Group 2 organometallic chemistry: Difference between revisions
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[[image:GOHRUQ.png|thumb|right|Magnesium anthracenide with three thf ligands.<ref>{{cite journal|author=Borislav Bogdanovic|title=Magnesium Anthracene Systems and their Application in Synthesis and Catalysis|journal=Accounts of Chemical Research |volume=21|year=1988|issue=7 |pages=261–267|doi=10.1021/ar00151a002}}</ref>]] '''Group 2 organometallic chemistry''' refers to the [[organic compound|organic derivatives]]s of any [[group 2 element]]. It is a subtheme to [[main group organometallic chemistry]].<ref>''Comprehensive Organometallic Chemistry'' by Mike Mingos, Robert Crabtree '''2007''' {{ISBN|978-0-08-044590-8}}</ref><ref>C. Elschenbroich, A. Salzer ''Organometallics : A Concise Introduction'' (2nd Ed) ('''1992''') from Wiley-VCH: Weinheim. {{ISBN|3-527-28165-7}}</ref> By far the most common group 2 organometallic compounds are the magnesium-containing [[Grignard reagent]]s which are widely used in [[organic chemistry]]. Other organometallic group 2 compounds are typically limited to academic interests. |
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==Characteristics== |
==Characteristics== |
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As the [[group 2 elements]] (also referred to as the alkaline earth metals) contain two [[valence electron]]s, their chemistries have similarities [[group 12 element|group 12]] organometallic compounds. Both readily assume a +2 [[oxidation state]]s with higher and lower states being rare, and are less electronegative than carbon. However, as the group two elements (with the exception of beryllium) have considerably low [[electronegativity]] the resulting C-M bonds are more highly polarized and [[ionic bond|ionic]]-like, if not entirely ionic for the heavier barium compounds. The lighter [[organoberyllium]] and [[organomagnesium]] compounds are often considered [[covalent bond|covalent]], but with some ionic bond characteristics owing to the attached carbon bearing a negative [[molecular dipole moment|dipole moment]]. This higher ionic character and bond polarization tends to produce high [[coordination number]]s and many compounds (particularly dialklys) are polymeric in solid or liquid states with highly complex structures in solution, though in the gaseous state they are often monomeric. |
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In many ways the chemistry of group 2 elements (the [[alkaline earth metals]]) mimics that of [[group 12 element]]s because both groups have filled [[s shell]]s for [[valence electron]]s. Thus, both groups have nominal [[Valence (chemistry)|valency]] 2 and [[oxidation state]] +2. All group 2 elements are electropositive towards carbon and [[electronegativity]] decreases down the row. At the same time the [[atomic radius]] increases resulting in increasingly ionic character, higher [[coordination number]]s, and increased ligand reactivity. |
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⚫ | [[Metallocene]] compounds with group 2 elements are rare, but some do exist. Bis(cyclopentadienyl)beryllium or beryllocene (Cp<sub>2</sub>Be), with a [[molecular dipole moment]] of 2.2 [[Debye|D]], is so-called slipped <sup>5</sup>η/<sup>1</sup>η sandwich. While magnesocene (Cp<sub>2</sub>Mg) is a regular metallocene, bis(pentamethylcyclopentadienyl)calcium (Cp<sup>*</sup>)<sub>2</sub>Ca is bent with an angle of 147°. |
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Many dialkyl group 2 metals are polymeric in the crystalline phase and resemble [[trimethylaluminium]] in [[three-center two-electron bond]]. In the gas-phase they are once again monomeric. |
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[[image: Me2Mg.png|right|thumb|322 px|[[Dimethylmagnesium]] is a polymer built up from 3-center, 2-electron bonded bridging methyl groups.<ref>{{cite journal | last1 = Weiss | first1 = E. | title = Die Kristallstruktur des Dimethylmagnesiums | journal = [[J. Organomet. Chem.]] | year = 1964 | volume = 2 | issue = 4 | pages = 314–321 | doi = 10.1016/S0022-328X(00)82217-2 }}</ref> [[Dimethylberyllium]] adopts the same structure.<ref>{{cite journal | last1 = Snow | first1 = A.I.|last2 = Rundle| first2=R.E.|title = Structure of Dimethylberyllium |
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|journal=Acta Crystallographica|year=1951|volume=4| issue = 4|pages=348–52|doi=10.1107/S0365110X51001100|hdl=2027/mdp.39015095081207|hdl-access=free}}</ref>]] |
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Low-valent organometallics with formal oxidation state 1 having a metal to metal bond are also known.<ref>{{cite journal|doi=10.1002/chem.201000580|pmid=20486240|title=Low-Valent Organometallics-Synthesis, Reactivity, and Potential Applications|year=2010|last1=Schulz|first1=Stephan|journal=Chemistry: A European Journal|volume=16|issue=22|pages=6416–28}}</ref> A representative is LMg-MgL with L = [(Ar)NC(NPri<sub>2</sub>)N(Ar)]<sup>−</sup>.<ref>{{cite journal|doi=10.1126/science.1150856|title=Stable Magnesium(I) Compounds with Mg-Mg Bonds|year=2007|last1=Green|first1=S. P.|last2=Jones|first2=C.|last3=Stasch|first3=A.|journal=Science|volume=318|pages=1754–7|pmid=17991827|issue=5857|bibcode = 2007Sci...318.1754G }}</ref> |
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==Synthesis== |
==Synthesis== |
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Mixed alkyl/aryl-halide compounds, which contain a single C-M bond and a C-X bond, are typically prepared by oxidative addition. Magnesium-containing compounds of this configuration are known as the [[Grignard reagent]]s, though some calcium Grignard's are known and more reactive and sensitive to decomposition. Calcium grignard's must be pre-activated prior to synthesis.<ref>{{cite journal|title=Highly Reactive Calcium for the Preparation of Organocalcium Reagents: 1-Adamantyl Calcium Halides and Their Addition to Ketones: 1-(1-Adamantyl)cyclohexanol|author=Reuben D. Rieke |author2=Tse-Chong Wu |author3=Loretta I. Rieke |journal=Org. Synth.|year=1995|volume=72|page=147|doi=10.15227/orgsyn.072.0147}}</ref> |
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There are three key reaction pathways for dialkyl and diaryl group 2 metal compounds. |
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*[[ |
*[[Salt metathesis reaction|metathesis]]: |
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:MX<sub>2</sub> + R-Y → MR<sub>2</sub> + Y-X' |
:MX<sub>2</sub> + R-Y → MR<sub>2</sub> + Y-X' |
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*via the [[Schlenk equilibrium]]: |
*via the [[Schlenk equilibrium]]: |
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:2 RMX → MR<sub>2</sub> + MX<sub>2</sub> |
:2 RMX → MR<sub>2</sub> + MX<sub>2</sub> |
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See for example the formation of [[dimethylmagnesium]]. |
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==Compounds== |
==Compounds== |
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Although organomagnesium compounds are widespread in the form of [[Grignard reagent]]s, the other organo-group 2 compound are almost exclusively of academic interest. Organoberyllium chemistry is limited due to the cost and toxicity of beryllium. [[Calcium]] is nontoxic and cheap but organocalcium compounds are difficult to prepare, [[strontium]] and [[barium]] compounds even more so. One use for these type of compounds is in [[chemical vapor deposition]]. |
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===Organoberyllium=== |
===Organoberyllium=== |
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{{Main|Organoberyllium chemistry}} |
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Beryllium derivatives and reagents are often prepared by alkylation of [[beryllium chloride]].<ref name=naglav>''Off the Beaten Track—A Hitchhiker's Guide to Beryllium Chemistry'' D. Naglav, M. R. Buchner, G. Bendt, F. Kraus, S. Schulz, Angew. Chem. Int. Ed. 2016, 55, 10562. {{doi|10.1002/anie.201601809}}</ref> Examples of known organoberyllium compounds are dineopentylberyllium,<ref>{{cite journal|doi=10.1039/J19710001308|title=Preparation of base-free beryllium alkyls from trialkylboranes. Dineopentylberyllium, bis(trimethylsilylmethyl)beryllium, and an ethylberyllium hydride|year=1971|last1=Coates|first1=G. E.|last2=Francis|first2=B. R.|journal=Journal of the Chemical Society A: Inorganic, Physical, Theoretical|page=1308}}</ref> beryllocene (Cp<sub>2</sub>Be),<ref>{{cite journal|doi=10.1002/cber.19590920233|title=Über Aromatenkomplexe von Metallen, XXV. Di-cyclopentadienyl-beryllium|year=1959|last1=Fischer|first1=Ernst Otto|last2=Hofmann|first2=Hermann P.|journal=Chemische Berichte|volume=92|page=482|issue=2}}</ref><ref>{{cite journal|doi=10.1071/CH9841601|title=A precise low-temperature crystal structure of Bis(cyclopentadienyl)beryllium|year=1984|last1=Nugent|first1=KW|last2=Beattie|first2=JK|last3=Hambley|first3=TW|last4=Snow|first4=MR|journal=Australian Journal of Chemistry|volume=37|page=1601|issue=8}}</ref><ref>{{cite journal|doi=10.1016/S0022-328X(00)92065-5|title=The molecular structure of beryllocene, (C5H5)2Be. A reinvestigation by gas phase electron diffraction|year=1979|last1=Almenningen|first1=A|journal=Journal of Organometallic Chemistry|volume=170|page=271|issue=3|last2=Haaland|first2=Arne|last3=Lusztyk|first3=Janusz}}</ref><ref>{{cite journal|doi=10.1107/S0567740872004820|title=Crystal structure of bis(cyclopentadienyl)beryllium at −120 °C|year=1972|last1=Wong|first1=C. H.|last2=Lee|first2=T. Y.|last3=Chao|first3=K. J.|last4=Lee|first4=S.|journal=Acta Crystallographica Section B|volume=28|page=1662|issue=6|doi-access=free}}</ref> ''diallylberyllium'' (by exchange reaction of diethyl beryllium with triallyl boron),<ref>{{cite journal|doi=10.1002/zaac.19744050111|title=Ein Beitrag zur Existenz von Allylberyllium- und Allylaluminiumverbindungen|year=1974|last1=Wiegand|first1=G.|last2=Thiele|first2=K.-H.|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=405|pages=101–108}}</ref> bis(1,3-trimethylsilylallyl)beryllium<ref>{{cite journal|doi=10.1002/anie.201001866|pmid=20575128|title=Bis(1,3-trimethylsilylallyl)beryllium|year=2010|last1=Chmely|first1=Stephen C.|last2=Hanusa|first2=Timothy P.|last3=Brennessel|first3=William W.|journal=Angewandte Chemie International Edition|volume=49|issue=34|pages=5870–4}}</ref> and Be(mes)2.<ref name=naglav/><ref>''Synthesis and structural characterization of the beryllium compounds [Be(2,4,6-Me3C6H2)2(OEt2)], [Be{O(2,4,6-tert-Bu3C6H2)}2(OEt2)], and [Be{S(2,4,6-tert-Bu3C6H2)}2(THF)].cntdot.PhMe and determination of the structure of [BeCl2(OEt2)2]'' Karin Ruhlandt-Senge, Ruth A. Bartlett, Marilyn M. Olmstead, and Philip P. Power Inorganic Chemistry 1993 32 (9), 1724-1728 {{doi|10.1021/ic00061a031}}</ref> Ligands can also be aryls<ref>{{cite journal|doi=10.1021/ic00061a031|title=Synthesis and structural characterization of the beryllium compounds [Be(2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>)<sub>2</sub>(OEt<sub>2</sub>)], [Be{O(2,4,6-tert-Bu<sub>3</sub>C<sub>6</sub>H<sub>2</sub>)}<sub>2</sub>(OEt<sub>2</sub>)], and [Be{S(2,4,6-tert-Bu<sub>3</sub>C<sub>6</sub>H<sub>2</sub>)}<sub>2</sub>(THF)].cntdot.PhMe and determination of the structure of [BeCl<sub>2</sub>(OEt<sub>2</sub>)<sub>2</sub>]|year=1993|last1=Ruhlandt-Senge|first1=Karin|last2=Bartlett|first2=Ruth A.|last3=Olmstead|first3=Marilyn M.|last4=Power|first4=Philip P.|journal=Inorganic Chemistry|volume=32|page=1724}}</ref> and alkynyls.<ref>{{cite journal|doi=10.1016/S0022-328X(00)87485-9|title=The crystal structure of dimeric methyl-1-propynyl- beryllium-trimethylamine|year=1971|last1=Morosin|first1=B|journal=Journal of Organometallic Chemistry|volume=29|page=7|last2=Howatson|first2=J.}}</ref> |
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{{see also|Berylliosis}} |
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===Organomagnesium=== |
===Organomagnesium=== |
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{{Also|Grignard reagent}} |
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The distinctive feature of the Grignard reagents is their formation from the organic halide and magnesium metal. Most other group II organic compounds are generated by [[salt metathesis]], which limits their accessibility. The formation of the Grignard reagents has received intense scrutiny. It proceeds by a [[single electron transfer|SET]] process. For less reactive organic halides, activated forms of magnesium have been produced in the form of [[Rieke magnesium]]. Examples of Grignard reagents are [[phenylmagnesium bromide]] and [[ethylmagnesium bromide]]. These simplified formulas are deceptive: Grignard reagents generally exist as dietherates, RMgX(ether)2. As such they obey the [[octet rule]]. |
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Organomagnesium compounds are widespread. They are commonly found as [[Grignard reagent]]s. The formation of alkyl or aryl magnesium halides (RMgX) from magnesium metal and an [[alkyl halide]] is attributed to a [[single electron transfer|SET]] process. Examples of Grignards are [[phenylmagnesium bromide]] and [[ethylmagnesium bromide]]. |
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Grignard reagents participate in the Schlenk equilibrium. Exploiting this reaction is a way to generate [[dimethylmagnesium]]. Beyond Grignard reagents, another organomagnesium compound is [[magnesium anthracene]]. This orange solid is used as a source of highly active magnesium. [[Butadiene]]-magnesium serves as a source for the butadiene dianion. [[Ate complex]]es of magnesium are also well known, e.g LiMgBu<sub>3</sub>.<ref>{{cite journal |doi=10.15227/orgsyn.089.0460|first1=Juan D.|last1=Arredondo|first2=Hongmei|last2=Li|first3=Jaume|last3=Balsells| |
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Relevant organic magnesium reagents outside the scope of Grignards are '''magnesium anthracene''' with magnesium forming a 1,4-bridge over the central hexagon used as a source of highly active magnesium and '''butadiene magnesium''' an adduct with [[butadiene]] and a source for the butadiene dianion. |
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title=Preparation of t-Butyl-3-Bromo-5-Formylbenzoate Through Selective Metal-Halogen Exchange Reactions|journal=Organic Syntheses|year=2012|volume=89|page=460|doi-access=free}}</ref> |
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===Organocalcium=== |
===Organocalcium=== |
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{{Main|Organocalcium chemistry}} |
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Further down this group [[calcium]] is nontoxic and cheap but '''organocalcium''' compounds are difficult to make. This is even more so for the remaining members [[strontium]] and [[barium]], and for the case of [[radium]] there are none known at all. One use for this type of compounds is in [[chemical vapor deposition]]. |
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Dimethylcalcium |
Dimethylcalcium is obtained by [[Salt metathesis reaction|metathesis]] reaction of [[Metal bis(trimethylsilyl)amides|calcium bis(trimethylsilyl)amide]] and [[methyllithium]] in [[diethyl ether]]:<ref>"Dimethylcalcium" Benjamin M. Wolf, Christoph Stuhl, Cäcilia Maichle-Mössmer, and Reiner Anwander ''J. Am. Chem. Soc.'' '''2018''', Volume 140, Issue 6, Pages 2373–2383 {{doi|10.1021/jacs.7b12984}}</ref> |
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:<math>\mathrm{Ca[N\{Si(CH_3 )_3\}_2]_2 + 2\ LiCH_3 \longrightarrow Ca(CH_3)_2 + 2\ Li[N\{Si(CH_3)_3\}_2]}</math> |
:<math>\mathrm{Ca[N\{Si(CH_3 )_3\}_2]_2 + 2\ LiCH_3 \longrightarrow Ca(CH_3)_2 + 2\ Li[N\{Si(CH_3)_3\}_2]}</math> |
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A well known organocalcium compound is ([[cyclopentadienyl|Cp]])calcium(I). Bis(allyl)calcium was described in 2009.<ref>"Bis(allyl)calcium" Phillip Jochmann, Thomas S. Dols, Thomas P. Spaniol, Lionel Perrin, Laurent Maron, Jun Okuda ''Angewandte Chemie International Edition'' Volume 48 Issue 31, Pages 5715–5719 2009 {{ |
A well known organocalcium compound is ([[cyclopentadienyl|Cp]])calcium(I).{{cn|date=January 2021}} Bis(allyl)calcium was described in 2009.<ref>"Bis(allyl)calcium" Phillip Jochmann, Thomas S. Dols, Thomas P. Spaniol, Lionel Perrin, Laurent Maron, Jun Okuda ''Angewandte Chemie International Edition'' Volume 48 Issue 31, Pages 5715–5719 2009 {{doi|10.1002/anie.200901743}}</ref> It forms in a metathesis reaction of [[allylpotassium]] and [[calcium iodide]] as a stable non-[[pyrophoric]] off-white powder: |
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:<chem>\overset{allylpotassium}{2KC3H5} + \overset{calcium\ iodide}{CaI2} ->[\ce{THF}][25^\circ \ce C] {(C3H5)2Ca} + 2KI</chem> |
:<chem>\overset{allylpotassium}{2KC3H5} + \overset{calcium\ iodide}{CaI2} ->[\ce{THF}][25^\circ \ce C] {(C3H5)2Ca} + 2KI</chem> |
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The bonding mode is [[hapticity|η]]<sup>3</sup>. This compound is also reported to give access to an [[hapticity|η]]<sup>1</sup> polymeric (CaCH<sub>2</sub>CHCH<sub>2</sub>)<sub>''n''</sub> compound.<ref>Lichtenberg, C., Jochmann, P., Spaniol, T. P. and Okuda, J. (2011), "The Allylcalcium Monocation: A Bridging Allyl Ligand with a Non-Bent Coordination Geometry". ''Angewandte Chemie International Edition'', 50: 5753–5756. {{doi|10.1002/anie.201100073}}</ref> |
The bonding mode is [[hapticity|η]]<sup>3</sup>. This compound is also reported to give access to an [[hapticity|η]]<sup>1</sup> polymeric (CaCH<sub>2</sub>CHCH<sub>2</sub>)<sub>''n''</sub> compound.<ref>Lichtenberg, C., Jochmann, P., Spaniol, T. P. and Okuda, J. (2011), "The Allylcalcium Monocation: A Bridging Allyl Ligand with a Non-Bent Coordination Geometry". ''Angewandte Chemie International Edition'', 50: 5753–5756. {{doi|10.1002/anie.201100073}}</ref> |
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The compound [(thf)<sub>3</sub>Ca{μ-C<sub>6</sub>H<sub>3</sub>-1,3,5-Ph<sub>3</sub>}Ca(thf)<sub>3</sub>] also described in 2009<ref>"Stable 'Inverse' Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]" Sven Krieck, Helmar Görls, Lian Yu, Markus Reiher and Matthias Westerhausen ''[[J. Am. Chem. Soc.]]'', '''2009''', 131 (8), pp 2977–2985 {{ |
The compound [(thf)<sub>3</sub>Ca{μ-C<sub>6</sub>H<sub>3</sub>-1,3,5-Ph<sub>3</sub>}Ca(thf)<sub>3</sub>] also described in 2009<ref>"Stable 'Inverse' Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]" Sven Krieck, Helmar Görls, Lian Yu, Markus Reiher and Matthias Westerhausen ''[[J. Am. Chem. Soc.]]'', '''2009''', 131 (8), pp 2977–2985 {{doi|10.1021/ja808524y}}</ref><ref>"Organometallic Compounds of the Heavier s-Block Elements—What Next?" J. David Smith ''[[Angew. Chem. Int. Ed.]]'' '''2009''', 48, 6597–6599 {{doi|10.1002/anie.200901506}}</ref> is an inverse [[sandwich compound]] with two calcium atoms at either side of an arene. |
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[[Olefin]]s tethered to [[cyclopentadienyl ligand]]s have been shown to coordinate to calcium(II), strontium(II), and barium(II):<ref name=schumann1>{{cite journal | author1 = H. Schumann | author2 = S. Schutte | author3 = H.-J. Kroth | author4= D. Lentz | title = Butenyl-Substituted Alkaline-Earth Metallocenes: A First Step towards Olefin Complexes of the Alkaline-Earth Metals | journal = Angew. Chem. Int. Ed. | year = 2004 | volume = 43 | pages = 6208–6211 | doi = 10.1002/anie.200460927}}</ref> |
[[Olefin]]s tethered to [[cyclopentadienyl ligand]]s have been shown to coordinate to calcium(II), strontium(II), and barium(II):<ref name=schumann1>{{cite journal | author1 = H. Schumann | author2 = S. Schutte | author3 = H.-J. Kroth | author4= D. Lentz | title = Butenyl-Substituted Alkaline-Earth Metallocenes: A First Step towards Olefin Complexes of the Alkaline-Earth Metals | journal = Angew. Chem. Int. Ed. | year = 2004 | volume = 43 | issue = 45 | pages = 6208–6211 | doi = 10.1002/anie.200460927| pmid = 15549740 | doi-access = free }}</ref> |
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:[[File:Olefine coordination at calcium strontium barium.png|400px|Olefin complexes of calcium, strontium and barium<ref name=schumann1/>]] |
:[[File:Olefine coordination at calcium strontium barium.png|400px|Olefin complexes of calcium, strontium and barium<ref name=schumann1/>]] |
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Organocalcium compounds have been investigated as catalysts.<ref>{{cite journal|doi=10.1021/om101063m|title=Cation Charge Density and Precatalyst Selection in Group 2-Catalyzed Aminoalkene Hydroamination|year=2011|last1=Arrowsmith|first1=Merle|last2=Crimmin|first2=Mark R.|last3=Barrett|first3=Anthony G. M.|last4=Hill|first4=Michael S.|last5=Kociok-KöHn|first5=Gabriele|last6=Procopiou|first6=Panayiotis A.|journal=Organometallics|volume=30|issue=6|pages=1493–1506}}</ref> |
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Organocalcium compounds are investigated as catalysts.<ref>Harder, S., Feil, F. and Knoll, K. (2001), ''Novel Calcium Half-Sandwich Complexes for the Living and Stereoselective Polymerization of Styrene'' . Angew. Chem. Int. Ed., 40: 4261–4264. {{doi|10.1002/1521-3773(20011119)40|22<4261::AID-ANIE4261>3.0.CO;2-J}}</ref><ref>''Calcium-Mediated Intramolecular Hydroamination Catalysis'' Mark R. Crimmin, Ian J. Casely, and Michael S. Hill Journal of the American Chemical Society 2005 127 (7), 2042-2043 {{DOI|10.1021/ja043576n}}</ref><ref>''2,5-Bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl Complexes of the Heavy Alkaline Earth Metals: Synthesis, Structures, and Hydroamination Catalysis'' Jelena Jenter, Ralf Köppe, and Peter W. Roesky Organometallics 2011 30 (6), 1404-1413 {{DOI|10.1021/om100937c}}</ref><ref>''Cation Charge Density and Precatalyst Selection in Group 2-Catalyzed Aminoalkene Hydroamination'' Merle Arrowsmith, Mark R. Crimmin, Anthony G. M. Barrett, Michael S. Hill, Gabriele Kociok-Köhn, and Panayiotis A. Procopiou Organometallics 2011 30 (6), 1493-1506 {{DOI|10.1021/om101063m}}</ref><ref>Penafiel, J., Maron, L. and Harder, S. (2014), ''Early Main Group Metal Catalysis: How Important is the Metal?''. Angew. Chem. Int. Ed. {{doi|10.1002/anie.201408814}}</ref> |
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===Organostrontium=== |
===Organostrontium=== |
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'''Organostrontium''' compounds have been reported as intermediates in [[Barbier reaction|Barbier-type]] reactions.<ref>{{Cite journal| doi = 10.1246/bcsj.77.341| title = The Barbier-Type Alkylation of Aldehydes with Alkyl Halides in the Presence of Metallic Strontium| year = 2004| last1 = Miyoshi | first1 = N.| last2 = Kamiura | first2 = K.| last3 = Oka | first3 = H.| last4 = Kita | first4 = A.| last5 = Kuwata | first5 = R.| last6 = Ikehara | first6 = D.| last7 = Wada | first7 = M.| journal = Bulletin of the Chemical Society of Japan| volume = 77| issue = 2| |
'''Organostrontium''' compounds have been reported as intermediates in [[Barbier reaction|Barbier-type]] reactions.<ref>{{Cite journal| doi = 10.1246/bcsj.77.341| title = The Barbier-Type Alkylation of Aldehydes with Alkyl Halides in the Presence of Metallic Strontium| year = 2004| last1 = Miyoshi | first1 = N.| last2 = Kamiura | first2 = K.| last3 = Oka | first3 = H.| last4 = Kita | first4 = A.| last5 = Kuwata | first5 = R.| last6 = Ikehara | first6 = D.| last7 = Wada | first7 = M.| journal = Bulletin of the Chemical Society of Japan| volume = 77| issue = 2| page = 341 }}</ref><ref>{{Cite journal| doi = 10.1246/cl.2005.760| title = The Chemistry of Alkylstrontium Halide Analogues: Barbier-type Alkylation of Imines with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Ikehara | first2 = D.| last3 = Kohno | first3 = T.| last4 = Matsui | first4 = A.| last5 = Wada | first5 = M.| journal = Chemistry Letters| volume = 34| issue = 6| page = 760 }}</ref><ref>{{Cite journal| doi = 10.1002/ejoc.200500484| title = The Chemistry of Alkylstrontium Halide Analogues, Part 2: Barbier-Type Dialkylation of Esters with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Matsuo | first2 = T.| last3 = Wada | first3 = M.| journal = European Journal of Organic Chemistry| volume = 2005| issue = 20| page = 4253 }}</ref> |
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===Organobarium=== |
===Organobarium=== |
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'''Organobarium''' compounds<ref>''Comprehensive organic functional group transformations'' [[Alan R. Katritzky]], Otto Meth-Cohn, [[Charles Rees|Charles Wayne Rees]]</ref> of the type (allyl)BaCl |
'''Organobarium''' compounds<ref>''Comprehensive organic functional group transformations'' [[Alan R. Katritzky]], Otto Meth-Cohn, [[Charles Rees|Charles Wayne Rees]]</ref> of the type (allyl)BaCl can be prepared by reaction of activated barium (Rieke method [[redox|reduction]] of [[barium iodide]] with lithium biphenylide) with allyl halides.<ref>{{Cite journal| doi = 10.1021/ja00023a058| title = Allylbarium in organic synthesis: unprecedented .alpha.-selective and stereospecific allylation of carbonyl compounds| year = 1991| last1 = Yanagisawa | first1 = A.| last2 = Habaue | first2 = S.| last3 = Yamamoto | first3 = H.| journal = Journal of the American Chemical Society| volume = 113| issue = 23| page = 8955 }}</ref><ref>{{Cite journal| doi = 10.1021/ja00093a010| title = Allylbarium Reagents: Unprecedented Regio- and Stereoselective Allylation Reactions of Carbonyl Compounds| year = 1994| last1 = Yanagisawa | first1 = A.| last2 = Habaue | first2 = S.| last3 = Yasue | first3 = K.| last4 = Yamamoto | first4 = H.| journal = Journal of the American Chemical Society| volume = 116| issue = 14| page = 6130 }}</ref> These allylbarium compounds react with carbonyl compounds. Such reagents are more alpha-selective and more stereoselective than the related Grignards or organocalcium compounds. The [[metallocene]] ([[Cp*]])<sub>2</sub>Ba has also been reported.<ref>{{Cite journal | first3 = J. C.| last3 = Huffman| journal = Journal of the Chemical Society, Chemical Communications| issue = 15| page = 1045 | first2 = T. P.| last2 = Hanusa| title = Solid state structure of bis(pentamethylcyclopentadienyl)barium, (Me5C5)2Ba; the first X-ray crystal structure of an organobarium complex| year = 1988| last1 = Williams | first1 = R. A.| doi = 10.1039/C39880001045 }}</ref> |
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===Organoradium=== |
===Organoradium=== |
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==See also== |
==See also== |
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* [[Organometallic chemistry]] |
* [[Organometallic chemistry]] |
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==References== |
==References== |
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{{reflist|30em}} |
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Latest revision as of 06:56, 13 December 2024
Group 2 organometallic chemistry refers to the organic derivativess of any group 2 element. It is a subtheme to main group organometallic chemistry.[2][3] By far the most common group 2 organometallic compounds are the magnesium-containing Grignard reagents which are widely used in organic chemistry. Other organometallic group 2 compounds are typically limited to academic interests.
Characteristics
[edit]As the group 2 elements (also referred to as the alkaline earth metals) contain two valence electrons, their chemistries have similarities group 12 organometallic compounds. Both readily assume a +2 oxidation states with higher and lower states being rare, and are less electronegative than carbon. However, as the group two elements (with the exception of beryllium) have considerably low electronegativity the resulting C-M bonds are more highly polarized and ionic-like, if not entirely ionic for the heavier barium compounds. The lighter organoberyllium and organomagnesium compounds are often considered covalent, but with some ionic bond characteristics owing to the attached carbon bearing a negative dipole moment. This higher ionic character and bond polarization tends to produce high coordination numbers and many compounds (particularly dialklys) are polymeric in solid or liquid states with highly complex structures in solution, though in the gaseous state they are often monomeric.
Metallocene compounds with group 2 elements are rare, but some do exist. Bis(cyclopentadienyl)beryllium or beryllocene (Cp2Be), with a molecular dipole moment of 2.2 D, is so-called slipped 5η/1η sandwich. While magnesocene (Cp2Mg) is a regular metallocene, bis(pentamethylcyclopentadienyl)calcium (Cp*)2Ca is bent with an angle of 147°.
Synthesis
[edit]Mixed alkyl/aryl-halide compounds, which contain a single C-M bond and a C-X bond, are typically prepared by oxidative addition. Magnesium-containing compounds of this configuration are known as the Grignard reagents, though some calcium Grignard's are known and more reactive and sensitive to decomposition. Calcium grignard's must be pre-activated prior to synthesis.[6]
There are three key reaction pathways for dialkyl and diaryl group 2 metal compounds.
- MX2 + R-Y → MR2 + Y-X'
- M'R2 + M → MR2 + M'
- via the Schlenk equilibrium:
- 2 RMX → MR2 + MX2
Compounds
[edit]Although organomagnesium compounds are widespread in the form of Grignard reagents, the other organo-group 2 compound are almost exclusively of academic interest. Organoberyllium chemistry is limited due to the cost and toxicity of beryllium. Calcium is nontoxic and cheap but organocalcium compounds are difficult to prepare, strontium and barium compounds even more so. One use for these type of compounds is in chemical vapor deposition.
Organoberyllium
[edit]Beryllium derivatives and reagents are often prepared by alkylation of beryllium chloride.[7] Examples of known organoberyllium compounds are dineopentylberyllium,[8] beryllocene (Cp2Be),[9][10][11][12] diallylberyllium (by exchange reaction of diethyl beryllium with triallyl boron),[13] bis(1,3-trimethylsilylallyl)beryllium[14] and Be(mes)2.[7][15] Ligands can also be aryls[16] and alkynyls.[17]
Organomagnesium
[edit]The distinctive feature of the Grignard reagents is their formation from the organic halide and magnesium metal. Most other group II organic compounds are generated by salt metathesis, which limits their accessibility. The formation of the Grignard reagents has received intense scrutiny. It proceeds by a SET process. For less reactive organic halides, activated forms of magnesium have been produced in the form of Rieke magnesium. Examples of Grignard reagents are phenylmagnesium bromide and ethylmagnesium bromide. These simplified formulas are deceptive: Grignard reagents generally exist as dietherates, RMgX(ether)2. As such they obey the octet rule.
Grignard reagents participate in the Schlenk equilibrium. Exploiting this reaction is a way to generate dimethylmagnesium. Beyond Grignard reagents, another organomagnesium compound is magnesium anthracene. This orange solid is used as a source of highly active magnesium. Butadiene-magnesium serves as a source for the butadiene dianion. Ate complexes of magnesium are also well known, e.g LiMgBu3.[18]
Organocalcium
[edit]Dimethylcalcium is obtained by metathesis reaction of calcium bis(trimethylsilyl)amide and methyllithium in diethyl ether:[19]
A well known organocalcium compound is (Cp)calcium(I).[citation needed] Bis(allyl)calcium was described in 2009.[20] It forms in a metathesis reaction of allylpotassium and calcium iodide as a stable non-pyrophoric off-white powder:
The bonding mode is η3. This compound is also reported to give access to an η1 polymeric (CaCH2CHCH2)n compound.[21]
The compound [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3] also described in 2009[22][23] is an inverse sandwich compound with two calcium atoms at either side of an arene.
Olefins tethered to cyclopentadienyl ligands have been shown to coordinate to calcium(II), strontium(II), and barium(II):[24]
Organocalcium compounds have been investigated as catalysts.[25]
Organostrontium
[edit]Organostrontium compounds have been reported as intermediates in Barbier-type reactions.[26][27][28]
Organobarium
[edit]Organobarium compounds[29] of the type (allyl)BaCl can be prepared by reaction of activated barium (Rieke method reduction of barium iodide with lithium biphenylide) with allyl halides.[30][31] These allylbarium compounds react with carbonyl compounds. Such reagents are more alpha-selective and more stereoselective than the related Grignards or organocalcium compounds. The metallocene (Cp*)2Ba has also been reported.[32]
Organoradium
[edit]The only known organoradium compound is the gas-phase acetylide.
See also
[edit]References
[edit]- ^ Borislav Bogdanovic (1988). "Magnesium Anthracene Systems and their Application in Synthesis and Catalysis". Accounts of Chemical Research. 21 (7): 261–267. doi:10.1021/ar00151a002.
- ^ Comprehensive Organometallic Chemistry by Mike Mingos, Robert Crabtree 2007 ISBN 978-0-08-044590-8
- ^ C. Elschenbroich, A. Salzer Organometallics : A Concise Introduction (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
- ^ Weiss, E. (1964). "Die Kristallstruktur des Dimethylmagnesiums". J. Organomet. Chem. 2 (4): 314–321. doi:10.1016/S0022-328X(00)82217-2.
- ^ Snow, A.I.; Rundle, R.E. (1951). "Structure of Dimethylberyllium". Acta Crystallographica. 4 (4): 348–52. doi:10.1107/S0365110X51001100. hdl:2027/mdp.39015095081207.
- ^ Reuben D. Rieke; Tse-Chong Wu; Loretta I. Rieke (1995). "Highly Reactive Calcium for the Preparation of Organocalcium Reagents: 1-Adamantyl Calcium Halides and Their Addition to Ketones: 1-(1-Adamantyl)cyclohexanol". Org. Synth. 72: 147. doi:10.15227/orgsyn.072.0147.
- ^ a b Off the Beaten Track—A Hitchhiker's Guide to Beryllium Chemistry D. Naglav, M. R. Buchner, G. Bendt, F. Kraus, S. Schulz, Angew. Chem. Int. Ed. 2016, 55, 10562. doi:10.1002/anie.201601809
- ^ Coates, G. E.; Francis, B. R. (1971). "Preparation of base-free beryllium alkyls from trialkylboranes. Dineopentylberyllium, bis(trimethylsilylmethyl)beryllium, and an ethylberyllium hydride". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 1308. doi:10.1039/J19710001308.
- ^ Fischer, Ernst Otto; Hofmann, Hermann P. (1959). "Über Aromatenkomplexe von Metallen, XXV. Di-cyclopentadienyl-beryllium". Chemische Berichte. 92 (2): 482. doi:10.1002/cber.19590920233.
- ^ Nugent, KW; Beattie, JK; Hambley, TW; Snow, MR (1984). "A precise low-temperature crystal structure of Bis(cyclopentadienyl)beryllium". Australian Journal of Chemistry. 37 (8): 1601. doi:10.1071/CH9841601.
- ^ Almenningen, A; Haaland, Arne; Lusztyk, Janusz (1979). "The molecular structure of beryllocene, (C5H5)2Be. A reinvestigation by gas phase electron diffraction". Journal of Organometallic Chemistry. 170 (3): 271. doi:10.1016/S0022-328X(00)92065-5.
- ^ Wong, C. H.; Lee, T. Y.; Chao, K. J.; Lee, S. (1972). "Crystal structure of bis(cyclopentadienyl)beryllium at −120 °C". Acta Crystallographica Section B. 28 (6): 1662. doi:10.1107/S0567740872004820.
- ^ Wiegand, G.; Thiele, K.-H. (1974). "Ein Beitrag zur Existenz von Allylberyllium- und Allylaluminiumverbindungen". Zeitschrift für anorganische und allgemeine Chemie. 405: 101–108. doi:10.1002/zaac.19744050111.
- ^ Chmely, Stephen C.; Hanusa, Timothy P.; Brennessel, William W. (2010). "Bis(1,3-trimethylsilylallyl)beryllium". Angewandte Chemie International Edition. 49 (34): 5870–4. doi:10.1002/anie.201001866. PMID 20575128.
- ^ Synthesis and structural characterization of the beryllium compounds [Be(2,4,6-Me3C6H2)2(OEt2)], [Be{O(2,4,6-tert-Bu3C6H2)}2(OEt2)], and [Be{S(2,4,6-tert-Bu3C6H2)}2(THF)].cntdot.PhMe and determination of the structure of [BeCl2(OEt2)2] Karin Ruhlandt-Senge, Ruth A. Bartlett, Marilyn M. Olmstead, and Philip P. Power Inorganic Chemistry 1993 32 (9), 1724-1728 doi:10.1021/ic00061a031
- ^ Ruhlandt-Senge, Karin; Bartlett, Ruth A.; Olmstead, Marilyn M.; Power, Philip P. (1993). "Synthesis and structural characterization of the beryllium compounds [Be(2,4,6-Me3C6H2)2(OEt2)], [Be{O(2,4,6-tert-Bu3C6H2)}2(OEt2)], and [Be{S(2,4,6-tert-Bu3C6H2)}2(THF)].cntdot.PhMe and determination of the structure of [BeCl2(OEt2)2]". Inorganic Chemistry. 32: 1724. doi:10.1021/ic00061a031.
- ^ Morosin, B; Howatson, J. (1971). "The crystal structure of dimeric methyl-1-propynyl- beryllium-trimethylamine". Journal of Organometallic Chemistry. 29: 7. doi:10.1016/S0022-328X(00)87485-9.
- ^ Arredondo, Juan D.; Li, Hongmei; Balsells, Jaume (2012). "Preparation of t-Butyl-3-Bromo-5-Formylbenzoate Through Selective Metal-Halogen Exchange Reactions". Organic Syntheses. 89: 460. doi:10.15227/orgsyn.089.0460.
- ^ "Dimethylcalcium" Benjamin M. Wolf, Christoph Stuhl, Cäcilia Maichle-Mössmer, and Reiner Anwander J. Am. Chem. Soc. 2018, Volume 140, Issue 6, Pages 2373–2383 doi:10.1021/jacs.7b12984
- ^ "Bis(allyl)calcium" Phillip Jochmann, Thomas S. Dols, Thomas P. Spaniol, Lionel Perrin, Laurent Maron, Jun Okuda Angewandte Chemie International Edition Volume 48 Issue 31, Pages 5715–5719 2009 doi:10.1002/anie.200901743
- ^ Lichtenberg, C., Jochmann, P., Spaniol, T. P. and Okuda, J. (2011), "The Allylcalcium Monocation: A Bridging Allyl Ligand with a Non-Bent Coordination Geometry". Angewandte Chemie International Edition, 50: 5753–5756. doi:10.1002/anie.201100073
- ^ "Stable 'Inverse' Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]" Sven Krieck, Helmar Görls, Lian Yu, Markus Reiher and Matthias Westerhausen J. Am. Chem. Soc., 2009, 131 (8), pp 2977–2985 doi:10.1021/ja808524y
- ^ "Organometallic Compounds of the Heavier s-Block Elements—What Next?" J. David Smith Angew. Chem. Int. Ed. 2009, 48, 6597–6599 doi:10.1002/anie.200901506
- ^ a b H. Schumann; S. Schutte; H.-J. Kroth; D. Lentz (2004). "Butenyl-Substituted Alkaline-Earth Metallocenes: A First Step towards Olefin Complexes of the Alkaline-Earth Metals". Angew. Chem. Int. Ed. 43 (45): 6208–6211. doi:10.1002/anie.200460927. PMID 15549740.
- ^ Arrowsmith, Merle; Crimmin, Mark R.; Barrett, Anthony G. M.; Hill, Michael S.; Kociok-KöHn, Gabriele; Procopiou, Panayiotis A. (2011). "Cation Charge Density and Precatalyst Selection in Group 2-Catalyzed Aminoalkene Hydroamination". Organometallics. 30 (6): 1493–1506. doi:10.1021/om101063m.
- ^ Miyoshi, N.; Kamiura, K.; Oka, H.; Kita, A.; Kuwata, R.; Ikehara, D.; Wada, M. (2004). "The Barbier-Type Alkylation of Aldehydes with Alkyl Halides in the Presence of Metallic Strontium". Bulletin of the Chemical Society of Japan. 77 (2): 341. doi:10.1246/bcsj.77.341.
- ^ Miyoshi, N.; Ikehara, D.; Kohno, T.; Matsui, A.; Wada, M. (2005). "The Chemistry of Alkylstrontium Halide Analogues: Barbier-type Alkylation of Imines with Alkyl Halides". Chemistry Letters. 34 (6): 760. doi:10.1246/cl.2005.760.
- ^ Miyoshi, N.; Matsuo, T.; Wada, M. (2005). "The Chemistry of Alkylstrontium Halide Analogues, Part 2: Barbier-Type Dialkylation of Esters with Alkyl Halides". European Journal of Organic Chemistry. 2005 (20): 4253. doi:10.1002/ejoc.200500484.
- ^ Comprehensive organic functional group transformations Alan R. Katritzky, Otto Meth-Cohn, Charles Wayne Rees
- ^ Yanagisawa, A.; Habaue, S.; Yamamoto, H. (1991). "Allylbarium in organic synthesis: unprecedented .alpha.-selective and stereospecific allylation of carbonyl compounds". Journal of the American Chemical Society. 113 (23): 8955. doi:10.1021/ja00023a058.
- ^ Yanagisawa, A.; Habaue, S.; Yasue, K.; Yamamoto, H. (1994). "Allylbarium Reagents: Unprecedented Regio- and Stereoselective Allylation Reactions of Carbonyl Compounds". Journal of the American Chemical Society. 116 (14): 6130. doi:10.1021/ja00093a010.
- ^ Williams, R. A.; Hanusa, T. P.; Huffman, J. C. (1988). "Solid state structure of bis(pentamethylcyclopentadienyl)barium, (Me5C5)2Ba; the first X-ray crystal structure of an organobarium complex". Journal of the Chemical Society, Chemical Communications (15): 1045. doi:10.1039/C39880001045.