Cationic Dialkyl Metal Compounds of Group 13 Elements (E = Al, Ga, In) Stabilized by the Weakly Coordinating Dianion [B12Cl12]2鈥?/sup>

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• 作者：Mathias Kessler ; Carsten Knapp ; Ardiana Zogaj
• 刊名：Organometallics
• 出版年：2011
• 出版时间：July 25, 2011
• 年：2011
• 卷：30
• 期：14
• 页码：3786-3792
• 全文大小：860K
• 年卷期：v.30,no.14(July 25, 2011)
• ISSN：1520-6041

文摘

The reactions of the trityl salt of the weakly coordinating dianion [B₁₂Cl₁₂]^{2鈥?/sup> ([Ph₃C]₂[B₁₂Cl₁₂]) with Et₃Al, Et₃Ga路(OEt₂) and Et₃In in 1,2-difluorobenzene yielded (Et₂Al)₂B₁₂Cl₁₂, [Et₂Ga(OEt₂)₂]₂[B₁₂Cl₁₂], and (Et₂In)₂B₁₂Cl₁₂. The products were characterized by NMR (1H, 11B, 13C), IR, and Raman spectroscopy. Investigation of the symmetric carbon鈥搈etal stretching vibration (Raman) of the [Et₂E]+ unit in (Et₂E)₂B₁₂Cl₁₂ (E = Al, In) compounds indicated a linear structure for E = In and a bent structure for E = Al. The latter was confirmed by a crystal structure determination of (Et₂Al)₂B₁₂Cl₁₂. While the reaction of the triethyl compounds Et₃E (E = Al, In) and Et₃Ga路(OEt₂) proceeded via 尾-hydride abstraction and release of ethylene, Me₃Al reacts with [Ph₃C]₂[B₁₂Cl₁₂] under methide transfer. The gaseous byproduct ethene was identified by IR spectroscopy, and solid byproducts (Ph₃CH or Ph₃CMe) were observed by NMR spectroscopy in solution. The formation of (Me₂Al)₂B₁₂Cl₁₂ was proven by X-ray diffraction and NMR spectroscopy. In the crystal structures of (Me₂Al)₂B₁₂Cl₁₂ and (Et₂Al)₂B₁₂Cl₁₂ the aluminum atoms are bound to two chlorine atoms, resulting in a distorted tetrahedral environment around aluminum. The aluminum鈥揷hlorine contacts are longer than a typical Al鈥揅l single bond but significantly shorter than the sum of the van der Waals radii. The bonding in both compounds can be described as ion-like. The underlying thermodynamics for 尾-hydride abstraction and methide transfer were investigated in the gas phase by DFT calculations, in 1,2-difluorobenzene solution by applying the COSMO solvation model, and in the solid state by Born鈥揌aber鈥揊ajans cycles using a volume-based approach to estimate lattice enthalpies. These estimations show that the reactions are unfavorable in the gas phase but become favorable when solvation and lattice energies are taken into account.}