Hyperelectronic Metal-Carborane Analogues of Cymantrene (MnCp(CO)3) Anions: Electronic and Structural Noninnocence of the Tricarbadecaboranyl Ligand

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• 作者：Ayman Nafady ; Robert Butterick III ; Maria Jos&eacute ; Calhorda ; Patrick J. Carroll ; Daesung Chong ; William E. Geiger ; Larry G. Sneddon
• 刊名：Organometallics
• 出版年：2007
• 出版时间：August 27, 2007
• 年：2007
• 卷：26
• 期：18
• 页码：4471 - 4482
• 全文大小：616K
• 年卷期：v.26,no.18(August 27, 2007)
• ISSN：1520-6041

文摘

The reduction of 1,1,1-(CO)₃-2-Ph-closo-1,2,3,4-MnC₃B₇H₉, 1, to the hyperelectronic dianion 1^2- hasbeen studied by electrochemistry, spectroscopy, X-ray crystallography, and DFT calculations. Dependingon the medium, this cymantrene derivative displays either a single two-electron wave or two separateone-electron waves in cyclic voltammetry scans, always at potentials (e.g., E_1/2 = -1.14 V vs ferrocenefor 1/1^- in THF) that are very far positive of that reported for MnCp(CO)₃ (-2.86 V). Reduction of thecorresponding Re compound 2 occurs in a single two-electron process. Both 1^- and 1^2- were isolated astheir decamethylcobaltocenium salts and characterized by X-ray crystallography. The hapticity of thetricarbadecaboranyl ligand is reduced from hexahapto (mages/gifchars/eta.gif" BORDER=0 >⁶) in 1 to tetrahapto (mages/gifchars/eta.gif" BORDER=0 >⁴) in 1^2-, mimicking anmages/gifchars/eta.gif" BORDER=0 >⁵/mages/gifchars/eta.gif" BORDER=0 >³ haptotropic rearrangement of a cyclopentadienyl ligand. The dianion 1^2- retains coordination tothe C7-B3-B4-C9 face of the tricarbadecaboranyl ligand, much like that found previously for theneutral isocyanide adduct (CNBu^t)(CO)₃MnC₃B₇H₉, 3, showing that the metal-ligand bonding reactssimilarly to gain of either two electrons or an electron pair donor. The monoanion 1^- also shows ligandslippage to an mages/gifchars/eta.gif" BORDER=0 >⁴ coordination in which relevant distances and angles are roughly intermediate of 1 and1^2-. The SOMO of 1^- is highly delocalized over the Mn-C₃B₇ framework. Although the tricarbadecaboranyl anion has a strongly electron-accepting ligand effect, the majority of the stabilization energyit imparts to nominally hyperelectronic metals originates from its flexibility in hapticity changes. Byanalogy to well-documented metal-chelate chemistry, the tricarbadecaboranyl group behaves as a"noninnocent" ligand in these electron-rich systems.