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• 作者：Jeffrey B. Bonanno ; Thomas P. Henry ; Peter T. Wolczanski ; Aaron W. Pierpont ; Thomas R. Cundari
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：February 19, 2007
• 年：2007
• 卷：46
• 期：4
• 页码：1222 - 1232
• 全文大小：379K
• 年卷期：v.46,no.4(February 19, 2007)
• ISSN：1520-510X

文摘

Treatment of (silox)₃Ta (1, silox = ^tBu₃SiO) with BH₃·THF and BCl₂Ph afforded (silox)₃Ta(BH₃) (2) and (silox)₃Ta(²-B,Cl-BCl₂Ph) (3), which are both remarkably stable Ta(III) compounds. NMe₃ and ethylene failed to removeBH₃ from 2, and no indication of BH₃ exchange with BH₃·THF-d₈ was noted via variable-temperature ¹H NMRstudies. Addition of BH₃·THF to (silox)₃TaH₂ provided the borohydride-hydride (silox)₃HTa(³-BH₄) (5), and itsthermolysis released H₂ to generate 2. Exposure of 2 to D₂ enabled the preparation of isotopologues(silox)₃Ta(BH_3-nD_n) (n = 0, 2; 1, 2-D; 2, 2-D₂; 3, 2-D₃) for isotopic perturbation of chemical shift studies, but thesefailed to distinguish between "inverse adduct" (i.e., (silox)₃TaBH₃) or (silox)₃Ta(²-B,H-BH₃) forms of 2. Computationalmodels (RO)₃Ta(BH₃) (R = H, 2'; SiH₃, 2^SiH SiMe₃, 2^SiMe, and Si^tBu₃, 2^SiBu) were investigated to assess the relativeimportance of steric and electronic effects on structure and bonding. With small R, ²-B,H structures were favored,but for 2^SiMe and 2^SiBu, the dative structure proved to be similar in energy. The electonic and vibrational featuresof both structure types were probed. The IR spectrum of 2 was best matched by the ²-B,H conformer of 2^SiBu. Inrelated computations pertaining to 3, small R models favored the oxidative addition of a BCl bond, while with R =Si^tBu₃ (3^SiBu), an excellent match with its X-ray crystal structure revealed the critical steric influence of the siloxligands.