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Evidence for Strong Tantalum-To-Boron Dative Interactions in (silox)3Ta(BH3) and (silox)3Ta(eta2-B,Cl-BCl2Ph) (Silox = tBu3SiO)1

Evidence for Strong Tantalum-To-Boron Dative Interactions in (silox)3Ta(BH3) and (silox)3Ta(eta2-B,Cl-BCl2Ph) (Silox = tBu3SiO)1

Jeffrey B Bonanno, Thomas P Henry, Peter T Wolczanski, Aaron W Pierpont, Thomas R Cundari

Inorg Chem. 2007 Feb 19;46(4):1222-32.

PMID: 17249656

Abstract:

Treatment of (silox)3Ta (1, silox = tBu3SiO) with BH3.THF and BCl2Ph afforded (silox)3Ta(BH3) (2) and (silox)3Ta(eta2-B,Cl-BCl2Ph) (3), which are both remarkably stable Ta(III) compounds. NMe3 and ethylene failed to remove BH3 from 2, and no indication of BH3 exchange with BH3.THF-d8 was noted via variable-temperature 1H NMR studies. Addition of BH3.THF to (silox)3TaH2 provided the borohydride-hydride (silox)3HTa(eta3-BH4) (5), and its thermolysis released H2 to generate 2. Exposure of 2 to D2 enabled the preparation of isotopologues (silox)3Ta(BH3-nDn) (n = 0, 2; 1, 2-D; 2, 2-D2; 3, 2-D3) for isotopic perturbation of chemical shift studies, but these failed to distinguish between "inverse adduct" (i.e., (silox)3Ta-->BH3) or (silox)3Ta(eta2-B,H-BH3) forms of 2. Computational models (RO)3Ta(BH3) (R = H, 2'; SiH3, 2SiH SiMe3, 2SiMe, and SitBu3, 2SiBu) were investigated to assess the relative importance of steric and electronic effects on structure and bonding. With small R, eta2-B,H structures were favored, but for 2SiMe and 2SiBu, the dative structure proved to be similar in energy. The electonic and vibrational features of both structure types were probed. The IR spectrum of 2 was best matched by the eta2-B,H conformer of 2SiBu. In related computations pertaining to 3, small R models favored the oxidative addition of a BCl bond, while with R = SitBu3 (3SiBu), an excellent match with its X-ray crystal structure revealed the critical steric influence of the silox ligands.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP12007351	Tantalum boride (1:2)		12007-35-1	Price

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