H. Jacobsen, H. Berke, S. Döring
Apr 9, 1999
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Organometallics
Abstract
A variety of donor adducts of tris(pentafluorophenyl)borane were experimentally generated by reaction of a Lewis base with an excess of B(C6F5)3 in pentane. In this way, nitrile complexes (C6F5)3B·NCR (R = CH3 1a, p-CH3−C6H4 1b, p-NO2−C6H4 1c), isonitrile complexes (C6F5)3B·CNR (R = C(CH3)3 3a, C(CH3)2CH2C(CH3)3 3b, 2,6-(CH3)2−C6H3 3c), and the phosphine adduct (C6F5)3B·P(C6H5)3 (6) could be prepared. The compounds were characterized by IR and NMR spectroscopy and by X-ray structure analyses (1a, 1c, 3a, 3b, and 6). Coordination of the nitriles as well as the isonitriles to the neutral Lewis acid leads to a substantial increase in the C⋮N bond strength. This is evident from a marked shift of the νC⋮N IR band to higher wavenumbers, and this interpretation is supported by the small but experimentally significant decrease of the C⋮N bond length observed by X-ray diffraction. The experimental work is complemented by a density functional study on the model complexes (C6F5)3B·L, L = CNCH3, NCCH3, PH3, CO. A de...