Carbodiphosphorane C(PPh3)2 as a Single and Twofold Lewis Base with Boranes: Synthesis, Crystal Structures and Theoretical Studies on [H3B{C(PPh3)2}] and [{(μ-H)H4B2}{C(PPh3)2}]+

The donor-acceptor complex [(H3B){C(PPh3)(2)}] (2) has been synthesized by treating B2H6 with C(PPh3)(2) and its geometry determined by X-ray structure analysis Treatment of 2 with DIME yields the complex [{(mu-H)H4B2}{C(PPh3)}][B2H7] (4), which teas also been isolated and structurally characterized Compound 4 is the first complex of a carbodiphosphorane where the carbon donor atone binds with its two-electron lone pairs to two main-group Lewis acids larger than protons This reaction is likely to occur via initial formation of [(H3B)(2)-{C(PPh3)(2)}] (6), which subsequently reacts with B2H6 with loss of a hydride, to yield 4 Quantum chemical calculations of 2, 4(+) and 6 show that the carbon-boron bonds in these complexes are very strong, and analysis of the bonding situation using the EDA, NBO and AIM methods reveals typical bonding patterns between the divalent carbon(0) moieties and one or two Lewis acids. The carbon donor atolls of the carbodiphosphorane moiety remains strongly negatively charged even in the cation 4(+). ((C) Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2009)