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The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2007, 4405 - 4412, DOI: 10.1039/b709249k

Insertion reactions of dicyclohexylcarbodiimide with aminoboranes, -boryls and -borylenes

Glesni A. Pierce, Natalie D. Coombs, David J. Willock, Joanna K. Day, Andreas Stasch and Simon Aldridge

Insertion reactions of dicyclohexylcarbodiimide with aminoboranes and with aminoboryl and -borylene transition metal complexes have been examined as potential routes to new boron-containing ligand systems. Reactions with systems containing two-coordinate boron centres are found to be significantly more facile than those with three-coordinate substrates. Thus, reaction of (dicyclohexylamino)boron dichloride ( 1a) with dicyclohexylcarbodiimide over 36 h at 50 °C generates the (structurally authenticated) guanidinate complex Cy2NC(NCy)2BCl2 ( 2a) via insertion into the BN bond. By contrast, the corresponding reaction with the cationic aminoborylene complex [CpFe(CO)2(BNCy2)]+[BArf4]– ( 4a) proceeds rapidly at ca.–30 °C, via initial insertion into the FeB bond to give [CpFe(CO)2C(NCy)2BNCy2]+[BArf4]– ( 5a). Consistent with related studies, a key factor in facilitating such insertion chemistry is thought to be the formation of an initial donor/acceptor complex between the diimide and the group 13 centre. Thus, DFT studies suggest that [CpFe(CO)2B(NCy2)(CyNCNCy)]+[BArf4]– is a potential intermediate in the reaction of 4a with CyNCNCy, and that further reaction to give the observed product, 5a, is strongly exergic (–183 kJ mol–1). By contrast, DFT calculations for the alternative isomer [CpFe(CO)2B(CyN)2CNCy2]+[BArf4]– ( 5a), formed by BN insertion, suggest that it is 112 kJ mol–1 less stable than 5a. Such experimental and computational findings imply that under reaction conditions where a suitable isomerisation pathway is available, cationic complexes such as 5a, which contain a four-membered boron-donor heterocycle are likely to be disfavoured with respect to alternative C-bound isomers.

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