Study of the bonding properties of the bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]ether toward Rh(I):: an hemilabile ligand exhibiting κ3N,N,O meridional or facial coordination mode

The bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]ether ligand (L-1) reacts with [Rh(COD)(THF)(2)][BF4] generated in situ, giving [Rh(COD)(L-1-kappa(2)N,N)][BF4] ([1][BF4]). The 1,5-cyclooctadiene ligand is displaced by carbon monoxide to generate [Rh(CO)(2)(Li)][BF4] ([2][BF4]) in which in the solid state, the ligand L-1 adopts a facial kappa(3)N,N,O bonding mode. This is the first example of such a coordination mode for this ligand, which generally prefers a 'T-shaped' meridional bonding mode. In solution [2][BF4] exists as a mixture of two isomers in rapid equilibrium on the NMR time scale, [Rh(CO)(2)(L-1-kappa(2)N,N)](+) ([2a](+)) and the major compound [Rh(CO)(2)(L-1-kappa(3)N,N,O)](+)[2b](+). [2][BF4] looses easily one molecule of carbon monoxide at room temperature leading to [Rh(CO)(L-1-kappa(3)N,N,O)][BF4] ([3][BF4]) in which L, adopts a 'T-shaped' meridional bonding mode. Carbon monoxide addition in solution regenerates rapidly [2][BF4]. The single-crystal X-ray structures of [1][BF4], [2b][BF4] and [3][BF4] are reported. (C) 2003 Elsevier B.V. All rights reserved.