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 (L1) reacts with [Rh(COD)(THF)2][BF4] generated in situ, giving [Rh(COD)(L1-κ2N,N)][BF4] ([1][BF4]). The 1,5-cyclooctadiene ligand is displaced by carbon monoxide to generate [Rh(CO)2(L1)][BF4] ([2][BF4]) in which in the solid state, the ligand L1 adopts a facial κ3N,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(L1-κ2N,N)]+ ([2a]+) and the major compound [Rh(CO)2(L1-κ3N,N,O)]+[2b]+. [2][BF4] looses easily one molecule of carbon monoxide at room temperature leading to [Rh(CO)(L1-κ3N,N,O)][BF4] ([3][BF4]) in which L1 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.