Substrate activation by the Wilkinson analogous complex C1Rh(P ～ O)(P O) containing η2 P O-chelated and η1 P-bonded (methoxyethyl) dicyclohexylphosphine as a hemilabile ligand

Article abstract of DOI:10.1016/S0022-328X(96)06551-5

In the presence of a variety of small molecules the pseudo 14-electron rhodium complex ClRh(P ～ O)(P O) (1, P O = η²(O,P)-chelated Cy₂PCH₂CH₂OCH₃ ligand; P ～ O= η¹(P)-coordinated) is shown to undergo a facile cleavage of its intramolecular ether moiety. The reaction of 1 with ethene, diphenylacetylene and carbon disulfide results in the irreversible coordination of the corresponding molecule to the metal yielding the complexes ClRh(C₂H₄)(P ～ O)₂ (2), ClRh(PhC=CPh)(P ～ O)₂ (3), ClRhCS₂(P ～ O)₂ (4), and ClRhCS(P ～ O)₂ (5). All compounds are obtained in excellent yields under very mild conditions. The structures of 4 and 5 were determined by single-crystal X-ray diffraction. The oxidative addition of HCl to the starting material 1 leads to the monochelated octahedrally coordinated complex Cl₂Rh(H)(P ～ O)(P O) (6). Complex 6 exhibits fluxional behavior on the ³¹P NMR time scale. Line-shape analysis of variable temperature ³¹P{¹H} NMR spectra of 6 affords the Eyring parameters ΔH? = 42.3kJ mol^-1 and ΔS? = -63.7 J mol^-1 K^-1, indicating an intramolecular exchange mechanism. The Rh-H bond in 6 is able to insert ethene to give the ethylrhodium(III) complex Cl₂RhC₂H₅(P ～ O)₂ (7). Subsequently, there follows a fast σ/π rearrangement to the complex Cl₂Rh(η²-C₂H₄)(H)(P ～ O)₂ (8) which undergoes a slow π/σ transformation to the monochelated product Cl₂Rh(C₂H₅)(P ～ O)(P O) (9).