Dihydride Complexes of the Cobalt and Iron Group Metals: An Investigation of Structure and Dynamic Behavior

Abstract

The previously reported cationic dihydride complexes (PP3)MH2+ (M = Co, Rh and Ir; PP3 = P(CH2CH2PPh2)3) have been prepared using improved synthetic methods. Variable-temperature 1H and 31P NMR spectra of these complexes reveal complex dynamic behavior. The hydride region 1H NMR spectra have been accurately simulated at all temperatures using a simple site permutation model after taking into consideration the opposite signs of the cis and trans H−P coupling constants. Partial deuteration of the hydride ligands in the rhodium and cobalt complexes is achieved by exposure to D2. In the partially deuterated samples, no evidence is found for a bound dihydrogen ligand, but the involvement of a dihydrogen species in the dynamic process which interchanges the two hydride positions remains a mechanistic possibility, as indicated by a kinetic isotope effect kH/kD = 1.3(1). The partially deuterated samples exhibit large and temperature-dependent isotope effects on the 1H NMR chemical shifts observed for the hydride ...