17-Electron, four-legged piano stool CpMoX 2L 2 complexes (X  halogen, L  tertiary phosphine). EPR evidence for the existence of a second isomer in solution

Abstract

Several 17-electron molybdenum(III) complexes of the type CpMoCl 2L 2 have been generated by either (1) reaction between CpMoCl 2 and the appropriate L, (2) reaction between MoCl 3(THF) 3, the appropriate L and CpTl, and (3) phosphine exchange from CpMoCl 2(PPh 3) 2. The iodide complexes CpMoI 2L 2 (L  PMePh 2, PPh 3) have been generated from the corresponding chloride and NaI. The complexes have been investigated by EPR ( X-band and Q-band) and cyclic voltammetry. The four-legged piano stool structure is found by single crystal X-ray diffraction studies of the PMePh 2 and PPh 3 dichloride compounds. However, this structure equilibrates in solution with at least one other isomeric form which is observable for the PMe 2Ph complexes by X-band EPR and for other complexes, including the previously reported CpMoCl 2(dppe), by Q-band EPR. Phosphine exchange equilibria show a thermodynamic stability trend that parallels the phosphine σ-donor strength.