Phosphinomethyl complexes of zirconium: A molecular orbital study of structure, bonding and reactivity problems

The electronic structure and geometry of bent sandwich phosphinomethyl complexes of Zr IV and Zr III have been investigated by means of molecular orbital calculations. A fragment MO approach and perturbation arguments are utilized to explain the unusual experimental structure of Cp 2 ZrCl(CH 2 PPh 2 ) ( 1 ). Various factors influencing monodentate (η 1 ) vs. bidentate (η 2 ) ligand coordination of a phosphinomethyl ligand in zirconocene derivatives are analyzed, allowing to extrapolate to other Cp 2 M(X)() systems (: potentially mono‐ or bidentate ligand) in general. Structural and chemical consequences of one electron reduction of 1 are interpreted on the basis of the MO calculations. is shown to possess an η 1 ‐phosphinomethyl ligand and to be unstable towards heterolytic loss of Cl − or CH 2 PPh   2 − . The ground state structure of d 1 ‐Cp 2 Zr(CH 2 PPh 2 ) is calculated to contain an η 2 ‐phosphinomethyl group, consistent with the observed ESR spectrum of the reduction product of 1 .