Bonding in Phosphanylphosphinidene Complexes of Transition Metals and their Correlation with Structures, 31P NMR Spectra, and Reactivities

Abstract

Theoretical studies of the bonding interactions and most important properties are carried out for isolable phosphanylphosphinidene complexes of transition metals. Three main types of phosphanylphosphinidene complexes are distinguished, based on the way in which the phosphanylphosphinidene ligand bonds to the metal center: (i) side‐on complexes of platinum, where the R2Pβ–Pα ligand mimics structural features of free singlet phosphanylphosphinidenes with short, polarized, double P–P bonds and two lone electron pairs on the terminal P atom. In this case, interactions between the platinum center and the phosphanylphosphinidene ligand are determined by π(PP)→s(Pt) donation and d(Pt)→π*(PP) back‐donation; (ii) terminal and bridging complexes of zirconium, where the R2P–P ligand is bonded to the metal center only by the terminal P atom. The metal–ligand interactions are a result of the singly occupied p orbitals of a terminal P atom overlapping with the singly occupied d orbitals of the Zr atom, which leads to multiple bonding; (iii) side‐on complexes of early transition metals, where the R2Pβ–Pα group is bonded to the metal through an R2Pβ–M single bond and a Pα=M double bond. The observed shortening of the P–P bond in these complexes is explained by a negative hyperconjugation, as a result of the interaction of the π(PαM) orbital with the σ*(PβC) orbitals.