A DFT/electron localization function (ELF) study of the bonding of phosphinidenes with N-heterocyclic carbenes

The bonding between model phosphinidene PH and two types of cyclic Arduengo 's carbenes, the aromatic C3H4N2 (1) and the related saturated C3H6N2 (2) s pecies, respectively, have been analyzed in terms of the electron localizat ion function (ELF). In a first step, the bare carbenes have been studied, a nd then, in a second step, the changes brought about by PH complexation hav e been treated. It has been shown that the bonding mode essentially results from a dative bond formed by the nucleophilic carbenic carbon of the ring and the PH acceptor site. Some back bonding from P creates a partial double -bond character around the C-P unit. The latter character is more pronounce d when PH is linked to the saturated carbene 2. A comparison of the ring ar omatic properties, in terms of nucleus-independent chemical shifts has been achieved, showing that complexation of 1 by PH diminishes the ring aromati city through relocalization of the electrons on the N atoms.