Chapter 9 - Coordination of N-heterocyclic carbene to Si–Si and P–P multiple bonded compounds

Abstract

Multiple bonded compounds of silicon and phosphorus are important in main group chemistry research. Considering silicon as a heavier analogue of carbon, two different silicon–silicon multiple bonded motifs are known, namely silicon–silicon double bond (known as disilene, the analogue of alkene) and silicon–silicon triple bond (known as disilyne, the analogue of alkyne). In the case of phosphorus, however, the only phosphorus–phosphorus multiple bonded motif is the phosphorus–phosphorus double bond (known as diphosphene, the analogue of an alkene). In all of these multiple bonded compounds, silicon and phosphorus centers are low-coordinated centers, which can therefore potentially be coordinated by a donor such as Lewis base. The coordination chemistry of N-heterocyclic carbene (NHC) to silicon–silicon and phosphorus–phosphorus multiple bonded motifs is discussed in this chapter. NHC coordinated to disilyne leads to a 1:1 complex that can react with Lewis acids such as ZnCl2 and MeOTf. NHC can also coordinate to the disilene motif in cyclotrisilene in a reversible manner. Depending on the cyclotrisilene used, it can form a zwitterionic compound and/or ring-opened NHC-coordinated disilenyl silylene. On the other hand, depending on substituent at the phosphorus center, NHC can directly cleave the phosphorus–phosphorus bond or it can reversibly coordinate to the diphosphene moiety. The reactivity of NHC-coordinated diphosphene has been enhanced with respect to diphosphene alone toward hydrolysis and hydrogenation reactions using NH3·BH3. Moreover, NHC-coordinated diphosphene can act as a ligand for the stabilization of the Au(I)-chloride moiety and its subsequent conversion to the monomeric Au(I)-hydride.