Cationic ligands between σ-donation and hydrogen-bridge-bond-stabilisation of ancillary ligands in coinage metal complexes with protonated carbodiphosphoranes.

A series of copper(I) and silver(I) complexes is reported containing the PCP-type tridentate ligand [(dppm)2CH]+ with a protonated carbodiphosphorane (CDPH) as cationic central donor group (dppm = 1,1-bis(diphenylphosphino)methane). In comparison to the previously reported gold complex [({dppm}2CH)AuCl]+ [Reitsamer et al., J. Organomet. Chem., 2017, 830, 150], the corresponding silver and copper complexes exhibit a κC-coordinated CDPH-group, which is absent in case of gold. For the series of silver complexes, we demonstrate that the κC-coordination of the CDPH-group is dependant on the ancillary ligand and that hydrogen bonding of the CDPH-group to the ancillary ligand can be competitive. The ability for such hydrogen bonding is a unique characteristic of protonated CDPs in comparison to other cationic ligands, which might offer benefits for applications in homogeneous catalysis by hemilability and substrate activation with this group.