Multimetallic Complexes Featuring a Bridging N‑heterocyclic Phosphido/Phosphenium Ligand: Synthesis, Structure, and Theoretical Investigation

By incorporating an N-heterocyclic phosphenium/phosphide (NHP) ligand into a chelating pincer ligand framework (PPP+/PPP–), we have elucidated several different and unprecedented binding modes of NHP ligands in homobimetallic, heterobimetallic, and trimetallic metal complexes. One-electron reduction of the previously reported (PPP)−/MII complexes (PPP)­M-Cl (M = Pd (1), Pt (2)) results in clean formation of the symmetric homobimetallic MI/MI complexes [(μ-PPP)­Pd]2 (5) and [(μ-PPP)­Pt]2 (6). The tridentate NHP ligand has also been utilized as a bridging linker in the M/Co heterobimetallic compounds (OC)3Co­(u-PPP)­M­(CO) (M = Pd (7), Pt (8)), synthesized via salt elimination from mixtures of 1 and 2 and Na­[Co­(CO)4]. Furthermore, an NHP-bridged trimetallic complex (PPP)2Pd3Cl2 (9) can be synthesized in a manner similar to precursor 1 (Pd­(PPh3)4 + (PPP)­Cl) via careful adjustment of reaction stoichiometry. Examination of the interatomic distances and angles in complexes 5–9, in tandem with density functional theory calculations have been used to evaluate and characterize the bonding interactions in these complexes.