Abstract
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.