Modular Design Strategy toward Second-Generation Tridentate Carbodiphosphorane N,C,N Ligands with a Central Four-Electron Carbon Donor Motif and Their Complexes

Abstract

The reaction of sym-bis(P-chlorodiphenyl)carbodiphosphorane (1) with difunctional nucleophiles leads to carbodiphosphoranes carrying two additional chelating N-donor functionalities. A proof of concept is demonstrated by the synthesis and characterization of sym-bis(3,5-dimethyl-1H-pyrazol-1-yl)carbodiphosphorane (CDP(3,5-MePz)2, 2) and sym-bis(pyridin-2-yloxy)carbodiphosphorane (CDP(O-2Py)2, 3). Due to their superbasic central two-/four-electron carbon donor functionality, these neutral ligands are electronically flexible to act as neutral six- or eight-electron donors, as pincer ligand templates, or as two geminally metal bridging ligands. Their potential to form mono- and dinuclear complexes involving two 6-ring or two 5-ring N,C-chelate ring motives has been explored. Complexes of 2 and 3 with fac-[M(CO)3] fragments (ls d6; M = Cr, Mo, W) were used as spectroscopic probes. They reveal a strong σ-donor and potential π-donor ability of the central carbon donor pushing electron density for enhanced M–CO back-bonding into the metal d orbitals. DFT calculations consolidate this observation. Dinuclear and multinuclear d10 Cu(I) complexes have been formed and structurally investigated upon treating these CDP ligands 2 and 3 with CuX (X = Cl, Br, I).