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

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).