Synthesis and Molecular Structure of a Palladium Complex Containing a λ5-Phosphinine-Based SPS Pincer Ligand

2,6-Bis(diphenylphosphino)-3,5-diphenylphosphinine (1) reacts with elemental sulfur to yield the corresponding 2,6-bis(diphenylphosphine sulfide)-3,5-diphenylphosphinine (2). Reaction of ligand 2 with [Pd(COD)Cl2] affords the square planar complex 4 resulting from the displacement of one chloride ligand. An X-ray crystal study reveals that complex 4 features a λ4-1-P-chlorophosphinine ligand which is bound to the palladium atom through the phosphorus atom. Reaction of 4 with methanol gives the corresponding P−OMe complex resulting from the nucleophilic substitution of the P−Cl bond. DFT calculations suggest that the formation of 4 results from the internal attack of the chloride counteranion onto the highly electrophilic P atom of the transient λ3-phosphinine complex [Pd(2)Cl]+ (3).