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)-3,5diphenylphosphinine (2). Reaction of ligand 2 with [Pd-(COD)Cl-2] 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 lambda(4)-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 lambda(3)-phosphinine complex [Pd(2)Cl](+) (3).