Different coordinating behaviour of the imino-phosphoranes Ph3PξNC(O)CH2Cl and Ph3PξNC(O)-2-NC5H4 towards MII complexes (M=Pd, Pt)

Abstract

The coordination behaviour of the iminophosphorane ligands Ph₃PNC(O)CH₂Cl and Ph₃PNC(O)-2-NC₅H₄ towards different Pd^II and Pt^II substrates has been explored. The iminophosphorane Ph₃PNC(O)CH₂Cl shows a poor coordination ability, always binding through the iminic N atom. Thus, Ph₃PNC(O)CH₂Cl reacts with PdCl₂(NCPh)₂, [M(C^∧P)(NCMe)₂]ClO₄ (M=Pd, Pt) and [Pd(dmba)(NCMe)₂]ClO₄ (2:1, 1:1 and 1:1 molar ratio, respectively, C^∧P=ortho-CH₂C₆H₄P(o-Tol)₂-C,P; dmba=C₆H₄CH₂NMe₂-2), resulting in the formation of trans-PdCl₂{N(PPh₃)C(O)CH₂Cl}₂, 1, [M(C^∧P){N(PPh₃)C(O)CH₂Cl}(NCMe)]ClO₄ (M=Pd, 2; Pt, 3) and [Pd(dmba){N(PPh₃)C(O)CH₂Cl}(NCMe)]ClO₄, 4. However, the iminophosphorane Ph₃PNC(O)-2-NC₅H₄ displays at least three different coordination modes, as a function of the starting material. The reaction of Ph₃PNC(O)-2-NC₅H₄ with PdCl₂(NCPh)₂ or PtCl₂ (1:1 molar ratio) gives cis-Cl₂M{N(PPh₃)C(O)-2-NC₅H₄} (M=Pd, 5; Pt, 6) in which the ligand acts as an N,N-chelate. The reaction with the bis-solvate orthometallated complexes [M(C^∧P)(NCMe)₂]ClO₄ (M=Pd, Pt) and [Pd(dmba)(NCMe)₂]ClO₄ (1:1 molar ratio) gives the bis-chelate complexes [M(C^∧P){NC₅H₄-2-C(O)NPPh₃}]ClO₄ (M=Pd 7, Pt 8) and [Pd(dmba){NC₅H₄-2-C(O)NPPh₃}]ClO₄, 9, in which the iminophosphorane ligand is coordinated through the pyridinic nitrogen atom and the carbonyl oxygen atom. The X-ray crystal structure of 9 has been determined. The reaction with [Pd(dmba)(PPh₃)(THF)]ClO₄ (1:1 molar ratio) gives the cationic derivative [Pd(dmba)(PPh₃){NC₅H₄-2-C(O)NPPh₃}]ClO₄, 10, in which the iminophosphorane ligand is coordinated only through the pyridinic nitrogen atom. Finally, the iminophosphorane reacts with [Pd(µ-Cl)(dmba)]₂ (2:1 molar ratio) resulting in the cleavage of the chlorine bridging system by the pyridinic N atom and formation of [Pd(dmba)Cl{NC₅H₄-2-C(O)NPPh₃}], 11.