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 PdII and PtII 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.