Synthesis and Skeletal Transformations of Trinuclear Palladium and Nickel Phosphido Complexes

Abstract

Trinuclear phosphido complexes of palladium and nickel were synthesized and characterized. [M{(2-Me2NC6H4)PPh}(OAc)]3 [M = Pd (2), Ni (6)] were obtained from the respective acetate, [Pd(OAc)2]3 or [Ni(OAc)2(H2O)4], in reactions with the secondary aminophosphane (2-Me2NC6H4)PHPh (1). The chloride derivative [Pd{(2-Me2NC6H4)PPh}Cl]3 (4a) was generated from the reaction of the chelating ligand 1 with Na2PdCl4. The reaction of the acetate 2 with p-toluenesulfonic acid (pTsOH) led to the formation of the tosylate analogue [Pd{(2-Me2NC6H4)PPh}(OTs)]3 (3). From the reaction of the tosylate trimer 3 with CsCl, CsBr or NaI, the substitution products [Pd{(2-Me2NC6H4)PPh}X]3 [X = Cl (4a), Br (4b), I (4c)] were isolated. From the reaction of the acetate 2 with HBF4 or HClO4 in acetonitrile, the solvent adduct [Pd(NP)(NCCH3)]33+ was isolated as the BF4– (5a) or ClO4– salt (5b). The phosphido-bridged complexes were characterized by single-crystal structural analyses (2, 4, 5a and 6), solution NMR experiments, and in the case of 2 and 4a by solid-state 31P cross-polarization magic-angle spinning NMR spectroscopy. The crystal structures show the six-membered (MP)3 cores in twist-boat or boat conformations that appear to be maintained in solution, according to NMR evidence. A search for (MP)3 structures in the Cambridge Structural Database reveals that these two conformations are the most common ones (46 % twist-boat, 21 % boat, 17 % chair).