Preparation and NMR studies of cobalt-containing diphosphine ligand chelated W, Ru, Au and Pd complexes: Suzuki cross-coupling reactions and carbonylation catalyzed by the Pd complex

Abstract

Treatment of a cobalt-containing diphosphine ligand, [{μ-P,P-PPh₂CH₂PPh₂}Co₂(CO)₄{μ-PPh₂CCPPh₂}] 1 with metal complexes W(CO)₆, Ru₃(CO)₁₂, AuCl(tht) (tht = tetrahydrothiophene) and (COD)PdCl₂ (COD = 1,5-cycloctadiene) gave 1-chelated metal complexes [(1)W(CO)₄] 3, [(μ-1)Ru₃(CO)₁₀] 4, [(1)(AuCl)₂] 5 and [(1)PdCl₂] 6, respectively. All these compounds were characterized by spectroscopic means whereas 3, 4 and 6 were also studied by X-ray diffraction. These compounds display chelating and bridging modes of metal–phosphine complexation. Variable-temperature ¹H and ³¹P NMR experiments were carried out for 3–6 and revealed that the fluxional behavior of each individual bridging dppm fragment was affected greatly by the bite angle of 1 in each metal complex. Suzuki cross-coupling reactions were satisfactorily catalyzed by 6 under mild conditions. The reactions of aryl halides or iodothiophenes with chloroform and alkali in biphasic solution utilizing a catalytic amount of 6 result into the formation of benzoic and thiophenic acids, respectively.