Synthesis and structural characterization of novel palladium complexes chelated by bulky cobalt-containing phosphine ligands: unusual palladium–cobalt bond formation

Abstract

The reaction of a bulky phosphine, [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 1 with P(OMe)3 gave a phosphite substituted tetracobalt-complex, [Co2(CO)4{P(OMe)3}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 5. Further reaction of 5 with (COD)PdCl2 yielded a 5 -coordinated palladium complex, [Co2(CO)4{P(OMe)3}}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl27. Similar results were obtained for the reaction of 1 with (COD)PdCl2, which yielded [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl26. Likewise, reaction of another bulky phosphine [(μ-Ph2PCH2PPh2)Co2(CO)4(μ-PPh2CCP(O)Ph2)] 3 with (COD)PdCl2 yielded [{μ-P,P-PPh2CH2PPh2}Co2(CO)3(μ-CO){μ-PPh2CCP(O)Ph2}]PdCl28. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium–cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-bromothiophene with boronic acid did not show encouraging signs.