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.