Palladium-catalysed formation of aroylcobalt complexes from iodoarene and tetracarbonylcobaltate anion. Syntheses, characterization and reactivities of model intermediate complexes

Abstract

The complex [Pd(PPh₃)₄] showed good catalytic activity for the formation of aroylcobalt complexes [Co(OCR)(CO)₃(PPh₃)] from RI (R = aryl), K[Co(CO)₄] and PPh₃. Attempts to isolate an intermediate Pd–Co complex in this catalytic reaction were unsuccessful, however a series of heterodinuclear complexes [(Ph₃P)(OC)RPtCo(CO)₃(PPh₃)](R = Ph 1a, C₆H₄Me-4 1b or Me 1c), [(Me₃P)₂(PhCO)PdCo(CO)₄]2 and [(Me₃P)₂PhPtCo(CO)₄]3 have been prepared from reactions of [MR(O₃SCF₃)(PR′₃)₂](M = Pt or Pd, R′= Me or Ph) with K[Co(CO)₄] as model intermediate complexes. Prior to the formation of complex 1, transient formation of [(Ph₃P)₂RPtCo(CO)₄] was confirmed by ³¹P NMR spectroscopy of the reaction solution. The reaction of [PtPh(O₃SCF₃)(PMe₃)₂] with K[Co(CO)₄] led to the isolation of the corresponding Pt–Co complex 3, while the palladium analogue resulted in the formation of the CO insertion product 2. Crystal structures of compounds 1a, 1c, 2 and 3 were determined by X-ray diffraction analyses. Addition of ligands L such as CO, Bu^tNC and PMe₃ to 3 in tetrahydrofuran induced heterolytic cleavage of the Pt–Co bond to form [PtPh(PMe₃)₂L][Co(CO)₄]. Thermolysis of complexes 1b and 1c under CO at 50 °C resulted in reductive elimination of Co(OCC₆H₄Me-4)(CO)₃(PPh₃) and Co(OCMe)(CO)₃(PPh₃), respectively, from the platinum centre. This strongly suggests the involvement of this type of heterodinuclear Pd–Co complex in the catalytic formation of aroylcobalt complexes.