The complex [Pd(PPh(3))(4)] showed good catalytic activity for the formation of aroylcobalt complexes [Co(OCR)(CO)(3)(PPh(3))] from RI (R = aryl), K[Co(CO)(4)] and PPh(3). Attempts to isolate an intermediate Pd-Co complex in this catalytic reaction were unsuccessful, however a series of heterodinuclear complexes [(Ph(3)P)(OC)RPtCo(CO)(3)(PPh(3))] (R = Ph 1a, C(6)H(4)Me-4 1b or Me 1c), [(Me(3)P)(2)(PhCO)PdCo(CO)(4)] 2 and [(Me(3)P)(2)PhPtCo(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 [(Ph(3)P)(2)RPtCo(CO)(4)] was confirmed by P-31 NMR spectroscopy Of the reaction solution. The reaction of [PtPh(O3SCF3)(PMe(3))(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(t)NC and PMe(3) to 3 in tetrahydrofuran induced heterolytic cleavage of the Pt-Co bond to form [PtPh(PMe(3))(2)L][Co(CO)(4)]. Thermolysis of complexes 1b and 1c under CO at 50 degrees C resulted in reductive elimination of Co(OCC(6)H(4)Me-4)(CO)(3)(PPh(3)) and Co(OCMe)(CO)(3)(PPh(3)), 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.