Mechanism of the palladium-catalyzed metal-carbon bond formation. Isolation of oxidative addition and transmetalation intermediates

To investigate the reaction mechanism of the Pd-catalyzed metal-carbon bond formation, the model compounds [eta(5)-1-Ph(2)P-2,4-Ph(2)C(5)H(2)](CO)(3)MI (M = Mo, 12; M = W, 13) have been prepared and their reactions studied under coupling conditions. Treatment of 12 and 13 with stoichiometric amounts of zerovalent palladium yields the complexes [eta(5)-1-Ph(2)P-2,4-Ph(2)C(5)H(2)](CO)(3)MPd(PPh(3))I (M = Mo, 16; M = W, 17) by oxidative addition of the M-I moieties on Pd-0. Subsequent reaction of intermediates 16 and 17 with 4-nitro-1-[2-(tributylstannyl)ethynyl]benzene(Bu(3)SnC=C(C6H4) p-NO2, 18) leads to the formation of the transmetalation products [eta(5)-1-Ph(2)P-2,4-Ph(2)C(5)H(2)](CO)(3)MPd(PPh(3))C=C(C6H4)p-NO2 (M = Mo, 19; W, 20), which have been isolated and characterized. Complexes 13 and 17 have been also characterized by X-ray analysis.