NEW NEUTRAL AND IONIC METHYL AND CHLORO PALLADIUM AND PLATINUM COMPLEXES CONTAINING HEMILABILE PHOSPHORUS NITROGEN LIGANDS - STUDY OF THE INSERTION OF CARBON-MONOXIDE INTO THE METAL METHYL BOND

The synthesis and properties are described for the complexes (PAN)MCl2 (M = Pd(II), Pt(II)), (PAN)2PdCl2, [(PAN)M(CH3]+Y- (M = Pd(II); Y- = Cl-, SO3CF3-, BF4-), and [(PAN)M(CH3)(CH3CN)]+Y-(M = Pd(II), Pt(II); Y- = SO3CF3-, BF4-) and further (PC3N)M(CH3)Cl (M = Pd(II), Pt(II)) and [(PC3N)Pd(CH3)(CH3CN)]+SO3CF3-, where PAN is the rigid ligand 1-(dimethylamino)-8-(diphenyl-phosphine)naphthalene and PC3N the more flexible ligand 1-(dimethylamino)-3-(diphenylphosphino)propane. For (PAN)2PdCl2, in which PAN acts as a monodentate phosphorus-bonded ligand, and for (PAN)Pd(CH3)Cl, in which PAN is a chelate, single-crystal X-ray structure determinations were carried out: (PAN)2PdCl2, space group P1BAR, a = 12.837 (2) angstrom, b = 17.518 (3) angstrom, c = 10.788 (3) angstrom, alpha = 91.07 (2)-degrees, beta = 112.87 (2)-degrees, gamma = 100.27 (2)-degrees, V = 2189.1 (6) angstrom3, Z = 2, R = 0.044, R(W) = 0.065; (PAN)Pd(CH3)Cl, space group P2(1)/n, a = 11.418 (1) angstrom, b = 15.088 (1) angstrom, c = 12.434 (1) angstrom, beta = 99.81 (1)-degrees, V = 2110.7 (3) angstrom3, Z = 4, R = 0.025, R(W) = 0.026. The investigations were mainly focused on the study of the carbonylation of the metal-carbon bond and in particular on the influence of the type of metal and ligand on the intimate steps of the mechanisms of the metal-acyl bond formation and on the magnitude of the rates. In the case of the reaction of (P-N)Pt(CH3)Cl (CH3 cis to P) evidence has been obtained for the formation of three intermediates with a terminal CO group in which the P-N (P-N = PAN, PC3N) ligand temporarily functions as a monodentate phosphorus-bonded ligand, i.e. [trans P, cis CH3 (Pt-CO)], [cis P, trans CH3 (Pt-CO)], and [cis P, cis CH3 (Pt-CO)], which for the first time were observed to occur together in one system. Subsequently the formation of the final metal-acyl product (P-N)Pt(C(O)CH3)Cl(C(O)CH3 cis to P) could be observed, in which the P-N ligand is again chelate-bonded. However, during the carbonylation of [(PAN)Pd(CH3)]+Y- and [(PAN)Pd(CH3)(CH3CN)]+Y- (Y- = SO3CF3-, BF4-), only the intermediate [(PAN)Pd(CH3)(CO)]+Y- (CH3 cis to P) could be detected, with the P-N ligand in the chelating form, before the formation of the acyl products [(PAN)Pd(C(O)CH3)]+Y- and [(PAN)Pd(C(O)CH3)(CH3CN)]+Y-, in which the C(O)CH3 group is cis to P. Several isomerization reactions are necessary to obtain these products. The reaction rates in terms of half-life times t1/2, were measured at 25 bar of CO in CD2Cl2 by means of NMR spectroscopy in a high-pressure tube and were compared with data for analogous bpy, dppp, and dppe complexes. The results show that generally the complexes with good leaving groups Y- in noncoordinating solvents reacted much faster than the chloride complexes. The influence of the metal and the bidentate ligands on the insertion is reflected in a decrease in rates in the order Pd(II) > Pt(II) and bpy > PAN > PC3N > dppp > dppe for (L-L)Pt(CH3)Cl and bpy > dppp much greater than PAN > PC3N > dppe for (L-L)Pd(CH3)Cl, while for [(L-L)Pd(CH3)(CH3CN)]+SO3CF3- the rate decreased in the order bpy > dppp > PC3N > PAN > dppe. Some general considerations are presented to rationalize the trends in the rates.