KINETICS AND CONFORMATION IN THE REVERSIBLE INSERTION OF AN ALKENE INTO A PLATINUM CARBON BOND IN A CHELATED (PENTENYL)PLATINUM COMPLEX

The synthesis and characterization, including detailed H-1, H-2, P-31, and C-13 NMR analysis of [(1,1-dideuterio-2,2-dimethyl-4-penten-1-yl-kappa3C1,4,5)(dmpe)PtII]BF4, 1-alpha-d2, and its 3,3-dideuterio isotopomer, 1-gamma-d2 (dmpe = 1,2-bis(dimethylphosphino)ethane), are described. Thermolysis of each 1-alpha-d2 and 1-gamma-d2 was carried out at 125-degrees-C in several solvents to yield a 1/1 mixture of 1-alpha-d2 and 1-gamma-d2. The rate of rearrangement is cleanly first order. Thermolysis of 1-alpha-d2 between 81 and 125-degrees-C in methylene chloride led to determinations of activation parameters, E(a) = 31.8(0.6) kcal/mol and DELTAS(double dagger) = -0.5(1.6) eu (100-degrees-C). An X-ray crystal structure determination was carried out on the compound. It crystallizes in the monoclinic space group P2(1)/n (No. 14), with a = 19.337(11) angstrom, b = 6.948(4) angstrom, c = 17.260(9) angstrom, beta = 122.34(6)degrees, V = 1959.3 angstrom, and Z = 4. The structure was solved with heavy atom techniques and refined to a final R factor of 4.18%. In the solid state, the coordinated vinyl group is slipped slightly out the plane of the molecule and is canted at a dihedral angle of 52-degrees from the molecular plane. The chelate ring shows only very slight distortions from a presumed strain-free shape. 2D NOESY spectra suggest that the in-plane conformation of the pentenyl chelate is at least partly populated in solution. (dmpe)Pt(CH2-c-C4H7)Cl, 11, was prepared. Thermolysis of 11 at 110-degrees-C yielded intractable metal-containing materials along with methylenecyclobutane and methylcyclobutane together in ca. 60% yield as the only identifiable organic products. Treatment of 11 with silver ion at low temperatures in acetone or methylene chloride yielded two products in a 1:7 (NMR) ratio, methylenecyclobutane and a material stable only below 0-degrees-C that is assigned the structure [(4-penten-1-yl-kappa3C1,4,5)(dmpe)PtII]BF4 on the basis of its NMR spectrum.