Reaction of Metal Carbonyls with Naked Enolates to Make a Metallocarbene Enolate and Alkylcarbonylmetalates

The KH-mediated deprotonation of acetophenone and propiophenone in THF led to the ion-pair and naked forms of the following crystalline enolates in good yield: ArC(CH2)0 ... K-(18-crown-6) [Ar = Ph, 4; 2-MeOC6H4, 5; 1,3,5-Me3C6H2,6], [PhC(CH2)0][K(kryptofix-2,2,2)], 7, and [PhC(--CHMe)O ... K(18-crown-6)], 8. The reaction of ion-pair 4 with [Cr(CO)5(THF)] led to the isolation of an alkylcarbonylmetalate, 9, [PhC(O)CH2Cr(CO)4CO ... K(18-crown-6)]n, a crystalline polymer in which the [PhC(O)CH2Cr(CO)5]- anion is bridged by [K(18-crown-6)]+ via the oxygen of the enolate and one of the carbonyl oxygens. The protonation of the Fischer carbene [(CO)5Cr=C(OMe)Me], 10, led to an alkylcarbonylmetalate analogue of 9. The X-ray analysis of [CH2(OMe)CCr(CO)4CO ... K(18-crown-6)], 11, revealed a decrease in the Cr-C(carbene) bond distance, and electron transfer from the anionic carbene to the trans CO. The trans Cr-C-0 has an increased Cr-C bond length, a decreased C-O bond length, and a Cr-C-O angle of 159.7(6)-degrees. The reaction of 4 with [Cr(CO)6] led to a Fischer-type metallacarbene, 12, from attack of the enolate on carbon monoxide; 12 was deprotonated by starting material to a dianionic metallacarbene enolate [(CO)5Cr--C(O-)CH=C(O-)Ph], 13. The alkylation and silylation of 13 led to the corresponding alkylated and silylated forms of 13, [(CO)5Cr=C(OMe)-CH=C-(OMe)Ph], 16, and [(CO)5Cr=C(OSiR2R')-CH=C(OSiR2R')Ph] [R = R' = Me, 17; R = Me, R' = Bu(t), 18]. An analogous metallacarbene enolate and its silylated form have been obtained for tungsten, [(CO)5W=C(O-)CH=C(O-)Ph ... {K(18-crown-6)}2], 19, and [ (CO)5W=C(OSiMe3)-CH=C(OSiMe3)Ph], 20. The reaction of the naked enolate 7 and [Cr(CO)6] led to a metallacarbene enolate which, due to the absence of stabilization by ion-pair formation, is much less stable than 13 or 19. Crystallographic details are as follows: 4 is monoclinic, space group P2(1)/n, a = 10.109(1) angstrom, b = 9.041(1) angstrom, c = 24.935(2) angstrom, beta = 96.94(l)-degrees, Z = 4, and R = 0.053; 7 is monoclinic, space group P2/n, a = 17.473(2) angstrom, b = 10.615(1) angstrom, c = 16.133(2) angstrom, beta = 99.75(1)-degrees, Z = 4, and R 0.040; 8 is monoclinic, space group P2(1)/c, a = 14.285(3) angstrom, b = 16.714(2) angstrom, c = 10.381(4) angstrom, = 107.88(2)-degrees, Z = 4, and R = 0.0 51; 9 is triclinic, space group P1BAR, a = 10.649(l) angstrom, b = 14.122(1) angstrom, c = 10.635(1) angstrom, alpha = 94.64(l)-degrees, beta = 98.04(l)-degrees, gamma = 108.81(l), Z = 2, and R = 0.031; 11 is triclinic, space group P1BAR, a 14.029(1) angstrom, b = 12.355(1) angstrom, c = 8.995(1) angstrom, a = 91.82(l)-degrees, beta = 91.17(l)-degrees, gamma = 91.89(l)-degrees, Z = 2, and R = 0.051.