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

Titanocene-Based Acetophenone Enolates: Synthesis and Structural Characterization of Mono, Bis, and Cationic Forms of Titanium Enolates and Some Aspects of Their Reactivity

The reaction of [cp2TiCl2] with potassium enolates derived from 2-MeOC6H4-COMe, 2, 4, 6-Me3C6H2COMe, and KH led to the metal–enolates [2-MeOC6H4C(CH2)OTi-(Cl)cp2](1), [2, 4, 6-Me3C6H2C(CH2)CTi(Cl)cp2] (2), and [{2-MeOC6H4C(CH2) 0}2Ticp2] (3) where the enolate is η1-O-bonded to the metal and the o-methoxy group does not interact with the metal. In order to increase the acidity and the template properties of the metal, complex 2 was ionized with CF3SO3Ag and AgBF4. The cationic form of 2 readily reacts with cyclohexanone to give [2, 4, 6-Me3C6H2C(O)CH=C6H10] (6) and a titanium oxo species. The cationic form, however, was isolated as an isocyanide adduct with ButNC, [2, 4, 6-Me3C6H2C(CH2)OTi-(CNBut)cp2]+X−(X− = CF3SO3, 8; X− = BF4, 9). The increased reactivity of the enolato functionality in the cationic form of 2 is demonstrated in the reaction with acetonitrile and benzonitrile, where the binding of the nitrile prompted attack by the nucleophilic enolate on the nitrile. The reaction led to β-keto enamine derivatives N, O-bonded to the [cp2Ti]2+ fragment, [2-MeOC6H4C(O) CH=C(Me) NHTicp2]+CF3SO3-(13) and [2, 4, 6-Me3C6H2C(O)CHC(R)-NHTicp2]+CF3SO3-(R = Me, 14; R = Ph, 15). Crystallographic details: 1 is orthorhombic, space group P212121, a = 7.690(1) Å, b = 14.113(2) Å, c = 15.685(2) Å, a = β = γ = 90°, Z = 4, and R = 0.034; 3 is orthorhombic, space group Aba2, a = 9.472(1) Å, b = 20.257(2) Å, c = 12.378(1) Å, α = β = γ = 90°, Z = 4, and R = 0.045; 14 is monoclinic, space group P21/n, a = 7.765(6) Å, b = 18.386(3) Å, c = 17.677(3) Å, α = γ = 90°, β = 100.6(3)°, Z = 4, and R = 0.088