SYNTHESIS AND STRUCTURES OF (MU-BIS(CARBENE))DIMETAL COMPLEXES OF CHROMIUM AND TUNGSTEN

Treatment of the alpha-lithio carbene anions (CO)5M1[C(X1R)C(R1)(R2)]Li (1) (M1 = Cr, W; X1R = OCH3, OCH2Ph, OCH2CH2Ph, N(CH3)2; R1, R2 = H, CH3, n-C3H7, Si(CH3)3) with the alpha,beta-unsaturated carbene complexes (CO)5M2[C(X2R)C(R4) = CHR3] (2) (M2 = Cr, W; X2R = OCH3, OCH2Ph, N(CH3)2; R3, R4 = H, CH3, Si(CH3)3, (-CH2-)3, (-CH2-)4, (-CH2-)6) produced the intermediate alpha-lithio (mu-bis(carbene))dimetal anions {(CO)5M1[C(X1R)C(R1)(R2)CH(R3)C(R4)C(X2R)]M2(CO)5}Li (3), which were subsequently quenched with various electrophilic reagents E-X (E-X = CH3OSO2CF3, CH2 = CHCH2Br, PhCH = CHCH2Br, PhCH2Br, (CH3)3SiCl, HCl) to afford the (mu-bis(carbene))dimetal complexes (CO)5M1[C(X1R)C(R1)(R2)CH(R3)C(R4)(R5)C(X2R)]M2(CO)5 (4a-z) (R1 = H, CH3, CH2CH = CH2, CH2CH = CHPh, CH2Ph) in 46-78% yields. Along with the desired (mu-bis(carbene))dimetal complexes (4) were produced small amounts of the vinyl ether derivatives (CO)5M1[C(X1R)C(R1)(R2)CH(R3)C(R4) = CH(OCH3)] (5). Complexes 4c-f,h,j-l,r-t,w,x, which each have two asymmetric carbon centers, were produced as one major diasteromer. Complexes 4j (M1 = M2 = W; X1R = X2R = OCH3; R1 = R2 = H; R3, R4 = (-CH2-)3; R5 = CH2CH = CH2), 4s (M1 = Cr, M2 = W, X1R = X2R = OCH3, R1 = R3 = R5 = H, R2 = R4 = CH3), and 4x (M1 = M2 = W; X1R = N(CH3)2; X2R = OCH3; R1 = R2 = H; R3, R4 = (-CH2-)3; R5 = CH2CH = CH2) were also characterized by single-crystal X-ray diffraction methods. Complex 4s crystallizes in the centric Pbca space group with cell constants a = 14.083 (7) angstrom, b = 18.032 (3) angstrom, c = 19.380 (5) angstrom, and D(calcd) = 1.81 g cm-3 for Z = 8. Least-squares refinement based on 2471 independent observed [F-omicron greater-than-or-equal-to 5-sigma(F-omicron)] reflections led to a final conventional R value of 0.044. Complexes 4j and 4x, which differ only in the heteroatom substituent X1R, crystallize in the centric Pbca space group with cell constants a = 11.931 (6) angstrom, b = 14.404 (8) angstrom, c = 31.496 (9) angstrom, and D(calcd) = 2.10 g cm-3 for Z = 8 and monoclinic P2(1)/c space group with cell constants a = 13.931 (3) angstrom, b = 12.729 (2) angstrom, c = 16.032 (2) angstrom, beta = 93.47 (2)-degrees, and D(calcd) = 2.03 g cm-3 for Z = 4, respectively. Both were refined via least squares, 4j to a conventional R value of 0.064 based on 2868 independent observed [F-omicron greater-than-or-equal-to 5-sigma(F-omicron)] reflections and 4x to 0.028 (based on 4037 reflections).