Synthesis, Characterization, and Equilibrium Studies of Group 6B Intramolecular Metalloesters: Crystal Structure of trans-(η5-C5H4)CH2CH2O2CW(CO)2PPh3

Article abstract of DOI:10.1021/ja00333a033

Treatment of <(η⁵-C5H4CH2CH2OH)M(CO)3PR3>⁺BF4^- (1a-d, M = Mo, W; R = Ph, p-tolyl) with base affords solely the neutral intramolecular metalloester, trans-(η⁵-C5H4)CH2CH2O2CM(CO)2PR3 (2).The X-ray structure of 2b (M = W; R = Ph) (space group P2₁/n, a = 8.127 Angstroem, b = 16.823 Angstroem, c = 17.623 Angstroem, β = 101.980 deg, V = 2357 (1) Angstroem³, Z = 4) was solved by heavy-atom and Fourier methods and refined by full-matrix least squares to S (goodness-of-fit) = 1.27 and R = 0.043 (5728 reflections).The structural results indicate that there is little or no strain upon coordination of the Cp and ester groups when coupled with the ethylene bridge.Equilibrium studies indicate that ΔH⁰ and ΔS⁰ are -1.1 +/- 0.6 kcal/mol and 3.2 +/- 2.0 eu and -1.9 +/- 0.2 kcal/mol and 4.5 +/- 0.6 eu for 2c (M = Mo; R = p-tolyl) and 2d (M = W; R = p-tolyl), respectively, for the reaction with MeOH in benzene to form the methyl ester and regenerate the alcohol-substituted Cp.Treatment of the analogous compound (1g), in which the alcohol is connected to the Cp by CH2, with methoxide yields an intramolecular metalloester (3) as well.Equilibrium data indicate that the intramolecular metalloester is more stable than the methyl ester, K_eq -1.The contrasting compounds with the (CH2)3 bridge (1e and 1f) yield only the intermolecular methyl esters (5e and 5f).The equilibrium constants are estimated to be >/=230 M^-1 (5e) and >/=117 M^-1 (5f).