Abstract
The standard molar enthalpies of formation, at 298.15 K, of five crystalline bent metallocenes, [M(η-C5H5)2L] (M = Mo, W, Ti) (LH2 = 1,2-benzenediol, C6H4-(OH)2; 2,3-napthalenediol, C10H6(OH)2; 9,10-phenanthrenediol, C14H8(OH)2), have been derived from enthalpies of hydrolyses in acid solution measured by precision solution-reaction calorimetry. The results were: ΔHf° [Mo(η-C5H5)2(O26H4),c] = -130.6±2.9, ΔHf°[Mo(η-C5H5)2(O2C10H6),c] = -80.3± 2.2, ΔHf° [ Mo(η-C5H5)2(O2C14H8,c] = -53.25 ± 10.4, ΔHf° [ W(η-C5H5)2 (O2C6H4),c] = -112.8 ±2.9, ΔHf° [Ti(η-C5H5)2(O2C14H8),c] = -322.6 ± 12.7 kJ mol-1. The metaloxygen bond strengths were evaluated as mean bond enthalpy terms (E). Comparison with corresponding values in similar comlexes reveals that small steric energy arises from the binding of a catechol type ligand to a metal atom. © 1988.