Kinetics and Mechanism of Nucleophilic Substitutions on Coordinated Polyenes and Polyenyls. 3. Activation of η5-Cyclopentadienyl Ligands toward Nucleophilic Attack through η5 → η3 Ring Slippage and a Comparison with Reaction at C5H4O in [Ru(η5-C5H5)(η4-C5H4O)(L)]+ (L = CH3CN, Pyridine, Thiourea)

Complexes of the types [Ru(η5-C5H5)(η4-C5H4O)]2(CF3SO3)2 (1) and [Ru(η5-C5H5)(η4-C5H4O)(L)]CF3SO3 (L = CH3CN (2), pyridine (3), thiourea (4)) react with tertiary phosphines to give (i) 1,1‘- (12) or (ii) 1,2-disubstituted ruthenocenes (13) depending primarily on the basicity of the entering phosphine and the nature of L. Path i proceeds via the intermediacy of [Ru(η3-C5H5)(η4-C5H4O)(PR3)]2 2+ (5) and [Ru(η3-C5H5)(η4-C5H4O)(PR3)(L)]+ (6−8); i.e., the hapticity of the C5H5 ligand is changed from η5 to η3 while forming an additional Ru−P bond. The η3 bonding mode was established by 1H and 13C{1H} NMR spectroscopies. The kinetics of these reactions were studied in detail, providing enthalpies and entropies of both activation and reaction. The conversions to 6−8 are exothermic (ΔH° = −5.5 to −16.9 kcal mol-1) but entropically unfavorable (ΔS° = −44.8 to −19.0 cal K-1 mol-1). The activation parameters and rate constants vary little with the phosphine, suggesting a preequilibrium between η5 and η3 species of the starting complexes where the latter reacts with the entering phosphine in the rate-determining step. The new η3-C5H5 complexes are, with the exception of 5, fluxional in solution due to an intramolecular enantiomeric equilibrium likely proceeding through a five-coordinate η1-C5H5 intermediate. Path ii proceeds via η3-cyclopentenoyl complexes of the type [Ru(η5-C5H5)(η3-C5H4O-2-PR3)(L)]+ (9−11). Furthermore, 3 and 4 react with small and basic phosphines PR3 = PMe3 and Me2PCH2PMe2 to give the half-sandwich complexes [Ru(η5-C5H4OH)(PR3)2L]+ (14, 15) together with free C5H4PR3 (16).