Chemistry of [(1H-hydronaphthalene)Mn(CO)3]:: The role of ring-slippage in substitution, catalytic hydrosilylation, and molecular crystal structure of [(η3-C10H9)Mn(CO)3P(OMe)3]

Reaction of [(eta(5)-C10H9)Mn(CO)(3)] (1) with L produced [(eta(3)-C10H9)Mn(CO)(3)L] (2, L = P(OMe)(3); 5, L = CO) in high yields. X-ray structural analysis of 2 confirmed an eta(3)-bonding mode of the 1-hydronaphthalene ring. Thermal treatment of 2 led to [(eta(5)-C10H9)Mn(CO)(2)P(OMe)(3)] (3). The eta(5)-1-hydronaphthalene ring in 1 is quite easily ring-slipped, eta(5)<-->eta(3). A kinetic study of the reaction of 1 with P(OMe)3 indicates that formation of 2 is first order in 1 and first order in P(OMe)3 with the following activation parameters: Delta H double dagger = 6.9 +/- 0.4 kcal/mol; Delta S double dagger = -32.6 +/- 1.5 eu. Quantitative comparison between the reactivity of the indenyl complex [(eta(5)-C9H7)Mn(CO)(3)] with P(OEt)(3) and 1 with P(OMe)(3) at 130 degrees C shows that the rate constant for 1 is 2 x 10(6) times faster than that of the indenyl complex. The tremendous rate enhancement in 1 was rationalized as a stabilization of 2 by the second benzene ring. The facile ring-slippage in 1 has been utilized in the synthesis of [(eta(6)-C10H8)Mn(CO)(2)P(OMe)(3)]BF4 and in the catalytic hydrosilylation of ketones. Complex 1 is an effective catalyst for the hydrosilylation of alkyl and aryl ketones with Ph2SiH2 as a silane source. The indenyl complex [(eta(5)-C9H7)Mn(CO)(3)] has no catalytic activity in the hydrosilylation of ketones. The facile ring-slippage in the eta(5)-1-hydronaphthalene ring plays a crucial role in the chemistry of 1.