HYDRIDE ION TRANSFER FROM CARBON-HYDROGEN BONDS TO CS2, COS, AND CO2 - SYNTHESIS, REACTIVITY, AND STRUCTURE OF (ETA-5-C6MENH7-N)MN(CO)LL' DERIVATIVES

A series of manganese complexes, endo-(eta5-C6MenH7-n)Mn(CO)LL' (n = 0 , 3,6; L, L'= CO, PR3), transfer hydride ion to CS2 and COS in THF to produce HCS2- and HC(O)S-, respectively, and the cation [(eta6-C6MenH6 -n)Mn(CO)LL']+. In THF, endo-(eta5-C6Me6H)Mn(CO)LL' (where L = CO and L' = P(OMe)3 (8c); L and L' = P(OMe)3 (12)) transfers hydride ion to C O2 to form HCO2-. The cationic precursors to these complexes, [(eta6-C 6MenH6-n)Mn(CO)LL']PF6 (n = 0, 3, 6; L, L' = CO, PR3), are prepared by the reaction of [(eta6-C6MenH6-n)Mn(CO)3]PF6 with Me3NO and PR3. The addition of borohydride reagents to these cations results in formation of the cyclohexadienyl complexes endo-(eta5-C6MenH7-n)Mn(CO)LL'. Kine tic data for the reaction of endo-(eta5-C6MenH7-n)Mn(CO)LL' with CS2 u nder pseudo-first-order conditions are presented. The rate data correl ate with the relative amounts of electron density on the metal, as ref lected in the carbonyl stretching frequencies, nu(CO). The methylated cyclohexadienyl complexes increase in reactivity as the relative elect ron density in the complex increases. Non-methylated complexes (eta5-C 6H7)Mn(CO)2L (L = CO, PR3) show no reactivity with CS2. Reactions of e ndo-(eta5-C6Et6H)Mn(CO)2PMe3 and two isomers of (eta5-C6Me3H4)Mn(CO)2P Me3 with CS2 are discussed. A stereoelectronic argument is presented t o explain the 3 x 10(4) rate enhancement of hydride ion transfer accom panying phosphine substitutions for carbonyls. The structures of two c omplexes, determined by X-ray analysis, are reported: 8c, orthorhombic , space group P2(1)2(1)2(1), a = 8.945 (6) angstrom, b = 12.911 (4) an gstrom, c = 16.528 (6) angstrom, Z = 4, R1 = 0.025 for 3861 averaged o bserved reflections; 12, triclinic, space group P1BAR, a = 10.606 (4) angstrom, b = 14.056 (8) angstrom, c = 16.162 (7) angstrom, 92.45 (5)d egrees, beta = 97.27 (4)degrees, gamma = 91.44 (6)degrees, Z = 4, R1 0 .055 for 4468 averaged observed reflections.