SPECTROSCOPIC CHARACTERIZATION AND DYNAMIC PROPERTIES OF CATIONIC ETA(2)-SILANE AND ETA(2)-H-2 COMPLEXES OF GENERAL STRUCTURE CP(CO)(L)FE(HSIR(3))(+) AND CP(CO)(L)FE(H-2)(+) (L=PET(3), PPH(3))

The eta(2)-H-2 complexes Cp(CO)(PEt(3))Fe(H-2)(+), 4, and Cp(CO)(PPh(3))Fe(H-2)(+), 9, were generated by protonation of the neutral monohydride complexes with H(OEt(2))(2)BAr'(4) (Ar' = 3,5-(CF3)(2)CsH3) at -78 degrees C in CD2Cl2. The eta(2)-H-2 bonding mode was verified by observation of J(HD) = 31.6 Hz for 4 and J(HD) = 31.7 Hz for 9 in the eta(2)-HD complexes. The classical trans dihydride Cp(CO)(PEt(3))Fe(H)(2)(+), 5, could be detected at low temperature but converts to the more stable eta(2)-H-2 complex at higher temperatures. The eta(2)-silane complex Cp(CO)(PEt(3))Fe(HSiEt(3))(+), 1, was prepared by protonation of Cp(CO)(PEt(3))FeSiEt(3) with H(OEt(2))(2)BAr'(4), and the nonclassical structure was verified by observation of a Si-H coupling constant of 62.4 Hz. A more convenient and general method involving displacement of H-2 from CP(CO)(PR(3))Fe(H-2)(+) by free silane was used to prepare a series of eta(2)-silane complexes including Cp(Co)(PEt(3))Fe(H(2)SiPh(2))(+), 12, Cp(CO)(PEt(3))Fe(H(2)SiMePh)(+), 13, Cp(CO)(PEt(3))Fe(H(3)SiPh)(+), 16, Cp(CO)(PPh(3))Fe(HSiEt(3))(+), 11, and Cp(CO)(PPh(3))Fe(H(2)SiMePh)(+), 15. Complex 13 exists as a pair of diastereomers which interconvert above -20 degrees C (Delta G(double dagger) = 12.6 kcal/mol). A mechanism involving pseudorotation in an Fe(IV) silyl hydride intermediate, Cp(CO)(PEt(3))-Fe(H)(SiMeHPh)(+), was proposed to account for this dynamic process. Similar dynamic properties were observed for 15 and 16.