UPS STUDY OF COMPOUNDS WITH METAL-SILICON BONDS - M(CO)(N)SICL3 (M=CO, MN, N=4, 5) AND FE(CO)(4)(SICL3)(2)

The (trichlorosilyl) (and -germyl)metal carbonyls Co(CO)(4)SiCl3, Co(C O)(4)GeCl3, Mn(CO)(5)SiCl3, and cis-Fe(CO)(4)(SiCl3)(2) have been synt hesized in high yields. He I photoelectron spectra (UPS) of the comple xes have been measured and interpreted on the basis of empirical argum ents and density functional theory (DFT) calculations. For cis/trans-F e(CO)(4)(SiCl3)(2) isomers the calculations predict the trans-isomer t o be more stable than cis by 15.2 kJ mol(-1). The cis-isomer is exclus ively present in the solid state and in the gas phase. UPS results sug gest the importance of charge polarization effects and the lack of pi- back-donation along TM-Si bonds. The calculated M-Si bond distances am ounted to 2.34 Angstrom (Co-Si), 2.43 Angstrom (Co-Ge), 2.47 Angstrom (Mn-Si), 2.41 Angstrom (trans-Fe-Si), and 2.45 Angstrom (cis-Fe-Si). F or Co(CO)(4)SiCl3, the DFT calculated Co-Si bond dissociation energy w as 317.7 kJ mol(-1), compared to 222.2 kJ mol(-1) for Co-C energy in C o(CO)(4)CCl3.