UPS Study of Compounds with Metal−Silicon Bonds: M(CO)<i>_n</i>SiCl₃ (M = Co, Mn; <i>n</i> = 4, 5) and Fe(CO)₄(SiCl₃)₂

Abstract

The (trichlorosilyl) (and -germyl)metal carbonyls Co(CO)4SiCl3, Co(CO)4GeCl3, Mn(CO)5SiCl3, and cis-Fe(CO)4(SiCl3)2 have been synthesized in high yields. He I photoelectron spectra (UPS) of the complexes have been measured and interpreted on the basis of empirical arguments and density functional theory (DFT) calculations. For cis/trans-Fe(CO)4(SiCl3)2 isomers the calculations predict the trans-isomer to be more stable than cis by 15.2 kJ mol-1. The cis-isomer is exclusively present in the solid state and in the gas phase. UPS results suggest the importance of charge polarization effects and the lack of π-back-donation along TM−Si bonds. The calculated M−Si bond distances amounted to 2.34 Å (Co−Si), 2.43 Å (Co−Ge), 2.47 Å (Mn−Si), 2.41 Å (trans-Fe−Si), and 2.45 Å (cis-Fe−Si). For Co(CO)4SiCl3, the DFT calculated Co−Si bond dissociation energy was 317.7 kJ mol-1, compared to 222.2 kJ mol-1 for Co−C energy in Co(CO)4CCl3.