ELECTRONIC-STRUCTURE FACTORS OF SI-H BOND ACTIVATION BY TRANSITION-METALS - VALENCE PHOTOELECTRON-SPECTRA OF (ETA-5-C5H4CH3)MN(CO)(PME3)HSICL3 AND (ETA-5-C5H4CH3)MN(CO)(PME3)HSIHPH2 (ME = CH3, PH = C6H5)

The valence photoelectron spectra of (η5-C5H4CH3)Mn(CO)(L)HSiCl3 and (η5-C5H4CH3)Mn(CO)(L)HSiHPh2, where L is CO or P(CH3)3, are compared to determine the effect of ligand substitution at the metal center on Si–H bond activation. Metal centers that are more electron rich may promote more complete oxidative addition of the Si–H bond to the metal. The shifts in the metal and ligand ionization energies and the relative intensities of ionizations in the He I and He II photoelectron experiments show that the metal in (η5-C5H4CH3)Mn(CO)(PMe3)HSiCl3 is best represented by a formal oxidation state of III (d4 electron count). This indicates nearly complete oxidative addition of the Si–H bond to the metal center and results in independent Mn–H and Mn–Si bonds. In contrast, the splitting and intensity pattern of the metal-based ionizations of (η5-C5H4CH3)Mn(CO)(PMe3)-HSiHPh2 reflect the formal d6 electron count of a metal corresponding to oxidation state I. The extent of electron charge density shift from the metal to the ligand is also small, as evidenced by the negligible shifts of these ionizations from those of the related (η5-C5H4CH3)Mn(CO)2(PMe3) complex. These observations indicate that the electronic structure of the Si–H interaction with the metal in this complex is in the initial stages of Si–H bond addition to the metal, before oxidative addition has become prevalent. Comparison with the previously reported photoelectron spectra of (η5-C5H5)Mn(CO)2HSiCl3 and (η5-C5H4CH3)Mn(CO)2HSiHPh2 shows that the Si–H bond interaction with the transition metal is affected more by alkyl and halogen substitutions on silicon than by substitution of a carbonyl with typical two-electron donor ligands at the metal center. © 1990, American Chemical Society. All rights reserved.