MeCpor Cp(CO)2Mn(H)SiR3 complexes (Cp = ~LCsHs, MeCp = ~IS-MeCsH4) are particularly well suited for investigating metal-hydrogen-silicon two-electron three-center bonding (4'5), since bonding in the Mn-H-Si triangle can be tuned by varying the substituents at silicon (R) (3' 5, 6). In order to study the influence of the metal on the three-center bond, we have now prepared a series of MeCp(CO)(L)Mn(H)SiR3 complexes, in which the electronic nature of the ligand, L, modifies the electron density at the metal. In Cp(CO)~Mn(H)SiR3 complexes a carbonyl ligand cannot be replaced by another ligand, L (~' 6). Instead, in the reaction with phosphines the silane HSiR3 is reductively eliminated and Cp(CO)2Mn-phosphine complexes are formed. In a different approach we reacted MeCp(CO)2MnL complexes [L = PMe3, PBu~, PPh3, P(OEt)3, P(OPh)3] photochemically with PhzSiH2 in hydrocarbon solution at ca . 10 ~ and obtained chiral MeCp(CO)(L)Mn(H)SiHPh2 (see Table 1) in high overall yields. For L = PPh3 we observed additional formation of the dicarbonyl hydrido silyl complex, MeCp(CO)2Mn(H)SiHPh2 by initial photochemical phosphine elimination from MeCp(CO)2MnPPh3 (7). When MeCp(CO)2MnPPr~ or MeCp(CO)2MnP(C6Hll)3 were reacted analogously with Ph2SiH2, only a small amount of MeCp(CO)zMn(H)SiHPh2, but no MeCp(CO)(L)Mn(H)SiHPh2 was formed. The different chemical behaviour of the latter phosphine complexes suggests that photochemical reaction of MeCp(CO)2MnL complexes with silanes is controlled mainly by steric rather than by electronic effects. Taking Tolman's cone