Complexes of the type (η5-CH3C5H4)(CO)2Mn(H)SiR1R2X where R1=phenyl, R2=1-naphthyl, and X=hydrogen, chlorine, fluorine, or methoxy have been prepared, and their chemical behavior has been studied. The different types of reactions they undergo are the following: (i) deinsertion reactions with formation of R1R2Si(H)X, (ii) cleavage of the Mn-Si bond with water or methanol, (iii) substitution reactions at silicon without cleavage of the Mn-Si bond, (iv) formation of salts by abstraction of H+, and (v) reaction with LiAlH4, which leads first to reduction of the function X and then to formation of the anion [(η-CH3CsH4(CO)2MnSiR1H2]-. © 1979, American Chemical Society. All rights reserved.