Trichlorostannyl complexes M(SnCl 3 )(Tp)L(PPh 3 ) (1, 2) and M(SnCl 3 )(Cp)L(PPh 3 ) (5, 6) [M ) Ru, Os; L ) P(OMe) 3 (a), P(OEt) 3 (b), PPh(OEt) 2 (c), PPh 3 (d)] were prepared by allowing chloro complexes MCl(Tp)L(PPh 3 ) and MCl(Cp)L(PPh 3 ) to react with an excess of SnCl 2 • 2H 2 O in ethanol. Treatment of trichlorostannyl complexes 1, 2, 5, and 6 with NaBH 4 in ethanol yielded tin trihydride derivatives M(SnH 3 )(Tp)L(PPh 3 ) (3, 4) and M(SnH 3 )(Cp)L(PPh 3 ) (7, 8). Reaction of these complexes with CCl 4 gave the trichlorostannyl precursors 1, 2, 5, and 6. Hydridochlorostannyl intermediates Os(SnH 2 Cl)(Tp)[P(OMe) 3 ](PPh 3 ) (9a) and Os(SnHCl 2 )(Tp)[P(OMe) 3 ](PPh 3 ) (10a) were also obtained. Reaction of trihydridostannyl complexes M(SnH 3 )(Tp)L(PPh 3 ) (3, 4) with CO 2 (1 atm) led to hydridobis(formate) derivatives M[SnH{OC(H)dO} 2 ](Tp)L(PPh 3 ) (11). In contrast, reaction of the related complexes M(SnH 3 )(Cp)L(PPh 3 ) (7, 8) with CO 2 (1 atm) led to the binuclear OH-bridging bis(formate) derivatives [M[Sn{OC(H)dO} 2 (µ-OH)](Cp)L(PPh 3 )] 2 (12, 13). A reaction path for the formation of 12 and 13, involving the mononuclear tin hydride complex M[SnH{OC(H)dO} 2 ](Cp)L(PPh 3 ), is discussed. The X-ray crystal structure of 12b is reported. Chlorobis(methyl)stannyl Ru(SnClMe 2 )(Cp)[P(OEt) 3 ](PPh 3 ) (15b) and trimethylstannyl complexes M(SnMe 3 )(Tp)[P(OMe) 3 ](PPh 3 ) (14a) and M(SnMe 3 )(Cp)[P(OEt) 3 ](PPh 3 ) (16b, 17b) were prepared by allowing trichlorostannyl compounds 1, 2, 5, and 6 to react with MgBrMe in diethyl ether. Trialkynylstannyl derivatives M[Sn(CtCR) 3 }(Tp)L(PPh 3 ) (18, 19) and Ru[Sn(CtCR) 3 }(Cp)[P(OEt) 3 ](PPh 3 ) (20b) (R ) Ph, p-tolyl) were also prepared from the reaction of trichlorostannyl complexes 1, 2, 5, and 6 with Li + (CtCR)in thf. The complexes were characterized by spectroscopy and by X-ray crystal structure determination of Ru(SnClMe 2 )(Cp)[P(OEt) 3 ](PPh 3 ) (15b).