Trichlorostannyl complex Co(SnCl 3 )(CO) 2 (PPh 3 ) 2 (1) was prepared by allowing the chloro compound CoCl(CO) 2 (PPh 3 ) 2 to react with SnCl 2 ·2H 2 O. Instead, treatment of the iodo complex CoI(CO) 2 [PPh(OEt) 2 ] 2 with SnCl 2 ·2H 2 O afforded a mixture of Co(SnCl 2 I)(CO) 2 [PPh(OEt) 2 ] 2 (2a) and Co(SnCl 3 )(CO) 2 [PPh(OEt) 2 ] 2 (2b) derivatives. Trichlorogermyl complexes Co(GeCl 3 )(CO) 2 L 2 (3, 4) [L = PPh 3 , PPh(OEt) 2 ] were prepared by allowing halo compounds CoX(CO) 2 L 2 (X = Cl, I) to react with GeCl 2 ·dioxane. Treatment of trihalostannyl complexes Co(SnCl 2 X)(CO) 2 L 2 (1, 2) (X = Cl, I) with NaBH 4 in ethanol yielded tin trihydrido derivatives Co(SnH 3 )(CO) 2 L 2 (5, 6). Instead, reaction of Co(SnCl 2 X)(CO) 2 [PPh(OEt) 2 ] 2 (2) with LiAlH 4 in THF yielded the hydrido CoH(CO) 2 [PPh(OEt) 2 ] 2 (7). Trimethylstannyl Co(SnMe 3 )(CO) 2 L 2 (8, 9) and trialkynylstannyl derivatives Co[Sn(CCPh) 3 ](CO) 2 L 2 (10, 11) were prepared by allowing trihalostannyl compounds Co(SnCl 2 X)(CO) 2 L 2 (1, 2) to react with MgBrMe and with Li + (PhCC) − , respectively, in THF. The complexes were characterised by spectroscopy (IR and 1 H, 31 P, 13 C, 119 Sn NMR) and by X-ray crystal structure determination of Co(SnCl 2 X)(CO) 2 [PPh(OEt) 2 ] 2 (2) and Co(GeCl 3 )(CO) 2 [PPh(OEt) 2 ] 2 (4).