The olefin(ylide) rhodium(I) complexes [(L)( iPr 3PCH 2)Rh(Cl] 2 ( 3: L = C 8H 14; 4: L = C 2H 4) have been prepared from [(L) 2RhCl] 2 ( 1, 2) and CH 2P iPr 3 in almost quantitative yield. Upon treatment of 3 and 4 with LiC 5H 5, the half-sandwich type compounds [C 5H 5Rh(CH 2P iPr 3)(L)] ( 5, 6) are obtained. Compound 5 (L = C 8H 14) reacts with carbon monoxide to give [C 5H 5Rh(CH 2P iPr 3)(CO)] ( 7) and with iodine to give [C 5H 5Rh(CH 2P iPr 3)I 2] ( 8). Displacement of the olefin ligand also occurs upon treatment of 5 with CH 3I, CH 2I 2 and CH 2ClI, leading to the formation of [C 5H 5RhCH 2X(CH 2P iPr 3)I] 9: X = H; 10: X = I; 11: X = Cl). The bis(ylide) rhodium(III) complexes [C 5H 5Rh(CH 2PR 3)(CH 2P iPr 3)I]I ( 12– 14), [C 5H 5Rh(CH 2P iPr 3)(CH 2AsPh 3)I]I ( 5) and [C 5H 5Rh(CH 2P iPr 3)(CH 2NEt 3)I]I ( 16) are obtained by nucleophilic substitution from 10 upon treatment with Pr 3, AsPh 3 and NEt 3, respectively. Reaction of 7 with CH 3I or CD 3I give a mixture of 8 and [C 5H 5RhCX 3(CH 2P iPr 3)(CO)I ( 17a: X = H; 17b: X = D). I contrast, treatment of 7 with dimethylsulfate gives only [C 5H 5RhCH 3(CH 2P iPr 3)-(CO)]SO 4Me ( 17c). The X-ray crystal structure of 17c has been determined. Compound 17c reacts with P iPr 3 to give the acetyl(ylide) rhodium(III) complex [C 5H 5RhCOCH 3(CH 2P iPr 3(P iPr 3)]SO 4Me ( 18).