Reactions of $Rh(ClO_4)(CO)(AsPh_3)_2$ with unsaturated nitriles and aldehyde, L, produce a series of new cationic rhodium (I) complexes, $[RhL(CO)(AsPh_3)_2]ClO_4$ (L = $CH_2$ = CHCN, $CH_2$ = C($CH_3$)CN, trans-$CH_3CH$ = CHCN, $CH_2$ = CH$CH_2$CN, trans-$C_6H_5CH$ = CHCN, and trans-$C_6H_5CH$ = CHCHD) where L are coordinated through the nitrogen and oxygen, respectively but not through the ${pi}$-system of the olefinic group. Dissociation constants for the reaction, $[RhL(CO)(AsPh_3)_2]ClO_4$ $ ightleftharpoons$ $Rh(ClO_4)(CO)(AsPh_3)_2$ + L, have been measured to be $1.20{ imes}10^{-4}$ M (L = $CH_2$ = CHCN), $1.05{ imes}10^{-4}$ M (L = $CH_2$ = C($CH_3$)CN, $3.26{ imes}10^{-5}$ M (L = trans-$CH_3$CH = CHCN) and $6.45{ imes}10^{-5}$ M (L = $CH_2$ = CH$CH_2$CN) in chlorobenzene at $25^{circ}C, and higher than those of triphenylphosphine complexes, $[RhL(CO)(AsPh_3)_2]ClO_4$ where L are the corresponding nitriles that are coordinated through the nitrogen atom. The differences in dissociation constants seem to be predominantly due to the differences in ${Delta}H$ (not due to the differences in ${Delta}S$). The weaker Rh-N (unsaturated nitriles) bonding in $AsPh_3$ complexes than in $PPh_3$ complexes (based on ${Delta}H$ values) suggests that the unsaturated nitriles in 2∼5 are good ${sigma}$-donor and poor ${pi}$-acceptor.