The oxidative addition of XRCN to PtL4 yields cis-and/or trans-F'tX(RCN)L, (X = C1, Br; R = (CHS)~, n = 1, 2, 3; L = PPh,, PPh,CH,, AsPh,). L is readily displaced by more basic phosphines or by a diphosphine. In each case the trans complex is the thermodynamically more stable isomer and cis-lrulzs isomerization catalyzed by free L occurs in dichloromethane.Insertion of CO in the u Pt-C bond takes place quantitatively in the case of cyanoethyl and cyanopropyl. Abstraction of X by AgBF, gives cis or tralzs cationic complexes with N-bonded CN group.Abstracted from the Ph.D Thesis of J . Renaud, University of Lausanne. Present address :