The carbene complexes cis-[PtCI,(PR,)(C(OR')(CH,R"))](1 ; R, = Me,Ph or Et,; R' = Me, Et, or Pr"; R" = Me, Et, or Ph) react rapidly with CD,OD to yield cis-[PtCI,(PR,){C(OR') (CD,R"))], then slowly by alkoxy-group exchange to cis-[PtCI,(PR,)(C(OCD,) (CD,R"))].Dimethylamine reacts by proton abstraction to form [PtCI-(PR,) (NMe,H){C(OR')=CHR"}].The carbene complexes react with chloride ions by R'CI elimination to form the acyls [Pt?(p-CI),(PR,),(COCH,R"),].Thermolyses of (1 ) produce the same products. These reactions are compared with those of related cationic carbene complexes. Treatment of (1) by PR, in the presence of Ag-[S(CF,)O,] leads to the cationic carbene complex trans-[PtCI(PR,),(C(OR')(CH,R"))] [S(CF,)O,] which can also be made by the action of R'SO,CF, on trans-[PtCI(PR,),(COCH,R")].