Alkali-metal reductions of various salts containing V(CO)6" in liquid ammonia provide high yields of the "super-reduced" species V(CO)53" which contains vanadium in its lowest known formal oxidation state. Although salts of V(CO)53" containing lithium, sodium, and various onium cations rapidly decompose above 0 °C, the trianion has been isolated and characterized as rather thermally stable rubidium and cesium salts, Rb3V(CO)5 and Cs3V(CO)5. A treacherously shock sensitive potassium salt, K3V(CO)5, is also described. Treatment of liquid ammonia solutions of Na3V(CO)5 with bis(triphenylphosphin)iminium chloride and tetraphenylphosphonium chloride provides thermally unstable, ammonia-insoluble solids believed to contain V(CO)53". These decompose on warming to room temperature to provide V(CO)5PPh3Y Main-group 4 electrophiles, including R3EX (R = alkyl, aryl; E = Sn, Pb; X = halide), react with V(CO)53' to provide moderate to high yields of the new organometallic derivatives, (R3Sn)V(CO)52~a nd (R3E)2V(CO)51". The dianions are the first reported organotin derivatives containing a transition metal in a formally negative oxidation state. Reactions of V(CO)53" in liquid ammonia with weak Bronsted acids including water, ammonium cation, and acetonitrile are also described. High yields (85-95%) of V(CO)5NH3~a re obtained by the treatment of V(CO)s3~i n liquid ammonia with 2 or more equiv of ammonium chloride. This amine-substituted anion is quite unstable in solution at room temperature but may be isolated as thermally stable Ph4As+ or Ph4P+ salts. Substantial interest in the synthesis and chemistry of metal carbonyl anions2,3 and other anionic organometallic compounds of the transition elements4 has developed in recent years. These useful materials are important as precursors to new organometallic and organic compounds,2,3 intermediates in homogeneous catalysis,5 photoactive substrates,6 and models for the study of ion pairing in solution.7,8 Our research group has been particularly interested in these compounds as sources of functional groups ("metalloanalogues") which chemically mimic more familiar electronically equivalent molecular fragments containing only nonmetals.9 Several years ago we recognized that there exist sufficiently far reaching parallels in the reactivity patterns of halides and metal carbonyl monoanions (e.g., Co(CO)4") and chalconides (especially S2") and metal carbonyl dianions (especially Fe(CO)42") to justify considering these transition-metal monoanions and dianions as pseudohalides and pseudochalconides, respectively.2 These ideas also led to the anticipation that previously unknown metal-carbonyl trianions, formally analogous to main-group trianions such as P3', might be stable entities.2,10 In the past several years we have prepared such species as well as more highly reduced materials ("carbonyl tetraanions") and have termed these species "super-reduced" since they contain transition metals in their lowest known formal oxidation states. Solutions of alkali metals in various solvents and sol...
