The chemistry of metal carbonyl anions : II. Synthesis and reactions of the pentacarbonylmetallate dianions of chromium, molybdenum, and tungsten with metallic monohalides

Abstract

Alkali metal amalgam reductions of M(CO) 6 in tetrahydrofuran (THF) have provided salts of the pentacarbonylmetallate dianions. Cesium amalgam reacts with M(CO) 6 at room temperature to yield Cs 2M(CO) 5, while sodium or potassium amalgams provide only (Na or K) 2Cr(CO) 5 in good yield in addition to a substantial amount of (Na or K) 2Cr 2(CO) 10. Molybdenum and tungsten carbonyl give primarily (Na or K) 2M 2(CO) 10 in THF even after 24 h of reflux; however, infrared evidence indicates the presence of monomeric dianions in these solutions. Reaction of the monomeric dianions with Ph 3MCl (M = Ge, Sn, Pb) provides air- and moisture-stable substituted carbonyl anions of the type Ph 3MM′(CO) 5 − (M′ = Cr, Mo, W) which have been isolated as tetraethylammonium salts. Pure Na 2Cr(CO) 5, prepared from the interaction of Cr(CO) 6 with sodium metal in liquid ammonia or HMPA, has also been used to provide similar substituted carbonyl anions of the type ECr(CO) 5 − where E = Me 3Sn and C 5H 5Fe(CO) 2. The triphenyltin derivatives have also been prepared independently by the interaction of Ph 3SnLi with M′(CO) 6 in THF at room temperature as well as from the reaction of Ph 3SnCl with M′ 2(CO) 10 2− in THF.