Reactions of metal carbonyls. Part VI. Formation of cationic carbonyl salts of manganese-(I) and -(II)

Abstract

The salt fac-[Mn(CO)₃(MeCN)₃]PF₆ has been prepared by heating under reflux [Mn(CO)₅Br] in acetonitrile. It rapidly undergoes substitution of the acetonitrile groups with phosphines and phosphites (L) to give the species fac-[Mn(CO)₃L(MeCN)₂]⁺, fac-[Mn(CO)₃L₂(MeCN)]⁺, cis-[Mn(CO)₂L₂(MeCN)₂]⁺, and mer-cis-[Mn(CO)₂L₃(MeCN)]⁺ under varying reaction conditions. These cations are also formed on treating the complexes [Mn(CO)_5–xL_xBr](x= 1–3) with AgPF₆ in acetonitrile. The dicarbonyl cations cis-[Mn(CO)₂{P(OMe)₂Ph}₂(MeCN)₂]⁺ and mer-cis-[Mn(CO)₂L₃(MeCN)]⁺ are oxidised by NOPF₆ to give trans-[Mn(CO)₂{P(OMe)₂Ph}₂(MeCN)₂]²⁺ and mer-trans-[Mn(CO)₂L₃(MeCN)]²⁺[L = P(OMe)₂Ph and P(OMe)₃]. Hydrazine reduction of the cation mer-trans-[Mn(CO)₂{P(OMe)₃}₃(MeCN)]²⁺ gives mer-trans-[Mn(CO)₂{P(OMe)₃}₃(MeCN)]⁺ which reacts further with P(OMe)₃ to give trans-[Mn(CO)₂{P(OMe)₃}₄]⁺. ¹H N.m.r. resonances of the nitrile methyl groups exhibit some unusual features which are discussed, together with steric factors governing the reactions.