Neutral and cationic mono- and bis-N-heterocyclic carbene complexes derived from manganese and rhenium carbonyl precursors

Synthesis of the manganese and rhenium bis-NHC complexes fac-M((IPr2Me2)-Pr-i)(2)(CO)(3)X ((IPr2Me2)-Pr-i = 1,3-diisopropyl-4-5-dimethylimidazol-2-ylidene; M = Mn, X = Br, 1; M = Re, X = Cl, 2) is achieved by treatment of M(CO)(5)X with 2 equiv of the free carbene. Halide abstraction by NaBAr4F (BAr4F = B{C6H5(3,5-CF3)(2)}(4)) yields the spectroscopically characterized agostic species [M((IPr2Me2)-Pr-i)(2)(CO)(3)]BAr4F (M = Mn, 3; M = Re, 4). These react rapidly with CO to form the tetracarbonyi compounds cis-[M((IPr2Me2)-Pr-i)(2)(CO)(4)]BAr4F (M = Mn, 5; M = Re, 6). Addition of 1 equiv of IPr (1,3-bis(2,6-diisopropylphenypimidazol-2-ylidene) to M(CO)(5)X yields the moriocarbene complexes M(IPr(CO)(4)X (M = Mn, 8; M = Re, 9), which, in the case of Re, affords the dichloromethane complex [Re(IPr)(CO)(4)(CH2Cl2)]BAr4F (11) upon reaction with AgOTf/NaBAr4F. Removal of halide from 8 and 9 by AgOTf/NaBAr4F in the presence of CO affords the cationic pentacarbonyl species [M(IPr)(CO)(5)]BAr4F (M = Mn, 13; M = Re, 14). Complexes 1, 2, 5, 6, 8, 9, 11, 13, and 14 have all been structurally characterized.