η-1,2,4,6-Tetramethylcycloheptatrienyl molybdenum chemistry

Abstract

Treatment of [Mo(CO)₆] with 1,3,5,7-tetramethylcycloheptatriene in octane gives a mixture of [Mo(η⁶-C₇H₄Me₄-1,3,5,7)(CO)₃]1, [Mo(η⁶-C₇H₄Me₄-1,2,4,6)(CO)₃]2 and [Mo(η⁶-C₇H₄Me₄-1,3,4,6)(CO)₃]3. The compounds 2 and 3 arise as a result of sequential 1,5-shifts of the 7-endo-hydrogen atom of the initially formed 1. Hydride abstraction from compounds 1–3 by [CPh₃][BF₄] gives [Mo(η⁷-C₇H₃Me₄-1,2,4,6)(CO)₃][BF₄]4. Compound 4 reacts with LiCl to yield [Mo(η⁷-C₇H₃Me₄-1,2,4,6)(CO)₂Cl]5 which reacts with 1 equivalent of Me₂PCH₂CH₂PMe₂(dmpe) to give [Mo(η³-C₇H₃Me₄-1,2,4,6)(dmpe)(CO)₂Cl]7. This is fluxional due to trigonal twist rearrangement and 1,2-shift of metal around the C₇ ring. Photolysis of 7 in toluene produces [Mo(η⁷-C₇H₃Me₄-1,2,4,6)(dmpe)Cl]9. Treatment of 4 with toluene affords the mixed-sandwich compound [Mo(η⁶-C₆H₅Me)(η⁷-C₇H₃Me₄-1,2,4,6)][BF₄]10 which yields [Mo(η⁷-C₇H₃Me₄-1,2,4,6)(CH₃COCHCOCH₃)(PPh₃)]11 upon treatment with sodium pentane-2,4-dionate and triphenylphosphine.