[3 + 2] cycloaddition of azido-bridged molybdenum(ii) complex with nitriles and alkynes
You-Xuan Chen1, Hsueh-Hui Yang2, Yu-Liang Lin1
1Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan, Republic of China. fcliu@gms.ndhu.edu.tw.
Abstract:
The azido-bridged molybdenum complex [N(CH3)4][(μ1,1-N3)3{Mo(η3-C3H5)(CO)2}2], 1, was synthesized and its reactions with unsaturated nitriles and alkynes were investigated. The isolated [3 + 2] cycloaddition products were the N(2), N(3) bound tetrazolate complexes [N(CH3)4][(μ1,1-N3)2(μ-N4C{R}-κ2N2:N3){Mo(η3-C3H5)(CO)2}2] (R = C(CN)C(CN)2 (2), C6H4NO2, (3)) and [N(CH3)4][(μ-N4C{R}-κ2N2:N3)2(μ1,1-N3){Mo(η3-C3H5)(CO)2}2] (R = C(CN)C(CN)2 (4), C6H4NO2 (5)), and the N(1), N(2) bound triazolate complexes [N(CH3)4][(μ-N3C2{R}2-κ2N1:N2)(μ1,1-N3)2{Mo(η3-C3H5)(CO)2}2] (R = CO2CH3 (6) and R = CO2CH2CH3 (7). The reactivity of these cycloaddition reactions could be determined by the electronic properties of both metal azide and dipolarophile. In the reaction of 1 with nitriles, at most two bridging azido groups can participate in the cycloaddition reactions and elevated temperature is required for the preparations of 3 and 5. In the case of alkynes, only one azido group is active for the reaction. These complexes are fluxional in solution, and isomers were found in 3 and 5. The molecular structures of the above complexes were determined by single-crystal X-ray diffraction analysis, which reveals a distorted octahedral geometry around each molybdenum atom, and the two metal atoms are connected through three bridging ligands. The formation of these heterocycles demonstrated the [3 + 2] cycloaddition reaction could also be applied to the less electron-rich azido-bridged molybdenum complex.
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