Add time:09/10/2019         Source:sciencedirect.com

The photogeneration mechanism of a series of 21 bis-nitrile imines with different types of linkage, and their subsequent thermal reactions, especially cycloadditions, are investigated by means of stationary and time-resolved methods. The short-living nitrile imines are efficiently photo-generated from the corresponding bis-2H-tetrazoles. Directly linked bis-2H-tetrazoles decompose according to a two-photon mechanism with different quantum yields of both steps. Both the transient bis-nitrile imines and the tetrazolyl-nitrile imines are indirectly detectable as their cycloaddition products tetrazolyl-Δ2-pyrazolines and bis-Δ2-pyrazolines. Exclusively, the formation of bis-Δ2-pyrazolines is detectables with all other bis-2H-tetrazoles. Quantum yields depend on the type of linkage. The decay kinetics of the bis-nitrile imines were investigated with the help of conventional flash photolysis. The rate of the cycloaddition to methylmethacrylate is discussed as a function of the linkage type and of substitution. Activation parameters of these reactions were determined.The Arrhenius parameters determined for the carbonyl-linked bis-nitrile imines under the variation of the solvent may suggest a non-concerted mechanism.

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