Organosilicon azoles: Structure, silylotropy and NMR spectroscopy

The present review summarizes comprehensive data (from the author's work and the literature) on structure and silylotropy rearrangements of organosilicon azoles (pyrazoles, imidazoles, thiazoles, 1,2,3- and 1,2,4-triazoles, tetrazoles and benzazoles) and related compounds by multinuclear 1H, 13C, 15N and 29Si NMR spectroscopy. Special emphasis is given to studies of silylated azoles by dynamic NMR spectroscopy. The structure of C- and N-trimethylsilyl derivatives of azoles, their bistrimethylsilyl analogs, and bicyclic organosilicon derivatives of azoles are discussed. The influence of the nature of the heterocycle and substituent on the equilibrium constants and the values of free activation energy of silylotropic transformations are analyzed. The catalytic effect of halogens and trimethylhalogensilanes on the silylotropy processes in N-trimethylsilylazoles is covered in detail. Critical analysis of literature data on structure of silicon-containing azoles is presented.