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Kinetics and mechanisms of the reactions of transient silylenes with amines
Author(s) -
Kostina Svetlana S.,
Singh Tishaan,
Leigh William J.
Publication year - 2011
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1908
Subject(s) - chemistry , silylene , reaction rate constant , diethylamine , amine gas treating , triethylamine , steric effects , kinetics , catalysis , equilibrium constant , medicinal chemistry , photochemistry , stereochemistry , organic chemistry , physics , quantum mechanics , silicon
The N–H insertion reactions of dimethyl‐, diphenyl‐, and dimesitylsilylene (SiMe 2 , SiPh 2 , and SiMes 2 , respectively) with n ‐butylamine (BuNH 2 ) and diethylamine (Et 2 NH) were studied in hexanes by steady‐state and laser photolysis methods. The process begins with the formation of the corresponding Lewis acid–base complexes, which decayed with second‐order kinetics at rates that show modest sensitivity to silylene and amine structures. The complexation process, which was also studied using triethylamine (Et 3 N), proceeds at rates close to the diffusion limit, but the rate constants vary systematically with steric bulk in the amine. Equilibrium constants were determined for the complexation of Et 2 NH and Et 3 N with SiMes 2 , which proceeds reversibly. The complexes of SiMe 2 and SiPh 2 with BuNH 2 and Et 2 NH decayed with pseudo‐first‐order rate coefficients in the 10 4 –10 5 s –1 range. This is consistent with upper limits of about 10 6 M –1 s –1 for the rate constants for amine‐catalyzed H‐migration, which is thought to be the dominant mechanism for product formation from the complexes. The results are compared to published kinetic data for the O–H insertion reactions of these silylenes with alcohols, which also proceeds via initial complexation followed by catalytic proton transfer. The results indicate that catalyzed H‐transfer in the amine complexes is at least 10 4 times slower than the analogous process in silylene–MeOH complexes. The experimental data are compared to the results of theoretical calculations of the SiMe 2 + NH 2 Me and SiMe 2 + MeOH potential energy surfaces, carried out at the Gaussian‐4 and B3LYP/6‐311 + G(d,p) levels of theory. Copyright © 2011 John Wiley & Sons, Ltd.