Mono- and di-alkyl-[1,3,5]-dithiazinanes and their N-borane adducts revisited. Structural and theoretical study

Structural analyses of a series of 5-alkyl-[1,3,5]-dithiazinanes [R = Me (1), iPr (2), tBu (3)], their N-BH3 adducts (1BH(3)-3BH(3)) and their 2-alkyl (R') derivatives are reported: R = Me, R' = Me (7); R = Me, R' iPr (8); R = iPr, R' = Me (10); R = tBu, R' = Me (11); and R = Me, R' = nBu (12). The reaction of 2-lithium-5-methyl-[1,3,5]-dithiazinane (4) with I-2 affords the bis-(5-methyl-[1,3,5]-dithiazinan-2-yl) (13). Isostructural compounds: [2,5,5]-trimethyl-[1,3,5]-dithiazinan-5-ium iodide (14), 5-borane-2,5-dimethyl-[1,3,5]-dithiazinane (15) and 2,5,5-trimethyl[1,3,5,6]-dithiazaborata (16) are compared. Structures of 7,8 and 10-13 were determined by B-11, C-13 and H-1 NMR and the X-ray diffraction analyses of 2, 1BH(3), 13 and 14 are reported. Optimization of two chair conformers of heterocycles 1-3,1BH(3)-3BH(3), 7, 9 (R = Me, R' = tBu), 13-16 were performed by HF/6-31++G and B3LYP/6-31G(d,p) methods and their minimum energy is compared. 2-Alkyl substituents or N-BH3 anchor the [1,3,5]-dithiazinane ring conformation allowing the analyses of steric and electronic interactions as well as the lone pairs effect in these molecules. (C) 2013 Elsevier B.V. All rights reserved.