Bis(tert-butyl)sulfurdiimide, S(NBut)2, and tris(tert-butyl)sulfurtriimide, S(NBut)3: structures by gas electron diffraction, X-ray crystallography and ab initio calculations

Abstract

The molecular structures of bis(tert-butyl)sulfurdiimide [S(NBu^t)₂] and tris(tert-butyl)sulfurtriimide [S(NBu^t)₃] have been investigated in the gas phase by electron diffraction and ab initio calculations, and in the solid phase by low-temperature X-ray diffraction. The structures of each were found to be similar in both phases, and the calculated structures agree well with those in the gas phase. Ab initio calculations at levels up to MP2(fc)/cc-pVTZ for S(NBu^t)₂ predict that the E/Z conformer (C_s symmetry) is the preferred arrangement by as much as 36.5 kJ mol⁻¹ over the E/E conformer. Important structural parameters [ab initio (r_e)/GED (r_a)/X-ray] for the E/Z conformer of S(NBu^t)₂ are S(1)–N(2) [152.9/153.8(3)/152.8(3) pm], S(1)–N(3) [155.5/156.5(4)/154.4(3) pm], N(2)–C(4) [147.3/146.2(4)/147.7(5) pm], N(3)–C(5) [147.9/147.0(4)/148.9(4) pm], N(2)–S(1)–N(3) [116.9/117.8(6)/117.4(2)°], S(1)–N(2)–C(4) [125.9/125.9(6)/128.1(2)°] and S(1)–N(3)–C(5) [117.1/116.7(7)/118.2(2)°]. One conformer of S(NBu^t)₃ with C_3h symmetry was located at the MP2(fc)/6-31G* level. The gas and solid-phase studies both returned C₃ structures, with the butyl groups moved a little out of the SN₃ plane. Important structural parameters [ab initio (r_e)/GED (r_a)/X-ray] for S(NBu^t)₃ are SN [152.8/153.5(3)/151.0(2), 151.0(2), 151.1(2) pm], N–C [148.7/147.2(4)/148.3(3), 148.5(3), 148.3(3) pm], C–C [152.8/150.8(2)/152.4(4), 152.6(4), 153.0(3) pm], SN–C [123.2/122.9(4)/126.2(2), 125.5(2), 126.0(2)°], C–C–C (mean) [110.4/108.3/110.0°] and NSN–C (mean) [180.0/173.0(5)/179.4°]. Theoretical predictions at the MP2(fc)/6-31G* level were used to restrain some of the refining parameters for both structures using the SARACEN method. The lowest energy structure of bis(tert-butyl)sulfurdiimide was found to be the E/Z conformer, and the structure of tris(tert-butyl)sulfurtriimide is such that each fragment with two NBu^t ligands has the E/Z conformation.