Decomposition of [2-Pyr(SiMe 3 ) 2 C] 2 SbCl into the Stibaalkene [2-Pyr(SiMe 3 ) 2 C−SbC(SiMe 3 )2-Pyr]: Solid, Solution, and ab Initio Study

The disubstituted antimony chloride complex [2-Pyr(SiMe 3 ) 2 C] 2 SbCl (Pyr = C 5 H 4 N), formed from the 2:1 reaction of [2-Pyr(SiMe 3 ) 2 CLi·tmeda] with SbCl 3, readily decomposes into the stibaalkene species [2-Pyr(SiMe 3 ) 2 CSb C(SiMe 3 )2-Pyr] via β-elimination of Me 3 SiCl. The stibaalkene species is an intensely colored, highly air and moisture sensitive, deep red oil. In thf solution the elimination of Me 3 SiCl occurs at temperatures ca. −40 °C; however, orange crystals of [2-Pyr(SiMe 3 ) 2 C] 2 SbCl were obtained from an Et 2 O solution maintained at −25 °C and the structure was determined by single-crystal X-ray diffraction. 1 H and 13 C NMR spectra of the crystals of [2-Pyr(SiMe 3 ) 2 C] 2 SbCl have been obtained in d 8 -toluene at −30 °C, and its decomposition to the stibaalkene was followed by recording spectra as the sample was warmed to 30 °C. DFT ab initio calculations have been conducted to investigate the role of the pyridyl groups in Me 3 SiCl elimination as well as the structure and stability of the final stibaalkene. These indicate that the formation of strong Sb−N bonds effectively localizes much of the double-bond character in a C C rather than Sb C bond, increasing its overall stability.