The dimerization of thiophosgene and trichlorothioacetyl chloride S-imides - Head-to-head and/or head-to-tail?

It has been shown that certain N-aryltrichoromethanesulfenamides Cl3C-S-NHAr can be dehydrochlorinated to form red-colored thiocarbonyl S-imides CCl2=S=NAr which dimerize spontaneously. The dimers so far obtained were first assigned the 1,4,2,5-dithiadiazinane structure but later shown to be the isomeric 1,4,2,3-dithiadiazinanes. It is proposed that both the so far unknown 1,4,2,5-dithiadiazinanes and the so far elusive thiocarbonyl S-imides (RRC)-R-1-C-2=S=NR3 might be made directly observable by introducing massive steric strain via bulky R in the starting chlorinated sulfenamides such as Cl3C-S-NHAr and CCl3CCl2-S-NHR. - According to PM7 and DFT type MO calculations of the enthalpies, the formation of the 1,4,2,5-dithiadiazinanes is thermodynamically favored over that of the 1,4,2,3-isomers. However, the activation energies for the cyclization reaction are lower for the head-to-head dimerization. Thus, the observed dimerization of thiocarbonyl S-imides under formation of 1,4,2,3-dithiadiazinanes is a kinetically controlled reaction.