Stable Boron Dithiolene Radicals

Whereas low-temperature (-78 degrees C) reaction of the lithium dithiolene radical 1. with boron bromide gives the dibromoboron dithiolene radical 2., the parallel reaction of 1. with (C6H11)(2)BCl (0 degrees C) affords the dicyclohexylboron dithiolene radical 3.. Radicals 2. and 3. were characterized by single-crystal X-ray diffraction, UV/Vis, and EPR spectroscopy. The nature of these radicals was also probed computationally. Under mild conditions, 3. undergoes unexpected thiourea-mediated B-C bond activation to give zwitterion 4, which may he regarded us an anionic dithiolene-modified carbene complex of the sulfenyl cation RS+ (R = cyclohexyl).