Reactivity and Structural Diversity in the Reaction of Guanidine 1,5,7-Triazabicyclo[4.4.0]dec-5-ene with COb>2b>, CSb>2b>, and Other Heterocumulenes
文摘
The guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) reacted with the heterocumulenes COb>2b>, CSb>2b>, iPrb>2b>NCNiPrb>2b>, p-tolylNCO, and p-tolylNCS to give three types of products: TBD–COb>2b> (<b>1b>) and TBD–p-tolylNCS (<b>5b>), resulting from the addition of the cumulene to TBD, TBD(–H)({iPrNH}–C=N{iPr}) (<b>3b>) and TBD(–H)(p-tolylNHCO) (<b>4b>), resulting from addition of the N–H bond of TBD to the C=N bond of the cumulene, and the dithiocarbamate salt [TBDH][TBD(–H)CSb>2b>] (<b>2b>) after transfer of a proton to a second molecule of TBD. Competition reactions indicated that the stability of the compounds decreases in the order <b>4b> > <b>5b> > <b>1b> > <b>2b> > <b>3b>. DFT calculations showed that the relative stabilities of the products are governed by both the Lewis acidity of the heterocumulene and the Brønsted basicity of the TBD(–H)–cumulene anion, whereas their distinct structures are determined by the latter, with the most basic site governing the geometry of the final product.