The first example of CoCl2-catalyzed reaction between 1,1'-carbonyldiazoles and carbonyl compounds was reported by TheĢ and Peterson in 1973, obtaining 2,2-di(pirazol-1-yl)propane from di(pyrazol-1-yl)methanone and acetone. The study was extended to several other ketones and aldehydes and to methyl-substituted di(pyrazol-1-yl)methanone derivatives, with the isolation of the corresponding di(pirazol-1-yl)alkanes by elimination of CO2. A reaction mechanism was subsequently proposed. The synthetic approach was then extended to functionalized aldehydes, with the aim of preparing pyrazole-based ligands to be applied in coordination, supramolecular, bioinorganic and organometallic chemistry. To the best of our knowledge, the cobalt-catalyzed reaction was never applied for the synthesis of di(benzotriazol-1-yl)methane derivatives, despite the fact that benzotriazole is considered an ideal synthetic auxiliary in organic chemistry [4]. For instance, di(benzotriazol-1-yl)phenylmethane was obtained following different synthetic approaches with variable selectivity [5]. In this communication we report the straightforward preparation of di(benzotriazol-1-yl)phenylmethane and di(benzotriazol-1-yl)pyridin-2-ylmethane from di(benzotriazol-1-yl)methanone and the proper aldehyde, using CoCl2 as catalyst under neat conditions. The products were characterized spectroscopically and their solid structures were ascertained by single-crystal X-ray diffraction.
