Click reactions of 2H-azaphosphirene chromium and molybdenum complexes and a surprisingly facile access to a 2H-1,4,2-diazaphosphole derivative
作者:Holger Helten、Gregor Schnakenburg、Rainer Streubel
DOI:10.1016/j.poly.2011.04.014
日期:2011.6
Ring expansion reactions of 2H-azaphosphirene chromium and molybdenum complexes 1a,b with dimethyl cyanamide, triflic acid, and, subsequently at ambient temperature, with triethylamine gave a mixture of the respective 2H-1,4,2-diazaphosphole complex 2a,b and the non-ligated heterocycle 3. If the deprotonation with NEt3 was carried out at low temperature, the selective formation of complexes 2a,b was observed, which were isolated in excellent yields and fully characterized (including single-crystal X-ray crystallography). Experimental and computational results revealed that the P, Cr and P, Mo bonds of 2H-1,4,2-diazaphosphole complexes are significantly weakened upon N-protonation of the heterocyclic ligand. When mixtures of 1a,b, TfOH, and Me2NCN were warmed to ambient temperature, the primarily formed N-protonated of 2H-1,4,2-diazaphosphole complexes 4a,b could be observed by P-31 NMR spectroscopy. The latter underwent decomplexation to give the N-protonated free ligand 5, which could be isolated and characterized by multinuclear NMR experiments. The neutral non-ligated heterocycle 3 was isolated from a one-pot reaction of 1b with TfOH and Me2NCN by adding NEt3 to a solution of intermediately formed 5. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.