A bromo-capped diruthenium(i,i) N-heterocyclic carbene compound for in situ bromine generation with NBS: catalytic olefin aziridination reactions

Abstract

A bromo-capped metal–metal bonded diruthenium(I,I) complex Ru₂(CO)₄(PIN)₂Br₂ (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene) generates bromine with N-bromosuccinimide (NBS) at room temperature. Cycloalkene and stilbene are readily brominated by stoichiometric reactions with 1 and NBS. An analysis of the dibrominated products suggests the formation of cyclic bromonium intermediates indicating in situ Br₂ generation. Complex 2, an iodide analogue of 1, is also synthesized. The reaction of 2 with N-iodosuccinimide releases I₂, which is confirmed by the starch-iodine test. The catalytic utility of 1 is examined for the bromination of phenol. Catalyst 1, in combination with NBS and base, exhibits regioselectivity towards monobrominated products. Furthermore, efficient olefin aziridination is demonstrated utilizing catalyst 1 in the presence of NBS, K₂CO₃ and TsNH₂.