High order cycloaddition reactions of M(CO)3-coordinated N-cyanoazepine with alkynes; M: Cr, Mo, W

Tricarbonyl(N-cyanoazepine)metal(0) complexes of chromium (2a), molybdenum (2b) and tungsten (2c) are formed when tricarbonyl-tris(acetonitrile)chromium(0), -molybdenum(0) and -tungsten(0), respectively, are treated photochemically with N-cyanoazepine (1). The resulting complexes are purified. UV photolysis of Cr(CO)3(η6-N-cyanoazepine) (2a) and RCCR (R: Ph, SiMe3) in toluene gives the [6+2]cycloadducts, tricarbonyl{η4:2-7,8-diphenyl-9-N-cyano-9-azabicyclo[4.2.1]-nona-2,4,7-triene}chromium(0), [(η4:2-C8H6N(CN)Ph2)Cr(CO)3] (3a) and tricarbonyl{η4:2-7,8-bis(trimethylsilyl)-9-N-cyano-9-azabicyclo[4.2.1]-nona-2,4,7-triene}chromium(0), [(η4:2-C8H6N(CN)(SiMe3)2)Cr(CO)3] (3b). Like 2a–c, these new bicyclic compounds were purified by chromatography, recrystallized and isolated as analytically pure crystalline solids in moderate yields and characterized by mass, IR and NMR spectroscopy. The heterobicyclotrienes (4a,b) are isolated from (3a,b) by treatment with cerium(IV) ammonium nitrate (R=SiMe3) or by heating in toluene (R=Ph).