Coupling of isocyanides to alkynes on manganese

Novel six-membered nitrogen-containing heterocycles bonded to manganese are produced from the reaction of [p-RC6H4CH2C(O)Mn(CO)4(CNC6H4-p-R′)] (1) R′=Me or OMe, R=H or Cl with various alkynes. Trapping of the alkynes by an unsaturated manganese-mono(iminoacyl) group generated in situ leads to formation of: [1-(p-tolyl)-2-(p-chlorobenzyl)-3,4,5,6-tetraphenyl-η5-azacyclohexadienyl]manganese tricarbonyl (2a), [1-(p-methoxy)-2-benzyl-3,4,5,6-tetraphenyl-η5-azacyclohexadienyl]manganese tricarbonyl (2b), [1-(p-tolyl)-2-(p-chlorobenzyl)-3,5-dihydro-4,6-diphenyl-η5-azacyclohexadienyl]manganese tricarbonyl (3a), [1-(p-methoxy)-2-(p-chlorobenzyl)-3,5-dihydro-4,6-diphenyl-η5-azacyclohexadienyl]manganese tricarbonyl (3b), [1-(p-tolyl)-2-(p-chlorobenzyl)-3,5-dimethyl-4,6-bis(carbomethoxy)-η5-azacyclohexadienyl]manganese tricarbonyl (4) and η4-azacyclohexadienyl complexes: [1-(p-tolyl)-2-(p-chlorobenzyl)-3,6-dimethyl-4,5-bis(carbomethoxy)-η4-azacyclohexadienyl]manganese tricarbonyl (5a), [1-(p-tolyl)-2-(p-chlorobenzyl)-3,6-bis(carbomethoxy)-4,5-dimethyl-η4-azacyclohexadienyl]manganese tricarbonyl (5b), [1-(p-tolyl)-2-(p-chlorobenzyl)-4,6-dimethyl-3,5-bis(carbomethoxy)-η4-azacyclohexadienyl]manganese tricarbonyl (5c) and [1-(p-tolyl)-2-(p-chlorobenzyl)-3,4,5,6-tetrakis(carbomethoxy)-η4-azacyclohexadienyl]manganese tricarbonyl (6). All these products result from coupling of one iminoacyl group and two molecules of alkyne. Surprisingly, reaction of 1 with hexafluoro-2-butyne led to formation of an unsaturated five-membered manganacycle [1,1,1,1-tetracarbonyl-2,3-bis(trifluoromethyl)-4-(p-chlorobenzyl)-5-p-tolyl]-5-azamanganacyclopentadiene (7). The structure, reactivity and formation mechanism of these complexes are discussed.