Heme/non-heme diiron(II) complexes and O2, CO, and NO adducts as reduced and substrate-bound models for the active site of bacterial nitric oxide reductase

As a first generation model for the reactive reduced active-site form of bacterial nitric oxide reductase, a heme/non-heme diiron(II) complex [(L-6)Fe-II center dot center dot center dot Fe-II-(Cl)](+) (2) {where L-6 = partially fluorinated tetraphenylporphyrin with a tethered tetradentate TMPA chelate; TMPA = tris(2-pyridyl)amine} was generated by reduction of the corresponding mu-oxo diferric compound [(L-6)Fe-III-O-Fe-III-Cl](+) (1). Coordination chemistry models for reactions of reduced NOR with O-2, CO, and NO were also developed. With O-2 and CO, adducts are formed, [(L-6)Fe-III(O-2(-))(thf)center dot center dot center dot Fe-II-Cl]B(C6F5)(4) (2a center dot O-2) {lambda(max) 418 (Soret), 536 nm; nu(O-O) = 1176 cm(-1), nu(Fe-O) = 574 cm(-1) and [(L-6)Fe-II(CO)(thf)Fe-II-Cl]B(C6F5)(4) (2a center dot CO) {nu(CO) 1969 cm(-1)}, respectively. Reaction of purified nitric oxide with 2 leads to the dinitrosyl complex [(L-6)Fe(NO)Fe(NO)-Cl]B(C6F5)(4) (2a center dot(NO)(2)) with nu(NO) absorptions at 1798 cm(-1) (non-heme Fe-NO) and 1689 cm(-1) (heme-NO).