Synthesis and Characterization of Reduced Heme and Heme/Copper Carbonmonoxy Species

Carbon monoxide readily binds to heme and copper proteins, acting as a competitive inhibitor of dioxygen. As such, CO serves as a probe of protein metal active sites. In our ongoing efforts to mimic the active site of cytochrome coxidase, reactivity toward carbon monoxide offers a unique opportunity to gain insight into the binding and spectroscopic characteristics of synthetic model compounds. In this paper, we report the synthesis and characterization of CO-adducts of (L)Fe", [(L)Fe"-Cuʹ](B(C6F5)4), and [(TMPA)Cuʹ(CHsCN)](B(C6F5)4), where TMPA - tris(2pyridylmethyl)amine and L = a tetraarylporphyrinate tethered in either the 5-position L) or 6-position L) to a TMPA copper binding moiety. Reaction of (L)Fe" {in THF (293 K): UV-vis 424 (Soret), 543-544 nm; NMR pyrrole 52-59 ppm (4 peaks); H NMR (from (L-d)Fe") pyrrole 53.3, 54.5, 55.8, 56.4 ppm} with CO in solution at RT yielded (L)Fe"-CO {in THF (293 K): UV-vis 413-414 (Soret), 532-533 nm; IR r(CO)pe 1976-1978 cmNMR pyrrole 8.8 ppm; NMR (from (-Feʹʹ-CO) pyrrole 8.9 ppm; C NMR (3(co)Fe 206.8-207.1 ppm (2 peaks)}. Experiments repeated in acetonitrile, acetone, toluene, and dichloromethane showed similar spectroscopic data. Binding of CO resulted in a change from five-coordinate, high-spin Fe(ll) to six-coordinate, low-spin Fe(ll), as evidenced by the upfield shift of the pyrrole resonances to the diamagnetic region (H and H NMR spectra). Addition of CO to [(L)Fe"-Cuʹ](B(C6F5)4) {in THF (293 K): UV-vis ( only) 424 (Soret), 546 nm; NMR pyrrole 54-59 ppm (multiple peaks); H NMR (from L-Fe"— Cuʹ](B(CeF5)4)) (3pyrroie 53.4 ppm (br)} gave the bis-carbonyl adduct [(L)Fe"-CO-Cuʹ-CO](B(C6F5)4) {in THF (293 K): UV-vis ( only) 413 (Soret), 532 nm;....