Carbon monoxide readily binds to heme and cooper proteins, acting as a competitive inhibitor of dioxygen. As such, CO serves as a probe of protein metal active sites. In our ongoing effect to mimic the active site of cytochrome c oxidase, 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-5/6)Fe-II, [(L-5/6)Fe-II...Cu-I](B(C6F5)(4)), and [(TMPA)Cu-I(CH3CN)](B(C6F5)(4)), where TMPA = tris(2-pyridylmethyl)amine and L-5/6 = a tetraarylporphyrinate tethered in either the 5-position (L-5) or 6-position (L-6) to a TMPA copper binding moiety. Reaction of (L-5/6)Fe-II {in THF (293 K): UV-vis 424 (Soret), 543-544 nm; H-1 NMR delta(pyrrole) 52-59 ppm (4 peaks); H-2 NMR (from (L-5-d(8))Fe-II) delta(pyrrole) 53.3, 54.5, 55.8, 56.4 ppm} with CO in solution at RT yielded ((5/6L))Fe-II-CO {in THF (293 K): UV-vis 413-414 (Soret), 532-533 nm; IR v(CO)Fe 1976-1978 cm(-1); H-1 NMR delta(pyrrole) 8.8 ppm; H-2 NMR (from (L-5-d(8))Fe-II-CO) delta(pyrrole) 8.9 ppm; C-13 NMR delta(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(II) to six-coordinate, low-spin Fe(II), as evidenced by the upfield shift of the pyrrole resonances to the diamagnetic region (H-1 and H-2 NMR spectra). Addition of CO to [(L-5/6)Fe-II...Cu-I](B(C6F5)(4)) {in THF (293 K): UV-vis (L-6 only) 424 (Soret), 546 nm; H-1 NMR delta(pyrrole) 54-59 ppm (multiple peaks); H-2 NMR (from [(L-5-d(8))Fe-II...Cu-I](B(C6F5)(4)) delta(pyrrole) 53.4 ppm (br)} gave the bis-carbonyl adduct [(L-5/6)Fe-II-CO...Cu-I-CO](B(C6F5)(4)) {in THF (293 K): UV-vis (L-6 only) 413 (Soret), 532 nm; IR v(CO)Fe 1971-1973 cm(-1), v(CO)Cu 2091-2093 cm(-1), similar to2070(sh) cm(-1); H-1 NMR delta(pyrrole) 8.7-8.9 ppm; H-2 NMR (from [L-5-d(8))Fe-II-CO...Cu-I-CO](B(C6F5)(4))) delta(pyrrole) 8.9 ppm; C-13 NMR delta(CO)Fe 206.8-208.1 ppm (2 peaks), delta(CO)Cu 172.4 (L-5), 178.2 (L-6) ppm}. Experiments in acetonitrile, acetone, and toluene exhibited spectral features similar to those reported. The [(L-5/6)Fe-II-CO and (CO...Cu-I-CO](B(C6F54)) compounds yielded (CO)Fe spectra analogous to those seen for (L-5/6)Fe-II-CO and (CO)Cu spectra similar to those seen for [(TMPA)Cu-I-CO](B(C6F5)(4)) {in THF (293 K): IR v(CO)Cu 2091 cm(-1), similar to2070(sh) cm(-1); C-13 NMR delta(CO)CU 180.3 ppm}. Additional IR studies were performed in which the [(L-5)Fe-II-CO... Cu-I-CO](B(C6F5)(4)) in solution was bubbled with argon in an attempt to generate the iron-only mono-carbonyl [(L-5)Fe-II-CO...Cu-I](B(C6F5)(4)) species; in coordinating solvent or with axial base present, decreases in characteristic IR-band intensities revealed complete loss of CO from copper variable loss of CO from the heme.