Synthesis, Characterization, and Laser Flash Photolysis Reactivity of a Carbonmonoxy Heme Complex

Abstract

We present here the synthesis, characterization, and flash photolysis study of [(F(8)TPP)Fe(II)(CO)(THF)] (1) [F(8)TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2-)]. Complex 1 crystallizes from THF/heptane solvent system as a tris-THF solvate, [(F(8)TPP)Fe(II)(CO)(THF)].3THF (1.3THF), with ferrous ion in the porphyrin plane (C(61)H(52)F(8)FeN(4)O(5); a = 11.7908(2) A, b = 20.4453(2) A, c = 39.9423(3), alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees; orthorhombic, P2(1)2(1)2(1), Z = 8; Fe-N(4)(av) = 2.00 A; N-Fe-N (all) = 90.0 degrees ). This complex (as 1.THF) has also been characterized by (1)H NMR [six-coordinate, low-spin heme; CD(3)CN, RT, delta 8.82 (s, pyrrole-H, 8H), 7.89 (s, para-phenyl-H, 8H), 7.46 (s, meta-phenyl-H, 4H), 3.58 (s, THF, 8H), 1.73 (s, THF, 8H)], (2)H NMR (pyrrole-deuterated analogue) [(F(8)TPP-d(8))Fe(II)(CO)(THF)] [THF, RT, delta 8.78 ppm (s, pyrrole-D)], (13)C NMR (on (13)CO-enriched adduct) [THF-d(8), RT, delta 206.5 ppm; CD(2)Cl(2), RT, delta 206.1 ppm], UV-vis [THF, RT, lambda(max), 411 (Soret), 525 nm], and IR [293 K, solution, nu(CO) 1979 cm(-)(1) (THF), 1976 cm(-)(1) (acetone), 1982 cm(-)(1) (CH(3)CN)] spectroscopies. In order to more fully understand the intricacies of solvent-ligand binding (as compared to CO rebinding to the photolyzed heme), we have also synthesized the bis-THF adduct [(F(8)TPP)Fe(II)(THF)(2)]. Complex 2 also crystallizes from THF/heptane solvent system as a bis-THF solvate, [(F(8)TPP)Fe(II)(THF)(2)].2THF (2.2THF), with ferrous iron in the porphyrin plane (C(60)H(52)F(8)FeN(4)O(4); a = 21.3216(3) A, b = 12.1191(2) A, c = 21.0125(2) A, alpha = 90 degrees, beta = 105.3658(5) degrees, gamma = 90 degrees; monoclinic, C2/c, Z = 4; Fe-N(4)(av) = 2.07 A; N-Fe-N (all) = 90.0 degrees ). Further characterization of 2 includes UV-vis [THF, lambda(max), 421 (Soret), 542 nm] and (1)H NMR [six-coordinate, high spin heme; THF-d(8), RT, delta 56.7 (s, pyrrole-H, 8H), 8.38 (s, para-phenyl-H, 8H), 7.15 (s, meta-phenyl-H, 4H)] spectroscopies. Flash photolysis studies employing 1 were able to resolve the CO rebinding kinetics in both THF and cyclohexane solvents. In CO saturated THF [[CO] approximately 5 mM] and at [1] congruent with 5 microM, the conversion of [(F(8)TPP)Fe(II)(THF)(2)] (produced after photolytic displacement of CO) to [(F(8)TPP)Fe(II)(CO)(THF)] was monoexponential, with k(obs) = 1.6 (+/-0.2) x 10(4) s(-)(1). Reduction in [CO] by vigorous Ar purging gave k(obs) congruent with 10(3) s(-)(1) in cyclohexane. The study presented in this report lays the foundation for applying fast-time scale studies based on CO flash photolysis to the more complicated heterobimetallic heme/Cu systems.

Isocyanide or nitrosyl complexation to hemes with varying tethered axial base ligand donors: synthesis and characterization

“…The Fe–N(imidazole) bond distances are ca. 2.02 Å, while the average Fe–N(porphyrin) bond distances are 1.99 Å, similar to our previously reported [(F 8 )Fe II ]·2THF complex [53]. Both structures are well ordered except the difluorophenyl group and toluene solvent molecule in complex ( 4 )-DIMPI (see “Materials and methods”).…”

New heme–dioxygen and carbon monoxide adducts using pyridyl or imidazolyl tailed porphyrins

“…Based on 2H-NMR spectra, where pyrrole-H positions have been replaced by deuterium [14, 38–42], [(F 8 )Fe II ] exhibits downfield resonances in acetone as solvent (Table 1), revealing a high-spin Fe II (d 6 , S = 2) complex state; this indicates pentacoordination with one axially ligated acetone molecule. In tetrahydrofuran (THF), downfield resonances are also observed, thus the complex is five- or six-coordinate with one or two axial THF molecules; a crystal structure of [(F 8 )Fe II (THF) 2 ] has been determined [43]). However, we find that acetonitrile (but only at low temperature, i.e., 233 K) and pyridine at all temperatures act as ‘strong’ ligands.…”

Organometallic alkane CH activation

“…More recently, CpRe(CO) 2 (n-heptane) was detected by FTIR at room temperature in heptane [41], and CpRe(CO) 2 (cyclopentane) (Scheme 10) was detected by NMR spectroscopy [42]. Structural evidence has been obtained for an iron porphyrin 15 heptane complex [43] and for a cyclohexane uranium complex [44].…”