We have synthesized and characterized via single-crystal X-ray diffraction methods iron(II), ruthenium(II), and osmium(II) carbonyl derivatives of (1-methylimidazole) (5,10,15,20-tetraphenylporphyrinate) [(5,10,15,20-tetraphenylporphyrinate ) TPP)], Fe(TPP)(CO)(1-MeIm)‚toluene, Ru(TPP)(CO)(1-MeIm)‚ chloroform, and Os(TPP)(CO)(1-MeIm)‚chloroform, together with the osmium(II) pyridine adduct Os(TPP)-(CO)(py)‚2benzene. The crystallographic results permit a detailed structural comparison between all of the six carbonyl metalloporphyrins which can be prepared from TPP, Fe, Ru, Os, and the two axial bases 1-methylimidazole and pyridine. The structures of all three (Fe, Ru, Os) 1-methylimidazole complexes display major saddle distortions, with the extent of the distortions being Fe > Ru ∼ Os. For the pyridine complexes, deviations from planarity of the porphyrin ring are about an order of magnitude smaller than those for the 1-methylimidazole species. The M-C-O bond angles in all complexes are in the range 176.8-179.3°. We also determined the 13 C and 17 O NMR isotropic chemical shifts, the 13 C NMR chemical shift tensor elements, and, for the three 1-MeIm adducts, the 17 O nuclear quadrupole coupling constants. We then used density functional theory (DFT) to relate the experimental spectroscopic results to the experimental structures. For the 13 C and 17 O isotropic shifts, there are excellent correlations between theory and experiment ( 13 C, R 2 value ) ∼0.99; 17 O, R 2 value ) ∼0.99), although the slopes ( 13 C, ∼-0.97; 17 O, ∼-1.27) deviate somewhat from the ideal values. For the 17 O nuclear quadrupole coupling constant, our results indicate an rms error between theory and experiment of 0.20 MHz, for experimental values ranging from (+)1.0 to (-)0.40 MHz, where the signs are deduced from the calculations. The ability to predict spectroscopic observables in metalloporphyrin systems having relatively well characterized structures by using density functional theory provides additional confidence in the application of these theoretical methods to systems where structures are much less certain, such as heme proteins.

The reaction of 1,3-diphenylallylethyl carbonate (1) with benzylamine to afford the secondary amine 2 is effectively catalyzed by Pd-complexes containing chiral ferrocenyl pyrazole ligands. The highest enantioselectivity (99% ee) was obtained using ligand 3a, 1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(1-adamantyl)-1H-pyrazole. Four different cationic Pd-allyl intermediates, 4a, 4c, 4j, and 4k (containing ligands 3a, 3c, 3j, and 3k, respectively), formed during the catalytic reaction were studied in solution by 2D-NMR spectroscopy, with the aim of clarifying configurational aspects. Depending on the size and shape of the substituent in position 3 of the pyrazole ring, it was found that the major diastereoisomeric form of these complexes either adopts an exo- syn-syn (ligands 3a and 3c, 1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]-ethyl}-3-phenyl-5-methyl-1H-pyrazole) or an exo-syn-anti configuration (ligands 3j, 1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(9-anthryl)-5-methyl-1H-pyrazole and 3k, 1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(9-triptycyl)-1H-pyrazole). This analysis allows the site of nucleophilic attack on the allyl ligand to be established unequivocally, i.e., the carbon atom trans to phosphorus. The reasons responsible for this pronounced site-selectivity are discussed. The Pd-allyl complexes [Pd(η3-PhCHCHCHPh)(3c)]PF6, 4c, and [Pd(η3-PhCHCHCHPh)(3k)]PF6, 4k, were characterized by X-ray diffraction. 4c crystallizes with 1 equiv of Et2O in the orthorhombic space group P212121:  a = 13.026(2) Å, b = 14.784(2) Å, c = 25.124(5) Å, Z = 4. Crystals of 4k contain 3 equiv of hexane and 1 equiv of acetone and H2O in the unit cell belonging to the trigonal system, space group P3221:  a = 24.07(3) Å, c = 22.48(3) Å, Z = 6.

We have investigated the 57Fe Mössbauer quadrupole splittings in the following compounds by using density functional theory, and in some cases via experiment:  Fe(CO)3(cyclo-butadiene), Fe(CO)5, Fe(CO)3(1,4−butadiene), CpFe(CO)2Me, Fe(CO)3(propenal), CpFe(CO)2Cl, (CO)(pyridine)(DMGBPh2)2Fe(II) (DMG = dimethylglyoximato), (CO)(pyridine)(DMGBBN)2Fe(II) (BBN = 9-borabicyclo[3.3.1]nonane), (CO)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(II), (CO)(pyridine)(5,10,15,20-tetraphenyl-porphinato)Fe(II), (nitrosobenzene)(pyridine)(5,10,15,20-tetraphenylporphinato)Fe(II), (pyridine)2(5,10,15,20-tetraphenylporphinato)Fe(II), (1-methylimidazole)2(5,10,15,20-tetramesitylporphinato)Fe(II), and (trimethylphosphine)2(2,3,7,8,12,13,17,18-octaethylporphinato)Fe(II). The electric field gradients at iron were evaluated by using a locally dense basis approach:  a Wachters' all electron representation for iron, a 6-311++G2d basis for all atoms directly bonded to iron, and either a 6-31G* basis for all other atoms or, in the case of the metalloporphyrins, a 6-31G*/3-21G* or 4-31G* basis, with the smaller basis being used on the peripheral atoms. Using a value of 0.16 × 10-28 m2 for the quadrupole moment of 57Fem, we find good agreement between theoretical and experimental quadrupole splittings:  a slope of 1.04, an R 2 value of 0.975, and a root-mean-square error of 0.18 mm s-1, for the 14 compounds examined. We have also investigated the effects of the CO ligand tilt and bend on the 57Fe quadrupole splittings in several heme models. The theoretical results provide no support for the very large (40°) Fe−C−O bond angles suggested by several diffraction studies on Physeter catodon carbonmonoxymyoglobin (P21 crystals). In contrast, the experimental results for (CO)(1-MeIm)(5,10,15,20-tetraphenylporphinato)Fe(II), which contains a linear and untilted Fe−CO, are in very close accord with the experimental values for CO-myoglobin:  0.35 mm s-1 for the model system versus 0.363−0.373 mm s-1 for MbCO, with V zz oriented perpendicular to the porphyrin plane, as found experimentally. Calculations on metalloporphyrins at the more distorted X-ray geometries yield quadrupole splittings around 2 mm s-1, inconsistent with experiment.

We have synthesized and studied via solid-state NMR, Mössbauer spectroscopy, single-crystal X-ray diffraction, and density functional theory the following Fe−O2 analogue metalloporphyrins:  Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(1-methylimidazole); Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(pyridine); Fe(5,10,15,20-tetraphenylporphyrinate)(4-nitroso-N,N-dimethylaniline)(pyridine); Fe(2,3,7,8,12,13,17,18-octaethylporphyrinate) (nitrosobenzene)(1-methylimidazole) and Co(2,3,7,8,12,13,17,18-octaethylporphyrinate)(NO). Our results show that the porphyrin rings of the two tetraphenylporphyrins containing pyridine are ruffled while the other three compounds are planar:  reasons for this are discussed. The solid-state NMR and Mössbauer spectroscopic results are well reproduced by the DFT calculations, which then enable the testing of various models of Fe−O2 bonding in metalloporphyrins and metalloproteins. We find no evidence for two binding sites in oxypicket fence porphyrin, characterized by very different electric field gradients. However, the experimental Mössbauer quadrupole splittings can be readily accounted for by fast axial rotation of the Fe−O2 unit. Unlike oxymyoglobin, the Mössbauer quadrupole splitting in PhNO•myoglobin does not change with temperature, due to the static nature of the Fe•PhNO subunit, as verified by 2H NMR of Mb•[2H5]PhNO. Rotation of O2 to a second (minority) site in oxymyoglobin can reduce the experimental quadrupole splittings, either by simple exchange averaging, or by an electronic mechanism, without significant changes in the Fe−O−O bond geometry, or a change in sign of the quadrupole splitting. DFT calculations of the molecular electrostatic potentials in CO, PhNO, and O2-metalloporphyrin complexes show that the oxygen sites in the PhNO and O2 complexes are more electronegative than that in the CO system, which strongly supports the idea that hydrogen bonding to O2 will be a major contributor to O2/CO discrimination in heme proteins.