Johann W. Buchler

Metallkomplexe mit tetrapyrrol-liganden : IX. Octaäthylporphinato-osmium(II)-carbonyl-komplexe mit trans-ständigen donator-liganden

Abstract By reaction of octaethylporphine [(OEP)H2] with osmium tetroxide in diethyleneglycil monomethyl ether at temperatures about 200°C, new octaethylporphinatoosmium (II) carbonyl complexes of the type (OEP)Os(CO)X are obtained in good yield after addition of a Lewis base X[where X = MeOH, EtOH, THF, C5H5N, PPh3, and AsPh3]. Treatment of these complexes with P(OMe)3 yields (OEP)Os[P(OMe)3]2, both axial ligands (CO and X) being replaced. All compounds are fully characterized by elemental analyses, electronic absorption, IR, NMR and mass spectra. The ligand X exerts a trans-effect on the carbonyl group: as the back-bonding capacity of X increases the carbonyl stretching frequency rises, indicating diminishing back bonding to the CO group. IR data show that back bonding onto the CO-ligand increases in the porphinatometal carbonyls (P)M(CO)X for different metals M in the order Fe

Electronic states and (π, π*) absorption and emission characteristics of strongly coupled porphyrin dimers: sandwich complexes of HfIV and ZrIV

Abstract Time-resolved and steady state optical measurements are reported for the sandwhich complexes consisting of two tetraphenylporphyrin macrocycles held within 3 A by either a Zr IV or Hf IV ion. Compared to monoporphyrins and weakly coupled bisporphyrins, the transition-metal sandwich complexes show new features in both the ground and excited state absorption spectra as well as a broad fluorescence red-shifted to ≈ 1 μm. A model is presented that describes the electronic states responsible for these optical features. The states arise from strong interactions between the porphyrin macrocycles and contain significant charge resonance character.

Effects of steric crowding on porphyrin conformation. Synthesis, crystal structure and molecular stereochemistry of μ-oxo-bis[(5,15-dimethyl-2,3,7,8,12,13,17,18-octaethylporphinato)iron(III)]

Abstract The preparation and structural characterization of [Fe(ODM)]2O is described. This μ-oxo iron(III) derivative has a nearly eclipsed arrangement of the two porphinato cores when viewed along the nearly linear Fe-O-Fe spine. This feature and the pronounced nonplanarity of the porphinato core are the consequence of significant steric congestion in the periphery of the molecule. The steric congestion also appears to have affected bond parameters in the core. However, the coordination group bond parameters are that expected for a high-spin iron(III) porphyrinate with FeN(ave)=2.065 A, FeO= 1.752(1) A and a FeOFe angle of 178.6(6)°. The iron(III) atom is displaced 0.53 A from the quasi D2d ruffled core. Crystal data: monoclinic, a= 22.593(10), b=15.138(5), c=20.368(6) A and β=103.04(2)°, Z=4, space group C2/c, 4199 observed data collected on an automated four- circle diffractometer.

Osmium and Cerium Porphyrins: Metalloporphyrins with Unnatural Metals as Models for Active Sites of Electron-Transfer Enzymes

Abstract Structure-function relationships can provide valuable insight into the function of enzymes. These relationships can be obtained by chemical variation or modification of the original enzyme. Many enzymes contain metal ions which either stabilize the tertiary structure or serve as active sites for the biochemical process catalyzed by the enzyme under consideration. This Comment is devoted to the use of “unnatural” metals in metalloporphyrins that may be regarded as enzyme models.

Metal complexes with tetrapyrrole ligands ☆: XV. A carbonylosmium porphodimethene: Synthesis, and determination of the crystal and molecular structure

A novel osmium porphodimethene, carbonyl (α, γ-dimethyl-α, γ-dihydrooctaethylporphinato) pyridineosmium(II) [Os(OEPMe2)CO · Py], has been prepared by reductive methylation of carbonyl(octaethylporphinato)pyridineosmium(II) [Os(OEP)CO · Py]. The constitution has been determined by elemental analysis, electronic absorption-, IR, NMR, and mass spectra. The syn-axial configuration of the two methyl and the carbonyl groups follows from an analysis of X-ray diffraction data collected with a Syntex P1 diffractometer. The compound crystallizes in an orthorhombic four-molecule unit cell (space group Pnma). The more important structural parameters have the following values: d[OsN(OEPMe2)] = 2.067 », d[OsN(Py)] = 2.230 », d[OsC(CO)] = 1.828 », and d[CO] = 1.15 »; the porphodimethene ligand shows a roof-like folding defined by an angle of 38.1° between the normals of the essentially planar pyrromethene halves of the macrocyle; the Os atom lies 0.18 » above the plane of the four N atoms of the (OEPMe2) ligand in the direction of the CO group. The decreased value of the CO stretching frequency in Os(OEPMe2)CO · Py (v(CO) = 1863 cm−1) compared with that in Os(OEP)CO · Py (v(CO) = 1902 cm−1) indicates an increased back-bonding to the CO group, and hence, a diminished back-bonding to the porphodimethene ligand.

Metallkomplexe mit Tetrapyrrol-Liganden, XXXI [1]. Neutrale und anionoide Bisporphinate des Gers und Praseodyms / Metal Complexes with Tetrapyrrole Ligands, XXXI [1]. Neutral and Anionoid Bisporphinates of Cerium and Praeseodymium

Abstract The preparation of the lanthanoid bisporphinates, bis[meso-tetra(p-tolyl)porphinato]-cerium(IV) [Ce(TTP)2**] and bis[meso-tetra(p-tolyl)porphinato]hydrogenpraseodymium-(III) [PrH(TTP)2] from Ce(acac)3 and Pr(acac)3 in boiling 1,2,4-trichlorobenzene is described. Ce(TTP)2 is a diamagnetic and rather inert CeIV derivative, PrH(TTP)2 is a paramagnetic PrIII complex and may be deprotonated to give the anion [Pr(TTP)2]- which is characterized by conductivity measurements, electrophoresis, and isolation of its tetra(n-butyl)ammonium or tetraphenylarsonium salt. The compounds are identified by UV/VIS, IR, 1H NMR, and mass spectra. The data are consistent with a sandwich-type square antiprismatic array of the two porphinate disks about the CeIV or PrIII ion as found earlier in the bis-phthalocyaninates U(Pc)2 or NdH(Pc)2.

Metallkomplexe mit Tetrapyrrol-Liganden, XXXIII [1] Darstellung von Azidochrom(III)-, Azidomangan(III)- und Azidoeisen(III)-Porphyrinen und deren Photolyse zu terminalen oder verbrückten Nitridometallporphyrinen / Metal Complexes with Tetrapyrrole Ligands XXXIII [1] Preparation of Azidochromium(III)-, Azidomanganese(III)-, and Azidoiron(III) Porphyrins and their Photolysis to Terminal or Bridged Nitridometal Porphyrins

Azidometal(III) porphyrins, e.g. M(TTP)N3 1 Aa-1 Ca (M = Cr, Mn, Fe), are transformed into nitrido complexes on irradiation with ultraviolet light. Thus, CrIII or MnIII complexes, e.g. Cr(TTP)N3 or Mn(TTP)N3, yield Crv and Mnv complexes with terminal nitride ligands, e.g. Cr(TTP)N (1Ab) or Mn(TTP)N (1Bb) with concomitant liberation of 1 mol of N2. However, the FeIII complex Fe(TTP)N3 produces the mixed-valence ,μ-nitrido-bis[iron(III,IV)] complex, [Fe(TTP)]2N (1Cg) and about 1.2 mol of N2 per mol of Fe. The azidometal(III) porphyrins are prepared from the corresponding hydroxo- or μ-oxo-metal(III) porphyrins and hydrazoic acid in benzene

Metallkomplexe mit Tetrapyrrol-Liganden, XXVIII. Mononukleare Nitridomangan(V)-Porphyrine: die ersten Mangan-Stickstoff-Dreifachbindungen/ Metal Complexes with Tetrapyrrole Ligands, XXVIII. Mononuclear Nitridomanganese(V) Porphyrins: the First Manganese Nitrogen Triple Bonds

Abstract The first complexes containing a manganese-nitrogen triple bond, nitrido(octaethylporphinato) manganese(V) [MnN(OEP)]** and nitrido[meso-tetra(p-tolyl)porphinato]manganese( V) [MnN(TTP)], are prepared by hypochlorite oxidation of the corresponding methoxomanganese( III) porphyrins, Mn(OEP)OMe and Mn(TTP)OMe, in the presence of ammonia. The red, pentacoordinated, diamagnetic species are identified by UV/VIS-, IR-, 1H NMR, and mass spectra. While the isoelectronic oxochromium(IV) or oxomolybdenum( IV) porphyrins behave as weak oxidants or reductants, respectively, the nitridomanganese( V) unit in the square pyramidal environment is chemically remarkably stable.

Metal complexes with tetrapyrrole ligands. 71. Heteroaggregation of cationic metal mono- and bisporphyrinates with anionic metal porphyrinates or indigosulfonates

The formation of binary or ternary porphyrin heteroaggregates of the type AB, BC, BC2 or ABC is investigated by UV-Vis spectrophotometry (1:1 mixtures and Jobs method of continuous variation), precipitation and electrophoresis. Components ae: A = anionic acceptor molecule, e.g. indigotetrasulfonate, (inds4)4−; B = cationic metal monoporphyrinate, e.g. the tetrakis (trimethylammoniophenyl)porphyrin derivative [Cu(ttm4ap)]4+ (2h-Cu), or cationic metal bisporphyrinate, e.g.[Ce(tm4pyp)2]7+ (3d, the carium(III) double-decker derived from tetrakis (4-methylpyridinio)porphyrin (1d); C = anionic metal complexes of tetrakis (4-sulfonatophenyl)porphyrin, [M(tpps4)]4− (2j-M, MCu, Zn, Ni, VO, Mn(H2O), OsO2, and OsL2 with L 1-methylimidazole). Aggregation in the binary system A/B always followed 1:1 stoichiometry for indigooligosulfonates (indsn)n− (n = 2, 3, 4) and [Cu(ttmnap)]n+ (n = 3, 4; 2g/2h-Cu) or (inds4)4− and [Ce(tm4pyp)2]7+ (3d). In the system B/C, pure samples of 2g-Cu or 2h-Cu and [Zn(tppsn)]n− (n = 3, 4; 2i-Zn, 2j-Zn) all formed 1:1 aggregates BC with each other. Impure samples produced spectral artifacts. [Ce(tm4pyp)2]7+ (3d) and [Ce(tH4pyp)2]8+ (3b-H8, prepared by N-protonation of Ce(typyp)2 (3b), the double-decker derived from tetrakis(4-pyridyl)porphyrin) (1b)) formed aggregates in ratios 1:1 with (inds4)4− and 1:2 with [M(tpps4)]4− (2j-M; M  Ni, Vo, Mn(OH2)) which were recognised by Job diagrams or precipitation and analysis, respectively. [Ce(ttm4ap)2]8+ (3h) and [M(tpps4)]4− (bd2j-M form 2:1 aggregates in solutions from which after weeks peculiar solids precipitate that are redissolved on shaking. The slow formation of these aggregates is also shown by electrophoresis, while solids containing [Ce(tm4pyp)2]7+ (3d) are rapidly deposited. The spectrophotometric analysis of a ternary system A/B/C, e.g. [inds4]4−/ [Ce(tm4pyp)2]7+/[Ni(tpps4)]4−, disclosed an interaction of all species, but no definite stoichiometry. Homoaggregation of [Ni(tpps4)]4− (2j-Ni) and [inds4]4− was not observed.

Metallkomplexe mit Tetrapyrrol-Liganden, XXIV [1]. Zur Kenntnis der Platin(IV)-Porphyrine / Metal Complexes with Tetrapyrrole Ligands, XXIV [1]. On the Knowledge of Platinum(IV) Porphyrins

Abstract The first platinum(IV) porphyrin, dichloromeso-tetra(p-tolyl)porphinatoplatinum(IV) [Pt(TPP)Cl2**], is prepared by oxidation of the corresponding platinum(II) complex [Pt(TTP)**] with hydrogen peroxide in acidic media and treatment with hydrogen chloride. Pt(TTP)Cl2 is thermally stable up to 200 °C. Electrochemical reduction yields Pt(TTP), presumably by a two-electron step. The platinum-to-porphyrin π-backbonding known to exist in Pt(TTP) decreases on oxidation to Pt(TTP)Cl2 but does not vanish. An improved synthesis of Pt(TTP) is described. Evidence for the accessibility of Pt(OEP)Cl2 and Pd(TTP)Cl2 is also presented.