Facial Isomers Research Articles

Ab Initio MO Study on Cationic Phosphenium Complexes of Group 6 Transition Metals,fac- andmer-[(bpy)(CO)3M{PN(Me)CH2CH2NMe}]+(M = Mo, W)

Quantum mechanical ab initio calculations at the RHF level of theory using effective core potentials (ECP) for the metals and several all-electron basis sets are reported for the facial and meridional isomers of cationic phosphenium complexes of group 6 transition metals, (M = Mo,W). Fully optimized geometries using the ECP by Stevens et al. are in good agreement with the experimental parameters for the related complex. The theoretically predicted relative thermodynamic stability of the meridional and facial isomers of Mo and W complexes also agrees well with experimental behavior. Structural consideration, M−P(phosphenium) bond rotational behavior, and Mulliken charge and orbital population analysis of component atoms in the central part based on the computational results reveal that (i) a phosphenium ligand has strong π-electron accepting character, which is stronger than that of a CO ligand, and (ii) a phosphenium ligand gets π-donation predominantly from a transition metal and little from amino groups...

A Matrix-Isolation Spectroscopic and Theoretical Investigation of Tris(8-hydroxyquinolinato)aluminum(III) and Tris(4-methyl-8-hydroxyquinolinato)aluminum(III)

Infrared and photoluminescence spectra of matrix-isolated and thin-film samples (both at 11 K) of tris(8-hydroxyquinolinato)aluminum(III) (Alq3) and tris(4-methyl-8-hydroxyquinolinato)aluminum(III) (Almq3) were collected and compared to vibrational spectra generated by B3LYP based density functional calculations. The present infrared spectral results suggest that both Alq3 and Almq3 exist primarily in the meridional or C1 isomeric form with little or no spectral evidence for the presence of the alternate, facial (C3 symmetry) geometric isomer. In addition, photoluminescence spectra of these molecules isolated in an argon matrix show vibronic structure in the emission band associated with the S1 → S0 transition.

Spectroscopic and electrochemical properties of [Mn(phen)(CO) 3(imidazole)](SO 3CF 3) complexes

The spectroscopic and electrochemical properties of [Mn(phen)(CO) 3(L)] + type complexes where L is an imidazole or an imidazole derivative containing a methyl, phenyl or NO 2 group, have been investigated. Introduction of the substituents to the σ-donor ligand has been found to produce significant changes in the electrochemical behaviour without significantly altering the fundamental electronic structure of the complexes. The oxidation potentials of the fac-[Mn(phen)(CO) 3L] + and mer-[Mn(phen)(CO) 3L] + isomers are very different, allowing detailed electrochemical studies to be made. Cyclic voltammetry of both the fac and mer isomers provides a complete description of a cyclic process involving the following reactions.

Complete analysis of the31P and19F NMR spectra of [(PF3)3Mo(CO)3

The product of the reaction of PF3 gas with cycloheptatriene molybdenum tricarbonyl to give [(PF3)3Mo(CO)3] was originally studied by IR and NMR spectroscopy and the product was described as the mer isomer based on the appearance of the CO stretching peaks in the IR spectra. This was unexpected since the starting organometallic must have the carbonyl groups in a fac configuration. The high-field 19F and 31P NMR spectra have now been completely analyzed by computer simulation and are best described by a mixture of mer and fac isomers. The values of the 2J(PP) and 1J(PF) coupling constants are in line with those from earlier measurements on cis- and trans-[(PF3)2Mo(CO)4]. The fine structure in the spectrum of the fac molecule can only be reproduced by inclusion of a long range, non-zero, 4J(FF′) coupling of 5.7 Hz between trans fluorine atoms. The gas-phase fluorine NMR spectrum run at three temperatures confirmed the presence of both fac and mer isomers in about the same ratio as in solution. Copyright © 2000 John Wiley & Sons, Ltd.

Tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III)

The preparation and properties of tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III) are described. The structure of the fac isomer has been established by X-ray diffraction techniques. Solvation characteristics of this complex have been assessed through solubility measurements in methanol–water mixtures. The complex is very inert in neutral solution but undergoes acid-catalysed aquation at lower pHs.

Geometrical isomerism and 19F NMR spectroscopy of octahedral perfluoroethyl- and perfluoropropyl-substituted β-diketonates and monothio-β-diketonates of rhodium(III)

In solution in acetone at room temperature, tris(perfluoropropanoyl and perfluorobutanoyl)benzoylmethanate complexes of rhodium(III) are shown by 19F NMR spectroscopy to exist as nearly statistical 1:3 mixtures of their respective fac and mer octahedral isomers, whereas the analogous perfluoroalkanoylthiobenzoylmethanate complexes have a fac-octahedral structure. For all four complexes studied, vicinal F-F coupling constants are too small (0-3 Hz) to lead to resolved multiplet peaks, so that perfluoroethyl groups show singlet resonances for their CF3 groups. Since four-bond coupling constants are significantly larger, ~9 Hz, perfluoropropyl groups show the expected multiplet resonances for their CF3 groups. In acetone, AB patterns, with geminal coupling constants equal to approx. 270 Hz, are observed for the CF2 groups next to the chelate ring (except for the perfluoropropanoylthiobenzoylmethanate complex). (These observations are modified by solvent. In toluene, one of the AB patterns of a mer-octahedral complex collapses to a single peak.) The AB spectra, which are subject to substituent and solvent effects, can be interpreted in terms of perfluoroalkyl groups rotating rapidly about the Cring-Calkyl bond, with an unsymmetric double potential well, giving unequal rotamer populations. Changes in the spectra were not noticeable over the temperature range accessible in the acetone and toluene solvents used.Key words: rotation, perfluoroalkyl groups, fluorine NMR spectra, fluorine-fluorine coupling constants, fluorinatedβ-diketonate complexes, monothio-beta-diketonates, rhodium complexes.

The Synthesis and Characterization of Facial and Meridional Isomers of Unsym-Cis-(Ethylenediamine-N, N-Di-3-Propionato)Cobalt(III) Complexes with Natural Aliphatic α-Amino Acids Containing Oxygen and Sulfur

In the reaction of sodium unsym-cis-(ethylenediamirte-N, N′-di-3-propionato)-(carbonato)cobaltate(III) dihydrate and the corresponding amino acid (S-serine, S-threonine, S-cysteine and R, S-methionine) at 70° C, both theoretically possible facial and meridional isomers of unsym-cis-(ethylenediamine-N, N′-di-3-propio-nato)(aminoacidato)cobalt(III) complex were prepared. The complexes were isolated chromatographically and characterized by elemental analyses, as well as electron absorption and infrared spectroscopy.

Synthesis, Structural Characterization, and MO Calculations of Vanadium Imido Complexes Containing Bidentate Phosphine Coligands.

Treatment of complex V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3) with 1,2-dimethoxyethane (dme) gives in quasi-quantitative yield the adduct V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(dme) (1). Interaction of 1 with bidentate phosphines gives V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(P-P) (P-P = depe, 2a; dppe, 2b) compounds. An X-ray analysis (monoclinic, space group P2(1)/c, a = 14.7387(14) Å, b = 10.6738(10) Å, c = 16.999(3) Å, beta = 90.954(2) degrees, Z = 4, R = 0.0544), carried out on complex 2a, shows a mer arrangement of the chloride ligands and a nonsymmetrical coordination of the diphosphine ligand. One of the phosphorus atoms occupies the trans position with respect to the organoimido ligand. MO calculations on the models V(NR)Cl(3)(H(2)PCH(2)CH(2)PH(2)) (R = H, C(6)H(5)) of complex 2a were performed. The mer isomer, which is more stable than the fac isomer, shows good agreement with the experimental data.

Tris 1-Nitroso-2-naphtholate Complex of Ruthenium(II): An Efficient Building Unit for Polynuclear Complexes

Reaction of 1-nitroso-2-naphthol (HL) with ruthenium trichloride afforded the facial isomer of [RuII(L)3]- (1), which has been isolated as the triethylammonium salt. Using [RuII(L)3]- as a tridentate ligand, a heterometallic trinuclear complex, viz., [{Ru(L)3}2Ni] (2), has been synthesized.

Thin-layer chromatography of facial and meridional isomers of Co(III) and Cr(III) complexes on polyacrylonitrile sorbent

The effect of facial–meridional geometrical isomerism of metal complexes on their chromatographic behaviour on a thin layer of polyacrylonitrile sorbent was examined. To that purpose the three following series of complexes were chromatographed: [Co(eddp)Am], where eddp is ethylenediamine-N,N′-3-propionato ligand, Am is glycinato, alaninato, valinato, leucinato, isoleucinato or isobutyrato ligands, [CoAm 3], where Am is glycinato, β-alaninato, valinato or leucinato ligands as well as two pairs of isomer complexes of [Macacphac 3] type, where M is Co(III) or Cr(III) and acacphac is 1-phenyl-1,3-butanedionato ion. For their chromatographic separation four mono- and thirteen polycomponent solvent systems were used. In all the examined cases meridional isomers were found to exhibit higher hR F values than corresponding facial isomers. Finally, some possible separation mechanisms are discussed.

Elucidation of the Wide Range of Reaction Pathways That Accompany the Electrochemical Oxidation of cis,mer-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)X] (dpm = Ph(2)PCH(2)PPh(2); X = Cl, Br).

The electrochemical oxidation of cis,mer-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Br] (dpm = Ph(2)PCH(2)PPh(2)), or (cis,mer)(0),()()has been examined in dichloromethane (0.1 M Bu(4)NPF(6)) by voltammetric, bulk electrolytic, in situ and ex situ spectroelectrochemical and simulation techniques. On the voltammetric time scale at 20 degrees C, the neutral 18-electron cis,mer Mn(I) species is oxidized to the corresponding 17-electron cation which at slow scan rates isomerizes to the trans cation. Simulations are consistent with a rate constant of 3.1 +/- 0.3 s(-1) for this isomerization process. Monitoring the reaction by in situ IR spectroscopy at low-temperature enables the identification of the nu(CO) bands of all four species ((cis,mer)(0); (cis,mer)(+); (trans)(0); (trans)(+)) in the resultant square reaction scheme that is operative under these thin layer electrolysis conditions. Additionally, 17-electron cis,fac-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Br](+) and its 18-electron (cis,fac)(0) counterpart, generated by a redox-induced catalytic isomerization reaction, are detected and characterized by IR spectroscopy (nu(CO)). Room-temperature bulk oxidative electrolysis experiments reveal that the trans cation, generated in bulk solution from the (cis,mer)(+) and (cis,fac)(+) isomers, slowly ejects bromide with a rate constant of 1.6 x 10(-3) s(-1) to form trans-[Mn(CO)(2)(eta(2)-dpm)(2)](+). The equivalent voltammetry in acetonitrile is complicated by an additional competing kinetic step which is attributed to reaction of this cation with the solvent. However, the major product formed upon oxidation at room temperature is still the trans cation. Less detailed studies on the oxidation of cis,mer-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Cl] only show significant differences under conditions of bulk electrolysis after trans-[Mn(CO)(2)(eta(2)-dpm)(2)](2+) is formed via expulsion of Cl(-).

Oxidative addition of chlorinated solvents (e.g. CH2Cl2 and CHCl3) with rhodium(I) complexes; crystal structure of mer-[Rh(py)3(CH2Cl)Cl2

Common chlorinated solvents (e.g. CH2Cl2 and CHCl3) readily reacted with [Rh2(C8H14)4(µ-Cl)2] (C8H14 = cyclooctene), in the presence of a monodentate, nitrogen donor ligand (L = py or 4-Butpy), to give the oxidative addition product [RhL3RCl2] (R = CH2Cl, CHCl2 or CH2Ph) which for R = CH2Cl and CH2Ph has been shown by X-ray analysis to adopt the mer configuration. NMR Spectroscopic measurements (13C and 15N) in solution were consistent with this configuration, although these NMR data cannot unambiguously distinguish between the mer and fac isomers.

η5-Pentamethylcyclopentadienyliridium(III) and -rhodium(III) Labeling of Amino Acids with Aromatic Side Chains – The Importance of Relativistic Effects for the Stability of Cp*Irııı Sandwich Complexes

η5-Pentamethylcyclopentadienyliridium(III) and -rhodium(III) sandwich complexes of the type [(η5-Cp*)M(η6-aa)](CF3SO3)2 (M = Ir, Rh; 3–14) containing L-tyrosine, L-tryptophan and L-phenylalanine derivatives (aa) can be prepared by treatment of [(η5-Cp*)ML3] (CF3SO3)2 [L = thf, (CH3)2CO, CH3CN] with the appropriate bioligand in thf for N-protected compounds and in CF3COOH for α-amino acids with unprotected amino groups. Coordination to the Cp*MIII fragments stabilizes the ketonic form of the tyrosine aromatic side chains, leading to a marked enhancement in the acidity of the p-hydroxy function. The crystal structure of [Cp*Ir(ActyrOMe)] (CF3SO3)2 (3b, ActyrOMe = N-acetyltyrosine methyl ester) confirms a marked distortion towards an η5-oxohexadienyl coordination mode as may be gauged from the tilting of the p-OH plane C13/C14/C15 by no less than θ = 12.9° from that of the remaining ring atoms. Facial isomers are present in an effective 1:1 ratio for all tryptophan derivatives. Whereas the Cp*IrIII sandwich complexes of aromatic α-amino acids are stable in polar solvents, rapid decay is observed for analogous Cp*RhIII complexes of N-unprotected derivatives in polar solvents. Comparative nonrelativistic and relativistic all-electron density functional calculations on the cationic sandwich complexes [Cp*M(η6-C6H5Me)]n+ (n = 2, M = Ir, Rh; n = 1, M = Ru) confirm that all three metals bind more tightly to Cp* than to toluene as gauged by the respective force constants (k1 > k2). A much larger relativistic enhancement of k2 for M = Ir (279 vs 207 Nm−1) could be responsible for the greater stability of Cp*IrIII complexes in solution.

Isomerism and redox properties of 1-ferrocenyl1,3-butanedionate complexes

The ferrocenyl diketone [(C 5H 5)Fe(C 5H 4)COCH 2COCH 3] has been used to form neutral metal complexes of the 1-ferrocenyl-l,3-butanedionate ligand [(C 5H 5)Fe(C 5H 4)COCHCOH 3] −: the aluminium complex of this ligand, [Al{(C 5H 5)Fe(C 5H 4)COCHCOCH 3} 3], has been characterised by 1H and 13C NMR as a 2:3 mixture of fac and mer isomers, having C 3 and C 1 molecular symmetry respectively. Electrochemical studies show that each peripheral 1-ferrocenyl-1,3-butanedionate ligand L of both M IIL 2 (M = Co, Ni, Cu) and M IIIL 3 (M = Al, Cr, Mn, Fe) complexes undergoes reversible one-electron oxidation at potential values essentially overlapping each other. This means that the central metal ions prevent any electronic communication between the two or three ferrocene fragments. In addition to these reversible ferrocene-centred oxidations, there are reversible one-electron reductions centred at M for MnL 3 and FeL 3 (but not for CrL 3 or AIL 3), but the metal-centre reductions of M IIL 2 are irreversible owing to further reactions following reduction.

Transition metal complexes of 1,3-dihydrobenzo[c]tellurophene: synthesis, spectroscopy and crystal structures

Reaction of 1,3-dihydrobenzo[c]tellurophene (L) with [Cu(MeCN)4]PF6 or AgBF4 yielded [CuL4]PF6 and [AgL4]BF4 respectively, which adopt distorted tetrahedral structures at the metal centre, with the tellurophene ligated via a Te-based lone pair, Cu–Te 2.587(2)–2.596(2) A; Ag–Te 2.7676(7)–2.8104(8) A. With palladium(II) and platinum(II) chlorides the neutral species [PdCl2L2] and [PtCl2L2] were formed readily. Infrared, 125Te-{1H} and 195Pt NMR spectroscopic studies showed that the former is the trans isomer, whereas the latter is the cis isomer. The 125Te-{1H} NMR spectra showed that in solution [RhCl3L3] is a mixture of mer and fac isomers in approximately 3∶2 ratio, whereas RuCl3 reacted with L in EtOH and hypophosphorous acid to give trans-[RuCl2L4] exclusively. The carbonyl derivatives fac-[MnCl(CO)3L2], [Mo(CO)5L], cis-[Mo(CO)4L2] and fac-[Mo(CO)3L3] have also been characterised through IR spectroscopy, 1H, 13C-{1H}, 55Mn, 95Mo and 125Te-{1H} NMR spectroscopy. For the molybdenum species δ(95Mo) and δ(125Te-{1H}) shift to high frequency with increasing substitution of the carbonyl ligands. The crystal structure of [Mo(CO)4L2] confirms the cis geometry and shows the Mo–CO bond lengths trans to L are about 0.10 A shorter than those trans to CO. The 1H NMR spectra of these complexes typically reveal AB quartets for the methylene protons, indicative of co-ordination through a Te-based lone pair in each case. The 125Te-{1H} NMR studies reveal a high frequency co-ordination shift except for the copper and silver species which show δ(125Te-{1H}) to low frequency of that for free L.

Electronic spectrum and crystal structure of fac-MoOCl 3(dppe)

X-ray analysis of the oxomolybdenum(V) complex MoOCl 3(dppe) (dppe = 1,2-bis(diphenylphosphino)ethane) shows that it is the facial isomer. (C 26H 24Cl 3MoOP 2, space group P2 1/ n, a = 13.217(1), b = 12.8935(8), c = 16.0578(9) A ̊ , β = 99.967(5)°, V = 2695.1(6) A ̊ 3, Z = 4, R = 0.038 for 6228 data with I > 1 σ( I).) The electronic absorption spectrum of the title compound is also compared with those of other oxomolybdenum(V) complexes.

Syntheses, characterization and facial–meridional isomerism of tungsten tricarbonyl diphosphine complexes

The complexes fac-[W(CO)3(η2-dppf)(η1-dppm)] 4f, fac-[W(CO)3(η2-dppm)(η1-dppf)] 5f, fac-[W(CO)3(η2-dppf)(η1-dppe)] 6f, fac-[W(CO)3(η2-dppe)(η1-dppf)] 7f, fac-[W(CO)3(η2-dppm)(η1-dppe)] 8f and fac-[W(CO)3(η2-dppe)(η1-dppm)] 9f have been prepared by treating fac-[W(CO)3(η2-diphos)(NCMe)] 1–3 [diphos = 1,1′-bis(diphenylphosphino)ferrocene (dppf), dppm (Ph2PCH2PPh2) or dppe (Ph2PCH2CH2PPh2)] with the corresponding diphosphines. The initially afforded facial isomers are converted into the meridional forms (4m–9m) in a subsequent, slow rearrangement process through opening of the chelated diphosphine ligand. A five-co-ordinate, square-pyramidal intermediate is presumed. In contrast, acid-assisted facial–meridional isomerization of 4f and 6f is likely via a seven-co-ordinate hydrido species. The new compounds have been characterized by elemental analyses and IR, mass and NMR spectroscopy.

Products from the photoreaction of (Me 3P)(OC) 4OsW(CO) 5 with CC1 4; synthesis and isomerization of Os(CO) 3(PMe 3)Cl 2

This paper reports the characterization of the fac-Os(CO) 3(PME 3)Cl 2 ( fac-2) product that is formed when (Me 3P)(OC) 4OsW(CO) 5 ( 1; a complex with a dative OsW bond) is irradiated (λ > 400 nm) in the presence of CCl 4. In an attempt to independently synthesize fac-2), Os 3(CO) 9(PMe 3) 3 was allowed to react with Cl 2. The product, however, was mer-cis-Os(CO) 3(PMe 3)Cl 2 ( mer-cis-2). The mer-cis isomer is converted to the fac isomer ( fac-2) by stirring under nitrogen in THF for nine days. The stereochemistry of each compound was confirmed by infrared and NMR spectroscopy and by X-ray crystallography. The [Os(CO) 2(PMe 3)(Cl)(μ-Cl)] 2 compound ( 3) was also formed as a minor product in the conversion of mer-cis-Os(CO) 3(PMe 3)Cl 2 to fac-Os(CO) 3(PMe 3)Cl 2. Irradiation (λ > 400 nm) of Os(CO) 4(PMe 3) in benzene in the presence of CCl 4 gave a product tentatively identified as fac-Os(CO) 3(PMe 3)(CCl 3)Cl ( 4), which results from the oxidative-addition of CCl 4 to OS(CO) 3(PMe 3).

(η6‐Arene)ruthenium(II) Labeling of Amino Acids and Peptides with Aromatic Side‐Chains

AbstractBis(arene)ruthenium(II) complexes of the type [(η6‐cymene)Ru(η6‐aa)](CF3SO3)n (2‐9) containing L‐tyrosine and L‐tryptophan derivatives may be prepared by treatment of [(η6‐cymene)Ru({CH3)2CO}3](CF3SO3)2 with the appropriate bioligand in CH2Cl2, for fully protected compounds and CF3COOH for α‐amino acids (aa) with unprotected amine or carboxylic acid groups. Whereas the tyrosine and tryptophan methyl ester complexes [(η6‐cymene)Ru(η6‐H2tyrOMe)](CF3SO3)3 (4) and [(η6‐cymene)Ru(η6‐H2trpOMe)](CF3‐SO3)3 (8) contain trications with protonated amino functions, the remaining compounds all exhibit dications. The crystal structure analysis of [(η6‐cymene)Ru(η6‐HtyrOH)](CF3SO3)2 (5) confirms a marked distortion towards an η5‐oxohexadienyl coordination with deprotonation of the aromatic side chain. Although facial isomers are formed in an effectively 1:1 ratio for all tryptophan derivatives fractional crystallization allowed an X‐ray structural characterization of the β‐isomer of [(η6‐cymene)Ru(η6‐ActrpOMe)](CF3SO3)2 (6). Chemospecific labeling of the tryptophan side chain was established for the mixed dipeptide phenylalanyltryptophan.

Synthesis, Properties, and Reactions of Monosulfonated Triphenylphosphine (PPh2(m-C6H4SO3K) = TPPMS) Complexes of Iridium(I). Crystal and Molecular Structure of [N(CH2C6H5)(C2H5)3+][PPh2(m-C6H4SO3)-]·H2O

Iridium complexes containing the TPPMS ligand (TPPMS = PPh2(m-C6H4SO3K)) have been prepared and studied in DMSO and H2O as a comparison to the PPh3 analogues in toluene. Measurements of the pH of the complexes show that most are almost neutral, but Ir(CO)(H)(TPPMS)3 is basic (pH = 10.7). The basicity of Ir(CO)(H)(TPPMS)3 is confirmed by its reaction with H2O to give Ir(CO)(H)2(TPPMS)3+. In aqueous solution, reaction of trans-Ir(CO)(OH)(TPPMS)2 with H2 produces only fac-Ir(CO)(H)3(TPPMS)2 not the usual mixture of facial and meridional isomers. This is attributed to a hydrogen-bonding interaction between the two cis-TPPMS ligands in H2O. Reaction of trans-Ir(CO)(Cl)(TPPMS)2 with CO in water produces [Ir(CO)2(TPPMS)2+]Cl- and [Ir(CO)3(TPPMS)2+]Cl sequentially in a reaction that is pH dependent. Reaction of trans-Ir(CO)(OH)(TPPMS)2 with CO results in products based on the water gas shift-reaction. These complexes of TPPMS are spectroscopically very similar to the PPh3 analogues, but display significantly diff...