First Row Transition Metal Complexes Research Articles

Accuracy of geometries: influence of basis set, exchange?correlation potential, inclusion of core electrons, and relativistic corrections

The geometries of a set of small molecules were optimized using eight different exchange–correlation (xc) potentials in a few different basis sets of Slater-type orbitals, ranging from a minimal basis (I) to a triple-zeta valence basis plus double polarization functions (VII). This enables a comparison of the accuracy of the xc potentials in a certain basis set, which can be related to the accuracies of wavefunction-based methods such as Hartree–Fock and coupled cluster. Four different checks are done on the accuracy by looking at the mean error, standard deviation, mean absolute error and maximum error. It is shown that the mean absolute error decreases with increasing basis set size, and reaches a basis set limit at basis VI. With this basis set, the mean absolute errors of the xc potentials are of the order of 0.7–1.3 pm. This is comparable to the accuracy obtained with CCSD and MP2/MP3 methods, but is still larger than the accuracy of the CCSD(T) method (0.2 pm). The best performing xc potentials are found to be Becke–Perdew, PBE and PW91, which perform as well as the hybrid B3LYP potential. In the second part of this paper, we report the optimization of the geometries of five metallocenes with the same potentials and basis sets, either in a nonrelativistic or a scalar relativistic calculation using the zeroth-order regular approximation approach. For the first-row transition-metal complexes, the relativistic corrections have a negligible effect on the optimized structures, but for ruthenocene they improve the optimized Ru–ring distance by some 1.4–2.2 pm. In the largest basis set used, the absolute mean error is again of the order of 1.0 pm. As the wavefunction-based methods either give a poor performance for metallocenes (Hartree–Fock, MP2), or the size of the system makes a treatment with accurate methods such as CCSD(T) in a reasonable basis set cumbersome, the good performance of density functional theory calculations for these molecules is very promising; even more so as density functional theory is an efficient method that can be used without problems on systems of this size, or larger.

Synthesis of a First-Row Transition Metal Parent Amido Complex and Carbon Monoxide Insertion into the Amide N−H Bond

The parent amido iron complex (dmpe)2Fe(H)(NH2) (dmpe = 1,2-bis(dimethylphosphino)ethane), the first such first-row transition metal complex, has been synthesized and characterized spectroscopically and crystallographically. This complex has been found to insert carbon monoxide into the amide N-H bond (rather than the M-N bond) to give trans-(dmpe)2Fe(H)(NHCHO). The mechanism of this transformation has been studied and is believed to occur through an unusual mechanism in which CO behaves as an apparent electrophile.

SYNTHESIS AND CHARACTERIZATION OF NOVEL MACROCYCLES AND THEIR COMPLEXES WITH TRANSITION METAL IONS

ABSTRACT Novel Schiff base macrocycles, 1,4,7,10-tetraazacyclododeca-5,6,11,12-tetraaminoisobutyric acid-4,6,10,12-tetraene (L1), 1,4,7,10-tetraazacyclododeca-5,6,11,12-tetraaminopiperizine-4,6,10,12-tetraene (L2) and 1,4,7,10-tetraazacyclodeca-5,6,11,-12-tetraaminouracil-4,6,10,12-tetraene (L3) containing pendant groups have been synthesized by reactions of oxamidediisobutyric acid, oxamidedipiperizine or oxamidediuracil, respectively, with ethylenediamine. Their first-row transition metal complexes of the types [M(L)Cl2] and [M(L)Cl2]Cl have been prepared. All of the compounds have been characterized on the basis of elemental analyses, IR, UV-Visible, EPR, NMR spectroscopy, magnetic moments and conductance measurements. The complex of divalent metal ions are non-ionic while those of trivalent metal ions are 1:1 electrolytes. For all of these complexes an octahedral stereochemistry has been proposed.

Unusual magnetic property associated with dimerization within a nickel tetramer.

A new ion-pair complex, 1-benzyl-4-aminopyridinium bis(maleonitriledithiolato)nickelate(III) (1), has been synthesized. The variable magnetic susceptibility results of 1 show a discontinuity around 184 K, which is phenomenologically similar to that observed for first-row transition metal complexes undergoing a spin crossover transition. The crystal structure analyses of 1 at high and low temperatures indicate that this unusual magnetic property is associated with a packing structure that changes from tetrameric spin clusters to dimers between neighboring spin carriers.

First-row transition metal complexes of sterically-hindered amidinates

Complexes of sterically-hindered amidinate ligands with first-row transition metals are described. The amidinate ligands feature bulky terphenyl substituents [2,6-(2,4,6-Me3Ph)2Ph or 2,6-(4-tBuPh)2Ph] attached to the backbone carbon atoms, providing bowl-shaped ligand environments. When employing divalent transition metal halides, bis-amidinate metal complexes are formed exclusively, whereas the use of Ni(acac)2 or CuCl allows access to mono-amidinate species. Additionally, the solid-state structure of one mono-amidinate [(LBut)Ni(acac)] and three bis-amidinate complexes [(LMe)2M; M = Mn, Co, Ni] are presented.

A periodic walk: a series of first-row transition metal complexes with the pentadentate ligand PY5.

A series of transition metal complexes derived from the pentadentate ligand PY5, 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine, illustrates the intrinsic propensity of this ligand to complex metal ions. X-ray structural data are provided for six complexes (1-6) with cations of the general formula [M(II)(PY5)(Cl)](+), where M = Mn, Fe, Co, Ni, Cu, Zn. In complexes 1-4 and 6, the metal ions are coordinated in a distorted-octahedral fashion; the four terminal pyridines of PY5 occupy the equatorial sites while the axial positions are occupied by the bridging pyridine of PY5 and a chloride anion. Major distortions from an ideal octahedral geometry arise from displacement of the metal atom from the equatorial plane toward the chloride ligand and from differences in pyridine-metal-pyridine bond angles. The series of complexes shows that M(II) ions are consistently accommodated in the ligand by displacement of the metal ion from the PY5 pocket, a tilting of the axial pyridine subunit, and nonsymmetrical pyridine subunit ligation in the equatorial plane. The displacement from the ligand pocket increases with the ionic radius of M(II). The axial pyridine tilt, however, is approximately the same for all complexes and appears to be independent of the electronic ground state of M(II). In complex 5, the Cu(II) ion is coordinated by only four of the five pyridine subunits of the ligand, resulting in a square-pyramidal complex. The overall structural similarity of 5 with the other complexes reflects the strong tendency of PY5 to enforce a distorted-octahedral coordination geometry. Complexes 1-6 are further characterized in terms of solution magnetic susceptibility, electrochemical behavior, and optical properties. These show the high-spin nature of the complexes and the anticipated stabilization of the divalent oxidation state.

Late first-row transition-metal complexes of texaphyrin.

The preparation of first-row transition-metal complexes of texaphyrin, a porphyrin-like, monoanionic penta-aza macrocyclic ligand, is reported. Specifically, the synthesis of organic-soluble Mn(II) (1), Co(II) (2), Ni(II) (3), Zn(II) (4), and Fe(III) (5) texaphyrin derivatives and their water-soluble counterparts (6-10) from appropriate metal-free, nonaromatic macrocyclic precursors is described. It was found that metal cations of sufficient reduction potential could act to oxidize the nonaromatic macrocyclic precursor in the course of metal insertion. Complexes were characterized by X-ray diffraction analysis, electrochemistry, flash photolysis, and EPR spectroscopy. The structural and electronic properties of these "expanded porphyrin" complexes are compared with those of analogous porphyrins. Notably, the texaphyrin ligand is found to support the complexation of cations in a lower valence and a higher spin state than do porphyrins. Interactions between the coordinated cation and the ligand pi system appear to contribute to the overall bonding. Texaphyrin complexes of Mn(II), Co(II), and Fe(III) in particular may possess sufficient aqueous stability to permit their use in pharmaceutical applications.

Silica-supported alkylidene complexes: their preparation, characterization and reactivity, especially towards olefins

When silica is employed as a bidentate ligand to bis(alkyl) complexes of the early first-row transition metals, rare terminal alkylidene fragments are readily formed and stabilized. These materials have the empirical formula (SiO) 2MCHEMe 3, where M is Ti, V, or Cr and E is C or Si, incorporating two covalent interactions with oxygens of the silica surface which serve to immobilize the grafted complexes. The silica-supported alkylidene complexes undergo several typical reactions, including electrophilic cleavage with H + and Br 2, metathetical exchange with acetone and styrene, and addition of a silane. Reaction with ethylene leads to oligomerization/polymerization, for which the material with M=Cr is particularly effective. The mechanism of initiation of polymerization, as well as the influence of the silica support (fumed versus precipitated) on the composition of the active sites, is discussed.

Synthesis and structural studies of diamagnetic first-row transition metal complexes with the rigid nitrogen ligand: bis[N-(2,6-diisopropylphenyl)imino]acenaphthene

Reported are the syntheses and characterization of diamagnetic copper(I) and iron(II) complexes with the bidentate nitrogen ligand bis[N-(2,6-diisopropylphenyl)imino]acenaphthene (o,o′-iPr2C6H3-BIAN). Namely, they are [Cu(o,o′-iPr2C6H3-BIAN)2](ClO4)(AcOH) (1), and [Fe(bipy)2(o,o′-iPr2C6H3-BIAN)](ClO4)2 (2), where bipy=2,2′-bipyridine, AcOH=acetic acid. Moreover, the crystal structure of the novel dimeric Cu(I) compound with the p-brominated derivative of the o,o′-iPr2C6H3-BIAN ligand, is also discussed. In [CuBr(o,o′-iPr2-p-BrC6H2-BIAN)]2 (3), the respective Cu(I) ion is in four-coordinate environment tetrahedrally surrounded by two imine nitrogen atoms of o,o′-iPr2-p-BrC6H2-BIAN, and by two bridging bromide atoms.

Synthesis and electrochemical properties of transition metal complexes of 2,2':6',2''-terpyridine 1,1''-dioxide.

The synthesis and characterization of a series of first-row transition metal complexes of 2,2‘:6‘,2‘ ‘-terpyridine 1,1‘ ‘-dioxide (terpyO2) are reported. Four new bis complexes [M(terpyO2)]X2 (M = Mn(II), Fe(II), Co(II), and Ni(II); X = ClO4- and BF4-) and one mono complex [Cu(terpyO2)(H2O)](ClO4)2 were isolated and characterized, and electrochemical properties were examined.

Density functional study of the first-row transition-metal complexes M–CH2, M–CHF, and M–CF2

Carbenes and fluorocarbenes are important intermediates in the hydrodechlorination of CFCs catalyzed by metal surfaces. However, the reaction mechanism at a molecular level is not completely understood. In this work, density functional calculations have been performed for the first-row transition-metal complexes M–CH2, M–CHF, and M–CF2 aiming to conbribute to the understanding of the metal/carbene interaction mechanism. Relative energies, geometries, and frequencies of the M–CXY complexes in different electronic states are reported. The binding mechanism is described through an analysis of the molecular orbitals. The binding energy of the M–CF2 is about 30% smaller than the respective M–CH2 binding energy. The electronic configuration of all complexes studied is presented in a diagram that allows one to predict qualitatively properties such as geometries, multiplicities, charge transfers, and relative bond lengths.

Pendant-Arm Tri- and Tetraazamacrocycles: Synthesis, Structure and Properties of their First-Row Transition Metal Complexes

Article Pendant-Arm Tri- and Tetraazamacrocycles: Synthesis, Structure and Properties of their First-Row Transition Metal Complexes was published on July 1, 2001 in the journal Reviews in Inorganic Chemistry (volume 21, issue 3-4).

2-(4′,4′-Dimethyl-3′,4′-dihydrooxazol-2′-yl)phenol: Some First-Row Transition Metal Complexes of This Naturally Occurring Binding Group

The synthesis and characterization of monomeric Mn III , Co II , Ni II , Cu II , and Zn II phenolates derived from a biologically relevant ligand, 2-(4',4'-dimethyl-3',4'-dihydrooxazol-2'-yl)phenol (1), are described. The addition of Mn(OAc) 2 ·4H 2 O to an ethanolic solution of 1 affords an unexpected 1:3 complex [Mn(OR){O(Ox)} 2 ] (2) [R=C 6 H 4 CONHC(Me 2 )CH 2 OH, Ox=2-(4,4-dimethyl-2-oxazolinyl)phenyl] in which one of the five-membered oxazoline rings is partially hydrolyzed. The complexes [M{O(Ox)} 2 ] [M=Co (3), Ni (4), Cu (6), or Zn (7)] were prepared in good yield by the reactions of 1 with the corresponding metal acetates. Novel formation of the six-coordinate Ni II complex 5 with neutral acetic acid was observed during the crystallization process. The complexes were characterized by elemental analysis, magnetic susceptibility, as well as EPR, 1 H NMR, electronic, and mass spectral techniques. Complexes 2, 3, 5, 6, and 7 were characterized by single crystal X-ray diffraction studies. Complex 2 is six-coordinate whereas complexes 3, 6, and 7 are four-coordinate with two oxazoline bidentate ligands. The geometry around the metal center is found to be distorted tetrahedral for all of the four-coordinate complexes. Complex 5 is octahedral with four coordination sites occupied by the two bidentate oxazoline ligands and the other two are occupied by two neutral acetic acid molecules. The hydroxy groups of the coordinated acetic acid are hydrogen-bonded to the phenolate oxygen atoms of the oxazoline ligands. The variable-temperature 1 H NMR spectroscopic studies of complex 7 indicate that the interconversion between the (M) and (P) helix is slow at low temperatures.

First-row transition metal complexes of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate)

Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with M(NO 3) 2· xH 2O (M=Mn, Co, Ni, Zn) in acetonitrile solutions produced a linear polymer [Mn(μ-C 6H 5C 4O 3)(C 6H 5C 4O 3)(H 2O) 3] n ( 1) and a series of isomorphous monomeric complexes [M(C 6H 5C 4O 3) 2(H 2O) 4] [M=Co ( 2), Ni ( 3), Zn ( 4)]. The complex 1 contains octahedral manganese with each metal centre being bridged μ-1,3 by a phenylsquarate ligand to two neighbouring metal atoms and further coordinated to a pendant phenylsquarate ligand group and three aqua ligands. The isomorphous monomeric complexes 2– 4 all contain two phenylsquarate ligand groups oriented trans to each other, but with the substituent phenyl group on the ligand oriented cis to the ligating oxygen atom. The coordination polyhedron in each of these monomers is completed by four aqua ligands. The polymeric manganese complex shows no significant antiferromagnetic coupling and no semiconductivity.

Coordination geometries of bis(4-amino-3-alkyl-1,2,4-triazole-5-thione) complexes of first-row transition metals: crystal structures of complexes with propyl and hydrogen in the 3-position. Relationship to the 3-methyl and 3-ethyl analogs

A series of bis bidentate complexes of 4-amino-3-propyl-1,2,4-triazole-5-thione, SN 4C 5H 10 (apt, 1) of the divalent ions Fe, Co, Ni, and Zn has been crystallized by direct combination of the ligand and metal nitrate or perchlorate hydrate salt in ethanol. The structures were determined by single-crystal X-ray diffraction techniques. In all the complexes, the triazole bonds to the metal ion through the amine and thione substituents on the five-membered ring. [Fe(apt) 2(H 2O) 2](ClO 4) 2 ( 2) has the like-ligands trans to each other. The FeN distances (2.259(5) Å) are elongated relative to the FeO bond lengths (2.092(5) Å). The compounds [Co(apt) 2(H 2O) 2](NO 3) 2·2H 2O ( 3), [Ni(apt) 2(H 2O) 2](NO 3) 2·2H 2O ( 4), and [Zn(apt) 2(H 2O) 2](NO 3) 2·2H 2O ( 5) are isostructural, with the water molecules cis to each other and the triazole ligands positioned with the amine groups cis and S atoms trans. A series of complexes of 4-amino-1,2,4-triazole-5-thione (aht, 6) of divalent Mn, Co, and Zn has also been crystallized by similar means and structurally characterized. [Mn(aht) 2(H 2O) 2](ClO 4) 2 ( 7) has the ligands arranged as in 3, though with a non-centrosymmetric packing (space group C 2). The cis MnN distances are significantly longer (2.377(2) Å) than the MnO distances (2.160(2) Å). [Co(aht) 2(H 2O) 2](ClO 4) 2 ( 8) possesses the trans geometry found in 2, though with comparable CoN and CoO bond lengths (2.175(3) and 2.082(3) Å). [Zn(aht) 2(H 2O) 2](ClO 4) 2 ( 9) is isostructural with 7. These structures are compared with those of two recently reported series of 4-amino-3-alkyl-1,2,4-triazole-5-thione complexes (alkyl=methyl and ethyl) in order to gauge the effect of the alkyl group on the coordination behavior of the triazole ligand towards the divalent first-row transition metals.

Electronic structure of [(CpCr)[(CO)3M]]mu-Cot (M = Cr, Fe): a theoretical study.

The electronic structure of two cyclooctatetraene-bridged dinuclear first-row transition metal complexes of the type [(CpM)[(CO)3M']]mu-Cot (M = Cr; M' = Fe (1), Cr (2)) was investigated by complete active space self-consistent field (CASSCF) calculations. In this context the differences in the binding capabilities of the complex fragments CpM and (CO)3M are discussed on the basis of extended Huckel molecular orbital (MO) calculations. The geometries used for the CASSCF calculations for complex 1 were obtained from the crystal structure. For 2 a model structure was established by geometry optimization using density functional methods. The CASSCF results agree well with the experimental findings and provide insight into the binding situation of the two compounds. Complex 1 can be regarded as being composed of a chromocene-like subunit CpCr(eta5-C5H5) and the fragment (CO)3Fe(eta3-C3H3). A direct metal-metal bond is found, involving one initially singly occupied orbital of each fragment, leading to a doublet ground state for 1 with the remaining unpaired electron localized at the chromium center. For 2 no such direct metal-metal bond can be recognized. A very weak direct metal-metal interaction is induced by electron donation from the Cot2- ligand into a formally unoccupied metal-metal binding orbital combination. In the quartet ground state all three unpaired electrons are localized at the chromium center of the formally doubly positive charged CpCr unit, on which complex fragment [(CO)3Cr(eta5-Cot)]2- acts like a cyclopentadienyl ligand. The coordination sphere of the chromium center of the CpCr unit resembles that of a metallocene metal center and its metal 3d occupation scheme corresponds to that of vanadocene.

Density functional predictions for metal and ligand nuclear shielding constants in diamagnetic closed-shell first-row transition-metal complexes

We use the well-established functionals LDA, BLYP, BP86, BP91 and B3LYP as well as the more recent HCTH, PBE and PBE0 functionals to investigate the density functional theory (DFT) metal nuclear magnetic shieldings in ten transition-metal complexes ([Co(CN)6]3−, [Co(NH3)6]3+, Cr(CO)6, [CrO4]2−, Fe(CO)5 , Fe(C5H5)2, [MnO4]−, [Mn(CO)6]+, VOCl3, VF5). We also investigate the 13C and 17O ligand shielding parameters in three first-row transition-metal carbonyl complexes [Cr(CO)6 , Ni(CO)4 and Fe(CO)5] as well as the 17O shielding parameters in three first-row transition-metal oxo complexes ([CrO4]2−, [MnO4]−, FeO4). We apply Malkin's sum-over-states density functional perturbation theory (SOS-DFPT) to our own HCTH functional and discuss the effect of the level shift correction to the DFT orbital energies on the calculated metal and ligand shieldings. For the metal chemical shifts the hybrid functionals are superior in quality to the non-hybrid functionals. Amongst this latter group HCTH and LDA provide the least errors. The large discrepancy between hybrid and non-hybrid functional paramagnetic shieldings is rationalised in terms of differences in the magnitude of their matrix element terms and eigenvalue differences. Our analysis of the dominant paramagnetic shielding contributions from the occupied-virtual MO excitations indicates that the poor performance of the non-hybrid functionals originates from their underestimation of the numerator (b∣lα∣j)(j∣lAβrA−3∣b) term rather than any deficiency in their description of the eigenvalue differences εb–εj. The relative increase in the magnitude of εb–εj following inclusion of a fraction of exact Hartree-Fock exchange is less than the corresponding increase in the (b∣lα∣j)(j∣lAβrA−3∣b) term. The net effect is a significant increase in the paramagnetic shielding terms for hybrid functionals. For the metal carbonyls the GGA functional 13C and 17O shielding parameters are superior in quality compared to the non-hybrid functionals with HCTH providing the best agreement with experiment. For the metal-oxo complexes, the 17O shieldings produced by the hybrid and non-hybrid functionals were found to be too deshielded and too shielded respectively, where the latter lie closer to the experimental values.

First-Row Transition-Metal Complexes of the 1-Methoxycyclobutenedionate(1-) Ion.

The synthesis and characterization by single-crystal X-ray crystallography of a series of monomeric first-row transition-metal complexes with the 1-methoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH(3)OC(4)O(3))(2)(H(2)O)(4)] (M = Mn, Co, Ni, Zn) are C(2) symmetric and crystallize in the monoclinic space group C2/c. The metal atom in each of these complexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) ligands, the methoxy substituent being oriented cis with respect to the ligating oxygen atom. The remaining coordination sites are filled by four aqua ligands. Monomers are linked by O-H.O hydrogen bonds to form arrays of stepped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C(4)O(4))(H(2)O)(2)].0.25H(2)O}(n)() is produced. This complex crystallizes in the tetragonal space group P4/n and has a structure similar to, but differing significantly from, those of a series of 3-dimensional cage squarates which have been reported previously.

New, Axially Chiral, Bimetallic Catalysts for Asymmetric Alkylation of Aldehydes with Diethylzinc

Axially chiral bis(salicylidene)ethylenediamine (H2salen)-type ligands 3 (cf. Schemes 1 and 3) are efficient ligands for the enantioselective addition of diethylzinc to aldehydes. There is ample evidence that an active bimetallic catalyst forms an effective chiral pocket (see Fig. 2); of a series of first-row transition-metal complexes with these ligands, the most stereoselective were the CoII complexes (see Fig. 1). Best ee values as well as the fastest rates (see Tables 2 and 3) were obtained with these CoII complexes when an EtO substituent was present at C(3) of the salicylaldehyde residues of ligand 3 (R1=EtO), i.e., complex [CoII(3′h)] produced up to 93% ee with aromatic aldehydes and 78% ee for aliphatic aldehydes (see Table 4).

Ion-molecule reactions in a quadrupole ion trap as a probe of the gas-phase structure of metal complexes

A method is described in which the coordination number in metal complexes can be determined using ion–molecule reactions in a quadrupole ion trap mass spectrometer. Complexes of first-row transition metals in the +2 oxidation state, including manganese through zinc, are electrosprayed, isolated in the ion trap and allowed to react with gases. The coordination number is ascertained by observing the reagent ligands that successfully react with the complex. It was generally observed that six-coordinate complexes are unreactive, five-coordinate complexes react with pyridine and ethylamine, four-coordinate complexes react with pyridine, ethylamine and ammonia and threecoordinate complexes react with all the reagent ligands studied, including water and methanol. The order of reactivity for a given complex reacting with the various reagent ligands is found to follow the order of the electron-donating ability of the reagent ligands. In addition, the effect of the metal center on the reactivity of the complexes in the gas phase is analogous to solution-phase trends; electronic structure strongly influences the gas-phase reactions. These results were then used to predict the complexation behavior of novel podand ligands for which condensed phase information is not available. The results indicate that ion–molecule chemistry in the gas phase may be useful in predicting the interactions between novel multidentate ligands and metals in solution. © 1998 John Wiley & Sons, Ltd.