Dichromium Complex Research Articles

SYNTHESIS AND CHARACTERIZATION OF MONONUCLEAR AND BINUCLEAR CHROMIUM(III) COMPLEXES OF α-BENZOIN OXIME

ABSTRACT Irradiation of a THF solution containing Cr(CO)6 and α-benzoin oxime (H2BNO) under various atmospheric conditions, of either argon or vacuum, gave two dichromium(III) complexes of the formulae [Cr(μ-OH)(BNIM)(HBNO)]2 (1) and [Cr(BNIM)(HBNO)(THF)]2O (2) where BNIM is the α-benzoin imine radical anion formed as a result of homolytic cleavage of the oxime N-OH bond. When a related reaction of α-benzoin oxime was carried out with Cr(NO)3 in open atmosphere, Cr(HBNO)3 (3) was obtained. Variable-temperature magnetic susceptibility measurements show a magnetic moment of 8.12 B.M. for the μ-dihydroxo complex (1) at room temperature. This high magnetic moment value strongly confirms the formulation of a dimer consisting of two benzoin imine radicals (S=1/2 coordinated to bridged dichromium(III)(S=3/2) ions. In contrast, the μ-oxo complex (2) shows a magnetic moment of 3.10 B.M. which is even smaller than that observed for the monomeric complex Cr(HBNO)3 (3) at room temperature. Moreover, IR spectral analysis was very informative in assigning the vibrations due to Cr2(OH)2 4+ and Cr2O4+ moieties for the complexes (1) and (2), respectively. Thermal gravimetric analysis (TGA) of complex (2) has shown decompositions due to coordinated THF molecules, followed by gradual decomposition of bezoin imine ligands. Interestingly, a low-energy transition in the Vis-near-IR region assigned as BNIM→Cr(III)LMCT transition was observed for the [Cr(BNIM)(HBNO)(THF)]2O complex.

Synthesis, Structures and Ethylene Polymerisation Behaviour of Low Valent β-Diketiminato Chromium Complexes

The preparation, reaction chemistry and ethylene polymerisation behaviour of low valent β-diketiminato chromium complexes are described. [(DDP)CrCl(µ-Cl)]2 (1) [DDPH = 2-{(2,6diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}pent-2-ene] is formed by treatment of CrCl3(THF)3 with LiDDP. Alkylation of 1 with AlMe3 results in the formation of the binuclear dimethyl complex [(DDP)CrMe(µ-Cl)]2 (2). In contrast, the attempted alkylation of 1 with benzylmagnesium chloride results in reduction to form the dichromium(II) complex [(DDP)Cr(µ-Cl)]2 (3). Depending on the conditions of crystallisation, 3 can be obtained as the THF adduct [3(THF)2·THF] or co-crystallised with a molecule of dibenzyl [3·Bz-Bz]. Cleavage of the dimeric unit in 1 can be achieved by the addition of carboxylates or β-diketonates to give [(DDP)CrCl(O2CR)(THF)] (R = Me 4a, Ph 4b) and [(DDP)CrCl({O(R)C}2CH)] (R = Me 5a, Ph 5b), respectively. Single crystal X-ray diffraction studies have been performed on 1, 2, 3(THF)2·THF, 3·Bz-Bz, 4a, and 5b. Complexes 1, 2 and 3(THF)2·THF are dimeric and have molecular C2h symmetry. Complex 3·Bz Bz is also dimeric but has its potential C2h symmetry removed by a significant tetrahedral distortion of the chromium coordination geometry. Compound 4a has an octahedral chromium centre coordinated to a single bidentate diketiminate ligand, a bidentate acetate, a chloride and a THF molecule. Complex 5b has a square pyramidal chromium with apical chloride and basal η2 diketiminate and diketonate ligands. The complex contains strong intramolecular C−H···π stabilising interactions. All the complexes are active in ethylene polymerisation on treatment with suitable aluminium activators, affording high molecular weight polyethylene.

Unique Axial Interaction of a Quadruply-Bonded Cr(II)-Cr(II) with Two Pt(II) Atoms in the Linearly Aligned Pt-Cr-Cr-Pt Supported by Four 6-Diphenylphosphino-2-pyridonate Ligands

Abstract Linearly aligned tetranuclear Pt(II)-Cr(II)-Cr(II)-Pt(II) complexes were prepared using a tridentate pyphos ligand (pyphos = 6-diphenylphosphino-2-pyridonate). The bonding between Cr(II) and Pt(II) was discussed on the basis of magnetic measurements. A dichromium complex, [Cr2(pyphos)4] (1), was prepared by the reaction of [Cr2(OAc)4] with the sodium salt of pyphos ligand. The complex 1 has four phosphorus atoms capable of holding transition metals at both of the axial positions of the Cr2 moiety. Three tetranuclear Pt(II)-Cr(II)-Cr(II)-Pt(II) complexes, i.e., [Cr2Pt2Me4(pyphos)4] (2), [Cr2Pt2Cl4(pyphos)4] (3), and [Cr2Pt2Cl2Me2(pyphos)4] (4), have been prepared by the addition of the respective platinum species, PtIIMe2, PtIICl2, and PtIIMeCl, to the axial positions of the Cr2 moiety of 1. Magnetic measurements of 1-4 together with a crystallographic study for the complexes 1 and 2 revealed that the quadruply-bonded Cr-Cr distance was delicately altered by the nature of the Pt atoms, i.e., the kind of substituents (Cl and/or Me) on the Pt atoms.

The effect of divergent-bite ligands on metal–metal bond distances in some paddlewheel complexes

In a paddlewheel type bimetal unit, the most frequent arrangement of the bridging ligands has a conformation such that the two donor orbitals are directed along approximately parallel lines. However, when a ligand has one of the two donor atoms derived from a six-membered ring and the other from a fused five-membered ring, the two donor orbitals will be directed divergently. Such divergent-bite ligands might be expected to elongate the M-M bonds. A Cr-Cr core supported by a set of four divergent-bite ligands, Cr2(CHIP)4, where CHIP is the anion of 1′,3′-dihydrospiro[cyclohexane-1,2′-[2H]imidazo[4,5-b]pyridine], has been synthesized and crystallographically characterized. It has a Cr-Cr distance of 2.016(1) Å, which is much longer than those in paddlewheel complexes with non-divergent dinitrogen ligands. This is the first example of a dichromium complex supported by a set of four divergent-bite ligands and no axial coordination. An analogous complex, namely Mo2(azin)4, where azin represents the anion of 7-azaindole, has also been characterized. Together with W2(azin)4, which was previously reported, the first series of quadruple bonds wrapped in a sheath of four divergent-bite ligands has been obtained. A comparison of the M-M bond lengths with those in a homologous series having a more flexible ligand, DTolF, which is the anion of di-p-tolylformamidine, reveals that the Cr-Cr quadruple bonds are much more sensitive to the effect of the bridging ligand geometry than are Mo-Mo and W-W quadruple bonds; this is very similar to the trend in susceptibility of quadruple bonds towards axial coordination.

Quadruply Bonded Dichromium Complexes with Variously Fluorinated Formamidinate Ligands.

Complexes of chromium with various amidinate anions of N,N'-di(biphenyl)formamidine (DbiPhF), N,N'-di(pentafluorophenyl)formamidine (DPh(F)()5F), N,N'-di(p-fluorophenyl)formamidine (DPh(p)(-)(F)F), N,N'-di(o-fluorophenyl)formamidine (DPh(o)(-)(F)F), N,N'-di(3,5-fluorophenyl)formamidine (DPh(3,5)(-)(F)F), and N,N'-di(m-fluorophenyl)formamidine (DPh(m)(-)(F)F) have been synthesized and structurally characterized to study the response of the M-M multiple bond to the donor capacity of the ligand by varying the substituents of the aromatic rings. All six of these dinuclear fluorinated amidinate derivatives of the chromium(II) compounds have the paddlewheel configuration. The synthetic route involves the reaction of CrCl(2) with the corresponding lithium salt of the ligands, LiDArF (where Ar = o-C(6)H(4)F, m-C(6)H(4)F, p-C(6)H(4)F, p-C(6)H(4)C(6)H(5), C(6)F(5), or 3,5-C(6)H(3)F(2)). Compounds [Cr(2)(DPh(p)(-)(F)F)(4)] (1), [Cr(2)(DPh(m)(-)(F)F)(4)] (2), [Cr(2)(DPh(3,5)(-)(F)F)(4)].C(6)H(14) (3.C(6)H(14)), and [Cr(2)(DbiPhF)(4)].0.7CH(2)Cl(2) (4.0.7CH(2)Cl(2)) show no variation in the Cr-Cr quadruple bond length, even though the ligands have very different basicities. In the solid state, [Cr(2)(DPh(F)()5F)(4)] (5) shows close axial contacts between the o-F atoms and the chromium metal centers. The (19)F NMR show an unresolved and broad signal for all o-F atoms that cannot be resolved even at very low temperature. To assess the efficiency of the contacts, [Cr(2)(DPh(o)(-)(F)F)(4)] (6) was prepared.( )()The crystal structure shows the same kind of Cr.F interactions as in 5, and an elongation of the Cr-Cr quadruple bond, compared with the values for the complexes 1, 2, 3, and 4. These new complexes reveal that the electronic contribution of the ligand basicity to the M-M bond is smaller and less important than the axial interactions of the chromium centers. Crystal data: for 1, orthorhombic, space group Fddd with a = 25.25(7) Å, b = 26.752(12) Å, c = 28.57(4) Å, alpha = beta = gamma = 90 degrees, and Z = 16; for 2, triclinic, space group P&onemacr; with a = 9.606(12) Å, b = 9.727(10) Å, c = 13.249(11) Å, alpha = 69.24(1) degrees, beta = 73.84(2) degrees, gamma = 84.24(2) degrees, and Z = 1; for 3.C(6)H(14), triclinic, P&onemacr; with a = 10.8274(10) Å, b = 13.739(2) Å, c = 18.152(4) Å, alpha = 83.25(1) degrees, beta = 75.61(2) degrees, gamma = 70.246(10) degrees, and Z = 2; for 4.0.7CH(2)Cl(2), triclinic P1 with a = 9.689(2) Å, b = 13.7088(3) Å, c = 16.844(3) Å, alpha = 69.90(3) degrees, beta = 87.10(3) degrees, gamma = 70.13(3) degrees, and Z = 1; for 5, monoclinic, C2/c with a = 19.114(3) Å, b = 18.957(3) Å, c = 29.923(6) Å, beta = 97.27(1) degrees, and Z = 4; for 6, triclinic, P&onemacr; with a =10.225(2) Å, b = 11.312(2) Å, c = 11.797(3) Å, alpha = 117.08(1) degrees, beta = 96.432(2) degrees, gamma = 107.52(2) degrees, and Z = 1.

Synthesis of multiply-bonded dichromium complexes with a variety of formamidinate ligands

A series of dichromium tetraformamidinate complexes with (ArNCHNAr) − where Ar is X 2C 6H 3 or XC 6H 4 and X is the remote substituent 3,5-Cl 2, 3,4-Cl 2, p-Cl, p-CF 3, m-CF 3, p-OCH 3 or m-OCH 3 has been synthesized, and the structures of four of the compounds determined by X-ray crystallography. The Cr–Cr bond distances of the complexes structurally characterized are 1.9072(10) Å [Cr 2(( p-ClC 6H 4N) 2CH) 4], 1.9162(10) Å [Cr 2((3,5-Cl 2C 6H 3N) 2CH) 4], 1.9018((8) Å [Cr 2(( m-CF 3C 6H 4N) 2CH) 4 ], and 1.9178(11) Å [Cr 2(( m-OCH 3C 6H 4N) 2CH) 4]. 1H NMR spectroscopy and electrochemistry were performed on the series. The diamagnetic anisotropy of the Cr–Cr bond was calculated from X-ray crystallographic and 1H NMR data and correlates with the Hammett constant of the formamidine ligands.

Quadruply bonded dichromium complexes with bridging α-metalla-carboxylates

X-ray crystallographic studies were carried out on quadruply bonded dichromium complexes with bridging α-metalla-carboxylates to examine the influence of these ligands on the Cr 4Cr bond distance. α-Metalla-carboxylic acids are the weakest carboxylic acids known to date. Cr 2(μ-FpAc) 4(FpAcH) 2 ( 1) (FpAc − = ( η 5-C 5H 5Fe(CO) 2(CH 2COO) −) has been prepared by adjusting the pH of a solution of CrCl 2 and FpAcH in water and ethanol (1:3) to about 8. 1 crystallizes in the monoclinic space group P2 1/n ( No. 14, Z = 2) with α = 11.8349(6), b = 13.605(2), c = 17.663(2) A ̊ , β = 98.802(10)°, V = 2810.3(5) A ̊ 3 . The Cr 4Cr bond distance was found to be 2.3070(8) Å. FpAcH molecules are axially bound to both ends of the Cr 2 unit in such a manner that the carboxylic CO group is coordinated to the Cr atom and the OH group forms a hydrogen bond to one of the equatorial O atoms of the bridging carboxylate O atoms. The axial CrO bond distance was found to be 2.246(2) Å and the OO distance of the hydrogen bond was found to be 2.722(3) Å, respectively.

Novel (fulvalene)dichromium alkyl and acyl complexes of the types FvCr2(CO)6−nLnRR′ and Et4N[FvCr2(CO)6−nLnR] (R, R′ = Me, CH2CN, COMe; L = CO, PMe2Ph; n = 0, 1, 2)

The compound FvCr2(CO)6Me2 (1) is obtained, via the intermediate formation of Et4N[FvCr2(CO)6Me] (2), by stepwise addition of 2 equivalents of methyl iodide to (Et4N)2[FvCr2(CO)6]; the analogous cyanomethyl compounds FvCr2(CO)6(CH2CN)2 (3) and Et4N[FvCr2(CO)6(CH2CN)] (4) are formed similarly. Compound 1 readily undergoes CO insertion upon treatment with 2 equivalents of PMe2Ph, giving rise to trans,trans-FvCr2(CO)4(PMe2Ph)2(COMe)2 (6), also in two steps via trans-FvCr2(CO)5(PMe2Ph)(Me)(COMe) (8). The neutral methyl "half" of 2 reacts similarly with PMe2Ph to form Et4N[trans-FvCr2(CO)5(PMe2Ph)(COMe)] (7), while the anionic "half" of 2 is alkylated with ClCH2CN to give FvCr2(CO)6(CH2CN)Me (5). Treatment of 5 with PMe2Ph also results in CO insertion into the Cr—Me bond to give trans-FvCr2(CO)5(PMe2Ph)(CH2CN)(COMe) (10). Although 3 is inert to both substitution and insertion reactions with PMe2Ph, the phosphine-substituted dialkyl (fulvalene)dichromium complex trans,trans-FvCr2(CO)4(PMe2Ph)2(CH2CN)2 (9) is prepared by reaction of ClCH2CN with (Et4N)2[FvCr2(CO)4(PMe2Ph)2]. Key words: chromium, metal–metal bonds, fulvalene.

The structure of dichromium tetraformate

Second-order perturbation theory (CASPT2) calculations using large basis sets have been used to study the CrCr bond in dichromium tetraformate, Cr 2(O 2CH) 4 The CrCr potential was found to have a double minimum with one short equilibrium at 1.94 Å, exhibiting considerable 3d-3d bonding, and a long equilibrium at 2.50 Å, which is essentially determined by the structure of the bridging ligands. The energy difference between the two minima is small (of the order of 0.1 eV) and the relative order depends on the level of theory used. Inclusion of relativistic effects and 3s,3p correlation (estimated from the corresponding effect in the 3 Σ u + state of Cr 2 locates the inner minimum 0.07 eV below the outer. The measured distance in Cr 2(O 2CCH 3) 4 is 1.966 Å. It is likely that addition of axial ligands like water will make the outer minimum more stable, thus explaining the variations in Cr{inCr} distances in dichromium complexes. The DFr approach is also applied and long, 2.296 and 2.487 \\rA, CrCr bond distances are found for Cr{in2}(O{in2}CH){in4} and Cr{in2}(O{in2}CCH{in3}){in4}, respectively. Addition of axial water ligands increases the CrCr distance by about 0.19 and 0.07 \\rA, respectively, for these two systems.

Synthesis, Structure and Magnetic Properties of Mono- and Dinuclear Chromium(III) Complexes with Tetrahydrosalen and Substituted Tetrahydrosalen Derivatives as Ligands. Crystal Structure of a Phenoxo-Bridged Dichromium(III) Complex.

Synthesis, Structure and Magnetic Properties of Mono- and Dinuclear Chromium(III) Complexes with Tetrahydrosalen and Substituted Tetrahydrosalen Derivatives as Ligands. Crystal Structure of a Phenoxo-Bridged Dichromium(III) Complex.

Syntheses, Structures and Magnetic Properties of Fluoro-Bridged Di- and Tetranuclear Chromium(III) Complexes with Tetrahydrosalen and Substituted Tetrahydrosalen Derivatives as Ligands. Crystal Structure of an Ethoxo-Fluoro-Bridged Dichromium(III) Complex and a Tetrafluoro-Bridged Tetrachromium(III) Complex.

Syntheses, Structures and Magnetic Properties of Fluoro-Bridged Di- and Tetranuclear Chromium(III) Complexes with Tetrahydrosalen and Substituted Tetrahydrosalen Derivatives as Ligands. Crystal Structure of an Ethoxo-Fluoro-Bridged Dichromium(III) Complex and a Tetrafluoro-Bridged Tetrachromium(III) Complex.

Dichromium cage complexes of cyclotetra-, cyclopenta-, and cyclohexa-phosphoxane

Metal-assisted assembly of cis-dimethylpiperidinophosphine oxide (DMP–PO) units around chromium carbonyl at progressively higher temperatures affords dichromium complexes of cyclotetraphosphoxane (two isomers), cyclopentaphosphoxane, and ultimatlely, the novel cyclohexaphosphoxane.

Thiolate-bridged dichromium complexes. Syntheses and crystal structures of [CpCr(CO)2(SPh)]2 and [CpCr(SPh)]2S

Thiolate-bridged dichromium complexes. Syntheses and crystal structures of [CpCr(CO)2(SPh)]2 and [CpCr(SPh)]2S

Ein μ 2-Benzylidenkomplex des Chroms mit ungepaarten Elektronen

The benzylidene-bridged dichromium complex [CpCr] 2(μ-Br) 2(μ-CHC 6H 5) ( 4) has been obtained by thermolysis of [CpCr(CH 2C 6H 5)] 2(μ-Br) 2. 1H NMR spectroscopy shows that 4 is antiferromagnetic and a barrier of 64.0 kJ mol −1 slows down the rotation of the phenyl group.

Structure of a methoxo-bridged dichromium complex

Structure of a methoxo-bridged dichromium complex

Preparation and structural characterization of the isostructural dichromium(II) and dimolybdenum(II) complexes, M2(O2CCH3)2[o-(NMe2)C6H4CH2]2, containing two four atom bridging ligands and surprisingly short M-M quadruple bonds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and structural characterization of the isostructural dichromium(II) and dimolybdenum(II) complexes, M2(O2CCH3)2[o-(NMe2)C6H4CH2]2, containing two four atom bridging ligands and surprisingly short M-M quadruple bondsF. Albert Cotton and Graham N. MottCite this: Organometallics 1982, 1, 2, 302–305Publication Date (Print):February 1, 1982Publication History Published online1 May 2002Published inissue 1 February 1982https://doi.org/10.1021/om00062a012RIGHTS & PERMISSIONSArticle Views130Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The thiocyanato adduct of chromium(II) acetate

The first dichromium complex with axially bonded anions, [NEt 4] 2[Cr 2(O 2CCH 3) 4(NCS) 2], was obtained by reactions of [NEt 4]NCS with [Cr 2(O 2CCH 3) 4(OH 2) 2] in ethanol.

Exchange interactions in di-µ-hydroxo-bis[bis(1,2-diaminoethane)-chromium(III)] salts. Structural, magnetochemical, and optical spectroscopic investigations

Chloride, bromide, iodide, and dichloride diperchlorate salts of the title complex have been prepared. The crystal structures of [Cr2(OH)2(en)4]Cl4·2H2O and [Cr2(OH)2(en)4]Br4·2H2O have been determined by single-crystal X-ray measurements on an automatic diffractometer, and refined to R 0.023 for the chloride and 0.031 for the bromide. Lattice constants are a= 8.165 0(8), b= 8.740 0(9), c= 9.790 2(7)A, α= 67.196(7), β= 87.937(7), and γ= 64.587(7)° for the chloride, and a= 8.211(2), b= 8.980(1), c= 10.024(1)A, α= 67.57(1), β= 88.90(1), and γ= 65.07(2)° for the bromide. Both structures belong to space group P and are strictly isomorphous. The symmetry of the dichromium complex is 2/m in both salts. Moreover, a normal probability plot analysis shows the cations to be identical in the two compounds. Powder magnetic-susceptibility data have been collected for all the four complexes between 1.5 K and room temperature. Single-crystal and Nujol-mull absorption spectra have been recorded between 7 and 40 K in the region of transitions from the electronic ground state 4A24A2 to the lowest levels of the first singly excited state 4A22E, and powder luminescence spectra obtained at <10 K. From the absorption and luminescence spectra the exchange splitting of the electronic ground state can be accurately determined. The exchange parameters J thus derived deviate by up to 10% from those obtained by fitting the magnetic-susceptibility data. These discrepancies indicate a slight temperature dependence of J. The values obtained for the biquadratic exchange parameter j from the magnetochemical fit have little if any physical significance. The exchange parameters (cm–1) for the four salts, determined spectroscopically at <40 K, are: J= 31.4 ± 0.4 and j= 0.08 ± 0.02 (chloride), 30.0 ± 0.3 and j= 0.11 ± 0.08 (bromide), 24.3 ± 0.9 and j= 0.08 ± 0.2 (iodide), and 22.2 ± 0.2 and j= 1.12 ± 0.6 (dichloride diperchlorate dihydrate).

Acetylene linkage at a di-metal centre: X-ray crystal structures of [Cr2(CO)(η-C5H5)2(PhC2Ph)2] and [Mo2(η-C5H5)2{(MeO2CC2CO2Me)-(HC2H)(MeO2CC2CO2Me)2}

A sequence of acetylene linking at a di-metal centre has been identified; X-ray diffraction studies have established the structures of di-chromium and di-molybdenum complexes containing two and four acetylene molecules, respectively.

Reactions of group vib hexacarbonyls with formamidines

The reaction of molybdenum and chromium hexacarbonyls with formamidines yields the tetrakis(formamidinato)dimolybdenum and dichromium complexes. In the case of molybdenum we were able to set up a reaction scheme for the formation of these complexes. An interesting feature of the chemistry of these complexes is the reaction with Mo(CO) 6 or Cr(CO) 6 to yield novel complexes in which an “M(CO) 3” species is bound to one of the aromatic groups. Their physical and chemical properties are discussed. The reaction of W(CO) 6 with formamidine did not produce a complex analogous to that obtained with Mo(CO) 6 or Cr(CO) 6 but, instead, a deep purple coloured complex.