Complexes CpM Research Articles

Protolysis of five-membered metallacyclocumulene complexes of zirconocene and hafnocene

The reactions of the five-membered metallacyclocumulene complexes Cp2M[η4ButC4But] (M = Zr, Hf) with an equimolar amount of HCl in dioxane at 20 °C result in linear complexes Cp2M(Cl)–C(But)=CH–CCBut, whereas the reaction with an excess of HCl affords Cp2MCl2 and trans-ButCH=CH–CCBut. The reaction of the latter hydrocarbon with an equivalent amount of the bis(trimethylsilyl)acetylene complex of zirconocene Cp2Zr(Me3SiC2SiMe3)(Py) leads to bis(trimethylsilyl)acetylene and a five-membered zircona-cycloallene complex. This complex can also be obtained in ‘one-pot’ via the reactions of five-membered zircona-cyclocumulene with two equivalents of HCl and subsequent treatment with magnesium in THF.

Group 4 Metallocene Complexes Supported by a Redox-Active O,C-Chelating Ligand

Group 4 metallocene complexes Cp2M[OC] (Cp = η5-C5H5; M = Ti (1) or Zr (2); [OC] = κ2-O,C-OC6H2-2-CPh2-4,6-tBu2) supported with a redox-active bidentate O,C-ligand were successfully synthesized through salt metathesis. X-ray crystallographic results showed that both complexes maintained similar bent metallocene coordination geometry. A close inspection of the structural parameters revealed a remarkably long Ti–C bond in 1, indicating concomitant intramolecular charge transfer upon metathesis and coordination. The electronic structure of 1 was investigated by electron paramagnetic resonance (EPR) measurements, revealing the presence of a Ti(III) center and one [OC]•– radical anion. In contrast, the diamagnetic complex 2 was found to comprise a Zr(IV) center and an alkyl/aryloxo dianion. Divergent catalytic reactivity was observed for the two group 4 derivatives in the reaction between alkenes and HBpin. Specifically, dehydrogenative boration products (i.e., vinyl boronate esters) were obtained exclusively in the presence of the Zr complex (18 examples, up to 90% yield), while the Ti compound selectively promoted the formation of alkyl boronate esters via hydroboration (19 examples, up to 99% yield).

An Air‐Stable Heterobimetallic Si2M2 Tetrahedral Cluster

AbstractAir‐ and moisture‐stable heterobimetallic tetrahedral clusters [Cp(CO)2MSiR]2 (M=Mo or W; R=SitBu3) were isolated from the reaction of N‐heterocyclic carbene (NHC) stabilized silyl(silylidene) metal complexes Cp(CO)2M=Si(SitBu3)NHC with a mild Lewis acid (BPh3). Alternatively, treatment of the NHC‐stabilized silylidene complex Cp(CO)2W=Si(SitBu3)NHC with stronger Lewis acids such as AlCl3 or B(C6F5)3 resulted in the reversible coordination of the Lewis acid to one of the carbonyl ligands. Computational investigations revealed that the dimerization of the intermediate metal silylidyne (M≡Si) complex to a tetrahedral cluster instead of a planar four‐membered ring is due to steric bulk.

An Air-Stable Heterobimetallic Si2 M2 Tetrahedral Cluster.

Air‐ and moisture‐stable heterobimetallic tetrahedral clusters [Cp(CO)2MSiR]2 (M=Mo or W; R=SitBu3) were isolated from the reaction of N‐heterocyclic carbene (NHC) stabilized silyl(silylidene) metal complexes Cp(CO)2M=Si(SitBu3)NHC with a mild Lewis acid (BPh3). Alternatively, treatment of the NHC‐stabilized silylidene complex Cp(CO)2W=Si(SitBu3)NHC with stronger Lewis acids such as AlCl3 or B(C6F5)3 resulted in the reversible coordination of the Lewis acid to one of the carbonyl ligands. Computational investigations revealed that the dimerization of the intermediate metal silylidyne (M≡Si) complex to a tetrahedral cluster instead of a planar four‐membered ring is due to steric bulk.

Adducts of Mn and Re vinylidenes with P–OR nucleophiles: Hydrolysis rather than the intramolecular Michaelis–Arbuzov rearrangement

The reactions of vinylidene complexes Ср(CO)2Mn = C=C(H)Ph (Mn1) and Cp(CO)2Re = C=C(H)Ph (Re1) with P–OR nucleophiles P(OR)R'R" (OR = R' = R" = OMe, OEt, OPri, OPh; OR = OEt, R' = R" = Ph; OR = R' = OEt, R" = Ph) proceed as nucleophilic addition to the Cα vinylidene atom to initially afford zwitter-ionic complexes Z-Ср(CO)2M¯−C[+P(OR)R'R"] = C(H)Ph which were identified by spectroscopic methods and, in some cases, their molecular structures were confirmed by X-ray diffraction. These adducts are extremely sensitive to water and hydrolyzed by water traces to afford the corresponding η2-phosphorylalkene complexes Cp(CO)2M{η2-E-HC[P(O)R'R"] = C(H)Ph}. The isotopic label experiments with D2O and H218O showed the hydrolysis to proceed with the phosphorus–oxygen bond cleavage and binding of the water hydrogen to the carbon atom bearing the > P=O group.

Theoretical study on [3]- and [4]radialene complexes CpM(C2nH2n) (n = 3, 4; M = Sc∼Ni): Special metal-aromatic interaction along with metal-alkene bonds

The coordination and electron configuration of radialene complexes CpM(C2nH2n) (n = 3, 4) are investigated. For M = Sc, Ti, Fe, Co, Ni, the ground states of CpM(C2nH2n) are low-spin states (singlet or doublet), while for M = V, Cr, Mn, the ground states are high-spin states (triplet or quartet). For M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, [3]radialene in the ground states of CpM(C6H6) are ŋ6-, ŋ6-, ŋ6-, ŋ4-, ŋ4-, ŋ4-, ŋ4-, and ŋ2-coordinated; and [4]radialene in the ground states of CpM(C8H8) are ŋ8-, ŋ8-, ŋ6-, ŋ4-, ŋ4-, ŋ4-, ŋ4-, and ŋ2-coordinated, respectively. Between metal atom and radialene in CpM(C2nH2n), the metal-alkene interactions, which are caused by the exocyclic CC π-bonds that donate the lone pair electrons to the empty d-orbitals of metal atom, are dominant and fundamental. Besides, the special π-backbonding metal-aromatic interactions, which is overlapped by the lone pair on metal atom and the empty 2π-aromatic orbital on the cyclic C3 or C4 ring of [n]radialenes, may also exist in some ground states of CpM(C2nH2n) complexes.

Totally complex submanifolds of a complex Grassmann manifold of 2-planes

A complex Grassmann manifold G2(Cm+2) of all 2-dimensional complex subspaces in Cm+2 has two nice geometric structures – the Kähler structure and the quaternionic Kähler structure. We study totally complex submanifolds of G2(Cm+2) with respect to the quaternionic Kähler structure. We show that the projective cotangent bundle P(T⁎CPm+1) of a complex projective space CPm+1 is a twistor space of the quaternionic Kähler manifold G2(Cm+2). Applying the twistor theory, we construct maximal totally complex submanifolds of G2(Cm+2) from complex submanifolds of CPm+1. Then we obtain many interesting examples. In particular we classify maximal homogeneous totally complex submanifolds. We show the relationship between the geometry of complex submanifolds of CPm+1 and that of totally complex submanifolds of G2(Cm+2).

Activation of M—H bond upon the complexation of transition metal hydrides with acids and bases

Features of the electronic structure of adducts of transition metal hydride complexes (Cp*M(dppe)H, dppe is the 1,2-(diphenylphosphino)ethane, M = Fe, Ru, Os; CpM(CO)3H, M = Mo, W) with acids and bases were analyzed with the ADF2014 program using energy decomposition analysis (EDA) by the Ziegler-Rauk method combined with the natural orbitals for chemical valence theory (ETS-NOCV). The nature of orbital interactions in the complex determines the reaction pathway: σMH → σ*OH interaction leads to the proton transfer to hydride ligand, nM → σ*OH leads to the metal atom protonation, nN → σ*MH implies the metal hydride deprotonation, and σMH → n*B corresponds to the hydride transfer to Lewis acid. It was shown that M-H bond polarization change has the similar character upon the formation of complexes with Bronsted and Lewis acids. The ease of polarization of M-H bonds in complexes CpM(CO)3H determines their reactivity as proton and hydride ion donors.

Integration of complex polynomial differential equations in higher dimension, a first step: Lie transverse structure

We prove that a one-dimensional holomorphic foliationswith generic singularities on a complex projective space ℂPm+1, m ≥ 2, exhibiting a Lie group transverse structure in some Zariski open subset, is logarithmic. That is, it is given by a system of m closed rational one-forms with simple poles. The foliation is given by a linear vector field in some affine space ℂm+1 ⊂ ℂPm+1 if, and only if, it exhibits only one singularity in this affine space. An application to foliations invariant under Lie group transverse actions is given.

HF‐measure: A new measurement for evaluating clusters in protein–protein interaction networks

Clustering of protein-protein interaction networks is one of the most prevalent methods for identifying protein complexes, detecting functional modules and predicting protein functions. In the past few years, many clustering methods have been proposed. However, it is still a challenging task to evaluate how well the protein clusters are identified. Even for two of the most popular measurements, F-measure and p-value, bias exists when evaluating the identified clusters. In this paper, we propose two new types of measurements to evaluate clusters more finely and distinctly. One is hF-measure(Tf) , a topology-free measurement and another is hF-measure(Tb) , a topology-based measurement. Unlike F-measure, the new measurements of hF-measure(Tf) and hF-measure(Tb) can discriminate between different types of errors. Both artificial test data and practical test data were used to evaluate the effectiveness of hF-measure(Tf) and hF-measure(Tb) . For the artificial test data, artificial errors were generated by replacing some cluster members with functionally similar or non-similar members. The practical test data was produced by seven clustering algorithms Markov Clustering, Molecular Complex Detection, HC-PIN, SPICI, CPM, Core-Attachment and RRW. The experimental results on artificial and practical test data both show that hF-measure(Tf) and hF-measure(Tb) evaluate clusters more accurately compared to F-measure. Especially, hF-measure(Tb) can capture the topology changes in clusters, which can also be used to the analysis of dynamic network.

High-yield synthesis of osmium complexes [(η6-C6H6)OsCl2]2, [CpOs(η6-C6H6)]+ and CpOs(η5-cyclohexadienyl)

The benzene complex [(η6-C6H6)OsCl2]2 (1) was obtained in 97% yield from thermal or microwave-assisted reaction of Na2OsCl6 with 1,3-cyclohexadiene in aqueous ethanol. Further reaction of 1 with TlCp gives [CpOs(η6-C6H6)]PF6 in 75% yield. Treatment of [CpM(η6-C6H6)]PF6 (M = Ru and Os) with NaBH4 in wet THF affords the cyclohexadienyl complexes CpM(η5-C6H7) in almost quantitative yields. The structure of [CpOs(η6-C6H6)]BArF (BArF = [B((3,5-(CF3)2)C6H3)4]) was confirmed by X-ray diffraction.

O-Alkylthiooxalato and dithiocarboxylato complexes of molybdenum and tungsten

The hydrosulfido complexes CpM(CO)3SH (M=Mo, W) react with one equivalent of O-alkyl oxalyl chlorides, RO2CCOCl, to form the corresponding O-alkylthiooxalato complexes CpM(CO)3SCOCO2R [M=Mo (1), W (2); R=Me (a), Et (b)]. The reaction of the hydrosulfido complexes with half equivalent of oxalyl or succinyl chlorides produces the bimetallic complexes [CpM(CO)3SCO]2 [M=Mo (3c), W (4c)] and [CpM(CO)3SCOCH2]2 [M=Mo (3d), W (4d)]. These new complexes have been characterized by elemental analysis, IR and 1H NMR spectroscopy. The solid state structures of CpMo(CO)3SCOCO2CH3 (1a) and CpW(CO)3SCOCO2CH2CH3 (2b) were determined by X-ray crystal structure analysis.

Theoretical Studies on the Structure and Bonding of Metallacyclocumulenes, -cyclopentynes, and -cycloallenes

In this paper, we compare the electronic structure of the hafnacycloallene complex Cp2HfC4RR′2R′′ (5Hf), which was previously described by Erker et al., with those of the titanium, zirconium, and hafnium complexes Cp2M(η4-RHC4HR) (3M; i.e. metallacyclopent-2,3,4-trienes, metallacyclocumulenes) and Cp2M(η4-R2C4R2) (4M; i.e. 1-metallacyclopent-3-ynes) using density functional theory (BP86/LANL2DZ) calculations. Moreover, the η3-phenylallenyl zirconocene complex 7Zr, which was synthesized by Wojcicki et al., is included for the comparison. These calculations and extended Hückel calculations show that the bonding in complex 5Hf is remarkably similar to that of complexes 4M and 7Zr. An analysis of the structural parameters and bonding reveals that the unique interaction of the internal carbon atoms along with the terminal carbon atoms with the bent-metallocene moiety is the reason for the unusual stability of these metallacycles. The molecular orbital analysis further suggests that complex 5Hf can react with another metal fragment to give the bimetallic complexes 9 and 10. The electronic structures of complexes 3M, 4M, 5Hf, and 7Zr have been comparatively studied to get a general understanding of the bonding in these metallacycles.

Are Metallocene−Acetylene (M = Ti, Zr, Hf) Complexes Aromatic Metallacyclopropenes?

The bonding nature of metallocene acetylene complexes Cp2M(eta(2)-H3SiC2SiH3) 1M and CP2M (eta(2)- HC2H) 1M' (M = Ti, Zr, Hf) wits studied by density functional theory method. It is found that this acetylene complex has indeed it metallacyclopropene moiety with two in-plane M-C sigma-bonds and one out-of-plane pi-bond interacting with the metal center, resulting in the formation of it delocalized three-center and two-electron (3c-2e) system. Along with its delocalized out-of-plane bonding, this complex has been characterized its aromatic on the basis of the computed stabilizing energy and negative nucleus-independent chemical shifts (NICS). The aromatic stabilization increases from Ti to Zr and Hf, and this is because of the increased charge separation between the CP2M fragment and the H3SiC2SiH3 (also HC2H) unit. The decrease of the M-C bond length from Zr to Hf is ttributed to the increased s character of both M and C hybridization of the M-C a-bonds.

Bi- and Trinuclear Complexes of Group 4 Metal and Palladium Bridged by OPPh2Groups: Synthesis and High Catalytic Activities in Double Hydrophosphinylation of 1-Octyne

The early−late heterobinuclear complexes Cp2M(μ-OPPh2)2PdMe2 (M = Ti (1), Zr (2), and Hf (3)) were synthesized by the reaction of PdMe2(tmeda) (tmeda = Me2NCH2CH2NMe2) with respective metallocene diphosphinite ligands Cp2M(OPPh2)2 prepared from Cp2MCl2 (M = Ti, Zr, and Hf) and LiOPPh2. The complexes 1−3 catalyzed the addition (hydrophosphinylation) of HP(O)Ph2 to 1-octyne to give mainly not the single-addition product n-Hex-CH═CHP(O)Ph2 (4a) or n-Hex-C{P(O)Ph2}═CH2 (4b) but the double-addition product n-Hex-CH{P(O)Ph2}CH2P(O)Ph2 (5) at 40 °C in low yields. The yield of 5 was, however, substantially improved to >95% for 2 and 3 when tertiary phosphine PR3 such as PMePh2 was added to the catalytic system. The stoichiometric reaction of the complexes 1−3 with the phosphorus substrate HP(O)Ph2 and PMePh2 afforded in situ the trinuclear complexes H(PMePh2)Pd(μ-OPPh2)3M(μ-OPPh2)3PdH(PMePh2), which were found to exhibit the high catalytic activities similar to those of their parent complexes 1−3 in the presence of PR3 and were thus proposed to be a practical catalyst. On the basis of the above findings, simple mixtures of mononuclear Cp2MCl2 and PdMe2(tmeda) complexes together with PMePh2 could be used successfully as precatalysts for the double hydrophosphinylation of 1-octyne with HP(O)Ph2 to give satisfactory results comparable to those attained with the preorganized binuclear complexes 2 and 3 with PMePh2 added.

Achieving Stable Hypercarbon CB62−-Based Cluster-Assembled Complexes: A General Strategy

A general strategy for designing stable hypercarbon CB62−-based cluster-assembled compounds CpM(CB6)q− (M = Li, Na, K, Be, Mg, and Ca) is proposed. This approach takes advantage of (1) the extra stability of a rigid organic aromatic Cp− deck, (2) the electrostatic interactions, (3) charge transfer based on orbital interaction, and (4) the good electronic match between the CB62− and CpM fragments. The nature and origin of various sandwich-type interactions and the requirements and technologies of the sandwiching decks’ assembly and stabilization are generally classified and comprehensively revealed. The quite crucial to perform fusion stability investigation is performed by comprehensive thermodynamic stability calculations. The electrostatic and orbital interactions and charge transfer in our designed hypercarbon complexes CpM(CB6)q− are revealed by detailed NBO analysis, orbital characterization, and frontier molecular orbital theory. Detailed analysis and comparison of the intrinsic difference of cluster-assembled compounds between hypercarbon phC CB62− and pentaatomic ptC CAl42− are performed.

PINCHING THEOREMS FOR A COMPACT MINIMAL SUBMANIFOLD IN A COMPLEX PROJECTIVE SPACE

AbstractWe give a formula for the Laplacian of the second fundamental form of an n-dimensional compact minimal submanifold M in a complex projective space CPm. As an application of this formula, we prove that M is a geodesic minimal hypersphere in CPm if the sectional curvature satisfies K≥1/n, if the normal connection is flat, and if M satisfies an additional condition which is automatically satisfied when M is a CR submanifold. We also prove that M is the complex projective space CPn/2 if K≥3/n, and if the normal connection of M is semi-flat.

Synthesis and dehydrocoupling reactivity of iron and ruthenium phosphine–borane complexes

The Fe and Ru phosphine-borane complexes CpM(CO)2PPh2 x BH3 (1, M = Fe, 4, M = Ru) were synthesized utilizing the reaction of the phosphine-borane anion Li[PPh2 x BH3] with the iodo complexes CpM(CO)2I. The Fe complex 1 reacted with PMe3 to yield CpFe(CO)(PMe3)(PPh2 x BH3) (2) and CpFe(PMe3)2(PPh2 x BH3) (3) whereas the Ru species 4 gave only CpRu(CO)(PMe3)(PPh2 x BH3) (5). The complexes 1-5 were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, MS, IR and X-ray crystallography for 1 to 4, and EA for 1, 2 and 4. The reactivity of 1 and 4 towards PPh2H x BH3 was explored. Although no stoichiometric reactions were detected under mild conditions, both 1 and 4 were found to function as dehydrocoupling catalysts to afford Ph2PH x BH2 x PPh2 x BH3 in the melt at elevated temperature (120 degrees C). The carbonyl Fe2(CO)9 also functioned as a dehydrocoupling catalyst under similar conditions. Complex 1 and Fe2(CO)9 represent the first reported active Fe complexes for the catalytic dehydrocoupling of phosphine-borane adducts.

DFT Studies on the Mechanism of Reactions between N2O and Cp2M(η2-alkyne) (M = Ti, Zr)

DFT calculations have been carried out to study the activation of N2O by the transition-metal alkyne complexes Cp2M(η2-alkyne) (M = Ti, Zr). The mechanism for the formation of the five-membered metallacyclic complexes Cp2M(RC═CR′NN(O)), which were obtained directly from the reactions of N2O with the metal alkyne complexes, and the conversion of the five-membered metallacyclic complexes Cp2M(RC═CR′NN(O)) via N2 loss to the oxametallacyclobutene complexes Cp2M(RC═CR′O) have been investigated in detail. An effort has been made to understand how the kinetically inert N2O can be activated. We concluded that N2O is best activated by metal fragments that possess high capability of π-back-bonding interactions with the π* orbitals of N2O.

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W−(CC) Bond, and the Vulnerability of the NHC Ligand toward Catalyst Deactivation during Ketone Hydrogenation

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OHmore » group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.« less