Synthesis and H NMR spectroscopic properties of substituted (η-tetraarylcyclobutadiene)(η-cyclopentadienyl)cobalt metallocenes

The reaction of diarylacetylenes with CoCl(PPh₃)₃ and sodium cyclopentadienylide or sodium carbomethoxycyclopentadienylide gave (η⁴-tetra-arylcyclobutadiene)(η⁵-cyclopentadienyl)cobalt and (η⁴-tetra-arylcyclobutadiene)(η⁵-carbomethoxycyclopentadienyl)cobalt, respectively, where aryl = para-XC₆H₄ (X = CF₃, F, MeO). The reaction was unsuccessful for the synthesis of (η⁴-tetra(para-methoxyphenyl)cyclobutadiene)(η⁵-cyclopentadienyl)cobalt, which was synthesised instead from dicarbonyl(η⁵-cyclopentadienyl)cobalt. In all of the examples starting with CoCl(PPh₃)₃ an intermediate (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallography. Heating the (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complexes resulted in clean conversion to the corresponding metallocenes. The influence of the para-aryl substituents on the ¹H NMR of the cyclopentadienyl moiety is tabulated, together with the influence of a range of R substituents in (η⁴-tetraphenylcyclobutadiene)(η⁵-RC₅H₄)cobalt (R = CO₂Me, CH₂OH, Me, CHO, CCH, CO₂H, CN, CONHR¹, 2-oxazolinyl, NH₂, NHAc, HgCl, Br, I, SiMe₃, SnMe₃, Ph).     

Synthesis, structure and electrochemistry of CO incorporated diruthenium metallacyclic compounds [Ru2(CO)6{μ-η:η:η:η-1,4-Fc2C5H2O}] and [Ru2(CO)6{μ-η:η:η:η-1,5-Fc2C5H2O}]

Ferrocenyl substituted ruthenium metallacyclic compounds, [Ru₂(CO)₆{μ-η¹:η¹:η²:η²-1,4-Fc₂C₅H₂O}] (1) and [Ru₂(CO)₆{μ-η¹:η¹:η²:η²-1,5-Fc₂C₅H₂O}] (2) have been synthesized and structurally characterized. Electrochemical studies for 1 and 2 and the respective quinone derivatives 3 and 4 show weak to no electrochemical coupling at the mixed-valent intermediate state which is dependent on the complex frameworks.     

Crystal and molecular structure of (μ-η2,η3-propargyl)- bis(cyclopentadienyl)tetracarbonyldimolybdenum tetrafluoroborate and (μ-η2,η3-1,1-dimethylpropargyl)- bis(cyclopentadienyl)tetracarbonyldimolybdenum tetrafluoroborate

An X-ray study of [(μ-η²,η³-HCCCH₂)Cp₂Mo₂(CO)₄]⁺(BF₄⁻) (1) and [(μ-η²,η³-HCCCMe₂)Cp₂Mo₂(CO)₄]⁺(BF₄⁻) (2) reveals their structures to be similar to the structure of neutral compounds of the series (μ-η²,η²-RCCR)Cp₂Mo₂(CO)₄, the difference between 1 and 2 being mainly due to the markedly different MoC⁺ bond lengths, which accounts for different stability and fluxional behavior of these compounds in solution.     

W(η-PhCCPh)3(η-Ph2PCCPPh2) as a ligand to prepare homo- and hetero-nuclear cluster complexes

Reaction of W(η²-PhCCPh)₃(NMe₃) (1) and Ph₂PCCPPh₂ (dppa) produces W(η²-PhCCPh)₃(η¹-Ph₂PCCPPh₂) (2), which contains a pendant phosphine group. Treatment of 2 with W(CO)₄(NCMe)₂ yields [W(η²-PhCCPh)₃](μ,η²-Ph₂PCCPPh₂)[W(CO)₄(NCMe)] (3). Compound 2 reacts with Os₃(CO)₁₀(NCMe)₂ to afford Os₃(CO)₁₀[(μ,η²-Ph₂PCCPPh₂)W(η²-PhCCPh)₃]₂ (4), and reacts with Ru₃(CO)₉(NCMe)₃ to afford Ru₃(CO)₉[(μ,η²-Ph₂PCCPPh₂)W(η²-PhCCPh)₃]₃ (5). The crystal structures of 2 and 3 are determined by an X-ray diffraction study.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.     

Cyclopentadienyl molybdenum dicarbonyl η-allyl complexes as catalyst precursors for olefin epoxidation. Crystal structures of Cp′Mo(CO)2(η-C3H5) (Cp′ = η-C5H4Me, η-C5Me5)

The complexes Cp′Mo(CO)₂(η³-C₃H₅) [Cp′ = η⁵-C₅H₅ (1), η⁵-C₅H₄Me (2), η⁵-C₅Me₅ (3)] have been prepared, structurally characterised by X-ray diffraction (2, 3), and tested as catalyst precursors for the epoxidation of olefins at 55 °C. Complex 1 gave a turnover frequency (TOF) of 310 mol mol_Mo⁻¹ h⁻¹ in the epoxidation of cis-cyclooctene with tert-butylhydroperoxide (TBHP, in decane) as oxidant, and 1,2-epoxycyclooctane was obtained quantitatively within 6 h. A similar result was obtained for complex 2, while the TOF for 3 was about one order of magnitude lower, suggesting a possible activity dependence on the ring substituents. For 1 the use of 1,2-dichloroethane as solvent increased the initial reaction rate to 361 mol mol_Mo⁻¹ h⁻¹, with no decrease in epoxide selectivity. Under these conditions the reaction rates for other olefins increased in the order 1-octene < trans-2-octene < cyclododecene < (R)-(+)-limonene < cis-cyclooctene, and, with the exception of limonene, the corresponding epoxide was the only product. For 1 the selective epoxidation of cis-cyclooctene could also be achieved in aqueous solution, using TBHP or H₂O₂ as oxidants, which gave epoxide yields of 99% and 27% at 24 h, respectively. The possibility of facilitating catalyst recycling by using ionic liquids as solvents was investigated.     

Synthesis, X-ray crystal structure, and reactivity of Pd2(μ-dotpm)2 (dotpm = bis(di-ortho-tolylphosphino)methane)

Alkylation of PdCl₂(dotpm) (dotpm = bis(di-ortho-tolylphosphino)methane) with n-butyllithium produces the binuclear Pd(0) complex Pd₂(μ-dotpm)₂ and the elimination byproducts 1-butene, cis-2-butene, trans-2-butene, butane, and octane. The dibutyl complex, Pd(dotpm)(n-Bu)₂, is presumed to be the reaction intermediate. The crystal structure of Pd₂(μ-dotpm)₂ reveals that the methylene groups of the bridging dotpm ligands are located on opposite sides of the Pd₂P₄ unit, forming an 8-membered ring that is in an elongated chair conformation. The four phosphorus atoms are not coplanar, and the P1-P2-P3-P4 ring has a torsion angle of 13.8°, which minimizes the spatial interactions among the o-tolyl rings. The Pd-Pd bond distance is 2.8560(6) Å, which indicates that there is a weak “closed-shell” bonding interaction between the d¹⁰-d¹⁰ metal centers. Each palladium atom has a nearly linear geometry, and the eight methyl groups of the dotpm ligands shield the open coordination sites on the metal centers. Four methyl groups shield the metal atoms above and below the Pd₂P₄ ring cavity, and four methyl groups block the open metal sites outside of the Pd₂P₄ ring. The Pd₂(μ-dotpm)₂ complex readily undergoes oxidative addition of dichloromethane to form the rigid A-frame complex Pd₂Cl₂(μ-CH₂)(μ-dotpm)₂.     

Synthesis and properties of carboxy-substituted half-sandwich ruthenium complexes with chelating bisphosphine ligands (η-C5H4CO2H)Ru(η-L)X (X = I, H)

Several Ru(II) complexes (η⁵-C₅H₄CO₂H)Ru(η²-L)I have been prepared by the hydrolysis of the ester linkage in (η⁵-C₅H₄CO₂t-Bu)Ru(η²-L)Cl with trimethylsilyl iodide. The hydrides (η⁵-C₅H₄CO₂H)Ru(η²-L)H may be prepared by reduction of the iodide complexes in KOH/MeOH solutions followed by acidification. Complexes with several chelating bisphosphine ligands have been prepared in this way. The carboxylate anions [(η⁵-C₅H₄CO₂)Ru(η²-L)H]⁻ are readily protonated by weak acids to give the carboxyCp complexes. The pK_a of the carboxy proton of (η⁵-C₅H₄CO₂H)Ru(dppe)H (dppe = 1,2-bis(diphenylphosphino)ethane) is 11.3 in DMSO. Protonation of the neutral hydride complex (η⁵-C₅H₄CO₂H)Ru(dppf)H gives the cationic dihydride (η⁵-C₅H₄CO₂H)Ru(dppf)H⁺₂; the dihydride structure has been confirmed by measuring the T₁ of its ¹H NMR hydride resonance over a range of temperatures. The oxidations of the halide complexes (η⁵-C₅H₄CO₂H)Ru(dppf)I and (η⁵-C₅H₄CO₂t-Bu)Ru(dppf)Cl (dppf = 1,1′-bis(diphenylphosphino)ferrocene) have been studied by cyclic voltammetry.     

Synthesis and characterization of isomeric 4- and 8-(σ-CHCHPh)-closo-ruthenacarboranes with η:η-phosphacarbocyclic ligand

Reactions of [3,3-(PPh₃)₂-3-Cl-3-H-3,1,2-closo-RuC₂B₉H₁₁] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph₃P)₂Cl}-5,6,10-(μ-H)₃-10-H-7,8-nido-C₂B₉H₈] (2) with NH₄PF₆ in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-8-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (4) and [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-4-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)-CHCHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η³:η²-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh₃ group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.     

Structural and X-ray powder diffraction studies of nano-structured lead(II) coordination polymer with η Pb?C interactions

A new nano-sized Pb(II) one-dimensional coordination polymer with η² Pb-C interactions, [Pb₂(μ₃-ba)₂(μ₂-ba)₂]_n (1) [ba⁻ = benzylacetylacetonate] has been synthesized and characterized by SEM, X-ray powder diffraction, IR spectroscopy and elemental analyses. Single-crystal X-ray diffraction shows the coordination number of Pb(II) ions is seven and the lead atoms have hemidirected coordination sphere containing involving Pb?C interactions, C₂O₇Pb. PbO nanoparticles were obtained by calcinations of the nano-sized compound 1 at 600 °C.     

Photochemical route to unusual tri-tungsten ferrocenylacetylene cluster [W3{μ-η,η- (H)CCFc}2(CO)12] and a dimetallacyclodecatetraene [W2{μ-η,η,η,η- (Fc)CC(H)C(H)C(Fc)C(Fc)C(H)C(H)C(Fc)}(CO)6]

Low temperature photoreaction between tungsten hexacarbonyl and ferrocenylacetylene yielded two unusual metal containing stable compounds, the tritungsten cluster, [W₃(μ-η²,η²- (H)CCFc)₂(CO)₁₂] (1), and ditungsten-1,4,5,8-ferrocenylcyclodecatetraene, [W₂{μ-η²,η²,η²,η²-(Fc)CC(H)C(H)C(Fc)C(Fc)C(H)C(H)C(Fc)}(CO)₆] (2). Both compounds were characterised by IR and ¹H and ¹³C NMR spectroscopy and their molecular structures established by single crystal X-ray diffraction methods.     

Mechanistic studies on the alcoholysis and aminolysis of [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}]

The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic [(MeZn)₂{μ-N(H)tBu}{μ-N(CH₂Py)₂}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the exchange of the μ-N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)₂(μ-OMe){μ-N(CH₂Py)₂}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridylmethyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Extensive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[μ-(MeO?H?NHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates with Zn[μ-(RNH ? H ? NHR)]Zn functionalities, respectively. We were able to detect the latter by ¹H NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition of the complex leading to the hexanuclear amide [{Zn(μ-N(H)Ph)}{MeZn(μ-N(H)Ph)}₂{μ-N(CH₂Py)₂}]₂ (4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)₂{μ-N(CH₂Py)₂}₂Zn{μ-(OMe₂Si)₂O}] (5). The X-ray structures of complexes 1-5 are discussed.     

Crystal structure and spectroscopic properties of polymeric adducts of the tetra-μ-haloaspirinate-dicopper(II)

Eight new copper(II) complexes with halo-aspirinate anions have been synthesized: [Cu₂(Fasp)₄(MeCN)₂]?·?2MeCN (1), [Cu₂(Clasp)₄(MeCN)₂]?·?2MeCN (2), [Cu₂(Brasp)₄(MeCN)₂]?·?2MeCN (3), {[Cu₂(Fasp)₄(Pyrz)]?·?2MeCN} _n (4), {[Cu₂(Clasp)₄(Pyrz)]?·?2MeCN} _n (5), [Cu₂(Brasp)₄(Pyrz)] _n (6), [Cu₂(Clasp)₄(4,4′-Bipy)] _n (7), and [Cu₂(Brasp)₄(4,4′-Bipy)] _n (8) (Fasp: fluor-aspirinate; Clasp: chloro-aspirinate; Brasp: bromo-aspirinate; MeCN: acetonitrile; Pyrz: pyrazine; 4,4′-Bipy: 4,4′-bipyridine). The crystal structure of two 2 and 4 have been determined by X-ray diffraction methods. All compounds have been studied employing elemental analysis, IR, and UV-Visible spectroscopic techniques. The results have been compared with previous data reported for complexes with similar structures.     

Structural investigations of β-CaAlF5 by coupling powder XRD, NMR, EPR and spectroscopic parameter calculations

β-CaAlF₅ was synthesized by solid-state reaction. The precise structure was refined from X-ray powder diffraction data in the monoclinic space group P2₁/c with lattice constants , , , and β=109.91° (Z=4). The structure exhibits isolated chains of octahedra sharing opposite corners.¹⁹F and ²⁷Al solid state NMR spectra were recorded using MAS and SATRAS techniques. An EPR spectrum was recorded for β-CaAlF₅:Cr³⁺. The experimental spectra were simulated in order to extract the NMR and EPR parameter values. Five fluorine sites and one low symmetry aluminium site were found in agreement with the refined structure.These parameters were calculated using empirical and ab-initio methods. The agreement obtained between the calculated ¹⁹F chemical shift values, ²⁷Al quadrupolar parameters, Cr³⁺ EPR fine structure parameters and the experimental results demonstrates the complementarity of XRD, magnetic resonance experiments and theoretical methodologies.     

Solid-state cis-trans isomerization reaction of (η-MeC5H4)W(CO)2P(OPr)3I

cis-(η⁵-MeC₅H₄)W(CO)₂P(OⁱPr)₃I (1) was converted to the trans isomer 2 in the solid state (90-110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2-60 min), cooling the tubes to room temperature and determining the conversion by solution ³¹P and ¹H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol⁻¹. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80-100 °C (10-60 min), yielding an activation energy of 52 ± 2 kJ mol⁻¹ (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.     

Synthesis and structures of the silyl bridged bis(indenyl) diruthenium complexes and a novel indenyl nonanuclear ruthenium cluster Ru9(μ6-C)(CO)14(μ3-η:η:η-C9H7)2

Thermal treatment of C₉H₇SiMe₂C₉H₇ and C₉H₇Me₂SiOSiMe₂C₉H₇ with Ru₃(CO)₁₂ in refluxing xylene gave the corresponding diruthenium complexes (E)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ [E = Me₂Si (1), Me₂SiOSiMe₂ (2)]. A desilylation product [(η⁵-C₉H₇)Ru(CO)]₂(μ-CO)₂ (3) was also obtained in the latter case. Similar treatment of C₉H₇Me₂SiSiMe₂C₉H₇ with Ru₃(CO)₁₂ gave a novel indenyl nonanuclear ruthenium cluster Ru₉(μ₆-C)(CO)₁₄(μ₃-η⁵:η²:η²-C₉H₇)₂ (5) with carbon-centered tricapped trigonal prism geometry, in addition to the diruthenium complex (Me₂SiSiMe₂)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ (4) and the desilylation product 3. Complex 4 can undergo a thermal rearrangement to form the product [(Me₂Si)(η⁵-C₉H₆)Ru(CO)₂]₂ (6). The molecular structures of 1, 2, 4, 5, and 6 were determined by X-ray diffraction.     

Bis(μ3-barbiturato−O,O,O′)-(μ2-aqua)- aqua-barium(II): crystal structure,spectroscopic and thermal properties

A polymeric coordination compound, [Ba(H₂O) ₂(Hba)₂] (1) (H₂ba – barbituric acid, C₄H₄N₂O₃), was obtained. The structure of 1 was solved using powder X-ray diffraction methods. The Ba²⁺ ion in 1 formed a three-capped trigonal prism. The BaO₉ polyhedra, connected with each other by the edges and faces, formed a chain. Several 4- and 12-membered cycles due to the bridging μ₂-H₂O and bridging μ₃-Hba^– also formed implementing a 3-D polymer structure. The structures of 1 and other thiobarbiturate complexes were compared. The replacement of a S atom by an O atom in the heterocyclic ligand Htba^? (thiobarbiturate ion) of the compound Ba(H₂O)₂(Htba)₂ resulted in changes of the coordination number Ba(II) and supramolecular structure. The intermolecular hydrogen bonds O–H?O and N–H?O formed a 3-D net where pronounced 2-D layers of Hba^– ions could be found. A new topological net in 1 was observed. The IR and thermal stability were investigated.     

Synthesis and characterization of dinuclear p-, m- and o-xylyl bridged complexes of molybdenum and tungsten. The crystal structures of μ-p-xylyl- bis(η-pentamethyl-cyclopentadienyltri- carbonylmolybdenum) and μ-m-xylyl-bis(η- pentamethylcyclopentadienyltricarbonyltungsten)

The reactions of (M = Mo, W) with α,α′-p-, m- and o-dichloro-xylenes yielded p-, m- and o-xylyl bridged dinuclear complexes of in high yields. All of such new complexes are stable to air and water, even stable in dilute acids and bases.     

Physical-mechanical properties of Zr-(Re)-doped β-rhombohedral boron

Effect of doping with Zr(Re) on the structure and physical-mechanical properties of β-rhombohedral boron has been studied. In all specimens p-type conductivity was found. Internal friction and dynamic shear modulus of the specimens were investigated at frequencies of torsion oscillations (0.5-5 Hz) in the temperature range 80<T<1000 K. The increase of Zr(Re) concentration in the samples results in increase of their hole concentration, this increasing and shifting the observed IF maxima to lower temperatures; activation energy of the maxima and frequency factor of the relaxation processes decrease by 10-15%. Effects of change of the structure-sensitive properties observed in Zr-(Re)-doped boron are analyzed in view of changes of activation energy necessary for the motion of twinning boundaries and stacking faults.