Unsaturation in binuclear cyclopentadienylchromium carbonyl thiocarbonyls: Viability of (η-C5H5)2Cr2(CS)2(CO)3 in contrast to (η-C5H5)2Cr2(CO)5

The cyclopentadienylchromium carbonyl thiocarbonyls Cp₂Cr₂(CS)₂(CO)_n (n = 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The lowest energy Cp₂Cr₂(CS)₂(CO)₄ structure can be derived from the experimentally characterized unbridged Cp₂Cr₂(CO)₆ structure by replacing the two terminal carbonyl groups furthest from the Cr-Cr bond with two terminal CS groups. The two lowest energy Cp₂Cr₂(CS)₂(CO)₃ structures have a single four-electron donor η²-μ-CS group and a formal Cr-Cr single bond of length ∼3.1 Å. In contrast to the carbonyl analogue Cp₂Cr₂(CO)₅ these Cp₂Cr₂(CS)₂(CO)₃ structures are viable with respect to disproportionation into Cp₂Cr₂(CS)₂(CO)₄ and Cp₂Cr₂(CS)₂(CO)₂ and thus are promising synthetic targets. The lowest energy Cp₂Cr₂(CS)₂(CO)₂ structures have all two-electron donor CO and CS groups and short CrCr distances around ∼2.3 Å suggesting the formal triple bonds required to give the chromium atoms the favored 18-electron configurations. These Cp₂Cr₂(CS)₂(CO)₂ structures are closely related to the known structure for Cp₂Cr₂(CO)₄. In addition, several doubly bridged structures with four-electron donor η²-μ-CS bridges are found for Cp₂Cr₂(CS)₂(CO)₂ at higher energies. The global minimum Cp₂Cr₂(CS)₂(CO) structure is a triply bridged triplet with a CrCr triple bond (2.299 Å by BP86). A higher energy singlet Cp₂Cr₂(CS)₂(CO) structure has a shorter Cr-Cr distance of 2.197 Å (BP86) suggesting the formal quadruple bond required to give each chromium atom the favored 18-electron configuration.     

Cyclopentadienyl chromium and tungsten complexes with halide, methyl and σ-phenylethynyl ligands: Structures of (η-C5H5)Cr(NO)2(-CC-C6H5), (η-C5H5)Cr(NO)2I and [(η-C5H4)-COOCH3]W(CO)3Cl

With copper(I) iodide as catalyst, σ-alkynyls, compounds (η⁵-C₅H₅)Cr(NO)₂(CC-C₆H₅) (5), [(η⁵-C₅H₄)-COOCH₃]Cr(NO)₂(CC-C₆H₅) (10), and [(η⁵-C₅H₄)-COOCH₃]W(CO)₃(CC-C₆H₅) (13), were prepared from their corresponding metal chloride 1, 6 and 12. Structures of compound 3, 5 and 12 have been solved by X-ray diffraction studies. In the case of 5, there is an internal mirror plane passing through the phenylethynyl ligand and bisecting the Cp ring. The phenyl group is oriented perpendicularly to the Cp with an eclipsed conformation. The twist angle is 0° and 118.4° for -CC-Ph and two NO ligands, respectively. The orientation is rationalized in terms of orbital overlap between ψ₃ of Cp, dπ of Cr atom, and π^∗ of alkynyl ligand, and complemented by molecular orbital calculation. The opposite correlation was observed on the chemical shift assignments of C(2)-C(5) on Cp ring in compounds 6 and 12, using HetCOR NMR spectroscopy. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data and compared with the calculations via density functional B3LYP correlation-exchange method.     

双核Fe配合物[(η5-C5H4)C6H10(C4H3S)Fe(CO)2]2的合成和晶体结构

由侧链带有噻吩的环戊二烯基配体C5H5C6H10C4H3S与Fe(CO)5在二甲苯中加热回流,合成了1个新颖的四羰基二铁配合物[(η5-C5H4)C6H10(C4H3S)Fe(CO)2]2。通过元素分析、IR、1H NMR对其结构进行了表征,用X-射线单晶衍射确定了其结构。X-射线单晶衍射表明配合物中有2个桥羰基和2个端羰基,Fe-Fe的键长为0.25465(10)nm。     

配合物{(n-Bu)2Sn[(η5-C5H5)Fe(η5-C5H4)COO]2}2的合成、谱学表征及晶体结构

合成了新型配合物{(n-Bu)₂Sn[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)COO]₂}₂，用元素分析、红外光谱和核磁共振谱( ¹H、¹³C、¹¹⁹Sn)进行了表征，并用X-射线单晶衍射分析法测定其晶体结构。晶体属单斜晶系，空间群P2₁/c，晶胞参数a=11.753(4)?，b=21.133(7)?，c=23.374(9)?，β=101.62(3)°，V=5687(4)?³，Z=4，D_c=1.614Mg·m^-3，μ(MoKα)=1.912mm^-1，F(000)=2800，最终可靠因子R₁=0.0827，wR₂=0.2085。配合物分子呈中心对称，是具有Sn₂O₂中心内环的二聚体结构;每个锡原子与5个O原子和2个C原子形成扭曲的五角双锥几何构型，其中5个O原子为赤道配位原子，而C-Sn-C为配合物的轴。     

Synthesis and X-ray investigation of novel Fe and Mn phenyltellurenyl-halide complexes: (CO)3FeBr2(PhTeBr), (η-C5H5)Fe(CO)2(PhTeI2) and CpMn(CO)2(PhTeI)

New complexes of transition metals with organotellurium halide ligands are reported. Iodination of [CpMn(CO)₂]₂(μ-Ph₂Te₂) leads to the Te-Te bond cleavage and formation of CpMn(CO)₂(PhTeI). Oxidative addition of PhTeBr₃ to Fe(CO)₅ gives the monomeric complex (CO)₃FeBr₂(PhTeBr) which is isostructural with the recently reported (CO)₃FeI₂(PhTeI). Insertion of phenyltellurenyl iodide (PhTeI) into the Fe-I bond of CpFe(CO)₂I forms CpFe(CO)₂(TeI₂Ph). Molecular structures of the reported complexes were determined by single-crystal X-ray diffraction analysis (XRD). A considerable shortening of metal-tellurium distances is observed.     

Dynamic behavior of [(η-C5H4CH3)Cr(CO)2(μ-SBu)Pt(PPh3)2] in solution

The structure and dynamic behavior of complex [(η⁵-C₅H₄CH₃)Cr(CO)₂(μ-SBu)Pt(PPh₃)₂] in solution was studied by multinuclear (¹H, ¹³C, ³¹P) NMR spectroscopy including a phase-sensitive NOESY experiment. Increasing temperature causes rupture of the Cr-Pt bond in the three-membered ring of the complex and rotation of the S-Pt(PPh₃)₂ unit around the Cr-S bond line, followed by formation of a new Cr-Pt bond to close the ring. All activation parameters for this dynamic process have been determined.     

Reactions of diferrocenyl dichalcogenides with [W(CO)5(THF)]: X-ray crystal structures of Fc2Te2 and [W2(μ-SeFc)2(CO)8] (Fc = [Fe(η-C5H5)(η-C5H4)])

Treatment of [W(CO)₅THF] with diferrocenyl diselenide, Fc₂Se₂, yielded the novel metal-metal bonded tungsten(I) complex, [W₂(μ-SeFc)₂(CO)₈] (1: Fc = ferrocenyl, [Fe(η⁵-C₅H₅)(η⁵-C₅H₄)]), which was characterised by NMR and IR spectroscopy, mass spectrometry, and X-ray crystallography. The corresponding tellurium derivative could not be prepared by an analogous route. The X-ray crystal structure of Fc₂Te₂ has also been determined.     

Derivatisation of boryl substituted titanium half-sandwich complexes - Molecular structures of [Ti{(η-C5H4)B(NiPr2)N(H)tBu}Cl2(NMe2)] and [{TiCl2(μ-{OB(NHMe2)-η-C5H4})}2-μ-O]

The half-sandwich complex [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}(NMe₂)₃] (6) was prepared from (η¹-C₅H₅)B(NiPr₂)N(H)iPr (5) and [Ti(NMe₂)₄] with cleavage of one equivalent of HNMe₂ and further converted into the corresponding constrained geometry complex [Ti{(η⁵-C₅H₄)B(NiPr₂)NiPr}(NMe₂)₂] (7) by elimination of a second equivalent of HNMe₂. Reaction of the half-sandwich complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}(NMe₂)₃] (R = iPr, tBu) with excess Me₃SiCl yielded the corresponding dichloro complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}Cl₂(NMe₂)] (R = tBu (10), iPr (11)). The intermediate species [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}Cl(NMe₂)₂] (9) could also be spectroscopically characterised. Partial hydrolysis of 10 and 11, respectively, resulted in formation of [{TiCl₂(μ-{OB(NHMe₂)-η⁵-C₅H₄})}₂-μ-O] (12). The molecular structures of 10 and 12 have been determined by X-ray crystallographic analyses. Complex 10, when activated with MAO, was found to be a highly active styrene polymerisation catalyst while being inactive towards the polymerisation of ethylene.     

A structural investigation of the carbocation complex [{Cp(CO)2Fe}2{μ-(C3H5)}]PF6

The reaction of the propanediyl complex [{Cp^∗(CO)₂Fe}₂{μ-(C₃H₆)}] (Cp^∗ = η⁵-C₅(CH₃)₅) with the hydride abstractor Ph₃CPF₆ in dry CH₂Cl₂ resulted in the formation of the carbocation complex [{Cp^∗(CO)₂Fe}₂{μ-(C₃H₅)}]PF₆. The complex formed triclinic crystals in the space group with Z = 1. In the structure one metal is bonded in the η²-fashion, forming a chiral metallacyclopropane structure with the carbocation, while the other is σ-bonded to the same carbocation ligand. However, NMR evidence indicates that the structure observed in the solid state is not preserved in solution because the metallacyclopropane ring opens up, giving a structure in which more positive charge is localized on the β-CH carbon and which could be fluxional.     

Crystal structure and spectral characteristics of {[(C6H5)NH]2C=NH(C6H5)}[B(C6H5)4]·C2H5OH

A novel compound of {[(C₆H₅)NH]₂C=NH(C₆H₅)}[B(C₆H₅)₄]·C₂H₅OH is prepared and examined by single crystal X-ray diffraction. Crystal data: C₄₅H₄₄BN₃O, M = 653.64, monoclinic, space group P2₁/c, unit cell parameters: a = 24.375(2) Å, b = 17.5829(15) Å, c = 18.090(1) Å, β = 105.277(2)°, V = 7479.0(11) ų, Z = 8, d _calc = 1.161 g/cm³, T = 293 K, R ₁ = 0.064. The structure contains two crystallographically independent cations, two anions, and two solvate ethanol molecules. Three types of interactions occur between them: interionic N-H(N)⋯π and N(H)⋯π⋯H(C), π-delocalized system of Ph rings of the anions, and interaction of ions with ethanol molecules N-H⋯O-H(O)⋯π. The compound is characterized by IR and luminescence spectra. At room temperature, the emission intensity grows with time of exposure to UV irradiation. Original Russian Text Copyright ? 2008 by T. M. Polyanskaya, E. A. Il’inchik, V. V. Volkov, M. K. Drozdova, O. P. Yur’eva, and G. V. Romanenko __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 3, pp. 512–521, May–June, 2008.     

Titanocene-based group-11 metal ions; solid-state structure of {[(η-C5H4SiMe3)2Ti(CCPh)2]2Ag}NO3

The reaction of [Ti](CCR)₂ {[Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; 1a, R = Fc, Fc = (η⁵-C₅H₄)Fe(η⁵-C₅H₅); 1b, R = Ph} with MX {2a, MX = [Cu(NCCH₃)₄]BF₄; M = Ag; 2b, X = ClO₄; 2c, X = NO₃} in a 2:1 molar ratio produces the trinuclear heterobimetallic (Ti₂M) or heptanuclear heterotrimetallic (Ti₂MFe₄) complexes [{[Ti](μ-σ,π-CCR)₂}₂M]X (R = Fc: 3a, M = Cu, X = BF₄; 3b, M = Ag, X = ClO₄. R = Ph: 3c, M = Cu, X = BF₄; 3d, M = Ag, X = ClO₄: 3e, M = Ag, X = NO₃) in high yield. Complexes 3c-3e are also accessible, when {[Ti](μ-σ,π-CCPh)₂}MX (M = Cu: 4a, X = FBF₃; M = Ag: 4b, X = OClO₃; 4c, X = ONO₂) is reacted with one equivalent of 1b. Transferring this reaction scheme to [Ti](CCSiMe₃)₂ (1c) only the formation of the heterobimetallic tweezer complex {[Ti](μ-σ,π-CCSiMe₃)₂}MX {4d, MX = [Cu(NCCH₃)]BF₄; 4e, MX = AgOClO₃} is observed which is attributed to the bulkiness of the acetylide-bound Me₃Si group. The solid-state structure of 3e is reported. In 3e, two [Ti](CCPh)₂ tweezer moieties are chelate-bound by their carbon-carbon triple bonds to a silver(I) ion, resulting in a pseudo-tetrahedral environment at the group-11 metal. is acting as counter-ion to cationic [{[Ti](CCPh)₂}₂Ag]⁺.Additionally, the result of cyclic voltammetric studies on [{[Ti](μ-σ,π-CCPh)₂}₂Cu]BF₄ (3c) is reported.     

Molecular Packing in the Crystal Structures of Mixed-Ligand Complexes [ZnPhen{(i-C4H9)2PS2}2] and [Zn(2,2′-Bipy){(i-C4H9)2PS2}2]

Volatile mixed-ligand complexes of Zn(i-Bu₂PS₂)₂ with Phen and 2,2-Bipy have been synthesized. The crystal structures of the complexes ZnPhen{(i-C₄H₉)₂PS₂}₂ and Zn(2,2-Bipy){(i-C₄H₉)₂PS₂}₂ were determined by single crystal X-ray diffractometry (CAD-4 diffractometer, MoK radiation, 2100 F_hkl, R = 0.0423 for the first complex and 2003 F_hkl, R = 0.0486 for the second). The crystals are monoclinic with cell dimensions a = 17.580(4), b = 9.969(2), c = 19.175(4) , = 90.33(3)°, V = 3360(1) ³, Z = 4, d _calc = 1.313 g/cm³, space group P2/n (for the Phen complex); a = 24.219(5), b = 11.386(2), c = 24.916(5) , = 97.70(3)°, V = 6809(2) ³, Z = 8, d _calc = 1.249 g/cm³, space group C2/c (for the 2,2-Bipy complex). The complexes are constructed from discrete monomer molecules. The coordination polyhedra of the Zn atoms are distorted tetrahedra formed by two S atoms of the two monodentate i-Bu₂PS ₂ ^- ligands and two N atoms of the cyclic bidentate Phen or 2,2-Bipy molecules. Intermolecular interactions and packings in the structures are analyzed.     

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.     

Mixed-ligand complex compounds [Pb(Phen)×{(iso-C4H9)2PS2}2] and [Pb(2,2′-Bipy){(iso-C4H9)2PS2}2] and formation of supramolecular assemblies in their crystal structures

Mixed-ligand complex compounds [Pb(Phen)(i-Bu₂PS₂)]₂ (I) and [Pb(2,2′-Bipy)(i-Bu₂PS₂)]₂ (II) were synthesized. Their structures were determined from X-ray diffraction data (X8 APEX diffractometer, MoK _α radiation, 6392 _Fhkl , R = 0.0233 for I and 3937 F _hkl , R = 0.0252 for II). Crystals I are triclinic: a = 10.2662(3) Å, b = 12.3037(2) Å, c = 14.8444(4) Å; α = 92.054(1)°, β = 103.473(1)°, γ = 105.561(1)°, V = 1746.89(8) ų, Z = 2, ρ_calc = 1.532 g/cm³, space group P . Crystals II are monoclinic: a = 9.3462(3) Å, b = 26.3310(12) Å, c = 28.5345(13) Å; β = 96.436(1)°, V = 6977.9(5) ų, Z = 8, ρ_calc = 1.489 g/cm³, space group P2₁/n. The structures are built from mononuclear molecules. In both structures, the intermolecular contacts between the Pb and S atoms of the neighboring mononuclear molecules form supramolecular assemblies involving two molecules. The environment of the Pb atoms in the assemblies is a pentagonal bipyramid, N₂S₄₊₁. The assemblies are joined into ribbons by π-π interactions of the Phen rings in I and C…C short contacts between the pyridine rings in II. Original Russian Text Copyright ? 2008 by R. F. Klevtsova, E. A. Sankova, T. E. Kokina, L. A. Glinskaya, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 1, pp. 123–131, January–February, 2008.     

(Cyclopentadienyl){(N,N-dimethylaminoethyl)cyclopentadienyl} complexes of zirconium: Crystal structure of [(η-C5H5)(η-C5H4CH2CH2NHMe2)ZrCl2]2[ZrCl6]

[(η⁵-C₅H₅)ZrCl₃] reacts with [C₅H₄CH₂CH₂NMe₂]Li yielding the coordination polymer [(C₅H₅)(C₅H₄CH₂CH₂NMe₂)ZrCl₂]_n (1) as a brown solid which is very sensitive to moisture. The reaction of 1 with 1.35 equivalent of HCl (methanolic solution) yields pale yellow green crystals of [(η⁵-C₅H₅)(η⁵-C₅H₄CH₂CH₂NHMe₂)ZrCl₂]₂[ZrCl₆] (2). Compound 2 was fully characterized on the basis of NMR data and X-ray crystal structure analysis. The formation of this product indicates the elimination of C₅H₄CH₂CH₂NMe₂ as well as C₅H₅ ligands from the Zr(IV) metal centre.     

Effect of high external pressures on the vibrational spectra of Zeise’s complexes, K[Pt(η-C2H4)Cl3] and [Pt(η-C2H4)Cl2]2

The pressure dependences (dν/dP) of the main IR and Raman bands of Zeise’s complexes, K[Pt(η²-C₂H₄)Cl₃] and [Pt(η²-C₂H₄)Cl₂]₂, have been determined for the first time for selected pressures up to ∼33 kbar with the aid of diamond-anvil cells. Neither complex undergoes a pressure-induced structural change throughout the pressure range investigated. The dν/dP values range from −0.13 to 0.79 cm⁻¹ kbar⁻¹. The negative values have proved particularly informative in identifying the location of the CC stretching modes of the Pt-ethylene groups, a topic of considerable disagreement in the literature.     

A comparison between the reaction of P2Ph4 with [{Co2(CO)6}2(μ-η:μ-η-HOCH2CCCCCH2OH)] and the reaction of [Co2(μ-PPh2)2(CO)6] with HOCH2CCCCCH2OH

Reaction of P₂Ph₄ with the diyne-diol complex [{Co₂(CO)₆}₂(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)] in toluene at 65 °C gives [{Co₂(μ-P₂Ph₄)(CO)₄}{Co₂(CO)₆}(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)] (1). Thermolysis of 1 at 95 °C leads to [{Co₂(CO)₅}₂(μ-P₂Ph₄)(μ-η²:μ-η²-HOCH₂CCCCCH₂OH)](2) and (μ₂-PPh₂)(μ₂-CO)(CO)₇] (3). The structures of 1-3 have been established by X-ray crystallography. In 1, a pseudoequatorial P₂Ph₄ ligand bridges the cobalt-cobalt bond of a Co₂(CC)(CO)₄ unit. By contrast, in isomeric 2, a pseudoaxial P₂Ph₄ ligand spans two Co₂(CC)(CO)₅ units, a new coordination mode for [{Co₂(CO)₅L}₂(μ-η²:μ-η²-diyne)] complexes. Complex 3 arises from dehydration-cyclocarbonylation of the diyne-diol in 1 to give a 2(5H)-furanone, a process that has not been previously reported. Reaction of HOCH₂CCCCCH₂OH with [Co₂(μ-PPh₂)₂(CO)₆] at 80 °C in toluene gave [Co₃(μ-PPh₂)₃(CO)₆], [Co₂(CO)₆(μ-η²-HOCH₂CCCCCH₂OH)] and [Co₂{μ-η⁴-PPh₂C(CCCH₂OH)C(CH₂OH)CO}(μ-PPh₂)(CO)₄] (4). The regiochemistry of 4 was confirmed by X-ray crystallography.     

Synthesis and reactions of cycloheptadienyl and cyclooctadienyl tungsten complexes: X-ray crystal structure of [W(CO)2(PPh3)2(η-C7H9)][BF4]

Protonation of the cycloheptatriene complex [W(CO)₃(η⁶-C₇H₈)] with H[BF₄] · Et₂O in CH₂Cl₂ affords the cycloheptadienyl system [W(CO)₃(η⁵-C₇H₉)][BF₄] (1). Complex 1 reacts with NaI to yield [WI(CO)₃(η⁵-C₇H₉)], which is a precursor to [W(CO)₂(NCMe)₃(η³-C₇H₉)][BF₄], albeit in very low yield. The dicarbonyl derivatives [W(CO)₂L₂(η⁵-C₇H₉)]⁺ (L₂=2PPh₃, 4, or dppm, 5) were obtained, respectively, by H[BF₄] · Et₂O protonation of [W(CO)₂(PPh₃)(η⁶-C₇H₈)] in the presence of PPh₃ and reaction of 1 with dppm. The X-ray crystal structure of 4 (as a 1/2 CH₂Cl₂ solvate) reveals that the two PPh₃ ligands are mutually trans and are located beneath the central dienyl carbon and the centre of the edge bridge. The first examples of cyclooctadienyl tungsten complexes [WBr(CO)₂(NCMe)₂(1-3-η:5,6-C₈H₁₁)] (6) and [WBr(CO)₂(NCMe)₂(1-3-η:4,5-C₈H₁₁)] (7) were synthesised by reaction of [W(CO)₃(NCR)₃] (R=Me or Prⁿ) with 3-Br-1,5-cod/6-Br-1,4-cod or 5-Br-1,3-cod/3-Br-1,4-cod (cod=cyclooctadiene), respectively. Complexes 6 and 7 are precursors to the pentahapto-bonded cyclooctadienyl tungsten species [W(CO)₂(dppm)(1-3:5,6-η-C₈H₁₁)][BF₄] and [W(CO)₂(dppe)(1-5-η-C₈H₁₁)][BF₄] · CH₂Cl₂.     

Functionalization of linear and cyclic siloxanes and a dendritic carbosilane with (η-C5H5)Fe(CO)2Si(CH3)2CHCH2 via hydrosilylation reaction

A series of multimetallic systems containing silicon-linked cyclopentadienyl dicarbonyl iron moieties including carbosilane dendrimers and cyclic and polymeric siloxanes have been prepared using hydrosilylation reactions. For this purpose the vinyl-substituted silyliron complex (η⁵-C₅H₅)Fe(CO)₂Si(CH₃)₂ CHCH₂ (1) was prepared by salt elimination reaction between Na[(η⁵-C₅H₅)Fe(CO)₂] and ClSi(CH₃)₂CHCH₂ and fully characterized. Hydrosilylation reaction of 1 with the appropriate Si-H functionalized molecules in the presence of Karstedt catalyst afforded the novel silyl carbonyl iron-functionalized cyclotetrasiloxane 2, dendrimer 3 and copolymer 4, in which the organometallic units are attached to the silicon-based frameworks through a two-methylene flexible spacer. The electrochemical behaviour of compounds 1-4 has been examined in dichloromethane, tetrahydrofuran and acetonitrile solutions using cyclic voltammetry.     

Isocyanide insertion reactivity of dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [{Nb(η-C5H4SiMe3)(CH2Ph)2}2(μ-1,4-NC6H4N)]

The reactivity of dinuclear niobium and tantalum imido complexes with the isocyanide compound 2,6-Me₂C₆H₃NC has been studied. The trialkyl complexes [{NbR₃(CH₃CN)}₂(μ-1,3-NC₆H₄N)], [{NbR₃(CH₃CN)}₂(μ-1,4-NC₆H₄N)] and [{TaR₃(CH₃CN)}₂(μ-1,4-NC₆H₄N)] (R=CH₂SiMe₃) gave [{Nb(η²-RCNAr)₂R}₂(μ-1,3-NC₆H₄N)] (1), [{Nb(η²-RCNAr)₂R}₂(μ-1,4-NC₆H₄N)] (2) and [{Ta(η²-RCNAr)₂R}₂(μ-1,4-NC₆H₄N)] (3) (R=CH₂SiMe₃; Ar=2,6-Me₂C₆H₃), from the isocyanide insertion in two of the metal alkyl carbon bonds. The reaction of the isocyanide reagent with the di-alkyl mono-cyclopentadienyl derivatives [{Nb(η⁵-C₅H₄SiMe₃)R₂}₂(μ-1,3-NC₆H₄N)] (R=Me, CH₂Ph, CH₂SiMe₃), [{Nb(η⁵-C₅H₄SiMe₃)R₂}₂(μ-1,4-NC₆H₄N)] (R=Me, CH₂Ph (4), CH₂SiMe₃) and [{Ta(η⁵-C₅Me₅)(CH₂SiMe₃)₂}₂(μ-1,4-NC₆H₄N)] yielded [{Nb(η⁵-C₅H₄SiMe₃)(η²-RCNAr)R}₂(μ-1,3-NC₆H₄N)] (R=Me (5), CH₂Ph (6), CH₂SiMe₃ (7)), [{Nb(η⁵-C₅H₄SiMe₃)(η²-RCNAr)R}₂(μ-1,4-NC₆H₄N)] (R=Me (8), CH₂Ph (9), CH₂SiMe₃ (10)) and [{Ta(η⁵-C₅Me₅)(η²-Me₃SiCH₂CNAr)CH₂SiMe₃}₂(μ-1,4-NC₆H₄N)] (11) (Ar=2,6-Me₂C₆H₃), respectively, from a single insertion process. The reaction with the mono-alkyl complex [{Nb(η⁵-C₅H₄SiMe₃)(Me)Cl}₂(μ-1,4-NC₆H₄N)] gave [{Nb(η⁵-C₅H₄SiMe₃)(η²-MeCNAr)Cl}₂(μ-1,4-NC₆H₄N)] (12), produced from the isocyanide insertion in the metal-alkyl carbon bond. The alkyl-amido complex [{Nb(η⁵-C₅H₄SiMe₃)(Me)NMe₂}₂(μ-1,4-NC₆H₄N)] gave, from the preferential isocyanide insertion in the metal-amide nitrogen bond, [{Nb(η⁵-C₅H₄SiMe₃)(η²-Me₂NCNAr)Me}₂(μ-1,4-NC₆H₄N)] (13). The molecular structure of one of the alkyl precursors, [{Nb(η⁵-C₅H₄SiMe₃)(CH₂Ph)₂}₂(μ-1,4-NC₆H₄N)] (4), has been determined.