Reaction Of Nickelocene Research Articles

Half‐Sandwich Nickel(II) NHC‐Picolyl Complexes as Catalysts for the Hydrosilylation of Carbonyl Compounds: Evidence for NHC‐Nickel Nanoparticles under Harsh Reaction Conditions

AbstractThe cationic [NiCp(Mes‐NHC‐CH2py]Br complex 2 a was prepared directly by the reaction of nickelocene with 1‐(2‐picolyl)‐3‐mesityl‐imidazolium bromide (1), and its PF6− derivative 2 b, by subsequent salt metathesis. X‐ray diffraction studies and Variable Temperature 1H NMR experiments run with 2 a and 2 b strongly suggest the bidentate coordination of the picolyl‐functionalized carbene to the nickel both in the solid state and in solution in both cases. These data suggest the absence of hemilabile behavior of the latter, even in the presence of a coordinating anion. Both complexes show similar activity in aldehyde hydrosilylation, further implying the absence of hemilability of the picolyl‐functionalized carbene, and effectively reduce a broad scope of aldehydes in the absence of additive under mild conditions. In the case of ketones, effective hydrosilylation is only observed in the presence of a catalytic amount of potassium t‐butoxide at 100 °C. Dynamic light scattering, scanning transmission electron microscopy and X‐ray photoelectron spectroscopy show evidence for the involvement of NHC‐picolyl‐Ni nanoparticles under these conditions.

Application of 1,2,3-triazolylidene nickel complexes for the catalytic oxidation of n-octane

Half-sandwich nickel complexes bearing a variety of mesoionic N-heterocyclic carbene ligands (η5-cyclopentadienyl)-iodo-{1-(R)-3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium-5-yl}nickel; where R = phenyl (3a); 2-ethoxy-2-oxoethyl (3b); propyl (3c); benzyl (3d) were synthesized by the reaction of nickelocene with the respective triazolium salts. The complexes were characterized by HRMS and multi-nuclear NMR, and the solid state structures of 3c and 3d were elucidated by single crystal X-ray diffraction analysis in which both complexes displayed a trigonal planar geometry. As catalysts for the oxidation of n-octane in the presence of oxidants under mild reaction conditions, all the complexes showed activity for the substrate yielding a range of oxygenated products. Under optimized reaction conditions, catalyst 3c with lighter substituents on the triazolium ring exhibited the highest catalytic activity of 15% total conversion to products. With H2O2 as the more productive oxidant, the preferential activation of internal carbons led to the observation of a mixture of octanones as the dominant product stream of the oxidation reaction.

A Bimetallic Iron–Nickel Cluster from the Reaction of Nickelocene with a Pentairon Carbonyl Carbide Cluster Complex

The new bimetallic Fe–Ni carbide containing cluster complex, Fe4Ni(Cp)2(CO)10(μ5-C), 4 was afforded by metal–metal exchange and metal cluster rearrangement processes in the reaction of Fe5(μ5-C)(CO)15, 1, with NiCp2 at 80 °C. A minor product Fe5(Cp)2(CO)10(μ5-C), 5, was also obtained from this reaction which contains no nickel and is a di-Cp substituted derivative of 1. Both compounds were characterized by a combination of IR, 1H NMR, mass spectrometry, elemental and single crystal X-ray diffraction analyses. Compound 4 consists of an open Fe4Ni(μ5-C) cluster framework with a carbide ligand where one iron atom bridges a butterfly arrangement of one nickel and three iron atoms.

Preparation of a N-Heterocyclic Carbene Nickel(II) Complex. Synthetic Experiments in Current Organic and Organometallic Chemistry

A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro–nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes·HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with paraformaldehyde, glyoxal, and hydrochloric acid is described. The reaction of NiCl2·6H2O with aqueous ammonia to give [Ni(NH3)6]Cl2, and the reaction of sodium in neat dicyclopentadiene at 160 °C to produce sodium cyclopentadienide in a one-pot synthesis are both delineated in the second part of this experiment. The reaction of [Ni(NH3)6]Cl2, with NaCp to yield [Ni(η5-C5H5)2] forms the third part. Finally, the procedure ends with the reaction of nickelocene with IMes·HCl to afford the nickel(II) half-sandwich complex [Ni(η5-C5H5)(IMes)Cl]. This sequence of experiments provides an excellent example of NHC–ligand preparation and its subsequent complexation to a transition metal and is a...

Coordination compounds of N, N′-olefin functionalized imidazolin-2-ylidenes

N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc) 2 or [Ni(CH 3CN) 6](BF 4) 2 by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX 2(NHC) 2] 3– 7 ( 3: M = Pd, X = Br, NHC = 1,3-di(3-butenyl)imidazolin-2-ylidene; 4: M = Pd, X = Br, NHC = 1,3-di(4-pentenyl)imidazolin-2-ylidene; 5: M = Pd, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 6: M = Ni, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 7: M = Ni, X = I, NHC = 1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for 4– 7 revealed that square-planar complexes with cis ( 5) or trans ( 4, 6, 7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η 5-cyclopentadienyl (η 5-Cp) monocarbene nickel complexes [NiBr(η 5-Cp)(NHC)] 8 and 9 ( 8: NHC = 1-methyl-3-allylimidazolin-2-ylidene; 9: NHC = 1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes 8 and 9 with silver tetrafluoroborate gave complexes [NiBr(η 5-Cp)(η 3-NHC)] 10 and 11. The X-ray structure analysis of 10 and 11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent.

Neutral, Radical [CpNi(dithiolene)] Complexes with Flexible, Nonplanar Seven‐Membered Rings: [CpNi{S2C2S2(CH2)2X}] (X = CH2, CF2, C=CH2, S, C=O)

AbstractNeutral, radical [CpNi(dithiolene)] complexes fused with seven‐membered rings, formulated as [CpNi{S2C2S2(CH2)2X}] (X = CH2, CF2, C=CH2, S), have been synthesized in 30–60 % yields from the reactions of nickelocene with the corresponding neutral, square‐planar, (dithiolene)nickel complexes [Ni{S2C2S2(CH2)2X}2]. [CpNi{S2C2S2(CH2)2X}] (X = C=O) was prepared from nickelocene and [1,3]dithiolo[4,5‐b][1,4]dithiepine‐2,6‐dione under thermal or photochemical conditions. All complexes exhibit reversible oxidation and reduction waves to the cation and anion form, respectively. The terminal groups (X) in the seven‐membered ring shift their redox potentials to anodic potentials in the following order: CF2 > C=O > S > C=CH2 > CH2. The singlet EPR responses of [CpNi{S2C2S2(CH2)2(X)}] appear at g ≈ 2.0514–2.0529 in dichloromethane solution at room temperature. An NIR absorption is observed at λmax ≈ 798–848 nm (ϵ ≈ 1700–2400 M–1 cm–1) in dichloromethane solution. The X‐ray structures of the five complexes show two‐legged piano‐stool geometries around the central nickel atom (formally NiIII) and strong distortions from planarity of the seven‐membered C2S2(CH2)2X rings. In the solid state, those radical (S = 1/2) species adopt either one‐dimensional alternating chain‐like motifs (X = CH2, C=CH2, S) or dimeric entities characterized by a singlet–triplet magnetic behavior (X = CF2, C=O). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Heterometallic Dithiolene Complexes Formed by Stepwise Displacement of Cyclopentadienyl Ligands from Nickelocene with CpMo(S2C2Ph2)2

The dithiolene ligand transfer reaction between Ni(S2C2Ph2)2 (1) and CpMo(CO)3Cl (2; Cp = eta-C5H5) affords the neutral paramagnetic molybdenum bis(dithiolene) complex CpM(S2C2Ph2)2 (3), which has been structurally characterized. As found in other d1 complexes of this type, one dithiolene ligand is planar while the other is significantly folded toward the Cp ligand. An unexpected second product of the reaction is the unusual trinuclear species Ni[Mo(S2C2Ph2)2Cp]2 (4), which in the solid state contains three different dithiolene bonding modes (terminal, bridging, and semi-bridging) in the same molecule. Complex 4 can also be synthesized by displacement of the diene ligands in Ni(cod)2 with 2 equiv of 3. In contrast, the reaction of nickelocene with 3 proceeds by displacement of the Cp ligands in a stepwise manner to give initially the dinuclear species NiMo(mu-S2C2Ph2)2Cp2 5, which then reacts further with 3 to produce 4.

Novel tetrahedral tetranickel cluster with alkylidyne ligand (NiCp) 4(μ 3-CR)

A novel tetrahedral (μ 3-alkylidyne)tetranickel cluster (NiCp) 4(μ 3-C(CH 2) 4CH 3) ( 4) was obtained in the reaction of nickelocene with potassium and 1-hexene. Compound 4 was characterised by means of MS and X-ray diffraction analysis. It crystallizes in the orthorhombic crystal system and Pna2 1 (No. 33) space group. Unit cell dimensions: a = 28.406(6) Å, b = 8.928(2) Å, c = 9.541(2) Å; Z = 4. The compound possesses 63 valence electrons, three more than the expected “magic number” for such type of clusters, and three of the four nickel atoms do not fulfil the 18VE rule. It is paramagnetic with the magnetic moment 3.54 μ B, what corresponds to three unpaired electrons per molecule. This was confirmed by molecular orbital calculations using the density functional theory (DFT).

New Synthetic Methods for η5-Cyclopentadienyl Nickel(III) Dithiolene Complexes Derived from Nickelocene

The reactions of nickelocene with the neutral square-planar metal dithiolene complexes [M(S2C2(R1)(R2))2] gave the η5-cyclopentadienyl nickel(III) dithiolene complexes [CpNi(S2C2(R1)(R2))] (R1, R2 = Ph (2); R1 = Ph, R2 = H (3); R1, R2 = Me (4)) in 58−62% yields. The monoanions of the square-planar dithiolene complexes [M(S2C2(R1)(R2))2]- reacted with nickelocenium to form [CpNi(S2C2(R1)(R2))] (R1, R2 = COOMe (5) or CN (6)) in 67% or 68% yield, respectively, when the R1 and R2 substituents are electron-withdrawing groups. The CpNi dithiolene complexes 3 and 5 were also obtained by the thermal reactions or photoreactions of nickelocene with 1,3-dithiol-2-one or 1,3-dithiol-2-thione derivatives, [EC(S2C2(R1)(R2))] (E = O, S; R1 = Ph, R2 = H; R1, R2 = COOMe). The most efficient synthetic method for the CpNi dithiolene complex was the reaction of the hexacoordinated platinum dithiolene complex [Pt(S2C2Ph2)2(dppe)] (dppe = bis(diphenylphosphino)ethane) with nickelocene (96% yield for complex 2). The structure of complex 6 was determined by X-ray crystal structure analysis. The electronic and ESR properties of the CpNi dithiolene complexes 2−6 were investigated.

Simple Synthesis of CpNi(NHC)Cl Complexes (Cp = Cyclopentadienyl; NHC = N-Heterocyclic Carbene)

The reaction of saturated and unsaturated imidazolium salts with nickelocene in refluxing THF results in the formation of NHC complexes of general formula CpNi(NHC)Cl (NHC = SIMes (2), IPr (3), SIPr (4)). This protonation of Cp2Ni was also tested using phosphonium salts, and the reaction of nickelocene with triethylphosphonium chloride leads to CpNi(PEt3)Cl (5). All compounds were characterized by NMR and X-ray crystallography. The catalytic activity of the NHC compounds was tested in aryl amination (Buchwald−Hartwig reaction) and in aryl halide dehalogenation reactions.

New insights into the reaction of nickelocene with methyllithium: the isolation and crystal structure of (NiCp) 3(μ 3-CH)

Thermolysis of the cyclopentadienylnickelmethyl complex [NiCp(CH 3)(η 2CH 2 CHC 4H 9)] in various solvents was studied. Separation of products by means of column chromatography allowed to isolate and crystallographically characterise (μ 3-methylidyne)tris(cyclopentadienylnickel) cluster (NiCp) 3(μ 3-CH) ( 1). Cluster 1 crystallised from a hexane/THF mixture in hexagonal crystal system and P6 3 space group. Ni–Ni and Ni–C(methylidyne) distances were 2.3558(10) and 1.823(4) Å, respectively. Detailed studies showed that cluster (NiCp) 3(μ 3-CH) ( 1) was produced during the chromatography on alumina. The plausible precursor to 1 is described as (NiCp) 6C.

Polymerization of alkynes on nickelocene based catalysts: considerations on polymerization mechanism

Abstract Novel nickelocene based catalysts were used for polymerization of 2-butyne, 1-phenyl-1-propyne, bis(trimethylsilyl)acetylene and trimethylsilylacetylene. The catalyst prepared in the reaction of nickelocene with organolithium compounds in the presence of alkyne was previously isolated and fully characterized. It enabled us to explain the mechanism of the polymerization. Polymerization of alkynes proceeds according to coordination-insertion mechanism. Coordinated acetylene molecule inserts into Ni C bond. An active catalytic species of polymerization appeared to be {CpNiR} stabilized by alkyne molecule. Cyclization is catalyzed by {CpNiH} species.

Nickelocene catalysts for polymerization of alkynes: mechanistic aspects

AbstractNovel nickelocene‐based catalysts were used for polymerization of diphenylacetylene and phenylacetylene. The catalyst obtained in the reaction of nickelocene with organolithium compounds in the presence of alkyne was previously isolated and fully characterized. This enabled us to explain the mechanism of the polymerization. Polymerization of alkynes proceeds according to a coordination–insertion mechanism. Coordinated acetylene molecule inserts into an NiC bond. An active catalytic species of polymerization appeared to be {CpNiR} stabilized by alkyne molecule. Cyclization is catalyzed by {CpNiH} species. The mechanism of polymerization and cyclization reaction was determined based on the composition of the reaction products formed, gel‐permeation chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry measurements. Copyright © 2004 John Wiley & Sons, Ltd.

Reactions of nickelocene with phenyl- and methyllithium in the presence of bis(trimethylsilyl)acetylene

Results of the reactions of nickelocene with phenyl- and methyllithium in the presence of bis(trimethylsilyl)acetylene have been reported. It was found that in the reaction of nickelocene with phenyllithium and bis(trimethylsilyl)acetylene three products were formed: di(cyclopentadienylnickel) complex with bis(trimethylsilyl)acetylene (NiCp) 2(μ–η 2–η 2-Me 3SiCCSiMe 3) ( 1); di(cyclopentadienylnickel) complex with phenyl(trimethylsilyl)acetylene (NiCp) 2(μ–η 2–η 2-PhCCSiMe 3) ( 2) and tetra(cyclopentadienylnickel) complex with 1,4-bis(trimethylsilyl)-1,3-butadiyne (NiCp) 4(μ,μ–η 2–η 2–η 2–η 2-Me 3SiCCCCSiMe 3) ( 3). Phenyl(trimethylsilyl)acetylene and 1,4-bis(trimethylsilyl)-1,3-butadiyne were the products of coupling and cross-coupling of {CpNiPh} and {CpNiCCSiMe 3} formed as intermediate products of the reactions. All products were characterized by spectroscopic methods and crystal and molecular structures of compounds 1 and 3 were determined by single crystal X-ray measurements.

The activation of CH bonds in internal alkenes and dienes by {NiCp} species formed in the reaction of nickelocene with alkali metals

Reactions of nickelocene with metallic sodium in the presence of internal alkenes: trans-3-hexene, cis-2-heptene and 2,3-dimethyl-2-butene have been studied. It was found that {NiCp} species generated in the reaction of nickelocene with sodium dehydrogenate internal alkenes to alkynes. The latter form then complexes with tri(cyclopentadienylnickel) (NiCp) 3RCCR and with di(cyclopentadienylnickel) (NiCp) 2RCCR. If the methyl group is adjacent to the alkene double bond, the activation of the CH bonds of this group leads to the formation of alkylidyne tri(cyclopentadienylnickel) clusters. In the reaction of nickelocene with lithium in the presence of 1,5-hexadiene, alkylidyne tri(cyclopentadienylnickel) cluster (NiCp) 3CCH 2CH 2CH 2CHCH 2 and intramolecularly stabilised complex Cp NiCH(CH 3)CH 2CH 2CH CH 2 were formed. In all the reactions studied di-, (NiCp) 2CpH, and tetra(cyclopentadienylnickel), (NiCp) 4H x , compounds were formed besides the other products.

Reactions of nickelocene with an Ru5 cluster: crystal structures of two nickel–ruthenium clusters containing C2 ligands

Reactions of nickelocene with Ru5(μ5-C2)(μ-SMe)2(μ-PPh2)2(CO)11 have given NiRu5(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)9Cp2 and Ni2Ru4(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)8Cp2 whose molecular structures have been determined. The NiRu5 cluster is related to other heterometallic clusters containing FeRu5, Ru6 or Co2Ru5 cores which contain two edge-fused squares supporting the C2 ligand, one carbon occupying the centre of each square face while retaining the C–C bond. However, there is no formal M–M interaction along the shared edge. Substitution of CO groups by Cp on one Ru atom has occurred. The structure of the Ni2Ru4 cluster is similar, with the six-membered ring having the boat conformation. The C2 ligand takes up two disordered (1∶1) positions, either parallel or perpendicular to the non-bonding Ni ⋯ Ni vector. Extended Huckel and density functional calculations have been carried out on Ni2Ru4(μ6-C2)(μ-SMe)2(μ-PPh2)2(CO)8Cp2 to rationalise these two observed coordination modes of the C2 unit to the metal framework. Results suggest that the two arrangements are isoenergetic and that the M–C bonding follows the Dewar–Chatt–Duncanson model as previously found for related C2-containing polynuclear organometallic clusters.

Reactions of nickelocene with diphenylmethyl- and triphenylmethyllithium

Reactions of nickelocene with diphenylmethyl- and triphenylmethyllithium have been studied. Several organonickel compounds were formed in these reactions. The products were separated by column chromatography and characterised by spectral methods. The presence of alkylated nickelocenes among products of both reactions has been confirmed. The crystal structures of two π-allyl cyclopentadienylnickel complexes have been determined by X-ray measurements. Bis(η 5-cyclopentadienyη 3-cyclopentenylnickel) ( 1) crystallises in orthorhombic crystal system with eight molecules in a unit cell; space group Pbca, unit cell dimensions: a=10.134(3), b=11.801(3), c=26.753(7) Å. Compound 4 contains triphenylmethyl group η 3-bonded to NiCp unit. It crystallises in triclinic crystal system with four molecules in the unit cell; space group P 1 ̄ ; unit cell dimensions: a=9.8747(9), b=10.6331(10), c=19.569(2) Å and α=93.793(8), β=102.000(8), γ=113.912(7)°.

Reactions of nickelocene with sodium in the presence of terminal alkenes

A novel reduction of nickelocene with metallic sodium in the presence of 1-pentene and 1-hexene was studied. It was found that two products of alkene activation were formed. The first one was a (μ 3-hydrido)-(μ 3-alkylidyne)-trinickel cluster ( 1) and the second one a (μ 3-alkylidyne)-trinickel cluster ( 3). Both types of clusters were characterised by spectroscopic methods and by single-crystal X-ray diffraction measurements. The first cluster crystallised from hexane in a monoclinic system in the C2/ c space group and the second one from methanol, also as a monoclinic system in the P2 1/ c space group.

Reaction of nickelocene with methyllithium in the presence of 2-butyne

Reaction of nickelocene with methyllithium in the presence of 2-butyne at the molar ratio of reactants 1:1:1 leads to the formation of several organinickel compounds. Five of these products were isolated and identified. A novel, 49-electron tri(cyclopentadienylnickel) nickel cluster (CpNi) 3·(CH 3CCCH 3) ( 5) was fully characterized by spectroscopic and X-ray measurements. Alkyne ligand is bonded to three nickel atoms via two σ and one π bonds (2σ+π bond system). Compound 5 crystallizes from hexane in a monoclinic crystal system and P2 1/ n space group. Corresponding unit cell parameters were determined as a=9.015(2) Å; b=14.608(3) Å; c=13.983(3) Å; β=108.47(3)°; V=1746.6(6) Å 3; Z=4.

Alkylation of cyclopentadienyl rings in the reactions of nickelocene with organolithium compounds

The reaction of nickelocene with tert-butyllithium has been studied. It was found that unstable species {CpNiC(CH 3) 3}, formed in this reaction, reacted further in two directions: β-H elimination and homolytic cleavage of Ni–C bond. Hydrogen elimination product formed trinickel cluster (NiCp) 3CCH(CH 3) 2 1, while t-butyl radical alkylated cyclopentadienyl rings to form several compounds. One of these compounds, {Ni[C 5H 4C(CH 3) 3]} 2[C 5H 5C(CH 3) 3] 3, has been isolated and fully characterised. The compound crystallizes from hexane in a triclinic crystal system and P 1 space group. Corresponding unit cell parameters were determined as a=7.520(2) Å; b=13.150(5) Å; c=13.625(4) Å; α=113.77(3)°; β=97.42(3)°; γ=90.02(3)°; V=1220.7(7) Å 3; Z=2. It is the first example of alkylation of cyclopentadienyl rings bonded to nickel by organolithium compounds.