Antoni Pietrzykowski

Reactions of nickelocene with methyl-, ethyl- and vinyl-lithium compounds. Hydrogen elimination and cyclopentadienyl ring hydrogenation

Abstract It has been shown that bis(cyclopentadienyl)(μ-cyclopentadiene)dinickel, (NiCP)2(η-C5H6), and (η5-cyclopentadienyl) (η3-cyclopentenyl)nickel, CpNi(η3-C5H7), are formed in the reaction of nickelocene with methyl-lithium and with 1-phenyl-2-methyl-propenyl-lithium. The compound (NiCp)2(μ-C5H6) can be only formed as a result of the reduction of the cyclopentadienyl ring bonded to the nickel atom whereas the formation of CpNi(η3-C5H7) can be explained by the further hydrogeneration of cyclopentadiene formed in the earlier reaction steps. (NiCp)2(μ-C5H6) has been fully characterised spectrometrically and its X-ray structure determined. It crystallises in the orthorhombic system, space group Pnma, with four molecules per unit cell.

From nickelocene to novel organonickel compounds

Abstract Nickelocene reacts with organolithium or -magnesium compounds forming unstable 16 VE species {CpNiR}. These species reacts further yielding many new organonickel compounds. The type of R group has a decisive influence on the course of {CpNiR} transformations. If R possesses easily accessible α- or β-hydrogen atoms, then hydrogen elimination is the main reaction course and many cyclopentadienylnickel clusters are formed. The absence of α- and β-hydrogen favours a coupling reaction with RR formation. Facile stabilisation of free radicals causes homolytic cleavage of the NiC bond with alkylation of cyclopentadienyl ring. Some kinds of R groups e.g. R=CHPh 2 facilitate formation of a carbene :CPh 2 which can react with nickelocene yielding alkylated nickelocene derivatives. {CpNiR} can also undergo intramolecular stabilisation as it occurs for R=CPh 3 . In most cases the above reactions proceed simultaneously yielding a complex mixture of several compounds. On the other hand some reactions proceed quite selectively forming products in high yield so they can be applied in syntheses.

THE ACTIVATION OF C-H BONDS IN TERMINAL OLEFINS BY CYCLOPENTADIENYLNICKEL SPECIES

Abstract The alkylidynetrinickel clusters (NiCp)3C(CH2)8CH3 1, (NiCp)3CCH3 2 and tetrakis(η5-cyclopentadienyl)dihydridotetranickel (NiCp)4H2 3 were isolated from the reaction mixture of nickelocene with phenyllithium in the presence of 1-decene. (NiCp)3C(CH2)4CH3 and the clusters 2 and 3 were obtained in reaction with 1-hexene. In the presence of 2,4,4-trimethyl-1-pentene, cluster 3 was obtained as the main product of the reaction. In the reaction with 1-decene, organic products (olefins, biphenyl, o-terphenyl, quartephenyl) were identified by GC/MS analyses. The structure of 3 has been determined by X-ray diffraction and characterized by 1H and 13C NMR, MS and IR. On the basis of organonickel and organic products formed, the mechanism of the sp2-hybridized C-H bond activation by cyclopentadienylnickel species has been discussed.

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 3 C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 P 2 1 / n space group. Corresponding unit cell parameters were determined as a =9.015(2) A; b =14.608(3) A; c= 13.983(3) A; β =108.47(3)°; V =1746.6(6) A 3 ; Z =4.

The first structurally characterized trinickel cluster with an open structure: Crystal and molecular structure of CpPh]Ni(μ-η2η2-PhCCPh)NiCp

Reaction of nickelocene with methyllithium in the presence of diphenylacetylene at the molar ratio of reactants 1:1:2 produces a trinickel cluster with an open structure. The cluster contains a bent arrangement of nickel atoms. Two of the alkyne units are linked via a carboncarbon bond to produce a nickelacyclopentadienyl ring, while the third alkyne unit remains independently coordinated to the cluster via two π -bonds. Two Cp groups are bonded to two terminal nickel atoms. The cluster crystallizes from methylene chloride with solvent molecules in a monoclinic crystal system and P 2 1 / n space group. Corresponding unit cell parameters were determined as: a =12.4385(13) A; b =24.994(3) A; c =13.9657(14) A; β =91.457(8)°; V =4340.4(8) A 3 ; Z =4.

Reactions of biscyclopentadienylnickel with lithium and magnesium aryls

Abstract The reaction of nickelocene with phenyllithium, ortho -, meta - and para -methylphenylmagnesium bromide, and 2-((dimethylamino)methyl) phenyllithium are studied. It was found that unstable compounds {CpNiC 6 H 4 R} (R  H, o -, m -, p -CH 3 ) are formed in those reactions. For R  CH 2 N(CH 3 ) 2 , a stable compound, CpNiC 6 H 4 CH 2 N(CH 3 ) 2 , is formed due to intramolecular coordination. In other cases, mainly coupling reactions occur and biphenyl, bitolyl and higher coupling products are formed. Compound (CpNiC 6 H 4 R) is also formed as a product of thermal decomposition of Cp{η 2− C 2 H 4 )NiC 6 H 4 R. It reacts further to form the same products as above. The mechanism of the coupling reactions is proposed and discussed.

(η3-allyl)(η5-cyclopentadienyl)nickel complexes

Abstract Unstable CpNi(vinyl) compounds of the type CpNi-CR′  CR 2 (R′  CH 3 , C 6 H 5 , R  CH 3 ) are formed in the reaction of nickelocene with vinyllithium or -magnesium compounds. CpNi(vinyl) reacts further to form π-allyl complexes and other compounds not yet fully characterized. For R′  CH 3 , π-allyl complex 1 is formed and for R′  C 6 H 5 two π-ally isomers anti - 2a and syn - 2b are formed. The mechanisms of α-, β-, γ- and η-H elimination and of hydrogen transfer reactions are discussed.

Triple C-H bond activation of a nickel-bound methyl group: synthesis and X-ray structure of a carbide cluster (NiCp)6(μ6-C).

A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(μ(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH(3))(η(2)-CH(2)═CHC(4)H(9))] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C(carbide) = 1.767(4)-2.109(4) Å) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) Å, Ni···Ni nonbonding distances = 3.107(2) and 3.108(2) Å). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, (13)C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds.

A new type of tetranuclear cyclopentadienylnickel cluster: synthesis and structural characterisation

Abstract A novel, 65-electron tetranuclear nickel cluster of the formula Cp3Ni4(CH3CCCH3)3 (6) was isolated and identified as the product of the reaction of nickelocene with methyllithium in the presence of 2-butyne at the molar ratio of reactants 1:1:1. The compound was fully characterised by spectroscopic and X-ray measurements. It crystallises from hexane in an orthorhombic crystal system and space group Pbcn. Corresponding unit cell parameters were determined as a=26.438(5), b=11.219(2), c=16.328(3) A; α=β=γ=90°; V=4843(2) A3; Z=8.

Reactions of methyl- and ethylaluminium compounds with alkoxyalcohols. The influence of alkoxyalcohol substituents on the structure of the complexes formed

Abstract Dimeric dimethylaluminium compounds {[Me 2 Al(μ-OCH 2 CH 2 O n Pr)] 2 ( 1 ), [Me 2 Al(μ-OCH(CH 3 )CH 2 O t Bu)] 2 ( 3 ), [Me 2 Al(μ-OCH 2 CH 2 CH 2 OEt)] 2 ( 5 ), [Me 2 Al(μ-OCH 2 CH 2 CH(Me)OMe)] 2 ( 7 ), [Me 2 Al(μ-OCH 2 CH 2 C(Me) 2 OMe)] 2 ( 9 )} and dichloroaluminium compounds {[Cl 2 Al(μ-OCH 2 CH 2 O n Pr)] 2 ( 2 ), [Cl 2 Al(μ-OCH(CH 3 )CH 2 O t Bu)] 2 ( 4 ), [Cl 2 Al(μ-OCH 2 CH 2 CH 2 OEt)] 2 ( 6 ), [Cl 2 Al(μ-OCH 2 CH 2 CH(Me)OMe)] 2 ( 8 ), [Cl 2 Al(μ-OCH 2 CH 2 C(Me) 2 OMe)] 2 ( 10 )} have been prepared. The molecular structures of compounds 2 , 3 , 6 , 8 , 9 and 10 have been determined by X-ray crystallography. All these compounds exist in the solid state as dimers with chelating ether-alkoxide ligands and five-coordinate aluminium atoms. Dichloroaluminium derivatives (compounds 2 , 4 , 6 , 8 and 10 ) exist as five-coordinate isomers also in solution, while dimethylaluminium ones (compounds 1 , 3 , 5 , 7 and 9 ) exist as an equilibrium mixture between four- and five-coordinate isomers. An increase of aluminium Lewis acidity in dichloroaluminium derivatives in comparison with dimethylaluminium ones results in substantial shortening of AlO distances. The R 2 Al⋯O (ether) R′ distance is mainly determined by the steric repulsion between the OR′ group and the two alkyl substituents on aluminium. The influence of electronic properties of R′ on Cl 2 Al⋯O (ether) R′ interaction was illustrated for compound 2 in comparison with literature data for analogous complexes.