Carl Krüger

The preparation, reactions and structure of bis[bis(tricyclohexylphosphine)nickel] dinitrogen, {[(C6H11)3P]2Ni}2N2

Abstract The treatment of nickel acetylacetonate with trimethylaluminium in the presence of tricyclohexylphosphine and nitrogen gives the dinitrogen complex {[(C6H11)3P]2Ni}2N2 (I). Intermediate methyl-nickel complexes can be isolated, and provide an insight into the mechanism of formation of (I). The nitrogen molecule is readily displaced to give [(C6H11)3P]2Ni. The reactions of this coordinatively unsaturated species are described. The structure of the dinitrogen complex has been determined by X-ray crystallography from 5977 reflections using an automatic diffractometer, and refined anisotropically for all 80 atoms to a final R-value of 11%. The molecule is shown to contain a linear Ni-N-N-Ni system in which the nitrogen molecule is enclosed in a cage formed by four of the cyclohexyl rings. The NN bond distance is 1.12 A.

Nickel(0)-induzierte CC-verknüpfung zwischen kohlendioxid und alkinen sowie alkenen

Abstract CO 2 and alkynes or alkenes undergo a 1/1 coupling in the presence of (Lig)Ni 0 complexes to give five-membered cyclic nickela complexes of types V and XVII. The influence of temperature and of the ligands upon the regioselectivity of the CC coupling in the case of monosubstituted olefins is reported, and the significance of these ring systems in preparative chemistry is emphasized. Oxanickelacyclopentenones (V) react with alkynes to form oxanickelacycloheptadienones (XIII). The structure of one of the compounds of this class has been determined by X-ray crystallography. Special features of these novel compounds, which can be readily prepared from CO 2 , are discussed together with the probable reaction mechanisms.

Synthesis of new ligands for transition metal complexes: menthyl- and neomenthyl-cyclopentadienes

Abstract Syntheses of (−)-menthylcyclopentadiene (MCp) and (+)-neomenthyl cyclopentadiene (NMCp) from (−)-menthol are described. These chiral ligands have been used to prepare (η5-MCp)2TiCl2, (η5-NMCp)2, TiCl2, (η5-MCp)2ZrCl2, (η5-NMCp)2ZrCl2, (η5-Cp)(η5-MCp)TiCl2 and (η5-Cp)(η5-NMCp)TiCl2. The structure and absolute configuration of (η5-Cp)(η5-MCp)TiCl2 has been established by X-ray analysis.

The Remarkable Features of (η4-Conjugated Diene)zirconocene and -hafnocene Complexes

Publisher Summary This chapter discusses the remarkable features of (η 4 -conjugated fiene) zirconocene and –hafnocene complexes. (η 4 -conjugated diene) transition-metal complexes are important as starting materials or reactive intermediates in many catalytic processes. They play an increasingly important role as stoichiometric substrates or reagents in organic synthesis. Group IV metallocenes readily form 1: l complexes with conjugated dienes in their s-trans conformation. Many (η 4 -diene) metallocenes of conjugated dienes, fixed in their s-cis conformation by a rigid carbon framework, have been obtained in high yields. Inner and outer methylene hydrogens appear as doublets at sufficiently low temperature. A hypsochromic shift is observed for long-wave absorption band on going from 5a to 3a. The diene moiety (plane C1, C2, C3, C4) of the ligands remains essentially planar. All four carbon atoms of the conjugated diene skeleton are clearly within bonding distance of the zirconium center. Isomeric (s-cis- and (s-trans-η 4 -conjugated diene)zirconocene and –hafnocene complexes exhibit pronounced differences in their characteristic structural data as well as their spectroscopic features. By the nature of its molecular mechanism, carbonyl-insertion reaction represents a typical reaction mode ofσ–alkyl transition-metal complexes. The pronounced alkyl metal character of (s-cis-butadiene)zirconocene should make the diene ligand in 5a much more amenable to electrophilic attack than in the isomeric (s-trans-η 4 -butadiene)ZrCp 2 (3a). The (conjugated-diene)zirconocene and –hafnocene systems are unique in that three isomeric organometallic species can be distinguished by physical and/or chemical means.

Synthesis, characterization and structural studies of mono- and polynuclear complexes of zinc(II) with 1,10-phenanthroline, 2,2′-bipyridine and 4,4′-bipyridine

Abstract Three complexes of the formula [Zn(2,2′-biny)(CCl3CO2)2(H2O)] (1). [Zn (1,10-phen) (CCl3CO2)2(H2O)] (1a) and [Zn(μ-4,4′-bipy)(4-4′-bipy)2(CCl3CO2)2(H2O)4]n (2) have been synthesized and characterized by elemental analysis, IR spectra, thermal analysis and single-crystal X-ray diffraction for 1 and 2 and X-ray powder pattern for 1a. The metal coordination in complex 1 is distorted trigonal bipyramidal with N(1), O(2) and O(5) defining the basal plane, O(3) and N(2) being in apical positions. The X-ray crystal structure of 2 reveals that the local coordination round the ZnII ion is a distorted octahedron, in which Zn(H2O)4 coordination planes are bridged by 4,4′-bipyridine to form an infinite chain structure. Two 4,4′-bipyridine molecules and two trichloroacetate anions exist in the lattice linked by intermolecular hydrogen bonds to coordinated water molecule. Complexes 1 and 1a have a similar pattern of bonding and showed identical TGA curve and almost similar X-ray powder diffractograms.

Transition metal allyls : IV. The (η3-allyl)2M complexes of nickel, palladium and platinum: reaction with tertiary phosphines

Abstract A series of 1 : 1 adducts have been prepared by treating the bis-η3-allyl complexes of nickel, palladium and platinum with tertiary phosphines. Investigations of their structure in solution as well as in the crystal have shown that both 18-electron (η3-allyl)2ML complexes as well as 16-electron (η1-allyl)-(η3-allyl)ML complexes may be formed.

Transition metal allyls ☆: III. The (η3-allyl)2M complexes of nickel, palladium and platinum: structural considerations

Abstract The structures of a series of (η 3 -allyl) 2 M complexes of nickel, palladium and platinum have been investigated with the help of 13 C NMR, 1 H NMR and Raman spectroscopy. The crystal structure of (η 3 -cyclooctatrienyl) 2 Ni has been determined by X-ray methods; the two nickel-bonded η 3 -allyl groups are mutually trans .

BIDENTATE PHOSPHINES OF HETEROARENES : 9,9-DIMETHYL-4,5-BIS(DIPHENYLPHOSPHINO)XANTHENE

Twofold lithiation of 9,9-dimethylxanthene with n-butyllithium and N,N,N′,N′-tetrametylethylenediamine (TMEDA) in boiling n-heptane followed by reaction with chlorodiphenylphosphine (Ph2PCl) yielded the title compound 4. The phosphine ligand was characterised by 1H NMR, 13C NMR, 31P NMR spectroscopy and single crystal X-ray structure analysis. The folded and deformed xanthene unit causes a remarkably short P…P distance of 4.1 A which in turn results in a large coupling 6JPP′ = 27.3 Hz.

Drei- oder Vierfach-Koordination des Aluminiums in Alkylaluminiumphenoxiden und deren Unterscheidung durch 27Al-NMR-Spektroskopie

The 27Al NMR spectra for a series of aryloxyaluminium compounds [RnAl(OAr)3−n]m (R  methyl, isobutyl; n  0–2; m  1, 2, 3) with various alkyl substituents in the 2 and 6 positions of the phenoxy rings have been measured. The δ(27Al) resonances give an indication of the number of aryloxy ligands and the coordination number of each Al atom. Monomeric R2AlOAr compounds have δ(27Al) resonances around 190 ppm whereas dimeric analogues give signals at 167 ppm. The 27Al NMR resonances for monomeric RAl(OAr)2 are found at ca. 100 ppm while those for [Al(OAr)3]2, where the aluminium atoms are solely bonded to aryloxy groups, lie at ca. 50 ppm. Characteristic shifts of the resonances were also observed for complexes of these compounds with THF, whereby it was found that the resulting change Δδ(27Al) decreases with increasing number of aryloxy ligands. The crystal structures of three selected compounds, 3, 8 and 11, were determined by X-ray crystallography.

Metallacycloalkanes: I. Preparation and characterisation of α,α′-bipyridyl-5-nickela-3,3,7,7-tetramethyl-trans-tricyclo[4.1.0.02,4]heptane

Abstract Oxidative addition of 2 molecules of 3,3-dimethylcyclopropene (I) to α,α′-bipyridyl(1,5-cyclooctadiene)nickel(0) (III) gave the title compound (IV) in over 90% yield. Complex IV was characterized by mass, 1 H NMR and 13 C NMR spectroscopy. Its structure was determined by X-ray diffraction ( a 13.7081(2), b 14.638(2), c 9.5139(1) A, β 110.82(1)°, C 2/ c , R = 0.05 for 1614 reflections).