Matthias Nolte

Preparation and catalytic application of a novel very rigid group 4 ansa-metallocene system

Abstract Treatment of 2,5-hexandione with cyclopentadiene in the presence of pyrrolidine yields the corresponding bisfulvene ( 5 ) that has been converted to the [4-cyclopentadienyliden-4,7,7-trimethyl-4,5,6,7-tetrahydroindenyl]lignad system, isolated as the dilithio compound 8 . Subsequent reaction with the group 4 metal halides MCl 4 (M = Ti, Zr, Hf) gives the rigid ansametallocene dichlorides 9a-c . Their reaction with methyllithium yields the corresponding dimethyl-ansa-metallocenes 10a-c . Complexes 9a-c and 10a-c were characterized by X-ray diffraction. The zirconium and hafnium systems all exhibit very low D1-M-D2 angles (D1 and D2 denote the centroids of the Cp-ring systems) at around 116°. Consequently the homogeneous metallocene/methylalumoxane Ziegler-type catalyst systems derived from the zirconium complex 9b produce low molecular weight propene oligomers (in contrast to high molecular weight polypropylene formed at the titanium containing 9a /MAO catalyst system), which is probably due to an electronic control of the k propagation /k termination -ratio of the propene polymerization process. It is forseeable that such ansa-metallocene derived catalyst systems favouring the formation of low molecular weight products instead of high molecular weight polyolefins will find increasing applications in organic synthesis.

Torsional isomerism of bent metallocene complexes. The structures of meso-and rac-bis(1-cyclohexyltetrahydroindenyl)zirconium dichloride in the solid state

Abstract Two molar equivalents of 1-cyclohexylindenyllithium were treated with ZrCl 4 (thf) 2 to give a ca . 1:1 mixture of meso - and rac -bis(1-cyclohexylindenyl)ZrCl 2 ( meso -/ rac - 4 ). Catalytic hydrogenation yielded a corresponding mixture of the bis(1-cyclohexyl-4,5,6,7-tetrahydroindenyl)ZrCl 2 diastereoisomers meso - 5 and rac - 5 . In both cases the diastereomers were separated by fractional crystallization. Complexes meso - and rac - 5 were characterized by an X-ray crystal structure study. In the crystal the molecular structure of complex rac - 5 is C 2 -symmetric, with the annulated six-membered ring systems arranged towards the open front side of the bent metallocene wedge and the cyclohexyl substituents oriented anti -periplanarly in the lateral sectors. In contrast complex meso - 5 has only one of the cyclohexyltetrahydroindenyl ligands arranged in this way, the cyclohexyl substituent of the other one pointing towards a central front position and the annulated six-membered ring being situated in the lateral position ( C 1 -symmetry).

On the structural features of the chiral organometallic Lewis-acid catalyst “(dibornacyclopentadienyl)zirconiumtrichloride”

Abstract 2-Bornenyllithium ( 3 ) was prepared from camphor by a variant of the Shapiro reaction and then reacted with 0.5 molar equivalents of ethylformate to give the dibornenylcarbinol 4 . Subsequent acid-catalyzed cyclization of 4 yielded “dibornacyclopentadiene” as a mixture of two diastereoisomers; their deprotonation with n-butyllithium produced a single “dibornacyclopentadienyllithium” reagent ( 6 ). Reaction of 6 with MCl 4 (M  Zr, Hf, Ti) gave the chiral organometallic Lewis-acids “(diborna-Cp)MCl 3 ”. “(+)-(Dibornacyclopentadienyl)zirconiumtrichloride” ( 7a ) was characterized by X-ray diffraction. The molecular structure of 7a provides a basis for discussing the stereochemical characteristics of the enantioselective arene hydroxyalkylation process catalysed by the optically active organometallic Lewis-acid “(dibornacyclopentadienyl)zirconiumtrichloride”.

Planar tetracoordinate carbon stabilized in a dimetallic hafnium/aluminium compound: Formation and crystal structure of Cp2Hf[μ-η1 : η2-MeCC(C6H11)][μ-CC(C6H11)]A1Me 2

The reaction of [Me2AlCCR]2, 1 (R = cyclohexyl), with an equimolar quantity of Cp2HfMe2, 2 gave the dimetallic mixed metal complex Cp2Hf(μ-η1 : η2-MeCCR)(μ-CCR)AlMe2, 3 and trimethylaluminium. An X-ray diffraction study of 3 revealed that it has a planar tetracoordinate carbon atom (C3) bridging between hafnium and aluminium. The four bond distances in the central plane to C3 are 1.280(9) [C3 C1], 1.562(8) [C3C4], 2.091(6) [C3A1], and 2.432(6) [C3Hf] A.

Synthesis of stable primary enamines from (butadiene)zirconocene and benzylic nitriles

Abstract (Butadiene)zirconocene adds two molar equivalents of benzyl cyanide to give the chiral nine-membered metallacycle 4. Controlled hydrolysis (CH3OH) of 4 yields the stable conjugated primary enamine 2,7-diamino-1,8-diphenyl-2,4,6-octatriene (6) (≥70% isolated). (2-Pyridyl)acetonitrile reacts similarly with the (butadiene)zirconocene reagent. Subsequent controlled hydrolysis now produces a non-conjugated primary enamine, namely 2,7-diamino-1,8-di(2-pyridyl)-1,4,7-octatriene (9). In this case, conjugative stabilization of a primary enamine is overcome by functional group stabilization by the 2-pyridyl substituent at the β-enamine position.

Structure of an oxazirconacyclohexadiene synthesized by thermolysis of difurylzirconocene

Abstract Thermolysis of bis(2-furyl)zirconocene 1 at 185°C gives 1,1-bis(η-cyclopentadienyl)-1-zircona-2-oxa-6-(2′-furyl)cyclohexa-3,5-diene 2 via a coupled σ,σ-exchange reaction. Complex 2 was characterized by X-ray diffraction and shown to be monomeric in the crystal and to have a non-planar twist-like oxametallacyclohexadiene ring conformation.

Torsional Isomerism of Bent Metallocene Complexes The Molecular Structure of Bis(isopropylcyclopentadienyl)zirconiumdichloride in the Solid State

Bis(isopropylcyclopentadienyl)zirconiumdichloride (1) was synthesized by the reaction of isopropylcyclopentadienyl lithium with 1/2 molar equivalent of zirconiumtetrachloride and then crystallized from methylenechloride. Complex 1 crystallizes in space group C2/c with cell parameters a = 24.492(3)A, b = 13.525(1)Å, c = 22.894(3)Å, β = 117.90(1)°, Z = 16, R = 0.046, Rw = 0.057. There are three independent molecular entities of 1 in the asymmetric unit. These represent torsional isomers differing in the relative positions of the isopropyl substituents at the Cp-rings. The three torsional isomers may be described as anti-, syn-, and gauchelike metallocene rotamers.

Metal atoms in the synthesis of metal clusters: III. HFe3(CO)9(CCSiMe3), synthesis and crystal structure☆

Abstract Vaporization of nickel atoms into a solution of bis(trimethylsilyl)acetylene and Fe(CO)5 in methylcyclohexane at −120°C unexpectedly afford (after chromatographic work-up and crystallization) deep red crystals of the new triangular cluster μ3-(δ,2π-trimethylsilylacetylene)tris[(tricarbonyl)iron]hydride 1 in low yield.

Konkurrierende Liganden: Theophyllin als nicht- und stark koordinierender Ligand in Quecksilber(II)-Komplexen / Competing Ligands: Theophylline as Non- and Strongly Coordinating Ligand in Mercury(II) Complexes

[{Hg(CF3)2}(ThpH)(H2O)](H2O) (1), [{Hg4(Thp)4}(ClO4)4(H2O)8](H2O)4 (2), [{Hg(ThpH)2} (NO3)](NO3) (3) and {Hg(Thp)Cl}(H2O) (4) (ThpH = theophylline, C7H8N4O2) have been synthesized by slow evaporation of aqueous solutions of the mercuric salts Hg(CF3)2, Hg(ClO4)2, Hg(NO3)2, or HgCl2 and theophylline. Their crystal structures were determined on the basis of single crystal X-ray data. The coordination polymers 1 and 2 crystallize with triclinic symmetry, P1̅ (no. 2), with a = 468.8(2), b = 1256.4(5), c = 1445.5(6) pm, α = 67.15(3), β = 89.21(3), γ = 89.40(3)° and a = 833.6(1), b = 1862.7(2), c = 2182.9(2) pm, α = 111.61(1), β = 90.98(1), γ = 95.51(1)°, respectively. 3 and 4 crystallize with monoclinic symmetry, Pc (no. 7), a =1194.1(1), b=1258.8(2), c=735.5(2) pm, β =96.96(2)° and P21/n (no. 14), a=1069.0(2), b =911.6(1), c=1089.9(2) pm and β = 96.87(2)°. In 1 the theophylline molecules are non-coordinating to mercury and leave the Hg(CF3)2 molecule unchanged. Only weak electrostatic attractions to one keto-oxygen atom of theophylline and one water molecule hold this co-crystallisate together. In 2, the theophyllinate anion, Thp−, strongly coordinates with both N(7) and N(9) to HgII forming a large ring with eight Hg atoms that incorporates the water molecules. One sort of nitrate ions in 3 is weakly attached to HgII with the theophylline molecules still bound strongly through N(9). The chloride ligand and the theophyllinate ion seem to have the same strengths as ligands in 4 as they are both attached to HgII with the shortest distances possible

Structures and dynamic features of dinuclear tartratozirconocene complexes

Abstract The reaction of dimethylzirconocene with 2R,3R-diethyltartrate proceeds with evolution of two equivalents of methane and yields the chiral diethyltartratozirconocene dimer 2. The analogous reaction between Cp2Zr(CH3)2 and 2S,3S-diethyltartrate furnishes ent-2 in almost quantitative yield. Complex 2 contains a dimetallatricyclic framework (tetraoxadizirconatricyclo[5.3.0.02,6]decane) in solution as well as in the solid state. Complex 2 was characterized by X-ray diffraction. It crystallizes in space group P21 with cell parameters a=9.494(1), b=20.122(2), c=9.915(1) A, β=108.36(1)°, Z=2, R=0.039 and Rw=0.046. In solution the tartratozirconocene dimer 2 undergoes an intramolecular automerization reaction (ΔG‡intra (265 K)≈13±1 kcal mol−1) which probably proceeds via a ten-membered metallacyclic intermediate or transition state. A cross-over experiment between the enantiomeric complexes 2 and ent-2 showed the activation barrier for intermolecular exchange of mononuclear dioxazirconacyclopentane units Cp2 ZrOCH(E)CH(E)O (ECO2C2H5) leading to equilibration with the isomeric dinuclear tartratozirconocene complex meso-2 to be at ΔG‡inter (290 K)≈22±1 kcal mol−1. Complex meso-2 shows NMR spectra compatible with a static ten-membered dimetallamonocyclic ring structure. The reaction of dimethylzirconocene with meso-dimethyltartrate yields the (meso-dimethyltartrato)zirconocene dimer 4 (two isomers, 4a and 4b in a 60:40 ratio, both of which possess dynamic dimetallatricyclic structures in solution (ΔG‡intra (224 K)≈11±1 kcal mol−1 (4a); ΔG‡intra (285 K)≈14±1 kcal mol−1 (4b); ΔG‡inter (300 K)=24.7±1.0 kcal mol−1 (4a→-4b). Crystallization from methylene chloride gives single crystals of the isomeric (meso-dimethyltartrato)zirconocene dimer 5a which contains a monocyclic ten-membered ring structure. Complex 5a crystallizes in space group P21/c with cell parameters a=11.261(2), b=14.511(2), c=11.562(2) A, β=117.81(1)°; Z=2, R=0.047 and Rw=0.063.