Rüger Schlund

Developing potentially useful organometallic Lewis acid catalysts: (η-cyclopentadienyl)zirconium trichloride derivatives

Abstract The organometallic Lewis acid (η-cyclopentadienyl)zirconium trichloride ( 2 ) was obtained from bis(cyclopentadienyl)zirconium dichloride ( 1 ) and chlorine by means of a radical induced metal-Cp bond cleavage. Reaction of 2 with tetrahydrofuran gave the CpZrCl 3 -bis(tetrahydrofuran) adduct 3 ; treatment of either 2 or 3 with excess dimethylformamide furnished CpZrCl 3 (dmf) 2 ( 4 ). (η-Methylcyclopentadienyl)bis(tetrahydrofuran)zirconium trichloride ( 7 ) was prepared by treatment of ZrCl 4 (thf) 2 ( 6 ) with one molar equivalent of the (methylcyclopentadienyl)thallium reagent 5 . Complexes 3, 4 and 7 were characterized by X-ray diffraction studies and their dynamic NMR spectra were recorded. Complex 3 crystallizes in space group P 2 1 / n with cell parameters a 8.155(1), b 13.342(2), c 15.775(1) A, β 104.81(1)°, Z = 4, R = 0.041, R w = 0.056. CpZrCl 3 (dmf) 2 ( 4 ) crystallizes in space group P 2 1 / c with cell parameters a 7.790(1), b 15.445(2), c 13.893(1) A, β 93.94(1)°, Z = 4, R = 0.032, R w = 0.052. Complex 7 crystallizes in space group P 2 1 / n with cell parameters a 10.242(2), b 12.836(2). c 13.683(1) A, β106.37 (1)°, Z = 4, R = 0.037, R w = 0.039. The (cyclopentadienyl)bis(tetrahydrofuran)zirconium trichloride adduct 3 selectively catalyzed the Diels-Alder addition of 2,3-dimethylbutadiene and methacrolein at ambient temperature to give 1,3,4-trimethyl-3-cyclohexenyl-1-carbaldehyde ( 13 ). However, the CpZrCl 3 -Lewis acid catalyzed rearrangement of 13 to 1,3,4-trimethylbicyclo[2.2.1]heptan-2-one ( 14 ) does not take place at a significant rate until ca. 150°C.

Gehinderte (RCp)M Rotation beit t-Alkyl Cp-substituierten (η4-s-cis-Butadien)zirconocen-Komplexen

Abstract Complex (CpCMe2C4H9)2ZrCl2 (7b) was prepared from ZrCl4 (0.5 equiv.) and [CpCMe2C4H9]Li, which in turn was obtained by adding methyllithium to 6-n-butyl-6-methyl fulvene. Compounds (CpCMe2-n-C10H21)2ZrCl2 (7c) and (CpC(C5H10)Me)2ZrCl2 (7d), respectively, were synthesized analogously. The t-alkyl-Cp-substituted complex 7d was charactherized by X-ray diffraction. The metallocene dihalide 7d crystallizes in space group C2/c, with cell parameters a 23.886(4),b 6.7129(9),c 14.128(1)A, β 93.076(8)°,Z = 4. Complex 7d is chiral in the crystal. Its bulky 1-methyl-cyclohexyl substituents are arranged trans to each other in the lateral sectors of the bent metallocene unit. Treatment of the (RCp)2ZrCl2 complexes 7b–d with “butadiene magnesium” yielded (s-c-η4-butadiene)(RCp)2Zr compounds (9b–d). For9b a chiral molecular geometry adopted in the solid state was revealed by its13C CP/MAS NMR spectrum. Analogous chiral molecular structures are favoured for 9b–d in solution according to their dynamic NMR spectra. Gibbs activation energies of topomerisation of the butadiene metallocene framework of complexes 9b–d uniformly amount to 13.3 ± 0.3 kcal/mol. Activation barriers of the hindered (RCp) M rotation for these complexes are estimated to be ΔG≠rot ≈ 10 ± 0.5 kcal/mol.

‘Agostic’ metal–alkenyl β-CH interaction in (C5H4Me)2ZrCl(CHCMe)ZrCl(C5H5)2

For the title compound (C5H4Me)2ZrCI(CHCMe)ZrCI(C5H5)2(7), which was prepared by hydrozirconation of (C5H4Me)2ZrCI(CCMe)(6), an ‘agostic’ zirconium–alkenyl β-CH interaction was demonstrated by n.m.r. and X-ray diffraction studies.

Unexpected open-chain molecular structure of a titanocenyl-substituted dimethyl ether

Abstract Reaction of (η-C 5 H 4 CH 3 ) 2 TiCl 2 with CH 3 OCH 2 MgCl yielded (η-C 5 H 4 -CH 3 ) 2 Ti(Cl)CH 2 OCH 3 ( 2a ). Complex 2a crystallizes in space group P 2 1 /n with cell constants a 8.162(1), b 11.004(2), c 15.297(2) A, β 96.40(1)°. In contrast to the three-membered metallacyclic zirconium compound of analogous composition (η-C 5 H 5 ) 2 Zr(Cl)CH 2 OCH 3 ( 1 ), the titanocenyl-substituted ether 2a has an open-chain (η 1 -O“-outside”) type structure.

Carbonylierung von Metallocenyliden Cp2M(R)(CHPPh3) des Zirconiums und Hafniums

Abstract The metallocene ylide Cp 2 Zr(Ph)( CHPPh 3 ) ( 1a ) reacts with carbon monoxide (ambient temperature, 40 bar) by insertion into the Zr C(ylide) bond to give Cp 2 Zr(Ph)[η 2 -C(CHPPh 3 ) O] ( 3a ). The “O-inside” orientation of the η 2 -acyl ligand of 3a has been revealed by X-ray diffraction. Complex 3a crystallizes in space group P 2 1 2 1 2 1 with cell parameters a 11.111(2), b 15.353(3), c 17.428(2)A, Z = 4. Carbonylation of Cp 2 M(C 2 H 5 )( CHPPh 3 ) (M = Zr, 1b ; Hf, 1c ) analogously yields the metal-containing stabilized ylides Cp 2 M(C 2 H 5 )[η 2 -C(CHPPh 3 ) O] ( 3b and 3c ). X-ray crystal structure analysis of the hafnium complex 3c : space group P 2 1 / n , a 10.521(1), b 15.431(2), c 16.863(1)A, β 94.28(1)°, Z = 4.

The three-membered metallacyclic structure of (η5-C5H5)2ZrCl-substituted dimethyl ether

The title compound cp2Z[graphic omitted]Me (3)(cp =η5-C5H5) was prepared by treating cp2ZrCl2 with MeOCH2MgCl in CH2(OMe)2; a three-membered metallacyclic onium-type structure was observed by X-ray diffraction.

Die bildung von β-CH agostischen alkenylzirconocen-komplexen bei der anormalen hydrozirconierung von alkinen

Abstract Some alkynes R 1 CCR 2 bearing bulky substituents undergo “abnormal” hydrozirconation reactions when treated with the reagent [Cp 2 Zr(H)Cl] x ( 1 ). The products obtained do not contain newly formed CH bonds. Dicyclopentadienylzirconacyclopentadiene systems ( 5 ) are formed instead. Extended Huckel calculations as well as the isolation of the product Cp 2 ZrCl[C(SiMe 3 )CPhH ] ( 3b ) in addition to Cp 2 ZrCl 2 and Cp 2 Zr[C(SiMe 3 )CPhCPhC (SiMe 3 )] ( 5b ) from Me 3 SiCCPh and 1 indicate that β-CH agostic alkenylmetallocene complexes may serve as important intermediates for this variant of hydrozirconation. The molecular structure of 3b was determined by an X-ray diffraction study. Complex 3b crystallizes in space group P 2 1 / n with cell constants a 9.641(2), b 18.066(3), c 11.762(1) A, β = 92.122(7)°, Z = 4. The ZrC(1)C(2) angle is 89.9° and the ZrH(2) distance is 2.29(2) A.

Dynamic NMR spectra and thermolysis of (RCp)2Zr(CH2OCH3)2: evidence for the insertion of a methylene group from a metallaoxirane into a ZrC σ-bond

Abstract The reaction of (RCp) 2 Zr(OCH 3 )Cl with two molar equivalents of ClMgCH 2 OCH 3 yields (RCp) 2 Zr(CH 2 OCH 3 ) 2 ( 6 ). Thermolysis of 6 at 70° gives ethylene and (RCp) 2 Zr(OCH 3 ) 2 . The low temperature dynamic NMR spectra of 6 indicate the presence of a η 2 -CH 2 OCH 3 ligand. It is suggested that the thermally-induced insertion of the meatallaoxirane methylene unit into the remaining ZrCH 2 OCH 3 σ-bond initiates the reaction sequence leading to CH 2 CH 2 and dimethoxyzirconocene.

Synthese und Thermolyse von α-Titanocenyl-substituierten Dimethylethern: die überraschende Bildung von [(CH3Cp)Ti(OCH3)Cl]4/ Syntheses and Thermolysis of a-Titanocenyl-Substituted Dimethylethers: the Unexpected Formation of [(CH3Cp)Ti(OCH3)Cl]4

Abstract Reaction of the Grignard-Reagent ClMgCH2OCH , (2) with (RCp)2TiCl2 (5a) (R = H). 5b (R = CH,) yields the titanocene(methoxymethyl)chlorides (RCp)2Ti(Cl)CH2OCH3, 7a and 7b. Thermal decomposition of 7b (2 min, 110 °C in toluene) yields the paramagnetic titanium (III) complex [(CH3Cp)Ti(OCH3)Cl]4 (8) in addition to the organic products ethylene and dimethvlether. The tetranuclear complex 8 crystallizes in space-group P21/n with a = 9.125(2), b = 8.899(1), c = 20.226(2) Å and β - 92.804(9)°. In 8 the Ti4-core is alternatingly doubly-bridged by μ-chloro- and μ-methoxy ligands.