Christian Sarter

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.

Zirconoxycarbene complexes obtained by regioselective coupling of (isoprene)zirconocene with hexacarbonyltungsten and a ketone. Crystal structure of Cp2ZrOC[W(CO)5]CH2ChC(CH3)CH2

Abstract (η4-Isoprene)zirconocene reacts with hexacarbonyltungsten to give the metallacyclic (π-allyl)zirconoxycarbene complex Cp2 ZrOC[W(CO) 5 ]CH 2 CHC(CH 3 )C H2 (14a), the structure of which has been determined by an X-ray diffraction study. Only one regioisomer is formed, that with the methyl substituent at the meso-position (C2) of the π-allyl-carbene ligand chain. Complex 14a undergoes insertion of one equivalent of acetone to give the nine-membered metallacyclic zirconoxycarbene complex Cp2 ZrOC[W(CO) 5 ]CH 2 CHC(CH 3 )CH 2 CR 1 R 2 O (18, R1 = R2 = CH3), which has an E-configurated endocyclic CC double bond. The chiral metallacycle 18 undergoes a thermally induced intramolecular enantiomerization, the activation barrier for which has been determined by dynamic 1H NMR spectroscopy to be ΔGent≠ (280 K) = 14.3 ± 0.3 kcal/mol. With pinacolone, 14a forms an analogous nine-membered metallacyclic zirconoxycarbene complex (only one diastereoisomer observed under thermodynamic control), which undergoes a stereo-unselective base-induced α-alkylation reaction to yield a 55/45 mixture of diastereomeric C6-monomethylated carbene complexes.

Molekülstruktur eines H2O-adduktes der organometall-Lewissäure CpZrCl3

Abstract Reaction of the organometallic Lewis acid CpZrCl3 with dry 18-crown-6-yields the 1 1 adduct CpZrCl3(18-crown-6) (1). Probably two of the six crown ether oxygens are coordinated to the metal center. Complex 1 exhibits a dynamic NMR behavior typical of CpZrCl3L2 type complexes. In contrast, CpZrCl3 reacts with 15-crown-5 in the presence of water to yield the 1 2 water addition product CpZrCl3(H2O)2(15-crown-5) (2). Complex 2 was characterized by an X-ray diffraction study. In an approximately octahedral coordination geometry the water molecules are found in positions oriented cis and trans to the Cp-ligand at the zirconium center, respectively. Each zirconium-bound water moiety is connected to a 15-crown-5 molecule by hydrogen bridges. Complex 2 crystallizes in the space group Pbcn with cell parameters a 15.838(4); b 26.086(6), c 10.664(2) A, Z = 8, R = 0.066, Rw = 0.065.

Synthesis of stable tail-to-tail-conjugated primary enamines containing hetarene substituents

Abstract A method is described that allows the preparation of stable conjugated primary enamines containing furyl or pyridyl substituents. In a template reaction (butadiene)zirconocene is 1,4-selectively coupled to two 2-cyanopyridine equivalents to give the nine-membered metallacycle 8b . Subsequent treatment with methanol removes the bent metallocene template and leads to the formation of 1,6-diamino-1,6-bis(2-pyridyl)-1,3,5-hexatriene ( 9b ). The 1,6- diamino-1,6-bis(2-furyl)-1,3,5-hexatriene system ( 9a ) was prepared analogously (69% isolated). Subsequent addition of benzonitrile to (butadiene)ZrCp 2 followed by 2-cyanopyridine or 2-cyanofurane gave the respective unsymmetrically substituted 1,6-diaminohexatrienes in good yield.

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.

Thermochemical heat treatment of steel substrates using borane-amine adducts as precursors

Abstract A novel approach to gas boronising has been carried out to systematically test organoboranes as precursors for low pressure gas boronising. The precursors of the group of borane–amine adducts were synthesised and subsequently applied to gas boronising of steel 42CrMo4 (AISI 4140). Characterisation of the boride layers was performed using glow discharge opticalemission spectroscopy, X-ray photoelectron spectroscopy, SEM, and metallography. Ultramicrohardness was also determined and the wear behaviour was simulated. With the precursors borane–triethylamine adduct and borane–diethylamine adduct gas boronising was possible. Single phased iron boride layers of type Fe2 B with a thickness of several micrometres were generated. The carbon, nitrogen, and oxygen contamination of the boride layers was low. The boride layers are not completely compact which results in a lower hardness compared with commercial powder pack boronised samples. The wear behaviour is similar to powder pack boronised steels and is significantly better than the untreated samples.