Normen Peulecke

An Alternative Mechanistic Concept for Homogeneous Selective Ethylene Oligomerization of Chromium‐Based Catalysts: Binuclear Metallacycles as a Reason for 1‐Octene Selectivity?

An alternative concept for the selective catalytic formation of 1-octene from ethylene via dimeric catalytic centers is proposed. The selectivity of the tetramerization systems depends on the capability of ligands to form binuclear complexes that subsequently build up and couple two separate metallacyclopentanes to form 1-octene selectively. Comparison of existing catalytic processes, the ability of the bis(diarylphosphino)amine (PNP) ligand to bridge two metal centers, and the experimental background support the proposed binuclear mechanism for ethylene tetramerization.

Synthesis of 1H-1,3-benzazaphospholes: substituent influence and mechanistical aspects

Abstract Various substituted carboxylic acid 2-chloro- and 2-bromoanilides 1a–j react with triethylphosphite in the presence of anhydrous NiCl2 or NiBr2 to give o-acylamido-benzenephosphonic acid esters 2a–g and 2j. Yields depend strongly on the substituents. 2-Fluoro-4,6-dibromoacetanilide 1g reacts only at 6-position, indicating an o-directed process. Based on substituent effects, we infer a mechanism via Ni(0) intermediates that insert into the carbon–halogen bond. The N-tertiary 2-bromoformanilide 4 does not undergo phosphonylation to 5 in the presence of the Ni-catalyst but reacts in the presence of Pd-catalysts. The subsequent reduction of the N-secondary o-acylamido-benzenephosphonic acid esters 2 with excess LiAlH4 is coupled with an intramolecular cyclisation to the 1H-1,3-benzazaphospholes 6 whereas the N-tertiary derivative 5 does not undergo cyclisation upon reduction. NMR data and the crystal structure of 6d are reported.

Si–H Activation in Titanocene and Zirconocene Complexes of Alkynylsilanes RC≡CSiMe2H (R=tBu, Ph, SiMe3, SiMe2H): A Model To Understand Catalytic Reactions of Hydrosilanes

An agostic interaction between the Si–H bond and the metal center (depicted on the right) is the characteristic feature of the title complexes, which could be prepared by acetylene exchange reactions. IR, NMR, and X-ray structural investigations reveal that the effect of the Si-H-metal interaction is considerably stronger at low temperatures and in the solid state. This mode of bond activation is important in active catalysts for hydrosilylation and dehydrogenative polysilane reactions.

Katalysatordesaktivierungen bei der Acetylen‐Polymerisation mit Titanocen‐ bzw. Zirconocen‐Komplexen des Bis(trimethylsilyl)acetylens

Bei der katalytischen Acetylen-Polymerisation mit den Metallocen-Alkin-Komplexen Cp2M(L)(η2-Me3SiC2SiMe3), 1: M = Ti, ohne L, 2: M = Zr, L = thf wurden unerwartete, katalytisch inaktive Nebenprodukte beobachtet. Die Reaktion von 1 mit Acetylen wurde NMR-spektroskopisch untersucht und gibt bei –20 °C quantitativ das Titanacyclopentadien Cp2Ti–CH=CH–C(SiMe3)=C(SiMe3) (3). Bei 0 °C lagert sich 3 um, wobei eine Kopplung zwischen einem Cp-Liganden und dem Titanacyclopentadien erfolgt und der Dihydroindenylkomplex 4 gebildet wird. In der entsprechenden Reaktion von 2 fallen unter analogen Bedingungen das Zirconacyclopentadien Cp2Zr–CH=CH–C(SiMe3)=C(SiMe3) (5) und der dimere acetylidverbruckte Komplex [Cp2ZrC(SiMe3)=CH(SiMe3)]2[μ-σ(1,2)-C≡C] (6) an. Wahrend sich 5 zu einer Mischung bisher nicht identifizierter paramagnetischer Species zersetzt, konnte 6 isoliert und mittels NMR-Spektroskopie und Kristallstrukturanalyse charakterisiert werden. Bei der Umsetzung von rac-(ebthi)Zr(η2-Me3SiC2SiMe3) (ebthi = ethylenbistetrahydroindenyl) mit 2-Ethinyl-pyridin wird der Komplex rac-(ebthi)ZrC(SiMe3)=CH(SiMe3)](σ-C≡CPy) 7 gebildet, von dem auch eine Kristallstrukturanalyse angefertigt wurde. Desactivation of Catalysts in the Polymerization of Acetylene by Bis(trimethylsilyl)acetylene Complexes of Titanocene or Zirconocene Unexpected inactive byproducts were observed in the catalytic polymerization of acetylene using metallocene alkyne complexes Cp2M(L)(η2-Me3SiC2SiMe3), 1: M = Ti, without L; 2: M = Zr, L = thf. The reaction of 1 was investigated in detail by NMR to give quantitatively at –20 °C the titanacyclopentadiene Cp2Ti–CH=CH–C(SiMe3)=C(SiMe3) (3). Around 0 °C 3 starts to rearrange to yield the dihydroindenyl complex 4 via coupling of one Cp-ligand with the titanacyclopentadiene. In the reaction of 2 under analogous conditions a zirconacyclopentadiene Cp2Zr–CH=CH–C(SiMe3)=C(SiMe3) (5) and the dimeric complex [Cp2Zr(C(SiMe3)=CH(SiMe3)]2[μ-σ(1,2)-C≡C] (6) were observed. Whereas 5 decomposes to a mixture of unidentified paramagnetic species, 6 was isolated and investigated by NMR spectroscopy and X-ray analysis. In the reaction of rac-(ebthi)Zr(η2-Me3SiC2SiMe3) (ebthi = ethylenbistetrahydroindenyl) with 2-ethynyl-pyridine the complex rac-(ebthi)ZrC(SiMe3)=CH(SiMe3)](σ-C≡CPy) 7 was obtained, which was investigated by an X-ray analysis.

Metalated 1,3-azaphospholes: synthesis of lithium-1,3-benzazaphospholides and reactivity towards organoelement and organometal halides

Abstract Metalation of benzazaphospholes 1a – e with t -BuLi provided the ambident anions 1a – e Li in high selectivity. A crystal structure analysis of 1b Li ·3THF reveals monomers and coordination of lithium at nitrogen. The tungsten pentacarbonyl complexes also react preferably at nitrogen as shown by the reaction of 2a and 2d with t -BuLi. Addition at the PC bond is a minor process in the case of 2a . Compounds 1a , c Li as well as 2d Li react with alkyl halides at phosphorus to give the 3-alkyl-1,3-benzazaphospholes 3a and 3d or the respective W(CO) 5 complex 4d . Even acetyl and pivaloyl chloride attack 1e Li at phosphorus affording the P -acyl derivatives 5e and 6e . Silylation can occur at nitrogen or phosphorus to give 7 and/or 8 depending on steric and electronic effects exerted by the substituent in position 2. The different effect of 2- t -butyl groups on the steric hindrance at N and P is illustrated by the molecular geometry of 1d determined by crystal structure analysis. Soft organometallic halides such as Me 3 SnCl, CpFe(CO) 2 I and CpW(CO) 3 Cl react with 1 Li preferably at phosphorus affording the stannyl or monomer organo-transition metal derivatives 9 – 11 . The products are characterized by multinuclear NMR data of all new compounds.

Activation and Deactivation by Temperature: Behavior of Ph2PN(iPr)P(Ph)N(iPr)H in the Presence of Alkylaluminum Compounds Relevant to Catalytic Selective Ethene Trimerization

Coordination, deprotonation, rearrangement, and cleavage of Ph(2)PN(iPr)P(Ph)N(iPr)H (1) by trialkylaluminum compounds R(3)Al (R=Me, Et) are reported that are relevant to the selective ethene trimerization system consisting of the ligand 1, CrCl(3)(THF)(3) and Et(3)Al that produces 1-hexene in more than 90% yield and highest purity. With increasing temperature and residence time first the formation of an adduct [Ph(2)PN(iPr)P(Ph)N(iPr)H][AlR(3)] (2), second the aluminum amide [Ph(2)PN(iPr)P(Ph)(AlR(3))N(iPr)][AlR(2)] (3) and third its rearrangement to the cyclic compound [N(iPr)P(Ph)P(Ph(2))N(iPr)][AlR(2)] (4) were observed. The cleavage of 3 by an excess of R(3)Al into an amidophosphane and an iminophosphane could be the reason for its rearrangement to complex 4, as well as to the cyclic dimer [R(2)AlN(iPr)P(Ph)(2)](2) (5). The chemistry of ligand 1 in the presence of alkylaluminum compounds gives hints on possible activation and deactivation mechanisms of 1 in trimerization catalysis.

Dehydrocoupling of Silanes Catalyzed by Zirconocene- and Titanocene Alkyne Complexes

Abstract The zirconocene- and titanocene alkyne complexes 1–10 were tested to be effective catalysts in the dehydrocoupling of hydrosilanes like PhMeSiH 2 and Ph 2 SiH 2 to give oligomers and of other examples, e.g., PhSiH 3 polymers with cyclic oligosilanes as byproducts.

Metalated 1,3‐Azaphospholes: 1H‐1,3‐Benzazaphosphole and 1,3‐Benzazaphospholide Tungsten(0) and Tungsten(II) Complexes

2-tert-Butyl-1H-1,3-benzazaphosphole (1a) reacts with tBuLi without addition to the P=C bond to form a lithium benzazaphospholide that affords the η1-(benzazaphospholide-P)tungsten(II) complex 2 upon reaction with [CpW(CO)3Cl]. It is sensitive to alcoholysis and to air oxidation yielding 1a and the P-oxo-benzazaphospholide complex 3, respectively. The (1,3-benzazaphosphole)pentacarbonyltungsten complex 4, obtained from 1b and [W(CO)5(THF)], reacts preferentially with tBuLi by lithiation of the NH function and is attacked by [CpW(CO)3Cl] at phosphorus to give the mixed valence bimetallic tungsten(II)-tungsten(0) benzazaphospholide complex 5. A side product, (3-tert-butyl-2-methyl-1,3-benzazaphosphole)pentacarbonyltungsten (6), is attributed to side-reaction where tBuLi adds to the P=C bond in 4. The composition of the products was determined from X-ray structure analysis of 3 and spectroscopic data.

The hydrosilylation of ald-and ketimines catalyzed by titanocene complexes

Different titanocene complexes 1–10 were tested in the catalytic hydrosilylation of ald-and ketimines with Ph2SiH2. The highest conversions were obtained with Cp2Ti(PhCCSiMe3) 1 up to 98 % at room temperature.

A Kinetic Model for Selective Ethene Trimerization to 1‐Hexene by a Novel Chromium Catalyst System

A numerical model for the kinetics of the selective trimerization of ethene to 1‐hexene has been developed on the basis of mechanistic investigations and extensive experimental parameter studies. The reaction is catalyzed by a homogeneous catalyst system, comprising the chromium source [CrCl3(thf)3], a Ph2PN(iPr)P(Ph)N(iPr)H ligand, and triethylaluminum as activator. The kinetic model is designed as a tool for laboratory data evaluation, design and planning of meaningful experiments in the multidimensional parameter space, and parameter identification, and, moreover, it includes all features needed to eventually facilitate the transfer of the laboratory results into the technical environment. In particular, the model is designed to deliver the intrinsic chemical kinetics of the homogeneous catalytic system and to rule out any undetected influence of phase‐transfer limitations. Key kinetic parameters are determined by fitting the numerical simulations to the experimental results. In general, the model calculations and experimental data are in excellent agreement. In conjunction with mechanistic investigations, the model helps to elucidate the complex reaction network.