Lajos Bencze

Characteristics of the one-component catalysts M(CO)3X2L2 (M = Mo or W, L = PPh3 or AsPh3, X = Cl OR Br) in the ring-opening polymerization of norbornene

Abstract M(CO) 3 X 2 L 2 complexes, (where M = Mo or W, X = Cl or Br, L = PPh 3 or AsPh 3 ) initiate the ring-opening polymerization of norbornene and norbornadiene. Of these one-component catalysts, tungsten derivatives are generally superior to those of molybdenum. Phosphine complexes are poor catalysts, but W(CO) 3 X 2 (AsPh 3 ) 2 compounds exhibit fair catalytic activity at 353 K. The catalytic activity is retained in the presence of air and moisture. The polymers produced from norbornene are moderately high- cis structure and somewhat blocky with respect to cis/trans distribution. The solvent generally has little effect on the polymer yield. However there was no polymerization in nitrobenzene, a large quantity of ethyl acrylate quenched the reaction and in CCl 4 solutions saturated chlorinated telomers were formed exclusively. Steric crowding at the metal centre caused by coordinating molecules, such as CO, alcohol, or even olefins, generally results in increased blockiness for the polymer. A non-cage-like ‘three-ligand sequence’, i.e. the simultaneous involvment of at least three coordination sites in the coordination sphere of the propagating species, is proposed to explain the experimental results. The catalysts are surprisingly tolerant towards alcohol and water. Both additives increase the cis/trans selectivity of the catalysts and the blockiness of the polymer. However, the addition of EtOH results in high- cis polymer with the main effect in r c , while water results in high- traras polymer with the main effect in r t .

Transition-metal alkyls and hydrides : III. Alkyl-olefin exchange reaction of grignard reagents catalyzed by nickel chloride☆

Abstract Anhydrous nickel chloride catalyzes the alkyl-olefin exchange reaction between Grignard reagents and α-olefins. The catalyst is especially effective in the case of gaseous olefins and long-chain alkylmagnesium halides. Olefins with internal double bonds do not undergo the reaction, while primary alkylmagnesium halides react more easily than secondary and tertiary ones. The reaction may involve a hydridic transition state or a direct hydride-ion migration between the ligands in the catalyst complex.

Mechanism of initiation of the metathesis of norbornene using W(CO)3Cl2(AsPh3)2 as catalyst

Low molecular-weight derivatives obtained during ring-opening polymerization of norbornene using W(CO)3Cl2(AsPh3)2 as catalyst indicate that a 2,3-hydrogen shift is a key step for the formation of the carbene initiator.

Transition metal alkyls and hydrides VIII. Nickel chloride catalyzed insertion of ethylene into arylmagnesium halides

Abstract Anhydrous nickel chloride catalyses the insertion of ethylene into the CMg-bond of arylmagnesium bromides and also the subsequent alkylolefin exchange reaction of the primary aralkyl metal derivatives. Other transition metal halides are less active. (2-Phenylethyl)magnesium bromide isomerises under these conditions to the 1-isomer, and this isomerization is promoted by olefins. The nickel catalyst complex probably contains both σ-alkyl (aralkyl or aryl) and π-olefin ligands, and direct hydride migration between these ligands is proposed as the mechanism for the exchange and isomerization in the presence of certain olefins.

Ring-opening polymerization of norbornene catalysed by W(CO)3Cl2(AsPh3)2 in the presence of other olefins

Abstract The steric course of ring-opening polymerization catalysed by W(CO) 3 Cl 2 (AsPh 3 ) 2 is strongly influenced by the presence of other cyclic or linear olefins, such as cyclooctene, cyclohexene, 1-hexene and 1,7-octadiene. The blockiness of the polymer increases linearly with the overall olefin concentration in the reaction mixture. This effect of the individual olefins is independent of whether or not they participate in the cross-metathesis reaction to a detectable extent. The results are in agreement with the existence of two major kinetically-distinct propagating metallacarbene species, one cis - and one trans -directing. Terminal olefins act as chain transfer agents. Based on polymer fractionation, 13 C NMR and GC-MS studies, two more kinds of selectivity of the catalyst was found besides the increase of σ c and r c r t , of the polymer: 1. The formation, exclusively, of oligomers of a nonsymmetric structure; 2. The lack of detectable products of the homometathesis of linear chain olefins. The results are explained by the reluctance to form CH 2 carbenes and the relatively high reaction rate of propagation, chain transfer and degenerate metathesis, compared to the productive metathesis of the terminal olefins.

Komplexkatalyse : VI. Ir-spektroskopische untersuchung der reaktion von nitrosylmolybdänkomplexen mit C2H5AlCl2, (C2H5)3Al, AlCl3 und kohlenmonoxid, ein beitrag zur klärung der struktur des katalytisch aktiven komplexes für die olefinmetathese

Abstract The reaction of di- and mono-nitrosylmolybdenum complexes with C 2 H 5 -AlCl 2 , AlCl 3 and Al(C 2 H 5 ) 3 under argon and CO was followed IR-spectroscopically. Some conclusions were reached concerning the nature of the catalyticactivity of the complex in olefin metathesis.

Komplexkatalyse : VII. Zur bildung von chloro-nitrosyl-dicarbonyl-molybdän(0)-komplexen bei der reaktion von dichloro-dinitrosyl- und trichloro-mononitrosyl-molybdän-verbindungen mit C2H5AlCl2 und kohlenmonoxid

Abstract The preparative isolation of the chloronitrosyldicarbonylmolybdenum(0) complexes MoCl(NO)(CO) 2 L 2 (L = PPh 3 , AsPh 3 ) from solutions of MoCl 3 (NO)/6 C 2 AlCl 2 /CO in CH 2 Cl 2 is described. From this it might be concluded that the catalytic active complex for olefin metathesis generated from dichlorodinitrosyl- or trichloromononitrosyl-molybdenum compounds with C 2 H 5 AlCl 2 could be a NO containing species.

Density functional studies of [(alkoxy-carbonyl)methyl]cobalt tricarbonyl triphenylphosphine complexes: an α-ester η3-coordination

Abstract Spectroscopic and structural data of 15 complexes with the general formula of RO(O)CCH 2 Co(CO) 3 PPh 3 indicate a novel coordination mode of the α-ester group to the central cobalt atom, which was found to be crucial in the formation of configurational chirality of the ester carbon atom. Stereoselective self-assembly, elongated ester carbonyl bond lengths, reduced carbonyl stretching frequencies, and 13 C/ 31 P NMR coupling constants show an activated α-ester group compared to the uncoordinated ester or to that in a more distal position. Density functional calculations were carried out to describe the nature of this new bonding, termed earlier as ‘autosolvation’.

Reaction of low valent transition metal complexes and their phosphine derivatives with Karl Fischer reagent

The Karl Fischer reagent reacts with many low valent transition metal complexes to bring about oxidation of the metal. The reaction can be used for the oxidimetric determination of these complexes in solution and must be taken into account when PIII ligands are determined in low valent metal complexes.

III. Modelling of the “well-defined” carbenes: Molecular mechanical studies on the olefin metathesis reaction☆

Abstract A new force field termed METHOD had been originally constructed to simulate the carbene complexes that initiate the metathesis of cyclic and acyclic olefins with or without the application of a Lewis acid cocatalyst. The largest and most studied group of them are the so-called Osborn carbenes. They can be regarded as derivatives of the WX 4 CR 2 (X  Cl, Br or I; R  H or alkyl group) carbenes in which one or more WX bonds are substituted to WO bonds, e.g. WX 4- n (OY) n CR 2 , where n = 1–4, Y  R, SO 2 CF 3 or SiPh 3 . In the present part of the work the force field is extended to all the mononuclear Osborn carbenes and some other structures related to them. Trigonal bipyramidal (TBP) structures are proposed for these compounds in which the carbene ligand occupies an equatorial site with its two substituents and with the two neopentoxo groups lying in the trigonal plane of the TBP. Parameter development was based on experiment al NMR, X-ray and IR data as well as on ab-initio calculations. Method 1 is composed of 16 new atom types and 571 new data in addition to the MMX parameters, and it is used within the well-documented computational software of Pcmodel-PI V4.0. The general transition metal force field of the original software is abandoned while all the seven MMX interactions are turned on and parametrized. Simulated structures fit ab initio and X-ray structures with high accuracy. Experimental (NMR) rotational barriers for WCc bonds are simulated with an average error of 0.563 kcal mol −1 .