Rhodium carbene complexes as hydrosilylation catalysts

The catalytic activity of various rhodium carbene complexes has been investigated. These complexes are active for the hydrosilylation of a wide variety of unsaturated organic molecules such as olefins, acetylenes and dienes. Their activity is comparable to other rhodium(I) complexes previously used as hydrosilylation catalysts. The yield of products is found to vary with catalyst, silane and organic substrate.     

Bis(pyrazole)- and bis(pyrazolyl)-palladium complexes as phenylacetylene polymerization catalysts

Two types of pyrazole-based palladium complexes were used to catalyze the polymerization of phenylacetylene. Catalysts with electron-withdrawing linkers, [{1,3-(3,5-R₂pzCO)₂C₆H₄}Pd₂Cl₂(μ-Cl)₂] (R = ^tBu (1), Ph (2), Me (3), [{2,6-(3,5-R₂pzCO)₂C₅H₃N)}PdCl₂] (R = ^tBu (4), Me (5)), show high conversion; whilst those with simple pyrazole ligands, [(3,5-R₂pz)₂PdCl₂] (R = H (6), Me (7), ^tBu (8)), [(3,5-^tBu₂pz)₂PdCl(Me)] (9), have much lower conversions. Conversion greatly improved when 9 was used to catalyze the co-polymerization of sulfur dioxide and phenylacetylene. Both types of catalysts produce predominantly trans–cisoidal polyphenylacetylene.     

Rhodium(I) and platinum(II) complexes of aminomethylphosphines as hydrogenation and hydroformylation catalysts

Hydrogenation of α-acetamidocinnamic acid with chiral aminomethylphosphine complexes of rhodium(I), [Rh(cyclo-octa-1, 5-diene) {(R₂PCH₂)₂NR¹}]-PF₆ (R = Ph or Cy, R¹ = D(+)-CHMePh, L-CHMeCO₂Et, (R)(+)-bornyl) shows no asymmetric induction. The hydroformylation of styrene using the catalyst mixture [PtCl₂(P–P)]/SnCl₂ shows asymmetric induction with up to 31% enantiomeric excess of 2-phenyl-propanol being observed.     

Acetamidine complexes as catalysts for ethylene polymerization

The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine (1a) and N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine (1b), and N,N′-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine (2), respectively. The addition of isomers (1a + 1b) to nickel (II) dibromide 2-methoxyethyl ether, (NiBr₂[O(C₂H₄OMe)₂]) gives a mixture of new nickel complexes, [NiBr₂{N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and [NiBr₂{N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine}] (3b). Similarly, ligand 2 reacts with nickel (II) dibromide 2-methoxyethyl ether to afford the complex [NiBr₂{N,N´-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine}] (4). The structures of the ligands and nickel complexes have been determined by single crystal X-ray diffraction.The addition of MAO to these complexes generates catalytically active species for the homopolymerization of ethylene. The polymer products are high molecular weight (80-169 K). At temperatures of up to 60 °C both catalysts are a single site giving a monomodal molecular weight distribution. However, at 70 °C the mixture (3a + 3b) shows a bimodal molecular weight distribution.     

Well-defined vanadium complexes as the catalysts for olefin polymerization

The design and synthesis of well-defined vanadium complexes as efficient catalysts for olefin polymerization remains an attractive project for organometallic and polymeric research. Recently, vanadium complexes with well-defined structures have been explored for olefin (co)polymerization by several groups around the world. This article summarizes our recent progress in well-defined vanadium complexes bearing a variety of chelating β-enaminoketonato, salicylaldiminato, iminopyrrolide and tetradentate amine trihydroxy ligands, and their applications in ethylene polymerization, ethylene/α-olefin copolymerization and ethylene/cycloolefin copolymerization. The application of the optimized catalysts in the copolymerization of ethylene and polar monomer such as 3-buten-1-ol, 5-hexen-1-ol, 10-undecen-1-ol and 5-norbornene-2-methanol is also discussed. Particular attention has been paid to the relationships between the catalytic behavior and the electronic and geometrical structure of the precatalyst.     

Mixed ligand platinum complexes as hydrogenation catalysts

PtLL′Cl₂ (L = PPh₃, L′ = sulphides, amines) are more effective catalysts for the hydrogenation of styrene to ethylbenzene, in the presence of SnCl₂·2H₂O than PtL₂Cl₂ or PtL′₂Cl₂; this effect is attributed to the ability of the weaker ligand L′ to function as a leaving group in the catalytic hydrogenation cycle.     

Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization

Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40°C. The highest value of catalyst activity was obtained at 40°C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF, almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg/mol·bar·h by Zr₂(Cy₄ Pyr ₄)Cl₄. The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming polymer, and its molecular mass distribution. Correspondence: Sajjad Mohebbi, Chemistry Department, University of Kurdistan, P.O. Box 66176-416, Sanandaj, Iran.     

Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization

Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40°C. The highest value of catalyst activity was obtained at 40°C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF, almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg/mol·bar·h by Zr₂(Cy₄ Pyr ₄)Cl₄. The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming polymer, and its molecular mass distribution.     

Metallocene complexes as homogeneous catalysts in olefin polymerization

Ansa metallocene dichloride complexes of titanium, zirconium, and hafnium can be activated by methyl aluminoxane (MAO) to give excellent catalysts for the homogeneous polymerization of ethylene and propylene. The symmetry of the corresponding metaliocene dichloride complexes is essential for the stereospecific polymerization of propylene (isotactic, syndiotactic or atactic). The application of fluorenyl groups instead of cyclopentadienyl groups greatly increases the activity of the catalysts. The first ansa bis(fluorenyl) complexes of zirconium and hafnium, (C₁₃H₈-C₂H₄-C₁₃Hs)MCl₂ (M = Zr, Hf), have been prepared. It was found that after the activation by MAO the zirconium derivative demonstrates a very high activity. Several model complexes are presented in order to discuss the mechanism of the polymerization.This paper was presented at the INEOS-94 Workshop The Modern Problems of Organometallic Chemistry (Moscow, May 21–27, 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–14, January, 1995.     

Rhodium complexes with dioximes as catalysts of hydroformylation and hydrogenation of 1-hexene

Rhodium(II) complexes with dioximes [Rh(Hdmg)₂(PPh₃)]₂ [I] (Hdmg=monoanion of dimethylglyoxime) and [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II] catalyse hydroformylation and hydrogenation reactions of 1-hexene at 1 MPa CO/H₂ and 0.5 MPa H₂ at 353 K, respectively. Hydroformylation with complex [I] produces 94% of aldehydes (n/iso=2.2) and 6% 2-hexene whereas the second catalyst [II] gives ca. 40% of aldehydes (n/iso=2.1) and 60% of 2-hexene. Corresponding Rh(III) complexes are inactive in hydroformylation except of RhH(Hdmg)₂(PPh₃) [III], which shows activity similar to [I]. Complexes [Rh(Hdmg)₂(PPh₃)]₂ [I], [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II], RhH(Hdmg)₂(PPh₃) [III] and [Rh(Hdmg)₂(PPh₃)₂]ClO₄ [V] catalyse 1-hexene hydrogenation with an average TON ca. 18 cycles/mol [Rh]×min. Complex [II] has also been found to catalyse hydrogenation of cyclohexene, 1,3-cyclohexadiene and styrene.     

Cyclopentadienyl titanium hydroxylaminato complexes as highly active catalysts for the polymerization of propylene

Half sandwich complexes of titanium bearing eta1 or eta2 bound nitroxide ligands are highly active catalysts for the polymerisation of propylene to high molecular weight atactic poly(propylene).     

Rhodium phosphine complexes immobilized on silica as active catalysts for 1-hexene hydroformylation and arene hydrogenation

In immobilizing the rhodium complexes [Rh(acac)(CO)(P)] (1) and [Rh(acac)(P)₂] (2) (P = Ph₂PCH₂CH₂Si(OMe)₃) onto SiO₂, acetylacetone is found to be released through protonation of the acac ligand by the acidic silica-OH groups. The resulting complexes [Rh(O-{SiO₂}(HO-{SiO₂})(CO)(P-{SiO₂})] (1a) and [Rh(O-{SiO₂})(HO-{SiO₂})(P-{SiO₂})₂] (2a) were successfully tested with respect to their catalytic action on 1-hexene hydroformylation as well as benzene and toluene hydrogenation. The reaction outcome, viz. the formation of aldehydes versus isomerization, depends strongly on the presence and concentration of a phosphine co-catalyst. Thus, while 1a gave only a 17% yield of aldehyde in the absence of phosphines, the yield is increased to 54% in the presence of phosphinated silica P-{SiO₂} or even 94% if PPh₃ is added to the solution. Without extra added phosphine, both 1a and 2a effect mainly the isomerization of 1-hexene to 2-hexene. Pre-catalyst 1a catalyzes also the hydrogenation of benzene at 10.5 atm H₂ and 90 °C to give cyclohexane with a TOF of 608 h⁻¹.     

Ansa bis(fluorenyl) complexes as homogeneous catalysts for propylene polymerization

Preparation and characterization of new ansa-metallocene complexes containing two substituted fluorenyl ligands connected by an R₂E bridge (R = Me, Ph; E = Si, Sn) are reported. The complexes, activated with methylaluminoxane (MAO), polymerize propylene. The degree of stereospecifity of the propylene polymerization depends on the size of the hetero atom in the bridge and the position of the substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2334–2339, September, 1996.     

Styrene polymerization using nickel(II) complexes as catalysts

Styrene polymerization is investigated with neutral and cationic Ni(II) complexes, i.e. Ni(bipy)Me₂, 1, Ni(bipy)Br₂, 2, Ni(phen)Br₂, 3, or Ni(Me₂phen)Br₂, 4, Ni(acac)₂, 5, (bipy = 2,2′-bipyridine, phen = phenanthroline, Me₂phen = 2,9-dimethyl-1,10-phenanthroline, acac = acetylacetonate), activated by [NHMe₂Ph][B(C₆F₅)₄] or B(C₆F₅)₃ as cocatalysts, in the presence of AlMe₃. The influence on the polystyrene features and the reaction kinetics of the nickel complex and boron activator, the Al/Ni or B/Ni molar ratios as well as the monomer concentration are studied. Catalytic systems derived from 2, 3 or 5 and [NHMe₂Ph][B(C₆F₅)₄] at a Ni:B:Al ratio of 1:1:5 are the most efficient at room temperature.     

Water-free neodymium 2,6-naphthalenedicarboxylates coordination complexes and their application as catalysts for isoprene polymerization

A series of four coordination polymers based on neodymium have been hydrothermally synthesized with different carboxylic acids as a linker. The structures of the compounds Nd(2)(2,6-ndc)(3)(H(2)O)(3)·H(2)O (1), Nd(2)(2,6-ndc)(2)(ox)(H(2)O)(2) (2), and Nd(2,6-ndc)(form) (3) (2,6-ndc = 2,6-naphthalenedicarboxylate; ox = oxalate; and form = formate) have been determined by single-crystal X-ray diffraction analysis. They exhibit rather dense networks built up from infinite chains of NdO polyhedra connected to each other through the 2,6-ndc ligand. Terminal and bridging aquo species are present in the coordination sphere of Nd for 1, whereas some of them are partially replaced by oxalate groups in 2 and fully substituted by formate groups in 3. The water-free phase 3 as well as the compound Nd(form)(3) (4) were considered for catalytic reaction for polymerization of isoprene in the presence of Al-based cocatalyst, affording cis-polyisoprene with good conversions. Residual Nd material with unchanged structure was found in the polymeric material. The neodymium luminescence of compounds 3 and 4 was also measured.     

Free-radical polymerization of phenylacetylene

The free-radical polymerization of phenylacetylene initiated by azobisisobutyronitrile at 50°C was studied in bulk and in the presence of benzene and toluene. The polymerization rate is approximately first-order with respect to the initiator concentration. The number-average molecular weight of the polymer is independent of the initiator concentration in bulk and is approximately proportional to the monomer concentration in the presence of the two diluents, but independent of their nature. The data are consistent with a mechanism based on first-order decay of active to inactive radicals. This step appears to exert the major control over kinetic and molecular chain lengths. Chain transfer to the monomer is concluded to be absent or to make only a small contribution to molecular termination.     

Tailored molybdenum imido alkylidene N-heterocyclic carbene complexes as latent catalysts for the polymerization of dicyclopentadiene

Three novel molybdenum imido alkylidene N-heterocyclic carbene (NHC) pre-catalysts, that is, Mo(N-t-Bu)(1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene)(CHCMe₂Ph)(OTf)₂ ( I1 , OTf = CF₃SO₃), Mo(N-t-Bu)(1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene)(CHCMe₂Ph)(OTf)(t-BuO) ( I2 ) and Mo(N-2,6-Me₂-C₆H₃)(1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)(CHCMe₂Ph)(OTf)₂ ( I3 ) are presented. Compared to complexes based on imidazol-2-ylidenes or imidazolin-2-ylidenes, (1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene) used in precatalysts I1 and I2 exerts a comparably strong trans effect to the triflate groups trans to the NHC, while (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) used in I3 has a weaker trans effect on the triflate. In combination with a suitable second anionic ligand at molybdenum, that is, OTf, t-BuO, compounds I1 – I3 require higher temperatures to become active and can thus be used as truly room temperature latent pre-catalysts, even for a highly reactive monomer such as dicyclopentadiene (DCPD). When used as latent precatalysts, I1 – I3 offer access to poly-DCPD with different degrees of cross-linking and glass-transition temperatures (T_g). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3028–3033