J. Boersma

Homogeneous vanadium-based catalysts for the Ziegler–Natta polymerization of α-olefins

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler–Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/α-olefin copolymers with high α-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.

Intramolecular Coordination in Group 3 and lanthanide Chemistry: An overview

Abstract The presence of potentially intramolecularly coordinating substituents in ligands can be an attractive alternative to steric bulk as an approach to stabilizing monomeric, solvent-free complexes of Lewis-acidic metal complexes. In addition, intramolecular coordination has proven to be a useful tool for the preparation of well-defined mixed-metal complexes. This paper gives an overview of the various types of ligands containing intramolecularly coordinating substituents that have been used in complexes with Group 3 and lanthanide metals. Emphasis is put on the synthesis of such complexes and on an analysis of the intramolecular coordination present. Their (potential) applications as catalysts in organic transformations and as precursors for lanthanide-oxide-containing ceramics are described.

Controlled radical polymerization of styrene in the presence of lithium molybdate(V) complexes and benzylic halides

Abstract The new lithium molybdate(V) complexes [LiMo(NAr) 2 ( C – N )R] ( C – N =C 6 H 4 (CH 2 NMe 2 )-2; R=( C – N ) ( 5 ), Me ( 6 ), CH 2 SiMe 3 ( 7 ), p -tolyl ( 8 )), have been generated in situ from reaction of the corresponding molybdenum(VI) complexes [Mo(NAr) 2 ( C – N )R] ( C – N =C 6 H 4 (CH 2 NMe 2 )-2; R=( C – N ) ( 1 ), Me ( 2 ), CH 2 SiMe 3 ( 3 ), p -tolyl ( 4 )) with n -BuLi. The nature of these radical anions was studied by EPR spectroscopy. The spectra of toluene solutions of in situ prepared complexes 5 – 8 revealed the presence of two different paramagnetic species, i.e. a molybdenum compound with distinct g iso - and A iso -values and an unidentified radical with a sometimes strong signal at g =1.986±0.001, lacking any hyperfine coupling. Extended Huckel calculations on the crystal structure of 5 showed that the single electron occupies a molybdenum centered orbital, merely d x 2 − y 2 in character. In situ prepared complexes 5 – 8 were successfully applied in the atom transfer radical polymerization (ATRP) of styrene using benzyl chloride as the initiator. The efficiency of the benzyl chloride initiator is rather poor (6–18%). Reaction of the lithium molybdate(V) complex 5 with (α-chloroethyl)benzene and (α-bromoethyl)benzene resulted in the formation of 1 , LiCl and LiBr, respectively. The molecular weights as well as the molecular weight distributions show that the catalytic system, BzCl/ 5 – 8 , catalyses styrene polymerization successfully but does not exercise much control over the polymerization reaction due to the poor initiator efficiency of benzyl chloride and probably the extreme air-sensitivity of the lithium molybdate(V) compounds. The unidentified radical ( g =1.986±0.001) is unable to initiate radical polymerization but possibly influences the ATRP activity.

On the way to chiral copper(I) arenethiolate catalysts for the enantioselective conjugate addition of methyl lithium and methyl magnesium iodide to benzylideneacetone

Selective conjugate addition (0 % enantiomeric excess (e.e.)) of organo- arenethiolatocuprates (from methyl lithium and 23 l-(R)-(dimethylamino)ethyl)phenyl- thiolatocopper(I), CuSAr*) to benzylideneacetone (BA) is found up to a LiMe/CuSAr* ratio of 2/l indicating the potential of the chiral SAr*-anion as non-transferable group; at higher ratios only 1,2-addition occurs. Reactions of methyl magnesium iodide with BA in the presence of a catalvtic amount of CuSAr* (9 mol%) result in exclusive conjugate addition with 57% e.e..

Preparation and properties of arylgold compounds. Scope and limitations of the auration reaction

Several ligand-free monoarylgold dichlorides (RC6H4AuCl2)2 (R = H, Me, Et, i-Pr, t-Bu, Ph) have been prepared from arenes and AuCl3; contrary to earlier reports, addition of ligands is not necessary in order to obtain thermally stable products. The auration is inhibited if the arenes contain potentially coordinating substituents. The properties and reactions of the arylgold dichlorides are discussed.

Application of N,S-chelating chiral zinc bis(arenethiolate) complexes as new precursor catalysts in the enantioselective addition of diethylzinc to aldehydes

Abstract The addition of diethylzinc to aldehydes in the presence of a catalytic amount of enantiomerically pure N,S -chelated bis {2-[( R )-1-(dimethylamino)ethyl]phenylthiolato}zinc, afforded the corresponding secondary alcohols in nearly quantitative yields with optical purities of up to 99 % e.e. under mild reaction conditions.

Multiple Use of Soluble Metallodendritic Materials as Catalysts and Dyes

Different sizes of core-functionalized metallodendritic wedges were prepared by anchoring sensor-active arylplatinum(II) sites at the focal point of Fréchet-type polyether dendritic wedges of various generations. The strong color of these metallodendrimers in the presence of SO2 was used to assess the permeability of nanofiltration membranes (molecular weight cut-off of 400 dalton) at ambient pressure. A primary result of these studies is that dendrimers do not have to be exceptionally large for successful retention. Hence, nanofiltration, membrane-capped. immersion vials were developed, which operate as sensor devices when loaded with metallodendrimers with good retention properties. Appropriate substitution of the dye site at the focal point of these metallodendritic wedges by a catalytically active group afforded dendritic catalysts that exhibit essentially the same physical properties (shape, retention) as the corresponding dyefunctionalized dendritic wedges. When this homogeneous catalyst is compartmentalized in membrane-capped vials, a unique and convenient method for its retrieval from product solutions is available. Moreover, such immobilized metallodendritic catalysts can be regenerated and stored for months without losing their activity; this provides access for the development of novel sustainable homogeneous catalysts.

Synthesis and coordination properties of ω-functionally-substituted dialkylzinc compounds

Abstract The synthesis and characterization are described of ω-functionally-substituted dialkylzinc compounds of the type Zn[(CH 2 ) 3 X] 2 , (X = OCH 3 , SCH 3 , N(CH 3 ) 2 ). For comparison, one higher homologue, viz. Zn[(CH 2 ) 4 OCH 3 ] 2 , was also prepared and studied. The chemical properties, degrees of association, dipole moments and NMR spectral data point to exclusive intramolecular coordination between zinc and the hetero-atoms present.

Synthesis and characterization of a stable bis-naphthyltin(II) compound.Bis[8-(dimethylamino)-1-naphthyl-C,N]tin(II) and its W(CO)5 adduct

Reaction of [8-(dimethylamino)-1-naphthyl-C, N]lithium with SnCl{2} affords the new monomeric stannylene bis[8-(dimethylamino)-1-naphthyl-C,N]tin(II) (3). The reaction between W(CO){5}(NME{3}) and 3 yields {bis[8-(dimethylamino)-1-naphthyl-C,N]tin(II)} tungsten pentacarbonyl (4). The crystal structures of 3 and 4 have been determined by X-ray diffraction methods. 3: C{2}{4}H{2}{4}N{2}Sn, orthorhombic, space group Pbca with a 22.383(4), b 30.865(5), c 12.127(2) @9 and Z = 16, final R = 0.067 for 4983 observed reflections. 4: C{2}{9}H{2}{4}N{2}O{5}SnW, a 12.509(3), b 15.191(1), c 9.780(1) @9, @a 98.42(1), @b 104.33(1), @c 107.27(1)}o{, space group P1, Z = 2, triclinic; R = 0.046 for 7116 observed reflections. The geometry about tin in 3 is distorted @j-trigonal bypyramidal, and that in 4 is distorted trigonal bipyramidal. In both 3 and 4 the 8-(dimethylamino)-1-naphthyl groups are C,N-chelate bonded, with the C(1) atoms at equatorial sites and the nitrogen atoms at axial sites. The Sn lone pair in 3 and the W(CO){5} moiety in 4 occupy the remaining equatorial sites. }1{H, }1{}3{C, and }1{}1{}9{Sn solution NMR spectroscopic studies of 3 and 4 show that at low temperature (=< - 15}o{C) they retain the structures found in the solid state. At higher temperatures fluxional processes become operative.

Organopalladium complexes with bidentate phosphorus and nitrogen containing ligands.

Organopalladium complexes containing the potentially P,N-bidentate ligands o-diphenylphosphino-N, N-dimethylbenzylamine (PN) and o-diphenylphosphino-amethyl-N, N-dimethylbenzylamine (PN*) have been studied. The palladium(O) complexes Pd(P-N), (P-N = PN or PN*) have been prepared; the ligands coordinate to the metal primarily through phosphorus, with the amine function coordinating not at all or only very weakly. Oxidative addition of several organic halides to these palladium(O) complexes afforded the corresponding monoorganopalladium(I1) complexes Pd(R)(X)(P-N) in which the donor ligands are P,N-bidentate coordinated. In solution the divalent species possess a Pd-N bond, and even in the presence of either free ligand, CO or X- there is no evidence for dissociation or displacement of the amine function from the metal centre. Complexes PdMe,(P-N) have been prepared from the corresponding dihalopalladium complexes by treatment with MeLi. Reaction of these dimethylpalladium species with the electrophiles MeI, MeBr and PhCH,Br resulted in replacement of one methyl group by halogen. The structures of Pd(Me)(Br)(PN) and Pd(C=CSiMe,)(Br)(PN) have been determined by X-ray diffraction studies. Pd(Me)(Br)o(PN) crystallizes in space group Cc with a 8.379(g), b 17.363(7) and c 14.818(6) A, /3 99.34(5)O, and 2 = 4; the structure was refined to Rf = 0.030. Pd(C=CSiMe,)(Br)(PN) ~stallizes in space group P2,/c with a 13.478(3), b 10.848(2) and c 19.212(3) A, j3 102.59(2)“, and 2 = 4; the structure was refined to R, = 0.038. Both complexes have a square planar configuration around palladium, with the organic group (Me, C+&SiMe3) trans to the amine function and the six-membered chelate ring in a boat conformation.