Zeev Goldschmidt

Titanium complexes of chelating dianionic amine bis(phenolate) ligands: an extra donor makes a big difference

Abstract Two dianionic amine bis(phenolate) ligands are introduced and their reactions with titanium tetra(iso-propoxide) studied; ligand 1 having a single N-donor group leads exclusively to a homoleptic Lig2Ti type complex whereas ligand 3 having an additional N-donor on a side arm leads exclusively to a LigTi(OPri)2 type complex.

Titanium(IV) complexes of trianionic amine triphenolate ligands

Abstract Two trianionic amine triphenolate ligands are introduced and their isopropoxide Ti(IV) complexes synthesized. The two complexes are mononuclear and C3-symmetrical on the NMR timescale. High barriers to inversion ( ΔG ‡ >65 KJ mol −1 ) between the enantiomers of each complex were found. The complex derived from the bulkier tripodal ligand shows a better resistance to hydrolysis.

Group IV complexes of an amine bis(phenolate) ligand featuring a THF sidearm donor: From highly active to living polymerization catalysts of 1-hexene

Abstract A new amine bis(phenolate) ligand bearing a THF donor on a sidearm and several dialkyl complexes of the group IV triad are introduced. The crystal structures of a zirconium dibenzyl complex and a titanium dibenzyl complex were solved, and revealed a strong binding of the oxygen donor of the THF group to the metal center. Upon activation with tris(pentafluorophenyl)borane the zirconium and the hafnium dibenzyl complexes lead to highly active 1-hexene polymerization catalysts. In comparison, titanium complexes (a dibenzyl complex and a dimethyl complex) lead to slower but living polymerization of 1-hexene at room temperature. Polymerization of neat 1-hexene under high dilution conditions was found to be living for an exceptionally long time of 6 days, leading to poly(1-hexene) of Mw=816 000 and PDI=1.09. A block copolymerization of 1-hexene and 1-octene at room temperature could be obtained using the titanium catalysts.

Living polymerization of 1-hexene due to an extra donor arm on a novel amine bis(phenolate) titanium catalyst

Abstract Two amine bis(phenolate) titanium dibenzyl complexes were synthesized in one-pot reactions starting from the ligand precursors and titanium tetra(isopropoxide). The catalyst derived from a ligand having an extra donor on a side arm leads to living polymerization of 1-hexene at room temperature, whereas the one derived from a ligand lacking it, leads to low molecular weight poly(1-hexene) with PDI values of around 2.0.

Reactions of coordinated cyclic polyolefins. The mechanism of the pericyclic [4,4]-sigmahaptotropic rearrangement; a kinetic study. Crystal structure of tricarbonyl[(2,3,4,5-η)bicyclo[4.2.1]nona-2,4-diene-7,7,8,8-tetracarbonitrile]iron

Abstract The novel [4,4]-sigmahaptotropic rearrangement II → IV, in which a σ-bonded group and a Fe(CO) 3 unit exchange bonding sites antarafacially across a four carbon skeleton, has been shown by kinetic data to involve a concerted, non-synchronous, one step process. First order rate constants for the rearrangement at 23°C are k 1.25 × 10 −6 s −1 (acetone) and k 2.2 × 10 −5 s −1 (methanol), with activation parameters Δ H # 21 kcal mol −1 and Δ S # −15 e.u. (acetone). The moderate value of the ratio of k in methanol to that in acetone, viz. 18, indicates that although a minor charge separation develops upon activation, no intermediate is formed. The least motion pathway mechanism is shown to involve a Berry pseudorotation about the metal, which maintains the bonding interaction between the metal and the organic fragment orbitals during the rearrangement. Topologically this rearrangement corresponds to a [σ2 a + (σ2 s + π2 a )] thermally allowed pericyclic reaction. The structure of the rearranged complex IV was determined by single-crystal X-ray diffraction.

Tantalum(v) complexes of an amine triphenolate ligand: a dramatic difference in reactivity between the two labile positionsElectronic supplementary information (ESI) available: synthetic and spectroscopic data for all complexes. See http://www.rsc.org/suppdata/dt/b2/b206759e/

A tetradentate trianionic amine triphenolate ligand leads to octahedral Ta(V) complexes of Cs-symmetry, in which the two labile positions that are in cis geometry exhibit a dramatic difference in reactivity, the position trans to a phenoxy group being the active one.

Novel zirconium complexes of amine bis(phenolate) ligands. Remarkable reactivity in polymerization of hex-1-ene due to an extra donor arm

Zirconium complexes of two dianionic amine bis(phenolate) ligands have been synthesized, their X-ray structures solved, and their activity as hex-1-ene polymerization catalysts studied; upon treatment with B(C6F5)3, an octahedral [ONNO]Zr(CH2Ph)2 complex, having an extra N-donor group on a side arm, shows exceptionally high polymerization activity and yields a high molecular weight poly(hex-1-ene), whereas a related pentacoordinate [ONO]Zr(CH2Ph)2 complex, having no extra donor group, shows only poor activity as a polymerization catalyst.

The solution structure and fluxional behaviour of cyclic and acyclic (diene) Fe(CO)2L complexes (L = phosphine, phosphite, isonitrile)

Variable temperature 13C and 31P NMR spectroscopy has been used to establish solution structures and conformer populations for a variety of cylic and acyclic (diene)Fe(CO)2L complexes (L = phosphine, phosphite, isonitrile). The solid state structures of (2,3-dimethylbutadiene)Fe(CO)2PPh3 and (trans,trans-2,4-hexadiene)Fe(CO)2PPh3 have been determined and used as a basis for molecular modelling of steric effects in these complexes.

Acetylation of alcohols in the pheromone biosynthesis of the tomato looper, Chrysodeixis chalcites (Lepidoptera: Noctuidae)

Abstract A series of C11–C14 alcohols, varying in the number, position and geometry of double bonds, was applied topically to the sex pheromone glands of the tomato looper, Chrysodeixis chalcites , in order to study the acetylation step in the pheromone biosynthesis of this moth. Each application contained one of the alcohols and (Z)-11-tetradecenol, in equimolar amounts, as a metabolic standard for comparison of the relative conversion of the alcohols to acetates in the terminal biosynthetic step. One secondary and one tertiary alcohol were also included in the study. All alcohols were converted to the corresponding acetates at similar relative rates indicating that this step has a very low substrate specificity. One alcohol, (Z)-9-dodecenol was applied to the glands of head ligated females, which produces very small amounts of pheromone, in order to investigate the relation between the total biosynthesis of the pheromone and the acetylation step. The decrease in pheromone biosynthesis due to ligation of the head did not affect the acetylation step.

Reactions of coordinated cyclic polyolefins. A kinetic study of the pericyclic [3,3]-sigmahaptotropic rearrangement

Abstract The reaction of tricarbonyl(tropone)iron with tetracyanoethylene (TCNE) was reinvestigated. Two primary cycloadducts, the 3 + 2 and 4 + 2 isomers are formed in a 96/4 ratio. The second order rate constant for the reaction is k 4.4 × 10 −2 M −1 s −1 (at 24°C, in acetone) with a free activation energy of Δ G # 19.2 kcal mol −1 The 3 + 2 cycloadduct undergoes a facile sigmahaptotropic rearrangement to the formal 5 + 2 adduct with rate constants of k 3.8 × 10 −10 s −1 (24°C, acetone) and k 5.1 × 10 −4 s −1 (24°C, methanol), and with activation parameters Δ H # 20 kcal mol −1 and Δ S # −7 e.u. (acetone). The kinetic results suggest that both the cycloaddition and the rearrangment are concerted, nonsynchronous, one-step reactions, involving a slightly polar transition state. Frontier molecular orbital considerations imply that the 3 + 2 and 4 + 2 cycloadditions are symmetry allowed reactions. The structural reorganization which takes place in the [3,3]-sigmahaptotropic rearrangement suggests that the metal migration proceeds by way of a Berry pseudorotation, and the simultaneous 1,3-sigmatropic shift occurs with configuration retention at the migrating carbon. A detailed molecular orbital analysis of the rearrangement is given.