Ph 3c Research Articles

A biphenylene-bridged dinuclear constrained geometry titanium complex for ethylene and ethylene/1-octene polymerizations

Permethylated cyclopentadienyl dinuclear constrained geometry titanium catalyst, [μ-(C 6H 4) 2-2,2′]{(η 5-C 5Me 3)[1-Me 2Si(η 1-N- t Bu)](TiCl 2)} 2 ( BPTi 2 ) linked by a biphenylene bridge was synthesized and tested in ethylene and ethylene/1-octene polymerizations upon activation by TIBA (triisobutylaluminum)/[Ph 3C][B(C 6F 5) 4]. When compared with the corresponding highly active, mononuclear analogs, Me 2Si(η 5-2-PhC 5Me 3)(η 1-N- t Bu)TiCl 2 ( PhTi 1 ) and Me 2Si(η 5-C 5Me 4)(η 1-N- t Bu)TiCl 2 ( MeTi 1 ), BPTi 2 exhibits significantly increased molecular weight of polymer (>two-fold), as well as high level of activity and 1-octene incorporations in ethylene and ethylene/1-octene polymerizations. Although the lower activity was observed at high 1-octene feeds, the combined effects of rigidity and electronic conjugation induced by the biphenylene bridge might be responsible for the observed polymerization properties of BPTi 2 .

Synthesis of (adamantylimido)vanadium(V)-alkyl complexes containing aryloxo ligands and their use as the catalyst precursors for ring-opening metathesis polymerization of norbornene, and ring-opening polymerization of tetrahydrofuran

Various (adamantylimido)vanadium(V) dialkyl complexes containing aryloxo ligands, V(NAd)(CH 2SiMe 3) 2(OAr) [Ad = 1-adamantyl ( 1); Ar = Ph ( a), 4-FC 6H 4 ( b), 2,6-F 2C 6H 3 ( c), 2,6-Me 2C 6H 3 ( d), C 6F 5 ( e)], have been prepared and identified. These complexes were employed as the catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of PMe 3 at 80 °C. The activity was strongly affected by the aryloxo substituent and increased in the order: C 6H 5 < 4-FC 6H 4 < 2,6-Me 2C 6H 3 << 2,6-F 2C 6H 3, C 6F 5. The same trend was observed in the ROMPs by the arylimido–aryloxo analogues, V(NAr′)(CH 2SiMe 3) 2(OAr) ( 2a– e; Ar′ = 2,6-Me 2C 6H 3), under the same conditions, and the activities by the arylimido analogues were generally higher than the adamantylimido analogues in most case. The (imido)vanadium(V) complexes containing O-2,6-F 2C 6H 3 ( 1, 2c) or OC 6F 5 ( 1, 2e) exhibited high catalytic activities, and these results strongly suggest that electronic as well as steric factors play a role. Living ring-opening polymerization of THF proceeded in the presence of V(NAd) (CH 2SiMe 3)(OAr) 2 (Ar = 2,6-Me 2C 6H 3, C 6F 5) and [Ph 3C][B(C 6F 5) 4], affording high molecular weight polymers with narrow molecular weight distributions (ex. M n = 2.11 × 10 5, M w / M n = 1.18).

Group 4 metallocene complexes with pendant nitrile groups

The preparation of a new functionalized cyclopentadienyl ligand bearing a nitrile pendant substituent, (C 5H 4CMe 2CH 2CN) − is reported. The corresponding lithium salt of this ligand ( 1) was prepared by the reaction of in situ lithiated acetonitrile with 6,6-dimethylfulvene. The ligand was subsequently utilized for the synthesis of group 4 metal complexes [(η 5–C 5H 4CMe 2CH 2CN) 2MCl 2] (M = Ti, 2; M = Zr, 3; M = Hf, 4), [(η 5–C 5H 5) (η 5–C 5H 4CMe 2CH 2CN)MCl 2] (M = Ti, 7; M = Zr, 8), and [(η 5-C 5Me 5) (η 5 C 5H 4CMe 2CH 2CN) 2ZrCl 2] ( 9). Alternative route to 2 comprised the preparation of half-sandwich complex [(η 5–C 5H 4CMe 2CH 2CN)TiCl 3] ( 6). The prepared compounds were characterized by common spectroscopic methods and the solid state structures of complexes 2, 3, 4, 7, and 9 were determined by the single-crystal X-ray diffraction analysis. In addition, compound 7 was converted to the corresponding dimethyl derivative [(η 5–C 5H 5) (η 5–C 5H 4CMe 2CH 2CN)TiMe 2] ( 10) and also treated with the chloride anion abstractor Li[B(C 6F 5) 4] to generate the cationic complex with the coordinated nitrile group, as suggested by the NMR spectroscopy. A formation of yet another cationic complex was observed upon treating compound 10 with (Ph 3C)[B(C 6F 5) 4].

Scandium and yttrium complexes of a heteroscorpionate [N,N,O]-donor-set ligand: Synthesis, characterization and catalytic activity in ethylene polymerization

New scandium and yttrium complexes ScL 2( bpzmp)(THF) {L = Cl ( 1); L = CH 2Si(CH 3) 3 ( 3)}, YL 2( bpzmp) {L = Cl ( 2); L = OTf ( 5)} and Y(CH 2SiMe 3) 2( bpzmp)(THF) ( 4) bearing the heteroscorpionate bpzmp ligand { bpzmp = (3,5- t Bu 2-2-phenoxo)bis(3,5-Me 2-pyrazol-1-yl)methane} have been synthesized and characterized by means of NMR and Mass spectroscopy. The tridentate monoanionic ligand resulted κ 3-coordinated to the metal via the oxygen and both the sp 2 nitrogen atoms of the heterocycles, producing complexes in C S symmetry. The behavior of 1– 4 in ethylene polymerization was investigated after proper activation with different activating agents. Complex 4, in combination with the Brönsted or Lewis acids [PhNMe 2H][B(C 6F 5) 4] or [Ph 3C][B(C 6F 5) 4], produced linear high molecular weight polyethylene in good yield.

Kinetic and Energetic Analysis of the Free Electron Transfer

In this paper, the bimolecular free (unhindered) electron transfer (FET) from various trityl-containing compounds to the solvent radical cations of n-BuCl is described. In good agreement with the previously studied cases, the FET involving trityl-derived compounds results in the formation of two different types of the radical cation, which undergo the subsequent fragmentation via two alternative reaction channels. This unusual effect is caused by the intramolecular rotational motion in the ground-state molecules around the arrow-marked bond Ar-//-X-CPh 3 (Ar = aromatic moiety; X = S, O, NH, CH 2), since such oscillations are directly connected with the electron distribution within the molecule. An unhindered electron jump from the donor trityl compound to the solvent radical cation, taking place in the subfemtosecond time range, generates the solute radical cation with the inherited geometry and the electron distribution of its precursor. Among the whole variety of produced radical cations, two extreme conformer states can be distinguished, namely, a planar and a twisted state. The planar type represents the structures with minimum energy, whereas the twisted type is destabilized by the increased value of the rotational barrier in the ionized state. The difference in the energetic profiles between planar and twisted radical cations plays a crucial role in their subsequent fragmentation. The planar radical cation follows the thermodynamically favored pathway generating ArX (*) and Ph 3C (+). A distinct part of the twisted radical cation dissociates faster than it relaxes into the more preferable planar conformation and, therefore, produces a thermodynamically unfavorable couple of products: ArX (+) and Ph 3C (*). This fragmentation channel is exclusively caused by FET. The undertaken quantum chemical calculations enable the judgment of the energetics of the different dissociation channels of the radical cations of the trityl derivatives.

Activation of C–CN bond of propionitrile: An alternative route to the syntheses of 5-substituted-1 H-tetrazoles and dicyano-platinum(II) species

Reaction of trans-[Pt(N 4CR) 2(PPh 3) 2] 1 (R = Me 1a, Et 1b, Ph 1c, CH 2CH 2Ph 1d) with propionitrile under reflux gives trans-[Pt(CN) 2(PPh 3) 2] 2 along with 5-substitued-1 H-tetrazoles N 4CR 3 (R = Me 3a, Et 3b, Ph 3c, CH 2CH 2Ph 3d) in moderated to good yield, respectively. Treatment of cis-[Pt(N 3) 2(PPh 3) 2] 5 with alkynes HC CR′ 6 (R′ = Ph 6a, p-MeC 6H 4 6b) under focused microwave irradiation leads, upon azide replacement, to the formation of the dialkynyl complexes trans-[Pt(C CR′) 2(PPh 3) 2] 7 (R′ = Ph 7a, p-MeC 6H 4 7b) which also furnish the dicyano-platinum complex 2 in refluxing propionitrile. In both cases, the reactions leading to the formation of 2 proceed via an unusual oxidative addition, involving NC–C bond cleavage of two propionitrile molecules, and a reductive elimination process.

Hydrodefluorination of non-activated C–F bonds by diisobutyl-aluminiumhydride via the aluminium cation [ i-Bu 2Al] +

A novel system for the hydrodefluorination (HDF) of non-activated C–F bonds at room-temperature is described. The reaction of i-Bu 2AlH with [Ph 3C][B(C 6F 5) 4] ( 1), [Ph 3C][Al(C 6F 5) 4] ( 2) and [Ph 3C][Al{OC(CF 3) 3} 4] ( 3) as precatalysts leads under formation of triphenylmethane to the aluminium cation [ i-Bu 2Al] + and the non-coordinating anions [M(C 6F 5) 4] − (M = B, Al) and [Al{OC(CF 3) 3} 4] −. The formed aluminium cation is very reactive towards C–F bonds and easily forms i-Bu 2AlF releasing a carbocation that abstracts the hydride of excess i-Bu 2AlH and yields the corresponding hydrocarbon. Thereby, the active species [ i-Bu 2Al] + is regenerated and can realize a catalytic cycle. For 1-fluorohexane as an example including non-activated C–F bonds different activities were found (TON: 1: 20; 2: 12; 3: 30) in cyclohexane as solvent.

Rare earth metal bis(alkyl) complexes bearing amino phosphine ligands: Synthesis and catalytic activity toward ethylene polymerization

Reactions of neutral amino phosphine compounds HL 1–3 with rare earth metal tris(alkyl)s, Ln(CH 2SiMe 3) 3(THF) 2, afforded a new family of organolanthanide complexes, the molecular structures of which are strongly dependent on the ligand framework. Alkane elimination reactions between 2-(CH 3NH)-C 6H 4P(Ph) 2 (HL 1) and Lu(CH 2SiMe 3) 3(THF) 2 at room temperature for 3 h generated mono(alkyl) complex (L 1) 2Lu(CH 2SiMe 3)(THF) ( 1). Similarly, treatment of 2-(C 6H 5CH 2NH)-C 6H 4P(Ph) 2 (HL 2) with Lu(CH 2SiMe 3) 3(THF) 2 afforded (L 2) 2Lu(CH 2SiMe 3)(THF) ( 2), selectively, which gradually deproportionated to a homoleptic complex (L 2) 3Lu ( 3) at room temperature within a week. Strikingly, under the same condition, 2-(2,6-Me 2C 6H 3NH)-C 6H 4P(Ph) 2 (HL 3) swiftly reacted with Ln(CH 2SiMe 3) 3(THF) 2 at room temperature for 3 h to yield the corresponding lanthanide bis(alkyl) complexes L 3Ln(CH 2SiMe 3) 2(THF) n ( 4a: Ln = Y, n = 2; 4b: Ln = Sc, n = 1; 4c: Ln = Lu, n = 1; 4d: Ln = Yb, n = 1; 4e: Ln = Tm, n = 1) in high yields. All complexes have been well defined and the molecular structures of complexes 1, 2, 3 and 4b– e were confirmed by X-ray diffraction analysis. The scandium bis(alkyl) complex activated by AlEt 3 and [Ph 3C][B(C 6F 5) 4], was able to catalyze the polymerization of ethylene to afford linear polyethylene.

Enantioselective methylalumination of α-olefins

The ability of various enantiopure zirconocenes to catalyze the asymmetric methylalumination of allylbenzene has been tested. The enantioselectivity of an ethylene(Ind) 2ZrCl 2/MAO system is the same as that of authentic methyl cation generated with Ph 3C + from ethylene(Ind) 2ZrMe 2, confirming that the methyl cation is the active catalyst from ethylene(Ind) 2ZrCl 2/MAO.

Half-sandwich dibenzyl complexes of scandium: Synthesis, structure, and styrene polymerization activity

Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C 5Me 4H)SiMe 2R (R = Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph) 2(THF)] and [Sc(η 5-C 5Me 4SiMe 2Ph)(CH 2Ph) 2(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η 5-C 5Me 4SiMe 2R)(CH 2SiMe 3) 2(THF)]. The four-coordinate complexes display η 1-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph) 2(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph)(THF) x ][BPh 3(CH 2Ph)]. Benzyl cation formed using [Ph 3C][B(C 6F 5) 4] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.

Titanium(IV) complexes with monocyclopentadienyl and phenoxy-alkoxo ligands: Synthesis, structures and catalytic properties for ethylene polymerization

Three monochlorotitanium complexes Cp′Ti(2,4- t Bu 2-6-(CPh 2O)C 6H 2O)Cl [Cp′ = η 5-C 5H 5 ( 2), η 5-C 5(CH 3) 5 ( 3), η 5-C 5H 2Ph 2CH 3 ( 4)] have been synthesized in high yields (>90%) by the reaction of corresponding Cp′TiCl 3 with the dilithium salt of ligand 2,4- t Bu 2-6-(CPh 2OH)C 6H 2OH ( 1). When activated by [Ph 3C] +[B(C 6F 5) 4] − and Al i Bu 3, complexes 2– 4 exhibit reasonable catalytic activity for ethylene polymerization, producing polyethylenes with moderate molecular weights and melting points. Addition of excess water to complex 2 gave the oxo-bridged complex [Ti(η 5-C 5H 5)(2,4- t Bu 2-6-(CPh 2O)C 6H 2O)] 2O ( 5). Complexes 4 and 5 were characterized by single crystal X-ray diffraction.

Manganese(II) halogeno complexes with neutral tris(3,5-diisopropyl-1-pyrazolyl)methane ligand: Synthesis and ethylene polymerization

Manganese(II) halogeno complexes containing a neutral tris(3,5-diisopropyl-1-pyrazolyl)methane (referred to as L1′) ligand have been examined on their catalytic performance in ethylene polymerization and ethylene/1-hexene copolymerization. The activities of [Mn(Cl 2)(L1′)] ( a) and [Mn(Br)(L1′)](Br) ( b) activated by Al( i-Bu) 3/(Ph 3C)[B(C 6F 5) 4] for ethylene polymerization go up to 1600 and 840 kg mol (cat) −1 h −1 with a bimodal molecular weight distribution ( M w/ M n) of 4.1 and 4.2, respectively. These results are different from the corresponding manganese(II) complexes with hydrotris(pyrazolyl)borate anion.

Synthesis and structures of o-phenylene-bridged Cp/phosphinoamide titanium complexes

Addition of R′ 2PCl to anilines substituted with di- or trimethylcyclopentadienyl unit at ortho-position affords ortho-phenylene-bridged Me 2Cp or Me 3Cp/phosophinoamide ligands, 2-(RMe 2C 5H 2)C 6H 4NHPR′ 2 (R = Me or H; R′ = Ph, iPr, or Cyclohexyl). Successive addition of Ti(NMe 2) 4 and Me 2SiCl 2 to the ligands affords the desired dichlorotitanium complexes, [2-(η 5-RMe 2C 5H)C 6H 4NPR′ 2− κ 2 N, P]TiCl 2 (R = H, R′ = Ph, 9; R = Me, R′ = Ph, 10; R = H, R′ = iPr, 11; R = Me, R′ = iPr, 12; R = H, R′ = Cy, 13; R = Me, R′ = Cy, 14). By using Zr(NMe 2) 4 instead of Ti(NMe 2) 4, a zirconium complex, [2-(η 5-Me 3C 5H)C 6H 4NP(iPr) 2− κ 2 N, P]ZrCl 2 ( 15) is prepared. Molecular structures of 10, 14 and [2-(η 5-Me 2C 5H 2)C 6H 4NPPh 2− κN]Ti(NMe 2) 2 ( 16) were determined. The metric parameters determined on the X-ray crystallographic studies and the chemical shifts of the 31P NMR signal indicate that the phosphorous atom coordinates to the titanium in the dichloro-complexes 9– 15. The titanium and zirconium complexes show negligible activity in ethylene and ethylene/1-hexene (co)polymerization when activated with MAO or iBu 3Al/[Ph 3C][B(C 6F 5) 4].

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system, as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph 3CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph 3CMe) and the triphenylcarbonium ion (“trityl ion”, Ph 3C +). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al 2Cl 3Me 4 −. Large excess of trityl chloride causes the formation of AlCl 4 −, and probably AlCl 3Me − and AlCl 2Me 2 − anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.

Rare earth metal bis(alkyl) complexes bearing a monodentate arylamido ancillary ligand: Synthesis, structure, and Olefin polymerization catalysis

The reaction of Ln(CH 2SiMe 3) 3(thf) 2 with 1 equiv. of the amine ligand 2,6- i Pr 2C 6H 3NH(SiMe 3) gave the corresponding amido-ligated rare earth metal bis(alkyl) complexes [2,6- i Pr 2C 6H 3N(SiMe 3)]Ln(CH 2SiMe 3) 2(thf) (Ln = Sc ( 1), Y ( 2), Ho ( 3), Lu ( 4)), which represent rare examples of bis(alkyl) rare earth metal complexes bearing a monodentate anionic ancillary ligand. In the case of Gd, a similar reaction gave the bimetallic complex Gd 2(μ-CH 2SiMe 2NC 6H 3 i Pr 2-2,6) 3(thf) 3 ( 5) through intramolecular C–H activation of a methyl group of Me 3Si on the amido ligand by Gd–CH 2SiMe 3 and the subsequent ligand redistribution. Complexes 1– 5 were structurally characterized by X-ray analyses. On treatment with 1 equiv of [Ph 3C][B(C 6F 5) 4] in toluene at room temperature, complexes 1– 4 showed high activity for the living polymerization of isoprene. The 1/[Ph 3C][B(C 6F 5) 4] system showed high activity also for the polymerization of 1-hexene and styrene.

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3- tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride ( 4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3- tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt ( 3a) followed by TiCl 4(THF) 2 in THF. THF-free complexes 5a– 5d were synthesized more conveniently by the direct reaction of MOM-protected ligands ( 2a– 2d) with TiCl 4 in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a– 5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene ( M w = 1,170,000, M w/ M n = 2.0) upon activation with Al( i Bu) 3/[Ph 3C][B(C 6F 5) 4] (TB). Ethylene polymerization activity of 5d activated with Al( i Bu) 3/TB reached 49.0 × 10 6 g mol (cat) −1 h −1.

Propylene polymerization catalyzed by constrained geometry (cyclopentadienyl)phenoxytitanium catalysts

Propylene polymerization was performed using three constrained geometry catalysts: 2-(tetramethylcyclopentadienyl)-4,6-di- tert-butylphenoxytitanium dichloride ( 1), 2-(tetramethylcyclopentadienyl)-6- tert-butylphenoxytitanium dichloride ( 2), and 2-(tetramethylcyclopentadienyl)-6-phenylphenoxytitanium dichloride ( 3) with Al( i Bu) 3/[Ph 3C] +[B(PhF 5)] 4 − as co-catalyst. The substituent effect of the ligand and the effect of the Al/Ti molar ratio on the catalytic properties were investigated. The catalytic activity decreases in the order of 1 > 2 > 3. The 13C NMR results show that the polymers are basically atactic polypropylene with some 2,1-insertion and 1,3-enchainment units in the polymer chain, and the end groups are mainly vinylidene (CH 2 CMe–) and vinyl (CH 2 CH–) together with a small amount of propenyl (CH 3CH CH–). A possible chain propagation and termination mechanism of the propylene polymerization was discussed.

Synthesis of the sterically crowded cycloheptatrienyl complexes [M(CO)(PPh 3) 2(η-C 7H 7)] + (M = Mo or W): X-ray crystal structures of [W(CO)(PPh 3) 2(η-C 7H 7)][BF 4] and [W(CO) 2(PPh 3)(η-C 7H 7)][BF 4] · CH 2Cl 2

The first examples of complexes of the sterically crowded, bis(triphenylphosphine) auxiliary M(PPh 3) 2(η-C 7H 7) (M = Mo or W) have been synthesised. [Mo(CO)(PPh 3) 2(η-C 7H 7)][PF 6] ( 1) was obtained by low-temperature reaction of [MoMe(CO)(PPh 3)(η-C 7H 7)] with [Ph 3C][PF 6] in the presence of PPh 3. The tungsten analogue [W(CO)(PPh 3) 2(η-C 7H 7)][BF 4] ( 3) was formed by reaction of [WI(CO)(PPh 3)(η-C 7H 7)] with Ag[BF 4] in acetone followed by addition of PPh 3. An X-ray crystallographic structural comparison of complex 3 with its mono-phosphine counterpart, [W(CO) 2(PPh 3)(η-C 7H 7)][BF 4] · CH 2Cl 2 ( 4) reveals that the principal structural differences between 3 and 4 resulting from replacement of a carbonyl ligand by PPh 3 are: (i) an increase in the sum of the angles between the tripodal ligands and (ii) an elongation of the W–PPh 3 bond length (from 2.4950(12) Å in 4 to 2.5360(6) and 2.5496(6) Å in the bis(phosphine) complex 3).

Copolymerization of propene with low amounts of ethene in propene bulk phase

Propene homopolymers and propene–ethene copolymers with small amount of ethene were synthesized using three catalyst systems [ p-CH 3OPh 2C(2,7-di- tert BuFlu)(Cp)]ZrCl 2/Me 2HNPh][B(C 6F 5) 4] ( Cat I), [ p-CH 3OPh 2C(2,7-di- tert BuFlu)(Cp)]ZrCl 2/[Ph 3C][B(C 6F 5) 4] ( Cat II) and [ p-CH 3OPh 2C(2,7-di- tert BuFlu)(Cp)]ZrCl 2/MAO ( Cat III) in propene bulk phase. The activity of the catalyst was dependent on the formed ion pair: Cat I showed the highest activity, up to 96,000 kg pol/mol Zr h, at the used polymerization conditions. The produced homo- and copolymers have high molecular weights, between 400 and 600 kg/mol. The ethene incorporation rate was nearly the same with the different catalyst systems; the amount of ethene in the copolymer was increasing linearly with the amount of ethene in feed. The syndiotacticity of the homopolymer was highest, [ rrrr]>90%, with Cat I when it was 81.4 with Cat II and 80.8 with Cat III. The small amount of ethene in the copolymer allows the control of the melting and crystallization behavior. Also the crystallization temperatures of the copolymers were found to depend on the used catalyst system.

Synthesis and reactivity of zirconium and hafnium complexes incorporating chelating diamido-N-heterocyclic-carbene ligands

Early transition metal complexes employing a diamido N-heterocyclic carbene (NHC) ligand set (denoted [NCN]) render the centrally disposed NHC moiety stable to dissociation. Aminolysis reactions with the mesityl-substituted ligand precursor ( Mes[NCN]H 2) and M(NMe 2) 4 (M = Zr, Hf) provide bis(amido)-NHC-metal complexes that can be further converted to chloro and alkyl derivatives. Activation of Mes[NCN]M(CH 3) 2 with [Ph 3C][B(C 6F 5) 4] yields { Mes[NCN]MCH 3}{B(C 6F 5) 4}, which is surprisingly inactive for the polymerization of 1-hexene. The zirconium cation did, however, show moderate ability to catalytically polymerize ethylene. The hafnium dialkyls are thermally stable with the exception of the diethyl complex, Mes[NCN]Hf(CH 2CH 3) 2, which undergoes β-hydrogen transfer and subsequent C–H bond activation with an ortho-methyl substituent on the mesityl group. The hafnium dialkyl complexes also insert carbon monoxide and substituted isocyanides to yield η 2-acyls and η 2-iminoacyls, respectively. In some circumstances, further C–C bond coupling occurs to yield enediolates and eneamidolate metallocycles. The molecular structures of Mes[NCN]Hf(CH 2CHMe 2) 2, Mes[NCN]Hf(η 2-(2,6-Me 2C 6H 3NCCH 3)(CH 3), Mes[NCN]Hf(η 2-(2,6-Me 2C 6H 3NCCH 3) 2, Mes[NCN]Hf(OC(CH 3) C(CH 3)NXy), and [ Mes[NCN]Hf(OC( i Bu) C( i Bu)O)] 2 are included.