Synthesis,structure and ethylene polymerization of group 4 complexes with phosphinoamide ligands

Group 4 complexes containing diphosphinoamide ligands [Ph₂PNR]₂MCl₂ (3: R = ^tBu, M = Ti; 4: R = ^tBu, M = Zr; 5: R = Ph, M = Ti; 6: R = Ph, M = Zr) were prepared by the reaction of MCl₄ (M = Ti; Zr) with the corresponding lithium phosphinoamides in ether or THF. The structure of [Ph₂PN^tBu]₂TiCl₂ (3) was determined by X‐ray crystallography. The phosphinoamides functioned as η²‐coordination ligands in the solid state and the Ti? N bond length suggests it is a simple single bond. In the presence of modified methylaluminoxane or i‐Bu₃Al/Ph₃BC(C₆F₅)₄, catalytic activity of up to 59.5 kg PE/mol cat h bar was observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Titanium and zirconium complexes with aminoiminophosphorane ligands

A series of titanium and zirconium complexes based on aminoiminophosphorane ligands [Ph₂P(Nt‐Bu)(NR)]₂MCl₂ ( 4 , M = Ti, R = Ph; 5 , M = Zr, R = Ph; 6 , M = Ti, R = SiMe₃; 7 , M = Zr, R = SiMe₃) have been synthesized by the reaction of the ligands with TiCl₄ and ZrCl₄. The structure of complex 4 has been determined by X‐ray crystallography. The observed very weak interaction between Ti and P suggests partial π‐electron delocalization through both Ti and P. The complexes 4–7 are inactive for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) or i‐Bu₃Al–Ph₃CB(C₆F₅)₄ under atmospheric pressure, and is probably the result of low monomer ethylene concentration and steric congestion around the central metal. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph₂P‐N‐PPh₂ at Group 4 metallocenes is presented herein. Coordination of N,N‐bis(diphenylphosphino)amine ( 1 ) to [(Cp₂TiCl)₂] (Cp=η⁵‐cyclopentadienyl) generated [Cp₂Ti(Cl)P(Ph₂)N(H)PPh₂] ( 2 ). The heterometallacyclic complex [Cp₂Ti(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Ti ) can be prepared by reaction of 2 with n‐butyllithium as well as from the reaction of the known titanocene–alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with the amine 1 . Reactions of the lithium amide [(thf)₃Li{N(PPh₂)₂}] with [Cp₂MCl₂] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp₂M(Cl){κ²‐N,P‐N(PPh₂)₂}] ( 4 Zr and 4 Hf ). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp₂Zr(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Zr ). Complexes 2 , 3 Ti , 4 Hf , and 3 Zr were characterized by X‐ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

The molecular composition of non-modified and acac-modified propoxide and butoxide precursors of zirconium and hafnium dioxides

Long-term storage at 0 °C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr₄O(OⁿPr)₁₄(ⁿPrOH)₂ in over 20% yield. The structure of this molecule can be described as a triangular Zr₃(μ₃-O)(OR)₁₀(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)₄(ROH) unit attached through a pair of (μ-OR) bridges. Mass spectrometric and ¹H NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be ~20% for n-propoxide and ~35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr(OⁿPr)(OⁱPr)₃(ⁱPrOH)]₂, from zirconium n-propoxide. A high yield has been observed (~90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)₃(acac)]₂ in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)₄ through very unstable M(acac)₃(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by ¹H NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XLII. Untersuchungen über Norbornylverbindungen des Titans,Zirconiums und Hafniums

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XLII. Investigations on Norbornyl Compounds of Titanium, Zirconium, and Hafnium It is reported about ¹³C-NMR, IR, and mass spectroscopic measurements of (1-Nor)₄M derivatives of Ti, Zr, and Hf and unsuccessful efforts for synthesis of 1-norbornyl titanium halides Furthermore, (2-Nor)₄Ti and (2-Nor)₄Zr were synthesized. These compounds are remarkably less stable than the corresponding 1-norbornyl derivatives and appear to be exo/endo isomer mixtures. At thermolyses of (2-Nor)₄Ti stable (2-Nor)₂Ti is formed. The stability of (7-Nor)₄Ti is comparable with that of (2-Nor)₄Ti.     

A proposal on an index of activities and selectivities of olefin polymerization catalysts by using 'paired interacting orbitals (PIO)' analysis

Olefin insertion and chain transfer to monomer on [O_h-CH₃MCl₄]^m(M = Ti, Zr, m = –1, –2: models of Ziegler-Natta catalysts) and [T_d-CH₃ML₂]^m(M = Ti, Zr; L = Cl, Cp m = 0, +1: models of metallocene catalysts) were analyzed by paired interacting orbitals (PIO) proposed by Fujimoto et al. Polymerization activities, molecular weights and regioselectivities of propylene insertion were easily predicted by using the total overlap population of all PIOs as an index of catalytic reactions.     

The ligand effect in Ti‐mediated living radical styrene polymerizations initiated by epoxide radical ring opening. 1. Alkoxide and bisketonate Ti complexes

Bisketonate and alkoxide Ti(III) complexes derived from Zn reduction of Ti(IV) precursors were evaluated as catalysts for the living radical polymerization (LRP) of styrene initiated by Ti‐catalyzed epoxide radical ring opening and mediated by reversible termination with Ti(III). No polymerization occurred with tris(2,2,6, 6‐tetramethyl‐3,5‐heptanedionato)titanium (III), whereas dichlorobis(2,2,6,6‐tetramethyl‐3,5‐heptanedionato)titanium (IV) affords only a free radical polymerization. Preliminary living features were displayed by (ⁱPrO)₂TiCl₂. Investigations of the effect of epoxide/Ti/Zn ratios, temperature, and nature of the epoxide demonstrated that (ⁱPrO)₃TiCl provides a linear dependence of M_n on conversion over a wide range of conditions with an optimum for [Sty]/[epoxide group]/[Ti]/[Zn] = 50/1/2/4 at 90 °C. However, the polydispersity could not be reduced below 1.4–1.5, with an initiator efficiency of 0.15. These results were rationalized in terms of a combination of decreased Ti oxophilicity and ligand exchange. The lowered oxophilicity decreases the initiation rate and broadens M_w/M_n. The fast alkoxide exchange promotes a weak dependence of the polymerization on reaction conditions and generates macromolecular Ti species with reduced ability to mediate LRP. Thus, while monofunctional epoxides provide homogeneous polymerizations and narrower M_w/M_n, difunctional initiators may lead to gel formation at high conversion. Nonetheless, all polymerizations were light gray to colorless and afforded white polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6028–6038, 2005     

A novel bifunctional Ti(IV) complex catalyzed asymmetric silylcyanation of aldehydes

A novel Lewis acid and Lewis base bifunctional Ti(IV) complex was formed in situ upon the treatment of ligand (R)‐3,3′‐bis(diphenylphosphinoyl)‐BINOL with Ti(PrO‐i)₄, which is proven to be an efficient catalyst in the asymmetric trimethylsilylcyanation of aldehydes. The corresponding cyanohydrins were obtained in high to excellent chemical yield (83–93%) albeit with moderate enantioselectivities (up to 51% enantiomeric excess). © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:31–35, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20652     

Poly(trimethylene carbonate)/Poly(malic acid) Amphiphilic Diblock Copolymers as Biocompatible Nanoparticles

Amphiphilic polycarbonate–poly(hydroxyalkanoate) diblock copolymers, namely, poly(trimethylene carbonate) (PTMC)‐b‐poly(β‐malic acid) (PMLA), are reported for the first time. The synthetic strategy relies on commercially available catalysts and initiator. The controlled ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) catalyzed by the organic guanidine base 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD), associated with iPrOH as an initiator, provided iPrO?PTMC?OH, which served as a macroinitiator in the controlled ROP of benzyl β‐malolactonate (MLABe) catalyzed by the neodymium triflate salt (Nd(OTf)₃). The resulting hydrophobic iPrO?PTMC‐b‐PMLABe?OH copolymers were then hydrogenolyzed into the parent iPrO?PTMC‐b‐PMLA?OH copolymers. A range of well‐defined copolymers, featuring different sizes of segments (M_n,NMR up to 9300 g mol^?1; Ð_M=1.28–1.40), were thus isolated in gram quantities, as evidenced by NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, differential scanning calorimetry, and contact angle analyses. Subsequently, PTMC‐b‐PMLA copolymers with different hydrophilic weight fractions (11–75 %) self‐assembled in phosphate‐buffered saline upon nanoprecipitation into well‐defined nano‐objects with D_h=61–176 nm, a polydispersity index <0.25, and a negative surface charge, as characterized by dynamic light scattering and zeta‐potential analyses. In addition, these nanoparticles demonstrated no significant effect on cell viability at low concentrations, and a very low cytotoxicity at high concentrations only for PTMC‐b‐PMLA copolymers exhibiting hydrophilic fractions over 47 %, thus illustrating the potential of these copolymers as promising nanoparticles.     

Synthesis and Characterization of Multiferrocenyl‐Substituted Group 4 Metallocene Complexes

The reaction of different metallocene fragments [Cp₂M] (Cp=η⁵‐cyclopentadienyl, M=Ti, Zr) with diferrocenylacetylene and 1,4‐diferrocenylbuta‐1,3‐diyne is described. The titanocene complexes form the highly strained three‐ and five‐membered ring systems [Cp₂Ti(η²‐FcC₂Fc)] ( 1 ) and [Cp₂Ti(η⁴‐FcC₄Fc)] ( 2 ) (Fc=[Fe(η⁵‐C₅H₄)(η⁵‐C₅H₅)]) by addition of the appropriate alkyne or diyne to Cp₂Ti. Zirconocene precursors react with diferrocenyl‐ and ferrocenylphenylacetylene under C? C bond coupling to yield the metallacyclopentadienes [Cp₂Zr(C₄Fc₄)] ( 3 ) and [Cp₂Zr(C₄Fc₂Ph₂)] ( 5 ), respectively. The exchange of the zirconocene unit in 3 by hydrogen atoms opens the route to the super‐crowded ferrocenyl‐substituted compound tetraferrocenylbutadiene ( 4 ). On the other hand, the reaction of 1,4‐diferrocenylbuta‐1,3‐diyne with zirconocene complexes afforded a cleavage of the central C? C bond, and thus, dinuclear [{Cp₂Zr(μ‐η¹:η²‐C?CFc)}₂] ( 6 ) that consists of two zirconocene acetylide groups was formed. Most of the complexes were characterized by single‐crystal X‐ray crystallography, showing attractive multinuclear molecules. The redox properties of 3 , 5 , and 6 were studied by cyclic voltammetry. Upon oxidation to 3 ⁿ⁺, 5 ⁿ⁺, and 6 ⁿ⁺ (n=1–3), decomposition occured with in situ formation of new species. The follow‐up products from 3 and 5 possess two or four reversible redox events pointing to butadiene‐based molecules. However, the dinuclear complex 6 afforded ethynylferrocene under the measurement conditions.     

Silylmethyl and related complexes II. Preparation,spectra, and thermolysis of the tetraneopentyls of titanium,zirconium, and hafnium

The preparation and characterisation of the Group IVA neopentyls (Me₃CCH₂)₄M (M = Ti, Zr, or Hf) is described. Spectroscopic data (IR, Raman, mass, ¹H NMR, and PE) are provided; IR and Raman bands have been assigned by comparison with results on Group IVB analogues (M = Ge or Sn). MC₄ stretching vibrations fall in the range 540–485 cm^?1, and bending modes at 240–283 cm^?1. Thermal decomposition gives neopentane as the sole detectable product; qualitatively, stability increases in the order M = Ti < Zr < Hf and for R₄M : R = Me ? Me₃CCH₂ ≈ Me₃SiCH₂. (Me₃CCH₂)₄Ti is aerobically oxidised in benzene to give (Me₃CCH₂O)₄Ti     

Preparation and crystal data of the New Pyrochlores Pb2[M1.5Te0.5]O6.5 (M = Ti,Zr, Sn,Hf)

From mixtures of PbO, MO₂ (M = Ti, Zr, Hf), SnO, and TeO₂, four new oxides Pb₂[M_1.5Te_0.5]O_6.5 have been obtained as yellow powders giving X-ray diffraction patterns characteristic of cubic pyrochlores, S.G. Fd3 m (No. 227), Z = 8, and a/Å values from 10.3529(1) (M = Ti) to 10.7406(1) (M = Zr). The best R factors, from 0.0465 (M = Ti) to 0.0242 (M = Hf), were obtained for Pb in 16(c) positions, M and Te (3:1) randomly distributed in 16(d), oxygen atoms in 48(f) and in a half of the 8(a) sites, and x values for the oxygen positional parameter (origin at center, 3 m) from 0.436 (M = Ti) to 0.421 (M = Zr). For the compounds of Ti and Zr the angles of the coordination polyhedra around the metals are reported. For seven-coordinated Pb^II the stereochemical influence of the nonbonded electron pair is shown. Apparent interatomic distances agree with those calculated.     

Evaluation of the dimethylsilyl-bis(2-methyl-4-phenyl-1-indenyl) ligand with group 4 triad metals in propene polymerizations with methylaluminoxane

Dimethylsilyl-bis(2-methyl-4-phenyl-1-indenyl)MCl₂ (M = Ti, Zr, Hf) complexes in combination with methylaluminoxanes produce isotactic polypropene. The Ti catalysts produce isotactic polypropene which is more stereoregular than that obtained with traditional, heterogeneous catalysts. Zr produces low molecular weight, weakly isotactic waxes at phenomenal rates greater than 32 · 10⁶ gPP/[(mol catalyst) · h · (mol/l monomer)]. Hf produces long, softer isotactic chains with good activities.     

Homoleptic alkenyls of the early transition metals and related compounds

The first stable homoleptic alkenyls of the early transition metals, MR_n, (R = C(Ph)=CMe₂; M = Ti, Zr, Hf, n = 4; and M = Cr, n = 3) and the related species (C₅H₅)₂MR₂ (M = Ti, Zr) and (C₅H₅)₂Zr(Cl)R have been prepared using appropriate organolithium reagents. Cleavage and insertion reactions are reported for the new compounds.     

Tetraalkyl titanium and zirconium metal chloride catalyst systems for ethylene polymerization

Coordination polymerization of olefins has become an industrially important, yet still poorly understood enterprise. The ethylene polymerization activity of (neophyl)_nZrCl_4-n shows a twentyfold increase from n = 4 to n = 3 and a further tenfold increase to n = 2. The heterogeneous MR₄/TiCl₄ catalysts (M = Ti, R = benzyl; M = Zr, R = benzyl, neophyl) have been developed. To explore the breadth of extendability, other metal chlorides (main group and transition metal) were substituted for TiCl₄. Indeed, excess AlCl₃ or MgCl₂ and the MR₄ compounds also produced ethylene polymerization catalysts. The inactivity of corresponding (neophyl)₄Ti systems is attributed to sterics. The abovementioned catalysts highlight the necessity of alkyl and chloride ligands at the transition metal catalyst centers.     

Structure evolution in the PbO-ZrO2-TiO2 sol-gel system: Part I — Characterization of prehydrolyzed precursors

In this investigation, several spectroscopic and analytical techniques were used to determine the chemical compositions and structures of the lead, zirconium, titanium, and Pb-(Zr, Ti) alkoxides involved in the sol-gel synthesis of PZT thin films. These techniques included ¹H, ¹³C, and ²⁰⁷Pb NMR; FT-IR; gas chromatography; Karl Fischer titration; and number-average molecular weights (M _n ) determined by cryoscopy. It was found that the titanium precursor had a M _n of 548 and a formula of [Ti(OCH₂CH₂OCH₃)₄]_1.6; the zirconium precursor had a M _n of 1015 and a formula of [Zr(OCH₂CH₂OCH₃)₄]_2.6; and the lead precursor had a formula Pb₆(OOCCH₃)₅(OCH₂CH₂OCH₃)₇. 4 H₂O and a molecular weight of 2131 (M _n =2113). It was observed that residual water from the incomplete dehydration of lead acetate trihydrate coupled with released water due to the esterification of acetic acid caused M-O-M (M=Pb, Zr, Ti) bonds in the Pb-(Zr, Ti) alkoxide. Two possible isomeric structures of the Pb-(Zr, Ti) alkoxide have been proposed. They are both cyclic and have a formula of Pb₂MMO₂(OR)₈(ROH)₂, (MM=Zr and/or Ti) and a molecular weight of 1336 (M _n =1386).     

Catenated polysulfur ligands: the pentasulfides of di-η5-cyclopentadienyl-zirconium(IV) and -hafnium(IV)

The thiols Cp₂M(SH)₂, where M = Ti and Zr, react to form the complexes Cp₂MS₅ when treated with mono- and di-sulfur transfer reagents. Treatment of Cp₂MCl₂ with Li₂S₂ and sulfur gave Cp₂MS₅, M = Ti, Zr and Hf, in better yield. The new Zr and Hf complexes have a six-membered MS₅ ring in a chair conformation similar to the previously observed for M = Ti. Variable temperature NMR studies show that the barriers to MS₅ ring inversion decrease in the order Ti > Hf > Zr.     

The bidentate behaviour of tetrahydroborate towards copper(II) and group(IV) metals in heterobimetallic complexes

Summary New heterobimetallic complexes of the type [Cu(TETA)-BH₄)₂M(BH₄)₂] (TETA = triethylene tetramine; M = Si, Ge, Sn, Ti and Zr) were prepared by the interaction of [Cu(TETA)Cl₂MCl₂] with an excess of KBH₄ in THF. The results indicate that the complexes are nonelectrolytes and the tetrahydroborate group links to the copper(II) atom and the group(IV) metal in a bidentate manner adopting C _2v symmetry.     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands

A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp₂M(Cl){κ²‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp₂MCl₂] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp₂Zr(H)Cl]. Salt metathesis reaction of [Cp₂Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp₂M(H){κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)₃Mg(Cl) {κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′₂Ti{κ²‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp₂′Ti(η²‐Me₃SiC₂SiMe₃)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.