Novel arene complexes of titanium(IV), zirconium(IV), and hafnium(IV)

Gillis, Daniel; Tudoret, Marie Jose; Baird, Michael C.

doi:10.1021/ja00059a079

Cited by 172 publications

(95 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The last hypothesis, however, is not supported by the EXAFS metrical data. Furthermore, the average EXAFS-derived Zr-C benzene distance is 2.35(±2) Å, in good agreement with singlecrystal diffraction-characterized benzene coordination to electrophilic d 0 centers (27,38). Although η 3 coordination is relatively uncommon for π-complexed arenes (39,40), the present results are consistent with the solid-state NMR results and DFT calculations, considering the overlap of four scattering shells.…”

Section: Resultssupporting

confidence: 89%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13 C-cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η 5 O rganometallic molecule-derived heterogeneous catalysts are of increasing interest owing to their enhanced thermal stability and activity vs. their homogeneous analogs, and their atomically precise tailorable metal-ligand structures vs. other heterogeneous catalysts (1, 2). Furthermore, it is becoming increasingly evident that the inorganic support in many systems is noninnocent and can function as both a ligand and an activator, with the chemically important but poorly understood nature of the catalyst-support interaction strongly modulating catalytic activity and selectivity (3, 4). When adsorbed on Lewis acidic, dehydroxylated alumina surfaces, group 4 complexes such as Cp 2 ZrR 2 (Cp = η 5 -C 5 H 5 ; A, R = H; B, R = CH 3 ) and Cp*Zr (CH 3 ) 3 [C, Cp* = η 5 -C 5 (CH 3 ) 5 ] were argued on the basis of highresolution solid-state NMR spectroscopy to transfer an alkyl anion to unsaturated, Lewis acidic surface sites as in Fig. 1 (complexes B, C → qualitative model D) (5, 6). The resulting catalysts are extremely active for olefin hydrogenation and polymerization, and analogous ion-paired species form the basis for large-scale industrial polymerization processes (7,8). However, kinetic poisoning experiments in which the catalytic sites are titrated in situ with H 2 O or t BuCH 2 OH indicate that ≤5% of D-type sites are catalytically significant, likely reflecting, among other factors, the established heterogeneity of alumina surfaces (5, 6, 9), hence rendering active site structural and chemical descriptions necessarily imprecise. In contrast to these results, chemisorption of such organozirconium precursors on SiO 2 , Al 2 O 3 , and SiO 2 -Al 2 O 3 surfaces having appreciable coverage by weakly acidic OH groups predominantly yields covalently bound, poorly electrophilic Etype species via Zr-CH 3 protonolysis with CH 4 evolution (5, 6, 10, 11). Although the E-type sites may be characterized in some detail by high-resolution solid-state NMR and extended X-ray adsorption fine structure spectroscopy (EXAFS), they display minimal catalytic turnover in the absence of added, complicating activators [e.g., methylalumoxane or B(C 6 F 5 ) 3 ], and the fraction of catalytically significant sites is unknown (12, 13). In such situations, it is experimentally impossible to unambiguously distinguish catalytically significant sites from inactive "spectator" sites, hence to fully understand the catalytic chemistry.-In marked contrast to the above results, chemisorption of these same organozirconium molecules on highly Brønsted "super...

show abstract

Section: Resultssupporting

confidence: 89%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…Indeed in some cases, it has been shown that a molecule of solvent would rather bind to the vacant site of the cation than [BF 20 ] -; this is a testament to the anion's non-coordinating nature [133][134][135] -can interact with cations sufficiently to form higher aggregates [137]. Marks et al [138] reported using similar PGSE NMR measurements in C 6 [121,122] quadruples or even hextuples in solution at higher concentrations.…”

Section: Anion and Solvent Interactionsmentioning

confidence: 99%

“…Other examples of halocarbon solvents bound to transition metals are known [144][145][146][147]. It is possible that the solvent-stabilised cations are resting states in the catalytic cycle and that the solvent needs to be removed from the metal centre before binding and subsequent polymerisation of the olefin can occur [4,126,148] 20 ] are even stabilised by a molecule of hydrocarbon solvent (toluene) in solution and the former also in the solid state [133][134][135].…”

Section: Anion and Solvent Interactionsmentioning

confidence: 99%

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

2015

View full text Add to dashboard Cite

The discovery of transition metal-catalysed polymerisation of olefins in the 1950s by Ziegler and Natta was of huge importance. Over the last 30 years, the interest in homogenous polymerisation has not only grown but has changed focus from primarily studying the metallocene complexes of Group 4 to widespread exploration of postmetallocene systems. This is a consequence of extensive patenting of the metallocene catalyst systems, as well as for general interest in the improvement of polyolefin catalysis. The plastics industry produces more than 10 7 tonnes of polyethylene, polypropylene and polystyrene each year worldwide, and the study of well-defined homogenous catalysts is invaluable in uncovering the mechanism of polymerisation and the fundamental properties of the active species. This short Tutorial Review gives an overview of homogenous transition metal Ziegler-Natta catalysis in general as well as an overview of a selection of Group 4 post-metallocene catalysts. An overview of the synthesis and reactions of alkyl cations relevant to olefin polymerisation is also given. Finally, this review summarises recent advances in bimetallic catalysts for olefin polymerisation.

show abstract

“…Instead, the formation of toluene or tert-butyl benzene was observed and the ring methyl-metallated complexes Ti(1-tBu-3-CH2CMe2-,/LCsHa)(CsHs)R [R = Bz (17); Nf (18)] were isolated as red oils at room temperature (Scheme 2). The metallacyclic complexes result from the intramolecular activation of one of the cyclopentadienyl-bonded tea-butyl groups with elimination of the corresponding hydrocarbon [14].…”

Section: Neutral Complexesmentioning

confidence: 99%

“…Several [M(CsHs_,Me,)(R)2(L),] + complexes have been reported [15][16][17][18], showing different structural dispositions. The 14-electron complex [Zr(CsMes)(CH3)2(THF)2] + adopts the same fourlegged piano-stool structure with cis CH 3 groups, w hereas the 1 6-electron com pound [Zr(CsMes)(CH3)2(dmpe)(THF)] + has a distorted octahedral structure with equatorial/axial coordination of the dmpe ligand trans to the phosphine ligand and the CsMe 5 ring, and the two mutually trans CH 3 groups occupy the other two equatorial positions [15].…”

Section: Cationic Complexesmentioning

confidence: 99%

Neutral and cationic di(tert-butyl) cyclopentadienyl titanium, zirconium and hafnium complexes dynamic NMR study of the ligand-free cations [M(1,3-tBu2-η5-C5H3)(η5-C5H5)(CH3)]+ (M = Zr, Hf)

Amor¹,

Cuenca²,

Galakhov³

et al. 1997

Journal of Organometallic Chemistry

View full text Add to dashboard Cite

Group 4 metal complexes containing the di(tert-butyl)cyclopentadienyl ligand (l,3-tBu2-r/5-CsH3) have been synthesized. The reaction of a mixture of 1,3-and 1,4-di(tert-butyl)cyclopentadiene isomers with KH in THF at -78°C gives the salt K+ [(1,]-(THF)I_3 2 as a white solid. Treatment of 2 with chlorotrimethylsilane in a 1:1 molar ratio gives the air-stable trimethylsilylcyclopentadienyl derivative Si(1,3-tBu2C5H3XCH3)3 3. The silyl derivative 3 is an excellent precursor for monocyclopentadienyl trichlorotitanium and zirconium compounds M (28)] as yellow oils which can be stored for weeks under an inert atmosphere. When the same reactions of (14) and (26) with B(C6Fs) 3 are carried out in a 2:1 molar ratio at room temperature, the complexes (29), Hf (30)] can be obtained as a mixture of syn-and anti-isomers as shown by NMR spectroscopic observations. The formation of (29) and (30) implies the stabilization of the 14-electron cationic intermediate by interaction with one methyl group of the neutral complexes (14) and (26). Complexes (27) and (28) undergo heterolytic dissociation of the Metal-MeB(C6Fs) 3 bonds, leading to the formation of the free [M(I,3-tBu2-r/5-CsH3)(r/5-CsHs)(CH3)] + 14-electron species, verified by 1H DNMR spectroscopy. When compound (27) was heated at 50°C the metallacyclic cation [Zr(1-tBu-3-CMezCH2-@-C5H3)(@-CsHs)] + (31) was formed. The alkyl derivatives synthesized and reported herein, activated with * Corresponding author. l X-ray diffraction studies.0022-328X/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved.Pll S0022-3 28X(97)00034-X 156 J.l. Amor et al. / Journal of Organometallic Chemistry 535 (1997) [155][156][157][158][159][160][161][162][163][164][165][166][167][168] MAO, B(C6Fs) 3 or [Ph3C][B(C6Fs)4], polymerize ethylene with very low activity. The molecular structure of [Ti(1,3-tBu2-r/5-C5H3)C1(/x-O)] 3 6 has been determined by X-ray diffraction methods. © 1997 Elsevier Science S.A.

show abstract

Novel arene complexes of titanium(IV), zirconium(IV), and hafnium(IV)

Cited by 172 publications

References 0 publications

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

Neutral and cationic di(tert-butyl) cyclopentadienyl titanium, zirconium and hafnium complexes dynamic NMR study of the ligand-free cations [M(1,3-tBu2-η5-C5H3)(η5-C5H5)(CH3)]+ (M = Zr, Hf)

Contact Info

Product

Resources

About

Novel arene complexes of titanium(IV), zirconium(IV), and hafnium(IV)

Cited by 172 publications

References 0 publications

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

Neutral and cationic di(tert-butyl) cyclopentadienyl titanium, zirconium and hafnium complexes dynamic NMR study of the ligand-free cations [M(1,3-tBu2-η5-C5H3)(η5-C5H5)(CH3)]+ (M = Zr, Hf)

Contact Info

Product

Resources

About

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites