Studies on the Coordination Patterns of Diamine-Bridged Tetraphenoxy Ligands with Group 3 and 4 Metals.

Alkane elimination reactions between the diamino- and dianilino-bridged tetrakis(phenolate) proligands and precursors M(CHSiMe)(THF), M(CHCH--NMe) (M = Sc and Y), and Hf(CHPh) were investigated. The diamino-bridged afforded nonsymmetric complex incorporating two metal centers in different coordination environments. This one and other dinuclear compounds , , and were characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study (for and ) and turned out to be symmetric in solution.

Dinuclear group IV metal complexes based on a bis(indenyl)-(/)-stilbene platform: a potential prototype of "photoswitchable" catalysts for olefin polymerization.

The preparation of dizirconium complexes based on a novel bis(indenyl)-(/)-stilbene platform was explored. Negishi coupling between the -generated diorganozincates obtained from the respective //-(/)-dibromostilbenes and the bromo-functionalized zirconocene (η-Cp*)(η-2-methyl-4-bromoindenyl)ZrCl, or, alternatively, the preparation of bis(indene)stilbene pro-ligands {//-(/)-BisIndSB}H through Negishi coupling of the corresponding dibromostilbenes with 4-bromoindene and subsequent metallation/transmetallation with Cp*ZrCl or Zr(NMe), allowed the preparation of a series of dinuclear complexes. These were analyzed by NMR spectroscopy and some of them by iASAP-mass spectrometry and by X-ray diffraction studies.

Hydrogenation of CO by a Bifunctional PC(sp )P Iridium(III) Pincer Complex Equipped with Tertiary Amine as a Functional Group.

Reversible hydrogen storage in the form of stable and mostly harmless chemical substances such as formic acid (FA) is a cornerstone of a fossil fuels-free economy. In the past, we have reported a primary amine-functionalized bifunctional iridium(III)-PC(sp )P pincer complex as a mild and chemoselective catalyst for the additive-free decomposition of neat formic acid. In this manuscript, we report on the successful application of a redesigned complex bearing tertiary amine functionality as a catalyst for mild hydrogenation of CO to formic acid.

-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new MeSi-bridged cyclopentadiene/indene proligands {MeSi(R-R-Cp)(R,R,R,R-Ind)H} (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding -symmetric group 4 -metallocene complexes (M = Zr, Hf), namely, {MeSi(MeCp)(Ind)}ZrCl (2a-Zr), {MeSi(MeCp)(2-Me,4-Ph-Ind)}MCl (2b-M), {MeSi(MeCp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2c-Zr), {MeSi(MeCp)(2-Me,4-Ph,5-OMe,6-Bu-Ind)}MCl (2d-M), {MeSi(MeCp)(2-R',4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl, R' = Me (2e-Zr), R' = Et (2f-Zr), {MeSi(2,5-Ph-3,4-Me-Cp)(2-Me,4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl (2g-Zr), {MeSi(MeCp)(2-Me,4-(3',6'-Bu-carbazol-4'-yl)-Ind)}ZrCl (2h-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph-Ind)}ZrCl (2i-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2j-Zr) and {MeSi(MeCp)(2-Me-4,5-[]anthracene-Ind)}MCl (2k-Zr) were synthesized and characterized by NMR spectroscopy and mass spectrometry. The solid-state molecular structures of 2b-Zr, 2d-Zr, 2e-Zr, 2f-Zr, 2j-Zr and 2k-Zr were determined by X-ray crystallography.

Ruthenium-Catalyzed Coupling Reactions of CO with C H and Hydrosilanes towards Silyl Esters.

A series of in situ-prepared catalytic systems incorporating Ru precursors and bidentate phosphine ligands has been probed in the reductive carboxylation of ethylene in the presence of triethylsilane as reductant. The catalytic production of propionate and acrylate silyl esters was evidenced by high-throughput screening (HTS) and implemented in batch reactor techniques. The most promising catalyst systems identified were made of Ru(H)(Cl)(CO)(PPh ) and 1,4-bis(dicyclohexylphosphino)butane (DCPB) or 1,1'-ferrocene-diyl-bis(cyclohexylphosphine) (DCPF).

{Cyclopentadienyl/Fluorenyl}-Group 4 ansa-Metallocene Catalysts for Production of Tailor-Made Polyolefins.

The development of new metallocene-based polymerization catalysts and innovative processes derived thereof still constitutes a challenge for the manufacturing of polyolefinic materials with tailored properties (e. g. particular microstructure or topology, ultra-high molecular weight, high melting transition, and their combinations) for contemporary commercial applications.

Rare-Earth Metal Complexes Supported by Polydentate Phenoxy-Type Ligand Platforms: C-H Activation Reactivity and CO/Epoxide Copolymerization Catalysis.

Mono- and dinuclear group 3 metal complexes incorporating polydentate bis(imino)phenoxy {NO} and bis(amido)phenoxy {NO} ligands were synthesized by alkane elimination reactions from the tris(alkyl) M(CHSiMe)(THF) and M(CHCH--NMe) (M = Sc, Y) precursors. Complex was used for the selective C-H activation of 2-phenylpyridine at the 2'-phenyl position affording the corresponding bis(aryl) product , which was found to be reacted reluctantly with weak electrophiles (styrene, imines, hydrosilanes). The mechanism of formation of was established by DFT calculations, which also corroborated high stability of the complex toward insertion of styrene, apparently stemming from the inability to form the corresponding adduct.

Paraffin-Inert Atmospheric Solid Analysis Probe: A Fast and Easy Approach To Characterize Extremely Air-Sensitive Organometallic Complexes by Mass Spectrometry.

Rational characterization of most organometallic compounds is hampered by their high reactivity, in particular, toward oxygen and water. Mass spectrometry experiments require physical introduction of the sample in the ionization source. So, the main challenge is to transfer air-sensitive organometallic compounds from inert atmosphere to the ionization source.

A Theoretical Outlook on the Stereoselectivity Origins of Isoselective Zirconocene Propylene Polymerization Catalysts.

The first three insertion steps of propylene for isoselective metallocenes from the one-carbon-bridged cyclopentadienyl-fluorenyl {Cp/Flu} and silicon-bridged ansa-bis(indenyl) {SBI} families were computed by using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the Solvation Model based on Density (SMD) continuum model. For C -symmetric {Cp/Flu}-type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain "stationary" insertion (or site epimerization backskip) and less stereoselective alternating mechanisms. For the C -symmetric {SBI}-type system, the computation results were in complete agreement with the sole operating chain migratory insertion mechanism.

Engineering of Syndiotactic and Isotactic Polystyrene-Based Copolymers via Stereoselective Catalytic Polymerization.

This contribution presents an updated overview of the different copolymers containing stereoregular polystyrene blocks. Special emphasis is placed on syndiospecific and isospecific copolymerization of styrene with co-monomers (ethylene and α-olefins, conjugated and non-conjugated dienes, styrene derivatives, etc.).

Conformationally dynamic titanium and zirconium cationic complexes of bis(naphthoxy)pyridine ligands: structure, "oscillation" and olefin polymerization catalysis.

Discrete ionic complexes {ONO}M(CHPh)((η-Ph)CHB(CF)) (M = Ti, 2-Ti; Zr, 2-Zr) have been prepared from the parent neutral dibenzyl precursors and B(CF). Also, a neutral dichloro complex {ONO}ZrCl(MeNH) (3) was synthesized by the reaction of a proligand {ONO}H (1-H2) with (MeN)ZrCl(DME). The compounds were characterized by NMR spectroscopy and X-ray crystallography (for 2-Zr and 3).

Synthesis and structure of the first discrete dinuclear cationic aluminum complexes.

The reactions of the charge neutral dinuclear aluminum tetraalkyl complexes of di-Schiff base ligands, i.e. [AlMe2{ON}-R-{ON}AlMe2] (1a, R = 1,3-propylene; 1b, R = 1,3-cyclohexylene) with B(C6F5)3 and [H(Et2O)2](+)[H2N{B(C6F5)3}2](-) were investigated.

Highly Stereocontrolled Ring-Opening Polymerization of Racemic Alkyl β-Malolactonates Mediated by Yttrium [Amino-alkoxy-bis(phenolate)] Complexes.

Yttrium [amino-alkoxy-bis(phenolate)]amido complexes have been used for the ring-opening polymerization (ROP) of racemic alkyl β-malolactonates (4-alkoxycarbonyl-2-oxetanones, rac-MLA(R) s) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the ortho-substituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)-disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLA(R) s (Pr ≥ 0.

Tandem C(sp(2))-OMe Activation/C(sp(2))-C(sp(2)) Coupling in Early Transition-Metal Complexes: Aromatic C-O Activation beyond Late Transition Metals.

We report on combined structural, kinetic, and computational studies unraveling the mechanism of a unique, highly selective intramolecular C(sp(2))-OMe cleavage/C(sp(2))-C(sp(2)) coupling tandem reaction in group 3 metal (Y and Sc) complexes of amidine-amidopyridinate ligands. The latter process represents a rare stoichiometric model of the nonredox cleavage of inert C(sp(2))-O bonds relevant to cross-coupling reactions of aromatic ethers catalyzed by late transition metals.

Heterobi- and -trimetallic Ion Pairs of Zirconocene-Based Isoselective Olefin Polymerization Catalysts with AlMe₃.

The reactivity towards AlMe3 of discrete cationic ansa-zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6-tBu2-Flu)(3-tBu-5-Et-Cp)}ZrMe2)] {Cp-Flu} and rac-[{Me2Si-(2-Me-4-Ph-Ind)2}ZrMe2] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe3 adduct (3 b) is reported. In the presence of excess AlMe3, the {SBI}-based AlMe3 adduct 3 b undergoes a slow decomposition via C-H activation in a bridging methyl unit to yield a new species (4 b) with a trimetallic {Zr(μ-CH2)(μ-Me)AlMe(μ-Me)AlMe2} core.

Beyond stereoselectivity, switchable catalysis: some of the last frontier challenges in ring-opening polymerization of cyclic esters.

Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis.

Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone.

Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone.

Exploring electronic versus steric effects in stereoselective ring-opening polymerization of lactide and β-butyrolactone with amino-alkoxy-bis(phenolate)-yttrium complexes.

A series of methoxy-amino-bis(phenol)s (ONOO(R(1),R(2)))H(2) possessing on the phenol rings R(1) ortho substituents with variable steric and electronic properties (R(1)=CMe(2)Ph, 1; CMe(2)tBu, 3; CMe(2)(4-CF(3)C(6)H(4)), 5; CPh(3), 9; Cl, 10) has been synthesized and further reacted with [Y{N(SiHMe(2))(2)}(3)](THF)(2) to give cleanly the corresponding yttrium compounds [Y(ONOO(R(1),R(2))){N(SiHMe(2))(2)}(thf)(n)] (Y-x); the solid-state structures of Y-3 and Y-10 have been determined. These amido complexes have been used as initiators for the ring-opening polymerization (ROP) of rac-lactide (LA) and rac-β-butyrolactone (BBL) to provide heterotactically enriched poly(lactic acid)s (PLAs) and syndiotactically enriched poly(3-hydroxybutyrate)s (PHBs), respectively, by means of a chain-end control mechanism. Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values.

Group 3 metal complexes supported by tridentate pyridine- and thiophene-linked bis(naphtholate) ligands: synthesis, structure, and use in stereoselective ring-opening polymerization of racemic lactide and beta-butyrolactone.

Scandium, yttrium and lanthanum amido complexes supported by tridentate bis(ortho-silyl-substituted naphtholate)-donor ligands ({ONO(SiPh3)}(2-) and {ONO(SitBuMe2)}(2-), donor = 2,6-pyridine; {OSO(SiPh3)}(2-), donor = 2,5-thiophene) have been prepared in high yields (72-96%) by reaction of the corresponding pro-ligand {OZO(SiR3)}H(2) and Ln[N(SiHMe(2))(2)](3)(THF)(n) precursor. The solid-state structures of {ONO(SiPh3)}La[N(SiHMe(2))(2)](THF) (3), {ONO(SitBuMe2)}Ln[N(SiHMe(2))(2)](THF) (Ln = Sc, 4; Y, 5) and {OSO(SiPh3)}Ln[N(SiHMe(2))(2)](THF) (Ln = Sc, 7; La, 9) have been determined by single-crystal X-ray diffraction studies. In all five complexes, the naphtholate rings twist in the same direction from the plane of the pyridine or thiophene linker, to give rise to C(s)-symmetric (non crystallographic) structures.

On the initiation mechanism of syndiospecific styrene polymerization catalyzed by single-component ansa-lanthanidocenes.

The mechanism of the initiation step of styrene polymerization promoted by single-component ansa-lanthanidocene catalysts [{Cp'XMe(2)Flu'}Ln(R)(ether)(n)] (Cp' = C(5)H(4); Flu' = 9-C(13)H(8); X = C or Si; R = allyl = CH(2)CHCH(2) or alkyl = CH(2)SiMe(3); ether = THF or Et(2)O, n = 0,1) has been studied from a combined experimental/theoretical perspective. First, detailed (13)C NMR studies conducted on syndiotactic oligostyrenes prepared by chain-growth polymerization with [{C(5)H(4)CMe(2)Flu'}Nd(eta(3)-1,3-C(3)H(3)(SiMe(3))(2))]/Mg(nBu)(2) (1:50) have shown that the insertion of styrene in these lanthanidocene systems proceeds selectively in a secondary (2,1) fashion, both at the initiation and propagation steps. Next, DFT studies of styrene insertion have been carried out on three model compounds, [{Cp'CMe(2)Flu'}Eu(eta(3)-allyl)(thf)] (I), [{Cp'SiMe(2)Flu'}Eu(eta(3)-allyl)(thf)] (II), and [{Cp'CMe(2)Flu'}Eu(eta(1)-CH(2)SiMe(3))(thf)] (III), in order to rationalize the influence of the ansa bridge (CMe(2) vs.

Allyl ansa-lanthanidocenes: single-component, single-site catalysts for controlled syndiospecific styrene and styrene-ethylene (Co)polymerization.

A series of new neutral allyl Group 3 metal complexes bearing ansa-bridged fluorenyl/cyclopentadienyl ligands [[Flu-EMe(2)-(3-R-Cp)]Ln(eta(3)-C(3)H(5))(THF)] (E=C, R=H, Ln=Y (2), La (3), Nd (4), Sm (5); R=tBu, Ln=Y (8), Nd (9); E=Si, R=H, Ln=Y (12), Nd (13)) were synthesized in good yields via salt metathesis protocols. The complexes were characterized by elemental analysis, NMR spectroscopy for diamagnetic complexes, and single-crystal X-ray diffraction studies for 2, 4, 9 and 12. Some of the allyl ansa-lanthanidocenes, especially 4, are effective single-component catalysts for the polymerization of styrene, giving pure syndiotactic polystyrenes (rrrr > 99 %) with low to high molecular weights (M(n)=6000-135,000 g mol(-1)) and narrow polydispersities (M(w)/M(n)=1.

Chiral fluorous dialkoxy-diamino zirconium complexes: synthesis and use in stereospecific polymerization of 1-hexene.

New catalysts for the isospecific polymerization of 1-hexene based on cationic zirconium complexes incorporating the tetradentate fluorous dialkoxy-diamino ligands [OC(CF(3))(2)CH(2)N(Me)(CH(2))(2)N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(2)NO)(2-)] and [OC(CF(3))(2)CH(2)N(Me)(1R,2R-C(6)H(10))N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(Cy)NO)(2-)] have been developed. The chiral fluorous diamino-diol [(ON(Cy)NO)H(2), 2] was prepared by ring-opening of the fluorinated oxirane (CF(3))(2)COCH(2) with (R,R)-N,N'-dimethyl-1,2-cyclohexanediamine. Proligand 2 reacts cleanly with [Zr(CH(2)Ph)(4)] and [Ti(OiPr)(4)] precursors to give the corresponding dialkoxy complexes [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3) and [Ti(OiPr)(2)(ON(Cy)NO)] (4), respectively.

Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes.

Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1).