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The synthesis and characterization of three complexes of the type (N‐(3‐tert‐butylsalicylidene)‐R)2TiCl2 [R=2,6‐difluorophenyl 1, R=2,6‐dimethylphenyl 2, R=phenyl 3] is reported and compared with the highly active R=2,3,4,5,6,–pentafluorophenyl 4. The complexes were tested for ethylene polymerization when activated with different co‐catalysts, giving high catalytic activity when activated with methylaluminoxane for complexes 3 and 4. Complex 3 is the only catalyst to be inactive when activated with diethylaluminum chloride. Unexpectedly, for complexes 1 and 2, no catalytic activity is recorded when butylated hydroxytoluene in methylaluminoxane is used to remove the trimethylaluminum, while the catalytic activity for complex 3 is retained. NMR study on the activation of the four complexes in the presence of common alkyl aluminum co‐catalysts suggests the formation of Ti(III) species in the presence of tri‐iso‐butylaluminum, and also the formation of NR−CH2 (R: −Al(CH2CH(CH3)2)2) bond from the N=C−H bond of the ligand explaining the absence of catalytic activity. Density functional theory calculations using B3LYP and a combination of basis sets (6‐31+G and cc‐pVTZ) were performed on the catalyst precursors and the activated species showing insights into the frontier orbitals, localizing the LUMO on the imino bond elucidating their reactivity. Mulliken charges are also reported and an unexpected relationship between the nitrogen on the ligands and the molecular weight is observed.

The solution structure and dynamics of three prototypical bis-indenyl ansa-zirconocenium methyl cations (Me2Si(2-methyl-4-phenyl-6-tert-butylindenyl)2ZrMe+, [1Me]+ Me2Si(2,4-dimethylindenyl)2ZrMe+, [2Me]+ Me2Si(indenyl)2ZrMe+, [3Me]+) paired with the weakly coordinating B(C6F5)4- anion have been investigated by NMR spectroscopy in aromatic hydrocarbons with different polarities (toluene, ϵr = 2.38; chlorobenzene, ϵr = 5.69; 1,2-difluorobenzene (ODFB), ϵr = 13.38). These highly electrophilic cations are stabilized by solvent coordination, as evidenced by the unequivocal identification of [1Me·C7H8]+B(C6F5)4-, a rare example of a toluene-stabilized ion pair that has been fully characterized in solution. Combining spectroscopic and DFT methods allowed us to evaluate how solvent coordination modulates the dynamic processes typical of this class of catalysts. An exchange between the two faces of coordinated toluene (face inversion, FI) occurs without solvent decomplexation (ΔH⧧FI = 14.6 kcal mol-1 ΔS⧧FI = 3 cal mol-1 K-1 ΔG⧧FI(298) = 13.7 kcal mol-1) and is about 20 times faster than the exchange between coordinated and free solvent (solvent decomplexation, SD, ΔH⧧SD = 17.9 kcal mol-1 ΔS⧧SD = 10 cal mol-1 K-1 ΔG⧧SD(298) = 14.9 kcal mol-1) and ion pair symmetrization (IPS, ΔH⧧IPS = 18.6 kcal mol-1 ΔS⧧IPS = 12 cal mol-1 K-1 ΔG⧧IPS(298) = 14.9 kcal mol-1). For the ion pairs [1-3Me·solvent]+B(C6F5)4-, IPS rate constants (kIPS) do not correlate with the solvent polarity (kIPS(ODFB) > kIPS(toluene) > kIPS(chlorobenzene)). For the more coordinating toluene and chlorobenzene solvents, ΔG⧧IPS nicely tracks with the amount of positive charge at the metal, increasing as the positive charge increases (qZrMe2,CM5; 1Me2 > 3Me2 > 2Me2). In contrast, in the less coordinating ODFB, differences in the IPS barriers for [1-3Me·ODFB]+B(C6F5)4- appear to correlate better with steric parameters, as measured by the percent buried volume on the open quadrants (%VBur,open) for the corresponding neutral precursors (%VBur,open = 34.8, 35.5, 34.6% for 1Me2, 2Me2, and 3Me2, respectively).

NMR spectroscopy has been exploited to investigate the reactions of Hf(IV) organometallic complexes with trialkylaluminum and dialkylzinc, with the aim of obtaining insights into the elementary steps of coordinative chain transfer polymerization (CCTP). Bis(cydopentadienyl)hafnium dimethyl (Cp2HfMe2, 1Me(2)) and [N-(2,6-diisopropylphenyl)-alpha-(2-isopropylphenyl)-6-(1-naphthalenyl)-2-pyridinemethanaminato]hafnium dimethyl (2Me(2)) complexes have been chosen as case studies for understanding the differences between poorly performing and highly active CCTP catalysts, in an attempt to assess the effect of the ancillary ligand on the transalkylation rate. 2Me(2) was found to react much more quickly with both AlEt3 and ZnEt2 in comparison to 1Me(2), mainly due to a remarkably lower activation enthalpy. In addition, while the ethylation rate was found to depend on the nature of the alkylating agent for 1Me(2), it does not for 2Me(2). This difference in reactivity was observed also in the case of the ion pairs obtained by reacting 1Me(2) and 2Me(2) with [CPh3][B(C6F5)(4)]. For the latter species, NMR indicated that two main deactivation pathways, namely anion decomposition and a -bond methatesis of Hf-alkyl groups, occur. Keywords

The fluxional behavior of zirconaaziridinium ion pairs [Cp2Zr(η2-CH2NMePh][X] (X– = MeB(C6F5)3– (1a), B(C6F5)4– (1b)) in solution has been investigated by means of 2D EXSY and line shape analysis NMR methods at different temperatures. It is found that two dynamic processes are operative: (i) the inversion of the absolute configuration of the coordinated nitrogen atom (PI process) and (ii) the dynamic symmetrization of the ion pair occurring through a 180° rotation around Zr–CH2 bond and anion relocation from one side of the cation to the other (BS process). Analysis of the kinetic data indicates that both processes necessitate nitrogen decoordination from the metal that, by the way, is not the rate-determining step; the nature of the borate anion has a negligible effect on the rates of both PI and BS processes.

Decamethylzirconocene cation [Cp*2ZrMe](+) (2) decomposes in bromobenzene-d(5) solution to generate sigma-aryl species [Cp*Zr-2(2-C6H4Br-kappa Br,C)][B(C6F5)(4)] (3). This a-bond metathesis reaction is catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay. In benzene-d(6) compound 2 decomposes via C H bond activation of one of the Cp* ligands to generate tucked-in compound [Cp*{eta(5):eta(1)-C5Me4(CH2)}Zr](+) (4). In the presence of Et3N, no formation of tucked-in compound 4 is observed, but instead an overall double C-H bond activation and C-N bond cleavage of the tertiary amine is observed, resulting in [Cp*Zr-2{C(Me)NEt-kappa C,N}](+) (6). A mechanism is proposed that nominates [Cp*2ZrNEt2](+) as an intermediate, the result of a C-H bond activation of Et3N, followed by beta-amide elimination. Attempted synthesis of this species by treatment of Cp*Zr-2(NEt2)Me with [Ph3C][B(C6F5)(4)] results, again, in formation of compound [6](+). The presence of Et3N also has an effect on the stability of THF adduct [Cp*2ZrMe(THF)](+) as the amine performs a nucleophilic THF ring-opening to generate [Cp*2ZrMe{O(CH2)(4)NEt3}](+) (7). The results show that amine coproducts, often generated in the synthesis of cationic transition-metal complexes, are not necessarily innocent.

Zirconaaziridinium inner sphere ion pairs (ISIPs) bearing alkyl chains of different lengths, [Cp2Zr(η2-CH2NR1R2)+···X−] (R1 = Me, R2 = C2H5, X− = MeB(C6F5)3−, ZrNC2BN; R1 = Me, R2 = C16H33, X− = MeB(C6F5)3−, ZrNC16BN; R1 = R2 = C18H37, X− = MeB(C6F5)3−, ZrNC18BN; R1 = Me, R2 = Ph, X− = MeB(C6F5)3−, ZrNPhBN; R1 = R2 = C18H37, X− = B(C6F5)4−, ZrNC18BT; R1 = Me, R2 = Ph, X− = B(C6F5)4−, ZrNPhBT), have been synthesized by the reaction of [Cp2ZrMe+···MeB(C6F5)3−] or [Cp2ZrMe+···B(C6F5)4−] with the suitable tertiary amine followed by selective C−H activation of one Me group of the coordinated amine and methane elimination. Subsequent reaction of ISIPs with THF afforded the corresponding outer-sphere ion pairs (OSIPs) ([ZrNC2THF][BN], [ZrNC16THF][BN], [ZrNC18THF][BN], [ZrNPhTHF][BN], [ZrNC18THF][BT], [ZrNPhTHF][BT]) in which the anion has been displaced into the second coordination sphere. The interionic structure in solution (i.e., the relative cation−anion position) and the self-aggregation level of both ISIPs...

A novel zinc silsesquioxane complex ([(c-C5H9)(7)Si7O11(OSiMePh2)](2)Zn4Me4 (1)) has been used as a model compound for silica-grafted zinc catalysts in the copolymerization of cyclohexene oxide and CO2. Complex 1 exists as a dimer in the solid state and is moderately active in the copolymerization, and polycyclohexene carbonates have been obtained with a carbonate content of 79-98%. Polymerizations with ZnEt2-treated silica particles resulted in polymer particles with (M) over bar (n) and (M) over bar (w) values and carbonate contents comparable to those of the polymers obtained with 1. It was further demonstrated that CO2 consumption can be followed online by monitoring the decrease of system pressure during the reaction. CO2 consumption has been interpreted in relation to both polycarbonate and cyclic carbonate formation. These measurements represent the intrinsic kinetics of this reaction, which appear to be directly related to CO2 pressure.

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution

The ionic metallocene complexes [Cp*(2)M][BPh(4)] (Cp* = C(5)Me(5)) of the trivalent 3d metals Sc, Ti, and V were synthesized and structurally characterized. For M = Sc, the anion interacts weakly with the metal center through one of the phenyl groups, but for M = Ti and V, the cations are naked. They each contain one strongly distorted Cp* ligand, with one (V) or two (Ti) agostic C-H...M interactions involving the Cp*Me groups. For Sc and Ti, these Lewis acidic species react with fluorobenzene and 1,2-difluorobenzene to yield [Cp*(2)M(kappaF-FC(6)H(5))(n)][BPh(4)] (M = Sc, n = 2; M = Ti, n = 1) and [Cp*(2)M(kappa(2)F-1,2-F(2)C(6)H(4))][BPh(4)], the first examples of kappaF-fluorobenzene and kappa(2)F-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C(6)F(5))(4)](-), both Sc and Ti form [Cp*(2)M(kappa(2)F-C(6)F(5))B(C(6)F(5))(3)] contact ion pairs. The nature of the metal-fluoroarene interaction was studied by density functional theory (DFT) calculations and by comparison with the corresponding tetrahydrofuran (THF) adducts and was found to be predominantly electrostatic for all metals studied.

Bisamidinate zirconium dichloride and dimethyl complexes with the sterically demanding amidinate ligands [PhC(NAr)(2))](-) (A) and [PhC(NAr)(NAr')](-) (B) (Ar = 2,6-(Pr2C6H3)-Pr-i; Ar' = 2,6-Me2C6H3) were prepared. The steric demand of ligand A induces the unusual trans geometry in trans-(A)(2)ZrCl2, whereas (A)(2)ZrMe2 and (B)(2)ZrX2 (X = Cl, Me) adopt the more usual cis-X-2 geometry. The dynamic behavior of these complexes in solution was studied by 1D and 2D H-1 NMR spectroscopy. Reaction of (A)(2)ZrMe2 with H-2 leads, after stepwise hydrogenolysis of the Zr-Me bonds, to cyclometalation of the two amidinate ligands. The same product was obtained by thermolysis of the dimethyl complex. The square pyramidal five-coordinate 10 valence electron cationic monomethyl species [(A)(2)ZrMe](+) was generated and structurally characterized. Remarkably, the compound is unreactive toward ethylene, H-2, and CO. The sterically slightly less encumbered species [(B)(2)ZrMe](+) does polymerize ethylene, albeit with modest activity.

Silsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3'-5,5'-tetrakis(tert-butyl)-2,2'-di-oxa-1,1'-biphenyl substituents. Both mono- and bidentate phosphites are prepared in good yields. Two types of silsesquioxanes are employed as starting materials. The monophosphinite I and the monophosphite 2 are prepared from the thallium silsesquioxide derived from a completely condensed silsesquioxane framework (c-C5H9)(7)Si7O12SiOTl. The diphosphite 3 is synthesized starting with the incompletely condensed monosilylated disilanol (cC(5)H(9))(7)Si7O9(OSiMePh2)(OH)(2). For monophosphite 2, the corresponding trans- [PtCl2(2)] complex 4 is characterized by NMR spectroscopy as well as by Xray crystallography, as the first example of a completely condensed oxo-functionalized silsesquioxane framework. The coordination of the bidentate ligand 3 towards Pd, Mo and Rh is studied, both by NMR spectroscopy as well as by X-ray crystallography. Various modes of coordination are shown to be possible. The molecular structures for the complexes trans- [PdCl2(3)] (5), cis-[Mo(CO)(4)(3)] (6) and the dinuclear complex [{Rh( mu-Cl)(CO)}(2)(kappa(2)-3)] (7) have been determined. In the rhodium-catalyzed hydro-formylation of I-octene high activities, with turnover frequencies of up to 6800 h(-1), are obtained with these new nanosized phosphorus ligands.

Silsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3'-5,5'-tetrakis(tert-butyl)-2,2'-di-oxa-1,1'-biphenyl substituents. Both mono- and bidentate phosphites are prepared in good yields. Two types of silsesquioxanes are employed as starting materials. The monophosphinite I and the monophosphite 2 are prepared from the thallium silsesquioxide derived from a completely condensed silsesquioxane framework (c-C5H9)(7)Si7O12SiOTl. The diphosphite 3 is synthesized starting with the incompletely condensed monosilylated disilanol (cC(5)H(9))(7)Si7O9(OSiMePh2)(OH)(2). For monophosphite 2, the corresponding trans- [PtCl2(2)] complex 4 is characterized by NMR spectroscopy as well as by Xray crystallography, as the first example of a completely condensed oxo-functionalized silsesquioxane framework. The coordination of the bidentate ligand 3 towards Pd, Mo and Rh is studied, both by NMR spectroscopy as well as by X-ray crystallography. Various modes of coordination are shown to be possible. The molecular structures for the complexes trans- [PdCl2(3)] (5), cis-[Mo(CO)(4)(3)] (6) and the dinuclear complex [{Rh( mu-Cl)(CO)}(2)(kappa(2)-3)] (7) have been determined. In the rhodium-catalyzed hydro-formylation of I-octene high activities, with turnover frequencies of up to 6800 h(-1), are obtained with these new nanosized phosphorus ligands.

International audience; The determination of the nature and structure of surface sites after chemical modification of large surface area oxides such as silica is a key point for many applications and challenging from a spectroscopic point of view. This has been, for instance, a long-standing problem for silica reacted with alkylaluminum compounds, a system typically studied as a model for a supported methylaluminoxane and aluminum cocatalyst. While Al-27 solid-state NMR spectroscopy would be a method of choice, it has been difficult to apply this technique because of large quadrupolar broadenings. Here, from a combined use of the highest stable field NMR instruments (17.6, 20.0, and 23.5 T) and ultrafast magic angle spinning (>60 kHz), high-quality spectra were obtained, allowing isotropic chemical shifts, quadnipolar couplings, and asymmetric parameters to be extracted. Combined with first-principles calculations, these NMR signatures were then assigned to actual structures of surface aluminum sites. For silica (here SBA-15) reacted with triethylaluminum, the surface sites are in fact mainly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands. Tetrahedral sites, resulting from the incorporation of Al inside the silica matrix, are also seen as minor species. No evidence for putative tri-coordinated Al atoms has been found.

Novel heptacyclic tetranuclear titanium complex containing penta- and hexacoordinated titanium centers was synthesised by the reaction of bis(o-phenol)phenylphosphine with titanium tetrachloride.

Ab initio quantum chemical calculations at the MP2 level were performed on the elementary reactions and structural reorganizations involved in activation and ligand binding by the “constrained geometry” olefin polymerization catalyst series R2Si(η5-R‘4C5)(R‘ ‘N)Ti(CH3)R‘ ‘‘ (R = H, CH3; R‘ = H, CH3; R‘ ‘ = CH3, t-Bu; R‘ ‘‘ = H, CH3, CH2CH2CH3, CH(CH3)2 ) in the presence of the organo-Lewis acid cocatalyst B(C6F5)3 and various solvation media. Calculated structures of the neutral precursors and resulting ion pairs are in good agreement with the experiment. Analysis of the R2Si(R‘4C5)(R‘ ‘N)TiR‘ ‘‘+ naked cations reveals the importance of α, β, and γ C−H/C−C agostic interactions in selectively stabilizing various conformations of the TiR‘ ‘‘ group as well as the diminished charge on Ti with the introduction of electron-donating ligand substituents. The calculated ion pair formation enthalpies for the process R2Si(η5-R‘4C5)(R‘ ‘N)Ti(CH3)R‘ ‘‘ + B(C6F5)3 → R2Si(η5-R‘4C5)(R‘ ‘N)TiR‘ ‘‘·H3CB(C6F5)3 are in good ...

The tetraphenylborate salt of the decamethyl titanocene cation, [Cp*2Ti][BPh4] (1, Cp* = C5Me5), was prepared by reaction of Cp*2TiH with [Cp2Fe][BPh4] and by reaction of Cp*2TiMe with [PhNMe2H][BPh4]. The crystal structure of 1 shows that the Cp*2Ti cation has a bent metallocene structure with agostic interactions with the metal center of two adjacent methyl groups on one of the Cp* ligands. Compound 1 reacts readily with THF to give the adduct [Cp*2Ti(THF)][BPh4] (2). In fluorobenzene, 1 forms the eta1-fluorobenzene adduct [Cp*2Ti(eta1-FC6H5)][BPh4] (3), which was structurally characterized. In contrast to the thermal stability of 3, addition of alpha,alpha,alpha-trifluorotoluene to either 1 or 2 results in C-F activation to give Cp*2TiF2 and PhCF2CF2Ph as the main products. This reactivity toward benzylic C-F bonds is also reflected in the reactivity toward the fluorinated borate anions [B(C6F5)4]- and {B(3,5-(CF3)2C6H3]4}-: reaction of Cp*2TiMe with their [PhNMe2H]+ salts results in a stable complex for the former anion, whereas rapid C-F activation is observed for the latter.