Structural Diversity in the Reactions of Dimetallic Alkyl Titanium Oxides with Isonitriles and Nitriles.

A detailed study of the reaction of the dinuclear [{Ti(eta(5)-C5Me5)R-2}(2)(mu-O)] (R = Me 1, CH2Ph 2) compounds with a series of organic isonitriles (R'NC, R' = tBu, iPr, CH2SiMe3, Xyl) (Xyl = 2,6-Me2C6H3) and nitriles (R'CN, R' = tBu, iPr, SiMe3) has been carried out. Single-crystal X-ray structural studies revealed a variety of reactivity and structural moieties. Theoretical calculations (density functional theory, DFT) were used to understand the mechanism of some uncommon reactions observed experimentally. Reactions of 1 and 2 with isocyanides tBuNC, iPrNC, and Me3SiCH2NC led to the formation of dimetallic eta(2)-iminoacyl species [{Ti(eta(5)-C5Me5)(R'NCR)R}(2)(mu-O)] (R = Me, R' = tBu 3, iPr 4, CH2SiMe3 5; R = CH2Ph, R' = CH2SiMe3 6). Complex 4 underwent net rearrangements at room temperature to give the imido-vinylamido derivative [Ti-2(eta(5)-C5Me5)(2)(mu-O)(mu-NiPr) {N(iPr)CMe=CMe2}Me] (7), whereas the reaction of complex 2 with XylNC rendered the N-C bond cleavage product [{Ti(eta(5)-C5Me5)(CH=CHPh)}(mu-O)(mu-kappa(2)-N,C-N(MeC6H3)CH2){Ti(eta(5)-C5Me5)}] (8). The reactions of 1 with nitriles tBuCN and iPrCN gave the ketimido products [{Ti(eta(5)-C5Me5)Me(CN(Me)R')}(2) (mu-O)] (R' = tBu 9, iPr 10), whereas the analogous processes with 2 gave the alkenyl-imido complexes [{Ti(eta(5)-C5Me5)(CH2Ph)(2)}(mu-O){Ti(eta(5)-C5Me5)(=NC(R')=C(H)Ph)(NCR')}] (R' = tBu 11, iPr 12) with the concomitant coordination of a nitrile molecule. Complex 1 reacts with Me3SiCN to afford the nitrile-isonitrile isomerization product [{Ti(eta(5)-C5Me5)Me-2}(mu-O){Ti(eta(5)-C5Me5)(kappa(2)-C,N-Me-2 CNSiMe3 )(CNSiMe3)] (13).Consorcio Madroño - Universidad de Alcal

Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides

The reactivity of the "tuck-over" species [Ti2(η5-C5Me5)(CH2Ph)3(μ-η5-C5Me4CH2-κC)(μ-O)] (1) and [Ti2(η5-C5Me5)(CH2CMe3)(μ-η5-C5Me4CH2-κC)(μ-CH2CMe2CH2)(μ-O)] (2) toward isocyanides has been examined both synthetically and theoretically. Treatment of 1with the isocyanides RNC, R = Me3SiCH2, 2,6-Me2C6H3, tBu,iPr, leads to a series of η2-iminoacyl species (3−6) where the molecule of isocyanide inserts into one of the terminal metal−alkyl bonds. The analogous reaction of the "tuck-over" metallacycle species 2 with 2,6-Me2C6H3NC andtBuNC results inthe initial insertion of one isocyanide into the terminal Ti−alkyl bondto form the iminoacyl complexes 7 and 8, followed by a secondinsertion into the metallacycle moiety to generate 9, in the case of tertbutylisocyanide. DFT calculations support the selective reactivity observed experimentally with a kinetic and thermodynamicpreference for RNC insertion on the terminal alkyl groups bound to both metallic centers over the alternative insertion on the "tuck-over"ligand.Ministerio de Economía y Competitividad Universidad de Alcal

A Bridging bis-Allyl Titanium Complex: Mechanistic Insights into the Electronic Structure and Reactivity

Treatment of the dinuclear compound [{Ti(η5-C5Me5)Cl2}2(μ-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti(η5-C5Me5)(μ-C3H5)}2(μ-O)] (1), structurally identified by single-crystal X-ray analysis. Density functional theory (DFT) calculations confirm that the electronic structure of 1 is a singlet state, and the molecular orbital analysis, along with the short Ti −Ti distance, reveal the presence of a metal −metal single bond between the two Ti(III) centers. Complex 1 reacts rapidly with organic azides, RN3 (R = Ph, SiMe3), to yield the allyl μ-imido derivatives [{Ti(η5-C5Me5)(CH2CH=CH2)}2(μ-NR)(μ-O)] [R = Ph(2), SiMe3(3)] along with molecular nitrogen release. Reaction of 2 and 3 with H2 leads to the μ-imido propyl species [{Ti(η5-C5Me5)(CH2CH2CH3)}2(μ-NR)(μ-O)] [R = Ph(4), SiMe3(5)]. Theoretical calculations were used to gain insight into the hydrogenation mechanism of complex 3 and rationalize the lower reactivity of 2. Initially, the μ-imido bridging group in these complexes activates the H2 molecule via addition to the Ti −N bonds. Subsequently, the titanium hydride intermediates induce a change in hapticity of the allyl ligands, and the nucleophilic attack of the hydride to the allyl groups leads to metallacyclopropane intermediates. Finally, the proton transfer from the amido group to the metallacyclopropane moieties affords the propyl complexes 4 and 5.Ministerio de Ciencia, Innovación y Universidades Universidad de Alcalá Generalitat de Cataluny

Ti(III) Catalysts for CO2/Epoxide Copolymerization at Unusual Ambient Pressure Conditions

Titanium compounds in low oxidation states are highly reducing species and hence powerful tools for the functionalization of small molecules. However, their potential has not yet been fully realized because harnessing these highly reactive complexes for productive reactivity is generally challenging. Advancing this field, herein we provide a detailed route for the formation of titanium(III) orthophenylendiamido (PDA) species using [LiBHEt3] as a reducing agent. Initially, the corresponding lithium PDA compounds [Li2(ArPDA)(thf)3] (Ar = 2,4,6-trimethylphenyl (MesPDA), 2,6-diisopropylphenyl (iPrPDA)) are combined with [TiCl4(thf)2] to form the heterobimetallic complexes [{TiCl(ArPDA)}(?-ArPDA){Li(thf)n}] (n = 1, Ar = iPr 3 and n = 2, Ar = Mes 4). Compound 4 evolves to species [Ti(MesPDA)2] (6) via thermal treatment. In contrast, the transformation of 3 into [Ti(iPrPDA)2] (5) only occurs in the presence of [LiNMe2], through a lithium-assisted process, as revealed by density functional theory (DFT). Finally, the Ti(IV) compounds 3?6 react with [LiBHEt3] to give rise to the Ti(III) species [Li(thf)4][Ti(ArPDA)2] (Ar = iPr 8, Mes 9). These low-valent compounds in combination with [PPN]Cl (PPN = bis(triphenylphosphine)iminium) are proved to be highly selective catalysts for the copolymerization of CO2 and cyclohexene epoxide. Reactions occur at 1 bar pressure with activity/selectivity levels similar to Salen? Cr(III) compounds.Comunidad de MadridUniversidad de AlcaláPrograma Estímulo a la Investigación de Jóvenes Investigadore

Reductive Hydrogenation of Sulfido-Bridged Tantalum Alkyl Complexes: A Mechanistic Insight

Hydrogenolysis of a series of alkyl sulfido-bridged tantalum(IV) dinuclear complexes [Ta(?5-C5Me5)R(?-S)]2 [R = Me, nBu (1), Et, CH2SiMe3, C3H5, Ph, CH2Ph (2), p-MeC6H4CH2 (3)] has led quantitatively to the Ta(III) tetrametallic sulfide cluster [Ta(?5-C5Me5)(?3-S)]4 (4) along with the corresponding alkane. Mechanistic information for the formation of the unique low-valent tetrametallic compound 4 was gathered by hydrogenation of the phenyl-substituted precursor [Ta(?5-C5Me5)Ph(?- S)]2, which proceeds through a stepwise hydrogenation process, disclosing the formation of the intermediate tetranuclear hydride sulfide [Ta2(?5-C5Me5)2(H)Ph(?-S)(?3-S)]2 (5). Extending our studies toward tantalum alkyl precursors containing functional groups susceptible to hydrogenation, such as the allyl-and benzylsubstituted compounds [Ta(?5-C5Me5)(?3-C3H5)(?-S)]2 and [Ta(?5-C5Me5)(CH2Ph)(?-S)]2 (2), enables alternative reaction pathways en route to the formation of 4. In the former case, the dimetallic system undergoes selective hydrogenation of the unsaturated allyl moiety, forming the asymmetric complex [{Ta(?5-C5Me5)(?3-C3H5)}(?-S)2{Ta(?5-C5Me5)(C3H7)}] (6) with only one propyl fragment. Species 2, in addition to the hydrogenation of one benzyl fragment and concomitant toluene release, also undergoes partial hydrogenation and dearomatization of the phenyl ring on the vicinal benzyl unity to give a ?5-cyclohexadienyl complex [Ta2(?5-C5Me5)2(?-CH2C6H6)(?-S)2] (7). The mechanistic implications of the latter hydrogenation process are discussed by means of DFT calculationsComunidad de MadridUniversidad de AlcaláPrograma Estímulo a la Investigación de Jóvenes Investigadore

N=N Bond Cleavage by Tantalum Hydride Complexes: Mechanistic Insights and Reactivity.

A series of dinuclear tantalum(IV) hydrides [{TaCpRX2}2(mu-H)2] (CpR = eta5-C5Me5, eta5-C5H4SiMe3, eta5-C5HMe4; X = Cl, Br) show the ability to promote the N=N bond cleavage in their reactions with azobenzene and benzo[c]cinnoline in absence of reducing reagents. Both, characterization of intermediate species and DFT studies point to a mechanism in two stages, in which the Ta-Ta bond splitting is key for the reduction of the N=N bond and its complete scission.Consorcio Madroño - Universidad de Alcal

Molecular Design of Cyclopentadienyl Tantalum Sulfide Complexes

Use of (Me3Si)2S and [Ta(η5-C5Me5)Cl4](1) in a 4:3 ratio afforded the trimetallic sulfide cluster [Ta3(η5-C5Me5)3Cl3(μ3-Cl)(μ-S)3(μ3-S)] (2) with loss of SiClMe3. A similar reaction between 1, TaCl5, and (Me3Si)2S in a 2:1:4 ratio resulted in the analogous complex [Ta3(η5-C5Me5)2Cl4(μ3-Cl)(μ-S)3(μ3-S)] (3). Single-crystal X-ray diffraction analyses of 2 and 3 showed in all cases trinuclear tantalum sulfide clusters. On the other hand, thermal treatment of 2 with SiH3Ph generated very cleanly the dinuclear tantalum(IV) sulfide complex [Ta2(η5-C5Me5)2Cl2(μ-S)2] (4) in a quantitative way. Likewise, we found that 4 was synthesized more easily by a one-pot reaction of 1, (Me3Si)2S, and SiH3Ph in toluene. Reactions of 4 with a series of alkylating reagents rendered the dinuclear peralkylated sulfide complexes [Ta2(η5-C5Me5)2R2(μ-S)2] (R = Me 5, Et 6, CH2SiMe3 7, C3H5 8, Ph 9). Single-crystal X-ray diffraction analyses of 4, 5, and 9 showed in all cases a trans disposition of the chloro or alkyl substituents. The short Ta−Ta distances (2.918(1)−2.951(1) Å) along with DFT calculations indicate a σ-Ta− Ta interaction. Complexes 5, 6, and 8 undergo trans−cis isomerization, and mechanistic proposals are discussed based on DFT calculations.Ministerio de Economía y Competitividad Universidad de Alcal

Synthesis and Characterization of Cyclopentadienyl Sulfur Niobium Complexes

A trimetallic sulfide cluster [Nb3(η5-C5Me5)3Cl3(μ3-Cl)(μ-S)3(μ3-S)] (2) has been synthesized from the reaction of [Nb(η5-C5Me5)Cl4] (1) with (Me3Si)2S in a 4:3 ratio by the release of SiClMe3. The trinuclear nature of complex 2 has been established by single crystal X-ray diffraction analysis. Thermal treatment of 2 with SiH3Ph generated the dinuclear niobium(IV) complex [Nb2(η5-C5Me5)2Cl2(μ-S)2] (3) in a quantitative way. Likewise, one-pot syntheses of 3 has been developed from reaction of 1, (Me3Si)2S, and SiH3Ph in toluene. A series of dinuclear sulfide niobium(IV) derivatives [Nb2(η5-C5Me5)2R2(μ-S)2] (R = Me 4, Et 5, CH2SiMe3 6, C3H5 7, CH2Ph 8, nBu 9) can easily be obtained from the reaction of 3 with 2 equiv of the corresponding alkylating reagents. Single crystal X-ray diffraction analyses of 6 and 7 showed in all cases a trans disposition of the substituents.Ministerio de Ciencia, Innovación y Universidades. Universidad de Alcalá

El aprendizaje activo del alumno mediante una metodología participativa en el aula

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