The first thermally stable half-sandwich titanium zwitterionic complex

Pinkas, Jiřı́; Varga, Vojtěch; Cı́sařová, Ivana; Kubišta, Jiřı́; Horáček, Michal; Mach, Karel

doi:10.1016/j.jorganchem.2007.01.022

Cited by 10 publications

(17 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…On the other hand, cases in which the three hydrogen atoms of a CH 3 -R group are simultaneously involved in agostic bonding with a same metallic center, were reported or proposed in the literature. 81,82 Thus, a topological description of multiple s C-H intermolecular agostic bonding is needed.…”

Section: Characterization Of Double R-bh 2 and R-ch 2 Interactions With A Metallic Centermentioning

confidence: 99%

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Zins

Silvi

Alikhani

2015

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes.

show abstract

Section: Characterization Of Double R-bh 2 and R-ch 2 Interactions With A Metallic Centermentioning

confidence: 99%

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Zins

Silvi

Alikhani

2015

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…The system for Cp′ = Cp* and OR′ = OSi(CH 2 CH 2 SiMePh 2 ) 3 also generated the zwitterionic [Cp*Ti(OR′)(Me)] (+) [MeB(C 6 F 5 ) 3 ] (−) complex in solution, which decomposed at room temperature with t 1/2 ≈ 48 h to give two decomposition products, the same as in the preceding case . Similar decomposition reactions were also acting in a recently attempted synthesis of dialkoxo-bridged cyclopentadienylsiloxo titanium cationic complexes. , Surprisingly, the lowest stability for complexes of this type was noticed for the expected [Cp*Ti(O t Bu)(Me)] (+) [MeB(C 6 F 5 ) 3 ] (−) complex, which decomposed immediately after mixing its precursors . The complete elimination of isobutene however indicated a different decomposition pathway …”

Section: Introductionmentioning

confidence: 58%

“…The application of the C 6 F 5 or OC 6 F 5 ligands as poor π-electron donor OR′ moieties yielded thermally unstable zwitterionic complexes with B(C 6 F 5 ) 3 . The only half-sandwich alkoxytitanium complexes of this type characterized in the solid state were the catalytically inactive zwitterionic dialkoxy complexes [Cp*Ti(OR′) 2 ] (+) [MeB(C 6 F 5 ) 3 ] (−) where R′ = t Bu or i Pr . Their X-ray crystal structures showed that the methyl carbon atom was σ-bonded to boron, and hydrogen atoms of the methyl group exerted an agostic interaction with the titanium atom, similarly to that known for zirconocene zwitterionic complexes …”

Section: Introductionmentioning

confidence: 96%

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

et al. 2009

Self Cite

View full text Add to dashboard Cite

Reaction of [(η5-C5Me5)TiMe3] with [(c-C5H9)7Si8O12(OH)] (SIPOSS) or [(c-C5H9)7Si7O9(OSiMe3)(OH)2)] (DIPOSS′) affords stoichiometrically the half-sandwich titanium-disiloxy-methyl complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2TiMe] (1) and [(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}TiMe] (2), respectively. Compound 2 consists of the two stereoisomers possessing the (η5-C5Me5) ligand and OSiMe3 group in syn- (2a) and anti-position (2b). The more abundant 2a (2a/2b ≈ 2:1) was isolated by fractional crystallization. Compounds 1 and 2a reacted rapidly with B(C6F5)3 to give zwitterionic complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2Ti](+)[(μ-Me)B(C6F5)3](−) (3) and syn-[(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}Ti](+)[(μ-Me)B(C6F5)3](−) (4a), respectively. Infrared spectra proved that 3 and 4a were thermally stable in the solid state, and the structure of 4a was determined by X-ray single-crystal analysis. In contrast, 1H, 13C, and 19F NMR spectra of 3 in toluene C7D8 revealed that it was completely dissociated into initial components at 25 °C; however, the features of 3 were dominating already at −35 °C. On the other hand, 4a was dissociated only slightly at 25 °C. Stable ionic complexes 7 and 8 were prepared by reacting [PhNHMe2]+[B(C6F5)4]− with 1 and 2, respectively. Both 7 and 8 contained the molecule PhNMe2 coordinated to the titanium cation, and 8 consisted of the syn- and anti-isomers 8a and 8b in abundances found for 2a/2b. Analogous reaction of 1 and 2 with [Ph3C]+[B(C6F5)4]− afforded impure ionic complexes 9 and 10. When dissolved in the presence of PhNMe2, the amine coordinated to the titanium cations, thus reproducing complexes 7 and 8a/8b, identified by 1H NMR spectra. All compounds 1−10 were inactive in polymerization of styrene to syndiotactic polymer. A low activity was achieved by adding of 2 equiv of AlMe3 to 3 or 4.

show abstract

“…These data provide evidence that the requirements defining metal–hydrogen agostic bond formation, namely, a comparable distance of Ti–C β and Ti–H and a Ti–C β –H angle smaller than 100°, are all fulfilled. The Ti–H distance below 2.0 Å and the Ti–C β –H angle close to 55° indicate the presence of a strong agostic Ti–H bond in comparison with the known Ti(III) compounds …”

Section: Resultsmentioning

confidence: 88%

Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

et al. 2014

Self Cite

View full text Add to dashboard Cite

Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1CCR2 into its Ti–H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1CCHR2)] (2a–e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti–H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a–4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RCC)2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a–2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1CCHR2)] 3a–3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a–3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d 8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a–4c, 5a, 6b, and 7.

show abstract

The first thermally stable half-sandwich titanium zwitterionic complex

Cited by 10 publications

References 45 publications

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

Contact Info

Product

Resources

About