Alkyne [2 + 2 + 2] Cyclotrimerization Catalyzed by a Low-Valent Titanium Reagent Derived from CpTiX3 (X = Cl, O-i-Pr), Me3SiCl, and Mg or Zn

Okamoto, Sentaro; Yamada, Takeshi; Tanabe, Yuki; Shimizu, Masaki

doi:10.1021/acs.organomet.8b00678

Cited by 20 publications

(21 citation statements)

References 118 publications

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“…By comparison, the use of monocyclopentadienyltitanium(III) halides [Ti(η 5 -C 5 R 5 )X 2 ] in organic synthesis has remained almost unexplored, although these derivatives have been known for decades . Nevertheless, half-sandwich titanium(III) species are receiving increasing attention as catalyst in organic synthesis . In particular, [Ti(η 5 -C 5 Me 5 )Cl 2 ] has been recently proposed as the active species in several radical processes, although the aggregated structure of this compound remains unknown in the literature .…”

Section: Introductionmentioning

confidence: 99%

The Puzzling Monopentamethylcyclopentadienyltitanium(III) Dichloride Reagent: Structure and Properties

et al. 2019

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Following the track of the useful titanocene [Ti( 5 -C5H5)2Cl] reagent in organic synthesis, the related half-sandwich titanium(III) derivatives [Ti( 5 -C5R5)Cl2] are receiving increasing attention in radical chemistry of many catalyzed transformations. However, the structure of the active titanium(III) species remains unknown in the literature. Herein, we describe the synthesis, crystal structure, and electronic structure of titanium( III) aggregates of composition [{Ti( 5 -C5Me5)Cl2}n]. The thermolysis of [Ti( 5 -C5Me5)Cl2Me] (1) in benzene or hexane at 180 ºC results in the clean formation of [{Ti( 5 -C5Me5)Cl(-Cl)}2] (2), methane and ethene. The treatment of 1 with excess pinacolborane in hexane at 65 ºC leads to a mixture of 2 and the paramagnetic trimer [{Ti( 5 -C5Me5)(-Cl)2}3] (3). The Xray crystal structures of compounds 2 and 3 show Ti-Ti distances of 3.267(1) and 3.219(12) Å, respectively. Computational studies (CASPT2//CASSCF and BS DFT methods) for dimer 2 reveal a singlet ground state and a relatively large singlet-triplet energy gap. Nuclear magnetic resonance (NMR) spectroscopy of 2 in aromatic hydrocarbon solutions and DFT calculations for several [{Ti( 5 -C5Me5)Cl2}n] aggregates are consistent with the existence of an equilibrium between the diamagnetic dimer [{Ti( 5 -C5Me5)Cl(-Cl)}2] and a paramagnetic tetramer [{Ti( 5 -C5Me5)(-Cl)2}4] in solution. In contrast, complex 2 readily dissolves in tetrahydrofuran to give a green-blue solution from which blue crystals of the mononuclear adduct [Ti( 5 -C5Me5)Cl2(thf)] (4) were grown.

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Section: Introductionmentioning

confidence: 99%

The Puzzling Monopentamethylcyclopentadienyltitanium(III) Dichloride Reagent: Structure and Properties

et al. 2019

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“…Reactions performed at lower temperatures (80 or 100 °C) afforded no naphthalene product; however, evolution of stoichiometric amounts of benzene signaled that β-hydrogen abstraction of Cp* 2 ZrPh 2 did occur. Moreover, low-valent Ti is competent for trimerization under mild conditions . Thus, the high reaction temperature may be more readily associated with the barrier for the generation of an active Ti II species.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, low-valent Ti is competent for trimerization under mild conditions. 39 Thus, the high reaction temperature may be more readily associated with the barrier for the generation of an active Ti II species. Notably, 2 is furnished in good yield at 1 mol % catalyst loading, while similar reactions employing Ni or Pd catalysts require 10 mol % catalyst loading to achieve comparable yields.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Group 4 Diarylmetallocenes as Bespoke Aryne Precursors for Titanium-Catalyzed [2 + 2 + 2] Cycloaddition of Arynes and Alkynes

Reiner

Tonks

2019

Inorg. Chem.

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Despite the ubiquity of reports describing titanium (Ti)-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes, the incorporation of arynes into this potent manifold has never been reported. The in situ generation of arynes often requires fluoride, which instead will react with the highly fluorophilic Ti center, suppressing productive catalysis. Herein, we describe the use of group 4 diarylmetallocenes, Cp R 2 MAr 2 (Cp R = C 5 H 5 , C 5 Me 5 ; M = Ti, Zr), as aryne precursors for the Ticatalyzed synthesis of substituted naphthalenes via coupling with 2 equiv of an alkyne. Fair-togood yields of the desired naphthalene products could be obtained with 1% catalyst loadings, which is roughly an order of magnitude lower than similar reactions catalyzed by palladium or nickel. Additionally, naphthalenes find broad applications in the electronics, photovoltaics, and pharmaceutical industries, urging the discovery of more economic syntheses. These results indicate that aryne transfer from a Cp R 2 M(η 2-aryne) complex to another metal is a viable route for the introduction of aryne fragments into organometallic catalytic processes.

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“…In 2017, Okamoto and co-workers demonstrated that low-valent titanium species catalyzed the [2+2+2] cycloadditions of alkynes using CpTi(Oi-Pr) 3 , CpTiCl 3 , or Ti(Oi-Pr) 4 combined with Mg or Zn powder as metal reductant in the presence of Me 3 SiCl that played a crucial role for the cycloaddition to proceed (Scheme 2). 62 Inter-, partially intra-, and intramolecular alkyne cyclotrimerization can be accomplished in THF (0.5 M) at 40-45 °C for 12-20 h. Under these optimized reaction conditions, the corresponding 1,3,5-and 1,2,4-trisubstituted benzenes were obtained as a mixture of regioisomers (up to 41:59) in 16-85% yield.…”

Section: Cyclotrimerization Of Alkynesmentioning

confidence: 99%

Recent Progress in Metal-Catalyzed [2+2+2] Cycloaddition Reactions

Matton¹,

Huvelle²,

Haddad³

et al. 2021

Synthesis

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Metal-catalyzed [2+2+2] cycloaddition is a powerful tool that allows rapid construction of functionalized 6-membered carbo- and heterocycles in a single step through an atom-economical process with high functional group tolerance. The reaction is usually regio- and chemoselective although selectivity issues can still be challenging for intermolecular reactions involving the cross-[2+2+2] cycloaddition of two or three different alkynes and various strategies have been developed to attain high selectivities. Furthermore, enantioselective [2+2+2] cycloaddition is an efficient means to create central, axial, and planar chirality and a variety of chiral organometallic complexes can be used for asymmetric transition-metal-catalyzed inter- and intramolecular reactions. This review summarizes the recent advances in the field of [2+2+2] cycloaddition.1 Introduction2 Formation of Carbocycles2.1 Intermolecular Reactions2.1.1 Cyclotrimerization of Alkynes2.1.2 [2+2+2] Cycloaddition of Two Different Alkynes2.1.3 [2+2+2] Cycloaddition of Alkynes/Alkenes with Alkenes/Enamides2.2 Partially Intramolecular [2+2+2] Cycloaddition Reactions2.2.1 Rhodium-Catalyzed [2+2+2] Cycloaddition2.2.2 Molybdenum-Catalyzed [2+2+2] Cycloaddition2.2.3 Cobalt-Catalyzed [2+2+2] Cycloaddition2.2.4 Ruthenium-Catalyzed [2+2+2] Cycloaddition2.2.5 Other Metal-Catalyzed [2+2+2] Cycloaddition2.3 Totally Intramolecular [2+2+2] Cycloaddition Reactions3 Formation of Heterocycles3.1 Cycloaddition of Alkynes with Nitriles3.2 Cycloaddition of 1,6-Diynes with Cyanamides3.3 Cycloaddition of 1,6-Diynes with Selenocyanates3.4 Cycloaddition of Imines with Allenes or Alkenes3.5 Cycloaddition of (Thio)Cyanates and Isocyanates3.6 Cycloaddition of 1,3,5-Triazines with Allenes3.7 Cycloaddition of Aldehydes with Enynes or Allenes/Alkenes3.8 Totally Intramolecular [2+2+2] Cycloaddition Reactions4 Conclusion

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Alkyne [2 + 2 + 2] Cyclotrimerization Catalyzed by a Low-Valent Titanium Reagent Derived from CpTiX₃ (X = Cl, O-i-Pr), Me₃SiCl, and Mg or Zn

Cited by 20 publications

References 118 publications

The Puzzling Monopentamethylcyclopentadienyltitanium(III) Dichloride Reagent: Structure and Properties

The Puzzling Monopentamethylcyclopentadienyltitanium(III) Dichloride Reagent: Structure and Properties

Group 4 Diarylmetallocenes as Bespoke Aryne Precursors for Titanium-Catalyzed [2 + 2 + 2] Cycloaddition of Arynes and Alkynes

Recent Progress in Metal-Catalyzed [2+2+2] Cycloaddition Reactions

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