Synthesis and Structure of Seven‐Membered Metallacycloalkynes

Suzuki, Noriyuki; Tsuchiya, Takashi; Aihara, Naoto; Iwasaki, Masakazu; Saburi, Masahiko; Chihara, Teiji; Masuyama, Yoshiro

doi:10.1002/ejic.201201245

Cited by 16 publications

(12 citation statements)

References 73 publications

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“…We employed hexapentaenes with cyclopentylidene ( 13c ), cyclohexylidene ( 13d ), and cycloheptylidene moieties ( 13e ). All of these compounds reacted with Cp 2 ZrCl 2 /Mg to give zirconacycles 14c – e in moderate to good yields (Scheme ) . These complexes 14c – e must show similar steric repulsion between their methyl groups and cyclopentadienyl rings to those of 14b .…”

Section: Resultsmentioning

confidence: 99%

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Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

et al. 2014

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Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts. Some [5]cumulene compounds reacted with zirconocene(II) species to afford 1-zirconacyclopent-3-yne complexes that have five-membered cycloalkyne structures. Only a few [5]cumulene compounds afforded η 2 -coordinated complexes in the presence of neutral ligands such as trimethylphosphine and tert-butyl isocyanide. Interconversion between the five-membered structure and the η 2 -complex was observed. Investigation of [5]cumulene derivatives of various cycloalkylidene moieties indicated that the η 2 -complex was preferred when the [5]cumulene has bulkier substituents. A [5]cumulene with 2,2,6,6-tetramethylcyclohexylidene groups much preferred the 1-zirconacyclopent-3-yne structure to η 2 -coordination. In sharp contrast, the η 2 -coordinated complex was favored for a [5]cumulene with 2,2,7,7-tetramethylcycloheptylidene groups in the presence of PMe 3 . Small differences in steric environments caused totally different reactivity in [5]cumulene complexes. DFT calculations on the formation enthalpy were consistent with the experimental results, although that cannot fully rationalize the difference.

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Section: Resultsmentioning

confidence: 99%

“… a Ref . b C3–C3* bond distance. c C2–Zr–C2* angle. d C2–C3–C3* angle. e Average values of two pseudoequivalent bonds in two independent molecules are shown. …”

Section: Resultsmentioning

confidence: 99%

Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

et al. 2014

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“…Yield: 0.113 g, 96%. 1 Synthesis of ( Ket guan)(Im Dipp N)Ti(S) (14). To a thawing solution of 1 (0.100 g, 0.104 mmol) in benzene (5 mL) was added SPPh 3 (0.031 g, 0.104 mmol) in one portion.…”

Section: ■ Summarymentioning

confidence: 99%

“…Accordingly, these metals are routinely utilized as potent Lewis acid activators or catalysts in preparative organic chemistry such as in Friedel–Crafts and Diels–Alder reactions. , On the industrial scale, the early metals are widely known for their utility in Ziegler–Natta catalysis for the polymerization of olefins such as ethylene . However, the chemistry of low-valent early metals (LVEMs), as defined by electron counts ≥ d 2 , is accessible and plays a critical role in a number of practical chemical transformations. , LVEMs have been utilized in natural product syntheses, − can induce the coupling and cyclization of alkenes and alkynes, ,− and are especially adept at McMurry and Pinacol reductive aldehyde and ketone coupling reactions. ,− …”

Section: Introductionmentioning

confidence: 99%

Redox Character and Small Molecule Reactivity of a Masked Titanium(II) Synthon

et al. 2019

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The two-electron reduction of the Ti(IV) guanidinate (Ketguan)(ImDippN)Ti(OTf)2 (2 OTf ) (Ketguan = [( t Bu2CN)C(NDipp)2]−; ImDippN– = 1,3-bis(Dipp)imidazolin-2-iminato; Dipp = 2,6-diisopropylphenyl) with an excess of KC8 generates the masked complex (Ketguan)(η6-ImDippN)Ti (1). Conversely, reduction of the chloride analogue (Ketguan)(ImDippN)TiCl2 (2 Cl ) with an excess of Na/Hg amalgam produces the Ti(III) compound (Ketguan)(ImDippN)TiCl (3), while treatment of 2 Cl with 3.0 equiv of KC8 affords a complicated mixture from which (ImDippN)(DippN)[η2-( t Bu2C)NC(NDipp)](THF)Ti (4) is isolated as the product of reductive ligand cleavage. These results clearly indicate that the success of early metal reduction chemistry is highly sensitive to the halide coligands and reaction conditions. Complex 1, despite possessing a Ti(IV) canonical form, behaves as a Ti(II) synthon and appreciable reducing agent. For instance, 1 effects the one-electron reduction of benzophenone and pyridine to give the Ti(III) products (Ketguan)(ImDippN)Ti(η1-OC·Ph2) (6) and [(Ketguan)(ImDippN)Ti]2[μ2-(NC5H5–H5C5N)] (7), providing an approximate chemical redox potential range for 1 between ca. −2.3 to −3.1 V (vs [Cp2Fe]0/+). Additionally, treatment of 1 with π-acids such as CNCy (Cy = cyclohexyl) or NC t Bu leads to the formation of the Ti(III) and Ti(IV) products (Ketguan)(ImDippN)Ti(CN)(CNCy) (9) and (ImDippN)[(DippN)(2- i PrC6H3-6-(η1-CH3CHCH2)N)C(NC t Bu2)]Ti[NC(H) t Bu] (10), respectively, via reduction of the π-acid substrate. The two-electron reduction proclivity of 1 is demonstrated by its reactivity with chalcogen sources (e.g., N2O) and organoazides to give the Ti(IV) products (Ketguan)(ImDippN)Ti(E) (E = O (13), S (14), Se (15), S2 (16), NSiMe3 (17), NAd (18)). In addition to illustrating the versatile Ti(II) synthon character of 1, the synthesis of these compounds shows that the 3N-coordinated [(Ketguan)(ImDippN)Ti] n+ manifold can readily accommodate metal–ligand multiple bonds, including relatively rare examples of terminally bound TiS and TiSe bonds. Taken altogether, the redox chemistry of 1, as a Ti(II) synthon, clearly shows the chemical diversity of low-valent early metals (LVEMs) and their ability to reductively activate a wide range of substrates.

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“…In the last decades, there has been increasing interest in the chemistry of strained metallacycles containing a triple CC bond or cumulated double CC bonds in the ring (see, e.g., refs − ). A remarkable property of these metallacycles is their surprisingly high thermal stability compared with the corresponding purely organic analogues.…”

Section: Introductionmentioning

confidence: 99%

Interaction of the Buchwald Seven-Membered Zirconacyclocumulene Complex with Carbonyl Compounds

et al. 2019

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The interaction of the Buchwald seven-membered zirconacyclocumulene Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )− C(C 2 SiMe 3 )=CSiMe 3 ] (1) with a 2-fold excess of benzophenone in toluene at 100 °C for 20 h results in the formation of Me 3 SiCC−CCSiMe 3 and a nine-membered dioxazirconacycle Cp 2 Zr[η 2 -OC(Ph) 2 C(SiMe 3 )C 2 C(SiMe 3 )C(Ph) 2 O] (5) containing [3]cumulene group in the ring. Analogous metallacycle (6) is formed on heating of 1 with fluorenone in toluene at 100 °C. A treatment of 5 with HCl in dioxane at 20 °C affords Cp 2 ZrCl 2 and cis-[3]cumulenic diol Ph 2 (HO)C(Me 3 Si)-CC 2 C(SiMe 3 )C(OH)Ph 2 (7) in 85% yield. The reaction of 1 with benzil (PhCO) 2 at 80 °C in benzene proceeds differently than with benzophenone and fluorenone. In this case, a nine-membered dioxazirconacycle Cp 2 Zr[η 2 -Me 3 SiCC(C 2 SiMe 3 )− C(SiMe 3 )C(C 2 SiMe 3 )OC(Ph)C(Ph)O] ( 10) is produced. The nature of products formed in the interaction of 1 with acenaphthenequinone proved to be temperature dependent. Thus, on carrying out the reaction at 20 °C, an 11-membered trioxazirconacycle (11) containing three CC bonds in the ring was isolated from the mixture, whereas at 80 °C the reaction gave a ten-membered tetraoxadizirconacycle (12) and octasubstituted cyclooctatetraene [(Me 3 Si)CC(CCSiMe 3 )] 4 (13). The structures of 5−7 and 10−13 have been determined by X-ray diffraction. The mechanism of the reactions found is discussed.

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Synthesis and Structure of Seven‐Membered Metallacycloalkynes

Cited by 16 publications

References 73 publications

Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

Redox Character and Small Molecule Reactivity of a Masked Titanium(II) Synthon

Interaction of the Buchwald Seven-Membered Zirconacyclocumulene Complex with Carbonyl Compounds

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