Selective propargylic C(sp3)–H activation of methyl-substituted alkynes versus [2 + 2] cycloaddition at a titanium imido template

The reaction of the titanium imido complex 1b with 2-butyne leads to the formation of the titanium azadiene complex 2a at ambient temperature instead of yielding the archetypical [2 + 2] cycloaddition product (titanaazacyclobutene) which is usually obtained by combining titanium imido complexes and internal alkynes. The formation of 2a is presumably caused by an initial propargylic C(sp³)–H activation step and quantum chemical calculations suggest that the outcome of this unexpected reactivity is thermodynamically favored. The previously reported titanaazacyclobutene I (which is obtained by reacting 1b with 1-phenyl-1-propyne) undergoes a rearrangement reaction at elevated temperature to give the corresponding five-membered titanium azadiene complex 2b.

An unexpected reactivity between a titanium imido complex and internal alkynes was unveiled yielding titanaazacyclobutenes instead of the expected [2 + 2] cycloaddition products.     

Stereoselective Synthesis of Tertiary Allylic Amines by Titanium-Catalyzed Hydroaminoalkylation of Alkynes with Tertiary Amines

Intermolecular hydroaminoalkylation reactions of symmetrical and unsymmetrical alkynes with tertiary amines take place in the presence of catalytic amounts of TiBn₄, Ph₃C[B(C₆F₅)₄], and a sterically demanding aminopyridinato ligand precursor. The resulting products, synthetically and pharmaceutically useful tertiary β,γ-disubstituted allylic amines, are formed in convincing yields and with excellent stereoselectivity. Particularly promising for future applications is the fact that even the industrial side product trimethylamine can be used as a substrate.     

Thin-layer chromatography of green leaves extracts: Zinc migrates into pheophytin on TLC silica plates with fluorescence indicator (F254)

JPC – Journal of Planar Chromatography – Modern TLC -     

Ring-Opening Metathesis Polymerization of Cyclooctyne Employing Well-Defined Tungsten Alkylidyne Complexes

Summary: The ring-opening metathesis polymerization of cyclooctyne was studied was studied in the presence of catalytic amounts of the tungsten alkylidyne complexes [RCW(NIm^tBu){OCMe(CF₃)₂}₂] ( 1a: R = CMe₃, 1b: R = Ph). The resulting polymers show relatively narrow polydispersities with the PDI ranging from 1.2 to 2.4. Treatment of 1b with cyclooctyne in dilute toluene or hexane solution afforded only low molecular weight oligomers. The mass spectra of these oligomers indicate the existence of macrocycles of the formula [C(CH₂)₆C]_n (n = 3–9). In contrast, reactions at high substrate concentration led to mixtures of cyclic oligomers and linear polymers, which is probably a result of ring-chain equilibria, established in agreement with the Jacobson-Stockmayer theory of macrocyclization. In contrast, treatment of neat cyclooctyne with a catalytic amount of the catalyst produced medium molecular weight polymers in good yields.     

Rapid and Simple Isolation of the Crystalline Molybdenum-Blue Compounds with Discrete and Linked Nanosized Ring-Shaped Anions: Na15[MoMoO462H14(H2O)70]0.5 [MoMoO457H14(H2O)68]0.5 · ca. 400 H2O and Na22[MoMoO442H14(H2O)58] · ca. 250 H2O

The blue mixed-crystal title compound Na₁₅[MoMoO₄₆₂H₁₄ (H₂O)₇₀]_0.5[MoMoO₄₅₇H₁₄ · (H₂O)₆₈]_0.5 · ca. 400 H₂O ≡ Na₁₅[ 1 a ]_0.5[ 1 b ]_0.5 · ca. 400 H₂O 1 , which crystallizes in the triclinic space group P 1 (a = 30.785(2), b = 32.958(2), c = 47.318(3) Å, α = 90.53(1), β = 89.86(1), γ = 96.85(1)°, V = 47665(6) ų, Z = 2, D_calc = 2.149 g cm^–3), precipitates within one day when an acidic (pH ≈ 1) aqueous solution of sodium molybdate (because of the extremely high solubility of the reaction product used in relatively high concentration) is reduced by sodium dithionite. 1 contains hitherto unknown pure molybdenum-oxide based, nanosized, ring-shaped, crystallographically independent cluster anions of the type {Mo₁₅₄} 1 a and {Mo₁₅₂} 1 b , the lacunary-type analogue of 1 a . Using the same reducing agent but in the presence of a reagent with a high affinity to the specific {Mo₂}-type building unit (also a leaving group) of 1 a , such as formic acid, the compound Na₂₂[MoMoO₄₄₂H₁₄(H₂O)₅₈] · ca. 250 H₂O 2 (space group P 1, a = 24.724(1), b = 35.726(2), c = 44.608(3) Å, α = 93.25(1), β = 93.51(1), γ = 106.72(1)°, V = 37552(4) ų, Z = 2, D_calc = 2.401 g cm^–3) is obtained in which the giant rings, having four missing {Mo₂} units compared to 1 a , are linked to chains. Until now, similar chain-type compounds could only be obtained using a non-well-defined synthetic method.