β‑H Abstraction/1,3‑CH Bond Addition as a Mechanism for the Activation of CH Bonds at Early Transition Metal Centers

This article describes the generalization of an overlooked mechanism for CH bond activation at early transition metal centers, namely 1,3‑CH bond addition at an η²-alkene intermediate. The X-ray-characterized [Cp₂Zr­(<i>c</i>-C₃H₅)₂] eliminates cyclo­propane by a β‑H abstraction reaction to generate the transient η²-cyclo­propene [Cp₂Zr­(η²-<i>c</i>-C₃H₄)] intermediate <b>A</b>. <b>A</b> rapidly cleaves the CH bond of furan and thiophene to give the furyl and thienyl complexes [Cp₂Zr­(<i>c</i>-C₃H₅)­(2-C₄H₃X)] (X = O, S), respectively. Benzene is less cleanly activated. Mechanistic investigations including kinetic studies, isotope labeling, and DFT computation of the reaction profile all confirm that rapid stereo­specific 1,3‑CH bond addition across the Zr­(η²-alkene) bond of <b>A</b> follows the rate-determining β‑H abstraction reaction. DFT computations also suggest that an α‑CC agostic rotamer of [Cp₂Zr­(<i>c</i>-C₃H₅)₂] assists the β‑H abstraction of cyclo­propane. The nature of the α‑CC agostic interaction is discussed in the light of an NBO analysis

β‑H Abstraction/1,3‑CH Bond Addition as a Mechanism for the Activation of CH Bonds at Early Transition Metal Centers

This article describes the generalization of an overlooked mechanism for CH bond activation at early transition metal centers, namely 1,3‑CH bond addition at an η²-alkene intermediate. The X-ray-characterized [Cp₂Zr­(<i>c</i>-C₃H₅)₂] eliminates cyclo­propane by a β‑H abstraction reaction to generate the transient η²-cyclo­propene [Cp₂Zr­(η²-<i>c</i>-C₃H₄)] intermediate <b>A</b>. <b>A</b> rapidly cleaves the CH bond of furan and thiophene to give the furyl and thienyl complexes [Cp₂Zr­(<i>c</i>-C₃H₅)­(2-C₄H₃X)] (X = O, S), respectively. Benzene is less cleanly activated. Mechanistic investigations including kinetic studies, isotope labeling, and DFT computation of the reaction profile all confirm that rapid stereo­specific 1,3‑CH bond addition across the Zr­(η²-alkene) bond of <b>A</b> follows the rate-determining β‑H abstraction reaction. DFT computations also suggest that an α‑CC agostic rotamer of [Cp₂Zr­(<i>c</i>-C₃H₅)₂] assists the β‑H abstraction of cyclo­propane. The nature of the α‑CC agostic interaction is discussed in the light of an NBO analysis

Chemo‑, Regio‑, and Stereoselective Silver-Catalyzed Aziridination of Dienes: Scope, Mechanistic Studies, and Ring-Opening Reactions

Silver complexes bearing trispyrazolylborate ligands (Tp^x) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = <i>p</i>-toluensulfonyl) units from PhINTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the CC bond is maintained in the aziridine product (<i>cis</i> or <i>trans</i>). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of β-amino alcohols have also been developed