Cyclic Bis‐alkylidene Complexes of Titanium and Zirconium: Synthesis, Characterization, and Reaction

• Published in: Chemistry : a European journal Vol. 26; no. 69; pp. 16472 - 16479
• Main Authors: Zhang, Yongliang, Wu, Botao, Zhong, Mingdong, Zhang, Wen‐Xiong, Xi, Zhenfeng
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 09.12.2020
• Subjects: Alkylidene; alkylidenes; Azo compounds; Carbon; Chemical synthesis; Chemistry; cyclic bis-carbene complexes; Cycloaddition; Electrons; group 4 metals; Heavy metals; metallacycles; metallacyclopentatriene; Metals; Organic chemistry; Organometallic compounds; Titanium; Zirconium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202003240

Transition‐metal alkylidenes have exhibited wide applications in organometallic chemistry and synthetic organic chemistry, however, cyclic Schrock‐carbene‐like bis‐alkylidenes of group 4 metals with a four‐electron donor from an alkylidene have not been reported. Herein, the synthesis and characterization of five‐membered cyclic bis‐alkylidenes of titanium (4 a,b) and zirconium (5 a,b) are reported, as the first well‐defined group 4 metallacyclopentatrienes, by two‐electron reduction of their corresponding titana‐ and zirconacyclopentadienes. DFT analyses of 4 a show a four‐electron donor (σ‐donation and π‐donation) from an alkylidene carbon to the metal center. The reaction of 4 a with N,N′‐diisopropylcarbodiimide (DIC) leads to the [2+2]‐cycloaddition product 6. Compound 4 a reacted with CO, affording the oxycyclopentadienyl titanium complex 7. These reactivities demonstrate the multiple metal–carbon bond character. The reactions of 4 a or 5 a with cyclooctatetraene (COT) or azobenzene afforded sandwich titanium complex 8 or diphenylhydrazine‐coordinated zirconacyclopentadiene 9, respectively, which exhibit two‐electron reductive ability. In for a Schrock: The synthesis and characterization of five‐membered cyclic Schrock‐carbene‐like bis‐alkylidenes of titanium and zirconium are realized. These Schrock‐carbene‐like bis‐alkylidenes show unique reactivity toward N,N′‐diisopropylcarbodiimide, CO, cyclooctatetraene, and azobenzene.