Multiple and Highly Selective Alkyne-Isonitrile C−C and C−N Couplings at Group 4 Metallocenes

• Published in: Chemistry : a European journal Vol. 22; no. 27; pp. 9169 - 9180
• Main Authors: Altenburger, Kai, Arndt, Perdita, Becker, Lisanne, Reiß, Fabian, Burlakov, Vladimir V., Spannenberg, Anke, Baumann, Wolfgang, Rosenthal, Uwe
• Format: Journal Article
• Language: English
• Published: WEINHEIM Blackwell Publishing Ltd 27.06.2016; Wiley
• Subjects: alkynes; Chemistry; Chemistry, Multidisciplinary; C−C coupling reactions; fused-ring systems; isocyanide; metallocenes; Physical Sciences; Science & Technology; fused-ring systems; NITRILE-NITRILE; C-C coupling reactions; CRYSTAL-STRUCTURE; alkynes; REACTIVITY; KETENIMINE COMPLEXES; isocyanide; metallocenes; H ACTIVATION; METAL-HETEROALLENE COMPLEXES; LIGANDS; MIGRATORY INSERTION; ZR; ISOCYANIDE INSERTION; C−C coupling reactions
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201601465

Reactions of the group 4 metallocene alkyne complexes [Cp′2M(η2‐Me3SiC2SiMe3)] [Cp′2=rac‐(ebthi)=rac‐1,2‐ethylene‐1,1′‐bis(η5‐tetrahydroindenyl): M=Ti, Zr, Hf; Cp′2=Cp*2 (Cp*=η5‐pentamethylcyclopentadienyl): M=Zr] with 2,6‐dimethylphenyl isocyanide (2‐xylyl isonitrile, XyNC) were investigated. Depending on the metal, the Cp′ ligand, and/or the stoichiometry, as well as the reaction temperature and time, different products were obtained. The products included simple end‐on coordination compounds of XyNC in addition to those of the coupling of Me3SiC2SiMe3 with two, three, or four isonitriles to form enimine complexes, aza‐metallacycloallenes, and fused heterocyclic systems, respectively. One example of the latter tricyclic compounds was subject to demetalation by using HCl. Molecular structures of the heterometallacycles were determined by X‐ray crystallography. The interconversion of the products was investigated by 1H NMR spectroscopy. Selective but strange: The reactions of titano‐, zircono‐ and hafnocene alkyne complexes with 2‐xylyl isonitrile afford enamine complexes, aza‐metallacycloallenes, and/or fused heterometallacycles, depending on the metal, the Cp′ ligand, and the stoichiometry applied. The alkyne always takes part in the coupling reactions. Furthermore, the metallocene is successfully expelled from the tricyclic complex to yield a highly functionalized pyrrole.