Formation of Homoleptic Tetracarbene versus cis-Chelating Dicarbene Complexes of Nickel(II) and Applications in Kumada–Corriu Couplings

✍ Scribed by Han Vinh Huynh; Ramasamy Jothibasu

• Book ID: 102168911
• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 182 KB
• Volume: 2009
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.200801149

✦ Synopsis

Abstract

The formation of mono‐ versus bis(chelate) Ni^II^ complexes bearing N‐heterocyclic dicarbene ligands can be controlled by the flexibility of the ligand bridge. A short methylene spacer exclusively gives rise to a dicationic bis(chelate) complex [Ni(^Me^CC^meth^)~2~]Br~2~ (1), whereas a more flexible propylene spacer affords a neutral monochelate complex [NiBr~2~(^Me^CC^prop^)] (2). Complex 2 was found to autoionize very slowly to the corresponding dicationic bis(chelate) over ca. 45 d in [D~6~]dmso. The formation of the bis‐ versus monochelate complex can be attributed to the different stabilities of the resulting metallacycles. The catalytic activity of monochelate 2 was tested in the Kumada–Corriu coupling of aryl halides with arylmagnesium reagents at ambient temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)