Synthesis of NHC complexes by template controlled cyclization of beta-functionalized isocyanides.

Flores-Figueroa A., Kaufhold O., Feldmann K. O., Hahn F. E.

Abstract

Starting from complexes of type [Ru(Cp)Cl(P-P)] (P-P = 2PPh3, 3a; P-P = 2PMe3, 3b: P-P = dppe, 3c; P-P = dppp, 3d) isocyanide complexes [Ru(Cp)(P-P)(CNR) 4a-4d (CNR = CN-CH2-CH2N3, 1) and 7a-7d (CN-C6H4-2N3, 2) have been prepared. Reduction of the azido functions of the coordinated isocyanide ligands with Zn/NH4Cl/H2O in methanol leads to coordinated 2-amino functionalized isocyanides which cyclize to yield the complexes with a saturated NH,NH-stabilized NHC ligand 5a-5d or a benzannulated NH,NH-stabilized NHC ligand 8a-8d. The Zn/NH4Cl/H2O reduction method is of general applicability and allowed the generation of complex 11 bearing three saturated NH,NH-stabilized NHC ligands.