Synthesis of NHC complexes by template controlled cyclization of β-functionalized isocyanides

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.