Synthesis of Palladium(II), -(III), and -(IV) Complexes with Acyclic Diaminocarbene Ligands

The reaction of [PdI­{C,N-C­(NHXy)­C6H4NH2-2}­CNXy]­TfO with XyNC (1:2, TfO
= CF3SO3, Xy = C6H3Me2-2,6) gives the cationic carbene complex [PdI­{C,C-C­(NHXy)­C6H4{NHC­(NHXy)}-2}­CNXy]­TfO
(4), while that of [PdCl2{C­(NHXy)­C6H4NH2-2}] with isocyanides (1:1, 50–60
°C) gives the neutral carbene complexes [PdCl2{C,C-C­(NHXy)­C6H4{NHC­(NHR)}-2}]
(R = tBu (8), Xy (9)), from which
mono- and dicationic derivatives [PdCl­{C,C-C­(NHXy)­C6H4{NHC­(NHXy)}-2}­L]­X (L = XyNC, X = TfO (10); L = PPh3, X = Cl (11)) and [Pd­{C,C-C­(NHXy)­C6H4{NHC­(NHXy)}-2}­(CNXy)2]­(TfO)2 (12), respectively, have been
isolated. Dehydrochlorination of complex 9 with TlTfO
and NaOAc (1:2:2) or with NEt3 (1:1) affords the dinuclear
complexes [(PdX)2{μ-N,C,C-C­(NXy)­C6H4{NHC­(NHXy)}-2}2] (X = OAc (13), Cl (14)), which in turn
react with PPh3 to give [PdX­{C,C-C­(NXy)­C6H4{NHC­(NHXy)}-2}­PPh3] (X = OAc (15), Cl (16)). Oxidative addition of 2-iodobenzoic
acid to 13 leads to the Pd­(IV) complex [{PdI­(C6H4CO2-2)}2{μ-N,C,C-C­(NXy)­C6H4{NHC­(NHXy)}-2}2] (17), while the reaction of 14 with PhICl2 affords the Pd­(III) derivative [(PdCl2)2{μ-N,C,C-C­(NXy)­C6H4{NHC­(NHXy)}-2}2] (18). The crystal structures of 4, 9, and 12 have been determined, and the atomic
connectivity in 18 has been established.