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

The reaction of [PdI{ C,N- C(═NHXy)C 6 H 4 NH 2 -2}CNXy]TfO with XyNC (1:2, TfO = CF 3 SO 3, Xy = C 6 H 3 Me 2 -2,6) gives the cationic carbene complex [PdI{ C,C -C(═NHXy)C 6 H 4 {NHC(NHXy)}-2}CNXy]TfO ( 4 ), while that of [PdCl 2 {C(═NHXy)C 6 H 4 NH 2 -2}] with isocyanides (1:1, 50–60 °C) gives the neutral carbene complexes [PdCl 2 { C,C -C(═NHXy)C 6 H 4 {NHC(NHR)}-2}] (R = t Bu ( 8 ), Xy ( 9 )), from which mono- and dicationic derivatives [PdCl{ C,C -C(═NHXy)C 6 H 4 {NHC(NHXy)}-2}L]X (L = XyNC, X = TfO ( 10 ); L = PPh 3, X = Cl ( 11 )) and [Pd{ C,C -C(═NHXy)C 6 H 4 {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 NEt 3 (1:1) affords the dinuclear complexes [(PdX) 2 {μ- N, C,C -C(═NXy)C 6 H 4 {NHC(NHXy)}-2} 2 ] (X = OAc ( 13 ), Cl ( 14 )), which in turn react with PPh 3 to give [PdX{ C,C -C(═NXy)C 6 H 4 {NHC(NHXy)}-2}PPh 3 ] (X = OAc ( 15 ), Cl ( 16 )). Oxidative addition of 2-iodobenzoic acid to 13 leads to the Pd(IV) complex [{PdI(C 6 H 4 CO 2 -2)} 2 {μ- N, C,C -C(═NXy)C 6 H 4 {NHC(NHXy)}-2} 2 ] ( 17 ), while the reaction of 14 with PhICl 2 affords the Pd(III) derivative [(PdCl 2 ) 2 {μ- N, C,C -C(═NXy)C 6 H 4 {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.