A systematic study on the synthesis, reactivity and structure of ortho-palladated aryloximes, including the first cyclopalladated aryloximato and iminoaryloxime complexes

Abstract

Complexes [Pd{C,N-Ar{C(Me)NOH}-2}(μ-Cl)]₂ (1) with Ar = C₆H₄, C₆H₃NO₂-5 or C₆H(OMe)₃-4,5,6, were obtained from the appropriate oxime, Li₂[PdCl₄] and NaOAc. They reacted with neutral monodentate C-, P- or N-donor ligands (L), with [PPN]Cl ([PPN] = Ph₃PNPPh₃), with Tl(acac) (acacH = acetylacetone), or with neutral bidentate ligands N⁁N (tetramethylethylenediamine (tmeda), 4,4′-di-tert-butyl-2,2′-bipyridine (^tBubpy)) in the presence of AgOTf or AgClO₄ to afford complexes of the types [Pd{C,N-Ar{C(Me)NOH}-2}Cl(L)] (2), [PPN][Pd{C,N-Ar{C(Me)NOH}-2}Cl₂] (3), [Pd{C,N-Ar{C(Me)NOH}-2}(acac)] (4) or [Pd{C,N-Ar{C(Me)NOH}-2}(N⁁N)]X (X = OTf, ClO₄) (5), respectively. Complexes 1 reacted with bidentate N⁁N ligands in the presence of a base to afford mononuclear zwitterionic oximato complexes [Pd{C,N-Ar{C(Me)NO}-2}(N⁁N)] (6). Dehydrochlorination of complexes 2 by a base yielded dimeric oximato complexes of the type [Pd{μ-C,N,O-Ar{C(Me)NO}-2}L]₂ (7). The insertion of XyNC into the Pd–C_aryl bond of complex 2 produced the mononuclear iminoaryloxime derivative [Pd{C,N-C(NXy)Ar{C(Me)NOH}-2}Cl(CNXy)] (8) which, in turn, reacted with [AuCl(SMe₂)] to give [Pd{μ-N,C,N-C(NXy)Ar{C(Me)NOH}-2}Cl]₂ (9) with loss of XyNC. Some of these complexes are, for any metal, the first containing cyclometalated aryloximato (6, 7) or iminoaryloxime (8, 9) ligands. Various crystal structures of complexes of the types 2, 3, 6, 7, 8 and 9 have been determined.