title: A Readily Accessible Chiral NNN Pincer Ligand with a Pyrrole Backbone and Its Ni(II) Chemistry: Syntheses, Structural Chemistry, and Bond Activations.
abstract: A new class of chiral C2-symmetric N-donor pincer ligands, 2,5-bis(2-oxazolinyldimethylmethyl)pyrroles (PdmBox)H, was synthesized starting from the readily available ethyl 2,2-dimethyl-3-oxobutanoate (1). The synthesis of the ligand backbone was achieved by oxidative enole coupling with CuC12followed by Paal-Knorr-type pyrrole synthesis. The corresponding protioligands (RPdmBox)H (R = iPr: 5a; Ph: 5b) were obtained by condensation with amino alcohols and subsequent zinc-catalyzed cyclization. Reaction of the lithiated ligands with [NiCl2(dme)] yielded the corresponding square-planar nickel(II) complexes [(RPdmBox)NiCl] (6a/b). Salt metathesis of 6a with the corresponding alkali or cesium salts in acetone led to the formation of air- and moisture-stable [(iPrPdmBox)NiX] (X = F (7), X = Br (8), X = I (9), X = N3(10), X = OAc (11). Furthermore, the conversion of [(iPrPdmBox)NiF] (7) with hydride transfer reagents such as PhSiH3led to the stable hydrido species [(iPrPdmBox)NiH] (27), the stoichiometric transformations of which were studied. Treatment of 6a with organometallic reagents such as ZnEt2, PhLi, PhC≡CLi, NsLi, or (4FBn)2Mg(THF)2gave the corresponding alkyl, alkynyl, or aryl complexes. The availability of the new nonisomerizable PdmBox pincer ligands allowed the comparative study of their ligation to square-planar complexes as helically twisted spectator ligands as opposed to the enforced planar rigidity of their iso-PmBox analogues and the way this influences the reactivity of the Ni complexes.
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Wenz
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kochan
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Hubert
authors.initials: H
authors.lastname: Wadepohl
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Lutz H
authors.identifier: http://orcid.org/0000-0002-7107-8169
authors.initials: LH
authors.lastname: Gade