Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C–H Bond to Form a Ni(II) Hydride

Abstract

The synthesis and characterization of a series of nickel(II) pincer complexes of the meta-phenylene-bridged bis-N-heterocyclic DIPPCCC ligand framework are reported. Characterization of the Ni(II)Cl complex revealed a square planar species with Cl– and the anionic carbon trans to one another. Formation of Ni(II) alkyl complexes derived from complex 1 was accomplished by addition of LiR [R = CH3 (2); CH2SiMe3 (3)]. Furthermore, we report a synthetic pathway to access the catalytically relevant Ni(II)H species (DIPPCCC)NiH (4), by direct oxidative addition of an aryl C–H bond across a Ni(0) center. Complexes 1–4 have been characterized by 1H and 13C NMR and electronic absorption spectroscopies as well as X-ray crystallography.

From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer

“…The Ni–O bond lengths were determined to be 187.60(13) pm and 190.11(13) pm, whereas the Ni–C carbene bonds have lengths between 184.06(19) pm and 184.82(19) pm, respectively. These values correspond to literature-known bond lengths of cis arranged bidentate ligands around Ni [42–44], but, as expected, they differ from those of [(PEt 3 )(Ph)Ni(imidazo[1,5- a ]quinolin-9-olate-1-ylidene)] [45] as well as Ni complexes with tridentate ligands [46–47]. …”

Nickel-catalyzed C–H/N–H annulation of aromatic amides with alkynes in the absence of a specific chelation system

“…The amidate anion, E , reacts with Ni(0) to give nickel complex H , which is sufficiently reactive to undergo oxidative addition to generate the nickel hydride species, I , because the complex is sufficiently electron rich. 11 , 13 The successive insertion of an alkyne into H–Ni and C–Ni bonds gives complex L . Reductive elimination, followed by protonation by t BuOH, affords the isoquinolinone with the regeneration of Ni(0) and KOBu t , with the concomitant formation of an alkene.…”

“…In the case of a Ni(0) catalyst, the nickel complex H would be expected to participate in the oxidative addition of C–H bonds to generate complex I . 9 , 11 Thus, no pre-coordination of an N(sp 2 ) atom to a nickel center would be required.…”

Dinuclear Nickel Complexes of Thiolate-Functionalized Carbene Ligands and Their Electrochemical Properties

“… 30 , 32 − 37 A number of exceptions have been reported for complexes bearing certain types of tridentate pincer ligands, showing dihedral angles α smaller than 5°. 38 − 40 …”