Oxidation of Ni(II) to Ni(IV) with Aryl Electrophiles Enables Ni-Mediated Aryl-CF3 Coupling

Accessing Pincer Bis(carbene) Ni(IV) Complexes from Ni(II) via Halogen and Halogen Surrogates

This communication describes the two-electron oxidation of ((DIPP)CCC)NiX ((DIPP)CCC = bis(diisopropylphenyl-benzimidazol-2-ylidene)phenyl); X = Cl or Br) with halogen and halogen surrogates to form ((DIPP)CCC)NiX3. These complexes represent a rare oxidation state of nickel, as well as an unprecedented reaction pathway to access these species through Br2 and halogen surrogate (benzyltrimethylammonium tribromide). The Ni(IV) complexes have been characterized by a suite of spectroscopic techniques and can readily reduce to the Ni(II) counterpart, allowing for cycling between the Ni(II)/Ni(IV) oxidation states.

Palladium-Catalyzed Arylation of Arylboronic Acids with Yagupolskii-Umemoto Reagents

A Pd-catalyzed Suzuki cross-coupling of arylboronic acids with Yagupolskii-Umemoto reagents was explored. In contrary to trifluoromethylations, the Pd-catalyzed reaction of R-B(OH)2 and [Ar2 SCF3 ](+) [OTf](-) provided the arylation products (R-Ar) in good to high yields. The reaction confirms that the S-Ar bonds of [Ar2 SCF3 ](+) [OTf](-) can be readily cleaved in the presence of Pd complexes. The relatively electron-poor aryl groups of asymmetric [Ar(1) Ar(2) SCF3 ](+) [OTf](-) salts are more favorably transferred compared to the electron-rich ones. This reaction represents the first report of utilization of [Ar2 SCF3 ](+) [OTf](-) as arylation reagents in organic synthesis.

Oxidatively-induced aromatic cyanation mediated by Ni(iii)

A Ni(ii) complex with two t-butylisocyanide ligands supported by a N3C(-) type tetradentate ligand was synthesized and characterized. Quantitative generation of the aromatic cyanation product, (tBu)N3C-CN, is observed by reacting this Ni(ii) complex with 1 equiv. of an oxidant. Reactivity studies suggest that this oxidatively-induced cyanation involves a heterolytic cleavage of the N-(t)Bu bond and is mediated by Ni(iii).

Ligand effects on the properties of Ni(iii) complexes: aerobically-induced aromatic cyanation at room temperature

Ligand effect studies on (^RN3C)Ni^IIIL₂ complexes reveal aerobically-induced aromatic cyanation with tBuNC at room temperature for the (^NpN3C)Ni system.

Copper-catalysed synthesis of trifluoromethyl(hetero)arenes from di(hetero)aryl-λ3-iodanes

Efficient regioselective copper-catalyzed trifluoromethylation of symmetrical and unsymmetrical diaryl-λ³-iodanes have been achieved for the synthesis of trifluoromethyl(hetero)arenes in good yield.

Gas-Phase and Computational Study of Identical Nickel- and Palladium-Mediated Organic Transformations Where Mechanisms Proceeding via M(II) or M(IV) Oxidation States Are Determined by Ancillary Ligands

Gas-phase studies utilizing ion-molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CH2CO2-C,O)M(CH3)](-) (M = Ni (5a), Pd (5b)) with allyl acetate proceed via oxidative addition to give M(IV) species [(CH2CO2-C,O)M(CH3)(η(1)-CH2-CH═CH2)(O2CCH3-O,O')](-) (6) that reductively eliminate 1-butene, to form [(CH2CO2-C,O)M(O2CCH3-O,O')](-) (4). The mechanism contrasts with the M(II)-mediated pathway for the analogous reaction of [(phen)M(CH3)](+) (1a,b) (phen = 1,10-phenanthroline). The different pathways demonstrate the marked effect of electron-rich metal centers in enabling higher oxidation state pathways. Due to the presence of two alkyl groups, the metal-occupied d orbitals (particularly dz(2)) in 5 are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from dz(2) to the C═C π* orbital is the key interaction leading to oxidative addition of allyl acetate to M(II). Upon collision-induced dissociation, 4 undergoes decarboxylation to form 5. These results provide support for the current exploration of roles for Ni(IV) and Pd(IV) in organic synthesis.