Oxidatively Triggered Carbon–Carbon Bond Formation in Ene-amide Complexes

Abstract

Ene-amides have been explored as ligands and substrates for oxidative coupling. Treatment of CrCl2, Cl2Fe(PMe3)2, and Cl2Copy4 with 2 equiv of {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}Li afforded pseudosquare planar {η(3)-C,C,N-(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Cr (1-Cr, 78%), trigonal {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Fe(PMe3) (2-Fe, 80%), and tetrahedral {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Co(py)2 (3-Co, 91%) in very good yields. The addition of CrCl3 to 1-Cr, and FeCl3 to 2-Fe, afforded oxidatively triggered C-C bond formation as rac-2,2'-di(2,6-(i)Pr2C6H3N═)2dicyclohexane (EA2) was produced in modest yields. Various lithium ene-amides were similarly coupled, and the mechanism was assessed via stoichiometric reactions. Some ferrous compounds (e.g., 2-Fe, FeCl2) were shown to catalyze C-arylation of {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}Li with PhBr, but the reaction was variable. Structural characterizations of 1-Cr, 2-Fe, and 3-Co are reported.

Oxygen-Induced Dimerization of Alkyl-Manganese(II) 2,6-Bisiminopyridine Complexes: Selective Synthesis of a New Ditopic NNN-Pincer Ligand

“…Interestigly, the Woclzansy group has reported recently that C-C couplingmediated by aza-enolate (iminate) complexes also requires oxidation of the metal center. 20 Scheme 3. Exchange reaction of (4-allyl-Mes HBIP)2 with Zn and Pd alkyls.…”

“…The need for an external trigger to switch the reaction outcome indicates that intermediate Mn­(II) dihydropyridinate complexes 1 are themselves unable to undergo dimerization but become activated when they react with oxygen. Interestigly, the Woclzansy group has reported recently that C–C coupling mediated by aza-enolate (iminate) complexes also requires oxidation of the metal center …”

Oxidative Additions to Ti(IV) in [(dadi)4–]TiIV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

“…Carbon–carbon bond formation is often a consequence of redox noninnocence (RNI) that induces radical character in certain ligands. − In many cases, a relatively simple coupling of carbon radicals occurs to form a single new bond, but sometimes the reactivity can be complicated. Figure illustrates some unusual C–C bond forming events discovered in these laboratories. − In A , the Ti­(III) complex, (smif)­{Li­(smif–smif)}­Ti, was shown to contain one C–C bond derived from coupling of smif (smif = 1,3-di­(2-pyridyl)-2-azaallyl) ligands that were reduced during the course of its synthesis. One mode of its decomposition generated dimer [(smif 2– )­Ti III ] 2 (μ-κ 3 ,κ 3 - N , N (py) 2 -smif,smif), which contained two new C–C bonds that can be construed as arising from coupling of a singlet diradical, or alternatively, a nucleophile/electrophile coupling .…”

Complexes of [(dadi)Ti(L/X)]m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon–Carbon Bond

“…The formation of a cyclopropanated backbone of (dadi) n suggested that reversible C–C bond formation could be a means of storing and releasing electrons in a redox noninnocent (RNI) fashion. ,− A possible hindrance to RNI is the transfer of a cyclopropane hydrogen subsequent to ring-opening, which would generate a nacnac fragment in place of the original diimine. The reactivity of {PhC 3 H 3 (-NC 6 H 4 -2-NAr) 2 }­Ti­(THF) ( 3 ) was probed via various potential oxidants and proton acceptors, and while most generated mixtures, the addition of Ph 2 CN 2 yielded a single product (>90%) that was dissymmetric.…”