763104-47-8Relevant academic research and scientific papers
Radical mechanisms in the reaction of organic halides with diiminepyridine cobalt complexes
Zhu, Di,Korobkov, Ilia,Budzelaar, Peter H. M.
, p. 3958 - 3971 (2012/07/14)
The formally Co(0) complex LCo(N2) (L = 2,6-bis(2,6- dimethylphenyliminoethyl)pyridine) can be prepared via either Na/Hg reduction of LCoCl2 or hydrogenolysis of LCoCH2SiMe3. In the latter reaction, LCoH could be trapped by reaction with N≡CC 6H4-4-Cl to give LCoN=CHC6H4-4-Cl. LCo(N2) reacts with many alkyl and aryl halides RX, including aryl chlorides, to give a mixture of LCoR and LCoX in a halogen atom abstraction mechanism. Intermediacy of free alkyl and aryl radicals is confirmed by the ring-opening of cyclopropylmethyl to crotyl, and the rearrangement of 2,4,6-tBu3C6H2 to 3,5- tBu2C6H3CMe2CH 2, before binding to Co. The organocobalt species generated in this way react further with activated halides R′X (alkyl iodides; allyl and benzyl halides) to give cross-coupling products RR′ in what is most likely again a halogen abstraction mechanism. DFT studies support the proposed radical pathways for both steps. MeI couples smoothly with LCoCH2SiMe 3 to give LCoI and CH3CH2SiMe3, but the analogous reaction of tBuI leads in part to radical attack at the 3 and 4 positions of the pyridine ring to form (tBu 2-L)CoI and (tBu2-L)CoI2.
Redox-active ligands and organic radical chemistry
Zhu, Di,Thapa, Indira,Korobkov, Ilia,Gambarotta, Sandro,Budzelaar, Peter H. M.
, p. 9879 - 9887 (2011/11/14)
Knowledge about bonding in diiminepyridine (L) halide, alkyl, and dinitrogen complexes of the metals iron, cobalt, and nickel is summarized, and two new examples are added to the set: L1Ni(Me) and L 1Ni(N2). Reactivity of
Olefin hydrogenation using diimine pyridine complexes of Co and Rh
Knijnenburg, Quinten,Horton, Andrew D.,Van Der Heijden, Harry,Kooistra, T. Martijn,Hetterscheid, Dennis G.H.,Smits, Jan M.M.,De Bruin, Bas,Budzelaar, Peter H.M.,Gal, Anton W.
, p. 151 - 159 (2008/10/09)
Square-planar cobalt diimine pyridine complexes LCoR (L = 2,6-[RN=CMe] 2C5H3N; R = n-C6H13 for Lhex, 2,6-(i-Pr)2C6H3 for L dip) are active in the hydrogenation of monosubstituted and disubstituted olefins; sterically more hindered trisubstituted olefins do not react. For the LdipCo system, a diamagnetic hydride intermediate was observed, although a small amount of paramagnetic product is also formed upon reaction of LdipCoR with H2. DFT studies suggest a traditional hydrogenation cycle starting with LCoH, except that intermediate LCo(R)(H2) transfers a hydrogen atom directly from H2 to the alkyl group in a σ-bond metathesis step, without going through a discrete CoIII intermediate. Autoclave experiments show that conversion is not linear in catalyst intake. Diffusion limitation was ruled out as an explanation, and we propose a concentration-dependent catalyst decay. At low catalyst intake conversion rates up to 2 × 104 (mol octene/mol Co/bar/h) can be reached. Reducing the steric bulk at the imine positions (Ldip → Lhex), or changing the metal from cobalt to rhodium, do not alter the activity or specificity of the hydrogenation much. For the LhexCo and LdipRh systems, no diamagnetic products corresponding to LdipCoH were observed.
Investigations into the mechanism of activation and initiation of ethylene polymerization by bis(imino)pyridine cobalt catalysts: Synthesis, structures, and deuterium labeling studies
Humphries, Martin J.,Tellmann, Kilian P.,Gibson, Vernon C.,White, Andrew J. P.,Williams, David J.
, p. 2039 - 2050 (2008/10/09)
The activation of bis(imino)pyridine cobalt(II) precatalysts by MAO leads initially to a bis(imino)pyridine cobalt(I) cationic species with no cobalt-C(alkyl) bond into which insertion can occur. Mechanistic studies have shown that the initiation of polym
Experimental and computational study of β-H transfer between cobalt (I) alkyl complexes and 1-alkenes
Tellmann, Kilian P.,Humphries, Martin J.,Rzepa, Henry S.,Gibson, Vernon C.
, p. 5503 - 5513 (2008/10/09)
Bis(imino)pyridine cobalt(I) alkyl complexes react with 1-alkenes by β-hydrogen transfer, providing a model reaction for the study of a commonly encountered chain transfer process in polymerization and oligomerization catalysis. The influence of steric effects on reaction rates is described. The theoretical models largely agree with the experimentally determined structures, provide a more detailed view of the species involved, and are consistent with the observed reactivities. Both experiment and theory support a stepwise pathway involving a cobalt-hydride intermediate.
The electronic structure of (diiminopyridine)cobalt(I) complexes
Knijnenburg, Quinten,Hetterscheid, Dennis,Martijn Kooistra,Budzelaar, Peter H. M.
, p. 1204 - 1211 (2007/10/03)
DFT calculations show that square-planar LCoIR complexes of a diiminopyridine ligand are best regarded as containing low-spin CoII antiferromagnetically coupled to a ligand radical anion. The lowest triplet state, corresponding to a 3dz2→π* excitation, is calculated to be only a few kcal/mol above the ground state, and is thermally accessible. The anomalous 1H NMR chemical shifts of the LCoR complexes are suggested to be due to thermal population of the triplet state at room temperature. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
