844642-16-6Relevant 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.
(Py)2Co(CH2SiMe3)2 as an easily accessible source of "coR2"
Zhu, Di,Janssen, Femke F. B. J.,Budzelaar, Peter H. M.
, p. 1897 - 1908 (2010/06/14)
(Py)2CoR2 (R = CH2SiMe3) is easily prepared from (Py)4CoCl2 and RLi. It is fairly stable at room temperature and serves as a convenient source of CoR2 for transfer to other ligands. Unfortunately, (Py)2CoR2 was obtained only as an oil, but the structure of the related complex (Py) 2CoR-2 (R- = CH2CMe2Ph) could be confirmed by a single-crystal X-ray diffraction study. Transfer of the CoR 2 fragment from (Py)2CoR2 or (TMEDA)CoR 2 to diiminepyridine-type ligands (1-6) was studied as a function of ligand steric and electronic properties. Reaction with N-2,6-dimethylphenyl (1) and N-2,4,6-trimethylphenyl (2) ligands produced diamagnetic monoalkyl complexes; the structure of (1)CoR was confirmed by X-ray diffraction. With the less shielding N-phenyl (3) and N-benzyl (4) ligands, 1H NMR indicated formation of diamagnetic CoI alkyl species, but they were not stable enough to allow isolation. Fluorinated ligand 5 appears to be less reactive and-despite its supposedly stronger φ-acceptor character-also does not lead to formation of a stable CoI alkyl complex. With PyBOX ligand 6, high-spin dialkyl complex (6)CoR2 was observed by 1H NMR. Based on these observations and DFT calculations, a mechanism is proposed for formation of diiminepyridine CoI alkyls that involves formation of a high-spin κ2 complex, spin flip to give a low-spin κ3 complex, and irreversible loss of an alkyl radical.
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.
