886364-57-4Relevant articles and documents
2,2′-Bipyridine-α,α′-trifluoromethyl-diol ligand: Synthesis and application in the asymmetric Et2Zn alkylation of aldehydes
Lauzon, Samuel,Ollevier, Thierry
supporting information, p. 11025 - 11028 (2021/11/03)
A chiral 2,2′-bipyridine ligand (1) bearing α,α′-trifluoromethyl-alcohols at 6,6′-positions was designed in five steps affording either the R,R or S,S enantiomer with excellent stereoselectivities, i.e. 97% de, >99% ee and >99.5% de, >99.5% ee, respectively. The key step for reaching high levels of stereoselectivity was demonstrated to be the resolution of the α-CF3-alcohol using (S)-ibuprofen as the resolving agent. An initial application for the 2,2′-bipyridine-α,α′-CF3-diol ligand was highlighted in the ZnII-catalyzed asymmetric ethylation reaction of aromatic, heteroaromatic, and aliphatic aldehydes. Synergistic electron deficiency and steric hindrance properties of the newly developed ligand afforded the corresponding alcohols in good to excellent yields (up to 99%) and enantioselectivities (up to 95% ee). As observed from single crystal diffraction analysis, the complexation of the 2,2′-bipyridine-α,α′-CF3-diol ligand generates an unusual hexacoordinated ZnII.
(Py)2Co(CH2SiMe3)2 as an easily accessible source of "coR2"
Zhu, Di,Janssen, Femke F. B. J.,Budzelaar, Peter H. M.
experimental part, 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.
