Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products
Molina DAC, Wititsuwannakul T, Hampel F, Hall MB, Gladysz JA (2021)
Publication Type: Journal article
Publication year: 2021
Journal
Abstract
Reactions of Li+ [(η5-C5H5)Re(NO)(PPh3)]− with 2- and 4-chloroquinoline or 1-chloroisoquinoline give the corresponding σ quinolinyl and isoquinolinyl complexes 3, 6, and 8. With 3 and 8 there is further protonation to yield HCl adducts, but additions of KH give the free bases. Treatment of 3 with HBF4⋅OEt2 or H(OEt2)2+ BArf− gives the quinolinium salts [(η5-C5H5)Re(NO)(PPh3)(C(NH)C(CH)4C(CH)(CH))]+ X− (3-H+ X−; X−=BF4−/BArf−, 94–98 %). Addition of CF3SO3CH3 to 3, 6, or 8 affords the corresponding N-methyl quinolinium salts. In the case of [(η5-C5H5)Re(NO)(PPh3)(C(NCH3)C(CH)4C(CH)(CH))]+ CF3SO3− (3-CH3+ CF3SO3−), addition of CH3Li gives the dihydroquinolinium complex (SReRC,RReSC)-[(η5-C5H5)Re(NO)(PPh3)(C(NCH3)C(CH)4C(CHCH3)(CH2))]+ CF3SO3− ((SReRC,RReSC)-5+ CF3SO3−, 76 %) in diastereomerically pure form. Crystal structures of 3-H+ BArf−, 3-CH3+ CF3SO3−, (SReRC, RReSC)-5+ Cl−, and 6-CH3+ CF3SO3− show that the quinolinium ligands adopt Re⋅⋅⋅C conformations that maximize overlap of their acceptor orbitals with the rhenium fragment HOMO, minimize steric interactions with the bulky PPh3 ligand, and promote various π interactions. NMR experiments establish the Brønsted basicity order 3>8>6, with Ka(BH+) values >10 orders of magnitude greater than the parent heterocycles, although they remain less active nucleophilic catalysts in the reactions tested. DFT calculations provide additional insights regarding Re⋅⋅⋅C bonding and conformations, basicities, and the stereochemistry of CH3Li addition.
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APA:
Molina, D.A.C., Wititsuwannakul, T., Hampel, F., Hall, M.B., & Gladysz, J.A. (2021). Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products. Chemistry - A European Journal. https://dx.doi.org/10.1002/chem.202101949
MLA:
Molina, Dante A. Castillo, et al. "Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products." Chemistry - A European Journal (2021).
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