期刊
ORGANOMETALLICS
卷 31, 期 9, 页码 3790-3797出版社
AMER CHEMICAL SOC
DOI: 10.1021/om300297y
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资金
- Department of Science and Technology (DST), India
- Indo-French Centre for the Promotion of Advanced Research (IFCPAR)
- DST
- CSIR
Treatment of [Rh(COD)(mu-Cl)](2) with excess (BuOK)-Bu-t and subsequent addition of 2 equiv of PIN center dot HBr in THF afforded [Rh(COD)(kappa C-2-PIN)Br] (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of 1 confirms ligand coordination to Rh(COD)Br through the carbene carbon featuring an unbound naphthyridine. Compound 1 is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h(-1) was achieved for the acrylonitrile. A similar Rh(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst-water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site via double hydrogen-bonding interactions, providing significant entropic advantage to the hydration process. The calculated transition state (TS) reveals multicomponent cooperativity involving proton movement from the water to the naphthyridine nitrogen and a complementary interaction between the hydroxide and the nitrile carbon. Bifunctional water activation and cooperative proton migration are recognized as the key steps in the catalytic cycle.
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