期刊
ORGANOMETALLICS
卷 40, 期 10, 页码 1416-1433出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.organomet.0c00776
关键词
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资金
- National Science Foundation [CHE-1360610]
- National Science Foundation MRI Program
- University of North Texas [CHE-1531468]
- Rigaku XtaLAB Synergy-S X-ray diffractometer [CHE-1726652]
The study synthesized sterically encumbered gold(I) acyclic diaminocarbene (ADC) complexes with different ligands and found that the bulky biaryl/terphenyl groups strongly influence product selectivity in gold-catalyzed reactions. The research also revealed how large aryl groups impact reaction mechanisms.
Two series of sterically encumbered gold(I) acyclic diaminocarbene (ADC) complexes were prepared by reaction of mono- and dialkylamines with gold-bound 2-mesitylphenyl isocyanide (monomesityl series) and 2,6-dimesitylphenyl isocyanide (dimesityl series). X-ray crystal structures and solution H-1 NMR data showed that the gold ADC complexes adopt major rotameric conformations with the bulky biaryl/terphenyl group and one alkyl group located syn to gold. This engenders substantial steric hindrance at the metal, as evidenced by the percent buried volume (%V-bur) parameters of 35.7-37.2 for the monomesityl series and 46.4-52.4 for the dimesityl series. Modest out-of-plane distortions of the ADC N-substituents in the dimesityl series were attributed to attractive CH center dot center dot center dot pi interactions between alkyl groups and mesityl rings on the basis of dispersion-corrected density functional theory calculations. Gold-catalyzed regiodivergent domino cyclization/hydroarylation reactions of a 1,6-enyne with indole revealed that the bulky biaryl/terphenyl substituents of the ligands exert a strong influence on product selectivity, with the bulkier dimesityl Au ADC catalysts inducing a shift away from the cyclopropane-fused product toward the normally disfavored alkene product. Incorporation of an even bulkier bis(2,6-diisopropylphenyl)-substituted terphenyl moiety into the ADC led to a gold catalyst that provided exclusive selectivity for the alkene product. Computational modeling suggested that bulky terphenyl groups hinder attack at the a-carbon in the initially formed organogold intermediate, allowing steric effects to override the intrinsic electronic preference for the cyclopropane product.
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