Tuning the Luminescence of Transition Metal Complexes with Acyclic Diaminocarbene Ligands

Organometallics featuring acyclic diaminocarbene (ADC) ligands have recently emerged as powerful emitters for use in OLEDs and other electroluminescent technologies. Owing to strong σ-donor properties and broad synthetic availability, ADCs...

Luminescent Cyclometalated Platinum(II) Complexes with Acyclic Diaminocarbene Ligands: Structural, Photophysical and Biological Properties

Four new cyclometalated Pt(II) complexes bearing acyclic diaminocarbene (ADC) ligands, [Pt(C^N)Cl{C(NHXyl)(NHR)}] [C^N = 2,6-difluorophenylpyridine (dfppy), phenylquinoline (pq); R = Pr 3a, 4a, CH2Ph 3b, 4b], were prepared by nucleophilic attack...

Highly Sterically Encumbered Gold Acyclic Diaminocarbene Complexes: Overriding Electronic Control in Regiodivergent Gold Catalysis

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 ¹H NMR data showed that the ADC-gold 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 percent buried volume (%<i>V</i>_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 <i>N</i>-substituents in the dimesityl series were attributed to attractive CH···π 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 ADC-Au catalysts inducing a shift away from the cyclopropane-fused product toward the normally disfavored alkene product. Incorporation of a yet 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.

Highly Sterically Encumbered Gold Acyclic Diaminocarbene Complexes: Overriding Electronic Control in Regiodivergent Gold Catalysis

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 ¹H NMR data showed that the ADC-gold 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 percent buried volume (%<i>V</i>_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 <i>N</i>-substituents in the dimesityl series were attributed to attractive CH···π 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 ADC-Au catalysts inducing a shift away from the cyclopropane-fused product toward the normally disfavored alkene product. Incorporation of a yet 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.