Azasilicon-bridged heterocyclic arylamines: Syntheses, structures and photophysical properties

The lithium κ¹-enamides, Me₂NSiMe₂CHC(Ph)-{2,6-(R¹)₂-4-(R²)C₆H₂}NLi·3THF (R¹ = ⁱPr, R² = H L1; R¹ = Et, R² = H L2; R¹ = Me, R² = H L3; R¹ = R² = Me L4; R¹ = Et, R² = Me L5), in the presence of titanium tetrachloride, undergo intermolecular rearrangement cyclization reactions resulting in 1,3-migration of the silicon groups and the elimination of dimethylamine affording five examples of bis-azasilicon-bridged heterocyclic arylamines, [{2,6-(R¹)₂-4-(R²)C₆H₂}N(Ph)CCSiMe₂]₂ (R¹ = ⁱPr, R² = H D1; R¹ = Et, R² = H D2; R¹ = Me, R² = H D3; R¹ = R² = Me D4; R¹ = Et, R² = Me D5) in good yield, respectively. The molecular structures of D1-D5 show the two fused N-Si-C-C-C rings to be co-planar indicative of extended π-conjugation, while their photophysical properties reveal them to be green/blue emitting with high luminescence quantum yields (Φ_F range: 75-99%). Furthermore, the compounds D serve as versatile reactants undergoing ring opening on hydrolysis to afford the saturated 1,4-diimines [{2,6-(R¹)₂-4-(R²)C₆H₂}N(Ph)C-CH₂]₂ (R¹ = ⁱPr, R² = H E1; R¹ = Et, R² = H E2; R¹ = Me, R² = H E3; R¹ = R² = Me E4; R¹ = Et, R² = Me E5). Alternatively, D can be employed in a redox-promoted cascade reaction to afford the conjugated 1,4-diimines, (E)-[{2,6-(R¹)₂-4-(R²)C₆H₂}NC(Ph)CH]₂ (R¹ = ⁱPr, R² = H F1; R¹ = Et, R² = H F2; R¹ = Me, R² = H F3; R¹ = R² = Me F4; R¹ = Et, R² = Me F5). In addition to D1-D5, E1-E3, E5, F2 and F3 have been the subject of single crystal X-ray diffraction studies.