Mapping of N−C Bond Formation from a Series of Crystalline Peri‐Substituted Naphthalenes by Charge Density and Solid‐State NMR Methodologies

Rees, Gregory J. and Pitak, Mateusz B. and Lari, Alberth and Day, Stephen P. and Yates, Jonathan R. and Gierth, Peter and Barnsley, Kristian and Smith, Mark E. and Coles, Simon J. and Hanna, John V. and Wallis, John D. (2021) Mapping of N−C Bond Formation from a Series of Crystalline Peri‐Substituted Naphthalenes by Charge Density and Solid‐State NMR Methodologies. Angewandte Chemie International Edition, 60 (44). pp. 23878-23884. ISSN 1433-7851

Abstract

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1 J NC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n-π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp 2 carbon atom in a series of crystalline peri-substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin-echo NMR measurements confirming, the 1 J NC couplings of ≈3-6 Hz for long C-N bonds (1.60-1.65 Å), and 1 J NC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å.