Conformational stabilisation of a 2-pyridyl imide by n→π* interaction in solid state

Figures & data

Figure 1. n→π* interaction in a carbonyl electrophile.

Figure 2. Syn and anti conformers of 2-pyridyl imide 1.

Figure 3. Structure of 2-pyridyl [5]polynorbornane 2. The left 2-pyridyl heterocycle is shown in the syn conformation, while the right is shown in the anti conformation.

Scheme 1. Reagents and conditions: (i) 130°C, DMF, 16 h, 72%.

Scheme 2. Synthesis of the bis(2-pyridyl) framework 2. Reagents and conditions: (i) RuH₂(CO)(PPh₃)₃, 100°C, DMF, 16 h, 46%; (ii) t-BuOOH, t-BuOK, −10°C – RT, THF, 16 h, 43%; (iii) 140°C, DMF, microwave, 30 min, 66%.

Figure 4. Calculated (a) transition state, (b) syn conformer and (c) anti conformer of imide 1, with annotated C3-N4-C2’-C3’ dihedral angles.

Table 1. Calculated (B3LYP/6-311 G* (298.15 K)) properties of conformers of imide 1.

Conformation	Transition State	Syn Conformer	Anti Conformer
E (kJmol^−1)	−2102582	−2102599	−2102597
ΔE (kJmol^−1)	0	−17.3	−14.8
Boltzmann Distribution	0.001	0.729	0.271
δ10s (ppm)	1.43	1.84	1.49
δ10a (ppm)	1.57	1.58	1.62
Torsion Angle* (°)^a	0.58	122.19	−53.22

^aDihedral angle of C3-N4-C2’-C3’.

Figure 5. VT ¹H NMR stackplot of 2-pyridyl imide 1 (1.670–1.565 ppm), CDCl₃, 500 MHz.

Figure 6. VT ¹H NMR stackplot of 2-pyridyl [5]polynorbornane 2 (9.00–0.75 ppm), CDCl₃, 500 MHz. Insets display the doublet assigned to the 31s and 33s protons.

Figure 7. (a) Asymmetric unit of 2-pyridyl imide 1 highlighting the n→π* interaction (orange) and (b) annotated n→π* interaction of 2-pyridyl imide 1.

Data availability statement

Deposition number 2356985 in the Cambridge Crystallographic Data Centre (CCDC) contains the supplementary crystallographic data for this paper.