Solid‐state NMR Spectroscopy of Iodine(I) Complexes

Abstract

Solid‐state NMR has been applied to a series of Barluenga‐type iodine(I) [L‐I‐L]PF6 (L=pyridine, 4‐ethylpyridine, 4‐dimethylaminopyridine, isoquinoline) complexes as their hexafluorophosphate salts, as well as their respective non‐liquid ligands (L), their precursor silver(I) complexes, and the respective N‐methylated pyridinium and quinolinium hexafluorophoshate salts. These results are compared and contrasted to the corresponding solution studies and single‐crystal X‐ray structures. As the first study of its kind on the solid‐state NMR behavior of halogen(I) complexes, practical considerations are also discussed to encourage wider utilization of this technique in the future.

Iodine(I) and Silver(I) Complexes Incorporating 3-Substituted Pyridines

“…19,32,43 The necessity of using more strongly polar deuterated solvents like MeCN for the NMR studies, however, does complicate analysis of the solutionstate NMR data for complexes 2a−5a, given that the observed 15 N NMR chemical shifts will be of an equilibrium of a complicated mixture of MeCN-solvated silver(I) complexes that exist in solution, e.g., 2a•(MeCN) n (n = 0−4). 45,46 Unfortunately, the diminished organic-solvent solubility that results from the Ag + cations proclivity to facilitate more intermolecular interactions only enabled 4a to be studied in CD 2 Cl 2 , with the 15 silver(I), which the essentially non-coordinating CD 2 Cl 2 solvent is incapable of, as demonstrated recently by solid-state NMR studies of similar silver(I) complexes. 46 Put in the context of previously reported analogous series of ligand (L) to Ag + to I + conversions for the structurally isomeric 4-substituted pyridines, meaningful electronic structure comparisons can be drawn.…”

“…45,46 Unfortunately, the diminished organic-solvent solubility that results from the Ag + cations proclivity to facilitate more intermolecular interactions only enabled 4a to be studied in CD 2 Cl 2 , with the 15 silver(I), which the essentially non-coordinating CD 2 Cl 2 solvent is incapable of, as demonstrated recently by solid-state NMR studies of similar silver(I) complexes. 46 Put in the context of previously reported analogous series of ligand (L) to Ag + to I + conversions for the structurally isomeric 4-substituted pyridines, meaningful electronic structure comparisons can be drawn. The 4-substituted analogues of iodine(I) complexes 3b (with different anions other than PF 6 ) and 5b, [I(4-aminopyridine) 2 ][anion] (anion = Cl, IBr 2 , I 7 ) and [I(4cyanopyridine) 2 ]PF 6 , are known; 24,47 however, no 15 N NMR data was reported for either of these iodine(I) complexes for comparison.…”

“…In contrast to halogen­(I), the silver­(I) cations are amenable to additional interactions supplemental to their linear coordination geometry, such as from weakly coordinating anions like triflate or potentially coordinating solvents like MeCN (as was reported for 1a ). ,, The necessity of using more strongly polar deuterated solvents like MeCN for the NMR studies, however, does complicate analysis of the solution-state NMR data for complexes 2a – 5a , given that the observed 15 N NMR chemical shifts will be of an equilibrium of a complicated mixture of MeCN-solvated silver­(I) complexes that exist in solution, e.g. , 2a ·(MeCN) n ( n = 0–4). , Unfortunately, the diminished organic-solvent solubility that results from the Ag + cations proclivity to facilitate more intermolecular interactions only enabled 4a to be studied in CD 2 Cl 2 , with the 15 N NMR resonance of −132.3 ppm being significantly different from the one taken in CD 3 CN (cf. −103.3 ppm).…”

Halogen Bonds of Halogen(I) Ions─Where Are We and Where to Go?

“…13,44,53,62 The coordination shifts are unaltered even in the absence of solvent. 108 Variations <±5 ppm are typically the consequence of acquiring NMR chemical shifts with low resolution in the 15 N dimension, or in worst case due to rapid chemical exchange with a contaminant proton complex. The iodine(I) complexes of tertiary amines show δ( 15 N) coord of ca.…”

“…−105 ppm . It cannot be stressed enough that the magnitude of the coordination shifts within a structurally closely related series of complexes is independent of substitution, counterion, and solvent (Table , entries 5, 9, and 10). ,,, The coordination shifts are unaltered even in the absence of solvent . Variations <±5 ppm are typically the consequence of acquiring NMR chemical shifts with low resolution in the 15 N dimension, or in worst case due to rapid chemical exchange with a contaminant proton complex.…”