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Controlling Tautomerization in Pyridine-Fused Phosphorus-Nitrogen Heterocycles

Journal Article · · Chemistry - A European Journal
 [1];  [2];  [3];  [3];  [3];  [4];  [3];  [2];  [3];  [3]
  1. University of Oregon, Eugene, OR (United States); OSTI
  2. University of Houston, TX (United States)
  3. University of Oregon, Eugene, OR (United States)
  4. Cornell University, Ithaca, NY (United States)
+ Show Author Affiliations

Inclusion of a second nitrogen atom in the aromatic core of phosphorus-nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X-ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs. To study the difference in solution vs. solid-state heterocycles, alkylated analogues that lock in the quinoidal tautomer were synthesized and their different 1H NMR and UV/Vis spectra studied. Ultimately, we determined that all heterocycles are the aromatic tautomer in solution and all but 2 e switch to the quinoidal tautomer in the solid state. Better understanding of this transformation and under what circumstances it occurs suggest future use in a switchable on/off hydrogen-bond-directed receptor that can be tuned for complementary hydrogen bonding.

Research Organization:
University of Oregon, Eugene, OR (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); National Institute of Health; Sloan Research Foundation
Grant/Contract Number:
SC0022147
OSTI ID:
1976302
Alternate ID(s):
OSTI ID: 1855305
Journal Information:
Chemistry - A European Journal, Journal Name: Chemistry - A European Journal Journal Issue: 22 Vol. 28; ISSN 0947-6539
Publisher:
WileyCopyright Statement
Country of Publication:
United States
Language:
English

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Figures / Tables (9)

Figure 1(p. 2)figure Figure 1
Figure 2(p. 3)figure Figure 2
Scheme 1(p. 3)figure Scheme 1
Figure 3(p. 4)figure Figure 3
Scheme 2(p. 4)figure Scheme 2
Figure 4(p. 5)figure Figure 4
Table 1(p. 5)table Table 1
Figure 5(p. 6)figure Figure 5
Figure 6(p. 6)figure Figure 6

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
NICS calculations
PN-heterocycles
quinoidal
tautomerization
x-ray crystallography