Are monophospha(III)amidines and -guanidines with ionizable hydrogens tautomeric? Towards a deeper understanding of two related hetero-element functional groups
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Date
2023
Authors
Masuda, Jason D.
Amrei, Leila M.
Boeré, René T.
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
Abstract
This paper presents definitive structural evidence for N,P(III)-monophosphaamidines in P=C and N=C isomeric forms from a combination of new syntheses, single-crystal X-ray diffraction (SC-XRD), solid-state NMR and FTIR. Evidence is also provided for C-amino-(σ2,λ3)-phosphaalkene and C-(σ3,λ3)-phosphinoimine tautomerism in solution using multi-nuclear NMR methods. Synthesis and SC-XRD structure determination of a trisubstituted N,N’,P(III)-monophosphaguanidine is presented, the first structure of a phospha(III)guanidine with two ionizable H atoms. The structural evidence is convincing for an N=C geometry, resulting in both N−H and P−H in the molecule. A detailed computational investigation using DFT methods is presented, with the goal of understanding the tautomeric structure preferences both at the fundamental level (parent molecules with all substituents on the heteroatoms being hydrogen) and using the full structures containing the very bulky 2,6-diisopropylphenyl (Dipp) substituents employed in this study. Arguments are espoused for treating phospha(III)amidines and -guanidines as new types of functional groups, similar to but distinct from the familiar organic analogues. Limited reactivity studies and a voltammetry study of one phospha(III)amidine are included with the supporting information.
Description
Open access article. Creative Commons Attribution 4.0 International Deed license (CC BY 4.0) applies
Keywords
Aminophosphaalkenes , Computational chemistry , Isomerism , Phosphinoimine , Hirshfeld atom refinement
Citation
Masuda, J. D., Amrei, L. M., & Boeré, R. T. (2023). Are monophospha(III)amidines and -guanidines with ionizable hydrogens tautomeric? Towards a deeper understanding of two related hetero-element functional groups. European Journal of Inorganic Chemistry, 26, Article e202300495. https://doi.org/10.1002/ejic.202300495