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Disulfonimides versus Phosphoric Acids in Bronsted Acid Catalysis: The Effect of Weak Hydrogen Bonds and Multiple Acceptors on Complex Structures and Reactivity.

ABSTRACT: In Brønsted acid catalysis, hydrogen bonds play a crucial role for reactivity and selectivity. However, the contribution of weak hydrogen bonds or multiple acceptors has been unclear so far since it is extremely difficult to collect experimental evidence for weak hydrogen bonds. Here, our hydrogen bond and structural access to Brønsted acid/imine complexes was used to analyze BINOL-derived chiral disulfonimide (DSI)/imine complexes. 1H and 15N chemical shifts as well as 1JNH coupling constants revealed for DSI/imine complexes ion pairs with very weak hydrogen bonds. The high acidity of the DSIs leads to a significant weakening of the hydrogen bond as structural anchor. In addition, the five hydrogen bond acceptors of DSI allow an enormous mobility of the imine in the binary DSI complexes. Theoretical calculations predict the hydrogen bonds to oxygen to be energetically less favored; however, their considerable population is corroborated experimentally by NOE and exchange data. Furthermore, an N-alkylimine, which shows excellent reactivity and selectivity in reactions with DSI, reveals an enlarged structural space in complexes with the chiral phosphoric acid TRIP as potential explanation of its reduced reactivity and selectivity. Thus, considering factors such as flexibility and possible hydrogen bond sites is essential for catalyst development in Brønsted acid catalysis.

SUBMITTER: Rothermel K

PROVIDER: S-EPMC6863592 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Disulfonimides versus Phosphoric Acids in Brønsted Acid Catalysis: The Effect of Weak Hydrogen Bonds and Multiple Acceptors on Complex Structures and Reactivity.

Rothermel Kerstin K Žabka Matej M Hioe Johnny J Gschwind Ruth M RM

The Journal of organic chemistry 20191002 21

In Brønsted acid catalysis, hydrogen bonds play a crucial role for reactivity and selectivity. However, the contribution of weak hydrogen bonds or multiple acceptors has been unclear so far since it is extremely difficult to collect experimental evidence for weak hydrogen bonds. Here, our hydrogen bond and structural access to Brønsted acid/imine complexes was used to analyze BINOL-derived chiral disulfonimide (DSI)/imine complexes. <sup>1</sup>H and <sup>15</sup>N chemical shifts as well as <su ...[more]

PMID: 31550152

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Project description:The crystalline forms of tris(pyridin-2-yl)phosphoric triamide, OP[NH-2Py]3 were investigated using single crystal X-ray diffraction, both as a metal complex [Co{(O)P[NH-2Py]2[NH-2PyH]}2]Cl3, compound 1, and as the purely organic pseudopolymorphs, the pure/anhydrate OP[NH-2Py]3, 2, monohydrate 2OP[NH-2Py]3·H2O, 3 and solvate 2OP[NH-2Py]3·2DMF·H2O, 4, respectively. An improved model of the metal organic framework (MOF) structure of Cu(ii)O6 {[Cu(OCHO)3][(CH3)2NH2]} n , 5 is also reported. Compound 1 is the first example of a discrete chelate phosphoric triamide (PT) complex with an [N]3P(O)-based backbone which in the PT compound acts as a flexible tridentate ligand. The structures 1, 3 and 4 crystallize in the monoclinic space group P21/n, while the anhydrous form 2 crystallizes in the R3̄ trigonal space group. 5 which was obtained as a byproduct of the synthesis process of coordination compounds of OP[NH-2Py]3, crystallizes in the monoclinic space group I2/c. Hydrogen bonding pattern analysis for the different solid state forms of OP[NH-2Py]3 (2-4) shows a 2D sheet of the N-H⋯N linked molecules for 2, and a 1D chain and a ten-membered ring motif, both formed via the hydrogen bonds N-H⋯O, N-H⋯N and O-H⋯O, for 3 and 4, respectively. Of note is the unusual absence of the expected hydrogen bond interaction N-H⋯O[double bond, length as m-dash]P of PT compounds and also a lack of any significant π interactions in structure 2. The role of the solvent/hydrate and substituent (aminopyridine) in the formation of the expected hydrogen bond interactions in the studied solid state forms is also investigated. For these structures, crystal packing analysis using 3D Hirshfeld surface (HS), 2D fingerprint plot (FP) and enrichment ratio (E) calculations confirm a competition between the pyridinyl nitrogen and phosphoryl oxygen atoms as H-bond acceptors to construct the N-H⋯N or N-H⋯O contacts. Moreover, the significant differences between the anhydrous form of OP[NH-2Py]3, 2, and the monohydrate and solvate forms, 3 and 4, can be correlated to the pseudo-infinite (in 2) versus finite values (in 3 and 4) for the upper values of d e and d i on the related full FPs.

Dataset Information

Disulfonimides versus Phosphoric Acids in Bronsted Acid Catalysis: The Effect of Weak Hydrogen Bonds and Multiple Acceptors on Complex Structures and Reactivity.

Publications

Disulfonimides versus Phosphoric Acids in Brønsted Acid Catalysis: The Effect of Weak Hydrogen Bonds and Multiple Acceptors on Complex Structures and Reactivity.

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