A Prototype for Catalyzed Amide Bond Cleavage:  Production of the [NH₃, H₂O]^•+Dimer from Ionized Formamide and Its Carbene Isomer

Abstract

The reaction of ionized formamide H(2)NCHO(*)(+) with water leads to an exclusive loss of CO from the complex. This contrasts with the unimolecular reaction of low-energy ionized formamide, which loses exclusively one hydrogen atom. The unimolecular loss of CO is not observed because it involves several H-transfers corresponding to high-energy barriers. Experimental and theoretical studies of the role of solvation by water on the fragmentation of ionized formamide leads to three different results: (i) In contrast with different systems previously studied, in which solvation plays only a role on one or two steps of a reaction, a molecule of water is efficient in the catalysis of the decarbonylation process because water catalyzes all the steps of the reaction of ionized formamide, including the final dissociation of the amide bond. (ii) The catalyzed isomerization of carbonylic radical cations into their carbene counterparts is shown to be an important step in the process. To study this step, a precise probe, characterizing the carbene structure by ion-molecule reaction, is for the first time described. (iii) Finally, decarbonylation of ionized formamide yields the [NH(3), H(2)O](*)(+) ion, which has not been generated and experimentally studied previously. By this method, the [NH(3), H(2)O](*)(+) ion is generated in abundance and with a low internal energy content, allowing one either to prepare, by ligand exchange, a series of other solvated radical cations or to generate covalent structures such as distonic ions. First results on related systems indicate that the conclusions obtained for ionized formamide are widespread.

Reactions of [NH3+·, H2O] with carbonyl compounds: A McLafferty rearrangement within a complex?

“…The [NH 3 ϩ⅐ , H 2 O] ion was generated in the cell by reaction with water of ionized aminohydroxycarbene HOCNH 2 ⅐ϩ m/z 45, produced in the external source by electron ionization of oxamide [3]. After transfer into the cell, the ion m/z 45 was allowed to react 1.5 s with water, then [NH 3 ϩ⅐ , H 2 O] m/z 35 was isolated by applying low-voltage single radio frequency (rf) pulses (soft shots) at the resonance frequencies of all unwanted ions.…”

“…In this case, the hot intermediate reacts by H ϩ transfer, whereas low energy collision induced dissociation of the solvated complex leads to H ⅐ abstraction [1]. CH 2 CHOH ⅐ϩ ϩ (CH 3 CHO) 3 3 [CH 2 CHOH ⅐ϩ , CH 3 CHO] ϩ (CH 3 CHO) 2 (1)…”

“…A variety of methods have been described for the preparation of solvated radical cations [2][3][4][5][6][7][8][9]. Among them, the preparation of the water solvated ammonia radical cation has been recently described [3] by use of a specific ion molecule reaction between ionized formamide (or its carbene isomer) and water (eq 2).…”

“…Among them, the preparation of the water solvated ammonia radical cation has been recently described [3] by use of a specific ion molecule reaction between ionized formamide (or its carbene isomer) and water (eq 2). The bimolecular reactions of the [NH 3 ϩ⅐ , H 2 O] ion allow the preparation of new ammonia solvated species [3]. The dissymetric repartition of the charge facilitates the replacement of water by the neutral reactant, allowing the production of ions such as [NH 3 …”

“…The bimolecular reactions of the [NH 3 ϩ⅐ , H 2 O] ion allow the preparation of new ammonia solvated species [3]. The dissymetric repartition of the charge facilitates the replacement of water by the neutral reactant, allowing the production of ions such as [NH 3 …”