Oxidative Addition of Ammonia to Form a Stable Monomeric Amido Hydride Complex

Abstract

The insertion of an iridium complex into an N-H bond in ammonia leads to a stable monomeric amido hydride complex in solution at room temperature. This reaction advances the transition-metal coordination chemistry of ammonia beyond its role for more than a century as an ancillary ligand. The precursor for this insertion reaction is an iridium(I) olefin complex with an aliphatic ligand containing one carbon and two phosphorus donor atoms. Kinetic and isotopic labeling studies indicate that olefin dissociates to give a 14-electron iridium(I) fragment, which then reacts with ammonia. This cleavage of the N-H bond under neutral conditions provides a foundation on which to develop future mild catalytic transformations of ammonia, such as olefin hydroamination and arene oxidative amination.

On the Ambiphilic Reactivity of Geometrically Constrained Phosphorus(III) and Arsenic(III) Compounds: Insights into Their Interaction with Ionic Substrates

“…It is also worth noting that the substrates cope of such compounds includes molecules such as ammonia,which hashistorically provendifficult to activate using precious metalc atalysts due to the unfavourable coordination/activation equilibrium. Newr outes resultingi nt he activation of NÀHb onds in ammonia are particularly appealing, becauseo ft he dearth of transition-metal systems capable of effecting such at ransformation, [7][8][9][10][11][12][13][14][15][16][17][18][19] and the relevance of NÀHa ctivation to an umber of potentially important industrialp rocesses. [20] More recently,g eometrically constrained compounds based on phosphorus(III) have also received significant attention in this field.…”

Density Functional Theoretical Study on the N-H Bond Activation by Ir Pincer Complexes

“…Although many factors control the kinetics and the thermodynamics of the coupling reaction, the relative stability can be affected by the electron density at the metal center. 2 The strongly electron donating ligand [Cy-PSiP] favored the amido hydride complex over the ammonia complex. 4 The coordination of ammonia would transfer considerable amount of electron density to the already electron-rich metalcenter in the presence of other electron donating ligand.…”

“…For example, the insertion of an Ir complex into an N-H bond in ammonia forms a stable amido hydride complex in solution at room temperature. 2 Recently, a report showed that Ir complexes supported by silyl pincer ligands undergo an N-H bond oxidative addition for both ammonia and aniline, which forms isolable [Cy-PSiP]Ir(H) (NHR) (R = H, or aryl;…”

“…2 An appropriate pincer ligand can be used to control the thermodynamics and kinetics of the chemical transformation between the two types of complexes. In this study the density functional theoretical (DFT) studies were conducted in order to determine the Gibbs energy of the activation of N-H bond coupling in 1 and the relative stability between the amido hydride complex and the amine complex.…”

“…4 The coordination of ammonia would transfer considerable amount of electron density to the already electron-rich metalcenter in the presence of other electron donating ligand. 2 In summary, the DFT calculations were performed for the N-H coupling reaction of the pincer type Ir (III) complexes. The transition states were successfully located, and the thermodynamic and kinetic results were consistent with the existing experimental data and previous computational results for the same types of complexes.…”