Cleavage of Nitrogen–Hydrogen Bonds of Ammonia Induced by Triruthenium Polyhydrido Clusters

Abstract

NÀH bond activation of amines has attracted increasing attention owing to its applicability to the synthesis of various amino compounds, and the development of a new and effective reaction system for the activation of ammonia must be one of the most important research targets in connection with the transformation of abundant and inexpensive ammonia into a useful amino compound.[1] However, successful examples of activation of the NÀH bond of ammonia are still rare because of both the high NÀH bond dissociation energy ( % 104 AE 2 kcal mol À1 ) [2] and the difficulty in forming an NÀH s complex.[3]The groups of Milstein [1g, i, j] and Hartwig [1k, q] showed independently that some mononuclear iridium(i) complexes exhibited activity towards oxidative addition of ammonia. A highly unsaturated 14 e species with T-shaped geometry was proposed as a reactive intermediate for the NÀH bond cleavage on the basis of kinetic studies.[1q] Some complexes containing a d 0 metal center, such as [Cp* 2 MH 2 ] (M = Zr, Hf; Cp* = pentamethylcyclopentadiene), [1b, c, e] [Cp* 2 ScR], [1f] and [(neopentyl) 3 Ta = C(H)(tBu)], [1h] also activated ammonia to generate amido and nitrido complexes. There have, thus far, been examples of bimetallic oxidative addition to ammonia. A trinuclear carbonyl cluster, [Os 3 (CO) 11 (L)] (L = c-C 6 H 8 or CH 3 CN), effectively activates ammonia with the participation of the two osmium centers to produce the m-amido complex [Os 3 (CO) 10 (m-H)(m-NH 2 )]. [1a, d] A multimetallic system may work more efficiently for bond activation than a monometallic complex owing to the cooperative action of the metal centers. Each metal center would be allotted a part as a binding site and an activation site, and the transition state of the bond-activation step may, therefore, be stabilized.

Activation of Linear Alkanes by a Hydrido Triruthenium Cluster and Associated Skeletal Rearrangements

“…4 Complex 1 fully realized the cooperative action of metal centers in the bondbreaking step of compounds such as saturated and unsaturated hydrocarbons, nitriles, 5 and ammonia. 6 It was also demonstrated that complex 1 is a suitable soluble model of adsorption sites for benzene 7 and pyridine 8 on a close-packed metal surface. …”

E–H Bond Activation of Ammonia and Water by a Geometrically Constrained Phosphorus(III) Compound

“…[8] New routes resulting in the activation of NÀHb onds in ammonia are particularly appealing because of the dearth of transition-metal systems capable of effecting such atransformation [9][10][11][12][13][14][15][16][17][18][19][20][21] and the relevance of N À H activation to an umber of potentially important industrial processes. [22] In addition to these high profile examples,r ecent studies have shown that complexes of phosphorus(III) with distorted geometry can cleave arange of polarized EÀHbonds (E=Oor N).…”

“…[9][10][11][12][13][14][15][16][17][18][19][20][21] Therefore,a dvances in main group mediated activation of ammonia are of great interest. [4, 5, 6c-d,24, 26, 27, 30-32] Ther eaction of 1 with ammonia gas (1 atm) results in the quantitative conversion of 1 to anew product, 2 (Scheme 2).…”

The Dehydrogenation of Alcohols through a Concerted Bimetallic Mechanism Involving an Amido‐Bridged Diiridium Complex

“…Noteworthy, to the best of our knowledge, this is the first example of a low-valent late metal mixed parent imido/amido complex ever reported. (14), Ir1-Ir2 2.7758(2), Ir1-Ir1' 2.8572(3), Ir1-H 1.788 (19); Ir1'-Ir1-Ir2 59.025(4), Ir1-Ir2-Ir1' 61.950 (8), N1-Ir1-N1' 73.58 (16), N1-Ir2-N1´ 73.79 (19), Ir1-N1-Ir2 86.90(13), Ir1-N1-Ir1' 89.90 (13). Ct represents the midpoints of the olefinic bonds.…”

“…[19] In this context, the transformation of a methoxo diiridium compound to imido clusters 2 and 3 upon interaction with ammonia can be viewed formally as a multiple activation of ammonia. The mere existence of parent imido complexes of late metals (Co triad and after) in low oxidation states is extremely rare, situation explained in terms of d p repulsions between the metal and the nucleophilic nitrogen centres.…”