Synthesis and Reactivity of a Coordinatively Unsaturated Ruthenium(II) Parent Amido Complex:  Studies of X−H Activation (X = H or C)

Abstract

Bu 2 ) 2 C 6 H 3 ) has been prepared by two independent routes that involve deprotonation of Ru-(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide complex (PCP)Ru(CO)(CtCPh) (5) and ammonia. In addition, complex 2 rapidly activates dihydrogen at room temperature to yield ammonia and the previously reported hydride complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H-H bond is attributed to the combination of a vacant coordination site for binding/activation of dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C-H activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated complex. The reaction of (PCP)Ru(CO)(Cl) with MeLi allows the isolation of (PCP)Ru(CO)-(Me) (8), and complex 8 undergoes an intramolecular C-H activation analogous to the amido complex 2 to produce methane and the cyclometalated complex. Determination of activation parameters for the intramolecular C-H activation transformations of 2 and 8 reveal identical ∆H q {18(1) kcal/mol} with ∆S q ) -23(4) eu and -18(4) eu, respectively. Density functional theory has been applied to the study of intermolecular activation of methane and dihydrogen by (PCP′)Ru(CO)(NH 2 ) to yield (PCP′)Ru(CO)(NH 3 )(X) (X ) Me or H; PCP′ ) 2,6-(CH 2 -PH 2 ) 2 C 6 H 3 ). The results indicate that the activation of dihydrogen is both exoergic and exothermic. In contrast, the addition of a C-H bond of methane across the Ru-NH 2 bond has been calculated to be endoergic and endothermic. The surprising endoergic nature of the methane C-H activation has been attributed to a large and unfavorable change in Ru-N bond dissociation energy upon conversion from Ru-amido to Ru-ammine.

Activation of Carbon−Hydrogen Bonds via 1,2-Addition across M−X (X = OH or NH2) Bonds of d6Transition Metals as a Potential Key Step in Hydrocarbon Functionalization: A Computational Study

“…29 Scheme 6 provides a comparison of the calculated distances for the four atoms that compose the active site for benzene C-H activation by (Tab)Ru(PH 3 )(C 6 H 6 )X for X ) CH 3 , 15c,49 NH 2 , and OH. It is readily apparent from the metric data that the X groups with a lone pair (NH 2 and OH) are quite similar to each other, while the methyl-activating ligand is more disparate.…”

Hydrogen−Deuterium Exchange between TpRu(PMe3)(L)X (L = PMe3 and X = OH, OPh, Me, Ph, or NHPh; L = NCMe and X = Ph) and Deuterated Arene Solvents: Evidence for Metal-Mediated Processes

“…For example, a combined experimental and computational 16 study suggests that the addition of H 2 across the Ru-N bond of (PCP)Ru(CO)(NH 2 ) (PCP ) 2,6-(CH 2 t Bu 2 ) 2 C 6 H 3 ) is thermally favorable, whereas the addition of a C-H bond of methane or benzene is disfavored. 20 …”

Net Hydrogenation of Pt−NHPh Bond Is Catalyzed by Elemental Pt

“…[5][6][7][8] Recently, C-H activation of hydrocarbons via net 1,2-addition of C-H bonds across metal-heteroatom bonds using late transition metals (with g6 d-electrons) bearing formally anionic ligands (e.g., -NHR or -OR) has been reported. [9][10][11][12][13][14] Despite interest in these C-H and H-H bond transformations, questions regarding the mechanism remain. 8 Thus, reaction of H 2 with 2 via a similar mechanism would involve Pt mediated 1,2-addition of H 2 to give ( t bpy)Pt(Me)(NH 2 Ph)(H) with aniline dissociation to form 3 and subsequent decomposition of 3 to methane, Pt(s), and free t bpy.…”

“…We initially presumed this straightforward pathway, which is consistent with the general notion of reactions with related systems. 5,7,8,13,19,20 Monitoring ( 1 H NMR) the reaction of 2 with H 2 and a plot of [2] versus time reveals an induction period ( Figure 2A). The observation of an induction period led us to consider Pt(s) as a heterogeneous catalyst.…”