Road Maps for Nitrogen‐Transfer Catalysis: The Challenge of the Osmium(VIII)‐Catalyzed Diamination

Abstract

Although the Sharpless dihydroxylation has been used on laboratory and industrial scales for several decades, an analogous osmium-catalyzed diamination is unknown. To explore the reaction of osmium(VIII) oxo-imido complexes with C=C bonds, density functional calculations have been performed. The calculations predict a chemoselective and perispecific [3+2] addition of the NH=Os=NH moiety of diimidodioxoosmium(VIII) to ethylene, yielding dioxoosma-2,5-diazolidine. At first sight, this metallacycle seems extremely stable; it is more stable than diimidoosma-2,5-dioxolane by 40 kcal mol(-1). However, a comparison of the thermodynamic reaction profiles for catalytic model cycles of dihydroxylation, aminohydroxylation, and diamination reveals that, contrary to common belief, the instability of the metal=N bond in the osmium(VIII) imido complex rather than the stability of the metal-N bond in the osmium(VI) intermediate causes most of the energy difference between the metallacycles. Substituents on the substrate have a small effect on the thermodynamic reaction profiles, whereas substituents on the imido ligands allow steric and electronic control of the reaction free enthalpies in the range of up to 25 kcal mol(-1). The results of this study help identify potential challenges in the development of the as-yet hypothetical title reaction and provide a modular concept for exploring novel catalytic routes.

Chemo‐ and Periselectivity in the Addition of [OsO2(CH2)2] to Ethylene: A Theoretical Study

“…Deubel and MuÇiz recently reported theoretical studies of the reaction pathways of the addition of [OsO 2 (NH) 2 ] to ethylene. [5] The calculations predict that the three possible [3+2] addition reactions are kinetically and thermodynamically favored over the two [2+2] additions, and that the diamination should be the most favored reaction. Pioneering experimental studies of the diamination of olefins with osmium trisimido compounds [OsO (NR) 3 ] have recently been reported by MuÇiz.…”

Theoretical Study of Ethylene Addition to O=W(=CH2)(CH3)2

“…The introduction of an imido group in OsO 2 (NH) 2 does not change the overall profile of the reaction. Deubel and Muñiz [4] reported that the three [3+2] addition reactions of ethylene which are possible for the system are clearly favoured over the [2+2] reactions. The authors predicted that the calculated activation barriers decrease with the order O/O > O/NH > NH/NH.…”

“…Various theoretical studies [1] have shown that the addition of olefins to OsO 4 initiates with a concerted [3+2] reaction rather than through a two-step process with initial [2+2] addition across an Os=O double bond. Subsequent work [2] has indicated that other metal oxides such as RuO 4 and ReO 3 − also prefer a [3+2] mechanism over a [2+2] reaction [3].…”

“…Subsequent work [2] has indicated that other metal oxides such as RuO 4 and ReO 3 − also prefer a [3+2] mechanism over a [2+2] reaction [3]. The introduction of an imido group in OsO 2 (NH) 2 does not change the overall profile of the reaction.…”

A Convenient and Highly Productive Aminohydroxylation Protocol Employing an Osmium‐Diamine Catalyst

“…[1] These reagents induce a completely chemoselective reaction in favour of diamination [2] and lead to monomeric osmium-diamine chelates with an unprecedented stability ( Figure 1). [3] The inherent properties of these products prompted us to examine whether or not such compounds themselves could act as catalyst precursors for oxidation chemistry.…”