Hydrogen- and Oxygen-Driven Interconversion between Imido-Bridged Dirhodium(III) and Amido-Bridged Dirhodium(II) Complexes

Abstract

The reaction of [Cp*RhCl(2)](2) (Cp* = eta(5)-C(5)(CH(3))(5)) with 2 equiv of p-toluenesulfonamide in the presence of KOH resulted in the formation of the sulfonylimido-bridged dirhodium(III) complex [(Cp*Rh)(2)(mu-NTs)(2)] (1a; Ts = SO(2)C(6)H(4)CH(3)-p). The imido complex 1a reacted with hydrogen donors such as H(2) and 2-propanol to give the sulfonylamido-bridged dirhodium(II) complex [(Cp*Rh)(2)(mu-NHTs)(2)] (2). Treatment of the (amido)rhodium(II) complex 2 with O(2) regenerated the (imido)rhodium(III) complex 1a. Complex 1a also underwent reversible protonation to afford the cationic amido- and imido-bridged dirhodium(III) complex [(Cp*Rh)(2)(mu-NHTs)(mu-NTs)](+) (4), which further reacted with H(2) or 2-propanol to give the (hydrido)bis(amido)dirhodium(III) complex [(Cp*Rh)(2)(mu-H)(mu-NHTs)(2)](+) (5). On the basis of DFT calculations and experimental results using 4 and 5, the reaction of 1a with H(2) proved to proceed via heterolytic cleavage of H(2) assisted by the sulfonyl oxygen atom followed by proton migration from the metal center. Furthermore, the redox interconversion between 1a and 2 was applied to catalytic aerobic oxidation of H(2) and an alcohol by using 1a as a well-defined dinuclear catalyst. The iridium complex [(Cp*Ir)(2)(mu-NTs)(2)] (1b) as well as a rhodium complex [Cp*RhCl(2)](2) without bridging imido ligands did not catalyze these aerobic oxidation reactions.

Synthesis and Reactivity of Coordinatively Unsaturated Dinuclear Ruthenium Bridging Imido Complexes

“…Anal. Calcd for C 38 [(Cp*Ru) 2 (μ-t-BuNCHNC 6 H 4 )(t-BuNC) 3 ] (5). To a solution of 2b (67 mg, 0.10 mmol) in THF (10 mL) was added t-BuNC (0.11 mL, 1.0 mmol).…”

Metall‐Ligand‐Kooperation

“…Der zweikernige Bis(tosylimido)‐verbrückte Rh III ‐Komplex 40 bewirkt die heterolytische Spaltung von H 2 zum Bis(amido)‐verbrückten Rh II ‐Komplex 41 (Schema ) 49. Eine DFT‐Studie zeigt, dass ein plausibler Reaktionsmechanismus mit der Sulfonyl‐vermittelten heterolytischen H 2 ‐Spaltung beginnt ( TS‐42 in Schema ), gefolgt von einem Protonentransfer vom Sulfonyl‐Sauerstoff zum Imid‐Stickstoff und der Protonenwanderung von Rh‐H zu einem weiteren Imid.…”

Bifunctional Transition Metal-Based Molecular Catalysts for Asymmetric Syntheses

“…Thus, the present bifunctional molecular catalyses can provide a wide substrate scope and applicability in organic synthetic chemistry. Thus, the rational design of the amine ligand that adjusts the balance of the electronic factors on the M/NH units in the bifunctional catalysts is crucially important to exploit further unprecedented catalyst performance [9,[77][78][79][80]. Finally, the industrial outlook for asymmetric reduction with bifunctional catalysts is bright, because of their excellent catalyst performance, wide substrate scope, operational simplicity, and economic viability as well as the growing awareness of the need for green chemistry [6].…”