Hydrogenation and protonation of parent imido complexes have attracted much attention in relation to industrial and biological nitrogen fixation. The present study reports the structure and properties of the highly unsaturated diiridium parent imido complex [(Cp*Ir)(2)(μ(2)-H)(μ(2)-NH)](+) derived from deprotonation of a parent amido complex. Because of the Lewis acid-Brønsted base bifunctional nature of the metal-NH bond, the parent imido complex promotes heterolysis of H(2) and deprotonative N-H cleavage of ammonia to afford the corresponding parent amido complexes under mild conditions.
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.
The mono(mesylamido)-bridged diiridium(III) complex [(Cp*IrCl)2(μ2-H)(μ2-NHMs)] (Cp* = η5-C5(CH3)5, Ms = SO2CH3) undergoes reversible dehydrochlorination to afford the unsaturated imido-bridged dinuclear complex [Cp*Ir(μ2-H)(μ2-NMs)IrClCp*] (
2
). The reaction of
2
with trimethylphosphine gives the simple adduct [Cp*Ir{P(CH3)3}(μ2-H)(μ2-NMs)IrClCp*], while the reaction with CO results in sequential formation of the mono- and dicarbonyl Ir(II) complexes [Cp*Ir(CO)(μ2-NHMs)IrClCp*] and [{Cp*Ir(CO)}2(μ2-NMs)] with concomitant umpolung of the bridging hydrido ligand in
2
to the amido proton.
The azido-bridged diruthenium and diiridium complexes [(LMCl)(2)(micro-N(3))(2)] (LM = CymRu, Cp*Ir; Cym = eta(6)-p-cymene, Cp* = eta(5)-C(5)(CH(3))(5)) are sequentially converted into the amido-bridged complexes [(LMCl)(2)(micro-NH(2))(micro-N(3))] and [(LMCl)(2)(micro-NH(2))(micro-H)] upon treatment with 2-propanol and a base.
Preparation of [Cp*Ir(µ 2 -NTs) 2 IrCp*] (1). A mixture of [Cp*IrCl 2 ] 2 (2.0002 g, 2.51 mmol), 1 TsNH 2 (0.8749 g, 5.11 mmol) and KOH (1.1680 g, 20.8 mmol) in CH 2 Cl 2 /H 2 O (20 mL/20 mL) was stirred for 8 h at room temperature. The resultant organic layer was washed with H 2 O (10 mL × 5) and chromatographed on alumina under air. A red band eluted with CH 2 Cl 2 was collected and evaporated to dryness. The resultant solid was recrystallized from CH 2 Cl 2 /diethyl ether (10 mL/100 mL) to yield 1 as dark red crystals (2.4022 g, 2.42 mmol, 96%).
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