Deoxygenation of aryl nitro compounds with disilanes

Abstract

Disilanes have been found to represent a new class of deoxygenating agents for aryl nitro compounds. Semiquantitative investigation of the effect of disilane structure on the deoxygenation of 2-nitrobiphenyl (1) at 240°, which yielded 2-aminobiphenyl (3) and carbazole (4), indicated only moderate reduction rate differences among those disilanes studied, with hexachlorodisilane (SisCle) and hexaphenyldisilane (SizPhe) being the most and least reactive, respectively. In contrast, the relative ratio of 4:3 was markedly dependent on disilane structure and varied between limits of ~70:1 and 1:35 for reduction with, respectively, cyclic 1,2-disilacyclopentene derivative 6 and SÍ2CI6. Deoxygenation of nitrobenzene (7a), o-nitrotoluene (7b), and p-nitrotoluene (7c) with hexamethyldisilane (SiaMes) gave their corresponding amines and azo coupling products, with AG1220o = 41 kcal/mol for the pseudo-first-order reduction of 7a in excess SisMes-Qualitative comparison of SisMee deoxygenation rates for 1 and 7a-c at 240°revealed that relative substrate reactivities were not in accord with expectations based on simple steric considerations. Failure of 2-nitrosobiphenyl to undergo deoxygenation by SiaMes has led to the suggestion that disilane reduction of 1 and, by extension, other nitro aromatics does not proceed in a stepwise fashion via nitroso intermediates. Mechanisms which accommodate this restriction and account for the observed stoichiometry and products are discussed in terms of possible transient nitrene species. Attempts to carry out low-temperature photochemical deoxygenation of 1 with SiaMee proved unsuccessful.

Organosilane Esters of 2-Fluoro-2,2-dinitroethanol as Potential Components of Explosives and Propellants

“…If the cleaving reagent was HC1 rather than ROH, one might profitably use an acceptor base in reaction 4, but the adverse effect of amines in the esterifications noted above and the expected (39) base-catalyzed disproportionation of Si2Cl6 to SiCl4 and higher polysilanes argue against this modification. A further complication to the preparation and stability of HE, polynitrodisilanes is a potential, internal redox cleavage of Si-Si by N02 groups, as suggested by the deoxygenation of aryl nitro compounds by disilanes at well-elevated temperatures (37).…”

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

“…Silanes and disilanes has long been known to promote the reduction of nitroarenes even in the absence of a metal catalyst and the reaction can be employed for the synthesis of heterocyclic compounds, but high temperatures are needed unless activated silanes are employed . Iron complexes have been found to catalyze the reduction of nitroarenes to anilines by phenylsilane …”

4,4′-Bipyridyl-Catalyzed Reduction of Nitroarenes by Bis(neopentylglycolato)diboron

“…We also checked other boron compounds: Reactions using hydroboranes, such as HBpin and H 3 B·NMe 3 , gave 2a in 6 and 3% yield, respectively (entries 10 and 11). Furthermore, Me 2 PhSiBpin was not effective for the reduction (entry 12). − …”