Ortho−Nitrosation of Anilines on a Ruthenium Hydridotris(pyrazolyl)borato Complex and Oxidation of the Resulting Coordinated Amine Groups

Nitrosation of anilines at the ortho
position was found to proceed
on a ruthenium hydridotris­(pyrazolyl)­borato (Tp) complex. Reactions
of [TpRuCl2(NO)] (1) with primary anilines
4-NH2C6H4R (R = tBu, H)
in the presence of excess Et3N in CH2Cl2 gave amine-chelated nitrosoarene complexes [TpRuCl­{N­(O)–C6H3R–NH2-κ2N,N}] (R = tBu (2a), H (2b)). Use of 2,4,6-trimethylaniline afforded an
aryldiazenido complex [TpRuCl2{NNC6H2(Me)3}] (3) without forming the nitrosation
product because of the introduction of the Me substituents at the
ortho positions. On the other hand, in the case of secondary amines
(N-methylanilines 4-NH­(Me)­C6H4R (R = tBu, H)), similar reactions gave amine-chelated
nitroso complexes [TpRuCl­{N­(O)–C6H3R–NHMe-κ2N,N}] (R = tBu (4a), H (4b)) and
imine-chelated nitroso complexes [TpRuCl­{N­(O)–C6H3R–NCH2-κ2N,N}] (R = tBu
(5a), H (5b)). Conversion of 4b into 5b by O2 was disclosed by 1H NMR monitoring. Moreover, oxidative reaction of 2a afforded an amide-chelated nitroso complex [TpRuCl­{N­(O)–C6H3(tBu)–NH-κ2N,N}] (6a) through
one-proton release from the NH2 group.