Quinoneimido Complexes of a Metalloporphyrin: Isolation, X‐ray Crystal Structures, and DFT Calculations

Abstract

Quinoneimine and quinoneimido ligands (designated here as QuNR and QuN À , respectively) bear close relevance to arylamido (ArNR À ) and arylimido (ArN 2À ) ligands (Scheme 1). [1] The latter two have been subjected to immense studies in the field of metal-ligand multiple-bonded complexes and in metal-catalyzed nitrogen/group-transfer catalysis. [2] While there are a large number of metal complexes of quinoneimines known in the literature, [3,4] quinoneimido complexes of transition metals are sparse. [5][6][7] In the early 1990s, Sharp and co-workers [5a,b] reported di-or tetranuclear rhodium complexes analogous to bridging quinoneimido complexes. Subsequently, bridging quinoneimido ligands were reported to exist in a few di-or trinuclear osmium [5c] and palladium/platinum [5d] complexes and hexanuclear osmium complexes, [5e] with the oxidation states of the metal ions being +2 or less. Terminal quinoneimido complexes of transition metals are extremely rare, which were once considered (as hypothetical species) in the oxidation of nickel o-phenylenediamine complexes [8] and were proposed to be the key intermediates in dirhodium-catalyzed carbazole formation from biaryl azides. [9] To the best of our knowledge, only one transition-metal complex bearing a terminal quinoneimido ligand has been isolated and reported in literature, that is, a mono(quinoneimido) nickel(II) complex recently reported by Stephan and Bai. [6] Herein we report the isolation, spectroscopy, and X-ray crystal structures of several terminal quinoneimido complexes of ruthenium(IV), which constitute the first quinoneimido complexes of a metalloporphyrin.Our approach to quinoneimido complexes came from an unexpected reaction of high-valent metal-oxo complexes [Ru VI A C H T U N G T R E N N U N G (por)O 2 ] (por = porphyrinato 2À ) with an aniline derivative, in contrast to the formation of the mono(quinoneimido) nickel(II) complex from reaction of a b-diketiminate nickel(II) complex with an aryl azide. [6] We previously reported that [Ru VI O 2 ] (por = ttp, [11a] 4-MeO-tpp, [11b] 4-Cl-tpp [11c] ) with 20 equiv of 2,6-dimethylaniline in ethanol for 8 h produced a red purple precipitate, which was found to be a mixture of quinoneimido complexes [Ru IV (OH)] (por = ttp: 2 a; 4-MeO-tpp: 2 b; 4-Cl-tpp: 2 c) (yield % 65 %). Complexes 2 probably resulted from the hydrolysis of 1 owing to the presence of a trace amount of water in the solvent. Indeed, stirring a mixture of [a] Dr.

Synthesis and Reactivity of a Cobalt-Supported Singlet Nitrene

“…Aryl imido 3 also rapidly reacts with t BuNH 2 to afford the green diamagnetic Co III quinone imido complex [(TIMMN mes )­Co III (NC 6 H 4 N t Bu)]­(PF 6 ) 2 ( 6 ) (Scheme , bottom). − Trivalent 6 is unstable in solution at room temperature and quickly decomposes into a complicated mixture of products. A quick 5-min reaction, carried out at −25 °C, followed by careful low-temperature workup, allowed for the isolation of 6 in 59% yield.…”