Nitrene Insertion into Aromatic and Benzylic C−H Bonds Catalyzed by Copper Complexes of Fluorinated Bis‐ and Tris(pyrazolyl)borates

Abstract

Fluorinated bis-and tris(pyrazolyl)boratocopper complexes catalyze the nitrene insertion to CÀ H bonds of aromatic hydrocarbons efficiently producing amination products in good to excellent yields at room temperature. Imidoiodanes, PhI=NTs (Ts = p-toluenesulfonyl) and PhI=NNs (Ns = p-nitrophenylsulfonyl) serve as the nitrene source. The bis(pyrazolyl)borate catalyst [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(NCMe) with PhI=NNs produced the arene CÀ H functionalized product of mesitylene in 87 % yield with only trace amounts of benzylic CÀ H insertion. The use of [H 2 B (3,5-(CF 3 ) 2 -4-(NO 2 )Pz) 2 ]Cu(NCMe) that has an even weakly donating pyrazolate generated the arene CÀ H insertion product exclusively. The tris(pyrazolyl)borate complex [HB(3,5-(CF 3 ) 2 Pz) 3 ] Cu(NCMe), in contrast, generated the benzylic amination product from mesitylene and PhI=NNs in 82 % yield with only very minor amounts of arene CÀ H functionalization. DFT calculations suggest that Cu-nitrene moiety generated from [HB (3,5-(CF 3 ) 2 Pz) 3 ]Cu(NCMe) and PhI=NNs activates the benzylic CÀ H bond of mesitylene via a hydrogen atom abstraction (HAA) followed by a radical rebound (RR) pathway, whereas the functionalization of sp 2 CÀ H bonds of mesitylene by [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(NNs) ensues possibly via a nitrene addition to the arene core.[a] T.

Carbonyl and Isocyanide Complexes of Copper and Silver Supported by Fluorinated Poly(pyridyl)borates

“…There are also no reports to our knowledge of bis­(2-pyridyl)­borate ligands such as 4 bearing substituents at the pyridyl ring 6-position, which due to their proximity to the coordinated metal atom should provide better protection to a metal site, relative to 6-unsubstitued bis­(2-pyridyl)­borate chelators such as [Ph 2 B­(Py) 2 ] − . Furthermore, based on the chemistry observed with pyrazolyl ring substituted bis­(pyrazolyl)­borates (e.g., 2 ), ,,,, we expect ligands of the type 4 with substituents at the pyridyl ring 6-position to be quite useful.…”

“…As a result, metal complexes of fluorinated ligands in comparison to their nonfluorinated, hydrocarbon counterparts usually display different properties such as relatively high thermal and oxidative stability, volatility, and unique reactivity profiles. − They are also ideal for applications in fluorous-biphase media and supercritical CO 2 . − Fluorinated poly­(pyrazolyl)­borates (which belong to a family known as scorpionates) , such as [HB­(3,5-(CF 3 ) 2 Pz) 3 ] − ( 1 , Pz = pyrazolyl, Figure ) and [H 2 B­(3,5-(CF 3 ) 2 Pz) 2 ] − ( 2 ) are a particularly useful group of ligands as they have facilitated the stabilization of rare species such silver­(I)-acetylene, copper­(I) and silver­(I)-organo azide, and silver­(I)-dimethyl diazomalonate complexes and to probe their chemistry under readily accessible conditions. They are also valuable in applications involving catalysis including those in supercritical CO 2 , − ethylene sensing, to olefin-paraffin separations . For example, fluorinated tris­(pyrazolyl)­borates have been useful in supporting catalytically active and fairly reactive copper complexes, without the ligand itself getting destroyed. , The silver complex [HB­(3,5-(CF 3 ) 2 Pz) 3 ]Ag is an effective mediator for the functionalization of inert C–Cl bonds of halocarbons as well as C–H bonds of saturated hydrocarbons via catalytic carbene insertion chemistry. ,,, The bis­(pyrazolyl)­borate [H 2 B­(3,5-(CF 3 ) 2 Pz) 2 ]Cu serves as an excellent nonporous material for the separation of ethylene from an ethylene/ethane mixture …”

Adducts of a Triangular Copper(I) Pyrazolate with Thiophenic Compounds Featuring Short Cu(I)–S Contacts

“…4-Nitro-3,5-bis­(trifluoromethyl)-1 H -pyrazole was prepared according to a literature method . Dias and co-workers used this pyrazole to prepare bis- or tris­(pyrazolyl)­borates and their Cu­(I), Ag­(I) complexes. , However, the coordination chemistry of this pyrazolyl ligand has not been extensively studied. In this paper, Cu 3 pz 3 was first synthesized by the reaction of 4-nitro-3,5-bis­(trifluoromethyl)­pyrazole with Cu 2 O in toluene at 80 °C.…”

Nitrene transfer from a sterically confined copper nitrenoid dipyrrin complex

“…Cu nitrenoid (Cu–NR) species are commonly invoked as the reactive intermediate for C–H bond activation and alkene aziridination (Fig. 1); 5,10,14–36 however, the fleeting nature of these highly reactive intermediates has precluded their spectroscopic observation and direct analysis of their reactivity profiles. In the absence of structural authentication and rigorous characterization, the intermediacy of a copper nitrenoid can be inferred from computational support 37,38 and through kinetic analysis of enantioselective aziridination.…”