Palladated azobenzenes and regiospecific aromatic metaloxylation

Reactions of m-chloroperoxybenzoic acid with dimeric cyclopalladated complexes derived from 2-phenyl-2-oxazolines

“…The most salient feature of the 1 H NMR spectrum of compound 3a was the presence of resonance signals in the region of 6.5-6.9 ppm assigned to two aromatic hydrogens of the C 6 H 4 fragment of the oxazoline ligand. Such a high-field shift for the signals of aromatic hydrogens in N,O-Pd(II) complexes compared to those of the starting CPCs was noted in other studies [41,44,49]. Complex 4a was isolated in 13 % yield when standard reaction conditions were used (EtOAc, rt, 18 h).…”

“…Oxygen insertion into the C-Pd bond of cyclopalladated complexes can be accomplished by any of the following reagents: m-chloroperoxybenzoic acid (m-CPBA) (used alone [34][35][36][37][38][39][40][41][42][43][44][45][46] or with an iron(III) porphyrin catalyst [37]), other peroxy acids [40], t-BuOOH (used alone [47][48][49][50] or with a catalyst [34,35,[47][48][49][50][51][52]), hydrogen peroxide in the presence of an iron(III) porphyrin catalyst [53], pentafluoroiodosylbenzene C 6 F 5 IO (alone [37,52], in a combination with t-BuOOH [37,52] or in the presence of an iron(III) porphyrin catalyst [37,52]), iodosylbenzene C 6 H 5 IO [54], [di(benzoyloxy)iodo]benzene PhI(O 2 CPh) 2 [55] and the molybdenum peroxide MoO(O 2 ) 2 ÁHMPAÁH 2 O (HMPA = hexamethylphosphoric triamide) [14,56]. The mechanisms involved in these transformations appear to be different [5]; however, in all cases, the C-Pd bond is transformed into the C-O-Pd moiety.…”

“…However, in spite of the number of studies focused on reactions of CPCs with m-CPBA, only a few rather similar types of palladacycles have been tested: (1) dinuclear complexes of the CN type derived from azoarenes ( Fig. 1, type A) [36,44,45], (2) mononuclear complexes based on azoarenes and having an additional cyclopentadienyl ligand (B) [20,39], (3) mononuclear complexes based on azoarenes with an SR (C) [40][41][42][43] or other chelating substituent (D) [34,35], (4) dinuclear complexes of the CS type obtained from dibenzyl sulfide, benzyl phenyl sulfide and benzyl phenyl sulfoxide (E) [38] and (5) mononuclear complexes derived from 2-(dimethylamino)methylnaphthalene (F) [47]. In this paper, we report our data for the reactions of m-CPBA with dimeric dichloro-and diacetato-bridged CPCs derived from 2-phenyl-2-oxazolines.…”

A new method for modification of CN-palladacycles

“…The retention of the Pd-C bond in mononuclear complex 4 (and, conse quently, in the starting dimer 3) is evidenced primarily by upfield shifts (under the influence of anisotropy of the PPh rings) of the signals for two aromatic protons, H (6) and H(5), nearest to this bond (to δ 6.21 and 6.29, respec tively; Fig. 1) compared to those in the spectra of trialkylphosphine derivatives of ortho palladated com plexes.…”

“…Organic peracids, 3-9 lead(IV) acetate, 10 tert butyl hydroperox ide, 11,12 molybdenum peroxides, 13,14 or iodosoarenes 15, 16 are used as oxidizing agents in these reactions, whereas simpler oxidants (for example, H 2 O 2 ) are unsuitable for this purpose. 6 The efficiency of these processes often strongly depends on the structure of palladacycle. In some cases, oxidation can be achieved only in the presence of a catalyst.…”