Cu(II)-silsesquioxanes as efficient precatalysts for Chan-Evans-Lam coupling

Abstract

Two cage copper(II)silsesquioxanes, namely, tricopper complex (PhSiO 1.5) 8 (CuO) 3 (TMEDA) 2 *(MeCN) 3 Cu-1 and hexacopper complex (MeSiO 1,5) 12 (CuO) 6 (Py) 6 *TMEDA Cu-2 were synthesized (in 30% and 16% yield, respectively) via TMEDA-assisted reactions (TMEDA ¼ tetramethylethylenediamine). Structural features of both products were established by X-ray diffraction study. Complexes Cu-1 and Cu-2, along with some Cu(II)-silsesquioxanes reported earlier, were evaluated for the first time as precatalysts for the homogeneous Chan-Evans-Lam (CEL) O-arylation of benzoic acids (the highest yield of phenylbenzoic ester was 84%). Observed catalytic activity was superior to reference catalyst Cu(OAc) 2 *H 2 O. Finally, an application of coppersilsesquioxanes allowed to observe the first example of CO CEL coupling under microwave activation characterized by (i) reduced loading of copper, (ii) low amount of added base, (iii) minimization of the time of reaction.

Polysiloxanes Grafted with Mono(alkenyl)Silsesquioxanes—Particular Concept for Their Connection

“…Interestingly, the Pt-based complexes are not particularly favorable towards the dehydrogenative silylation [110,111] in contrast to 8-9 group of the periodic table, i.e., iron [112], rhodium [113], iridium [114] and cobalt [115] complexes, specifically known for this selectivity [116,117]. This observation is reflected in NMR spectra (Figure 4) and the appearance of new signals in 1 H NMR derived from -CH=CH-Si-bond, i.e., 5.61-5.67, 6.11-6.23 ppm and in 13 C NMR: 130.30, 143.60 ppm. They are shifted in comparison to the signals of the terminal -CH=CH 2 bond in the -allyl group ( 1 H NMR: 4.84-4.91, 5.73-5.87 ppm and 13 C NMR: 113.54, 133.99 ppm respectively).…”

“…They are soluble in organic solvents like DCM, CHCl 3 , THF, acetone, and toluene, but not in, e.g., methanol, MeCN, and hexane (for products with Ph groups). They were isolated (Table S1) and characterized by means of spectroscopic ( 1 H, 13 C and 29 Si NMR as well as FT-IR, see Supplementary Materials) methods. Depending on the content of Si-H in the PS1 and PS2, as well as the alkyl chain via which the SQs core is attached to the polysiloxane, and finally on the presence of iBu or Ph inert substituents, the resulting 1-5RT 8 @PS1-2 differ in the morphology (Figure 7).…”

“…The synthetic protocol was optimized to ensure a complete Si-H consumption along with the avoidance of side-products. As a result, we obtained 20 new compounds, characterized by spectroscopic methods ( 1 H, 13 C, 29 Si NMR, and FT IR; see Supporting Information). These compounds not previously been described.…”

“…Nuclear magnetic resonance spectroscopy (NMR) measurements ( 1 H, 13 C, and 29 Si NMR) were conducted using spectrometers: Bruker Ultrashield 300 MHz and 400 MHz respectively (Faellanden, Switzerland) with CDCl 3 as a solvent. Chemical shifts are reported in ppm with reference to the residual solvent signals (CHCl 3 ) peaks for 1 H and 13 C and to TMS for 29 Si.…”

“…The cage-type polysilsesquioxanes derivatives, commonly known as silsesquioxanes (SQs), for their three-dimensional nanosized structures, have attracted considerable attention not only from the synthetic perspective (tunable possibility for modification), but also for their application feature (thermal stability) [1][2][3][4]. These systems, thanks to their unique properties, have influenced almost all branches of science and have found numerous examples of applications also in everyday life, e.g., optoelectronics (OLEDs) [5][6][7], dendrimers [8][9][10][11], catalysts [12,13], medicine and biochemistry (drug delivery systems, dental applications) [14][15][16], lithium and fuel batteries, and conductive matrices [17][18][19][20], food industries, cosmetics, and many more [21][22][23][24][25][26][27][28][29][30][31].…”