Canopied trans-chelating bis(N-heterocyclic carbene) ligand: synthesis, structure and catalysis

Abstract

The terphspan scaffold was employed to support a bis(N-heterocyclic carbene) ligand () that provides a m-terphenyl canopy over one side of its metal complexes. Single-crystal X-ray diffraction studies on a silver complex of {[Ag()]AgBr(2)}(2) revealed an unusual tetranuclear silver core with a Ag-Ag bond distance of 3.0241(8) A with as a trans-chelating ligand (C-Ag-C = 171 degrees ). A preliminary X-ray structure of pseudo-square planar [PdCl(2)()] showed a similar binding mode of (C-Pd-C = 177 degrees ). High yields were obtained in Suzuki-Miyaura coupling reactions utilizing [PdCl(2)()] as the procatalyst and the results were compared with analogous complexes of trans-spanning diphosphine () and diphosphinite () complexes. The diphosphinite complex, [PdCl(2)()], decomposes to [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) at room temperature.

Crystal structure of bis(μ 2-chlorido)-bis(di-p-tolylhydroxyphosphine-κP)-bis(di-p-tolylphosphite-κP)dipalladium(II), C56H58Cl2O4P4Pd2

“…The dimerized title complex consists of a di-nuclear chlorido-bridged palladium entity consisting of hydrogen bridged through the oxygen atoms of the di-p-tolylphosphite groups on both phorsphorous atoms. The average O· · · O and P-O distances are 2.4057(27) Å and 1.546(2) Å respectively and are comparable to other similar compounds found in literature [7][8][9][10][11]. The asymmetric unit contains a monomer of the title complex while the other monomer is generated through the (1−x, 2−y, 1−z) symmetry.…”

Chelating Bis(N‐Heterocyclic Carbene) Palladium‐Catalyzed Reactions

“…With respectt ot he Suzuki-Miyaura reaction performed in organic solvent, trans-chelating Pd-bis(NHC) complex 79 (Figure 14, below) with at erphspan scaffoldw as evaluatedi n the work of Smith and co-workers. [46] The coupling reaction was carried out in 1,4-dioxane at 100 8C, and the complex showedm oderate to high efficacyi nt he coupling of various aryl halides, including those that were sterically hindered. In the work of Hahna nd co-workers, pincer-type palladium complexes, such as 47 (Figure 7), were employed as precatalysts in the Suzuki-Miyaura reactioni nD MSO.…”

Synthesis of bis(N-heterocyclic carbene) palladium complexes derived from (S,S)-1,2-bis(1-hydroxypropyl)benzene

“…Compound (R,R)-10b was isolated as a pale brown powder (0.263 g, 0.277 mmol, 92%). mp > 155.4 C (Dec. (m,2H,ArH). 13 C NMR (125 MHz, CDCl 3 ) d 11.6 (CH 3 ), 27.1 (CH 2 ), 63.1 (NeCH 2 ePh), 72.2 (CH), 112.…”

“…1 H NMR (500 MHz, CD 2 Cl 2 ) d 0.73 (t, J ¼ 7.6 Hz, 6H, 2 Â CH 3 ), 2.00e2.12 (m, 2H, CH 2 ), 2.22e2.31 (m, 2H, CH 2 ), 3.91 (s, 6H, 2 Â NeCH 3 ), 5.86 (t, J ¼ 7.6 Hz, 2H, 2 Â CH), 6.65 (d, J ¼ 1.3 Hz, 2H, ImH), 6.90 (d, J ¼ 1.3 Hz, 2H, ImH), 7.53e7.56 (m, 2H, ArH), 7.66e7.69 (m,2H,ArH). 13 C NMR (125 MHz, CD 2 Cl 2 ) d 11.4 (CH 3 ), 29.4 (CH 2 ), 39.5 (NeCH 3 ), 61.4 (CH), 118.…”

“…Methyl iodide (1.62 mL, 3.69 g, 26.0 mmol) was added to a solution of (R,R)-8 (0.513 g, 1.30 mmol) in DME (15 mL) and the mixture was refluxed for 5 h. After the solvent was removed under reduced pressure, the residue was washed with hexane (10 mL Â 3) and Et 2 O (10 mL Â 3), and dried in vacuo to give (R,R)-9a as a pale yellow powder (0.863 g, 1.27 mmol, 98% (m,2H,ArH),7.62e7.65 (m,2H,ArH),7.71e7.75 (m,4H,ArH),8.02e8.04 (m,4H,ArH),9.85 (s,2H,2 Â N]¼CHeN) 13 C NMR (100 MHz, DMSO-d 6 ) d 10.4 (CH 3 ), 27.9 (CH 2 ), 33.6 (NeCH 3 ), 58.0 (CH), 113. 7, 113.8, 126.6, 126.8, 127.9, 130.1, 130.4, 31.9, 135.0, 141.8 (aromatic).…”