Palladium, [ N , N ′‐1,2‐ethanediylidenebis[2,6‐dimethylbenzenamine‐κN]][(3,4‐ η )‐2,5‐furandione] ( ^DMP DAB–Pd–MAH)

Abstract

image [2721487‐84‐7] C 22 H 22 N 2 O 3 Pd (MW 468.85) InChI = 1S/C18H20N2.C4H2O3.Pd/c1‐13‐7‐5‐8‐14(2)17(13)19‐11‐12‐20‐18‐15(3)9‐6‐10‐16(18)4;5‐3‐1‐2‐4(6)7‐3;/h5‐12H,1‐4H3;1‐2H;/b19‐11+,20‐12+;; InChiKey = WHOQNDZHEHSRKP‐GAMUHHASSA‐N (palladium(0) compound used as a precursor to phosphine palladium(0) complexes, 1–5 and as a catalyst precursor for cross‐coupling reactions, 1,6 CH activation reactions, 7 and enantioselective allylation reactions 4,8 ) Alternative Names : (1 E ,2 E )‐ N 1, N 2‐bis(2,6‐dimethylphenyl)ethane‐1,2‐diimine 2,5‐dihydrofuran‐2,5‐dione palladium, [κ 2 ‐ N , N ′‐bis(2,6‐dimethylphenyl)ethan‐1,2‐diimine][ η 2 ‐maleic anhydride]palladium(0). Physical Data : m.p. 121 °C (dec). Solubility : fully soluble (≥20 mg mL −1 ) in acetone, dichloromethane, tetrahydrofuran (THF), 2‐methyltetrahydrofuran (MeTHF); partially soluble in toluene (5 mg mL −1 ), ethyl acetate (2.5 mg mL −1 ); poorly soluble (≤2 mg mL −1 ) in pentane, n ‐hexane, n ‐heptane, diethyl ether, tert ‐butylmethyl ether (TBME); insoluble in isopropanol (<1 mg mL −1 ); soluble but decomposes in acetonitrile, chloroform; poorly soluble and decomoposes in dimethylsulfoxide (DMSO), N,N ‐dimethylformamide (DMF), methanol, ethanol; insoluble in water. Form Supplied in : red/purple crystalline solid. Preparative Methods : commercially available. There are two reported procedures 1 for preparing DMP DAB–Pd–MAH by reacting N , N ′‐1,2‐ethanediylidenebis(2,6‐dimethylbenzenamine) ( DMP DAB) and maleic anhydride (MAH) 9 with either Pd 2 dba 3 ·CHCl 3 10 or “Pd(dba) 2 ” (actually Pd 2 dba 3 ·dba). 11 These palladium sources can be prepared from a variety of palladium(II) starting materials according to the method of Zalesskiy and Ananikov, 12 or purchased from commercial sources. Recystallization of crude “Pd(dba) 2 ” is not required, since purification of DMP DAB–Pd–MAH removes residual dba and colloidal palladium(0) (see below). N , N ′‐1,2‐ethanediylidenebis(2,6‐dimethylbenzenamine) ( DMP DAB) is prepared from glyoxal (40% wt/wt solution in water) and 2,6‐dimethylaniline in methanol with 13 or without 14 formic acid as a catalyst. Purification : colloidal palladium(0) can be removed from DMP DAB–Pd–MAH by dissolving the solid in a minimum amount of acetone, dichloromethane, or THF, followed by filtration through a bed of Celite ™ and subsequent solvent removal from the filtrate. Uncoordinated N , N ′‐1,2‐ethanediylidenebis(2,6‐dimethylbenzenamine) ( DMP DAB), maleic anhydride, and/or residual dibenzylideneacetone (dba) from the synthesis can be removed by slurrying solid DMP DAB–Pd–MAH in TBME (∼30 mL g −1 of solid), followed by filtration and washing with TBME. Analysis of Reagent Purity : 1 H NMR spectroscopic analysis is suitable for routine purity determination. In d 6 ‐acetone (solvent residual peak at 2.05 ppm), DMP DAB–Pd–MAH has diagnostic resonances at 8.55 ppm (s, 2 H ) for the N=CH–CH=N protons, 3.57 ppm (s, 2 H ) for the coordinated maleic anhydride, and 2.30 ppm (s, 12 H ) for the four Ar–CH 3 groups. Elemental analysis is also suitable for establishing bulk purity. Handling, Storage, and Precautions : solid DMP DAB–Pd–MAH is shelf‐stable when stored at room temperature in a closed container under ambient atmosphere.