Palladium-Assisted Formation of Carbon−Carbon Bonds. Part 10.¹ Insertion Reactions of Isocyanides into the Pd−C Bond of Orthopalladated Primary Amines. Synthesis of 2-R-Aminoisoindolinium Salts (R = ^tBu, 2,6-Xylyl)

Abstract

The palladated primary amines [Pd{C 6 H 3 CH 2 NH 2 -2-X-5}(μ-Br)] 2 [X = H ( 1a ), OMe ( 1b ), NO 2 ( 1c ), F ( 1d )] react with isocyanides (Pd:RNC = 1:1) to give [Pd{C 6 H 3 CH 2 NH 2 -2-X-5}Br(RNC)] [R = Xy = C 6 H 3 Me 2 -2,6, X = H ( 2a ), OMe ( 2b ), NO 2 ( 2c ), F ( 2d ), R = t Bu, X = H ( 3a ), OMe ( 3b ), NO 2 ( 3c ), F ( 3d )]. When XyNC reacts with 1a (Pd:RNC = 1:2) or with 2a (Pd:RNC = 1:1), the complex [Pd{(C NXy)C 6 H 4 CH 2 NH 2 -2}(XyNC)Br] ( 4a ) is obtained. The reactions of complexes 1 with isocyanides in the ratio Pd:RNC = 1:3 lead to Pd(I) complexes [Pd 2 Br 2 L 4 ] [L = XyNC ( 5 ); L = t Bu ( 6 )]. On the basis of NMR data we propose the following reaction pathway for this reduction process: (1) formation of the corresponding monomer 2 or 3, (2) insertion of one molecule of the isocyanide into the Pd−C bond of 2 or 3 to give [Pd{(C NR)C 6 H 3 CH 2 NH 2 -2-X-5}(RNC)Br], (3) cleavage of the N−Pd bond and coordination of a new isocyanide molecule to give complexes [Pd{(C NR)C 6 H 3 CH 2 NH 2 -2-X-5}(RNC) 2 Br] [detected in solution for R = Xy, X = H ( 7a ) and isolated as an acetylated derivative of this complex [Pd{(C NXy)C 6 H 4 CH 2 NHC(O)Me-2}(XyNC) 2 Br] ( 8a )], and (4) decomposition of these complexes to give 5 or 6 . The organic product of these reactions was not identified. By refluxing mixtures of complexes 1 with RNC and TlOTf (Pd:RNC:TfO = 1:1:1) the corresponding isoindolinium triflates 9·OTf [R = Xy, X = H ( 9a·OTf ), OMe ( 9b·OTf ), F ( 9d·OTf )] or 10·OTf [R = t Bu, X = H ( 10a·OTf ), OMe ( 10b·OTf ), F ( 10d·OTf )] were isolated and characterized. A mechanism of formation of these isoindolinium triflates is proposed. When the reaction between 1a and XyNC (Pd:RNC = 1:1) was carried out in refluxing toluene in the absence of TlOTf, or when 2a was refluxed in toluene, an insertion of the isocyanide occurs in both cases to give [Pd{(C NXy)C 6 H 4 CH 2 NH 2 -2}Br] 2 ( 11 ). If 1a or 2a is reacted with XyNC (Pd:RNC = 1:1.25 or 1:0.25, respectively), the complex [PdBr 2 {2-(XyNH)-isoindole} 2 ] ( 12 ) is formed. A proposal for the reaction pathway of this process is discussed. The crystal structures of 3d, 9a·OTf, and 12 have been determined.