Orthometalation of Primary Amines. 4.¹ Orthopalladation of Primary Benzylamines and (2-Phenylethyl)amine

By the refluxing of an acetonitrile solution of [Pd(OAc) 2 ] 3 and primary amines 4-XC 6 H 4 CH 2 NH 2 (F, Cl, NO 2, OMe), 3,5-X 2 C 6 H 3 CH 2 NH 2 (X = OMe), or PhCH 2 CH 2 NH 2 (Pd:amine = 1:1) and subsequent addition of excess NaBr, the corresponding orthometalated complexes [Pd{C 6 H 3 (CH 2 NH 2 )-2,X-5}(μ-Br)] 2, [Pd{C 6 H 3 (CH 2 NH 2 )-2,(OMe) 2 -4,6}(μ-Br)] 2, or [Pd{C 6 H 3 (CH 2 NH 2 )-2}(μ-Br)] 2 are obtained. Alternatively, the hydrochloride of 4-XC 6 H 4 CH 2 NH 2 (X = F, NO 2 ) can also be used to prepare the corresponding [Pd{C 6 H 3 (CH 2 NH 2 )-2,X-5}(μ-Cl)] 2 complexes. These results show that primary benzylamines can be orthometalated even if the substituents are electron-withdrawing groups and that 2-(phenyl)ethylamine can be orthometalated in spite of the six-membered ring that it forms. These reactions occur via intermediate complexes [Pd(OAc) 2 L 2 ], which react with [Pd(OAc) 2 ] 3 to give the dimeric species [Pd(OAc)(μ-OAc)L] 2 (L = amine), from which in turn the orthometalated complexes are formed. Each of these steps has been studied, and both types of intermediates have been isolated for all the amines. PPh 3 reacts with the orthometalated complexes to give the corresponding products of the bridge splitting. The crystal structures of [Pd(OAc)(μ-OAc)L] 2 (L = 4-O 2 NC 6 H 4 CH 2 NH 2 ) and [Pd{C 6 H 4 (CH 2 CH 2 NH 2 )-2}Br(PPh 3 )] have been determined by X-ray diffraction.