The first orthopalladation of a primary nitrobenzylamine. Synthesis of chiral cyclopalladated complexes derived from (S)-α-methyl-4-nitrobenzylamine

Abstract

By refluxing a mixture of (S)-α-methyl-4-nitrobenzylamine and Pd(O₂CMe)₂(1 : 1) in acetone, complexes (S,S)-[{Pd[C₆H₃{CH(Me)NH₂}-2-NO₂-5](µ-X)}₂](X = MeCO₂1a or Cl 1b) are obtained. Complex 1b can also be obtained by treating (S)-α-methyl-4-nitrobenzylamine hydrochloride with Pd(O₂CMe)₂(1 : 1) in acetone. These complexes are the first orthometallated complexes containing a primary amine with an electron-withdrawing group in the benzene ring. Complex 1a reacted with an excess of NaBr or Nal to give (S,S)-[{Pd[C₆H₃{CH(Me)NH₂}-2-NO₂-5](µ-X)}₂](X = Br 1c or I 1d). Triphenylphosphine reacted with 1b or 1c to give (S)-[Pd{C₆H₃[CH(Me)NH₂]-2-NO₂-5}X(PPH₃)](X = Cl 2a or Br 2b). The reaction of complex 1b with AgClO₄(1 : 1) and an excess of pyridine (py) gave (S)-[Pd{C₆H₃[CH(Me)NH₂]-2-NO₂-5}(py)₂]ClO₄3. Complex 1c reacted with 3 equivalents of RCCR (R = CO₂Me) to give a tri-insertion reaction product, the crystal structure of which has been determined: space group P2₁2₁2₁, a= 11.0969(14), b= 17.197(2), c= 19.604(3)Å, R(F)= 0.041. The planar co-ordination at palladium is not significantly disturbed by a short contact of 2.600 Å to the C atom of a CO₂Me group. A cationic derivative of this complex has also been prepared.