Synthesis and spectroscopic and structural characterization of different configurations of the tridentate amine ligand N,N ',N ''-trimethyldiethylenetriamine coordinated to platinum

Different configurations of the tridentate amine ligand N,N',N"-trimethyldi ethylenetriamine coordinated to platinum have been characterized both in th e solid state and in solution. Four isomers are possible: two isomers have a mirror symmetry (R,S configurations at the terminal nitrogen atoms) and t he terminal N-Me's anti or syn with respect to the central N-Me (anti-(R,S) and syn-(R,S) isomers, respectively), two more isomers have R,R and S,S co nfigurations at the terminal nitrogen atoms and constitute a couple of enan tiomers (rac denotes a 1:1 mixture of the two enantiomers). In the experime ntal conditions used, only one symmetrical isomer was isolated in the solid state (1) which, in solution, slowly isomerizes into a non-symmetrical iso mer (2) and subsequently into a second symmetrical isomer (3). NMR and, cry stallographic studies have shown that the first species isolated (1) is the syn-(R,S) isomer having all three methyl groups on the same side of the pl atinum coordination plane, such a configuration allows steric interaction b etween bis-axial 1,3-substituents within the chelate rings to be reduced. T his isomer is also the preferred one in water solution where the ratios 1:2 :3 are approximately 52:36:12. In a separate work the guanine derivatives [ Pt(Me(3)dien)G](n+) were used to investigate cis-amine-G intramolecular int eractions without the complication arising from cis-G to cis-G interactions present in cis-PtA(2)G(2) intrastrand crosslink models (A, is two unidenta te or one didentate amine ligand and G is a unidentate guanine derivative). [Pt(NO3){syn -(R,S)-Me(3)dien}] (NO3) crystallizes in the orthorhombic spa ce group P2(1)2(1)2(1) with one molecule in the asymmetric unit. (C) 2000 E lsevier Science B.V. All rights reserved.