DIPLATINUM AND HETERONUCLEAR COMPLEXES DERIVED FROM (TMEDA)PT(1-MEU)2 (TMEDA = N,N,N',N'-TETRAMETHYLETHYLENEDIAMINE, 1-MEU = 1-METHYLURACILATE-N(3)) - STERIC EFFECT OF THE TMEDA LIGAND ON THE ORIENTATION OF THE 2ND METAL

The reaction of (tmeda)Pt(1-MeU)2 (tmeda = N,N,N,N'-tetramethylethylenediamine, I-MeU = 1-methyluracilate-N3) toward several electrophiles (H+, Ag+, Cu2+, PdCl42-, cis-(NH3)2Pt(II), (dien)Pt(II), enPdCl2) has been studied using H-1 NMR spectroscopy (H+, Ag+, Pd(II), Pt(II)) and X-ray structure crystallography (Cu2+). (tmeda)Pt (1-MeU)2 exists in solution in two rotamers (head-head and head-tail) which exhibit two separate acid-base equilibria between the neutral and monoprotonated species. Ag+, Cu2+, and PdCl42- bind to (tmeda)Pt(1-MeU)2 via the exocyclic O4 oxygens in the well-known fashion with metals facing each other. In contrast, amine-containing species(cis-NH3)2Pt(II), (dien)Pt(II), (en)Pd(II)) bind to (tmeda)Pt(1-MeU)2 via a single O4 oxygen in a face-back fashion, which leads to a short contact between the entering second metal and H5 of the bridging 1-MeU. This situation is reflected in a large downfield shift (Pt, 1.64 ppm; Pd, 1.13-1.28 ppm) of this resonance in the H-1 NMR spectrum. The X-ray structure of {[(tmeda)Pt(1-MeU)2]2Cu}(ClO4)2 is reported. As a consequence of the steric bulk of the tmeda ligand, the tilt between the metal coordination planes (32.3-degrees) and the Pt-Cu separation (2.9843 (1) angstrom) are considerably larger than in related compounds derived from cis-(NH3)2Pt(II).