N-15 NMR-STUDIES OF TETRAZOLE COMPLEXES OF PENTAAMMINECOBALT(III) - IMPLICATIONS CONCERNING THE TRANSITION-STATE FOR LINKAGE ISOMERIZATION

Synthesis of the N1-bonded (5-methyltetrazolato)pentaamminecobalt(III) complex utilizing sodium azide enriched in N-15 at the terminal nitro gen has produced a complex enriched specifically at the N2 and N4 ring positions. This has permitted the assignment of all four nitrogen sig nals in the natural-abundance N-15 NMR spectrum of the complex. A simi lar natural-abundance NMR spectrum for a novel chelated amidine comple x which is also N1 bonded is reported along with its synthesis and pur ification. Following the N-15 NMR of the linkage isomerization of the enriched complex in solution to the N2-bonded form has also permitted an eta5 and certain eta3 transition-state structures to be eliminated from consideration for the isomerization process. The data suggest an eta2 transition state is utilized. A subsequent N2-to-N3 isomerization of the N2-bonded complex has also been discovered from the N-15 NMR s tudy. The enrichment study also indicates that previous assignments of ring nitrogen signals N1 and N4 in similar N2-bonded tetrazolato comp lexes of cobalt(III) may be in error.