H-1-DETECTED MULTINUCLEAR NMR EXPERIMENTS FOR THE MEASUREMENT OF SMALL HETERONUCLEAR COUPLING-CONSTANTS IN TRANSITION-METAL COMPLEXES

The scalar coupling constants between protons, nitrogens, and phosphor us in the metal complex hosphine)bis[bis(1-pyrazolyl)methane]ruthenium (II) chloride, [RuCl(PPh3)(BPM)(2)]Cl-+(-) (1), were measured with a s et of specially adapted NMR experiments. The absolute sign of the coup ling constants was determined by relating the signs of the measured co uplings to that of a one-bond proton-carbon coupling constant. A compl ete set of coupling constants > \0.4\ Hz was obtained with use of a si ngle sample with 99% N-15-labeled bis-pyrazolyl ligands. The data show that the two-bond N-15-N-15 and P-31-N-15 couplings across the metal center are significantly larger, if the two metal-ligating atoms are t rans rather than cis with respect to one another. Furthermore, all tra ns couplings (2)J(PN) and (2)J(NN) are positive, while the correspondi ng cis couplings are negative or too small to be measured. The conform ation dependence of the scalar coupling constants supports the rapid s tructural characterization of catalytically active organometallic comp lexes by NMR spectroscopy. The proposed set of NMR experiments include s HSQC experiments with small flip angles, a quantitative long-range N -15-N-15 correlation experiment, and DQ/ZQ experiments for the determi nation of the sign and size of J(NN) and J(PN) coupling constants in l inear spin systems.