Structural and spectroscopic characterization of iridium trihydride complexes: evidence for proton-proton exchange coupling

Protonation of the neutral iridium dihydrides {eta}-C{sub 5}H{sub 5}Ir(L)H{sub 2} with HBF{sub 4} {times} Et{sub 2}O affords cationic trihydride complexes of the form (({eta}-C{sub 5}H{sub 5})Ir(L)H{sub 3})BF{sub 4} (L = various phosphine and phosphite ligands). The {sup 1}H NMR spectra of the cations in the hydride region at low temperature display AB{sub 2}X spin systems (X = {sup 31}P), which are simplified to AB{sub 2} spin systems in the {sup 1}H({sup 31}P) spectra. The values for J{sub A-B} derived by computer fitting of the observed spectra are extremely large, ranging from 61 to 1,565 Hz. In general, J{sub A-B} is inversely proportional to the basicity of the ligand L. The J{sub A-B} values are strongly temperature dependent, increasing rapidly over the temperature range 150-200 K. Coupling constants have not been evaluated at temperatures higher than 200 K due to the onset of A/B site exchange, which causes line broadening and eventual coalescence of the two resonances. In derivatives partially labeled with deuterium in the hydride ligands, no H-D coupling was resolved. In a tritiated derivative, {sup 3}H NMR was used to detect J{sub H-T}, which was substantially reduced from the expected value. a neutron diffraction study of ({eta}-C{sub 5}H{sub 5})Ir(PMe{submore » 3})H{sub 3}BF{sub 4} (21) has been carried out. Compound 21 crystallizes in the space group P2{sub 1}2{sub 1}2{sub 1} (Z = 4) with a = 8.840 (2) {angstrom}, b = 9.971 (1) {angstrom}, c = 14.278 (2) {angstrom} c = 14.278 (2) {angstrom}, and V = 1,258.5 (5) {angstrom}{sup 3} (130 K).« less