Parahydrogen induced polarization and the oxidative addition of hydrogen to iridium tribromostannyl carbonylate anions.
Activation of dihydrogen by a system composed of (Bu(4)N)[IrBr(2)(CO)(2)] (1) and tin dibromide in varying ratios was studied using parahydrogen induced polarization (PHIP) which allows the detection of transient dihydrides not observable in conventional (1)H NMR spectra. While the oxidative addition of dihydrogen to neutral and cationic Ir(I) species is common, there are only a few examples of H(2) addition to anionic complexes. Tin dibromide reacts with iridium(I) complex 1 in acetone forming equilibrium mixtures of cis- and trans-tribromostannyl derivatives [IrBr(n)()(SnBr(3))(2)(-)(n)()(CO)(2)](-), n = 0,1, the existence of which is inferred from the stereochemistries of the dihydrogen addition products determined using PHIP. The sigma-donating effect of the SnBr(3)(-) ligand facilitates the oxidative addition to the iridium center. The structures of the dihydrides formed upon addition of dihydrogen are assigned on the basis of hydride chemical shifts and values of (2)J((1)H-(117,119)Sn). The only dihydride observed in conventional (1)H NMR spectra is cis-trans-cis-[IrH(2)(SnBr(3))(2)(CO)(2)](-), the identity of which was confirmed using the (13)C labeled Ir(I) precursor. Both [IrBr(2)(CO)(2)](-) and its tribromostannyl derivatives catalyze cis-pairwise addition of dihydrogen to phenylacetylene.
Permin
Alexei
A
Department of Chemistry, University of Rochester, Rochester, New York 14627, USA. RSE7@chem.rochester.edu
Eisenberg
Richard
R