Stereoselective Formation of Rhodium and Iridium Hydrides via Intramolecular Hydrogen Bonding

Article abstract of DOI:10.1021/ja00243a039

Dihydrogen addition to Ir(CH3)I (R = Ph, i-Pr), under ambient conditions, results in protonation of the iridium amide bond to give an iridium amine monohydride complex, IrH(CH3)I.IrH(CH3)I crystallizes in the triclinic space group PI<*> with a = 11.412(2) Angstroem, b = 14.712(3) Angstroem, c = 9.913(1) Angstroem, α = 106.97(1) deg, β = 112.41(1) deg, γ = 70.99(1) deg (Z = 2, R_w = 0.040).When these derivatives are heated under dihydrogen in toluene at 80 deg C, the iridium amine dihydrides, IrH2I, are produced.The analogous rhodium amides, Rh(CH3)I, yield only dihydride products, RhH2I, under 1 atm of dihydrogen at room temperature.One of these, RhH2I, has been crystallographically characterized; the complex belongs to the monoclinic space group P2₁/n having the following cell dimensions: a = 10.287(1) Angstroem, b = 21.317(1) Angstroem, c = 13.740(2) Angstroem, β = 110.296(6) deg (Z = 4, R_w = 0.034).Reaction of M(η²-C8H14) (M = Rh, Ir) with H2 in the presence of CH2X2 (X = Cl, Br, I) also yields the amine dihydrides, MH2X.IrH2Cl, prepared by this route, was analyzed by X-ray crystallography and found to be a member of the monoclinic space group P2₁/a with a = 28.064(3) Angstroem, b = 10.817(1) Angstroem, c = 12.695(2) Angstroem, β = 97.27(1) deg (Z = 4, R_w = 0.039).As shown by spectroscopic and crystallographic information, all of these M(III) amine hydride species possess a common structural feature: the amine N-H bond is syn to the metal-halide linkage.This orientation, as well as the concomitant stereoselectivity of these reactions, appears to be a direct consequence of intramolecular N-H...X hydrogen bonding.