Site Selectivity in Electrophilic (H+, CH3+) Abstraction on Os(H)2X2(PiPr3)2

While protonation (HBF4 or HO3SCF3 = HOTf) or methylation (MeOTf) of Os(H)2X2L2 (L = PiPr3, X = Cl, Br) abstracts halide and causes aggregation to form (L2OsH2)2(μ-X)3+, protonation of Os(H)2I2L2 forms a species whose −7.5 ppm 1H NMR chemical shift has a short T1min characteristic of an H2 complex (or short H/H contact). This is also supported by a significant isotopic perturbation of resonance for OsH3I2L2+, although no J(HD) is observed in OsHD2I2L2+. In contrast, Os(H)2I2L2 is converted by MeOTf into L2Os(H)2(OTf)I, then L2Os(H)2(OTf)2, a non-octahedral Lewis acid which binds H2O to form the intramolecularly hydrogen bonded L2Os(H)2(OTf)2(H2O), whose intramolecular fluxionality has been characterized (1H and 31P NMR). The complexes L2Os(H)2(ORf)2 (ORf = OCH2CF3 and OCH(CF3)2) are synthesized from L2Os(H)2Cl2 and TlORf. The X-ray structure of L2Os(H)2(OCH2CF3)2 shows evidence for O→Os π-donation. Protonation of L2Os(H)2(ORf)2 (Rf = CH(CF3)2) with HBF4 forms (L2OsH2)2(μ-F)3+, which is also inefficiently formed by fluoride abstraction (25 °C) by L2Os(H)2(OCH2CF3)2, even in the solid state. Protonation of the monochloride L2Os(H)3Cl gives equimolar (L2OsH2)2(μ-Cl)3+ and L2OsH7+, but the initial site of protonation remains unknown. Crystal data for [OsH2(PiPr3)2(OTf)2][OsH2(PiPr3)2(OTf)2(H2O) ] at −172 °C: a = 19.916(3) Å, b = 20.260(4), c = 19.824(3), α = 115.54(1)°, β = 115.03(1), γ = 63.57(1) with Z = 4 in space group P1̄. Crystal data for (PiPr3)2OsH2(OCH2CF3)2 at −175 °C: a = 8.831(2), b = 16.680(4), c = 19.820(5), β = 93.97(1)° with Z = 4 in space group P21/c.