Reactions of aquatitanium(II) with hypervalent chromium species.

Titanium(ii) solutions, prepared by dissolving titanium metal in triflic acid and HF, react readily with derivatives of Cr(vi), Cr(v) and Cr(iv). Reductions of Cr(vi) and Cr(iv), carried out with [Co(NH(3))(5)Br](2+) as a scavenger for Cr(ii), yield no detectable Co(2+), indicating that 2e(-) steps, bypassing Cr(v) and Cr(iii), are not operative. Catalysis by Ti(iv) is observed only for reduction of Cr(vi). Rates for reduction by Ti(iii) are remarkably similar to those for the corresponding reductions by Ti(ii). The addition of Ti(iii) to triflic acid and HF results in rapid and quantitative disproportionation to Ti(ii) and Ti(iv).