Osmium(II) Alkyl Precursors to Alkane Coordination Complexes: Synthesis and Isotopic Labeling Via Dialkylzinc Reagents

Abstract

In two previous articles, we reported detailed studies of σ-alkane complexes prepared by low-temperature protonation of the osmium alkyl complexes (C5Me5)Os(dfmpm)R, where dfmpm = (F3C)2PCH2P(CF3)2 and R = methyl (1), ethyl (2), propyl (3), butyl (4), or isobutyl (5). This paper describes the preparation and characterization of these complexes, in addition to labeled isotopologues of complexes 2–4 in which deuterium and/or carbon-13 labels are incorporated into the alkyl group. The isotopologues were prepared from labeled alkyl halides RX (X = Br, I) via dialkylzinc reagents ZnR2. Several standard methods to make the labeled alkyl halides were found to be problematic. The problems arise for three reasons: (1) the cost of labeled starting materials limits reaction scales to ca. 1 g; (2) many standard methods to make alkyl halides (e.g., from alcohols), also convert ether solvents into alkyl halides, which contaminate the desired product; and (3) the intermediate volatilities of the alkyl halides and dialkylzinc reagents make small-scale purifications less straightforward.