Formylborane Formation with Frustrated Lewis Pair Templates

Boranes R2BH react with carbon monoxide by forming the respective borane carbonyl compounds R2BH(CO). The formation of (C6F5)2BH(CO) derived from the Piers borane, HB(C6F5)2, is a typical example. Subsequent CO‐hydroboration does not take place, since the formation of the formylborane is usually endothermic. However, an “η2‐formylborane” was formed by CO‐hydroboration with the Piers borane at vicinal phosphane/borane frustrated Lewis pair (FLP) templates. Subsequent treatment with pyridine liberated the intact formylborane from the FLP framework, and (pyridine)(C6F5)2BCHO was then isolated as a stable compound. This product underwent typical reactions of carbonyl compounds, such as Wittig olefination.