On the mechanism of the silicon-tethered reductive Pauson–Khand reaction

The reductive Pauson–Khand reaction (PKR) of tethered vinyl silanes likely proceeds as usual to the bicyclopentenones , but rapid loss of the allylic silane initiates a fragmentation process culminating in propargylic carbon reduction. Damp nitrile solvents are crucial for efficient reaction, and under dry conditions additional products are obtained including dimerized cyclopentadienones and 5-(1-amino-alkylidine) cyclopentenes. Solvent incorporated enones likely arise from enolate attack on a cobalt coordinated nitrile. A unified reaction mechanism is proposed. The first example of a PKR with an allyloxy ethynylsilane is also reported.