Comparative chemistry of η3-oxaallyl and η3-allyl rhodium(I) complexes in the hydrosilylation of cyclopropyl ketones: observation of an unprecedented rearrangement

Add time:08/16/2019    Source:sciencedirect.com

Addition of η3-oxaallyl bis(triphenylphosphine)rhodium(I) (1) or η3-allyl bis(triphenylphosphine)rhodium(I) (2) to a mixture of cyclopropyl phenyl ketone and triethylsilane promotes two competitive catalytic reactions. Complex 1 gives high yields of the silyl ether 13, while complex 2 favors an unprecedented cyclopropyl carbinyl ring-opening reaction providing good yields of enol silane (Z)- and (E)-14 (4.1 Z/E ratio). Studies of catalyst turnover provide evidence that two monomeric rhodium complexes account for the competing reactions. The cyclopropyl carbinyl catalysis occurs under a narrow reaction regime with a specific set of ketone substrates suitable for the reaction. Chemicals such as triethylsilane activate the catalysis leading to 13, while triphenylphosphine strongly inhibits the formation of 14. A mechanism involving a polar transition state for the cyclopropyl carbinyl rearrangement is proposed.

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