Atom Transfer Radical Addition of Activated Primary Alkyl Chlorides Using In Situ Generated [Cp*Ru^II(Cl)(PR₃)] Catalysts

Atom transfer radical addition (ATRA) of halogenated compounds with alkenes is well established but primary alkyl chlorides are understudied because of the difficult C-Cl bond activation. In this paper, we show that TONs of 61 can be achieved in the ATRA of ethyl chloroacetate onto styrene with [Cp*Ru(Cl)(2)(PPh3)] and 1,1'-azobis(cyclohexanecarbonitrile) (ACHN) as a radical initiator, representing a three-fold improvement compared to previous reports. New catalyst precursors of the type [Cp*Ru(Cl)(2)(PR3)] were synthesized and tested (R=Me, Et, Cy, Ph, p-CF3C6H4 and p-MeOC6H4). The kinetic reaction profiles were studied using in situ ATR-FTIR spectroscopy. Among these complexes, [Cp*Ru(Cl)(2)(PPh3)] gave the best yields while [Cp*Ru(Cl)(2)(PMe3)] showed the highest rate. While rates correlate with redox potentials (electronics), our investigation reveals that substrate sterics are important for the overall yield. Density functional theory calculations suggest an open-shell singlet pathway, where polymerization is kinetically disfavored, explaining the selectivity towards ATRA products.