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.