An efficient direct carboxylation of a series of benzyl chlorides with CO₂ catalyzed by Pd(OAc)₂/dicyclohexyl (2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (SPhos) was developed to afford the corresponding phenylacetic acids in combination with Mn powder as a reducing reagent and MgCl₂ as an indispensable additive. The reaction proceeded smoothly under 1 atm CO₂. The application of Mn powder instead of a sensitive reducing reagent represents an operationally simple access to phenylacetic acids. Notably, MgCl₂ is able to stabilize the (SPhos)₂Pd^II(Bn)(Cl)(η¹-CO₂)(MgCl₂) adduct and thus facilitates CO₂ insertion into the Pd^II−C bond, which is supported by a DFT study.

The effects of insertion of nitrogen atoms on the N―H bond strength of azaphenalene and on the stability of the corresponding radicals were comprehensively investigated using density functional theory. The N―H bond dissociation enthalpy of azaphenalene is found to be strengthened in all cases, but the magnitudes are various with the replaced sites and are additive. It is correlated with the coefficient of frontier molecular orbital; that is, it is correlated with the electron density distribution of the outer electrons. The computational results explain why the product substituted with two CH groups by N atoms in the phenalenyl skeleton yielded radical easily, whereas the product replaced with six nitrogen atoms failed. In addition, the effects of insertion of nitrogen atoms in other aromatic nitrogen-containing compounds, including carbazole, indole, and pyrrole, were also studied. All the understanding about the insertion effects of nitrogen atoms would be helpful in designing novel molecules for specific applications, such as functional materials and antioxidants. Copyright © 2011 John Wiley & Sons, Ltd.