N‑Methylation of Aniline Derivatives with CO2 and Phenylsilane Catalyzed by Lanthanum Hydridotriarylborate Complexes bearing a Nitrogen Tridentate Ligand

A lanthanum amide complex, La­(L)­[N­(SiHMe2)2]­(thf) (L = N,N″-bis­(pentafluorophenyl)­diethylenetriamine dianion, 1a), upon activation with B­(3,4,5-F2C6H2)3 (2a), showed excellent catalytic activity for N-methylation of N-alkylaniline derivatives with CO2 in the presence of PhSiH3. A catalytically active lanthanum hydridotriarylborate complex, [La­(L)­(thf)2]­[HB­(3,4,5-F3C6H2)3] (5aa), was generated via hydride abstraction from the Si–H moiety of 1a by moderate Lewis acid 2a in THF. DFT studies of the CO2 hydrosilylation step clarified the following multiple noncovalent interactions as key factors for locating the HB­(3,4,5-F2C6H2)3 anion and B­(3,4,5-F3C6H2)3 near the lanthanum center in the transition states of CO2 reduction and Si–O bond formation: (1) π–π interaction between the electron-deficient C6F5 ring on ligand L and the 3,4,5-F3C6H2 ring of the HB­(3,4,5-F3C6H2)3 anion and (2) C–H···F hydrogen bonds between the ortho-C–H bond of B­(3,4,5-F3C6H2)3 and the fluorine atoms of L.