The para-selective C−H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N−H-activated cyclometalate formed in situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N−H metalation (as opposed to C−H metalation in meta-selective processes) and form a redox active ruthenium species, to enable site-selective radical addition at the para position
