Selectivity\nof Ru and Fe P<sup>R</sup><sub>2</sub>N<sup>R’</sup><sub>2</sub> Catalysts Toward Acceptorless Dehydrogenation\nof Benzylamine

The\nperformance of six ruthenium catalysts and two iron catalysts\nwere evaluated toward the acceptorless dehydrogenation of benzylamine.\nAll catalysts shared the common structure [M(Cp/Cp*)(P<sup>R</sup><sub>2</sub>N<sup>R’</sup><sub>2</sub>)(MeCN)]PF<sub>6</sub> (M = Fe, Ru; Cp = cyclopentadienyl; Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl;\nP<sup>R</sup><sub>2</sub>N<sup>R’</sup><sub>2</sub> = 1,5-R′-3,7-R-1,5-diaza-3,7-diphosphacyclooctane)\nin which the P<sup>R</sup><sub>2</sub>N<sup>R’</sup><sub>2</sub> ligands contain a pendant tertiary amine that enables cooperative\ncatalytic mechanisms. Catalytic activity and selectivity were evaluated\nto identify the optimal catalyst structural features. The iron catalyst\n[Fe(Cp)(P<sup>Ph</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)(MeCN)]PF<sub>6</sub> demonstrated near-exclusive selectivity for the acceptorless\ndehydrogenative coupled product, <i>N</i>-benzylidenebenzylamine.\nThe absence of the hydrogen-borrowed (dibenzylamine) product indicates\nthat this iron catalyst strongly favors dehydrogenation pathways over\nhydrogenation. This was confirmed through the control reactions. The\nperformance of [Fe(Cp)(P<sup>Ph</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)(MeCN)]PF<sub>6</sub> was optimized, but the catalyst was\nineffective toward a broader scope of substrates.