Reduction of Hexaazatrinaphthylenes by Masked Divalent Lanthanide Dinitrogen Reagents
Arpan Mondal, Christopher G. T. Price, Alexander Steiner, Jinkui Tang, Richard A. Layfield
Abstract
High Resolution Image Download MS PowerPoint Slide The oxidation state +2 is of interest in rare-earth chemistry since it allows these conventionally redox-inactive metals to be used as reducing agents. However, the divalent oxidation state is difficult to form for most rare-earth elements, and the ensuing compounds are often unstable. Here, we describe an approach to rare-earth reduction chemistry that circumvents the divalent oxidation state by using compounds of trivalent rare earths that store reducing electrons on the dinitrogen ligand [N 2 ] 2–, akin to “masked” divalent reactivity. Thus, the dinitrogen complexes [ ( Cp 2 ttt M ) 2 ( μ ‐1, 2‐N 2 ) ] ( 1 M, M = Y, Gd, Tb, Dy, Cp ttt = 1,2,4-C 5 t Bu 3 H 2 ) reduce hexaazatrinaphthylene and its hexamethyl derivative to give trimetallic [ ( Cp 2 ttt M ) 3 ( R 6 HAN ) ], where the [R 6 HAN] 3– ligands (R = H, 2 M; R = Me, 3 M ) form with S = 1/2, and with elimination of N 2 . The structures of 2 M and 3 M reveal that the tert -butyl substituents strongly influence the core geometry of these trimetallic complexes. Analysis of the magnetism and electronic structure of 2 Gd and 3 Gd identifies ferromagnetic metal-radical exchange, with coupling constants of J = +2.87 cm –1 and +3.07 cm –1, respectively (−2 J formalism). The unusual ferromagnetic exchange is a consequence of charge transfer to the gadolinium 5d, 6s, and 6p orbitals from the radical ligands.