1,4-dicyanobenzene as a scaffold for the preparation of bimetallic actinide complexes exhibiting metal-metal communication.

Reaction of two equivalents of [(C5Me4Et)2U(CH3)(Cl)] (6) or [(C5Me5)2Th(CH3)(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [((C5Me4Et)2(Cl)U)(2)(mu-(N=C(CH3)-C6H4-(CH3)C=N))] (8) and [((C5Me5)2(Br)Th)2(mu-(N=C(CH3)-C6H4- (CH3)C==N))] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U IV/U IV (5f2-5f2) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the pi system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U IV/U IV system decrease substantially compared to the related monometallic ketimide chloride complex, [(C5Me5)2U(Cl)(-N=C(CH3)-(3,4,5-F(3)-C6H2))] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C5Me4Et)(2)U(CH3)(Cl)] (6) and [(C5Me5)2Th(CH3)(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C5Me4Et)2UCl2] (3), [(C5Me4Et)2U(CH3)2] (4), [(C5Me4Et)2U(-N==C(CH3)-C6H4-C==N)2] (10), and 11.