1,4-Dicyanobenzene as a Scaffold for the Preparation of Bimetallic Actinide Complexes Exhibiting Metal-Metal Communication

• Published in: Chemistry : a European journal 2008-09, Vol.14 (26), p.7782-7790
• Main Authors: Schelter, Eric J., Veauthier, Jacqueline M., Graves, Christopher R., John, Kevin D., Scott, Brian L., Thompson, Joe D., Pool-Davis-Tournear, Jaime A., Morris, David E., Kiplinger, Jaqueline L.
• Format: Article
• Language: English
• Subjects: actinides; bimetallic complexes; electrochemistry; electronic communication; magnetic properties
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800585

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(μ‐{NC(CH3)‐C6H4‐(CH3)CN})] (8) and [{(C5Me5)2(Br)Th}2(μ‐{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 UIV/UIV (5f2–5f2) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the π system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f–f bands for the bimetallic UIV/UIV system decrease substantially compared to the related monometallic ketimide chloride complex, [(C5Me5)2U(Cl){‐NC(CH3)‐(3,4,5‐F3‐C6H2)}] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C5Me4Et)2U(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. Bridging the gap: Nitrile insertion chemistry with 1,4‐dicyanobenzene has been used to prepare discrete dinuclear ThIV/ThIV (5f0–5f0) and UIV/UIV (5f2–5f2) organometallic complexes in which the two metal centers are covalently connected by a 1,4‐phenylenediketimide bridging ligand (see picture). The uranium system displays appreciable electronic communication between the UIV centers through the π system of the dianionic diketimide bridging ligand.