A New Binucleating Ligand Based on Anthracene and Its Cofacial Dirhodium(I) and Diiridium(I) Complexes

A new bis(beta-keto enamine) ligand (2a, ABIH(2)) containing a 1,8-anthracenediyl bridging group has been synthesized by a four-step procedure that relies on the Pd-catalyzed cross-coupling between (3,5-dimethylisoxazol-4-yl)trialkyltin and 1,8-dibromoanthraquinone or -anthracene. The molecular structures of the 1,8-bis(3,5-dimethylisoxazol-4-yl)anthraquinone (8) and -anthracene (10) intermediates were determined by X-ray analysis. Crystal data for 8: orthorhombic, space group Pbca; a = 14.351 (2), b = 11.932 (1), c = 23.278 (2) Å; V = 3986 (1) Å(3); Z = 8; R = 0.057 for 2615 reflections. Crystal data for 10: orthorhombic, space group P2(1)2(1)2(1); a = 7.104 (1), b = 12.805 (1), c = 22.280 (2) Å; V = 2026.7 (6) Å(3); Z = 4; R = 0.066 for 3423 reflections. The rigid ABIH(2) ligand, whose chelating moieties are constrained to be cofacial, allows the preparation of a new family of cofacial bimetallic complexes (ABI)[ML(2)](2) with controllable environments around the metal centers. Two novel cofacial binuclear complexes 4 and 5, with ML(2) = dicarbonylrhodium(I) and (eta(4)-1,5-cyclooctadiene)iridium(I), have been synthesized by reaction of ABIH(2) with [(&mgr;-Cl)Rh(CO)(2)](2) and [(&mgr;-Cl)Ir(COD)](2), respectively. NMR data indicate the formation of meso and racemic atropisomers for 2a, 4, and 5.