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

A new bis(β-keto enamine) ligand (2a,
ABIH2) 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)
Å3; Z = 8; R = 0.057 for 2615
reflections. Crystal data for 10:  orthorhombic, space
group P212121;
a = 7.104
(1), b = 12.805 (1), c = 22.280 (2) Å;
V = 2026.7 (6) Å3; Z = 4;
R = 0.066 for 3423 reflections. The
rigid
ABIH2 ligand, whose chelating moieties are constrained to
be cofacial, allows the preparation of a new family of
cofacial bimetallic complexes
(ABI)[ML2]2 with controllable
environments around the metal centers. Two novel
cofacial binuclear complexes 4 and 5, with
ML2 = dicarbonylrhodium(I) and
(η4-1,5-cyclooctadiene)iridium(I),
have been synthesized by reaction of ABIH2 with
[(μ-Cl)Rh(CO)2]2 and
[(μ-Cl)Ir(COD)]2, respectively.
NMR
data indicate the formation of meso and racemic atropisomers for
2a, 4, and 5.