Synthesis and characterization of 9,10‐bis(arylimino)‐9,10‐dihydrophenanthrenes, the structure of (<i>Z,Z</i>)‐9,10‐bis(phenylimino)‐9,10‐dihydrophenanthrene and PdCl₂‐[(<i>E,E</i>)‐9,10‐bis(phenylimino)‐9,10‐dihydrophenanthrene] in the solid state and in solution

Abstract

Abstract The synthesis and characterization of substituted phenanthrene‐9,10‐quinone diimines of the type 9,10‐bis(arylimino)‐9,10‐dihydrophenanthrene (aryl‐BIP) is described. These rigid bisnitrogen ligands have been synthesized by a metal‐mediated cyclodehydrogenation reaction from the aromatic open‐chain diimine analogues derived from benzil. All aryl‐BIP compounds adopt a Z,Z configuration in solution except for ( o ‐ i Pr‐phenyl)‐BIP, which mainly exists in the E,Z form. All non‐cyclic BIP compounds undergo a configurational change into the E,E isomer upon coordination to palladium. NDDO calculations on phenyl‐BIP and its palladium dichloride complex have revealed that the energy of the LUMO is very much dependent on the puckering of the phenanthrene backbone and is in all cases lower than, for instance, that of the aromatic diimine of acenaphthene‐1,2‐quinone or open‐chain diimines. The structures of phenyl‐BIP and PdCl 2 ‐(phenyl‐BIP) in the solid state have been determined by X‐ray diffraction. Phenyl‐BIP is triclinic, space group P̄, a = 12.392(1), b = 12.478(1), c = 14.633(2) Å, α = 109.36(1), β = 91.57(1), γ = 115.82(1)°, Z = 4, final R = 0.0556 for 4494 reflections with I &gt; 2.5σ( I ). PdCl 2 ‐(phenyl‐BIP) is monoclinic, space group P 2 1 / c, a = 20.5148(9), b = 10.6756(9), c = 23.2007(16) Å, β = 105.13(1)°, Z = 4, final R = 0.0701 for 2569 reflections with I &gt; 2.5σ( I ).