A New Dichroic, Nitroso‐Bridged Complex of Rhenium: Di‐μ 2 ‐chloro[μ 2 ‐(η 2 ‐ N , O )‐ N , N ‐dimethyl‐4‐nitrosoaniline]bis[tricarbonylrhenium( I )]

The dimeric μ 2 ‐amino‐phenoxy complexes of rhenium [(CO) 3 Re(μ 2 ‐O ∩ NH 2 )] 2 ( 1 ) do not react with the C ‐nitroso compounds R−C 6 H 4 NO [R = NMe 2 ( 2 ), H ( 2′ )] in the presence of AlCl 3 by a condensation reaction to give the desired azo dye complexes [(CO) 3 Re(μ 2 ‐O ∩ N=NC 6 H 4 R)] 2 . Instead, they react to give the novel neutral η 2 ‐ N , O ‐bridged C ‐nitroso complexes [{CO) 3 ReCl} 2 ONC 6 H 4 R] ( 3 , 3′ ) by means of a substitution reaction. Both complexes yield golden gleaming crystals, and their solutions are deeply blue ( 3 ) or violet ( 3′ ) due to the broad UV/Vis absorption at λ = 617 ( 3 ) and 505 nm ( 3′ ). Single crystals of 3 , 3′ show nonlinear optical properties, they are dichroic and have a red and blue ( 3 ) or violet and green ( 3′ ) side. The molecular structures of 3 , 3′ have been determined by single‐crystal X‐ray analyses. Both compounds contain two face‐joined octahedra, with two chloro and the NO ligands as bridges. The C ‐nitroso groups together with the NC 2 moiety of NMe 2 ( 3 ) lie almost exactly within the symmetry plane of the molecules. Both the N atoms of 3 have a trigonal‐planar geometry. 3 and 3′ are the first single, neutral and dinuclear C ‐nitroso complexes with the rare non‐assisted μ‐(η 2 ‐ N , O ) bridge and only single atoms as additional bridges. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)