Preparation and characterization of ruthenium(II), rhodium(III) and iridium(III) complexes of isocyanide bearing the azo group

Reactions of [(eta (6)-arene)RuCl2](2) (1) (eta (6)-arene = p-cymene (1a), 1,3,5-Me3C6H3 (1b), 1,2,3-Me3C6H3 (1c) 1,2,3-Me4C6H2(1d), 1,2,3,5-Me4C6H2 (1e) and C6Me6 (1f)) or [Cp*MCl2](2) (M = Rh (2), Ir (3); Cp* = C5Me5) with 4-isocyanoazobenzene (RNC) and 4,4'-diisocyanoazobenzene (CN-R-NC) gave mononuclear and dinuclear complexes, [(eta (6)-arene)Ru(CNC6H4N=NC6H5)Cl-2] (4a-f). [Cp*M(CNC6H4N=NC6H5)Cl-2] (5: M = Rh; 6: M = Ir), [{(eta (6) -arene)RuCl2}(2){mu -CNC6H4N=NC6H4NC}] (8a-f) and [(Cp*MCl2)(2)(mu -CNC6H4N=NC6H4NC)}] (9: M = Rh; 10: M = Ir), respectively. It was confirmed by X-ray analyses of 4a and 5 that these complexes have trans-forms for the -N=N- moieties. Reaction of [Cp*Rh(dppf)(MeCN)](PF6)(2) (dppf = 1,1'-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC6H4N=NC6H5)](PF6)(2) (7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF3SO3), giving a rectangular tetranuclear complex 11b, [{(eta (6)-1,3,5-Me3C6H3)Ru(mu -Cl}(4)(mu -CNC6H4N=NC6H4NC)(2)](CF3SO3)(4) bridged by four Cl atoms and two mu -diisocyanoazobenzene ligands. Photochemical reactions of the ruthenium complexes (4 and 8) led to the decomposition of the complexes, whereas those of 5, 7, 9 and 10 underwent a trans-to-cis isomerization. In the electrochemical reactions the reductive waves about -1.50 V for 4 and -1.44 V for 8 are due to the reduction of azo group, [-N=N-] [-N=N-]2 -. The irreversible oxidative waves at ca. 0.87 V for the 4 and at ca. 0.85 V for 8 came from the oxidation of Ru(II) Ru(III). (C) 2001 Elsevier Science B.V. All rights reserved.