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

Abstract

Reactions of [(η 6-arene)RuCl 2] 2 ( 1) (η 6-arene= p-cymene ( 1a), 1,3,5-Me 3C 6H 3 ( 1b), 1,2,3-Me 3C 6H 3 ( 1c) 1,2,3,4-Me 4C 6H 2( 1d), 1,2,3,5-Me 4C 6H 2 ( 1e) and C 6Me 6 ( 1f)) or [Cp*MCl 2] 2 (M=Rh ( 2), Ir ( 3); Cp*=C 5Me 5) with 4-isocyanoazobenzene (RNC) and 4,4′-diisocyanoazobenzene (CN–R–NC) gave mononuclear and dinuclear complexes, [(η 6-arene)Ru(CNC 6H 4NNC 6H 5)Cl 2] ( 4a– f), [Cp*M(CNC 6H 4NNC 6H 5)Cl 2] ( 5: M=Rh; 6: M=Ir) , [{(η 6-arene)RuCl 2} 2{μ-CNC 6H 4NNC 6H 4NC}] ( 8a– f) and [(Cp*MCl 2) 2(μ-CNC 6H 4NNC 6H 4NC)}] ( 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)](PF 6) 2 (dppf=1,1′-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC 6H 4NNC 6H 5)](PF 6) 2 ( 7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF 3SO 3), giving a rectangular tetranuclear complex 11b, [{(η 6-1,3,5-Me 3C 6H 3)Ru(μ-Cl} 4(μ-CNC 6H 4NNC 6H 4NC) 2](CF 3SO 3) 4 bridged by four Cl atoms and two μ-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).