Reactivity with aryldiazonium cations of hydrazine complexes of ruthenium and osmium
Graphical abstract
The reaction of bis(hydrazine) complexes [M(NH2NH2)2L4](BPh4)2 (M = Ru, Os) with aryldiazonium salt affording bis(amine) [M(NH3)2L4](BPh4)2, chloro-amine [MCl(NH3)L4]BPh4, and bis(hydrazone) derivatives [M{NH2NC(CH3)2}2L4](BPh4)2 is described.
Introduction
The chemistry of hydrazine complexes of transition metals has developed extensively in recent years [1], [2], mainly due to their close relationship with the dinitrogen fixation process [3], [4]. Many hydrazine complexes have thus been synthesised and several reactivity studies have been reported [1], [2]. Among the former, oxidation of coordinated NH2NH2 to give stable 1,2-diazene derivatives [M]–NHNH [3] and reduction to ammonia are the most interesting [4], [5]. Deprotonation reactions with strong bases, affording both 1,2-diazene and dinitrogen derivatives [2], as well as the reaction with ketones yielding hydrazone derivatives, have also received attention [6]. However, although several reactivity studies have been reported, none of them concerns the reaction of coordinated hydrazine with aryldiazonium cations [ArN2]+.
We are interested in the chemistry of diazo complexes of transition metals and have reported the synthesis and reactivity of mono- and bis(hydrazine) complexes of the iron triad [7] of the type [M(CO)(NH2NH2)L4](BPh4)2 and [M(NH2NH2)2L4](BPh4)2 (L = phosphites). Oxidation with Pb(OAc)4 at low temperature of these complexes was extensively studied, affording new examples of mono- and bis(1,2-diazene) derivatives. We have now extended these studies to include reactivity with aryldiazonium salts of mono- and bis(hydrazine) complexes. This paper reports the results of these investigations.
Section snippets
General comments
All synthetic work was carried out in an appropriate atmosphere (Ar, N2) using standard Schlenk techniques or a vacuum atmosphere dry-box. All solvents were dried over appropriate drying agents, degassed on a vacuum line, and distilled into vacuum-tight storage flasks. RuCl3·3H2O and OsO4 were Pressure Chemical Co. (USA) products, used as received. Triethylphosphite P(OEt)3 was an Aldrich product, purified by distillation. Hydrazine NH2NH2 was prepared by decomposition of hydrazine cyanurate
Results and discussion
The bis(hydrazine) complex [Os(NH2NH2)2{P(OEt)3}4](BPh4)2 was reacted with aryldiazonium cations [ArN2]+ in CH2Cl2 to give the bis(amine) complex [Os(NH3)2{P(OEt)3}4](BPh4)2 (1) in about 80% yield (Scheme 1).
The formation of amine complex 1 was surprising, but can be explained as due to the reaction of the coordinate hydrazine with the aryldiazonium cation to give a tetrazene complex [A] (Scheme 2), which is probably unstable and decomposes, with loss of the arylazide molecule ArN3 and
Conclusions
Depending on both the nature of the solvent and the metal centre, the reaction of bis(hydrazine) complexes [M(NH2NH2)2L4](BPh4)2 (M = Ru, Os) with aryldiazonium salt affords bis(amine) [M(NH3)2L4](BPh4)2, chloro-amine [MCl(NH3)L4](BPh4), and bis(hydrazone) derivatives [M{NH2NC(CH3)2}2L4](BPh4)2.
Acknowledgment
We thank Mrs. Daniela Baldan, from the Università Ca’ Foscari Venezia, for her technical assistance.
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