Research paperHalf-sandwich hydrazine complexes of iridium: Preparation and reactivity
Graphical abstract
The preparation and oxidation with Pb(OAc)4 of both mono- and bis(hydrazine) complexes of iridium(III) are described.
Introduction
The chemistry of transition metal complexes containing hydrazine and other partially reduced dinitrogen ligands such as diazene RNNH has attracted interest in recent years [1], [2], [3], [4], [5], not only because of their relationship with dinitrogen fixation process intermediates [6], [7], [8], but also because their properties led us to consider this class of complexes as having identity and chemistry in itself [1], [2], [3], [5], with potentially interesting developments.
A large number of hydrazine and substituted hydrazine complexes of several metals have been reported recently [1], [2], [3], [4], [5] and several studies on their oxidation [8] and reduction [5], [6], [7], [9] reactions have revealed their interesting properties, e.g., in convertion of metal-bonded hydrazine to diazene.
However, despite many studies on these issues, the chemistry of hydrazine complexes of iridium has been relatively under-developed when compared with other metals and, except for cluster [(Cp∗Ir)4(µ3-S)2(µ2-H)2(N2H4)2](BF4)2 [10], only two papers on the preparation of hydrazine complexes of iridium have appeared in the literature [11].
We have a long-standing interest in the “diazo” chemistry of transition metals and have reported the synthesis and reactivity of hydrazine, diazene and diazoalkane complexes of Ru and Os stabilised by half-sandwich fragments of the type [M(η5-C5H5)(R1NHNH2)(PPh3)L]BPh4, [M(η5-C5H5)(R1NNH)(PPh3)L]BPh4, [M(η5-C5H5)(Ar1Ar2CN2)(PPh3)L]BPh4, [M(η5-C9H7)(R1NHNH2)(PPh3)L]BPh4 [MRu, Os; R1H, Me, Ph; LP(OR)3] [12], [13].
We have now extended our study to iridium, and report here the synthesis and oxidation reactions of both mono- and bis(hydrazine) iridium(III) complexes stabilised by pentamethylcyclopentadienyl half-sandwich fragments.
Section snippets
General comments
All synthetic work was carried out under an appropriate atmosphere (Ar, N2) with standard Schlenk techniques or in an inert atmosphere dry-box. All solvents were dried over appropriate drying agents, degased on a vacuum line, and distilled into vacuum-tight storage flasks. IrCl3·3H2O (Pressure Chemical Co. (USA) and pentamethylcyclopentadiene C5Me5H (STREM) were used as received. Phosphites P(OMe)3 and P(OEt)3 were Aldrich products, used as received. Hydrazines CH3NHNH2 and C6H5NHNH2 were
Results and discussion
Half-sandwich phosphite complexes of iridium IrCl2(η5-C5Me5)[P(OR)3] (1) were prepared by reacting the dimeric species [IrCl2(η5-C5Me5)]2 with phosphites in refluxing methanol or ethanol, as shown in Scheme 1.
The reaction proceeds with break of the dimer and coordination of the phosphite, affording neutral dichloro derivatives 1, which were isolated in good yield (about 90%) and characterised.
Treatment of chloro compounds IrCl2(η5-C5Me5)[P(OR)3] with an excess of hydrazine R1NHNH2 in the
Conclusions
We demonstrate in this work that both mono- and bis(hydrazine) complexes of iridium can be prepared with half-sandwich complexes IrCl2(η5-C5Me5)[P(OR)3] as precursors. Oxidation with Pb(OAc)4 at −40 °C allowed both mono- and bis(aryldiazene) derivatives to be obtained.
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