Abstract
Reaction of [OsI2(C6H6)(PMeBut2)] with Na[ONCMe2] in methanol, in presence of KPF6′, afforded the oximato compound [Os(C6H6)(η2-ONCMe2)(PMeBut2)]PF6 which on further reaction with HNCPh2 gave the azavinylidene complex [Os(C6H6)(NCPh2)(PMeBut2)]PF6′. By using a similar synthetic route, the bis(tert-butylphosphine)osmium(II) derivatives [OsX2(arene)(PHBut2)], [Os(arene)(η2-ONCMe2)(PHBut2)]PF6 and [Os(arene)(NCPh2)(PHBut2)]PF6(arene = C6H6 or C6H3Me3-1,3,5; X = Cl or I) were obtained, in most cases almost quantitatively. The NMR spectra of all the latter complexes and of [Os(C6H6)(η2-ONCMe2)(PMeBut2)]PF6 are temperature-dependent and thus indicative of a dynamic behaviour in solution. The most reasonable explanation for these observations is that due to a hindered rotation around the Os–P axis conformational isomers are formed. The energy barrier for the conversion significantly depends on the type of the non-phosphine ligands co-ordinated to osmium and is, for arene = C6H6, in [Os(arene)(NCPh2)(PHBut2)]PF6 higher than in [OsX2(arene)(PHBut2)] and in the mesitylene complexes higher than in the benzene derivatives. For [Os(C6H6)(NCPh2)(PHBut2)]PF6, a value of ΔG‡ for the rotational barrier of ca. 60 kJ mol–1 has been calculated.
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