Bis(acetylacetonato)bis(cyclooctene)ruthenium(II), cis-[Ru(acac)(2)(eta(2)-C8H14)(2)]: a synthetic precursor to trans- and cis-bis(acetylacetonato)ruthenium(II) complexes

Reduction of [Ru(acac)(3)] with zinc amalgam or zinc dust in hot THF contai ning some water in the presence of an excess of cyclooctene generated in so lution cis-[Ru(acac)(2)(eta(2)-C8H14)(2)], which cannot be isolated in soli d form but has been identified on the basis of its H-1 NMR spectrum. It is a useful synthetic precursor because the co-ordinated olefins are easily di splaced by many ligands. Treatment with pyridine, tert-butyl isocyanide, te rtiary phosphines, phosphites and triphenylarsine (L) at room temperature g ave red-brown complexes trans-[Ru(acac)(2)L-2], which isomerise in solution to the more stable cis compounds on heating. In contrast, the similarly pr epared trimethylamine complex, trans-[Ru(acac)(2)(NMe3)(2)], does not under go trans to cis isomerisation. Reaction of cis-[Ru(acac)(2)(eta(2)-C8H14)(2 )] with acetonitrile or triphenylstibine (L') gave monosubstitution product s cis-[Ru(acac)(2)(eta(2)-C8H14)L'], which react on heating with an excess of L' to give cis-[Ru(acac)(2)L'(2)]. Treatment of cis-[Ru(acac)(2)(eta(2)- C8H14)(2)] (1 mol) with Ph2PCH2PPh2 (dppm) (2 mol) at room temperature gave trans-[Ru(acac)(2)(eta(1)-dppm)(2)], whereas the ligands Ph2P(CH2)(m)PPh2 (L-L, m = 2, dppe; m = 3, dppp) under the same conditions gave oligomers [{ Ru(acac)(2)(L-L)}(n)], which probably contain mutually trans-phosphorus ato ms. On heating all three compounds are converted into cis-[Ru(acac)(2)(L-L) ]. Treatment of trans-[Ru(acac)(2)L-2] (L = NMe3 or PPh3) with CO at room t emperature and pressure gave trans-[Ru(acac)(2)(CO)L], which, in the case o f L = PPh3, isomerises to the cis compound on heating; reaction of trans-[R u(acac)(2)(AsPh3)(2)] with CO under the same conditions gave cis-[Ru(acac)( 2)(CO)(AsPh3)] directly. The structures of trans-[Ru(acac)(2)(CNBut)(2)], t rans-[Ru(acac)(2)(PMePh2)(2)], cis-[Ru(acac)(2)(CNBut)(2)] (in the form of a molecular adduct with [Ru(acac)(3)]), cis-[Ru(acac)(2)(PMePh2)(2)] and tr ans-[Ru(acac)(2)(eta(1)-dppm)(2)] have been determined by X-ray crystallogr aphy, and trends in the metal-ligand distances are discussed. The formation of trans-[Ru(acac)(2)L-2] from cis-[Ru(acac)(2)(eta(2)-C8H14)(2)] may proc eed via a square-pyramidal intermediate [Ru(acac)(2)L].