Sulfido-bridged tetranuclear titanium-iridium complexes with an unconventional tetrahedral iridium center

A general route to the complexes [CpTi(mu(3)-S)(3)M-3(diolefin)(3)] (M = Rh, diolefin = cod, nbd, tfbb; M = Ir, diolefin = cod) consists of the reactions of the anion [Cp2Ti2(mu-S)(2)(S)(2)](2-), obtained by mono-deprotonation of Cp2Ti(SH)(2) with butyllithium in THF, with the appropriate complexes [{M(mu-Cl)(diolefin)}(2)]. Replacement of the diolefin by carbon monoxide in [CpTi(mu(3)-S)(3)M-3(diolefin)(3)] gives the carbonyl derivatives [CpTi(mu(3)-S)(3)M-3(CO)(6)]. Further reactions of the carbonyliridium complex with tertiary phosphine and phosphite ligands produce the 62-e valence clusters [CpTi(mu(3)-S)(3)Ir-3(mu-CO)(CO)(3)(PR3)(3)] (PR3 = PPh3, PMe3, P(OMe)(3), PMePh2). Remarkable features in the structure of these compounds, as found for [CPTi(mu(3)-S)(3)Ir-3(mu-CO)(CO)(3)(P(OMe)(3)}] by X-ray diffraction studies, are a distorted tetrahedral metal framework with short Ir-Ir distances and a tetrahedral coordination of the iridium atom closest to the titanium. A delocalized bonding scheme can be proposed for the iridium triangle and, at least, an interaction between the tetrahedral iridium and the titanium atom. The complexes [CpTi(mu(3)-S)(3)Ir-3(mu-CO)(CO)(3)(PR3)(3)] quickly exchange all their carbonyl ligands with (CO)-C-13 under normal conditions to give the labeled complexes. Indeed, an equilibrium between the compounds [CpTi(mu(3)-S)(3)Ir-3(mu-(CO)-C-13)((CO)-C-13)(3)(PR3)(3)] and [CpTi(mu(3)-S)(3)Ir-3(mu-(CO)-C-13)((CO)-C-13)(4)(PR3)(2)] and free phosphine exists under an atmosphere of (CO)-C-13. In addition, these compounds are fluxional, since they exhibit a single carbonyl resonance in the low-temperature C-13{H-1} NMR spectrum, probably due to very fast carbonyl scrambling. Furthermore, the reaction of [CpTi(mu(3)-S)(3)Ir-3{mu-CO)(CO)(3)(PPh3)(3)] with HBF4 gives the unsymmetric and nonfluxional hydride of formula [CpTi(mu(3)-S)(3)Ir-3(mu-CO)(H)(CO)(3)(PPh3)(3)]BF4.