Rhenium-platinum mixed-metal spiked-triangle clusters. Synthesis and X-ray characterization of the cluster anions [Re2Pt(mu-H)(2)(CO)(9){Re(CO)(5)}](-) and [Re2Pt(mu-H)(2)(CO)(9){HRe2(CO)(9)}](-)

The spiked-triangle cluster [Re2Pt(mu-H)(2)(CO)(9){HRe(CO)(5)}] (1), which contains a HRe(CO)(5) molecule bound to the Pt vertex of a Re2Pt triangle, reacts with methanolic NEt(4)OH to give the red anion [Re2Pt(mu-H)(2)(CO)(9){Re(CO)(5)}](-) (2), whose structure has been determined by single-crystal X-ray analysis of its NEt(4)(+) salt. NMR monitoring showed the intermediate formation of a carbomethoxy derivative 3, arising from the attack of OMe(-) on a carbonyl df the HRe(CO)(5) group. The deprotonation of 1 can be performed also by a base as weak as pyridine. The anion 2 in solution is thermally unstable, and at room temperature it gives rise to complex mixtures. The main component has been identified, by X-ray analysis of its NEt(4)(+) salt, as the anion [Re2Pt(mu-H)(2)(CO)(9){HRe2(CO)(9)}](-) (4), containing a HRe2(CO)(9)(-) complex bound to the Pt vertex of a Re2Pt triangle, through a Re(mu-H)Pt bond. The anions 2 and 4 are better obtained by treating [Re2Pt(mu-H)(2)(CO)(8)(COD)](COD = 1,5-cyclooctadiene) with [Re(CO)(5)](-) or [HRe2(CO)(9)](-), respectively, in the presence of CO. Experiments have been performed to clarify the origin of the [HRe2(CO)(9)](-) fragment bound to Pt in 4. The reaction between free [HRe(CO)(5)] and [Re(CO)(5)](-) produces in high yields the anion [HRe2(CO)(9)](-), but this one does not displace Re(CO)(5)(-) from 2. The reaction between [Re(CO)(5)](-) and the complex 1 gives instantaneously the anion 2. No reaction occurs upon treatment of the anion 2 with [HRe(CO)(5)]. Variable-temperature NMR has revealed the occurrence in both the anions 3 and 4 of an intramolecular dynamic process equalizing the two hydrides bound to the Pt atom, with E(a) = 70(1) and 74(7) kJ/mol, respectively.