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

The spiked-triangle cluster [Re2Pt(μ-H)2(CO)9HRe(CO)5] (1), which contains a HRe(CO)5 molecule bound to the Pt vertex of a Re2Pt triangle, reacts with methanolic NEt4OH to give the red anion [Re2Pt(μ-H)2(CO)9Re(CO)5] - (2), whose structure has been determined by single-crystal X-ray analysis of its NEt4+ salt. NMR monitoring showed the intermediate formation of a carbomethoxy derivative 3, arising from the attack of OMe- on a carbonyl of 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 NEt4+ salt, as the anion [Re2Pt(μ-H)2(CO)9HRe2(CO) 9]- (4), containing a HRe2(CO)9- complex bound to the Pt vertex of a Re2Pt triangle, through a Re(μ-H)Pt bond. The anions 2 and 4 are better obtained by treating [Re2Pt(μ-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 Ea = 70(1) and 74(7) kJ/mol, respectively.