The series Os4(µx-η2-C2Ph2)(CO)14–n(n = 0, 1, 2;x = n+ 2) — Models for site-specific surface catalysts

Abstract

The cluster Os4(µ-η2-C2Ph2)(CO)14(1) has been prepared from the reaction of Os4(CO)14and C2Ph2in CH2Cl2at 25 °C. Other minor products include the known clusters Os3(µ3-η2-C2Ph2)(CO)10and Os3(µ-η4-C4Ph4)(CO)9. The structure of 1 reveals an approximately planar C2Os4skeleton with a dimetallacyclobutene ring (C—C = 1.32(4) Å) and a flat butterfly Os4unit (Os—Os range = 2.859(2)–2.916(2) Å). The13C{1H} NMR spectrum of 1 indicates the carbonyl ligands are rigid at room temperature. Stirring 1 in CH2Cl2for 2 days (ambient temperature) afforded Os4(µ3-η2-C2Ph2)(CO)13(2). The Os atoms in 2 also have an almost flat butterfly arrangement (Os—Os range = 2.7392(7)–2.8947(6) Å) with the alkyne ligand located over one of the Os3triangles. The13C NMR data for 2 are consistent with rapid rotation on the NMR timescale of the hinge Os(CO)3units at 21 °C, but slow rotation at –50 °C. Heating 2 at 40 °C gave Os4(µ4-η2-C2Ph2)(CO)12(3) after 2 days. Cluster 3 has the common butterfly arrangement of Os atoms with the C2Ph2bound to all four metal atoms (Os—Os range = 2.7457(5)–2.8742(5) Å). The13C{1H} NMR spectra of 3 at 21 and 90 °C indicate there is rapid CO exchange of the carbonyls of the two types of Os(CO)3units, but not between the units. The spectrum at –90 °C indicates one of the rotations (presumed to be that involving the carbonyls of the wingtip Os(CO)3units) is slowed on the NMR timescale. Compounds 1–3 form a unique series of clusters that have an alkyne ligand bound to two, three, and four metal atoms. Compound 1 is a model for a corner, compound 2 for a planar surface, and compound 3 a step site, in site-specific surface catalysts.Key words: osmium cluster, diphenylacetylene, dimetallacyclobutene, carbonyl exchange, surface catalysis.