Synthesis, structural characterization and thermal reactivities of osmium carbonyl clusters containing 4,6-dimethylpyrimidine-2-thione

Yat Kun Au, Kung Kai Cheung, Wing Tak Wong

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The reaction of the labilized cluster [Os3(CO)10(MeCN)2] and bis(4,6-dimethylpyrimidin-2-yl) disulfide affords two major products [Os3(CO)10(μ-dmpymt)2] 1 (36%) and [Os3(CO)10(μ-SH)(μ-dmpymt)] 2 (19%) (dmpymt = 4,6-dimethylpyrimidine-2-thione). Cluster 2 is formed from C-S bond cleavage of one of the dmpymt ligands at ambient conditions. Thermolysis of cluster 1 in n-heptane (98 °C) for 1 h produces an isomeric cluster of 1, [Os3(CO)10(μ-dmpymt)2] 3 (62%), which contains two dmpymt ligands co-ordinated across the same non-bonding Os⋯Os edge. Thermolysis of cluster 3 in n-heptane for 2 h affords the cluster [Os3(CO)9(μ-dmpymt)(μ3-η 2-dmpymt)] 4 as the major product (42%) in addition to a minor product [Os3(CO)8(μ-η2-dmpymt)(μ 3-η2-dmpymt)] 5 (9%). Cluster 4 contains two dmpymt moieties co-ordinating in μ and μ3-η2 modes respectively. Cluster 5 has two dmpymt moieties bonding in the μ3-η2 and μ-η2 modes respectively. Further thermolysis of cluster 4 in n-octane (125 °C) leads to a much higher yield of cluster 5 (60%) at the expense of cluster 4. Chemical activation of cluster 1 using Me3NO in CH2Cl2 at -78 °C also produces clusters 4 and 5 in 20 and 15% yield respectively. A new, orange product (31%) is also formed but remains uncharacterized. When cluster 4 is allowed to stand under ambient conditions over a period of ten days, it isomerizes to the cluster [Os3(CO)9(μ-dmpymt)(μ-η2-dmpymt)] 6 in almost quantitative yield (87%). Cluster 6 contains one dmpymt ligand co-ordinating in the μ-η2 five-electron donating mode. Cluster 5 undergoes carbonylation to form cluster 4 (62%) under a CO atmosphere in CH2Cl2 while cluster 4 also changes back to cluster 3 (47%) in refluxing n-hexane (69 °C) under a CO atmosphere. Formation of clusters 3-5 is thus reversible. Mechanisms for the formation of 3, 4 and 6 have also been proposed. All the clusters 1-6 isolated have been fully characterized by conventional spectroscopic methods as well as single-crystal X-ray analyses.
Original languageEnglish
Pages (from-to)1047-1057
Number of pages11
JournalJournal of the Chemical Society, Dalton Transactions
Issue number6
Publication statusPublished - 1 Dec 1995
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)


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