Ruthenium and Rhodium Sulfur Macrocycle Chemistry
Macrocycle chemistry involving the transition elements has enjoyed considerable attention in the last two decades. It was suggested that sulfur macrocycles could replace phosphines in catalyts leading to less contamination from free phosphine. The work presented here involves the use of the thiacycle 1,4,7-trithiacyclononane aneS3 as a tridentate supporting ligand for catalytically relevant ligands (vinyl, thioacyl). A better understanding of the role of macrocycles in the reactivity of transition metal complexes could provide valuable information relating to catalytic activity. This is illustrated by the discovery of the first example of a catalytic process (demercuration) supported by the aneS3 ligand described here.
Reaction of [Ru(CR=CHR')Cl(CO)(PPh3)2] (R, R' = H, Ph etc.) with aneS3 results in the loss of a phosphine and chloride ligands to yield [Ru(CR=CHR')(CO)(PPh3)(aneS3)]+, an example of a vinyl complex incorporating a thiacycle. The structure of the parent ethenyl vinyl compound is shown below (phenyl groups omitted for clarity).
The same reaction was attempted with the corresponding thiocarbonyl vinyl complexes [Ru(CR=CHR')Cl(CS)(PPh3)2]. However, due to the propensity of the CS ligand to enter into migratory insertion reactions, a thioacyl complexes [Ru(η2-SCCR=CHR)(PPh3)(aneS3)]+ ((R, R' = H, Ph) were obtained through insertion of thiocarbonyl into the vinyl Ru-C bond as shown below:
This suggests that coordination of the aneS3 ligand is the driving force for the insertion reaction. This was not found to be the case for all the complexes studied. The silyl complex [RuCl(SiMe2OEt)(CS)(PPh3)2] reacted with aneS3 to yield the non-migrated product [Ru(SiMe2OEt)(CS)(PPh3)(aneS3)]+. A further interesting case is that of the compound [RuCl(C6H5)(CS)(PPh3)2] which forms the non-migrated complex with aneS3 under mild conditions but goes on ultimately to yield the migrated species [Ru(η2-SCC6H5)(PPh3)(aneS3)]+ after heating:
The species [Rh(PPh3)2(aneS3)]PF6 was prepared in order to provide a synthetically versatile starting material for rhodium aneS3 chemistry, similar to the role of its corresponding Tp analogue [RhTp(PPh3)2]. However, the deposition of elemental mercury in test reactions with organomercury reagents led to the discovery that it catalysed the demercuration of mercury(bisacetylides) Hg(CCR)2 to di-ynes. This represents the first example of a well-defined aneS3 complex in catalysis. The catalytic cycle is shown below:
Further details of this work can be found in the following articles:
J. C. Cannadine, A. F. Hill, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Organometallic macrocycle chemistry 5. Sigma-vinyl and sigma-aryl complexes of ruthenium(II) ligated by 1,4,7-trithiacyclononane (aneS3). Organometallics, 1996, 15, 5409.
A. F. Hill and J. D. E. T. Wilton-Ely. Synthesis and catalytic application of [Rh(PPh3)2(aneS3)]PF6. Organometallics, 1997, 16, 4517.
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