Chemical Overview

 Ruthenium and Rhodium Scorpionate Chemistry


Since the discovery by Trofimenko of the hydrotris(pyrazol-1-yl)borate (Tp) ligand, it has been used to stabilise a wide variety of transition metal complexes. The research presented briefly here describes versatile ruthenium and rhodium systems that provide excellent entrypoints for metal-bound functional group transformations supported by the Tp ligand. The term 'scorpionate' has been used to describe the interchange between bidentate and tridentate coordination modes of the Tp ligand, in which the third pyrazole ring (the 'scorpion's tail') can curl round to bind with the metal centre.

[RhI2{=C(SMe)2}{HB(pz)3}]

[Rh{η2-C2(CO2Me)2}{HB(pz)3}(PPh3)]

[Rh(η2-SCNMe2){HB(pz)3}(PPh3)]Cl

First prepared in the Hill group, [RuCl{HB(pz)3}(PPh3)2] has proved a versatile starting material for ruthenium Tp chemistry. My work in the area involved a thorough investigation of this compound for the generation of carbene complexes. This was achieved through ligand substitution and subsequent transformations centred around the labile phosphine and chloride ligands of [RuCl{HB(pz)3}(PPh3)2]. Examples bearing cabene, vinylidene, allenylidene, isonitrile and acetylide ligands were successfully isolated.

The reaction of [RuHCl(CO)(PPh3)3] with KTp under very mild conditions was found to yield the species [RuH(CO){k2-HB(pz)3}(PPh3)2] in which the Tp ligand is coordinated in a bidentate manner. Despite the fact that this coordination mode of the Tp ligand has led to the term 'scorpionate' ligand being coined, this is a relatively rare observation for the unsubstituted Tp ligand (as opposed to the bulky 3,4,5-trimethyl analogue, Tp*). Vigorous heating leads to closure of the 'scorpions tail' and tridenate coordination for the Tp ligand.

The highly reactive species [Rh{HB(pz)3}(PPh3)2] was prepared as a direct response to the lack of starting materials bearing the Tp ligand capable of reacting with organic reagents. It was found that one or both of the phosphines could be replaced to provide access to alkyne [Rh{η2-C2(CO2Me)2}{HB(pz)3}(PPh3)] (see right) and thiocarbamoyl [Rh(η2-SCNMe2){HB(pz)3}(PPh3)]Cl (bottom right) functionality as just two examples. Double alkylation of the carbon disulfide adduct [Rh(η2-SCS){HB(pz)3}(PPh3)] with iodomethane resulted in the carbene complex [RhI2{=C(SMe)2}{HB(pz)3}] through loss of the remaining phosphine ligand. This molecule is shown as an interactive structural model at the top right of the page.

 

 

Further details of this work can be found in the following articles:

I. D. Burns, A. F. Hill, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Polyazolyl chelate chemistry 6. Bidentate coordination of HB(pz)3 (pz = pyrazol-1-yl) to ruthenium and osmium. Crystal structure of [RuH(CO)(PPh3)2{k2-HB(pz)3}]. Organometallics, 1998, 17, 1552.

A. F. Hill, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Synthesis and reactivity of [TpRu(PPh3)2] (Tp = hydrotris(pyrazol-1-yl)borate). Organometallics, 1998, 17, 3152.

A. F. Hill, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Polyazolyl chelate chemistry 8. Organometallic dihydrobis(pyrazol-1-yl)borato complexes of ruthenium. Organometallics, 1998, 17, 4249.

B. Buriez, I. D. Burns, A. F. Hill, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Polyazolyl chelate chemistry 7. Reactivity of the complexes [MCl(PPh3)2(HB(pz)3)] (M = Ru, Os; pz = pyrazol-1-yl). Organometallics, 1999, 18, 1504.

B. Buriez, D. J. Cook, K. J. Harlow, A. F. Hill, T. Welton, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Unprecedented coupling of vinylidene and allenylidene ligands with dithiocarbamates. X-ray structure of [Ru{C(=C=CPh2)SC(NMe2)S}(S2CNMe2)(PPh3)]. J. Organomet. Chem., 1999, 578, 264.

 

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