Chemical Overview

 Ruthenium and Osmium Phosphavinyl Chemistry


The discovery in the Hill group of the first example of phospha-alkyne hydroruthenation provided a versatile, coordinatively-unsaturated analogue of the highly reactive vinyl complexes [RuCl(P=CHtBu)(CA)(PPh3)2] (A = O, S). This promised a fascinating chemistry through reaction at both the metal centre and at the phosphorus centre itself. The thorough investigation of the chemistry of the phosphavinyl ligand is detailed briefly below as well as the extention of the preparative methodology to osmium.

[Ru(P=CHtBu)(O2CH)(CO)(PPh3)2]

[RuCl{P(HgFc)=CHtBu)(CO)(PPh3)2]

[Ru{P(=O)CtBuC(=O)(CNtBu)2(PPh3)2]

 

Perhaps the most significant body of work to come out of my four years at Imperial College is the research carried out on the phosphavinyl complexes of ruthenium [RuCl(P=CHtBu)(CA)(PPh3)2] (A = O, S). The crystal structure (shown on right) of the formate derivative [Ru(P=CHtBu)(O2CH)(CO)(PPh3)2] clearly shows the phosphavinyl ligand to be coordinated in a bent manner indicating a nucleophilic reactivity for the trigonal phosphorus centre. The formate ligand is shown detached from the ruthenium centre. In fact, one oxygen is bound much more strongly than the other.

This reactivity was exploited in the preparation of a range of highly novel phosphaalkene ligands bearing alkyl, organogold and organomercury substituents. An example of the latter [RuCl2{P(HgFc)=CHtBu}(CO)(PPh3)2] is shown in the interactive representation to the right. These ligands are stabilised through ligation to a transition metal and would be otherwise unstable in the free state. It is also noteworthy that, in contrast to the majority of previously reported examples, these phosphaalkene ligands do not require kinetically-stabilising substituents (e.g. SiMe3 groups).

On reaction of [RuCl(P=CHtBu)(CO)(PPh3)2] with excess isocyanide, an interesting rearrangement involving the carbonyl and phosphavinyl ligands takes place to provide the complex [Ru{κ2-P(=O)CRC(=O)}(CNR)2(PPh3)2] (R = tBu) containing the first example of a phosphavinyl ligand containing a formally pentavalent phosphorus (crystal structure shown to the right).

The highly reactive osmium starting material [OsHCl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) was employed in an attempt to prepare the first osmium phosphavinyl complex. The product, however, was found to be a species displaying a diphosphacycle ligand containing both phosphavinyl and phosphaalkene motifs [Os(P=CRP(=CHR)}Cl(CO)(PPh3)2] (R = tBu) as shown below:

This work was made possible by a collaboration with Prof. Cameron Jones at Cardiff University and his provision of tertiarybutylphospha-alkyne.

 

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

R. B. Bedford, A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Coordinative activation of phospha-alkynes: methyl neopentylidene phosphorane complexes of ruthenium(II): crystal structure of [Ru(MeP=CHBut)Cl(I)(CO)(PPh3)2]. J. Chem. Soc., Dalton Trans., 1997, 139.

R. B. Bedford, A. F. Hill, C. A. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Novel synthesis of heterodinuclear phospha-alkenyl complexes: x-ray structure of [Ru{P(AuPPh3)=CHBut}Cl2(CO)(PPh3)2]. Chem. Commun., 1997, 179.

A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. A metallacyclic l5-phospha-alkenyl complex of ruthenium(II): x-ray structure of [Ru{k2-P(=O)CButC(=O)}(CNBut)2(PPh3)2]. Chem. Commun., 1998, 367.

R. B. Bedford, A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Phospha-alkyne hydrometallation: synthesis and reactivity of the complexes [Ru(P=CHCMe3)Cl(CA)(PPh3)2] (A = O, S). Organometallics, 1998, 17, 4744.

A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely. Mercuriophospha-alkene-P complexes: crystal structure of [Ru{P(=CHBut)HgC5H4Fe(h-C5H5)}Cl2(CO)(PPh3)2]. J. Chem. Soc., Dalton Trans., 1998, 1419.

A. F. Hill, C. Jones and J. D. E. T. Wilton-Ely. Phospha-alkyne hydro-osmiation: synthesis of [Os{k1P,k1P'-P=CRP(=CHR)}Cl(CO)(PPh3)2]. Chem. Commun., 1999, 451.

 

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