Organoruthenium chemistry is the chemistry of organometallic compounds containing a carbon to ruthenium chemical bond. Several organoruthenium catalysts are of commercial interest [1] and organoruthenium compounds have been considered for cancer therapy. [2] The chemistry has some stoichiometric similarities with organoiron chemistry, as iron is directly above ruthenium in group 8 of the periodic table. The most important reagents for the introduction of ruthenium are ruthenium(III) chloride and triruthenium dodecacarbonyl.
In its organometallic compounds, ruthenium is known to adopt oxidation states from -2 ([Ru(CO)4]2−) to +6 ([RuN(Me)4]−). Most common are those in the 2+ oxidation state, as illustrated below.
As with other late transition metals, ruthenium binds more favorably with soft ligands. [3] The most important ligands for ruthenium are:
While monodentate phosphine ligands such as triphenylphosphine and tricyclohexylphosphine are most common, bidentate phosphine ligands can also be useful in organoruthenium compounds. BINAP, in particular, is a useful asymmetric ligand for many asymmetric ruthenium catalysts. [4] [5] [6] [7]
NHC ligands have become very common in organoruthenium complexes. [8] [9] NHC ligands can be prepared with precise steric and electronic parameters, and can be chiral for use in asymmetric catalysis. [10] NHCs, as strongly donating L-type ligands, are often used to replace phosphine ligands. A notable example is 2nd generation Grubbs catalyst, in which a phosphine of the 1st generation catalyst is replaced by an NHC.
The parent compound ruthenocene is unreactive because it is coordinatively saturated and contains no reactive groups. Shvo catalyst ([Ph4(η5-C4CO)]2H]}Ru2(CO)4(μ-H)) is also coordinatively saturated, but features reactive OH and RuH groups that enable it to function in transfer hydrogenation. [11] It is used in hydrogenation of aldehydes, ketones, via transfer hydrogenation, in disproportionation of aldehydes to esters and in the isomerization of allylic alcohols.
Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium features a reactive chloro group, which is readily substituted by organic substrates.
One example of an Ru-arene complex is (cymene)ruthenium dichloride dimer, which is the precursor to a versatile catalyst for transfer hydrogenation. [12] Acenaphthylene forms a useful catalyst derived from triruthenium dodecacarbonyl. [13] The hapticity of the hexamethylbenzene ligand in Ru(C6Me6)2 depends on the oxidation state of the metal centre: [14] The compound Ru(COD)(COT) is capable of dimerizing norbornadiene:
Multinuclear organo-ruthenium complexes have been investigated for anti-cancer properties. The compounds studied include di-, tri-, and tetra-nuclear complexes and tetrara-, hexa-, and octa- metalla-cages. [2]
The main ruthenium carbonyl is triruthenium dodecacarbonyl, Ru3(CO)12. The analogues of the popular reagents Fe(CO)5 and Fe2(CO)9 are not very useful. Ruthenium pentacarbonyl decarbonylates readily:
Carbonylation of ruthenium trichloride gives a series of Ru(II) chlorocarbonyls. These are the precursors to Ru3(CO)12.