Organoruthenium chemistry
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.
Ligands
[edit]As with other late transition metals, ruthenium binds more favorably with soft ligands.[3] The most important ligands for ruthenium are:
- halides, especially chloride.
- phosphines, especially triphenylphosphine.
- N-heterocyclic carbenes (NHCs).
- cyclopentadienyl ligands.
- various arenes and dienes
- carbon monoxide.
- hydride, notably in the Shvo catalyst.
- metal carbenes, notably in the Grubbs catalyst.
Phosphine ligands
[edit]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]
N-Heterocyclic carbene ligands
[edit]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.
Cyclopentadienyl ligands
[edit]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.
Arene and alkene ligands
[edit]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:
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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]
Carbonyls
[edit]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:
- Ru3(CO)12 + 3 CO ⇌ 3 Ru(CO)5
Carbonylation of ruthenium trichloride gives a series of Ru(II) chlorocarbonyls. These are the precursors to Ru3(CO)12.
References
[edit]- ^ Synthesis of Organometallic Compounds: A Practical Guide Sanshiro Komiya Ed. S. Komiya, M. Hurano 1997
- ^ a b Babak, Maria V.; Wee, Han Ang (2018). "Chapter 6. Multinuclear Organometallic Ruthenium-Arene Complexes for Cancer Therapy". In Sigel, Astrid; Sigel, Helmut; Freisinger, Eva; Sigel, Roland K. O. (eds.). Metallo-Drugs:Development and Action of Anticancer Agents. Metal Ions in Life Sciences. Vol. 18. Berlin: de Gruyter GmbH. pp. 171–198. doi:10.1515/9783110470734-012. PMID 29394025.
- ^ Barthazy, P.; Stoop, R. M.; Wörle, M.; Togni, A.; Mezzetti, A. (2000). "Toward Metal-Mediated C-F Bond Formation. Synthesis and Reactivity of the 16-Electron Fluoro Complex [RuF(dppp)2]PF6 (dppp = 1,3-Bis(diphenylphosphino)propane)". Organometallics. 19: 2844–2852. doi:10.1021/om0000156.
- ^ Example: Organic Syntheses, Coll. Vol. 10, p.276 (2004); Vol. 77, p.1 (2000). Link
- ^ Example: Organic Syntheses, Organic Syntheses, Coll. Vol. 9, p.589 (1998); Vol. 71, p.1 (1993). Link
- ^ Example: Organic Syntheses, Coll. Vol. 9, p.169 (1998); Vol. 72, p.74 (1995). Link
- ^ Example: Organic Syntheses, Vol. 81, p.178 (2005). Link
- ^ Öfele, K.; Tosh, E.; Taubmann, C.; Herrmann, W.A. (2009). "Carbocyclic Carbene Metal Complexes". Chemical Reviews. 109 (8): 3408–3444. doi:10.1021/cr800516g. PMID 19449832.
- ^ Samojłowicz, C.; Bieniek, M.; Grela, K. (2009). "Ruthenium-Based Olefin Metathesis Catalysts Bearing N-Heterocyclic Carbene Ligands". Chemical Reviews. 109 (8): 3708–3742. doi:10.1021/cr800524f. PMID 19534492.
- ^ Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-Laponnaz, S.; César, V. (2011). "Synthetic Routes to N-Heterocyclic Carbene Precursors" (PDF). Chemical Reviews. 111 (12): 2705–2733. doi:10.1021/cr100328e. PMID 21235210.
- ^ Conley, B.; Pennington-Boggio, M.; Boz, E.; Williams, T. (2010). "Discovery, Applications, and Catalytic Mechanisms of Shvo's Catalyst". Chemical Reviews. 110 (4): 2294–2312. doi:10.1021/cr9003133. PMID 20095576.
- ^ Organic Syntheses, Organic Syntheses, Vol. 82, p.10 (2005).Link
- ^ Example: Organic Syntheses, Organic Syntheses, Vol. 82, p.188 (2005). Link
- ^ Huttner, Gottfried; Lange, Siegfried; Fischer, Ernst O. (1971). "Molecular Structure of Bis(Hexamethylbenzene)-Ruthenium(0)". Angewandte Chemie International Edition in English. 10 (8): 556–557. doi:10.1002/anie.197105561.