Tm ligands
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By reacting Methimazole (or a closely related compound) and sodium borohydride together a sulfur ligand which is similar to the Tp ligands can be made. The donor atoms in this ligand class are similar to thioureas. Several research groups including Tony Hill's group [1]have been working on this ligand class. These ligands are an example of the scorpionate ligands.
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[edit] Ruthenium, rhodium, osmium and related metals
- It was shown that the reaction of a 16VE ruthenium vinyl [RuCl(CO)(CH=CHPh)(PPh3)] with NaTm forms a zero valent ruthenium complex [B(mt)3Ru(CO)(PPh3)] which has a boron metal bond. If the ruthenium starting material is replaced with a osmium complex [OsHCl(CO)(PPh3)3] then an intermediate is formed which decomposes into [B(mt)3Os(CO)(PPh3)].
Here it can be seen that the boron binds to the metal, the osmium complex is an 18 VE complex, where the metal is formally in the zero oxidation state. The carbonyl stretching frequency is very low for this complex because the metal is so electron rich. The ruthenium complex is not shown because it has the same structure.
M.R.StJ.Foreman, A.F.Hill, A.J.P.White and D.J.Williams, Organometallics, 2004, 23, 913.
A.F.Hill, G.R.Owen, A.J.P.White and D.J.Williams, Angew. Chem.,Int. Ed. Engl., 1999, 38, 2759.
- In the case of the reaction of [RuHCl(CO)(PPh3)3] with NaTm, it is possible to isolate [RuTmH(CO)(PPh3)3] which on treatment with phenylacetylene forms the zerovalent [B(mt)3Ru(CO)(PPh3)] complex.
Here it can be seen that the hydrogen atom attached to the boron is being transferred to the metal, it is thought that if the hydrogen is transferred totally to the metal that a reductive elimination reaction (opposite of oxidative addition) can occur to form the zero valent metal borane complex.
M.R.StJ.Foreman, A.F.Hill, G.R.Owen, A.J.P.White and D.J.Williams, Organometallics, 2003, 22, 4446.
- If the ruthenium is replaced with rhodium then the corresponding compound is a chloride complex rather than a carbonyl complex.
This complex should be comapired with the osmium complex, here to provide the metal with 18 valence electrons one fewer electrons is needed, so as a result the carbonyl seen in the ruthenium and osmium complexes has been replaced with a chloride ligand.
I.R.Crossley, M.R.St. J.Foreman, A.F.Hill, A.J.P.White and D.J.Williams, Chem. Comm., 2005, 221.
[edit] Molybdenum
A large number of molybdenum complexes have been made, many of these mirror in some ways the chemistry of the Tp and cyclopentadienyl ligands. These very sulfur rich molybdenum complexes might be possible models for a molybdenum sulfide surface used in Hydrodesulfurization.
M.R.StJ.Foreman, A.F.Hill, N.Tshabang, A.J.P.White, D.J.Williams, Organometallics, 2003, 22, 5593.
M.Garner, M.-A.Lehmann, J.Reglinski and M.D.Spicer, Organometallics, 2001, 20, 5233.
[edit] Tungsten
It is possible by the reaction of [WBrL2(CO)2(CN-i-Pr2)] to form a Tm complex [WTm(CO)2(CN-i-Pr2)].
M.R.St. J.Foreman, A.F.Hill, A.J.P.White and D.J.Williams, Organometallics, 2003, 22, 3831.
[edit] Zinc and cadmium complexes
A large number of zinc and cadmium complexes of these Tm class ligands have been made as models for enzymes.
An example of a cadmium complex, here the zinc is bonded to by the Tm liagnd and a thiolate ligand.
S.Bakbak, C.D.Incarvito, A.L.Rheingold and D.Rabinovich, Inorganic Chemistry, 2002, 41, 998.
[edit] Actinide complexes
A uranium complex of Bm has been reported, to the uranium are attached three THF ligands and two Bm ligands. Note that the hydrides attached to the boron atoms are much closer to the uranium atom than the two phenyl groups. This suggests that the hydrides are partway between being attached to the boron and the metal.
L.Maria, A.Domingos, I.Santos, Inorganic Chemistry, 2001, 40, 6863.
[edit] Action as a nucleophile
In addition to acting as a ligand, Tm and Bm ligands can react with electrophiles such as dichloromethane to form cationic S, S' alkylated products.
I.R.Crossley, A.F.Hill, E.R.Humphrey, M.K.Smith, N.Tshabang and A.C.Willis, Chem. Comm., 2004, 1878.
