Organoscandium chemistry

Organoscandium chemistry is an area with organometallic compounds focused on compounds with at least one carbon to scandium chemical bond.^[2][3] The interest in organoscandium compounds is mostly academic but motivated by potential practical applications in catalysis, especially in polymerization. A common precursor is scandium chloride, especially its THF complex.^[4]

Structure of (C₅H₅)Sc(CH₂tms)₂(thf) (tms = Si(CH₃)₃, thf = tetrahydrofuran).^[1]

As with the other elements in group 3 – e.g. yttrium, forming organoyttrium compounds – and the lanthanides, the dominant oxidation state for scandium in organometallic compounds is +3 (electron configuration [Ar] 3d¹4s²). The members of this group also have large ionic radii with vacant s,p and d orbitals (88 pm for Sc³⁺ compared to 67 pm for Al³⁺) and as a result they behave as hard Lewis acids and tend to have high coordination numbers of 9 to 12. The metal to ligand chemical bond is largely ionic.

Illustrative complexes

Sc(III) derivatives

Many organoscandium(III) compounds have at least one cyclopentadienyl-type ligand. The reaction of scandium trichloride with two equivalents of sodium cyclopentadienide (NaCp) produces the chloride-bridged dimer:

2 ScCl₃ + 4 NaCp → [Cp₂Sc(μ-Cl)]₂ + 4 NaCl

Cp₃Sc is a polymer wherein one third of the Cp ligands serving as bridging ligands.^[5]

Bulkier cyclopentadienide ligands give monoscandium derivatives, e.g. (C₅Me₅)₂ScCl.^[6] The corresponding alkyls polymerize alkenes.^{[7] [8]}

The synthesis of a tris(allyl)scandium complex is analogous to the above methods, involving the reaction of ScCl₃ with allyl potassium in THF solution, The product is Sc(C₃H₅)₃(THF)₂ wherein two allyl ligands are η³ coordinated and one allyl ligand is η¹.^[9]

Sc(II) and Sc(I) derivatives

Organoscandium compounds in lower oxidation states have been prepared.^[10][11]