Organoscandium chemistry explained

Organoscandium chemistry is an area with organometallic compounds focused on compounds with at least one carbon to scandium chemical bond.^{[1] [2]} 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.^[3]

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:

2ScCl₃ + 4NaCp → [Cp₂Sc(μ-Cl)]₂ + 4NaClCp₃Sc is a polymer wherein one third of the Cp ligands serving as bridging ligands.^[4]

Bulkier cyclopentadienide ligands give monoscandium derivatives, e.g. (C₅Me₅)₂ScCl.^[5] The corresponding alkyls polymerize alkenes.^{[6] [7]}

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.^[8]

Sc(II) and Sc(I) derivatives

Organoscandium compounds in lower oxidation states have been prepared.^{[9] [10]}

Notes and References

1. Synthesis of Organometallic Compounds: A Practical Guide Sanshiro Komiya Ed. 1997
2. C. Elschenbroich, A. Salzer Organometallics : A Concise Introduction (2nd Ed) (1992) from Wiley-VCH: Weinheim.
3. Book: 10.1002/9780470132524.ch31. Tetrahydrofuran Complexes of Selected Early Transition Metals. Inorganic Syntheses. 1982. Manzer. L. E.. 135–140. 21.
4. 10.1039/DT9730002487. Crystal Structure of di-µ-chloro-bis[di-η-cyclopentadienylscandium(III)]. 1973. Atwood. Jerry L.. Smith. Karl D.. J. Chem. Soc., Dalton Trans.. 22. 2487–2490.
5. 10.1039/C8DT02623H. Solid-state ⁴⁵Sc NMR Studies of Cp*₂Sc–X and Cp*₂ScX(THF). 2018. Huynh. Winn. Culver. Damien B.. Tafazolian. Hosein. Conley. Matthew P.. Dalton Transactions. 47. 37. 13063–13071. 30160275.
6. 10.1021/ja00235a031. σ-Bond Metathesis for Carbon-Hydrogen Bonds of Hydrocarbons and Sc-R (R = H, alkyl, aryl) Bonds of Permethylscandocene Derivatives. Evidence for Noninvolvement of the π System in Electrophilic Activation of Aromatic and Vinylic C-H Bonds. 1987. Thompson. Mark E.. Baxter. Steven M.. Bulls. A. Ray. Burger. Barbara J.. Nolan. Michael C.. Santarsiero. Bernard D.. Schaefer. William P.. Bercaw. John E.. Journal of the American Chemical Society. 109. 203–219.
7. 10.1021/ja054544i. Naked (C₅Me₅)₂M Cations (M = Sc, Ti, and V) and Their Fluoroarene Complexes. 2005. Bouwkamp. Marco W.. Budzelaar. Peter H. M.. Gercama. Jeroen. Del Hierro Morales. Isabel. De Wolf. Jeanette. Meetsma. Auke. Troyanov. Sergei I.. Teuben. Jan H.. Hessen. Bart. Journal of the American Chemical Society. 127. 41. 14310–14319. 16218625.
8. 10.1039/C1CC14180E. Allyl Complexes of Scandium: Synthesis and Structure of Neutral, Cationic and Anionic Derivatives. 2011. Standfuss. Sabine. Abinet. Elise. Spaniol. Thomas P.. Okuda. Jun. Chemical Communications. 47. 41. 11441–11443. 21946865.
9. Polly L. Arnold. F. Geoffrey. N. Cloke. Peter B. Hitchcock. John F. Nixon. amp. 1996. The First Example of a Formal Scandium(I) Complex: Synthesis and Molecular Structure of a 22-Electron Scandium Triple Decker Incorporating the Novel 1,3,5-Triphosphabenzene Ring . J. Am. Chem. Soc.. 118. 32. 7630–7631. 10.1021/ja961253o.
10. 5. Ana Mirela Neculai. Dante Neculai. Herbert W. Roesky. Jörg Magull. Marc Baldus. Ovidiu Andronesi. Martin Jansen. 2002. Stabilization of a Diamagnetic Sc^IBr Molecule in a Sandwich-Like Structure . Organometallics. 21. 2590–2592. 10.1021/om020090b. 13.