Optically active bis(β-diketonate) complexes of titanium?

Dalton Transactions Pub Date: 2010-09-07 DOI: 10.1039/C0DT00828A

Abstract

The 2,2′-bis(methylene)biphenyl bridged bis(diketonate) (Tol2Bob)TiIV fragment is resolved by reaction of the isopropoxide complex with (R)-1,1′-bi-2-naphthol, which selectively forms (S,Δ)-(Tol2Bob)Ti(R-BINOL). The binaphtholate ligand can be cleaved from titanium by careful treatment with trifluoromethanesulfonic acid to give (S,Δ)-(Tol2Bob)Ti(OTf)2, which has a half-life toward racemization of at least 34 h at 51 °C. Racemization of the (Tol2Bob)TiIV fragment is strongly accelerated under protic conditions, probably due to protonolysis of one of the diketonate ligands. Analogous optically active titanium bis(diketonates) can also be prepared by using an optically active 2,2′-bis(methylene)-1,1′-binaphthyl bridged bis(diketonate) ligand, Tol2Bobbinap, prepared from (R)-BINOLH2. Complexation of (R)-Tol2BobbinapH2 with Ti(OiPr)4 gives only a single diastereomer with the Λ configuration at titanium. The bis(diketonate)titanium(IV) fragment gives rise to characteristic signals in circular dichroism spectra which can be used to identify the configuration at the metal centre.

Graphical abstract: Optically active bis(β-diketonate) complexes of titanium
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