Ketoximate Derivatives of Titanium Alkoxides and Partial Hydrolysis Products Thereof

Abstract

Crystalline oximate derivatives of titanium alkoxides [Ti(OR)2(ON=CR′R″)2]2 were obtained when Ti(OR)4 (R = iPr, Et) was treated with various oximes (cyclopentanone oxime, cyclohexanone oxime, acetoxime, ethyl methyl ketoxime or 2,4‐pentandione dioxime). Formation of bis‐substituted derivatives was favored in each case, and only one mono‐substituted derivative, [Ti(OiPr)3(ON=C6H10)]2, was isolated. Two isomers were observed for [Ti(OR)2(ON=CR′R″)2]2, differing by the mutual orientation of the oximate ligands. The NO groups of the oximate ligands are side‐on coordinated to one titanium atom in each case. Three partially hydrolyzed derivatives, viz. Ti6O6(OiPr)6(ON=CR2)6 (CR2 = CMe2 or C5H8) and Ti4O2(OiPr)8(ON=CMe–CH2–CMe=NO)2 were also structurally characterized. In these derivatives the NO groups bridge two titanium atoms.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Modification of Titanium Isopropoxide with Aromatic Aldoximes

“…The behavior of 3 in solution was inves- tigated by NMR spectroscopy and serves as an example for the other derivatives. As also observed for [Ti(OiPr) 2 -(ON=C 6 H 10 ) 2 ] 2 , [6] signals corresponding to exchange of the OiPr groups (δ CH = 4.58 and 4.06 ppm) were present in the EXSY spectrum ( Figure 6). Furthermore, the oximate ligands are dynamic in solution; this can possibly be explained by interconversion of the two isomers (Figure 1).…”

“…Only one isomer crystallized exclusively in either case. As for the reactions with aliphatic oximes, [6] there is no apparent correlation of the formed isomer with the properties of the applied oxime. As the isomers interconvert in solution (see below) the preferred crystallization of one isomer is obviously a crystal packing effect.…”

“…Different to Ti 6 O 6 (OiPr) 6 -(ON=CR 2 ) 6 (CR 2 =CMe 2 or C 5 H 8 ), [6] for example, the two titanium atoms are not bridged by the NO group, but instead only by the oxygen atom of the oximate. Another noteworthy difference to the structures of 1-3 is that the mutual orientation of the side-on coordinated oximate ligands in the two halves of the compound are different.…”

“…The Ti-O and Ti-N bond lengths of 1 and 2 (Table 1) are in the same range as that of derivatives with aliphatic oximate ligands. [6] The alkoxido bridges are asymmetric; the bridging Ti-O bond lengths differ by up to 13 pm (in 1; see Table 1) with the longer Ti-O distance trans to the terminal OiPr ligand. In all structures discussed in this article, the phenyl rings are coplanar with the C=N-O groups, and oximate ligands bonded to the same titanium atom are nearly coplanar with each other.…”

“…[6] Disubstituted derivatives (two oximate ligands per titanium atom) were found even if a 1:1 ratio of Ti(OR) 4 and oxime was employed. Two isomers were observed (Figure 1), which differ by the mutual orientation of the side-on coordinated oximate ligands.…”