Alkoxide donor-functionalized

Internally tailoring of the alkoxide ligand with additional coordination sites leads to the class of functionalized ligands. When required, the alkoxide ligands can support these coordination sites using the effect of chelation. The idea donor functionalization of alkoxide ligands is developed in Scheme 9. Such modification of the tritox ligand as expressed in Fig. 9 represents a simple case of functionalization (monovalent, Do = OEt, n = 1). 

Scheme 9. Possible donor-functionalizations of alkoxide ligands...

A mixed-alkylated heterobimetallic Ln/Al complex was reported by the Evans group [191]. In a two-step reaction the donor-functionalized europium(II) alkoxide [Eu(OCH2CH2OMe)2] was combined with [Me2Al(OCH2CH2 OMe)]2 and trimethylaluminum to yield a polymetallic Eu(II)/Al(III) compound (Scheme 37, Fig. 31). 

Aspinall, H.C., Bickley, J.F., Gaskell, J.M., Jones, A.C., Labat, G, Chalker, P.R., et al. (2007) Precursors for MOCVD and ALD of rare earth oxides - complexes of the early lanthanides with a donor-functionalized alkoxide ligand. Inorganic Chemistry, 46, 5852-5860. 

One subset of Schiff base complexes are the hydrazone complexes which have a R—C=N—N functional group instead of the R C=N—C functionality. These compounds have been prepared as models for bromoperoxidase389 and other biological systems.390 In the solid state, the hydrazones have coordination patterns similar to those of the Schiff bases and the majority of the complexes are oxovanadium(V) hexadentate or pentacoordinate complexes with tridentate 02N donor sets (see Table 5). While most structures contain alkoxide donors,390-403 complexes have been reported with diols and catechols,129,404,405 hydroxamic acids,288,391 hydroxy quinolinate,406, 7 and benzoylhydrazine.408 In addition, dioxo,375,409-412 oxo-bridged... 

Kimura and co-workers have synthesized a series of alkoxide complexes with the alcohol functionality as a pendent arm.447 674 737 A zinc complex of l-(4-bromophenacyl)-l, 4,7,10-tetraaza-cyclododecane was also synthesized by the same workers to mimic the active site of class II aldolases. The X-ray structure shows a six-coordinate zinc center with five donors from the ligand and a water molecule bound. The ketone is bound with a Zn—O distance of 2.159(3) A (Figure 12). Potentiometric titration indicated formation of a mixture of the hydroxide and the enolate. Enolate formation was also independently carried out by reaction with sodium methoxide, allowing full characterization.738... 

On the basis of these studies and some calculations by Rappe and Goddard (19) it would seem incontrovertible that the oxo ligand prevents reduction of the metal and perhaps also enhances the rate of reforming an alkylidene complex from a metallacyclobutane complex. The next question was whether other strong n-donor ligands such as alkoxides could take over the oxo s function (lib). 

The low affinity of the alkali metals for neutral P-donor ligands has hampered efforts to synthesize complexes in which there is a genuine R3P-M interaction (see Section I). However, this poor affinity may be overcome by incorporating a remote phosphine functionality into a potentially chelating anionic ligand, such as a phosphine-substituted alkoxide, amide, or aryl, and several alkali metal complexes of such ligands have been isolated. 

Among the polydentate carbene ligands, particular interest has recently been placed on cyclic polycarbenes. ImidazoUum precursors like 23 [89] or 24 [90, 91], which upon C2 deprotonation would lead to tetradentate or even hexadentate double-pincer NHC ligands, have been prepared. Their interesting coordination chemistry will be discussed in Sect. 4. Finally, Arnold et al. developed and reviewed NHC ligands which are functionalized with additional anionic (alkoxide or amido) donor groups [92]. 

In the absence of a proton donor, the alkoxide ion generated by carbanion addition to the carbonyl function can interact with a carbon-halogen bond in the 8 2 displacement reaction. Reactions of this type have led to some novel carbon chain forming processes. Ketones are converted to homologated enones in good yield by... 

---