Alkoxo ligands

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

Hiroi et al. also reported the Cp lr complex-catalyzed Oppenauer-type oxidation of primary alcohols in acetone and butanone [31]. These authors prepared a novel Ir-ligand bifunctional catalyst 6 having an amido-alkoxo ligand, the... 

Hiroi et al. also reported the asymmetric lactonization of meso-diols catalyzed by a Cp Ir complex bearing a chiral amido-aUcoxo ligand (Scheme 5.33) [72]. The reaction of meso-diol 34 in acetone/dichloromethane solvent at 30 °C for 45 h in the presence of a Cp lr catalyst bearing a chiral amido-alkoxo ligand 35 gave a corresponding lactone 36 in quantitative yield, with 80% ee. 

For rhodium and iridium compounds alkoxo ligands take over the role of the basic anion. Using /z-alkoxo complexes of ( -cod)rhodium(I) and iridium(I)— formed in situ by adding the /r-chloro bridged analogues to a solution of sodium alkoxide in the corresponding alcohol and azolium salts—leads to the desired NHC complexes even at room temperature [Eq. (10)]. Using imidazolium ethoxyl-ates with [(r " -cod)RhCl]2 provides an alternative way to the same complexes. By this method, it is also possible to prepare benzimidazolin-2-ylidene complexes of rhodium(I). Furthermore, an extension to triazolium and tetrazolium salts was shown to be possible. ... 

Scheme 12.5 Representative alkoxide and diketonate-based SOLnC PMS. Complex oligomerization occurs mainly in the presence of small alkoxo ligands (e.g., O/Pr).

FIGURE 9.1 The 51V chemical shifts of monoanionic alkoxovanadates are shown as a function of their pKa values. Only a selection from all the alkoxo ligands is identified. The solid lines provide a guide for viewing the data, which was taken from the work of Tracey and coworkers [3]. 

The significance of [Fe4S4]n+ (193) and [Mn4X4]"+ (194) (where X = oxo, chloro, or alkoxo ligands) in biological systems, has made the synthesis and properties of iron and manganese alkoxide cubes... 

Two trinuclear heterobimetallic molecules with alkoxo ligands are known BaNb2(OPr )i2 (Pr OI I)2 (146) contains a non-linear Nb(q2-0)2Ba(q2-0)2Nb core while LaNb2(OPr )13 (147) contains a non-linear Nb(//2-0)3La(q2-0)2Nb core.285... 

Allyltitanium compounds and Ti enolates derived from mono-Gp chloro titanium complexes with two chiral alkoxo ligands add to aldehydes with high enantioface discrimination.973... 

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