Indium alkoxides

Although hydrolysis of tin alkoxides and alkoxochlorides, especially in the mixture with indium alkoxides, is used extensively, such as forpreparation of conductive ITO (solid solution of indium and tin oxides) layers, only few fundamental works on hydrolysis of Sn(OR)4 are known, and they have been summarized in a comprehensive review [702], Bradley proved the formation of oligomeric molecules as first hydrolysis products of [Sn(OPri)4 PrOH]2 by... 

Taking into account the observed analogy in the molecular structures of rare earth and indium alkoxides, the butoxide of the latter should exist only as solvates [IiqfOBu lyLj]. 

ROP [65, 74]. The indium alkoxide (11) was a good initiator, with 100 equivalents of SS-lactide being converted to PLA in 200 min, at 50°C. When compared with the analogous aluminium initiators, the indium complexes showed comparable rates but lower-molecular-weight PLA. All the PLA formed from rac-lactide was atactic [65]. 

Potassium hydride and potassium hexamethyldisilazide are the most commonly used metal sources to generate the alkoxide . But recently, the indium(I)-mediated tandem carbonyl addition-oxy-Cope rearrangement of y-pentadienyl anions to cyclohexenones and conjugated aromatic ketones has been reported. For example, indium alkoxide 8.32, obtained after the addition of 5-bromopenta-1,3-diene (8.31) to the aromatic conjugated ketones 8.30, undergoes a spontaneous oxy-Cope rearrangement to give 8.33 in 55% yield (Scheme 8.9). 

The diastereoselective production of homoallylic indium alkoxides can be accomplished by a kinetic resolution process [194]. The indium-mediated reaction of benzaldehyde with 2-butenyl bromide has always been observed to be unselec-tive. The use of alkoxide or halide modifiers in the reactions of allylindium reagents has previously been shown to provide synthetically useful reagents [195], Upon addition of 2-butenylindium sesquibromide to benzaldehyde it was determined that newly formed syn and anti homoallylic alcohols undergo decomposition at a similar rate, but as the concentration of the anti homoallylic alcohol reaches zero, the rate of decomposition of the syn alcohol slows dramatically. Thus, the syn homoallylic alcohol can be obtained in high diastereoselectivity, albeit low yield. 

Indium(III) alkoxides are readily prepared by the treatment of trihalide with NaOR.127 The chemistry of these compounds has been little studied, no doubt because they are insoluble materials in which the indium atom optimizes its coordination number by cross-linking via oxygen. The isopropoxides of aluminum and gallium react128 with In(OPr )3 to give In[M(OPr )4]3 (M = A1, Ga) which are volatile and monomeric in solution. The structure involves six-coordination at the smaller metal centre. 

Studies of the alkoxides of this group started in the middle of 1960s when Funk [602], Mehrotra [1129], and Reinmann [1349] nearly simultaneously reported the synthesis of Ga(OR)j. Indium isopropoxide was first described by Mehrotra in 1972 [1106] (the preparation ofIn(OMe)3 on reaction of InC13 with 50 equivalents of NaOMe reported by Runge et al. [1374] should apparently be questioned). Of the modem studies of primary interest are the preparation of indium (I) phenoxides stabilized by bulky ligands, reported by Roesky etal. [1362,1434], and that of the bimetallic butoxide, In Sn(OBu )3, described byVeith etal. [1685],... 

The reduced yttrium complex was active for the polymerization of 55-lactide, 74% conversion in 3 h (0.2 M, THF, 25°C). When the complex was oxidized, using FcBArF, the polymerization was completely stopped, and it was restarted when the complex was reduced back. The authors provide good evidence that the polymerization switch operates by changing the electron density of the yttrium-alkoxide bond during oxidation/reduction cycles. Polymerizations with the indium analogue... 

Okuda and Arnold have reported a series of 5- and 6-coordinate chiral indium complexes (e.g. 12), analogous to those previously discussed with yttrium (Table 4), which show varying activities for the polymerization of rac-lactide [71]. The homoleptic species was fluxional, interconverting between a 5-coordinate and fac- and mer-isomers of a 6-coordinate complex. It resulted in controlled polymerization and some stereoselectivity (max. P, = 0.63 and max. Ps = 0.64). MALDI-ToF mass spectrometry confirmed that the chiral alkoxide ligand was an initiating group. 

One of the main interests in indium amides has been their potential utility as single-source precursors for indium nitride materials. They also serve as starting materials in the synthesis of various other indium compounds. For instance, amides such as In(NEt2)3 and In[N(SiMe3)t-Bu]3 react with alcohols or thiols to produce indium(III) alkoxides or thiolates, respectively. 

An interesting indium(I) alkoxide [(2,4,6-(CF3)3C6H20)In]2 (93), featuring two-coordinate, bent indium sites, has been reported." This compound is synthesized from Cpin and 2,4,6-(CF3)3C6H20H in hexane, and features a planar In202 core. The reaction of Sn(/i-t-BuO)3Tl or... 

Mixed-metal alkoxide complexes of thallium are also known. For example, Sn(/u-t-BuO)3Tl has both Sn(II) and T1(I) ions." The thallium site is unreactive as a donor for metal carbonyls. However, as indicated earlier, the indium(I) site of the indium analogue shows Lewis-base character. The Sn(IV)/Tl(I) mixed alkoxide [Sn(EtO)eTl2] exists as a one-dimensional polymer. This adduct reacts quantitatively with SnCl2 to form the homoleptic, mixed-valent [Sn2(OEt)6]n. Thallium-titanium double alkoxides have been synthesized using thallium alkoxide as one of the starting materials. ... 

Complexes ( )- and (R,R)-2 are highly active and controlled for the polymerization of rac-LA yielding a linear relationship between the observed PLA molecular weights and the added monomer, assuming both alkoxides initiate the polymerization, with low molecular weight distributions (Figure 36)." The rate of polymerization with these complexes is first order in lactide concentration with values comparable with the tri-dentate diaminophenolate indium complexes desaibed in Section 2. " -The rates of polymerization are much faster than any of the known chiral aluminum salen systems, which require elevated temperatures and days to reach full conversion." -... 

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