Indium complex chiral

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

Zhu, C. Yuan, F. Gu, W. Pan, Y. (2003) The first example of enantioselective isocyanosilylation of meso-epoxides with TMSCN catalyzed by novel chiral organogallium and indium complexes., Chem. Commun., 692-693. 

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. 

As a logical extension of the discrete bifunctional catalytic systems described above, Lectka et al. developed the homogeneous salicylate indium complex 22, containing the chiral nucleophile (alkaloid) and the Lewis acid (In(OTf)3) in a single unit, which exhibited excellent catalytic activity and stereoselectivity (90% yield, 99% ee, and 10 1 diastereomeric ratio (dr)) (Scheme 4.20) [47, 48]. Mechanistic studies revealed that the chiral nucleophiles form zwitterionic enolates that react with the metal-coordinated imines to form a ternary complex 23 in which C—C bond formation occurs. 

Catalytic asymmetric Diels-Alder reactions in ionic liquids, using an air- and moisture-stable chiral BlNOL-indium complex prepared from ( S)-BINOL and InClj, have also reported [46]. The reactions of various dienes with 2-methacrolein or 2-bromoacrolein proceeded in an ionic hquid with good yields and excellent enantioselectivities (up to 98% ee). The chiral In(lll) catalyst immobilized in ionic liquid [hmim][PF 5] could be reused seven times without any significant loss in catalytic activity (Scheme 7.13). 

Dinuclear indium complexes bearing chiral salen-type ligands 10.3.1 Chiral indium salen complexes... 

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." -... 

Figure 34 Synthesis of chiral salen indium complexes with cyclohexyl backbones...

Fig. 8.146 Two plausible pathways for the formation of chiral indium complex.

A simpler preparation of catalytic chiral indium complex based on BINOL ligand were reported by Shibasaki et al. in their asymmetric alkynylation of aldehydes [317]. InBrs was the Lewis acid of choice and the authors proposed a dual role for this bifunctional catalyst, both in activating the alkyne triple bond and the carbonyl moiety. These characteristics, and the inclusion of the chiral BINOL ligand into the In(III) center, had allowed the asymmetric addition of terminal alkynes to aldehydes with just the addition of a mild amine base (Figure 8.150). Positive nonlinear effect was observed with BINOL of varying optical enrichment, and thus the active catalytic species was expected by the authors to be most likely bimetallic in nature. 

Complexes of other metals such as gallium, indium, lead, and antimony have also been used as Lewis acids. Catalytic enantioselective meso-epoxide ring-opening reactions using a chiral gallium(III) catalyst (Ga-Li-linked-BINOL) have been reported (Scheme 84).348 The chemical yields are much improved by linking two BINOL units. 

A chiral BINOL-indium(in) complex has been used to catalyse the addition of allyltributylstannane to aldehydes in high ee.184... 

Chiral BINOL-indium(ni) complexes have been employed in several enantioselective allylations (i) in the ionic liquid, hexylmethylimidazolium-PF6, for aldehydes,190 (ii) a moisture tolerant version, for a wide variety of aldehyde types,191 and (iii) a recyclable example, useful for aromatic, aliphatic, and a,/S-unsaturated ketones.192... 

The enantioselective addition of allyltributylstannanes to aldehydes and ketones has been performed in the presence of various chiral indium(III) complexes derived from (R)-BINOL,136 (S )-BINOL,137,138 and PYBOX.139,140... 

The indium-induced Reformatsky reaction with stoichiometric amounts of chiral amino alcohols such as cinnco-nine and cinchonidine gives optically active /3-hydroxy esters with 40%-70% ee (Table 19). In contrast to the smooth reaction with uncomplexed indium-based Reformatsky reagents, ketones do not react with the complexed indium Reformatsky reagents. Other chiral ligands, including (—)-spartein, (—)-norephedrine, (+)-(l-methylpyrrolidin-2-yl)diphenylmethanol, (+)-Dibutyl tartrate and (+)-l,l -bi-2-naphthol, are not effective for this reaction.324... 

Indium and zinc complexes bearing chiral diaminophenolate ligands... 

As discussed above, A1 catalysts supported by salen ligands are some of the most isoselective catalysts for the polymerization of racemic lactide. However, slow polymerization rates and high water/air sensitivity preclude their use in an industrial setting. " We were interested in exploiting chiral indium salen complexes to achieve high activity, selectivity and control over the polymerization process. Although achiral indium salen complexes had been reported previously, " prior to our work there was only one example of a chiral indium salen complex, which was not used as a catalyst for polymerization." ... 

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