Synthesis ligand-centred reactions

Simultaneously to the disclosure of 112-117 by Liddle, Le Floch reported that complex 88 could be converted to complex 121, which is analogous to 112-117, by reaction with potassium bis(trimethylsilyl)amide.48 The second deprotonation of one of the methanide ligands to give a methandiide-methanide complex is noteable because amides, especially silyl-amides, are not usually basic enough to effect a second deprotonation at a carbon centre (cf. synthesis of 1-8) and it was suggested that coordination to the electropositive neodymium polarised the C-H bond sufficiently to activate it. 

Boron atoms in transition metal clusters Denuding the boron atom of B-H interactions in transition metal boron clusters Transition metal boride clusters at the molecular level Recent advances in the chemistry of carborane metal complexes incorporating d and /block elements The interplay of alkylidyne and carbaborane ligands at metal centres. I. Synthesis of electronically unsaturated mixed-metal complexes. II. Proton-mediated reactions... 

In 2003, Bonini et al. reported a new synthesis of ferrocenyloxazolines based on an iodide-mediated ring expansion of A-ferrocenoyl-aziridine-2-carboxylic esters. The thus-formed ligands were successfully employed as palladium chelates for the test reaction, since they allowed the product to be formed in quantitative yields and good to high enantioselectivities (Scheme 1.69). According to the results, it seemed that the additional chiral centre present in the oxazoline backbone of these ligands did not play a major role for the asymmetric induction and the activity of the corresponding catalysts. 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

The Stille coupling of 2-chloro-5-tributylstannylpyridine with an enantiopure 2-iodo-cyclohexenon (7.29.) derivative formed the basis of the total synthesis of (+)-epibatidine. The reaction is a nice example of the chemical inertness of arylstannanes and the mildness of the coupling conditions. Both the enone moiety and the chiral ally lie centre remained untouched in the process. The effective coupling required the use of a soft ligand, triphenylarsine and the addition of copper(I) iodide as co-catalyst.40... 

The reaction of phosphorus-donor ligands with silver(I) ions has traditionally been centred on tertiary arylphosphines. The synthesis of complexes with tertiary phosphites has often been... 

From the properties outlined in the previous section it might well be expected that synthesis of an amino acid via reaction at a ligand coordinated to a chiral metal centre could lead to a chiral... 

The final aldol reaction used in our synthesis of spongistatin 1 was one of the more remarkable reactions of this type our group has witnessed over the years. The aldol union of ketone 64 with ( )-4-chloro-2,4-pentadienal 65 required the creation of the (475) stereochemistry in the resultant alcohol 66. Formally, this would require 1,5-syn induction from the ketone 64, which is opposite to that observed previously for boron aldol reactions with simple [i-alkoxy methyl ketones. However, ketone 64 is densely packed with stereocentres, and predicting the influence of these remote centres on the reaction outcome was not possible with any degree of certainty. It was hoped that should 64 display undesirable 1,5-anti bias, this may be overturned by appropriate choice of Ipc ligands on boron. 

It is clear from the preceding section that the field of tethered arene-metal complexes is dominated by ruthenium and by arene-phosphines as ligands. In part, this situation has arisen because of the current surge of interest in the catalytic properties of ruthenium complexes in organic synthesis.85,86 Moreover, the tethered arene complexes are usually air-stable, crystalline solids with a well-defined, half-sandwich molecular geometry that, in principle, can lock the configuration at the metal centre. These compounds should, therefore, be ideal both for the study of the stereospecificity of reactions at the metal centre and for stereospecific catalysis. 

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