Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds

Abstract

Publisher Summary This chapter discusses chiral metal atoms in optically active organo-transition-metal compounds. An important approach to stereochemical problems is to make use of the concept of chirality. The chiral center most frequently encountered is the asymmetric carbon atom––a tetrahedral C atom––bonded to four different substituents. Chiral molecules may be studied by a great many techniques. Occasionally, optically active ligands have been employed in organo-transition-metal chemistry to demonstrate the stereospecificity of reactions at metal–ligand bonds with respect to the α-carbon atom of the ligand. The chapter focuses on organo-transition-metal compounds having chiral metal atoms whose optical activity have been demonstrated. The principle of introducing a diastereoisomer relationship into a pair of mirror-image isomers is the basis for each optical resolution. After the preparation of diastereoisomers by the introduction of an optically active resolving agent, the next problem in an optical resolution is to separate the diastereoisomers. The optical purity of enantiomers has been determined by nuclear magnetic resonance (NMR) spectroscopy with the help of optically active shift-reagents. Thus, for racemization, the steric effect seems to be most important. Metal–alkyl bonds can be carbonylated, and metal–acyl bonds can be decarbonylated. Optically active organo-transition-metal compounds exhibit extremely large specific rotations, usually exceeding the specific rotations encountered in organic chemistry by a factor of one or two powers of ten.