THE REACTIONS OF ELECTROPHILES WITH ORGANOTIN COMPOUNDS AND RHODIUM-OLEFIN COMPLEXES

The stereochemistry of bromodemetallation reactions of triisopropyl-sec-butyltin and diisopropyl-neopentyl-sec-butyltin were investigated as a function of solvent. A dramatic solvent effect is observed; for aprotic solvents a fair correlation is observed between the stereochemistry of reaction and such solvent parameters as E(,T) or Z values. As the polarity of the solvent increased, based on E(,T) or Z values, greater net inversion is observed. However, this correlation is not seen in protic solvents. The alcohols, methanol, ethanol and n-propanol all give more retention of configuration at carbon than is predicted by the E(,T) or Z values.

The stereochemistry of the halodemetallation of triisopropyl-sec-butyltin and diisopropyl-neopentyl-sec-butyltin with iodine, iodinemonochloride and iodinemonobromide was investigated. In the cases of the heteronuclear electrophiles, the alkyl halide product obtained is primarily the iodide, indicating that reaction occurs via predominantly polar mechanisms. In acetonitrile the following stereochemical trend is observed: (UNFORMATTED TABLE FOLLOWS)

I(,2) < Br(,2) < IBr < ICl

increasing inversion

(TABLE ENDS)

In methanol a radically different stereochemical trend is found: (UNFORMATTED TABLE FOLLOWS)

ICl < IBr < I(,2) < Br(,2)

increasing inversion

(TABLE ENDS)

Some very intimate and specific solvent-solute and metal-electrophile interactions are postulated as rationale for explaining these results.

In a separate, unrelated study, some cyclopentadienylrhodium(I) - olefin complexes have been reacted with electrophilic mercury salts. In all cases investigated attack by the electrophile occurs at the metal center with subsequent loss of the olefin. It was anticipated and hoped that reaction could occur at the complexed olefin but this was never realized.

If these reactions are performed in halogenated hydrocarbon solvents, the halogen becomes incorporated into the evantual organometallic product. Presumably this halogen abstraction from solvent can occur via a rhodium(II) species generated from one-electron oxidation of the rhodium(I) complex by the mercury(II) salt.