Studies of the catalysis of cyanide addition and substitution
The chiral diphenylphosphinites of menthol and binaphthol have been prepared. The zerovalent palladium complexes of these phosphinites were found to be poor catalysts for the hydrocyanation of alkenes. The enantiomeric purity of the exo-norbornane carbonitrile produced from the hydrocyanation of norbornene catalysed by Pd(DI0P)(_2) was found to be considerably lower than originally surmised. In the same reaction, the zerovalent palladium complexes of BPPM and BINAP were found to give the highest reported enantiomeric purities for a transition metal catalysed hydrocyanation reaction. The mechanism of transition metal catalysed asymmetric hydrocyanation was examined. Preliminary mechanistic investigations were conducted using (DIOP) platinum(O) alkene complexes. The formation of a platinum hydrido cyanide complex was observed by (^i)H and (^31)P N.M.R. spectroscopy. The novel complex (DIOP) palladium(O) ethene has been prepared and isolated, yielding the first crystal structure of a palladium ethene complex. Oxidative addition of HCN to the complex generated (DIOP) palladium hydrido cyanide. The complex also underwent other oxidative addition reactions; some may involve one electron processes. The use of PNP salts to effect the introduction of CN" by addition or substitution reactions is described. The salts are particularly suited to reactions with hydrolysis sensitive substrates. The salts are used under both phase transfer and stoichiometric conditions.