|Abstract or Summary
- The methanolysis of phosphorus trichloride coordinated to nickel
(0) has been studied. Free phosphorus trichloride reacts with methanol
to give dimethyl hydrogen phosphonate, methyl chloride, and hydrogen
chloride. The reaction involves a rearrangement on phosphorus using
the lone pair, in which the coordination number increases from three
to four. In the complex Ni(PC1₃)₄, tetrakis(trichlorophosphine)-nickel(0), the lone pair is already involved in coordinate bonding and
the coordination number is already four. Attack of methanol might be
on the complex itself, with the metal-phosphorus bond retained throughout
the reaction, or might be on free phosphorus ligand in equilibrium
with a partly dissociated complex.
The reaction of methanol with tetrakis (trichlorophosphine)nickel(0)
in hydrocarbon solvents was found to be quite slow, to involve a series
of various colored heterogeneous intermediates, and to give eventually
a clear green solution. Hydrogen chloride, methyl chloride, dimethyl
hydrogen phosphonate, and nickel in the plus two oxidation state were
identified as the major reaction products. These were identified by
vacuum line separation and characterization, gas chromatography,
and spectroscopic techniques.
No specific reduction product was identified. It was established that
hydrogen was not formed. It is postulated that a reduced organo-phosphorus
species was formed, such as a hypophosphite, possibly
through the intermediate formation of a hydrido-nickel complex. Such
a species could be formed by oxidative addition of hydrogen chloride
to a nickel(0) complex. Experimental evidence of an indirect nature is
presented to support this suggestion.
With free phosphorus trichloride, methanolysis in the presence of
a tertiary amine (which consumes hydrogen chloride as it is formed,
but is otherwise inert) permits synthesis of the unrearranged tertiary
phosphite ester. An attempt to use this technique in studying methanolysis
of the nickel(0) complex was unsuccessful. An unexpected
direct reaction took place between triethylamine and tetrakis-(trichlorophosphine)nickel(0). Methanolysis of the unidentified
product of this reaction also gave oxidized nickel(II) species.
Reaction of tetrakis(trichlorophosphine)nickel(0) with sodium
methoxide in methanol causes hydrogen chloride to be consumed as
fast as it is formed and also involves methoxide ion, a more reactive nucleophile than methanol. The product of this reaction, in hydrocarbon
solvents, was tetrakis(trimethyl phosphite)nickel(0). Conditions
for obtaining this product in the pure state, conveniently, and
in good yield were developed. The method is recommended as the
preferred method of synthesis of this compound.