Dimethylcuprate-Mediated Transformation of Acetate to Dithioacetate

Dithiocarboxylic
acids, RCS2H, and their esters, RCS2R′,
are useful reagents that can be synthesized by
the reaction of carbon disulfide with organometallic reagents. Here
the coinage-metal-mediated transformation of acetate to dithioacetate
is explored in the gas phase using multistage mass spectrometry experiments
in a linear ion trap mass spectrometer in conjunction with density
functional theory (DFT) calculations. The ion–molecule reactions
between coinage-metal dimethylmetalate anions [CH3MCH3]− (M = Au, Ag, Cu), formed via double decarboxylation
of the metal acetate anions, [CH3CO2MO2CCH3]−, and carbon disulfide, were examined.
Only [CH3CuCH3]− reacts with
CS2 with a reaction efficiency of 0.8% of the collision
rate to yield the adduct [CH3CuS2CCH3]− (77.5%) as well as CH3CS2– (22.5%). Collision-induced dissociation (CID)
of the adduct [CH3CuS2CCH3]− gives CH3CS2– as the major
product, with a small amount of [CuS2CCH2]− being formed via loss of methane. DFT calculations
reveal the following. (i) [CH3CuCH3]− reacts via oxidative addition to form a Cu­(III) intermediate, followed
by reductive elimination of CH3CS2–, which is captured by Cu to form [CH3CuS2CCH3]−. This energetic adduct can fragment via
loss of CH3CS2– or can be
collisionally cooled by the helium bath gas used in the experiments.
(ii) Loss of CH4 from [CH3CuS2CCH3]− also involves a Cu­(III) intermediate
and results in formation of the metalladithiolactone [Cu­(CH2CS2)]−.