The reaction of Fe
2(S
2C
2H
4)(CO)
6 with
cis-Ph
2PCH=CHPPh
2 (dppv) yields Fe
2(S
2C
2H
4)(CO)
4(dppv),
1(CO)
4, whereinthe dppv li
gand is chelated to a sin
gle iron center. NMR analysis indicates that in
1(CO)
4, the dppv li
gand spansaxial and basal coordination sites. In addition to the axial-basal isomer, the 1,3-propanedithiolate and azadithiolatederivatives exist as dibasal isomers. Density functional theory (DFT) calculations indicate that the axial-basalisomer is destabilized by nonbondin
g interactions between the dppv and the central NH or CH
2 of the lar
gerdithiolates. The Fe(CO)
3 subunit in
1(CO)
4 under
goes substitution with PMe
3 and cyanide to afford
1(CO)
3(PMe
3)and (Et
4N)[
1(CN)(CO)
3], respectively. Kinetic studies show that
1(CO)
4 reacts faster with donor li
gands than doesits parent Fe
2(S
2C
2H
4)(CO)
6. The rate of reaction of
1(CO)
4 with PMe
3 was first order in each reactant,
k = 3.1 ×10
-4 M
-1 s
-1. The activation parameters for this substitution reaction,
ges/
gifchars/Delta.
gif" BORDER=0 >
Hges/entities/thermod.gif"> = 5.8(5) kcal/mol and
ges/
gifchars/Delta.
gif" BORDER=0 >
Sges/entities/thermod.gif"> = -48(2)cal/de
g·mol, indicate an associative pathway. DFT calculations su
ggest that, relative to Fe
2(S
2C
2H
4)(CO)
6, theenhanced electrophilicity of
1(CO)
4 arises from the stabilization of a "rotated" transition state, which is favored bythe unsymmetrically disposed donor li
gands. Oxidation of MeCN solutions of
1(CO)
3(PMe
3) with Cp
2FePF
6 yielded[Fe
2(S
2C
2H
4)(
ges/entities/m
gr.
gif">-CO)(CO)
2(dppv)(PMe
3)(NCMe)](PF
6)
2. Reaction of this compound with PMe
3 yielded [Fe
2(S
2C
2H
4)(
ges/entities/m
gr.
gif">-CO)(CO)(dppv)(PMe
3)
2(NCMe)](PF
6)
2.
