Magnesium reduction of
RuCl2(CO)2L2 in the presence
of equimolar L in THF gives Ru(CO)2L3 (L = PPh3 (1),
PMePh2 (2), PEt3 (3),
P
i
Pr2Me (4)).
The corresponding reduction of
RuCl2(CO)2(PEt3)2
in the presence of equimolar L‘ (L‘ = P(2-furyl)3
(5) or AsPh3 (6)) gives
Ru(CO)2(PEt3)2L‘ but
gives a mixture of
Ru(CO)2(PEt3)3
-
n
L
n
(n = 0−3) species when L‘ =
PPh3. Comparisons show that 3 or
5 reacts slowly with L‘‘ = (H)2, CO, or
PhC⋮CPh to
form Ru(CO)2L‘‘(PEt3)2
and free PEt3 or P(2-furyl)3 but
rapidly with 4 or 6 to give
the
analogous products. The reaction of PhC⋮CPh with
Ru(CO)2(PEt3)2L‘ is
faster for L‘ = PEt3
than for P(2-furyl)3. All of these reactions are
proposed to take place by preliminary ligand
loss of L‘, this being slower for 3 and 5 than
for 1, 4, and 6. Reaction of
O2 with complexes
containing the readily dissociated L‘ species gives simply
Ru(η2-O2)(CO)2L2,
but for Ru(CO)2(PEt3)3, this is accompanied by an apparent
bimolecular electron transfer involving the intact
complex to give
Ru(CO)(CO3)(PEt3)3.
X-ray structure determinations of
Ru(CO)2(PEt3)3
(bis
equatorial CO in trigonal bipyramid (TBP)),
Ru(CO)2(P
i
Pr2Me)3
(two isomers: bis axial CO
in TBP and also square pyramidal), and
Ru(η2-PhCCPh)(CO)2(PEt3)2
(cis carbonyls and trans
phosphines) are reported. It is shown that all of the
Ru(CO)2L3 species exist in solution
as
two isomers in rapid equilibrium. Ab initio MP2
calculations on the unhindered
Ru(CO)2(PH3)3 model shows a preference for a trigonal
bipyramidal structure with only a weak
preference for CO to be at the equatorial site. It is shown that
this pattern cannot be
generalized to all π-acid ligands since ethylene is calculated to
have a strong preference for
an equatorial site in a TBP. Integrated quantum chemical and
molecular mechanics
calculations on
Ru(CO)2(PEt3)3 and
Ru(CO)2(P
i
Pr2Me)3
give structures in excellent agreement
with the X-ray results and confirm that the geometry and relative
energetic preference for
the observed structural isomers is strongly influenced, or even
dominated by, the steric effect
of the phosphine ligands.
is prepared by the reaction of Rf 2 PPdClPh 2 PCH 2 CH 2 PPh 2 1 with AgSbF 6 in the presence of benzaldehyde in 92% yield, and the structure determined by X-ray diffraction analysis.
Diastereomeric pentacoordinate hypervalent stiboranes with an Sb−Fe bond {4a and 4b:
RfRfm*Sb*FeCp(CO)2 {Rf = o-C6H4C(CF3)2O-, Rfm* = o-C6H4C*(CF3)(Me)O-} were synthesized by the reaction of stiboranide anion, RfRfm*Sb*-Li+ (3-Li), with CpFeI(CO)2 in the
presence of AgBF4. The carbonyl group of 4 was replaced with triphenylphosphine by
irradiation with a tungten lamp to give a mixture of four diastereomers {5a−5d: RfRfm*Sb*Fe*Cp(CO)(PPh3)}. Each of the diastereomers was separated by TLC, and the relative stereochemistry was determined by X-ray crystallographic analysis. The thermal equilibration
from the pure diastereomer of 5 indicated that the isomerization took place through inversion
(pseudorotation) at the central antimony atom. The pseudorotational barriers of 5 were much
higher than those of Rf2Sb*Cl and RfRfm*Sb*(p-CH3C6H4). These results are consistent with
the electron-donating properties of the group 8 transition metal fragment. Hypervalent
stiboranes {6, Rf2Sb*Fe*Cp(CO)(PMe3); 7, Rf2Sb*Fe*Cp(CO)(PEt3)} were also prepared by
similar procedures. The order of pseudorotational barriers [2 {Rf2Sb*Fe*Cp(CO)(PPh3)} (32.8,
33.2 kcal/mol) > 7 (32.5, 32.9 kcal/mol) > 6 (32.2, 32.7 kcal/mol)] suggests that the steric
effect of the iron ligand also played a role. The pseudorotational barriers of the corresponding
ruthenium compounds, RfRfm*Sb*RuCp(CO)2 (12a and 12b), were slightly higher than those
of the corresponding iron compounds (4a and 4b).
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