180
D. Peña et al. / Inorganica Chimica Acta 439 (2016) 178–185
(8) (9 mg, 15 %). Crystals of 8 suitable for X-ray structure determi-
nation were obtained by slow evaporation of an acetonitrile solu-
tion at room temperature.
P = 175.8°], due to steric interactions between the large phosphine
ligands and CO ligands.
When cyanoethylditertbutylphosphine is used as ligand in the
reaction with [Re2(CO)8(MeCN)2] one compound characterized as
[Re2(CO)9{j
1(P)-tBu2P(CH2)2CN}] (2) is obtained, its structure
2.7. Photolysis of 8 in dichloromethane
(Scheme 3) was readily solved from the spectroscopic data. The
IR spectrum of 2 is characteristic of a monosubstituted dinuclear
compound closely related to that of [Re2(CO)9L] (L = PR3 and
RCN), where the phosphine ligand occupies an equatorial site
(symmetry Cs) [37,39,42–45]. The 31P{1H} NMR spectrum shows
A
solution of diax-[Re2(CO)8(PPh3){j
1(P)-p-MeOC6H4P(CH2-
CH@CH2)2}] (8, 36 mg, 0.033 mmol) in CH2Cl2 (15 mL) was exposed
to UV–Vis light for 4 h. The solvent was removed under vacuum
and the residue was purified by TLC (silica gel, CH2Cl2/hexane,
one singlet at d 59.1 ppm, indicating a j
1-coordination of the phos-
2:8 v/v), which gave cis-[Re(CO)4{j
1(P)-p-MeOC6H4P(CH2
phorus atom. As expected, the 1H and 13C{1H} NMR spectra shows
very small differences compared to those of the free ligand, which
confirm only phosphorus–rhenium bonding.
CH@CH2)2}Cl] (7) (12 mg, 36%) and cis-[Re(CO)4(PPh3)Cl] (13 mg,
33%).
Thermal treatment of [Re2(CO)8(MeCN)2] with diallyldiisopropy-
laminophosphine in refluxing cyclohexane yields two compounds
2.8. Crystal structure determination for 1, 4, and 8
characterized as diax-[Re2(CO)8{
and [Re2(CO)8{
3(P,C,C)-iPr2NP(CH2CH@CH2)2}] (4). At lower
temperature, any reaction was observed.
The IR
j
1(P)-iPr2NP(CH2CH@CH2)2}2] (3)
Intensity data were recorded at room temperature on a Rigaku
AFC-7S diffractometer equipped with a Mercury CCD detector
l:j
using monochromated Mo
Ka radiation (k = 0.71070 Å). An
m
(CO) frequencies for 3 are closely related to the analo-
gous disubstituted complex 1. A singlet in the 31P{1H} NMR
spectrum at d 60.7 indicates that both phosphines are equivalent
as observed in 1; the 1H and 13C{1H} NMR signals of the phosphine
ligand do not display significant differences in comparison to those
empirical absorption correction (multi-scan) was applied using
the CRYSTALCLEAR package. The structures were solved by direct
methods and refined by full-matrix least-squares on F2 using the
SHELXTL-PLUS package. All non hydrogen atoms were refined
anisotropically, and hydrogen atoms were added at calculated
positions (C–H = 0.93–0.97 Å) and refined as riding with
of the free ligand, suggesting j
1(P)-coordination. The spectroscopic
data of 3 (IR and NMR) shows that its molecular structure is a
direct analog of 1 (Scheme 4).
Uiso(H) = 1.2Ueq
.
The IR spectrum of 4 in the carbonyl stretching region indicates
the presence of an octacarbonyl compound similar to that of
3. Results and discussion
[Mn2(CO)8{l:j a
3(P,C,C)-Ph2PCH@CH2}] [41], which contains
bridging phosphine ligand coordinated by the phosphorus atom
3.1. Thermal treatment of [Re2(CO)8(MeCN)2] with hemilabile
phosphines
and an alkenyl unit. In the 31P{1H} NMR spectrum, a low-field sin-
i
glet was observed at d 62.9 [d 30.1, uncoordinated Pr2NP(CH2-
CH@CH2)2]. The 1H NMR spectrum for 4 displays a total of ten
signals, which reveals the absence of equivalence for the allylic
protons. The signal of one of the methylene protons adjacent to
the phosphorus atom in the coordinated allyl moiety is notably
Reaction of [Re2(CO)8(MeCN)2] and cyanoethyldiphenylphos-
phine in refluxing cyclohexane gave only one product, which
was characterized as diax-[Re2(CO)8{j
1(P)-Ph2P(CH2)2CN}2] (1)
(Scheme 2); its IR spectrum in the carbonyl region is very similar
shifted to low-field (d 6.10, Hb⁄) with respect to the signal of its
a
to those found for octacarbonyl disubstituted compounds [M2-
geminal proton (d 1.96, Ha⁄), while the methylene protons in the
a
(CO)8{j
1(P)-PR3}2] (M = Mn, Re) with ax,ax bonding geometries
uncoordinated allyl unit do not show such differences. This is con-
[38–40]. The 31P{1H} NMR spectrum of 1 shows only a singlet at
d 7.1 ppm, this indicates that the disubstituted derivative contains
two equivalent phosphorus atoms; while the simplicity of the 1H
and 13C{1H} NMR spectra suggests a symmetric structure for the
coordinated ligands. The molecular structure of complex 1 was
confirmed by an X-ray crystallographic study and revealed that
the symmetric unit contains four independent diax-[Re2(CO)8{j1
(P)-Ph2P(CH2)2CN}2] units (Fig. 1). Each rhenium atom contains
four terminal CO ligands and an axially positioned phosphine
ligand. The average distances Re–Re = 3.053 Å and Re–P = 2.365 Å
are similar to those observed in the related compounds [Re2(CO)8
(P)2] (P = PTh3, PMePh2, PPh3), which also adopt a similar diaxial
conformation [38,40]. The average N–C distances [N„C = 1.14 Å]
are clearly related to uncoordinated carbon–nitrogen triple bonds
[41]. The Re–Re–P average angles are slightly distorted [Re–Re–
sistent to what was found for [Os3(CO)10{l:j
3(P,C,C)–RP(CH2-
C@CH2)2}] [R = iPr2N, p-MeOC6H4], wherein the coordination of
one the allyl groups is evident [30]. The single crystal X-ray
structure of 4 (Fig. 2) revealed a dinuclear rhenium with eight
terminal carbonyl ligands and a bridging phosphine ligand. Its
structure shows one of the methylene protons (H11B) in the
p-
coordinated allyl unit located near to a carbonyl group (CO14A)
[H11BÁ Á ÁO14A = 2.7903(73) Å], which may be inducing an elec-
tronic effect that explains its greatly different chemical shift in
the 1H NMR spectrum with respect to H11A. The Re1–Re2 [3.084
(1) Å] bond is slightly longer than that obtained for compound 1
[Re–Re = 3.053 Å] due to the presence of a bridging allylphosphine
unit [Re1–C12 = 2.353(8) Å and Re1–C13 = 2.313(7) Å], which
is similar to that observed in [Os3(CO)10
{
l
:
j
3(P,C,C)–
3(P,
{l:j
3(P,C,C)-Ph2PCH2-
RP(CH2C@CH2)2}] [30] [R = iPr2N, p-MeOC6H4], [Mn2(CO)8{
l:j
C,C)-Ph2PCH@CH2}] [41] and [Rh6(CO)14
CH@CH2}] [29].
Additionally, two compounds were obtained, [Re2(CO)9{
j
1(P)-
l:j
3(P,C,C)-p-
p-MeOC6H4P(CH2CH@CH2)2}] (5) and [Re2(CO)8{
MeOC6H4P(CH2CH@CH2)2}] (6), from the reaction of [Re2(CO)8
(MeCN)2] with diallyl(p-methoxyphenyl)phosphine in refluxing
cyclohexane (Scheme 5). Complex 5 was easily characterized by
its spectroscopic data; its IR spectrum is similar to those found
for monosubstituted compounds [M2(CO)9{j
1(P)-PR3}] (M = Mn,
Re), where the phosphole ligand is bonded to an axial site (symme-
Scheme 2. Reaction of [Re2(CO)8(MeCN)2] with cyanoethyldiphenylphosphine.
try C4v). The simplicity of 31P{1H}, 1H and 13C{1H} NMR spectra of 5