Reactions of the Dirhenium(II) Complexes Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with Isocyanides. 11.1 A Triply Bonded Dirhenium Complex Containing a Labile Acetonitrile Ligand. Synthesis, Structural Characterization, and Reactivity

Article abstract of DOI:10.1021/ic9604831

The reaction of the open bioctahedral form of Re₂Cl₄(μ-dppm)₂(CO)(CNXyl) (1), where XylNC = 2,6-dimethylphenyl isocyanide, with TlO₃SCF₃ in the presence of acetonitrile proceeds with retention of stereochemistry at the dirhenium unit to afford the complex [Re₂Cl₃(μ-dppm)₂(CO)(CNXyl)(NCCH ₃)]O₃SCF₃ (3). The single-crystal X-ray structure determination of 3 shows that a Re=Re bond is retained (the Re-Re distance is 2.378(3) A?) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with TlO₃SCF₃ in a noncoordinating solvent to produce the unsymmetrical complex [Re₂Cl₃(μ-dppm)₂(CO)(CNXyl)]O ₃-SCF₃ (2), through loss of this same chloride ligand of 1 and CO transfer from the adjacent Re center. The acetonitrile ligand of 3 is very labile and is readily displaced by XylNC and t-BuNC, with retention of stereochemistry, to produce complexes of stoichiometry [Re₂Cl₃(μ-dppm)₂(CO)(CNXyl)(CNR)]O ₃SCF₃ (R = Xyl, 4a; R = t-Bu, 4b). In a noncoordinating solvent, the nitrile ligand of 3 is lost and 2 is formed following CO transfer; this conversion is reversed upon the reaction of 2 with acetonitrile. When 3 is treated with CO, the acetonitrile ligand is again displaced, but in this instance the reaction is accompanied by a structure change to produce an edge-sharing bioctahedral complex of the type [Re₂(μ-CO)(μ-Cl)(μ-dppm)₂Cl ₂(CO)(CNXyl)O₃SCF₃ (5).

Full text of DOI:10.1021/ic9604831

6784
Inorg. Chem. 1996, 35, 6784-6788
Reactions of the Dirhenium(II) Complexes Re2X4(µ-dppm)2 (X ) Cl, Br; dppm )
Ph2PCH2PPh2) with Isocyanides. 11.1 A Triply Bonded Dirhenium Complex Containing a
Labile Acetonitrile Ligand. Synthesis, Structural Characterization, and Reactivity of
[(XylNC)(CH3CN)ClRe(µ-dppm)2ReCl2(CO)]O3SCF3
Wengan Wu, J. Anand Subramony, Phillip E. Fanwick, and Richard A. Walton*
Department of Chemistry, Purdue University, 1393 Brown Building,
West Lafayette, Indiana 47907-1393
ReceiVed May 2, 1996X
The reaction of the open bioctahedral form of Re2Cl4(µ-dppm)2(CO)(CNXyl) (1), where XylNC ) 2,6-
dimethylphenyl isocyanide, with TlO3SCF3 in the presence of acetonitrile proceeds with retention of stereochemistry
at the dirhenium unit to afford the complex [Re2Cl3(µ-dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3 (3). The single-
crystal X-ray structure determination of 3 shows that a RetRe bond is retained (the Re-Re distance is 2.378(3)
Å) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with
TlO3SCF3 in a noncoordinating solvent to produce the unsymmetrical complex [Re2Cl3(µ-dppm)2(CO)(CNXyl)]O3-
SCF3 (2), through loss of this same chloride ligand of 1 and CO transfer from the adjacent Re center. The
acetonitrile ligand of 3 is very labile and is readily displaced by XylNC and t-BuNC, with retention of
stereochemistry, to produce complexes of stoichiometry [Re2Cl3(µ-dppm)2(CO)(CNXyl)(CNR)]O3SCF3 (R ) Xyl,
4a; R ) t-Bu, 4b). In a noncoordinating solvent, the nitrile ligand of 3 is lost and 2 is formed following CO
transfer; this conversion is reversed upon the reaction of 2 with acetonitrile. When 3 is treated with CO, the
acetonitrile ligand is again displaced, but in this instance the reaction is accompanied by a structure change to
produce an edge-sharing bioctahedral complex of the type [Re2(µ-CO)(µ-Cl)(µ-dppm)2Cl2(CO)(CNXyl)]O3SCF3
(5).
Introduction
Experimental Section
Starting Materials and General Procedures. The compounds Re2-
Cl4(dppm)2(CO)(CNXyl), 1,3 and TlO3SCF35 were prepared according
to the literature procedures. However, 1 was recrystallized from CH2-
Cl2/Et2O to remove trace amounts of the CH3CN solvent prior to use.
2,6-Dimethylphenyl isocyanide, XylNC, was purchased from Fluka
Chemical Corp., CO gas was obtained from Matheson Gas Products
Co., and TlPF6 was purchased from Strem Chemicals. These reagents
were used as received. Solvents were obtained from commercial
sources and were deoxygenated by purging with dinitrogen gas prior
to use. All reactions were performed under an atmosphere of dry
Our recent investigations into the chemistry of multiply
bonded dirhenium(II) complexes containing π-acceptor ligands
have revealed that differences in halide and isocyanide ligands,
and/or the nature of the reaction solvent, can affect the formation
of different isomeric forms of the products.2,3 A prime example
is the reaction between Re2Cl4(dppm)2(CO) and XylNC, where
XylNC ) xylyl isocyanide. When acetone is used as the
solvent, this reaction yields an edge-sharing bioctahedral
complex (XylNC)ClRe(µ-Cl)(µ-CO)(µ-dppm)2ReCl2,4 whereas
in acetonitrile an open bioctahedral isomeric form of this
complex, (XylNC)Cl2Re(µ-dppm)2ReCl2(CO), 1, is formed.3
We have previously reported that complex 1 reacts with TlO3-
SCF3 in the presence of a further equivalent of XylNC to afford
the complex [(XylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3,3 which
is another example of a molecule with an open bioctahedral
structure. In examining further the reactions of 1, we have found
that it reacts with TlO3SCF3, in a noncoordinating solvent such
as dichloromethane, to give the unsymmetrical, coordinatively
unsaturated complex [(XylNC)(CO)ClRe(µ-dppm)2ReCl2]O3-
SCF3, 2, while in acetonitrile the complex [(XylNC)(MeCN-
)ClRe(µ-dppm)2ReCl2(CO)]O3SCF3, 3, which contains a mixed
CO/isocyanide/nitrile ligand set, is produced. The synthesis,
characterization, and reactivity of 2 and 3 are described,
including details of the interconversion of 2 and 3.
1
dinitrogen. Infrared, H and 31P{1H} NMR, and cyclic voltammetric
measurements were carried out as described previously.2 Elemental
microanalyses were performed by Dr. H. D. Lee of the Purdue
University Microanalytical Laboratory.
A. Synthesis of [Re2Cl3(dppm)2(CO)(CNXyl)]O3SCF3, 2.
A
quantity of 1 (50.0 mg, 0.0347 mmol) was allowed to react with 13.5
mg of TlO3SCF3 (0.0382 mmol) in 15 mL of dichloromethane solvent.
Within a period of 2 h, the starting red-purple suspension changed color
to pale green. The reaction was stopped after 16 h, a white solid (TlCl)
was filtered off, and the pale green filtrate was reduced in volume to
ca. 1 mL. A small volume of i-Pr2O (0.5 mL) was added to this
concentrated filtrate, and the solvents were allowed to slowly evaporate
at 25 °C. The title complex, [Re2Cl3(dppm)2(CO)(CNXyl)]O3SCF3,
2, was collected as a crop of tiny green crystals after 4 h; yield 53.0
mg (>95%). Anal. Calcd for C61H53Cl3F3NO4P4Re2S: C, 47.09; H,
3.43; N, 0.90. Found: C, 46.12; H, 3.35; N, 0.99. When 1,2-
dichloroethane was used as the reaction solvent, a similar result was
obtained.
B. Synthesis of [Re2Cl3(dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3,
3. (i) From Re2Cl4(dppm)2(CO)(CNXyl), 1. A mixture of 1 (50.0
mg, 0.0347 mmol) and TlO3SCF3 (13.5 mg, 0.0382 mmol) was treated
with 15 mL of dichloromethane and 25 µL of acetonitrile. The resulting
X Abstract published in AdVance ACS Abstracts, October 15, 1996.
(1) Part 10: Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1996,
35, 5484.
(2) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1995, 34, 5810.
(3) Wu, W.; Fanwick, P. E.; Walton, R. A. J. Cluster Sci. 1996, 7, 155.
(4) Cotton, F. A.; Dunbar, K. R.; Price, A. C.; Schwotzer, W.; Walton,
R. A. J. Am. Chem. Soc. 1986, 108, 4843.
(5) Woodhouse, M. E.; Lewis, F. D.; Marks, T. J. J. Am. Chem. Soc.
1982, 104, 5586.
S0020-1669(96)00483-1 CCC: $12.00 © 1996 American Chemical Society

Reactions of Re2X4(µ-dppm)2 with Isocyanides
Inorganic Chemistry, Vol. 35, No. 23, 1996 6785
Table 1. Crystallographic Data for
mixture was stirred at 25 °C for 3 h. The reaction was stopped after
20 h, and the white precipitate of TlCl was filtered off. The volume
of the red filtrate was reduced to ca. 1 mL, and 20 mL of Et2O was
added to induce precipitation of 3 as a red powder. The product was
filtered off and washed with Et2O; yield 53.0 mg (96%). Anal. Calcd
for C63H56Cl3F3N2O4P4Re2S: C, 47.38; H, 3.53; N, 1.75. Found: C,
46.27; H, 3.44; N, 1.61.
[Re2Cl3(µ-dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3‚CH3CN (3)
empirical
formula
fw
space group P21/n (No. 14)
a, Å
Re2Cl3SP4F3O4N3C65H59
Z
4
F
calcd, g/cm3
1.616
1637.93
µ, cm-1 (Mo, KR) 40.67
transm factors
0.56/0.87
17.556(3)
14.988(3)
25.699(7)
93.98(7)
6745(5)
min/max
b, Å
c, Å
data with I >
3.0σ(I)
5276
Two modifications of this procedure were used, but neither resulted
in any significant differences in the product purity or yield. First, a
mixture of 1 (50.0 mg, 0.0347 mmol) and TlO3SCF3 (13.5 mg, 0.0382
mmol) was treated with 15 mL of dichloromethane until the reaction
suspension changed color to pale green; only at this point was the 25
µL of acetonitrile then added to the reaction mixture. The resulting
mixture was stirred at 25 °C for 24 h. During this period, the reaction
mixture changed color from green to yellow and finally to orange-red;
yield 52.0 mg (94%). Second, acetonitrile (15 mL) was used as the
reaction solvent and the reaction carried out at 25 °C for 19 h; yield
85%.
b
â, deg
Ra/Rw
0.041/0.049
V, Å3
largest shift/error 0.08
GOFc
0.341
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) {∑w(|Fo| - |Fc|)2/∑w|Fo| }1/2; w
) 1/σ2(|Fo|). c Goodness-of-fit ) [∑w(|Fo| - |Fc|)2/(Nobservns - Nparams)]1/2.
of the carbonyl complex [(XylNC)ClRe(µ-Cl)(µ-CO)(µ-dppm)2ReCl-
(CO)]O3SCF3, 5. The green product was filtered off and dried; yield
38.5 mg (86%). Anal. Calcd for C62H53Cl3F3NO5P4Re2S: C, 47.02;
H, 3.37; N, 0.88. Found: C, 47.41; H, 3.57; N, 0.98. The identity of
this complex was also based on a comparison of its spectroscopic and
electrochemical data with those of the known compound [(XylNC)-
ClRe(µ-Cl)(µ-CO)(µ-dppm)2ReCl(CO)]PF6.6
X-ray Crystallography. Single crystals of the complex [Re2Cl3(µ-
dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3, 3, which were suitable for
X-ray diffraction analysis were grown from an acetonitrile solution by
slow evaporation of the solvent at 25 °C. A red plate of 3, having
approximate dimensions of 0.40 × 0.40 × 0.23 mm, was mounted on
a glass fiber in a random orientation. The data collection was performed
on an Enraf-Nonius CAD4 computer-controlled diffractometer with
graphite-monochromatized Mo KR radiation at 293 K. The cell
constants for data collection were based on 25 reflections obtained in
the range 16 < θ < 18°, measured by the computer-controlled diagonal-
slit method of centering. Three standard reflections were measured
after every 5000 s of beam time during data collection to monitor the
crystal stability. Lorentz and polarization corrections were applied to
the data set. An empirical absorption correction7 was also applied,
but no correction for extinction was made. Calculations were performed
on an AlphaServer 2100 computer by the use of the MolEN8 structure
determination package.
(ii) From Re2Cl4(dppm)2(CO). A mixture of the monocarbonyl
complex Re2Cl4(dppm)2(CO) (50.0 mg, 0.0381 mmol), 1 equiv of
XylNC (5.0 mg, 0.0381 mmol), and TlO3SCF3 (15.0 mg, 0.0424 mmol)
was treated with 10 mL of acetonitrile. A green suspension formed
first and then changed color to red. The reaction was stopped after 7
h, the white precipitate of TlCl was filtered off, and the red filtrate
was concentrated to ca. 3 mL. Complex 3 was collected as red crystals
after slow evaporation of the remaining solvent at 25 °C; yield 53.2
mg (87%).
C. Interconversion of 2 and 3. (i) Reaction of 2 with Acetoni-
trile. A quantity of 2 (20.0 mg, 0.0129 mmol) was dissolved in 8 mL
of acetonitrile and the resulting solution then stirred at 25 °C for 18 h.
The reaction mixture changed color from green to brown within ca. 10
min and then slowly converted to an orange solution during the course
of the reaction. The red compound 3 was isolated when the solvent
was evaporated and the residue washed with Et2O; yield 20.0 mg (97%).
(ii) Thermolysis of 3 to 2. A solution of 3 (80.0 mg, 0.0501 mmol)
in 25 mL of dichloromethane was heated to reflux for 18 h. A green
solution formed during this period. The volume of this solution was
reduced to ca. 1 mL, and 20 mL of Et2O was added to induce
precipitation. A pale tan solid was collected by filtration. The IR and
solution 1H and 31P{1H} NMR spectra of this product showed it to be
a mixture of 2 and 3 in an approximate 50/50 ratio; yield 72.5 mg.
Longer reaction times afforded similar results. However, when this
product mixture was redissolved in fresh dichloromethane and the
procedure of heating and product isolation repeated several times, a
much higher conversion of 3 to 2 (>80%) was achieved.
D. Reactions of [Re2Cl3(dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3,
3, with Isocyanides RNC. (i) R ) Xylyl. A quantity of 3 (40.0 mg,
0.0250 mmol) was mixed with XylNC (3.5 mg, 0.0267 mmol) and 15
mL of dichloromethane, and the mixture was stirred at 25 °C for 20 h.
A red suspension formed initially but redissolved completely in about
2 h. The volume of the solution was reduced to ca. 1 mL, and 20 mL
of Et2O was then added to induce precipitation of the red complex
[Re2Cl3(dppm)2(CO)(CNXyl)2]O3SCF3, 4a, which was filtered off and
washed with Et2O; yield 31.5 mg (75%). The identity of this product
was based on a comparison of its spectroscopic and electrochemical
properties with those of a sample prepared by the previously reported
method.3
Compound 3 crystallized in the monoclinic crystal system. The
systematic absences observed for the data set were consistent with space
group P21/n. The structure was solved by a combination of direct
methods (SIR92)9 and difference Fourier syntheses. All non-hydrogen
atoms except C(21) in this structure were refined anisotropically. Atom
C(21) was refined with isotropic thermal parameters. The hydrogen
atoms were calculated by the use of idealized geometries with C-H
) 0.95 Å and U(H) ) 1.3Ueq(C). Their contributions were added to
the structure factor calculations, but their positions were not refined.
During the course of the structure refinement, a CH3CN molecule from
the crystallization solvent was found cocrystallized with the complex
in the asymmetric unit. Atoms of this solvent molecule were located
and refined satisfactorily. The structure was refined in full-matrix least
squares where the function minimized was ∑w(|Fo| - |Fc|)2, where w
is the weighting factor defined as w ) 1/σ2(Fo). Corrections for
anomalous scattering were applied to the anisotropically refined atoms.10
The final residuals for 3 were R ) 0.041 and Rw ) 0.049 with GOF )
0.341. The highest peak in the final difference Fourier was 0.94 e/Å3.
(ii) R ) tert-Butyl. The reaction of 3 (60.0 mg, 0.0376 mmol) with
t-BuNC (5 µL, 0.0442 mmol) in 15 mL of dichloromethane for 16 h at
25 °C afforded a red solution. A workup procedure similar to that
described in section D(i) gave the red complex [Re2Cl3(dppm)2-
(CO)(CNXyl)(CN-t-Bu)]O3SCF3, 4b; yield 54.2 mg (88%). Anal.
Calcd for C66H62Cl3F3N2O4P4Re2S: C, 48.37; H, 3.81; N, 1.71.
Found: C, 48.06; H, 3.75; N, 1.72.
The crystallographic data for compound 3 are given in Table 1, while
important intramolecular bond lengths and angles are given in Table
2.
(6) Anderson, L. B.; Cotton, F. A.; Dunbar, K. R.; Falvello, L. R.; Price,
A. C.; Reid, A. H.; Walton, R. A. Inorg. Chem. 1987, 26, 2717.
(7) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(8) Fair, C. K. MolEN Structure Determination System; Delft Instru-
ments: Delft, The Netherlands, 1990.
E. Reaction of [Re2Cl3(dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3,
3, with CO. A suspension of 3 (45.0 mg, 0.0281 mmol) in 15 mL of
dichloromethane was slowly purged with CO gas for 5 min and the
resulting mixture then stirred at 25 °C for 19 h. A green solution
formed during this period. The solvent was removed, and the residue
was redissolved in a minimum amount of dichloromethane (ca. 0.5
mL). An excess of Et2O (ca. 2.0 mL) was added to induce precipitation
(9) Altomare, A.; Cascarano, G.; Gaicovazzo, C.; Burla, M. C.; Polidori,
G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(10) Cromer, D. T. International Tables for X-ray Crystallography;
Kynoch: Birmingham, U.K., 1974; Vol. IV: (a) Table 2.3.1; (b) Table
2.2B.

6786 Inorganic Chemistry, Vol. 35, No. 23, 1996
Wu et al.
pattern, whereas the analogous bromo complex2 shows a distinct,
well-resolved AA′BB′ pattern with multiplets centered at δ -9.0
and -14.5. The cyclic voltammetric properties of 2 in 0.1 M
TBAH-CH2Cl2 (scan rate 200 mV s-1, potentials vs Ag/AgCl)
show a reversible couple, corresponding to a one-electron
oxidation of the bulk complex, with an E1/2 value of +0.96 V,
and an irreversible reduction at Ep,c ) -0.89 V (there is a
coupled process at Ep,a ) -0.28 V with ip,a , ip,c). This
behavior is very similar to that reported for [Re2Br3(µ-
dppm)2(CO)(CNXyl)]O3SCF3 which has E1/2(ox) ) +0.99 V
and Ep,c ) -0.77 V.2
If the reaction between 1 and TlO3SCF3 is carried out in the
presence of acetonitrile, the coordinatively saturated species 3,
which contains a mixed CO/XylNC/CH3CN ligand set, is
formed. An alternative approach to the synthesis of 3 utilizes
the reaction of the monocarbonyl complex Re2Cl4(µ-dppm)2-
(CO)11 with 1 equiv each of XylNC and TlO3SCF3 in acetoni-
trile. This reaction proceeds through the intermediacy of 1,
which is known to be formed by the reaction of Re2Cl4(µ-
dppm)2(CO) with XylNC in acetonitrile.3
We had shown previously3 that the reaction of 1 with TlO3-
SCF3 in the presence of XylNC affords the bis(xylyl isocyanide)
complex [Re2Cl3(µ-dppm)2(CO)(CNXyl)2]O3SCF3 (4a), which
has been structurally characterized. Note also that the tert-butyl
isocyanide complex Re2Cl4(µ-dppm)2(CO)(CN-t-Bu), which is
essentially isostructural with 1, reacts in a similar such fashion
with TlPF6 and an additional equivalent of t-BuNC to form [Re2-
Cl3(µ-dppm)2(CO)(CN-t-Bu)2]PF6.12,13 The reaction of the
acetonitrile-containing complex 3 with the isocyanide ligands
XylNC and t-BuNC affords the complexes 4a and 4b, respec-
tively, through displacement of the labile CH3CN ligand. The
properties of the different samples of 4a, as obtained by these
two different routes, are identical. These conversions support
a close structural relationship among 3, 4a, and 4b, which has
been confirmed by a single-crystal X-ray structure determination
of 3. An ORTEP14 drawing of the dirhenium cation of 3 is
shown in Figure 1. The structure of 3 very closely resembles
that of 4a,3 with Re-Re bond distances in accord with the
retention of a RetRe bond (2.378(3) Å for 3 and 2.3833(8) Å
for 4a3). The comparable Re-C, Re-Cl, and Re-P distances
in the two structures are similar. The Re-N distance of 2.12(4)
Å is normal for a nitrile ligand bound to a dirhenium(II) center.15
As expected, the absence of an electronic barrier to rotation
about the RetRe bond in 3, results in a partially staggered
rotational geometry. The torsional angles P(1)-Re(1)-Re(2)-
P(2), P(4)-Re(1)-Re(2)-P(3), Cl(11)-Re(1)-Re(2)-C(20),
and C(10)-Re(1)-Re(2)-N(30) have values of 22.55(13),
27.68(13), 27.36(34), and 25.70(50)°, respectively, somewhat
larger on average than the comparable angles in the structure
of 4a (20.2, 10.6, 24.3, and 17.8°, respectively).3 These
differences reflect compromises between steric effects and the
conformational requirements of the µ-dppm ligands within these
compact dinuclear complexes.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for
[Re2Cl3(µ-dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3‚CH3CN (3)a
Distances
Re(1)-Re(2)
Re(1)-Cl(11)
Re(1)-Cl(12)
Re(1)-P(1)
2.378(3)
2.412(11)
2.550(11)
2.502(11)
2.469(12)
1.92(5)
Re(2)-P(3)
2.489(11)
2.12(4)
2.03(5)
1.15(5)
1.17(5)
1.41(5)
1.07(6)
1.49(8)
Re(2)-N(30)
Re(2)-C(20)
C(10)-O(10)
C(20)-N(20)
N(20)-C(21)
N(30)-C(30)
C(30)-C(31)
Re(1)-P(4)
Re(1)-C(10)
Re(2)-Cl(21)
Re(2)-P(2)
2.467(11)
2.476(12)
Angles
Re(2)-Re(1)-Cl(11) 107.5(3) Re(1)-Re(2)-N(30) 102.2(10)
87.7(11)
Re(2)-Re(1)-Cl(12) 161.6(3) Re(1)-Re(2)-C(20)
Re(2)-Re(1)-P(1)
Re(2)-Re(1)-P(4)
Re(2)-Re(1)-C(10)
98.6(3) Cl(21)-Re(2)-N(30) 88.4(10)
91.8(3) Cl(21)-Re(2)-C(20) 81.7(11)
81.9(13) Cl(21)-Re(2)-P(3)
80.5(4)
86.0(4)
166.4(4)
93.7(11)
87.5(11)
87.6(11)
89.0(11)
Cl(11)-Re(1)-Cl(12) 90.0(4) Cl(21)-Re(2)-P(2)
Cl(11)-Re(1)-P(1)
Cl(11)-Re(1)-P(4)
Cl(11)-Re(1)-C(10) 169.9(13) P(2)-Re(2)-C(20)
Cl(12)-Re(1)-P(1)
Cl(12)-Re(1)-P(4)
Cl(12)-Re(1)-C(10)
P(1)-Re(1)-P(4)
P(1)-Re(1)-C(10)
P(4)-Re(1)-C(10)
93.3(4) P(2)-Re(2)-P(3)
84.0(4) P(2)-Re(2)-N(30)
85.7(4) P(3)-Re(2)-N(30)
84.3(4) P(3)-Re(2)-C(20)
80.3(13) N(30)-Re(2)-C(20) 169.9(15)
169.6(4) Re(1)-C(10)-O(10) 176(4)
88.7(13) Re(2)-C(20)-N(20) 172(3)
92.3(13) C(20)-N(20)-C(21) 169(4)
Re(1)-Re(2)-Cl(21) 169.4(3) Re(2)-N(30)-C(30) 176(4)
Re(1)-Re(2)-P(2)
Re(1)-Re(2)-P(3)
94.4(3) N(30)-C(30)-C(31) 177(6)
98.5(3)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Scheme 1. Reactions of the Bioctahedral Complex
Re2Cl4(µ-dppm)2(CO)(CNXyl), 1
Results and Discussion
The reactions of the bioctahedral dirhenium(II) complex Re2-
Cl4(µ-dppm)2(CO)(CNXyl), 1, which we have examined in the
present investigation, are summarized in Scheme 1. Important
spectroscopic data for the reaction products 2-5 are summarized
in Table 3.
The conversion of 1 to the coordinatively unsaturated complex
2, upon reaction of the former with TlO3SCF3, occurs through
labilization of the Re-Cl bond which is trans to the XylNC
ligand and CO transfer from the adjacent Re center. This
reaction course therefore resembles that reported previously for
the reactions of TlO3SCF3 with the analogous bromo analogue
of 1 (i.e., Re2Br4(µ-dppm)2(CO)(CNXyl)) and with the t-BuNC-
containing derivative Re2Br4(µ-dppm)2(CO)(CN-t-Bu).2 The IR
and 1H NMR spectroscopic properties and electrochemical
properties of 2 closely resemble those of these bromo ana-
logues.2 The only significant spectroscopic difference is seen
in the 31P{1H} spectra; for 2, a fairly broad singlet (fwhm )
0.28 ppm) is observed which is probably an unresolved AA′BB′
The conversions of 3 into 4a and 4b occur with retention of
stereochemistry as shown by the structural characterizations of
(11) Cotton, F. A.; Daniels, L. M.; Dunbar, K. R.; Falvello, L. R.; Tetrick,
S. M.; Walton, R. A. J. Am. Chem. Soc. 1985, 107, 3524.
(12) Fanwick, P. E.; Price, A. C.; Walton, R. A. Inorg. Chem. 1987, 26,
3086.
(13) Fanwick, P. E.; Price, A. C.; Walton, R. A. Inorg. Chem. 1988, 27,
2601.
(14) Johnson, C. K. ORTEP II. Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
(15) (a) Barder, T. J.; Cotton, F. A.; Falvello, L. R.; Walton, R. A. Inorg.
Chem. 1985, 24, 1258. (b) Fanwick, P. E.; Qi, J.-S.; Shih, K.-Y.;
Walton, R. A. Inorg. Chim. Acta 1990, 172, 65. (c) Derringer, D. R.;
Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. Polyhedron 1991, 10, 79.

Reactions of Re2X4(µ-dppm)2 with Isocyanides
Inorganic Chemistry, Vol. 35, No. 23, 1996 6787
Table 3. Spectroscopic Data for Dirhenium Complexes Derived from the Reactions of Re2Cl4(µ-dppm)2(CO)(CNXyl) (1)
IR, cm-1 b
1H NMR, δc,d
-CH2- of dppm
compd
no.a
ν(CN)
2154 (ms)
ν(CO)
CH3 of XylNC
31P{1H} NMR,δc,e
2
3
2030 (vs)
6.12 (m, 2H), 5.77 (m, 2H)
5.74 (m, 2H), 5.57 (m, 2H)
6.20 (m, 2H),5.88 (m, 2H)
6.15 (m, 2H),5.80 (m, 2H)
4.72 (m, 2H),4.56 (m, 2H)
2.03 (s, 6H)
-9.1 (s)
2288 (vw),f 2094 (vs)
2144 (m), 2116 (vs)
2172 (m), 2112 (vs)
2188 (m)
1958 (vs)
2.60 (s, vbr, 6H)g
1.84 (s, 6H),1.65 (s, 6H)
1.62 (s, 6H)j
-7.1, -7.4
-8.5,i -8.8i
-7.1, -11.1
-6.0, -8.9
4ah
4b
5
1944 (s)
1962 (vs)
1966 (vs), 1768 (s)
2.17 (s, 6H)
a Compound numbering as shown in Scheme 1. b IR spectra recorded as Nujol mulls. Abbreviations: ms ) medium strong, vw ) very weak,
vs ) very strong, m ) medium. c NMR spectra recorded on CDCl3 solutions of the complexes. Abbreviations: m ) multiplet, vbr ) very broad,
s ) singlet. d Resonances for the phenyl ring protons occur in the range δ ) 6.8-8.0. e With the exception of compound 2, resonances appear as
AA′BB′ multiplets. Unless otherwise indicated, the centers of the two multiplets are quoted. f The ν(CN) mode of the coordinated MeCN. g The
methyl resonance of the coordinated CH3CN is at δ ) 2.25 (s, 3H). h Data for this complex taken from ref 3. i Most intense component. j The
resonance for the t-BuNC ligand is at δ ) 1.35 (s, 9H).
Chart 1. Structural Isomers of the Dirhenium Cation
[Re2Cl3(µ-dppm)2(CO)(CNXyl)(CN-t-Bu)]+ with the µ-dppm
Ligands Omitted for Clarity
Figure 1. ORTEP14 representation of the dirhenium cation [Re2Cl3-
(µ-dppm)2(CO)(CNXyl)(NCCH3)]+ as present in 3. The thermal el-
lipsoids are drawn at the 50% probability level except for those of the
Cl3(µ-dppm)2(CO)(CNXyl)(CN-t-Bu)]+ cation has now been
identified in four quite distinct stereochemistries (see Chart 1).
Another noteworthy feature of the reaction chemistry sum-
marized in Scheme 1 is the reversibility of interconversion of
2 and 3. While the presence of only trace amounts of
acetonitrile cause the conversion of 2 to 3, this reaction can be
reversed upon heating solutions of the nitrile complex 3,
provided the acetonitrile can be removed from the system by
distillation. In the case of salts of the bis(isocyanide) complex
cations of the type [Re2X3(µ-dppm)2(CO)(CNR)2]+ which
possess the open bioctahedral structure [(RNC)2XRe(µ-dppm)2-
ReX2(CO)]+ (this work and refs 12 and 13), we observed no
corresponding loss of RNC ligands under these same conditions.
Presumably, other nitrile-containing complexes which are similar
to 32,13 will very likely exhibit nitrile ligand loss upon mild
thermolysis.
The final reaction shown in Scheme 1 is the carbonylation
of 3 under mild conditions to form the bis(carbonyl) complex
5. This reaction product is analogous to that obtained from the
reaction of the t-BuNC analogue of 3 (i.e., [Re2Cl3(µ-dppm)2-
(CO)(CN-t-Bu)(NCCH3)]PF6) and CO, which affords the edge-
sharing bioctahedral complex [Re2(µ-Cl)(µ-CO)(µ-dppm)2Cl2-
(CO)(CN-t-Bu)]PF6.13 The latter complex, which has been
structurally characterized by X-ray crystallography,6 and its
xylNC analogue have spectroscopic and electrochemical proper-
ties very similar to those recorded for the triflate salt 5 (see
Table 3), thereby supporting the structural formulation given
in Scheme 1 for complex 5. Furthermore, when a solution of
5 in 1,2-dichloroethane is refluxed for 4 h, it converts to the
all-cis edge-sharing bioctahedral form of this complex. The
latter species has been shown6 to be the thermodynamically
favored form of these two isomers, and this transformation is
diagnostic of the structure shown for 5 in Scheme 1.
phenyl group atoms of the dppm ligands and the xylyl group atoms of
the XylNC ligand, which are circles of arbitrary radius.
3 (Figure 1) and 4a (R ) Xyl).3 This observation also accords
with the structural identity of the complex cation [Re2Cl3(µ-
dppm)2(CO)(CN-t-Bu)2]+ which can be prepared through the
reaction of [Re2Cl3(µ-dppm)2(CO)(CN-t-Bu)(NCR)]PF6, a close
structural analogue of 3, with t-BuNC.12,13 Furthermore,
complexes of the type [Re2Cl3(µ-dppm)2(CO)(CN-t-Bu)(NCR)]-
PF6, where R ) CH3 or C2H5, which are obtained by the reaction
of Re2Cl4(µ-dppm)2(CO)(CN-t-Bu) with TlPF6 in the presence
of an excess of the nitrile RCN,13 almost certainly have a
structure closely akin to that of 3, with t-BuNC in place of
XylNC. Interestingly, the product which is produced when [Re2-
Cl3(µ-dppm)2(CO)(CN-t-Bu)(NCCH3)]PF6 is reacted with Xy-
lNC is an isomer of 4b.13 The spectroscopic properties of this
product13 differ from those of 4b (Table 3), but reveal that, like
those in 4b, the CO, t-BuNC, and XylNC ligands are all
terminally bound. Since the conversions of 3 to 4a and 4b
proceed with retention of stereochemistry (Scheme 1), the isomer
which is formed from the treatment of [Re2Cl3(µ-dppm)2(CO)-
(CN-t-Bu)(NCCH3)]PF6 with XylNC13 must possess a structure
very similar to that shown in Scheme 1 for 4b, but with the
t-BuNC and XylNC ligands switched, i.e. with the XylNC ligand
syn to the CO (Chart 1). Of further note is our earlier finding13
that [Re2Cl3(µ-dppm)2(CO)(CNXyl)(CN-t-Bu)]PF6 exists in two
other structural forms, both of which are based upon the edge-
sharing bioctahedral geometry (Chart 1). These other isomers
are of the types [Re2(µ-Cl)(µ-CO)(µ-dppm)2Cl2(CNXyl)(CN-
t-Bu)]PF6 and [Re2(µ-Cl)(µ-CNXyl)(µ-dppm)2Cl2(CO)(CN-t-
Bu)]PF6, in which the three π-acceptor ligands have an all-cis
arrangement relative to one another.13 Accordingly, the [Re2-

6788 Inorganic Chemistry, Vol. 35, No. 23, 1996
Wu et al.
Concluding Remarks
ligands are in an all-cis disposition relative to one another on
one side of the molecule.
The reaction chemistry which is summarized in Scheme 1
confirms that, for dirhenium(II) halide complexes of the type
Re2X4(µ-dppm)2(CO)(CNR) which possess the same type of
open bioctahedral structure as represented by 1, the most labile
Re-X bond is the one which is trans to the RNC ligand. This
behavior is independent of the nature of the halide (X can be
Cl or Br) and the isocyanide ligand (R can be t-Bu or Xyl).1-3,13
The sequence of substitution reactions shown in the conversion
of complex 1 to 3, and then to 4a and 4b, occurs with retention
of stereochemistry when the added ligand is a nitrile or
isocyanide. This same situation seems to hold in the case of
the reactions of bromo analogues of 1 (i.e., Re2Br4(µ-dppm)2-
(CO)(CNR), where R ) t-Bu or Xyl) with nitriles.2,16 However,
this is not so when XylNC is reacted with the tetrabromo
complex Re2Br4(µ-dppm)2(CO)(CNXyl); in this system, the
reaction chemistry is quite complicated, and edge-sharing bis-
(µ-bromo)-bridged species are the major products.1
From the present study and one earlier investigation,13 we
have established that the dirhenium cation [Re2Cl3(µ-dppm)2-
(CO)(CNXyl)(CN-t-Bu)]+ can exist in one of four distinct
isomeric forms (see Chart 1). We also note that the bioctahedral
complex [Re2Cl3(µ-dppm)2(CO)(CNXyl)(NCCH3)]O3SCF3 (3),
in which the Re-Re bond is formally of order 3.0, is the second
isomeric form of this cation to be isolated and characterized.
The other isomer is the edge-sharing bioctahedral species
[Re2(µ-CO)(µ-Cl)(µ-dppm)2Cl2(CNXyl)(NCCH3)]PF6,13 which
has an all-cis arrangement of CO, CNXyl, and NCCH3 ligands.
The latter complex is prepared13 from the reaction of the other
isomer of 1, i.e., the edge-sharing bioctahedral form Re2(µ-
CO)(µ-Cl)(µ-dppm)2Cl3(CNXyl),4 with TlPF6 in the presence
of acetonitrile.13 This reaction, like the conversion of 1 to 3,
proceeds with retention of stereochemistry.
The carbonylation of 3 to afford the bis(carbonyl) complex
5, which has an edge-sharing bioctahedral structure with one
of the CO ligands in a bridging mode, is typical of all those
reactions we have studied1,6,13,17 in which a species of stoichi-
ometry [Re2X3(µ-dppm)2(CO)2(CNR)]n+ is formed (n ) 0 or
1). This ligand set, in which two CO ligands and one RNC
ligand are present, always gives this type of edge-sharing
bioctahedral geometry in one of two isomeric forms, viz., that
shown for 5 in Scheme 1, or one in which the three π-acceptor
Acknowledgment. We thank the National Science Founda-
tion, through Grant No. CHE94-09932 to R.A.W., for support
of this work.
Supporting Information Available: Tables giving full details of
the crystal data and data collection parameters (Table S1), atomic
positional parameters (Tables S2 and S3), anisotropic thermal param-
eters (Table S4), bond distances (Table S5), and bond angles (Table
S6) for 3 (9 pages). An X-ray crystallographic file, in CIF format, is
available on the Internet. Ordering and access information is given
on any current masthead page.
(16) Wu, W.; Walton, R. A. Unpublished results.
(17) Cotton, F. A.; Dunbar, K. R.; Falvello, L. R.; Walton, R. A. Inorg.
Chem. 1985, 24, 4180.
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