Reactions of the dirhenium(II) complexes Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPH2) with isocyanides

Article abstract of DOI:10.1021/ic000064a

A study of the reactions between the triply bonded dirhenium(II) complexes Re₂Cl₄(μ-LL)₂, where LL = Ph₂PCH₂PPh₂ (dppm), Ph₂PC( = CH₂)PPh₂ (dppE), or Cy₂PCH₂PCy₂ (dcpm), with the isocyanides t-BuNC and XylNC (Xyl = 2,6-dimethylphenyl) show that complexes of the type Re₂Cl₄(μ-LL)2(CNR), Re₂Cl₄(μ-LL)₂(CNR)₂, and [Re₂Cl₃(μ-LL)₂(CNR)₃]⁺ are formed sequentially. Several of these have been structurally characterized by X-ray crystallography: Re₂Cl₄(μ-dppm)₂(CNXyl) (2), Re₂Cl₄(μ-dcpm)₂(CNXyl) (11), Re₂Cl₄(μ-dppE)₂(CN-t-Bu)₂ (6), Re₂Cl₄(μ-dcpm)₂(CN-t-Bu)₂ (12), and [Re₂Cl₃(μ-dppE)₂(CN-t-Bu)₃]Cl (7). Complex 2 has an A-frame-like structure with a single μ-Cl bridging ligand, whereas for 11 the structure is like that of 2 but without this bridge, viz., Cl₂Re(μ-dppm)₂ReCl₂(CNXyl) with a Re - Cl bond approximately collinear with Re≡Re. The symmetrical complexes 6 and 12 are essentially isostructural and have an anti-arrangement of the two t-BuNC ligands. Complex 7 has the open bioctahedral structure [(t-BuNC)₂ClRe(μ-dppE)₂ReCl₂(CN-t-Bu)]⁺, which is quite different from that of the edge-sharing bioctahedron found in salts of the [Re₂Cl₃(μ-dppm)₂(CNXyl)₃]⁺ cation and its neutral congener Re₂Cl₃(μ-dppm)₂(CNXyl)₃; preliminary crystallographic data for the latter compound show the structure to be (XylNC)ClRe(μ-Cl)(μ-CNXyl)(μ-dppm)₂ReCl(CNXyl) with an all-cis arrangement of XylNC ligands. The Re - Re bond distances of 2, 6, 7, 11, and 12 occur in the range 2.289-2.380 A and are consistent in all instances with the retention of a Re≡Re bond, albeit weakened by some degree of Re→CNR(π*) back-bonding.

Full text of DOI:10.1021/ic000064a

2676
Inorg. Chem. 2000, 39, 2676-2683
Reactions of the Dirhenium(II) Complexes Re2X4(µ-dppm)2 (X ) Cl, Br; dppm )
Ph2PCH2PPh2) with Isocyanides. 21.1 A Comparison with the Complexes Re2Cl4(µ-dppE)2
and Re2Cl4(µ-dcpm)2 (dppE ) Ph2PC(dCH2)PPh2; dcpm ) Cy2PCH2PCy2) and the
Structural Characterization of Complexes of the Types Re2Cl4(µ-LL)2(CNR),
Re2Cl4(µ-LL)2(CNR)2, and [Re2Cl3(µ-LL)2(CNR)3]+ (LL ) dppm, dppE, dcpm;
R ) t-Bu, Xyl)
Yan Ding, Shan-Ming Kuang, Michael J. Siwajek, Phillip E. Fanwick, and
Richard A. Walton*
Department of Chemistry, Purdue University, 1393 Brown Building,
West Lafayette, Indiana 47907-1393
ReceiVed January 18, 2000
A study of the reactions between the triply bonded dirhenium(II) complexes Re2Cl4(µ-LL)2, where LL ) Ph2-
PCH2PPh2 (dppm), Ph2PC(dCH2)PPh2 (dppE), or Cy2PCH2PCy2 (dcpm), with the isocyanides t-BuNC and XylNC
(Xyl ) 2,6-dimethylphenyl) show that complexes of the type Re2Cl4(µ-LL)2(CNR), Re2Cl4(µ-LL)2(CNR)2, and
[Re2Cl3(µ-LL)2(CNR)3]+ are formed sequentially. Several of these have been structurally characterized by X-ray
crystallography: Re2Cl4(µ-dppm)2(CNXyl) (2), Re2Cl4(µ-dcpm)2(CNXyl) (11), Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6),
Re2Cl4(µ-dcpm)2(CN-t-Bu)2 (12), and [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7). Complex 2 has an A-frame-like structure
with a single µ-Cl bridging ligand, whereas for 11 the structure is like that of 2 but without this bridge, viz.,
Cl2Re(µ-dppm)2ReCl2(CNXyl) with a Re-Cl bond approximately collinear with RetRe. The symmetrical
complexes 6 and 12 are essentially isostructural and have an anti-arrangement of the two t-BuNC ligands. Complex
7 has the open bioctahedral structure [(t-BuNC)2ClRe(µ-dppE)2ReCl2(CN-t-Bu)]+, which is quite different from
that of the edge-sharing bioctahedron found in salts of the [Re2Cl3(µ-dppm)2(CNXyl)3]+ cation and its neutral
congener Re2Cl3(µ-dppm)2(CNXyl)3; preliminary crystallographic data for the latter compound show the structure
to be (XylNC)ClRe(µ-Cl)(µ-CNXyl)(µ-dppm)2ReCl(CNXyl) with an all-cis arrangement of XylNC ligands. The
Re-Re bond distances of 2, 6, 7, 11, and 12 occur in the range 2.289-2.380 Å and are consistent in all instances
with the retention of a RetRe bond, albeit weakened by some degree of RefCNR(π*) back-bonding.
Introduction
Cl2(µ-dppm)2(CO)(CNXyl)3]2+ 12,13
. Several of the analogous
bromo complexes are also known.3,4,9 These compounds exist
in a variety of stable isomeric forms that are notable for the
dependence of the Re-Re bond order on the structure of the
isomer, and the rich metal-based redox chemistry that they
exhibit.3,5-17
The reactions of Re2Cl4(µ-dppm)2 (dppm ) Ph2PCH2PPh2)
with CO lead to the incorporation of up to three of these ligands
into the dimetal coordination sphere to afford the complexes
Re2Cl4(µ-dppm)2(CO),2,3 Re2Cl4(µ-dppm)2(CO)2,2 and [Re2Cl3-
(µ-dppm)2(CO)3]+.4 In addition, several extensive series of
dirhenium(II) complexes have been isolated and structurally
characterized which contain a combination of CO along with
up to three xylyl isocyanide ligands, viz., Re2Cl4(µ-dppm)2(CO)-
(CNXyl),3,5 [Re2Cl3(µ-dppm)2(CO)(CNXyl)2]+,5-11 and [Re2-
Although earlier work had also led to the isolation of several
dirhenium(II) isocyanide complexes of the types Re2Cl4(µ-
dppm)2(CNR),18 [Re2Cl3(µ-dppm)2(CNR)2]PF6,19,20 and [Re2-
Cl3(µ-dppm)2(CNR)3]PF6,20 these compounds have remained
inadequately characterized and their chemistry little explored.
To establish the structural identity of these types of complexes,
we have performed a comparative study of the reaction chem-
(1) Part 20: Chantler, J.; Kort, D. A.; Fanwick, P. E.; Walton, R. A. J.
Organomet. Chem. 2000, 596, 27.
(2) 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.
(3) Cotton, F. A.; Dunbar, K. R.; Price, A. C.; Schwotzer, W.; Walton,
R. A. J. Am. Chem. Soc. 1986, 108, 4843.
(11) Wu, W.; Fanwick, P. E.; Walton, R. A. J. Cluster Sci. 1997, 8, 547.
(12) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1997, 36, 3810.
(13) Ding, Y.; Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1999,
38, 1918.
(4) Fanwick, P. E.; Price, A. C.; Walton, R. A. Inorg. Chem. 1987, 26,
3920.
(5) Wu, W.; Fanwick, P. E.; Walton, R. A. J. Cluster Sci. 1996, 7, 155.
(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) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chim. Acta 1996, 242,
81.
(8) Wu, W.; Fanwick, P. E.; Walton, R. A. J. Am. Chem. Soc. 1996, 118,
13091.
(14) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1995, 34, 5810.
(15) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1996, 35, 5484.
(16) Wu, W.; Fanwick, P. E.; Walton, R. A. J. Chem. Soc., Chem. Commun.
1997, 755.
(17) Wu, W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1998, 37, 3122.
(18) Anderson, L. B.; Barder, T. J.; Esjornson, D.; Walton, R. A.; Bursten,
B. E. J. Chem. Soc., Dalton Trans. 1986, 2607.
(9) Ding, Y.; Kort, D. A.; Wu, W.; Fanwick, P. E.; Walton, R. A. J.
Organomet. Chem. 1999, 573, 87.
(10) Wu, W.; Fanwick, P. E.; Walton, R. A. Organometallics 1997, 16,
1538.
(19) Anderson, L. B.; Barder, T. J.; Walton, R. A. Inorg. Chem. 1985, 24,
1421.
(20) Anderson, L. B.; Barder, T. J.; Cotton, F. A.; Dunbar, K. R.; Falvello,
L. R.; Walton, R. A. Inorg. Chem. 1986, 25, 3629.
10.1021/ic000064a CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/19/2000

Reactions of Dirhenium(II) Complexes Re2X4(µ-dppm)2
Inorganic Chemistry, Vol. 39, No. 12, 2000 2677
The mixture was filtered, and the green filtrate was reduced in volume
to ca. 5 mL. An excess of diethyl ether was added to afford a green
precipitate of 7, which was filtered off, washed with 20 mL of diethyl
ether, and dried under reduced pressure; yield, 143 mg (60%). Anal.
Calcd for C67H71Cl4N3P4Re2: C, 51.70; H, 4.60. Found: C, 51.00; H,
4.91.
istry of the triply bonded dirhenium(II) complexes Re2Cl4(µ-
dppm)2,21,22 Re2Cl4(µ-dppE)2 (dppE ) Ph2PC(dCH2)PPh2),23
and Re2Cl4(µ-dcpm)2 (dcpm ) Cy2PCH2PCy2)24 with tert-butyl
isocyanide (t-BuNC) and 2,6-dimethylphenyl isocyanide (Xy-
lNC) and, in so doing, have been able to clarify the structures
of several of these isocyanide complexes.
4. Synthesis of [Re2Cl3(µ-dppE)2(CN-t-Bu)3]PF6 (8). The reaction
between 4 (131 mg, 0.10 mmol) and t-BuNC (45 µL, 0.40 mmol) was
performed as described in section B.3 in the presence of an equivalent
of TlPF6 (35 mg, 0.10 mmol). After 24 h, the green reaction mixture
was filtered and the green filtrate worked up in the usual way to afford
green microcrystals of 8; yield, 92 mg (55%). Anal. Calcd for C68H73-
Cl5F6N3P5Re2 (i.e., 8‚CH2Cl2): C, 46.65; H, 4.20; N, 2.40. Found: C,
46.12; H, 4.22; N, 2.85. The presence of lattice CH2Cl2 was confirmed
Experimental Section
A. Starting Materials and General Procedures. The complexes
Re2Cl4(µ-dppm)2 (1),25 Re2Cl4(µ-dppE)2 (4),23 and Re2Cl4(µ-dcpm)2
(10)24 were prepared by the standard reported procedures, as was the
complex Re2Cl4(µ-dppm)2(CNXyl) (2),18 and the reagent TlO3SCF3.26
The neutral dirhenium(II,I) complex Re2Cl3(µ-dppm)2(CNXyl)3 (3) was
prepared from [Re2Cl3(µ-dppm)2(CNXyl)3]O3SCF3 by use of cobal-
tocene as the reducing agent and a procedure similar to that described
previously starting with the analogous [PF6]- salt.20 Samples of 2,6-
dimethylphenyl isocyanide (XylNC) were purchased from Fluka
Chemical Corp., whereas TlPF6, t-BuNC, and (η5-C5H5)2Co were
obtained from Strem Chemicals. These commercial reagents were used
as received. Solvents were obtained from commercial sources and were
deoxygenated by purging with dinitrogen before use. All reactions were
performed under an atmosphere of dinitrogen.
Routine IR spectra, NMR spectra, and cyclic voltammetric measure-
ments were determined as described previously.14 Elemental micro-
analyses were performed by Dr. H. D. Lee of the Purdue University
Microanalytical Laboratory.
CAUTION! Special precautions should be taken in handling
thallium(I) compounds, which are toxic.
B. Reactions of Re2Cl4(µ-dppE)2 (4) with Isocyanides. 1. Synthesis
of Re2Cl4(µ-dppE)2(CNXyl) (5). A quantity of 4 (65 mg, 0.05 mmol)
was dissolved in 30 mL of dichloromethane, and a solution of XylNC
(5.2 mg, 0.04 mmol) in dichloromethane (5 mL) was added dropwise
with stirring while maintaining a temperature of -10 °C. The reaction
mixture was stirred for a further 30 min and then allowed to warm to
room temperature, and the solvent was removed under reduced pressure.
The residue was washed with diethyl ether and dried. The 31P{1H} NMR
spectrum of the product (recorded in CDCl3) showed that it consists of
the desired complex 5 (see Results and Discussion), unreacted starting
material 4,23 and a small amount of an unidentified impurity. The
amount of the latter species increased when the reaction was performed
at room temperature and with an increase in the mole proportions of
XylNC used. This impurity exhibits an AA′BB′ pattern in its 31P{1H}
NMR spectrum with δ ) +26.8 and +8.8 for the centers of the two
multiplets.
1
by H NMR spectroscopy.
5. Synthesis of [Re2Cl3(µ-dppE)2(CN-t-Bu)2]O3SCF3 (9). A mixture
of the bis(t-butyl isocyanide) complex 6 (100 mg, 0.07 mmol) and TlO3-
SCF3 (24 mg, 0.07 mmol) in 30 mL of dichloromethane was stirred at
room temperature for 48 h. The resulting pale-green solution was filtered
to remove insoluble impurities, the volume of the filtrate was reduced
to about 3 mL, and diethyl ether (15 mL) was added to afford a pale-
yellow-green precipitate of 9, which was filtered off, washed with 20
mL of diethyl ether, and dried under reduced pressure; yield, 72 mg
(65%). Anal. Calcd for: C63H62Cl3F3N2O3P4Re2S: C, 47.68; H, 3.94.
Found: C, 47.45; H, 3.57.
The analogous green hexafluorophosphate salt [Re2Cl3(µ-dppE)2(CN-
t-Bu)2]PF6 was produced when TlPF6 was used in place of TlO3SCF3.
Its spectroscopic and electrochemical properties are essentially identical
to those of 6 with the exception of the presence of a band at 841(vs)
cm-1 in its IR spectrum, due to the [PF6]- anion, in place of a triflate
band at 1267(vs) cm-1
.
C. Reactions of Re2Cl4(µ-dcpm)2 (10) with Isocyanides. 1.
Synthesis of Re2Cl4(µ-dcpm)2(CNXyl) (11). A mixture of 10 (100
mg, 0.075 mmol) and XylNC (10 mg, 0.075 mmol) was stirred in
acetone (10 mL) for 1 day. The orange microcrystalline sample of 11
was collected by vacuum filtration, washed with acetone, and dried
under reduced pressure; yield, 0.076 g (69%). Anal. Calcd for C59H101
-
Cl4NP4Re2: C, 48.45; H, 6.96; Cl, 9.70. Found: C, 48.07; H, 7.28; Cl,
9.81.
The reaction of 11 with a further quantity of XylNC (1.5 equiv) in
acetone at room temperature for 5 days led to the formation of a purple
powder, which cyclic voltammetric measurements showed was a
mixture of products. We were unable to obtain the bis(xylyl isocyanide)
complex Re2Cl4(µ-dcpm)2(CNXyl)2.
2. Synthesis of Re2Cl4(µ-dcpm)2(CN-t-Bu)2 (12). A mixture of 10
(100 mg, 0.075 mmol) and t-BuNC (17 µL, 0.165 mmol) was stirred
in acetone (10 mL) for 1 day, and the green insoluble product, 12, was
collected by vacuum filtration, washed with acetone, and dried under
reduced pressure; yield, 0.089 g (79%). Anal. Calcd for C60H110Cl4N2P4-
Re2: C, 48.12; H, 7.40; Cl, 9.47. Found: C, 48.81; H, 7.71; Cl, 9.68.
D. Reactions of Re2Cl4(µ-dppm)2 (1) with t-BuNC. 1. Excess
t-BuNC. A mixture of 1 (128 mg, 0.10 mmol) and 4 equiv of t-BuNC
(45 µL, 0.40 mmol) in 30 mL of dichloromethane was stirred for 48 h
at room temperature. The reaction mixture was filtered, the volume of
the green filtrate was reduced to ca. 5 mL, and diethyl ether (40 mL)
was added to precipitate a green solid which was filtered off, washed
with 20 mL of diethyl ether, and dried under reduced pressure; yield,
98 mg (64%). The spectroscopic and electrochemical properties of this
product showed that it was the chloride salt [Re2Cl3(µ-dppm)2(CN-t-
Bu)3]Cl (13), by comparison with the properties of the previously
characterized [PF6]- salt.20 This compound resembled closely the
analogous dppE complex 7 (see section B.3).
2. Two Equivalents of t-BuNC. A stoichiometric quantity of t-BuNC
(22.5 µL, 0.20 mmol) was added to a solution of 1 (128 mg, 0.10 mmol)
in 30 mL of dichloromethane. The mixture was stirred at room
temperature and worked up after set periods of time (5 min, 30 min,
or 2 days) by evaporating the reaction mixture to dryness under reduced
pressure. In addition, the reaction was performed for 1 min, and the
product was precipitated by the addition of a large excess of diethyl
ether. The products from these four reactions were characterized by
2. Synthesis of Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6). A quantity of
t-BuNC (22.5 µL, 0.20 mmol) was added to a solution of 4 (131 mg,
0.10 mmol) in 30 mL of dichloromethane. The resulting mixture was
stirred for 24 h at room temperature and then filtered. The volume of
the brown solution was then reduced to about 3 mL, and an excess of
diethyl ether (20 mL) was added to give a brown precipitate of 6, which
was filtered off, washed with 20 mL of diethyl ether, and dried under
reduced pressure; yield, 108 mg (73%). This complex was recrystallized
from 1,2-C2H4Cl2/diethyl ether to afford brown crystals. Anal. Calcd
for C65H68Cl7N2P4Re2 (i.e., 6‚1.5C2H4Cl2): C, 48.14; H, 4.22; N, 1.73.
Found: C, 48.04; H, 4.21; N, 1.69. The presence of lattice 1,2-C2H4-
1
Cl2 was confirmed by H NMR spectroscopy.
3. Synthesis of [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7). The reaction
between 4 (200 mg, 0.15 mmol) and t-BuNC (68 µL, 0.60 mmol) was
performed in 40 mL of dichloromethane at room temperature for 48 h.
(21) Ebner, J. R.; Tyler, D. R.; Walton, R. A. Inorg. Chem. 1976, 15, 833.
(22) Barder, T. J.; Cotton, F. A.; Dunbar, K. R.; Powell, G. L.; Schwotzer,
W.; Walton, R. A. Inorg. Chem. 1985, 24, 2550.
(23) Kuang, S.-M.; Fanwick, P. E.; Walton, R. A. Inorg. Chim. Acta,
accepted for publication.
(24) Cotton, F. A.; Yokochi, A.; Siwajek, M. J.; Walton, R. A. Inorg. Chem.
1998, 37, 372.
(25) Cutler, A. R.; Derringer, D. R.; Fanwick, P. E.; Walton, R. A. J. Am.
Chem. Soc. 1988, 110, 5024.
(26) Woodhouse, M. E.; Lewis, F. D.; Marks, T. J. J. Am. Chem. Soc.
1982, 104, 5586.

2678 Inorganic Chemistry, Vol. 39, No. 12, 2000
Ding et al.
Table 1. Crystallographic Data for the Dirhenium Isocyanide Complexes Re2Cl4(µ-dppm)2(CNXyl)(2), Re2Cl4(µ-dppE)2(CN-t-Bu)2‚3C2H4Cl2
(6), [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7), Re2Cl4(µ-dcpm)2(CNXyl)‚(CH3)2CO (11), and Re2Cl4(µ-dcpm)2(CN-t-Bu)2‚CH2Cl2 (12)
2
6
7
11
12
empirical formula
fw
space group
a, Å
b, Å
C59H53Cl4NP4Re2
1414.10
P43212 (No. 96)
15.0903(4)
15.0903(4)
26.1521(7)
90
90
90
5955.3(5)
4
1.577
4.385
Mo KR (0.71073)
203
C68H76Cl10N2P4Re2
1772.20
P21/n (No. 14)
14.4494(2)
34.0915(5)
15.5458(2)
90
92.3135(7)
90
7651.6(3)
4
1.538
3.677
Mo KR (0.71073)
193
0.049
0.145
1.050
C67H71Cl4N3P4Re2
1556.44
P1h (No. 2)
12.679(4)
14.422(3)
19.997(4)
97.13
108.39(3)
90.07(3)
3439.8(13)
2
1.608
3.806
Mo KR (0.71073)
293
0.036
0.090
1.026
C62H107Cl4NOP4Re2
1520.66
P2h1/c (No. 14)
23.2164(5)
12.4916(3)
25.3930(5)
90
106.0421(11)
90
7077.5(5)
4
1.422
3.741
Mo KR (0.71073)
293
0.052
0.117
1.007
C61H112Cl6N2P4Re2
1582.60
P1h (No. 2)
13.9247(2)
15.0320(3)
16.9804(3)
87.0330(12)
77.0095(10)
79.2906(10)
3402.80(15)
2
1.544
3.970
Mo KR (0.71073)
295
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
F
calcd, g/cm3
µ, mm-1
radiation (λ,Å)
temp, K
R(Fo)a
0.071
0.178
1.161
2
0.026
0.060
1.044
Rw(Fo )b
2
GOF
a R ) ∑||Fo| - |Fc||/∑|Fo| with Fo > 2σ(Fo ). b Rw ) [∑w(|Fo | - |Fc2|)2/∑w|Fo | ]1/2
.
2
2
2 2
31P{1H} NMR spectroscopy on CD2Cl2 solutions. Further details are
presented under Results and Discussion.
thermal parameters. All the other nonhydrogen atoms were refined
anisotropically. The absolute structure was determined by refinement.
The enantiomer chosen has the absolute structure parameter of 0.020-
(15).
For the complex Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6), three 1,2-dichlo-
roethane molecules from the crystallization solvents were found
cocrystallized with 6 in the asymmetric unit. They were included in
the analysis and refined satisfactorily. All non-hydrogen atoms were
refined anisotropically.
No solvent of crystallization or disorder problems were encountered
in the structure solution of [Re2Cl3(µ-dppE)3(CN-t-Bu)3]Cl (7), and all
non-hydrogen atoms were refined anisotropically.
During the structure analysis of Re2Cl4(dcpm)2(CNXyl) (11), a
solvent molecule, acetone, was found to be cocrystallized with the
complex in the asymmetric unit. It was included in the analysis and
was refined satisfactorily. Another solvent molecule, which was badly
disordered, was removed by the use of the squeeze option in
PLATON.31 All nonhydrogen atoms were refined with anisotropic
thermal parameters.
E. X-ray Crystallography. Single crystals of Re2Cl4(µ-dppm)2-
(CNXyl) (2) were grown by the slow diffusion of diethyl ether into a
dichloromethane solution of the complex whereas single crystals of
Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6) and [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7)
were obtained by the slow diffusion of di-isopropyl ether vapor into
1,2-dichloroethane solutions of the complexes. With Re2Cl4(µ-dcpm)2-
(CNXyl) (11) and Re2Cl4(µ-dcpm)2(CN-t-Bu)2 (12), crystals were grown
by layering acetone on top of dichloromethane solutions of the
complexes at room temperature. The crystals were mounted on glass
fibers in random orientations. The data collections for 2, 6, 11, and 12
were performed on a Nonius KappaCCD diffractometer. For 7, intensity
data were collected on a four-circle Rigaku AFC7R diffractometer in
the variable ω-scan mode at the Department of Chemistry of the Chinese
University of Hong Kong. In all instances, Mo KR radiation (λ )
0.71073 Å) was used. The crystallographic data for all five compounds
are given in Table 1.
The structures of 6, 11, and 12 were solved by the use of the
Patterson heavy-atom method, whereas direct methods were used for
2 and 7 to reveal the positions of the Re atoms. The remaining
nonhydrogen atoms were located in succeeding difference Fourier
syntheses. The hydrogen atoms were placed in calculated positions
according to idealized geometries with C-H ) 0.95 Å, and U(H) )
1.3 Ueq(C) for 6, 11, and 12 and U(H) ) 1.2 Ueq(C) for 2 and 7. They
were included in the refinement but constrained to ride on the atom to
which they were bonded. Empirical absorption corrections were applied;
SCALEPACK27 was used in 2, 6, 11, and 12, whereas the method of
Kopfmann and Huber28 was used for 7. All the structures were refined
There are two-half independent molecules of Re2Cl4(µ-dcpm)2(CN-
t-Bu)2 (12) in the asymmetric unit as well as a molecule of dichlo-
romethane, one of the solvents used in recrystallization. All nonhy-
drogen atoms were refined anisotropically.
The largest remaining peak in the final difference maps of 2, 6, 7,
11, and 12 were 1.51, 1.52, 0.49, 1.14, and 1.10 e/Å3, respectively.
Results and Discussion
The clarification of the nature of the products that are formed
upon the reactions of Re2Cl4(µ-dppm)2, Re2Cl4(µ-dppE)2, and
Re2Cl4(µ-dcpm)2 with t-BuNC and XylNC focuses first on
establishing unambiguously the structure of the previously
isolated 1:1 complex Re2Cl4(µ-dppm)2(CNXyl) and, by implica-
tion, that of its t-BuNC analogue.18 The second part of this
presentation deals with the nature of 1:1, 1:2, and 1:3 isocyanide
complexes that are formed on reacting Re2Cl4(µ-dppE)2 and Re2-
Cl4(µ-dcpm)2 with t-BuNC and XylNC, and their comparison
with the related complexes of Re2Cl4(µ-dppm)2. The key aspects
of the reactions leading to the 1:2 and 1:3 complexes are shown
in Scheme 1.
A. The Structural Identity of Re2Cl4(µ-dppm)2(CNXyl)
(2). The spectroscopic and electrochemical properties of com-
plexes of the type Re2Cl4(µ-dppm)2(CNR) (R ) Me, t-Bu, or
Xyl) are very similar to one another and signal a close structural
relationship between all three complexes.18 IR spectroscopy
indicated the presence of isomers in the solid state and in
2
in full-matrix least squares where the function minimized was ∑w(|Fo|
- |Fc| )2 and the weighting factor w has the form w ) 1/[σ2(Fo ) +
2
2
(AP)2 + BP], where P ) (Fo + 2Fc2)/3. The calculations were
2
performed on an AlphaServer 2000 for 6, 11, and 12 and a PC29 for 2
and 7. The final refinements were performed by the use of the program
SHELXL-97.30
A disorder problem was encountered during the refinement of the
structure of Re2Cl4(dppm)2(CNXyl) (2). There was only half an
independent molecule in the asymmetric unit. The XylNC ligand was
disordered with the terminal chlorine atom Cl(2). This disorder is
generated by a 2-fold axis through the bridging chlorine atom Cl(12)
and the midpoint of the Re-Re bond. Both Cl(2) and the XylNC ligand
were set at 50% occupancy. The xylyl group was refined with isotropic
(27) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307.
(28) Kopfmann, G.; Huber, R. Acta Crystallogr. 1968, A24, 348.
(29) Farrugia, L. J. WinGX-A Windows Program for Crystal Structure
Analysis; University of Glasgow: Glasgow, U.K., 1998.
(30) Sheldrick, G. M. SHELXL97. A Program for Crystal Structure
Refinement; University of Gottingen: Gottingen, Germany, 1997.
(31) Sluis, P. V. D.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194.

Reactions of Dirhenium(II) Complexes Re2X4(µ-dppm)2
Inorganic Chemistry, Vol. 39, No. 12, 2000 2679
Scheme 1. 1:2 and 1:3 Isocyanide Complexes Derived
from Re2Cl4(µ-LL)2 (LL ) dppm, dppE, or dcpm)a
Figure 1. ORTEP32 representation of the structure of the dirhenium
complex Re2Cl4(µ-dppm)2(CNXyl) (2). This representation shows one-
half of the disorder involving the terminal XylNC and Cl ligands which
are trans to the bridging Cl ligand. The thermal ellipsoids are drawn
at the 50% probability level, except for the phenyl group atoms of the
dppm ligands and the xylyl group atoms of the XylNC ligands which
are circles of arbitrary radius.
a (a) See also data reported in ref 20. (b) This compound was
identified in solution only. (c) Reaction performed for PP ) dppm or
dppE only.
solutions of these complexes in organic solvents; these isomers
contain terminally bound RNC ligands. A partial crystal structure
determination on Re2Cl4(µ-dppm)2(CN-t-Bu) showed it to have
the A-frame-like structure Cl2Re(µ-Cl)(µ-dppm)2ReCl(CN-t-Bu)
with a Re-Re distance of ca. 2.30 Å.18 This structure is
represented in I. A disorder involving the terminal t-BuNC and
Table 2. Important Bond Distances (Å) and Bond Angles (deg) for
the Complex Re2Cl4(µ-dppm)2(CNXyl) (2)a
Distances
2.3195(9)
1.90(3)
2.533(3)
2.539(3)
Re-Re′
Re′-Cl(2)
Re-P(1)
Re-P(2)
2.342(7)
2.461(3)
2.431(3)
Re-C(1)
Re-Cl(1)
Re-Cl(12)
Angles
Re′-Re-C(1)
Re-Re′-Cl(2)
P(1)-Re-P(2)
C(1)-Re-Cl(1)
Re′-Re-Cl(1)
87.9(8)
114.2(3)
Re′-Re-Cl(12)
62.82(4)
Cl(2)-Re′-Cl(12) 173.65(19)
163.78(10) Cl(1)-Re-Cl(12)
88.11(8)
54.36(8)
175(3)
121.5(8)
150.00(7)
C(1)-Re-Cl(12) 150.3(8)
Re-Cl(12)-Re′
N-C(1)-Re
Cl ligands trans to the Cl-bridge frustrated our attempts to
adequately solve the structure.18 This same type of disorder has
been found in the fully refined structures of the analogous
carbonyl complexes Re2X4(µ-dppm)2(CO) (X ) Cl3 or Br14),
and in the structure determination of Re2Cl4(µ-dppm)2(CNXyl)
(2) as described herein. An ORTEP32 representation of the
structure of 2 is shown in Figure 1. Important structural
parameters are given in Table 2. The disorder is generated by
a 2-fold axis that passes through the bridging Cl atom Cl(12)
and bisects the Re-Re bond. The Re-Re distance for 2 of
2.3195(9) Å is similar to the analogous triply bonded Re-Re
distances for Re2Cl4(µ-dppm)2(CO)3 and Re2Br4(µ-dppm)2-
(CO),14 which are 2.338(1) Å and 2.336(1) Å, respectively. The
slightly shorter bond for 2 accords with the weaker π-accepting
ability of XylNC compared with CO and, therefore, a diminished
weakening of the Re-Re π and/or δ bonding components
through RefRNC (π*) back-bonding (relative to RefCO(π*)).
B. The Reactions of Re2Cl4(µ-dppE)2 (4) and Re2Cl4(µ-
dcpm)2 (10) with Isocyanides. This study was prompted by
our interest in comparing the reactivity and redox properties of
the previously described complex Re2Cl4(µ-dppm)2 (1)25,33 with
a Numbers in parentheses are estimated standard deviations in the
least significant digits. The unlabeled Re atom in Figure 1 is denoted
Re′ in this table.
those of the more recently synthesized complex Re2Cl4(µ-dcpm)2
(10).24 We had anticipated some differences in reactivity because
of the greater basicity of the dcpm ligand compared with dppm.
In contrast, a close similarity between the reactivity of 1 and
its dppE analogue Re2Cl4(µ-dppE)2 (4) was to be expected.23
Preliminary experiments demonstrated that the spectroscopic
and electrochemical properties of 1:1 complex Re2Cl4(µ-dppE)2-
(CNXyl) (5) resembled those of Re2Cl4(µ-dppm)2(CNXyl) (2).
The important spectroscopic data for 5 are presented in Table
3. A cyclic voltammogram (CV), recorded on a solution of 5
in 0.1 M n-Bu4NPF6-CH2Cl2, shows a reversible oxidation at
E1/2 ) +0.33 V and an irreversible oxidation at Ep,a ) +1.40
V vs Ag/AgCl. The corresponding CV of 2 shows processes at
+0.31 V and +1.27 V vs Ag/AgCl.18 This similarity implies
that these complexes possess, not unexpectedly, a close structural
relationship. Both display AA′BB′ patterns in their 31P{1H}
NMR spectra. Note that the presence of two terminal ν(CN)
modes in the IR spectrum of 5 (Table 3), just as observed
previously for 2,18 signifies the presence of two isomers in the
solid state, one of which possesses structure I.
(32) (a) Johnson, C. K. ORTEP II, Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976. (b) Farrugia, L. J. J. Appl.
Crystallogr. 1997, 565.
(33) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms,
2nd ed.; Oxford University Press: Oxford, U.K.; 1993; Chapter 2 and
references therein.
Although the µ-dcpm complex 10 reacts with 1 equiv of
XylNC in acetone to afford the 1:1 complex Re2Cl4(µ-dcpm)2-

2680 Inorganic Chemistry, Vol. 39, No. 12, 2000
Ding et al.
Table 3. Selected Spectroscopic Data for Isocyanide Complexes of Dirhenium(II)
IR, cm-1 a
chem shift, δb
complex
no.
v(CN) and v(CO)
31P{1H} NMR
Re2Cl4(µ-dppE)2(CNXyl)
5
6
7
8
9
11
12
13
2070(s), ∼2000(sh)
+16.8(m), +9.8(m)c
+10.8(s)
Re2Cl4(µ-dppE)2(CN-t-Bu)2
[Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl
[Re2Cl3(µ-dppE)2(CN-t-Bu)3]PF6
[Re2Cl3(µ-dppE)2(CN-t-Bu)2]O3SCF3
Re2Cl4(µ-dcpm)2(CNXyl)
2103(vs)
2170(m-w), 2141(vs), 2106(s)
2176(m-w), 2142(vs), 2110(s)
2163(s), 2105(sh)
2036(s), 2004(m)
2096(s), 2065(vs)
+10.2(m), +4.3(m)
+10.2(m), +4.3(m)
+7.3(m), +1.5(m)
-15.0(m)
Re2Cl4(µ-dcpm)2(CN-t-Bu)2
[Re2Cl3(µ-dppm)2(CN-t-Bu)3]Cl
-10.0(s,br)
-5.6(m), -12.3(m)
2142(vs), 2111(s)
a IR spectra recorded as Nujol mulls or KBr pellets. All compounds that contain the triflate anion have a strong band at ∼1270 cm-1. Abbreviations:
s ) strong, m ) medium, w ) weak, br ) broad, sh ) shoulder. b NMR spectra recorded on CD2Cl2 solutions unless otherwise indicated.
Abbreviations: s ) singlet, m ) multiplet. For AA′BB′ patterns, the centers of the two multiplets are given. c Spectrum recorded in CDCl3.
Table 4. Important Bond Distances (Å) and Bond Angles (deg) for
the Complex Re2Cl4(µ-dcpm)2(CNXyl)‚(CH3)2CO (11)a
Distances
Re(1)-Re(2)
Re(1)-C(10)
Re(1)-Cl(11)
Re(1)-P(1)
2.2887(3)
1.952(6)
2.4331(14)
2.4923(14)
2.5142(14)
2.6165(15)
Re(2)-Cl(21)
Re(2)-Cl(22)
Re(2)-P(4)
2.3652(15)
2.3750(14)
2.4414(14)
2.4704(14)
1.190(7)
Re(2)-P(2)
Re(1)-P(3)
N(10)-C(10)
N(10)-C(11)
Re(1)-Cl(12)
1.416(7)
Angles
89.14(15) P(3)-Re(1)-Cl(12)
C(10)-Re(1)-Re(2)
87.20(5)
C(10)-Re(1)-Cl(11) 162.00(16) Re(1)-Re(2)-Cl(21) 113.81(4)
Re(2)-Re(1)-Cl(11) 108.82(4) Re(1)-Re(2)-Cl(22) 109.33(4)
C(10)-Re(1)-P(1)
Re(2)-Re(1)-P(1)
Cl(11)-Re(1)-P(1)
C(10)-Re(1)-P(3)
Re(2)-Re(1)-P(3)
Cl(11)-Re(1)-P(3)
P(1)-Re(1)-P(3)
91.05(16) Cl(21)-Re(2)-Cl(22) 136.71(6)
89.72(4) Re(1)-Re(2)-P(4)
90.21(5) Cl(21)-Re(2)-P(4)
90.44(16) Cl(22)-Re(2)-P(4)
95.79(4) Re(1)-Re(2)-P(2)
86.69(5) Cl(21)-Re(2)-P(2)
174.31(5) Cl(22)-Re(2)-P(2)
93.90(4)
88.64(5)
84.96(5)
99.10(4)
88.12(5)
88.64(5)
166.81(5)
C(10)-Re(1)-Cl(12) 77.62(16) P(4)-Re(2)-P(2)
Re(2)-Re(1)-Cl(12) 166.47(4) N(10)-C(10)-Re(1) 175.5(5)
Cl(11)-Re(1)-Cl(12) 84.49(5) C(10)-N(10)-C(11) 169.2(6)
Figure 2. ORTEP32 representation of the structure of the dirhenium
complex Re2Cl4(µ-dcpm)2(CNXyl) (11). The thermal ellipsoids are
drawn at the 50% probability level except for the cyclohexyl group
atoms of the dcpm ligands and the xylyl group atoms of the XylNC
ligands which are circles of arbitrary radius.
P(1)-Re(1)-Cl(12)
87.76(5)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
are, as expected, longer than the distances Re(2)-Cl(21) and
Re(2)-Cl(22). The distance of 2.4331(14) Å for Re(1)-Cl-
(11) is ca. 0.05 Å longer than both of the Re(2)-Cl distances,
partly because of the trans effect of the XylNC ligand. The
distance Re(1)-Cl(12) of 2.6161(15) Å is the longest for all
the Re-Cl bonds, and is typical of axial Re-Cl coordination
in dirhenium(II) complexes.5,14,34 This relatively weak bond is
characterized by a significant deviation from linearity with the
RetRe bond; the angle Re(2)-Re(1)-Cl(12) is 166.47(4)°.
This compound possesses a partially staggered structure in the
solid state as reflected by the torsional angles P(1)-Re(1)-
Re(2)-P(2), P(3)-Re(1)-Re(2)-P(4), C(11)-Re(1)-Re(2)-
Cl(21), and C(10)-Re(1)-Re(2)-Cl(22) which are 35.9°, 32.3°,
34.1°, and 36.6°, respectively.
Like the other 1:1 complexes with XylNC, complex 11 shows
two terminal ν(CN) modes in its IR spectrum and an AA′BB′
pattern in its 31P{1H} NMR spectrum, although a clear resolution
into two multiplets does not occur, and a single broad multiplet
is observed instead (see Table 3). The CV of 11 (recorded in
0.1 M n-Bu4NPF6-CH2Cl2) resembles those for 218 and 5 (Table
3) in showing two one-electron oxidations, with E1/2 values of
+1.29 V and +0.11 V vs Ag/AgCl; the ∆Ep ()Ep,a - Ep,c)
values are 75 and 70 mV, respectively.
(CNXyl) (11), the solid-state structure of this compound is
different from that of 2 and, by implication, from its aforemen-
tioned dppE analogue 5. The ORTEP32 representation of the
structure of 11 is shown in Figure 2, and important bond
distances and angles are given in Table 4. This structure is
related to that of 2 (see Figure 1 and structure I) by the breaking
of the µ-Cl bridge of 2 and the simple rotation of the [ReCl2-
(CNR)] unit so that it assumes the relationship to the adjacent
[ReCl2] unit that is shown in structure II. This is presumably a
relatively low-energy process and could account for the presence
of two isomers. It is tempting to propose that the same pair of
isomers are present in samples of 2, 5, and 11 (i.e., structures
I and II), but that the structure of isomer I has been determined
in 2, whereas isomer II is the one characterized from the crystals
of 11. Supporting this possibility is our earlier discovery that
the monocarbonyl complexes Re2X4(µ-dppm)2(CO) (X ) Cl,
Br)3,14 have two structural isomers, one of which has the same
structure as that of I, whereas the other has an open structure
like that of II, with terminal halide and CO ligands; because of
a disorder problem the exact location of the CO ligand could
not be determined.14
The Re-Re distance of 2.2887(3) Å for the unbridged
isomeric form 11 is similar to that of 2, supporting the presence
of a Re-Re multiple bond in both instances. The Re-Cl
distances at the higher coordination number Re center Re(1)
(34) Wu, W.; Subramony, J. A.; Fanwick, P. E.; Walton, R. A. Inorg. Chem.
1996, 35, 6784.

Reactions of Dirhenium(II) Complexes Re2X4(µ-dppm)2
Inorganic Chemistry, Vol. 39, No. 12, 2000 2681
Table 5. Important Bond Distances (Å) and Bond Angles (deg) for
the Complex Re2Cl4(µ-dppE)2(CN-t-Bu)2‚3C2H4Cl2 (6)a
Distances
Re(1)-Re(2)
Re(1)-C(10)
Re(1)-Cl(11)
Re(1)-P(1)
2.3497(4)
2.016(8)
2.4512(17)
2.4520(19)
2.4605(19)
2.5779(18)
2.016(7)
Re(2)-Cl(22)
2.4330(17)
2.4696(19)
2.4797(19)
2.5793(19)
1.154(9)
Re(2)-P(4)
Re(2)-P(2)
Re(2)-Cl(21)
C(10)-N(10)
C(20)-N(20)
Re(1)-P(3)
Re(1)-Cl(12)
Re(2)-C(20)
1.154(9)
Angles
88.3(2) Re(1)-Re(2)-Cl(22) 106.20(5)
C(10)-Re(1)-Re(2)
C(10)-Re(1)-Cl(11) 166.4(2)
C(20)-Re(2)-P(4)
90.1(2)
97.51(5)
88.54(6)
85.0(2)
94.91(5)
93.11(6)
166.48(6)
Re(2)-Re(1)-Cl(11) 104.84(5) Re(1)-Re(2)-P(4)
C(10)-Re(1)-P(1)
Re(2)-Re(1)-P(1)
Cl(11)-Re(1)-P(1)
C(10)-Re(1)-P(3)
Re(2)-Re(1)-P(3)
Cl(11)-Re(1)-P(3)
P(1)-Re(1)-P(3)
89.55(19) Cl(22)-Re(2)-P(4)
99.90(5) C(20)-Re(2)-P(2)
91.69(6) Re(1)-Re(2)-P(2)
90.1(2)
Cl(22)-Re(2)-P(2)
94.61(5) P(4)-Re(2)-P(2)
85.32(6) C(20)-Re(2)-Cl(21) 78.2(2)
165.47(7) Re(1)-Re(2)-Cl(21) 165.06(5)
C(10)-Re(1)-Cl(12) 80.0(2)
Re(2)-Re(1)-Cl(12) 167.57(5) P(4)-Re(2)-Cl(21)
Cl(11)-Re(1)-Cl(12) 86.64(6) P(2)-Re(2)-Cl(21)
Cl(22)-Re(2)-Cl(21) 87.59(6)
Figure 3. ORTEP32 representation of the structure of the dirhenium
complex Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6). The thermal ellipsoids are
drawn at the 50% probability level except for the phenyl group atoms
of the dppE ligands which are circles of arbitrary radius.
76.73(6)
89.93(6)
P(1)-Re(1)-Cl(12)
P(3)-Re(1)-Cl(12)
C(20)-Re(2)-Re(1)
84.24(6) N(10)-C(10)-Re(1) 175.0(7)
81.39(6) N(20)-C(20)-Re(2) 173.2(6)
88.1(2)
C(10)-N(10)-C(11) 174.7(8)
C(20)-N(20)-C(21) 167.4(7)
C(20)-Re(2)-Cl(22) 165.7(2)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Table 6. Important Bond Distances (Å) and Bond Angles (deg) for
the Complex Re2Cl4(µ-dcpm)2(CN-t-Bu)2‚CH2Cl2 (12)a
Distances
Re(1)-Re(1)′
Re(1)-C(10)
Re(1)-Cl(12)
Re(1)-P(2)
2.3797(3)
1.989(4)
2.4451(10)
2.4912(10)
2.5096(10)
2.6113(10)
1.156(5)
Re(2)-Re(2)′
Re(2)-C(20)
Re(2)-Cl(22)
Re(2)-P(3)
2.3804(3)
1.979(4)
2.4555(9)
2.4988(10)
2.5076(9)
2.5945(11)
1.160(5)
Re(1)-P(1)
Re(2)-P(4)
Re(1)-Cl(11)
C(10)-N(10)
Re(2)-Cl(21)
C(20)-N(20)
Angles
C(10)-Re(1)-Re(1)′ 86.57(11) C(20)-Re(2)-Re(2)′ 84.38(11)
C(10)-Re(1)-Cl(12) 164.53(11) C(20)-Re(2)-Cl(22) 164.50(12)
Re(1)′-Re(1)-Cl(12) 108.60(3) Re(2)′-Re(2)-Cl(22) 111.12(3)
C(10)-Re(1)-P(2)
Re(1)′-Re(1)-P(2)
Cl(12)-Re(1)-P(2)
C(10)-Re(1)-P(1)
93.12(11) C(20)-Re(2)-P(3)
95.65(2) Re(2)′-Re(2)-P(3)
88.49(3) Cl(22)-Re(2)-P(3)
90.28(11) C(20)-Re(2)-P(4)
92.51(11)
97.00(2)
86.12(3)
92.70(11)
98.58(2)
84.82(3)
163.98(3)
Figure 4. ORTEP32 representation of the structure of one of the
independent molecules of the dirhenium complex Re2Cl4(µ-dcpm)2(CN-
t-Bu)2 (12). The unlabeled Re atom is Re(2)′. The thermal ellipsoids
are drawn at the 50% probability level except for the cyclohexyl group
atoms of the dcpm ligands which are circles of arbitrary radius.
Re(1)′-Re(1)-P(1) 101.02(2) Re(2)′-Re(2)-P(4)
Cl(12)-Re(1)-P(1)
P(2)-Re(1)-P(1)
C(10)-Re(1)-Cl(11) 80.70(11) C(20)-Re(2)-Cl(21) 80.34(12)
Re(1)′-Re(1)-Cl(11) 166.36(3) Re(2)′-Re(2)-Cl(21) 164.60(3)
Cl(12)-Re(1)-Cl(11) 84.41(4) Cl(22)-Re(2)-Cl(21) 84.19(4)
P(2)-Re(1)-Cl(11)
P(1)-Re(1)-Cl(11)
N(10)-C(10)-Re(1) 174.1(4) N(20)-C(20)-Re(2) 176.0(4)
C(10)-N(10)-C(11) 169.8(4) C(20)-N(20)-C(21) 172.2(4)
a Data for the two independent molecules in the unit cell are
compared. Numbers in parentheses are estimated standard deviations
in the least significant digits.
83.97(3) Cl(22)-Re(2)-P(4)
163.15(3) P(3)-Re(2)-P(4)
Several attempts to isolate a pure sample of the 1:2 complex
Re2Cl4(µ-dcpm)2(CNXyl)2 were unsuccessful.35 Similarly, we
had not obtained the analogous 1:2 complexes Re2Cl4(µ-dppm)2-
(CNR)2 (R ) Xyl or t-Bu) in an earlier study,20 although the
1:3 species [Re2Cl3(µ-dppm)2(CNR)3]+ were isolated; the latter
will be discussed in more detail later in this section. However,
with the use of t-butyl isocyanide we were able to obtain the
bis-isocyanide complexes Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6) and
Re2Cl4(µ-dcpm)2(CN-t-Bu)2 (12) in ca. 75% yield. The spec-
troscopic properties of 6 and 12 established the presence of
terminal t-BuNC ligands and a symmetric structure as demon-
strated by a singlet in the 31P{1H} NMR spectra (Table 3). These
conclusions were confirmed by single-crystal X-ray structure
demonstrations of both complexes. The ORTEP32 representa-
80.26(3) P(3)-Re(2)-Cl(21)
84.02(3) P(4)-Re(2)-Cl(21)
81.89(3)
84.08(3)
tions of the structures are shown in Figures 3 and 4, and
important bond distances and angles are given in Tables 5 and
6. Both complexes possess the same open bioctahedral structure
with axial Re-Cl bonds and an anti-arrangement of t-BuNC
ligands. These two structures resemble those of the triply bonded
dirhenium(II) bioctahedral complexes of the type Re2X4(µ-
dppm)2(CO)(CN-t-Bu) (X ) Cl, Br)3,14 which have this same
type of bioctahedral structure.
(35) Siwajek, M. J., Ph.D. Thesis, Purdue University, 1999.

2682 Inorganic Chemistry, Vol. 39, No. 12, 2000
Ding et al.
The Re-Re distances for 6 and 12 are 2.3497(4) Å and
2.3797(3) Å, respectively, and closely resemble the distance of
2.3805(14) Å found in the structure of Re2Br4(µ-dppm)2(CO)-
(CN-t-Bu).14 As expected, the axial Re-X bonds (those collinear
with RetRe) are longer than the corresponding equatorial
Re-X bonds by 0.13-0.17 Å. The Re-Re-Clax bond angles,
which are in the range 164.6-167.6° (Tables 5 and 6) for these
two complexes, are similar to the angle of 166.5° found in the
structure of compound 11 (Table 4). Because the two crystal-
lographically independent dirhenium molecules in the crystal
of 12 are located about inversion centers, they are each required
to possess rigorously eclipsed rotational geometries. No such
requirement exists in the crystal of 6, and the molecule in the
asymmetric unit has a partially staggered rotational geometry
with values for the torsional angles P(1)-Re(1)-Re(2)-P(2),
P(3)-Re(1)-Re(2)-P(4), Cl(11)-Re(1)-Re(2)-C(20), and
Cl(10)-Re(1)-Re(2)-Cl(22) of 18.2°, 24.3°, 27.8°, and 23.6°,
respectively.
this end, we reinvestigated the reaction between Re2Cl4(µ-
dppm)2 (1) and t-BuNC in dichloromethane in the absence of
TlO3SCF3 or TlPF6. Under these conditions, and with the
presence of an excess of t-BuNC (four or more equivalents),
the chloride salt [Re2Cl3(µ-dppm)2(CN-t-Bu)3]Cl (13) was
formed; its spectroscopic properties, which are given in Table
3, are essentially identical with those of the previously isolated
[PF6]- salt.20 Compound 13 will be considered in more detail
later in this section. We next studied the reactions between 1
and 2 equiv of t-BuNC in dichloromethane as a function of
time; see Experimental section D.2 for details of the procedures
that were followed. In all instances, the nature of the product-
(s) was monitored by 31P{1H} NMR spectroscopy on CD2Cl2
solutions. When t = 1 min, the NMR spectrum showed the
presence of only one product that exhibited a symmetrical
AA′BB′ pattern with multiplets centered at δ ) -5.9 and δ )
-10.0. This is the same 1:1 complex Re2Cl4(µ-dppm)2(CN-t-
Bu) we had isolated in an earlier study.18 With an increase in
time (t = 5 min), the spectrum consisted of an AA′BB′ pattern
caused by an unknown species (multiplets centered at δ ) -9.7
and δ ) -13.8) along with a singlet (δ ) -9.72), which
overlapped the downfield of these two multiplets; this resonance
is assigned to the symmetrical 1:2 complex Re2Cl4(µ-dppm)2-
(CN-t-Bu)2. With a further increase in time (t ) 30 min) the
resonance caused by Re2Cl4(µ-dppm)2(CN-t-Bu)2 remained
unchanged, whereas the AA′BB′ pattern caused by the unknown
species decreased in intensity as a new AA′BB′ pattern (δ )
-5.7 and δ ) -12.4) emerged as a result of the formation of
the tris-isocyanide complex cation [Re2Cl3(µ-dppm)2(CN-t-
Bu)3]+.20 At t ) 2 days, the spectrum showed the presence of
Re2Cl4(µ-dppm)2(CN-t-Bu)2 along with some [Re2Cl3(µ-dppm)2-
(CN-t-Bu)3]+. These experiments provide good evidence for the
formation of Re2Cl4(µ-dppm)2(CN-t-Bu)2 and also demonstrate
the ease with which the tris-isocyanide cation is generated.
Despite the close structural relationship established between
6 and 12, these complexes display some differences in their
CV properties (recorded on solutions in 0.1 M n-Bu4NPF6-
CH2Cl2). The single scan CV of 6 showed broad waves at Ep,a
) +0.72 V and Ep,c ) -1.24 V vs Ag/AgCl, whereas the CV
of 12 showed major processes at E1/2(ox) ) +1.30 V (∆Ep )
60 mV) and Ep,c ) -1.19 V vs Ag/AgCl, along with coupled
processes at Ep,a ) +0.96 V and Ep,c ) +0.41 V vs Ag/AgCl.
As mentioned previously, we had not isolated the analogous
bis-isocyanide complex Re2Cl4(µ-dppm)2(CN-t-Bu)2 in our
earlier study of the reactions between this dirhenium(II) complex
and t-BuNC,20 because of the reaction conditions we used, in
which KPF6 or TlPF6 were added to the reaction mixtures. In
the presence of these reagents, the 1:2 complex Re2Cl4(µ-
dppm)2(CN-t-Bu)2 would have converted to [Re2Cl3(µ-dppm)2-
(CN-t-Bu)2]PF6 because of the labilization of one of the Re-
Cl bonds.20 This was confirmed in the present study by the
reactions of Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6), a close analogue
of the unknown complex Re2Cl4(µ-dppm)2(CN-t-Bu)2, with
TlO3SCF3 and TlPF6, which produce a complex of stoichiometry
[Re2Cl3(µ-dppE)2(CN-t-Bu)2]Y (Y ) O3SCF3 or PF6). The spec-
troscopic properties of the triflate salt 9 (given in Table 3) close-
ly resemble those of the green isomeric form of [Re2Cl3(µ-
As we have established previously,20 and confirmed in this
study (see above), the reaction of an excess of t-BuNC with
Re2Cl4(µ-dppm)2 affords the complex [Re2Cl3(µ-dppm)2(CN-
t-Bu)3]Cl. Salts of the analogous XylNC-containing complex
[Re2Cl3(µ-dppm)2(CNXyl)3]+ have also been isolated,20 and it
is clear from differences between the spectroscopic and elec-
trochemical properties of the t-BuNC and XylNC species that
they possess different structures.20 Previous attempts to obtain
X-ray quality crystals of these complexes were unsuccess-
ful.20
20
dppm)2(CN-t-Bu)2]PF6 which shows ν(CN) modes in its IR
spectrum at 2160(s) and 2127(m) cm-1, and an AA′BB′ pattern
in its 31P{1H} NMR spectrum. The CV of a 0.1 M n-Bu4NPF6-
CH2Cl2 solution of 9 displays a one-electron oxidation at E1/2(ox)
) +0.64 V and an irreversible reduction process at Ep,c ) -1.31
V vs Ag/AgCl. These processes can be contrasted with those
at E1/2 ) +0.65 V and Ep,c ) -1.64 V vs Ag/AgCl in the CV
of [Re2Cl3(µ-dppm)2(CN-t-Bu)2]PF6. Conductivity measure-
ments on a 1.0 × 10-3 M solution of 9 in acetonitrile confirmed
that it behaved as a 1:1 electrolyte (Λm ) 136 Ω-1 cm2 mol-1).
Based on the aforementioned properties, we propose that 9 has
a structure similar to that of its dppm analogue, structure III.
In the present study we find that the complex Re2Cl4(µ-dppE)2
(4) reacts with t-BuNC to afford the tris-isocyanide complexes
[Re2Cl3(µ-dppE)2(CN-t-Bu)3]Y, where Y ) Cl (7) or PF6 (8),
thereby establishing the similarity of this system to Re2Cl4(µ-
dppm)2. These two complexes possess spectroscopic properties
very similar to one another (Table 3) and to [Re2Cl3(µ-dppm)2-
20
(CN-t-Bu)3]PF6 and [Re2Cl3(µ-dppm)2(CN-t-Bu)3]Cl (13)
(Table 3). Therefore, we are confident in assigning them similar
structures. The IR spectra of these pairs of dppm and dppE
complexes show ν(CN) modes which are characteristic of
terminally bound t-BuNC ligands, an interpretation that is
confirmed by a single-crystal X-ray structure determination of
[Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7). This complex possesses an
open bioctahedral structure which is related to that of the bis-
isocyanide complex Re2Cl4(µ-dppE)2(CN-t-Bu)2 (6) by the
replacement of a Cl ligand trans to one of the t-BuNC ligands
by another t-BuNC ligand, thereby generating a dirhenium(II)
cationic species. An ORTEP32 representation of this structure
is shown in Figure 5 and important bond distances and angles
are given in Table 7.
In view of the preceding observations, it seemed very likely
that Re2Cl4(µ-dppm)2(CN-t-Bu)2 could in fact be isolated. To

Reactions of Dirhenium(II) Complexes Re2X4(µ-dppm)2
Inorganic Chemistry, Vol. 39, No. 12, 2000 2683
[2.3497(4) Å]. This distance is also similar to that of the RetRe
bond in the triflate salt of the isomeric form of the cation [Re2-
Cl3(µ-dppm)2(CO)(CNXyl)2]+ [2.3833(8) Å]5 in which there are
two XylNC ligands trans to one another and the CO is bound
to the adjacent Re atom. As is typical for this type of dirhenium
complex, the axial Re-Cl bonds of 7 [Re(1)-Cl(1) and Re-
(2)-Cl(3)] are longer than the equatorial bond Re(2)-Cl(2) by
ca. 0.14 Å. The angles Re(1)-Re(2)-Cl(3) ) 164.83(7)° and
Re(2)-Re(1)-Cl(1) ) 171.74(10)° show some deviation from
linearity, whereas the three Re-C-N angles are within the
narrow range 172-175°, signifying the absence of a significant
degree of RefCNR(π*) back-bonding. As is the case with the
bis-isocyanide complex 6, the tris-isocyanide 7 has a partially
staggered rotational geometry with torsional angles P(1)-Re-
(1)-Re(2)-P(2), P(3)-Re(1)-Re(2)-P(4), C(20)-Re(1)-Re-
(2)-Cl(2), and C(10)-Re(1)-Re(2)-C(30) of 18.8°, 24.5°,
28.1°, and 28.6°, respectively.
With the structures of the [Re2Cl3(µ-dppE)2(CN-t-Bu)3]+ and
[Re2Cl3(µ-dppm)2(CN-t-Bu)3]+ firmly established, it is now
appropriate to consider the structure of the previously reported
XylNC complex [Re2Cl3(µ-dppm)2(CNXyl)3]+.20 Although at-
tempts to structurally characterize the Cl-, [PF6]-, and [O3SCF3]-
salts of this cation have so far been unsuccessful, we were able
to obtain X-ray quality single crystals of the neutral paramag-
netic congener Re2Cl3(µ-dppm)2(CNXyl)3 (3). This compound
was obtained by the one-electron reduction of the triflate salt
through the use of cobaltocene in acetone. Crystals were grown
by the slow diffusion of diethyl ether into a dichloromethane
solution of the complex. Although the structure was that of the
edge-sharing bioctahedron (XylNC)ClRe(µ-Cl)(µ-CNXyl)(µ-
dppm)2ReCl(CNXyl), with an all-cis arrangement of XylNC
ligands and a Re-Re distance of 2.73 Å, the poor quality of
the data set prevented us from obtaining a fully refined,
publishable structure. However, the present study has enabled
us to clarify the nature of the structural difference that exists
between the pair [Re2Cl3(µ-dppm)2(CN-t-Bu)3]+ and [Re2Cl3-
(µ-dppm)2(CNXyl)3]+.20
Figure 5. ORTEP32 representation of the structure of the dirhenium
cation in the complex [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7). The thermal
ellipsoids are drawn at the 50% probability level except for the phenyl
group atoms of the dppE ligands and the tert-butyl group atoms of the
t-BuNC ligands which are circles of arbitrary radius.
Table 7. Important Bond Distances (Å) and Bond Angles (deg) for
the Complex [Re2Cl3(µ-dppE)2(CN-t-Bu)3]Cl (7)a
Distances
Re(1)-Re(2)
Re(1)-C(20)
Re(1)-C(10)
Re(1)-P(1)
Re(1)-P(3)
Re(1)-Cl(1)
Re(2)-C(30)
2.3451(10)
2.054(12)
2.099(14)
2.468(4)
2.498(4)
2.571(4)
2.05(2)
Re(2)-Cl(2)
Re(2)-P(4)
Re(2)-P(2)
Re(2)-Cl(3)
C(10)-N(10)
C(20)-N(20)
C(30)-N(30)
2.427(3)
2.448(4)
2.477(4)
2.566(3)
1.16(2)
1.15(2)
1.13(2)
Angles
C(20)-Re(1)-C(10) 163.6(7)
C(20)-Re(1)-Re(2) 89.5(4)
C(10)-Re(1)-Re(2) 106.7(4)
Re(1)-Re(2)-P(2)
Cl(2)-Re(2)-P(2)
P(4)-Re(2)-P(2)
C(30)-Re(2)-Cl(3)
97.51(8)
93.48(12)
166.30(12)
75.4(4)
C(20)-Re(1)-P(1)
C(10)-Re(1)-P(1)
Re(2)-Re(1)-P(1)
C(20)-Re(1)-P(3)
C(10)-Re(1)-P(3)
Re(2)-Re(1)-P(3)
P(1)-Re(1)-P(3)
86.5(4)
94.0(5)
Re(1)-Re(2)-Cl(3) 164.83(7)
Concluding Remarks
97.13(9) Cl(2)-Re(2)-Cl(3)
89.62(11)
79.68(13)
86.74(13)
91.7(4)
96.09(9)
84.65(11)
86.6(5)
89.7(5)
85.8(5)
P(4)-Re(2)-Cl(3)
P(2)-Re(2)-Cl(3)
The synthesis and unambiguous structural characterization
of a series of organic isocyanide complexes of the types Re2-
Cl4(µ-LL)2(CNR), Re2Cl4(µ-LL)2(CNR)2, and [Re2Cl3(µ-LL)2-
(CNR)3]Cl, where LL ) dppm, dppE, or dcpm and R ) t-Bu
or Xyl, has for the first time allowed for an understanding of
the isomer chemistry that is possible with this class of
compounds. The present study provides the clarification of the
structural chemistry that is a necessary prelude to exploring the
reaction chemistry of these compounds toward other π-acceptor
ligands. These studies are currently underway.
97.05(8) C(30)-Re(2)-P(4)
165.26(12) Re(1)-Re(2)-P(4)
C(20)-Re(1)-Cl(1) 82.8(4)
C(10)-Re(1)-Cl(1) 81.2(4)
Cl(2)-Re(2)-P(4)
C(30)-Re(2)-P(2)
Re(2)-Re(1)-Cl(1) 171.74(10) N(10)-C(10)-Re(1) 172.0(14)
P(1)-Re(1)-Cl(1)
P(3)-Re(1)-Cl(1)
79.5(2)
85.9(2)
N(20)-C(20)-Re(1) 174.9(10)
N(30)-C(30)-Re(2) 175.1(12)
C(10)-N(10)-C(11) 163(2)
C(20)-N(20)-C(21) 172(2)
C(30)-Re(2)-Re(1) 90.3(4)
C(30)-Re(2)-Cl(2) 165.0(3)
Re(1)-Re(2)-Cl(2) 104.58(9) C(30)-N(30)-C(31) 167.8(12)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Supporting Information Available: Five X-ray crystallographic
files in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
The Re-Re distance for 7 is 2.3451(10) Å, a value which is
almost identical to its bis-isocyanide precursor complex 6
IC000064A