Unsymmetrical dirhenium complexes that contain [Re2]6+ and [Re2]5+ cores complexed by tridentate ligands with P2O and P2N donor sets

Article abstract of DOI:10.1021/ic010983g

The quadruply bonded dirhenium(III) complex (n- Bu₄N)₂Re₂Cl₈ reacts with tridentate ligands that contain essentially planar P,O,P donor sets to afford the complexes Re₂Cl₆(η³-L

Full text of DOI:10.1021/ic010983g

Inorg. Chem. 2002, 41, 405−412
6+
5+
Unsymmetrical Dirhenium Complexes That Contain [Re ] and [Re ]
2
2
Cores Complexed by Tridentate Ligands with P O and P N Donor Sets
2
2
Shan-Ming Kuang, Phillip E. Fanwick, and Richard A. Walton*
Department of Chemistry, Purdue UniVersity, 1393 Brown Building,
West Lafayette, Indiana 47907-1393
Received September 19, 2001
The quadruply bonded dirhenium(III) complex (n-Bu
planar P,O,P donor sets to afford the complexes Re
4
N)
Cl
2
Re
2
Cl
8
reacts with tridentate ligands that contain essentially
3
2
6 1 1
(η -L ) (3) (L ) bis[2-(diphenylphosphino)phenyl]ether)
1
4
and (n-Bu N)[Re
2
Cl
7
(η -L
2
)] (4) (L
2
) 4,6-bis(diphenylphosphino)dibenzofuran). Spectroscopic and electrochemical
3
data support the unsymmetrical structure Cl
4
ReReCl
2
(η -L
1
) in the case of 3, while 4 contains monodentate P-bound
(µ-O CCH Cl (H O) reacts with ligands L , L
), bis[2-(diphenylphosphino)ethyl]amine (L ), and N,N-bis[2-(diphen-
) to give the paramagnetic complexes Re (µ-O CCH
Re Re bonds. The lability of the µ-acetato ligands in 5−9 has been demonstrated by the reactions of
compounds 5 (n ) 1) and 7 (n ) 3) with 4-Ph PC CO H, 2-Ph PC CO H, and quinoline-4-carboxylic acid to
L
2
; both complexes contain Re&Re bonds. The synthon cis-Re
,6-bis(diphenylphosphinomethyl)pyridine (L
ylphosphino)ethyl]trimethylacetamide (L
2
2
3
)
2
4
2
2
1
2
,
2
3
4
3
5
2
2
3
)Cl
4
n
(η -L ) (5−9) with
3.5
2
6
H
4
2
2
6
H
4
2
give complexes 10−12 (from 5) and 13−15 (from 7), respectively. These products contain uncoordinated donor
atoms that can be used to produce mixed-metal assemblies. Compounds 5 and 7 also react with terephthalic acid
3
3
(
1,4-C
6
H
4
(CO
2
H) to give [Re
2
Cl
4
(η -L
1
)]
2
(µ-O
2
CC
6
H
4
CO
2
) (16) and [Re
2
Cl
4
(η -L
3
)]
2
2 6 4 2
(µ-O CC H CO ) (17) in which
electronic coupling between the paramagnetic sets of dirhenium units is very weak. Single-crystal X-ray structure
determinations have been carried out on complexes 5−8, 11, 12, and 14−16.
2 3
[Re Cl6-x(PR )
2+x]n (x ) 0, 1, or 2; n ) +2, +1, 0, or -1).2-7
Introduction
Through our structural characterization of compound II we
found that the Re-Re‚‚‚Fe unit was linear although, as
expected, the Fe center was at a nonbonding distance to the
The genesis of the present study was our recent discovery
of the first example of a 1,3-Re
encountered in the Re-Re quadruply bonded complex Cl
ReReCl (dppf), where dppf ) 1,1′-bis(diphenylphosphino)-
2 6 3 2
Cl (PR ) type isomer (I) as
4
-
closest Re center (∼3.5 Å). Upon replacing the Cp
2
Fe unit
2
by a suitable donor ligand atom we reasoned that it should
be possible to obtain unsymmetrical compounds (like II) in
which the trans 1,3 arrangement of P donors is maintained
but a significant bonding interaction would exist in one of
the axial sites of the Re-Re bond. The stability of such an
arrangement is of interest in light of the tendency of the
Re&Re bond to be cleaved by certain bidentate and
1
ferrocene (II). The search for a “missing” isomer of this
(
(
(
(
2) Cotton, F. A.; Frenz, B. A.; Ebner, J. R.; Walton, R. A. Inorg. Chem.
1976, 15, 1630.
3) Cotton, F. A.; Dunbar, K. R.; Falvello, L. R.; Tomas, M.; Walton, R.
A. J. Am. Chem. Soc. 1983, 105, 4950.
4) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Inorg. Chem.
Commun. 1999, 2, 28.
type had been stimulated by the earlier work of Cotton and
others on the synthetic and structural chemistry of a variety
of isomers of dirhenium complexes of the general type
5) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Inorg. Chem. 1999,
38, 3384 and relevant references cited therein.
*
To whom correspondence should be addressed. E-mail: rawalton@
purdue.edu.
1) Reddy, N. D.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 2001, 40,
732.
(6) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Inorg. Chem. 1999,
38, 3889.
(7) Uzelmeier, C. E.; Bartley, S. L.; Fourmigu e´ , M.; Rogers, R.;
Grandinetti, G.; Dunbar, K. R. Inorg. Chem. 1998, 37, 6706.
(
1
1
0.1021/ic010983g CCC: $22.00 © 2002 American Chemical Society
Inorganic Chemistry, Vol. 41, No. 2, 2002 405
Published on Web 12/22/2001

Kuang et al.
Chart 1
ethanol (50 mL) for 12 h gave a green powder that was filtered off
and washed with ethanol (2 × 5 mL) and diethyl ether (2 × 5 mL)
7 2
and dried; yield 92 mg (61%). Anal. Calcd for C52H62Cl NOP -
Re
7.83. The use of longer reaction times produced this same product.
B. Synthesis of Complexes of the Type Re (µ-O CCH )Cl
η -L), where L ) Bis[2-(diphenylphosphino)phenyl]ether (L
2
: C, 45.27; H, 4.53; Cl, 17.73. Found: C, 44.43; H, 4.43; Cl,
1
2
2
3
4
-
3
(
4
1
),
), 2,6-Bis(diphen-
3
), Bis[2-(diphenyl-phosphino)-
,6-Bis(diphenylphosphino)dibenzofuran (L
2
ylphosphinomethyl)pyridine (L
ethyl]amine (L
methylacetamide (L
mixture of cis-Re (µ-O
and L (108 mg, 0.20 mmol) was refluxed in 60 mL of ethanol for
6 h, the reaction mixture allowed to cool to 25 °C, and the yellow-
brown crystalline product filtered off and washed with ethanol (2
4
), or N,N-Bis[2-(diphenylphosphino)ethyl]tri-
3
5
). (i) Re
2
(µ-O
2
CCH
3
)Cl
4
(η -L
1
) (5). A
2
2
CCH Cl
3
)
2
4
(H O)
2
2
(2) (67 mg, 0.10 mmol)
1
1
×
5 mL) and diethyl ether (2 × 5 mL); yield 59 mg (53%). Anal.
Calcd for C38
H, 2.79.
H31Cl
4 3 2
O P Re
2
: C, 41.05; H, 2.79. Found: C, 41.14;
8
tridentate phosphine donors. Accordingly, we have examined
3
2
(ii) Re (µ-O
2
CCH
3
)Cl
4
(η -L
2
) (6). A procedure similar to B(i)
in place of L and a
reaction time of 3 days; yield 54 mg (49%). Anal. Calcd for C38
the reactions of an assortment of such ligands (see L
in Chart 1) with the dirhenium(III) precursors (n-Bu
Re Cl (1) and cis-Re (µ-O CCH Cl (H O)
1
-L
N)
5
was used with 107 mg (0.20 mmol) of L
2
1
4
2
-
H
29
-
2
8
2
2
)
3 2
4
2
2
(2). The studies
Cl
4
O
3
P
2
Re
2
: C, 41.13; H, 2.63. Found: C, 41.11; H, 2.69.
involving the dirhenium(III) acetate complex 2 proved to
3
(iii) Re
2
(µ-O
2 3 4 3
CCH )Cl (η -L ) (7). The reaction between 2 (67
be the most fruitful and led to a series of paramagnetic
mg, 0.10 mmol) and 2,6-bis(diphenylphosphinomethyl)pyridine (L
(95 mg, 0.20 mmol) was carried out in refluxing ethanol for 4 h as
described in B(i); yield 89 mg (85%). Anal. Calcd for C33
NO Re : C, 37.79; H, 2.88. Found: C, 38.37; H, 2.98. Recrys-
tallization from 1,2-dichloroethane/benzene gave 7 as brown crystals
of composition 7‚C
iv) Re (µ-O CCH
B(iii) was used with the salt bis(diphenylphosphinoethyl)amine
hydrochloride (L ‚HCl) (100 mg, 0.22 mmol) in place of L ; yield
2 mg (81%). Anal. Calcd for C30 NO Re : C, 35.51; H,
.18. Found: C, 35.67; H, 3.26.
Compound 8 was also obtained by the reaction of Re
CCH Cl with an excess of L ‚HCl in refluxing ethanol for 2
3
)
5+
[Re
2
]
core complexes, including ones in which two such
units are coupled together. Some of these results have been
4
H30Cl -
9
the subject of a preliminary report.
2
P
2
2
Experimental Section
6 6
H .
3
(
2
2
3
)Cl
4
4
(η -L ) (8). A procedure identical to
4
N)
(2) were prepared by standard literature
procedures, as were the phosphine ligands L -L shown in Chart
was isolated as its HCl salt and used as such.
2 2 8 2
Re Cl (µ-
(1)10 and cis-Re
The dirhenium complexes (n-Bu
O CCH ) Cl (H O)
2 3 2 4 2 2
11
4
3
1
5
8
3
H32Cl
4
P
2 2
2
1
2-15
14
1.
Ligand L
4
Solvents were obtained from commercial sources and were deoxy-
genated by purging with dinitrogen prior to use. All reactions were
performed under an atmosphere of dinitrogen.
2 2
(µ-O -
3
)
4
2
4
weeks; yield 36%. This procedure is not a convenient one and was
not pursued further with other ligands.
3
A. (i) Synthesis of Re
Re Cl
phenyl]ether (L
2
Cl
6
(η -L
1
) (3). A mixture of (n-Bu
4
N)
2
-
2
8
(1) (114 mg, 0.10 mmol) and bis[2-(diphenylphosphino)-
3
(v) Re
2
(µ-O
2
CCH
3
)Cl
4
(η -L
5
) (9). The use of L
5
(105 mg, 0.20
1
) (108 mg, 0.20 mmol) was refluxed in 60 mL of
mmol) in place of L
time of 2 days; yield 63 mg (57%). This product was recrystallized
from dichloromethane/diethyl ether to give brown microcrystals.
Anal. Calcd for C36
4
‚HCl afforded compound 9 after a reaction
ethanol for 2 h, the reaction mixture allowed to cool to 25 °C and
filtered, and the red solid washed with ethanol (2 × 5 mL) and
diethyl ether (2 × 5 mL); yield 98 mg (93%). Anal. Calcd for
H42Cl NO P Re
6 3 2 2
2 2
(i.e., 9‚CH Cl ): C, 36.53; H,
38 6 2 2 2
C H34Cl O P Re (i.e., 3‚EtOH): C, 39.02; H, 2.93; Cl, 18.19.
3.58. Found: C, 35.77; H, 3.27.
Found: C, 39.69; H, 2.76; Cl, 18.10. The presence of lattice ethanol
C. Carboxylate-Exchange Reactions of Re
2
(µ-O
2 3 4
CCH )Cl -
1
was confirmed by H NMR spectroscopy.
η3-L
3
(
1
) (5) and Re
(µ-O CCH )Cl
2 2 3 4
(η -L
3
) (7). Since all reactions
1
(
ii) Synthesis of (n-Bu
n-Bu N) Re Cl
ylphosphino)dibenzofuran (L
4
N)[Re
2
Cl
7
(η -L
2
)] (4). The reaction of
were carried out with the use of essentially identical procedures,
details of representative reactions only are given.
(
4
2
2
8
(1) (114 mg, 0.10 mmol) and 4,6-bis(diphen-
) (107 mg, 0.20 mmol) in refluxing
2
3
(
i) Synthesis of Re
mixture of 5 (111 mg, 0.10 mmol) and 4-Ph
.12 mmol) was refluxed in 50 mL of ethanol for 3 days. The
2
(µ-O
2
6
CC H
4
-4-PPh
2
)Cl
4
(η -L
1
) (10). A
2
PC
6 4 2
H CO H (36 mg,
(
8) (a) Jaecker, J. A.; Robinson, W. R.; Walton, R. A. J. Chem. Soc.,
0
Dalton Trans. 1975, 698. (b) Costello, M. T.; Schrier, P. W.; Fanwick,
P. E.; Walton, R. A. Inorg. Chim. Acta 1993, 212, 157.
9) Kuang, S.-M.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. Commun.,
in press.
reaction mixture was cooled to 25 °C and filtered and the yellow
powder washed with ethanol (2 × 5 mL) and diethyl ether (2 × 5
mL); yield 100 mg (74%). Recrystallization from dichlorometh-
ane/diethyl ether gave yellow microcrystals. Anal. Calcd for
(
(
(
(
10) (a) Barder, T. J.; Walton, R. A. Inorg. Chem. 1982, 21, 2510. (b)
Barder, T. J.; Walton, R. A. Inorg. Synth. 1985, 23, 116.
11) Chakravarty, A. R.; Cotton, F. A.; Cutler, A. R.; Walton, R. A. Inorg.
Chem. 1986, 25, 3619.
12) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995,
C
56
H
44Cl
6
O
P
3 3
Re
5.91; H, 2.93.
ii) Synthesis of Re
use of 2-Ph PC CO
11 in crystalline form; yield 22%. Anal. Calcd for C55
Re : C, 48.64; H, 3.12. Found: C, 46.64; H, 3.07. Although the C
2
2 2
(i.e., 10‚CH Cl ): C, 46.61; H, 3.07. Found: C,
4
3
(
2
(µ-O
2 6
CC H
4
-2-PPh
2
)Cl
4
(η -L
1
) (11). The
1
4, 3081.
13) Haenel, M. W.; Jakubik, D.; Rothenberger, E.; Schroth, G. Chem. Ber.
991, 124, 1705.
2
6
H
4
2
H and the same procedure as C(i) afforded
(
4 3 3
H42Cl O P -
1
2
(
(
14) Dahlhoff, W. V.; Nelson, S. M. J. Chem. Soc. A 1971, 2184.
15) Nuzzo, R. G.; Haynie, S. L.; Wilson, M. E.; Whitesides, G. M. J.
Org. Chem. 1981, 46, 2861.
microanalysis of this complex was consistently low, the composition
of this product was confirmed by X-ray crystallography.
406 Inorganic Chemistry, Vol. 41, No. 2, 2002

Unsymmetrical Dirhenium Complexes
iii) Synthesis of Re (µ-O C-4-C10 N)Cl
complex was obtained as insoluble red crystals from the reaction
between 5 and quinoline-4-carboxylic acid for 2 days using the
3
(
2
2
H
6
4
(η -L
1
) (12). The title
positions according to idealized geometries with C-H ) 0.95 Å
and U(H) ) 1.3Ueq(C). They were included in the refinement but
constrained to ride on the atom to which they are bonded. An
empirical absorption correction using SCALEPACK18 was applied.
The final refinements were performed by the use of the program
34
procedure described in C(i); yield 61%. Anal. Calcd for C46H -
4 3 2
Cl NO P Re
2
: C, 45.10; H, 2.80. Found: C, 44.93; H, 2.75.
3
19
(iv) Synthesis of Re
2 2 6 4
(µ-O CC H -4-PPh
2
)Cl
4
(η -L
3
) (13). The
SHELXL-97. For 12 the absolute structure was determined by
2
0
use of 7 (105 mg, 0.10 mmol) in place of 5 and a procedure similar
to C(i) give the desired product; yield 76%. Anal. Calcd for C50
Cl NO Re : C, 46.37; H, 3.19. Found: C, 46.00; H, 3.30.
v) Synthesis of Re
procedure similar to C(i) gave 14 as insoluble yellow crystals; yield
refinement. The enantiomer chosen had a Flack parameter of
-0.017(7). Crystallographic drawings were done using the program
ORTEP.21
41
H -
4
P
2 3
2
3
The structure solutions and refinements of all nine compounds
proceeded without significant problems. The C and O atoms of
the solvent molecules present in the structures of 7 and 14-16 were
refined with anisotropic thermal parameters. Unidentified and
disordered solvent molecules were present in the crystals of 11 and
(
2
(µ-O
2 6
CC H
4
-2-PPh
2
)Cl
4 3
(η -L ) (14). A
3
4
6%. Anal. Calcd for C52
6.57; H, 3.53. Found: C, 46.03; H, 3.15.
vi) Synthesis of Re (µ-O C-4-C10 N)Cl
H
47Cl
4
NO
3
P
3
Re
2
(i.e., 14‚EtOH): C,
3
(
2
2
H
6
4
(η -L
3
) (15). The title
16, but in neither case could the disorder be adequately modeled.
complex was obtained as red crystals with the use of a procedure
Accordingly, these molecules were removed with the squeeze option
in PLATON.22 In the cases of 6 and 11, two independent dirhenium
molecules are present in the asymmetric unit.
Full structural details for the nine compounds are provided in
the Supporting Information. The most important bond distances and
bond angles are given in the captions to Figures 1-9, which show
the ORTEP representations of the structures.
similar to C(i); yield 57%. Anal. Calcd for C43
H
39Cl
4
N
2
O
3
P
2
Re
2
(
i.e., 15‚EtOH): C, 42.76; H, 3.25. Found: C, 42.51; H, 3.02.
3
(
vii) Synthesis of [Re
2
Cl
4
(η -L
1
)]
2
(µ-O
2
CC
6
H
4
CO
2
) (16). A
mixture of 5 (111 mg, 0.10 mmol) and terephthalic acid (8.3 mg,
0.05 mmol) was refluxed in 50 mL of n-butanol for 12 h. The cooled
reaction mixture was filtered, and the brown powder was washed
with ethanol (2 × 5 mL) and diethyl ether (2 × 5 mL); yield 84
E. Physical Measurements. Infrared spectra were recorded in
mg (74%). Anal. Calcd for C80
Found: 41.23; H, 3.10.
8 6 4 4
H60Cl O P Re : C, 42.34; H, 2.66.
-
1
the region 4000-400 cm as KBr pellets and from 700 to 150
-
1
cm as Nujol mulls on a Perkin-Elmer 2000 FT-IR spectrometer.
This complex was also obtained by an alternative procedure. A
solution of 5 (111 mg, 0.10 mmol) in acetonitrile (40 mL) was
Electronic absorption spectra were recorded with use of a Cary
1
31
1
3
00 spectrophotometer, while H and P{ H} NMR spectra were
4 2
treated with HBF ‚Et O (0.20 mL) and the mixture stirred at room
obtained on a Varian INOVA 300 spectrometer. Proton resonances
were referenced internally to the residual protons in the incompletely
deuterated solvent. The 31P{ H} spectra were recorded at 121.6
temperature for 24 h. The clear green solution that resulted was
treated with a solution of disodium terephthalate (11 mg, 0.05
mmol) in ethanol (5 mL), the mixture was stirred at room
temperature for another 24 h and filtered, and the volume of the
filtrate was reduced to about 10 mL. Benzene (10 mL) was added,
and the slow evaporation of the solvents over a period of days gave
1
MHz, with 85% H
measurements were carried out with use of a BAS Inc. model CV-
7 instrument in conjunction with a BAS model RXY recorder and
3 4
PO as an external standard. Cyclic voltammetric
2
were recorded on dichloromethane solutions that contained 0.1 M
tetra-n-butylammonium hexafluorophosphate (TBAH) as supporting
electrolyte. E1/2 values, determined as (Ep,a + Ep,c)/2, were
referenced to the silver/silver chloride (Ag/AgCl) electrode at 25
brown crystals; yield 36 mg (31%).
3
(viii) Synthesis of [Re
2
Cl
4
(η -L
3 2 2 6 4 2
)] (µ-O CC H CO ) (17). The
reaction of 7 (105 mg, 0.10 mmol) with terephthalic acid (8.3 mg,
0
.05 mmol) was carried out in refluxing n-propanol for 1 week;
°
C and were uncorrected for junction potentials. Under our ex-
8 2 4 4 4
yield 78 mg (73%). Anal. Calcd for C70H58Cl N O P Re : C, 39.22;
perimental conditions E1/2 ) +0.47 V vs Ag/AgCl for the ferro-
cenium/ferrocene couple. Differential pulsed voltammetric (DPV)
measurements and magnetic data were recorded in the Laboratory
of Professor Kim R. Dunbar at Texas A&M University. Conductiv-
ity measurements were obtained with the use of a YSI model 35
conductance meter.
H, 2.73. Found: C, 39.14; H, 2.82.
D. Single-Crystal X-ray Crystallography. Single crystals of
, 6, 8, 11, 12, 14, and 15 were harvested directly from the reaction
5
mixtures. Crystals of 7 were obtained by recrystallization from 1,2-
dichloroethane/benzene while suitable crystals of 16 were grown
from a mixed acetonitrile/benzene/ethanol solvent system. Subse-
quent structure analysis showed that several of the single crystals
chosen for the structure analyses contained solvent molecules; these
Elemental microanalyses were performed by Dr. H. D. Lee of
the Purdue University Microanalytical Laboratory.
particular crystals were of compositions 7‚C
EtOH, and 16‚2EtOH.
6 6
H , 14‚EtOH, 15‚
Results and Discussion
The crystals were mounted on glass fibers in random orientations.
The data collections were carried out at 150((1) K with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å) on a Nonius
KappaCCD diffractometer. Lorentz and polarization corrections
were applied to the data sets. The key crystallographic data are
given in Table 1.
The reactions of (n-Bu
ylphosphino)phenyl]ether (L
4
N)
2
Re
2 8
Cl (1) with bis[2-(diphen-
1
) and 4,6-bis(diphenylphosphi-
no)dibenzofuran (L ) (see Chart 1) afford the red complex
2
3
Re
(
2
Cl
6
(η -L
1
) (3) and the green complex (n-Bu
4
N)[Re
2
Cl
7
-
η1-L
2
)] (4), respectively. Compound 3 is formally very
The structures of 6 and 8 were solved by using the structure
solution program SHELXS-9716 while the structures of 5, 7, 11,
(17) Beurskens, P. T.; Admirall, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF92
Program System; Technical Report; Crystallography Laboratory,
University of Nijmegen, Netherlands, 1992.
(18) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307.
(19) Sheldrick, G. M. SHELXL-97. A Program for Crystal Structure
Refinement; University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
1
2, and 14-16 were solved with the use of the structure solution
17
program PATTY in DIRDIF92. The remaining non-hydrogen
atoms were located in succeeding difference Fourier syntheses.
Hydrogen atoms bound to carbon were placed in calculated
(
(
20) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
21) Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
(16) Sheldrick, G. M. SHELXS-97. A Program for Structure Solution;
University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
(22) Sluis, P. V. D.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194.
Inorganic Chemistry, Vol. 41, No. 2, 2002 407

Kuang et al.
Figure 1. ORTEP20 representation of the structure of Re2(µ-O2CCH3)Cl4
3
(
η -L1) (5). Thermal ellipsoids are drawn at the 50% probability level, except
for the carbon atoms of the Ph2P groups, which are circles of arbitrary
radius. Selected bond distances (Å) and bond angles (deg) are as follows:
Re(1)-Re(2) 2.2454(3), Re(1)-O(1) 2.089(4), Re(1)-O(12) 2.351(3),
Re(1)-Cl(1) 2.3731(15), Re(2)-O(2) 2.091(4), Re(2)-Cl(22) 2.3230(16),
Re(2)-Cl(23) 2.3006(16), Re(2)-Cl(21) 2.3095(16); P(1)-Re(1)-P(2)
1
49.84(5), O(1)-Re(1)-Cl(1) 162.58(11), O(2)-Re(2)-Cl(22) 167.29(12),
Cl(23)-Re(2)-Cl(21) 136.10(6).
Figure 2. ORTEP20 representation of the structure of Re2(µ-O2CCH3)-
3
Cl4(η -L2) (6). The thermal ellipsoids are drawn at the 50% probability
level, except for the carbon atoms of the Ph2P groups, which are circles of
arbitrary radius. Selected bond distances (Å) and bond angles (deg) are as
follows: Re(1)-Re(2) 2.2403(4), Re(1)-O(1) 2.059(4), Re(1)-O(1d)
2
2
.285(4), Re(1)-Cl(1) 2.3929(15), Re(2)-O(2) 2.063(5), Re(2)-Cl(23)
.3407(19), Re(2)-Cl(22) 2.306(2), Re(2)-Cl(21) 2.3085(18); P(1)-
Re(1)-P(2) 150.11(6), O(1)-Re(1)-Cl(1) 162.86(13), O(2)-Re(2)-
Cl(23) 166.95(19), Cl(22)-Re(2)-Cl(21) 139.12(7).
similar to the product obtained in the reaction between (n-
4 2 2 8
Bu N) Re Cl and 1,1′-bis(diphenylphosphino)ferrocene (dppf)
that affords the unsymmetrical quadruply bonded complex
1
4 2
Cl ReReCl (dppf), while the salt 4 may well be related
closely to the intermediate formed in the conversion of 1 to
-
3
which involves the sequential displacement of two Cl
ligands.
All indications are that 3 is structurally very similar to
1
Re
L
(
2
Cl
ligand in place of the unbound Fe atom of Re
see structure representation II). Like Re Cl (dppf), com-
pound 3 is diamagnetic and shows a singlet at δ ) +24.7 in
6
(dppf), but with a weak axially bound O atom of the
1
2
Cl (dppf)
6
2
6
3
1
1
its P{ H} NMR spectrum (recorded in (CD
field of that of the free ligand (δ ) -21.0 in (CD
cyclic voltammogram (CV) of a solution of 3 in 0.1 M n-Bu
NPF -CH Cl shows potentials at E1/2(red) ) -0.02 V and
1/2(red) ≈ -1.35 V vs Ag/AgCl, which is very similar to
3
)
2
SO) down-
3 2
)
SO). A
4
-
6
2
2
E
408 Inorganic Chemistry, Vol. 41, No. 2, 2002

Unsymmetrical Dirhenium Complexes
2
0
Figure 3. ORTEP representation of the structure of Re2 (µ-O2CCH3)-
20
Figure 5. ORTEP representation of the structure of Re2(µ-O2CC6H4-
3
Cl4(η -L3) (7). The thermal ellipsoids are drawn at the 50% probability
3
2
-PPh2)Cl4(η - L1) (11). The thermal ellipsoids are drawn at the 50%
probability level, except for the carbon atoms of the Ph2P groups, which
are circles of arbitrary radius. Selected bond distances (Å) and bond angles
deg) are as follows: Re(1)-Re(2) 2.2390(3), Re(1)-O(1) 2.069(4), Re-
1)-O(23) 2.378(4), Re(1)-Cl 2.3707(17), Re(2)-O(2) 2.077(4), Re(2)-
Cl(22) 2.3288(16), Re(2)-Cl(23) 2.3010(18), Re(2)-Cl(21) 2.3219(17);
P(2)-Re(1)-P(3) 149.65(16), O(1)-Re(1)-Cl(11) 162.86(13), O(2)-
Re(2)-Cl(22) 167.68(13), Cl(23)-Re(2)-Cl(21) 138.92(6).
level, except for the carbon atoms of the Ph2P groups, which are circles of
arbitrary radius. Selected bond distances (Å) and bond angles (deg) are as
follows: Re(1)-Re(2) 2.2804(4), Re(1)-O(1) 2.094(4), Re(1)-N(11)
(
(
2
2
.310(5), Re(1)-Cl(11) 2.3715(16), Re(2)-O(2) 2.053(5), Re(2)-Cl(21)
.3496(18), Re(2)-Cl(22) 2.260(2), Re(2)-Cl(23) 2.293(2); P(1)-Re(1)-
P(2) 158.21(6), O(1)-Re(1)-Cl(11) 164.27(14), O(2)-Re(2)-Cl(21)
66.98(14), Cl(22)-Re(2)-Cl(23) 137.50(8).
1
Figure 4. ORTEP20 representation of the structure of Re2(µ-O2CCH3)-
3
Cl4(η -L4) (8). The thermal ellipsoids are drawn at the 50% probability
level, except for the carbon atoms of the Ph2P groups, which are circles of
arbitrary radius. Selected bond distances (Å) and bond angles (deg) are as
follows: Re(1)-Re(2) 2.2596(3), Re(1)-O(11) 2.090(4), Re(1)-N(3)
.327(5), Re(1)-Cl(11) 2.3954(13), Re(2)-O(12) 2.058(4), Re(2)-Cl(21)
.3367(16), Re(2)-Cl(22) 2.3094(16), Re(2)-Cl(23) 2.3191(18); P(1)-
Re(1)-P(2) 156.95(5), O(11)-Re(1)-Cl(11) 164.85(11), O(12)-Re(2)-
Cl(21) 163.77(13), Cl(22)-Re(2)-Cl(23) 143.65(6).
20
Figure 6. ORTEP representation of the structure Re2(µ-O2C-4-C10H6N)-
2
2
3
Cl4(η -L1) (12). The thermal ellipsoids are drawn at the 50% probability
level, except for the carbon atoms of the Ph2P groups, which are circles of
arbitrary radius. Selected bond distances (Å) and bond angles (deg) are as
follows: Re(1)-Re(2) 2.2536(4), Re(1)-O(1) 2.090(5), Re(1)-O(12)
2
.360(4), Re(1)-Cl(11) 2.3577(18), Re(2)-O(2) 2.070(5), Re(2)-Cl(22)
the dirhenium-based redox chemistry observed for Re
dppf), with E1/2 ) -0.03 V and Ep,c ≈ -1.5 V vs Ag/AgCl.
Electronic absorption spectral measurements on dichlo-
2
Cl
6
-
2.3227(18), Re(2)-Cl(21) 2.260(2), Re(2)-Cl(23) 2.316(2); P(1)-Re(1)-
1
P(2) 151.53(7), O(1)-Re(1)-Cl(11) 162.29(13), O(2)-Re(2)-Cl(22)
(
1
68.07(14), Cl(21)-Re(2)-Cl(23) 139.37(9).
romethane solutions of Re
have their δ f δ* transitions at 834 nm (ꢀ ) 1408) and
2
Cl
6
2
(dppf) and 3 show that they
distance of 2.24 Å; unfortunately the C
6 4 6 4
H OC H fragment
3
of the ligand L did not refine satisfactorily and the result
1
8
(
6
50 nm (ꢀ ) 1420), respectively; the symmetrical dirhenium-
III) complex (n-Bu N) Re Cl has its δ f δ* transition at
67 nm (ꢀ ) 1600) with use of our experimental conditions.
was unacceptable. We have not yet been able to grow a
suitable single crystal of 3 for a full structure determination.
However, the structural identity of 3 was further supported
by its low-resolution mass spectrum (as determined by
MALDI) which showed an intense peak at m/z ca. 1090
4
2
2
8
Further support for this close relationship comes from a
comparison of their low-frequency IR spectra (recorded as
Nujol mulls), which show very similar absorption patterns,
with bands at 519 (s), 508 (m-s), 485 and 478 (s), and 346
+
+
(
calcd for [Re
2 5 1
Cl (L )] , i.e., [M - Cl] , m/z 1088).
1
A solution of (n-Bu
4
N)[Re
2
Cl
7 2
(η -L )] (4) in acetone (1.0
-
1
(
2 6
vs) cm in the case of Re Cl (dppf) and 520 (s), 498 (m-
-
3
×
10 M) has a conductivity in accord with that expected
for a 1:1 electrolyte (Λ
-
1
s), 478 (m-s), and 342 (vs) cm for 3. The bands at ∼345
-
1
2
-1
m
) 97 Ω cm mol ). The
-
1
cm are assigned to ν(Re-Cl). This conclusion was
electronic absorption spectrum of a dichloromethane solution
confirmed by a partial X-ray structure determination of a
crystal of 3 grown from dichloromethane which showed it
2
3
of 4 shows a δ f δ* transition at 695 nm (ꢀ ) 1710), a
value intermediate between those measured for (n-Bu N)
SO
4
2
-
1
2 6
to be similar to Re Cl (dppf), with a Re-Re quadruple bond
1
Re
2
Cl
8
and 3. The H NMR spectrum of 4 in (CD
3
)
2
+
confirms the presence of [n-Bu
4
N] , but these solutions
(23) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms,
2nd ed.; Oxford University Press: Oxford, U.K., 1993.
decompose. However, freshly prepared solutions of 4 in CD
2
-
Inorganic Chemistry, Vol. 41, No. 2, 2002 409

Kuang et al.
Figure 9. ORTEP20 representation of the structure of the tetrarhenium
3
complex [Re2Cl4(η -L1)]2(µ-O2CC6H4CO2) (16). The thermal ellipsoids are
drawn at the 50% probability level, except for the carbon atoms of the
Ph2 P groups, which are circles of arbitrary radius. Selected bond dis-
tances (Å) and bond angles (deg) are as follows: Re(1)-Re(2) 2.2424(4),
Re(1)-O(1) 2.067(4), Re(1)-O(12) 2.376(4), Re(1)-Cl(1) 2.3672(18),
Re(2)-O(2) 2.064(5), Re(2)-Cl(22) 2.3308(18), Re(2)-Cl(21) 2.3033(18),
Re(2)-Cl(23) 2.3097(19); P(1)-Re(1)-P(2) 149.78(6), O(1)-Re(1)-
Cl(1) 163.76(14), O(2)-Re(2)-Cl(22) 166.39(15), Cl(21)-Re(2)-Cl(23)
Figure 7. ORTEP20 representation of the structure Re2(µ-O2CC6H4-2-
3
PPh2)Cl4(η -L3) (14). The thermal ellipsoids are drawn at the 50%
probability level, except for the carbon atoms of the Ph2P groups, which
are circles of arbitrary radius. Selected bond distances (Å) and bond angles
(
deg) are as follows: Re(1)-Re(2) 2.2651(4), Re(1)-O(1) 2.120(5),
138.41(7).
Re(1)-N(101) 2.331(6), Re(1)-Cl(11) 2.374(2), Re(2)-O(2) 2.043(6),
Re(2)-Cl(22) 2.343(2), Re(2)-Cl(23) 2.301(2), Re(2)-Cl(21) 2.313(2);
P(1)-Re(1)-P(2) 152.58(7), O(1)-Re(1)-Cl(11) 165.46(15), O(2)-
Re(2)-Cl(22) 167.31(16), Cl(23)-Re(2)-Cl(21) 135.28(9).
occurs. This was also confirmed by monitoring the CV of a
solution of 4 in 0.1 M TBAH-CH Cl over a period of
2
2
several hours. A freshly prepared solution shows an irrevers-
ible oxidation at Ep,a ) +1.25 V and a reversible reduction
at E1/2 ) -0.35 V vs Ag/AgCl, behavior that is different
from that seen in the CV of 3 (vide supra). When this solution
is allowed to stand for several hours, processes that are
2
-
characteristic of the [Re
2 8
Cl ]
anion grow in at E1/2 ) +1.20
2
4
V and E1/2 ) -0.87 V vs Ag/AgCl, although the majority
species is still 4. Interestingly, the CV of 4 resembles closely
n
that reported for a solution of the salt (Ph
Ph )] in (n-Bu N)BF -CH Cl (E1/2 ) -0.34 V vs SCE).
This observation, coupled with that of two singlets in the
4
As)[Re
2
Cl
7
(PBu -
2
5
2
4
4
2
2
31
1
P{ H} NMR spectrum of 4, indicating the presence of both
free and bound P atoms in the L ligand, implies that 4 may
2
1
well involve η -bound L
2
, so that it resembles structurally a
2
0
Figure 8. ORTEP representation of the structure of Re2(µ-O2C-4-
-
compound of the type [Re
donor atoms strongly bound to the [Re
[Cl ReReCl (P)] ).
4 3
2
Cl
7
(PR
3
)] in only having eight
3
C10H6N)Cl4(η -L3) (15). The thermal ellipsoids are drawn at the 50%
6
+
2
]
core (i.e.,
probability level, except for the carbon atoms of the Ph2P groups, which
are circles of arbitrary radius. The hydrogen-bonding interaction between
the EtOH molecule and the N atom of the 4-quinoline carboxylate ligand
is also shown (the H atom is omitted). Selected bond distances (Å) and
bond angles (deg) are as follows: Re(1)-Re(2) 2.2694(3), Re(1)-O(1)
-
23,25-28
This type of compound is the
logical intermediate in the formation of a compound such
as 3; the latter would be formed after the loss of an additional
-
2
2
2
.101(4), Re(1)-N(101) 2.329(5), Re(1)-Cl(11) 2.3667(14), Re(2)-O(2)
.061(4), Re(2)-Cl(22) 2.3313(15), Re(2)-Cl(21) 2.304(2), Re(2)-Cl(23)
.3177(18); P(1)-Re(1)-P(2) 155.89(6), O(1)-Re(1)-Cl(11) 165.02(12),
[Cl] ligand and the coordination of the second P atom along
with the more weakly bound axial O(ether) atom. The reason
that the reaction of (n-Bu
this first stage may be related to the rigid nature of L
compared to the more flexible ligand L . Note that 4 does
even under forcing
4 2 2 8 2
N) Re Cl with L terminates at
O(2)-Re(2)-Cl(22) 165.48(12), Cl(21)-Re(2)-Cl(23) 137.91(6).
2
Cl
2
are quite stable and show two singlets with similar
1
31
1
intensities in the P{ H} NMR spectrum at δ ) +1.2 and
not react further with an excess of L
2
δ ) -21.0, the latter resonance being shifted a little upfield
reaction conditions.
The reactions of (n-Bu N) Re Cl with ligands L and L
4 2 2 8 3 4
in refluxing ethanol gave insoluble brown and green products,
respectively, but neither product was soluble in solvents
without decomposition. Accordingly, they were not inves-
1
of that of the free ligand (δ ) -16.7 in CD
NMR spectrum in CD Cl
2
Cl
2
). The H
2
2
shows a complex set of phenyl H
resonances in the region δ ) +9.3 to δ +6.8 and confirms
+
the 1:1 stoichiometry of L
2
to [n-Bu
4
N] . Upon allowing
these solutions to stand, the 31P{ H} and H NMR spectra
1
1
(
24) Cameron, C. J.; Tetrick, S. M.; Walton, R. A. Organometallics 1984,
slowly change and reveal the presence of a small amount of
3, 240.
+
free ligand L
2
, an increase in the amount of [n-Bu
4
N]
(25) Ferry, J.; Gallagher, J.; Cunningham, D.; McArdle, P. Inorg. Chim.
Acta 1989, 164, 185.
present relative to compound 4, but no change in the relative
(
26) (a) McArdle, P.; Rabbitte, M.; Cunningham, D. Inorg. Chim. Acta
31
1
intensities of the two singlets in the P{ H} NMR spectrum.
A quantity of (n-Bu N) Re Cl can be isolated upon workup
of these “aged” solutions, so it is apparent that some
decomposition of 4 to (n-Bu N) Re Cl and L eventually
1995, 229, 95. (b) Ferry, J.; Gallagher, J.; Cunningham, D.; McArdle,
P. Inorg. Chim. Acta 1990, 172, 79.
4
2
2
8
(
(
27) Bakir, M.; Walton, R. A. Polyhedron 1987, 6, 1925.
28) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Inorg. Chem. 2001,
40, 5716.
4
2
2
8
2
410 Inorganic Chemistry, Vol. 41, No. 2, 2002

Unsymmetrical Dirhenium Complexes
tigated further, although we note that neither contains
Table 2. Cyclic Voltammetric Half-Wave Potentials for Dirhenium
Complexes of Ligands L1-L5
+
1
4 3 2
[n-Bu N] as shown by H NMR measurements on (CD ) -
compd no.
E1/2(ox), Va
E1/2(red), Va
SO solutions.
The type of tridentate coordination of L
is present in 3, is encountered in the paramagnetic [Re ]
2
1
that we propose
5
6
7
8
9
0
1
12
3
4
+0.42
+0.42
+0.36
+0.30
+0.33
+0.39
+0.37
+0.44
+0.37
+0.34
+0.40
-1.03
-1.00
-1.09
-1.10
-1.11
-1.02
-1.06
-0.97
-1.06
-1.10
-1.01
5
+
3
complex Re
the reaction between cis-Re
in refluxing ethanol. Complexes analogous to 5 are formed
when the ligands L -L (see Chart 1) are used in place of
; this gives rise to compounds 6-9. The reagent for the
2
(µ-O
2
CCH
3
)Cl
4
(η -L
1
) (5) which is formed by
2
(µ-O
2
CCH Cl (H O) (2) and
3
)
2
4
2
2
1
1
L
1
2
5
1
1
1
reduction process is probably the ethanol solvent, a conclu-
sion that is supported by earlier work of Cotton and
co-workers.29 The crystal structures of 5-8 (Figures 1-4)
show that they have the same structure, with Re-Re
15
6
7
b
b
1
1
+0.43
-1.00
+0.39b
-1.05
b
a
Data are based upon single-scan cyclic voltammograms measured on
3
.5
0.1 M TBAH-CH2Cl2 solutions and referenced to the Ag/AgCl electrode
distances for the Re Re bonds in the range 2.2403(4)-
.2804(4) Å. The small variation in Re-Re distances
with a scan rate (ν) of 200 mV/s at a Pt-bead electrode. The E1/2 values are
2
p p,a
for one-electron processes with ip,a ) ip,c. Values of ∆E , i.e., E - Ep,c,
b
for the individual processes are in the range 60-120 mV. These processes
are broadened due to weak electronic coupling between the pairs of
dirhenium units.
probably reflects some differences in the strength of the axial
Re-O and Re-N binding, the Re-Re distance with the
pyridyl-containing ligand L being the longest of the set.
3
The parameters for the two dirhenium molecules present in
the asymmetric unit of 6 are very similar; only one set of
these parameters is given in the caption to Figure 2. In spite
series of compounds. The cyclic voltammograms of 0.1 M
TBAH-CH Cl solutions show a one-electron oxidation and
2 2
a one-electron reduction for each of the compounds, the E1/2
of the considerably greater flexibility of ligand L
1
compared
values of which are listed in Table 2. Attempts to oxidize
to L , we see little significant difference between the struc-
2
these compounds chemically to afford salts of the diamag-
+
tural parameters of 5 and 6, although the axial Re-O bond
distance Re(1)-O(1d) in 6 (2.285(4) Å) is a little shorter
than is the comparable distance Re(1)-O(12) of 2.351(3) Å
netic cations [Re
cessful.
2
2 3
(µ-O CCH )Cl
4
(L
n
)] have not been suc-
Solid samples of 5-9 were quite stable in air for extended
periods, and their solutions in polar solvents likewise showed
little sign of decomposition when kept under dinitrogen.
However, these compounds readily undergo carboxylate
exchange reactions in refluxing alcohol solvents. This type
in 5. The nonplanarity of the C
by a dihedral angle of 55.1°, a value which is similar to that
present in other complexes of L that are discussed later.
6 4 1
H rings of L in 5 is reflected
1
The Re-P bond distances of 5-8, which are not given in
the captions to Figures 1-4, fall in the range 2.40-2.49 Å
and seem to show only small variations with the Re-Lax
interaction. The compound with the shortest Re-P bond
lengths (6) also shows the largest P-Re-P angle (158.21°).
The torsional angles that define the extent of rotation of
the ligand sets about the Re-Re bonds are all less than 5°,
signifying that the rotational geometries are very close to
being fully eclipsed; for example, for 5 the angles Cl(1)-
Re(1)-Re(2)-Cl(22), P(2)-Re(1)-Re(2)-Cl(23), O(1)-
Re(1)-Re(2)-O(2), and P(1)-Re(1)-Re(2)-Cl(21) are
of behavior was examined in detail in the case of the
3
reactions of Re
2
(µ-O
) (7) with 4-Ph
H, quinoline-4-carboxylic acid, and terephthalic acid
1,4-C (CO H) ). These reactions afforded complexes
0-17, which are either of the type Re
) (where Ar ) 4-Ph PC , 2-Ph PC
n ) 1 or 3) or of the type [Re
2
CCH
3
)Cl
4
(η -L
1
) (5) and Re
2
(µ-
3
2 3 4
O CCH )Cl (η -L
3
2
PC
6
H
4
CO H, 2-Ph PC
2
2
6 4
H -
CO
2
(
6
H
4
2
2
3
1
2
(µ-O
, or 4-C10
(µ-O CC
where n ) 1 or 3), the latter pair of compounds containing
2
CAr)Cl
N and
CO
4
(η -
L
n
2
H
6 4
2
6
H
4
H
6
3
2
Cl
4
(η -L
n
)]
2
2
6
H
4
2
)
(
5
+
two [Re
2
]
units that are linked via a terephthalate bridge.
The structural identity of this series of complexes was
established by X-ray crystal structure determinations on 11,
4.1°, 2.6°, 1.9°, and 0.0°, respectively.
As expected, compounds 5-9 give only broad poorly
1
2, 14, 15, and 16 (Figures 5-9). These compounds retain
1
defined resonances in their H NMR spectra and no
3
the same type of Re(µ-O
present in 5 and 7. The Re-Re distances are in the range
.2390(3)-2.2694(3) Å and are very similar to the distances
2
CR)Cl
4 n
(η -L ) structure that is
resonances in the 31P NMR spectra. The magnetic moment
B
of 5, which is 1.40 µ at 300 K, is effectively constant down
2
to ∼4 K, and Curie law behavior is observed. A rising
absorption in the electronic absorption spectrum of a dichlo-
romethane solution of 5, at the low-energy limit of our
measurements (900 nm), signals the presence of the expected
encountered for complexes 5-8. The two molecules present
in the asymmetric unit of 11 have essentially identical
parameters; only one set of parameters is given in the caption
to Figure 5. Like the set of complexes 5-8, compounds 11,
5
+
2
low-energy δ f δ* transition for a complex of the [Re ]
core.
1
2, and 14-16 all have essentially eclipsed rotational
2
3
geometries (the relevant torsional angles (ø) are all less than
In accord with the structural similarity of compounds 5-9,
we observe very similar electrochemical behavior for this
6
2
°) and Re-P distances that fall in the very narrow range
.41-2.45 Å. Other features of note include the presence of
ethanol solvent molecules in the crystals of 14-16. While
the EtOH present in 16 does not interact with the coupled
dirhenium units, an EtOH molecule is hydrogen-bonded to
(
29) (a) Angaridis, P.; Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A.
Polyhedron 2001, 20, 755. (b) Cotton, F. A.; Dikarev, E. V.;
Petrukhina, M. A. Inorg. Chem. 1999, 38, 3384.
Inorganic Chemistry, Vol. 41, No. 2, 2002 411

Kuang et al.
the Cl atom (Cl(11)) of one of the Re-Cl bonds of 14, and
to the N atom of the quinoline carboxylate ligand of 15; the
latter of these interactions is depicted in Figure 8. The
parameters for these hydrogen-bonded interactions are as
follows: 14, Cl(11)‚‚‚H(901) 2.722(3) Å and Cl(11)‚‚‚
H(901)-O(901) 168.1(6)°; 15, N(14)‚‚‚H(901) 2.051(7) Å
and N(14)‚‚‚H(901)-O(901) 173.0(6)°. In the structure of
complex 16, in which there are two dirhenium units coupled
through a terephthalate bridge, the deviation from planarity
K), which show the absence of a significant antiferromagnetic
5+
34
interaction between the [Re
of 16 is 2.80 µ at 300 K.
Concluding Remarks
The use of the tridentate P,O,P and P,N,P ligands L
2
]
units. The magnetic moment
B
1
+
-L
and
5
6
(
Chart 1) provides new types of unsymmetrical [Re
2
]
5+
3
[
Re
2
]
complexes. The compound Re
N) Re Cl and is formally a quadruply
bonded Re(IV)Re(II) complex, resembles closely Re Cl
dppf) (dppf ) 1,1′-bis(diphenylphosphino)ferrocene). How-
ever, unlike Re Cl (dppf), compound 3 contains a weak axial
ligand coordination although this does not significantly affect
its spectroscopic properties compared to those of Re Cl
, reacts with
to afford the stable salt (n-Bu N)[Re Cl
)] (4), which we believe contains P-bound η -ligand
2 6 1
Cl (η -L ) (3), which
is formed from (n-Bu
4
2
2
8
2
6
-
2 2 6 4 2 2
of the [Re O CC H CO Re ] unit is reflected by the torsional
1
(
angles O(1)-C(10)-C(11)-C(16) and O(2)-C(10)-C(11)-
C(12), which have values of 11.4(10)° and 13.3(10)°,
respectively.
The cyclic voltammetric properties of 10-15 resemble
closely those of 5-9 (Table 2). While the potentials for the
tetrarhenium complexes 16 and 17 are very similar to those
of all the complexes listed in Table 2, each of the processes
2
6
2
6
-
(
(
(
dppf). Ligand L
2 1
, which is a rigid variant of L
n-Bu N) Re Cl
4
2
2
8
4
2
7
-
1
1
η -L
2
coordination and would very likely have a structure similar
(E
1/2(ox) and E1/2(red)) differ in showing clear evidence for
1
to that of the intermediate (n-Bu
presumably formed in the conversion of (n-Bu
to 3. The five-ligand set L -L reacts with cis-Re
CCH Cl (H O)
type Re (µ-O CCH
the nonbridging tridentate coordination of L
4
N)[Re
2
Cl
7
(η -L
1
)] that is
broadening due to electronic coupling between the pairs of
4
N)
2
Re
2
Cl
8
5+
2
[Re ]
dirhenium units that are present in these compounds.
1
5
2
(µ-O
2
-
However, we were unable to resolve the pairs of sequential
one-electron redox processes and estimate that ∆E1/2 is <40
mV for both E1/2(ox) and E1/2(red). Accordingly, the value
3
)
2
4
2
2
to afford paramagnetic complexes of the
3
2
2
3
)Cl
4
(η -L
n
) (5-9), all of which involve
to one of the
n
for the comproportionation constant K
c
for the equilibrium
Re atoms. The lability of the acetate ligand in these
complexes toward carboxylates that contain other donor sites
represented in eq 1,
Kc
2 6 4 2 6 4 6
(i.e., 4-Ph PC H , 2-Ph PC H , and 4-C10H N) provides a
2
+
+
[
Re - - -Re ] + [Re - - -Re ]
y\ z 2[Re - - -Re ] (1)
2
2
2
2
2
2
route to systems that have the potential to be used to obtain
new types of mixed-metal assemblies. These studies are
currently underway. The exchange of terephthalate for acetate
shows that the µ-terephthalate bridged paramagnetic tetrar-
henium complexes 16 and 17 can easily be obtained. Other
dicarboxylic acids, which can also serve as linkers between
dirhenium units and are of different lengths and involve
different degrees of conjugation, will be used to develop this
chemistry further.
where
K ) exp(∆E /25.69)
c
1/2
is very small, well less than the value of 100 that is typically
the order of magnitude expected for a weakly coupled
This result is in accord with
the evidence reported by Chisholm and co-workers that
terephthalate is at best a poor linker ligand for electronic
valence trapped system.3
0-32
3
0
Acknowledgment. R.A.W. thanks the John A. Leighty
Endowment Fund for support of this work. We are most
grateful to Professor Kim R. Dunbar (Texas A&M Univer-
sity) for providing access to equipment for recording the DPV
of 16 and the magnetic susceptibilities of 5 and 16 and to
Dr. Jitendra K. Bera and Dr. Galan Mascoros Hose Raman
for obtaining these data for us.
coupling, and relates to our recent findings concerning the
+
linking of symmetrical [Re
2
Cl
4
(µ-dppm)
2
] and [Re
2
Cl
2
(µ-
2
+
33
dppm)
Support for the conclusion that electronic coupling in 16 and
7 is at most very weak comes from a study of the
temperature range magnetic properties of 16 (from 300 to 2
2
]
units via terephthalate and related ligands.
1
Supporting Information Available: X-ray crystallographic files
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
30) Cayton, R. H.; Chisholm, M. H.; Huffman, J. C.; Lobkovsky, E. B. J.
Am. Chem. Soc. 1991, 113, 8709.
(
(
(
31) Cotton, F. A.; Lin, C.; Murillo, C. A. Inorg. Chem. 2001, 40, 478.
32) Ren, T.; Zou, G.; Alvarez, J. C. Chem. Commun. 2000, 1197.
33) Bera, J. K.; Angaridis, P.; Cotton, F. A.; Petrukhina, M. A.; Fanwick,
P. E.; Walton, R. A. J. Am. Chem. Soc. 2001, 123, 1515.
IC010983G
(34) Bera, J. K.; Hose Raman, G. M. Unpublished results.
412 Inorganic Chemistry, Vol. 41, No. 2, 2002