Cyanide adducts on the diruthenium core of [Ru2(L) 4]+ (L = ap, CH3ap, Fap, or F3ap). Electronic properties and binding modes of the bridging ligand

Article abstract of DOI:10.1021/ic030195m

The products of the reaction between CN^- and four different diruthenium complexes of the type Ru₂(L)₄Cl where L = 2-CH₃ap (2-(2-methylanilino)pyridinate anion), ap (2-anilinopyridinate anion), 2-Fap (2-(2-fluoroanilino)pyridinate anion), or 2,4,6-F₃ap (2-(2,4,6-trifluoroanilino)pyridinate anion) are reported. Mono- and/or dicyano adducts of the type Ru₂(L)₄(CN) and Ru₂(L)₄(CN)₂ are found exclusively as reaction products when either the 2-CH₃ap or the ap derivative is reacted with CN^-, but diruthenium complexes with formulations of the type Ru₂(F_xap)₃[μ-(o-NC)F_x-1- ap](μ-CN) or Ru₂(F_xap)₄(μ-CN) ₂ (x = 1 or 3) are also generated when Ru₂(Fap) ₄Cl or Ru₂(F₃ap)₄Cl is reacted with CN^-. More specifically, four products formulated as Ru ₂(Fap)₄(CN), Ru₂(Fap)₄(CN) ₂, Ru₂(Fap)₃[μ-(o-NC)ap](μ-NC), and Ru₂(Fap)₄(μ-CN)₂ can be isolated from a reaction of CN^- with the Fap derivative, but the exact type and yield of these compounds depend on the temperature at which the experiment is carried out. In the case of the F₃ap derivative, the only diruthenium complex isolated from the reaction mixture has the formulation Ru₂(F₃ap)₃[μ-(o-NC)F₂ap](μ-CN) and this compound has structural, electrochemical, and spectroscopic properties quite similar to that of previously characterized Ru ₂(F₅ap)[μ-(o-NC)F₄ap](μ-CN). Both the mono- and dicyano derivatives synthesized in this study possess the isomer type of their parent chloro complexes. The Ru-Ru bond lengths of Ru ₂(ap)₄(CN) and Ru₂(2-CH₃ap) ₄(CN) are longer than those of Ru₂(ap)₄Cl and Ru₂(CH₃ap)₄Cl, respectively, and this is accounted for by the strong σ-donor properties of the CN^- ligand as compared to Cl^-. The Ru-C bonds in Ru₂(ap) ₄(CN)₂ are significantly shorter than those in Ru ₂(ap)₄(CN), thus revealing a greatly enhanced Ru-CN interaction in the dicyano adduct, a result which is also indicated by the fact that v_CN in Ru₂(ap)₄(CN)₂ is 50 cm^-1 higher than v_CN in Ru₂(ap) ₄(CN). Although both (4,0) Ru₂(ap)₄(CN) ₂ and (3,1) Ru₂(Fap)₄(CN)₂ possess the same formulation, there are clear structural differences between the two complexes and this can be explained by the fact that the two cyano derivatives possess a different binding symmetry of the bridging ligands. Each mono- and dicyano adduct was electrochemically investigated in CH₂Cl ₂ containing TBAP as supporting electrolyte. Ru₂(ap) ₄(CN), Ru₂(CH₃ap)_4- (CN), and Ru₂(Fap)₄(CN) undergo one reduction and two oxidations. The two dicyano adducts of the ap and Fap derivatives are characterized by two reductions and one oxidation. The potentials of these processes are all negatively shifted in potential by 400-720 mV with respect to half-wave potentials for the same redox couples of the monocyano derivatives, with the exact value depending upon the specific redox reaction.

Full text of DOI:10.1021/ic030195m

Inorg. Chem. 2003, 42, 6230−6240
Cyanide Adducts on the Diruthenium Core of [Ru2(L)4]+ (L ) ap, CH ap,
3
Fap, or F3ap). Electronic Properties and Binding Modes of the Bridging
Ligand
,†
John L. Bear,* Wei-Zhong Chen,‡ Boacheng Han,†,| Shurong Huang,† Li-Lun Wang,†
,†
,‡
Antoine Thuriere,† Eric Van Caemelbecke,†,§ Karl M. Kadish,* and Tong Ren*
Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003, Department of
Chemistry, UniVersity of Miami, Coral Gables, Florida 33146, and Department of Chemistry,
Houston Baptist UniVersity, Houston, Texas 77074-3298
Received June 13, 2003
The products of the reaction between CN- and four different diruthenium complexes of the type Ru2(L)4Cl where
L ) 2-CH ap (2-(2-methylanilino)pyridinate anion), ap (2-anilinopyridinate anion), 2-Fap (2-(2-fluoroanilino)pyridinate
3
anion), or 2,4,6-F ap (2-(2,4,6-trifluoroanilino)pyridinate anion) are reported. Mono- and/or dicyano adducts of the
3
type Ru2(L)4(CN) and Ru2(L)4(CN)2 are found exclusively as reaction products when either the 2-CH ap or the ap
3
derivative is reacted with CN-, but diruthenium complexes with formulations of the type Ru2(F ap)3[µ-(o-NC)F
-
x-1
x
ap](µ-CN) or Ru2(F ap)4(µ-CN)2 (x ) 1 or 3) are also generated when Ru2(Fap)4Cl or Ru2(F ap)4Cl is reacted with
x
3
CN-. More specifically, four products formulated as Ru2(Fap)4(CN), Ru2(Fap)4(CN)2, Ru2(Fap)3[µ-(o-NC)ap](µ-CN),
and Ru2(Fap)4(µ-CN)2 can be isolated from a reaction of CN- with the Fap derivative, but the exact type and yield
of these compounds depend on the temperature at which the experiment is carried out. In the case of the F ap
3
derivative, the only diruthenium complex isolated from the reaction mixture has the formulation Ru2(F ap)3[µ-(o-
3
NC)F ap](µ-CN) and this compound has structural, electrochemical, and spectroscopic properties quite similar to
2
that of previously characterized Ru (F ap)[µ-(o-NC)F ap](µ-CN). Both the mono- and dicyano derivatives synthesized
2
5
4
in this study possess the isomer type of their parent chloro complexes. The Ru−Ru bond lengths of Ru2(ap)4(CN)
and Ru2(2-CH ap)4(CN) are longer than those of Ru2(ap)4Cl and Ru2(CH ap)4Cl, respectively, and this is accounted
3
3
for by the strong σ-donor properties of the CN- ligand as compared to Cl-. The Ru−C bonds in Ru2(ap)4(CN)2 are
significantly shorter than those in Ru2(ap)4(CN), thus revealing a greatly enhanced Ru−CN interaction in the dicyano
adduct, a result which is also indicated by the fact that νCN in Ru2(ap)4(CN)2 is 50 cm-1 higher than νCN in Ru2-
(ap)4(CN). Although both (4,0) Ru2(ap)4(CN)2 and (3,1) Ru2(Fap)4(CN)2 possess the same formulation, there are
clear structural differences between the two complexes and this can be explained by the fact that the two cyano
derivatives possess a different binding symmetry of the bridging ligands. Each mono- and dicyano adduct was
electrochemically investigated in CH Cl2 containing TBAP as supporting electrolyte. Ru2(ap)4(CN), Ru2(CH ap)4-
2
3
(CN), and Ru2(Fap)4(CN) undergo one reduction and two oxidations. The two dicyano adducts of the ap and Fap
derivatives are characterized by two reductions and one oxidation. The potentials of these processes are all negatively
shifted in potential by 400−720 mV with respect to half-wave potentials for the same redox couples of the monocyano
derivatives, with the exact value depending upon the specific redox reaction.
Introduction
supramolecules.1-3 Notably, Cotton and co-workers have
realized molecular triangles, squares, cages, and loops based
on connecting Mo2/Rh2 units at either equatorial or axial
positions.1,2 Work from the laboratories of Cotton,4,5 Dun-
bar,6,7 Ku¨hn,8-10 Bear,11 and Ren12,13 has demonstrated that
Recent years have witnessed a rapid development in
utilizing dimetallic paddlewheel complexes as synthons for
* Authors to whom correspondence should be addressed. E-mail:
kkadish@uh.edu.
† University of Houston.
(1) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759.
(2) Cotton, F. A.; Lin, C.; Murillo, C. A. Proc. Natl. Acad. Sci., U. S. A.
2002, 99, 4810.
(3) Wong, K.-T.; Lehn, J.-M., Peng, S.-M.; Lee, G.-H. Chem. Commum.
2000, 2259.
‡ University of Miami.
| Current address: Department of Chemistry, University of Wisconsins
Whitewater, Whitewater, WI 53190.
§ Houston Baptist University.
6230 Inorganic Chemistry, Vol. 42, No. 20, 2003
10.1021/ic030195m CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/03/2003

Cyanide Adducts on the Diruthenium Core [Ru2(L)4]+
electron-rich Ru2 and Rh2 units form both linear arrays and
2-D nets through axial coordination of di- and tetratopic
linkers. Among potential ditopic linkers is the cyano (CN-)
ligand, which is especially interesting due to its ability to
mediate strong spin-spin couplings.14,15 Recently, metal-
cyano complexes have been used as N-donor ligands at Ru2
centers to form both extended arrays16,17 and molecular
complexes.18
Diruthenium complexes supported by N,N′-bidentate
ligands exhibit rich redox activities and magnetic properties,
and their axial cyano adducts could become unique building
blocks. Bear and co-workers19 have demonstrated that Ru2-
(dpf)4 (dpf ) diphenylformamidinate) readily forms both
mono- and dicyano adducts, and the latter was carefully
characterized. The structure of Ru2(dpf)4(CN)2 demonstrates
that the aryl groups flanking both axial positions prevent the
coordinated CN- groups from functioning as N-donor
ligands.
In contrast to Ru2(dpf)4Cl, the reaction between Ru2(F5-
ap)4Cl (F5ap ) 2-pentafluoroanilinopyridinate) and NaCN
under reflux conditions affords three dicyano products where
the cyano ligands are all in bridging modes.20 Nothing has
been published on the reactions of CN- with other known
Ru2 complexes containing ap or substituted ap bridging
ligands, and we now report that by controlling the reaction
conditions, both mono- and dicyano adducts on the Ru2(ap)4
and Ru2(Fap)4 core can be preferentially synthesized where
the CN- ligands are axially coordinated in both cases. The
difference in the coordination mode of CN- ligands between
the Ru2 complexes of ap (axial) and F5ap (µ-C) is likely
attributed to the labile nature of F5ap ligand, which is clearly
a consequence of perfluorination on the aniline ring. Natu-
rally, one would be intrigued about the reactivity toward CN-
ligands by the Ru2 complexes with ligands of medium
basicity, i.e., partially fluorinated ap anions Fap and F3ap.
Reactions between CN- and Ru2(Fxap)4Cl (x ) 1 or 3) and
characterizations of products isolated from these reactions
are also reported.
Experimental Section
General Remarks. Potassium cyanide and sodium cyanide were
purchased from Aldrich, tetra-n-butylammonium perchlorate (TBAP)
was purchased from Fluka, and silica gel was purchased from Merck
or Aldrich. THF was distilled over Na/benzophenone under an N2
atmosphere prior to use. Absolute dichloromethane (water content
<0.005%, sealed under nitrogen) was purchased from Fluka and
used as received for the electrochemical measurements. Potassium
bromide was purchased from International Crystal Laboratories and
was stored at 40 °C in a vacuum oven prior to use.
1H NMR spectra were recorded on a Bruker AVANCE300 NMR
spectrometer with chemical shifts (δ) referenced to the residual
CHCl3. IR spectra were recorded on a Perkin-Elmer 2000 FTIR
spectrometer or a FTIR Nicolet 550 Magna-IR spectrometer using
KBr disks. UV-vis spectra were obtained with a Perkin-Elmer
Lambda-900 UV-vis spectrophotometer or a Hewlett-Packard
model 8453 diode array spectrophotometer. Magnetic susceptibility
was measured at 298 K with a Johnson Matthey Mark-I magnetic
susceptibility balance or was determined by the Evan’s method.21,22
Electron spin resonance (ESR) spectra were recorded on a Bruker
ER 100E spectrometer. The g values were measured with respect
to diphenylpicrylhydrazyl (DPPH, g ) 2.0036 ( 0.0003). Mass
spectra were recorded on a Finnigan TSQ 700 instrument at the
University of Texas, Austin. Standard fast atom bombardment was
used, and m-nitrobenzyl alcohol (NBA) was used as the liquid
matrix.
Cyclic voltammograms were obtained using an EG&G Princeton
Applied Research (PAR) model 173 potentiostat/galvanostat or an
IBM model EC 225 voltammetric analyzer using a three-electrode
system which consisted of a platinum button (1.0 mm diameter) or
a glassy carbon working electrode (3.0 mm diameter), a platinum
wire counter electrode, and a homemade saturated calomel reference
electrode (SCE) as the reference electrode. The SCE was separated
from the bulk of the solution by a fritted-glass bridge of low porosity
that contained the solvent/supporting electrolyte mixture. TBAP
(0.1 M) was used as the supporting electrolyte for the cyclic
voltammetric measurements. The ferrocenium/ferrocene couple in
CH2Cl2, 0.1 M TBAP was observed at 0.49 V vs SCE under our
experimental conditions.
Synthesis of Starting Compounds. Ru2(ap)4Cl,23 Ru2(CH3-
ap)4Cl,24 Ru2(Fap)4Cl,25 and Ru2(F3ap)4Cl24 were prepared as
described in the literature.
(4) Cotton, F. A.; Kim, Y. J. Am. Chem. Soc. 1993, 115, 8511.
(5) Cotton, F. A.; Kim, Y.; Ren, T. Inorg. Chem. 1992, 31, 2723.
(6) Miyasaka, H.; Campos-Ferna´ndez, C. S.; Cle´rac, R.; Dunbar, K. R.
Angew. Chem., Int. Ed. Engl. 2000, 39, 3831.
(7) Miyasaka, H.; Cle´rac, R.; Campos-Ferna´ndez, C. S.; Dunbar, K. R.
Inorg. Chem. 2001, 40, 1663.
(8) Zuo, J.-L.; Herdtweck, E.; Ku¨hn, F. E. J. Chem. Soc., Dalton Trans.
2002, 1244.
(9) Zuo, J.-L.; Herdtweck, E.; Biani, F. F. D.; Santos, A. M.; Ku¨hn, F. E.
New J. Chem. 2002, 26, 889.
(10) Zuo, J.-L.; Biani, F. F. d.; Santos, A. M.; Ko¨hler, K.; Ku¨hn, F. E.
Eur. J. Inorg. Chem. 2003, 449.
(11) Bear, J. L.; Han, B.; Wu, Z.; Caemelbecke, E. V.; Kadish, K. M. Inorg.
Chem. 2001, 40, 2275.
(12) Ren, T.; Xu, G. Comments Inorg. Chem. 2002, 23, 355.
(13) Ren, T.; Zou, G.; Alvarez, J. C. Chem. Commun. 2000, 1197.
(14) Dunbar, K. R.; Heintz, R. A. Prog. Inorg. Chem. 1997, 45, 283.
(15) Miller, J. S.; Manson, J. L. Acc. Chem. Res. 2001, 34, 563.
(16) Liao, Y.; Shum, W. W.; Miller, J. S. J. Am. Chem. Soc. 2002, 124,
9336.
Synthesis of (4,0) Ru2(ap)4(CN) (1). Potassium cyanide (15 mg,
0.23 mmol) in 5 mL of methanol was added to a THF solution of
Ru2(ap)4Cl (200 mg, 0.22 mmol in 40 mL), and the mixture was
stirred under argon while the progress was monitored by thin-layer
chromatography (TLC). Upon the complete disappearance of
Ru2(ap)4Cl (ca. 2 h), the reaction mixture was filtered through a
2-cm silica gel pad deactivated with Et3N. Solvent removal from
the filtrate resulted in a green solid which was recrystallized from
THF/hexanes to afford 1 as green microcrystals. Yield: 181 mg,
(91% based on Ru). Rf (v/v/v, CH2Cl2/hexanes/triethylamine ) 3/6/
1), 0.85. UV-vis [λmax, nm (ꢀ, M-1 cm-1)]: 462 (4410), 763 (5800).
IR, ν(CtN)/cm-1: 2038 (s). MS-FAB (m/e, based on 101Ru): 906
[MH+]. ømol(corrected) ) 5.64 × 10-3 emu, µeff ) 3.67 µB.
(21) Evans, J. J. Chem. Soc. 1959, 2003.
(17) Yoshioka, D.; Mikuriya, M.; Handa, M. Chem. Lett. 2002, 1044.
(18) Zhang, L.-Y.; Chen, J.-L.; Shi, L.-X.; Chen, Z.-N. Organometallics
2002, 21, 5919.
(19) Bear, J. L.; Han, B.; Huang, S.; Kadish, K. M. Inorg. Chem. 1996,
35, 3012.
(22) Loliger, J.; Scheffold, R. J. Chem. Educ. 1972, 49, 646.
(23) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A. Inorg. Chem. 1985,
24, 172.
(24) Kadish, K. M.; Wang, L.-L.; Thuriere, A,; Van Caemelbecke, E.; Bear,
J. L. Inorg. Chem. 2003, 42, 834.
(20) Bear, J. L.; Li, Y.; Cui, J.; Han, B.; Caemelbecke, E. V.; Phan, T.;
Kadish, K. M. Inorg. Chem. 2000, 39, 857.
(25) Bear, J. L.; Wellhoff, J.; Royal, G.; Van Caemelbecke, E.; Eapen, S.;
Kadish, K. M. Inorg. Chem. 2001, 40, 2282.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6231

Bear et al.
Synthesis of Ru2(ap)4(CN)2 (2). Potassium cyanide (150 mg,
2.2 mmol) dissolved in 10 mL of methanol was added to a CH2Cl2
solution of Ru2(ap)4Cl (200 mg, 0.22 mmol in 50 mL), and the
solution was stirred with concurrent air bubbling for 6 h, during
which the color of the reaction mixture changed from green to royal
blue. The reaction mixture was washed with a copious amount of
water to remove excess KCN. Solvent removal from the organic
phase yielded a purple solid, which was purified via silica column
chromatography to afford both 2 as the major product (130 mg,
63%) and 1 as the minor product. Rf ) 0.65. UV-vis [λmax, nm (ꢀ,
M-1 cm-1)]: 568 (3640), 996 (4060). IR, ν(CtN)/cm-1: 2095 (m),
2093 (m, b), 2080 (m, b), 1608 (s), 1489 (s), 1464 (s), 1421 (s),
1342 (m), 1292 (m), 1241 (s), 1196 (m), 1162 (w), 1105 (m), 1032
(w), 942 (w), 891 (w), 840 (w), 795 (w), 756 (m), 722 (w), 670
(w), 643 (w) cm-1
.
6. UV-vis, λmax (nm): 677 and 808. IR (KBr pellet): 1976 (m),
1736 (s), 1538 (m, b), 1434 (s), 1366(s), 1220 (s), 1012 (m, b),
911 (m), 843 (m, b), 771 (m), 685 (m, b), 522 (s) cm-1
.
7. UV-vis, λmax (nm): 703 and 974. MS (m/e, fragment): 1003
[Ru2(Fap)4(µ-CN)2]+. IR (KBr pellet): 2045 (m), 1720(s), 1607
(s), 1494 (m) 1460 (s), 1379 (m), 1271 (m), 1192 (m) 1103 (s),
1023 (m), 847 (m), 804 (m), 754 (s), 713 (m), 622(m) cm-1
.
1
2082 (m). MS-FAB (m/e, based on 101Ru): 905 [M+ - CN]. H
Synthesis of Ru2(F3ap)3[µ-(o-NC)F2ap](µ-CN) (8). This com-
pound was obtained by reacting the (3,1) isomer of Ru2(F3ap)4Cl
(100 mg, 0.089 mmol) with sodium cyanide (18 mg, 0.37 mmol)
in 50 mL of fresh distilled THF. The reaction mixture was left
open to the atmosphere while being refluxed overnight. The solution
was dark green in the beginning and then gradually changed to
dark blue. The solution was left to evaporate under the hood, after
which it was extracted using CH2Cl2 and water. The organic layer
was collected and evaporated under the hood. The remaining dark
blue residue was purified on a silica gel column using 100% CH2-
Cl2 as the eluent. Three bands (green, purple, and blue) were
observed in the column, but only the green fraction could be
isolated. The title compound was obtained by slow evaporation of
this fraction with a yield of 26%. This yield increased to 44% when
the reaction was carried out at 70 °C. UV-vis [λmax, nm (10-3ꢀ,
mol-1 L cm-1)]: 674 (4.37) and 795 (6.95). MS (m/e, fragment):
1128 [Ru2(F3ap)3[µ-(o-NC)F2ap)](µ-CN)]+. IR (KBr pellet): 1993
(m), 1703 (m), 1600 (s), 1512 (s), 1466 (s), 1445 (s), 1424 (s),
1326 (m), 1305 (w), 1264 (m), 1207 (m), 1119 (s), 1031 (s), 860
NMR (CDCl3): 9.18-8.99 (m, 4H, aromatic), 7.66-6.76 (m, 16H,
aromatic), 6.98-6.56 (m, 8H, aromatic), 5.56 (m, 8H, aromatic).
Synthesis of (4,0) Ru2(CH3ap)4(CN) (3). The title compound
was synthesized following a procedure similar to the one used for
the reaction between Ru2(F5ap)4Cl and NaCN.20 Ru2(CH3ap)4Cl
(100 mg, 0.10 mmol) was dissolved in 100 mL of fresh anhydrous
THF prior to addition of excess NaCN (90 mg, 1.84 mmol). The
reaction mixture was refluxed at 70 °C in air for 48 h. The color
of the solution remained green for the whole time the experiment
was carried out. The solvent was removed under vacuum, after
which the excess NaCN was removed from the reaction mixture
by extraction with H2O. The organic layer was dried over MgSO4
before removing the solvent by rotary evaporation. The compound
was purified on a silica gel column using acetone/n-hexane (3:7
v/v) as eluent and was recovered in a 55% yield. MS (m/e,
fragment): 961 [Ru2(CH3ap)4CN]+. UV-vis [λmax, nm (ꢀ × 10-3
,
M-1 cm-1)]: 463 (2.8), 756 (4.3).
Synthesis of Ru2(Fap)4(CN) (4), Ru2(Fap)4(CN)2 (5), Ru2-
(Fap)3[µ-(o-NC)ap](µ-CN) (6), and Ru2(Fap)4(µ-CN)2 (7). All
four compounds were isolated during the reaction between the (3,1)
isomer of Ru2(Fap)4Cl (50 mg, 0.051 mmol) and NaCN (10 mg,
0.20 mmol) in 30 mL of fresh distilled THF under two different
experimental conditions, but the exact type of diruthenium complex
and its yield varied drastically with the experimental conditions.
In both experiments, the reaction mixtures were left open to the
atmosphere but in one case the reflux was done at room temperature
while in the other it was carried out at 70 °C. Two bands (dark
green and blue) were observed in the column when the reaction
was carried at room temperature while three bands (green, blue,
and green-blue) were found from the reaction at 70 °C. Ru2(Fap)4-
(CN)2 5 was obtained from reactions at both room temperature and
70 °C, but Ru2(Fap)3[µ-(o-NC)ap)](µ-CN) 6 was obtained only from
the reaction at 70 °C. Compound 6 was isolated from the green
band after it was subjected to column chromatography using a
column packed with silica gel and 100% CH2Cl2 as eluent (yield
4%). Compound 5 was isolated from the blue band after it was
subjected to column chromatography several times using CH2Cl2/
hexanes (1:9 v/v) as eluent. The yield of 5 was 23 and 12% from
the room temperature and 70 °C reactions, respectively.
(w), 855 (w), 824 (w), 813 (w), 754 (m), 731 (w) cm-1
.
Attempt to Rearrange 2. Compound 2 (50 mg) and 10-fold
KCN dissolved in 20 mL of THF were refluxed in air. After
overnight reflux, 1 was detected as the major product, and some
unidentified compounds were found near the baseline of TLC plate.
Reflux of 2 without KCN gave similar results.
Structural Determination of Compounds 1-3, 5, and 8. Single
crystals of the five structurally characterized compounds were grown
as follows: slow evaporation of a saturated THF solution (1), slow
diffusion of methanol into CH2Cl2 solution (2), slow evaporation
of a CH2Cl2 solution containing 0.1 M TBAP (3), or slow diffusion
of n-hexane into a CH2Cl2 solution (5 and 8). The X-ray intensity
data were measured using Mo KR (λ ) 0.71073 Å) either at 300
K on a Bruker SMART1000 CCD-based X-ray diffractometer
system (1 and 2) or at 223 K on a Siemens SMART platform
diffractometer equipped with a 1K CCD area detector (3, 5, and
8). For X-ray crystallographic analysis, crystals of dimension 0.49
× 0.27 × 0.03 mm3 (1) and 0.25 × 0.21 × 0.05 mm3 (2) were
mounted in quartz capillaries with mother liquors, and crystals of
dimension 0.40 × 0.12 × 0.25 mm (3), 0.40 × 0.40 × 0.06 mm3
(5), and 0.20 × 0.18 × 0.16 mm3 (8) were mounted on quartz fiber
and placed in a steam of dry nitrogen gas at -50 °C. Data were
measured using omega scans of 0.3° per frame such that a
hemisphere (1271 frames) was collected. No decay was indicated
for any of five data sets by the re-collection of the first 50 frames
at the end of each data collection. The frames were integrated with
the SAINT software package26 using a narrow-frame integration
algorithm, which also corrects for the Lorentz and polarization
effects. Absorption corrections were applied using SADABS
supplied by George Sheldrick.
Two other compounds were isolated during workup of the
column (at room temperature and 70 °C) but no crystal structure
could be obtained to confirm their formulation; one was obtained
during purification of the dark green fraction while the other was
isolated from the green-blue fraction. On the basis of their
electrochemical behavior and mass spectral data, we formulate the
dark green compound as Ru2(Fap)4(CN) (4) and the blue-green
product as Ru2(Fap)4(µ-CN)2 (7).
4. MS (m/e, fragment): 978 [Ru2(Fap)4CN]+.
5. UV-vis [λmax, nm (ꢀ × 10-3, M-1 cm-1)]: 457 (sh, 2.63),
564 (5.47), 669 (sh, 4.95), and 862 (5.19) nm (sh: shoulder peak).
MS (m/e, fragment): 1002 [Ru2(Fap)4(CN)2]+. IR (KBr pellet):
The structures were solved and refined using the SHELXTL
(Version 5.1) software package in the space groups P1h for crystals
1, 2, and 8; C2/c for 3; and P21/c for 5. Positions of all
6232 Inorganic Chemistry, Vol. 42, No. 20, 2003

Cyanide Adducts on the Diruthenium Core [Ru2(L)4]+
Table 1. Crystal Data for Compounds 1-3, 5, and 8
1‚2THF‚H2O
2‚CH2Cl2‚MeOH
3‚2CH2Cl2
5‚CH2Cl2
8‚0.5CH2Cl2‚0.5C6H14
chemical formula
formula weight
space group
a, Å
b, Å
c, Å
C53H54N9O3Ru2
1067.2
P1h
C48H42Cl2N10ORu2
1048.0
P1h
C51H48N9Ru2Cl4
1130.92
C2/c
19.2291(7)
15.6453(5)
17.4068(6)
C47H34N10F4Ru2Cl2
1087.88
P21/c
16.708(1)
15.5031(9)
17.046(1)
C48H28N10F11Ru2Cl0.5
1170.67
P1h
10.010(6)
13.705(10)
19.698(16)
74.01(8)
79.31(8)
86.68(7)
2553(3)
2
16.378(4)
16.456(4)
17.651(4)
73.140(4)
89.864(4)
89.870(5)
4553(2)
4
16.2682(9)
16.7828(9)
17.1006(9)
88.568(1)
88.568(1)
83.802(1)
4637.8(4)
4
R, deg
â, deg
108.710(1)
97.861(1)
γ, deg
V, Å3
4960.0(3)
4
4374.0(4)
4
Z
T, °C
27
0.71073
1.388
0.642
0.069
27
0.71073
1.529
0.830
0.053
-50
-50
-50
λ(Mo KR), Å
0.71073
1.514
0.870
0.029
0.076
0.71073
1.652
0.878
0.030
0.083
0.71073
1.677
F
calc, g cm-3
µ, cm-1
R
0.772
0.030
0.086
wR2
0.202
0.151
Scheme 1. Mono-(1) and Bis-cyano (2) Complexes of [Ru2(ap)4]
Core
non-hydrogen atoms of diruthenium moieties were revealed by
direct method. In the case of crystal 1, the asymmetric unit contains
one diruthenium molecule, one water molecule, and two THF
molecules. In the case of 2, the asymmetric unit contains two
independent diruthenium molecules, two methanol, and two dichlo-
romethane solvent molecules. The asymmetric unit of 3 consists
of one-half molecule that is related to the other half by a
crystallographic axis coincident with the Ru1-Ru2-C25 vector
plus one molecule of methylene chloride solvent. The asymmetric
unit of 5 consists of one diruthenium molecule and one molecule
of methylene chloride solvent. Each of the four fluorine atoms in
5 is disordered over two different ortho carbon sites and was refined
with occupancy constraint. The asymmetric unit of 8 contains two
independent diruthenium molecules plus solvent molecules (one
CH2Cl2 and one hexane). With all non-hydrogen atoms being
anisotropic and all hydrogen atoms in calculated position and riding
mode, the structure was refined to convergence by least-squares
method on F2, SHELXL-93, incorporated in SHELXTL.PC V
5.03.27-29 Relevant information on the data collection and the figures
of merit of final refinement are listed in Table 1.
Scheme 2. Formation of Mono- and Dicyano Adducts on Ru2(ap)4
Nevertheless, continuous air bubbling through this solution
over an extended period of time led to a gradual shift in the
solution color from green to deep purple. TLC analysis
revealed a buildup of the new purple product which was
separated from the residual 1 by column chromatography
and identified as the dicyano adduct, 2 (see Scheme 2). The
difference in reaction products involving the cyano and
alkynyl ligands is likely due to the lower affinity of the CN-
ligand toward the Ru2(ap)4 core. Hence, the overwhelmingly
predominant species produced from Ru2(ap)4Cl under anaer-
obic conditions is Ru2(ap)4(CN), while {Ru2(ap)4(CN)2}- is
only formed in trace amounts (which is undetected by TLC).
Aerobic oxidation of the anionic CN- complex to Ru2(ap)4-
(CN)2 facilitates a shift of the equilibrium toward the neutral
dicyano adduct formation and eventually resulted in 2 as the
major product, as shown in Scheme 2. The coexistence of
mono- and dicyano adducts was also noted in the reaction
between Ru2(dpf)4Cl and excess NaCN.19
Results and Discussion
Reaction between Ru2(ap)4Cl and CN-. Ru2(ap)4Cl in
THF readily undergoes a metathesis reaction with 1 equiv
of KCN in an inert atmosphere to afford the monocyano
adduct Ru2(ap)4(CN) (1) in nearly quantitative yield (see
Scheme 1). It was noted in previous syntheses of Ru2(dpf)4-
and Ru2(ap)4-alkynyl compounds that the presence of excess
LiCCZ under anaerobic conditions always yielded a solution
whose color was significantly different from that of the
monoalkynyl adduct,19,30-32 and this was interpreted as due
to the high tendency for formation of [Ru2(C2Y)2]- in the
absence of O2. To our surprise, the addition of KCN in large
excess to a solution of Ru2(ap)4Cl under argon did not result
in the appearance of any new product other than 1.
Isolation of bridging dicyano complexes from refluxing
Ru2(F5ap)4Cl with CN- 20 prompted us to examine the
possible formation of a µ-cyano-Ru2(ap)4 product. However,
further reflux of 2 with or without KCN only led to its
decomposition, giving 1 (major) and very polar unidentified
products (minor) that were immobilized on silica TLC plate.
(26) SAINT V 6.035 Software for the CCD Detector System 1999 Bruker-
AXS Inc.
(27) SHELXTL 5.03 (WINDOW-NT Version), Program library for Struc-
ture Solution and Molecular Graphics 1998 Bruker-AXS Inc.
(28) Sheldrick, G. M. SHELXS-90, Program for the Solution of Crystal
Structures; University of Go¨ttigen: Go¨ttigen, Germany, 1990.
(29) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structures; University of Go¨ttigen: Go¨ttigen, Germany, 1993.
(30) Xu, G.; Ren, T. Organometallics 2001, 20, 2400.
(31) Ren, T. Organometallics 2002, 21, 732.
Compound 1 is paramagnetic and has an effective mag-
netic moment of 3.67 µB, indicating an S ) 3/2 ground state
that is common to all Ru2(ap)4Lax compounds (Lax is a
(32) Xu, G.; Ren, T. J. Organomet. Chem. 2002, 655, 239.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6233

Bear et al.
Table 2. Reaction Products between Ru2(L)4Cl and Cyanide (L ) ap, CH3ap, Fap, F3ap, or F5ap)
cyano adducts
isomer type
bridging ligand, L
mono-CN
bis-CN
rearranged cyano products
(4,0)
(4,0)
(3,1)
ap
CH3ap
Fap
Ru2(ap)4(CN) (1)
Ru2(CH3ap)4(CN) (3)
Ru2(Fap)4(CN) (4)
Ru2(ap)4(CN)2 (2)
Ru2(Fap)4(CN)2 (5)
Ru2(Fap)3[µ-(o-NC)ap](µ-CN) (6)
Ru2(Fap)4(µ-CN)2 (7)
Ru2(F3ap)4[µ-(o-NC)F2ap](µ-CN) (8)
Ru2(F5ap)3[µ-(o-NC)F4ap](µ-CN)
Ru2(F5ap)4(µ-CN)2 (2 isomers)
(3,1)
(3,1)
F3ap
F5apa
a Taken from ref 20.
monoanionic axial ligand). Similar to the Ru2(ap)4(C2Y)2 type
complexes, compound 2 is diamagnetic, which facilitates its
NMR characterization.
Reaction between Ru2(L)4Cl and CN- where L )
CH3ap, Fap, or F3ap. Table 2 summarizes the type of diru-
thenium complexes obtained when reacting either the (3,1)
or (4,0) isomer of Ru2(L)4Cl with CN-. The product isolated
when reacting (3,1) Ru2(F3ap)4Cl and NaCN is Ru2(F3ap)3-
[µ-(o-NC)F2ap)](µ-CN) (8) regardless of whether the reaction
is carried out at room temperature or at 70 °C. In contrast,
Ru2(Fap)3[µ-(o-NC)ap)](µ-CN) (6) is isolated only when the
reaction between NaCN and (3,1) Ru2(Fap)4Cl is carried out
at 70 °C. Indeed, at room temperature, this reaction gives
Ru2(Fap)4(CN) (4), Ru2(Fap)4(CN)2 (5), and Ru2(Fap)4(µ-
CN)2 (7) and there is no trace of 6. The reaction between
(4,0) Ru2(ap)4Cl and NaCN yields Ru2(ap)4(CN) (major) and
Ru2(ap)4(CN)2 (minor) while the reaction between (4,0)
Ru2(CH3ap)4Cl and NaCN yields only the monocyano adduct,
Ru2(CH3ap)4(CN) (see Table 2). Thus the mono- and/or
dicyano adducts appear as the only products of the reaction
that can be isolated from the reaction mixture when the
starting materials exist in a (4,0) isomeric form. Indeed, a
reaction between the (3,1) isomer of Ru2(F5ap)4Cl and excess
NaCN20 is known to produce only the three edge-sharing
diruthenium complexes, Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN)
and Ru2(F5ap)4(µ-CN)2 (two isomers) (see Table 2). The
present work shows that the (3,1) isomer also forms mono-
and dicyano adducts since both axial cyano adducts and
rearranged cyano products are found in the reaction mixture
when reacting the (3,1) isomer of Ru2(Fap)4Cl with CN-.
The summary of products formed in Table 2 also implies
that mono- and/or dicyano adducts of the (3,1) isomers are
more likely to be formed when the “ap-type” ligand is more
basic. A similar conclusion could also be drawn for the (4,0)
isomers (see Table 2), but preliminary data on Ru2(F5ap)4Cl
and Ru2(3,5-F2ap)4Cl indicate that both mono- and dicyano
products are also found in the reaction between CN- and
the (4,0) isomers of diruthenium complexes containing an
“ap-type” bridging ligand,33 i.e., F5ap or 3,5-F2ap which are
both less basic than Fap.
Figure 1. ORTEP diagram of Ru2(ap)4(CN) at 30% probability level. H
atoms have been omitted for clarity.
Figure 2. ORTEP plot (40% equiprobability envelopes) of Ru2(CH3ap)4-
(CN). Hydrogen atoms have been omitted for clarity.
Figures 1 and 2, respectively, and some selected bond lengths
and angles are collected in Table 3. Similar to both the parent
compound, Ru2(ap)4Cl, and the alkynyl analogues, Ru2(ap)4-
(C2Y),34-36 ap ligands in the monocyano complexes adopt
the (4,0) arrangement where all pyridyl nitrogens (Np)
coordinate to the Ru1 center while all anilino nitrogens (Na)
coordinate to the Ru2 center. The coordination sphere of the
Ru1 center can be described as octahedral with Ru2 and CN-
as fifth and sixth ligands while that of Ru2 is square
Molecular Structures of Monocyano Complexes 1 and
3. The axially coordinating nature of the cyano ligands in
both 1 and 3 were ascertained through single-crystal X-ray
diffraction studies. The ORTEPs of 1 and 3 are shown in
(34) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A.; Tocher, J. H.
Polyhedron 1985, 4, 1475.
(33) Bear, J. L.; Kadish, K. M.; Van Caemelbecke, E. Manuscript in
preparation.
(35) Chakravarty, A. R.; Cotton, F. A. Inorg. Chim. Acta 1986, 113, 19.
(36) Zou, G.; Alvarez, J. C.; Ren, T. J. Organomet. Chem. 2000, 596, 152.
6234 Inorganic Chemistry, Vol. 42, No. 20, 2003

Cyanide Adducts on the Diruthenium Core [Ru2(L)4]+
Table 3. Selected Bond Lengths (Å) and Angles (deg) for Compounds
1 and 3
1
3
Ru(1)-N(2)
Ru(1)-N(4)
Ru(1)-N(6)
Ru(1)-N(8)
Ru(1)-C(1)
Ru(1)-Ru(2)
Ru(2)-N(3)
Ru(2)-N(5)
Ru(2)-N(7)
Ru(2)-N(9)
N(1)-C(1)
2.107(6) Ru(1)-N(1)
2.111(6) Ru(1)-N(3)
2.091(6) Ru(2)-N(2)
2.095(6) Ru(2)-N(4)
2.210(8) Ru(1)-C(25)
2.336(2) Ru(1)-Ru(2)
2.041(6) N(5)-C(25)
2.037(6)
2.098(3)
2.098(3)
2.056(3)
2.048(2)
2.174(5)
2.304 (5)
1.073(11)
2.040(6)
2.021(6)
1.015(10)
N(2)-Ru(1)-Ru(2)
N(4)-Ru(1)-Ru(2)
N(6)-Ru(1)-Ru(2)
N(8)-Ru(1)-Ru(2)
C(1)-Ru(1)-Ru(2)
N(3)-Ru(2)-Ru(1)
N(5)-Ru(2)-Ru(1)
N(7)-Ru(2)-Ru(1)
N(9)-Ru(2)-Ru(1)
N(1)-C(1)-Ru(1)
87.99(18) N(1)-Ru(1)-Ru(2)
88.30(19) N(3)-Ru(1)-Ru(2)
88.74(19) N(2)-Ru(2)-Ru(1)
87.81(18) N(4)-Ru(2)-Ru(1)
178.9(2) C(25)-Ru(1)-Ru(2)
89.93(18) N(5)-C(25)-Ru(1)
89.09(18)
88.66(18)
90.14(18)
177.7(9)
87.83(7)
87.75(7)
89.01(7)
88.88(7)
180
169(4)
Figure 3. ORTEP diagram of Ru2(ap)4(CN)2 at 30% probability level. H
atoms have been omitted for clarity.
N(2)-Ru(1)-Ru(2)-N(3) 14.0(2)
N(4)-Ru(1)-Ru(2)-N(5) 15.5(2)
N(6)-Ru(1)-Ru(2)-N(7) 16.0(2)
N(8)-Ru(1)-Ru(2)-N(9) 16.3(2)
N(1)-Ru(1)-Ru(2)-N(2) 21.50(10)
N(3)-Ru(1)-Ru(2)-N(4) 21.41(10)
pyramidal. The Ru-Ru bond lengths (2.336(2) Å in 1 and
2.304(5) Å in 3), while comparable to those in Ru2(ap)4-
(C2Y) (ca. 2.33 Å),12 are longer than those of the parent
molecule Ru2(ap)4Cl (2.275(3) Å), and the elongation is
attributed to the strong σ-donor nature of the CN- ligand in
comparison with Cl-. On the other hand, the Ru-C bond
lengths (2.210(8) Å in 1 and 2.174(5) Å in 3) are significantly
longer than the Ru-C distances in Ru2(ap)4(C2Y) type
compounds (2.08-2.10 Å),12 reflecting the weaker basicity
of CN- as compared to an alkynyl ligand. Nevertheless, the
similarity in both overall structural features and magnetism
implies that compounds 1 and 3 are isoelectronic to other
known Ru2(ap)4Lax compounds.
While the majority of bond lengths and angles around Ru2
agree within experimental error with what is seen for 1 and
3, molecule 3 exhibits a significantly larger N-Ru-Ru′-
N′ torsional angle (21.5°) than 1 (15.5°) due to the o-methyl
substitution on the anilino ring in 3. Unusually short CN-
bond lengths of 1.015(10) Å (1) and 1.073(11) Å (3) are
also noteworthy, but this feature has previously been reported
in dimolybdenum compounds37 and was attributed to a
libration of the crystal structure.38 While the Ru-Ru-C
angle is equal or close to 180° in both molecules, the Ru-
C-N angle is still linear in 1 (177.7(9)°) but clearly bent in
3 (169(4)°). The large variance in Ru-C-N angles is likely
due to the lack of a significant Ru2 f π*(CN) back-donation.
Molecular Structures of Dicyano Complexes 2 and 5.
There are two independent diruthenium molecules (2A and
2B) in the asymmetric unit of crystal 2 but only one in that
of 5. The ORTEPs of 2A and 5 are shown in Figures 3 and
4, respectively, and the selected bond lengths and angles for
molecules 2A, 2B, and 5 are listed in Table 4. The Ru-Ru
Figure 4. Thermal ellipsoid plot (40% equiprobability envelopes) of the
(3,1) isomer of Ru2(Fap)4(CN)2. H atoms have been omitted for clarity.
bond lengths, 2.451(3), 2.447(3), and 2.456(5) Å in 2A, 2B,
and 5, respectively, are identical to each other within
experimental error and much longer than the Ru-Ru bonds
of 1 and 3 (ca. 2.32 Å). The Ru-C bond lengths in the
dicyano adducts (1.99-2.02 Å) are shortened by ca. 0.18 Å
from the Ru-C bond lengths of the monocyano adducts.
2
Clearly, the dz (Ru) orbital is polarized toward the C center
to form a strong σ (Ru-C) bond and is no longer available
for Ru-Ru σ-bonding. Evidence corroborating an enhance-
ment of the Ru-C bond in 2 can also be found from the IR
data. Both νCN stretches in 2 are ca. 50 cm-1 higher than
those found for the monocyano adduct 1, which is attributed
to an enhanced Ru-CN bonding.39
Table 4 reveals a peculiar pattern of deviation from the
4-fold symmetry about the Ru2 core. In the (4,0) molecule
2A, there are two short Ru-Np bonds (Ru1-N3 and Ru1-
N5 where Np stands for a pyridyl-nitrogen) and two long
Ru-Np bonds (Ru1-N7 and Ru1-N9) at the “0” site (Ru1),
and each short bond is always trans to a long one. The same
pattern also holds for Ru-Na bonds at the “4” site (Ru2) in
2A (Na stands for an anilino nitrogen). In the (3,1) molecule
5, the Ru1 center (“1” site) has two short (Ru1-N1 and
(37) Dunbar, K. R.; Szalay, P. S. Inorg. Chem. Commun. 2000, 49.
(38) Drago, R. S. Physical Methods in Chemistry; Saunders: Philadelphia,
1977.
(39) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 5th ed.; Wiley: New York, 1997; Vol. B.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6235

Bear et al.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Dicyano Complexes 2 and 5
2A 2B
5
Ru(1)-C(1)
2.01(3)
2.01(2)
2.03(2)
2.07(2)
2.13(2)
2.451(3)
2.01(4)
2.11(2)
2.10(2)
2.04(2)
2.06(2)
1.17(4)
1.13(4)
89.5(6)
87.5(6)
84.0(6)
83.5(6)
172.8(9)
177(3)
83.8(6)
84.6(6)
89.6(6)
89.6(7)
171.8(10)
179(4)
22.5(9)
24.8(9)
20.8(9)
23.7(9)
Ru(3)-C(47)
2.03(4)
2.00(2)
2.12(2)
2.06(2)
2.04(2)
2.447(3)
2.02(4)
2.11(2)
2.06(2)
2.05(2)
2.10(2)
1.17(4)
1.14(4)
83.9(6)
89.5(7)
89.6(6)
84.6(6)
171.9(10)
177(3)
89.6(7)
83.7(6)
84.4(6)
87.6(6)
172.9(9)
179(3)
22.6(9)
23.6(9)
20.5(9)
24.8(8)
Ru(1)-N(1)
2.002(4)
2.108(3)
2.154(3)
1.988(4)
2.000(5)
2.456(5)
2.130(4)
1.986(3)
2.001(3)
2.158(3)
1.993(5)
1.140(6)
1.153(6)
95.6(1)
Ru(1)-N(3)
Ru(3)-N(13)
Ru(1)-N(3)
Ru(1)-N(5)
Ru(3)-N(15)
Ru(1)-N(5)
Ru(1)-N(7)
Ru(3)-N(17)
Ru(1)-N(8)
Ru(1)-N(9)
Ru(3)-N(19)
Ru(1)-C(45)
Ru(1)-Ru(2)
Ru(3)-Ru(4)
Ru(1)-Ru(2)
Ru(2)-C(2)
Ru(4)-C(48)
Ru(2)-N(2)
Ru(2)-N(4)
Ru(4)-N(14)
Ru(2)-N(4)
Ru(2)-N(6)
Ru(4)-N(16)
Ru(2)-N(6)
Ru(2)-N(8)
Ru(4)-N(18)
Ru(2)-N(7)
Ru(2)-N(10)
Ru(4)-N(20)
Ru(2)-C(46)
N(1)-C(1)
N(11)-C(47)
N(9)-C(45)
N(2)-C(2)
N(12)-C(48)
N(10)-C(46)
N(3)-Ru(1)-Ru(2)
N(5)-Ru(1)-Ru(2)
N(7)-Ru(1)-Ru(2)
N(9)-Ru(1)-Ru(2)
C(1)-Ru(1)-Ru(2)
N(1)-C(1)-Ru(1)
N(4)-Ru(2)-Ru(1)
N(6)-Ru(2)-Ru(1)
N(8)-Ru(2)-Ru(1)
N(10)-Ru(2)-Ru(1)
C(2)-Ru(2)-Ru(1)
N(2)-C(2)-Ru(2)
N(14)-Ru(4)-Ru(3)
N(16)-Ru(4)-Ru(3)
N(18)-Ru(4)-Ru(3)
N(20)-Ru(4)-Ru(3)
C(48)-Ru(4)-Ru(3)
N(11)-C(47)-Ru(3)
N(13)-Ru(3)-Ru(4)
N(15)-Ru(3)-Ru(4)
N(17)-Ru(3)-Ru(4)
N(19)-Ru(3)-Ru(4)
C(47)-Ru(3)-Ru(4)
N(12)-C(48)-Ru(4)
N(1)-Ru(1)-Ru(2)
N(3)-Ru(1)-Ru(2)
N(5)-Ru(1)-Ru(2)
N(8)-Ru(1)-Ru(2)
C(45)-Ru(1)-Ru(2)
N(9)-C(45)-Ru(1)
N(2)-Ru(2)-Ru(1)
N(4)-Ru(2)-Ru(1)
N(6)-Ru(2)-Ru(1)
N(7)-Ru(2)-Ru(1)
C(46)-Ru(2)-Ru(1)
N(10)-C(46)-Ru(2)
82.78(9)
79.83(9)
91.4(1)
166.2(1)
172.7(4)
79.20(10)
91.01(10)
92.39(10)
82.69(9)
162.5(1)
176.2(4)
15.86(15)
19.46(13)
24.46(13)
18.66(15)
N(3)-Ru(1)-Ru(2)-N(4)
N(5)-Ru(1)-Ru(2)-N(6)
N(7)-Ru(1)-Ru(2)-N(8)
N(9)-Ru(1)-Ru(2)-N(10)
N(13)-Ru(3)-Ru(4)-N(14)
N(15)-Ru(3)-Ru(4)-N(16)
N(17)-Ru(3)-Ru(4)-N(18)
N(19)-Ru(3)-Ru(4)-N(20)
N(1)-Ru(1)-Ru(2)-N(2)
N(3)-Ru(1)-Ru(2)-N(4)
N(5)-Ru(1)-Ru(2)-N(6)
N(8)-Ru(1)-Ru(2)-N(7)
Table 5. Selected Average Bond Lengths (Å) and Bond Angles (deg) of Ru2(L)4(Lax)2 (L ) ap or Fap and Lax ) CN or C2C6H5)
(3,1) isomer (4,0) isomer
Ru2(Fap)4(C2C6H5)2 Ru2(ap)4(C2C6H5)2
a
b
Ru2(Fap)4(CN)2 (5)
Ru2(ap)4(CN)2 (2)
bond lengths (Å)
2.469(6)
Ru-Ru
Ru-C
C-N
Ru-Na
Ru-Np
2.456(5)
1.997(5)
1.145(6)
2.026(3)
2.106(4)
2.451
2.01
1.15
2.06
2.08
2.4707(3)
1.988(2)
2.002(6)
2.020(4)
2.130(4)
2.050(2)
2.067(3)
bond angles (deg)
161.0(17)
90.33(10)
83.08(11)
18.2
Ru-Ru-C
164.4(12)
88.50(9)
85.24(10)
19.6
172.3(9)
86.1(6)
86.9(6)
22.9
163.0(1)
Ru-Ru-Na
Ru-Ru-Np
N-Ru-Ru-N
85.6(1)
87.0(1)
22.4
a Reference 41. b Reference 42.
Ru1-N8) bonds that are trans to two long (Ru1-N3 and
Ru1-N5) bonds. In addition to the disparity among Ru-N
distances, average Ru-Ru-C angles in 2 (172.5°) and 5
(164.1°) deviate significantly from linearity. As elaborated
for diruthenium dialkynyl complexes, these distortions have
an electronic origin, a second-order Jahn-Teller ef-
fect.12,19,30,40 As in the case of the monoadduct, compounds
2 and 5 are isoelectronic with previously characterized Ru2-
(ap)4(C2Y)2.
X-ray structures of diphenylacetylide analogues of 2 and
5 were previously reported,41,42 and some relevant bond
lengths and angles are gathered in Table 5 along with those
of 2 and 5 for comparison purpose.
selected averaged bond lengths and bond angles of 8 along
with those of Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN)20 for com-
parison purposes. Compound 8 and previously characterized
Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN)20 possess a similar coor-
dination sphere around the Ru2 core. These two compounds
also exhibit similar bond lengths and bond angles (Table 6)
despite the fact that F5ap is more bulky and more electron
withdrawing than the F3ap ligand. In both cases, the
coordination sphere of the two Ru atoms can be described
as a distorted octahedral with Ru1 attached to three Np and
one Na centers and Ru2 attached to one Np and three Na
centers. The edge-sharing motif is completed with the two
octahedrons fusing along a common equatorial edge defined
by C45 and C46 centers. Two of the F3ap ligands are chelated
to Ru centers, while the other two are in three-atom bidentate
bridging modes. The Ru-Ru bond length of 8 (see Table 6)
is similar to that of Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN)20 but
is 0.36 Å longer than its parent compound Ru2(F3ap)4Cl.24
The elongation of the bond is consistent with a decrease in
Molecular Structure of Compound 8. The molecular
structure of 8 is given in Figure 5 while Table 6 summarizes
(40) Lin, C.; Ren, T.; Valente, E. J.; Zubkowski, J. D. J. Chem. Soc., Dalton
Trans. 1998, 571.
(41) Wellhoff, J. M.S. Thesis, University of Houston, Houston, TX, 2000.
(42) Huang, S. R. Ph.D. Dissertation, University of Houston, Houston, TX,
1994.
6236 Inorganic Chemistry, Vol. 42, No. 20, 2003

Cyanide Adducts on the Diruthenium Core [Ru2(L)4]+
Table 7. Half-Wave Potentials (V vs SCE) for Redox Processes of
Ru2(L)4(Lax)n (L ) ap, CH3ap, or Fap; Lax ) Cl or CN; and n ) 1 or 2)
in CH2Cl2 Containing TBAP as Supporting Electrolyte
E
1/2, V vs SCE
isomer bridging
axial
7+/6+
6+/5+
5+/4+
type
ligand, L ligand, Lax Ru2
Ru2
Ru2
ref
(4,0)
ap
Cl-
0.37
0.43
-0.24
0.41
0.46
0.47
0.52
-0.21
-0.86
-0.73
-1.24a
-0.89
-0.73
-0.77
-0.68
-1.08
42
b
b
24
b
25
b
CN-
2 CN-
Cl-
1.30
1.02a
1.44
1.08a
1.43
1.47
0.92
(4,0)
(3,1)
CH3ap
Fap
CN-
Cl-
CN-
2 CN-
b
a Ep at 0.1 V/s. b This work.
Figure 5. Thermal ellipsoid plot (40% equiprobability envelopes) of the
(3,1) isomer of Ru2(F3ap)3[µ-(o-CN)F2ap](µ-CN). H atoms have been
omitted for clarity.
Table 6. Selected Average Bond Lengths (Å) and Bond Angles (deg)
of Ru2(Fxap)3[µ-(o-NC)Fx-1ap)](µ-CN) (x ) 3 or 5)
x ) 3
x ) 5a
bond lengths (Å)
2.644
Ru-Ru
2.647
1.980
1.988
1.173
1.227
2.063
2.102
Ru-C(45)
Ru-C(46)
C(45)-N(9)
C(46)-N(10)
Ru-Na
2.086
1.986
1.174
1.232
2.057
2.092
Figure 6. Cyclic voltammograms of Ru2(Fap)4(CN) and Ru2(Fap)4(CN)2
in CH2Cl2 containing 0.1 M TBAP. Scan rate ) 0.1 V/s.
Ru-Np
and one oxidation. Each electrochemical process is proposed
to involve the dimetal unit. The half-wave potentials in CH2-
Cl2, 0.1 M TBAP are given in Table 7, and cyclic voltam-
mograms for Ru2(Fap)4(CN) and Ru2(Fap)4(CN)2 are shown
in Figure 6. The Ru26+/5+ and Ru25+/4+ couples of Ru2(Fap)4-
(CN)2 are located at E1/2 ) -0.21 and -1.08 V and are both
negatively shifted with respect to the same electrode reactions
of Ru2(Fap)4(CN) (E1/2 ) 0.52 and -0.68 V). The largest
bond angles (deg)
163.0
Ru(1)-C(45)-N(9)
C(46)-N(10)-C(44)
Ru-Ru-Na
161.6
142.6
114.5
120.3
143.3
114.9
119.8
Ru-Ru-Np
a Reference 20.
bond order (b.o.) upon going from (3,1) Ru2(F3ap)4Cl (b.o.
) 2.5) to 8 (b.o. ) 0.5). Also, in general, the averaged Ru-
(1)-N bond distance is 0.27 Å longer than the averaged Ru-
(2)-N distance and this was also the case for Ru2(F5ap)3[µ-
(o-NC)F4ap)](µ-CN).20
shift is seen for the Ru26+/5+ process (∆E1/2 ) 730 mV) while
5+/4+
the smallest (400 mV) is seen for Ru2
.
A similar trend in E1/2 is seen when comparing the Ru26+/5+
5+/4+
and Ru2
couples of Ru2(ap)4(CN) (Figure 7) and Ru2-
As previously discussed for Ru2(F5ap)3[µ-(o-NC)F4ap)]-
(µ-CN), the C45-N9 cyanide ligand is σ-bonded to Ru(1)
and π-bonded to Ru(2), resulting in an asymmetry of the
bridging cyanide ligand.20 This phenomenon is also seen in
8 where the C45-N9 cyanide ligand bridges two ruthenium
atoms. In addition, the Ru1-C45-N9 angle of 163.0° (see
Table 6) also suggests that the cyanide group of Ru2(F3ap)3-
[µ-(o-NC)F2ap)](µ-CN) bridges the two ruthenium atoms in
a σ-π mode. Similar to the case of the F5ap derivative, the
bond length of C(45)-N(9) (1.174 Å) is slightly shorter than
that of C(46)-N(10) (1.232 Å). The σ-π binding modes of
CN- are consistent with the low frequency of CN- vibrations
(less than 2000 cm-1), the latter of which are influenced by
π back-donation from the Ru2 dimetal core.7,39
(ap)4(CN)2 (Figure 8), but Ru2(ap)4(CN)2 is less stable than
Ru2(Fap)4(CN)2 in CH2Cl2 and undergoes a loss of one CN-
ligand to give a mixture of [Ru2III,III(ap)4(CN)]+ and Ru2
-
III,III
(ap)4(CN)2 in solution, prior to carrying out the experiment.
This is evident from Figure 8, which shows a reversible
process at E1/2 ) -0.73 V, which also appears in the cyclic
voltammogram of Ru2(ap)4(CN) (see Figure 7).
This reaction sequence of Ru2(ap)4(CN)2 is given in
Scheme 3 where the process at E1/2 ) -0.73 V corresponds
to the reduction of Ru2(ap)4(CN) and that at -0.29 and -1.25
V correspond to the electrode reaction of Ru2(ap)4(CN)2.
As seen in Figure 8, the two reduction processes of the
dicyano adduct have larger currents than the single reduction
in the case of the monocyano adduct, thus indicating that
Ru2(ap)4(CN)2 is the predominant species in solution under
these experimental conditions. The third reduction in Figure
8 (the second reduction of Ru2(ap)4(CN)2) is irreversible and
is accompanied by an increased formation of [Ru2(ap)4(CN)]-.
Electrochemistry of Ru2(L)4(CN)x (L ) ap or Fap). The
three investigated mono-CN complexes, which are in a Ru2
oxidation state in their air-stable form, undergo one reduction
and two oxidations, while the two dicyano species, which
contain a Ru2 core, are characterized by two reductions
5+
6+
Inorganic Chemistry, Vol. 42, No. 20, 2003 6237

Bear et al.
Scheme 3
160 mV for the CH3ap derivative. This is because the π-back-
bonding effect (which results from a good overlap between
the π*Ru-Ru orbital and the empty π*CN orbital) between CN-
4+
and the dimetal core stabilizes the Ru2 oxidation state of
each compound. There is only a small effect of the axial
ligand on the oxidation of the compounds, thus revealing
that the lowest unoccupied molecular orbital (LUMO) is
more sensitive to axial ligation than the highest occupied
molecular orbital (HOMO), a result consistent with the fact
that the reduction of Ru2(L)4Cl (L ) ap, Fap, or CH3ap) has
been proposed to involve the π* orbital while the oxidation
the δ* orbital.24
Figure 7. Cyclic voltammogram of Ru2(ap)4(CN) in CH2Cl2 containing
0.1 M TBAP at a scan rate of 0.1 V/s.
Electrochemical and Spectroscopic Properties of Ru2-
(Fxap)3[µ-(o-NC)Fx-1ap](µ-CN) (x ) 1, 3, or 5). Figure 9
illustrates cyclic voltammograms of Ru2(Fxap)3[µ-(o-NC)-
Fx-1 ap)](µ-CN) (x ) 1, 3, or 5) in CH2Cl2 containing 0.1
M TBAP. Each redox reaction of the compounds in Table 8
(labeled as I, II, and III in Figure 9) shifts in a cathodic
direction upon going from x ) 5 to x ) 1, and this is
attributed to a higher electronic density of the diruthenium
core owing to a decrease in the electron-withdrawing
properties of the equatorial bridging ligands. A similar trend
was reported in the case of Ru2(Fxap)4Cl (x ) 0, 1, 3, or 5)
where the data were analyzed in terms of LFER between
E1/2 and Σσ for the substituents on the anilino part of the
bridging ligand.24 In fact, similar correlations between E1/2
and Σσ exist for the three redox reactions of Ru2(Fxap)3[µ-
(o-NC)Fx-1ap)](µ-CN) (x ) 1, 3, or 5) as shown in Figure
10. The correlation coefficients (R2) for the E1/2 vs Σσ plots
in Figure 10 are 0.996 for the first reduction and 0.999 for
both oxidations and the fact that the plots give good fits
suggests that 6 should indeed be formulated as Ru2(Fap)3-
[µ-(o-NC)ap)](µ-CN), although no X-ray crystal structure
could be obtained to confirm this structure. The first
reduction of Ru2(Fxap)3[µ-(o-NC)Fx-1ap)](µ-CN) exhibits a
F value of 108 mV and this is virtually the same as what is
seen for the first oxidation where F ) 111 mV, thus
suggesting that the electron is added or removed from the
same orbital. This is indeed the case as discussed in the next
paragraph.
Figure 8. Cyclic voltammogram of Ru2(ap)4(CN)2 in CH2Cl2 containing
0.1 M TBAP after reversing the scan after (a) the first, (b) the second, and
(c) the third reduction. Scan rate ) 0.1 V/s.
The well-resolved ESR spectrum of Ru2(F3ap)3[µ-(o-NC)-
F2ap)](µ-CN) (8) shows a rhombic signal with three g values
(g1 ) 2.118, g2 ) 2.042, g3 ) 1.944) and resembles the ESR
spectra19,20,43 of Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN), [Ru2(F5ap)4-
(CtCC6H5)2]-, and [Ru2(dpf)4(CtCC6H5)2]-, all of which
Thus, the reoxidation currents for the process at -0.73 V
are larger than those obtained when the potential is termi-
nated at -1.00 V. This is shown in Figure 8c.
As seen in Table 7, the reduction of each “ap-type”
complex shifts in a positive direction upon switching the axial
ligand from Cl- to CN-, with the magnitude of the potential
shift ranging from 90 mV for the ap and Fap derivatives to
(43) Bear, J. L.; Li, Y.; Han, B.; Van Caemelbecke, E.; Kadish, K. M.
Inorg. Chem. 1997, 36, 5449.
6238 Inorganic Chemistry, Vol. 42, No. 20, 2003

Cyanide Adducts on the Diruthenium Core [Ru2(L)4]+
Figure 10. Linear free energy relationship for the redox reactions of the
(3,1) isomer of Ru2(Fxap)3[µ-(o-NC)Fx-1ap](µ-CN) (x ) 1, 3 or 5) (open
circle: second oxidation, open square: first oxidation and open triangle:
first reduction).
Figure 9. Cyclic voltammograms of Ru2(Fxap)3[µ-(o-NC)Fx-1ap](µ-CN)
(x ) 1, 3 or 5) in CH2Cl2 containing 0.1 M TBAP. Scan rate ) 0.1 V/s.
characterized) since the purification of the reaction mixture
reveals that Ru2(F3ap)3[µ-(o-NC)F2ap)](µ-CN) is not the only
product formed during the reaction.
Table 8. Half-Wave Potentials (V vs SCE) of
Ru2(Fxap)3[µ-(o-NC)Fx-1ap](µ-CN) (x ) 1, 3, or 5) in CH2Cl2
Containing 0.1 M TBAP
The direct precursor of Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-CN)
has been identified as one of the two geometric isomers of
Ru2(F5ap)4(µ-CN)2,20 and the formation of Ru2(Fxap)4(µ-CN)2
(x ) 1 or 3) appears therefore to be the key step in the overall
conversion of Ru2(Fxap)4Cl to Ru2(Fxap)3[µ-(o-NC)Fx-1ap)]-
(µ-CN).
As shown in Scheme 4, three different routes can be
proposed for the formation of Ru2(Fxap)4(µ-CN)2 (b). First
of all, the reaction product (b) could be simply a rearrange-
ment of the reaction product (a) (see route 2 in Scheme 4)
due to a preferred electronic configuration or a more
thermodynamically stable structure (although no experimen-
tal data has yet been obtained to support this mechanism).
Routes 1 and 3 can also be proposed for formation of reaction
product (b) but it is not clear at this time how a second CN-
ligand can be added to the monocyano product Ru2(Fxap)4-
(CN) or [Ru2(Fxap)4(CN)Cl]- without forming the dicyano
adduct Ru2(Fxap)4(CN)2 as an intermediate. One possibility
is that the monocyano adduct undergoes a structural rear-
rangement prior to addition of a second ligand, but no trace
of such a product has yet been found in the reaction mixture.
oxidation
reduction
6+
5+
4+
Ru27+/Ru2
(III)
Ru26+/Ru2
Ru25+/Ru2
(I)
x
4Σσa
(II)
5
3
1
4.64
1.92
0.72
1.45
1.20
1.08
0.96
0.68
0.52
-0.01
-0.32
-0.43
a Because one of the F atoms on the chelating Fxap ligand is substituted
by one of the bridging cyanides, the value of Σσb was calculated based on
only three fluorine atoms on the ligand. b Zuman, P. Substituent Effects in
Organic Polarography; Plenum Press: New York, 1967.
have been assigned as diruthenium(II,III) complexes. The
magnetic susceptibility of 8 was calculated using the Evan’s
method and the room temperature magnetic moment of 1.45
µB is consistent with the presence of only one unpaired
electron in the compound. On the basis of the ESR and
magnetic properties, 8 is therefore proposed to have the
electronic configuration σ2π2δ2δ*2π*2σ*1. The same elec-
tronic structure was given to Ru2(F5ap)3[µ-(o-NC)F4ap)](µ-
CN),20 a compound with a similar structural type and whose
ESR features and magnetic properties resemble what is seen
in the case of 8. This electronic configuration implies that
the HOMO and LUMO are both the σ* orbital, thus resulting
in virtually the same F value for the first reduction and the
first oxidation of the series Ru2(Fxap)3[µ-(o-NC)Fx-1ap)](µ-
CN) (x ) 1, 3, or 5) as shown in Figure 10.
Summary
In the present study, we have structurally and electro-
chemically examined the products of the reaction between
CN- and four different diruthenium complexes of the type
Ru2(L)4Cl where L is ap or a substituted ap ligand. The type
of reaction products varies with the nature of the bridging
ligand and in some cases with the experimental conditions
themselves. More specifically, only mono- and/or dicyano
adducts are found as reaction products when L ) ap or CH3-
ap but compounds with the structural type Ru2(Fxap)3[µ-(o-
NC)Fx-1ap](µ-CN) or Ru2(Fxap)4(µ-CN)2 are also isolated
Proposed Mechanism of Rearrangement. Table 2 shows
that when the product formulated as Ru2(Fxap)3[µ-(o-NC)-
F
x-1ap)](µ-CN) (x ) 1 or 5) is obtained in the reaction
between CN- and Ru2(Fxap)4Cl, the reaction mixture also
contains one or two additional compounds with the structural
type Ru2(Fxap)4(µ-CN)2. This is most likely also true for
Ru2(F3ap)4Cl (although as discussed in the Experimental
Section all products of the reaction were not isolated and
Inorganic Chemistry, Vol. 42, No. 20, 2003 6239

Bear et al.
Scheme 4
when L ) Fap or F3ap. Interestingly, the reaction between
CN- and the (3,1) isomer of Ru2(L)4Cl where L is an “ap-
type” ligand is more likely to form a mono- or dicyano
adduct as the basicity of the bridging ligand increases. Both
mono- and dicyano derivatives possess the isomer type of
their parent chloro complexes, but Ru-Ru bond lengths in
the monocyano derivatives are larger than those in their
respective chloro derivatives owing to the strong σ-donor
properties of the CN- axial ligand. The crystal structure and
the IR data of Ru2(ap)4(CN)2 reveal a greatly enhanced
interaction between the CN group and the dimetal core in
the dicyano complex. All synthesized mono- and dicyano
adducts were also electrochemically investigated in CH2Cl2.
Ru2(ap)4(CN), Ru2(CH3ap)4(CN), and Ru2(Fap)4(CN) exhibit
a similar behavior, and the three compounds undergo one
reversible reduction and two oxidations within the solvent
potential range investigated.
Acknowledgment. This work is supported in part by both
the University of Miami and the Petroleum Research Fund/
ACS (36595-AC3). The support of the Robert A. Welch
Foundation (J.L.B., Grant E-918; K.M.K., Grant E-680) is
also gratefully acknowledged. We thank Dr. J. D. Korp for
performing the X-ray analyses as well as Tuan Phan and
Dr. Giribabu for help in electrochemical measurements.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determination of compounds 1-3,
5 and 8. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC030195M
6240 Inorganic Chemistry, Vol. 42, No. 20, 2003