Linkage and redox isomerism in ruthenium complexes of catecholate, semi-quinone, and o-acylphenolate ligands derived from tri- and tetrahydroxy-9,10-anthracenediones

Article abstract of DOI:10.1021/ic010068v

The complexes Ru(CO)₂L₂(PHAQ-2H) (PHAQ = 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3-trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L = PPh₃, PCy₃, PBu₃), and Ru(CO)(dppe)(PBu₃)(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO)₂(PBu₃)₂(AG-2H) crystallizes in the space group P2₁/n (No. 14 var) with a = 13.317(2), b = 15.628(2), c = 21.076(3) A, β = 101.660(10)°, Z = 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO)₂L₂(PHAQ-2H)]¹⁺ and [Ru(CO)(dppe)(PBu₃)(PHAQ-2H)]¹⁺ were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy₃)₂(PUR-H), is also reported.

Full text of DOI:10.1021/ic010068v

Inorg. Chem. 2001, 40, 4361-4367
4361
Linkage and Redox Isomerism in Ruthenium Complexes of Catecholate, Semi-quinone, and
o-Acylphenolate Ligands Derived from Tri- and Tetrahydroxy-9,10-anthracenediones
Melvyn Rowen Churchill,* Kim M. Keil, Brian P. Gilmartin, Joshua J. Schuster, and
Jerome B. Keister*
Department of Chemistry, University at Buffalo, the State University of New York,
Buffalo, New York 14260-3000
Thomas S. Janik
Department of Chemistry, Fredonia State University, the State University of New York,
Fredonia, New York 14063
ReceiVed January 18, 2001
The complexes Ru(CO)2L2(PHAQ-2H) (PHAQ ) 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3- trihydroxy-
9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L ) PPh3, PCy3, PBu3), and
Ru(CO)(dppe)(PBu3)(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO)2-
(PBu3)2(AG-2H) crystallizes in the space group P21/n (No. 14 Var) with a ) 13.317(2), b ) 15.628(2), c )
21.076(3) Å, â ) 101.660(10)°, Z ) 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The
electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO)2L2(PHAQ-2H)]1+
and [Ru(CO)(dppe)(PBu3)(PHAQ-2H)]1+ were generated by chemical oxidation. One example of an o-acylphenolate
complex, HRu(CO)(PCy3)2(PUR-H), is also reported.
Introduction
anthracenedione (alizarin), including 1,2-catecholate, 1,9-
acylphenolate, and 1,2-semi-quinone complexes.4 In this paper
we present the syntheses and characterizations of ruthenium
complexes (Figure 1) of the PHAQs purpurin, anthragallol, and
quinalizarin.
Metal complexes of polyhydroxy-9,10-anthracenediones
(PHAQs)1 have been used as dyes and as indicators.2,3 Relatively
few organometallic complexes have been reported. As ligands
PHAQs offer three features of interest to organometallic
chemistry. (1) They can exhibit linkage isomerism, acting as
chelates via the 1,2-, 2,3-, or the 1,9-oxygen atoms and other
adjacent oxygen atoms. (2) As 1,2-chelates they display ligand-
based redox chemistry. (3) The complexes are deeply colored,
allowing for applications of the complexes as optical sensor
components or as molecular recognition elements. We recently
reported some ruthenium complexes of 1,2-dihydroxy-9,10-
Experimental Section
Starting Materials. Dichloromethane was distilled under nitrogen
from calcium hydride before use. Purpurin was obtained from Aldrich.
Quinalizarin was obtained from Pfaltz & Bauer. Anthragallol was
prepared according to a literature procedure.5 Ru3(CO)12 was obtained
from Strem. Other chemicals were of reagent grade purity and were
used as received. All reactions were carried out under a blanket of
nitrogen and with nitrogen-saturated solvents using standard Schlenk
procedures. However, workup and spectral analyses were conducted
without exclusion of air.
Physical Methods of Characterizations. Infrared spectra were
recorded on a Nicolet Magna 550 spectrophotometer. 1H NMR spectra
were obtained on Varian Associates Gemini 300 or Varian Associates
VXR-400S instruments, using deuteriochloroform as solvent and TMS
as reference. 13C NMR spectra were recorded on the Gemini 300 or
the VXR-400S instrument in deuteriochloroform and referenced to
TMS. 31P NMR spectra were recorded on the VXR-400S instrument
in deuteriochloroform, and chemical shifts are reported relative to
o-phosphoric acid. UV/visible spectra (300-800 nm) were recorded
using a Hewlett-Packard 8452A diode array spectrophotometer. EPR
spectra were recorded on an IBM/Bruker X-band ER-200 SRC
spectrometer, with a microwave power of 20 mW, in dichloromethane
solutions. Spectral parameters were determined by comparison of
experimental spectra with spectra simulated using Bruker WINEPR
Simfonia (ver. 1.25) software.
* To whom correspondence should be addressed.
(1) Throughout this paper the following abbreviations are used: purpurin
(1,2,4-trihydroxy-9, 10-anthracenedione), PUR; anthragallol (1,2,3-
trihydroxy-9, 10-anthracenedione), AG; quinalizarin (1,2,5,8-tetrahy-
droxy-9, 10-anthracenedione), QAL. The removal of one hydroxyl
proton is indicated by “-H” and of two hydroxyl protons as “-2H”;
removal of three hydroxyl protons and O-methylation is indicated by
“-3H+Me”.
(2) For example, see: (a) Capitan, F.; Roman, M. Inf. Quim Anal. 1967,
21, 208. (b) Roman, M.; Fernandez-Gutierrez, A. Bol. Soc. Quim. Peru
1975, 41, 1. (c) Maties, R.; Jimenez, F.; Arias, J. J.; Roman, M. Anal.
Let. 1997, 30, 2059. (d) Capitan, F.; Arrebola Ramirez, A.; Jimenez
Linares, C. Analyst (London) 1986, 111, 739. (e) Fieser, L. F. J. Chem.
Educ. 1930, 7, 2609.
(3) (a) DelMedico, A.; Auburn, P. R.; Dodsworth, E. S.; Lever, A. B. P.;
Pietro, W. J. Inorg. Chem. 1994, 33, 1583. (b) DelMedico, A.; Pietro,
W. J.; Lever, A. B. P. Inorg. Chim. Acta 1998, 281, 126. (c)
DelMedico, A.; Fielder, S. S.; Lever, A. B. P.; Pietro, W. J. Inorg.
Chem. 1995, 34, 1507. (d) Masoud, M. S.; Tawfik, M. S.; Zayan, S.
E. Synth. React. Inorg. Met.-Org. Chem. 1984, 14, 1. (e) Wunderlich,
C.-H.; Bergerhoff, G. Chem. Ber. 1994, 127, 1185. (f) Bulatov, A.
V.; Khidekel, M. L.; Egorochkin, A. N.; Panicheva, M. V.; Sennikov,
P. G. Transition Met. Chem. 1983, 8, 289. (g) Merrell, P. H., Inorg.
Chim. Acta 1979, 32, 99. (h) Bakola-Christianopoulou, M. N.
Polyhedron 1984, 3, 729.
(4) Churchill, M. R.; Keil, K. M.; Bright, F. V.; Pandey, S.; Baker, G.
A.; Keister, J. B. Inorg. Chem. 2000, 39, 5807.
(5) Seuberlich, C. Ber. 1877, 10, 38.
10.1021/ic010068v CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/20/2001

4362 Inorganic Chemistry, Vol. 40, No. 17, 2001
Churchill et al.
λ
max(ꢀ) 498 (8.5 × 103) nm. Anal. Calcd for C51H73O6P2Ru: C, 64.81;
H, 7.78. Found: C, 65.01; H, 7.88.
Ru(CO)2(PCy3)2(PUR-2H). IR (CH2Cl2): 2031.6 s, 1966.4 s cm-1
.
1H NMR (CDCl3): δ 15.937 (s, 1 H), 8.279 (m, 2 H), 7.598 (m, 2 H),
6.135 (s, 1 H), 2.2-1.0 (m, 66 H) ppm. 31P{1H} NMR (CDCl3): δ
38.22 ppm. UV/vis (CH2Cl2): λmax(ꢀ) 362 (2.0 × 104), 512 (4.8 ×
103), 546 (8.0 × 103), 586 (7.1 × 103) nm. Anal. Calcd for C52H72O7P2-
Ru: C, 64.25; H, 7.46. Found: C, 64.39; H, 7.65.
Ru(CO)(dppe)(PBu3)(PUR-2H). A solution of Ru3(CO)12 (247.7
mg, 539 µmol), dppe (650 mg, 1.63 mmol), and purpurin (418 mg,
1.63 mmol) in toluene (30 mL) was heated at reflux under a nitrogen
atmosphere for 3.5 h. Then PBu3 (411 µL, 1.65 mmol) was added, and
the solution was heated at reflux for 8 more hours. The products were
separated by TLC on silica eluting with 2% ethyl acetate in dichloro-
methane. The second, purple band was extracted with ethyl acetate.
Yield, 532 mg, 33%.
Ru(CO)(dppe)(PBu3)(PUR-2H). IR (CH2Cl2): 1948.0 cm-1. 1H NMR
(CDCl3): δ 16.12 (s, 1 H), 8.94 (dd, 2 H, J ) 8, 11 Hz), 8.54 (m, 1
H), 8.26 (m, 1 H), 7.86 (m, 2 H), 7.68 (m, 1 H), 7.64-7.42 (m, ca. 11
H), 7.37 (d, 1 H, J ) 6 Hz), 6.94 (m, 1 H), 6.71 (m, 3 H), 6.01 (s, 1
H), 3.05 (m, 1 H), 2.60 (m, 1 H), 2.47 (m, 1 H), 2.05 (m, 1 H), 1.26
(m, 6 H), 1.05 (m, 6 H), (m, 6 H), 0.71 (t, 9 H, J ) 7 Hz) ppm. 31P-
{1H} NMR (CDCl3): δ 60.55 (dd, 1 PA), 44.98 (dd, 1 PB), 18.00 (dd,
1 PC) ppm, JAB ) 12 Hz, JAC ) 23 Hz, JBC ) 334 Hz. UV/vis (CH2-
Cl2): λmax(ꢀ) 520 (1.2 × 104), 552 (1.7 × 104), 592 (1.5 × 104) nm.
Anal. Calcd for C53H57O6P3Ru: C, 64.69; H, 5.84. Found: C, 64.60;
H, 5.80.
Ru(CO)(dppe)(PBu3)(PUR-3H+Me). A solution of Ru(CO)(dppe)-
(PBu3)(PUR-2H) (51.5 mg, 52.4 µmol), potassium t-butoxide (57 mg,
520 µmol), and methyl iodide (150 µL, 240µmol) in 5 mL of THF
was stirred under argon for 5 days. The solution was evaporated, and
the residue was separated by TLC on silica eluting with 10% ethyl
acetate in dicloromethane. The second, blue band was extracted with
ethyl acetate, yielding 29.3 mg, 56%, upon evaporation.
Ru(CO)(dppe)(PBu3)(PUR-3H+Me). IR (CH2Cl2): 1943.3 cm-1. 1H
NMR (CDCl3): δ 8.94 (dd, 2 H, J ) 8, 11 Hz), 8.30 (m, 1 H), 8.25
(m, 1 H), 8.03 (m, 1 H), 7.82 (m, 2 H), 7.66 (m, 1 H), 7.6-7.3 (m, 10
H), 7.20 (m, 1 H), 6.95 (m, 2 H), 6.67 (m, 2 H), 6.18 (s, 1 H), 3.78 (s,
3 H), 3.02 (dm, 1 H), 2.57 (dm, 1 H), 2.42 (m, 1 H), 2.07 (m, 1 H),
1.26 (m, 6 H), 1.15 (m, 6 H), 1.06 (m, 6 H), 0.68 (t, 9 H, J ) 7 Hz)
ppm. 31P{1H} NMR (CDCl3): δ 60.04 (dd, 1 PA), 43.48 (dd, 1 PB),
17.79 (dd, 1 PC) ppm, JAB ) 12 Hz, JAC ) 23 Hz, JBC ) 348 Hz.
UV/vis (CH2Cl2): λmax(ꢀ) 384 (3800), 562 (1.2 × 104), 594 (1.0 ×
104) nm. Anal. Calcd for C54H59O6P3Ru: C, 64.99; H, 5.96. Found:
C, 65.27; H, 6.15.
Figure 1. Structures of complexes derived from purpurin (PUR),
anthragallol (AG), and quinalizarin (QAL). 1: Ru(CO)2(PR3)2(PUR-
2H) (R1 ) OH, R2 ) H, L′ ) CO); Ru(CO)2-n(PR3)2+n(QAL-2H) (R1
) H, R2 ) O H, L′ ) CO or PR3). 2: Ru(CO)(PBu3)(dppe)(PUR-2H)
(R1 ) OH, R2 ) H); Ru(CO)(PBu3)(dppe)(QAL-2H) (R1 ) H, R2 )
OH); Ru(CO)(PBu3)(dppe)(PUR-3H+Me) (R1 ) OMe, R2 ) H). 3:
Ru(CO)2-n(PR3)2+n(AG-2H) (L′ ) CO or PR3). 4: Ru(CO)(PBu3)-
(dppe)(AG-2H) (R ) H); Ru(CO)(PBu3)(dppe)(AG-3H+Me) (R) Me).
5: HRu(CO)(PCyc3)2(1,9-PUR-H). 6: HRu(CO)(PCyc3)2(4,10-PUR-
H).
Electrochemistry. The electrochemical procedures were conducted
as described previously.4 All potentials are reported relative to the
ferrocene/ferrocinium couple as 0 V.
Ru(CO)2(PBu3)2(PUR-2H). A solution of Ru3(CO)12 (103 mg, 161
µmol), PBu3 (240 µL, 960 µmol), and purpurin (126 mg, 492 µmol) in
toluene (30 mL) was heated at reflux under an argon atmosphere for
14 h. The resulting red solution was evaporated to dryness, and the
residue was applied as a dichloromethane solution to a silica gel
preparative TLC plate. Elution with first dichloromethane and then 3%
acetone in dichloromethane gave a red colored leading band, which
was extracted with acetone. Yield: 136 mg, 167 µmol, 35%. Recrys-
tallization from methanol gave red crystals.
Ru(CO)2(PBu3)2(PUR-2H). IR (hexanes): 2037.6 vs, 1973.1 s cm-1
.
1H NMR (CDCl3): δ 15.642 (s, 1 H), 8.274 (m, 2 H), 7.604 (m, 2 H),
6.182 (s, 1 H), 1.705 (m, 12 H), 1.49 (br, 12 H), 1.353 (m, 12 H),
0.874 (t, 18 H, J ) 7 Hz) ppm. 13C{1H} NMR (CDCl3): δ 197.2 (br,
2 C), 179.79 (1 C), 179.69 (1 C), 176.64 (1 C), 165.25 (1 C), 164.55
(1 C), 136.16 (1 C), 134.38 (1 C), 131.60 (1 C), 131.24 (1 C), 126.40
(1 C), 125.26 (1 C), 114.45 (1 C), 106.19 (1 C), 105.84 (1 C), 25.12
(6 C), 24.27 (t, 6 C, JPC ) 7 Hz), 22.85 (t, 6 C, JPC ) 13 Hz), 13.42
(6 C) ppm. 31P{1H} NMR (CDCl3): δ 20.56 ppm. UV/vis (CH2Cl2):
Ru(CO)(dppe)(PBu3)(QAL-2H).
A
solution of Ru3(CO)12
(104.5 mg, 163.4 µmol), dppe (197 mg, 495 µmol), and quinalizarin
(133 mg, 489 µmol) in toluene (30 mL) was heated at reflux under a
nitrogen atmosphere for 4.5 h. Then PBu3 (140 µL, 560 µmol) was
added, and the solution was heated at reflux for 8 more hours. The
products were separated by TLC on silica eluting with 2% ethyl acetate
in dichloromethane. The second, blue-green band was extracted. Re-
crystallization from dichloromethane/methanol yielded 146 mg, 30%.
λ
max(ꢀ) 512 (1.2 × 104), 542 (2.0 × 104), 582 (1.7 × 104) nm. Anal.
Ru(CO)(dppe)(PBu3)(QAL-2H). IR (CH2Cl2): 1946.9 cm-1 1H
.
Calcd for C40H60O7P2Ru: C, 58.88; H, 7.41. Found: C, 59.53; H, 7.49.
NMR (CDCl3): δ 15.080 (s, 1 H), 14.014 (s, 1 H), [8.991 (dd, 2 H,
J ) 7.6, 10.8 Hz), 8.142 (m, 2 H), 7.780 (m, 2 H), 7.707 (m, 1 H),
7.634 (m, 2 H), 7.472 (m, 6 H), 7.111 (d, 2 H), 6.840 (m, 2 H), 6.756
(m, 4 H), 6.452 (d, 1 H, J ) 8.0 Hz), 2.99 (m, 1 H), 2.78 (m, 1 H),
2.40 (m, 1 H), 1.87 (m, 1 H), 1.4-1.1 (m, 18 H), 0.757 (t, 9 H, J )
7.2 Hz) ppm;] minor - 14.873 (s, 1 H), 14.137 (s, 1 H), 6.000 (d, 1 H,
J ) 8.4 Hz), 31P{1H} NMR (CDCl3): δ major isomer, 60.437 (dd, 1
PA), 46.081 (dd, 1 PB), 18.819 (dd, 1 PC), JAB ) 11.5 Hz, JAC ) 22.5
Hz, JBC ) 339.1 Hz; minor isomer, 60.466 (dd, 1 PA), 45.167 (dd, 1
Ru(CO)2(PCy3)2(PUR-2H) and HRu(CO)(PCy3)2(PUR-H). A
solution of Ru3(CO)12 (108 mg, 170 µmol), PCy3 (400 mg, 1.42 mmol),
and purpurin (182 mg, 707 µmol) in toluene (30 mL) was heated at
reflux under an argon atmosphere for 11 h. The resulting red solution
was evaporated to dryness, and the residue was applied as a dichloro-
methane solution to silica gel preparative TLC plates. Elution with
dichloromethane gave a green colored leading band, which overlapped
with a brown band, a blue band, and a trailing red band. Extraction of
the green/brown band with ethyl acetate gave 147 mg (31%) HRu-
(CO)(PCy3)2(PUR-H). Extraction of the red band with ethyl acetate
gave 85 mg, 17%, of Ru(CO)2(PCy3)2(PUR-2H).
PB), 19.526 (dd, 1 PC) ppm, JAB ) 11.5 Hz, JAC ) 21.4 Hz, JBC
)
339.5 Hz; major/minor ) 3.9. UV/vis (CH2Cl2): λmax(ꢀ) 410 (5800),
584 (1.4 × 104), 622 (2.2 × 104), 674 (1.9 × 104) nm. Anal. Calcd for
C53H57O7P3Ru: C, 63.66; H, 5.74. Found: C, 63.36; H, 5.85.
Ru(CO)(mer-PBu3)3(QAL-2H) and Ru(cis-CO)2(trans-PBu3)2-
(QAL-2H). A solution of Ru3(CO)12 (101.5 mg, 159 µmol), PBu3 (240
µL, 960 µmol), and quinalizarin (127.7 mg, 469 µmol) in toluene (20
mL) was heated at reflux under an argon atmosphere for 6 h. The
HRu(CO)(PCy3)2(PUR-H). IR (CH2Cl2): 1898.1 cm-1 1H NMR
.
(CDCl3): δ 15.550 (s, 1 H), 8.308 (m, 2 H), 8.040 (s, 1 H), 7.682 (m,
2 H), 6.546 (s, 1 H), 2.0-0.9 (m, 66 H), -15.283 (t, 1 H, JPH ) 19.6
Hz) ppm; minor isomer, -15.440 (t, PPH 19.6 Hz) ppm; major/minor
) 11.7. 31P{1H} NMR (CDCl3): δ 43.713 ppm. UV/vis (CH2Cl2):

Linkage and Redox Isomerism
Inorganic Chemistry, Vol. 40, No. 17, 2001 4363
resulting blue solution was evaporated to dryness, and the residue was
applied as a dichloromethane solution to a silica gel preparative TLC
plate. Elution with dichloromethane gave purple, blue, red, and purple
bands; the blue band was extracted with ethyl acetate, 357 mg. Repeated
TLCs were necessary to separate the bis- and trisphosphine complexes.
Ru(CO)(mer-PBu3)3(AG-2H) and Ru(CO)2(PBu3)2(AG-2H). A
solution of Ru3(CO)12 (105.1 mg, 164 µmol), PBu3 (234 µL, 940 µmol),
and anthragallol (122 mg, 476 µmol) in toluene (30 mL) was heated at
reflux under an argon atmosphere for 7 h. The resulting green solution
was evaporated to dryness, and the residue was applied as a dichloro-
methane solution to a silica gel preparative TLC plate. Elution with
2% ethyl acetate in dichloromethane gave two green bands, which were
extracted with ethyl acetate. The top band (89 mg, 18%) was identified
as a mixture of two isomers of Ru(CO)(mer-PBu3)3(AG-2H). The
second band (149 mg, 37% based on Ru) was Ru(CO)2(PBu3)2(AG-
2H).
Ru(CO)2(PBu3)2(QAL-2H). IR (CH2Cl2): 2036.1 vs, 1970.8 s cm-1
.
1H NMR (CDCl3): δ 14.18 (s, 1 H), 13.72 (s, 1 H), 7.63 (d, 1 H, J )
8 Hz), 7.05 (s, 2 H), 6.60 (d, 1 H, J ) 8 Hz), 1.68 (m 12 H), 1.45 (dm,
12 H), 1.34 (m, 12 H), 0.89 (t, 18 H, J ) 7 Hz) ppm. 31P{1H} NMR
(CDCl3): δ 21.90 (s) ppm. UV/vis (CH2Cl2): λmax(ꢀ) 584 (2.3 × 104),
622 (1.9 × 104) nm.
Ru(CO)2(PBu3)2(AG-2H). IR (CH2Cl2): 2035.4 vs, 1968.0 s cm-1
.
Ru(CO)(mer-PBu3)3(QAL-2H). IR (CH2Cl2): 1928.0 cm-1. 1H NMR
(CDCl3): δ a, 14.70 (s, 1 H), 13.98 (s, 1 H), 7.60 (d, 1 H, J ) 8 Hz),
7.01 (m, 2 H), 6.40 (d, 1 H, J ) 8 Hz) ppm; b, 14.72 (s, 1 H), 13.96
(s, 1 H), 7.62 (d, 1 H, J ) 8 Hz), 7.01 (m, 2 H), 6.47 (d, 1 H, J ) 8
Hz) ppm; 2.0-1.2 (m, 54 H), 1.0-0.8 (m, 27 H) ppm. 31P{1H} NMR
(CDCl3): δ a (62%), 26.098 (t, JPP ) 23.1 Hz, 1 P), 15.494 (d, 2 P)
ppm; b (38%), 26.75 (t JPP ) 24 Hz, 1 P), 15.30 (d, 2 P) ppm.
1H NMR (CDCl3): δ 12.640 (s, 1 H), 8.14 (m, 2 H), 7.59 (m, 2 H),
7.14 (s, 1 H), 1.72 (m, 12 H), 1.39 (br, 24 H), 0.875 (t, 18 H, J ) 7
Hz) ppm. 13C{1H} NMR (CDCl3): δ 198.26 (br, 2 C), 187.02 (1 C),
182.85 (1 C), 169.57 (1 C), 156.20 (1 C), 154.11 (1 C), 135.50 (1 C),
135.38 (1 C), 133.48 (1 C), 133.21 (1 C), 127.19 (1 C), 126.49 (1 C),
123.71 (1 C), 112.40 (1 C), 110.44 (1 C), 26.07 (6 C), 25.09 (t, 6 C,
JPC ) 6 Hz), 23.50 (t, 6 C, JPC ) 13 Hz), 14.31 (6 C) ppm. 31P{1H}
NMR (CDCl3): δ 18.67 ppm. UV/vis (CH2Cl2): λmax(ꢀ) 372 (3.0 ×
104), 456 (6.7 × 103) nm.
Ru(CO)(dppe)(PBu3)(AG-2H). A solution of Ru3(CO)12 (243 mg,
379 µmol), dppe (457 mg, 1.15 mmol), and anthragallol (299 mg, 1.17
mmol) in toluene (30 mL) was heated at reflux under a nitrogen
atmosphere for 3 h. Then PBu3 (100 µL, 396 µmol) was added, and
the solution was heated at reflux for 4 more hours. The products were
separated by TLC on silica eluting with dichloromethane. Two green
bands and a pine green band trailed by a dark green band were extracted
with ethyl acetate. The pine green band was predominantly Ru(CO)2-
(PBu3)2(AG-2H). The dark green band yielded 262 mg, 23%.
Ru(CO)(dppe)(PBu3)(AG-2H). IR (CH2Cl2): 1944.2 cm-1. 1H NMR
(CDCl3): δ 12.218 (s, 1 H), 8.679 (m, 2 H), 8.111 (m, 4 H), 7.7-7.4
(m, 15 H), 7.052 (s, 1 H), 7.036 (m, 1 H), 6.915 (m, 2 H), 2.974 (dm,
1 H), 2.668 (dm, 1 H), 2.431 (m, 1 H), 2.010 (m, 1 H), 1.4-1.1 (m, 18
H), 0.780 t, 9 H, J ) 7 Hz) ppm; minor isomer resonances were not
assigned. 31P{1H} NMR (CDCl3): δ minor isomer, 59.691 (dd, 1 PA),
42.072 (dd, 1 PB), 16.409 (dd, 1 PC), JAB ) 11.6 Hz, JAC ) 23.3 Hz,
JBC ) 358.7 Hz; major isomer, 59.207 (dd, 1 PA), 40.142 (dd, 1 HB),
18.498 (dd, 1 PC), JAB ) 11.5 Hz, JAC ) 22.5 Hz, JBC ) 359.5 Hz,
major/minor ) 4.2. UV/vis (CH2Cl2): λmax(ꢀ) 316 (1.2 × 104), 394
(3.0 × 104), 472 (6.8 × 103), 498 (5.8 × 103) nm. Anal. Calcd for
C53H57O6P3Ru: C, 64.692; H, 5.839. Found: C, 64.50; H, 6.09.
Ru(CO)(dppe)(PBu3)(AG-3H+Me). A solution of Ru(CO)(dppe)-
(PBu3)(AG-2H) (52 mg, 53 µmol), potassium t-butoxide (59 mg, 560
µmol), and methyl iodide (150 µL, 240 µmol) in 8 mL of THF was
stirred under argon for 46 h. The solution was evaporated, and the
residue was separated by TLC on silica eluting with 3% ethyl acetate
in dichloromethane. The top, green band was extracted with ethyl
acetate, yielding 25 mg, 46%, upon evaporation. The second green band
contained 7 mg, 13%, of recovered starting material.
Ru(CO)(dppe)(PBu3)(AG-3H+Me). IR (CH2Cl2): 1943.9 cm-1. 1H
NMR (CDCl3): δ 8.712 (dd, 2 H), 8.14 (m, 4 H), 7.7-7.4 (m, 13 H),
7.230 (s, 1 H), 6.991 (m, 2 H), 6.926 (m, 3 H), 3.789 (s, 3 H), 2.920
(m, 1 H), 2.715 (m, 1 H), 2.400 (m, 1 H), 1.990 (m, 1 H), 1.4-1.1 (m,
18 H), 0.758 (t, 9 H, J ) 7 Hz) ppm. 31P{1H} NMR (CDCl3): δ 59.06
(dd, 1 PA), 40.43 (dd, 1 HB), 20.91 (dd, 1 PC), JAB ) 12 Hz, JAC ) 23
Hz, JBC ) 360 Hz. UV/vis (CH2Cl2): λmax(ꢀ) 324 (1.6 × 104), 388
(2.3 × 104), 606 (2.7 × 103) nm. Anal. Calcd for C54H59O6P3Ru: C,
64.99; H, 5.96. Found: C, 64.89; H, 5.84.
Ru(CO)(mer-PBu3)3(AG-2H). IR (CH2Cl2): 1922.8 cm-1. 1H NMR
(CDCl3): δ 12.544 (s, 0.34 H, a), 12.475 (s, 0.66 H, b), 8.152 (a and
b, m, 2 H), 7.571 (a and b, m, 2 H), 7.122 (s, 0.66 H, b), 7.070 (s,
0.34 H, a), 1.9-1.25 (m, 48 H), 1.001 (t, 8.2 H, J ) 7 Hz), 0.953 (t,
2.9 H, J ) 7 Hz), 0.893 (t, 15.8 H, J ) 7 Hz) ppm. 31P{1H} NMR
(CDCl3): δ a (34%), 24.54 (t, JPP ) 24 Hz, 1 P), 13.20 (d, 2 P) ppm;
b (66%), 24.36 (t, JPP ) 24 Hz, 1 P), 14.38 (d, 2 P) ppm.
[Ru(CO)(dppe)(PBu3)(QAL-2H)]SbCl6, [Ru(CO)(dppe)(PBu3)-
(PUR-2H)]PF6, [Ru(CO)(dppe)(PBu3)(AG-2H)]PF6, [Ru(CO)2-
(PBu3)2(QAL-2H)]SbCl6, [Ru(CO)2(PBu3)2(PUR-2H)]SbCl6, and
[Ru(CO)2(PBu3)2(AG-2H)]SbCl6. Semi-quinone complexes were pre-
pared by adding a stoichiometric amount of ferrocinium hexafluoro-
phosphate or tris(4-bromophenyl)ammoniumyl hexachloroantimonate
to a dichloromethane solution of the appropriate complex. IR and EPR
spectra were then immediately recorded. IR (CH2Cl2): [Ru(CO)(dppe)-
(PBu3)(QAL-2H)]SbCl6, 1977.5 cm-1; [Ru(CO)(dppe)(PBu3)(PUR-2H)]-
PF6, 1975.9 cm-1; [Ru(CO)(dppe)(PBu3)(AG-2H)]PF6, 1976.8 cm-1
;
[Ru(CO)2(PBu3)2(QAL-2H)]SbCl6, 2062.7 s, 2009.7 s cm-1; [Ru(CO)2-
(PBu3)2(PUR-2H)]SbCl6, 2059.8 vs, 2002.2 s cm-1; and [Ru(CO)2-
(PBu3)2(AG-2H)]SbCl6, 2063.6 vs, 2010.5 s cm-1. EPR (CH2Cl2):
[Ru(CO)(dppe)(PBu3)(QAL-2H)]SbCl6, g 2.004, A(31P) ) 26.0, 23.5
G, A(1H or 31P) ) 1.5 G, A(101Ru) ) A(99Ru) ) 4 G; [Ru(CO)(dppe)-
(PBu3)(PUR-2H)]PF6, g 2.005, A(31P) ) 19.0, 21.0 G, A(1H or 31P) )
1.2 G, A(101Ru) ) A(99Ru) ) 3.5 G; [Ru(CO)(dppe)(PBu3)(AG-2H)]-
PF6, g 2.004, A(31P) ) 26.0, 24.0 G, A(1H or 31P) ) 2.0 G, A(101Ru) )
A(99Ru) ) 4.5 G; [Ru(CO)2(PBu3)2(QAL-2H)]SbCl6, g 2.005, A(31P2)
) 25.6 G, A(1H) ) 2.4 G, A(101Ru) ) A(99Ru) ) 4 G; [Ru(CO)2(PBu3)2-
(PUR-2H)]SbCl6, g 2.004, A(31P) ) 20.1 G, A(101Ru) ) A(99Ru) ) ca.
4 G; [Ru(CO)2(PBu3)2(AG-2H)]SbCl6, g 2.004, A(31P) ) 25 G, A(101Ru)
) A(99Ru) ) ca. 4 G.
Crystal Structure Analysis of trans-Ru(CO)2(PBu3)2(AG-2H).
Crystals suitable for X-ray diffraction studies were obtained by vapor
diffusion of 2,2,3-trimethylbutane into a toluene solution of the complex.
The crystal chosen for the analysis, a thick green plate of dimensions
0.38 × 0.46 × 0.72 mm, was sealed into a thin-walled glass capillary
and mounted on a Siemens R3m/V diffractometer. The crystal belongs
to the monoclinic system (2/m symmetry) in space group P21/n. Cell
constants were derived from a least-squares fit to 50 carefully centered
reflections, chosen as {hkl} sets with 2θ(Mo KR) ) 24-30° and well-
dispersed in reciprocal space. Data were collected as described
previously6 and were collected for Lorentz and polarization factors and
for absorption (T ) 0.647 f 0.698).
Ru(CO)2(PPh3)2(AG-2H). A solution of Ru3(CO)12 (102.4 mg, 160
µmol), PPh3 (265.3 mL, 1040 µmol), and anthragallol (119.9 mg, 468
µmol) in toluene (20 mL) was heated at reflux under an argon
atmosphere for 3.5 h. The resulting green solution was evaporated to
dryness, and the residue was applied as a dichloromethane solution to
a silica gel preparative TLC plate. Elution with 4% ethyl acetate in
dichloromethane gave four bands; the third, green one was extracted
with ethyl acetate. Evaporation gave Ru(CO)2(PPh3)2(AG-2H) (188.8
mg, 43%).
All calculations were performed under the SHELXTL PLUS (Release
4.11 VMS) program package.7 The analytical scattering factors for
Ru(CO)2(PPh3)2(AG-2H). IR (CH2Cl2): 2044.4 vs, 1982.1 s w cm-1
.
(6) Churchill, M. R.; Lashewycz, R. A.; Rotella, F. J. Inorg. Chem., 1977,
16, 265.
(7) Sheldrick, G. M. SHELXTL PLUS (Release 4.11 VMS); Siemens
Analytical Instruments Inc.; Madison, WI, 1990. (See also Siemens
SHELXTL PLUS Manual, 2nd ed., 1990).
1H NMR (CDCl3): δ 12.306 (s, 1 H), 8.107 (m, 2 H), 7.706 (m, 1 H),
7.578 (m, 12 H), 7.370 (m, 18 H), 7.277 (m, 1 H), 6.608 (s, 1 H) ppm.
31P{1H} NMR (CDCl3): δ 18.94 (s) ppm. UV/vis (CH2Cl2): λmax(ꢀ)
382 (2.3 × 104), 462 (8.4 × 103), 492 sh nm.

4364 Inorganic Chemistry, Vol. 40, No. 17, 2001
Table 1. Crystallographic Data for Ru(CO)2(PBu3)2((AG-2H)
Churchill et al.
empirical formula
fw
C40H60O7P2Ru
815.9
wavelength, Å
space group
a, Å
0.710730
P21/n (No. 14 Var)
13.317(2)
b, Å
c, Å
15.628(2)
21.076(3)
â, deg
101.660(10)
4295.9(11)
4
1.261
0.472
R ) 8.68%, wR ) 11.82%
R ) 11.77%, wR ) 12.21%
vol, Å3
Z
calcd density, Mg/m3
µ(mm-1
)
final R indices [I > 2σ(I)]a
R indices (all data)a
a R(%) ) 100 ∑||Fo| - |Fc||/∑|Fo| and wR(%) ) 100 [∑w(|Fo| -
2
|Fc|)2/∑w|Fo| ]1/2
neutral atoms8a were corrected for anomalous dispersion.8b The structure
was solved by direct methods, difference-Fourier techniques, and least-
squares refinement. All non-hydrogen atoms were refined anisotropi-
cally. All hydrogen atoms of the PBu3 ligands and those four bonded
to atoms C(5) f C(8) were included in optimized positions with d(C-
H) ) 0.96 Å.9 The molecule is well defined but (using the usual
crystallographic parlance, Vide infra) one OH group of the anthragallol-
2H is disordered and occupies two alternative sites, defined as O(1X)
and O(1Y).
Figure 2. Molecular geometry of Ru(CO)2(PBu3)2(AG-2H). Hydrogen
atoms in the disordered portion of the structure, i.e., those on O(1X),
O(1Y), C(1), and C(4), are not shown.
isomeric form maintains the hydrogen bond to the 9-oxo moiety
and also would appear to be favored on steric grounds. However,
electronic stabilization or kinetic control are also possible.
The products formed from dppe were too insoluble to allow
for facile characterization, so further substitution using PBu3
was accomplished (Figure 1). Ru(CO)(dppe)(PBu3)(QAL-2H)
is a highly soluble, deep blue compound, while Ru(CO)(dppe)-
(PBu3)(AG-2H) is dark green, and Ru(CO)(dppe)(PBu3)(PUR-
2H) is red. The 31P NMR spectrum of each indicates predomi-
nantly one isomer with PBu3 occupying one site cis to the PAHQ
chelate and one end of the dppe ligand occupying the other.
The large trans P-P coupling constant of 350 Hz, compared
with the small cis values of 12 and 23 Hz, is diagnostic.
Data for the crystallographic study are collected in Table 1.
Results
Coordination chemistry of hydroxyanthraquinones has not
received much attention recently. A 1,2- versus 1,9-chelation
has previously been established for alizarin.3a-c,4 The PHAQs
used in this study offer a variety of additional coordination
modes. In particular, purpurin and anthragallol both can act as
1,2- or 1,9-chelates, but the former can additionally act as a
4,10-univalent chelate and the latter as a 2,3-divalent chelate.
Quiinalizarin can act as a 1,9-, 8,9-, or 5,10- univalent chelate.
All of these, in principle, can act as bimetallic, dual compartment
ligands.
1,2-Catecholate Complexes. Reaction of Ru3(CO)12, PR3,
and PHAQ in the ratios 1:3:6 in refluxing toluene generate Ru-
(CO)2(PR3)2(PHAQ-2H) (PHAQ ) PUR, R ) Bu, Cyc;
PHAQ) AG, R ) Bu, Ph; PHAQ ) QAL, R ) Bu) and Ru-
(CO)(PR3)3(PHAQ-2H) (PHAQ ) QAL, AG; R ) Bu) (Figure
1). Characterizations of Ru(CO)2L2(PHAQ-2H) are straightfor-
ward, by comparison to previously reported catecholate com-
plexes. The observation of two CO stretches in the IR spectra
and a single 31P resonance for each complex indicate that all
are Ru(cis-CO)2(trans-PR3)2(chelate) complexes. The 1H NMR
spectra show the expected numbers of free O-H resonances,
and the expected aromatic proton resonances can be observed
for the PBu3 and PCy3 complexes, although the aromatic region
is largely obscurred for the PPh3 complex. Proton resonances
for hydroxy substituents in the 1-, 4-, 5-, or 8- positions have
chemical shifts of 14-16 ppm, which is due to hydrogen
bonding to the central quinone oxygens. Ru(CO)(PBu3)3(PHAQ-
2H) exists as mixtures of two meridianal isomers in a ca. 6:4
ratio.
The complexes are highly stable to heat, water, and air. All
are quite soluble in dichloromethane, and the PBu3 complexes
are soluble in hydrocarbons.
The o-methylated complexes Ru(CO)(dppe)(PBu3)(AG-
3H+Me) and Ru(CO)(dppe)(PBu3)(PUR-3H+Me) were pre-
pared by reaction with methyl iodide and potassium t-butoxide.
Thus, base-promoted reactions of the remaining phenolic
hydroxyls are feasible to further functionalize these complexes.
Description of the Molecular Structure for Ru(CO)2-
(PBu3)2(AG-2H). Figure 2 shows the overall disordered struc-
ture and the atomic labeling scheme. Selected bond lengths and
angles are collected in Table 2.
As mentioned above, the crystal structure suffers from
disorder. The final model has the rather high discrepancy index
of R ) 8.68% for the observed data (I > 2σ(I) or |Fo| > 4σ-
(|Fo|)). The averaging of intensities of common reflections yields
a value of Rint ) 0.86%, indicating that the intensities have been
measured with precision. The crystallographic model is clearly
subject to some problems, which are caused, no doubt, by
disorder. One may loosely define the disorder in the following
fashion. There are two possible sites for the OH group adjacent
to the O(1)-Ru(1)-O(2) chelate system, that centered on O(1X)
has an occupancy of 0.341(18) while that centered on O(1Y)
has an occupancy of 0.659(18). This description is, of course,
facile. It must be recognized that each crystallographic site may
be occupied by an entire molecule in one of two possible
orientations (the two being inter-related by a C2 rotation about
the bisector of the O(1)-Ru(1)-O(2) chelate “bite”). The outer
surfaces of the two such orientations must have approximately
the same energy profile, and the sites of the outermost atoms
Anthragallol could form 1,2- or 2,3-catecholate products. The
main product was shown to have 2,3-coordination in the case
of Ru(CO)2(PBu3)2(AG-2H) (vide infra) (Figure 2). The factors
which give rise to 2,3-chelation are unknown at this time. This
(8) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. 4 (a) pp 99-101, (b) pp 149-150.
(9) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.

Linkage and Redox Isomerism
Inorganic Chemistry, Vol. 40, No. 17, 2001 4365
Table 2. Selected Bond Lengths (Å) and Angles (Deg) for
Ru(CO)2(PBu3)2(AG-2H)
and P(1)-Ru(1)-P(2) ) 171.9(1)°) and mutually cis carbonyl
ligands (Ru(1)-C(21) ) 1.905(14), Ru(1)-C(22) ) 1.844(14)
Å, and C(21)-Ru(1)-C(22) ) 88.3(6)°). The anthragallol-
2H ligand is bonded to the ruthenium(II) center via the oxygen
atoms associated with C(2) and C(3) (Ru(1)-O(1) ) 2.084(8),
Ru(1)-O(2) ) 2.098(8) Å, with the chelate “bite angle” O-
(1)-Ru(1)-O(2) ) 80.6(3)°), rather than via the possible, but
less symmetrical, coordination through those oxygen atoms on
C(1) [O(1x), see structure A] and C(2) [O(1)].
Oxygen-carbon distances within the disordered anthragallol-
2H system include O(1)-C(2) ) 1.306(14) and O(2)-C(3) )
1.295(14) Å, each of which is essentially a single bond. These
bond lengths are shorter than those found for most catecholates
(cf. Ru(CO)2(PPh3)2(O2C6H4),10c 1.347(4) Å), However, the
values are very similar to those found in two aluminum
complexes derived from1,2-dihydroxy- and 1,2,4-trihydroxy-
anthraquinone (1.30-1.32 Å).3e Also, comparison of the single
bonds for the free C-OH (1.349(7) Å) and the phenolate
C-ORu (1.308(8) Å) of HRu(CO)(PPh3)2(alizarinate) suggests
that this distance of 1.3 Å is the norm for phenolate C-O single
bonds of hydroxyanthraquinone ligands.4 The linkages O(9)-
C(9) ) 1.225(17) and O(10)-C(10) ) 1.218(19) Å are clearly
typical CdO double bonds. The final oxygen atom occupies
two possible sites with O(1X)-C(1) ) 1.270(31) and O(1Y)-
C(4) ) 1.304(19) Å, occupancies being 0.341(18) for O(1X)
and 0.659(18) for O(1Y). These bond lengths are consistent with
C-OH systems.
(A) Ruthenium-Ligand Bond Lengths
Ru(1)-P(1)
Ru(1)-P(2)
Ru(1)-O(1)
2.405(4)
2.407(4)
2.084(8)
Ru(1)-O(2)
Ru(1)-C(21)
Ru(1)-C(22)
2.098(8)
1.905(14)
1.844(14)
(B) Carbon-Oxygen Distances
O(1)-C(2)
O(2)-C(3)
O(9)-C(9)
O(10)-C(10)
1.306(14)
1.295(14)
1.225(17)
1.218(19)
O(1X)-C(1)a
O(1Y)-C(4)a
O(21)-C(21)
O(22)-C(22)
1.270(31)
1.304(19)
1.104(18)
1.171(18)
(C) Carbon-Carbon Distances In the Anthragallol-2H Ligand
C(1)-C(2)
1.407(17)
1.476(16)
1.389(18)
1.399(18)
1.498(17)
1.374(17)
1.442(17)
1.498(17)
1.433(19)
C(5)-C(6)
1.351(23)
1.324(31)
1.414(23)
1.391(20)
1.356(21)
1.402(21)
1.502(19)
1.356(21)
1.509(19)
C(2)-C(3)
C(6)-C(7)
C(3)-C(4)
C(7)-C(8)
C(4)-C(11)
C(11)-C(12)
C(12)-C(1)
C(9)-C(12)
C(12)-C(11)
C(11)-C(10)
C(8)-C(14)
C(14)-C(13)
C(13)-C(5)
C(10)-C(13)
C(13)-C(14)
C(14)-C(9)
(D) Angles Around the Ruthenium Atom
P(1)-Ru(1)-P(2)
P(1)-Ru(1)-O(1)
P(1)-Ru(1)-O(2)
P(1)-Ru(1)-C(21)
P(1)-Ru(1)-C(22)
P(2)-Ru(1)-O(1)
P(2)-Ru(1)-O(2)
P(2)-Ru(1)-C(21)
171.9(1) P(2)-Ru(1)-C(22)
86.5(2) O(1)-Ru(1)-O(2)
86.8(2) O(1)-Ru(1)-C(21)
93.9(4) O(1)-Ru(1)-C(22)
93.6(5) O(2)-Ru(1)-C(21)
86.1(3) O(2)-Ru(1)-C(22)
88.8(2) C(21)-Ru(1)-C(22)
90.3(4)
93.4(5)
80.6(3)
98.1(5)
173.5(5)
178.4(5)
93.0(5)
88.3(6)
The crystal structure is stabilized by the stacking of an-
thragallol-2H systems (see Figure 1S in Supporting Information).
1,9-Complex. Reaction of Ru3(CO)12, PCy3, and PUR in the
ratios 1:6:3 generates two significant products, Ru(CO)2(PCy)2-
(PUR-2H) and HRu(CO)(PCy3)2(PUR-H) (Figure 1). The latter
complex has a acylphenolate ligand, as we have shown
previously for RuH(CO)(PPh3)2(1,9-AL-H).4 However, there are
two possible linkage isomers for purpurin, via the 1,9- or 4,-
10-oxygen atoms. The singlet 31P signal indicates a trans
a O(1X) and O(1Y) represent the two sites for the disordered oxygen
atoms. Occupancies are 0.341(18) for O(1X) and 0.659(18) for O(1Y).
in the two orientations should, in general, coincide. To a first
approximation, the Ru(PBu3)2(CO)2 moieties of the two over-
lapping images overlap well, although the ends of the n-butyl
groups do show substantial excursions (treated as “thermal
motion”), with U(eq) values (in Å2) of 0.29(3) for C(44), 0.27-
(3) for C(54), 0.26(3) for C(74), etc. The two possible
orientations of the anthragallol-2H ligand are shown below. That
designated A has a 34% occupancy and that designated B a
66% occupancy.
1
arrangment of PCy3 ligands. The H NMR and IR spectra are
similar to those of RuH(CO)(PPh3)2(AL-H), the structure of
which we previously determined by X-ray crystallography. The
1H NMR spectrum contains HO resonances at 15.55 and 8.04
ppm; the lower field signal is due the hydrogen-bonded 1- or
4-hydroxyl. The other signal is 1 ppm downfield of the chemical
shift for the 2-OH moiety of RuH(CO)(PCy3)2(1,9-AL-H).4
Because of the difference in chemical shifts for the free hydroxyl
of RuH(CO)(PCy3)2(PUR-H) compared with RuH(CO)(PCy3)2-
(1,9-AL-H) we favor the 4,10- isomer for the former. Two
isomers due to the relative orientations of the cis-(H)(CO)
ligands are expected but one predominates by 11.7:1.
The analogous reaction with anthragallol did not produce a
significant yield of the corresponding AG-H complex.
Electrochemistry. The electrochemistry of these complexes
was surveyed using cyclic voltammetry. All of the 1,2-
catecholates exhibit a reversible to quasi-reversible 1-e oxidation,
at potentials of -0.13 to +0.30 V, associated with catecholate/
semiquinone couples, and reversible to quasi-reversible reduc-
tions associated with the 9,10-anthraquinone moiety at -1.70
to -2.1 V. The greatest number of reversible redox couples
was found for Ru(CO)(dppe)(PBu3)(QAL-2H) (Figure 3). We
attribute the couple at +0.67 V to 1-e oxidation of the 5,8-
While we have not located the hydrogen atoms on atoms
O(1X) in A or O(1Y) in B, they are probably involved in
hydrogen bonding to the nearby quinonic oxygen atoms. The
disordered OH groups will probably result in imprecise overlap
of the two orientations of this ligand at other atomic sites.
Therefore, all bond lengths in this ligand, and even more, the
esd’s on these bond lengths, should be taken cum grano salis.
The central ruthenium(II) moiety has a slightly distorted
octahedral coordination environment with mutually trans PBu3
ligands (Ru(1)-P(1) ) 2.405(4), Ru(1)-P(2) ) 2.407(4) Å,
(10) (a) Connelly, N. G.; Manners, I.; Protheroe, J. R. C.; Whiteley, M.
W. J. Chem. Soc., Dalton Trans. 1984, 2713. (b) Bohle, D. S.;
Goodson, P. A. J. Chem. Soc., Chem. Commun. 1992, 1205. (c) Bohle,
D. S.; Carron, K. T.; Christensen, A. N.; Goodson, P. A.; Powell, A.
K. Organometallics 1994, 13, 1355.

4366 Inorganic Chemistry, Vol. 40, No. 17, 2001
Table 3. Cyclic Voltammetric Data
Churchill et al.
complex
(Ep,a+Ep,c)/2 [Ep,a1] (V)
∆Ep (mV)
ipc/ipa
(Ep,a+ Ep,c)/2 (V)
∆Ep (mV)
ipc/ipc
Ru(CO)2(PBu3)2(PUR-2H) (800 mV/s)
Ru(CO)(dppe)(PBu3)(PUR-2H) (400 mV/s)
Ru(CO)2(PCy3)2(PUR-2H) (100 mV/s)
Ru(CO)(dppe)(PBu3)(AG-2H) (800 mV/s)
Ru(CO)2(PBu3)2(AG-2H) (400 mV/s)
+0.22
0.0
+0.18
-0.13
+0.17
88
84
66
85
61
0.84
0.45
0.81
0.91
0.79
[-1.92]
[-2.1]
-1.81
-1.70
[-2.12]
-1.70
-1.81
60
72
0.82
0.92
Ru(CO)2(PBu3)2(QAL-2H) (1000 mV/s)
Ru(CO)(dppe)(PBu3)(QAL-2H) (500 mV/s)
+0.30
+0.67
87
102
133
69
0.82
0.66
0.90
1.0
72
96
0.55
0.81
+0.03
RuH(CO)(PCy3)2(PUR-H) (400 mV/s)
+0.04
-1.61
62
1.0
[+0.39]
[+0.82] (2e)
Figure 4. EPR spectrum for [Ru(CO)(dppe)(PBu3)(QAL-2H)]1+
.
Figure 3. Cyclic voltammogram of Ru(CO)(dppe)(PBu3)(QAL-2H)
at 500 mV/s in dichloromethane (0.1 M NBu4BF4).
group.4 The hexafluorophosphate complexes can be isolated and
are stable to air for extended periods, but we did not obtain
analytically pure compounds. The hexachloroantimonate salts
decompose over a 24 h period, forming Ru(CO)2Cl2(PBu3)2.
hydroquinone moiety, since no similar oxidation was present
in the CVs of Ru(CO)(dppe)(PBu3)(AG-2H) or Ru(CO)(dppe)-
(PBu3)(PUR-2H). Electrochemical data are summarized in Table
3.
Discussion
Transition metal complexes of catecholate ligands have
received considerable attention because of their relationship to
biologically important quinoids and catechols and because of
their unique structural, magnetic, and electronic properties.12
Although metal complexes of 1,2-dihydroxyanthracenediones
have been used as dyes and indicators2, except for alizarin3 and
purpurin,3f the chemistry of metal complexes of these catecho-
lates has been unexplored. Although no complex was character-
ized, 5,10- and 8,9-chelation was proposed to account for the
selective esterification of the 1- and 2-hydroxyl groups by
reaction of a quinalizarin-Cu(II) complex with acyl halides.13
No complexes of anthragallol appear to have been characterized
previously.
We have shown that, as expected, catecholates and semi-
quinones can be prepared from anthragallol, purpurin, and
quinalizarin, and additionally purpurin can act as a univalent
acylphenolate ligand, and the preferred catecholate complex
from anthragallol is the 2,3- isomer. Base-promoted function-
alization of free hydroxyls is feasible. These ligand systems,
therefore, provide for complexes with a variety of coordination
modes, redox states, and photophysical properties which can
be tuned via substitutuion on the metal and the anthraquinone
ring. Although the catecholate/semiquinone redox couple is
largely ligand based, the oxidation potential for Ru(CO)2(dppe)-
(PBu3)(PHAQ-2H) is 0.2-0.3 V lower than that of the corre-
sponding Ru(CO)2(PBu3)2(PHAQ-2H). The uncoordinated hy-
droxyls can be used to attach the complexes to supports or to
linkers capable of selective binding of the complexes to
biologically important targets. Finally, the solubilities of the
The CV of RuH(CO)(PCy3)2(PUR-H) displays a reversible
1-e oxidation at +0.04 V, irreversible oxidation waves at Ep,a
+0.39 (1-e) and +0.82 (2-e) V, and a reversible 1-e reduction
at -1.61 V. For comparison, RuH(CO)(PCy3)2(1,9-AL-H)
displays a single reversible 1-e oxidation at +0.076 V, which
we assigned to a metal-centered couple, and two reductions at
-1.40 and -1.67 V.4 The two irreversible oxidations observed
for RuH(CO)(PCy3)2(PUR-H) are likely associated with the
PUR-H ligand.
Semi-quinone Complexes. Chemical oxidation, using fer-
rocinium hexafluorophosphate or tris(4-bromophenyl)ammoni-
umyl hexachloroantimonate (for those complexes with oxidation
potentials more positive than that of ferrocene), was used to
generate the semi-quinone complexes [Ru(CO)(dppe)(PBu3)-
(PHAQ-2H)]1+ (PHAQ ) PUR, AG, and QAL) and [Ru(CO)2-
(PBu3)2(PHAQ-2H)]SbCl6, which were characterized in situ
(dichloromethane solution). The IR spectra of the semi-quinone
complexes show that the CO stretches are shifted to higher
frequency by ca. 20-30 cm-1 versus the neutral precursor. In
each case the EPR spectrum is a triplet near g 2.00, with
hyperfine coupling to two 31P nuclei in positions cis to the
PHAQ ligand (A(31P) ca. 20-25 G) and to 99Ru and 101Ru (ca.
4 G for each). The spectrum of [Ru(CO)2(PBu3)2(QAL-2H)]1+
also shows resolvable coupling to an aromatic ring proton.
Hyperfine coupling to the 31P nucleus in the plane of the PHAQ
ring, where present, is too small to resolve. A representative
spectrum, for [Ru(CO)(dppe)(PBu3)(QAL-2H)]1+ is shown in
Figure 4. The spectra are very similar to those of [Ru(CO)2-
(PPh3)L(o-O2C6Cl4)]1+, reported by previously by Connelly et
al.10a and by Balch11 (e.g., L ) PPh3, g 2.002 (t, A(31P) 25.2
G), and of analogous alizarinate complexes reported by our
(12) (a) Pierpont, C. G.; Lange, C. W. Prog. Inorg. Chem. 1994, 41, 331.
(b) Pierpont, C. G.; Buchanan, R. M. Coord. Chem. ReV. 1981, 38,
45.
(11) Balch, A. L. J. Am. Chem. Soc. 1973, 95, 2723.
(13) Mellidis, A. S.; Papageorgiou, V. P. Tetrahedron Lett. 1986, 27, 5881.

Linkage and Redox Isomerism
Inorganic Chemistry, Vol. 40, No. 17, 2001 4367
complexes are easily adjustable by choice of appropriate
phosphine ligands.
semiquinone redox couple will allow redox-based switching of
the ligands’ donor properties toward the second metal atom.
Attempts to prepare such bimetallic complexes are underway.
Since these ligands can coordinate via the 1,9- or 4(5),10-
oxygens, the catecholate complexes of purpurin, anthragallol,
and quinalizarin should be able to coordinate a second metal
atom as acetylacetonate analogues. Homobimetallic complexes
of 1,4-dihydoxoanthracenedione, in which both metals are
chelated by the acylphenolate structure, have been characterized
previously.14 Bimetallic complexes of these catecholate-acyl-
phenolate ligands should be accessible by base-promoted
metathesis reactions with a second metal salt. The catecholate/
Acknowledgment. Research contributions from Mark Przy-
bylski and Peter Bruschi are acknowledged. This work was
funded in part by a grant from the Petroleum Research Fund to
J.B.K.
Supporting Information Available: Listings of crystal data,
crystallographic data collection information, solution and refinement
information, atomic coordinates and equivalent isotropic displacement
coefficients, bond lengths, bond angles, anisotropic displacement
coefficients and hydrogen atom coordinates with their isotropic
displacement coefficients (10 pages), diagram of packing of molecules
within the unit cell (1 page). This material is available free of charge
via the Internet at http://pubs.acs.org.
(14) (a) Pierpont, C. G.; Francesconi, L. C.; Hendrickson, D. N. Inorg.
Chem. 1978, 17, 3470. (b) Maroney, M. J.; Day, R. O.; Psyris, T.;
Fleury, L. M.; Whitehead, J. P. Inorg. Chem. 1989, 28, 173. (c) Sadler,
G. G.; Gordon, N. R. Inorg. Chim. Acta 1991, 180, 271. (d) Coble,
H. D.; Holtzclaw, H. F., Jr. J. Inorg. Nucl. Chem. 1974, 36, 1049.
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