Ruthenium complexes with tetraphenylimidodiphosphinate: Syntheses, structures, and applications to catalytic organic oxidation

Article abstract of DOI:10.1021/ic800018d

Treatment of Ru(PPh₃)₃Cl₂ with K(tpip) (tpip^- = [N(Ph₂PO)₂]^-) afforded Ru(tpip)(PPh₃)₂Cl (1), which reacted with 4-t-Bu-C ₆H₄CN, SO

Full text of DOI:10.1021/ic800018d

Inorg. Chem. 2008, 47, 4383-4391
Ruthenium Complexes with Tetraphenylimidodiphosphinate: Syntheses,
Structures, and Applications to Catalytic Organic Oxidation
Wai-Man Cheung, Ho-Yuen Ng, Ian D. Williams, and Wa-Hung Leung*
Department of Chemistry, The Hong Kong UniVersity of Science and Technology, Clear Water
Bay, Kowloon, Hong Kong, People’s Republic of China
Received January 4, 2008
Treatment of Ru(PPh3)3Cl2 with K(tpip) (tpip- ) [N(Ph2PO)2]-) afforded Ru(tpip)(PPh3)2Cl (1), which reacted with
4-t-Bu-C6H4CN, SO2(g), and NH3(g) to give Ru(tpip)(PPh3)2Cl(4-t-BuC6H4CN) (2), Ru(tpip)(PPh3)2Cl(SO2) (3), and
fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4), respectively. Reaction of [Ru(CO)2Cl2]x with K(tpip) in refluxing tetrahydrofuran
(THF) led to isolation of the K/Ru bimetallic compound K2Ru2(tpip)4(CO)4Cl2 (5). Photolysis of cis-Ru(tpip)2(NO)Cl
in MeCN and wet CH2Cl2 afforded cis-Ru(tpip)2(MeCN)Cl (6) and cis-Ru(tpip)2(H2O)Cl (7), respectively. Refluxing
6 in neat THF yielded Ru(tpip)2(THF)Cl (8). Treatment of Ru(CHR)Cl2(PCy3)2 (Cy ) cyclohexyl) with [Ag(tpip)]4
afforded cis-Ru(tpip)2(CHR)(PCy3) [R ) Ph (9), OEt (10)]. Complex 9 is capable of catalyzing oxidation of alcohols
and olefins with N-methylmorpholine N-oxide and iodosylbenzene, respectively. The crystal structures of 2-7 and
9 were determined.
Chart 1
Introduction
Ru complexes in oxygen-rich ligand environments are of
interest because they are relevant to the active sites of oxide-
based heterogeneous Ru catalysts, which have found ap-
plications in organic oxidations.1 In order to gain insight into
the molecular mechanisms of oxide-supported Ru catalysts,
we sought to investigate the organometallic chemistry of Ru
compounds containing oxygen donor ligands. We were
particularly interested in π-donating phosphinate ligands that
are compatible with both hard and soft metal centers.
Previous studies demonstrated that the facially coordinated
tris(phosphinate) ligands [(η5-C5H5)Co{P(O)(OR)2}3]- can
stabilize low-valence organoruthenium2,3 as well as high-
valence Ru oxo4 and nitrido5 complexes. To further explore
the organometallic chemistry of chelating phosphinate ligands,
we set out to synthesize Ru complexes with bidentate
imidodiphosphinate ligands.
Imidodiphosphinates[N(R2PO)2]- (Chart1), suchastetraph-
enylimidodiphosphinate (R ) Ph) or tpip-, which are
considered to be inorganic analogues of acetylacetonates
(acac-), can form stable complexes with a variety of metals.6
Metal-tpip complexes have received much attention recently
because of their applications as NMR shift agents,7 lumi-
(3) (a) Leung, W.-H.; Chan, E. Y. Y.; Williams, I. D.; Wong, W.-T.
Organometallics 1997, 16, 3234. (b) Leung, W.-H.; Chan, E. Y. Y.;
Wong, W.-T. Organometallics 1998, 17, 1245.
* To whom correspondence should be addressed. E-mail: chleung@
ust.hk.
(4) (a) Power, J. M.; Evertz, K.; Henling, L.; Marsh, R.; Schaefer, W. P.;
Labinger, J. A.; Bercaw, J. E. Inorg. Chem. 1990, 29, 5058. (b) Kelson,
E. P.; Henling, L. M.; Schaefer, W. P.; Labinger, J. A.; Bercaw, J. E.
Inorg. Chem. 1993, 32, 2863.
(1) See for example: (a) Yamaguchi, K.; Mori, K.; Mizugaki, T.; Ebitani,
K.; Kaneda, K. J. Am. Chem. Soc. 2000, 122, 7144. (b) Matsushita,
T.; Ebitani, K.; Kaneda, K. Chem. Commun. 1999, 265. (c) Yamaguchi,
K.; Mizuno, N. Chem.sEur. J. 2003, 9, 4353. (d) Wu, D. L.; Wight,
A. P.; Davis, M. E. Chem. Commun. 2003, 758. (e) Tada, M.; Coquet,
R.; Yoshida, J.; Kinoshita, M.; Iwasawa, Y. Angew. Chem., Int. Ed.
2007, 46, 7220. (f) Cheung, W.-H.; Yu, W.-Y.; Yip, W.-P.; Zhu, N.-
Y.; Che, C.-M. J. Org. Chem. 2002, 67, 7716.
(5) Yi, X.-Y.; Lam, T. C. H.; Sau, Y.-K.; Zhang, Q.-F.; Williams, I. D.;
Leung, W.-H. Inorg. Chem. 2007, 46, 7193.
(6) (a) Haiduc, I. In ComprehensiVe Coordination Chemistry II; McClev-
erty, J. A., Meyer, T. J., Eds.; Elsevier Pergamon: Amsterdam, 2003;
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176, 451.
(2) Kläui, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 627.
10.1021/ic800018d CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 10, 2008 4383
Published on Web 04/09/2008

Cheung et al.
nescent materials,8 and catalysts for organic oxidations.9
While main-group, lanthanide, and early transition-metal
complexes with tpip- have been well documented, relatively
few late transition-metal-tpip complexes have been isolated.6
To our knowledge, organoruthenium compounds containing
tpip- are unknown to date. This is in sharp contrast to the
well-explored Ru(acac)2 system, whose members exhibit
interesting redox10 and organometallic chemistry11 and can
serve as building blocks for coordination polymers.10a,12
Vaissermann and co-workers9a,b reported that Ag(I)- and
Cu(II)-tpip complexes can catalyze aerobic co-oxidation of
hydrocarbons and aldehydes, demonstrating that tpip- is
stable toward oxidants and thus may find applications in
organic oxidations. This prompted us to investigate the
catalytic activity of Ru(tpip) complexes in organic oxidations.
Herein we describe the synthesis, crystal structures, and
electrochemistry of mono- and bis(tpip) complexes of Ru
and their applications in catalytic oxidation of alcohols and
olefins.
AgNO3 (0.1 M in MeCN), respectively. Potentials were reported
with reference to the ferrocenium/ferrocene (Cp2Fe+/0) couple.
Elemental analyses were performed by Medac Ltd. (Surrey, U.K.).
K(tpip),13 [Ag(tpip)]4,9a Ru(PPh3)3Cl2,14 [Ru(CO)2Cl2]x,15 cis-
Ru(tpip)2(NO)Cl,16 and Ru(CHR)(PCy3)2Cl2 (Cy ) cyclohexyl, R
) Ph, OEt)17 were prepared according to literature methods. Other
reagents were purchased from commercial sources and used as
received.
Preparation of Ru(tpip)(PPh3)2Cl (1). A suspension of
Ru(PPh3)3Cl2 (96 mg, 0.10 mmol) and 1 equiv of K(tpip) (46 mg,
0.10 mmol) in THF (10 mL) was heated at reflux for 3 h. The
solvent was pumped off, and the residue was washed with Et2O.
Recrystallization from CH2Cl2/hexane afforded dark-brown crystals.
1
Yield: 91 mg, 85%. H NMR (CDCl3): δ 6.82–7.48 (m, 40H).
31P{1H} NMR (CDCl3): δ 28.35 (s, tpip), 64.73 (s, PPh3). Anal.
Calcd for C60H50ClNO2P4Ru·H2O: C, 65.8; H, 4.8; N, 1.3. Found:
C, 65.9; H, 4.6; N, 1.2.
Preparation of Ru(tpip)(PPh3)2(4-t-Bu-C6H4CN)Cl (2). To a
solution of 1 (40 mg, 0.037 mmol) in CH2Cl2 was added 1 drop of
4-tert-butylbenzonitrile. The pale-brown solution turned yellow
immediately. The solvent was pumped off, and the residue was
washed with hexane. Recrystallization from CH2Cl2/hexane afforded
yellowish-orange crystals. Yield: 30 mg, 65%. 1H NMR (CDCl3):
δ 1.28 (s, 9H, t-Bu), 6.37 (d, J ) 8.4 Hz, Hm of 4-t-Bu-C6H4CN),
7.08–8.23 (m, 52H). 31P{1H} NMR (CDCl3): δ 23.97 (d, J ) 3.3
Hz, tpip-), 51.18 (d, J ) 3.3 Hz, PPh3). IR (KBr) νCN (cm-1): 2227.
Anal. Calcd for C71H63ClN2O2P4Ru: C, 69.0; H, 5.1; N, 2.3. Found:
C, 69.0; H, 5.3; N, 2.1.
Experimental Section
General Considerations. All manipulations were carried out
under nitrogen by standard Schlenk techniques. Solvents were
purified, distilled, and degassed prior to use. NMR spectra were
recorded using a Bruker ARX 300 or Varian Mercury 300
spectrometer operating at 300, 75.5, 121.5, and 282.5 MHz for 1H,
13C, 31P, and 19F, respectively. Chemical shifts (δ, ppm) were
reported with reference to SiMe4 (1H and 13C), H3PO4 (31P), and
CF3C6H5 (19F). Infrared spectra were recorded using a PerkinElmer
16 PC FT-IR spectrophotometer and mass spectra using a Finnigan
TSQ 7000 spectrometer. Cyclic voltammetry was performed using
a Princeton Applied Research (PAR) model 273A potentiostat. The
working and reference electrodes were glassy carbon and Ag/
Preparation of Ru(tpip)(PPh3)2(SO2)Cl (3). SO2(g) was bubbled
through a solution of 1 (40 mg, 0.037 mmol) in CH2Cl2 (20 mL)
for 15 s, during which the solution color changed from pale-brown
to orange. The solvent was pumped off, and the residue was washed
with hexane. Recrystallization from CH2Cl2/hexane afforded orange
1
crystals. Yield: 36 mg, 85%. H NMR (CDCl3): δ 6.80–7.85 (m,
50H). 31P{1H} NMR (CDCl3): δ 27.46 (s, tpip), 32.36 (s, PPh3).
IR (KBr) VSO (cm-1): 1247. Anal. Calcd for C60H50ClNO4P4RuS:
C, 63.1; H, 4.4; N, 1.2. Found: C, 63.0; H, 4.4; N, 1.2.
(7) Barkaoui, L.; Charrouf, M.; Rager, M. N.; Denise, B.; Platzer, N.;
Ruddler, R. Bull. Soc. Chim. Fr. 1997, 134, 167.
Preparation of fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4). NH3(g) was
bubbled through a solution of 1 (40 mg, 0.037 mmol) in CH2Cl2
(20 mL) for 30 s, during which the color of the solution changed
from pale-brown to yellowish-green. The solvent was pumped off,
and the residue was washed with hexane. Recrystallization from
CH2Cl2/hexane afforded yellowish-green crystals. Yield: 31 mg,
(8) (a) Magennis, S. W.; Parsons, S.; Pikramenou, Z. Chem.sEur. J. 2002,
24, 5761. (b) Magennis, S. W.; Parsons, S.; Corval, A.; Woollins,
J. D.; Pikramenou, Z. Chem. Commun. 1999, 61. (c) Bassett, A. P.;
Van Deun, R.; Nockemann, P.; Glover, P. B.; Kariuki, B. M.; Van
Hecke, K.; Van Meervelt, L.; Pikramenou, Z. Inorg. Chem. 2005, 44,
6140. (d) Glover, P. B.; Bassett, A. P.; Nockemann, P.; Kariuki, B. M.;
Van Deun, R.; Pikramenou, Z. Chem.sEur. J. 2007, 13, 6308.
(9) (a) Rudler, H.; Denise, B.; Gregorio, J. R.; Vaissermann, J. Chem.
Commun. 1997, 2299. (b) Rudler, H.; Denise, B. J. Mol. Catal. A
2000, 154, 277. (c) Yi, X.-Y.; Ng, G. K. Y.; Williams, I. D.; Leung,
W.-H. Inorg. Chim. Acta 2006, 359, 3581.
1
73%. H NMR (CDCl3): δ 1.65 (br s, 3H, NH3), 2.25 (br s, 3H,
NH3), 3.01 (br s, 3H, NH3), 7.09–7.71 (m, 50H). 31P{1H} NMR
(CDCl3): δ 11.00 (s, tpip), 50.69 (s, PPh3). Anal. Calcd for
C60H59ClN4O2P4Ru: C, 63.9; H, 5.3; N, 5.0. Found: C, 63.4; H,
5.3; N, 5.0.
(10) (a) Hasegawa, T.; Lau, T. C.; Taube, H.; Schaefer, W. P. Inorg. Chem.
1991, 30, 2921. (b) Oomura, K.-i.; Ooyama, D.; Satoh, Y.; Nagao,
N.; Nagao, H.; Howell, F. S.; Mukaida, M. Inorg. Chim. Acta 1998,
269, 342. (c) Baird, I. R.; Cameron, B. R.; Skerlj, R. T. Inorg. Chim.
Acta 2003, 353, 107. (d) Baird, I. R.; Rettig, S. J.; James, B. R.; Skov,
K. A. Can. J. Chem. 1999, 77, 1821. (e) Majumdar, P.; Falvello, L. R.;
Tomás, M.; Goswami, S. Chem.sEur. J. 2001, 7, 5222. (f) Ghumaan,
S.; Sarkar, B.; Patra, S.; van Slageren, J.; Fiedler, J.; Kaim, W.; Lahiri,
G. K. Inorg. Chem. 2005, 44, 3210. (g) Wu, A.; Masland, J.; Swartz,
R. D.; Kaminsky, W.; Mayer, J. M. Inorg. Chem. 2007, 46, 11190.
(h) Maji, S.; Sarkar, B.; Mobin, S. M.; Fiedler, J.; Kaim, W.; Lahiri,
G. K. Dalton Trans. 2007, 2411.
Preparation of K2Ru2(tpip)4(CO)4Cl2 (5). A suspension of
[Ru(CO)2Cl2]x (23 mg, 0.10 mmol) and 2 equiv of K(tpip) (91 mg,
0.20 mmol) in THF (10 mL) was heated at reflux for 3 h. The
solvent was pumped off, and the residue was extracted with Et2O.
Recrystallization from CH2Cl2/Et2O/hexane afforded yellow crys-
tals. Yield: 67 mg, 63%. 1H NMR (CDCl3): δ 6.74–7.99 (m, 40H).
31P{1H} NMR (CDCl3): δ 13.95 (s), 22.03 (s), 30.52 (d, J ) 3.6
Hz), 33.58 (d, J ) 3.6 Hz). IR (KBr) VCO (cm-1): 1974, 2051. Anal.
(11) (a) Bennett, M. A.; Byrnes, M. J.; Kovácˇik, I. J. Organomet. Chem.
2004, 689, 4463. (b) Bennett, M. A.; Byrnes, M. J.; Willis, A. C.
Organometallics 2003, 22, 1018. (c) Bennett, M. A.; Heath, G. A.;
Hockless, D. C. R.; Kovacik, I.; Willis, A. C. J. Am. Chem. Soc. 1998,
120, 932.
(13) Wang, F. T.; Najdzionek, J.; Leneker, K. L.; Wasserman, H.; Braitsch,
D. M. Synth. React. Inorg. Met. Org. Chem. 1978, 8, 119.
(14) Stephenson, T. A.; Wilkinson, G. Inorg. Nucl. Chem. 1966, 28, 945.
(15) Colton, R.; Farthing, R. H. Aust. J. Chem. 1971, 24, 903.
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W.-H. Polyhedron 2007, 26, 4631.
(12) (a) Toma, L. M.; Toma, L. D.; Delgado, F. S.; Ruiz-Pérez, C.; Sletten,
J.; Cano, J.; Clemente-Juan, J. M.; Lloret, F.; Julve, M. Coord. Chem.
ReV. 2006, 250, 2176. (b) Yeung, W.-F.; Lau, P.-H.; Lau, T.-C.; Wei,
H.-Y.; Sun, H.-L.; Gao, S.; Chen, Z.-D.; Wong, W.-T. Inorg. Chem.
2005, 44, 6579.
(17) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996,
118, 100.
4384 Inorganic Chemistry, Vol. 47, No. 10, 2008

Ruthenium Complexes with Tetraphenylimidodiphosphinate
Calcd for C100H80Cl2K2N4O12P8Ru2: C, 56.4; H, 3.8; N, 2.6. Found:
C, 56.9; H, 4.0; N, 2.7.
General Procedure for Ru-Catalyzed Oxidation of Alcohols.
The oxidant (0.2 mmol) was added to a solution of Ru catalyst
(0.002 mmol) and alcohol (0.08 mmol) in CH2Cl2 (2 mL), and the
reaction mixture was stirred at room temperature. The organic
products were analyzed by GLC using bromobenzene as the internal
standard.
Preparation of cis-Ru(tpip)2(MeCN)Cl (6). A solution of cis-
Ru(tpip)2(NO)Cl (30 mg, 0.030 mmol) in CH2Cl2/MeCN (100 mL,
9:1 v/v) was irradiated with UV light (9 W, Hg lamp) for 1 h,
during which the pale-purple solution turned yellow. The solvent
was removed, and the residue was extracted with CH2Cl2. Recrys-
tallization from CH2Cl2/Et2O/hexane afforded yellow crystals. Yield:
26 mg, 85%. µeff (CDCl3, Evans method18) ) 1.7µB. Anal. Calcd
for C50H43ClN3O4P4Ru·CH2Cl2: C, 55.9; H, 4.1; N, 3.8. Found:
C, 55.9; H, 4.0; N, 3.8.
Preparation of cis-Ru(tpip)2(H2O)Cl (7). A solution of cis-
Ru(tpip)2(NO)Cl (30 mg, 0.030 mmol) in wet CH2Cl2 (100 mL)
was irradiated with UV light (9 W, Hg lamp) for 1 h, during which
the pale-purple solution turned dark-orange. The solvent was
removed, and the residue was extracted with CH2Cl2. Recrystalli-
zation from CH2Cl2/Et2O/hexane in air afforded pale-brown crystals.
Yield: 14 mg, 48%. Anal. Calcd for C48H42ClN2O5P4Ru·1/2H2O:
C, 57.9; H, 4.4; N, 2.8. Found: C, 57.7; H, 4.2; N, 2.7.
Preparation of cis-Ru(tpip)2(THF)Cl (8). A solution of 6 (30
mg, 0.030 mmol) in THF (10 mL) was heated at reflux overnight,
during which the yellow solution turned pale-orange. The solvent
was pumped off, and the residue was extracted with Et2O. Addition
of excess hexane afforded an orange solid. Yield: 24 mg, 76%.
Anal. Calcd for C52H48ClN2O5P4Ru: C, 60.0; H, 4.7; N, 2.7. Found:
C, 59.6; H, 4.8; N, 2.4.
General Procedure for Ru-Catalyzed Oxidation of Olefins.
Iodosylbenzene (0.2 mmol) was added to a solution of Ru catalyst
(0.002 mmol) and olefin (0.08 mmol) in CH2Cl2 (2 mL), and the
reaction mixture was stirred at room temperature under nitrogen.
The organic products were analyzed by GLC using bromobenzene
as the internal standard.
X-ray Crystallography. Details concerning the crystallographic
data for complexes 2-7 and 9 are summarized in Table 1.
Preliminary examinations and intensity data collection were per-
formed on a Bruker SMART-APEX 1000 area-detector diffracto-
meter using graphite-monochromatized Mo KR radiation (λ )
0.70173 Å). The collected frames were processed using the software
SAINT.20 The data were corrected for absorption using the program
SADABS. Structures were solved by direct methods and refined
by full-matrix least-squares on F2 using the SHELXTL software
package.21 Unless stated otherwise, non-hydrogen atoms were
refined with anisotropic displacement parameters. Selected bond
lengths and angles for complexes 2-7 and 9 are listed in Tables
2-6.
Preparation of cis-Ru(tpip)2(CHPh)(PCy3) (9). To a solution
of Ru(dCHPh)(PCy3)2Cl2 (41 mg, 0.050 mmol) in CH2Cl2 (10 mL)
was added 0.5 equiv of [Ag(tpip)]4 (52 mg, 0.025 mmol), and the
reaction mixture was stirred at room temperature (RT) for 2 h. The
solvent was pumped off, and the residue was extracted with CH2Cl2/
Et2O (1:1 v/v). Addition of hexane and concentration to 2 mL
Results and Discussion
Syntheses. A. Ru(II) Complexes. The syntheses of Ru-
(tpip) complexes are summarized in Scheme 1. Treatment
of Ru(PPh3)3Cl2 with K(tpip) in refluxing THF led to
isolation of brown crystals analyzed as the mono(tpip)
complex Ru(tpip)(PPh3)2Cl (1). Ru(II)-bis(tpip) complexes
could not be isolated even when excess K(tpip) was used,
indicating the reluctance of Ru(II) to bind to two hard
bis(phosphinate) ligands. It may be noted that similar
reactions with analogous chalcogen ligands K[N(R2PQ)2] (R
) Ph, i-Pr; Q ) S, Se) led to formation of the five-coordinate
bis(chelate) complexes Ru[N(R2PQ)2]2(PPh3).22 The 31P{1H}
NMR spectrum of 1 displayed two singlets at δ 28.35 and
64.73, which were assigned to the tpip- and PPh3 ligands,
respectively. The 31P resonance for the tpip- ligand was
shifted downfield relative to that for K(tpip) (δ 14.2 in
CDCl3). A preliminary X-ray diffraction study revealed that
1 is monomeric and has a pseudo-trigonal-bipyramidal
structure, with the two PPh3 ligands and one PdO group in
the equatorial plane. Unfortunately, the structure could not
be refined satisfactorily because of poor crystal quality.
Compound 1 is stable in the solid state but air-sensitive
in solutions. It readily reacts with Lewis bases to give
octahedral adducts. For example, treatment of 1 with 4-tert-
butylbenzonitrile led to isolation of Ru(tpip)(PPh3)2Cl(4-t-
Bu-C6H4CN) (2). While reaction of 1 with SO2(g) afforded
the sulfur dioxide adduct Ru(tpip)(PPh3)2Cl(SO2) (3), reaction
with NH3(g) led to dissociation of the tpip- ligand and
1
afforded green crystals. Yield: 39 mg, 60%. H NMR (CDCl3): δ
1.12–2.36 (m, 33H, Cy), 6.94–7.23 (m, 12H, Ph), 7.29 (t, J ) 7.7
Hz, 2H, Hm of CHPh), 7.31–7.51 (m, 12H, Ph), 7.70 (t, J ) 7.7
Hz, 1H, Hp), 8.28–8.83 (m, 16H, Ph), 8.94 (d, J ) 7.7 Hz, 2H, Ho
of CHPh), 22.46 (d, J ) 7.5 Hz, 1H, CHPh). 31P{1H} NMR
(CDCl3): δ 21.84 (m), 26.75 (m), 27.17 (m), 28.06 (s), 34.85 (m).
13C{1H} NMR (CDCl3): δ 295.07 (s, RudC). Anal. Calcd for
C73H79N2O4P5Ru: C, 67.2; H, 6.1; N, 2.2. Found: C, 66.8; H, 6.3;
N, 2.2.
Preparation of cis-Ru(tpip)2(CHOEt)(PCy3) (10). This com-
pound was prepared similarly to 9, using Ru(dCHOEt)(PCy3)2Cl2
(40 mg, 0.050 mmol) in place of Ru(dCHPh)(PCy3)2Cl2. Yield:
43 mg, 67%. 1H NMR (CDCl3): δ 0.89 (m, 3H, CH2CH3), 1.13–2.56
(m, 33H, Cy), 3.88–1.86 (m, 2H, CH2CH3), 6.90–8.43 (m, 40H,
Ph), 16.62 (s, 1H, CHPh). 31P{1H} NMR (CDCl3): δ 22.83 (m),
23.12 (m), 27.14 (m), 33.05 (m), 44.62 (s). 13C{1H} NMR (CDCl3):
δ 290.60 (d, J ) 18 Hz, RudC). Anal. Calcd for C69H79N2O5P5Ru ·1/2-
Et2O: C, 65.1; H, 6.7; N, 2.1. Found: C, 65.4; H, 6.3; N, 1.8.
Ru-Catalyzed Ring-Closing Metathesis of Diethyl Diallylma-
lonate. This reaction was carried out according to a literature
procedure.19 To a solution of 9 (4 mg, 0.003 mmol) in CDCl3 (0.5
mL) in a NMR tube was added a 20-fold excess of diethyl
diallylmalonate (15 µL, 0.061 mmol) at room temperature. The
progress of the reaction was monitored by 1H NMR spectroscopy.
The percent ring closure was calculated on the basis of the ratio of
the amounts of the four ꢀ hydrogens in the product (Hp) and starting
material (Hs), i.e., % ring closure ) Hp/(Hp + Hs).19
(20) Sheldrick, G. M. SADABS; University of Göttingen: Göttingen,
Germany, 1997.
(21) Sheldrick, G. M. SHELXTL-Plus V5.1 Software Reference Manual;
Bruker AXS Inc.: Madison, WI, 1997.
(18) Schubert, E. M. J. Chem. Educ. 1992, 69, 62.
(19) Sanford, M. S.; Henling, L. M.; Grubbs, R. H. Organometallics 1998,
17, 5384.
(22) Leung, W.-H.; Zheng, H. G.; Chim, J. L. C.; Chan, J.; Wong, W.-T.;
Williams, I. D. J. Chem. Soc., Dalton Trans. 2000, 423.
Inorganic Chemistry, Vol. 47, No. 10, 2008 4385

Cheung et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Ru(tpip)(PPh3)2Cl(X)
X
4-t-Bu-C6H4CN (2)
SO2 (3)
Bond Lengths
Ru(1)-O(1)
Ru(1)-O(2)
Ru(1)-P(3)
Ru(1)-P(4)
Ru(1)-Cl
2.1611(15)
2.1613(16)
2.1185(17)
2.3314(7)
2.3473(7)
2.3568(6)
2.1326(6)
1.5135(18)
1.5209(18)
1.586(2)
2.1557(14)
2.2895(6)
2.2866(6)
2.3885(5)
1.9792(17)
1.5046(15)
1.5110(15)
1.5963(19)
1.593(2)
Ru(1)-X
P(1)-O(1)
P(2)-O(2)
P(1)-N(2)/(1)
P(2)-N(2)/(1)
1.590(2)
Bond Angles
O(1)-Ru(1)-O(2)
P(3)-Ru(1)-P(4)
O(1)-Ru(1)-P(3)
O(2)-Ru(1)-P(4)
O(1)-Ru(1)-P(4)
O(2)-Ru(1)-P(3)
Cl(1)-Ru(1)-X
Cl(1)-Ru(1)-O(1)
Cl(1)-Ru(1)-O(2)
Cl(1)-Ru(1)-P(3)
Cl(1)-Ru(1)-P(4)
X-Ru(1)-O(1)
87.89(6)
101.24(2)
86.45(4)
84.41(4)
172.25(4)
174.29(4)
167.98(5)
86.07(4)
87.48(4)
92.863(19)
94.50(2)
82.80(6)
87.60(6)
90.96(5)
95.93(5)
122.69(11)
91.35(6)
104.61(2)
172.15(5)
169.76(5)
83.17(5)
80.80(5)
175.94(2)
86.27(5)
85.75(5)
93.23(2)
85.27(2)
89.72(5)
94.94(5)
90.83(2)
93.69(2)
123.47(14)
X-Ru(1)-O(2)
X-Ru(1)-P(3)
X-Ru(1)-P(4)
P(1)-N(2)/(1)-P(2)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4)
Bond Lengths
Ru(1)-N(1)
Ru(1)-N(3)
Ru(1)-P(1)
P(3)-N(10)
P(3)-O(2)
2.190(2)
Ru(1)-N(2)
2.1659(18)
2.4572(6)
2.2844(7)
1.584(2)
2.1132(18) Ru(1)-Cl(4)
2.3204(6) Ru(1)-P(2)
1.576(2)
P(4)-N(10)
1.5012(17) P(4)-O(1)
1.5005(17)
Bond Angles
Cl(1)-Ru(1)-N(1) 90.67(5)
Cl(1)-Ru(1)-N(3) 167.38(5)
Cl(1)-Ru(1)-N(2) 82.31(5)
Cl(1)-Ru(1)-P(1)
P(1)-Ru(1)-N(1)
P(1)-Ru(1)-N(3)
98.48(2)
87.58(5)
93.82(5)
Cl(1)-Ru(1)-P(2)
89.57(2)
P(1)-Ru(1)-N(2) 167.41(6)
P(1)-Ru(1)-P(2)
P(2)-Ru(1)-N(2)
N(1)-Ru(1)-N(2)
N(2)-Ru(1)-N(3)
101.68(2)
90.88(6)
79.84(7)
85.07(7)
P(2)-Ru(1)-N(1) 170.60(5)
P(2)-Ru(1)-N(3)
N(1)-Ru(1)-N(3)
90.73(6)
87.00(7)
P(3)-N(10)-P(4) 141.86(14)
formation of the triammine complex fac-[Ru(NH3)3(PPh3)2Cl]-
[tpip] (4), which contains a tpip- counteranion. The ease of
displacement of the tpip- ligand in 1 by NH3 indicates that
the interaction between Ru(II) and the hard tpip- ligand is
not strong. The 31P{1H} NMR spectrum of 2 showed two
doublets at δ 23.97 and 51.18 (3JPP ) 3.3 Hz) that were
assigned to the tpip- and PPh3 ligands, respectively. The
corresponding signals for 3 appeared as two singlets at δ
27.34 and 32.36. The NMR data for 2 and 3 are consistent
with their solid-state structures (see below), in which the
two PPh3 are cis to each other and trans to the tpip- ligand.
The 31P{1H} NMR spectrum of 4 showed two singlets at δ
11.0 and 50.69 that were assigned to the tpip- anion and
the PPh3 ligands, respectively, consistent with the solid-state
structure.
Reaction of [Ru(CO)2Cl2]x with 2 equiv of K(tpip) in
refluxing THF afforded the K/Ru bimetallic compound
4386 Inorganic Chemistry, Vol. 47, No. 10, 2008

Ruthenium Complexes with Tetraphenylimidodiphosphinate
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
K2Ru2(tpip)4(CO)4Cl2 (5)
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
cis-Ru(tpip)2(CHPh)(PCy3) (9)
Bond Lengths
Bond Lengths
Ru(1)-C(1)
Ru(1)-O(1)
Ru(1)-O(3)
K(1A)-O(1)
K(1A)-O(4)
K(1A)-Cl(1)
N(1)-P(2)
1.858(3) Ru(1)-C(2)
2.1341(16) Ru(1)-O(2)
2.1277(17) Ru(1)-Cl(1)
2.6988(17) K(1A)-O(3)
2.7051(19) K(1)-O(4)
3.1915(8) N(1)-P(1)
1.595(2) N(2)-P(3)
1.602(2) P(1)-O(1)
1.5359(17) P(3)-O(3)
1.5050(18)
1.849(3)
Ru(1)-C(1)
Ru(1)-O(2)
Ru(1)-O(4)
P(1)-O(1)
P(3)-O(3)
N(1)-P(1)
N(2)-P(3)
1.864(5) Ru(1)-O(1)
2.173(3) Ru(1)-O(3)
2.242(3) Ru(1)-P(5)
1.522(3) P(2)-O(2)
1.533(3) P(4)-O(4)
1.590(4) N(1)-P(2)
1.591(4) N(2)-P(4)
2.103(3)
2.110(3)
2.3397(13)
1.516(3)
1.516(3)
1.601(4)
1.584(4)
2.0949(16)
2.3820(6)
2.8039(17)
2.6288(17)
1.585(2)
1.583(2)
1.5275(17)
1.5247(18)
N(2)-P(4)
Bond Angles
89.73(11) O(3)-Ru(1)-O(4)
P(2)-O(2)
P(4)-O(4)
O(1)-Ru(1)-O(2)
O(1)-Ru(1)-O(3) 170.67(11) O(1)-Ru(1)-O(4)
O(2)-Ru(1)-O(3)
C(1)-Ru(1)-O(1)
C(1)-Ru(1)-O(3)
C(1)-Ru(1)-P(5)
P(5)-Ru(1)-O(2) 177.05(9)
P(5)-Ru(1)-O(4)
P(3)-N(2)-P(4)
90.44(11)
81.36(11)
86.09(11)
91.22(16)
170.39(16)
93.21(9)
Bond Angles
85.65(11) C(1)-Ru(1)-O(1)
85.24(12) O(2)-Ru(1)-O(4)
89.41(17) C(1)-Ru (1)-O(2)
98.54(17) C(1)-Ru(1)-O(4)
88.54(14) P(5)-Ru(1)-O(1)
C(1)-Ru(1)-C(2)
C(1)-Ru(1)-O(2)
C(1)-Ru(1)-Cl(1)
C(2)-Ru(1)-O(2)
C(2)-Ru(1)-Cl(1)
O(1)-Ru(1)-O(3)
O(2)-Ru(1)-O(3)
O(3)-Ru(1)-Cl(1)
Cl(1)-K(1A)-O(3)
96.72(9)
177.84(9)
177.62(9)
94.98(9)
89.43(6)
83.93(5)
96.81(9)
89.01(8)
90.20(8)
96.22(7)
82.65(6)
85.25(6)
88.87(5)
63.28(4)
C(1)-Ru(1)-O(3)
C(2)-Ru(1)-O(1)
C(2)-Ru(1)-O(3)
O(1)-Ru(1)-O(2)
O(1)-Ru(1)-Cl(1)
P(5)-Ru(1)-O(3)
P(1)-N(1)-P(2)
91.89(9)
122.2(3)
94.62(9)
127.9(2)
O(2)-Ru(1)-Cl(1) 171.65(5)
Cl(1)-K(1A)-O(1) 61.14(4)
Cl(1)-K(1A)-O(4) 142.75(4)
Scheme 1. Syntheses of Ru(tpip) Complexesa
Cl(1)-K(1A)-O(4A) 114.86(4)
O(1)-K(1A)-O(3)
61.48(5)
O(1)-K(1A)-O(4) 126.95(6)
O(1)-K(1A)-O(4A) 133.44(6)
O(3)-K(1A)-O(4A) 163.58(6)
Ru(1)-C(1)-O(10) 174.6(2)
O(3)-K(1A)-O(4)
88.07(5)
O(4)-K(1A)-O(4A) 85.73(6)
Ru(1)-C(2)-O(20) 177.1(2)
P(1)-N(1)-P(2)
126.13(13)
P(3)-N(2)-P(4)
132.71(14)
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
cis-Ru(tpip)2(X)Cl
X
MeCN (6)
H2O (7)
Bond Lengths
2.0523(19)
2.0262(19)
2.0265(19)
2.0272(19)
2.3034(7)
2.002(3)
Ru(1)-O(1)
Ru(1)-O(2)
Ru(1)-O(3)
Ru(1)-O(4)
Ru-Cl
2.048(3)
2.033(3)
2.018(3)
2.046(3)
2.3294(11)
2.060(3)
1.513(3)
1.520(3)
1.590(4)
1.583(4)
1.527(3)
1.535(3)
1.581(4)
1.574(4)
Ru-X
P(1)-O(1)
P(2)-O(2)
P(1)-N(1)
P(2)-N(1)
P(3)-O(3)
P(4)-O(4)
P(3)-N(2)
P(4)-N(2)
1.522(2)
1.526(2)
1.583(3)
1.583(3)
1.521(2)
1.528(2)
1.590(2)
1.579(2)
a (i) Ru(PPh3)3Cl2, THF, reflux; (ii) L, CH2Cl2, RT; (iii) NH3(g), CH2Cl2,
RT; (iv) [Ru(CO)2Cl2]x, THF, reflux; (v) Ru(NO)Cl3 ·xH2O, acetone, reflux
(ref 16); (vi) hν, L/CH2Cl2; (vii) THF, reflux; (viii) AgNO3, MeOH, RT
(ref 9a); (ix) Ru(dCHR)(PCy3)2Cl2.
Bond Angles
90.31(8)
84.40(8)
87.24(8)
95.14(9)
175.30(6)
85.74(8)
177.47(8)
89.47(9)
91.52(6)
94.60(8)
175.19(9)
91.42(6)
90.16(9)
90.97(6)
89.20(7)
127.44(16)
129.43(16)
O(1)-Ru(1)-O(2)
O(1)-Ru(1)-O(3)
O(1)-Ru(1)-O(4)
O(1)-Ru(1)-X
O(1)-Ru(1)-Cl(1)
O(2)-Ru(1)-O(3)
O(2)-Ru(1)-O(4)
O(2)-Ru(1)-X
O(2)-Ru(1)-Cl(1)
O(3)-Ru(1)-O(4)
O(3)-Ru(1)-X
O(3)-Ru(1)-Cl(1)
O(4)-Ru(1)-X
92.27(11)
90.19(12)
88.38(11)
88.38(12)
177.83(9)
88.87(11)
174.63(11)
88.78(11)
89.45(8)
96.46(11)
177.19(11)
91.17(9)
85.91(11)
89.78(8)
Scheme 2. Ru-Catalyzed RCM of Diethyl Diallylmalonate
of cis-Ru(acac)2(CO)2 (1988 and 2057 cm-1)23 and Ru(LOEt)-
(CO)2Cl (LOEt ) [(η5-C5H5)Co{P(O)(OEt)2}3]-) (1964 and
-
2044 cm-1).24 The 31P{1H} NMR spectrum displayed two
doublets at δ 30.52 and 33.58 (J ) 3.6 Hz), which were ten-
tatively assigned to the κ2-tpip- ligands, and two broad singlets
at δ 13.95 and 22.03, which were attributed to the κ1-tpip-
ligands (refer to the solid-state structure of 5 described below).
O(4)-Ru(1)-Cl(1)
X-Ru-Cl(1)
P(1)-N(1)-P(2)
P(3)-N(2)-P(4)
90.33(9)
126.1(2)
130.1(2)
B. Ru(III) Complexes. Previously, we reported the syn-
thesis of photoactive Ru{N(Ph2PQ)}2(NO)Cl from Ru(NO)-
K2Ru2(tpip)4(CO)4Cl2 (5), which was isolated as pale-yellow
crystals. 5 is air-sensitive in solutions and readily turns gray
upon exposure to air. The IR spectrum of 5 showed two νCO
bands at 1974 and 2051 cm-1, which are comparable to those
(23) Calderazzo, F.; Floriani, C.; Henzi, R.; L’Eplattenier, F. J. Chem. Soc.
A 1969, 1378.
Inorganic Chemistry, Vol. 47, No. 10, 2008 4387

Cheung et al.
Figure 1. Molecular structure of Ru(tpip)2(PPh3)2Cl(4-t-Bu-C6H4CN) (2).
The ellipsoids are drawn at the 30% probability level.
Figure 3. Molecular structure of fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4). The
ellipsoids are drawn at the 30% probability level.
green crystals by reaction of Ru(CHPh)Cl2(PCy3)2 with
[Ag(tpip)]4. An analogous Fischer carbene complex, cis-
Ru(tpip)2(CHOEt)(PCy3) (10), was prepared similarly from
Ru(CHOEt)Cl2(PCy3)2 and [Ag(tpip)]4. It should be noted
that reaction of Ru(CHPh)Cl2(PCy3)2 with K[N(Ph2PS)2]
afforded five-coordinate Ru[N(Ph2PS)2]2(CHPh), whereas
reaction with K[N(Ph2PSe)2] led to formation of a mixture
of Ru[N(Ph2PSe)2]2(CHPh) and Ru[N(Ph2PSe)2][PhP(Se)-
NPPh2](CHPh), the latter of which contains a monoselenide
ligand.25 In contrast, compound 9 is six-coordinate and
contains a PCy3 ligand. The 31P{1H} NMR spectrum of 9
showed four multiplets at δ 21.84, 26.75, 27.17, and 34.85
due to the two mutually cis tpip- ligands as well as a singlet
at δ 28.06 attributable to PCy3. The signal from the carbene
proton (RudCHPh) appeared as a doublet at δ 22.46 (3JPH
) 7.5 Hz) located further downfield than that of
Ru[N(Ph2PS)2]2(CHPh) (δ 18.16).25 The corresponding
resonance for 10 was found further upfield (δ 16.62). The
13C chemical shifts for the carbene carbons in 9 and 10 (δ
295.07 and 290.60, respectively) are typical of Ru(IV)
carbene complexes.
Complex 9 is capable of catalyzing ring-closing metathesis
(RCM) of dienes, although its catalytic activity is consider-
ably less than that of Grubbs’ catalyst, presumably because
it is coordinately saturated. For example, RCM of diethyl
diallylmalonate in the presence 5 mol % of 9 was complete
in 24 h (Scheme 2).
Crystal Structures. The molecular structures of 2 and 3
are shown in Figures 1 and 2, respectively. Selected bond
lengths and angles are compiled in Table 2. In each complex,
the geometry around Ru is pseudo-octahedral, with the two
PPh3 ligands trans to tpip-. The average Ru-O and Ru-P
distances in 2 (2.158 and 2.288 Å, respectively) and 3
(2.1399 and 2.3394 Å, respectively) are comparable to those
Figure 2. Molecular structure of Ru(tpip)2(PPh3)2Cl(SO2) (3). The ellipsoids
are drawn at the 30% probability level.
Cl3L2 (L ) PPh3 or H2O) and K[N(Ph2PQ)2] (Q ) O, S,
Se).16 Irradiation of CH2Cl2 solutions of Ru{N(Ph2PQ)}2-
(NO)Cl (Q ) S, Se) using UV light led to release of NO.
Unfortunately, we were not able to crystallize the Ru(III)
photoproducts for structural characterization. In this work,
we found that photolysis of cis-Ru(tpip)2(NO)Cl in CH2Cl2/
MeCN gave cis-Ru(tpip)2(MeCN)Cl (6), which could be
isolated as air-stable crystals. Similarly, the aqua compound
cis-Ru(tpip)2Cl(H2O) (7) was prepared by photolysis of cis-
Ru(tpip)2(NO)Cl in wet CH2Cl2. Compound 6 is paramag-
netic, with a measured magnetic moment of 1.7µB that is
consistent with an S ) 1/2 spin state. No reaction was found
when 6 was refluxed with excess pyridine (10-fold) in
CH2Cl2 for 2 h. Refluxing 6 in neat THF overnight led to
isolation of an orange solid characterized as Ru(tpip)2(THF)Cl
(8). Attempts to prepare Ru(tpip)3 by reaction of 6 or 8 with
1 equiv of K(tpip) in CH2Cl2 failed.
(24) Leung, W.-H.; Chan, E. Y. Y.; Wong, W.-T. Inorg. Chem. 1999, 38,
136.
C. Ru(IV) Complexes. No reaction was found between
Ru(CHPh)Cl2(PCy3)2 and K(tpip). The carbene complex cis-
Ru(tpip)2(CHPh)(PCy3) (9) could be isolated as air-stable
(25) Leung, W.-H.; Lau, K.-K.; Zhang, Q.-F.; Wong, W.-T.; Tang, B.
Organometallics 2000, 19, 2084.
4388 Inorganic Chemistry, Vol. 47, No. 10, 2008

Ruthenium Complexes with Tetraphenylimidodiphosphinate
Figure 4. Molecular structure of K2Ru2(tpip)4(CO)4Cl2 (5). The ellipsoids are drawn at the 30% probability level.
Figure 6. Molecular structure of cis-Ru(tpip)2(H2O)Cl (7). The ellipsoids
are drawn at the 30% probability level.
Figure 5. Molecular structure of cis-Ru(tpip)2(MeCN)Cl (6). The ellipsoids
are drawn at the 30% probability level.
of Ru(LOEt)(PPh3)2Cl (2.183 and 2.267 Å, respectively).3a
The Ru-Cl distance in 3 [2.3568(6) Å] is slightly shorter
than that in 2 [2.3885(5) Å]. The SO2 ligand in 3 binds to
Ru in a planar fashion (sum of bond angles of S ) 360°).
The Ru-S distance of 2.1326(6) Å in 3 is similar to that in
cis-Ru[N(Ph2PS)2]2(PPh3)(SO2) [2.140(4) Å].22
The molecular structure of 4 is shown in Figure 3; selected
bond lengths and angles are listed in Table 3. The geometry
around Ru is pseudo-octahedral with three facially coordi-
nated NH3 ligands. The average Ru-N distance of 2.156 Å
is slightly shorter than that in [Ru(NH3)5(Me2SO)][PF6]2
(2.217 Å).26 The Ru-N bonds trans to PPh3 [2.190(2) and
2.1659(18) Å] are longer than that trans to Cl [2.1132(18)
Å] as a result of the trans influence of PPh3.
tpip)(κ1-tpip)(CO)2Cl} fragments linked together via two
K-O bridges. In each fragment, the Ru has pseudo-
octahedral geometry with two mutually cis carbonyls. The
Ru-O bonds trans to the CO ligands [2.1341(16) and
2.1277(17) Å] are longer than that trans to Cl [2.0949(16)
Å] because of the trans influence of the carbonyl group. The
K atom is five-coordinate, binding to the chloride, one
oxygen atom of the κ2-tpip- ligand, both oxygen atoms of
the κ1-tpip- ligand, and one oxygen atom of the κ2-tpip-
ligand in the adjacent fragment. The K-O distances are in
the range 2.6988(17)–2.8039(17) Å. The K-Cl distance is
rather long [3.1915(8) Å], indicating that the K-Cl interac-
tion is weak.
The structures of 6 and 7 are shown in Figures 5 and 6,
respectively. Selected bond lengths and angles are compiled
in Table 5. The geometry around Ru in each complex is
pseudo-octahedral, with the acetonitrile/aqua ligand cis to
the chloride. The average Ru-O distance and the Ru-Cl
distance in 6 [2.033 and 2.3034(7) Å, respectively] and 7
Figure 4 shows the molecular structure of 5; selected bond
lengths and angles are listed in Table 4. Compound 5 can
be viewed as consisting of two symmetry-related {KRu(κ2-
(26) March, F. C.; Ferguson, G. Can. J. Chem. 1971, 49, 3590.
Inorganic Chemistry, Vol. 47, No. 10, 2008 4389

Cheung et al.
Table 8. Ru-Catalyzed Oxidation of Alcoholsa
entry catalyst
alcohol
oxidant time (h) product (% yieldb)
1
2
3
4
5
6
7
8
1
1
5
5
6
7
9
9
1
5
7
9
9
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH(OH)Me NMO
PhCH(OH)Me NMO
PhCH(OH)Me NMO
PhCH(OH)Me NMO
TBHP
NMO
TBHP
NMO
NMO
NMO
TBHP
NMO
2
1.5
2
2
1
2
3
1
2
PhCHO (67)
PhCHO (98)
PhCHO (49)
PhCHO (67)
PhCHO (9)
PhCHO (66)
PhCHO (93)
PhCHO (100)
PhC(O)Me (82)
PhC(O)Me (54)
PhC(O)Me (64)
PhC(O)Me (83)
cyclohexanone (80)
9
10
11
12
13
2
1.5
2
cyclohexanol
NMO
2
a Experimental conditions: a mixture of alcohol (0.2 mmol), oxidant (0.2
mmol), and catalyst (0.002 mmol, 1 mol %) in CH2Cl2 (2 mL) was stirred
at room temperature under nitrogen. b Yield based on the amount of oxidant
used.
Table 9. Ru-Catalyzed Oxidation of Olefinsa
entry catalyst substrate time (h)
products (% yieldb)
Figure 7. Molecular structure of cis-Ru(tpip)2(CHPh)(PCy3) (9). The
1
2
3
1
7
9
styrene
styrene
styrene
3
3
2
styrene oxide (6), benzaldehyde (7)
benzaldehyde (3)
styrene oxide (35),
benzaldehyde (15)
styrene oxide (31),
ellipsoids are drawn at the 30% probability level.
Table 7. Formal Potentials (E1/2) for Ru(tpip) Complexesa
E1/2 (V vs Cp2Fe+/0
)
4
5
10
9
styrene
2
2
benzaldehyde (12)
complex
reduction
oxidation
cyclohexene
cyclohexene oxide (45),
cyclohexenone (trace)
cyclooctene oxide (58)
cis-stilbene oxide (40)
Ru(tpip)(PPh3)2Cl(4-t-Bu-C6H4CN) (2)
Ru(tpip)(PPh3)2Cl(SO2) (3)
cis-Ru(tpip)2(NO)Cl
trans-Ru[N(Ph2PS)2]2(NO)Cl
cis-Ru(tpip)2(MeCN)Cl (6)
cis-Ru(tpip)2(H2O)Cl (7)
0.16
0.63c
6
7
9
9
cycloctene
cis-stilbene
2
2
-1.54b
-1.15b
-1.07
-1.20
-1.47b
a Experimental conditions: a mixture of olefin (0.2 mmol), iodosylbenzene
(0.20 mmol), and catalyst (0.002 mmol, 1 mol %) in CH2Cl2 (2 mL) was
stirred at room temperature under nitrogen. b Yield based on the amount of
PhI formed.
0.84
0.66
0.56
cis-Ru(tpip)2(THF)Cl (8)
cis-Ru(tpip)2(CHPh)PCy3 (9)
cis-Ru(tpip)2(CHOEt)PCy3 (10)
Ru[N(Ph2PS)2]2(CHPh)
-0.05
-0.24
0.05
reflecting the trend of the trans influences, tpip- < PCy3 <
carbene.
a Potentials were measured at a glassy carbon electrode in CH2Cl2
solutions containing 0.1 M [n-Bu4N][PF6] as the supporting electrolyte using
a scan rate of 100 mV s-1 b Irreversible, Epc value. c Irreversible, Epa value.
.
Electrochemistry. Formal potentials of the Ru(tpip) com-
plexes were determined using cyclic voltammetry (Table 7).
The cyclic voltammogram (CV) of 2 in CH2Cl2 showed a
reversible couple at 0.16 V versus Cp2Fe+/0, which was
assigned to the metal-centered Ru(III/II) couple. Under the
same conditions, the ligand K(tpip) was redox-inactive in
the potential range -2.0 to 1.0 V. Compound 3 exhibited
an irreversible oxidation wave at 0.63 V, indicating that the
Ru(II) state is stabilized by the π-acidic SO2 ligand. No
couples were observed for the dicarbonyl complex 5. The
CV for cis-Ru(tpip)2(NO)Cl displayed an irreversible wave
at -1.54 V that was tentatively assigned to the Ru(II/I)
reduction. The reduction for trans-Ru(NO){N(Ph2PS)2}2Cl
occurred at a less-negative potential (-1.15 V), suggesting
that the thiophosphinate ligand is more capable of stabilizing
the Ru(I) state than is the PdO analogue. 6 exhibited two
reversible redox couples at -1.07 and 0.84 V that were
assigned to the Ru(III/II) and Ru(IV/III) couples, respec-
tively. Although the acac- analogue of 6 is unknown, the
Ru(III/II) potential for cis-Ru(acac)2(MeCN)Cl may be
assumed to lie between those of trans-[Ru(acac)2Cl2]- and
cis-Ru(acac)2(MeCN)2, which were determined to be -0.45
and 0.26 V versus the normal hydrogen electrode, respec-
tively12a (approximately -1.12 and -0.41 V vs Cp2Fe+/0 in
[2.036 and 2.3294(11) Å, respectively] are shorter than those
in the Ru(II) compounds 2 and 3, as a result of the smaller
ionic radius of Ru3+ as opposed to Ru2+. The Ru-O(aquo)
distance of 2.060(3) Å in 7 is similar to the average [2.029(7)
Å] of those in [Ru(H2O)6](OTs)3 (TsO- ) p-toluenesul-
fonate).27 The Ru-O(tpip) distances in the Ru(III) complexes
were found to increase in the order Ru-O(trans to H2O)
[2.018(3) Å] < Ru-O(trans to PdO) [2.0262(19)-2.046(3)
Å] < Ru-O(trans to Cl) [2.048(3) Å] < Ru-O(trans to
MeCN) [2.0625(19) Å], which is suggestive of the order of
the trans influences, H2O < tpip- < Cl- < MeCN.
Figure 7 shows the molecular structure of 9; selected bond
lengths and angles are listed in Table 6. The geometry around
Ru is pseudo-octahedral, with the benzylidene and PCy3
ligands adjacent to each other. The Ru-C [1.864(5) Å] and
Ru-P [2.3397(13) Å] distances are comparable to those in
[Ru(dCHPh)(Tp)(PCy3)(H2O)][PF6] [Tp- ) hydridotris(pyra-
zolyl)borate] [1.878(4) and 2.3822(13) Å, respectively].19
The Ru-O distances were found to increase in the order
Ru-O(trans to PdO) (average of 2.107 Å) < Ru-O(trans
to P) [2.173(3) Å] < Ru-O(trans to carbene) [2.242(3) Å],
(27) Berhard, P.; Bürgi, H.-B.; Hauser, J.; Lehmann, H.; Ludi, A. Inorg.
Chem. 1982, 21, 3936.
4390 Inorganic Chemistry, Vol. 47, No. 10, 2008

Ruthenium Complexes with Tetraphenylimidodiphosphinate
MeCN28). Thus, the electrochemical data indicated that tpip-
is a stronger electron donor than acac-. The Ru(IV/III)
potentials for 7 and 8 were less anodic than that of 6,
suggesting that the O-donor ligands H2O and THF are more
capable of stabilizing the Ru(IV) state than is N-bound
MeCN. Unlike that for 6 and 7, the Ru(III/II) reduction for
complex 8 at -1.47 V is irreversible. The CV of 9 displayed
a reversible couple at -0.05 V, which was assigned as a
metal-centered couple [formally, the Ru(V/IV) couple]. A
more-negative potential was found for the Fischer carbene
analogue 10 (-0.24 V). The Ru(V/IV) potential for
Ru[N(Ph2PS)2]2(CHPh) (0.05 V) was similar to that for 9,
suggesting that for the Ru(IV) carbene system, the donor
strength of tpip- is comparable to that of the thiophosphinate
analogue.
Ru-Catalyzed Oxidation. The catalytic activity of Ru(t-
pip) complexes in the oxidation of alcohols was studied, and
the results are summarized in Table 8. Both mono- and
bis(tpip) complexes of Ru can catalyze selective oxidation
of benzyl alcohol and methylbenzyl alcohol to benzaldehyde
and acetophenone, respectively, in moderate to good yield.
N-Methylmorpholine N-oxide (NMO) appears to be a better
terminal oxidant than tert-butylhydroperoxide (TBHP) for
the catalytic alcohol oxidation. However, prolonged oxidation
of benzyl alcohol using NMO led to formation of benzoic
acid, whereas no overoxidation of benzyl alcohol was found
using TBHP. The catalytic activity of the Ru(IV)-bis(tpip)
complexes is comparable to that of the Ru(II) complex 1
but greater than that of the Ru(III) counterparts. Complex 6
is not an active oxidation catalyst, possibly because substitu-
tion at the low-spin d5 Ru(III) center is slow. Ru(tpip)
complexes can also catalyze oxidation of secondary aliphatic
alcohols. For example, oxidation of cyclohexanol with NMO
in the presence of 1 mol % of 9 afforded cyclohexanone in
80% yield.
The catalytic oxidation of olefins with iodosylbenzene and
Ru(tpip) complexes was also studied (Table 9). For example,
oxidation of styrene with 1 mol % of the Ru(IV) complex 9
afforded styrene oxide and benzaldehyde in 35 and 25%
yield, respectively. A similar yield of styrene oxide was
obtained using the Fischer carbene complex 10 as the
catalyst. In contrast, the Ru(II) and Ru(III) complexes are
less active in olefin epoxidation. The oxidation of cyclohex-
ene, cyclooctene, and cis-stilbene with 9 afforded the
corresponding epoxides as major products, indicating that
the Ru(tpip) oxo-active species is a selective oxidant.
An attempt to isolate the active intermediate(s) for the
Ru(tpip)-catalyzed oxidation was made. The reaction between
9 and iodosylbenzene was monitored by NMR spectroscopy.
Treatment of 9 in CDCl3 with 2 equiv of iodosylbenzene at
room temperature resulted in the formation of a brown
species 11, which could be isolated as an air-stable solid by
addition of a large amount of hexane to the reaction mixture.
1
The H NMR spectrum of 11 showed the absence of the
resonance at δ 22.46, indicating the loss of the carbene group.
The 31P{1H} NMR spectrum of 11 displayed two singlets at
δ 20.33 and 50.88. The resonance at δ 20.33, which is within
the range found for diamagnetic Ru(tpip) complexes, was
attributed to tpip- ligand(s), whereas the one at δ 50.88
possibly was due to a coordinated PCy3 (or OPCy3) ligand
(31P resonances for uncomplexed PCy3 and OPCy3 were
found at approximately δ 9.7 and 46.7, respectively). The
ESI mass spectrum showed a molecular ion peak at m/z 933
corresponding to [Ru(tpip)2]+. However, no signals due to
Ru(tpip) species having a PCy3 ligand were observed.
Isolated 11 can oxidize benzyl alcohol and PPh3 to give
benzaldehyde and OPPh3 in 35 and 41% yield, respectively,
but no reaction was found between 11 and styrene, suggesting
that a different Ru active species is responsible for the
9-catalyzed epoxidation. On the basis of the above evidence,
we believe that 11 is a high-valence Ru-bis(tpip) complex,
possibly an oxo species containing a PCy3 ligand. Unfortu-
nately, despite many attempts, we were not able to obtain a
crystalline sample of 11 for structure determination. Ad-
ditional experimental work is required in order to identify
the active species of the Ru-catalyzed oxidation.
Concluding Remarks. In summary, transmetalation of
K(tpip) or [Ag(tpip)]4 with a variety of Ru chloride com-
pounds has been studied. For the reactions of Ru(PPh3)3Cl2
and [Ru(CO)2Cl2]x, only mono(κ2-tpip) complexes were
isolated, indicating the reluctance of Ru(II) to bind four hard
PdO groups in the coordination sphere. Ru-bis(tpip)
complexes could be synthesized using nitrosyl and carbene
complexes of Ru as starting materials. Photolysis of cis-
Ru(tpip)2(NO)Cl produced Ru(tpip)2(solv)Cl complexes that
may serve as useful precursors to Ru(III)-bis(tpip) com-
plexes. The cyclic voltammetry study showed that tpip- is a
stronger electron donor than acac-. Thus, one may expect
that higher-valence Ru(tpip) complexes should be easily
accessible and may exhibit interesting chemistry. cis-
Ru(tpip)2(CHPh)(PCy3) can catalyze oxidation of alcohols
and olefins with NMO and iodosylbenzene, respectively.
Acknowledgment. We thank Dr. Herman H. Y. Sung for
solving the crystal structures. Financial support from the
Hong Kong Research Grants Council (Project 602104) is
gratefully acknowledged.
Supporting Information Available: Tables of crystal data, final
atomic coordinates, anisotropic thermal parameters, and complete
lists of bond lengths and angles for complexes 2-7 and 9 (in CIF
format). This material is available free of charge via the Internet at
http://pubs.acs.org.
(28) Assuming that the Cp2Fe+/0 couple in MeCN occurs at 0.665 V versus
the normal hydrogen electrode (Gennett, T.; Milner, D. F.; Weaver,
M. J. J. Phys. Chem. 1985, 89, 2789).
IC800018D
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