Ruthenium complexes of six-electron-donor NUPHOS-Type diphosphines: Highly selective catalysts for the hydrocarboxylation of terminal alkynes

Article abstract of DOI:10.1021/om050014j

The ruthenium-p-cymene complexes [p-cymene)Ru(1,2,3,4-Me ₄-NUPHOS)Cl][SbF₆] and [(p-cymene)Ru(1,4-Et ₂-2,3-cyclo-C₆H₈-NUPHO S)Cl][SbF₆] were prepared by reaction of [(p-cymene)RuCl₂

Full text of DOI:10.1021/om050014j

Organometallics 2005, 24, 2633-2644
2633
Ruthenium Complexes of Six-Electron-Donor
NUPHOS-Type Diphosphines: Highly Selective Catalysts
for the Hydrocarboxylation of Terminal Alkynes
Simon Doherty,*,‡ Julian G. Knight,*,‡ Rakesh K. Rath,‡ William Clegg,‡
Ross W. Harrington,‡ Colin R. Newman,§ Robert Campbell,§ and Hiren Amin‡
School of Natural Sciences, Chemistry, Bedson Building, The University of Newcastle upon
Tyne, Newcastle upon Tyne, NE1 7RU, U.K., and Centre for the Theory and Applications of
Catalysis, School of Chemistry, The Queen’s University of Belfast, David Keir Building,
Stranmillis Road, Belfast, BT9 5AG, U.K.
Received January 6, 2005
The ruthenium-p-cymene complexes [(p-cymene)Ru(1,2,3,4-Me4-NUPHOS)Cl][SbF6] (2a)
and [(p-cymene)Ru(1,4-Et2-2,3-cyclo-C6H8-NUPHOS)Cl][SbF6] (2b) have been prepared by
reaction of [(p-cymene)RuCl2]2 with the corresponding NUPHOS diphosphine in the presence
of NaSbF6. The chloro ligand can be abstracted from these monocations to afford [(p-cymene)-
Ru(P,P,η2(C)-1,2,3,4-Me4-NUPHOS)][SbF6]2 (3a) and [(p-cymene)Ru(P,P,η2(C)-1,4-Et2-2,3-
cyclo-C6H8-NUPHOS)][SbF6]2 (3b), respectively, in which the diphosphine coordinates as a
six-electron donor, bonded through both diphenylphosphino groups and one of the double
bonds of the butadiene tether. In stark contrast, it proved markedly more difficult to abstract
the chloro ligand from either the BIPHEP or the MeO-BIPHEP monocations [(p-cymene)-
Ru(BIPHEP)Cl][SbF6] (4a) and [(p-cymene)Ru(MeO-BIPHEP)Cl][SbF6] (4b), and even after
prolonged reaction times at elevated temperature [(p-cymene)Ru(BIPHEP)][SbF6]2 (5a) and
[(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 (5b) formed as a 30% mixture with unreacted 4a and
4b, respectively. The structures of 2a, as its perchlorate salt, and 2b have been determined
by single-crystal X-ray crystallography and are compared with that of their BIPHEP
counterpart 4a. Unfortunately, it has not been possible to prepare the corresponding dppb
complex [(p-cymene)Ru(dppb)Cl][SbF6] to undertake a comparative study, since [(p-cymene)-
RuCl2]2 reacts with dppb under the same conditions as those used to prepare 2a,b to afford
the bridged dimer [{(p-cymene)RuCl2}2(µ-dppb)] (6), the identity of which has been confirmed
by a single-crystal X-ray study. Interestingly, 3a undergoes rapid hydrolysis in the presence
of pyridine to give [(p-cymene)Ru{Ph2(O)PC(H)MeCMeCMeCMePPh2}][SbF6] (7), which
contains an unusual unsymmetrical bisphosphine monoxide pincer ligand formed by oxidation
of one of the diphenylphosphino groups of 1,2,3,4-Me4-NUPHOS and a highly regioselective
syn addition of Ru and H across the butadiene double bond proximate to the phosphine
oxide. Dications 3a,b catalyze the regioselective anti-Markovnikov addition of benzoic acid
to 1-pentyne and 1-octyne to give the corresponding alk-1-en-1-yl esters with cis-to-trans
ratios as high as 95:5, while the corresponding BIPHEP and MeO-BIPHEP complexes were
significantly less selective, catalyst mixtures formed from 4b giving a 70:30 mixture of cis
and trans alk-1-en-1-yl ester. In contrast, selectivity was reversed with catalyst mixtures
generated from 6, which were 90% selective for Markovnikov addition to 1-octyne, as might
have been predicted for a ruthenium catalyst coordinated by a single phosphine, albeit one-
half of a bidentate diphosphine. Catalysts based on NUPHOS diphosphines are also highly
active and selective for anti-Markovnikov addition of benzoic acid to phenylacetylene and
give (Z)-styryl benzoate in yields of up to 85% and selectivities as high as 99:1 with no
evidence for the formation of terminal olefin. In our hands, solutions formed by activation
of 4a,b with AgSbF6 catalyze the regio- and stereoselective anti-Markovnikov hydrocar-
boxylation of phenylacetylene, which was somewhat surprising considering that an earlier
report has claimed that 5b reacts with phenylacetylene to form a stable catalytically inactive
cyclometalation/insertion product.
Introduction
Biaryl-based diphosphines are proving to be among
the most versatile and effective of ligands for asym-
metric catalysis,1 with noteworthy examples including
the ruthenium-catalyzed asymmetric hydrogenation of
(1) (a) Seyden-Penne, J. Chiral Auxiliaries and Ligands in Asym-
metric Catalysis: Wiley: New York, 1995. (b) Noyori, R. Asymmetric
Catalysis in Organic Synthesis; Wiley: New York, 1994. (c) Ojima, I.
Ed. Catalytic Asymmetric Synthesis, 2nd ed.; Wiley-VCH: New York,
2000.
* To whom correspondence should be addressed. E-mail: s.doherty@
ncl.ac.uk.
‡ The University of Newcastle upon Tyne.
§ The Queen’s University of Belfast.
10.1021/om050014j CCC: $30.25 © 2005 American Chemical Society
Publication on Web 04/19/2005

2634 Organometallics, Vol. 24, No. 11, 2005
Doherty et al.
olefins2 and carbonyl compounds3 as well as ring-
opening polymerizations,4 palladium-catalyzed trans-
formations such as inter- and intramolecular Heck
reactions,5 hydroaminations (conjugate additions),6 hy-
drocyanations,7 Diels-Alder cycloadditions,8 aldol and
Mannich-type reactions,9 and the ene reaction10 and
rhodium-catalyzed cycloisomerizations,11 reductive aldol
reactions,12 kinetic resolutions,13 and 1,6-additions to
enynones.14 Moreover, biaryl-based diphosphines have
recently proven to be the ligand of choice for several
achiral transformations, forming optimum catalysts for
the carbonylation of heterocyclic chlorides,15 the chemo-
and regioselective intermolecular trimerization of al-
kynes,16 Grignard cross-couplings,17 and Buchwald-
Hartwig aminations.18
Chart 1
We have recently prepared an entirely new class of
diphosphine, NUPHOS, which is based on a 1,3-buta-
diene tether and a potential alternative to biaryl
diphosphines such as BINAP and BIPHEP (Chart 1).19
Preliminary studies have revealed that these diphos-
phines can coordinate as either 4e- or 6e-donors to
ruthenium, with the third pair of electrons arising from
coordination of one of the carbon-carbon double bonds
of the butadiene tether (eq 1).20 Following this discovery,
a survey of the literature revealed an increasing number
of examples of biaryl diphosphines that coordinate in
this manner, the first of which was reported by Pathak
as early as 1994.21 Pregosin subsequently prepared a
number of related examples of six-electron-donor MeO-
BIPHEP and BINAP ruthenium complexes, each sup-
ported by six-electron-donor hydrocarbons such as a
deprotonated pyrrole, the benzene ring of indole, and
p-cymene.22 Biaryl diphosphines coordinated in this
P,P,η2(C)-manner are now routinely identified by a
combination of 31P and 13C chemical shift data, the latter
of which is obtained using long-range correlation.23 In
selected cases 2D NMR exchange spectroscopy has
shown that the double bond is weakly coordinated and
undergoes slow dissociative exchange.22,23 More recently,
James and co-workers have shown that [RuCl2(BINAP)-
(bipy)] undergoes aerobic oxidation in methanol to give
[RuCl(BINAPO)(bipy)][PF6], which contains a six-
electron (P,O,η2-naphthyl) BINAP monoxide.24
(2) For a comprehensive and informative review see: (a) Noyori, R.
Angew. Chem., Int. Ed. 2002, 41, 2008. See also: (b) Kitamura, M.;
Tsukamoto, M.; Bessho, Y.; Yoshimura, M.; Kobs, U.; Widhalm, M.;
Noyori, R. J. Am. Chem. Soc. 2002, 124, 6649. (b) Jeulin, S.; Duprat
de Paule, S.; Ratovelomanana-Vidal, V.; Genet, J.-P.; Champion, N.;
Dellis, P, Proc. Nat. Acad. Sci. 2004, 101, 5799. (c) Kitamura, M.;
Kasahara, I.; Manabe, K.; Noyori, R.; Takaya, H. J. Org. Chem. 1988,
53, 708. (d) Noyori, R.; Ikeda, T.; Ohkuma, T.; Widhalm, M.; Kitamura,
M.; Takaya, H.; Akutagawa, S.; Sayo, N.; Saito, T.; Taketomi, T.;
Kumobayashi, H. J. Am. Chem. Soc. 1989, 111, 9134. (e) Noyori, R.
Tetrahedron 1994, 50, 4259.
(3) (a) Noyori, R.; Ohkuma, Angew. Chem., Int. Ed. 2001, 40, 40.
(b) Sandoval, C. A.; Ohkuma, T.; Muniz, K.; Noyori, R. J. Am. Chem.
Soc. 2003, 125, 13490. (c) Qui, L.; Wu, J.; Chan, S.; Au-Yeung, T. T.-
L.; Ji, J.-X.; Guo, R.; Pai, C.-C.; Zhou, Z.; Li, X.; Fan, Q.-H.; Chan, A.
S. C. Proc. Nat. Acad. Sci. 2004, 101, 5815.
(4) Ameroso, D.; Fogg, D. E. Macromolecules 2000, 33, 2815.
(5) (a) Ozawa, F.; Kubo, A.; Hayashi, T. J. Am. Chem. Soc. 1991,
113, 1417. (b) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.;
Nishioka, E.; Yanagi, K.; Moriguchi, K. Organometallics 1993, 12, 4188.
(6) (a) Hii, K. K.; Li, K. Chem. Commun. 2003, 1132. (b) Li, K.;
Cheng, X.; Hi, K. K. Eur. J. Org. Chem. 2004, 959. (c) Hamashima,
Y.; Somei, H.; Shimura, Y.; Tamura, T.; Sodeoka, M. Org. Lett. 2004,
6, 1861.
(7) Hodgson, M.; Parker, D. J. Organomet. Chem. 1987, 325, C27.
(8) (a) Ghosh, A. K.; Matsuda, H. Org. Lett. 1999, 1, 2157. (b) Oi,
S.; Terada, E.; Ohuchi, K.; Kato, T.; Tachibana, Y.; Inoue, Y. J. Org.
Chem. 1999, 64, 8660. (c) Hiroi, K.; Watanabe, K. Tetrahedron:
Asymmetry 2001, 12, 3067. (d) Pignat, K.; Vallotto, J.; Pinna, F.;
Strukul, G. Organometallics 2000, 19, 5160.
(9) (a) Sodeoka, M.; Tokunoh, R.; Miyazaki, F.; Hagiwara, E.;
Shibasaki, M. Synlett 1997, 464. (b) Fujimura, O. J. Am. Chem. Soc.
1998, 120, 10032. (c) Fujii, A.; Hagiwara, E.; Sodeoka, M. J. Am. Chem.
Soc. 1999, 121, 5450.
Reasoning that the coordinated biaryl double bond of
[(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 could act to “sta-
bilize” an otherwise coordinatively unsaturated 16-
electron complex, this dication has been used to catalyze
(10) (a) Hao, J.; Hatano, M.; Mikami, K. Org. Lett. 2000, 2, 4059.
(b) Aikawa, K.; Kainuma, S.; Hatano, M.; Mikami, K. Tetrahedron Lett.
2004, 45, 183. (c) Becker, J. J.; Van Orden, L. J.; White, P. S.; Gagne´,
M. R. Org. Lett. 2002, 4, 727. (d) Koh, J. H.; Larsen, A. O.; Gagne´, M.
R. Org. Lett. 2001, 3, 1233.
(11) (a) Lei, A.; Waldkirch, J. P. He, M.; Zhang, X. Angew. Chem.,
Int. Ed. 2002, 41, 4526. (b) Fairlamb, I. J. S. Angew. Chem., Int. Ed.
2004, 43, 1048. (c) Tong, X.; Dao, L.; Zhang, Z.; Zhang, X. J. Am. Chem.
Soc. 2004, 126, 7601. (d) Mikami, K.; Yusa, Y.; Hatano, M.; Waka-
bayashi, K.; Aikawa, K. Chem. Commun. 2004, 98.
(12) Morken, J. P.; Duffrey, M. O.; Taylor, S. J. J. Am. Chem. Soc.
2000, 112, 4528.
(13) (a) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2003, 125, 8078
(b) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2002, 124, 10296.
(14) Hayashi, T.; Tokunaga, N.; Inoue, K. Org. Lett. 2004, 6, 305.
(15) Albaneze-Walker, J.; Bazaral, C.; Leavey, T.; Dormes, P. G.;
Murry, J. A. Org. Lett. 2004, 6, 2097.
(16) Tanaka, K.; Shirasaka, K. Org. Lett. 2003, 5, 4697.
(17) Ogasawara, M.; Yoshida, K.; Hayashi, T. Organometallics 2000,
19, 1567.
(19) (a) Doherty, S.; Knight. J. G.; Robins, E. G.; Scanlan, T. H.;
Champkin, P. A.; Clegg, W. J. Am. Chem. Soc. 2001, 123, 5110. (b)
Doherty, S.; Robins, E. G.; Nieuwenhuyzen, M.; Knight, J. G.; Champ-
kin, P. A.; Clegg, W. Organometallics 2002, 21, 1383. (c) Doherty, S.;
Newman, C. R.; Rath, R. K.; Hardacre, C.; Nieuwenhuyzen, M.; Knight,
J. G. Org. Lett. 2003, 5, 3863. (d) Doherty, S.; Goodrich, P.; Hardacre,
C.; Luo, H.-K.; Rooney, D. W.; Seddon, K. R.; Styring, P. Green Chem.
2004, 6, 63. (e) Doherty, S.; Newman, C. R.; Rath, R. K.; Hardacre, C.;
Nieuwenhuyzen, M.; Knight, J. G. Organometallics 2004, 23, 1055. (f)
Doherty, S.; Knight, J. G.; Hardacre, C.; Luo, H.-K.; Newman, C. R.;
Nieuwenhuyzen, M. Organometallics 2004, 23, 6127.
(20) Doherty, S.; Newman, C. R.; Hardacre, C.; Nieuwenhuyzen, M.;
Knight, J. G. Organometallics 2003, 22, 1452.
(21) Pathak, D. D.; Adams, H.; Bailey, N. A.; King, P. J.; White, C.
J. Organomet. Chem. 1994, 479, 237.
(22) Feiken, N.; Pregosin, P. S.; Trabesinger, G.; Albinati, A.; Evoli,
G. L. Organometallics 1997, 16, 5756.
(23) (a) Feiken, N.; Pregosin, P. S.; Trabesinger, G.; Scalone, M.
Organometallics 1997, 16, 537. (b) den Reijer, C. J.; Dotta, P.; Pregosin,
P. S.; Albinati, A. Can. J. Chem. 2001, 79, 693.
(18) (a) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805 (b) Hartwig, J. F. Acc. Chem. Res. 1998, 31,
852.
(24) Cyr, P. W.; Rettig, S. J.; Patrick, B. O.; James, B. R. Organo-
metallics 2002, 21, 4672.

Ruthenium Complexes of NUPHOS-Type Diphosphines
Organometallics, Vol. 24, No. 11, 2005 2635
Scheme 1
characteristic of the p-cymene ring. A similar procedure
was used to prepare the corresponding BIPHEP and
known MeO-BIPHEP complexes [(p-cymene)Ru-
(BIPHEP)Cl][SbF6] (4a) and [(p-cymene)Ru(MeO-
BIPHEP)Cl][SbF6] (4b), respectively, again identified by
a characteristic pair of doublets in the 31P NMR
spectrum. We also attempted to prepare the correspond-
ing dppb complex [(p-cymene)Ru(dppb)Cl][SbF6] to com-
pare the performance of catalysts based on diphosphines
containing a four-carbon sp2-hydridized tether with that
containing solely sp3-hybridized carbon atoms. However,
under the same conditions as those used to prepare
2a,b, and regardless of the ruthenium:diphosphine
stoichiometry, dppb reacts with [(p-cymene)RuCl2]2 to
afford the diphosphine-bridged dimer [{(p-cymene)-
RuCl2}2(µ-dppb)] (6) (eq 2), the identity of which was
unequivocally established by a single-crystal X-ray
study (vide infra).
the anti-Markovnikov addition of benzoic acid to ter-
minal alkynes.25 While good cis/trans ratios were ob-
tained for addition to 1-pentyne and 1-octyne, the
dication was reported to be completely inactive for the
reaction between phenylacetylene and benzoic acid,
which was attributed to the formation of a stable,
inactive cyclometalation-alkyne insertion product (vide
infra). Herein, we report the results of a comparative
study between the ruthenium-based chemistry of
NUPHOS-type diphosphines and BIPHEP/MeO-
BIPHEP, which has revealed several noteworthy dif-
ferences including (i) a much greater propensity for
NUPHOS diphosphines to coordinate in a P,P,η2(C)-
manner than BIPHEP or MeO-BIPHEP, (ii) markedly
higher cis-to-trans ratios for anti-Markovnikov addition
of benzoic acid to terminal alkynes with NUPHOS-based
catalysts compared with their biaryl-based counterparts,
and (iii) efficient and highly regio- and stereoselective
addition of benzoic acid to phenylacetylene using cata-
lysts based on NUPHOS.
The chemical shift of δ 24.8 in the 31P NMR spectrum
of 6 is similar to that of 25.0 reported for [{(C6H6)-
RuCl2}]2(µ-dppb),26 while the intensities of the reso-
nances associated with methylene protons of dppb
relative to the aromatic signals of the p-cymene frag-
ment are entirely consistent with this dimeric formula-
tion. Formation of 6 is perhaps not surprising, since
there are a number of reports of four-carbon-bridged
diphosphines such as dppb and DIOP that bridge two
ruthenium atoms. For instance, the reaction of dppb and
DIOP with [(C6H6)RuCl2]2 to give [{(C6H6)RuCl2}2(µ-
dppb)] and [{(C6H6)RuCl2}2(µ-DIOP)], respectively, re-
ported by James and co-workers,26 is particularly rel-
evant, as is the reaction between dppb and the bis(allyl)
dimer [{Ru(η3:η3:C10H16)(µ-Cl)Cl}2] to afford [{Ru(η3:η3:
C10H16)Cl2}2(µ-dppb)].27
Although we have previously shown that the ruthe-
nium complex [RuCl2(1,2,3,4-Me4-NUPHOS)(en)] rap-
idly dissociates a chloro ligand in chloroform to give
[RuCl(P,P,η2(C)-1,2,3,4-Me4-NUPHOS)(en)]Cl and that
these two complexes cleanly and quantitatively inter-
convert in a solvent-dependent equilibrium that involves
reversible formation of six-electron-donor NUPHOS
diphosphines, we found no evidence for such a process
occurring with 2a,b, in either dichloromethane, THF,
chloroform, or methanol.20 However, the chloro ligand
in 2a,b can be abstracted by reaction with a slight
excess of AgSbF6 to afford [(p-cymene)Ru(P,P,η2(C)-
NUPHOS)][SbF6]2 (3a,b), in which one of the CdC
double bonds of the butadiene tether is coordinated in
an η2-manner to the metal center (Scheme 1). Definitive
evidence for the presence of the P,P,η2(C)-coordinated
Results and Discussion
Synthesis and Spectroscopic Characterization
of Ruthenium(II) Complexes. Reaction of NUPHOS
diphosphines 1a,b with [(p-cymene)RuCl2]2 in dichloro-
methane in the presence of sodium hexafluoroanti-
monate gave salts of the monocations [(p-cymene)Ru-
(1,2,3,4-Me4-NUPHOS)Cl][SbF6] (2a) and [(p-cymene)-
Ru(1,4-Et2-2,3-cyclo-C6H8-NUPHOS)Cl][SbF6] (2b), re-
spectively, in good yields (Scheme 1). Both complexes
were isolated as orange-yellow solids after crystalliza-
tion and were characterized by NMR spectroscopy, mass
spectrometry, and elemental analysis. The 31P NMR
spectra of both 2a and 2b contain a pair of well-resolved
doublets associated with the diastereotopic diphenylphos-
1
phino groups. The methyl region of the H NMR spec-
trum of 2a contains a set of four equal intensity signals
associated with the four-carbon tether of NUPHOS,
while that of 2b is more complex due to the methylene
protons of the cyclohexyl ring; both spectra contain a
set of four well-resolved high-field-shifted doublets
(26) Fogg, D. E.; James, B. R. J. Organomet. Chem. 1993, 462, C21.
(27) Cadierno, V.; Garcia-Garrido, S. E.; Gimeno, J. Inorg. Chim.
Acta. 2003, 347, 41.
(25) den Reijer, C. J.; Drago, D.; Pregosin, P. S. Organometallics
2001, 20, 2982.

2636 Organometallics, Vol. 24, No. 11, 2005
Doherty et al.
diphosphine was provided by the distinctive 31P NMR
spectrum, which contained two well-separated pairs of
doublets, one at δ 78.9 (3a), 82.1 (3b) and the other at
much higher field, δ 6.5 (3a), 9.0 (3b), the latter in the
region expected for a P,P,η2(C)-coordinated diphosphine
and associated with the diphenylphosphino group ad-
jacent to the coordinated double bond. Since Pregosin
has warned against relying on 31P NMR spectroscopy
as the sole technique for identifying this type of
interaction,22,23a C-H long-range correlation was also
used to unequivocally assign the resonances associated
with the carbon atoms of the η2-coordinated double
bond. In the case of 3a, long-range correlation identified
a doublet at δ 62 and a doublet of doublets at δ 102,
which we confidently assign to the two carbon atoms of
the η2-coordinated double bond. These resonances show
two and three cross-peaks, respectively, which arise
from two- and three-bond J(C-H) coupling to the
protons of neighboring methyl groups. The doublet at δ
62 clearly correlates with only two sets of methyl
protons, a singlet and a doublet, and must therefore
belong to the carbon bonded to phosphorus, while the
doublet of doublets at δ 102 shows cross-peaks to three
sets of methyl protons, two singlets and a doublet. This
long-range correlation study can also be used to assign
the two carbon atoms associated with the uncoordinated
double bond. In a similar manner the pattern of cross-
peaks in the C-H long-range correlation of 3b has been
used to identify each of the carbon atoms of the
monocyclic NUPHOS tether.
While the chloro ligand in 2a was readily abstracted
under mild reaction conditions, that in 4a,b proved
much more difficult to remove, so much so that it was
impossible to isolate pure samples of the corresponding
6e-donor BIPHEP and MeO-BIPHEP complexes [(p-
cymene)Ru(BIPHEP)][SbF6]2 (5a) and [(p-cymene)Ru-
(MeO-BIPHEP)][SbF6]2 (5b), respectively. Typically,
treatment of a dichloromethane solution of [(p-cymene)-
Ru(BIPHEP)Cl][SbF6] (4a) or [(p-cymene)Ru(MeO-
BIPHEP)Cl][SbF6] (4b) with an excess of AgSbF6 gave
a 30:70 mixture of 5a,b and 4a,b even after heating at
reflux for 12 h. In each case a 31P NMR spectrum of the
crude reaction mixture clearly showed two sets of
signals, a major pair of doublets corresponding to
unreacted 4a/b together with two minor exchange-
broadened signals at ca. δ 65 and 3 associated with 5a/
b. In stark contrast, the formation of 3a,b occurs rapidly
and quantitatively under mild conditions, i.e., in dichloro-
methane at room temperature. Such facile conversion
of a four-electron NUPHOS diphosphine into its six-
electron P,P,η2(C)-coordinated counterpart is consistent
with our previous studies in which [RuCl2(1,2,3,4-Me4-
NUPHOS)(en)] (en ) ethylenediamine) rapidly dissoci-
ates chloride in chloroform to give [RuCl(P,P,η2(C)-
1,2,3,4-Me4-NUPHOS)(en)][Cl] (eq 1), whereas its BINAP
counterpart is indefinitely stable in solution.20 Thus,
NUPHOS-type diphosphines clearly demonstrate a much
greater propensity to coordinate in a P,P,η2(C)-manner
than BINAP, BIPHEP, or MeO-BIPHEP, which we
tentatively suggest to be associated with an inherently
greater conformational flexibility of the 1,3-butadiene
tether as well as an intrinsically more favorable η2-
coordination of the butadiene fragment compared with
the aromatic system of a biaryl fragment.
The reaction of 3a with pyridine was examined in an
attempt to demonstrate that the CdC double bond of
the P,P,η2(C)-coordinated NUPHOS was of sufficient
substitutional lability to form the dication [(p-cymene)-
Ru(1,2,3,4-Me4-NUPHOS)(py)][SbF6]2. However, rather
than forming the desired adduct, addition of pyridine
to a dichloromethane solution of 3a, generated in situ
by abstraction of chloride from 2a with AgSbF6, resulted
in rapid and quantitative hydrolysis to afford [(p-
cymene)Ru{Ph2(O)PC(H)MeCMeCMeCMePPh2}]-
[SbF6] (7), which was initially identified by a combina-
tion of 1H NMR spectroscopy and FAB mass spectrometry
and subsequently by a single-crystal X-ray study (eq 3).
Two low-field singlets at δ 73.4 and 68.5 in the 31P NMR
3
spectrum of 7 are consistent with a small or zero JPP
for a P,O-coordinated bis(phosphine)monoxide, as ob-
served for Pd, Pt, Rh, and most recently ruthenium
complexes of BINAP monoxide. Several unusual fea-
1
tures in the H NMR spectrum of 7 provided the first
indication that an unexpected transformation had oc-
curred. In particular, a low-field doublet of quartets of
intensity 1H at δ 5.02 corresponds to the methine proton
of the newly formed CHMe adjacent to the phosphine
oxide, while its methyl substituent appears as a doublet
of doublets at δ 1.53. As expected, the methyl groups at
the 2- and 3-positions of the butadiene tether appear
as singlets at δ 1.15 and 0.73, and the remaining methyl
group adjacent to the diphenylphosphino fragment
appears as a doublet at δ 1.45. The most likely origin
of the adventitious water involved in this transforma-
tion is the pyridine, which was not dried prior to use,
the pyridine acting to remove the HSbF6 generated
during the hydrolysis. In a comparative series of experi-
ments compound 3a did not react with dry pyridine to
form the desired adduct [(p-cymene)Ru(1,2,3,4-Me4-
NUPHOS)(py)][SbF6]2, nor did it undergo hydrolysis in
the absence of pyridine. Overall, formation of 7 involves
oxidation of one of the diphenylphosphino groups and
a highly selective syn addition of Ru and H across the
double bond of the butadiene tether adjacent to the
phosphine oxide, presumably via a hydride intermedi-
ate.
Crystal Structures of [(p-cymene)Ru(1,2,3,4-Me4-
NUPHOS)Cl][ClO4] (2a), [(p-cymene)Ru(1,4-Et2-2,3-
cyclo-C6H8-NUPHOS)Cl][SbF6] (2b), [(p-cymene)-
Ru(P,P,η2(C)-1,2,3,4-Me4-NUPHOS)][SbF6]2 (3a), [(p-
cymene)Ru(BIPHEP)Cl][SbF6] (4a), [{(p-cymene)-
RuCl2}2(µ-dppb)] (6), and [(p-cymene)Ru{Ph2(O)-
PC(H)MeCMeCMeCMePPh2}][SbF6] (7). The marked
difference in reactivity between 2a,b and 4a, particu-
larly with respect to halide abstraction, prompted us to
undertake single-crystal X-ray analyses of each of these
compounds, the molecular structures of which are
shown in Figures 1-3, with selected bond lengths and

Ruthenium Complexes of NUPHOS-Type Diphosphines
Organometallics, Vol. 24, No. 11, 2005 2637
Figure 3. Molecular structure of [(p-cymene)Ru(1,2,3,4-
Me4-NUPHOS)][SbF6]2 (3a), illustrating the P,P,η2(C)-
coordination of Me4-NUPHOS. Hydrogen atoms and hexa-
fluoroantimonate anions have been omitted for clarity.
Ellipsoids are at the 30% probability level.
Figure 1. Molecular structure of [(p-cymene)Ru(1,2,3,4-
Me4-NUPHOS)Cl][ClO4] (2a). Hydrogen atoms, dichloro-
methane molecules of crystallization, minor disorder com-
ponents, and the perchlorate anion have been omitted for
clarity. Ellipsoids are at the 30% probability level.
related complexes of C4-bridged biaryl diphosphines,31
as are the corresponding Ru-P distances, which lie
between 2.335(2) and 2.4082(17) Å. The Ru-Cl bond
lengths are also unexceptional, with that of 2.3976(18)
Å in 4a slightly shorter than those of 2.4114(13) and
2.4056(10) Å in 2b and 2a, respectively. The dihedral
angle of 66.7° between the least-squares plane contain-
ing the two sp2-carbon atoms and their substituents in
2a is slightly larger than the corresponding angles of
60.1° and 60.7° in 2b and 4a, respectively.
A single-crystal X-ray structure determination of 3a
has also been undertaken in order to determine the
influence of P,P,η2(C)-coordination on the metal-
diphosphine bonding and coordination geometry at the
metal center. A perspective view of the molecular
structure of 3a is shown in Figure 3, and a selection of
bond lengths and angles is listed in Table 3. The
structure reveals that the NUPHOS diphosphine coor-
dinates in a P,P,η2(C)-manner and occupies a facial
coordination environment, bonded through both phos-
phorus atoms and one of the double bonds of the
butadiene tether. The remaining facial coordination
sites are occupied by the η6-p-cymene fragment, which
exhibits a marked deviation from planarity with C(2)
and C(5) displaced by 0.0574 and 0.0456 Å, respectively,
out of the mean plane of the six carbon atoms. The
C(13)-C(14) bond length of 1.441(11) Å shows the
elongation expected upon η2-coordination32 compared
with that of 1.311(11) Å for the uncoordinated double
bond C(11)-C(12). The Ru-C(13) and Ru-C(14) bond
lengths of 2.237(7) and 2.211(7) Å are very similar, as
has previously been noted for the related complex [(η6-
Figure 2. Molecular structure of [(p-cymene)Ru(1,4-Et2-
2,3-cyclo-C6H8-NUPHOS)Cl][SbF6] (2b). Hydrogen atoms,
chloroform molecules of crystallization, and the hexa-
fluoroantimonate anion have been omitted for clarity.
Ellipsoids are at the 30% probability level.
angles listed in Table 1 and crystal data presented in
Table 4. Since the structures of each of these compounds
are based on p-cymene ruthenium complexes of C4-
bridged tropos diphosphines and are clearly related,
they will be described together. The coordination of the
metal is similar in all complexes and is best described
as octahedral, with three sites occupied by the η6-p-
cymene fragment and the remaining three by two
diphenylphosphino groups and a chloro ligand. The six
Ru-C(arene) distances in all three complexes fall
between 2.247(7) and 2.345(6) Å and are within
the range expected on the basis of related complexes
such as [(arene))Ru(BINAP)Cl]+,27,28 [(p-cymene)Ru-
(BDPBzP)I]I,29 and [(p-cymene)Ru(dppf)Cl][PF6].30 The
natural bite angles of 88.50(3)° (2a), 87.05(6)° (2b), and
89.68(7)° (4a) are comparable to those reported for
(31) (a) Tudor, M. D.; Becker, J. J.; White, P. S. Gagne´, M. R.
Organometallics 2000, 19, 4376. (b) Tominaga, H.; Sakai, K.; Tsubo-
mura, T. J. Chem. Soc., Chem. Commun. 1995, 2273. (c) Wicht, D. K.;
Zhuravel, M. A.; Gregush, R. V.; Glueck, D. S.; Guzei, I. A.; Liable-
Sands, L. M.; Rheingold, A. L. Organometallics 1998, 17, 1412. (d)
Alcock, N. W.; Brown, J. M.; Perez-Torrente, J. Tetrahedron Lett. 1992,
33, 389. (e) Brown, J. M.; Perez-Torrente, J. J.; Alcock, N. W.
Organometallics 1995, 14, 1195. (f) Motoyama, Y.; Murata, K.; Kuri-
hara, O.; Naitoh, T.; Aoki, K.; Nishiyama, H. Organometallics 1998,
17, 1251. (g) Motoyama, Y.; Kurihara, O.; Murata, K.; Aoki, K.;
Nishiyama, H. Organometallics 2000, 19, 1025.
(28) Mashima, K.; Kusano, K.; Sato, N.; Matsumara, Y.; Nozaki, K.;
Kumobayashi, H.; Hori, Y.; Ishizaki, T.; Akutagawa, S.; Takaya, H. J.
Org. Chem. 1994, 59, 3064.
(29) Bianchini, C.; Barbaro, P.; Scapacci, G.; Zanobini, F. Organo-
metallics 2000, 19, 2450.
(32) (a) Motoyama, Y.; Murata, K.; Kurihara, O.; Naitoh, T.; Aoki,
K.; Nishiyama, H. Organometallics 1998, 17, 1251. (b) Motoyama, Y.;
Kurihara, O.; Murata, K.; Aoki, K.; Nishiyama, H. Organometallics
2000, 19, 1025.
(30) Jensen, S. B.; Rodger, S. J.; Spicer, M. D. J. Organomet. Chem.
1998, 556, 151.

2638 Organometallics, Vol. 24, No. 11, 2005
Table 1. Selected Bond Distances (Å) and Angles (deg) for 2a, 2b, and 4a
compound 2a compound 2b compound 4a (molecule a)
Doherty et al.
Ru-P(1)
2.3526(12)
2.3944(9)
2.4056(10)
2.299(4)
2.267(4)
2.265(4)
2.311(4)
2.266(4)
2.270(4)
1.352(5)
1.489(6)
1.350(5)
1.422(7)
1.359(7)
1.456(6)
1.402(6)
1.428(6)
1.398(6)
Ru-P(1)
2.3450(15)
2.4081(16)
2.4114(13)
2.331(6)
2.300(6)
2.268(6)
2.343(6)
2.284(6)
2.288(6)
1.342(8)
1.509(8)
1.337(8)
1.434(9)
1.427(10)
1.425(10)
1.407(9)
1.412(9)
1.411(9)
Ru(1)-P(1)
Ru(1)-P(2)
Ru(1)-Cl(11)
Ru(1)-C(2)
Ru(1)-C(3)
Ru(1)-C(4)
Ru(1)-C(5)
Ru(1)-C(6)
Ru(1)-C(7)
C(23)-C(28)
C(28)-C(29)
C(29)-C(30)
C(2)-C(3)
2.340(2)
Ru-P(2)
Ru-P(2)
2.3732(19)
2.3976(18)
2.303(8)
Ru-Cl(1)
Ru-C(2)
Ru-Cl(1)
Ru-C(2)
Ru-C(3)
Ru-C(3)
2.284(8)
Ru-C(4)
Ru-C(4)
2.265(7)
Ru-C(5)
Ru-C(5)
2.344(7)
Ru-C(6)
Ru-C(6)
2.265(7)
Ru-C(7)
Ru-C(7)
2.247(7)
C(23)-C(24)
C(24)-C(25)
C(25)-C(26)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
C(23)-C(26)
C(26)-C(31)
C(31)-C(32)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
1.391(10)
1.512(10)
1.402(10)
1.403(11)
1.376(10)
1.436(10)
1.395(10)
1.403(10)
1.422(10)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
P(1)-Ru-P(2)
88.50(3)
84.32(4)
89.75(3)
118.4(3)
125.1(4)
127.2(3)
120.9(3)
P(1)-Ru-P(2)
87.01(5)
85.11(5)
90.29(5)
120.3(4)
126.5(5)
128.0(5)
121.1(4)
P(1)-Ru(1)-P(2)
P(1)-Ru(1)-Cl(11)
P(2)-Ru(1)-Cl(11)
P(1)-C(23)-C(28)
C(23)-C(28)-C(29)
C(28)-C(29)-C(30)
C(29)-C(30)-P(2)
89.68(7)
84.61(7)
90.14(7)
121.9(5)
124.2(6)
127.9(6)
123.8(5)
P(1)-Ru-Cl(1)
P(1)-Ru-Cl(1)
P(2)-Ru-Cl(1)
P(2)-Ru-Cl(1)
P(1)-C(23)-C(24)
C(23)-C(24)-C(25)
C(24)-C(25)-C(26)
C(25)-C(26)-P(2)
P(1)-C(23)-C(26)
C(23)-C(26)-C(31)
C(26)-C(31)-C(32)
C(31)-C(32)-P(2)
Table 2. Selected Bond Distances (Å) and Angles
(deg) for 3a
Table 4. Selected Bond Distances (Å) and Angles
(deg) for 7
Ru-P(1)
Ru-P(2)
Ru-C(2)
Ru-C(3)
Ru-C(4)
Ru-C(5)
Ru-C(6)
Ru-C(7)
Ru-C(13)
Ru-C(14)
2.315(2)
2.315(2)
2.355(9)
2.260(8)
2.292(7)
2.379(8)
2.282(8)
2.246(8)
2.237(7)
2.211(7)
C(11)-C(12)
C(12)-C(13)
C(13-C(14)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
1.311(11)
1.499(11)
1.441(11)
1.402(12)
1.410(11)
1.400(11)
1.435(11)
1.420(11)
1.337(12)
Ru-P(1)
Ru-O
2.2814(10)
2.163(2)
2.223(3)
2.228(4)
2.243(4)
2.252(4)
2.289(4)
2.286(4)
2.180(4)
1.514(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
C(23)-C(24)
C(24)-C(25)
C(25)-C(26)
1.439(6)
1.381(6)
1.447(6)
1.396(6)
1.418(6)
1.415(6)
1.333(5)
1.528(5)
1.560(5)
Ru-C(25)
Ru-C(2)
Ru-C(3)
Ru-C(4)
Ru-C(5)
Ru-C(6)
Ru-C(7)
P(2)-O
P(1)-Ru-P(2)
91.16(8)
Ru-C(14)-P(1)
Ru-C(14)-C(18)
Ru-C(14)-C(13)
C(14)-Ru-C(13)
69.8(3)
122.2(6)
72.1(4)
37.8(3)
P(1)-Ru-O
P(1)-Ru-C(25)
88.74(7)
79.87(9)
O-Ru-C(25)
P(2)-O-Ru
79.29(11)
112.72(13)
Ru-C(13)-C(17)
Ru-C(13)-C(12)
Ru-C(13)-C(14)
117.7(5)
114.7(5)
70.1(4)
81.6° in [RuCl(P,P,η2-naphthyl-BINAPO)(phen)][PF6] is
greater than that of 77.37° in [RuCl2(BINAP)(phen)].24
The two Ru-P bond lengths are identical [2.315(2) Å]
and slightly shorter than those of 2.3944(9) and
2.3526(12) Å in 2a, which is presumably associated with
the additional positive charge on 3a. Although the
natural bite angle of 91.16(8)° is slightly larger than
that in 2a, it falls within the range expected for
ruthenium complexes of six-electron-donor diphosphines
such as MeO-BIPHEP.22
Table 3. Selected Bond Distances (Å) and Angles
(deg) for 6
Ru-P
2.3487(9)
2.4195(8)
2.4140(8)
2.217(3)
2.159(3)
2.182(3)
2.213(3)
2.245(3)
2.234(3)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(2)
1.374(5)
1.391(5)
1.376(7)
1.413(5)
1.403(5)
1.421(5)
1.424(5)
1.395(5)
1.426(5)
Ru-Cl(1)
Ru-Cl(2)
Ru-C(2)
Ru-C(3)
Ru-C(4)
Ru-C(5)
Ru-C(6)
Ru-C(7)
Although the spectroscopic data for 6, in particular
the relative intensities of the resonances in the 1H NMR
spectrum, were consistent with its formulation as a
dppb-bridged dimer, a single-crystal X-ray study was
undertaken to unequivocally confirm its identify, the
result of which is shown in Figure 5. A selection of bond
lengths and angles is listed in Table 3. The molecular
structure clearly shows two (p-cymene)RuCl2 fragments
connected through a dppb bridge in a piano stool
configuration. The two Ru-C bonds that lie trans to the
phosphorus atoms, namely, Ru-C(6) (2.245(3) Å) and
Ru-C(7) (2.234(3) Å) are slightly longer than the
remaining four Ru-C bonds [d(Ru-C)av ) 2.193 Å].
Similar bond length patterns have previously been
noted for [(C6H6)RuCl2(PMePh2)] and [(p-cymene)RuCl2-
P-Ru-Cl(1)
P-Ru-Cl(2)
83.04(3)
88.44(3)
Cl(1)-Ru-Cl(2)
88.30(3)
indole)Ru(MeO-BIPHEP-Bu)][BF4]2 [2.34(3) and 2.31(3)
Å]. The dihedral angle of 75.7° between the least-
squares planes defined by C(13)C(14)C(17)C(18) and
C(11)C(12)C(15)C(16) is significantly larger than that
of 66.1° in 2a, reflecting the dramatic conformational
changes experienced upon η2-coordination of C(13)-
C(14). A similar increase in dihedral angle occurs upon
changing from P,P coordination in [CpRuI(BINAP)]
(66°) to P,P,η2-naphthyl coordination in [CpRu(BINAP)]
(80°).21 James has also noted that the dihedral angle of

Ruthenium Complexes of NUPHOS-Type Diphosphines
Organometallics, Vol. 24, No. 11, 2005 2639
Figure 6. Molecular structure of [(p-cymene)Ru{Ph2(O)-
PC(H)MeCMeCMeCMePPh2}][SbF6] (7). Hydrogen atoms
and dichloromethane molecule of crystallization have been
omitted for clarity. Ellipsoids are at the 30% probability
level.
Figure 4. Molecular structure of [(p-cymene)Ru(BIPHEP)-
Cl][SbF6] (4a). Hydrogen atoms, dichloromethane mol-
ecules of crystallization, and the hexafluoroantimonate
anion have been omitted for clarity. Ellipsoids are at the
30% probability level.
C(sp3) σ-bond.35 The PdO bond length of 1.514(2) Å falls
within the range expected for a coordinated phosphine
oxide and is very similar to that of 1.493(4) Å in [(p-
cymene)Ru{P,O-(S)-BINAPO}][SbF6]34 and 1.518(3) Å
in [RuCl(BINAPO)(bipy)][PF6],24 and the P(1)-Ru-O(1)
bite angle of 88.74(7)° is similar to that of 87.71(12)° in
[RuCl(BINAPO)(phen)][PF6].24 The Ru-O(1)-P(1) bond
angle of 112.72(13)° presumably reflects the size of the
chelate ring, since the corresponding angles of 98.6(2)°
and 97.2(1)° in [RuCl(BINAPO)(phen)][PF6] and [RuCl-
(BINAPO)(bipy)][PF6], respectively, are much smaller,
which was suggested to be due to η2-coordination of the
two carbon atoms of the naphthyl ring proximate to the
PdO group.24 In contrast, the PdO-M angle in com-
plexes in which BINAPO acts solely as a heterobi-
dentate P,O-chelate is much larger: 165.9(3)° in [(p-
cymene)RuCl(P,O-BINAPO][SbF6]34 and 161.5(5)° in [(p-
cymene)OsCl(P,O-BINAPO][SbF6].36
Catalysis: Ruthenium-Catalyzed Addition of
Benzoic Acid to 1-Alkynes. The clear structural
similarity between biaryl-based diphosphines such as
BIPHEP and NUPHOS-type diphosphines and the
ability of both to coordinate to ruthenium in a P,P,η2(C)-
manner prompted us to undertake a comparison of their
performance in the ruthenium-catalyzed addition of
benzoic acid to terminal alkynes. The regio- and stereo-
selective addition of carboxylic acids to terminal alkynes
has evolved as a highly versatile reaction since the
resulting enol esters are important reagents and inter-
mediates in organic synthesis;37 for example, enol esters
resulting from Markovnikov addition are widely used
for the acylation of alcohols and amines.38 More recently
the catalytic intramolecular Markovnikov addition of a
hydroxy group to an unactivated terminal triple bond
has been applied to the synthesis of functional furans39
Figure 5. Molecular structure of [{(p-cymene)RuCl2}2(µ-
dppb)] (6). Hydrogen atoms and dichloromethane and
hexane molecules of crystallization have been omitted for
clarity. Ellipsoids are at the 30% probability level.
(PMePh2)]33 and attributed to the bond-lengthening
trans effect of the tertiary phosphine ligand. The p-
cymene ring is essentially planar, with maximum and
mean deviations from the least-squares mean plane of
the six carbon atoms of -0.0218 and 0.0012 Å, respec-
tively.
Finally, a single-crystal X-ray study of 7 was under-
taken to confirm its formulation and to establish the
relative stereochemistry of the two new stereocenters.
A perspective view of the molecular structure is shown
in Figure 6, and selected bond lengths and angles are
listed in Table 4. The X-ray study reveals that 7 results
from oxidation of one end of 1,2,3,4,Me4-NUPHOS and
regioselective syn addition of Ru and H to the double
bond proximate to the newly formed phosphine oxide,
to afford a ligand that can most aptly be described as
an unsymmetrical bis(phosphine) monoxide pincer,
which coordinates in a P,O,η1(C)-terdentate manner to
form two five-membered rings. The Ru-P(1) and Ru-
O(1) bond lengths of 2.2814(10) and 2.163(2) Å, respec-
tively, are typical for a bisphosphine monoxide (BPMO)
P,O-coordinated to ruthenium(II),34 and Ru-C(25)
[2.223(3) Å] is within the range expected for a Ru-
(35) Fang, X.; Watkin, J. G.; Scott, B. L.; John, K. D.; Kubas, G. J.
Organometallics 2002, 21, 2336.
(36) Faller, J. W.; Parr, J. Organometallics 2001, 20, 697.
(37) (a) Fischmeister, C.; Bruneau, C. Dixneuf, P. H. In Ruthenium
in Organic Synthesis; Murahashi, S.-I., Ed.; Wiley-VCH: New York,
2004; Chapter 8, p 189. (b) Bruneau, C.; Dixneuf, P. H. Chem.
Commun. 1997, 507.
(33) Bennett, M. A.; Robertson, G. B.; Smith, A. K. J. Organomet.
Chem. 1972, 43, C41.
(34) Faller, J. W.; Parr, J. Organometallics 2000, 19, 1829.
(38) Kita, Y.; Akai, S.; Yoshigi, M.; Nakajima, Y.; Yasuda, H.;
Tamura, Y. Tetrahedron Lett. 1984, 25, 6067.

2640 Organometallics, Vol. 24, No. 11, 2005
Doherty et al.
Table 5. Summary of Crystal Data and Structure Determination for 2a, 2b, 3a, 4a, 6, and 7
2a
2b
3a
4a
6
7
formula
C
42H46ClP2Ru+‚
C
46H52ClP2Ru+‚
C
42H46P2Ru2+
‚
C
46H42P2ClRu+‚
C
48H56P2Ru2‚
C
42H47OP2Ru+‚
ClO4-‚2CH2Cl2
1018.6
SbF6- ‚2CHCl3
1277.8
2SbF6-‚CH2Cl2
1270.2
SbF6-‚2CH2Cl2
1198.9
2CH2Cl2‚C6H14
1294.8
SbF6-‚CH2Cl2
1051.5
fw
cryst syst
space group
T (K)
monoclinic
P21
monoclinic
P21/c
monoclinic
C2/c
triclinic
P1h
triclinic
P1h
monoclinic
P21/c
150
150
150
150
150
150
a (Å)
13.564(3)
14.897(3)
13.853(3)
10.1035(5)
28.610(5)
18.303(5)
24.3186(11)
29.7261(13)
16.5645(7)
14.7948(13)
17.8716(15)
19.9255(17)
97.429(1)
94.401(2)
111.458(1)
4818.0(7)
4
10.4797(5)
11.8099(14)
13.5696(12)
92.326(9)
108.030(5)
112.768(8)
1447.7(2)
1
11.2957(15)
13.4324(11)
31.891(3)
b (Å)
c (Å)
R (deg)
â (deg)
117.49(3)
97.250(6)
123.608(1)
96.170(13)
γ (deg)
V (Å3)
2483.1(9)
2
99 089
11 363, 0.0501
519
5248.4(16)
4
94 570
9109, 0.0637
556
9972.8(8)
8
34 471
8765, 0.0708
555
4810.8(9)
4
57 077
10 946, 0.0630
486
Z
reflns measd
unique data, Rint
params
34 205
20 141
34 205
6574, 0.0396
283
1167
R (F, F2 > 2σ)
Rw (F2, all data)
GOF on F2
max., min. electron
density (e/Å3)
0.0403
0.1153
1.114
0.0569
0.1599
1.108
0.0627
0.1509
1.038
0.0714
0.0413
0.0474
0.1390
1.074
0.2019
0.1035
1.022
1.039
0.67, -0.45
0.99, -0.72
1.28, -1.36
2.29, -1.68
0.78, -1.00
0.93, -1.02
and enol lactones40 while anti-Markovnikov addition has
been used for the synthesis of functional dienes and
aldehydes.37
boxylation, the product of phenylacetylene insertion was
reported to be stable with respect to further reaction.25
Preliminary results for addition of benzoic acid to
1-pentyne, 1-octyne, and phenylacetylene (eq 4) using
catalysts based on Me4-NUPHOS, 1,4-Et2-2,3-cyclo-
C6H8-NUPHOS, and dppb, as well as BIPHEP and
MeO-BIPHEP for comparison, are summarized in Table
6. Catalysts were typically generated in situ by abstrac-
tion of chloride from the corresponding precursor with
AgSbF6 prior to addition of substrate, since crystalline
samples of the six-electron-donor dications are generally
very insoluble in the small volume of solvent used to
perform the catalysis. In the case of 1-octyne, compara-
tive testing was also conducted with catalyst generated
by activation of [(p-cymene)RuCl2]2 with AgSbF6 in
order to evaluate the influence of the diphosphine. Prior
to this study, Pregosin has previously reported that the
dication [(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 catalyzes
the highly regioselective addition of benzoic acid to
1-pentyne and 1-octyne under mild conditions to give
the anti-Markovnikov addition product with a cis-to-
trans ratio of 70:30 and that the same catalyst was
completely inactive for addition to phenylacetylene (vide
infra). All three alkynes were reported to react with [(p-
cymene)Ru(MeO-BIPHEP)][SbF6]2 via cyclometalation-
alkyne insertion to afford 8 as the thermodynamic
product (eq 5). However, while the 1-pentyne and
1-octyne insertion products both catalyzed hydrocar-
The dication generated by activation of 2a with
AgSbF6 catalyzes the highly regioselective anti-
Markovnikov addition of benzoic acid to both 1-pentyne
and 1-octyne to give the corresponding alk-1-en-1-yl
ester with a cis-to-trans ratio of 92:8 and no evidence
for the Markovnikov addition product (entries 2 and 6).
For comparison, under the same conditions the MeO-
BIPHEP-based catalyst also gave the anti-Markovnikov
addition product exclusively, but with a significantly
lower stereoselectivity of 70:30 (entry 12), consistent
with the performance first reported by Pregosin.25
Surprisingly, catalyst performance was found to be
highly sensitive to 6,6′-substitution of the biaryl tether,
since replacement of MeO-BIPHEP with its tropos
counterpart BIPHEP resulted in a marked improvement
in the cis-to-trans ratio from 70:30 to 85:15 (entry 10).
Such a dramatic dependence of selectivity on the biaryl
substitution prompted us to investigate the influence
of the NUPHOS tether by comparing the performance
of catalysts generated from acyclic and monocyclic
NUPHOS diphosphines, 2a and 2b, respectively. The
cis-to-trans ratio of 66:8 for addition to 1-pentyne
catalyzed by 2b/AgSbF6 (entry 4) was markedly lower
than that of 92:8 obtained with its Me4-NUPHOS
counterpart, as was that of 66:11 for addition to 1-octyne
(39) (a) Seiller, B.; Bruneau, C.; Dixneuf, P. H. Tetrahedron 1995,
51, 13089. (b) Seiller, B.; Bruneau, C.; Dixneuf, P. H. Chem. Commun.
1994, 493.
(40) Jimenez Tenorio, M.; Puerta, M. C.; Valerga, P.; Moreno-
Dorado, F. J.; Guerra, F. M.; Massanet, G. M. Chem. Commun. 2001,
2324.

Ruthenium Complexes of NUPHOS-Type Diphosphines
Organometallics, Vol. 24, No. 11, 2005 2641
Table 6. Ruthenium-Catalyzed Addition of Benzoic Acid to Terminal Alkynes
a Reaction conditions: 5 mol % of catalyst, benzoic acid (0.87 mmol), and alkyne (0.99 mmol) in 1.0 mL of C2H4Cl2, 25 °C, 96 h (1-
pentyne); 60 °C, 24 h (1-ocytne); 60 °C, 20 h (phenylacetylene). b Combined isolated yields after purification by column chromatography.
Average of three runs.
(entry 8). However, it should be noted that these cis-
to-trans ratios are still significantly higher than that
of 70:30 obtained with MeO-BIPHEP. More surprising
was the marked difference in regioselectivity between
catalysts generated from 2a and 2b, the former giving
anti-Markovnikov addition product exclusively, while
the latter gave 23 and 26% of the Markovnikov addition
to 1-octyne and 1-pentyne, respectively. Dixneuf has
studied the effect of varying the length of the tether in
diphosphines of type Ph2P(CH2)nPPh2 (n ) 1-4) on the
addition of carboxylic acids to terminal alkynes and
established that catalysts based on 1,4-bis(diphenyl-
phosphino)butane give optimum selectivity for anti-
Markovnikov addition (95%), while those based on
dppm, dppe, and dppp are less selective, with dppm
giving 80% selectivity for Markovnikov addition.41 In-
terestingly, both compounds 2a,b are active for the
hydrocarboxylation of terminal alkynes in the absence
of silver salt, which is somewhat unexpected, since
abstraction of halide was considered to be necessary to
generate the active 16-electron species 3a,b, albeit
stabilized by weak coordination of the butadiene double
bond. In fact, the performance of 2a in the absence of
silver salt was comparable to that obtained when
activated with AgSbF6 (entries 1 and 5 versus 2 and 6).
In contrast, in the absence of silver salt 2b gave
markedly higher regio- and stereoselectivities for addi-
tion to both 1-pentyne and 1-octyne than its AgSbF6-
activated counterpart. In this regard, Goossen recently
reported that addition of silver nitrate to catalyst
mixtures generated from [(p-cumene)RuCl2]2 and either
PPh3 or P(furyl)3 resulted in a significant enhancement
in activity, while maintaining the same selectivity for
Markovnikov addition.42
Unfortunately, we have been unable to prepare the
corresponding dppb-based catalyst precursor [(p-
cymene)Ru(dppb)Cl][SbF6] to carry out a direct com-
parison with 2a,b, since reaction between [(p-cymene)-
RuCl2]2 and dppb in the presence of NaSbF6 resulted
in the rapid formation of a dark brown intractable solid.
(41) Doucet, H.; Martin-Vaca, B.; Bruneau, C.; Dixneuf, P. H. J.
Organomet. Chem. 1995, 60, 7247.
(42) Goossen, L. J.; Paetzold, J.; Koley, D. Chem. Commun. 2003,
706.

2642 Organometallics, Vol. 24, No. 11, 2005
Doherty et al.
However, the dppb-bridged dimer [{(p-cymene)RuCl2}2-
(µ-dppb)] (6) has been isolated as the sole product of
reaction in the absence of sodium salt. Catalyst mixtures
generated by activation of 6 with AgSbF6 were highly
selective for Markovnikov addition to 1-octyne, affording
91% of the oct-1-en-2-yl benzoate together with trace
quantities of the anti-Markovnikov addition product
(entry 14). Even in the absence of silver salt, 6 catalyzed
the Markovnikov hydrocarboxylation of 1-octyne, albeit
giving much lower yields of product (entry 13). This
reversal of regioselectivity is consistent with 6 acting
as 2 equiv of a mono-phosphine-based catalyst, i.e. in
much the same manner as [(arene)Ru(PR3)Cl2]; such
catalysts are highly selective for Markovnikov addition
to phenylacetylene and propyne.43 Goossen et al. have
recently demonstrated that catalysts generated in situ
from [(p-cumene)RuCl2]2 and a monodentate phosphine
are highly selective and give up to 97% Markovnikov
addition, the best yields being obtained with tri-2-furyl
phosphine and an additive such as a silver salt or an
inorganic base. The regioselectivity was reversed in the
presence of organic bases such as pyridines, which gave
99% selectivity for anti-Markovnikov addition. To dem-
onstrate the influence of the phosphine on catalyst
performance, we investigated the hydrocarboxylation of
1-octyne in the presence of catalyst generated by activa-
tion of [(p-cymene)RuCl2]2 with AgSbF6 and obtained
66% selectivity for anti-Markovnikov addition with a 2:1
ratio of the resulting (E)- and (Z)-oct-1-en-1-yl benzoate
and in low overall yield (entry 15).
To complete a comparative study between the per-
formance of catalysts generated from 2a,b with those
based on BIPHEP/MeO-BIPHEP, we have also inves-
tigated the hydrocarboxylation of phenylacetylene and
found that catalyst mixtures generated by activation of
2a or 2b with 1 equiv of AgSbF6 are highly active and
regioselective for anti-Markovnikov addition, giving up
to 99% selectivity for (Z)-styryl benzoate (entries 17 and
19). Interestingly, in an earlier report Pregosin claimed
that [(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 was inactive
for addition of benzoic acid to phenylacetylene, reason-
ing that the stability of the cyclometalation-phenyl-
acetylene insertion product 8 was responsible for this
inactivity, as it did not react further to afford organic
products, while the corresponding 1-octyne insertion
product was capable of catalyzing the corresponding
addition reaction. Intrigued by such a dramatic differ-
ence in catalyst performance for a seemingly minor
change in catalyst architecture, we performed the
hydrocarboxylation of phenylacetylene and found that,
in our laboratory, catalyst mixtures generated by acti-
vation of 4a,b with AgSbF6 were highly selective for
anti-Markovnikov addition, giving (Z)-styryl benzoate
as the major enol ester (entries 20 and 21) and only
trace amounts (ca. 2%) of the Markovnikov addition
product. Although the highly regio- and stereoselective
anti-Markovnikov hydrocarboxylation of phenylacetyl-
ene using catalysts formed from 4a,b is contrary to an
earlier report from the Pregosin group, it should be
noted that the catalysts involved in our study were
generated in situ and the yields of enol ester are
significantly lower than those obtained with catalysts
formed from 2a,b.
Conclusions
Abstraction of a chloro ligand from the ruthenium-
p-cymene
complexes
[(p-cymene)Ru(1,2,3,4-Me4-
NUPHOS)Cl][SbF6] (2a) and [(p-cymene)Ru(1,4-
Et2-2,3-cyclo-C6H8-NUPHOS)Cl][SbF6] (2b) occurs
rapidly and quantitatively at room temperature to
afford [(p-cymene)Ru(P,P,η2(C)-1,2,3,4-Me4-NUPHOS)]-
[SbF6]2 (3a) and [(p-cymene)Ru(P,P,η2(C)-1,4-Et2-2,3-
cyclo-C6H8-NUPHOS)][SbF6]2 (3b), respectively, in which
the diphosphine is coordinated as a six-electron donor,
bonded through both diphenylphosphino groups and one
of the double bonds of the butadiene tether. In contrast,
complexes of BIPHEP and MeO-BIPHEP are markedly
more reluctant to form the corresponding 6e-donor
complexes. Compound 3a rapidly hydrolyses in the
presence of pyridine to give [(p-cymene)Ru{Ph2(O)PC-
(H)MeCMeCMeCMePPh2}][SbF6] (7), which contains a
new unsymmetrical bisphosphine monoxide pincer ligand
formed by oxidation of one of the diphenylphosphino
groups of 1,2,3,4-Me4-NUPHOS and a highly regio-
selective syn addition of Ru and H across the butadiene
double bond proximate to the phosphine oxide. Dications
3a,b are highly efficient catalysts for the regioselective
anti-Markovnikov addition of benzoic acid to 1-pentyne
and 1-octyne and give the corresponding alk-1-en-1-yl
ester with cis-to-trans ratios up to 95:5, markedly higher
than that of 70:30 obtained with MeO-BIPHEP-based
catalysts. Catalysts 3a,b are also highly active and
selective for anti-Markovnikov addition of benzoic acid
to phenylacetylene, giving (Z)-styryl benzoate in up to
85% yield and 95:5 selectivity. In our hands, catalyst
mixtures formed from 4a or 4b and AgSbF6 are active
for the hydrocarboxylation of phenylacetylene and give
the (Z)-styryl benzoate as the major enol ester, which
was somewhat of a surprise, considering an earlier
report by Pregosin claimed that [(p-cymene)Ru(MeO-
BIPHEP)][SbF6]2 (5b) reacted with phenylacetylene to
afford a thermodynamically stable and catalytically
inactive insertion/cyclometalation product. This study
has revealed marked differences between the coordina-
tion chemistry of NUPHOS-based diphosphines and
their biaryl-based counterparts, BIPHEP and MeO-
BIPHEP, and highlighted potential advantages of using
NUPHOS diphosphines for the ruthenium-catalyzed
addition of carboxylic acids to alkynes. As a result of
these encouraging studies, we have initiated further
studies to explore the scope of NUPHOS diphosphines
in ruthenium-catalyzed transformations.
Experimental Section
General Procedures. All manipulations involving air-
sensitive materials were carried out in an inert atmosphere
glovebox or using standard Schlenk line techniques under an
atmosphere of nitrogen or argon in oven-dried glassware. Di-
ethyl ether and hexane were distilled from potassium/sodium
alloy and dichloromethane, chloroform, and 1,2-dichloro-
ethane from calcium hydride. BIPHEP and MeO-BIPHEP
were purchased from Strem, dppb and benzoic acid from
Avocado, and the terminal alkynes phenylacetylene, 1-octyne,
and 1-pentyne from Aldrich. Unless otherwise stated, com-
(43) (a) Ruppin, C.; Dixneuf, P. H.; Lecolier, S. Tetrahedron Lett.
1988, 27, 5365. (b) Kabouche, Z.; Bruneau, C.; Dixneuf, P. H.
Tetrahedron Lett. 1991, 32, 5359. (c) Philippot, K.; Devanne, D.;
Dixneuf, P. H. Chem. Commun. 1990, 1119. (d) Ruppin, C.; Dixneuf,
P. H. Tetrahedron Lett. 1986, 27, 6323. (e) Bruneau, C.; Neveux, M.;
Kabouche, Z.; Dixneuf, P. H. Synlett 1991, 755.

Ruthenium Complexes of NUPHOS-Type Diphosphines
Organometallics, Vol. 24, No. 11, 2005 2643
mercially purchased materials were used without further
purification. Deuteriochloroform was predried with calcium
hydride and vacuum transferred and stored over 4 Å molecular
sieves. The ruthenium complexes [(p-cymene)RuCl2]244 and [(p-
cymene)Ru(MeO-BIPHEP)Cl][SbF6]23b were prepared as previ-
ously described. 1H and 31P{1H} and 13C{1H} NMR spectra
were recorded on a JEOL LAMBDA 500 or Bruker AC 200,
AMX 300, and DRX 500 machines. Purification of reaction
products was carried out by column chromatography on
reagent silica gel (60-200 mesh).
(d, JHH ) 6.5 Hz, 1H, p-cymene), 6.61 (d, JHH ) 6.0 Hz, 1H,
p-cymene), 6.35 (d, JHH ) 6.0 Hz, 1H, p-cymene), 5.82 (d, JHH
) 6.5 Hz, 1H, p-cymene), 2.79 (d, JPH ) 9.8 Hz, 3H, CH3), 2.72
(m, 1H, CHMe2), 2.35 (br s, 6H, 2 × CH3), 2.0 (br s, 3H,
p-cymene CH3), 1.1 (d, JHH ) 6.8 Hz, 3H, CHMe2), 0.89 (d, JPH
) 11.3 Hz, 3H, CH3), 0.59 (d, JHH ) 6.8 Hz, 3H, CHMe2). 13C
NMR (125.13 MHz, (CD3)2CdO, δ): 161.4 (d, JPC ) 28.0 Hz,
CMe), 140.8-122.5 (m, C6H5 + p-cymene), 108.0 (s, C6H4),
106.1 (s, C6H4), 105.7 (d, JPC ) 7.1, 5.0 Hz, η2-CdC), 103.9 (s,
C6H4), 103.6 (s, C6H4), 65.1 (d, JPC ) 30 Hz, η2-CdC), 33.8 (s,
CHMe2), 27.3 (d, JPC ) 8.0 Hz, CMe), 26.7 (s, CMe), 24.8 (s,
CHMe2), 23.9 (d, JPC ) 7.1 Hz, CMe), 22.8 (s, CHMe2), 21.6 (s,
p-cymene Me), 17.3 (s, CMe). MS (FAB+): calcd M2+ 714; found
950 [M + SbF6]+. Anal. Calcd for C42H46F12P2RuSb2 C, 42.56;
H, 3.91. Found: C, 42.87; H, 4.11.
Synthesis of [(p-cymene)Ru(1,2,3,4-Me4-NUPHOS)Cl]-
[SbF6] (2a). A solution of 1,2,3,4-Me4-NUPHOS (0.200 g, 0.42
mmol) and NaSbF6 (0.108 g 0.42 mol) in dichloromethane was
added to [(p-cymene)RuCl2]2 (0.12 g, 0.2 mmol), and the
resulting mixture was stirred at room temperature for 12 h,
after which time it was filtered through Celite and the solvent
removed to give 2a as a spectroscopically pure yellow-orange
powder in quantitative yield. Crystallization by slow diffusion
of a concentrated dichloromethane solution layered with
hexane gave 2a as orange crystals in 86% yield (0.35 g).
Although we were unable to grow crystals of the hexafluoro-
antimonate salt of 2a suitable for analysis by single-crystal
X-ray crystallography, crystals of the corresponding perchlo-
rate salt, prepared by replacement of NaSbF6 with NaClO4 in
the above procedure, were obtained by slow diffusion of hexane
into a concentrated dichloromethane solution at room tem-
Synthesis of [(p-cymene)Ru(P,P,η2(C)-1,4-Et2-2,3-cyclo-
C6H8-NUPHOS)][SbF6]2 (3b). Compound 3b was prepared
according to the procedure described above for 3a and was
isolated as yellow crystals in 60% yield by slow diffusion of
hexane into a dichloromethane solution at room temperature.
31P{1H} NMR (121.4 MHz, CDCl3, δ): 82.1 (d, 2JPP ) 38.7 Hz,
2
1
PA), 9.0 (d, JPP ) 38.7 Hz, PB). H NMR (500.1 MHz, CDCl3,
δ): 7.89-7.24 (m, 16H, C6H5), 6.90 (br s, 2H, C6H5), 6.81 (br
s, 2H, C6H5), 6.34 (d, JHH ) 6.6 Hz, 1H, p-cymene CH), 6.31
(d, JHH ) 6.6 Hz, 1H, p-cymene CH), 5.65 (d, JHH ) 6.6 Hz,
2H, p-cymene CH), 3.06 (m, 1H, Cy-H), 2.87 (m, 1H, Cy-H),
2.73 (d br, JHH ) 10.1 Hz, 1H, Cy-H), 2.51 (d br, JHH ) 10.1
Hz, 1H, Cy-H), 2.27 (m, 1H, Cy-H), 2.26 (sept, JHH ) 6.6 Hz,
1H, CHMe2), 2.21 (br d, JHH ) 10.1 Hz, 1H, Cy-H), 2.04 (m,
1H, Cy-H), 1.78 (s, 3H, p-cymene CH3), 1.77 (m, 1H, Cy-H),
1.18-1.0 (m, 2H, CH2CH3), 0.76 (t, JHH ) 7.6 Hz, 3H, CH3),
0.43 (t, JHH ) 7.6 Hz, 3H, CH2CH3). 13C NMR (125.13 MHz,
CD2Cl2, δ): 136.1-125.4 (m, C6H5 + p-cymene + CdC), 117.4
(s, p-cymene), 105.8 (s, p-cymene), 102.1 (dd, JPC ) 6.1, 4.0
Hz, η2-CdC), 101.8 (s, p-cymene), 99.3 (s, p-cymene), 96.7 (s,
p-cymene), 62.6 (d, JPC ) 26 Hz, η2-CdC), 30.8 (s, Cy-CH2),
30.1 (s, p-cymene-CHMe2), 27.6 (s, p-cymene-CMe), 29.6 (s, Cy-
CH2), 27.3 (s, Cy-CH2), 25.4 (Cy-CH2), 22.2 (s, p-cymene-
CHMe2), 21.9 (s, CH2CH3), 20.9 (d, JPC ) 4.9 Hz, CH2CH3),
19.7 (s, p-cymene-CHMe2), 13.1 (s, CH2CH3), 12.5 (s, CH2CH3).
MS (FAB+): calcd M2+ 768; found 1003 [M + SbF6]+. Anal.
Calcd for C46H52F12P2RuSb2 C, 44.58; H, 4.23. Found: C, 44.91;
H, 4.57.
2
perature. 31P{1H} NMR (121.4 MHz, CDCl3, δ): 39.8 (d, JPP
2
1
) 60.5 Hz, PA), 27.9 (d, JPP ) 60.5 Hz, PB). H NMR (500.1
MHz, CDCl3, δ): 7.8-6.9 (m, 20H, C6H5), 6.05 (d, JHH ) 6.0
Hz, 1H, p-cymene), 5.94 (d, JHH ) 7.0 Hz, 1H, p-cymene), 4.38
(br d, JHH ) 7.0 Hz, 1H, p-cymene), 4.26 (d, JHH ) 7.0 Hz, 1H,
p-cymene), 3.05 (sept, JHH ) 6.9 Hz, 1H, CHMe2), 1.91 (s, 3H,
p-cymene-CH3), 1.79 (d, JPH ) 11.6 Hz, 3H, CH3), 1.43 (d, JPH
) 10.5 Hz, 3H, CH3), 1.37 (d, JHH ) 6.9 Hz, 3H, CH(CH3)2),
1.32 (s, 3H, CH3), 0.97 (d, JHH ) 6.9 Hz, 3H, CH(CH3)2), 0.93
(s, 3H, CH3). MS (FAB+): calcd M+ 749; found 749 [M]+, 714
[M - Cl]+, 615 [M - p-cymene]+. Anal. Calcd for C42H46ClF6P2-
RuSb C, 51.21; H, 4.71. Found: C, 51.63; H, 5.01.
Synthesis of [(p-cymene)Ru(1,4-Et2-2,3-cyclo-C6H8-
NUPHOS)Cl][SbF6] (2b). Compound 2b was prepared ac-
cording to the procedure described above for 2a and was
isolated as orange-yellow crystals in 60% yield by slow
diffusion of hexane into a chloroform solution at room tem-
2
perature. 31P{1H} NMR (121.4 MHz, CDCl3, δ): 37.9 (d, JPP
Synthesis of [(p-cymene)Ru(BIPHEP)Cl][SbF6] (4a).
Compound 4a was prepared according to the procedure
described above for 2a and was isolated as deep orange crystals
in 78% yield by slow diffusion of hexane into a chloroform
solution at room temperature. X-ray quality crystals were
grown by diffusion of hexane into a concentrated dichloro-
methane solution. 31P{1H} NMR (121.4 MHz, CDCl3, δ): 40.8
(d, JPP ) 63.0 Hz, PPh2), 29.1 (d, JPP ) 63.0 Hz, PPh2). 1H
2
1
) 66.0 Hz, PA), 22.0 (d, JPP ) 66.0 Hz, PB). H NMR (500.1
MHz, CDCl3, δ): 7.87-7.15 (m, 20H, C6H5), 6.15 (d, JHH ) 6.8
Hz, 1H, p-cymene), 5.68 (d, JHH ) 6.1 Hz, 1H, p-cymene), 5.36
(br d, JHH ) 6.1 Hz, 1H, p-cymene), 4.63 (d, JHH ) 6.8 Hz, 1H,
p-cymene), 3.10 (sept, JHH ) 6.8 Hz, 1H, CHMe2), 2.56 (m, 2H,
CH2CH3), 2.30 (m, 2H, CH2CH3), 2.24 (m, 1H, Cy-H), 1.82 (s,
3H, p-cymene-CH3), 1.6-1.4 (m, 6H, Cy-H), 1.41 (d, JHH ) 6.8
Hz, 3H, CH(CH3)2), 1.1 (br m, 1H, Cy-H), 0.96 (d, JHH ) 6.8
Hz, 3H, CH(CH3)2), 0.38 (t, JHH ) 7.4 Hz, CH2CH3), 0.24 (t,
JHH ) 7.4 Hz, CH2CH3). MS (FAB+): calcd M+ 803; found 803
[M]+, 768 [M - Cl]+, 669 [M - p-cymene]+. Anal. Calcd for
C46H52ClF6P2RuSb.2CHCl3 C, 45.11; H, 4.26. Found: C, 45.47;
H, 4.41.
NMR (500.1 MHz, CDCl3, δ): 7.87-7.14 (m, 26H, C6H5
+
biphenyl), 6.66 (dd, J ) 7.2, 1.7 Hz, 1H, biphenyl), 6.27 (dd, J
) 7.0, 1.6 Hz, 1H, biphenyl), 5.83 (d, JHH ) 6.7 Hz, 1H,
p-cymene-CH), 5.36 (d, JHH ) 6.1 Hz, 4H, p-cymene-CH), 4.48
(d, JHH ) 6.1 Hz, 1H, p-cymene-CH), 4.42 (d, JHH ) 6.1 Hz,
4H, p-cymene-CH), 2.99 (sept, JHH ) 6.8 Hz, 2H, CHMe2), 1.83
(s, 3H, p-cymene-CH3), 1.29 (d, JHH ) 6.8 Hz, 3H, p-cymene-
CHMe2), 0.96 (d, JHH ) 6.8 Hz, 3H, p-cymene-CHMe2). 13C
NMR (125.13 MHz, CDCl3, δ): 146-122 (m, C6H5 + biphenyl),
114.2 (s, p-cymene), 108.6 (s, p-cymene), 103.2 (s, p-cymene),
101.6 (s, p-cymene), 96.9 (s, p-cymene-CH), 85.9 (s, p-cymene-
CH), 29.5 (s, p-cymene-CHMe2), 21.7 (s, p-cymene-CHMe2),
20.6 (s, p-cymene-CHMe2), 18.2 (s, p-cymene-CH3). Anal. Calcd
for C46H42ClF6P2RuSb‚2CH2Cl2, 48.09; H, 3.87. Found: C,
48.39; H, 4.13.
Synthesis of [(p-cymene)Ru(P,P,η2(C)-1,2,3,4-Me4-
NUPHOS)][SbF6]2 (3a). A solution of 2a (0.100 g, 0.1 mmol)
in dichloromethane (4 mL) was treated with AgSbF6 (0.034 g,
0.1 mmol) and stirred for 30 min at room temperature. The
resulting mixture was filtered through Celite and the solvent
removed under reduced pressure to afford 3a as a spectro-
scopically pure yellow powder, which was crystallized by slow
diffusion of toluene into a dichloromethane solution at room
temperature (0.09 g 76%). 31P{1H} NMR (121.4 MHz, CDCl3,
δ): 78.9 (d, 2JPP ) 38.7 Hz, PA), 6.5 (d, 2JPP ) 38.7 Hz, PB). 1H
NMR (500.1 MHz, CDCl3, δ): 8.09-6.96 (m, 20H, C6H5), 6.91
Attempted Preparation of [(p-cymene)Ru(BIPHEP)]-
[SbF6]2 (5a) and [(p-cymene)Ru(MeO-BIPHEP)][SbF6]2
(5b). Initially, a solution of 4a (0.100 g, 0.097 mmol) in
dichloromethane (4 mL) was treated with AgSbF6 (0.033 g,
0.097 mmol) and stirred for 1 h at room temperature, after
(44) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1981, 21, 74.

2644 Organometallics, Vol. 24, No. 11, 2005
Doherty et al.
which time there was no sign of reaction, as evidenced by 31
P
procedure a solution of 2a (0.0423 g, 0.043 mmol) and 1-octyne
(0.130 mL, 0.88 mmol) in 1,2-dichloroethane (1 mL) was stirred
for 24 h at 60 °C, then cooled to room temperature, diluted
with dichloromethane (20 mL), washed with NaHCO3, and
dried over MgSO4. The crude residue was purified by column
chromatography over silica gel (60-200 mesh, 5% ethyl acetate
in hexane).
General Procedure for Ruthenium-Catalyzed Addi-
tion of Benzoic Acid to 1-Pentyne. The catalytic hydrocar-
boxylation of 1-pentyne was performed according to methods
A and B described above for 1-ocytne in dichloromethane for
96 h at 35 °C. The crude residue was purified by column
chromatography over silica gel (60-200 mesh, 5% ethyl acetate
in hexane).
General Procedure for Ruthenium-Catalyzed Addi-
tion of Benzoic Acid to Phenylacetylene. The catalytic
hydrocarboxylation of phenylaceylene was performed according
to methods A and B described above for 1-ocytne in 1,2-
dichloroethane for 20 h at 60 °C. The crude residue was
purified by column chromatography over silica gel (60-200
mesh, 5% ethyl acetate in hexane).
NMR spectroscopy. The solution was subsequently refluxed
for 24 h, then filtered through Celite. The solvent was removed
and the 31P NMR spectrum of the this crude product recorded,
which contained two distinct sets of resonances, a major pair
of doublets associated with 4a and a minor set of broad
resonances at δ 65.1 and 5.0 corresponding to approximately
20% of the desired product. A similar level of conversion was
obtained during the reaction of 4b with AgSbF6 under similar
conditions, as evidenced by characteristic 31P resonances at δ
67.1 and 7.7.
Synthesis of [{(p-cymene)RuCl}2(µ-dppb)] (6). A solu-
tion of dppb (0.200 g, 0.47 mmol) and [(p-cymene)RuCl2]2 (0.280
g, 0.46 mmol) in dichloromethane (20 mL) was stirred for 4 h,
after which time the reaction mixture was filtered and the
solvent removed to give 6 as a spectroscopically pure orange-
red solid in 98% yield (0.465 g). Crystals suitable for single-
crystal X-ray structure determination were grown by slow
diffusion of hexane into a dichloromethane solution at room
temperature. 31P{1H} NMR (121.4 MHz, CDCl3, δ): 24.9 (s,
1
PPh2). H NMR (500.1 MHz, CDCl3, δ): 7.6 (dt, J ) 9.6, 1.2
Hz, 8H, C6H5), 7.38 (m, 12H, C6H5), 5.11 (d, JHH ) 6.0 Hz, 4H,
p-cymene-CH), 4.94 (d, JHH ) 6.0 Hz, 4H, p-cymene-CH), 2.26
(sept, JHH ) 6.9 Hz, 2H, CHMe2), 2.11 (br, 4H, dppb-CH2), 1.71
Crystal Structure Determinations. Crystals of 2a, 2b,
3a, 4a, 6, and 7 were examined with Mo KR radiation (λ )
0.71073 Å) on Bruker SMART and Bruker-Nonius KappaCCD
diffractometers at 150 K. Selected crystal data are given in
Table 5, and further details of the structure determination are
in the Supporting Information. Semiempirical absorption
corrections were applied, based on repeated and symmetry-
equivalent reflections.46 The structures were solved by direct
methods and refined by least-squares methods on all unique
F2 values, with anisotropic displacement parameters, and with
constrained riding hydrogen atoms; U(H) was set at 1.2 (1.5
for methyl groups) times Ueq of the parent atom. Disorder over
two distinct positions was resolved and refined for the anion
(s, 6H, p-cymene-CH3), 0.8 (br, 4H, dppb-CH2), 0.67 (d, JHH
)
6.9 Hz, 12H, p-cymene-CHMe2). 13C NMR (125.13 MHz, CDCl3,
δ): 132.4 (s, C6H5), 131.6 (d, JPC ) 42 Hz, C6H5), 129.7 (s,
C6H5), 127.4 (s, C6H5), 106.5 (s, p-cymene), 92.8 (s, p-cymene),
89.6 (d, JPC ) 4.0 Hz, p-cymene-CH), 84.8 (d, JPC ) 5.7 Hz,
p-cymene-CH), 29.2 (s, p-cymene-CHMe2), 23.9 (d, JPC ) 12.1
Hz, PCH2CH2), 21.8 (d, JPC ) 28.0 Hz, PCH2), 20.2 (s,
p-cymene-CHMe2), 16.2 (s, p-cymene-CH3). Anal. Calcd for
C52H56Cl4P2Ru2 C, 55.50; H, 5.43. Found: C, 55.89; H, 5.55.
Attempted Preparation of [(p-cymene)Ru(1,2,3,4-Me4-
NUPHOS)(py)][SbF6]2. A dichloromethane solution of 3a
(0.08 g, 0.067 mmol) and pyridine (6.4 µl, 0.08 mmol) was
stirred for 30 min, during which time the color changed from
pale yellow to brown-yellow. The reaction mixture was filtered,
the solvent removed, and the residue crystallized by slow
diffusion of hexane into a concentrated dichloromethane
solution at room temperature to afford 7 as a yellow crystalline
solid in 87% yield (0.057 g). 31P{1H} NMR (121.4 MHz, CDCl3,
δ): 73.3 (s, PPh2), 68.4 (s, PPh2). 1H NMR (500.1 MHz, CDCl3,
δ): 8.10 (t, J ) 7.5 Hz, 2H, C6H5), 7.8 (dd, J ) 11.0 Hz, 7.5
Hz, 2H, C6H5), 7.7-7.4 (m, 10H, C6H5), 7.30 (t, J ) 7.6 Hz,
2H, C6H5), 7.17 (dt, J ) 7.7, 3.0 Hz, 2H, C6H5), 6.98 (dd, J )
11.0, 7.5 Hz, 2H, C6H5), 6.16 (d, JHH ) 9.5 Hz, 1H, p-cymene),
5.74 (d, JHH ) 9.5 Hz, 1H, p-cymene), 5.64 (d, JHH ) 9.5 Hz,
1H, p-cymene), 5.01 (dq, JPH ) 17.8 Hz, JHH 12.5 Hz, Ph2P-
(O)CHMe), 4.70 (d, JHH ) 9.5 Hz, 1H, p-cymene), 2.23 (s, 3H,
p-cymene-CH3), 1.49 (dd, JPH ) 17.8 Hz, JHH ) 12.5 Hz, 1H,
Ph2P(O)CHMe), 1.45 (d, JPH ) 9.1 Hz, 3H, CMe), 1.42 (sept,
JHH ) 7.0 Hz, 1H, p-cymene-CHMe2), 1.16 (s, 3H, CMe), 0.98
(d, JHH ) 7.0 Hz, 3H, CHMe2), 0.78 (d, JHH ) 7.0 Hz, 3H,
CHMe2), 0.74 (s, 3H, CMe). Anal. Calcd for C42H47F6OP2RuSb
C, 52.19; H, 4.90. Found: C, 52.58; H, 5.13.
i
and one Pr group of 2a, the anions of 2b and 3a, and the
dichloromethane solvent molecule of 4a. More extensive
disorder could not be modeled for solvent molecules in most
of the structures, and these were treated with the SQUEEZE
procedure of PLATON.47 2a was found to be an inversion twin,
with 23(3)% of the second component, and 4a was a nonmero-
hedral twin, with approximately 2:1 ratio of the two compo-
nents; merging of symmetry-equivalent reflections is not
possible before refinement in this case. The largest features
in final difference syntheses are close to heavy atoms and
disordered groups. Programs were Bruker AXS SMART and
SAINT, Nonius COLLECT and EvalCCD, and SHELXTL.48
Acknowledgment. We gratefully acknowledge the
EPSRC (R.K.R.), the University of Newcastle upon Tyne
and the McClay Trust (C.R.N.) for funding and Johnson
Matthey for generous loans of palladium salts.
Supporting Information Available: For 2a, 2b, 3a, 4a,
6, and 7 details of structure determination, atomic coordinates,
bond lengths and angles, and displacement parameters in CIF
format. This material is available free of charge via the
Internet at http://pubs.acs.org. Observed and calculated struc-
ture factor tables are available from the authors upon request.
General Procedure for Ruthenium-Catalyzed Addi-
tion of Benzoic Acid to 1-Octyne. Method A. In a typical
procedure a solution of 2a (0.0423 g, 0.043 mmol) in 1,2-
dichloroethane (1 mL) was treated with AgSbF6 (0.0147 g,
0.043 mmol) and stirred for 0.5 h, after which time benzoic
acid (0.106 g, 0.87 mmol) and 1-octyne (0.130 mL, 0.88 mmol)
were added. The resulting reaction mixture was stirred for 24
h at 60 °C, then cooled to room temperature, diluted with
dichloromethane (20 mL), washed with NaHCO3, and dried
over MgSO4. The crude residue was purified by column
chromatography over silica gel (60-200 mesh, 5% ethyl acetate
in hexane). The E/Z ratio and the regioselectivity were
OM050014J
(45) Rotem, M.; Shvo, Y. J. Organomet. Chem. 1993, 448, 189.
(46) Sheldrick, G. M. SADABS; University of Go¨ttingen: Germany,
1997.
(47) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(48) (a) SMART and SAINT software for CCD diffractometers;
Bruker AXS Inc.: Madison, WI, 2001. (b) COLLECT software for
KappaCCD; Nonius BV: Delft, The Netherlands, 1998. (c) Duisenberg,
A. J. M.; Kroon-Batenburg, L. M. J.; Schreurs, A. M. M. J. Appl.
Crystallogr. 2003, 36, 220. (d) Sheldrick, G. M. SHELXTL user manual,
version 6; Bruker AXS, Inc.; Madison, WI, 2001.
1
determined by H NMR spectroscopy.44
General Procedure for Ruthenium-Catalyzed Addi-
tion of Benzoic Acid to 1-Octyne. Method B. In a typical