Efficient transfer hydrogenation of ketones catalyzed by the bis(isocyanide)-ruthenium(II) complexes trans,cis,cis,-[RuX2(CNR) 2(dppf)] (X = Cl, Br; dppf = 14 -bis(diphenylphosphino)ferrocene): Isolation of active mono- And dihydride intermediates

Article abstract of DOI:10.1021/om0400651

The bis(isocyanide) - ruthenium(II) complexes trans,cis,cis-[RuX ₂(CNR)₂(dppf)] (X = Cl, R = CH₂Ph (2a), Cy (2b), ^tBu (2c), 2,6-C₆H₃Me₂ (2d), (S)-(-)-C(H)MePh (2e); X = Br, R = CH₂Ph (3a), Cy (3b), _tBu (3c), 2,6-C₆H₃Me₂ (3d), (S)-(-)-C(H)MePh (3e)) have been prepared by reaction of the bis(allyl)-ruthenium(II) derivative [Ru(η³-2-C₃H ₄Me)₂(dppf)] (1) with the appropriate isocyanide ligand, in CH₂Cl₂ at room temperature and in the presence of the corresponding hydrogen halide HX. The structure of the compound trans,cis,cis-[RuCl₂(CN-2,6-C₆H₃Me ₂)₂(dppf)] (2d) has been confirmed by X-ray crystallography. The catalytic activity of complexes 2a-e and 3a-e in the transfer hydrogenation of acetophenone by propan-2-ol has been studied, and the most active complex, trans,cis,cis-[RuCl₂(CNCH₂Ph) ₂(dppf)] (2a), has been also tested as a catalyst in the transfer hydrogenation of a large variety of ketones. The hydride derivatives cis,cis-[RuHCl(CN-2,6-C₆H₃Me₂) ₂(dppf)] (4) and cis,cis,cis-[RuHCl₂(CN-2,6-C ₆H₃Me₂)₂(dppf)] (5) have been isolated and characterized. Although both hydride complexes catalyze the transfer hydrogenation of acetophenone in the absence of base, the reactions proceed ca. 5 times faster with 5 than with 4, pointing out that the real active species are dihydride-ruthenium complexes.

Full text of DOI:10.1021/om0400651

4836
Organometallics 2004, 23, 4836-4845
Efficien t Tr a n sfer Hyd r ogen a tion of Keton es Ca ta lyzed
by th e Bis(isocya n id e)-Ru th en iu m (II) Com p lexes
tr a n s,cis,cis-[Ru X2(CNR)2(d p p f)] (X ) Cl, Br ; d p p f )
1,1′-Bis(d ip h en ylp h osp h in o)fer r ocen e): Isola tion of
Active Mon o- a n d Dih yd r id e In ter m ed ia tes†
Victorio Cadierno,* Pascale Crochet, J osefina D´ıez, Sergio E. Garc´ıa-Garrido, and
J ose´ Gimeno*
Departamento de Quı´mica Orga´nica e Inorga´nica, Instituto Universitario de Quı´mica
Organometa´lica “Enrique Moles” (Unidad Asociada al CSIC), Facultad de Qu´ımica,
Universidad de Oviedo, E-33071 Oviedo, Spain
Received May 5, 2004
The bis(isocyanide)-ruthenium(II) complexes trans,cis,cis-[RuX2(CNR)2(dppf)] (X ) Cl, R
t
) CH2Ph (2a ), Cy (2b), Bu (2c), 2,6-C6H3Me2 (2d ), (S)-(-)-C(H)MePh (2e); X ) Br, R )
CH2Ph (3a ), Cy (3b), tBu (3c), 2,6-C6H3Me2 (3d ), (S)-(-)-C(H)MePh (3e)) have been prepared
by reaction of the bis(allyl)-ruthenium(II) derivative [Ru(η3-2-C3H4Me)2(dppf)] (1) with the
appropriate isocyanide ligand, in CH2Cl2 at room temperature and in the presence of the
corresponding hydrogen halide HX. The structure of the compound trans,cis,cis-[RuCl2(CN-
2,6-C6H3Me2)2(dppf)] (2d ) has been confirmed by X-ray crystallography. The catalytic activity
of complexes 2a -e and 3a -e in the transfer hydrogenation of acetophenone by propan-2-ol
has been studied, and the most active complex, trans,cis,cis-[RuCl2(CNCH2Ph)2(dppf)] (2a ),
has been also tested as a catalyst in the transfer hydrogenation of a large variety of ketones.
The hydride derivatives cis,cis-[RuHCl(CN-2,6-C6H3Me2)2(dppf)] (4) and cis,cis,cis-[RuH2(CN-
2,6-C6H3Me2)2(dppf)] (5) have been isolated and characterized. Although both hydride
complexes catalyze the transfer hydrogenation of acetophenone in the absence of base, the
reactions proceed ca. 5 times faster with 5 than with 4, pointing out that the real active
species are dihydride-ruthenium complexes.
In tr od u ction
continuous interest in catalytic TH, since alcohols can
be obtained in high yields, under relatively mild condi-
tions, avoiding the use of H2 gas.1
Transfer hydrogenation (TH) of ketones by ruthe-
nium(II) catalysts is currently one of the most appealing
synthetic routes to alcohols and constitutes a good
alternative to the widely used catalytic hydrogenation.1
Despite the fact that the latter route has a much greater
potential for industrial applications,2 there has been a
To date, a multitude of ruthenium complexes have
proven to be efficient catalyst precursors in the TH of
ketones, and there is both experimental and theoretical
evidence regarding the role of ruthenium hydrides
as the active catalytic species.1 In general, they are
rarely detected but can be easily generated in situ in
the presence of a base as promoter, transferring the
hydride group from the R-hydrogen of a secondary
* To whom correspondence should be addressed. E-mail: vcm@
uniovi.es (V.C.), jgh@uniovi.es (J .G.).
† This work is respectfully dedicated to the memory of Dr. J uan
Carlos Del Amo, who was a victim of the March 11th tragedy in
Madrid.
i
alcohol, i.e. PrOH/NaOH.1 In fact, only a few isolated
ruthenium hydride complexes have been used as cata-
lysts (the presence of a base is not required in this case).
These include the following examples (see Chart 1):
[N(PPh3)2][Ru4H3(CO)12] (A; only one isomer is repre-
sented),3 [RuH(H2)(P(CH2CH2PPh2)3)][BPh4] (B),4 [RuH-
(MeCONH)(PCy3)2(CO)(iPrOH)] (C),5 [RuH2(PPh3)4] (D),6
[K][RuH3(CO)(Cy2P(CH2)4PCy2)]‚KBHsBu3 (E),7 [RuH-
(1) For general reviews and personal accounts on transition-metal-
catalyzed transfer hydrogenation of ketones see: (a) Zassinovich, G.;
Mestroni, G.; Gladiali, S. Chem. Rev. 1992, 92, 1051. (b) Noyori, R.;
Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97. (c) Palmer, M. J .; Wills,
M. Tetrahedron: Asymmetry 1999, 10, 2045. (d) Ohkuma, T.; Noyori,
R. In Comprehensive Asymmetric Catalysis; J acobs, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. 1, Chapter 6.1. (e)
Noyori, R.; Yamakawa, M.; Hashiguchi, S. J . Org. Chem. 2001, 66,
7931. (f) Ba¨ckvall, J . E. J . Organomet. Chem. 2002, 652, 105. (g)
Carmona, D.; Lamata, M. P.; Oro, L. A. Eur. J . Inorg. Chem. 2002,
2239. (h) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008. (i) Everaere,
K.; Mortreux, A.; Carpentier, J . F. Adv. Synth. Catal. 2003, 345, 67.
(j) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev., in
press.
(3) Bhaduri, S.; Sharma, K.; Mukesh, D. J . Chem. Soc., Dalton
Trans. 1993, 1191.
(4) Bianchini, C.; Farnetti, E.; Graziani, M.; Peruzzini, M.; Polo, A.
Organometallics 1993, 12, 3753.
(2) In classical hydrogenations very large substrate to catalyst ratios
can be reached, allowing their application to large-scale preparations
(the highest ratio is about 2 × 106; more than 103-104 times higher
than in TH). See for example: Doucet, H.; Ohkuma, T.; Murata, K.;
Yokozawa, T.; Kozawa, M.; Katayama, E.; England, A. F.; Ikariya, T.;
Noyori, R. Angew. Chem., Int. Ed. 1998, 37, 1703.
(5) Yi, C. S.; He, Z.; Guzei, I. A. Organometallics 2001, 20, 3641.
(6) (a) Mizushima, E.; Yamaguchi, M.; Yamagishi, T. Chem. Lett.
1997, 237. (b) Aranyos, A.; Csjernyik, G.; Szabo´, K. J .; Ba¨ckvall, J . E.
Chem. Commun. 1999, 351.
(7) Drouin, S. D.; Amoroso, D.; Yap, G. P. A.; Fogg, D. E. Organo-
metallics 2002, 21, 1042.
10.1021/om0400651 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/08/2004

Efficient Transfer Hydrogenation of Ketones
Organometallics, Vol. 23, No. 21, 2004 4837
Ch a r t 1
(aminoamido)(η6-arene)] (F ),1e [RuH(η6-arene)(PkP)] (G;
PkP ) binap, MeO-biphep),8 and the Shvo catalyst (H).9
In the context of our studies on ruthenium-catalyzed
TH of ketones by propan-2-ol,10 we have recently
reported that the carbonyl-halide dimers [{RuX(µ-X)-
(CO)(PkP)}2] (X ) Cl, Br; PkP ) 1,1′-bis(diphenylphos-
phino)ferrocene (dppf), 1,1′-bis(diisopropylphosphino)-
ferrocene (dippf)) (I; see Figure 1) are valuable precursors
of extremely active catalytic species.11,12 The effective-
ness of these dimers is probably associated with their
ability to generate the transient five-coordinate mono-
nuclear species [RuX2(CO)(PkP)] in solution, via halide-
bridge cleavage, which readily provides the required
vacant site for the ketone coordination.13 Nevertheless,
no detailed mechanism was proposed, since all attempts
to isolate or detect any catalytic intermediate were
unsuccessful.
F igu r e 1. Structures of the dimers [{RuX(µ-X)(CO)-
(PkP)}2] (I) and [{RuX(µ-X)(CNR)(PkP)}2] (II).
To gain insight into the outcome of these catalytic
processes, we believed it of interest to prepare the
related isocyanide dimers [{RuX(µ-X)(CNR)(PkP)}2] (II;
see Figure 1), since an appropriate modulation of the
electronic and/or steric properties of the isocyanide
ligands could favor the isolation of intermediate spe-
cies.14 Since compounds I are readily obtained via HX-
promoted releasing of η3-allyl units in the complexes
[RuX(η3-2-C3H4R)(CO)(PkP)] (R ) H, Me),11,15 we de-
vised the synthesis of the analogous isocyanide dimers
II by the treatment of the known bis(allyl)-ruthenium-
(II) complex [Ru(η3-2-C3H4Me)2(dppf)] (1)16 with HX in
the presence of a stoichiometric amount of CNR ligands.
(8) Geldbach, T. J .; Pregosin, P. S. Helv. Chim. Acta 2002, 85, 3937.
(9) Pa`mies, O.; Ba¨ckvall, J . E. Chem. Eur. J . 2001, 7, 5052 and
references therein.
(10) (a) Crochet, P.; Gimeno, J .; Garc´ıa-Granda, S.; Borge, J .
Organometallics 2001, 20, 4369. (b) Cadierno, V.; Crochet, P.; Garc´ıa-
AÄ lvarez, J .; Garc´ıa-Garrido, S. E.; Gimeno, J . J . Organomet. Chem.
2002, 663, 32. (c) Crochet, P.; Gimeno, J .; Borge, J .; Garc´ıa-Granda,
S. New J . Chem. 2003, 27, 414. (d) Cadierno, V.; Crochet, P.; D´ıez, J .;
Garc´ıa-AÄ lvarez, J .; Garc´ıa-Garrido, S. E.; Gimeno, J .; Garc´ıa-Granda,
S.; Rodr´ıguez, M. A. Inorg. Chem. 2003, 42, 3293. (e) Cadierno, V.;
Crochet, P.; D´ıez, J .; Garc´ıa-AÄ lvarez, J .; Garc´ıa-Garrido, S. E.; Garc´ıa-
Granda, S.; Gimeno, J .; Rodr´ıguez, M. A. Dalton 2003, 3240. (f)
Crochet, P.; Ferna´ndez-Zumel, M. A.; Beauquis, C.; Gimeno, J . Inorg.
Chim. Acta 2003, 356, 114.
(11) Cadierno, V.; Crochet, P.; D´ıez, J .; Garc´ıa-Garrido, S. E.;
Gimeno, J .; Garc´ıa-Granda, S. Organometallics 2003, 22, 5226.
(12) These examples belong to the limited series of catalysts bearing
ligands with no N-H functionalities. It is well-known that the presence
of an NH group in the catalyst is usually required to achieve efficient
ketone transfer hydrogenations. See ref 1 and: (a) Noyori, R.; Ohkuma,
T. Angew. Chem., Int. Ed. 2001, 40, 40 and references therein. (b)
Rautenstrauch, V.; Hoang-Cong, X.; Churlaud, R.; Abdur-Rashid, K.;
Morris, R. H. Chem. Eur. J . 2003, 9, 4954 and references therein.
(13) Although several 16-electron species [RuX2(CO)(PR3)2] (PR3
)
monodentate phosphine) are known,11 only the involvement of
[RuCl2(CO)(PiPr3)2] in catalysis (hydrosilylation of alkynes) has been
reported: (a) Katayama, H.; Tanaguchi, K.; Kobayashi, M.; Sagawa,
T.; Minami, T.; Ozawa, F. J . Organomet. Chem. 2002, 645, 192. (b)
Katayama, H.; Nagao, M.; Moriguchi, R.; Ozawa, F. J . Organomet.
Chem. 2003, 676, 49.

4838 Organometallics, Vol. 23, No. 21, 2004
Cadierno et al.
Sch em e 1
In this respect, it should be mentioned that Geneˆt and
co-workers have reported that the treatment of the
related bis(allyl) compounds [Ru(η3-2-C3H4Me)2(PkP)]
(PkP ) optically active diphosphine) with HX (X ) Cl,
Br) in acetone yields the halide-bridged dimeric species
[{RuX(µ-X)(acetone)(PkP)}2],17 which are extremely ef-
ficient catalysts for the enantioselective hydrogenation
of prochiral olefins and keto groups.18
In this paper we report that, in contrast to our
expectations, the release of the η3-allyl groups in [Ru-
(η3-2-C3H4Me)2(dppf)] (1) in the presence of isocyanides
leads instead to the selective formation of the mono-
nuclear bis(isocyanide)-ruthenium(II) complexes trans,-
cis,cis-[RuX2(CNR)2(dppf)] (X ) Cl, Br; R ) CH2Ph, Cy,
tBu, 2,6-C6H3Me2, (S)-(-)-C(H)MePh) (2a -e and 3a -
e). These complexes have also proven to be efficient
catalysts in transfer hydrogenation of ketones by pro-
pan-2-ol. We also report the isolation and catalytic
activity of the hydride complexes cis,cis-[RuHCl(CN-
2,6-C6H3Me2)2(dppf)] (4) and cis,cis,cis-[RuH2(CN-2,6-
C6H3Me2)2(dppf)] (5).
properly prepared using 2 equiv of benzyl isocyanide (95
and 93% yield, respectively) (Scheme 1). Other com-
plexes, trans,cis,cis-[RuX2(CNR)2(dppf)] (X ) Cl, R ) Cy
(2b), tBu (2c), 2,6-C6H3Me2 (2d ), (S)-(-)-C(H)MePh (2e);
t
X ) Br, R ) Cy (3b), Bu (3c), 2,6-C6H3Me2 (3d ), (S)-
(-)-C(H)MePh (3e)), containing alkyl- and aryl-sub-
stituted isocyanides, including the optically active (S)-
(-)-R-methylbenzyl isocyanide, have been similarly
obtained (91-97% yields; Scheme 1). We note that,
despite the large number of six-coordinate compounds
of general formula [RuX2(CNR)2(PR3)2] reported in the
literature (PR3 ) monodentate phosphine; several ste-
reoisomers have been described),20 to the best of our
knowledge complexes 2a -e and 3a -e represent the
first examples of isocyanide complexes with the stoichi-
ometry [RuX2(CNR)2(PkP)] containing a chelating diphos-
phine ligand.21,22
Resu lts a n d Discu ssion
Syn th esis of th e Bis(isocya n id e)-Ru th en iu m (II)
Com p lexes tr a n s,cis,cis-[Ru X2(CNR)2(d p p f)] (X )
t
Cl, R ) CH2P h (2a ), Cy (2b), Bu (2c), 2,6-C6H3Me2
(2d ), (S)-(-)-C(H)MeP h (2e); X ) Br , R ) CH2P h
t
(3a ), Cy (3b), Bu (3c), 2,6-C6H3Me2 (3d ), (S)-(-)-
C(H)MeP h (3e)). Treatment of the bis(allyl)-ruthe-
nium(II) complex [Ru(η3-2-C3H4Me)2(dppf)] (1) with 2
equiv of the appropriate HX acid, in dichloromethane
at room temperature and in the presence of 1 equiv of
benzyl isocyanide, generates the corresponding mono-
nuclear bis(isocyanide) derivatives trans,cis,cis-[RuX2-
(CNCH2Ph)2(dppf)] (X ) Cl (2a ), Br (3a )) along with
several unidentified species,19 with release of 2-meth-
ylpropene. As expected, complexes 2a and 3a can be
Compounds 2a -e and 3a -e have been isolated as air-
stable yellow solids. They have been characterized by
means of standard spectroscopic techniques (IR and 1H,
31P{1H}, and 13C{1H} NMR) and elemental analyses, all
data being in agreement with the proposed trans,cis,-
(20) For references dealing with the chemistry of the bis(isocyanide)
complexes [RuX2(CNR)2(PR3)2] see: (a) Prater, B. E. Inorg. Nucl. Chem.
Lett. 1971, 7, 1071. (b) Prater, B. E. J . Organomet. Chem. 1971, 27,
C17. (c) Cenini, S.; Fusi, A.; Capparella, G. J . Inorg. Nucl. Chem. 1971,
33, 3576. (d) Prater, B. E. J . Organomet. Chem. 1972, 34, 379. (e) Chatt,
J .; Richards, R. L.; Royston, G. H. D. J . Chem. Soc., Dalton Trans.
1973, 1433. (f) Crociani, B.; Richards, R. L. J . Organomet. Chem. 1978,
144, 85. (g) Gussoni, D.; Mercati, G.; Morazzoni, F. Gazz. Chim. Ital.
1979, 109, 545. (h) Tsuihiji, T.; Akiyama, T.; Sugimori, A. Bull. Chem.
Soc. J pn. 1979, 52, 3451. (i) J effrey, J . C.; Rauchfuss, T, B. Inorg. Chem.
1979, 18, 2658. (j) Albers, M. O.; Coville, N. J .; Nicolaides, C. P.;
Webber, R. A. J . Organomet. Chem. 1981, 217, 247. (k) Fehlhammer,
W. P.; Bartel, K.; Weinberger, B.; Plaia, U. Chem. Ber. 1985, 118, 2220.
(l) Yamamoto, Y.; Tanase, T.; Date, T.; Koide, Y.; Kobayashi, K. J .
Organomet. Chem. 1990, 386, 365. (m) Katsuki, K.; Ooyama, Y.;
Okamoto, M.; Yamamoto, Y. Inorg. Chim. Acta 1994, 217, 181. (n)
Werner, H.; Stark, A.; Steinert, P.; Gru¨nwald, C.; Wolf, J . Chem. Ber.
1995, 128, 49. (o) Lindner, E.; Gepra¨gs, M.; Gierling, K.; Fawzi, R.;
Steimann, M. Inorg. Chem. 1995, 34, 6106. (p) Werner, H.; Bank, J .;
Wolfsberger, W. Z. Anorg. Allg. Chem. 1999, 625, 2178. (q) Al Dulaimi,
J . P.; Clark, R. J . H.; Humphrey, D. G. Dalton 2000, 933. (r) Clot, O.;
Wolf, M. O.; Yap, G. P. A. J . Organomet. Chem. 2001, 637-639, 145.
(21) The closely related cationic bis(isocyanide)-carbonyl complex
cis,cis-[RuCl(CO)(CNtBu)2(dppf)][BF4] has been recently reported:
Kawano, H.; Nishimura, Y.; Onishi, M. Dalton 2003, 1808.
(14) Despite the fact that the chemistry of isocyanide-halide-
phosphine complexes of ruthenium(II) has been largely explored, the
dimeric species [{RuX(µ-X)(CNR)L2}2] (L ) monodentate phosphine;
L2 ) chelate diphosphine) have been unknown until now: (a) Seddon,
E. A.; Seddon, K. R. In The Chemistry of Ruthenium; Elsevier:
Amsterdam, 1984. (b) Schro¨der, M.; Stephenson, T. A. In Comprehen-
sive Coordination Chemistry; Wilkinson, G., Ed.; Pergamon Press:
Oxford, U.K., 1987; Vol. 4, p 384. (c) Hill, A. F. In Comprehensive
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon: New York, 1995; Vol. 7, p 327.
(15) It is well-known that η3-allyl groups act as labile ligands,
generating free coordination sites in acidic media: Braterman, P. S.
In Reactions of Coordinated Ligands: Braterman, P. S., Ed.; Plenum
Press: New York, 1986; Vol. 1, p 103.
(16) Smith J r., D. C.; Cadoret, J .; J afarpour, L.; Stevens, E. D.;
Nolan, S. P. Can. J . Chem. 2001, 79, 626.
(17) These species are usually generated in situ and have not been
characterized. See for example: (a) Geneˆt, J . P.; Pinel, C.; Mallart, S.;
J uge´, S.; Thorimbert, S.; Laffitte, J . A. Tetrahedron: Asymmetry 1991,
2, 555. (b) Geneˆt, J . P.; Pinel, C.; Mallart, S.; J uge´, S.; Cailhol, N.;
Laffitte, J . A. Tetrahedron Lett. 1992, 33, 5343. (c) Geneˆt, J . P.; Pinel,
C.; Ratovelomanana-Vidal, V.; Mallart, S.; Pfister, X.; Can˜o de An-
drade, M. C.; Laffite, J . A. Tetrahedron: Asymmetry 1994, 5, 665. (d)
Geneˆt, J . P.; Pfister, X.; Ratovelomanana-Vidal, V.; Pinel, C.; Laffite,
J . A. Tetrahedron Lett. 1994, 35, 4559. (e) Geneˆt, J . P.; Pinel, C.;
Ratovelomanana-Vidal, V.; Mallart, S.; Pfister, X.; Bischoff, L.; Can˜o
de Andrade, M. C.; Darses, S.; Galopin, C.; Laffite, J . A. Tetrahedron:
Asymmetry 1994, 5, 675.
(22) The preparation of the complexes [RuCl2(CNR)2(dppm)] has
been unsuccessfully attempted. Thus, while the thermal reaction of
t
trans-[RuCl2(CNR)4] (R ) Ph, Bu) with an excess of dppm generates
the compounds cis,cis,trans-[RuCl2(CNR)2(κ1P-dppm)2] (R ) Ph) and
mer-[RuCl(CNR)3(dppm)][Cl] (R ) Ph, tBu), treatment of trans-[RuCl2-
(dppm)2] with 2 equiv of isocyanides in different reaction conditions
affords trans,trans,trans-[RuCl2(CNR)2(κ1P-dppm)2] (R ) Ph, tBu),
t
trans-[RuCl(CNR)2(dppm)(κ1P-dppm)][PF6] (R ) Ph, Bu), and trans-
(18) For an overview see: Ratovelomanana-Vidal, V.; Geneˆt, J . P.
J . Organomet. Chem. 1998, 567, 163.
[Ru(CNR)2(dppm)2][PF6]2 (R ) Ph, tBu): (a) Ruiz, J .; Riera, V.; Vivanco,
M. J . Chem. Soc., Dalton Trans. 1995, 1069. (b) Ruiz, J .; Mosquera,
M. E. G.; Riera, V. J . Organomet. Chem. 1997, 527, 35. By using the
unsymmetrical diphosphine Ph2PCH2PtBu2, a mixture of cis,trans-
[RuCl2(CNtBu)2(Ph2PCH2PtBu2)] (characterized only by 31P{1H} NMR
spectroscopy) and two isomers of mer-[RuCl(CNtBu)3(Ph2PCH2PtBu2)]+
is obtained: (c) Mosquera, M. E. G.; Ruiz, J .; Riera, V.; Garcı´a-Granda,
S.; Salvado´, M. A. Organometallics 2000, 19, 5533.
(19) Analysis of the reaction mixtures by IR and NMR spectroscopy
reveals that complexes 2a and 3a are the only isocyanide-containing
species present in solution. This fact indicates clearly that the
formation of mononuclear derivatives [RuX2(CNR)2(dppf)] is strongly
favored vs the formation of the expected dimers [{RuX(µ-X)(CNR)-
(dppf)}2].

Efficient Transfer Hydrogenation of Ketones
Organometallics, Vol. 23, No. 21, 2004 4839
Sch em e 2
The isocyanide groups are bound to ruthenium in a
nearly linear fashion (Ru-C(1)-N(1) ) 174.6(2)°; Ru-
C(10)-N(2) ) 177.5(2)°) with metal-carbon bond dis-
tances of 1.960(3) Å (Ru-C(1)) and 1.946(3) Å (Ru-
C(10)). These bonding parameters fit well with those
reported in the literature for other isocyanide-ruthe-
nium(II) complexes.14a,20l,o,r,22c
Ca ta lytic Tr a n sfer Hyd r ogen a tion of Keton es.
The easy access to complexes trans,cis,cis-[RuX2(CNR)2-
(dppf)] (2a -e and 3a -e) prompted us to check their
catalytic activity in the transfer hydrogenation of ke-
tones. We note that, despite the large number of
ruthenium(II) catalysts reported for this particular
transformation, no isocyanide-ruthenium species have
been used to date.1 The classical transfer hydrogenation
of acetophenone by propan-2-ol was used as a model
reaction (see Scheme 2). Thus, in a typical experiment,
the ruthenium catalyst precursors 2a -e and 3a -e (0.4
mol %) and NaOH (9.6 mol %) were added to a 0.1 M
F igu r e 2. ORTEP-type view of the structure of trans,cis,-
cis-[RuCl2(CN-2,6-C6H3Me2)2(dppf)] (2d ) showing the crys-
tallographic labeling scheme. Hydrogen atoms have been
omitted for clarity. Thermal ellipsoids are drawn at the
10% probability level. Selected bond distances (Å) and
angles (deg): Ru-Cl(1) ) 2.4268(7); Ru-Cl(2) ) 2.4164-
(6); Ru-P(1) ) 2.4784(6); Ru-P(2) ) 2.4551(6); Ru-C(1)
) 1.960(3); Ru-C(10) ) 1.946(3); C(1)-N(1) ) 1.159(3);
C(10)-N(2) ) 1.150(3); N(1)-C(2) ) 1.404(3); N(2)-C(11)
) 1.411(4); Fe-C* ) 1.6428(4); Fe-C** ) 1.6401(4); P(1)-
Ru-P(2) ) 98.17(2); P(1)-Ru-C(1) ) 87.70(7); P(1)-Ru-
C(10) ) 172.85(8); P(1)-Ru-Cl(1) ) 95.16(2); P(1)-Ru-
Cl(2) ) 85.42(2); P(2)-Ru-C(10) ) 86.27(7); P(2)-Ru-C(1)
) 171.65(7); P(2)-Ru-Cl(1) ) 95.07(2); P(2)-Ru-Cl(2) )
90.03(2); Cl(1)-Ru-Cl(2) ) 174.72(3); Cl(1)-Ru-C(1) )
90.28(7); Cl(1)-Ru-C(10) ) 89.99(8); Cl(2)-Ru-C(1) )
84.50(7); Cl(2)-Ru-C(10) ) 89.00(8); C(1)-Ru-C(10) )
87.32(10); Ru-C(1)-N(1) ) 174.6(2); C(1)-N(1)-C(2) )
167.3(3); Ru-C(10)-N(2) ) 177.5(2); C(10)-N(2)-C(11) )
163.9(3); C*-Fe-C** ) 178.94(3). C* and C** denote the
centroids of the cyclopentadienyl rings C(31), C(32), C(33),
C(34), C(35) and C(36), C(37), C(38), C(39), C(40), respec-
tively.
i
solution of acetophenone (5 mmol) in PrOH at 82 °C,
the reaction being monitored by gas chromatography.
Selected results are summarized in Figure 3.
All of the complexes have proven to be active and
efficient catalysts leading to nearly quantitative conver-
sions (yield g96%) of acetophenone into 1-phenylethanol
within 0.5-8 h (22 h in the case of 3d ; see Figure 3).
The complex trans,cis,cis-[RuCl2(CNCH2Ph)2(dppf)] (2a )
shows the best performance, achieving 99% of conver-
sion in 30 min (TOF ) 500 h-1). Remarkably, the
catalytic activity of complex 2a is retained at lower
catalyst loadings; i.e. using 0.025 mol % of 2a , acetophe-
i
none (0.1 M solution in PrOH; ketone/Ru/NaOH ratio
4000/1/24) can be reduced in 98% yield within 5 h (TOF
) 780 h-1).23 From the results depicted in Figure 3, the
following features deserve comment. (i) There is a strong
influence of the isocyanide substituents on the catalytic
activity, increasing in the order CH2Ph > C(H)MePh .
Cy > tBu ≈ 2,6-C6H3Me2. This indicates clearly that the
steric requirements of the isocyanide ligands play a
crucial role in the reaction. (ii) The catalytic perfor-
mances shown by the chloride complexes 2a -e are, in
all cases, better than those of their bromide counterparts
3a -e, due probably to the higher ability of the Ru-Cl
bonds to favor the formation of the corresponding
hydride-ruthenium(II) species. (iii) No chiral induction
(0% ee) is observed when the optically active complexes
trans,cis,cis-[RuX2{CN-(S)-C(H)MePh}2(dppf)] (2e and
3e) are used as catalysts even at temperatures lower
than 82 °C.
cis stereochemistry (see the Experimental Section for
details). Key spectroscopic features are as follows: (i;
IR) the presence of two strong ν(CN) absorption bands
in the range 2081-2180 cm-1, in accord with a mutually
cis disposition of the isocyanide ligands, (ii; 31P{1H}
NMR) the appearance of a singlet signal at 17.74-21.17
ppm, indicative of equivalent phosphorus nuclei of the
dppf ligand; (iii; 13C{1H} NMR) only one signal for the
isocyanide groups, at the expected downfield chemical
shifts (δ 149.90-162.82 ppm), which appears as a
2
doublet of doublets. The J CP values observed, in the
ranges 111.1-129.9 and 21.5-25.3 Hz, clearly reveal
that each isocyanide group is located in a trans and cis
disposition with respect to the phosphorus nuclei of the
diphosphine. Moreover, the structure of the complex
trans,cis,cis-[RuCl2(CN-2,6-C6H3Me2)2(dppf)] (2d ) has
been unequivocally confirmed by a single-crystal X-ray
diffraction study. An ORTEP view of the molecular
structure is depicted in Figure 2; selected bond distances
and angles are listed in the caption. The ruthenium
atom is in a slightly distorted octahedral environment
with the two chloride ligands oriented mutually trans.
The most active complex, 2a , has been tested in the
hydride transfer hydrogenation of other ketones (results
are shown in Tables 1 and 2). Thus, it has been shown
to be particularly efficient in the reduction of dialkyl
ketones (see Table 1), even when long-chain substitu-
ents are present: i.e., 2-octanone (98% of conversion
i
(23) Using 0.1 mol % of 2a , acetophenone (0.1 M solution in PrOH;
ketone/Ru/NaOH ratio 1000/1/24) is reduced in 98% yield within 1 h
(TOF ) 980 h-1).

4840 Organometallics, Vol. 23, No. 21, 2004
Cadierno et al.
F igu r e 3. Catalytic transfer hydrogenation of acetophenone by the complexes trans,cis,cis-[RuX2(CNR)2(dppf)] (2a -e
i
and 3a -e). Conditions: reactions were carried out at 82 °C using 5 mmol of acetophenone (0.1 M in PrOH). Ketone/Ru/
NaOH ratio: 250/1/24. Yield of 1-phenylethanol determined by GC (the values are the average of two runs).
Ta ble 1. Ca ta lytic Tr a n sfer Hyd r ogen a tion of Dia lk yl Keton es by Com p lex 2a a
a
i
b
Conditions: reactions were carried out at 82 °C using 5 mmol of ketone (0.1 M in PrOH). Ketone/Ru/NaOH ratio: 250/1/24. Yield
of the corresponding alcohol after 10 min. Final yield and time are given in parentheses, determined by GC. The values given in the table
are the average of two runs.
within 45 min; TOF ) 330 h-1; entry 4). Nevertheless,
it should be noted that its catalytic activity is signifi-
cantly reduced in the case of ketones containing bulky
substituents: i.e., 3-methyl-2-butanone and pinacolone
(TOF ) 160 and 10 h-1, respectively; entries 5 and 6).
A large variety of aryl ketones have been also efficiently
transformed into the corresponding alcohols using 2a
as catalyst (see Table 2). In comparison to acetophenone,
slower reductions have been observed for its ortho-,
meta-, and para-substituted derivatives (TOF ) 60-
330 h-1) regardless of the presence of electron-with-
drawing (Cl, Br; entries 1-4) or electron-donating (OMe;
entries 5-7) groups.24 These observations do not allow
us to propose the turnover-limiting step in the catalytic
cycle: i.e., ketone coordination vs hydride transfer from
the metal to the coordinate ketone.25 The effectiveness
of 2a is clearly demonstrated in the transfer hydrogena-
tion of R-tetralone (entry 9), 1-indanone (entry 10), and
propiophenone (entry 11), since the reduction of such
substrates is usually difficult.1
Remarkably, the catalytic activity shown by com-
plexes 2a -e and 3a -e is, under the same reaction
conditions, comparable to that found for the dimeric
species [{RuX(µ-X)(CO)(dppf)}2] (X ) Cl, Br) (I; see
Figure 1), despite the ability of the latter to generate
the unsaturated mononuclear species [RuX2(CO)(dppf)]
in solution (i.e. for the reduction of acetophenone 97%
of conversion was attained within 3 (X ) Cl) or 10 h (X
) Br); to be compared with results in Figure 3).11 We
also note that the catalytic activity shown by the
complex trans,cis,cis-[RuCl2(CNCH2Ph)2(dppf)] (2a ) is
(24) The catalytic activity is not attenuated when the methoxy group
is introduced in an ortho position (TOF ) 500 h-1; see entry 5 in Table
2). This effect, attributed to chelate coordination of 2-methoxyacetophe-
none to ruthenium, has been previously described. See for example:
Evans, D. A.; Nelson, S. G.; Gagne´, M. R.; Muci, A. R. J . Am. Chem.
Soc. 1993, 115, 9800.
(25) (a) Faller, J . W.; Lavoie, A. R. Organometallics 2001, 20, 5245.
(b) Faller, J . W.; Lavoie, A. R. Organometallics 2002, 21, 3493.

Efficient Transfer Hydrogenation of Ketones
Organometallics, Vol. 23, No. 21, 2004 4841
Ta ble 2. Ca ta lytic Tr a n sfer Hyd r ogen a tion of Ar yl-Alk yl Keton es by Com p lex 2a a
a
i
b
Conditions: reactions were carried out at 82 °C using 5 mmol of ketone (0.1 M in PrOH). Ketone/Ru/NaOH ratio: 250/1/24. Yield
of the corresponding alcohol after 10 min. Final yield and time are given in parentheses, determined by GC. The values given in the table
are the average of two runs.
Sch em e 3
higher than that reported by Ba¨ckvall and co-workers
for the five-coordinate species [RuCl2(PPh3)3] (TOF )
1500 vs 890 h-1 for the reduction of cyclohexanone into
cyclohexanol).26
Syn th esis a n d Ca ta lytic Activity of th e Hyd r id e
Com p lexes cis,cis-[Ru HCl(CN-2,6-C6H3Me2)2(d p p f)]
(4) a n d cis,cis,cis-[Ru H2(CN-2,6-C6H3Me2)2(d p p f)]
(5). Since metal-hydride derivatives are commonly
proposed as active species in transfer hydrogenation
reactions,1 we sought the preparation of such com-
pounds starting from the isocyanide-halide complexes
2a -e and 3a -e. The complex trans,cis,cis-[RuCl2(CN-
2,6-C6H3Me2)2(dppf)] (2d ) was chosen as the model
precursor due to its low catalytic activity. With this
complex, we could anticipate a relatively favorable
stabilization of the hydride intermediates.
In agreement with our expectations, we have found
that the treatment of 2d with 1 equiv of NaOEt, in
yield) (Scheme 3), via classical â-hydrogen elimination
EtOH at 80 °C, cleanly generates the monohydride
on the intermediate ethoxide complex.27 In addition,
complex cis,cis-[RuHCl(CN-2,6-C6H3Me2)2(dppf)] (4; 94%
when 2 equiv of NaOEt is used, the dihydride derivative
cis,cis,cis-[RuH2(CN-2,6-C6H3Me2)2(dppf)] (5) is formed
(26) Chowdhury, R. L.; Ba¨ckvall, J . E. J . Chem. Soc., Chem.
Commun. 1991, 1063.
along with minor amounts (∼5%) of its isomer trans,-

4842 Organometallics, Vol. 23, No. 21, 2004
Cadierno et al.
cis,cis-[RuH2(CN-2,6-C6H3Me2)2(dppf)] (6) (Scheme 3).28,29
Workup of this mixture allowed the selective isolation
of complex 5 (83% yield).
Hydride complexes 4 and 5 have been obtained as
yellow air-sensitive solids that can be stored under
nitrogen at room temperature for short periods (2-3
days) without apparent decomposition. They have been
characterized by IR and NMR (1H, 31P{1H} and 13C{1H})
spectroscopy as well as elemental analyses (details are
given in the Experimental Section). The hydride ligand
in 4 gives rise to a strong ν(Ru-H) IR absorption band
1
at 1998 cm-1 and, in the H NMR spectrum, to a triplet
signal at δ -14.19 ppm that indicates equivalent
coupling (2J HP ) 22.9 Hz) to two cis-disposed phosphorus
nuclei. In accord with this, a singlet resonance is
observed for the dppf ligand in the 31P{1H} NMR
spectrum (δ 34.74 ppm). 13C{1H} NMR also supports the
proposed stereochemistry for 4, showing a single iso-
cyanide resonance at 169.78 ppm (dd, 2J CP ) 107.8 and
F igu r e 4. Catalytic transfer hydrogenation of acetophe-
none in the absence of base using trans,cis,cis-[RuCl2(CN-
2,6-C6H3Me2)2(dppf)] (2d ), cis,cis-[RuHCl(CN-2,6-C6H3-
Me2)2(dppf)] (4), and cis,cis,cis-[RuH2(CN-2,6-C6H3Me2)2-
(dppf)] (5). Conditions: reactions were carried out at 82
°C using 5 mmol of acetophenone (0.1 M in PrOH). Ketone/
Ru ratio: 250/1. Yield of 1-phenylethanol determined by
GC (the values are the average of two runs).
2
27.5 Hz). Two hydride (δH -7.08 (ddd, J HP ) 78.9 and
2
2
33.4 Hz, J HH ) 5.0 Hz) and -6.62 (ddd, J HP ) 27.5
and 22.8 Hz, 2J HH ) 5.0 Hz) ppm), isocyanide (δC 178.38
(dd, 2J CP ) 89.1 and 9.1 Hz) and 181.07 (dd, 2J CP ) 11.3
and 8.3 Hz) ppm) and Ph2P (δP 42.97 and 51.22 (d, 2J PP
) 25.7 Hz) ppm) resonances are observed in the NMR
spectra of 5, indicative of an all-cis stereochemistry for
this complex. As expected, two ν(Ru-H) absorptions are
also observed in the IR spectra of 5 at 1955 and 1999
i
As far as the catalytic activity of both hydride
complexes is concerned, the following features should
be noted (see Figures 3 and 4): (i) the reactions in the
absence of base proceed ca. 5 times faster with 5 than
with 4, (ii) using the same ruthenium loading (0.4 mol
%), the catalytic activity of the dihydride complex 5
without NaOH is similar to that found for the dichloride
complex 2d in the presence of NaOH, and (iii) the
activity of monohydride 4 in the absence of NaOH is,
in contrast, remarkably lower than that of 2d with
NaOH. This indicates that the dihydride species 5 is
remarkably more active than the monohydride 4. All
these observations support that the hydrogen transfer
reactions catalyzed by the system trans,cis,cis-[RuX2-
(CNR)2(dppf)] (2a -e and 3a -e) and an excess of NaOH
proceed essentially via the dihydride intermediates cis,-
cis,cis-[RuH2(CNR)2(dppf)]. Although ruthenium(II) di-
hydride derivatives are commonly proposed as active
species in TH processes catalyzed by octahedral Ru(II)
dichloride complexes associated with a base, little
experimental evidence has been published to date. Thus,
in the study of catalytic TH reactions promoted by
[RuCl2(PPh3){(2-(4′-phenyloxazolin-2′-yl)ferrocenyl)diphe-
nylphosphine}], the detection by NMR spectroscopy of
two ruthenium(II) dihydride species is mentioned, but
no details are given.31 Only the isolated and well-
characterized complex [RuH2(PPh3)4] has been experi-
mentally proven to be an efficient catalyst, its activity
being comparable to that of the system [RuCl2(PPh3)3]/
NaOH.26
cm-1
.
To assess whether mono- or dihydride complexes 4
and 5 are active species, the transfer hydrogenation of
acetophenone with propan-2-ol was carried out in the
absence of NaOH. We have found that both complexes
are able to reduce acetophenone into 1-phenylethanol
(96 and 95% yields, respectively (TOF ) 50 and 10 h-1);
see Figure 4).30 To the best of our knowledge, there is
no precedent of mono- and dihydride species containing
the same ruthenium(II) fragment which are active in
TH of ketones in the absence of base.
(27) Several monohydride-ruthenium(II) complexes containing iso-
cyanide ligands are known: (a) Bancroft, G. M.; Mays, M. J .; Prater,
B. E.; Stefanini, F. P. J . Chem. Soc. A 1970, 2146. (b) Christian, D. F.;
Roper, W. R. J . Chem. Soc., Chem. Commun. 1971, 1271. (c) Christian,
D. F.; Clark, G. R.; Roper, W. R.; Waters, J . M.; Whittle, K. R. J . Chem.
Soc., Chem. Commun. 1972, 458. (d) Grundy, K. R. Inorg. Chim. Acta
1981, 53, L225. (e) Burns, I. D.; Hill, A. F.; Thompsett, A. R.; Alcock,
N. W.; Claire, K. S. J . Organomet. Chem. 1992, 425, C8. (f) J ime´nez-
Tenorio, M.; Puerta, M. C.; Valerga, P. Inorg. Chem. 1994, 33, 3515.
(g) Lindner, E.; Pautz, S.; Fawzi, R.; Steimann, M. Organometallics
1998, 17, 3006. (h) Rocchini, E.; Rigo, P.; Mezzetti, A.; Stephan, T.;
Morris, R. H.; Lough, A. J .; Forde, C. E.; Fong, T. P.; Drouin, S. D.
Dalton 2000, 3591. (i) Huang, D.; Koren, P. R.; Folting, K.; Davidson,
E. R.; Caulton, K. G. J . Am. Chem. Soc. 2000, 122, 8916. (j) Coalter, J .
N., III; Huffman, J . C.; Caulton, K. G. Organometallics 2000, 19, 3569.
(k) Caballero, A.; Go´mez-de la Torre, F.; J alo´n, F. A.; Manzano, B. R.;
Rodr´ıguez, A. M.; Trofimenko, S.; Sigalas, M. P. Dalton 2001, 427.
(28) The complexes cis,cis,trans-[RuH2(CNtBu)2(PMe3)2] and cis,mer-
[RuH2(CNCH2Ph){κ3P,P,P-PhP(CH2CH2CH2PCy2)2}] are, to the best
of our knowledge, the only ruthenium(II) dihydride complexes contain-
ing isocyanide ligands reported to date: (a) Chiu, K. W.; J ones, R. A.;
Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. J . Chem. Soc., Dalton
Trans. 1981, 2088. (b) J ia, G.; Meek, D. W.; Gallucci, J . C. Inorg. Chem.
1991, 30, 403.
With regard to the mechanism, we assume that the
first step in the catalytic cycle involves the dissociation
of one isocyanide ligand from [RuHY(CNR)2(dppf)] to
form the pentacoordinate species [RuHY(CNR)(dppf)],
which readily provide the required vacant site for
coordination of the ketone (see Scheme 4). Experimental
(29) Key spectroscopic data for 6 in C6D6 (obtained from the crude
2
reaction mixture): δP 41.24 (s) ppm; δH -5.85 (t, 2H, J HP ) 25.0 Hz,
Ru-H) ppm.
(30) (a) As expected, trans,cis,cis-[RuCl2(CN-2,6-C6H3Me2)2(dppf)]
(2d ) is almost inactive in the absence of NaOH (see Figure 4). (b) We
also note that, in the absence of any ruthenium(II) source, NaOH
catalyzes the reduction of acetophenone into 1-phenylethanol (ac-
etophenone/base ) 250/24) in only 5% yield after 4 h (13% yield after
24 h). This fact clearly indicates the crucial role of the metal in the
catalytic system [RuX2(CNR)2(dppf)]/NaOH.
(31) Nishibayashi, Y.; Takei, I.; Uemura, S.; Hidai, M. Organome-
tallics 1999, 18, 2291.

Efficient Transfer Hydrogenation of Ketones
Organometallics, Vol. 23, No. 21, 2004 4843
techniques. Solvents were dried by standard methods and
distilled under nitrogen before use. All reagents were obtained
from commercial suppliers and used without further purifica-
tion, with the exception of the compound [Ru(η3-2-C3H4Me)2-
(dppf)] (1), which was prepared by following the method
reported in the literature.16 Infrared spectra were recorded on
a Perkin-Elmer 1720-XFT spectrometer. The C, H, and N
analyses were carried out with a Perkin-Elmer 2400 mi-
croanalyzer. Gas chromatographic measurements were made
on Hewlett-Packard HP6890 equipment using an HP-INNO-
WAX cross-linked poly(ethylene glycol) (30 m, 250 µm) or a
Supelco Beta-Dex 120 (30 m, 250 µm) column. Optical rotations
(R) were measured an a Perkin-Elmer 343 polarimeter. NMR
spectra were recorded on a Bruker DPX-300 instrument at 300
MHz (1H), 121.5 MHz (31P), or 75.4 MHz (13C) using SiMe4 or
85% H3PO4 as standards. DEPT experiments have been
carried out for all the compounds reported.
Sch em e 4
support of this dissociation relies on the fact that the
catalytic activity of dihydride 5 is completely inhibited
in the presence of free 2,6-dimethylphenyl isocyanide
([isocyanide]/[Ru] ) 50/1).32 The rest of the steps could
be analogous to those proposed by Ba¨ckvall and co-
workers for the transfer hydrogenation of ketones
catalyzed by [RuH2(PPh3)3], and therefore, no further
comment is warranted.1f
Syn th esis of tr a n s,cis,cis-[Ru X2(CNR)2(d p p f)] (X ) Cl,
t
R ) CH2P h (2a ), Cy (2b), Bu (2c), 2,6-C6H3Me2 (2d ), (S)-
(-)-C(H)MeP h (2e); X ) Br , R ) CH2P h (3a ), Cy (3b), tBu
(3c), 2,6-C6H3Me2 (3d ), (S)-(-)-C(H)MeP h (3e)). The corre-
sponding isocyanide (2 mmol) was added, at room temperature,
to a solution of the complex [Ru(η3-2-C3H4Me)2(dppf)] (1; 0.765
g; 1 mmol) in 50 mL of dichloromethane. The appropriate HX
acid (2.2 mL of a 1.0 M solution in diethyl ether; 2.2 mmol)
was then added and the reaction mixture stirred at room
temperature for 15 min. After the solvent was removed under
reduced pressure, the resulting yellow solid residue was
washed with hexanes (3 × 30 mL) and vacuum-dried. 2a : yield
95% (0.913 g). Anal. Calcd for FeRuC50H42Cl2N2P2: C, 62.51;
H, 4.41; N, 2.92. Found: C, 62.74; H, 4.57; N, 2.85. IR (KBr,
cm-1): ν 2140 and 2178 (CtN). 31P{1H} NMR (CD2Cl2): δ
19.40 (s) ppm. 1H NMR (CD2Cl2): δ 4.27 and 4.73 (br, 4H each,
C5H4), 4.64 (s, 4H, NCH2), 7.20-7.90 (m, 30H, Ph) ppm. 13C-
{1H} NMR (CD2Cl2): δ 48.35 (s, NCH2), 71.85 and 76.38 (br,
CH of C5H4), 80.32 (m, C of C5H4), 126.50-139.00 (m, Ph),
Con clu sion s
In this paper we have described an efficient and
straightforward synthetic protocol for the stereoselective
preparation of rare examples of bis(isocyanide)-ruthe-
nium(II) complexes, namely trans,cis,cis-[RuX2(CNR)2-
(dppf)] (2a -e and 3a -e), starting from the readily
available bis(allyl) derivative [Ru(η3-2-C3H4Me)2(dppf)]
(1). This route is based on the HX-promoted releasing
of the η3-allyl units of 1 in the presence of isocyanide
ligands. Recently, we have also used this synthetic
methodology for the preparation of the dimeric ruthe-
nium(II) species [{RuX(µ-X)(CO)(PkP)}2] (I; see Figure
1).11 Halide complexes 2a -d and 3a -d have proven to
be suitable catalysts for transfer hydrogenation of
ketones by propan-2-ol in the presence of base, repre-
senting novel examples of efficient catalysts containing
ligands with no N-H functionalities.12 In addition, the
hydride complexes cis,cis-[RuHCl(CN-2,6-C6H3Me2)2-
(dppf)] (4) and cis,cis,cis-[RuH2(CN-2,6-C6H3Me2)2(dppf)]
(5), belonging to the scarce series of ruthenium(II)
hydride-isocyanide derivatives,27,28 have also been
isolated and characterized. These complexes catalyze
the TH of acetophenone in the absence of base, showing
that they are intermediates in the catalytic transforma-
tions using their halide precursors as catalysts. As far
as we know, these are the first examples of related
ruthenium hydride complexes of the types LnRuHX and
LnRuH2 which are both active catalysts in TH of ketones
without base. The catalytic activity of the dihydride
complex 5 can be compared to that shown by its
dichloride precursor 2d in the presence of an excess of
base. This fact suggests that dihydride derivatives are
the active species in the catalytic cycle. Moreover, the
lability of these intermediates toward dissociation of one
isocyanide ligand, leading to the putative formation of
16e species [RuH2(CNR)(dppf)], supports the observed
catalytic activity.
2
153.67 (dd, J CP ) 129.9 and 22.5 Hz, CtN) ppm. 2b: yield
96% (0.907 g). Anal. Calcd for FeRuC48H50Cl2N2P2: C, 61.03;
H, 5.33; N, 2.97. Found: C, 61.15; H, 5.01; N, 2.98. IR (KBr,
cm-1): ν 2135 and 2164 (CtN). 31P{1H} NMR (CD2Cl2): δ
20.55 (s) ppm. 1H NMR (CD2Cl2): δ 1.25-1.75 (m, 20H, CH2),
3.70 (m, 2H, NCH), 4.27 and 4.66 (br, 4H each, C5H4), 7.20-
7.80 (m, 20H, Ph) ppm. 13C{1H} NMR (CD2Cl2): δ 23.11, 25.48,
and 33.14 (s, CH2), 54.72 (s, NCH), 71.70 and 76.18 (br, CH of
C5H4), 80.72 (m, C of C5H4), 127.20-137.50 (m, Ph), 151.13
(dd, 2J CP ) 121.9 and 21.5 Hz, CtN) ppm. 2c: yield 96% (0.857
g). Anal. Calcd for FeRuC44H46Cl2N2P2: C, 59.21; H, 5.19; N,
3.14. Found: C, 59.39; H, 5.07; N, 3.11. IR (KBr, cm-1): ν 2139
1
and 2169 (CtN). 31P{1H} NMR (CD2Cl2): δ 21.17 (s) ppm. H
NMR (CD2Cl2): δ 1.39 (s, 18H, CH3), 4.35 and 4.73 (br, 4H
each, C5H4), 7.30-7.85 (m, 20H, Ph) ppm. 13C{1H} NMR (CD2-
Cl2): δ 30.72 (s, CH3), 56.99 (s, C(CH3)3), 71.41 and 75.74 (br,
CH of C5H4), 80.49 (m, C of C5H4), 126.50-137.50 (m, Ph),
2
150.31 (dd, J CP ) 120.7 and 24.7 Hz, CtN) ppm. 2d : yield
95% (0.939 g). Anal. Calcd for FeRuC52H46Cl2N2P2: C, 63.17;
H, 4.69; N, 2.83. Found: C, 63.01; H, 4.76; N, 2.90. IR (KBr,
cm-1): ν 2100 and 2146 (CtN). 31P{1H} NMR (CD2Cl2): δ
1
18.63 (s) ppm. H NMR (CD2Cl2): δ 2.15 (s, 12H, CH3), 4.34
and 4.76 (br, 4H each, C5H4), 7.00-8.30 (m, 26H, Ph) ppm.
13C{1H} NMR (CD2Cl2): δ 18.54 (s, CH3), 71.50 and 76.13 (br,
CH of C5H4), 80.14 (m, C of C5H4), 125.60-136.40 (m, Ph),
2
162.82 (dd, J CP ) 126.8 and 24.8 Hz, CtN) ppm. 2e: yield
94% (0.929 g). Anal. Calcd for FeRuC52H46Cl2N2P2: C, 63.17;
H, 4.69; N, 2.83. Found: C, 63.29; H, 4.51; N, 2.75. IR (KBr,
cm-1): ν 2131 and 2169 (CtN). 31P{1H} NMR (CD2Cl2): δ
Exp er im en ta l Section
3
19.60 (s) ppm. 1H NMR (CD2Cl2): δ 1.43 (d, 6H, J HH ) 6.8
The manipulations were performed under an atmosphere
of dry nitrogen using vacuum-line and standard Schlenk
Hz, CH3), 4.31 (br, 4H, C5H4), 4.60 and 4.84 (br, 2H each,
3
C5H4), 4.87 (quartet, 2H, J HH ) 6.8 Hz, NCH), 7.19-8.10 (m,
30H, Ph) ppm. 13C{1H} NMR (CD2Cl2): δ 25.57 (s, CH3), 56.55
(s, NCH), 71.68, 72.06, 76.14 and 76.37 (br, CH of C5H4), 80.31
(m, C of C5H4), 126.00-139.75 (m, Ph), 153.24 (dd, 2J CP ) 121.1
(32) The lability of the isocyanide ligands can also explain the
similar catalytic activity shown by complexes 2a -e and 3a -e and the
dimeric species [{RuX(µ-X)(CO)(dppf)}2] (X ) Cl, Br) (I).

4844 Organometallics, Vol. 23, No. 21, 2004
Cadierno et al.
and 22.4 Hz, CtN) ppm. [R]20 ) -16.7° mL dm-1 g-1 (c )
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for 2d
D
0.001 M in CHCl3). 3a : yield 93% (0.976 g). Anal. Calcd for
FeRuC50H42Br2N2P2: C, 57.22; H, 4.03; N, 2.67. Found: C,
57.41; H, 4.16; N, 2.63. IR (KBr, cm-1): ν 2141 and 2180 (Ct
N). 31P{1H} NMR (CD2Cl2): δ 19.16 (s) ppm. 1H NMR (CD2-
Cl2): δ 4.32 (br, 4H, C5H4), 4.72 (br, 8H, C5H4 and NCH2),
7.20-7.80 (m, 30H, Ph) ppm. 13C{1H} NMR (CD2Cl2): δ 48.34
(s, NCH2), 71.62 and 76.68 (br, CH of C5H4), 81.77 (m, C of
chem formula
fw
FeRuC52H46Cl2N2P2
988.67
T (K)
296(2)
wavelength (Å)
cryst syst
space group
cryst size, mm
a, Å
1.541 84
monoclinic
P21/c (No. 14)
0.28 × 0.12 × 0.10
9.5193(2)
15.2348(3)
31.1384(5)
90
98.135(1)
90
4
2
C5H4), 127.00-137.50 (m, Ph), 153.01 (dd, J CP ) 119.8 and
21.5 Hz, CtN) ppm. 3b: yield 91% (0.940 g). Anal. Calcd for
FeRuC48H50Br2N2P2: C, 55.78; H, 4.88; N, 2.71. Found: C,
55.65; H, 4.92; N, 2.75. IR (KBr, cm-1): ν 2137 and 2169 (Ct
N). 31P{1H} NMR (CD2Cl2): δ 20.27 (s) ppm. 1H NMR (CD2-
Cl2): δ 1.30-1.75 (m, 20H, CH2), 3.76 (m, 2H, NCH), 4.33 and
4.77 (br, 4H each, C5H4), 7.20-7.85 (m, 20H, Ph) ppm. 13C-
{1H} NMR (CD2Cl2): δ 23.13, 25.33, and 33.20 (s, CH2), 54.71
(s, NCH), 71.63 and 76.41 (br, CH of C5H4), 81.63 (m, C of
b, Å
c, Å
R, deg
â, deg
γ, deg
Z
V, Å3
4470.39(15)
1.469
7.408
F
calcd, g cm-3
µ, mm-1
2
C5H4), 127.00-137.60 (m, Ph), 150.43 (dd, J CP ) 121.1 and
F(000)
2024
23.4 Hz, CtN) ppm. 3c: yield 95% (0.932 g). Anal. Calcd for
FeRuC44H46Br2N2P2: C, 53.84; H, 4.72; N, 2.85. Found: C,
53.71; H, 4.89; N, 2.93. IR (KBr, cm-1): ν 2133 and 2162 (Ct
N). 31P{1H} NMR (CD2Cl2): δ 21.07 (s) ppm. 1H NMR (CD2-
Cl2): δ 1.38 (s, 18H, CH3), 4.39 and 4.78 (br, 4H each, C5H4),
7.15-7.75 (m, 20H, Ph) ppm. 13C{1H} NMR (CD2Cl2): δ 31.10
(s, CH3), 57.32 (s, C(CH3)3), 71.78 and 76.12 (br, CH of C5H4),
θ range, deg
2.87-64.09
-10 e h e 11
-17 e k e 16
-35 e l e 32
98.9
index ranges
completeness to θ ) 64.09
no. of data collected
no. of unique data
no. params/restraints
refinement method
goodness of fit on F2
R1a (I > 2σ(I))
26 943
7350 (Rint ) 0.0491)
2
725/0
81.11 (m, C of C5H4), 125.35-137.80 (m, Ph), 149.90 (dd, J CP
full-matrix least squares on F2
1.033
) 111.1 and 23.0 Hz, CtN) ppm. 3d : yield 97% (1.045 g). Anal.
Calcd for FeRuC52H46Br2N2P2: C, 57.96; H, 4.30; N, 2.60.
Found: C, 57.81; H, 4.44; N, 2.70. IR (KBr, cm-1): ν 2081 and
2125 (CtN). 31P{1H} NMR (CD2Cl2): δ 17.74 (s) ppm. 1H NMR
(CD2Cl2): δ 2.21 (s, 12H, CH3), 4.37 and 4.79 (br, 4H each,
C5H4), 7.00-7.95 (m, 26H, Ph) ppm. 13C{1H} NMR (CD2Cl2):
δ 18.79 (s, CH3), 71.33 and 76.49 (br, CH of C5H4), 81.37 (m,
0.0288
0.0726
0.0351
wR2a (I > 2σ(I))
R1 (all data)
wR2 (all data)
0.0762
largest diff peak and hole, e Å-3 0.311 and -0.358
a
R1 ) ∑(|Fo| - |Fc|)/∑|Fo|; wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
2
C of C5H4), 126.90-136.65 (m, Ph), 161.56 (dd, J CP ) 124.3
and 25.3 Hz, CtN) ppm. 3e: yield 91% (0.980 g). Anal. Calcd
for FeRuC52H46Br2N2P2: C, 57.96; H, 4.30; N, 2.60. Found: C,
57.78; H, 4.21; N, 2.62. IR (KBr, cm-1): ν 2130 and 2165 (Ct
N). 31P{1H} NMR (CD2Cl2): δ 19.54 (s) ppm. 1H NMR (CD2-
mL) and filtered over Kieselguhr. Evaporation of the solvent
gave a yellow solid, which was washed with hexanes (5 × 10
mL) and vacuum-dried. Yield: 83% (0.077 g). Anal. Calcd for
FeRuC52H48N2P2: C, 67.90; H, 5.26; N, 3.05. Found: C, 67.82;
H, 5.24; N, 3.01. IR (KBr, cm-1): ν 1955 and 1999 (Ru-H),
2014 and 2073 (CtN). 31P{1H} NMR (C6D6): δ 42.97 and 51.22
3
Cl2): δ 1.46 (d, 6H, J HH ) 6.7 Hz, CH3), 4.36 (br, 4H, C5H4),
3
4.68 and 4.89 (br, 2H each, C5H4), 4.92 (quartet, 2H, J HH
)
6.7 Hz, NCH), 7.20-7.85 (m, 30H, Ph) ppm. 13C{1H} NMR
(CD2Cl2): δ 25.72 (s, CH3), 56.55 (s, NCH), 71.76, 71.93, 76.52,
and 76.56 (br, CH of C5H4), 81.41 (m, C of C5H4), 126.00-
2
1
(d, J PP ) 25.7 Hz) ppm. H NMR (C6D6): δ -7.08 (ddd, 1H,
2
2J HP ) 78.9 and 33.4 Hz, J HH ) 5.0 Hz, Ru-H), -6.62 (ddd,
2
2
1H, J HP ) 27.5 and 22.8 Hz, J HH ) 5.0 Hz, Ru-H), 2.09 and
2.15 (s, 6H each, CH3), 3.94 (br, 4H, C5H4), 4.29 (br, 2H, C5H4),
4.56 and 4.88 (br, 1H each, C5H4), 6.55-8.40 (m, 26H, Ph) ppm.
13C{1H} NMR (C6D6): δ 19.12 and 19.17 (s, CH3), 70.89, 71.51,
2
139.85 (m, Ph), 152.52 (dd, J CP ) 120.0 and 22.4 Hz, CtN)
ppm. [R]20 ) -14.3° mL dm-1 g-1 (c ) 0.001 M in CHCl3).
D
Syn t h esis of cis,cis-[R u H Cl(CN-2,6-C6H 3Me2)2(d p p f)]
(4). NaOEt (2.02 mL of a 0.05 M solution in ethanol; 0.101
mmol) was added at room temperature to a solution of the
complex trans,cis,cis-[RuCl2(CN-2,6-C6H3Me2)2(dppf)] (2d ;
0.100 g; 0.101 mmol) in 20 mL of ethanol. The reaction mixture
was heated at 80 °C for 2 h and then evaporated to dry-
ness. The solid residue was extracted with toluene (ca. 20 mL)
and filtered over Kieselguhr. Evaporation of the solvent gave
a yellow solid, which was washed with hexanes (3 × 10 mL)
and vacuum-dried. Yield: 94% (0.091 g). Anal. Calcd for
FeRuC52H47N2P2Cl: C, 65.45; H, 4.96; N, 2.94. Found: C,
65.31; H, 4.87; N, 2.95. IR (KBr, cm-1): ν 1998 (Ru-H), 2063
and 2114 (CtN). 31P{1H} NMR (C6D6): δ 34.74 (s) ppm. 1H
2
71.96, and 72.25 (d, J CP ) 5.1 Hz, CH of C5H4), 74.71, 75.08,
3
75.58, and 77.39 (d, J CP ) 9.4 Hz, CH of C5H4), 83.39 and
1
83.88 (d, J CP ) 76.1 Hz, C of C5H4), 125.50-142.60 (m, Ph),
2
2
178.38 (dd, J CP ) 89.1 and 9.1 Hz, CtN), 181.07 (dd, J CP
11.3 and 8.3 Hz, CtN) ppm.
)
Gen er a l P r oced u r e for Ca ta lytic Tr a n sfer Hyd r oge-
n a tion of Keton es. Under an inert atmosphere, the ketone
(5 mmol), the ruthenium catalyst precursor (0.02 mmol, 0.4
mol % of Ru), and 45 mL of propan-2-ol were introduced into
a Schlenk tube fitted with a condenser and heated at 82 °C
for 15 min. Then NaOH was added (5 mL of a 0.096 M solution
in propan-2-ol, 9.6 mol %) and the reaction monitored by gas
chromatography. The corresponding alcohol and acetone were
the only products detected in all cases. The identity of the
alcohols was assessed by comparison with commercially avail-
able (Aldrich Chemical Co. or Acros Organics) pure samples.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of Com p lex 2d .
Crystals suitable for X-ray diffraction analysis were obtained
by slow diffusion of pentane into a saturated solution of the
complex in dichloromethane. The most relevant crystal and
refinement data are collected in Table 3. A yellow single crystal
with prismatic shape was mounted on a glass fiber and
transferred to a Bruker SMART 6K CCD area-detector three-
circle diffractometer (Cu KR radiation, λ ) 1.541 84 Å).33 X-ray
data were collected at 296(2) K, with a combination of three
2
NMR (C6D6): δ -14.19 (t, 1H, J HP ) 22.9 Hz, Ru-H), 2.08
(s, 12H, CH3), 3.93 (br, 4H, C5H4), 4.43 and 5.06 (br, 2H each,
C5H4), 6.55-8.40 (m, 26H, Ph) ppm. 13C{1H} NMR (C6D6): δ
17.64 (s, CH3), 70.02, 70.57, 74.51, and 74.91 (br, CH of C5H4),
2
80.49 (m, C of C5H4), 125.30-139.15 (m, Ph), 169.78 (dd, J CP
) 107.8 and 27.5 Hz, CtN) ppm.
Syn th esis of cis,cis,cis-[Ru H2(CN-2,6-C6H3Me2)2(d p p f)]
(5). NaOEt (4.04 mL of a 0.05 M solution in ethanol; 0.202
mmol) was added at room temperature to a solution of
the complex trans,cis,cis-[RuCl2(CN-2,6-C6H3Me2)2(dppf)]
(2d ; 0.100 g; 0.101 mmol) in 20 mL of ethanol. The reaction
mixture was heated at 80 °C for 2 h and then evaporated to
dryness. The solid residue was extracted with toluene (ca. 20

Efficient Transfer Hydrogenation of Ketones
Organometallics, Vol. 23, No. 21, 2004 4845
runs at different æ and 2θ angles. The data were collected
using 0.3° wide ω scans (8 s/frame at 2θ ) 40° and 25 s/frame
at 2θ ) 100°) with a crystal-to-detector distance of 4.0 cm. The
substantial redundancy in data allows empirical absorption
corrections (SADABS)34 to be applied using multiple measure-
ments of symmetry-equivalent reflections (ratio of minimum
to maximum apparent transmission 0.663 230). A total number
of 26 943 reflections were collected, with 7350 independent
reflections (Rint ) 0.0491). The unit cell parameters were
obtained by full-matrix least-squares refinements of 9668
reflections. The raw intensity data frames were integrated
with the SAINT program,35 which also applied corrections for
Lorentz and polarization effects.
The software package WINGX was used for space group
determination, structure solution, and refinement.36 The space
group determination was based on a check of the Laue
symmetry and systematic absences and ascertained from the
structure solution. The structure was solved by Patterson
interpretation and phase expansion using DIRDIF,37 completed
with difference Fourier syntheses, and refined with full-matrix
least squares using SHELXL-97.38 Weighted R factors (Rw) and
all goodness of fit values S are based on F2; conventional R
factors (R) are based on F. All non-hydrogen atoms were
refined with anisotropic displacement parameters. All hydro-
gen atoms were located by difference maps and refined
2
isotropically. The function minimized was [∑w(Fo - Fc2)/
∑w(Fo2)]1/2, where w ) 1/[σ2(Fo2) + (0.0439P)2 + 2.2802P] with
σ2(Fo2) from counting statistics and P ) (max (Fo2, 0) + 2Fc2)/
3. Atomic scattering factors were taken from ref 39. Geo-
metrical calculations were made with PARST.40 Plots were
made with PLATON.41
Ack n ow led gm en t. We are indebted to the Minis-
terio de Ciencia y Tecnolog´ıa (MCyT) of Spain (Projects
BQU2000-0227 and BQU2003-00255) and the Gobierno
del Principado de Asturias (Project PR-01-GE-6) for
financial support. S.E.G.-G. thanks the MCyT for the
award of a Ph.D. grant. V.C. and P.C. thank also the
MCyT for “Ramo´n y Cajal” contracts.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for the structure determination of com-
plex 2d . This material is available free of charge via the
Internet at http://pubs.acs.org.
(33) SMART version 5.625, Area-Detector Software Package; Bruker
AXS, Madison, WI, 1997-2001.
OM0400651
(34) Sheldrick, G. M. SADABS version 2.03: Program for Empirical
Absorption Correction; University of Go¨ttingen, Go¨ttingen, Germany,
1997-2001.
(38) Sheldrick, G. M. SHELXL97: Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1997.
(39) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV (present distributor: Kluwer Aca-
demic: Dordrecht, The Netherlands).
(40) Nardelli, M. Comput. Chem. 1983, 7, 95.
(41) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool;
University of Utrecht, Utrecht, The Netherlands, 2000.
(35) SAINT+ NT version 6.04, SAX Area-Detector Integration
Program; Bruker AXS Madison, WI,, 1997-2001.
(36) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(37) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF Program System; Technical Report of the Crystallographic
Laboratory, University of Nijmegen, Nijmegen, The Netherlands, 1999.