New mechanism for the intermolecular hydroamination of alkynes: Catalysis by dinuclear ruthenium complexes with a rigid dicyclopentadienyl ligand

Article abstract of DOI:10.1021/om049377u

The dinuclear ruthenium complex {(η⁶-C₅H ₃)₂(SiMe₂)₂}Ru₂(CO) ₃(C₂H₄)H⁺BF₄ ^-(1) catalyzes the intermolecular hydroamination of arylalkynes (e.g., phenylacetylene) with arylamines (e.g., p-toluidine) to give imines (e.g., (Ph(Me)C=N(p-MeC₆H₄)). Although the catalyst has a limited lifetime (up to 6 turnovers), details of the reaction mechanism have been elucidated by isolation and characterization (X-ray and/or NMR) of six of the seven intermediates and reaction-terminating species. The mechanism is fundamentally different from all previously proposed mechanisms for alkyne hydroamination. The rigid doubly bridged bis((dimethylsily)cyclopentadienyl) ligand is an important feature of the catalyst that facilitates this new type of hydroamination mechanism.

Full text of DOI:10.1021/om049377u

5662
Organometallics 2004, 23, 5662-5670
Articles
New Mechanism for the Intermolecular Hydroamination
of Alkynes: Catalysis by Dinuclear Ruthenium
Complexes with a Rigid Dicyclopentadienyl Ligand
David P. Klein, Arkady Ellern,† and Robert J. Angelici*
Department of Chemistry, Iowa State University, Ames, Iowa 50011
Received August 11, 2004
The dinuclear ruthenium complex {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(C2H4)H+BF4- (1) catalyzes
the intermolecular hydroamination of arylalkynes (e.g., phenylacetylene) with arylamines
(e.g., p-toluidine) to give imines (e.g., (Ph(Me)CdN(p-MeC6H4)). Although the catalyst has
a limited lifetime (up to 6 turnovers), details of the reaction mechanism have been elucidated
by isolation and characterization (X-ray and/or NMR) of six of the seven intermediates and
reaction-terminating species. The mechanism is fundamentally different from all previously
proposed mechanisms for alkyne hydroamination. The rigid doubly bridged bis((dimethyl-
silyl)cyclopentadienyl) ligand is an important feature of the catalyst that facilitates this
new type of hydroamination mechanism.
Introduction
There are few reports3 of hydroaminations involving
catalytic species that contain more than one metal
center; however, the hydroamination of arylalkynes by
arylamines is catalyzed by ruthenium carbonyl, Ru3-
(CO)12.3 For this reaction, the authors proposed an
amine activation mechanism but could not exclude
alkyne coordination as a possible first step in the
catalytic cycle.3a
Hydroamination of alkynes with amines to give either
the corresponding enamine (R′, R′′ * H) or imine (R′,
R′′ ) H) (eq 1) is of great interest because of its potential
commercial applications. Hydroamination has been
Recently, our group reported the stoichiometric hy-
droamination of alkenes in the reaction (eq 2) of amines
-
with {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(C2H4)H+BF4 (1),
shown to be catalyzed by a wide variety of early- and
late-transition-metal complexes, as well as lanthanide
and actinide complexes.1 Two different mechanisms
have been proposed for these reactions: (1) activation
of the amine and (2) activation of the alkyne. Amine
activation occurs by formation of a metal-imide or
metal-amide complex, which reacts further either by
a [2 + 2] cycloaddition or by insertion of the alkyne into
the metal-nitrogen bond. Alkyne activation occurs by
η2 coordination of the alkyne to the metal through the
triple bond, which is subsequently attacked by the
amine. Mechanistic studies of this latter route primarily
involve the intramolecular hydroamination of alkynes.2
which contains the doubly linked bis(dimethylsilylcy-
clopentadienyl) ligand.4 Addition of 3 equiv of amine
yields the alkylated amine as a result of a Markovnikov
addition of the amine to the coordinated olefin. Attempts
to make this system catalytic were unsuccessful, pre-
sumably because the alkylated ammonium ion (+NH2-
R1R2) is unable to reprotonate the Ru-Ru bond.5 The
hydroamination of alkynes generally occurs more readily1
than that of alkenes; therefore, we explored the use of
1 as a catalyst for alkyne hydroamination. Herein, we
report the results of these catalytic experiments, with
* To whom correspondence should be addressed. E-mail:
angelici@iastate.edu.
† Molecular Structure Laboratory, Iowa State University.
(1) For reviews of alkyne hydroamination see: (a) Alonso, F.;
Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104, 3079. (b) Pohlki, F.;
Doye, S. Chem. Soc. Rev. 2003, 32, 104. (c) Mu¨ller, T. E. In Encyclo-
pedia of Catalysis; Horva´th, I. T., Ed.; Wiley-Interscience: New Jersey,
2003; Vol. 3, p 492. (d) Mu¨ller, T. E., Beller, M. Chem. Rev. 1998, 98,
675.
(3) (a) Uchimaru, Y. Chem. Commun. 1999, 1133. (b) Tokunaga, M.;
Eckert, M.; Wakatsuki, Y. Angew. Chem., Int. Ed. 1999, 38, 3222. (c)
Kondo, T.; Okada, T.; Suzuki, T.; Mitsudo, T. J. Organomet. Chem.
2001, 622, 149.
(4) Ovchinnikov, M. V.; LeBlanc, E.; Guzei, I. A.; Angelici, R. J. J.
Am. Chem. Soc. 2001, 123, 11494.
(5) Klein, D. P.; Angelici, R. J. Unpublished results.
(2) (a) Mu¨ller, T. E.; Berger, M.; Grosche, M.; Herdtweck, E.;
Schmidtchen, F. P. Organometallics 2001, 20, 4384. (b) Mu¨ller, T. E.;
Grosche, M.; Herdtweck, E.; Pleier, A.-K.; Walter, E.; Yan, Y.-K.
Organometallics 2000, 19, 170. (c) Mu¨ller, T. E.; Pleier, A.-K. J. Chem.
Soc., Dalton Trans. 1999, 583.
10.1021/om049377u CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/20/2004

Intermolecular Hydroamination of Alkynes
Organometallics, Vol. 23, No. 24, 2004 5663
Table 1. Hydroamination of Acetylenes Catalyzed
by 1, 2, 3a,b, and 8
rate at 25 °C (entry 2). Increasing the catalyst (1)
concentration by a factor of 3 increased the yield to 29%,
but the number of turnovers remained at 2.9 (entry 8).
A 3-fold increase in the amine concentration does not
change the yield of the reaction (3.5 turnovers, 12%
yield, entry 9).
TOb
entrya
acetylene
PhCtCH
amine
solvent
(% yield)
1
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
3.3 (11)
NR
2c
PhCtCH
PhCtCH
PhCtCH
PhCtCH
PhCtCH
PhCtCH
PhCtCH
PhCtCH
n-hexCtCH
Me3SiCtCH
o-MeC6H4CtCH p-MeC6H4NH2 CD2Cl2
p-FC6H4CtCH p-MeC6H4NH2 CD2Cl2
p-CF3C6H4CtCH p-MeC6H4NH2 CD2Cl2
PhCtCMe
PhCtCPh
3d,e
4f
3.5 (12)
5.0 (17)
NR
The reaction of phenylacetylene with p-toluidine is
also catalyzed by {(η5-C5H3)2(SiMe2)2}Ru2(CO)2(µ-CO)-
{µ2-η1:η1-C(Ph)dC(H)} (2; see Scheme 1) in the presence
of equimolar HBF4‚OEt2, which immediately protonates
the amine to give 1 equiv of RNH3+BF4-; this reaction
gives a slightly higher yield (entry 3, 12% yield, 3.5
turnovers) than with 1 as the catalyst (entry 1). When
approximately 4.5 equiv of RNH3+BF4- is added (entry
4), the number of turnovers increases to 5.0 (17% yield).
The hydroamination reaction is not catalyzed by 2 in
the absence of acid (entry 5), and catalyst 2 is essential
to the reaction, as no hydroamination occurs when
phenylacetylene is combined with p-toluidine and HBF4‚
OEt2 under the standard reaction conditions (entry 6).
The p-toluidine complex {(η5-C5H3)2(SiMe2)2}Ru2(CO)3-
{NH2(p-MeC6H4)}H+BF4- (8) also catalyzes the reaction
of p-toluidine and phenylacetylene (entry 7) to give the
imine product in 14% yield (4.1 turnovers).
As observed in studies of other hydroamination reac-
tions,3 aliphatic alkynes are not as reactive as aryl-
alkynes; this is evident in the reaction of 1-octyne with
p-toluidine (entry 10), which gives only a 6.2% yield (1.8
turnovers) of N-(2-octylidene)-4-methylaniline, as com-
pared with a 11% yield for the same reaction with
phenylacetylene. Under the same conditions, (trimeth-
ylsilyl)acetylene does not react (entry 11), presumably
because of the bulky nature of the SiMe3 group. Phen-
ylacetylene with an o-methyl group is also unreactive
(entry 12), again presumably due to a steric effect.
Reduction of the electron density in the phenyl ring by
incorporation of an electron-withdrawing p-fluoro group
increases the yield of the reaction to 20% (5.8 turnovers,
entry 13). However, the more strongly electron-with-
drawing p-trifluoromethyl group results in no reaction
(entry 14). Internal alkynes (entries 15 and 16) do not
react with p-toluidine in the presence of catalyst. In an
attempt to increase the overall rate of reaction by
increasing the temperature, the higher boiling solvents
(CD3)2SO and (CD3)2CO (entries 17-19) were used, but
they inactivated the catalyst, most likely by coordination
to the metal center.
5e
6g
7h
8i
NR
4.1 (14)
2.9 (29)
3.5 (12)
1.8 (6.2)
NR
9j
10
11
12
13
14
15
16
NR
5.8 (20)
NR
NR
NR
p-MeC6H4NH2 CD2Cl2
p-MeC6H4NH2 CD2Cl2
17i,k PhCtCH
p-MeC6H4NH2 (CD3)2SO NR
p-MeC6H4NH2 (CD3)2CO NR
p-MeC6H4NH2 (CD3)2CO NR
18
PhCtCH
PhCtCH
PhCtCH
PhCtCH
19i,l
20
n-PrNH2
PhNHMe
PhNH2
CD2Cl2
CD2Cl2
CD2Cl2
NR
NR
3.6 (12)
0.82 (2.8)
21
22d,e PhCtCH
23m
PhCtCH
p-MeC6H4NH2 CD2Cl2
a Conditions (unless otherwise indicated): all reaction mixtures
contain 0.35 mmol of acetylene, 0.35 mmol of amine, 0.012 mmol
(3.3 mol %) of 1, and 0.6 mL of CD2Cl2; 40 ( 1.0 °C, 18 h.
b Turnovers (TO) are determined from NMR product integrations
vs N,N-dimethylacetamide as internal standard; percent yields are
based on NMR yields relative to the indicated acetylene and are
the average of two runs ((10%). c 25.0 ( 0.1 °C. d 0.012 mmol of
HBF4‚OEt2 added. e 2 catalyst. f 0.35 mmol of acetylene, 0.35 mmol
of p-toluidine, 0.056 mmol of (p-MeC6H4)NH3+BF4-, and 0.012
mmol (3.3 mol %) of 2 added. g 0.35 mmol of acetylene, 0.47 mmol
of amine and 0.12 mmol of HBF4‚OEt2 added. h 8 catalyst. i 0.035
mmol of (10 mol %) 1. j 1.05 mmol of amine. k 18 h at 50 ( 1 °C.
l 18 h at 65 ( 1 °C. m {(η5-C5H5)2Ru2(CO)2(µ-CO){µ2-η1:η2-C(Ph)-
-
CH2}+BF4 catalyst.
special attention directed at understanding the mech-
anism of this catalytic hydroamination reaction. The
mechanistic study was accomplished by independent
syntheses and characterizations of some of the proposed
intermediates in the catalytic cycle and by studies of
the inactivation of the catalyst. Of particular note is the
importance of the doubly linked bis((dimethylsilyl)-
cyclopentadienyl) ligand and the Ru-Ru unit in pro-
moting the catalysis by 1.
Results and Discussion
From studies of the reactions of phenylacetylene with
different amines, it is evident that the pKa and steric
properties of the amines affect their reactions. Amines
with a higher pKa (n-propylamine, pKa(H2O) ) 10.8,6
entry 20) or larger cone angle (N-methylaniline, cone
angle 126°,7 entry 21) than p-toluidine (pKa(H2O) ) 5.1,6
cone angle 111°)7 do not react; however, a decrease in
amine pKa(H2O) to 4.6 by the use of aniline6 (entry 22)
results in the same yield of the product imine (3.6
turnovers, 12% yield). The reaction is not catalyzed by
the nonbridged cyclopentadienyl complex {(η5-C5H5)2-
Ru2(CO)2(µ-CO){µ2-η1:η2-C(Ph)dCH2}+BF4- (0.82 turn-
overs, entry 23), which indicates the importance of the
bridging (η5-C5H3)2(SiMe2)2 ligand. In {(η5-C5H5)2Ru2-
Intermolecular Hydroamination Catalyzed by
Complexes 1, 2, 3a,b, and 8. Catalytic reactions (eq
1) of alkynes with amines to give an imine (A) are
summarized in Table 1. Typically, 0.35 mmol of an
alkyne is reacted with 0.35 mmol of an amine in the
presence of 0.012 mmol of a catalyst precursor (1, 2,
3a,b, or 8) for 18 h at 40 °C; longer reaction times did
not give yields any higher than those reported in Table
1. These reactions gave no evidence for other products,
and there was also no evidence of anti-Markovnikov
addition. Unreacted alkyne, amine, and vinylidene
complex 6 (see below) were the only other species
present at the end of the reaction. The reaction of
phenylacetylene with p-toluidine (eq 1) at 40 °C is
catalyzed by complex 1 to give N-(p-tolyl)phenylmeth-
ylimine in 11% yield, corresponding to 3.3 turnovers
(entry 1); this reaction does not occur at a significant
(6) Perrin, D. D. Dissociation Constants of Organic Bases in Aqueous
Solution; Butterworth: London, 1972.
(7) Seligson, A. L.; Trogler, W. C. J. Am. Chem. Soc. 1991, 113, 2520.

5664 Organometallics, Vol. 23, No. 24, 2004
Klein et al.
Scheme 1
(CO)2(µ-CO){µ2-η1:η2-C(Ph)dCH2}+BF4-, the -C(Ph)d
CH2 group is the same as that in 3a, but the cyclopen-
tadienyl ligands are oriented trans to each other,8 which
may be a reason for the inactivity of the nonbridged
complex in hydroamination catalysis.
Considering the above data, the best catalytic per-
formance is achieved in a system that utilizes a primary
arylamine, a phenylacetylene with a moderately elec-
tron-withdrawing group, the weakly coordinating sol-
vent methylene chloride, and the preformed catalyst
precursor 2 in the presence of excess HBF4‚OEt2.
Although there are other more efficient routes for the
synthesis of the arylimines produced in these reactions,
the low reactivity and relatively short lifetimes of the
catalyst have allowed us to understand the mechanism
of the catalytic reactions and events that lead to
inactivation of the catalyst, as described in the next
section.
removal of the ethylene and H+ ligands by the known
nucleophilic amine attack (eq 2) to give NH(p-MeC6H4)-
Et and amine complex 5 (step A).4 In step B, phenyl-
acetylene displaces the amine to give complex 2, which
then undergoes protonation by the p-toluidinium ion to
give an equilibrium mixture of complexes 3a,b (step C).
One or both of these cationic complexes is activated to
attack by p-toluidine (step D) to give the cationic
complex 4. In step E, the enaminium ligand is displaced
directly by p-toluidine or the amine first deprotonates
the enaminium ligand followed by displacement of the
enamine by another molecule of amine to give {(η5-
C5H3)2(SiMe2)2}Ru2(CO)3(NH2(p-MeC6H4)) (5), which is
in equilibrium with the protonated complex 8. The
observed imine product (A) is formed by a 1,3-hydrogen
shift in the enamine (step I). The catalytic reaction ends,
due to the conversion of 2 to the bridging vinylidene
complex (6), which is catalytically inactive and is the
only Ru-containing product observed at the end of the
reaction (step G). In the following paragraphs we
describe the evidence for each of the steps in the
proposed mechanism.
Proposed Mechanism for the Hydroamination
of Alkynes as Catalyzed by Complexes 1, 2, 3a,b,
and 8. On the basis of results of the catalytic reactions
described above, as well as experiments described below,
a mechanism for the hydroamination of phenylacetylene
is proposed in Scheme 1. In this mechanism, when
complex 1 is the catalyst precursor, the first step is the
The only Ru-containing species observed in 1H NMR
spectra of CD2Cl2 solutions of the catalytic reactions of
phenylacetylene, p-toluidine, and 1 is complex 2, which
is the resting state of the catalyst. This complex has
been independently synthesized (Scheme 2) by the
(8) Dyke, A. F.; Knox, S. A. R.; Morris, M. J.; Naish, P. J. J. Chem.
Soc., Dalton Trans. 1983, 1417.

Intermolecular Hydroamination of Alkynes
Organometallics, Vol. 23, No. 24, 2004 5665
Scheme 2
reaction of {(η5-C5H3)2(SiMe2)2}Ru2(CO)4H+BF4 with
NMe2H to give {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NHMe2),
which is subsequently reacted with phenylacetylene at
50 °C to give 2. This synthesis makes use of the known
-
reaction of {(η5-C5H3)2(SiMe2)2}Ru2(CO)4H+BF4 with
-
Figure 1. Thermal ellipsoid drawing of {(η5-C5H3)2-
(SiMe2)2}Ru(CO)2(µ-CO){µ2-η1:η1-C(Ph)dC(H)} (2) with 50%
ellipsoid probability and labeling scheme. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and
angles (deg): Ru(1)-Ru(2), 2.7661(4); Ru(1)-C(17), 2.082-
(3); Ru(2)-C(18), 2.103(3); C(17)-C(18), 1.311(4); C(18)-
C(19), 1.486(4); Ru(1)-Cp(centroid), 1.913; Ru(2)-Cp-
(centroid), 1.920; C(15)-Ru(1)-C(16), 82.7(1); C(15)-
amines to give amine complexes.9 Formation of 2 occurs
by displacement of the NHMe2 ligand from the amine
complex. Complex 2 contains an µ2-η1:η1-phenylacety-
lene ligand that bridges both Ru atoms through both C
atoms of the carbon-carbon triple bond. The unsym-
metrical nature of complex 2 is evident in the 1H NMR
spectrum, which shows two inequivalent Cp fragments;
each fragment shows a triplet and two doublets, with
resonances for the Cp hydrogen atoms at δ 5.21 (m),
5.26 (m), 5.66 (m), 5.69 (m), 6.41 (t), and 6.43 (t). The
lack of symmetry in the (η5-C5H3)2(SiMe2)2 ligand is also
reflected in the four different resonances for the four
Si-Me groups with signals at 0.27, 0.37, 0.45, and 0.52
ppm. The resonance for the acetylenic proton is observed
as a singlet at 8.46 ppm, which is 0.85 ppm downfield
from that observed in the bridging vinylidene isomer
(6, Scheme 1).10 The 13C NMR spectrum, which is
consistent with the structure of 2, exhibits 4 signals for
the Si-Me groups, 10 resonances for the Cp fragments,
3 signals for the CO ligands, and 1 broad resonance at
104.13 ppm for the acetylenic carbons. The infrared
spectrum of 2 in the ν(CO) region shows absorptions at
1996 (vs), 1965 (s), and 1772 (w) cm-1, the last signal
for a bridging CO group.
Ru(1)-C(17), 83.6(1);
C(16)-Ru(1)-C(17), 101.8(1);
Ru(1)-C(17)-C(18), 113.8(2); Ru(2)-C(18)-C(17), 106.9-
(2); C(17)-C(18)-C(19), 127.6(3); Ru(2)-C(18)-C(19),
125.4(2); Ru(1)-C(16)-Ru(2), 85.6(1); C(15)-Ru(1)-Ru-
(2)-C(25), 4.6; C(20)-C(19)-C(18)-C(17), 13; Ru(2)-
C(18)-C(17)-Ru(1), 2.3; Cp(centroid)-Ru(1)-Ru(2)-Cp-
(centroid), 1.2; Cp-Cp fold angle, 122.68.
(1.20 Å). This bond is only 2.24° out of parallel with the
Ru-Ru bond. The C(17), C(18), and C(19) atoms of the
phenylacetylene ligand and the two Ru centers lie in
the same plane, as evidenced by the torsion angles Ph-
(centroid)-C(18)-C(17)-Ru(1) (1°) and Ru(2)-C(18)-
C(17)-Ru(1) (2°).
The resting state of the catalyst during the reaction
is complex 2, as it is observed during the course of the
reaction by the presence of Si-Me resonances at 0.27,
1
0.37, 0.45, and 0.52 ppm in the H NMR spectrum in
The molecular structure of 2 has been determined by
X-ray diffraction (Figure 1) and exhibits a Ru-Ru bond
that is bridged by both the phenylacetylene unit and a
carbon monoxide. The Ru(1)-Ru(2) bond length of
2.7661 Å is elongated (0.11 Å) compared to that in the
bridging vinylidene isomer 6 (2.6551 Å).10 The Cp-Cp
fold angle (122.68°) in 2 is 4° larger than that in the
bridging vinylidene complex, which is consistent with
the longer Ru-Ru bond distance. The Ru-Cp(centroid)
distances (average 1.91 Å) are nearly identical with
those in the bridging vinylidene complex (6, average
1.92 Å), and there is virtually no twist between the two
Cp fragments ( Cp(centroid)-Ru(1)-Ru(2)-Cp(cen-
troid) ) 1.2°). The terminal CO ligands lie nearly in the
same plane shared by the two Ru atoms and the Cp
centroids. Interestingly, the carbon-carbon distances
of the bridging phenylacetylene (C(17)-C(18)) in 2 and
6 are identical at 1.31 Å,10 a distance that is between
that of a carbon-carbon double (1.34 Å) and triple bond
as little as 1 h after the start of the reaction, when the
reaction has proceeded to only 3% completion (1 turn-
over). Also, 2 was observed in the catalyst mixture
during the reaction of phenylacetylene and n-propyl-
amine (Table 1, entry 20); this reaction is not catalytic
because 2 is not protonated by the weakly acidic
n-propylammonium ion. To determine if complex 2 is
involved in the catalytic cycle, it was used as the catalyst
in the presence of 1 equiv of HBF4‚OEt2; these condi-
tions resulted in the same yield of A (Table 1, entry 3).
In the catalytic reactions, the p-toluidinium ion (pKa-
(H2O) ) 5.1) or the protonated iminium form of the
product A (pKa(H2O, calculated) ≈ 4.9)11 serves as the
acid for the protonation of 2 to give complexes 3a,b (step
C). This protonation of 2 occurs at either the internal
or terminal carbon of the phenylacetylene ligand and
can be observed after 1 h as a mixture of 2, 3a,b, 8,
and A in the 1H NMR spectrum of a CD2Cl2 solution of
-
2 to which 1 equiv of (4-MeC6H4)NH3+BF4 is added.
The protonation reaction is greatly simplified by the use
(9) Ovchinnikov, M. V.; Guzei, I. A.; Angelici, R. J. Organometallics
2001, 20, 691.
(10) Ovchinnikov, M. V.; Klein, D. P.; Guzei, I. A.; Choi, M.-G.;
Angelici, R. J. Organometallics 2002, 21, 617.
(11) Calculated using Advanced Chemistry Development (ACD)
Software Solaris V4.67, 2004, located within Scifinder Scholar 2001.

5666 Organometallics, Vol. 23, No. 24, 2004
Klein et al.
of HBF4‚OEt2 as the acid and cleanly gives the three
isomers 3a,b, and 7 (Scheme 1, step C) in the ratio 2:1:
0.01 (3a:3b:7). The IR spectrum of the mixture in CH2-
Cl2 exhibits bands at 2071 (s), 2048 (w), 2018 (vs), and
1994 (s) cm-1, which indicates that there are no bridging
CO groups in either of the major isomers. Although the
isomers could not be separated, the mixture gave a
correct elemental analysis and the complexes were
characterized by their NMR spectra as described below.
The protonation of 2 (step C) is apparently reversible,
as the 3a/3b/7 mixture reacts with a 30-fold excess of
Et3N completely within 5 min at room temperature to
give a 20% yield of 2, but the other 80% of the
Ru-containing products could not be identified and
presumably resulted from other reactions of 3a/3b/7
with Et3N.
The 1H NMR spectrum of the major isomer, 3a,
exhibits four doublets and two triplets for the Cp proton
resonances, indicating a completely unsymmetrical
environment for the bridging (η5-C5H3)2(SiMe2)2 ligand.
The low symmetry is also reflected in the four signals
for the methyl groups bonded to silicon at -0.79, 0.49,
0.72, 0.74 ppm; the peaks at 0.49 and -0.79 ppm are
broad and shifted upfield due to shielding of the methyl
groups by the phenyl group of the bridging vinyl moiety.
The geminal protons exhibit 1H NMR resonances at 4.51
and 3.37 ppm with a coupling constant of 2 Hz, which
is typical for geminal protons in bridging vinyl ligands.8
The upfield position (3.37 ppm) of one of the geminal
protons is consistent with shielding by the phenyl group.
The geminal resonance at 3.37 ppm, along with those
of the Si-Me groups at 0.49 and -0.79 ppm, is broad
in the room-temperature spectrum of 3a, presumably
because of restricted rotation of the phenyl group; such
broad signals have been observed in the methyl groups
of the (η5-C5H3)2(SiMe2)2 ligand in diruthenium com-
plexes containing the diphenylacteylene ligand.10 Cool-
ing a CD2Cl2 solution containing 3a to -25 °C gives an
1H NMR spectrum with a sharp resonance at 3.32 ppm
for the geminal proton and four sharp Si(CH3) reso-
nances at -0.88, 0.43, 0.67, and 0.69; these sharp
resonances are consistent with a slow rotation of the
phenyl group at the lower temperature. In the low-
Figure 2. Thermal ellipsoid drawing of the cation in [{(η5-
C5H3)2(SiMe2)2}Ru(CO)3{trans-µ2-η1:η2-C(H)dC(H)Ph}][BF4]-
(7) with 50% ellipsoid probability and labeling scheme.
Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): Ru(1)-Ru(2), 2.878(3); Ru-
(1)-C(8), 2.105(8); Ru(2)-C(8), 2.118; Ru(2)-C(7), 2.385;
C(7)-C(8), 1.389(14); C(6)-C(7), 1.493(14); Ru(1)-Cp-
(centroid), 1.925; Ru(2)-Cp(centroid), 1.859;
C(8)-
Ru(1)-Ru(2), 47.2(2); C(6)-C(7)-C(8), 125.6(9); Ru(1)-
C(8)-C(7), 129.9(8); Ru(2)-C(8)-C(7), 82.91; Ru(1)-
C(8)-Ru(2), 85.95; Ru(1)-C(8)-C(7)-C(6), 8.9; Cp-
(centroid)-Ru(1)-Ru(2)-Cp(centroid), 3.9; Cp-Cp fold
angle, 125.1.
those (4.51 and 3.37 ppm) for 3a, resonances for the
geminal protons (3.80 and 4.17 ppm) of the vinyl ligand
in 3b are shifted much closer to each other. Although
these protons are coupled to each other in the COSY
NMR spectrum, the coupling constant was too small to
measure, similar to what is observed in the σ-bonded
vinyl ligand of [Ru2{η1-C(Ph)dCH2}(µ-CO)2(CO)2(µ-
dppm)2]+.13a
The final isomer obtained from the protonation of 2
is 7; in this isomer, the proton adds to the carbon in 2
that bears the phenyl group, and the two vinyl protons
are trans to each other. These vinyl protons exhibit 1H
NMR resonances at 4.84 and 9.91 ppm that have a
coupling constant of 11 Hz, as expected for bridging
vinyl protons with a trans geometry.8 The 1H NMR
spectrum also exhibits four resonances for the Si(CH3)2
methyl groups at 0.63, 0.69, 0.70, and 0.94 ppm and four
resonances for the cyclopentadienyl protons at 5.09,
5.70, 6.19, and 6.71 ppm (the peaks at 5.09 and 5.70
integrating for two protons each). Isomer 7 is more
stable thermodynamically than 3a,b, as heating (50 °C)
of a dichloroethane solution of the 3a/3b/7 mixture for
18 h resulted in quantitative formation of isomer 7
(Scheme 1, step F). The molecular structure (Figure 2)
of 7 has been determined by X-ray diffraction and
confirms the trans geometry of the bridging vinyl ligand.
Complex 7 contains a Ru-Ru bond (2.878(3) Å) that is
0.11 Å longer than that in parent complex 2 and 0.03 Å
longer than that in the related ruthenium phosphine
1
temperature H NMR spectrum, the ratio of the two
major isomers changes to approximately 4:1 (3a:3b),
with the amount of 7 staying the same; this change in
isomer ratio with temperature also indicates that the
interconversion of isomers 3a,b is rapid.
The room-temperature 1H NMR spectrum of 3b shows
that it has a structure similar to that of 3a. In contrast
to the bridging vinyl group in 3a, it is the phenyl group
in 3b that is coordinated to the ruthenium to give a
bridging η3-benzyl derivative. Freely rotating phenyl
groups exhibit one doublet and three triplets due to the
plane of symmetry. However, in 3b there is no plane of
symmetry, as indicated by the four resonances for the
benzyl group at 6.81 (d), 6.94 (d), 7.65 (m), and 7.69 (m);
a similar pattern was observed by King for the η3-benzyl
ligand in CpMo(CO)2(η3-CH2C6H5).12 Complex 3b ex-
hibits four resonances for the Si(CH3)2 groups at 0.84,
0.58, 0.55, and 0.52 ppm and six resonances for the Cp
protons at 5.05, 5.42, 5.63, 5.94, 6.18, and 6.50 ppm,
due to the low symmetry of the complex. Compared to
complex
[Ru2(CO)4(trans-µ2-η1:η2-CHdCHPh)(µ-
dppm)2]+.13b The σ-Ru(1)-C(8) bond of the vinyl ligand
is 2.105(8) Å, and the olefinic portion of the vinyl ligand
is unsymmetrically bonded in an η2 fashion to Ru(2),
with the bridging C(8) atom being 0.27 Å closer than
(12) King, R. B.; Fronzaglia, A. J. Am. Chem. Soc. 1966, 88, 709.

Intermolecular Hydroamination of Alkynes
Organometallics, Vol. 23, No. 24, 2004 5667
the terminal C(7) atom (2.385 Å) to Ru(2). The unsym-
metrical nature of this bond may be partially rational-
ized by steric repulsions between the Cp fragment on
Ru(2) and the phenyl group, as indicated by a 2.457 Å
distance between hydrogen atoms on C(5) of the cyclo-
pentadienyl group and C(21) of the phenyl group. The
C(8)-C(7) bond distance of the vinyl moiety is 1.389 Å,
0.07 Å longer than that in the phenylacetylene ligand
in 2 but only slightly longer than a normal CdC double
bond (1.34 Å). The double-bond character of the C(8)-
C(7) bond is also supported by the 125.6(9) and 129.9-
(8)° angles for C(6)-C(7)-C(8) and Ru(1)-C(8)-C(7),
respectively.
3a/3b at room temperature. The ν(CO) bands at 2025
(vs) and 1965 (vs) cm-1 are at somewhat higher wave-
numbers than those of the analogous ethylene complex,
{(η5-C5H3)2(SiMe2)2}Ru2(CO)3(C2H4) (2000 (vs), 1950
(vs), 1923 (w) cm-1),4 with the minor absorbance in 4
(corresponding to 1923 cm-1) presumably being ob-
scured by the broad peak at 1965 cm-1. The higher
wavenumbers of these bands in 4 are due to the
electron-withdrawing nature of the phenyl ring and the
ammonium group on the coordinated olefin. Attempts
to isolate 4 were unsuccessful.
Also present after 5 min in the reaction of p-toluidine
with 3a,b in CD2Cl2 is approximately 6% of the proto-
nated amine complex 8, as indicated by resonances at
0.33, 0.43, 0.45, and 0.52 ppm for the methyl groups
Attempts to use 7 as a catalyst precursor resulted in
no catalytic activity, and although 7 is not directly
involved in the catalytic reactions, its isomers 3a,b are
proposed to react (step D) by undergoing amine attack
on the η2-coordinated vinyl group at the carbon bearing
the phenyl group. This proposed site of attack is based
on the structure of the imine product A, in which the N
and Ph groups are bonded to the same carbon. As seen
in other examples of amine attack on olefins coordinated
to positive metal centers,14 the amine attack on the vinyl
group in 3a is presumably promoted by its η2 coordina-
tion to a positive Ru center, but benzyl isomer 3b is not
similarly activated. Knox and co-workers8 previously
reported the reaction of BH4- with Cp2Ru2(CO)2(µ-CO)-
(µ2-η1:η2-CHdCH2)+ to give products resulting from H-
attack on both the R- and â-carbons of the bridging vinyl
ligand. The R-attack is analogous to that proposed in
step D. In an attempt to characterize products of the
nucleophilic reactions (step D), we added a 30-fold
excess of p-toluidine at room temperature to a CD2Cl2
solution of the mixture of 3a,b. Within 5 min of the
1
located on the SiMe2 groups in the H NMR spectrum;
complete conversion of 4 to 8 was achieved after
approximately 18 h at room temperature. Complex 8
was isolated from the reaction of a 30-fold excess of
p-toluidine with isomers 3a,b in a CH2Cl2 solution after
18 h at room temperature (Scheme 1, steps D, E, H).
1
The H NMR spectrum of 8 exhibits one resonance for
the bridging hydride ligand at -18.98 ppm, four reso-
nances for the methyl groups of the bridging SiMe2
groups, one resonance for the p-methyl group of the
coordinated amine at 2.25 ppm, one resonance for the
-NH2 group at 5.42 ppm, five resonances at 5.12, 5.61,
5.64, 5.78, and 5.90 ppm for the Cp fragments, and
resonances at 6.85 and 7.03 ppm for the aryl protons of
the coordinated amine. The IR spectrum of 8 in CH2Cl2
exhibits only terminal ν(CO) bands (2052 (vs), 2004 (vs),
and 1960 (w) cm-1) that are shifted to wavenumbers
slightly higher than those (2050 (vs), 2002 (vs), 1954
(w) cm-1) of the previously characterized protonated
pyrrolidine complex {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NH-
(CH2CH2)2)H+BF4-,9 as expected for the less electron-
donating p-toluidine ligand.
1
amine addition, the H NMR spectrum indicates the
formation of 4 (Scheme 1, step D). The 1H NMR
spectrum of 4 exhibits resonances at 0.21 and 0.16 ppm
for the methyl groups on (η5-C5H3)2(SiMe2)2 and reso-
nances for the Cp fragments at 4.93 (d), 5.21 (d), 5.49
(t), and 6.01 (t) ppm. These resonances are similar to
those of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(C2H4),4 whose
resonances for the {(η5-C5H3)2(SiMe2)2} ligand occur at
0.35, 0.44 (SiCH3) and 4.88, 5.48, 5.79 (Cp H). Reso-
nances for the two geminal protons of the coordinated
enaminium ion are observed at 5.24 (d) and 5.70 (d) ppm
with a coupling constant of 1.6 Hz, which is consistent
with geminal protons in coordinated vinylic olefins.15
The geometry of these protons is also supported by the
1H-13C-coupled NMR spectrum, which indicates that
these protons reside on the same carbon, with a 13C
chemical shift of 127.2 ppm. Aromatic resonances for
the p-toluidine group are observed as broad doublets at
4.86 and 5.76 ppm (p-MeC6H4), shifted upfield due to
shielding by the adjacent phenyl ring. The methyl group
of the p-toluidine fragment is observed at 2.28 ppm, and
the protons of the phenyl ring are observed at 7.08 (m,
4 H) and 7.24 (t, 1 H) ppm. Complex 4 is also observed
in the IR spectrum of a solution formed by the addition
of a 30-fold excess of p-toluidine to a CH2Cl2 solution of
When the reaction of 3a,b with p-toluidine (30-fold
excess) in CD2Cl2 at room temperature was conducted
in the presence of a 30-fold excess of phenylacetylene,
still the only product was 8. Thus, intermediate 5 does
not react with phenylacetylene under these conditions
to give 2, which indicates that 5 is converted to 8 faster
than it is converted to 2. The slow conversion of 5 to 2
is consistent with the observation that, in the synthesis
of 2, the reaction of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3-
(NHMe2) with phenylacetylene requires heating to 50
°C (Scheme 2). The fact that the 3a,b-catalyzed reaction
of phenylacetylene with p-toluidine requires 40 °C
indicates that the conversion of 5 to 2 does occur at this
temperature (entry 2, Table 1). While 8 probably forms
during the catalytic reaction, it is in equilibrium with
5 (step H), which is supported by the observation that
8 catalyzes the reaction of phenylacetylene with p-
toluidine (30-fold excess) in CD2Cl2 at 40 °C to give the
expected imine product (entry 7, Table 1). Attempts to
prepare 5 by reaction of 1 with p-toluidine according to
eq 2 and by the deprotonation of 8 with Et3N were
unsuccessful.
While the results discussed above provide good evi-
dence for the proposed catalytic cycle (Scheme 1), it is
also necessary to account for the short lifetime (up to 6
turnovers) of the catalyst. Since the vinylidene complex
6 is the only form of ruthenium that exists in the
(13) (a) Gao, Y.; Jennings, M. C.; Puddephatt, R. J. Dalton 2003,
261. (b) Gao, Y.; Jennings, M. C.; Puddephatt, R. J. Can. J. Chem.
2001, 79, 915.
(14) Bush, R. C.; Angelici, R. J. J. Am. Chem. Soc. 1986, 108, 2735.
(15) Chang, T. C. T.; Coolbaugh, T. S.; Foxman, B. M.; Rosenblum,
M.; Simms, N.; Stockman, C. Organometallics 1987, 6, 2394.

5668 Organometallics, Vol. 23, No. 24, 2004
Klein et al.
from P2O5. N-methylaniline and n-propylamine were stirred
with KOH overnight and fractionally distilled, and p-toluidine
was recrystallized first from ethanol and then from boiling
hexanes. Complexes {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(C2H4)H+-
BF4- (1),4 {(η5-C5H3)2(SiMe2)2}Ru2(CO)4H+BF4-,17and (η5-C5H5)2-
Ru2(CO)2(µ-CO){µ2-η1:η2-C(Ph)dCH2}+BF4- 8 were prepared by
reported methods. All other compounds were used as received
from Aldrich. Solution infrared spectra were recorded on a
Nicolet-560 spectrometer using NaCl cells with a 0.1 mm path
length. 1H and 13C NMR spectra were recorded on Bruker
DRX-400, Varian VXR-300, and Bruker AC-200 spectrometers
using deuterated solvent signals as internal references. El-
emental analyses were performed on a Perkin-Elmer 2400
Series II CHNS/O analyzer.
reaction solution when the catalyst becomes inactive,
it is the formation of 6 that terminates the reaction. The
two most likely routes to the formation of 6 are direct
isomerization of 2 to 6 and the deprotonation of the
R-carbon in 7. Heating a CD2Cl2 solution of 2 at 40 °C
(the temperature of the catalytic studies) for 18 h
resulted in the formation of 6 in approximately 40%
yield (Scheme 1, step G). Thus, it is possible that the
isomerization of 2, the predominant species in the
catalytic reactions, is responsible for the formation of
6. To determine if 6 is formed by the deprotonation of
7, a 30-fold excess of p-toluidine was reacted with 7 at
room temperature, but even after 18 h 50% of 7
remained, and there was no evidence for 6; however,
the 1H NMR spectrum indicated the formation of other
unidentifiable Ru-containing products. Thus, it is the
isomerization of 2 to 6 (step G) that appears to be the
major reason for the inactivation of the catalyst.
Synthesis of {(η5-C5H3)2(SiMe2)2}Ru2(CO)2(µ-CO){µ2-η1:
η1-C(Ph)dC(H)} (2). Anhydrous gaseous NMe2H (23 mL, 0.94
mmol) was bubbled by syringe into a CH2Cl2 (20 mL) solution
of {(η5-C5H3)2(SiMe2)2}Ru2(CO)4H+BF4- (200 mg, 0.310 mmol).
After 1 h, solvent was removed under vacuum, the residue was
redissolved in 10 mL of hexanes, and phenylacetylene (0.34
mL, 3.1 mmol) was added. The solution was then heated to
50 °C for 30 min while the reaction mixture turned from red
to orange. Upon cooling, reduction of the solvent volume to
about 3 mL caused the precipitation of 2, which was separated
by filtration. The product was then washed with 10 mL of
hexanes, followed by three additional washes with cold hex-
anes (5 mL), each wash being removed by filtration. Drying
under vacuum gave 110 mg of 2 (56% yield). Crystals suitable
for X-ray diffraction were grown by layering a CH2Cl2 (3 mL)
solution of 2 (50 mg) with hexanes (30 mL), and cooling to -30
°C. 1H NMR (400 MHz, CD2Cl2): δ 0.27 (s, 3 H, Si(CH3)), 0.37
(s, 3 H, Si(CH3)), 0.45 (s, 3 H, Si(CH3)), 0.52 (s, 3 H, Si(CH3)),
5.21 (m, 1 H, Cp H), 5.26 (m, 1 H, Cp H), 5.66 (m, 1 H, Cp H),
5.69 (m, 1 H, Cp H), 6.41 (t, J ) 2 Hz, 1 H, Cp H), 6.43 (t, J
) 2.4 Hz, 1 H, Cp H), 7.10 (t, J ) 7.2 Hz, 1 H, Ph H), 7.26 (t,
J ) 7.2 Hz, 2 H, Ph H), 7.42 (m, 2 H, Ph H), 8.46 (s, 1 H,
PhCtCH). 13C NMR (50 MHz, CD2Cl2): δ -3.08, -2.24, 2.11,
6.56 (Si(CH3)), 91.69, 92.50, 93.71, 96.11, 97.22, 97.52, 99.31,
100.82 (Cp C), 104.19 (br, PhCtCH), 114.13, 114.33 (Cp C),
129.70, 128.15, 129.09, 142.83 (Ph C), 204.05, 204.76 (CO),
236.97 (µ-CO). IR (CH2Cl2): ν(CO) (cm-1) 1996 (vs), 1965 (s),
1772 (w). Anal. Calcd for C25H24O3Ru2Si2: C, 47.60; H, 3.84.
Found: C, 47.29; H, 4.22.
Conclusion
These investigations show that the dinuclear com-
plexes 1, 3a,b, and 8 containing the doubly bridged
cyclopentadienyl ligand (η5-C5H3)2(SiMe2)2 catalyze the
hydroamination of arylalkynes by reaction with aryl-
amines. The catalytic activity of these complexes is a
result of the unique bridging nature of the cyclopenta-
dienyl ligand, as the nonbridged complex {(η5-C5H5)2-
Ru2(CO)2(µ-CO){µ2-η1:η2-C(Ph)dCH2}}+BF4-, an ana-
logue of 3a, does not catalyze the reaction. The proposed
mechanism (Scheme 1) is based on the isolation and
structural characterization (X-ray and/or NMR) of the
following intermediates (or close analogues): 1, 2, 3a,b,
4, 6, 7, and 8. The role of 2 as an intermediate in the
catalytic cycle is supported by its presence during the
reaction and its ability to catalyze the reaction in the
presence of HBF4‚OEt2. When intermediates 3a,b are
reacted with p-toluidine at room temperature, they give
the expected imine A, as well as complexes 4 and 8.
Thus, key identified intermediates react as expected,
according to Scheme 1, under the conditions of the
catalytic reactions. The inactivation of the catalyst
occurs primarily by the isomerization of 2 to its vi-
nylidene isomer 6, which is not catalytic. The present
catalytic system, although not as useful for the synthesis
of imines as other methods, does reveal details of the
mechanism by which diruthenium complexes catalyze
the hydroamination of alkynes. The mechanism is
fundamentally different from those proposed for hy-
droamination reactions that are catalyzed by mono-
nuclear transition-metal complexes.
Synthesis of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(µ2-PhC2-
H2)+BF4 (3a,b). Reaction of 2 (50 mg, 0.079 mmol) in CH2-
-
Cl2 (10 mL) with HBF4‚OEt2 (15 µL, 0.12 mmol) resulted in a
darkening of the solution. After 1 h, solvent was reduced under
vacuum to approximately 3 mL, and Et2O (30 mL) was added
to yield an orange oil. Careful decanting of the solvent gave
an oily residue, which was dissolved in CH2Cl2 (5 mL); addition
of hexanes (40 mL) to this solution precipitated the mixture
of 3a,b. Filtration, followed by drying under vacuum, gave 40.8
mg (72% yield) of a mixture of two isomers, 3a,b. Major isomer,
3a: 1H NMR (400 MHz, CD2Cl2, -25 °C) δ -0.88 (s, 3 H, Si-
(CH3)), 0.43 (s, 3 H, Si(CH3)), 0.67 (s, 3 H, Si(CH3)), 0.69 (s, 3
H, Si(CH3)), 3.32 (d, J ) 2 Hz, 1 H, C(Ph)dC(H)2), 4.45 (d, J
) 2 Hz, 1 H, C(Ph)dC(H)2), 5.32 (m, 1 H, Cp H), 5.58 (m, 1 H,
Cp H), 5.62 (m, 1 H, Cp H), 5.79 (m, 1 H, Cp H), 6.03 (m, 1 H,
Cp H), 6.89 (t, J ) 2 Hz, 1 H, Cp H), 7.33 (m, 5 H, C(Ph H)d
C(H)2); 13C NMR (100 MHz, CD2Cl2, -25 °C): δ -7.53, 0.24,
3.90, 5.79 (Si(CH3)), 69.65 (C(Ph)dC(H)2), 81.86, 93.70, 94.33,
95.62, 98.54, 109.12 (Cp C), 128.57, 128.89, 152.38, 172.02 (Ph
C), 193.93, 195.60, 206.49 (CO). Minor isomer, 3b: 1H NMR
(400 MHz, CD2Cl2, -25 °C) δ 0.47 (s, 3 H, Si(CH3)), 0.50 (s, 3
H, Si(CH3)), 0.53 (s, 3 H, Si(CH3)), 0.80 (s, 3 H, Si(CH3)), 3.73
(s, 1 H, C(Ph)dC(H)2), 4.14 (s, 1 H, C(Ph)dC(H)2), 5.03 (m, 1
H, Cp H), 5.40 (t, J ) 2.4 Hz, 1 H, Cp H), 5.60 (m, 1 H, Cp H),
5.91 (d, J ) 2 Hz, 1 H, Cp H), 6.16 (m, 1 H, Cp H), 6.51 (m, 1
Experimental Section
General Considerations. All reactions were carried out
under an inert atmosphere of dry argon using standard
Schlenk techniques. Diethyl ether, methylene chloride, and
hexanes were purified on alumina using a Solv-Tek solvent
purification system, similar to that reported by Grubbs.16
Methylene chloride-d2 was stirred overnight with calcium
hydride and then refluxed for 4 h and distilled over calcium
hydride. Acetone-d6 was distilled from CaSO4, and DMSO-d6
was vacuum-distilled from NaOH. Dichloroethane was distilled
(16) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(17) Ovchinnikov, M. V.; Angelici, R. J. J. Am. Chem. Soc. 2000,
122, 6130.

Intermolecular Hydroamination of Alkynes
Organometallics, Vol. 23, No. 24, 2004 5669
Table 2. Crystal Data and Structure Refinement
Details for 2 and 7
H, Cp H), 6.71 (d, J ) 7.2 Hz, 1 H, o-H of Ph), 6.93 (d, J ) 7.8
Hz, 1 H, o-H of Ph), 7.57 (m, 1 H, p-H of Ph), 7.66 (m, 2 H,
m-H of Ph); 13C NMR (100 MHz, CD2Cl2, -25 °C): δ -4.42,
-2.38, 0.88, 1.50 (Si(CH3)), 65.89 (C(Ph)dC(H)2), 78.81, 87.22,
90.84, 99.11, 100.18, 101.12 (Cp C), 78.44, 125.83, 132.26,
134.68, 136.45 (Ph C), 196.45, 197.97, 201.37 (CO). Resonances
in the 13C NMR spectrum of 3a,b are assigned on the basis of
a heteronuclear (1H-13C) coupling experiment. The 13C NMR
spectrum of the mixture also contained the correct number of
resonances for the quaternary carbon atoms of both 3a and
3b; however, these peaks could not be assigned. IR (3a,b, CH2-
Cl2): ν(CO) (cm-1) 2071 (s), 2048 (w), 2018 (vs), 1994 (s). Anal.
Calcd for C25H25O3Ru2Si2BF4: C, 41.79; H, 3.51. Found: C,
41.80; H, 3.90.
2
7
empirical formula
formula wt
temo, K
wavelength, Å
cryst syst
space group
unit cell dimens
a, Å
C
25H24O3Ru2Si2
C
25H25BF4O3Ru2Si2
630.76
173(2)
718.58
193(2)
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
P21
35.495(7)
8.7563(16)
15.913(3)
90
105.490(5)
90
4766.2(15)
8
9.280(10)
12.903(14)
12.147(13)
90
b, Å
c, Å
R, deg
â, deg
108.389(17)
90
Synthesis of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3{trans-µ2-η1:
η2-C(H)dC(H)Ph}+BF4- (7). A dichloroethane (10 mL) solu-
tion of 2 (50 mg, 0.079 mmol) was treated with HBF4‚OEt2
(15 µL, 0.12 mmol) and heated to 50 °C for 12 h. The solvent
was reduced under vacuum to approximately 3 mL, and
hexanes (50 mL) was added to precipitate 7. Filtration of the
solution, followed by solvent removal under vacuum, gave 7
(43 mg, 76%). Crystals suitable for X-ray diffraction were
grown by layering a CH2Cl2 (2 mL) solution of 7 (25 mg) with
Et2O (25 mL) and cooling to -30 °C. 1H NMR (400 MHz, CD2-
Cl2): δ 0.63 (s, 3 H, Si(CH3)), 0.69 (s, 3 H, Si(CH3)), 0.70 (s, 3
H, Si(CH3)), 0.94 (s, 3 H, Si(CH3)), 4.84 (d, J ) 10.8 Hz, 1 H,
C(H)dCPh(H)), 5.09 (m, 2 H, Cp H), 5.70 (m, 2 H, Cp H), 6.19
(m, 1 H, Cp H), 6.71 (m, 1 H, Cp H), 7.29 (m, 5 H, C(H)dC(Ph
H)H), 9.91 (d, J ) 10.8 Hz, 1 H, C(H)dCPh(H)). 13C NMR (100
MHz, CD2Cl2): δ -3.72, -1.40, 2.31, 5.86 (Si(CH3)), 82.35,
93.10, 93.49, 93.94, 96.66, 97.14, 98.89, 102.00, 105.64, 118.21
(Cp C), 83.94, 137.70 (µ-vinyl); 126.20, 128.75, 129.62, 141.63,
(Ph C), 193.13, 196.51 (CO). IR (CH2Cl2): ν(CO) (cm-1) 2072
(s), 2017 (vs), 1986 (w). Anal. Calcd for C25H25O3Ru2Si2BF4:
C, 41.79; H, 3.51. Found: C, 41.41; H, 3.78.
γ, deg
V, Å3
1380(3)
2
Z
calcd density, Mg/m3 1.758
1.729
abs coeff, mm-1
F(000)
1.393
2512
1.234
712
cryst size, mm3
θ range for data
collecn, deg
0.47 × 0.25 × 0.12 0.30 × 0.10 × 0.10
2.38-28.26
1.77-28.20
index ranges
-46 e h e 37,
-11 e k e 11,
-21 e l e 21
18 794
5522 (R(int) )
0.0637)
empirical
-12 e h e 12,
-15 e k e 16,
-15 e l e 15
10 309
5556 (R(int) )
0.0748)
semiempirical from
equivalents
5556/1/334
no. of rflns collected
no. of indep rflns
abs cor
no. of data/restraints/ 5522/0/293
params
goodness of fit on F2
final R indices
1.048
1.119
R1 ) 0.0287,
wR2 ) 0.0745
R1 ) 0.0332,
wR2 ) 0.0765
R1 ) 0.0489,
wR2 ) 0.1210
R1 ) 0.0764,
wR2 ) 0.1585
1.779 and -1.042
(I > 2σ(I))
R indices (all data)
Synthesis of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3[NH2(p-Me-
largest diff peak and 0.983 and -0.687
hole, e/Å3
C6H4)]H+BF4 (8). To a CH2Cl2 (10 mL) solution of the
-
mixture of isomers 3a,b (25 mg, 0.035 mmol) was added
p-toluidine (112 mg, 1.04 mmol), and the solution was stirred
for 18 h. The volume of the solution was then reduced to 2
mL under vacuum. Addition of 30 mL of Et2O, followed by
filtration, gave 8 as a maroon powder (16.5 mg, 65% yield).
1H NMR (400 MHz, CD2Cl2): δ -18.98 (s, 1H, Ru-H-Ru),
0.33 (s, 3 H, Si(CH3)), 0.43 (s, 3 H, Si(CH3)), 0.45 (s, 3 H, Si-
(CH3)), 0.52 (s, 3 H, Si(CH3)), 2.25 (s, 3 H, p-CH3C6H4NH2),
5.12 (m, 1 H, Cp H), 5.42 (m, 2 H, p-CH3C6H4NH2), 5.61 (t, J
) 2 Hz, 1 H, Cp H), 5.64 (m, 1 H, Cp H), 5.78 (m, 2 H, Cp H),
5.90 (m, 1 H, Cp H), 6.85 (d, J ) 8 Hz, 2 H, p-CH3C6H4NH2),
7.03 (d, J ) 8 Hz, 2 H, p-CH3C6H4NH2). 13C NMR (100 MHz,
CD2Cl2): δ -3.00, 2.17, 3.67 (Si(CH3)), 20.77 (NH2(p-MeC6H4)),
70.87, 81.50, 87.94, 89.77, 93.88, 95.22, 99.08, 102.89, 103.83,
104.59 (Cp C), 120.03, 130.34, 135.17, 144.89 (Ph C), 196.00,
197.50, 203.40 (CO). IR (CH2Cl2): ν(CO) (cm-1) 2052 (vs), 2004
(vs), 1960 (w). Anal. Calcd for C21H28BF4NO3Ru2Si2: C, 39.84;
H, 3.90; N, 1.94. Found: C, 39.80; H, 3.91; N, 1.80.
to their literature-reported data ((n-hexyl)MeCdN(p-MeC6H4)),18
data from their independent syntheses ((Ph)MeCdN(p-MeC6H4)
and (Ph)MeCdN(Ph)),19 or data from a newly prepared sample
by an extension of a literature method (below) ((p-FC6H4)-
MeCdN(p-MeC6H4)).19
Synthesis of (p-FC6H4)MeCdN(p-MeC6H4). In a reaction
analogous to that used in the synthesis of (p-MeOC6H4)MeCd
N(p-MeC6H4),19 mercury(II) acetate (2.56 g, 8.03 mmol) was
added to a THF (16 mL) solution of p-FC6H4CtCH (0.92 mL,
8.03 mmol) and p-toluidine (0.857 g, 8.00 mmol). The reaction
mixture was stirred for 1.75 h, after which 35 mL of 0.5 N
aqueous NaOH was added. Immediately following the NaOH
addition, sodium borohydride (0.605 g, 16.8 mmol) in 2 N
NaOH (8 mL) was added, and the reaction mixture was stirred
for an additional 3 h. The product was extracted with two
portions of diethyl ether (15 mL), and the ether extract was
dried with anhydrous sodium sulfate and filtered. The ether
was removed under vacuum, and the residue was recrystal-
lized from hexanes to give (p-FC6H4)MeCdN(p-MeC6H4) (0.42
General Procedure for the Catalytic Hydroamination
Reaction. In a typical catalytic run, the catalyst precursor
(approximately 5-7 mg) was loaded into an NMR tube, and
the tube was run through three vacuum/Ar flush cycles. Under
Ar, the alkyne, the amine, 5 µL of N,N-dimethylacetamide
(DMAC, internal standard), and 0.6 mL of dry CD2Cl2 were
then added. The solution was then frozen with liquid nitrogen
and subjected to three freeze/pump/thaw cycles; the tube was
flame-sealed under dynamic vacuum on the fourth cycle. The
NMR tube was then placed in a constant-temperature oil bath
at 40.0 ( 1.0 °C, and the 1H NMR spectrum was recorded after
18 h. The yield of the imine was determined by the ratio of
the methyl peak of the p-MeC6H4 or the -C(dNR)Me group of
the imine to the reference -C(O)Me peak of DMAC. Results
of these reactions are summarized in Table 1. Imines were
1
g, 23% yield). Mp: 97-99 °C. H NMR (400 MHz, CD2Cl2): δ
2.20 (s, 3 H, CH3CdN), 2.34 (s, 3 H, p-MeC6H4NdC), 6.65 (m,
2 H), 7.13 (m, 4 H), 7.98 (m, 2 H). 13C NMR (100 MHz, CD2-
Cl2): δ 17.28 (CH3CdN), 20.90 (p-MeC6H4), 115.31 (d, J ) 21.8
Hz, p-FC6H4), 119.63 (p-MeC6H4), 129.54 (d, J ) 8.4 Hz,
p-FC6H4), 129.82 (p-MeC6H4), 133.04 (p-MeC6H4), 136.36 (d,
J ) 2.7 Hz, p-FC6H4), 149.37 (p-MeC6H4), 163.30 (d, J ) 247.9
Hz, p-FC6H4), 164.21 (CdN). Anal. Calcd for C15H14FN: C,
79.27; H, 6.21; N, 6.16. Found: C, 79.04; H, 6.46; N, 6.14.
Molecular Structure Determinations of 2 and 7. The
crystal evaluations and data collections were performed at 173
(18) Hartung, C. G.; Tillack, A.; Trauthwein, H.; Beller, M. J. Org.
Chem. 2001, 66, 6339.
(19) Barluenga, J.; Aznar, F. Synthesis 1975, 704.
1
identified by comparison of their H NMR spectra in CD2Cl2

5670 Organometallics, Vol. 23, No. 24, 2004
Klein et al.
K (2) or 193 K (7) on a Bruker CCD-1000 diffractometer with
Mo KR (λ ) 0.710 73 Å) radiation and a detector-to-crystal
distance of 5.03 cm. The data (Table 2) were collected using
the full-sphere routine and were corrected for Lorentz and
polarization effects. The absorption correction was based on
fitting a function to the empirical transmission surface, as
sampled by multiple equivalent measurements using SADABS
software.20,21
The structure solutions were accomplished by direct meth-
ods. All non-hydrogen atoms were refined by using a full-
matrix anisotropic approximation. All hydrogen atoms were
placed in the structure factor calculations at idealized positions
and were allowed to ride on the neighboring atoms with
relative isotropic displacement coefficients.
Acknowledgment. This work was supported by the
National Science Foundation through Grant No. CHE-
9816342.
Supporting Information Available: CIF files and tables
giving crystallographic data for 2 and 7, including atomic
coordinates, bond lengths and angles, and anisotropic dis-
placement parameters, low-temperature (-25 °C) 1H, 13C,
COSY, and HETCOR NMR data for 3a,b, 1H, COSY, and
HETCOR NMR data for 4, and HETCOR NMR data for 7. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(21) All software and sources of the scattering factors are contained
in the SHELXTL (version 5.1) program library (G. Sheldrick, Bruker
Analytical X-ray Systems, Madison, WI).
OM049377U