Hydrofunctionalization of alkenes promoted by diruthenium complexes [{(η5-C5H32 (SiMe2)2}(CO)3(η2 -CH2=CH-R)(μ-H]+featuring a kinetically inert proton on a

Full text of DOI:10.1021/ja0116573

11494
J. Am. Chem. Soc. 2001, 123, 11494-11495
Scheme 1. Synthesis of Complexes 2a-bH+TfO- (R ) H
(a), CH3 (b))
Hydrofunctionalization of Alkenes Promoted by
Diruthenium Complexes
[{(η5-C5H3)2(SiMe2)2}Ru2(CO)3(η2-CH2dCH-R)(µ-H)]+
Featuring a Kinetically Inert Proton on a
Metal-Metal Bond
Maxim V. Ovchinnikov, Eric LeBlanc, Ilia A. Guzei,† and
Robert J. Angelici*
Department of Chemistry
Iowa State UniVersity, Ames, Iowa 50011
ReceiVed July 9, 2001
Metal-assisted nucleophilic attack on unsaturated ligands is a
reaction of great synthetic importance and represents one of the
most common and well-studied reactions in organometallic
chemistry.1 For example, amines and alkoxides attack a carbon
of coordinated alkenes in transition metal complexes if the metal
is sufficiently electropositive to promote such an attack (eq 1).2
The reaction of [{(η5-C5H3)2(SiMe2)2}Ru2(CO)4(µ-H)]+ (1H+)
with Me3NO‚2H2O in the presence of the desired alkene forms
complexes {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(η2-CH2dCH-R) (2a-
b; R ) H, Me) in 72 and 65% isolated yields, respectively, as
air- and moisture-sensitive yellow solids (Scheme 1; see Sup-
porting Information for experimental details). Addition of 1 equiv
of HBF4‚OEt2 or CF3SO3D to solutions of complexes 2a-b in
CH2Cl2 at room temperature gives the hydride-bridged dinuclear
Ru complexes 2a-bH+ in quantitative yields. Complex 2bH+BF4-
exists as a mixture (2.3:1 ratio) of two isomers with Ru
coordinated to different faces of the propylene ligand. The CO
stretching frequencies of 2a-bH+ are approximately 40 cm-1
higher than those of 2 and fall within the range where amine
attack on coordinated alkenes is expected to occur.2 An X-ray
One of the simplest approaches to making the metal in a complex
more positive is to add a proton (H+) to the metal center.3
However, either most protonated metal complexes containing
unsaturated ligands do not react with nucleophiles because the
metal is not sufficiently electropositive, or the nucleophiles simply
deprotonate the metal to give the unreactive neutral metal
complex. We recently reported4 the synthesis of the cationic
dinuclear complex [{(η5-C5H3)2(SiMe2)2}Ru2(CO)4(µ-H)]+ (1H+)
whose carbon monoxide ligands are activated to attack by amine
nucleophiles (eq 2) because of the positive charge on the complex
-
diffraction study of 2aH+BF4 (Figure 1)6 reveals an eclipsed
orientation of the terminal CO and ethylene ligands on the two
-
Ru atoms. The Ru-Ru distance in 2aH+BF4 (3.1306(6) Å) is
similar to that in complex 1H+BF4 (3.1210(5) Å).7 Complexes
-
2a-bH+ are slow to undergo deprotonation relative to reaction
of the alkene with nucleophiles as the unprotonated complexes
2a-b are not detected among the products of reactions of 2a-
bH+ with nucleophiles (vide infra). The deuterated complex
2aD+TfO- in wet acetone-d6 solution (∼5% H2O) did not undergo
measurable H-D exchange after 1 day at 25 °C. As for 1H+,4
this low kinetic acidity is attributed to a combination of the
bulkiness of the dimethylsilyl linkers in the (η5-C5H3)2(SiMe2)2
bridging ligand and the rigidity of the molecule.
and the slow rate of deprotonation of the bridging hydride by the
amines. In this communication we report the synthesis of
protonated alkene complexes [{(η5-C5H3)2(SiMe2)2}Ru2(CO)3(η2-
CH2dCH-R)(µ-H)]+ (2a-bH+) and the activation of the alkene
ligand in these complexes to attack by amines and other
nucleophiles to give the alkylated nucleophiles. This type of
reaction with amine nucleophiles is a key step in the catalytic
intermolecular hydroamination of alkenes, a process of great
current interest and importance.5
Reactions of 2a-bH+BF4 with amines (NH3, MeNH2,
-
Me2NH, morpholine, p-CH3C6H4NH2) yield amine complexes
{(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NHR1R2) (NHR1R2 ) NH3, MeNH2,
(5) For leading references, see: (a) Kawatsura, M.; Hartwig, J. F. J. Am.
Chem. Soc. 2000, 122, 9546. (b) Beller, M.; Eichberger, M.; Trauthwein, H.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2225. (c) Tian, S.; Arredondo, V. M.;
Stern, C. L.; Marks, T. J. Organometallics 1999, 18, 2568. (d) Mu¨ller, T. E.;
Beller, M. Chem. ReV. 1998, 98, 675. (e) Casalnuovo, A. L.; Calabrese, J. C.;
Milstein, D. J. Am. Chem. Soc. 1988, 110, 6738.
* To whom correspondence should be addressed. E-mail: angelici@
iastate.edu.
† Iowa State University, Molecular Structure Laboratory.
(1) (a) McDaniel, K. F. In ComprehensiVe Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E W., Eds.; Pergamon Press: Oxford,
New York 1995; Vol. 12, p 601. (b) Collman, J. P.; Hegedus, L. S.; Norton,
J. R.; Finke, R. G. Principles and Applications of Organotransition Metal
Chemistry; University Science Books: Mills Valley, CA, 1987; Chapter 7.
(c) Yamamoto, A. J. Organomet. Chem. 2000, 600, 159. (d) Brunet, J. J.;
Neibecker, D.; Niedercorn, F. J. Mol. Catal. 1989, 49, 235.
(2) Bush, R. C.; Angelici, R. J. J. Am. Chem. Soc. 1986, 108, 2735.
(3) (a) Angelici, R. J. Acc. Chem. Res. 1995, 28, 52. (b) Kristja´nsdo´ttir, S.
S.; Norton, J. R. In Transition Metal Hydrides: Recent AdVances in Theory
and Experiments; Dedieu, A., Ed.; VCH: New York, 1991; Chapter 10. (c)
Bullock, R. M. Comments Inorg. Chem. 1991, 12, 1.
(6) Crystal data: (173(2) K) C19H23BF4O3Ru2Si2, MW ) 644.50, mono-
clinic, P21/c, a ) 18.2230(9) Å, b ) 15.9109(8) Å, c ) 17.2675(8) Å, â )
108.5284(10)°, Z ) 8, V ) 4747.1(4) Å3, µ ) 1.423 mm-1, 9689 unique
reflections, R1 ) 0.0511 (0.0616 for all data), wR2 ) 0.1411 (0.1485 for all
data). Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-162940 (2aH+BF4-). Copies
of the data can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK, (fax: +44 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk).
(4) (a) Ovchinnikov, M. V.; Angelici, R. J. J. Am. Chem. Soc. 2000, 122,
6130. (b) Ovchinnikov, M. V.; Guzei, I. A.; Angelici, R. J. Organometallics
2001, 20, 691.
(7) Details of the X-ray and neutron diffraction studies of 1H+ will be
published separately: Ovchinnikov, M. V.; Wang, X.; Schultz, A. J.; Angelici,
R. J. Manuscript in preparation.
10.1021/ja0116573 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/27/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 46, 2001 11495
Scheme 2. Proposed Mechanism for the Reaction of 2a-bD+
with Aminesa
Figure 1. Thermal ellipsoid drawing, with 30% probability ellipsoids,
[{(η5-C5H3)2(SiMe2)2}Ru2(CO)3(η2-CH2dCH2)(µ-H)]+ in 2aH+BF4- show-
ing the labeling scheme. Selected bond distances (Å) and angles (deg)
are as follows: Ru(1)-Ru(2), 3.1306(6); Ru(1)-H(1) ) Ru(2)-H(1),
1.743(1); Ru(1)-C(6), 1.901(7); Ru(1)-C(7), 1.899(7); Ru(2)-C(17),
1.889(7); Ru(2)-C(18), 2.237(7); Ru(2)-C(19), 2.242(7); C(18)-C(19),
1.340(12); Ru(1)-Cp(centroid), 1.872(3); Ru(2)-Cp(centroid), 1.868(3);
Ru(1)-H(1)-Ru(2), 128(1); Ru(2)-Ru(1)-C(6), 89.28(19); Ru(2)-
Ru(1)-C(7), 101.6(2); C(6)-Ru(1)-C(7), 91.2(3); Ru(1)-Ru(2)-
C(17), 88.8(2); C(6)-Ru(1)-Ru(2)-C(17), 5.5(3); C(7)-Ru(1)-
Ru(2)-C(17), 96.5(3); Cp(centroid)-Ru(1)-Ru(2)-Cp(centroid),
3.16(17); Cp-Cp fold angle (angle between the planes of the Cp rings),
131.3(3).
a (η5-C5H3)2(SiMe2)2 ligands are omitted.
The scope of this reaction is relatively broad: complexes 2a-
bH+BF4 react with several representative nucleophiles (PMe3,
-
-OMe, -SMe) to give the hydrofunctionalized alkenes and, in
most cases (Table 1; entries 2, 4), readily identifiable Ru-
-
containing products.10 Reactions of 2a-bH+BF4 with these
nucleophiles occur rapidly (t1/2 < 1 s) to give organic products
with high Markovnikov regioselectivities (except PMe3). Surpris-
ingly, the reaction of complex 2bH+BF4 with PMe3 gives a
-
+
+
mixture of n-PrPMe3 and i-PrPMe3 in a 1.6:1 ratio.
Although a detailed mechanism for the reactions of 2a-bH+
with nucleophiles is yet to be established, on the basis of
experiments with deuterium-labeled complex 2aD+TfO-, we
propose the mechanism shown in Scheme 2. It involves initial
nucleophilic attack by the amine on the coordinated alkene to
produce the cationic intermediate A, which is either deprotonated
to B or undergoes reductive elimination of the alkylated am-
monium salt to form an unsaturated diruthenium intermediate that
coordinates an amine to give 3. Intermediate B could also undergo
reductive elimination of the alkylated amine. This mechanism is
consistent with the reaction of the deuterium-labeled 2aD+TfO-
with morpholine which gives N-ethylmorpholine (CH2D-CH2-
N(CH2CH2)2O) that is ∼93 ( 5% deuterated at the methyl
position and no other. No intermediates were observed by FT-IR
Table 1. Hydrofunctionalization of Alkenes Promoted by 2a-bH+
(R ) H (a), CH3 (b))
1
or H NMR spectroscopy during the course of the reactions.
Reductive eliminations involving a µ-H have only recently been
characterized11 in the formation of alkanes and arenes from
Pd2R2(µ-H)(dppm)2+ and proposed in the formation of formamides
in reaction 2.4
In conclusion, we have demonstrated that the alkene complexes
2a-bH+, featuring a kinetically inert bridging proton on a metal-
metal bond and a doubly linked dicyclopentadienyl ligand, react
with a variety of nucleophiles to give hydrofunctionalized alkenes
with predominantly Markovnikov regioselectivity. Future studies
will be directed toward hydroamination and other hydrofunction-
alization reactions of alkenes that are catalyzed by 2a-bH+ and
its derivatives.
Acknowledgment. Dedicated to Professor Jiabi Chen, a good friend
and colleague, on the occasion of his 60th birthday. This work was
supported by the National Science Foundation through Grant No. CHE-
9816342.
Me2NH)8 (3) and the corresponding alkylated amines in a 1:1
1
ratio as determined by H NMR spectroscopy (Table 1; entry 1;
-
Scheme 2). The reactions of 2bH+BF4 give Markovnikov
addition products with >95% regioselectivity. In contrast to
reaction of 1H+ (eq 2),4 even weakly nucleophilic amines (p-
CH3C6H4NH2, pKa ) 5.10)9 react with 2aH+BF4-. Rates of
reactions of 2aH+BF4- with morpholine are approximately 102-
103 times faster than those of complex 1H+ (t1/2 ) 5 min for
Supporting Information Available: Full experimental details,
including the preparations of 2a-b and 2a-bH+ and their reactions
(PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
1H+, t1/2 < 1 s for 2aH+BF4-);4 the reaction of 2aH+BF4 with
-
JA0116573
p-CH3C6H4NH2 was found to be slowest (t1/2 ) 15 min, 25 °C,
CDCl3) among the amines studied. The absence of the depro-
tonated complexes 2a-b and formamides among the products in
these reactions is consistent with relatively slow rates of depro-
tonation of 2a-bH+ and faster rates of nucleophilic attack on
the coordinated alkene than on CO.2
(8) Complexes {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NHR1R2) (3) (NHR1R2
)
morpholine, p-CH3C6H4NH2) undergo rapid decomposition in CDCl3 solution
(9) Perrin, D. D. Dissociation Constants of Organic Bases in Aqueous
Solution; Butterworth: London, 1972.
(10) See Supporting Information.
(11) Stockland, R. A., Jr.; Anderson, G. K.; Rath, N. P. J. Am. Chem. Soc.
1999, 121, 7945.