Ruthenium amidinato-carbene complexes containing a Ru-Si bond: Formation and reversible α-silyl group migration from the metal to the carbene ligand

Article abstract of DOI:10.1021/om010775w

Reactions of the coordinatively unsaturated complexes [(η⁶-C₆Me₆)Ru{η-ⁱPrNC(Me) = NⁱPr}]⁺X^- with Me₃SiCHN₂ resulted in the formation of the amidinato-carbene complexes [(η⁶-C₆Me₆)Ru{=CHNⁱPrC(Me) = NⁱPr}(SiMe₃)]⁺ X^-, in which a trimethylsilyl group is bonded to the ruthenium atom. Migration of the silyl group to the carbene ligand occurred on reaction with CO, whereas the reverse reaction was promoted by photochemical dissociation of CO.

Full text of DOI:10.1021/om010775w

4996
Organometallics 2001, 20, 4996-4998
Ru th en iu m Am id in a to-Ca r ben e Com p lexes Con ta in in g a
Ru -Si Bon d : F or m a tion a n d Rever sible r-Silyl Gr ou p
Migr a tion fr om th e Meta l to th e Ca r ben e Liga n d
Taizo Hayashida and Hideo Nagashima*
Institute of Advanced Material Study, Graduate School of Engineering Sciences, and
CREST, J apan Science and Technology Corporation (J ST), Kyushu University, Kasuga,
Fukuoka 816-8580, J apan
Received August 24, 2001
Summary: Reactions of the coordinatively unsaturated
complexes [(η6-C6Me6)Ru{η-iPrNC(Me)dNiPr}]+X- with
Me3SiCHN2 resulted in the formation of the amidinato-
the viewpoints of organic and organometallic chemistry.5
Reactions of coordinatively unsaturated Ru(II) com-
plexes with diazoalkanes were reported recently: [CpRu-
(tmeda)]+TFPB- (tmeda ) tetramethylethylenediamine,
TFPB ) tetrakis{3,5-bis(trifluoromethyl)phenyl}borate)
reacted with trimethylsilyldiazomethane (Me3SiCHN2)
to give [CpRu(tmeda)(dCHSiMe3)]+(TFPB)-,2g whereas
treatment of RuHCl(CO)(PtBu2Me)2 with diazomethane
itself resulted in the formation of Ru(CH3)Cl(CO)(PtBu2-
Me)2 via a ruthenium-carbene intermediate, Ru(dCH2)-
HCl(CO)(PtBu2Me)2.2e These results prompted us to
investigate the reactions of 1 and 2 with Me3SiCHN2.
Although no reaction took place when 1 was treated
with this reagent, the cationic complexes [(η6-C6Me6)-
Ru{η-iPrNC(Me)dNiPr}]+X- (2a , X ) TFPB; 2b, X )
PF6) reacted instantly. The products were amidinato-
carbene complexes having a trimethylsilyl group on
carbene complexes [(η6-C6Me6)Ru{dCHNiPrC(Me)dNi-
Pr}(SiMe3)]+X-, in which a trimethylsilyl group is
bonded to the ruthenium atom. Migration of the silyl
group to the carbene ligand occurred on reaction with
CO, whereas the reverse reaction was promoted by
photochemical dissociation of CO.
Coordinatively unsaturated transition-metal com-
plexes have received considerable attention in terms of
possible intermediates of homogeneous catalysis.1 In
particular, such complexes of ruthenium have been
investigated actively in recent years.2 We recently
have prepared novel organoruthenium amidinates,
(η5-C5Me5)Ru(η-amidinate) (1)3a and [(η6-C6R6)Ru(η-
amidinate)]+X- (2),3b which have formally 16 valence
electrons and are highly reactive toward coordination
of several 2-electron-donor ligands3a,b and oxidative
addition of allylic substrates.3c,d In our further studies
of the reactivity of 1 and 2, we were interested in their
reactions with diazoalkanes. The reactions of certain
metal complexes with diazoalkanes represent a route
to transition metal carbene complexes.4 Numerous
studies have been undertaken of such reactions from
the ruthenium, [(η6-C6Me6)Ru{dCHNiPrC(Me)dNiPr}-
(SiMe3)]+X- (3a , X ) TFPB; 3b, X ) PF6). Furthermore,
the trimethylsilyl group of these new carbene complexes
migrates readily from the metal center to the carbene
ligand by coordination of CO or isocyanide to form 4 or
5, respectively. The reverse carbon to metal R-silyl group
migration involving elimination of CO occurs upon
irradiation of 4. To our knowledge, this is the first
example of the formation of amidinato-carbene com-
plexes by the reaction of organometallic complexes with
diazoalkanes6 and a rare case of experimental proof of
the reversible R-silyl group migration from a metal to a
carbene ligand.7,8
(1) For a review: Poli, R. Chem. Rev. 1996, 96, 2135-2204.
(2) (a) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Chem. Soc.,
Chem. Commun. 1988, 278-280. (b) Caulton, K. G. New J . Chem.
1994, 18, 25-41. (c) J ohnson, T. J .; Folting, K.; Streib, W. E.; Martin,
J . D.: Huffman, J . C.; J ackson, S. A.; Eisenstein, O.; Caulton, K. G.
Inorg. Chem. 1995, 34, 488-499. (d) Heyn, R. H.; Macgregor, S. A.;
Nadasdi, T. T.; Ogasawara, M.; Eisenstein, O.; Caulton, K. G. Inorg.
Chim. Acta 1997, 259, 5-26. (e) Huang, D.; Spivak, G. J .; Caulton, K.
G. New J . Chem. 1998, 22, 1023-1025. (f) Huang, D.; Streib, W. E.;
Bollinger, J . C.; Caulton, K. G.; Winter, R. F.; Scheiring, T. J . Am.
Chem. Soc. 1999, 121, 8087-8097. (g) Gemel, C.; Huffman, J . C.;
Caulton, K. G.; Mauthner, K.; Kirchner, K. J . Organomet. Chem. 2000,
593-594, 342-353. (h) Mashima, K.; Kaneyoshi, H.; Kaneko, S.;
Mikami, A.; Tani, K.; Nakamura, A. Organometallics 1997, 16, 1016-
1025. (i) Haack, K.-J .; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
Angew. Chem., Int. Ed. Engl. 1997, 36, 285-288. (j) Tenorio, M. J .;
Mereiter, K.; Puerta, M. C.; Valerga, P. J . Am. Chem. Soc. 2000, 122,
11230-11231.
(3) (a) Yamaguchi, Y.; Nagashima, H. Organometallics 2000, 19,
725-727. (b) Hayashida, T.; Yamaguchi, Y.; Kirchner, K.; Nagashima,
H. Chem. Lett., in press. (c) Kondo, H.; Yamaguchi, Y. Nagashima, H.
Chem. Commun. 2000, 1075-1076. (d) Kondo, H.; Kageyama, A.;
Yamaguchi, Y.; Haga, M.; Kirchner, K.; Nagashima, H. Bull. Chem.
Soc. J pn., in press.
(4) (a) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. Rev. 1995, 139,
281-311. (b) Sutton, D. Chem. Rev. 1993, 93, 995-1022. (c) Herrmann,
W. A. Angew. Chem., Int. Ed. Engl. 1978, 17, 800-812. (d) Schwab,
P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc. 1996, 118, 100-110.
(e) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1996, 118, 8737-8738.
As shown in Scheme 1, the reaction of 2a or 2b with
Me3SiCHN2 in CH2Cl2 at -78 °C leads to immediate
(5) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; pp 783-823. (b)
Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
2nd ed.; Wiley-Interscience: New York, 1994; pp 270-310. (c) Do¨rwald,
F. Z. Metal Carbenes in Organic Synthesis; Wiley-VCH: Weinheim,
Germany, 1999. (d) Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565-
1604. (e) Herndon, J . W. Coord. Chem. Rev. 2000, 206-207, 237-262.
(6) Metal amidinato-carbene complexes obtained by other routes:
(a) Hitchcock, P. B.; Lappert, M. F.; McLaughlin, G. M.; Oliver, A. J .
J . Chem. Soc., Dalton Trans. 1974, 68-74. (b) Do¨tz, K. H.; Kroll, F.;
Harms, K. J . Organomet. Chem. 1993, 459, 169-176. (c) Feng. S. G.;
White, P. S.; Templeton, J . L. Organometallics 1994, 13, 1214-1223.
(7) Although R-silyl migration is well investigated in main group
organometallic chemistry,15 it is rarely observed in the organotransition
metal chemistry.8,15 The only example for silyl group migration from
a metal to a carbene ligand: Berry, D. H.; Koloski, T. S.; Carroll, P. J .
Organometallics 1990, 9, 2952-2962.
(8) Reversible migration reactions of a silyl group from a metal to a
silylene ligand: Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95,
1351-1374.
10.1021/om010775w CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/02/2001

Communications
Organometallics, Vol. 20, No. 24, 2001 4997
Sch em e 1
liberation of N2 to afford the air- and moisture-stable
amidinato-carbene complex containing the Ru-Si(CH3)3
moiety 3a or 3b, respectively, in good yield.9 The struc-
tures of 3a and 3b were determined by their 1H and
13C NMR spectra: existence of the metal-carbene bond
F igu r e 1. ORTEP drawing of 3b with thermal ellipsoids
drawn at the 30% probability level. All hydrogen atoms
except H36 and the counteranion are omitted for clarity.
Representative bond distances (Å) and angles (deg) are as
follows: Ru1-C21 ) 1.900(5), Ru1-N1 ) 2.053(4), Ru1-
Si1 ) 2.4476(15), N1-C16 ) 1.292(7), N2-C16 ) 1.372(7),
N2-C21 ) 1.349(6); C21-Ru1-N1 ) 76.64(19), Ru1-N1-
C16 ) 115.5(3), N2-C21-Ru1 ) 119.4(4).
1
is suggested by the H and 13C resonances appearing
at characteristically lower field (for example, 3a in CD2-
Cl2; δH 10.7 ppm, δC 246 ppm). The 13C-1H coupling
constant of the carbene carbon atom was 162 Hz,
indicative of the sp2 character of this carbon atom. The
methyl groups of the two iPr groups of the amidinato-
carbene ligand are magnetically inequivalent and give
1
four doublets in the H NMR spectrum and four signals
Sch em e 2
in the 13C NMR spectrum. These spectroscopic features
were supported by the X-ray structure determina-
tion of 3b, whose molecular structure is illustrated in
Figure 1.10 There is a trimethylsilyl group (Ru-Si )
2.448(1) Å) and a carbene moiety (Ru-Ccarbene
)
1.900(5) Å) bonded to the ruthenium center. The Ru-C
bond distance is similar to those of the known amino-
carbene complexes of ruthenium.11 The carbene carbon
is bonded with a proton and one nitrogen atom of the
amidinate ligand. The other nitrogen atom of the
amidinate is coordinated to the ruthenium atom. The
resulting five-membered ruthenacycle consisting of the
ruthenium atom and the amidinato-carbene ligand is
planar. Such a planar structure of an amidinato-
carbene-metal unit has been seen in the tungsten
ported by Templeton,6c in which delocalization of the
positive charge provides several possible resonance
structures.
The unprecedented formation of 3 must involve cleav-
age of the C-SiMe3 bond in Me3SiCHN2, which resulted
in subsequent Ru-Si and C-N bond formation. As a
clue to enable an understanding of the mechanism of
these multiple reactions, we have discovered experi-
mentally that silyl group migration from the carbene
carbon atom to ruthenium can occur. As shown in
Scheme 2, trimethylsilyl group migration from the
ruthenium to the carbene ligand was accomplished
quantitatively by treatment of 3a or 3b with a typical
π-acid, σ-donor such as CO or CNtBu to give the
complexes 4 and 5, respectively.12 No rearrangement
occurred when either 3a or 3b was treated with phos-
phines, pyridine, or olefins such as ethyl vinyl ether and
acrylonitrile. The migration resulted in a typical higher
complexes [Tp′(CO)2W{dC(OR)N(R′)C(Me)dN(H)}]X re-
(9) In a typical example for 3, to a solution of 2 (40 mg, 0.032 mmol)
dissolved in CH2Cl2 (ca. 3 mL) was added a hexane solution of Me3-
SiCHN2 (10% solution, 0.048 mmol) dropwise at -78 °C. The color of
the solution changed immediately from dark blue to red, and the
reaction mixture was warmed to room temperature with stirring for
10 min. After removal of the solvent, the resulting crude product
was purified by recrystallization from CH2Cl2/pentane at -35 °C to
give 3a as red crystals (33 mg, 0.024 mmol, 77%). 1H NMR (600 ΜΗz,
CD2Cl2): δ -0.18 (s, Si(CH3)3), 1.24 (d, J ) 7.0 Hz, 3H; CH(CH3)2),
1.31 (d, J ) 5.1 Hz, 3H; CH(CH3)2), 1.35 (d, J ) 6.6 Hz, 3H; CH(CH3)2),
1.38 (d, J ) 6.8 Hz, 3H; CH(CH3)2), 2.20 (s, 18H; C6Me6), 2.45 (s, 3H;
CCH3), 4.06 (sep, J ) 6.8 Hz, 1H; CH(CH3)2), 4.37 (sep, J ) 6.7 Hz,
1H; CH(CH3)2), 7.56 (s, 4H; p-(CF3)2C6H3), 7.72 (t, J ) 2.2 Hz, 8H;
o-(CF3)2C6H3), 10.7 (s, 1H; RudCH). Other data are given in the
Supporting Information.
1
field shift of the H and 13C resonances of the CH group
bonded with the ruthenium atom; for example, the δH
and δC values of 4a appeared at 3.72 and 56 ppm with
J CH ) 126 Hz due to the sp3 carbon atom. The 29Si NMR
signal of 4a appeared at 3.85 ppm, which is higher than
(10) Crystal data for 3b: C24H45F6N2PRu; Mr ) 635.75, monoclinic,
a ) 18.580(3) Å, b ) 20.311(3) Å, c ) 16.596(3) Å, â ) 110.411(3), U
) 5868.6(17) Å3, T ) 293 K, space group C2/c (No. 15), Z ) 8, µ(Mo
KR) ) 0.683 mm-1, 6225 reflections measured, 6225 unique (Rint
)
0.000), 4542 observed (>2σ), final residuals R1 ) 0.0601, wR2 ) 0.1581
(I > 2σ(I)); R1 ) 0.0869, wR2 ) 0.1782 (all data).
(12) In a typical example for 4: in a Schlenk tube, a CH2Cl2 solution
(ca. 3 mL) of 3a (54 mg, 0.040 mmol) was stirred under a CO
(11) (a) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L.; Thomas, S. J .
Chem. Soc., Dalton Trans. 1979, 1929-1942. (b) Adams, R. D.; Chen,
G.; Tanner, J . T.; Yin, J . Organometallics 1990, 9, 595-601. (c)
Blenkiron, P.; Pilette, D.; Corrigan, J . F.; Taylor, N. J .; Carty, A. J . J .
Chem. Soc., Chem. Commun. 1995, 2165-2166. (d) Morran, P. D.;
Mawby, R. J .; Wilson, G. D.; Moore, M. H. Chem. Commun. 1996, 261-
262. (e) Enders, D.; Gielen, H.; Raabe, G.; Runsink, J .; Teles, J . H.
Chem. Ber. 1997, 130, 1253-1260. (f) Yam, V. W.; Chu, B. W.; Cheung,
K. Chem. Commun. 1998, 2261-2262. (g) Mul, W. P.; Elsevier, C. J .;
Vuurman, M. A.; Smeets, W. J . J .; Spek, A. L.; de Boer, J . L. J .
Organomet. Chem. 1997, 532, 89-100.
atmosphere at room temperature for 2 h. The color of the solution
changed from red to yellow. After removal of the solvent, the product
3a was obtained as a yellow solid (54 mg, 0.039 mmol, 98%). 1H NMR
(600 ΜΗz, CD2Cl2): δ 0.09 (s, Si(CH3)3), 1.16 (d, J ) 6.8 Hz, 3H; CH-
(CH3)2), 1.23 (d, J ) 7.1 Hz, 3H; CH(CH3)2), 1.33 (d, J ) 7.1 Hz, 3H;
CH(CH3)2), 1.43 (d, J ) 7.1 Hz, 3H; CH(CH3)2), 2.07 (s, 3H; CCH3),
2.15 (s, 18H; C6Me6), 3.48 (sep, J ) 7.0 Hz, 1H; CH(CH3)2), 3.52 (sep,
J
) 7.1 Hz, 1H; CH(CH3)2), 3.72 (s, 1H; Ru-CH), 7.56 (s, 4H;
p-(CF3)2C6H3), 7.72 (t, J ) 2.2 Hz, 8H; o-(CF3)2C6H3). IR (KBr): ν˜ 1963
cm-1 (CO). Other data are given in the Supporting Information.

4998 Organometallics, Vol. 20, No. 24, 2001
Communications
Sch em e 3
F igu r e 2. ORTEP drawing of 4b with thermal ellipsoids
drawn at the 30% probability level. All hydrogen atoms
except H36 and the counteranion are omitted for clarity.
Representative bond distances (Å) and angles (deg) are
as follows: Ru1-C21 ) 2.097(11), Ru1-N1 ) 1.960(8),
Ru1-C25 ) 1.836(9), N1-C16 ) 1.294(13), N2-C16 )
1.339(13), N2-C21 ) 1.497(13); C21-Ru1-N1 ) 75.0(4),
Ru1-N1-C16 ) 125.0(8), N2-C21-Ru1 ) 107.1(6),
Ru1-C21-Si1 ) 119.7(5).
that of 3a by 20 ppm (3a ; 24.61 ppm). The existence of
a coordinated CO is suggested by the IR and 13C NMR
spectra (νCO 1963 cm-1; δCO 203 ppm). These spectral
changes on going from 3a to 4a correspond to the R-
silyl migration from [(amidinato)(H)CdRuSiMe3] to
[(amidinato)(H)(Me3Si)CRuCO]. The crystal structure
of 4b is consistent with the NMR data as shown in
Figure 2.13 There is a trimethylsilyl group bonded to
the R-carbon on the ruthenium atom. The Ru-C dis-
tance of 2.097 (11) Å is in the range of typical Ru-C
single bonds. The R-carbon is trisubstituted, and pyra-
midalization of the R-carbon resulted in loss of the
planarity of the ruthenacycle that had been present in
3. The complexes 4 and 5 were formed by R-trimethyl-
silyl group migration from the ruthenium atom to the
carbene ligand. Interestingly, the reverse migration
from the carbon atom to the ruthenium could be effected
by photochemical dissociation of the CO ligand in 4a ,
which photoirradiation of 4a (500 W Xe lamp, room
temperature, 5 h) gave rise to regenerated 3a in 73%
yield.
As described above, the reaction of cationic, coordi-
natively unsaturated ruthenium complexes 2 with Me3-
SiCHN2 gave the amidinato-carbene silyl complexes 3,
having a Ru-Si bond. A possible mechanism of the
conversion of 2 to 3 is illustrated in Scheme 3. The
initial step of the reaction may be formation of the
ruthenium-carbene intermediate A with concomitant
liberation of N2. Subsequent migration of an amidinate
nitrogen atom in A from the ruthenium center to the
carbon atom to form B follows. Such a ruthenium-
carbene formation was reported by Kirchner.2f At-
tempted detection of this silylcarbene intermediate by
NMR spectroscopy at low temperature failed because
the reaction was too rapid.14 In this sense, a reaction
pathway via A′ cannot be excluded at present.
The carbon-to-ruthenium trimethylsilyl group migra-
tion from the coordinatively unsaturated intermediate
B leads to formation of 3. As described above, this
pathway is supported by the following experimental
evidence: (1) existence of the metal fragment B was
demonstrated by isolation of the CO and isocyanide
adducts 4 and 5 and (2) the observation that B could
be photochemically generated from 4; this led to forma-
tion of 3. Experimental evidence for reversible R-tri-
methylsilyl group migration between the ruthenium
atom and the carbene ligand presented in this paper is
quite unique in the chemistry of silyl group rearrange-
ments.7,8,15,16 We are currently investigating detailed
mechanisms of the formation of 3 and the reversible
R-silyl migration.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details and analytical data for new complexes and
tables of X-ray structural data, including data collection
parameters, positional and thermal parameters, and bond
lengths and angles for 3b and 4b. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM010775W
(14) Experiments to detect intermediates in the reaction of 2a with
Me3SiCHN2 were carried out as follows: a CD2Cl2 solution (ca. 0.4 mL)
of 2a (10.8 mg, 8.5 µmol) was treated with a hexane solution of
Me3SiCHN2 (12 µmol) at -78 °C, and the mixture was immediately
(∼5 min) subjected to 1H NMR measurement at -80 °C. Only 3a was
observed as the organometallic product.
(13) Crystal data for 4b: C25H45F6N2OPRuSi; Mr ) 663.76, ortho-
rhombic, a ) 22.250(4) Å, b ) 9.234(3) Å, c ) 15.137(3) Å, U )
3110.1(12) Å3, T ) 293 K, space group Pna21 (No. 33), Z ) 4,
µ(Mo KR) ) 0.650 mm-1, 4682 reflections measured, 4682 unique
(Rint ) 0.000), 2155 observed (>2σ), final residuals R1 ) 0.0498,
wR2 ) 0.1263 (I > 2σ(I)); R1 ) 0.1777, wR2 ) 0.1730 (all data).
(15) (a) Auner, N.; Weis, J . Organosilicon Chemistry II; VCH:
Weinheim, Germany, 1996. (b) Brook, M. A. Silicon in Organic,
Organometallic, and Polymer Chemistry; Wiley-Interscience: New
York, 2000.
(16) Shelby, Q. D.; Lin, W.; Girolami, G. S. Organometallics 1999,
18, 1904-1910 and references sited therein.