Thermal Si-C bond cleavage of LRhH(SiAr3)(μ-H) (μ-Cl)RhH(SiAr3)L (Ar = C6H5, C 6H4F-p; L = P(i-Pr)3) to give LRhH(μ-SiAr3)(μ-SiAr2)(μ-Cl)RhHL containing sym

Article abstract of DOI:10.1021/om9804677

The reaction of dinuclear rhodium complex LRhH(SiPh₃)(μ-H) (μ-Cl)RhH(SiPh₃)L (1; L = P(i-Pr)₃) with excess HSi(C₆H₄F-p)₃ leads to replacement of the SiPh₃ ligands with the Si-(C<

Full text of DOI:10.1021/om9804677

Organometallics 1998, 17, 5721-5727
5721
Th er m a l Si-C Bon d Clea va ge of
LRh H(SiAr 3)(µ-H)(µ-Cl)Rh H(SiAr 3)L (Ar ) C6H5, C6H4F -p;
L ) P (i-P r )3) To Give LRh H(µ-SiAr 3)(µ-SiAr 2)(µ-Cl)Rh HL
Con ta in in g Sym m etr ica lly Br id gin g Tr ia r ylsilyl a n d
Dia r ylsilylen e Liga n d s
Take-aki Koizumi, Kohtaro Osakada,* and Takakazu Yamamoto*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, J apan
Received J une 8, 1998
The reaction of dinuclear rhodium complex LRhH(SiPh3)(µ-H)(µ-Cl)RhH(SiPh3)L (1; L )
P(i-Pr)3) with excess HSi(C6H4F-p)3 leads to replacement of the SiPh3 ligands with the Si-
(C6H4F-p)3 group to give LRhH[Si(C6H4F-p)3](µ-H)(µ-Cl)RhH[Si(C6H4F-p)3]L (2) at room
temperature. HSiPh2(C6H4F-p) and HSiPh(C6H4F-p)2 also react with 1 to give LRhH[SiPh2-
(C6H4F-p)](µ-H)(µ-Cl)RhH[SiPh2(C6H4F-p)]L (3) and LRhH[SiPh(C6H4F-p)2](µ-H)(µ-Cl)RhH-
[SiPh(C6H4F-p)2]L (4), respectively. Heating of benzene or toluene solution of 1 and 2 at 60
°C results in Si-C bond cleavage of a triarylsilyl ligand and affords LRhH(µ-SiAr3)(µ-SiAr2)-
(µ-Cl)RhHL (7, Ar ) Ph; 8, Ar ) C6H4F-p) accompanied by liberation of benzene and
fluorobenzene, respectively. The NMR (1H and 31P) spectra of 7 and 8 indicate symmetrical
coordination of the bridging triarylsilyl and diarylsilylene groups to two Rh centers. The
reaction of 1 to form 7 at 55-70 °C obeys first-order kinetics with the kinetic parameters:
∆Gq ) 112 kJ mol-1, ∆Hq )129 kJ mol-1, and ∆Sq ) 58 J mol-1 deg-1 at 298 K. Complexes
2-4 also undergo thermal Si-C bond cleavage of a triarylsilyl ligand to liberate fluorobenzene
as the organic product. The rate constants of the reaction increase in the order 2 < 4 < 3 <
1.
Sch em e 1
In tr od u ction
Late transition metal complexes often cleave Si-C
bonds of organosilicon compounds or Si-containing
organic ligands under mild conditions. Scheme 1 sum-
marizes several reaction patterns previously reported.
Complexes of Fe and Ru with 2-silylethyl ligand undergo
â-silyl group elimination to form a new metal-Si bond
(i).1 The reaction is involved in the transition-metal-
catalyzed transsilylation of vinylsilane and related
reactions as the crucial step.2 A mononuclear Pt com-
plex3 and a dinuclear Ru complex4 containing a trim-
ethylsilylmethyl ligand undergo scission of Si-Me or
CH2-Si bond to give methylene-group-coordinated metal
complexes (ii). A (triorganosilyl)iridium(III) complex was
reported to yield a thermal reaction product containing
a triflate-substituted diorganosilyl ligand. The reaction
most probably proceeds through R-elimination of the
organic group to give a silylene-coordinated intermedi-
ate followed by its reaction with a triflate counterion to
form a Si-OTf bond (iii).5 The oxidative addition of an
unstrained or strained C-Si bond to low-valent Rh and
Ru complexes was studied in detail (iv).6 Synthetic
organic reactions involving similar oxidative addition
of the Si-C bond to a Cu or a Pd complex were recently
reported.7
(1) (a) Randolph, C. L.; Wrighton, M. S. J . Am. Chem. Soc. 1986,
108, 3366. (b) Wakatsuki, Y.; Yamazaki, H.; Nakano, M.; Yamamoto,
Y. J . Chem. Soc., Chem. Commun. 1991, 703.
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349. (b) Seki, Y.; Takeshita, K.; Kawamoto, K. J . Organomet. Chem.
1989, 369, 117. (c) Suzuki, T.; Mita, I. J . Organomet. Chem. 1991, 414,
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1997, 16, 292.
10.1021/om9804677 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 11/25/1998

5722 Organometallics, Vol. 17, No. 26, 1998
Koizumi et al.
Sch em e 2
Dinuclear complexes of Pt, Ru, and Rh, which contain
a nonbridging silyl ligand, provide another kind of Si-C
bond activation. Scheme 2 depicts the oxidative addition
of an Si-C bond in a triorganosilyl group bonded to one
metal to the other metal center to afford a complex with
a bridging diorganosilylene ligand. Such reactions in
bimetallic systems occur smoothly, probably because of
the high stability of the bridging coordination of the
silylene group of the product as well as of the Si-C bond
to be activated and the metal center, which are close to
each other.8b,9
In this paper, we report the thermally induced Si-C
bond cleavage of LRhH(SiAr3)(µ-H)(µ-Cl)RhH(SiAr3)L
type complexes to afford new dinuclear Rh complexes
with bridging triarylsilyl and diarylsilylene ligands.
Part of this work has been reported in a preliminary
form.10
F igu r e 1. Perspective drawing of complex 1. The molecule
has a crystallographic C2 symmetry around the midpoint
of the Rh-Rh bond. Selected bond distances (Å) and angles
(deg): Rh-Rh, 2.815(1); Rh-Cl, 2.413(2); Rh-P, 2.314(2);
Rh-Si, 2.289(2); Rh-H(1), 1.59(2); Rh-H(2), 1.37(5); Rh-
Rh-Cl, 54.32(4); Rh-Rh-P, 150.97(6); Rh-Rh-Si, 101.74-
(6); Rh-Rh-H(1), 27.(1); Rh-Rh-H(2), 119.(1); Cl-Rh-
P, 98.98(7); Cl-Rh-Si, 127.97(6); Cl-Rh-H(1), 81.(1);
Cl-Rh-H(2), 165.(2); P-Rh-Si, 104.58(8); P-Rh-H(1),
167.6(2); P-Rh-H(2), 82.(1); Si-Rh-H(1), 84.(1); Si-Rh-
H(2), 65.(2); H(1)-Rh-H(2), 93.(2); Rh-Cl-Rh, 71.37(8);
Rh-H(1)-Rh, 126.
Resu lts
Exch a n ge Rea ction of LRh H(SiP h 3)(µ-H)(µ-Cl)-
Rh H(SiP h 3)L (1) w ith Tr ia r ylsila n e a t Room Tem -
p er a tu r e. LRhH(SiPh3)(µ-H)(µ-Cl)RhH(SiPh3)L (1, L )
P(i-Pr)3)11 reacts with HSi(C6H4F-p)3 in a 1:10 molar
ratio at room temperature to give LRhH[Si(C6H4F-p)3]-
(µ-H)(µ-Cl)RhH[Si(C6H4F-p)3]L (2) in 78% yield, as
shown in eq 1. The molecular geometries of 1 and 2 are
shown in Figures 1 and 2, respectively. Two Rh centers
having triarylsilyl and P(i-Pr)3 ligands are bridged by
hydrido and chloro ligands, similarly to the previously
F igu r e 2. Perspective drawing of complex 2. The molecule
has a crystallographic C2 symmetry around the midpoint
of the Rh-Rh bond. Selected bond distances (Å) and angles
(deg): Rh-Rh, 2.810(2); Rh-Cl, 2.415(4); Rh-P, 2.309(4);
Rh-Si, 2.293(4); Rh-H(1), 1.55; Rh-H(2), 1.30; Rh-Rh-
Cl, 54.42(8); Rh-Rh-P, 151.6(1); Rh-Rh-Si, 101.0(1);
Rh-Rh-H(1), 25; Rh-Rh-H(2), 136; Cl-Rh-P, 98.5(1);
Cl-Rh-Si, 127.2(1); Cl-Rh-H(1), 80; Cl-Rh-H(2), 164;
P-Rh-Si, 104.7(2); P- Rh-H(1), 168; P-Rh-H(2), 67; Si-
Rh-H(1), 85; Si-Rh-H(2), 67; H(1)-Rh-H(2), 111; Rh-
Cl-Rh, 71.2(1); Rh-H(1)-Rh, 130.
(7) (a) Ito, H.; Sensui, H.; Arimoto, K.; Miura, K.; Hosomi, A. Chem.
Lett. 1997, 639. (b) Nishihara, Y.; Ikegashira, K.; Mori, A.; Hiyama,
T. Chem. Lett. 1997, 1233. (c) Ikegashira, K.; Nishihara, Y.; Hiraba-
yashi, K.; Mori, A.; Hiyama, T. Chem. Commun. 1997, 1039.
(8) (a) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.; Pugh,
N. J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem. Soc.,
Dalton Trans. 1980, 659. (b) Takao, T.; Yoshida, S.; Suzuki, H.; Tanaka,
M. Organometallics 1995, 14, 3855. (c) Osakada, K.; Koizumi, T.;
Yamamoto, T. Bull. Chem. Soc. J pn. 1997, 70, 189.
(9) (a) Hoyano, J . K.; Elder, M.; Graham, W. A. G. J . Am. Chem.
Soc. 1969, 91, 4568. (b) Crozat, M. M.; Watkins, S. F. J . Chem. Soc.,
Dalton Trans. 1972, 2512. (c) Hencken G.; Weiss, E. Chem. Ber. 1973,
106, 1747. (d) Simon, G. L.; Dahl, L. F. J . Am. Chem. Soc. 1973, 95,
783. (e) Cowie, M.; Bennet, M. J . Inorg. Chem. 1977, 16, 2321, 2325.
(f) McDonald, R.; Cowie, M. Organometallics 1990, 9, 2468. (g) Wang,
W.-D.; Eisenberg, R. J . Am. Chem. Soc. 1990, 112, 1833. (h) Wang,
W.-D.; Hommeltoft, S. I.; Eisenberg, R. Organometallics 1988, 7, 2417.
(i) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J . Organometallics 1991,
10, 2537; 1996, 15, 2871. (j) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J .
Inorg. Chim. Acta 1994, 222, 345. (k) Campion, B. K.; Heyn, R. H.;
Tilley, T. D. Organometallics 1992, 11, 3918. (l) Suzuki, H.; Takao, T.;
Tanaka, M.; Moro-oka, Y. J . Chem. Soc., Chem. Commun. 1992, 476.
(m) Tobita, H.; Shinagawa, I.; Ohnuki, S.; Abe, M.; Izumi, H.; Ogino,
H. J . Organomet. Chem. 1994, 473, 187. (n) Simons, R. S.; Tessier, C.
A. Organometallics 1996, 15, 2604. (o) Bourg, S.; Boury, B.; Carre´, F.;
Corriu, R. J . P. Organometallics 1997, 16, 3097.
reported X-ray structure of LRhH[Si(C6H4OCF3-p)3](µ-
H)(µ-Cl)RhH[Si(C6H4OCF3-p)3]L. The Rh-Rh distances
(2.810(2) and 2.815(1) Å) are in the range of that
previously reported for dinuclear organorhodium com-
plexes with the Rh-Rh bond.8c,9 g-j,12 Two nonbridging
hydrido ligands of 1 and 2 are situated at anti positions
of the Rh-Cl-Rh-H1(bridging) four-membered ring
(12) (a) Isobe, K.; de Miguel, A. V; Bailey, P. M.; Okeya, S.; Maitlis,
P. M. J . Chem. Soc., Dalton Trans. 1983, 1441. (b) Okeya, S.; Meanwell,
N. J .; Taylor, B. F.; Isobe, K.; de Miguel, A. V.; Maitlis, P. M. J . Chem.
Soc., Dalton Trans. 1984, 1453. (c) Isobe, K.; Okeya, S.; Meanwell, N.
J .; Smith, A. J .; Adams, H.; Maitlis, P. M. J . Chem. Soc., Dalton Trans.
1984, 1215.
(10) Osakada, K.; Koizumi, T.; Yamamoto, T. Angew. Chem., Int.
Ed. Engl. 1998, 37, 349.
(11) Osakada, K.; Koizumi, T.; Yamamoto, T. Organometallics 1997,
16, 2063.

Si-C Bond Cleavage To Afford New Rh Complexes
Organometallics, Vol. 17, No. 26, 1998 5723
F igu r e 4. Changes in the 1H NMR spectra (hydrido
region) during thermal reaction of 1 to give 7 at 70 °C.
Signals a and b are assigned to bridging and nonbridging
hydrido ligands of 1, while signal c is assigned to the
hydrido ligands of 7.
F igu r e 3. 1H NMR spectrum of the reaction product of
HSi(C6H4Me-p)3. The signals in the range of δ -15.5 to
-16.1 are assigned to nonbridging hydrido ligands of (a)
1, (b) 6′, and (c) 6.
plane in order to reduce steric repulsion between the
triarylsilyl ligands. The NMR (1H and 31P) spectra of 2
are similar to those of 1 and are consistent with the
crystal structure.
reactivity of HSiAr3 (Ar ) C6H4Me-p, C6H4F-p) with
initially formed mononuclear RhCl(H)(SiAr3)L2.
Th er m a l Si-C Bon d Clea va ge Rea ction of 1 a n d
2. Heating of a benzene or toluene solution of 1 and 2
at 60 °C leads to the conversion of the complexes to
LRhH(µ-SiAr3)(µ-SiAr2)(µ-Cl)RhHL (7, Ar ) Ph; 8, Ar
) C6H4F-p), as shown in eq 3. Gas chromatographic
Triarylsilanes with electron-withdrawing substitu-
ents, HSiPh2(C6H4F-p), HSiPh(C6H4F-p)2, and HSi-
(C6H4CF3-p)3, also react with 1 at room temperature to
give dinuclear complexes LRhH[SiPh2(C6H4F-p)](µ-H)-
(µ-Cl)RhH[SiPh2(C6H4F-p)]L (3), LRhH[SiPh(C6H4F-p)2]-
(µ-H)(µ-Cl)RhH[SiPh(C6H4F-p)2]L (4), and LRhH[Si(C6H4-
CF3-p)3](µ-H)(µ-Cl)RhH[Si(C6H4CF3-p)3]L (5), respec-
tively. Complexes 3 and 4 were isolated and character-
ized by NMR spectroscopy, and their spectra are similar
to those of 1 and 2, while complex 5 was characterized
in situ by NMR spectroscopy without isolation.
The reaction of HSi(C6H4Me-p)3 with 1 in a 4:1 molar
ratio leads to the formation of a mixture of LRhH[Si-
(C6H4Me-p)3](µ-H)(µ-Cl)RhH[Si(C6H4Me-p)3]L (6), LRhH-
[Si(C6H4Me-p)3](µ-H)(µ-Cl)RhH(SiPh3)L (6′), and unre-
acted 1 in a molar ratio of 44:12:44 (eq 2). Figure 3
analyses of the product showed quantitative formation
of benzene and fluorobenzene, respectively. The X-ray
structure of 8, having symmetrical coordination of the
triarylsilyl and diarylsilylene ligands, was shown in our
1
preliminary report.10 The H NMR spectra of 7 and 8
exhibit signals due to two equivalent hydrido ligands
at δ -17.40 and -17.60, respectively. The splitting
pattern assigned to the AA′ part of an AA′MM′XX′
pattern indicates nonbridging coordination of the hy-
drido ligand. In agreement with the presence of two
unequivalent Si centers bridging to two Rh centers, the
29Si{1H} NMR spectrum of 7 contains signals at δ 157.8
and 28.7. The former signal appears as a triplet of
triplets, while the latter is observed as a triplet. The
former signal may be assigned to the Si of the SiPh2
ligand because the 29Si NMR signal of most bridging
diorganosilylene ligands bonded to two transition metal
centers was observed at lower magnetic field positions
than δ 80.8b,9k,n,13
1
depicts the H NMR spectrum of the mixture. The four
signals in the range of δ -15.5 to -16.1 are assigned to
the nonbridging hydrido ligands of the complexes. The
signal at δ -15.78 due to 1 overlaps with that due to 6
(δ -15.81), whereas two signals at δ -15.59 and -16.01
with equal intensity are assigned to the two nonbridging
hydrido ligands of 6′ having an unsymmetrical struc-
ture. Similar reaction in a 10:1 molar ratio leads to for-
mation of not only 1, 6, and 6′ (6:68:26) but also a new
complex (ca. 25% of the product) formed through further
reaction of 6 and 6′ under the reaction conditions.
Complex 1 was prepared by reacting HSiPh3 with
RhClL2 to form RhCl(H)(SiPh3)L2 initially, which was
followed by its further reaction with HSiPh3.11 Attempts
to obtain 2 and 6 by a similar reaction of the triarylsi-
lane with RhClL2 were unsuccessful owing to the low
The 1H and 31P{1H} NMR spectra obtained during the
reaction contain signals of the above starting complexes
and the product only. Figure 4 shows a decrease in the
1H NMR signal intensity of the hydrido of 1 and an
increase in that of 7 during the reaction at 70 °C. The
first-order plots of the reaction obtained from peak
(13) (a) Bikovetz, A. L.; Kuzmin, O. V.; Vdovin, V. M.; Krapivin, A.
M. J . Organomet. Chem. 1980, 194, C33. (b) Malisch, W.; Ries, W.
Angew. Chem., Int. Ed. Engl. 1980, 17, 120. (c) Malisch, W.; Wekel,
H.-U.; Grob, I.; Ko¨hler, F. H. Z. Naturforsch. 1982, 37b, 601. (d)
Kawano, Y.; Tobita, H.; Ogino, H. J . Organomet. Chem. 1992, 428,
125. (e) Tobita, H.; Shinagawa, I.; Ohnuki, S.; Abe, M.; Izumi, H.;
Ogino, H. J . Organomet. Chem. 1994, 473, 187. (f) Takao, T.; Suzuki,
H. Organometallics 1994, 13, 2554.

5724 Organometallics, Vol. 17, No. 26, 1998
Koizumi et al.
Dinuclear Fe and Ru complexes with bridging methyl-
ene and carbonyl ligands and a terminal triorganosilyl
ligand undergo smooth silyl ligand exchange on addition
of triorganosilane.13d,14 Our previous study on the reac-
tion of diarylsilane with mer-RhCl(H)(SiHAr2)(PMe3)3
established the facile exchange of the diarylsilyl ligand
through reductive elimination of diarylsilane from the
complex followed by its oxidative addition.15 Measure-
ment of the equilibrium constants revealed the relative
stability of the Rh-Si bond in the order Rh-SiH(C6H4F-
p)2 > Rh-SiHPh2 > Rh-SiH(C6H4Me-p)2. Reactions in
eq 1 turn the SiPh3 ligand of 1 into the fluorinated
triarylsilyl ligand of the product, whereas exchange of
the SiPh3 ligand of 1 on addition of HSi(C6H4Me-p)3
gives 6 and 6′ together with unreacted 1. These results
seem to suggest a lower thermodynamic stability of the
Rh-Si(C6H4Me-p)3 bond than the Rh-Si(C6H4F-p)3
bond of the present dinuclear complexes.
F igu r e 5. First-order plots of reaction of 1 to 7 obtained
from changes in 1H NMR peak intensity of the hydrido
ligand of 1 at (a) 328, (b) 333, (c) 338, and (d) 343 K.
The bridging coordination of a triorganosilyl group to
Na, Al, and B to form the M-Si-M bond is regarded
as an analogue of the M-H-M three-center, two-
electron bond of nontransition metals.16 Most of the silyl
ligand bridged dinuclear transition metal complexes
contain an SiHR2 ligand that is bonded to one metal
through a σ-bond and to another metal through the Si-
H-M three-center, two-electron bond, as shown in
Chart. Such µ-η1,η2-coordination of the ligand renders
the distances between the two M-Si bonds different.9,17
There have been only a few reports on transition metal
complexes with bridging triorganosilyl ligands. A di-
nuclear platinum complex with bridging SiMeCl2 ligand
was reported although no crystallographic study was
done.18 Dinuclear or tetranuclear copper complexes with
a sterically demanding Si(SiMe3)3 group as the bridging
ligands were characterized structurally.19 A diplatinum
complex with symmetrically bridging triorganophos-
phine that is isolobal to the triorganosilyl anion was
reported by Braunstein and co-workers.20
Complex 8 obtained in this study showed unique
structural properties as follows. The distances between
Rh centers and the Si atom of the triarylsilyl ligand are
similar (2.444(4) and 2.487(3) Å) and are significantly
longer than the bonds between Si of the silylene ligand
and Rh centers (2.290(3) and 2.250(3) Å) as well as the
Rh-Si σ-bond distances already reported (2.203-2.379
Å). They are comparable even to the Rh-Si distance in
a Rh-H-Si three-center, two-electron bond (2.487 Å).
This contrasts with the previous observation that the
Cu complexes containing Si(SiMe3)3 ligands showed no
significant differences in the distances between the
bridging and nonbridging Cu-Si bonds.
Ta ble 1. Kin etic Resu lts of Th er m a l Rea ction of
LRh H(SiAr 3)(µ-H)(µ-Cl)Rh H(SiAr 3)L a n d
LRh H(SiAr Ar ′2)(µ-H)(µ-Cl)Rh H(SiAr 2Ar ′)L
complex
Ar
Ar′
temp/K
k/s-1
1
C6H5
-
-
-
-
-
328
333
338
343
333
333
333
2.16 × 10-5
4.41 × 10-5
8.51 × 10-5
1.82 × 10-4
1.42 × 10-5
3.01 × 10-5
1.96 × 10-5
2
3
4
C6H4F-p
C6H4F-p
C6H5
C6H5
C6H4F-p
intensity relative to an internal standard are linear at
55-70 °C and indicate the first-order kinetics with
respect to [1], as shown in Figure 5. Table 1 summarizes
the rate constants. The kinetic parameters were ob-
tained from the temperature dependence of the rate
constants as ∆Gq ) 112 kJ mol-1, ∆Hq ) 129 kJ mol-1
,
and ∆Sq ) 58 J mol-1 deg-1 at 298 K.
The thermal reaction of 3 and 4 gives fluorobenzene
rather than benzene. The selective activation of an Si-
C6H4F-p bond should afford LRhH[µ-SiPh2(C6H4F-p)]-
[µ-SiPh(C6H4F-p)](µ-Cl)RhHL and LRhH[µ-SiPh(C6H4F-
1
p)2][µ-SiPh(C6H4F-p)](µ-Cl)RhHL, respectively. The H
NMR spectrum of the product of the reaction of 4 shows
the hydrido signal (δ - 17.60) whose complicated peak
pattern indicates the presence of isomers caused by a
difference in position of the Ph group in the bridging
SiPh(C6H4F-p) and SiPhn(C6H4F-p)3-n (n ) 1,2) ligands.
The rate constants of the reaction increase in the order
2 < 4 < 3 < 1 as shown in Table 1, suggesting that the
introduction of fluorine at the para position of the
triarylsilyl ligand retards the Si-C bond cleavage
reaction.
(14) (a) Tobita, H.; Kawano, Y.; Shimoi, M.; Ogino, H. Chem. Lett.
1987, 2247. (b) Akita, M.; Hua, R.; Oku, T.; Tanaka, M.; Moro-oka, Y.
Organometallics 1996, 15, 4162.
(15) Osakada, K.; Sarai, S.; Koizumi, T.; Yamamoto, T. Organome-
tallics 1997, 16, 3973.
Discu ssion
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Chem., Int. Ed. Engl. 1989, 28, 923.
The dinuclear Rh complexes LRhH(SiAr3)(µ-H)(µ-Cl)-
RhH(SiAr3)L undergo exchange of the triarylsilyl ligand
on addition of another triarylsilane and thermal Si-C
bond activation of an SiAr3 ligand to form a product with
bridging triarylsilyl and diarylsilylene ligands. The
exchange of the organosilyl ligand was also reported to
occur in several other mononuclear and dinuclear
transition metal complexes containing a M-Si bond.

Si-C Bond Cleavage To Afford New Rh Complexes
Organometallics, Vol. 17, No. 26, 1998 5725
Sch em e 3
to retard the initial reaction involving activation of the
Rh-Si bond of nonbridging triarylsilyl ligand turning
it into a semibridging one. The pathway contains a
smaller number of reaction steps than the other and
does not require sterically congested intermediate com-
plexes. Although the σ-bond metathesis reaction was
uncommon in electron rich late transition metal com-
plexes with phosphine ligands, such a sterically rigid
system with close Rh-H and Si-aryl bonds may enable
the electronically disfavored bond activation involving
the four-center transition state.
The pathways in Schemes 3 and 4 seem to be more
favored than the others, while it is not feasible to decide
which of the mechanisms is operative for the Si-C bond
cleavage reaction.21 Other reactions involving Rh-Rh
bond splitting or a shift of the bridging chloro ligand to
a terminal position may also trigger the Si-C bond
cleavage.
Sch em e 4
Recently, the triorganosilyl ligand transfer from one
metal to the other in a dinuclear metal system was
found by Braunstein, Girolami, Akita, and their respec-
tive co-workers.3,22 These reactions should involve a
triorganosilyl group bridging a dinuclear complex as the
transition-state species or the unstable intermediate
since these reactions proceed very rapidly under mild
conditions. The present study has provided the di-
nuclear Rh complexes with bridging triarylsilyl ligands.
The complexes have high thermal stability despite the
significantly longer Rh-Si bond than the common Rh-
Si single bond observed in the crystal structure. The
formation of the complexes involves a change in the
coordination of a nonbridging triarylsilyl ligand to a
bridging one, which corresponds to the process of
converting the nonbridging triorganosilyl ligand in the
dinuclear complexes to a high-energy species during the
above triorganosilyl ligand transfer reaction.
Several pathways are conceivable for the thermal
reaction of 1 and 2 to give 7 and 8, respecitvely. Scheme
3 shows a pathway involving R-elimination of an aryl
group of the triarylsilyl ligand of the starting complex
followed by reductive elimination of arene and a change
in coordination of the diarylsilylene group to a more
stable bridging one. The reaction of 3 and 4 leading to
selective formation of fluorobenzene and the rate con-
stants in the order 2 < 4 < 3 < 1 can be rationalized by
assuming that the reaction involves formation of an
intermeidate (A) as the rate determining step. Fluoro
substituents of the produced diarylsilylene ligand de-
stabilize the intermediate and retard the reaction, while
the Si-C6H4F-p bond is cleaved more readily than the
Si-Ph bond to leave a smaller number of fluorine
substituents in the diarylsilylene ligand. On the other
hand, products with diarylsilyl (SiHAr2) or chlorodiar-
ylsilyl (SiClAr2) ligands, which may be expected from
the chloro(hydrido)rhodium intermediate having a Rhd
Si double bond, were not formed at all.
Scheme 4 depicts a plausible reaction pathway in-
volving an intramolecular σ-bond metathesis type reac-
tion of a Si-Ar bond with a Rh-H bond. The direct
elimination of Ar-H followed by a change in the
coordination mode of a hydrido and a triarylsilyl ligand
between bridging and nonbridging will lead to the
product. The positive activation entropy of the reaction
is consistent with the mechanism. The elimination of
fluorobenzene from the reaction of 3 and 4 can be
attributed to the relief of the mismatching of polariza-
tion of the Siδ+-Cδ- and Rhδ+-Hδ- bonds in the initial
reaction caused by the electron-withdrawing fluorine
substituent. The fluorine substituent serves also to
stabilize the Rh-Si bond of the starting complex and
Exp er im en ta l Section
Gen er a l Con sid er a tion s, Mea su r em en t, a n d Ma ter ia ls.
Manipulation of Rh complexes was carried out under nitrogen
or argon using standard Schlenk techniques. RhClL2, 1, and
triarylsilanes were prepared according to the literature.23
HSiPh(C6H4F-p)2 and HSiPh2(C6H4F-p) were prepared from
reactions of FC6H4MgBr with HSiPhCl2 and with HSiPh2Cl,
respectively. NMR spectra (1H and 31P) were recorded on a
J EOL EX-400 spectrometer. 31P{1H} and 29Si{1H} NMR spec-
tra were referenced to external 85% H3PO4 and to external
SiMe4, respectively. Elemental analyses were carried out by
(21) Rate constants of the thermal reaction of 1 are increased
significantly by addition of HSiPh3 (60 °C, [1]0 ) 0.053 mM in benzene);
105k (s-1) ) 4.41 ([HSiPh3] ) 0), 7.32 ([HSiPh3]/[1] ) 1.02), 13.2
([HSiPh3]/[1] ) 2.00), and 11.5 ([HSiPh3]/[1] ) 4.00). There seem to
be two possible rationales for the remarkable influence of the additive.
Added HSiPh3 may shift an equilibrium of reductive elimination of
HSiPh3 and its reoxidative addition to regenerate 1 and serve to
increase the concentration of 1 in the equilibrated mixture. Alterna-
tively, the Si-C bond cleavage reaction involving a different mecha-
nism from that without addition of HSiPh3 may occur in the presence
of added HSiPh3. The observations do not seem to provide any clue to
elucidate the mechanism.
(22) (a) Braunstein, P.; Knorr, M.; Hirle, B.; Reinhard, G.; Schubert,
U. Angew. Chem., Int. Ed. Engl. 1992, 31, 1583. (b) Knorr, M.;
Braunstein, P.; Tiripicchio, A.; Ugozzoli, F. Organometallics 1995, 14,
4910. (c) Knorr, M.; Hallauer, E.;. Huch, V.; Veith, M.; Braunstein, P.
Organometallics 1996, 15, 3868. (d) Braunstein, P.; Knorr, M. J .
Organomet. Chem. 1995, 500, 21. (e) Akita, M.; Oku, T.; Hua, R.; Moro-
oka, Y. J . Chem. Soc., Chem. Commun. 1993, 1670.
(23) (a) Werner, H.; Wolf, J .; Ho¨hn, A. J . Organomet. Chem. 1985,
287, 395. (b) Price, F. P. J . Am. Chem. Soc. 1947, 69, 2600. (c) Benkeser,
R. A.; Foster, D. J . J . Am. Chem. Soc. 1952, 74, 5314. (d) Steward, O.
W.; Pierce, O. R. J . Am. Chem. Soc. 1961, 83, 1916.

5726 Organometallics, Vol. 17, No. 26, 1998
Koizumi et al.
Ta ble 2. Cr ysta l Da ta a n d Deta ils of Str u ctu r e
Refin em en t of 1 a n d 2
a Yanaco MT-5 CHN autocorder. Gas chromatographic mea-
surement was carried out on a Shimadzu GC-8A equipped with
a 2 m Silicone OV-1 packed column.
compd
formula
mol wt
cryst syst
space group
a (Å)
1
C
2
P r ep a r a tion of 2-5. To a toluene (5 mL) solution of 1 (41
mg, 0.038 mmol) was added HSi(C6H4F-p)3 (120 mg, 0.38
mmol) at room temperature. After stirring for 2 h at that
temperature, the solvent was reduced to ca. 2 mL under
vaccum. Removal of a small amount of insoluble solid followed
by addition of pentane to the filtrate resulted in separation of
54H75ClP2Si2Rh2 C54H69ClF6P2Si2Rh2
1083.57
monoclinic
C2/c (No. 15)
21.140(5)
10.465(4)
24.313(3)
92.27(1)
5374
4
7.89
2256
1.340
1191.51
monoclinic
C2/c (No. 15)
21.400(9)
10.678(4)
24.277(10)
93.49(3)
5537
4
7.87
2448
1.430
b (Å)
c (Å)
â (deg)
V (Å3)
Z
1
2 as yellow crystals (35 mg, 78%). H NMR: δ 7.59 (dd, 12H,
ortho, J (HH) ) 6 Hz, J (HF) ) 7 Hz), 6.90 (dd, 12H, meta,
J (HH) ) 6 Hz, J (HF) ) 9 Hz), 1.54 (m, 6H, P-CH, J ) 7 Hz),
0.82 (br, 36H, CH3), -12.55 (tt, 1H, Rh-H-Rh, J (Rh-H) )
58 Hz, J (P-H) ) 25 Hz), -16.07 (AA′ part of an AA′MM′XX′
pattern, 2H, Rh-H). 31P{1H} NMR: δ 54.2 (AA′ part of an
AA′XX′ pattern). Anal. Calcd for C54H68ClF6P2Rh2Si2: C, 54.43;
H, 5.84. Found: C, 53.98; H, 5.97.
µ (cm-1
F(000)
)
Dcalcd (g cm-3
)
crystal size
0.3 × 0.4 × 0.4
0.3 × 0.5 × 0.5
(mm × mm × mm)
2 θ range (deg)
measrd reflcns
unique reflcns
used reflcns (I> 3σ(I)) 2255
no. of variables
5.0-50.0
4507
4355
5.0-55.0
5339
5360
1804
303
Reactions of HSiPh2(C6H4F-p) and of HSiPh(C6H4F-p)2 with
1 gave complexes LRhH[SiPh2(C6H4F-p)](µ-H)(µ-Cl)RhH[SiPh2-
(C6H4F-p)]L (3) (68%) and LRhH[SiPh(C6H4F-p)2](µ-H)(µ-Cl)-
RhH[SiPh(C6H4F-p)2]L (4) (28%), respectively. Data of 3
282
R
0.042
0.032
1.35
0.061
0.041
2.15
1
(obtained in a toluene solvated form). H NMR (C6D6): δ 7.76
a
Rw
(d, 8H, ortho hydrogen of SiPh, J ) 6 Hz), 7.74 (t, 4H, ortho
hydrogen of SiC6H4F-p, J (HH) ) J (HF) ) 8 Hz), 7.13-7.23
(m, 12 H, meta and para hydrogen of SiPh), 6.87 (t, 4H, meta
hydrogen of SiC6H4F-p, J (HH) ) J (HF) ) 8 Hz), 1.7 (br, 6H,
P-CH), 0.7-1.0 (br, 36H, CH3), -12.28 (tt, 1H, Rh-H-Rh,
J (Rh-H) ) 58 Hz, J (P-H) ) 25 Hz), -15.83 (AA′ part of an
AA′MM′XX′ pattern, 2H, Rh-H). 31P{1H} NMR: δ 53.6 (AA′
part of an AA′XX′ pattern). Anal. Calcd for C54H73ClF2P2Rh2-
Si2‚C7H8: C, 60.47; H, 6.74. Found: C, 60.23; H, 6.36. Data of
4: 1H NMR (C6D6): δ 7.74 (d, 4H, ortho hydrogen of SiPh, J
) 6 Hz), 7.67 (dd, 8H, ortho hydrogen of SiC6H4F-p, J (HH) )
J (HF) ) 8 Hz), 7.12-7.22 (m, 6 H, meta and para hydrogen of
SiPh), 6.91 (t, 8H, meta hydrogen of SiC6H4F-p, J (HH) ) J (HF)
) 8 Hz), 1.6 (br, 6H, P-CH), 0.7-1.0 (br, 36H, CH3), -12.42
(tt, 1H, Rh-H-Rh, J (Rh-H) ) 59 Hz, J (P-H) ) 23 Hz),
-15.98 (AA′ part of an AA′MM′XX′ pattern, 2H, Rh-H). 31P-
{1H} NMR: δ 53.9 (AA′ part of an AA′XX′ pattern). Anal. Calcd
for C54H71ClF4P2Rh2Si2: C, 56.13; H, 6.19. Found: C, 55.68;
H, 5.80.
GOF
a
Weighting scheme [σ(Fo)2]-1
.
benzene in a quantitative amount. The 31P{1H} NMR spectrum
of the reaction mixture showed peaks due to 7 only. Addi-
tion of pentane to the reaction mixture led to the separa-
tion of 7 as yellow orange crystals that were collected by
filtration, washed with pentane, and dried in vacuo (71 mg,
29%). The low isolated yield is due to loss of the product
during the isolation. 1H NMR (C6D6, 400 MHz at 25 °C): δ
6.9-8.2 (m, 25H, aromatic), 1.18 (m, 6H, P-CH-CH3, J ) 7.3
Hz), 0.95 (qd, 18H, P-CH-CH3, J ) 7.3 Hz), -17.40 (AA′ part
of an AA′MM′XX′ pattern, 2H, Rh-H). 31P{1H} NMR (C6D6,
160 MHz at 25 °C): δ 57.4 (AA′ part of an AA′XX′ pattern).
29Si{1H} NMR (C6D6, 80 MHz at 25 °C): δ 157.8 (t, J ) 50
Hz), 28.7 (tt, J ) 50 and 8 Hz). Anal. Calcd C48H69ClP2Rh2Si2:
C, 57.34; H, 6.92; Cl, 3.53. Found: C, 57.67; H, 7.01; Cl, 2.93.
1
Similar heating of a toluene solution of 2 gave 8 (51%). H
Similar reaction of HSi(C6H4CF3-p)3 with 1 led to conversion
of the Rh complex to LRhH[Si(C6H4CF3-p)3](µ-H)(µ-Cl)RhH-
[Si(C6H4CF3-p)3]L (5), which showed NMR signals similar to
1 and 2. Isolation of 5 as crystals was not feasible. Data of 5:
1H NMR (C6D6): δ 7.58 (d, 12H, ortho, J ) 7 Hz), 7.47 (d, 12H,
meta, J ) 7 Hz), 1.42 (m, 6H, P-CH), 0.7 (br, 36H, CH3),
-12.69 (tt, 1H, Rh-H-Rh, J (Rh-H) ) 56 Hz, J (P-H) ) 25
Hz), -16.21 (AA′ part of an AA′MM′XX′ pattern, 2H, Rh-H).
31P{1H} NMR: δ 54.9 (AA′ part of an AA′XX′ pattern).
NMR: δ 6.76-7.88 (m, 20H, aromatic), 1.12 (m, 6H, P-CH-
CH3), 0.86 (qd, 18H, P-CH-CH3) -17.60 (AA′ part of an
AA′MM′XX′ pattern, 2H, Rh-H). 31P{1H} NMR (C6D6, 160
MHz at 25 °C): δ 58.2 (AA′ part of an AA′XX′ pattern). 29Si-
{1H} NMR (C6D6, 80 MHz at 25 °C): δ 155.2 (t, J ) 50 Hz),
21.9 (tt, J ) 50 and 8 Hz). Anal. Calcd for C48H64ClF5P2Rh2-
Si2: C, 52.63; H, 5.89. Found: C, 52.81; H, 5.89.
Kin etic Stu d y. To an NMR tube containing 1 (23 mg) was
introduced C6D6 (0.40 mL) by vacuum-transfer technique.
Change of peak intensity of hydrido peaks was monitored
relative to tetramethylsilane as internal standard by keeping
the temperature of the NMR probe at 60 °C. Kinetic measure-
ment of 1 at the other temperatures and of 2-4 were carried
out analogously.
Rea ction of 1 w ith HSi(C6H4Me-p)3. To a toluene (1 mL)
solution of 1 (91 mg, 0.084 mmol) was added HSi(C6H4Me-p)3
(102 mg, 0.34 mmol). The solution was stirred for 24 h at room
temperature. After removing the solvent under vacuum, the
1
product was dissolved in C6D6 and was analyzed by H NMR
spectroscopy. The spectrum contains a mixture of 1, 6, and 6′
in a molar ratio of 44:12:44.
X-r a y Cr ysta llogr a p h ic Stu d y. The data were collected
on a Rigaku AFC5R diffractometer at ambient temperature
(23 °C) using the ω-scan mode. Correction for Lorentz and
polarization effects, and an empirical absorption correction (Ψ-
scan) were applied. Atomic scattering factors were taken from
the literature.24 The structure was solved by a combination of
direct method and subsequent Fourier technique. The posi-
tional and thermal parameters of non-hydrogen atoms were
refined anisotropically. Hydrido ligands were located by dif-
ference Fourier technique and refined isotropically (1) or
included in the calculation without further refinement (2). The
other hydrogens were located by assuming ideal positions
The product of similar reaction in a 1:10 molar ratio
contained not only 1, 6, and 6′ but also a new complex that
showed the 1H hydrido signal at δ -17.25 and the 31P{1H}
signal at δ 57.1. Positions and the coupling pattern of the
signals are similar to those of 7 and 8. Thus, the complex may
be tentavely assigned to LRhH[µ-Si(C6H4Me-p)2][µ-Si(C6H4Me-
p)3](µ-Cl)RhHL formed via the Si-C bond cleavage of 6 at room
temperature. Isolation nor further characterization of the
complex was infeasible.
P r ep a r a t ion of 7 a n d 8. A toluene (5 mL) solution of
1 (264 mg, 0.24 mmol) was heated for 2 h at 70 °C. The color
of the solution turned from yellow to orange during the
reaction. GC analysis of the solution showed formation of
(24) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham, England, 1974; Vol. IV.

Si-C Bond Cleavage To Afford New Rh Complexes
Organometallics, Vol. 17, No. 26, 1998 5727
(d(C-H) ) 0.95 Å) and included in the structure calculation
without further refinement of the parameters. Crystal data
and results of structure refinement were summarized in
Table 2.
istry of Education, Science, Sports, and Culture, J apan.
T.K. is grateful for the fellowship from J SPS (J apan
Society for Promotion of Science).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data of complexes 1 and 2 (12 pages). Ordering
information is given on any current masthead page.
Ack n ow led gm en t. This work was financially sup-
ported by Grants-in-Aid for Scientific Research (No.
09940229) and for Scientific Research on Priority Areas
(“Interelement Linkage”, No. 09239212) from the Min-
OM9804677