Structure and properties of halogeno(hydrido)(triorganosilyl)rhodium(III) complexes, RhX(H)(SiRn1R3-n2)(PPh3) 2 (X = Cl, I; R1 = OSiMe3, OEt, R2 = Me). Influence of the alkoxy groups and halo ligand on stability and reactivity of the complexes

Article abstract of DOI:10.1021/om010862o

Silylrhodium(III) complexes RhX(H)(SiR_n¹R_3-n²)(PPh₃) ₂ (1: X = I, R¹ = OSiMe₃, R² = Me, n = 1; 2: X = I, R¹ = OEt, n = 3; 3: X = I, R¹ = OEt, R² = Me, n = 2; 4: X = I, R¹ = OEt, R² = Me, n = 1; 5: X = Cl, R¹ = OSiMe₃, R² = Me, n = 1; 6: X = Cl, R¹ = OEt, n = 3; 7: X = Cl, R¹ = OEt, R² = Me, n = 2; 8: X = Cl, R¹ = OEt, R² = Me, n = 1) were prepared by oxidative addition of HSiR_n¹R_3-n² to RhX(PPh₃)₃ and characterized by means of NMR (¹H, ¹³C{¹H}, ³¹P{¹H}, and ²⁹Si{¹H}) and IR spectroscopy as well as elemental analyses. X-ray crystallography of 1, 2, and 6 showed a distorted square-pyramidal coordination around the Rh center that is bonded to the silyl ligand at the apical position and to halo and hydrido ligands in trans positions in the basal plane. The Rh-Si bonds in 2 and 6 are the shortest among Rh-Si bonds of the silylrhodium complexes reported to date. ²⁹Si{¹H} NMR spectra of 1-8 show that the J(RhSi) value increases with an increase in the number of alkoxy substituents on the Si atom. Complex 2 reacted with HSiMe₂(OSiMe₃), HSi(OEt)₂Me, and HSi(OEt)Me₂, respectively, to cause exchange of the silyl group between the Rh complex and the organosilane, forming an equilibrium mixture. Complexes 5-8 undergo thermally induced coupling of their chloro and triorganosilyl ligands at 60 °C to liberate the respective chloro(triorgano)silane. The reaction obeys first-order kinetics in the Rh complex with the observed rate constants in the order 5 ? 8 > 7 > 6. The OEt groups at the Si retard the coupling of chloro and triorganosilyl ligands significantly. Formation of ISiMe₂(OEt)₂ from 4 takes place at a slightly slower rate than the reaction of 6, while complexes 2 and 3 do not undergo coupling of their iodo and silyl ligands at 60 °C.

Full text of DOI:10.1021/om010862o

Organometallics 2002, 21, 825-831
825
Str u ctu r e a n d P r op er ties of
Ha logen o(h yd r id o)(tr ior ga n osilyl)r h od iu m (III)
Com p lexes, Rh X(H)(SiR1 R23-n )(P P h 3)2 (X ) Cl, I;
n
R1 ) OSiMe3, OEt, R2 ) Me). In flu en ce of th e Alk oxy
Gr ou p s a n d Ha lo Liga n d on Sta bility a n d Rea ctivity of
th e Com p lexes
Yasushi Nishihara, Miwa Takemura, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, J apan
Received October 2, 2001
Silylrhodium(III) complexes RhX(H)(SiR1 R23-n)(PPh3)2 (1: X ) I, R1 ) OSiMe3, R2 ) Me,
n
n ) 1; 2: X ) I, R1 ) OEt, n ) 3; 3: X ) I, R1 ) OEt, R2 ) Me, n ) 2; 4: X ) I, R1 ) OEt,
R2 ) Me, n ) 1; 5: X ) Cl, R1 ) OSiMe3, R2 ) Me, n ) 1; 6: X ) Cl, R1 ) OEt, n ) 3; 7:
X ) Cl, R1 ) OEt, R2 ) Me, n ) 2; 8: X ) Cl, R1 ) OEt, R2 ) Me, n ) 1) were prepared by
oxidative addition of HSiR1 R2
to RhX(PPh3)3 and characterized by means of NMR (1H,
3-n
n
13C{1H}, 31P{1H}, and 29Si{1H}) and IR spectroscopy as well as elemental analyses. X-ray
crystallography of 1, 2, and 6 showed a distorted square-pyramidal coordination around the
Rh center that is bonded to the silyl ligand at the apical position and to halo and hydrido
ligands in trans positions in the basal plane. The Rh-Si bonds in 2 and 6 are the shortest
among Rh-Si bonds of the silylrhodium complexes reported to date. 29Si{1H} NMR spectra
of 1-8 show that the J (RhSi) value increases with an increase in the number of alkoxy
substituents on the Si atom. Complex 2 reacted with HSiMe2(OSiMe3), HSi(OEt)2Me, and
HSi(OEt)Me2, respectively, to cause exchange of the silyl group between the Rh complex
and the organosilane, forming an equilibrium mixture. Complexes 5-8 undergo thermally
induced coupling of their chloro and triorganosilyl ligands at 60 °C to liberate the respective
chloro(triorgano)silane. The reaction obeys first-order kinetics in the Rh complex with the
observed rate constants in the order 5 = 8 > 7 > 6. The OEt groups at the Si retard the
coupling of chloro and triorganosilyl ligands significantly. Formation of ISiMe2(OEt)2 from
4 takes place at a slightly slower rate than the reaction of 6, while complexes 2 and 3 do not
undergo coupling of their iodo and silyl ligands at 60 °C.
In tr od u ction
past decades probably owing to their relationship to the
mechanisms of Rh complex-catalyzed synthetic organic
reactions such as hydrosilylation of alkene and carbonyl
compounds and silylformylation of alkenes and al-
kynes.16-18 Oxidative addition of di- or triorganosilanes
to 16- or 14-electron Rh(I) complexes provides a conve-
nient route to silylrhodium(III) complexes. RhCl(PPh3)3
The structure and chemical properties of silylrhodium
complexes containing phosphine or cyclopentadienyl as
ancillary ligands1-15 have attracted attention during the
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10.1021/om010862o CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/01/2002

826 Organometallics, Vol. 21, No. 5, 2002
Nishihara et al.
Sch em e 1
activity for addition of organosilanes or their coupling
reactions.22,23 In this paper we report preparation of
silylrhodium(III) complexes with an alkoxy group on Si
and their chemical properties, which vary depending on
the halo ligand and on the number of OR substituents
at Si.
Resu lts
RhI(PPh3)3 reacts with organosilanes, HSiMe2OSiMe3,
HSi(OEt)3, HSi(OEt)2Me, and HSi(OEt)Me2, at room
temperature to produce silylrhodium(III) complexes,
RhI(H)(SiR1nR23-n)(PPh3)2 (1: R1 ) OSiMe3, R2 ) Me,
n ) 1; 2: R1 ) OEt, n ) 3; 3: R1 ) OEt, R2 ) Me, n )
2; 4: R1 ) OEt, R2 ) Me, n ) 1), respectively (eq 1).
Analogous oxidative addition reactions of alkoxy-
substituted triorganosilanes to RhCl(PPh3)3 form the
chloro(hydrido)silylrhodium(III) complexes, RhCl(H)-
(SiR1nR23-n)(PPh3)2 (5: R1 ) OSiMe3, R2 ) Me, n ) 1;
6: R1 ) OEt, n ) 3; 7: R1 ) OEt, R2 ) Me, n ) 2; 8: R1
) OEt, R2 ) Me, n ) 1) (eq 2). Table 1 shows yields,
analytical results, and IR data.
reacts with HSiCl3 to give stable RhCl(H)(SiCl3)(PPh3)2.4
The reactions of HSiR3 with chloroiridium(I) and dichlo-
roplatinum(II) complexes containing PPh3 ligands, how-
ever, produce ClSiR3 via initial oxidative addition of
HSiR3 to give the Ir(III) or Pt(IV) intermediate followed
by coupling of the chloro and silyl ligands.19 Recently,
we reported the oxidative addition of di- or triorganosi-
lanes with RhCl{P(i-Pr)3}2 and [Rh(PMe3)4]Cl to pro-
duce the rhodium(III) complexes with silyl, hydrido, and
chloro ligands.20,21 These complexes undergo coupling
of their chloro and silyl ligands, giving chlorosilanes and
hydridorhodium species as depicted in Scheme 1. Oxi-
dative addition of HSiR3 to Rh(I) occurs reversibly,
whereas reductive elimination of ClSiR3 is irreversible.20f
To obtain further insights into such coupling of halo
and silyl ligands, we prepared several chloro(silyl)-
rhodium(III) and iodo(silyl)rhodium complexes contain-
ing PPh3 ligands. Comparison of the stability and
reactivity of iodo(silyl)rhodium(III) complexes with those
of chloro(silyl)rhodium complexes is of interest because
iodorhodium complexes often exhibit unique catalytic
(16) (a) Ojima, I. In Organic Transition-Metal Chemistry; Ishii, Y.,
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of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley:
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p 1479. (e) Marciniec, B., Ed. Comprehensive
Handbook on Hydrosilylation; Pergamon: Oxford, U.K., 1992. (f)
Marciniec, B.; Gulinski, J . J . Organomet. Chem. 1993, 446, 15.
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Corey, E. R. Organometallics 1987, 6, 1595. (d) Chang, L. S.; Corey, J .
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A.; Sato, S. J . Am. Chem. Soc. 1990, 112, 6120. (g) Matsuda, I.;
Sakakibara, J .; Nagashima, H. Tetrahedron Lett. 1991, 32, 7431. (h)
Bergens, S.; Noheda, P.; Whelan, J .; Bosnich, B. J . Am. Chem. Soc.
1992, 114, 2128. (i) Ikeda, S.; Chatani, N.; Kajikawa, Y.; Ohe, K.;
Murai, S. J . Org. Chem. 1992, 57, 2. (j) Wright, M. E.; Cochran, B. B.
J . Am. Chem. Soc. 1993, 115, 2059. (k) Zhou, J .-Q.; Alper, H.
Organometallics 1994, 13, 1586. (l) Chen, R. M.; Chien, K.-M.; Wong,
K.-T.; J in, B. Y.; Luh, T. Y.; Hsu, J .-H.; Fann, W. J . Am. Chem. Soc.
1997, 119, 11321.
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K.; Sarai, S.; Koizumi, T.; Yamamoto, T. Organometallics 1997, 16,
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1997, 16, 2063. (d) Osakada, K.; Koizumi, T.; Yamamoto, T. Bull. Chem.
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Osakada, K. J . Organomet. Chem. 2000, 611, 323.
Figures 1-3 depict molecular structures of complexes
1, 2, and 6 as determined by X-ray crystallography.
Table 2 summarizes selected bond distances and angles
of the complexes. The molecules contain distorted
square-pyramidal coordination with the silyl ligand at
the apical site and the iodo or chloro ligand and the
hydrido ligand in trans positions in the basal plane. We
previously reported the reaction of triarylsilane with
RhCl{P(i-Pr)3}2 to give RhCl(H)(SiAr3){P(i-Pr)3}2, which
have square-pyramidal coordination analogous to 1-8.20c
The exclusive formation of the square-pyramidal com-
plexes with PPh3 and P(i-Pr)3 as ancillary ligands
among several possible structures is ascribed to a large
trans effect of the silyl ligand, which may exclude
structures with a ligand at the trans coordination site
of the silyl ligand. RhCl(H)(SiCl3)(PPh3)24 also contains
the chloro, silyl, and hydrido ligands in meridional sites
in this order in octahedral coordination; a C-H bond of
a PPh3 ligand coordinates weakly to the site trans to
(22) Ojima, I.; Clos, N.; Donovan, J .; Ingallina, P. Organometallics
1990, 9, 3127.
(21) Si-SR coupling of silyl(thiolato)rhodium(III) complexes. (a)
Osakada, K.; Hataya, K.; Yamamoto, T. J . Chem. Soc., Chem. Commun.
1995, 2315. (b) Baruah, J . B.; Osakada, K.; Yamamoto, T. Organome-
tallics 1996, 15, 456. (c) Osakada, K.; Hataya, K.; Yamamoto, T. Inorg.
Chim. Acta 1997, 259, 203.
(23) (a) Mori, A.; Takahisa, E.; Kajiro, H.; Hirabayashi, K.; Nishi-
hara, Y.; Hiyama, T. Chem. Lett. 1998, 443. (b) Mori, A.; Takahisa,
E.; Kajiro, H.; Nishihara, Y.; Hiyama, T. Polyhedron 2000, 19, 567. (c)
Mori, A.; Takahisa, E.; Kajiro, H.; Hirabayashi, K.; Nishihara, Y.;
Hiyama, T. Macromolecules 2000, 33, 1115.

Halogeno(hydrido)(triorganosilyl)rhodium(III)
Organometallics, Vol. 21, No. 5, 2002 827
Ta ble 1. Yield s, An a lytica l Resu lts, a n d IR Da ta of
Com p lexes 1-8
anal. (%)b
H
IRc
yield
(%)a
complex
C
I or Cl ν(RhH)
RhI(H)(SiMe2OSiMe3) (PPh3)2 (1)
88 54.39 5.24 14.19 2124
(54.55) (5.14) (14.06)
RhI(H){Si(OEt)3}(PPh3)2 (2)
RhI(H){Si(OEt)2Me}(PPh3)2 (3)
RhI(H){Si(OEt)Me2}(PPh3)2 (4)
86 55.15 5.04 13.82 2060
(54.91) (5.05) (13.81)
75 55.33 4.98 14.26 2076
(55.42) (4.99) (14.28)
76 56.01 5.02 14.60 2086
(55.96) (4.93) (14.78)
RhCl(H)(SiMe2OSiMe3) (PPh3)2 (5)d 86 62.52 5.52
4.03 2149
(62.34) (5.88) (4.14)
RhCl(H){Si(OEt)3}(PPh3)2 (6)
RhCl(H){Si(OEt)2Me}(PPh3)2 (7)
RhCl(H){Si(OEt)Me2}(PPh3)2 (8)
79 60.94 5.82
(60.98) (5.60) (4.29)
97 61.62 5.59
(61.77) (5.56) (4.45)
89 63.97 5.48
3.94 2060
F igu r e 3. ORTEP drawing of RhCl(H){Si(OEt)3}(PPh3)2
(6) at 50% ellipsoid level.
4.23 2095
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 1, 2, a n d 6
4.56 2103
(63.96) (5.64) (4.72)
1a
2
6
a
Yields are before recrystallization, but their purity was
confirmed by 1H and 31P{1H} NMR spectra. Calculated values
b
Rh-Xb
Rh-P1
Rh-P2
Rh-Si
2.724(1)
2.320(2)
2.298(2)
2.291(2)
2.731(1)
2.303(2)
2.297(2)
2.282(2)
2.7011(8)
2.324(2)
2.313(2)
2.251(2)
2.401(2)
2.319(2)
2.319(2)
2.251(2)
are in parentheses. c cm-1 in KBr disks. Obtained as 5‚0.5C7H8.
d
The presence of solvated toluene was confirmed by 1H NMR.
X-Rh-P1b
95.04(6)
99.08(6)
92.47(6)
95.75(6)
155.99(7)
109.17(7)
102.46(8)
96.07(8)
90.54(4)
94.64(4)
162.11(6)
114.81(5)
96.78(6)
96.54(6)
90.10(7)
89.81(7)
166.02(7)
115.35(9)
95.90(8)
96.77(8)
X-Rh-P2b
P1-Rh-P2 152.82(8)
Si-Rh-Xb
106.27(7)
Si-Rh-P1 101.17(9)
Si-Rh-P2
97.00(9)
a
Data of two crystallographically independent molecules are
b
shown. X ) I for 1 and 2; X ) Cl for 6.
depending on substituents on the Si atom (Table 1). The
wavenumbers of the peaks for the series of the iodo and
chloro complexes decrease in the order 1 > 4 > 3 > 2
and 5 > 8 > 7 > 6, respectively, indicating that the
Rh-H bond becomes weaker on introduction of the
alkoxy group on the Si center. This effect of the silyl
ligand in cis position of the hydrido ligand on the IR
data is much more significant than that of the Cl and I
ligands, with a different trans influence, in trans
F igu r e 1. ORTEP drawing of RhI(H)(SiMe2OSiMe3)-
(PPh3)2 (1) at 50% ellipsoid level. One of the two crystal-
lographically independent molecules is shown.
1
positions of the hydrido ligand. The H, 13C{1H}, and
31P{1H} NMR data of complexes 1-8 are listed in Tables
3 and 4. The NMR spectra of the complexes suggest that
the structure in solution is the same as that in crystals
of 1, 2, and, 6. The 1H NMR spectra of 1-4 show a
characteristic Rh-H signal at δ -10.89 to -11.30 as a
doublet of triplets with coupling constants of 25-26 Hz
(J (RhH)) and 13-14 Hz (J (PH)). The hydrido signals
of the chloro complexes 5-8 are observed at higher
magnetic field (δ -13.98 to -14.09) with similar cou-
pling constants. The 13C{1H} NMR signal of the ipso
carbon of PPh3 ligands of the complexes appears as an
apparent triplet due to virtual coupling. These data
indicate that the two PPh3 ligands are in cis position to
the hydrido ligand and are situated mutually in trans
positions.
F igu r e 2. ORTEP drawing of RhI(H){Si(OEt)3}(PPh3)2 (2)
at 50% ellipsoid level.
the silyl ligand. The Rh-Si bond distances (2.291(2),
2.282(2) Å) of 1 are similar to the Rh-Si single bond of
RhCl(H)(SiPh3){P(i-Pr)3}2 (2.299(2) Å)20c and are shorter
than those of octahedral RhH(SiPh3)(SAr)(PMe3)3 (2.342-
(1) Å)21c due to the absence of a ligand in trans position
to the silyl ligand in the pentacoordinated complexes.
The Rh-Si distances in 2 (2.251(2) Å) and 6 (2.251(2)
Å) are even shorter than that in 1 and than the Rh-Si
single bond distances of the complexes already reported.
Slight elongation of the Si-O bond of 1 (1.640(5) Å)
compared with 2 (1.629(4), 1.634(4), 1.614(4) Å) was also
noted.24
Table 5 summarizes the 29Si{1H} NMR data of 1-8
at -50 °C. The complexes give a doublet of triplets due
to coupling with a Rh and two P nuclei. Complexes 1,
4, 5, and 8 with a monoalkoxysilyl ligand show a J (RhSi)
of 29 Hz, while other complexes exhibit larger coupling
constants, 37 Hz for 3 and 7 and 49 Hz for 2 and 6,
respectively. This increase of J (RhSi) with the increase
(24) The typical Si-O bond distance of siloxanes is 1.60 Å. See:
Lickiss, P. D.; Litster, S. A.; Redhouse, A. D.; Wisener, C. J . J . Chem.
Soc., Chem. Commun. 1991, 173.
The IR peaks of the ν(RhH) vibration in the solid state
are observed at 2149-2060 cm-1, whose positions vary

828 Organometallics, Vol. 21, No. 5, 2002
Ta ble 3. 1H NMR Da ta for Com p lexes 1-8a
Nishihara et al.
Rh-H
Si-Me
Si-OCH2CH3
Si-OCH2CH3
Ph
1
2
3
4
5
6
7
8
-11.27 (dt, 1H, J (RhH) ) 25 Hz,
J (PH) ) 13 Hz)
-0.18 (s, 9H)
7.02-7.08 (m, 18H)
7.94-8.01 (m, 12H)
7.00-7.15 (m, 18H)
7.95-8.02 (m, 12H)
7.00-7.15 (m, 18H)
7.95-8.02 (m, 12H)
6.99-7.15 (m, 18H)
7.95-8.02 (m, 12H)
7.00-7.10 (m, 18H)
7.96-8.01 (m, 12H)
7.04-7.07 (m, 18H)
7.95-8.02 (m, 12H)
7.04-7.06 (m, 18H)
7.96-8.02 (m, 12H)
7.02-7.07 (m, 18H)
7.96-8.03 (m, 12H)
0.47 (s, 6H)
-10.89 (dt, 1H, J (RhH) ) 26 Hz,
J (PH) ) 13 Hz)
0.91 (t, 9H, J ) 7 Hz)
0.81 (t, 6H, J ) 7 Hz)
0.70 (t, 3H, J ) 7 Hz)
3.62 (q, 6H, J ) 7 Hz)
3.36-3.57 (m, 4H)
-11.30 (dt, 1H, J (RhH) ) 26 Hz,
J (PH) ) 14 Hz)
0.41 (s, 3H)
0.39 (s, 6H)
-11.07 (dt, 1H, J (RhH) ) 26 Hz,
J (PH) ) 14 Hz)
3.20 (q, 2H, J ) 7 Hz)
-14.09 (dt, 1H, J (RhH) ) 24 Hz,
J (PH) ) 14 Hz)
-0.17 (s, 9H)
0.47 (s, 6H)
-13.98 (dt, 1H, J (Rh-H) ) 24 Hz,
J (PH) ) 14 Hz)
0.90 (t, 9H, J ) 7 Hz)
0.83 (t, 6H, J ) 7 Hz)
0.72 (t, 3H, J ) 7 Hz)
3.61 (q, 6H, J ) 7 Hz)
3.38-3.56 (m, 4H)
-14.06 (dt, 1H, J (RhH) ) 24 Hz,
J (P-H) ) 15 Hz)
-14.06 (dt, 1H, J (RhH) ) 24 Hz,
J (PH) ) 14 Hz)
0.42 (s, 3H)
0.38 (s, 6H)
3.24 (q, 2H, J ) 7 Hz)
a
300 MHz at 25 °C in benzene-d6.
Ta ble 4. 13C{1H} a n d 31P {1H} NMR Da ta of
Com p lexes 1-8
(OEt)3 complexes (δ -39.78 for 2 and δ -34.01 for 6)
are much lower than those of the other complexes.
Dialkoxysilyl complexes show the signal at the positions
(δ 13.45 for 3 and δ 15.44 for 7) between the trialkox-
ysilyl complexes and the monoalkoxy complexes (δ
42.73-54.14 for 1, 4, 5, and 8). This order of δ values,
Si(OEt)3 < Si(OEt)2Me < Si(OEt)Me2, is observed also
in the 29Si{1H} NMR spectra of the corresponding
triorganosilanes, as listed in Table 5.26 The magnitude
of difference in δ values between the complex and the
1
13C{1H} NMRa
CH3 CH2 orthoc metac para
31P{1H}
ipsod NMRb
Si-Me
1 1.84, 13.53e
128.43 135.20 130.39 133.41
43.5
(4.6)
(7.3)
(21.9) (126.8)
2
17.74 59.12 128.20 135.22 130.21 133.39
(5.5) (5.5) (21.9) (120.2)
17.81 58.79 128.23 135.09 130.23 133.74 42.4
(5.5) (7.3) (21.9) (125.8)
17.81 58.90 128.36 135.15 130.34 133.66 42.3
(5.5) (7.3) (21.9) (124.7)
128.54 135.15 130.45 133.16 42.2
(5.9) (5.8) (22.4) (128.7)
17.96 58.90 128.53 135.38 130.52 133.28 41.5
(5.5) (5.5) (21.9) (122.5)
17.70 58.65 128.34 135.07 130.32 133.39 40.6
(5.5) (5.5) (21.9) (125.6)
17.54 58.48 128.16 134.80 130.10 132.99 40.0
(3.7) (7.3) (21.9) (127.9)
43.1
3 5.19
4 9.71
5 1.86, 12.06e
6
nR2
triorganosilane, ∆δ (δcomplex - δHSiR 3-n), increases
significantly with a decrease in the number of alkoxy
ligands at Si. The ∆δ increases in the order 2 (18.25) <
3 (29.47) < 4 (49.35) = 1 (50.62) in the iodo(silyl)-
rhodium(III) complexes and in the order 6 (24.02) < 7
(31.46) < 8 (48.19) = 5 (48.93) in the chloro(silyl)-
rhodium(III) complexes. Complexes 1, 4, 5, and 8,
having different alkoxy groups or different halo ligands,
give quite similar ∆ δ values (48.19-50.62).
Hexacoordinated hydrido(silyl)rhodium complexes mer-
RhCl(H)(SiHAr2)(PMe3)3 were reported to react with
added diarylsilanes to cause silyl group exchange via
reductive elimination of diarylsilane and reoxidative
addition of the other diarylsilane to the RhCl(PMe3)3.20b
Analogous silyl group exchange reactions were con-
ducted with the pentacoordinated iodo(silyl)rhodium-
(III) complexes 1-4. Typically, complex 2 reacts with a
mixture of an excess of HSiMe(OEt)2 and HSi(OEt)3 at
50 °C to give an equilibrium mixture of 2 and 3 (eq 3).
7 4.39
8 8.08
a
b
100 MHz at 25 °C in benzene-d6. 121 MHz at 25 °C in
benzene-d6. Coupling constants, J (RhP) (Hz), are given in paren-
theses. c Observed splittings of the signals (Hz) are given in
d
parentheses. Apparent triplet due to virtual coupling. Observed
splittings of the signals (Hz) are given in parentheses. e OSiMe3
carbons.
Ta ble 5. 29Si{1H} NMR Da ta of Com p lexes 1-8a
chemical shift (ppm)b
coupling constant (Hz)
1
nR2
complex δcomplex δHSiR
∆δc
1J (RhSi)
2J (PSi)
3-n
1d
2
3
44.42
-39.78
13.45
54.14
42.73
-34.01
15.44
52.98
-6.20
-58.03
-16.02
4.79
-6.20
-58.03
-16.02
4.79
50.62
18.25
29.47
49.35
48.93
24.02
31.46
48.19
29.4
49.2
36.8
29.4
29.4
49.6
36.8
29.4
7.4
9.2
7.4
7.4
7.4
9.2
7.4
7.4
4
5d
6
7
8
a
b
79.3 MHz at -50 °C in CD2Cl2. Relative to SiMe4. cf. δ -16.3
c
d
1
nR2
for HSiMe3. δcomplex - δHSiR
.
1, 5, and HSiMe2OSiMe3
exhibit OSiMe3 signals at δ 6.67,3-6n.62, and 10.30, respectively.
The reactions with HSiMe2(OEt) and with HSiMe2-
(OSiMe3) lead to attainment of the equilibrium between
2 and 4 and between 1 and 2, respectively. Equilibrium
constants of the reactions were determined by measur-
in the number of alkoxy substituents on Si is explained
by more p-character of the Si-OR bond than that of the
Si-C(sp3) bond, which leaves more s-character of the
Rh-Si bond (Bent’s rule).25 The difference of halo
ligands of the complexes does not influence the magni-
tude of the coupling constants. The 29Si{1H} NMR peak
positions vary depending on the number of alkoxy
substituents on the Si center. The chemical shifts of Si-
1
ing the relative H NMR peak area ratios of the Si-H
and Rh-H signals in the range 278-318 K (Table 6).
Figure 4 shows van’t Hoff plots of the reaction, which
gives the thermodynamic parameters ∆H° ) 1.37 kJ
mol-1 and ∆S° ) 12 J mol-1 K-1 for HSi(OEt)2Me at
(26) Williams, E. A. In The Chemistry of Organic Silicon Com-
pounds; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1989;
Chapter 8.
(25) Bent, H. A. Chem. Rev. 1961, 61, 275.

Halogeno(hydrido)(triorganosilyl)rhodium(III)
Organometallics, Vol. 21, No. 5, 2002 829
Ta ble 6. Equ ilibr iu m Con sta n ts of Rea ction of 2
w ith HSiR3
Ka
temp (K)
SiR3 ) SiMe2OSiMe3
Si(OEt)Me2
Si(OEt)2Me
278
288
298
308
318
0.1011
0.1013
0.1015
0.1018
0.1020
0.346
0.337
0.331
0.323
2.27
2.31
2.36
2.40
2.44
a
K ) [HSi(OEt)3][RhI(H)(SiR3)(PPh3)2][HSiR3]-1[2]-1
.
F igu r e 4. Van’t Hoff plots of 2 with complexes 1, 3, and
4. The equilibrium constants were obtained from NMR
peak area ratios of the solutions of 2 with a mixture of
excess HSi(OEt)3 and triorganosilanes.
298 K. Measurement of analogous silyl exchange reac-
tions of 2 with HSiMe2OSiMe3 and with HSi(OEt)Me2
gave ∆H° ) 0.17 kJ mol-1 and ∆S° ) -19 J mol-1 K-1
,
,
and ∆H° ) -1.56 kJ mol-1 and ∆S° ) -14 J mol-1 K-1
F igu r e 5. (a) Time-yield curve and (b) first-order polts
of thermal decomposition of 4-8 at 60 °C in benzene-d6.
respectively, at 298 K. The relative facility in formation
of the complexes in these equilibrium silyl ligand
exchanges is 3 > 2 > 4 = 1, which is not directly related
to the number of alkoxy groups of the complexes.
The iodo(triorganosilyl)rhodium complexes 2 and 3
are stable above 60 °C in solution. Complex 4, however,
showed a decrease by 7% after being heated for 2 h at
60 °C. Thermal decomposition of chloro complex 6 at
60 °C occurs more rapidly (16% decrease in 2 h), and it
forms 80% of ClSi(OEt)3 after 24 h (eq 4). Complex 7
Discu ssion
The silylrhodium(III) complexes in this study have
similar structures but different reactivities toward
coupling of the halo and silyl ligands, a process that
depends on the kind of halo and silyl ligands. They have
meridional arrangement of halo, silyl, and hydrido
ligands in square-pyramidal coordination with the silyl
ligand in the apical position; the coordination is quite
similar to that in RhCl(H)(SiAr3){P(i-Pr)3}2. The struc-
ture is the thermodynamically favored one among the
possible structures because the complexes have a flex-
ible and labile pentacoordinated Rh center and because
the complexes are equilibrated to halorhodium(I) com-
plexes via rapid reductive elimination of triorganosilane
and its reoxidative addition. A theoretical study on
oxidative addition of SiH4 to RhCl(PH3)2 suggests a
greater stability of the structure RhCl(H)(SiH3)(PH3)2
with the Cl and silyl ligands with much larger Si-Rh-
Cl angles (135.8-136.6°) than the structures of 1-8.27
The calculated and observed stable pentacoordinated
structures differ depending on the substituents at the
Si and P centers, suggesting a small difference in the
stability of the two structures.
shows the first-order coupling of the chloro and trior-
ganosilyl ligands, as plotted in Figure 5a. Complexes 5
and 8, with fewer OEt groups, undergo rapid thermal
decomposition that is almost complete within 0.5 h. This
contrasts with the reactions of 4 and 6, which require
24 h or longer for complete consumption of the com-
plexes. The reactions of 4-8 obey first-order kinetics.
Figure 5b shows the first-order plots of the reactions at
60 °C. The observed rate constants increase in the order
4 (1.04 × 10-5 s-1) < 6 (2.01 × 10-5 s-1) < 7 (5.59 ×
10-4 s-1) < 5 (2.9 × 10-3 s-1) = 8 (3.7 × 10-3 s-1). The
complexes having fewer alkoxy substituents on Si
undergo much faster decomposition. Reductive elimina-
tion of the ClSiR3 is easier than that of ISiR3 from the
Rh complex with the same alkoxy-silyl ligand.
The geometry of the Rh(III) complexes with the silyl
ligand in cis position to the hydrido ligand and halo
ligand in this study allows direct coupling of the hydrido
and silyl ligands, and that of the halo and silyl ligands.
The pentacoordinate complexes RhCl(H)(SiAr3){P(i-
(27) Koga, N.; Morokuma, K. J . Am. Chem. Soc. 1993, 115, 6883.

830 Organometallics, Vol. 21, No. 5, 2002
Nishihara et al.
Sch em e 2
Pr)3}2, without alkoxy groups on Si, undergo reductive
elimination of ClSiAr3 even at room temperature. The
hydridorhodium(I) product is soon captured by the
rhodium(III) complex to form bimetallic rhodium prod-
ucts such as {P(i-Pr)3}(Ar3Si)HRh(µ-H)(µ-Cl)RhH(SiAr3)-
{P(i-Pr)3}. In sharp contrast, chlororhodium complexes
5-8 with OEt or OSiMe3 groups on the Si center are
stable at room temperature. Thermally induced elimi-
nation of ClSiMen(OR)3-n from 5-8 takes place at 60
°C. The reaction rates vary significantly depending on
the number of alkoxy groups on the Si center; the
observed rate constants decrease in the order 5 = 8 >
7 > 6 with an increase of the number of alkoxy groups.
The reaction giving ClSi(OEt)3 from 6 at 60 °C proceeds
at a slightly faster rate than the thermal reaction of 4
to give ISiMe2(OEt) at the same temperature. Other
iodo complexes 2 and 3 are stable even at 60 °C. These
results indicate that introduction of OEt (or OSiMe3)
groups on Si retards the reductive elimination due to
the stable Rh-Si bond and that coupling of chloro-
(triorgano)silane from the Rh(III) center is more facile
than that of iodo(triorganosilane). A markedly different
thermal stability was observed between iodo complexes
1-4 and chloro complexes 5-8 toward coupling of the
halo and silyl ligands.
than ∆H° in many of the reactions, the obtained
thermodynamic parameters do not provide important
information about relative stability of the Rh-Si bond.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
under a nitrogen or an argon atmosphere using standard
Schlenk techniques. Hexane and toluene were distilled from
sodium and benzophenone prior to use or purchased from
Kanto Chemicals Co. Ltd. RhCl(PPh3)3 and RhI(PPh3)3 were
prepared according to published procedures.28 NMR spectra
(1H, 13C{1H}, 29Si{1H}, and 31P{1H}) were recorded on J EOL
EX-400 or Varian Mercury 300 spectrometers. Residual peaks
of solvent were used as the reference for 1H NMR (benzene-
d6, δ 7.15; dichloromethane-d2, δ 5.32; toluene-d8, δ 2.09). 13C-
{1H} NMR signals were referenced with the solvent signals,
while 85% H3PO4 (δ 0) and tetramethylsilane (δ 0) were used
as an external standard for 31P{1H} and 29Si{1H} NMR
measurements, respectively. The IR spectra were recorded on
a Shimadzu FTIR-8100A spectrometer in KBr. Elemental
analyses were carried out with a Yanaco MT-5 CHN auto-
corder.
P r ep a r a t ion of Com p lexes 1-8. To a toluene (25 mL)
dispersion of RhI(PPh3)3 (800 mg, 0.80 mmol) was added
HSiMe2OSiMe3 (157 µL, 0.80 mmol) at room temperature. The
dispersed reddish brown solid was gradually dissolved on
stirring to give a pale yellow solution. After 2 h, the solution
was concentrated and 30 mL of hexane was added to give a
pale yellow precipitate; the latter was collected by filtration,
washed with hexane (15 mL x 3 times), and dried in vacuo to
give 1 as a pale yellow solid (683 mg, 88%). Recrystallization
from toluene/hexane afforded pale yellow crystals suitable for
X-ray crystallography. Complexes 2-4 and 6 were prepared
analogously.
Reductive elimination of haloalkane via concerted
coupling of the halo and alkyl (or aryl) ligands is not
common in the chemistry of alkyltransition metal
complexes. On the other hand, the concerted intramo-
lecular coupling of the chloro and organosilyl ligands
of the Rh(III) complexes takes place easily. A series of
RhCl(H)(SiR3)(PR′3)n (R ) Ar, H; PR′3 ) PMe3, P(i-Pr)3)
type complexes form ClSiR3 smoothly at room temper-
ature only when the Cl and silyl ligands are in mutually
cis positions in a square-pyramidal or octahedral coor-
dination. Coupling of Cl and SiR3 in Ir(III) and Pt(IV)
complexes with chloro and silyl ligands was previously
proposed in the reaction of an excess of organosilanes
with chloro complexes of Ir(I) and Pt(II) by Chalk and
Harrod.19
The Rh-Si bonds of 2 and 6 are shorter than that of
1 and than almost all the Rh-Si bond reported so far.
Previously we reported that the Rh-Si bond of RhCl-
(H){Si(CtCPh)3}{P(i-Pr)3}2 was much shorter than that
of RhCl(H)(SiAr3){P(i-Pr)3}2, which suggests a signifi-
cant effect of the electron-withdrawing alkynyl group
on the Si-Rh bond distance. Crystallographic studies
and NMR spectroscopic studies of the complexes re-
vealed a shortening of the Rh-Si bond and an increase
in J (RhSi) caused by introduction of the alkoxy group
at Si. These results indicate that the OR groups render
the σ-bond between Rh and Si more stable. The smaller
magnitude of δ∆ values of the complexes with larger
OEt groups of the Si center seems to suggest a strength-
ening of the covalent σ-coordination bond.
Complexes 5, 7, and 8 were prepared analogously, but the
products were isolated quickly after the reaction for 1 h in
order to avoid decomposition of the complexes.
E q u ilibr iu m Con st a n t s of t h e R ea ct ion of 2 w it h
Tr ior ga n osila n es. To a toluene-d8 (0.7 mL) solution of 2 (10
mg, 1.1 × 10-2 mmol) in an NMR sample tube were added
HSi(OEt)2Me (16.7 µL, 10 × 10-2 mmol) and HSi(OEt)3 (18.4
µL, 9.8 × 10-2 mmol). The tube was sealed and heated at 50
°C for 2 h in an oil bath. Subsequently it was set in an NMR
probe and kept at fixed temperatures (278, 288, 298, 308, and
318 K) for 30 min. The equilibrium constants between 2 and
1
3 were determined by comparison of the H NMR peak areas
of the Si-H hydrogen signals of the two hydrosilanes (δ 4.78
for HSi(OEt)2Me and δ 4.52 for HSi(OEt)3) and the Rh-H
hydrogen signals of the complexes (δ -10.99 for 2 and δ -11.16
for 3). The equilibrium constants at each temperature in the
reaction of 2 with various hydrosilanes are shown in Table 6.
Th er m a l Rea ction s of 4-8. A solution of 6 (19.4 mg, 0.036
mmol) in carefully dried and digassed benzene-d6 (0.6 mL) was
NMR measurement of complex 2 with various orga-
nosilanes gave thermodynamic parameters of complexes
1-4 via reductive elimination of HSiMen(OR)3-n, fol-
lowed by oxidative addition of organosilane (Scheme 2).
The ∆G° or ∆H° do not correlate directly with the
number of OR groups of the complexes nor with relative
stability of the Rh-Si bonds that are estimated based
on the rate constants of coupling of complexes 5-8 or
J (RhSi) values. Since the magnitude of T∆S° is larger
(28) Osborn, J . A.; J ardine, F. H.; Young, J . F.; Wilkinson, G. J .
Chem. Soc. A 1966, 1711.

Halogeno(hydrido)(triorganosilyl)rhodium(III)
Organometallics, Vol. 21, No. 5, 2002 831
Ta ble 7. Cr ysta l Da ta a n d Deta ils of th e Str u ctu r e Refin em en t of 1, 2, a n d 6
1
2
6
formula
mol wt
cryst syst
space group
a (Å)
C
41H82IOP2Si2Rh
C42H46IO3P2SiRh
918.67
C42H46ClO3P2SiRh‚C7H8
919.36
939.03
triclinic
P1h (No. 2)
17.838(5)
18.828(4)
15.023(3)
104.37(2)
101.63(2)
115.85(2)
4112(2)
4
triclinic
P1h (No. 2)
13.171(3)
13.706(3)
12.637(2)
112.62(1)
101.99(2)
88.50(2)
2056.2(8)
2
triclinic
P1h (No. 2)
13.053(3)
18.541(4)
10.173(3)
101.35(2)
92.20(2)
103.58(2)
2337(1)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
µ (mm-1
F(000)
)
1.334
1968
1.517
1.308
928
1.484
0.555
956
1.306
Dcalcd (g cm-3
)
cryst size
0.25 × 0.20 × 0.13
5.0-50.0
10 877
6177
873
0.50 × 0.30 × 0.05
5.0-55.0
9421
5320
455
0.45 × 0.45 × 0.05
5.0-55.0
10 709
5229
483
2θ range (deg)
no. of unique reflns
no. of used reflns
no. of variables
R
0.036
0.026
0.040
0.030
0.058
0.057
a
Rw
a
Weighting scheme [σ(Fo)2]-1
.
prepared in an NMR tube under argon. The sample was
degassed and sealed. Heating the sample at 60 °C for 24 h
caused consumption of the complex and formation of ClSi-
(OEt)3 (80%). Reactions of 4, 5, 7, and 8 were carried out in
an NMR sample tube under Ar. Heating a benzene-d6 solution
of 5 (55 min), 7 (3 h), and 8 (0.5 h) at 60 °C gave ClSiMe2-
OSiMe3 (76%), ClSi(OEt)2Me (66%), and ClSi(OEt)Me2 (61%),
respectively. These products were characterized by comparison
of the NMR peak positions with the authentic samples.
Byproducts were also observed in the reaction mixtures in
7-13% yields. They did not give satisfactory GC-mass data
and were not characterized unambiguously, although they may
be tentatively assigned to the corresponding siloxanes formed
via condensation of the above products during the reaction.
Kinetic measurement of the reactions was carried out by
1H NMR spectra using the solution prepared as above.
X-r a y Diffr a ction . Single crystals of 1, 2, and 6 suitable
for X-ray diffraction studies were grown from toluene-hexane.
Crystallographic data and details of refinement are sum-
marized in Table 7. The crystals were sealed in glass capillary
tubes and mounted on a Rigaku AFC-5R or AFC-7R automated
four-cycle diffractometer. Intensities were collected for Lorentz
and by using diffractometer and ω-2θ scan methods, and an
empirical absorption correction (ψ scan) was applied. The
intensities of three standard reflections, measured every 150
reflections, were monitored throughout the data collection.
Calculations were carried out using the program package
teXsan for Windows. The structures were solved by the
Patterson method. A full matrix least-squares refinement was
used for the non-hydrogen atoms with anisotropic thermal
parameters. All non-hydrogen atoms were refined with aniso-
tropic thermal parameters, whereas all hydrogen atoms were
located by assuming the ideal geometry and included in the
structure calculation without further refinement of the pa-
rameters.29
Ack n ow led gm en t. This work was financially sup-
ported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, Sports, Technology
and Culture of J apan.
Su p p or tin g In for m a tion Ava ila ble: Table of crystal-
lographic data and complete tables of non-hydrogen and
selected hydrogen parameters, bond lengths and angles,
calculated hydrogen atom parameters, anisotropic thermal
parameters, and intermolecular contacts for 1, 2, and 6. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM010862O
(29) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham, England, 1974; Vol. 4.