Rh(I) and Rh(III) silyl PMe3 complexes. Syntheses, reactions and 103Rh NMR spectroscopy

Article abstract of DOI:10.1016/S0022-328X(97)00433-6

Synthetic approaches to Rh(I) silyls are described. The complexes L_nRhSiR₃ (L=PMe₃; 6, n=4, R₃=(OEt)₃; 7, n=4, R₃=Me(OMe)₂; 21, n=3, R₃=Ph₃) resulted from the reactions of MeRhL₄ (1) with the corresponding silanes HSiR₃. Complex 21 was prepared alternatively from PhRhL₃ (2) and HSiPh₃, while analogous reactions of HSi(OEt)₃, HSiMe(OMe)₂ and HSi(OMe)₃ led to the bis(silyl)hydrides fac-L₃Rh(SiR₃)₂(H) (8, R₃=(OEt)₃; 9, R₃=Me(OMe)₂; 13, R₃=(OMe)₃). Like in analogous iridium-based systems, the outcome of these reactions largely depends on the nature of substituents at the silicon atom. Synthesis of Rh(I) silyls inaccessible by this route, namely those with alkyl substituents at the silicon, L_nRhSiR₃ (19, n=3, R₃=PhMe₂; 22, n=4, R₃=Me₃), was achieved utilizing nucleophilic attack of the corresponding silyllithiums at [L₄Rh]Cl. The solid-state structure of 19 was determined by X-ray crystallography. C₁₇H₃₈P₃SiRh, Fw=466.38 monoclinic, C2/m, a=13.304(3) A, b=13.814(2) A, c=13.123(4) A, β=110.66(3) deg, V=2257(1) A³, Z=4, d_calcd=1.373 g cm^-3, μ=1.019 mm^-1. A series of di(hydrido)silyls fac-L₃Rh(H)₂(SiR₃) (10, R₃=(OEt)₃; 15, R₃=PhMe₂; 16, R₃=Ph₃) was synthesized using oxidative additions of HSiR₃ to HRhL₄ (3). Complexes 10, 15, 16 are thermodynamically stable with respect to H-H and Si-H reductive-elimination reactions at ambient conditions. Complex 8 reductively eliminates HSi(OEt)₃ reversibly at room temperature and complex 13 is capable upon heating of mediating dehydrogenative Si-Si coupling of HSi(OMe)₃ and redistribution of [(MeO)₃Si]₂. ¹⁰³Rh NMR data obtained for MeRhL₄ (1), HRhL₄ (3), L₃RhSiPhMe₂ (19), L₃RhSiPh₃ (21) and for the di(hydrido) silyls (10, 15, 16) allowed to qualitatively evaluate steric and electronic effects of methyl, silyl, and hydride ligands on the ¹⁰³Rh chemical shift.

Full text of DOI:10.1016/S0022-328X(97)00433-6

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.
Journal of Organometallic Chemistry 551 1998 81–92
103
ž /
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Rh I and Rh III silyl PMe3 complexes. Syntheses, reactions and Rh
1
NMR spectroscopy
a
a
a,2
Michael Aizenberg , Juergen Ott , Cornelis J. Elsevier b,), David Milstein
a
Department of Organic Chemistry, The Weizmann Institute of Science, RehoÕot 76100, Israel
b
Anorganisch Chemisch Laboratorium, J.H. Õan’t Hoff Research Institute, UniÕersiteit Õan Amsterdam, Nieuwe Achtergracht 166, 1018 WV
Amsterdam, Netherlands
Received 1 May 1997
Abstract
Ž .
Ž
Ž
.
3
Synthetic approaches to Rh I silyls are described. The complexes LnRhSiR3 LsPMe3; 6, ns4, R3 s OEt ; 7, ns4,
Ž
.
.
Ž .
R3sMe OMe 2; 21, ns3, R3sPh3 resulted from the reactions of MeRhL4 1 with the corresponding silanes HSiR3. Complex 21
was prepared alternatively from PhRhL3 2 and HSiPh3, while analogous reactions of HSi OEt , HSiMe OMe and HSi OMe led to
Ž .
Ž
.
Ž
.
Ž
.
3
2
3
Ž
.
Ž
. Ž . Ž
Ž
.
Ž
.
Ž
. .
3
the bis silyl hydrides fac-L3Rh SiR3
H
8, R3s OEt ; 9, R3sMe OMe 2; 13, R3s OMe . Like in analogous iridium-based
2
3
Ž .
systems, the outcome of these reactions largely depends on the nature of substituents at the silicon atom. Synthesis of Rh I silyls
Ž
.
inaccessible by this route, namely those with alkyl substituents at the silicon, LnRhSiR3 19, ns3, R3 sPhMe2; 22, ns4, R3 sMe3 ,
w
x
was achieved utilizing nucleophilic attack of the corresponding silyllithiums at L4Rh Cl. The solid-state structure of 19 was determined
˚
˚
˚
Ž .
Ž .
Ž .
by X-ray crystallography. C17H38P3SiRh, Fws466.38 monoclinic, C2rm, as13.304 3 A, bs13.814 2 A, cs13.123 4 A,
bs110.66 3 deg, Vs2257 1 A , Zs4, dcalcds1.373 g cmy3, ms1.019 mmy1. A series of di hydrido silyls fac-L3Rh H SiR3
3
˚
Ž .
Ž .
Ž
.
Ž . Ž
.
2
Ž
Ž
.
.
Ž .
10, R3s OEt ; 15, R3sPhMe2; 16, R3sPh3 was synthesized using oxidative additions of HSiR3 to HRhL4 3 . Complexes 10, 15,
3
16 are thermodynamically stable with respect to H–H and Si–H reductive-elimination reactions at ambient conditions. Complex 8
Ž
.
reductively eliminates HSi OEt reversibly at room temperature and complex 13 is capable upon heating of mediating dehydrogenative
3
Si–Si coupling of HSi OMe and redistribution of MeO Si . 103Rh NMR data obtained for MeRhL4 1 , HRhL4 3 , L3RhSiPhMe2
Ž
.
wŽ
Ž
.
x
Ž .
Ž .
3
3
2
.
Ž
.
Ž
.
Ž
.
19 , L3RhSiPh3 21 and for the di hydrido silyls 10, 15, 16 allowed to qualitatively evaluate steric and electronic effects of methyl,
silyl, and hydride ligands on the 103Rh chemical shift. q 1998 Elsevier Science S.A.
Keywords: Comlexes; Silyls; NMR spectroscopy
Ž
.
Ž
.
w
x
1. Introduction
and PMe3 3-RhSiMe2 SiMe SiMe3 2. 17,18 Several
reports dealing with catalytic and mechanistic aspects of
rhodium-mediated transformations of organosilicon sub-
The vast majority of mononuclear silyl complexes of
rhodium described so far are those of Rh III 1–9 .
There are a few examples of Cp Rh V silyls 10–15 .
Ž
.
w
w
x
w
x
strates are available 1,2,5,6,8,16–25 .
)
Ž .
x
We have been studying synthetic ways to, and reac-
tivity of, silyl complexes of rhodium and iridium be-
cause of their possible involvement in useful catalytic
reactions of organosilicon compounds. Their isolation
and characterization may allow to carry out and study
some of the postulated steps of these catalyses. In
addition, silyl ligands, which are known for high s-
donicity and trans-influence, when bound to an elec-
tron-rich metal center may lead to novel chemistry, like
the above mentioned catalytic C–F activation.
Ž .
Silyl complexes of Rh I remain quite rare. In addition
Ž
.
to PMe3 3RhSiMe2 Ph, which we used in C–F activa-
w x
tion reactions of polyfluorobenzenes 8 and which is
described in detail here, the following complexes were
Ž
.
Ž
.
w x
4
reported: Rh tripsi CO and Rh tripsi PPh3,
Ž
.
w x
Ž
.
Ž
Ž
. .Ž
.
w
x
PMe3 3RhSiPh3, 5 dtbpm Rh Si OEt PMe3 , 16
3
)
Corresponding author.
1 Dedicated to Professor Peter Maitlis in recognition of his pio-
Earlier we have investigated competitive reductive
eliminations from facial iridium III methyl-hydrido-
silyl complexes and cyclometalation of the resulting
neering work and outstanding contribution to organometallic chem-
istry and homogeneous catalysis.
Ž
.
2 Also corresponding author.
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

(
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82
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
Ž .
w
x
iridium I silyl intermediates 26–28 . Here we report
on synthetic approaches to, spectroscopic characteriza-
Ž .
tion and properties of, electron-rich rhodium I silyls. A
num ber of related bis silyl hydrido- and
Ž
.
.
Ž
.
Ž
di hydrido silyl-complexes of Rh III and their reduc-
tive-elimination reactions are described as well. We
show in which aspects rhodium-based systems resemble
those of iridium and in which these two systems differ
from each other. Part of these results was communi-
w
x
cated 8,29 .
2. Results
(
)
(
)
3
2.1. Reactions of MeRh PMe3 and PhRh PMe3 with
4
silanes
Scheme 2.
Ž
Reaction of RRhLn 1, RsMe, ns4; 2, RsPh,
X
.
ns3; LsPMe3 with hydrosilanes R3SiH leads either
to C–H or to C–Si coupling, or to both these processes.
Ž . Ž
.
Ž
Ž
.
L 3 Rh H SiR 3
10, R 3 s OEt ; 11, R 3 s
3
Ž
.2 . Ž
.
Me OMe
Scheme 2 .
2
( )
2.1.1. ReactiÕity of alkoxysilanes. Formation of Rh I
Reactions of the phenyl complex 2 with silanes 4 and
(
)
(
)
silyls and Rh III bis silyl hydrides
Ž .
Ž .
Ž
.
5 do not lead to Rh I silyls. Instead, the bis silyls 8 or
9 are formed even when a 1:1 ratio of the reactants is
Rhodium I silyl complexes of the general formula
. .
Ž
Ž
.
Ž
L4RhSiR3 6, R3 s OEt ; 7, R3 sMe OMe
are
major products of the reactions between 1 and one
Ž . Ž .
Ž
.
used, half of 2 remaining unreacted Scheme 2 . The
3
2
reactions are cleaner when carried out at lower tempera-
Ž
.
Ž
.
or HSiMe OMe
2
equivalent of HSi OEt
4
5
Ž
.
tures. The analogous reaction between 2 and HSi OMe
3
3
Ž
.
Scheme 1 . In both cases there is some concurrent
Ž
.
12 is less selective and produces a 4:1 mixture of
. . Ž
Ž .
C–Si coupling leading to the formation of HRhL4 3 ,
Ž
Ž
.
Ž
.
fac-L R h S i O M e
H
13
14 even at y208C.
Complexes 8, 9, 13 are assigned on the basis of their
and
fac-
3
3
2
which is produced in f5–10% yield at room tempera-
Ž . Ž
Ž
. . Ž
.
L3Rh H Si OMe
2
3
31
Ž
.
Ä1
4
ture or below . P H NMR spectra of 6 and 7
31
1
Ä1
4
Ž
measured at 208C are featureless, exhibiting as does the
P H and H NMR data which are completely analo-
31
Ä1
4
.
spectrum of complex 1 very broad signals in the region
gous. P H NMR spectra exhibit doublet-of-doublets
and doublet-of-triplets patterns with small coupling con-
of d y22 to y24 ppm. However, 1H NMR and
31
Ä1
4
Ž .
stants 1JP – Rh f78 and f100 Hz indicative of Rh III .
1H NMR spectra contain appropriately split and inte-
grated signals due to hydrides and two silyl groups. The
facial configuration follows from the aforementioned
low-temperature P H NMR 6 data allow to un-
Ž
.
Ž
.
Ž
.
equivocally assign them as tetrakis phosphine -
Ž .
rhodium I silyls. As expected, 6 adopts at low tempera-
Ž
.
ture y938C a trigonal bipyramidal structure, with the
low values of 1JP – Rh of the doublet-of-doublets signals
3
silyl group occupying an axial position.
If in the reactions between 1 and 4 or 5 two equiva-
lents of the silanes are used, one equivalent of PMe3 is
liberated and smooth double additions take place to
and from apparent inequivalence of the two sets of
methoxy groups of 9 in both proton and carbon NMR
spectra. It is further confirmed by the high value of
2JSi – P, trans s183 Hz observed in the 29Si NMR spec-
trum of 9. The dihydridosilyls 10, 11, 14 were identified
Ž
.
Ž
. Ž . Ž
produce the bis silyl hydrides fac-L3Rh SiR3 H 8,
2
Ž
.
Ž
. .
R3 s OEt ; 9, R3 sMe OMe in 90–95% yield, the
3
2 Ž
.
rest being corresponding di hydrido silyls fac-
Ž
.
by comparison of their completely analogous NMR
spectra with those of independently prepared authentic
Ž
.
Ž . Ž
.Ž
Ž
.
samples of fac- Me3P Rh H SiR3 10, R3 s OEt ;
3
2
3
15, R3 sPhMe2; 16, R3 sPh3; see Section 5 for de-
.
tails .
3 For PMe3 complexes of Rh III that have meridional arrange-
Ž
.
1
ment, JP – Rh of the signals due to mutually trans phosphines is
expected to have a value of 93–105 Hz. See for example, Refs.
w
x
Scheme 1.
30–32 .

(
)
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
83
1
.
2.1.2. ReactiÕity of alkylsilanes
HSiEt3 17 reacts with 1 in a benzene solution to
produce almost exclusively CH3SiEt3 and HRhL4 3 .
tion 2.1.3 . In the H NMR spectrum signals due to
C6 H6 and Me2 SiPh2 are observed.
Ž
.
Ž .
(
)
2.1.3. ReactiÕity of HSiPh3 20
The reaction between 1 and 20, as reported by Thorn
w x
Only traces of methane are formed. When the reactants
are mixed in toluene-d8 at y788C and the course of the
reaction is monitored by NMR during gradual warming
to room temperature, no intermediate is observed.
The analogous reaction between 2 and 17 in C6 D6
leads to complicated mixtures in which the products of
both C–H and C–Si coupling, namely C6 H6 and
C6 H5SiEt3, are present. Organometallic complexes that
could be assigned include HRhL4 , L3 RhSiEt3,
and Harlow, 5 leads to the formation of L3RhSiPh3
Ž
.
21 accompanied by the liberation of methane and
trimethylphosphine. Similarly, the analogous reaction of
complex 2 results in quantitative production of 21 and
Ž
Ž ..
benzene Eq. 1 .
C H Rh PMe q HSiPh3
Ž
.
6
5
3
3
20
2
Ž . Ž
. Ž
.
™ C H q PMe RhSiPh3
1
Ž .
Ž
.
L3Rh H SiEt3 the latter two tentatively . At early
6
6
3
3
2
21
stages of the 1:1 reaction between 2 and 17, the analysis
is still possible. After 3 h, when about 2r3 of the initial
amounts of PhRhL3 and HSiEt3 are still present accord-
ing to 1H NMR, the L3RhSiEt3rC6 H5SiEt3 ratio is
about 5.6. After 1 day it decreases to approximately 1.5,
apparently because of the instability of L3RhSiEt3 un-
der these conditions. Unsaturated species such as HRhL3
and L3RhSiEt3, that are initially formed, react further in
the presence of free PMe3, HSiEt3 and C6 D6 to form 3
1
Complex 21 was identified by its H NMR spectral
data. Its room temperature P H NMR spectrum ex-
31
Ä1
4
hibits a very broad doublet at d y17.6 ppm with
1
Ž .
apparent JP – Rh f142 Hz indicative of Rh I .
( )
2.2. Synthesis of Rh I silyls using silyllithium reagents
w
x
The cationic complex RhL4 Cl reacts with LiSiR3
Ž .
Ž
.
R3 s PhMe2 ; Me3 to form the Rh I silyls
Ž . Ž
.
Ž
.
Ž
.
and L3Rh H SiEt3 in a mixture of fluxional andror
L3RhSiMe2 Ph 19 and L4RhSiMe3 22 as shown in
2
Ž .
partially deuterated complexes.
Eq. 2 .
Ž
.
Reaction of complex 2 with HSiMe2 Ph 18 is also
Rh PMe
ClqLiSiR ™LiClq PMe RhSiR3
Ž .
19, ns3, R3 sMe2 Ph
22, ns4, R3 sMe3
Isolation of 19 and especially 22 is complicated by
formation of the undesired HRhL4 3 . Complex 19 can
be purified albeit with significant losses by recrystal-
lization from cold pentane. Purification of 22 is difficult
because of similar solubility to that of HRhL4, both
Ž
.
3
3
3
n
4
complicated. After 3 h at room temperature according to
Ž
NMR analysis all silane 18 about 20% excess with
2
Ž .
.
respect to the amount of 2 taken is consumed. The
Ž
.
Ž
resulting mixture contains unreacted 2 f25% , 3 f
.
Ž . Ž
. Ž
.
Ž .
7% , L3Rh H SiPhMe2 15, f28% , which was
2
Ž
.
identified by NMR and also synthesized independently,
31
Ä1
4
and a complex that exhibits in P H NMR a doublet
1
Ž
d y17.2 with JP – Rh s146 Hz 19, f40%, see Sec-
Fig. 1. Perspective view of a molecule of 19. Hydrogen atoms are omitted for clarity.

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)
84
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
Table 2
being highly soluble in common organic solvents. Iden-
tification of 19 and 22 is based on their NMR data and
˚
Ž .
Selected interatomic bond lengths A in the molecule of 19
Atoms
Ž . Ž .
Bond length
Atoms
Bond length
Ž
.
on X-ray structural analysis 19 . At room temperature
both compounds are fluxional on the 31 P NMR time
Ž .
Ž .
Ž
.
.
.
Ž .
Rh 1 –P 1
2.3094 9
P 2 –C 21
1.827 3
31
Ä1
4
Ž . Ž .
Ž .
Ž .
Ž
Ž .
Rh 1 –P 2
2.2708 6
P 2 –C 22
1.833 3
scale. Complex 19 exhibits in P H NMR the afore-
1
Ž .
Ž
.
.
Ž .
Ž .
Ž
Ž .
Ž .
Rh 1 –P 2a
2.2708 6
P 2 –C 23
1.832 3
Ž .
1.903 3
mentioned doublet at d y17.2 ppm with JP – Rh s146
Ž .
P 1 –C 11
Ž .
Rh 1 –Si
2.3804 10
Ž .
Si–C 1
Hz. Upon cooling a toluene solution of 19 to y808C, it
transforms into two broad signals in 1:2 ratio at d y26
Ž .
Ž
Ž
.
Ž
.
Ž .
1.903 3
Ž .
1.917 3
1.831 3
Si–C 1a
Ž .
Ž .
Ž .
1.831 3
Ž .
1.841 4
P 1 –C 11a
Si–C 2
1
Ž .
Ž
.
and y12 ppm with apparent JP – Rh f115 and 149 Hz
P 1 –C 12
31
Ä1
4
respectively. The P H NMR spectrum of complex
22, which is virtually non-observable at room tempera-
ture, converts at y558C into well-resolved doublet-of-
doublets and doublet-of-quartets integrated as 3:1 at d
selected bond distances and angles are presented in
Ž .
Tables 1 and 2. Complex 19 is among the few Rh I
1
silyls characterized by X-ray crystallography. Like its
closest analog 21, complex 19 adopts a distorted square
planar coordination geometry. However, the distortion
of 19 towards tetrahedral structure is less expressed:
y28.2 and y15.4 ppm with JP – Rh s158 and 91 Hz.
1H NMR spectra of 19 and 22 contain signals of
appropriate intensity due to PMe3 and SiR3 groups in
accordance with the proposed formulae.
Ž
.
Ž . Ž .
Ž .
Ž .
P 2a –Rh 1 –P 2 and P 1 –Rh 1 –Si angles in a
2.3. X-ray structure of 19
Ž . Ž .
molecule of 19 are 159.98 3 and 156.43 3 deg com-
pared to 148.21 3 and 143.24 3 reported for 21 5 . In
accordance with the strong trans-influence of silyl lig-
Ž .
ands the bond P 1
Ž .
longer than P 2
length of 2.3804 10 A is substantially by 0.063 A
Ž .
Ž .
w x
A ruby-red single crystal of 19 was grown from its
concentrated pentane solution at y208C. A perspective
view of a molecule of 19 is presented in Fig. 1 and
˚
Ž .
Si–Rh 1 is about 0.04 A
P–Rh 1 . The Rh 1 –Si bond
trans to
Ž .
Ž .
trans to
˚
˚
.
Ž
.
Ž
Table 1
longer than that in triphenylsilyl analog 21. Since this is
contrary to steric requirements of the silyl groups in
question, electronic factors are likely to be responsible
Crystallographic parameters for the structure of 19
Empirical formula
Formula mass, amu
Color and habit
Crystal size, mm
Crystal system
C17 H38 P3SiRh
466.38
Red prisms
0.6=0.6=0.6
monoclinic
for this. However, the higher deviation of P
trans to
Si –Rh–Si angle from linearity in 21 may also play a
role.
Ž
.
Space group
C2rm No. 12
Ž .
13.304 3
˚
a, A
(
)
2.4. ReactiÕity of the bis silyl hydrides 8 and 13
˚
Ž .
13.814 2
b, A
Ž
Ž
. . Ž . Ž .
H
3 2
fac-L3Rh Si OEt 8 reacts in a benzene solu-
˚
Ž .
110.66 3
Ž .
2257 1
c, A
13.123 4
Ž .
tion at room temperature with CO to form mixtures of
b, deg
3
˚
two carbonyl-containing complexes assigned as mer-
V, A
Z
4
Ž
.Ž
Ž
. .
Ž
. Ž
Ž
. .
L3Rh CO Si OEt
and L2 Rh CO Si OEt . De-
3
2
3
y3
Ž
.
Density calcd , g cm
1.373
1.019
pending on the amount of the added CO, mixtures with
different ratios of the products are formed that allows to
m, mmy1
Diffractometer
CAD 4 Enraf–Nonius
Ž
assign the NMR and IR spectra obtained see Section
˚
Ž
.
Ž
.
Radiation wavelength, A
Monochromator
Temperature, K
Mode
Mo Ka ls0.71073
.
5 . Both complexes contain only one triethoxysilyl group
Graphite
per rhodium.
110
v
Reaction of 8 with 1.3 equivalents of CDCl3 in
benzene at room temperature leads to the formation of
umax , deg
26.97
1
0.9
y16FhF16
y17FkF0
y16F1F16
Scan speed, deg miny1
Scan width, deg
Collection range
Ž
.Ž
.Ž
Ž
. .
mer-L3Rh Cl CDCl2 Si OEt in 80% yield over 3 h,
3
Ž
.
indicating like the reaction with CO above that 8 is
capable of easy loss of triethoxysilane in solution. How-
ever, no reductive elimination of hexaetoxydisilane from
8 was observed in any of these experiments.
No. of reflections
Collected
5129
To test whether Si–Si bond formation can be opera-
tive in these systems, we carried out several experi-
Independent
2558
Ž
.
R int
0.0422
Ž
Ž
. . Ž . Ž
.
ments on thermolysis of fac-L3Rh Si OMe
H
13 .
Heating a benzene solution of 13 at 558C for 3 days
Ž . Ž . .
Datarrestraintsrparameters
Solution
Refinement
2553r0r202
3
2
Patterson
Full-matrix least-squares on F2
Ž
results in its conversion to fac-L3Rh H Si OMe
14 as a major product. Of the organosilicon com-
2
3
Ž
Ž ..
Final R indices I)2s I
R1
wR2
Ž
.
0.0312
0.0777
Ž
.
Ž
.
Ž
.
pounds formed, MeO Si-Si OMe
2% yield and
3
3
MeO Si 10% yield were identified by 1H NMR,
Ž
.
Ž
.
4

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)
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
85
Table 3
103Rh NMR chemical shifts ppm of Me3 P nRhR and
Ž .
w
x
trans-influence of silyl ligands 27,33,34 may facilitate
phosphine dissociation, resulting in intermolecular ex-
change of the phosphine ligands in the 16-e complexes.
It is worthy of note that for sterically non-demanding
Ž
.
Ž
.
Ž
.
Me3P 3Rh H 2 SiR3 complexes
a
Ž103
y802
y735
.
Rh
Compound
d
Ž
Ž
Ž
Ž
Ž
Ž
Ž
.
PMe3 3RhSiMe2 Ph, 19
Ž
.
Ž
.Ž
.
silyl groups, such as EtO Si, Me OMe Si and
3
2
.
PMe3 3RhSiPh3, 21
Me3Si, saturated 5-coordinate L4RhSiR3 complexes are
formed, while with the bulkier Ph3Si and PhMe2 Si
ligands 4-coordinate L3RhSiR3 are produced. Another
important observation is the fact that in the reaction
between PhRhL3, 2, with the small reactive alkoxysi-
.
Ž . Ž
Ž
. .
3
.
PMe3 3Rh H Si OEt , 10
y1222
y1108
y1091
y735
.
Ž .2Ž
PMe3 3Rh H SiMe2 Ph , 15
.
Ž .2Ž
.
PMe3 3Rh H SiPh3 , 16
2
.
PMe3 4RhH, 3
PMe3 4RhMe, 1
y490b
.
a In ppm towards high frequency, scaled to J s3.16 MHz, T s293
Ž
.
Ž
.
lanes HSi OEt or HSiMe OMe , the initially formed
3
2
b
Ž
.
K unless otherwise specified; at 223 K; d Rh sy482 ppm at 233
transient L3RhSiR3 species are substantially more reac-
tive towards Si–H oxidative addition than the starting
phenylrhodium complex. This results in the fast double
addition and the formation of bis silyls fac-
L3Rh H SiR3 8 and 9 even when a 1:1 ratio of the
reactants is used. For comparison, when one starts with
the saturated methyl complex 1, the intermediate
L3RhSiR3 species are captured with the extra phos-
phine present, thus allowing to isolate the saturated
L4RhSiR3 complexes 6 and 7.
Ž
.
K; inaccurate extrapolation gives d Rh sy434 ppm at 293 K.
Ž
.
29Si-INEPT NMR and GC-MS. Similar thermolyses
Ž .Ž
.
2
Ž
.
carried out in the presence of an excess of HSi OMe
3
result in higher yields of these products. Heating phos-
Ž
.
phine-deficient bis trimethoxysilyl complexes of
Ž
rhodium obtained by partial oxidation of the PMe3
groups of 13 allows to get in the presence of 100
equivalents of HSi OMe 97% and 250% yields of
.
Ž
.
Ž .
As expected, all the Rh I silyls are highly air and
moisture sensitive. Upon exposure to air these com-
pounds are quickly oxidized andror hydrolyzed.
Ž
.
Ž
.
3Ž
.
Ž
MeO Si-Si OMe and MeO Si respectively see
3
3
4
4
.
Section 5 for details .
2.5. Rh NMR chemical shifts data
(
)
(
)
(
)
3.2. Rhodium III bis silyl hydrides and di hydrido silyls
103Rh NMR chemical shifts obtained for 4-coordinate
Rh I silyls 19 and 21, 6-coordinate Rh III
Ž
.
As expected, Rh III complexes are readily formed in
these electron-rich systems. Starting with sterically
non-demanding reactive alkoxysilanes one can easily
Ž . .
Ž
Ž
.
Ž .
di hydrido silyls 10, 15, 16 and 5-coordinate Rh I hy-
dride and methyl complexes 3 and 1 are compiled in
Table 4.
Ž
.
Ž .Ž
.
synthesize bis silyl complexes L3Rh H SiR3 8, 9,
2
Ž
.
Ž . Ž
.
13 and di hydrido silyls L3Rh H SiR3 10, 11, 14.
2
The latter species can be obtained using bulkier arylsi-
Ž
.
lanes as well 15, 16 . All of these complexes have a
facial arrangement of ligands with the strong trans-di-
recting hydrides and silyls in mutually cis positions.
3. Discussion
( )
3.1. Rhodium I silyls
Ž
.
Ž
.
Formation of the di hydrido silyls of rhodium III from
HRhL4 3 and HSiR3 is a facile straightforward reac-
tion, which takes place at room temperature with quanti-
tative yields indicating that under these conditions such
species are thermodynamically quite stable with respect
to Si–H or H–H reductive eliminations. A few Rh III
bis silyl hydrides are known, 7,16 and one of them,
namely fac- PMe3 3Rh h -SiMe2CH CH2 SiMe2 H ,
Ž .
Ž .
As described, Rh I silyl complexes with alkoxy,
alkyl, aryl and mixed substituents at silicon can be
formed in solution and some of them can be isolated.
The synthetic pathways involve either reactions of
methyl or phenyl rhodium complexes with the corre-
Ž
.
Ž
.
w
x
2
Ž .
sponding hydrosilanes A , or nucleophilic attack of
silyl anions at the cationic rhodium center B . Both
Ž
.
Ž
.Ž .
2 w x
Ž .
was crystallographically characterized 7 . An iridium
Ž .Ž . .
analog fac- PMe3 3Ir H Si OEt
3 2
solution 27 . However, no reactivity of these com-
pathways have their limitations: route B is limited
mainly by the accessibility of silyllithium reagents,
while route A is applicable for alkoxy- and arylsilanes,
that is, for those bearing electronegative substituents at
the silicon, and not to trialkylsilanes.
Ž
x
.
Ž
was observed in
w
Both the 16-e L3RhSiR3 and the 18-e L4RhSiR3
complexes were found to be non-rigid at room tempera-
ture on the NMR time scale, giving rise to broad signals
4 In general, these reactions result in decomposition to mixtures
Ž .
due to easy oxidation of PMe3 and Rh I center and due to high
affinity of silicon for oxygen. However, upon careful hydrolysis of 6
in 31 P H NMR. Whereas fluxionality is quite common
for 5-coordinate monovalent d8 complexes, it is rare for
their 4-coordinate counterparts. The well-known strong
Ä1
4
in the absence of oxygen, the silyl ligand is lost and the cationic
w
cis- L4RhH2
NMR, see Ref. 35 .
is produced cleanly. It was identified by its 31P
xq
w
x

(
)
86
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
5, 6
plexes, e.g., Si–Si bond formation, was reported.
Our findings demonstrate that H–Si reductive elimina-
tion from 8 is a facile reversible process that takes place
at room temperature. This is exemplified by trapping of
cations. First, it implies that the product-forming steps
and even the mechanisms of catalytic reactions involv-
ing organosilicon compounds may depend on the nature
of the substrate used. Second, it renders alkylsilyl-
w
Ž
.
x
Ž
Ž .
Ž .
the transient L3RhSi OEt species with CO as Rh I
rhodium I complexes inaccessible via the reactions of
3
.
Ž
silyls and with CDCl3 in a form of an oxidative-ad-
methyl- or arylrhodium complexes with alkylsilanes.
Importantly, however, we have shown here that this
.
dition product . Reductive elimination of Si–Si
bonds 7, 8 from 13 is likely to be thermodynamically less
Ž .
approach allows to generate rhodium I alkoxy- and
w
x
favorable 45 than that of Si–H bonds. Nevertheless,
using an excess of HSi OMe , reductive elimination of
MeO SiSi OMe can be induced, albeit the outcome
is complicated by the formation of MeO Si by redis-
tribution processes. The Si–Si reductive elimination
becomes more pronounced under phosphine-deficient
phenylsilyls, such as 6, 7, 19 and 21, which are isolable,
but are highly unstable to air and moisture. It should be
noted that their electron-rich iridium analogs are not
available because of facile cyclometalation reactions
Ž
.
3
Ž
.
Ž
.
3
3
Ž
.
4
9
w
x
17,18,26–28,47,48 . Similarly, while nucleophilic at-
w
x
tack of PhMe2 SiLi and Me3SiLi at RhL4 Cl leads to
10
Ž .
conditions.
the formation of Rh I dimethylphenyl- and trimethyl-
silyl complexes 19 and 22, respectively, the reaction of
w
x
3.3. Comparison of Rh and Ir systems
IrL4 Cl with PhMe2 SiLi leads to the orthometalated
Ž
.
w x
Ir III complex 28 . We have not observed formation of
rhodasilacycles in these systems, which is, again, in line
with the relatively lower propensity of rhodium to un-
dergo oxidative-addition reactions.
w
x
In contrast to methyl- and phenyliridium, 26,27
both methyl- and phenylrhodium PMe3 complexes 1
and 2, when reacted with hydrosilanes, do not lead to
stable primary oxidative-addition adducts. Moreover,
even monitoring the reaction between 1 and HSiEt3 at
low-temperature did not allow to spectroscopically de-
tect the product of Si–H oxidative addition. This is not
3.4. Rhodium-103 NMR data
The nuclear shielding of transition metal nuclei like
103Rh is mainly determined by the paramagnetic contri-
bution s p to the overall shielding, which may accord-
Ž
.
unexpected, since rhodium III complexes have a higher
w
x
propensity to reductively eliminate C–H 46 bonds than
Ž
.
Ž .
do their isostructural iridium III analogs. Significantly,
C–Si bond formation at the rhodium centers, like in the
iridium systems, is substantially more expressed for
alkylsilyl ligands. Thus, the selectivity of the reaction
between MeRhL4 and HSiEt3 is completely shifted to
C–Si coupling, contrary to that of alkoxy- and phenylsi-
lanes for which C–H bond formation prevails. As dis-
ing to the Ramsey Eq. 3 be described by changes in
the average excitation energy, D Eav , the d-orbital ra-
dius, -ryd 3 ), and the angular imbalance of charge,
SQN.
sss d ys psAycP D E y1 P-rdy3 )PSQN
Ž
.
av
3
Ž .
w
x
cussed previously 26,27 the reasons are both thermo-
dynamic, i.e. strengthening of M–Si bonds for silyls
that bear electronegative substituents at the silicon, and
kinetic, i.e. low directionality of the silicon-centered
orbitals that are involved in M–Si bonding. The de-
scribed phenomenon, being common for iridium and
rhodium, has important mechanistic and synthetic impli-
The 103Rh NMR shifts for 1, 3, 10, 15, 16, 19, 21
see Table 4 fall within the range expected for Rh I
Ž
.
Ž .
Ž
.
and Rh III compounds containing ligands of intermedi-
ate to strong ligand field strength for the respective
w
x
coordination geometries 49 . As the ligand field split-
ting term D Eav is large for the 4- and 5- as well as for
the currently described 6-coordinate compounds,
11
small changes in their structure will be clearly reflected
in the Rh chemical shift. The D Eav term will in fact
govern the magnitude of s p and hence it may for
qualitative purposes be invoked for comparison within
this series.
5 Mitchell et al. reported NMR evidence for a degenerate re-
versible Si–Si reductive-elimination process from two analogous
Ž
.
w x
unsaturated Rh III silyl complexes. See Ref. 17 .
6
Ž
.
Hofmann et al. prepared a EtO 3Si analog of 6 and 7 with one
PMe3 and a chelating Bu2 P 2CH2 ligand dtbpm . According to
Žt
.
Ž
.
Comparing the shifts for 19 and 21, the increase of
d Rh with increasing bulk of the SiR3 group is readily
Ž
.
their data no Si–Si coupling could be induced from this complex. See
w
x
Ref. 16 .
7 Examples of stoichiometric Si–Si reductive elimination from
5
w
x
.
isolated complexes are rare. See Refs. 36–38
8 For dehydrogenative coupling of hydrosilanes, catalysed by plat-
11
w
x
As discussed by Mann, 49 although most 6-coordinate com-
w
x
Ž
inum metals, see Refs. 39–44 .
pounds have much higher shifts due the presence of small, weak-field
donor ligands which leads to smaller D E compared to square planar
9 Facilitation of C–H reductive elimination by loss of phosphine
.
w
x
ligands is known. See Ref. 46 .
ones, the advent of compounds having larger, strong-field ligands has
extended the range of shifts of 6-coordinate compounds to very low
values indeed.
10
We did not identify other redistribution products of these reac-
tions.

(
)
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
87
Ž .
explained by the larger deviation from the square planar
geometry for 21, as inferred from the P–Rh–P and
both 4-coordinate 16-e and 5-coordinate 18-e Rh I
silyls can be prepared, and determined the X-ray struc-
ture for one of them, namely L3RhSiMe2 Ph. We have
Ž
. w x
P–Rh–Si angles for 19 and 21 see above . 5 This
structural feature is accompanied by a diminished over-
lap between the dx2yy2 orbital and ligand orbitals,
Ž
.
also described syntheses of a series of rhodium III
Ž
.
Ž
.
bis silyl hydrides and di hydrido silyls. Whereas the lat-
ter are thermodynamically stable at room temperature
with respect to H–H and H–Si reductive-elimination
reactions, the former are prone to Si–H and on moder-
ate heating to Si–Si reductive eliminations.
Comparison with related iridium silyl systems
demonstrated that, along with the expected differences
in reactivities of second and third row metals, there
exists an important common factor of major importance,
that is, the effect of the substituents at the silicon atom
causing a smaller ligand field splitting and hence larger
y1
Ž
.
Ž .
term, resulting in the higher d Rh for 21.
D Eav
The compounds 10, 15, 16 have rather low 103Rh
chemical shifts for 6-coordinate compounds, which is
readily accounted for by the presence of six strong-field
ligands. Their shifts are at higher frequencies compared
)
Ž
.Ž
.
S iR L
3
to th e related H R h C p
an d
Ž
) .Ž
.
w x
H2 Rh Cp SiR3 2 , 14 in agreement with the smaller
ligand field splitting by PMe3 ligands in 10, 15, 16
Ž
) .Ž
.
compared to Cp) in HmRh Cp SiR3 n. Within the
on reductive-elimination reactivity.
103
Ž
.
Ž .
Ž
.
series 10, 15, 16 a steady increase in d Rh is observed,
reflecting the increase in relative steric bulk of the SiR3
group. A similar argumentation as in the case of 19
versus 21, i.c. an increasing perturbation of the quasi-
Rh NMR spectra of selected Rh I - and Rh III -
silyl compounds have been measured and a qualitative
understanding of the 103Rh chemical shifts as a function
of their structural features has been established.
Ž
.
octahedral environment when going from the Si OEt
3
to SiMe2 Ph and SiPh3 analogue, pertains in this case.
We note a similar trend in the 103Rh NMR data for
5. Experimental
2
Ž
) .Ž
.
Ž
.
compounds HRh Cp SiR3 L LsCO, h -C2 H4 ob-
w
x
tained by Ruiz et al. 14 which was not discussed by
these authors. The notion of increasing deviation from
octahedral geometry in the series 10, 15, 16 is, albeit
circumstantially, corroborated by X-ray data on a series
5.1. General
The compounds described herein are air and moisture
sensitive and were handled as reported in detail else-
w
x
w
x
Ž
.
of similar iridium compounds 50 . The trend of dimin-
where 27 . HSiPh3, HSiPhMe2 , and HSi OEt were
purchased from Aldrich; HSiEt3 was purchased from
3
Ž
ishing Ptrans-Si–Rh–Si angles and other relevant an-
.
Ž
.
Ž
.
Ž
.
gles in PMe3 3IrH2 SiR3 reflects a more perturbed
quasi-octahedral geometry in case of the more bulky
Petrarch System HSiMe OMe was synthesized from
HSiMeCl2 and HC OMe
degassed by purging with dry N2 before use.
Ž
.
w
2x
53 , Liquid silanes were
3
12
SiR3 group.
Ž
.
w
x
Ž
.
w
x
56
For 5-coordinate compounds the ligand field splitting
will be slightly smaller than for 4-coordinate square
M eRh PM e3
,
54,55 PhRh PM e3
PMe 4Rh Cl, 35 LiSiMe2 Ph,
,
4
Ž
.
w4 x w
Ž
.
x
w x
HRh PMe3
57,58 and Hg SiMe3
,
54
4
w
x
w
x
Ž
.
w
3 x
planar systems. 51 The energy of the dx2yy2 orbital
and hence D E are mainly determined by the ligands in
59 were synthesized accord-
2
ing to published procedures. 31 P, H, 13C NMR spectra
were measured in C6 D6 as a solvent unless otherwise
specified and were referenced as described elsewhere.
1
w
x
the basal plane of 5-coordinate compounds, 52 but the
energy of the dz 2 orbital will be influenced by the
apical ligand. It is therefore expected that the 103Rh
shifts for 3 and 1 will be close to but higher than those
of 19 and 21, as is indeed observed. The low frequency
shift of 3 relative to 1 is in qualitative agreement with
the higher s-donor capacity of H compared to CH3.
w
x
27 Variable-temperature NMR spectra obtained in
Ž
toluene-d8 were referenced to external 85% H3PO4 0.0
31
Ä1
4
Ž
.
ppm, P H NMR and to the residual signals of
C6 D5CD2 H 2.10 ppm, H NMR . 29Si NMR spectra
1
.
1
were recorded using an inverse H–29 Si method and
were referenced to the external Me3SiCl at d q29.9
ppm. All NMR spectra except for those of the 103Rh
Ž
.
4. Conclusions
nucleus see Section 5.2 were obtained using Bruker
AMX400 spectrometer.
Ž .
We have reported two synthetic ways to Rh I silyl
complexes, namely: i reactions of tertiary silanes with
MeRhL4 or PhRhL3 and ii nucleophilic attack of silyl
Ž .
5.2. Rh NMR measurements
Ž .
w
x
anions at RhL4 Cl. We have described the scope and
limitations of these two strategies, demonstrated that
The instrumentation and procedures used to obtain
inverse two-dimensional P H - Rh 60,61 and H-
31
1
103
Ä1
4
w
x
103
w
x
Rh NMR 62,63 spectra were described in detail
elsewhere. 61,63 The spectral resolution in the 103Rh
w
x
12
Ž
.
domain was better than 3 Hz 1 ppm . All measure-
ments, except that of MeRh PMe3
Ž
.
Ž
.
Ž . Ž .
In PMe3 3IrH2 SiR3 the Ptrans-Si –Rh–Sis157.3 1 8 average
t
Ž
.
4
Ž .
Ž .
Ž .
1 , were carried
for SiHPh2 , 146.4 1 8 for SiPh3 and 141.8 1 8 for SiClBu2.

(
)
88
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
Ž2
.
Ž
.
out at 293 K in C6 D6. The data for 1 were obtained at
trans to Si; 1.44 d JH – P s7.8 Hz , 9H, P C H3
3
Ž3
.
Ž
.
two temperatures 223 and 233 K in toluene-d8 and
were extrapolated to 293 K. Chemical shifts are re-
ported relative to Js3.16 MHz. Signals at higher
frequencies are taken as positive.
trans to H; 1.36
t
JH – H s 7.0 Hz , 18H,
Ž
.
Ž3
.
2Si OCH2C H3 3; 4.10 symm. m JH – H s7.0 Hz ,
Ž
.
.
3
12H, 2Si OC H2CH3
(
)
(
(
) ) ( ) ( )
5.6. Fac- Me3 P 3 Rh SiMe OMe 2
H
9
2
(
)
(
) ( )
5.3. Me3 P 4 RhSi OEt 3
10
This complex was prepared from 1 or 2 analogously
to 8 using 5 instead of 4. As in the case of 8, complex 9
is produced contaminated with the corresponding di hy-
Ž
.
To a solution of 21 mg 0.05 mmol of 1 in 1 ml of
Ž
Ž
.
C6 D6 was added by a microsyringe 8 mg 0.049 mmol
Ž .
.
Ž
.
drido silyl 11 f10% .
Ž
.
3
of HSi OEt
4 . NMR analysis after 2 h showed
formation of 6 in f92% yield, the rest being
. Ž .
31
Ä1
4
Ž
.
Ž1
P H NMR C6 D6 : d y26.7 dd JP – Rh s77.7
2
.
Ž1
Hz, JP – P s29.0 Hz , 2P trans to Si; y19.4 dt JP – Rh
Ž
HRh PMe3 3 .
4
1
s103.0 Hz, 2JP – P s29.0 Hz , 1P trans to H. H NMR
31
.
Ä1
4
Ž
.
P H NMR C6 D6 : d y23.4 very broad signal
Ž2
31
Ž
.
Ä1
4
Ž
C6 D6 : d y10.63 d of pseudo q JH – P, trans s122.0
with a shoulder at y22.8. P H NMR C6 D5CD3,
y938C : d y25.9 dd JP – Rh s151.9 Hz, 2JP – P s50.7
.
Ž1
Hz, Jq f17 Hz , 1H, Rh–H; 0.68 s, 6H 2SiC H3; 1.21
.
Hz , 3P ; y11.7 dq JP – Rh f101 Hz, 2JP – P f51 Hz ,
Ž
Ž1
.
2nd order symm. 3-line m outer lines’ separation Ds
.
eq
.
Ž
.
.
3
Ž2
1
6.0 Hz , 18H, 2P C H3 trans to Si; 1.28 d JH – P s7.4
Ž
.
Ž3
1P trans to Si. H NMR C6 D6 : d 1.31 t JH – H s6.9
ax
.
Ž
Hz , 9H, P C H3 trans to H; 3.57 s and 3.59 s, 6H
.
Ž
.
.
Ž
.
3
Hz , 9H, Si OCH2C H3 3; 1.37 br s, 36H, 4P C H3
;
3
13
Ž
.
each, 2Si OC H3 .
2
Ä1
4 Ž .
Ž3
4.03 q JH – H s6.9 Hz , 6H, Si OC H2CH3
Ž
.
C H NMR C6 D6 : d 7.34 app
.
3
Ž
.
tdd Jt s9.8 Hz, Jd1 s4.2 Hz, Jd2 s1.9 Hz , 2SiCH3;
3
2
Ž1
24.11 dtd JC – P s21.6 Hz, JC – P, cis s6.4 Hz, JC – Rh
(
)
(
) ( )
5.4. Me3 P 4 RhSiMe OMe 2
7
.
Ž
.
Ž
.
f1.3 Hz , P CH3 trans to H; 24.94 m, 2P CH3
3
3
.
Ž
.
trans to Si; 50.10 br s and 50.39 br s, 2Si OCH3
Ž
.
2
A solution of 21 mg 0.05 mmol of 1 in 4 ml of
toluene was cooled to y208C in a drybox freezer and to
it was added in four portions over 2 h a similarly
29
Ä1
4
Ž
.
Ž2
Si H NMR C6 D6 : d 36.8 dm JSi – P, trans s183
.
Hz .
Ž
.
precooled solution of 1.05 equivalents of HSiMe OMe
2
(
)
( (
( ) ( ( ) ) ( )
Me3 P 3 Rh H 2 Si OMe 3 14
) ) ( ) (
)
13 and fac-
5.7. Fac- Me3 P 3 Rh Si OMe 3
H
2
Ž .
5 in 1 ml of toluene. After the addition was complete,
the reaction mixture was allowed to warm up to room
temperature and was left overnight. Then the solvent
was removed under vacuum and the oily residue was
dissolved in C6 D6. The P H NMR analysis indi-
(
)
Ž
.
Ž
.
61 mg 0.15 mmol of 2 and 30 mg 0.30 mmol of
Ž
. Ž
.
HSi OMe 12 were each dissolved in 2 ml of toluene,
31
3
Ä1
4
cooled to y208C in a drybox freezer and combined.
After 24 h at y208C the reaction mixture was allowed
to warm to room temperature and all volatile compo-
nents were removed under vacuum. The yellow oily
residue was dissolved in C6 D6. The NMR analysis
indicated the presence of 80% of 13, the rest being 14.
cated the presence in the solution of f75% of 7,
Ž
.
f17.5% of HRh PMe3 4, and f7.5% of the double
addition product 9.
P H NMR C6 D6 : d y24 very br. 1H NMR
31
Ä1
.
4
Ž
.
Ž
Ž
.
C6 D6 : d 0.61 s, 3H, SiC H3; 1.30 br s, 36H 4P C H3 ;
3
Ž
.
.
2
3.62 s, 6H, Si OC H3
5.7.1. Characterization of 13
31
Ä1
4
Ž
.
Ž
P H NMR C6 D6 : d y26.1 dd 1JP – Rh
s
(
)
( ( ) ) ( ) ( )
5.5. Fac- Me3 P 3 Rh Si OEt 3 H 8
2
2
.
78.3Hz, JP – P s29.8 Hz , 2P trans to Si; y18.8 dt
JP – Rh s99.0 Hz, 2JP – P s29.8 Hz , 1P trans to H. H
1
Ž1
.
This complex was prepared by adding two equiva-
lents of 4 to 1 ml of a benzene solution of 1 21 mg,
0.05 mmol at room temperature over 15 min. 8 was
isolated after removal of the volatile components of the
Ž2
Ž
Ž
.
NMR C6 D6 : d y10.79 d of pseudo q JH – P, trans
s
.
.
122.0 Hz, Jq s16.0 Hz , 1H, Rh–H; 1.23 2nd order
Ž
.
.
symm. 3-line m outer lines’ separation Ds6.4 Hz ,
Ž2
reaction mixture as a brownish oil in f95% purity,
Ž
.
18H, 2P C H3 trans to Si; 1.38 d JH – P s7.9 Hz ,
3
Ž
.
Ž
.
di hydrido silyl 10 see Section 5.8 being the side
product. Alternatively, 8 can be prepared from 2 and
Ž
.
Ž
.
9H, P C H3 trans to H; 3.76 s, 18H, 2Si OC H3
.
3
3
Ž
two equivalents of 4 in toluene at y208C see the
5.7.2. Characterization of 14
31
31
.
Ä1
4
Ä1
4
Ž
.
Ž1
procedure for 13 in Section 5.7 . p P H NMR
P H NMR C6 D6 : d y24.6 dt JP – Rh s85.6Hz,
2
2
Ž1
Ž
.
Ž1
C6 D6 : d y26.0 dd JP – Rh s77.7 Hz, JP – P s29.3
.
JP – P s26.8 Hz , 1P trans to Si; y14.0 dd JP – Rh
s
2
1
.
Ž1
1
.
Hz , 2P trans to Si; y19.4 dt JP – Rh s99.3 Hz,
97.5 Hz, JP – P s26.8 Hz , 2P trans to H. H NMR
2
Ž2
.
Ž
.
Ž
.
JP – P s29.3 Hz , 1P trans to H. H NMR C6 D6 : d
C6 D6 : d y10.51 d of pseudo t JH – P, trans s120.0
Ž2
.
Ž2
.
.
y10.76 d of pseudo q JH – P, trans s124.4 Hz, Jq s
Hz, Jt s20.0 Hz , 2H, Rh–H; 1.09 d JH – P s6.1 Hz ,
Ž2
.
Ž
.
18.5 Hz , 1H, Rh–H; 1.29 2nd order symm. 3-line m
9H, P C H3 trans to Si; 1.25 d JH – P s7.0 Hz ,
3
X
Ž
.
Ž
.
Ž
.
Ž
.
18H, 2P C H3 trans to H; 3.82 s, 6H, Si OC H3 .
3
outer lines separation Ds6.2 Hz , 18H, 2P C H3
3
3

(
)
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
89
(
)
( ) ( ( ) ) ( )
5.8. Fac- Me3 P 3 Rh H 2 Si OEt 3 10
was recrystallized from pentane at y208C to yield a
dark red solid, pure enough for further experiments. The
yield at best was 42%. The analytical sample and red
single crystals, suitable for X-ray analysis, were ob-
tained by slow evaporation of the solvent from a con-
The synthetic procedure and the yield were the same
as for the dimethylphenylsilyl analog 15 see Section
.
5.9 , except that 18 mg 0.110 mmol of HSi OEt
3
Ž
.
Ž
.
.
Ž
was used.
centrated pentane solution of 19 at y308C.
31
P H NMR C6 D6 : d y24.5 dt with 29Si satel-
31
Ä1
4
Ž
.
2
Ä1
4
Ž
.
Ž
.
P H NMR C6 D6 : d y17.2 d Js146 Hz .
2
31
Ž1
Ä1
4
Ž
.
lites JP – Rh s85.2 Hz, JP – P s26.5 Hz, JP – Si, trans
f
P H NMR C6 D5CD3, y808C : d y26, very br d
.
Ž1
1
Ž1
.
Ž1
JP – Rh f115 Hz , 1P trans to Si; y12 br d JP – Rh
229 Hz , 1P trans to Si; y13.7 dd JP – Rh s98.7 Hz,
f
2
1
.
Ž
.
.
Ž
.
JP – P s26.5 Hz , 2P trans to H. H NMR C6 D6 : d
149 Hz , mutually trans 2P. H NMR C6 D6 : d 0.79
Ž2
Ž
Ž
.
Ž
.
w
y10.53 d of pseudo t JH – P, trans s118.2 Hz, Jt s19.4
br s, 6H, Si C H3 2; 1.08 br s, 27H, 3P C H3 3; 7.91 m,
2H; 7.31 t 7.4 Hz , 2H; 7.19 m, 1H , SiC6 H5.
.
Ž2
.
Ž
.
.
.
x
Hz , 2H, Rh–H; 1.10 d JH – P s6.0 Hz , 9H, P C H3
3
Ž2
trans to Si; 1.29 d JH – P s7.0 Hz , 18H, 2P C H3
.
Ž
3
Ž3
.
[
(
) ]
( )
trans to H; 1.39
t
JH – H s 7.0 Hz , 9H,
Ž3
.
JH – H s 7.0 Hz , 6H,
5.12. Reaction of Rh PMe3 Cl with LiSiMe3 . Forma-
4
Ž
Ž
.
(
)
Si OCH2C H3
;
4.13
q
tion of Me3 P 4 RhSiMe3 22
3
.
.
3
Si OC H2CH3
A solution of LiSiMe3 was generated from 350 mg
(
)
( ) (
) (
)
Ž
.
5.9. Fac- Me3 P 3 Rh H 2 SiMe2 Ph 15
Hg SiMe3 and 30 mg Li sand in 1 ml of THF over 1
2
day. After removing excess Li and free Hg, that was
formed, the resulting brown solution was immediately
used in the next step. To 76 mg 0.170 mmol of
Ž
. Ž .
To a solution of HRh PMe3 45 mg, 0.110 mmol
4
Ž
.
Ž
.
Ž
.
in C6 H6 3 ml was added 19 mg 0.140 mmol of
HSiMe2 Ph. After 15 min the solvent and the excess
silane were removed under vacuum to leave 50 mg
w
Ž
. x
Rh PMe3 Cl suspended in 5 ml of THF approxi-
4
mately 2-fold excess of LiSiMe3 was added dropwise
Ž
.
w
Ž
.
x
97% of an analytically pure yellow-white solid.
upon stirring. After 30 min all Rh PMe3 Cl dissolved
and the dark yellow-brown solution was formed. The
solvent was removed under vacuum to leave a sticky
4
P H NMR C6 D6 : d y24.4 dt with 29Si satel-
31
Ä1
4
Ž
.
2
2
Ž1
lites JP – Rh s85.4 Hz, JP – P s24.3 Hz, JP – Si, trans
f
.
Ž1
1
Ž
.
146 Hz , 1P trans to Si; y16.0 dd JP – Rh s100.0 Hz,
brown solid. This was extracted with pentane 2=3 ml
2
.
Ž
.
JP – P s24.3 Hz , 2P trans to H. H NMR C6 D6 : d
and the extract was evaporated to dryness to yield 40
1
Ž2
y10.12 d of pseudo t JH – P, trans s121.8 Hz, Jt s19.0
mg of orange-brown powder, which was shown by H
and 31 P H NMR to consist of 22 and 3 in f3:2 ratio.
Ä1
4
.
Ž
.
Hz , 2H, Rh–H; 0.89 br s, 6H, Si C H3 2; 0.98 d
Ž2
.
.
Ž
.
JH – P s6.0 Hz , 18H, 2P C H3 trans to H; 1.09 d
Complex 22 exhibited the following spectral data.
3
31
Ž2
Ž
.
w
Ä1
4
Ž
.
JH – P s6.0 Hz , 9H, P C H3 trans to Si; 8.03 m,
P H NMR C6 D6 : extremely broad signal be-
3
tween d y17 and y30 ppm. 31 P H NMR C6 D5CD3,
Ä1
4
Ž
Ž
.
x
2H; 7.35 t 7.4 Hz , 2H; 7.19 m, 1H , SiC6 H5.
y558C : d y28.2 dd JP – Rh s158.1 Hz, 2JP – P s50.3
.
Ž1
2
Ž1
(
)
( ) ( ) ( )
5.10. Fac- Me3 P 3 Rh H 2 SiPh3 16
.
Hz , 3P ; y15.4 dq JP – Rh s91.1 Hz, JP – P s50.3
eq
1
.
Ž
.
Hz , 1P trans to Si. H NMR C6 D6 : d 0.68 s, 9H,
ax
1H NMR
Ž
.
Ž
.
This compound was prepared earlier and was fully
characterized 5 . In the present work it was synthesized
completely analogously to the above described di hy-
drido silyls, using equimolar amounts of reactants, and
Si C H3 3; 1.19 br s, 36H, 4P C H3
.
Ž3
.
w x
Ž
d
.
.
C6 D5CD3, y558C : d 0.83 br s, 9H, Si CH H3 3; 1.09
Ž2
Ž
.3.
Ž
JH – P s5.1 Hz , 9H, P C H3
unique; 1.25 br s,
.
Ž
.
.
3
27H 3P C H3
31
Ä1
4
Ž
.
was isolated in 95% yield. P H NMR C6 D6 : d
2
y25.0 dt with 29Si satellites JP – Rh s89.2 Hz, JP – P
Ž1
(
)
( (
) ) ( ) ( )
5.13. ReactiÕity of fac- Me3 P 3 Rh Si OEt 3 H 8
2
2
.
s21.7 Hz, JP – Si, trans f154 Hz , 1P trans to Si;
2
Ž1
y17.6 dd JP – Rh s102.1 Hz, JP – P s21.7 Hz , 2P
.
5.13.1. Reaction with CO
1
Ž
.
w x
Ž
.
trans to H. H NMR C6 D6 : as reported 5 .
A solution of 10 mg 0.015 mmol of 8 in 4 ml of
C6 H6 was transferred to a Fischer–Porter pressure flask
and was pressurized with 10 psi of CO. After 3 h of
stirring at room temperature the solvent was removed
(
)
( )
5.11. Me3 P 3 RhSiMe2 Ph 19
31
1
Ä1
4
w
Ž
.
x
Ž
To a suspension of Rh PMe3 Cl 150 mg, 0.339
under vacuum. P H , H NMR and IR analyses of
the yellow oil indicated the formation of 67% of
4
.
Ž
.
mmol in THF 10 ml , 0.8 ml of a 0.53 M solution of
Ž
.
Ž
.
Ž
Ž
. . . .
L2 CO Rh Si OEt and 33% of L3 CO Rh Si OEt .
3
10 mg 0.015 mmol of 8 were dissolved in 1 ml
C6 D6 under a nitrogen atmosphere and transferred to
Ž
.
Ž
Ž
LiSiMe2 Ph 1.25 equiv. in THF was added upon stir-
ring. The reaction mixture gradually turned brown-red.
After 40 min stirring, the mixture was evacuated and
2
3
Ž
.
Ž
.
Ž
the dry residue formed was extracted with pentane two
portions of 3 ml each . After filtration, the extract was
evacuated to yield 88 mg of a red oily material. This
a NMR tube equipped with a rubber septum. The gas
room of the NMR tube was flushed three times with
CO. Every time the solution was shaken well which led
.

(
)
90
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
Ž .
Ž
.
to a gradual loss of the yellow color. NMR and IR
c A solution of 12 mg 0.02 mmol of 13 and 244
Ž
.
Ž
.
analyses indicated
a
product ratio of 20% of
mg 2.00 mmol HSi OMe in 1.5 ml C6 D6 was
warmed up to 558C. The reaction progress was followed
by periodical measurement of P H NMR of the
solution. After 40 h 13 had completely converted to 14
and the sample was cooled to room temperature. NMR
wŽ . x
analysis indicated a yield of 10% of MeO Si and
3 2
40% of MeO Si, as quantified by addition of an
3
Ž
.
Ž
Ž
. .
Ž
.
Ž
Ž
. .
L2 CO Rh Si OEt and 80% of L3 CO Rh Si OEt
.
2
3
3
31
Ä1
4
(
)
( ( ) )
5.13.1.1. Characterization of L2 CO 2 Rh Si OEt 3
.
31
Ä1
4
Ž
.
Ž1
.
P H NMR C6 D6 : d y25.5 d JRh – P s110.5Hz .
1H NMR C6 D6 : d 1.13 vt Js3.8Hz , 18H,
Ž
.
Ž
.
.
Ž
.
Ž 3
q
Ž
.
2P C H3
;
1.40 t,
JH – H s 7.0 Hz , 9H,
3
Ž
.
.
Ž3
.
4 Ž
.
Si OCH2C H3
;
4.42
JH – H s 7.0 Hz , 6H,
internal standard HSiMe2 Ph .
3
Ž
Ž
.
Ž .
Ž
.
Ž .
Ž
.
Si OC H2CH3 3. IR Film : yCO s1975 s , 1925 vs .
d To a solution of 12 mg 0.02 mmol of 13 in 1.5
Ž
.
Ž
.
ml of C6 D6 244 mg 2.00 mmol of HSi OMe was
3
(
)
( (
) )
.
5.13.1.2. Characterization of L3 CO Rh Si OEt
.
added. About 10% of the PMe3-groups were oxidised to
Me3PO by treatment of the sample with a small amount
of air. Warming up of the reaction mixture to 558C over
3
31
Ä1
4
Ž
.
Ž1
P H NMR C6 D6 : d y26.0 d JRh – P s112.0Hz .
1
Ž
.
Ž2
.
H NMR C6 D6 : d 1.23 br d JP – H s5.4 Hz , 27H,
Ž
.
Ž 3
.
w
Ž
.
x
3P C H3
;
1.38
t
JH – H s 7.0 Hz , 9H,
40 h resulted in the formation of 97% of MeO Si
3
3
2
Ž
.
Ž3
.
Ž
and 250% of MeO Si, as quantified by addition of an
31
.
Si OCH2C H3
;
4.41
Ž
q
.
JH – H s 7.0 Hz , 6H,
3
4
Ž
.
Ž .
Ž .
Ž
.
Ä1
4
Si OC H2CH3 3. IR Film : yCO s1948 s , 1900 s .
internal standard HSiMe2 Ph . P H NMR of the
sample showed 20% of 14, the rest being decomposition
products. 29Si-INEPT-NMR C6 D6 :
d
y51.7
5.13.2. Reaction with CDCl3
Ž
.
.
Ž
.
To a solution of 16 mg 0.025 mmol of 8 in 2 ml of
C6 H6, a solution of 4 mg CDCl3 in 1 ml of C6 H6 was
added upon stirring. After 3 h of stirring at room
temperature all volatile components were removed un-
Ž
w
Ž
.
x
.
ŽŽ
.
.
MeO 3Si 2 ; y78.8 MeO Si .
4
Ž . .
Ž
Ž
e 12 mg 0.02 mmol of 13 and 10 mg 0.02 mmol
wŽ
.
x
of MeO 3Si 2 were dissolved in 1.5 ml of C6 D6 and
transferred to a screw capped NMR tube. The reaction
31
1
Ä1
4
31
Ä1
4
der vacuum. P H and H NMR analyses showed the
progress was monitored by P H NMR. After 40 h at
558C the reaction mixture contained 53% of 14 as a
major organometallic product. 1H NMR showed the
disappearance of 50% of MeO Si and the appear-
ance of significant amounts of MeO Si.
formation of 80% of a product identified as mer-
Ž
.Ž . .
L3Rh Cl CDCl2 Si OEt .
3
.Ž
Ž
31
Ä1
4
Ž
.
Ž1
P H NMR C6 D6 : d y8.2 dd JRh – P s95.0
wŽ
.
x
2
3
2
.
Ž1
Hz, JP – P s30.0 Hz , 2P; 3.7 dt JRh – P s128.7 Hz,
Ž
.
2
4
JP – P s30.0 Hz , 1P. 1H NMR C6 D6 : d 1.10 t
.
.
Ž
.
3
2
Ž
Ž
.
.
Ž
JH – H s7.0 Hz , 9H, Si OCH2C H3 3; 1.35 d JP – H
5.15. X-ray crystallography
.
Ž
Ž2
.
s10.5 Hz , 9H, P C H3 3; 1.58 t JP – H s3.5 Hz ,
Ž
.
.
.
3
Ž3
.
JH – H s 7.0 Hz , 6H,
18H, 2P C H3 3; 3.90 q
From the batch of crystals obtained from a concen-
trated pentane solution of 19, a red prismatic crystal of
dimensions 0.6=0.6=0.6 mm was chosen for the
analysis. The data were collected using a CAD4
Enraf–Nonius diffractometer, equipped with a graphite
monochromator Mo K a, ls0.71073 A . Unit cell
dimensions were determined from 25 reflections. De-
tails of crystal parameters and data collection are given
in Table 3. Three standards were collected 50 times
each with no changes in intensities and 11% changes in
azimuthal scan. The data were corrected for absorption
based on a psi scan. The structure was solved by
Ž
Si OC H2CH3
(
)
( ( ) ) ( )
5.14. Thermolyses of fac- Me3 P 3 Rh Si OMe 3 H
2
13
(
)
˚
Ž
.
All following thermolyses were carried out in
screw-capped NMR tubes. The inner surface of the
NMR tubes was silylated with Me3SiCl prior to the
experiments. The yields are reported with regard to the
used amount of 13.
Ž .
Ž
.
a A solution of 23 mg 0.04 mmol of 13 in 1.5 ml
of C6 D6 was warmed up to 558C. After 72 h the 31 P
NMR follow-up of the reaction showed a complete
transformation of 13 to 14 and an unknown decomposi-
Ž
.
Ž
. w x
automated Patterson analysis SHELXS-86 64 and
Ž
. w x
Fourier method SHELXL-93 , 65 refined using full-
1
tion product. H NMR and GC-MS indicated the pres-
ence of 2%
MeO Si : H NMR C6 D6 :d 3.52 s coincidental
with the signal due to added authentic sample of
matrix least-squares refinement based on F2. Hydro-
w
Ž
.
x
Ž
.
MeO Si
and 10% MeO Si.
3
Ž
2
4
1
w
Ž
.
x
.
Ž
Table 4
3
2
Ž
.
Selected bond angles deg in the molecule of 19
Atoms Bond angle Atoms
Ž .
1
w
Ž
.
x
. Ž
.
Ž
.
Bond angle
MeO Si . MeO 4Si: H NMR C6 D6 : d 3.43 s.
3
2
Ž .
Ž .
A 6-fold excess 15 mg, 0.12 mmol of
b
Ž
.
Ž . Ž .
Ž
.
Ž .
Ž
.
Ž
.
.
.
P 2a –Rh 1 –P 2 159.98 3
Ž . Ž . Ž .
C 23 –P 2 –C 22
100.36 13
Ž
.
Ž
Ž
.
Ž
.
.
Ž .
Ž
Ž
.
.
Ž .
P 2a –Rh 1 –P 1 94.04 2
C 11a –P 1 –C 11 96.1 2
HSi OMe was added to a solution of 12 mg 0.02
3
Ž
.
Ž . Ž .
Ž
Ž .
Ž .
Ž
P 2a –Rh 1 –Si 89.94 2
C 11a –P 1 –C 12 100.63 12
Ž . Ž .
.
mmol of 13 in 1.5 ml C6 D6. The solution was treated
as in a . P H , 1H and GC-MS were measured,
31
Ž . Ž . Ž .
P 1 –Rh 1 –Si 156.43 3
C 1 –Si–C 1a 97.7 2
Ž . Ž .
Ž .
Ä1
4
Ž
Ž
.
Ž .
Ž
.
Ž
.
Ž
C 21 –P 2 –C 23 101.37 14 C 1 –Si–C 2
101.38 10
showing the signals of 14 and the formation of 4% of
.
Ž . Ž .
Ž
.
C 21 –P 2 –C 22 97.12 14
w
Ž
.
x
Ž
.
MeO Si and 10% of MeO Si.
3
2
4

(
)
M. Aizenberg et al.rJournal of Organometallic Chemistry 551 1998 81–92
91
w
x
17 G.P. Mitchell, T.D. Tilley, G.P.A. Yap, A.L. Rheingold,
gens were found from the difference Fourier map and
refined in a free mode with individual temperature
factors. Scattering factors, including anomalous terms
Ž
.
Organometallics 14 1995 5472.
w
w
w
x
Ž
.
18 G.P. Mitchell, T.D. Tilley, Organometallics 15 1996 3477.
19 H. Kono, H. Wakao, I. Ojima, Chem. Lett. 1975 189.
20 M.D. Fryzuk, L. Rosenberg, S.J. Rettig, Organometallics 10
x
Ž
.
w
x
for Rh, Si and P, were taken from the literature. 66 For
202 parameters the following final discrepancy factors
x
Ž
.
1991 2537.
w
w
w
x
Ž
.
21 M.D. Fryzuk, L. Rosenberg, S.J. Rettig, Organometallics 15
were obtained: R1 based on F s0.0312 and wR2
X
X
2
Ž
.
1996 2871.
Ž
.
Ž
Ž ..
based on F s0.077 I)2s I ; R1 s0.0344, wR2
x
22 P.I. Djurovich, A.R. Dolich, D.H. Berry, J. Chem. Soc. Chem.
2
Ž
.
Ž
.
s0.04389 all data . GOF on F s1.180, largest
Ž
.
Commun. 1994 1897.
3
˚
electron density 1.473 eAy . Selected interatomic bond
x
23 R. Takeuchi, N. Tanouchi, J. Chem. Soc. Chem. Commun.
lengths and angles are listed in Tables 1 and 2. The
molecule is occupying a mirror plane of symmetry with
atoms C12, P1, Rh1, Si, C2, C3, C4, C5, C6, and C7
lying precisely on this plane.
Ž
.
1993 1319.
w
w
x
x
Ž
.
24 T.H. Chan, G.Z. Zheng, Tetrahedron Lett. 34 1993 3095.
25 Y. Kawanami, K. Yamamoto, Bull. Chem. Soc. Jpn. 69 1996
Ž
.
1117.
w
x
26 M. Aizenberg, D. Milstein, Angew. Chem. Int. Ed. Engl. 33
Complete lists of bond lengths and angles, and tables
of thermal parameters and hydrogen atom coordinates
have been deposited at the Cambridge Crystallographic
Data Centre.
Ž
.
1994 317.
w
w
w
x
Ž
.
27 M. Aizenberg, D. Milstein, J. Am. Chem. Soc. 117 1995 6456.
28 M. Aizenberg, D. Milstein, Organometallics 15 1996 3317.
29 M. Aizenberg, D. Milstein, Abstracts of the 10th International
x
Ž
.
x
Symposium on Homogeneous Catalysis. Princeton, USA August
11–16, 1996, p. B45.
w
w
w
x
30 T.B. Marder, W.C. Fultz, J.C. Calabrese, R.L. Harlow, D.
Acknowledgements
Ž
.
Milstein, J. Chem. Soc. Chem. Commun. 1987 1543.
x
31 T.B. Marder, D.M.-T. Chan, W.C. Fultz, D. Milstein, J. Chem.
We thank Dr. F. Frolow for measuring the X-ray
structure of complex 19 and J.M. Ernsting for measur-
ing the 103Rh NMR spectra. C.J.E. thanks the Nether-
lands Foundation for the Advancement of Pure Science
Ž
.
Soc. Chem. Commun. 1988 996.
x
32 A.A. Zlota, F. Frolow, D. Milstein, J. Am. Chem. Soc. 112
Ž
.
1990 6411.
w
w
x
x
Ž
.
33 J. Chatt, C. Eaborn, S. Ibekwe, Chem. Commun. 1966 700.
34 R.N. Haszeldine, R.V. Parish, J.H. Setchfield, J. Organomet.
Ž
.
NWO for a travel grant. The research performed in
Ž
.
Chem. 57 1973 279, and references therein.
Israel was supported by the Israel Science Foundation.
M.A. thanks the Clore Foundations, Jerusalem, Israel
for a scholarship. D.M. is the holder of the Israel Matz
Professorial Chair of Organic Chemistry.
w
x
35 R.A. Jones, F. Mayor Real, G. Wilkinson, A.M.R. Galas, M.B.
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Ž
.
1980 511.
w
w
x
36 K.T. Kobayashi, T. Hayashi, H. Yamashita, M. Tanaka, Chem.
Ž
.
Lett. 1988 1411.
x
Ž
.
37 J. Kiso, K. Tamao, M. Kumada, J. Organomet. Chem. 76 1974
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w
x
x
Ž
.
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w x
1
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Ž
.
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Ž
.
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w
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w
x
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.
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.
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