Oxidative addition reactions of silyl halides with the (PNP)Rh fragment

Article abstract of DOI:10.1021/om800216h

The (PNP)Rh fragment, where PNP is the bis(o-diisopropylphosphinophenyl) amide pincer ligand, has been shown to undergo a series of silicon-halogen oxidative addition reactions. (PNP)Rh(SPrⁱ ₂) (1) reacted with certain silyl halides with formation of (PNP)Rh(Silyl)(Hal) and release of SPr₂ⁱ. The reactions with 1.1 equiv of Me₃Si-I, Cl₃Si-Cl, or MeCl ₂Si-Cl proceeded to completion, the reactions with 1.1 equiv of Me₂ClSi-Cl or Me₃Si-Br produced an equilibrium mixture of (PNP)Rh(Silyl)(Hal) and (PNP)Rh(SPrⁱ₂) (1), and the reaction with Me₃Si-Cl did not proceed at all. (PNP)Rh(SiMe ₃)(Cl) was instead prepared via the reaction of (PNP)Rh(Me)(CH ₂Ph) with Me₃Si-Cl, which proceeds with concomitant elimination of ethylbenzene. The reaction of (PNP)Rh(SPrⁱ ₂) (1) with Me₂SiHCl led to the exclusive formation of (PNP)Rh(SiMe₂Cl)(H) (14), containing a borderline Si...H contact. (PNP)Rh(SPr₂ⁱ) (1) and (PNP)Rh(SiMe ₂Cl)(Cl) (7) displayed similar rates in the reaction with PhBr that results in (PNP)Rh(Ph)(Br), presumably via the rate-limiting elimination of either SPr₂ⁱ or Me₂SiCl₂.

Full text of DOI:10.1021/om800216h

Organometallics 2008, 27, 6257–6263
6257
Oxidative Addition Reactions of Silyl Halides with the (PNP)Rh
Fragment
Sylvain Gatard, Chun-Hsing Chen, Bruce M. Foxman, and Oleg V. Ozerov*
Department of Chemistry, Brandeis UniVersity, MS 015, 415 South Street, Waltham, Massachusetts 02454
ReceiVed March 7, 2008
The (PNP)Rh fragment, where PNP is the bis(o-diisopropylphosphinophenyl)amide “pincer” ligand,
has been shown to undergo a series of silicon-halogen oxidative addition reactions. (PNP)Rh(SPri2) (1)
reacted with certain silyl halides with formation of (PNP)Rh(Silyl)(Hal) and release of SPri2. The reactions
with 1.1 equiv of Me3Si-I, Cl3Si-Cl, or MeCl2Si-Cl proceeded to completion, the reactions with 1.1 equiv
of Me2ClSi-Cl or Me3Si-Br produced an equilibrium mixture of (PNP)Rh(Silyl)(Hal) and (PNP)Rh(SPri2)
(1), and the reaction with Me3Si-Cl did not proceed at all. (PNP)Rh(SiMe3)(Cl) was instead prepared via
the reaction of (PNP)Rh(Me)(CH2Ph) with Me3Si-Cl, which proceeds with concomitant elimination of
ethylbenzene. The reaction of (PNP)Rh(SPri2) (1) with Me2SiHCl led to the exclusive formation of
(PNP)Rh(SiMe2Cl)(H) (14), containing a borderline Si · · · H contact. (PNP)Rh(SPri2) (1) and
(PNP)Rh(SiMe2Cl)(Cl) (7) displayed similar rates in the reaction with PhBr that results in (PNP)Rh(Ph)(Br),
presumably via the rate-limiting elimination of either SPri2 or Me2SiCl2.
Scheme 1
Introduction
Oxidative addition (OA) and its reverse (RE) are among the
most fundamental reactions in organometallic chemistry.1 OA/
RE reactions involving carbon-element bonds are a customary
focus because of their importance in the syntheses of organic
compounds.2 OA/RE reactions involving silicon, the heavier
congener of carbon, receive less attention.3-9 We have previ-
ously reported a series of OA and RE reactions, as well as ligand
exchange reactions, occurring at a Rh(I) center10,11 supported
by the diarylamido-based PNP pincer ligand.12,13 The (PNP)Rh
fragment is especially convenient for these studies, as it is
compatible with a large variety of reactions, potentially allowing
for well-defined comparisons of the kinetic and thermodynamic
parameters. For example,10b we showed that (PNP)Rh(SPri2)
(1) reacts with PhBr to give the Rh(III) OA product (PNP)-
Rh(Ph)(Br) (3) via a dissociative mechanism with intermediate
generation of the unsaturated (PNP)Rh fragment 2 (Scheme 1).14
Herein, we report our studies of Si-Hal OA reactions with the
(PNP)Rh fragment. Our work provides insight into the relative
thermodynamic affinity of the (PNP)Rh fragment toward
addition of various halosilanes and how it compares with its
affinity toward addition of other species.
* Corresponding author. E-mail: ozerov@brandeis.edu.
(1) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley-Interscience: New York, 2001; pp 149-173. (b)
van Leeuwen, P. W. N. M. Homogeneous Catalysis: Understanding the
Art; Kluwer Academic Publishers: Dordrecht, 2004; pp 271-298 and 387-
402.
(2) Negishi, E. I., Ed. Handbook of Organopalladium Chemistry for
Organic Synthesis; Wiley-Interscience: New York, 2002.
(3) Yoo, H.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 2006, 128,
6038.
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1980, 193, 127. (b) Uson, R.; Oro, L. A.; Ciriano, M. A.; Gonzalez, R. J.
Organomet. Chem. 1981, 205, 259.
(5) Zlota, A. A.; Frolow, F.; Milstein, D. J. Chem. Soc., Chem. Commun.
1989, 1826.
(6) Yamashita, H.; Kawamoto, A. M.; Tanaka, M.; Goto, M. Chem. Lett.
1990, 2107.
(7) Clark, H. C.; Hampden-Smith, M. J. Coord. Chem. ReV. 1987, 79,
229.
(8) (a) Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M.; Goto,
M. J. Am. Chem. Soc. 1988, 110, 4417. (b) Yamashita, H.; Tanaka, M.;
Goto, M. Organometallics 1997, 16, 4696.
(9) Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M. Chem. Lett.
1990, 1447.
(10) (a) Gatard, S.; C¸ elenligil-C¸ etin, R.; Guo, C.; Foxman, B. M.;
Ozerov, O. V. J. Am. Chem. Soc. 2006, 128, 2808. (b) Gatard, S.; Guo, C.;
Foxman, B. M.; Ozerov, O. V. Organometallics 2007, 26, 6066.
(11) For other reports on the chemistry of (PNP)Rh complexes, see the
following:(a) Weng, W.; Guo, C.; C¸ elenligil-C¸ etin, R.; Foxman, B. M.;
Ozerov, O. V. Chem. Commun. 2006, 197. (b) Weng, W.; Guo, C.; Moura,
C. P.; Yang, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2005, 24,
3487. (c) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman, B. M. J. Am.
Chem. Soc. 2004, 126, 4792. (d) Winter, A. M.; Eichele, K.; Mack, H.-G.;
Potuznik, S.; Mayer, H. A.; Kaska, W. C. J. Organomet. Chem. 2003, 682,
149.
(12) For reviews on the chemistry of diarylamido-based PNP complexes,
see: (a) Liang, L.-C. Coord. Chem. ReV. 2006, 250, 1152. (b) Ozerov, O. V.
In The Chemistry of Pincer Compounds; Morales-Morales, D., Jensen, C.,
Eds.; Elsevier: Amsterdam, 2007; pp 287-309.
(13) The diarylamido-based PNP ligand used in this work is preceded
and to some degree inspired by the Fryzuk amido/(bis)phosphine ligand13a,b
of the [(R2PCH2SiMe2)N] type that has more recently been employed by
Caulton et al.:13c,d
(a) Fryzuk, M. D. Can. J. Chem. 1992, 70, 2839–2845. (b)
Fryzuk, M. D.; Berg, D. J.; Haddad, T. S. Coord. Chem. ReV.
1990, 99, 137. (c) Ingleson, M. J.; Fullmer, B. C.; Buschhorn,
D. T.; Fan, H.; Pink, M.; Huffman, J. C.; Caulton, K. G. Inorg.
Chem. 2008, 47, 407. (d) Ozerov, O. V.; Watson, L. A.; Pink,
M.; Caulton, K. G. J. Am. Chem. Soc. 2007, 129, 6003.
(14) The instability of the “naked” (PNP)Rh fragment precludes its
characterization. While we do not know its precise structure and whether
it is truly a 14-electron three-coordinate fragment, it behaves as a kinetic
equivalent of such. A recent study by Caulton et al. demonstrated that a
closely related (PNP*)Rh fragment (where PNP* is the Fryzuk-type ligand
(tBu2PCH2SiMe2) 2N) favors a Rh(III) ground state resulting from the
intramolecular OA of a C-H bond. Verat, A. Y.; Pink, M.; Fan, H.;
Tomaszewski, J.; Caulton, K. G. Organometallics 2008, 27, 166.
10.1021/om800216h CCC: $40.75
2008 American Chemical Society
Publication on Web 11/06/2008

6258 Organometallics, Vol. 27, No. 23, 2008
Gatard et al.
as has been shown for Pd/Pt systems.15,16 (PNP)Rh(Me)(Cl) (10)
was found to react with PhCH2MgCl to give a 95:5 mixture of
two new compounds that we have identified as
(PNP)Rh(Me)(CH2Ph) (13) and (PNPRh(CH2Ph)217 (14) on the
basis of solution NMR data. While we have not performed
rigorous kinetic measurements (as we did with 11/12),10a the
rates of C-C RE for 13 and especially 14 are much lower than
those for 11 or 12, insofar as the workup at 22 °C (ca. 30 min)
does not result in significant degradation (<5%). When a C6D6
solution of a 95:5 mixture of 13/14 was treated with 1.1 equiv
of Me3SiCl and allowed to stand for 3 days, >95% conversion
to (PNP)Rh(SiMe3)(Cl) (6) was observed in situ by NMR
methods with concomitant production of ethylbenzene and
bibenzyl (Scheme 3).
Scheme 2
Interestingly, the isolation of a (PNP)Rh(R)(R′) precursor
apparently is not always necessary. When (PNP)Rh(Me)(Cl)
(10) was treated first with 1.1 equiv of Me3SiBr and then with
1.1 equiv of PhLi and allowed to stand for 24 h at ambient
temperature, 5 was the major product of the reaction (NMR
evidence) and was isolated in 40% yield (unoptimized yield of
14 mg) upon workup as an analytically pure solid. This is rather
surprising, as it appears to indicate that PhLi reacted with 10
faster than with Me3SiBr.
Solution NMR Characterization of the Si-Hal OA
Products. All of the Si-X OA products (4-9) demonstrated
time-averaged Cs symmetry at 22 °C in the NMR experiments.
These compounds are rich in NMR information and were fully
characterized by 1H, 13C, 31P, and 29Si NMR in solution (Table
1 and the Experimental Section). The 31P chemical shift (δ
36-42 ppm) and the JP-Rh (100-112 Hz) data for the
silicon-halogen oxidative addition products 4-9 are similar
to those previously observed for (PNP)Rh(H)(Cl),11c (PNP)-
Rh(Me)(Cl) (10),11c and (PNP)Rh(Ar)(X).10a In the series of
(PNP)Rh(SiMe3)(Hal) complexes (4-6), the nature of the halide
has very little effect on the chemical 29Si chemical shift or the
JSi-Rh or JSi-P values. On the other hand, in the series of
(PNP)Rh(SiMe3-nCln)(Cl) complexes (6-9), the JSi-Rh and JSi-P
values steadily increase with increasing n. This is indicative of
a stronger interaction of the silyl group with Rh as the number
of electron-withdrawing substituents on Si increases. A similar
trend in the corresponding coupling constants was reported by
Tanaka et al. for (Me3-nClnSi)(Cl)Pt(PEt3)2 complexes.8
Results and Discussion
Reactions of Si-Hal-Containing Compounds with
(PNP)Rh(SPri2) (1). Complex 1 proved to be a viable (PNP)Rh
synthon in reactions with halobenzenes,10b and we set out to
explore its reactivity in Si-Hal OA reactions. We initially
focused on the reactions of 1 with Me3Si-Hal reagents (Scheme
2). No oxidative addition product was observed in the reactions
of 1 with Me3Si-Cl. The OA of Me3SiBr to (PNP)Rh is
approximately isoergic with the binding of SPri2 (Keq ) 0.8(1)
for the conversion from 1 to 5). The reaction of 1.1 equiv of
Me3Si-I with 1 proceeded to completion, giving 4 as product.
This is in contrast to the OA reactions of Ph-Hal, where Hal )
Cl, Br, and I, all leading to thermodynamically favorable OA
reaction with 1. The intrinsic bond energetics must play a role
here, but the conical Me3Si group must also create greater steric
encumbrance compared to the flat, “wedge-like” Ph group in
the OA products.
The second set of compounds we explored were compounds
with a varying number of Cl and Me groups on Si (Scheme 2).
As mentioned before, 1 did not react with Me3SiCl. The reaction
of 1 with Me2SiCl2 required 35 equiv of Me2SiCl2 to proceed
to >95% conversion to 7 (<24 h, 70 °C), while the reactions
of 1 with 1.1 equiv of MeSiCl3 or SiCl4 proceeded completely
to form the OA products 8 and 9, respectively. The incomplete
conversion in the reaction with Me2SiCl2 is a thermodynamic
issue (Keq ) 1.0(1) from a set of exchange reactions), similarly
to Me3SiBr. We have also tested the reactivity of 1 with
Me3SiOTf, Me3SiOSiMe3, and Me3SiSiMe3 and found that 1
remained unchanged after extended thermolysis (48 h, 85 °C,
C6D6) in the presence of these reagents.
Tanaka et al. studied the reactions of Pt(0) phosphine
complexes with the same set of Si-Hal reagents as used in
Scheme 2 here.8 Interestingly, the thermodynamic trends in the
Tanaka work are the same as observed in this work: higher
thermodynamic preference for OA of heavier halogen-silicon
bonds and for OA of Si-Cl bonds with more Cl substituents
on Si.
Synthesis of (PNP)Rh(SiMe3)(Br) (5) and (PNP)-
Rh(SiMe3)(Cl) (6) via C-C Elimination at Rh. We recently
described complexes (PNP)Rh(Ph)(Me) (11) and (PNP)RhPh2
(12).10a Both undergo clean C-C RE to generate the (PNP)Rh
fragment (2) in situ (Scheme 3). However, both 11 and 12 are
too short-lived to be conveniently isolable on the experimental
time scale. We surmised that C(sp3)-C(sp3) RE should proceed
more slowly than either C(sp2)-C(sp2) or C(sp3)-C(sp2) RE,
Structural Characterization of 7. The solid-state structure
of 7 was established in the course of a single-crystal X-ray
diffraction study (Figure 1). The environment about Rh is best
described as approximately square pyramidal with the silyl
ligand occupying the apical position. Silyl is a ligand of strong
trans-influence, and square pyramid with a strong trans-influence
ligand trans to an empty site is a common motif for five-
coordinate d6 complexes.18 Among the PNP-supported Rh
complexes in our work, analogous structures have been deter-
mined in the solid state for (PNP)Rh(Ph)(Br) (3, apical Ph) and
(15) (a) Hartwig, J. F. Inorg. Chem. 2007, 46, 1936. (b) Braterman,
P. S.; Cross, R. J.; Young, G. B. J. Chem. Soc., Dalton Trans. 1977, 1892.
(16) (a) Ananikov, V. P.; Musaev, D. G.; Morokuma, K. Organometallics
2005, 24, 715. (b) Ananikov, V. P.; Musaev, D. G.; Morokuma, K. Eur.
J. Inorg. Chem. 2007, 5390.
(17) 13 is presumably formed via benzyl/methyl exchange between 13
and PhCH2MgCl.
(18) (a) For analysis of the structural preferences of five-coordinate d6
complexes see the following: Lam, W. H.; Shimada, S.; Batsanov, A. S.;
Lin, Z.; Marder, T. B.; Cowan, J. A.; Howard, J. A. K.; Mason, S. A.;
McIntyre, G. J. Organometallics 2003, 22, 4557. (b) Rachidi, I. E.-I.;
Eisenstein, O.; Jean, Y. New J. Chem. 1990, 14, 671. (c) Riehl, J.-F.; Jean,
Y.; Eisenstein, O.; Pelissier, M. Organometallics 1992, 11, 729. (d) Olivan,
M.; Eisenstein, O.; Caulton, K. G. Organometallics 1997, 16, 2227.

OxidatiVe Addition Reactions of Silyl Halides
Organometallics, Vol. 27, No. 23, 2008 6259
Scheme 3
Table 1. Selected NMR Data for 4-9
Scheme 4
δ, 31P,
ppm
1JP-Rh
Hz
,
δ, 29Si,
ppm
1JSi-Rh
Hz
,
2JSi-P
,
Hz
compd
4
5
6
7
8
9
39.5
37.2
36.4
38.7
40.8
42.1
113
110
112
109
104
100
60.7
59.5
58.5
66.7
42.5
28
28
29
39
57
87
8
8
8
8
10
12
For 15, it is conceivable to propose two bonding descriptions:
either a classical silyl hydride formalism (true OA product) or
an η2-Si-H nonclassical σ-complex. η2-Si-H complexes of Rh
have been characterized for addition of Si-H to Rh(III),21 but
not Rh(I), as is the case here. Both the solution NMR data and
the results of a solid-state X-ray diffraction on a single crystal
of 15 (Figure 2) point to the identity of 15 being a borderline
case. The hydridic resonance in 15 was found at δ -15.6 ppm
-12.5
(PNP)Rh(Me)(Cl) (10, apical Me).10a,11c The environment about
Si is pseudotetrahedral (angles about Si range from 102° to 118°)
with no structural evidence of interaction between Rh and the
substituents on Si. The Rh-P, Rh-N, and Rh-Cl distances
are unremarkable and comparable to those observed in 3 and
10.10a,11c The Rh-Si distance in 7 (2.2777(9) Å) is only slightly
1
in the H spectrum as a doublet of doublets of triplets, owing
to the coupling to 29Si (31 Hz), 103Rh (24 Hz), and 31P (11 Hz),
respectively. The 29Si resonance of 15 (δ 49.3 ppm) displays
coupling to the hydride (31 Hz), 103Rh (23 Hz), and 31P (6 Hz).
JSi-H values have been proposed as indicators of the presence
of a residual Si-H interaction. Schubert’s arbitrary proposal
of 10-20 Hz as the lower limit for Si-H bonding is frequently
used.22 The value of 31 Hz falls slightly above this criterion.
However, in a more recent review,23Nikonov cogently argued
shorter than the Rh-Si distance of 2.314(2)
Å in
(Me3P)3Rh(H)2(SiClPh2) reported by Osakada et al.19
Reaction of (PNP)Rh(SPri2) (1) with Me2SiHCl and the
Structure of 15. The reaction of 1 with Me2SiHCl offered
insight into the competition between Si-H and Si-Cl OA.
Complex 15 was formed exclusively after thermolysis (18 h,
70 °C). Given the conditions, it is reasonable to assume that
the preference for 15 over the unobserved Si-Cl OA product
is thermodynamic and not merely kinetic.
Figure 2. ORTEP20 drawing (50% probability ellipsoids) of 15
showing selected atom labeling. Hydrogen atoms (except Rh-H)
and the rotational disorder of the Me2SiCl group are omitted for
clarity. Rotational disorder of the SiClMe2 group is not shown.
Selected bond distances (Å) and angles (deg) follow: Rh1-P1,
2.3081(4); Rh1-P2, 2.3056(4); Rh1-N1, 2.0642(13); Rh1-Si1,
2.2600(5); Rh1-H1, 1.50(2); Si1-H1, 1.93(2); P1-Rh1-P2,
156.195(16); P1-Rh1-N1, 80.62(4); P2-Rh1-N1, 82.58(4);
P1-Rh1-Si1, 100.928(17); P2-Rh1-Si1, 102.866(17);
N1-Rh1-Si1, 136.83(4); P1-Rh1-H1, 97.3(8); P2-Rh1-H1,
94.8(8); N1-Rh1-H1, 165.7(8).
Figure 1. ORTEP20 drawing (50% probability ellipsoids) of 7
showing selected atom labeling. Hydrogen atoms are omitted for
clarity. Selected bond distances (Å) and angles (deg) follow:
Rh1-Si1, 2.2777(9); Rh1-P1, 2.3249(8); Rh1-P2, 2.3256(8);
Rh1-N1, 2.027(2); Rh1-Cl1, 2.3511(7); Si1-Rh1-P1,
96.46(3); Si1-Rh1-P2, 97.43(3); P1-Rh1-P2, 159.42(3);
Si1-Rh1-N1, 91.56(8); P1-Rh1-N1, 80.38(7); P2-Rh1-N1,
84.13(7); Si1-Rh1-Cl1, 96.24(3); P1-Rh1-Cl1, 99.42(3);
P2-Rh1-Cl1, 94.09(3); N1-Rh1-Cl1, 172.17(8).

6260 Organometallics, Vol. 27, No. 23, 2008
Gatard et al.
Scheme 5
of a molecule via RE) should be similar to the binding energy
of the fragment being lost,25 these results are consistent with
the greater thermodynamic preference for the OA of MeSiCl3
to the (PNP)Rh fragment compared to the OA of Me2SiCl2 and
coordination of SPri2. 1 is roughly isoergic with 7 (vide supra),
and the similarity of their apparent rates of reaction with PhBr
is consistent with a dissociative mechanism in both cases. At
this point, however, we cannot conclusively establish the
intrinsic mechanism of the reaction of (PNP)Rh (2) with silyl
halides.
that JSi-H values should be evaluated with caution and that
several factors need to be taken into account. For example, JSi-H
values in free trialkylsilanes are intrinsically smaller than JSi-H
values in silanes bearing electron-withdrawing substituents on
Si (such as Cl). It is thus unreasonable to apply the same
arbitrary “cutoff” value for different silanes.
For a true silyl hydride structure for 15, a Y-shaped geometry
is expected with an acute H-Rh-Si angle.18 It is worth noting
that acute H-Ta-PMe3 and H-Re-PMe3 angles have been
previously shown to result in JH-P coupling as large as 75 Hz;
nonclassical H-P interactions were not invoked.24
Conclusion
Investigation of Si-Hal oxidative addition reactions to the
(PNP)Rh fragment led to a few interesting findings. The
thermodynamic favorability of the oxidative addition reactions
increases for Me3Si-Hal compounds in the series Cl < Br < I.
The oxidative addition of the Si-Cl bond becomes more
favorable with the increasing number of Cl substituents on the
Si atom. On the other hand, Si-H addition is preferred over
the Si-Cl addition when Me2SiHCl is used as a substrate.
(PNP)Rh(SPri2) (1) serves as a convenient precursor for the
(PNP)Rh fragment 2 (via SPri2 dissociation) only for those
reactions where oxidative addition of Si-Hal is more favorable
than coordination of SPri2. The less thermodynamically stable
oxidative addition products can nonetheless be prepared by using
C-C reductive elimination to access (PNP)Rh (2) irreversibly.
Oxidative addition of PhBr proceeds at similar rates with
(PNP)Rh(SPri2) (1) and with (PNP)Rh(SiMe2Cl)(Cl) (7). By
The 29Si-103Rh coupling in 15 (23 Hz) is lower than for a
presumably classical single Rh-Si bond in 7 (39 Hz); however,
comparison of these values should also be made with caution
because of the different structures of 15 and 7. In the square-
pyramidal 7, the silyl ligand is trans to the empty site, which
may lead to enhanced Rh-Si bonding.
The solid-state structure of 15 was determined by X-ray
diffractometry (Figure 2). The N1-Rh1-Si1 angle of 136.83(4)°
is consistent with both a Y-shaped OA product structure and a
nonclassical silane complex. The hydrogen atom in question
was located and its position was refined isotropically. Applying
caution appropriate to the determination of hydrogen positions
by X-ray diffractometry, we note that the Si-H distance is quite
long (1.93(2) Å) and is near 2 Å, another arbitrary “cutoff”
criterion introduced by Schubert.22 At the same time the Rh-Si
distance in 15 (2.2600(5) Å) is actually slightly shorter than
the unambiguous Rh-Si single bond in 7 (2.2777(9) Å). The
chemistry of Si-H addition to transition metals truly offers a
continuum of structures in terms of the bonding situation. Our
data indicate that 15 is at the end of this continuum, approaching
or embodying an OA product.
analogy with the earlier studies of the reactivity of 1,10b
a
dissociative mechanism is proposed for the reaction of PhBr
with 7, intimating initial loss of Me2SiCl2.
The rigid PNP ligand ensures that the (PNP)Rh framework
endures a wide variety of ligand exchange, oxidative addition,
and reductive elimination reactions and thus permits us to
concentrate on straightforward kinetic and thermodynamic
comparisons. The present study allows us to not only analyze
the Si-Hal oxidative addition reactivity but also place it into
the context of other reactions of (PNP)Rh.
Experimental Section
Oxidative Addition of PhBr. We previously showed that
the OA reaction of PhBr with 1 proceeds via a dissociative
mechanism (Scheme 5).10b We surmised that the Si-Cl OA
products may enter a similar reaction (Scheme 5), where the
initial step, analogous to the simple SPri2 dissociation, would
be the loss of the chlorosilane via Si-Cl RE. To test this
hypothesis, we performed thermolyses of 1, 7, and 8 with 1.1
equiv of PhBr in C6D6. After 40 min at 75 °C, the reactions
with 1 and 7 resulted in similar conversions to 3 (88% and 80%,
respectively), whereas no conversion was detected in the reaction
with 8 (31P NMR evidence). Since the activation energy for a
dissociative reaction (be that plain ligand dissociation or loss
General Considerations. Unless specified otherwise, all ma-
nipulations were performed under an argon atmosphere using
standard Schlenk line or glovebox techniques. Ethyl ether and
pentane were dried and deoxygenated (by purging) using a solvent
purification system by MBraun and stored over molecular sieves
in an Ar-filled glovebox. C6D6 was dried over NaK/Ph2CO, distilled,
and stored over molecular sieves in an Ar-filled glovebox. Fluo-
robenzene was dried with CaH2, then distilled and stored over
molecular sieves in an Ar-filled glovebox. (PNP)Rh(Cl)(Me)11c and
(PNP)Rh(SPri2)10b were prepared according to modified published
procedures. Silicon tetrachloride, MeSiCl3, Me2SiCl2, Me3SiCl,
Me3SiBr, Me3SiI, Me2SiHCl, Me3SiSiMe3, Me3SiOTf, and
Me3SiOSiMe3 were degassed prior to use and stored over molecular
sieves in an Ar-filled glovebox. All other chemicals were used as
received from commercial vendors. NMR spectra were recorded
on a Varian iNova 400 (1H NMR, 399.755 MHz; 13C NMR, 100.518
MHz; 31P NMR, 161.822 MHz) and a Varian iNova 500 (29Si NMR,
(19) Osakada, K.; Sarai, S.; Koizumi, T.; Yamamoto, T. Organometallics
1997, 16, 3973.
(20) Ortep-3 for Windows. Farugia, L. J. Appl. Crystallogr. 1997, 30,
565.
(21) Taw, F. L.; Bergman, R. G.; Brookhart, M. Organometallics 2004,
23, 886.
(22) Schubert, U. AdV. Organomet. Chem. 1990, 30, 151.
(23) Nikonov, G. I. AdV. Organomet. Chem. 2005, 53, 217.
(24) (a) Ozerov, O. V.; Watson, L. A.; Pink, M.; Caulton, K. G. J. Am.
Chem. Soc. 2004, 126, 6363. (b) Clark, J. R.; Pulvirenti, A. L.; Fanwick,
P. E.; Sigalas, M.; Eisenstein, O.; Rothwell, I. P. Inorg. Chem. 1997, 36,
3623. (c) Parkin, B. C.; Clark, J. C.; Visciglio, V. M.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1995, 14, 3002.
(25) There is some debate in the literature pertaining to this approxi-
mation:(a) Zhang, S.; Dobson, G. R. Inorg. Chim. Acta 1991, 181, 103. (b)
Asali, K. J.; Awad, H. H.; Kimbrough, J. F.; Lang, B. C.; Watts, J. M.;
Dobson, G. R. Organometallics 1991, 10, 1822. (c) Bryndza, H. E.;
Domaille, P. J.; Paciello, R. A.; Bercaw, J. E. Organometallics 1989, 8,
379. (d) Klassen, J. K.; Selke, M.; Sorensen, A. A.; Yang, G. K. J. Am.
Chem. Soc. 1990, 112, 1267.

OxidatiVe Addition Reactions of Silyl Halides
Organometallics, Vol. 27, No. 23, 2008 6261
1
1
100 MHz) spectrometer. For H and 13C{1H} NMR spectra, the
The reaction was monitored by 31P{1H} NMR and H NMR at
residual solvent peak was used as an internal reference. 31P{1H}
NMR spectra were referenced externally using 85% H3PO4 at 0
ppm. 29Si{1H} NMR were referenced internally using tetrameth-
ylsilane at 0 ppm. The signal-to-noise ratios of the 29Si{1H} NMR
spectra of (PNP)Rh(I)(SiMe3) (4), (PNP)Rh(Br)(SiMe3) (5), and
(PNP)Rh(Cl)(SiMe3) (6) were dramatically improved by addition
of the relaxation agent Cr(acac)3 (5-10 mg) to the sample.26
(PNP)Rh(I)(SiMe3) (4). (PNP)Rh(SPri2) (1) (60.0 mg, 0.092
mmol) was treated with Me3SiI (14.4 µL, 0.101 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube and heated at 70 °C for 18 h,
resulting in a color change from orange to black. Analysis by
31P{1H} NMR showed only 4. The resultant solution was evaporated
to dryness, and the residue was extracted with ether and filtered
through Celite. The filtrate was evaporated to dryness to yield a
green solid residue. This residue was dissolved in pentane and
recrystallized at -35 °C to afford 4 by precipitation. Yield: 0.040
regular intervals until the ratio of products remains unchanged over
time (<27 h at 65 °C). The ratio of free isopropyl sulfide to free
bromotrimethylsilane was determined by integrating signals of the
CH protons of isopropyl sulfide against the methyl protons of
bromotrimethylsilane for each experiment. Trace amounts of
(PNP)Rh(H)(Br) and an unknown product were detected in the
31P{1H} NMR. The equilibrium constant was determined to be Keq
) 0.8(1); the error was taken to be double the standard deviation
calculated by MS Excel.
(PNP)Rh(Cl)(SiMe3) (6). (PNP)Rh(Me)(Cl) (10) (50.0 mg, 0.086
mmol) was treated with PhCH2MgCl (95 µL of a 1.0 M solution
in Et2O, 0.095 mmol) in C6D6 (0.7 mL) in a J. Young NMR tube.
After 10 min at ambient temperature, 13 (95%) and 14 (5%) were
observed by 1H and 31P{1H} NMR. The solution passed through a
short plug of silica using fluorobenzene as eluent, and the resulting
solution was evaporated to dryness. The residue was redissolved
in C6D6 (0.7 mL) and treated with Me3SiCl (12 µL, 0.095 mmol).
After 3 days at ambient temperature, NMR analysis revealed the
1
g (60%). H NMR (C6D6): δ 7.72 (d, 2H, 8 Hz, Ar-H of PNP),
7.12 (s, 2H, Ar-H of PNP), 6.78 (d, 2H, 8 Hz, Ar-H of PNP), 2.92
(m, 2H, CHMe2), 2.72 (m, 2H, CHMe2), 2.16 (s, 6H, Ar-CH3 of
PNP), 1.68 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.40 (app. quartet
(dvt), 6H, 8 Hz, CHMe2), 1.18 (app. quartet (dvt), 6H, 8 Hz,
CHMe2), 1.10 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 0.41 (s, 9H,
SiMe3). 13C{1H} NMR (C6D6): δ 160.0 (vt, 10 Hz, C-N of PNP),
132.2 (s, CAr of PNP), 131.4 (s, CAr of PNP), 125.6 (vt, 3 Hz, CAr
of PNP), 123.4 (vt, 18 Hz, CAr of PNP), 117.5 (vt, 5 Hz, CAr of
PNP), 28.5 (vt, 9 Hz, CH(CH3)2), 27.2 (vt, 9 Hz, CH(CH3)2), 22.8
(s, Ar-CH3), 20.5, 20.3, 19.9, 18.9 (four s, CH(CH3)2), 11.1 (s,
Si(CH3)3). 31P{1H} NMR (C6D6): δ 39.5 (d, 113 Hz). 29Si{1H} NMR
(C6D6): δ 60.7 (dt, JRh-Si ) 28 Hz, JP-Si ) 8 Hz, Rh-Si). Anal.
Found (Calcd) for C29H49INP2RhSi: 47.46 (47.61); 6.59 (6.75).
(PNP)Rh(Br)(SiMe3) (5). (PNP)Rh(Me)(Cl) (10) (30.0 mg,
0.052 mmol) was treated with Me3SiBr (7.0 µL, 0.057 mmol) in
C6D6 (0.7 mL) in a J. Young NMR tube followed by addition of
PhLi (28.4 µL, 0.057 mmol). After 24 h at ambient temperature, 5
1
formation of 6 as well as ethylbenzene (selected data: H NMR
(C6D6): δ 2.43 (q, 2H, 8 Hz, C6H5-CH2-CH3), 1.06 (t, 3H, 8 Hz,
1
C6H5-CH2-CH3)) and bibenzyl (selected data: H NMR (C6D6): δ
2.73 (s, 4H, C6H5-CH2-CH2-C6H5)). Complex 6 was not isolated
but characterized by NMR in solution instead; data for 6 follow.
1H NMR (C6D6): δ 7.72 (d, 2H, 8 Hz, Ar-H of PNP), 7.12 (s, 2H,
Ar-H of PNP), 6.78 (d, 2H, 8 Hz, Ar-H of PNP), 2.77 (m, 2H,
CHMe2), 2.69 (m, 2H, CHMe2), 2.15 (s, 6H, Ar-CH3 of PNP), 1.62
(app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.32 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 1.25 (app. quartet (dvt), 6H, 8 Hz, CHMe2),
1.11 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 0.40 (s, 9H, SiMe3).
13C{1H} NMR (C6D6): δ 160.4 (vt, 10 Hz, C-N of PNP), 132.2 (s,
CAr of PNP), 131.3 (s, CAr of PNP), 125.5 (vt, 3 Hz, CAr of PNP),
123.1 (vt, 18 Hz, CAr of PNP), 117.6 (vt, 5 Hz, CAr of PNP), 27.4
(vt, 9 Hz, CH(CH3)2), 26.7 (vt, 9 Hz, CH(CH3)2), 21.1 (s, Ar-CH3),
20.4, 20.1, 19.4, 18.9 (four s, CH(CH3)2), 8.6 (s, Si(CH3)3). 31P{1H}
NMR (C6D6): δ 36.4 (d, 112 Hz, P(Pri)2). 29Si{1H} NMR (C6D6):
δ 58.5 (dt, JRh-Si ) 29 Hz, JP-Si ) 8 Hz, Rh-Si).
1
was the main product observed by H and 31P{1H} NMR. The
solution was treated with a drop of water and then evaporated to
dryness, and the residue was extracted with Et2O and filtered
through Celite. The filtrate was evaporated to dryness to yield a
green residue. This residue was dissolved in Et2O and recrystallized
Attempted Reaction of (PNP)Rh(SPri2) (1) with TMSCl.
(PNP)Rh(SPri2) (1) (20.0 mg, 0.031 mmol) was dissolved in neat
Me3SiCl (0.7 mL) in a J. Young NMR tube. After 48 h at 85 °C,
1 was the only compound observed by 31P{1H} NMR.
1
at -35 °C to afford 5. Yield: 14 mg (40%). H NMR (C6D6): δ
7.72 (d, 2H, 8 Hz, Ar-H of PNP), 7.12 (s, 2H, Ar-H of PNP), 6.78
(d, 2H, 8 Hz, Ar-H of PNP), 2.86 (m, 2H, CHMe2), 2.72 (m, 2H,
CHMe2), 2.16 (s, 6H, Ar-CH3 of PNP), 1.65 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 1.34 (app. quartet (dvt), 6H, 8 Hz, CHMe2),
1.23 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.11 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 0.40 (s, 9H, SiMe3). 13C{1H} NMR (C6D6): δ
160.3 (vt, 10 Hz, C-N of PNP), 132.2 (s, CAr of PNP), 131.4 (s,
CAr of PNP), 125.6 (vt, 3 Hz, CAr of PNP), 123.4 (vt, 18 Hz, CAr of
PNP), 117.6 (vt, 5 Hz, CAr of PNP), 27.8 (vt, 9 Hz, CH(CH3)2),
27.0 (vt, 9 Hz, CH(CH3)2), 21.7 (s, Ar-CH3), 20.4, 20.2, 19.6, 18.9
(four s, CH(CH3)2), 9.5 (s, Si(CH3)3). 31P{1H} NMR (C6D6): δ 37.2
(d, 110 Hz). 29Si{1H} NMR (C6D6): δ 59.5 (dt, JRh-Si ) 28 Hz,
JP-Si ) 8 Hz, Rh-Si). Anal. Found (Calcd) for C29H49BrNP2RhSi:
50.81 (50.88); 7.11 (7.21).
(PNP)Rh(Cl)(SiClMe2) (7). (PNP)Rh(SPri2) (1) (30.0 mg, 0.046
mmol) was treated with Me2SiCl2 (139 µL, 1.15 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube and heated at 70 °C for 24 h,
resulting in a color change from orange to black. A mixture of 7
(95%) and 1 (5%) was observed by 31P{1H} NMR. Another portion
of Me2SiCl2 (56 µL, 0.46 mmol) was added, and after 24 h at 70
°C, 7 was the only compound observed by 31P{1H} NMR. The
resultant solution was evaporated to dryness, and the residue was
extracted with ether and filtered through Celite. The filtrate was
evaporated to dryness to yield a dark solid residue. This residue
was triturated three times with pentane and dried to give (PNP)-
Rh(Cl)(SiClMe2). Yield: 0.014 g (47%). NMR data for (PNP)-
Determination of Keq for the Reaction of (PNP)Rh(SiPr2)
(1) with Me3SiBr. (PNP)Rh(SiPr2) (1) (20.0 mg, 30.8 µmol) in
C6D6 (total volume brought to 0.70 mL) was treated with Me3SiBr
(three different experiments were conducted for three different
amounts of Me3SiBr: 20 µL, 0.15 mmol, 0.22 M; 41 µL, 0.31 mmol,
0.44 M; 81 µL, 0.62 mmol, 0.88 M) in a J. Young NMR tube. The
samples were placed in an oil bath, which was preheated to 65 °C.
1
Rh(Cl)(SiClMe2) follow. H NMR (C6D6): δ 7.76 (d, 2H, 8 Hz,
Ar-H of PNP), 7.12 (s, 2H, Ar-H of PNP), 6.76 (d, 2H, 8 Hz, Ar-H
of PNP), 2.92 (m, 2H, CHMe2), 2.77 (m, 2H, CHMe2), 2.15 (s,
6H, Ar-CH3 of PNP), 1.60 (app. quartet (dvt), 6H, 8 Hz, CHMe2),
1.30 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.19 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 1.07 (app. quartet (dvt), 6H, 8 Hz, CHMe2),
0.88 (s, 6H, SiClMe2). 13C{1H} NMR (C6D6): δ 159.9 (vt, 10 Hz,
C-N of PNP), 132.2 (s, CAr of PNP), 131.5 (s, CAr of PNP), 126.0
(vt, 3 Hz, CAr of PNP), 122.4 (vt, 18 Hz, CAr of PNP), 117.8 (vt,
5 Hz, CAr of PNP), 27.4 (vt, 9 Hz, CH(CH3)2), 26.8 (vt, 9 Hz,
CH(CH3)2), 20.9 (s, Ar-CH3), 20.4, 19.8, 19.4, 18.7 (four s,
CH(CH3)2). 31P{1H} NMR (C6D6): δ 38.7 (d, 109 Hz). 29Si{1H}
(26) Utilization of Cr(acac)3 for the enhancement of 29Si NMR signal-
to-noise ratios in the spectra of transition metal silyl complexes has been
reported by Krentz and Pomeroy; the addition of Cr(acac)3 was reported to
have no significant effect on chemical shifts: Krentz, R.; Pomeroy, R. K.
Inorg. Chem. 1985, 24, 2976.

6262 Organometallics, Vol. 27, No. 23, 2008
Gatard et al.
NMR (C6D6): δ 66.7 (dt, JRh-Si ) 39 Hz, JP-Si ) 8 Hz, Rh-Si).
Anal. Found (Calcd) for C28H46Cl2NP2RhSi: 50.80 (50.91); 6.99
(7.01).
C6D6 in a J. Young NMR tube. NMR analysis 10 min after the
addition revealed formation of 13 and 14 in a 95:5 ratio, which
were characterized in solution in situ. NMR data for 13 follow. 1H
NMR (C6D6): δ 7.85 (d, 2H, 8 Hz, Ar-H of PNP), 7.50 (d, 2H, 8
Hz, C6H5), 7.11 (t, 1H, 8 Hz, C6H5), 6.99 (t, 2H, 8 Hz, C6H5), 6.92
(s, 2H, Ar-H of PNP), 6.86 (d, 2H, 8 Hz, Ar-H of PNP), 3.56 (m,
2H, Rh-CH2-C6H5), 2.35 (m, 2H, CHMe2), 2.22 (1 multiplet + 1
singlet overlapping, 10 H, CHMe2 + Ar-CH3 of PNP), 1.58 (m,
3H, Rh-CH3), 1.24 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.07
(app. quartet (dvt), 6H, 8 Hz, CHMe2), 0.94 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 0.72 (app. quartet (dvt), 6H, 8 Hz, CHMe2).
31P{1H} NMR (C6D6): δ 32.2 (d, 120 Hz). Selected NMR data for
Determination of Keq for the Reaction of (PNP)Rh(SiPr2)
(1) with Me2SiCl2. (PNP)Rh(SiPr2) (1) (20.0 mg, 30.8 µmol) in
C6D6 (total volume brought to 0.70 mL) was treated with Me2SiCl2
(three different experiments were conducted with three different
amounts of Me3SiBr: 19 µL, 0.15 mmol, 0.22 M; 37 µL, 0.31 mmol,
0.44 M; 74 µL, 0.62 mmol, 0.88 M) in a J. Young NMR tube. The
samples were placed in an oil bath, which was preheated to 65 °C.
1
The reaction was monitored by 31P{1H} NMR and H NMR at
regular intervals until the ratio of products remained unchanged
over time (<27 h at 65 °C). The ratio of free isopropyl sulfide to
free dichlorodimethylsilane was determined by integrating signals
of the CH protons of isopropyl sulfide against the methyl protons
of dichlorodimethylsilane for each experiment. Trace amounts of
(PNP)Rh(H)(Cl) were detected by 31P{1H} NMR. The equilibrium
constant was determined to be Keq ) 1.0(1); the error was taken to
be double the standard deviation calculated by MS Excel.
(PNP)Rh(Cl)(SiCl2Me) (8). (PNP)Rh(SPri2) (1) (30.0 mg, 0.046
mmol) was treated with MeSiCl3 (6.0 µL, 0.051 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube and heated at 70 °C for 3 h,
resulting in a color change from orange to green. 8 was the only
compound observed by 31P{1H} NMR. The resultant solution was
evaporated to dryness, and the residue was extracted with ether
and filtered through Celite. The filtrate was evaporated to dryness
to yield a green solid residue. This residue was recrystallized at
-35 °C from pentane to afford 8. Yield: 0.020 g (64%). 1H NMR
(C6D6): δ 7.78 (d, 2H, 8 Hz, Ar-H of PNP), 7.15 (s, 2H, Ar-H of
PNP), 6.76 (d, 2H, 8 Hz, Ar-H of PNP), 3.07 (m, 2H, CHMe2),
2.78 (m, 2H, CHMe2), 2.15 (s, 6H, Ar-CH3 of PNP), 1.63 (app.
quartet (dvt), 6H, 8 Hz, CHMe2), 1.37 (s, 3H, SiCl2Me), 1.31 (app.
quartet (dvt), 6H, 8 Hz, CHMe2), 1.15 (app. quartet (dvt), 6H, 8
Hz, CHMe2), 1.07 (app. quartet (dvt), 6H, 8 Hz, CHMe2). 13C{1H}
NMR (C6D6): δ 159.8 (vt, 10 Hz, C-N of PNP), 132.3 (s, CAr of
PNP), 131.7 (s, CAr of PNP), 126.7 (vt, 3 Hz, CAr of PNP), 122.3
(vt, 18 Hz, CAr of PNP), 118.5 (vt, 5 Hz, CAr of PNP), 27.5 (vt, 9
Hz, CH(CH3)2), 27.0 (vt, 9 Hz, CH(CH3)2), 20.9 (s, Ar-CH3), 20.4,
19.6, 19.4, 18.8 (four s, CH(CH3)2). 31P{1H} NMR (C6D6): δ 40.8
(d, 104 Hz). 29Si{1H} NMR (C6D6): δ 42.5 (dt, JRh-Si ) 57 Hz,
JP-Si ) 10 Hz, Rh-Si). Anal. Found (Calcd) for C27H43Cl3NP2RhSi:
47.49 (47.62); 6.42 (6.36).
1
14 follow. H NMR (C6D6): δ 3.79 (m, Rh-CH2-C6H5). 31P{1H}
NMR (C6D6): δ 30.2 (d, 125 Hz).
(PNP)Rh(H)(SiClMe2) (15). (PNP)Rh(SPri2) (1) (50.0 mg, 0.077
mmol) was treated with Me2SiHCl (12.0 µL, 0.085 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube. After 18 h at 70 °C, analysis
1
by H and 31P{1H} NMR revealed quantitative formation of 15.
The resultant solution was evaporated to dryness, and the residue
was extracted with ether and filtered through Celite. The filtrate
was evaporated to dryness to yield an orange solid residue. This
residue was recrystallized from Et2O at -35 °C to afford 15. Yield:
1
0.031 g (62%). H NMR (C6D6): δ 7.57 (d, 2H, 8 Hz, Ar-H of
PNP), 6.96 (s, 2H, Ar-H of PNP), 6.78 (d, 2H, 8 Hz, Ar-H of PNP),
2.66 (m, 2H, CHMe2), 2.25 (s, 6H, Ar-CH3 of PNP), 2.08 (m, 2H,
CHMe2), 1.24 (app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.08 (app.
quartet (dvt), 12H, 8 Hz, CHMe2), 1.04 (m, 6H, SiClMe2), -15.6
2
1
2
(dtt, JH-Si ) 31 Hz, JH-Rh ) 24 Hz, JH-P ) 11 Hz, Rh-H).
13C{1H} NMR (C6D6): δ 161.5 (vt, 10 Hz, C-N of PNP), 131.9
(two s, CAr of PNP), 125.4 (vt, 3 Hz, CAr of PNP), 122.4 (vt, 18
Hz, CAr of PNP), 115.5 (vt, 5 Hz, CAr of PNP), 26.5 (vt, 9 Hz,
CH(CH3)2), 23.9 (vt, 9 Hz, CH(CH3)2), 20.4 (s, Ar-CH3), 19.4, 18.7,
17.0, 17.4 (four s, CH(CH3)2), 15.8 (s, SiCl(CH3)2). 31P{1H} NMR
(C6D6): δ 41.0 (d, 146 Hz). 29Si NMR (C6D6): δ 49.3 (dtt, 2JSi-H
31 Hz, JSi-Rh ) 23 Hz, JSi-P ) 6 Hz, Rh-Si).
)
1
2
Oxidative Addition of PhBr to (PNP)Rh(SPri2) (1),
(PNP)Rh(Cl)(SiClMe2) (7), and (PNP)Rh(Cl)(SiCl2Me) (8). Solu-
tions of 1 (18.8 mg, 0.029 mmol), 7 (19.1 mg, 0.029 mmol), and
8 (20 mg, 0.029 mmol), each in 0.7 mL of C6D6, were prepared in
three separate J. Young NMR tubes. Equal amounts of bromoben-
zene (3.2 µL, 0.032 mmol) were introduced into each NMR tube.
These three samples were placed into a 75 °C oil bath. The progress
of the reaction was monitored by 31P NMR. After 40 min at 75 °C,
the conversions to (PNP)Rh(Ph)(Br) (3) were as follows: 1, 88%;
7, 80%; and 8, <3%. N.B.: (PNP)Rh(Cl)(Ph) was also observed in
the 1H and 31P{1H} NMR spectra of the reaction of (PN-
P)Rh(Cl)(SiClMe2) with bromobenzene, ostensibly owing to the
post-OA Cl/Br exchange.
Attempted Reaction of (PNP)Rh(SPri2) with Me3SiSiMe3.
(PNP)Rh(SPri2) (1) (20 mg, 0.031 mmol) and Me3SiSiMe3 (6.9 µL,
0.034 mmol) were introduced into a J. Young tube in 0.8 mL of
C6D6. The sample was placed in an oil bath that was preheated at
85 °C. After 48 h at 85 °C, 1 was the only compound observed by
1H and 31P{1H} NMR.
(PNP)Rh(Cl)(SiCl3) (9). (PNP)Rh(SPri2) (1) (30.0 mg, 0.046
mmol) was treated with SiCl4 (6.0 µL, 0.051 mmol) in C6D6 (0.7
mL) in a J. Young NMR tube and heated at 70 °C for 3 h, resulting
in a color change from orange to green. The resultant solution was
evaporated to dryness, and the residue was extracted with ether
and filtered through Celite. The filtrate was evaporated to dryness
to yield a green solid residue. This residue was recrystallized from
Et2O at -35 °C to afford 9. Yield: 0.016 g (48%). 1H NMR (C6D6):
δ 7.75 (d, 2H, 8 Hz, Ar-H of PNP), 7.11 (s, 2H, Ar-H of PNP),
6.77 (d, 2H, 8 Hz, Ar-H of PNP), 3.13 (m, 2H, CHMe2), 2.81 (m,
2H, CHMe2), 2.12 (s, 6H, Ar-CH3 of PNP), 1.69 (app. quartet (dvt),
6H, 8 Hz, CHMe2), 1.31 (app. quartet (dvt), 6H, 8 Hz, CHMe2),
1.10 (app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.02 (app. quartet (dvt),
6H, 8 Hz, CHMe2). 13C{1H} NMR (C6D6): δ 159.4 (vt, 10 Hz,
C-N of PNP), 132.3 (s, CAr of PNP), 131.9 (s, CAr of PNP), 127.4
(vt, 3 Hz, CAr of PNP), 122.3 (vt, 18 Hz, CAr of PNP), 118.8 (vt,
5 Hz, CAr of PNP), 27.6 (vt, 9 Hz, CH(CH3)2), 26.9 (vt, 9 Hz,
CH(CH3)2), 20.9 (s, Ar-CH3), 20.4, 19.4, 19.3, 18.7 (four s,
CH(CH3)2). 31P{1H} NMR (C6D6): δ 42.1 (d, 100 Hz). 29Si{1H}
NMR (C6D6): δ -12.5 (dt, JRh-Si ) 87 Hz, JP-Si ) 12 Hz, Rh-Si).
Anal. Found (Calcd) for C26H40Cl4NP2RhSi: 44.66 (44.52); 5.90
(5.74).
Attempted Reaction of (PNP)Rh(SPri2) with Me3SiOTf.
(PNP)Rh(SPri2) (1) (20 mg, 0.031 mmol) and Me3SiOTf (6.2 µL,
0.034 mmol) were introduced in a J. Young tube in 0.8 mL of
C6D6. The sample was placed in an oil bath that was preheated at
85 °C. After 48 h at 85 °C, 1 was the only compound observed by
1H and 31P{1H} NMR.
Attempted Reaction of (PNP)Rh(SPri2) with Me3SiOSiMe3.
(PNP)Rh(SPri2) (1) (20 mg, 0.031 mmol) was introduced in a J.
Young tube in neat Me3SiOSiMe3. The sample was placed in an
oil bath that was preheated at 85 °C. After 48 h at 85 °C, 1 was
(PNP)Rh(Me)(CH2Ph) (13) and (PNP)Rh(CH2Ph)2 (14).
(PNP)Rh(Me)(Cl) (10) (25.0 mg, 0.043 mmol) was treated with
PhCH2MgCl (47 µL of 1.0 M solution in Et2O, 0.047 mmol) in
1
the only compound observed by H and 31P{1H} NMR.

OxidatiVe Addition Reactions of Silyl Halides
Organometallics, Vol. 27, No. 23, 2008 6263
Acknowledgment. Support of this research by the NSF
(CHE-0517798), Alfred P. Sloan Foundation (Research
Fellowship to O.V.O.), Department of Energy (DE-FG02-
86ER13615), the donors of the Petroleum Research Fund,
and Brandeis University is gratefully acknowledged. We also
thank the National Science Foundation for the partial support
of this work through grant CHE-0521047 for the purchase
of a new X-ray diffractometer. We are grateful to Dr. Sara
Kunz for assistance with NMR experiments and to Prof.
Ka´lma´n J. Szabo´ for useful suggestions regarding collection
of the 29Si NMR spectra. We are especially thankful to
Mayank Puri for the equilibrium constant data.
Supporting Information Available: Crystallographic informa-
tion for 7 and 15 in the form of CIF files, experimental details,
and pictorial NMR spectra for select compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM800216H