Highly active cationic rhodium(I) precatalysts for the ambient temperature ring-opening polymerization of [1]silaferrocenophanes and tetramethyldisilacyclobutane

Article abstract of DOI:10.1021/om020492j

The highly active cationic rhodium(I) precatalysts for the ambient temperature ring-opening polymerization (ROP) of [1]silaferrocenophanes and tetramethyldisilacyclobutane were studied. The prolonged exposure of the resulting polyferrocene solution to the catalyst resulted in a dramatic molecular weight decline. It was found that the addition of dmpe effectively arrested the catalytic activity with [Rh(1,5-cod)(dmpe)]PF₆.

Full text of DOI:10.1021/om020492j

Organometallics 2002, 21, 4377-4384
4377
High ly Active Ca tion ic Rh od iu m (I) P r eca ta lysts for th e
Am bien t Tem p er a tu r e Rin g-Op en in g P olym er iza tion of
[1]Sila fer r ocen op h a n es a n d
Tetr a m eth yld isila cyclobu ta n e
Karen Temple, Sebastian Dziadek, and Ian Manners*
Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario, M5S 3H6, Canada
Received J une 21, 2002
The cationic rhodium(I) complexes [Rh(1,5-cod)2]A (A ) OTf, PF6, 1,5-cod ) 1,5-
cyclooctadiene) have been shown to exhibit high catalytic activity for the transition metal-
mediated ring-opening polymerization (ROP) of silicon-bridged [1]ferrocenophanes (e.g.,
fcSiMe2 (1a ), fc ) Fe(η5-C5H4)2), to quantitatively afford high molecular weight (Mn > 105)
polyferrocenylsilanes (e.g., [fcSiMe2]n (2a )). However, prolonged exposure of the resulting
polyferrocene solution to the catalyst resulted in a dramatic molecular weight decline.
Transition metal-catalyzed ROP of tetramethyldisilacyclobutane (6) and copolymerization
of this species with 1a also proved readily feasible with [Rh(1,5-cod)2]OTf forming high
molecular weight polycarbosilane homopolymer (7) (Mn ) 4.20 × 105 to 1.08 × 106, PDI )
1.39-2.08) and poly(carbosilane-r-ferrocenylsilane) (8) copolymer (Mn ) 4.63 × 105, PDI )
1.86), respectively. While [Rh(1,5-cod)(dmpe)]PF6 (dmpe ) bis(dimethylphosphinoethane))
proved less active as a ROP catalyst, this species represents the first phosphine-ligated
catalyst for the ROP of 1a , and moreover, in this case no subsequent depolymerization of
the resulting poly(ferrocenyldimethylsilane) (2a ) was detected. The cleavage of the polyfer-
rocene backbone in the presence of [Rh(1,5-cod)2]OTf was modeled through the catalytic
reaction of Fc2SiMe2 (Fc ) Fe(η5-C5H5)(η5-C5H4)) with the rhodium complex (9 mol %), which
resulted in Cp-Si bond cleavage affording ferrocene as the sole, isolable product. The
presence of 1,5-cod inhibited the catalytic activity of both [Rh(1,5-cod)2]OTf and [Rh(1,5-
cod)(dmpe)]PF6, suggesting that elimination of a 1,5-cod ligand is necessary to generate the
true active catalytic species. The addition of dmpe effectively arrested the catalytic activity
with [Rh(1,5-cod)(dmpe)]PF6; this is presumably a result of the displacement of the 1,5-cod
ligand by dmpe, which would generate catalytically inactive [Rh(dmpe)2]PF6.
In tr od u ction
An area of significant recent interest concerns poly-
ferrocenes (e.g., 2a ), which are readily accessible via the
ROP of strained [1]metallocenophanes (e.g., 1) and their
analogues.8-11 Due to the unique backbone comprised
of alternating repeat units of ferrocene and silicon, these
The incorporation of main group and transition ele-
ments into polymer chains continues to attract attention
due to the interesting physicochemical properties of the
resulting materials.1 Synthetic routes to inorganic
polymers have traditionally employed condensation and
ionically-initiated ring-opening polymerization (ROP)
processes.1,2 However, key synthetic advances involving
the polymerization of silanes, germanes, and stannanes
using transition metal catalysis have recently gained
much attention.3-5 In addition, our group has recently
reported a rhodium-mediated route for the formation
of polyphosphinoboranes.6,7
(6) Dorn, H.; Singh, R. A.; Massey, J . A.; Lough, A. J .; Manners, I.
Angew. Chem., Int. Ed. 1999, 38, 3321.
(7) Dorn, H.; Singh, R. A.; Massey, J .; Nelson, J . M.; J aska, C.;
Lough, A. J .; Manners, I. J . Am. Chem. Soc. 2000, 122, 6669.
(8) Manners, I. Can. J . Chem. 1998, 76, 371.
(9) Review: Kulbaba, K.; Manners, I. Macromol. Rapid Commun.
2001, 22, 711.
(10) Resendes, R.; Nelson, J . M.; Fischer, A.; J a¨kle, F.; Bartole, A.;
Lough, A. J .; Manners, I. J . Am. Chem. Soc. 2001, 123, 2116.
(11) For the work of other groups on the synthesis of ring-opened
polyferrocenes, see, for example: (a) Brandt, P. F.; Rauchfuss, T. B.
J . Am. Chem. Soc. 1992, 114, 1926. (b) Stanton, C. E.; Lee, T. R.;
Grubbs, R. H.; Lewis, N. S.; Pudelski, J . K.; Callstrom, M. R.; Erickson,
M. S.; McLaughlin, M. L. Macromolecules 1995, 28, 8713. (c) Mizuta,
T.; Onishi, M.; Miyoshi, K. Organometallics 2000, 19, 5005. (d)
Compton, D. L.; Brandt, P. F.; Rauchfuss, T. B.; Rosenbaum, D. F.;
Zukoski, C. F. Chem. Mater. 1995, 7, 2342. (e) Heo, R. W.; Somoza, F.
B.; Lee, T. R. J . Am. Chem. Soc. 1998, 120, 1621. (f) Brunner, H.;
Klankermayer, J .; Zabel, M. J . Organomet. Chem. 2000, 601, 211. (g)
Herberhold, M.; Hertel, F.; Milius, W.; Wrackmeyer, B. J . Organomet.
Chem. 1999, 582, 352. (h) Antipin, M. Y.; Vorontsov, I. I.; Dubovik, I.
I.; Papkov, V.; Cervantes-Lee, F.; Pannell, K. H. Can. J . Chem. 2000,
78, 1511. (i) Calleja, G.; Carre´, F.; Cerveau, G.; Labbe´, P.; Coche-
Gue´rente, L. Organometallics 2001, 20, 4211.
(1) (a) Manners, I. Science 2001, 294, 1664. (b) Archer, R. D.
Inorganic and Organometallic Polymers; Wiley-VCH: Weinheim, 2001.
(2) Nguyen, P.; Go´mez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99,
1515.
(3) For reviews, see: (a) Gauvin, F.; Harrod, J . F.; Woo, H.-G. Adv.
Organomet. Chem. 1998, 42, 363. (b) Reichl, J . A.; Berry, D. H. Adv.
Organomet. Chem. 1999, 43, 197.
(4) (a) Imori, T.; Tilley, T. D. J . Chem. Soc., Chem. Commun. 1993,
1607. (b) Imori, T.; Lu, V.; Cai, H.; Tilley, T. D. J . Am. Chem. Soc.
1995, 117, 9931. (c) Babcock, J . R.; Sita, L. R. J . Am. Chem. Soc. 1996,
118, 12481.
(5) Aitken, C. T.; Harrod, J . F.; Samuel, E. J . Am. Chem. Soc. 1986,
108, 4059.
10.1021/om020492j CCC: $22.00 © 2002 American Chemical Society
Publication on Web 09/19/2002

4378 Organometallics, Vol. 21, No. 21, 2002
Temple et al.
polymers exhibit electrochromism and redox activity
and become semiconducting upon doping.9,12,13 As a
result of such physical properties, these materials are
attracting attention as charge dissipation coatings,
variable refractive index sensing materials, and mag-
affording the corresponding [2]platinaferrocenophanes,
3 and 4, respectively.29-31 With a labile 1,5-cod ligand,
netic ceramic precursors over
a range of length
scales.14-19 In addition to the previously reported ther-
mal, anionic, and cationic ROP routes,10,20,21 the ambient
temperature transition metal-catalyzed polymerization
promoted by a variety of Pt and Pd complexes, as well
as the Rh(I) complex [Rh(coe)2(µ-Cl)]2 (coe ) cy-
clooctene), provides a mild and more convenient route
to these novel materials.22-25 Moreover, this facile
synthetic methodology also permits molecular weight
control and access to complex polymer architectures,
such as block, star, and graft copolymers.24-26
4 proved an equally effective catalyst for the ROP of 1a
as its parent compound, Pt(1,5-cod)2. In contrast, the
absence of catalytic activity for 3 was attributed to the
presence of more strongly coordinating phosphine ligands.
The importance of facile dissociation of the remaining
ligands was convincingly illustrated by the complete
lack of polymer formation when catalytic amounts of 4
were added to 1a in neat 1,5-cod. Furthermore, when
used in conjunction with BH3‚THF cocatalyst, which
serves as a phosphine ligand abstraction agent, complex
3 becomes catalytically active, affording low molecular
weight, cyclic polymers.32 Recent mechanistic studies
point to the formation of platinum colloids as the active
catalytic species.27
ROP of 1a with platinum catalysts normally requires
ca. 24 h to reach high conversion (ca. 100%). With this
in mind, we have recently examined cationic organo-
rhodium complexes with the intention of developing a
more active catalytic system. In this paper we report
the high catalytic activity of the cationic Rh(I) complexes
[Rh(1,5-cod)2]A (1,5-cod ) 1,5-cyclooctadiene, A ) OTf,
PF6) for the ROP of [1]silaferrocenophanes (1a -1c) and
also tetramethyldisilacyclobutane (6). In addition, the
discovery of the first effective ROP catalyst bearing
phosphine ligands, namely, [Rh(1,5-cod)dmpe]PF6 (dmpe
) bis(dimethylphosphino)ethane), is described.
Since the discovery of transition metal-catalyzed ROP
of 1a in 1995,22,23 efforts have been directed at unravel-
ing the mechanisms of these reactions.27-32 The inser-
tion of a platinum fragment into a strained Si-C bond
has been proposed as the first step in the mechanism.
With this in mind, we and Sheridan have reported the
oxidative-addition of Pt(PEt3)3 and Pt(1,5-cod)2 to 1a ,
(12) (a) Rulkens, R.; Lough, A. J .; Manners, I.; Lovelace, S. R.; Grant,
C.; Geiger, W. E. J . Am. Chem. Soc. 1996, 118, 12683. (b) Foucher, D.
A.; Honeyman, C. H.; Nelson, J . M.; Tang, B. Z.; Manners, I. Angew.
Chem. Int. Ed. Engl. 1993, 32, 1709.
(13) Papkov, V. S.; Gerasimov, M. V.; Dubovik, I. I.; Sharma, S.;
Dementiev, V. V.; Pannell, K. H. Macromolecules 2000, 33, 7107.
(14) Resendes, R.; Berenbaum, A.; Stojevic, G.; J a¨kle, F.; Bartole,
A.; Zamanian, F.; Dubois, G.; Hersom, C.; Balmain, K.; Manners, I.
Adv. Mater. 2000, 12, 327.
(15) Massey, J . A.; Chan, V. Z.-H.; Ostermann, J . M.; Enchelmaier,
R.; Spatz, J . P.; Mo¨ller, M.; Winnik, M. A.; Manners, I. J . Am. Chem.
Soc. 2001, 123, 3147.
(16) MacLachlan, M. J .; Ginzburg, M.; Coombs, N.; Coyle, T. W.;
Raju, N. P.; Greedan, J . E.; Ozin, G. A.; Manners, I. Science 2000, 287,
1460.
(17) MacLachlan, M. J .; Ginzburg, M.; Coombs, N.; Raju, N. P.;
Greedan, J . E.; Ozin, G. A.; Manners, I. J . Am. Chem. Soc. 2000, 122,
3878.
(18) Kulbaba, K.; Resendes, R.; Cheng, A.; Bartole, A.; Safa-Sefat,
A.; Coombs, N.; Stover, H. D. H.; Greedan, J . E.; Ozin, G. A.; Manners,
I. Adv. Mater. 2001, 13, 732.
(19) Espada, L. I.; Shadaram, M.; Robillard, J .; Pannell, K. H. J .
Inorg. Organomet. Polym. 2000, 10, 169.
(20) Foucher, D. A.; Tang, B.-Z.; Manners, I. J . Am. Chem. Soc. 1992,
114, 6246.
(21) (a) Rulkens, R.; Lough, A. J .; Manners, I. J . Am. Chem. Soc.
1994, 116, 797. (b) Ni, Y.; Rulkens, R.; Manners, I. J . Am. Chem. Soc.
1996, 118, 4102.
Resu lts a n d Discu ssion
Tr a n sition Meta l-Ca ta lyzed ROP of 1a Usin g
[Rh (1,5-cod )2]A (A ) OTf, P F 6) a s a P r eca ta lyst. The
transition metal-mediated ROP of [1]silaferrocenophanes
(e.g., 1a ) by platinum complexes normally requires ca.
24 h to reach 100% conversion. Therefore, we explored
the catalytic potential of [Rh(1,5-cod)2]A with the hopes
of discovering a more efficient catalyst. Thus, on addi-
tion of catalytic amounts of [Rh(1,5-cod)2]A (ca. 1 mol
%) to 1a in toluene, the solution immediately became
highly viscous and changed from the initial red color to
amber, characteristic of polyferrocenylsilane formation.
Analysis of the reaction mixture by 1H NMR spec-
troscopy confirmed ROP to be 100% completed within
2 min.33 The resulting polymer was immediately iso-
(29) Sheridan, J . B.; Lough, A. J .; Manners, I. Organometallics 1996,
15, 2195.
(30) Sheridan, J . B.; Temple, K.; Lough, A. J .; Manners, I. Dalton
Trans. 1997, 711.
(31) For an independent report of 3, see: ref 28.
(32) Temple, K.; Lough, A. J .; Sheridan, J . B.; Manners, I. Dalton
Trans. 1998, 2799.
(22) Ni, Y.; Rulkens, R.; Pudelski, J . K.; Manners, I. Makromol.
Rapid. Commun. 1995, 16, 637.
(23) Reddy, N. P.; Yamashita, H.; Tanaka, M. Chem. Commun. 1995,
2263.
(24) Go´mez-Elipe, P.; Resendes, R.; Macdonald, P. M.; Manners, I.
J . Am. Chem. Soc. 1998, 120, 8348.
(25) Resendes, R.; Massey, J .; Dorn, H.; Power, N.; Winnik, M.;
Manners, I. Angew. Chem., Int. Ed. 1999, 38, 2570.
(26) Resendes, R.; Massey, J . A.; Temple, K.; Cao, L.; Power-Billard,
K. N.; Winnik, M. A.; Manners, I. Chem. Eur. J . 2001, 7, 2414.
(27) Temple, K.; J a¨kle, F.; Sheridan, J . B.; Manners, I. J . Am. Chem.
Soc. 2001, 123, 1355.
(33) The ambient-temperature Rh(I)-catalyzed polymerizations of
1a -1c dissolved in C6D6 to give a 0.25 M solution with 1.4 mol % [Rh-
(1,5-cod)2]OTf are complete (100% conversion) by 1H NMR spectroscopy
by the time the spectrum can be run (ca. 2 min). Similar concentrations
using the Pt(0) catalysts result in 80% polymer within 2 h and require
24 h to reach full conversion. When reactions are performed in CH2-
Cl2, enough heat is generated during the polymerization to cause the
solution to reflux.
(28) Reddy, N. P.; Choi, N.; Shimada, S.; Tanaka, M. Chem. Lett.
1996, 649.

Highly Active Cationic Rh(I) Precatalysts
Organometallics, Vol. 21, No. 21, 2002 4379
Ta ble 1. In flu en ce of P r olon ged Rea ction Tim es
on th e GP C-Der ived Molecu la r Weigh ts of
P olyfer r ocen ylsila n e 2a F or m ed fr om th e
[Rh (1,5-cod )]2A-Ca ta lyzed ROP of 1a in THF
A
time (h)
Mn
PDI
OTf
0.25
4
1.00 × 105
1.50 × 104
oligomersa
7.90 × 103
1.01 × 105 d
1.78 × 105
1.60 × 105
3.60 × 104
1.95 × 105
1.90
1.67
20
20b
20b
0.25
2
1.15
1.22
2.05
2.01
1.64
2.14
PF6
48
48c
Oligomers soluble in hexanes at 25 °C, Mn < 1.5 × 103. After
a
b
reduction of polymer, isolated after 20 h, by treatment with
lated by precipitation into hexanes, affording a fibrous
orange polymer of high molecular weight. Generally, Mn
values ranged between 1.00 × 105 and 1.94 × 105,
although values up to Mn ) 4.81 × 105 have also been
observed, with corresponding PDI values falling be-
tween 1.40 and 2.10 by GPC analysis.
In contrast to the platinum catalytic systems, failure
to isolate 2a within ca. 2 h led to significant apparent
decreases in molecular weight as measured by GPC. The
results are rather dramatic. Specifically, addition of [Rh-
(1,5-cod)2]A to 1a in either toluene, THF, or CH2Cl2 was
accompanied by the normal rapid increase in solution
viscosity indicative of high polymer formation. After 2
h, a marked decrease in viscosity was observed, ir-
respective of the counterion or solvent employed. Pre-
cipitating aliquots at selected time intervals revealed a
continuous decrease in the molecular weights as indi-
cated by GPC (Table 1).
It is important to bear in mind that partial oxidation
of polyferrocenes can cause artificially low apparent
molecular weights to be observed by GPC in THF due
to the associated decrease in the hydrodynamic radius.34
However, attempts to reduce samples of 2a generated
using [Rh(1,5-cod)2]OTf with a 10% v/v solution of
hydrazine in MeOH only occasionally resulted in partial
regeneration of the higher molecular weight fraction
(Table 1). Similar results were observed with [Rh(1,5-
cod)2]PF6 as a precatalyst. This indicated that although
some degree of oxidation appears to occur, the decline
in molecular weight is real and chain cleavage is
observed.
In an effort to gain more insight into the cause of the
decreasing molecular weights, we turned our attention
to the reaction of [Rh(1,5-cod)2]OTf (ca. 1 mol %) with
narrow polydispersity samples of polyferrocenylsilane
5 (Mn ) 1.10 × 105, PDI ) 1.12).21 Importantly,
hydrazine (7.90 × 103:1.01 × 105 ) 1:2). c After reduction of
d
polymer, isolated after 48 h, by treatment with hydrazine. This
experiment was repeated several times and the Mn ≈ 105 peak
was often not observed.
molecular weights decreased in a fashion similar to that
observed for the poly(ferrocenyldimethylsilane) gener-
ated using rhodium(I) precatalysts (Table 2).
Reduction of the polymer by treatment with hydrazine
again resulted in a bimodal distribution with partial
regeneration of a high molecular weight fraction (Mn ≈
1.2 × 105, PDI ≈ 1.2), in addition to a low molecular
weight fraction (Mn ≈ 1.4 × 104, PDI ≈ 2.5). To
investigate the ability of the triflate anion to react with
the silicon-carbon bonds of a polyferrocenylsilane,
sodium triflate was added to a THF solution of mono-
disperse 5. No decrease in molecular weight or broaden-
ing of the molecular weight distribution was observed
over a period of 11 days.
In an effort to probe the generality of the [Rh(1,5-
cod)2]OTf precatalyst for the ROP of [1]silaferro-
cenophanes, we also investigated the Rh-mediated ROP
behavior of the unsymmetrically substituted monomer
1b and 1c. Similar rates of polymerization were ob-
served for monomers 1a and 1b.33 In contrast, steric
effects appeared to play a role in the ROP of 1c, which
proceeded at a noticeably slower rate. Trends in molec-
ular weight decline for polyferrocenylsilane 2b with
respect to reaction time paralleled that observed with
2a , while the decline detected for polymer 2c over time
was less dramatic. It should be noted that molecular
weights remained more uniform in the case of 2c,
reaching a plateau typically around Mn ) 5 × 104 after
24 h. This may be a consequence of the bulkier phenyl
groups, which may inhibit chain cleavage reactions in
ring-opened polymer 2c.
Tr a n sition Meta l-Ca ta lyzed ROP of 1a Usin g
[R h (1,5-cod )d m p e]OTf a s a P r eca t a lyst . In sharp
contrast to the dramatic decrease in the observed
molecular weights with [Rh(1,5-cod)2]A precatalysts,
substitution of a 1,5-cod ligand for dmpe affords an
effective catalyst for the ROP of 1a without subsequent
(34) Go´mez-Elipe, P.; Temple, K.; Manners, I. Unpublished work.
Gel-permeation chromatography gives molecular weight data based
on the hydrodynamic size of the polymer molecules. Oxidation of the
main chain ferrocene units leads to contraction of the polymer coils
due to poorer polymer/solvent interactions, and so an apparent decrease
in molecular weight is detected. If the oxidized polymer is reduced back
to the neutral material, the original hydrodynamic size and GPC-
derived molecular weight is restored. For an introduction to GPC,
see: Young, R. J .; Lovell, P. A. Introduction to Polymers, 2nd ed.;
Chapman and Hall: New York, 1991; pp 211-221.

4380 Organometallics, Vol. 21, No. 21, 2002
Temple et al.
Ta ble 2. In flu en ce of [Rh (1,5-cod )2]OTf on th e GP C-Der ived Molecu la r Weigh ts of P olyfer r ocen ylsila n e 5
time (h)
0
44
66
102
102a,b
Mn
PDI
1.10 × 105
4.80 × 104
3.40 × 104
2.50 × 104
1.2 × 105
1.4 × 104
1.12
1.48
1.59
1.80
1.20
2.51
a
b
After reduction by treatment of the polymer with hydrazine. Bimodal molecular weight distribution with an approximate molecular
weight (Mn) 2:1 ratio of the fractions of 1.2 × 105:1.4 × 104.
chain cleavage. Thus, 1a underwent metal-catalyzed
ROP initiated by [Rh(1,5-cod)dmpe]OTf in C6D6 to afford
high polymer 2a with quantitative conversion attained
after 4 h (Mn ) 1.0 × 105, PDI ) 1.94).35 Equally
important, prolonged exposure of the polymer to the
catalyst solution over 1 week had no significant effect
on the resulting molecular weight.
In light of the inability of Wilkinson’s catalyst, Rh-
(PPh3)3Cl, to induce ROP of 1a ,22 the catalytic activity
of [Rh(1,5-cod)dmpe]OTf is significant. This further
contrasts with Pd and Pt systems, where strongly
binding phosphine ligands hinder catalytic ROP activ-
ity,29 although Tanaka and co-workers have demon-
strated catalytic dimerization reactions with Pd
phosphine complexes.28 Thus, [Rh(1,5-cod)dmpe]OTf
represents the first phosphine-ligated catalyst to pro-
duce high molecular weight polymer 2a .
which also renders them effective as ROP monomers.
The resulting polycarbosilanes represent an important
class of inorganic polymers that attract interest as
ceramic precursors to â-SiC.1 Transition metal-catalyzed
polymerization of cyclic carbosilanes by Pt(IV) com-
plexes was discovered in the 1960s. Numerous other
precatalysts have been explored for the metal-mediated
ROP of silacyclobutanes ranging from anionic species
such as IrCl6 and RuCl6 to neutral organorhodium
complexes typically bearing phosphine ligands.36 In the
case of the Ru catalyst, polymers were of low molecular
weight, while the Ir complexes resulted in low conver-
sion. Neutral rhodium-based systems generated intrac-
table gums, with Wilkinson’s catalyst proving most
effective, affording 50% conversion after 4 h.37 Recently,
Neckers and co-workers reported the discovery of a
highly active catalyst, Pt(acac)2, which photocatalyzes
the ROP of 6, affording high molecular weight polymer
within 15 min.38,39 Nonetheless, H2PtCl6 presently
remains the general catalyst of choice despite requiring
elevated reaction temperatures.40
2-
2-
In h ibition of Ca ta lytic Activity via th e Ad d ition
of 1,5-cod or d m p e. Mechanistic studies of the Pt(1,5-
cod)2-catalyzed polymerization of 1a have shown initial
insertion to afford 4 with the loss of 1,5-cod followed by
dissociation of the second ligand prior to polymerization.
Evidence for the second step was provided by the
complete lack of polymer formation when the polymer-
ization of 1a was initiated by 4 in neat 1,5-cod.30 Further
evidence pointing to the necessary elimination of the
remaining ligands on platinum lies in the inability of 3
to induce ROP of 1a in the absence of the phosphine
ligand abstracting BH3‚THF complex as a cocatalyst.32
Consequently, the effect of 1,5-cod on the catalytic
activity of [Rh(1,5-cod)2]OTf and [Rh(1,5-cod)dmpe]OTf
and dmpe on that of [Rh(1,5-cod)dmpe]OTf was expected
to provide insight into the ROP mechanism for the Rh
catalysts. Thus, equimolar amounts of 1a and 1,5-cod
were dissolved in C6D6 to which [Rh(1,5-cod)2]OTf (<1
mol %) was added. After 12 h at room temperature, the
formation of less than 5% of polymer 2a was detected
The ROP of 1a appears to mirror the polymerization
of sila- and disilacyclobutanes in a number of key
respects. Tanaka and co-workers isolated 1-platina-2-
silacyclopentanes via the oxidative-addition of Pt(PEt3)3
to a variety of silacyclobutanes.41 Indeed, complexes 3
and 4 model analogous insertions of platinum fragments
into the strained Si-C bond of 1a . As a result of the
impressive catalytic rate for the polymerization of 1a ,
we therefore decided to investigate the ability of [Rh-
(1,5-cod)2]OTf to initiate the ROP of 6. Thus, catalytic
amounts of [Rh(1,5-cod)2]OTf (<1 mol %) were added
to a solution of [CH2SiMe2]2 in CDCl3 at room temper-
ature. A pronounced increase in viscosity was noted
1
after only 45 min, and H NMR spectroscopy revealed
the appearance of new resonances appearing at δ ) 0.04
and -0.25, consistent with the formation of polymer 7.
Integration of the signals indicated an 85% conversion
to polymer at that time. Isolation of the resulting
polymer 7 via precipitation into MeOH afforded a white
fibrous material of very high molecular weight in 80%
1
by H NMR spectroscopy. In the case of [Rh(1,5-cod)-
dmpe]OTf, the addition of 1 equiv of either 1,5-cod or
dmpe completely inhibited formation of polymer 2a
under similar experimental conditions. Therefore these
studies for the rhodium-based catalysts also point to the
necessary elimination of weakly coordinated 1,5-cod
before catalytic activity is achieved. With excess dmpe,
the anticipated displacement of the 1,5-cod ligand in
[Rh(1,5-cod)dmpe]OTf by the diphosphine to yield [Rh-
(dmpe)2]OTf arrested catalytic activity. Indeed, when
small quantities of [Rh(dmpe)2]OTf were added to a
solution of 1a in C6D6, no polymer was detected after 1
week at room temperature.
(36) For examples of transition metal-catalyzed ROP of carbosilanes,
see: (a) Kriner, W. A. J . Polym. Sci., Part A-1 1966, 4, 444. (b) Cundy,
C. S.; Lappert, M. F. J . Chem. Soc., Chem. Commun. 1972, 445, and
references therein. (c) Poletaev, V. A.; Vdovin, V. M.; Nametkin, N. S.
Dokl. Akad. Nauk SSSR 1973, 208, 1112. (d) Lienhard, M.; Ruskin,
I.; Verdecia, G.; Wiegand, C.; Apple, T.; Interrante, L. V. J . Am. Chem.
Soc. 1997, 119, 12020. (e) Peckham, T. J .; Nguyen, P.; Bourke, S. C.;
Wang, Q.; Harrison, D. G.; Zoricak, P.; Russell, C.; Liable-Sands, L.
M.; Rheingold, A. L.; Lough, A. J .; Manners, I. Organometallics 2001,
20, 3035.
(37) Cundy, C. S.; Eaborn, C.; Lappert, M. J . Organomet. Chem.
1972, 44, 291.
P olym er iza tion of Disila cyclobu ta n e (6) a n d th e
Cop olym er iza tion of 1a a n d 6 Ca ta lyzed by [Rh -
(1,5-cod )2]OTf. Silacyclobutanes possess ring strain,
(38) Wu, X. S.; Neckers, D. C. Macromolecules 1999, 32, 6003.
(39) Wang, F.; Neckers, D. C. Macromolecules 2001, 34, 6202.
(40) Interrante, L. V.; Wu, H. J .; Apple, T.; Shen, Q.; Ziemann, B.;
Narsavage, D. M.; Smith, K. J . Am. Chem. Soc. 1994, 116, 12085.
(41) For insertion of Pd or Pt into a silacyclobutane, see: (a)
Yamashita, H.; Tanaka, M.; Honda, K. J . Am. Chem. Soc. 1995, 117,
8873. (b) Tanaka, Y.; Yamashita, H.; Shimada, S.; Tanaka, M.
Organometallics 1997, 16, 3246.
(35) [Rh(1,5-cod)(dmpe)]PF6 proved less efficient as a catalyst than
[Rh(1,5-cod)2]PF6, displaying ROP rates similar to those observed with
Pt(0) catalysts.

Highly Active Cationic Rh(I) Precatalysts
Organometallics, Vol. 21, No. 21, 2002 4381
yield (Mn ) 1.08 × 106, PDI ) 1.39). Thus, [Rh(1,5-cod)2]-
OTf represents a highly active catalyst for the ROP of
6, with only the platinum-based photocatalyst, Pt(acac)2,
exhibiting superior catalytic activity.38,39 Importantly,
in contrast to the degradation of 2a following [Rh(1,5-
cod)2]OTf-initiated ROP of 1a , no decrease in molecular
weight was detected for 7. Indeed, the molecular weights
of 7 were unchanged over a period of 7 days.
F igu r e 1. 29Si NMR spectrum (C6D6) of copolymer 8.
We previously reported that random copolymers
derived from 1a and 6 and benzosilacyclobutane are
readily accessible via platinum-catalyzed ROP.42 Con-
sequently, the catalytic effect of [Rh(1,5-cod)2]OTf on
both 1a and 6 to afford high molecular weight ho-
mopolymers 2a and 7 led us to explore the possible
copolymerization of these two monomers. Previous
copolymerization studies have shown that tetrameth-
yldisilacyclobutane undergoes transition metal-medi-
ated ROP at a slower rate than the dimethyl[1]-
silaferrocenophane.24 Therefore, to effectively copolym-
erize these two monomers, a higher concentration of the
less reactive species was used. Thus compounds 1a and
6 in a 1:9 mol ratio were dissolved in THF, after which
a catalytic amount of [Rh(1,5-cod)2]OTf (<1 mol %) was
added. An immediate dramatic increase in the viscosity
was accompanied by a color change from orange-red to
amber. Due to the decreases in molecular weight when
the [Rh(1,5-cod)2]A catalyzes the polymerization, the
polymer was precipitated prior to complete consumption
of 6. Therefore, after stirring for 20 min at room
temperature, the solution was precipitated into MeOH,
yielding an orange-colored gum (8) in 45% yield.
segments. In contrast, the second resonance falling
slightly upfield at δ ) -3.66 is indicative of the
switching group, CH2SiMe2fc. Noteworthy is the con-
spicuous absence of signals due to segments analogous
to homopolymer 2a at δ ) -6.41. Similarily, the
resonances due to the methyl groups of homopolyferro-
cenylsilane (fcSiMe2fc), which typically fall at δ ) 0.58
1
and δ ) -0.55 in H and 13C NMR spectra, respectively,
were not observed. Consequently, copolymer 8 is com-
prised of segments derived from 6 with a single dim-
ethylferrocenylsilane unit intermittently interrupting
this homo-oligocarbosilane backbone. On the basis of the
29Si NMR spectrum, the carbosilane segments average
three repeat units.
Switching groups detected in both the 1H and 13C
NMR spectra provided further evidence supporting the
1
formation of a random copolymer. The H NMR spec-
trum displayed resonances at δ ) 0.41 and 0.44, which
correlate with the methyl groups flanking the ferrocene
moiety (CH2SiMe2fcSiMe2CH2). The resonances at δ )
0.14 and 0.20 correspond to the methylene switching
groups (CH2SiMe2fcSiMe2CH2). Thus, the presence of
these two sets of distinct switching group resonances
arises from the unusual structure of short carbosilane
segments, interrupted by single ferrocenylsilane moe-
ities, and not due to head-to-head linkages. The 13C
NMR spectrum also proved informative. The resonance
at δ ) 2.9 shouldering the signal of the methyl groups
of polycarbosilane segments (cf. δ ) 3.1) was assigned
to the switching group CH2SiMe2CH2SiMe2fc. Simi-
larly, a series of peaks, observed between δ ) 6.4-7.5,
was attributed to SiMe2CH2SiMe2fc switching groups.
More intense signals at δ ) 3.1 and 7.9 were attributed
to the methyl and methylene resonances of homocar-
bosilane segments. Finally, the cyclopentadienyl ligands
were found to resonate at δ ) 71.6 and 73.4, which are
similar to the values for 2a . Importantly, no degradation
of the backbone was detected upon leaving the reaction
solution in the presence of the catalyst for prolonged
periods of time.
GPC revealed a monomodal distribution of high
molecular weight (Mn ) 4.63 × 105, PDI ) 1.86). The
29Si NMR spectrum (Figure 1) proved interesting and
surprisingly showed only two detectable resonances. The
peak at δ ) 0.21 is similar to that observed for the
corresponding homopolymer 7 and was therefore at-
tributed to the silicon resonances of polycarbosilane
Modelin g th e Catalytic Depolym er ization Ch em -
(42) Sheridan, J . B.; Go´mez-Elipe, P.; Manners, I. Macromol. Rapid.
Commun. 1996, 17, 319.
istr y: Rea ction of F c2SiMe2 (F c ) (η5-C5H5)(η5-

4382 Organometallics, Vol. 21, No. 21, 2002
Temple et al.
C5H4)F e) w ith [Rh (1,5-cod )2]OTf. To model the de-
polymerization of polyferrocenylsilane 2a, we investigated
the reaction of Fc2SiMe2 (Fc ) Fe(η5-C5H5)(η5-C5H4))
with a catalytic amount (10 mol %) of [Rh(1,5-cod)2]OTf.
During the reaction, the initially orange-colored solution
discolored somewhat, taking on a slight green hue. After
The homopolymerization of tetramethyldisilacyclobu-
tane (6) and copolymerization with 1a also proved facile
using the cationic rhodium(I) precatalysts. Significantly,
no subsequent polymer degradation was observed. The
absence of chain cleavage reactions may be due to the
absence of repeating ferrocenylsilane units in these
materials. Mechanistic studies showed that the presence
of 1,5-cod arrested catalytic activity of all rhodium(I)
precatalysts studied, suggesting that 1,5-cod may dis-
sociate from the rhodium center prior to ROP. Catalytic
activity of [Rh(1,5-cod)(dmpe)]OTf was also completely
inhibited in the presence of dmpe presumably due to
the substitution of the 1,5-cod ligand for dmpe, thereby
rendering the rhodium complex ineffective toward the
ROP of 1a . Further studies will be directed at expanding
the range of rhodium ROP catalysts bearing chelating
diphosphine ligands and will also focus on the mecha-
nism of the catalytic chain cleavage reactions.
1
1 week at room temperature, the H NMR resonances
corresponding to Fc2SiMe2 had disappeared, while a new
signal at δ ) 4.05, characteristic of ferrocene, was
detected. The formation of ferrocene was confirmed by
13C NMR and mass spectrometry. Furthermore, when
the reaction was conducted in a deuterated solvent
(C6D6), no Fe(η5-C5H4D)(η5-C5H5) was detected in the
product as determined by mass spectrometry. The fate
of the SiMe2 fragment remains unknown, with numer-
1
ous H NMR peaks appearing in the region δ ) 0.43-
0.12, upfield of the methyl resonance in Fc2SiMe2 (δ )
0.50).
Exp er im en ta l Section
Ma ter ia ls. Solvents were dried by standard procedures and
distilled immediately prior to use. [1]Silaferrocenophanes (1a -
1c) were synthesized as described in the literature.20,27 [Rh-
(1,5-cod)2]OTf was purchased from Strem, while [Rh(1,5-
cod)2]PF6, [Rh(1,5-cod)dmpe]PF6,44 Fc2SiMe2,45 and polymer 521
were synthesized as described in the literature.
Equ ip m en t. All reactions and manipulations were per-
formed under an inert atmosphere (prepurified N2) using
either standard Schlenk techniques or an inert-atmosphere
glovebox (Innovative Technologies), except for the polymers
for which manipulations were carried out in air. The reactions
and polymerizations were monitored by 1H NMR spectroscopy.
Solution NMR spectra were recorded on Varian XL 400
These results indicate that [Rh(1,5-cod)2]OTf can
cause Si-Cp bond cleavage in a model compound and,
thus, suggest a similar mechanism may be operating
in the case of high molecular weight polymer. Interest-
ingly, no reaction occurred when Me3SiPh was treated
with [Rh(1,5-cod)2]OTf, indicating that this Rh(I) com-
plex is not active toward Si-Ph bonds at room temper-
ature and that the presence of repeating ferrocenyl-
silane units may be a prerequisite for Si-C bond
cleavage.43 A detailed knowledge of the catalytic depo-
lymerization mechanism is desirable and will be the
subject of future work.
1
instruments. H NMR spectra (400 MHz) were referenced to
residual protonated solvent, and 13C NMR spectra (100.5 MHz)
were referenced to the residual carbons of the deuterated
solvent. 29Si NMR (79.5 MHz) spectra were referenced exter-
nally to TMS utilizing a normal (proton-decoupled) pulse
sequence. Molecular weight distributions were analyzed by gel
permeation chromatography using a Waters Associates 2690
Separations Unit. Ultrastyragel columns with a pore of 500,
103, and 105 Å and a Waters 410 differential refractometer
were used. A flow rate of 1.0 mL/min was used, and samples
were dissolved in a THF solution of 0.1% tetra-n-butylammo-
nium bromide. Polystyrene standards purchased from Aldrich
were used for calibration purposes.
Su m m a r y
Catalytic amounts of the rhodium(I) complexes [Rh-
(1,5-cod)2]A (A ) OTf, PF6) initiate the ROP of 1a -1c
to yield high molecular weight polymers 2a -2c. While
activity of these catalysts proved remarkably high with
quantitative conversion within 2 min in the case of 2a
and 2b, prolonged exposure of the polymer in the
reaction medium resulted in oxidation and apparent
degradation of 2a .33 Evidence for Cp-Si bond cleavage
was provided through the reaction of Fc2SiMe2 and [Rh-
(1,5-cod)2]OTf, which afforded ferrocene as the sole,
isolable product. Although significantly less active than
[Rh(1,5-cod)2]A (A ) OTf, PF6), [Rh(1,5-cod)(dmpe)]OTf
represents the first phosphine-ligated transition metal
complex to be catalytically active toward the ROP of 1a .
Moreover, no subsequent cleavage of the resulting
polyferrocenylsilane chains was detected in this case.
ROP of 1a -1c Usin g [Rh (1,5-cod )2]OTf a s a P r eca ta -
lyst. As the experimental conditions were identical for mono-
mers 1a -1c, the ROP of only one example, 1a , will be
described. Silaferrocenophane (1a ) (0.28 g, 1.16 mmol) was
dissolved in toluene (4.0 mL). To this red solution was added
the catalyst [Rh(1,5-cod)2]OTf (ca. 0.3 mol %), which had been
previously dissolved in THF (0.1 mL) The solution rapidly
changed from red to amber. The resulting polymer (2a ) was
precipitated into hexanes (ca. 250 mL) after 2 min, isolated
by filtration, and dried under high vacuum. Repeated reactions
1
were monitored by H NMR spectroscopy and were complete
by the time the NMR experiment was over. Yield 2a : 182 mg
1
(65%). H NMR (δ, C6D6) monomer 1a : 0.35 (s, 6H, fcSiMe2),
3.95 (br, 4H, Cp), 4.40 (br, 4H, Cp); polymer 2a : 0.58 (s,
fcSiMe2), 4.02 (br, Cp), 4.23 (br, Cp). GPC analysis: Mn ) 1.00
× 105, PDI ) 1.94. 1H NMR (δ, C6D6) monomer 1b: 0.32 (s,
3H, fcSiMe(CH2CH3), 0.88 (q, 2H, fcSiMe(CH2CH3), 1.12 (t, 3H,
fcSiMe(CH2CH3), 3.95 (m, 4H, Cp), 4.41 (m, 4H, Cp); polymer
2b: 0.28 (s, fcSiMe(CH2CH3), 1.00 (br, fcSiMe(CH2CH3), 1.17
(43) While triflic acid is known to cleave Si-Ar bonds to generate
Si-OTf bonds (see Schro¨ck, R.; Angermaier, K.; Schmidbaur, H. Z.
Naturforsch. 1995, 50, 613, and references therein), it should be noted
that Rh-catalyzed depolymerization of 2a was observed irrespective
of the counteranion (OTf or PF6) employed.
(44) Green, M.; Kuc, T. A.; Taylor, S. H. J . Chem. Soc. (A) 1971,
2334.
(45) Guillaneux, D.; Kagan, H. B. J . Org. Chem. 1995, 60, 2502.

Highly Active Cationic Rh(I) Precatalysts
Organometallics, Vol. 21, No. 21, 2002 4383
(br, fcSiMe(CH2CH3), 4.10 (br, Cp), 4.12 (br, Cp), 4.28 (br, Cp).
GPC analysis (isolated after 5 min): Mn ) 1.51 × 105, PDI )
bimodal distribution. GPC analysis: Mn ) 1.2 × 105, PDI )
1.2; Mn ) 1.4 × 104, PDI ) 2.5 with an approximate ratio of
2:1.
1
2.05. H NMR (δ, C6D6) monomer 1c: 0.56 (s, 3H, fcSiMePh),
3.97 (br, 2H, Cp), 4.40 (br, 2H, Cp), 4.38 (br, 2H, Cp), 4.43 (br,
2H, Cp), 7.26 (br, 3H, fcSiMePh), 7.91 (br, 2H, fcSiMePh);
polymer 2c: 0.72, (s, fcSiMePh), 0.74 (s, fcSiMePh), 0.76 (s,
fcSiMePh), 3.97 (br, Cp, fcSiMePh,), 4.06 (br, Cp, fcSiMePh),
4.14 (br, Cp, fcSiMePh), 4.21 (br, Cp, fcSiMePh), 7.24 (br,
fcSiMePh), 7.75 (br, fcSiMePh). GPC analysis (isolated after
1.5 h): Mn ) 9.57 × 104, PDI ) 2.12.
Attem p ted Rea ction of Na OTf w ith 5. Polymer 5 (0.08
g, Mn ) 1.10 × 105, PDI ) 1.12) and NaOTf (0.11 g, 0.64 mmol)
were dissolved in THF (4 mL). After stirring the reaction at
room temperature for 11 days, the polymer was purified by
precipitation into MeOH (ca. 20 mL) after 24 and 48 h. GPC
analysis: (24 h) Mn ) 9.40 × 104, PDI ) 1.16; (48 h) Mn
)
1.01 × 105, PDI ) 1.12. No appreciable change was detected
after 11 d.
Effects of Rea ction Tim e on th e ROP of 1a -1c Ca ta -
lyzed Usin g [Rh (1,5-cod )2]OTf a s a P r eca ta lyst in THF .
In a typical experiment when 1a (0.74 g, 3.09 mmol) was
dissolved in ca. 5 mL of THF containing a catalytic amount of
[Rh(1,5-cod)2]OTf (<1 mol %), the solution viscosity increased
very rapidly followed by a continuing decrease in solution
viscosity with respect to time. Removing aliquots at given time
intervals and purifying the polymer via precipitation into
hexanes (ca. 50 mL) revealed an apparent decrease in molec-
ular weight by GPC analysis: see Table 1 for 2a . 2b (over 132
h): Mn ranged from 1.36 × 105 to 3.61 × 104, PDI ) 1.75-
2.12; 2c (over 24 h), 6.00 × 104 to 3.28 × 104, PDI ) 2.12-
2.85.
ROP of 1a In itia ted by [Rh (1,5-cod )(d m p e)]OTf P r e-
ca ta lyst. In a typical experiment, 1a (0.08 g, 0.33 mmol) was
dissolved in 0.5 mL of C6D6, after which a catalytic amount of
[Rh(1,5-cod)(dmpe)]OTf (<1 mol %) was added. The solution
became immobile after 4 h, accompanied by a color change
from red to amber, characteristic of polymer formation. After
1 week at room temperature, the solution remained immobile.
The polymer 2a was then precipitated into hexanes (ca. 100
mL), isolated by filtration, and dried at reduced pressure.
Yield: 68 mg (85%). 1H NMR (δ, C6D6) monomer 1a : 0.35 (6H,
Me), 3.95 (4H, Cp), 4.40 (4H, Cp); polymer 2a : 0.58 (6H, Me),
4.02 (4H, Cp), 4.23 (4H, Cp). GPC analysis: Mn ) 1.54 × 105
to 3.44 × 105, PDI ) 1.61-2.13.
Effects of Rea ction Tim e on th e ROP of 1a Ca ta lyzed
Usin g [Rh (1,5-cod )2]OTf a s a P r eca ta lyst in CH2Cl2. When
a catalytic amount of [Rh(1,5-cod)2]OTf (<1 mol %) was added
to a CH2Cl2 (5 mL) solution of 1a (435 mg, 1.80 mmol), a trend
of decreasing molecular weights was observed that was similar
to that in THF. Thus, the solution immediately became viscous
and amber in color followed by a pronounced decrease in
viscosity. Aliquots were precipitated into hexanes (50 mL) at
the 0.2, 3, 24, 48, and 72 h. GPC analysis: 2a over a period of
72 h, Mn ranged from 2.33 × 105 to 4.95 × 104, PDI ) 1.45-
2.23.
Red u ction of 2a a fter Obser ved Decr ea ses in GP C-
Der ived Molecu la r Weigh ts. Complex 1a (0.20 g, 0.83 mmol)
dissolved in THF (5 mL) was exposed to catalytic amounts of
[Rh(1,5-cod)2]OTf (<1 mol %). An aliquot was precipitated into
hexanes (50 mL) after 15 min, and the remaining reaction
medium was allowed to stir for 20 h. The samples were
subjected to purification and reduction via reprecipitation into
a 10% solution of hydrazine in MeOH in an attempt to return
the polymer to its original GPC-derived molecular weight. GPC
results: (after 15 min) monomodal distribution Mn ) 1.00 ×
105, PDI ) 1.77; (20 h followed by reduction) bimodal distribu-
tion, Mn ) 7.90 × 103, PDI ) 1.11, Mn ) 1.08 × 105, PDI )
1.31 (ratio ) 2.1).
Effect of th e P r eca ta lyst’s Cou n ter a n ion on th e Ap -
p a r en t Decr ea se in Molecu la r Weigh t. Complex 1a (0.20
g, 0.83 mmol) was dissolved in ca. 5 mL of THF. On addition
of catalytic amounts of [Rh(1,5-cod)2]PF6 (<1 mol %), the
solution become highly viscous, with quantitative conversion
to polymer within 15 min as evidenced by 1H NMR. GPC:
(after 15 min) Mn ) 1.78 × 105, PDI ) 2.05. However,
extending the reaction time led to a decrease in molecular
weight by GPC. GPC: (2 h) Mn ) 1.60 × 105, PDI ) 2.01; (48
h) Mn ) 3.60 × 104, PDI ) 1.64. In this case, reprecipitation
into a 10% solution of hydrazine in MeOH reduced the polymer
back to high GPC-derived molecular weight. GPC analysis: Mn
) 1.95 × 105, PDI ) 2.14. This experiment was repeated
several times, and the regeneration of the fraction with Mn ≈
105 was often not complete and a lower Mn fraction (ca. 104)
remained.
Effects of Rea ction Tim e on th e ROP of 1a -1c Ca ta -
lyzed Usin g [Rh (1,5-cod )d m p e]OTf a s a P r eca ta lyst. In
a similar reaction, 1a (0.25 g, 1.03 mmol) was dissolved in
toluene (ca. 4 mL). A catalytic amount of [Rh(1,5-cod)(dmpe)]-
OTf (<1 mol %) was added. At selected time intervals, aliquots
of the reaction medium were removed, precipitated, and dried
under reduced pressure prior to GPC analysis: (4 h) Mn ) 1.00
× 105, PDI ) 1.94; (1 week) Mn ) 1.54 × 105, PDI ) 1.63.
In h ibition Stu d ies for th e Rh od iu m -Ca ta lyzed P olym -
er iza tion of 1a . A. Equimolar amounts of 1,5-cod (25 µL, 0.21
mmol) and 1a (0.05 g, 0.21 mmol) were dissolved in ca. 0.5
mL of C6D6. To this solution was added a catalytic amount of
[Rh(1,5-cod)2]OTf (<1 mol %). Monitoring by 1H NMR revealed
less than 5% conversion to polymer after 12 h at room
temperature.
B. [1]Silaferrocenophane 1a (0.05 g, 0.21 mmol) and 1,5-
cod (25 µL, 0.21 mmol) were dissolved in 0.5 mL of C6D6. To
this solution was added a small amount of the [Rh(1,5-cod)-
dmpe]PF6 precatalyst (<1 mol %). No polymerization occurred
over a period of 7 days as monitored by 1H NMR spectroscopy.
C. When equimolar amounts of 1a (0.05 g, 0.21 mmol) and
dmpe (35 µL, 0.21 mmols) were dissolved in 0.5 mL of C6D6
followed by a catalytic amount of [Rh(1,5-cod)dmpe]PF6 pre-
catalyst (<1 mol %), no reaction was observed over a period of
1
1 week as monitored by H NMR spectroscopy.
At t em p t ed R OP of 1a Usin g [R h (d m p e)2]OTf a s a
P r eca ta lyst. To a solution of 1a (0.05 g, 0.21 mmol) dissolved
in CH2Cl2 (ca. 5 mL) was added a catalytic amount of [Rh-
(dmpe)2]OTf (<1 mol %). The reaction was allowed to stir at
room temperature for over 1 week. Throughout this time,
polymer formation was not detected by 1H NMR spectroscopy.
R OP of 6 Ca t a lyzed Usin g [R h (1,5-cod )2]OTf a s a
P r eca ta lyst. Compound 6 (0.05 g, 0.35 mmol) was dissolved
in ca. 0.5 mL of CDCl3 to which a catalytic amount of [Rh-
(1,5-cod)2]OTf (<1 mol %) was added. Within 15 min the
solution became immobile, and the reaction reached 85%
conversion after 45 min. Yield: 40 mg (80%). 1H NMR (δ,
CDCl3) monomer: -0.01 (4H, [CH2SiMe2]2), 0.22 (12H, [CH2-
SiMe2]2); polymer 7: -0.25 (4H, [CH2SiMe2]2), 0.04 (12H, [CH2-
SiMe2]2). GPC analysis: Mn ) 1.08 × 106, PDI ) 1.39.
Rea ction of [Rh (1,5-cod )2]OTf w ith P olym er 5. Polymer
5 (0.08 g, Mn ) 1.10 × 105, PDI ) 1.12) was dissolved in THF
(4 mL) containing ca. 1 mol % [Rh(1,5-cod)2]OTf. Aliquots were
precipitated into hexanes (50 mL) at 44, 66, and 102 h. GPC
ROP of 6 In itia ted by [Rh (1,5-cod )2]OTf a s th e P r e-
ca ta lyst: Th e Effect of P r olon ged Rea ction Tim es. In a
typical experiment when 6 (0.25 g, 1.74 mmol) was dissolved
in ca. 5 mL of THF containing a catalytic amount of [Rh(1,5-
cod)2]OTf (<1 mol %), the viscosity of the solution increased
and remained high for the duration of the experiment. Aliquots
of the reaction mixture were removed at specific time intervals.
analysis: (44 h) Mn ) 4.80 × 104, PDI ) 1.48; (66 h) Mn
)
3.40 × 104, PDI ) 1.59; (102 h) Mn ) 2.50 × 104, PDI ) 1.80.
Attempts to reduce the samples, after 102 h, by reprecipitating
into a 10% v/v solution of hydrazine in MeOH produced a

4384 Organometallics, Vol. 21, No. 21, 2002
Temple et al.
The resulting polymer (7) was purified by precipitation into
hexanes (ca. 50 mL). GPC analysis: Mn values ranged from
4.20 × 105 to 6.60 × 105 and the PDI from 1.58 to 2.08 over a
reaction period of 5 days with no significant molecular weight
decline detected.
and recrystallized from hexane at 25 °C. Yield: 0.15 g (85%).
1H NMR (δ, C6D6): 4.05 (10H, Cp). 13C NMR (δ, C6D6): 68.3
(Cp). MS (EI, 70 eV): m/z 186 [M+ ) Fc] 121 [M+ - Cp], 56
[M+ - 2Cp]. Comparison with an authentic sample of ferrocene
confirmed the identity of the product of this reaction.
Attem p ted Rea ction of P h SiMe3 w ith [Rh (1,5-cod )2]-
OTf. PhSiMe3 (0.12 g, 0.80 mmol) was dissolved in C6D6
followed by the addition of a catalytic amount of [Rh(1,5-cod)2]-
OTf (ca. <1 mol %). The reaction was monitored over a period
of 1 week by 1H NMR spectroscopy. No reaction was detected.
Cop olym er iza tion of 1a a n d 6 Ca ta lyzed Usin g [Rh -
(1,5-cod )2]OTf P r eca ta lyst. After dissolving compounds 1a
(0.04 g, 0.16 mmol) and 6 (0.20 g, 1.39 mmol) in 2 mL of THF,
a catalytic amount of [Rh(1,5-cod)2]OTf (<1 mol %) was added
to the solution. In addition to a color change from orange-red
to light amber, a dramatic increase in viscosity was noted
within less than 30 s. After stirring for 20 min at room
temperature, the solution was precipitated into ca. 100 mL of
MeOH, yielding an orange-colored elastomer 8. Yield: 108 mg
Ack n ow led gm en t. We are grateful to Dr. Douglas
Neckers and Ms. Fei Wang (Bowling Green State
University) and Dr. Xiaosong Wu (DSM Desotech, Inc.)
for their helpful suggestions concerning the synthesis
of 6. We also would like to thank Prof. J . B. Sheridan
(Rutgers University, Newark, NJ ) for many helpful
discussions. This research was supported by the Natural
Science and Engineering Research Council of Canada
(NSERC). K.T. is grateful to NSERC for a postgraduate
scholarship (1997-2000) and a University of Toronto
Fellowship (2001). S.D. is thankful for support provided
by the Deutscher Akademischer Austauschdienst (DAAD)
for financial support. In addition, I.M. gratefully ac-
knowledges the Ontario Government for a PREA Award
(1999-2003), the University of Toronto for a McLean
Fellowship (1997-2003), and the Canadian Government
for a Canada Research Chair.
1
(45%). H NMR (δ, C6D6): -0.06 (SiMeCH2SiMe2), 0.14, 0.20
(switching group, SiMe2CH2fc), 0.27 (CH2SiMe2CH2), 0.41, 0.44
(switching group, CH2SiMe2fc), 4.12 (fcSiMe2CH2), 4.32 (fcSiMe2-
CH2). 13C NMR (δ, C6D6): 1.1 (CH2SiMe2fc), 2.9 (switching
group, CH2SiMe2CH2SiMe2fc), 3.1 (CH2SiMe2CH2), 6.4-7.5
(switching group, SiMe2CH2SiMe2fc), 7.9 (SiMe2CH2SiMe2),
71.6 (Cp), 73.4 (Cp). 29Si NMR (δ, C6D6): 0.21 (CH2SiMe2CH2),
-3.66 (CH2SiMe2fc). GPC analysis: Mn ) 4.63 × 105, PDI )
1.86.
Rea ction of F c2SiMe2 w ith [Rh (1,5-cod )2]OTf. To an
orange solution of Fc2SiMe2 (0.20 g, 0.47 mmol) in toluene (ca.
3.5 mL) was added a catalytic amount of [Rh(1,5-cod)2]OTf
(0.02 g, 0.04 mmol, 9 mol %). During the reaction the solution
became slightly green. After allowing the reaction to stir over
1 week, the resulting solution was analyzed by NMR spec-
troscopy. The product was purified by filtration through Celite
OM020492J