Base-promoted silicon-hydrogen bond activation of silanes by iridium(III) porphyrin complexes

Article abstract of DOI:10.1021/om701144a

Iridium(III) porphyrin silyls were synthesized in moderate to high yields conveniently from the reactions of iridium(III) porphyrin carbonyl chloride and methyl with silanes, via silicon-hydrogen bond activation (SiHA) in solvent-free conditions and nonpolar solvents. Base was found to promote the SiHA reactions. Specifically, K₃PO₄ accelerated the SiHA with iridium porphyrin carbonyl chloride, while KOAc promoted the SiHA by iridium porphyrin methyl. Mechanistic experiments suggested that iridium(III) porphyrin carbonyl chloride initially formed iridium porphyin cation, which then reacted with silanes likely via heterolysis to give iridium porphyrin hydride. Iridium porphyrin hydride further reacted with silanes to yield iridium porphyrin silyls. On the other hand, iridium(III) porphyrin methyl and silyls underwent either oxidative addition or σ-bond metathesis to form the products. In the presence of base, a pentacoordinated silicon hydride species likely formed and reacted with iridium porphyrin methyl to form iridium porphyrin anion, which could further react with silanes to yield iridium porphyrin hydride after protonation. Ir(ttp)H finally reacted with excess silanes to give iridium porphyrin silyl complexes.

Full text of DOI:10.1021/om701144a

4034
Organometallics 2008, 27, 4034–4042
Articles
Base-Promoted Silicon-Hydrogen Bond Activation of Silanes by
Iridium(III) Porphyrin Complexes
Baozhu Li and Kin Shing Chan*
Department of Chemistry, The Chinese UniVersity of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China
ReceiVed NoVember 14, 2007
Iridium(III) porphyrin silyls were synthesized in moderate to high yields conveniently from the reactions
of iridium(III) porphyrin carbonyl chloride and methyl with silanes, via silicon-hydrogen bond activation
(SiHA) in solvent-free conditions and nonpolar solvents. Base was found to promote the SiHA reactions.
Specifically, K3PO4 accelerated the SiHA with iridium porphyrin carbonyl chloride, while KOAc promoted
the SiHA by iridium porphyrin methyl. Mechanistic experiments suggested that iridium(III) porphyrin
carbonyl chloride initially formed iridium porphyin cation, which then reacted with silanes likely via
heterolysis to give iridium porphyrin hydride. Iridium porphyrin hydride further reacted with silanes to
yield iridium porphyrin silyls. On the other hand, iridium(III) porphyrin methyl and silyls underwent
either oxidative addition or σ-bond metathesis to form the products. In the presence of base, a
pentacoordinated silicon hydride species likely formed and reacted with iridium porphyrin methyl to
form iridium porphyrin anion, which could further react with silanes to yield iridium porphyrin hydride
after protonation. Ir(ttp)H finally reacted with excess silanes to give iridium porphyrin silyl complexes.
or σ-bond metathesis.12,13 One key supporting evidence for the
Introduction
oxidative addition is the isolation of an iridium(V) silyl
intermediate,whichhasbeencharacterizedbyX-raydiffraction.7,11
Silicon-hydrogen bond activation (SiHA) is an important
process for both catalytic applications in organic synthesis1–3
andthesynthesisoftransitionmetalsilyls.4Recently,silicon-hydrogen
bond activation has been utilized for the catalytic functional-
ization of hydrocarbons by transition metal complexes, and
transition metal silyls are proposed as the intermediates.2,3 The
preparation of transition metal silyls from the reactions of metal
halides with silanes has been extensively utilized.5
The silicon-hydrogen bond activation with the late high-
valent transition metal such as rhodium(III) or iridium(III)
complexes is interesting.5–7 So far, the mechanistic possibilities
of silicon-hydrogen bond activation by these late transition
metal complexes can be heterolysis,8,9 oxidative addition,7,10,11
Our group has reported that silicon-hydrogen bonds activa-
tion by rhodium(III) porphyrins (por) can provide a facile
synthetic route to rhodium silyl complexes.8 We have reported
that rhodium(III) porphyrin halides and methyls reacted with
silanes to give high yields of rhodium porphyrin silyls via
silicon-hydrogen bond activation in solvent-free conditions.
Rh(por)Cl was proposed to undergo ionization into
Rh(por)+Cl-, which then underwent silylation to yield rhodium
porphyrin silyls. On the other hand, Rh(por)Me reacted with
silanes via either oxidative addition or σ-bond metathesis
(Scheme 1). These reactions are mechanistically puzzling since
cis-interaction on the same face of a porphyrin by the methyl
group and silane could be sterically very demanding.
* Corresponding author. E-mail: ksc@cuhk.edu.hk.
(1) (a) Yang, J.; Brookhart, M. J. Am. Chem. Soc. 2007, 129, 12656–
12657. (b) Yamanoi, Y.; Taira, T.; Sato, J.-I.; Nakamula, I.; Nishihara, H.
Org. Lett. 2007, 22, 4543–4546.
(2) Tsukada, N.; Hartwig, J. F. J. Am. Chem. Soc. 2005, 127, 5022–
5023.
(3) Yamanoi, Y.; Nishihara, H. Tetrahedron Lett. 2006, 47, 7157–7161.
(4) (a) Casty, G. L.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1997, 16, 4746–4754. (b) Turculet, L.; Feldman, J. D.;
Tilley, T. D. Organometallics 2004, 23, 2488–2502. (c) Mork, B. V.; Tilley,
T. D.; Schultz, A. J.; Cowan, J. A. J. Am. Chem. Soc. 2004, 126, 10428–
10440.
To broaden the synthetic scope and to gain further mechanistic
understanding of these metalloporphyrin-based SiHA, we have
explored the SiHA chemistry with high-valent iridium(III)
porphyrins. In addition, the base-promoted SiHA was discov-
ered. Herein, we now report the successful results of these
studies.
(10) Fernandez, M. J.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1984,
3, 2063–2066.
(5) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175–292.
(6) Taw, F. L.; Bergman, R. G.; Brookhart, M. Organometallics 2004,
4, 886–890.
(7) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics 2006, 25,
4471–4482.
(8) Zhang, L. R.; Chan, K. S. Organometallics 2006, 25, 4822–4829.
(9) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2002,
21, 3376–3387.
(11) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000,
122, 1816–1817.
(12) (a) Radu, N. S.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 5863–
5864. (b) Ziegler, T.; Folga, E. J. Organomet. Chem. 1994, 478, 57–65.
(c) Woo, H.-G.; Walzer, J. F.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114,
7047–7055.
(13) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46,
2578–2592.
10.1021/om701144a CCC: $40.75
2008 American Chemical Society
Publication on Web 07/22/2008

Silicon-Hydrogen Bond ActiVation of Silanes
Organometallics, Vol. 27, No. 16, 2008 4035
Table 2. Solvent-Free SiHA of Silanes by Ir(ttp)Cl(CO)
Scheme 1. Mechanism of SiHA of Silanes with Rh(ttp)Cl or
Rh(ttp)Me
entry
HSiR3
temp (°C)
time
product (% yield)b
1
2
3
4
HSiEt3, 2a
200
200
200
140
200
140
200
4 days Ir(ttp)SiEt3 2b (84)
HSi(OEt)3 3a
HSiBnMe2 4a
H3SiPh 5a
H2SiPhMe 6a
H2SiPh2 7a
6 h
1 day
5 h
Ir(ttp)Si(OEt)3 3b (54)
Ir(ttp)SiBnMe2 4b (78)
Ir(ttp)SiPhH2 5b (90)
Ir(ttp)SiPhMeH 6b (34)
5
0.5 h
6
2 days Ir(ttp)SiPh2H 7b (68)
6 h Ir(ttp)SiPh2Me 8b (42)
7a
HSiPh2Me 8a
a 30% yield of Ir(ttp)SiPhMeH 6b was also generated according to
1H NMR analysis of the crude reaction mixture. b Average yield of
duplicate experiments.
the more hindered HSiPr3 or HSitBuMe2. However, the rate of
SiHA was also dependent on the solubility of Ir(ttp)Cl(CO) 1a
in silane. A better solvent, such as H2SiPhMe or HSiPhMe2,
gave a faster rate (Table 2, entries 5 and 7), while a poor solvent
such as HSiEt3 gave a slower rate (Table 2, entry 1).
Iridium porphyrin silyls are thermally stable when the silyl
group is trisubstituted. However, the monosubstituted Ir(ttp-
)SiPhH2 5b decomposed at 200 °C even in a nitrogen atmo-
sphere. Therefore, the reaction of Ir(ttp)Cl(CO) 1a and H3SiPh
5a was carried out at a lower temperature of 140 °C (Table 2,
entry 4). Ir(ttp)SiPhH2 5b and Ir(ttp)SiPhMeH 6b could not be
purified by column chromatography on alumina or recrystalli-
zation from CH2Cl2/MeOH. However, these two complexes
could be purified simply by washing off the impurities with
methanol under N2.
ForHSiPh2Me8aonly,besidestheSiHAreaction,silicon-carbon
bond activation (SiCA) was also observed. When 8a reacted
with Ir(ttp)Cl(CO) 1a at 200 °C, according to 1H NMR analysis,
Ir(ttp)H16,17 initially formed. Then both the SiHA product 8b
and SiCA product 6b were generated slowly and simultaneously
in the ratio of 1.00 to 1.16 with the slow disappearance of
Ir(ttp)H.18 In addition, Ir(ttp)H also reacted with HSiPh2Me to
generate both 8b and 6b at 200 °C in about 1.00 to 0.71 ratio,18
which suggested that Ir(ttp)H was the intermediate for the
parallel formation of both 8b and 6b in the reaction of 1a and
8a at 200 °C.
Figure 1. Structures of iridium porphyrin complexes.
Table 1. Temperature Optimization of SiHA
entry
temp (°C)
time
% 2ba
1
2
3
4
120
140
200
200
9 days
6 days
4.5 h
trace
10
6
4 days
84
a Average yield of duplicate experiments.
Results and Discussion
Optimization in Solvent-Free Conditions. Initially, Ir(ttp)-
Cl(CO) 1a (Figure 1) reacted with HSiEt3 2a in solvent-free
conditions at 120 °C (Table 1, entry 1). However, only a trace
amount of Ir(ttp)SiEt3 2b was obtained even after 9 days, while
Ir(ttp)H 1d was observed as the major product according to
the 1H NMR analysis of the crude reaction mixture. When the
reaction temperature was increased to 200 °C, after 4.5 h,
Ir(ttp)H was generated as the major product together with
Ir(ttp)SiEt3 2b isolated in a low yield of 6% (Table 1, entry 3).
After 4 days, Ir(ttp)SiEt3 2b was isolated in 84% yield (Table
1, entry 4). Therefore, the temperature of 200 °C was employed
for subsequent studies.
Base-Promoted SiHA with Ir(ttp)Cl(CO). Yamanoi and his
co-worker reported that a base, especially K3PO4, can promote
catalysis of a SiHA reaction.3 Our group also found that 2,6-
dimethylpyridine can increase the rate of SiHA of Rh(ttp)X (X
) Cl and OTf) and HSiEt3.8 We therefore examined the
possibility of base-promoted SiHA.
When the optimized solvent-free conditions at 200 °C were
applied to the reactions of Ir(ttp)Cl(CO) 1a with various silanes,
moderate to good yields of iridium porphyrin silyl complexes
were obtained (eq 1, Table 2). Ir(ttp)Cl(CO) 1a dissolved in
alkyl-substituted silanes only upon heating, but dissolved in
aromatic silanes even at room temperature.
The yields of the products depended on the steric hindrance
of silanes.8 Cone angles obtained from phosphines have been
used as a measure of steric hindrance, and cone angles of silanes
are identical to the corresponding phosphines14 [H3SiPh (101°),
HSi(OEt)3 (109°), H2SiPh2 (128°), HSiEt3 (132°), HSiPr3 (132°),
HSiPh2Me (136°)].15 In general, more bulky silanes with larger
cone angles reacted with slower rates and gave lower yields.
No SiHA product was found when Ir(ttp)Cl(CO) 1a reacted with
Table 3 and eq 2 show the successful results of base-promoted
SiHA reaction of Ir(ttp)Cl(CO) 1a and HSiEt3 2a in solvent-
free conditions. Addition of 5 equiv of K3PO4 enhanced the
reaction rate and yield slightly (Table 3, entries 3 and 2), while
addition of 10 equiv of K3PO4 enhanced the reaction rate and
yield remarkably even at a lower temperature of 140 °C (Table
3, entry 4). However, the addition of 20 equiv of K3PO4
decreased the reaction yield slightly (Table 3, entry 5), and this
may be due to the decomposition of intermediates or the
occurrence of a side reaction caused by excess base. The optimal
amount of K3PO4 was therefore found to be 10 equiv.
We further screened other salts with anions of different
basicity and nucleophilicity in the reaction of Ir(ttp)Cl(CO) and
HSiEt3. The pKa values for conjugated acids have been used to
(14) Tolman, C. A. Chem. ReV. 1977, 77, 313–348.
(15) (a) Hester, D. M.; Sun, S.; Harper, A. W.; Yang, G. K. J. Am.
Chem. Soc. 1992, 114, 5234–5240. (b) Goikhman, R.; Milstein, D. Chem.-
Eur. J. 2005, 11, 2983–2988.
(16) Yeung, S. K.; Chan, K. S. Organometallics 2005, 24, 6426–6430.
(17) Wayland, B. B.; Van Voorhees, S. L.; Wilker, C. Inorg. Chem.
1986, 25, 4039–4042.
(18) See the Supporting Information for details.

4036 Organometallics, Vol. 27, No. 16, 2008
Li and Chan
Table 3. Base-Promoted SiHA of HSiEt3 in Solvent-Free Conditions
Scheme 3. Mechanism of SiHA and SiCA of Ir(ttp)Cl(CO)
and HSiPh2Me
entry
base
equiv
temp (°C)
time (days)
% 2ba
1
2
3
4
5
6
7
8
9
none
none
0
0
5
200
140
140
140
140
140
140
140
140
140
140
4
6
1
1
1
1
1
5
6
5
5
84
10
46
88
80
16
37
50
4
K3PO4
K3PO4
K3PO4
K2CO3
KOH
KF
CsCl
KI
KOAc
10
20
10
10
10
10
10
10
Table 4. SiHA of Silanes by Ir(ttp)Cl(CO)
10
11
14
12
a Average yield of duplicate experiments.
Scheme 2. Mechanism of Base-Promoted SiHA of
Ir(ttp)Cl(CO) with HSiEt3
entry
silane
solvent
time
product (% yield)a
1
2
3
4
HSiEt3 2a
HSiEt3 2a
His(OEt)3 3a benzene
benzene
9 days Ir(ttp)SiEt3 2b (58)
cyclohexane 9 days Ir(ttp)SiEt3 2b (60)
6 h
Ir(ttp)Si(OEt)3 3b (85)
Ir(ttp)Si(OEt)3 3b (88)
His(OEt)3 3a cyclohexane 12 h
a Average yield of duplicate experiments.
formation of the Ir(ttp)H intermediate. Furthermore, in an
independent experiment, Ir(ttp)H reacted with HSiEt3 to give
92% yield of Ir(ttp)SiEt3 at 140 °C after 2 days (eq 4).
Scheme 3 illustrates the proposed mechanism for the reaction
of Ir(ttp)Cl(CO) with HSiPh2Me with SiHA, SiCA, and silyl
exchange reactions. Ir(ttp)Cl(CO) reacts with HSiPh2Me to give
Ir(ttp)H initially, which then reacts with excess HSiPh2Me to
yield both SiHA product 8b and SiCA product 6b concurrently.
We do not know the details of the SiCA, as iridium porphyrin
silyls could undergo slower reactions (2 days) to give 6b or
8b in HSiPh2Me solvent to give a mixture of 8b and 6b (eqs
5 and 6).
SiHA in Solvents. We have reported that the SiHA of silanes
with rhodium porphyrin complexes should be carried out in
solvent-free conditions due to the competitive activation of
solvent, such as benzene and dichloromethane.8 However,
iridium porphyrin complexes appeared to be less reactive toward
solvents. So the SiHA reaction was carried out in a nonpolar
solvent, such as benzene or cyclohexane.
Table 4 and eq 7 show the results of SiHA of silanes by
Ir(ttp)Cl(CO) 1a in benzene and cyclohexane. For HSiEt3 2a,
the reaction rate was slower than that in neat solvent-free
conditions, as expected by the lower concentration of 2a used
(Table 4, entries 1 and 2 vs Table 2, entry 1). The lower yielding
reaction of 2b is likely due to the lower reactivity of 2a.
However, a higher yield was obtained for HSi(OEt)3 3a even
in a solvent (Table 4, entries 3 and 4 vs Table 2, entry 2). The
faster rate and higher yield may be due to the better solubility
of Ir(ttp)Cl(CO) in solvent and the higher reactivity of HSi(O-
Et)3. Therefore, benzene and cyclohexane were both suitable
solvents for this reaction. Ir(ttp)Cl(CO) 1a also underwent rate-
enhanced SiHA in benzene in the presence of K3PO4 (eq 8).
compare the basicities of anions [H2O (15.7) > H3PO4 (12.32)
> H2CO3 (10.3) > HOAc (4.76) > HF (3.17) > HCl (-8.0) >
HI (<-9.0)].19 In general, a stronger base can promote SiHA
of silane effectively (Table 3, entries 4 and 7). However, a very
strong base such as KOH gave lower product yield, which was
likely due to base-promoted decomposition of either the
intermediate or the product. Since Ir(ttp)SiEt3 in the presence
of KOH (10 equiv) remained stable at 200 °C in benzene-d6
for 3 days, an intermediate was likely decomposed by a strong
base. One possible route is the conversion of the weakly basic
Ir(ttp)H intermediate into Ir(ttp)-, which further undergoes
thermal decomposition.20
Mechanistic Studies. Scheme 2 illustrates the proposed
mechanism for the SiHA. Initially, Ir(ttp)Cl(CO) ionizes into
Ir(ttp)+Cl- upon heating. This step is supported by the rate-
enhanced reaction with Ir(ttp)(BF4)(CO)21 1c bearing a more
labile anion. At 200 °C, Ir(ttp)Cl(CO) required 4 days to give
Ir(ttp)SiEt3 in 84% yield (Table 2, entry 1). Ir(ttp)(BF4)(CO)
only took 1 day to complete the reaction to produce 61% yield
of 2b (eq 3). The slightly lower yield may be caused by the
lower stability of 1c at high temperature.21 Then Ir(ttp)+ forms
a silane complex A, which reacts to give the observed
intermediate Ir(ttp)H together with Et3SiCl presumably. Further
reaction of Ir(ttp)H with excess silane produces the iridium
porphyrin silyl product. In the presence of a strong base (K3PO4,
KOH, KF), Ir(ttp)H is formed more rapidly by the facile attack
on the silicon atom in the iridium-silane complex by a base.
The intermediate Ir(ttp)H then reacts with excess silane to yield
Ir(ttp)SiEt3. Indeed, when the reaction mixture of Ir(ttp)Cl(CO)
1a and 100 equiv of HSiEt3 2a with the addition of K3PO4 in
benzene-d6 was heated for 1.5 h at 140 °C in a sealed NMR
tube, Ir(ttp)H was observed first without any Ir(ttp)SiEt3.18
Therefore, the base-promoted SiHA is due to the accelerated
Ir(ttp)Cl(CO) + HSiEt3 10 equivK PO , benzene8 Ir(ttp)SiEt3 (8)
3
4
100 equiv N2, dark, 140 oC, 3 days
2b 92%
SiHA with Ir(ttp)Me. The SiHA by more electron-rich
Ir(ttp)Me 1b bearing a nondissociating methyl group was also
successful (Table 5, eq 9). In solvent-free conditions, 1b reacted
with HSiEt3 2a to give 83% yield of Ir(ttp)SiEt3 2b at 200 °C
after 5 days (Table 5, entry 2). However, 1b reacted with
HSi(OEt)3 3a only to produce 16% yield of Ir(ttp)Si(OEt)3 3b
(19) http://daecr1.harvard.edu/pdf/evans_pKa_table.pdf.
(20) Ogoshi, H.; Setsune, J.-I.; Yoshida, Z.-I. J. Organomet. Chem. 1978,
159, 317–328.
(21) Song, X.; Chan, K. S. Organometallics 2007, 26, 965–970.

Silicon-Hydrogen Bond ActiVation of Silanes
Organometallics, Vol. 27, No. 16, 2008 4037
Table 5. Silicon-Hydrogen Bond Activation by Ir(ttp)Me
Scheme 4. Mechanism of SiHA of Ir(ttp)Me and Ir(ttp)SiR3
with Silanes
entry
HSiR3
temp (°C) time (days)
product (% yield)b
1
2
HSi(OEt)3, 3a
HSiEt3, 2a
HSiEt3, 2a
HSiEt3, 2a
HSi(OEt)3, 3a
200
200
150
200
200
7
5
8
7
4
Ir(ttp)Si(OEt)3 3b (16)
Ir(ttp)SiEt3 2b (83)
Ir(ttp)SiEt3 2b (12)
Ir(ttp)SiEt3 2b (10)
Ir(ttp)Si(OEt)3 3b (8)
3
4a
5a
a In benzene solvent, Ir(ttp)Me:silane ) 1:100. b Average yield of
duplicate experiments.
Scheme 5. Mechanism of SiHA of Ir(ttp)Me and Silane with
Base
Table 6. Base-Promoted SiHA of HSiEt3 by Ir(ttp)Me in
Solvent-Free Conditions
by theoretical methods since it is experimentally difficult.22
A
entry
base
% 2b
entry
base
KF
CsCl
KI
% 2ba
dissociative mechanism via homolysis of Ir(ttp)Me is unlikely
since the Ir-Me bond is stronger than the Rh-Me bond, which
is about 58 kcal/mol23 and will require a very long reaction
time. An alternative dissociative mechanism via heterolytic
cleavage of Ir-Me is not probable since Ir-/Me+ or Ir+/Me-
ion pairs are unstable and the energetic requirement would be
expected to be even much higher than that of homolysis.21
1
2
3
4
none
12
44
14
trace
5
6
7
8
15
6
9
K3PO4
K2CO3
KOH
KOAc
60
a Average yield of duplicate experiments.
(Table 5, entry 1). The lower yield was attributed to the poor
reactivity and selectivity, since most Ir(ttp)Me remained and
Ir(ttp)Et generated via carbon-oxygen bond activation reaction
was also observed. At 150 °C, a poor yield of 2b was produced
(Table 5, entry 3). When the reaction was carried out in benzene
solvent, a higher reaction temperature of 200 °C was required,
but still poor product yields were observed (Table 5, entries 4
and 5).
While we do not understand very well the mechanism of the
base-promoted SiHA by Ir(ttp)Me, we speculate in Scheme 5
that a base (B ) K2PO4- and OAc-) can attack Et3SiH to form
a pentavalent BEt3SiH-,21 which is more reactive to convert
Ir(ttp)Me into Ir(ttp)-. Then rapid proton abstraction of Ir(ttp)-
with Et3SiH or other proton source forms Ir(ttp)H, which
subsequently undergoes facile SiHA with Et3SiH to produce
1
Ir(ttp)SiEt3. Indeed, Ir(ttp)H was observed by H NMR spec-
Base-Promoted SiHA with Ir(ttp)Me. To further enhance
the SiHA by Ir(ttp)Me, the base effect on SiHA was examined.
Table 6 and eq 10 list the results of the base-promoted SiHA
by Ir(ttp)Me. We were delighted to find that the addition of
K3PO4 or KOAc gave higher product yields (Table 6, entries 2
and 8), although KOH and CsCl proved to be detrimental.
troscopy when the reactions were run only in the presence of
base, such as K3PO4 or KOAc, while no Ir(ttp)H was found
without the addition of base. This proposed mechanism further
accounts for the effect of base strength. In the presence of weak
base, such as CsCl or KI, the formation of BEt3SiH- is
disfavored. On the other hand, in the presence of very strong
base, such as KOH, Ir(ttp)- is formed rapidly, but undergoes
facile competitive decomposition, and only a trace amount of
Ir(ttp)SiEt3 is observed.
SiHA with Iridium Porphyrin Silyls. The SiHA reaction
was also observed with the electron-rich Ir(ttp)SiEt3 and
Ir(ttp)SiBnMe2 complexes. Ir(ttp)SiBnMe2 4b reacted with
HSiEt3 2a at 200 °C in 4 days to give 20% of Ir(ttp)SiEt3 2b
and 71% of 4b was recovered, while Ir(ttp)SiEt3 2b reacted
with HSiBnMe2 to give 82% of Ir(ttp)SiBnMe2 4b after 2 days,
and 2b was completely consumed (eqs 11 and 12). The higher
conversion of Ir(ttp)SiEt3 into 4b (eq 12) is likely due to the
preferred formation of a less hindered Ir(ttp)SiBnMe2 complex.
X-ray Structure. The structures of Ir(ttp)Si(OEt)3 (3b) and
Ir(ttp)SiBnMe2 (4b) were confirmed by single-crystal X-ray
diffraction studies and are shown in Figures 2 and 3 (30%
thermal ellipsoids). Crystals were grown from CH2Cl2/MeOH
solution. Details of data collection and processing parameters
are given in Table 7. Tables 8 and 9 list selected bond lengths
and angles for 3b and 4b, respectively.
From Figures 2 and 3 and Table 8, the coordination sphere
of the iridium atom of Ir(ttp)Si(OEt)3 3b forms a triclinic
geometry with the four porphyrinato nitrogen atoms occupying
the basal sites, while the silicon atom resides at the axial site.
The mean bond length of Ir-N bonds is 2.030 Å, which is
longer than the reported five-coordinated organorhodium(III)
porphyrin (2.013 Å for Rh(tmp)SiPh2Me).8 The Ir-Si length
is 2.277 Å, which is slightly shorter than that of reported Rh-Si
(2.329 Å for Rh(tmp)SiPh2Me, 2.305 Å for Rh(tpp)SiMe3 and
Mechanism of SiHA with Ir(ttp)Me and Ir(ttp)SiR3.
Scheme 4 shows the proposed reaction pathways for the reaction
of Ir(ttp)Me or Ir(ttp)SiR3 with silanes without the addition of
base. Oxidative addition can occur via the formation of an Ir(V)
intermediate since an Ir(V) intermediate in SiHA has been
reported by Bergman and co-workers.11 Alternatively, σ-bond
metathesis or σ-complex-assisted metathesis13 via a four-
centered transition state is also possible. The distinction between
oxidative addition and σ-bond metathesis has been attempted
(22) (a) Vastine, B. A.; Hall, M. B. J. Am. Chem. Soc. 2007, 129, 12068–
12069. (b) Webster, C. E.; Hall, M. B. Coord. Chem. ReV. 2003, 238, 315–
331.
(23) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc. 1991,
113, 5305–5311.

4038 Organometallics, Vol. 27, No. 16, 2008
Li and Chan
Figure 2. Molecular structure of Ir(ttp)Si(OEt)3 (30% thermal ellipsoids).
Figure 3. Molecular structure of Ir(ttp)SiBnMe2 (30% thermal ellipsoids).
2.32 Å for Rh(oep)SiEt3).8,25 It is also shorter than that of Ir-Si
in iridium complexes.26 The Ir atom lies almost at the center of
the mean plane of the porphyrin ring. The Ir-Si bond length
of Ir(ttp)SiBnMe2 4b is 2.328 Å, which is longer than that of
Ir(ttp)Si(OEt)3 3b. The Ir atom is also located at the center of
the mean plane of the porphyrin ring.
Conclusion
We have discovered that iridium porphyrin silyl complexes
were synthesized from the reactions of iridium(III) porphyrin
carbonyl chloride and methyl with silanes via silicon-hydrogen
bond activation in both solvent and solvent-free conditions.
SiHA reactions were promoted by basic additives. K3PO4
facilitated the SiHA of silane by Ir(ttp)Cl(CO) most efficiently,
while KOAc acceleratd the SiHA with Ir(ttp)Me best. Prelimi-
nary mechanistic experiments suggested that iridium porphyrin
carbonyl chloride initially formed iridium porphyrin cation,
which then reacted with silanes to generate iridium porphyrin
hydride. Ir(ttp)H further reacted with excess silane via
silicon-hydrogen bond activation reaction to yield iridium
porphyrin silyls. On the other hand, the silicon-hydrogen bond
activation reaction of silanes by iridium(III) porphyrin methyl
and silyls likely underwent oxidative addition or σ-bond
metathesis. In the presence of base, an anionic pentacoordinated
silicon hydride species likely formed, which would further react
with iridium porphyrin methyl to generate iridium porphyrin
(24) (a) Corriu, R. J. P.; Guerin, C.; Henner, B. J. L.; Wang, Q.
Orgnaometallics 1991, 10, 3200–3250. (b) Wan, Y. J.; Verkade, J. G. J. Am.
Chem. Soc. 1995, 117, 141–156. (c) Damrauer, R.; Crowell, A. J.; Craig,
C. F. J. Am. Chem. Soc. 2003, 125, 10759–10766. (d) Kinrade, S. D.; Del
Nin, J. W.; Schach, A. S.; Sloan, T. A.; Wilson, K. L.; Knight, C. T. G.
Science 1995, 285, 1542–1546. (e) Damrauer, R.; O’Connell, B.; Danahey,
S. E.; Simon, R. Organometallics 1989, 8, 1167–1171.
(25) (a) Tse, K.-S.; Mu, B.-M.; Mak, C. W.; Chan, K. S. J. Organomet.
Chem. 1998, 568, 257–261. (b) Mizutani, T.; Uesaka, T.; Ogoshi, H.
Organometallics 1995, 14, 341–346.
(26) (a) Goikaman, R.; Aizenberg, M.; Kraatz, H.-B.; Milstein, D. J. Am.
Chem. Soc. 1995, 117, 5865–5866. (b) Simons, R. S.; Gallucci, J. C.; Tessier,
C. A.; Youngs, W. J. J. Organomet. Chem. 2002, 654, 224–228. (c) Klei,
S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2001, 20, 3220–
3222. (d) Diversi, P.; Marchetti, F.; Ermini, V.; Matteoni, S. J. Organomet.
Chem. 2000, 593-594, 154–160.

Silicon-Hydrogen Bond ActiVation of Silanes
Organometallics, Vol. 27, No. 16, 2008 4039
Table 7. Crystal Data for Ir(ttp)Si(OEt)3 and Ir(ttp)SiBnMe2
3b
4b
empirical formula
cryst syst
space group
fw
C54 H51Ir N4O3Si
triclinic
P1
C57H49IrN4Si · 1/4CH2Cl2
monoclinic
P21/c
j
1024.28
1031.52
a (Å)
b (Å)
c (Å)
11.743 (6)
12.886 (6)
16.755 (8)
83.320 (10)
84.748 (9)
85.872 (10)
2
1.359
2.736
2503 (2)
13.780 (2)
51.702 (9)
15.311 (3)
90
97.874 (4)
90
R (deg)
ꢀ (deg)
γ (deg)
Z
8
Dcalc (mg/m3)
1.268
2.555
10806 (3)
absorp coeff (mm-1
V (Å3)
)
F(000)
1036
4164
cryst size (mm)
no. of reflns collcd
absorp corr
0.50 × 0.40 × 0.30
0.50 × 0.40 × 0.30
13 356
57 969
SADABS
SADABS
max. and min. transmn
refinement method
1.0000 and 0.480014
full-matrix least-squares on F2
8740/16/577
1.072
0.0545/0.1436
0.0677/0.1555
0.1018/0.8042
1.0000 and 0.500568
full-matrix least-squares on F2
19 016/156/1216
1.138
0.0986/0.2632
0.1371/0.2851
0.1040/232.8366
no. of data/restraints/params
goodness-of-fit on F2
b
final R1a/wR2 [I > 2σ(I)]
b
final R1a/wR2 (all data)
c
w1/w2
2
2 2
2
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. b wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2
.
c Weighting scheme w-1 ) σ2(Fo2) + (w1P)2 + w2P, where P ) (Fo
+
2
2Fc )/3.
Table 8. Selected Bond Lengths and Angles of Ir(ttp)Si(OEt)3
were run in duplicate, and the yields obtained were average yields.
Samples for microanalysis were recrystallized from CH2Cl2/MeOH
and were then dried at 40-60 °C under vacuum (0.005 mmHg)
for 3 days. Ir(ttp)Cl(CO)16 1a, Ir(ttp)Me16,17 1b, Ir(ttp)(BF4)(CO)21
1c, and Ir(ttp)H16,17 1d were prepared according to the literature.
1H NMR spectra were recorded on a Bruker DPX-300 (300
MHz). Chemical shifts were reported with reference to the residual
solvent protons in CDCl3 (δ 7.26 ppm) as the internal standard.
Chemical shifts (δ) were reported in parts per million (ppm)
downfield from TMS. Coupling constants (J) are reported in hertz
(Hz). 13C NMR spectra were recorded on a Bruker DPX 300 (75
MHz) spectrometer and referenced to CDCl3 (δ 77.1 ppm) spectra.
High-resolution mass spectra (HRMS) were performed on a
Thermofinnign MAT 95 XL in FAB (using 3-nitrobenzyl alcohol
(NBA) matrix and CH2Cl2 as the solvent) and ESI model (MeOH/
CH2Cl2, 1:1, as the solvent).
Bond Lengths (Å)
Ir(1)-N(1)
Ir(1)-N(3)
Ir(1)-Si(1)
Si(1)-O(2)
2.040 (6)
2.029 (6)
2.277 (3)
1.616 (9)
Ir(1)-N(2)
Ir(1)-N(4)
Si(1)-O(1)
Si(1)-O(3)
2.022 (6)
2.029 (6)
1.552 (11)
1.604 (10)
Bond Angles (deg)
N(1)-Ir(1)-Si(1)
N(3)-Ir(1)-Si(1)
O(1)-Si(1)-Ir(1)
O(3)-Si(1)-Ir(1)
O(1)-Si(1)-O(3)
90.88 (19)
N(2)-Ir(1)-Si(1)
N(4)-Ir(1)-Si(1)
O(2)-Si(1)-Ir(1)
O(1)-Si(1)-O(2)
O(3)-Si(1)-O(2)
95.1 (2)
92.9 (2)
109.6 (3)
103.9 (8)
102.7 (6)
94.3 (2)
112.7 (5)
113.3 (4)
113.6 (8)
Table 9. Selected Bond Lengths and Angles of Ir(ttp)SiBnMe2
Bond Lengths (Å)
Ir(1)-N(1)
2.036 (12) Ir(1)-N(2)
2.025 (13) Ir(1)-N(4)
2.328 (5) Si(1)-C(61)
1.852 (6) Si(1)-C(63)
2.026 (14)
Ir(1)-N(3)
Ir(1)-Si(1)
Si(1)-C(62)
2.030 (13)
1.865 (2)
1.85 (3)
Reactions of Ir(ttp)Cl(CO) 1a with Silanes. General Proce-
dure. The reaction of Ir(ttp)Cl(CO) 1a with triethylsilane (2a) is
described as a typical example. Triethylsilane (1.1 mL, 500 equiv)
was added to Ir(ttp)Cl(CO) (12.5 mg, 0.014 mmol), and the mixture
was degassed by the freeze-pump-thaw method (3 cycles). Then
the mixture was heated at 200 °C for 4 days in N2. The crude
product was purified by column chromatography on alumina eluting
with hexane. A purple solid of Ir(ttp)SiEt3 2b (11.5 mg, 0.0118
mmol, 84%) was produced. Rf ) 0.52 (hexane/CH2Cl2 ) 5:1). 1H
NMR (CDCl3, 300 MHz): δ -3.22 (q, 6 H, J ) 7.8 Hz), -1.25 (t,
9 H, J ) 7.8 Hz), 2.68 (s, 12 H), 7.50 (d, 8 H, J ) 8.4 Hz), 7.96
(t, 8 H, J ) 6.0 Hz), 8.51 (s, 8 H). 13C NMR (CDCl3, 75 MHz):
δ 0.1, 5.3, 21.7, 29.9, 124.8, 127.6, 127.7, 131.3, 133.4, 133.8,
137.3, 138.8, 143.8. HRMS (FAB): calcd for (C54H51N4SiIr)+ m/z
976.3507; found m/z 976.3526. Anal. Calcd for C54H51N4SiIr: C,
66.43; H, 5.26; N, 5.74. Found: C, 66.43; H, 5.24; N, 5.64.
Bond Angles (deg)
N(1)-Ir(1)-Si(1)
N(3)-Ir(1)-Si(1)
C(61)-Si(1)-Ir(1) 110.4 (8)
C(63)-Si(1)-Ir(1) 110.2 (8)
C(61)-Si(1)-C(63) 109.4 (15)
93.5 (4)
92.7 (4)
N(2)-Ir(1)-Si(1)
N(4)-Ir(1)-Si(1)
C(62)-Si(1)-Ir(1) 110.8 (9)
C(61)-Si(1)-C(62) 106.6 (14)
C(63)-Si(1)-C(62) 109.8 (14)
92.3 (5)
91.6 (4)
anion. Ir(ttp)H was produced after protonation and finally reacted
with excess silane to give iridium porphyrin silyl complexes.
Experimental Section
Unless otherwise noted, all chemicals were obtained from
commercial suppliers and used before purification. Hexane for
chromatography was distilled from anhydrous calcium chloride.
Thin-layer chromatography was performed on precoated alumina
plates for analysis of reaction mixture. All reactions were carried
out in a Teflon screw-head stoppered tube in N2 in the absence of
light by aluminum foil wrapping. The purification of iridium silyl
complexes was carried out by flash column chromatography in air
using aluminum (90 active neutral, 70-230 mesh). All reactions
Reaction between Ir(ttp)Cl(CO) 1a and Triethylsilane (2a).
Triethylsilane (1.0 mL, 500 equiv) and Ir(ttp)Cl(CO) (11.2 mg,
0.012 mmol) were heated at 120 °C for 9 days. Only trace amount
1
of Ir(ttp)SiEt3 2b was observed according to H NMR.
Reaction between Ir(ttp)Cl(CO) 1a and Triethylsilane (2a).
Triethylsilane (1.0 mL, 500 equiv) and Ir(ttp)Cl(CO) (11.2 mg,
0.012 mmol) were heated at 200 °C for 4.5 h. A purple solid of

4040 Organometallics, Vol. 27, No. 16, 2008
Li and Chan
Ir(ttp)SiEt3 2b (0.7 mg, 0.0007 mmol, 6%) was obtained after
column chromatography.
13C NMR (CDCl3, 75 MHz): δ 21.8, 124.5, 126.2, 127.5, 127.7,
131.4, 132.0, 133.8, 134.0, 137.4, 138.9, 143.2. HRMS (FAB): calcd
for (C60H47N4SiIr)+ m/z 1044.3194; found m/z 1044.3209. Anal.
Calcd for C60H47N4SiIr: C, 69.00; H, 4.54; N, 5.36. Found: C, 69.11;
H, 4.54; N, 5.38.
Reaction between Ir(ttp)Cl(CO) 1a and Triethylsilane (2a).
Triethylsilane (1.2 mL, 500 equiv) and Ir(ttp)Cl(CO) (14.1 mg,
0.015 mmol) were heated at 140 °C for 6 days under N2. A purple
solid of Ir(ttp)SiEt3 2b (1.5 mg, 0.0015 mmol, 10%) was obtained
after column chromatography.
Reaction between Ir(ttp)Cl(CO) 1a and Diphenylmethylsi-
lane (8a). Diphenylmethylsilane (1.5 mL, 500 equiv) and Ir(ttp)-
Cl(CO) (14.0 mg, 0.015 mmol) were heated at 200 °C for 6 h under
N2. A purple solid of Ir(ttp)SiPh2Me 8b (6.7 mg, 0.0063 mmol,
42%) was obtained after column chromatography. Rf ) 0.51
(hexane/CH2Cl2 ) 5:1). 1H NMR (CDCl3, 300 MHz): δ -3.07 (s,
3 H), 2.68 (s, 12 H), 4.61 (d, 4 H, J ) 7.2 Hz), 6.46 (t, 4 H, J )
7.5 Hz), 6.77 (t, 2 H, J ) 7.2 Hz), 7.46 (q, 8 H, J ) 7.5 Hz), 7.78
(d, 4 H, J ) 7.8 Hz), 7.89 (d, 4 H, J ) 7.8 z), 8.42(s, 8 H). 13C
NMR (CDCl3, 75 MHz): δ -8.2, 21.8, 124.7, 126.1, 127.1, 127.6,
127.7, 131.4, 131.6, 133.6, 133.7, 133.9, 137.4, 138.9, 143.4. HRMS
(FAB): calcd for (C61H49N4SiIr)+ m/z 1058.3350; found m/z
1058.3367. Anal. Calcd for C54H51N4O3SiIr: C, 69.22; H, 4.67; N,
5.29. Found: C, 69.21; H, 4.65; N, 5.03. Ir(ttp)SiPhMeH 6b (4.4
Reaction between Ir(ttp)Cl(CO) 1a and Triethoxysilane (3a).
Triethoxyslane (1.3 mL, 500 equiv) and Ir(ttp)Cl(CO) (13.3 mg,
0.014 mmol) were heated at 200 °C for 6 h under N2. A purple
solid of Ir(ttp)Si(OEt)3 3b (7.7 mg, 0.0076 mmol, 54%) was
obtained after column chromatography. Rf ) 0.28 (hexane/CH2Cl2
1
) 5:1). H NMR (CDCl3, 300 MHz): δ -0.22 (t, 9 H, J ) 6.9
Hz), 0.91 (q, 6 H, J ) 6.9 Hz), 2.68 (s, 12 H), 7.50 (d, 8 H, J )
8.1 Hz), 7.99 (d, 8 H, J ) 8.1 Hz), 8.58 (s, 8 H). 13C NMR (CDCl3,
75 MHz): δ 17.3, 21.8, 55.1, 124.3, 127.7, 127.8, 131.2, 133.9,
137.4, 139.2, 143.6. HRMS (FAB): calcd for (C54H51N4SiIr)+ m/z
1024.3354; found m/z 1024.2260. Anal. Calcd for C54H51N4O3SiIr:
C, 63.32; H, 5.02; N, 5.47. Found: C, 63.15; H, 4.98; N, 5.38.
1
mg, 0.0045 mmol, 30%) was also generated according to the H
Reaction between Ir(ttp)Cl(CO) 1a and Benzyldimethylsi-
lane (4a). Benzyldimethylsilane (1.2 mL, 500 equiv) and Ir(ttp)-
Cl(CO) (13.6 mg, 0.015 mmol) were heated at 200 °C for 1 day
under N2. A purple solid of Ir(ttp)SiBnMe2 4b (11.8 mg, 0.0117
mmol, 78%) was obtained after column chromatography. Rf ) 0.55
(hexane/CH2Cl2 ) 5:1). 1H NMR (CDCl3, 300 MHz): δ -3.83 (s,
6 H), -2.21 (s, 2 H), 2.69 (s, 12 H), 5.32 (t, 2 H, J ) 3.6 Hz),
6.47 (t, 3 H, J ) 3.6 Hz), 7.50 (t, 8 H, J ) 7.2 Hz), 7.96 (d, 4 H,
J ) 7.5 Hz), 8.04 (d, 4 H, J ) 7.5 Hz), 8.58 (s, 8 H). 13C NMR
(CDCl3, 75 MHz): δ -7.3, 21.7, 21.1, 123.2, 125.2, 127.5, 128.1,
128.2, 131.8, 133.9, 134.3, 137.9, 139.2, 144.0. HRMS (FAB): calcd
for (C57H49N4SiIr)+ m/z 1010.3350; found m/z 1010.3340. Anal.
Calcd for C54H51N4O3SiIr: C, 67.76; H, 4.89; N, 5.54. Found: C,
67.65; H, 4.948; N, 5.41.
NMR spectrum of the crude reaction mixture.
Reaction of Ir(ttp)Cl(CO) 1a and Diphenylmethylsilane (8a).
Diphenylmethylsilane (1.4 mL, 500 equiv) was added to Ir(ttp)-
Cl(CO) (13.4 mg, 0.014 mmol), and the mixture was degassed by
the freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 200 °C under N2. The reaction mixture was monitored
by 1H NMR spectroscopy by taking aliquots of the reaction mixture.
After 1 day, the ratio of Ir(ttp)SiPh2Me 8b to Ir(ttp)SiPhMeH 6b
was about 1.00:1.16.
Reaction of Ir(ttp)Cl(CO) 1a with Silanes with Base Added.
General Procedure. The reaction of Ir(ttp)Cl(CO) 1a with trieth-
ylsilane (2a) with addition of K3PO4 is described as a typical
example. Triethylsilane (1.1 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (12.6 mg, 0.014 mmol) and K3PO4 (29.7 mg, 0.140
mmol, 10 equiv), and the mixture was degassed by the freeze-
pump-thaw method (3 cycles). Then the mixture was heated at
140 °C for 1 day under N2. The crude product was purified by
chromatography on alumina eluting with hexane. A purple solid
of Ir(ttp)SiEt3 2b (12.0 mg, 0.0123 mmol, 88%) was produced.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
K3PO4. Triethylsilane (1.3 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (14.8 mg, 0.016 mmol) and K3PO4 (17.0 mg, 0.080
mmol, 5 equiv). Then the mixture was heated at 140 °C for 1 day
under N2. A purple solid of Ir(ttp)SiEt3 2b (7.2 mg, 0.0074 mmol,
46%) was obtained after column chromatography.
Reaction between Ir(ttp)Cl(CO) 1a and Phenylsilane (5a).
Phenylsilane (1.0 mL, 500 equiv) and Ir(ttp)Cl(CO) (15.6 mg, 0.017
mmol) were heated at 140 °C for 5 h under N2. A dark brown
solid of Ir(ttp)SiH2Ph 5b (14.8 mg, 0.0153 mmol, 90%) was
obtained when the reaction mixture was washed by MeOH. 1H
1
NMR (CDCl3, 300 MHz): δ -2.16 (s, 2 H, JSi-H ) 202.8 Hz),
2.69 (s, 12 H), 4.33 (d, 2 H, J ) 6.3 Hz), 6.37 (t, 2 H, J ) 6.3 Hz),
6.76 (t, 1 H, J ) 6.3 Hz), 7.51 (d, 8 H, J ) 7.5 Hz), 7.88 (d, 4 H,
J ) 7.2 Hz), 8.00 (d, 4 H, J ) 7.2 Hz), 8.53 (s, 8 H). 13C NMR
(CDCl3, 75 MHz): δ 21.7, 124.2, 126.1, 127.5, 127.6, 131.3, 131.4,
133.6, 133.9, 137.3, 138.7, 143.0. HRMS (FAB): calcd for
(C54H43N4SiIr)+ m/z 968.2881; found m/z 968.2872.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
K3PO4. Triethylsilane (1.4 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (15.8 mg, 0.017 mmol) and K3PO4 (72.2 mg, 0.340
mmol, 20 equiv). Then the mixture was heated at 140 °C for 1 day
under N2. A purple solid of Ir(ttp)SiEt3 2b (13.3 mg, 0.0136 mmol,
80%) was obtained after column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
K2CO3. Triethylsilane (1.0 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (12.2 mg, 0.013 mmol) and K2CO3 (18.0 mg, 0.130
mmol, 10 equiv). Then the mixture was heated at 140 °C for 1 day
under N2. A purple solid of Ir(ttp)SiEt3 2b (2.0 mg, 0.0021 mmol,
16%) was obtained after column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
KOH. Triethylsilane (1.0 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (12.2 mg, 0.013 mmol) and KOH (7.3 mg, 0.130
mmol, 10 equiv). Then the mixture was heated at 140 °C for 1 day
under N2. A purple solid of Ir(ttp)SiEt3 2b (4.7 mg, 0.0048 mmol,
37%) was obtained after column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
KF. Triethylsilane (1.3 mL, 500 equiv) was added to a mixture of
Ir(ttp)Cl(CO) (15.3 mg, 0.017 mmol) and KF (9.9 mg, 0.170 mmol,
10 equiv). Then the mixture was heated at 140 °C for 5 days under
Reaction between Ir(ttp)Cl(CO) 1a and Phenylmethylsilane
(6a). Phenylmethylsilane (0.8 mL, 500 equiv) and Ir(ttp)Cl(CO)
(11.2 mg, 0.012 mmol) were heated at 200 °C for 0.5 h under N2.
A purple solid of Ir(ttp)SiPhMeH 6b (4.0 mg, 0.0041 mmol, 34%)
was obtained when the reaction mixture was washed by MeOH. Rf
1
) 0.46 (hexane/CH2Cl2 ) 5:1). H NMR (CDCl3, 300 MHz): δ
1
-3.45 (d, 3 H, J ) 3.3 Hz), -2.24 (q, 1 H, J ) 3.3 Hz, JSi-H
)
200.1 Hz), 2.68 (s, 12 H), 4.34 (d, 2 H, J ) 6.9 Hz), 6.40 (t, 2 H,
J ) 7.5 Hz), 6.78 (t, 1 H, J ) 7.4 Hz), 7.53 (t, 8 H, J ) 5.7 Hz),
7.86 (d, 4 H, J ) 8.4 Hz), 7.98 (d, 4 H, J ) 8.4 Hz), 8.49 (s, 8 H).
13C NMR (CDCl3, 75 MHz): δ -9.8, 21.8, 124.5, 126.2, 127.5,
127.7, 127.8, 130.6, 131.4, 133.7, 134.0, 137.4, 138.9, 143.3. HRMS
(FAB): calcd for (C55H45N4SiIr)+ m/z 982.3037; found m/z 982.3032.
Reaction between Ir(ttp)Cl(CO) 1a and Diphenylsilane
(7a). Diphenylsilane (1.6 mL, 500 equiv) and Ir(ttp)Cl(CO) (16.0
mg, 0.017 mmol) were heated at 140 °C for 2 days under N2. A
purple solid of Ir(ttp)SiPh2H 7b (12.1 mg, 0.0116 mmol, 68%) was
obtained after column chromatography. Rf ) 0.56 (hexane/CH2Cl2
1
1
) 5:1). H NMR (CDCl3, 300 MHz): δ -1.76 (s, 1 H, JSi-H
)
204.6 Hz), 2.68 (s, 12 H), 4.50 (d, 4 H, J ) 7.5 Hz), 6.39 (t, 4 H,
J ) 7.5 Hz), 6.75 (t, 2 H, J ) 7.5 Hz), 7.48 (t, 8 H, J ) 7.5 Hz),
7.72 (d, 4 H, J ) 7.5 Hz), 7.95 (d, 4 H, J ) 7.5 Hz), 8.45 (s, 8 H).

Silicon-Hydrogen Bond ActiVation of Silanes
Organometallics, Vol. 27, No. 16, 2008 4041
N2. A purple solid of Ir(ttp)SiEt3 2b (8.3 mg, 0.0085 mmol, 50%)
was obtained after column chromatography.
Reaction of Ir(ttp)(BF4)(CO) 1c and Triethylsilane (2a)Tri-
ethylsilane (1.0 mL, 500 equiv) was added to Ir(ttp)(BF4)(CO) (12.8
mg,0.013mmol),andthemixturewasdegassedbythefreeze-pump-thaw
method (3 cycles). Then the mixture was heated at 200 °C for 1
day under N2. The crude product was purified by chromatography
on alumina eluting with hexane. A purple solid of Ir(ttp)SiEt3 2b
(7.7 mg, 0.0079 mmol, 61%) was obtained.
Reaction of Ir(ttp)H 1d and Triethylsilane (2a). Triethylsilane
(1.3 mL, 500 equiv) was added to Ir(ttp)H (14.0 mg, 0.016 mmol),
and the mixture was degassed by the freeze-pump-thaw method
(3 cycles). Then the mixture was heated at 140 °C for 2 days under
N2. The crude product was purified by chromatography on alumina
eluting with hexane. A purple solid of Ir(ttp)SiEt3 2b (14.4 mg,
0.0147 mmol, 92%) was produced.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
CsCl. Triethylsilane (1.2 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (14.0 mg, 0.015 mmol) and CsCl (25.3 mg, 0.150
mmol, 10 equiv). Then the mixture was heated at 140 °C for 6
days under N2. A purple solid of Ir(ttp)SiEt3 2b (0.6 mg, 0.0006
mmol, 4%) was obtained after column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
KI. Triethylsilane (1.1 mL, 500 equiv) was added to a mixture of
Ir(ttp)Cl(CO) (13.2 mg, 0.014 mmol) and KI (23.2 mg, 0.140 mmol,
10 equiv). Then the mixture was heated at 140 °C for 5 days under
N2. A purple solid of Ir(ttp)SiEt3 2b (1.9 mg, 0.0020 mmol, 14%)
was obtained after column chromatography.
Reaction of Ir(ttp)H 1d and Diphenylmethylsilane (8a).
Diphenylmethylsilane (1.0 mL, 500 equiv) was added to Ir(ttp)H
(9.0 mg, 0.010 mmol), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 200 °C under N2. The reaction mixture was monitored
by 1H NMR spectroscopy by taking aliquots of the reaction mixture.
After 2 h, the ratio of Ir(ttp)SiPh2Me 8b to Ir(ttp)SiPhMeH 6b was
about 1.00:0.71.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) with
KOAc. Triethylsilane (1.2 mL, 500 equiv) was added to a mixture
of Ir(ttp)Cl(CO) (14.4 mg, 0.016 mmol) and KOAc (15.7 mg, 0.160
mmol, 10 equiv). Then the mixture was heated at 140 °C for 5
days under N2. A purple solid of Ir(ttp)SiEt3 2b (1.9 mg, 0.0019
mmol, 12%) was obtained after column chromatography.
Reactions of Ir(ttp)Cl(CO) 1a with Silanes in Solvent.
General Procedure. The reaction of Ir(ttp)Cl(CO) 1a with trieth-
ylsilane (2a) in benzene is described as a typical example.
Triethylsilane (0.22 mL, 100 equiv) was added to Ir(ttp)Cl(CO)
(12.9 mg, 0.014 mmol) in benzene (1.0 mL), and the mixture was
degassed by the freeze-pump-thaw method (3 cycles). Then the
mixture was heated at 200 °C for 9 days under N2. The crude
product was purified by chromatography on alumina eluting with
hexane. A purple solid of Ir(ttp)SiEt3 2b (7.9 mg, 0.0081 mmol,
58%) was produced.
Reactions of Ir(ttp)Me 1b with Silanes. General Procedure.
The reaction of Ir(ttp)Me 1b with triethylsilane (2a) is described
as a typical example. Triethylsilane (1.0 mL, 500 equiv) was added
to Ir(ttp)Me (11.1 mg, 0.013 mmol), and the mixture was degassed
by the freeze-pump-thaw method (3 cycles). Then the mixture
was heated at 200 °C for 5 days under N2. The crude product was
purified by chromatography on alumina eluting with hexane. A
purple solid of Ir(ttp)SiEt3 2b (10.5 mg, 0.0108 mmol, 83%) was
obtained.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane 2a in
Cyclohexane. Triethylsilane (0.22 mL, 100 equiv) was added to
Ir(ttp)Cl(CO) (12.6 mg, 0.014 mmol) in cyclohexane (1.0 mL). Then
the mixture was heated at 200 °C for 9 days under N2. A purple
solid of Ir(ttp)SiEt3 2b (8.2 mg, 0.0084 mmol, 60%) was obtained
after column chromatography.
Reaction between Ir(ttp)Me 1b and Triethylsilane (2a).
Triethylsilane (1.2 mL, 500 equiv) and Ir(ttp)Me (13.4 mg, 0.015
mmol) were heated at 150 °C for 8 days under N2. A purple solid
of Ir(ttp)SiEt3 2b (1.8 mg, 0.0018 mmol, 12%) was obtained after
column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethoxylsilane (3a) in
Benzene. Triethoxylsilane (0.24 mL, 100 equiv) was added to
Ir(ttp)Cl(CO) (12.2 mg, 0.013 mmol) in benzene (1.0 mL). Then
the mixture was heated at 200 °C for 6 h under N2. A purple solid
of Ir(ttp)Si(OEt)3 3b (11.3 mg, 0.0110 mmol, 85%) was obtained
after column chromatography.
Reaction between Ir(ttp)Me 1b and Triethoxysilane (3a).
Triethoxysilane (1.1 mL, 500 equiv) and Ir(ttp)Me (10.9 mg, 0.012
mmol) were heated at 200 °C for 7 days under N2. A purple solid
of Ir(ttp)Si(OEt)3 3b (2.0 mg, 0.0019 mmol, 16%) was obtained
after column chromatography.
Reactions of Ir(ttp)Me 1b with Silanes in Benzene. General
Procedure. The reaction of Ir(ttp)Me 1b with triethylsilane (2a)
in benzene is described as a typical example. Triethylsilane (0.24
mL, 100 equiv) was added to Ir(ttp)Me (12.9 mg, 0.015 mmol) in
benzene (1.0 mL), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 200 °C for 7 days under N2. The crude product was
purified by chromatography on alumina eluting with hexane. A
purple solid of Ir(ttp)SiEt3 2b (1.5 mg, 0.0015 mmol, 10%) was
produced.
Reaction of Ir(ttp)Cl(CO) 1a with Triethoxylsilane (3a) in
Cyclohexane. Triethoxylsilane (0.26 mL, 100 equiv) was added
to Ir(ttp)Cl(CO) (12.9 mg, 0.014 mmol) in cyclohexane (1.0 mL).
Then the mixture was heated at 200 °C for 12 h under N2. A purple
solid of Ir(ttp)Si(OEt)3 3b (12.6 mg, 0.0123 mmol, 88%) was
obtained after column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) in
Benzene with K3PO4 Added. Triethylsilane (0.26 mL, 100 equiv)
was added to a mixture of Ir(ttp)Cl(CO) (14.4 mg, 0.016 mmol)
and K3PO4 (34.0 mg, 0.160 mmol, 10 equiv) in benzene (1.0 mL),
and the mixture was degassed by the freeze-pump-thaw method
(3 cycles). Then the mixture was heated at 140 °C for 3 days under
N2. The crude product was purified by chromatography on alumina
eluting with hexane. A purple solid of Ir(ttp)SiEt3 2b (14.6 mg,
0.015 mmol, 92%) was produced.
Reaction of Ir(ttp)Me 1b with Triethoxylsilane (3a) in
Benzene. Triethoxylsilane (0.26 mL, 100 equiv) was added to
Ir(ttp)Me (11.9 mg, 0.014 mmol) in benzene (1.0 mL). Then the
mixture was heated at 200 °C for 4 days under N2. A purple solid
of Ir(ttp)Si(OEt)3 3b (1.1 mg, 0.0011 mmol, 8%) was obtained after
column chromatography.
Reaction of Ir(ttp)Cl(CO) 1a with Triethylsilane (2a) in
Benzene-d6 with K3PO4 Added in a Sealed NMR Tube. Trieth-
ylsilane (90 µL, 100 equiv) was added to a mixture of Ir(ttp)Cl(CO)
(5.4 mg, 0.006 mmol) and K3PO4 (12.3 mg, 0.058 mmol, 10 equiv)
in benzene-d6 (0.5 mL), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 140 °C in the presence of light under vacuum. When the
reaction was traced by 1H NMR, after 1.5 h, Ir(ttp)H was observed
first without any Ir(ttp)SiEt3.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with
Base Added. General Procedure. The reaction of Ir(ttp)Me 1b
with triethylsilane (2a) with addition of K3PO4 is described as a
typical example. Triethylsilane (1.2 mL, 500 equiv) was added to
a mixture of Ir(ttp)Me (13.1 mg, 0.015 mmol) and K3PO4 (31.8
mg, 0.150 mmol, 10 equiv), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 150 °C for 8 days under N2. The crude product was

4042 Organometallics, Vol. 27, No. 16, 2008
Li and Chan
purified by chromatography on alumina eluting with hexane. A
purple solid of Ir(ttp)SiEt3 2b (6.4 mg, 0.0066 mmol, 44%) was
produced.
degassed by the freeze-pump-thaw method (3 cycles). Then the
mixture was heated at 200 °C for 2 days under N2. The crude
product was purified by chromatography on alumina eluting with
hexane. A purple solid of Ir(ttp)SiPh2Me 8b (4.2 mg, 0.0040 mmol,
33%) was obtained, and a 31% yield of Ir(ttp)SiPhMeH 6b was
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with
KOH. Triethylsilane (1.1 mL, 500 equiv) was added to a mixture
of Ir(ttp)Me (12.3 mg, 0.014 mmol) and KOH (7.8 mg, 0.140 mmol,
10 equiv). Then the mixture was heated at 150 °C for 8 days under
N2. Only a trace amount of Ir(ttp)SiEt3 2b was observed according
1
produced according to H NMR of the crude mixture.
Reaction of Ir(ttp)SiPhMeH (6b) with Diphenylmethylsi-
lane (8a). Diphenylmethylsilane (1.5 mL, 500 equiv) was added
to Ir(ttp)SiPhMeH (14.6 mg, 0.015 mmol), and the mixture was
degassed by the freeze-pump-thaw method (3 cycles). Then the
mixture was heated at 200 °C for 2 days under N2. The crude
product was purified by chromatography on alumina eluting with
hexane. A purple solid of Ir(ttp)SiPh2Me 8b (6.4 mg, 0.0060 mmol,
40%) was produced, and 46% recovery yield of Ir(ttp)SiPhMeH
1
to H NMR.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with
K2CO3. Triethylsilane (1.0 mL, 500 equiv) was added to a mixture
of Ir(ttp)Me (11.8 mg, 0.013 mmol) and K2CO3 (18.0 mg, 0.130
mmol, 10 equiv). Then the mixture was heated at 150 °C for 8
days under N2. A purple solid of Ir(ttp)SiEt3 2b (1.8 mg, 0.0018
mmol, 14%) was produced.
1
6b was obtained according to H NMR of the crude mixture.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with KF.
Triethylsilane (1.2 mL, 500 equiv) was added to a mixture of
Ir(ttp)Me (12.8 mg, 0.015 mmol) and KF (8.7 mg, 0.150 mmol, 10
equiv). Then the mixture was heated at 150 °C for 8 days under
N2. A purple solid of Ir(ttp)SiEt3 2b (2.2 mg, 0.0023 mmol, 15%)
was produced.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with
CsCl. Triethylsilane (1.3 mL, 500 equiv) was added to a mixture
of Ir(ttp)Me (14.1 mg, 0.016 mmol) and CsCl (26.9 mg, 0.160
mmol, 10 equiv). Then the mixture was heated at 150 °C for 8
days under N2. A purple solid of Ir(ttp)SiEt3 2b (0.9 mg, 0.0010
mmol, 6%) was produced.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with KI.
Triethylsilane (1.1 mL, 500 equiv) was added to a mixture of
Ir(ttp)Me (12.1 mg, 0.014 mmol) and KI (23.2 mg, 0.140 mmol,
10 equiv). Then the mixture was heated at 150 °C for 8 days under
N2. A purple solid of Ir(ttp)SiEt3 2b (1.2 mg, 0.0013 mmol, 9%)
was produced.
Reaction of Ir(ttp)SiEt3 2b with Benzyldimethylsilane (4a).
Benzyldimethylsilane (1.0 mL, 500 equiv) was added to Ir(ttp)SiEt3
(12.2 mg, 0.012 mmol), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 200 °C for 2 days under N2. The crude product was
purified by chromatography on alumina eluting with hexane. A
purple solid of Ir(ttp)SiBnMe2 4b (9.9 mg, 0.0098 mmol, 82%)
was produced.
Reaction of Ir(ttp)SiBnMe2 4b with Triethylsilane (2a).
Triethylsilane (1.2 mL, 500 equiv) was added to Ir(ttp)SiBnMe2
(15.2 mg, 0.015 mmol), and the mixture was degassed by the
freeze-pump-thaw method (3 cycles). Then the mixture was
heated at 200 °C for 4 days under N2, and 4b was not consumed
completely. The crude product was purified by chromatography on
alumina eluting with hexane. A purple solid of Ir(ttp)SiEt3 2b (2.9
mg, 0.0030 mmol, 20%) was produced, and Ir(ttp)SiBnMe2 4b (10.8
mg, 0.0106 mmol, 71%) was recovered.
Reaction of Ir(ttp)Me 1b with Triethylsilane (2a) with KOAc.
Triethylsilane (1.2 mL, 500 equiv) was added to a mixture of
Ir(ttp)Me (13.3 mg, 0.015 mmol) and KOAc (14.7 mg, 0.150 mmol,
10 equiv). Then the mixture was heated at 150 °C for 8 days under
N2. A purple solid of Ir(ttp)SiEt3 2b (8.8 mg, 0.0090 mmol, 60%)
was produced.
Reaction of Ir(ttp)SiPh2Me (8b) with Diphenylmethylsilane
(8a). Diphenylmethylsilane (1.2 mL, 500 equiv) was added to
Ir(ttp)SiPh2Me (12.2 mg, 0.012 mmol), and the mixture was
Acknowledgment. We thank the Research Grants Council
of Hong Kong of the SAR of China for financial support
(No. 400105).
Supporting Information Available: Crystallographic data for
3b and 4b and spectra for 5b and 6b. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM701144A