Alkylation of rhodium porphyrins using ammonium and quinolinium salts

Article abstract of DOI:10.1021/om500438s

Alkylation of rhodium(III) porphyrins [Rh^III(por)] was achieved under relatively mild conditions in up to 98% yields, where readily available ammonium and quinolinium salts were utilized as the alkylating agents. This transformation tolerates air and water, thus serving as a convenient method to prepare a variety of alkyl- and benzyl-Rh^III(por) complexes. Preliminary mechanistic studies support an S_N2-like reaction pathway involving a Rh^I(por) anion intermediate.

Full text of DOI:10.1021/om500438s

Article
pubs.acs.org/Organometallics
Alkylation of Rhodium Porphyrins Using Ammonium and
Quinolinium Salts
Samuel J. Thompson and Guangbin Dong*
Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
S
* Supporting Information
ABSTRACT: Alkylation of rhodium(III) porphyrins [RhIII(por)] was achieved
under relatively mild conditions in up to 98% yields, where readily available
ammonium and quinolinium salts were utilized as the alkylating agents. This
transformation tolerates air and water, thus serving as a convenient method to
prepare a variety of alkyl- and benzyl-RhIII(por) complexes. Preliminary
mechanistic studies support an SN2-like reaction pathway involving a RhI(por)
anion intermediate.
Scheme 1. Alkylation of Rhodium Porphyrins
INTRODUCTION
■
Metal−carbon σ-bond formation plays a critical role in
organotransition metal chemistry, ranging from fundamental
mechanistic studies to new catalyst development.1 Among the
numerous metal-alkyl complexes discovered to date, alkyl-
rhodium(III) porphyrins [RhIII(por)s] are intriguing organo-
metallic compounds. First, they serve as the key intermediate in
the RhII(por) metalloradical-mediated C−H activation of
alkanes;2 second, they have been utilized as unique substrates
to study anti-Markovnikov hydrofunctionalization of olefins;3
and third, they represent a potential model for mimicking the
B12 coenzyme process.4 Hence, developing efficient strategies
to access various alkyl-RhIII(por)s remains an important area of
research.
The first alkylation of RhIII(por)s was reported by Ogoshi in
1972 involving treatment of RhIII(OEP)Cl (OEP =
2,3,7,8,12,13,17,18-octaethylporphyrin) with MeLi to give
RhIII(OEP)Me (Scheme 1a).5 A more versatile method was
later developed through the reduction of RhIII(por)s with
NaBH4, forming an air-sensitive RhI(por) anion that is
subsequently quenched with excess alkyl halides (Scheme
1b).6 Olefin insertion into the RhIII(por)−H bond represents
an atom-economical approach to form alkyl-RhIII(por)
complexes;3,7 however, the alkyl groups that can be introduced
via this approach are limited (Scheme 1c). The activation of
alkane C−H bonds by RhII(por) metalloradicals serves as
another important method to form Rh−C bonds, which was
first reported by Wayland2a,b and later expanded by Chan
(Scheme 1d).8 In addition, Chan and co-workers have
developed various novel C−C activations of ketones, esters,
amides, nitriles, ethers, and strained and unstrained alkanes
with RhIII(por)s, providing alkyl-RhIII(por) products.9 Fur-
thermore, they found reactions with trialkylamines led to C−N
bond cleavage, affording alkyl-rhodium(III) porphyrins albeit in
modest yields (Scheme 1e).10 Herein, we disclose an efficient
complementary approach to access a range of alkyl-RhIII(por)
complexes from stable RhIII(por) halides [e.g., Rh(TPP)X; TPP
= 5,10,15,20-tetraphenylporphyrinato dianion, X = I or Cl]
using widely available ammonium/quinolinium salts as
alkylating reagents (Scheme 1f).11
RESULTS AND DISCUSSION
■
1. Reaction Discovery. While examining the role of water
in the Rh(por)-mediated C−H activation of toluene,2a,b
tetrabutylammonium hydroxide (50 equiv) was added as a
phase-transfer catalyst to a solution of Rh(TPP)I in toluene at
125 °C. To our surprise, the major product from this reaction
was Rh(TPP)(n-butyl) complex (ca. 72% yield) instead of
Rh(TPP)(benzyl) (minor product, ca. 17% yield). After
switching the solvent from toluene to benzene, the competitive
C−H activation was completely circumvented and Rh(TPP)Bu
Received: April 26, 2014
Published: July 7, 2014
© 2014 American Chemical Society
3757
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
(2a) was isolated in 98% yield using only 1.2 equiv of
tetrabutylammonium hydroxide (eq 1). Using the Rh(TPP)Cl
as the substrate worked equally well. The reaction temperature
can be lowered to 80 °C, yielding 82% Rh(TPP)Bu over 8 h
(eq 2). The more sterically encumbered Rh(TMP)I (TMP =
5,10,15,20-tetramesitylporphyrinato dianion) (3) also under-
went alkylation, forming Rh(TMP)Bu (4) in 80% yield,
although requiring a longer reaction time (eq 3).
Figure 1. ORTEP structure of Rh(TPP)(n-butyl) (2a) (displacement
ellipsoids are scaled to the 50% probability level; all solvent molecules
and hydrogen atoms are omitted for clarity).
This alkylation reaction was found to be insensitive to
oxygen and water. Nevertheless, under degassed conditions the
Rh(TPP)Bu was still obtained in 98% yield, showing no
participation of oxygen. Tributylamine was detected via GC and
high-resolution mass spectrometry after the reaction was
complete (vide infra, Mechanistic Studies), supporting that
the butyl group comes from the ammonium salt.12 Stimulated
by the convenience and efficiency of this transformation, we
envisioned that a simple general process could be developed to
synthesize various alkyl-RhIII(por)s.
To examine the reaction scope, other commercially available
ammonium hydroxides were tested (Table 1). In general, the
Table 1. Alkylation with Commercially Available
Ammonium Hydroxides
(TPP)Rh−I ⎯⎯R⎯⎯4⎯N⎯⎯O⎯⎯H⎯⎯⎯(⎯1⎯.2⎯⎯e⎯q⎯⎯u⎯i⎯v→) (TPP)Rh−R
C6H6, 120 °C, air, 2 h
1a
2a−d
Figure 2. ORTEP structure of Rh(TPP)(n-propyl) (2b) (displace-
ment ellipsoids are scaled to the 50% probability level; all solvent
molecules and hydrogen atoms are omitted for clarity).
a
entry
R =
yield (%)
1
2
3
4
n-butyl
n-propyl
ethyl
98 (2a)
90 (2b)
91 (2c)
56 (2d)
methyl
a
All yields are isolated yields.
reaction proceeded smoothly in high yields for various alkyl
ammonium hydroxides. While not necessary, using excess
ammonium hydroxide was found to have no effect on the
reaction. The lower yield for the methyl substrate is likely
attributed to the instability of the methyl compound (2d)
during isolation (entry 4, Table 1).
X-ray Structures. Figures 1−3 show the molecular structures
of the n-butyl (2a), n-propyl (2b), and ethyl (2c) metal
complexes, respectively (at the 50% probability level). The Rh−
C bond length of 2a was 2.054 Å, and for both 2b and 2c it was
2.048 Å, which are similar to the reported Rh−C bond lengths
of Rh(TTP)(n-heptyl) (TTP = 5,10,15,20-tetratolylporphyr-
inato dianion) (2.048 Å).13 The Rh−N bond lengths (average)
are close to 2.028 Å for both 2b and 2c with a slight decrease to
2.017 Å for 2a, possibly due to a disorder in the crystal packing.
The Npor−Rh−Calkyl bond angle (average) was comparable for
all three structures (90.94−92.18°), aligning the alkyl group
orthogonally to the porphyrin plane.
Figure 3. ORTEP structure of Rh(TPP)(ethyl) (2c) (displacement
ellipsoids are scaled to the 50% probability level; all solvent molecules
and hydrogen atoms are omitted for clarity).
Hence, it would be highly desirable if ammonium halides could
be used directly as the precursors for this alkyl-transfer reaction.
To examine the feasibility, tetrabutylammonium bromide
(TBAB) was employed as a model substrate (Table 2).
When heating 3 equiv of TBAB with Rh(TPP)I in benzene and
water (4:1 v/v), no reaction was observed. However, upon the
2. Alkylation with Quaternary Ammonium Halide
Salts. In contrast to ammonium hydroxides, halogen-based
ammonium salts are more readily available and easy to prepare.
3758
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
Table 2. Conditions for the Alkylation with
Tetrabutylammonium Bromide
Table 4. Reaction with Tetraalkylammonium Salts
R4N−X (3equiv), NaOH (15 equiv)
(TPP)Rh−I ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→⎯ (TPP)Rh−R
Bu4NBr (3 equiv), NaOH (15 equiv)
(TPP)Rh−I ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ (TPP)Rh−Butyl
C6H6/H2O (4:1 ), 120 °C, air, 5 h
C6H6/H2O (4:1 ), 120 °C, air, 5 h
1a
2a−e
a
1a
2a
entry
R =
X =
yield (%)
a
entry
change from standard conditions
yield (%)
1
2
3
4
5
n-octyl
n-butyl
n-propyl
ethyl
Br
Br
Br
Br
l
91 (2e)
89 (2a)
67 (2b)
48 (2c)
42 (2d)
1
2
3
4
5
none
89
0
b
c
no NaOH
1 equiv NaOH
80 °C, 12 h
1 equiv Bu4NBr
2
methyl
83
61
a
b
All yields are isolated yields. Use of n-Pr4NCl resulted in 61% yield.
c
a
Use of Et4NI resulted in 46% yield.
All yields are isolated yields.
treatment of Rh(TPP)I with commercially available benzyl-
trimethylammonium chloride afforded benzyl-RhIII(TPP) in
73% yield (entry 1, Table 5). The yield was further increased to
addition of excess 0.5 M NaOH (15 equiv), the reaction
proceeded smoothly in 5 h to give n-butyl-RhIII(TPP) (2a) in
89% yield (entries 1 and 2, Table 2). In contrast, using only 1
equiv of NaOH was not effective (entry 3, Table 2). The
reaction temperature can also be lowered to 80 °C to yield
complex 2a in 83% yield in 12 h (entry 4, Table 2). When the
loading of TBAB was decreased to 1 equiv, the yield was
reduced to 61% (entry 5, Table 2).
Table 5. Reaction with Benzyltrimethylammonium Salts
The counterion effect of the ammonium salts was
subsequently investigated (Table 3). Higher yields were
a
entry
1
R =
X =
yield (%)
Table 3. Counter Anion Effect in Alkylation
H
H
Cl
OH
Br
Cl
Br
Cl
Br
Br
Cl
73 (5a)
84 (5a)
64 (5b)
62 (5c)
61 (5d)
74 (5e)
88 (5f)
78 (5g)
70 (5h)
Bu4N−X (3 equiv), NaOH (15 equiv)
b
2
(TPP)Rh−I ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ (TPP)Rh−Butyl
C6H6/H2O (4:1 ), 120 °C, air, 5 h
1a
3
4
5
6
7
8
9
p-methyl
p-methoxy
p-nitro
2a
a
entry
X =
yield (%)
1
2
3
4
l
82
89
74
72
o-iodo
Br
Cl
F
o-bromo
p-bromo
p-chloro
a
All yields are isolated yields.
a
b
All yields are isolated yields. BnMe3NOH was used in 1.2 equiv, and
no NaOH was added.
obtained with bromide and iodide salts. The instability of
chloride and fluoride salts under basic conditions has been
reported, which likely accounts for the slightly diminished
yields.14 It is interesting to note that although simple alkyl
halides (e.g., n-BuI) are better electrophiles, they are much less
effective alkylating agents for this transformation (eq 4). This is
likely due the instability of alkyl halides under basic conditions,
thus making the use of ammonium salts advantageous.
84% when using benzyltrimethylammonium hydroxide (entry
2, Table 5). This reaction is highly selective for the benzyl
transfer, as only trace amounts of the methyl-RhIII(TPP) were
detected, even though the methyl group is statistically three
times more abundant than the benzyl group.
This reaction was found to be general for other benzyl-
derived trimethylammonium substrates, which can be easily
prepared via treatment of the corresponding benzyl halide with
trimethylamine.16 Notably, the alkylations proceeded well for
both electron-rich and electron-poor substrates (61−88%
yields), serving as a convenient approach for preparing
benzyl-Rh(TPP) derivatives.17 Aryl halides are compatible
under the reaction conditions. While the trimethylammonium
salt strategy works well for the benzyl-transfer reaction, use of
the butyltrimethylammonium salt18 provided the methyl
derivative as the only product (eq 5). These results suggest
the trend in reactivity for this transformation is benzyl > methyl
> other alkyl groups.
With the optimized conditions in hand, reactions of
Rh(TPP)I with several tetraalkylammonium halide salts were
pursued in the presence of NaOH at 120 °C (Table 4). In
general, alkylated RhIII(TPP) complexes were obtained in
moderate to high yields. A general trend was observed where
the tetraalkylammonium salts with longer chain lengths
afforded greater yields. The ethyl (2c) and methyl (2d)
ammonium salts are much less sterically shielded than the
longer alkyl chain analogues, likely allowing for hydroxide-
promoted side reactions15 to occur, contributing to the lower
observed yields of 48% and 42%, respectively.
To synthesize more complex alkyl-RhIII(por)s, it would be
more attractive to employ unsymmetrical ammonium salts that
can selectively transfer only one alkyl group. To our delight,
An X-ray structure for 5d is shown in Figure 4. The Rh−C
bond length (2.048 Å), R−N bond length (average) (2.027 Å),
3759
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
suggesting that this approach can potentially be used to prepare
more valuable and functionalized alkyl-Rh(por)s.20 In contrast,
the benzyl-derived quinolinium salt gave a poor yield likely due
to its labile nature.21 A stronger counteranion effect was
observed, where the bromide substrates generally provide
higher yields than the iodide counterparts.22 At the conclusion
of these reactions, free quinoline was detected through high-
23
1
resolution mass spectrometry and H NMR.
When investigating the alkylation with the unprotected alkyl
alcohol-substituted quinolinium salts, an unexpected trans-
formation was observed with the 3-bromopropanol-derived
substrate. Instead of giving 3-hydroxylpropyl-Rh(TPP), a new
complex was isolated in a good yield and identified as 3-
(quinolin-2(1H)-one)propyl-Rh(TPP) (7) (Figure 5). While
Figure 4. ORTEP structure of Rh(TPP)(p-nitrobenzyl) (5d)
(displacement ellipsoids are scaled to the 50% probability level; all
solvent molecules and hydrogen atoms are omitted for clarity).
and Npor−Rh−Calkyl bond angle (average) (91.37°) for 5d do
not have any significant variances from 2a−2c. The relatively
large p-nitrobenzyl group does not seem to affect the planarity
of the porphyrin ring, and the electron-withdrawing nature of
the nitro group does not significantly affect the length of the
Rh−C bond.
3. Alkylation with Quinolinium Salts. To overcome the
competition challenge for nonbenzyl alkyl transfer (Me vs other
alkyl groups), pyridinium salts were pursued as an ammonium
equivalent, avoiding alkyl selectivity issues. However, simple
pyridinium salts were found highly moisture sensitive. Although
the corresponding lutidinium salts were more stable, they were
unsuccessful for transferring alkyl groups presumably due to the
steric hindrance. Finally, the quinolinium salts were found to be
the more suitable reagent, which can be easily prepared from
the neat reaction of quinoline with the corresponding alkyl
halides at 120 °C.19
Figure 5. Rearrangement to form quinolinone-derived alkyl-Rh(por)s.
still unclear, we propose 7 was formed through an intermediate
(7′) that is likely generated via intramolecular alkoxide
nucleophilic attack of the electrophilic 2-position of the
quinolinium species. Hence, this approach provides a new
method for preparing quinolinone-derived alkyl-Rh(por)s.
Crystals of 7 grew as single orange plates, with the structure
shown in Figure 6. The Rh−C bond length (2.043 Å) was
slightly shorter than the previous compounds, while its Rh−N
Rh(TPP)I reacted with a range of alkyl quinolinium salts
under the standard conditions, yielding the alkyl-rhodium(III)
porphyrins in modest to good yields (24−84%, Table 6). A
similar trend was observed (vide supra, Table 4) where yields
improved with increasing length of the alkyl chain. Note that N-
1-(3-OTBS)-propyl-RhIII(TPP) (6a) was afforded in 84% yield,
Table 6. Alkylation with Quinolinium Salts
a
entry
R =
yield (%)
1
2
3
4
5
6
CH2CH2CH2OTBS
n-octyl
84 (6a)
70 (2e)
64 (6b)
53 (2a)
55 (2b)
37 (2c)
24 (2d)
n-pentyl
n-butyl
n-propyl
ethyl
Figure 6. ORTEP structure of Rh(TPP)(3-(quinolin-2(1H)-one)-
propyl) (7) (displacement ellipsoids are scaled to the 50% probability
level; all solvent molecules and hydrogen atoms are omitted for
clarity).
b
7
methyl
a
b
All yields are isolated yields. The counteranion was iodide.
3760
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
bond length (average) (2.024 Å) and Npor−Rh−Calkyl bond
angle (average) (91.56°) were similar. The quinolin-2(1H)-one
substituent appears to be undistorted, with bond lengths [N5−
C48 (1.380 Å), O1−C48 (1.254 Å)] and a N5−C48−O bond
angle (121.3°) similar to what has been reported for a free
quinolinone.24
Rh(TPP)Bu in 4% yield (eq 7). The low efficiency of this
reaction disfavors the C−N bond cleavage pathway through
tributylamine that could come from decomposition of the
tetraalkylammonium salts.
While our attempts of using a radical-clock probe derived
from methylcyclopropane were proven unsuccessful,27 we did
find that this reaction was completely insensitive to radical
inhibitors. For example, addition of radical scavengers, such as
BHT and TEMPO,28 in large excess (10 equiv), did not
significantly affect the reaction yields (eqs 8 and 9). Running
either under air or under O2-free conditions gave almost
identical outcomes (vide supra). Thus, a radical-mediated C−N
bond cleavage approach (pathway A) is unlikely.
MECHANISTIC STUDIES
■
Chan’s earlier research demonstrated that heating Rh(TPP)I
and NaOH led to the generation of a reactive RhIII(TPP)OH
species that serves as a precursor to the [RhII(TPP)]2 dimer.25
Similarly, under our conditions, the production of
[RhII(TPP)]2 was confirmed through EPR spectroscopy,
where a discrete rhodium(II) porphyrin complex with oxygen,
RhII(TPP)−O2 radical (g = 2.003, C6H6, 25 °C), was observed
similarly to the reported value in the literature (g = 2.033,
toluene, −160 °C).26 In addition, we demonstrated the
[RhII(TPP)]2 dimer can serve as an active intermediate for
the alkylation reaction. Irradiation of the Rh(TPP)Me complex
resulted in the known [RhII(TPP)]2 dimer,2b which upon
treatment with Bu4NOH followed by heating provided the
desired Rh(TPP)Bu (2a) in 76% yield (eq 6).
RhIII(por)-Hydride Approach. RhII(por) radicals are
known to abstract aliphatic hydrogens, forming RhIII(por)−H
species.2,8 Under strong basic conditions, the Hofmann
elimination of alkyl ammoniums may generate olefins, which
could further react with RhIII(por)−H intermediates to give
alkyl-RhIII(por)s (pathway B).3,7 This RhIII(por)−H mecha-
nism could potentially account for nonmethyl/benzyl alkyla-
tion. To examine the feasibility of this approach, a competitive
cross experiment was designed. When a large excess of 1-
hexene (40 equiv) was added with 1.2 equiv of Bu4NOH,
Rh(TPP)Bu (2a) was the only product isolated (eq 10). In
On the basis of the above observation, three possible
mechanisms are proposed (Scheme 2): (A) homolytic C−N
Scheme 2. Proposed Mechanistic Pathways for Alkyl
Transfer to Rhodium(III) Porphyrins
addition, an isotope labeling experiment was conducted. When
a large excess of (E)-1-D-oct-1-ene (>99% deuterium)29 (40
equiv) was added along with 3 equiv of n-Oct4NBr,
Rh(TPP)(n-octyl) (2e) was isolated with no observed
deuterium incorporation (eq 11). The absence of the cross
hexyl product and cross deuterium labeled product ruled out
the RhIII(por)−H-mediated olefin-insertion mechanism (path-
way B).
Direct Nucleophilic Substitution Approach. Quaternary
ammonium salts are rarely utilized as electrophilic alkylating
agents.30 However, during the study of methionine synthase-
catalyzed methyl-transfer reaction, Pandit and co-workers
reported that N-dealkylation of some quaternary ammonium
salts can occur with soft nucleophiles, such as thiolate anions,
cobaloxime, and cobalamin.31 In these alkyl-transfer processes,
an SN2 mechanism was proposed. Thus, it is reasonable to
hypothesize that a similar SN2-like displacement of one alkyl
group from ammonium salts can occur with anionic
nucleophilic RhI(por) species (pathway C).
bond cleavage of trialkylamine or ammonium with a RhII(por)
radical, (B) RhIII(por)−H addition across an olefin that is
generated via Hofmann elimination of an ammonium
hydroxide, (C) direct nucleophilic substitution (i.e., an SN2-
like pathway) of the ammonium with anionic RhI(por) or its
equivalent.
RhII(por) Radical Approach. RhII(por) radical-mediated
C−N bond cleavage of amines was previously reported by
Chan.10 However, under our conditions, substitution of the
tetraalkylammonium salt with tributylamine resulted only in
3761
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
While it was challenging to perform accurate kinetic studies
for this reaction due to its heterogeneous nature, our
hypothesis for an SN2 pathway is supported by the following
observations: first, trialkylamine and quinoline (the leaving
groups) were found at the end of the reactions. For example,
after the alkylation of complex 1a was complete with
tetrabutylammonium hydroxide, tributylamine was produced
in 111% yield based on RhIII(por) (93% based on the
Bu4NOH)32 (eq 12).
Scheme 3. Proposed Mechanism for Alkylation of
RhIII(por)s
Second, the involvement of an anionic RhI(TPP) species was
strongly supported in an epoxide-opening experiment (eq 13).
tion. The resulting RhI(TPP) anion is trapped by the
ammonium cation, furnishing the alkyl transfer. The newly
generated RhIII(TPP)OH is expected to re-enter the reaction
cycle. This proposed activation mode is analogous to the
bimetallic oxidation of palladium(II) to palladium(III)
proposed by Ritter.38
While the proposed mechanism remains to be further
investigated, we hypothesize that the reason that the
[RhII(por)]2 dimer works much better than mononuclear
RhI(por) sodium salt is due to the counterion effect. When the
RhI(por) anion is generated with NaBH4, the cation is sodium,
forming a reasonably tight ion pair, which would likely slow the
nucleophilic substitution process. In the proposed approach
involving the [RhII(por)]2 dimer, the cation for the RhI(por)
anion is the ammonium (substrate itself), thus facilitating the
subsequent substitution reaction, which is supported by the
experiment using Bu4NBH4 as the reagent (vide supra, eq 15).
Groves first discovered anionic RhI(por) was able to open
epoxides regioselectively at the less substituted position.33 We
found treatment of 1,2-epoxyhexane with Rh(TPP)I under the
standard alkyl-transfer conditions afforded the epoxide ring-
opening product (8) in 62% yield by alkylating at the less
substituted carbon without forming the other regioisomer (eq
13). This result indicates that an SN2-like nucleophilic addition
pathway is possible under the standard alkyl-transfer con-
ditions.
When the anionic RhI(TPP) complex, independently
prepared through NaBH4 reduction of RhIII(TPP)I,6,34 was
treated with Bu4NOH under the standard conditions, the
Rh(TPP)Bu product was formed in only 2% yield (eq 14). This
suggests the mononuclear anion with a sodium cation is likely
not the major pathway for alkylation. However, in situ reduction
and alkylation of RhIII(TPP)I with Bu4NBH4 afforded the
Rh(TPP)Bu product in 64% yield (eq 15), which indicates the
RhI(TPP)/ammonium ion pair may be the key for the success
of this transformation.
CONCLUSION
■
In summary, a new carbon−metal bond forming reaction
between RhIII(por)Xs and ammonium/quinolinium salts was
systematically studied. A range of quaternary ammonium and
alkyl quinolinium salts were found to be effective for alkyl
transfer, serving as a convenient approach to synthesize various
alkyl-RhIII(por) complexes. Preliminary mechanistic studies
support a RhI(por) anion-mediated SN2-like pathway. Studies
of the properties of these new alkyl-RhIII(por) complexes
prepared in this work are ongoing.
EXPERIMENTAL SECTION
■
General Considerations. Unless stated otherwise, all reactions
were carried out under air in vials sealed with PTFE-lined caps,
purchased from Qorpak. All deuterated solvents were purchased from
Cambridge Isotopes Laboratories, Inc. [Rh(CO)2Cl]2 was purchased
from Strem. (TPP)RhI,39 (TPP)RhCl,40 and (TMP)RhI2b were
synthesized following literature procedures. Ammonium hydroxides
were purchased from Acros as molar solutions in water. A 0.5 M
NaOH stock solution was used for all necessary reactions. GC yield of
tributylamine was determined through a standard curve with decane as
an internal standard. High-resolution mass spectra (HRMS) were
obtained on a Karatos MS9 and are reported as m/z (relative
intensity). Accurate masses are reported for the molecular ion [M +
H]+, [M+], or [M]. 1H NMR and 13C NMR spectra were recorded on
The remaining question is how the RhI(TPP)/ammonium
ion pair is formed under the hydroxide environment. While
alkylamines have been shown to reduce water-soluble rhodium
porphyrins under basic conditions by Fu and co-workers,35 the
high recovery of tributylamine postreaction (vide supra, eq 12)
disfavors the amine acting as the ultimate reductant in our
system. On the other hand, disproportionation of RhII(por)s to
RhI(por) and RhIII(por) is known to be promoted by various
nucleophiles.36 Thus, combining the knowledge from the
experiment with [RhII(TPP)]2 (vide supra, eq 6) and Chan’s
earlier observation,25 we propose a mechanism involving
anionic RhI(por) generated via hydroxide-triggered dispropor-
tionation (Scheme 3).
1
a Varian Gemini (400 or 500 MHz for H, 101, 125, or 151 MHz for
13C). Chemical shifts are reported as parts per million (ppm) using
residual solvent signals as internal standard (CHCl3, δ = 7.26 ppm for
1H NMR, δ = 77.00 ppm for 13C NMR; DMSO, δ = 2.49 ppm for 1H
NMR, δ = 39.50 ppm for 13C NMR). Metal complex Rh−C bonds
required −3 ppm 13C{1H} decoupling in some instances for 13C NMR
spectroscopy. Infrared spectra were obtained from a Nicolet iS5 FTIR
spectrometer. A Rayonet photoreactor fitted with UV lamps (300 nm)
was used for photolysis. Electron paramagnetic resonance (EPR)
spectra at 298 K were recorded on a Bruker EMX Plus (X-Band)
Collectively, heating Rh(TPP)I and hydroxide in solution
first generates the [RhII(TPP)]2 dimer through the Chan-
proposed25 RhIII(TPP)OH intermediate and elimination of
hydrogen peroxide or its equivalent.37 Nucleophilic attack of
the hydroxide onto [RhII(por)]2 initiates the disproportiona-
3762
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
spectrometer. All other solvents and reagents were reagent grade and
were purchased and used as received.
Synthesis of [Rh(TPP)(ethyl)] (2c) from Et4NOH. This product
was prepared as described above for 2a, giving 8.2 mg (91% yield) of
2c as a red solid. Rf = 0.97 (dichloromethane). H NMR (400 MHz,
CDCl3): δ 8.70 (s, 8H), 8.21 (m, 4H), 8.12 (m, 4H), 7.75 (m, 12H),
−4.43 (m, 3H), −4.84 (m, 2H). 13C NMR (151 MHz, CDCl3): δ
143.1, 142.2, 134.0, 133.8, 131.5, 127.6, 126.7, 126.6, 122.4, 13.0, 10.4
(d, J = 27.2 Hz). IR (KBr): ν 2954, 2925, 2856, 2060, 1996, 1808,
1595, 1445, 1358 cm−1. HRMS: calcd C46H33N4Rh [M] 744.1760;
found 744.1755.
1
Synthesis of [Rh(TPP)(n-butyl)] (2a) from [Rh(TPP)I] (1a). To
(TPP)RhI (1a, 16.5 mg, 0.020 mmol, 1 equiv) in 1.5 mL of benzene
was added tetrabutylammonium hydroxide (16 μL of a 1.5 M solution
in water, 0.024 mmol, 1.2 equiv). The solution was sealed, heated to
120 °C, and stirred for 2 h. The reaction was monitored by TLC
analysis, and when complete, the solution was extracted with
dichloromethane, dried over anhydrous magnesium sulfate, filtered,
and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (dichloromethane/hexanes, 1:4)
solution to give 15.2 mg (98% yield) of 2a as a red solid. Rf = 0.94
(dichloromethane). 1H NMR (400 MHz, CDCl3): δ 8.70 (s, 8H), 8.17
(m, 8H), 7.88−7.52 (m, 12H), −0.81 (t, J = 7.3 Hz, 3H), −1.55 (m, J
= 6.3 Hz, 2H), −4.46 (m, J = 7.5 Hz, 2H), −4.92 (m, 2H). 13C NMR
(151 MHz, CDCl3): δ 143.1, 142.2, 134.0, 133.7, 131.4, 127.6, 126.7,
126.6, 122.4, 29.6, 19.3, 15.3 (d, J = 27.3 Hz), 12.4. IR (KBr): ν 3026,
2957, 2920, 2868, 2851, 1810, 1595, 1531, 1445, 1351 cm−1. HRMS:
calcd C48H37N4Rh+ [M+] 772.2073; found 772.2062.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from [Rh(TPP)Cl] (1b). The
procedure above was followed, starting with (TPP)RhCl (1b, 16.3 mg,
0.019 mmol), to give 14.7 mg (97% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) at 80 °C. To (TPP)RhI (1a,
21.6 mg, 0.026 mmol, 1 equiv) in 1.5 mL of benzene was added
tetrabutylammonium hydroxide (21 μL of a 1.5 M solution in water,
0.031 mmol, 1.2 equiv). The solution was sealed, heated to 80 °C, and
stirred for 8 h. The reaction was monitored by TLC analysis, and when
complete, the solution was extracted with dichloromethane, dried over
anhydrous magnesium sulfate, filtered, and concentrated under
vacuum. The crude product was purified by column chromatography
on silica gel (dichloromethane/hexanes, 1:4) solution to give 16.4 mg
(82% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(methyl)] (2d) from Me4NOH (ref 41).
This product was prepared as described above for 2a, giving 6.9 mg
(56% yield) of 2d as a bright red solid. Rf = 0.77 (4:1
1
dichloromethane/hexanes). H NMR (400 MHz, CDCl3): δ 8.71 (s,
8H), 8.19 (m, 4H), 8.14 (m, 4H), 7.73 (m, 12H), −5.80 (d, J = 2.9
Hz, 3H). HRMS: calcd C45H31N4Rh [M] 730.1604; found 730.1603.
General Procedure for Alkylation with Tetrabutylammo-
nium Halides. To (TPP)RhI (1a, 1 equiv) were added corresponding
tetrabutylammonium halide (3 equiv), 0.5 M NaOH (15 equiv in
NaOH), and benzene (1.5 mL). The reaction was heated to 120 °C
and stirred for 5 h, monitoring by TLC analysis. When complete, the
solution was extracted with dichloromethane, dried over anhydrous
magnesium sulfate, filtered, and concentrated under vacuum. The
crude product was purified by column chromatography on silica gel
(dichloromethane/hexanes, 1:4) solution to give 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from n-Bu4NI. Isolated: 6.0
mg (82% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from n-Bu4NBr. Isolated: 7.6
mg (89% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from n-Bu4NCl. Isolated: 7.4
mg (74% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from n-Bu4NF. Isolated: 6.1
mg (72% yield) of 2a as a red solid.
Reaction of Butyl Iodide (4 equiv) with [Rh(TPP)I] (1a). To
(TPP)RhI (1a, 13.2 mg, 0.016 mmol, 1 equiv) were added butyl
iodide (7.2 μL, 0.063 mmol, 4 equiv), 0.5 M NaOH (0.48 mL, 0.24
mmol, 15 equiv), and 1.5 mL of benzene. The solution was sealed,
heated to 120 °C, and stirred for 5 h. The reaction was monitored by
TLC analysis, and when complete, the solution was dried over
anhydrous magnesium sulfate, filtered, and concentrated under
Synthesis of [Rh(TPP)(n-butyl)] (2a) under Air-Free Conditions.
To a Schlenk flask were added (TPP)RhI (1a, 9.5 mg, 0.011 mmol, 1
equiv), 1.5 mL of benzene, and tetrabutylammonium hydroxide (9 μL
of a 1.5 M solution in water, 0.013 mmol, 1.2 equiv). The solution was
freeze−pump−thawed for five cycles and filled under argon gas. The
solution was heated to 120 °C and stirred for 2 h, then extracted with
dichloromethane, dried over anhydrous magnesium sulfate, filtered,
and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (dichloromethane/hexanes, 1:4)
solution to give 8.6 mg (98% yield) of 2a as a red solid.
1
vacuum. Only trace amounts of product were detected via H NMR
analysis.
Reaction of Butyl Iodide (100 equiv) with [Rh(TPP)I] (1a). To
(TPP)RhI (1a, 22.2 mg, 0.026 mmol, 1 equiv) were added butyl
iodide (0.3 mL, 2.6 mmol, 100 equiv), 0.5 M NaOH (0.78 mL, 0.39
mmol, 15 equiv), and 1.5 mL of benzene. The solution was sealed,
heated to 120 °C, and stirred for 5 h. The reaction was monitored by
TLC analysis, and when complete, the solution was extracted with
dichloromethane, dried over anhydrous magnesium sulfate, filtered,
and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (dichloromethane/hexanes, 1:4)
solution to give 5.4 mg (27% yield) of 2a as a red solid.
Synthesis of [Rh(TMP)(n-butyl)] (4) from [Rh(TMP)I] (3). To
(TMP)RhI (3, 13.2 mg, 0.013 mmol, 1 equiv) in 1.5 mL of benzene
was added tetrabutylammonium hydroxide (43 μL of a 1.5 M solution
in water, 0.065 mmol, 5 equiv). The solution was sealed, heated to 120
°C, and stirred for 12 h. The reaction was monitored by TLC analysis,
and when complete, the solution was extracted with dichloromethane,
dried over anhydrous magnesium sulfate, filtered, and concentrated
under vacuum. The crude product was purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:8) solution
to give 9.7 mg (80% yield) of 4 as a red solid. Rf = 0.73 (1:1
Synthesis of [Rh(TPP)(n-octyl)] (2e) from n-Oct4NBr. To
(TPP)RhI (1a, 13.9 mg, 0.016 mmol, 1 equiv) were added
tetraoctylammonium bromide (26 mg, 0.048 mmol, 3 equiv), 0.5 M
NaOH (0.48 mL, 0.24 mmol, 15 equiv), and 1.5 mL of benzene. The
solution was sealed, heated to 120 °C, and stirred for 5 h. The reaction
was monitored by TLC analysis, and when complete, the solution was
extracted with dichloromethane, dried over anhydrous magnesium
sulfate, filtered, and concentrated under vacuum. The crude product
was purified by column chromatography on silica gel (dichloro-
methane/hexanes, 1:4) solution to give 12.7 mg (91% yield) of 2e as a
1
dichloromethane/hexanes). H NMR (600 MHz, CDCl3): δ 8.45 (s,
8H), 7.26 (s, 4H), 7.24 (s, 4H), 2.61 (s, 12H), 1.92 (s, 12H), 1.84 (s,
12H), −0.85(t, J = 7.8 Hz, 3H), −1.40 (m, 2H), −4.24 (m, 2H),
−4.80 (m, 2H). 13C NMR (151 MHz, CDCl3): δ 142.5, 139.0, 138.9,
138.5, 137.3, 130.5, 127.6, 119.4, 25.3, 21.7, 21.6, 21.5, 19.8, 14.7 (d, J
= 27.8 Hz), 11.9. IR (KBr): ν 2952, 2918, 2849, 1623, 1544, 1455,
1351, 1069, 1003 cm−1. HRMS: calcd C60H61N4Rh [M] 940.3951;
found 940.3960.
Synthesis of [Rh(TPP)(n-propyl)] (2b) from n-Pr4NOH. This
product was prepared as described above for 2a, giving 8.2 mg (90%
yield) of 2b as a red solid. Rf = 0.97 (dichloromethane). 1H NMR (400
MHz, CDCl3): δ 8.70 (s, 8H), 8.21−8.13 (m, 4H), 8.12 (m, 4H), 7.74
(m, 12H), −1.72 (t, J = 7.3 Hz, 3H), −4.42 (m, 2H), −4.96 (m, 2H).
13C NMR (151 MHz, CDCl3): δ 143.1, 142.2, 134.1, 133.7, 131.4,
127.6, 126.6, 122.4, 20.4, 17.8 (d, J = 27.3 Hz), 10.8. IR (KBr): ν 2962,
2924, 2869, 2848, 1541, 1440, 1357, 1009 cm−1. HRMS: calcd
C46H33N4Rh [M] 758.11917; found 758.1909.
1
red solid. Rf = 0.86 (4:1 dichloromethane/hexanes). H NMR (400
MHz, CDCl3): δ 8.70 (s, 8H), 8.21 (d, J = 6.8 Hz, 4H), 8.11 (d, J = 6.8
Hz, 4H), 7.80−7.68 (m, 12H), 0.84 (td, J = 14.9 Hz, J = 7.6 Hz, 2H),
0.60 (t, J = 7.3 Hz, 3H), 0.51 (dt, J = 15.1 Hz, J = 7.6 Hz, 2H), 0.03
(dt, J = 15.3 Hz, J = 7.7 Hz, 2H), −0.53 (dt, J = 15.1 Hz, J = 7.6 Hz,
2H), −1.57 (m, 2H), −4.48 (dt, J = 15.8 Hz, J = 7.9 Hz, 2H), −4.92
(m, 2H). 13C NMR (101 MHz, CDCl3): δ 143.1, 142.2, 134.0, 133.7,
131.4, 127.5, 126.7, 126.6, 122.4, 31.2, 27.8, 27.4, 26.9, 26.1, 22.7, 22.3,
14.0 (d, J = 28.1 Hz). IR (KBr): ν 2967, 2920, 2850, 1648, 2462, 1356,
3763
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
1010, 752 cm−1. HRMS: calcd C48H45N4Rh [M] 828.2699; found
828.2701.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from n-Bu4NBr. This
product was prepared as described above for 2e, giving 8.2 mg (89%
yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-propyl)] (2b) from n-Pr4NBr. This
product was prepared as described above for 2e, giving 7.6 mg (67%
yield) of 2b as a red solid.
Synthesis of [Rh(TPP)(ethyl)] (2c) from Et4NBr. This product
was prepared as described above for 2e, giving 5.5 mg (48% yield) of
2c as a red solid.
Synthesis of [Rh(TPP)(o-bromobenzyl)] (5f). This product was
prepared as described above for 5a, giving 16.4 mg (88% yield) of 5f as
a red solid. Rf = 0.75 (4:1 dichloromethane/hexanes). H NMR (400
1
MHz, CDCl3): δ 8.68 (s, 8H), 8.18 (m, 4H), 8.13 (m, 4H), 7.75 (m,
12H), 6.18 (m, 2H), 5.76 (td, J = 3.6 Hz, 1H), 2.55 (dd, J = 1.7 Hz,
1H), −3.48 (d, J = 3.3 Hz, 2H). 13C NMR (151 MHz, CDCl3): δ
143.3, 142.3, 113.8, 131.6, 127.6, 126.7, 124.8, 122.6, 8.6 (d, J = 28.4
Hz). IR (KBr): ν 2978, 2927, 2893, 2844, 1781, 1561, 1440, 1358
cm−1. HRMS: calcd C51H34N4BrRh [M] 884.1022; found 884.1052.
Synthesis of [Rh(TPP)(p-bromobenzyl)] (5g). This product was
prepared as described above for 5a, giving 12.0 mg (78% yield) of 5g
1
Synthesis of [Rh(TPP)(methyl)] (2d) from Me4NI. This product
was prepared as described above for 2e, giving 4.7 mg (42% yield) of
2d as a red solid.
as a red solid. Rf = 0.88 (4:1 dichloromethane/hexanes). H NMR
(400 MHz, CDCl3): δ 8.69 (s, 8H), 8.18 (m, 4H), 8.08 (m, 4H), 7.76
(m, 12H), 5.97 (d, J = 8.4 Hz, 2H), 2.79 (d, J = 8.4 Hz, 2H), −3.83 (d,
J = 3.8 Hz, 2H). 13C NMR (151 MHz, CDCl3): δ 143.0, 142.1, 140.2,
133.9, 131.7, 128.9, 127.6, 126.7, 126.1, 122.6, 117.1, 10.4 (d, J = 27.8
Hz). IR (KBr): ν 3058, 3021, 2925, 2843, 1704, 1635, 1353, 1013
cm−1. HRMS: calcd C51H34N4BrRh [M] 884.1022; found 884.1179.
Synthesis of [Rh(TPP)(p-chlorobenzyl)] (5h). This product was
prepared as described above for 5a, giving 9.1 mg (70% yield) of 5h as
Synthesis of [Rh(TPP)(benzyl)] (5a) from BnMe3NCl. To
(TPP)RhI (1a, 10.4 mg, 0.012 mmol, 1 equiv) were added
benzyltrimethylammonium chloride (6.7 mg, 0.036 mmol, 3 equiv),
0.5 M NaOH (0.36 mL, 0.18 mmol, 15 equiv), and 1.5 mL of benzene.
The solution was sealed, heated to 120 °C, and stirred for 5 h. The
reaction was monitored by TLC analysis, and when complete, the
solution was extracted with dichloromethane, dried over anhydrous
magnesium sulfate, filtered, and concentrated under vacuum. The
crude product was purified by column chromatography on silica gel
(dichloromethane/hexanes, 1:4) solution to give 7.5 mg (73% yield)
1
a red solid. Rf = 0.78 (4:1 dichloromethane/hexanes). H NMR (400
MHz, CDCl3): δ 8.68 (s, 8H), 8.18 (m, 4H), 8.08 (m, 4H), 7.75 (m,
12H), 5.82 (d, J = 8.3 Hz, 2H), 2.85 (d, J = 8.4 Hz, 2H), −3.82 (d, J =
3.8 Hz, 2H). 13C NMR (101 MHz, CDCl3): δ 143.0, 142.1, 133.9,
131.7, 127.6, 126.7, 126.0, 125.7, 122.60, 10.5 (d, J = 21.6). IR (KBr):
ν 3048, 3019, 2923, 2848, 1597, 1440, 1351, 1010 cm−1. HRMS: calcd
C51H34N4ClRh [M] 840.1527; found 840.1511.
Synthesis of [Rh(TPP)(benzyl)] (5a) from BnMe3NOH. To
(TPP)RhI (1a, 13.0 mg, 0.015 mmol, 1 equiv) in 1.5 mL of benzene
was added benzyltrimethylammonium hydroxide (46 μL of a 40% w/w
solution in water, 0.019 mmol, 1.2 equiv). The solution was sealed,
heated to 120 °C, and stirred for 2 h. The reaction was monitored by
TLC analysis, and when complete, the solution was extracted with
dichloromethane, dried over anhydrous magnesium sulfate, filtered,
and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (dichloromethane/hexanes, 1:4)
solution to give 10.4 mg (84% yield) of 3a as a red solid.
Synthesis of [Rh(TPP)(methyl)] (2d) from n-BuMe3NBr. To
(TPP)RhI (1a, 10.1 mg, 0.012 mmol, 1 equiv) was added
butyltrimethylammonium bromide (7.1 mg, 0.036 mmol, 3 equiv),
0.5 M NaOH (0.36 mL, 0.18 mmol, 15 equiv), and 1.5 mL of benzene.
The solution was sealed, heated to 120 °C, and stirred for 5 h. The
reaction was monitored by TLC analysis, and when complete, the
solution was extracted with dichloromethane, dried over anhydrous
magnesium sulfate, filtered, and concentrated under vacuum. The
crude product was purified by column chromatography on silica gel
(dichloromethane/hexanes, 1:4) solution to give 4.0 mg (46% yield)
of 2d as a red solid.
1
of 5a as a red solid. Rf = 0.81 (4:1 dichloromethane/hexanes). H
NMR (400 MHz, CDCl3): δ 8.66 (s, 8H), 8.18 (m, 4H), 8.12 (m,
4H), 7.74 (m, 12H), 6.43 (t, J = 1.6 Hz, 1H), 5.89 (t, J = 7.6 Hz, 2H),
2.98 (d, J = 8 Hz, 2H), −3.76 (d, J = 3.6 Hz, 2H). 13C NMR (151
MHz, CDCl3): δ 143.0, 142.2, 133.9, 133.9, 131.5, 127.6, 126.7, 126.6,
125.9, 124.5, 123.54, 122.5, 12.5 (d, J = 27.0 Hz). HRMS: calcd
C51H35N4Rh [M] 806.1917; found 806.1932.
Synthesis of [Rh(TPP)(p-methylbenzyl)] (5b). This product was
prepared as described above for 5a, giving 6.4 mg (64% yield) of 5b as
1
a red solid. Rf = 0.81 (4:1 dichloromethane/hexanes). H NMR (400
MHz, CDCl3): δ 8.86 (s, 8H), 8.19 (m, 4H), 8.08 (m, 4H), 5.68 (d, J
= 7.6 Hz, 2H), 2.89 (d, J = 7.6 Hz, 2H), 1.70 (s, 3H), −3.74 (d, J = 4.0
Hz, 2H). 13C NMR (101 MHz, CDCl3): δ 143.0, 142.3, 134.0, 133.9,
131.5, 127.5, 126.7, 126.6, 124.6, 122.4, 20.99, 14.5 (d, J = 28.3 Hz).
IR (KBr): ν 3045, 2972, 2921, 2851, 1651, 1534, 1444, 1351, 1019
cm−1. HRMS: calcd C52H37N4Rh [M] 820.2073; found 820.2053.
Synthesis of [Rh(TPP)(p-methoxybenzyl)] (5c). This product
was prepared as described above for 5a, giving 12.1 mg (62% yield) of
1
5c as a red solid. Rf = 0.54 (4:1 dichloromethane/hexanes). H NMR
(400 MHz, CDCl3): δ 8.66 (s, 8H), 8.19 (m, 4H), 8.10 (m, 4H), 7.74
(m, 12H), 5.44 (d, J = 8.8 Hz, 2H), 3.43 (s, 3H), 2.95 (d, J = 8.8 Hz,
2H), −3.74 (d, J = 3.6 Hz, 2H). 13C NMR (151 MHz, CDCl3): δ
143.1, 142.3, 133.9, 131.5, 127.5, 126.6, 125.7, 122.4, 114.3, 111.6,
55.6, 12.8 (d, J = 26.6 Hz). IR (KBr): ν 3051, 3021, 2922, 2851, 2828,
1672, 1603, 1506, 1445, 1343 cm−1. HRMS: calcd C52H37N4Rh [M]
836.2022; found 836.2017.
Synthesis of [Rh(TPP)(CH2CH2CH2OTBS)] (6a). To (TPP)RhI
(1a, 12.0 mg, 0.014 mmol, 1 equiv) were added 1-(3-((tert-
butyldimethylsilyl)oxy)propyl)quinolin-1-ium bromide (16.1 mg,
0.042 mmol, 3 equiv), 0.5 M NaOH (0.42 mL, 0.21 mmol, 15
equiv), and 1.5 mL of benzene. The solution was sealed, heated to 120
°C, and stirred for 5 h. The reaction was monitored by TLC analysis,
and when complete, the solution was extracted with dichloromethane,
dried over anhydrous magnesium sulfate, filtered, and concentrated
under vacuum. The crude product was purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 10.7 mg (84% yield) of 6a as a dark red solid. Rf = 0.62 (4:1
Synthesis of [Rh(TPP)(p-nitrobenzyl)] (5d). This product was
prepared as described above for 5a, giving 12.0 mg (61% yield) of 5d
1
as a red solid. Rf = 0.59 (4:1 dichloromethane/hexanes). H NMR
(400 MHz, CDCl3): δ 8.70 (s, 8H), 8.13 (m, 4H), 8.04 (m, 4H), 7.76
(m, 12H), 6.68 (d, J = 8.8 Hz, 2H), 2.88 (d, J = 8.8 Hz, 2H), −3.84 (d,
J = 4.0 Hz, 2H). 13C NMR (151 MHz, CDCl3): δ 143.0, 141.8, 133.9,
133.8, 131.9, 127.8, 126.8, 124.5, 122.8, 121.0, 8.3 (d, J = 28.2 Hz). IR
(KBr): ν 2964, 2930, 2915, 2856, 1652, 1521, 1489, 1440, 1331 cm−1.
HRMS: calcd C51H34N5O2Rh [M] 851.1768; found 851.1755.
Synthesis of [Rh(TPP)(o-iodobenzyl)] (5e). This product was
prepared as described above for 5a, giving 10.8 mg (74% yield) of 5e
1
dichloromethane/hexanes). H NMR (500 MHz, CDCl3): δ 8.70 (s,
8H), 8.19 (m, 4H), 8.11 (m, 4H), 7.74 (m, 12H), 0.89 (t, J = 6.4 Hz,
2H), 0.24 (s, 9H), −0.86 (s, 6H), −4.25 (m, 2H), −4.95 (m, 2H). 13C
NMR (151 MHz, CDCl3): δ 143.1, 142.2, 134.0, 133.8, 131.5, 127.6,
126.6, 122.4, 30.5, 25.3, 17.4, 10.3 (d, J = 28.4 Hz), −5.9. IR (KBr): ν
3046, 3021, 2927, 2851, 1744, 1655, 1593, 1516, 1348, 1012, 701
cm−1. HRMS: calcd C53H49N4OSiRh [M] 888.2731; found 888.2718.
Synthesis of [Rh(TPP)(n-octyl)] (2e) from 1-n-Octylquinolin-
1-ium Bromide. This product was prepared as described above for
4a, giving 8.7 mg (70% yield) of 2e as a red solid.
1
as a red solid. Rf = 0.79 (4:1 dichloromethane/hexanes). H NMR
(400 MHz, CDCl3): δ 8.68 (s, 8H), 8.16 (m, 8H), 7.74 (m, 12H), 6.44
(dd, J = 6.7 Hz, 1.2 Hz, 1H), 6.01 (td, J = 7.8 Hz, 1.2 Hz, 1H), 5.80
(td, J = 7.2 Hz, 1.6 Hz, 1H), 2.46 (dd, J = 7.7 Hz, 1.1 Hz, 1H), −3.45
(d, J = 7.8 Hz, 2H). 13C NMR (151 MHz, CDCl3): δ 143.7, 142.2,
137.5, 133.9, 133.8, 131.7, 127.6, 126.7, 122.6, 14.5 (d, J = 22.0 Hz).
IR (KBr): ν 2969, 2927, 2848, 2821, 1736, 1670, 1551, 1353, 1012
cm−1. HRMS: calcd C51H34N4RhI [M] 932.0883; found 932.0886.
3764
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
Synthesis of [Rh(TPP)(n-pentyl)] (6b) from 1-n-Pentylquino-
lin-1-ium Bromide. This product was prepared as described above
for 6a, giving 7.6 mg (64% yield) of 6b as a red solid. Rf = 0.84 (4:1
monium hydroxide (10 μL of a 1.5 M solution in water, 0.016 mmol,
1.2 equiv), and 1.5 mL of benzene. The solution was sealed, heated to
120 °C, and stirred for 2 h. The reaction was monitored by TLC
analysis, and when complete, the solution was extracted with
dichloromethane, dried over anhydrous magnesium sulfate, filtered,
and concentrated under vacuum. The crude product was purified by
column chromatography on silica gel (dichloromethane/hexanes, 1:4)
solution to give 9.3 mg (93% yield) of 2a as a red solid.
Radical Inhibitor (TEMPO) Effect on Alkylation with n-
Bu4NOH. To (TPP)RhI (1a, 16.1 mg, 0.019 mmol, 1 equiv) were
added TEMPO (29.7 mg, 0.19 mmol, 10 equiv), tetrabutylammonium
hydroxide (15 μL of a 1.5 M solution in water, 0.023 mmol, 1.2 equiv),
and 1.5 mL of benzene. The solution was sealed, heated to 120 °C,
and stirred for 2 h. The reaction was monitored by TLC analysis, and
when complete, the solution was extracted with dichloromethane,
dried over anhydrous magnesium sulfate, filtered, and concentrated
under vacuum. The crude product was purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 11.9 mg (81% yield) of 2a as a red solid.
1
dichloromethane/hexanes). H NMR (400 MHz, CDCl3): δ 8.69 (s,
8H), 8.21 (m, 4H), 8.11 (d, 4H), 7.80−7.66 (m, 12H), −0.26 (t, J =
7.3 Hz, 3H), −0.49 (m, 2H), −1.59 (dt, J = 14.7, J = 7.4 Hz, 2H),
−4.47 (m, 2H), −4.93 (m, 2H). 13C NMR (151 MHz, CDCl3): δ
143.1, 142.2, 134.0, 133.7, 131.4, 127.5, 126.7, 126.6, 122.4, 29.7, 20.6,
15.7 (d, J = 27.2), 14.1, 12.7. IR (KBr): ν 3025, 2956, 2914, 2845,
1603, 1448, 1351, 1009 cm−1. HRMS: calcd C49H39N4Rh [M]
786.2230; found 786.2239.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from 1-n-Butylquinolin-
1-ium Bromide. This product was prepared as described above for
4a, giving 6.2 mg (53% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-propyl)] (2b) from 1-n-Propylquino-
lin-1-ium Bromide. This product was prepared as described above
for 4a, giving 7.1 mg (55% yield) of 2b as a red solid.
Synthesis of [Rh(TPP)(ethyl)] (2c) from 1-Ethylquinolin-1-
ium Bromide. This product was prepared as described above for 4a,
giving 5.1 mg (37% yield) of 2c as a red solid.
Competition Reaction of 1-Hexene and n-Bu4NOH with
[Rh(TPP)I]. To (TPP)RhI (1a, 14.9 mg, 0.018 mmol, 1 equiv) were
added 1-hexene (88 μL, 0.71 mmol, 40 equiv), tetrabutylammonium
hydroxide (12 μL of a 1.5 M solution in water, 0.018 mmol, 1.2 equiv),
and 1.5 mL of benzene. The solution was sealed, heated to 120 °C,
and stirred for 2 h. The reaction was monitored by TLC analysis, and
when complete, the solution was extracted with dichloromethane,
dried over anhydrous magnesium sulfate, filtered, and concentrated
under vacuum. The crude product was purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 13.4 mg (96% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(methyl)] (2d) from 1-Methylquinolin-
1-ium Iodide. This product was prepared as described above for 4a,
giving 2.2 mg (24% yield) of 2d as a red solid.
Synthesis of [Rh(TPP)(3-(quinolin-2(1H)-one)propyl)] (7). To
(TPP)RhI (1a, 16.4 mg, 0.019 mmol, 1 equiv) were added 1-(3-
hydroxypropyl)quinolin-1-ium bromide (15.2 mg, 0.06 mmol, 3
equiv), 0.5 M NaOH (0.57 mL, 0.29 mmol, 15 equiv), and 1.5 mL
of benzene. The solution was sealed, heated to 120 °C, and stirred for
5 h. The reaction was monitored by TLC analysis, and when complete,
the solution was extracted with dichloromethane, dried over
anhydrous magnesium sulfate, filtered, and concentrated under
vacuum. The crude product was purified by column chromatography
on silica gel (chloroform/hexanes, 5:1) solution to give 9.3 mg (56%
yield) of 7 as a red solid. Rf = 0.07 (1:1 dichloromethane/hexanes). 1H
NMR (400 MHz, CDCl3): δ 8.68 (s, 8H), 8.17 (m, 4H), 7.90 (m,
4H), 7.79−7.62 (m, 12H), 7.30 (dd, J = 7.7 Hz, J = 1.5 Hz, 1H), 7.26
(m, 1H) 7.15 (ddd, J = 8.6 Hz, J = 7.3 Hz, J = 1.6 Hz, 1H), 7.04 (m,
1H), 6.09 (d, J = 9.3 Hz, 1H), 4.90 (d, J = 8.4 Hz, 1H), 0.73 (t, J = 7.9
Hz, 2H), −4.08 (dt, J = 15.7 Hz, J = 7.9 Hz, 2H), −4.92 (m, 2H). 13C
NMR (125 MHz, CDCl3): δ 160.4, 143.1, 142.0, 138.1, 137.8, 134.1,
133.7, 130.4, 128.3, 127.6, 126.6, 122.5, 121.3, 121.0, 120.19, 113.1,
37.3, 24.5, 8.7 (d, J = 28.7). IR (KBr): ν 3063, 3024, 2962, 2905, 2836,
2759, 1650, 1583, 1442, 1352, 1074, 1012 cm−1. HRMS: calcd
C56H40N5ORh [M] 901.2288; found 901.2292.
Competition Reaction of (E)-1-D-Oct-1-ene28 and n-Bu4NBr
with [Rh(TPP)I]. To (TPP)RhI (1a, 12.2 mg, 0.015 mmol, 1 equiv)
were added (E)-1-D-oct-1-ene (65 mg, 0.58 mmol, 40 equiv),
tetrabutylammonium bromide (24 mg, 0.043 mmol, 3 equiv), 0.5 M
NaOH (0.45 mL, 0.23 mmol, 15 equiv), and 1.5 mL of benzene. The
solution was sealed, heated to 120 °C, and stirred for 5 h. The reaction
was monitored by TLC analysis, and when complete, the solution was
extracted with dichloromethane, dried over anhydrous magnesium
sulfate, filtered, and concentrated under vacuum. The crude product
was purified by column chromatography on silica gel (dichloro-
methane/hexanes, 1:4) solution to give 10.1 mg (84% yield) of 2a as a
red solid.
Synthesis of [Rh(TPP)(2-hydroxyhexyl] (8). To (TPP)RhI (1a,
14.5 mg, 0.017 mmol, 1 equiv) was added 1,2-epoxyhexane (61 μL,
0.51 mmol, 30 equiv), 0.5 M NaOH (0.51 mL, 0.26 mmol, 15 equiv),
and 1.5 mL of benzene. The solution was sealed, heated to 120 °C,
and stirred for 1 h. The reaction was monitored by TLC analysis, and
when complete, the solution was dried over anhydrous magnesium
sulfate, filtered, and concentrated under vacuum. The crude product
was purified by preparative TLC (silica/dichloromethane) to give 8.7
mg (62% yield) of 8 as a red solid. Rf = 0.43 (4:1 dichloromethane/
hexanes). 1H NMR (400 MHz, CDCl3): δ 8.75 (s, 8H), 8.20 (m, 4H),
8.11 (m, 4H), 7.82−7.70 (m, 12H), 0.21 (d J = 11.3 Hz, J = 4.2 Hz,
3H), 0.05 (m, 2H), −0.65 (m, 2H), −1.03 (dt, J = 22.2 Hz, J = 7.3 Hz,
1H), −1.48 (td, J = 14.0 Hz, J = 7.0 Hz, 1H), −2.79 (d, J = 7.1 Hz,
1H) −4.13 (d, J = 1.6 Hz, 1H), −4.90 (m, 2H). 13C NMR (151 MHz,
CDCl3): δ 143.2, 141.8, 134.1, 133.6, 131.9, 131.8, 127.7, 126.7, 122.7,
70.0, 32.4, 26.5, 21.3, 20.6 (d, J = 28.5), 13.4. IR (KBr): ν 3424, 3059,
2958, 2915, 2853, 1640, 1603, 1445, 1353, 1074 cm−1. HRMS: calcd
C50H41N4ORh+ [M+] 816.23300; found 816.23210.
Evaluation of [RhII(TPP)]2 as Precursor for Alkylation with n-
Bu4NOH. To a J. Young tube were added (TPP)Rh-Me (2d, 4.7 mg,
0.006 mmol, 1 equiv) and 0.5 mL of C6D6 (freshly distilled over
sodium and stored under argon). The solution was freeze−pump−
thawed three times and filled with argon gas. The solution was
irradiated at 300 nm for 10 h, at which time full conversion to the
1
[(TPP)RhII]2 dimer was obtained based on H NMR spectroscopy.
To this reaction was then added excess 1.5 M tetrabutylammonium
hydroxide (50 μL, 0.08 mmol) under an inert atmosphere. After 1 h
1
no change was observed via H NMR spectroscopy, and the reaction
was heated to 120 °C for 10 h with complete conversion. The reaction
was concentrated and purified by preparative TLC (silica/dichloro-
methane) to give 3.5 mg of 2a as a red solid in 76% yield.
Evaluation of NBu3 for Alkylation of [Rh(TPP)I]. To (TPP)RhI
(1a, 9.8 mg, 0.012 mmol, 1 equiv) was added tributylamine (83 μL,
0.35 mmol, 29 equiv), 0.5 M NaOH (0.36 mL, 0.18 mmol, 15 equiv),
and 1.5 mL of benzene. The solution was sealed, heated to 120 °C,
and stirred for 5 h. The reaction was monitored by TLC analysis, and
when complete, the solution was extracted with dichloromethane,
dried over anhydrous magnesium sulfate, filtered, and concentrated
under vacuum. The crude product was purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 0.4 mg (4% yield) of 2a as a red solid.
Synthesis of [Rh(TPP)(n-butyl)] (2a) from NaBH4. Following a
modified procedure,6 to a Schlenk flask was added (TPP)RhI (1a, 22.3
mg, 0.026 mmol) to 18 mL of ethanol, and the solution was degassed
with nitrogen for 20 min. Afterward, a degassed solution of NaBH4 (12
mg, 0.32 mmol) in 0.5 mL of 0.5 M NaOH was added to the flask
under nitrogen. The solution was heated to 60 °C for 2 h, whereupon
the solution became dark brown. The reaction was cooled to room
temperature, and 1.5 M Bu4NOH (1 mL, 1.5 mmol) was added. After
stirring 2 h the solution was concentrated and purified by column
Radical Inhibitor (BHT) Effect on Alkylation with n-Bu4NOH.
To (TPP)RhI (1a, 11.3 mg, 0.013 mmol, 1 equiv) were added
butylhydroxytoluene (28.6 mg, 0.13 mmol, 10 equiv), tetrabutylam-
3765
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 0.4 mg (2% yield) of 2a as a red solid.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gbdong@cm.utexas.edu.
Notes
■
Synthesis of [Rh(TPP)(n-butyl)] (2a) from Bu4NBH4. To a
flame-dried vial were added (TPP)RhI (1a, 10.2 mg, 0.012 mmol, 1
equiv) and 1.5 mL of degassed benzene (distilled over CaH2). At room
temperature was added tetrabutylammonium borohydride (16 mg,
0.06 mmol, 5 equiv) under nitrogen. The solution was heated to 120
°C for 1 h. The solution was concentrated and purified by column
chromatography on silica gel (dichloromethane/hexanes, 1:4) solution
to give 5.9 mg (64% yield) of 2a as a red solid.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank UT Austin, CPRIT, and the Welch Foundation (F-
1781) for funding. G.D. is a Searle Scholar. Dr. Vincent Lynch
is acknowledged for X-ray crystallography. Mrs. Angela
Spangenberg and Dr. Steve Sorey are acknowledged for their
NMR advice. Dr. Ian Riddington is acknowledged for high-
resolution mass spectrometry. Johnson Matthey is also thanked
for their donation of metal salts. We thank Dr. Alpay Dermenci
for proofreading the manuscript and Ms. Rachel Whittaker for
checking reproducibility of the experiment.
X-ray Diffraction Analyses. Single crystals of 2a−2c were grown
from concentrated carbon tetrachloride solutions layered with hexane
at −20 °C over 24 h, forming red prisms (2a crystals formed as a
trimer). Crystals of 5d and 7 were grown from concentrated
chloroform solutions layered with hexanes at −20 °C over 24 h,
forming red prisms and orange plates, respectively (5d crystals formed
as a trimer). Diffraction data for 2a, 2b, and 7 were collected at 100 K
using a Rigaku SCX-Mini diffractometer with a Mercury 2 CCD using
graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å),
obtaining data with ω-scans (scan range of 0.5°). Data reductions
were performed using the Rigaku Americas Corporation’s Crystal
Clear version 1.40. For 2a, each of the three CCl4 molecules was
disordered along with three phenyl rings on two of the Rh complexes.
One CCl4 molecule was modeled using a three-component disorder
model. All other entities were modeled using a two-component
disorder model. The disorder was modeled in essentially the same
manner for each entity. For 7, a large channel near 1/2, y, 1/2
appeared to be occupied with three molecules of chloroform. These
molecules were intricately disordered. Attempts to model the disorder
were unsatisfactory. The contributions to the scattering factors due to
these solvent molecules were removed by use of the utility SQUEEZE
in PLATON98.
Diffraction data for 2c were collected at 153 K using a Rigaku
AFC12 diffractometer with a Saturn 724+ CCD using a graphite
monochromator with Mo Kα radiation (λ = 0.71073 Å), obtaining
data with ω-scans (scan range of 0.5°). Data reductions were
performed using the Rigaku Americas Corporation’s Crystal Clear
version 1.40. A molecule of carbon tetrachloride was disordered near a
crystallographic inversion center at 1, 1/2, 0. Diffraction data for 5d
were collected at 133 K using a Nonius Kappa CCD diffractometer
using a Bruker AXS Apex II detector and a graphite monochromator
with Mo Kα radiation (λ = 0.710 75 Å), obtaining data with ω-scans
(scan range of 0.7°). Data reductions were performed using SAINT
V8.27B. The structure was solved by direct methods using SIR97 and
refined by full-matrix least-squares on F2 with anisotropic displacement
parameters for the non-H atoms using SHELXL-97. Two molecules of
solvent, one molecule of chloroform, and one molecule of n-hexane
were badly disordered near a crystallographic inversion center near 0,
1/2, 0. Attempts to model the disorder were unsatisfactory. The
contributions to the scattering factors due to these solvent molecules
were removed by use of the utility SQUEEZE in PLATON98.
Structures were solved with direct methods using SIR97 for 2a−2b,
5d, and 7 and Superflip for 2c, all being refined by full-matrix least-
squares on F2 with anisotropic displacement parameters for the non-H
atoms using SHELXL-97. Structure analysis was aided by use of the
programs PLATON98 and WinGX. The hydrogen atoms on carbon
were calculated in ideal positions with isotropic displacement
parameters set to 1.2Ueq of the attached atom (1.5Ueq for methyl
hydrogen atoms). Details of crystal data, data collection, and structure
refinement can be found in the Supporting Information. The
crystallographic data (excluding structure factors) are available as
Supporting Information CIF files.
REFERENCES
■
(1) (a) Collman, J. P.; Hegedus, L. Principles and Applications of
Organotransition Metal Chemistry; University Science Books: Mill
Valley, CA, 1980. (b) Hartwig, J. F. Organotransition Metal Chemistry:
From Bonding to Catalysis; University Science Books: Sausalito, CA,
2010.
(2) (a) Sherry, A. E.; Wayland, B. B. J. Am. Chem. Soc. 1990, 112,
1259. (b) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc. 1991,
113, 5305. (c) Cui, W.; Wayland, B. B. J. Porphyrins Phthalocyanines
2004, 8, 103.
(3) Sanford, M. S.; Groves, J. T. Angew. Chem., Int. Ed. 2004, 43, 588.
(4) (a) Wayland, B. B.; Van Voorhees, S. L.; Del Rossi, K. J. J. Am.
Chem. Soc. 1987, 109, 6513. (b) Wayland, B. B.; Woods, B. A.; Minda,
V. M. J. Chem. Soc., Chem. Commun. 1982, 634. (c) Farnos, M. D.;
Woods, B. A.; Wayland, B. B. J. Am. Chem. Soc. 1986, 108, 3659.
(d) Geno, M. K.; Halpern, J. J. Am. Chem. Soc. 1987, 109, 1238.
(e) Van Voorhees, S. L.; Wayland, B. B. Organometallics 1985, 4, 1887.
(5) Yoshida, Z.; Ogoshi, H.; Omura, T.; Watanabe, E.; Kurosaki, T.
Tetrahedron Lett. 1972, 11, 1077.
(6) Ogoshi, H.; Setsune, J.; Omura, T.; Yoshida, Z. J. Am. Chem. Soc.
1975, 97, 6461.
(7) (a) Fu, X. F.; Basickes, L.; Wayland, B. B. Chem. Commun. 2003,
520. (b) Mak, K. W.; Xue, F.; Mak, T. C. W.; Chan, K. S. J. Chem. Soc.,
Dalton Trans. 1999, 3333. (c) Paonessa, R. S.; Thomas, N. C.;
Halpern, J. J. Am. Chem. Soc. 1985, 107, 4333.
(8) (a) Chan, K. S.; Chiu, P. F.; Choi, K. S. Organometallics 2007, 26,
1117. (b) Chan, Y. W.; Chan, K. S. Organometallics 2008, 27, 4625.
(c) Choi, K. S.; Chiu, P. F.; Chan, K. S. Organometallics 2010, 29, 624.
(9) (a) Zhang, L.; Chan, K. S. J. Organomet. Chem. 2006, 691, 3782.
(b) Fung, H. S.; Li, B. Z.; Chan, K. S. Organometallics 2010, 29, 4421.
(c) Fung, H. S.; Li, B. Z.; Chan, K. S. Organometallics 2012, 31, 570.
(d) Chan, C. S.; Lee, S. Y.; Chan, K. S. Organometallics 2013, 32, 151.
(e) Zhang, L.; Chan, K. S. J. Organomet. Chem. 2007, 692, 2021.
(f) Chan, K. S.; Li, Z. L.; Fung, C. W.; Zhang, L. Organometallics 2007,
26, 20. (g) Chan, K. S.; Li, X. Z.; Zhang, L.; Fung, C. W.
Organometallics 2007, 26, 2679. (h) Lai, T. H.; Chan, K. S.
Organometallics 2009, 28, 6845. (i) Lee, S. Y.; Lai, T. H.; Choi, K.
S.; Chan, K. S. Organometallics 2011, 30, 3691. (j) Chan, Y. W.; Chan,
K. S. J. Am. Chem. Soc. 2010, 132, 6920. (k) To, C. T.; Choi, K. S.;
Chan, K. S. J. Am. Chem. Soc. 2012, 134, 11388. (l) Tse, M. K.; Chan,
K. S. J. Chem. Soc., Dalton Trans. 2001, 510. (m) Chan, K. S.; Li, X. Z.;
Dzik, W. I.; de Bruin, B. J. Am. Chem. Soc. 2008, 130, 2051.
(10) Chan, K. S.; Au, C. C.; Lai, T. H. J. Organomet. Chem. 2010, 695,
1370.
ASSOCIATED CONTENT
* Supporting Information
■
(11) For a related one-pot procedure of preparing the [R-RhIII-
salophen] complex from a Rh(I) dimer, R4NOH, and a free salophen
ligand see: Anderson, D. J.; Eisenberg, R. Organometallics 1996, 15,
1697.
S
1
Starting material procedures, iodide counteranion data, H and
13C characterization, and X-ray crystallography data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(12) Tributylamine was detected from the crude mixture. HRMS:
calcd C12H27N+ [M + H]+ 186.221 60; found 186.221 30.
3766
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767

Organometallics
Article
(13) Chan, Y. W.; Chan, K. S. Organometallics 2008, 27, 4625.
(14) Landini, D.; Maia, A.; Rampoldi, A. J. Org. Chem. 1986, 51,
3187.
(41) Wayland, B. B.; Van Voorhees, S. L.; Wilker, C. Inorg. Chem.
1986, 25, 4039.
(15) (a) Chempath, S.; Boncella, J. M.; Pratt, L. R.; Henson, N.;
Pivovar, B. S. J. Phys. Chem. C 2010, 114, 11977. (b) Li, N.; Leng, Y.;
Hickner, M. A.; Wang, C.-Y. J. Am. Chem. Soc. 2013, 135, 10124.
(16) Menger, F. M.; Venkataram, U. V. J. Am. Chem. Soc. 1986, 108,
2980.
(17) (a) Collman, J. P.; Boulatov, R. Inorg. Chem. 2001, 40, 2461.
(b) Boschi, T.; Licoccia, S.; Paolesse, R.; Tagliatesta, P. Organometallics
1989, 8, 330. (c) Choi, K. S.; Chiu, P. F.; Chan, C. S.; Chan, K. S. J.
Chin. Chem. Soc. 2013, 60, 779 and refs 2b 8a, and 8c..
(18) For preparation of n-butyltrimethylammonium bromide, see:
Dai, K.; Nomoto, K.; Ueno, S.; Tomono, K.; Miyamura, K. Bull. Chem.
Soc. Jpn. 2011, 84, 312.
(19) Krieg, R.; Eitner, A.; Gunther, N.; Halbhuber, K. J. Biotechnol.
̈
Histochem. 2007, 82, 235.
(20) Secondary alkyl quinolinium salts were found not successful for
the alkylation.
(21) N-Benzylquinolinium bromide resulted in only a 2% yield.
(22) See Supporting Information, Table S1, for comparison to
substrates with iodide as the counteranion.
(23) Free quinoline was detected from the crude mixture. HRMS:
calcd C9H7N+ [M + H]+ 130.065 10; found 130.065 20.
(24) Zhang, C.-G.; Luo, Y.-H. Acta. Crystallogr., Sect E: Struct. Rep.
Online 2012, 68, o188.
(25) Choi, K. S.; Lai, T. H.; Lee, S. Y.; Chan, K. S. Organometallics
2011, 30, 2633.
(26) Wayland, B. B.; Newman, A. R. Inorg. Chem. 1981, 20, 3093.
The EPR spectrum can be found in the Supporting Information, Table
S2.
(27) The ammonium substrate was found to be unstable under the
alkylation conditions. See the Supporting Information for character-
ization.
(28) (a) Jahn, U. In Radicals and Synthesis III; Heinrich, M. R.;
Gansauer, A., Eds.; Topics in Current Chemistry 320; Springer: Berlin,
̈
Germany, 2012; pp 129−132. (b) Hawker, C. J. Acc. Chem. Res. 1997,
30, 373.
(29) Sevov, S. S.; Zhou, J.; Hartwig, J. F. J. Am. Chem. Soc. 2014, 136,
3200.
(30) (a) Niyazymbetov, M. E.; Rudashevskaya, T. Y.; Petrosyan, V. A.
Russ. Chem. Bull. 1990, 39, 1318. (b) Hunig, S.; Quast, H.; Brenninger,
̈
W.; Frankenfield, E. Org. Synth. 1969, 49, 107.
(31) (a) Hilhorst, E.; Chen, T.; Iskander, A. S.; Pandit, U. K.
Tetrahedron 1994, 50, 7837. (b) Hilhorst, E.; Iskander, A. S.; Chen, T.;
Pandit, U. K. Tetrahedron 1994, 50, 8863.
(32) It is expected that some tributylamine came from self-
decomposition of the ammonium hydroxide.
(33) Han, Y.-Z.; Sanford, M. S.; Englanda, M. D.; Groves, J. T. Chem.
Commun. 2006, 549.
(34) The use of Na/Hg for reduction of Rh(TPP)I to the RhI(TPP)
anion followed by Bu4NOH addition did not give alkylation.
(35) Ling, Z.; Yun, L.; Liu, L.; Wu, B.; Fu, X. Chem. Commun. 2013,
49, 4214.
(36) (a) Wayland, B. B.; Balkus, K. J., Jr.; Farnos, M. D.
Organomettalics 1989, 8, 950. (b) Wayland, B. B.; Sherry, A. E.;
Bunn, A. G. J. Am. Chem. Soc. 1993, 115, 7675.
(37) After the Rh(por) alkylation was completed under exhaustively
anaerobic conditions, pure PPh3 was added to the reaction mixture
under argon and gently heated for 30 min. A significant amount of
OPPh3 was observed, which is consistent with the results shown by
Chan.25 For more detailed information, see the SI.
(38) (a) Powers, D. C.; Ritter, T. Nat. Chem. 2009, 1, 302.
(b) Powers, D. C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T. J. Am.
Chem. Soc. 2009, 131, 17050. (c) Powers, D. C.; Xiao, D. Y.; Geibel,
M. A. L.; Ritter, T. J. Am. Chem. Soc. 2010, 132, 14350.
(39) Collman, J. P.; Boulatov, R. J. Am. Chem. Soc. 2000, 122, 11812.
(40) Tse, A. K.; Wu, B.-M.; Mak, T. C.; Chan, K. S. J. Organomet.
Chem. 1998, 568, 257.
3767
dx.doi.org/10.1021/om500438s | Organometallics 2014, 33, 3757−3767