Syntheses of acyl rhodium porphyrins by aldehydic carbon-hydrogen bond activation with Rh(III) porphyrin chloride and methyl

Article abstract of DOI:10.1021/om0507878

Rhodium(III) porphyrin chloride reacted with aryl aldehydes in solvent-free conditions to give acyl rhodium porphyrins. Selective aldehydic without any aromatic carbon-hydrogen bond activation (CHA) was observed. At lower temperature, reduction and side products were found. Alkanals reacted poorly. On the other hand, Rh(III) porphyrin methyl reacted more cleanly with both aryl and alkyl aldehydes. These reactions provided a facile, convenient synthesis of acyl rhodium porphyrins. These activations are unique CHA by high-valent Rh(III) species. Preliminary mechanistic experiments suggested that the rhodium(III) porphyrin chloride initially formed a cationic rhodium(III) porphyrin via chloride dissociation and then underwent oxidative addition or heterolysis to yield the product. On the other hand, rhodium(III) porphyrin methyl underwent either oxidative addition or σ bond metathesis.

Full text of DOI:10.1021/om0507878

260
Organometallics 2006, 25, 260-265
Syntheses of Acyl Rhodium Porphyrins by Aldehydic
Carbon-Hydrogen Bond Activation with Rh(III) Porphyrin
Chloride and Methyl
Kin Shing Chan* and Cheuk Man Lau
Department of Chemistry, The Chinese UniVersity of Hong Kong, Shatin,
New Territories, Hong Kong, China
ReceiVed September 12, 2005
Rhodium(III) porphyrin chloride reacted with aryl aldehydes in solvent-free conditions to give acyl
rhodium porphyrins. Selective aldehydic without any aromatic carbon-hydrogen bond activation (CHA)
was observed. At lower temperature, reduction and side products were found. Alkanals reacted poorly.
On the other hand, Rh(III) porphyrin methyl reacted more cleanly with both aryl and alkyl aldehydes.
These reactions provided a facile, convenient synthesis of acyl rhodium porphyrins. These activations
are unique CHA by high-valent Rh(III) species. Preliminary mechanistic experiments suggested that the
rhodium(III) porphyrin chloride initially formed a cationic rhodium(III) porphyrin via chloride dissociation
and then underwent oxidative addition or heterolysis to yield the product. On the other hand, rhodium(III)
porphyrin methyl underwent either oxidative addition or σ bond metathesis.
Table 1. Optimization of CHA of PhCHO with Rh(ttp)Cl
Carbon-hydrogen bond activation (CHA) by cationic and
related low-valent late transition metal complexes has emerged
as an exciting area of research with potential industrial applica-
tions.1,2 Numerous catalytic applications in organic synthesis
have appeared for the direct functionalization of hydrocarbons.
The catalytic conversions of methane into methyl derivatives
mark one of the milestones.3-5 An advantage of late transition
metal complexes over early transition ones is the broader
functional group tolerance in substrates.
The CHA of aldehydes with transition metal complexes gives
acyl metal complexes. Acyl transition metal complexes are
important compounds and proposed intermediates formed in the
hydroacylation of alkenes6 and alkynes.7 Most complexes
reported are low-valent ones, and the activations occur through
classical oxidative addition pathways. One typical example is
the reaction of the Wilkinson type complex (RhI(R3P)3Cl) with
aldehydes.8 The activation of aldehydes by high-valent rhod-
ium(III) complexes to form acyl rhodium complexes is much
less well-known.9
% yield of
Rh(ttp)COPh, 2a
% yield of
Rh(ttp)Bn, 3
entry
temp/°C
time
1
2
3
4
5
6
130
150
1 day
1 day
1.5 days
2 days
0.5 h
none
38%
51%
43%
28%
79%
none
5%
28%
17%
18%
none
180
200
1 day
In extending our previous success of CHA of PhCN solvent
in refluxing conditions with Rh(ttp)Cl (ttp ) tetrakis-4-
tolylporphyrinatio dianion) to give metacyanophenyl rhodium
porphyrins,10 we have discovered that aldehydes reacted with
both Rh(ttp)Cl and Rh(ttp)Me in solvent-free conditions selec-
tively at the aldehydic carbon-hydrogen bond. These reactions
provide convenient syntheses of Rh(ttp)COR and illustrate a
unique type of CHA by high-valent rhodium(III) complexes.
* To whom correspondence should be addressed. E-mail: ksc@
cuhk.edu.hk.
Results and Discussion
(1) (a) Shilov, A. E.; Shul’pin G. B. Chem. ReV. 1997, 97, 2879-2932.
(b) Rukebgm V.; Sirlin, C.; Pfeller, M. Chem. ReV. 2002, 102, 1731-1789.
(c) Labinger, J. A.; Bercaw, J. E. Nature 2002, 507, 507-514. (d) Lersch,
M.; Tilset, M. Chem. ReV. 2005, 105, 2471-2526.
(2) (a) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1973.
(b) Tellers, D. M.; Yung, C. M.; Arndtsen, B. A.; Adamson, D. R. Bergman,
R. G. J. Am. Chem. Soc. 2002, 124, 1400-1410.
(3) (a) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560-564. (b) Periana, R. A.; Mironov, O.;
Taube, D.; Bhalla, G.; Jones, C. J. Science 2003, 301, 814-818.
(4) Bar-Nahum, I.; Khenkin, A. M.; Neumann, R. J. Am. Chem. Soc.
2004, 126, 10236-10237.
The reactions of Rh(ttp)Cl (1) with PhCHO revealed that the
solvent, temperature, and extent were crucial in controlling
product selectivity and yield (Table 1, eq 1). As Rh(ttp)Cl was
found to react with various solvents, such as 1,2,4-trichloroben-
zene, dibutyl ether, and NMP above 150 °C, solvent-free
conditions, i.e., PhCHO as a reagent and solvent, were used.
At 200 °C in 1 day, Rh(ttp)Cl gave Rh(ttp)COPh (2a) in 79%
yield in the absence of light under nitrogen. Selective activation
of the aldehydic carbon-hydrogen bond occurred without any
aromatic CHA. Below 150 °C, little reaction occurred. At 150
°C, the CHA product Rh(ttp)COPh (2a) and the “reduction
(5) Lin, M.; Shen, C.; Garcia-Zaya, E. A.; Sen, A. J. Am. Chem. Soc.
2001, 123, 1000-1001.
(6) Marder, T. B.; Roe, D. C.; Milstein D. Organometallics 1988, 7,
1451-1453.
(7) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 11492-11493.
(8) Milstein, D. Organometallics 1982, 1, 1549-1551.
(9) An example of activation of aldehydes by a cationic methyl Rh(III)
complex has been reported, but the mechanism is not defined. Corkey, B.
K.; Taw, F. L.; Bergman, R. G.; Brookhart, M. Polyhedron 2004, 23, 2943-
2954.
(10) (a) Zhou, X.; Wang, R.-J.; Mak, T. C. W.; Chan, K. S. Inorg. Chim.
Acta 1998, 270, 551-554. (b) Zhou, X.; Wang, R.-J.; Xue, F.; Mak, T. C.
W.; Chan, K. S. J. Organomet. Chem. 1999, 580, 22-25. (c) Zhou, X.;
Tse, M. K.; Wu, D.-D.; Mak, T. C. W.; Chan, K. S. J. Organomet. Chem.
2000, 598, 80-86.
10.1021/om0507878 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/25/2005

Syntheses of Acyl Rhodium Porphyrins
Organometallics, Vol. 25, No. 1, 2006 261
Table 2. Activation of Aryl Aldehydes with Rh(ttp)Cl
Table 4. Optimization of CHA of PhCHO with Rh(ttp)Me
entry
temp (°C)
time (h)
2a (yield %)
6 recovered (%)
% yield of
Rh(ttp)COAr,
1
2
100
200
48
0.5
12
82
40
0
entry FG time
2
% yield of Rh(ttp)R
V) supports the rationale.12 To our delight, Rh(ttp)Me reacted
much faster with PhCHO in solvent-free conditions to give a
slightly higher yield of Rh(ttp)COPh.
The optimal temperature of aldehydic CHA of prototypical
PhCHO with Rh(ttp)Me (6) was found to be 200 °C (Table 4,
eq 4). At 100 °C in 2 days, only 12% yield of CHA product
was obtained and 40% yield of Rh(ttp)Me was recovered. At
200 °C, fast and complete reaction occurred. PhCHO reacted
with Rh(ttp)Me (6) to afford PhCORh(ttp) (2a) in 82% yield
within 0.5 h. No Rh(ttp)Bn (3) was formed.
1
2
3
4
5
6
7
8
H
F
1 day
1 day
2a 79%
2b 45%
2c 20%
2c 57%
2d 17%
2d 38%
2e 50%
Me 1 h
1 day
tBu 1 h
1 day
CF3 1 day
OMe 1 day
(4-CHOC6H4CH2)Rh(ttp), 4 (4%)
(4-CHOC6H4CH(Me)2)Rh(ttp), 5 (2%)
MeRh(ttp), 6 (11%)
Table 3. CHA of Aliphatic Aldehydes by Rh(ttp)Cl
Rh(ttp)Me also underwent aldehydic CHA with other aryl
aldehydes at a faster rate, with broader functional group
compatibility and cleaner product formation than Rh(ttp)Cl
(Table 5, eq 5). In general, most reactions required less than 1
day to complete. Fluoro-, chloro-, and trifluoromethyl groups
are compatible. Even the electron-rich 4-anisoylaldehyde yielded
56% of anisoyl rhodium porphyrin without any other CHA or
side product. Unfortunately, 4-N,N-dimethylbenzaldehyde gave
complex, unidentified products. In most of these reactions, clean
products were formed with little side products.
entry
R
temp (°C)
time (h)
Rh(ttp)COR (yield %)
1
2
3
C2H5
C7H15
tBu
100
200
200
48
24
48
7a (3)
7b (0)
7c (10)
product” Rh(ttp)Bn (3) were formed nearly at the same time. 3
slowly disappeared on further heating with slight increase in
the yield of 2a. A similar pattern was observed at 180 and 200
°C. At 200 °C in 1 day, the total yields of the products were
79% with the same yield obtained at 150 °C in 1.5 days.
Synthetically, the synthesis of thermally stable Rh(ttp)COPh (2a)
was optimized to occur at 200 °C in 1 day.
It is also gratifying that aliphatic aldehydes reacted with
Rh(ttp)Me to give moderate yields of Rh(ttp)COR (Table 6, eq
6). Selective aldehydic CHA occurred even with enolizable
aldehyde.
When the optimized reaction conditions were applied to
various 4-susbstitued aryl aldehydes, moderate to good yields
of Rh(ttp)COAr were obtained in 1 day at 200 °C (Table 2, eq
2). Substrates bearing alkyl carbon-hydrogen bonds such as
4-MeC6H4CHO and 4-tBuC6H4CHO gave mainly 4-MeC6H4-
CORh(ttp) (2c) and 4-tBuC6H4CORh(ttp) (2d), respectively.
Small amounts of alkyl CHA products (4-CHOC6H4CH2)Rh(ttp)
(4) and (4-CHOC6H4C(Me)2CH2)Rh(ttp) (5) were observed only
initially and nearly simultaneously with aldehydic CHA products
in about 1 h. Competitive aliphatic and benzylic CHA therefore
occurred. Upon prolonged heating, 4 and 5 disappeared with
increasing yields of the corresponding rhodium complexes 2c
and 2d. Apparently, 4 and 5 likely underwent further CHA with
excess aryl aldehydes to afford corresponding acyl complexes
similar to that of Rh(ttp)Bn (3) with PhCHO. Little substrate
electronic effect on rate was noted. Surprisingly, the most
electron rich 4-methoxylphenyl aldehyde produced no acyl
rhodium complex but only 11% yield of Rh(ttp)Me (6), in which
the Me group likely comes from the MeO group of anisoyl
aldehyde. A limitation for the preparation of anisoyl complex
exists.
For aliphatic aldehydes, Rh(ttp)Cl reacted inefficiently to give
only either mixtures of products or lower yields of acyl rhodium
porphyrins (Table 3, eq 3). Presumably, other carbon-hydrogen
bonds, especially those at the R-carbonyl positions, form
enolizable carbonyls, which compete to give complex mix-
tures.11 More efficient synthesis is desirable.
We reasoned that the electron-rich Rh(ttp)Me would be more
difficult to reduce to Rh(ttp)Bn, and cleaner CHA would then
be expected. In fact, the more negative reduction potential of
Rh(ttp)Me (E1/2 ) -1.43 V) than that of Rh(ttp)Cl (E1/2 ) -1.01
The IR stretching ν(CdO) of the benzoyl rhodium complexes
appears between 1690 and 1720 cm-1. On the other hand, the
carbonyl frequencies in RCORh(oep)13 range from 1684 to 1709
cm-1 (oep ) octaethylporphyrinato) and are lower than that in
RCORh(ttp). Likely, the Rh to CO back π-bonding is stronger
with the more electron rich oep ligand, resulting in lower
carbonyl stretching frequencies.
X-ray Data. Single-crystal analyses were carried out for
compounds 2, 3, and 4. Crystal data, collection, and processing
parameters are listed in the Supporting Information. Notably,
the para-substitutents on the benzaldehyde do not affect the bond
lengths between Rh-C(O) as they are all similar to the Rh-
C(O) (1.988(5) Å) in (oep)RhC(O)NH(C8H3(CH3)2) reported
by Wayland (Table 7).14 Moreover, the bond angles are not
affected by the para-substitutents. All rhodium atoms do not
lie in the porphyrin plane but deviate from the plane defined
by the 24-atom least-squares plane (Supporting Information).
Mechanism: Rh(ttp)Cl. We postulate that Rh(ttp)Cl reacts
as an electrophile in CHA (Scheme 1)10,15 analogous to its
electrophilic aromatic substitution with PhCN to give meta-
cyanophenyl rhodium porphyrin. Such electrophilic aromatic
substitution has also been reported with Rh(oep)OTf.15 Rh(ttp)Cl
initially dissociates to give a cationic, electrophilic Rh(ttp)
species likely as an ion-pair (Rh(ttp)+Cl-). Coordination of
(12) (a) Kadish, K. M.; Yao, C. L.; Anderson, J. E.; Cocolios, P. Inorg.
Chem. 1985, 24, 4515-4520. (b) Guilard, R.; Kadish, K. M. Chem. ReV.
1988, 88, 1121-1146. (c) Anderson, J. E.; Yao, C. L.; Kadish, K. M. Inorg.
Chem. 1986, 25, 718-719.
(13) Del Rossi, K. J.; Zhang, X. X.; Wayland, B. B. J. Organomet. Chem.
1995, 504, 47-56.
(14) Poszmik, G.; Carroll, P. J.; Wayland, B. B. Organometallics 1993,
12, 3410-3417.
(11) Aoyama, Y.; Tanaka, T.; Yoshia, H.; Toi, H.; Ogoshi, H. J.
Organomet. Chem. 1987, 329, 251-256.
(15) Aoyama, Y.; Yoshida, T.; Sakurai, K. I.; Ogoshi, H. Organometallics
1986, 5, 168-173.

262 Organometallics, Vol. 25, No. 1, 2006
Chan and Lau
Table 5. CHA of Para-Substituted Benzaldehydes by
Rh(ttp)Me
Rh(ttp)Bn reacted with PhCHO at 200 °C in 1 day to give
Rh(ttp)COPh in 49% yield (eq 10).
Mechanism: Rh(ttp)Me. Since the Rh-Me bond in
Rh(ttp)Me is strong (about 57 kcal/mol)18 and is unlikely to
undergo facile and complete homolysis at 200 °C within a few
hours, homolysis is unlikely. Concerted pathways are more
reasonable. We propose that Rh(ttp)Me undergoes either clas-
sical oxidative addition or σ bond metathesis19 with PhCHO.
The oxidative addition demands a Rh(V) intermediate complex,
which exists but is less common. The σ bond metathesis does
not require a formal Rh(V) species.9,20,21 They are, however,
mechanistically very difficult to distinguish unless a stable
intermediate is isolated. At this stage, we cannot rule out one
from the other, and to firmly establish the detailed pathway,
further experiments are necessary.
entry
FG
time (h)
yield (%)
1
2
3
4
5
6
7
8
H
0.5
8
2a (82)
2b (76)
2f (53)
2e (54)
2c (73)
2d (39)
2g (56)
2h (0)
F
Cl
24
16
16
48
16
60
CF3
Me
tBu
OMe
NMe2
Table 6. CHA of Aliphatic Aldehydes by Rh(ttp)Me
In summary, we have discovered a facile synthesis of
Rh(ttp)COR from the reactions of Rh(ttp)Cl and Rh(ttp)Me with
aldehydes in solvent-free conditions. The reactions involve
selective aldehydic CHA with high-valent Rh(III) species.
Preliminary mechanistic experiments suggest Rh(tttp)Cl likely
activates aldehydes in an electrophilic manner with the parallel
formation of Rh(ttp)COPh and Rh(ttp)H. Rh(ttp)H further
activates PhCHO consecutively to yield Rh(ttp)COPh. The
mechanism of CHA of PhCHO with Rh(ttp)Me is different from
that of Rh(ttp)Cl and likely operates through oxidative addition
or σ bond methathesis.
entry
R
temp (°C)
time (h)
yield (%)
1
2
3
C2H5
C7H15
tBu
100
200
200
24
48
48
7a (60)
7b (41)
7c (37)
Table 7. Selected Bond Lengths and Bond Angles of
Compounds 2a, 2b, and 2e
FG
H, 2a
1.950(5) Å 1.976(7) Å 1.941(7) Å
117.8(4)° 117.1(5)° 118.3(5)°
F, 2b
CF3, 2e
bond length (Rh-CO)
bond angle (Rh-C(O)-Caryl
)
Experimental Section
Scheme 1. Mechanism of Aldehydic CHA with Rh(ttp)Cl
General Procedures. Unless otherwise noted, all reagents were
purchased from commercial suppliers and used without purification.
Hexane for chromatography was distilled from anhydrous calcium
chloride. Tetrahydrofuran (THF) was distilled from sodium ben-
zophenone ketyl prior to use. Benzonitrile was distilled from
anhydrous P2O5. Thin-layer chromatography was performed on
precoated silica gel 60 F254 plates. Silica gel (Merck, 70-230 and
230-400 mesh) was used for column chromatography.
1H NMR spetra were recorded on a Bruker DPX 300 (300 MHz)
spectrometer. Spectra were referenced internally to the residual
proton resonance in C6D6 (δ 7.15 ppm) or CDCl3 (δ 7.26 ppm) or
with tetramethylsilane (TMS, δ 0.00 ppm) as the internal standard.
Chemical shifts (δ) were reported in parts per million (ppm). 13C
NMR spectra were recorded on a Bruker DPX 300 (75 MHz)
spectrometer and referenced to CDCl3 (δ 77.10 ppm). Coupling
constants (J) were reported in hertz (Hz). High-resolution mass
spectra (HRMS) were performed on a Thermofinnigan MAT 95
XL (FABMS).
aldehydic oxygen of PhCHO directs the aldehydic CHA to give
Rh(ttp)COPh and HCl. Rh(ttp)OTf (8) was therefore indepen-
dently synthesized from metathesis of Rh(ttp)Cl and AgOTf (eq
7)15 and indeed underwent faster aldehydic CHA than Rh(ttp)Cl
to give 89% yield of Rh(ttp)COPh (2a) at 200 °C in 15 min
(eq 8).
Preparation of Starting Materials. 5,10,15,20-Tetratolypor-
phyrinato)rhodium(III) Chloride, Rh(ttp)Cl (1).10a H2ttp (350
mg, 0.51 mmol) and RhCl3‚xH2O (209 mg, 1.00 mmol) were
refluxed in PhCN (30 mL) in air for 3 h. After removal of solvent,
the mixture was purified by column chromatography on silica gel
Rh(ttp)+Cl- can also be reduced by PhCHO to give Rh(ttp)H
and an acylium ion in a parallel manner with the direct CHA.
Rh(ttp)H then reacts with PhCHO to give Rh(ttp)COPh, which
can be further reduced by Rh(ttp)H to give Rh(ttp)Bn. Sup-
porting evidence has been obtained by an independent experi-
ment. Rh(ttp)H was synthesized by the reductive protonation
of Rh(ttp)Cl with NaBH4/HOAc.16 At 200 °C in half an hour,
Rh(ttp)H reacted with PhCHO to give both 35% of Rh(ttp)COPh
and 4% of Rh(ttpp)Bn (eq 9).17
(17) Wayland, B. B.; Woods, B. A.; Minda, V. M. Chem. Commun. 1982,
634-635. Reaction of Rh(ttp)H with PhCHO to give Rh(ttp)CH(OH)Ph,
which undergoes further reaction and disproportionation to give Rh(ttp)Bn,
is also possible.
(18) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc. 1991,
113, 5305-5311.
(19) Thompson, M. E.; Baxteer, S. M.; Bulls, A. R.; Burger, B. J.; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem.
Soc. 1987, 109, 203-219.
(20) Examples of an Ir(V) intermediate have been reported in the silane
activation. (a) Klei, S. R.; Tilley T. D.; Bergman R. G. J. Am. Chem. Soc.
2000, 122, 1816-1817.
Finally, Rh(ttp)Bn undergoes CHA with PhCHO to give
Rh(ttp)COPh, like that of Rh(ttp)Me with PhCHO. Indeed,
(21) Examples of Rh(V) organometallic complexes: Gomez, M.; Kisenyi,
J. M.; Sunley, G. J.; Maitlis, P. M. J. Organomet. Chem. 1985, 296, 197-
207.
(16) Wayland, B. B.; Van Voorhees, S. L.; Wilker, C. Inorg. Chem. 1986,
25, 4039-4042.

Syntheses of Acyl Rhodium Porphyrins
Organometallics, Vol. 25, No. 1, 2006 263
eluting with CH2Cl2. 1 was then dried under vacuum at 80 °C to
remove the coordinated PhCN. Purplish red solid 1 was obtained
after recrystallization from CH2Cl2/MeOH (368 mg, 0.39 mmol,
76% yield). Rf ) 0.30 (CH2Cl2). H NMR (300 MHz, CDCl3): δ
2.71 (s, 12 H), 7.54 (d, 8 H, J ) 8.1 Hz), 8.07 (d, 4 H, J ) 6.9
Hz), 8.12 (d, 4 H, J ) 6.9 Hz), 8.94 (s, 8 H).
200 °C under N2 in the dark for 1 day. The dark red crude product
was purified by column chromatography on silica gel eluting with
hexane/CH2Cl2 (4:1). 4-FC6H5CORh(ttp) (2b) was obtained as a
red solid (22 mg, 0.024 mmol, 45% yield). Rf ) 0.54 (hexane/
CH2Cl2 ) 1:1). 1H NMR (300 MHz, CDCl3): δ 2.42 (dd, 2 H, J )
5.4, J ) 8.4 Hz), 2.71 (s, 12 H), 5.68 (t, 2 H, J ) 8.7 Hz), 7.53 (t,
8 H, J ) 6.1 Hz), 7.95-7.977 (m, 4 H), 8.03-8.07 (m, 8 H), 8.78
(s, 8 H). HRMS (FABMS): calcd for (C55H40N4OFRh)+ m/z
894.2236, found m/z 894.2256. IR (KBr, cm-1): ν (CdO) 1711
(s). Anal. Calcd for C55H40N4ORhF‚3H2O: C, 70.13; H, 4.28; N,
5.95. Found: C, 70.39; H, 4.50; N, 5.84. A single crystal for X-ray
diffraction analysis was grown from CH2Cl2/MeOH.
1
(5,10,15,20-Tetratolyporphyrinato)(methyl)rhodium(III),
Rh(ttp)Me (6).22 A suspension of Rh(ttp)Cl (98 mg, 0.11 mmol)
in EtOH (50 mL) and a solution of NaBH4 (40 mg, 1.08 mmol) in
aqueous NaOH (0.1 M, 2 mL) were purged with N2 for 15 min
separately. A solution of NaBH4 was added slowly to the suspension
of Rh(ttp)Cl via a cannula. The mixture was heated at 50 °C under
N2 for 1 h to give a brown solution. The solution was then cooled
to 0 °C under N2, and methyl iodide (0.7 mL, 10.8 mmol) was
added via a syringe. A reddish orange suspension was formed. After
stirring at room temperature for another 15 min under N2, the
reaction mixture was worked up by extraction with CH2Cl2 and
washed with H2O. The combined organic extract was dried
(anhydrous MgSO4), filtered, and rotatory evaporated. The reddish
orange residue was purified by column chromatography over silica
gel (250-400 mesh), eluting with a solvent mixture of hexane/
CH2Cl2 (4:1). The major orange fraction was collected and gave 6
as a reddish orange solid (73 mg, 0.095 mmol, 86% yield), which
was further purified by recrystallization from CH2Cl2/CH3OH. Rf
Method B. Rh(ttp)CH3 (30 mg, 0.038 mmol) was mixed with
4-fluorobenzaldehyde (1.0 mL) in a Telfon screw-capped flask
under nitrogen at 200 °C in the dark for 8 h to yield 4 as a red
solid (26 mg, 0.029 mmol, 76% yield).
(5,10,15,20-Tetratolyporphyrinato)(4-chlorobenzoyl)rhodium-
(III), 4-ClC6H5CORh(ttp) (2f). Method B. Rh(ttp)CH3 (30 mg,
0.038 mmol) was mixed with 4-chlorobenzaldehyde (938 mg) in a
Telfon screw-capped flask under nitrogen at 200 °C in the dark
for 8 h to yield 4-ClC6H5CORh(ttp) (2f) as a red solid (16 mg,
1
0.020 mmol, 53% yield). Rf ) 0.70 (hexane/CH2Cl2 ) 1:1). H
NMR (300 MHz, CDCl3): δ 2.33 (d, 2 H, J ) 8.1 Hz), 2.71 (s, 12
H), 5.94 (d, 2 H, J ) 8.1 Hz), 7.53 (t, 8 H, J ) 6.6 Hz), 7.90-7.93
(m, 4 H), 8.03-8.06 (m, 4 H), 8.79 (s, 8 H). IR (KBr, cm-1):
ν(CdO) 1703 (s). Anal. Calcd for C55H40ClN4ORh‚H2O: C, 71.08;
H, 4.56; N, 6.03. Found: C, 70.68; H, 4.35; N, 5.97.
1
) 0.72 (hexane/CH2Cl2 ) 1:1). H NMR (CDCl3, 300 MHz) δ
-5.83 (d, 3 H, J ) 3.0 Hz), 2.96 (s, 12 H), 7.52 (d, 8 H, J ) 8.1
Hz), 8.00-8.09 (m, 8 H), 8.72 (s, 8 H). HRMS (FABMS): calcd
for (C49H39N4Rh)+ m/z 786.2224, found m/z 786.2242.
(5,10,15,20-Tetratolyporphyrinato)(4-r,r,r-trifluoromethyl-
benzoyl)rhodium(III), 4-CF3C6H5CORh(ttp) (2e). Method A2.
Rh(ttp)Cl (47 mg, 0.054 mmol) was dissolved in 4-R,R,R-
trifluoromethylbenzaldehyde (2.0 mL) and heated at 200 °C under
N2 in the dark for 1 day. Excess 4-R,R,R-trifluoromethylbenzal-
dehyde was removed, and the dark red crude products were then
purified by column chromatography on silica gel eluting with
hexane/CH2Cl2 (4:1). One fraction was collected. A reddish purple
solid, 4-CF3C6H5CORh(ttp) (2f) (26 mg, 0.021 mmol, 38% yield),
Reactions of Aromatic Aldehydes with Rh(ttp)Cl (1). (5,10,-
15, 20-Tetratolyporphyrinato)(benzoyl)rhodium(III), C6H5CORh-
(ttp) (2a), and (5,10,15,20-Tetratolyporphyrinato)(benzyl)-
rhodium(III), C6H5CH2Rh(ttp) (3): General Procedure. Method
A1. Rh(ttp)Cl (47 mg, 0.054 mmol) was dissolved in benzaldehyde
(2.0 mL) and formed a bright red reaction mixture. The bright red
reaction mixture was heated at 150 °C under N2 in the dark for 1.5
days, after which the mixture turned dark red. Excess benzaldehyde
was removed, and the dark red crude products were then isolated
by column chromatography on silica gel eluting with hexane/CH2Cl2
(4:1). Two fractions were collected. Red, solid C6H5CORh(ttp) (2a)
was collected as major product (24 mg, 0.028 mmol, 52% yield).
1
was obtained. Rf ) 0.54 (hexane/CH2Cl2 ) 1:1). H NMR (300
MHz, CDCl3): δ 2.48 (d, 2 H, J ) 8.1 Hz), 2.71 (s, 12 H), 6.25
(d, 2 H, J ) 8.1 Hz), 7.53 (d, 8 H, J ) 7.8 Hz), 7.90-7.93 (m, 4
H), 8.03-8.06 (m, 4 H), 8.79 (s, 8 H). HRMS (FABMS): calcd
for (C56H40N4OF3Rh)+ m/z 944.2204, found m/z 944.2220. IR (KBr,
cm-1): ν(CdO) 1691 (s). Anal. Calcd for C56H40N4F3ORh‚H2O:
C, 69.86; H, 4.19; N, 5.82. Found: C, 69.96; H 4.26; N, 5.73.
1
Rf ) 0.42 (hexane/CH2Cl2 ) 1:1). H NMR (300 MHz, CDCl3):
δ 2.43 (dd, 2 H, J ) 1.2, 8.1 Hz), 2.70 (s, 12 H), 5.98-6.00 (m,
2 H), 6.40 (t, 1 H, J ) 7.8 Hz), 7.53-7.56 (m, 8 H), 7.95-8.07
(m, 8 H), 8.76 (s, 8 H). HRMS (FABMS): calcd for (C55H41N4ORh)+
m/z 876.2330, found m/z 876.2303. IR (KBr, cm-1): ν(CdO) 1716
(s). Anal. Calcd for C55H41N4ORh‚H2O: C, 73.82; H, 4.62; N, 6.26.
Found: C, 73.66; H, 4.64; N, 5.90. A single crystal for X-ray
diffraction analysis was grown from CH2Cl2/MeOH. An orange-
red solid, C6H5CH2Rh(ttp) (3), was collected as minor product (13
mg, 0.015 mmol, 28% yield). Rf ) 0.52 (hexane/CH2Cl2 ) 1:1).
1H NMR (300 MHz, CDCl3): δ -3.80 (d, 2 H, J ) 3.6 Hz), 2.67
(s, 12 H), 2.94 (d, 2 H, J ) 6.5 Hz), 5.84-5.89 (m, 2 H), 6.38 (t,
1 H, J ) 7.4 Hz), 7.45-7.56 (m, 8 H), 7.98-8.08 (m, 8 H), 8.67
(s, 8 H).
Method B. Rh(ttp)CH3 (30 mg, 0.038 mmol) was mixed with
4-R,R,R-trifluoromethylbenzaldehyde (1.0 mL) in a Telfon screw-
capped flask under nitrogen at 200 °C in the dark for 2 days to
yield 5 as a reddish purple solid (14 mg, 0.015 mmol, 39% yield).
(5,10,15,20-Tetratolyporphyrinato)(4-methylbenzoyl)rhodium-
(III), 4-CH3C6H5CORh(ttp) (2c) and (5,10,15,20-Tetratolypor-
phyrinato)(4-formylbenzyl)rhodium(III), 4-CHOC6H5CH2Rh-
(ttp) (4). Method A2. Rh(ttp)Cl (47 mg, 0.054 mmol) was dissolved
in 4-methylbenzaldehyde (2.0 mL) and heated at 200 °C under N2
in the dark for 2 h. Then excess 4-methylbenzaldehyde was
removed, and the dark red crude products were then isolated by
column chromatography on silica gel eluting with hexane/CH2Cl2
(4:1). A red solid, 4-CH3C6H5CORh(ttp) (2c) (14 mg, 0.016 mmol,
Method A2. Rh(ttp)Cl (47 mg, 0.054 mmol) was added into
benzaldehyde (2.0 mL). The bright red reaction mixture was heated
at 200 °C under N2 in the dark for 1 day only and 2a was isolated
(24 mg, 0.043 mmol, 79% yield).
1
30% yield), was collected. Rf ) 0.45 (hexane/CH2Cl2 ) 1:1). H
NMR (300 MHz, CDCl3): δ 1.87 (s, 3 H), 2.35 (d, 2 H, J ) 8.1
Hz), 2.70 (s, 12 H), 5.76 (d, 2 H, J ) 8.1 Hz), 7.53 (d, 8 H, J )
8.1 Hz), 7.92-7.95 (m, 4 H), 8.05-8.08 (m, 4 H), 8.76 (s, 8 H).
HRMS (FABMS): calcd for (C56H43N4ORh)+ m/z 890.2486, found
m/z 890.2472. IR (KBr, cm-1): ν(CdO) 1704 (s). Anal. Calcd for
C56H43N4ORh‚H2O: C, 73.28; H, 4.72; N, 6.10. Found: C, 73.50;
H, 4.70; N, 5.98. An orange-red solid, 4-CHOC6H5CH2Rh(ttp) (4)
(26 mg, 0.030 mmol, 55% yield), was collected. Rf ) 0.35 (hexane/
Method B. Rh(ttp)CH3 (30 mg, 0.038 mmol) was mixed with
benzaldehyde (1.0 mL) in a Telfon screw-capped flask under
nitrogen at 200 °C in the dark for 30 min. Only the red solid (2a)
was obtained as the major product (20 mg, 0.027 mmol, 70% yield).
(5,10,15,20-Tetratolyporphyrinato)(4-fluorobenzoyl)rhodium-
(III), 4-FC6H5CORh(ttp) (2b). Method A2. Rh(ttp)Cl (47 mg,
0.054 mmol) was mixed with 4-fluorobenzaldehyde (2.0 mL) at
1
CH2Cl2 ) 1:1). H NMR (300 MHz, CDCl3): δ -3.80 (d, 2 H, J
(22) Ogoshi, H.; Setsune, J.; Omura, T.; Yoshida, Z. J. Am. Chem. Soc.
1975, 97, 6461-6466.
) 3.0 Hz), 2.70 (s, 12 H), 2.97 (d, 2 H, J ) 7.8 Hz), 6.35 (d, 2 H,

264 Organometallics, Vol. 25, No. 1, 2006
Chan and Lau
J ) 7.8 Hz), 7.53-7.56 (m, 8 H), 7.94-8.08 (m, 8 H), 8.70 (s, 8
cm-1): ν(CdO) 1717 (s). Anal. Calcd for C51H41N4ORh‚2H2O:
C, 70.83; H, 5.24; N, 6.48. Found: C, 70.46; H, 4.81; N, 6.21.
H), 9.44 (s, 1 H). 13C NMR (75 MHz, CDCl3) δ 9.81 (d, JRh-C
)
27 Hz), 22.0, 24.0, 123.2, 125.2, 128.0, 132.0, 132.2, 134.2, 134.4,
137.8,139.8,143.6,192.3.HRMS(FABMS): calcdfor(C56H45N4Rh)+
m/z 890.2486, found m/z 890.2482. IR (KBr, cm-1): ν(CdO) 1693
(s).
Method B. Rh(ttp)Me (30 mg, 0.038 mmol) was added into
propanal (1.0 mL). The bright red reaction mixture was heated at
100 °C under N2 in the dark for 1 day. Excess propanal was
removed. The dark red crude products were then isolated by column
chromatography on silica gel eluting with hexane/CH2Cl2 (4:1).
Bright red solid 7b was collected (19 mg, 0.023 mmol, 60% yield).
Method B. Rh(ttp)CH3 (30 mg, 0.038 mmol) was mixed with
4-methylbenzaldehyde (1.0 mL) in a Telfon screw-capped flask
under nitrogen at 200 °C in the dark for 16 h to yield 12a (6 mg,
0.021 mmol, 54% yield).
5,10,15,20-Tetratolyporphyrinato)(hexylformyl)rhodium-
(III), CH3(CH2)5CORh(ttp) (7b). Method B. Rh(ttp)Me (30 mg,
0.038 mmol) was added into heptanal (1.0 mL). The bright red
reaction mixture was heated at 200 °C under N2 in the dark for 3
days. Excess heptanal was removed. The dark red crude products
were then isolated by column chromatography on silica gel eluting
with hexane/CH2Cl2 (4:1). Bright red solids of CH3(CH2)5CORh(ttp)
(7b) were collected (14 mg, 0.016 mmol, 41% yield). Rf ) 0.67
(hexane/CH2Cl2 ) 1:1). 1H NMR (300 MHz, CDCl3): δ -3.12 (t,
2 H, J ) 7.2 Hz), -1.40 (p, 2 H, J ) 9.0 Hz), -0.88 (q, 2 H, J )
9.0 Hz), 0.47 (d, 2 H, J ) 5.7 Hz), 0.53 (m, 2 H), 0.86 (d, 3 H, J
) 7.2 Hz), 2.70 (s, 12 H), 7.57 (d, 8 H, J ) 7.3 Hz), 8.01-8.09
(m, 8 H), 8.79 (s, 8 H). HRMS (FABMS): calcd for (C55H49N4ORh)+
m/z 884.2953, found m/z 884.2956. IR (KBr, cm-1): ν(CdO) 1716
(s). Anal. Calcd for C55H49N4ORh‚2H2O: C, 71.57; H, 6.00; N,
6.07. Found: C, 71.61; H, 5.60; N, 6.05.
(5,10,15,20-Tetratolyporphyrinato)(4-tert-butylbenzoyl)rhod-
ium(III), 4-tBuC6H5CORh(ttp) (2d), and (5,10,15,20-Tetratoly
porphyrinato)(4-formylphenyl-1,1-dimethylethyl)rhodium-
(III), 4-CHOC6H4(Me)2CH2Rh(ttp) (5). Method A2. Rh(ttp)Cl
(47 mg, 0.054 mmol) was dissolved in 4-tert-butylbenzaldehyde
(2.0 mL) and heated at 200 °C under N2 in the dark for 1 h. Then
excess 4-tert-butylbenzaldehyde was removed, and the dark red
crude products were then isolated by column chromatography on
silica gel eluting with hexane/CH2Cl2 (4:1). Red solids of 4-tBuC6H5-
CORh(ttp) (2d) (9 mg, 0.0092 mmol, 17% yield) were collected.
1
Rf ) 0.43 (hexane/CH2Cl2 ) 1:1). H NMR (300 MHz, CDCl3):
δ 0.95 (s, 9 H), 2.42 (d, 2 H, J ) 8.3 Hz), 2.70 (s, 12 H), 5.96 (d,
2 H, J ) 8.3 Hz), 7.52 (d, 8 H, J ) 8.1 Hz), 7.95-7.98 (m, 4 H),
8.04-8.07 (m, 4 H), 8.74 (s, 8 H). HRMS (FABMS): calcd for
(C59H49N4ORh)+ m/z 932.2956, found m/z 932.2974. IR (KBr,
cm-1): ν(CdO) 1710 (s). Anal. Calcd for C59H49N4ORh‚2H2O:
C, 73.13; H, 5.51; N, 5.78. Found: C, 73.25; H, 5.22; N, 5.69.
Another orange fraction, 4-CHOC6H4(Me)2CH2Rh(ttp) (5), was also
collected (3 mg, 0.0011 mmol, 2% yield). Rf ) 0.69 (hexane/CH2Cl2
(5,10,15,20-Tetratolyporphyrinato)(tert-butylformyl)rhodium-
t
(III), BuCORh(ttp) (7c). Method A. Rh(ttp)Cl (47 mg, 0.054
mmol) was dissolved in tert-butylaldehyde (2.0 mL) and heated at
200 °C under N2 in the dark for 1 day. Then excess tert-
butylaldehyde was removed, and the dark red crude products were
then isolated by column chromatography on silica gel eluting with
1
) 1:1). H NMR (300 MHz, CDCl3): δ -3.79 (d, 2 H, J ) 3.0
t
hexane/CH2Cl2 (4:1). Red solids of BuCORh(ttp) (7c) (11 mg,
Hz), 1.25 (s, 9 H), 2.70 (s, 12 H), 2.92 (d, 2 H, J ) 9.0 Hz), 5.87
(d, 2 H, J ) 9.0 Hz), 7.52-7.56 (m, 8 H), 8.01 (t, 8 H, J ) 7.5
Hz), 8.65 (s, 8 H). 13C NMR (75 MHz, CDCl3): δ 13.0 (d, JRh-C
) 28 Hz), 22.1, 31.2, 122.9, 123.5, 124.6, 127.8, 127.9, 131.8,
134.3, 134.4, 137.6, 138.3, 139.9, 143.6, 194.5. HRMS (FABMS):
calcd for (C59H49N4ORh)+ m/z 932.3288, found m/z 932.2956. IR
(KBr, cm-1): ν(CdO) 1704 (s).
Method B. Rh(ttp)CH3 (30 mg, 0.038 mmol) was mixed with
4-tert-butylbenzaldehyde (1.0 mL) in a Telfon screw-capped flask
under nitrogen at 200 °C in the dark for 16 h to yield 2d (26 mg,
0.028 mmol, 73% yield).
0.013 mmol, 24% yield) were collected. Rf ) 0.52 (hexane/CH2Cl2
1
) 1:1). H NMR (300 MHz, CDCl3): δ -2.36 (s, 9 H), 2.70 (s,
12 H), 7.53 (d, 8 H, J ) 9.0 Hz), 7.96-8.05 (m, 8 H), 8.70 (s, 8
H). HRMS (FABMS): calcd for (C53H45N4ORh)+ m/z 857.2700,
found m/z 857.2721. IR (KBr, cm-1): ν(CdO) 1732 (s). Anal.
Calcd for C53H49N4ORh‚H2O: C, 72.75; H, 5.42; N, 6.41. Found:
C, 72.61; H, 5.60; N, 6.05.
Method B. Rh(ttp)Me (30 mg, 0.038 mmol) was added into tert-
butylaldehyde (1.0 mL). The bright red reaction mixture was heated
at 200 °C under N2 in the dark for 3 days. Excess solvent was
removed. The dark red crude products were then isolated by column
chromatography on silica gel eluting with hexane/CH2Cl2 (4:1).
Bright red solid 7c was collected (16 mg, 0.018 mmol, 48% yield).
(5,10,15,20-Tetratolyporphyrinato)(4-methoxylbenzoyl)rhod-
ium(III), 4-MeOC6H5CORh(ttp) (2g). Method B. Rh(ttp)CH3 (30
mg, 0.038 mmol) was dissolved in anisaldehyde (1.0 mL) in a
Telfon screw-capped flask under nitrogen at 200 °C in the dark
for 16 h to yield 4-MeOC6H5CORh(ttp) (2g) (21 mg, 0.021 mmol,
(5,10,15,20-Tetratolyporphyrinato)rhodium(III) Trifate, Rh-
(ttp)OTf (8).15 Rh(ttp)Cl (50 mg, 0.057 mmol) and the silver triflate
(25.6 mg, 0.11 mmol) were put into the dried CH2Cl2 (100 mL)
and stirred for 1.5 days at room temperature. The color of the
mixture changed from red to reddish brown after 1.5 days. Then
the product was isolated on silica gel eluting with CH2Cl2/EA (9:
1). 4 was collected as orange solids (22 mg, 0.023 mmol, 40%
1
56% yield) as a red solid. Rf ) 0.52 (hexane/CH2Cl2 ) 1:1). H
NMR (300 MHz, CDCl3): δ 2.42 (d, 2 H, J ) 8.5 Hz), 2.70 (s, 12
H), 3.45 (s, 3 H), 5.47 (d, 2 H, J ) 8.5 Hz), 7.53 (d, 8 H, J ) 8.1
Hz), 7.95-8.08 (m, 8 H), 8.76 (s, 8 H). HRMS (FABMS): calcd
for (C56H43N4O2Rh)+ m/z 906.2422, found m/z 906.2436. IR (KBr,
cm-1): ν(CdO) 1704 (s). Anal. Calcd for C56H43N4ORh‚2H2O:
C, 71.33; H, 5.02; N, 5.94. Found: C, 71.71; H, 4.72; N, 5.77.
1
yield). Rf ) 0.32 (hexane/CH2Cl2 ) 1:1). H NMR (300 MHz,
CDCl3): δ 2.70 (s, 12 H), 7.48-7.61 (m, 8 H), 7.98-8.05 (m, 8
H), 8.76 (s, 8 H). HRMS (FABMS): calcd for (C49H36N4RhO3F3S)+
m/z 771.1990, found m/z 771.1998.
Reaction of Aliphatic Aldehydes with Rh(ttp)Cl (1). (5,10,-
15,20-Tetratolyporphyrinato)(ethylformyl)rhodium(III), CH3CH2-
CORh(ttp) (7a). General Procedure. Method A. Rh(ttp)Cl (47
mg, 0.054 mmol) was dissolved in propanal (2.0 mL) and heated
at 100 °C under N2 in the dark for 2 days. Then excess propanal
was removed. The dark red crude products were then isolated by
column chromatography on silica gel eluting with hexane/CH2Cl2
(4:1). A red solid, CH3CH2CORh(ttp) (7a) (1 mg, 0.0016 mmol,
Reaction of Rh(ttp)OTf with PhCHO. Rh(ttp)OTf (15) (10 mg,
0.010 mmol) was dissolved in benzaldehyde (1.0 mL) and heated
at 200 °C under N2 in the dark. After 15 min, C6H5CORh(ttp) (2)
(7.8 mg, 0.0089 mmol, 89% yield) was obtained.
(5,10,15,20-Tetratolyporphyrinato)rhodium(III) Hydride,
Rh(ttp)H (9).16 A suspension of Rh(ttp)Cl (100 mg, 0.11 mmol)
in MeOH (50 mL) and a solution of NaBH4 (17 mg, 0.45 mmol)
in aqueous NaOH (0.1 M, 2 mL) were purged with N2 for 15 min
separately. The solution of NaBH4 was added slowly to the
suspension of Rh(ttp)Cl via a cannula. The mixture was heated at
50 °C under N2 for 1 h to give a brown solution. The solution was
then cooled to 0 °C under N2, and 0.1 M HCl (40 mL) was added
1
3% yield), was collected. Rf ) 0.52 (hexane/CH2Cl2 ) 1:1). H
NMR (300 MHz, CDCl3): δ -3.14 (q, 2 H, J ) 7.5 Hz), -1.69
(t, 3 H, J ) 7.2 Hz), 2.70 (s, 12 H), 7.26 (d, 8 H, J ) 7.8 Hz), 8.05
(d, 8 H, J ) 6.3 Hz), 8.80 (s, 8 H). HRMS (FABMS): calcd for
(C51H41N4ORh)+ m/z 828.2335, found m/z 828.2330. IR (KBr,

Syntheses of Acyl Rhodium Porphyrins
Organometallics, Vol. 25, No. 1, 2006 265
via a syringe. A brick red suspension was formed. After stirring at
room temperature for another 15 min under N2, the brick red
precipitate was collected after filtration and washing with water (2
× 10 mL). The brick red residue for 9 was obtained (80 mg, 0.10
mmol, 92% yield) and vacuum-dried. 1H NMR (C6D6, 300 MHz):
δ -40.12 (d, 1 H, JRh-H ) 43.5 Hz), 2.42 (s, 12 H), 7.16 (d, 4 H,
J ) 8.2 Hz), 7.35 (d, 4 H, J ) 8.2 Hz), 7.95 (d, 4 H, J ) 8.1 Hz),
8.22 (d, 4 H, J ) 8.1 Hz), 9.03 (s, 8 H).
Reaction of Rh(ttp)H with PhCHO. Rh(ttp)H (9) (20 mg, 0.026
mmol) was dissolved in PhCHO (1.0 mL) to form a dark red
solution and was then heated at 200 °C for 30 min. Both C6H5-
CORh(ttp) (2a) (8.0 mg, 0.0091 mmol, 35% yield) and C6H5CH2-
Rh(ttp) (3) (1.0 mg, 0.0010 mmol, 4% yield) were obtained after
chromatography.
Acknowledgment. We thank H. S. Chan for the X-ray
crystallographic determination and the Research Grants Council
of the HKSAR, China (CUHK 400105), for financial support.
Supporting Information Available: Text, tables, and figure
of crystallographic data for complexes 2a, 2b, and 2e. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0507878