Direct observation of aldehyde insertion into rhodium-aryl and -alkoxide complexes

Article abstract of DOI:10.1021/ja017401e

Several organorhodium(I) complexes of the general formula (PPh₃)₂(CO)RhR (R = p-tolyl, o-tolyl, Me) were isolated and were shown to insert aryl aldehydes into the aryl-rhodium(I) bond. Under nonaqueous conditions, these reactions provided ketones in good yield. The stability of the arylrhodium(I) complexes allowed these reactions to be run also in mixtures of THF and water. In this solvent system, diarylmethanols were generated exclusively. Mechanistic studies support the formation of ketone and diarylmethanol by insertion of aldehyde into the rhodium-aryl bond and subsequent β-hydride elimination or hydrolysis to form diaryl ketone or diarylmethanol products. Kinetic isotope effects and the formation of diarylmethanols in THF/water mixtures are inconsistent with oxidative addition of the acyl carbon-hydrogen bond and reductive elimination to form ketone. Moreover, the intermediate rhodium diarylmethoxide formed from insertion of aldehyde was observed directly during the reaction. Its structure was confirmed by independent synthesis. This complex undergoes β-hydrogen elimination to form a ketone. This alkoxide also reacts with a second aldehyde to form esters by insertion and subsequent β-hydrogen elimination. Thus, reactions of arylrhodium complexes with an excess of aldehyde formed esters by a double insertion and β-hydrogen elimination sequence.

Full text of DOI:10.1021/ja017401e

Published on Web 01/29/2002
Direct Observation of Aldehyde Insertion into Rhodium-Aryl
and -Alkoxide Complexes
Christopher Krug and John F. Hartwig*
Department of Chemistry, Yale UniVersity, P.O. Box 208107,
New HaVen, Connecticut 06520-8107
Received October 26, 2001. Revised Manuscript Received December 1, 2001
Abstract: Several organorhodium(I) complexes of the general formula (PPh3)2(CO)RhR (R ) p-tolyl, o-tolyl,
Me) were isolated and were shown to insert aryl aldehydes into the aryl-rhodium(I) bond. Under nonaqueous
conditions, these reactions provided ketones in good yield. The stability of the arylrhodium(I) complexes
allowed these reactions to be run also in mixtures of THF and water. In this solvent system, diarylmethanols
were generated exclusively. Mechanistic studies support the formation of ketone and diarylmethanol by
insertion of aldehyde into the rhodium-aryl bond and subsequent â-hydride elimination or hydrolysis to
form diaryl ketone or diarylmethanol products. Kinetic isotope effects and the formation of diarylmethanols
in THF/water mixtures are inconsistent with oxidative addition of the acyl carbon-hydrogen bond and
reductive elimination to form ketone. Moreover, the intermediate rhodium diarylmethoxide formed from
insertion of aldehyde was observed directly during the reaction. Its structure was confirmed by independent
synthesis. This complex undergoes â-hydrogen elimination to form a ketone. This alkoxide also reacts
with a second aldehyde to form esters by insertion and subsequent â-hydrogen elimination. Thus, reactions
of arylrhodium complexes with an excess of aldehyde formed esters by a double insertion and â-hydrogen
elimination sequence.
Introduction
(I)-catalyzed reactions that form alcohols and amines by addition
of aryl main group reagents to aldehydes and imines. We
Insertion of alkenes into late transition metal-carbon bonds1
is a common organometallic reaction in catalytic processes that
form small molecules as well as macromolecules. Insertions of
electrophilic heterocumulenes, such as CO2 and isocyanates, are
also known, but fewer catalytic processes involving these
insertions have been developed.2 In contrast, directly observed
insertions of aldehydes into late metal-carbon bonds are rare
and have been limited to reactions of metallacycles.3 Indeed,
insertion of aldehydes into a late metal-carbon bond should
be less favorable than insertion of olefins. The carbon-oxygen
π-bond is stronger than the carbon-carbon π-bond,4 and the
resulting alkoxides are often less stable kinetically than the
starting alkyl. These trends make detection of aldehyde insertion
products difficult. Insertion of CO2 and isocyanates generates
more stable carboxylate and carbamate products.
recently reported a rhodium-catalyzed Heck-type coupling of
imines with arenes that appeared to involve imine insertion,11
and Yamamoto12,13 has developed palladium- and platinum-
catalyzed reactions that form amines and carbinols, perhaps by
insertion of aldehydes or imines. Recently, Tamaru and Mori
have independently developed nickel-catalyzed intra- and
intermolecular additions of π-allyl donors to aldehydes, and
these reactions may involve insertion of aldehyde into a metal-
allyl linkage.14 With an interest in observing new insertion
(6) (a) Oi, S.; Moro, M.; Inoue, Y. Chem. Commun. 1997, 1621. (b) Oi, S.;
Moro, M.; Inoue, Y. Organometallics 2001, 20, 1036. (c) Oi, S.; Moro,
M.; Fukuhara, H.; Kawanishi, T.; Inoue, Y. Tetrahedron Lett. 1999, 40,
9259.
(7) Hayashi, T.; Ishigedani, M. J. Am. Chem. Soc. 2000, 122, 976.
(8) Batey, R. A.; Thadani, A. N.; Smil, D. V. Org. Lett. 1999, 1, 1683.
(9) (a) Li, C. J.; Meng, Y. J. Am. Chem. Soc. 2000, 122, 9538. (b) Huang, T.;
Meng, Y.; Venkatraman, S.; Wang, D.; Li, C. J. J. Am. Chem. Soc. 2001,
123, 7451.
(10) Fu¨rstner, A.; Krause, H. AdV. Synth. Catal. 2001, 343, 343.
(11) Ishiyama, T.; Hartwig, J. F. J. Am. Chem. Soc. 2000, 122, 12043.
(12) (a) Nakamura, H.; Iwama, H.; Yamamoto, Y. J. Am. Chem. Soc. 1996,
118, 6641. (b) Nakamura, H.; Nakamura, K.; Yamamoto, Y. J. Am. Chem.
Soc. 1998, 120, 4242. (c) Gevorgyan, V.; Quan, L. G.; Yamamoto, Y.
Tetrahedron Lett. 1999, 40, 4089.
(13) For late metal-catalyzed reactions between vinyl or aryl groups and ketones,
see: (a) Quan, L. G.; Lamrani, M.; Yamamoto, Y. J. Am. Chem. Soc. 2000,
122, 4827. (b) Quan, L. G.; Gevorgyan, V.; Yamamoto, Y. J. Am. Chem.
Soc. 1999, 121, 3545.
Nevertheless, catalytic cycles that may occur by aldehyde or
related imine insertions have been emerging. Miyaura,5 Oi,6
Hayashi,7 Batey,8 Li,9 and Fu¨rstner10 have developed rhodium-
(1) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and
Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, 1987.
(2) Braunstein, P.; Matt, D.; Nobel, D. Chem. ReV. 1988, 88, 747.
(3) (a) Carmona, E.; Gutie´rrez-Puebla, E.; Mar´ın, J. M.; Monge, A.; Paneque,
M.; Poveda, M. L.; Ruiz, C. J. Am. Chem. Soc. 1989, 111, 2883. (b)
Hartwig, J. F.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1989,
111, 2717.
(4) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry; Harper and Row: New York, 1987; p 162.
(14) For other late metal-catalyzed reactions between aryl or allyl groups and
aldehydes, see: (a) Cheng, C. H.; Majumdar, K. K. Org. Lett. 2000, 2,
2295. (b) Shibata, K.; Kimura, M.; Shimizu, M.; Tamaru, Y. Org. Lett.
2001, 3, 2181. (c) Sato, Y.; Takimoto, M.; Mori, M. J. Am. Chem. Soc.
2000, 122, 1624. (d) Sato, Y.; Takimoto, M.; Hayashi, K.; Katsuhara, T.;
Takagi, K.; Mori, M. J. Am. Chem. Soc. 1994, 116, 9771. (e) Larock, R.
C.; Doty, M. J.; Cacchi, S. J. Org. Chem. 1993, 58, 4579.
(5) (a) Sakai, M.; Ueda, M.; Miyaura, N. Angew. Chem., Int. Ed. 1998, 37,
3279. (b) Ueda, M.; Miyaura, N. J. Org. Chem. 2000, 65, 4450. (c) Ueda,
M.; Miyaura, N. J. Organomet. Chem. 2000, 595, 31.
9
1674 VOL. 124, NO. 8, 2002 J. AM. CHEM. SOC.
10.1021/ja017401e CCC: $22.00 © 2002 American Chemical Society

Aldehyde Insertion into Rh−Aryl and −Alkoxide Complexes
A R T I C L E S
processes, we sought to prepare discrete organometallic com-
plexes that would insert aldehydes and imines. Thus, we targeted
potential intermediates in these new catalytic processes. Here,
we describe the preparation of stable, phosphine-ligated aryl-,
alkyl-, and alkoxo-rhodium(I) complexes that allow for the
direct observation of aldehyde insertions to form alkoxide
intermediates. These alkoxide intermediates generate ketone or
diarylmethanol products, depending on reaction conditions.
Results and Discussion
Preparation of Rhodium-Aryl Complexes. Many of the
reported systems for addition of arylmetalloids to aldehydes and
imines involve cationic and often “ligandless” rhodium com-
plexes generated in situ. Discrete arylrhodium complexes would
be difficult to isolate in these systems. In addition to these
catalysts, we found that the rhodium analogue of Vaska’s
complex provided 5 to 10 turnovers for the addition of potassium
phenyltrifluoroborate to benzaldehyde in THF/water mixtures.
Although this catalyst is less reactive than the most active
species generated in situ, the Vaska-type system would be more
amenable to isolation of potential intermediates, while remaining
relevant to catalytic chemistry.
Figure 1. Ortep diagram of 1. Representative bond lengths (Å) and bond
angles (deg): Rh(1)-P(1) 2.3141; Rh(1)-P(2) 2.3016; Rh(1)-C(1) 1.862;
Rh(1)-C(2) 2.090; C(1)-O(1) 1.131; P(1)-Rh(1)-P(2) 174.7; C(1)-Rh-
(1)-C(2) 172.7; P(1)-Rh(1)-C(2) 88.33; P(2)-Rh(1)-C(1) 90.70.
Table 1. Yields of Diaryl Ketone Product in the Reaction of
Organorhodium Complexes and Aryl Aldehydesa
Triphenylphosphine-ligated arylrhodium(I) complexes can
be difficult to isolate in pure form,15-18 but rhodium-aryl
compounds with a mixed phosphine and CO ligation sphere
are stable. Complexes of the general formula (PPh3)2Rh(CO)-
Ar have been reported. Although we found that literature
procedures generate product mixtures,17 as determined by 31P
NMR spectroscopy of crude reaction solutions, reaction of 1
equiv of bis(p-tolyl)zinc with (PPh3)2Rh(CO)Cl in THF at room
temperature did give the desired p-tolyl rhodium complex 1 as
a yellow crystalline material in 77% yield (Figure 1). Single
crystals suitable for X-ray analysis were grown from a THF/
pentane solution at -35 °C.18 This method allowed for the
preparation of the o-tolyl and methyl analogues 2 and 3 in 70%
and 59% yields, respectively (eq 1).
entry
Rh complex
Ar
yield (%)
1
2
3
4
5
6
7
8
1
1
1
1
1
1
2
3
Ph
68
75
2-naphthyl
2-naphthyl
o-tolyl
p-F3CC6H4
p-OMeC6H4
Ph
53b
78
38c
74
57d
<10e
Ph
a Reaction conditions: 1.5 equiv of aldehyde in C6D6, [Rh] ) 0.013 M.
80 min at 85 °C. b 10 equiv of aldehyde was used. c 4 h reaction time. d 16
h reaction time. e 8 h reaction time.
ucts. Heating of 3 at 85 °C for 8 h with benzaldehyde formed
acetophenone, but in less than 10% yield (Table 1, entry 8).
Aldehyde insertions were limited to aryl aldehydes; heating of
1 in C6D6 in the presence of 1-hexanal did not form the
1
corresponding ketone, as determined by GC-MS or H NMR
spectroscopy.
Reactions of Aldehydes To Form Ketones. We investigated
the reactivity of these isolated organorhodium(I) complexes with
various unsaturated substrates. Reaction of p-tolyl 1 with aryl
aldehydes in C6D6 gave diaryl ketones in good yields in most
cases after 80 min at 85 °C (Table 1). Reactions of o-tolyl 2
and methyl 3 with benzaldehyde were less selective or gave
lower yields of the desired ketone. Heating of 2 and benzalde-
hyde in benzene-d6 gave 2-methylbenzophenone (57% yield by
1H NMR spectroscopy), along with several unidentified prod-
A 31P NMR signal at 37.3 ppm (JPRh ) 195 Hz) correspond-
ing to the known dimer [Rh(µ-CO)(PPh3)2]2 (4) was generated
by the reaction with aldehyde.19 As the reaction progressed,
complex 4 underwent decomposition, as determined by obtain-
ing at various time intervals 31P NMR spectra of reaction
solutions containing tris(2,4,6-trimethoxyphenyl)phosphine as
internal standard. Yet, we were able to isolate complex 4 from
the reaction between 1 and p-F3CC6H4CHO at room temperature
in THF. Its structure was confirmed by X-ray diffraction.
Toluene was produced in 19-25% yield as a side product of
the reactions between p-tolyl 1 and aryl aldehydes. We
considered that hydrolysis by traces of adventitious water or
simple thermal decomposition of 1 could form the toluene side
product. Thus, a solution of 1 was heated at the temperature of
the reaction in the absence of aldehyde. Although about 10%
(15) (a) Takesada, M.; Yamazaki, H.; Hagihara, N. Nippon Kagaku Zasshi 1968,
89, 1121. (b) Kulzick, M. A.; Price, R. T.; Andersen, R. A.; Muetterties,
E. L. J. Organomet. Chem. 1987, 333, 105. (c) Yamamoto, M.; Onitsuka,
K.; Takahashi, S. Organometallics 2000, 19, 4669. (d) Zecchin, S.;
Schiavon, G.; Pilloni, G.; Martelli, M. J. Organomet. Chem. 1976, 110,
C45.
(16) Keim, W. J. Organomet. Chem. 1968, 14, 179.
(17) Dahlenburg, L.; Mirzaei, F.; Yardimcioglu, A. Z. Naturforsch. 1982, 37B,
310.
(18) For the only other aryl-rhodium(I) complex that has been structurally
characterized, see: Boyd, S. E.; Field, L. D.; Hambley, T. W.; Partridge,
M. G. Organometallics 1993, 12, 1720.
(19) Evans, D.; Yagupsky, G.; Wilkinson, G. J. Chem. Soc. A 1968, 2660.
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1675

A R T I C L E S
Krug and Hartwig
Scheme 1
Scheme 2
thaldehyde and 2-naphthaldehyde-d1 occurred with rate constants
of 9.8 and 9.9 × 10-4 s-1, indicating the absence of a deuterium
isotope effect in the rate determining step. Second, reaction of
1 with 2-naphthaldehyde at room temperature for 24 h generated
the proposed alkoxide intermediate 6. This intermediate 6 was
1
observed directly by H and 31P NMR spectroscopy. It ac-
cumulated as roughly 25% of the reaction mixture after 20 h at
room temperature.
1
Independent synthesis was used to demonstrate that the H
and 31P NMR signals of the intermediate corresponded to
insertion product 6. Reaction of (PPh3)2Rh(CO)Cl and sodium
2-naphthyl-p-tolylmethoxide led to formation of the same
species, which was isolated from a cold toluene/Et2O solution
in 56% yield. As required by the insertion mechanism, heating
of this isolated complex in C6D6 gave diaryl ketone in 80%
of 1 had undergone decomposition, an 1H NMR spectrum
acquired after 80 min at 85 °C showed that no toluene had
formed.
Mechanistic Studies on the Formation of Ketones. Tsuji20
and more recently Pignolet,21 Goldman,22 O’Connor,23 and
Crabtree24 reported on the rhodium(I)-catalyzed decarbonylation
of aldehydes. In addition, catalytic hydroacylation of olefins
has been reported.25,26 These processes have been shown to
occur by initial C-H bond cleavage of the aldehyde. Thus, we
investigated whether the formation of ketone from a reaction
between 1 and aryl aldehydes occurred by initial cleavage of
the aldehyde C-H bond as shown at the top of Scheme 1.
Ketone and toluene would then form from competing C-C and
C-H reductive elimination from the phenacyl hydride 5.
Alternatively, the ketone could form as shown at the bottom
of Scheme 1. Insertion of aldehyde would form diarylmethoxide
6, and subsequent â-hydrogen elimination would form ketone.
â-Hydrogen elimination from alkoxo complexes is a common
route to hydride complexes27 and has been observed directly in
related iridium alkoxo complexes.28 In either the C-H activation
or insertion mechanism, the rhodium dimer 4 would form from
decomposition of the resulting unstable rhodium hydride 7
(Scheme 1).
1
yield by H NMR spectroscopy (eq 2).
Because the insertion mechanism does not directly account
for the formation of toluene, we further evaluated the origin of
this side product. We reasoned that RhH(CO)(PPh3)3 would
generate hydride 7 by phosphine dissociation and, therefore,
could serve as a model for the reactivity of the initial hydride
product RhH(CO)(PPh3)2. Reaction of RhH(CO)(PPh3)3 with
p-tolyl complex 1 consumed the hydride and formed toluene in
27% yield (1H NMR spectroscopy) and dimeric 4, after 2 h at
85 °C. Thus, an independent side reaction of the hydride product
with p-tolyl 1 most likely accounts for the formation of the small
amounts of toluene in the reaction of 1 with aryl aldehydes.
Reactions of Aldehydes To Form Diarylmethanols. The
intermediacy of diarylmethoxide 6 in the formation of ketone
suggested that aldehydes would react with 1 to form alcohols
in the presence of water by hydrolysis of 6. This reaction
sequence would account for the formation of arylmethanols in
some of the catalytic chemistry described in the Introduction.
Thus, arylrhodium complexes 1 and 2 were treated with
aldehydes at room temperature and at 55 °C in a mixture of
THF and water. These reactions gave diarylmethanols and
(PPh3)2Rh(CO)OH29 after 24-72 h (Scheme 2). Reactions of
o-tolyl 2 were slower than were those of p-tolyl 1, presumably
because the greater steric hindrance of 2 prevents association
of aldehyde. Reactions that formed alcohol in aqueous THF were
faster than those that formed ketone in the less polar benzene.
Several experiments strongly favor insertion of aldehyde and
subsequent â-H elimination. First, reactions of 1 with 2-naph-
(20) Tsuji, J.; Ohno, K. Tetrahedron Lett. 1967, 2173.
(21) Doughty, D. H.; Pignolet, L. H. J. Am. Chem. Soc. 1978, 100, 7083.
(22) Abu-Hasanayn, F.; Goldman, M. E.; Goldman, A. S. J. Am. Chem. Soc.
1992, 114, 2520.
(23) O’Conner, J. M.; Ma, J. J. Org. Chem. 1992, 57, 5075.
(24) Beck, C. M.; Rathmill, S. E.; Park, Y. J.; Chen, J.; Crabtree, R. H.; Liable-
Sands, L. M.; Rheingold, A. L. Organometallics 1999, 18, 5311.
(25) (a) Barnhart, R. W.; Wang, X.; Noheda, P.; Bergens, S. H.; Whelan, J.;
Bosnich, B. J. Am. Chem. Soc. 1994, 116, 1821. (b) Fairlie, D. P.; Bosnich,
B. Organometallics 1988, 7, 936. (c) Fairlie, D. P.; Bosnich, B. Organo-
metallics 1988, 7, 946.
(26) (a) Lenges, C. P.; Brookhart, M. J. Am. Chem. Soc. 1997, 119, 3165. (b)
Lenges, C. P.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 1998, 120,
6965.
(27) (a) Blum, O.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 4582. (b) Ritter,
J. C. M.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 6826. (c) Blum,
O.; Milstein, D. J. Organomet. Chem. 2000, 593-594, 479.
(28) Zhao, J.; Hesslink, H.; Hartwig, J. F. J. Am. Chem. Soc. 2001, 123, 7220.
(29) Li, P. C. H.; Thompson, M. Analyst 1994, 119, 1947.
9
1676 J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002

Aldehyde Insertion into Rh−Aryl and −Alkoxide Complexes
A R T I C L E S
Scheme 3
Aldrich and used as received. Benzaldehyde and p-anisaldehyde were
purchased from Aldrich and were distilled prior to use. Both were
degassed via three freeze-pump-thaw cycles. All aldehyde substrates
were stored in a glovebox to slow oxidation to the corresponding
carboxylic acid. Me2Zn (2.0 M in toluene), p-tolylmagnesium bromide
(1.0 M in Et2O), and o-tolylmagnesium chloride (1.0 M in THF) were
purchased from Aldrich and used as received. KF3BPh,8 (PPh3)2Rh-
(CO)Cl,32 bis(p-tolyl)zinc,33 and bis(o-tolyl)zinc33 were prepared ac-
cording to literature procedures. 2-Naphthaldehyde-d1 was prepared by
an analogous procedure to that reported for PhCDO.34 RhD(CO)(PPh3)3
was prepared in an analogous manner to RhH(CO)(PPh3)3 using NaBD4
and EtOD.19
Kinetic experiments were performed on a General Electric Omega
300- or 500-MHz instrument. All yields determined by 1H NMR were
calculated using 1,3,5-trimethoxybenzene or Cp2Fe as an internal
standard. A pulse delay of 80 s (5 × T1) was used to compensate for
the slow relaxation time of Cp2Fe.
Insertions of Aldehydes into Rhodium Diarylmethoxide
Complexes. Reactions with 6 with an excess of aldehyde formed
ester in competition with ketone, and this competitive formation
of ester accounts for the lower yield of ketone noted in entry 3
of Table 1. This ester could form by insertion of aldehyde into
the rhodium alkoxo complex and subsequent â-hydrogen
elimination from the resulting alkoxo complex. Thus, we tested
whether ester would form from addition of aldehyde to isolated
alkoxide 6. Indeed, reaction of diarylmethoxide 6 with an excess
of 2-naphthaldehyde gave the diarylmethyl-2-naphthoate 8 in
53% yield (Scheme 3). Although metal-catalyzed Tishchenko
reactions are known,26b,30 direct observation of aldehyde inser-
tions into alkoxo complexes are rare. Recently, Han and
Hillhouse reported the only previously observed insertion of
aldehydes into late metal alkoxo complexes.31
Conclusions. This work represents a rare example of directly
observed insertion of aldehydes into a late transition metal-
carbon and -oxygen bonds, particularly in unstrained systems.
These data support the mechanism proposed by several groups
for the rhodium-catalyzed formation of aryl methanols and aryl
methylamines, as well as our proposed insertion of a tethered
imine into a rhodium(III) aryl group.11 Further studies on new
insertions and on the detailed mechanism of the insertion
chemistry reported here are in progress.
Preparation of trans-Carbonyl(p-tolyl)bis(triphenylphosphine)-
rhodium(I) (1).17 In a 20 mL scintillation vial equipped with a magnetic
stir bar were placed 0.250 g (0.360 mmol) of (PPh3)2Rh(CO)Cl and
0.0900 g (0.360 mmol) of bis(p-tolyl)zinc. Dry THF (8 mL) was added
via syringe, and the resulting solution was stirred for 0.5 h at room
temperature. The solution was filtered through Celite and concentrated
under reduced pressure. Degassed ethyl alcohol was added to the
concentrated solution via cannula, giving a yellow precipitate. The
supernatant was removed via cannula, and the product was washed
1
with pentane and dried in vacuo, yielding 1 in 77% yield. H NMR
(300 MHz, C6D6): δ 2.09 (s, 3H), 6.45 (d, J ) 7.8 Hz, 2H), 6.87 (d,
J ) 7.8 Hz, 2H), 6.99-7.04 (m, 18H), 7.64-7.71 (m, 12H). 31P NMR
(121.6 MHz, C6D6): 35.2 (JPRh ) 159 Hz).
Preparation of trans-Carbonyl(o-tolyl)bis(triphenylphosphine)-
rhodium(I) (2).17 The title compound was prepared in 70% yield in
an analogous manner to that of 1, but using bis(o-tolyl)zinc. 1H NMR
(300 MHz, C6D6): δ 1.95 (s, 3H), 6.49 (t, J ) 7.2 Hz, 1H), 6.56 (d,
J ) 7.5 Hz, 1H), 6.78 (t, J ) 7.5 Hz, 1H), 6.99-7.03 (m, 18H), 7.07
(d, J ) 7.2 Hz, 1H), 7.60-7.71 (m, 12H). 31P NMR (121.6 MHz,
C6D6): 35.6 (JPRh ) 160 Hz).
Experimental Section
General. Unless noted otherwise, all manipulations were carried out
under an inert atmosphere using a nitrogen-filled glovebox or standard
Schlenk techniques. All glassware was oven-dried for approximately
1 h prior to use. THF, diethyl ether, toluene, and pentane were distilled
from sodium benzophenone ketyl under nitrogen. CH2Cl2 was dried
over CaH2 and distilled under nitrogen. Ethyl alcohol, deuterium oxide,
and H2O were degassed prior to use by nitrogen sparging for 1 h. C6D6,
and THF-d8 were purchased from Cambridge Isotope Laboratories, Inc.,
dried over sodium benzophenone ketyl, and vacuum transferred prior
to use. Column chromatography was performed using Merck silica gel
60 (230-400 mesh). Preparatory thin-layer chromatography plates were
purchased from Analtech.
Preparation of trans-Carbonyl(methyl)bis(triphenylphosphine)-
rhodium(I) (3).17 The title compound was prepared in 59% yield in
1
an analogous manner to that of 1, but using dimethylzinc. H NMR
(300 MHz, C6D6): δ -0.08 (dt, J ) 7.8 Hz, 3H), 7.01-7.06 (m, 18H),
7.86-7.88 (m, 12H). 31P NMR (202.4 MHz, C6D6): 43.2 (JPRh ) 159
Hz).
Preparation of trans-Carbonyl[(2-naphthyl)(p-tolyl)methoxy]bis-
(triphenylphosphine)rhodium(I) (6). Into a 20 mL scintillation vial
equipped with magnetic stir bar were placed 0.100 g (0.145 mmol) of
(PPh3)2Rh(CO)Cl and 0.117 g (0.434 mmol) of (2-naphthyl)(p-tolyl)-
sodium methoxide.35 The components were dissolved in 5 mL of dry
THF, and the resulting solution was stirred at room temperature for 1
h. The volatile materials were removed under reduced pressure, and
the product was extracted into toluene. The solution was filtered through
Celite and concentrated under reduced pressure. Slow addition of Et2O
and cooling to -35 °C gave the title compound in 56% yield. 1H NMR
(400 MHz, C6D6): δ 2.19 (s, 3H), 5.72 (s, 1H), 6.78-6.84 (m, 5H),
6.97-7.05 (m, 18H), 7.28-7.37 (m, 4H), 7.61-7.64 (m, 2H), 7.89-
7.94 (m, 12H). 13C NMR (100.6 MHz, CDCl3): δ 21.3, 85.9, 123.9,
1H NMR spectra were obtained on either a General Electric QE Plus
300-MHz spectrometer or Bruker DPX 400- or 500-MHz spectrometers.
1H NMR spectra were recorded relative to residual protiated solvent.
13C NMR spectra were obtained at 100.6 MHz on a Bruker DPX 400-
MHz instrument, and chemical shifts were recorded relative to the
solvent resonance. Both H NMR and 13C NMR chemical shifts are
1
reported in parts per million downfield from tetramethylsilane. 31P NMR
spectra were obtained at 121.6 or 202.4 MHz on a General Electric
Omega 300-MHz or 500-MHz instrument and chemical shifts are
reported relative to 85% H3PO4. Elemental analysis was performed by
Robertson Microlit Laboratories, Inc., Madison, NJ. High-resolution
mass spectrometry was performed by the University of Illinois at
Urbana-Champaign on a Micromass 70-VSE instrument.
1
124.2, 124.8, 126.5, 126.9, 126.9 (overlap of signals observed by H/
13C correlation spectroscopy), 127.5, 127.7, 127.9, 128.3 (vt, J ) 3.9
Hz), 130.0, 132.1, 133.3, 133.5 (vt, J ) 20.5 Hz), 133.9, 135.0 (vt,
J ) 6.5 Hz), 148.1, 149.2, 190.4 (dt, JCRh ) 62.5 Hz, JCP ) 19.3 Hz).
p-Chlorobenzaldehyde, p-trifluoromethylbenzaldehyde, o-tolualde-
hyde, 2-naphthaldehyde, and 2-naphthoyl chloride were purchased from
(32) Evans, D.; Osborn, J. A.; Wilkinson, G. Inorg. Synth. 1968, 11, 99.
(33) De Graaf, P. W. J.; Boersma, J.; Van der Kerk, G. J. M. J. Organomet.
Chem. 1977, 127, 391.
(30) (a) Murahashi, S.; Naota, T.; Ito, K.; Maeda, Y.; Taki, H. J. Org. Chem.
1987, 52, 4319. (b) Ito, T.; Horino, H.; Koshiro, Y.; Yamamoto, A. Bull.
Chem. Soc. Jpn. 1982, 55, 504.
(34) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
(35) Prepared by deprotonation of the corresponding (2-naphthyl)(p-tolyl)-
methanol with excess NaH in THF, giving a viscous oil upon filtration
and removal of all volatile materials.
(31) Han, R.; Hillhouse, G. L. J. Am. Chem. Soc. 1997, 119, 8135.
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1677

A R T I C L E S
Krug and Hartwig
31P NMR (202.4 MHz, C6D6): 28.4 (JPRh ) 149 Hz). Anal. Calcd for
C55H45O2P2Rh: C, 73.17; H, 5.02. Found: C, 72.94; H, 5.25.
Representative Procedure for the Reactions of Complexes 1-3
with Aldehydes in C6D6. To a small vial were weighed 9.0 mg (0.011
mmol) of 1 and about 1 mg of Cp2Fe. C6D6 (0.7 mL) was added via
syringe, and the yellow suspension was transferred to an NMR tube,
which was subsequently warmed in a 55 °C oil bath for 5 min to ensure
temperature for 1.5 h. The volatile materials were removed using rotary
evaporation, and the products were extracted into EtOAc (1 × 20 mL).
The organic extract was washed with water, NaHCO3, and brine and
dried over anhydrous MgSO4. The solution was filtered, and all volatile
materials were removed in vacuo. The title compound was isolated in
pure form following preparatory TLC (5% EtOAc/hexanes) as a clear
oil in 66% yield. 1H NMR (500 MHz, C6D6): δ 2.07 (s, 3H), 6.99 (d,
J ) 7.5 Hz, 2H), 7.13-7.23 (m, 4H), 7.43-7.61 (m, 10H), 7.97 (s,
1H), 8.35 (dd, J ) 8.5 Hz, J ) 1.5 Hz, 1H), 8.87 (s, 1H). 13C NMR
(100.6 MHz, CDCl3): δ 21.1, 77.6, 125.0, 125.3, 126.0, 126.1, 126.2,
126.6, 127.3, 127.4, 127.6, 127.7, 128.1, 128.2, 128.3, 128.4, 129.3,
129.4, 131.3, 132.4, 132.9, 133.1, 135.6, 137.2, 137.7, 137.8, 165.8.
HRMS calcd for C29H22O2: 402.1620; found 402.1624.
1
complete dissolution of 1. An H NMR spectrum was acquired, and
the solution was transferred to a small vial equipped with a magnetic
stir bar. Aldehyde (1.5 equiv) was added via syringe (or as a solid) to
the solution, and the vial was capped and placed in an 85 °C oil bath
1
for a specified period of time (Table 1). An H NMR spectrum was
acquired following completion of the reaction, and a yield was
calculated on the basis of the amount of ketone formed relative to the
amount of 1 used in the reaction.
Representative Procedure for Kinetic Experiments of 1 with
2-Naphthaldehyde. To a small vial was weighed 9.0 mg (0.011 mmol)
of 1. C6D6 (0.7 mL) was added via syringe, and the suspension was
transferred to an NMR tube. The contents were warmed to 50 °C for
2-3 min or until 1 was entirely dissolved. Ten equivalents of
2-naphthaldehyde or 2-naphthaldehyde-d1 were added to the yellow
solution, and the sample was placed in the NMR probe at 60 °C. The
intensity of the doublet at δ ) 6.37 in the 1H NMR spectrum of 1 was
Synthesis of Benzhydrol from KF3BPh and Benzaldehyde Using
Rhodium Catalysis. To a small vial equipped with stir bar were placed
80 mg (0.75 mmol) of benzaldehyde, 287 mg (1.55 mmol) of KF3-
BPh, and 52 mg (0.075 mmol) of (PPh3)2Rh(CO)Cl. THF (1.5 mL)
was added, and the vial was capped with a piercable septum. Degassed
H2O (1.0 mL) was added via syringe, and the mixture was stirred at
80 °C for 15 h. The mixture was removed from the oil bath, diluted
with H2O (15 mL), and extracted with EtOAc (1 × 20 mL). The organic
extract was washed with brine, dried over anhydrous MgSO4, and
filtered. All volatile materials were removed using rotary evaporation.
The solid residue that remained was purified by chromatography on
silica gel using 10% EtOAc in hexane to give a 43% yield of pure
benzhydrol. 1H NMR (400 MHz, CDCl3): δ 2.23 (d, J ) 3.2 Hz, 1H),
5.87 (d, J ) 3.6 Hz, 1H), 7.28-7.41 (m, 10 H).
Representative Procedure for the Reactions of Complexes 1 and
2 with Aldehydes in THF-d8 and D2O. To a small vial were weighed
9.0 mg (0.011 mmol) of 1 and about 1 mg of Cp2Fe or 1,3,5-
trimethoxybenzene. Addition of THF-d8 (0.7 mL) via syringe generated
a clear, yellow solution. An 1H NMR spectrum was acquired, and the
solution was transferred to a small vial equipped with a magnetic stir
bar. Aldehyde (20 equiv) was added via syringe (or as a solid) to the
solution, and the vial was capped with a piercable septum. Degassed
D2O (0.1 mL) was added via syringe, and the resulting solution was
stirred at the specified temperature and period of time (Scheme 2). An
1H NMR spectrum was acquired following completion of the reaction,
and a yield was calculated on the basis of the amount of carbinol formed
relative to the amount of 1 or 2 used in the reaction.
1
monitored over 2 h by acquiring H NMR spectra every 30 s. Rate
constants were determined by fitting the data to an exponential decay
using KaleidaGraph software.
Independent Preparation of Diarylmethanols and Diaryl Ketones.
All products that are not commercially available have been reported
previously14a,37-42 and were synthesized according to the following
procedure: Into a 50 mL two-neck round-bottom flask equipped with
a magnetic stir bar was placed 1.00 g of aldehyde. Dry Et2O (7-9
mL) was then added via syringe. The solution was cooled to 0 °C, and
1.5 equiv of p-tolylmagnesium bromide was added dropwise via syringe.
The solution was allowed to warm to room temperature, and the solution
was stirred for 1 h. Upon formation of a precipitate, 3-5 mL of dry
THF was added, and the solution was stirred for an additional hour.
Excess Grignard reagent was then quenched with aqueous ammonium
chloride, and the organic products were extracted with Et2O (1 × 40
mL). The extracts were washed with brine, dried over MgSO4, and
filtered, and the volatile materials were removed under reduced pressure.
No further purification of the crude alcohol was performed.
The crude alcohol (500 mg) was placed into a 50 mL two-neck
round-bottom flask equipped with a stir bar. Dry CH2Cl2 (8 mL) was
added via syringe. While stirring, 1.5 equiv of pyridinium chlorochro-
mate was added as a solid, giving a dark-colored solution. After 2 h,
the solution was filtered through Celite, and the ketone product was
purified using silica gel chromatography (CH2Cl2 eluent). 4-Methyl-
benzophenone:36 1H NMR (300 MHz, C6D6) δ 2.00 (s, 3H), 6.87 (d,
J ) 8.1 Hz, 2H), 7.13-7.05 (m, 3H), 7.76-7.71 (m, 4H). 4-Methyl-
4′-trifluoromethylbenzophenone:37 1H NMR (300 MHz, C6D6) δ 2.00
(s, 3H), 6.88 (d, J ) 8.4 Hz, 2H), 7.20 (d, J ) 8.4 Hz, 2H), 7.46 (d,
J ) 8.1 Hz, 2H), 7.61 (d, J ) 8.4 Hz, 2H). (4-Methylphenyl)naphthyl
ketone:38 1H NMR (300 MHz, C6D6) δ 2.03 (s, 3H), 6.92 (d, J ) 7.8
Hz, 2H), 8.19 (s, 1H), 8.04 (dd, J ) 8.7 Hz, J ) 1.8 Hz, 1H), 7.26 (m,
2H), 7.47-7.58 (m, 3H), 7.79 (d, J ) 8.1 Hz, 2H). 4-Methyl-2′-
methylbenzophenone:36 1H NMR (300 MHz, C6D6) δ 1.96 (s, 3H), 2.28
(s, 3H), 6.85 (d, J ) 8.1 Hz, 2H), 6.86-7.18 (m, 4H), 7.80 (d, J ) 8.1
Hz, 2H). 4-Methyl-4′-methoxybenzophenone:36 1H NMR (300 MHz,
C6D6) δ 2.03 (s, 3H), 3.19 (s, 3H), 6.65 (d, J ) 9.0 Hz, 2H), 6.92 (d,
J ) 8.4 Hz, 2H), 7.76 (d, J ) 8.4 Hz, 2H), 7.86 (d, J ) 8.7 Hz, 2H).
2-Methylbenzophenone:36 1H NMR (400 MHz, C6D6) δ 2.25 (s, 3H),
6.88-7.15 (m, 7H), 7.78-7.80 (m, 2H). (4-Methylphenyl)(phenyl)-
methanol:36 1H NMR (400 MHz, CDCl3) δ 2.18 (s, 1H), 2.34 (s, 3H),
5.84 (s, 1H), 7.16 (d, J ) 8.4 Hz, 2H), 7.29 (s, 1H), 7.33-7.41 (m,
Reaction between HRh(CO)(PPh3)3 and 1. Into a small vial were
placed 10 mg (0.012 mmol) of 1 and about 1 mg of 1,3,5-trimethoxy-
benzene. C6D6 (0.7 mL) was added, and the suspension was transferred
to an NMR tube. The sample was warmed in a 70 °C oil bath for 5
min and occasionally shaken until 1 was completely dissolved. An 1H
NMR spectrum was acquired, and the sample was transferred to a vial
containing 11 mg (0.012 mmol) of HRh(CO)(PPh3)3. The sample was
1
heated at 85 °C for 2 h. An H NMR spectrum was acquired, and the
yield of toluene produced was calculated to be 27%.
Reaction between Rhodium Alkoxide 6 and 2-Naphthaldehyde.
Into a small vial were placed 9.0 mg (0.010 mmol) of 6 and 16 mg
(0.10 mmol, 10 equiv) of 2-naphthaldehyde. The reagents were
dissolved in 0.7 mL of C6D6. 1,3,5-Trimethoxybenzene (1 mg) was
added to the solution, and the solution was transferred to an NMR tube.
An 1H NMR spectrum was acquired. The sample was heated at 85 °C
1
for 0.5 h, after which time alkoxide 6 was consumed. An H NMR
spectrum was acquired, from which a 57% yield of [(p-tolyl)(2-
naphthyl)methyl] 2-naphthoate was calculated.
Independent Preparation of [(p-Tolyl)(2-naphthyl)methyl] 2-Naph-
thoate. Into a 25 mL round-bottom flask equipped with a magnetic
stir bar were placed 80.0 mg (0.322 mmol) of (p-tolyl)(2-naphthyl)-
methanol and 184 mg (0.967 mmol, 3 equiv) of 2-naphthoyl chloride.
Dry CH2Cl2 (4 mL) was added via syringe. Et3N (0.670 mL, 4.81 mmol,
15 equiv) was added, and the resulting solution was stirred at room
(36) Commercially available.
(37) French, F. A.; DoAmaral, J. R.; Blanz, E. J.; French, D. A. J. Med. Chem.
1971, 14, 862.
(38) Myata, A.; Matsunaga, K.; Ishikawa, M. JP Patent 07089894 A2, 1995.
9
1678 J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002

Aldehyde Insertion into Rh−Aryl and −Alkoxide Complexes
A R T I C L E S
6H). (2-methylphenyl)(phenyl)methanol:36 1H NMR (300 MHz,
CDCl3): δ 2.14 (s, 1H), 2.27 (s, 3H), 6.03 (s, 1H), 7.15-7.35 (m,
8H), 7.52-7.55 (m, 1H). (2-Methylphenyl)(4′-methylphenyl)methanol:
(s, 3H), 6.00 (s, 1H), 7.17 (d, J ) 8.4 Hz, 2H), 7.32 (d, J ) 8.0 Hz,
2H), 7.42-7.51 (m, 3H), 7.79-7.86 (m, 3H), 7.92 (s, 1H). (4-
Methylphenyl)(2′-methoxyphenyl)methanol:14a 1H NMR (400 MHz,
CDCl3) δ 2.13 (s, 1H), 2.34 (s, 3H), 3.80 (s, 3H), 5.79 (s, 1H), 6.87 (d,
J ) 8.8 Hz, 2H), 7.16 (d, J ) 8.4 Hz, 2H), 7.27 (d, J ) 7.6 Hz, 2H),
7.29 (d, J ) 9.0 Hz, 2H).
39
1H NMR (400 MHz, CDCl3) δ 2.15 (s, 1H), 2.31 (s, 3H), 2.40 (s,
3H), 6.05 (s, 1H), 7.19-7.25 (m, 3H), 7.29-7.34 (m, 4H), 7.61 (d,
J ) 1.2 Hz, 1H). (2-Methylphenyl)(4′-chlorophenyl)methanol:40 1H
NMR (300 MHz, CDCl3) δ 2.16 (s, 1H), 2.26 (s, 3H), 6.00 (s, 1H),
7.15-7.18 (m, 2H), 7.22-7.33 (m, 6H). (4-Methylphenyl)(4′-chlo-
rophenyl)methanol:41 1H NMR (400 MHz, CDCl3) δ 2.14 (s, 1H), 2.31
(s, 3H), 5.73 (s, 1H), 7.11-7.29 (m, 8H). (4-Methylphenyl)(2-naph-
thyl)methanol:42 1H NMR (400 MHz, CDCl3) δ 2.29 (s, 1H), 2.35
Acknowledgment. This work was supported by the Depart-
ment of Energy, Office of Basic Energy Sciences.
Supporting Information Available: Full structural charac-
terization of 1. This information is available free of charge via
the Internet at http://www.pubs.acs.org.
(39) Okubo, M.; Hayashi, S.; Matsunaga, M.; Uematsu, Y. Bull. Chem. Soc.
Jpn. 1981, 54, 2337.
JA017401E
(40) Barkow, A.; Gruetzmacher, H.-F. Int. J. Mass Spectrom. Ion Processes
1995, 142, 195.
(42) Artico, M.; Stefancich, G.; Silvestri, R.; Massa, S.; Apuzzo, G.; Simonetti,
(41) Pourbaix, C.; Carreaux, F.; Carboni, B. Org. Lett. 2001, 3, 803.
G. Eur. J. Med. Chem. 1992, 27, 693.
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1679