Aromatic and aldehyde carbon-hydrogen bond activation at cationic Rh(III) centers. Evaluation of electronic substituent effects on aldehyde binding and C-H oxidative addition

Article abstract of DOI:10.1016/j.poly.2004.09.005

Cationic rhodium methyl complexes, [Cp*(L)Rh(Me)(CH ₂Cl₂)]⁺ (L = PMe₃, P(OMe) ₃) react with benzene to yield the corresponding phenyl complexes, [Cp*(L)Rh(Ph)(CH₂Cl₂)]⁺. Reactions of [Cp*(L)Rh(Me)(CH₂Cl₂)]⁺ with p-X-substituted benzaldehydes (X = -CF₃, -CH₃, and -OMe) produce acyl aldehyde adducts, [Cp*(L)Rh(C(O)C₆H ₄X)(p-XC₆H₄CHO)]⁺. In the case of L = PMe₃, decarbonylation of the aldehyde adducts occurs cleanly to form [Cp*(PMe₃)Rh(C₆H₄X)(CO)] ⁺. For L = P(OMe)₃, decarbonylation is a more complicated process. Cationic rhodium methyl complexes, [Cp(PMe3)Rh(Me)(CH2Cl2)] BAr4′(1) and [Cp(P(OMe)3)Rh(Me)(CH2Cl2)]BAr4′(3), react with benzene to yield the corresponding phenyl complexes, [Cp(PMe3)Rh(Ph)(CH2Cl2)] BAr4′(6) and [Cp(P(OMe)3)Rh(Ph)(CH2Cl2)]BAr4′(7). First-order rate constants observed in 1.1 M benzene in CD₂Cl₂ at 25°C are (2.1 ± 0.2) × 10^-5 s^-1 and (1.9 ± 0.2) × 10^-5 s^-1, respectively. Reactions of 1 and 3 with p-X-substituted benzaldehydes (X = -CF₃, -CH₃, and -OMe) initially produce the σ-aldehyde adducts, [Cp(L)Rh(Me)(p-XC6H4CHO)] BAr4′ (L = PMe₃ (15), P(OMe)₃ (16)). Exchange of free with bound aldehyde occurs via a dissociative process and quantitative NMR rate measurements show that complexes of 1 exchange faster than those of 3 and that less basic aldehydes exchange faster than more basic aldehydes (p-CF ₃C₆H₄CHO > p-CH₃C ₆H₄CHO > p-CH₃OC₆H ₄CHO). The aldehyde adducts undergo C-H bond activation to produce initially methane plus acyl aldehyde adducts, [Cp(L)Rh(C(O)C6H4X)(p-XC6H4CHO)] BAr4′ (L = PMe₃ (17), P(OMe)₃ (18)). Rates of C-H activation are correlated with aldehyde exchange rates; activation barriers of weakly bound aldehydes are lower than more strongly bound aldehydes. In the case of L = PMe₃, decarbonylation of the aldehyde adducts occurs cleanly to form aryl carbonyl complexes, [Cp(PMe3)Rh(C6H4X)(CO)]BAr4′. For L = P(OMe)₃, decarbonylation is a more complicated process; some intermediates and products have been identified by NMR spectroscopy.

Full text of DOI:10.1016/j.poly.2004.09.005

Polyhedron 23 (2004) 2943–2954
www.elsevier.com/locate/poly
Aromatic and aldehyde carbon–hydrogen bond activation at
cationic Rh(III) centers. Evaluation of electronic substituent
effects on aldehyde binding and C–H oxidative addition
a
a
b,
a,
*
Britton K. Corkey , Felicia L. Taw , Robert G. Bergman *, Maurice Brookhart
a
Department of Chemistry, University of North Carolina at Chapel Hill, CB #3290, Chapel Hill, NC 27599-3290, USA
Department of Chemistry, University of California and Division of Chemical Sciences, Lawrence Berkeley National Laboratory,
b
Berkeley, CA 94720-1460, USA
Received 4 June 2004; accepted 2 September 2004
Available online 26 October 2004
Dedicated to Malcolm L.H. Green for his pathbreaking contributions to organometallic chemistry, his international collegiality, his wit,
and his warmth
Abstract
Cationic rhodium methyl complexes, ½CpꢀðPMe3ÞRhðMeÞðCH2Cl2ÞꢁBAr0 ð1Þ and ½CpꢀðPðOMeÞ ÞRhðMeÞðCH2Cl2ÞꢁBAr0 ð3Þ,
4
3
4
react with benzene to yield the corresponding phenyl complexes, ½CpꢀðPMe3ÞRhðPhÞðCH2Cl2ÞꢁBAr0 ð6Þ and
4
½CpꢀðPðOMeÞ ÞRhðPhÞðCH2Cl2ÞꢁBAr0 ð7Þ. First-order rate constants observed in 1.1 M benzene in CD2Cl2 at 25 ꢀC are
3
4
(2.1 0.2) · 10ꢂ5 sꢂ1 and (1.9 0.2) · 10ꢂ5
s
ꢂ1, respectively. Reactions of 1 and 3 with p-X-substituted benzaldehydes (X =
–CF3, –CH3, and –OMe) initially produce the r-aldehyde adducts, ½CpꢀðLÞRhðMeÞðp-XC6H4CHOÞꢁBAr0 (L = PMe3 (15),
4
P(OMe)3 (16)). Exchange of free with bound aldehyde occurs via a dissociative process and quantitative NMR rate measurements
show that complexes of 1 exchange faster than those of 3 and that less basic aldehydes exchange faster than more basic aldehydes (p-
CF3C6H4CHO > p-CH3C6H4CHO > p-CH3OC6H4CHO). The aldehyde adducts undergo C–H bond activation to produce initially
methane plus acyl aldehyde adducts, ½CpꢀðLÞRhðCðOÞC6H4XÞðp ꢂ XC6H4CHOÞꢁBAr0 (L = PMe3 (17), P(OMe)3 (18)). Rates of
4
C–H activation are correlated with aldehyde exchange rates; activation barriers of weakly bound aldehydes are lower than more
strongly bound aldehydes. In the case of L = PMe3, decarbonylation of the aldehyde adducts occurs cleanly to form aryl carbonyl
complexes, ½CpꢀðPMe3ÞRhðC6H4XÞðCOÞꢁBAr0 . For L = P(OMe)3, decarbonylation is a more complicated process; some intermedi-
4
ates and products have been identified by NMR spectroscopy.
ꢁ 2004 Elsevier Ltd. All rights reserved.
Keywords: C–H bond activation; Rhodium(III); Benzene activation; Aldehyde activation
1. Introduction
plexes, take place at metal centers in relatively low for-
mal oxidation states. This has led to the general
perception that electron-rich complexes are required in
order to make this important oxidative addition process
exergonic and therefore capable of generating stable
products.
However, the platinum-based alkane functionaliza-
tion reactions observed many years ago by Shilov
and his coworkers [1], and the dehydrogenation
Early examples of the oxidative addition reactions of
alkane C–H bonds, leading to hydrido(alkyl)metal com-
*
Corresponding authors. Present address: Department of Chemis-
try, Los Alamos National Laboratory, Mailstop J514, Los Alamos,
USA. Tel.: +1 505 6673968; fax: +1 505 6679905.
E-mail address: ftaw@lanl.gov (F.L. Taw).
0277-5387/$ - see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.09.005

2944
B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
reactions subsequently observed using high-valent irid-
ium and rhenium complexes by the Crabtree [2] and
Felkin [3] groups, were early indications that more
electron-deficient metal centers could also undergo
C–H oxidative addition. More recently, direct observa-
tion of C–H oxidative addition reactions at iridium
(III) [4], as well as analogous reactions that take place
in Pt(II) complexes [5], have made clear that such
processes can occur at metal centers that are relatively
electrophilic, and in some cases can be overall exer-
gonic. This has given rise to a substantial increase in
the number of studies directed toward alkane activa-
tion reactions involving higher-valent late transition
metal complexes in recent years.
NMR resonance of the Rh–CH3 group exhibited a signal
at 1.19 ppm (dd, 2JP–C = 37.1 Hz, 1JRh–C = 22.0 Hz).
+ BAr'4
-
+ NaBAr'4
- NaCl
CH2Cl2
Cp*
Rh
Cp*
Rh
Me
Me
Cl
(MeO)3P
(MeO)3P
ClCH2Cl
4
3
ð1Þ
2.2. Carbon–hydrogen bond activation studies
In contrast to BergmanÕs cationic iridium (III) com-
plex, ½CpꢀðPMe3ÞIrðMeÞðCH2Cl2ÞꢁBAr0 ð5Þ [4b], the
4
analogous rhodium methyl complex 1 does not react
with alkanes to any appreciable extent, even at 45
ꢀC. Addition of 500 equivalents of pentane to a
CD2Cl2 solution of 1 resulted in the observation of
only trace amounts of methane (by 1H NMR) over
the course of several days at 25 ꢀC. Similar results
were obtained with the corresponding Rh phosphite
compound 3. Given the inertness toward alkanes, stud-
ies of C–H bond activations using 1 and 3 focused on
the more reactive substrates: benzene and aryl
aldehydes.
The cationic Ir(III) C–H oxidative addition reactions
referred to above lead to relatively rare examples of
organometallic positively-charged Ir(V) intermediates
[6]. Many of these have been generated only in transient
form, but a few have been found to be stable enough to
isolate or detect in solution. In contrast to this growing
body of research on Ir(III) C–H activation, much less
attention has been directed toward the search for analo-
gous reactions at Rh(III). In view of the fact that penta-
methylcyclopentadienylrhodium(I) complexes were
ultimately discovered to undergo C–H oxidative addition
reactions analogous to those of their iridium congeners
[7], we felt it would be interesting to look for Rh(III)-
to-Rh(V) C–H oxidative addition reactions in related sys-
tems as well. This manuscript reports the results of our
investigation of C–H bond activations of benzene and
2.3. Carbon–hydrogen bond activation of benzene
Rhodium methyl complexes 1 and 3 react with ben-
zene to yield methane and the cationic rhodium phenyl
complexes 6 and 7, respectively (Eq. (2)). To further ver-
ify the structure of product 6, this compound was inde-
pendently synthesized and fully characterized by NMR
spectroscopy and X-ray diffraction studies (see below).
Product 7 was directly isolated from the C–H activation
reaction of benzene and characterized by NMR
spectroscopy.
aryl aldehydes by ½CpꢀðLÞRhðMeÞðCH2Cl2ÞꢁBAr0
4
(L = PMe3 (1), P(OMe)3 (3)).
2. Results and discussion
+ BAr'4
-
+ BAr'4
-
Cp*
Rh
Cp*
Rh
2.1. Synthesis of cationic rhodium(III) methyl complexes,
[Cpꢀ(L)Rh(Me)(CH2Cl2)]BAr04
Me
Me
(L = PMe3
P(OMe)3 (3), Ar0 = 3,5-(CF3)2C6H3)
(1),
+ CH2Cl2
L
L
Keq
ClCH2Cl
L = PMe3 (1)
L = P(OMe)3 (3)
L = PMe3 (8)
L = P(OMe)3 (9)
Synthesis of ½CpꢀðPMe3ÞRhðMeÞðCH2Cl2ÞꢁBAr0 ð1Þ
4
by treatment of Cp*(PMe3)Rh(Me)(Cl) (2) with
NaBAr04 has been previously reported by us [8]. This com-
plex was fully characterized by NMR spectroscopy and
X-ray diffraction studies. The phosphite analogue
½CpꢀðPðOMeÞ ÞRhðMeÞðCH2Cl2ÞꢁBAr0 ð3Þ was synthe-
-
+ BAr'4
Cp*
Ph
Rh
L
k1
ClCH2Cl
3
4
L = PMe3 (6)
L = P(OMe)3 (7)
sized in a similar manner (Eq. (1)). The rhodium methyl
chloride complex, Cp*(P(OMe)3)Rh(Me)(Cl) (4), was
prepared by reaction of previously reported Cp*(P(O-
Me)3)RhCl2 [9] with MeLi. The 1H NMR spectrum of 3
ð2Þ
The rates of these reactions are sufficiently slow that
clean conversions can be achieved only by using high ra-
tios of benzene to rhodium complex. Under these condi-
tions, the reactions exhibit clean pseudo-first order
kinetics, as determined by integrations of H NMR sig-
nals. Table 1 summarizes the observed first-order rate
3
in CD2Cl2 showed signals at 3.78 (d, JP–H = 11.4 Hz)
4
for P(OMe)3, 1.63 ppm (d, JP–H = 4.2 Hz) for Cp*,
3
and 1.02 ppm (dd, JP–H = 5.5 Hz, JRh–H = 1.5 Hz) for
2
the Rh–CH3 group. The 31P{1H} NMR signal appeared
1
1
at 126.9 ppm (d, JRh–P = 269 Hz), and the 13C{1H}

B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
2945
Table 1
First-order rate constants for C–H activation of benzene by 1, 3, 5, and 10
½CpꢀðLÞMðMeÞðCH2Cl2ÞꢁBAr04
L = PMe3
L = P(OMe)3
Rate ratio
M = Rha
M = Irb
(2.1 0.2) · 10ꢂ5 sꢂ1
(8.4 0.8) · 10ꢂ3 sꢂ1
(1.9 0.2) · 10ꢂ5 sꢂ1
(3.0 0.3) · 10ꢂ4 sꢂ1
(1/3) = 1.1
(5/10) = 28.0
a
1.1 M C6H6 in CD2Cl2, 25 2 ꢀC.
0.26 M C6H6 in CD2Cl2, 0 ꢀC.
b
constants for the reactions of 1 and 3 (0.02 M) with
1
2.4. Independent synthesis and characterization of
[Cpꢀ(PMe3)Rh(Ph)(CH2Cl2)]BAr04 (6)
1.1 M benzene in CD2Cl2 at 25 2 ꢀC. For compari-
son, the reported rate constants [10] for the correspond-
ing iridium analogues 5 and ½CpꢀðPðOMeÞ ÞIrðMeÞ
To verify the identity of the product derived from
C–H activation of benzene by rhodium methyl complex
1, the cationic rhodium phenyl complex (6) was inde-
pendently synthesized by adding NaBAr04 to a dichloro-
methane solution of previously reported Cp*(PMe3)Rh
(Ph)(Cl) [11]. X-ray quality, orange–red crystals of 6
were isolated in 70% yield. This compound is more ther-
mally and air-sensitive than the rhodium methyl com-
plex 1, but can be stored under inert conditions at ꢂ30
ꢀC for extended periods of time. An ORTEP diagram
of 6 is shown in Fig. 1, with some selected bond dis-
tances and bond angles listed in Table 2. The bond dis-
tance between Rh and the ipso aryl carbon of the phenyl
3
ðCH2Cl2ÞꢁBAr0 ð10Þ reacting at 0 ꢀC with 0.26 M ben-
4
zene in CD2Cl2 are also listed.
In general, the iridium complexes 5 and 10 are far
more reactive toward benzene than rhodium analogues
1 and 3. Correcting for benzene concentrations, 5 reacts
with benzene ca. 103 times faster than either 1 or 3 at a
considerably lower temperature (0 ꢀC vs. 25 ꢀC). A sig-
nificant feature of these comparisons is that, in the case
of the Ir examples, the PMe3 complex exhibits a rate ca.
30· that of the P(OMe)3 complex; in contrast, the rates
are comparable in the rhodium systems. Bergman has
postulated that these reactions occur through the 16-
electron species 11 and 12 (Eq. (3)) and that, while the
presumably more electrophilic species 12 is expected to
be more reactive (k1 for P(OMe)3 > k1 for PMe3), the va-
lue of Keq for P(OMe)3 is much less than Keq for (PMe3),
resulting in KeqðPMe Þk1ðPMe Þ > KeqðPðOMeÞ Þk1ðPðOMeÞ Þ [10].
˚
ring is 2.026(8) A, which is shorter than the Rh–CH3
˚
bond length (2.106(5) A) of complex 1 [8], as is expected
for a metal bonded to an sp2-hybridized carbon versus
an sp3 carbon. However, the Rh–Cl distance of phenyl
˚
complex 6 is 2.512(2) A and differs only by 0.02 A rela-
˚
3
3
3
3
˚
tive to the bond distance of 2.488(1) A observed for the
Rh–Cl bond of methyl complex 2 [8].
In the case of the rhodium complexes, it appears that
the k1ðPMe Þ : k1ðPðOMeÞ Þ ratio is counterbalanced by the
3
3
KeqðPðOMeÞ Þ : KeqðPMe Þ ratio, and the observed rates of
3
3
benzene activation are essentially equal (see Eq. (2)).
The assumptions that Rh phosphite complex 9 is more
electrophilic than the Rh phosphine complex 8 and that
KeqðPMe Þ > KeqðPðOMeÞ Þ receive independent support from
2.5. Carbon–hydrogen bond activation of aryl aldehydes
Bergman has shown that the iridium (III) complex
Cp*(PMe3)Ir(Me)(OTf) reacts rapidly with benzalde-
hyde at ꢂ80 ꢀC to form an g1-(O)-bound aldehyde
3
3
observations described below in connection with the C–
H bond activation of aryl aldehydes.
+ BAr'4
-
+ BAr'4
-
Cp*
Ir
Cp*
Ir
Me
Me
+ CH2Cl2
L
L
Keq
ClCH2Cl
L = PMe3 (5)
L = PMe3 (11)
L = P(OMe)3 (10)
L = P(OMe)3 (12)
+ BAr'4
-
Cp*
Ph
ClCH2Cl
L = PMe3 (13)
Ir
L
k1
L = P(OMe)3 (14)
ð3Þ
1
Reactions of 1 and 3 in 2.2 M benzene in CD2Cl2 at 25 2 ꢀC give
pseudo first-order rate constants of (3.2 0.2) · 10ꢂ5 sꢂ1 and
(3.8 0.4) · 10ꢂ5 ꢂ1, respectively. These data establish a clear
dependence of the rate on benzene concentration.
Fig. 1. ORTEP diagram of [Cp*(PMe3)Rh(Ph)(CH2Cl2)]+ (6, BAr40ꢂ
counterion omitted for clarity).
s

2946
B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
Table 2
Selected bond distances and bond angles for complex 6
The trends follow the expected electronic effects. For
both series 15a–15c and 16a–16c the order of dissocia-
tion is p-CF3C6H4CHO > p-CH3C6H4CHO > p-CH3-
OC6H4CHO which inversely parallels the order of
basicity of the aldehydes. In comparing 15a–15c with
16a–16c in each of the three pairs the barrier to dissoci-
ation of aldehyde from the more electron-deficient
P(OMe)3 complex is ca. 1.7 kcal/mol higher than that
for the more electron-rich PMe3 complex. The strongest
Rh(III)-aldehyde interaction is between the more electro-
philic phosphite complex 16 and the most electron-rich
aldehyde, p-CH3OC6H4CHO. The weakest interaction
is between the less electrophilic PMe3 complex 15 and
the most electron-deficient aldehyde, p-CF3C6H4CHO.
The C–H activation chemistry of aryl aldehydes by
rhodium complexes 1 and 3 is similar to the iridium
Bond distance
˚
(A)
Bond angle
(ꢀ)
Rh(1)–C(24)
Rh(1)–P(1)
Rh(1)–C(11)
Rh(1)–Cl(1)
2.195(6)
2.374(2)
2.026(8)
2.512(2)
C(24)–Rh(1)–P(1)
C(11)–Rh(1)–Cl(1)
P(1)–Rh(1)–C(11)
P(1)–Rh(1)–Cl(1)
101.5(2)
98.3(2)
87.9(3)
84.9(8)
adduct [12]. Upon warming to ꢂ60 ꢀC, the adduct
undergoes C–H bond activation and decarbonylation
to form the iridium phenyl carbonyl complex,
[Cp*(PMe3)Ir(Ph)(CO)]OTf, and methane. Similarly,
the cationic rhodium methyl complexes 1 and 3 react
with aryl aldehydes (tolualdehyde, anisaldehyde, and
4-(trifluoromethyl)benzaldehyde) in CD2Cl2 at ꢂ80 ꢀC
to form g1-aldehyde adducts (Eq. (4)).
O
H
X
+ BAr'4
+ BAr'4
-
-
Cp*
Rh
Cp*
Rh
(X = CF3, CH3, OMe)
Me
O
Me
L
L
ð4Þ
Cl2CH2
CD2Cl2
L = PMe3 (1)
L = P(OMe)3 (3)
H
X
L = PMe3; X = CF3 (15a), CH3 (15b), OMe (15c)
L = P(OMe)3; X = CF3 (16a), CH3 (16b), OMe (16c)
When reactions with 1 and 3 are carried out using
1
excess aldehyde as substrate, H NMR resonances for
chemistry but more complex in the case of 3. Deinser-
tion products can react with 3 which complicates kinetic
measurements and gives rise to a mixture of products.
The most definitive kinetic studies were carried out using
a large excess of aldehyde. First, this approach ensures
that the equilibrium between the methylene chloride ad-
ducts 1 and 3 and the aldehyde adducts 15a–15c and
16a–16c lies strongly in favor of the aldehyde adducts.
Second, and critical in the case of 3, the C–H activation
reactions result in generation of the Rh acyl aldehyde
adducts 17 and 18. Little deinsertion occurs under these
conditions. The aldehyde adduct intermediate 15 or 16
builds up to high concentrations and clean first-order
kinetics for conversion to 17 or 18, respectively, are
exhibited over ca. two half-lives (Eq. (5)). Rates and free
energies of activation are summarized for these C–H
bond activation reactions in Tables 4 and 5.
the aldehydic proton of both the bound and free alde-
hydes can be detected at low temperatures. The lack of
rhodium coupling to the aldehydic hydrogen supports
the g1 structure. Upon warming, these resonances
broaden and coalesce. The rates for loss of bound alde-
hydes from Rh were assessed by measuring the changes
in line-width at half-height of the aldehydic protons
and applying the slow exchange equation, k = p(Dw).
A key finding is that the linewidth and thus the rate
of exchange of the bound aldehyde is independent of
the concentration of free aldehyde. This clearly indi-
cates the exchange occurs through a dissociative proc-
ess. Table 3 summarizes the DGà values obtained from
line broadening experiments together with 1H NMR
shifts for free and bound aldehyde at ꢂ88 ꢀC.
Table 3
Kinetic parameters for dissociation of bound aldehyde and 1H NMR shifts (in ppm) for free and bound aldehyde at ꢂ88 ꢀC
[Cp*(L)Rh(Me)(XC6H4CHO)]+(g1-aldehyde adduct)
k (sꢂ1
)
T ( 2 ꢀC)
DGà (kcal/mol)
d CHO (bound)
d CHO (free)
L = PMe3, X = CF3 (15a)
L = PMe3, X = CH3 (15b)
L = PMe3, X = OMe (15c)
L = P(OMe)3, X = CF3 (16a)
L = P(OMe)3, X = CH3 (16b)
L = P(OMe)3, X = OMe (16c)
50
60
ꢂ58
ꢂ38
ꢂ28
ꢂ18
0
10.8 0.1
11.7 0.2
12.1 0.2
12.4 0.1
13.4 0.2
13.7 0.1
9.38
9.13
8.97
9.33
9.02
8.88
10.02
9.87
9.79
10.02
9.86
9.79
75
115
105
110
7

B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
2947
Table 4
kobs of C–H activation using 50 equivalents of aldehyde (20 2 ꢀC)
[Cp*(L)Rh(Me)(XC6H4CHO)]+(g1-aldehyde adduct)
L = PMe3 (15)
5.4 0.4 · 10ꢂ4 ꢂ1
2.1 0.1 · 10ꢂ4 ꢂ1
9.0 0.5 · 10ꢂ5 sꢂ1
L = P(OMe)3 (16)
5.2 0.3 · 10ꢂ5 ꢂ1
1.2 0.4 · 10ꢂ5 ꢂ1
2.9 0.3 · 10ꢂ6 sꢂ1
Rate ratio (15/16)
X = CF3 (a)
X = CH3 (b)
X = OMe (c)
s
s
10
18
31
s
s
Table 5
DGà for activation of aldehydic C–H bonds (20 2 ꢀC)
[Cp*(L)Rh(Me)(XC6H4CHO)]+(g1-aldehyde adduct)
L = PMe3 (15)
L = P(OMe)3 (16)
X = CF3 (a)
X = CH3 (b)
X = OMe (c)
21.5 0.1 kcal/mol
22.1 0.1 kcal/mol
22.6 0.2 kcal/mol
22.9 0.1 kcal/mol
23.7 0.1 kcal/mol
24.6 0.1 kcal/mol
+ BAr'4
Similarly, the more electron-deficient aldehydes show
faster rates of dissociation and higher rates of C–H bond
activation (15a > 15b > 15c; 16a > 16b > 16c). These
rate trends can be rationalized by considering the ex-
pected substituent effects on the ground state aldehyde
complexes relative to the transition state for C–H bond
activation (Scheme 1). In the r-aldehyde complexes
there will be substantial partial positive charge on the
carbonyl carbon due to polarization of the C@O p bond
upon binding to the Lewis acidic Rh center. Ground
state energies of these r-complexes will be significantly
affected by resonance and inductive effects of para sub-
stituents. In the four-centered transition state for C–H
bond activation, Lewis acidic rhodium will no longer
be bound exclusively to oxygen, thus para-substituent
effects, especially p effects, should be less significant in
affecting relative transition state energies. In short, elec-
tron-donating substituents will stabilize the aldehyde ad-
ducts 15 and 16 more than the corresponding transition
states and thus retard the rate of C–H bond activation.
-
-
+ BAr'4
-CH4
X-C6H4CHO
Cp*
Rh
Cp*
Rh
O
Me
O
L
L
CD2Cl2
X
O
H
H
X
X
L = PMe3 (15)
L = P(OMe)3 (16)
L = PMe3 (17)
L = P(OMe)3 (18)
ð5Þ
As noted earlier, C–H bond activation of benzene by
1 and 3 occurs at essentially equal rates. In these cases
benzene is a weakly binding substrate and does not com-
pete with CH2Cl2. That is, no benzene adduct is ob-
served during the activation reaction. In the case of
aryl aldehyde activation, the aldehyde adducts, 15a–
15c and 16a–16c, rather than the CH2Cl2 adducts,
are the more stable species, and as shown in Scheme 1,
C–H bond activation is initiated from these species.
The rates of C–H bond activation of these complexes
correlate qualitatively with the rates of dissociation of
the aldehydes. The more electron-rich PMe3 complexes
show higher rates of dissociation and higher rates of
C–H bond activation than their P(OMe)3 congeners.
+
+
+ BAr'4
-
Cp*
Rh
Cp*
Rh
Cp*
Rh
O
O
- CH4
Me
O
Me
O
L
L
L
X
X
H
H
X
H
X
L = PMe3 (15)
L = P(OMe)3 (16)
(transition state)
+ BAr'4
-
Cp*
Rh
O
L
X
O
H
X
L = PMe3 (17)
L = P(OMe)3 (18)
Scheme 1.

2948
B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
-
-
+ BAr'4
+ BAr'4
Cp*
Rh
Cp*
Rh
When 5 equivalents of tolualdehyde is allowed to un-
13CO
Me
Me
dergo reaction with cationic Rh methyl complex 1 at
room temperature, facile C–H bond activation and
decarbonylation occurs, as evidenced by extrusion of
methane and formation of ½CpꢀðPMe3ÞRhðC6H4CH3Þ
ðCOÞꢁBAr04 ð19Þ. X-ray quality orange crystals of 19
were isolated via pentane layering of the reaction
mixture. The ORTEP diagram is shown in Fig. 2, with
some selected bond distances and bond angles listed in
Table 6.
(MeO)3P
(MeO)3P
CD2Cl2
Cl2CH2
13CO
3
20'
ð6Þ
The correspoꢀnding 13C-labeled Rh tolyl carbonyl
0
13
complex,
½Cp ðPðOMeÞ ÞRhðC6H4CH3Þð COÞꢁBAr4
3
ð210Þ, was generated by an analogous reaction using
½CpꢀðPðOMeÞ ÞRhðC6H4CH3ÞðCH2Cl2ÞꢁBAr0 ð22Þ, as
3
4
Contrary to the reaction described above between 1
and tolualdehyde, the reactions of Rh phosphite com-
plex 3 with aryl aldehydes do not result in clean forma-
tion of decarbonylation products. A variety of species
can be detected by 1H and 31P{1H} NMR spectroscopy.
The concentrations of these species fluctuate as a func-
tion of time, and vary with the particular aldehyde used
along with the initial ratio of Rh complex to aldehyde.
In the case of the reaction between 3 and tolualdehyde,
several reaction products and intermediates have been
identified by independent synthesis. Prior to proposing
a sequence of reactions for the C–H activation and
decarbonylation process, generation of potential inter-
mediates is outlined below.
shown in Scheme 2. The independent synthesis and
characterization of 22 is detailed in Section 4. Inter-
estingly, formation of 210 by exposure of a CD2Cl2
solution of 22 to 13CO was accompanied by forma-
tion of a rhodium acyl carbonyl complex (230), which
results from migratory insertion of carbon monoxide
from 210 followed by trapping with additional 13CO
(Scheme 2). Addition of excess P(OMe)3 to a mixture
of 210 and 230 led to the Rh bis-phosphite acyl com-
ꢀ
0
0
13
plex ½Cp ðPðOMeÞ Þ Rhð CðOÞC6H4CH3ÞꢁBAr4 ð24 Þ.
3
2
To generate Rh tolyl aldehyde adduct 25, excess tol-
ualdehyde was added to a CD2Cl2 solution of 22
(Scheme 2). NMR parameters for these species,
which have been generated in situ, are summarized
in Section 4.
The 13C-labeled Rh methyl 0carb0onyl complex,
ꢀ
13
½Cp ðPðOMeÞ ÞRhðMeÞð COÞꢁBAr4 ð20 Þ, was readily
Scheme 3 summarizes a proposed reaction sequence
which accounts for the various species observed during
the C–H activation and decarbonylation process involv-
ing cationic Rh methyl 3 and tolualdehyde. This reac-
tion proceeds over the course of several days at room
temperature, and was monitored by NMR spectroscopy.
As noted above, treatment of 3 with excess tolual-
dehyde (25–50 equivalents) results in immediate for-
mation of Rh aldehyde adduct 16b. After ca. 4
days, the C–H activation product, Rh acyl aldehyde
18b, is formed as the major species (Scheme 3). Ex-
change of free aldehyde with bound aldehyde in 18b
is rapid at room temperature, but distinct aldehydic
proton resonances for free and g1-bound aldehyde
3
generated in situ by exposure of a CD2Cl2 solution of
3 to 13CO at 25 ꢀC (Eq. (6)).
1
could be observed by H NMR spectroscopy at ꢂ88
ꢀC. Treatment of 18b with one equivalent of
P(OMe)3 results in complete conversion to the Rh
bis-phosphite acyl complex ½CpꢀðPðOMeÞ Þ RhðCðOÞ-
3
2
C6H4CH3ÞꢁBAr0 ð24Þ. In addition to the presence of
4
18b as the major species, the Rh tolyl carbonyl com-
plex ½CpꢀðPðOMeÞ ÞRhðC6H4CH3ÞðCOÞꢁBAr0 ð21Þ and
Fig. 2. ORTEP diagram of [Cp*(PMe3)Rh(C6H4CH3)(CO)]+ (19,
BAr04ꢂ counterion omitted for clarity).
3
4
the Rh methyl carbonyl complex ½CpꢀðPðOMeÞ Þ-
3
RhðMeÞðCOÞꢁBAr04 ð20Þ were also detected, along with
small amounts of unidentified rhodium compounds
(Scheme 3). Formation of 20 can be attributed to
transfer of CO from 21 to either 3 (CO displaces coor-
dinated dichloromethane) or 16b (CO displaces coor-
dinated aldehyde).
Table 6
Selected bond distances and bond angles for complex 19
˚
Bond distance (A)
Bond angle (ꢀ)
C(16)–Rh(1)–P(1) 124.3(2)
Rh(1)–C(16) 2.246(7)
Rh(1)–P(1)
Rh(1)–C(6)
Rh(1)–C(1)
C(1)–O(2)
2.298(3)
2.091(8)
1.879(8)
1.134(10)
C(6)–Rh(1)–C(1)
P(1)–Rh(1)–C(6)
P(1)–Rh(1)–C(1)
89.4(3)
87.2(2)
89.0(3)
Treatment of 3 with 5 equivalents of tolualdehyde re-
sults in formation of 16b, which decays predominantly
to 20 and 21. In this case we see very little build-up of
Rh(1)–C(1)–O(2) 174.6(8)

B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
2949
-
+ BAr'4
-
O
13C
+ BAr'4
-
+ BAr'4
Cp*
Rh
Cp*
Rh
Cp*
Rh
13CO
+
(MeO)3P
(MeO)3P
Cp*
(MeO)3P
(MeO)3P
Cl2CH2
13CO
13CO
23'
21'
22
O
P(OMe)3
O
H
+ BAr'4
-
-
+ BAr'4
Cp*
Rh
Cp*
Rh
13C
(MeO)3P
P(OMe)3
O
24'
H
25
Scheme 2.
O
+ BAr'4
-
-
+ BAr'4
Cp*
H
Me
Me
Rh
Rh
(MeO)3P
(MeO)3P
CH2Cl2
Cl2CH2
O
3
H
16b
O
H
CH4
+ BAr'4
-
-
+ BAr'4
+ BAr'4
-
Cp*
Rh
Cp*
Rh
Cp*
O
Me
+
Rh
+
(MeO)3P
(MeO)3P
(MeO)3P
CO
CO
O
21
20
H
18b
(major species)
P(OMe)3
+ BAr'4
-
Cp*
O
Rh
(MeO)3P
P(OMe)3
24
Scheme 3.
18b due to the low concentration of aldehyde present.
After 16 days, the only identifiable product remaining
is Rh methyl carbonyl 20, which presumably, is the most
stable species. When anisaldehyde or 4-(trifluoro-
methyl)benzaldehyde are used in the reaction with 3,
similar reactivity patterns emerge. However, the Rh acyl
anisaldehyde adduct (the analogue of 18b) is more stable
than the Rh acyl tolualdehyde adduct (18b) due to the

2950
B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
1
˚
tighter binding of the more basic anisaldehyde. The least
basic aldehyde, 4-(trifluoromethyl)benzaldehyde, forms
the least stable Rh acyl aldehyde adduct.
catalyst (Chemalog) and 4 A molecular sieves. H and
13C NMR chemical shifts were referenced to residual
1H and 13C NMR signals of the deuterated solvents,
respectively. 31P NMR chemical shifts were referenced
to an 85% H3PO4 sample used as an external standard.
Elemental analyses were performed by Atlantic Micro-
lab Inc. of Norcross, GA.
3. Conclusions
The work described here has provided new insights
into the primary steps involved in C–H activation reac-
tions that occur at cationic Group 9 M(III) centers. It
has also revealed significant differences between the
way such reactions take place at rhodium and iridium.
Specifically, the focus on rhodium in this work has al-
lowed us to measure the rates of exchange of free and
bound aldehyde in the rhodium aldehyde complexes 15
and 16. It has also revealed that in the presence of high
concentrations of aldehyde, Rh acyl complexes, formed
by decarbonylation of aryl aldehydes, can be stabilized
by coordination of a second molecule of aldehyde, lead-
ing to cationic Rh acyl aldehyde complexes that are sta-
ble enough to be characterized in solution.
Our ability to observe the coordination and ex-
change of aldehyde at cationic Rh(III), and the subse-
quent C–H activation reaction, has allowed us to
examine and compare the electronic effects on both
processes. The factors that contribute to strong or
weak aldehyde binding to the Rh+ center appear to
be dominated by r-donation effects, as one would ex-
pect for a relatively electrophilic metal center. The
rates of exchange and C–H activation are strongly
correlated. The primary influence on the overall
C–H activation rate is a ground state effect: when
the aldehyde is strongly bound to the Rh+ center, this
binding retards its rearrangement to the transition
state for C–H activation. Conversely, a more loosely-
held aldehyde rearranges more easily to the transition
state, facilitating the C–H activation process. Thus
this system reflects a property often noted for en-
zymes: strong coordination of substrate to an active
site does not necessarily promote efficient catalysis,
and in fact can have the opposite effect [13]. The opti-
mum situation for catalysis involves relatively weak
binding of substrate in the ground state, so that this
interaction does not counteract the binding energy of
the rearranging substrate to the active site in the tran-
sition state.
4.2. Materials
All solvents were deoxygenated and dried via passage
over a column of activated alumina [14]. Deuterated sol-
vents (Cambridge Isotope Laboratories) were purified
˚
by vacuum transfer from CaH2 and stored over 4 A
molecular sieves. Unless otherwise noted, all chemicals
were purchased from Aldrich and used without further
purification. 13C-labeled CO was purchased from Cam-
bridge Isotope Laboratories. NaBAr04 was purchased
from Boulder Scientific and used without further purifi-
cation. Solutions of 1.5 M MeLi and PhLi in Et2O were
purchased from Acros and used without further purifi-
cation. Organometallic complexes 1 [8], 2 [15], Cp*(P(O-
Me)3)RhCl2 [9], and Cp*(PMe3)Rh(Ph)(Cl) [11] have
been previously reported and were synthesized accord-
ing to literature procedures.
4.3. Spectral data for BAr40ꢂ
The 1H and 13C NMR resonances of the BAr40
(Ar0 = 3,5-(CF3)2C6H3) counteranion in CD2Cl2 were
essentially invariant for all cationic complexes discussed
here and spectroscopic data are not repeated for each
1
compound. H NMR (400 MHz, CD2Cl2) d 7.73 (s, 8
H, Hortho), 7.57 (s, 4 H, Hpara). 13C{1H} NMR
1
(101 MHz, CD2Cl2) d 161.9 (q, JC–B = 49.8, Cipso),
135.0 (s, Cortho), 129.0 (q, JC–F = 31.4, Cmeta), 124.7
1
(q, JC–F = 272.6, CF3), 117.7 (s, Cpara).
2
4.4. Synthesis of [Cpꢀ(P(OMe)3)Rh(Me)(CH2Cl2)]
BAr04 (3)
A vial was charged with 172 mg (0.412 mmol) of 4 and
408 mg (0.461 mmol) of NaBAr04. The reactants were dis-
solved in 5 mL of CH2Cl2 and the resulting mixture was
stirred for 5 min. The contents were filtered and stored at
ꢂ35 ꢀC for 24 h. Red–orange crystals of 3 were isolated in
55% yield. 1H NMR (300 MHz, CD2Cl2) d 5.33 (s,
3
4. Experimental
CH2Cl2), 3.78 (d, JP–H = 11.4 Hz, 9 H, P(OMe)3), 1.63
4
(d, JP–H = 4.2 Hz, 15 H, Cp*), 1.02 (dd, JP–H = 5.5
3
2
4.1. General considerations
Hz, JRh–H = 1.5 Hz, 3 H, Me). 31P{1H} NMR (121.5
1
126.9 (d, JRh–P = 268.6 Hz,
MHz, CD2Cl2)
d
Unless otherwise noted, all reactions and manipula-
tions were performed using standard high-vacuum, Sch-
lenk, or drybox techniques. Argon and nitrogen were
purified by passage through columns of BASF R3-11
P(OMe)3). 13C{1H} NMR (101 MHz, CD2Cl2) d 103.3
(s, Cp*–Ar), 54.34 (d, JP–C = 8.0 Hz, P(OMe)3), 54.19
2
3
(s, CH2Cl2), 9.16 (d, JP–C = 1.4 Hz, Cp*–Me), 1.19
(dd, 2JP–C = 37.1 Hz, 1JRh–C = 22.0 Hz, Me).

B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
2951
4.5. Synthesis of Cp*(P(OMe)3)Rh(Me)(Cl) (4)
15 H, Cp*). 31P{1H} NMR (162 MHz, CD2Cl2) d
121.7 Hz (d, JRh–P = 268.4 Hz, P(OMe)3).
1
To a flame-dried Schlenk flask under argon, 2.5 g (6.9
mmol) of Cp*(P(OMe)3)RhCl2 was dissolved in 100 mL
dry ether. The solution was cooled to ꢂ78 ꢀC and meth-
yllithium (7.6 mmol in THF) was added to the solution,
which was then brought to room temperature. The reac-
tion was opened to air and quenched with 10 mL of
water, the ether phase was removed, and the red/orange
product isolated by roto-evaporation. The crude prod-
uct was dissolved in 20 mL CH2Cl2 to which hexanes
were added (50 mL) until the solution became cloudy.
Red–orange crystals were isolated in 50% yield. 1H
4.8. Generation of [Cpꢀ(P(OMe)3)Rh(Me)(p-CH3C6H4
CHO)]BAr04 (16b)
In a J-Young NMR tube 15.0 mg (0.01 mmol) of 3
was dissolved in 0.5 mL CD2Cl2, and tolualdehyde (5
equivalents, 6.0 lL, 0.055 mmol) was added to the solu-
tion. At ꢂ68 ꢀC, 16b and the aldehydic protons of both
the bound and free aldehyde were observable by NMR
1
spectroscopy. H NMR (300 MHz, CD2Cl2, ꢂ68 ꢀC) d
3
9.11 (s, 1 H, CH3C6H4CO-H), 3.69 (d, JP–H = 11.7
3
4
Hz, 9 H, P(OMe)3), 1.64 (d, JP–H = 4.2 Hz, 15 H,
NMR (300 MHz, CD2Cl2) d 3.68 (d, JP–H = 11.4 Hz,
9 H, P(OMe)3), 1.61 (d, JP–H = 4.1 Hz, 15 H, Cp*),
4
3
2
Cp*), 0.96 (dd, JP–H = 5.4 Hz, JRh–H = 1.6 Hz, 3 H,
Me). 31P{1H} NMR (121.5 MHz, CD2Cl2, ꢂ68 ꢀC) d
3
2
0.73 (dd, JP–H = 5.1 Hz, JRh–H = 2.1 Hz, 3 H, Me).
31P{1H} NMR (121.5 MHz, CD2Cl2) d 138.36 (d,
1JRh–P = 259.9 Hz, P(OMe)3). 13C{1H} NMR (101
1
132.1 Hz (d, JRh–P = 266 Hz, P(OMe)3).
1
MHz, CD2Cl2) d 100.00 (vt, JRh–C = 2JP–C = 4. 2 Hz,
4.9. Generation of [Cpꢀ(P(OMe)3)Rh(C(O)C6H4CH3)
(p-CH3C6H4CHO)]BAr04 (18b)
2
Cp*–Ar), 53.00 (d, JP–C = 4.38 Hz, P(OMe)3), 8.94 (d,
1
J = 2.25 Hz, Cp*–Me), ꢂ2.57 (dd, JRh–C = 22.2 Hz
2JP–C = 20.6 Hz, Me).
In a J-Young NMR tube 15.0 mg (0.01 mmol) of 3
was dissolved in 0.5 mL CD2Cl2 and 50 lL of tolualde-
hyde was added to the solution. After 3 days, the solu-
tion was cooled to ꢂ68 ꢀC to allow for the resolution
(by NMR spectroscopy) of the aldehydic proton of
bound aldehyde in 18b.1H NMR (300 MHz, CD2Cl2,
4.6. Synthesis of [Cpꢀ(PMe3)Rh(Ph)(CH2Cl2)]BAr04 (6)
A Schlenk flask was charged with 50 mg (0.117
mmol) of Cp*(PMe3)Rh(Ph)(Cl) and 109 mg (0.123
mmol) of NaBAr04 and sealed with a rubber stopper.
The flask was placed in an ice bath and 5 mL of CH2Cl2
was introduced via syringe. The contents of the flask
were stirred for 5 min and then filtered through Celite
supported by a glass frit. The filtrate was concentrated
in vacuo and the flask placed in a freezer (ꢂ30 ꢀC) for
3 d. Orange–red crystals of 6 (110 mg, 0.082 mmol) were
isolated in 70% yield and can be stored at ꢂ30 ꢀC for
3
ꢂ68 ꢀC) d 9.58 (s, 1 H, CH3C6H4CO–H), 3.81 (d, JP–H
4
= 11.1 Hz, 9 H, P(OMe)3), 1.71 (d, JP–H = 5.3 Hz, 15
H, Cp*). 31P{1H} NMR (121.5 MHz, CD2Cl2, ꢂ68
1
ꢀC) d 115.4 Hz (d, JRh–P = 235 Hz, P(OMe)3).
4.10. Synthesis of [Cpꢀ(PMe3)Rh(C6H4CH3)(CO)]
BAr04 (19)
1
weeks. H NMR (400 MHz, CD2Cl2, 0 ꢀC) d 7.19 (br
A Schlenk flask was charged with 30 mg (0.023
mmol) of 1 and 1 mL of dichloromethane. A dichloro-
methane solution of tolualdehyde (0.115 mmol) was
added via syringe and the contents of the flask were al-
lowed to stir overnight. To afford crystals, 1 mL of pen-
tane was added and the flask placed in a freezer at ꢂ30
ꢀC. After 6 d, 12 mg (0.0093 mmol) of X-ray quality or-
m, 2 H, Ph), 7.07 (br m, 3 H, Ph), 5.33 (s, CH2Cl2),
4
1.51 (d, JP–H = 2.7 Hz, 15 H, Cp*), 1.46 (d, JP–H
2
= 10.1 Hz, 9 H, PMe3). 31P{1H} NMR (162 MHz,
1
CD2Cl2, 0 ꢀC) d 1.1 (d, JRh–P = 168.2 Hz, PMe3).
13C{1H} NMR (101 MHz, CD2Cl2, 0 ꢀC) d 158.3 (dd,
2
1JRh–C = 32.0 Hz, JP–C = 17.5 Hz, Ph–Cipso), 136.2 (d,
2JRh–C = 4.6 Hz, Ph–Cortho), 130.2 (s, Ph–Cmeta), 125.1
(s, Ph–Cpara), 103.1 (s, Cp*–Ar), 54.1 (s, CH2Cl2),
1
ange crystals were isolated in 39% yield. H NMR (400
3
MHz, CD2Cl2) d 6.99 (d, J = 7.7 Hz, 2 H, tolyl-Ar),
6.91 (d, JH–H = 7.7 Hz, 2 H, tolyl-Ar), 2.28 (s, 3 H, to-
1
15.31 (d, JP–C = 32.0 Hz, PMe3), 9.66 (s, Cp*–Me).
3
4
lyl-Me), 1.84 (d, JP–H = 2.9 Hz, 15 H, Cp*), 1.50 (d,
2JP–H = 10.8 Hz, 9 H, PMe3). 31P{1H} NMR (162
4.7. Synthesis of [Cpꢀ(P(OMe)3)Rh(Ph)(CH2Cl2)]
BAr04 (7)
1
MHz, CD2Cl2) d 4.1 (d, JRh–P = 129.1 Hz, PMe3).
13C{1H} NMR (101 MHz, CD2Cl2) d 188.8 (dd,
2
1JRh–C = 72.5 Hz, JP–C = 21.9 Hz, CO), 138.5 (br m,
In a J-Young NMR tube, 15.9 mg (0.01 mmol) of 3
was dissolved in 0.5 mL of 1.1 M benzene in CD2Cl2.
After 24 h, the volatile materials were removed to yield
Cipso of tolyl-Ar), 136.0 (s, tolyl-Ar), 131.9 (s, tolyl-
Ar), 130.1 (s, tolyl-Ar), 107.6 (s, Cp*–Ar), 20.59 (s,
1
tolyl-Me), 16.43 (d, JP–C = 35.6 Hz, PMe3), 9.89 (s,
1
a light orange powder in quantitative yields. H NMR
3
(400 MHz, CD2Cl2) d 7.30 (m, 5 H, Ph), 3.74 (d, JP–
H = 11.2 Hz, 9 H, P(OMe)3), 1.56 (d, JP–H = 4.4 Hz,
Cp*–Me). Anal. Calc. for C53H43OBF24PRh: C, 49.10;
H, 3.34. Found: C, 48.93; H, 3.12%.
4

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B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
3
H, m-Ar–H), 3.68 (d, JP–H = 10.8 Hz, 9 H, P(OMe)3),
4.11. Synthesis of [Cpꢀ(P(OMe)3)Rh(p-C6H4CH3)
(CH2Cl2)]BAr04 (22)
4
2.13 (s, 3 H, tolyl-CH3), 1.50 (d, JP–H = 4.5 Hz, 15 H,
Cp*). 31P{1H} NMR (121.5 MHz, CD2Cl2, ꢂ68 ꢀC) d
1
126.8 Hz (d, JRh–P = 260 Hz, P(OMe)3).
In the glove box, a vial was charged with 36 mg
(0.075 mmol) of Cp*(P(OMe)3)Rh(C6H4 CH3)(Cl) (see
below for synthesis of this compound) and 72 mg
(0.081 mmol) of NaBAr04. The reactants were dissolved
in 2 mL of CH2Cl2. The contents were filtered and
stored at ꢂ35 ꢀC for 24 h. An orange powder was iso-
lated in 40% yield. 1H NMR (300 MHz, CD2Cl2) d
4.14. Generation of [Cpꢀ(P(OMe)3)Rh(Me)(13CO)]
BAr04 (200)
In a J-Young NMR tube15.0 mg (0.011 mmol)of 3 was
dissolved in 0.5 mL CD2Cl2. The solution was subject to
three freeze–pump–thaw cycles, at which point the head-
space of the tube was backfilled with 13CO. Upon shaking
of the tube, the solution turned from orange to light yel-
6.95 (d, J = 8.1 Hz, 2 H, tolyl-H), 7.26 (d, J = 7.2 Hz,
3
H, tolyl-H), 3.68 (d, JP–H = 10.8 Hz,
2
P(OMe)3), 2.24 (s, 3 H, tolyl-CH3), 1.48 (d, JP–H = 4.5
9
H,
4
1
Hz, 15 H, Cp*). 31P{1H} NMR (121.5 MHz, CD2Cl2)
low. H and 31P NMR spectroscopy showed complete
1
1
d 126.8 Hz (d, JRh–P = 260 Hz, P(OMe)3). 13C{1H}
conversion of 3 to 200. H NMR (300 MHz, CD2Cl2) d
3.77 (d, JP–H = 12.0 Hz, 9 H, P(OMe)3), 1.87 (d,
3
NMR (75.5 MHz, CD2Cl2) d 131.1 (s, tolyl-Ar) 102.6
(s, Cp*–Ar), 54.72 (d, JP–C = 7.6 Hz, P(OMe)3), 20.44
(s, tolyl-Me), 8.71 (s, Cp*–Me).
2
3
4JP–H = 4.8 Hz, 15 H, Cp*), 0.78 (dd, JP–H = 3.9 Hz,
2JRh–H = 2.1 Hz, 3 H, Me). 31P{1H} NMR (121.5 MHz,
1
CD2Cl2) d 121.6 Hz (d, JRh–P = 217 Hz, P(OMe)3).
4.12. Synthesis of Cp*(P(OMe)3)Rh(C6H4CH3)(Cl)
13C{1H} NMR (101 MHz, CD2Cl2) d 187.1 (dd,
1JRh–C = 70.7 Hz, 2JP–C = 32.0 Hz, 13CO).
To a flame dried Schlenk flask under argon,
Cp*(P(OMe)3)RhCl2 was dissolved in 40 mL dry THF
and the resulting solution was cooled to ꢂ78 ꢀC. To-
lyl-lithium (2.3 equivalents, 321 mg, 3.28 mmol) [16]
was dissolved in 10 mL of THF, and the resulting solu-
tion was cooled to ꢂ78 ꢀC and cannula-transferred into
a stirred solution of Cp*(P(OMe)3)RhCl2 at which point
the color changed from red to orange. After being
brought to room temperature the solvent was removed
to yield an orange foam, which was then extracted with
3 · 20 mL toluene and filtered through celite. Concen-
tration of this solution under vacuum yielded a red oil
which, upon addition of pentane and cooling to ꢂ78
4.15. Generation of [Cpꢀ(P(OMe)3)Rh(C6H4CH 3)(13 CO)]
BAr04 (210)
A J-Young tube with 35 mg of 22 in 0.5 mL CD2Cl2
was freeze–pump-thawed three times and backfilled with
13CO. The solution was shaken, and excess 13CO was
evacuated from the headspace and backfilled with argon
1
while the solution was frozen. H, 13C and 31P NMR
spectroscopy showed the presence of both 210 and 230
1
(see below) in solution. H NMR (300 MHz, CD2Cl2)
d 6.98 (d, J = 7.8 Hz, 2 H, tolyl-H), 7.05 (d, J = 7.8
Hz, 2 H, tolyl-H), 3.63 (d, JP–H = 12.0 Hz, 9 H,
3
1
4
P(OMe)3), 2.25 (s, 3 H, tolyl-CH3), 1.77 (d, JP–H = 4.8
ꢀC afforded an orange powder in 46% yield. H NMR
(300 MHz, CD2Cl2) d 7.36 (d, J = 7.2 Hz, tolyl-H),
6.80 (d, J = 7.6 Hz, tolyl-H), 3.49 (d, JP–H = 11.4 Hz,
Hz, 15 H, Cp*). 31P{1H} NMR (121.5 MHz, CD2Cl2)
3
1
2
d 116.9 Hz (dd, JRh–P = 215 Hz, JP–C = 32.8 Hz,
P(OMe)3). 13C{1H} NMR (101 MHz, CD2Cl2) d 187.5
4
9 H, P(OMe)3), 2.22 (s, tolyl-Me), 1.50 (d, JP–H = 4.1
Hz, 15 H, Cp*), 31P{1H} NMR (121.5 MHz, CD2Cl2)
(dd, JRh–C = 68.3 Hz, JP–C = 38.4 Hz, 13CO).
1
2
1
d 135.56 (d, JRh–P = 247.0 Hz, P(OMe)3). 13C{1H}
NMR (101 MHz, CD2Cl2) d 139.41 (s, tolyl-Ar),
131.97 (s, tolyl-Ar), 128.93 (s, tolyl-Ar), 101.60 (d,
3
J = 4.6 Hz, Cp*–Ar), 53.66 (d, JP–C = 4.6 Hz,
4.16. Generation of [Cpꢀ(P(OMe)3)Rh(13C(O)-
C6H4CH3)(13CO)]BAr04 (230)
P(OMe)3), 21.14 (s, tolyl-C H3), 9.29 (d, J = 1.61 Hz,
Cp*–Me).
A J-Young tube charged with 35 mg of 22 in 0.5 mL
CD2Cl2. The contents were freeze–pump-thawed three
times and backfilled with 13CO. The solution was shaken,
and excess 13CO was evacuated from the headspace and
4.13. Synthesis of [Cpꢀ(P(OMe)3)Rh(C6H4CH3)
(p-CH3C6H4CHO)] BAr04 (25)
1
backfilled with argon while the solution was frozen. H,
13C and 31P NMR spectroscopy showed the presence of
In a J-Young NMR tube 15.0 mg (0.010 mmol) of 22
was dissolved in 0.5 mL CD2Cl2 and 25 lL of tolualde-
hyde was added to the solution. The solution was cooled
to ꢂ68 ꢀC to allow for the resolution of the aldehydic
proton of bound aldehyde. 1H NMR (300 MHz,
CD2Cl2, ꢂ68 ꢀC) d 8.98 (s, p-CH3C6H4CO-H), 6.95 (d,
J = 7.7 Hz, 2 H, tolyl-H), 7.26 (d, partially obscured, 2
both 210 and 230 in solution. 1H NMR (300 MHz,
3
CD2Cl2) d 7.31 (m, 4 H, Ar–H), 3.74 (d, JP–H = 11.7
Hz, 9 H, P(OMe)3), 2.39 (s, 3 H, tolyl-CH3), 1.88 (d,
4JP–H = 3.9 Hz, 15 H, Cp*). 31P{1H} NMR (121.5
1
114.7 (ddd, JRh–P = 226 Hz,
MHz, CD2Cl2)
d
2
2JP–C = 35.2 Hz, JP–C = 12.1 Hz, P(OMe)3). 13C{1H}
1
NMR (101 MHz, CD2Cl2) d 223.6 (ddd, JRh–C
=

B.K. Corkey et al. / Polyhedron 23 (2004) 2943–2954
2953
2
23.3 Hz, JP–C = 10.9,2JC–C = 3.0 Hz, Rh–acyl-13CO),
Table 7
Crystallographic data and collection parameters for 6 and 19
188.5 (ddd, JRh–C = 74.7 Hz, JP–C = 34.8Hz,2JC–C
3.0 Hz, Rh–13CO).
=
1
2
6
19
Empirical formula
Formula weight
Crystal system
Space group
RhPC52H43BF24Cl2
1339.46
monoclinic
P21/c
RhPBC53H43F24
1317.79
triclinic
O
4.17. Generation of [Cp*(P(OMe)3)2Rh(13C(O)C6H4
CH3)]BAr04 (240)
ꢀ
P1
˚
a (A)
12.5934(22)
18.824(3)
24.160(4)
ꢂ
12.3960(5)
12.7232(6)
18.3440(8)
76.5570(10)
86.1510(10)
84.6820(10)
2798.67(21)
2
A J-Young tube containing a mixture of 210 and 230 in
CD2Cl2 solution (product from synthesis of 210) was
brought into the glove box where 3.1 lL of trimethyl
phosphite was introduced. After 1 day at room tempera-
ture, the resulting yellow solution was decanted from pre-
cipitate, at which point 240 was the only species detected in
solution. Alternatively, 240 can be generated by the addi-
tion of trimethyl phosphite to a solution of 18b. 1H NMR
(300 MHz, CD2Cl2) d 7.35 (m, 2 H, tolyl-Hortho), 7.19 (d,
J = 8.1 Hz, 2 H, tolyl-Hmeta), 3.72 (t, J = 5.7 Hz, 18 H,
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
94.260(7)
ꢂ
3
˚
V (A )
5711.3(15)
4
1.558
Z
Dcalc (Mg/m3)
Radiation
1.564
Mo Ka
0.53
0.129
Mo Ka
0.47
0.098
l (mmꢂ1
Rf
)
Rw
0.131
1.8114
0.086
2.1963
4
P(OMe)3), 2.39 (s, 3 H, tolyl-CH3), 1.66 (t, JP–H = 4.6
Hz, 15 H, Cp*). 31P{1H} NMR (121.5 MHz, CD2Cl2) d
119.1 (dd, JRh–P = 244 Hz, JP–C = 11.9 Hz, P(OMe)3).
Goodness-of-fit
1
2
13C{1H} NMR (75.5 MHz, CD2Cl2) d 233.21 (dt,
5. Supplementary material
2
1JRh–C = 29.1 Hz, JP–C = 12.2 Hz, Rh–13CO-tolyl),
CCDC-240673 (6) and -240674 (19) contain the sup-
plementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.
ac.uk/data_request/cif, by emailing data_request@
ccdc.cam.ac.uk, or by contacting The Cambridge Crys-
tallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
142.90 (s, tolyl-Ar), 128.8 (br d, tolyl-Ar), 128.5 (br d, to-
lyl-Ar), 125.1 (s, tolyl-Ar), 106.1 (m, Cp*–Ar), 55.17 (m,
P(OMe)3), 21.27 (tolyl-Me), 9.67 (s, Cp*–Me).
4.18. Kinetics of C–H activation reactions of aldehydes
using 1 and 3
Reactions using 10–20 mg of 1 or 3 (0.03 M) with
aldehydes (1.5 M) were carried out in J-Young NMR
tubes in CD2Cl2. Values of kobs were determined by inte-
gration of the rhodium–methyl and Cp* peaks relative
to the invariant BAr04 peaks during reaction of 1 and 3
with 50 equivalents of aldehyde over the course of days
at room temperature.
Acknowledgement
B.K.C., F.L.T., and M.B. acknowledge the National
Science Foundation (CHE-0107810) for support of this
work and R.G.B. acknowledges support by the Direc-
tor, Office of Energy Research, Office of Basic Energy
Sciences, Chemical Sciences Division, of the US Depart-
ment of Energy under Contract No. DE-AC03-7600098.
4.19. Determination of DGà for dissociative exchange of
aldehydes in 15 and 16
Solutions of 10 mg of 1 or 3 in CD2Cl2 were com-
bined with 5 equivalents of aldehyde and cooled to
ꢂ88 ꢀC. At this temperature, the natural w1/2 of the alde-
hydic proton was determined. The w1/2 was again meas-
ured at a temperature where the width had reached 5–10
times the natural line width. Rate constants for ex-
change and DGà were calculated from this data using
the slow exchange equation k = p(Dw).
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