Substituent Effects on Reactions of [RhCl(COD)]2 with Diazoalkanes

Article abstract of DOI:10.1021/acs.organomet.8b00889

The reactions of [RhCl(COD)]₂ with a series of diazoalkanes with different substitutents were investigated. The outcomes of the reactions were found to be substituent-dependent via four different pathways. (1) The reactions with diazoindenes produced ??⁵-cyclopentadienyl complexes. (2) The reaction with diazofluorene produced a mixture of olefin and azine compounds. (3) The reactions with monosubstituted diazoalkanes RCHN₂ (R = Ph, MeO₂C) produced olefins RCHa?CHR. (4) The reaction with the disubstituted diazoalkane Ph₂CN₂ produced the azine Ph₂Ca?N-Na?CPh₂ only. Computational studies have been carried out to understand the interesting substituent effect by comparing the kinetics and thermodynamics of the reaction pathways. It was found that the reactions with diazocyclopentadiene, diazoindene, and Ph₂CN₂ are kinetically controlled, while the reactions with RCHN₂ and diazofluorene are both thermodynamically and kinetically controlled.

Full text of DOI:10.1021/acs.organomet.8b00889

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Substituent Effects on Reactions of [RhCl(COD)]2 with Diazoalkanes
Mingxu Cui,† Shujuan Lin,† Herman H. Y. Sung, Ian D. Williams,* Zhenyang Lin,*
and Guochen Jia*
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
S
* Supporting Information
ABSTRACT: The reactions of [RhCl(COD)]2 with a series of
diazoalkanes with different substitutents were investigated. The outcomes
of the reactions were found to be substituent-dependent via four different
pathways. (1) The reactions with diazoindenes produced η5-cyclo-
pentadienyl complexes. (2) The reaction with diazofluorene produced a
mixture of olefin and azine compounds. (3) The reactions with
monosubstituted diazoalkanes RCHN2 (R = Ph, MeO2C) produced
olefins RCHCHR. (4) The reaction with the disubstituted diazoalkane
Ph2CN2 produced the azine Ph2CN−NCPh2 only. Computational
studies have been carried out to understand the interesting substituent
effect by comparing the kinetics and thermodynamics of the reaction
pathways. It was found that the reactions with diazocyclopentadiene,
diazoindene, and Ph2CN2 are kinetically controlled, while the reactions
with RCHN2 and diazofluorene are both thermodynamically and kinetically controlled.
attacked by the terminal nitrogen of a diazo molecule to give
azine complexes D (reaction 4). For carbene transfer reactions
to work efficiently, the formation of the reactive carbene
species should proceed easily and the side reactions 2−4 of the
carbene species should be minimized. Thus, a good under-
standing of processes for the generation and reactions of
carbene intermediates is important for rationalizing the results
of catalytic reactions and their further development.
INTRODUCTION
■
There has been interest in rhodium-catalyzed carbene transfer
reactions using diazoalkanes R2CN2 as the carbene source, for
example, cyclopropanations, H−X insertions, ylide formations,
and cross-couplings.1,2 It is generally believed that the catalytic
reactions proceed by initial formation of carbene intermediates
A (reaction 1, Scheme 1) followed by the reactions of the
Studies of the reactions of diazoalkanes R2CN2 with
rhodium complexes can give important information regarding
generation and reactivity of carbene intermediates.3 Previous
studies in this direction have led to the isolation of a number of
carbene complexes with Rh(I),4−9 Rh(II)10,11 and Rh(III)10,12
centers (reaction 1). Both experimental and computational
evidence7 supports the hypothesis that carbene complexes are
formed via η1-C-diazoalkane complexes LnRh−C(N2)R2.
While much is known about the formation of carbene
complexes from reactions of diazoalkanes with rhodium
complexes, reported examples of reactions of diazoalkanes
with rhodium complexes to give complexes B, C1, C2, and D
via reactions 2−4 are rather limited. The alkyl complex
Cp*RhCl{CCl(CO2Me)(o-C6H4−OMe)} was obtained from
the reaction of [Cp*RhCl2]2 with (MeO2C)(p-MeOC6H4)-
CN2.10 Cyclopentadienyl complexes of the type (η5-C5R4X)-
RhL2 were obtained from the reactions of diazocyclopenta-
dienes C5R4N2 (R = H, Ph, and Cl) with [RhCl(L)2]2 (L = 1/
2 COD,13−17 CO,18 and CH2CH2).17 Olefin complexes
L2ClRh(η2-olefin) were obtained from the reaction of
[RhCl(PiPr3)2]2 with CH2N2,19 and the reaction of RhCl-
Scheme 1. Generation and Reactions of Rhodium Carbene
Complexes
carbene intermediates with partner substrates. The efficiency of
a catalytic system for carbene transfer reactions could be
adversely affected by side-reactions of the carbene intermedi-
ates. For example, carbene intermediates A may undergo
intramolecular migratory insertion reactions to give alkyl
complexes LnRh−C(X)R2 (B) (reaction 2). The carbene
carbon of A could be attacked by the C(N2) carbon of a diazo
molecule to give dinitrogen complexes LnRh(N2) (C1) or
olefin complexes LnRh(η2-olefin) (C2) (reaction 3); and
Received: December 9, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(C2H4)(SbiPr3)2 with EtO2CHN2.5 As related reactions,
Rh(II) complexes catalyzed dimerization of diazoalkanes to
give olefins.20,21 Dinitrogen complexes (PiPr3)2XRh(η2-N2)
were obtained from the reactions of [RhCl(PiPr3)2]2 with
Scheme 2. Reactions of [RhCl(COD)]2 with Diazoindenes
19
(EtO2C)HCN2 and PhCHN2,22 and the reaction of
Rh(O2CCF3)(PiPr3)2 with PhCHN2.23 Azine derivatives were
obtained from the reactions of CpRh(SbiPr3)(CPh2) with
8
Ph2CN2 and from the reaction of Rh2(OAc)4 with
diazofluorene.24 Factors determining the reactivity of the
carbene intermediate species and the tendency for reactions
2−4 to occur are not well systematically investigated, defined,
or understood.
In our effort to address these deficiencies, we have studied
the reactions of [RhCl(COD)]2 with a series of diazoalkanes.
Experimentally, we have identified the products of the
reactions of [RhCl(COD)]2 with various diazoalkanes such
as diazoindenes, diazofluorene, Ph2CN2, PhCHN2, and
(MeO2C)CHN2. The outcomes of the reactions were found
to be substituent-dependent. The reactions with diazoindenes
produced η5-cyclopentadienyl complexes. The reactions with
the monosubstituted diazoalkanes RCHN2 (R = Ph, MeO2C)
produced olefins RCHCHR. The reaction with the
disubstituted diazoalkane Ph2CN2 produced the azine
Ph2CN−NCPh2 only. The reaction with diazofluorene
produced a mixture of olefin and azine compounds. We have
also carried out computational studies to understand the
interesting substituent effect by comparing the kinetics and
thermodynamics of the energy profiles of the pathways leading
to the formation of complexes analogous to B−D for each
representative diazoalkanes. The findings from these inves-
tigations are reported here.
Complexes 3 are presumably formed via chlorine migratory
insertion reaction of rhodium indenylidene complexes 2.
Similar reactions occurred between diazocyclopentadienes
1
C5R4N2 (R = H, Ph, and Cl) and [RhCl(L)2]2 (L = /2
COD,13−17 and CH2CH2)17 to give η5-chlorocyclopenta-
dienyl complexes.
The structures of the complexes 3a (Figure 1) and 3c
(Figure 2) have been confirmed by X-ray diffraction. The
RESULTS AND DISCUSSION
■
Reactions of [RhCl(COD)]2 with Diazoalkanes. Rh(I)-
diene complexes have been actively investigated as catalysts or
catalytic precursors for carbene transfer reactions using
diazoalkanes as the carbene sources.25−28 Thus, it is naturally
of interest in investigating the stoichiometric reactions of
Rh(I)-diene complexes with diazoalkanes. However, reported
stoichiometric reactions of Rh(I)-diene complexes with
diazoalkanes are rare and limited to the reactions of
Figure 1. Molecular structure of 3a. Selected bond distances (Å):
Rh(1)−C(1) 2.180(4), Rh(1)−C(2) 2.247(4), Rh(1)−C(3)
2.235(4), Rh(1)−C(4) 2.379(4), Rh(1)−C(9) 2.381(4), Rh(1)−
C(21) 2.122(4), Rh(1)−C(22) 2.124(4), Rh(1)−C(25) 2.127(4),
Rh(1)−C(26) 2.132(4), Cl(1)−C(1) 1.735(4), C(1)−C(2)
1.424(6), C(1)−C(9) 1.448(6), C(2)−C(3) 1.424(6), C(3)−C(4)
1.457(6), C(4)−C(9) 1.434(6), C(21)−C(22) 1.395(6), C(25)−
C(26) 1.398(7).
diazocyclopentadienes C5R4N2 (R = H, Ph, and Cl) with
COD,13−17 and CH2CH2).17 To
1
[RhCl(L)2]2 (L =
/
2
systematically investigate the effect of substituents of
diazoalkanes on the reactions of Rh(I)-diene complexes with
diazoalkanes, we have studied the reactions of [RhCl(COD)]2
with diazoindenes, diazofluorene, and monosubstituted and
disubstituted diazoalkanes.
structural features are similar to those of (η5-C9R7)Rh(η4-cod)
(R = H, Me) reported in the literature.29 The solid-state
structures are supported by the solution NMR data. For
1
example, the H NMR spectrum of 3a displayed the olefinic
First, the reaction of [RhCl(COD)]2 with diazoindene 1a
was investigated. When 2.2 equiv of diazoindene 1a was added
to a solution of [RhCl(COD)]2 in C6D6, gas evolution
CH signal of COD at 3.69 and 3.54 ppm and the
cyclopentadienyl CH signal at 6.40 ppm. In the 13C{1H}
NMR spectrum of 3a, the olefinic CH signals of COD were
observed at 75.5 and 74.7 ppm, and the five cyclopentadienyl
signals at 112.2, 110.4, 110.4, 93.0, 91.1, and 90.6 ppm.
Next, the reaction of diazofluorene with [RhCl(COD)]2 was
investigated. After a mixture of diazofluorene and [RhCl-
(COD)]2 in a molar ratio of 2:1 in C6D6 was kept at room
temperature for 10 min, the in situ NMR indicates that
[RhCl(COD)]2 remains unchanged, while the diazofluorene
was completely converted to a mixture of olefin 4 and azine 5
in a molar ratio of 3:1. The expected rhodium carbene or η5-
fluorenyl complexes were not detectable. The result suggests
that [RhCl(COD)]2 catalyzed the homo coupling reactions of
1
(presumed to be N2) was observed. The in situ H NMR
spectrum (collected 10 min after mixing the reagents) showed
that most of the diazoindene was consumed and the reaction
1
produced a new species displaying a characteristic doublet H
signal at 6.41 ppm with JH−Rh = 1.92 Hz. The new complex can
be isolated as a yellow powder in 80% yield and was identified
to be η5-indenyl rhodium complex 3a (Scheme 2).15 Similarly,
the reactions of [RhCl(COD)]2 with the diazoindenes 1b and
1c produced η5-indenyl rhodium complexes 3b and 3c,
respectively. Thus, the substitutents of diazoindenes have no
effect on the pathways leading to the formation of the η5-
indenyl complexes.
diazofluorene. With 2.5 mol % of [RhCl(COD)]2,
a
B
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
proposed previously for metal-mediated coupling of diazo-
alkanes to give olefins20,30 and azines.31
It is noted that different products were obtained in
previously reported reactions of diazofluorene (N2CC12H8)
with rhodium(I) complexes, including diazo complexes,19
carbene complexes5 and azine compounds.24
To further study the substituent effect on the outcomes of
the reactions of [RhCl(COD)]2 with diazoalkanes, the
reactions with Ph2CN2, PhHCN2 and (MeO2C)HCN2 were
carried out. After a toluene solution of the disubstituted
diazoalkane Ph2CN2 was stirred at room temperature for 10
min in the presence of 2.5 mol % of [RhCl(COD)]2, the in situ
NMR indicates that the [RhCl(COD)]2 remains unchanged,
and all Ph2CN2 was converted to the azine Ph2CN−N
CPh2 (9), which can be isolated in 97% yield. Azine 9 is
presumably formed by nucleophilic attack on the carbene
carbon of intermediate 10 by the terminal nitrogen of Ph2CN2
(Scheme 5).
Figure 2. Molecular structure of 3c. Selected bond distances (Å):
Rh(1)−C(1) 2.1670(16), Rh(1)−C(2) 2.2404(17), Rh(1)−C(3)
2.2362(16), Rh(1)−C(4) 2.3977(16), Rh(1)−C(5) 2.3564(15),
Rh(1)−C(31) 2.1227(17), Rh(1)−C(32) 2.1267(17), Rh(1)−
C(35) 2.1286(16), Rh(1)−C(36) 2.1517(16), Cl(1)−C(1)
1.7319(17), C(1)−C(2) 1.441(2), C(1)−C(5) 1.443(2), C(2)−
C(3) 1.440(2), C(3)−C(4) 1.468(2), C(4)−C(5) 1.424(2), C(31)−
C(32) 1.410(3), C(35)−C(36) 1.415(2).
Scheme 5. Reaction of [RhCl(COD)]2 with Ph2CN2
quantitative conversion was achieved within 10 min (Scheme
3).
Scheme 3. Reaction of [RhCl(COD)]2 with Diazofluorene
In a closely related reaction, the carbene complex CpRh-
(SbiPr3)(CPh2) reacted with Ar2CN2 (Ar = Ph, p-tolyl) to
give Ph2CN−NCAr2.8 It is noted that products other
than azines were obtained in reported reactions of Ph2CN2
with Rh(I) complexes, such as carbene complexes,5,6 diazo
complexes,19,23,32,33 and dinitrogen complex.32
Under conditions similar to those for the reaction with the
disubstituted diazoalkane Ph2CN2, [RhCl(COD)]2 reacted
with the monosubstituted diazoalkane PhHCN2 completely to
give a mixture of trans-stilbene (11a) and cis-stilbene (11b) in
a molar ratio of 1:1, while [RhCl(COD)]2 remains unchanged
(Scheme 6). A similar catalytic reaction occurred for
(MeO2C)HCN2, giving a mixture of dimethyl fumarate
(12a) and dimethyl maleate (12b) in 1:1 molar ratio. Olefins
11 and 12 are presumably formed via the reaction of the
carbene intermediates 13 with the diazoalkanes to give
intermediates 14 followed by elimination of N2 and
dissociation of the olefins from the metal center (Scheme 6).
Scheme 4 shows a plausible mechanism for the formation of
the olefin 4 and the azine 5 from the catalytic reaction. The
Scheme 4. Proposed Mechanism for [RhCl(COD)]2-
Catalyzed Reactions of Diazofluorene
Scheme 6. Reactions of [RhCl(COD)]2 with Phenyl
Diazomethane and Methyl Diazoacetate
complex [RhCl(COD)]2 initially reacted with diazofluorene to
produce the rhodium fluorenylidene 6. Nucleophilic attack of
the carbene carbon by the C(N2) carbon of diazofluorene
would give the intermediate 7, which then loses N2 to form
olefin 4 and regenerate [RhCl(COD)]2. Nucleophilic attack of
the carbene carbon by the terminal nitrogen of diazofluorene
would give intermediate 8, which then evolves to azine 5 and
regenerates [RhCl(COD)]2. Similar pathways have been
C
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The reactions with RCHN2 (R = Ph, MeO2C) to give 11
and 12 are interesting as they represent rare examples of
homodimerization of diazoalkanes to give olefins catalyzed by
Rh(I) complexes, although similar reactions catalyzed by
Rh(II) complexes are now well-documented.20 Several types of
products have been isolated from the reactions of Rh(I)
complexes with monosubstituted diazoalkanes RCHN2, such as
carbene complexes,7,9 diazoalkane complexes,6,19,23,34 olefin
complexes,5 and dinitrogen complexes.22,23
the suffix FD, and those evolving from the reaction with phenyl
diazomethane are named with the suffix PM.
Carbene Formation. In all the reactions described above,
the formation of carbene species is the initial step. Therefore,
we have first calculated the energy profiles for the formation of
carbene complexes. The results are presented in Figure 3.
Computational Studies. We have shown that three
possible products are experimentally produced in the reactions
of [RhCl(COD)]2 with diazoalkanes, depending on the
substituents of the diazoalkanes. Taking the reaction with
diazocyclopentadiene (C5H4N2) as an example, the plausible
pathways for the formation of these products are summarized
in Scheme 7. The dimeric complex [RhCl(COD)]2 could react
with C5H4N2 to give initially active Rh-carbene species 15.
Scheme 7. Plausible Mechanisms for the Formation of
Three Side Products
Figure 3. Calculated energy profiles for the formation of carbene
complexes from chloro-rhodium dimer complex [RhCl(COD)]2 with
diazocyclopentadiene (C5H4N2) (pink line), 3-tert-butyl-diazoindene
(blue line), diazofluorene (C13H8N2) (red line), and phenyl
diazomethane (C7H6N2) (black line). The relative free energies and
electronic energies (in parentheses) are given in kcal/mol.
It is generally accepted that reactions of diazoalkanes with
transition metal compounds to give carbene complexes
proceed through η1-C-coordinated diazoalkane intermediates.9
Reaction of [RhCl(COD)]2 with neutral ligands L to give
RhCl(COD)L is very common. As shown in Figure 3, the
reaction of [RhCl(COD)]2 with diazocyclopentadiene
(C5H4N2) to give η1-C-coordinated diazoalkane complex
1DC is thermodynamically unfavored by 11.4 kcal/mol. The
dissociation of N2 from diazoalkane complex 1DC to give Rh-
carbene intermediate 2DC is thermodynamically favored by
12.6 kcal/mol with a kinetic barrier of 12.0 kcal/mol. The
overall reaction of [RhCl(COD)]2 with C5H4N2 to give Rh-
carbene species 2DC is thermodynamically favored by 1.2
kcal/mol with a kinetic barrier of 23.4 kcal/mol. The reaction
of [RhCl(COD)]2 with C5H4N2 could also give other initial
products RhCl(COD)(η1-N-C5H4N2), RhCl(COD)(η2-CC-
C5H4N2), and RhCl(COD)(η2-NC-C5H4N2). However, our
computational work suggests that these species are unlikely to
be involved in the formation of carbene complex 2DC (see the
Supporting Information for details).
There exist three competing pathways starting from Rh-
carbene species 15: (a) chloride migratory-insertion to give
chlorocyclopentadienyl complex 16; (b) nucleophilic attacking
of the diazo carbon (C(N2)) on the carbene carbon to give
intermediate 17 which evolves to homocoupling olefin product
19; and (c) nucleophilic attacking of the terminal N of the
diazo reagent on the carbene carbon to generate intermediate
18 which evolves to azine 20.
The experimental results described above indicate that the
thermodynamics and kinetics of the competing reaction
pathways are influenced by the substituents of the diazoalkanes
or carbene intermediates. To understand the effect of
substituents of diazoalkanes on the reaction pathways, we
have calculated the energy profiles for the reactions of
[RhCl(COD)]2 with four representative diazoalkanes, namely,
diazocyclopentadiene, 3-tert-butyl-diazoindene, diazofluorene,
and PhCHN2.
To study the substituent effect on carbene formation, the
energy profiles for the reactions of [RhCl(COD)]2 with 3-tert-
butyl-diazoindene, diazofluorene and PhCHN2 were also
carried out. The profiles were found to be similar to that of
the reaction with diazocyclopentadiene. Compared with the
reaction with diazocyclopentadiene, the formation of inden-
ylidene complex 2ID from the reaction of [RhCl(COD)]2 with
In the following discussion of the computational results,
species evolving from the reaction with diazocyclopentadiene
are named with the suffix DC, those evolving from the reaction
with diazoindene are named with the suffix with ID, those
evolving from the reaction with diazofluorene are named with
D
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 4. Calculated energy profiles for the possible reaction pathways of chloro-rhodium cyclopentadienylidene intermediate (2DC). The relative
free energies and electronic energies (in parentheses) are given in kcal/mol.
2-tert-butyl-diazoindene is both thermodynamically and kineti-
cally more favorable. The reaction is thermodynamically
favored by 13.5 kcal/mol with an appreciably low barrier of
19.5 kcal/mol. Following the trend, the formation of
fluorenylidene complex 2FD from the reaction of [RhCl-
(COD)]2 with diazofluorene is even more favorable both
thermodynamically and kinetically. The reaction is thermody-
namically favored by 16.7 kcal/mol with a barrier of 18.2 kcal/
mol. The reaction of PhCHN2 with [RhCl(COD)]2 to give
carbene complex 2PM should be kinetically most favorable
with an overall barrier of 16.9 kcal/mol. Interestingly, carbene
(2PM) formation was found to be thermodynamically slightly
less favorable (the free energy change is −15.4 kcal/mol) than
that from the reaction with diazofluorene (the free energy
change is −16.7 kcal/mol).
(R = Ph, CH2Ph).26,35 The energy profiles for the reactions of
Rh(RPCP)(N2) with PhCHN2 resemble those shown in
Figure 3. For example, the complex Rh(N2)(iPrPCP) reacts
with PhCHN2 to give the diazoalkane complex Rh(η1-C-
PhCHN2)(iPrPCP) in an endothermic process (by 18.1 kcal/
mol). The intermediate Rh(η1-C-PhCHN2)(iPrPCP) evolves
to the carbene complex Rh(CHPh)(iPrPCP) exothermically
with a kinetic barrier of 11.0 kcal/mol, which is similar to those
(10.2−12.0 kcal/mol) calculated for the transformation of
1PM, 1ID, and 2DC to the corresponding carbene complexes.
Reactions of Carbene Complexes. The experimentally
observed variation in the preference of the reaction pathways is
likely caused by the difference in the kinetics and
thermodynamics of reactions of carbene intermediates as a
result of the effect of the substituents of the carbene
intermediates and diazoalkanes. To study the effect, we
calculated the energy profiles for the three possible reaction
pathways shown in Scheme 7 for the reactions of Rh-carbene
species 2DC, 2ID, 2FD, and 2PM.
The calculated energy profiles for the reactions of rhodium
cyclopentadienylidene complex 2DC are shown in Figure 4.
The formation of chlorocyclopentadienyl complex 4DC from
2DC involves migratory-insertion and rearrangement steps.
The migratory-insertion to give the η2-CCl-coordinated
complex 3DC is thermodynamically favored by 4.0 kcal/mol
with a small barrier of 3.5 kcal/mol. The rearrangement of
3DC to 4DC is thermodynamically favored by 22.1 kcal/mol
with a barrier of 8.3 kcal/mol. Overall, the formation of η5-
chlorocyclopentadienyl complex 4DC from Rh-carbene species
2DC is thermodynamically favored by 26.1 kcal/mol.
Except in the case of diazofluorene, the overall carbene
formation barriers for reactions with diazoalkanes seem to be
related to the stability of the η1-C-diazoalkane complexes. The
overall carbene formation barrier is higher if the formation of
the η1-C-diazoalkane complex is thermodynamically less
favorable. As can be seen from Figure 3, while the overall
barriers (from [RhCl(COD)]2) vary from 16.9 to 23.4 kcal/
mol, the barriers from the η1-C-diazoalkane complexes 1PM,
1ID, and 2DC are within a small range of 10.2−12.0 kcal/mol.
In related works, energy profiles for the formation of
rhodium carbene complexes from reactions of Rh(I)
complexes with diazoalkanes have been previously described
for the reactions of the pincer complexes Rh(N2)(RPCP)
9
i
(RPCP = 2,6-(R2PCH2)2C6H3 (R = H, Pr) with PhCHN2
and the reactions of RhCl(2,5-Ph2-NBD) with (MeO2C)RCN2
E
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Cyclopentadienylidene complex 2DC evolves to olefin
complex 5DC by nucleophilic attack on the carbene carbon
by the C(N2) carbon of diazocyclopentadiene via transition
20,30
state TS2−5DC
.
The process is thermodynamically favored
by 82.2 kcal/mol with a barrier of 14.0 kcal/mol (TS2−5DC).
For comparison, the reaction of Rh2(O2CH)4(CPh-
(CO2Me) with (MeO2C)CHN2 to give the olefin (MeO2C)-
CHCPh(CO2Me) was reported to have a barrier of ca. 18
kcal/mol.20
Cyclopentadienylidene complex 2DC evolves to azine
complex 6DC by nucleophilic attack on the carbene carbon
by the terminal nitrogen of diazocyclopentadiene via transition
31
state TS2−6DC
.
The process is also thermodynamically
favored (by 36.3 kcal/mol) with a barrier (13.7 kcal/mol)
similar to that (14.0 kcal/mol) for the formation of olefin
complex 5DC.
As can be seen from the profiles, all three pathways are
thermodynamically favored, with the formation of olefin
complex 5DC being most favorable and that of chlorocyclo-
pentadienyl complex 4DC being least favorable. Kinetically,
the pathway leading to the formation of cyclopentadienyl
complex 4DC is mostly favored, consistent with the
experimental isolation of η5-cyclopentadienyl complex 16.
Figure 5a shows the energy profiles calculated for the
reactions of rhodium indenylidene 2ID. Overall, the calculated
energy profiles are similar to those calculated for the reaction
of rhodium cyclopentadienylidene 2DC. Like those from the
reactions of 2DC, the formations of η5-indenyl complex 4ID,
olefin complex 5ID, and azine complex 6ID from the reactions
of 2ID are all thermodynamically favored, with the formation
of the olefin complex being most favored and that of the
chloroindenyl complex being least favored. The overall barriers
for the formations of 4ID, 5ID, and 6ID are 11.5, 16.0, and
16.2 kcal/mol, respectively. Thus, the formation of η5-indenyl
complex 4ID is the most kinetically favored, consistent with
our observation that η5-indenyl complexes (3a, 3b, and 3c)
were isolated experimentally.
The calculated energy profiles for the conversions of the
rhodium fluorenylidene intermediate (2FD) are shown in
Figure 5b. Different from the cases of 2DC and 2ID, the
chlorine migratory insertion reaction of 2FD to give η5-
fluorenyl complex 4FD was found to be thermodynamically
unfavorable (by 2.4 kcal/mol), indicating that this process is
unlikely. Like the cases from the reactions of 2DC and 2ID,
the homocoupling pathways to give the olefin (5FD) and azine
(6FD) complexes are both thermodynamically favorable (by
57.5 and 28.5 kcal, respectively). The barrier for the formation
of olefin complex 5FD (14.7 kcal/mol) is similar to (or slightly
lower than) that for the formation of azine complex 6FD (17.7
kcal/mol), consistent with the experimental observation that a
mixture of olefin (4) and azine (5) were produced.
Figure 5c shows the energy profiles calculated for the
reactions of rhodium phenylcarbene 2PM. The energy profiles
clearly indicate that chloride migration reaction should not
occur because the reaction will produce thermodynamically
unfavorable products (3PM or 4PM). In contrast, the
formation of olefin complex 5PM and azine complex 6PM
are both thermodynamically and kinetically feasible, with the
formation of the olefin complex being appreciably more
favorable (by 6.7 kcal/mol). The results are therefore
consistent with the experimental observation that [RhCl-
(COD)]2 catalyzes the coupling reaction of PhHCN2 to give
PhHCCHPh.
Figure 5. Calculated energy profiles for the conversions of
chlororhodium indenylidene (2ID), fluorenylidene intermediate
(2FD), and phenylcarbene (2PM). The relative free energies and
electronic energies (in parentheses) are given in kcal/mol.
Comments on the Reactions of Carbene Complexes.
General Comments. The computational work described above
represents the first study systematically comparing the kinetics
and thermodynamics of the reaction types of diazoalkanes with
rhodium complexes to give complexes B, C1, C2, and D via
the reactions 2−4 shown in Scheme 1. Several interesting
observations were noted from the computational results.
Among the three reaction pathways of the carbene
intermediates, the chlorine migratory insertion to give η5-
pentadienyl complexes is thermodynamically least favored,
while nucleophilic attacking of the diazo carbon (C(N2)) on
the carbene carbon to give olefin complexes is thermodynami-
cally most favored. However, the relative kinetic barriers for
the three pathways can vary with the substituents of the
diazoalkanes affecting the observed product.
Chlorine Migratory Insertion Reactions. The initial
chlorine migratory insertion reactions of the carbene species
to give the corresponding η2-CCl complexes are kinetically
F
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
feasible as indicated by the low reaction barriers (being 3.5,
9.2, 10.3, and 8.7 kcal/mol calculated for 2DC, 2ID, 2FD, and
2PM, respectively). However, these processes, with the
exception of the reaction of 2DC, are in general thermody-
namically unfavorable. The free energy changes for the
migratory reactions of 2DC, 2ID, 2FD, and 2PM are −4.0,
5.9, 8.1, and 7.2 kcal/mol, respectively.
(C6H4Me)2, Ph(CF3), C12H8) and EtO2CCHN2 have been
shown to produce trans-RhCl(CRR)(SbiPr3)2 and trans-
RhCl{(E)-(EtO2CCHCH(CO2Et)}(SbiPr3)2, respectively.5
Interestingly, reported Rh-catalyzed carbene transfer reac-
tions usually involve disubstituted diazoalkanes with at least
one electron-withdrawing group. We suspect that such
diazoalkanes are less likely to undergo transition metal
mediated homocoupling reactions. In supporting our hypoth-
esis and findings, in the presence of 1 mol % Rh2(OPiv)4 (Piv
= pivaloyl) catalyst, an equimolar mixture of Ph(MeO2C)CN2
and EtO2CCHN2 rapidly afforded the cross-coupling product
Ph(MeO2C)CCH(CO2Et) and the homocoupling product
(EtO2C)HCCH(CO2Et), but the homocoupling product
Ph(MeO2C)CC(CO2Me)Ph was not produced in the
catalytic reaction.20
The thermodynamics of the chlorine migratory insertion
reactions of the carbene species could be altered if the initially
formed η2-CCl complexes can rearrange to more stable species.
Our computational work confirms that η2-CCl complexes
3DC, 3ID, and 3FD can rearrange to the corresponding
thermodynamically more stable η5-pentadienyl complexes with
a low kinetic barrier. As a result, both 2DC and 2ID can
rearrange to η5-pentadienyl complexes in a thermodynamically
favorable process. In the case of 2FD, the stabilization effect is
not enough, such that the formation of η5-pentadienyl complex
4FD from 2FD is still not favorable. The trend in the relative
stability of cyclopentadienylidene, indenylidene, and fluoreny-
lidene complexes with respect to the formation of the
corresponding η5-chlorocyclopentdienyl complexes can be
related to the strength of the Rh-η5-pentadienyl interactions
in the η5-pentadienyl complexes. The average Rh−C(ring)
distances of the η5-pentadienyl complexes are in the order of
cyclopentadienyl complex 4DC (2.31 Å) < indenyl complex
4ID (2.34 Å) < fluorenyl complex 4FD (2.38 Å), suggesting
that the Rh-(η5-chlorocyclopentadienyl) bond is the strongest
and the Rh-(η5-chlorofluorenyl) bond is the weakest. Thus, the
formation of chlorocyclopentadienyl complex 4DC is most
favored, and the formation of the chlorofluorenyl complex 4FD
is least favored. Interestingly, rearrangement of η2-C−Cl
complex 3PM (derived from phenyl carbene complex 2PM)
to give η3-cyclohexadienyl complex 4PM is thermodynamically
unfavored, probably because the delocalization of electrons in
the aromatic ring of 3PM is disrupted in the formation of η3-
cyclohexadienyl complex 4PM.
CONCLUSIONS
■
In summary, we have investigated the reactions of [RhCl-
(COD)]2 with a series of diazoalkanes containing different
substitutents. The outcomes of the reactions were found to be
substituent-dependent. The reactions with diazocyclopenta-
diene and diazoindenes produced η5-cyclopentadienyl com-
plexes. The complex [RhCl(COD)]2 catalyzed dimerization of
RCHN2 (R = Ph, MeO2C) to give olefins RCHCHR,
dimerization of diazofluorene to give a mixture of olefin and
azine compounds, and dimerization of Ph2CN2 to give the
azine Ph2CN−NCPh2. Computational studies suggest
that the reactions of diazocyclopentadiene, diazoindenes, and
Ph2CN2 are kinetically controlled, while the reactions of
RCHN2 and diazofluorene are both thermodynamically and
kinetically controlled.
The results have the following implications: (1) Reactions of
monosubstituted diazoalkanes with Rh(I) complexes to give
carbene complexes are kinetically more favorable than those of
disubstituted diazoalkanes. (2) Reactions of diazocyclopenta-
dienes and diazoindenes with Rh(I)-halo complexes can easily
produce η5-pentadienyl complexes due to facile halogen
migratory inserion reactions of the halo-rhodium carbene
complexes. (3) The barriers for metal-mediated coupling
reactions of diazoalkanes to give olefins are sensitive to steric
effect. Coupling reactions of sterically less bulky monosub-
stituted diazoalkanes to give olefins can be kinetically and
thermodynamically very favorable. (4) Bulky diazoalkanes tend
to react with Rh(I) complexes to give azines, because the
competing reactions to give olefins can be kinetically retarded.
Dimerization Reactions. The reactions of the carbene
species with diazoalkanes to give olefin or azine complexes are
all thermodynamically favored, with the formation of the olefin
complexes being significantly more favorable.
Interestingly, the barriers for reactions of carbene species
2DC, 2ID, 2FD, and 2PM to form the corresponding azine
complexes are similar to each other (being 13.7, 16.2, 14.7, and
13.6 kcal/mol, respectively). In contrast, the barriers for
reactions of carbene species 2DC, 2ID, 2FD, and 2PM to form
the corresponding olefin complexes vary appreciably and are in
the order of 2PM (7.1 kcal/mol) < 2DC (14.0 kcal/mol) <
2ID (16.0 kcal/mol) < 2FD (17.7 kcal/mol). The trend in the
barriers appears to be related to the steric effect. Especially, the
barrier for the reaction of 2PM with the monosubstituted
diazoalkane PhCHN2 is appreciably lower than those of the
reactions of 2DC, 2ID, and 2FD as PhCHN2 is a
monosubstituted diazoalkane, while the others are disubsti-
tuted diazoalkanes.
Our computational results suggest that the barriers for
metal-mediated coupling reactions of disubstituted diazoal-
kanes to give olefins are similar to, or even higher than those to
give diazines. In contrast, the barriers for metal-mediated
coupling reactions of monosubstituted diazoalkanes to give
olefins are lower than those to give diazines. Supporting these
trend predicted from the computational results, we found in
the literature that the reactions of trans-RhCl(CH2CH2)-
(SbiPr3)2 with RR′CN2 [RR′ = Ph2, Ph(C6H4Me),
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out
under a nitrogen atmosphere using standard Schlenk techniques
unless otherwise stated. Solvents were distilled under nitrogen from
sodium benzophenone (hexane), sodium (toluene), or CaH2
(dichloromethane (DCM)). Methanol was bubbled with N2 before
use. The starting materials [RhCl(COD)]2,36 C5H4N2PPh3,37
diazofluorene,38 diphenyl diazomethane,39 phenyl diazomethane,40
and methyl diazoacetate40 were prepared following the procedure
described in the literatures. Diazoindenes 1a−c were synthesized by
the routes described in the Supporting Information. All other reagents
were purchased from commercial suppliers and used without further
purification. Microanalyses were performed by M−H-W Laboratories
1
(Phoenix, AZ). H and 13C{1H} NMR spectra were collected on a
Bruker-400 spectrometer (400 MHz). H and 13C NMR shifts are
1
relative to TMS.
Caution! Diazo compounds are explosive and assumed to be toxic. All
operations involving with diazo compounds should be carried out with
G
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
care. A safety shield should be used during heating or distillation of diazo
compounds.
(97%). The product was confirmed to be benzophenone azine. The
NMR data are consistent with the literature41 reported ones.
Preparation of Rh(η5-C5H5Cl)(COD) (16). This complex has
been previously prepared by Shaver et al.16,17 by reacting [RhCl-
(COD)]2 with C5H4N2. Herein, we used an alternative synthetic
route by reacting [RhCl(COD)]2 with C5H4N2PPh3, a safer precursor
to C5H4N2. A mixture of C5H4N2PPh3 (72 mg, 0.20 mmol) and
[RhCl(COD)]2 (100 mg, 0.20 mmol) in toluene (6 mL) was stirred
overnight at room temperature. After removing volatiles under
vacuum, the mixture was purified by flashing silica gel column
chromatography with hexane/DCM (v/v 10:1) as the eluent to afford
the air stable yellow solid of 16. Yield: 43 mg (68%). The NMR data
are consistent with the literature17 reported ones.
Reaction of [RhCl(COD)]2 with Phenyl Diazomethane. To a
solution of [RhCl(COD)]2 (2.5 mg, 5 × 10−3 mmol) in toluene (2
mL) was added a toluene solution of phenyl diazomethane (3.2 mL,
0.062 M, ca. 24 mg, 0.2 mmol) dropwise at room temperature. After
stirring for 10 min, the solvents were removed under vacuum. The
residues were dissolved with CDCl3 for in situ NMR analysis. The
phenyl diazomethane was consumed completely and only olefin
products were observed. The molar ratio of trans isomer 11a to cis
1
isomer 11b determined by integrals of H NMR is 1:1.
Reaction of [RhCl(COD)]2 with Methyl Diazoacetate. To a
solution of [RhCl(COD)]2 (2.5 mg, 5 × 10−3 mmol) in C6D6 (2 mL)
in a degassed NMR tube was added methyl diazoacetate (17 μL, ca.
20 mg, 0.2 mmol) at room temperature. An in situ 1H NMR spectrum
was collected after standing the mixture for 10 min. The methyl
diazoacetate was consumed completely and only olefin products were
observed. The molar ratio of dimethyl fumarate (12a) to dimethyl
Preparation of Rh{η5-C9H5(Ph)Cl}(COD) (3a). To a solution of
[RhCl(COD)]2 (87 mg, 0.18 mmol) in toluene (5 mL) was added a
DCM solution of 1a (2 mL, 0.2 M, ca. 87 mg, 0.4 mmol) dropwise at
room temperature. After stirring for 10 min, the solvents were
removed under vacuum. The orange residue was washed with hexane
(3 mL × 3) and methanol (3 mL × 3) and dried under vacuum to
give a yellow powder. Yield: 121 mg (80%). Anal. Calcd for
1
maleate (12b) determined by integrals of H NMR is 1:1.
X-ray Crystallography. Single crystals of 3a and 3c suitable for
X-ray diffraction were grown from a saturated hexane solution in −20
°C fridge. A suitable specimen was selected and mounted in Cryoloop
in Paratone, and intensity data were collected at 100 K on a Rigaku
Oxford-Diffraction SuperNova diffractometer (Cu Kα). Using Olex2
GUI42 the structure was solved with the ShelXS43 structure solution
program using Direct Methods and refined with the ShelXL44
refinement package. Further crystallographic details are summarized
in Tables S1 and S2. Crystallographic data have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC 1871356 (complex 3a) and CCDC
1871359 (complex 3c). Copies of these data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Computational Detail. All of the structures presented in the
energy profiles are optimized at DFT level using the M06
functionals.45 The solvation effect was considered using the
polarizable continuum model (PCM),46 and the solvent was assigned
as toluene corresponding to the experiment. The Rh atom is
described by the effective core potentials of lanl2dz47 with one set of
polarization functions (ζf = 1.350).48 The 6-311+G(d) basis set was
used for the Cl atom. Other atoms, including H, C, and N, were
described by 6-31G(d) standard basis set. Vibrational frequency
calculations were carried out to confirm the nature of stationary
points, as transition states (only one imaginary frequency) or the local
minima (no imaginary frequency). Intrinsic reaction coordinate
(IRC) calculations49 were also employed to further demonstrate the
transition states connect the relevant local minima. On the basis of the
optimized structures obtained in the aforementioned calculation, the
single-point energies calculations were performed using DFT-
D350mpirical dispersion correction and larger basis set, that is 6-
311G(d,p) for the H, C, and N atoms. All of the DFT calculations
were carried out using Gaussian 09 packages.51
1
C23H22ClRh: C, 63.25; H, 5.08. Found: C, 63.49; H, 5.03. H NMR
(400 MHz, C6D6): δ 7.46−7.44 (m, 2H), 7.36−7.34 (m, 2H), 7.20−
7.16 (m, 2H), 7.14−7.04 (m, 3H), 6.41 (d, JH−Rh = 1.92 Hz, 1H),
3.72−3.67 (m, 2H), 3.56−3.51 (m, 2H), 1.93−1.78 (m, 4H), 1.74−
1.70 (m, 2H), 1.62−1.56 (m, 2H). 13C{1H} NMR (100.6 MHz,
C6D6, 293 K): δ 135.2, 129.1, 126.9, 124.3, 123.7, 118.2, 117.7, 112.2,
110.4, 110.4, 93.0 (d, JC−Rh = 5.2 Hz), 91.1 (d, JC−Rh = 4.1 Hz), 90.6
(d, JC−Rh = 5.2 Hz), 75.5 (d, 2C, JC−Rh = 13.3 Hz), 74.7 (d, 2C, JC−Rh
= 13.5 Hz), 32.19, 30.82.
Preparation of Rh{η5-C9H5(tBu)Cl}(COD) (3b). This complex
was prepared as described for 3a, starting from 1b (3.2 mL 0.2 M
solution in DCM, ca. 127 mg, 0.64 mmol) and [RhCl(COD)]2 (150
mg, 0.30 mmol) in toluene (6 mL). Yield: 221 mg (83%). Anal. Calcd
1
for C21H26ClRh: C, 60.52; H, 6.29. Found: C, 60.42; H, 6.43. H
NMR (400 MHz, C6D6): δ 7.37 (t, JH−H = 7.6 Hz, 2H), 7.09 (t, JH−H
= 7.6 Hz, 1H), 7.04−7.00 (m, 1H), 6.08 (d, JH−Rh = 1.96 Hz, 1H),
4.09−4.05 (m, 2H), 3.79−3.74 (m, 2H), 1.94−1.78 (m, 4H), 1.67−
1.64 (m, 2H), 1.17 (s, 9H). 13C{1H} NMR (100.6 MHz, C6D6, 293
K): δ 123.5, 123.4, 119.6, 117.8, 112.1, 111.6, 102.8 (d, JC−Rh = 4.2
Hz), 92.7 (d, JC−Rh = 4.5 Hz), 89.1 (d, JC−Rh = 5.4 Hz), 74.7 (d, 2C,
J
C−Rh = 13.7 Hz), 71.0 (d, 2C, JC−Rh = 13.8 Hz), 33.0, 32.1, 30.9, 30.7.
Preparation of Rh{η5-C9H4(Ph)2Cl}(COD) (3c). This complex
was prepared as described for 3a, starting from 1c (130 mg, 0.44
mmol) and [RhCl(COD)]2 (99 mg, 0.20 mmol) in toluene (5 mL).
Yield: 156 mg (76%). Anal. Calcd for C29H26ClRh: C, 67.91; H, 5.11.
1
Found: C, 68.11; H, 5.31. H NMR (400 MHz, C6D6): δ 7.68−7.66
(m, 2H), 7.51 (s,, JH−H = 8.1 Hz, 1H), 7.39 (s, JH−H = 8.2 Hz, 1H),
7.23−7.20 (m, 2H), 7.18−7.14 (m, 5H), 7.10−7.04 (m, 4H), 7.01−
6.98 (m, 1H), 3.87−3.75 (m, 4H), 2.00−1.82 (m, 4H), 1.75−1.59
(m, 4H). 13C{1H} NMR (100.6 MHz, C6D6, 293 K): δ 134.1, 133.9,
132.0, 130.4, 128.6, 128.2, 127.6, 126.9, 124.6, 123.9, 118.1, 117.7,
112.6 (d, JC−Rh = 5.5 Hz), 111.2, 110.5, 91.5 (d, JC−Rh = 3.9 Hz), 91.3
(d, JC−Rh = 4.3 Hz), 75.7 (d, 2C, JC−Rh = 12.7 Hz), 75.6 (d, 2C, JC−Rh
= 12.3 Hz), 31.6, 31.1.
ASSOCIATED CONTENT
* Supporting Information
■
S
Reaction of [RhCl(COD)]2 with Diazofluorene. To a solution
of [RhCl(COD)]2 (2.5 mg, 5 × 10−3 mmol) in toluene (2 mL) was
added a toluene solution of diazofluorene (2 mL, 0.1 M, ca. 38 mg 0.2
mmol) dropwise at room temperature. After stirring for 10 min, the
solvents were removed under vacuum. The residues were totally
dissolved with CDCl3 for in situ NMR analysis. The diazofluorene
was consumed completely to give 4 and 5. The molar ratio of olefin 4
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00889.
Additional experimental and computational details,
NMR spectra and crystallographic data (PDF)
Cartesian coordinates of all the calculated structures
(XYZ)
1
to azine 5 determined by integrals of H NMR is 3:1.
Reaction of [RhCl(COD)]2 with Diphenyl Diazomethane. To
a solution of [RhCl(COD)]2 (2.5 mg, 5 × 10−3 mmol) in toluene (2
mL) was added a toluene solution of diphenyl diazomethane (2 mL,
0.1 M, ca. 39 mg, 0.2 mmol) dropwise at room temperature. After
stirring for 10 min, the solvents were removed under vacuum. The
residues were purified by silica gel column chromatography with
hexane/EtOAC (v/v 10:1) to afford a pale yellow solid. Yield: 35 mg
Accession Codes
CCDC 1871356 and 1871359 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
H
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(6) Schwab, P.; Werner, H. A series of rhodium(I) complexes,
including carbene, vinylidene and allenylidene derivatives, with the
bifunctional arsine Pri2AsCH2CH2OMe as ligand. J. Chem. Soc., Dalton
Trans. 1994, 3415−3425.
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
(7) Vigalok, A.; Milstein, D. Direct Synthesis of Thermally Stable
PCP-Type Rhodium Carbenes. Organometallics 2000, 19, 2061−
2064.
Corresponding Authors
*E-mail: chwill@ust.hk.
*E-mail: chzlin@ust.hk.
*E-mail: chjiag@ust.hk.
(8) Werner, H.; Schwab, P.; Bleuel, E.; Mahr, N.; Windmuller, B.;
Wolf, J. Carbenerhodium complexes of the half-sandwich-type:
synthesis, substitution, and addition reactions. Chem. - Eur. J. 2000,
6, 4461−4470.
(9) Cohen, R.; Rybtchinski, B.; Gandelman, M.; Rozenberg, H.;
Martin, J. M. L.; Milstein, D. Metallacarbenes from diazoalkanes: an
experimental and computational study of the reaction mechanism. J.
Am. Chem. Soc. 2003, 125, 6532−6546.
ORCID
Zhenyang Lin: 0000-0003-4104-8767
Guochen Jia: 0000-0002-4285-8756
Author Contributions
†M.C. and S.L. contributed equally to this work.
(10) Werle, C.; Goddard, R.; Philipps, P.; Fares, C.; Furstner, A.
Structures of Reactive Donor/Acceptor and Donor/Donor Rhodium
Carbenes in the Solid State and Their Implications for Catalysis. J.
Am. Chem. Soc. 2016, 138, 3797−3805.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by the Hong Kong Research Grants
Council (Project No.: 602113, 16321516).
■
(11) Kornecki, K. P.; Briones, J. F.; Boyarskikh, V.; Fullilove, F.;
Autschbach, J.; Schrote, K. E.; Lancaster, K. M.; Davies, H. M.; Berry,
J. F. Direct spectroscopic characterization of a transitory dirhodium
donor-acceptor carbene complex. Science 2013, 342, 351−354.
(12) Tindall, D. J.; Werle, C.; Goddard, R.; Philipps, P.; Fares, C.;
Furstner, A. Structure and Reactivity of Half-Sandwich Rh(+3) and
Ir(+3) Carbene Complexes. Catalytic Metathesis of Azobenzene
Derivatives. J. Am. Chem. Soc. 2018, 140, 1884−1893.
REFERENCES
■
(1) For reviews, see (a) Xia, Y.; Qiu, D.; Wang, J. Transition-Metal-
Catalyzed Cross-Couplings through Carbene Migratory Insertion.
Chem. Rev. 2017, 117, 13810−13889. (b) Xiao, Q.; Zhang, Y.; Wang,
J. Diazo compounds and N-tosylhydrazones: novel cross-coupling
partners in transition-metal-catalyzed reactions. Acc. Chem. Res. 2013,
46, 236−247.
(13) Sunkel, K.; Stramm, C.; Lang, M.; Kempinger, W.; Hofmann, J.
̈
Coordination chemistry of perhalogenated cyclopentadienes XXII.
Reaction of tetrabromodiazocyclopentadiene with some halide
bridged Rh(I), Ru(II) and Ru(III) complexes. Molecular structure
of [C5Br5]Rh(COD), a complex with an η1,η4-coordinated cyclo-
pentadienyl ligand. Inorg. Chim. Acta 1998, 269, 111−116.
(14) Reimer, K. J.; Shaver, A. Pentachlorocyclopentadienyl
derivatives of manganese and rhodium. Inorg. Chem. 1975, 14,
2707−2716.
(2) For examples of recent work, see (a) Rodriguez, K. X.; Pilato, T.
C.; Ashfeld, B. L. An unusual stereoretentive 1,3-quaternary carbon
shift resulting in an enantioselective Rh(II)-catalyzed formal [4 + 1]-
cycloaddition between diazo compounds and vinyl ketenes. Chem. Sci.
2018, 9, 3221−3226. (b) Wang, K.; Chen, P.; Ji, D.; Zhang, X.; Xu,
G.; Sun, J. Rhodium-Catalyzed Regioselective N2-Alkylation of
Benzotriazoles with Diazo Compounds/Enynones via a Nonclassical
Pathway. Angew. Chem., Int. Ed. 2018, 57, 12489−12493. (c) Zhang,
Z.; Sheng, Z.; Yu, W.; Wu, G.; Zhang, R.; Chu, W. D.; Zhang, Y.;
Wang, J. Catalytic asymmetric trifluoromethylthiolation via enantio-
selective [2,3]-sigmatropic rearrangement of sulfonium ylides. Nat.
Chem. 2017, 9, 970−976. (d) Zhou, Q.; Li, S.; Zhang, Y.; Wang, J.
Rhodium(II)- or Copper(I)-Catalyzed Formal Intramolecular Car-
bene Insertion into Vinylic C(sp2)-H Bonds: Access to Substituted
1H-Indenes. Angew. Chem., Int. Ed. 2017, 56, 16013−16017.
(e) Deng, Y.; Massey, L. A.; Rodriguez Nunez, Y. A.; Arman, H.;
Doyle, M. P. Catalytic Divergent [3 + 3]- and [3 + 2]-Cycloaddition
by Discrimination Between Diazo Compounds. Angew. Chem., Int. Ed.
2017, 56, 12292−12296. (f) Chen, Z.-S.; Huang, X.-Y.; Chen, L.-H.;
Gao, J.-M.; Ji, K. Rh(II)/Pd(0) Dual Catalysis: Regiodivergent
Transformations of Alkylic Oxonium Ylides. ACS Catal. 2017, 7,
7902−7907. (g) Lubcke, M.; Yuan, W.; Szabo, K. J. Trifluorome-
thylthiolation-Based Bifunctionalization of Diazocarbonyl Com-
pounds by Rhodium Catalysis. Org. Lett. 2017, 19, 4548−4551.
(h) Yuan, W.; Eriksson, L.; Szabo, K. J. Rhodium-Catalyzed Geminal
Oxyfluorination and Oxytrifluoro-Methylation of Diazocarbonyl
Compounds. Angew. Chem., Int. Ed. 2016, 55, 8410−8415.
(3) For a review, see Werner, H. Half-Sandwich-Type Complexes
with Non-Fischer-Type Carbene Ligands: Synthesis, Molecular
Structure, Substitution, and C−C Coupling Reactions. Organo-
metallics 2005, 24, 1036−1049.
(4) Palacios, L.; Miao, X.; Di Giuseppe, A.; Pascal, S.; Cunchillos, C.;
Castarlenas, R.; Perez-Torrente, J. J.; Lahoz, F. J.; Dixneuf, P. H.; Oro,
L. A. Synthesis of a Square-Planar Rhodium Alkylidene N-
Heterocyclic Carbene Complex and Its Reactivity Toward Alkenes.
Organometallics 2011, 30, 5208−5213.
(5) Werner, H.; Schwab, P.; Bleuel, E.; Mahr, N.; Steinert, P.; Wolf,
J. A New Family of Carbenerhodium(I) Complexes: Ligand Variation
as The Key to Success. Chem. - Eur. J. 1997, 3, 1375−1384.
(15) Quinn, S.; Shaver, A. Insertion reactions of diazoindene with
some rhodium and manganese halides. Inorg. Chim. Acta 1981, 50,
141−146.
(16) Day, V. M.; Stults, B. R.; Reimer, K. J.; Shaver, A. Reactions of
diazocyclopentadienes. Preparation and structure of halogen sub-
stituted pentahaptocyclopentadienylrhodium complexes. J. Am. Chem.
Soc. 1974, 96, 1227−1229.
(17) Reimer, K. J.; Shaver, A. Insertion Reactions of Diazocyclo-
pentadienes with Halo-Transition Metal-Complexes. J. Organomet.
Chem. 1975, 93, 239−252.
(18) Cheong, M.; Basolo, F. Substituent effects on the rates of
carbon monoxide substitution of (η5-C5H4X)Rh(CO)2. Organo-
metallics 1988, 7, 2041−2044.
(19) Werner, H.; Mahr, N.; Wolf, J.; Fries, A.; Laubender, M.;
Bleuel, E.; Garde, R.; Lahuerta, P. Synthesis, Molecular Structure, and
Reactivity of Rhodium(I) Complexes with Diazoalkanes and Related
Substrates as Ligands. Organometallics 2003, 22, 3566−3576.
(20) Hansen, J. H.; Parr, B. T.; Pelphrey, P.; Jin, Q.; Autschbach, J.;
Davies, H. M. Rhodium(II)-catalyzed cross-coupling of diazo
compounds. Angew. Chem., Int. Ed. 2011, 50, 2544−2548.
(21) Doyle, M. P.; Hu, W.; Phillips, I. M.; Wee, A. G. H. A New
Approach to Macrocyclization via Alkene Formation in Catalytic
Diazo Decomposition. Synthesis of Patulolides A and B. Org. Lett.
2000, 2, 1777−1779.
(22) Werner, H.; Mahr, N.; Frenking, G.; Jonas, V. Synthetic,
Structural, and Theoretical Studies on a Novel Rhodium(I) Complex
Containing a π-Allyl-Type Ylide Ligand. Organometallics 1995, 14,
619−625.
(23) Werner, H.; Mahr, N.; Schneider, M. E.; Bosch, M.; Wolf, J.
Acetylacetonato, pentachlorophenolato and carboxylato rhodium(I)
complexes and their reactivity in the C−C coupling reaction of olefins
and diazoalkanes. Polyhedron 2004, 23, 2645−2657.
́
I
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(24) Bertani, R.; Michelin, R. A.; Mozzon, M.; Sassi, A.; Basato, M.;
Biffis, A.; Martinati, G.; Zecca, M. Catalytic activity of dicationic
platinum(II) and rhodium(II) complexes towards 9-diazofluorene.
Inorg. Chem. Commun. 2001, 4, 281−284.
(32) Werner, H.; Schwab, P.; Mahr, N.; Wolf, J. Vinylidene
Transition−Metal Complexes, XX[1] Synthesis, Reactions, and
Molecular Structure of Bis(arsane) and Bis(stibane) Rhodium(I)
Complexestrans-[RhCl(L)(EiPr3)2] (E = As, Sb) Including the
Rhodium−Mediated Rearrangement of Alkynes to the Isomeric
Allenes. Chem. Ber. 1992, 125, 2641−2650.
(33) Werner, H.; Schneider, M. E.; Bosch, M.; Wolf, J.; Teuben, J.
H.; Meetsma, A.; Troyanov, S. I. Cationic and Neutral
Diphenyldiazomethanerhodium(I) Complexes as Catalytically Active
Species in the C−C Coupling Reaction of Olefins and Diphenyldiazo-
methane. Chem. - Eur. J. 2000, 6, 3052−3059.
(34) Dias, E. L.; Brookhart, M.; White, P. S. Rhodium(I)-Catalyzed
Homologation of Aromatic Aldehydes with Trimethylsilyldiazo-
methane. J. Am. Chem. Soc. 2001, 123, 2442−2443.
(35) For theoretical studies on carbene formation from Rh(II)
systems, see (a) Nakamura, E.; Yoshikai, N.; Yamanaka, M.
Mechanism of C−H Bond Activation/C−C Bond Formation
Reaction between Diazo Compound and Alkane Catalyzed by
Dirhodium Tetracarboxylate. J. Am. Chem. Soc. 2002, 124, 7181−
7192. (b) Bonge, H. T.; Hansen, T. Computational study of
cyclopropanation reactions with halodiazoacetates. J. Org. Chem.
2010, 75, 2309−2320.
(36) Chatt, J.; Venanzi, L. M. Olefin Co-ordination Compounds.
Part VI. Diene Complexes of Rhodium (I). J. Chem. Soc. 1957, 4735−
4741.
(37) (a) Ramirez, F.; Levy, S. Reaction of Diazocyclopentadiene
with Triphenylphosphine. J. Org. Chem. 1958, 23, 2036−2037.
(b) Weil, T.; Cais, M. A Simplified Procedure for the Preparation of
Diazocyclopentadiene and Some Related Compounds. J. Org. Chem.
1963, 28, 2472−2472.
(38) Zeng, W.; Eric Ballard, T.; Tkachenko, A. G.; Burns, V. A.;
Feldheim, D. L.; Melander, C. Mimicking the biological activity of
diazobenzo[b]fluorene natural products with electronically tuned
diazofluorene analogs. Bioorg. Med. Chem. Lett. 2006, 16, 5148−5151.
(39) Pasquini, L. M.; Hashmi, S. M.; Sommer, T. J.; Elimelech, M.;
Zimmerman, J. B. Impact of surface functionalization on bacterial
cytotoxicity of single-walled carbon nanotubes. Environ. Sci. Technol.
2012, 46, 6297−6305.
(40) Zhou, Y.; Trewyn, B. G.; Angelici, R. J.; Woo, L. K. Catalytic
reactions of carbene precursors on bulk gold metal. J. Am. Chem. Soc.
2009, 131, 11734−11743.
(41) (a) Han, W.; Zhang, G.; Li, G.; Huang, H. Rh-catalyzed
sequential oxidative C-H and N-N bond activation: conversion of
azines into isoquinolines with air at room temperature. Org. Lett.
2014, 16, 3532−3535. (b) Laouiti, A.; Rammah, M. M.; Rammah, M.
B.; Marrot, J.; Couty, F.; Evano, G. Copper-catalyzed oxidative
alkynylation of diaryl imines with terminal alkynes: a facile synthesis
of ynimines. Org. Lett. 2012, 14, 6−9.
(42) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. OLEX2: a complete structure solution, refinement
and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341.
(43) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(44) Sheldrick, G. M. Crystal structure refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8.
(45) (a) Zhao, Y.; Truhlar, D. G. The M06 suite of density
functionals for main group thermochemistry, thermochemical
kinetics, noncovalent interactions, excited states, and transition
elements: two new functionals and systematic testing of four M06-
class functionals and 12 other functionals. Theor. Chem. Acc. 2008,
120, 215−241. (b) Zhao, Y.; Truhlar, D. G. Density functionals with
broad applicability in chemistry. Acc. Chem. Res. 2008, 41, 157−167.
(c) Truhlar, D. G. Molecular modeling of complex chemical systems.
J. Am. Chem. Soc. 2008, 130, 16824−16827. (d) Zhao, Y.; Truhlar, D.
G. Benchmark energetic data in a model system for Grubbs II
metathesis catalysis and their use for the development, assessment,
and validation of electronic structure methods. J. Chem. Theory
Comput. 2009, 5, 324−333.
(25) Wolf, J.; Brandt, L.; Fries, A.; Werner, H. Rhodium-Catalyzed
Synthesis of Trisubstituted Olefins from Ethene Derivatives and
Diazoalkanes. Angew. Chem., Int. Ed. Engl. 1990, 29, 510−512.
(26) Liu, S.; Jiang, J.; Chen, J.; Wei, Q.; Yao, W.; Xia, F.; Hu, W. A
DFT calculation-inspired Rh(I)-catalyzed reaction via suppression of
α-H shift in α-alkyldiazoacetates. Chem. Sci. 2017, 8, 4312−4317.
(27) (a) Chen, D.; Zhu, D. X.; Xu, M. H. Rhodium(I)-Catalyzed
Highly Enantioselective Insertion of Carbenoid into Si-H: Efficient
Access to Functional Chiral Silanes. J. Am. Chem. Soc. 2016, 138,
1498−1501. (b) Chen, D.; Zhang, X.; Qi, W. Y.; Xu, B.; Xu, M. H.
Rhodium(I)-catalyzed asymmetric carbene insertion into B-H bonds:
highly enantioselective access to functionalized organoboranes. J. Am.
Chem. Soc. 2015, 137, 5268−5271. (c) Ma, X.; Jiang, J.; Lv, S.; Yao,
W.; Yang, Y.; Liu, S.; Xia, F.; Hu, W. An Ylide Transformation of
Rhodium(I) Carbene: Enantioselective Three-Component Reaction
through Trapping of Rhodium(I)-Associated Ammonium Ylides by β-
Nitroacrylates. Angew. Chem. 2014, 126, 13352−13355.
(28) For examples of reactions catalyzed by related Rh(I)-diene
complexes, see (a) Zhou, Y.; Zhang, Y.; Wang, J. Rh(I)-Catalyzed
Arylation of α-Diazo Phosphonates with Aryl Boronic Acids:
Synthesis of Diarylmethylphosphonates. Chin. J. Chem. 2017, 35,
621−627. (b) Feng, S.; Mo, F.; Xia, Y.; Liu, Z.; Liu, Z.; Zhang, Y.;
Wang, J. Rhodium(I)-Catalyzed C-C Bond Activation of Siloxyvi-
nylcyclopropanes with Diazoesters. Angew. Chem., Int. Ed. 2016, 55,
15401−15405. (c) Liu, Z.; Xia, Y.; Feng, S.; Zhang, Y.; Wang, J.
Rh(I)-Catalyzed coupling of 2-bromoethyl aryldiazoacetates with
tertiary propargyl alcohols through carbene migratory insertion. Org.
Chem. Front. 2016, 3, 1691−1698. (d) Xia, Y.; Feng, S.; Liu, Z.;
Zhang, Y.; Wang, J. Rhodium(I)-Catalyzed Sequential C(sp)-C(sp3)
and C(sp3)-C(sp3) Bond Formation through Migratory Carbene
Insertion. Angew. Chem., Int. Ed. 2015, 54, 7891−7894. (e) Xia, Y.;
Liu, Z.; Feng, S.; Ye, F.; Zhang, Y.; Wang, J. Rh(I)-catalyzed cross-
coupling of alpha-diazoesters with arylsiloxanes. Org. Lett. 2015, 17,
956−959. (f) Xia, Y.; Liu, Z.; Liu, Z.; Ge, R.; Ye, F.; Hossain, M.;
Zhang, Y.; Wang, J. Formal carbene insertion into C-C bond: Rh(I)-
catalyzed reaction of benzocyclobutenols with diazoesters. J. Am.
Chem. Soc. 2014, 136, 3013−3015. (g) Yada, A.; Fujita, S.; Murakami,
M. Enantioselective insertion of a carbenoid carbon into a C-C bond
to expand cyclobutanols to cyclopentanols. J. Am. Chem. Soc. 2014,
136, 7217−7220. (h) Tsoi, Y. T.; Zhou, Z.; Yu, W. Y. Rhodium-
catalyzed cross-coupling reaction of arylboronates and diazoesters and
tandem alkylation reaction for the synthesis of quaternary α, α-
heterodiaryl carboxylic esters. Org. Lett. 2011, 13, 5370−5373.
(29) Kakkar, A. K.; Jones, S. F.; Taylor, N. J.; Collins, S.; Marder, T.
B. The hapticity of η-indenyl complexes: molecular structures of [(η5-
C9R7)Rh(η4-cod)](R = H, Me)(cod = cyclo-octa-5-diene). J. Chem.
Soc., Chem. Commun. 1989, 1454−1456.
(30) (a) Collman, J. P.; Rose, E.; Venburg, G. D. Reactivity of
ruthenium 5,10,15,20-tetramesitylporphyrin towards diazoesters:
formation of olefins. J. Chem. Soc., Chem. Commun. 1993, 934−935.
(b) Basato, M.; Tubaro, C.; Biffis, A.; Bonato, M.; Buscemi, G.;
Lighezzolo, F.; Lunardi, P.; Vianini, C.; Benetollo, F.; Del Zotto, A.
Reactions of diazo compounds with alkenes catalysed by [RuCl-
(cod)(Cp)]: effect of the substituents in the formation of cyclo-
propanation or metathesis products. Chem. - Eur. J. 2009, 15, 1516−
1526. (c) Ye, X.; Yang, L.; Wu, Z.; Ren, G.; Lu, Y.; Sun, T.; Lei, Q.;
Fang, W.; Xie, H. Exploring the reaction mechanism of a cationic
terminal iridium methylene complex with ethyl diazoacetate, a Lewis
base and dihydrogen: a quantum chemistry study. New J. Chem. 2014,
38, 4115−4119.
(31) Rivilla, I.; Sameera, W. M.; Alvarez, E.; Diaz-Requejo, M. M.;
Maseras, F.; Perez, P. J. Catalytic cross-coupling of diazo compounds
with coinage metal-based catalysts: an experimental and theoretical
study. Dalton Trans 2013, 42, 4132−4138.
J
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(46) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum mechanical
continuum solvation models. Chem. Rev. 2005, 105, 2999−3094.
(47) (a) Wadt, W. R.; Hay, P. J. Ab initio effective core potentials for
molecular calculations. Potentials for main group elements Na to Bi. J.
Chem. Phys. 1985, 82, 284−298. (b) Hay, P. J.; Wadt, W. R. Ab initio
effective core potentials for molecular calculations. Potentials for K to
Au including the outermost core orbitals. J. Chem. Phys. 1985, 82,
299−310.
̈
̈
(48) Hollwarth, A.; Bohme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi,
̈
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
A set of d-polarization functions for pseudo-potential basis sets of the
main group elements Al-Bi and f-type polarization functions for Zn,
Cd, Hg. Chem. Phys. Lett. 1993, 208, 237−240.
(49) (a) Fukui, K. Formulation of the reaction coordinate. J. Phys.
Chem. 1970, 74, 4161−4163. (b) Fukui, K. The path of chemical
reactions - the IRC approach. Acc. Chem. Res. 1981, 14, 363−368.
(50) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and
accurate ab initio parametrization of density functional dispersion
correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010,
132, 154104.
(51) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.
K
DOI: 10.1021/acs.organomet.8b00889
Organometallics XXXX, XXX, XXX−XXX