Synthesis of Carbophosphinocarbene and Their Donating Ability: Expansion of the Carbone Class

Article abstract of DOI:10.1021/acs.organomet.0c00618

In recent years, carbones (CL2) have established themselves to be reliable ligands in organometallic and catalytic reactions. With its superb donating ability as well as a second lone pair for extra coordination, it distinguishes itself from the widely used carbenes and phosphines. However, a lack of modular structural diversity in carbones has limited its use. A carbophosphinocarbene (CPC), a subclass of carbones containing a carbene and phosphine as flanking groups, offers an easy structural modification. In this work, we report a new modular synthetic procedure for CPCs by using readily available starting materials. In addition, the phosphine moiety can be easily exchanged and directly used out of the bottle. The resulting CPCs offer a strong donating ability. Their electronic properties have been determined using Ga and Au complexes.

Full text of DOI:10.1021/acs.organomet.0c00618

pubs.acs.org/Organometallics
Article
Synthesis of Carbophosphinocarbene and Their Donating Ability:
Expansion of the Carbone Class
Shu-kai Liu, Wen-Ching Chen,* Glenn P. A. Yap, and Tiow-Gan Ong*
Cite This: https://dx.doi.org/10.1021/acs.organomet.0c00618
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: In recent years, carbones (CL2) have established
themselves to be reliable ligands in organometallic and catalytic
reactions. With its superb donating ability as well as a second lone
pair for extra coordination, it distinguishes itself from the widely
used carbenes and phosphines. However, a lack of modular
structural diversity in carbones has limited its use. A carbophos-
phinocarbene (CPC), a subclass of carbones containing a carbene
and phosphine as flanking groups, offers an easy structural
modification. In this work, we report a new modular synthetic
procedure for CPCs by using readily available starting materials. In
addition, the phosphine moiety can be easily exchanged and
directly used out of the bottle. The resulting CPCs offer a strong donating ability. Their electronic properties have been determined
using Ga and Au complexes.
from NHCs in terms of chemical reactivity.2 Other unique
INTRODUCTION
■
features of CDCs have also been unraveled by the works of
England and our laboratory, demonstrating redox and
photoactive properties that NHCs are lacking.3 Definitely,
these complementary features should permit CDCs to define
their own kind of new conceptual reactivity as opposed to
traditional ligands such as NHCs and phosphines.
Carbodicarbenes A (CDCs) are classified in the family of
carbones (CL2) that feature a dicoordinated central carbon
(C0). This C0 bears two lone electron pairs with N-
heterocyclic carbenes (NHCs) as flanking ligands (L) (Scheme
1). Due to the two lone pairs on the central carbon, CDCs
Scheme 1. General Structures of CDC (A), CDP (B), and
CPC (C) and Reported CPCs
The origin of carbones can be historically traced back to the
discovery of carbodiphosphorane B ((PPh3)2C or CDP) by
Ramirez around 1965.4 However, it was Bertrand,5 Petz,6
Roesky,7 Driess,8 Kira9 and Frenking10 who are responsible for
putting this octet-defying carbogenic species including
silylones and germylones on the map of contemporary
chemistry with interest spanning almost all the conventional
disciplines of chemistry. Of those carbones, carbodicarbenes
and bisylides by Ong,2,11 Stephan,12 Meek,13 Gessner14 and
Fu
̈
rstner15 emerged as notable models in their supporting role
for main-group chemistry, transition-metal complexes, and
catalysis. The success of these cases can be attributed to the
presence of framework diversity in these carbone classes,
enabling the possibility of modulating the steric and electronic
of these ligands for specific reaction conditions.
have been regarded as ligands with strong σ-donation.1 Despite
sharing some similarities to NHCs as electron-rich scaffolds,
CDCs possess low-lying empty p orbitals adjacent to the center
carbon containing lone pairs, rendering these two reactive sites
capable of undergoing 1,2-addition reactions with a series of
organic molecules. This unique property distinguishes CDCs
Special Issue: Organometallic Chemistry of the Main-
Group Elements
Received: September 17, 2020
https://dx.doi.org/10.1021/acs.organomet.0c00618
© XXXX American Chemical Society
Organometallics XXXX, XXX, XXX−XXX
A

Organometallics
pubs.acs.org/Organometallics
Article
Slightly different from A and B, the carbophosphinocarbenes
C (CPCs) are another subset of the C(0) class with their
center carbons flanked by NHC and phosphine. The chemical
implication invoked by this ligand framework is promising. The
two different flanking pendants of CPCs could interplay
synergistically, bringing new distinct properties manifested
between those of the known CDC and CDP. Most
importantly, this platform would allow chemists a great
flexibility to tune the electronic and steric environment of
this ligand. Unfortunately, the CPC scaffold has been
overlooked so far, and only a few known CPCs have been
reported, as illustrated in Scheme 1.11a,15 The lack of a sound
synthetic strategy has hampered the expansion of the CPC
class. Current known procedures of synthesizing CPCs are
ineffective, due to the involvement of overly reactive
phosphorus ylide intermediates.16 In this report, we aim to
address the framework diversity of CPCs by creating a simple
synthetic strategy based on commercially available starting
materials. At the same time, we also investigate and evaluate
the donating strength of CPCs by preparing Ga and Au
complexes.
Scheme 2. Synthetic Route of CPC and Other Known
Derivatives
RESULTS AND DISCUSSION
■
There is no library of ligands concerning scaffolds related to
the CPC moiety, and thus we began our plan to synthesize
ligands. Commercially available N-methylphenylenediamine
hydrochloride salt and glycolic acid were chosen as starting
materials and allowed to react to afford the benzimidazole
derivative 1 in excellent yield of 90% (Scheme 2). Chloroacetic
acid could also be used as an alternative for making 1, albeit in
lower yield (30%).17 Subsequently, the highly hygroscopic
phosphonium salt 2a was prepared in 90% yield via refluxing 1
with PPh3 in 1,4-dioxane solution. An anion exchange with
sodium triflate is used to reduce hydromancy and to increase
its solubility in organic solvents. A direct methylation using
methyl trifluoromethanesulfonate effectively transformed 2a to
the CPC precursor 3a. As illustrated at the bottom of Scheme
2, a total of 10 different CPC precursors (3a−j) were
successfully obtained in good yields using similar preparation
steps (for further details see the Supporting Information). Aryl,
alkyl, or a combination of those (a−d) with certain degrees of
steric modulation and electronic variants (e−j) are possible. As
expected, this new preparation route offered a tremendous
improvement in the overall yield of the reaction (77%) with
step reduction in comparison to our previously reported
method (36%).11a The key strategy underlying the present
achievement is the absence of any formation of a reactive
phosphine ylide. In the previous method the phosphine moiety
was introduced via a nucleophilic attack of the ylide at the N-
heterocyclic thioether derivative to form the precursor. The
ylide’s absence in combination with the direct use of the
phosphine allows the use of alkylated species, which are
sensitive to transylidation.18 In addition, the product
purification for more soluble phosphines (e.g., d−g) can be
more effectively carried out.
carbodicarbene (∼110 ppm)1c but downfield with respect to
the carbodiphosphorane B (∼15 ppm).18a We attributed these
large NMR shift differences to the π-accepting ability of the
flanking ligands embedded within the carbone. The CDC
contained two flanking NHCs with vacant p orbitals capable of
delocalizing electron density away from the center carbon. This
generates a weak shielding effect and thus leads to a downfield
shift in 13C resonances. As expected, CPC has a more upfield
shift in comparison to CDC, as its flanking phosphine is a poor
π-acceptor.19
Further closer examination of 13C NMR of CPCs 4e−h
containing PAr3 revealed signals at around 64−65 ppm for the
center carbon. The upfield trend of 13C NMR in the CPCs was
consistently observed with an increase in number of the alkyl
group. For example, 4b containing one cyclohexyl substituent
has a signal at 55.6 ppm, while that of 4d appears at 43.3 ppm
with three cyclohexyl groups (Scheme 2). This upfield
phenomenon may be correlated directly to the higher σ-
donating strength of PCy3 in comparison to PPh3. In contrast
to 13C NMR, the phosphine resonance moves oppositely
toward the downfield region as the number of alkyl
substituents of CPCs increased (4a (−18.9 ppm) > 4b
(−10.3 ppm) > 4c (−4.9 ppm) > 4d (−4.0 ppm)). This
phenomenon in 31P NMR could be rationalized by an electron-
withdrawing effect invoked by the aryl group that had pulled
the electron density away from the C(0) center to the
phosphorus center, generating a stronger shielding effect over
the P atom for an upfield shift. This trend of correlation is
The free carbone of CPC 4a in 70% yield could be isolated
through a double-deprotonation process using 2 equiv of
sodium amide base (Scheme 2). Other analogous precursors 3
could also be converted to free carbone 4 except for 3i,j (vide
infra). A 31P NMR study of 4a shows a large upfield shift,
moving from 22.2 to −18.9 ppm with respect to its precursor
3a. Similarly, the 13C NMR shift of the center carbon of 4a
appears at 64 ppm, substantially upfield with respect to the
B
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
further exemplified by 4h. Bearing fluorine within the moiety,
4h has the most upfield signal of all CPCs at −23.9 ppm. In
that sense, results obtained from 31P NMR studies could be
used to quantify the π-back-bonding ability of the carbones.
X-ray crystal analyses have been carried out for 4c,d,f,
obtained from a slow evaporation of fluorobenzene at −20 °C
or benzene at room temperature (Figure 1). The pertinent
of a similar cyclization via carbene CH insertion observed by
Bertrand,20 we propose that the transformation of this reaction
occurred via generation of the unstable carbone 4j as depicted
in Scheme 3. Since the methyl group at the ortho position of
Scheme 3. Proposed Mechanism of the Phosphorine 5j from
3j
the tolyl substituent was in close range with the reactive site of
the carbone, a facile intramolecular abstraction occurred to
form a six-membered cyclic transition state to give II-4j.
Rearrangement and concomitant C−N bond cleavage
proceeded to generate product 5j.
To evaluate the electronic properties of the CPC ligands, the
synthesis of metal complexes bearing CPCs is necessary. We
selected gallium and gold complexes as our target of
investigation, because of the experimental simplicity and
literature precedent of using these complexes for measuring
the donating strength. The CPC-ligated gallium complexes
(6a−h, Scheme 4) were prepared by reacting equimolar
Figure 1. X-ray crystal structures of CPC 4c,d,f with thermal
ellipsoids drawn at the 30% probability level and hydrogen atoms
omitted for clarity.
crystal structure of 4a was reported previously by Ong’s
laboratory.11a We note that the structure of 4c flanked with
PPhCy2 features two chemically different molecules in a unit
cell. Thus, we have averaged the structural parameters for the
following discussion. The C1−C2 and C1−P1 bond lengths in
4a,c,d,f are consistently the same with average values of ∼1.33
and ∼1.65 Å, respectively, suggesting a minimum steric
influence of substituents on the topology of the structures.
Among these structures, steric bulk invoked by three
cyclohexyl groups has resulted in 4d having the largest C2−
C1−P1 angle of 149.25° (Table 1).
Scheme 4. Formation of Ga-CPC Complex 6: Overview of
∑
ClGaCl, the Resulting TEP(GaCl3), and the TEP23 of PR3
Table 1. Overview of Specific Bond Lengths of CDP, CDC,
and CPCs
C1−C2 (Å)
C1−P1 (Å) C2−C1−C3/C2−C1−P1 (deg)
CDP18b
CDC1c
4a11a
4c
4d
4f
1.629(3)
143.8(6)
1.318−1.346
1.3378(17)
1.3392(19)
1.3262(18)
1.345(2)
134.8−146.1
143.04(10)
137.94(11)
149.25(12)
144.09(15)
amounts of the ligand and GaCl3 in pentane solution. The
target main-group complexes precipitated readily out of the
solution and were fully characterized by NMR and MS
analysis. Single-crystal X-ray structural analyses confirmed the
coordination of the CPC 4a−f to GaCl3. Unfortunately, we
were unable to get suitable crystals of the complexes with
CPCs 4g,h. As expected, GaCl3 changes its geometry from
trigonal planar to a trigonal-pyramidal-like geometry. The C1−
Ga1 bond length varies from 1.9369(13) to 1.964(2) Å for the
CPCs (6a−f). These bond lengths are shorter in comparison
to CAACs (∼2.0463 Å)21 or NHCs (∼1.994 Å).22 The
electronic variation had no dramatic consequence over the
Ga−carbone bond length of the CPC. Because of a decrease in
the electron density due to the GaCl3 coordination, the average
C1−C2 (∼1.431 Å) and C1−P1 (1.707 Å) bond distances of
all these CPCs were lengthened in comparison to the free CPC
(1.337 and 1.65 Å). Notably, the C2−C1−P1 angle became
1.6435(12)
1.6629(14)
1.6441(13)
1.6454(19)
a
a
There are two chemically distinct molecules in the unit cell; average
values are given.
It should be noted that we failed to obtain free carbones 4i,j,
in spite of attempts using various kinds of bases for
deprotonation. We could not identify products associated
with the deprotonation reaction of 3i, but we successfully
isolated the air-stable bright orange compound 5j (60% yield),
which is attributed to the decomposition of the carbone as an
intermediate. 5j is a phosphorine heteroarene, as confirmed by
a single-crystal X-ray diffraction experiment and NMR
spectroscopy (see the Supporting Information). On the basis
C
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
more acute, an indication of a change of the CPC from sp2
toward sp3 hybridization.
radii of 3.45 Å. Interestingly, we could not find such a
noncovalent interaction in complex 6e (see Figure 2). This
interaction seems to widen the angle of ∑ClGaCl, which can
cause a deception of the true geometry angle. On the basis of
this observation, we concluded that the presence of this
noncovalent interaction negatively affects the Gandon method
and makes predicting the donor strength of the CPC in a more
precise manner harder.
To avoid the problem associated with nonbonding
interactions in the Gandon method, we needed to find a
more effective alternate to quantify each CPC. More
importantly, we needed a method that is not dependent on
the single-crystal X-ray structures. The Huynh electronic
parameter (HEP) seems to be the perfect choice to measure
the donating ability of the carbones. Huynh et al. reported a
parameter based on the 13C NMR chemical shift of the carbene
carbon atom of the complexes trans-[PdBr2(iPr2-bimy)(L)]
and [(iPr2-bimy)Au-L]+ as a probe for gauging the donating
strength of the ligand L.24 Similar to Gandon’s method, this
method mainly measures the σ-donating ability of the ligand.
The preparation of [(iPr2-bimy)Au-L][BF4] complexes (7)
was needed, in which L was our CPC ligand. A previously
reported synthetic protocol based on the starting compound
(iPr2-bimy)Au-Cl was not suitable, as it was plagued by a facile
ligand redistribution process leading to the unwanted by-
product [(iPr2-bimy)2Au]+, which made the purification step
unmanageable (Scheme 5). Therefore, an alternative route was
developed to prepare [(iPr2-bimy)Au-L][BF4].
Another important structural feature of these Ga complexes
of 6 is the sum of the Cl−Ga−Cl angles (∑ClGaCl). The
Gandon group recently reported that the degree of the
pyramidalization of the L→GaCl3 complex correlated with the
TEP (Tolman electronic parameter) donating strength over a
wide range of ligands such as phosphines, carbenes (NHC/
CAAC), and several CDC/CDPs. It was found that a stronger
donor will concentrate the π-character of the gallium orbitals
toward the chlorine atoms. This effect leads to the compacting
of the three Cl−Ga−Cl angles. As a result, the sum of angles
around Cl−Ga provides useful information about the donor
strength of CPC ligands.21 In Scheme 4, the ∑ClGaCl values and
their calculated TEP values are given for each CPC-Ga
complex. In view of these structural parameters, the complex 6f
(313.3°) bearing the 4f ligand has the smallest value of
∑ClGaCl, while 6a bearing the 4a ligand has the largest value
(320.0°). Subsequent conversion of the ∑ClGaCl values gives
TEP values of 2031.7 and 2043.3 cm−1 on the basis of Gandon
protocol, respectively (see the Supporting Information).
Importantly, the donor strength predicted by the Gandon
method showed that the CPCs are more strongly donating
ligands (2043−2031 cm−1) in comparison to NHCs and
CAACs (2051−2046 cm−1). As shown in Scheme 4, the
donation ability strength of CPC is ranked in order of weakest
to strongest as 4a < 4e < 4d < 4b < 4c < 4f on the basis of the
Gandon protocol. Notwithstanding its accuracy in predicting
electronic features for common ligands, we observed an
anomaly within the carbone system in this method. For
example, 4d flanked by PCy3 is supposed to be more electron
rich than 4b (PPh2Cy), 4c (PPhCy2), and 4f (p-PTol3) but the
Gandon method predicted otherwise. This is counterintuitive
to our conventional chemical electronic knowledge of these
ligands, as flanking phosphine fragments should account for
most of the donor strength of CPCs.
Scheme 5. Formation of Complexes 7 and 8 and Their
Resulting HEPs
Gandon and co-workers briefly noted that noncovalent
interactions and crystal forces influence the conformation of
structures, which might affect the accuracy of the measure-
ment. A detailed examination of these structures revealed a
noncovalent interaction between the electronegative chloride
atoms and flanking NHC containing an empty p orbital. The
nonbonding interaction varies from 3.281 Å (6c) to 3.415 Å
(6f; see Figure 2), which is within the combined van der Waals
The isolable [(iPr2-bimy)Au-py][BF4] (9; see the Support-
ing Information for further information) is used as an
intermediate in the synthesis step, the desirable complexes 7
were obtained in good yield with full characterization via NMR
and MS experiments. Crystals of 7a suitable for X-ray analyses
were grown by diffusion of pentane into a saturated
dichloromethane solution at −30 °C. The Au−C bond of 7a
(2.052(2) Å) is slightly long, warranting no further detailed
discussion. On the basis of 13C NMR studies of complexes 7,
the HEP revealed the following order of the weakest to the
strongest carbone ligands: 4h < 4a < 4e < 4f < 4g < 4b < 4c <
4d. Similarly to Gandon’s method with GaCl3 we observed 4a
to be the most weakly donating ligand, while 4d is now seen as
the most strongly donating ligand. We were also able to
analyze CPCs 4h (p-P(PhF)3) and 4g (p-P(Anisyl)3) with this
method. These two were missing in the Gandon method due
to a lack of crystal structures. Again, the anomaly occurring in
Figure 2. X-ray crystal structures of Ga-CPCs 6e,f with thermal
ellipsoids drawn at the 30% probability level. Solvent and hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): 6e, Ga1−C1 1.9425(15), C1−C2 1.4352(29), C1−P1
1.7017(15), C2−C1−P1 117.03(11); 6f, Ga1−C1 1.964(2), C1−
C2 1.419(3), C1−P1 1.715(2), C2−C1−P1 121.96(15), C2···Cl3
3.415.
D
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Gandon’s method with alkylated phosphines is not observed
here. The more electron rich phosphine PCy3 in 4d is the
strongest donor among the CPCs, in line with our intuitive
thoughts. In addition, the HEP was measured with our
previously reported CDCs as well with the following ranking:
CDC1 < CDC2 < CDC3. The result is also in line with our
expectation that CDC3 is the most strongly donating ligand
followed by CDC2 and CDC1, which have approximately
equal donating strengths. On comparison of the results of
CPCs and CDCs, the HEP reveals that CDC3 is more strongly
donating than CPC 4d. CDC1 and CDC2 are ranked in the
lower midrange, showing that most of the newly synthesized
CPCs are more strongly donating ligands. The reason may be
the donating strength of the free ligand itself. Imidazolylidene
is known to be a stronger donor than the phosphines and
therefore makes CDC3 the strongest member. On the other
hand, the benzimidazolylidene strength is similar to that of the
phosphines, leading to a lower rank.
Chemical Science and Technology, Taiwan International
Graduate Program, Academia Sinica and National Chiao
Tung University, Hsin-chu, Taiwan; orcid.org/0000-
0002-8627-5253
Glenn P. A. Yap − The Department of Chemistry and
Biochemistry, University of Delaware, Newark, Delaware
19716, United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00618
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Ministry of Science
& Technology of Taiwan (MOST-107-2113-M-001-034-MY2,
MOST-109-2113-M-001-038, and MOST-108-2113-M-001-
026-MY3 grants) and the grant of an Academia Sinica
Investigator Award (AS-IA-108-M04). S.L. thanks Academia
Sinica and TIGP for financial and technical support.
CONCLUSION
■
In conclusion, we have shown a new, convenient, and efficient
synthetic pathway for the gram-scale synthesis of CPCs. This
short and highly modular synthesis allows the use of most
commercially available alkyl and aryl phosphines out of the
bottle without involving the reactive phosphorus ylide. In
addition, it can be considered the most customizable ligand
next to the current NHCs and phosphines. TEP(GaCl3) and
the HEP studies reveal the excellent donating ability of CPCs,
easily surpassing those of CAACs and NHCs. A majority of the
presented CPCs are more strongly donating than previously
reported CDCs. Our group is currently conducting further
research and analysis of the properties of the CPCs and their
application.
REFERENCES
■
(1) For recent reviews, see: (a) Doddi, A.; Peters, M.; Tamm, M. N-
Heterocyclic Carbene Adducts of Main Group Elements and Their
Use as Ligands in Transition Metal Chemistry. Chem. Rev. 2019, 119,
6994−7112. (b) Liu, S.-k.; Shih, W.-C.; Chen, W.-C.; Ong, T.-G.
Carbodicarbenes and their Captodative Behavior in Catalysis.
ChemCatChem 2018, 10, 1483−1498. (c) Liu, S.; Chen, W.-C.;
Ong, T.-G. Synthesis and Structure of Carbodicarbenes and Their
Application in Catalysis. In Modern Ylide Chemistry: Applications in
Ligand Design, Organic and Catalytic Transformations; Gessner, V. H.,
Ed.; Springer International: Cham, Switzerland, 2018; pp 51−71.
(2) Chen, W.-C.; Shih, W.-C.; Jurca, T.; Zhao, L.; Andrada, D. M.;
Peng, C.-J.; Chang, C.-C.; Liu, S.-k.; Wang, Y.-P.; Wen, Y.-S.; Yap, G.
P. A.; Hsu, C.-P.; Frenking, G.; Ong, T.-G. Carbodicarbenes:
Unexpected π-Accepting Ability during Reactivity with Small
Molecules. J. Am. Chem. Soc. 2017, 139, 12830−12836.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00618.
■
sı
(3) (a) Chan, S.-C.; Gupta, P.; Engelmann, X.; Ang, Z. Z.; Ganguly,
R.; Bill, E.; Ray, K.; Ye, S.; England, J. Observation of Carbodicarbene
Ligand Redox Noninnocence in Highly Oxidized Iron Complexes.
Angew. Chem., Int. Ed. 2018, 57, 15717−15722. (b) Chan, S.-C.; Ang,
Z. Z.; Gupta, P.; Ganguly, R.; Li, Y.; Ye, S.; England, J.
Carbodicarbene Ligand Redox Noninnocence in Highly Oxidized
Chromium and Cobalt Complexes. Inorg. Chem. 2020, 59, 4118−
4128. (c) Hsu, Y.-C.; Wang, V. C.-C.; Au-Yeung, K.-C.; Tsai, C.-Y.;
Chang, C.-C.; Lin, B.-C.; Chan, Y.-T.; Hsu, C.-P.; Yap, G. P. A.; Jurca,
T.; Ong, T.-G. One-Pot Tandem Photoredox and Cross-Coupling
Catalysis with a Single Palladium Carbodicarbene Complex. Angew.
Chem., Int. Ed. 2018, 57, 4622−4626.
Experimental details and characterization data (PDF)
Accession Codes
CCDC 2031833−2031844 contain the supplementary crys-
tallographic 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
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(4) (a) Ramirez, F.; Desai, N. B.; Hansen, B.; McKelvie, N.
Hexaphenylcarbodiphosphorane, (C6H5)3PCP(C6H5)3. J. Am. Chem.
Soc. 1961, 83, 3539−3540. (b) Desai, N. B.; McKelvie, N.; Ramirez,
AUTHOR INFORMATION
Corresponding Authors
■
̈
F. A New Synthesis of 1,1-Dibromoolefins via Phosphine-Dibromo-
Wen-Ching Chen − Institute of Chemistry, Academia Sinica,
Taipei, Taiwan; Email: cwc590317@gmail.com
Tiow-Gan Ong − Institute of Chemistry, Academia Sinica,
Taipei, Taiwan; The Department of Applied Chemistry,
National Chiao Tung University, Hsin-chu, Taiwan; The
Department of Chemistry, National Taiwan University,
Taipei, Taiwan; orcid.org/0000-0001-9817-6300;
Email: tgong@gate.sinica.edu.tw
methylenes. the Reaction of Triphenylphosphine with Carbon
Tetrabromide. J. Am. Chem. Soc. 1962, 84, 1745−1747.
(5) (a) Melaimi, M.; Parameswaran, P.; Donnadieu, B.; Frenking,
G.; Bertrand, G. Synthesis and Ligand Properties of a Persistent, All-
Carbon Four-Membered-Ring Allene. Angew. Chem., Int. Ed. 2009, 48,
́
4792−4795. (b) Fernandez, I.; Dyker, C. A.; DeHope, A.; Donnadieu,
B.; Frenking, G.; Bertrand, G. Exocyclic Delocalization at the Expense
of Aromaticity in 3,5-bis(π-Donor) Substituted Pyrazolium Ions and
Corresponding Cyclic Bent Allenes. J. Am. Chem. Soc. 2009, 131,
11875−11881. (c) Lavallo, V.; Dyker, C. A.; Donnadieu, B.; Bertrand,
G. Synthesis and Ligand Properties of Stable Five-Membered-Ring
Allenes Containing Only Second-Row Elements. Angew. Chem., Int.
Ed. 2008, 47, 5411−5414. (d) DeHope, A.; Donnadieu, B.; Bertrand,
Authors
Shu-kai Liu − Institute of Chemistry, Academia Sinica, Taipei,
Taiwan; The Department of Applied Chemistry, National
Chiao Tung University, Hsin-chu, Taiwan; Sustainable
E
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
G. Grubbs and Hoveyda-type ruthenium complexes bearing a cyclic
bent-allene. J. Organomet. Chem. 2011, 696, 2899−2903. (e) Wein-
stein, C. M.; Martin, C. D.; Liu, L.; Bertrand, G. Cross-Coupling
Reactions between Stable Carbenes. Angew. Chem., Int. Ed. 2014, 53,
6550−6553.
6047−6048. (l) Frenking, G.; Hermann, M.; Andrada, D. M.;
Holzmann, N. Donor-acceptor bonding in novel low-coordinated
compounds of boron and group-14 atoms C-Sn. Chem. Soc. Rev. 2016,
45, 1129−1144.
(11) (a) Chen, W.-C.; Shen, J.-S.; Jurca, T.; Peng, C.-J.; Lin, Y.-H.;
Wang, Y.-P.; Shih, W.-C.; Yap, G. P. A.; Ong, T.-G. Expanding the
Ligand Framework Diversity of Carbodicarbenes and Direct
Detection of Boron Activation in the Methylation of Amines with
CO2. Angew. Chem., Int. Ed. 2015, 54, 15207−15212. (b) Chen, W.-
C.; Lee, C.-Y.; Lin, B.-C.; Hsu, Y.-C.; Shen, J.-S.; Hsu, C.-P.; Yap, G.
P. A.; Ong, T.-G. The Elusive Three-Coordinate Dicationic Hydrido
Boron Complex. J. Am. Chem. Soc. 2014, 136, 914−917. (c) Chen,
W.-C.; Hsu, Y.-C.; Lee, C.-Y.; Yap, G. P. A.; Ong, T.-G. Synthetic
Modification of Acyclic Bent Allenes (Carbodicarbenes) and Further
Studies on Their Structural Implications and Reactivities. Organo-
metallics 2013, 32, 2435−2442.
(12) (a) Pranckevicius, C.; Liu, L.; Bertrand, G.; Stephan, D. W.
Synthesis of a Carbodicyclopropenylidene: A Carbodicarbene based
Solely on Carbon. Angew. Chem., Int. Ed. 2016, 55, 5536−5540.
(b) Dobrovetsky, R.; Stephan, D. W. Catalytic Reduction of CO2 to
CO by Using Zinc(II) and In Situ Generated Carbodiphosphoranes.
Angew. Chem., Int. Ed. 2013, 52, 2516−2519. (c) Pranckevicius, C.;
Fan, L.; Stephan, D. W. Cyclic Bent Allene Hydrido-Carbonyl
Complexes of Ruthenium: Highly Active Catalysts for Hydrogenation
of Olefins. J. Am. Chem. Soc. 2015, 137, 5582−5589.
(13) (a) Marcum, J. S.; Roberts, C. C.; Manan, R. S.; Cervarich, T.
N.; Meek, S. J. Chiral Pincer Carbodicarbene Ligands for
Enantioselective Rhodium-Catalyzed Hydroarylation of Terminal
and Internal 1,3-Dienes with Indoles. J. Am. Chem. Soc. 2017, 139,
15580−15583. (b) Roberts, C. C.; Matías, D. M.; Goldfogel, M. J.;
Meek, S. J. Lewis Acid Activation of Carbodicarbene Catalysts for Rh-
Catalyzed Hydroarylation of Dienes. J. Am. Chem. Soc. 2015, 137,
6488−6491. (c) Goldfogel, M. J.; Roberts, C. C.; Meek, S. J.
Intermolecular Hydroamination of 1,3-Dienes Catalyzed by Bis-
(phosphine)carbodicarbene−Rhodium Complexes. J. Am. Chem. Soc.
2014, 136, 6227−6230.
(6) (a) Petz, W. Addition compounds between carbones, CL2, and
main group Lewis acids: A new glance at old and new compounds.
Coord. Chem. Rev. 2015, 291, 1−27. (b) Petz, W.; Neumuller, B. New
̈
platinum complexes with carbodiphosphorane as pincer ligand via
ortho phenyl metallation. Polyhedron 2011, 30, 1779−1784. (c) Petz,
̈
W.; Oxler, F.; Neumuller, B. Syntheses and crystal structures of linear
̈
coordinated complexes of Ag+ with the ligands C(PPh3)2 and
(HC{PPh3}2)+. J. Organomet. Chem. 2009, 694, 4094−4099.
(d) Petz, W.; Kutschera, C.; Neumuller, B. Reaction of the
̈
Carbodiphosphorane Ph3PCPPh3 with Platinum(II) and -(0)
Compounds: Platinum Induced Activation of C−H Bonds. Organo-
metallics 2005, 24, 5038−5043.
(7) (a) Mondal, K. C.; Roesky, H. W.; Schwarzer, M. C.; Frenking,
̈
G.; Niepotter, B.; Wolf, H.; Herbst-Irmer, R.; Stalke, D. A Stable
Singlet Biradicaloid Siladicarbene: (L:)2Si. Angew. Chem., Int. Ed.
2013, 52, 2963−2967. (b) Li, Y.; Mondal, K. C.; Roesky, H. W.; Zhu,
H.; Stollberg, P.; Herbst-Irmer, R.; Stalke, D.; Andrada, D. M. Acyclic
Germylones: Congeners of Allenes with a Central Germanium Atom.
J. Am. Chem. Soc. 2013, 135, 12422−12428.
(8) (a) Xiong, Y.; Yao, S.; Inoue, S.; Epping, J. D.; Driess, M. A
Cyclic Silylone (“Siladicarbene”) with an Electron-Rich Silicon(0)
Atom. Angew. Chem., Int. Ed. 2013, 52, 7147−7150. (b) Xiong, Y.;
Yao, S.; Tan, G.; Inoue, S.; Driess, M. A Cyclic Germadicarbene
(“Germylone”) from Germyliumylidene. J. Am. Chem. Soc. 2013, 135,
5004−5007. (c) Zhou, Y.-P.; Karni, M.; Yao, S.; Apeloig, Y.; Driess,
M. A Bis(silylenyl)pyridine Zero-Valent Germanium Complex and Its
Remarkable Reactivity. Angew. Chem., Int. Ed. 2016, 55, 15096−
15099.
(9) (a) Ishida, S.; Iwamoto, T.; Kabuto, C.; Kira, M. A stable silicon-
based allene analogue with a formally sp-hybridized silicon atom.
Nature 2003, 421, 725−727. (b) Iwamoto, T.; Masuda, H.; Kabuto,
C.; Kira, M. Trigermaallene and 1,3-Digermasilaallene. Organo-
metallics 2005, 24, 197−199. (c) Iwamoto, T.; Abe, T.; Kabuto, C.;
Kira, M. A missing allene of heavy Group 14 elements: 2-
germadisilaallene. Chem. Commun. 2005, 5190−5192. (d) Kira, M.;
Iwamoto, T.; Ishida, S.; Masuda, H.; Abe, T.; Kabuto, C. Unusual
Bonding in Trisilaallene and Related Heavy Allenes. J. Am. Chem. Soc.
2009, 131, 17135−17144. (e) Kira, M. An isolable dialkylsilylene and
its derivatives. A step toward comprehension of heavy unsaturated
bonds. Chem. Commun. 2010, 46, 2893−2903.
(10) (a) Tonner, R.; Frenking, G. C(NHC)2: Divalent Carbon(0)
Compounds with N-Heterocyclic Carbene LigandsTheoretical
Evidence for a Class of Molecules with Promising Chemical
Properties. Angew. Chem., Int. Ed. 2007, 46, 8695−8698. (b) Tonner,
R.; Frenking, G. Divalent Carbon(0) Chemistry, Part 1: Parent
Compounds. Chem. - Eur. J. 2008, 14, 3260−3272. (c) Tonner, R.;
Frenking, G. Divalent Carbon(0) Chemistry, Part 2: Protonation and
Complexes with Main Group and Transition Metal Lewis Acids.
Chem. - Eur. J. 2008, 14, 3273−3289. (d) Takagi, N.; Shimizu, T.;
Frenking, G. Divalent E(0) Compounds (E = Si−Sn). Chem. - Eur. J.
2009, 15, 8593−8604. (e) Takagi, N.; Shimizu, T.; Frenking, G.
Divalent Silicon(0) Compounds. Chem. - Eur. J. 2009, 15, 3448−
3456. (f) Tonner, R.; Frenking, G. Tolman’s Electronic Parameters
for Divalent Carbon(0) Compounds. Organometallics 2009, 28,
3901−3905. (g) Klein, S.; Tonner, R.; Frenking, G. Carbodicarbenes
and Related Divalent Carbon(0) Compounds. Chem. - Eur. J. 2010,
16, 10160−10170. (h) Esterhuysen, C.; Frenking, G. Distinguishing
Carbones from Allenes by Complexation to AuCl. Chem. - Eur. J.
2011, 17, 9944−9956. (i) Himmel, D.; Krossing, I.; Schnepf, A.
Dative Bonds in Main-Group Compounds: A Case for Fewer Arrows!
Angew. Chem., Int. Ed. 2014, 53, 370−374. (j) Frenking, G. Dative
Bonds in Main-Group Compounds: A Case for More Arrows! Angew.
Chem., Int. Ed. 2014, 53, 6040−6046. (k) Himmel, D.; Krossing, I.;
Schnepf, A. Dative or Not Dative? Angew. Chem., Int. Ed. 2014, 53,
(14) (a) Scherpf, T.; Wirth, R.; Molitor, S.; Feichtner, K.-S.;
Gessner, V. H. Bridging the Gap between Bisylides and Methandiides:
Isolation, Reactivity, and Electronic Structure of an Yldiide. Angew.
Chem., Int. Ed. 2015, 54, 8542−8546. (b) Scharf, L. T.; Gessner, V. H.
Metalated Ylides: A New Class of Strong Donor Ligands with Unique
Electronic Properties. Inorg. Chem. 2017, 56, 8599−8607. (c) Scharf,
L. T.; Andrada, D. M.; Frenking, G.; Gessner, V. H. The Bonding
Situation in Metalated Ylides. Chem. - Eur. J. 2017, 23, 4422−4434.
(d) Weber, P.; Scherpf, T.; Rodstein, I.; Lichte, D.; Scharf, L. T.;
Gooßen, L. J.; Gessner, V. H. A Highly Active Ylide-Functionalized
Phosphine for Palladium-Catalyzed Aminations of Aryl Chlorides.
Angew. Chem., Int. Ed. 2019, 58, 3203−3207. (e) Scherpf, T.;
Schwarz, C.; Scharf, L. T.; Zur, J.-A.; Helbig, A.; Gessner, V. H. Ylide-
Functionalized Phosphines: Strong Donor Ligands for Homogeneous
Catalysis. Angew. Chem., Int. Ed. 2018, 57, 12859−12864. (f) Kroll,
A.; Steinert, H.; Scharf, L. T.; Scherpf, T.; Mallick, B.; Gessner, V. H.
A diamino-substituted carbodiphosphorane as strong C-donor and
weak N-donor: isolation of monomeric trigonal-planar L·ZnCl2.
Chem. Commun. 2020, 56, 8051−8054.
́
(15) (a) Alcarazo, M.; Suarez, R. M.; Goddard, R.; Furstner, A. A
̈
New Class of Singlet Carbene Ligands. Chem. - Eur. J. 2010, 16,
9746−9749. (b) Alcarazo, M.; Lehmann, C. W.; Anoop, A.; Thiel, W.;
Furstner, A. Coordination chemistry at carbon. Nat. Chem. 2009, 1,
̈
295−301.
(16) Bestmann, H. J.; Zimmerman, R. 1.6 - Synthesis of
Phosphonium Ylides. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Eds.; Pergamon: Oxford, 1991; pp 171−202.
(17) Dumat, B.; Bordeau, G.; Faurel-Paul, E.; Mahuteau-Betzer, F.;
Saettel, N.; Metge, G.; Fiorini-Debuisschert, C.; Charra, F.; Teulade-
Fichou, M.-P. DNA Switches on the Two-Photon Efficiency of an
Ultrabright Triphenylamine Fluorescent Probe Specific of AT
Regions. J. Am. Chem. Soc. 2013, 135, 12697−12706.
F
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
(18) (a) Yogendra, S.; Schulz, S.; Hennersdorf, F.; Kumar, S.;
Fischer, R.; Weigand, J. J. Reductive Ring Opening of a Cyclo-
Tri(phosphonio)methanide Dication to a Phosphanylcarbodiphos-
pho-rane: In Situ UV-Vis Spectroelectrochemistry and Gold
Coordination. Organometallics 2018, 37, 748−754. (b) Vincent, A.
T . ; W h e a t l e y , P . J . C r y s t a l s t r u c t u r e o f b i s -
(triphenylphosphoranylidene)-methane [hexaphenylcarbodiphos-
phorane, Ph3P:C:PPh3]. J. Chem. Soc., Dalton Trans. 1972, 617−622.
(19) Wilson, D. J. D.; Couchman, S. A.; Dutton, J. L. Are N-
Heterocyclic Carbenes “Better” Ligands than Phosphines in Main
Group Chemistry? A Theoretical Case Study of Ligand-Stabilized E2
Molecules, L-E-E-L (L = NHC, phosphine; E = C, Si, Ge, Sn, Pb, N,
P, As, Sb, Bi). Inorg. Chem. 2012, 51, 7657−7668.
(20) Weinstein, C. M.; Junor, G. P.; Tolentino, D. R.; Jazzar, R.;
Melaimi, M.; Bertrand, G. Highly Ambiphilic Room Temperature
Stable Six-Membered Cyclic (Alkyl)(amino)carbenes. J. Am. Chem.
Soc. 2018, 140, 9255−9260.
(21) El-Hellani, A.; Monot, J.; Tang, S.; Guillot, R.; Bour, C.;
Gandon, V. Relationship between Gallium Pyramidalization in L·
GaCl3 Complexes and the Electronic Ligand Properties. Inorg. Chem.
2013, 52, 11493−11502.
́
(22) Marion, N.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Stevens,
E. D.; Fensterbank, L.; Malacria, M.; Nolan, S. P. Synthesis,
Characterization, and Structure of [GaCl3(NHC)] Complexes.
Organometallics 2007, 26, 3256−3259.
(23) (a) Tolman, C. A. Steric effects of phosphorus ligands in
organometallic chemistry and homogeneous catalysis. Chem. Rev.
1977, 77, 313−348. (b) Chen, L.; Ren, P.; Carrow, B. P. Tri(1-
adamantyl)phosphine: Expanding the Boundary of Electron-Releasing
Character Available to Organophosphorus Compounds. J. Am. Chem.
Soc. 2016, 138, 6392−6395. (c) Brink, A.; Roodt, A.; Steyl, G.; Visser,
H. G. Steric vs. electronic anomaly observed from iodomethane
oxidative addition to tertiary phosphine modified rhodium(i)
acetylacetonato complexes following progressive phenyl replacement
by cyclohexyl [PR3 = PPh3, PPh2Cy, PPhCy2 and PCy3]. Dalton
Trans. 2010, 39, 5572−5578.
(24) (a) Huynh, H. V. Electronic Properties of N-Heterocyclic
Carbenes and Their Experimental Determination. Chem. Rev. 2018,
118, 9457−9492. (b) Huynh, H. V.; Han, Y.; Jothibasu, R.; Yang, J. A.
13C NMR Spectroscopic Determination of Ligand Donor Strengths
Using N-Heterocyclic Carbene Complexes of Palladium(II). Organo-
metallics 2009, 28, 5395−5404. (c) Guo, S.; Sivaram, H.; Yuan, D.;
Huynh, H. V. Gold and Palladium Hetero-Bis-NHC Complexes:
Characterizations, Correlations, and Ligand Redistributions. Organo-
metallics 2013, 32, 3685−3696. (d) Teng, Q.; Huynh, H. V. A unified
ligand electronic parameter based on 13C NMR spectroscopy of N-
heterocyclic carbene complexes. Dalton Trans. 2017, 46, 614−627.
G
https://dx.doi.org/10.1021/acs.organomet.0c00618
Organometallics XXXX, XXX, XXX−XXX