Pd(II) Complexes with Chelating Phosphinoferrocene Diaminocarbene Ligands: Synthesis, Characterization, and Catalytic Use in Pd-Catalyzed Borylation of Aryl Bromides

Article abstract of DOI:10.1021/acs.organomet.9b00398

We developed a novel, straightforward route toward Pd(II)-aminocarbene complexes bearing a P-chelating phosphinoferrocenyl substituent based on a three-component reaction of 1′-(diphenylphosphino)-1-isocyanoferrocene (1) with [PdCl₂(cod)] (cod = cycloocta-1,5-diene) and nucleophilic amines. Depending on the type of the amine, the reaction produced acyclic diaminocarbenes and their saturated (imidazolin-2-ylidene) and unsaturated (imidazol-2-ylidene) cyclic counterparts (NHCs). Using (S)-2-(chloromethyl)pyrrolidine as the nucleophile, this method afforded a separable pair of stable diastereomeric bicyclic imidazolin-2-ylidene carbenes with different configurations of the planar-chiral ferrocene unit. The prepared P-chelating carbenes were characterized using spectroscopic methods, X-ray crystallography, and DFT methods. The last were used to explain the formation of isomeric open diaminocarbenes featuring NHR groups at the wing-tip position, trends in Pd-Cl bond lengths reflecting similar trans influences of the particular carbene and phosphine donors, and the results from cyclic voltammetric measurements. Furthermore, the carbenes were used as defined (pre)catalysts in Miyaura borylation of aryl bromides with bis(pinacolato)diboron. When applying the optimized catalytic system (1 mol % Pd catalyst, KOAc as the base, 2-propanol, 85 °C), this reaction produced a range of simple and substituted arylboronate pinacol esters in high yield and without biaryl side products.

Full text of DOI:10.1021/acs.organomet.9b00398

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Pd(II) Complexes with Chelating Phosphinoferrocene
Diaminocarbene Ligands: Synthesis, Characterization, and Catalytic
Use in Pd-Catalyzed Borylation of Aryl Bromides
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Karel Skoch, Jirí Schulz, Ivana Císarova, and Petr Stepnicka*
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
S
* Supporting Information
ABSTRACT: We developed a novel, straightforward route
toward Pd(II)-aminocarbene complexes bearing a P-chelating
phosphinoferrocenyl substituent based on a three-component
reaction of 1′-(diphenylphosphino)-1-isocyanoferrocene (1)
with [PdCl2(cod)] (cod = cycloocta-1,5-diene) and nucleo-
philic amines. Depending on the type of the amine, the
reaction produced acyclic diaminocarbenes and their saturated
(imidazolin-2-ylidene) and unsaturated (imidazol-2-ylidene)
cyclic counterparts (NHCs). Using (S)-2-(chloromethyl)pyrrolidine as the nucleophile, this method afforded a separable pair of
stable diastereomeric bicyclic imidazolin-2-ylidene carbenes with different configurations of the planar-chiral ferrocene unit. The
prepared P-chelating carbenes were characterized using spectroscopic methods, X-ray crystallography, and DFT methods. The
last were used to explain the formation of isomeric open diaminocarbenes featuring NHR groups at the wing-tip position, trends
in Pd−Cl bond lengths reflecting similar trans influences of the particular carbene and phosphine donors, and the results from
cyclic voltammetric measurements. Furthermore, the carbenes were used as defined (pre)catalysts in Miyaura borylation of aryl
bromides with bis(pinacolato)diboron. When applying the optimized catalytic system (1 mol % Pd catalyst, KOAc as the base,
2-propanol, 85 °C), this reaction produced a range of simple and substituted arylboronate pinacol esters in high yield and
without biaryl side products.
a
Chart 1. Examples of Ferrocene Phosphino-NHC Ligands
INTRODUCTION
■
The discovery of persistent carbenes and their transition metal
complexes1,2 has led to a remarkable paradigm shift in the
design of ancillary ligands for transition metal chemistry and
catalysis. In particular, N-heterocyclic carbenes (NHCs)3
emerged as attractive alternatives to ubiquitous phosphine
ligands. Similarly to phosphine donors, the coordination
properties of NHCs can be easily varied by changing the
organic scaffold and substituents and, thus, advantageously
fine-tuned to a specific purpose.4
Perhaps unsurprisingly, research on NHCs has recently
intertwined with the chemistry of ferrocene-based ligands,
which is another rapidly developing research area.5 Now, the
use of ferrocene fragments in the design of NHCs is no longer
uncommon, with applications ranging from mere pendant
substituents to the very molecular scaffold and carriers of
molecular chirality.6 Among these applications, compounds
featuring phosphinoferrocenyl substituents stand out for
combining NHC (most typically an imidazol-2-ylidene) with
phosphine donor moieties, in addition to their ability to form
P,C-chelate complexes.7 Representative examples of such
compounds, A,8 B,9 C,10 and D,10a,11 shown in Chart 1,12
have been synthesized using conventional methods, namely N-
alkylation of suitable imidazoles with ferrocenylmethylating
agents13 followed by deprotonation of the resulting imidazo-
lium salts.
a
The ligands are shown in their generic form with unspecified
substituents R and, for C, also with unspecified planar chirality.
These compounds, however, inevitably contain methylene
linking groups between the imidazolylidene fragment and the
ferrocene group. We hypothesized that this type of compound
albeit without a linker should be easily accessible through
nucleophilic additions across coordinated isocyanides.
Although this approach has been known for a century,14 it
has only been rarely used to prepare carbene complexes with
Received: June 13, 2019
© XXXX American Chemical Society
A
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phosphine substituents,15 primarily due to the lack of suitable
synthetic precursors, i.e., phosphino-isocyanides.
The analogous imidazolin-2-ylidene carbene 4a resulted
from the reaction of [PdCl2(cod)]/1 with N-(2-chloroethyl)-
methylamine generated in situ from the corresponding
hydrochloride and triethylamine (Scheme 2). In this reaction,
Recently, Duan and Matthey16 and our group17 have
reported the synthesis of the first phosphines bearing
isocyanide substituents potentially suitable for the preparation
of chelate complexes (compounds E and 1 in Chart 2). Having
a
Scheme 2. Synthesis of Cyclic Carbenes 4 and 6
Chart 2. Phosphino-Isocyanides Relevant to This Study
demonstrated that isocyanide 1 readily inserts into Pd−C
bonds to produce Pd(II) imidoyl complexes,18 we decided to
extend our studies toward the synthesis of new phosphino-
ferrocene−carbene complexes via reactions of Pd-1 species
with amine nucleophiles. Resulting from these efforts, this
contribution describes the synthesis and structural character-
ization of open and cyclic diaminocarbene Pd(II) complexes
and their application in Pd-catalyzed Miyaura borylation19 of
aryl bromides with bis(pinacolato)diboron.
a
cod = cycloocta-1,5-diene.
RESULTS AND DISCUSSION
■
Syntheses. Repeated initial attempts to prepare defined Pd-
1 complexes (such as PdCl2(1)n) as starting materials for
further reactivity studies failed, only resulting in ill-defined,
dark, and insoluble (probably polymeric) materials. Hence, we
resorted to a one-pot approach based on a simultaneous
addition of a Pd precursor and an amine to 1.20 Indeed, the
reaction of 1 with [PdCl2(cod)] (cod = cycloocta-1,5-diene)
and with a slight excess of primary (MeNH2, i-PrNH2) and
secondary (Me2NH, i-Pr2NH) amines produced acyclic
diaminocarbenes 2 and 3 in moderate-to-good yields (35−
64%; isopropyl-substituted amines gave consistently better
yields) after chromatographic purification (Scheme 1). In
the base additive (NEt3), used in excess, facilitates intra-
molecular alkylation in the intermediate carbene which closes
the imidazoline ring.21 However, this transformation proved
rather delicate. Although the reaction with [(ClCH2CH2)-
NH2Me]Cl/NEt3 produced imidazolin-2-ylidene carbene 4a in
a 85% isolated yield, we were unable to isolate a similar
product from the reaction with the bulkier (2-chloroethyl)-
isopropylamine. The reaction most likely proceeded as
expected but mainly produced other unidentified products
that could not be separated from the desired carbene complex.
Ultimately, imidazol-2-ylidene complexes 6 were prepared
analogously, using amino acetals (MeO)2CHCH2NHR (R =
Me, i-Pr) as protected building blocks (nucleophiles).22 In the
first step, the reaction of the acetals with [PdCl2(cod)]/1
produced stable acyclic carbenes 5 in good yields (Scheme 2).
Similarly to the 2a and 2b pair, compound 5a was isolated as a
mixture of isomers21b (≈2:1 ratio, 85% overall yield), whereas
5b was isolated as a single isomer (73%). After adding HCl (in
dioxane) to dichloromethane solutions of 5, these diamino-
carbenes smoothly transformed into the corresponding
imidazol-2-ylidene complexes 6a and 6b, which were isolated
by column chromatography at yields exceeding 90%. Bulky
(AdaNH2, AdaNHCH2CH2Cl, and AdaNHCH2CH(OMe)2;
Ada = 1-adamantyl) and the less nucleophilic aromatic
(MesNH2, MesNHCH2CH2Cl, and MesNHCH2CH(OMe)2;
Mes = mesityl) amines did not react or produced complex
mixtures under similar reaction conditions.
a
Scheme 1. Synthesis of Acyclic Carbenes 2 and 3
a
cod = cycloocta-1,5-diene.
Structural Characterization. NMR spectra of the isolated
compounds were fully consistent with the formulation.
Diagnostic 13C{1H} NMR resonances (Table 1) due to
carbene carbons were observed as 31P-coupled doublets at δC
193−200 for acyclic and imidazolin-2-ylidene carbenes,
whereas those of imidazol-2-ylidene complexes 6 appeared at
higher fields (δC ≈ 164) and showed no interactions with the
phosphorus atom in the cis position. The ferrocene moieties
particular, the reaction with methylamine afforded the diprotic
carbene 2a as a mixture of two isomers21b (vide infra) in a ratio
of approximately 2:1, whereas a similar reaction with
isopropylamine produced carbene 2b as a single isomer. The
reactions with dimethylamine (generated in situ from Me2NH·
HCl and NEt3) and with diisopropylamine furnished the
respective monoprotic carbenes 3a and 3b.
1
gave rise to eight separate CH resonances in both H and 13C
NMR spectra of all compounds, thus suggesting that the
B
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a
The carbene planes, {N1, C11, N2}, are oriented nearly
perpendicularly to the coordination plane (the interplanar
angles φ are ≈80°; see Table 2), and the N1−C11−N2 angles
decrease from open carbenes through cyclic imidazolin-2-
ylidene to their imidazol-2-ylidene counterparts (N.B. the N−
C−N angles of cyclic carbenes are similar to those determined
for the respective free ligands).23 The saturated C3N2 ring in
the structure of 4a is twisted at the C12−C13 bond (the
torsion angle N1−C12−C13−N2 is 8.4(3)°), whereas the
unsaturated carbene rings in 6a and 6b are planar and
delocalized. The bridging ferrocene units are only marginally
tilted (by ≈3−6° in the series). To facilitate chelate
coordination, the substituents at the cyclopentadienyl rings
are nearly eclipsed (τ = 5−13°), and the attached NCN
moieties are rotated by ≈40° from the planes of their parent
cyclopentadienyl rings (see ψ angles in Table 2).
Table 1. Selected Spectroscopic Data for Carbenes 2−6
carbene
νcarbene
δC [2JPC
]
δP
b
2a
2b
3a
3b
5a
5b
4a
6a
6b
1581
1570
1572
1546
1560
1547
1541, 1497
1571, 1497
1541, 1492
199.8, 191.9
17.8, 17.7
17.8
193.45 [6]
194.55 [7]
193.19 [8]
17.9
16.3
196.25 [7], 198.43 [7]
197.49 [8]
194.68 [2]
164.76
18.0, 17.2
16.8
18.4
17.2
18.1
162.68
a
νcarbene = frequencies of carbene bands (in cm−1) in IR spectra
recorded in Nujol mulls, δC = chemical shift of the carbene carbon (in
ppm) and JPC coupling constants (in Hz), when observed, δP = 31P
2
NMR shifts (in ppm). For solubility reasons, the NMR spectra were
recorded in CD2Cl2−CD3OD. Chemical shifts from 2D spectra.
b
Another noteworthy feature is the variability in Pd−Cl bond
lengths. Pd−Cl2 bonds located trans to the carbene in the open
diaminocarbenes are slightly but statistically significantly
longer than Pd−Cl1 bonds trans to the phosphine moiety,
whereas the opposite is found in the structures of the cyclic
carbenes 4a, 6a, and 6b. This observation is in line with the
notion that the trans influence of phosphines is similar to that
of NHC carbenes based on both structural24 and reactivity9c
data. Otherwise, however, Pd-donor distances match the data
reported for complexes with C-type ligands, [PdCl2(C-
κ2P,C)].10b,c
The fact that compound 2b, isolated as a single isomer,
according to NMR analysis, was structurally characterized as
the seemingly more sterically crowded anti isomer bond led us
to further analyze its solid-state structure and, especially, to
compare the DFT-computed energies and structures of both
isomers of open carbenes 2 (see Chart 3). Three different
functionals (B3LYP, PBE0, and TPSS), used to eliminate a
possible bias, consistently indicated that the syn isomers of 2a
and 2b are energetically favored and that the energy difference
between the isomers is significantly larger in compound 2b
featuring the bulkier terminal substituent (Table 3) than in
compound 2a.
ferrocene moieties had fixed conformations, which render their
CH groups diastereotopic. In addition, pairs of 1H NMR
signals attributable to protons in the α-position of the
cyclopentadienyl rings were observed at markedly lower fields
(up to δH ≈ 6), presumably due to shielding anisotropy.
31P{1H} NMR signals occurred at δP 16−18.
Complexes 2−6 displayed IR bands attributable to carbene
νNCN vibrations in the range 1490−1580 cm−1 (see Table 1),
in addition to νNH bands above 3000 cm−1 in the protic
carbenes. In electrospray ionization (ESI) mass spectra, they
showed ions resulting from the [M − Cl]+ and/or [M − HCl
− Cl]+ fragments.
The structures of compounds 2b, 3a, 3b, 4a, 5b, 6a, and 6b
were determined by single-crystal X-ray diffraction analysis,
often in solvated form (see the Experimental Section).
Molecular diagrams are shown in Figure 1, and pertinent
geometric data are outlined in Table 2. Additional structural
diagrams are available in the Supporting Information.
The coordination planes, {PdP(C)Cl2}, in all structurally
characterized compounds are distorted from the ideal square-
planar geometry for two main reasons. First, the coordination
bonds to carbene carbons are substantially shorter than the
bonds to the remaining donor atoms. Second, the interligand
angles slightly depart from the ideal 90° (by maximum 5°),
thus reflecting the spatial congestion and steric demands of the
chelating phosphinocarbene ligands (N.B. the bite angles
associated with the P-chelating aminocarbene ligands fall in the
rather narrow range 86−90°).
The computed structure of syn-2b differed only marginally
from that determined in the solid state, thereby validating our
approach (the average absolute deviation from experimental
bonds distances was 0.056 Å, with a maximum of 0.138 Å for
the N(i-Pr)-H bond). Because the NCN moieties are rotated
with respect to the coordination planes (vide supra), the
isopropyl substituent is positioned above the coordination
Figure 1. Views of the molecular structures of representative carbene complexes 2b (molecule 1), 3a, 4a, and 6a (further structural diagrams are
available in the Supporting Information).
C
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Chart 3. Isomers of Acyclic Carbenes 2
a
The adopted prefixes relate to the relationship between the terminal
substituents R and the central Pd−C bond (R = Me, i-Pr).
Table 3. Free Energy Differences (ΔG at 298 K in kcal
mol−1) Between the Isomers of Complexes 2a and 2b
a
Calculated Using Three Different DFT Functionals
compound
ΔG(B3LYP)
ΔG(PBE0)
ΔG(TPSS)
syn-2a/anti-2a
syn-2b/anti-2b
−0.1
−0.8
−0.1
−0.8
+0.1
−1.5
a
Calculated with the specified functionals at the def2-TZVP:cdd-
(Fe,Pd)-D3 level of theory. Solvent effects (dichloromethane) have
been approximated using the PCM model. For details, see the
Experimental Section and the Supporting Information. The preferred
isomer is indicated in bold.
plane in the structure of syn-2b, with one of its CH hydrogens
directed toward the palladium and with the methyl groups
extending away from the central atom, without much
crowding. One of the methyl groups is oriented to form
supportive intramolecular C−H···Cl contacts, as observed in
the solid-state structure (molecule 2: C63···Cl21 = 3.680(4) Å,
angle at H = 147°) and further confirmed by AIM analysis (a
bond critical point with hydrogen-bond characteristics,
according to the Koch−Popelier definition, was located
between the hydrogen atom of the CH3 group and the Pd-
bound chloride25). Conversely, the analysis of DFT-optimized
structural data and calculated parameters of the anti isomer
revealed the lack of such stabilizing interaction and suggested
possible steric crowding between the methyl groups and a
phenyl substituent (Figure 2). In addition, the syn isomers in
Figure 2. Space filling diagrams for DFT-optimized structures of syn-
and anti-2b, as viewed perpendicularly to the coordination plane
(top) and along the C11−Pd bond (bottom); note: the color code is
the same as that used in Figure 1.
D
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which both NH hydrogens point away from the central Pd-
carbene bond can experience additional stabilization in the
solid state through cooperative hydrogen bonds, as shown in
the crystal structure of syn-2b (see Figure 3).
Figure 3. Simplified view of H-bonded chains in the structure of
solvated 2b; for clarity, the phenyl rings and CH hydrogens are
omitted, and the bulky ferrocene units are replaced with ribbons
connecting pivotal atoms (molecule 1 in black, molecule 2 in red).
Hydrogen bond lengths (in Å): N1···Cl4, 3.283(3); N2···Cl3,
3.204(3); N3···Cl12, 3.169(3); N4···Cl1, 3.207(3).
Preparation of Chiral Carbene 7. To extend our
synthetic endeavors, we used the fixed geometry of the
ferrocene core to prepare an optically pure P-chelated carbene
complex. For this purpose, we treated [PdCl2(cod)]/1 with
(S)-2-(chloromethyl)pyrrolidine, which is accessible from (S)-
proline.26 Gratifyingly, this reaction proceeded as expected
(Scheme 3), producing bicyclic carbene 7 as a mixture of
Figure 4. ECD (top) and UV−vis (bottom) and spectra of (S,Rp)-7
(red line) and (S,Sp)-7 (blue line).
a
Scheme 3. Synthesis of Chiral Carbene 7
a
cod = cycloocta-1,5-diene.
diastereoisomers in a 3:2 ratio and 65% overall yield. We were
able to separate the isomers by chromatography and to
structurally authenticate the major product as (S,Rp)-7 by X-
ray diffraction analysis (vide infra).
Figure 5. View of the molecular structure of (S,Rp)-7. Selected
distances and angles (in Å and deg): Pd−Cl1, 2.3722(9); Pd−Cl2,
2.3532(8); Pd−P, 2.2559(8); Pd−C11, 1.962(3); Cl1−Pd−Cl2,
91.00(3); P−Pd−C11, 90.54(8); C11−N1, 1.348(4); C11−N2,
1.327(3); N1−C11−N2, 108.7(2); τ = 8.9(2), φ = 74.8(2), ψ =
45.7(3) (for definitions, see Table 2).
The diastereoisomers could be clearly distinguished by their
NMR spectra (see the Supporting Information); the diagnostic
carbene 13C NMR and the 31P NMR signals were identified at
δC 198.08/190.88 and at δP 18.8/16.3 for (S,Rp)-7 and (S,Sp)-
7, respectively. However, the fact that the isomers differ in
configuration at the planar-chiral ferrocene unit was more
clearly expressed in electronic circular dichroism (ECD)
spectra, showing a nearly (albeit not ideally, due to their
diastereomeric relationship) mirror-symmetric response in the
region dominated by ferrocene d−d transitions (Figure 4).27
The molecular structure of (S,Rp)-7 is presented in Figure 5,
along with selected structural parameters. The comparison of
the parameters with the values derived from the aforemen-
tioned structures (Table 2) revealed only marginal differences,
thus suggesting that the annelation of the carbene moiety has
no significant impact on the overall structure. The five-
membered ring around the carbene moiety, {N1, C11, N2,
C12, C3}, is only marginally twisted (N1−C12−C13−N2 =
10.2(3)°; cf. the structure of 4a), whereas the appended ring
{N2, C13, C26−C28} adopts an approximate envelope
conformation with the C26 atom at the tip position.28
DFT Computations and Electrochemistry. In addition
to explaining differences among isomers (vide supra), DFT
computations (PBE0/def2-TZVP:sdd(Fe,Pd)-D3) were used
to follow possible changes in bonding in the series of
diaminocarbenes 3a, 4a, and 6a. The inspection of frontier
orbitals (Figure 6 and Figure S13) showed that the HOMO is
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3a (0.28 V) through 4a (0.35 V) to 6a (0.48 V). This indicates
not only an increase in the overall electron-withdrawing nature
of the carbene substituents (in the same order), and
consequently their lower donating ability,4,30 but also the
conjugated nature of the compounds, wherein differences in
“substituent” are relayed to the central ferrocene core. Notably,
all potentials were lower than that of [PdCl2(dppf-κ2P,P′)]
(0.58 V;31 dppf = 1,1′-bis(diphenylphosphino)ferrocene)
under similar conditions, thus attesting to the easier oxidation
of carbene complexes and, hence, to the higher electron
density at their ferrocene core.
Despite the dominant contribution of chlorine-based orbitals
to the HOMO, the assignment of the observed redox transition
as a standard one-electron oxidation of the ferrocene unit was
corroborated by changes in DFT-computed electron density.
For all studied compounds, the difference electron density,
ρ(M) − ρ(M+), calculated for the molecule in its native state
(M) and for the corresponding cation at the same geometry
(M+; the electron transfer is fast and precedes any possible
structural change), suggested that the electron is almost
exclusively removed from the ferrocene iron (see Figure 6 and
Figure S13).
Catalytic Evaluation. The catalytic properties of Pd(II)
complexes with phosphinoferrocene carbene ligands were
examined in Pd-catalyzed Miyaura borylation of aryl bromides
with bis(pinacolato)diboron.19 This reaction, directly convert-
ing the ubiquitous starting materials into useful synthetic
building blocks,32 often employs dppf as the supporting ligand
for palladium and, hence, allows comparisons in terms of
catalyst efficiency. As a model reaction, we chose the
borylation of 4-bromotoluene into ester 9a and used the
imidazole carbene 6b as (pre)catalyst (Scheme 4).
Figure 6. Frontier orbitals (isosurfaces at 0.05 au) and electron
density difference map, ρ(M) − ρ(M+), at the geometry of M
(isosurfaces at 0.02 au) for carbene complex 3a. Diagrams for
compounds 4a and 6a are presented in the Supporting Information.
mainly contributed from the chloride ligands (≈75%, mostly
3p orbitals, according to the NBO analysis), with a smaller
contribution from Pd (≈10%) and P (≈4%). The contribu-
tions from the Fe orbitals ranged from 1% to 3%. Conversely,
the LUMO orbitals were more delocalized and mainly
consisted of the orbitals of one P−Ph moiety, of the palladium
(15−20%), of the carbene carbon, and of chloride ligands.
DFT computations closely reproduced the observed
variation in Pd−Cl bond lengths. However, these changes
were not straightforwardly reflected in the electronic structure
of the model carbenes 3a, 4a, and 6a, particularly in the
calculated electron density ρ(r), in its Laplacian ∇2ρ(r) and in
bond ellipticity (ε) at bond critical points (see Table S2).29
Nonetheless, the same parameters indicated that the carbene
carbon was more strongly coordinated and with a more
significant contribution of π-back bonding, as reflected by the
higher ellipticity values for the Pd−C bonds, than the
phosphorus atom.
Using the ferrocene moiety as a probe at the molecular level,
we also studied the electrochemical behavior of representative
carbenes 3a, 4a, and 6a by cyclic (CV) voltammetry at the
platinum disc electrode in dichloromethane. In the anodic
region, these compounds displayed an electrochemically
reversible redox change (Figure 7). Only for the open carbene
3a, the redox wave was broader and asymmetric, presumably
due to diminished reversibility and/or adsorption phenomena.
The half-wave potentials determined from CV increased from
Scheme 4. Testing Catalytic Reaction
Initial reaction tests revealed that strictly inert conditions
(i.e., oven-dried glassware, dry base additives and solvent, and
rigorous exclusion of air) are essential for obtaining boronate
esters in good yields. The results from subsequent optimization
experiments (Table 4) illustrate that the yield of boronate ester
9a varies greatly in different solvents (Table 4, entries 1−6).
When using potassium acetate, which is commonly applied in
this reaction,33 the best yield of 9a was obtained in
isopropanol, whose relative permittivity (εr) is approximately
intermediate between those of toluene and DMSO, which
represent the extreme cases among the tested solvents.34
Lowering the amount of KOAc from 3 equiv to 2 equiv had no
significant effect on the reaction yield; however, further
decreasing this amount to 1.5 equiv lowered the yield to
92% (entries 3, 7, and 8). The survey of base additives (entries
3 and 9−14) also showed remarkable differences. For instance,
the reaction in the presence of NaOAc proceeded with full
conversion of the substrate 8a but mainly produced (62%)
4,4′-dimethylbiphenyl as the “homocoupling” product. Stron-
ger bases such as KOH and t-BuOK also activated the primary
product 9a toward Suzuki−Miyaura cross-coupling, producing
4,4′-dimethylbiphenyl. Conversely, less homocoupling product
Figure 7. Cyclic voltammograms of 3a, 4a, and 6a (recorded at the Pt
disc electrode at the scan rate of 0.1 V s−1); the potentials are
expressed in relation to ferrocene/ferrocenium.
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a
a
Table 4. Summary of the Optimization Experiments
Table 6. Reaction Scope Tests
b
entry
solvent
base (equiv)
NMR yield (%)
1
2
3
4
5
6
7
8
toluene
1,4-dioxan
i-PrOH
MeCN
DMF
DMSO
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
KOAc (3.0)
KOAc (3.0)
KOAc (3.0)
KOAc (3.0)
KOAc (3.0)
KOAc (3.0)
KOAc (2.0)
KOAc (1.5)
NaOAc (2.0)
CsOAc (2.0)
K2CO3 (2.0)
K3PO4 (2.0)
KOH (2.0)
t-BuOK (2.0)
61(0)
54(0)
99(0)
17(0)
27(0)
31(0)
98(0)
92(0)
38(62)
95(1)
76(9)
92(7)
82(18)
73(27)
substrate 8
(Ar in ArBr)
yield of
9 (%)
substrate 8
(Ar in ArBr)
yield of
9 (%)
4-tolyl (a)
3-tolyl (b)
2-tolyl (c)
mesityl (d)
1-naphthyl(e)
2-naphthyl (f)
94
94
88
40
66
90
4-C6H4OMe (g)
4-C6H4NHAc (h)
4-C6H4CHO (i)
4-C6H4Cl (j)
4-C6H4F (k)
4-C6H4CF3 (l)
4-C6H4NO2 (m)
78
97
92
85
95
92
94
b
9
10
11
12
13
14
a
Conditions: aryl bromide (1.0 mmol), bis(pinacolato)diboron (1.2
mmol), 1 mol % 4a, KOAc (2 mmol), i-PrOH (4 mL), 85 °C, 6 h.
b
The isolated yields are an average of two independent runs. After 24
h.
a
Conditions: 4-bromotoluene (1.0 mmol), bis(pinacolato)diboron
b
(1.2 mmol), 1 mol % of 6b, solvent (4 mL), 85 °C, 24 h. NMR
yields are an average of two independent runs. The yield of the
homocoupling product (4,4′-dimethylbiphenyl) is given in paren-
theses.
featuring the strongly electron-donating methoxy substituent.
Other compounds reacted smoothly, affording the correspond-
ing boronates in yields exceeding 85%. No biaryls were
detected among the products of these reactions.
was obtained in reactions with K2CO3, giving 9a in a 76%
yield, and with K3PO4 and CsOAc, which ensued in >90%
yields of the boronate ester, with only minor amounts of the
biphenyl (7% and 1%, respectively). Lastly, no reaction was
observed when substrate 8a was replaced by the corresponding
chloride.
CONCLUSION
■
Although the synthetic approach presented in this contribution
is based on time-tested methods, it provides an efficient and
convenient access to a range of novel, structurally unique
chelating phosphino-diaminocarbene ligands. In particular, the
family of phosphinoferrocene imidazol-2-ylidenes was ex-
tended by their hitherto unknown saturated counterparts
(imidazolin-2-ylidenes) and by their analogous open protic
diaminocarbenes. However, even for phosphinoferrocene
imidazol-2-ylidenes, the newly introduced, one-pot approach
proved more efficient than the conventional convergent
approach (synthesis of a heterocyclic precursor, deprotonation,
and coordination). More importantly, compounds derived
from phosphinoferrocene isocyanide 1 bear a carbene moiety
directly bonded to the ferrocene core (i.e., without any
inserted spacer, typical of previously reported compounds),
which in turn increases the stereochemical rigidity and allows
for electronic conjugation between the ferrocene unit and the
carbene moiety.
Subsequent experiments revealed significant differences
between precatalysts (Table 5). Of the tested compounds, 4a
a
Table 5. Comparison of the Precatalysts
b
b
catalyst
NMR yield (%)
catalyst
NMR yield (%)
2a
2b
3a
3b
89(6)
77(3)
88(3)
98(1)
4a
6a
6b
98(0)
91(2)
98(0)
90(2)
[PdCl2(dppf)]
a
Conditions: 4-bromotoluene (1.0 mmol), bis(pinacolato)diboron
(1.2 mmol), KOAc (2.0 mmol), 1 mol % of catalyst, i-PrOH (4 mL),
b
85 °C, 6 h. NMR yields are an average of two independent runs. The
yield of the homocoupling product (4,4′-dimethylbiphenyl) is given
in parentheses.
Aminocarbene ligands (especially heterocyclic) are often
matched against phosphines. This is perhaps inevitable,
especially when considering the dominant role of the dppf
ligand in coordination chemistry and catalysis.35 In this
particular case, the electrochemical data suggested that the
reported phosphinoferrocene diaminocarbene ligands are more
electron rich (hence, better donating) ligands than dppf, in
agreement with general trends. When applied in Miyaura
borylation of aryl bromines, some of the prepared Pd(II)
complexes featuring P,C-chelating phosphinoferrocene carbene
ligands outperformed the benchmark catalyst [PdCl2(dppf)] in
both activity and selectivity.
and 6a reacted selectively and achieved quantitative (within
the margins of experimental error) yields of 9a within 6 h of
reaction. The efficiency of compound 3b was close to those of
4a and 6a, albeit with minor amounts of 4,4′-dimethybiphenyl;
the benchmark catalyst, [PdCl2(dppf)], behaved very similarly.
Other investigated phosphinocarbene complexes performed
relatively worse, producing 77−91% of 9a and 2−6% of the
homocoupling product.
On the basis of the aforementioned results, the more easily
accessible precatalyst 4a was chosen for the following scope
experiments. The reactions were performed in i-PrOH using
KOAc as the base (2 equiv) at 85 °C for 6 h. The results
outlined in Table 6 indicate that nonfunctionalized aryl halides
react typically very well in the absence of pronounced steric
crowding. Nonetheless, even mesityl bromide could be
converted into the respective boronate ester 9d with a 40%
isolated yield when the reaction time was extended to 24 h.
Among the functionalized aryl halides, the lowest yield of the
coupling product was achieved when using p-anisyl bromide
EXPERIMENTAL SECTION
■
Materials and Methods. The syntheses were performed under
argon using standard Schlenk techniques and oven-dried glassware.
Isocyanide 117 and [PdCl2(dppf)]36 were prepared by following the
literature methods. The syntheses of N-(2,2-dimethoxyethyl)-2-
propanamine, N-(2-chloroethyl)methylamine hydrochloride, and
(S)-2-(chloromethyl)pyrrolidine hydrochloride are described in the
G
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Supporting Information. Other chemicals were purchased from
commercial suppliers (Sigma-Aldrich or Alfa-Aesar) and were used
as received. Anhydrous dichloromethane used for syntheses was
obtained from an in-house PureSolv MD5 solvent purification system
(Innovative Technology). Triethylamine and isopropanol utilized
during catalytic tests were dried by adding some CaH2 and by
distillation. The solvents used for crystallizations and for chromatog-
raphy (reagent grade from Lach-Ner) were utilized as received.
1H, 31P{1H}, and 13C{1H} NMR spectra were recorded with a
Varian Unity Inova 400, a Bruker AVANCE 400 (1H, 400 MHz; 31P,
162 MHz; and 13C, 101 MHz; 11B, 128 MHz) or a Bruker AVANCE
III 600 (1H, 600 MHz; 13C, 151 MHz) spectrometer at 25 °C.
Chemical shifts (δ in ppm) are quoted relative to internal
tetramethylsilane (1H and 13C), to external 85% aqueous H3PO4
(31P), and to external BF3·OEt2 (11B). IR spectra in Nujol mulls were
acquired with a Thermo Nicolet 6700 instrument over the 400−4000
cm−1 range. Electrospray ionization (ESI) mass spectra were recorded
on a Compact QTOF-MS spectrometer (Bruker Daltonics).
Electronic circular dichroism (ECD) spectra were collected on a
Jasco 815 spectrometer over the spectral range 220−400 nm using a
0.01 cm cylindrical quartz cell at room temperature (experimental
setup: 0.1 nm step, 20 nm min−1 scan range, 4 s response time, and 1
nm spectral bandwidth). The spectra were corrected on the baseline.
The samples were dissolved in dichloromethane to 0.1 mM. Optical
rotations were determined on an AUTOPOL IV automatic polar-
imeter (Rudolph Research Analytical). Elemental analyses were
performed on a PE 2400 Series II CHNS/O elemental analyzer
(PerkinElmer). The amount of clathrated solvent(s) was verified by
NMR analysis.
isomer). MS ESI+: m/z 531 ([M − HCl − Cl]+), 567 ([M − Cl]+).
IR (Nujol) νmax/cm−1: 3443 br w, 3197 br m, 3054 m, 1581 vs
(carbene), 1252 w, 1200 w, 1169 m, 1099 s, 1050 w, 1030 s, 999 w,
934 m, 824 m, 746 s, 695 s, 628 m, 571 w, 526 s, 498 s, 480 s, 444 m.
Anal. Calcd for C24H23Cl2FeN2PPd·0.1 CHCl3 (615.5): C, 47.03%;
H, 3.78%; N, 4.55%; Found: C, 47.03%; H, 3.96%; N, 4.26%.
Synthesis of 2b. Compound 2b was prepared analogously to 2a,
starting from isocyanide 1 (79 mg, 0.20 mmol), [PdCl2(cod)] (57
mg, 0.20 mmol), and neat isopropyl amine (26 μL, 0.30 mmol).
Isolation as described above gave pure 2b as an orange solid (single
isomer). Yield: 81 mg (64%). Crystals used for structure
determination were obtained from chloroform/hexane.
3
1H NMR (CD2Cl2, 400 MHz): δ 0.39 (d, JHH = 6.5 Hz, 3 H,
CHMe2), 1.30 (d, 3JHH = 6.5 Hz, 3 H, CHMe2), 4.14 (dt, J′ = 2.6 Hz,
1.2 Hz, 1 H, CH of fc), 4.30 (dt, J′ = 2.6 Hz, 1.2 Hz, 1 H, CH of fc),
4.38 (dt, J′ = 2.6 Hz, 1.2 Hz, 1 H, CH of fc), 4.43 (td, J′ = 2.5 Hz, 1.3
Hz, 1 H, CH of fc), 4.54 (br s, 1 H, CH of fc), 4.58 (m, 1 H,
CHMe2), 5.11 (br s, 1 H, CH of fc), 5.50 (br s, 1 H, CH of fc), 5.56
(br s, 1 H, CH of fc), 7.32−7.62 (m, 10 H, PPh2), 8.12 (br d, 3JHH
=
9.2 Hz, 1 H, i-PrNH), 8.86 (br s, 1 H, fcNH). 13C{1H} NMR
(CD2Cl2, 151 MHz): δ 21.74 (CHMe2), 23.11 (CHMe2), 54.62 (d,
4JHH = 3 Hz, CHMe2), 63.30 (CH of fc), 66.12 (CH of fc), 66.20 (d,
1JPC = 63 Hz, Cipso-P of fc), 68.52 (CH of fc), 68.73 (CH of fc), 71.90
(d, 2JPC = 6 Hz, CH of fc), 74.21 (d, 3JPC = 5 Hz, CH of fc), 74.57 (d,
3JPC = 10 Hz, CH of fc), 78.20 (d, 2JPC = 20 Hz, CH of fc), 104.15 (d,
4JPC = 3 Hz, Cipso-N of fc), 128.28 (d, JPC = 12 Hz, CH of PPh2),
129.53 (d, JPC = 11 Hz, CH of PPh2), 129.63 (d, 1JPC = 55 Hz, Cipso-P
of PPh2), 131.09 (d, 1JPC = 55 Hz, Cipso-P of PPh2), 131.11 (d, 4JPC
=
4
3 Hz, CHpara of PPh2), 131.28 (d, JPC = 3 Hz, CHpara of PPh2),
Electrochemical measurements were performed using a μAUTO-
LAB III multipurpose potentiostat (Eco Chemie) at room temper-
ature and using a three-electrode cell with a platinum disc electrode
(2 mm diameter) as the working electrode, a platinum sheet auxiliary
electrode, and a double-junction Ag/AgCl (3 M KCl) reference
electrode. The analyzed compounds were dissolved in anhydrous
dichloromethane to give a solution containing 1 mM of the analyte
and 0.1 M Bu4N[PF6] (Fluka, puriss. for electrochemistry) as the
supporting electrolyte. The solutions were deaerated with argon
before the measurements and then kept under an argon blanket.
Decamethylferrocene (Alfa-Aesar) was added as an internal standard
for the final scans, and the redox potentials were converted into the
ferrocene/ferrocenium scale by subtracting 0.548 V.37
Syntheses. Synthesis of 2a. A solution of isocyanide 1 (79 mg,
0.20 mmol) in dry dichloromethane (2 mL) was added to a stirring
solution of [PdCl2(cod)] (57 mg, 0.20 mmol) in the same solvent (3
mL), immediately followed by a methylamine solution (0.12 mL of 2
M in THF, 0.25 mmol). The resulting mixture was stirred at room
temperature overnight (a precipitate gradually separated during this
time) and then evaporated under vacuum. The crude product was
purified by column chromatography (silica gel, dichloromethane−
methanol 20:1). The first, minor brown band was discarded, and the
following, tailing orange band was collected and evaporated under
vacuum to give 2a as an orange solid. Yield: 62 mg (52%). The
compound is a 2:1 mixture of isomers.
133.21 (d, JPC = 10 Hz, CH of PPh2), 134.59 (d, JPC = 12 Hz, CH of
2
PPh2), 193.45 (d, JPC = 6 Hz, carbene C). 31P{1H} NMR (CD2Cl2,
162 MHz): δ 17.8 (s). MS ESI+: m/z 559 ([M − HCl − Cl]+), 596
([M − Cl]+). IR (Nujol) νmax/cm−1: 3187 br m, 3034 br m, 1570 s,
1527 m, 1293 w, 1247 w, 1169 s, 1099 m, 1029 m, 1000 w, 932 w,
821 m, 745 s, 695 s, 628 w, 536 w, 520 s, 479 s, 443 w. Anal. Calcd for
C26H27Cl2FeN2PPd (631.6): C, 49.44%; H, 4.31%; N, 4.44%. Found:
C, 49.29%; H, 4.46%; N, 4.16%.
Synthesis of 3a. To a stirring solution of [PdCl2(cod)] (57 mg,
0.20 mmol) in anhydrous dichloromethane (3 mL), the following
reagents were added, in rapid succession: isocyanide 1 (79 mg, 0.20
mmol), dissolved in the same solvent (2 mL), and a solution of
dimethylamine, prepared separately by mixing dimethylamine hydro-
chloride (24.5 mg, 0.30 mmol) and triethylamine (0.1 mL, 0.7 mmol)
in dry dichloromethane (2 mL). The deep red mixture was stirred
overnight and then washed with saturated aqueous NH4Cl and
evaporated under vacuum. The crude product was purified by column
chromatography (silica gel, dichloromethane−methanol 10:1). The
first minor band containing some impurities was discarded, and the
following major orange−brown band due to the product was collected
and evaporated. The resulting solid was redissolved in chloroform (2
mL) and crystallized by layering with hexane (10 mL). The orange
crystals of 3a, which separated during several days, were isolated by
suction and dried under vacuum. Yield: 43 mg (35%). Crystals used
for structure determination were obtained from chloroform/hexane.
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 2.47 (s, 3 H, NMe),
3.41 (s, 3 H, NMe), 4.32 (td, J′ = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.42
(td, J′ = 2.6 Hz, 1.5 Hz, 1 H, CH of fc), 4.63 (td, J′ = 2.6 Hz, 1.4 Hz,
1 H, CH of fc), 4.66 (dq, J′ = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.82 (m,
1 H CH of fc), 4.87 (dt, J′ = 2.6 Hz, 1.5 Hz, 1 H, CH of fc), 5.69 (dt,
J′ = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 5.86 (dq, J′ = 2.6 Hz, 1.3 Hz, 1 H,
CH of fc), 7.38−7.44 (m, 5 H, PPh2), 7.46−7.51 (m, 1 H, PPh2),
7.54−7.60 (m, 2 H, PPh2), 7.65−7.71 (m, 2 H, PPh2). The signals of
the NH protons were not observed due to H−D exchange. 13C{1H}
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ, major isomer, 2.94 (s, 3
H, NMe), 4.26 (td, J′ = 2.6 Hz, 1.3 Hz, 1 H, CH of fc), 4.38 (td, J′ =
2.7 Hz, 1.5 Hz, 1 H, CH of fc), 4.59−4.61 (m, 2 H, 2× CH of fc),
4.75 (m, 1 H, CH of fc), 4.77 (td, J′ = 2.7 Hz, 1.3 Hz, 1 H, CH of fc),
5.48 (td, J′ = 2.7 Hz, 1.3 Hz, 1 H, CH of fc), 5.73 (dq, J′ = 5.0 Hz, 1.3
Hz, 1 H, CH of fc), 7.35−7.56 (m, 6 H, PPh2), 7.59−7.69 (m, 4 H,
PPh2); minor isomer, 2.30 (s, 3 H, NMe), 4.32 (td, J′ = 2.6 Hz, 1.4 Hz,
1 H, CH of fc), 4.41 (td, J′ = 2.7 Hz, 1.5 Hz, 1 H, CH of fc), 4.64 (td,
J′ = 2.6 Hz, 1.3 Hz, 1 H, CH of fc), 4.66 (td, J′ = 2.5 Hz, 1.3 Hz, 1 H,
CH of fc), 4.80 (m, 1 H, CH of fc), 4.82 (td, J′ = 2.6 Hz, 1.2 Hz, 1 H,
CH of fc), 5.57 (dt, J′ = 2.6 Hz, 1.2 Hz, 1 H, CH of fc), 5.77 (dq, J′ =
5.2 Hz, 1.3 Hz, 1 H, CH of fc), 7.35−7.56 (m, 6 H, PPh2), 7.59−7.69
(m, 4 H, PPh2). The signals of the NH protons were not observed
due to H−D exchange. 13C NMR spectra could not be obtained given
the low solubility of the compound. 31P{1H} NMR (CD2Cl2/
CD3OD, 162 MHz): δ 17.75 (s, major isomer), 17.77 (s, minor
NMR (CD2Cl2/CD3OD, 151 MHz): δ 38.49 (NMe), 48.09 (d, 4JPC
3 Hz, NMe), 64.04 (CH of fc), 65.80 (d, 1JPC = 62 Hz, Cipso-P of fc),
=
66.51 (CH of fc), 68.57 (CH of fc), 68.73 (CH of fc), 72.89 (d, 2JPC
=
6 Hz, CH of fc), 74.62 (d, 3JPC = 4 Hz, CH of fc), 74.83 (d, 3JPC = 11
Hz, CH of fc), 79.07 (d, 2JPC = 21 Hz, CH of fc), 103.65 (d, 4JPC = 3
Hz, Cipso-N of fc), 128.39 (d, JPC = 12 Hz, CH of PPh2), 128.91 (d,
H
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
4
3
2
JPC = 11 Hz, CH of PPh2), 130.76 (d, JPC = 54 Hz, Cipso of PPh2),
131.09 (d, 4JPC = 3 Hz, CHpara of PPh2), 131.22 (d, 1JPC = 56 Hz, Cipso
of PPh2), 131.60 (d, 4JPC = 3 Hz, CHpara of PPh2), 132.05 (d, JPC = 10
Hz, CH of PPh2), 134.69 (d, JPC = 12 Hz, CH of PPh2), 194.55 (d,
2JPC = 7 Hz, carbene C). 31P{1H} NMR (CD2Cl2/CD3OD, 162
MHz): δ 17.9 (s). MS ESI+: m/z 475 ([M − PdCl]+), 545 ([M −
HCl − Cl]+). IR (Nujol) νmax/cm−1: 3454 br w, 3212 br m, 3053 m,
1572 vs (carbene), 1342 m, 1310 w, 1267 m, 1219 w, 1167 s, 1099 s,
1029 s, 999 w, 948 w, 889 m, 821 m, 749 s, 694 s, 663 w, 629 w, 537
m, 526 s, 518 s, 498 s, 479 s, 443 w. Anal. Calcd for
C25H25Cl2FeN2PPd·0.2 CHCl3 (641.4): C, 47.18%; H, 3.96%; N,
4.37%. Found: C, 47.05%; H, 4.36%; N, 4.31%.
(dddd, JHH = 1.7 Hz, JHH = 11.7 and 10.3 Hz, JHH = 8.7 Hz, 1 H,
MeNCH2), 3.72−3.86 (m, 2 H, fcNCH2), 4.39 (td, JHH = 2.7 Hz, 1.4
Hz, 1 H, CH of fc), 4.46 (td, JHH = 2.7 Hz, 1.3 Hz, 1 H, CH of fc),
4.72 (td, JHH = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.80−4.84 (m, 2 H,
CH of fc), 4.87 (dt, JHH = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 5.59 (dt,
J
HH = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 5.90 (m, 1 H, CH of fc), 7.37−
7.43 (m, 2 H, PPh2), 7.45−7.50 (m, 4 H, PPh2), 7.65−7.74 (m, 4 H,
PPh2). 13C{1H} NMR (CD2Cl2/CD3OD, 151 MHz): δ 37.81 (NMe),
1
51.43 (MeNCH2), 53.36 (fcNCH2), 64.79 (CH of fc), 66.56 (d, JPC
= 63 Hz, Cipso-P of fc), 67.21 (CH of fc), 67.86 (CH of fc), 68.63
(CH of fc), 73.25 (d, 3JPC = 6 Hz, CH of fc), 74.57 (d, 2JPC = 11 Hz,
3
2
CH of fc), 74.64 (d, JPC = 4 Hz, CH of fc), 79.42 (d, JPC = 22 Hz,
CH of fc), 102.26 (d, 4JPC = 2 Hz, Cipso-N of fc), 128.46 (d, JPC = 12
Hz, CH of PPh2), 129.13 (d, JPC = 11 Hz, CH of PPh2), 130.56 (d,
1JPC = 55 Hz, Cipso of PPh2), 131.37 (d, 4JPC = 3 Hz, CHpara of PPh2),
131.61 (d, JPC = 10 Hz, CH of PPh2), 131.73 (d, 4JPC = 3 Hz, CHpara
of PPh2), 132.20 (d, 1JPC = 57 Hz, Cipso of PPh2), 134.64 (d, JPC = 11
Hz, CH of PPh2), 194.68 (d, 2JPC = 2 Hz, carbene C). 31P{1H} NMR
(CD2Cl2/CD3OD, 162 MHz): δ 18.4 (s). IR (Nujol) νmax/cm−1:
3091 w, 3069 w, 1541 s (carbene), 1497 s (carbene), 1315 m, 1274 s,
1171 w, 1124 w, 1101 m, 1095 m, 1021 w, 936 w, 821 m, 761 m, 747
m, 733 m, 700 s, 652 w, 628 w, 616 m, 541 m, 528 s, 508 s, 483 s, 465
w, 443 w. MS ESI+: m/z 557 ([M − HCl − Cl]+), 593 ([M − Cl]+).
Anal. Calcd for C26H25Cl2FeN2PPd (629.6): C, 49.60%; H, 4.00%; N,
4.45%. Found: C, 49.71%; H, 3.98%; N, 4.27%.
Synthesis of 5a. Neat (methylamino)acetaldehyde dimethylacetal
(26 μL, 0.20 mmol) was added to a suspension of [PdCl2(cod)] (57
mg, 0.20 mmol) in dichloromethane (4 mL), thereby dissolving the
solid educt and changing the color from yellow to orange. Next, a
solution of 1 (79 mg, 0.20 mmol) in dichloromethane (4 mL) was
introduced, and the red mixture was stirred at room temperature for
18 h. The crude product obtained by evaporation of the mixture was
purified by column chromatography (silica gel, dichloromethane−
methanol 10:1). The second, major red band was collected and
evaporated, leaving 5a as a red glassy solid. Yield: 121 mg, 85%. The
compound is a mixture of isomers in a ratio of approximately 2:1.
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ, major isomer, 2.60 (d, J
= 0.4 Hz, 3 H, NMe), 3.14 (dd, J = 13.7 Hz, 7.8 Hz, 1 H, NCH2),
3.37 (s, 3 H, OMe), 3.52 (s, 3 H, OMe), 4.35 (td, JHH = 2.6 Hz, 1.3
Hz, 1 H, CH of fc), 4.44 (td, JHH = 2.7 Hz, 1.5 Hz, 1 H, CH of fc),
4.60 (m, 1 H, CH of fc), 4.62 (dd, JHH = 3.4 Hz, 1.1 Hz, 1 H, NCH2),
4.64 (td, JHH = 2.5 Hz, 1.1 Hz, 1 H, CH of fc), 4.83 (m, 1 H, CH of
fc), 4.87 (dd, JHH = 7.4 Hz, 3.4 Hz, CH(OMe)2), 4.93 (dt, JHH = 2.7
Hz, 1.3 Hz, 1 H, CH of fc), 5.87 (m, 1 H, CH of fc), 7.38−7.68 (m,
10 H, PPh2); minor isomer, 2.87 (dd, JHH = 15.1 Hz, 4.2 Hz, 1 H,
NCH2), 3.18 (t, JHH = 3.9 Hz, 1 H, NCH2), 3.37 (s, 6 H, OMe), 3.55
Synthesis of 3b. Diisopropylamine (34 μL, 0.25 mmol) and
isocyanide 1 (79 mg, 0.20 mmol in 4 mL of dichloromethane) were
successively added to a solution of [PdCl2(cod)] (57 mg, 0.20 mmol)
in dichloromethane (2 mL). The mixture was stirred at room
temperature overnight and evaporated under vacuum. The residue
was purified by chromatography (silica gel, dichloromethane−
methanol 20:1). Evaporation of the second band afforded 3b as an
orange−red solid. Yield: 73 mg (54%). Single crystals used for
structure determination were formed upon layering a solution of the
compound in chloroform−ethyl acetate with hexane.
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 0.50 (d, 3JHH = 6.8 Hz,
3 H, CHMe2), 1.08 (d, 3JHH = 7.4 Hz, 3 H, CHMe2), 1.32 (d, 3JHH
=
3
7.3 Hz, 3 H, CHMe2), 1.41 (d, JHH = 6.6 Hz, 3 H, CHMe2), 3.62
(septet, 3JHH = 7.3 Hz, 1 H, CHMe2), 4.36 (td, JHH = 2.6 Hz, 1.3 Hz,
1 H, CH of fc), 4.39 (dq, JHH = 2.7 Hz, 1.3 Hz, 1 H, CH of fc), 4.47
(td, JHH = 2.7 Hz, 1.5 Hz, 1 H, CH of fc), 4.61 (td, JHH = 2.6 Hz, 1.4
Hz, 1 H, CH of fc), 4.70 (dt, JHH = 2.6 Hz, 1.4 Hz, 1 H, CH of fc),
4.83 (m, 1 H, CH of fc), 5.75 (dt, JHH = 2.7 Hz, 1.3 Hz, 1 H, CH of
fc), 5.82 (br sept, JHH ≈ 6.7 Hz, 1 H, CHMe2), 5.90 (dq, JPH = 4.7
Hz, 3JHH = 1.3 Hz, 1 H, CH of fc), 7.33−7.39 (m, 2 H, PPh2), 7.41−
7.53 (m, 6 H, PPh2), 7.59−7.65 (m, 2 H, PPh2). The NH signals were
not observed due to H−D exchange. 13C{1H} NMR (CD2Cl2/
CD3OD, 151 MHz): δ 19.20 (CHMe2), 19.65 (CHMe2), 20.07
3
3
4
(CHMe2), 21.63 (CHMe2), 47.84 (CHMe2), 64.01 (d, JPC = 4 Hz,
1
CHMe2), 64.48 (CH of fc), 66.15 (d, JPC = 61 Hz, Cipso-P of fc),
66.45 (CH of fc), 68.43 (CH of fc), 68.87 (CH of fc), 72.82 (d, 3JPC
=
6 Hz, CH of fc), 74.14 (d, 3JPC = 5 Hz, CH of fc), 75.19 (d, 2JPC = 11
Hz, CH of fc), 79.09 (d, 2JPC = 20 Hz, CH of fc), 103.75 (d, 4JPC = 3
Hz, Cipso-N of fc), 128.29 (d, JPC = 12 Hz, CH of PPh2), 129.22 (d,
1
JPC = 11 Hz, CH of PPh2), 131.03 (d, JPC = 55 Hz, Cipso of PPh2),
131.05 (d, JPC = 3 Hz, CHpara of PPh2), 131.35 (d, JPC = 3 Hz,
4
4
CHpara of PPh2), 131.38 (d, JPC = 53 Hz, Cipso of PPh2), 132.98 (d,
1
JPC = 9 Hz, CH of PPh2), 134.52 (d, JPC = 12 Hz, CH of PPh2),
193.19 (d, 2JPC = 8 Hz, carbene C). 31P{1H} NMR (CD2Cl2/CD3OD,
162 MHz): δ 16.3 (s). IR (Nujol) νmax/cm−1: 3438 br m, 3413 m,
3335 br m, 3130 w, 3092 m, 3078 m, 3052 m, 1546 vs (carbene),
1320 s, 1218 w, 1204 w, 1188 m, 1168 m, 1141 m, 1105 m, 1093 m,
1059 w, 1048 w, 1036 m, 1019 w, 1000 w, 941 w, 907 w, 838 s, 749 s,
702 m, 694 s, 649 m, 636 m, 539 m, 525 m, 498 m, 483 s, 469 m, 441
m. MS ESI+: m/z 601 ([M − HCl − Cl]+). Anal. Calcd for
C29H33N2Cl2FePPd·0.66 CH2Cl2 (729.8): C, 48.81%; H, 4.74%; N,
3.84%. Found C, 48.72%; H, 4.74%; N, 3.47%.
3
(s, 3 H, NMe), 4.17 (t, JHH = 4.6 Hz, 1 H, CH(OMe)2), 4.36 (td,
HH = 2.6 Hz, 1.3 Hz, 1 H, CH of fc), 4.45 (td, JHH = 2.7 Hz, 1.5 Hz, 1
J
H, CH of fc), 4.60 (m, 1 H, CH of fc), 4.66 (m, 1 H, CH of fc), 4.71
(dt, JHH = 2.8 Hz, 1.5 Hz, 1 H, CH of fc), 4.84 (m, 1 H, CH of fc),
5.66 (dt, JHH = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 5.86 (m, 1 H, CH of
fc), 7.38−7.68 (m, 10 H, PPh2). Signals of the NH protons were not
observed due to H−D exchange. 13C{1H} NMR (CD2Cl2/CD3OD,
151 MHz): δ major isomer, 38.55 (NMe), 56.02 (OMe), 56.30
4
(OMe), 62.56 (d, JPC = 3 Hz, NCH2), 64.43 (CH of fc), 65.77 (d,
Synthesis of 4a. Anhydrous triethylamine (0.20 mL, 1.4 mmol)
was added to a suspension of N-(2-chloroethyl)methylamine
hydrochloride (39 mg, 0.30 mmol) in dry dichloromethane (3 mL),
causing the solid educt to rapidly dissolve. Next, solid [PdCl2(cod)]
(57 mg, 0.20 mmol) and a dichloromethane solution of 1 (79 mg,
0.20 mmol in 3 mL) were introduced in rapid succession. The
resulting mixture was stirred overnight and then evaporated, leaving a
residue, which was purified by column chromatography (silica gel,
dichloromethane−methanol 20:1). The major orange band contain-
ing the product was collected and evaporated, affording compound 4a
as an orange glassy solid. Evaporation with chloroform gave a
microcrystalline solid. Yield: 107 mg (85%). Crystals used for
structure determination were grown by recrystallization from
chloroform/methanol.
1JPC = 63 Hz, Cipso-P of fc), 66.64 (CH of fc), 68.73 (CH of fc), 68.81
3
3
(CH of fc), 72.95 (d, JPC = 7 Hz, CH of fc), 74.61 (d, JPC = 5 Hz,
CH of fc), 74.90 (d, 2JPC = 11 Hz, CH of fc), 79.00 (d, 2JPC = 21 Hz,
CH of fc), 103.68 (d, JPC = 3 Hz, Cipso-N of fc), 104.53
4
(CH(OMe)2), 128.47 (d, JPC = 11 Hz, CH of PPh2), 129.12 (d,
JPC = 10 Hz, CH of PPh2), 130.65 (d, JPC =55 Hz, Cipso of PPh2),
1
130.95 (d, 1JPC = 55 Hz, Cipso of PPh2), 131.22 (d, 4JPC = 3 Hz, CHpara
of PPh2), 131.66 (d, 4JPC = 2 Hz, CHpara of PPh2), 132.21 (d, JPC = 10
Hz, CH of PPh2), 134.62 (d, JPC = 11 Hz, CH of PPh2), 196.25 (d,
2JPC = 7 Hz, carbene C); minor isomer, 47.94 (NMe), 55.97 (NCH2),
1
56.19 (OMe), 56.66 (OMe), 64.72 (CH of fc), 65.70 (d, JPC = 63
Hz, Cipso-P of fc), 66.75 (CH of fc), 68.83 (CH of fc), 68.86 (CH of
fc), 73.06 (d, 3JPC = 4 Hz, CH of fc), 74.60 (d, 3JPC = 4 Hz, CH of fc),
74.98 (d, 2JPC = 11 Hz, CH of fc), 79.08 (d, 2JPC = 21 Hz, CH of fc),
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 2.81 (ddd, JHH = 12.2
3
Hz, 10.3 Hz, 2JHH = 8.7 Hz, 1 H, MeNCH2), 3.05 (s, 3 H, NMe), 3.49
103.24 (d, JPC = 2 Hz, Cipso-N of fc), 103.49 (CH(OMe)2), 128.42
4
I
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
(d, JPC = 11 Hz, CH of PPh2), 128.99 (d, JPC = 11 Hz, CH of PPh2),
131.06 (d, 4JPC = 3 Hz, CHpara of PPh2), 131.14 (d, 1JPC = 55 Hz, Cipso
of PPh2), 131.16 (d, 1JPC = 55 Hz, Cipso of PPh2), 131.54 (d, 4JPC = 3
Hz, CHpara of PPh2), 132.25 (d, JPC = 10 Hz, CH of PPh2), 134.47 (d,
Cipso-P of fc), 67.84 (CH of fc), 69.85 (CH of fc), 73.36 (d, JPC = 6
2
3
Hz, CH of fc), 74.18 (d, JPC = 3 Hz, CH of fc), 74.87 (d, JPC = 11
Hz, CH of fc), 73.32 (d, 2JPC = 22 Hz, CH of fc), 100.83 (d, 4JPC = 2
Hz, Cipso-N of fc), 124.35 (CH of imidazole), 124.66 (CH of
imidazole), 128.30 (d, JPC = 12 Hz, CH of PPh2), 129.22 (d, JPC = 10
Hz, CH of PPh2), 130.05 (d, 1JPC = 56 Hz, Cipso of PPh2), 130.31 (d,
2
JPC = 11 Hz, CH of PPh2), 198.43 (d, JPC = 7 Hz, carbene C).
31P{1H} NMR (CD2Cl2/CD3OD, 162 MHz): δ 18.0 (s, major
isomer), 17.2 (s, minor isomer). IR (Nujol) νmax/cm−1: 3445 br w,
3176 br m, 1560 vs (carbene), 1307 m, 1275 m, 1214 w, 1188 m,
1170 m, 1123 m, 1101 s, 1071 s, 1031 s, 999 w, 973 m, 900 m, 824 m,
750 s, 695 s, 630 w, 538 m, 525 m, 498 m, 481 s, 442 w. MS ESI+: m/
z 619 ([M − HCl − Cl]+), 657 ([M − Cl]+). Anal. Calcd for
C28H31Cl2FeN2O2PPd (691.7): C, 48.62%; H, 4.52%; N, 4.05.
Found: C, 48.30%; H, 4.49%; N, 3.97%.
JPC = 10 Hz, CH of PPh2), 130.57 (d, JPC = 3 Hz, CHpara of PPh2),
4
131.60 (d, 1JPC = 58 Hz, Cipso of PPh2), 131.63 (d, 4JPC = 3 Hz, CHpara
of PPh2), 134.69 (d, JPC = 11 Hz, CH of PPh2), 164.76 (carbene C).
31P{1H} NMR (CD2Cl2/CD3OD, 162 MHz): δ 17.2 (s). IR (Nujol)
νmax/cm−1: 3160 w, 3086 m, 1571 m, 1497 s, 1307 s, 1296 m, 1246 m,
1202 w, 1171 m, 1141 w, 1126 m, 1097 s, 1042 s, 1034 s, 999 m, 974
w, 880 w, 840 s, 747 s, 702 s, 695 s, 684 s, 628 w, 542 m, 518 s, 509 s,
481 s, 446 m. MS ESI+: m/z 555 ([M − HCl − Cl]+), 590 ([M −
Cl]+). Anal. Calcd for C26H23Cl2FeN2PPd·CH2Cl2 (712.5): C,
45.51%; H, 3.54%; N, 3.93%. Found: C, 45.45%; H, 3.40%; N, 3.77%.
Synthesis of 6b. Compound 6b was prepared similarly from 5b
(105 mg, 0.15 mmol) and isolated as an orange brown glassy solid.
Yield: 89 mg (93%). The compound was crystallized from
dichloromethane/hexane.
Compound 5b. Compound 5b was prepared similarly to 5a, using
[PdCl2(cod)] (57 mg, 0.20 mmol), N-(2,2-dimethoxyethyl)-2-
propanamine (44 mg, 0.30 mmol), and 1 (79 mg, 0.20 mmol). The
crude product was purified by chromatography (silica gel, dichloro-
methane−methanol 20:1) and isolated as an orange−brown glassy
solid (105 mg, 73%). Single crystals were grown from dichloro-
methane/hexane.
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 0.45 (d, 3JHH = 6.8 Hz,
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 0.52 (d, 3JHH = 6.8 Hz,
3 H, CHMe2), 1.40 (d, 3JHH = 6.6 Hz, 3 H, CHMe2), 3.21 (dd, JHH
=
3 H, CHMe2), 1.44 (d, 3JHH = 6.7 Hz, 3 H, CHMe2), 4.44 (dt, JHH
=
15.8 Hz, 4.0 Hz, 1 H, NCH2), 3.29 (dd, JHH = 15.8 Hz, 4.6 Hz, 1 H,
NCH2), 3.38 (s, 3 H, OMe), 3.48 (s, 3 H, OMe), 4.10 (t, JHH = 4.3
Hz, 1 H, CH(OMe)2), 4.37 (m, 2 H, CH of fc), 4.47 (td, JHH = 2.7
Hz, 1.4 Hz, 1 H, CH of fc), 4.62 (td, JHH = 2.6 Hz, 1.3 Hz, 1 H, CH of
fc), 4.65 (dt, JHH = 2.6 Hz, 1.5 Hz, 1 H, CH of fc), 4.85 (m, 1 H, CH
of fc), 5.71 (septet, 3JHH = 6.7 Hz, 1 H, CHMe2), 5.74 (dt, JHH = 2.7
2.7 Hz, 1.3 Hz, 1 H, CH of fc), 4.49 (td, JHH = 2.7 Hz, 1.4 Hz, 1 H,
CH of fc), 4.61 (td, JHH = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 4.71 (td,
HH = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.89 (dt, JHH = 2.6 Hz, 1.4 Hz, 1
H, CH of fc), 4.97 (dt, JHH = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 5.11
(sept, 3JHH = 6.8 Hz, 1 H, CHMe2), 5.83 (dt, JHH = 2.8 Hz, 1.4 Hz, 1
H, CH of fc), 5.91 (m, 1 H, CH of fc), 6.85−6.90 (m, 2 H, PPh2),
6.88 (d, JHH = 2.1 Hz, 1 H, CH of imidazole), 7.15−7.22 (m, 2 H,
PPh2), 7.23 (dd, JHH = 2.1 Hz, J = 0.4 Hz, 1 H, CH of imidazole),
J
3
Hz, 1.4 Hz, 1 H, CH of fc), 5.82 (ddd, JPH = 3.4 Hz, JHH = 2.6 Hz,
3
1.3 Hz, 1 H, CH of fc), 7.38−7.47 (m, 7 H, PPh2), 7.51−7.54 (m, 1
H, PPh2), 7.57−7.64 (m, 2 H, PPh2). The signals due to NH protons
were not observed. 13C{1H} NMR (CD2Cl2/CD3OD, 151 MHz): δ
20.20 (CHMe2), 20.22 (CHMe2), 49.81 (s, NCH2), 54.87 (OMe),
3
7.29−7.34 (m, 1 H, PPh2), 7.40−7.46 (m, 2 H, PPh2), 7.48−7.53 (m,
1 H, PPh2), 7.56−7.63 (m, 2 H, PPh2). 13C{1H} NMR (CD2Cl2/
CD3OD, 151 MHz): δ 21.43 (CHMe2), 23.31 (CHMe2), 54.38
(CHMe2), 66.65 (CH of fc), 67.22 (CH of fc), 67.79 (CH of fc),
68.58 (d, 1JHH = 62 Hz, Cipso-P of fc), 69.87 (CH of fc), 73.02 (d, 3JPC
4
55.78 (OMe), 62.21 (d, JPC = 4 Hz, CHMe2), 64.62 (CH of fc),
66.51 (d, 1JPC = 62 Hz, Cipso-P of fc), 66.79 (CH of fc), 68.03 (CH of
fc), 69.00 (CH of fc), 72.82 (d, 3JPC = 7 Hz, CH of fc), 74.53 (d, 3JPC
= 6 Hz, CH of fc), 74.12 (d, 2JPC = 4 Hz, CH of fc), 75.10 (d, 3JPC
11 Hz, CH of fc), 78.99 (d, 2JPC = 21 Hz, CH of fc), 101.27 (d, JPC
=
=
= 5 Hz, CH of fc), 75.26 (d, 2JPC = 11 Hz, CH of fc), 78.73 (d, 2JPC
=
4
20 Hz, CH of fc), 103.62 (d, JPC = 3 Hz, Cipso-N of fc), 104.71
2 Hz, Cipso-N of fc), 119.33 (CH of imidazole), 125.53 (CH of
(CH(OMe)2), 128.47 (d, JPC = 12 Hz, CH of PPh2), 129.15 (d, JPC
=
imidazole), 128.33 (d, 2JPC = 12 Hz, CHortho of PPh2), 129.36 (d, 3JPC
1
10 Hz, CH of PPh2), 130.78 (d, JPC = 56 Hz, Cipso of PPh2), 131.37
= 10 Hz, CHmeta of PPh2), 129.91 (d, JPC = 56 Hz, Cipso of PPh2),
1
4
1
(d, JPC = 3 Hz, CHpara of PPh2), 131.37 (d, JPC = 54 Hz, Cipso of
4
130.98 (d, 4JPC = 3 Hz, CHpara of PPh2), 131.23 (d, 1JPC = 56 Hz, Cipso
of PPh2), 131.29 (d, 3JPC = 9 Hz, CHmeta of PPh2), 131.65 (d, 4JPC = 3
Hz, CHpara of Ph), 134.71 (d, 2JPC = 11 Hz, CHortho of PPh2), 162.68
(carbene C). 31P{1H} NMR (CD2Cl2/CD3OD, 162 MHz): δ 18.1
(s). MS ESI+: m/z 583 ([M − HCl − Cl]+), 619 ([M − Cl]+), 679
([M + Na]+). IR (Nujol) νmax/cm−1: 3160 w, 3122 m, 3096 m, 3065
w, 1636 m, 1572 m, 1492 s (carbene), 1482 s (carbene), 1418 m,
1311 m, 1287 m, 1231 m, 1247 w, 1171 m, 1131 m, 1099 m, 1073 w,
1061 w, 1044 w, 1031 m, 1000 w, 957 w, 888 w, 871 m, 847 w, 829 m,
821 m, 744 s, 708 s, 691 s, 658 w, 643 w, 629 m, 560 w, 541 m, 531
m, 512 s, 482 s, 462 w, 445 m. Anal. Calcd for C28H27Cl2FeN2PPd
(656.0): C, 51.29%; H, 4.15%; N, 4.27%. Found: C, 50.91%; H,
3.99%; N, 4.19%.
PPh2), 131.60 (d, JPC = 3 Hz, CHpara of PPh2), 133.09 (d, JPC = 10
Hz, CH of PPh2), 134.63 (d, JPC = 11 Hz, CH of PPh2), 197.49 (d,
2JPC = 8 Hz, carbene C). IR (Nujol) νmax/cm−1: 3197 br m, 1714 m,
1547 s (carbene), 1304 w, 1219 w, 1169 w, 1123 m, 1095 m, 1072 m,
1032 m, 971 w, 915 w, 817 m, 748 m, 697 s, 678 w, 630 w, 536 m,
525 s, 486 s, 474 s, 444 w. MS ESI+: m/z 647 ([M − HCl − Cl]+),
683 ([M − Cl]+). Anal. Calcd for C30H35Cl2FeN2O2PPd·0.66CH2Cl2
(775.8): C, 47.47%; H, 4.72%; N, 3.61%. Found: C, 47.21%; H,
4.62%; N, 3.55%.
Synthesis of 6a. Complex 5a (102 mg, 0.15 mmol) was dissolved
in dry dichloromethane (10 mL), and the solution was treated with
HCl (1 mL of 4 M solution in dioxane, 0.25 mmol). After stirring
overnight, the reaction mixture was evaporated, and the residue was
purified by chromatography (silica gel, dichloromethane−methanol
50:1). A single rusty brown band was collected and evaporated,
producing 6a as a rusty brown glassy solid (91 mg, 97%). Crystals
suitable for X-ray diffraction analysis were grown from dichloro-
methane/hexane.
Compound 7. (S)-2-(Chloromethyl)pyrrolidine hydrochloride (49
mg, 0.30 mmol) was dissolved in dry dichloromethane (3 mL). To
this solution, the following reagents were successively added:
anhydrous triethylamine (0.10 mL, 0.7 mmol), [PdCl2(cod)] (57
mg, 0.20 mmol), and a dichloromethane solution of isocyanide 1 (79
mg, 0.20 mmol in 2 mL). The orange reaction mixture was stirred
overnight and then evaporated under vacuum. The crude product was
purified by chromatography over a silica gel column with dichloro-
methane−methanol 20:1, yielding the product as a 3:2 mixture of
diastereoisomers (83 mg, 63%; see Chart 4). The diastereoisomers
were separated by chromatography over silica gel (dichloromethane−
methanol 50:1) and subsequent chromatographic purification on a
1H NMR (CD2Cl2/CD3OD, 400 MHz): δ 3.45 (s, 3 H, NMe),
4.49 (td, J = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 4.60 (td, J = 2.7 Hz, 1.4
Hz, 1 H, CH of fc), 4.65 (dt, J = 2.7 Hz, 1.3 Hz, 1 H, CH of fc), 4.76
(td, J = 2.6 Hz, 1.3 Hz, 1 H, CH of fc), 4.88 (m, 1 H, CH of fc), 4.97
(dt, J = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 5.78 (dt, J = 2.7 Hz, 1.3 Hz, 1
H, CH of fc), 5.93 (m, 1 H, CH of fc), 6.67 (d, 3JHH = 2.0 Hz, CH of
imidazole), 7.08−7.13 (m, 2 H, PPh2), 7.10 (d, 3JHH = 2.0 Hz, CH of
imidazole), 7.18−7.24 (m, 2 H, PPh2), 7.28−7.34 (m, 1 H, PPh2),
7.38−7.43 (m, 2 H, PPh2), 7.46−7.51 (m, 1 H, PPh2), 7.64−7.77 (m,
2 H, PPh2). 13C{1H} NMR (CD2Cl2/CD3OD, 151 MHz): δ 38.11
Sepacore Flash System X50 (Buchi) using gradient elution with a
̈
similar solvent mixture. Yield of (S,Rp)-7: orange solid; 46 mg (35%).
Single crystals were obtained from chloroform/hexane. Yield of
(S,Sp)-7: orange solid; 31 mg (24%).
1
(NMe), 66.55 (CH of fc), 67.23 (CH of fc), 67.77 (d, JPC = 62 Hz,
J
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
m/z 583 ([M − HCl − Cl]+). Anal. Calcd for C28H27Cl2FeN2PPd
(655.6): C, 51.29%; H, 4.15%; N, 4.27%. Found: C, 51.46%; H,
4.26%; N, 4.08%.
Chart 4. Labeling Scheme of Proline Carbene 7
Catalytic Borylation of Aryl Bromides. A Schlenk tube was
charged successively with aryl bromide (1.0 mmol), bis(pinacolato)-
diboron (304 mg, 1.2 mmol), the catalyst (0.01 mmol), base (2.0
mmol), and anhydrous isopropanol (or other solvent during the
screening experiments; 4 mL). After degassing for five freeze−pump−
thaw cycles, the mixture was transferred into an oil bath kept at 85 °C.
After heating for 6 h, the reaction mixture was cooled to room
temperature and diluted with ethyl acetate (5 mL) and water (10
mL). The organic layer was separated and the aqueous residue
extracted with ethyl acetate (3× 5 mL). The combined organic layers
were washed with brine, dried over MgSO4, and evaporated. In the
screening experiments, anisole (108 mg, 1.0 mmol) was added as an
internal standard, and the mixture was analyzed by NMR spectros-
copy. During the preparative experiments, the filtered reaction
mixture was evaporated, and the crude product was purified by
column chromatography over silica gel using hexane−ethyl acetate
mixtures as the eluent (30:1 to 3:1 depending on the compound).
X-ray Crystallography. Full-set diffraction data were collected
with a Bruker D8 VENTURE Kappa diffractometer equipped with a
Duo PHOTON100 detector, a IμS microfocus sealed tube source,
and a Cryostream cooler at 150 K using Mo Kα radiation. The
structures were solved by direct methods (SHEXLT-201438) and
refined by least-squares against F2 with SHELXL-2014 or SHELXL-
2017.39 All non-hydrogen atoms were refined with anisotropic
displacement parameters. The NH hydrogens were located on
difference electron density maps and refined as riding atoms with
Uiso(H) set to 1.2Ueq(N). Hydrogens residing on the carbon atoms
(CHn) were included in their theoretical positions and refined
similarly. Particular details on structure refinement are as follows.
Compound 2a crystallizes as a chloroform solvate and with two
Analytical data for (S,Rp)-7. [α]20 = −295 (c = 0.33, CH2Cl2).
589
1H NMR (CD2Cl2, 600 MHz): δ 1.39 (tdt, JHH = 11.8 Hz, 10.3 Hz,
9.0 Hz, 1 H, Pro-4), 1.68 (m, 1 H, Pro-3), 1.83 (m, 1 H, Pro-4), 2.09
(dtdd, JHH = 13.3 Hz, 8.9 Hz, 4.5 Hz, 2.0 Hz, 1 H, Pro-3), 2.97 (m, 1
H, Pro-6), 3.30 (tt, JHH = 10.5 Hz, 6.5 Hz, 1 H, Pro-5), 3.50 (dd, 2JHH
3
3
2
= 10.4 Hz, JHH‑syn = 6.9 Hz, 1 H, Pro-6), 3.76 (t, JHH‑anti ≈ JHH
=
10.4 Hz, 1 H, Pro-6), 4.35 (td, J = 2.7 Hz, 1.4 Hz, 1 H, CH of fc),
4.43 (td, J = 2.7 Hz, 1.4 Hz, 1 H, CH of fc), 4.53 (ddd, JHH = 11.2 Hz,
8.7 Hz, 6.8 Hz, 1 H, Pro-2), 4.66 (td, J = 2.6 Hz, 1.3 Hz, 1 H, CH of
fc), 4.78 (tdd, J = 2.6 Hz, 1.7 Hz, 1.2 Hz, 1 H, CH of fc), 4.79 (dt, J =
2.6 Hz, 1.7 Hz, 1.2 Hz, 1 H, CH of fc), 4.80 (dt, J = 2.7 Hz, 1.4 Hz, 1
H CH of fc), 5.70 (dt, J = 2.8 Hz, 1.4 Hz, 1 H, CH of fc), 5.98 (ddt, J
= 3.9 Hz, 2.6 Hz, 1.3 Hz, 1 H, CH of fc), 7.35−7.39 (m, 2 H, PPh2),
7.40−7.46 (m, 4 H, PPh2), 7.66−7.73 (m, 4 H, PPh2). 13C{1H} NMR
(CD2Cl2, 151 MHz): δ 24.59 (Pro-3), 30.89 (Pro-4), 46.55 (Pro-2),
57.76 (Pro-6), 64.09 (Pro-5), 65.51 (CH of fc), 67.01 (CH of fc),
68.16 (d, 1JPC = 62 Hz, Cipso-P of fc), 68.28 (CH of fc), 68.36 (CH of
fc), 72.72 (d, 3JPC = 6 Hz, CH of fc), 74.21 (d, 3JPC = 3 Hz, CH of fc),
74.26 (d, 2JPC = 11 Hz, CH of fc), 79.58 (d, 2JPC = 22 Hz, CH of fc),
101.71 (d, 4JPC = 1 Hz, Cipso-N of fc), 128.17 (d, JPC = 12 Hz, CH of
PPh2), 128.69 (d, JPC = 11 Hz, CH of PPh2), 130.79 (d, 4JPC = 3 Hz,
CHpara of PPh2), 131.30 (d, 4JPC = 3 Hz, CHpara of PPh2), 130.86 (d,
1JPC = 54 Hz, Cipso of PPh2), 131.57 (d, JPC = 10 Hz, CH of PPh2),
132.42 (d, 1JPC = 57 Hz, Cipso of PPh2), 134.49 (d, JPC = 11 Hz, CH of
PPh2), 196.08 (d, 3JPC = 4 Hz, carbene). 31P{1H} NMR (CD2Cl2, 162
MHz): δ 18.8 (s). IR (Nujol) νmax/cm−1: 3072 w, 3049 w, 1497 s
(carbene), 1436 s, 1325 w, 1269 m, 1168 m, 1098 m, 1067 w, 1032 m,
999 w, 933 w, 825 m, 746 s, 694 s, 629 m, 529 m, 508 s, 481 s, 440 m.
MS ESI+: m/z 583 ([M − HCl − Cl]+), 619 ([M − Cl]+). MS ESI−:
m/z 691 ([M + Cl]−). Anal. Calcd for C28H27Cl2FeN2PPd (655.6):
C, 51.29%; H, 4.15%; N, 4.27%. Found: C, 51.27%; H, 4.00%; N,
4.12%.
̅
structurally independent complex molecules (space group P1). Two
of the solvent molecules in the asymmetric unit were refined, but the
remaining ones, disordered within large structural voids (approx-
imately 12% of the unit cell volume), could not be adequately
modeled and, hence, were removed from the refinement by PLATON
SQUEEZE.40 One of the solvating methanol molecules in the
structure of 4a·2MeOH and the solvent molecules in the structures of
5b·CH2Cl2 and 6b·1/2CH2Cl2 were similarly treated.
Selected crystallographic data and structure refinement parameters
are outlined in the Supporting Information (Table S1). PLATON41
was used to create all structural diagrams and to perform geometric
calculations. The numerical values are rounded to one decimal place
of their estimated standard deviations (ESDs). Parameters pertaining
to atoms in constrained positions are presented without ESDs.
DFT Calculations. Theoretical calculations were performed using
the Gaussian 09 program package.42 The reported energies
correspond to Gibbs free energies obtained from full geometry
optimizations (starting from atomic coordinates determined by X-ray
diffraction analysis where possible) using meta-GGA (TPSS)43 and
hybrid (B3LYP,44,45 PBE046) density functionals in conjunction with
the Stuttgart effective core potential47 used for the transition metals
(Fe, Pd) and with the def2-TZVP48 basis set used for the remaining
elements (C, H, N, P, Cl) with added Grimme’s D3 dispersion
correction.49 The solvent effects (dichloromethane) were approxi-
mated using the polarized continuum model (PCM).50 Topological
analysis of the electron density according to the atoms in molecules
(AIM) method51 and orbital composition analysis were performed
using the Multiwfn software package (version 3.6).52 Molecular
orbitals were visualized using the Avogadro program.53
Analytical data for (S,Sp)-7. [α]20589 = +277 (c = 0.38, CH2Cl2). 1H
NMR (CD2Cl2, 600 MHz): δ 0.27 (qd, JHH = 11.1 Hz, 8.3 Hz, 1 H,
Pro), 1.52 (dtdd, JHH = 13.2 Hz, 8.4 Hz, 3.5 Hz, 1.4 Hz, 1 H, Pro),
1.72 (m, 1 H, Pro), 1.82 (dddt, JHH = 12.9 Hz, 10.9 Hz, 10.0 Hz, 7.7
Hz, 1 H, Pro), 3.29 (dt, JHH = 11.6 Hz, 8.3 Hz, 1 H, Pro), 3.48 (t, JHH
= 10.4 Hz, 1 H, Pro), 3.62 (ddd, JHH = 11.6 Hz, 10.1 Hz, 3.4 Hz, 1 H,
Pro), 3.76 (td, JHH = 10.5 Hz, 1.4 Hz, 1 H, Pro), 4.13 (qd, JHH = 10.4
Hz, 5.7 Hz, 1 H, Pro), 4.39 (td, J = 2.6 Hz, 1.4 Hz, 1 H, CH of fc),
4.43 (td, J = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.67 (m, 2 H, CH of fc),
4.71 (td, J = 2.6 Hz, 1.4 Hz, 1 H, CH of fc), 4.79 (m, 1 H, CH of fc),
5.44 (dt, J = 2.8 Hz, 1.7 Hz, 1 H, CH of fc), 5.98 (ddtd, 3JPH = 4.0 Hz,
JHH = 2.7 Hz, 1.3 Hz, 0.5 Hz, 1 H, CH of fc), 7.36−7.40 (m, 2 H,
PPh2), 7.43−7.49 (m, 4 H, PPh2), 7.67−7.76 (m, 4 H, PPh2).
13C{1H} NMR (CD2Cl2, 151 MHz): δ 25.84 (Pro), 30.44 (Pro),
46.27 (Pro), 58.47 (Pro), 64.86 (Pro), 65.19 (d, 1JPC = 62 Hz, Cipso-P
of fc), 65.30 (CH of fc), 67.03 (CH of fc), 67.06 (CH of fc), 73.35 (d,
2
3JPC = 6 Hz, CH of fc), 74.30 (d, JPC = 12 Hz, CH of fc), 74.44 (d,
3JPC = 3 Hz, CH of fc), 79.84 (d, 2JPC = 23 Hz, CH of fc), 102.55 (d,
4JPC = 1 Hz, Cipso-N of fc), 128.15 (d, JPC = 12 Hz, CH of PPh2),
129.30 (d, JPC = 10 Hz, CH of PPh2), 130.99 (d, 4JPC = 4 Hz, CHpara
of PPh2), 131.15 (d, 1JPC = 54 Hz, Cipso of PPh2), 131.34 (d, 4JPC = 3
Hz, CHpara of PPh2), 131.99 (d, JPC = 9 Hz, CH of PPh2), 132.77 (d,
1JPC = 55 Hz, Cipso of PPh2), 134.53 (d, JPC = 11 Hz, CH of PPh2),
190.88 (carbene). 31P{1H} NMR (CD2Cl2, 162 MHz): δ 16.3 (s). IR
(Nujol) νmax/cm1 3068 w, 3042 w, 1495 s (carbene), 1437 s, 1307 w,
1265 m, 1168 m, 1097 m, 1067 w, 1031 m, 999 w, 937 w, 888 w, 824
m, 746 s, 695 s, 628 s, 540 w, 529 m, 508 s, 481 s, 442 m. MS ESI+:
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00398.
K
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Further experimental details, characterization data for
Article
Wiley: Chichester, 2008. (c) Atkinson, R. C. J.; Gibson, V. C.; Long,
N. J. The syntheses and catalytic applications of unsymmetrical
the coupling products 9, additional structural diagrams,
summary of the crystallographic data and structure
refinement parameters, as well as copies of the NMR
spectra (PDF)
Cartesian coordinates of the DFT optimized structures
(XYZ)
́
ferrocene ligands. Chem. Soc. Rev. 2004, 33, 313−328. (d) Gomez
́
Arrayas, R.; Adrio, J.; Carretero, J. C. Recent Applications of Chiral
Ferrocene Ligands in Asymmetric Catalysis. Angew. Chem., Int. Ed.
2006, 45, 7674−7715.
(6) For reviews, see: (a) Bildstein, B.; et al. J. Organomet. Chem.
2001, 617−618, 28−38. (b) Siemeling, U. Singlet Carbenes Derived
from Ferrocene and Closely Related Sandwich Complexes. Eur. J.
Inorg. Chem. 2012, 2012, 3523−3536.
Accession Codes
CCDC 1922546−1922553 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.
(7) Gaillard, S.; Renaud, J.-L. When phosphorus and NHC (N-
heterocyclic carbene) meet each other. Dalton Trans. 2013, 42,
7255−7270.
(8) (a) Gischig, S.; Togni, A. Synthesis and Coordination Chemistry
of a New Chiral Tridentate PCP N-Heterocyclic Carbene Ligand
Based on a Ferrocene Backbone. Organometallics 2004, 23, 2479−
2487. (b) Gischig, S.; Togni, A. A Dinuclear Copper(I) Complex
Containing a Bridging Chiral Tridentate Carbene Ligand. Organo-
metallics 2005, 24, 203−205. (c) Gischig, S.; Togni, A. PdII
Complexes of Tridentate PCP N-Heterocyclic Carbene Ligands:
Structural Aspects and Application in Asymmetric Hydroamination of
Cyano Olefins. Eur. J. Inorg. Chem. 2005, 2005, 4745−4754.
(9) (a) Seo, H.; Park, H.; Kim, B. Y.; Lee, J. H.; Son, S. U.; Chung,
Y. K. Synthesis of P- and S-Functionalized Chiral Imidazolium Salts
and Their Rh and Ir Complexes. Organometallics 2003, 22, 618−620.
(b) Shi, J.-C.; Yang, P.-Y.; Tong, Q.; Wu, Y.; Peng, Y. Highly efficient
and stable palladium/imidazolium salt-phosphine catalysts for
Suzuki−Miyaura cross-coupling of aryl bromides. J. Mol. Catal. A:
Chem. 2006, 259, 7−10. (c) Visentin, F.; Togni, A. Synthesis and
Characterization of Palladium(II) π-Allyl Complexes with Chiral
Phosphinocarbene Ligands. Kinetics and Mechanism of Allylic
Amination. Organometallics 2007, 26, 3746−3754. (d) Shi, J.; Yang,
P.; Tong, Q.; Jia, L. Palladium-catalyzed aminations of aryl halides
with phosphine-functionalized imidazolium ligands. Dalton Trans.
AUTHOR INFORMATION
Corresponding Author
*E-mail: petr.stepnicka@natur.cuni.cz.
■
ORCID
̌
Karel Skoch: 0000-0001-6406-989X
̌
̌
̌
Petr Stepnicka: 0000-0002-5966-0578
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Czech Science Foundation
(Project 17-02495S) and by the Charles University Research
Centre program (Project UNCE/SCI/014). The authors
́
́
thank Dr. L. Bednarova for recording the ECD and UV−vis
spectra.
́
̌
́
́
2008, 938−945. (e) Csizmadiova, J.; Meciarova, M.; Almassy, A.;
̌
́
Horvath, B.; Sebesta, R. Ferrocene phosphane−carbene ligands in Cu-
catalyzed enantioselective 1,4-additions of Grignard reagents to α,β-
unsaturated carbonyl compounds. J. Organomet. Chem. 2013, 737,
47−52.
REFERENCES
■
(1) For early examples, see: (a) Wanzlick, H. W.; Kleiner, H. J.
Nucleophile Carben-Chemie. Darstellung des Bis-[1.3-diphenyl-
imidazolidinyliden-(2)]. Angew. Chem. 1961, 73, 493. (b) Ofele, K.
(10) (a) Labande, A.; Daran, J.-C.; Manoury, E.; Poli, R. New (1-
Phosphanylferrocen-1′- and −2-yl)methyl-Linked Diaminocarbene
Ligands: Synthesis and Rhodium(I) Complexes. Eur. J. Inorg. Chem.
2007, 2007, 1205−1209. (b) Debono, N.; Labande, A.; Manoury, E.;
Daran, J.-C.; Poli, R. Palladium Complexes of Planar Chiral
Ferrocenyl Phosphine-NHC Ligands: New Catalysts for the
Asymmetric Suzuki−Miyaura Reaction. Organometallics 2010, 29,
̈
lcemal, S.; Daran, J.-C.;
Manoury, E.; Poli, R.; Cetinkaya, B.; Labande, A. Palladium(II)
complexes with planar chiral ferrocenyl phosphane−(benz)imidazol-
2-ylidene ligands. New J. Chem. 2014, 38, 338−347.
̈
(11) (a) Gulcemal, S.; Labande, A.; Daran, J.-C.; Çetinkaya, B.; Poli,
R. Rhodium(I) Complexes of New Ferrocenyl Benzimidazol-2-
ylidene Ligands: The Importance of the Chelating Effect for Ketone
Hydrosilylation Catalysis. Eur. J. Inorg. Chem. 2009, 2009, 1806−
1815. (b) Labande, A.; Debono, N.; Sournia-Saquet, A.; Daran, J.-C.;
Poli, R. Oxidation-promoted activation of a ferrocene C−H bond by a
rhodium complex. Dalton Trans. 2013, 42, 6531−6537. (c) Debono,
N.; Daran, J.-C.; Poli, R.; Labande, A. A rhodium(I) dicarbonyl
complex with a redox-active ferrocenyl phosphine-NHC ligand:
Enhanced reactivity of the metal centre through ferrocene oxidation.
Polyhedron 2015, 86, 57−63.
̈
1,3-Dimethyl-4-imidazolinyliden-(2)-pentacarbonylchrom ein neuer
ubergangsmetall-carben-komplex. J. Organomet. Chem. 1968, 12,
̈
̈
P42−P43. (c) Wanzlick, H.-W.; Schonherr, H. J. Direct Synthesis
of a Mercury Salt-Carbene Complex. Angew. Chem., Int. Ed. Engl.
1968, 7, 141−142. (d) Igau, A.; Grutzmacher, H.; Baceiredo, A.;
Bertrand, G. Analogous α,α′-bis-carbenoid, triply bonded species:
synthesis of a λ3-phosphino carbene-λ5-phosphaacetylene. J. Am.
Chem. Soc. 1988, 110, 6463−6466. (e) Arduengo, A. J., III; Harlow,
R. L.; Kline, M. A Stable Crystalline Carbene. J. Am. Chem. Soc. 1991,
1879−1882. (c) Loxq, P.; Debono, N.; Gu
̧
̈
113, 361−363. See also: (f) Herrmann, W. A.; Kocher, C. N-
Heterocyclic Carbenes. Angew. Chem., Int. Ed. Engl. 1997, 36, 2162−
2187.
(2) Bourissou, D.; Guerret, O.; Gabbaï, F. P.; Bertrand, G. Stable
Carbenes. Chem. Rev. 2000, 100, 39−92.
(3) Recent reviews: (a) Hahn, F. E.; Jahnke, M. C. Heterocyclic
Carbenes: Synthesis and Coordination Chemistry. Angew. Chem., Int.
́
Ed. 2008, 47, 3122−3172. (b) de Fremont, P.; Marion, N.; Nolan, S.
P. Carbenes: synthesis, properties, and organometallic chemistry.
Coord. Chem. Rev. 2009, 253, 862−892. (c) Hopkinson, M. N.;
Richter, C.; Schedler, M.; Glorius, F. An overview of N-heterocyclic
carbenes. Nature 2014, 510, 485−496.
(12) Related compounds, in which the phosphorus atom is a part of
a phosphaferrocene moiety, have been described by Ganter et al:
Willms, H.; Frank, W.; Ganter, C. Hybrid Ligands with N-
Heterocyclic Carbene and Chiral Phosphaferrocene Components.
Chem. - Eur. J. 2008, 14, 2719−2729.
(13) (a) Perevalova, E. G., Reschetova, M. D., Grandberg, K. I., Eds.
Methods of Organoelement Compounds, volume Organoiron Compounds,
Ferrocene; Nauka: Moscow, 1983 (in Russian). (b) Boev, V. I.;
(4) (a) Nelson, D. J.; Nolan, S. P. Quantifying and understanding
the electronic properties of N-heterocyclic carbenes. Chem. Soc. Rev.
2013, 42, 6723−6753. (b) Huynh, H. V. Electronic Properties of N-
Heterocyclic Carbenes and Their Experimental Determination. Chem.
Rev. 2018, 118, 9457−9492.
(5) (a) Togni, A., Hayashi, T., Eds. Ferrocenes: Homogeneous
Catalysis, Organic Synthesis, Materials Science; VCH: Weinheim, 1995.
̌
̌
̌
(b) Stepnicka, P., Ed. Ferrocenes: Ligands, Materials and Biomolecules;
L
DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Snegur, L. V.; Babin, V. N.; Nekrasov, Yu. S. α-Metallocenylalkylation.
Russ. Chem. Rev. 1997, 66, 613−636. (c) Rockett, B. W.; Marr, G.
Ferrocene: Annual survey covering the year 1989. J. Organomet. Chem.
1991, 416, 327−398 and previous “annual surveys.” .
(14) Boyarskiy, V. P.; Bokach, N. A.; Luzyanin, K. V.; Kukushkin, V.
Y. Metal-Mediated and Metal-Catalyzed Reactions of Isocyanides.
Chem. Rev. 2015, 115, 2698−2779 and references cited therein. .
(15) (a) Yu, I.; Wallis, C. J.; Patrick, B. O.; Mehrkhodavandi, P.
Template Synthesis of Donor-Functionalized NX-Carbenes (X = P,
Si). Organometallics 2009, 28, 6370−6373. (b) Yu, I.; Wallis, C. J.;
Patrick, B. O.; Diaconescu, P. L.; Mehrkhodavandi, P. Phosphine-
Tethered Carbene Ligands: Template Synthesis and Reactivity of
Cyclic and Acyclic Functionalized Carbenes. Organometallics 2010,
29, 6065−6076.
J. 2005, 11, 1833−1853. (b) Tang, Y.-Q.; Lu, J.-M.; Wang, X.-R.;
Shao, L.-X. Palladium(II)−N-heterocyclic carbene complexes derived
from proline: synthesis and characterization. Tetrahedron 2010, 66,
7970−7974. (c) Ma, M.-T.; Lu, J.-M. Dinuclear Pd(II)−NHC
complex derived from proline and its application toward Mizoroki−
Heck reaction performed in water. Appl. Organomet. Chem. 2012, 26,
175−179. (d) Zhao, Y.; Gilbertson, S. R. Synthesis of Proline-Based
N-Heterocyclic Carbene Ligands. Org. Lett. 2014, 16, 1033−1035.
(27) (a) Scott, D. R.; Becker, R. S. Comprehensive Investigation of
the Electronic Spectroscopy and Theoretical Treatments of Ferrocene
and Nickelocene. J. Chem. Phys. 1961, 35, 516−531. (b) Salzner, U.
Quantitatively Correct UV-vis Spectrum of Ferrocene with
TDB3LYP. J. Chem. Theory Comput. 2013, 9, 4064−4073.
(28) The ring puckering parameters are Q2 = 0.341(3) Å, φ2 =
138.5(6)°. For reference, see: Cremer, D.; Pople, J. A. General
definition of ring puckering coordinates. J. Am. Chem. Soc. 1975, 97,
1354−1358.
(16) (a) Zhang, L.; Yu, W.; Liu, C.; Xu, Y.; Duan, Z.; Mathey, F. he
Chemistry of ortho-(Diarylphosphino)aryl Isocyanides. Organometal-
lics 2015, 34, 5697−5702. (b) Zhang, L.; Liu, C.; Duan, Z.; Mathey,
F. A Straightforward Synthesis of 1,2-Azaphosphindoles. Eur. J. Inorg.
Chem. 2017, 2017, 2504−2509.
(29) Additional interactions can come into a play in this case, e.g.,
sterics (the cis-Cl−Pd−C angles are typically the most acute among
interligand angles) cooperating with cis influence of the carbene
ligand: Abernethy, C. D.; Codd, G. M.; Spicer, M. D.; Taylor, M. K. A
Highly Stable N-Heterocyclic Carbene Complex of Trichloro-oxo-
vanadium(V) Displaying Novel Cl−Ccarbene Bonding Interactions. J.
Am. Chem. Soc. 2003, 125, 1128−1129.
̌
̌
̌
̌
́
̌
(17) Skoch, K.; Císarova, I.; Schulz, J.; Siemeling, U.; Stepnicka, P.
Synthesis and characterization of 1′-(diphenylphosphino)-1-isocya-
noferrocene, an organometallic ligand combining two different soft
donor moieties, and its Group 11 metal complexes. Dalton Trans.
2017, 46, 10339−10354.
̌
̌
̌
̌
́
̌
(18) Skoch, K.; Císarova, I.; Uhlík, F.; Stepnicka, P. Divergent
reactivity of isomeric phosphinoferrocene nitrile and isocyanide in
Pd(II) complexes: Synthesis of conventional coordination compounds
and P-chelated carbenes. Dalton Trans. 2018, 47, 16082−16101.
(19) Ishiyama, T.; Murata, M.; Miyaura, N. Palladium(0)-Catalyzed
Cross-Coupling Reaction of Alkoxydiboron with Haloarenes: A Direct
Procedure for Arylboronic Esters. J. Org. Chem. 1995, 60, 7508−7510.
(30) An easier oxidation of Ir(I)-NHC complexes with imidazolin-2-
ylidenes as compared to their counterparts featuring analogous
̈
imidazol-2-ylidene ligands was noted in: Leuthausser, S.; Schwarz, D.;
Plenio, H. Tuning the Electronic Properties of N-heterocyclic
Carbenes. Chem. - Eur. J. 2007, 13, 7195−7203.
(31) Gusev, O. V.; Peterleitner, M. G.; Kal’sin, A. M.; Vologdin, N.
V. Cyclic Voltammetry of 1,1′-bis(Diarylphosphino)metallocenes and
Their Complexes with Palladium(II). Russ. J. Electrochem. 2003, 39,
1293−1299.
́
́
(20) Eberhard, M. R.; van Vliet, B.; Duran Pachon, L.; Rothenberg,
G.; Eastham, G.; Kooijman, H.; Spek, A. L.; Elsevier, C. J. A simple
building-block route to (phosphanyl-carbene)palladium complexes via
intermolecular addition of functionalised phosphanes to isocyanides.
Eur. J. Inorg. Chem. 2009, 2009, 1313−1316.
(32) (a) Ishiyama, T.; Miyaura, N. Metal-Catalyzed Reactions of
Diborons for Synthesis of Organoboron Compounds. Chem. Rec.
2004, 3, 271−280. (b) Lennox, A. J. J.; Lloyd-Jones, G. C. Selection
of boron reagents for Suzuki−Miyaura coupling. Chem. Soc. Rev. 2014,
43, 412−443. (c) Fyfe, J. W. B.; Watson, A. J. B. Recent
Developments in Organoboron Chemistry: Old Dogs. New Tricks.
Chem. 2017, 3, 31−55.
(33) Selected examples: (a) Ishiyama, T.; Ishida, K.; Miyaura, N.
Synthesis of pinacol arylboronates via cross-coupling reaction of
bis(pinacolato)diboron with chloroarenes catalyzed by palladium(0)−
tricyclohexylphosphine complexes. Tetrahedron 2001, 57, 9813−9816.
(b) Tang, W.; Keshipeddy, S.; Zhang, Y.; Wei, X.; Savioe, J.; Patel, N.
D.; Yee, N. K.; Senanyake, C. H. Efficient Monophosphorus Ligands
for Palladium-Catalyzed Miyaura Borylation. Org. Lett. 2011, 13,
(21) (a) Hashmi, A. S. K.; Lothschutz, C.; Bohling, C.; Hengst, T.;
̈
̈
Hubbert, C.; Rominger, F. Carbenes Made Easy: Formation of
Unsymmetrically Substituted N-Heterocyclic Carbene Complexes of
Palladium(II), Platinum(II) and Gold(I) from Coordinated Isonitriles
and their Catalytic Activity. Adv. Synth. Catal. 2010, 352, 3001−301.
(b) Hashmi, A. S. K.; Lothschutz, C.; Bohling, C.; Rominger, F. From
̈
̈
Isonitriles to Carbenes: Synthesis of New NAC− and NHC−
Palladium(II) Compounds and Their Catalytic Activity. Organo-
metallics 2011, 30, 2411−2417. (c) Hashmi, A. S. K.; Yu, Y.;
Rominger, F. Efficient One-Pot Synthesis of Unsymmetrical Gold(I)
N-Heterocyclic Carbene Complexes and Their Use as Catalysts.
Organometallics 2012, 31, 895−904.
́
1366−1369. (c) Pandarus, V.; Gingras, G.; Beland, F.; Ciriminna, R.;
(22) Riedel, D.; Wurm, T.; Graf, K.; Rudolph, M.; Rominger, F.;
Hashmi, A. S. K. From Isonitriles to Unsaturated NHC Complexes of
Gold, Palladium and Platinum. Adv. Synth. Catal. 2015, 357, 1515−
1523.
(23) (a) Arduengo, A. J., III; Dias, H. V. R.; Harlow, R. L.; Kline, M.
Electronic stabilization of nucleophilic carbenes. J. Am. Chem. Soc.
1992, 114, 5530−5534. (b) Arduengo, A. J., III; Goerlich, J. R.;
Marshall, W. J. A stable diaminocarbene. J. Am. Chem. Soc. 1995, 117,
11027−11028.
(24) See, for instance: Slattery, J.; Thatcher, R. J.; Shi, Q.;
Douthwaite, R. E. Comparison of donor properties of N-heterocyclic
carbenes and N-donors containing the 1H-pyridin-(2E)-ylidene motif.
Pure Appl. Chem. 2010, 82, 1663−1671.
(25) Koch, U.; Popelier, P. L. A. Characterization of C-H−O
hydrogen bonds on the basis of the charge density. J. Phys. Chem.
1995, 99, 9747−9754. The calculated parameters were: ρ(r) = 0.009
au, ∇2ρ(r) = 0.026 au.
(26) For examples of proline-derived NHCs, see: (a) Kremzow, D.;
̈
Seidel, G.; Lehmann, C. W.; Furstner, A. Diaminocarbene- and
Fischer-Carbene Complexes of Palladium and Nickel by Oxidative
Pagliaro, M. Clean and fast cross-coupling of aryl halides in one-pot.
Beilstein J. Org. Chem. 2014, 10, 897−901. (d) Lu, H.; Wang, S.; Li, J.;
Zou, D.; Wu, Y.; Wu, Y. Efficient synthesis of pyrazine boronic esters
via palladium-catalyzed Miyaura borylation. Tetrahedron Lett. 2017,
58, 839−842.
(34) Reichardt, C.; Welton, T.; Eds. Solvents and Solvent Effects in
Organic Chemistry, 4th ed.; Wiley-VCH: Weinheim, 2011.
(35) (a) Gan, K.-S.; Hor, T. S. A. 1,1’-Bis(diphenylphosphino)-
ferrocene. Coordination Chemistry, Organic Syntheses, and Catalysis.
In Ferrocenes: Homogeneous Catalysis, Organic Synthesis Materials
Science; Togni, A., Hayashi, T., Eds.; Wiley-VCH: Weinheim, 1995;
ch. 1, pp 3−104. (b) Chien, S. W.; Hor, T. S. A. The Coordination
and Homogeneous Catalytic Chemistry of 1,1’-Bis-
(diphenylphosphino)ferrocene and its Chalcogenide Derivatives. In
̌
̌
̌
Ferrocenes: Ligands, Materials and Biomolecules; Stepnicka, P., Ed.;
Wiley: Chichester, 2008; ch. 2, pp 33−116. (c) Bandoli, G.; Dolmella,
A. Ligating ability of 1,1’ -bis(diphenylphosphino)ferrocene: a
structural survey (1994 − 1998). Coord. Chem. Rev. 2000, 209,
161−196.
́
(36) Corain, B.; Longato, B.; Favero, G.; Ajo, D.; Pilloni, G.; Russo,
Insertion: Preparation, Structure, and Catalytic Activity. Chem. - Eur.
U.; Kreissl, F. R. Heteropolymetallic complexes of 1,1’-bis-
M
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Organometallics
Article
(diphenylphosphino)ferrocene (dppf). III*. Comparative physico-
chemical properties of (dppf)MCl2 (M = Co, Ni, Pd, Pt, Zn, Cd, Hg).
Inorg. Chim. Acta 1989, 157, 259−266.
(53) (a) Avogadro: An Open-Source Molecular Builder and
Visualization Tool, version 1.2.0. http://avogadro.openmolecules.
net/. (b) Hanwell, M. D.; Curtis, D. E.; Lonie, D. C.; Vandermeersch,
T.; Zurek, E.; Hutchison, G. R. Avogadro: an advanced semantic
chemical editor, visualization, and analysis platform. J. Cheminf. 2012,
4, 17.
̀
(37) Barriere, F.; Geiger, W. E. Use of Weakly Coordinating Anions
to Develop an Integrated Approach to the Tuning of ΔE1/2 Values by
Medium Effects. J. Am. Chem. Soc. 2006, 128, 3980−3989.
(38) Sheldrick, G. M. SHELXT−Integrated space-group and crystal-
structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015,
71, 3−8.
(39) Sheldrick, G. M. Crystal structure refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(40) Spek, A. L. PLATON SQUEEZE: a tool for the calculation of
the disordered solvent contribution to the calculated structure factors.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 9−18.
(41) Spek, A. L. Structure validation in chemical crystallography.
Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148−155.
(42) 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.
(43) Tao, J.; Perdew, J. P.; Staroverov, V. N.; Scuseria, G. E.
Climbing the Density Functional Ladder: Nonempirical Meta−
Generalized Gradient Approximation Designed for Molecules and
Solids. Phys. Rev. Lett. 2003, 91, 146401.
(44) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-
Salvetti correlation-energy formula into a functional of the electron
density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785.
(45) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J.
Ab Initio Calculation of Vibrational Absorption and Circular
Dichroism Spectra Using Density Functional Force Fields. J. Phys.
Chem. 1994, 98, 11623−11627.
(46) Ernzerhof, M.; Scuseria, G. E. Assessment of the Perdew−
Burke−Ernzerhof exchange-correlation functional. J. Chem. Phys.
1999, 110, 5029−5036.
(47) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Energy-adjusted ab initio pseudopotentials for the second and third
row transition elements. Theor. Chim. Acta 1990, 77, 123−141.
(48) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence,
triple zeta valence and quadruple zeta valence quality for H to Rn:
Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7,
3297−3305.
(49) (a) 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. (b) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the
damping function in dispersion corrected density functional theory. J.
Comput. Chem. 2011, 32, 1456−1465.
(50) (a) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical
Continuum Solvation Models. Chem. Rev. 2005, 105, 2999−3093.
(b) Scalmani, G.; Frisch, M. J. Continuous surface charge polarizable
continuum models of solvation. J. Chem. Phys. 2010, 132, 114110.
(51) (a) Bader, R. F. W. Atoms in Molecules: A Quantum Theory;
Oxford University Press: Oxford, U.K., 1990. (b) Bader, R. F. W. A
quantum theory of molecular structure and its applications. Chem.
Rev. 1991, 91, 893−928.
(52) Lu, T.; Chen, F. Multiwfn: A multifunctional wavefunction
analyzer. J. Comput. Chem. 2012, 33, 580−592.
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DOI: 10.1021/acs.organomet.9b00398
Organometallics XXXX, XXX, XXX−XXX