An Isolable Mononuclear Palladium(I) Amido Complex

Article abstract of DOI:10.1021/jacs.1c04965

Mononuclear Pd(I) species are putative intermediates in Pd-catalyzed reactions, but our knowledge about them is limited due to difficulties in accessing them. Herein, we report the isolation of a Pd(I) amido complex, [(BINAP)Pd(NHArTrip)] (BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene, ArTrip = 2,6-bis(2′,4′,6′-triisopropylphenyl)phenyl), from the reaction of (BINAP)PdCl2 with LiNHArTrip. This Pd(I) amido species has been characterized by X-ray crystallography, electron paramagnetic resonance, and multiedge Pd X-ray absorption spectroscopy. Theoretical study revealed that, while the three-electron-two-center π-interaction between Pd and N in the Pd(I) complex imposes severe Pauli repulsion in its Pd-N bond, pronounced attractive interligand dispersion force aids its stabilization. In accord with its electronic features, reactions of homolytic Pd-N bond cleavage and deprotonation of primary amines are observed on the Pd(I) amido complex.

Full text of DOI:10.1021/jacs.1c04965

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An Isolable Mononuclear Palladium(I) Amido Complex
Jian Liu, Melissa M. Bollmeyer, Yujeong Kim, Dengmengfei Xiao, Samantha N. MacMillan, Qi Chen,
Xuebing Leng, Sun Hee Kim,* Lili Zhao,* Kyle M. Lancaster,* and Liang Deng*
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ABSTRACT: Mononuclear Pd(I) species are putative intermedi-
ates in Pd-catalyzed reactions, but our knowledge about them is
limited due to difficulties in accessing them. Herein, we report the
isolation of a Pd(I) amido complex, [(BINAP)Pd(NHArTrip)]
(BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene, ArTrip
= 2,6-bis(2′,4′,6′-triisopropylphenyl)phenyl), from the reaction of
(BINAP)PdCl2 with LiNHArTrip. This Pd(I) amido species has
been characterized by X-ray crystallography, electron paramagnetic resonance, and multiedge Pd X-ray absorption spectroscopy.
Theoretical study revealed that, while the three-electron−two-center π-interaction between Pd and N in the Pd(I) complex imposes
severe Pauli repulsion in its Pd−N bond, pronounced attractive interligand dispersion force aids its stabilization. In accord with its
electronic features, reactions of homolytic Pd−N bond cleavage and deprotonation of primary amines are observed on the Pd(I)
amido complex.
A common feature of the aforementioned reactive Pd(I)
intermediates is the presence of π-donorsligands whose
coordinating atoms bear nonbonding lone pairs, e.g., halides,
superoxide, and amido in the aforementioned caseswithin
Pd’s inner coordination sphere. Such mononuclear Pd(I)
species reported to date are exceedingly reactive and have only
been observed using spectroscopic methods in γ-ray-irradiated
Pd(II)Cl2 and Pd(II)(acac)2 and thermalized Pd(II)-ex-
changed zeolites,12−14 where their stability is conferred by
immobilization within the lattice framework. Certain Pd(0)
and Pd(II) complexes are reported to undergo chemical and
electrochemical redox reactions to produce mononuclear
paramagnetic Pd(I) complexes.15−19 These include three
INTRODUCTION
■
Palladium is a frequently used metal in the modern molecular
chemists’ catalyst arsenal and can be found in a variety of
useful organic reactions, such as Wacker oxidations, cross-
couplings, C−H bond functionalization, and hydrogenation
reactions.1 Underlying the broad utility of Pd are the multiple
oxidation states accessible, which suit them well to the
formation and cleavage of covalent bonds. Pd compounds
most commonly occur as diamagnetic, closed-shell Pd(0),
Pd(II), and Pd(IV) complexes. Paramagnetic, open-shell Pd
compounds are far less prevalent, but are now receiving
increased attention.2−5 Paramagnetic Pd(I) species, for
example, are implicated as intermediates in some Pd-catalyzed
reactions, but sparse data are available concerning their
electronic structures and reactivity. In Pd-catalyzed C−C
bond-forming reactions, Pd(I) halide species LnPdIX (L =
phosphine; X = Br, I) are proposed to form via single-electron
transfer reactions of photoexcited Pd(0) phosphine complexes
with organic halides,6−8 as well as in the reactions of Pd(0)
phosphine complexes with fluoroalkyl halides (Figure 1A).9 In
the reactions of Pd(0) species with dioxygen, which is a key
step in Pd-catalyzed aerobic oxidation reactions, Pd(I)
superoxide species LnPdI(η1-OO•) are proposed as intermedi-
ates en route to Pd(II) peroxides LnPdII(η2-O2) (Figure 1A).10
The formation of the Pd(I) intermediates has also been
envisaged in thermolysis or photolysis of Pd(II) compounds.
For example, photolysis-induced decomposition of (PNP)Pd-
(II) alkyl (PNP = phosphine-amido-phosphine) complexes
was proposed to proceed through (PNP)Pd(I) intermediates
that dimerized to yield diamagnetic, dinuclear Pd(I) complexes
(Figure 1A).11
isolable complexes, [(PBut )2 Pd]X (X
= PF6 ,
3
CB11Cl11H)18,19 and [(PBut3)2Pd(NCMe)](CB11Cl11H).19
These mononuclear Pd(I) complexes, however, are not
supported by π-donating ligands. To our knowledge, isolable
Pd(I) complexes bearing π-donating ligand have remained
elusive. The challenge of accessing mononuclear Pd(I)
complexes bearing π-donating ligands likely originates from
severe Pauli repulsion: conventional wisdom dictates that π-
interactions between the nd orbitals of low-valent platinum-
group metals (Ru, Rh, Pd, Os, Ir, Pt) and the lone pairs of π-
donors (Figure 1B) should enforce severe Pauli repulsion,20,21
leading to the destabilization of the metal−ligand multiple
Received: May 16, 2021
Published: July 7, 2021
https://doi.org/10.1021/jacs.1c04965
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© 2021 American Chemical Society
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Figure 1. Research background on Pd(I) species bearing π-donating ligands. (A) Examples of reactive Pd(I) intermediates containing π-donating
ligands. (B) Pauli repulsion in metal−ligand π-interaction. (C) Cartoon illustrating how London dispersion forces stabilize an M−X bond.
Figure 2. Synthetic route to the Pd(I) amido complex and its molecular structure. (A) Reaction giving Pd(I) amido complex
[(BINAP)Pd(NHArTrip)] (1) and the byproducts 2−4. (B) Molecular structure of 1, showing one of the two crystallographically independent
molecules in the unit cell with 30% thermal ellipsoids and a partial atom-numbering scheme. Hydrogen atoms, except the one on N1, are omitted
for clarity. Selected distances (Å) and angles (deg): Pd1−N1 2.063(2), Pd1−P1 2.3314(7), Pd1−P2 2.2883(7), N1−C45 1.377(3), P2−Pd1−P1
92.20(2), N1−Pd1−P1 108.06(6), N1−Pd1−P2 154.04(6), C45−N1−Pd1 135.29(18). (C) Proposed route for the formation of 1 and the
byproducts 2−4.
bond. Pauli repulsion has been used to explain the high
reactivity of low-valent platinum-group metal amido, alkoxide,
imido, oxo, and nitride species.22−24 So far, low-valent
platinum-group metal complexes containing π-donor ligands
are restricted to the nd6−nd8 metal ions.25−27 Analogous
isolable complexes containing a nd9-platinum-group metal
center are unknown.
phenyl). The Pd(I) amido complex is isolated from the
reaction of (BINAP)PdCl2 with LiNHArTrip and has been
characterized by single-crystal X-ray diffraction, electron
paramagnetic resonance spectroscopy, and multiedge Pd X-
ray absorption spectroscopy. Electronic structure calculations
indicate that the Pd(I) amido complex is S = 1/2 with a three-
electron two-center π-interaction between the Pd and N atoms
and that the Pd−N bond indeed presents severe destabilizing
Pauli repulsion. However, dispersion forces28 (Figure 1C)
between BINAP and the bulky amido ligand aids the
stabilization of the complex. Further reactivity studies evaluate
Herein we report the first nd9 platinum-group metal terminal
amido complex, namely, the Pd(I) complex [(BINAP)Pd-
(NHArTrip)] (BINAP = 2,2′-bis(diphenylphosphino)-1,1′-
binaphthalene, ArTrip = 2,6-bis(2′,4′,6′-triisopropylphenyl)-
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Figure 3. Spectroscopic data of Pd complexes. (A−C) EPR spectra of 1 (black line) and simulations (red line) at 9 GHz CW, 34 GHz electron spin
echo field sweep (derivative), and 94 GHz CW EPR. The minor features at the right in the 94 GHz EPR spectrum come from the Mn2+ impurities
from Critoseal in the W-band tube. (D) Overlay of the smoothed second derivatives of Pd K-edge XAS spectra of Pd0(IPr)2 (5, blue), 1 (red), and
(BINAP)PdII(OAc)2 (6, black). (E) Experimental (red) and TDDFT-calculated (black) Pd L3-edge XAS spectra of 1. The B3LYP functional and
SARC-ZORA basis set were used for Pd, with ZORA-def2-TZVP(-f) used for all other atoms. Contributions of individual orbitals were obtained
̈
from Lowdin population analysis of the QROs. Orbitals are plotted at an isovalue of 0.03 au with hydrogen atoms removed for clarity.
the lability of the Pd−N bond. When subjected to thermolysis,
photoirradiation, or coordination of exogenous ligands, the
Pd(I) amido complex undergoes homolytic Pd−N bond
cleavage to release the aminyl radical [NHArTrip]•. In addition,
the Pd(I) amido complex can react with primary alkyl and aryl
amines to release NH2ArTrip. These observations showcase the
unique reactivity of low-valent, odd-electron platinum-group-
metal amido complexes.
[(BINAP)Pd(NDArTrip)] (1-d) shows the N−D stretch at
2538 cm−1 (Figure S5). In addition to 1, three amine
byproducts, the amino-imine 2, the aniline featuring an alkene
side arm 3, and the free aniline 4 (Figure 2A), are observed.
These amines are likely formed from the decomposition
reactions of the aminyl radical [NHArTrip]•. Consequently, 1 is
proposed to form via a homolytic Pd−N bond cleavage
reaction of a Pd(II) bisamido intermediate, (BINAP)Pd-
(NHArTrip)2, that can be produced by the interaction of A with
LiNHArTrip (Figure 2C). Single crystals of 1 were obtained by
cooling a diethyl ether solution at −30 °C for 2 days. An X-ray
diffraction study revealed that there are two crystallo-
graphically independent molecules in the unit cell, with similar
structure metrics. As the representative, Figure 2B depicts the
structure of one of the molecules. The three-coordinate Pd(I)
complex has a P−Pd−P angle of 92.20(2)° and two unequal
P−Pd−N angles of 108.06(6)° and 154.04(6)°. While the sum
of the three angles (354.3°) indicates an idealized planar
geometry for the Pd center, the presence of two unequal P−
Pd−N angles differentiates 1 from trigonal-planar three-
coordinate Pd(0) complexes (Pri2PCH2CH2CH2PPri2)Pd-
RESULTS AND DISCUSSION
■
Synthesis and Molecular Structure of [(BINAP)Pd-
(NHArTrip)]. The Pd(I) amido complex [(BINAP)Pd-
(NHArTrip)] (1) was obtained via the reaction of (BINAP)-
PdCl2 with two equivalents of LiNHArTrip. Mixing the two
reagents in toluene at −78 °C produced a blue solution, whose
31P NMR spectrum features two signals with an AB-splitting
pattern, suggesting the formation of a Pd(II) monoamido
intermediate, presumably (BINAP)Pd(NHArTrip)Cl (A).
When warmed to room temperature, the solution turned
green. Recrystallization led to the isolation of the Pd(I) amido
complex 1 as a green crystalline solid in 51% yield (Figure 2A).
The composition of 1 is supported by elemental analysis (C,
H, N) and cold electrospray mass spectroscopy (Figure S6),
and its structure has been confirmed by single-crystal X-ray
diffraction (Figure 2B). The infrared spectrum of 1 features an
N−H stretch at 3295 cm−1. The deuterated isotopologue
30
(PCy3)29 and Pd(PPh3)3 and T-shaped three-coordinate
Pd(II) complexes (PBut3)Pd(C6H4-4-OCH3)(N(C6H3-3,5-
(CF3)2)2)31 and (IPr)Pd(3-methylnorborn-2-yl)(NHC6H4-4-
CH3) (IPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazole-2-yli-
dene).32 The Pd−N bond distance in 1 is 2.063(2) Å, which is
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slightly longer than those of the three-coordinate Pd(II) amido
complexes (sIPr)Pd(3-methylnorborn-2-yl)(NHC6H4-4-
OCH3) (sIPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazolin-2-
ylidene) (2.037(3) Å) and (IPr)Pd(3-methylnorborn-2-yl)-
(NHC6H4-4-CH3) (2.011(3) Å).32 Counter to the knowledge
that the trans influence of the amido ligand would elongate the
transoid Pd−P bond, the 2.2883(7) Å Pd1−P2 bond is shorter
than the 2.3314(7) Å Pd1−P1 bond. The shortening of the
Pd−P bond distance might be caused by the joint effect of Pd-
to-phosphine π-backdonation (vide infra) and the attractive
dispersion forces between the phenyl groups on the P atom
and the proximal 2,4,6-triisopropylphenyl group on the amido
ligand (vide infra). In addition, the bond distances within the
amido ligand of 1 itself are typical of anilido ligands in metal
complexes31,32 and are different from those of the parent
phenylaminyl radical [NHPh]•33 and the arylaminyl complexes
complexes. For example, the spectra of the Pd(I) species
generated by γ-ray irradiation on Pd(II) compounds have their
g⊥-values in the range 2.0 to 2.1 and g∥-values in the range 2.1
to 2.6,40 the spectrum of [(PBut3)2Pd][CB11Cl11H] has the g-
values of g⊥ = 2.338, g = 1.971,19 and that of [(PBut3)2Pd-
∥
(NCMe)][CB11Cl11H] shows g⊥ = 2.088, g = 2.314.19 For the
∥
reference, EPR of Pd(III) generally displays axial spectra with
g∥ and g⊥ values of 2.01−2.05 and 2.28−2.31, respectively,
although isotropic and rhombic EPR spectra have also been
reported.41 The 31P hyperfine constant values (HFCs)
determined by globally fitting the frozen-solution EPR spectra
of 1 for 31P1 are A1 = 535, A2 = 535, and A3 = 631 MHz. The
values for 31P2 are A1 = 205, A2 = 210, and A3 = 260 MHz.
Deduction of atomic spin density from the isotropic (Aiso) and
dipolar (T) contributions to the HFCs42 yields a spin density
of 13.0% on P1, of which 4.3% resides in the 3s orbital and
8.7% in a 3p orbital, and a spin density on P2 is 6.4%, where
1.7% resides in the 3s orbital and 4.7% in the 3p orbital. Thus,
total spin density on two P nuclei is ca. 20% based on the EPR
experiments. A(105Pd) and A(14N) contributions to the spectra
could not be resolved.
(Table S1),34−37 which hints at the monoanionic nature of
1−
[NHArTrip
]
in 1. Notably, the core structure of 1 is
reminiscent of Hillhouse’s nickel(I) amido complexes
[(dtbpe)Ni(NHDipp)] (dtbpe = 1,2-bis(di-tert-
butylphosphino)ethane) and [(dtbpe)Ni(NHDmp)] (Dmp =
2,6-dimesitylphenyl).38,39
Spectroscopic and Electronic Structure Features of
[(BINAP)Pd(NHArTrip)]. Complex 1 features an S = 1/2 ground
spin-state as indicated by the measured magnetic moment of
2.1(1) μB. Continuous wave (CW) and field-swept echo-
detected (FSE) electron paramagnetic resonance (EPR)
spectra were obtained for 1 (Figures 3A−C and S74). The
X-band (9 GHz) CW-EPR spectrum obtained at room
To probe the electronics of the Pd center in 1, Pd K- and L-
edge XAS data for 1, the Pd(0) complex [Pd0(IPr)2] (5), and
the Pd(II) complex [(BINAP)PdII(OAc)2] (6) were collected.
As shown in Figures 3 D and S75 and Table 1, the rising-edge
energies obtained from the K-edge (1s → valence/continuum)
for the series of compounds shift toward higher energies with
increasing formal oxidation state, although it has been noted
that factors such as coordination environment and ligand
identity can shift rising-edge energies to degrees similar to
shifts caused by oxidation state changes.43 Pre-edge features
arising from the metal 1s → nd transitions are also
conventionally used to assess physical oxidation states. Such
excitations are not expected for the Pd(0) complexes because
of their d10 configuration, but will occur in the case of formally
Pd(I) and Pd(II) complexes. Such features are not resolved in
the experimental Pd K-edge spectra likely owing to the weak
intensity of these quadrupole-allowed but dipole-forbidden
transitions as well as the core-hole lifetime broadening
endemic to second- and third-row metal K-edge XAS.
temperature shows a four-line pattern centered at giso
≈
2.052 with Aiso(31P1) = 202 G (567 MHz) and Aiso(31P2) = 80
G (225 MHz) (Figure S74). The anisotropy of the g-values
and the 31P A-values were resolved at low temperatures by
obtaining spectra at the X-, Q- (35 GHz), and W-band (94
GHz). Figure 3A−C shows the frozen-solution multifrequency
EPR spectra obtained for 1 along with simulations using
globally fit spin-Hamiltonian parameters. The g-values
obtained are g1 = 2.0085, g2 = 2.0350, and g3 = 2.1115. The
small g-value is consistent with the density functional theory
(DFT)-calculated electronic structure, as discussed below
(Table 2), but is unusual among the few known Pd(I)
To complement the K-edge data, the Pd L2,3-edge (2p →
valence/continuum) XAS data were obtained, where dipole-
allowed Pd 2p → 4d transitions gives rise to intense features
that probe the energetics and covalency of the Pd ligand
field.44 Experimental Pd L2,3-edge spectra are shown in Figures
3 E and S75−S77 for 1 and 6. L3 and L2 mainlines in these
spectra can be assigned to excitations from the Pd 2p orbitals
into singly or unoccupied Pd 4d orbitals. Satellite features at
higher energies relative to the mainline result from transitions
into higher lying levels of primarily ligand character (vide
infra). The L3 and L2 mainlines for 1 are shifted by ca. 2 eV to
lower energy relative to 6 (Table 1). Areas of L2,3-edge
mainlines can be used to quantify metal nd character in valence
acceptor orbitals, providing a direct probe of covalency and
physical oxidation state.43 This approach has been applied to
Pd L2,3-edges, where an increase in the L2,3-edge area of PdAl3
and PdCl2 compared to Pd metal was attributed to d-count
depletion.45 In the present case, the total L2,3-edge mainline
area of 1 is ca. half that of 6, consistent with Pd-localized
reduction.
Table 1. Experimental Pd K-Edge and L2,3-Edge Energies
K-edge
(eV)
L3 pre-edge max L2 pre-edge max
(eV) (eV)
total L3 + L2
mainline area
5
1
6
24 347
24 351
24 353
nd nd
nd
3174.5
3176.4
3331.7
3333.6
1.66(0.03)
4.02(0.16)
Table 2. Experimental and DFT-Calculated EPR Parameters
for 1
a
experimental
calculated
g tensor
[2.0085, 2.0350, 2.1115]
[205, 210, 260]
[535, 535, 631]
NR
[2.0216, 2.0408, 2.1065]
[237, 242, 298]
[535, 537, 650]
[105, 31.1, 80.8]
[2.6, 3.3, 24.7]
A(31P1)/MHz
A(31P2)/MHz
A(105Pd)/MHz
A(14N)/MHz
NR
a
Calculations used crystallographic coordinates with the B3LYP
hybrid density functional, D3 correction for dispersion, the SARC-
ZORA basis set on Pd, and the ZORA-def2-TZVP(-f) basis set on all
other atoms.
Hybrid DFT calculations were carried out to interrogate the
electronic structure of 1. All calculations used the dispersion-
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Figure 4. DFT calculations of the Pd(I) amido complex. (A) Selected molecular orbitals of 1; hydrogen atoms on ligands were omitted. (B) EDA-
NOCV results (in kcal/mol). Fragments of (BINAP)Pd and NHArTrip are given in the table in singlet (S) or doublet (D) electronic states. (C)
Short interligand H···H contacts with distances of less than 2.4 Å (purple lines).
corrected B3LYP-D3 hybrid density functional46,47 with the
segmented all-electron relativistically contracted (SARC)-
ZORA basis on Pd48 and ZORA-def2-TZVP(-f) basis set on
all other atoms. All calculations used crystallographic
coordinates. Veracity of the electronic structure calculations
was judged by comparison of calculated spectroscopic
parameters to experiment. Spin-Hamiltonian parameters
calculated for 1 agree well with experiment (Table 2).
Specifically, the g-values as well as the magnitudes and
asymmetry of the 31P HFCs are effectively reproduced by
experiment. Calculated Mulliken spin densities comprise 9.5%
3p and 3.9% 3s on P1 and 5.7% 3p and 2.7% 3s on P2, in
splendid agreement with analysis of the experimentally
obtained HFCs (vide supra). The calculation yielded low 14N
and 105Pd HFC values, consistent with the fact that these
features are unresolved in the EPR data.
The single-point DFT solutions were used as starting points
for time-dependent DFT (TDDFT) calculations of the X-ray
absorption spectroscopy (XAS) data obtained for 1 and 6.
TDDFT has been used previously to calculate L2,3-edge XAS
spectra for second-row transition metals and was shown to
adequately reproduce the structure of experimental L3-edges
without including the contributions from spin−orbit coupling
that yield the L3−L2 splitting.49 TDDFT reproduced the
overall envelope of L3 features in the experimental spectra
(Figures 3E and S80). The satellite features to higher energy of
the L3 mainlines comprise transitions into ligand-localized
molecular orbitals with minimal Pd 4d character. The mainline
transition in 1 primarily comprises the Pd 2p → SOMO
excitation, while for (BINAP)PdII(OAc)2 the mainline consists
of the Pd 2p LUMO excitation as well as transitions to two
additional low-lying MOs with ca. 10% contributions from Pd
4d orbitals. Calculated total Pd 4d character in all acceptor
orbital holes against summed L3 and L2 mainline areas gives a
correlation with R2 = 0.97 (Figure S82). Formally PdI complex
1 exhibits 30% lower overall d vacancy than the PdII complex,
providing further support for metal-centered reduction relative
to formally PdII-containing 6.
The experimentally validated DFT calculations indicate that
1 bears a three-electron two-center Pd−N π-bond, and its
electronic configuration can be described as
2
8
2
1
2
2
2
̈
(πd +p ) (dz ,dxz,dz ,dx −y ) (π*d ‑p ) . Lowdin orbital popula-
xy
N
xy
N
tions show that the SOMO is highly delocalized, although
there is a substantial (40%) Pd 4d contribution, consistent
with the observed anisotropy in g-values obtained for 1 (Figure
4A). Major contributors to the SOMO come from the P-
donors (10.3% 3p) and the amide (10.4% N 2p). The sum of
the spin density on the NHArTrip fragment, 0.22, precludes
description of 1 as an aminyl radical complex. Relevant
comparisons include the aminyl radical species [(bipy)Rh(N-
(Trop)2)][OTf] (0.56, bipy = bipyridine, Trop = 5H-
dibenzo[a,d]cyclohepten-5-yl),26 [(Ph2B(CH2PBut2)2)Cu(N-
(tolyl-p)2)] (0.69),36 [(Me3NN)Cu(NPh2)] (0.58, Me3NN =
2,4-bis(2,4,6-trimethylphenylimido)pentyl),37 [(PNP)NiCl]-
[OTf] (0.69),35 and [(PNP)Re(CO)3][OTf] (0.83),34 which
feature higher spin density on their N-ligands. On the other
hand, the spin-density distribution on 1 is closer to that of
Hillhouse’s Ni(I) amido complex [(dtbpe)Ni(NHDmp)],39
where the unpaired spin locates essentially on the nickel center
(0.76 on nickel and 0.07 on nitrogen, as shown in Figure S89).
To gain further insight into the nature of the Pd−N bond in
1, we did bonding analysis by using the state-of-the-art energy
decomposition analysis (EDA)50 with the natural orbitals for
the chemical valency (NOCV) approach (see SI for
details).51−53 The most important numerical results are
provided in Figure 4B, while more detailed information can
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Figure 5. Reactivity of 1. (A) Thermolysis-, light irradiation-, and ligand-coordination-induced decomposition reactions of 1, as well as its reactions
with primary amines and a phenol. (B) Hammett plot with para-substituted 2,6-dimethylaniline (kX/kH = relative rate constants for para-X-
substituted 2,6-dimethylanilines versus 2,6-dimethylaniline; σp = Hammett substituent constant, ρ = reaction constant). (C) Kinetic isotope effect
kH/kD for the reactions of 1 with 2,6-dimethylaniline.
be found in Table S3 and Figures S84−S88. The interacting
neutral fragments of (BINAP)Pd0 and NHArTrip have
comparable orbital energy (i.e., ΔEorb = −72.0 kcal/mol)
with that of the ionic fragments of [(BINAP)PdI]+ and-
[NHArTrip]− (i.e., ΔEorb = −73.7 kcal/mol), implying the two
resonant structures exist for 1, but the neutral fragments are
slightly favored because of the smaller orbital energy (see
Figure S88a). This also agrees very well with the spectroscopic
data and spin density analysis as shown in Figure S88b. It
donating ligand. Being different from the aforementioned
fleeting Pd(I) species, it is stable at ambient temperature,
which facilitates studies of its reactivity. When 1 is subjected to
thermolysis, light irradiation, or coordination with exogenous
ligands, it undergoes Pd−N bond homolytic cleavage reactions
to yield anilines and Pd(0) species (Figure 5A). In these
reactions, the arylaminyl radical dimerization product 2, the
alkane-chain dehydrogenation product 3, and the aniline
NH2ArTrip (4) are observed, implicating the radical inter-
revealed that there is significant Pauli repulsion (i.e., ΔEPauli
=
mediate [NHArTrip •
] in these reactions (Figure S19). In
123.1 kcal/mol) within the Pd−N interaction by using the
neutral interacting fragments. Nonetheless, the favorable
attractive interactions, including the electrostatic energy
(ΔEelstat = −92.3 kcal/mol) and orbital interaction energy
(ΔEorb = −72.0 kcal/mol), can compensate and even exceed
the Pauli repulsion ΔEPauli by 41.2 kcal/mol. It should be
emphasized that the dispersion energy (ΔEdisp = −31.3 kcal/
mol) contributing 16% of total attractive forces leads to a
summed bond dissociation energy (De) of 50.9 kcal/mol,
which helps to stabilize the Pd(I) amido species at ambient
temperature. The dispersion forces can be discerned from the
short interligand H···H contacts between BINAP and NHArTrip
in the optimized structure of 1 (Figure 4C). The ionic
interacting fragments have similar Pauli repulsion and orbital
energies but with a significant strong electrostatic energy
(ΔEelstat = −163.5 kcal/mol), which is understandable between
the cation [(BINAP)PdI]+ and anion [NHArTrip]− fragments
and thus leads to a larger intrinsic energy ΔEint of −139.0 kcal/
mol and bond dissociation energy (De) of 121.3 kcal/mol. It
should be mentioned that, in addition to the thermodynamic
factors, the stabilization of 1 apparently benefits from steric
protection of the Pd−N bond by the bulky substituents.
Reactivity of [(BINAP)Pd(NHArTrip)]. Complex 1 is the
first isolable d9 platinum-group-metal complex bearing a π-
addition, two Pd(0) complexes, [(BINAP)Pd(2,6-(CH3)2-
C6H3NC)2] (7) and [(BINAP)Pd(η2-3,5-(CF3)2-
C6H3CHCH2)] (8), have been isolated in the corresponding
reaction and structurally authenticated by X-ray diffraction
studies (Figures S29 and S34).
The decomposition reaction of 1 under white light
irradiation (6 W LED) at room temperature shows zero-
order kinetics with a kinetic constant kirri = 1.6 × 10−8 mol·L−1·
s−1 (Figure S23), whereas the thermal decomposition reaction
at 348 K is a first-order reaction with a rate constant ktherm
=
1.1 × 10−4 s−1 (Figure S27). The thermal- and light-
irradiation-induced decomposition reactions of 1 might result
from amido-to-palladium(I) electron transfer to form
(BINAP)Pd0(NHArTrip)•. The absorption spectrum of 1 in
toluene shows an intense feature at 808 nm (7300 mol−1·L·
cm−1). TDDFT calculations suggest that the band principally
arises due to what is best described as a π → π* transition with
ligand-to-metal charge transfer (LMCT) character: the
principal donor orbital is the Pd−N π-bonding SOMO−1,
whose largest contributor is the N 2p, while the acceptor
orbital is the Pd−N π* SOMO, which is dominated by Pd 4d
character (Figure S79). Either transition fully populates the
Pd−N antibonding MO and thus promotes bond cleavage.
Kinetics study on the reactions of 1 with an excess amount of
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3,5-bis(trifluoromethyl)styrene in benzene at 30 °C revealed
pseudo-first-order kinetics on the concentrations of both 1 and
the alkene (Figures S41−S47). This suggests that the ligand-
coordination-induced-decomposition reaction might proceed
via an associative mechanism or involve ligand exchange
equilibria.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c04965.
Experimental procedures, characterization, data, compu-
tational details, and Cartesian coordinates (PDF)
When 1 is treated with phenols and amines, e.g., 2,6-di(tert-
butyl)-4-methylphenol, 2,6-di(isopropyl)aniline, 2,6-dimethy-
laniline, n-butyl amine, and n-octyl amine, the free aniline
NH2ArTrip (4) was formed in high yields. The reaction with the
phenol allows the isolation of the Pd(0) complex (2,6-di-tert-
butyl-4-methylenecyclohexa-2,5-dienone)palladium(0) (9) in
67% yield (Figure 5A), whose structure has been confirmed by
X-ray diffraction (Figures S48 and S49). The reactions with
amines produced blue-purple mixtures, and the attempts to
isolate palladium-containing species from the mixture were
unsuccessful. These reactions likely start with a proton-transfer
step between the basic amido ligand in 1 and the H−X (X = O,
N) bonds in phenols and amines, rather than a hydrogen-
atom-abstraction mechanism as (i) a linear Hammett plot with
a positive reaction constant ρ = +0.77 was obtained for the
reactions of 1 with anilines bearing different para-substituents
(Figure 5B), (ii) no obvious kinetic isotope effect was
observed in the reactions 1 with 2,6-Me2C6H3NH2 and 2,6-
Me2C6H3ND2 (Figure 5C), and (iii) no reaction took place
when 1 was treated with substrates bearing weak C−H bonds,
e.g., xanthene (73.3 kcal/mol in DMSO) and cyclohexa-1,4-
diene (67 kcal/mol in the gas phase), whose C−H bond
dissociation energies are much lower than those of the O−H
bond of 2,6-di(tert-butyl)-4-methylphenol (78 kcal/mol in
DMSO) and the N−H bonds of amines (≥89 kcal/mol in
DMSO).54 Thus, the formation of the Pd(0) complex 9 can be
explained by the sequential steps of proton transfer followed by
electron transfer and hydrogen atom abstraction reactions
(Figure S55). Notably, as anilido anions are generally less basic
than aliphatic amido anions,54 the capability of 1 to react with
aliphatic amines to form NH2ArTrip demonstrates the unique
reactivity of the d9 Pd amido species. The elucidation of the
mechanism of the reaction of 1 with aliphatic amines needs
further study.
Accession Codes
CCDC 2059309−2059313 and 2070924 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
Sun Hee Kim − Western Seoul Center, Korea Basic Science
Institute (KBSI), Seoul 03759, Republic of Korea;
Department of Chemistry and Nano Science, Ewha Womans
University, Seoul 03760, Republic of Korea; orcid.org/
0000-0001-6557-1996; Email: shkim7@kbsi.re.kr
Lili Zhao − Institute of Advanced Synthesis, School of
Chemistry and Molecular Engineering, Nanjing Tech
University, Nanjing 211816, China; orcid.org/0000-
0003-2580-6919; Email: ias_llzhao@njtech.edu.cn
Kyle M. Lancaster − Department of Chemistry and Chemical
Biology, Cornell University, Ithaca, New York 14853, United
States; orcid.org/0000-0001-7296-128X;
Email: kml236@cornell.edu
Liang Deng − State Key Laboratory of Organometallic
Chemistry, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Chinese Academy
of Sciences, Shanghai 200032, China; orcid.org/0000-
0002-0964-9426; Email: deng@sioc.ac.cn
Authors
Jian Liu − State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, University of
Chinese Academy of Sciences, Chinese Academy of Sciences,
Shanghai 200032, China
Melissa M. Bollmeyer − Department of Chemistry and
Chemical Biology, Cornell University, Ithaca, New York
14853, United States
Yujeong Kim − Western Seoul Center, Korea Basic Science
Institute (KBSI), Seoul 03759, Republic of Korea;
Department of Chemistry and Nano Science, Ewha Womans
University, Seoul 03760, Republic of Korea; orcid.org/
0000-0001-7667-996X
Dengmengfei Xiao − Institute of Advanced Synthesis, School
of Chemistry and Molecular Engineering, Nanjing Tech
University, Nanjing 211816, China
Samantha N. MacMillan − Department of Chemistry and
Chemical Biology, Cornell University, Ithaca, New York
14853, United States; orcid.org/0000-0001-6516-1823
Qi Chen − State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, University of
Chinese Academy of Sciences, Chinese Academy of Sciences,
Shanghai 200032, China
Xuebing Leng − State Key Laboratory of Organometallic
Chemistry, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Chinese Academy
CONCLUSION
■
In summary, the first isolable, room-temperature-stable Pd(I)
complex bearing a π-donating ligand [(BINAP)Pd-
(NHArTrip)], which also represents the first platinum-group-
metal amido complex with an nd9 electronic configuration, has
been synthesized from the salt elimination reaction of
(BINAP)PdCl2 with LiNHArTrip. The Pd(I) amido complex
features a long Pd−N bond and inequivalent N−Pd−P angles.
EPR and XAS spectroscopies indicate that the Pd−N bond in
the Pd(I) amido complex is highly covalent. Theoretical
studies accord with the spectroscopic data and further revealed
that pronounced dispersion forces between the BINAP and the
bulky amido ligand NHArTrip help the stabilization of this
complex. Reactivity studies revealed that the Pd−N bond in
[(BINAP)Pd(NHArTrip)] can undergo homolytic cleavage
reaction to release the aminyl radical [NHArTrip]• when the
complex is subjected to heat, light irradiation, or ligand
coordination. The Pd(I) complex can also react with primary
amines to yield NH2ArTrip. The reactivity profile of the Pd(I)
amido complex points out the potential synthetic utility of low-
valent platinum-group-metal species bearing π-donating
ligands for the design of new reactions.
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(10) Jaworski, J. N.; McCann, S. D.; Guzei, I. A.; Stahl, S. S.
Detection of palladium(I) in aerobic oxidation catalysis. Angew.
Chem., Int. Ed. 2017, 56, 3605−3610.
(11) Fafard, C. M.; Adhikari, D.; Foxman, B. M.; Mindiola, D. J.;
Ozerov, O. V. Addition of ammonia, water, and dihydrogen across a
single Pd-Pd bond. J. Am. Chem. Soc. 2007, 129, 10318−10319.
(12) Fujiwara, S.; Nakamura, M. Electron spin resonance of Pd(I). I.
γ-irradiated bis(acetylacetonato)palladium(II). J. Chem. Phys. 1970,
52, 6299−6301.
(13) Fujiwara, S.; Nakamura, M. Electron spin resonance of Pd(I).
II. γ-irradiated single crystals of K2PdCl4 and (NH4)2PdCl4. J. Chem.
Phys. 1971, 54, 3378−3380.
(14) Taarit, Y. B.; Vedrine, J. C.; Dutel, J. F.; Naccache, C. EPR
investigation of structure and reactivity of Pd(I) species generated in
synthetic mordenite-type zeolite. J. Magn. Reson. 1978, 31, 251−257.
(15) Lane, G. A.; Geiger, W. E.; Connelly, N. G. Palladium(I).pi.-
radicals. Electrochemical preparation and study of their reaction
pathways. J. Am. Chem. Soc. 1987, 109, 402−407.
(16) Luo, J.; Tran, G. N.; Rath, N. P.; Mirica, L. M. Detection and
characterization of mononuclear Pd(I) complexes supported by N2S2
and N4 tetradentate ligands. Inorg. Chem. 2020, 59, 15659−15669.
(17) Blake, A. J.; Gould, R. O.; Hyde, T. I.; Schröder, M.
Stabilisation of monovalent palladium by tetra-aza macrocycles. J.
Chem. Soc., Chem. Commun. 1987, 0, 431−433.
(18) Troadec, T.; Tan, S. Y.; Wedge, C. J.; Rourke, J. P.; Unwin, P.
R.; Chaplin, A. B. One-electron oxidation of [M(PtBu3)2] (M = Pd,
Pt): Isolation of monomeric [Pd(PtBu3)2]+ and redox-promoted C-H
Bond cyclometalation. Angew. Chem., Int. Ed. 2016, 55, 3754−3757.
(19) MacInnis, M. C.; DeMott, J. C.; Zolnhofer, E. M.; Zhou, J.;
Meyer, K.; Hughes, R. P.; Ozerov, O. V. Cationic two-coordinate
complexes of Pd(I) and Pt(I) have longer metal-ligand bonds than
their neutral counterparts. Chem. 2016, 1, 902−920.
(20) Bickelhaupt, F. M.; Jan Baerends, E. Kohn-Sham density
functional theory: Predicting and understanding chemistry. Rev.
Comput. Chem. 2007, 15, 1−86.
(21) Caulton, K. G. The influence of Pi-stabilized unsaturation and
filled repulsions in transition-metal chemistry. New J. Chem. 1994, 18,
25−41.
(22) Bryndza, H. E.; Tam, W. Monomeric metal hydroxides,
alkoxides, and amides of the late transition metals: synthesis,
reactions, and thermochemistry. Chem. Rev. 1988, 88, 1163−1188.
(23) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G.
Formation, reactivity, and properties of nondative late transition
metal-oxygen and -nitrogen bonds. Acc. Chem. Res. 2002, 35, 44−56.
(24) Gunnoe, T. B. Reactivity of ruthenium(II) and copper(I)
complexes that possess anionic heteroatomic ligands: Synthetic
exploitation of nucleophilicity and basicity of amido, hydroxo, alkoxo,
and aryloxo ligands for the activation of substrates that possess polar
bonds as well as nonpolar C-H and H-H bonds. Eur. J. Inorg. Chem.
2007, 2007, 1185−1203.
(25) Fryzuk, M. D.; Montgomery, C. D. Amides of the platinum
group metals. Coord. Chem. Rev. 1989, 95, 1−40.
(26) Buttner, T.; Geier, J.; Frison, G.; Harmer, J.; Calle, C.;
Schweiger, A.; Schonberg, H.; Grutzmacher, H. A stable aminyl
radical metal complex. Science 2005, 307, 235−238.
of Sciences, Shanghai 200032, China; orcid.org/0000-
0003-3291-8695
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c04965
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Mr. Chenglu Lu for the cold electron spray mass
spectrometry measurements and Mr. Jianfeng Zhang for
elemental analysis. L.D. is thankful for the financial support
from the National Natural Science Foundation of China
(grants 21725104, 21690062, 22061160464, and 21821002),
the Science and Technology Commission of Shanghai
Municipality (grant 19XD1424800), and K. C. Wong
Education Foundation. K.M.L. thanks the NSF for support
of this research via CHE-1954515. M.M.B. is an NSF Graduate
Research Fellow. XAS data were obtained at SSRL, which is
supported by the DOE, Office of Science, Office of Basic
Energy Sciences, under Contract No. DE-AC02-76SF00515.
The SSRL Structural Molecular Biology Program is supported
by the U.S. DOE Office of Biological and Environmental
Research and by NIH/NIGMS (including P41GM103393).
S.H.K. thanks the NRF of Korea for support of this research
(NRF-2017M3D1A1039380). L.Z. is thankful for the financial
support from National Natural Science Foundation of China
(Grant No. 21973044), the State Key Laboratory of Materials-
oriented Chemical Engineering (Project No. KL19-11), and
the high-performance center of Nanjing Tech University for
supporting the computational resources.
REFERENCES
■
(1) Hartings, M. Reactions coupled to palladium. Nat. Chem. 2012,
4, 764.
(2) Powers, D. C.; Ritter, T. Palladium(III) in synthesis and
catalysis. Top. Organomet. Chem. 2011, 503, 129−156.
(3) Liu, Q.; Dong, X.; Li, J.; Xiao, J.; Dong, Y.; Liu, H. Recent
advances on palladium radical involved reactions. ACS Catal. 2015, 5,
6111−6137.
(4) Bonney, K. J.; Proutiere, F.; Schoenebeck, F. Dinuclear Pd(I)
complexes-solely precatalysts? Demonstration of direct reactivity of a
Pd(I) dimer with an aryl iodide. Chem. Sci. 2013, 4, 4434−4439.
(5) Cui, P.; Iluc, V. M. Redox-induced umpolung of transition metal
carbenes. Chem. Sci. 2015, 6, 7343−7354.
(6) Parasram, M.; Chuentragool, P.; Sarkar, D.; Gevorgyan, V.
Photoinduced formation of hybrid aryl Pd-radical species capable of
1,5-HAT: Selective catalytic oxidation of silyl ethers into silyl enol
ethers. J. Am. Chem. Soc. 2016, 138, 6340−6343.
(7) Zhao, B.; Shang, R.; Wang, G.-Z.; Wang, S.; Chen, H.; Fu, Y.
Palladium-catalyzed dual ligand-enabled alkylation of silyl enol ether
and enamide under irradiation: Scope, mechanism, and theoretical
elucidation of hybrid alkyl Pd(I)-radical species. ACS Catal. 2020, 10,
1334−1343.
(8) Torres, G. M.; Liu, Y.; Arndtsen, B. A. A dual light-driven
palladium catalyst: Breaking the barriers in carbonylation reactions.
Science 2020, 368, 318−323.
(27) Driver, M. S.; Hartwig, J. F. A rare, low-valent alkylamido
complex, a diphenylamido complex, and their reductive elimination of
amines by three-coordinate intermediates. J. Am. Chem. Soc. 1995,
117, 4708−4709.
(28) Liptrot, D. J.; Power, P. P. London dispersion forces in
sterically crowded inorganic and organometallic molecules. Nat. Rev.
Chem. 2017, 1, 1−12.
(29) Perez, P. J.; Calabrese, J. C.; Bunel, E. E. Synthesis,
characterization, and reactivity of [((iPr)2P(CH2)3P(iPr)2)(PCy3)-
PdH][OR]. Organometallics 2001, 20, 337−345.
(30) Tejel, C.; Asensio, L.; del Rio, M. P.; de Bruin, B.; Lopez, J. A.;
Ciriano, M. A. Developing synthetic approaches with non-innocent
metalloligands: easy access to Ir(I)/Pd(0) and Ir(I)/Pd(0)/Ir(I)
cores. Angew. Chem., Int. Ed. 2011, 50, 8839−8843.
(9) Chen, Q.-Y.; Yang, Z.-Y.; Zhao, C.-X.; Qiu, Z.-M. Studies on
fluoroalkylation and fluoroalkoxylation. Part 28. Palladium(0)-
induced addition of fluoroalkyl iodides to alkenes: an electron
transfer process. J. Chem. Soc., Perkin Trans. 1 1988, 1, 563−567.
10758
https://doi.org/10.1021/jacs.1c04965
J. Am. Chem. Soc. 2021, 143, 10751−10759

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
(31) Yamashita, M.; Hartwig, J. F. Synthesis, structure, and reductive
elimination chemistry of three-coordinate arylpalladium amido
complexes. J. Am. Chem. Soc. 2004, 126, 5344−5345.
(52) Mitoraj, M.; Michalak, A. Applications of natural orbitals for
chemical valence in a description of bonding in conjugated molecules.
J. Mol. Model. 2008, 14, 681−687.
(53) Mitoraj, M.; Michalak, A.; Ziegler, T. A combined charge and
energy decomposition scheme for bond analysis. J. Chem. Theory
Comput. 2009, 5, 962−975.
(32) Hanley, P. S.; Marquard, S. L.; Cundari, T. R.; Hartwig, J. F.
Reductive elimination of alkylamines from low-valent, alkylpalladium-
(II) amido complexes. J. Am. Chem. Soc. 2012, 134, 15281−15284.
(54) Warren, J. J.; Tronic, T. A.; Mayer, J. M. Thermochemistry of
proton-coupled electron transfer reagents and its implications. Chem.
Rev. 2010, 110, 6961−7001.
(33) Penkert, F. N.; Weyhermuller, T.; Bill, E.; Hildebrandt, P.;
̈
Lecomte, S.; Wieghardt, K. Anilino radical complexes of cobalt(III)
and manganese(IV) and comparison with their phenoxyl analogues. J.
Am. Chem. Soc. 2000, 122, 9663−9673.
(34) Radosevich, A. T.; Melnick, J. G.; Stoian, S. A.; Bacciu, D.;
Chen, C. H.; Foxman, B. M.; Ozerov, O. V.; Nocera, D. G. Ligand
reactivity in diarylamido/bis(phosphine) PNP complexes of Mn-
(CO)3 and Re(CO)3. Inorg. Chem. 2009, 48, 9214−9221.
(35) Adhikari, D.; Mossin, S.; Basuli, F.; Huffman, J. C.; Szilagyi, R.
K.; Meyer, K.; Mindiola, D. J. Structural, spectroscopic, and
theoretical elucidation of a redox-active pincer-type ancillary applied
in catalysis. J. Am. Chem. Soc. 2008, 130, 3676−3682.
(36) Mankad, N. P.; Antholine, W. E.; Szilagyi, R. K.; Peters, J. C.
Three-coordinate copper(I) amido and aminyl radical complexes. J.
Am. Chem. Soc. 2009, 131, 3878−3880.
(37) Wiese, S.; Badiei, Y. M.; Gephart, R. T.; Mossin, S.; Varonka,
M. S.; Melzer, M. M.; Meyer, K.; Cundari, T. R.; Warren, T. H.
Catalytic C-H amination with unactivated amines through copper(II)
amides. Angew. Chem., Int. Ed. 2010, 49, 8850−8855.
(38) Mindiola, D. J.; Hillhouse, G. L. Terminal amido and imido
complexes of three-coordinate nickel. J. Am. Chem. Soc. 2001, 123,
4623−4624.
(39) Iluc, V. M.; Hillhouse, G. L. Hydrogen-atom abstraction from
Ni(I) phosphido and amido complexes gives phosphinidene and
imide ligands. J. Am. Chem. Soc. 2010, 132, 15148−15150.
(40) Nakamura, M.; Fujiwara, S. Electron spin resonance of Pd(I).
III* The nature of the metal-ligand bonds in square planar complexes
of palladium(I). J. Coord. Chem. 1972, 1, 221−227.
(41) Khusnutdinova, J. R.; Rath, N. P.; Mirica, L. M. Stable
mononuclear organometallic Pd(III) complexes and their C-C bond
formation reactivity. J. Am. Chem. Soc. 2010, 132, 7303−7305.
(42) Morton, J. R.; Preston, K. F. Atomic parameters for
paramagnetic resonance data. J. Magn. Reson. 1978, 30, 577−582.
(43) MacMillan, S. N.; Lancaster, K. M. X-ray spectroscopic
interrogation of transition-metal-mediated homogeneous catalysis:
Primer and case studies. ACS Catal. 2017, 7, 1776−1791.
(44) Boysen, R. B.; Szilagyi, R. K. Development of palladium L-edge
X-ray absorption spectroscopy and its application for chloropalladium
complexes. Inorg. Chim. Acta 2008, 361, 1047−1058.
(45) Sham, T. K. L-edge x-ray-absorption spectra of PdAl3 and
PdCl2: A study of charge redistribution in compounds of an element
with a nearly full 4d shell. Phys. Rev. B: Condens. Matter Mater. Phys.
1985, 31, 1903−1908.
(46) Elstner, M.; Hobza, P.; Frauenheim, T.; Suhai, S.; Kaxiras, E.
Hydrogen bonding and stacking interactions of nucleic acid base
pairs: A density-functional-theory based treatment. J. Chem. Phys.
2001, 114, 5149−5155.
(47) 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.
(48) Rolfes, J. D.; Neese, F.; Pantazis, D. A. All-electron scalar
relativistic basis sets for the elements Rb-Xe. J. Comput. Chem. 2020,
41, 1842−1849.
(49) He, W.; Kennepohl, P. Direct experimental evaluation of
ligand-induced backbonding in nickel metallacyclic complexes.
Faraday Discuss. 2019, 220, 133−143.
(50) Ziegler, T.; Rauk, A. On the calculation of bonding energies by
the Hartree Fock Slater method. Theoret. Chim. Acta. 1977, 46, 1−10.
(51) Mitoraj, M.; Michalak, A. Donor-acceptor properties of ligands
from the natural orbitals for chemical valence. Organometallics 2007,
26, 6576−6580.
10759
https://doi.org/10.1021/jacs.1c04965
J. Am. Chem. Soc. 2021, 143, 10751−10759