E–H (E?=?N, O) bond activation by a nucleophilic palladium carbene

Article abstract of DOI:10.1016/j.poly.2017.10.007

E–H bond cleavage by [{PC(sp²)P}Pd(PMe₃)] (1, PC(sp²)P = ⁱPr₂P–C₆H₄–C–C₆H₄–PⁱPr₂) of alcohols led to a series of new square-planar tri

Full text of DOI:10.1016/j.poly.2017.10.007

Accepted Manuscript
E-H (E = N, O) Bond Activation by a Nucleophilic Palladium Carbene
Cezar C. Comanescu, Vlad M. Iluc
PII:
S0277-5387(17)30648-4
https://doi.org/10.1016/j.poly.2017.10.007
POLY 12870
DOI:
Reference:
Polyhedron
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Accepted Date:
30 June 2017
6 October 2017
Please cite this article as: C.C. Comanescu, V.M. Iluc, E-H (E = N, O) Bond Activation by a Nucleophilic Palladium
Carbene, Polyhedron (2017), doi: https://doi.org/10.1016/j.poly.2017.10.007
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E-H (E = N, O) Bond Activation by a Nucleophilic Palladium Carbene
Cezar C. Comanescu and Vlad M. Iluc*
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana
46556, United States
ABSTRACT
E-H bond cleavage by [{PC(sp2)P}Pd(PMe3)] (1, PC(sp2)P = iPr2P-C6H4-C-C6H4-PiPr2) of
alcohols led to a series of new square-planar tridentate palladium alkoxides,
[{PC(sp3)HP}Pd(OiPr)] (3), [{PC(sp3)HP}Pd(OtBu)] (4), and [{PC(sp3)HP}Pd(OPh)] (5,
PC(sp3)HP = bis[2-(di-iso-propylphosphino)phenyl]methyl). The analogous reaction with
amines led to the formation of [{PC(sp3)HP}Pd(NPh2)] (6) and [{PC(sp3)HP}Pd(NHMes)]
(7). The molecular structure of 7 was further probed by a CO2 insertion reaction into the Pd-
N bond, yielding the corresponding carbamate 8. The molecular structures of 3-8 were
determined by single-crystal X-ray diffraction and conform to the corresponding solution
structures as determined by NMR spectroscopy. The reactivity of carbene 1 towards alcohols
and amines is dictated by the nucleophilic/basic character at the carbene backbone carbon
atom, the pKa and bond dissociation energy of the E-H bond (E =N, O), and the steric
properties of the organic substrates used.
1. Introduction
Current synthetic strategies mediated by organometallic complexes typically rely on
improving ligand design in order to both stabilize the reactive coordinated metal and enhance
its reactivity in envisioned transformations [1]. Pincer complexes featuring a PCP tridentate
backbone fulfill these requirements and have been widely studied since the pioneering work
-1-

of Shaw et al. on group 9 and 10 metals supported by the 2,6-bis[di-t-
butylphosphino)methyl]phenyl ligand [2]. Nowadays, pincers have become ubiquitous in
organometallic chemistry and are employed commonly in many catalytic reactions [3, 4].
Our efforts are currently directed towards studying metal-ligand cooperation and
involve the design of various diphosphine supporting ligands, which generate a PCP pincer
framework upon coordination to a metal center [5-12]. These pincer-supported metal
complexes can lead to carbenes [13-17] that engage in further reactivity with a plethora of
substrates [13, 16-22]. We previously described the synthesis of the nucleophilic carbene
i
[{PC(sp2)P}Pd(PMe3)] (1, PC(sp2)P = Pr2P-C6H4-C-C6H4-PiPr2) by a dehydrochlorination
reaction from [{PC(sp3)HP}PdCl] 2 [16]. The reactivity of 1 was investigated toward the
slightly acidic C-H bonds of acetone, CH3CN, fluorene, 9,10-dihydroanthracene and
phenylacetylene [19], and toward Si-H (substituted silanes, Ph4-nSiHn, n=1-3) and Ge-H
bonds (substituted germanes, Ph4-nGeHn, n=1-3) [20]. With the exception of silanes and
germanes, which yielded both types of isomers (hydride and silyl/germyl), the other reactions
produced the addition of the E-H bond across the Pd-C bond to afford the PC(sp3)HP pincer
framework, a result anticipated given the basic character at the backbone carbene carbon.
Carbene 1 also reacted with a primary alcohol (CH3OH) and a primary amine, para-toluidine;
these reactions supported the basicity of the backbone carbon [16]. We decided to expand the
scope of the O-H and N-H addition reactions to other primary, secondary, and tertiary
alcohols and amines since E-H bond activation through metal-ligand cooperation mechanisms
is understudied and could provide new reaction avenues. Herein, we report 1,2-addition
reactions across the Pd-C bond of carbene 1 via the heterolytic splitting of E-H (E = N, O)
bonds. These reactions allowed the synthesis and characterization of novel palladium(II)
amides and alkoxides supported by a PCP pincer.
-2-

2. Experimental
2.1. Materials and methods
All experiments were carried out under protective air- and moisture-free, N2
atmosphere (glovebox techniques). All solvents were dried prior to use and kept over 4 Å
molecular sieves. All commercial chemicals were used as received, except where otherwise
specified. Deuterated solvents were purchased from Cambridge Isotope Laboratories. C6D6
was dried by reflux over CaH2 and filtered prior to use. NMR spectra were recorded on a
Varian 300 spectrometer at ambient probe temperature or Bruker 400 and 500. Chemical
shifts are reported in ppm relative to residual internal protonated solvent for 1H and 13C{1H}
NMR spectra; J values are given in Hz. All assignments are based on one-dimensional 1H and
13C experiments unless noted otherwise. Compounds [{PC(sp2)P}Pd(PMe3)] (1) and
[{PC(sp3)HP}PdCl] (2) were synthesized following literature procedures previously reported
by us [16]. CHN analyses were performed on a CE-440 elemental analyzer or by Midwest
Microlab. The diffraction experiments were carried out on a Bruker AXS SMART CCD
three-circle diffractometer with a sealed tube using graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å). The crystals were mounted on a plastic loop and used for the
diffraction experiments. Anisotropic thermal parameters were refined for all non-hydrogen
atoms. The hydrogens were placed according to a riding model. Gaussian 03 (revision D.02)
was used for all reported calculations. The B3LYP (DFT) method was used to carry out the
geometry optimizations on model compounds specified in text using the LANL2DZ basis set.
The validity of the true minima was checked by the absence of negative frequencies in the
energy Hessian.
-3-

2.2. Synthesis of metal complexes
2.2.1. [{PC(sp3)HP}Pd(OiPr)] (3). In a 20 mL scintillation vial, 29.1 mg of
[{PC(sp2)P}Pd(PMe3)] (1, C28H45P3Pd, 0.05 mmol) was dissolved in THF. Subsequently, 0.5
mL iPrOH 0.1 M (in THF) was added at RT via a syringe and a fast color change from dark
brown to dark red occurred. After the removal of volatiles under a reduced pressure,
[{PC(sp3)HP}Pd(OiPr)] (3) was isolated in high yield (89.2 %) as a light brown solid.
(C28H44OP2Pd, 565.02 g/mol, 25.2 mg). Recrystallization from a concentrated Et2O solution
afforded X-ray quality single crystals suitable for molecular structure elucidation. 1H and
1
31P{1H} NMR spectra confirmed the product to be analytically pure. For 3: H NMR (500
MHz, C6D6, 298 K) δ 7.27 (d, J = 7.9 Hz, 2H, ArH), 7.12 (ddt, J = 7.6, 3.7, 1.9 Hz, 2H, ArH),
7.05 (t, J = 7.6 Hz, 2H, ArH), 6.91 (t, J = 7.4 Hz, 2H, ArH), 5.69 (s, 1H, benzylic bachbone),
4.41 (hept, J = 5.8 Hz, 1H, -OCH(CH3)2), 2.39 (ddt, J = 13.6, 9.8, 5.2 Hz, 4H, -CH(CH3)2),
1.74 (d, J = 5.8 Hz, 6H, -OCH(CH3)2), 1.49 (q, J = 7.7 Hz, 6H, -CH(CH3)2), 1.37 (q, J = 8.1
Hz, 6H, -CH(CH3)2), 1.13 (q, J = 7.6 Hz, 6H, -CH(CH3)2), 1.08 (q, J = 6.7 Hz, 6H, -
CH(CH3)2). 31P{1H} NMR (202 MHz, C6D6, 298 K) δ 43.94 (s). 13C{1H} NMR (126 MHz,
C6D6, 298 K) δ 160.04 (t, J = 15.0 Hz, ArC), 134.35 (t, J = 16.7 Hz, ArC), 132.15 (s, ArC) ,
129.90 (s, ArC) , 127.69 (t, J = 8.5 Hz, ArC), 124.85 (t, J = 3.2 Hz, ArC), 71.92 (s, -
OCH(CH3)2), 47.38 (s, benzylic backbone) , 32.34 (s, -OCH(CH3)2) , 25.70 (t, J = 9.1 Hz, -
CH(CH3)2), 25.38 (t, J = 11.2 Hz, -CH(CH3)2), 19.40 (t, J = 3.7 Hz, -CH(CH3)2), 18.66 (t, J =
2.0 Hz, -CH(CH3)2), 18.37 (t, J = 2.8 Hz, -CH(CH3)2), 17.71 (s, -CH(CH3)2). Anal. Calcd for
C28H44OP2Pd: C, 59.52; H, 7.85. Found: C, 59.61; H, 7.63.
2.2.2. [{PC(sp3)HP}Pd(OtBu)] (4). Method A: 58.1 mg of [{PC(sp2)P}Pd(PMe3)] (1, 0.1
mmol) and 9.5 µL of t-BuOH (C4H10O, 74.1 g/mol, 7.4 mg, 0.1 mmol) were dissolved in 4
mL of THF at RT and stirred for 48 h. Aliquots taken at different times during the reaction
showed it to be incomplete and after 48 h at RT a modest conversion of 27% was achieved
-4-

(by analysis of the crude reaction 1H and 31P{1H} NMR spectra). The identity of the alkoxide
[{PC(sp3)HP}Pd(OtBu)] (4) was established by synthesizing it independently by a metathesis
reaction (Method B, see below) and comparison of NMR spectra. The reaction also affords
two asymmetric (2 pairs of doublets in the 31P{1H} NMR spectra) products that were not
identified. Method B: In a 20 mL scintillation vial, was dissolved 54.1 mg of
[{PC(sp3)HP}PdCl] (2, C25H37ClP2Pd, 541.39 g/mol, 0.1 mmol) in THF and precooled to -35
°C, before adding 1 mL solution of KOtBu 0.1 M in THF. The solution changed color from
off-white to deep red within minutes. The solution was then warmed up to RT, allowed to
react for 2 additional hours, filtered over Celite, and then the volatiles were removed under a
reduced pressure, affording 4 as a red solid. Crystallization from a concentrated hexanes
solution afforded 52.7 mg of analytically pure 4 (C29H46OP2Pd, 579.04 g/mol) by 1H and
31P{1H} spectroscopy as X-ray quality crystals, in 91.1% yield. For 4: 1H NMR (500 MHz,
C6D6, 298 K) δ 7.20 (dtd, J = 4.9, 3.7, 1.3 Hz, 2H, ArH), 7.14 (d, J = 7.8 Hz, 2H, ArH), 7.03
(tdd, J = 8.1, 2.2, 1.2 Hz, 2H, ArH), 6.91 (t, J = 7.4 Hz, 2H, ArH), 5.71 (s, 1H, benzylic
backbone), 2.72 – 2.61 (m, 2H, -CH(CH3)2), 2.46 – 2.35 (m, 2H, -CH(CH3)2), 1.73 (s, 9H, -
OC(CH3)3), 1.61 (dd, J = 14.9, 7.8 Hz, 6H, -CH(CH3)2), 1.21 (dd, J = 15.1, 7.9 Hz, 6H, -
CH(CH3)2), 1.16 (dd, J = 14.6, 7.6 Hz, 6H, -CH(CH3)2), 1.09 (dd, J = 12.8, 5.8 Hz, 6H, -
CH(CH3)2). 31P NMR (202 MHz, C6D6, 298 K) δ 40.67 (s). 13C NMR (101 MHz, C6D6,
298K) δ 160.09 (t, J = 15.1 Hz, ArC), 134.54 (t, J = 16.6 Hz, ArC), 132.15 (s, ArC), 129.86
(t, J = 1.3 Hz, ArC), 127.79 – 127.60 (m, ArC), 124.87 (t, J = 3.0 Hz, ArC), 70.10 (s, -
OC(CH3)3),47.67 (s, benzylic backbone), 37.16 (s, -OC(CH3)3), 26.00 (t, J = 11.0 Hz, -
CH(CH3)2), 24.90 (t, J = 8.5 Hz, -CH(CH3)2), 20.00 (t, J = 3.8 Hz, -CH(CH3)2), 19.28 (t, J =
2.8 Hz, -CH(CH3)2), 18.46 (t, J = 2.1 Hz, -CH(CH3)2), 17.37 (s, -CH(CH3)2). Anal. Calcd for
C29H46OP2Pd: C, 60.15; H, 8.01. Found: C, 59.99; H, 7.64.
-5-

2.2.3. [{PC(sp3)HP}Pd(OPh)] (5). 58.1 mg of [{PC(sp2)P}Pd(PMe3)] (1, 0.1 mmol) and 9.4
mg of phenol (C6H6O, 94.11 g/mol) were stirred in THF at RT, and the color changed
instantly from brown to deep red. After 10 min of additional stirring, removal of volatiles
under a reduced pressure, extraction in diethyl ether, and recrystallization, 52.3 mg of
analytically pure 5 (C31H42OP2Pd, 599.03 g/mol) was obtained in 87.3% yield, as crystals of
suitable quality for X-ray analysis. For 5: 1H NMR (400 MHz, C6D6, 298 K) δ 7.48 – 7.37
(m, 4H, ArH), 7.26 (dd, J = 7.8, 0.4 Hz, 2H, ArH), 7.07 – 6.98 (m, 4H, ArH), 6.89 (t, J = 7.4
Hz, 2H, ArH), 6.77 (tt, J = 6.9, 1.4 Hz, 1H, ArH), 5.97 (s, 1H, benzylic backbone), 2.33 –
2.20 (m, 2H, -CH(CH3)2), 2.18 – 2.05 (m, 2H, -CH(CH3)2), 1.23 (dtd, J = 8.3, 7.2, 5.8 Hz,
12H, -CH(CH3)2), 1.07 (dd, J = 14.9, 7.7 Hz, 6H, -CH(CH3)2), 0.92 (q, J = 7.1 Hz, 6H, -
CH(CH3)2). 31P NMR (162 MHz, C6D6, 298 K) δ 47.20 (s). 13C NMR (101 MHz, C6D6, 298
K) δ 172.60 (s, ArC), 159.25 (t, J = 14.9 Hz, ArC), 133.56 (t, J = 17.1 Hz, ArC), 132.21 (s,
ArC), 130.24 (s, ArC), 129.20 (s, ArC), 127.53 (t, J = 8.7 Hz, ArC), 125.32 (t, J = 3.2 Hz,
ArC), 120.46 (s, ArC), 112.07 (s, ArC), 46.57 (t, J = 1.7 Hz, benzylic backbone), 25.64 (t, J =
9.7 Hz, -CH(CH3)2), 24.84 (t, J = 11.5 Hz, -CH(CH3)2), 18.91 (t, J = 3.1 Hz, -CH(CH3)2),
18.32 (t, J = 2.9 Hz, -CH(CH3)2), 18.20 (t, J = 1.6 Hz, -CH(CH3)2), 17.81 (s, -CH(CH3)2).
Anal. Calcd. for C31H42OP2Pd: C, 62.16; H, 7.07. Found: C, 62.51; H, 7.73.
2.2.4. [{PC(sp3)HP}Pd(NPh2)] (6). Method A: 58.1 mg of [{PC(sp2)P}Pd(PMe3)] (1, 0.1
mmol) and 16.9 mg of Ph2NH (C12H11N, 169.23 g/mol) were stirred in THF at RT for 18 h.
Aliquots from the reaction mixture taken at 3, 6, and 12 h showed the reaction to be
incomplete. Final 1H and 31P{1H} NMR data assess the product to be pure. After solvent
removal, extraction in diethyl ether and recrystallization, 54.6 mg of analytically pure (by 1H
and 31P{1H} spectra) amide 6 was obtained in 81% yield, as crystals of suitable quality for X-
ray analysis. Method B: To 1 g of Ph2NH (C12H11N, 169.23 g/mol, 5.9 mmol) dissolved in
hexanes and cooled at -78 °C, was added dropwise 3.68 mL of nBuLi 1.6 M in hexanes. The
-6-

solution formed a white precipitate and was warmed slowly to RT, continued stirring for 30
min and the volatiles were then removed under a reduced pressure, affording a white powder
of Ph2NHLi (0.9094 g, 5.19 mmol) in 88% yield. This powder was then kept in the freezer in
the glovebox at -35 °C for future use. In a 20 mL scintillation vial was added 54.1 mg of
[{PC(sp3)HP}PdCl] (2, C25H37ClP2Pd, 541.39 g/mol, 0.1 mmol), dissolved in Et2O and
cooled to -35 °C, followed by 1 mL solution of Ph2NLi 0.1 M in Et2O. The solution changed
color from off-white to deep yellow within 2 hours. The solution was then warmed up to RT,
filtered over Celite and the volatiles were removed under a reduced pressure affording 6 as a
yellow solid. Crystallization from a concentrated hexanes solution afforded 58.6 mg of
analytically pure (by 1H and 31P{1H} spectroscopy) 6 (C37H47NP2Pd, 674.16 g/mol) as X-ray
quality crystals, in 87% yield. For 6: 1H NMR (500 MHz, C6D6, 298 K) δ 7.96 – 7.87 (m, 2H,
ArH), 7.58 (dd, J = 8.6, 1.0 Hz, 2H, ArH), 7.36 (d, J = 7.9 Hz, 2H, ArH), 7.29 – 7.24 (m, 2H,
ArH), 7.19 (dd, J = 8.6, 7.1 Hz, 2H, ArH), 7.10 – 7.04 (m, 2H, ArH), 6.99 (dtd, J = 4.7, 3.6,
1.2 Hz, 2H, ArH), 6.90 (t, J = 7.4 Hz, 2H, ArH), 6.75 (tt, J = 7.2, 1.1 Hz, 1H, ArH), 6.68 (tt, J
= 7.2, 1.1 Hz, 1H, ArH), 6.19 (s, backbone Ar2CH-), 2.20 – 2.11 (m, 2H, -CH(CH3)2), 1.88 –
1.79 (m, 2H, -CH(CH3)2), 1.10 (dd, J = 15.4, 7.8 Hz, 6H, -CH(CH3)2), 1.00 (td, J = 8.5, 7.1
Hz, 6H, -CH(CH3)2), 0.93 (qd, J = 7.2, 1.3 Hz, 12H, -CH(CH3)2). 31P NMR (202 MHz, C6D6,
298 K) δ 46.63 (s). 13C NMR (126 MHz, C6D6, 298 K) δ 158.64 (t, J = 14.2 Hz, ArC), 158.10
(s, ArC), 157.46 (s, ArC), 134.09 – 133.12 (m, ArC), 132.22 (s, ArC), 130.25 (s, ArC),
128.55 (s, ArC), 128.49 (s, ArC), 127.07 (t, J = 7.6 Hz, ArC), 125.08 (t, J = 3.0 Hz, ArC),
121.31 (s, ArC), 120.99 (s, ArC), 115.80 (s, ArC), 115.19 (s, ArC), 49.53 (t, J = 1.9 Hz,
backbone Ar2CH-), 25.45 (t, J = 9.7 Hz, -CH(CH3)2), 25.04 (t, J = 11.0 Hz, -CH(CH3)2),
18.54 (t, J = 2.9 Hz, -CH(CH3)2), 18.29 (s, -CH(CH3)2), 17.90 (s, -CH(CH3)2), 17.69 (s, -
CH(CH3)2). Anal. Calcd. for C37H47NP2Pd: C, 65.92; H, 7.03; N, 2.08. Found: C, 65.81; H,
6.97; N, 1.98.
-7-

2.2.5. [{PC(sp3)HP}Pd(NHMes)] (7). Method A: 58.1 mg of [{PC(sp2)P}Pd(PMe3)] (1, 0.1
mmol) and 13.5 mg of MesNH2 ((CH3)3C6H2NH2, 135.21 g/mol) were stirred in THF at RT
for 18 h. Aliquots from the reaction mixture taken at 3, 6, and 12 h showed the reaction to be
incomplete. Final 1H and 31P{1H} NMR data assess the product to be pure. After solvent
removal, extraction in diethyl ether and recrystallization, 55.7 mg of analytically pure (by 1H
and 31P{1H} spectra) amide 7 was obtained in 87% yield, as crystals of suitable quality for X-
ray analysis. Method B: 1 mL of a cold 0.1 M Et2O solution of LiNHMes (C9H12LiN, 141.14
g/mol) was added dropwise, under stirring, to a cold (-35 °C) solution of 54.1 mg
of[{PC(sp3)HP}PdCl] (2, C25H37ClP2Pd, 541.39 g/mol, 0.1 mmol). The reaction mixture
turned orange and remained dark orange until the end of the reaction (2 h). Aliquots of the
reaction mixture showed the reaction to be incomplete before the 2 h mark. After subsequent
warm up to RT, removal of Et2O, extraction with n-pentane and filtration over a plug of
Celite (to remove LiCl formed as a by-product), the red residue was found to be pure by 1H
and 31P{1H} spectroscopy. Compound 7 (C34H49NP2Pd, 640.14 g/mol) was obtained in 86%
isolated yield (55.1 mg). Recrystallization from a concentrated Et2O solution yielded deep
orange crystals of X-ray quality. For 7: 1H NMR (500 MHz, C6D6, 298 K) δ 7.22 (d, J = 7.9
Hz, 2H, ArH), 7.07 (ddd, J = 14.1, 9.0, 5.2 Hz, 5H, ArH), 6.94 (d, J = 1.9 Hz, 1H, ArH), 6.91
(t, J = 7.4 Hz, 2H, ArH), 5.82 (s, 1H, backbone Ar2CH-), 3.18 (s, 3H, -NH(C6H2(CH3)3), 2.44
(s, 3H, -NH(C6H2(CH3)3), 2.34 (s, 3H, -NH(C6H2(CH3)3), 2.27 – 2.14 (m, 4H, -CH(CH3)2),
1.28 (s, 1H, -NHMes), 1.19 (dd, J = 15.3, 8.0 Hz, 6H, -CH(CH3)2), 1.11 (dd, J = 15.3, 8.1 Hz,
6H, -CH(CH3)2), 0.99 (dd, J = 14.5, 7.3 Hz, 6H, -CH(CH3)2), 0.95 (q, J = 7.0 Hz, 6H, -
CH(CH3)2). 31P{1H} NMR (202 MHz, C6D6, 298 K) δ 43.36 (s). 13C NMR (126 MHz, C6D6,
298 K) δ 159.75 (t, J = 14.8 Hz, ArC), 158.83 (s, ArC), 134.44 (t, J = 16.7 Hz, ArC), 132.01
(s, ArC), 130.61 (s, ArC), 130.12 (s, ArC), 128.96 (s, ArC), 127.84 (s, ArC), 124.95 (t, J =
2.9 Hz, ArC), 121.70 (s, ArC), 119.79 (s, ArC), 116.55 (s, ArC), 49.78 (s, backbone Ar2CH-),
-8-

25.42 (t, J = 9.5 Hz, -CH(CH3)2), 24.86 (t, J = 11.1 Hz, -CH(CH3)2), 22.44 (s, -
NH(C6H2(CH3)3), 21.10 (s, -NH(C6H2(CH3)3), 20.07 (s, -NH(C6H2(CH3)3), 18.58 (t, J = 2.6
Hz, -CH(CH3)2), 18.52 (t, J = 2.4 Hz, -CH(CH3)2), 18.34 (s, -CH(CH3)2), 17.47 (s, -
CH(CH3)2). Anal. Calcd. for C34H49NP2Pd: C, 63.79; H, 7.72; N, 2.19. Found: C, 63.71; H,
7.53; N, 1.78.
2.2.6. [{PC(sp3)HP}Pd{OC(O)NHMes}] (8). In a 100 mL round-bottomed flask, 32.0 mg of
7 (0.05 mmol) was dissolved in THF at RT with stirring and the flask was sealed with a
rubber septum and brought outside the glovebox covered in aluminium foil to avoid light
exposure. 1.2 mL of CO2 (0.05 mmol) were injected through the septum with an air-tight
syringe. The color changed gradually from red to yellow within 20 min. The flask was then
brought back in the box and the volatiles were removed under reduced pressure. The resulting
solids were extracted with n-pentane and the solution filtered over Celite. The volatiles were
removed again under a reduced pressure, affording 31.1 mg of 8 (C35H49NO2P2Pd, 684.15
g/mol), in 91% yield. Recrystallization from a concentrated n-pentane solution at -35 °C in
the glovebox yielded X-ray quality crystals suitable for analysis; overall yield: 74% (25.3
mg). For 8: 1H NMR (500 MHz, C6D6, 298 K) δ 7.25 (d, J = 7.9 Hz, 2H, ArH), 7.07 (dtd, J =
5.1, 3.8, 1.2 Hz, 2H, ArH), 7.03 (t, J = 7.5 Hz, 2H, ArH), 6.91 (t, J = 7.4 Hz, 2H, ArH), 6.89
(s, 2H, ArH), 6.77 (s, 1H, -OC(O)NHMes), 6.14 (s, 1H, backbone Ar2CH-), 2.56 (s, 6H, -CH3
in positions 2,6 of the trimethylphenyl Mes –NH(C6H2(CH3)3), o,o’-Mes), 2.55 – 2.48 (m,
2H, -CH(CH3)2), 2.36 – 2.27 (m, 2H, -CH(CH3)2), 2.21 (s, 3H, -CH3 in position 4 of the
trimethylphenyl Mes –NH(C6H2(CH3)3); p-Mes), 1.37 (dd, J = 15.7, 8.4 Hz, 6H, -CH(CH3)2),
1.32 (dd, J = 15.6, 8.4 Hz, 6H, -CH(CH3)2), 1.08 (dd, J = 14.5, 7.2 Hz, 6H, -CH(CH3)2), 1.03
(dd, J = 14.3, 7.0 Hz, 6H, -CH(CH3)2). 31P NMR (202 MHz, C6D6, 298 K) δ 49.45 (s). 13C
NMR (126 MHz, C6D6, 298 K) δ 160.56 (s, -OC(O)NHMes), 159.06 (t, J = 15.1 Hz, ArC),
137.80 (s, ArC), 135.08 (s, ArC), 133.62 (t, J = 16.7 Hz, ArC), 133.05 (s, ArC), 132.25 (s,
-9-

ArC), 130.13 (s, ArC), 128.74 (s, ArC), 127.26 (t, J = 8.7 Hz, ArC), 125.28 (t, J = 3.0 Hz,
ArC), 45.97 (t, J = 2.1 Hz, backbone Ar2CH-), 25.43 (t, J = 9.8 Hz, -CH(CH3)2), 24.99 (t, J =
11.2 Hz, -CH(CH3)2), 21.04 (s, -CH3, p-Mes), 19.74 (s, -CH3, o,o’-Mes), 19.23 (t, J = 3.1 Hz,
-CH(CH3)2), 18.79 (t, J = 3.0 Hz, -CH(CH3)2), 18.25 (s, -CH(CH3)2), 18.09 (s, -CH(CH3)2).
Anal. Calcd. for C35H49NO2P2Pd: C, 61.45; H, 7.22; N, 2.05. Found: C, 61.15; H, 7.16; N:
1.67.
3. Results and discussion
3.1. Synthesis and characterization of new metal complexes
The reaction of carbene 1 with alcohols and amines was carried out under mild
conditions (at ambient temperature in THF or Et2O as a solvent). For example, the reaction of
1 with iPrOH was fast and occurred within 30 min at ambient temperature, carried out with
either an equivalent of iPrOH or in neat iPrOH; the corresponding iso-propoxide, 3, was
isolated in a near-quantitative yield as a red solid. The 1H NMR spectrum of 3 indicates that
the backbone proton resonates at 5.69 ppm as a singlet, while the iso-propoxide moiety
displays a septet for the methine –OCHMe2 (3JHH = 5.8 Hz) and a doublet for the methyls at
1.74 ppm (3JHH = 5.8 Hz). The phosphines give rise to a singlet resonance in the 31P{1H}
NMR spectrum at δ 43.9 ppm, indicative of equivalent magnetic environments. In the
13C{1H} spectrum, the backbone carbon resonates at δ 47.4 ppm as a singlet, while the iso-
propoxide methine carbon displays a shift at 71.9 ppm and the methyl carbons at 32.3 ppm.
-10-

Scheme 1. Synthesis of compounds 3-5.
A single-crystal structure elucidation for 3 (Figure 1) further corroborates the
assignment from NMR spectra, showing a square-planar geometry around the metal center
(∑angles = 360.42(7)°), with near-identical Pd-P distances and a Pd(1)-O(1) distance of
2.092(2) Å, comparable to the Pd-O distance in the methoxide homologue (2.055(4) Å) [16],
and in other related palladium alkoxide complexes (2.081-2.090 Å) [23-25]. The Pd-C(sp3)
distance of 2.071(3) Å is within the expected range displayed by this PCP framework
coordinated to a Pd(II) center [16-20]. The molecular structure of 3 shows a rare case of
hydrogen bonding between M-OR and a free iPrOH molecule. Hydrogen bonding usually
occurs in dimeric alkoxide complexes when M-OR and M-O(H)R vectors are approximately
parallel [26], and this explains the typical occurrence of such H-bonds in dinuclear species
that can accommodate these H-bonds intramolecularly [26]. Although iPrOH is used as a
reactant in the current synthesis, it might also be produced by an undesired hydrolysis of the
metal iso-propoxide product.
-11-

Figure 1. Molecular structure representation of [{PC(sp3)HP}Pd(OiPr)] (3). Most hydrogen
atoms are omitted for clarity. Selected distances (Å) and angles (°): Pd(1)–C(1) 2.070(3);
Pd(1)–O(1) 2.092(2); Pd(1)–P(1) 2.3241(8); Pd(1)–P(2) 2.2761(8); O(1)–C(31) 1.400(4);
P(2)–Pd(1)–P(1) 158.70(3); C(1)–Pd(1)–O(1) 178.08(10); C(31)–O(1)–Pd(1) 117.35(18);
C(1)–Pd(1)–P(1) 81.59(8); C(1)–Pd(1)–P(2) 84.04(8); O(1)–Pd(1)–P(1) 97.48(6); O(1)–
Pd(1)–P(2) 97.31(6).
Choosing the simplest tertiary alcohol, tert-butanol, as the organic substrate, resulted
in a lower conversion (~30% as indicated by NMR spectra of crude reaction mixtures) of 1 to
the expected PCP palladium tert-butoxide (4) than 3. To confirm the identity of 4, a salt
metathesis reaction between 2 and KOtBu at -35 °C was carried out. The spectral data of the
product obtained by this route match those of the crude reaction mixtures when 1 was used.
-12-

The 1H NMR spectrum of 4 shows the resonating backbone proton at 5.71 ppm as a
singlet, while the three equivalent methyl groups of the OtBu moiety display a sharp signal at
1.73 ppm. The phosphines are equivalent and give rise to a singlet at δ 40.7 ppm in the
corresponding 31P{1H} NMR spectrum. The 13C{1H} NMR spectrum displays a shift at δ
47.6 ppm, characteristic for the benzylic position, while the OtBu moiety displays two singlet
resonances at δ 70.1 ppm (OC(CH3)3) and δ 37.1 ppm (OC(CH3)3). Heterolytic cleavage of
the tBuO-H bond is harder to achieve and lower yielding compared to that of stronger acids
like MeOH or iPrOH, but the steric properties of tBuOH likely play a role as well.
Figure 2. Molecular structures of alkoxide [{PC(sp3)HP}Pd(OtBu)] (4). Most hydrogen
atoms were omitted for clarity. Selected distances (Å) and angles (°): Pd–C 2.0831(14); Pd–O
2.0898(10); Pd–P(1) 2.2769(4); Pd–P(2) 2.3203(4); O–C(51) 1.3955(18); C–Pd–O 178.27(5);
P(1)–Pd–P(2) 155.649(14); C–Pd–P(1) 83.73(4); C–Pd–P(2) 82.21(4); O–Pd–P(1) 97.81(3);
O–Pd–P(2) 96.61(3).
-13-

A concentrated hexanes solution of 4 afforded X-ray quality single crystals. The solid
state molecular structure (Figure 2) showed a square-planar geometry at the metal center
(Σangles = 360.36(4)°). The Pd–C distance of 2.0831(14) Å is typical for a Pd-C(sp3) bond,
while the Pd–O distance of 2.0898(10) Å is similar to that found in the alkoxide complex 3
(2.092(2) Å) and other alkoxides [23-25]. The bulkiness of the tBuO moiety forces some
bending of the PCP framework, as shown by the more acute P-Pd-P angle of 155.649(14)°.
The reaction between phenol and 1 afforded the phenoxide derivative
[{PC(sp3)HP}Pd(OPh)] (5) within seconds. The 1H NMR spectrum of 5 displays a single
shift for the C-H backbone proton at 5.97 ppm, while the 31P{1H} spectrum confirms the
equivalence of the phosphines, which display a singlet at δ 47.2 ppm. The main spectral
feature of the 13C{1H} NMR spectrum is the backbone carbon resonating at 46.6 ppm as a
triplet due to the coupling to the two equivalent phosphorus nuclei (2JCP = 1.7 Hz). X-ray
crystallography (Figure 3) reveals a square-planar geometry at the Pd(II) center (Σangles
=
358.92(3)°), with a Pd–O distance of 2.0901(9) Å, typical for analogous Pd(II) alkoxide
complexes (2.055 – 2.090 Å) [16, 23-25] and close to the Pd-O distance in a related PCP
palladium phenoxide reported by Fulmer in 2011 (2.0900(12) Å) [23].
-14-

Figure 3. Molecular structure representation of phenoxide [{PC(sp3)HP}Pd(OPh)] (5).
Selected distances (Å) and angles (°): Pd–C 2.0692(11); Pd–O 2.0901(9); Pd–P(1) 2.3223(4);
Pd–P(2) 2.2651(4); O–C(51) 1.3145(18); C–Pd–O 175.17(5); P(2)–Pd–P(1) 161.902(12); C–
Pd–P(1) 82.22(3); C–Pd–P(2) 84.94(3); O–Pd–P(1) 98.65(3); O–Pd–P(2) 93.11(3); C(51)–O–
Pd 122.98(10).
In a previous communication, we reported the N-H bond activation of p-toluidine by
palladium carbenes and the synthesis of the corresponding anilide
[PC(sp3)HP]Pd(NHC6H4CH3) [16]. Since many active catalysts exhibit an enhanced
reactivity precisely due to the steric congestion around a metal center, we decided to extend
the scope of the amide synthesis to sterically encumbered Pd(II) amides, which could furnish
reactive sites at the metal center. The synthesis of palladium amides was straightforward and
high yielding, consisting in treating [{PC(sp2)P}Pd(PMe3)] (1) with the corresponding amine
(diphenylamine or 2,4,6-trimethylphenyl amine) in THF at ambient temperature (Scheme 2).
Figure 4. Molecular structure representation of amide [{PC(sp3)HP}Pd(NPh2)] (6). Selected
distances and angles: Pd – C 2.114(4); Pd – N 2.1284(17); Pd – P(1) 2.3145(6); Pd – P(2)
-15-

2.2985(6); C – C(21) 1.498(4); C – C(11) 1.611(5); N – C(31) 1.381(3); N – C(41) 1.391(3);
C – Pd – N 170.15(16); P(2) – Pd – P(1) 164.81(2); C – Pd – P(2) 84.12(10); N – Pd – P(2)
96.74(5); N – Pd – P(1) 98.24(5); C – Pd – P(1) 80.69(10); C(41) – N – Pd 118.57(14); C(31)
– N – Pd 120.45(14).
The palladium PCP diphenylamide complex [{PC(sp3)HP}Pd(NPh2)] (6) was
synthesized by a straightforward reaction between carbene complex [{PC(sp2)P}Pd(PMe3)]
(1) with Ph2NH for 18 h at ambient temperature. A parallel strategy was reacting the pincer
chloride [{PC(sp3)HP}PdCl] (2) with Ph2NLi. Both methods afforded 6 in high yield.
Spectroscopic data for 6 are in agreement with its proposed structure; the backbone proton
resonates at 6.19 ppm as a singlet in the 1H NMR spectrum, while the backbone carbon is
found at 49.5 ppm as a triplet (2JC-P = 1.9 Hz) due to coupling to two equivalent phosphorus
nuclei (46.6 ppm in the 31P{1H} NMR spectrum). The two phenyl rings of NPh2 are
equivalent and give rise to only 4 signals in the corresponding 13C{1H} NMR spectrum. The
single crystal structure of 6 (Figure 4) agrees with the spectroscopic data and shows a square-
planar geometry at the metal center (Σangles at palladium 359.79(7)°). C-Pd-P angles are
smaller than 90° (84.12(10)° and 80.69(10)°), while the P-Pd-N angles are larger (96.74(5)
and 98.24(5)°); as a consequence, the Pd-C distance of 2.114(4) Å is larger than in
[{PC(sp3)HP}PdCl] (2). The Pd-N distance of 2.1284(17) Å is slightly longer than other Pd-
N distances in this series (2.0860(14) Å for [{PC(sp3)HP}Pd(NHC6H4CH3)][16] and 2.111(3)
Å – for [{PC(sp3)HP}Pd(NHMes)] 7).
-16-

Scheme 2. Synthesis of 6.
N-H activation of MesNH2 (Mes = 2,4,6-trimethylphenyl) by carbene 1 occurs within
3 h at ambient temperature and [{PC(sp3)HP}Pd(NHMes)] (7) is obtained in high yield.
Alternatively, reacting the lithiated salt LiNHMes with an equivalent of [{PC(sp3)HP}PdCl]
(2) yielded 7 as an orange powder. The 1H NMR spectrum of 7 indicates that the backbone
proton can be identified at 5.82 ppm as a singlet, while the amide NH proton resonates at 1.28
ppm also as a singlet. The two equivalent phosphorus nuclei display a singlet at 43.3 ppm.
The 1H NMR spectrum of 7 also shows 3 distinct methyl shifts (3.18, 2.44, and 2.34 ppm) for
the 2,4,6-trimethylanilide moiety, consistent with an anagostic interaction between the metal
center and one of the ortho methyl groups on the mesityl substituent. Additionally, the Pd-
H(o-C6H4(CH3)3) distance of 2.763 Å and the Pd-H-C(59) angle of 120.55° are both in line
with the description of an anagostic interaction observed in square-planar, d8 Pd(II)
complexes (vide infra).
Contrary to the 3-center-2-electron M-H-C bonds that are agostic [27], the anagostic
interactions, while still being special cases of hydrogen bonding, can vary in nature between
-17-

purely electrostatic (typical hydrogen bonding) to partially covalent, with relatively larger M-
H bonds (2.3-2.9 Å) and a more obtuse M-H-C angle of 110-170° [28-30]. Metal complexes
featuring agostic or anagostic interactions differ greatly from a structural and spectroscopic
viewpoint; the chemical shift of the anagostic protons is downfield of uncoordinated CH in
the corresponding 1H NMR spectrum, in line with the predominantly electrostatic description
of the interaction [27-30]. Anagostic interactions are typical for square-planar, d8 metal
complexes (Rh(I), Pt(II) [30, 31], or Pd(II) [32]). For example, [Rh(cyclo-octa-1,5-
diene)(Fe{η5-C5H4(2-C5H4N)}(η5-C5H4PPh2)]PF6 shows an aromatic C-H⋅⋅⋅Rh interaction,
[RhCl(i-Pr2POXy)(PMe3)]2 (Xy =2,3-xylyl) shows a phenyl C-H⋅⋅⋅Rh interaction, trans-
PtCl2(quinoline-8-carbaldehyde)PEt3, shows an aldehyde C-H⋅⋅⋅Pt interaction, and cis-[Pt(o-
Ph2PC6H4NC(O)C6H4][o-Ph2PC6H4NHC(O)Ph)] shows a typical hydrogen bond [30]. Our
group has previouslys investigated anagostic interactions in a series of Pd(II) complexes
(diacetates and dichlorides) supported by a diphosphine ligand (PC(sp3)H2P = iPr2P-C6H4-
CH2-C6H4-PiPr2), all of them conforming to the general definition given for anagostic
complexes regarding the Pd-H bond distance, C-H⋅⋅⋅Pd angle, and different chemical shift for
the two inequivalent backbone protons experiencing an interaction with the palladium center
[17, 32, 33].
-18-

Scheme 3. Synthesis of 7 and 8.
Figure 5. Molecular structure representation of [{PC(sp3)HP}Pd(NHMes)] (7). Selected
distances and angles: Pd – C 2.101(4); Pd – N 2.111(3); Pd – P(1) 2.3253(10); Pd – P(2)
2.2621(9); N – C(51) 1.364(5); C – C(11) 1.533(5); C – C(21) 1.512(5); C – Pd – N
-19-

172.55(14); P(2) – Pd – P(1) 161.93(4); C – Pd – P(2) 84.62(10); N – Pd – P(2) 92.53(9); N –
Pd – P(1) 100.02(9); C – Pd – P(1) 81.30(10); C(51) – N – Pd 141.4(3).
A single crystal X-ray diffraction investigation (Figure 5) confirmed the proposed
structure of 7: the metal center has a distorted square-planar geometry (Σangles = 358.47(10)°),
with individual angles strongly deviating from 90°; for example, the N-Pd-P angles are
84.62(10) and 81.30(10)°. The Pd-Cbackbone distance (2.101(4) Å) is longer than in the
palladium pincer chloride 2 (2.0738(19) Å), while the Pd-N distance of 2.111(3) Å is similar
to typical Pd-N distances [24, 34-41]. The Pd-N-C(51) angle of 141.4(3)° accounts for a
drastic bending of the planar amide moiety. This wide angle is structurally enforced by the
relatively bulky mesityl moiety.
Because initial attempts to crystallize 7 were failing, we decided to probe its structure
by running a CO2 reaction resulting in the near-quantitative formation of the carbamate
complex 8. Compound 8 shows only two shifts corresponding to the methyl protons of the
mesityl group in the 1H NMR spectrum, a spectral feature typical for symmetrical species.
This is consistent with the lack of an anagostic interaction due to an increased distance
between palladium center and the mesityl moiety.
The 1H NMR spectrum of 8 also shows a singlet resonance at 6.14 ppm,
corresponding to the backbone proton, and at 6.77 ppm for the amide proton –OC(O)NHMes
that is severely deshielded (1.28 ppm in 7). The phosphorus nuclei are chemically equivalent
and thus display a single shift at 49.4 ppm. The 13C{1H} spectrum shows the backbone
carbon at 45.9 ppm as a triplet (2JC-P = 2.1 Hz), while the carbamate carbon resonates
downfield at 159.1 ppm, exhibiting a larger phosphorus coupling (2JC-P = 15.1 Hz) than the
typical 2-bond coupling 2JCP, which is found in the range 1.3 – 7.1 Hz [16, 19]. The o,o’-
-20-

methyl groups of the mesityl moiety are equivalent and appear as a singlet at 19.7 ppm (no
anagostic interaction), while the para methyl resonates at 21.0 ppm in the 13C{1H} NMR
spectrum.
Figure 6. Molecular structure representation of [{PC(sp3)HP}Pd{OC(O)NHMes}] (8).
Selected distances (Å) and angles (°): Pd(1) – C(1) 2.073(4); Pd(1) – O(31) 2.134(2); Pd(1) –
P(12) 2.2829(10); Pd(1) – P(11) 2.3249(10); N(1) – C(3) 1.371(5); N(1) – C(51) 1.422(5);
C(3) – O(31) 1.300(4); C(3) – O(32) 1.238(4); C(1) – Pd(1) – P(12) 84.38(10); C(1) – Pd(1) –
P(11) 80.32(10); O(31) – Pd(1) – P(12) 98.54(7); O(31) – Pd(1) – P(11) 98.65(7); P(12) –
Pd(1) – P(11) 158.12(4); C(3) – N(1) – C(51) 123.2(3); O(32) – C(3) – O(31) 125.0(3); O(32)
– C(3) – N(1) 121.3(3).
The investigation of the molecular structure of 8 (Figure 6) revealed two independent
molecules in the unit cell bound by two O…H-N hydrogen bonds (O and N atoms belong to
different molecules). Each unit has similar metrical parameters; the palladium center is
square planar (Σangles at palladium 361.89(34)°), with a Pd-Cbackbone distance of 2.073(4) Å
-21-

and a Pd-O distance of 2.134(2) Å; the C=O distance of 1.238(4) Å resembles that of a
typical C=O double bond found in other carbonyl compounds (1.23 Å) [42].
3.2. DFT calculations
Scheme 4. Mechanism of OH activation. Enthalpies are listed in parenthesis.
Given the basicity of the carbene carbon in 1 and the acidity of the E-H (E = O, N)
bonds studied herein, there is the possibility that the reactions occur by the deprotonation of
the substrates. Our previous studies of the Si-H and Ge-H activation reactions showed [20],
however, a concerted addition of the E-H bond to the Pd-C moiety. We found that, in the case
of Ge-H containing substrates, only the corresponding palladium germyl product was
observed. On the other hand, the activation of Si-H activation of substituted silanes results in
the formation of a mixture of isomers, the expected palladium silyl complex and a palladium
hydride with a silyl functionalized backbone carbon. The lack of regioselectivity was
attributed to small differences in electronegativity between the hydrogen and the silicon
atom.
-22-

Given that Si-H and Ge-H bonds are less polarized than the E-H (E = O, N) bonds
studied herein, we decided to perform DFT calculations in order to determine the addition
mechanism of E-H bonds. DFT calculations were carried out with methanol for simplicity.
We found (Scheme 4) that, initially, the alcohol forms an adduct with the carbene due to the
presence of a negatively charged carbon in the backbone (9-A). Similarly to our previous
observations for the Si-H activation process [20], we were able to identify a transition state,
9-B, where the O-H bond is cooperatively activated by the nucleophilic carbon and the metal
center. Unlike in our previously reported study, due to the presence of a more polar E-H bond
in the alcohols series, only one isomer (the palladium alkoxide) is observed as a product, the
transition state that would lead to the formation of the metal hydride being energetically
unfavorable. Furthermore, we were not able to locate a 5-coordinated intermediate. In the
present case, one of the phosphine arms dissociates from palladium to form a 4-coordinated
complex, where the trimethylphosphine ligand is still coordinated to the metal center (9-C).
We were not able to locate the transition state with PMe3 as the leaving group. Finally, the
product, 9-D, is generated through the re-association of the phosphine arm and the
subsequent loss of PMe3.
4. Conclusions
The reactivity of the nucleophilic palladium(II) carbene 1, [{PC(sp2)P}Pd(PMe3)],
toward N-H and O-H bond activation was expanded. The studied reactions yielded in
moderate-to-excellent yields the alkoxides [{PC(sp3)HP}Pd(OiPr)], [{PC(sp3)HP}Pd(OtBu)]
and [{PC(sp3)HP}Pd(OPh)], and amides [{PC(sp3)HP}Pd(NPh2)] and
[{PC(sp3)HP}Pd(NHMes)]. While iPrOH and PhOH produced the corresponding alkoxides in
a near-quantitative yield, the reaction with a sterically encumbered alcohol (tBuOH) to give 4
-23-

was lower yielding. An alternative pathway to 4 was a metathesis reaction of the parent
pincer [{PC(sp3)HP}PdCl] (2) with KOtBu.
DFT calculations using methanol as a substrate indicate that the addition of O-H
bonds to 1 proceeds through a concerted mechanism, similarly to what was found previously
for the addition of Si-H and Ge-H bonds to 1. This finding is interesting given that O-H
bonds are more acidic than Si/Ge-H bonds.
The N-H activation reactivity of 1 was exemplified by its reactions with a primary
(MesNH2) and secondary (Ph2NH) amine, yielding the corresponding amide complexes.
Amide [{PC(sp3)HP}Pd(NHMes)] exhibits an interesting case of an anagostic interaction,
and as a result, the three methyl groups of the mesityl moiety are chemically non-equivalent.
The structure of [{PC(sp3)HP}Pd(NHMes)] was further probed by a CO2 insertion reaction
leading to the quantitative formation of the carbamate [{PC(sp3)HP}Pd{OC(O)NMes}],
which no longer exhibits an anagostic interaction due to an increased distance between
palladium and the mesityl group. These metal complexes enhance the family of pincer
compounds supported by the PC(sp3)HP tridentate backbone and open new avenues in E-H
(E = N, O) bond activation by late transition metal carbenes with potential applications to
catalysis.
Acknowledgment
We thank Dr. Allen Oliver for crystallographic assistance. This work was partially supported
by the University of Notre Dame. V.M.I. acknowledges support from the National Science
Foundation (NSF) CAREER Program (CHE-1552397).
Appendix A. Supplementary material
-24-

NMR spectra and X-ray data for compounds 3-8, and DFT calculation results. CCDC
1558876-1558881 contain the supplementary crystallographic data for compounds 3-8. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Graphical abstract pictogram:
Graphical abstract synopsis
Atom-efficient E-H (E=N, O) bond activation by a unique palladium(II) carbene furnishes new
palladium amides and alkoxide complexes, suggesting the versatility of nucleophilic metal carbenes
in various cooperative metal-ligand bond activation reactions.
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