Unsymmetrical RPNPR′ pincer ligands and their group 10 complexes

Article abstract of DOI:10.1039/c1dt10265f

Two new unsymmetrical ^RPNP^R′-type pincer ligands based on a bis(tolyl)amine framework have been synthesized and characterized by a variety of techniques, including X-ray crystallography. These ligands have been coordinated to Ni, Pd, and Pt precursors to provide a number of well-characterized group 10 halides. Conversion of these metal halides to metal hydrides was accomplished using borohydride reagents, or by direct interaction of the ligand with the zerovalent metal precursor. The insertion of oxygen into these hydrides in an attempt to prepare metal hydroperoxides has been examined; however, we were unable to obtain stable and isolable hydroperoxide species. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10265f

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This article is published as part of the Dalton Transactions themed issue entitled:
Pincers and other hemilabile ligands
Guest Editors Dr Bert Klein Gebbink and Gerard van Koten
Published in issue 35, 2011 of Dalton Transactions
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Articles in the issue include:
PERSPECTIVE:
Cleavage of unreactive bonds with pincer metal complexes
Martin Albrecht and Monika M. Lindner
Dalton Trans., 2011, DOI: 10.1039/C1DT10339C
ARTICLES:
Pincer Ru and Os complexes as efficient catalysts for racemization and deuteration of alcohols
Gianluca Bossi, Elisabetta Putignano, Pierluigi Rigo and Walter Baratta
Dalton Trans., 2011, DOI: 10.1039/C1DT10498E
Mechanistic analysis of trans C–N reductive elimination from a square-planar macrocyclic aryl-
copper(III) complex
Lauren M. Huffman and Shannon S. Stahl
Dalton Trans., 2011, DOI: 10.1039/C1DT10463B
CSC-pincer versus pseudo-pincer complexes of palladium(II): a comparative study on
complexation and catalytic activities of NHC complexes
Dan Yuan, Haoyun Tang, Linfei Xiao and Han Vinh Huynh
Dalton Trans., 2011, DOI: 10.1039/C1DT10269A
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PAPER
Unsymmetrical RPNPR¢ pincer ligands and their group 10 complexes†
Raymond B. Lansing, Jr.,a Karen I. Goldberg*b and Richard A. Kemp*a,c
Received 18th February 2011, Accepted 6th April 2011
DOI: 10.1039/c1dt10265f
Two new unsymmetrical RPNPR¢-type pincer ligands based on a bis(tolyl)amine framework have been
synthesized and characterized by a variety of techniques, including X-ray crystallography. These ligands
have been coordinated to Ni, Pd, and Pt precursors to provide a number of well-characterized group 10
halides. Conversion of these metal halides to metal hydrides was accomplished using borohydride
reagents, or by direct interaction of the ligand with the zerovalent metal precursor. The insertion of
oxygen into these hydrides in an attempt to prepare metal hydroperoxides has been examined; however,
we were unable to obtain stable and isolable hydroperoxide species.
Introduction
The search for new ligands that can direct specific electronic or
steric effects upon metal ions is one that continues unabated. Pin-
cer ligands, which are multidentate ligands that afford increased
thermal and kinetic stabilities to metal complexes, have been
highly-developed over the past decades; however, new types of pin-
cer ligands are still desired.1,2 Pincer ligands have been synthesized
with a wide range of donor atoms to serve as attachment points
to metals, and these pincer–metal complexes have been used in a
variety of applications, most importantly in catalytic chemistry.3–6
In this current submission we restrict ourselves to a family of
RPNPR¢-pincer ligands based on a backbone framework recently
investigated by Kaska,7 Liang,8 Mindiola,9–11 and Ozerov.4,12–16 In
the vast majority of these RPNPR¢-pincer ligands, both R and R¢
are the same alkyl or aryl fragment, thus producing PNP ligands
with symmetrical ends (Fig. 1). However, very recently the group
of Liang has shown that an unsymmetrical RPNPR¢-pincer (R =
Fig. 1 Symmetrical versions of the PNP-framework.
pincer ligands. We have recently demonstrated the first direct
insertion of O2 into a Pd–H bond to form the Pd–OOH complex,23
and have examined this reaction computationally.24 Therefore, in
order to learn more about these O2 reactions it was of interest to
us to expand our approaches and prepare new unsymmetrical
RPNPR¢-pincer ligands, as well as to examine their abilities to
form new late metal halide and hydride complexes. We report
herein the detailed syntheses and characterization of two new
unsymmetrical ligands based on the bis(tolyl)amine backbone
(R = Me in Fig. 1). Also reported are the preparations of new
Ni, Pd, and Pt halide complexes utilizing these ligands, and the
conversion of these halides into the corresponding metal hydrides.
Lastly, the reactivities of O2 with these metal hydrides are also
briefly presented.
i
Ph, R¢ = Pr) ligand based on a phenyl backbone (R = H) can
be prepared and coordinated to Ni and Al.17,18 We have been
interested in expanding the range of unsymmetrical RPNPR¢-pincer
ligands for application in the preparation of new late transition
metal complexes of Ni, Pd, and Pt.
Our research groups have had long-standing efforts in the
syntheses, characterization, and use of pincer-containing metal
compounds.19–22 In a more focused application, we have been
examining the insertion of O2 into transition metal hydrides
containing various symmetric phosphine- and carbene-based
Results and discussion
Synthesis and characterization of unsymmetrical ligands 1 and 2
aDepartment of Chemistry and Chemical Biology, University of New Mexico,
MSC03 2060, Albuquerque, New Mexico, 87131, USA. E-mail: rakemp@
unm.edu; Fax: 1-505-272-7336; Tel: 1-505-272-7609
The unsymmetrical bis(tolyl)amine ligands 1 and 2 were both
prepared similarly to the method employed by Liang (Scheme 1).17
The same dibromo-substituted amine precursor was used in each
preparation.25 The key step in the syntheses of the unsymmetrical
ligands 1 and 2 is to add the dialkylchlorophosphine first, prior to
the addition of the diphenylchlorophosphine, due to the higher
electrophilic character of the diphenylchlorophosphine. If the
bDepartment of Chemistry, Box 351700, University of Washington, Seattle,
Washington, 98195, USA. E-mail: goldberg@chem.washington.edu
cAdvanced Materials Laboratory, Sandia National Laboratories, 1001
University Blvd, SE, Albuquerque, New Mexico, 87106, USA
† CCDC reference numbers: 812749 (1), 812750 (3), 812751(4), 812752 (5),
812753 (6), 812754 (7), and 812755 (10). For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1dt10265f
8950 | Dalton Trans., 2011, 40, 8950–8958
This journal is
The Royal Society of Chemistry 2011
©

Liang,17 we saw no compelling reason to obtain the single-crystal
structure of 2.
Halide-containing Pd and Pt metal complexes prepared from 1
and 2
After the new unsymmetrical ligands 1 and 2 were prepared we
next investigated the coordination chemistry of these ligands to
Ni, Pd, and Pt. Treatment of (COD)PdCl2 with either 1 or 2 in
THF in the presence of NEt3 for one hour gave (PhPNPiPr)PdCl (3)
or (PhPNPCy)PdCl (4), respectively◦(Scheme 2). The synthesis of 3
required one hour of reflux at 80 C, resulting in a 96% yield of
Scheme 1 Preparation of unsymmetrical ligands 1 and 2.
1
a red solid. The 31P{ H} NMR spectrum of 3 reveals two signals
order of addition is reversed, mixtures of products including the
symmetrically-substituted ligands are formed.17 PhPNPiPr ligand 1
can be isolated in 39% yield as an off-white solid after precipitation
from a diethyl ether/pentane mixture at -35 ◦C.
corresponding to the two distinct phosphorus environments within
the molecule. A doublet exists at 54.0 ppm with JPP = 437.2 Hz,
corresponding to the –PiPr2 phosphorus atom, and another
doublet is found further upfield at 25.7 ppm with JPP = 437.2 Hz,
corresponding to the –PPh2 phosphorus environment. The large
JPP values for the two signals are characteristic of phosphines
in the trans-orientation, which suggests that the binding mode is
similar to other PNP metal halides (square planar geometry). The
solid-state structure of 3 was determined using X-ray diffraction
analysis. A single crystal suitable for X-ray diffraction analysis
was grown from the slow evaporation of a benzene solution at
room temperature. The structure of 3 is depicted in Fig. 3, along
with selected bond lengths and angles. As shown, the geometry
of 3 is confirmed to be approximately square planar around the
metal center. The P–Pd–P angle is 163.724(15)◦. The two Pd–P
Ligand 1 was completely characterized by 1H, 13C, and 31P
multinuclear NMR spectra, elemental analysis, and single crystal
1
X-ray diffraction studies. The 31P{ H} NMR spectrum as expected
showed two distinct resonances for the two non-equivalent P atoms
present. A single crystal suitable for X-ray diffraction analysis
was grown from a concentrated solution of 1 in diethyl ether at
-30 ◦C, and the molecular structure of 1 is shown in Fig. 2. The
structure of 1 largely resembles the structure seen by Liang in
his related RPNPR¢-ligand,17 and as such requires little need for
extensive discussion. Even though the two tolyl rings attached to
N1 that make up the ligand backbone are twisted by 54.9◦ relative
to each other, the Ph- and iPr-substituents are large enough to lead
to a somewhat crowded environment around the location of the
N1–H1A bond.
Scheme 2 Preparation of halide-containing Pd and Pt complexes.
Fig. 2 Molecular structure of 1 (thermal ellipsoids at 50% probability
level). Hydrogen atoms bound to carbon omitted for clarity.
The PhPNPCy ligand 2 can be prepared in an analogous fashion
to 1 in 33% isolated yield as an off-white solid after deposition
from a diethyl ether/pentane mixture at -30 ◦C. 2 was also
fully characterized by multinuclear NMR spectra and elemental
1
analysis. The 13C{ H} NMR spectra for 1 and 2 both showed
fewer resonances than expected, presumably due to overlapping
and broadened peaks. Inequivalent P atoms were again seen in
Fig. 3 Molecular structure of 3 (thermal ellipsoids at 50% probability
1
the 31P NMR spectrum, and the H NMR spectrum was more
level). Hydrogen atoms bound to carbon omitted for clarity. Selected
complex than in 1 as the Cy groups replaced the iPr groups. As the
X-ray structure of 1 so resembled the prior structure reported by
◦
˚
distances (A) and angles ( ): Pd1–Cl1 2.314(4); Pd1–P1 2.300(4); Pd1–P2
2.278(4), Pd1–N1 2.028(1); P1–Pd1–P2 163.72(1); N1–Pd1–Cl1 179.12(4).
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8950–8958 | 8951
©

˚
˚ ˚
and 2.272(1) A, the Pt–N bond length is 2.028(3) A, and the Pt–
bond lengths are 2.278(4) and 2.300(4) A, and the Pd–N bond
˚
˚
length is 2.028(1) A. The N–Pd–Cl bond angle is expected to be
Cl bond length is 2.321(1) A, very close to the values found in
180◦ and experimentally is found to be so (179.12(4)◦). The other
bond lengths and angles show no remarkable differences from
previously-characterized related complexes, and so no further
discussion is warranted.
the structure of the Pd analogue 3. Other bond distances and
angles showed no remarkable differences from 3. As the structure
of 5 visually resembled 3 closely, no separate figure is shown
although the structural files have been deposited in the Cambridge
Structural Database (CSD) (see Supplementary Information†).
(PhPNPCy)PtCl (6) was prepared analogously, and exhibited similar
NMR spectra to 5 with details presented in the Experimental
section. X-ray quality crystals of 6 were deposited from the
gradual evaporation of solvent from a concentrated solution of 6
in benzene. The crystal structure confirmed the expected distorted
square-planar geometry around the metal center. All other bond
distances and angles around Pt were not significantly different
from the Pd analogue 4. As with 5, no separate figure is shown
although the structural files for 6 have been deposited in the CSD
(see Supplementary Information†). Crystallographic data for all
compounds are in Tables 1 and 2.
Similarly, the 31P{ H} NMR spectrum of 4 exhibits two reso-
1
nances for the inequivalent phosphorus environments. A doublet
at 46.5 ppm (JPP = 437.5 Hz, –PCy2) and another doublet at
25.7 ppm (JPP = 437.4 Hz, –PPh2) are present, consistent with the
spectrum of 3. Again, the coupling constant values are consistent
with earlier complexes and suggests a square planar geometry.
The solid-state structure of 4 was determined by X-ray diffraction
analysis (Fig. 4). A single crystal suitable for X-ray study was
grown from the slow evaporation of a benzene solution at room
temperature. A list of selected bond lengths and angles for 4 are
shown in Fig. 4. The environment around the central Pd atom
is very similar to 3 in terms of Pd–P, Pd–N, and Pd–Cl bond
lengths; however, the N–Pd–Cl angle of 4 deviates slightly more
from linearity (176.23(4)◦) than was seen in 3.
Hydrido-containing group 10 metal complexes prepared from 1
and 2
New metal hydrides containing these new ligands 1 and 2 were
prepared from all three Group 10 metals—Ni, Pd, and Pt,
albeit by different synthetic routes. Due to the reactivity of
the N–H bond, it is possible to directly prepare the M(II)–
H complex via direct oxidative addition of the ligand to a
M(0) precursor. Previously, Ozerov has shown that this N–H
oxidative addition reaction to M(0) can occur, but due to the
demanding conditions often required for Group 10 metals it can
be difficult to obtain pure products.13 We decided to approach
the preparation of unsymmetrical PNP-ligated Ni–H complexes
via this direct one-step, oxidative route rather than attempting to
convert (RPNPR¢)NiCl precursor complexes using hydride sources.
We have previously documented the difficulty in determining
the optimal hydride reagent to use to obtain analytically-pure
products in the conversion of pincer-Ni halides to hydrides.19
The syntheses of the unsymmetric metal hydrides,
(PhPNPiPr)NiH (7) and (PhPNPCy)NiH (8), were performed
via the oxidative addition route using either 1 or 2 as the starting
amine. Harsh, forcing conditions were fortunately not required.
Equimolar amounts of the starting amine and Ni(COD)2 were
stirred at room temperature for 15 min, and the volatiles removed
Fig. 4 Molecular structure of 4 (thermal ellipsoids at 50% probability
level). Hydrogen atoms ◦bound to carbon omitted for clarity. Selected
˚
distances (A) and angles ( ): Pd1–Cl1 2.3171(4); Pd1–P1 2.2843(4); Pd1–P2
2.3046(4), Pd1–N1 2.0229(13); P1–Pd1–P2 164.233(16); N1–Pd1–Cl1
176.23(4).
The Pt-containing analogs of 3 and 4 were also prepared
via similar synthetic routes (Scheme 2). (PhPNPiPr)PtCl (5) was
1
to form brown solids in both cases (Scheme 3). The 31P{ H}
NMR spectrum of 7 revealed two doublets, corresponding to
the two different phosphorus environments. The first doublet
appeared at 58.9 ppm with a JPP = 244.2 Hz (–PiPr2) and the
second doublet appeared at 31.4 ppm with a JPP = 244.1 Hz
1
generated in 75% yield as a yellow solid. The 31P{ H} NMR
spectrum of 5 reveals two signals for the two inequivalent phos-
phorus environments, both containing Pt satellites—a doublet at
43.7 ppm (JPPt = 2754.5 Hz and JPP = 401.6 Hz) for the –PiPr2
phosphorus atom, and a second doublet at 24.7 ppm (JPPt
=
2673.9 Hz and JPP = 401.9 Hz) for the –PPh2 environment. In
both cases, the JPPt coupling constants are consistent with other
similar structures, and the large JPP values are characteristic of
phosphines binding in the trans-orientation, in an approximate
square-planar motif. The proposed molecular structure of 5
was confirmed by X-ray diffraction analysis. A single crystal
suitable for X-ray diffraction analysis was grown from the slow
evaporation of a benzene solution at room temperature. The
crystal structure confirmed a distorted square-planar geometry
around the metal center. The two Pt–P bond lengths are 2.282(9)
Scheme 3 Preparation of Ni hydrides using direct addition route.
8952 | Dalton Trans., 2011, 40, 8950–8958
This journal is
The Royal Society of Chemistry 2011
©

Table 1 Crystallographic data for the structures of 1, 3, and 4
1
3
4
Empirical formula
Formula weight
T/K
C32H37NP2
497.57
228(2)
0.45 ¥ 0.19 ¥ 0.16
Orthorhombic
Pna21
15.4380(11)
22.8418(16)
8.1278(5)
90
90
90
2866.1(3)
4
1.153
C35H39ClNP2Pd
677.46
183(2)
0.60 ¥ 0.43 ¥ 0.28
Monoclinic
P21/n
9.6912(6)
11.5459(7)
28.3155(17)
90
98.821(3)
90
3130.8(3)
4
1.437
0.805
C44H50ClNP2Pd
796.64
188(2)
Crystal size/mm
Crystal system
Space group
0.50 ¥ 0.23 ¥ 0.11
Triclinic
¯
P1
˚
a/A
11.3446(3)
11.7317(3)
15.4507(4)
93.6470(10)
109.9500(10)
93.1420(10)
1922.61(9)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Volume/A
Z
Dc/g cm-3
1.376
0.667
828
56344
16083
442
m(Mo-Ka)/mm-1
F(000)
0.172
1064
36855
5539
1396
107611
15154
361
Total reflections
Unique reflections
Parameters
316
Rint
0.039
1.121
0.0297
1.239
0.0289
1.142
GOF on F2
Final R1, wR2 (I >
2s(I)), (all data)
0.0373, 0.0980
0.0579, 0.1208
0.0325, 0.0856
0.0411, 0.0962
0.0348, 0.0929
0.0461, 0.0929
Table 2 Crystallographic data for the structures of 5, 6, 7, and 10
5
6
7
10
Empirical formula
Formula weight
T/K
C35H39ClNP2Pt
766.15
183(2)
0.21 ¥ 0.09 ¥ 0.06
Monoclinic
P21/c
9.7018(3)
11.5256(4)
28.4989(10)
90
100.733(2)
90
3130.97(18)
4
1.625
4.694
C44H50ClNP2Pt
885.32
183(2)
C32H37NNiP2
556.28
228(2)
C40.5H45NP2Pd
714.12
183(2)
Crystal size/mm
Crystal system
Space group
0.32 ¥ 0.16 ¥ 0.09
0.51 ¥ 0.46 ¥ 0.34
Monoclinic
P21/c
12.3808(8)
14.9010(10)
18.6532(11)
90
122.533(4)
90
2901.3(3)
4
1.274
0.800
1176
31034
5933
328
0.25 ¥ 0.12 ¥ 0.07
Triclinic
Triclinic
¯
¯
P1
P1
˚
a/A
11.3219(5)
11.7353(5)
15.5010(6)
93.810(2)
110.178(2)
92.996(2)
1922.65(14)
2
11.3866(5)
11.4791(5)
14.9377(7)
91.051(2)
108.575(2)
94.265(2)
1843.81(14)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Volume/A
Z
Dc/g cm-3
1.529
3.834
892
43159
13063
442
1.286
0.618
742
41162
10335
392
m(Mo-Ka)/mm-1
F(000)
1524
47085
7789
367
Total reflections
Unique reflections
Parameters
Rint
0.0764
1.024
0.0320, 0.0601
0.0501, 0.0656
0.0381
1.157
0.0411, 0.1260
0.0514, 0.1336
0.0445
1.063
0.0447, 0.1158
0.0649, 0.1317
0.0375
1.162
0.0364, 0.1020
0.0445, 0.1162
GOF on F2
Final R1, wR2 (I > 2s(I)),
(all data)
(–PPh2). The large JPP values indicate that the phosphine donor
atoms are coordinated to the metal in a trans-orientation. The 1H
NMR spectrum of 7 exhibits a doublet of doublets for the Ni–H
with the other crystallographically-characterized compounds
discussed above. The hydride ligand attached to Ni was located
and refined; the process used to refine the H atom is discussed in
the Experimental section. Interestingly, in previous work done
by our group, the hydrides in a series of related (RPCP)NiH
complexes could also be located in the X-ray pattern and refined
to give accurate Ni–H bond lengths.19
resonance at -18.1 ppm with JHP = 58.2 Hz (–PiPr2) and JHP
=
68.4 Hz (–PPh2). The molecular structure of 7 was determined
by X-ray diffraction analysis (Fig. 5). A single crystal suitable
for X-ray study was grown from a concentrated solution of 7 in
diethyl ether at -30 ◦C. A list of selected bond lengths and angles
for 7 are also shown in Fig. 5. The crystal structure of 7 confirms
the distorted square-planar geometry around the metal center.
The P–Ni–P bond angle is 173.78◦, which is also consistent
1
The 31P{ H} NMR spectrum of 8 reveals a pair of doublets
corresponding to the two significantly different phosphorus en-
vironments. The first doublet appeared at 49.6 ppm with a JPP
=
244.9 Hz (–PCy2) and the second doublet appeared at 31.8 ppm
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8950–8958 | 8953
©

a virtual triplet for the hydride ligand at -9.91 ppm. The X-ray
structure of 10 is shown in Fig. 6. Interestingly, in the case of 10
we were able to locate and refine the hydride ligand at a Pd1–
˚
H1 distance of 1.55(3) A (see discussion in Experimental section).
The single crystal X-ray structure displays an approximate square
planar geometry around the palladium center with a P–Pd–P angle
of 165.11(2)◦ as compared to 164.23(2)◦ of 4. The Pd–N bond
˚
distance of 10 (2.0833(19) A) is slightly elongated from that of
˚
4 (2.023(1) A), which is due to the trans-influence of the hydride
ligand. All other noted bond distances and angles are similar to
earlier complexes that have been structurally-characterized.
Fig. 5 Molecular structure of 7 (thermal ellipsoids at 50% probability
level). Hydrogen atoms bound to carbon omitted for clarity. Selected
◦
˚
distances (A) and angles ( ): Ni1–P1 2.1353(8); Ni1–P2 2.1344(8), Ni1–N1
1.921(2); P1–Ni1–P2 173.77(3).
with a JPP = 244.2 Hz (–PPh2), with the large JPP values indicating
1
a trans-orientation of the two phosphine donor atoms. The H
NMR spectrum of 8 contains a doublet of doublets for the Ni–H at
-18.15 ppm with JHP = 58.9 Hz (–PCy2) and JHP = 64.4 Hz (–PPh2).
Unfortunately, even after multiple attempts to grow crystals, a
sample for X-ray diffraction analysis was not obtained.
The Pd and Pt hydrides (PhPNPiPr)PdH (9), (PhPNPCy)PdH (10),
and (PhPNPiPr)PtH (11) were prepared via conversion of the four
Fig. 6 Molecular structure of 10 (thermal ellipsoids at 50% probability
R
(RPNPR¢)MCl precursors using Super-Hydrideꢀ reagent (LiEt3BH
level). Hydrogen atoms bound to carbon omitted for clarity. Selected
◦
˚
distances (A) and angles ( ): Pd1–P1 2.2692(6); Pd1–P2 2.2614(6), Pd1–N1
2.0833(19); Pd1–H1 1.55(3); P1–Pd1–P2 165.11(2); N1–Pd1–H1 179.5(13).
in THF). Use of other traditional metal hydride sources was
also attempted; however, none proved as effective as Super-
Hydride solution. The general synthetic procedure to prepare
these hydrides is shown in Scheme 4. The RPNPR¢-containing
metal chloride precursor was treated with an equimolar amount
of Super-Hydride solution in THF for 2–5 h at room temperature,
and removal of the volatiles in all cases gave brown solids. These
Reactions of Group 10 hydrides with oxygen
Examining the interaction of metal hydrides with O2 is of interest
with respect to the discovery of new partial oxidation catalysts.26
We have previously shown that O2 can insert into a Pd–H bond
to form a Pd–OOH species, which we fully characterized by X-
ray crystallography.23 In an attempt to prepare new, isolable metal
hydroperoxides, each of the Group 10 metal hydrides prepared
in this work (7–11) were treated with gaseous O2 under pressure
in a medium-wall NMR tube fitted with a J. Young valve. This
technique is similar to that previously described by us.23
R
solids were redissolved in pentane, filtered through Celiteꢀ filter
aid, and the volatiles again removed to give orangish-brown solids.
Detailed NMR and characterization data for these compounds
are given in the Experimental section. X-ray quality crystals could
not be grown of either (PhPNPiPr)-containing complex (9 or 11);
however, gradual deposition at -30 ◦C from a concentrated diethyl
ether solution of the (PhPNPCy)-containing 10 did produce high-
1
quality orangish-brown crystals. The 31P{ H} NMR of 10 exhibits
The two nickel PNP-based hydrides 7 and 8 were first in-
vestigated in these oxygen reactions. Compounds 7 and 8 were
each treated with O2 at 70 psig (4.76 atm.) in toluene-d8 and an
immediate color change from brown to green was noted. These
complexes reacted much faster with O2 than the Pd RPNPR¢-based
a pair of doublets at 54.5 ppm (JPP = 354.5 Hz, –PCy2) and
31.5 ppm (JPP = 354.5 Hz, –PPh2) which showed the characteristic
1
downfield shift from 4. The H NMR spectrum of 10 displays
1
metal hydrides 9 and 10 (vide infra). In the 31P{ H} NMR spectra,
the peaks corresponding to either 7 or 8 disappeared followed
1
by the formation of several new peaks. In the H NMR spectra,
the Ni–H peak disappears with no formation of resonances that
can be confidently assigned to either a Ni–OH or Ni–OOH
species. Attempts to grow crystals of components of the reaction
mixture were unsuccessful. Unfortunately, the formation of a
number of products is reminiscent of our previous work using
RPCP–NiH complexes with O2, in which we observed attack on
and destruction of the R groups of the RPCP-ligand framework,
presumably by highly reactive Ni–OOH species.27
Scheme 4 Preparation of Pd and Pt hydrides using borohydride route.
8954 | Dalton Trans., 2011, 40, 8950–8958
This journal is
The Royal Society of Chemistry 2011
©

The two new Pd-based hydrides 9 and 10 were also examined
using similar conditions. Each compound was treated with O2
under pressure, and after a day the reaction turned from dark
brown to an orange/red solution. As in the Ni–H cases above,
Preparation of PhPNPiPr
1
nBuLi (2.4 mL, 6.03 mmol, 2.5 M in hexane) was added drop-
wise to a solution of bis(2-bromo-4-methylphenyl)amine (1.07 g,
3.02 mmol) in diethyl ether (50 mL) at -35 ◦C. The solution
was allowed to warm to room temperature (RT) and was stirred
for 3 h. The reaction mixture was cooled back to -30 ◦C and
a diethyl ether (5 mL) solution of diisopropylchlorophosphine
(0.460 g, 3.02 mmol) was added dropwise. The reaction mixture
was stirred at RT overnight. The yellow solution was cooled down
1
the 31P{ H} NMR spectrum showed disappearance of the starting
Pd–H complexes and formation of a mixture of new, unidentified
compounds. These new compounds are likely the Pd–OOH and
Pd–OH species, as we have seen these species in our RPCP–
PdH work earlier. The 1H NMR spectrum of each reaction
also showed disappearance of the respective Pd–H resonance.
Unfortunately, despite much effort, single crystals suitable for
X-ray diffraction analysis could not be isolated for any of these
presumed hydroperoxides or hydroxides.
The platinum PhPNPiPr-based hydride 11 was also treated with
O2 under identical conditions as above. The NMR tubes were
pressurized with 70 psig (4.76 atm.) of O2 in toluene-d8 with
no immediate color change observed. The system was closely
monitored over several days with no change in the color in either
solution, nor in the NMR chemical shifts of the Pt–H complex.
The lack of reactivity with O2 is likely attributable to the stronger
M–H bond strength of Pt relative to Pd.
◦
n
to -35 C and BuLi (0.71 mL, 1.76 mmol, 2.5 M in hexane)
was added dropwise. The solution was stirr◦ed at RT for 3 h. The
reaction mixture was cooled down to -35 C and a diethyl ether
(5 mL) solution of diphenylchlorophosphine (0.390 g, 1.76 mmol)
was added dropwise. The reaction mixture was stirred at RT
R
overnight, filtered through Celiteꢀ filter aid, and evaporated to
dryness under reduced pressure, resulting in an orange residue.
The orange residue was dissolved into diethyl ether (20 mL) and
5 mL of degassed deionized water was added. The solution was
then dried with MgSO4, filtered through Celite, and evaporated
to dryness under reduced pressure resulting in an orange oil. The
oil was dissolved into a solution of diethyl ether and layered with
pentane (3 : 1) and cooled to -35 ◦C. This resulted in an off-white
1
solid of 1 (0.590 g, 39%). H NMR (C6D6, 250.13 MHz): d 7.66
Conclusions
(dd, 1H, JHP = 10.51 and JHP = 3.25, NH), 7.49 (dt, 4H, Ar) 7.40
(dd, 1H, Ar) 7.24 (dd, 1H, Ar), 7.09 (m, 7H, Ar), 6.90 (m, 3H, Ar),
2.16 (s, 3H, Ar–Me), 1.96 (s, 3H, Ar–Me), 1.88 (m, 2H, CHMe2),
In this submission we report the synthesis and characterization
of two new unsymmetrically-substituted examples of the RPNPR¢
pincer ligands based on the bis(tolyl)amine backbone which
should prove useful to a wide range of chemists. The coordination
chemistry of these unsymmetric ligands has been demonstrated
via the preparation of Group 10 metal halides and hydrides.
While the Pd(II) and Pt(II) hydrides were prepared via borohydride
reduction of the metal halide complexes, the Ni hydrides were
prepared using direct interaction of the ligands with a Ni(0)
precursor. Full characterization of these products, including X-
ray crystallography, is reported. Lastly, the Group 10 hydrides
were treated with gaseous oxygen in attempts to isolate metal
hydroperoxides. Unfortunately, only mixtures of products were
obtained and individual products could not be isolated.
1.02 (dd, 6H, CHMe2), 0.88 (dd, 6H, CHMe2). 31P{ H} NMR
1
(C6D6, 101.26 MHz): d -14.5 (bs, PiPr2), -16.5 (d, JPP = 8.10,
1
PPh2). Observable 13C{ H} NMR (C6D6, 62.89 MHz): d 147.7 (d,
JCP = 19.0, C), 144.9 (d, JCP = 19.9, C), 136.9 (d, JCP = 11.1, C),
134.7 (s, CH), 134.3 (d, JCP = 19.9, CH), 133.7 (s, CH), 131.3 (s,
CH), 130.7 (d, JCP = 7.4, CH), 128.8 (s, CH), 128.7 (s, CH) 122.1
(d, JCP = 15.7, C), 119.7 (s, CH), 116.9 (s, CH), 23.6 (d, JCP = 11.1,
CHMe2), 20.9 (s, Ar–Me), 20.8 (s. Ar–Me) 20.5 (d, JCP = 19.0,
CHMe2), 19.3 (d, JCP = 9.2, CHMe2). Anal. Calcd for C32H37NP2:
C, 77.24; H, 7.49; N, 2.81. Found: C, 77.49; H, 7.85; N, 2.68.
Preparation of PhPNPCy
2
nBuLi (8.15 mL, 20.37 mmol, 2.5 M in hexane) was added
dropwise to a solution of bis(2-bromo-4-methylphenyl)amine
(3.62 g, 10.19 mmol) in diethyl ether (80 mL) at -5 ◦C. The
solution was stirred at RT for 3 h. The reaction mixture was
cooled down to -35 ◦C and a diethyl ether (5 mL) solution of
dicyclohexylchlorophosphine (2.37 g, 10.19 mmol) was added
dropwise. The reaction mixture was stirred at RT overnight.
The yellow solution was cooled down to -30 ◦C and nBuLi
(4.08 mL, 10.19 mmol, 2.5 M in hexane) was added dropwise.
The solution was stirred◦at RT for 3 h. The reaction mixture
was cooled down to -35 C and a diethyl ether (5 mL) solution
of diphenylchlorophosphine (2.25 g, 10.19 mmol) was added
dropwise. The reaction mixture was stirred at RT overnight,
filtered through Celite, and evaporated to dryness under reduced
pressure resulting in an orange residue. The orange residue was
redissolved into diethyl ether (20 mL) and 5 mL of degassed DI
water was added. The solution was dried with MgSO4, filtered
through Celite, and evaporated to dryness under reduced pressure
resulting in an orange oil. The orange oil was redissolved into a
solution of diethyl ether and layered with pentane (1 : 3) and cooled
Experimental
General procedures
All procedures and manipulations were carried out under argon
using an MBRAUN glove box or by standard Schlenk techniques.
All solvents used were of high purity (anhydrous) or were dried
by using standard methods. All reagents were purchased from
Acros, Aldrich, Alfa Aesar, or Strem and were used as received.
The starting bis(2-bromo-4-methylphenyl)amine was prepared ac-
cording to the literature procedure.25 NMR spectra were obtained
at room temperature on a Bruker AMX 250 MHz spectrometer or
on a Bruker AC 250 MHz spectrometer with a Tecmag MacSpect
upgrade. All chemical shifts are reported in (d) ppm with 1H and
13C spectra referenced to tetramethylsilane or to their respective
residual solvent peaks. 31P NMR spectra were referenced externally
using 85% H3PO4 at d 0 ppm. All coupling constants are given
in Hz. Elemental analyses were performed by Columbia Analytical
Services of Tucson, AZ.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8950–8958 | 8955
©

to -35 ◦C. This resulted in an off-white solid of 2 (1.92 g, 33%). 1H
NMR (C6D6, 250.13 MHz): d 7.70 (dd, 1H, JHP = 10.13 and JHP
133.9 (d, JCP = 30.1, CH), 132.5 (s, CH), 131.4 (dd, JCP = 43.0 and
JCP = 3.8, C), 130.6 (s, CH), 129.0 (s, CH), 128.8 (d, JCP = 5.0, CH),
126.9 (JCP = 6.0, CH), 126.3 (d, JCP = 6.8, CH), 121.3 (d, JCP = 47.5,
=
3.25, NH), 7.49 (m, 5H, Ar) 7.28 (m, 2H, Ar), 7.11 (m, 6H, Ar),
6.91 (m, 3H, Ar), 2.18 (s, 3H, Me), 1.96 (s, 3H, Me), 1.88–1.38
C), 119.5 (d, JCP = 40.0, C), 117.0 (d, JCP = 12.8, CH), 116.5 (JCP
=
1
(m, Cy), 1.38–0.95 (m, Cy). 31P{ H} NMR (C6D6, 101.26 MHz):
14.3, CH), 34.4 (d, JCP = 21.3, CH), 28.7 (s, CH2), 28.3 (s, CH2),
27.1 (s, CH2), 27.0 (s, CH2), 25.8 (s, CH2), 20.4 (s, Ar–Me), 20.0
(s, Ar–Me). Anal. Calcd for C38H44ClNP2Pd: C, 63.51; H, 6.17; N,
1.95; Found: C, 63.14; H, 6.16; N, 1.87.
1
d -16.5 (d, JPP = 7.7, PPh2), -23.5 (bs, PCy2). Observable 13C{ H}
NMR (C6D6, 62.89 MHz): d 148.0 (d, JCP = 19.0, C), 144.1 (d,
JCP = 19.5, C), 137.1 (d, JCP = 10.6, C), 134.7 (s, CH), 134.4 (d,
JCP = 19.9, CH), 134.0 (s, CH), 131.4 (s, CH), 130.7 (d, JCP = 7.9,
CH), 128.8 (s, CH), 128.7 (s, CH) 121.8 (d, JCP = 16.2, C), 119.5
(s, CH), 116.9 (s, CH), 33.6 (d, JCP = 11.6, CH), 30.9 (JCP = 17.6,
CH2), 29.2 (d, JCP = 7.4, CH2), 27.4 (d, JCP = 12.5, CH2), 27.3 (d,
JCP = 7.4, CH2), 26.8 (s, CH2), 21.0, (s, Ar–Me), 20.9 (s, Ar–Me).
Anal. Calcd for C38H45NP2: C, 79.00; H, 7.85; N, 2.42; Found: C,
78.82; H, 7.93; N, 2.22.
Preparation of (PhPNPiPr)PtCl 5
PhPNPiPr (1) (0.093 g, 0.190 mmol) and (COD)PtCl2 (0.070 g,
0.190 mmol) were placed into a round bottom flask along with
20 mL of THF and one equiv. of NEt3. The yellow solution was
refluxed for 2.5 h, filtered through Celite, and the volatiles were
removed under reduced pressure resulting in a yellow solid. The
solid was washed with cold pentane and dried under vacuum to
give 5 (0.102 g, 75%). A single crystal suitable for X-ray diffraction
analysis was grown from the slow evaporation of a benzene
Preparation of (PhPNPiPr)PdCl 3
PhPNPiPr (1) (0.051 g, 0.180 mmol) and (COD)PdCl2 (0.089 g,
0.180 mmol) were placed into a round bottom flask along with
20 mL of THF and one equiv. of NEt3. The red solution was
refluxed for 1 h, filtered through Celite, and the volatiles were
removed under reduce pressure, resulting in a red solid. The red
solid was washed with cold pentane and dried under vacuum to
give 3 (0.110 g, 96%). A single crystal suitable for X-ray diffraction
analysis was grown from the slow evaporation of a benzene
1
solution at room temperature. H NMR (C6D6, 250.13 MHz):
d 8.00 (m, 4H, Ar), 7.78 (dd, 1H, Ar) 7.68 (dd, 1H, Ar) 6.99 (m,
8H, Ar), 6.78 (td, 2H, Ar), 2.52 (m, 2H, CHMe2), 2.13 (s, 3H, Ar–
Me), 1.94 (s, 3H, Ar–Me), 1.43 (dd, 6H, CHMe2), 1.08 (dd, 6H,
1
CHMe2). 31P{ H} NMR (C6D6, 101.26 MHz): d 43.7 (d, JPPt
=
=
2754.5 and JPP = 401.6, PiPr2), 24.7 (d, JPPt = 2673.9 and JPP
1
401.9, PPh2). Observable 13C{ H} NMR (C6D6, 62.89 MHz): d
162.0 (d, JCP = 18.1, C), 161.6 (d, JCP = 20.4, C), 135.1 (s, CH),
134.0 (d, JCP = 10.6, CH), 132.6 (d, JCP = 45.3, C), 132.4 (s, CH),
131.6 (d, JCP = 52.1 and JCP = 3.0, C), 130.6 (s, CH), 128.9 (s, CH),
1
solution at room temperature. H NMR (C6D6, 250.13 MHz):
d 7.96 (m, 4H, Ar), 7.78 (dd, 1H, Ar) 7.68 (dd, 1H, Ar) 6.99
(m, 7H, Ar), 6.78 (td, 3H, Ar), 2.28 (m, 2H, CHMe2), 2.11 (s,
3H, Ar–Me), 1.91 (s, 3H, Ar–Me), 1.43 (dd, 6H, CHMe2), 1.07
128.7 (s, CH), 127.3 (s, CH), 126.7 (d JCP = 6.8, CH), 121.5 (d, JCP
=
1
(dd, 6H, CHMe2). 31P{ H} NMR (C6D6, 101.26 MHz): d 54.0 (d,
55.8, C), 119.5 (d, JCP = 48.3, C), 116.8 (d, JCP = 11.3, CH), 116.4
(JCP = 12.1, CH), 25.3 (d, JCP = 28.0, CHMe2), 20.3 (s, Ar–Me),
20.0 (s, Ar–Me), 18.4 (s, CHMe2), 17.9 (s, CHMe2). Anal. Calcd
for C32H36ClNP2Pt: C, 52.86; H, 4.99; N, 1.93; Found: C, 52.46;
H, 5.14; N, 1.71.
1
JPP = 437.2, PiPr2), 25.7 (d, JPP = 437.2, PPh2). Observable 13C{ H}
NMR (C6D6, 62.89 MHz): d 161.8 (d, JCP = 20.4, C), 161.5 (d, JCP
=
25.1, C), 135.2 (s, CH), 134.0 (d, JCP = 12.1, CH), 133.1 (s, CH),
132.5 (s, CH), 131.5 (d, JCP = 43.1 and JCP = 3.7, C), 130.5 (s, CH),
129.0 (s, CH), 128.8 (s, CH), 126.9 (d, JCP = 7.0, CH), 126.3 (d
JCP = 7.0, CH), 121.3 (d, JCP = 46.5, C), 119.2 (d, JCP = 39.4, C),
Preparation of (PhPNPCy)PtCl 6
116.9 (d, JCP = 13.0, CH), 116.5 (JCP = 14.3, CH), 25.2 (d, JCP
21.3, CHMe2), 20.4 (s, Ar–Me), 20.2 (s, Ar–Me), 18.8 (d, JCP
=
=
PhPNPCy (2) (0.056 g, 0.096 mmol) and (COD)PtCl2 (0.036 g,
0.096 mmol) were placed into a round bottom flask along with
20 mL of THF and one equiv. of NEt3. The yellow solution
was refluxed for 2.5 h, filtered through Celite, and the volatiles
were removed under reduced pressure resulting in a yellow solid.
The yellow solid was washed with cold pentane and dried under
vacuum to give 6 (0.067 g, 87%). A single crystal suitable for
X-ray diffraction analysis was grown from the slow evaporation
of a benzene solution at room temperature. 1H NMR (C6D6,
250.13 MHz): d 8.03 (m, 4H, Ar), 7.90 (dd, 1H, Ar) 7.81 (dd,
1H, Ar) 6.97 (m, 8H, Ar), 6.75 (td, 2H, Ar), 2.15 (s, 3H, Ar–
3.7, CHMe2), 18.1 (s, CHMe2). Anal. Calcd for C32H36ClNP2Pd:
C, 60.20; H, 5.68; N, 2.19; Found: C, 60.55; H, 5.69; N, 2.08.
Preparation of (PhPNPCy)PdCl 4
PhPNPCy (2) (0.191 g, 0.330 mmol) and (COD)PdCl2 (0.094 g,
0.330 mmol) were placed into a round bottom flask along with
20 mL of THF and one equiv. of NEt3. The red solution was
refluxed for 1 h, filtered through Celite, and the volatiles were
removed under reduced pressure resulting in a red solid. The red
solid was washed with cold pentane and dried under vacuum to
give 4 (0.129 g, 84%). A single crystal suitable for X-ray diffraction
analysis was grown from the slow evaporation of a benzene
1
Me), 1.93 (s, 3H, Ar–Me), 2.60–0.99 (m, 22H, Cy). 31P{ H} NMR
(C6D6, 101.26 MHz): d 36.2 (d, JPPt = 2749.2 and JPP = 402.4,
PCy2), 24.4 (d, JPPt = 2673.0 and JPP = 402.3, PPh2). Observable
1
1
solution at room temperature. H NMR (C6D6, 250.13 MHz): d
13C{ H} NMR (C6D6, 62.89 MHz): d 162.0 (d, JCP = 17.4, C),
8.00 (m, 4H, Ar), 7.83 (dd, 1H, Ar) 7.74 (dd, 1H, Ar) 6.99 (m, 8H,
161.6 (d, JCP = 19.6, C), 135.1 (s, CH), 134.0 (d, JCP = 10.6, CH),
132.7 (d, JCP = 52.0, C), 132.6 (s, CH), 132.3 (s, CH2), 131.7 (d,
JCP = 53.6, C), 130.6 (s, CH), 128.9 (s, CH), 128.7 (s, CH), 127.3
(d, JCP = 7.5, CH), 126.8 (d, JCP = 6.7, C), 121.5 (d, JCP = 55.8,
C), 119.7 (d, JCP = 46.0, C), 116.9 (d, JCP = 10.6, CH), 116.4
(JCP = 11.3, CH), 34.7 (d, JCP = 27.9, CH), 28.4 (s, CH2), 28.3 (d,
Ar), 6.77 (td, 2H, Ar), 2.13 (s, 3H, Ar–Me), 1.91 (s, 3H, Ar–Me),
1
2.48–0.91 (m, 22H, Cy). 31P{ H} NMR (C6D6, 101.26 MHz): d
46.5 (d, JPP = 437.5, PCy2), 25.7 (d, JPP = 437.4, PPh2). Observable
1
13C{ H} NMR (C6D6, 62.89 MHz): d 162.0 (d, JCP = 20.4, C),
161.6 (d, JCP = 25.7, C), 135.2 (s, CH), 134.0 (d, JCP = 11.3, CH),
8956 | Dalton Trans., 2011, 40, 8950–8958
This journal is
The Royal Society of Chemistry 2011
©

JCP = 6.3, CH2), 27.2 (s, CH2), 27.0 (d, JCP = 6.2, CH2), 26.1 (s, CH2),
20.4 (s, Ar–Me), 20.0 (s, Ar–Me). Anal. Calcd for C38H44ClNP2Pt:
C, 56.54; H, 5.49; N, 1.74; Found: C, 56.98; H, 6.35; N, 1.98.
brown solid. The brown solid was dried under vacuum to give
9 (0.081 g, 84%). H NMR (C6D6, 250.13 MHz): d 7.96 (m, 2H,
Ar), 7.83 (m, 4H, Ar) 6.98 (m, 8H, Ar), 2.05 (m, 2H, CHMe2),
1
2.21 (s, 3H, Ar–Me), 2.00 (s, 3H, Ar–Me), 1.22 (dd, 6H, CHMe2),
1
0.90 (dd, 6H, CHMe2) -9.97 (vt, 1H, JHP = 5.25, Pd–H). 31P{ H}
Preparation of (PhPNPiPr)NiH 7
NMR (C6D6, 101.26 MHz): d 63.4 (d, JPP = 354.2, PiPr2), 31.4 (d,
JPP = 354.3, PPh2).
PhPNPiPr (1) (0.103 g, 0.160 mmol) and Ni(COD)2 (0.160 mL,
0.160 mmol) were placed into a round bottom flask along with
20 mL of benzene and stirred at RT for 15 min. The volatiles were
removed under reduced pressure, resulting in a brown residue.
The brown residue was washed with cold pentane and dried under
vacuum to give 7 as a brown solid (0.081 g, 84%). A single crystal
suitable for X-ray diffraction analysis was g◦rown from the slow
evaporation of a diethyl ether solution at -30 C. 1H NMR (C6D6,
250.13 MHz): d 7.95–7.75 (m, 6H, Ar), 7.10–6.85 (m, 10H, Ar)
2.05 (m, 2H, CHMe2), 2.21 (s, 3H, Ar–Me), 2.02 (s, 3H, Ar–Me),
Preparation of (PhPNPCy)PdH 10
(PhPNPCy)PdCl (4) (0.100 g, 0.140 mmol) and Super-Hydride
solution (0.140 mL, 0.140 mmol) were placed into a round bottom
flask along with 20 mL of THF and stirred at RT for 3 h. The
volatiles were removed under reduced pressure, resulting in a
brown residue. The brown residue was redissolved into pentane
and filtered through Celite, again resulting in a brown solution.
The volatiles were removed under reduced pressure to give a brown
solid. The brown solid was dried under vacuum to give 10 (0.083 g,
87%). A single crystal suitable for X-ray diffraction analysis was
grown from the slow evaporation of a diethyl ether solution at
-30 ◦C. 1H NMR (C6D6, 250.13 MHz): d 7.99 (m, 4H, Ar), 7.90–
7.75 (m, 2H, Ar), 7.14–6.86 (m, 10H, Ar), 2.23 (s, 3H, Ar–Me),
1.23 (dd, 6H, CHMe2), 0.95 (dd, 6H, CHMe2) -18.1 (dd, 1H, JHP
=
68.4 and JHP = 58.9, Ni–H). 31P{ H} NMR (C6D6, 101.26 MHz): d
1
58.9 (d, JPP = 244.2, PiPr2), 31.4 (d, JPP = 244.1, PPh2). Observable
1
13C{ H} NMR (C6D6, 62.89 MHz): d 161.4 (dd, JCP = 21.4 and
JCP = 3.5, C), 160.9 (dd, JCP = 25.1 and JCP = 2.3, C), 134.5 (s, CH),
133.8 (d, JCP = 12.5, CH), 133.0 (s, CH), 132.5 (s, CH), 130.0 (s,
CH), 128.6 (d, JCP = 9.9, CH), 128.5 (s, CH), 124.6 (d, JCP = 7.0,
2.16 (s, 3H, Ar–Me), 2.01–0.95 (m, 22H, Cy), -9.91 (vt, 1H, JHP
=
=
1
4.75, Pd–H). 31P{ H} NMR (C6D6, 101.26 MHz): d 54.5 (d, JPP
C), 124.5 (d, JCP = 42.3, C), 124.1 (d, JCP = 5.4, CH), 122.5 (d, JCP
=
34.2, C), 115.6 (d, JCP = 10.8, CH), 115.0 (JCP = 11.1, CH), 23.7
(d, JCP = 25.7, CHMe2), 20.5 (s, Ar–Me), 20.3 (s, Ar–Me), 19.5 (d,
JCP = 5.7, CHMe2), 18.3 (s, CHMe2). Anal. Calcd for C32H37NP2Ni:
C, 69.09; H, 6.70; N, 2.52; Found: C, 69.27; H, 6.88; N, 2.27.
354.5, PCy2), 31.5 (d, JPP = 354.5, PPh2).
Preparation of (PhPNPiPr)PtH 11
(PhPNPiPr)PtCl (5) (0.043 g, 0.060 mmol) and Super-Hydride
solution (0.060 mL, 0.060 mmol) were placed into a round bottom
flask along with 20 mL of THF and stirred at RT for 2 h. The
volatiles were removed under reduced pressure resulting in a brown
residue. The brown residue was redissolved into pentane and
filtered through Celite to again give a brown solution. The volatiles
were removed under reduced pressure, resulting in a brown solid.
The brown solid was dried under vacuum to give 11 (0.035 g, 85%).
1H NMR (C6D6, 250.13 MHz): d 8.05–7.71 (m, 6H, Ar), 7.11–6.96
(m, 10H, Ar), 2.13 (m, 2H, CHMe2), 2.11 (s, 3H, Ar–Me), 2.00 (s,
3H, Ar–Me), 1.18 (dd, 6H, CHMe2), 0.93 (dd, 6H, CHMe2), -11.6
Preparation of (PhPNPCy)NiH 8
PhPNPCy (2) (0.100 g, 0.104 mmol) and Ni(COD)2 (0.140 mL,
0.140 mmol) were placed into a round bottom flask along with
20 mL of benzene and stirred at RT for 15 min. The volatiles
were removed under reduced pressure resulting in a brown solid.
The brown solid was washed with cold pentane and dried under
vacuum to give 8 as a brown solid (0.083 g, 87%). 1H NMR (C6D6,
250.13 MHz): d 8.00–7.78 (m, 6H, Ar) 7.14–6.85 (m, 10H, Ar),
2.22 (s, 3H, Ar–Me), 2.02 (s, 3H, Ar–Me), 2.22–0.85 (m, Cy),
-18.15 (dd, JHP = 58.9 and JHP = 68.4, Ni–H). 31P{ H} NMR
1
1
(vt, 1H, JHP = 14.1 and JHPt = 1031.8, Pt–H). 31P{ H} NMR (C6D6,
101.26 MHz): d 59.8 (d, JPPt = 2860.3 and JPP = 361.4, PiPr2), 34.5
(d, JPPt = 2824.0 and JPP = 361.3, PPh2).
(C6D6, 101.26 MHz): d 49.6 (d, JPP = 244.9, PCy2), 31.8 (d, JPP
=
1
244.2, PPh2). Observable 13C{ H} NMR (C6D6, 62.89 MHz): d
161.6 (dd, JCP = 21.9 and JCP = 3.6, C), 160.9 (dd, JCP = 25.3 and
JCP = 2.4, C), 134.4 (s, CH), 133.8 (d, JCP = 12.4, CH), 132.7 (d,
JCP = 31.0, CH), 132.4 (s, CH), 129.9 (s, CH), 128.8 (s, CH), 128.6
(s, CH), 124.6 (d, JCP = 6.1, C), 124.6 (d, JCP = 42.0, C), 124.2 (d,
JCP = 5.4, CH), 122.6 (d, JCP = 34.3, C), 115.6 (d, JCP = 10.4, CH),
115.1 (JCP = 11.7, CH), 33.3 (d, JCP = 26.0, CH), 29.8 (d, JCP = 4.1,
CH2), 28.6 (s, CH2) 27.4 (s, CH2), 27.0 (s, CH2), 26.6 (s, CH2), 20.6
(s, Ar–Me), 20.3 (s, Ar–Me).
Reactions of (PhPNPR¢)MH with O2
An approximate 0.04 mmol sample of the metal hydride 7, 8, 9, 10,
or 11 was placed into a medium-walled NMR tube fitted with a J.
Young valve. Approximately 0.6 mL of C7D8 was added to dissolve
the metal hydride. The sample was degassed using several freeze-
pump-thaw cycles, and then pressurized to 70 psig (4.76 atm.) O2
for 30 min. The tube was shaken several times during this period.
The reaction progress was monitored by 31P and 1H NMR spectra
taken during the reaction. The tube was then placed in a -35 ◦C
freezer in order to attempt to isolate the crystallized product(s).
Preparation of (PhPNPiPr)PdH 9
R
(PhPNPiPr)PdCl (3) (0.103 g, 0.160 mmol) and Super-Hydrideꢀ
solution (LiEt3BH in THF, 0.160 mL, 0.160 mmol) were placed
into a round bottom flask with 20 mL of THF and stirred at RT for
5 h. The volatiles were removed under reduced pressure, resulting
in a brown residue. The brown residue was redissolved into pentane
and filtered through Celite resulting in a brown solution. The
volatiles were removed under reduced pressure, resulting in a
X-ray data collection
Data for X-ray crystallographic determination were collected and
solved with the assistance of Dr. Diane Dickie of the University of
New Mexico. Crystallographic data were collected on a Bruker X8
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 8950–8958 | 8957
©

APEX CCD-based X-ray diffractometer using monochromated
3 M. Albrecht and G. van Koten, Angew. Chem., Int. Ed., 2001, 40,
3750–3781.
4 M. E. van der Boom and D. Milstein, Chem. Rev., 2003, 103, 1759–1792.
5 J. T. Singleton, Tetrahedron, 2003, 59, 1837–1857.
6 D. Benito-Garagorri and K. Kirchner, Acc. Chem. Res., 2008, 41, 201–
213.
7 A. M. Winter, K. Eichele, H.-G. Mack, S. Potuznik, H. A. Mayer and
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3682.
˚
Mo-Ka radiation (l = 0.71073 A). The single crystals were coated
in oil (Paratone-NTM) and mounted on nylon cryoloops (Hampton
Research). Bruker APEX2 was used to collect and process the
data.28 The structures were solved by either the direct or Patterson
method with XSHEL and were refined by full matrix least-
squares method on F2 with SHELXTL.29 All non-hydrogens were
refinedanisotropically and hydrogen atoms were fixed atcalculated
geometric positions with the exception of hydrogens attached to
metals. All H atoms were refined in calculated positions with the
exception of the M–H bonds in 7 and 10. We initially allowed the
hydrogen attached to the metal atom to vary in position. However,
when doing this, two large residual electron density peaks appeared
11 B. L. Tran, D. Adhikari, H. Fan, M. Pink and D. J. Mindiola, Dalton
Trans., 2010, 39, 358–360.
˚
at a distance of approximately 0.8–0.9 A from the metal. We believe
12 M. Ohff, A. Ohff, M. E. van der Boom and D. Milstein, J. Am. Chem.
Soc., 1997, 119, 11687–11688.
that the large residual electron density is likely due to the Fourier
series truncation effect because of a lack of collected data as the
two residual electron density peaks are located on a symmetry
axis containing the metal atoms.30 To solve this issue, we initially
13 O. V. Ozerov, C. Guo, L. Fan and B. M. Foxman, Organometallics,
2004, 23, 5573–5580.
14 O. V. Ozerov, C. Guo, V. A. Papkov and B. M. Foxman, J. Am. Chem.
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15 A. S. Goldman, A. H. Roy, Z. Huang, R. Ahuja, W. Schinski and M.
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16 A. T. Radosevich, J. G. Melnick, S. A. Stoian, D. Bacciu, C.-H. Chen,
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9214–9221.
˚
constrained the Ni–H bond length to be 1.50 A, and the Pd–H
˚
bond length to be 1.7 A and then allowed the M–H bond to vary
during refinement. The value of the M–H bond lengths resulting
˚
˚
from this model treatment at 1.95(3) A for 7 and 1.55(3) A for 10,
within the range seen earlier for other M–H bonds. SQUEEZE
in PLATON was used to treat disordered solvent molecules.31
Crystallographic figures were generated using Diamond 3.1g.32
All crystallographic data are located in Tables 1 and 2.
17 L.-C. Liang, P.-S. Chien and P.-Y. Lee, Organometallics, 2008, 27, 3082–
3093.
18 P.-Y. Lee and L.-C. Liang, Inorg. Chem., 2009, 48, 5480–5487.
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21 A. Mrutu, K. I. Goldberg and R. A. Kemp, Inorg. Chim. Acta, 2010,
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Acknowledgements
This work was financially supported by the Department of
Energy via a grant (DE-FG02-06ER15765) to RAK and KIG.
The Bruker X-ray diffractometer was purchased via a National
Science Foundation CRIF:MU award to the University of New
Mexico (CHE-0443580). We thank Dr. Diane Dickie of UNM for
assistance with the X-ray data analysis. Sandia is a multiprogram
laboratory operated by Sandia Corporation, a Lockheed Martin
Company, for the United States Department of Energy under
Contract No. DE-AC04-94AL85000.
22 G. R. Fulmer, W. Kaminsky, R. A. Kemp and K. I. Goldberg,
Organometallics, 2011, DOI: 10.1021/om101150.
23 M. C. Denney, N. A. Smythe, K. L. Cetto, R. A. Kemp and K. I.
Goldberg, J. Am. Chem. Soc., 2006, 128, 2508–2509.
24 J. M. Keith, R. P. Muller, R. A. Kemp, K. I. Goldberg, W. A. Goddard
III and J. Oxgaard, Inorg. Chem., 2006, 45, 9631–9633.
25 H. Gilman and E. A. Zuech, J. Org. Chem., 1961, 26, 3481–3484.
26 B. J. Boro, R. Lansing, K. I. Goldberg and R. A. Kemp, Inorg. Chem.
Comm., 2011, DOI: 10.1016/j.inoche.2011.1001.1014.
27 B. J. Boro, Ph.D Dissertation, University of New Mexico,
2009.
28 Bruker APEX2, (2007) Bruker AXS, Inc., Madison, Wisconsin, USA.
29 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
A64, 112–122.
30 P. Muller, ed., Crystal Structure Refinement: A Crystallographer’s Guide
to SHELXL, Oxford University Press, New York, 2006.
31 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
32 K. Brandenburg, Diamond, (1999) Crystal Impact GbR, Bonn, Ger-
many.
Notes and references
1 C. J. Moulton and B. L. Shaw, J. Chem. Soc., Dalton Trans., 1976,
1020–1024.
2 D. Morales-Morales, and C. Jensen, ed., The Chemistry of Pincer
Compounds, Elsevier Science, Amsterdam, 2007.
8958 | Dalton Trans., 2011, 40, 8950–8958
This journal is
The Royal Society of Chemistry 2011
©