Reactions of cyclopalladated complexes with HPPh2resulting in ligand phosphination

Article abstract of DOI:10.1016/j.jorganchem.2016.12.023

Reactions of a dinuclear chloro-bridged cyclopalladated complex (CPC) derived from N,N-dimethylbenzylamine with HPPh₂under a variety of conditions resulted in the phosphination of the cyclopalladated ligand. The best yield (77%) of the reaction product, ortho-(diphenylphosphino)-N,N-dimethylbenzylamine, was achieved using 4.5 equiv. of HPPh₂in toluene in the presence of Cs₂CO₃at 40?°C. The scope of the reaction was explored with a range of enantiopure and achiral C,N, C,S and C,P CPCs having either five- or six-membered rings and containing either an sp²or sp³C[sbnd]Pd bond. The corresponding N,P, S,P, and P,P ligands or their oxides were isolated in 30–70% yields. Reactions of HPPh₂in toluene with CPCs derived from D-camphor methyloxime and 2-tert-butyl-4,4-dimethyl-2-oxazoline provided unique mononuclear Pd(II) complexes with a terminal PPh₂ligand in 16 and 52% yield, respectively. Structures of all new compounds were supported by¹H,¹³C{¹H}, DEPT,³¹P{¹H}, and 2D NMR spectra.

Full text of DOI:10.1016/j.jorganchem.2016.12.023

Journal of Organometallic Chemistry 830 (2017) 155e166
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactions of cyclopalladated complexes with HPPh2 resulting in ligand
phosphination
Jonathan E. Kukowski, Valeria A. Stepanova 1, Irina P. Smoliakova*
Department of Chemistry, University of North Dakota, Grand Forks, ND 58202-9024, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of
a dinuclear chloro-bridged cyclopalladated complex (CPC) derived from N,N-dime-
Received 26 November 2016
Received in revised form
15 December 2016
Accepted 20 December 2016
Available online 23 December 2016
thylbenzylamine with HPPh2 under a variety of conditions resulted in the phosphination of the cyclo-
palladated ligand. The best yield (77%) of the reaction product, ortho-(diphenylphosphino)-N,N-
dimethylbenzylamine, was achieved using 4.5 equiv. of HPPh2 in toluene in the presence of Cs2CO3 at
40 ꢀC. The scope of the reaction was explored with a range of enantiopure and achiral C,N, C,S and C,P
CPCs having either five- or six-membered rings and containing either an sp2 or sp3CePd bond. The
corresponding N,P, S,P, and P,P ligands or their oxides were isolated in 30e70% yields. Reactions of HPPh2
in toluene with CPCs derived from D-camphor methyloxime and 2-tert-butyl-4,4-dimethyl-2-oxazoline
provided unique mononuclear Pd(II) complexes with a terminal PPh2 ligand in 16 and 52% yield,
respectively. Structures of all new compounds were supported by 1H, 13C{1H}, DEPT, 31P{1H}, and 2D NMR
spectra.
Keywords:
Cyclopalladated complex
Reactions at the CePd bond
Phosphination
Diphenylphosphine
CeH functionalization via palladacycles
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
planar-chiral phosphine-oxazolines from
a
paracyclophane-
derived mononuclear CPC and KPPh2 [4c]. Our group has studied
the influence of LiPPh2 preparation method on reactions with a
dimeric N,N-dimethylbenzylamine-derived CPC [4d]. We have also
reported the reaction of sp2CePd CPCs with KPPh2 to give corre-
sponding N,P, S,P, P,P and S,P,S ligands [4e,4f], an approach that we
later extended to sp3CePd CPCs [4g].
The use of HPPh2 in phosphination reactions with CPCs is ad-
vantageous because of its low cost. Additionally, the solvent choice
is much broader than for metal phosphides due to low solubility of
KPPh2 and variability of LiPPh2 aggregate structure, a significant
factor in the product distribution [4d]. HPPh2 has been used in a
variety of CeP coupling reactions involving palladium catalysts.
These are predominantly hydrophosphination transformations
using either HPPh2 or its phosphine-borane analog with activated
alkenes [6] or alkynes [7]. Pd-catalyzed substitution reactions have
The broad variety and undeniable significance of Pd-catalyzed
transformations in organic synthesis make studies of stoichio-
metric reactions at the CePd bond of cyclopalladated complexes
(CPCs) important, as they may provide insight on mechanisms of
the related catalytic processes [1,2]. Cyclopalladation followed by
reaction at the CePd bond is also an attractive two-step method for
regioselective ligand functionalization, especially in cases where
alternative methods are problematic or do not exist [3]. The
introduction of a phosphino group to cyclopalladated ligands with
an amino or other donor moiety [4] results in the formation of
aminophosphines or related N,P and S,P bidentate hemilabile li-
gands. Metal complexes of such difunctional compounds are effi-
cient catalysts in a variety of transformations [5].
Several studies have been reported involving CPCs as reactants
in phosphination reactions. A dinuclear chloro-bridged CPC derived
from N,N-dimethylaminomethylferrocene has been reacted with
lithium phosphides (LiPAr1Ar2) to obtain the corresponding ami-
nophosphines [4a,4b]. Bolm et al. have described the preparation of
been reported for vinyl halides [8], triflates [9], and a-amido enol
phosphates [10], as well as functionalized aryl (pseudo)halides [11]
and compounds containing allylic hydroxy, alkoxy, or acyloxy
groups [12].
Here we report the reactions of HPPh2 with dimeric chloro-
bridged C,N, C,S and C,P CPCs {[Pd(
m
-Cl)(
k
2-C,E)]2 (E ¼ N, S or P)}
containing either an sp2 or sp3CePd bond to give corresponding N,P,
S,P and P,P bidentate ligands including amino-, pyridinyl-, oxazo-
linyl-, oximo-, and sulfidophosphines as well as diphosphines
* Corresponding author.
E-mail address: irina.smoliakova@UND.edu (I.P. Smoliakova).
Present address: Department of Chemistry and Biochemistry, University of
1
Wisconsin La Crosse, La Crosse, WI 54601, USA.
http://dx.doi.org/10.1016/j.jorganchem.2016.12.023
0022-328X/© 2016 Elsevier B.V. All rights reserved.

156
J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
(Scheme 1).
2. Results and discussion
2.1. Reactions of dimeric chloro-bridged CPCs with HPPh2
Our initial work involved reactions of the dinuclear CPC 1
derived from N,N-dimethylbenzylamine with HPPh2 in THF at rt
(Scheme 2). Experiments were carried out in THF using two reagent
ratios: the stoichiometric 1:2 ratio required for the formation of
aminophosphine 2 and a 1:4.5 ratio to determine the effect of
excess HPPh2. The resulting mixtures were quite complex; how-
ever, the desired aminophosphine 2 was isolated from all reactions
in yields of 10e35% depending on the reagent ratio and reaction
time (1e18 h). The best yield of compound 2, 35%, was obtained
using a 1:4.5 reagent ratio (Table 1, entry 4).
In our studies of reactions between CPCs and metal phosphides,
we determined that these transformations are affected by solvent
coordinating properties and polarity [4d]. Therefore, the non-
coordinating solvent toluene was used to compare results with
those from reactions in THF. While reactions in THF provided the
product using either of the two reagent ratios, the aminophosphine
formation in toluene occurred only with 4.5 equiv. of HPPh2, giving
the highest isolated yield of 40%. Likewise for the 1:4.5 reactions in
THF, the highest yield of 2 in PhMe was obtained after 18 h (Table 1,
entry 7). When the optimal conditions for THF and toluene at rt
were used in the reaction with CH2Cl2 as the solvent, 2 was isolated
with a similar yield of 37% (entry 9).
Next, the temperature was varied. In our previous investigation
involving reactions of CPCs with KPPh2 [4e], we reported that lower
temperatures favor the formation of palladium coordination com-
plexes and disfavor the formation of the desired aminophosphine.
The same trend was observed for reactions with HPPh2. Increasing
the temperature to 40 ꢀC and then 80 ꢀC gave comparably higher
yields of the aminophosphine. However, palladium black appeared
on the flask when the temperature was raised to 100 ꢀC and none of
the product was isolated.
We investigated the effect of several bases on the reaction
outcome. The results are summarized in Table 2. Compared to re-
actions without a base, the use of the mild NaOAc slightly improved
yields of aminophosphine 2 when the temperature and solvent
were kept similar (entries 1e3). The use of the stronger K2CO3
further increased the product yield to 70%. However, when K3PO4
was used, the aminophosphine yield dropped to 33%. The highest
yield (77%) of aminophosphine 2 was achieved using Cs2CO3 in
PhMe at 40 ꢀC. The product yield decreased when either higher
temperatures or shorter reaction times were used. Replacement of
Cs2CO3 with a more soluble base, NaOSiMe3, furnished the desired
aminophosphine in 4 and 26% yield at 40 and 80 ꢀC, respectively
(entries 17 and 18).
Scheme 2. Reactions of CPCs 1 and 3 with HPPh2.
Table 1
Reagent molar equiv. and solvent effect at rt.
Entry
HPPh2, equiv.
Solvent
Time, h
Yield of 2, %
1
2
3
4
5
6
7
8
9
2
2
THF
THF
1.5
3
33
10
21
35
0
16
40
0
4.5
4.5
2
4.5
4.5
9
THF
THF
1.5
18
18
1
18
18
18
PhMe
PhMe
PhMe
PhMe
CH2Cl2
4.5
37
Table 2
Base effect in reactions of CPC 1 with 4.5 equiv. of HPPh2.
Entry
Base
Solvent
T, ꢀC
Time, h
Yield of 2, %
1
2
3
NaOAc
NaOAc
NaOAc
K2CO3
K2CO3
K2CO3
PhMe
PhMe
CH2Cl2
PhMe
PhMe
PhMe
CH2Cl2
PhMe
PhMe
THF
PhMe
PhMe
CH2Cl2
PhMe
PhMe
PhMe
PhMe
PhMe
rt
18
18
18
18
18
18
18
18
18
1.5
18
18
18
18
4
56
67
68
70
43
35
56
33
0
40
40
40
40
60
40
40
rt
40
40
40
40
80
40
40
40
80
4
5a
6
7
8
K2CO3
K3PO4
9b
10b
11
12a
13
14
15
16
17
18
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
NaOSiMe3
NaOSiMe3
NaOSiMe3
9
77
60
61
45
39
0
4
18
18
4
26
a
The m-OAc analog of CPC 1 was used as the starting material.
2 equiv. of HPPh2 were used.
b
bridged dimeric CPC 1 was converted to the corresponding
mononuclear adduct using two equivalents of PPh3. Next, the PPh3
adduct was reacted with 4.5 equiv. of HPPh2 in toluene at 40 ꢀC in
the presence of 9 equiv. of Cs2CO3. Although the formation of
aminophosphine 2 was observed, the compound was isolated in
only 40% yield. This result suggests that the use of PPh3 is not ad-
vantageous for the synthesis of P-containing bidentate ligands us-
ing HPPh2, possibly due to competition from the alternative
phosphorus nucleophile in coordinating to the Pd center.
In our studies of reactions between CPCs and metal phosphides,
we preferred dimeric complexes, while the Sokolov and Bolm
groups used mononuclear CPCs with PPh3 as an auxiliary ligand. In
the present study, we also investigated whether a mononuclear
derivative of CPC 1 is capable of reacting with HPPh2. The chloro-
After determining optimal conditions for the reaction of com-
plex 1 with HPPh2, we investigated the reactant scope. First, (S,S)-
CPC 3, an optically active a-methyl-substituted analog of CPC 1, was
tested (Scheme 1). By performing the reaction in toluene at 80 ꢀC
instead of the optimal 40 ꢀC for CPC 1, the yield of compound 4 was
nearly doubled from 37 to 70%.
It is noteworthy that enantiopure aminophosphine 4, also
known as (S)-AMPHOS, is an efficient ligand in asymmetric metal-
catalyzed hydroxylations of prochiral carbonyl compounds [13].
Scheme 1. Reaction of [Pd(
m
-Cl)(
k
2-C,E)]2 (E ¼ N, S or P) with HPPh2.

J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
157
There are a few methods for the synthesis of aminophosphine 4, its
HPPh2.
achiral analog 2 and related benzylamine-derived N,P ligands
[5a,14]. The most common approach is lithiation with n-BuLi fol-
lowed by treatment with ClPPh2. This approach allows preparation
of 2 in 35e90% [15]. For comparison, the reaction of CPC 2 with
KPPh2 provided 63% of aminophosphine 4 [4f].
CPCs 5, 7, and 10 were likewise reacted with HPPh2 at either 40
or 80 ꢀC in toluene to give corresponding P,P, S,P, and N,P ligands
(Scheme 3). Only traces of diphosphine monoxide 6 were isolated
unless the crude mixture was deliberately exposed to air before
purification. Similarly, the reaction of complex 7 also gave the
corresponding phosphine oxide in addition to the desired S,P ligand
after exposure to air during purification. By contrast, the pyridine-
based six-membered C,N CPC 10 reacted to give novel amino-
phosphine 11 in good yield despite the low solubility of the starting
complex.
To the best of our knowledge, there are only two papers
describing preparation of either [2-(diphenylphosphino)benzyl]
diphenylphosphine, its monoxide 6, the corresponding dioxide or a
phosphine-borane adduct. The Ghosh group used a multistep
approach with a key reaction being the borophosphorylation of [2-
(bromomethyl)phenyl]diphenylphosphine oxide using n-BuLi/
Ph2P(BH3)H [16]. The other method, reported by our group, fur-
nished the diphosphine dioxide in 35% and is based on the reaction
of CPC 5 with KPPh2 [4f]. Using the same method, we also reported
the preparation of compound 8 in 51% yield. Likewise, Salmeia et al.
synthesized the compound in 40% yield by lithiation of (2-
bromobenzyl)methylsulfide with n-BuLi followed by treatment
with ClPPh2 [17].
While introduction of the PAr2 group to an aromatic ring is
usually accomplished via the lithiation of appropriate substrates,
the basic method for the formation of an sp3CeP bond is the SN2
reaction of a metal phosphide with alkyl halides or related com-
pounds having good leaving groups [5a]. Recently, we reported a
method for sp3CeP bond formation using KPPh2 reactions with
CPCs having an sp3CePd bond [4g]. Based on the results of that
study, we predicted that phosphination of cyclopalladated ligands
at an sp3-hybridized carbon could also be accomplished using
The previously reported [18] C,N CPC 12 derived from 2-tert-
butyl-4,4-dimethyl-2-oxazoline was chosen as a model compound
to determine the optimal conditions for phosphination reactions
leading to the formation of an sp3CeP bond. The complex reacted
with HPPh2 in the presence of Cs2CO3 in toluene at 40 ꢀC; however,
no signals of free iminophosphine 13 were detected in the 31P{1H}
NMR spectrum of the crude mixture. Instead, complexes 14 and 15
were isolated in 24 and 52% yield, respectively (Scheme 4). After
varying reaction conditions (Table 3), the best yield of iminophos-
phine 13, 56%, was obtained using 9 equiv. of HPPh2 in CH2Cl2 at
35 ꢀC (entry 7).
In another attempt to increase the yield of the products and
render the reaction more selective, the phosphination was per-
formed at rt with 4.5 equiv. of HPPh2 and in the presence of pyri-
dine, which can act both as a ligand and a base. Complex 14 was
found to be the major product with no free iminophosphine 13
formed. When the temperature was increased to 40 ꢀC,
m-Cl-m-PPh2
complex 14 was isolated in 27% yield along with 5% of compound 15
(Scheme 5). When 2 equiv. of both pyridine and HPPh2 were used,
complex 14 was obtained in 40% yield. Signals belonging to com-
plex 15 and the free iminophosphine were not detected in the 31P
{1H} NMR spectrum of the crude mixture.
Complex 14 was previously reported as a product in the re-
actions of CPC 12 with KPPh2 [4g]. The structure of the novel
complex 15 was determined by using 1H, 13C{1H}, DEPT, 31P{1H} and
2D NMR spectroscopy. According to the NMR data, compound 15
contains a C,N cyclopalladated ligand of the starting reagent 12,
iminophosphine 13 as a monodentate auxiliary ligand, and a ter-
minal PPh2 ligand. The presence of two PPh2 groups in the complex
and their cis geometry are supported by the presence of two dou-
blets in the 31P{1H} NMR spectrum at
d 7.8 and 116.8 ppm with
coupling constant 2JPP ¼ 38 Hz [19]. The signal at
d 116.8 ppm was
assigned to the PPh2 ligand; the low-field position of the doublet
suggests non-bridging coordination of this ligand to the metal [20].
The cis position of the CH2 fragment of the cyclopalladated ligand
and the terminal PPh2 ligand in complex 15 is suggested based on
the transphobia concept [21]. There are several reports of
Scheme 3. Reaction of CPCs 5, 7, and 10 with HPPh2.

158
J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
Scheme 4. Reactions of HPPh2 with CPC 12 having an sp3CePd bond.
Table 3
providing phosphine oxides 17 and 19 in 60% yield (Scheme 6).
Our group has previously reported the preparation of CPC 20
derived from the O-methyloxime of L-fenchone [25] and its sub-
sequent reaction with KPPh2 at rt in THF [4g]. In those reactions, the
corresponding free N,P ligand 21 was isolated in 51% yield whereas
the reaction with 9 equiv. of HPPh2 in CH2Cl2 at 35 ꢀC gave an
improved 65% yield (Scheme 7).
We have also previously reported the preparation of CPC 22
derived from the O-methyloxime of D-camphor [26] and its re-
actions with KPPh2 [4g], furnishing the corresponding free N,P
ligand (23) in 21% yield while its oxide (24) was not isolated. By
contrast, in reactions of complex 22 with 9 equiv. of HPPh2 in the
Yields of compounds 13e15 depending on the condition used.
Entry
HPPh2, equiv.
Solvent
T, ꢀ
C
Time, h
Yield, %
13
14
15
1
2
3
4
5
6
7
8
9
4.5
4.5
9
9
9
4.5
9
4.5
2
PhMe
PhMe
PhMe
PhMe
PhMe
CH2Cl2
CH2Cl2
THF
40
80
rt
40
80
35
35
40
40
18
18
48
18
18
18
18
18
18
0
24
0
0
0
0
0
0
0
52
29
33
15
18
18
0
18
13
15
25
18
56
0
15
14
THF
0
14
Scheme 5. Reaction of CPC 12 with HPPh2 in the presence of pyridine at 40 ꢀC for 18 h.
mononuclear Pd(II) complexes containing a terminal phosphido
group. Zhuravel et al. and Mazzeo et al. have reported complexes in
which the PePd bond was stabilized by intramolecular chelation of
the ligand [19c,20]. Madadi et al. have recently reported disilyl- and
dibenzoylphosphido complexes of type PdI(i-Pr2-bimy)2PR2 and
PdI(n-Bu2-bimy)2PR2, which are stabilized by the presence of N-
heterocyclic carbene ligands [22]. Moncarz et al. as well as Pican
and Gaumont isolated phosphido-borane complexes with the
structure Pd(L)(Ar)P(BH3)R1R2 (L ¼ diphos or another P,P or P,N
presence of Cs2CO3 in CH2Cl2 (both at rt and 35 ꢀC) no signal of the
N,P ligand was observed in 31P{1H} NMR spectra of the crude
mixtures or isolated fractions. When the optimized conditions for
the phosphination of CPC 1 were used, the major product was
found to be the unique Pd(II) complex 25. The compound contains a
terminal PPh2 group, a chloride ligand, and an N,P ligand. The 1H
NMR spectrum provided evidence that the NOMe group in the
cyclopalladated ligand was converted to NOH, with the oxime
signal appearing at 9.02 ppm. The 31P{1H} NMR spectrum of the
complex contained two doublets with a rather small coupling
constant (12.2 Hz), suggesting the cis position of two P atoms
(Scheme 8) [4e]. An interesting feature of the 13C{1H} NMR spec-
trum is the long-range coupling observed between the terminal
phosphido group and C3 of the camphor bicycle (4JCP ¼ 4.8 Hz).
HRMS data confirmed the presence of a cation corresponding to
complex 25 minus a chloride ion. The proposed structure was
further supported by testing the substance for halides using AgBF4,
ligand) [23]. Mononuclear k-PPh2 Pd(II) complexes were proposed
as intermediates in Pd-catalyzed phosphination reactions [24], but
they have not been isolated to our knowledge.
To examine the reactivity of other aliphatic CPCs, complexes 16
and 18 containing benzylic CePd bonds were reacted with 9 equiv.
of HPPh2 in CH2Cl2 at 35 ꢀC. In both cases, partial oxidation of the
ligand was observed. The crude mixtures were therefore oxidized
prior to purification either with 30% H2O2 or by exposure to air

J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
159
Scheme 6. Reactions of complexes 16 and 18 with HPPh2.
The yields of N,P ligands 13, 21 and 23 as well as the phosphine
oxide 17 (30e65%) obtained in this study were consistently higher
than those reported for the related KPPh2 reactions with CPCs
having an sp3CePd bond [4g]. It is noteworthy that the alternative
method for the phosphination of the alkyl fragment, based on the
SN2 reaction of alkyl halides with metal phosphides, was success-
fully used for preparation of enantiopure phosphino-oxazolines
[27]. However, a major obstacle to the generality of this method
for preparation of bidentate hemilabile ligands is the need for
regioselective halogenation of the alkyl moiety before the phos-
phination step.
Scheme 7. Reaction of CPC 20 with HPPh2 to form product 21.
2.2. Mechanistic considerations
We suggest that the first step of the reaction between HPPh2 and
complex [Pd(m
-Cl)LC]2 (structure A in Scheme 10 where LC is a
cyclopalladated ligand) is the formation of the corresponding
mononuclear CPC, PdClLC(HPPh2) (B). The 31P{1H} NMR spectra of
the 1:2.5 and 1:4.5 mixtures of CPC 12 and HPPh2 in toluene-d8
(recorded at 20 ꢀC after freezing to ꢁ95 ꢀC) contained a prominent
signal at
d
ꢁ1.2 ppm. We assigned this signal to the P atom of HPPh2
in PdClLC(HPPh2) (LC ¼ cyclopalladated 2-tert-butyl-2,2-dimethyl-
2-oxazoline). Although there are several known Pd(II) complexes
with HPPh2 as a terminal ligand [19b,25,28], to the best of our
knowledge, there has been only one report of an analogous C,N
cyclopalladated complex [29]. Díez et al. described the preparation
and spectral characterization of an HPPh2 adduct of benzo[h]
quinoline-derived CPC PdCl(bzqC)(HPPh2). The reported 31P NMR
data of the complex include the chemical shift, 20.2 ppm, and the
Scheme 8. Reaction of CPC 22 with HPPh2 furnishing complex 25.
after which a precipitate was observed.
In an attempt to free the N,P ligand from coordination with
palladium, the workup was altered by addition of 1,2-
bis(diphenylphosphino)ethane at the end of the reaction; howev-
er, this was not effective. A series of experiments were then per-
formed where one parameter of the reaction conditions was
changed: different temperatures (rt, 40 ꢀC, and 80 ꢀC), solvents
(toluene, CH2Cl2, and THF), and molar equivalents of HPPh2 (3.2,
3.9, 4.5, and 9) were explored. However, the free N,P ligand was not
isolated in any of these experiments with only one exception. At rt
with 9 equiv. of HPPh2 in toluene, oximophosphine 23 was ob-
tained in 21% yield along with the oxidized analog 24 (9%, Scheme
9). Noteworthy, the N,P ligand was not isolated from reactions in
toluene using the same ratio of reactants at 40 ꢀC and 80 ꢀC.
coupling constant, JPH ¼ 376 Hz. In non-decoupled 31P NMR
1
spectra of CPC 12/HPPh2/Cs2CO3 reaction mixtures, the proposed
complex PdClLC(HPPh2) (LC ¼ cyclopalladated 2-tert-butyl-2,2-
dimethyl-2-oxazoline) gave a broad doublet with a coupling con-
stant 1JPH ¼ 375 Hz.
Díez et al. also prepared the Pt analog PtCl(bzqC)(HPPh2), which
was converted to [Pt(
By analogy, we suggest that in the presence of Cs2CO3 or another
base, complexes of type B undergo a transformation to [Pd( -PPh2)
LC]2 (C, Scheme 10). Previously, we showed that in the presence of
chloride ions, the diphosphido-bridged complex [Pd(
-PPh2)LC]2
(C) derived from 2-tert-butyl-4,4-dimethyl-2-oxazoline is
m
-PPh2)(bzqC)]2 in the presence of K2CO3 [29].
m
m

160
J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
Scheme 9. Preparation of compounds 23 and 24.
Scheme 10. Proposed mechanism of N,P ligand formation by reaction of CPC with HPPh2.
converted to the corresponding mono-chloro-mono-phosphido-
bridged analog, LCPd( -Cl)PdLC (D), and a small amount
-PPh2)(
of the trinuclear complex LCPd( -Cl)PdLC
-PPh2)( -Cl)Pd( -PPh2)(
without prior coordination to palladium. This is supported by the
fact that the 31P NMR spectra of HPPh2 with or without Cs2CO3 are
identical.
m
m
m
m
m
m
[4g]. So, it is reasonable to suggest that CPC/HPPh2/Cs2CO3 reaction
The last step of the phosphination reaction is expected to be
reductive elimination. The isolation of Pd(HPPh2)4 (see our X-ray
data for this complex in the Supporting Information; the crystal-
lographic structure of this compound was previously reported by
Leoni et al. [31]) from a reaction mixture of CPC 1 with 4.5 equiv. of
HPPh2 in the presence of Cs2CO3 supports reductive elimination of
Pd(0)Ln from a Pd(II) intermediate. The formation of this and other
Pd(0) species containing HPPh2 as a ligand may explain why an
excess of the reactant is needed. In general, all complexes having a
PPh2 ligand cis to a CePd bond (e.g., compounds CeF) could be
considered as species that potentially undergo reductive
mixtures should also contain complexes of type D (Scheme 10) and
possibly trinuclear derivatives LCPd(
m
-PPh2)(
PdLC (the latter complex is not shown).
In the presence of an additional 2 equiv. of HPPh2, complex
[Pd(
-PPh2)LC]2 (C) is expected to give PdLC(k¸ -PPh2)(HPPh2) (E),
whereas LCPd( -Cl)PdLC provides two complexes, E and B
-PPh2)(
m-Cl)Pd(m-PPh2)(m-Cl)
m
m
m
(Scheme 10). Complex E may also be formed from its chloro-analog
B in the presence of PPh2 ions or, perhaps more likely, from the
Pd(II) phosphido complexes C and D, since HPPh2 (pKa 22.9 in
DMSO) [30] cannot be deprotonated by Cs2CO3 (HCOꢁ3 has pKa 10.3)

J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
161
elimination. However, there is some indication that the complexes
with a bridging PPh2 ligand, C and D, are unlikely to go through
reductive elimination to produce an N,P ligand. In our previous
study [4d], we found that complex D derived from N,N-dime-
thylbenzylamine slowly undergoes reductive PeP coupling in
CH2Cl2 at rt to produce Ph2PꢁPPh2, the mononuclear complex
LPdIICl[PPh2P(O)Ph2] and Pd(0) black. In another study [4g], we
showed that at rt in the presence of chloride ions, two
diphosphido-bridged complexes of type C derived from D-camphor
O-methyloxime and 2-tert-butyl-2,2-dimethyl-2-oxazoline readily
undergo ligand metathesis instead of reductive elimination. Both
types of complexes, C and D, provided N,P ligands only in the
presence of at least one additional equivalent of MPPh2 (M ¼ Li or
K) [4d,4g]. These data suggest that in order to undergo reductive
elimination with the formation of a CeP bond, a Pd(II) complex
should have a terminal rather than bridging phosphido ligand. In
order to have a complex with a terminal PPh2 group, the CPC/
HPPh2/Cs2CO3 reaction mixture must have at least 2 equiv. of HPPh2
per palladium atom. The most plausible intermediate that may
undergo reductive elimination to give CeP coupling appears to be
at ꢁ1.2 ppm, as previously mentioned (Fig. 1). As the samples were
kept at rt, this signal gave way to a singlet at ꢁ1.53 ppm, which was
assigned to the previously reported complex of type D, LCPd(
m-
PPh2)(
m
-Cl)PdLC (LC ¼ cyclopalladated 2-tert-butyl-2,2-dimethyl-2-
oxazoline). Two doublets in the 31P{1H} NMR spectrum (still dou-
blets in the non-decoupled spectrum) were also observed at 79.0
and 70.9 ppm (2JPP ¼ 48 Hz) after 14 h when the molar ratio of
HPPh2 to CPC was 1:4.5. When the ratio was 1:2.5, these signals
were present after 72 h and were still prominent after ten days,
when signals corresponding to free iminophosphine 13 and com-
plex 15 were first observed. The fact that the CeP coupling products
13 and 15 were not detected until after these two doublets were
present suggests that they may belong to a key intermediate from
which reductive elimination occurs. The chemical shift value and
the proximity of the signals at 79.0 and 70.9 ppm suggest that they
belong to similar Pd-bound P-containing groups. The value of the
coupling constant, 48 Hz, points to the cis position of these two
ligands. We propose that these doublets belong to [PdLC( -PPh2)2]ꢁ
k
(LC ¼ cyclopalladated tert-butyl-2,2-dimethyl-2-oxazoline). In the
case of the 1:4.5 ratio of reactants, signals for complex 15 were
present after 18 h at rt, implying that CeP bond formation is faster
with excess HPPh2.
k
[PdLC( -PPh2)2]ꢁ (F, Scheme 10). Related anionic complexes of the
type [PdLC(
k
-OAc)2]ꢁ and [PdLCBr2]ꢁ (where LC is a C,P CPC with a
benzylic sp3CePd bond) have previously been implicated as species
undergoing reductive elimination leading to CeO and CeBr bond
formation [32], respectively.
There is no reason to believe that reductive elimination from
[PdLC( -PPh2)2]ꢁ with an sp2CePd bond takes place through a
k
different route than a traditionally proposed three-membered
In 1:2.5 and 1:4.5 reaction mixtures of CPC 12 and HPPh2 in the
presence of Cs2CO3, initial 31P{1H} NMR spectra of the mixtures
frozen to ꢁ95 ꢀC and recorded at rt contained a broad signal
transition state [33]. To give Pd(0) species, complexes [PdLC(
k-
PPh2)2]ꢁ with an sp2CePd bond may actually have two transition
states, one with Pd, P and C atoms and the other with Pd and two P
Fig. 1. Proton-coupled 31P NMR spectra of CPC 12/HPPh2/Cs2CO3/toluene-d8 reaction mixtures frozen to ꢁ95 ꢀC and kept at rt for: a) 10 min (4.5 equiv. HPPh2), b) 4 h (4.5 equiv.
HPPh2), and c) 10 days (2.5 equiv. HPPh2). (LC ¼ cyclopalladated tert-butyl-2,2-dimethyl-2-oxazoline).

162
J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
atoms, since one of the PPh2 ligands is cis to both C and P atoms.
Interestingly, products of PeP coupling were observed in the ma-
jority of reactions involving CPCs with an sp2CePd bond. Ph2PP(O)
PPh2 was isolated in some of those reactions, and the corre-
and 23), a phosphinosulfide (8) and monooxides of two diphos-
phines (6 and 19) were obtained in 30e77% yield, which is com-
parable to yields reported for preparation of these or similar P-
containing bidentate ligands by other methods. Reactions in
toluene involving CPCs derived from 2-tert-butyl-4,4-dimethyl-2-
oxazoline and D-camphor methyloxime provided unique stable
Pd(II) terminal phosphido complexes 15 and 25. 31P{1H} NMR
monitoring of reaction mixtures of HPPh2 and sp3CePd CPC 12
sponding
adduct
of
the
type
LCPdIICl[PPh2P(O)Ph2]
(LC ¼ cyclopalladated N,N-dimethylbenzylamine) was also obtained
in low yield when NaOSiMe3 was used as a base. However, in the
same reactions of CPCs having an sp3CePd bond, neither Ph2PP(O)
PPh2 nor complexes LCPdIICl[PPh2P(O)Ph2] were isolated or detec-
ted. Thus, in reactions with CPCs containing an sp2CePd bond, PeP
coupling competes with CeP bond formation during the reductive
elimination step. The absence of PeP coupling products in reactions
with CPCs having an sp3CePd bond indicates that the SN2-like
mechanism of the reductive elimination step may be favored over
the concerted pathway involving a three-atom transition state. In
the case of an SN2 mechanism, the PPh2 ion is more likely to attack
the carbon than the phosphorus atom bonded to two bulky phenyl
groups (vide infra).
suggests that the anionic Pd(II) complex [PdLC( -PPh2)2]ꢁ, previ-
k
ously implicated in reactions of LiPPh2 with CPCs, is likely to be a
key intermediate undergoing reductive elimination to form a CeP
bond. The described method offers the possibility of using other
commercially available secondary phosphines for the introduction
of the PR2 (where R s Ph) or PR1R2 moieties to ligands capable of
cyclopalladation, whereas previously reported methods involving
MPR2 require their preparation from other highly air- and
moisture-sensitive compounds. Currently we are studying re-
actions of CPCs with various secondary phosphines and exploring
the possibility of catalytic synthesis of N,P and related hemilabile
bidentate ligands using HPR2.
Little is known about the mechanism of the reductive elimina-
tion step from Pd(II) complexes to give an sp3CꢁE bond, where
E ¼ N, P or O [4g,33,34]. Similar to the sp2CꢁE couplings, concerted
sp3CeN bond formation through a three-membered transition state
has been proposed for the reductive elimination of norbornyl-
amines from alkylpalladium(II) amido complexes [34c]. However,
an SN2-like mechanism for our phosphination reactions cannot be
excluded. The two most probable SN2 pathways include 1) nucle-
ophilic attack by the exogenous PPh2 ion on the sp3-hybridized
carbon bonded to Pd(II) and 2) dissociation of the PPh2 ligand from
a Pd(II) complex, e.g., F, followed by SN2 attack of the phosphide ion
on the carbon.
4. Experimental
4.1. General methods and instrumentation
All reactions of HPPh2 were carried out under an argon atmo-
sphere using Schlenk techniques. Purifications by column chro-
matography were carried out using Natland silica gel 60 (230
mesh). Preparative thin-layer chromatography (TLC) was carried
out using 200 ꢂ 250 mm glass plates with an unfixed layer of
Natland or Merck silica gel 60 (230 mesh). Analytical TLC was
To shed light on possible mechanisms of the reductive elimi-
nation step, three experiments were performed with complex 15,
which has a terminal PPh2 ligand cis to the Pd-bound carbon atom.
The compound was heated for 18 h at 75 ꢀC in acetonitrile, at 80 ꢀC
in toluene in the presence of 4 equiv. of PPh3 as an auxiliary ligand,
and at 80 ꢀC in toluene with 9 equiv. of Cs2CO3 and 4 equiv. of
HPPh2. Only in the latter case did the free iminophosphine form
(NMR data showed >80% conversion), suggesting that either
nucleophilic attack of the exogenous PPh2 ion is required to pro-
duce an sp3CeP bond and/or substitution of the iminophosphine
performed on Whatman silica gel 60 (F254) 250
mm precoated
plates. Compounds were visualized on TLC plates using UV light
(254 nm) and/or iodine stains. Routine 1H (500 MHz), 13C{1H}
(126 MHz) and 31P{1H} (202 MHz) NMR spectra as well as DEPT,
COSY and HSQC spectra were recorded on a Bruker AVANCE 500
NMR spectrometer. Chemical shifts are reported in ppm with SiMe4
as an internal standard (1H and 13C) or P(OEt)3 as an external
standard (31P). Spin-spin coupling constants, J, are given in Hz.
Spectra of the products obtained were recorded in CDCl3 unless
otherwise stated. Melting points were measured on a Laboratory
Devices Mel-Temp apparatus and are uncorrected. Optical rotations
were measured at room temperature on a Rudolph Autopol III
automatic polarimeter or a JASCO P-2000 series digital polarimeter
using a 1-dm tube. Elemental analyses were carried out by Atlantic
Microlabs Inc., Norcross, GA. Mass spectrometry analyses were
conducted on an Agilent 1100 HPLC coupled to a high resolution
Time of Flight MS G1689A Series 6200. Samples were injected
directly to the mass spectrometer. Electrospray ionization was
performed in a positive mode. Drying gas (N2) was set to 350 ꢀC at a
flow rate of 12 L/min and the nebulizer gas (N2) pressure was set to
25 psi. The MS data were acquired in the full scan mass range of
100e1000 m/z.
moiety by PPh2 is necessary to form the [PdLC( -PPh2)2]ꢁ inter-
k
mediate, which then undergoes reductive elimination. The results
of the experiments also show that intramolecular reductive elimi-
nation is unlikely for neutral Pd(II) intermediates with terminal
PPh2 ligands cis to sp3CePd bonds at 75e80 ꢀC in coordinating and
non-coordinating solvents.
The iminophosphine formed as a result of the reductive elimi-
nation step can exist in the reaction mixture as a free ligand or be
coordinated to Pd(0) or Pd(II) to form various complexes. Two
different types of Pd(II) complexes with N,P ligands,15 and 25, were
isolated in our study. It is noteworthy that Pd(0) complexes with
N,P ligands have been reported [35]. For example, Pd(0) complexes
with N,P ligands 2 and 4 were studied by the van Koten group [35g].
Both complexes Pd(2)3 and Pd(4)3 have three ligands coordinated
to the metal through phosphorus atoms.
Benzene, toluene, tetrahydrofuran, and their deuterated analogs
were dried by refluxing over K/benzophenone ketyl, distilled under
Ar, and stored over potassium. Acetone was purified by distillation
over KMnO4. Other solvents were distilled over CaH2. Starting
cyclopalladated complexes were prepared using previously re-
ported methods [18b,25,26,36].
3. Conclusions
A general procedure for the formation of sp2CeP and sp3CeP
bonds using reactions of dimeric dichloro-bridged CPCs with
commercially available and inexpensive HPPh2 has been developed.
The scope of complexes that can be used in the reaction include
five- and six-membered C,N, C,S and C,P palladacycles having either
an sp2 or and sp3CePd bond. Achiral or enantiopure amino- (2 and
4), pyridinyl- (11 and 17), imino- (13), and oximophosphines (21
4.2. Preparation of N,P, S,P, and P,P ligands or their oxides
4.2.1. General procedure for phosphination reactions
The CPC was placed into an Ar-filled 10-mL Schlenk flask with
nine equivalents of Cs2CO3, a rubber septum was inserted, and the

J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
163
2
solvent was introduced by syringe (1 mL per 5 mg of complex,
unless noted otherwise). The flask was lowered into an oil bath
heated to the reaction temperature. Once the CPC was completely
dissolved, HPPh2 was added dropwise for 2 min either as a neat
liquid or as a 1 M toluene solution. The reaction mixture was stirred
in an Ar atmosphere for 18 h. The solvent was removed at reduced
pressure and the crude mixture was separated by preparative thin
layer chromatography on silica gel. Additional experimental details
are described in the Supporting Information.
128.5 (d, JCP ¼ 7, o-PPh), 128.6 (C(6)H of C6H4), 129.1 (C(5)H of
3
C6H4), 130.3 (d, JCP ¼ 5, m-PPh), 133.9 (C(3)H of C5H4N), 134.0 (p-
PPh), 136.1 (d, 1JCP ¼ 12, ipso-PPh), 136.1 (C(4)H of C5H4N), 136.6 (d,
2JCP ¼ 8, quat. C(1) of C6H4), 144.1 (d, 1JCP ¼ 10, quat. C(2) of C6H4),
149.1 (C(6)H of C5H4N), 160.4 (quat. C(2) of C5H4N). 31P{1H} NMR (
d,
ppm): ꢁ29.5. HRMS: [M þ H]þ calcd for C24H21NPþ 354.14116,
found 354.14506.
4.2.6. 2-Methyl-2-(4,4-dimethyloxazolin-2-yl)
propyldiphenylphosphine (13)
4.2.2. ortho-(Diphenylphosphino)benzyldiphenylphosphine
monooxide (6)
Rf 0.61 (6:1 hexaneeethyl acetate). 1H NMR (
d, ppm): 1.17 (s, 6H,
C(CH3)2), 1.30 (s, 6H, NC(CH3)2), 2.43 (d, 2H, 2JHP ¼ 3.6, PCH2), 3.66
Rf 0.27 (10:1 benzeneeacetone). 1H NMR (
d
, ppm): 4.10 (dd, 2H,
(s, 2H, OCH2), 7.29 (br. m, 5H, m- and p-PPh), 7.44 (dt, JHH ¼ 7.5,
3
2JHP ¼ 14.8, 4JHP ¼ 5.1, P(O)CH2), 6.81 (m, 1H, C(6)H arom), 7.07 (m,
4H, o-PPh), 7.11 (m, 1H, C(5)H arom), 7.29 (m, 7H, C(4)H arom, m-
PPh, p-PPh), 7.38 (m, 4H, m-P(O)Ph), 7.47 (m, 2H, p-P(O)Ph), 7.74 (m,
3JHP ¼ 1.4, 4H, o-PPh). 13C{1H} NMR (
d
, ppm): 27.5 (d, JCP ¼ 9.7,
3
C(CH3)2), 28.2 (NC(CH3)2), 36.5 (d, 2JCP ¼ 17.2, PCH2C(CH3)3), 41.1 (d,
1JCP ¼ 16.8, PCH2), 66.8 (NC(CH3)2), 78.7 (OCH2), 128.3 (d, 3JCP ¼ 6.5,
4H, o-P(O)Ph), 7.83 (m,1H, C(3)H arom). 13C{1H} NMR (
d
, ppm): 35.5
m-PPh), 129.1 (p-PPh)), 132.9 (d, JCP ¼ 19.5, o-PPh), 139.6 (d,
2
1
3
3
(dd, JCP ¼ 65.4, JCP ¼ 26.4, P(O)CH2), 127.7 (d, JCP ¼ 2.0, C(5)H
1JCP ¼ 12.6, ipso-PPh), 170.9 (d, 3JCP ¼ 2.2, OC]N). 31P{1H} NMR (
d,
arom), 128.8 (d, 3JCP ¼ 11.7, m-PPh), 128.9 (d, 3JCP ¼ 6.8, m-P(O)Ph),
ppm): ꢁ37.8. HRMS: [M þ H]þ calcd for C21H27NOPþ 340.18303,
4
3
129.1 (p-PPh), 129.7 (d, JCP ¼ 1.9, C(4)H arom), 131.3 (t, JCP ¼ 4.1,
found 340.18302.
2
6
C(3)H arom), 131.7 (dd, JCP ¼ 9.4, JCP ¼ 0.9, o-P(O)Ph), 132.0 (d,
4JCP ¼ 2.6, p-P(O)Ph), 133.0 (d, JCP ¼ 99.4, ipso-PPh), 133.9 (d,
4.2.7. cis-(C,P1)-Diphenylphosphido-[2-methyl-2-(4,4-
dimethyloxazolin-2-yl)propyl-C,N][2-methyl-2-(4,4-
dimethyloxazolin-2-yl)propyldiphenylphosphine-P2]palladium(II)
(15)
1
2JCP ¼ 18.9, o-PPh), 134.7 (C(6)H arom), 136.6 (dd, JCP ¼ 10.1,
2
2JCP ¼ 7.5, quat. C(2) arom), 136.7 (d, JCP ¼ 8.8, quat. C(1) arom),
1
1
137.5 (d, JCP
¼
20.1, ipso-P(O)Ph arom). 31P{1H} NMR
(d,
ppm): ꢁ30.67 (d, 4JPP ¼ 6.0) and 15.43 (d, 4JPP ¼ 6.0). HRMS: [M þ
Mp 154e156 (dec). Rf 0.72 (7:1 benzeneeacetone). 1H NMR (
d,
H]þ calcd for C31H27NPþ 477.1577, found 477.1618.
ppm, C6D6): 0.50 (s, 6H, C(CH3)2), 1.15 (s, 2H, PdCH2C(CH3)2), 1.20 (s,
6H, C(CH3)2), 1.19 (s, 6H, NC(CH3)2), 1.22 (s, 6H, NC(CH3)2), 1.43 (d,
2H, 2JHP ¼ 2.1, PCH2), 3.31 (s, 2H, OCH2), 3.41 (s, 2H, OCH2), 7.01 (2,
2H, 3JHH ¼ 7.5, p-PPh), 7.05 (br. m, 2H, p-PPh), 7.16 (br. m, 4H, o-PPh),
4.2.3. ortho-(Diphenylphosphino)benzylmethylsulfide (8)
Rf 0.82 (benzene). 1H NMR (
d, ppm): 1.99 (s, 3H, CH3), 3.96 (d,
2H, 4JHP ¼ 1.7, CH2), 6.92 (dd, 1H, 3JHH ¼ 7.9, 3JHP ¼ 3.5, C(6)H arom),
7.15 (t, 1H, 3JHH ¼ 7.3, C(5)H arom), 7.28 (m, 4H, o-PPh), 7.33 (br m,
6H, m-PPh and p-PPh), 7.47 (br m, 2H, C(3)H arom and C(4)H arom).
7.23 (dt, 4H, JHH ¼ 7.5, JHP ¼ 1.6, 4H, o-PPh), 8.12 (dt, JHH ¼ 8.6,
3
3
3
2JHP ¼ 1.2, 4H, m-PPh), 8.19 (dt, 3JHH ¼ 8.9, 4JHP ¼ 1.3, 4H, m-PPh). 13
C
{1H} NMR (
d
, ppm, C63D6): 25.57 (C(CH3)2), 26.08 (NC(CH3)2), 27.05
13C{1H} NMR (
d
, ppm): 15.4 (CH3), 36.8 (d, 3JCP ¼ 24.8, SCH2), 127.2
(NC(CH3)2), 28.4 (d, JCP ¼ 9.7, C(CH3)2), 29.8 (CH2PdPPd), 40.4
(C(4)H arom), 128.5 (d, 3JCP ¼ 6.9, m-PPh), 128.6 (d, 1JCP ¼ 23.5, ipso-
(PdCH2C(CH3)3), 40.4 (d, JCP
¼
2.9, PCH2C(CH3)3), 41.8 (d,
2
2
3
PPh), 129.0 (p-PPh), 129.6 (d, JCP ¼ 4.6, quat. C(2) arom), 132.0 (d,
1JCP ¼ 77.3, PCH2), 64.3 (NC(CH3)2), 65.1 (d, JCP ¼ 3.2, NC(CH3)2),
3JCP ¼ 9.6, C(3)H arom), 133.8 (d, 2JCP ¼ 19.8, o-PPh), 134.1 (p-PPh),
136.2 (d, 2JCP ¼ 13.4, C(6)H arom), 136.8 (d, 3JCP ¼ 10.4, C(5)H arom),
79.8 (OCH2), 80.2 (OCH2), 126.0 (p-PPh), 126.1 (d, 3JCP ¼ 2.6, m-PPh),
3
4
127.1 (d, JCP ¼ 2.6, m-PPh), 127.5 (d, JCP ¼ 1.5, p-PPh), 131.1 (d,
2JCP ¼ 11.3, o-PPh), 133.6 (d, 2JCP ¼ 12.7, o-PPh), 142.2 (d, 1JCP ¼ 7.9,
142.8 (d, 1JCP ¼ 24.9, quat. C(1) arom). 31P{1H} NMR (
, ppm): ꢁ31.3.
d
HRMS: [M þ H]þ calcd for C20H20PSþ 323.1028, found 323.1014.
ipso-PPh), 143.4 (d, 1JCP ¼ 55.3, ipso-PPh), 180.4 (OC]N), 183.7 (d,
3JCP ¼ 6.6, OC]N). 31P{1H} NMR (
d
, ppm, C6D6): 7.8 (d, JPP ¼ 38,
2
2
4.2.4. 2-(Diphenyloxophosphino)-1-[(methylthio)methyl]benzene
PdPPh2CH2), 116.8 (d, JPP ¼ 38, PdPPh2). 31P{1H} NMR (
d, ppm,
(9)
CDCl3): ꢁ5.4 (d, 2JPP ¼ 38, PdPPh2CH2), 102.5 (d, 2JPP ¼ 38, PdPPh2).
Anal. calcd for C42H52Cl2N2O2P2Pd2: C, 52.41; H, 5.45; N, 2.91%.
Found: C, 52.02; H, 5.54; N, 2.86%.
Rf 0.29 (5:1 benzeneeacetone). 1H NMR (
d
, ppm): 1.85 (s, 3H,
3
3
CH3), 4.09 (s, 2H, CH2), 7.04 (dd, 1H, JHH ¼ 7.1, JHP ¼ 14.7, C(6)H
arom), 7.18 (t, 1H, 3JHH ¼ 8.2, C(5)H arom), 7.46 (m, 4H, o-PPh), 7.50
(br m, 1H, C(4)H arom), 7.53 (m, 2H, p-PPh), 7.65 (m, 4H, m-PPh),
4.2.8. (1S,4R)-cis-(P,P)-Chloro(diphenylphosphido){1-
[(diphenylphosphino)methyl]-7,7-dimethylbicyclo[2.2.1]heptan-2-
one oxime}palladium (25)
7.74 (dd, 1H, JHH ¼ 8.2, JHP ¼ 4.1, C(3)H arom). 13C{1H} NMR (
d,
3
4
3
ppm): 15.4 (CH3), 36.3 (CH2), 126.2 (d, JCP ¼ 12.6, C(6)H arom),
2
128.6 (d, JCP ¼ 11.9, o-PPh), 130.7 (br s, C(3)H arom), 131.1 (d,
Mp 180e182 (dec). Rf 0.57 (24:1 CH2Cl2eCH3OH). [
a
]
¼ ꢁ133ꢀ
D
1JCP ¼ 10.4, C(5)H arom), 131.5 (d, 2JCP ¼ 7.9, quat. C(2) arom), 131.9
(c 0.165, acetone). 1H NMR (
d
, ppm): 0.66 (ddd, JHH(6exo) ¼ 13.7,
2
4
3
3
(d, JCP ¼ 2.8, p-PPh), 132.0 (d, JCP ¼ 9.7, m-PPh), 132.4 (d,
1JCP ¼ 37.7, ipso-PPh), 133.3 (C(4)H arom.), 133.5 (d, 1JCP ¼ 12.9, quat.
3JHH(5endo) ¼ 9.4, JHH(5exo) ¼ 4.3, 1H, H(6endo)), 0.82 (s, 3H, CH3),
0.83 (s, 3H, CH3), 0.85 (m, 1H, H(6exo)), 1.05 (ddd, 2JHH(5exo) ¼ 13.7,
C(1) arom). 31P{1H} NMR (
d
, ppm): 16.9. HRMS: [M þ H]þ calcd for
3JHH(6endo) ¼ 9.4, JHH(6exo) ¼ 4.2, 1H, H(5endo)), 1.63 (dddd,
3
C
20H20PSOþ 339.0977, found 339.0969.
2JHH(5endo) ¼ 12.1, 3JHH(6exo) ¼ 8.9, 3JHH(6endo) ¼ 4.3, 3JHH(4) ¼ 0.9, 1H,
H(5exo)), 1.88 (dd, 3JHH(5exo) ¼ 7.6, 3JHH(3exo) ¼ 3.5, 1H, H4), 1.94 (d,
2
2
4.2.5. 2-[2-(Diphenylphosphino)benzyl]pyridine (11)
Rf 0.64 (7:1 benzeneeacetone). 1H NMR (
2JHH(3exo) ¼ 18.4, 1H, H(3endo)), 2.04 (dd, JHP ¼ 16.2, JHH ¼ 14.6,
2
2
d
, ppm): 4.45 (d,
1H, PCHA), 2.13 (dd, JHH ¼ 14.6, JHP ¼ 6.9, 1H, PCHB), 2.54 (br d,
2JHH(3endo) ¼ 18.4, 1H, H(3exo), 7.11 (m, 4H, o-PPh), 7.21 (dt,
2JHH ¼ 7.2, 3JHH ¼ 1.3,1H, p-PPh), 7.29 (m, 4H, o- and p-PPh), 7.52 (m,
7H, o-, m-, and p-PPh), 7.76 (m, 2H, m-PPh), 8.18 (m, 2H, m-PPh),
4JHP ¼ 1.6, 2H, CH2), 6.92 (m, 2H, C(3)H of C5H4N and C(3)H of C6H4),
7.00 (ddd, 3JHH ¼ 7.5, 3JHH ¼ 4.7, 4JHH ¼ 1.5, 1H, C(5)H of C5H4N), 7.14
(dt, 3JHH ¼ 7.5, 3JHP ¼ 1.5, 1H, C(3)H of C6H4), 7.27 (br m, 12H, o-, m-,
p-PPh, C(5)H and C(3)H of C6H4), 7.40 (td, 3JHH ¼ 7.5, 4JHH ¼ 1.5, 1H,
9.03 (s,1H, NOH). 13C{1H} NMR (
d, ppm): 19.2 (CH3), 20.0 (CH3), 27.4
H(5) of C5H4N), 8.46 (dd, 3JHH ¼ 4.7, 4JHH ¼ 1.5, 1H, H(6) of C5H4N).
(C(5)H2), 28.6 (d, 1JCP ¼ 24.6, PCH2), 29.4 (C(6)H2), 41.8 (d, 4JCP ¼ 4.8,
3
3
13C{1H} NMR (
d
, ppm): 42.7 (d, JCP ¼ 17, CH2), 121.0 (C(5)H of
C(3)H2), 42.8 (C(4)H), 51.3 (d, JCP ¼ 9.1, quat. C(7)), 57.9 (d,
2
C5H4N), 123.7 (d, JCP ¼ 2, C(3)H of C6H4), 126.8 (C(4)H of C6H4),
2JCP ¼ 1.9, quat. C(1)), 127.0 (ipso-PPh), 127.4 (d, 2JCP ¼ 11.4, o-PPh),

164
J.E. Kukowski et al. / Journal of Organometallic Chemistry 830 (2017) 155e166
2
2
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127.7 (d, JCP ¼ 11.4, o-PPh), 128.0 (d, JCP ¼ 11.4, o-PPh), 129.0 (d,
3JCP ¼ 11.4, o-PPh), 129.3 (d, 4JCP ¼ 2.6, p-PPh), 129.4 (d, 4JCP ¼ 2.6, p-
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3
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tional groups
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[M e Clꢁ]þ calcd for C34H36NOP2Pdþ 642.1301, found 642.1280.
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CPC 12 and 9 equiv. of Cs2CO3 were placed in a J. Young NMR
tube at rt. The tube was vacuumed and filled with Ar 5 times. Under
an Ar atmosphere, degassed toluene-d8 was added. The concen-
tration of CPC solutions was ca. 5 mg/mL. Then the NMR tube was
frozen by placing it in liquid nitrogen. The specified amount of
HPPh2 was added and 31P{1H} NMR spectra were recorded at rt.
c) X.-Y. Yang, Y.-X. Jia, W. Tay, Y. Li, S.A. Pullarkat, P.-H. Leung, Mechanistic
insights into the role of PC- and PCP-type palladium catalysts in asymmetric
hydrophosphination of activated alkenes incorporating potential coordinating
heteroatoms, Dalton Trans. 45 (2016) 13449e13455;
Acknowledgment
d) R.J. Chew, P.-H. Leung, Our odyssey with functionalized chiral phosphines:
from optical resolution to asymmetric synthesis to catalysis, Chem. Rec. 16
(2016) 141e158 and references cited therein;
We would like to acknowledge the University of North Dakota
for financial support. We also would like to thank Victor G. Young,
Jr. and the X-Ray Crystallographic Laboratory in the Department of
Chemistry at the University of Minnesota for elucidation of the
molecular structure of Pd(HPPh2)4. Dr. Alena Kubatova and her
students at the University of North Dakota are also acknowledged
for providing mass spectral data for some of our compounds.
e) C. Baillie, J. Xiao, Catalytic synthesis of phosphines and related compounds,
Curr. Org. Chem. 7 (2003) 477e514 and references cited therein.
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Appendix A. Supplementary data
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