Oxidative ring expansion of a low-coordinate palladacycle: Synthesis of a robust T-shaped alkylpalladium(II) complex

Article abstract of DOI:10.1016/j.ica.2020.119948

The synthesis of an unusual T-shaped alkylpalladium(II) complex featuring a cyclometalated tri-tert-butylphosphineoxide ligand by oxidation of the corresponding cyclometalated tri-tert-butylphosphine complex with PhIO is reported. We speculate that this reaction proceeds by formation of a transient palladium oxo intermediate and there are structural similarities with a late transition metal exemplar: Milstein's seminal pincer ligated Pt(IV) oxo (Nature 2008, 455, 1093–1096).

Full text of DOI:10.1016/j.ica.2020.119948

Inorganica Chimica Acta 513 (2020) 119948
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Oxidative ring expansion of a low-coordinate palladacycle: Synthesis of a
robust T-shaped alkylpalladium(II) complex
⁎
Matthew J.G. Sinclair, Adrian B. Chaplin
Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
A R T I C L E I N F O
A B S T R A C T
Keywords:
The synthesis of an unusual T-shaped alkylpalladium(II) complex featuring a cyclometalated tri-tert-butylpho-
sphineoxide ligand by oxidation of the corresponding cyclometalated tri-tert-butylphosphine complex with PhIO
is reported. We speculate that this reaction proceeds by formation of a transient palladium oxo intermediate and
there are structural similarities with a late transition metal exemplar: Milstein’s seminal pincer ligated Pt(IV) oxo
Palladium
Cyclometallation reactions
Terminal oxo complexes
Low-coordinate complexes
Agostic interactions
(
Nature 2008, 455, 1093–1096).
1
. Introduction
As intermediates in important palladium catalysed organic
transformations, the structure and onward reactivity of low-coordinate
Pd(II) organometallics is of fundamental mechanistic interest [1]. With
direct relevance to C–C cross coupling reactions, the synthesis of
complexes of the form [Pd(PR )(aryl)(halide)] by oxidative addition of
3
aryl halides to palladium(0) precursors is a particularly notable, but not
isolated example [2]. Compared to aryl variants, unsaturated Pd(II)
+
alkyls have proven to be more elusive, with cationic [Pd(PtBu
3
) (Me)]
2
(
A) the most pertinent exemplar to this work [3]. As part of ongoing
work in our laboratories exploring the chemistry of Pd(I) and Pt(I)
metalloradicals [4], we serendipitously discovered that aerobic
oxidation of [Pd(PtBu
3
)
2
][PF ] in the weakly coordinating solvent
6
Scheme 1. Discovery and rational synthesis of cyclometalated Pd(II) complexes
1 and 2.
1
,2-difluorobenzene (DFB) [5] resulted in the consecutive formation of
2
novel cyclometalated Pd(II) complexes [Pd(κP,C-PtBu
PtBu )] (1) and [Pd(κO,C-O]PtBu CMe CH )(PtBu )] (2) as the
major organometallic products on prolonged exposure to air (Scheme 1)
6]. We herein disclose our preliminary investigation of the latter step,
involving ring expansion of a coordinatively unsaturated palladacycle.
2
CMe
2
CH
2
)
+
2
+
(
3
2
2
2
3
F
on a practically useful scale. Isolated 1·BAr
4
is characterised by
3
1
[
NMR spectroscopy in DFB solution by P resonances at δ 57.8 (PtBu )
3
and −0.6 (PtBu
2
), which display diagnostically large trans-phosphine
2
13
J
PP coupling of 317 Hz [8], and a metal alkyl C resonance at δ 26.2
2
2
. Results and discussion
(dd,
J
PC = 23, 3 Hz). The easily handled reagent PhIO was identified
F
as an effective oxidant [9] and enabled quantitative oxidation of 1·BAr
4
F
The identity of
1
was verified by independent synthesis
to 2·BAr
4
within 1 h at RT in DFB (10 eqv PhIO). The product was
F
4
–
F
4
F
as the [BAr
]
salt (1·BAr
; Ar = 3,5-(CF
3
)
2
6
C H
3
), by metathesis
subsequently obtained in 55% isolated yield and fully characterised.
of the previously reported four-coordinate acetate derivative
The formation of 2 is associated with significant downfield shifts of the
2
F
31
[
Pd(κP,C-PtBu
2
CMe
2
CH
2
)(PtBu
3
)(OAc)]·HOAc [7] with Na[BAr
4
] under
P resonances to δ 90.0 (O]PtBu
2
) and 72.6 (PtBu
3
), with no appre-
3
13
biphasic conditions (Scheme 1). This method subsequently proved to be
ciable JPP coupling (< 2 Hz), and a metal alkyl C resonance at δ 38.6
(app. t, 2
JPP = 3 Hz) in DFB solution.
the most expedient method for obtaining analytically pure samples of 1
⁎
Corresponding author.
E-mail address: a.b.chaplin@warwick.ac.uk (A.B. Chaplin).
https://doi.org/10.1016/j.ica.2020.119948
Received 15 June 2020; Received in revised form 27 July 2020; Accepted 5 August 2020
Available online 07 August 2020
0
020-1693/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(
http://creativecommons.org/licenses/by/4.0/).

M.J.G. Sinclair and A.B. Chaplin
Inorganica Chimica Acta 513 (2020) 119948
F
4
F
4
Structural elucidation of 1·BAr
and 2·BAr
using X-ray diffraction
vs 2.020(3) Å cf. 2.029(6) Å in A) and the expected reduction in ring
strain, as gauged by the large increase of the P2/O1–Pd1–C1 angle from
68.2(2) to 87.91(9)° (cf. 91.4(2)/95.1(2)° in A).
was frustrated by whole molecule structural disorder of both the pal-
ladium-based cations and counteranions in the high symmetry P2 3
1
space group. Consequently, single crystalline samples of the corre-
The formation of 2 can be reconciled by idealised mechanisms in-
volving (a) ring strain promoted hemi-labile coordination of the teth-
–
sponding [PF
6
] salts, which can be prepared in a similar manner and
do not suffer from such crystallographic problems, where analysed
ered phosphine or (b) intermediate formation of a palladium oxo de-
F
(
Fig. 1). The solid-state structures of 1·PF and 2·PF are notable for the
6
6
rivative (Scheme 2). In order to probe the former, 1·BAr
4
was reacted
adoption of distorted T-shaped geometries (P2/O1–Pd1–P3 angles >
with 2,6-(tBu
2
PO)
2
C
5
H
3
N (PONOP) at RT in DFB leading to the for-
F
1
70°; cf. 173.40(5)° in A) and an agostic interaction with the PtBu
3
6
mation of 3·BAr
4
by substitution of PtBu
3
, dissociation of the tethered
ligand, with that in 2·PF significantly more pronounced than in 1·PF
6
phosphine donor, and the (unusual) partial chelation of the pincer li-
31
(
Pd1∙∙∙C14 = 2.770(3) vs 2.825(7) Å) and in turn A (2.900(2) Å).
gand; as evidenced by singlet P resonances at δ 182.6, 180.0, and
Transformation from palladacyclobutane to palladacyclopentane is as-
sociated with a marked reduction of the Pd1–C1 bond length (2.075(6)
−12.0 (PtBu
2
) in an integral 1:1:1 ratio, and a doublet of doublets
1
3
2
metal alkyl C resonance at δ 24.2 ( JPC = 70, 34 Hz). Whilst the X-ray
structure of isolated 3 indicates the palladacycle is retained in the solid
state (Fig. 2), the solution-phase behaviour suggests outer-sphere
phosphine oxidation is a viable option. As a gauge for the timescales
associated with such a mechanism, the oxidation of PtBu with PhIO
3
(
t > 9 h) was studied, but the corresponding rate is incongruent with
the formation of 2 under equivalent conditions (t < 1 h). Corre-
spondingly, we favour an inner-sphere explanation, with the formation
of a discrete metal oxo at one extreme and concerted O-atom transfer
into the Pd–P bond at the other [10]. Whilst the formation of terminal
oxo complexes beyond the “oxo wall” between groups 8 and 9 is rare
[
11,12], a directly pertinent platinum example supported by an anionic
PCN pincer ligand has been reported and, moreover, its onward re-
activity involves intramolecular O-atom transfer (B → C, Scheme 2)
[
10]. On this basis, whilst we currently cannot definitively distinguish
between the two possibilities, we postulate a discrete terminal oxo
derivative is involved.
Complex 2 is remarkably stable in solution, with no reaction evident
upon exposure to air for 2 months. Moreover, whilst complete decom-
position of 1 to [Pd(PtBu
3
)
2
], PtBu and palladium black was observed
3
on placing under H in DFB at RT (t < 2 days), 2 persists for > 3 days
2
under the same conditions and only upon heating to 50 °C was any
evidence of a reaction evident.
Fig. 1. Solid-state structures of 1·PF
0% and 50% probability, respectively; minor disordered components and
anions omitted for clarity. Selected bond lengths (Å) and angles (deg): 1·PF
Pd1-P2, 2.2976(11); Pd1-P3, 2.3250(11); Pd1-C1, 2.075(6); Pd1-C14, 2.825(7);
6
and 2·PF
6
. Thermal ellipsoids drawn at
3
6
;
P2-Pd1-P3, 175.38(4); P2-Pd1-C1, 68.2(2); 2·PF
6
; Pd1-O1, 2.093(2); Pd1-P3,
.2387(6); Pd1-C1, 2.020(3); Pd1-C14, 2.770(3); P2-O1, 1.525(2); O1-Pd1-P3,
71.55(5); O1-Pd1-C1, 87.91(9); Pd1-O1-P2, 114.79(10).
2
1
F
Fig. 2. Solid-state structure of 3·BAr
4
. Thermal ellipsoids drawn at 30% prob-
ability; anion omitted for clarity. Selected bond lengths (Å) and angles (deg):
Pd1-P2, 2.2837(7); Pd1-P3, 2.3831(7); Pd1-N13, 2.229(2); Pd1-C1, 2.082(3);
P2-Pd1-N13, 162.56(6); P2-Pd1-C1, 67.40(8); C1-Pd1-P3, 171.23(9).
Scheme 2. Possible reaction mechanisms and associated evidence/precedents.
2

M.J.G. Sinclair and A.B. Chaplin
Inorganica Chimica Acta 513 (2020) 119948
1
3
3
. Conclusions
(HMBC, PdCH
app. t, JPC = 5, PtBu
PC = 4, JPC = 1, PtBu
2
C), 39.8 (dd,
J
PC = 7,
J
PC = 2, PtBu {C}), 38.7
3
2
(
2
{C}), 31.7 (d, JPC = 4, PtBu
2
{Me}), 31.1 (d,
2
4
2
In summary, we report the synthesis of an unusual T-shaped alkyl-
J
3
{Me}), 29.0 (s, Me), 26.2 (dd, JPC = 23,
palladium(II) complex featuring a cyclometalated tri-tert-butylpho-
sphineoxide ligand by oxidation of the corresponding cyclometalated
tri-tert-butylphosphine complex with PhIO. We speculate that this re-
action may include transient formation of a palladium oxo inter-
mediate, however, further work is needed to substantiate this claim.
3, PdCH ).
2
3
1
1
): δ 57.8 (d, 2JPP = 317, 1P,
P{ H} NMR (162 MHz, DFB/C
6 6
D
2
PtBu
3
), −0.6 (d,
J
PP = 317, 1P, PtBu ).
2
Anal. Calcd for C56
H
65BF24
P
2
Pd (1373.28 g mol−1): C, 48.98; H,
4.77; N, 0.00. Found: C, 48.91; H, 4.65; N, 0.00.
4
. Experimental
4.4. Preparation of [Pd(κ P2 ,C-PtBu
2
CMe
2
CH
2
)(PtBu
CH
3
)][PF
6
] 1·PF
6
4.1. General experimental methods
To
a
solution of [Pd(κ P2 ,C‑PtBu
2
CMe
2
2
)(PtBu
3
)(OAc)]·HOAc
(
130.6 mg, 207.9 μmol) in MTBE (5 mL) was added a solution of PtBu
3
All manipulations were performed under an inert atmosphere of argon
in pentane (0.27 mL of a 0.78 M solution, 210 µmol) and the resulting
using Schlenk and glovebox techniques unless otherwise stated. Glassware
was oven dried at 150 °C overnight and flame-dried under vacuum prior to
use. Molecular sieves were activated by heating at 300 °C in vacuo over-
solution was stirred for 5 min at room temperature, before being
transferred onto a 5 mL degassed aqueous suspension of Na[PF ]
6
(35.4 mg, 211 μmol). The biphasic mixture was stirred vigorously for 5
mins and hexane (5 mL) was added. The yellow precipitate was isolated
by filtration and washed with hexane (3 × 5 mL). The product was then
extracted into DFB, precipitated by addition of excess hexane, isolated
by filtration and dried in vacuo. Yield: 78.4 mg (58%). Single crystals
suitable for X-ray diffraction were obtained by slow diffusion of hexane
into a DFB solution at room temperature.
night. CD
2
Cl was dried over activated molecular sieves (3 Å) and stored
2
under an argon atmosphere. 1,2-F
2
C
6
H
4
(DFB) was pre-dried over Al
2
O ,
3
distilled from calcium hydride and dried over two successive batches of 3 Å
molecular sieves under argon. t-Butyl methyl ether (MTBE) was sparged
with argon prior to use. All other anhydrous solvents were purchased from
Aldrich or Acros, freeze–pumpthaw degassed, and stored over 3 Å mole-
2
cular sieves under argon. [Pd(PtBu
3
)
2
][PF
6
] [4a], Pd(κP,C‑PtBu
2
PO)
CMe
2
C
5
CH )
2
3
N
F
1
3
(
PtBu
3
)(OAc)]·HOAc [7], Na[BAr
4
] [13], PhIO [14], 2,6-(tBu
2
2
H
H NMR (300 MHz, DFB/C D ): δ 2.32 (app. t, JPH = 5.7, 2H,
6
6
3
3
(
PONOP) [15] were prepared using literature procedures. All other reagents
PdCH ), 1.38 (d, J = 13.3, 6H, Me), 1.35 (d, J = 14.4, 18H,
2
2
PH
PH
3
are commercially available and were used as received. NMR spectra were
recorded on Bruker spectrometers at 298 K. Chemical shifts are quoted in
ppm and coupling constants in Hz. NMR spectra in DFB were recorded
PtBu ) 1.23 (d,
J
= 12.7, 27H, PtBu ).
PH
3
3
1
1
2
P{ H} NMR (122 MHz, DFB/C D ): δ 57.6 (d,
6
6
J
PP
= 317, 1P,
2
PtBu ), −0.6 (d,
3
J
PP
=
317, 1P, PtBu ), −142.4 (septet,
2
3
1
1
using an internal capillary of C
solution of O]P(OMe) in C
PO ). High resolution (HR) ESI-MS were recorded on a Bruker Maxis Plus
6
6
D
6
.
P NMR spectra are referenced to a
J
= 710, 1P, PF ).
PF
6
−1
3
6
D (0.025 mmol L , δ 3.80 relative to 85%
3
4
4.5. NMR scale reactions of 1·BArF and PtBu3 with PhIO
4
H
spectrometer. Microanalyses were performed at the London Metropolitan
University by Stephen Boyer.
F
4
A suspension of PhIO (22.1 mg, 100 μmol) in a solution of 1·BAr
(
13.9 mg, 10.0 μmol) in DFB (0.5 mL) within a J. Young’s valve NMR
31
4.2. NMR scale reaction of [Pd(PtBu
3
)
2
][PF
6
] with air
tube was monitored by P NMR spectroscopy, with constant mixing at
room temperature when not in the spectrometer. Quantitative conver-
F
A solution of [Pd(PtBu ][PF ] (6.6 mg, 10 μmol) in DFB (0.5 mL)
3
)
2
6
sion to 2·BAr
4
was observed within 1 h.
within an open NMR tube containing an internal sealed capillary of
A suspension of PhIO (22.1 mg, 100 μmol) in a solution of PtBu
3
O]P(OMe)
3
in C
6
D was held at room temperature and monitored
6
(
15 μL of a 0.67 M solution in hexane, 10 μmol) in DFB (0.5 mL) within
31
periodically over 1 month using NMR spectroscopy, topping up with
solvent as necessary to maintain a constant volume. During this
a J. Young’s valve NMR tube was monitored by P NMR spectroscopy,
with constant mixing at room temperature when not in the spectro-
2
+
+
time, the consecutive formation of [Pd(κP,C-PtBu
2
2
2
CMe CH
2
CMe CH
2
)(PtBu
2
)(PtBu
3
3
)]
)]
meter. Quantitative conversion to O]PtBu (δ 64.4 ppm) [16] was
3
2
(
(
δ
57.8 and −0.6) and [Pd(κO,C-O]PtBu
observed within 24 h.
δ 90.0 and 72.6) was observed as the major organometallic products
4
.6. Preparation of [Pd(κ O2 ,C-O]PtBu
2
CMe
2
CH
)(PtBu
2
)(PtBu
3
)][BArF
4
] 2·BArF
4
along with other unidentified species.
.3. Preparation of [Pd(κ 2P ,C-PtBu
)][BArF
] 1·BArF
A suspension of [Pd(κ 2P ,C-PtBu
F
4
2
CMe
2
CH
2
)(PtBu
3
4
4
2
CMe CH
2
2
3
)][BAr
4
] (73.1 mg,
5
3.2 μmol) and PhIO (119.6 mg, 543.4 μmol) in DFB (5 mL) was stirred
To
a
solution of [Pd(κ P2 ,C‑PtBu
2
2
CMe CH
2
)(PtBu )(OAc)]·HOAc
3
for 30 min at room temperature. The solution was filtered into hexane
(20 mL) affording a yellow precipitate that was isolated by filtration,
washed with hexane (3 × 5 mL) and dried in vacuo. Yield: 40.7 mg
(55%). Single crystals suitable for X-ray diffraction were obtained by
slow diffusion of hexane into a DFB solution at room temperature.
(
56.6 mg, 90.1 μmol) in MTBE (5 mL) was added a solution of PtBu
3
in
pentane (0.12 mL of a 0.78 M solution, 94 µmol) and the resulting
solution was stirred at room temperature for 5 min before being
F
transferred onto a 5 mL degassed aqueous suspension of Na[BAr
4
]
(
79.9 mg, 90.2 μmol). The biphasic mixture was stirred vigorously for
1
F
5
min and the organic phase transferred dropwise into excess hexane,
H NMR (500 MHz, DFB/C D ): δ 8.17–8.12 (m, 8H, Ar ), 7.50
6
6
F
3
affording a yellow precipitate that was isolated by filtration and dried in
vacuo. Yield: 63.2 mg (51%). Single crystals suitable for X-ray diffrac-
tion were obtained by slow diffusion of hexane into a DFB solution at
room temperature.
(br, 4H, Ar ), 2.77 (d,
J
=
10.0, 2H, PdCH ), 1.44
PH
2
3
3
(d,
J
PH
= 13.0, 6H, Me), 1.27 (d, JPH = 13.5, 18H, O]PtBu ),
2
3
1.25 (d,
J
PH
= 13.1, 27H, PtBu ).
3
1
F
H NMR (300 MHz, CD Cl ): δ 7.76–7.68 (m, 8H, Ar ), 7.56
2
2
F
3
(
br, 4H, Ar ), 2.83 (d,
J
PH
=
10.1, 2H, PdCH
2
), 1.61
1
F
3
3
H NMR (500 MHz, DFB/C
6
D
6
): δ 8.17–8.12 (m, 8H, Ar ), 7.50 (br,
(d,
J
= 13.0, 6H, Me), 1.48 (app. d,
J
= 13.3, 45H,
PH
PH
F
3
3
4
6
2
H, Ar ), 2.33 (app. t, JPH = 5.7, 2H, PdCH
2
), 1.38 (d, JPH = 13.4,
O]PtBu + PtBu ).
2
3
3
3
13
1
H, Me), 1.35 (d,
J
PH = 14.3, 18H, PtBu
2
), 1.23 (d,
J
PH = 12.7,
C{ H} NMR (126 MHz, DFB/C D selected data only): δ 53.9
6
6,
1
1
7H, PtBu
3
).
(d,
(d,
J
= 53, PdCH C), 39.9 (d,
J
= 14, PtBu {C}), 38.7
PC
PC
2
PC
3
1
3
1
1
2
C{ H} NMR (126 MHz, DFB/C
6
D
6, selected data only): δ 51.9
J
= 47, O]PtBu {C}), 38.6 (app. t,
J
= 3, PdCH ), 30.7
2
PC
2
3

M.J.G. Sinclair and A.B. Chaplin
Inorganica Chimica Acta 513 (2020) 119948
2
2
{Me}), 27.8 (s, Me), 27.5 (s, 2
1.36 (d, 3JPH = 14.2, 18H, PtBu
O), 1.20 (d, 3
JPH = 12.4, 18H,
(
d,
J
PC = 3, PtBu
3
J
PC = 22,
), 72.6
), 73.8
kV) positive ion: 525.2611
O]PtBu
2
{Me}).
PtBu O).
2
3
1
1
13
1
P{ H} NMR (162 MHz, DFB/C
s, 1P, PtBu ).
P{ H} NMR (121 MHz, CD
6
D
6
): δ 90.0 (s, 1P, O]PtBu
2
C{ H} NMR (126 MHz, DFB/C
6
D
6, selected data only): δ 46.0
1
1
(
3
(d,
J
PC = 25, PdCH
2
C), 38.7 (d,
J
PC = 9, PtBu
2
{C}), 38.4
3
1
1
1
2
2
Cl
2
): δ 91.0 (s, 1P, O]PtBu
2
(s, PtBu
2
O{C}), 35.9 (d,
J
PC = 33, PtBu
2
O{C}), 32.0 (d,
J
PC = 3,
2
2
(
s, 1P, PtBu
3
).
PtBu
2
{Me}), 30.8 (d,
J
PC = 5, Me), 27.0 (d,
J
PC = 3, PtBu O
2
2
O{Me}), 24.2 (dd, 2JPC = 70, 34,
HR ESI-MS (MeCN, 180 °C,
4
{Me}), 27.1 (d,
J
PC = 3, PtBu
2
+
(
[M] , calcd 525.2611) m/z.
PdCH ).
2
Pd (1389.33 g mol−1): C, 48.41; H,
31
P{ H} NMR (162 MHz, DFB/C
(s, 1P, PtBu O), −12.0 (s, 1P, PtBu
P{ H} NMR (162 MHz, CD Cl ): δ 182.1 (s, 1P, PtBu
).
kV) positive ion: 706.3263
1
D
): δ 182.6 (s, 1P, PtBu
O), 180.0
Anal. Calcd for C56
H
65BF24OP
2
6
6
2
2
4
.72; N, 0.00. Found: C, 48.29; H, 4.87; N, 0.00.
2
).
3
1
1
2
2
2
O), 178.9
4
.7. Preparation of [Pd(κ O2 ,C-O]PtBu
2
CMe
2
CH
2
)(PtBu
3
)][PF
6
] 2·PF
6
(s, 1P, PtBu
2
O), −12.6 (s, 1P, PtBu
2
HR ESI-MS (MeCN, 180 °C,
4
A suspension of [Pd(κ P2 ,C-PtBu
CMe CH
)(PtBu
([M] calcd 706.3270) m/z.
+
2
2
2
3
6
)][PF ] (61.2 mg,
9
3.4 μmol) and PhIO (620.0 mg, 2.814 mmol) in DFB (5 mL) was stirred
Anal. Calcd for C56
H
78BF24NO
2
P
3
Pd (1570.40 g mol−1): C, 49.68;
vigorously for 15 min at room temperature. The solution was filtered
into hexane (20 mL), affording a yellow precipitate which was isolated
by filtration, washed with hexane (3 × 5 mL) and dried in vacuo.
Analytically pure material was obtained by recrystallisation from di-
chloromethane/hexane. Yield: 6.5 mg (10%). Single crystals suitable
for X-ray diffraction were obtained by slow diffusion of hexane into a
DFB solution at room temperature.
H, 5.00; N, 0.89. Found: C, 49.77; H, 5.01; N, 0.86.
4.10. NMR scale reaction of 2·BArF
with air
4
A solution of 2·BArF
(13.9 mg, 10.0 μmol) in DFB (0.5 mL) within an
4
open NMR tube containing an internal sealed capillary of O]P(OMe)
3
in C
6
D was held at room temperature and monitored periodically
6
over 2 months, topping up with solvent as necessary to maintain a
1
3
31
H NMR (500 MHz, DFB/C
6
D
6
): δ 2.76 (d, JPH = 10.1, 2H, PdCH
2
),
constant volume. No reaction was apparent from analysis by P NMR
3
1
.44 (d,
J
PH
=
).
13.0, 6H, Me), 1.31–1.18 (m, 45H,
spectroscopy.
O]PtBu
2
+ PtBu
3
1
): δ 2.84 (d, 3
4.11. NMR scale reactions of 1·BArF
and 2·BArF
H NMR (500 MHz, CD
2
Cl
2
J
PH = 10.0, 2H, PdCH
2
),
4
4
with H .
2
3
3
1
.62 (d,
J
PH = 13.1, 6H, Me), 1.49 (app. d,
J
PH = 13.3, 45H,
O]PtBu
2
+ PtBu
3
).
Solutions of 1·BArF
4
(13.8 mg, 10.1 μmol) and 2·BAr
F
4
3
1
1
P{ H} NMR (162 MHz, DFB/C
6
D
6
): δ 90.0 (s, 1P, O]PtBu
2
), 72.7
(13.8 mg, 10.0 μmol) in DFB (0.5 mL) within J. Young’s valve
1
(
s, 1P, PtBu
3
), −142.4 (septet,
J
PF = 710, 1P, PF ).
6
NMR tubes (the former containing an internal sealed capillary of
3
1
1
P{ H} NMR (162 MHz, CD
2
Cl
2
J
): δ 89.2 (s, 1P, O]PtBu
2
), 72.0
O]P(OMe)
3
in C
6
D ) were freeze–pumpthaw degassed and placed
6
1
(
s, 1P, PtBu
3
), −144.5 (septet,
PF = 710, 1P, PF
6
).
under an atmosphere of H (1 bar). Reactions were monitored by NMR
2
+
HR ESI-MS (MeCN, 180 °C, 4 kV) positive ion: 525.2605 ([M]
calcd 525.2611) m/z.
spectroscopy, with constant mixing at room temperature when not in
F
the spectrometer. The reaction of 1·BAr
4
with H
2
generated PtBu
3
(
δ 62.9), [Pd(PtBu
3
)
2
] (δ 84.4) and palladium black over 40 h. No re-
was observed after 72 h at room temperature.
.8. NMR scale reaction of 1·BArF
with PONOP
action of 2·BAr
F
with H
4
4
4
2
Subsequent heating at 50 °C, however, resulted in complete
A solution of 1·BArF
(13.8 mg, 10.1 μmol) and PONOP (3.9 mg,
decomposition of 2·BArF
to a palladium mirror within 18 h.
4
4
1
1 μmol; δ 156.0) in DFB (0.5 mL) was prepared in a J. Young’s valve
NMR tube containing an internal sealed capillary of O]P(OMe)
3
in
Declaration of Competing Interest
3
1
C
6
D . Analysis by
6
P NMR spectroscopy after 30 min at room
temperature indicated complete conversion to [Pd(PONOP)
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
(
PtBu
2
CMe
2
CH
2
)][BArF
4
]
(δ 182.6, 180.0 and −12.0) and PtBu
3
(
δ 62.8).
4.9. Preparation of [Pd(PONOP)(PtBu
2
CMe
2
CH
2
)][BArF
4
] 3·BArF
4
Acknowledgements
A solution of [Pd(κ P2 ,C-PtBu
)][BAr
F
] (55.1 mg,
2
2
CMe CH
2
)(PtBu
3
4
We gratefully acknowledge the EPSRC (DTP studentship; M.J.G.S),
University of Warwick, and Royal Society (UF100592, UF150675;
A.B.C.) for financial support. Crystallographic data were collected using
an instrument that received funding from the ERC under the European
Union’s Horizon 2020 research and innovation programme (grant
agreement No 637313).
4
0.0 μmol) and PONOP (15.1 mg, 44.0 μmol) in DFB (2 mL) was stirred
for 30 min at room temperature. The solution was concentrated in vacuo
and transferred dropwise into excess hexane, affording a pale blue
precipitate that was isolated by filtration and dried in vacuo. Yield:
3
3.1 mg (53%). Single crystals suitable for X-ray diffraction were ob-
tained by slow diffusion of hexane into a DFB solution at room tem-
perature.
Appendix A. Supplementary data
1
H NMR (500 MHz, DFB/C
6
D
6
, selected data only): δ 8.17–8.12
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2020.119948.
F
F
3
(
m, 8H, Ar ), 7.50 (br, 4H, Ar ), 1.82 (d,
J
PH = 7.0, 2H, PdCH
2
),
3
3
3
1
1
.41 (d,
.20 (d,
J
PH = 14.2, 18H, PtBu
2
), 1.31 (d,
J
PH = 14.6, 6H, Me),
J
PH = 14.1, 18H, PtBu
2
O), 1.06 (d, 3JPH = 12.4, 18H,
References
PtBu
2
O).
1
3
H NMR (400 MHz, CD
2
Cl
2
): δ 7.79 (t,
J
HH = 7.8, 1H, py),
[
1] (a) J.F. Hartwig, Organotransition Metal Chemistry-From Bonding to Catalysis,
University Science Books, 2010;
F
F
7
.76–7.68 (m, 8H, Ar ), 7.56 (br, 4H, Ar ), 7.35 (app. t, J = 6, 1H,
3
3
(b) U. Christmann, R. Vilar, Angew. Chem. Int. Ed. 44 (2005) 366–374.
py), 6.72 (d, JHH = 7.9, 1H, py), 1.92 (d, JPH = 7.0, 2H, PdCH
2
),
), 1.51 (d, 3
JPH = 14.5, 6H, Me),
.60 (d, 3
[2] (a) J.P. Stambuli, M. Bühl, J.F. Hartwig, J. Am. Chem. Soc. 124 (2002) 9346–9347;
1
J
PH = 14.3, 18H, PtBu
2
4

M.J.G. Sinclair and A.B. Chaplin
Inorganica Chimica Acta 513 (2020) 119948
(
(
(
(
b) M. Yamashita, J.F. Hartwig, J. Am. Chem. Soc. 126 (2004) 5344–5345;
c) J.P. Stambuli, C.D. Incarvito, M. Bühl, J.F. Hartwig, J. Am. Chem. Soc. 126
2004) 1184–1194;
M.P. Mingos, R. Vilar, A.J.P. White, D.J. Williams, Chem. Commun. (2000)
1525–1526.
[7] W.H. Henderson, J.M. Alvarez, C.C. Eichman, J.P. Stambuli, Organometallics 30
(2011) 5038–5044.
d) M. Yamashita, I. Takamiya, K. Jin, K. Nozaki, Organometallics. 25 (2006)
4
588–4595;
[8] P.S. Pregosin, NMR in Organometallic Chemistry, Wiley-VCH, 2012.
[9] N.R. Deprez, M.S. Sanford, Inorg. Chem. 46 (2007) 1924–1935.
[10] For an illustrative example of concerted insertion into a M–P bond see: E.A.
LaPierre, M.L. Clapson, W.E. Piers, L. Maron, D.M. Spasyuk, C. Gendy, Inorg. Chem.
57 (2017) 495–506.
(
(
(
e) J.P. Stambuli, Z. Weng, C.D. Incarvito, J.F. Hartwig, Angew. Chem. Int. Ed. 46
2007) 7674–7677;
f) F. Barrios-Landeros, B.P. Carrow, J.F. Hartwig, J. Am. Chem. Soc. 131 (2009)
8
141–8154;
(
g) P.S. Hanley, D. Marković, J.F. Hartwig, J. Am. Chem. Soc. 132 (2010)
[11] E. Poverenov, I. Efremenko, A.I. Frenkel, Y. Ben-David, L.J.W. Shimon, G. Leitus,
L. Konstantinovski, J.M.L. Martin, D. Milstein, Nature 455 (2008) 1093–1096.
[12] (a) D. Delony, M. Kinauer, M. Diefenbach, S. Demeshko, C. Würtele,
M.C. Holthausen, S. Schneider, Angew. Chem. Int. Ed. 58 (2019) 10971–10974;
(b) D. Munz, Chem. Sci. 9 (2018) 1155–1167;
6
302–6303;
(
(
(
(
h) P.S. Hanley, J.F. Hartwig, J. Am. Chem. Soc. 133 (2011) 15661–15673;
i) P.S. Hanley, S.L. Marquard, T.R. Cundari, J.F. Hartwig, J. Am. Chem. Soc. 134
2012) 15281–15284;
j) S. Sugawara, M. Abe, Y. Fujiwara, M. Wakioka, F. Ozawa, Y. Yamamoto, Eur. J.
(c) K. Ray, F. Heims, F.F. Pfaff, Eur. J. Inorg. Chem. 2013 (2013) 3784–3807;
(d) R.S. Hay-Motherwell, G. Wilkinson, B. Hussain-Bates, M.B. Hursthouse,
Polyhedron 12 (1993) 2009–2012.
Inorg. Chem. (2015) 534–541;
(
k) D.M. Peacock, Q. Jiang, P.S. Hanley, T.R. Cundari, J.F. Hartwig, J. Am. Chem.
Soc. 140 (2018) 4893–4904.
[13] (a) W.E. Buschmann, J.S. Miller, K. Bowman-James, C.N. Miller, Inorg. Synth. 33
(2002) 83–91;
[
[
3] M.D. Walter, P.S. White, M. Brookhart, New. J. Chem. 37 (2013) 1128–1133.
4] (a) T. Troadec, S.-Y. Tan, C.J. Wedge, J.P. Rourke, P.R. Unwin, A.B. Chaplin,
Angew. Chem. Int. Ed. 55 (2016) 3754–4375;
(b) A.J. Martínez-Martínez, A.S. Weller, Dalton Trans. 48 (2019) 3551–3554.
[14] K. Li, A.E. Weber, L. Tseng, S.J. Malcolmson, Org. Lett. 19 (2017) 4239–4242.
[15] S. Kundu, W.W. Brennessel, W.D. Jones, Inorg. Chem. 50 (2011) 9443–9453.
(
b) Q. Simpson, M.J.G. Sinclair, D.W. Lupton, A.B. Chaplin, J.F. Hooper, Org. Lett.
2
0 (2018) 5537–5540.
3
[16] O]PtBu prepared independently using an adapted literature proceedure (C.R.
[
[
5] S.D. Pike, M.R. Crimmin, A.B. Chaplin, Chem. Commun. 53 (2017) 3615–3633.
6] For a related oxidation reaction involving a palladium(I) dimer see: V. Durà-Vilà, D.
Hilliard, N. Bhuvanesh, J.A. Gladysz, J. Dalton Trans. 41 (2012) 1742–1754) was
31
characterised by P NMR spectroscopy by a signal at δ 64.4.
5