Expanding the allyl analogy: accessing
η
3
-
P,B,P
diphosphinoborane complexes of group 10†
Marcus W. Drover
and
Jonas C. Peters
*
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena,
California, 91125, USA
Abstract
Using the diphosphinoborane, (PPh
2
)
2
BMes (Mes = 2,4,6-Me
3
C
6
H
3
), we report the first examples
of
η
3
-
P,B,P
-ligated complexes using Ni(0) and Pt(
II
). Reaction of (PPh
2
)
2
BMes with Ni(COD)
2
or
Pt(COD)Me
2
(COD = 1,5-cyclooctadiene) results in gradual COD displacement to give [
η
3
-
P,B,P
-
(PPh
2
)
2
BMes]Ni(COD) (
3
) or [
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Pt(CH
3
)
2
(
6
). Complex
3
serves as a
versatile Ni-containing synthon for the preparation of square planar or tetrahedral Ni(0)
complexes. Notably, the M–B interaction in these systems is non-negligible – with coordination
resulting in an upfield shift of
ca.
80 ppm in the
11
B NMR spectrum. We also show that treatment
of the Pt
IV
halide precursor, [PtMe
3
I]
4
with this ligand framework results in migration of X-type
ligands (CH
3
−
and I
−
) to boron and reductive elimination of ethane (C
2
H
6
) to give a distorted
square planar zwitterionic Pt
II
complex, Pt[
κ
2
-
P,P
-(PPh
2
)
2
B(Mes)(CH
3
)][
κ
2
-
P,P
-(PPh
2
)
2
B (Mes)
(I)] (
10
). This reactivity suggests the feasibility of (PPh
2
)
2
BMes-ligand-induced labilization of M–
X ligands.
Introduction
Allyl ligands [C
3
H
5
]
−
represent a cornerstone of organometallic chemistry, stabilizing
transition and main group elements in a
η
1
- or
η
3
-bonding fashion. Drawing inspiration
from the ‘all-carbon’-based allyl fragment, related ligands have emerged incorporating a
Z
-
type
1
accepting boron atom
in lieu
of carbon. Shapiro and co-workers, for example, reported
that the zwitter-ionic bis(triphenylphosphinemethylenido)borane ligand coordinates in an
η
3
-
C,B,C
fashion to both Zr(
IV
) and Pd(
II
) (Chart 1A).
2
By analogy, Emslie and co-workers
found that vinylboranes (R
2
C=CR–BR
2
) serve as precursors to
η
3
-
B,C,C
coordinated
complexes of Ni(0) and Pt(0) adopting borataallyl coordination modes (Chart 1A).
3
In a
similar vein, our group and others have characterized related
η
3
-
B,C,C
complexes using
(phosphine)borane-based ligand platforms, where the metal centre engages in bonding with
both boron and a
π
-acidic aryl ring.
4
–
6
Building on our group’s previous efforts in
P,B
-
containing coordination complexes of late transition metals, we wished to explore direct P–
†
Electronic supplementary information (ESI) available:
1
H,
31
P,
11
B, and
13
C NMR spectra for all complexes as well as
crystallographic data for 2, 3, 5, 6, and 10. CCDC 1581574–1581579 contains the supplementary crystallographic data for this paper.
For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt00058a
*
jpeters@caltech.edu.
Conflicts of interest
There are no conflicts to declare.
HHS Public Access
Author manuscript
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Published in final edited form as:
Dalton Trans
. 2018 March 12; 47(11): 3733–3738. doi:10.1039/c8dt00058a.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
B linkages as isolobal fragments to C=C bonds
e.g.
, [R
2
C=CR–CR
2
]
−
vs.
R
2
P=B(R)–PR
2
.
This approach has been highlighted by isolation of the
η
6
-
P
3
,
B
3
-containing arene complex
[{
η
6
-[(P
t
Bu)(BMes)]
3
}Cr(CO)
3
]7 and the
η
2
-
P,B
phosphinoborane complexes,
Pt(PPh
3
)
2
(
η
2
-R
2
P=B(C
6
F
5
)
2
) (R = Cy or
t
Bu), providing evidence for alkene-type
coordination of P=B multiple bonds (Chart 1B).
8
We now disclose that the
diphosphinoborane, (PPh
2
)
2
BMes (
1
: Mes = 2,4,6-Me
3
C
6
H
3
) first prepared by Power and
co-workers,
9
serves as a practical starting point from which
η
3
-
P,B,P
bonded complexes of
group 10 transition metals can be accessed.
Generation of [
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Ni(COD) (
2
; COD = 1,5-cyclooctadiene) was
achieved by combination of (PPh
2
)
2
BMes with Ni(COD)
2
in benzene at ambient
temperature, which provides a dark brown solution (Scheme 1). Monitoring the reaction by
1
H NMR spectroscopy evidences loss of cyclooctadiene (C
6
D
6
:
δ
H
= 5.58 and 2.21 ppm)
and formation of a new
C
s
-symmetric Ni(0) complex. Notably, three unique mesityl –CH
3
signals are observed (each of integration 3H) at
δ
= 2.58, 2.13, and 1.30 ppm, indicative of
both (1) hindered B–C bond rotation and (2) the absence of a B–Ni decoordination/
recoordination process (where the boron atom transiently dissociates only to reassociate on
the opposite face of the molecule). Further, by
1
H NMR spectroscopy, coalescence of the
ortho
-CH
3
(mesityl) groups is not observed at elevated temperature (95 °C, tol-d
8
). It is
noteworthy that this phenomenon is observed for all
η
3
-
P,B,P
-(PPh
2
)
2
BMes complexes
discussed herein. A strong Ni–B interaction is corroborated by
11
B NMR spectroscopy [
δ
B
=
+4.0; Δ
δ
= −81.0
cf.
1
] (Fig. 1), while
31
P NMR spectroscopy provides a new signal at
δ
P
=
−16.6 (Δ
δ
= −16.5
cf.
1
) – coupling between
11
B and
31
P is not observed. High-resolution
FAB-MS also provides a [M]
+
signal consistent with the molecular formula of
2
at
m
/
z
=
666.229 (calcd 666.229).
Orange/brown crystals of
2
can be obtained from a saturated Et
2
O solution at −35 °C
allowing for unambiguous structural determination using single crystal X-ray diffraction
(Fig. 2). Complex
2
crystallizes in the triclinic space group,
P
1
‒
and features a tetrahedral
Ni(0) complex bonded to PBP and COD co-ligands having Ni(1)–P(1) and Ni(1)–P(2) bond
lengths of 2.183(1) and 2.190(1) Å and a Ni(1)–B(1) bond distance of 2.329(4) Å. This
distance is considerably shorter than that noted for a related compound, [(Ph
3
P)
2
Ni(
η
3
-
B,C,C
-VB
Ph
)] (VB
Ph
= (
E
)-PhHC=CH–B(C
6
F
5
)
2
(
d
Ni–B
= 2.660(3) Å)).
3
The boron centre
also retains sp
2
-hybridization [∑(X–B–X) = 360°] and upon coordination, little perturbation
in P–B bond length is noted [1.888(4)/1.907(4) Å
cf.
1.879(2)/1.901(2) Å for
1
]. Consistent
with increased planarization, the sum of angles at phosphorus, [∑(X–P–X) = 340.2° and
342.7°] also increase by
ca.
20° [318.8° and 324.5° for
1
]. These data indicate that
coordination of
1
involves some degree of P–B–P communication/
π
-orbital overlap,
signifying that the ligand is electronically distinct from its relative, bis(diphenylphosphino)
methane (dppm). Highlighting the electrophilic nature of boron in this family of compounds,
treatment of
1
with NiCl
2
or NiBr
2
(dme) (dme = 1,2-dimethoxyethane) in THF or Et
2
O
leads to rapid B–P bond rupture, forming the known tetrahedral Ni(0)-species, Ni(PPh
2
H)
4
10
and MesBX
2
(X = Cl, Br). We posit that the H-atoms in Ni(PPh
2
H)
4
10
arise from radical H-
atom transfer (HAT), presumably from solvent.
Drover and Peters
Page 2
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
To evaluate the effect of co-ligand on
η
3
-
P,B,P
bonding and to further study the nature of the
Ni–B interaction, we next ventured to treat complex
2
with L-type ligands. Dissolution of
complex
2
in coordinating solvents: MeCN-d
3
, pyridine-d
5
, or THF-d
8
did not result in Ni–
B dissociation as judged by
11
B and
31
P NMR spectroscopy. Conversely, treatment of a
benzene solution of complex
2
with 2,2
′
-bipyridine (2,2
′
-bpy) slowly (4 days) produces a
dark purple solution, identified as the tetrahedral Ni(0) complex, [
η
3
-
P,B,P
-
(PPh
2
)
2
BMes]Ni(2,2
′
-bpy) (
3
) along with free COD (Scheme 1). This complex displays two
deshielded resonances in the
1
H NMR spectrum at
δ
= 9.92 and 8.92 ppm for each of its two
ortho
-CH pyridyl groups, indicating
C
s
-symmetry. Further,
11
B NMR spectroscopy supports
a maintained interaction between Ni and B [
δ
B
= −7.7], while
31
P NMR spectroscopy
provides a new signal at
δ
P
= −20.9. Purple blocks, suitable for X-ray analysis were obtained
from a concentrated THF/pentane solution at −35 °C (Fig. 3). Complex
3
possesses similar
Ni(1)–P(1) and Ni(1)–P(2) bond lengths to complex
2
of 2.1625(6) and 2.1751(9) Å, albeit a
shorter Ni(1)–B(1) bond length of 2.201(3) Å. For the 2,2
′
-bpy ligand, all bond lengths are
consistent with redox innocence.
11
By analogy, the COD ligand of complex
2
is readily displaced by the
π
-accepting ligands
2,6-dimethylphenylisonitrile (CNXyl) or diphenylacetylene to give complexes
4
and
5
,
respectively (Scheme 1). For the bis(CNXyl) analogue
4
a single
11
B and
31
P NMR
resonance at
δ
B
= +4.8 ppm and
δ
P
= −8.5 ppm is observed. Three broad signals are
observed by IR spectroscopy at
ν
(
CN
) = 2078, 2039, and 1993 cm
−1
(
cf.
2123 cm
−1
for free
CNXyl), again indicating moderate
π
-back donation. Over a period of hours complex
4
decomposes in solution to as yet unidentified species, obviating analysis by X-ray
crystallography. For the square planar complex
5
, NMR spectroscopy supports the formation
of a
C
s
-symmetric complex (
δ
B
= +6.7 ppm and
δ
P
= −8.1 ppm) and the IR spectrum
exhibits a feature at 1823 cm
−1
(consistent with
π
-back donation by
η
3
-
P,B,P
-Ni
0
). The
solid-state structure of complex
5
was also obtained (Fig. 3). By contrast to complexes
2
and
3
, for complex
5
, Ni(1)–P(1) and Ni(1)–P(2) bonds of 2.2040(7) and 2.1905(9) Å represent a
slight elongation at the cost of the Ni(1)–B(1) bond [2.254(3) Å], which is slightly
shortened. Complex
5
is structurally similar to the
η
2
-alkyne complex, reported by Hillhouse
et al.
[dtbpe]Ni(
η
2
-PhCuCPh) (dtbpe = 1,2-bis(di-
tert
-butyl)phosphinoethane) for which
ν
(
CC
) = 1790 cm
−1
.
12
Expansion of the ligand platform to Pt
II
was also established. Combination of
1
and
Pt(Me)
2
(COD) in benzene at ambient temperature provides a light yellow solution over a
period of four days (Scheme 2). NMR spectroscopic analysis of a C
6
D
6
solution of this
mixture provides evidence for two Pt-containing species in a 9: 1 ratio: [
η
3
-
P,B,P
-
(PPh
2
)
2
BMes] Pt(Me)
2
(
6
) and the known complex, Pt(PHPh
2
)
2
(Me)
2
.
13
Complex
6
could
be purified and separated by recrystallization from Et
2
O at −35 °C in 88% yield. By analogy
to complex
2
, the
1
H NMR spectrum of
6
features three diagnostic signals, each of
integration of 3H at
δ
= 2.81, 2.78, and 2.06 ppm for the mesityl group, while for the
platinum-methyl groups, an apparent triplet is observed at
δ
= 2.18 ppm [
3
J
Pt,H
= 80 Hz] that
corresponds to
δ
c
= 4.52 ppm (t,
2
J
C,P
= 27.8 Hz) with
195
Pt satellites (
1
J
C,Pt
= 688 Hz) in
the
13
C NMR spectrum. Coordination of Pt
II
to the PBP unit is also evidenced by
31
P and
Drover and Peters
Page 3
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
11
B NMR spectroscopy, which provides a signal at
δ
P
= −21.6 [
1
J
Pt,P
= 839 Hz] and
δ
B
=
+7.9 ppm [Δ
δ
B
= −77.1
cf.
1
].
The solid-state structure of complex
6
is depicted in Fig. 4. The four-coordinate geometry is
best described as square planar, having Pt(1)–P(1) and Pt(1)–P(2) contacts of 2.305(3) and
2.318(2) Å and a Pt(1)–B(1) distance of 2.403(11) Å. The Pt(1)–C(1) and Pt(1)–C(2) bond
lengths are non-exceptional.
Given the halophilic nature of
1
, we wondered if capture of an X-type ligand by B could be
performed in a controlled manner – in effect promoting metal–ligand cooperativity.
14
–
19
As
a result,
1
was treated with 0.25 equiv. of the Pt
IV
precursor, [PtMe
3
I]
4
resulting in slow
effervescence of C
2
H
6
[
δ
H
= 0.80 ppm] as judged by
1
H NMR spectroscopy. By
31
P NMR
spectroscopy, consumption of the ligand and the appearance of a broad multiplet centred at
δ
P
= −35.7 was observed (see ESI, Fig. S28†) over a period of four days. Removal of
volatiles
in vacuo
and recrystallization of the resulting solid from Et
2
O at −35 °C, provided
colourless prisms suitable for single crystal analysis. Analysis of the resulting crystal data
provides evidence for Pt[
κ
2
-
P,P
-(PPh
2
)
2
B(Mes)(I)][
κ
2
-
P,P
-(PPh
2
)
2
B(Mes) (CH
3
)] (
10
) (Fig.
5). Notably, the B–C
H
3
resonance for complex
10
appears as a phosphorus-coupled triplet at
δ
H
= 1.45 [
3
J
P,H
= 19.4 Hz]. We posit that coordination of ‘PtMe
3
I’ to
1
provides the
octahedral Pt
IV
complex
7
, which is susceptible to halide abstraction by
1
, providing the
coordinatively unsaturated five-coordinate complex
8
. Reductive elimination of ethane
(C
2
H
6
) from
8
thus provides complex
9
, which upon methyl abstraction by another
equivalent of
1
gives complex
10
. Abstraction of X-type halide and methyl groups by group
13 Lewis acids is well documented.
20
–
24
The crystal structure of
10
features a distorted
square planar Pt(
II
) centre (
τ
4
= 0.23)
25
bonded by four phosphorus atoms. By contrast to
complex
6
, each boron atom in the ligand is sp
3
-hybridized in nature, owing to association
of the X-type iodide or methyl anion causing the P–B bond lengths elongate: [2.036(4) and
2.064(4) Å
cf.
1.85(1) and 1.89(1) Å for
6
].
Conclusion
In close, we have provided here the first examples of Ni
0
and Pt
II
compounds containing a
P–B–P diphosphinoborane ligand. This work expands the scope of P–B bond coordination
complexes beyond that of the known
η
6
-PvB and
η
2
-PvB coordination modes and illustrates
the use of diphosphinoboranes as modular
η
3
-
P,B,P
chelates.
Experimental section
General considerations
All experiments were carried out employing standard Schlenk techniques under an
atmosphere of dry nitrogen or argon employing degassed, dried solvents in a solvent
purification system supplied by SG Water, LLC. Combustion analyses were carried out by
Midwest Microlabs (Indianapolis). N.B. The results provided represent the best analysis
values obtained. Multinuclear NMR spectroscopy has been provided (see ESI†) to illustrate
sample homogeneity. Non-halogenated solvents were tested with a standard purple solution
of sodium benzophenone ketyl in tetrahydrofuran in order to confirm effective moisture
Drover and Peters
Page 4
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
removal. (PPh
2
)
2
BMes
9
was prepared according to a literature procedure. All other reagents
were purchased from commercial vendors and used without further purification unless
otherwise stated.
Physical methods
Fourier transform infrared ATR (FT-IR ATR) spectra were collected on a Thermo Scientific
Nicolet iS5 Spectrometer with diamond ATR crystal. NMR data were collected on a Varian
400 MHz instrument with chemical shifts reported in ppm relative to C
6
D
6
or THF-d
8
, using
residual solvent resonances as internal standards. N.B. In some instances, not all aromatic
carbon atoms are viewed due to overlap with residual C
6
D
6
.
31
P chemical shifts are reported
in ppm relative to 85% aqueous H
3
PO
4
.
11
B{
1
H} NMR spectra were acquired using quartz
NMR tubes.
(PPh
2
)
2
BMes (1)
This compound was prepared as previously, however the
1
H and
13
C NMR data were not
provided.
9
Also, in our hands a
11
B{
1
H} NMR chemical shift of 85.0 ppm was recorded in
C
6
D
6
or 1: 1 C
6
D
6
:THF, which is different from that reported (30.0 ppm).
1
H NMR (400
MHz, C
6
D
6
, 298 K):
δ
= 7.29 (m, 8H;
o
-PPh
2
), 6.90 (m, 8H;
m
-PPh
2
), 6.89 (m, 4H;
p
-
PPh
2
), 6.69 (s, 2H; Mes), 2.20 (s, 3H; Mes), 2.18 (s, 6H; Mes).
13
C{
1
H} NMR (100 MHz,
C
6
D
6
, 298 K):
δ
= 137.61 (t,
J
C,P
= 2.1 Hz), 137.28 (t,
J
C,P
= 5.9 Hz), 134.61 (t,
J
C,P
= 7.9
Hz), 134.19 (t,
J
C,P
= 6.4 Hz), 128.42 (t,
J
C,P
= 4.2 Hz), 128.00 (under C
6
D
6
), 127.92 (t,
J
C,P
= 4.2 Hz), 22.51 (t,
J
C,P
= 2.5 Hz), 21.38.
31
P{
1
H} NMR (161.9 MHz, C
6
D
6
, 298 K):
δ
=
−0.01.
11
B{
1
H} NMR (128 MHz, C
6
D
6
, 298 K):
δ
= 85.0.
[
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Ni(COD) (2)
In the glovebox,
1
(45 mg, 0.090 mmol) and Ni(COD)
2
(25 mg, 0.091 mmol) were added to
a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the
orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed
in vacuo
and the resulting orange oil was washed with pentane to afford an orange/brown solid.
Recrystallization from saturated Et
2
O at −35 °C gave orange crystals (56 mg, 93%).
1
H
NMR (400 MHz, THF-d
8
, 298 K):
δ
= 7.40 (m, 4H; PPh
2
), 7.08 (m, 12H; PPh
2
), 6.89 (t,
3
J
H,H
= 7.2 Hz, 4H; PPh
2
), 6.66 (s, 1H; Mes), 6.44 (s, 1H; Mes), 5.09 (s, 2H; COD), 4.27 (s,
2H; COD), 2.83 (br, 2H; COD), 2.58 (s, 3H; Mes), 2.47 (br m, 4H; COD), 2.27 (br m, 2H;
COD), 2.13 (s, 3H; Mes), 1.30 (s, 3H; Mes).
13
C{
1
H} NMR (100 MHz, C
6
D
6
, 298 K):
δ
=
141.36, 139.78, 136.70 (t,
J
C,P
= 33 Hz), 135.46, 134.86 (t,
J
C,P
= 5.4 Hz), 133.74 (t,
J
C,P
=
5.1 Hz), 132.05 (t,
J
C,P
= 23 Hz), 128.40, 93.07, 87.63, 32.13, 31.06, 25.86, 23.26, 21.17.
31
P{
1
H} NMR (161.9 MHz, THF-d
8
, 298 K):
δ
= −16.6 (br).
11
B{
1
H} NMR (128 MHz,
THF-d
8
, 298 K):
δ
= +4.03 (br).
FAB-MS (
m/z
):
666.229 (calcd 666.229).
Anal. calcd
for
C
41
H
43
BNiP
2
(666.23): C, 73.80; H, 6.50. Found: C, 72.20; H, 7.11.
[
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Ni(2,2
′
-bipy) (3)
In the glovebox,
2
(30 mg, 0.045 mmol) and 2,2
′
-bipyridine (7.0 mg, 0.048 mmol) were
added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added
and the orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed
in
Drover and Peters
Page 5
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
vacuo
and the resulting purple oil was recrystallized from pentane at −35 °C to give purple
crystals (14 mg, 44%) N.B. Low yields are due to the high solubility of complex
3
in
pentane.
1H NMR (400 MHz, C6D6, 298 K):
δ
= 9.92 (d,
3
J
H,H
= 5.6 Hz, 1H; bpy), 8.92
(d,
3
J
H,H
= 5.7 Hz, 1H; bpy), 7.75 (m, 4H; PPh
2
), 7.50 (m, 4H; PPh
2
), 7.25 (d,
3
J
H,H
= 8.3
Hz, 1H; bpy), 7.09 (d,
3
J
H,H
= 8.1 Hz, 1H; bpy), 7.02 (s, 1H; Mes), 7.00–6.76 (m, 15H; Ar),
6.60 (m, 2H; Ar), 3.24 (s, 3H; Mes), 2.47 (s, 3H; Mes), 2.24 (s, 3H; Mes).
13
C{
1
H} NMR
(100 MHz, C
6
D
6
, 298 K):
δ
= 152.39, 150.10, 142.15 (m), 140.62 (m), 135.89, 134.18,
129.82, 129.20, 128.60, 127.34, 123.47, 122.49, 121.32, 120.69, 26.40, 22.90 (br), 21.44.
31
P{
1
H} NMR (161.9 MHz, C
6
D
6
, 298 K):
δ
= −20.9 (br).
11
B{
1
H} NMR (128 MHz,
C
6
D
6
, 298 K):
δ
= −7.68 (br).
Anal. calcd
for C
43
H
39
BN
2
NiP
2
(714.20): C, 72.21; H, 5.50;
N, 3.92. Found: C, 70.19; H, 5.50; N, 3.74.
[
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Ni(CNXyl)
2
(4)
In the glovebox,
2
(15 mg, 0.015 mmol) and 2,6-dimethylphenylisocyanide (5.9 mg, 0.030
mmol) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene
was added and the resulting orange/green solution was allowed to stir for 30 min at 25 °C.
The solvent was removed
in vacuo
and the resulting brown solid was washed with pentane to
afford a brown solid (9.2 mg, 50%). This compound is unstable in solution (
t
1/2
= 60 min)
providing a mixture of as yet unidentified species including a broad resonance at
δ
B
= 31.2
ppm for the boroxin, (MesBO)
3
26
for which
1
H NMR (400 MHz, C
6
D
6
, 298 K)
δ
= 6.67 (s,
2H), 2.49 (s, 6H), 2.14 (3H).
1
H NMR (400 MHz, C
6
D
6
, 298 K):
δ
= 7.77 (m, 4H; PPh
2
),
7.72 (m, 4H; PPh
2
), 7.07–6.68 (m, 20H; Ar), 2.98 (s, 3H; Mes), 2.45 (s, 3H; Mes), 2.30 (s,
6H; CNXyl), 2.23 (s, 6H; CNXyl), 2.11 (s, 3H; Mes).
13
C{
1
H} NMR (100 MHz, C
6
D
6
, 298
K):
δ
= 141.98, 141.67, 137.81, 137.47, 137.13, 136.70 (t,
J
C,P
= 6.2 Hz), 135.01, 134.73,
134.26, 134.01 (t,
J
C,P
= 6.0 Hz), 128.81, 128.76, 128.59, 126.96, 126.88, 125.84, 28.38,
26.62, 25.63, 19.13, 19.10.
31
P {
1
H} NMR (161.9 MHz, C
6
D
6
, 298 K):
δ
= −8.5.
11
B{
1
H}
NMR (128 MHz, C
6
D
6
, 298 K):
δ
= 4.75 (br).
FT-IR ATR (neat solid, cm
−1
):
2078, 2039,
1993 (br,
ν
(
CN
)). Appropriate elemental analysis could not be obtained for complex
4
due
to decomposition.
[
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Ni(
η
2
-C
2
Ph
2
) (5)
In the glovebox,
2
(21 mg, 0.031 mmol) and diphenylacetylene (5.5 mg, 0.031 mmol) were
added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added
and the orange solution was allowed to stir for 2 days at 25 °C. The solvent was removed
in
vacuo
and the resulting orange solid was washed with pentane to afford an orange solid.
Recrystallization from Et
2
O or pentane at −35 °C gave orange crystals (16 mg, 70%).
1
H
NMR (400 MHz, C
6
D
6
, 298 K):
δ
= 8.17 (d,
3
J
H,H
= 7.1 Hz, 4H; Ph
2
C
2
), 7.52 (m, 4H;
PPh
2
), 7.47 (m, 4H; PPh
2
), 7.13 (t,
3
J
H,H
= 7.5 Hz, 6H; Ar), 7.03 (t,
3
J
H,H
= 7.4 Hz, 2H; Ar),
6.84 (m, 6H), 6.74 (m, 2H), 6.59 (t,
3
J
H,H
= 7.6 Hz, 4H; Ar), 2.85 (s, 3H; Mes), 2.60 (s, 3H;
Mes), 2.08 (s, 3H; Mes).
13
C{
1
H} NMR (100 MHz, C
6
D
6
, 298 K):
δ
= 141.31, 140.49,
136.51, 136.35 (t,
J
C,P
= 6.2 Hz), 133.07, 133.86 (m), 133.51 (m), 133.36 (t,
J
C,P
= 6.0 Hz),
131.07, 128.99, 128.82, 128.74, 128.56, 128.42, 128.21, 127.94, 127.39, 25.78, 25.03,
21.26.
31
P{
1
H} NMR (161.9 MHz, C
6
D
6
, 298 K):
δ
= −8.1.
11
B {
1
H} NMR (128 MHz,
Drover and Peters
Page 6
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
C
6
D
6
, 298 K):
δ
= 6.67 (br).
FT-IR ATR (neat solid, cm
−1
):
1823 (
ν
(CC)).
Anal. calcd
for C
47
H
41
BNiP
2
(736.21): C, 76.57; H, 5.61. Found: C, 74.29; H, 5.76.
[
η
3
-
P,B,P
-(PPh
2
)
2
BMes]Pt(CH
3
)
2
(6)
In the glovebox,
1
(60 mg, 0.12 mmol) and Pt(Me)
2
(COD) (40 mg, 0.12 mmol) were added
to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene was added and the
orange solution was allowed to stir for 4 days at 25 °C. The solvent was removed
in vacuo
and the resulting yellow solid was recrystallized from saturated Et
2
O at −35 °C to give
yellow crystals (77 mg, 88%). N.B. Heating this reaction mixture results in decomposition to
Pt(0) and undesired organic by-products.
1
H NMR (400 MHz, C
6
D
6
, 298 K):
δ
= 7.47 (m,
4H; PPh
2
), 7.42 (m, 4H; PPh
2
), 6.81 (m, 8H; PPh
2
), 6.72 (s, 1H; Mes), 6.66 (s, 1H; Mes),
6.62 (t,
3
J
H,H
= 7.6 Hz, 4H; PPh
2
), 2.81 (s, 3H; Mes), 2.78 (s, 3H; Mes), 2.17 (s with
195
Pt
satellites,
3
J
H,Pt
= 80 Hz, 6H; Pt–C
H
3
), 2.06 (s, 3H; Mes).
13
C{
1
H} NMR (100 MHz, C
6
D
6
,
298 K):
δ
= 142.64, 140.08, 136.30 (t,
J
C,P
= 5.1 Hz), 133.60 (t,
J
C,P
= 4.8 Hz), 129.74,
129.62, 129.41, 128.82, 128.54 (t,
J
C,P
= 6.1 Hz), 128.24 (t,
J
C,P
= 6.0 Hz), 124.75 (t,
J
= 33
Hz), 25.50, 25.45, 21.21, 4.52 (t with
195
Pt satellites,
J
C,Pt
= 688 Hz,
J
C,P
= 27.8 Hz; Pt–
CH
3
).
31
P{
1
H} NMR (161.9 MHz, CD
2
Cl
2
, 298 K):
δ
= −21.6 (br t,
1
J
Pt,P
= 853 Hz).
11
B{
1
H} NMR (128 MHz, CD
2
Cl
2
, 298 K):
δ
= +7.9 (br).
Anal. calcd
for C
35
H
37
BP
2
Pt
(725.21): C, 57.94; H, 5.14. Found: C, 59.23; H, 5.08.
Pt[
κ
2
-
P,P
-(PPh
2
)
2
B(Mes)(I)][
κ
2
-P,P-(PPh
2
)
2
B(Mes)(CH
3
)] (10)
In the glovebox,
1
(30 mg, 0.12 mmol, 2 equiv.) and [Pt(Me)
3
(I)]
4
(11 mg, 0.03 mmol, 0.25
equiv.) were added to a 20 mL vial equipped with a stir bar. Approximately 2 mL of benzene
was added and the colorless solution was allowed to stir for 4 days at 25 °C. The solvent was
removed
in vacuo
and the resulting pale yellow solid was recrystallized from saturated Et
2
O
at −35 °C to give clear colorless crystals (14 mg, 38%).
1
H NMR (400 MHz, C
6
D
6
, 298 K):
δ
= 7.92 (br; 4H PPh
2
), 7.77 (br, 4H; PPh
2
), 7.05 (br, 12H; PPh
2
), 6.92 (t,
3
J
H,H
= 7.6 Hz,
4H; PPh
2
), 6.82 (t,
3
J
H,H
= 7.6 Hz, 4H; PPh
2
), 6.77 (s, 2H; Mes), 6.75 (t,
3
J
H,H
= 7.6 Hz, 4H;
PPh
2
), 6.69 (s, 2H; Mes), 6.63 (t,
3
J
H,H
= 7.6 Hz, 4H; PPh
2
), 6.56 (t,
3
J
H,H
= 7.6 Hz, 4H;
PPh
2
), 2.23 (s, 6H; Mes), 2.15 (s, 9H (6H + 3H); Mes), 2.08 (s, 3H; Mes), 1.45 (t,
3
J
H,P
=
19.4 Hz, 3H; B–C
H)
3
.
13
C{
1
H} NMR (100 MHz, THF-d
8
, 298 K):
δ
= 142.08 (m), 140.85
(m), 137.07 (m), 136.44, 136.25 (m), 135.91 (m), 134.90 (m), 134.35, 133.26, 132.07,
130.90, 129.87, 129.68 (m), 129.30 (m), 128.85, 128.61 (m), 128.41, 128.25, 127.99,
127.25, 26.64, 26.26, 20.56, 20.55, 8.66 (br, B–
CH
3
).
31
P{
1
H} NMR (161.9 MHz, C
6
D
6
,
298 K):
δ
= −35.65 (m).
11
B{
1
H} NMR (128 MHz, C
6
D
6
, 298 K):
δ
= 4.94.
Anal. calcd
for C
67
H
65
B
2
IP
4
Pt (1337.29): C, 60.16; H, 4.90. Found: C, 58.05; H, 4.96.
Supplementary Material
Refer to Web version on PubMed Central for supplementary material.
Acknowledgements
This work was supported by the NIH (GM070757), NSERC (Banting PDF award to MWD), and the Resnick
Sustainability Institute at Caltech (Postdoctoral award to MWD). We thank Larry Henling and Mike Takase for
assistance with X-ray crystallography.
Drover and Peters
Page 7
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
References
1. Green MLH. J. Organomet. Chem. 1995; 500:127–148.
2. Jiang F, Shapiro PJ, Fahs F, Twamley B. Angew. Chem., Int. Ed. 2003; 42:2651–2653.
3. Kolpin KB, Emslie DJH. Angew. Chem., Int. Ed. 2010; 49:2716–2719.
4. Nesbit MA, Suess DLM, Peters JC. Organometallics. 2015; 34:4741–4752.
5. Macmillan SN, Harman WH, Peters JC. Chem. Sci. 2014; 5:590–597.
6. Emslie DJH, Cowie BE, Kolpin KB. Dalton Trans. 2012; 41:1101–1117. [PubMed: 21983808]
7. Kaufmann B, Nöth H, Paine RT, Polborn K, Thomann M. Angew. Chem., Int. Ed. 2003; 32:1446–
1448.
8. Amgoune A, Ladeira S, Miqueu K, Bourissou D. J. Am. Chem. Soc. 2012; 134:6560–6563.
[PubMed: 22480251]
9. Bartlett RA, Dias H, Power PP. Inorg. Chem. 1988; 27:3919–3922.
10. Langer J, Görls H, Gillies G, Walther D. Z. Anorg. Allg. Chem. 2005; 631:2719–2726.
11. Scarborough CC, Wieghardt K. Inorg. Chem. 2011; 50:9773–9793. [PubMed: 21678919]
12. Waterman R, Hillhouse GL. Organometallics. 2003; 22:5182–5184.
13. Kakeya M, Tanabe M, Nakamura Y, Osakada K. J. Organomet. Chem. 2009; 694:2270–2278.
14. Figueroa JS, Melnick JG, Parkin G. Inorg. Chem. 2006; 45:7056–7058. [PubMed: 16933903]
15. Bouhadir G, Bourissou D. Chem. Soc. Rev. 2016; 45:1065–1079. [PubMed: 26567634]
16. Schindler T, Lux M, Peters M, Scharf LT, Osseili H, Maron L, Tauchert ME. Organometallics.
2015; 34:1978–1984.
17. Cowie BE, Emslie DJH. Organometallics. 2015; 34:2737–2746.
18. Braunschweig H, Dewhurst RD, Schneider A. Chem. Rev. 2010; 110:3924–3957. [PubMed:
20235583]
19. Khusnutdinova JR, Milstein D. Angew. Chem., Int. Ed. 2015; 54:12236–12273.
20. Sircoglou M, Bouhadir G, Saffon N, Miqueu K, Bourissou D. Organometallics. 2008; 27:1675–
1678.
21. Devillard M, Nicolas E, Appelt C, Backs J, Mallet-Ladeira S, Bouhadir G, Slootweg JC, Uhl W,
Bourissou D. Chem. Commun. 2014; 50:14805–14808.
22. Fischbach A, Bazinet PR, Waterman R, Tilley TD. Organometallics. 2008; 27:1135–1139.
23. Thibault M-H, Boudreau J, Mathiotte S, Drouin F, Sigouin O, Michaud A, Fontaine F-G.
Organometallics. 2007; 26:3807–3815.
24. Boudreau J, Fontaine F-G. Organometallics. 2011; 30:511–519.
25. Yang L, Powell DR, Houser RP. Dalton Trans. 2007; 60:955–964.
26. Cole SC, Coles MP, Hitchcock PB. Dalton Trans. 2003:3663.
Drover and Peters
Page 8
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Fig. 1.
11
B{
1
H} NMR spectra of ligand 1 and complexes
2
and
3
(128 MHz, C
6
D
6
, 298 K).
Drover and Peters
Page 9
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Fig. 2.
ORTEP depiction of the solid-state molecular structure of 2 (displacement ellipsoids are
shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and
angles (°). Ni(1)–P(1) 2.183(1), Ni(1)–P(2) 2.190(1), Ni(1)–B(1) 2.329(4), P(1)–Ni(1)–P(2)
85.46(4), P(1)–B(1)–P(2) 102.8(2).
Drover and Peters
Page 10
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Fig. 3.
ORTEP depiction of the solid-state molecular structure of 3 and 5 (displacement ellipsoids
are shown at the 50% probability, hydrogens omitted for clarity).
Drover and Peters
Page 11
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Fig. 4.
ORTEP depiction of the solid-state molecular structure of 6 (displacement ellipsoids are
shown at the 50% probability, hydrogens omitted for clarity). Selected bond lengths [Å] and
angles (°). Pt(1)–P(1) 2.305(3), Pt(1)–P(2) 2.318(2), Pt(1)–B(1) 2.403(11), Pt(1)–C(1)
2.093(9), Pt(1)–C(2) 2.103(12), P(1)–Pt(1)–P(2) 81.08(9), P(1)–B(1)–P(2) 106.9(5).
Drover and Peters
Page 12
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Fig. 5.
Generation of complex
10
and ORTEP depiction of the solid-state molecular structure of 10
(displacement ellipsoids are shown at the 50% probability, hydrogens omitted for clarity).
Drover and Peters
Page 13
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Chart 1.
Overview of boron-based ligand platforms.
Drover and Peters
Page 14
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript
Scheme 1.
Generation of
η
3
-
P,B,P
-(PPh
2
)
2
BMes Ni complexes.
Drover and Peters
Page 15
Dalton Trans
. Author manuscript; available in PMC 2019 March 12.
Author Manuscript
Author Manuscript
Author Manuscript
Author Manuscript