Investigation of Steric Factors Involved in the Formation of Terminal Cationic Platinum Arylborylene Complexes

Article abstract of DOI:10.1021/om501141g

The abstraction of halido ligands from Pt^II diphosphine boryl complexes has previously been shown to yield one of two isomeric products: either T-shaped cationic boryl complexes or square-planar cationic borylene complexes. However, the latter product has only been observed in one case, that of a mesitylboryl ligand, which converts to a mesitylborylene ligand upon halido abstraction. In an effort to test the efficacy of this reaction in the presence of different steric and electronic influences, Pt^II diphosphine boryl complexes were prepared with both 4-tert-butylphenyl and duryl (2,3,5,6-tetramethylphenyl) groups. Halide abstraction from the 4-tert-butylphenyl complex resulted in a T-shaped cationic boryl complex. However, subjecting the duryl-substituted complexes to the same conditions exclusively results in terminal cationic borylene complexes, a difference we attribute to the greater steric hindrance between the boron-bound bromide and the methyl groups at the 2- and 6-positions of the duryl group. This outcome indicates that the electronic effect of alkylation at the para position is not a factor for this borylene formation reaction. (Chemical Equation Presented).

Full text of DOI:10.1021/om501141g

Article
pubs.acs.org/Organometallics
Investigation of Steric Factors Involved in the Formation of Terminal
Cationic Platinum Arylborylene Complexes
Nicole Arnold, Holger Braunschweig,* Peter B. Brenner, Rian Dewhurst, Thomas Kramer,
and Krzysztof Radacki
̈ ̈ ̈
̈
Institut fur Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074 Wurzburg, Germany
*
S Supporting Information
II
ABSTRACT: The abstraction of halido ligands from Pt diphosphine boryl
complexes has previously been shown to yield one of two isomeric products:
either T-shaped cationic boryl complexes or square-planar cationic borylene
complexes. However, the latter product has only been observed in one case,
that of a mesitylboryl ligand, which converts to a mesitylborylene ligand upon
halido abstraction. In an effort to test the efficacy of this reaction in the
II
presence of different steric and electronic influences, Pt diphosphine boryl
complexes were prepared with both 4-tert-butylphenyl and duryl (2,3,5,6-
tetramethylphenyl) groups. Halide abstraction from the 4-tert-butylphenyl
complex resulted in a T-shaped cationic boryl complex. However, subjecting
the duryl-substituted complexes to the same conditions exclusively results in
terminal cationic borylene complexes, a difference we attribute to the greater
steric hindrance between the boron-bound bromide and the methyl groups at
the 2- and 6-positions of the duryl group. This outcome indicates that the
electronic effect of alkylation at the para position is not a factor for this borylene formation reaction.
INTRODUCTION
tBu, Mes) has been studied extensively. The strong trans
■
11,12
influence of these boryl complexes
allows for the easy
Synthetically important boron-based catalytic functionalizations
of organic substrates have greatly improved since the discovery
of transition-metal-catalyzed hydroboration in 1985. Common
abstraction of the bromo ligand with formation of cationic, T-
1
shaped, in most cases non-agostic-free boryl complexes trans-
+
[
Pt{B(Br)R}(PCy ) ] via reaction with a salt of a weakly
3
2
to all these synthetic protocols is the intermediacy of transition-
f
f
2
coordinating anion (e.g., Na[BAr ] (Ar = 3,5-(CF ) C H ),
metal−boron bonds. In the last two decades the investigation
4 3 2 6 3
K[B(C F ) ], Na [B Cl ], Ag[Al(Pftb) ] (Pftb = OC-
of the bonding modes of boron-based ligands in transition-
6
5
4
2
12 12
4
6
,13−15
3
(
CF ) ))
and formation of poorly soluble bromide salts
metal chemistry has developed immensely. Boron-based
ligands with only one substituent, such as borylene, iminoboryl
3 3
in CH Cl reaction medium. In the case of R = Mes, the T-
2
2
shaped boryl complex, which could be detected at −80 °C, is
not the thermodynamic product. In this case the kinetic
product of the halide abstraction reaction reacts further upon
(
−BNR), and oxoboryl (−BO) ligands, represent a
particularly interesting class of compounds, because the
boron atom in these ligands is in general both electronically
and sterically unsaturated.
warming to yield the cationic terminal borylene complex trans-
+
We have recently established a synthetic protocol for the
[Pt(BMes)Br(PCy
3
)
2
] resulting from a formal 1,2-halide shift,
4,5
6
stabilization of BN
and BO triple bonds in the
whereas the both electronically and sterically related o-tolyl-
coordination sphere of the platinum fragment [Pt(PCy ) ]
substituted T-shaped cationic boryl complex does not react any
3
2
1
4,16
(
Cy = cyclohexyl), allowing for the investigation of these
further.
systems at ambient temperature. A more common class of
compounds with monosubstituted boron-centered ligands are
terminal borylene complexes, the first of which were prepared
through a double salt elimination reaction of Na [M(CO) ] (M
This unexpected reactivity posed two questions. (1) Does
the steric demand of 2,6-substitution at the boron-bound aryl
substituent in T-shaped cationic complexes trans-[Pt{B(Br)-
+
2
5
R}(PCy ) ] induce the halide shift and borylene formation, or
3 2
7
−9
=
Cr, Mo) and Cl B{N(SiMe ) },
in which the borylene
is the electron-donating effect of para alkyl groups responsible
for this? (2) What is the influence of the steric interaction of
the phosphine substituents? In order to answer these questions,
2
3 2
moiety is stabilized by the electron-donating and sterically
shielding amino substituent. Later, Aldridge et al. established a
synthetic route to terminal borylene complexes via halide
abstraction from the boron atom in the case of a resulting
10
Special Issue: Mike Lappert Memorial Issue
Received: November 12, 2014
mesityl-substituted cationic borylene complex.
In our group the chemistry of platinum boryl complexes of
the general formula trans-[Pt{B(Br)R}Br(PCy ) ] (e.g., R =
3
2
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/om501141g | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
we synthesized the complexes trans-[Pt{B(Ar)Br}Br(PR ) ]
moieties are oriented nearly perpendicular to the PtP axis.
3
2
2
(
4
Ar = Dur = 2,3,5,6-tetramethylphenyl, R = Cy, iPr; Ar = C H -
-tBu, R = Cy) as precursors for the formation of cationic
Long Pt−Br1 bond distances (1a, 2.618(1) Å; 1b, 2.610(1) Å)
indicate the strong trans influence of the boryl moieties (Table
1). The dihedral angle Pt−B−C1−C2 in 1a (31.4(5)°) is
significantly larger than those of trans-[Pt{B(Br)Mes}Br-
(PCy ) ] (1d; 9.2(5)°) and 1b (4.3(7)°).
6
4
complexes. While the duryl-substituted derivatives both form
new cationic terminal borylene complexes (regardless of the
phosphine ligands), the C H -4-tBu-substituted representative
6
4
3
2
does not form such a compound.
Table 1. Selected Bond Distances (Å) and Angles (deg) in
1a,b
RESULTS AND DISCUSSION
■
Syntheses of Platinum Boryl Complexes. The platinum
boryl complexes of the general formula trans-[Pt{B(Ar)Br}Br-
1
a
1b
Pt−B
Pt−Br1
Pt−P1
Pt−P2
B−Br2
P1−Pt−P2
Pt−B−C1−C2
2.004(4)
2.618(1)
2.336(1)
2.370(1)
2.039(4)
170.9(1)
31.4(1)
1.977(6)
2.610(2)
2.340(2)
2.340(2)
1.989(6)
170.4(1)
4.3(7)
(
1
PR ) ] (1a, R = Cy, Ar = Dur; 1b, R = Cy, Ar = C H -4-tBu;
3
2
6
4
c, R = PiPr , Ar = Dur) were prepared by oxidative addition of
3
the B−Br bond of the corresponding aryldibromoboranes
Br BAr to the corresponding low-valent platinum complexes
2
[
Pt(PR ) ] (Scheme 1).
3 2
Scheme 1. Synthesis of Platinum Boryl Complexes 1a−c
Synthesis of Cationic T-Shaped Boryl and Square-
Planar Borylene Complexes. The boryl complexes 1a−c
f
f
were mixed with equimolar quantities of Na[BAr ] (Ar = 3,5-
4
(
CF ) C H ) in CD Cl (Scheme 2). The reaction mixtures
3 2 6 3 2 2
Scheme 2. Synthesis of Cationic Boryl Complex 2b and
Cationic Borylene Complexes 2a,c via Bromide Abstraction
In a typical reaction, the aryldibromoborane was dissolved in
hexanes or benzene and added dropwise to an equimolar yellow
solution of the platinum complex. Because of its high reactivity,
the addition of Br B(C H -4-tBu) was perfomed at −78 °C.
2
6
4
The reactions were monitored by multinuclear NMR spectros-
copy at room temperature, revealing the consumption of the
starting materials within 30 min. New high-field-shifted
3
1
1
195
P{ H} NMR signals flanked by Pt satellites (1a, δ 21.3,
1J = 3033 Hz; 1b, δ 19.7, J = 2774 Hz; 1c, δ 28.5, J
3
1
1
=
PPt
PPt
PPt
1
1
1
050 Hz) and broad low-field-shifted B{ H} NMR signals
(1a, δ 73.7; 1b, δ 74.0; 1c, δ 74.1) in all cases indicated the
formation of boryl complexes 1a−c.
Compounds 1a−c were isolated from the reaction mixtures
as colorless powders upon cooling the solutions to −35 °C in
good yields (59−74%). Crystals suitable for X-ray diffraction
analysis of 1a,b could be obtained by crystallization from
saturated solutions in methylene chloride at −35 °C.
The molecular structures of 1a,b display trans-confiugured,
slightly distorted square planar geometries around the platinum
centers, respectively (Figure 1). In both complexes, the boryl
both turned yellow, and colorless solids precipitated. The
resulting suspensions were filtered, and the retained yellow
reaction mixtures were monitored via multinuclear NMR
spectroscopy. New downfield-shifted singlet resonances, with
195
respect to the precursors 1a−c, flanked by Pt satellites were
31
1
detected in the P{ H} NMR spectra of the cationic complexes
f
1
trans-[Pt(BDur)Br(PCy ) ][BAr ] (2a, δ 44.8, J = 2075
3
2
4
PPt
f
Hz), trans-[Pt{B(Br)(C H -4-tBu)}(PCy ) ][BAr ] (2b, δ
1.8, JPPt = 2833 Hz), and trans-[Pt{B(Dur)}Br(PiPr ) ]
6
4
3 2
4
1
4
[
3 2
f
1
1
BAr ] (2c, δ 55.8, J = 2102 Hz). The J coupling
4 PPt PPt
1
1
constants in 2b ( J = 2833 Hz) and 1b ( J = 2812 Hz) are
PPt
PPt
very similar, indicating the formation of a T-shaped, cationic
boryl platinum complex. The corresponding coupling constants
in 2a,c display values that are about 1000 Hz smaller than those
of the corresponding precursors, respectively, suggesting the
presence of cationic borylene complexes. Notable is the
detection of 11B{ H} NMR resonances of 2a at δ 101 (fwhm
1
≈
2400 Hz) and 2c at δ 99.6 (fwhm ≈ 2400 Hz), the first
Figure 1. Molecular structures of 1a,b in the crystal. Phosphine
substituents have been simplified. One molecule of cocrystallized
methylene chloride in 1b and the hydrogen atoms of both structures
have been omitted for clarity. Thermal ellipsoids are displayed at the
11
1
B{ H} NMR resonances to be reported for platinum-bound
borylenes. Storing the reaction mixtures of 2a,c at −35 °C
yielded colorless crystals within 2−4 days in moderate to good
yields (69−74%). Unfortunately, 2b is too unstable in solution
50% probability level.
B
dx.doi.org/10.1021/om501141g | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
to be isolated, due to rehalogenation and reversion back to the
starting material 1b.
The X-ray-derived molecular structures of 2a,c display
slightly distorted square-planar geometries around the platinum
centers (Figure 2). The Pt−B bond distances in 2a (1.861(5)
methyl groups in ortho positions of the aryl substituent. These
results seem to indicate a propulsive force for the halide shift
from the boron atom to the platinum center following the
halide abstraction reaction, whereas evidence for the halide shift
due to electronic effects of the phosphine substituent was not
obtained.
CONCLUSION
■
In order to investigate whether the ortho substitution pattern of
the boron-bound aryl group is a prerequisite for the halide shift
and borylene formation, platinum boryl complexes with
alternative aryl substituents at the boron atom were treated
f
with Na[BAr ]. The 4-tert-butylphenyl-substituted complex
4
forms a T-shaped cationic boryl complex. In contrast, the two
duryl complexes undergo formal boron-to-metal halide shifts
and formation of the corresponding cationic borylene
complexes. These results indicate that (1) the steric demand
of the boron substituent is more important for the boron-to-
platinum halide shift than the substituent’s electron donation
ability and (2) the influence of the phosphine coligand appears
to play a minor role.
Figure 2. Molecular structures of 2a,c. Thermal ellipsoids of the
f
−
phosphine substituents, counterions ([BAr ] ), cocrystallized mole-
4
cules of methylene chloride (one in 2c, two in 2a), and all hydrogen
atoms have been omitted for clarity. Thermal ellipsoids are displayed
at the 50% probability level.
Å) and 2c (1.863(5) Å) are identical within experimental
uncertainty (Table 2) and are similar to that in the only other
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed in
dried glassware under an atmosphere of dry argon using standard
Schlenk-line or glovebox techniques. Solvents (benzene, hexane, and
methylene chloride) were dried according to standard procedures and
Table 2. Selected Bond Distances (Å) and Angles (deg) in
2
a,c
stored under argon over molecular sieves (4 Å). C D , d -Tol, and
2
a
2c
6
6
8
CD Cl were degassed by three freeze−pump−thaw cycles and stored
2
2
Pt−B
Pt−Br1
Pt−P1
Pt−P2
P1−Pt−P2
1.861(5)
2.531(1)
2.362(2)
2.368(2)
174.4(1)
1.863(5)
2.531(1)
2.352(1)
2.355(1)
171.5(1)
under argon over molecular sieves (4 Å). Routine NMR spectra were
recorded on a Bruker Avance 400 spectrometer. The NMR spectra of
1
the products were acquired on a Bruker Avance 500 ( H, 500.13 MHz;
11
13
31
B, 160.47 MHz; C, 125.76 MHz; P, 202.46 MHz) NMR
1
13
1
spectrometer. The H and C{ H} NMR spectra were referenced to
external tetramethylsilane via the residual proton signal of the solvent
1
13
11
1
(
H) or the solvent itself ( C). B{ H} NMR spectra were referenced
cationic borylene complex reported thus far, trans-[Pt(BMes)-
, and 31P{ H} NMR spectra were referenced to
1
+
14
to external BF
external 85% H PO . The chemical shift δ is reported in ppm.
·OEt
3 2
Br(PCy ) ] (2d; 1.859(3) Å). Both of these bond distances
3
2
3
4
are ca. 7% shorter than in the precursor neutral boryl complex
a (2.004(4) Å). This indicates the multiple-bond character
Microanalyses for C, H, and N were performed on either a
1
7
1
LecoCHNS-932 or a Carlo Erba Model 1106 instrument. Br BDur,
2
1
8
19−21
22
between the metal center and the boron atom, which was
examined previously using a simplified model of 2d through
calculation of Kohn−Sham orbitals. Two orbitals with
considerable Pt−B σ-bonding character and two orthogonal
orbitals with π-bonding character were found therein. The Pt−
Br bond distances of the borylene complexes 2a (2.531(1) Å)
and 2c (2.531(1) Å) are similar to that of 2d (2.542(1) Å).
In order to understand the driving force for the formation of
either cationic T-shaped or square-planar borylene complexes
by the abstraction of a bromido ligand, we found substantial
differences in the spatial constitution of the corresponding
precursors by comparison of their structural parameters. While
the bond distances and angles around the platinum centers in
the four complexes are very similar, the dihedral angles Pt−B−
C1−C2 in 1b (4.3(7)°) and trans-[Pt{B(Br)o-Tol}Br(PCy ) ]
Br B(C H -4-tBu), [Pt(PCy ) ],
and [Pt(PiPr ) ] were
2
6
4
3
2
3 3
prepared according to published procedures.
Synthesis of trans-[Pt{B(Br)Dur}Br(PCy ) ] (1a). A solution of
3 2
Br BDur (40.3 mg, 0.132 mmol) in hexane (5 mL) was added
2
dropwise to a stirred solution of [Pt(PCy ) ] (100 mg, 0.132 mmol) in
3
2
hexane (5 mL). Colorless crystals of 1a were isolated from the reaction
1
mixture upon cooling to −65 °C for 1 day (yield 103 mg, 74%). H
NMR (500.13 MHz, d -Tol, 70 °C): δ 6.92 (s, 1H, Dur), 3.19 (s, 6H,
8
CH -o, Dur), 3.01 (m, 6H, CH-i of Cy), 2.26−2.12 (m, 12H, Cy), 2.16
3
(
s, 6H, CH -m of Dur), 1.81−1.57 (m, 30H, Cy), 1.21−1.13 (m, 18H,
3
13
1
q
Cy). C{ H} NMR (125.76 MHz, d -Tol, 70 °C): δ 150.1 (s, C of
Dur), 139.4 (s, CCH -o of Dur), 134.5 (s, CCH -m of Dur), 134.3 (s,
CH, Dur), 36.4 (vt, N = | JCP + JCP| = 26.4 Hz, C , Cy), 31.3 (m, C ,
Cy), 28.0 (m, C , Cy), 27.1 (s, CH -o of Dur), 27.2 (m, C , Cy), 20.8
8
3
3
1
3
1
3,5
2
,6
4
3
31
1
(
2
s, CH -m of Dur). P{ H} NMR (202.46 MHz, d -Tol, 25 °C): δ
3
8
1
11
1
1.4 (s, J = 3036 Hz). B{ H} NMR (128.38 MHz, d -Tol, 25
PPt
8
3
2
1
6
°C): δ 73.7 (br s, fwhm ≈ 2550 Hz). Anal. Calcd for C46
C, 52.13; H, 7.51. Found: C, 52.70; H, 7.72.
H
79BBr P Pt:
2 2
(
(
1e, 3.2(4)°) are significantly smaller than those in 1a
14
31.4(1)°) and 1d (9.2(5)°) (Table 3). The last two
Synthesis of trans-[Pt{B(Br)(C H -4-tBu)}Br(PCy ) ] (1b). A
6
4
3 2
complexes indicate a greater steric hindrance due to the two
pale yellow solution of [Pt(PCy ) ] (80 mg, 0.11 mmol) and a
3
2
solution of Br B(C H -4-tBu) (32.2 mg, 0.106 mmol) in 2 mL of
2
6
4
Table 3. Pt−B−C1−C2 Dihedral Angles in the Boryl
Complexes 1a,b,d,e
hexanes were cooled to −78 °C. The solution of the borane was added
dropwise to the platinum complex with continuous stirring. After the
mixture was stored at ambient temperature and stirred over a period of
1
h, the volume was reduced by half and stored for 1 day at −35 °C for
1
a
1b
1d
1e
crystallization. The solvent was removed in vacuo, and the colorless
solid was gently washed with hexanes to separate the phosphine−
Pt−B−C1−C2
31.4(1)
4.3(7)
9.2(5)
3.2(4)
C
dx.doi.org/10.1021/om501141g | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
f
f
borane adduct Cy P·BBr (Ph-4-tBu). trans-[Pt{B(Br)(Ph-4-tBu)}Br-
BAr ), 7.56 (br s, 4H, BAr ), 7.41 (br s, 1H, CH-p of Dur), 3.05 (m,
4 4
3
2
1
(
PCy ) ] was dried under vacuum (yield 66.2 mg, 59%). H NMR
6H, CH of iPr), 2.69 (s, 6H, CH -o of Dur), 2.20 (s, 6 H, CH -m of
Dur), 1.36 (q, 36 H, CH of iPr). C{ H} NMR (CD Cl , 100.61
3 2 2
MHz, 24 °C): δ 162.1 (q, J = 49.8 Hz, C-ipso, BAr ), 142.4 (s,
CCH -o of Dur), 142.2 (s, CH, Dur), 137.3 (s, CCH -o of Dur), 135.2
3 3
(s, C-o, BAr ), 129.2 (qq, J = 30.9 Hz, C-m of BAr ), 124.9 (q, J
= 273 Hz, CF , BAr ), 117.8 (sep, J = 3.8 Hz, C-p, BAr ), 27.8 (br
3 4 CF 4
3
2
3
3
13
1
(
500.13 MHz, d -Tol, 70 °C): δ 8.80 (br s, 2H, H-o of C H -4-tBu),
8
6
4
1
f
7
2
1
.32 (d, 2H, H-m of C H -4-tBu), 2.80 (m, 6H, CH-i of Cy), 2.42−
6
4
CB 4
.31 (m, 6H, Cy), 1.95−1.88 (m, 6H, Cy), 1.81−1.51 (m, 30H, Cy),
13
1
f
2
f
1
.37−0.97 (m, 18H, Cy), 1.21 (s, 9H, tBu). C{ H} NMR (125.76
4 CF 4 CF
q
f
3
f
MHz, d -Tol, 70 °C): δ 155.8 (s, C , C-ipso of C H -4-tBu), 129.3 (s,
8
6
4
q
q
C , C(CH ) of C H -4-tBu), 128.4 (s, C , C(tBu) of C H -4-tBu),
s, C, iPr), 21.9 (s, CH -o of Dur), 20.2 (s, CH of iPr), 18.6 (s, CH -m
3
3
6
4
6
4
3 3 3
of Dur). 31P{ H} NMR (CD Cl , 202.46 MHz, 24 °C): δ 55.8 (s, J
2 2 PPt
11 1
1
1
1
25.5 (s, CH-o of C H -4-tBu), 124.5 (s, CH-m of C H -4-tBu), 36.4
6
4
6
4
1
3
1
3,5
(
vt, N = | J + J | = 27.4 Hz, C , Cy), 31.5 (m, C , Cy), 30.7 (m,
= 2102 Hz). B{ H} NMR (CD Cl , 160.46 MHz, 24 °C): δ 99.6 (br
CP
CP
2
2
3
,5
2
4
2,6
f
C , Cy), 28.1 (vt, N = | J + J | = 11.5 Hz, C , Cy), 28.0 (vt, N =
s, fwhm ≈ 2400 Hz), −7.6 (s, BAr ). Anal. Calcd for
CP
2,6
CP
4
2
4
4
|
JCP + J | = 10.6 Hz, C , Cy), 27.1 (m, C , Cy), 31.3 (s, CH of
C H B BrF P Pt: C, 44.98; H, 4.27. Found: C, 45.35; H, 4.26.
CP
3
60 68
2
24 2
31
1
C H -4-tBu). P{ H} NMR (202.46 MHz, d -Tol, 70 °C): δ 22.3 (s,
Crystallographic Data. The crystal data of 1a,b and 2a,c were
collected on a Bruker X8APEX diffractometer with a CCD area
detector and multilayer mirror monochromated Mo Kα radiation. The
structures were solved using direct methods, refined with the Shelx
software package, and expanded using Fourier techniques. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included in structure factor calculations. All hydrogen atoms were
assigned to idealized geometric positions.
Crystal data for 1a: C46
block, 0.774 × 0.656 × 0.466 mm , orthorhombic space group P2
a = 14.3925(8) Å, b = 17.5114(11) Å, c = 18.3676(11) Å, V =
4629.2(5) Å , Z = 4, ρcalcd = 1.521 g cm , μ = 4.857 mm , F(000) =
2152, T = 100(2) K, R1 = 0.0265, wR2 = 0.0428, 9867 independent
reflections (2θ ≤ 53.64°), and 473 parameters.
Crystal data for 1b: C46
block, 0.24 × 0.19 × 0.15 mm , triclinic space group P1
13.0435(17) Å, b = 14.2865(18) Å, c = 14.9344(18) Å, α =
6
4
8
1
11
1
JPPt = 2842 Hz). B{ H} NMR (128.38 MHz, d -Tol, 23 °C): δ 74.0
8
(
7
br s, fwhm ≈ 1600 Hz). Anal. Calcd for C H BBr P Pt: C, 52.13; H,
46
79
2 2
.51. Found: C, 52.27; H, 7.69.
Synthesis of trans-[Pt{B(Br)Dur}Br(PiPr ) ] (1c). Neat [Pt-
3
2
(
PiPr ) ] was heated under vacuum to 60 °C. The obtained yellow
3 3
oil ([Pt(PiPr ) ]; 206 mg, 0.399 mmol) was dissolved in benzene. A
3
2
solution of Br BDur (121 mg, 0.399 mmol) in 2 mL of benzene was
2
added dropwise with continuous stirring. After 1 h the solvent was
removed under vacuum at 50 °C. The remaining colorless solid was
H79BBr P Pt, M = 1059.75, colorless
2 2 r
3
2 2 ,
1 1 1
crystallized from hexanes at −35 °C within 4 days (yield 206.3 mg,
1
3
−3
−1
6
3%). H NMR (400.13 MHz, C D , 24 °C): δ 6.95 (s, 1H, CH of
6
6
Dur), 3.16−3.08 (m, 6H, CH of iPr), 2.11 (s, 6H, CH -m of Dur),
3
13
1
1
.35−1.16 (m, 36H, CH of iPr, 6H, CH -o of Dur). C{ H} NMR
3
3
q
(
C D , 100.61 MHz, 24 °C): δ 150.6 (s, C of Dur), 138.7 (s, CCH -o
H
79BBr
P
2
2
Pt, M
r
= 1059.75, colorless
6
6
3
3
of Dur), 134.5 (br s, CCH -m of Dur), 134.2 (s, CH of Dur), 26.1 (t,
̅
, a =
3
1
JPC = 28.2 Hz, CH of iPr), 20.9 (s, CCH -m of Dur), 20.4 (br s, CH
3
3
3
31
1
8
0.703(4)°, β = 89.627(4)°, γ = 72.306(4)°, V = 2613.8(6) Å , Z = 2,
of iPr), 19.7 (s, CCH -o of Dur). P{ H} NMR (161.98 MHz, C D ,
3
6
6
−3
−1
1
11
1
ρcalcd = 1.347 g cm , μ = 4.301 mm , F(000) = 1076, T = 100(2) K,
R1 = 0.0611, wR2 = 0.0907, 11241 independent reflections (2θ ≤
2
4 °C): δ 28.5 (s, J = 3050 Hz). B{ H} NMR (128.38 MHz,
PPt
C D , 24 °C): δ ca. 74.1 (br s, fwhm ≈ 1990 Hz). Anal. Calcd for
C H BBr P Pt: C, 40.99; H, 6.88. Found: C, 40.61; H, 7.07.
6
6
5
3.84°), and 472 parameters.
2
8
56
2 2
f
Crystal data for 2a: C H B BrF P Pt, M = 1843.07, colorless
Synthesis of trans-[Pt(BDur)Br(PCy ) ][BAr ] (2a). trans-[Pt-
78 91
2
24
2
r
3
2
4
3
f
block, 0.24 × 0.18 × 0.09 mm , triclinic space group P1
̅
, a =
{
B(Br)(Dur)}Br(PCy ) ] (1a; 20 mg, 19 μmol) and Na[BAr ] (16.7
3
2
4
1
3.0971(9) Å, b = 17.3259(14) Å, c = 20.8371(15) Å, α = 71.694(4)°,
mg, 18.9 μmol) were mixed in CD Cl . The colorless reaction mixture
2
2
3
β = 75.300(4)°, γ = 85.345(4)°, V = 4342.1(6) Å , Z = 2, ρ
= 1.410
turned yellow, and a colorless solid precipitated. After filtration and
calcd
−3
−1
g cm , μ = 2.203 mm , F(000) = 1856, T = 100(2) K, R1 = 0.0567,
wR2 = 0.1335, 17726 independent reflections (2θ ≤ 52.74°), and 977
parameters.
storage at −35 °C for 3 days, colorless crystals of trans-[Pt(BDur)-
f
1
Br(PCy ) ][BAr ] were isolated (yield 25.7 mg, 74%). H NMR
(
3
2
4
f
500.13 MHz, CD Cl , 23 °C): δ 7.99 (m, 8H, BAr ), 7.75 (br s, 4H,
2 2 4
f
Crystal data for 2c: C H B BrCl F P Pt, M = 1687.62, colorless
BAr ), 7.49 (br s, 1H, CH-p of Dur), 2.88 (m, 6H, CH-i of Cy), 2.79
61 69
2
2
24
2
r
4
3
block, 0.35 × 0.27 × 0.22 mm , monoclinic space group P2 /n, a =
(
s, 6H, CH -o of Dur), 2.31 (s, 6H, CH -m, Dur), 2.21−2.01 (m, 12H,
1
3
3
13
1
1
6
3
4.935(6) Å, b = 24.927(13) Å, c = 18.515(8) Å, β = 97.572(9)°, V =
Cy), 1.95−1.71 (m, 30H, Cy), 1.26−1.09 (m, 18H, Cy). C{ H}
3
−3
−1
1
833(5) Å , Z = 4, ρ
= 1.640 g cm , μ = 2.867 mm , F(000) =
calcd
NMR (125.76 MHz, CD Cl , 23 °C): δ 162.4 (q, J = 49.9 Hz, CH-
2
2
CB
f
352, T = 100(2) K, R1 = 0.0621, wR2 = 0.0727, 14513 independent
reflections (2θ ≤ 53.54°), and 873 parameters.
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC 1032889−1032892. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
ipso of BAr ), 142.4 (s, CCH -o of Dur), 141.9 (s, CH, Dur), 137.3 (s,
4
3
f
2
CCH -m of Dur), 135.4 (br s, C-o of BAr ), 129.5 (qq, J = 31.5 Hz,
C-m of BAr ), 125.2 (q, J = 272 Hz, CF , BAr ), 118.0 (sep, J =
4
3
3
4
CF
f
1
f
3
4
CF
3
4
CF
f
1
3
1
.0 Hz, C-p of BAr ), 37.6 (vt, N = | J + J | = 26.6 Hz, C , Cy),
4 CP CP
3,5 2 4 2,6
0.7 (s, C , Cy), 27.5 (vt, N = | J + J | = 11.4 Hz, C , Cy), 26.2
CP
CP
4
31
1
(
s, C , Cy), 21.5 (s, CH -o of Dur), 18.6 (s, CH -m of Dur). P{ H}
3
3
1
NMR (202.46 MHz, CD Cl , 23 °C): δ 44.8 (s, J = 2075 Hz).
2
2
PPt
1
1
1
B{ H} NMR (160.46 MHz, CD Cl , 23 °C): δ 101 (br s, fwhm ≈
2
2
f
2
5
100 Hz), −7.3 (s, BAr ). Anal. Calcd for C H B BrF P Pt: C,
ASSOCIATED CONTENT
4
78 91
2
24 2
■
0.83; H, 4.98. Found: C, 50.30; H, 4.93.
f
*
S
Supporting Information
Synthesis of trans-[Pt{B(Br)(C H -4-tBu)}(PCy ) ] [BAr ] (2b).
6
6
3 2
4
f
4
Equimolar amounts of 1b (50 mg, 43 μmol) and Na[BAr ] (41.8 mg,
CIF file giving crystallographic data for 1a,b and 2a,c. This
material is available free of charge via the Internet at http://
pubs.acs.org.
4
2.7 μmol) were mixed in CD Cl . The colorless reaction mixture
2 2
31
turned yellow, and a colorless solid precipitated. Although fitting
P
and 11B NMR data were obtained, it was not possible to isolate the
resulting unstable product due to facile rehalogenation and re-
31
1
AUTHOR INFORMATION
formation of the precursor 1b. P{ H} NMR (161.98 MHz, CD Cl ,
■
*
2
2
1
11
1
24 °C): δ 41.8 (s, J = 2833 Hz). B{ H} NMR (128.38 MHz,
Corresponding Author
E-mail for H.B.: h.braunschweig@uni-wuerzburg.de.
PPt
f
CD Cl , 24 °C): δ 24.3 (br s), −7.4 (s, BAr ).
2
2
4
f
Synthesis of trans-[Pt(BDur)Br(PiPr ) ][BAr ] (2c). trans-[Pt-
3
2
4
f
Notes
{
B(Br)Dur}Br(PiPr ) ] (30 mg, 37 μmol) and Na[BAr ] (32.4 mg,
3
2
4
3
3.6 μmol) were mixed in CD Cl (4 mL). The solution turned
The authors declare no competing financial interest.
2
2
yellow, and a colorless solid precipitated. After the solids were filtered
off and the solution was stored at −35 °C over 3 days, colorless
ACKNOWLEDGMENTS
f
crystals of trans-[Pt(BDur)Br(PiPr ) ][BAr ] were isolated (yield 40.5
■
3
2
4
1
mg, 69%). H NMR (500.13 MHz, CD Cl , 24 °C): δ 7.72 (m, 8H,
This work was supported by an ERC Advanced Grant to H.B.
2
2
D
dx.doi.org/10.1021/om501141g | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
REFERENCES
■
(
(
1) Man
̈
nig, D.; No
̈
th, H. Angew. Chem., Int. Ed. 1985, 24, 878−879.
2) Irvine, G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice,
C. R.; Robins, E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Chem.
Rev. 1998, 98, 2685−2722.
(
3) Braunschweig, H.; Dewhurst, R. D.; Schneider, A. Chem. Rev.
2
010, 110, 3924−3957.
4) Braunschweig, H.; Kupfer, T.; Radacki, K.; Schneider, A.; Seeler,
F.; Uttinger, K.; Wu, H. J. Am. Chem. Soc. 2008, 130, 7974−7983.
5) Braunschweig, H.; Radacki, K.; Rais, D.; Uttinger, K. Angew.
Chem., Int. Ed. 2006, 45, 162−165.
6) Braunschweig, H.; Schneider, A.; Radacki, K. Science 2010, 328,
45−347.
7) Braunschweig, H.; Colling, M.; Kollann, C.; Stammler, H. G.;
Neumann, B. Angew. Chem., Int. Ed. 2001, 40, 2298−2300.
8) Blank, B.; Colling-Hendelkens, M.; Kollann, C.; Radacki, K.; Rais,
D.; Uttinger, K.; Whittell, G. R.; Braunschweig, H. Chem. Eur. J. 2007,
3, 4770−4781.
9) Braunschweig, H.; Kollann, C.; Englert, U. Angew. Chem., Int. Ed.
998, 37, 3179−3180.
10) Aldridge, S.; Calder, R. J.; Rossin, A.; Dickinson, A. A.; Willock,
(
(
(
3
(
(
1
(
1
(
D. J.; Jones, C.; Evans, D. J.; Steed, J. W.; Light, M. E.; Coles, S. J.;
Hursthouse, M. B. Dalton Trans. 2002, 2020.
(
11) Zhu, J.; Lin, Z. Y.; Marder, T. B. Inorg. Chem. 2005, 44, 9384−
390.
12) Braunschweig, H.; Brenner, P.; Mu
Uttinger, K. Chem. Eur. J. 2007, 13, 7171−7176.
13) Braunschweig, H.; Herbst, T.; Rais, D.; Seeler, F. Angew. Chem.,
Int. Ed. 2005, 44, 7461−7463.
14) Braunschweig, H.; Radacki, K.; Uttinger, K. Angew. Chem., Int.
Ed. 2007, 46, 3979−3982.
15) Arnold, N.; Braunschweig, H.; Brenner, P.; Jimenez-Halla, J. O.
C.; Kupfer, T.; Radacki, K. Organometallics 2012, 31, 1897−1907.
16) Braunschweig, H.; Radacki, K.; Uttinger, K. Chem. Eur. J. 2008,
4, 7858−7866.
17) Braunschweig, H.; Ye, Q.; Radacki, K. Chem. Commun. 2012, 48,
9
(
̈
ller, A.; Radacki, K.; Rais, D.;
(
(
(
(
1
(
2
(
(
701−2001.
18) Paetzold, P.; Hoffmann, J. Chem. Ber. 1980, 113, 3724−3733.
19) Otsuka, S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J. Am.
Chem. Soc. 1976, 98, 5850−5858.
(
20) Mann, B. E.; Musco, A. J. Chem. Soc., Dalton Trans. 1980, 5,
7
(
(
76−785.
21) Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 113−119.
22) Matsuda, T.; Otsuka, S.; Yoshida, T. Inorg. Synth. 1979, 28,
122−123.
E
dx.doi.org/10.1021/om501141g | Organometallics XXXX, XXX, XXX−XXX