Wolfphos in sheep's clothing: The first trinuclear triboryl- and other boryl platinum complexes featuring a flexible phosphine ligand

Article abstract of DOI:10.1002/zaac.201200556

Studies on the reactivity of the novel bis(phosphine) platinum complex [Pt{P(CH₂Cy)₃}₂] towards haloboranes are presented. The resulting complexes of the general formula trans-[Pt{B(R) R′}X{P(CH₂Cy)₃}₂] were isolated in good to excellent yields (82-91 %) and the molecular structure of trans-[Pt{B(Br)Fc}Br{P(CH₂Cy)₃}₂] is reported. The reactions of 1,4-(Br₂B)₂C₆H₄ and 1,3,5-(Br₂B)₃C₆H₃ with two and three equivalents of the platinum precursor yield the corresponding di- and trinuclear boryl platinum complexes, respectively. The structural characterization of the first trinuclear triboryl complex 1,3,5-trans-[Pt(BBr) Br{P(CH₂Cy)₃}₂]₃C₆H ₃ extends the number of possible structural motifs in boryl platinum chemistry by a noteworthy example and confirms that P(CH₂Cy) ₃ has flexible steric bulk. Copyright

Full text of DOI:10.1002/zaac.201200556

Job/Unit: Z12556
/KAP1
Date: 04-03-13 18:07:15
Pages: 6
ARTICLE
DOI: 10.1002/zaac.201200556
Wolfphos in Sheep’s Clothing: The First Trinuclear Triboryl- and Other
Boryl Platinum Complexes Featuring a Flexible Phosphine Ligand
Holger Braunschweig,*[a] Peter Brenner,[a] and Krzysztof Radacki[a]
Dedicated to Professor Heinrich Nöth on the Occasion of His 85th Birthday
Keywords: Boron; Platinum; Complex; Boryl; Phosphine; Flexible steric bulk
Abstract. Studies on the reactivity of the novel bis(phosphine)
platinum complex [Pt{P(CH2Cy)3}2] towards haloboranes are pre-
lents of the platinum precursor yield the corresponding di- and
trinuclear boryl platinum complexes, respectively. The structural
sented. The resulting complexes of the general formula characterization of the first trinuclear triboryl complex 1,3,5-trans-
trans-[Pt{B(R)RЈ}X{P(CH2Cy)3}2] were isolated in good to [Pt(BBr)Br{P(CH2Cy)3}2]3C6H3 extends the number of possible struc-
excellent yields (82–91%) and the molecular structure of tural motifs in boryl platinum chemistry by a noteworthy example and
trans-[Pt{B(Br)Fc}Br{P(CH2Cy)3}2] is reported. The reactions of
confirms that P(CH2Cy)3 has flexible steric bulk.
1,4-(Br2B)2C6H4 and 1,3,5-(Br2B)3C6H3 with two and three equiva-
The oxidative addition reaction of the B–X bond (X = F, Cl,
Br, I) to phosphine platinum complexes is now well investi-
gated[5] and has proven beneficial for the synthesis of model
compounds for intermediates in transition-metal-catalyzed bo-
rylation reactions.[6] A suitable platinum precursor for the iso-
lation of boron-centered ligands, especially in unprecedented
coordination modes, is [Pt(PCy3)2] (1, Cy = cyclohexyl)[7] be-
cause the addition of B–X bonds forms complexes of the gene-
ral formula trans-[Pt{B(R)RЈ}X(PCy3)2] commonly with high
selectivity.[8] Aside from the sterically crowded platinum pre-
cursor [Pt(PCy3)2], several different phosphine platinum com-
plexes can be used as precursors for the preparation of boryl
platinum complexes, e.g. [Pt(PPh3)4], [Pt(PPh3)3],[9] [Pt(PiPr3)
3],[10] [Pt(PEt3)4].[11] All these complexes react with dissoci-
ation of at least one phosphine ligand, which can form adducts
with the Lewis-acidic haloboranes, both necessitating un-
wanted workup steps and lowering the yield of the goal com-
pounds. An alternative to these [Pt(PR3)2+n] complexes might
be [Pt(η2-C2H4)(PPh3)2], but its reactivity is restricted to only
a few haloboranes, e.g. ClBcat (cat = 1,2-O2C6H4).[12] Particu-
larly for boryl platinum complexes featuring phosphine ligands
with sterically less demanding substituents, there is a lack of
suitable precursors.
Introduction
The stabilization of low valent transition metal complexes
without the disadvantage of lowering the reactivity by steric
overcrowding of the central metal atom is a general problem
in organometallic chemistry and homogeneous catalysis. Some
carbene-type ligands with flexible steric bulk of the NHC type
(NHC: N-heterocyclic carbenes; Glorius et al.) and also one
of the CAAC-type [CAAC: cyclic (alkyl)(amino)carbene;
Bertrand et al.], found applications e.g. in the activation of
aryl chlorides in Suzuki cross-coupling reactions,[1] the
Suzuki-Miyaura cross-coupling of sterically hindered aryl
chlorides,[2] and the α-arylation of propiophenone.[3]
In order to generate an easy-to-prepare platinum complex
featuring a phosphine ligand with flexible substituents at the
phosphorus atoms that has both the potential to either stabilize
low-valent metal complexes or free the coordination site when
required, we have developed the unusual Wolfphos ligand
P(CH2Cy)3. The corresponding platinum precursor
[Pt{P(CH2Cy)3}2] (2) can be thought of as an easy to handle
and bench-stable derivative of the elusive bisphosphine plati-
num complex [Pt(PMe3)2].
Recently we showed that the reactivity of 2 is unprecedented
in allowing for the investigation of the dehydrocoupling reac-
tion of catBH and its mechanism.[4] A remarkable finding of
this project was the likely formation of a PtIV intermediate as
the key compound of the catalytic cycle of this reaction.
Herein we report the preparation and characterization of a
handful of new boryl platinum complexes, among them the
first representative of a triboryl complex with an aryl spacer,
accessible through an oxidative addition protocol without the
formation of any byproducts.
* Prof. Dr. H. Braunschweig
Fax: +49-931-31-84623
E-Mail: h.braunschweig@uni-wuerzburg.de
[a] Institut für Anorganische Chemie
Julius-Maximilians-Universität Würzburg
Am Hubland
Results and Discussion
In order to generalize the reactivity of the novel platinum
species [Pt{P(CH2Cy)3}2] (2), we reacted the compound with
97074 Würzburg, Germany
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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H. Braunschweig, P. Brenner, K. Radacki
ARTICLE
several haloboranes BXRRЈ (X = R = Br, RЈ = Fc, NMe2; X =
Compound 3 crystallizes in the monoclinic space group
Br, R = RЈ = NMe2; X = R = RЈ = I). The observation of P21/c. The molecular structure exhibits the expected, slightly
the reactions with NMR spectroscopy reveals the quantitative distorted, square-planar trans-configured boryl platinum com-
formation of boryl platinum complexes of the general formula plex. The bond lengths at the central metal atom are very sim-
[Pt{B(R)(RЈ)}X{P(CH2Cy)3}2] [X = R = Br, RЈ = Fc (3), NMe2 ilar to those of trans-[Pt{B(Br)Fc}Br(PCy3)2] and trans-
(4); X = Br, R = RЈ = NMe2 (5); X = R = RЈ = I (6)] within [Pt{B(Br)Fc}Br(PiPr3)2] whereas the P1–Pt–P2 angle of
minutes at ambient temperature, whereas the formation of 5 is 177.3(1)° is the largest observed in boryl platinum complexes
complete within 2 d at 40 °C (Scheme 1). Remarkably, the re- and is very close to the ideal 180° in a perfectly square planar
action of 2 with BI3 is very selective even in presence of an arrangement. This finding might be explained by the large ste-
excess of haloborane and at elevated temperatures. The com- ric demand of the phosphine ligand that results in the maxi-
pounds 3–6 can be isolated as amorphous, analytically pure mum avoidance of the cyclohexyl groups. The phosphine sub-
compounds by evaporation of the solvent.
stituents have an eclipsed orientation concerning the phos-
phine-bound methylene carbon atoms, whereas two cyclohexyl
groups each point towards the vacant coordination sites at the
central platinum atom. The third cyclohexyl substituent is ori-
ented towards the boryl moiety, whereas the unrestricted rota-
tion around the methylene carbon atom allows for the avoid-
ance of the cyclohexyl ring and the {B(Br)Fc} group. A mea-
sure for the steric demand is given through the percent buried
volume[13] which gives a value[14] of 28.9%. This volume is
about one quarter smaller than that of the free phosphine ligand
(39.7%) and even smaller than that of PCy3 (31.8%).
Scheme 1. Synthesis of novel boryl complexes by B–X-oxidative ad-
dition (3: X = R = Br, RЈ = Fc, 4: NMe2; 5: X = Br, R = RЈ = NMe2;
6: X = R = RЈ = I).
The strikingly selective reactivity of 2 towards highly reac-
tive haloboranes such as BI3 motivated us to investigate its
reactivity towards dibromoboranes with aryl spacers, which
are known to react unselectively with 1. Mixing of 1,4-
C6H4(BBr2)2 with two equivalents of 2 yields 1,4-trans-
[Pt(BBr)Br{P(CH2Cy)3}2]2(C6H4) (7) as a slightly yellow,
moderately air sensitive solid in 74% yield. Monitoring the
reaction with NMR spectroscopy reveals the formation of a
single phosphorus-containing product in the 31P{1H} NMR
spectrum as a singlet signal in the expected range with plati-
The (boryl)(halogeno)platinum complexes 3–5 exhibit
31P{1H} NMR signals shifted about 10–20 ppm to lower fre-
quencies (11.9–0.8 ppm) relative to the signal of 2 (δ =
23.5 ppm), whereas the signal of 6 occurs at –9.0 ppm. Both
the relative chemical shift as well as the P–Pt coupling con-
stant feature values that are similar to those of the related sys-
tems trans-[Pt{B(R)(RЈ)}X(PCy3)2] (1JP,Pt = 2647–2959 Hz).
By layering a saturated solution of 3 in benzene with hexanes,
red crystals suitable for X-ray diffraction analysis could be
isolated (Figure 1).
1
num satellites (δ = 3.9, JP,Pt = 2750 Hz) (Scheme 2).
Scheme 2. Synthesis of di- and trinuclear boryl platinum complexes
with aryl spacers.
Figure 1. Molecular structure of trans-[Pt{B(Br)Fc}Br{P(CH2Cy)3}2]
as derived from X-ray crystallography. Thermal ellipsoids depicted at
the 50% probability level. For clarity, hydrogen atoms and one mole-
cule of co-crystallized benzene are removed and cyclohexyl groups are
simplified. Selected bond lengths /pm and angles /°: Pt–B 198.9(4),
Pt–Br1 261.15(6), P1–Pt–P2 175.95(3), B–Pt–Br1 177.3(1).
The reaction of
2
with three equivalents of
1,3,5-(BBr2)3C6H3 in benzene takes 16 h at 65 °C for full
transformation of the starting materials to 1,3,5-trans-
2
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Trinuclear Boryl Pt Complexes Featuring a Flexible Phosphine Ligand
[Pt(BBr)Br{P(CH2Cy)3}2]3C6H3 (8) as confirmed by NMR 198.6(9) pm, Pt–Br 261.94(8) pm, Pt–P1 231.5(2) pm, Pt–P2
spectroscopy. A new signal in the 1H NMR (δ = 9.56 ppm) for 232.3(2) pm, P1–Pt–P2 176.05(7)°, B–Pt–Br 169.4(3)°]. It
the aryl protons and a single 31P NMR resonance at δ = 3.4 should be noted that compound 8 represents the first trinuclear
(1JP,Pt = 2745 Hz) reveals the formation of a symmetric prod- triboryl complex.
uct.
Compound 8 crystallizes in the tetragonal space group
P42/n with two molecules in the asymmetric unit (Figure 2).
Conclusions
Reactivity studies of the novel bis(phosphine) platinum
complex [Pt{P(CH2Cy)3}2] (2) towards haloboranes disclose a
strikingly selective reactivity of 2. The resulting complexes
trans-[Pt{B(R)RЈ}X{P(CH2Cy)3}2] [X = R = Br, RЈ = Fc (3),
NMe2 (4); X = Br, R = RЈ = NMe2 (5); X = R = RЈ = I (6)] were
isolated in higher yields (82–91%) than their PCy3 derivatives
throughout, whereas the investigation of the molecular struc-
ture of 3 indicated structural similarities of the respective PCy3
systems. Whereas the high yield of the dinuclear complex 1,4-
trans-[Pt(BBr)Br{P(CH2Cy)3}2]2(C6H4) (7) compared to that
of the PCy3-substituted dinuclear complex again corroborates
the selective reactivity, the formation and structural characteri-
zation of the first trinuclear triboryl complex 1,3,5-trans-
[Pt(BBr)Br{P(CH2Cy)3}2]3C6H3 (8) extends the number of
possible structural motifs in boryl platinum chemistry by a
noteworthy example and confirms that the P(CH2Cy)3 ligand
has flexible steric bulk.
Experimental Section
Figure 2.
Molecular
structure
of
1,3,5-trans-[Pt(BBr)Br-
All manipulations were conducted either in an atmosphere of dry argon
or in vacuo using standard Schlenk line or glovebox techniques.
{P(CH2Cy)3}2]3C6H3 (8) as derived from X-ray crystallography. Ther-
mal ellipsoids depicted at the 50% probability level. For clarity, only
one of two molecules in the asymmetric unit is displayed, hydrogen
atoms are removed and phosphine substituents are simplified. Selected
bond lengths /pm and angles /° for one exemplary platinum fragment:
Pt–B 198.6(9), Pt–Br 261.94(8), Pt–P1 231.5(2), Pt–P2 232.3(2),
average C–C 140.5, P1–Pt–P2 176.05(7), B–Pt–Br1 169.4(3), P1–Pt–
C–C ca. 100.0.
BBr2Fc,[17] BBr2NMe2,[18] BBr(NMe2)2,[18] BI3,[19] 1,4-(Br2B)2C6H4,
[20]
and 1,3,5-(Br2B)3C6H3
were prepared according to published pro-
cedures. Solvents were dried according to standard procedures, de-
gassed, and stored in an argon atmosphere over activated molecular
sieves. C6D6 was degassed by three freeze-pump-thaw cycles and
stored over molecular sieves. Reagents were dried and purified by
standard procedures. NMR spectra were acquired with a Bruker AMX
400 or a Bruker Avance 500 NMR spectrometer. Chemical shifts are
given in ppm and are referenced against external Me4Si (1H, 13C),
BF3·Et2O (11B), and H3PO4 (85%, 31P). Assignments were made from
the analysis of 1H,13C-HMQC, and 1H,13C-HMBC NMR spectroscopic
experiments. Microanalyses (C, H, N) were performed with a Leco
Instruments elemental analyzer, type CHNS 932.
The molecular structure confirms the formation of a sym-
metric, trinuclear triboryl complex with an aryl spacer, in
which every platinum atom is coordinated in a square planar
trans arrangement. The clean formation of a trinuclear boryl
complex is unprecedented and corroborates the concept of flex-
ible steric bulk, given that [Pt(PCy3)2] decomposes when
treated with the triborylaryl reagent due to dissociation of the
more rigid phosphine, followed by phosphine-borane adduct
formation.[16] Because of the structural similarities of every
single central platinum atom, only one complex fragment is
discussed in detail. The Pt–P axes are oriented nearly orthogo-
nal to the plane defined by the aryl carbon atoms (P–Pt–C–C
≈100°). Similar to the arrangement in 3, the phosphorus-bound
methylene carbon atoms are eclipsed, whereas two cyclohexyl
rings are each oriented towards the free coordination site at the
platinum atom. The third cyclohexyl ring at each phosphine is
situated above the metal–boron bond and adopts an umbrella-
like position, shielding and kinetically stabilizing the Pt–B
bond. The average C–C distance in the central phenyl ring
(140.5 pm) lies in the typical range of that in benzene. The
bonding distances and angles at the platinum center lie in the
X-ray Crystallography: The crystal data of 3 were collected with a
Bruker APEX diffractometer with a CCD area detector and graphite
monochromated Mo-Kα radiation, those of 8 were collected with a
Bruker SMART-APEX diffractometer with a CCD area detector and
multi-layer mirror monochromated Mo-Kα radiation. The structures
were solved by direct methods, refined with the SHELX software
package (G. Sheldrick, Acta Crystallogr. Sect. A, 2008, 64, 112–122)
and expanded using Fourier techniques. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included in structure fac-
tors calculations. All hydrogen atoms were assigned to idealized geo-
metric positions.
The unit cell of 8 contains benzene and hexane molecules, which were
treated as a diffuse contribution to the overall scattering without spe-
cific atom positions by SQUEEZE/PLATON.
Crystal Data for 3: C55H90BBr2FeP2Pt, Mr = 1234.78, red block,
expected range for platinum boryl complexes [Pt–B 0.15ϫ0.12ϫ0.10 mm3, monoclinic space group P21/c,
a
=
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H. Braunschweig, P. Brenner, K. Radacki
ARTICLE
14.785(5) Å, b = 16.227(4) Å, c = 23.083(6) Å, β = 105.610(7)°, V = (br. m, 18 H, CH2Cy). 11B NMR (128.4 MHz, C6D6, 294 K): δ = 35.0
5334(3) Å3, Z = 4, ρcalcd. = 1.538 g·cm–3, μ = 4.485 mm–1, F(000) =
2516, T = 174(2) K, R1 = 0.0437, wR2 = 0.0688, 13237 independent
reflections [2θ Յ 5664°] and 559 parameters.
(FWHM ca. 1100 Hz). 13C{1H} NMR (100.6 MHz, C6D6, 296 K): δ =
3
43.0 (vbr. s, NMe2, CH2Cy), 36.3 (s, Cy), 34.8 (vt, N = |1JP,C + JP,C
|
= 15 Hz), 26.7 (s, Cy), 26.5 (s, Cy). 31P{1H} NMR (162.0 MHz, C6D6,
1
294 K): δ = 11.8 (s, JP,Pt = 2960 Hz).
Crystal Data for 8: C132H237B3Br6P6Pt3, Mr = 3107.20, color-
less block, 0.385ϫ0.294ϫ0.172 mm3, tetragonal space group
P42/n, a = 41.7816(16) Å, b = 41.7816(16) Å, c = 18.0650(15) Å, α =
trans-[Pt(BI2)I{P(CH2Cy)3}2] (6): To
a
yellow solution of
[Pt{P(CH2Cy)3}2] (20.0 mg, 23.8 μmol) in C6D6 (0.5 mL) colorless,
solid BI3 (9.4 mg, 24 μmol) was added. The reaction mixture decol-
ored immediately. By evaporation of the solvent in high vacuum trans-
[Pt(BI2)I{P(CH2Cy)3}2] was isolated as a colorless solid (25 mg,
84%). Elemental analysis (calculated for C42H78BI3P2Pt): C 40.49
90.00°, β = 90.00°, γ = 90.00°, V = 31536(3) Å3, Z = 8, ρcalcd.
=
1.309 g·cm–3, μ = 4.276 mm–1, F(000) = 12624, T = 102(2) K, R1 =
0.0852, wR2 = 0.1235, 29931 independent reflections [2θ Յ 51.36°]
and 1403 parameters.
1
(40.96); H 5.99 (6.38)%. H NMR (400.1 MHz, C6D6, 294 K): δ - =
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository numbers CCDC-916114 (3) and CCDC-916113 (8)
(Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk).
2.34–2.30 (br. s, 12 H, CH2Cy), 2.12–2.04 (m, 12 H, CH2Cy), 2.02–
1.90 (m, 6 H, CH2Cy), 1.88–1.70 (m, 12 H, CH2Cy), 1.67–1.57 (m, 6
H, CH2Cy), 1.48–1.29 (m, 12 H, CH2Cy), 1.24–1.08 (m, 18 H,
CH2Cy). 11B NMR (128.4 MHz, C6D6, 297.7 K): δ = 37.0. 13C{1H}
NMR (100.6 MHz, C6D6, 296 K): δ = 35.5 (m, CH2Cy), 34.8 (s,
CH2Cy), 33.5 (m, CH2Cy), 26.6 (s, CH2Cy), 26.3 (m, CH2Cy).
31P{1H} NMR (162.0 MHz, C6D6, 298 K): δ = –8.7 (1JP,Pt = 2668 Hz).
trans-[Pt{B(Br)Fc}Br{P(CH2Cy)3}2] (3):
A yellow solution of
1,4-trans-[Pt(BBr)Br{P(CH2Cy)3}2]2(C6H4) (7): [Pt{P(CH2Cy)3}2]
(20 mg, 24 μmol) and 1,4-C6H4(BBr2)2 (3.5 mg, 8.1 μmol) are diluted
in C6D6. After 1 h, the solvent of the reaction mixture is evaporated
off yielding 1,4-trans-[Pt(BBr)Br{P(CH2Cy)3}2]2(C6H4) as a moder-
ately air-sensitive, colorless solid (17 mg, 74%). Elemental analysis
(calculated for C92H162B2Br4P2Pt): C 51.49 (52.03); H 7.36 (7.69)%.
1H NMR (400.1 MHz, C6D6, 296 K): δ = 8.72 (s, 4 H, C6H4), 2.20–
1.05 (vbr. m, 156 H, Cy). 11B NMR (128.4 MHz, C6D6, 296 K): due to
unresolved coupling to 31P and 195Pt nuclei, no signal can be detected.
13C{1H} NMR (162.0 MHz, C6D6, 296 K): δ = 137.33 (br. s, C6H4),
36.8–35.0 (m, CH2Cy), 34.0 (m, CH2Cy), 27.1–26.4 (m, CH2Cy).
[Pt{P(CH2Cy)3}2] (100 mg, 119 μmol) in C6D6 (0.5 mL) was
mixed with BBr2Fc (42.3 mg, 119 μmol). The solvent of the
red reaction mixture was allowed to evaporate, yielding trans-
[Pt{B(Br)Fc}Br{P(CH2Cy)3}2] as a red, crystalline solid (116 mg,
82%). Elemental analysis (calculated for C52H87BBr2FeP2Pt·C6H6): C
1
54.69 (54.77); H 7.36 (7.58)%. H NMR (400.1 MHz, C6D6, 296 K):
δ = 4.71 (br. vt, 2 H, C5H4B), 4.34 (br. vt, 2 H, C5H4B), 4.24 (br. s, 5
H, C5H5), 2.29–2.18 (m, 6 H, CH2Cy), 2.14–1.10 (vbr. m, 66 H, Cy).
11B{1H} NMR (128.4 MHz, C6D6, 294 K): δ = 82.0. 13C{1H} NMR
(100.6 MHz, C6D6, 296 K): δ = 76.3, 71.9 ([(η5-C5H5)Fe(η5-C5H4)]),
69.9 ([(η5-C5H5)Fe(η5-C5H4)]), 40.8 (br. s, CH2Cy), 35.8 (vt, N =
1
31P{1H} NMR (162.0 MHz, C6D6, 296 K): δ = 3.9, JP,Pt = 2750 Hz.
4
3
|2JP,C + JP,C| = 3 Hz), 34.9 (s, CH2Cy), 33.6 (vt, N = |1JP,C + JP,C| =
16 Hz), 26.8 (s, CH2Cy), 26.4 (s, CH2Cy). 31P{1H} NMR (400.1 MHz,
C7D8, 296 K): δ = 4.0 (1JP,Pt = 2807 Hz).
1,3,5-trans-[Pt(BBr)Br{P(CH2Cy)3}2]3(C6H3)
(8):
Yellow
[Pt{P(CH2Cy)3}2] (70 mg, 83 μmol) and brown 1,3,5-(Br2B)3C6H3
(16 mg, 27 μmol) were mixed in C6D6 (0.5 mL) and heated to 65 °C
for 16 h. Evaporation of the solvent and gentle washing of the light
brown residue with cold hexanes (0.5 mL) yielded 1,3,5-trans-
[Pt(BBr)Br{P(CH2Cy)3}2]3(C6H3) as a colorless, crystalline solid
trans-[Pt{B(Br)NMe2}Br{P(CH2Cy)3}2] (4): A yellow solution of
[Pt{P(CH2Cy)3}2] (20.0 mg, 24 μmol) was mixed with BBr2(NMe2)
(5.11 mg, 23.8 μmol), leading to a colorless reaction mixture. Evapora-
tion of the solvent yielded 4 as a colorless, amorphous solid (22.8 mg,
91%). Elemental analysis (calculated for C44H84BBr2NP2Pt): C 50.58
(55 mg,
64%).
Elemental
analysis
(calculated
for
C132H237B3Br6P6Pt3): C 51.21 (51.02); H 7.61 (7.69)%. 1H NMR
(400.1 MHz, C6D6, 296 K): δ = 9.56 (s, 3 H, C6H3), 2.34–2.05 (m, 90
H, CH2Cy), 1.87–1.83 (m, 36 H, CH2Cy), 1.74–1.70 (m, 18 H,
CH2Cy), 1.54–1.51 (m, 36 H, CH2Cy), 1.30–1.17 (m, 54 H, CH2Cy).
11B NMR (128.4 MHz, C6D6, 296 K): δ = due to unresolved coupling
to 31P and 195Pt nuclei, no signal can be detected. 13C{1H} NMR
(100.6 MHz, C6D6, 296 K): δ = 152.1 (s, C6H3), the boron-bound car-
bon atom resonance could not be detected due to unresolved coupling;
36.3 (s, CH2Cy), 34.9 (s, CH2Cy), 34.6 (s, CH2Cy), 34.4 (s, CH2Cy),
34.3 (s, CH2Cy), 26.8 (s, CH2Cy), 25.5 (s, CH2Cy). 31P{1H} NMR
(162.0 MHz, C6D6, 296 K): δ = 3.4 (1JP,Pt = 2745 Hz).
1
(50.10); H 7.67 (8.03); N 1.09 (1.33)%. H NMR (400.1 MHz, C6D6,
297 K): δ = 3.12 (s, 3 H, NMe2), 2.98 (s, 3 H, NMe2), 2.26–2.21 (m,
6 H, CH2Cy), 2.08–1.97 (m, 24 H, CH2Cy), 1.77–1.61 (m, 18 H,
CH2Cy), 1.43–1.34 (m, 12 H, CH2Cy), 1.24–1.09 (m, 18 H, CH2Cy).
11B NMR (128.4 MHz, C6D6, 298 K): δ = 36.4. 13C{1H} NMR
(100.6 MHz, C6D6, 296 K): δ = 45.0 (s, NMe2), 40.8 (s, NMe2), 35.9
(m, CH2Cy), 34.6 (m, CH2Cy), 33.7 (m, CH2Cy), 26.7 (m, CH2Cy),
26.5 (s, CH2Cy). 31P{1H} NMR (162.0 MHz, C6D6, 298 K): δ = 6.7
(1JP,Pt = 2750 Hz).
trans-[Pt{B(NMe2)2}Br{P(CH2Cy)3}2]
(5):
[Pt{P(CH2Cy)3}2]
(20 mg, 24 μmol) and BBr(NMe2)2 (4.3 mg, 24 μmol) were incorpo-
rated in C6D6 (0.5 mL) yielding a colorless reaction mixture. After 2
d at 60 °C the reaction was judged complete with NMR spectroscopy.
By evaporation of the solvent in high vacuum and gentle washing of
the remaining solid with hexanes, trans-[Pt{B(NMe2)2}-
Br{P(CH2Cy)3}2] was isolated as a spectroscopically pure, colorless
solid (21.4 mg, 88%). Elemental analysis (calculated for
C46H90BBrN2P2Pt): C 53.93 (54.22); H 8.60 (8.90); N 2.35 (2.75)%.
1H NMR (400.1 MHz, C6D6, 296 K): δ = 2.93 (s, 12 H, NMe2), 2.09–
2.01 (br. m, 30 H, CH2Cy), 1.76–1.71 (br. m, 12 H, CH2Cy), 1.65–
1.61 (br. m, 6 H, CH2Cy), 1.43–1.34 (br. m, 12 H, CH2Cy), 1.23–1.10
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft (DFG) for financial
support. The authors thank Dr. Justin Wolf for inspiration.
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Received: December 19, 2012
Published Online: ᭿
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H. Braunschweig, P. Brenner, K. Radacki
ARTICLE
H. Braunschweig*, P. Brenner, K. Radacki ..................... 1–6
Wolfphos in Sheep’s Clothing: The First Trinuclear Triboryl-
and Other Boryl Platinum Complexes Featuring a Flexible
Phosphine Ligand
6
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