Synthesis and Reactivity of Platinum(II) cis-Dialkyl, cis-Alkyl Chloro, and cis-Alkyl Hydrido Bis-N-heterocyclic Carbene Chelate Complexes

Article abstract of DOI:10.1021/acs.organomet.5b00204

Platinum(II) cis-dimethyl and cis-dineopentyl complexes bearing the alkyl-substituted bis-NHC ligands L^t-Bu, L^Me, and L^i-Pr (L^t-Bu = 1,1′-di-tert-butyl-3,3′-methylenediimidazolin-2,2′-diylidene, L^Me = 1,1′-dimethyl-3,3′-methylenediimidazolin-2,2′-diylidene, L^i-Pr = 1,1′-diisopropyl-3,3′-methylenediimidazolin-2,2′-diylidene) as well as novel cis-alkyl chloro and cis-alkyl hydrido compounds were synthesized. The reactivity of the dimethyl complexes toward dichloromethane and methanol was investigated. Reductive elimination of alkanes from cis-alkyl hydrido complexes requires much higher temperatures than in related bisphosphine systems, which limits their applicability for the generation of reactive, bent platinum(0) d¹⁰-ML₂ fragments for bond-activation chemistry. The platinum(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction in most cases. (Figure Presented).

Full text of DOI:10.1021/acs.organomet.5b00204

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Platinum(II) cis-Dialkyl, cis-Alkyl Chloro,
and cis-Alkyl Hydrido Bis‑N‑heterocyclic Carbene Chelate Complexes
Matthias Brendel,§ Rene Engelke,§,† Vidya G. Desai,‡ Frank Rominger, and Peter Hofmann*
́
Organisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Platinum(II) cis-dimethyl and cis-dineopentyl
complexes bearing the alkyl-substituted bis-NHC ligands Lt‑Bu
,
LMe, and Li‑Pr (Lt‑Bu = 1,1′-di-tert-butyl-3,3′-methylenediimid-
azolin-2,2′-diylidene, LMe = 1,1′-dimethyl-3,3′-methylenedi-
imidazolin-2,2′-diylidene, Li‑Pr = 1,1′-diisopropyl-3,3′-
methylenediimidazolin-2,2′-diylidene) as well as novel cis-
alkyl chloro and cis-alkyl hydrido compounds were synthesized.
The reactivity of the dimethyl complexes toward dichloro-
methane and methanol was investigated. Reductive elimination
of alkanes from cis-alkyl hydrido complexes requires much
higher temperatures than in related bisphosphine systems,
which limits their applicability for the generation of reactive,
bent platinum(0) d10-ML2 fragments for bond-activation chemistry. The platinum(II) complexes were characterized by NMR
and IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction in most cases.
the reaction, could hamper reactions of the 14 VE fragment or
interfere with product formation. This problem can be avoided
with the second route based upon irreversible reductive
elimination of e.g. a gaseous alkane from an appropriate cis-
dialkyl or a cis-alkyl hydrido Pt(II) precursor. In case of
established bisphosphine systems, cis-neopentyl hydrido
platinum(II) complexes were successfully used. The reductive
elimination takes place at room temperature for [(dtbpm)-
PtNpH]3a (dtbpm = bis(di-tert-butylphosphino)ethane; Np =
neopentyl) and above 45 °C in case of [(dcpe)PtNpH] (dcpe =
bis(dicyclohexylphosphino)ethane).2a However, bis-NHC che-
late complexes of platinum bearing two cis-alkyl ligands are
scarce. Jamali et al. synthesized the dialkyl complex
[Lt‑BuPtMe2] by reaction of an in situ generated silver cluster
with [PtMe2(μ-SMe2)]2. Following this procedure with the
isopropyl-substituted ligand Li‑Pr, a cluster containing two silver
and four platinum centers was formed.8 A dimethyl platinum-
(II) complex bearing an aryl-substituted bis-NHC ligand was
synthesized by the reaction of the same platinum precursor
with the isolated bis(carbene).9
INTRODUCTION
■
Hydrocarbons are major constituents of natural gas and
petroleum. Thus, the selective transformation of C−H bonds
to other functional groups is a field of great interest not only in
academic but in industrial research as well. One option to
activate C−H or other relative inert bonds is the oxidative
addition to electron-rich, low-valent complexes of late transition
1
1
metals like d10-ML2 fragments (isolobal to CH2). Whitesides
et al.2 and our group3 were able to confirm this by experiments
with platinum complexes of chelating bisphosphines. The
reactivity of these fragments depends on the electron density at
the metal center and the bite angle of the ligand. MO model
calculations suggest a higher reactivity for smaller bite angles in
bond-activation reactions due to an increase of the total energy
and an electronic structure change of the frontier orbitals.4 It is
well recognized that the replacement of phosphine ligands by
N-heterocyclic carbenes (NHCs) can provide complexes with
enhanced catalytic performance and higher ligand-to-metal
bond stability.5 The first chelating bis(carbene) complex used
in catalysis was described by Herrmann et al. in 1995, who
tested LMePdI2 successfully as a catalyst in the Heck reaction.6
There are two possible routes to access the desired
platinum(0) fragments bearing bis-NHC units as spectator
ligands: Either the direct conversion of a platinum(0) precursor
with a preformed bis(carbene), or reductive elimination from a
bis-NHC platinum(II) compound. We successfully applied the
first strategy to synthesize [Lt‑BuPt(η2-cod)] (cod = 1,5-
cyclooctadiene) as the first example of a bis-NHC platinum(0)
complex.7 This one-step approach provides a fast access to
complexes bearing differently substituted bis-NHCs. However,
the olefin ligand, which has to dissociate prior to or in course of
The goal of this study was the development of a flexible
protocol for the synthesis of cis-dialkyl platinum(II) complexes
bearing methyl and neopentyl groups, which do not allow β-H
elimination. These compounds incorporating the bis-NHC
chelate ligands Lt‑Bu, LMe, and Li‑Pr (Figure 1) should then be
further functionalized via cis-alkyl chloro to cis-alkyl hydrido
complexes in order to investigate the reductive elimination of
alkanes from the latter.
Received: March 11, 2015
© XXXX American Chemical Society
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[Li‑PrPtMe2] (2c) were synthesized by the reaction of the
corresponding bis(imidazolium) salts, potassium tert-butoxide,
and [(cod)PtMe2] in THF or toluene at room temperature in
yields between 61% and 87% (Scheme 1). As the products are
unreactive toward water, it was possible to quench the reaction
mixtures, and the complexes were extracted with dichloro-
methane.
Figure 1. Bis-NHC ligands used in this study.
RESULTS AND DISCUSSION
■
Our first strategy for the preparation of platinum(II) dialkyl
complexes with chelating bis-NHC ligands started with the
synthesis of the corresponding dichloro complexes. Analo-
gously to our work on bisphosphine platinum(II) complexes,3a
these compounds should then in a second step be trans-
formable with alkyl lithium reagents into the corresponding cis-
dialkyl analogs.
Scheme 1. Synthesis of the Dimethyl Complexes 2a−c
The reaction of [(cod)PtCl2] with the isolated bis(carbene)
Lt‑Bu in dichloromethane afforded the cis-dichloro complex
[Lt‑BuPtCl2] (1) in 52% yield. Single crystals suitable for X-ray
analysis precipitated from the reaction mixture at room
temperature (Figure 2). The six-membered platinacycle exhibits
Suitable single crystals for X-ray crystallography were
obtained by slow evaporation of THF solutions of the
complexes. The structures of the two new compounds 2b
(C1-symmetry) and 2c (Cs-symmetry) are depicted in Figure 3.
Figure 2. Solid-state molecular structure of 1 with ellipsoids drawn at
the 50% probability level. Hydrogen atoms of tert-butyl groups and a
non-coordinated dichloromethane molecule are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Pt−C1 1.982(5), Pt−C6
1.974(5), Pt−Cl12 2.3731(13), Pt−Cl13 2.3764(14), C1−Pt−C6
84.6(2), Cl12−Pt−Cl13 88.02(5), N5−C11−N7 107.8(4).
the typical boat conformation found in methylene-bridged bis-
NHC complexes, resulting in two diastereotopic methylene
protons denominated exo- and endo-H. Due to the weaker trans
influence of the chloro ligands, the platinum−carbene bond
lengths in 1 are shorter than those in [Lt‑BuPtMe2].8 In
comparison to the dimethyl complex, the bite angle in the
dichloro complex of 84.6(2)° is 1.6(2)° larger.
Figure 3. Solid-state molecular structures of 2b and 2c with ellipsoids
drawn at the 50% probability level. A non-coordinated THF molecule
in case of 2c is omitted for clarity. Selected bond lengths (Å) and
angles (deg): [LMePtMe2] (2b), Pt−C1 2.011(4), Pt−C6 2.024(4),
Pt−C12 2.090(5), Pt−C13 2.127(4), C1−Pt−C6 84.56(17), C12−
Pt−C13 85.9(2), N5−C11−N7 108.9(3); [Li‑PrPtMe2] (2c), Pt−C1
2.013(5), Pt−C7 2.104(5), C1−Pt−C1′ 85.5(3), C7−Pt−C7′
86.6(3), N5−C6−N5′ 109.0(6).
This air-stable compound has a very low solubility in most
common organic solvents. In DMSO-d6 the solubility was
1
sufficient for the recording of a H NMR spectrum, which
shows two doublets at 5.97 and 6.18 ppm for the bis-NHC
ligand’s methylene bridge. Hence, the inversion of the
platinacycle’s boat conformers does not take place at room
temperature in solution.
Presumably due to the low solubility of 1, reactions with alkyl
lithium compounds were not successful, and another route had
to be developed for the synthesis of cis-platinum(II) dialkyl
complexes. Starting from [(cod)PtCl2], the alkyl groups were
introduced prior to the bis-NHC ligand. In contrast to the
preparation of 1, the bis(carbenes) were generated in situ as
they turned out to be very temperature-sensitive. The dimethyl
complexes [Lt‑BuPtMe2] (2a), [LMePtMe2] (2b), and
The bite angles of the bis-NHC ligands in the two structurally
characterized dimethyl complexes are similar and lie between
85.5(3)° in 2c and 83.0(1)° in 2a.8 In comparison to the latter,
the platinum−carbene bond lengths in 2b and 2c are about
0.03 Å shorter.
In the 1H NMR spectra, the methyl ligands appear as singlets
between 0.2 and 0.3 ppm complemented by platinum satellites
2
with J coupling constants of 66−68 Hz. The protons of the
bis-NHC ligands’ methylene bridges give rise to two doublets
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2
with J coupling constants between 12 and 13 Hz. As in
complex 1, this shows the rigidity of the six-membered
platinacycles’ boat conformations at room temperature. In
each compound, one of the methylene protons, which was
identified by ROESY as the one directing toward the metal
center (endo-H), additionally couples with the platinum atom
(4J = 11−19 Hz). Remarkably, in complex 2b all protons couple
with the metal center except for the exo-H of the methylene
bridge. The 13C NMR signals of the carbene carbon atoms
between 180.52 and 186.89 ppm are shifted to higher field in
comparison to the platinum(0) complex [Lt‑BuPt(η2-cod)]
(193.49 ppm).7
High-temperature NMR measurements in DMSO-d6 for 2b
bearing the N-methyl-substituted bis(carbene) showed coa-
lescence of the methylene protons at 57 °C. As expected, the
inversion takes place at higher temperatures with increasing
Figure 5. Main component of the solid-state structural isomers of 3
with ellipsoids drawn at the 50% probability level.
isomerization might in case of the bis-NHC system be slower
because of the strong platinum−carbene bonds hampering an
opening of the chelate ring.
1
steric bulk of the ligand’s substituents. Figure 4 shows the H
Due to the nonplanar chelate ring, seven diastereotopic
products for the oxidative addition are in principle possible.
1
The H NMR spectrum in Figure 6 was recorded 8 days after
1
Figure 4. Determination of the methylene protons coalescence point
using VT H NMR spectroscopy of 2c.
Figure 6. H NMR spectrum of 2b after 8 days in CD2Cl2.
1
[LMePtMe2] was dissolved in CD2Cl2. It shows no remaining
starting material, but a complicated product mixture. The
integrals over the selected regions are in accordance with the
formation of oxidative addition products: six protons for the
methyl ligands at high field, six protons for the methyl
substituents of the bis-NHC in the area around 4 ppm as well
as two and four protons at lower field representing the
methylene bridge and the imidazole protons, respectively. The
deuterated chloromethylene ligand is not visible. In a COSY
experiment, the diastereotopic sets of the methylene bridges of
three main products (marked #, ○, and ^ in Figure 6) could be
identified. These compounds were observed in a ratio of about
10:3:2.
NMR spectra for 2c with a coalescence temperature of 76 °C.
In the tert-butyl system 2a, no inversion was observed until 150
°C. In spite of this high temperature, no decomposition of the
complex was visible in its NMR spectra.
While the sterically most crowded dimethyl complex 2a
based on ligand Lt‑Bu is stable in dichloromethane at room
temperature, 2b and 2c slowly reacted with this solvent within
about 5 days. X-ray structure analysis of single crystals formed
by slow evaporation of a dichloromethane solution of
[LMePtMe2] showed that oxidative addition to the complex
takes place (Figure 5). The octahedral, 5-fold C-ligated
platinum(IV) complex [LMePtMe2(CH2Cl)Cl] (3) is the
product of a formal cis-addition of a C−Cl bond to Pt(II)
andwith about 50%is the main component of the crystals.
It is superimposed by several other stereoisomers holding the
chloromethylene moiety in a cis- or trans-arrangement to the
chloro ligand. The only group not involved in this multiple
disorder pattern is the chloro ligand. Due to this disorder, we
refrain from a geometrical discussion. Known structurally
characterized compounds resulting from the oxidative addition
of dichloromethane to platinum(II) dimethyl complexes exhibit
trans arrangements of the methyl ligands due to a fast
isomerization of the initially formed cis product.10 This
Also in case of [Li‑PrPtMe2] single crystals were harvested
from a dichloromethane solution. However, their X-ray analysis
revealed them as the known complex [Li‑PrPtCl2].11 Due to the
isopropyl groups, superimpositions of the signals did not allow
an interpretation of the NMR data of the product mixture in
this case.
When dissolved in methanol-d4, each of the three dimethyl
complexes reacted to a new species within about 1 day at room
temperature. These transformations were accompanied by the
appearance of a singlet at 0.20 ppm and a triplet at 0.18 ppm in
1
the H NMR spectra, indicating the formation of methane and
C
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monodeuterated methane, respectively. Subsequently, the new
compounds further reacted to a complicated product mixture of
several secondary products. This reactivity was investigated in
detail for 2c. A quantitative transformation to the first product
(4) without the observation of byproducts is observed after 2
days at 5 °C in methanol. In comparison to the dimethyl
complex, Cs-symmetry is broken: the isopropyl methine
1
hydrogens give rise to two septets in the H NMR spectrum.
A signal at 0.45 ppm representing a platinum bound methyl
group has an integral of three protons and, in contrast to the
product from the reaction with deuterated methanol, a new
singlet with the same integral at 3.77 ppm is observed. This
group obviously originates from the solvent andin
accordance with the formation of methanesuggests that the
product is a platinum(II) methoxy methyl complex (Scheme
2). Although various attempts to obtain single crystals for X-ray
analysis were not successful, the LIFDI mass spectrum and a
correct elemental analysis confirm the identity of 4.
Scheme 2. [Li‑PrPtMe2] Reacts with Methanol under
Liberation of Methane To Give the Methoxy Methyl
Complex 4
Figure 7. Solid-state molecular structures of 5a and 5b with ellipsoids
drawn at the 50% probability level. Hydrogen atoms of tert-butyl
groups are omitted for clarity. Selected bond lengths (Å) and angles
(deg): [Lt‑BuPtNp2] (5a), Pt−C1 2.050(3), Pt−C6 2.059(3), Pt−C12
2.101(3), Pt−C13 2.098(3), C1−Pt−C6 81.77(11), C12−Pt−C13
86.25(11), N5−C11−N7 109.2(2); [LMePtNp2] (5b) (two independ-
ent molecules were found in the unit cell; the values given are
averaged), Pt−C1 2.021, Pt−C6 2.018, Pt−C12 2.108, Pt−C13 2.116,
C1−Pt−C6 82.3, C12−Pt−C13 89.3, N5−C11−N7 108.7.
The syntheses of [Lt‑BuPtNp2] (5a) and [LMePtNp2] (5b)
were performed in a similar procedure to that of the dimethyl
complexes using [(cod)PtNp2] as precursor (Scheme 3). In
Scheme 3. Preparation of the Dineopentyl Complexes 5a
and 5b
acetyl chloride with methanol. The products were obtained as
colorless solids in 94% (6a) and 79% (6b) yield.
Scheme 4. Synthesis of Bis-NHC cis-Methyl Chloro
Complexes
contrast to known procedures using a Grignard reagent to
prepare this platinum(II) complex,12 we developed a synthesis
employing neopentyl lithium to give [(cod)PtNp2] in high
yield and purity.
The dineopentyl complexes were isolated as colorless solids
in 76% (5a) and 67% (5b) yield, respectively. As the rotation of
the neopentyl groups is sterically hindered in both complexes,
the hydrogen atoms of the platinum-bound methylene groups
are diastereotopic and give rise to two doublets in the 1H NMR
spectra. Single crystals were obtained from a saturated
dichloromethane solution (5a) and by layering a THF solution
of 5b with n-hexane. The solid-state structures show a slight
decrease of the bite angles in comparison to the corresponding
dimethyl complexes (Figure 7). In the dimethyl as well as in the
dineopentyl complexes, the platinum−carbene bonds in
compounds bearing LMe and Li‑Pr are shorter than those in
In contrast to the dimethyl complexes, the solubility in THF
and toluene is low, and NMR data were obtained from CD2Cl2
solutions. Due to the asymmetric substitution, the signal sets
for the imidazole rings and ligand substituents are doubled in
comparison to the starting materials. Single crystals were
obtained from a dichloromethane solution in case of 6a. The
solid-state structure shows that the shorter platinum−carbene
bond distance is trans to the chloro ligand (Figure 8).
For the synthesis of the neopentyl chloro complex 7 the
employment of AcCl/MeOH led to the formation of side
products. Better results were obtained by slow addition of a
hydrogen chloride stock solution in diethyl ether to a saturated
THF solution of the dineopentyl complex (Scheme 5). The
product precipitated and was obtained in 91% yield.
complexes of the bulky Lt‑Bu
.
The methyl chloro bis-NHC platinum(II) complexes 6a and
6b were synthesized from the corresponding dimethyl
complexes by reaction with 1 equiv of hydrochloric acid
(Scheme 4). The acid was generated in situ by the reaction of
The solid-state structure shows that the bite-angle of
84.38(9)° in 7 is larger than in the dineopentyl complex
(Figure 9). As in the other alkyl chloro complexes, the
D
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Scheme 6. Preparation of the Alkyl Hydrido Complexes 8
and 9
coupling constants of 1047 and 1083 Hz, respectively. The
rotation of the sterically demanding neopentyl ligand in 9 is
hindered at room temperature resulting in two doublets for its
2
methylene groups with J couplings of 12 Hz between the
hydrogen atoms and 78−84 Hz to the metal center. Whereas
the 13C resonance of the neopentyl methylene group in 9 is
only slightly shifted to higher field compared to that of the
dineopentyl complex 5a, the 13C signal of the methyl ligand in
8 is shifted 15.7 ppm upfield in comparison to the methyl
ligands of 2a and is observed at −23.91 ppm.
Crystallization from a saturated THF solution yielded single
crystals of 8. Due to the strong trans influence of the hydrido
ligand, the platinum−carbene bond opposite to it is weakened
and exhibits the longest NHC carbon-to-metal distance of the
platinum(II) complexes discussed in this study with 2.072(4) Å
(Figure 10). The platinum−hydride bond length measures
Figure 8. Solid-state molecular structure of 6a with ellipsoids drawn at
the 50% probability level. A non-coordinated dichloromethane
molecule is omitted for clarity. Selected bond lengths (Å) and angles
(deg): Pt−C1 2.060(4), Pt−C6 1.961(4), Pt−Cl 2.3724(13), Pt−C12
2.121(8), C1−Pt−C6 85.21(17), Cl−Pt−C12 86.6(3), N5−C11−N7
108.9(3).
Scheme 5. Preparation of the cis-Neopentyl Chloro Complex
7
platinum−carbene bond trans to the chloro ligand is the shorter
one.
Figure 10. Solid-state molecular structure of 8 with ellipsoids drawn at
the 50% probability level. Hydrogen atoms of tert-butyl groups and a
non-coordinated THF molecule are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Pt−C1 2.036(4), Pt−C6 2.072(4), Pt−
H12 1.72(4), Pt−C13 2.114(4), C1−Pt−C6 84.14(15), H−Pt−C13
79.0(14), N5−C11−N7 108.5(3).
Figure 9. Solid-state molecular structure of 7 with ellipsoids drawn at
the 50% probability level. Hydrogen atoms of tert-butyl groups and a
non-coordinated dichloromethane molecule are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Pt−C1 1.970(2), Pt−C6
2.061(2), Pt−Cl 2.3894(5), Pt−C12 2.097(2), C1−Pt−C6 84.38(9),
Cl−Pt−C12 90.07(6), N5−C11−N7 108.54(19).
1.72(4) Å and is longer than that in the neopentyl hydrido
bisphosphine systems (dcpe: 1.56(5) Å;2a dtbpm: 1.58(5) Å3a).
This is in line with the IR stretching frequency of 2002 cm−1 in
8, which is lower than 2010 cm−1 in [(dcpe)PtNpH].2a In the
bis-NHC neopentyl hydrido complex 9, an even lower
frequency of 1986 cm−1 is observed.
Alkyl hydrido complexes were synthesized for the Lt‑Bu
systems, as the steric bulk of the tert-butyl groups is expected
to facilitate the reductive elimination and makes the complexes
less prone to side reactions resulting from oxidative additions.
Lt‑BuPtMeH (8) and Lt‑BuPtNpH (9) are accessible from the
reaction of the appropriate alkyl chloro complexes with 5−10
equiv of sodium trimethoxyborohydride at 65 °C (Scheme 6).
The products were obtained by extraction with toluene in yields
of 78% (8) and 87% (9).
As stated in the introduction, reductive elimination of
neopentane from bisphosphine platinum(II) neopentyl hydrido
complexes takes place at rather mild temperatures. In case of
the bis-NHC complexes 8 and 9, no reaction was observed
within 2 days in THF-d8 at 65 °C. After 1 day at 100 °C in
toluene-d8, about 20% of 9 had reductively eliminated
1
neopentane, giving rise to a singlet in the H NMR spectrum
at 0.90 ppm. The conversion of 8 is about 5 times slower, which
is attributed to less steric bulk of the methyl ligand. In both
reactions, a yellow suspension is formed. The solid is hardly
soluble in any common organic solvent, and the reaction
1
In the H NMR spectra, the hydrido ligands give rise to
singlets at −7.58 (8) and −7.12 ppm (9) with 1J(Pt,H)
E
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92.4 Hz, 4H, Pt-CH2), 2.12−2.34 (m, 8H, CCH−CH2), 4.88 (s,
2J(Pt,H) = 37.5 Hz, 4H, CCH-CH2). 13C{1H} NMR (75.47 MHz,
CDCl3): δ 29.80 (CCH-CH2), 35.56 (3J(Pt,C) = 50.0 Hz, CH3),
36.08 (1J(Pt,C) = 884.1 Hz, Pt-CH2), 36.69 (C(CH3)3), 100.50 (s+sat,
1J(Pt,C) = 44.6 Hz, CC).
product(s) could not be identified to date. First experiments
show that the addition of electron-deficient olefins lowers the
required temperatures to a certain extent. This is attributed to
the associative formation of platinum(0) olefin complexes.
Nevertheless, the high temperatures needed limit the scope of
the neopentyl hydrido complexes as precursors for reactive d10-
ML2 fragments in bond-activation reactions, as potential
activation products might not be stable under these conditions.
The chemistry of the cis-alkyl hydrido complexes 8 and 9 will
be reported in due course.
[Lt‑BuPtCl2] (1). Lt‑Bu (50 mg, 0.19 mmol) and [(cod)PtCl2] (72 mg,
0.19 mmol) were dissolved in dichloromethane (5 mL) and stirred for
2 h at room temperature. The colorless, crystalline product was
isolated by filtration, washed two times with 0.5 mL of dichloro-
methane, and dried in vacuo. Yield: 53 mg (52%). Anal. Calcd for
C16H26Cl4N4Pt (526.37): C, 31.44; H, 4.29; N, 9.17. Found: C, 32.17;
H, 4.44; N, 8.75 (the one non-coordinated dichloromethane molecule
1
visible in the crystal structure is included). H NMR (300.13 MHz,
CONCLUSION
■
2
DMSO-d6): δ 1.85 (s, 18H, CH3), 5.97 (d, J(H,H) = 13 Hz, 1H,
In summary, we have presented the syntheses of cis-dimethyl
and cis-dineopentyl platinum(II) complexes bearing alkyl-
substituted bis-NHC chelate ligands. The reactivity of the cis-
dimethyl complexes toward methanol and dichloromethane was
investigated. In the first case, cis-methoxy methyl complexes are
formed. Oxidative addition of dichloromethane does not take
place with the bulky tert-butyl-substituted complex. In case of
methyl substitution, a 5-fold C-ligated platinum(IV) product
was structurally characterized. By the reaction of the cis-dialkyl
complexes with hydrogen chloride, the corresponding cis-alkyl
chloro complexes were prepared, which were further function-
alized to cis-alkyl hydrido compounds. Reductive elimination of
alkanes from these complexes requires high temperatures of
about 100 °C, which limits their usefulness as convenient
precursors for 14 VE fragments of the d10-ML2 type in bond-
activation reactions. Therefore, future studies in this field
should better focus on employment of the conveniently
accessible platinum(0) complex Lt‑BuPt(η2-cod) as the source
for the desired reactive intermediates.
CH2), 6.18 (d, 2J(H,H) = 13 Hz, 1H, CH2), 7.55 (d, 3J(H,H) = 2 Hz,
3
2H, CH-Im), 7.60 (d, J(H,H) = 2 Hz, 2H, CH-Im). Due to the low
solubility of 1a, a 13C NMR spectrum could not be measured. MS
(FAB): m/z (%) 526.1 (4) [M + H]+, 491.1 (29) [M − Cl]+, 454.2
(100) [M − 2Cl − H]+, 398.1 (75) [M − 2Cl − t-Bu]+.
[Lt‑BuPtMe2] (2a). A colorless suspension of [(cod)PtMe2] (300
mg, 0.90 mmol), Lt‑BuH2Br2 (380 mg, 0.90 mmol), and potassium tert-
butoxide (303 mg, 2.70 mmol) in toluene (40 mL) was stirred for 12 h
at room temperature. Dichloromethane (20 mL) and water (40 mL)
were added, and the organic phase was separated. The aqueous phase
was extracted three times with 15 mL of dichloromethane. The
combined organic phases were dried over magnesium sulfate. All
volatile compounds were removed in vacuo. The remaining solid was
washed with diethyl ether and dried in vacuo to give a colorless
powder. Yield: 265 mg (61%). Mp: 157 °C dec. Anal. Calcd for
C17H30N4Pt (485.52): C, 42.05; H, 6.23; N, 11.54. Found: C, 41.78;
1
H, 6.14; N, 11.35. H NMR (300.51 MHz, THF-d8): δ 0.20 (s+sat,
2J(Pt,H) = 68 Hz, 6H, Pt-CH3), 1.72 (s, 18H, N-C(CH3)3), 5.39 (d,
2J(H,H) = 12 Hz, 1H, exo-CH2), 6.39 (d+sat, 2J(H,H) = 12 Hz,
4J(Pt,H) = 19 Hz, 1H, endo-CH2), 7.04 (d, 3J(H,H) = 2 Hz, 2H, CH-
3
Im), 7.11 (d, J(H,H) = 2 Hz, 2H, CH-Im). 13C{1H} NMR (125.47
MHz, THF-d8): δ −8.25 (s+sat, 1J(Pt,C) = 609 Hz, Pt-CH3), 31.54 (s
+sat, 4J(Pt,C) = 8 Hz, N-C(CH3)3), 58.50 (N-C(CH3)3), 63.90
(CH2), 117.47 (s+sat, 3J(Pt,C) = 24 Hz, CH-Im), 118.27 (s+sat,
3J(Pt,C) = 19 Hz, CH-Im), 186.89 (N2C-Im). IR (KBr, cm−1):
3132(w); 3097(w); 2974(m); 2795(m); 2360(w); 2340(w); 1477(s);
1368(s); 1229(s); 825(m). MS (LIFDI, CH2Cl2): m/z (%) 485.2
(100) [M]+•.
EXPERIMENTAL SECTION
■
General Methods. All manipulations were performed under an
inert atmosphere of argon using standard Schlenk and glovebox
techniques. Dichloromethane, diethyl ether, n-hexane, THF, and
toluene were taken from an MBraun SPS-800 solvent purification
system. Pentane was distilled from sodium, methanol from
magnesium, and DMSO from calcium hydride. All solvents were
degassed by freeze−pump−thaw cycles, saturated with argon, and
[LMePtMe2] (2b). A colorless THF suspension (20 mL) of
[(cod)PtMe2] (150 mg, 0.45 mmol), LMeH2Br2 (152 mg, 0.45
mmol), and potassium tert-butoxide (106 mg, 0.95 mmol) was stirred
for 24 h at room temperature. Water (40 mL) and dichloromethane
(20 mL) were added to the light yellow suspension, and the organic
phase was separated. The aqueous phase was extracted three times
with 20 mL of dichloromethane. After back-extraction of the combined
organic phases with water (20 mL), they were dried over magnesium
sulfate. All volatile compounds were removed in vacuo. The remaining
colorless solid was washed three times with 4 mL of diethyl ether.
Yield: 158 mg (87%). Mp: 237 °C dec. Anal. Calcd for C11H18N4Pt
(401.38): C, 32.92; H, 4.52; N, 13.96. Found: C, 32.79; H, 4.48; N,
13.67. 1H NMR (300.13 MHz, THF-d8): δ 0.30 (s+sat, 2J(Pt,H) = 66
stored over molecular sieves (3 Å). Chemicals were prepared
13
according to published procedures: Lt‑Bu
,
1,1′-di-tert-butyl-3,3′-
methylenediimidazolium dibromide (Lt‑BuH2Br2),7 1,1′-dimethyl-3,3′-
methylenediimidazolium dibromide (LMeH2Br2),14 1,1′-diisopropyl-
3,3′-methylenediimidazolium dibromide (Li‑PrH2Br2),14 [(cod)-
PtCl2],15 and [(cod)PtMe2].16 Neopentyl lithium was synthesized
according to a procedure by Schrock et al.17a using ultrasonic
irradiation as described by Matsumoto et al.17b NMR data are reported
in units of δ relative to tetramethylsilane referenced to the residual
solvent resonance as internal standard.
[(cod)PtNp2]. At −30 °C a colorless solution of neopentyllithium
(673 mg, 8.62 mmol) in diethyl ether (30 mL) was added dropwise
over a period of 20 min to a colorless suspension of [(cod)PtCl2]
(1.075 g, 2.87 mmol) in diethyl ether (30 mL). The yellowish reaction
mixture was stirred for 2 h and allowed to warm to 5 °C during that
time. The resulting yellow suspension was hydrolyzed with 30 mL of a
saturated ammonium chloride solution. After the organic phase was
separated and the aqueous phase extracted four times with 8 mL of
diethyl ether, the combined organic phases were dried over
magnesium sulfate. All volatile compounds were removed in vacuo.
The remaining brown crude product was purified by column
chromatography with petroleum ether, dissolved in pentane, and
crystallized at −15 °C. Pale yellow crystals were obtained as product.
Yield: 1.024 g (80%). Mp: 111−112 °C. Anal. Calcd for C18H34Pt
(445.54): C, 48.52; H, 7.69. Found: C, 48.60; H, 7.69. 1H NMR
4
Hz, 6H, Pt-CH3), 3.66 (s+sat, J(Pt,H) = 3,6 Hz, 6H, N-CH3), 5.53
2
2
(d, J(H,H) = 12 Hz, 1H, exo-CH2), 5.84 (d+sat, J(H,H) = 12 Hz,
4J(Pt,H) = 11 Hz, 1H, endo-CH2), 6.87 (d+sat, 3J(H,H) = 2 Hz,
4J(Pt,H) = 7 Hz, 2H, CH-Im), 7.08 (d+sat, J(H,H) = 2 Hz, 4J(Pt,H)
3
= 4 Hz, 2H, CH-Im). 13C{1H} NMR (75.47 MHz, THF-d8): δ −8.34
1
3
(s+sat, J(Pt,C) = 584 Hz, Pt-CH3), 36.52 (s+sat, J(Pt,C) = 23 Hz,
N-CH3), 63.21 (s+sat, 3J(Pt,C) = 43 Hz, CH2), 118.77 (s+sat,
3J(Pt,C) = 19 Hz, CH-Im), 120.62 (s+sat, 3J(Pt,C) = 23 Hz, CH-Im),
185.08 (s+sat, 1J(Pt,C) = 788 Hz, N2C-Im). IR (KBr, cm−1): 3145(w);
3106(w); 2946(m); 2900(m); 2788(s); 1563(w); 1457(s); 1368(s).
MS (LIFDI, toluene): m/z (%) 401.1 (100) [M]+•.
[Li‑PrPtMe2] (2c). Li‑PrH2Br2 (355 mg, 0.90 mmol), potassium tert-
butoxide (212 mg, 1.89 mmol), and [(cod)PtMe2] (300 mg, 0.90
mmol) were suspended in THF (40 mL) and stirred at room
2
(300.53 MHz, CDCl3): δ 1.05 (s, 18H, CH3), 1.88 (s+sat, J(Pt,H) =
F
DOI: 10.1021/acs.organomet.5b00204
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
temperature for 24 h. The light pink suspension was concentrated to
half of its volume in vacuo, and dichloromethane (40 mL) and water
(20 mL) were added. The phases were separated, and the aqueous
phase was extracted three times with dichloromethane (5 mL). The
combined organic phases were dried over magnesium sulfate, and two-
thirds of the solvent was removed in vacuo. The brownish solution was
layered with diethyl ether (10 mL) and stored overnight at −60 °C.
The colorless solid was washed with cold diethyl ether and dried in
vacuo. Yield: 230 mg (78%). Mp: 260 °C dec. Anal. Calcd for
C15H26N4Pt (457.18): C, 39.38; H, 5.73; N, 12.25. Found: C, 39.33;
H, 5.66; N, 11.90. 1H NMR (300.51 MHz, DMSO-d6): δ 0.17 (s+sat,
2H, CH-Im). 13C{1H} NMR (125.76 MHz, CD2Cl2): δ 31.56 (N-
1
C(CH3)3), 34.18 (s+sat, J(Pt,C) = 706 Hz, Pt-CH2), 35.36 (s+sat,
3J(Pt,C) = 45 Hz, Pt-CH2-C(CH3)3), 36.10 (Pt-CH2-C(CH3)3), 58.69
3
(N-C(CH3)3), 64.28 (s+sat, J(Pt,C) = 64 Hz, CH2), 117.81 (s+sat,
3J(Pt,C) = 23 Hz, CH-Im), 118.86 (s+sat, 3J(Pt,C) = 18 Hz, CH-Im),
188.44 (N2C-Im). IR (KBr, cm−1) = 3138(w); 3109(w); 2974(s);
2943(s); 2927(s); 2888(s); 2777(s); 1471(m); 1435(s); 1404(s);
1360(s); 1229(s); 821(m). MS (LIFDI, toluene) m/z (%) 526.3 (100)
[M − Np]+.
[LMePtNp2] (5b). A colorless THF suspension (80 mL) of
[(cod)PtNp2] (500 mg, 1.12 mmol), LMeH2Br2 (372 mg, 1.10
mmol), and potassium tert-butoxide (303 mg, 2.70 mmol) was stirred
for 12 h at room temperature. Water and dichloromethane were
added. The organic phase was separated, and the aqueous phase was
extracted three times with 15 mL of dichloromethane. The organic
phase was dried over magnesium sulfate. All volatile compounds were
removed in vacuo. The remaining solid was washed with diethyl ether.
Yield: 380 mg (67%). Mp: 242 °C dec. Anal. Calcd for C19H34N4Pt
(513.58): C, 44.43; H, 6.67; N, 10.91. Found: C, 44.63; H, 6.51; N,
3
2J(Pt,H) = 66 Hz, 6H, Pt-CH3), 1.14 (d, J(H,H) = 7 Hz, 6H, N-
CH(CH3)2), 1.41 (d, 3J(H,H) = 7 Hz, 6H, N-CH(CH3)2), 5.03 (sept,
2
3J(H,H) = 7 Hz, 2H, N-CH(CH3)2), 5.67 (d+sat, J(H,H) = 13 Hz,
4J(Pt,H) = 12 Hz, 1H, endo-CH2), 5.79 (d, 2J(H,H) = 13 Hz, 1H, exo-
CH2), 7.27 (d, 3J(H,H) = 2 Hz, 2H, CH-Im), 7.32 (d, 3J(H,H) = 2 Hz,
2H, CH-Im). 13C{1H} NMR (75.56 MHz, DMSO-d6): δ −7.51 (s+sat,
1J(C,Pt) = 581 Hz, Pt-CH3), 22.62 (N-CH(CH3)2), 23.41 (N-
CH(CH3)2), 49.44 (N-C(CH3)2), 61.89 (CH2), 115.63 (CH-Im),
119.73 (CH-Im), 180.52 (N2C-Im). IR (ATR, cm−1) = 3132(m);
2961(m); 2870(m); 2791(m); 1520(w); 1449(m); 1410(s); 1366(m);
1351(m); 1281(m); 1237(m); 1215(s); 1194(m); 1179(s); 1004(m);
797(m); 707(s); 669(s); 529(m); 534(m). MS (LIFDI, THF): m/z
(%) 456.9 (100) [M]+•.
1
10.59. H NMR (500.13 MHz, THF-d8): δ 0.84 (s, 18H, Pt-CH2-
2
2
C(CH3)3), 1.22 (d+sat, J(H,H) = 12 Hz, J(Pt,H) = 80 Hz, 2H, Pt-
CH2), 2.06 (d+sat, 2J(H,H) = 12 Hz, 2J(Pt,H) = 72 Hz, 2H, Pt-CH2),
3.66 (s, 6H, N-CH3), 5.55 (d, 2J(H,H) = 12 Hz, 1H, exo-CH2), 6.15 (d
2
4
+sat, J(H,H) = 12 Hz,, J(Pt,H) = 14 Hz, 1H, endo-CH2), 6.78 (d,
3J(H,H) = 2 Hz, 2H, CH-Im), 7.11 (d, 3J(H,H) = 2 Hz, 2H, CH-Im).
13C{1H} NMR (125.76 MHz, THF-d8): δ 34.82 (s+sat,1J(Pt,C) = 673
Hz, Pt-CH2), 36.42 (s+sat, 3J(Pt,C) = 44 Hz, Pt-CH2-C(CH3)3), 37.07
[Li‑PrPt(OMe)Me] (4). 2a (211 mg, 0.46 mmol) was dissolved at 5
°C in methanol (15 mL) and stirred at this temperature for 2 days. All
volatiles of the slightly turbid reaction mixture were removed in vacuo.
The colorless product was dried in vacuo. Yield: 218 mg (100%). Mp:
107 °C dec. Anal. Calcd for C15H26N4OPt (473.48): C, 38.05; H, 5.53;
N, 11.83. Found: C, 37.81; H, 5.43; N, 11.95. 1H NMR (500.13 MHz,
3
(s+sat, J(Pt,C) = 23 Hz, N-CH3), 36.59 (s, Pt-CH2-C(CH3)3), 63.10
(s+sat, 3J(Pt,C) = 48 Hz, CH2), 119.02 (s+sat, 3J(Pt,C) = 19 Hz, CH-
Im), 120.73 (s+sat, 3J(Pt,C) = 21 Hz, CH-Im), 187.88 (s+sat, 1J(Pt,C)
= 753 Hz, N2C-Im). IR (KBr, cm−1) = 3130(w); 2948(s); 2935(s);
2889(s); 2768(s); 1658(w); 1470(s); 1421(s). MS (LIFDI, toluene):
m/z (%) 512.9 (100) [M]+•.
3
THF-d8): δ 0.45 (s, 3H, Pt-CH3), 1.21 (d, J(H,H) = 7 Hz, 3H, N-
CH(CH3)2), 1.27 (d, 3J(H,H) = 7 Hz, 3H, N-CH(CH3)2), 1.44
2
(pseudo-t, 6H, N-CH(CH3)2), 3.77 (s, 3H, OCH3), 4.90 (d, J(H,H)
= 12 Hz, 1H, exo-CH2), 5.19 (sept, 3J(H,H) = 9 Hz, 1H, N-
CH(CH3)2), 6.13 (sept, 3J(H,H) = 7 Hz, 1H, N-CH(CH3)2), 6.95 (d,
3J(H,H) = 2 Hz, 1H, CH-Im), 7.00 (d, 3J(H,H) = 2 Hz, 1H, CH-Im),
7.33−7.42 (m, 2H, endo-CH2 and CH-Im), 8.16 (s, 1H, CH-Im).
13C{1H} NMR (125.76 MHz, THF-d8): δ −5.27 (Pt-CH3), 22.30 (N-
CH(CH3)2), 22.73 (N-CH(CH3)2), 23.68 (N-CH(CH3)2), 24.42 (N-
CH(CH3)2), 49.68 (N-C(CH3)2), 50.66 (N-C(CH3)2), 55.50
(OCH3), 61.09 (CH2), 115.36 (CH-Im), 115.43 (CH-Im), 120.11
(CH-Im), 120.92 (CH-Im), 156.28 (N2C-Im), 181.86 (N2C-Im). IR
(ATR, cm−1) = 2963(w); 2872(w); 2792(w); 2742(w); 1455(w);
1416(s); 1356(m); 1285(w); 1211(s); 1177(m); 1131(w); 1062(s);
1006(w); 880(w); 801(w); 717(m); 693(m); 674(m). MS (LIFDI,
THF): m/z (%) 472.9 (100) [M]+•.
[Lt‑BuPtMeCl] (6a). Acetyl chloride (14.5 μL, 0.20 mmol) was
added to a solution of 2a (99 mg, 0.20 mmol) in dichloromethane (20
mL) and methanol (0.3 mL). The reaction mixture was stirred for 2 h
at room temperature. All volatile compounds were removed in vacuo.
The remaining solid was washed with THF. Yield: 97 mg (94%). Mp:
266 °C dec. Anal. Calcd for C16H27ClN4Pt (505.95): C, 37.98; H,
5.38; N, 11.07. Found: C, 37.76; H, 5.34; N, 10.78. 1H NMR (300.51
MHz, CD2Cl2): δ 0.38 (s+sat, 2J(Pt,H) = 59 Hz, 3H, Pt-CH3), 1.78 (s,
2
9H, N-C(CH3)3), 1.83 (s, 9H, N-C(CH3)3), 5.30 (d, J(H,H) = 12
2
4
Hz, 1H, exo-CH2), 6.48 (d+sat, J(H,H) = 12 Hz, J(Pt,H) = 18 Hz,
1H, endo-CH2), 7.00 (d, 3J(H,H) = 2 Hz, 1H, CH-Im), 7.02 (d,
3J(H,H) = 2 Hz, 1H, CH-Im), 7.09 (m, 2H, CH-Im). 13C{1H} NMR
1
(125.76 MHz, CD2Cl2): δ −6.74 (s+sat, J(Pt,C) = 553 Hz, Pt-CH3),
[Lt‑BuPtNp2] (5a). [(cod)PtNp2] (1.737 g, 3.90 mmol) and
31.52 (N-C(CH3)3), 31.82 (N-C(CH3)3), 59.53 (N-C(CH3)3), 64.44
(s+sat, 3J(Pt,C) = 71 Hz, CH2), 118.37 (s+sat, 3J(Pt,C) = 22 Hz, CH-
Im), 118.71 (CH-Im), 118.87 (CH-Im), 155.79 (N2C-Im), 182.61
(N2C-Im). IR (KBr, cm−1): 3130(m); 2976(m); 2926(m); 2360(w);
2340(w); 1416(s); 1380(s); 1236(s). MS (LIFDI, CH2Cl2): m/z (%)
505.3 (100) [M]+•.
L
t‑BuH2Br2 (1.881 g, 4.29 mmol) were suspended in dimethyl sulfoxide
(50 mL) and toluene (50 mL). Over a period of 1.5 h, a solution of
potassium tert-butoxide (1.531 g, 13.65 mmol) in dimethyl sulfoxide
(5 mL) and toluene (20 mL) was added, and the deep red solution
was stirred for 12 h at room temperature. All volatile compounds apart
from dimethyl sulfoxide were removed in vacuo. Dichloromethane
(200 mL) and water (200 mL) were added to the remaining brown
suspension. The organic phase was separated, and the aqueous phase
was extracted four times with dichloromethane (50 mL). After the
organic phase had been back-extracted three times with water (40
mL), the combined aqueous phases were extracted a last time with
dichloromethane (35 mL). The combined organic phases were dried
over magnesium sulfate and concentrated to 20 mL in vacuo. The
colorless product crystallized at 8 °C and was washed with diethyl
ether. Yield: 1.767 g (76%). Mp: 256 °C dec. Anal. Calcd for
C25H46N4Pt (597.74): C, 50.23; H, 7.76; N, 9.37. Found: C, 49.97; H,
[LMePtMeCl] (6b). Acetyl chloride (14.5 μL, 0.20 mmol) was added
to a solution of 2b (75 mg, 0.19 mmol) in dichloromethane (30 mL)
and methanol (1 mL). The reaction mixture was stirred for 1 h at
room temperature. All volatile compounds were removed in vacuo.
The remaining solid was washed with toluene. Yield: 62 mg (79%).
Mp: 270 °C dec. Anal. Calcd for C10H15ClN4Pt (421.79): C, 28.48; H,
1
3.58; N, 13.28. Found: C, 28.40; H, 3.62; N,13.01. H NMR (600.13
MHz, CD2Cl2): δ 0.44 (s+sat, 2J(Pt,H) = 56 Hz, 3H, Pt-CH3), 3.71 (s,
3H, N-CH3), 3.96 (s, 3H, N-CH3), 5.41 (d, 2J(H,H) = 13 Hz, 1H, exo-
CH2), 6.07 (d+sat, 2J(H,H) = 13 Hz, 1H, endo-CH2), 6.82 (d, 3J(H,H)
= 2 Hz, 1H, CH-Im), 6.85 (d, 3J(H,H) = 2 Hz, 1H, CH-Im), 7.03 (d,
3J(H,H) = 2 Hz, 1H, CH-Im), 7.05 (d, 3J(H,H) = 2 Hz, 1H, CH-Im).
13C{1H} NMR (150.90 MHz, CD2Cl2): δ −6.07 (s, Pt-CH3), 37.47
(N-CH3), 37.65 (N-CH3), 63.27 (CH2), 118.81 (CH-Im), 119.47
(CH-Im), 121.55 (CH-Im), 122.05 (CH-Im), 155.21 (N2C-Im),
181.77 (N2C-Im). IR (KBr, cm−1): 3153(w); 3084(w); 2948(m);
1
7.72; N, 9.26. H NMR (300.13 MHz, CD2Cl2): δ 0.79 (s, 18H, Pt-
CH2-C(CH3)3), 1.09 (d+sat, 2J(H,H) = 12 Hz, 2J(Pt,H) = 76 Hz, 2H,
2
Pt-CH2), 1.70 (s, 18H, N-C(CH3)3), 1.74 (d+sat, J(H,H) = 12 Hz,
2
2J(Pt,H) = 79 Hz, 2H, Pt-CH2), 5.13 (d, J(H,H) = 12 Hz, 1H, exo-
3
2
CH2), 6.87 (d, J(H,H) = 2 Hz, 2H, CH-Im), 6.87 (d+sat, J(H,H) =
4
3
12 Hz, J(Pt,H) = 20 Hz, 1H, endo-CH2), 7.02 (d, J(H,H) = 2 Hz,
G
DOI: 10.1021/acs.organomet.5b00204
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
2918(m); 2797(s); 1668(w); 1564(m); 1464(s); 1434(s); 1401(s);
1248(s). MS (LIFDI, CH2Cl2): m/z (%) 422.0 (100) [M + H]+.
[Lt‑BuPtNpCl] (7). To a solution of 5a (195 mg, 0.33 mmol) in THF
(15 mL) a solution of hydrogen chloride in diethyl ether (0.36 mL, 1.0
M) was added with a syringe pump over a period of 2 h at room
temperature. The colorless suspension was stirred for 30 min, and all
volatile compounds were removed in vacuo. The colorless solid was
washed three times with 6 mL of toluene and dried in vacuo. Yield:
166 mg (91%). Mp: 227 °C dec. Anal. Calcd for C20H35ClN4Pt
(562.06): C, 42.74; H, 6.28; N, 9.97. Found: C, 42.12; H, 6.02; N,
9.76. 1H NMR (300.51 MHz, CD2Cl2): δ 0.79 (s, 9H, Pt-CH2-
C(CH3)3), 1.64 (s, 2H, Pt-CH2), 1.81 (s, 9H, N-C(CH3)3), 1.82 (s,
118.57 (s+sat, J(Pt,C) = 17 Hz, CH-Im), 184.18 (N2C-Im), 191.14
(N2C-Im). IR (THF, cm−1) = 3141(w); 2979(s); 2926(s); 2846(m);
1986(s, Pt-H); 1413(s); 1372(s); 1292(s); 699(m). MS (LIFDI,
toluene): m/z (%) 455.2 (100) [M − NpH]+•.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, and CIF files, giving NMR spectra and
crystallographic data. The Supporting Information is available
free of charge on the ACS Publications website at DOI:
10.1021/acs.organomet.5b00204.
2
9H, N-C(CH3)3), 5.27 (d, J(H,H) = 12 Hz, 1H, exo-CH2), 6.52 (d
2
4
+sat, J(H,H) = 12 Hz, J(Pt,H) = 18 Hz, 1H, endo-CH2), 6.98 (d,
3J(H,H) = 2 Hz, 1H, CH-Im), 7.02 (d, 3J(H,H) = 2 Hz, 1H, CH-Im),
AUTHOR INFORMATION
■
3
3
7.07 (d, J(H,H) = 2 Hz, 1H, CH-Im), 7.09 (d, J(H,H) = 2 Hz, 1H,
CH-Im). 13C{1H} NMR (125.76 MHz, CD2Cl2): δ 31.50 (N-
C(CH3)3), 32.01 (N-C(CH3)3), 32.54 (Pt-CH2), 34.57 (s+sat,
3J(Pt,C) = 36 Hz, Pt-CH2-C(CH3)3), 35.62 (Pt-CH2-C(CH3)3),
59.43 (N-C(CH3)3), 59.52 (N-C(CH3)3), 64.56 (CH2), 118.37 (CH-
Im), 118.72 (CH-Im), 118.77 (CH-Im), 118.79 (CH-Im), 157.48
(N2C-Im), 183.73 (N2C-Im). IR (KBr, cm−1) = 3130(m); 2975(s);
2943(s); 2889(m); 2847(m); 1418(s); 1376(s); 1322(m); 1235(s);
1211(s); 718(m). MS (LIFDI, CH2Cl2): m/z (%) 562.3 (100) [M +
H]+.
Corresponding Author
*E-mail: ph@oci.uni-heidelberg.de.
Present Addresses
†R.E.: Freudenberg Filtration Technologies SE & Co. KG, D-
69465 Weinheim, Germany.
‡V.G.D.: Department of Chemistry, DMs College of Arts,
Science and Commerce, Post-Graduate Research Centre,
Assagao, Mapusa, Bardez-Goa, 403507 India
[Lt‑BuPtMeH] (8). A colorless THF suspension (40 mL) of 6 (50
mg, 0.10 mmol) and sodium trimethoxyborohydride (64 mg, 0.50
mmol) was stirred at 65 °C for 1 h. All volatile compounds were
removed in vacuo. Toluene (40 mL) was added, and the solution was
stirred for 15 min, filtered, and evaporated to dryness. The remaining
solid was washed with n-hexane. Yield: 37 mg (78%). Mp: 162 °C dec.
Anal. Calcd for C16H28N4Pt (471.50): C, 40.76; H, 5.98; N, 11.88.
Found: C, 41.06; H, 6.00; N, 11.71. 1H NMR (300.13 MHz, THF-d8):
Author Contributions
§M.B. and R.E. contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Support of this work by the Deutsche Forschungsgemeinschaft
(through SFB 623 “Molecular Catalysts: Structure and
Functional Design”) is gratefully acknowledged.
1
2
δ −7.58 (s+sat, J(Pt,H) = 1047 Hz, 1H, Pt-H), 0.48 (s+sat, J(Pt,H)
= 68 Hz, 3H, Pt-CH3), 1.74 (s, 9H, N-C(CH3)3), 1.78 (s, 9H, N-
2
C(CH3)3), 5.58 (d, J(H,H) = 12 Hz, 1H, exo-CH2), 6.16 (d+sat,
2J(H,H) = 12 Hz, J(Pt,H) = 17 Hz, 1H, endo-CH2), 7.00 (d+sat,
4
3J(H,H) = 2 Hz, 4J(Pt,H) = 8 Hz, 1H, CH-Im), 7.10 (d, J(H,H) = 2
3
REFERENCES
■
Hz, 2H, CH-Im), 7.18 (d, J(H,H) = 2 Hz, 1H, CH-Im). 13C{1H}
3
(1) (a) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507−514.
(b) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471−2526.
(2) (a) Hackett, M.; Ibers, M. A.; Jernakoff, P.; Whitesides, G. M. J.
Am. Chem. Soc. 1986, 108, 8094−8095. (b) Hackett, M.; Whitesides,
G. M. J. Am. Chem. Soc. 1988, 110, 1436−1448. (c) Hackett, M.;
Whitesides, G. M. J. Am. Chem. Soc. 1988, 110, 1449−1462.
NMR (75.47 MHz, THF-d8): δ −23.91 (Pt-CH3), 30.23 (s+sat,
4
4J(Pt,C) = 21 Hz, N-C(CH3)3), 31.78 (s+sat, J(Pt,C) = 7 Hz, N-
C(CH3)3), 58.47 (N-C(CH3)3), 58.65 (N-C(CH3)3), 63.91 (CH2),
116.46 (CH-Im), 117.46 (CH-Im), 117.71 (CH-Im), 118.52 (CH-
Im), 183.18 (N2C-Im), 189.66 (N2C-Im). IR (THF, cm−1) =
3129(m); 2975(s); 2904(s); 2795(m); 2002(s, Pt-H); 1446(s);
1372(s); 1261(s); 705(m). MS (LIFDI, toluene): m/z (%) 455.2
(100) [M − CH4]+•.
(3) (a) Hofmann, P.; Heiss, H.; Neiteler, P.; Muller, G.; Lachmann, J.
̈
Angew. Chem., Int. Ed. 1990, 29, 880−882. (b) Hofmann, P.; Unfried,
G. Chem. Ber. 1992, 125, 659−661.
[Lt‑BuPtNpH] (9). A colorless THF suspension (50 mL) of 7 (208
mg, 0.37 mmol) and sodium trimethoxyborohydride (470 mg, 3.70
mmol) was stirred at 65 °C for 5 h. All volatile compounds were
removed in vacuo. Toluene (50 mL) was added, and the solution was
stirred for 15 min, filtered, and evaporated to dryness. The remaining
colorless solid was washed with n-hexane. Yield: 170 mg (87%). Mp:
206 °C dec. Anal. Calcd for C20H36N4Pt (527.61): C, 45.53; H, 6.88;
N, 10.62. Found: C, 45.51; H, 6.79; N, 10.73. 1H NMR (500.13 MHz,
(4) Hofmann, P.; Heiss, H.; Muller, G. Z. Naturforsch. B 1987, 42,
̈
395−409.
(5) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290−
1309. (b) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47,
3122−3172. (c) Díez-Gonzal
́
ez, S.; Marion, N.; Nolan, S. P. Chem.
Rev. 2009, 109, 3612−3676. (d) Glorius, F.; Droge, T. Angew. Chem.,
̈
Int. Ed. 2010, 49, 6940−6952.
(6) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R.
̈
1
toluene-d8): δ −7.12 (s+sat, J(Pt,H) = 1083 Hz, 1H, Pt-H), 1.61 (s,
J. Angew. Chem., Int. Ed. 1995, 34, 2371−2374.
(7) Brendel, M.; Braun, C.; Rominger, F.; Hofmann, P. Angew. Chem.,
Int. Ed. 2014, 53, 8741−8745.
9H, Pt-CH2-C(CH3)3), 1.62 (s, 9H, N-C(CH3)3), 1.68 (s, 9H, N-
2
2
C(CH3)3), 2.28 (d+sat, J(H,H) = 12 Hz, J(Pt,H) = 84 Hz, 1H, Pt-
CH2), 2.53 (d+sat, 2J(H,H) = 12 Hz, 2J(Pt,H) = 78 Hz, 1H, Pt-CH2),
4.04 (d, J(H,H) = 12 Hz, 1H, exo-CH2), 5.98 (d+sat, J(H,H) = 12
́
(8) Jamali, S.; Milic, D.; Kia, R.; Mazloomi, Z.; Abdolahi, H. Dalton
2
2
Trans. 2011, 40, 9362−9365.
4
3
Hz, J(Pt,H) = 17 Hz, 1H, endo-CH2), 6.09 (d, J(H,H) = 2 Hz, 1H,
(9) Huffer, A.; Jeffery, B.; Waller, B. J.; Danopoulos, A. A. C.R. Chim.
2013, 16, 557−565.
CH-Im), 6.16 (d, 3J(H,H) = 2 Hz, 1H, CH-Im), 6.32 (d, 3J(H,H) = 2
Hz, 1H, CH-Im), 6.33 (d, J(H,H) = 2 Hz, 1H, CH-Im). 13C{1H}
3
(10) Abo-Amer, A.; McCready, M. S.; Zhang, F.; Puddephatt, R. J.
Can. J. Chem. 2012, 90, 46−54.
4
NMR (125.76 MHz, THF-d8): δ 30.17 (s+sat, J(Pt,C) = 22 Hz, N-
C(CH3)3), 30.45 (Pt-CH2), 31.84 (N-C(CH3)3), 35.36 (s+sat,
(11) Khlebnikov, V.; Heckenroth, M.; Muller-Bunz, H.; Albrecht, M.
̈
3J(Pt,C) = 60 Hz, Pt-CH2-C(CH3)3), 35.49 (Pt-CH2-C(CH3)3),
Dalton Trans. 2013, 42, 4197−4207.
3
58.45 (N-C(CH3)3), 58.60 (N-C(CH3)3), 63.94 (s+sat, J(Pt,C) = 63
(12) (a) Brainard, R. L.; Miller, T. M.; Whitesides, G. M.
Organometallics 1986, 5, 1481−1490. (b) Klein, A.; van Slageren, J.;
3
Hz, CH2), 116.37 (s+sat, J(Pt,C) = 23 Hz, CH-Im), 117.30 (s+sat,
3J(Pt,C) = 20 Hz, CH-Im), 117.89 (s+sat, 3J(Pt,C) = 22 Hz, CH-Im),
́ ̌
Zalis, S. J. Organomet. Chem. 2001, 620, 202−210.
H
DOI: 10.1021/acs.organomet.5b00204
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(13) Douthwaite, R. E.; Haussinger, D.; Green, M. L. H.; Silcock, P.
̈
J.; Gomes, P. T.; Martins, A. M.; Danopoulos, A. A. Organometallics
1999, 18, 4584−4590.
(14) Scherg, T.; Schneider, S. K.; Frey, G. D.; Schwarz, J.;
Herdtweck, E.; Herrmann, W. A. Synlett 2006, 18, 2894−2907.
(15) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.
Soc. 1976, 98, 6521−6528.
(16) Bassan, R.; Bryars, K. H.; Judd, L.; Platt, A. W. G.; Pringle, P. G.
Inorg. Chim. Acta 1986, 121, L41−L42.
(17) (a) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100,
3359−3370. (b) Kyushin, S.; Ikarugi, M.; Takatsuna, K.; Goto, M.;
Matsumoto, H. J. Organomet. Chem. 1996, 510, 121−133.
I
DOI: 10.1021/acs.organomet.5b00204
Organometallics XXXX, XXX, XXX−XXX