Transition Metal Cooperative Lewis Pairs Using Platinum(0) Diphosphine Monocarbonyl Complexes as Lewis bases

Article abstract of DOI:10.1021/acs.organomet.9b00568

The platinum(0)-diphosphine complex [Pt(CO)(L1)] (3, where L1 = 1,2-C₆H₄(CH₂P^tBu₂)₂) and its diphosphinite analogue [Pt(CO)(L2)] (11, where L2 = 1,2-C₆H₄(OP^t

Full text of DOI:10.1021/acs.organomet.9b00568

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Transition Metal Cooperative Lewis Pairs Using Platinum(0)
Diphosphine Monocarbonyl Complexes as Lewis bases
Krishna Mistry, Paul G. Pringle,* Hazel A. Sparkes, and Duncan F. Wass*
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ABSTRACT: The platinum(0)-diphosphine complex [Pt(CO)(L1)] (3, where L1 = 1,2-C6H4(CH2PtBu2)2) and its diphosphinite
analogue [Pt(CO)(L2)] (11, where L2 = 1,2-C6H4(OPtBu2)2) act as Lewis bases in conjunction with the main group Lewis acid
B(C6F5)3 to form frustrated or cooperative Lewis pairs. These systems activate dihydrogen, ethene/carbon monoxide, and
phenylacetylene, leading to products that depend on the exact ligand used. These subtle changes to ligand structure influence
reactivity, most notably in hydrogen activation where a variety of dinuclear species of the type [(diphos)Pt(μ-H)3Pt(diphos)]+ or
[(diphos)Pt(μ-H)(μ-CO)Pt(diphos)]+ are observed. Activation of ethene with the Lewis pair leads to a previously reported
coupling product and the mechanism is probed. The basicity of [Pt(CO)(L)] is demonstrated by deprotonation of phenylacetylene.
Preliminary studies with an analogous palladium complex [Pd(CO)(L1)] 33 suggests related chemistry may be exploited for this
metal. These results provide further examples of cooperative Lewis pair behavior in which one of the components is based on a
transition metal complex.
pling.15,24,25 Erker et al. reported a similar intramolecular
INTRODUCTION
■
zirconocene system (2, Figure 1) capable of a variety of FLP-
The concept of frustrated Lewis pairs (FLPs) has led to major
advances in small molecule activation and catalysis by main
type transformations.26
We were intrigued by the possibility that transition metal
group systems.1−7 There are now many examples where
FLPs need not be limited to electrophilic complexes acting as
activation chemistry is still observed despite a persistent
the Lewis acid, and suitable electron rich, nucleophilic
interaction between Lewis acidic and basic fragments,8−11 and
transition metal complexes could act as the Lewis basic
perhaps a more accurate description of these systems would be
component of such a system. We have previously reported
cooperative Lewis pairs: the two Lewis centers working
cooperative Lewis pair chemistry using the platinum(0)
together to activate small molecules. Initially, FLP chemistry
complex [Pt(CO)(L1)] (3) (L1 = 1,2-bis(ditert-
butylphosphinomethyl)benzene) as a Lewis base in con-
focused on main group compounds for the active Lewis
centers. We12−16 and others17−22 have extended the field into
junction with the main group Lewis acid B(C6F5)3. This
the use of transition metal components as either the Lewis acid
or the Lewis base (Figure 1).23 We reported the intermolecular
system will activate carbon dioxide, dihydrogen, and ethene/
carbon monoxide, leading to the expected activation products
zirconocene aryloxide/phosphine, (1, Figure 1), which was
in some cases (4 and 5) and unprecedented reactivity in others
capable of a variety of transformations including activation of
(6) (Scheme 1).13 Further examples of FLP-type chemistry
H2, CO2, THF, and alkyl halides.16 An intermolecular variant
with late transition metals have also now emerged.20−22 In this
of this system also demonstrated FLP-type reactivity, including
present contribution, we explore a wider set of platinum(0)
catalytic imine hydrogenation and amine-boranes dehydrocou-
complexes of this family and show that subtle changes to ligand
structure can have a profound influence on reactivity.
Received: August 20, 2019
Figure 1. Early transition metal cooperative Lewis pairs (counterions
omitted for clarity).
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cycles for L1. The molecular structures of [Pt(CO)(L1)] and
[Pt(CO)(L2)] are shown in Figure 3. The two structures are
Scheme 1. Small Molecule Activation by 3/B(C6F5)3
RESULTS AND DISCUSSION
■
Figure 3. Crystal structures of [Pt(CO)(L1)] 3 (left) and
[Pt(CO)(L2)] 11 (right). Thermal ellipsoids at 50%. Hydrogen
atoms omitted for clarity.
Synthesis of [Pt(CO)(L)]. An advantage of transition metal
FLPs is that steric and electronic modification can be readily
achieved synthetically by simple changes to the ligand
structures in sharp contrast to the often challenging syntheses
associated with, for example, modified fluorinated aryl borane
Lewis acids. In order to alter the electronics of the Pt(0) Lewis
base, a range of related diphos ligands were synthesized L2−L5
(Figure 2).
similar and show the expected conformation of the seven
membered chelates. There was no significant difference in the
Pt−CO bond length in the solid state (Pt1−C1 1.853(12) and
1.8773(16) for [Pt(CO)(L1)] and [Pt(CO)(L2)] respec-
tively), but the electronic effect of the ligand backbone is
apparent when comparing the infrared (IR) data for the
carbonyl complexes. The IR stretching frequency for the
carbonyl ligand in [Pt(CO)(L2)] (ν(CO) = 1933 cm−1) is
significantly higher than for [Pt(CO)(L1)] (ν(CO) = 1907
cm−1). This is consistent with L1 producing a more electron
rich metal center than L2 in the analogous carbonyl complexes
[Pt(CO)(L)].
Figure 2. Series of ligands synthesized.
Reaction of 11/B(C6F5)3 and 3/B(C6F5)3 with Dihy-
drogen. Upon combination of 11 with B(C6F5)3 in
chlorobenzene, there was no significant change in chemical
shifts in either the 11B{1H} or 31P{1H} NMR spectra, but line-
Based on the previously successful route to [Pt(CO)(L1)]
(3), the general synthesis of [Pt(CO)(L)] started from the
combination of [Pt(nbe)3)] (nbe = norbornene) with the
selected diphos to form mono norbornene complexes [Pt-
(nbe)(L)]13,27 (Scheme 2). The coordinated nbe was
broadening was apparent for the 31P{1H} NMR signal (w1/2
=
45 Hz). The solution did not change color but did exhibit
thermochromic properties; upon freezing the solution in liquid
nitrogen, its color changed from bright orange to a very dark
purple. These observations mimic what is seen when 3 and
B(C6F5)3 are combined in chlorobenzene (line-broadening in
the 31P{1H} NMR spectrum and a dark green frozen
solution).13 The color changes indicate that some interaction
between the borane and the Pt(0) complex does take place.
We have previously investigated the interaction of 3 and
B(C6F5)3 by DFT calculations. It was calculated that an adduct
could be formed by coordination of B(C6F5)3 to the oxygen of
the CO or directly to the Pt atom in the complex.13 Low
temperature NMR spectroscopy studies showed sharpening of
the 31P{1H} NMR signal but no significant change in δP or
1JPPt values. Although there appears to be some interaction
between the Lewis acid and the Lewis base, the evidence
suggests that this interaction is weak and dynamic in solution.
Since similar interactions in the 3/B(C6F5)3 system did not
inhibit small molecule activation, further studies on the
reactivity of 11 were carried out.
Scheme 2. Synthesis of Pt(0) Complexes of L2−L5
displaced by bubbling CO through the reaction mixture
followed by removal of the CO atmosphere, solvent, and
displaced nbe to form a mixture of the desired product
[Pt(CO)(L)] and precursor [Pt(nbe)(L)]. These CO/vacuum
cycles were repeated until full conversion of the [Pt(nbe)(L)]
to [Pt(CO)(L)] was observed by 31P{1H} NMR spectroscopy.
With L2, the synthesis of [Pt(CO)(L2)] (11) was successful
using this procedure. Unfortunately, for L3−L5, this sequence
did not proceed smoothly; however, under a CO atmosphere,
the formation of a dicarbonyl [Pt(CO)2(L)]27 L = L3−L5 is
observed and confirmed by the use of 13CO (see Figure S1).
Removal of the CO atmosphere and the toluene solvent led to
full conversion back to the starting material [Pt(nbe)(L)], with
no evidence of the formation of [Pt(CO)(L)] even after
several CO/vacuum cycles. Attempts to isolate the dicarbonyl
complex either led to degradation or formation of [Pt(nbe)-
(L)].
The reaction of 11/B(C6F5)3 with dihydrogen resulted in a
color change of the mixture from orange to bright pink within
15 min. To facilitate study by NMR spectroscopy, the reaction
was repeated with [Pt(13CO)(L2)] (11*). The reaction
1
mixture was analyzed by in situ H, 11B{1H}, 13C{1H}, 19F,
and 31P{1H} NMR spectroscopy. After 15 min, the 13C{1H}
NMR spectrum showed the presence of three 13C-enriched
The specific synthetic procedure to obtain complexes with
diphosphine L1 and diphosphinite L2 varied; at least seven
CO/vacuum cycles were required to achieve full conversion to
the mono carbonyl complex for L2 compared to only three
products (Figure 4, A). The signal at δC = 249.2 ppm appeared
1
to be a broad 1:1:1:1 quartet with a coupling constant JCB
=
49.3 Hz, indicating it was directly bonded to boron. This was
confirmed in the 11B{1H} NMR spectrum (Figure 4, B) which
B
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combinations of two Pt atoms in a binuclear species:
195Pt−195Pt, 195Pt−Pt, and Pt−Pt (ca. 1:4:4 ratio).29 The
corresponding hydride signal in the 1H NMR spectrum is at δH
= −1.92 ppm with the same multiplicity indicating the hydride
is also bridging. The 31P{1H} NMR spectrum also has the
distinctive multiplicities expected for a binuclear Pt species
which has been described by Otsuka for similar binuclear
trihydrido species30 and is also observed for analogues of
18.31−33
1
The final signal in the H NMR spectrum at δH = −5.72
ppm (Figure 3C) corresponds to a signal at δP = 185.6 ppm in
the 31P{1H} NMR spectrum (Figure 4D) and is attributed to
the trihydrido binuclear platinum species 20; this was also
confirmed by mass spectrometry. Over time, the composition
of this reaction mixture did not change except for the gradual
degradation of formyl borate species 21 over 4−5 days.
The diversity of species observed came as a surprise, given
that we have previously reported the analogous cationic species
15 and the counterion [HB(C6F5)3] are the only products of
dihydrogen activation with L1 after 16 h.13 The activation of
dihydrogen was repeated with 3/B(C6F5)3 to examine if
species analogous to those derived from 11/B(C6F5)3 were
formed at earlier stages of the reaction. The reaction was
monitored by NMR spectroscopy and after 15 min, the
presence of 21, and analogous species 15 and 17, were
detected (Figure 5, A). As previously observed, after longer
Figure 4. In situ 13C{1H} (A), 11B{1H} (B), 1H (C), and 31P{1H} (D)
NMR spectra of the reaction between 11*/B(C6F5)3 and H2 after 15
min. Expansions in C show the 1H−13C splitting. D shows the
31P{1H} NMR spectrum of reaction using 11.
showed a doublet at δB = −16.7 ppm (1JBC = 49 Hz). When
1
using 11*, a proton signal at δH = 10.80 ppm in the H NMR
spectrum (Figure 4C) then exhibited a 1J coupling to 13C (1JHC
= 151 Hz). This product was assigned to formyl borate anion
21 (Scheme 3). This species has been previously reported by
Stephan et al. while investigating the reaction of syngas (50:50
CO/H2) with the main group FLP, PtBu3/B(C6F5)3.28
Scheme 3. Reaction of 3 or 11/B(C6F5)3 with H2 after 15
a
min
Figure 5. In situ 13C{1H} NMR spectra of the reaction between 3*/
B(C6F5)3 and H2 after 15 min (A) and 16 h (B).
periods (16 h), the NMR spectra simplified with 15 being
formed as the major platinum-containing species.13 There was
also a trace amount (<5%) of 19 detected in the H NMR
1
a
Percentages of various Pt products are based on 1H NMR
spectroscopic data. Ratio of 21:[HB(C6F5)3] is 45:55 for L1 and
90:10 for L2.
spectrum after 15 min which was persistent over time.
Previously, two possible reaction pathways were proposed
for dihydrogen activation by the Pt(0)/B(C6F5)3 Lewis pair
(Scheme 4). In pathway a, classic organometallic oxidative
The signal at δC = 178.4 ppm in the 13C{1H} NMR
spectrum corresponds to the CO ligand in the mononuclear
cation 16. The associated signals in the 31P{1H} NMR
spectrum occur at δP = 174.5 and 163.0 ppm (Figure 4D) and
Scheme 4. Previously Proposed13 Pathways for Dihydrogen
Activation by the Pt(0)/B(C6F5)3 Lewis Pair
1
the hydride signal in the H NMR spectrum at δH = −4.15
ppm (Figure 4C).
The final signal in the 13C{1H} NMR spectrum occurs at δC
= 231.6 ppm and exhibits a 1:8:18:8:1 quintet of binomial
quintets and corresponds to species 18. This splitting pattern is
indicative of a bridging CO ligand in a binuclear platinum
species with two equivalent 195Pt atoms and four equivalent 31
P
atoms. The signal is a composite of three subspectra occurring
from the different isotopic combinations of the platinum
nuclei. The only isotope of Pt that is NMR active is 195Pt (I =
1/2) and is 33.8% abundant; therefore there are three possible
C
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addition of H2 to give the cis-dihydride, with loss of CO, is
then followed by hydride abstraction by B(C6F5)3 and
reassociation of CO. In pathway b, the H2 molecule is
bound between the platinum and boron centers in an
encounter complex and is then heterolytically cleaved in a
concerted process to form the final dihydrogen activation
products.13
The starting complexes 3 or 11 do react with dihydrogen in
the absence of B(C6F5)3 to form the cis-[Pt(H)2(L)], but this
is very slow (maximum 40% conversion over 1 week)
compared to the much more rapid reactions reported here;
this species also reverts to [Pt(CO)(L)] when the hydrogen
atmosphere is removed. There is no NMR spectroscopic
evidence of the cis-dihydride when dihydrogen is introduced to
solutions of either of the Pt(0)/B(C6F5)3 Lewis pair systems.
We previously suggested this evidence supports the more FLP-
like pathway b; however, the formation of an equilibrium with
very low concentrations of the cis-dihydride which is then
rapidly intercepted by B(C6F5)3 to pull the reaction over to the
observed products via pathway a is also possible. Indeed, the
observed complexes in this present study are neatly explained
by pathway a (Scheme 5). Oxidative addition of H2 gives the
two B(C6F5)3 molecules, and one molecule of dihydrogen
seem highly likely on the basis of the high reaction order
required.
It should be noted that Minghetti et al. have extensively
studied the chemical transformation of [Pt2(μ-H)3(L)2]+ to
[Pt2(μ-H)(μ-CO)(L)2]+ (L = dppe, 1,2-bis(diphenyl-
phosphino)ethane) by the simple addition of CO to a solution
of [Pt2(μ-H)3(L)2]+.32 Studies of similar binuclear trihydrido
species have shown that the structures are dynamic, with
hydrido ligand exchange between bridging and terminal
sites.30,31,34,35 This suggests equilibria between all of the
species observed here are possible.
Reaction of 11/B(C6F5)3 with Ethene. The reaction of
11/B(C6F5)3 with ethene in chlorobenzene resulted in a color
change from orange to pale pink over 1 h. The reaction
mixture was monitored by NMR spectroscopy; after 1 h, the
31P{1H} NMR spectrum displayed two doublets at δP = 173.4
ppm (2JPP = 15 Hz, 1JPPt = 2219 Hz) and δP = 137.5 ppm (2JPP
1
= 15 Hz, JPPt = 4662 Hz). Analysis of the 11B{1H} NMR
spectrum showed a single sharp peak at δB = −22 ppm
1
indicating a 4-coordinate boron species and the H NMR
spectrum displayed two broad signals at δH = 2.87 and 1.90
ppm. When the reaction was repeated with 11* a broad quartet
was observed in the 13C{1H} NMR spectrum at δC = 278.7
ppm (1JCB = 52 Hz). Attempts to crystallize the product were
unsuccessful, but the presence of the low field signal in the
13C{1H} NMR spectrum is strong evidence for the final
activation product being the cyclic complex 27 (Scheme 6).
Scheme 5. Proposed Pathways for the Formation of
a
Dihydrogen Activation Products
Scheme 6. Proposed Pathway for the Activation of Ethene
by 3 or 11
The 11/B(C6F5)3 Lewis pair appears to have activated
ethene in a similar manner to 3/B(C6F5)3, except that the rate
of reaction is significantly faster, the former only taking 1 h to
have detectable product signals versus 16 h for the latter. The
ethene/CO coupled product 27 was also stable when the
solvent and ethene atmosphere were removed and the solid
residue redissolved with only minor amounts (<3%) of
decomposition.
Previous mechanistic studies would suggest an initial
activation of the ethene occurs to form a product related to
the structure of 24 or 25 and then further reaction with the
CO to form the final product.13 To investigate this, the mono
ethene complex 23 was formed by subjecting 11 to at least two
ethene/vacuum cycles. The formation of 23 is favorable, as
after just one ethene cycle, over 95% of 11 had converted to
23. B(C6F5)3 was then added to a solution of 23 in
chlorobenzene and the mixture instantly turned cloudy.
Addition of CO to the reaction mixture resulted in a pale
pink solution with almost quantitative conversion to the
ethene/CO coupled product 27, analogous to previous
a
Anions omitted for clarity.
cis-dihydride complex with loss of CO. This species is present
in low concentration but then reacts with B(C6F5)3 to abstract
a hydride and form the highly reactive species [Pt(H)(L)]+.
This formally 14 electron species can react with [Pt(CO)(L)]
to form [Pt2(μ-H)(μ-CO)(L)2]+ (17 and 18). Alternatively,
[Pt(H)(L)]+ can react with a further molecule of [Pt(H)2(L)]
to give [Pt2(μ-H)3(L)2]+ (19 and 20); this again lends support
to the intermediacy of [Pt(H)2(L)]. Finally, it could also react
directly by recoordination of CO to give [Pt(H)(CO)-
(L)]+(15 and 16). The ratio of these various species is linked
to the stereoelectronic properties of the ligand used. The
possibility of the anions [HB(C6F5)3] or 21 being associated
with any of these cationic species further adds complexity but
does not detract from the main reaction sequence. Alternative
pathways for the formation of binuclear species involving the
concerted reaction of two platinum mono carbonyl complexes,
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observations with the formation of 26 from 3/B(C6F5)3 and
ethene.13
this metal of interest. The palladium monocarbonyl complex,
[Pd(CO)(L1)] 33, has been reported, serendipitously isolated
when investigating intermediates of the methoxycarbonylation
of ethene to form methyl propionate.37−39 The target complex
33 was synthesized in 50% yield in two steps: first combining
[Pd(dba)2] and L1 in the presence of HCl to form dichlorido
species [PdCl2(L1)] (32, Scheme 9) and then treatment with
base under a CO atmosphere.
Reaction of [Pt(CO)(L)] (L = L1 or L2)/B(C6F5)3 with
Phenylacetylene. Terminal alkynes react with FLPs either by
deprotonation or 1,2-addition to form an E-alkene.15,16,36 The
chemoselectivity has been found to depend predominantly on
the basicity of the phosphine, although a balance of several
parameters, including sterics, is necessary to control the
reactivity.
The Lewis pair 3/B(C6F5)3 was treated with an excess of
phenylacetylene and an instant color change from bright
orange to a dark red/brown was observed. After 2 h, analysis of
the 31P{1H} NMR spectrum showed full conversion of the
starting material to the cationic fragment of 28 (Scheme 7).
The anionic fragment has been previously reported in the
literature so assignment from the 11B{1H} NMR and 19F NMR
spectra was unambiguous.36
Scheme 9. Synthesis of [Pd(CO)(L1)] 33
When 33 and B(C6F5)3 were combined in chlorobenzene at
room temperature, an orange solution formed. No significant
change in chemical shift was observed in the 31P{1H} or
11B{1H} NMR spectra but broadening of the 31P{1H} NMR
signal was seen (w1/2 = 55 Hz). When 33/B(C6F5)3 was
treated with H2 (1 bar), a color change from orange to yellow
was observed over 6 h. Analysis of the 31P{1H} NMR spectrum
showed quantitative conversion to a new species at δP = 42.0
ppm which appeared as a singlet. This signal corresponds to a
quintet observed in the hydride region of the 1H NMR
spectrum (δH = −9.96 ppm, 2JHP = 43 Hz, Figure S3, A). This
species is tentatively assigned, from the NMR spectroscopic
data, as Pd(I) species 34, analogous to the Pt species 17
(Scheme 10). The presence of 34 was detected in positive ion
Scheme 7. Reaction of [Pt(CO)(L)]/B(C6F5)3 with PhCCH
The reaction of 11/B(C6F5)3 with phenylacetylene did not
proceed as cleanly although the major product remains the
result of deprotonation of phenylacetylene 29. Upon addition
of phenylacetylene to 11/B(C6F5)3 in chlorobenzene there was
an immediate color change from bright orange to dark red. Full
conversion of the starting material was observed and ca. 90% of
the product formed was assigned to complex 29 (Scheme 7).
Scheme 10. Reaction of 33/B(C6F5)3 with H2 in
Chlorobenzene at Room Temperature
1
Analysis of the 31P{1H} and H NMR spectra revealed a
second phosphorus-containing species, the binuclear Pt(I)
cation 18.
To investigate the mechanism of phenylacetylene activation
for both systems, phenylacetylene was added to the 3* or 11*
in the absence of B(C6F5)3 (Scheme 8). With 3*, a gradual
ESI-MS analysis of the reaction mixture. The 11B{1H} NMR
spectrum showed a sharp signal at δB = −16.2 ppm and a broad
signal at δB = −2.8 ppm, and collectively with the observation
of a broad singlet at δH = 10.80 ppm in the 1H NMR spectrum,
the anion was confirmed to be 21 (Scheme 10). Clearly, the
chemistry of this Pd system is promising but distinct from the
Pt analogues and warrants further investigation.
Scheme 8. Reaction of [Pt(13CO)(L)] with PhCCH
CONCLUSIONS
■
[Pt(CO)(L2)] (11) has been synthesized and compared to
[Pt(CO)(L1)] (3) for cooperative Lewis pair reactivity with
B(C6F5)3. While broadly similar reactivity is observed with
substrates such as hydrogen, ethene, and phenylacetylene,
there are important differences. Notably, a more complex
picture of bridging hydride species emerges in the hydrogen
activation reactions. A new synthesis of [Pd(CO)(L1)] (33) is
reported, and with B(C6F5)3, this complex shows promising
results for cooperative activation of hydrogen.
color change of the solution over 16 h from orange to pale
yellow was observed. Two doublets observed in the 31P{1H}
NMR spectrum (at δP = 47.3 and 42.5 ppm, JPP = 24 Hz)
2
indicated the formation of 30. Similar chemistry was observed
with 11 (δP = 190.5 and 184.9 ppm, 2JPP = 15.9 Hz) although
the conversion to the product 31 occurred much faster in this
case (2 h). Addition of B(C6F5)3 to chlorobenzene solutions of
30 or 31 showed ca. 60% conversion to the products 28 and
29.
Synthesis and Reactivity of [Pd(CO)(L1)] (33)/B(C6F5)3
Pairs. The great utility of palladium complexes in catalysis
made an analogous cooperative Lewis pair system based on
EXPERIMENTAL DETAILS
■
General Experimental Details. Unless otherwise stated, all
reactions were carried out under an inert atmosphere (N2 or Ar) using
standard Schlenk line or glovebox (MBraun O2 < 0.1 ppm, H2O < 0.1
ppm) techniques. All glassware was dried in an oven (200 °C) for at
least 2 h or flame-dried before use. Common laboratory solvents
(DCM, diethyl ether, hexane, THF, acetonitrile and toluene) were
E
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purified using an anhydrous Grubbs-type solvent system and then
degassed by at least three freeze/pump/thaw cycles. Nonstandard
solvents (pentane, benzene, chlorobenzene, and fluorobenzene) were
purchased from Sigma-Aldrich, distilled from CaH2, and degassed by
at least three freeze/pump/thaw cycles. Deuterated solvents (CDCl3,
CD2Cl2, d5-PhBr, d5-PhCl, d6-benzene, and d8-toluene) were obtained
from commercial sources, distilled from CaH2, and degassed by at
least three freeze/pump/thaw cycles. Unless otherwise stated,
reagents were purchased from commercial sources and used without
further purification. Reagent gases (CO2 and 13CO2) were dried prior
to use by passing through a −78 °C trap. Catechol was dried by
azeotroping with toluene three times before use. Phenylacetylene was
purified by distillation before use and stored over 4 Å molecular sieves
in an Ar glovebox. [Pt(norbornene)3] was synthesized according to a
literature method.40 3 was synthesized as reported previously.13
NMR spectra were recorded on Jeol ECS 300, Jeol ECP (Eclipse)
300, Jeol ECS 400, Bruker Nano 400, Varian VNMRS 500, and
Bruker Avance III HD 500 cryo-spectrometers in the solvents stated.
Chemical shifts are given in parts per million (ppm) and coupling
constants (J) are given in Hertz (Hz). For paramagnetic NMR, line
C22H41O2P2 [M + H]+ = 399.2576, obs. 399.2568; Elem. Anal. (calcd.
for C22H40O2P2) C 66.49 (66.31), H 10.13 (10.12).
Synthesis of 1,2-bis((Dicyclohexylphosphanyl)oxy)benzene (L3).
Catechol (125 mg, 1.13 mmol) in THF (5 mL) was added dropwise
at room temperature to a suspension of NaH (60 mg, 2.49 mmol) in
THF (4 mL). A white suspension and effervescence was seen.
Dicyclohexylchlorophosphine (0.5 mL, 2.26 mmol) was added to the
reaction mixture dropwise. After stirring for 3 h at room temperature,
the reaction mixture was filtered through celite under N2 (extra care
was taken to exclude water traces). The solvent was removed in vacuo
to yield an oily solid. Recrystallization from hexane at −20 °C yielded
white crystals (368 mg, 65%). Crystals suitable for X-ray analysis were
1
obtained from a saturated solution in hexane at −40 °C. H NMR
(500 MHz; C6D6) δH 7.50 (2H, m, Ar CH), 6.84 (2H, m, Ar CH),
2.15−2.01 (4H, m, Cy CH2/CH), 1.88−1.53 (24H, m, Cy CH2/CH),
1.44−1.14 (16H, m, Cy CH2/CH); 13C{1H} NMR (126 MHz; C6D6)
δC 150.5 (dd, J = 8.8, 2.1 Hz, Ar C), 122.0 (s, Ar CH), 119.4 (d, J =
18.7 Hz, Ar CH), 38.7 (d, J = 19.1 Hz, Cy CH), 28.3 (d, J = 18.3 Hz,
Cy CH2), 27.5−27.2 (m, Cy CH2), 26.8 (d, J = 1.0 Hz, Cy CH2);
31P{1H} NMR (202 MHz; C6D6) δP 144.9 (s, PtBu2); HR-MS (ESI)
m/z calcd. for C30H48O2P2Na for [M + Na]+ = 502.3130; obs. =
502.3139; Elem. Anal. (calcd. for C30H48O2P2) C 69.01 (68.77), H
8.24 (8.02).
1
widths (w1/2) are given in Hz. H and 13C{1H} NMR chemical shifts
(δ) are reported in ppm and are referenced internally relative to the
residual solvent signal. 11B{1H}, 19F, 27Al{1H}, and 31P{1H} were
referenced to BF3·OEt2, CFCl3, Al(NO3)3, and 85% H3PO4 as
external standards, respectively. Data is reported as follows: chemical
shift (δ, ppm), integration, multiplicity (s = singlet, d = doublet, t =
triplet, q = quartet, qu = quintet, dd = doublet of doublets, dt =
doublet of triplets, td = triplet of doublets, ququ = quintet of quintets,
m = multiplet, app = apparent, br = broad signal), coupling constants
(J, Hz), and assignment. Electrospray ionization mass spectra (ESI-
MS) were recorded by the mass spectrometry service at the University
of Bristol on a Bruker Dalronics microTOF II. Elemental analyses
were carried out by the Microanalytical Laboratory in the School of
Chemistry, University of Bristol. X-ray diffraction experiments were
carried out at 100 K on a Bruker APEX II diffractometer using Mo−
Kα radiation (λ = 0.71073 Å). The data collections were performed
using a CCD area detector from a single crystal mounted on a glass
fiber. Intensities were integrated, and absorption corrections based on
equivalent reflections using SADABS were applied. The structures
were all solved using Superflip,41 and structures were refined against
all F2 in ShelXL201542 using Olex2.43 All of the non-hydrogen atoms
were refined anisotropically. All of the hydrogen atoms were located
geometrically and refined using a riding model. Compound 3 is
modelled as a two component twin and refined against an hklf 5 file
twin fractions 0.46:0.54. The slightly larger residual are attributed to
the twinning in the structures.
Synthesis of 1,2-bis(Dicyclohexylphosphino)xylene (L4). KOtBu
(1.27 g, 11.3 mmol) was added to a solution of o-xylene (620 μL, 5.15
mmol) in Et2O (5 mL). The white suspension was cooled to −78 °C
and n-BuLi (∼1.6 M in hexanes, 7.4 mL, 11.8 mmol) was added
dropwise while maintaining the temperature. The intense orange
colored solution was allowed to warm to room temperature and then
refluxed for 2 h. The reaction mixture was then cooled again to −78
°C and a solution of ClPCy2 (2.5 mL, 11.3 mmol) in Et2O (5 mL)
was added dropwise and the temperature was maintained for 1 h. The
reaction was warmed to room temperature and degassed H2O was
added slowly. The product was extracted with DCM (4 × 8 mL), and
the organic fractions were combined and dried over Na2SO4. The
crude product was washed with hot MeOH to yield L4 as a white
solid (934 mg, 36%).
1H NMR (400 MHz; CDCl3) δH 7.14 (2H, m, Ar CH), 7.05 (2H,
m, Ar CH), 3.03 (4H, br s, PCH2), 1.88−1.63 (20H, m, Cy CH2/
CH), 1.57−1.47 (4H, m, Cy CH2/CH), 1.34−1.12 (20H, m, Cy
CH2/CH); 31P{1H} NMR (162 MHz; CDCl3) δP −2.86 (s, PCy2).
Synthesis of 1,2-bis(Diphenylphosphino)xylene (L5). KPPh2 (0.5
M in THF, 5.03 mL, 2.51 mmol) was added dropwise to a solution of
α,α′-dichloro-o-xylene (200 mg, 1.14 mmol) in THF (10 mL) at −78
°C and the reaction was stirred for 24 h at room temperature.
Degassed, deionized H2O (1 mL) was added to the reaction to
quench any remaining KPPh2, and the solution was passed through a
silica column, washing with THF (2 × 10 mL). The volatiles were
removed in vacuo, and the product was washed with hexane (3 × 15
mL) to yield a white solid (0.319 g, 59%).
Synthesis of 1,2-bis(Ditert-butylphosphinooxy)benzene (L2).
Catechol (596 mg, 5.41 mmol) in THF (10 mL) was added
dropwise at room temperature to a suspension of NaH (286 mg,
11.91 mmol) in THF (10 mL). Effervescence of hydrogen gas and the
formation of a white suspension was observed. The reaction was left
to stir at room temperature until effervescence had subsided
(approximately 30 min). Di-tert-butylchlorophosphine (2.05 mL,
10.83 mmol) was added dropwise to the reaction mixture and was
heated at 60 °C for 72 h. Reaction progress was monitored by
31P{1H} NMR spectroscopy and upon consumption of the starting
chlorophosphine the reaction mixture was filtered through celite
under N2 (extra care was taken to exclude water traces). The solvent
was removed in vacuo to yield a colorless oily solid. Recrystallization
from hexane at −20 °C yielded a white crystalline solid (1.38 g, 56%).
Upon workup, the P−O bond hydrolysis product bond formed. After
several unsuccessful attempts to isolate the pure product, the crude
product was carried forward to the next step. Crystals suitable for X-
ray analysis were obtained by slow evaporation of a pentane solution
1H NMR (400 MHz; CDCl3) δH 7.35−7.28 (20H, m, Ph CH),
6.90 (2H, m, Ar CH), 6.73 (2H, m, Ar CH), 3.30 (4H, s, CH2);
2
13C{1H} NMR (100 MHz; CDCl3) δC 138.4 (d, JCP = 15.1 Hz, Ar
C), 135.1, Ar CH), 133.2 (d, 1JCP = 19.1 Hz, Ph C), 130.7 (s, Ar CH),
128.8 (s, Ph-CH), 128.5 (s, Ph CH), 126.0 (s, Ph CH), 33.4 (d, 1JCP
=
17.4, CH2); 31P{1H} NMR (162 MHz; CDCl3) δP −13.5 (s, PPh2).
[Pt(CO)(L2)] (11). A solution of L2 (250 mg, 0.5 mmol) in toluene
(5 mL) was added dropwise to a solution of Pt(nbe)3 (200 mg, 0.5
mmol) in toluene (5 mL) at −78 °C. After 2 h stirring at −78 °C a
yellow suspension formed. The reaction was left to warm to room
temperature and stir overnight. CO was bubbled through the
suspension for 20 min during which time the reaction mixture
changed to a dark orange solution. This solution was filtered to
remove any Pt(0) nanoparticles. The solvent was removed in vacuo
and the solid redissolved in toluene (5 mL). CO was bubbled through
for 20 min, and the solvent removed in vacuo and redissolved in
toluene (5 mL). This CO/vacuum cycle was repeated five times. The
product was extracted with pentane (3 × 3 mL) and recrystallization
from this solution at −78 °C yielded orange crystals (164 mg, 61%).
1
of L2 at −40 °C. H NMR (400 MHz; C6D6) δH 7.69 (2H, m, Ar
CH), 6.82 (2H, m, Ar CH), 1.21 (36H, d,3 JHP = 11.6 Hz, CH3);
13C{1H} NMR (100 MHz; C6D6) δC 150.2 (dd, J = 9.8, 1.7 Hz, Ar
C), 121.6 (m, Ar CH), 118.7 (d, J = 22.9 Hz, Ar CH), 35.8 (d, J =
27.0 Hz, C(CH3)3), 27.6 (d, J = 15.9 Hz, C(CH3)3); 31P{1H} NMR
(162 MHz; C6D6) δP 153.1 (s, PtBu2); HR-MS (ESI) m/z calcd. for
F
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Article
Crystals suitable for X-ray analysis were obtained from a saturated
solution in pentane at −40 °C.
1H NMR (500 MHz; d8-toluene) δH 7.11 (2H, m, Ar CH), 6.91
(2H, m, Ar CH), 3.49 (2H, br, CH2), 1.22 (36H, m, CH3); 13C{1H}
NMR (125 MHz; d8-toluene) δC 224.7 (t, JCP = 44.1 Hz, JCPt = 2095
Hz, Pt-13CO), 135.0 (m, Ar C), 130.8 (br s, Ar CH), 122.7 (br s, Ar
CH), 33.9 (br, CH2), 29.4 (br s, CCH3), 26.9 (m, CCH3); 31P{1H}
NMR (202 MHz; d8-toluene) δP 69.7 (d, 2JPC = 44.1 Hz, 1JPPt = 3680
Hz, PtBu2).
1H NMR (500 MHz; d8-toluene) δH 7.03 (2H, m, Ar CH), 6.69
3
(2H, m, Ar CH), 1.28 (36H, br d, JHP = 14.0 Hz, CH3); 13C{1H}
NMR (125 MHz; d8-toluene) δC 147.4 (m, Ar C), 128.0 (br s, Ar
CH), 124.5 (br s, Ar CH), 42.4 (app t, JCP = 5.1 Hz, JCPt = 75.3 Hz,
CCH3), 29.5 (m, CCH3); 31P{1H} NMR (202 MHz; d8-toluene) δP
218.2 (s, JPPt = 4062 Hz, PtBu2); HR-MS (ESI) m/z calcd. for
C23H41O3P2Pt [M + H]+ = 622.2176, obs. 622.2169; Elem. Anal.
(calcd. for C23H40O3P2Pt) C 44.81 (44.44), H 6.57 (6.49); IR νCO
1933 cm−1.
Reaction of 11/B(C6F5)3 with H2. A Youngs NMR tube was
charged with a solution of 11 (31.0 mg, 0.050 mmol) and B(C6F5)3
(25.5 mg, 0.050 mmol) in d5-chlorobenzene (0.7 mL). The orange
solution was frozen in liquid nitrogen, and the tube was evacuated.
The solution was thawed and allowed to warm to room temperature.
The tube was backfilled with H2 (1 bar) and shaken. A color change
from orange to bright pink was observed over 30 min, which
intensified over time. Three cationic (16 10%, 18 85%, 20 5%)
species (% within Pt-containing species) and two anionic species
([HB(C6F5)3] 10% and 21 90%) (% within B-containing species were
identified in solution.
In Situ Synthesis of [Pt(13CO)2(L3)] (12). A Youngs NMR tube was
charged with a solution of Pt(nbe)3 (13.3 mg, 0.028 mmol) and L3
(14.0 mg, 0.028 mmol) in d8-toluene (0.7 mL). The solution was
frozen in liquid nitrogen and the tube was evacuated. The solution
was thawed and allowed to warm to room temperature. The tube was
backfilled with 13CO (1.2 bar). The solution changed from colorless
to pale yellow. The product was not isolated.
2
13C{1H} NMR (75 MHz; d8-toluene; −60 °C) δC 183.4 (t, JCP
=
16: 1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH),
1.11−1.02 (36H, m, CCH3), −4.15 (1H, dd, 1JHPt = 755 Hz, 2JHP(trans)
1
15.7 Hz, JCPt = 1743 Hz, Pt13CO); 31P{1H} NMR (122 MHz; d8-
toluene; −60 °C) δP 151.2 (t,2JCP = 15.7 Hz, 1JPPt = 3569 Hz, PtBu2).
In Situ Synthesis of [Pt(13CO)2(L4)] (13). A Youngs NMR tube was
charged with a solution of Pt(nbe)3 (26.5 mg, 0.055 mmol) and L4
(27.7 mg, 0.055 mmol) in d8-toluene (0.7 mL). The solution was
frozen in liquid nitrogen and the tube was evacuated. The solution
was thawed and allowed to warm to room temperature. The tube was
backfilled with 13CO (1.2 bar). The solution changed from colorless
2
= 159 Hz, JHP(cis) = 24.3 Hz, Pt-H); 31P{1H} NMR (202 MHz; d5-
2
PhCl) δP 174.5 (d, 1JPPt = 3301 Hz, JPP = 15.0 Hz, PtBu2), 163.0 (d,
2
1JPPt = 2294 Hz, JPP = 15.0 Hz, PtBu2).
18: 1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH),
1.27−1.16 (36H, m, CCH3), −1.92 (1H, 1:8:18:8:1 ququ, 1JHPt = 475
Hz, 2JHP = 38 Hz, Pt(μ-H)Pt); 31P{1H} NMR (202 MHz; d5-PhCl) δP
1
2
3
182.2 (m, JPPt = 4029 Hz, JPPt = 131 Hz, JPP = 38 Hz, PtBu2). 20:
to pale yellow. The product was not isolated.
1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH), 1.27−
2
13C{1H} NMR (75 MHz; d8-toluene; −60 °C) δC 184.1 (t, JCP
=
1
1.16 (36H, m, CCH3), −5.72 (1H, 1:8:18:8:1 ququ, JHPt = 393 Hz,
1
11.4 Hz, JCPt = 1820 Hz, Pt-13CO); 31P{1H} NMR (122 MHz; d8-
2JHP = 41.3 Hz, Pt(μ-H)3Pt); 31P{1H} NMR (202 MHz; d5-PhCl) δP
1
toluene; −60 °C) δP 0.37 (t,2JCP = 11.3 Hz, JPPt = 3114 Hz, PtBu2).
1
2
3
185.6 (m, JPPt = 3459 Hz, JPPt = 153 Hz, JPP = 10.1 Hz, PtBu2).
In Situ Synthesis of [Pt(CO)2(L5)]. A Youngs NMR tube was
charged with a solution of Pt(nbe)3 (28.6 mg, 0.063 mmol) and L5
(28.4 mg, 0.060 mmol) in d8-toluene (0.7 mL). The solution was
frozen in liquid nitrogen and the tube was evacuated. The solution
was thawed and allowed to warm to room temperature. The tube was
backfilled with CO (1.2 bar) and the immediate formation of Pt
nanoparticles was seen. The solution was filtered to yield a dark red
solution. Attempts to isolate the product led to further degradation.
1H NMR (400 MHz; d8-toluene) δH 7.63−7.51 (8H, m, Ph CH),
7.15−7.03 (12H, m, Ph CH), 6.62 (2H, m, Ar CH), 6.10 (2H, m, Ar
CH), 3.62 (4H, m, CH2); 31P{1H} NMR (162 MHz; d8-toluene) δP
−9.2 (br s, 1JPPt = 3335 Hz, PPh2); νCO (d8-toluene) 1997, 1953 cm−1.
Synthesis of [Pt(13CO)(L2)] (11*). A Youngs NMR tube was
charged with a solution of 11 (30.5 mg, 0.049 mmol) in d8-toluene
(0.7 mL). The solution was frozen in liquid nitrogen and the tube was
evacuated. The solution was thawed and allowed to warm to room
temperature. The tube was backfilled with 13CO (1.2 bar). The
solution was mixed and left for 5 min before removing the solvent in
vacuo. The solid was redissolved in d8-toluene. This cycle was
repeated three more times to ensure majority of the 12CO had been
exchanged for 13CO. This species was confirmed in solution by NMR
spectroscopy only.
[HB(C6F5)3]: 1H NMR (500 MHz; d5-PhCl) δH 3.94 (br q, 1JHB
=
80.1 Hz, BH); 11B{1H} NMR (128 MHz; d5-PhCl) δB − 27.7 (br s,
BH); 19F NMR (471 MHz; d5-PhCl) δF − 131.5 (6F, br, o-C6F5), −
163.9 (3F, br, p-C6F5), − 166.2 (6F, br, m-C6F5).
21: H NMR (500 MHz; d5-PhCl) δH 10.80 (br s, CH); 11B{1H}
1
NMR (128 MHz; d5-PhCl) δB −2.4 (br, OB), −16.7 (br s, BCO); 19
F
NMR (471 MHz; d5-PhCl) δF −130.3 (6F, br, o-C6F5), −132.6 (6F,
br, o-C6F5), −157.6 (3F, br, p-C6F5), −159.2 (3F, br, p-C6F5), −164.8
(6F, br, m-C6F5), −165.2 (6F, br, m-C6F5).
Reaction of 11*/B(C6F5)3 with H2. A Youngs NMR tube was
charged with a solution of 11* (20.0 mg, 0.032 mmol) and B(C6F5)3
(16.4 mg, 0.032 mmol) in d5-chlorobenzene (0.7 mL). The orange
solution was frozen in liquid nitrogen and the tube was evacuated.
The solution was thawed and allowed to warm to room temperature.
The tube was backfilled with H2 (1 bar) and shaken. A color change
from orange to a bright pink was observed over 30 min which
intensified over time. 13CO enriched analogues of the previous species
were identified.
16: 1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH),
1
1.11−1.02 (36H, m, CCH3), −4.15 (1H, ddd, JHPt = 755 Hz,
2JHP(trans) = 159 Hz, 2JHP(cis) = 24.3 Hz, 2JHC = 3.5 Hz, PtH); 13C{1H}
NMR (125 MHz; d5-PhCl) δC 178.4 (dd, 1JCPt = 1212 Hz, 2JCP = 124
1H NMR (500 MHz; d8-toluene) δH 7.03 (2H, m, Ar CH), 6.69
2
Hz, JCP = 6.2 Hz, Pt13CO); 31P{1H} NMR (202 MHz; d5-PhCl) δP
3
(2H, m, Ar CH), 1.29 (36H, br d, JHP = 14.1 Hz, CH3); 13C{1H}
1
2
1
174.5 (d, JPPt = 3301 Hz, JPP = 15.0 Hz, PtBu2), 163.0 (d, JPPt
=
2
1
NMR (125 MHz; d8-toluene) δC 228.8 (t, JCP = 56.5 Hz, JCPt
=
2
2294 Hz, JPP = 15.0 Hz, PtBu2).
1964 Hz, Pt13CO), 147.4 (m, Ar C), 128.0 (br s, Ar CH), 124.5 (br s,
18: 1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH),
1.27−1.16 (36H, m, CCH3), −1.92 (1H, 1:8:18:8:1 ququ, 1JHPt = 475
Ar CH), 51.1 (app t, JCP = 5.4 Hz, JCPt = 75.0 Hz, CCH3), 38.2 (m,
2
CCH3); 31P{1H} NMR (202 MHz; d8-toluene) δP 218.2 (d, JPC
=
Hz, JHP = 38 Hz, JH13C = 4.5 Hz, Pt(μ-H)Pt); 13C{1H} NMR (125
MHz; d5-PhCl) δC 231.6 (1:8:18:8:1 ququ, 1JCPt = 753 Hz, 2JCP = 38
Hz, Pt(μ-13CO)Pt) ; 31P{1H} NMR (202 MHz; d5-PhCl): δP 182.2
2
2
1
56.5 Hz, JPPt = 4062 Hz, PtBu2).
Synthesis of [Pt(13CO)(L1)] (3*). A Youngs NMR tube was charged
with a solution of 3 (29.6 mg, 0.048 mmol) in d8-toluene (0.7 mL).
The solution was frozen in liquid nitrogen and the tube was
evacuated. The solution was thawed and allowed to warm to room
temperature. The tube was backfilled with 13CO (1.2 bar). The
solution was mixed and left for 5 min before removing the solvent in
vacuo. The solid was redissolved in d8-toluene. This cycle was
repeated three more times to ensure most of the 12CO had been
exchanged for 13CO. This species was confirmed in solution by NMR
spectroscopy only. NMR data is in agreement with the literature.13
(m, JPPt = 4029 Hz, JPPt = 131 Hz, JPP = 38 Hz, PtBu2).
1
2
3
20: 1H NMR (500 MHz; d5-PhCl) δH 6.99−6.77 (4H, m, Ar CH),
1.27−1.16 (36H, m, CCH3), −5.72 (1H, 1:8:18:8:1 ququ, 1JHPt = 393
Hz, 2JHP = 41.3 Hz, Pt(μ-H)Pt); 31P{1H} NMR (202 MHz; d5-PhCl)
δP 185.6 (m, JPPt = 3459 Hz, JPPt = 153 Hz, 3JPP = 10.1 Hz, PtBu2).
21: 1H NMR (500 MHz; d5-PhCl) δH 10.80 (br d, 1JHC = 151 Hz,
13CH11B{1H} NMR (128 MHz; d5-PhCl) δB −2.4 (br, OB), −16.7
(br d, 1JBC = 49 Hz, B13C);); 13C{1H} NMR (125 MHz; d5-PhCl) δC
1
2
G
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249.2 (br q, 1JCB = 53 Hz, B13CO); 19F NMR (471 MHz; d5-PhCl) δF
−130.3 (6F, br, o-C6F5), −132.6 (6F, br, o-C6F5), −157.6 (3F, br, p-
C6F5), −159.2 (3F, br, p-C6F5), −164.8 (6F, br, m-C6F5), −165.2 (6F,
br, m-C6F5).
repeated twice more. This species was confirmed in solution by NMR
spectroscopy only.
1H NMR (400 MHz; d8-toluene) δH 7.06 (2H, m, Ar CH), 6.72
(2H, m, Ar CH), 2.04 (4H, m, 1JHPt = 55.6 Hz), 1.29 (36H, br d, 3JHP
= 14.1 Hz, CH3); 13C{1H} NMR (100 MHz; d8-toluene) δC 147.7
(m, Ar C), 127.3 (s, Ar CH), 124.3 (br s, Ar CH), 42.4 (m, CCH3),
29.5 (m, CCH3); 31P{1H} NMR (162 MHz; d8-toluene) δP 198.0 (s,
1JPPt = 3840 Hz, PtBu2).
Reaction of 3*/B(C6F5)3 with H2. A Youngs NMR tube was
charged with a solution of [Pt(13CO)(L1)] (18.4 mg, 0.030 mmol)
and B(C6F5)3 (15.3 mg, 0.030 mmol) in d5-chlorobenzene (0.7 mL).
The orange solution was frozen in liquid nitrogen and the tube was
evacuated. The solution was thawed and allowed to warm to room
temperature. The tube was backfilled with H2 (1 bar) and shaken. A
color change from orange to a pale yellow was observed over 16 h.
Three cationic (15 55%, 17 40%, 19 5%) species (% within Pt-
containing species) and two anionic species ([HB(C6F5)3] 55% and
21 45%) (% within B-containing species) were identified in solution
after 15 min.
Synthesis of [Pt(PhCCH)(L1)] (30). A Youngs NMR tube was
charged with a solution of 3* (20.0 mg, 0.032 mmol) and B(C6F5)3
(16.6 mg, 0.032 mmol) in d5-chlorobenzene (0.7 mL). Phenyl-
acetylene was added in excess (ca. 30 μL) and an instant color change
from bright orange to a dark redish brown color was observed. Species
30 was identified in solution.
1H NMR (400 MHz; d5-PhCl) δH 7.12−6.96 (5H, m PhCC),
7.12−6.96 (4H, m, Ar CH), 3.73−2.90 (4H, br, PCH2), 1.04−0.91
(36H, m, CCH3), −4.15 (1H, dd, 1JHPt = 755 Hz, 2JHP(trans) = 159 Hz,
2JHP(cis) = 24 Hz, PtH); 11B{1H} NMR (128 MHz; d5-PhCl) δB −21.1
(br s, CCB(C6F5)3); 19F NMR (376 MHz; d5-PhCl) δF −138.1 (6F,
br, o-C6F5), −170.2 (3F, br, p-C6F5), −173.5 (6F, br, m-C6F5);
31P{1H} NMR (162 MHz; d5-PhCl) δP 43.4 (d, 1JPPt = 2994 Hz, 2JPP
15: 1H NMR (500 MHz; d5-PhCl) δH 7.20−7.02 (4H, m, ArCH),
3.71−3.10 (br, 4H, PCH2), 1.26−1.09 (36H, m, CCH3), −4.55 (1H,
1
2
2
dd, JHPt = 734 Hz, JHP(trans) = 145 Hz, JHP(cis) = 16 Hz, PtH);
13C{1H} NMR (125 MHz; d5-PhCl) δC 178.2 (dd, JCPt = 1305 Hz,
1
2JCP = 113 Hz, 2JCP = 8.8 Hz, Pt13CO); 31P{1H} NMR (122 MHz; d5-
PhCl) δP 43.4 (d, 1JPPt = 2987 Hz, 2JPP = 19 Hz), 34.2 (d, 1JPPt = 2004
1
2
= 19 Hz, PtBu2), 34.2 (d, JPPt = 2018 Hz, JPP = 19 Hz, PtBu2).
Synthesis of [Pt(PhCCH)(L2)] (31). A Youngs NMR tube was
charged with a solution of 11* (20.0 mg, 0.032 mmol) and B(C6F5)3
(16.5 mg, 0.032 mmol) in d5-chlorobenzene (0.7 mL). Phenyl-
acetylene was added in excess (ca. 30 μL) and an instant color change
from bright orange to a dark red color was observed. Species 31 was
identified in solution.
2
Hz, JPP = 19 Hz).
17: 1H NMR (500 MHz; d5-PhCl) δH 7.20−7.02 (4H, m, ArCH),
3.71−3.10 (br, 4H, PCH2), 1.08−0.93 (36H, m, CCH3), −5.75 (1H,
1:8:18:8:1 ququ, 1JHPt = 496 Hz, JHP = 35 Hz, Pt(μ-H)Pt); 13C{1H}
2
1
NMR (125 MHz; d5-PhCl) δC 212.88 (1:8:18:8:1 ququ, JCPt = 805
2
Hz, JCP = 33 Hz, Pt(μ-13CO)Pt); 31P{1H} NMR (122 MHz; d5-
1
2
3
PhCl) δP 46.4 (m, JPPt = 3755 Hz, JPPt = 144 Hz, JPP = 23 Hz).
1H NMR (400 MHz; d5-PhCl) δH 7.19−6.73 (5H, m PhCC),
6.99−6.77 (4H, m, Ar CH), 1.11−1.02 (36H, m, CCH3), −4.15 (1H,
1
19: H NMR (500 MHz; d5‑PhCl) δH 6.99−6.77 (4H, m, ArCH),
1.27−1.16 (36H, m, CCH3), −7.48 (1H, 1:8:18:8:1 ququ, 1JHPt = 393
1
2
2
2
Hz, JHP = 41 Hz, Pt(μ-H)3Pt); 31P{1H} NMR (122 MHz; d5-PhCl)
dd, JHPt = 755 Hz, JHP(trans) = 159 Hz, JHP(cis) = 24 Hz, Pt-H);
11B{1H} NMR (128 MHz; d5-PhCl) δB −21.1 (br s, CCB(C6F5)3);
19F NMR (376 MHz; d5-PhCl) δF −138.1 (6F, br, o-C6F5), −170.2
(3F, br, p-C6F5), −173.5 (6F, br, m-C6F5); 31P{1H} NMR (162 MHz;
δP 50.8 (br).
Reaction of 11/B(C6F5)3 with C2H4. A Youngs NMR tube was
charged with a solution of 11 (17.2 mg, 0.028 mmol) and B(C6F5)3
(14.2 mg, 0.028 mmol) in d5-chlorobenzene (0.7 mL). The orange
solution was frozen in liquid nitrogen and the tube was evacuated.
The solution was thawed and allowed to warm to room temperature.
The tube was backfilled with C2H4 (1 bar) and shaken. A color
1
2
d5-PhCl) δP 174.5 (d, JPPt = 3301 Hz, JPP = 15.0 Hz, PtBu2), 163.0
(d, JPPt = 2294 Hz, JPP = 15.0 Hz, PtBu2).
1
2
Synthesis of [PdCl2(L1)] (32). Pd(dba)2 (879 mg, 1.53 mmol) and
L1 (605 mg, 1.53 mmol) were combined and stirred in THF (30 mL)
for 2 d at room temperature. The red-orange solution was filtered, and
the solvent was removed in vacuo. The resulting orange solid was
dissolved in Et2O (35 mL) and HCl (2.5 mL, 1 M in Et2O) was
added. Over 1 h, a dark yellow precipitate had formed. The solid was
isolated and washed with Et2O (3 × 30 mL) and THF (1 × 30 mL).
The product was dissolved in DCM and the insoluble material was
filtered off. The desired product was then isolated as a yellow solid by
precipitation from a DCM solution by slow addition of Et2O (540 mg,
62%). NMR data is in agreement with the literature.44 1H NMR (400
MHz; CD2Cl2) δH 7.38 (2H, m, Ar CH), 7.22 (2H, m Ar CH), 3.43
1
change from orange to pale pink was observed over 1 h. H NMR
(400 MHz; d5-PhCl) δH 6.94−6.70 (4H, m, Ar CH), 2.87 (2H, br m,
BCCH2), 1.90 (2H, br m, PtCH2), 1.19−1.08 (36H, m, CCH3);
11B{1H} NMR (128 MHz; d5-PhCl) δB −22.0 (br s, CB(C6F5)3); 19
F
NMR (376 MHz; d5-PhCl) δF −137.2 (6F, br, o-C6F5), −167.1 (3F,
br, p-C6F5), −172.1 (6F, br, m-C6F5); 31P{1H} NMR (162 MHz; d5-
PhCl) δP 173.4 (d, 1JPPt = 2219 Hz, 2JPP = 15.0 Hz, PtBu2), 137.5 (d,
2
1JPPt = 4662 Hz, JPP = 15.0 Hz, PtBu2).
Reaction of 11*/B(C6F5)3 with C2H4. A Youngs NMR tube was
charged with a solution of 11* (15.8 mg, 0.025 mmol) and B(C6F5)3
(13.0 mg, 0.025 mmol) in d5-chlorobenzene (0.7 mL). The orange
solution was frozen in liquid nitrogen and the tube was evacuated.
The solution was allowed to warm to room temperature. The tube
was backfilled with C2H4 (1 bar) and shaken. A color change from
orange to pale pink was observed over 1 h.
3
(4H, m, CH2), 1.60 (36 H, d, JHP = 14.0 Hz, C(CH3)3); 31P{1H}
NMR (162 MHz; CD2Cl2) δP 37.2 (s, PtBu2).
Synthesis of [Pd(CO)(L1)] (33). Compound 32 (100 mg, 0.17
mmol) was dissolved in EtOH (CO saturated) and then the yellow
suspension was sparged with CO and kept under a CO atmosphere
(CO balloon). NEt3 (50 μL, 0.35 mmol) was added, and then the
reaction mixture was sparged with CO. A darkening of the reaction
mixture was seen, and a yellow precipitate formed in a dark orange
solution. The yellow solid was isolated as the desired product (49 mg,
55%).
1H NMR (400 MHz; d5-PhCl) δH 6.94−6.70 (4H, m, Ar CH), 2.87
(2H, br m, BCCH2), 1.90 (2H, br m, PtCH2), 1.19−1.08 (36H, m,
1
CCH3); 11B{1H} NMR (128 MHz; d5-PhCl) δB −22.0 (br d, JBC
=
52.4 Hz, 13CB(C6F5)3); 13C{1H} NMR (100 MHz; d5-PhCl) δC 278.7
(br q, JCB = 52.4 Hz, B13CO); 19F NMR (471 MHz; d5-PhCl) δF
1
1H NMR (400 MHz; d8-toluene) δH 7.13 (2H, m, Ar CH), 6.90
(2H, m, Ar CH), 3.10 (4H, m, CH2), 1.21 (36H, m, C(CH3)3);
13C{1H} NMR (125 MHz; d8-toluene) δC 130.0 (br s, Ar CH), 122.0
(br s, Ar CH), 33.5 (br, CH2), 29.0 (br s, CCH3), 26.0 (m, CCH3)
135.0 (m, Ar C), (note: Pt-CO not observed); 31P{1H} NMR (400
MHz; d8-toluene) δP 50.0 (s, PtBu2); IR νCO 1955 cm−1.
−137.2 (6F, br, o-C6F5), −167.1 (3F, br, p-C6F5), −172.1 (6F, br, m-
C6F5); 31P{1H} NMR (162 MHz; d5-PhCl) δP 173.4 (d, 1JPPt = 2219
Hz, 2JPP = 15.2 Hz, PtBu2), 137.5 (d, 1JPPt = 4662 Hz, 2JPP = 15.2 Hz,
PtBu2).
Synthesis of [Pt(C2H4)(L2)] (23). A Youngs NMR tube was charged
with a solution of 11 (25.4 mg, 0.041 mmol) in d8-toluene (0.7 mL).
The solution was frozen in liquid nitrogen and the tube was
evacuated. The solution was thawed and allowed to warm to room
temperature. The tube was backfilled with C2H4 (1.2 bar). The
solution was shaken and left for 5 min before removing the solvent in
vacuo. The solid was redissolved in d8-toluene. This cycle was
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00568.
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sı
H
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Selected NMR spectra (PDF)
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CCDC 1950779−1950781 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Paul G. Pringle − School of Chemistry, University of Bristol,
Bristol BS8 1TS, U.K.; orcid.org/0000-0001-7250-4679;
Email: paul.pringle@bristol.ac.uk
Duncan F. Wass − Cardiff Catalysis Institute, School of
Chemistry, Cardiff University, Cardiff CF10 3AT, U.K.;
orcid.org/0000-0002-0356-7067; Email: wassd@
cardiff.ac.uk
Authors
Krishna Mistry − School of Chemistry, University of Bristol,
Bristol BS8 1TS, U.K.
Hazel A. Sparkes − School of Chemistry, University of Bristol,
Bristol BS8 1TS, U.K.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.9b00568
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The EPSRC CDT in Chemical Synthesis is thanked for
financial support to K.M.
■
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