Transformation of a phosphorus-bound Cp* moiety in the coordination sphere of manganese carbonyl complexes

Article abstract of DOI:10.1021/om300808t

The reaction of Cp PCl₂ with K[Mn(CO)₅] yields two novel anionic products, [Mn₂(CO)₈(μ-PC ₁₁H₁₄O)]^- (1^-) and [Mn ₂(CO)₈(μ-PHCp)]^- (2^-), instead of the expected phosphinidene complexes with a delocalized Mn-P-Mn bond system. By treating these anionic complexes with [Ph₃PAuCl], they are converted into corresponding neutral derivatives [Mn₂(CO)₈(μ- PC₁₁H₁₄O)(μ-AuPPh₃)] (3) and [Mn ₂(CO)₈(μ-PHCp)(μ-AuPPh₃)] (4). NMR investigations and X-ray structural analyses for 1^-, 3, and 4 show that the compounds 1^- and 3 as well as 2^- and 4 reveal similar molecular structures in which the neutral complexes 3 and 4 contain AuPPh₃ units bridging Mn-Mn bonds. In comparison to 1 and 3, complexes 2 and 4 possess one additional H atom bound at the P atom. The structures of 1 and 3 include a novel bicyclic unit consisting of a C ₅ ring of the former Cp* moiety conjugated to a CCC(O)P four-membered ring. The latter is built by a CO group of a former Mn carbonyl fragment connecting a P and a C atom of the cycle. One of the methyl groups of the Cp* ligand became a CH₂ unit, resulting in two isomers containing an exocyclic CH₂ moiety in the positions three or five of the C₅ ring. Both isomers were found in the reaction mixture, with one as the major isomer. The proposed reaction pathway is based on XRD, NMR, and MS data and includes the reduction of a transient [CpP(Mn(CO)₅) ₂] complex by [Mn(CO)₅]^-, a proton transfer from the neutral to the reduced complex, and a successive reduction of the protonated species. The neutral bicyclic compound 3, containing a 2-phosphacyclobutanone ring, is light sensitive and decomposes to tetramethylfulvene, possibly by a radical decarbonylation mechanism via a transient phosphacyclobutane derivative, [C₅(CH₃) ₄(CH₂)P(Mn(CO)₄)₂AuPPh₃] (5), detected by NMR spectroscopy.

Full text of DOI:10.1021/om300808t

Article
pubs.acs.org/Organometallics
Transformation of a Phosphorus-Bound Cp* Moiety in the
Coordination Sphere of Manganese Carbonyl Complexes
Nikolay A. Pushkarevsky,*,† Sergey N. Konchenko,† Alexander V. Virovets,† and Manfred Scheer*,‡
†Nikolaev Institute of Inorganic Chemistry, Siberian Division of RAS, Akad. Lavrentieva Street 3, 630090 Novosibirsk, Russia
‡Institut fur Anorganische Chemie, Universitat Regensburg, 93040, Regensburg, Germany
̈
̈
S
* Supporting Information
ABSTRACT: The reaction of Cp*PCl2 with K[Mn(CO)5] yields two novel anionic products, [Mn2(CO)8(μ-PC11H14O)]−
(1−) and [Mn2(CO)8(μ-PHCp*)]− (2−), instead of the expected phosphinidene complexes with a delocalized Mn−P−Mn bond
system. By treating these anionic complexes with [Ph3PAuCl], they are converted into corresponding neutral derivatives
[Mn2(CO)8(μ-PC11H14O)(μ-AuPPh3)] (3) and [Mn2(CO)8(μ-PHCp*)(μ-AuPPh3)] (4). NMR investigations and X-ray
structural analyses for 1−, 3, and 4 show that the compounds 1− and 3 as well as 2− and 4 reveal similar molecular structures in
which the neutral complexes 3 and 4 contain AuPPh3 units bridging Mn−Mn bonds. In comparison to 1 and 3, complexes 2 and
4 possess one additional H atom bound at the P atom. The structures of 1 and 3 include a novel bicyclic unit consisting of a C5
ring of the former Cp* moiety conjugated to a CCC(O)P four-membered ring. The latter is built by a CO group of a former Mn
carbonyl fragment connecting a P and a C atom of the cycle. One of the methyl groups of the Cp* ligand became a CH2 unit,
resulting in two isomers containing an exocyclic CH2 moiety in the positions three or five of the C5 ring. Both isomers were
found in the reaction mixture, with one as the major isomer. The proposed reaction pathway is based on XRD, NMR, and MS
data and includes the reduction of a transient [Cp*P(Mn(CO)5)2] complex by [Mn(CO)5]−, a proton transfer from the neutral
to the reduced complex, and a successive reduction of the protonated species. The neutral bicyclic compound 3, containing a 2-
phosphacyclobutanone ring, is light sensitive and decomposes to tetramethylfulvene, possibly by a radical decarbonylation
mechanism via a transient phosphacyclobutane derivative, [C5(CH3)4(CH2)P(Mn(CO)4)2AuPPh3] (5), detected by NMR
spectroscopy.
M, W), Co(CO)3),5,6 a double bond (type C, MLn
=
INTRODUCTION
■
8
MoCp(CO)I,7 VCp(CO)2 ), or a triple bond (type D, MLn
Carbene complexes of transition metals bearing a CR2 unit are
important compounds in organic syntheses and catalyses such
as metathesis, polymerization, and oxidation of olefins.1 Their
isolobal relatives are phosphinidene complexes containing a PR
unit that can be bound on up to four metal fragments. They
show a high variety in coordination modes and structural
features2 and are valuable synthons for the design of
organophosphorus derivatives containing low-coordinate phos-
phorus centers. Whereas big efforts in the reactivity of terminal
phosphinidene complexes have been made,2a,3 the class of 2-
fold bridging complexes possessing a delocalized M−P−M
bond is comparatively rather underdeveloped. Depending on
the valence electron (VE) number of the coordinated metal
fragments MLn, the formed molecules possess no bond (type A,
MLn = M(CO)5 (M = Cr, Mo, W), MnCp(CO)2, Fe(CO)4,
CpCo(CO)2),4 a single bond (type B, MLn = Cp(CO)2 (M =
= MoCp(CO)7) between the metal centers. Rarely, they tend
to dimerize and form type E complexes (MLn = Fe(CO)3 ).
9
Type B or E complexes are usually achieved if complex
fragments with an odd number of VEs are used. For even-
numbered complex moieties usually type A complexes are
formed, and only by using electron-deficient fragments are the
multiple-bonded species C and D observed. The delocalized 3c-
4e M−P−M bond in A is responsible for the electron-deficient
P atom and provides its strong electrophilic reactivity pattern.
Thus, most commonly μ-phosphinidene complexes easily react
with nucleophiles to form the addition products F.
Received: August 27, 2012
Published: January 24, 2013
© 2013 American Chemical Society
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Cp*PCl2 with KMn(CO)5. Surprisingly, the aforementioned
reaction leads to a rapid reduction of the resulting species
accompanied by deprotonation and rearrangement reactions
and the formation of novel types of bicyclic phosphorus-
containing complexes. The results are reported herein.
RESULTS AND DISCUSSION
■
Synthesis. The reaction of Cp*PCl2 with an excess of
KMn(CO)5 (Scheme 1) was not accompanied by a drastic
color change, and the 31P NMR spectra of the reaction mixture
did not contain any signals at low field either. These features
usually correspond to the formation of a M−P−M delocalized
bond of type A−D compounds.20 After the evaporation of the
solvents, the only neutral reaction product that could be
extracted with hexane was Mn2(CO)10 (as shown by IR
spectroscopy). The other products seemed to be ionic and were
soluble only in polar solvents such as THF and DME. After
washing off the formed Mn2(CO)10 with hexane, the remaining
solid was extracted with ether. Addition of 18-crown-6 and
cooling led to the precipitation of red crystals identified as the
ionic compound [K(18-crown-6)(Et2O)][Mn2(CO)8(μ-
C11H14OP)] ([K(18-crown-6)(Et2O)][1]) by X-ray crystal
structure analysis (Figure 1). The structure of the anion
shows substantial changes of the former Cp* substituent. Its
ring is distorted and one additional CO group bridges the C2
atom of the Cp* ring and the P1 atom. So, a four-membered
ring is formed in addition to the initial five-membered one. The
P atom binds two Mn(CO)4 fragments that are additionally
connected by a Mn−Mn bond.
Only two anionic products were detected by measuring an
ESI mass spectrum of the DME solution of the remaining solid
after the extraction of Mn2(CO)10: the one with the mass of
527.0 corresponds exactly to the anion [1]−, while the other
one, with a mass of 501.1, has one CO group less than [1]−.
Low tube lens voltage settings (20 V) were applied to avoid
decomposition of the reaction components. The relative
intensities (100% and 70%) indicate that both compounds
are present in the reaction mixture in comparable amounts.
Unfortunately, we did not succeed in crystallizing the second
ionic compound separately from the reaction mixture (vide
infra).
Besides the nature of the complex fragment also the
properties of the substituent R at the phosphinidene P atom
can decisively influence the structure and reactivity of the
compounds. The Ruiz group has shown the influence of the
mesityl substituent, which can move to a transition metal and
act as an additional ligand, providing type G-like and other
complexes.7,10 A unique reaction behavior appears when the P
atom bears a Cp* group. The resulting complex [Cp*P{W-
(CO)5}2]11 shows a rich subsequent chemistry, which was
intensively investigated in our group. The lability and the
coordination properties of the η1-bound Cp* group12 allow its
shifting to the metal atom after thermal activation, forming an
intermediate containing a phosphorus−tungsten triple bond of
the formula [Cp*(CO)2WP→(CO)5].13 This transient
compound serves as a versatile precursor in reactions with
unsaturated species such as alkynes,14 phosphaalkynes,15 and
binuclear carbonyl complexes containing a metal−metal triple
bond.16 With nitriles, the μ-phosphinidene complex undergoes
migration reactions of the Cp* substituent to form novel P-
containing heterocycles.17 UV radiation induces elimination of
a Cp* radical to yield stable triphospha- or arsadiphosphaallyl
radicals in the reaction with diphosphenes.18 Only if MesCP
reacts with [Cp*P{W(CO)5}2] a ring expansion of the Cp*
substituent has been found so far,15 and primary phosphines
provoke hydrophosphination reactions to expand the Cp*
moiety, yielding diphosphanorbornene derivatives.19
With this versatile and rich chemistry of the tungsten
derivative in mind, we tried to extend the general concept of
bridging phosphinidene complexes to Mn-substituted deriva-
tives of the type [Cp*P{Mn(CO)5}2], which are unknown up
to now. As reactions of dihalogenophosphines with anionic
metallates represent the most usual way for the synthesis of
such phosphinidene complexes, we have studied the reaction of
Scheme 1. Synthesis of the Anionic Phosphorus Complexes of Manganese and the Subsequent Transformation into the Neutral
Gold Derivatives
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Figure 1. Cation and anion of [K(18-crown-6)(Et2O)][Mn2(CO)8(μ-
C11H14OP)] ([K(18-crown-6)(Et2O)][1]) (thermal ellipsoids at the
50% probability level, only one part of the disordered bicyclic moiety
P1,C1−C6 is shown). Hydrogen atoms are omitted for clarity.
Selected bond distances (Å): Mn(1)−P(1) 2.2337(19); Mn(1)−
Mn(2) 2.8545(14); Mn(2)−P(1) 2.2606(19); P(1)−C(6) 1.838(12);
P(1)−C(1) 1.913(14); C(6)−O(6) 1.221(12); C(6)−C(2)
1.585(18); C(1)−C(2) 1.565(19); C(2)−C(3) 1.595(19); C(3)−
C(4) 1.30(2); C(4)−C(5) 1.35(2); C(1)−C(5) 1.509(19); C(1)−
C(11) 1.66(2); C(2)−C(21) 1.486(19); C(3)−C(31) 1.46(2);
C(4)−C(41) 1.533(18); C(51)−C(5) 1.43(2).
Figure 2. Molecular structure of complex 4 in the crystal (thermal
ellipsoids at the 40% probability level). Hydrogen atoms are omitted
for clarity. Selected bond distances (Å): Au(1)−P(2) 2.3125(7);
Au(1)−C(74) 2.760(4); Au(1)−C(84) 2.673(3); Au(1)−Mn(2)
2.6794(5); Au(1)−Mn(1) 2.6968(4); Mn(1)−P(1) 2.2934(9);
Mn(1)−Mn(2) 3.0775(6); Mn(2)−P(1) 2.2682(8); P(1)−H(1)
1.26(3); P(1)−C(1) 1.882(3).
To study the anionic products individually, we converted the
ionic part of the reaction mixture into neutral derivatives by
treatment with PPh3AuCl. This reaction proceeded without any
noticeable decomposition, and the neutral products could be
separated by chromatography on TLC plates (silica). The first
bright yellow fraction was obtained apart from the others and
could be crystallized from hexane. The subsequent X-ray
structure analysis identified the crystals as the complex
[Mn2(CO)8(μ-PHCp*)(μ-AuPPh3)] (4) (Figure 2). Unlike
the anion [1]−, this neutral cluster contains an intact Cp*
group σ-bound to the P atom and an AuPPh3 fragment bridging
the Mn atoms. The heterocyclic P atom carries an additional
proton (cf. Crystal Structure Determination for a more detailed
discussion).
The next two fractions were eluted as orange bands so close
to each other that they could only be separated (yet not
completely) after multiple runs on a TLC plate with hexane as
an eluent. The second light orange fraction contained only
traces of a product of which no single crystals could be
obtained. The third orange fraction included as much
compound as the first one and was slightly contaminated by
the tail of the previous fraction. We succeeded in getting
suitable single crystals for an X-ray structure analysis of this
fraction by crystallization from n-hexane. The crystals were
identified as the neutral cluster [Mn2(CO)8(μ-C11H14OP)-
(AuPPh3)] (3) (Figure 3). In the bicyclic section, the structure
of this compound is reminiscent of that of the anion 1−. Like in
4, the fragment AuPPh3 is bridging two Mn atoms, forming a
neutral molecule.
Crystal Structure Determination. Suitable crystals for an
X-ray analysis of [K(18-crown-6)(Et2O)][1] were obtained by
crystallization of the anionic reaction products after addition of
crown ether. The crystal structure (Figure 1) shows the
transformation of the Cp* substituent during the formation of
the anion [1]−. Along with the P atom and an additional CO
group, it forms a bicyclic ligand with adjacent four- and five-
membered rings. The ring system is disordered over two
positions, which were refined with equal occupancies. Both
rings are almost planar, revealing an angle of 72° between the
planes. The distance C6−O6 (∼1.22 Å) is typical for a CO
double bond. A more detailed understanding of the geometry
and the bonding situation of the ring system could not be
deduced solely from the crystallographic data due to a
significant overlap of the disordered fragments, which crucially
affected the C−C bond distances and did not allow localizing of
the hydrogen atoms. The same structure of the anion 1− of a
somewhat poorer quality was obtained for the salt without 18-
crown-6, [K(Et2O)2][1] (cf. Supporting Information). After
treatment of the mixture of the ionic products with PPh3AuCl,
the crystal structures for both resulting neutral products have
fortunately been determined. The molecular structure of 3
(Figure 3) reveals the same bicyclic unit as the anion [1]−. The
four-membered rings in both compounds possess similar
geometrical parameters (the maximum differences of the
corresponding bond lengths are 0.05 Å). The distances
between the remaining three C atoms of the five-membered
ring (C3−C5) and from these atoms to their adjacent carbon
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moiety featuring both ionic structures (cf. Supporting
Information). In comparison to the initial Cp* moiety, the
C2 atom became quaternized, unlike the atoms C3−C5.
According to the X-ray data, the atoms C3, C4, and C5 as well
as all the adjacent C atoms lie nearly in one plane. Such a
planarity can be explained by a chain of sp2-hybridized carbon
atoms. Hence, supposing the bicyclic moiety is neutral and
electron-even, two conjugated double bonds in the chain C31−
C3−C4−C5−C51 must be present: either between C3C31
and C4C5 or between C3C4 and C5C51 (see the
NMR Study section for further insight). In the structure of 3,
the bonds C3−C4 and C5−C51 (both 1.33 Å) are significantly
shorter than C4−C5, C3−C4, and C4−C41 (1.47−1.52 Å).
The thermal ellipsoids of the carbon atoms are not stretched
significantly along the bonding direction. Thus, these shorter
distances can be considered as double bonds (typical values are
1.33−1.38 Å for double bonds and 1.44−1.52 Å for single
bonds for similar conjugated structures with five-membered
rings21). Therefore, atom C51 represents a CH2 group and not
a CH3 group like in the initial Cp* fragment. The length of the
bond C4−C41 is in the range 1.47−1.59 Å in all structures and
can be regarded as a single bond.
In the crystal structure of the second neutral main product, 4
(Figure 2), an intact Cp* moiety is σ-bound at the P atom. The
environment of the P atom is not planar (which would be
expected for the bridging phosphinidene complexes with a
delocalized M−P−M bond), but distorted tetrahedral with
three vertices occupied by two Mn and one C atom. The fourth
position can be assigned to a H atom, which was found from
the difference electron map and refined isotropically without
further restraints. The existence of this H atom was further
confirmed by NMR and MS data (vide infra). Thus, the
[Cp*PH] fragment donates three electrons to the two Mn
fragments. The counting of one further VE from the AuPPh3
fragment and 8e− from the four CO groups yields 34e− for the
dimanganese fragment, which supports the existence of a Mn−
Mn single bond according to the 18 VE rule. A related
dimanganese complex, [Mn2(CO)8(μ-PCyH)(μ-AuPPh3)],22
with a bridging (μ-PHR) phosphido ligand and (μ-AuPPh3)
unit reveals very similar structural and spectroscopic properties.
The Mn−Mn bond length in 4 (3.076 Å) lies within the normal
range of known Mn−Mn distances (2.664−3.244 Å for
Figure 3. Molecular structure of complex 3 in the crystal (thermal
ellipsoids at the 40% probability level). Hydrogen atoms are omitted
for clarity. Selected bond distances (Å): Au(1)−P(2) 2.326(4);
Au(1)−C(74) 2.718(18); Au(1)−C(84) 2.649(17); Au(1)−Mn(1)
2.669(2); Au(1)−Mn(2) 2.719(2); Mn(1)−P(1) 2.255(5); Mn(1)−
Mn(2) 3.081(4); Mn(2)−P(1) 2.259(5); P(1)−C(6) 1.828(18);
P(1)−C(1) 1.947(17); C(6)−O(6) 1.23(2); C(1)−C(2) 1.63(2);
C(2)−C(3) 1.49(3); C(3)−C(4) 1.33(2); C(4)−C(5) 1.47(2);
C(1)−C(5) 1.42(2); C(1)−C(11) 1.54(2); C(2)−C(21) 1.43(3);
C(3)−C(31) 1.48(3); C(4)−C(41) 1.52(2); C(5)−C(51) 1.33(2);
C(2)−C(6) 1.59(2).
atoms (C31−C51) sufficiently differ in compounds 3, [K(18-
crown-6)(Et2O)][1], and [K(Et2O)2][1], however. These
differences may be attributed to the disorder of the bicyclic
Figure 4. Sections of the 1H NMR spectra (a) of a mixture of 3a and 3b in C6D6 and (b, c) after decomposition under diffuse sunlight. The lower
field part of the NMR spectrum contains signals of CH2 groups; the higher field part, those of CH3 groups. The lower field part is multiplied by 8 for
clarity. The asterisk denotes a minor signal of unknown origin.
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complexes with a (CO)4Mn−Mn(CO)4 fragment and 3.040−
3.136 Å for compounds of the type Mn2(CO)8(μ-AuPR3)(μ-
PR2) according to the Cambridge Structural Database). The
Mn−Mn distance in 3 (3.081 Å) is almost the same as in 4. In
the structure of [1]− the Mn−Mn bond is noticeably shorter
(2.855 Å), which agrees with the absence of the second
bridging group (μ-AuPPh3) and is typical for phosphorus-
bridged dimanganese complexes containing a Mn2(CO)8(μ-
PR2) fragment21 (2.846−2.951 Å). The cycles P1Mn1Mn2Au1
in the structures of 3 and 4 are nearly planar. Two CO groups
in each cluster may be considered as semibridging between the
Mn and Au atoms (C74O74 and C84O84), and the angles
Mn−C−O lie in the range 170−174°. The C···Au distances
vary from 2.649 to 2.760 Å.
of 3b had disappeared (Figure 4b), and the signals of 3a were
reduced by a factor of about seven in four days (Figure 4c). At
the same time, three new resonances increased that coincide
with those known for tetramethylfulvene (Me4Fv) (the
corresponding signals have also been found in the 13C
spectrum).24 No further signals of noticeable intensity have
been monitored in the 1H NMR spectrum, which indicates that
the decomposition of the isomers 3 into Me4Fv is the main
reaction route.
Along with the signals of Me4Fv, a new set of weaker signals
containing one methylene and four methyl resonances
appeared in the mixture and decreased after a prolonged
irradiation concurrently with those for the isomers of 3. We
were able to separate small amounts of the corresponding
1
compound 5 as a narrow band on a TLC plate. Its H NMR
NMR Study. The NMR spectroscopic investigations provide
further information about the structure of the reaction
products. In the 1H NMR spectrum of 4, three different
sharp resonances for the three CH3 groups are found that are
typical for a σ-bound Cp* moiety.23 The P−H resonance at
5.20 ppm reveals a doublet (1JPH = 308 Hz), and the
corresponding doublet in the 31P spectrum arises at 181 ppm.
The second fraction of the chromatographic separation
containing 3 reveals two similar sets of signals with a ratio of
spectrum contains two characteristic CH2 multiplets noticeably
shifted to a higher field in comparison with the signals of 3. The
13C and 31P NMR spectra of 5 show the same number of
resonances as those of 3a and 3b, although the signals of the
phosphorus atom and the carbon atom of a CH2 group are
shifted to higher field. 13C DEPT measurements confirm that
the signal at 28 ppm belongs to a CH2 group. Nevertheless, this
chemical shift and the shifts of the corresponding protons in
1
1
about 4:1 in the H NMR spectra (Figure 4a). Both sets show
the H NMR are too much shifted upfield to represent a
proton signals around 5 ppm that correspond to CH2 groups
and an additional four signals of four different CH3 groups with
appropriate integral values. The presence of one CH2 and four
CH3 resonances for each set was also proven by a 13C DEPT
experiment that shows all the corresponding resonances as two
sets of similar signals. The 31P NMR spectrum reveals two
resonances at lower field with the same ratio of intensities at
290 and 277 ppm. Due to this similarity and the fact that the
mass spectra illustrate only the presence of two compounds in
the mixture of the anionic products, we suppose the presence of
two isomers of compound 3 (namely, 3a and 3b) in the
reaction mixture. They differ in the position of the CH2 group
in the five-membered carbon ring (Figure 5). It was further
shown by the X-ray data of 3 (vide supra) and [K(OEt2)2][1]
(see Supporting Information) that 3a is the more abundant
isomer.
terminal CH2 group. This fact, as well as the large H−H
coupling constant of 14 Hz, allows the assignment of this
resonance to a bridging CH2 group. In addition, the 31P NMR
chemical shift of the P atom (233 ppm) indicates the presence
of a μ-PR2 ligand (cf. 249 ppm for the related complex
[Mn2(CO)8(μ-PCy2)(μ-AuPPh3)]).25 Hence, one can propose
that 5 represents a phosphacyclobutane derivative originated
from the elimination of a CO group from the four-membered
cycle of 3a, followed by a radical-induced cyclization with the
terminal CH2 group and a rearrangement of the conjugated
double bonds (Scheme 2). The transient compound 5 is then
degraded under prolonged irradiation to give Me4Fv. The
stereochemistry of the isomer 3b does not allow it to be
transformed into 5 by an analogous pathway. Still, it is possible
that 3b is decomposed to give Me4Fv via other transient
Scheme 2. Proposed Reaction Route of the Light-Induced
Decomposition of 3
Figure 5. Proposed structures for both isomers of 3.
As already mentioned, separation of isomers 3a and 3b was
not possible by column chromatography, and they were eluted
together as an orange band. While trying to separate the
isomers by TLC, 3b disappears according to NMR monitoring.
A light-induced decomposition was supposed, which was
proven by a separate experiment. After the chromatographic
separation, a sealed NMR tube containing a C6D6 solution of
1
both isomers was exposed to diffuse sunlight, and H NMR
spectra were taken periodically. The intensity of the signals of
both 3a and 3b subsided gradually. After two days, the signals
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Scheme 3. Proposed Pathway of the Reaction of Cp*PCl2 with KMn(CO)5: (a) Substitution of Cl− by Pentacarbonylmanganate
Units; (b) Reduction of the Obtained Complex by a Third Equivalent of [Mn(CO)5]−; (c) Abstraction of a Proton from the
Neutral Complex by the Reduced Complex, Followed by a Mesomeric Stabilization of the Obtained Anion; (d) Intramolecular
Nucleophilic Attack of a CO Group, Accompanied by Rearrangement and Formation of a Four-Membered Ring; (e) Binding of
a Proton by the Reduced Phosphinidene Complex to Form a Neutral Protonated Complex with a μ-P(H)Cp* Unit
species, which are not monitored by NMR spectroscopy owing
to their low concentration or instability. The mentioned
photodecomposition is not known for 2-phosphacyclobuta-
nones. To the best of our knowledge, there are only two reports
on 2-phosphacyclobutanones as stable compounds to date,26
and one example represents a ligand of a W complex.13a
However, the all-carbon analogues, the cyclobutanones,
represent a broadly studied class of compounds. Their
photochemical decarbonylation leading to the formation of
1,3-biradical was shown to be the predominant pathway for
triplet-sensitized reactions.27−30 The further photodecomposi-
tion of 5 can be facilitated by coordination of the P atom to two
metal centers, as well as by the release of the stable Me4Fv in
the reaction course. Imine elimination (PriNCMe2) was
reported for a μ-PNiPr2 ligand coordinated to two metal
centers upon α-C−H activation,31 which is somewhat
comparable to the process found in 5. For 5, decomposition
products with Mn, Au, and P atoms could not be isolated or
identified. The 31P NMR spectrum of the reaction mixture
indicates the formation of a large number of unknown P-
containing species.
derivatives, all the characteristic signals of the ionic compounds
(especially those of the central P atom and the CH2 group) are
shifted to higher field, revealing higher electron density. It is
noteworthy that in contrast to the neutral congeners no
noticeable decomposition of the ionic salts is observed by
irradiation with visible light, which is indicated by the absence
of the signals at higher field (for the CH2 group) or those
corresponding to tetramethylfulvene.
Reaction Pathway. On the basis of the X-ray structures of
all the main reaction products and the NMR evidence of the
isomers [1a]− and [1b]−, the following reaction pathway can be
proposed. It should be again mentioned that in the majority of
the reactions of RPHal2 with various transition metal-centered
anions the main reaction products are phosphinidene
complexes of the type A−D, diphosphenes RPPR, and
their derivatives.6,9−11,32 Both types of compounds are easily
identified by their low-field shifts in the 31P NMR spectra,33
which were not observed for the discussed reactions. The
absence of these phosphinidene complexes as reaction products
is rather unusual since such complexes are also formed in
−
similar reactions of the metalate monoanions Co(CO)4 and
1
−
Interestingly, the resonances in the H, 13C, and 31P NMR
CpMo(CO)3 with Ph*PCl2, which possesses the more
spectra of the reaction mixture of Cp*PCl2 with KMn(CO)5
are similar to those of the compounds 4, 3a, and 3b with only
slightly different chemical shifts. No other resonances are
present in the spectra. Hence, we suppose that the mixture of
ionic compounds is consistent with the corresponding anions
[1a]−, [1b]−, and [2]− (Scheme 1) and that the reaction with
Ph3PAuCl results in the formation of the neutral derivatives 3a,
3b, and 4.
sterically demanding Ph* substituent (Ph* = 2,4,6-
tBu3C6H2).5 Thus, in the present case a fast conversion of an
initially generated phosphinidene complex of type A might be
the reason. Thus, one can propose the formation of the
dimanganese complex [Cp*P{Mn(CO)5}2] in the early stage
of the reaction (Scheme 3a) since a halogen substitution usually
proceeds rapidly even at low temperatures.34 The anionic
nature of the characterized products 1 and 2 indicates that not
only the substitution but also the reduction of the initially
formed neutral complexes occurs (Scheme 3b), which is
possibly accompanied by the elimination of CO groups. The
only suitable reduction agent in the reaction mixture is
[Mn(CO)5]−. This assumption is supported by the exper-
imental detection of Mn2(CO)10 as a byproduct of the reaction
and by the observation that the maximum yields of the anionic
The 1H NMR spectrum of the anion [2]− features a doublet
with a large coupling constant corresponding to the P−H bond
(3.49 ppm, J = 317 Hz) for which an analogous doublet arises
at 149 ppm in the 31P NMR spectrum. The signals of both
isomers of [1]− reveal similar chemical shifts, and the same
ratios of intensity (approximately 3:1 for 1a:1b) were found for
their neutral derivatives. In comparison to the neutral
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Article
products are achieved when the reagents KMn(CO)5 and
Cp*PCl2 are reacted in the ratio of 3:1 (Scheme 3).
ligands are present, and by converting a Cp*P moiety a PC2
three-membered ring is formed.
The presence of the anions 2− with one additional H atom
and 1− without a terminal H atom as the major products
indicates that a H atom transfer also occurred during the
reaction. The four-membered cycle in 1− containing an
additional CO unit evidently arises from an eliminated CO
group of a former Mn(CO)5 unit. In order to form a C−C(O)
bond, the CO ligand is presumably attacked by the negatively
charged C(2) atom (of the C5 cycle) that has been formed by a
rearrangement after hydrogen atom transfer (Scheme 3c).
Reactions including a carbanion attack of the C atom in metal
carbonyls are widely known. The opening of the Mn(1)−CO
bond and the formation of the P−C(O) bond that closes the
PC3 cycle as well as the formation of the Mn(1)−Mn(2) bond
and the loss of a Mn(2)−CO ligand can either be a concerted
process or a sequence of subsequent reactions (Scheme 3d).
The formation of the two different isomers 1a− and 1b− is
possible if the formation of the corresponding carbanion occurs
after abstraction of H+ from the neutral complex Cp*P{Mn-
(CO)5}2. The abstraction of H+ from a C(3)- or C(4)-bound
CH3 group forms the conjugated anion I, which is capable of
attacking the CO ligand at the Mn complex fragment (Scheme
3c); the abstraction of H+ from the CH3 groups bound at C(2)
or C(5) results in the formation of the isomer II. An
appropriate basic species to abstract the proton is the anionic
complex Cp*P{Mn(CO)n}2− (n = 4 or 5), which is formed by
the reduction of the initial nucleophilic substitution product by
It should be noted that if the reaction proceeds according to
Scheme 3 and anions 1− and 2− are the only products, their
amounts have to be equal. In fact, the concentration of the
isomers of 1− was shown to exceed that of 2− by a factor of 1.5
to 3.2 depending on the reaction setup (according to NMR
spectra). It can be explained by the competition of another base
that is also capable of abstracting a proton from the neutral
species Cp*P{Mn(CO)5}2. Since anionic products containing
additional protons are limited to 2−, some other neutral
protonated products must be present in the reaction mixture.
After washing the ionic products with hexane, noticeable
amounts of only one additional compound containing a
Cp*PH2 moiety were detected (besides Mn2(CO)10). This
compound could be characterized only by NMR spectroscopy.
It shows all the signals of a σ-bound Cp* substituent24 (1H
NMR in C6D6 [ppm]: 1.66 d, 6H, 4 Hz, CH3 at C2 and C5;
1.60 s, 6H, CH3 at C3 and C4; 0.95 d, 3H, 14 Hz, C(1)−CH3)
and a doublet at 4.36 ppm with a large coupling constant of 320
Hz in the 1H NMR spectrum. This corresponds to a PH2 group
since in the 31P NMR spectrum a triplet at 4.9 ppm revealing
the same coupling constant is detected. These signals cannot be
assigned to free Cp*PH2.24 This compound may arise from a
further protonation of the anion 2− and may represent a
Cp*PH2 phosphine coordinated to a Mn carbonyl complex.
The 1H NMR pattern and the coupling constants of this
compound are similar to those of (Cp*PH2)Cr(CO)5.38
An alternative pathway of the reaction can be proposed by a
transfer of a H radical from a neutral phosphinidene complex
initially formed by its reduced radical anion, followed by a
radical attack on the CO carbon atom to form the four-
membered cycle. This way is not very likely since the radical
attack on a coordinated CO group is an unusual process and
shown by calculations to be energetically less favorable.39
Another quite possible pathway would include fast conversion
of the initial phosphinidene complex into a radical anion, which
could either react with itself to provide a H radical transfer or
gain and release H atoms by separate pathways. To check this
possibility, we reacted Cp*PCl2 and KMn(CO)5 with CoCp2 as
an innocent 1e reduction agent (the redox potential of
CoCp2+/0, −0.85 V vs SCE,40 is close to that of
−
Mn(CO)5 (Scheme 3b). After abstraction of a proton, this
anion will turn into Cp*P(H){Mn(CO)n}2 (Scheme 3e), which
is further reduced to form anion 2−. Any participation of water
traces or the solvent as a H atom source can be excluded since
the solvents had been thoroughly dried prior to use and
experiments using THF-d8 as solvent did not reveal any
deuterated products. Another possible base, such as Mn-
−
(CO)5 , can be excluded since the formed HMn(CO)5 would
be rather unreactive under the used conditions. Only traces of
such a complex among the neutral reaction products could be
detected by 1H NMR spectroscopy at high field, but the
intensity of the appropriate signal is negligible. Moreover, the
basicity of P-centered anions must be higher than that of
Mn(CO)5 (pKa of the conjugated acid is 15.1 in THF35). In
−
41
−
0.5Mn2(CO)10/Mn(CO)5 , −0.69 V vs SCE ) in the molar
all reactions the ratio of 1a− to 1b− was found to be 2.5:1 (1H
NMR data). This may be explained by the higher stability of I
with respect to II owing to the better delocalization of the
negative charge over the conjugated diene system in I. In order
to prove the participation of a base in the abstraction of a
proton from the Cp* substituent and the formation of the
anions 1−, we performed the same reaction in the presence of
NaN(SiMe3)2, which is a strong base (the pKa of the
conjugated acid is 25.8 in THF36). Although it is a weak
nucleophile, it should not be competitive in substitution
reactions. The reagents were used in the ratio CpPCl2:KMn-
(CO)5:NaN(SiMe3)2 = 1:2:1 to exclude the possibility of the
reduction stage b (Scheme 3), and the anionic reaction mixture
was treated with PPh3AuCl. The NMR spectra of the reaction
products showed approximately the same ratio of the isomers
3a and 3b as in the initial reaction, but the concentration of 4
was lowered by a factor of 4. Hence, the presence of an
additional base actually facilitates the formation of the carbonic
products. A similar carbanion-mediated process is supposed by
1
ratio 1:2:1. The H NMR spectra of the reaction mixture did
not contain characteristic signals of complex 2−, and only traces
of 1− were detected. Instead, they contained signals of a σ-
bound Cp* group and a signal of the [CoCp2]+ cation, which
means the reduction actually took place. Possibly, faster
reduction results in a complete conversion of the transient
phosphinidene complexes to the radical anion (Scheme 3b),
which is incapable of further reaction with itself or acquiring a
H atom under the reaction conditions. The presence of radical
species is indirectly supported by a noticeable shift of all
resonances to higher field, the biggest found for [CoCp2]+ as a
consequence of the interaction. In summary the proposed
pathway of proton transfer reactions (Scheme 3) seems to be
the most realistic one, although the proceeding of other
pathways cannot be completely ruled out.
CONCLUSIONS
■
The reaction of K[Mn(CO)5] with Cp*PCl2 has been shown
to be a rare example of an intra- and intermolecular
rearrangement reaction involving the reduction of an initially
the reaction of N(SiMe3)2 with Cp*2PCl.37 Here no CO
−
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Organometallics
Article
3JPH = 15 Hz). 13C{1H} NMR: 239, 227 (both br s, Mn−CO), 237.8
(d, COb, 1JPC = 7 Hz), 236.1 (d, COa, 1JPC = 11 Hz), 162.9 (d, JPC
= 1 Hz), 140.5 (s), 135.7 (d, JPC = 2 Hz; the last three signals
correspond to the atoms C(2)a, C(3)a, and C(4)a), 156.9 (s), 150.6
(d, JPC = 2 Hz), 132.9 (d, JPC = 8 Hz; the last three signals correspond
formed phosphinidene species, H atom transfer, and the
formation of a new bicyclic ligand by activating the Cp* moiety
along with an incorporation of a CO ligand. On the basis of a
used excess of the reducing anion [Mn(CO)5]− several
reactivity centers are necessary for such a complex reaction
process such as the presence of a labile CO ligand and a Cp*
group that is acidic enough to be diprotonated by a P-centered
anion. This combination of reaction centers is unique for the
formation of phosphinidene complexes, which usually occurs
directly in one step to form conventional complexes of type A−
D. Moreover, to the best of our knowledge, the observed
reduction of planar phosphinidene complexes of the type
RP(MLn)2 has not yet been reported. We believe that the
reductive activation of phosphinidene complexes might present
a useful way for the synthesis of novel P-heterocyclic ligands
and metal complexes.
a
to the atoms C(2)b, C(4)b, and C(5)b), 102.8 (d, CH2 , 3JPC = 9 Hz),
b
5
1
99.1 (d, CH2 , JPC = 6 Hz), 87.6 (d, C(1)a, JPC = 33 Hz), 82.4 (d,
C(1)b, JPC = 33 Hz), 56.6 (d, C(3)b, JPC = 20 Hz), 49.0 (d, C(5)a,
1
2
a
2
2JPC = 19 Hz), 20.9 (d, C(1)−CH3 , JPC = 7 Hz), 19.0 (d, C(1)−
b
CH3 , 2JPC = 9 Hz), 17.5 (d, J = 1 Hz), 12.3 (d, J = 2 Hz), 10.4 (d, J =
b
2 Hz; the last three signals correspond to the atoms C(2)−CH3 ,
b
b
C(4)−CH3 , and C(5)−CH3 ), 14.0 (d, J = 4 Hz), 11.3 (s), 10.5 (s;
a
the last three signals correspond to the atoms C(2)−CH3 , C(3)−
a
a
CH3 , and C(4)−CH3 ). The CH2 groups are confirmed by a DEPT
135 experiment. 31P NMR: 260a (s, br), 243b (s, br). IR (νCO): 1711
(m), 1899 (s), 1922 (m), 1939 (s), 1946 (w,sh), 1968 (w,sh), 1978
(s), 2039 (s) cm−1.
Anion 2− (based on the subtraction of the signals of 1a− and 1b−
1
from the spectrum of the mixture of compounds): H NMR: 3.49 (d,
EXPERIMENTAL SECTION
1
1H, PH, JPH = 317 Hz), 2.00 (s, 6H, C(2)−CH3 and C(5)−CH3),
■
5
All manipulations were performed under argon or nitrogen by using
Schlenk techniques or gloveboxes. The starting reagents were prepared
according to the known methods: K[Mn(CO)5]42 and Cp*PCl2.24 All
solvents were distilled in an inert atmosphere by using common drying
agents. TLC plates (Merck silica gel 60) were dried in an oven and
transferred into the glovebox.
1.75 (d, 6H, C(3)−CH3 and C(4)−CH3, JPH = 2 Hz), 0.97 (d, 3H,
C(1)−CH3, 3JPH = 18 Hz). 13C{1H} NMR: 143.4 (d, C(3) and C(4),
3JPC = 3 Hz), 133.6 (d, C(2) and C(5), JPC = 5 Hz), 60.1 (s, C(1)),
2
2
17.6 (d, C(1)−CH3, JPC = 7 Hz), 11.8 (d, C(2)−CH3 and C(5)−
CH3, JP1C = 3 Hz), 11.3 (s, C(3)−CH3 and C(4)−CH3). 31P NMR:
3
149 (d, JPH = 320 Hz).
The NMR spectra were recorded on a Bruker Avance 400
spectrometer (1H: 400.132 MHz, 13C{1H}: 100.632 MHz, 31P:
162.016 MHz) in THF-d8 or CD2Cl2. Chemical shifts (δ, ppm)
were referenced to 85% H3PO4 (31P) or to the signals of the solvent
(1H and 13C, δH = 3.58 ppm (THF-d8), 5.31 ppm (CD2Cl2); δC = 25.2
ppm (THF-d8), 54.0 ppm (CD2Cl2)). Mass spectra of ionic
compounds were measured on a Finnigan ThermoQuest TSQ 7000
spectrometer (ESI, solutions in DME, negative region, tube lens 20 V).
IR spectra were recorded in THF solutions. Elemental analysis was
carried out on a Eurovector EuroEA3000 CHN analyzer.
Reaction of Cp*PCl2 with KMn(CO)5. Synthesis of [K(OEt2)2]-
[1]. A solution of Cp*PCl2 (0.200 g, 0.844 mmol) in 5 mL of THF
was added under stirring to a suspension of KMn(CO)5 (0.600 g, 2.56
mmol) in 10 mL of THF at −60 °C. The initially slightly green
solution was stirred at this temperature for one hour. During this time,
the color turned to yellow. The stirring was continued overnight at
room temperature. The resulting orange, turbid solution was filtered to
remove the precipitated (KCl), and the filtrate was evaporated to
dryness. The remaining solid was washed with hexane until the
washings were no longer colored by Mn2(CO)10 (3 × 30 mL) and
then dried in a vacuum. The solid mixture of ionic compounds was
used for the NMR (as a solution in THF-d8) and MS studies as well as
for the subsequent reactions. Yields (based on the composition,
determined by NMR): 1−, 46%; 2−, 31%. The pure crystalline product
[K(OEt2)2][1] (mixture of isomers) was obtained by the extraction of
the product mixture with ether followed by crystallization at −30 °C.
The crystalline product [K(18-crown-6)(Et2O)][1] was obtained in a
mixture with salts of 2− after the addition of an approximately
equimolar amount (with respect to the starting phosphine) of dry 18-
crown-6 ether to the ether extract followed by cooling at 4 °C
overnight. Single crystals suitable for X-ray diffraction were taken from
the group of formed crystals. ESI-MS of the solid mixture of products:
527.0 (1−), 501.1 (2−).
Syntheses of 3, 4, and 5. At −78 °C, a solution of PPh3AuCl
(0.40 g, 0.81 mmol) in 10 mL of THF was added dropwise to a
solution of the mixture of the anionic salts from the above-described
reaction (0.40 g, ca. 0.71 mmol 1− + 2−) in 10 mL of THF. After half
an hour the mixture was allowed to warm to room temperature,
filtered, and evaporated to a volume of ca. 2 mL. According to NMR
spectroscopy, the reaction proceeds nearly quantitatively. Half of the
mixture was separated by column chromatography (silica gel, hexane−
toluene mixtures), and compound 4 (first band, bright yellow) and a
mixture of 3a and 3b (second band, orange) were obtained. The other
half of the product mixture was separated by TLC (silica plates,
hexane), and compounds 4 (first band), 5 (second weak band, yellow-
orange), and 3a (third band) were isolated. Two weak bands, which
came in front of the second and after the third ones, contained very
small amounts of products, which could not be characterized. The
plates were cut and extracted with THF. The solutions were dried
under vacuum, and all the compounds were recrystallized separately
from hexane. Isolated yields (based on the amount of starting
material): 90 mg (27%) for 4 and 62 mg (18%) for 3a. Compound 5
was characterized only by NMR due to the small amounts formed.
Compound 3a: 1H NMR (CD2Cl2): 7.62−7.42 (m, 15H, Ph), 5.15
2
2
(d, 1H, CH2, JHH = 7 Hz), 4.69 (d, 1H, CH2, JHH = 6 Hz), 1.88 (s,
3H), 1.84 (s, 3H), 1.43 (s, 3H, the last three signals correspond to the
C(2)−CH3, C(3)−CH3, and C(4)−CH3 groups), 1.62 (d, 3H, C(1)−
3
1
CH3, JPH = 16 Hz). 13C{1H} NMR: 225.3 (d, CO, JPC = 10 Hz),
162.3 (d, JPC = 2 Hz), 139.5 (s), 137.0 (d, JPC = 2 Hz; the last three
signals correspond to the atoms C(2), C(3), and C(4)), 134.6 (d, 6C,
o-Ph, 2JPC = 14 Hz), 132.4 (d, i-Ph, 1JPC = 45 Hz), 131.7 (d, 3C, p-Ph,
4JPC = 2 Hz), 129.7 (d, 6C, m-Ph, JPC = 11 Hz), 104.6 (d, 1C, CH2,
3
3JPC = 9 Hz), 90.3 (d, C(1), JPC = 37 Hz), 51.1 (d, C(5), JPC = 21
Hz), 20.6 (d, 1C, C(1)−CH3, 2JPC = 5 Hz), 13.5 (d, 1C, 3JPC = 5 Hz),
11.8 and 10.8 (both s, 1C, the last three signals correspond to the
atoms C(2)−CH3, C(3)−CH3, and C(4)−CH3). The CH2 group is
confirmed by a DEPT 135 experiment. 31P NMR: 290 (s, 1P, PMn2),
65 (s, 1P, PPh3). IR (νCO): 1701 (m), 1912 (s), 1942 (s), 1960 (m),
2007 (s), 2050 (s) cm−1.
1
2
Compounds [K(OEt2)2][1] and [K(18-crown-6)(Et2O)][1] (atom
numbering is consistent with that shown for crystal structures)
(mixture of the isomers a and b, only signals of the anionic part are
given, THF-d8): 1H NMR: 4.98 (d, 4JPH = 6 Hz), 4.66 (d, 4JPH = 6 Hz;
the last two signals correspond to the CH2a group), 4.72 (dd, 5JPH = 2
Hz, 2JHH = 0.6 Hz), 4.58 (dd, 5JPH = 3 Hz, 2JHH = 0.6 Hz; the last two
Compound 3b (based on the subtraction of the signals of 3a from
the spectra of the mixture of isomers): 1H NMR (CD2Cl2): 7.62−7.42
(m, 15H, Ph), 5.00 (br s, 1H, CH2), 4.89 (br s, 1H, CH2), 1.82 (br s,
3H), 1.58 (s, 3H; the last two signals correspond to two of the three
Me groups C(2)−CH3, C(4)−CH3, and C(5)−CH3), 1.70 (d, 3H,
C(1)−CH3, 3JPH = 17 Hz). 13C{1H} NMR: 155.5 (s), 147.7 (s), 135.6
(d, JPC = 8 Hz; the last three signals correspond to the atoms C(2),
b
signals correspond to the CH2 group), 1.87 (m), 1.73 (m), 1.42 (s;
b
b
the last three signals correspond to the C(2)−CH3 , C(4)−CH3 , and
C(5)−CH3b groups), 1.80 (m), 1.75 (m), 1.19 (s; the last three signals
a
a
a
correspond to the C(2)−CH3 , C(3)−CH3 , and C(4)−CH3
b
a
3
groups), 1.48 (d, C(1)−CH3 , JPH = 15 Hz), 1.44 (d, C(1)−CH3 ,
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Organometallics
Article
2
C(4), and C(5)), 134.8 (d, 6C, o-Ph, JPC = 14 Hz), 132.2 (d, i-Ph,
model. In [K(18-crown-6)(Et2O)][1] the P-CO-C5Me4CH2 fragment
is disordered over two positions with equal weights and significant
overlap. Therefore H atom positions in this fragment were not
localized. The other H atoms were placed in the geometrical positions.
Full details of X-ray structural determinations can be found in the
Supporting Information and in CIF files that were deposited in the
Cambridge Crystallographic Data Centre under the deposition codes.
1JPC = 45 Hz), 132.0 (br s, 3C, p-Ph), 129.8 (d, 6C, m-Ph, JPC = 12
Hz), 102.4 (d, 1C, CH2, JPC = 6 Hz), 84.5 (d, C(1), JPC = 38 Hz),
59.4 (d, C(3), JPC = 21 Hz), 18.5 (d, 1C, C(1)−CH3, JPC = 6 Hz),
16.9, 13.0, 10.7 (all s, 1C, the last three signals correspond to the
atoms C(2)−CH3, C(4)−CH3, and C(5)−CH3). The CH2 group is
confirmed by a DEPT 135 experiment. 31P NMR: 277 (s, 1P, PMn2),
65 (s, 1P, PPh3).
3
4
1
3
2
1
Compound 4: H NMR (CD2Cl2): 7.59−7.40 (m, 15H, Ph), 5.20
ASSOCIATED CONTENT
* Supporting Information
■
(d, 1H, PH, 1JPH = 308 Hz), 1.94 (s, 6H, C(2)−CH3 and C(5)−CH3),
S
5
1.75 (d, 6H, C(3)−CH3 and C(4)−CH3, JPH = 4 Hz), 1,68 (d, 3H,
Details giving experimental and crystal data for [K(18-crown-
6)(Et2O)][1], [K(OEt2)2][1], 3a, and 4 and figures giving the
NMR spectra of all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org. CCDC
Nos. 901837 ([K(OEt2)2][1]), 919318 ([K(18-crown-6)-
(Et2O)][1]), 901838 (3a), and 901839 (4) contain supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
C(1)−CH3, 3JPH = 17 Hz). 13C{1H} NMR: 139.8 (s, C(3) and C(4)),
2
2
138.7 (d, C(2) and C(5), JPC = 6 Hz), 134.7 (d, 6C, o-Ph, JPC = 15
1
4
Hz), 132.6 (d, i-Ph, JPC = 45 Hz), 131.6 (d, 3C, p-Ph, JPC = 2 Hz),
3
1
129.6 (d, 6C, m-Ph, JPC = 11 Hz), 60.1 (d, C(1), JPC = 6 Hz), 21.9
(d, 1C, C(1)−CH3, 2JPC = 3 Hz), 12.0 (d, 2C, C(2)−CH3 and C(5)−
4
5
CH3, JPC = 2 Hz), 11.6 (d, 2C, C(3)−CH3 and C(4)−CH3, JPC = 2
Hz). 31P NMR: 181 (d, 1P, PH, JPH = 310 Hz), 63 (s, 1P, PPh3).
1
Anal. Calcd for C36H31AuMn2O8P2: C, 45.02; H, 3.25. Found: C,
44.62; H, 3.40. IR (νCO): 1932 (s), 1954 (s), 1980 (s), 2018 (s), 2061
(m) cm−1.
1
Compound 5: H NMR: 7.60−7.42 (m, 15H, Ph), 3.81 (dd, 1H,
AUTHOR INFORMATION
Corresponding Author
2
2
2
■
CH2, JHH = 14 Hz, JPH = 7 Hz), 3.16 (dd, 1H, CH2, JHH = 14 Hz,
2JPH = 3 Hz), 1.94 (br s, 3H), 1.91 (m, 3H), 1.80 (br s, 3H), 1.55 (s,
3H, all four signals correspond to CH3 groups). 13C{1H} NMR: 134.6
*Tel: +49 941 943 4441. Fax: 49 941 943 4439. E-mail:
manfred.scheer@ur.de. Tel: + 7-383-3165831. Fax: + 7-383-2-
344489. E-mail: nikolay@niic.nsc.ru.
2
1
(d, 6C, o-Ph, JPC = 15 Hz), 132.4 (d, i-Ph, JPC = 45 Hz), 131.7 (d,
3C, p-Ph, 4JPC = 2 Hz), 129.6 (d, 6C, m-Ph, 3JPC = 11 Hz), 28.0 (d, 1C,
CH2, 1JPC = 13 Hz), 18.7 (s, 1C), 12.0 (s, 1C), 11.2 (br s, 2C, the last
three signals correspond to all the CH3 groups). The CH2 group is
confirmed by a DEPT 135 experiment. 31P NMR: 233 (s, 1P, PMn2),
65 (s, 1P, PPh3).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Light Irradiation of the Mixture of the Isomers 3a and 3b.
The mixture of the isomers 3a and 3b (obtained after chromatographic
separation) was dissolved in C6D61and sealed in a NMR tube, which
was exposed to diffused sunlight. H NMR spectra were periodically
monitored. The isomer 3b fully disappeared after two days, while the
concentration of the predominant isomer 3a decreased by a factor of
2.5 (the residual proton signals of C6D6 were used as reference).
Simultaneously with the decomposition of 3a and 3b, the formation of
tetramethylfulvene was noticed, which was identified on the basis of
This work was supported by the Deutsche Forschungsgemein-
schaft, the German Academic Exchange Service (N.A.P.), and
the Russian Foundation for Basic Research (grant no. 10-03-
00385 and the state contract no. 02.740.11.0628).
REFERENCES
■
(1) Recent reviews on carbene chemistry: (a) Herndon, J. W. Coord.
Chem. Rev. 2011, 255, 3. (b) Arduengo, A. J.; Bertrand, G. Chem. Rev.
24
the known H and 13C spectra. The remaining 3a had decomposed
almost completely after further three days, but no other signals in the
region of CH3 and CH2 groups were monitored in the mixture. The
31P NMR spectra showed an increasing number of resonances of low
intensity during the decomposition (without a predominant one),
which could not be assigned to any known compound.
1
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X-ray Structure Determination of the Compounds [K(18-
crown-6)(Et2O)][1], 3a, and 4. Crystals of [K(18-crown-6)(Et2O)]-
[1] were obtained from a cooled ether solution (−28 °C), while 3a
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