Synthesis of η1-α-phosphinocarbene complexes of manganese and mechanistic insight into their base-induced transformations

Article abstract of DOI:10.1021/om2000772

A series of η¹-α-phosphinocarbene complexes of manganese, Cp(CO)₂Mn=C(R)PR′R′′ (3; 3a: R = Ph, R′ = H, R′′ = Mes; 3b: R = Me, R′ = H, R′′ = Mes; 3c: R = Ph, R′ = R′′ = Ph; 3d: R = Ph, R′ = R′′ = N(i-Pr)₂; 3e: R = Ph, R′ = Me, R′′ = Mes), was generated at low temperature upon nucleophilic addition of the primary phosphine H₂PMes and secondary phosphines HPPh₂, HP(N(i-Pr)₂)₂, or (±)-HPMeMes to the cationic carbyne complexes Cp(CO)₂Mn⁺=C-R ([1] ⁺; [1a]⁺: R = Ph; [1b]⁺: R = Me), followed by deprotonation of the resulting α-phosphoniocarbene intermediates Cp(CO)₂Mn=C(R)P⁺(H)R′R′′ ([2a-e] ⁺). The η¹-α-phosphinocarbene complexes 3c-e derived from secondary phosphines were found to be highly thermolabile, giving upon intramolecular CO insertion the η³-phosphinoketene complexes Cp(CO)Mn(η³-C(O)C(Ph)PR′R′′) (4c: R′ = R′′ = Ph, 4d: i-Pr₂N; RR/SS-4e: R′ = Me, R′′ = Mes) in 80-95% yield. The η¹-α- phosphinocarbene complexes 3a,b, bearing a mesityl substituent, were isolated in 57-65% yield. The availability of the phosphorus lone pair in such compounds was assessed by their reaction with borane, giving the corresponding adducts Cp(CO)₂Mn=C(R)P(BH₃)HMes (5a, R = Ph; 5b, R = Me). Complexes 3a,b slowly rearrange in a nonpolar solvent (benzene) to afford a mixture of the η³-phosphinoketene complexes Cp(CO) Mn(η³-C(O)C(R)PHMes) (4a, R = Ph; 4b, R = Me) and the η¹-phosphaalkene complexes Cp(CO)₂Mn(η ¹-P(Mes)=C(H)R (6a, R = Ph; 6b, R = Me), and ultimately pure 6a,b as a mixture of E/Z stereoisomers (6a, E/Z 60:40; 6b, E/Z 55:45). By contrast, a stereoselective rearrangement of 3a,b into E-6a,b was observed in a polar solvent (THF), the process being considerably accelerated in the presence of catalytic amounts of base. Deprotonation of 3a by n-BuLi at -80 °C affords the dicarbonyl phosphidocarbene anion [Cp(CO)₂Mn=C(Ph)PMes]Li ([7a]Li), which undergoes an instantaneous CO insertion process upon addition of traces of weak acids (H₂O, t-BuOH) to give the cyclic monocarbonylacyl anion [Cp(CO)₂Mn(η²-C(O)C(Ph)=PMes]Li ([8a]Li, R = Ph). Besides, deprotonation of 3a,b by t-BuOLi affords directly the cyclic monocarbonylacyl anions [8a,b]Li. The protonation of [8a]Li with various proton sources (HBF₄?Et₂O, NH ₄Cl_aq, [Et₃NH]Cl) leads to a stereoselective formation of E-6a, illustrating the key role of this anion in the stereoselective 3a → E-6a rearrangement. Alkylation of [8a]Li by MeI resulted in formation of η³-phosphinoketene complex RR/SS-4e as a single pair of diastereomers, whereas its treatment with iodine resulted in thermally unstable η³-phosphinoketene complex Cp(CO)Mn(η³-C(O)C(Ph)PIMes) (11), evolving at room temperature into the η¹-phosphaalkene product Cp(CO)₂Mn(η ¹-P(Mes)=C(I)Ph) (12) of Z conformation. The solid-state structures of 3b, 4c, 4d, RR/SS-4e, and Z-12 are reported.

Full text of DOI:10.1021/om2000772

ARTICLE
pubs.acs.org/Organometallics
Synthesis of η1-r-Phosphinocarbene Complexes of Manganese and
Mechanistic Insight into Their Base-Induced Transformations
Dmitry A. Valyaev,†,‡ No€el Lugan,*,† Guy Lavigne,† and Nikolai A. Ustynyuk‡
†Laboratoire de Chimie de Coordination du CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex 4, France
‡A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov Str., GSP-1, B-334, 119991
Moscow, Russia
S Supporting Information
b
ABSTRACT: A series of η1-R-phosphinocarbene complexes of manga-
nese, Cp(CO)2MndC(R)PR0R00 (3; 3a: R = Ph, R0 = H, R00 = Mes; 3b:
R = Me, R0 = H, R00 = Mes; 3c: R = Ph, R0 = R00 = Ph; 3d: R = Ph, R0 = R00
= N(i-Pr)2; 3e: R = Ph, R0 = Me, R00 = Mes), was generated at low
temperature upon nucleophilic addition of the primary phosphine
H2PMes and secondary phosphines HPPh2, HP(N(i-Pr)2)2, or (()-
HPMeMes to the cationic carbyne complexes Cp(CO)2MnþtCꢀR
([1]þ; [1a]þ: R = Ph; [1b]þ: R = Me), followed by deprotonation of the
resulting R-phosphoniocarbene intermediates Cp(CO)2MndC(R)Pþ-
(H)R0R00 ([2aꢀe]þ). The η1-R-phosphinocarbene complexes 3cꢀe
derived from secondary phosphines were found to be highly thermolabile,
giving upon intramolecular CO insertion the η3-phosphinoketene com-
plexes Cp(CO)Mn(η3-C(O)C(Ph)PR0R00) (4c: R0 = R00 = Ph, 4d: i-
Pr2N; RR/SS-4e: R0 = Me, R00 = Mes) in 80ꢀ95% yield. The η1-R-
phosphinocarbene complexes 3a,b, bearing a mesityl substituent, were
isolated in 57ꢀ65% yield. The availability of the phosphorus lone pair in
such compounds was assessed by their reaction with borane, giving the
corresponding adducts Cp(CO)2MndC(R)P(BH3)HMes (5a, R = Ph; 5b, R = Me). Complexes 3a,b slowly rearrange in a nonpolar
solvent (benzene) to afford a mixture of the η3-phosphinoketene complexes Cp(CO)Mn(η3-C(O)C(R)PHMes) (4a, R = Ph; 4b, R =
Me) and the η1-phosphaalkene complexes Cp(CO)2Mn(η1-P(Mes)dC(H)R (6a, R = Ph; 6b, R = Me), and ultimately pure 6a,b as a
mixture of E/Z stereoisomers (6a, E/Z 60:40; 6b, E/Z 55:45). By contrast, a stereoselective rearrangement of 3a,b into E-6a,b was
observed in a polar solvent (THF), the process being considerably accelerated in the presence of catalytic amounts of base. Deprotonation
of 3a by n-BuLi at ꢀ80 ꢀC affords the dicarbonyl phosphidocarbene anion [Cp(CO)2MndC(Ph)PMes]Li ([7a]Li), which undergoes an
instantaneous CO insertion process upon addition of traces of weak acids (H2O, t-BuOH) to give the cyclic monocarbonylacyl anion
[Cp(CO)2Mn(η2-C(O)C(Ph)dPMes]Li ([8a]Li, R = Ph). Besides, deprotonation of 3a,b by t-BuOLi affords directly the cyclic
monocarbonylacyl anions [8a,b]Li. The protonation of [8a]Li with various proton sources (HBF4 Et2O, NH4Claq, [Et3NH]Cl) leads to
3
a stereoselective formation of E-6a, illustrating the key role of this anion in the stereoselective 3a f E-6a rearrangement. Alkylation of
[8a]Li by MeI resulted in formation of η3-phosphinoketene complex RR/SS-4e as a single pair of diastereomers, whereas its treatment
with iodine resulted in thermally unstable η3-phosphinoketene complex Cp(CO)Mn(η3-C(O)C(Ph)PIMes) (11), evolving at room
temperature into the η1-phosphaalkene product Cp(CO)2Mn(η1-P(Mes)dC(I)Ph) (12) of Z conformation. The solid-state structures
of 3b, 4c, 4d, RR/SS-4e, and Z-12 are reported.
’ INTRODUCTION
LnMdC(R)PR02, have remained extremely scarce and their
reactivity has been virtually unexplored.5ꢀ7
Historically, Fischer and Reitmeiter were the first to isolate an
η1-R-phosphinocarbene complex of tungsten, (CO)4(L)WdC-
(NEt2)P(Me)Ph (L = CO, HP(Me)Ph), albeit in very low yield
(3ꢀ4%), upon nucleophilic attack of a phosphide, [PMePh]K,
Since the seminal finding by Fischer and Maasb€ol some 40
years ago,1 thousands of heteroatom-stabilized carbene com-
plexes LnMdC(R)X (X = OR0, NR02, SR0, SnR03) have been
synthesized in view of their anticipated application scope in
organic synthesis.2 Although the case of transition-metal R-P-
substituted carbene complexes has been examined on several
occasions,3,4 the true phosphorus-containing homologues of
Fischer carbenes, η1-R-phosphinocarbenes of the type
Received: January 27, 2011
Published: March 22, 2011
r
2011 American Chemical Society
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|

Organometallics
ARTICLE
Scheme 1
onto the electrophilic carbyne atom of the cationic carbyne
complex [(CO)5WtCꢀNEt2]þ.5 The main reaction product
in that case was a dimeric phosphorus-free species resulting from
a reductive coupling of two carbyne units of the starting
precursor.5 Adopting a conceptually similar synthetic route, Yu
et al.6 recently reported that the cationic isonitrile complex
[Cp(CO)FeꢀCtN(CH2)3PPh2]BF4 undergoes nucleophilic
attack by [PPh2]K to give, after protonation, the iron η1-R-
phosphinocarbene complex [Cp(CO)FedC(PPh2)NH(CH2)3-
PPh2]BF4. This complex, however, was seen to undergo sponta-
neous elimination of diphenylphosphine to restore the initial
isonitrile complex.6 Besides, Bertrand and co-workers proposed a
totally different approach consisting in the elaboration of a stable
R-phosphinocarbene ligand to be subsequently reacted with a
transition-metal precursor. The method was applied to (i-
Pr2N)2P(Ar)C: and illustrated by the synthesis of the Rh(I)
or highly reactive10dꢀf R-phosphoniocarbene complexes of the
type [LnMdC(R)PR3]þ is well documented. Likewise, we have
observed that the primary phosphine H2PMes as well as second-
ary phosphines HPPh2, HP(N(i-Pr)2)2, or (()-HPMeMes read-
ily reacts with the cationic manganese carbyne complexes
[Cp(CO)2MntCR]BX4 ([1]BX4; [1a]BX4: R = Ph, X = Cl or
Ph; [1b]BCl4: R = Me)11 under very mild conditions (CH2Cl2,
ꢀ40 to ꢀ80 ꢀC) to give the corresponding thermolabile R-
phosphoniocarbene
adducts,
[Cp(CO)2MndC(Ph)-
P(H)R0R00]BX4 ([2]BX4; Scheme 1). Complexes [2]BCl4 each
display two bands in the νCO region; for a typical example
[2a]BCl4: IR (CH2Cl2) 2020, 1960 cmꢀ1 (νCO)), at a position
very similar to that of their closely related analogue [Cp(CO)2-
MndC(Ph)PMe3]BCl4.10b Although compounds [2]BCl4 were
found to be stable for several hours below ꢀ40 ꢀC, they generally
decompose at room temperature, which prevents their isolation
in analytically pure form. Yet, complex [2e]BPh4, generated
upon reaction of [1a]BPh4 with HP(N(i-Pr)2)2, could be
isolated in 92% yield and fully characterized by NMR, high-
complexes
L2ClRhdC(2,6-C6H3(CF3)2)P(N(i-Pr)2)2
(L2 = (CO)2, η4-cod, η4-nbd).7a,b Such a synthetic method,
which could be later extended to the case of a cyclic R,R0-bis-
phosphinocarbene,7c,d rests on the availability of stable R-phos-
phinocarbenes, which remains highly challenging.8 Clearly, the
search for a simple and general route to transition-metal η1-R-
phosphinocarbene complexes is still of current interest.
lighting its carbene character (13C{1H} NMR δ 325.2 (d, 1JPC
24.5 Hz, MndC)).
=
Deprotonation of the transient R-phosphoniocarbene [2a,
b]BCl4 at low temperature cleanly afforded the corresponding
η1-R-phosphinocarbene complexes Cp(CO)2MndC(Ph)PH-
Mes (3a,b, Scheme 1) in reasonable yields. Optimal results were
obtained using either neutral alumina, for [2a]BCl4, or NEt3, for
[2b]BCl4, as bases. Noticeably, the deprotonation of [2a]BPh4
generated upon reaction of [1a]BPh4 with H2PMes at low
temperature was found to occur spontaneously when the solu-
tion was allowed to warm up to room temperature, leading to 3a
as the sole product.
Addition of NEt3, or 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU), to cold CH2Cl2 solutions of R-phosphoniocarbene
complexes [2c,d]BCl4 did produce a color change, but the
expected η1-R-phosphinocarbene derivatives could never be
isolated. These complexes were found to be barely stable
enough to be identified by IR spectroscopy, and only during
the course of the deprotonation of 2e could an IR spectrum
attributable to 3e be recorded (IR (CH2Cl2): 1957, 1898
(νCO)). Actually, workup led instead to the new η3-phosphi-
noketene complexes Cp(CO)Mn(η3-C(O)C(Ph)PR0R00)
(4cꢀe, Scheme 1), which were fully characterized, including
by X-ray diffraction (see below and the Supporting In-
formation). These complexes may be regarded as deriving from
the expected η1-R-phosphinocarbene complexes 3cꢀe upon
coordination of the phosphorus atom to manganese and con-
comitant CO insertion into the manganeseꢀcarbene bond.12
They could be subsequently obtained in almost quantitative
yield upon treatment of [1a]BPh4 with the appropriate
For our part, inspired by Fischer’s seminal work and engaged
for some time in a general program aimed at exploiting the
availability, ease of use, and high reactivity of cationic manganese
carbyne complexes derived from cymantrene,9 we envisioned
that the deprotonation R-phosphoniocarbene complexes10 result-
ing from nucleophilic attack of secondary and/or primary
phosphine on such carbyne species would possibly afford η1-R-
phosphinocarbene complexes. In a preliminary communication
of the present work,11 such an approach was found to be viable,
offering multiple advantages, such as (i) the simplicity of the
procedure, (ii) the absence of constraints about the steric bulk of
phosphorus substituents, and (ii) the simplicity and diversity of
the phosphorus sources, often being commercially available. The
present report gives a detailed description of the synthesis of
these η1-phosphinocarbene complexes of manganese and pro-
vides an account of their intrinsic reactivity.
’ RESULT AND DISCUSSION
Synthesis and Characterization of the η1-r-Phosphino-
carbene Complexes Cp(CO)2MndC(R)PHMes (3; 3a: R = Ph,
R00 = Mes; 3b: R = Me, R00 = Mes) and of the η3-Phosphino-
ketene Complexes Cp(CO)Mn(η3-C(O)C(Ph)PR0R00) (4; 4c: R0 =
R00 = Ph; 4d: R0 = R00 = i-Pr2N; 4e: R0 = Me, R00 = Ph). Synthesis.
The interaction of tertiary phosphines with electrophilic transi-
tion-metal carbyne complexes [LnMtCR]þ to afford stable10aꢀc
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ARTICLE
Scheme 2
Figure 1. ORTEP drawing of 3b (ellipsoids set at the 50% probability
level). Selected bond lengths [Å] and angles [deg]: Mn1ꢀC3 = 1.859(2),
C3ꢀP1 = 1.811(2), C3ꢀC4 = 1.522(4); P1ꢀC21 = 1.837(2); P1ꢀH1 =
1.33(3); Mn1ꢀC3ꢀC4 = 124.96(17); Mn1ꢀC3ꢀP1 = 124.83(13);
C4ꢀC3ꢀP1 = 109.84(16); C3ꢀP1ꢀC21 = 107.98(11); C3ꢀP1ꢀH1
= 101.0(12); C3ꢀP1ꢀH1 = 94.3(11).
is only partially delocalized over the PꢀCcarbeneꢀMn bonds. Yet,
the corresponding bond length (P1ꢀC3 = 1.811(2) Å) appears
to be significantly shorter than the other one (P1ꢀC21 =
1.837(2) Å), indicating that a certain degree of delocalization
of the phosphorus lone pair occurs in the direction of the carbene
carbon atom. Such a difference in the environment of the
heteroatom in amino- and η1-R-phosphinocarbene complexes
was previously predicted on the basis of a DFT analysis of model
tungsten carbene complexes of the type (CO)5WdC(R)XR0
(X = N, P),18 but we are observing here for the first time an
effective pyramidalization around P. Indeed, in the only ante-
cedent of structurally characterized η1-R-phosphinocarbene
complex, namely, (η4-nbd)ClRhdC(Ar)P(Ni-Pr2)2 (Ar =
C6H3(CF3)2-2,6),7a the phosphorus atom was found to exhibit
a trigonal-planar arrangement (∑PR = 358.3ꢀ) indicative of a
significant contribution of the betaine σ-phosphavinyl form (η4-
nbd)ClRhꢀꢀC(Ar)dPþ(Ni-Pr2)2 in that case,19 certainly fa-
vored by the presence of the two amino substituents on
phosphorus.
secondary phosphine, followed by addition of DBU at low
temperature, and final warming to room temperature.
Analogous η3-phosphinoketene complexes Cp(CO)Mn-
(η3-C(O)C(R)PHMes) (4a,b) were obtained from 3a,b upon
standing, along with the η1-phosphaalkene derivatives Cp-
(CO)2Mn(η1-P(Mes)dC(H)Ph) (6a,b). A specific paragraph
will be devoted to the overall isomerization process (vide
infra).
Spectroscopic and Structural Characterization of the η1-R-
Phosphinocarbene Complexes 3a,b. Complexes 3a,b display
characteristic low-field 13C{1H} NMR resonances at δ 358.2 and
366.5 ppm, respectively, with strong 1JCP direct coupling constants
of 76 and 81 Hz, respectively, attributable to the carbene carbon
atoms. 31P{1H} NMR spectra show singlets at δ 18.9 and 10.2 ppm,
respectively. The IR spectra of 3a,b in CH2Cl2 solution (3a: 1957,
1898 cmꢀ1; 3b: 1970, 1906 cmꢀ1) display νCO stretching bands at
frequencies much higher than those of homologous aminocarbene
complexes such as Cp(CO)2MndC(Me)NHMe,13a for instance
νCO 1947, 1875 cmꢀ1, in a domain one would actually expect for
non-heteroatom-substituted carbene complexes such as Cp-
(CO)2MndCPh213b (νCO: 1968, 1910 cmꢀ1). These data indicate
that the present phosphinocarbene ligands are much less of electron
donors than aminocarbene ligands and already suggest that the lone
pair on phosphorus participates only very weakly in the carbene-to-
metal bonding, contrary to the lone pair of the nitrogen atom in the
parent aminocarbene complexes. The solid-state structure of 3b
corroborates such an analysis.
Finally, it is worth mentioning that examination of the NMR
data in the temperature range 173ꢀ298 K reveals that complexes
3a,b experience dynamic processes in solution. For complex 3b,
the observed motion translates into an exchange of o-Me groups
of the mesityl substituent; examination of the coalescence
behavior of the corresponding signals led to a ΔGq value of
11.1 kcal mol .
ꢀ1 20 Such an exchange could be rationalized either
in terms of a fast rotation [NMR time-scale] of the mesityl group
around the PꢀCipso bond or in terms of an inversion of
configuration at the phosphorus atom. However, we favor the
first exchange pathway (Scheme 2a), considering that the value
of the activation barrier of the present process, 11.1 kcal molꢀ1
,
A perspective view of complex 3b is shown in Figure 1. The
carbene ligand displays the typical vertical coordination mode,14
in which the carbene plane lies in the mirror plane of the
Cp(CO)2Mn fragment ([cntꢀMn1ꢀC3ꢀP1]) = 7.1ꢀ; ideal,
0ꢀ), the PHMes substituent being on the Cp side. Noticeably, the
manganeseꢀcarbene bond length (Mn1ꢀC3 = 1.859(2) Å)
appears to be among the shortest MndC bonds found in
piano-stool Mn(I) carbene complexes,15 including the non-
heteroatom-substituted ones, and the phosphorus atom shows
a significant pyramidalization (∑PR = 303ꢀ). This situation is in
sharp contrast with the one found in homologous aminocarbene
complexes, which invariably display (i) a long interatomic
MndC bond distance,16 actually being of the same magnitude
as a MnꢀC single bond, as found, for instance, in the Mn acyl
complex Cp(CO)2MnꢀꢀC(O)Ph (1.951 Å),17 and (ii) a trigo-
nal-planar environment around N. This indicates that the
phosphorus lone pair in the present phosphinocarbene complex
compares well with the value of the rotation barrier of the mesityl
group in t-BuMesPH, 13.2 kcal molꢀ1 21
,
and is considerably
lower than the known unimolecular phosphorus inversion barrier
for the free secondary phosphine (()-Phi-PrPH, which exceeds
23.3 kcal mol .
ꢀ1 22 Yet, it has to be taken into consideration that a
possible contribution of the σ-phosphavinyl form Cp-
(CO)2MnꢀꢀC(Me)dPþHMes to the structure of 3b may
significantly lower the inversion barrier at phosphorus,23 thus
preventing totally excluding the latter hypothesis. Upon cooling,
1
the H NMR spectra of complex 3a showed a more intricate
evolution. In addition to changes in the 2.70ꢀ2.20 ppm region
likely due, as above, to the hindered rotation of the Mes
substituent, a second dynamic process that translates, in parti-
cular, into the splitting of the C5H5 resonance (Δδ = 0.38 ppm at
173 K) was clearly observed. Concomitantly, a splitting of the 31
P
resonances was also detected. Examination of the coalescence
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to those found in other manganese η2-ketene complexes25 with,
in particular, a manganese-to-central carbon atom distance
(Mn1ꢀC2 = 1.904(5) Å) longer than the manganese-to-term-
inal carbon atom distance (Mn1ꢀC3 2.165(4) Å) and an
elongated C2ꢀC3 bond (C2ꢀC3 = 1.473(6) Å) and a bent
ketene moiety due to coordination (C3ꢀC2ꢀO2 = 135.0(4)ꢀ).
The overall structure is similar to that of the related cationic
tungsten complexes [Cp(CO)(L)W(η3-C(O)C(R)PR2)]X
(L = PMe3, R0 = Me, X = Cl; L = MeNtC, R = Ph, R0 = Tol,
X = BF4), obtained upon reaction of chlorophosphine on
cationic tungsten η2-ketenyl complexes.27
Reactions of η1-r-Phosphinocarbene Complexes 3a,b
with Lewis Acids and Relevant Modulation of the Electron
Donicity of the Carbene Ligand. Keeping in mind the pyrami-
dal arrangement of the phosphorus atom revealed by the X-ray
diffraction study, we envisioned probing the availability of the
phosphorus lone pair by coordination to a Lewis acid. The
reaction of 3a,b with the borane dimethylsulfide adduct at low
temperature led to spectroscopically quantitative conversion of
the starting compounds into the corresponding 5a,b adducts
(Scheme 3). Both complexes were fully characterized in solution
by IR and NMR spectroscopy. A comparison of the IR spectra of
3a,b, 5a,b, and 2a,b reveals a significant blue shift of the νCO
stretching frequencies following the order ÆνCOæ 3a,b < ÆνCOæ 5a,
b < ÆνCOæ 2a,b, illustrating, as expected, that coordination of
borane to the phosphorus atom in the η1-R-phosphinocarbene
complexes increases the electron acceptor ability of the overall
carbene ligand, but not as much as a protonation at phosphorus.
Although such an experiment brings further evidence for the
availability of the phosphorus lone pair in the η1-R-phosphino-
carbene complexes 3a,b, the thermal stability of the resulting R-
phosphinocarbene complexes/borane adduct was found to be
disappointingly low as compared with that of classical secondary
phosphine/borane adducts,28 and only 5a could to be isolated in
a pure form.
Further examination of the NMR spectra of 5a in the 273ꢀ193
K range revealed, qualitatively, the same dynamic behavior as for
3a, i.e., a decoalescence of the o-Me signals—magnetically
equivalent at 273 K—at 243 K, followed by an additional
decoalescence of the Cp resonance at δ 5.28 ppm into two
distinct singlets at δ 5.76 (minor) and 5.51 (major) ppm, at 213
K. Concomitant splitting of the 31P singlet at 28.8 ppm into two
singlets at δ 30.8 (minor) and 28.0 (major) ppm was observed at
213 K. As for 3a, the two dynamic processes are tentatively
rationalized in terms of a fast rotation [NMR time-scale] of the
mesityl group around the PꢀCipso bond and a fast rotation
[NMR time-scale] of the carbene moiety around the MnꢀC axis.
Examination of the coalescence behavior of the appropriate
signals led to estimated rotation barriers of 10.9 and 9.3 kcal
molꢀ1 for the respective processes (Scheme 4).20
Figure 2. ORTEP drawing of RMnRP-4e (ellipsoids are shown at the
30% probability level). Selected bond lengths [Å] and angles [deg]:
Mn1ꢀP1 = 2.1924(13), Mn1ꢀC1 = 1.770(5), Mn1ꢀC2 = 1.904(5),
Mn1ꢀC3 = 2.165(4), C1ꢀO1 = 1.160(6), C2ꢀO2 = 1.196(5), C2ꢀC3
= 1.473(6), C3ꢀP1 = 1.760(5), C4ꢀP1 = 1.821(5); O2ꢀC2ꢀC3 =
135.0(4), C2ꢀC3ꢀP1 = 114.3(2).
behavior of the latter two signals in the 173ꢀ298 K range led to a
ΔGq value of 8.8 kcal molꢀ1 for the dynamic process involved.
We tentatively attribute the second fluxional process to the fast
rotation [NMR time-scale] of the carbene moiety around the
MndC bond (Scheme 2b). It is noteworthy that the value of such a
rotation barrier—8.8 kcal molꢀ1—is of the same magnitude as the
3
one corresponding to the rotation barrier found in piano-stool
Mn(I) vinylidene complexes (8.6ꢀ13.5 kcal molꢀ1).24
Spectroscopic and Structural Characterization of the η3-
Phosphinoketene Complexes 4aꢀe. The IR spectra of com-
plexes 4aꢀe in solution in CH2Cl2 display two bands, namely, a
strong one in a 1918ꢀ1932 cmꢀ1 range, attributed to the νCO of
the unique carbonyl ligand, and a medium one in a 1697ꢀ
1720 cmꢀ1 range, attributed to the νCdCdO of the ketene ligand,
which thus appears at a frequency close to that of η2-ketene
ligands in the parent Cp(CO)2Mn(η2-C(O)CRR) complexes.25
The 13C{1H} NMR spectra of 4aꢀe show distinct signals for the
carbonyl ligands (MnꢀCO: δ 230.4ꢀ234.1 ppm) and for the
carbonyl of the ketene ligand (CdCdO: δ 237.5ꢀ239.9 ppm).
The Csp2 carbon atom of the ketene moiety CdCdO appears at
very high field (CdCdO: δ ꢀ36.2 to ꢀ24.7 ppm). The 31P
NMR spectra show a remarkable dispersion of signals due to the
phosphorus atoms of the phosphinoketene ligand, which appear
in a δ ꢀ41.4 (4a) to 110.4 (4d) ppm range (C6D6). Noticeably,
the η3-phosphinoketene complex 4e (resulting from reaction of
[1a]BPh4 with (()-HPMeMes), which possesses two stereo-
genic centers, namely, the manganese and the phosphorus atoms,
is obtained as a single pair of diastereoisomers. The actual RR/SS
stereochemistry of 4e was determined by single-crystal X-ray
diffraction analysis and was corroborated by 2D ROESY NMR
experiments.
For complex 5b, the magnetic inequivalence of the o-Me and
m-H signals of the Mes substituent reveals a rigid [NMR time-
scale] structure in solution at 273 K, but the relative instability of
the complex in solution precluded a full analysis of its dynamic
behavior.
A perspective view of complex 4e, isolated in the crystal in the
RMnRP form, is shown in Figure 2.26 The phosphinoketene ligand
is indeed coordinated to the metal through P1 and through the
carbon atoms C2 and C3 of the ketene moiety. The methyl
substituent on P1 is located on the same side as the Cp ligand,
conferring a RMnRP configuration to the complex. The Mn1ꢀP1
bond is slightly shorter than typical MnꢀP bonds in phosphorus-
substituted Mn(I) piano-stool complexes (average value of
2.212 Å). Metrical features within the ketene moiety are similar
Versatile Rearrangement of the η1-r-Phosphinocarbene
Complexes 3a,b Observed in a Nonpolar Solvent and under
Basic Catalysis Conditions. Generation of the η1-R-Phosphi-
docarbene Complex [7d]Li and Its Subsequent Isomeriza-
tion into the Monocarbonyl Acyl Complex [8d]Li via Acid-
Catalyzed Migratory CO Insertion. The η1-R-phosphinocar-
bene complexes 3a,b can be stored in the solid state at ꢀ20 ꢀC for
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Scheme 3
temperature, which is fully consistent with literature data.29 The
observed rearrangement of the η1-R-phosphinocarbenes 3a,b
into the η1-phosphaalkene complexes 6a,b is reminiscent of the
non-stereoselective migration of the i-Pr2N group reported for
the rhodium complex (CO)2ClRhdC(Ar)P(NiPr2)2, which was
proposed to take place via a formal 1,2-amino group shift.7a,b
With such a mechanistic proposal in mind, the present occur-
rence of η3-phosphinoketene complexes 4a,b as apparent inter-
mediates on the way to the final products 6a,b appeared rather
puzzling, possibly indicating the occurrence of a competitive
reaction pathway.
Scheme 4
The structure of 6a,b was established by the characteristic 1H,
31P, and 13C NMR signals of the η1-P(Mes)dC(H)R ligands,
which are similar to those reported for η1-P(Mes)dCPh2
transition-metal complexes.30 In the present case, the E or Z
geometries around the PdC bond were inferred from additional
NOE experiments.
Scheme 5
Interestingly, the rearrangement was found to proceed faster
in THF solution (ca. 36 h, and 1.5 h for 3a, and 3b, respectively)
than in benzene or CH2Cl2, affording in fine the η1-phosphaalk-
ene complexes 6a,b, in that case with ca. 95% E-selectivity. Again,
the η3-phosphinoketenes complexes 4a,b were appearing in the
course of the rearrangement. Keeping in mind that THF—unlike
benzene and dichloromethane—can facilitate proton transfer
processes and that related carbene-to-alkene rearrangements of
group 6 Fischer-type alkoxycarbene complexes have been pre-
viously shown to be base-catalyzed,31 we decided to examine the
influence of an added base on the rearrangement processes
encountered here. In a typical experiment, the addition of a
catalytic amount (ca. 15%) of Et3N to a solution of 3a in CH2Cl2
at 25 ꢀC resulted in its faster and spectroscopically quantitative
conversion into 4a within 2ꢀ3 min, whereas the subsequent
rearrangement of 4a into E-6a still required 3ꢀ4 h. It was found
later that acceleration of this second step requires an excess of
Et3N (ca. 5 equiv), then leading to reaction completion within 5
min. By contrast, Et3N did not affect the transformation of 3b
under the same reaction conditions, probably due to its lower
PꢀH bond acidity. Effectively, the addition of a stronger base like
DBU was found to promote the immediate and quantitative
rearrangement of both 3a and 3b in CH2Cl2, affording the η1-
phosphaalkene species 6a and 6b with >99% E-selectivity. Let us
recall that the base-catalyzed rearrangement of transition-metal
alkoxycarbene complexes (CO)5MdC(CH2R)OR0 is typically
Z-stereoselective.31
several months without significant decomposition. However,
they cleanly rearrange in solution at room temperature to afford
the corresponding η3-phosphinoketene complexes Cp(CO)Mn-
(η3-C(O)C(R)P(H)Mes), 4a,b, along with the corresponding
η1-phosphaalkene complexes Cp(CO)2Mn(η1-P(Mes)dC-
(H)R) (6a,b, Scheme 5). Selected 31P NMR monitoring data
relative to this rearrangement are given in Table 1. Complex 4a,
which was fully characterized by IR and NMR spectroscopy,
apparently forms as a single pair of diastereoisomers. Attempts to
establish its stereochemistry by NMR remained inconclusive,
due to the unavoidable presence of 3a and 6a in the samples.
Complexes 6a,b should be regarded as the thermodynamic
products of the rearrangement process, since they are the sole
remaining compounds observed after 3ꢀ4 days of reaction, then
appearing as equilibrated mixtures of E/Z stereoisomers (6a:
60:40 E/Z ratio; 6b: 55:45 E/Z ratio). No further interconver-
sion of these E- and Z-isomers was observed for 6a,b at room
While looking for plausible explanations for the unexpected
role of a CO insertion in the rearrangement process and
eventually the origin of its stereoselectivity, we were led to
investigate the deprotonation of the η1-R-phosphinocarbene
complexes 3a and 3b. Treatment of 3a with n-BuLi in THF
at ꢀ80 ꢀC led smoothly to the formation of a deep red solution of
the unprecedented anionic R-phosphidocarbene complex
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1
Table 1. H and 31P NMR Monitoring of the Rearrangement of the η1-r-Phosphinocarbene Complexes 3a,b at 298 K
entry
complex
solvent, catalyst
C6D6
reaction time
product(s), yield (E:Z ratio)
1
3a
1 d
4a, 65% þ 6a, 34% (47:53)
6a, 100% (60:40)
2
3ꢀ4 d
3ꢀ4 d
4 h
3
3b
3a
C6D6
6b, 100% (55:45)
4
THF-d8
4a, 67% þ 6a, 33% (95:5)
6a, 100% (95:5)
5
THF-d8
36 h
6
3b
3a
THF-d8
30 min
1.5 h
3b, 15% þ 4b, 5% þ 6b, 80% (95:5)
6d, 100% (95:5)
7
THF-d8
8
CD2Cl2, NEt3 (15%)
CD2Cl2, NEt3 (15%)
CD2Cl2, NEt3 (500%)
CD2Cl2, NEt3 (500%)
CD2Cl2, DBU (1%)
CD2Cl2, DBU (1%)
2ꢀ3 min
3ꢀ4 h
5 min
30 min
1 min
1 min
4a, 100%
9
6a, 100%(99:1)
10
11
12
13
6a, 100%(99:1)
3b
3a
3b
3b, 90% þ 6b, 10% (55:45)
6a, 100% (99:1)
6b, 100% (99:1)
[Cp(CO)2MndC(Ph)PMes]Li, [7a]Li, which appeared to be
stable at room temperature for several hours (Scheme 5). Later
on, it was found that complex [7a]Li can be also generated in one
pot upon reaction of the carbyne precursor [1a]BPh4 in THF
with MesPH2, followed by addition of two equivalents of n-BuLi
at ꢀ80 ꢀC. Although the formation of such anionic R-phosphi-
docarbene complexes is unprecedented, it is clearly reminiscent
of the formation of anionic amidocarbene complexes upon
deprotonation of Fischer-type aminocarbene complexes.32
Complex [7a]Li exhibits a three-band pattern in the νCO
region (IR (THF): 1882 (vs), 1811 (s), 1772 (s) cmꢀ1 (νCO)),
very similar to the one observed for the carbene anion
[Cp0(CO)2MndC(OEt)CH2]Li (IR (THF): 1870 (vs), 1795
(s), 1745 (s) cmꢀ1 (νCO))33 or for the η1-allenyl anion
[Cp0(CO)2MnꢀC(Ph)dCdC(Tol)Nu]Li (Nu = H, STol,
PPh2) (IR (THF): 1873 (vs), 1798 (s), 1755 (s) cmꢀ1
(νCO)).34 The occurrence of a three-band pattern in these
anionic dicarbonyl species was previously ascribed to an inter-
action of lithium cations with the oxygen atom of a CO group,35
and it seems likely that the same phenomenon takes place here.
Attempts to further characterize raw [7a]Li by NMR failed due
to its extreme moisture sensitivity and unavoidable presence of
paramagnetic impurities, whereas all attempts to purify it in-
variably led to the orange monocarbonyl acyl anion [Cp(CO)2-
Mn(η2-C(O)C(Ph)dPMes]Li, [8a]Li (IR (THF): 1888
(s) cmꢀ1 (νCO); 1620 (m) cmꢀ1 (νCdO)) (Scheme 5). It was
soon found that the latter reaction is in fact acid-catalyzed.
Indeed, addition of traces of water to a THF solution of [7a]Li
was found to trigger its instantaneous and quantitative isomer-
ization into [8a]Li, even at ꢀ80 ꢀC. Parallel treatment of the η1-
R-phosphinocarbene complex 3b by n-BuLi under the same
reaction conditions led directly to the formation of the mono-
carbonyl species [8b]Li. The antecedent η1-R-phosphidocar-
bene complex could not be intercepted in that case presumably
due to the intrinsic existence of a proton source, namely, the
methyl group in R-position relative to the carbenic carbon
center.36 Finally, the monocarbonylacyl anions [8a,b]Li could
be conveniently generated through a deprotonation of carbene
complexes with t-BuOLi, at ꢀ40 ꢀC, in THF (Scheme 5).
The structure of [8a,b]Li was unambiguously established by
13C{1H} NMR spectroscopy, revealing in particular signals at δ
267.6ꢀ274.2 (s (br), CdO) and 233.6ꢀ235.6 (s (br),
MnꢀCO), along with the characteristic signal of the carbon of
Scheme 6
the four-membered ring (δ 143.2ꢀ146.4 (d, 1JPC = 57ꢀ60 Hz,
PdC)). The latter data are in agreement with those reported for
the related neutral iron complex Cp(CO)Fe(η2-C(O)-
C(R)dPPR2) (R = Ni-Pr2), exhibiting the same metallacyclic
structure.37
The present observation of an acid-catalyzed rearrangement of
the dicarbonyl anion [7a,b]ꢀ into the monocarbonyl acyl
derivatives [8a,b]ꢀ can be rationalized in terms of the proposed
reaction sequence shown in Scheme 6 involving (i) a partial
protonation of [7]ꢀ by a proton source, such as water, t-BuOH,
or, in the case of 3b, the η1-R-phosphinocarbene carbene com-
plex itself, giving the elusive hydridodicarbonyl species {9}; (ii) a
fast migratory CO insertion of the σ-phosphaalkenyl fragment
concomitant with coordination of the phosphorus atom to
produce monocarbonylhydride {10}; and (iii) deprotonation
of {10} by the remaining [7]ꢀ to give the final [8]ꢀ.
The ease of the isomerization of {9} into {10} can be under-
stood in terms of the enhanced electrophilicity of its carbonyl
groups resulting from a reduction of the negative charge on the
metal center upon protonation. This is reminiscent of earlier
observations on the oxidative activation of the anionic acyl
complex [Cp0(CO)2MnꢀC(O)Tol-p]ꢀ38 or neutral σ-alkyl39
and σ-alkenyl40 transition-metal complexes toward migratory
CO insertion.
Finally, the protonation of [8a]Li with various proton sources
(HBF4 Et2O, NH4Claq, [Et3NH]Cl) leads to a stereoselective
3
formation of E-6a (Scheme 5). The protonation of [8b]Li
proceeds similarly with the same E-stereoselectivity and typically
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Scheme 7
faster than for [8a]Li when using weak acids (for [8b]Li reaction
takes 15ꢀ20 min for completion, instead of 2 h required in the
case of [8a]Li). Interestingly, the transient formation of the η3-
phosphinoketene complexes 4a and 4b was observed by IR
spectroscopy only with the weakest proton donor, [Et3NH]þ.
On the basis of the above observations, we propose that the
base-catalyzed rearrangement of η1-R-phosphinocarbene com-
plexes 3a,b into the η1-phosphalkene complexes 6a,b and—
depending on the reaction conditions—the η3-phosphaketene
complexes 6a,b proceeds in THF or CH2Cl2 through acidicꢀba-
sic processes involving the anionic monocarbonyl acyl complexes
[8a,b]ꢀ as the key transient species. The latter would arise from
initial deprotonation of 3a,b into the η1-R-phosphidocarbene
complex [7a,b]ꢀ followed by a CO insertion. Reversible pro-
tonation at the phosphorus atom would lead to the η3-phosphi-
noketenes 4a,b, which may or may not accumulate, depending on
the strength of the base used as catalyst.41 Competitive proton-
ation at the central carbon atom and concomitant CO deinser-
tion would produce 6a,b as the final product, under an exclusive
E configuration.
In an effort to assess the above intermolecular acidicꢀbasic
process for the overall rearrangement 3a,b f 6a,b in THF—and
to exclude an alternate direct intramolecular concerted 1,2-
hydrogen shift,42 which, we consider, could competitively oper-
ate in C6D6 to give the observed E/Z mixture of 6a,b (Table 1)—
we carried out crossover experiments with a mixture of the
closely related Cp(CO)2MndC(p-Tol)PHMes, 3a0, and deut-
erated d-3a complexes, in THF solution (see Experimental
Section). Unfortunately, such an experiment did not shed light
on the reaction mechanism since an unexpected quasi-instanta-
neous H/D exchange was found to occur between the two
complexes, affording a statistical mixture of four possible carbene
products, 3a0, d-3a0, 3a, and d-3a, generated before any other
transformation.
Figure 3. Perspective view of complex of Z-12 (ellipsoids set at the 30%
probability level). Selected bond lengths [Å]: Mn1ꢀP1 2.1611(8),
P1ꢀC3 1.674(3), P1ꢀC31 1.827(3), C3ꢀC21 1.486(4), C3ꢀI1
2.112(3).
diastereoisomer. On the other hand, reaction with iodine at
ꢀ80 ꢀC led to a thermally unstable species tentatively identified
as the η3-phosphinoketene complex Cp(CO)2Mn(η3-C(O)C-
(Ph)PIMes), 11, on the basis of its IR spectrum (IR (THF):
1945 (s) (νCO), 1736 (m) (νCdCdO)). Upon warming to room
temperature, the latter was found to rearrange into the η1-
phosphaalkene complex Cp(CO)2Mn(η1-P(Mes)dC(I)Ph),
12 (Scheme 7). Examination of the crude reaction mixture
(after filtration through Celite) revealed two signals in the 31P
NMR, at δ 297 ppm (ca. 98%) and 302.3 ppm (ca. 2%),
tentatively attributed to each the two isomers of 12. After
purification and recrystallization, the major compound was
isolated in 92% yield and identified as the Z isomer on the basis
of a single-crystal X-ray diffraction analysis. A perspective view of
the complex is given in Figure 3. The transformation 11 f Z-12
illustrates the possibility of a concerted 1,2-shift of the mobile
group with concomitant CO deinsertion in manganese η3-
phosphinoketene complexes to give an η1-phosphaalkene of Z
conformation. This supports our view that the nonselective
rearrangement of the η1-R-phosphinocarbene 3a,b into E- and
Z-6a,b in a nonpolar solvent and in the absence of base may
indeed be the result of competitive mechanisms, i.e., a concerted
Reactions of the Monocarbonyl Acyl Anion [8a]Li and the
η3-Phosphinoketene Derivatives with Electrophiles. Hoping
to get additional clues about the η1-R-phosphinocarbene/η1-
phospha-alkene rearrangement, we decided to examine the
reactivity of the anion [8a]ꢀ toward electrophilic reagents in
complement to the above protonation reactions.
The monocarbonyl acyl anion [8a]Li, generated upon treat-
ment of the η1-R-phosphinoketene complex 3a with t-BuOLi at
ꢀ80 ꢀC, was found to react readily with MeI to afford the η3-
phosphinoketene complex RR/SS-4e (Scheme 7) in 95% yield
and in a totally diastereoselective manner, in favor of the RR/SS
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1,2-shift of the mobile proton responsible for the formation of
the Z isomer and an acidicꢀbasic process giving the E isomer, the
latter pathway being largely favored in THF or in CH2Cl2 in the
presence of base.
300, DPX 300, Avance 400, and Avance 500 spectrometers and
referenced to the residual signals of deuterated solvent (1H and 13C)
and to 85% H3PO4 and BF3 OEt2 (31P and 11B, respectively, external
3
standard). Elemental analyses were performed on a Perkin-Elmer 2400
CHN analyzer.
Preparation of MesPD2. Mesitylphosphine (0.76 g, 5 mmol) was
dissolved in a mixture of THF (5 mL) and D2O (3 mL, 150 mmol, >97%
of deuterium), and a catalytic amount of CF3COOD (12 μL, 0.1 mmol)
was added. The solution was stirred at room temperature for 12 h; then
THF was carefully evaporated under vacuum. The resulting emulsion
was extracted with pentane (3 ꢁ 5 mL), the combined extracts were
filtered through Celite and dried over CaH2, and the pentane was
evaporated under vacuum. The product thus obtained—containing ca.
15% of residual protons based on 1H and 31P NMR spectra—was treated
again as described above to afford in fine MesPD2 (0.68 g, 88% yield)
with more than 96% isotopic purity, based on NMR analysis.
’ CONCLUSION
Whereas η1-R-phosphinocarbene complexes have long been
regarded as elusive, except in rare specific examples, the present
account has revealed a simple and rational synthetic pathway to
such compounds, illustrated here by the case of manganese, and
exploiting the ability of phosphines to form “phosphoniocarbene”
adducts with the electrophilic center of a cationic carbyne
complex. Indeed, when such adducts are generated from a
primary or a secondary phosphine, their simple deprotonation
gives readily the desired η1-R-phosphinocarbene complex. Here,
the fully characterized η1-R-phosphinocarbene complex 3, de-
rived from mesitylphosphine, was found to exhibit a fascinating
reactivity characterized by a versatile behavior in the presence of
different bases, in relevance to the mobility of the hydrogen atom
remaining on its R-phosphorus center. Deprotonation of 3 by n-
BuLi was found to yield the unprecedented R-phosphidocarbene
complex [7]ꢀ, which proved to be highly sensitive to traces of
moisture and could be engaged in a proton-catalyzed isomeriza-
tion to the acyl complex [8]ꢀ, a transformation understood as an
unprecedented example of proton-induced migratory CO inser-
tion. The key compound [8]ꢀ, also directly accessible from 3
upon treatment with t-BuOLi, is ultimately converted into the
phosphaalkene complex 6 in a regioselective way upon stoichio-
metric addition of acids, affording the E derivative. By contrast,
electrophilic addition of iodine to the same compound [8]ꢀ gives
the iodide-substituted phosphaalkene Z-12 with opposite regios-
electivity. The present work sheds new light on hitherto un-
known and apparently complicated transformations of R-
phosphinocarbene complexes, which are in fact perfectly ratio-
nalizable in terms of basic fundamental concepts.
1
MesPH2: H NMR (400.1 MHz, C6D6, 298 K) δ 6.82 (s, 2H, m-H
(Mes)), 3.72 (d, 1JPH = 203.8 Hz, 2H, PH2), 2.32 (s, 6H, o-CH3 (Mes)),
2.20 (s, 3H, p-CH3 (Mes)); 31P{1H} NMR (162.0 MHz, C6D6, 25 ꢀC)
δ ꢀ155.9 (s).
MesPHD: 1H NMR (400.1 MHz, C6D6, 298 K) δ 6.82 (s, 2H, m-H
(Mes)), 3.70 (d (br), 1JPH = 203.8 Hz, 1H, PHD), 2.32 (s, 6H, o-CH3
(Mes)), 2.20 (s, 3H, p-CH3 (Mes)); 31P{1H} NMR (162.0 MHz, C6D6,
25 ꢀC) δ ꢀ156.9 (t, 1JPD = 31.7 Hz).
MesPD2: 1H NMR (400.1 MHz, C6D6, 298 K) δ 6.82 (s, 2H, m-H
(Mes)), 2.32 (s, 6H, o-CH3 (Mes)), 2.20 (s, 3H, p-CH3 (Mes));
31P{1H} NMR (162.0 MHz, C6D6, 298 K) δ ꢀ157.9 (qv, 1JPD = 31.7
Hz).
Synthesis of [Cp(CO)2MndC(Ph)PH(Ni-Pr2)2]BPh4 ([2d]BPh4).
The carbyne complex [1a]BPh4 (292 mg, 0.5 mmol) was suspended in
CH2Cl2 (20mL) atꢀ50 ꢀC, and HP(Ni-Pr2)2 (95μL, 0.5 mmol) was added
dropwise via syringe under vigorous stirring. The reaction mixture was
allowed to slowly reach room temperature (ca. 1 h), giving a green solution
of [2d]BPh4, which was filtered through Celite, concentrated to ca. 3 mL, and
precipitated with diethyl ether (20 mL). The green solid obtained was washed
with ether (3 ꢁ 10 mL) and dried under vacuum to afford 375 mg of
[2d]BPh4 as a green powder (92% yield).
[2d]BPh4: 1H NMR (300.1 MHz, CD2Cl2, 298 K) δ 8.12 (d, 1JHP
=
’ EXPERIMENTAL SECTION
546 Hz, 1H, PH), 7.60ꢀ6.70 (m, 25H, Ph), 5.09 (s, 5H, C5H5), 3.66 (m,
4H, CH(CH3)2), 1.44 (d, 3JHH = 7.0 Hz, 6H, CH(CH3)2), 1.13 (d, 3JHH
= 7.0 Hz, 6H, CH(CH3)2); 31P NMR (121.5 MHz, CD2Cl2, 298 K)
δ 25.5 (dt, 1JHP = 546 Hz, 3JHP = 14.0 Hz); 13C{1H} NMR (75.45 MHz,
All manipulations were carried out using standard Schlenk techniques
under an atmosphere of dry nitrogen. Tetrahydrofuran and diethyl ether
used for the synthesis were distilled under nitrogen from sodium
benzophenone ketyl just prior to use. Other solvents (pentane, hexane,
toluene, dichloromethane) were purified following standard procedure
and stored under nitrogen. The following reagent grade chemicals BCl3
(1.0 M solution in heptane), BH3 SMe2 (2.0 M solution in toluene), n-
BuLi (1.6 M solution in hexanes), NaBPh4, MeI, I2, D2O, CF3COOD,
Et3N, DBU, Ph2PH, and t-BuOLi were obtained from commercial
sources. Triethylamine and DBU were distilled over CaH2 before use.
Manganese complexes Cp(CO)2MndC(R)OEt (R = Me, Ph, p-Tol)43
and [Cp(CO)2MntCꢀPh]BPh4 ([1a]BPh4)9a and phosphines HP-
(Ni-Pr2)2,44 MesPH2,45 and Mes(Me)PH46 were prepared according to
known procedures.
A liquid nitrogen/ethanol slush bath was used to maintain samples at
the desired low temperature. Chromatographic purification of the
complexes was performed on silica (0.060ꢀ0.200 mm, 60 Å) or alumina
(neutral, 0.050ꢀ0.200 mm, dried under vacuum at 150 ꢀC during 4 h
and stored under nitrogen) obtained from Acros Organics. Deuterium-
enriched silica for purification of the deuterated phosphinocarbene
complex d-3a was prepared by repetitive drying of SiO2 at 150 ꢀC and
saturation with D2O (three times). Solution IR spectra were recorded in
0.1 mm CaF2 cells using a Perkin Elmer 983 G infrared spectro-
photometer and are given in cmꢀ1 with relative intensity in parentheses.
1H, 31P, 11B, and 13C NMR spectra were obtained on Bruker Avance
CD2Cl2, 298 K) δ 325.2 (d, 1JCP = 24.7 Hz, MndC), 229.4 (d, 3JCP
10.6 Hz, MnꢀCO), 164.1ꢀ121.3 (Ph), 95.0 (s, C5H5), 48.8 (d, 2JCP
4.7 Hz, CH(CH3)2), 23.5 (d, 3JPC = 1.7 Hz, CH(CH3)2), 22.8 (d, 3JPC
=
=
=
3.8 Hz CH(CH3)2)); IR (CH2Cl2) 2018 (s), 1943 (s) (νCO). Anal.
Calcd for C50H59BMnN2O2P: C, 73.53; H, 7.23; N, 3.43. Found: C,
72.90; H, 7.54; N, 3.25.
Synthesis of Cp(CO)2MndC(Ph)PHMes (3a) from [1a]BPh4. A
sample of the carbyne complex [1a]BPh4 (292 mg, 0.5 mmol) was
suspended in CH2Cl2 (20 mL) at ꢀ40 ꢀC, and a solution of MesPH2
(76μL, 0.5 mmol) in CH2Cl2 (1 mL) was added dropwise via syringe under
stirring. After stirring for 30 min, a homogeneous green solution was
obtained. IR monitoring showed the phosphinocarbene complex 3a to be
the sole reaction product (IR (CH2Cl2): 1973 (s), 1910 (s) (νCO)). The
solvent was removed under vacuum, and the green residue was purified by a
rapid column chromatography on silica (2 ꢁ 10 cm), under a nitrogen
atmosphere. The green band of 3a waselutedwithpurehexanetoafford162
mg of crude product after solvent removal (78% yield). Subsequent
recrystallization from pentane at ꢀ20 ꢀC afforded 135 mg of analytically
pure 3a as black crystals (65% yield).
3a: 1H NMR (300.1 MHz, toluene-d8, 298 K) δ 6.99 (t, 3JHH = 6.6
3
Hz, 2H, m-H (Ph)), 6.81 (t, JHH = 6.6 Hz, 1H, p-H (Ph)), 6.80 (d,
1JHP = 260.4 Hz, 1H, PHMes), 6.69 (s, 2H, m-H (Mes)), 6.61
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(d, 3JHH = 7.3 Hz, 2H, o-H (Ph)), 4.49 (s, 5H, C5H5), 2.52 (s, 6H, o-CH3
(Mes)), 2.04 (s, 3H, p-CH3 (Mes)); 31P NMR (121.5 MHz, toluene-d8,
to a solution of Cp(CO)2MndC(Me)OEt (600 mg, 2.4 mmol) in
hexane (40 mL) cooled to ꢀ60 ꢀC, under vigorous stirring. After stirring
for an additional 15 min, the supernatant was removed by means of a
cannula tipped with filter paper. The pale yellow precipitate of [1b]BCl4
was washed with hexane (20 mL) and then suspended in CH2Cl2
(30 mL). A solution of MesPH2 (0.37 mL, 2.4 mmol) in CH2Cl2 (2 mL)
was added dropwise at ꢀ80 ꢀC via syringe. This resulted in the
formation of a deep blue solution of [2b]BCl4 (IR (CH2Cl2): 2022
(s), 1962 (s) (νCO)). An excess of Et3N (0.68 mL, 4.8 mmol) was then
added, causing the reaction medium to turn deep green. IR monitoring
showed the phosphinocarbene complex 3b to be the sole reaction
product (IR (CH2Cl2): 1970 (s), 1906 (s) (νCO)). The cold solution
was rapidly filtered through a short column of alumina, and the volatiles
were removed under vacuum. The green-brown residue was purified by
rapid column chromatography on silica (2 ꢁ 10 cm), under a nitrogen
atmosphere. The deep green band of 3b was eluted with pure hexane,
affording 600 mg of crude product after solvent removal (70% yield).
Subsequent recrystallization of the product from pentane at ꢀ20 ꢀC
afforded 490 mg of analytically pure 3b as green-black crystals (58%
yield), some of them being suitable for an X-ray diffraction analysis.
3b: 1H NMR (300.1 MHz, C6D6, 298 K) δ 6.84 (s, 2H, m-H (Mes)),
6.39 (d, 1JHP = 261.5 Hz, 1H, PHMes), 4.72 (s, 5H, C5H5), 3.16 (d, 3JHP
= 14.5 Hz, 3H, MndCꢀCH3), 2.43 (s, 6H, o-CH3 (Mes)), 2.19 (s, 3H,
p-CH3 (Mes)); 31P NMR (121.5 MHz, C6D6, 298 K) δ 10.15 (dq, 1JHP
= 261.5 Hz, 3JHP = 14.5 Hz); 13C{1H} NMR (75.45 MHz, C6D6, 298 K)
1
298 K) δ 18.9 (d, JHP = 260.4 Hz); 13C{1H} NMR (125.8 MHz,
toluene-d8, 240 K) δ 358.2 (d, 1JCP = 75.5 Hz, MndCꢀP), 233.0 (s (br),
MnꢀCO), 142.9ꢀ118.2 (Ph and Mes), 90.5 (s, C5H5), 24.1 (s (br),
o-CH3 (Mes)), 20.9 (s, p-CH3 (Mes)); IR (CH2Cl2) 1973 (s), 1910 (s)
(νCO). Anal. Calcd (%) for C23H22MnO2P: C, 66.35; H, 5.29. Found: C,
66.33; H, 5.54.
Synthesis of Cp(CO)2MndC(Ph)PDMes (d-3a). A sample of
the carbyne complex [1a]BPh4 (175 mg, 0.3 mmol) was suspended in
CH2Cl2 (10 mL) at ꢀ40 ꢀC, and a solution of MesPD2 (46 μL, 0.3
mmol) in CH2Cl2 (0.5 mL) was added dropwise via syringe. After
stirring for 30 min, a homogeneous green solution was obtained. The
solvent was removed under vacuum, and the green residue was purified
by column chromatography on a deuterium-enriched silica column (1 ꢁ
3 cm), under a nitrogen atmosphere. The green band of d-3a was eluted
with pure hexane. The resulting green solution was filtered through
Celite, concentrated, and crystallized at ꢀ20 ꢀC, affording 77 mg of d-3d
as black crystals (62% yield). The isotopic purity of the compound thus
prepared was estimated by 1H and 31P NMR spectra to be higher
than 93%.
d-3a: 31P NMR (162.0 MHz, C6D6, 298 K) δ 17.7 (t, 1JPD = 40.1 Hz,
PDMes).
Synthesis of Cp(CO)2MndC(p-Tol)PHMes (3a0). Boron
trichloride (4.4 mL of 1.0 M solution in heptane, 4.4 mmol) was added
rapidly to a solution of Cp(CO)2MndC(p-Tol)OEt (650 mg, 2 mmol)
in hexane (40 mL) cooled to ꢀ60 ꢀC, under vigorous stirring. After
stirring for an additional 15 min, the supernatant was removed by means
of a cannula tipped with filter paper. The pale yellow precipitate of
[Cp(CO)2MntC(p-Tol)]BCl4, [1a0]BCl4 was washed with hexane
(20 mL) and then suspended in CH2Cl2 (30 mL). A solution of
MesPH2 (0.3 mL, 2 mmol) in CH2Cl2 (2 mL) was added dropwise at
ꢀ80 ꢀC via syringe. This resulted in the formation of a deep green
solution of [Cp(CO)2MndC(p-Tol)PH2Mes]BCl4, [2a0]BCl4 (IR
(CH2Cl2): 2021 (s), 1958 (s) (νCO)). The cold solution was rapidly
filtered through a short column of alumina, which was subsequently
washed with cold (ꢀ80 ꢀC) ether (30 mL). [NOTE: the alumina used
for the filtration should be thoroughly dried, otherwise the yield in 3a0
drastically decreases.] The resulting solution was evaporated under
vacuum at ca. ꢀ20 ꢀC, giving a green-brown residue, which was
extracted with a 4:1 hexaneꢀCH2Cl2 mixture (4 ꢁ 15 mL), whereas
the extracts were filtered through Celite. The resulting green solution
was concentrated under vacuum and left overnight at ꢀ20 ꢀC to give 3a0
as a microcrystalline material. After removal of the supernatant by
decantation, the residue was washed with pentane (2 ꢁ 10 mL) and
finally dried under vacuum to afford 404 mg of 3a0 obtained as a brown
microcrystalline solid (47% yield).
1
δ 366.5 (d, JCP = 81.0 Hz, MndCꢀP), 232.6 (s (br), MnꢀCO),
2
143.1ꢀ128.4 (Ph and Mes), 90.4 (s, C5H5), 47.7 (d, JCP = 11.5 Hz,
MndCꢀCH3), 23.5 (d, 3JCP = 11.5 Hz, o-CH3 (Mes)), 20.9 (s, p-CH3
(Mes)); IR (CH2Cl2) 1970 (s), 1906 (s) (νCO). Anal. Calcd for
C18H20MnO2P: C, 61.02; H, 5.65. Found: C, 60.73; H, 5.49.
Synthesis of Cp(CO)Mn(η3-C(O)C(Ph)PPh2) (4c). A sample of
the carbyne complex [1a]BPh4 (292 mg, 0.5 mmol) was suspended in
CH2Cl2 (20 mL) at ꢀ50 ꢀC, and Ph2PH (87 μL, 0.5 mmol) was added
dropwise via syringe under vigorous stirring. IR monitoring showed the
reaction to be complete within 30 min, giving a green solution of
[Cp(CO)2MndC(Ph)PPh2H]BPh4 ([2c]BPh4) (IR (CH2Cl2): 2020
(s), 1960 (s) (νCO)). The reaction mixture was cooled to ꢀ80 ꢀC and
treated with one equivalent of DBU (76 μL, 0.5 mmol). This resulted in
the formation of a brown solution of a thermally unstable intermediate.
Upon subsequent warming up to ꢀ20 ꢀC, the color of the solution
turned red and the IR monitoring showed complex 4c to be the only
reaction product (IR (CH2Cl2) 1932 (s) (νCO), 1700 (m) (νCdCdO)).
After solvent removal under vacuum at ꢀ20 ꢀC, the resulting red, waxy
residue was extracted with a 2:1 tolueneꢀpentane mixture (4 ꢁ 5 mL) at
the same temperature and separated from [DBUH]BPh4 by filtration
through Celite. Pentane (40 mL) was added to the combined extracts,
and the solution was left overnight at ꢀ20 ꢀC, causing complex 4c to
crystallizeout as a microcrystalline powder. Thesupernatant was removed,
and theprecipitate waswashedwith pentane (2 ꢁ 10 mL) and driedunder
vacuum to afford 180 mg of 4c as a brown microcrystalline solid (80%
yield). Crystals of 4c suitable for an X-ray diffraction analysis were grown
from a diethyl etherꢀhexane mixture, at room temperature.
Complex 3a (358 mg, 43% yield) could be prepared according to the
same procedure from Cp(CO)2MndC(Ph)OEt (620 mg, 2 mmol),
BCl3 (4.4 mL of 1.0 M solution in heptane, 4.4 mmol), and MesPH2
(0.3 mL, 2 mmol).
3a0: 1H NMR (400.1 MHz, C6D6, 298 K) δ 6.85 (d, 3JHH = 8.0 Hz,
2H, o-H (p-Tol)), 6.83 (d, 1JPH = 260.6 Hz, 1H, PHMes), 6.71 (s, 2H, m-
H (Mes)), 6.62 (d, 3JHH = 8.0 Hz, 2H, m-H (p-Tol)), 4.53 (s, 5H, C5H5),
2.57 (s, 6H, o-CH3 (Mes)), 2.03 (s, 3H, p-CH3 (Mes)), 2.02 (s, 3H, p-
4c: 1H NMR (300.1 MHz, C6D6, 298 K) δ 6.90ꢀ7.70 (m, 15H, Ph),
4.65 (s, 5H, C5H5); 31P NMR (121.5 MHz, C6D6, 298 K) δ 25.85 (s);
13C{1H} NMR (75.45 MHz, C6D6, 298 K) δ 238.6 (d, 2JCP = 24.4 Hz,
2
CH3 (p-Tol)). 31P NMR (162.0 MHz, C6D6, 298 K) δ 18.5 (d, 1JPH
=
P-CdCdO), 231.6 (d, JCP = 34.8 Hz, Mn-CO), 138.4ꢀ124.5 (Ph),
85.7 (s, C5H5), ꢀ28.6 (d, 1JCP = 32.2 Hz, P-CdCdO); IR (CH2Cl2)
1932 (s) (νCO), 1700 (m) (νCdCdO). Anal. Calcd for C26H20MnO2P:
C, 69.33; H, 4.44. Found: C, 68.83; H, 4.87.
260.6 Hz); 13C{1H} NMR (100.6 MHz, CD2Cl2, 253 K) δ 360.1
(d, 1JPC = 76.1 Hz, MndCꢀP), 233.0 (s (br), MnꢀCO), 143.4ꢀ118.2
(p-Tol and Mes), 90.8 (s, C5H5), 24.1 (d, 3JPC = 11.1 Hz, o-CH3 (Mes)),
21.0 (s, p-CH3 (Mes)), 20.8 (s, p-CH3 (p-Tol)); IR (CH2Cl2) 1971 (s),
1909 (s) (νCO). Anal. Calcd for C24H24MnO2P: C, 66.98; H, 5.58.
Found: C, 67.16; H, 5.72.
Synthesis of Cp(CO)Mn(η3-C(O)C(Ph)P(Ni-Pr2)2) (4d). A
solution of complex [2d]BPh4 generated from [1a]BPh4 (292 mg, 0.5
mmol) and HP(Ni-Pr2)2 (95 μL, 0.5 mmol) as described above was
cooled to ꢀ80 ꢀC and treated with DBU (76 μL, 0.5 mmol) to give an
intense red-violet solution containing a thermally unstable intermediate.
Synthesis of Cp(CO)2MndC(Me)PHMes (3b). Boron trichlor-
ide (5.3 mL of 1.0 M solution in heptane, 5.3 mmol) was added rapidly
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The cooling bath was removed, and the reaction mixture was allowed to
slowly reach room temperature (ca. 1 h), giving a red solution of
complex 4d (IR (CH2Cl2): 1918 (s) (νCO), 1697 (m) (νCdCdO)). The
solvent was removed under vacuum, and then the product was thor-
oughly extracted with ether (6 ꢁ 10 mL). The combined extracts were
filtered through Celite, and the solvents were removed under vacuum.
The remaining microcrystalline orange powder was washed with pen-
tane (2 ꢁ 10 mL) and dried under vacuum to afford 235 mg of pure 4d
(95% yield). Crystals of 4d suitable for an X-ray diffraction analysis were
grown from a diethyl etherꢀhexane mixture, at room temperature.
4d: 1H NMR (300.1 MHz, C6D6, 298 K) δ 7.53 (d, 3JHH = 7.3 Hz,
2H, o-H (Ph)), 7.25 (t, 3JHH = 7.4 Hz, 2H, m-H (Ph)), 7.15 (t, 3JHH = 7.2
Synthesis of Cp(CO)2MndC(Ph)P(BH3)(H)Mes (5a). A solu-
tion of BH3 ꢁ SMe2 (0.18 mL of 2.0 M solution in toluene, 0.36 mmol)
was added dropwise to a solution of complex 3a (125 mg, 0.3 mmol) in
CH2Cl2 (10 mL) cooled to ꢀ30 ꢀC under stirring. After 30 min, IR
monitoring revealed the presence of complex 5a as the sole reaction
product (IR (CH2Cl2): 2003 (s), 1941 (s) (νCO)). The volatiles were
removed under vacuum at ca. ꢀ10 ꢀC, and the residue was extracted
with a 4:1 hexaneꢀCH2Cl2 mixture (3 ꢁ 5 mL). The combined extracts
kept at ꢀ10 ꢀC were rapidly filtered through Celite into the flask cooled
at ꢀ10 ꢀC, concentrated at ca. 0 ꢀC until the beginning of the crystal-
lization, and finally left at ꢀ20 ꢀC overnight. The precipitate thus
obtained was separated by decantation, washed with pentane (2 ꢁ
5 mL), and dried under vacuum to afford 97 mg of complex 5a as a green
microcrystalline powder (75% yield).
Although quite stable in the solid state, complex 5a was seen to
gradually decompose in solution at room temperature, with concomitant
formation of paramagnetic impurities. Accordingly, samples suitable for
NMR analysis were prepared upon dissolution of 5a in CD2Cl2 at
ꢀ40 ꢀC followed by a rapid filtration through Celite directly into the
NMR tube, which was then inserted into a precooled (ꢀ40 ꢀC)
NMR probe.
3
Hz, 1H, p-H (Ph)), 4.63 (s, 5H, C5H5), 4.24 (d sept, JHP = 11.0 Hz,
3JHH = 7 Hz, 2H, CH(CH3)2), 3.87 (sept (br), 3JHP = 7.4 Hz, 3JHH = 6.6
Hz, 2H, CH(CH3)2), 1.35 (d (br) 3JHH = 5.4 Hz, 6H, CH(CH3)2), 1.13
3
3
(d, JHH = 7.0 Hz, 3H, CH(CH3)2), 1.07 (d, JHH = 7.0 Hz, 3H,
CH(CH3)2); 31P NMR (121.5 MHz, C6D6, 298 K) δ 110.4 (dd, 3JHP
=
11.0 Hz, JHP = 7.4 Hz); 13C{1H} NMR (75.45 MHz, C6D6, 298 K)
3
δ 237.5 (d, 2JCP = 28.5 Hz, PꢀC=CdO), 234.1 (d, 2JCP = 47.0 Hz, Mn-
2
CO), 137.8ꢀ125.4 (Ph), 85.5 (s, C5H5), 51.0 (s (br), 49.4 (d, JCP
=
3
12.0 Hz, CH(CH3)2), 25.0 (s, CH(CH3)2), 23.4 (d, JCP = 6.0 Hz,
1
CH(CH3)2), 23.1 (s (br), CH(CH3)2), ꢀ36.2 (d, JCP = 43.0 Hz,
5a: 1H NMR (400.1 MHz, CD2Cl2, 298 K) δ 7.11 (m, 3H, m-H þ p-
H (Ph)), 7.06 (d (br), 1JHP = 395 Hz, 1H, PH(BH3)Mes), 6.79 (m, 2H,
o-H (Ph)), 6.44 (s, 2H, m-H (Mes)), 5.28 (s, 5H, C5H5), 2.26 (s, 3H, p-
CH3 (Mes)), 2.18 (s, 6H, o-CH3 (Mes)), 1.70ꢀ0.60 (two singlets at
1.32 and 0.93 on the broad multiplet background, 3H, PH(BH3)Mes));
1H NMR (400.1 MHz, CD2Cl2, 193 K) δ 7.29 (s (br), 1H, m-H (Mes)),
P-CdCdO); 13C{1H} NMR (125.8 MHz, CD2Cl2, 193 K) δ 245.2
2
2
(d, JCP = 26.5 Hz, P-CdCdO), 233.3 (d, JCP = 43.0 Hz, Mn-CO),
135.7ꢀ122.2 (Ph), 86.1 (s, C5H5), 52.9, 48.1 (s, CH(CH3)2), 41.5, 34.9,
(s (br), CH(CH3)2), 21.3, 25.5, 27.9, 29.6 (s, CH(CH3)2), ꢀ34.6
1
(d, JCP = 42.5 Hz, P-CdCdO); IR (CH2Cl2) 1918 (s) (νCO), 1697
1
(m) (νCdCdO). Anal. Calcd for C26H38O2MnN2P: C, 62.90; H, 7.66; N,
5.65. Found: C, 63.25; H, 7.42; N, 5.58.
7.01 (d (br), JHP = 400 Hz, 1H, PH(BH3)Mes), 7.20ꢀ6.70 (m, 5H,
Ph), 6.60 (s, 1H, m-H (Mes)), 5.76 (s, C5H5 minor isomer), 5.51
(s, C5H5 major isomer), 2.43 (s, 3H, o-CH3 (Mes)), 2.20 (s, 3H, p-CH3
(Mes)), 1.60 (s, 3H, o-CH3 (Mes)), 1.30ꢀ0.70 (m, 3H, PH-
(BH3)Mes)); 31P NMR (162.0 MHz, CD2Cl2, 233 K) δ 28.8 (d (br),
1JHP = 400.5 Hz); 31P{1H} NMR (162.0 MHz, CD2Cl2, 193 K) δ 30.8
(s, minor isomer), 28.0 (s, major isomer); 11B{1H} NMR (128.4 MHz,
CD2Cl2, 233 K) δ ꢀ33.6 (s); 13C{1H} NMR (100.6 MHz, CD2Cl2, 213
K) δ 230.6 (s (br), Mn-CO), 145.7ꢀ125.6 (Ph and Mes), 93.0 (s,
C5H5), 24.2, 21.7 (s, o-CH3 (Mes)), 21.3 (s, p-CH3 (Mes)); IR
(CH2Cl2) 2003 (s), 1941 (s) (νCO). Anal. Calcd (%) for
C23H25BMnO2P: C, 64.19; H, 5.81. Found: C, 64.00; H, 6.09.
Formation of Cp(CO)2MndC(Me)P(BH3)(H)Mes (5b). A so-
lution of BH3 ꢁ SMe2 (0.12 mL of 2.0 M solution in toluene, 0.24
mmol) was added dropwise to a solution of complex 3b (70 mg, 0.2
mmol) in CH2Cl2 (5 mL) cooled to ꢀ40 ꢀC under stirring. After 30 min,
IR monitoring revealed the presence of complex 5b as the sole reaction
product (IR (CH2Cl2): 1998 (s), 1932 (s) (νCO)). The volatiles were
removed under vacuum at ca. ꢀ20 ꢀC, giving 5b as a brown solid. All
attempts to prepare an analytically pure sample of the latter by crystal-
lization failed due to the thermal instability of the compound. A sample
suitable for NMR analysis was prepared upon dissolution of crude 5b in
CD2Cl2 at ꢀ40 ꢀC followed by a rapid filtration through Celite directly
into the NMR tube, which was then rapidly inserted into a precooled
(ꢀ40 ꢀC) NMR probe. A gradual increase in the temperature of the
sample allowed us to obtain good quality 1H spectra in a ꢀ40 to 0 ꢀC
temperature range (rapid decomposition was observed at room tem-
perature over 1ꢀ2 min).
Synthesis of RR/SS-Cp(CO)Mn(η3-C(O)C(Ph)P(Me)Mes)
(RR/SS-4e). A sample of the carbyne complex [1a]BPh4 (292 mg,
0.5 mmol) was suspended in CH2Cl2 (20 mL) at ꢀ50 ꢀC, and
Mes(Me)PH (83 μL, 0.5 mmol) was added dropwise via syringe under
vigorous stirring. IR monitoring showed the reaction to be complete
within 30 min, giving a green-brown solution of [Cp(CO)2MndC-
(Ph)P(Me)(Mes)H]BPh4 ([2e]BPh4) (IR (CH2Cl2): 2018 (s), 1958
(s) (νCO)). The reaction mixture was cooled to ꢀ80 ꢀC and treated with
one equivalent of DBU (76 μL, 0.5 mmol). This resulted in the
formation of a brown solution containing an elusive thermally unstable
intermediate (IR (CH2Cl2): 1957 (s), 1898 (s) (νCO)). Upon subse-
quent warming to room temperature, the color of the solution turned
red. At that stage, IR monitoring revealed complex 4e as the sole reaction
product (IR (CH2Cl2) 1930 (s) (νCO), 1720 (m, br) (νCdCdO)). After
the solvent was removed under vacuum, the red, waxy residue was
extracted with ether (4 ꢁ 5 mL) and separated from [DBUH]BPh4 by
filtration through Celite. The combined extracts were evaporated under
vacuum, giving the crude complex 4e, an analytically pure sample of
which was prepared by recrystallization from an etherꢀhexane mixture
to afford 183 mg of 4e as a red microcrystalline solid (85% yield),
containing some crystals suitable for an X-ray diffraction analysis.
RR/SS-4e: 1H NMR (400.1 MHz, C6D6, 298 K) δ 7.56 (d, 3JHH = 7.6
Hz, 2H, o-H (Ph)), 7.26 (t overlapped with residual solvent protons,
3JHH = 7.8 Hz, 2H, m-H (Ph)), 7.12 (t, 3JHH = 7.4 Hz, 1H, p-H (Ph)),
6.80 (d, 4JPH = 4.8 Hz, 1H, m-H (Mes)), 6.56 (s, 1H, m-H (Mes)), 4.39
(d, JPH = 1.2 Hz, 5H, C5H5), 2.81 (s, 3H, o-CH3 (Mes)), 2.59 (s, 3H, o-
CH3 (Mes)), 2.07 (s, 3H, p-CH3 (Mes)), 1.58 (d, 2JPH = 11.7 Hz, 3H,
PCH3); 31P NMR (162.0 MHz, C6D6, 298 K) δ ꢀ7.8 (s); 13C{1H}
1
5b: H NMR (400.1 MHz, CD2Cl2, 273 K) δ 6.98 (s, 2H, m-H
(Mes)), 6.81 (d (br), 1JHP = 398 Hz, 1H, PH(BH3)Mes), 5.35 (s, 5H,
C5H5), 3.08 (d, 3JHP = 18.0 Hz, 3H, MndC-CH3), 2.51 (s, 3H, o-CH3
(Mes)), 2.32 (s, 3H, p-CH3 (Mes)), 2.28 (s, 3H, o-CH3 (Mes)),
1.90ꢀ0.60 (m (br), 3H, PH(BH3)Mes)); 31P NMR (162.0 MHz,
2
NMR (100.6 MHz, C62D6, 298 K) δ 238.7 (d, JCP = 20.8 Hz,
P-CdCdO), 230.9 (d, JCP = 29.0 Hz, Mn-CO), 142.3ꢀ124.4 (Ph
and Mes), 85.2 (s, C5H5), 23.0 (d, 3JPC = 4.2 Hz, o-CH3 (Mes)), 21.3 (d,
1
3JPC = 16.6 Hz, o-CH3 (Mes)), 20.8 (s, p-CH3 (Mes)), 13.4 (d, 1JPC
=
CD2Cl2, 233 K) δ 26.8 (d (br), JHP = 404 Hz); 11B{1H} NMR
26.3 Hz, PCH3), ꢀ24.7 (d, 1JCP = 33.2 Hz, P-CdCdO); IR (CH2Cl2)
1930 (s) (νCO), 1720 (m, br) (νCdCdO). Anal. Calcd for
C24H24MnO2P: C, 66.98; H, 5.58. Found: C, 66.69; H, 5.73.
(128.4 MHz, CD2Cl2, 233 K) δ ꢀ21.0 (s); 13C{1H} NMR (100.6 MHz,
CD2Cl2, 233 K) δ 341.6 (d (br), 1JCP = 27.0 Hz, MndC-P), 231.3 (s
(br), Mn-CO), 143.2ꢀ130.2 (Mes), 92.1 (s, C5H5), 48.6 (d, 2JCP = 13.0
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Hz, MndC-CH3), 26.2, 23.9 (s, o-CH3 (Mes)), 21.2 (s, p-CH3 (Mes));
IR (CH2Cl2) 1998 (s), 1932 (s) (νCO).
3JPH = 26.9 Hz, 3JHH = 7.7 Hz, 3H, PdC(H)CH3); 31P NMR (121.5
MHz, C6D6, 298 K) δ 274.3 (s (br)); 13C{1H} NMR (75.45 MHz,
C6D6, 298 K) δ 230.1 (d, 2JPC = 26.7 Hz, Mn-CO), 154.9 (d, 1JPC = 50.9
Evolution of Cp(CO)2MndC(Ph)PHMes (3a) in Benzene
Solution. Complex 3a (42 mg, 0.1 mmol) was dissolved in 0.5 mL of
C6D6, and the solution was filtered through a plug of Celite directly into
an NMR tube for monitoring. The composition of the solution was
analyzed by integration of the 1H and 31P NMR signals. After 30 min at
room temperature, NMR monitoring revealed the presence of 3a (87%),
4a (∼10%), and 6a (∼3%). After 24 h, 3a was present in only trace
amounts (∼1%), with 4a being the major compound (65%), along with
6a (34%; 53:47 E/Z ratio). After 3 days, NMR monitoring showed 4a in
only trace amounts (∼3%), 6a being then the main product (97% yield;
60:40 E/Z ratio).
Hz, PdC(H)CH3), 139.7ꢀ128.4 (Mes), 82.1 (s, C5H5), 21.5 (d, 3JPC
=
6.6 Hz, o-CH3 (Mes)), 20.9 (s, p-CH3 (Mes)), 16.8 (d, 2JPC = 5.9 Hz,
PdC(H)CH3).
NMR Monitoring of the Isomerization of Cp(CO)2MndC-
(Ph)PHMes (3a) in THF-d8 Solution. A sample of the carbene
complex 3a (42 mg, 0.1 mmol) was dissolved in THF-d8 (0.5 mL) at
room temperature, and the solution was filtered through a plug of Celite
directly into an NMR tube for monitoring. The composition of the
solution was analyzed by integration of the 1H and 31P NMR signals. The
resulting data are given in Table S1 (see Supporting Information). The
transformation was complete after ca. 36 h, giving 6a as the only product
(94:6 E/Z ratio).
4a: 1H NMR (300.1 MHz, C6D6, 298 K) δ 7.56 (d, 3JHH = 7.5 Hz,
2H, o-H (Ph)), 7.20 (t, 3JHH = 7.5 Hz, 2H, m-H (Ph)), 7.09 (t, 3JHH = 7.0
Hz, 1H, p-H (Ph)), 6.65 (d, 4JPH = 3.9 Hz, 2H, m-H, (Mes)), 5.94 (d,
1JPH = 392 Hz, 1H, PHMes), 4.36 (s, 5H, C5H5), 2.58 (s, 6H, o-CH3
(Mes)), 2.05 (s, 3H, p-CH3 (Mes)); 31P NMR (121.5 MHz, C6D6, 298
K) δ ꢀ41.4 (d, 1JPH = 392 Hz); 13C{1H} NMR (125.8 MHz, toluene-d8,
233 K) δ 239.9 (d, 2JPC = 18.9 Hz, P-CdCdO), 230.4 (d, 2JPC = 27.7
Hz, Mn-CO), 85.6 (s, C5H5), 22.5 (s, p-CH3 (Mes)), 22.1 (d, 3JPC = 6.3
Hz, o-CH3 (Mes)), ꢀ28.2 (d, 1JPC = 31.5 Hz, P-CdCdO).
3a: 31P NMR (121.5 MHz, THF-d8, 298 K) δ 14.8 (d, 1JHP = 260.5
Hz).
4a: 1H NMR (300.1 MHz, THF-d8, 298 K) δ 7.50 (m, 2H, o-H (Ph)),
7.20 (m, 2H, m-H (Ph)), 7.00 (m, 1H, p-H (Ph)), 6.94 (s, 2H, m-H
(Mes)), 6.45 (d, 1JHP = 390.5 Hz, 1H, PHMes), 4.66 (s, 5H, C5H5), 2.60
(s, 6H, o-CH3 (Mes)), 2.26 (s, 3H, p-CH3 (Mes)); 31P NMR (121.5
MHz, THF-d8, 298 K) δ ꢀ44.0 (d, 1JHP = 390.8 Hz).
E-6a: 1H NMR (300.1 MHz, THF-d8, 298 K) δ 8.41 (d, 2JHP = 18.0
Hz, 1H, PdC(H)Ph), 7.53 (m, 2H, o-H (Ph)), 7.29 (m, 2H, m-H (Ph)),
7.16 (m, 1H, p-H (Ph)), 6.97 (s, 2H, m-H (Mes)), 4.55 (s, 5H, C5H5),
2.53 (s, 6H, o-CH3 (Mes)), 2.31 (s, 3H, p-CH3 (Mes)); 31P NMR (121.5
MHz, THF-d8, 298 K) δ 279.7 (s (br)).
E-6a: 1H NMR (300.1 MHz, C6D6, 298 K) δ 8.51 (d, 2JPH = 18.1 Hz,
3
1H, PdC(H)Ph), 7.68 (d, JHH = 7.9 Hz, 2H, o-H (Ph)), 7.28
(t overlapped with residual benzene protons, 3JHH = 7.9 Hz, 2H, m-H
(Ph)), 7.11 (t, 3JHH = 7.0 Hz, 1H, p-H (Ph)), 6.83 (s, 2H, m-H (Mes)),
4.19 (d, JPH = 2 Hz, 5H, C5H5), 2.55 (s, 6H, o-CH3 (Mes)), 2.19 (s, 3H,
p-CH3 (Mes)); 31P NMR (121.5 MHz, C6D6, 298 K) δ 281.6 (s (br));
13C{1H} NMR (75.45 MHz, C6D6, 298 K) δ 229.6 (d, 2JPC = 25.8 Hz,
Mn-CO), 166.9 (d, 1JPC = 46.8 Hz, PdC(H)Ph), 141.0ꢀ125.8 (Ph þ
Mes), 82.8 (s, C5H5), 22.4 (d, 3JPC = 6.5 Hz, o-CH3 (Mes)), 20.9 (s, p-
CH3 (Mes)).
NMR Monitoring of the Isomerization of Cp(CO)2MndC-
(Me)PHMes (3b) in THF-d8 Solution. The carbene complex 3b (36
mg, 0.1 mmol) was dissolved in THF-d8 (0.5 mL) at room temperature,
and the solution was filtered through a plug of Celite directly into an
NMR tube for monitoring. The composition of the solution was
analyzed by integration of the 1H and 31P NMR signals. The resulting
data are given in Table S2 (see Supporting Information). The transfor-
mation was complete after ca. 1.5 h, giving 6b as the main product (98:2
E/Z ratio).
Z-6a: 1H NMR (300.1 MHz, C6D6, 298 K) δ 7.81 (d, 2JPH = 12.9 Hz,
1H, PdC(H)Ph), 6.98 (t, 3JHH = 7.0 Hz, 1H, m-H (Ph)), 6.90 (d, 3JHH
=
7.0 Hz, 2H, o-H (Ph)), 6.69 (t, 3JHH = 7.0 Hz, 1H, p-H (Ph)), 6.78 (s,
2H, m-H (Mes)), 4.19 (s, 5H, C5H5), 2.53 (s, 6H, o-CH3 (Mes)), 2.13
(s, 3H, p-CH3 (Mes)); 31P NMR (121.5 MHz, C6D6, 298 K) δ 273.0 (s
(br)); 13C{1H} NMR (75.45 MHz, C6D6, 298 K) δ 229.8 (d, 2JPC = 25.6
Hz, Mn-CO), 153.2 (d, 1JPC = 46.8 Hz, PdC(H)Ph), 141.0ꢀ125.8 (Ph
þ Mes), 82.6 (s, C5H5), 21.5 (d, 3JPC = 6.5 Hz, o-CH3 (Mes)), 20.95 (s,
p-CH3 (Mes)).
1
3b: H NMR (300.1 MHz, THF-d8, 298 K) δ 6.94 (s, 2H, m-H
(Mes)), 6.47 (d, 1JHP = 261.5 Hz, 1H, PH), 5.20 (s, 5H, C5H5), 2.97 (d,
3JHP = 13.9 Hz, 3H, MndC-CH3), 2.40 (s, 6H, o-CH3 (Mes)), 2.28 (s,
3H, p-CH3 (Mes)); 31P NMR (121.5 MHz, THF-d8, 298 K) δ 6.6 (dq,
1JHP = 260.8 Hz, 3JHP = 13.5 Hz).
1
4b: H NMR (300.1 MHz, THF-d8, 298 K) δ 6.94 (s, 2H, m-H
Evolution of Cp(CO)2MndC(Me)PHMes (3b) in Benzene
Solution. Complex 3b (35 mg, 0.1 mmol) was dissolved in 0.5 mL of
C6D6, and the solution was filtered through a plug of Celite directly into
an NMR tube for monitoring. The composition of the solution was
analyzed by integration of the 1H and 31P NMR signals. Traces (>1%) of
the η3-phosphinoketene complex 4b could be detected by 31P NMR
after 2ꢀ3 h of reaction. A clean and quantitative isomerization of 3b into
6b (55:45 E/Z ratio) was observed when the solution was kept for 4 days
at room temperature.
(Mes)), 5.64 (d, 1JHP = 390.0 Hz, 1H, PH), 4.76 (s, 5H, C5H5), 2.40 (s,
6H, o-CH3 (Mes)), 2.28 (s, 3H, p-CH3 (Mes)), 1.39 (d, 3JHP = 7.6 Hz,
3H, MndCꢀCH3); 31P NMR (121.5 MHz, THF-d8, 298 K) δ ꢀ24.85
(d, 1JHP = 390.0 Hz).
E-6b: 1H NMR (300.1 MHz, THF-d8, 298 K) δ 7.29 (dq, 2JHP = 15.2
Hz, 3JHH = 8.0 Hz, 1H, PdC(H)CH3), 6.95 (s, 2H, m-H (Mes)), 4.46 (s,
5H, C5H5), 2.47 (s, 6H, o-CH3 (Mes)), 2.30 (s, 3H, p-CH3 (Mes)), 2.14
(dd, 3JHP = 29.8 Hz, 3JHH = 8 Hz, 3H, PdC(H)CH3); 31P NMR (121.5
MHz, THF-d8, 298 K) δ 278.0 (s (br)).
4b: 31P NMR (121.5 MHz, C6D6, 298 K) δ ꢀ22.2 (d, 1JPH = 393 Hz).
1
Crossover Experiment of the Isomerization of d-3a and
3a0 in THF-d8 Solution. Samples of d-3a (25 mg, 0.06 mmol) and 3a0
(26 mg, 0.06 mmol) were dissolved in THF-d8, and the resulting
solution was filtered through a plug of Celite directly into an NMR
tube. The composition of the solution was analyzed by integration of the
1H and 31P NMR signals. After 10ꢀ15 min at room temperature, an H/
D exchange process between the η1-phosphinocarbene complexes was
observed, resulting in a mixture of the four different complexes 3a, d-3a,
3a0, and d-3a0. Further evolution led to a mixture of the corresponding
deuterated and nondeuterated η3-phosphinoketene complexes and
finally to the formation of all possible varieties of η1-phosphaalkene
complexes with an E-selectivity of ca. 90%. Mass spectrometry analysis
(EI) of the resulting mixture revealed the deuteration of p-tolyl
E-6b: H NMR (300.1 MHz, C6D6, 298 K) δ 7.29 ppm (dq over-
2
3
lapped with residual solvent protons, JPH = 15 Hz, JHH = 8 Hz, 1H,
PdC(H)CH3), 6.80 (s, 2H, m-H (Mes)), 4.19 (s, 5H, C5H5), 2.50 (s,
3
3
6H, o-CH3 (Mes)), 2.25 (dd, JPH = 30.1 Hz, JHH = 7.9 Hz, 3H,
PdC(H)CH3), 2.17 (s, 3H, p-CH3 (Mes)); 31P NMR (121.5 MHz,
C6D6, 298 K) δ 278.8 (s (br)); 13C{1H} NMR (75.45 MHz, C6D6, 298
2
1
K) δ 229.7 (d, JPC = 30 Hz, Mn-CO), 161.2 (d, JPC = 54.5 Hz,
PdC(H)CH3), 139.7ꢀ128.4 (Mes), 81.9 (s, C5H5), 22.3 (d, 3JPC = 7.4
2
Hz, o-CH3 (Mes)), 20.9 (s, p-CH3 (Mes)), 19.2 (d, JPC = 14.7 Hz,
PdC(H)CH3).
Z-6b: 1H NMR (300.1 MHz, C6D6, 298 K) δ 6.97 (dq, 2JPH = 18 Hz,
3JPH = 8 Hz, 1H, PdC(H)CH3), 6.78 (s, 2H, m-H (Mes)), 4.15 (s, 5H,
C5H5), 2.48 (s, 6H, o-CH3 (Mes)), 2.16 (s, 3H, p-CH3 (Mes)), 1.71 (dd,
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derivatives (ca. 35% of d-6a0) as well as the presence of a significant
amount of 6a (ca. 45% of d-6a).
thoroughly dried. If not, [8a]Li will be quantitatively formed instead of
[7a]Li.]
3a: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 14.9 (d, 1JPH = 260
Hz); d-3a: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 13.6 (d, 1JPD = 40.2
Hz); 3a0: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 14.8 (d, 1JPH = 259.5
In Situ Formation of [Cp(CO)2MndC(Ph)PMes]Li ([7a]Li)
from the Carbyne Complex [1a]BPh4. A sample of the carbyne
complex [1a]BPh4 (292 mg, 0.5 mmol) was suspended in THF (7 mL)
at ꢀ80 ꢀC, and MesPH2 (76 μL, 0.5 mmol) was added dropwise via
syringe under strirring. The reaction mixture was allowed to warm to
room temperature over a period of 30 min, affording a green solution of
3a. The solution was cooled again to ꢀ80 ꢀC, and n-BuLi (0.65 mL of 1.6
M solution in hexane, 1.0 mmol) was added dropwise, affording a red
solution containing complex [7a]Li as the sole reaction product,
identified by IR (IR (THF): 1882 (vs), 1811 (s), 1772 (s) (νCO)).
Attempted in Situ Formation of [Cp(CO)2MndC(Me)-
PMes]Li. Addition of n-BuLi to a solution of complex 3b in THF led
exclusively and repeatedly to an orange solution of the anionic mono-
carbonyl species [Cp(CO)2Mn(η2-C(O)C(Me)dPMes]Li ([8b]Li).
The anionic dicarbonyl species analogous to [7a]Li, namely,
[Cp(CO)2MndC(Me)PMes]Li, could never be intercepted.
Hz); d-3a0: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 13.5 (d, 1JPD
=
40.2 Hz).
4a: 31P NMR (162.0 MHz, THF-d8, 298 K) δ ꢀ43.7 (d, 1JPH = 400.5
Hz); 4a0: (162.0 MHz, THF-d8, 298 K) δ ꢀ43.9 (d, 1JPH = 401 Hz); d-
4a þ d-4a0: 31P NMR (162.0 MHz, THF-d8, 298 K) δ ꢀ44.0 to ꢀ45.3 (t
overlapped with each other).
E-6a: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 281.4 (s (br)); d-E-
6a: 31P NMR (162.0 MHz, THF-d8, 298 K) δ 280.7 (s (br)); Z-6a: 31
P
NMR (162.0 MHz, THF-d8, 298 K) δ 273.7 (s (br)); d-Z-6a: 31P NMR
(162.0 MHz, THF-d8, 298 K) δ 273.1 (s (br)); E-6a0: 31P NMR (162.0
MHz, THF-d8, 298 K) δ 275.4 (s (br)); d-E-6a: 31P NMR (162.0 MHz,
THF-d8, 298 K) δ 274.5 (s (br)); Z-6a0: 31P NMR (162.0 MHz, THF-
d8, 298 K) δ 267.0 (s (br)); d-Z-6a0: 31P NMR (162.0 MHz, THF-d8,
298 K) δ 266.4 (s (br)).
In Situ Formation of [Cp(CO)2Mn(η2-C(O)C(R)dPMes]Li
([8a]Li, R = Ph; [8b]Li, R = Me) for NMR Analysis. The appro-
priate carbene complex, 3a or 3b (0.15 mmol), was dissolved in 0.5 mL
of THF-d8 at ꢀ20 ꢀC, and 20 mg (0.25 mmol) of t-BuOLi was added.
After warming to room temperature, the solution was filtered through a
plug of Celite directly into an NMR tube. The signals of t-BuOꢀ and t-
BuOH (1H NMR (300.1 MHz, THF-d8, 298 K) δ 3.30 (s (br), OH),
1.19 (s (br), CH3); 13C{1H} NMR (300.1 MHz, THF-d8, 298 K) δ 31.0
(s (br), CH3)) could be easily separated from those of [8a]Li or [8b]Li.
[8a]Li: 1H NMR (300.1 MHz, THF-d8, 298 K) δ 7.76 (d, 4JHP = 4.6
Hz, 2H, m-H (Mes)), 7.04 (m, 2H, m-H (Ph)), 6.86 (m, 1H, p-H (Ph)),
6.53 (m, 1H, o-H (Ph), 6.38 (m, 1H, o-H (Ph)), 4.20 (s, 5H, C5H5), 2.66
(s, 3H, o-CH3 (Mes)), 2.36 (s, 3H, o-CH3 (Mes)), 2.07 (s, 3H, p-CH3
(Mes)); 31P NMR (121.5 MHz, THF-d8, 298 K) δ ꢀ75.4 (s); 13C{1H}
NMR (75.45 MHz, THF-d8, 298 K) δ 267.6 (s (br), PdC-CdO), 233.6
Synthesis of Cp(CO)2Mn(η1-E-P(R)dC(H)Ph (E-6a: R = Ph;
E-6b: R = Me). A catalytic amount of DBU (3 μL, 0.02 mmol) was
added at room temperature to a solution of 3a (85 mg, 0.2 mmol) in
CH2Cl2 (2 mL), causing an immediate color change of the reaction
mixture from green to orange and the quantitative transformation of 3a
(IR (CH2Cl2) 1973 (s), 1910 (s) (νCO)) into the η1-phosphaalkene
complex E-6a (IR (CH2Cl2) 1958 (s), 1900 (s) (νCO)), observed upon
IR monitoring. The solvent was removed under vacuum, and the residue
was dissolved in ether (10 mL), cooled to ꢀ80 ꢀC, and filtered quickly
through a short column of alumina. The solvents were thoroughly
removed under vacuum, leading to 82 mg of E-6a, recovered as an
orange oil (95% yield, ca. 99% purity based on 1H and 31P NMR data).
Similar treatment of 3b (70 mg, 0.2 mmol) gave E-6b as an orange oil
(65 mg, 93% yield, ca. 99% purity based on 1H and 31P NMR data).
Reaction of Cp(CO)2MndC(Ph)PHMes (3a) with Et3N. A
solution of 3a (85 mg, 0.2 mmol) in CH2Cl2 (2 mL) was treated with a
catalytic amount of Et3N (5 μL, 0.035 mmol) at room temperature. After
2ꢀ3 min of stirring, the color of the reaction mixture changed from
green to red-orange, and IR monitoring revealed the quantitative
transformation of 3a (IR (CH2Cl2): 1973 (s), 1910 (s) (νCO)) into
4a (IR (CH2Cl2): 1930 (s) (νCO), 1700 (m) (νCdCdO)). Subsequent
transformation of 4a into the final reaction product E-6a (IR (CH2Cl2):
1958 (s), 1900 (s) (νCO)) was finally observed upon stirring for an
additional 4 h at room temperature.
(s (br), Mn-CO), 150.0 (d, 2JCP = 21.0 Hz, i-C (Ph)), 143.2 (d, 1JCP
=
60.0 Hz, PdC), 140.7 (d, 1JCP = 21.0 Hz, i-C (Mes)), 136.9, 129.8, (s, o,
p-C (Mes)), 125.3ꢀ125.9 (o,m,p-C (Ph)), 120.2 (s, m-C (Mes)), 81.8
(d, JCP = 6.0 Hz, C5H5), 20.0, 20.3 (s, o-CH3 (Mes)), 18.4 (s (br), p-CH3
(Mes)).
[8b]Li: 1H NMR (300.1 MHz, THF-d8, 298 K) δ 6.96 (s, 2H, m-H
(Mes)), 4.33 (s, 5H, C5H5), 2.66 (s, 3H, o-CH3 (Mes)), 2.37 (s, 3H, o-
CH3 (Mes)), 2.05 (s, 3H, p-CH3 (Mes)), 1.57 (d, 3JHP = 8.1 Hz, PdC-
CH3); 31P NMR (121.5 MHz, THF-d8, 298 K) δ ꢀ50.3 (s); 13C{1H}
NMR (75.45 MHz, THF-d8, 298 K) δ 274.2 (s (br), PdC-CdO), 235.6
(s (br), Mn-CO), 146.4 (d, 1JCP = 57.0 Hz, PdC), 141.9 (d, 1JCP = 18.5
Hz, i-C (Mes)), 131.1, 138.3 (s, o,p-C (Mes)), 127.2 (s, m-C (Mes)),
Addition of an excess of Et3N (140 μL, 1 mmol) to the solution of 4a
was found to induce a significant acceleration of the reaction, giving 6a
within 5 min. The latter was isolated in ∼95% yield as described above.
Examination of the crude reaction mixture by NMR showed 6a to form
in a 97:3 E/Z ratio under these reaction conditions.
2
81.7 (s, C5H5), 21.8 (d, JCP = 29.0 Hz, PdC-CH3), 20.2 (s, o-CH3
(Mes)), 19.9 (s (br), p-CH3 (Mes)).
In Situ Formation of [Cp(CO)2Mn(η2-C(O)C(R)dPMes]Li
([8a]Li: R = Ph; [8b]Li: R = Me) and Subsequent Protonation
with [Et3NH]Cl or [NH4]Claq. Complex 3a (42 mg, 0.1 mmol) was
dissolved in THF (3 mL) at ꢀ40 ꢀC and treated with t-BuOLi (15 mg,
0.2 mmol). After stirring for 5 min at ꢀ40 ꢀC, IR monitoring showed
total conversion of 3a into [8a]Li (IR (THF) 1888 (vs) (νCO), 1620
(m) (νCdCdO)). The reaction mixture was allowed to reach room
temperature and was acidified with [Et3NH]Cl (50 mg, 0.35 mmol). An
IR spectra recorded right after acidification showed partial conversion of
[8a]Li into a mixture of 4a (IR (THF) 1932 (s) (νCO), 1725 (m, br)
(νCdCdO)) and 6a (IR (THF) 1959 (s), 1903 (s) (νCO)). A total
conversion into 6a was observed after stirring at room temperature for
an additional 2 h. The solution was then filtered through Celite, and the
solvent was removed under vacuum to afford 6a as an orange oil.
Examination of the residue by NMR showed 6a to form in a 98:2 E/Z
ratio. Similar treatment of [8a]Li with an excess of [NH4]Claq also led to
its quantitative conversion into 6a (98:2 E/Z ratio) upon stirring for ca.
In Situ Formation of [Cp(CO)2MndC(Ph)PMes]Li ([7a]Li)
from 3a and Subsequent Isomerization into [Cp(CO)2Mn(η2-
C(O)C(Ph)dPMes]Li ([8a]Li). A Schlenk tube was charged with
complex 3a (42 mg, 0.1 mmol) and cooled to ꢀ80 ꢀC, and freshly
distilled THF (4 mL) was added. Further addition of n-BuLi (65 μL of
1.6 M solution in hexane, 0.1 mmol) via syringe under stirring was found
to afford a deep red solution of [7a]Li (IR (THF): 1882 (vs), 1811 (s),
1772 (s) (νCO)). The reaction medium was allowed to reach room
temperature and was stirred at 25 ꢀC for one more hour, during which IR
monitoring did not show any significant change. Addition of traces of
water to the solution (for example, simply by contact with a slightly wet
glass pipet or a small piece of paper) resulted in an instantaneous
reaction involving the formation of an orange solution of [8a]Li (IR
(THF) 1888 (vs) (νCO), 1620 (m) (νCdO), 1605 (w), 1561 (w)
(νCdC)). [NOTE: Given that the reaction is extremely sensitive to
the presence of mobile protons, all glassware and solvents should be
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2 h at room temperature. Again, complex 4a was not observed by IR
monitoring during the course of this reaction.
on an Oxford Diffraction Gemini diffractometer (4e), or on a Bruker D8
APEX II diffractometer (12), at 180 K. All calculations were performed
on a PC-compatible computer using the WinGX system.47 Full crystal-
lographic data are given in Table S3 (see Supporting Information). The
structures were solved using the SIR92 program,48 which revealed in
each instance the position of most of the non-hydrogen atoms. All
remaining non-hydrogen atoms were located by the usual combination
of full matrix least-squares refinement and difference electron density
syntheses by using the SHELXL97 program.49 Atomic scattering factors
were taken from the usual tabulations. Anomalous dispersion terms for
Mn and P atoms were included in Fc. All non-hydrogen atoms were
allowed to vibrate anisotropically. All the hydrogen atoms—except H1
in the structure of 3b—were set in idealized position (R3CH, CꢀH =
0.96 Å; R2CH2, CꢀH = 0.97 Å; RCH3, CꢀH = 0.98 Å; C(sp2)ꢀH =
0.93 Å; Uiso 1.2 or 1.5 time greater than the Ueq of the carbon atom to
which the hydrogen atom is attached), and their positions were refined
as “riding” atoms. The hydrogen H1 atom attached to P1 in the structure
of 3b was located from a difference electron density synthesis; its
position and isotropic thermal parameters were refined. Selected bond
distances and angles for complexes 3b, 4c, 4d, 4e, and 12 are given in
Tables S4 to S6 (see Supporting Information).
A similar experiment carried out from complex 3b (35 mg, 0.1 mmol)
led to the quantitative formation of 6b (97:3 E/Z ratio), via [8b]Li (IR
(THF) 1879 (vs) (νCO), 1625 (s) (νCdO)) during 15ꢀ20 min at room
temperature. Here too, the transient formation of 4b could be observed
only upon quenching with [Et3NH]Cl.
Reaction of [Cp(CO)2Mn(η2-C(O)C(Ph)dPMes]Li ([8a]Li)
with MeI. A solution of complex [8a]Li, generated in situ upon addition
of solid t-BuOLi (24 mg, 0.3 mmol) to a solution of 3a (125 mg, 0.3
mmol) in THF (5 mL) at ꢀ40 ꢀC, was cooled to ꢀ80 ꢀC, and MeI (28
μL, 0.45 mmol) was added dropwise. The reaction mixture was slowly
warmed to room temperature, diluted with THF (10 mL), and cooled
again to ꢀ80 ꢀC. The cold solution was filtered rapidly through a short
column of alumina and then evaporated to dryness under vacuum. NMR
analysis of the crude product revealed the presence of the RR/SS
diastereomer of 4e as the only product (31P NMR δ ꢀ7.8). The residue
was extracted with a 1:1 etherꢀhexane mixture (3 ꢁ 10 mL), and the
combined extracts were filtered through Celite, concentrated under
vacuum, and cooled to ꢀ20 ꢀC overnight. The precipitate was separated
by decantation, washed with pentane (2 ꢁ 5 mL), and thoroughly dried
to afford 122 mg of pure RR/SS-4e as a red microcrystalline solid (95%
yield). Analytical and spectroscopy data for the product obtained were
identical to those described above in the synthesis of 4e from [1a]BPh4
and HP(Me)Mes. Crystals of RR/SS-4e suitable for X-ray diffraction
analysis were grown from a diethyl etherꢀhexane mixture, at room
temperature.
’ ASSOCIATED CONTENT
S
Supporting Information. NMR monitoring data of the
b
isomerization of 3a and 3b in THF-d8 solution; perspective views
of complexes 4c and 4d, including selected bond distances and
angles, full crystallographic data for all complexes studied by
X-ray diffraction. This material is available free of charge via the
Internet at http://pubs.acs.org.
Reaction of [Cp(CO)2Mn(η2-C(O)C(Ph)dPMes]Li ([8a]Li)
with Iodine. A solution of complex [8a]Li, generated in situ upon
addition of solid t-BuOLi (16 mg, 0.2 mmol) to a solution of 3a (83 mg,
0.2 mmol) in THF (10 mL) at ꢀ40 ꢀC, was cooled to ꢀ80 ꢀC, and solid
iodine (51 mg, 0.2 mmol) was added under a slow nitrogen flow. This
caused an immediate color change of the solution from orange to deep
red. IR monitoring showed the presence of a mixture of the η3-
phosphinoketene complex 11 (IR (THF): 1945 (s) (νCO), 1736 (m)
(νCdCdO)), along with the η1-phosphaalkene complex 12 (IR (THF):
1963 (s), 1912 (νCO)). The reaction mixture was allowed to warm
slowly to room temperature and then stirred for an additional hour to
afford an orange solution containing 12 as the only product (IR
monitoring). The reaction mixture was diluted with THF (10 mL),
cooled to ꢀ80 ꢀC, and filtered through a short column of alumina. The
volatiles were removed under vacuum. At that stage, 31P NMR monitor-
ing of the crude reaction mixture showed a main signal subsequently
attributed to Z-12 (δ 297.1 ppm, 98%), along with a minor signal
tentatively attributed to E-12 (δ 302.3, ∼2%). The crude reaction
mixture was dissolved in a 1:1 etherꢀhexane mixture (30 mL), filtered
through Celite, concentrated under vacuum, and cooled to ꢀ20 ꢀC
overnight. The solid was separated by decantation, washed with pentane
(2 ꢁ 5 mL), and thoroughly dried to afford 100 mg of pure Z-12 as an
orange microcrystalline material (92% yield). Crystals of Z-12 suitable
for X-ray diffraction analysis were grown from a diethyl etherꢀhexane
mixture, at room temperature.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: noel.lugan@lcc-toulouse.fr.
’ ACKNOWLEDGMENT
Financial support of the CNRS (France) and the Russian
Foundation for Basic Research (grant PICS No. 09-03-91060
Russia/France, CNRS No. 4873) is acknowledged.
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