A direct, modular, and efficient construction of the P-C-P structural motif through coupling of manganese carbyne complexes with phosphines

Article abstract of DOI:10.1002/chem.201304239

Easily available carbyne complexes of manganese were used as a source of carbyne fragments in an unconventional synthesis of backbone-substituted diphosphinomethanes and cyclic P-ylides upon coupling with secondary or tertiary phosphines, respectively, followed by demetalation under mild conditions. Copyright

Full text of DOI:10.1002/chem.201304239

DOI: 10.1002/chem.201304239
Communication
&
Organophosphorus Chemistry
A Direct, Modular, and Efficient Construction of the PꢀCꢀP
Structural Motif through Coupling of Manganese Carbyne
Complexes with Phosphines
Dmitry A. Valyaev,[a, b] Stꢀphanie Bastin,[a, b] Kamil I. Utegenov,[c] Noꢁl Lugan,*[a, b]
Guy Lavigne,[a, b] and Nikolai A. Ustynyuk[c]
We first observed that the MnI phosphoniocarbene complex
[Mp=C(Me)PPh2H]BCl4 [2a]BCl4 (here and thereafter, Mp=
Cp(CO)2Mn) generated in situ upon addition of PPh2H to the
methylcarbyne precursor [MpꢁCMe)]BCl4, [1Me]BCl4 at low tem-
perature,[1b,d,e] can uptake a second molecule of phosphine to
give the cationic complex [4aa-H]BCl4 featuring a newly
formed pendant PꢀCꢀP structural motif containing ligand re-
sulting formally from the coupling of the carbyne fragment
and two secondary phosphines (Scheme 1). Deprotonation of
the latter upon purification on an alumina column afforded
a neutral diphosphine complex 4aa in a nearly quantitative
yield.
Abstract: Easily available carbyne complexes of manga-
nese were used as a source of carbyne fragments in an
unconventional synthesis of backbone-substituted diphos-
phinomethanes and cyclic P-ylides upon coupling with
secondary or tertiary phosphines, respectively, followed by
demetalation under mild conditions.
To date, transition-metal phosphoniocarbene complexes LnM=
+
C(R)PR’3 , which are easily available from electrophilic carbyne
precursors and phosphines,[1,2] have found only limited applica-
tion in synthetic chemistry, with the notable exception of
Grubbs type ruthenium phosphoniocarbene complexes being
among the most active initiators
The [2a]BCl4!4aa transformation is likely to proceed via
the formation of an elusive semi-ylide intermediate,
[3aa]BCl4,[5] resulting from the nucleophilic attack of the
in olefin metathesis.[2,3] Yet, a fur-
ther exploitable aspect of their
reactivity rests on the strong
electrophilicity of their carbenic
atom—inherent to the presence
of the adjacent positively
charged phosphorus fragment—
favoring further coupling with
incoming nucleophiles.[4] Based
ꢀ
Scheme 1. Coupling of [MpꢁCMe)]BCl4 with two equivalents of secondary phosphines (BCl4 anions omitted for
clarity). Conditions: i) CH2Cl2,ꢀ808C. ii) Warming to RT. iii) Deprotonation with Al2O3 (4aa) or Et3N (4ab). iv) HB-
F4·OEt2 (2 equiv), hn, CH2Cl2. v) hn, CH2Cl2.
on this, we report herein a con-
ceptually new route to back-
bone-substituted diphosphino-
methane and cyclic P-ylide deriv-
atives using a fully controlled stepwise carbyne/phosphine/
phosphine coupling involving MnI phosphoniocarbene com-
plexes as key reactive species.
second PPh2H molecule onto the highly electrophilic carbene
atom, the latter undergoing a proton migration from the phos-
phonium fragment to the central carbon atom with concomi-
tant metal coordination to form the protonated diphosphine
complex [4aa-H]BCl4, ultimately giving 4aa upon deprotona-
tion. Though the key irreversible transformation [3aa]BCl4!
[4aa-H]BCl4 may proceed through the stepwise formation of
a manganese cis-hydride species by 1,3-H shift followed by re-
ductive elimination,[6] the occurrence of a direct concerted 1,2-
proton migration from the phosphonium moiety to the ylidic
carbon remains an alternate mechanistic possibility.
[a] Dr. D. A. Valyaev, S. Bastin, N. Lugan, G. Lavigne
Laboratoire de Chimie de Coordination du CNRS (UPR 8241)
205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France)
Fax: (+33)561553003
E-mail: noel.lugan@lcc-toulouse.fr
[b] Dr. D. A. Valyaev, S. Bastin, N. Lugan, G. Lavigne
Universitꢀ de Toulouse, UPS, INPT, 31077 Toulouse Cedex 4 (France)
[c] K. I. Utegenov, Prof. Dr. N. A. Ustynyuk
Stepwise addition of molar equivalents of PPh2H followed by
PCy2H to [1Me]BCl4 at ꢀ808C led in the end to a mixture of two
diphosphine complexes 4aa and 4ab in approximately 1:2.5
ratio (Scheme 1), finally isolated in 18% and 49% yield, respec-
tively (see the Supporting information for details of the 4aa/
A. N. Nesmeyanov Institute of Organoelement Compounds (INEOS)
Russian Academy of Sciences
28 Vavilov str., GSP-1, B-334, Moscow (Russia)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304239.
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Communication
4ab separation). Gratifyingly, the inversion of the order of
phosphines addition—that is, PCy2H followed by PPh2H—al-
lowed to optimize the heterocoupling process affording 4ab
in 93% isolated yield (4aa/4ab ratio in the crude product was
ca. 1:50). Interestingly, regardless of the order of phosphines
addition, the diphosphine ligand in 4ab was systematically
found coordinated to the metal through the PPh2 moiety,
which is consistent with the occurrence of a proton migration
in [3ab]BCl4 from the less basic phosphonium site. The struc-
ture of 4ab featuring the pendant PCy2 termination was con-
firmed by single-crystal XRD (Figure 1).[7]
Table 1. Photochemical demetalation of MnI complexes 6, 4aa, and
[4ab-H]BF4.[a]
Complex
Solvent
Additive
Time
Product
Yield [%]
6
6
toluene
THF
–
–
4 h
30 min
PPh3
PPh3
Mp(THF)
PPh3·BH3
Mp(SMe2)
PPh3
traces
60[b]
60[b]
95[c]
76[c]
92[c]
85[c]
19[c]
88[c]
90[c]
97[c]
[d]
6
THF
BH3·SMe2
1 h
6
6
4aa
4aa
4aa
[4ab-H]BF4
CH2Cl2
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
–
10 min
45 min
4 h
40 min
15 min
10 min
[e]
CH2Cl2
–
BH3·SMe2
HBF4·OEt2
PPh3
5aa
[f]
5aa[h]
5aa[i]
[g]
–
5ab[i]
[a] Photolysis of 8–12 mm solution of MnI phosphine complex in 125 mL
of the appropriate solvent with immersed medium pressure Hg lamp
(150 W) using Pyrex filter jacket at 15–208C for the indicated time period.
[b] Yield estimated by IR spectroscopy in the n(CO) region. [c] Yield of the
isolated product. [d] 1.25 equiv. [e] 1% vol. [f] 2.5 equiv. [g] 2.0 equiv.
[h] After deboration with DABCO. [i] After deprotonation with 2m NaOHaq.
mately 30 min led to an equilibrium mixture of 6, PPh3 and
Mp(THF). This equilibrium could be easily shifted to the right
upon addition of BH3·SMe2 as a phosphine scavenger, to afford
PPh3·BH3 and Mp(SMe2) in good yield. This represents the first
evidence for a selective PPh3 ligand photodissociation upon
bulk photolysis of Mp(PR3) complexes.[9] We were pleased to
observe that the irradiation of 6 in CH2Cl2 caused its very rapid
destruction with liberation of PPh3 and formation of an insolu-
ble metal-containing product. As a working hypothesis, we
considered that this decomplexation process could include
a CO dissociation step followed by a fast decomposition of the
resulting solvent adduct Cp(CO)(PPh3)Mn(CH2Cl2).[10] However,
the competitive dissociation of PPh3 (like in THF) and photo-
Figure 1. A perspective view of 4ab (ellipsoids at the 30% probability level).
The selectivity observed in PPh2H/PCy2H coupling can be
reasonably ascribed to the different electrophilic and steric
properties of the phosphoniocarbene intermediates. Unlike
[2a]BCl4 showing the uptake of both phosphines at very low
temperature (ꢀ808C), the reaction of the less electrophilic and
more bulky [2b]BCl4 with PPh2H takes place only between
ꢀ20–08C, leading to the rapid [3ab]BCl4![4ab-H]BCl4
rearrangement. The lower selectivity observed in the reaction
of [2a]BCl4 with PCy2H at ꢀ808C could be explained by a
partial scrambling of the semi-ylide complex [3ab]BCl4
under such reaction conditions ([2a]BCl4+PCy2HÐ[3ab]BCl4Ð
[2b]BCl4+PPh2H) to form some PPh2H rapidly trapped by com-
plex [2a]BCl4.
Having in mind the aim to exploit this original carbyne/
phosphine/phosphine coupling for the synthesis of valuable
chemicals, we next focused on means to efficiently liberate the
resulting diphosphines from the robust manganese complexes
(4!5, Scheme 1). Inspired by the high yield photochemical lib-
eration of cyclopentadienes[8] or allene[6b] from cymantrene de-
rivatives, we first investigated the behavior of the model com-
plex Mp(PPh3) (6) under visible light irradiation in different sol-
vents (Table 1).
chemical electron transfer from 6 to the solvent,[11] followed by
+
degradation of Mp(CH2Cl2)[12] and 6 , respectively, could also
C
be implicated in the demetalation process.
Application of the most effective CH2Cl2 demetalation proto-
col to the diphosphine complex 4aa appeared to be disap-
pointedly sluggish, giving 5aa in low yield after prolonged ir-
radiation time. We ascribe the drastic difference in behavior
between 4aa and 6 to the primary transformation of the
former into a mixture of chelate diphosphine complexes
Cp(CO)Mn(k2-PPh2CHMePPh2) (see the Supporting information),
undergoing demetalation with low rate and chemoselectivity.
To our delight, in situ treatment of 4aa with borane or acid
providing protection of the pendant phosphine moiety toward
coordination, allowed a rapid and nominal liberation of 5aa.
Finally, 5ab could also be quantitatively liberated from the iso-
lated [4ab-H]BF4 upon irradiation, without any additive.
The overall two-step preparation of 5aa and 5ab highlights
a novel unconventional route to backbone-substituted diphos-
phinomethanes[13] from simple and readily available building
blocks,[14] which could complement the set of traditional syn-
thetic methods for this type of ligands in terms of simplicity
and modularity.
Complex 6 appeared to be stable upon prolonged irradia-
tion in toluene. Conversely, its irradiation in THF after approxi-
Beyond the utilization of simple secondary phosphines, we
were prompted to extend the scope of this coupling process
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Communication
Acknowledgements
Financial support from CNRS and the PICS grant 4873 (CNRS)/
09-03-91060 (RFBR) is gratefully acknowledged. D. A. V. thanks
CNRS for a temporary researcher position.
Keywords: carbyne complexes · demetalation · diphosphines ·
phosphoniocarbene complexes · phosphorus ylides
Scheme 2. Coupling of carbyne complex [1Ph]BPh4 with tertiary diphosphines
(BPh4ꢀ anions omitted for clarity).
to tertiary diphosphines, in an intramolecular manner, first
using dppm as a model substrate (see Scheme 2).[15] The reac-
tion of phenylcarbyne [1Ph]BPh4 with dppm was found to pro-
ceed at ꢀ808C in CH2Cl2 to give a red solution of the thermally
unstable intermediate [7]BPh4, which underwent a spontaneous
demetalation above ꢀ208C producing insoluble brown man-
ganese decomposition products and a yellow solution of the
cationic cyclic semi-ylide [8]BPh4, isolated in 83% yield as a sol-
vate with one CHCl3 molecule. Following the same protocol
and now using our newly prepared diphosphine 5ab
(Scheme 1), the unsymmetrical cyclic semi-ylide [8ab]BPh4, fi-
nally constructed in a fully controlled and highly convergent
manner from two different carbynes and two different secon-
dary phosphine moieties, was obtained in 90% yield. Both
compounds were fully characterized, including single-crystal
XRD (see Figure 2 for [8ab]BPh4 and Figure 30S in the Sup-
porting information for [8]BPh4·CHCl3).
[1] For the trapping of carbyne complexes with external phosphines, see:
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N. Lugan, G. Lavigne, N. A. Ustynyuk, Organometallics 2011, 30, 2318–
2332.
[2] For intramolecular migration of metal-coordinated phosphine to the
carbyne ligand, see: a) P. E. Romero, W. E. Piers, R. McDonald, Angew.
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[7] CCDC-957227 (4ab), CCDC-957228 ([8]BPh4·CHCl3), and CCDC-957229
([8ab]BPh4) contain the supplementary 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
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Figure 2. A perspective view of [8ab]BPh4 (ellipsoids at the 30% probability
level, BPh4ꢀ anion is not shown).
[9] Bulk photolysis of structurally closed (h5-C5H4Me)Mn(CO)2(PPh3) by visi-
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In conclusion, we have demonstrated that readily available
electrophilic manganese carbyne complexes[14] can serve as
stoichiometric carbyne synthons being potentially useful for
organophosphorus chemistry.[16] We are now exploring the ap-
plication scope of such carbyne/phosphine/phosphine cou-
pling processes and its possible development in asymmetric
version.
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[10] The early formation of Cp(CO)Mn(PPh3)2 was observed upon photolysis
of 6 in CH2Cl2 showing CO photolability in this solvent (see the Sup-
porting information).
[14] For the preparation of manganese carbyne complexes deriving from in-
dustrially produced Mp(CO), see: E. O. Fischer, G. Besl, F. R. Kreissl in
Synthetic Methods of Organometallic and Inorganic Chemistry, Vol. 7, (Ed.:
W. A. Herrmann), George Thieme, Stuttgart, 1997, pp. 208–209 and the
Ref. [1e].
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diphosphoranes from dppm and CS2 was recently reported: a) S. Stallin-
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Commun. 2007, 510–512; b) C. Reitsamer, S. Stallinger, W. Schuh, H. Ko-
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3514.
[16] During the last decade nucleophilic carbyne (alkylidyne) complexes
were shown to be excellent homogeneous catalysts in highly challeng-
ing alkyne metathesis processes. For a recent comprehensive review on
their application, see: A. Fꢃrstner, Angew. Chem. 2013, 125, 2860–2887;
Angew. Chem. Int. Ed. 2013, 52, 2794–2819.
[11] The photooxidation of some organometallic compounds containing Cp
and/or CO and/or PR3 ligands in chlorinated solvents (CH2Cl2, CHCl3,
CCl4) is well documented, see for representative examples: a) O. Traver-
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[12] a) P.-F. Yang, G. K. Yang, J. Am. Chem. Soc. 1992, 114, 6937–6938;
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[13] Compound 5aa was prepared from Ph2PLi and 1,1-dichloroethane in
80% yield, see: C.-L. Lee, Y.-P. Yang, S. J. Rettig, B. R. James, D. A. Nelson,
M. A. Lilga, Organometallics 1986, 5, 2220–2228. Non-substituted ana-
logue of 5ab - Ph2PCH2PCy2 was prepared in 75% yield by the reaction
of Ph2PCH2Li with Cy2PCl, see: T. E. Wolff, L. P. Klemann, Organometallics
1982, 1, 1667–1670.
Received: October 30, 2013
Published online on January 30, 2014
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