Angewandte
Chemie
Manganese Complexes
Umpolung of Methylenephosphonium Ions in Their Manganese
Half-Sandwich Complexes and Application to the Synthesis of Chiral
Phosphorus-Containing Ligand Scaffolds**
Dmitry A. Valyaev,* Oleg A. Filippov, Noꢀl Lugan,* Guy Lavigne, and Nikolai A. Ustynyuk
Abstract: Half-sandwich manganese methylenephosphonium
2
=
complexes [Cp(CO)2Mn(h -R2P C(H)Ph)]BF4 were obtained
in high yield through a straightforward reaction sequence
involving a classical Fischer-type manganese complex and
a secondary phosphine as key starting materials. The addition
of various nucleophiles (Nu) to these species took place
Scheme 1. Respective regioselectivities observed in the addition of
nucleophiles to iminium (left), methylenephosphonium salts (center),
and manganese methylenephosphonium complexes (right,
{Mp}=CpMn(CO)2).
regioselectively at the double-bonded carbon center of the
+
=
coordinated methylenephosphonium ligand R2P C(H)Ph to
produce the corresponding chiral phosphine complexes
1
[Cp(CO)2Mn(k -R2P C(H)(Ph)Nu)], from which the phos-
MeOꢀ)[3a,b,4a] at the electropositive phosphorus center
(Scheme 1). In attempts to explore the reactivity of manga-
ꢀ
phines were ultimately recovered as free entities upon simple
irradiation with visible light. The synthetic potential of this
umpolung approach is illustrated herein by the preparation of
novel chiral pincer-type phosphine–NHC–phosphine ligand
architectures.
nese methylenephosphonium complexes [Cp(CO)2Mn-
2
=
(h -R2P C(H)Ph)]BF4, readily available from half-sandwich
MnI Fischer carbenes and secondary phosphines as key
starting materials, we observed that the coordinated methyl-
enephosphonium moiety undergoes regioselective addition of
nucleophiles at the carbon center, thus mimicking the
reactivity mode of iminium salts (Scheme 1; in this scheme
and thereafter {Mp} = Cp(CO)2Mn). This key observation
inspired the development of an unconventional synthetic
methodology toward a wide variety of organophosphorous
derivatives, as illustrated herein by a simple route to a novel
family of chiral pincer-type phosphine–NHC–phosphine
ligands (NHC = N-heterocyclic carbene).
I
minium salts are of utmost importance in organic syn-
thesis,[1] owing in particular to their key role as intermediates
in many enantioselective organocatalytic transformations of
carbonyl compounds.[2] However, the synthetic utility of their
phosphorus analogues, methylenephosphonium ions,[3,4]
remains limited to
a
few examples of [2+2][4h,j] and
[2+4][4b,e,g] cycloaddition, the ene reaction,[4b,e] electrocyclic
cyclization with an arene ring,[4e,f] stereoselective rearrange-
ment to give phosphaalkenes,[4d] and the phospha-Stork
reaction.[4l] Whereas the reactivity of iminium salts is gov-
erned by the strong electrophilicity of the carbon atom
(Scheme 1), the methylenephosphonium salts undergo regio-
selective addition of nucleophiles (Nu = Fꢀ, Clꢀ, and
Earlier investigations in our laboratories had previously
+
ꢁ ꢀ
established that the cationic manganese carbyne [{Mp}
C
Ph]BPh4 ([2]BPh4) reacts sequentially with diphenylphos-
phine and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to give
the h1-phosphinocarbene complex 3a, which undergoes facile
CO insertion to form the h3-phosphinoketene complex 4a
(see structures in Scheme 2).[5] We have now found that
further protonation of 4a with HBF4·OEt2 leads to the
quantitative formation of the cationic complex [5a]+ with
a h2-methylenephosphonium ligand (Scheme 2).[6,7] This reac-
tion is a rare example of controlled CO deinsertion from
a ketene ligand in a mononuclear complex, a reaction
[*] Dr. D. A. Valyaev, Dr. N. Lugan, Dr. G. Lavigne
Laboratoire de Chimie de Coordination du CNRS (UPR 8241)
205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4 (France)
and
Universitꢀ de Toulouse
UPS, INPT, 31077 Toulouse Cedex 4 (France)
E-mail: dmitry.valyaev@lcc-toulouse.fr
previously only explicitly induced by chloride abstraction
2
= =
within the complex [(tBu2PCH2PtBu2)(Cl)Ir(h -Ph2C C O)]
+ [8,9]
=
to afford [(tBu2PCH2PtBu2)(CO)Ir CPh2] .
Dr. O. A. Filippov, Prof. Dr. N. A. Ustynyuk
A. N. Nesmeyanov Institute of Organoelement Compounds
(INEOS), Russian Academy of Sciences
A DFT study of the protonation-induced CO deinsertion
in 4a with CF3OH as a model of a strong acid revealed that
the reaction occurs through the initial formation of a hydro-
gen-bonded adduct involving the oxygen atom of the ketene
28 Vavilov Street, GSP-1, B-334, Moscow (Russia)
[**] Financial support from the CNRS and the PICS grant 4873 (CNRS)/
09-03-91060 (RFBR) is gratefully acknowledged. O.A.F. is grateful to
the Russian Scientific Foundation (grant 14-13-00801) for financial
support of DFT calculations. D.A.V. thanks the IDEX-UNITI for
a starting grant.
ligand, followed by proton transfer to the Cb atom with
+
ꢀ
concomitant Ca Cb bond cleavage to afford [5a] (see the
Supporting Information for full details). The calculated TS
energy of 3.8 kcalmolꢀ1 (SMD method, CH2Cl2) is consistent
with the experimental observation of a rapid transformation
4a![5a]+ at ꢀ808C.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
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