Stepwise formation of σ-alkynyl, vinylidene, and vinylphosphonium complexes of manganese(I)

Article abstract of DOI:10.1021/om050146c

Reaction of methyl propiolate with the diphosphinomethanide complex [Mn(CO)₄{(PPh₂)₂CH}] (1) produces simultaneously the insertion of the alkyne into the C-H bond, giving [Mn(CO)₄{(PPh₂)₂C-C(H)=C(CO₂Me)H}] (2), and the deprotonation of the alkyne mediated by the diphosphinomethanide ligand, affording the σ-alkynyl derivative fac-[Mn(C≡C-CO ₂Me)(CO)₃(dppm)] (3). Protonation of 3 with HBF ₄ at 200 K affords the corresponding vinylidene compound fac-[Mn(C=C(H)CO₂Me)(CO)₃(dppm)]BF₄ (5), which, on raising the temperature to 243 K, undergoes the spontaneous insertion of the vinylidene ligand into a Mn-P bond.

Full text of DOI:10.1021/om050146c

2542
Organometallics 2005, 24, 2542-2545
Stepwise Formation of σ-Alkynyl, Vinylidene, and
Vinylphosphonium Complexes of Manganese(I)
Javier Ruiz,*,† Roberto Quesada,† Maril´ın Vivanco,† Eduardo E. Castellano,‡ and
Oscar E. Piro§
Departamento de Quı´mica Orga´nica e Inorga´nica, Facultad de Qu´ımica, Universidad de
Oviedo, 33071 Oviedo. Spain, Instituto de Fı´sica de Sao Carlos, Universidade de Sao Paulo,
C.P. 369, 13560 (SP), Brazil, and Departamento de F´ısica, Facultad de Ciencias Exactas,
Universidad Nacional de la Plata and Instituto IFLP (CONICET), C.C. 67,
1900 La Plata, Argentina
Received March 1, 2005
Scheme 1
Summary: Reaction of methyl propiolate with the diphos-
phinomethanide complex [Mn(CO)4{(PPh2)2CH}] (1) pro-
duces simultaneously the insertion of the alkyne into the
C-H bond, giving [Mn(CO)4{(PPh2)2C-C(H)dC(CO2-
Me)H}] (2), and the deprotonation of the alkyne mediated
by the diphosphinomethanide ligand, affording the
σ-alkynyl derivative fac-[Mn(CtC-CO2Me)(CO)3(dppm)]
(3). Protonation of 3 with HBF4 at 200 K affords the
corresponding vinylidene compound fac-[Mn(CdC(H)-
CO2Me)(CO)3(dppm)]BF4 (5), which, on raising the tem-
perature to 243 K, undergoes the spontaneous insertion
of the vinylidene ligand into a Mn-P bond.
Introduction
The chemistry of transition metal σ-alkynyl complexes
has attracted much attention from organometallic chem-
ists since a long time ago.1 The special nature of the
metal-carbon bond in these systems, the capability of
transforming alkynyl complexes to other organometallic
derivatives such as vinylidenes, and the fascinating
properties of some akynyl complexes, which range from
optical nonlinearity to electrical conductivity, are the
origin of that interest.2 Transition metal σ-alkynyl
complexes are usually prepared by reaction of halo
complexes with alkynilating agents, such as alkynyl
compounds of alkali metals, copper(I), or trimethylstan-
nyl.2 The synthesis of these complexes can also be
carried out by direct reaction of the halo complexes with
terminal alkynes, using an external base as deproto-
nating agent.3 Interestingly, in a few cases deprotona-
tion of the alkyne is achieved by a ligand of the starting
complex acting as an internal base. This is the case in
the hydride complexes [(NP3)RhH] (NP3 ) tetradentate
ligand N(CH2CH2PPh2)3) and cis-[FeH2(P-P)2] (P-P )
R2PCH2CH2PR2; R ) Me, Et, nPr), which react with
phenyl acetylene to give the alkynyl complexes [(NP3)-
RhCtCPh]4 and trans-[Fe(CtCPh)2(P-P)2],5 respec-
tively, through the elimination of H2. In relation with
this, here we describe the synthesis of the σ-alkynyl
complex of manganese(I) fac-[Mn(CtC-CO2Me)(CO)3-
(dppm)] by direct reaction of the diphosphinomethanide
complex [Mn(CO)4{(PPh2)2CH}] with methyl propiolate,
which supposes an unprecedented way of forming
σ-alkynyl derivatives. The stepwise transformation of
this compound into vinylidene and vinylphosphonium
derivatives is also described throughout this paper.
Results and Discussion
Treatment of the diphosphinomethanide complex
[Mn(CO)4{(PPh2)2CH}] (1) with an excess of methyl
propiolate in refluxing toluene gives a mixture of
compounds [Mn(CO)4{(PPh2)2C-C(H)dC(CO2Me)H}] (2)
and fac-[Mn(CtC-CO2Me)(CO)3(dppm)] (3) in similar
ratio (Scheme 1), which are separated by column chro-
matography. Compound 2 contains a vinyl-substituted
diphosphinomethanide ligand resulting from the inser-
tion of the alkyne into a P2C-H bond of 1, whereas the
σ-alkynyl complex 3 can be assumed to be formed
through substitution of a CO ligand by the alkyne
followed by a deprotonation of the alkyne mediated by
the diphosphinomethanide ligand (see Scheme 1).
* To whom correspondence should be addressed. E-mail: jruiz@
fq.uniovi.es.
† Universidad de Oviedo.
‡ Universidade de Sao Paulo.
§ Universidad Nacional de la Plata and Instituto IFLP (CONICET).
(1) Nast, R. Coord. Chem. Rev. 1982, 47, 89.
(2) For a recent review covering the synthesis, properties, and
application in materials science of metal alkynyls, see: Long, N. J.;
Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586.
(3) For examples of manganese(I) carbonyl complexes with σ-bonded
alkynyl ligands, see: Miguel, D.; Riera, V. J. Organomet. Chem. 1985,
293, 379.
(4) Bianchini, C.; Laschi, F.; Ottaviani, F.; Peruzzini, M.; Zanello,
P. Organometallics 1988, 7, 1660.
(5) Field, L. D.; George, A. V. J. Organomet. Chem. 1993, 454, 217.
10.1021/om050146c CCC: $30.25 © 2005 American Chemical Society
Publication on Web 04/14/2005

Notes
Organometallics, Vol. 24, No. 10, 2005 2543
Scheme 2
Figure 1. ORTEP drawing of compound 3, showing only
one of the two conformations adopted by the CO2Me group.
Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): C6-C7 1.208(2), Mn-C7
1.980(2), Mn-P1 2.3060(4), Mn-P2 2.3165(4); C7-C6-C4
173.6(2), Mn-C7-C6 174.7(1), P1-Mn-P2 72.84(2), P1-
C8-P2 95.51(7).
alkenyl phosphonium residue arising from the insertion
of the vinylidene ligand into a manganese-phosphorus
bond of the transient vinylidene complex 5. This process
leads to a coordination vacancy in the coordination
sphere of the metal, which is occupied by the oxygen
atom of the carboxylate group. The 31P{1H} NMR
spectrum of 4 displays two doublets (63.1 and 26.4 ppm,
2J(PP) ) 34 Hz) according to the presence of two
1
The H and 13C NMR spectra of 2 show resonances
consistent with the alkenyl substituent on the diphos-
phinomethanide ligand. Moreover, its nature is strongly
supported by the X-ray structure elucidation of the
closely related fac-[Mn(CNtBu)(CO)3{(PPh2)2C-C(H)d
C(CO2Me)H}], obtained as the sole product in the
reaction of fac-[Mn(CNtBu)(CO)3{(PPh2)2CH}] with meth-
yl propiolate.6 On the other hand, the IR spectrum of 3
exhibits a typical pattern for a fac-tricarbonyl complex
1
nonequivalent phosphorus atoms. The H NMR spec-
trum shows a new doublet of doublets resonance (6.45
ppm, 3J(PH) ) 25, 4J(PH) ) 7 Hz) for the vinylic proton
incorporated into the complex.
The structure of 4 was definitively elucidated by X-ray
crystallography (Figure 2). The manganese atom is in
an octahedral arrangement, being part of two fused five-
membered metallacycles: MnO(4)C(4)C(6)C(7), which
is essentially planar, and MnP(1)C(8)P(2)C(7), which is
bent at manganese. The C(6)-C(7) bond length (1.342-
(3) Å) of the inserted vinylidene is in agreement with a
double-bond character.
in the νCO region (2016(vs), 1950(s), 1935(s) cm-1
)
together with a weak band corresponding to the CtC
stretching vibration (2093 cm-1). The presence of the
1
newly formed dppm ligand is corroborated by the H
NMR spectrum of 3, which gives signals for the two
nonequivalent methylenic hydrogens in the appropriate
region (4.80(m) and 4.37(m) ppm). The solid-state mo-
lecular structure of 3 was determined by X-ray analysis
(Figure 1). The crystal structure reveales the presence
of the alkynyl ligand, with C6-C7 (1.208(2) Å) and Mn-
C7 (1.9801(16) Å) bond lengths typical of a triple and
single bond, respectively.7 It is worth remarking that
formation of 3 as described above represents a rare
synthetic approach for σ-alkynyl derivatives from a
terminal alkyne and a complex containing the depro-
tonating agent as a ligand (diphosphinomethanide),
which remains attached to the metal after proton
abstraction (dppm).
Efforts to extend this reaction to nonactivated termi-
nal alkynes such as HCtCPh have been unfruitful,
because much decomposition occurs, and only an insig-
nificant amount of the target σ-alkynyl derivative was
spectroscopically detected in the reaction mixture.
Addition of 1 equiv of HBF4 to a solution of 3 in CH2-
Cl2 at room temperature leads to the quantitative
formation of 4 (Scheme 2). Complex 4 features a new
Figure 2. ORTEP drawing of the cationic complex 4.
Hydrogen atoms of phenyl and methyl groups are omitted
for clarity. Selected bond distances (Å) and angles (deg):
C6-C7 1.342(3), Mn-C7 2.033(2), Mn-P1 2.3156(6), Mn-
O4 2.095(2); C6-C7-P2 120.9(2), Mn-C7-P2 119.0(1),
Mn-C7-C6 116.3(2), P1-C8-P2 108.2(1).
(6) Ruiz, J.; Quesada, R.; Riera, V.; Castellano, E.; Piro, O. Orga-
nometallics 2004, 23, 175.
(7) Val´ın, M. L.; Moreiras, D.; Solans, X.; Miguel, D.; Riera, V. Acta
Crystallogr. Sect. C, Cryst. Struct. Commun. 1986, C42, 977.

2544 Organometallics, Vol. 24, No. 10, 2005
Notes
The intermediate vinylidene compound fac-[Mn(Cd
C(H)CO2Me)(CO)3(dppm)]BF4 (5) (see Scheme 2), re-
sulting from protonation of the alkynyl ligand, was not
observed when performing the reaction at room tem-
perature. However, the addition of HBF4 at 200 K to a
NMR sample of 4 instantaneously changes the color of
the solution from yellow to red and allows spectroscopic
detection of the vinylidene complex 5. Thus the 1H NMR
spectrum showed the presence of the CdCH- proton
as a new signal at 5.9 ppm, whereas the 31P{1H} NMR
spectrum gave a singlet signal at 11.5 ppm, showing
that phosphorus atoms remain equivalent. Below 243
K, 5 is the unique species detected, and above this
temperature formation of 4 took place readily and
quantitatively. Although a structure for 5 consisting of
the η2-alkyne tautomer of the proposed vinylidene
derivative cannot be totally excluded, it seems to be
unlikely on the basis of similar results previously
reported,13 as well us considering the absence of P-H
coupling in the CdCH- proton resonance.
Migratory insertion is an important reaction pathway
for transition metal vinylidene complexes, with several
examples being known of insertion of vinylidene ligands
into metal-carbon σ-bonds,8 and also into metal-
nitrogen,9 metal-oxygen,10 and metal-halide bonds.11
However, although a plethora of vinylidene complexes
containing phosphines as ancillary ligands have been
described, with some of them displaying important
catalytic applications,12 only a few examples of vi-
nylidene insertion into a metal-phosphorus bond have
been reported.13 This phosphorus-carbon bond forming
process is of great interest, as it represents a potential
catalyst deactivation pathway for vinylidene complex-
catalyzed organic transformations. It must be noted that
related insertion of allenylidene14 and alkyne15 ligands
into metal-phoshorus bond has been described recently.
There is no doubt that oxygen coordination is a
driving force in the insertion reaction and product
stabilization; thus insertion proceeds giving exclusively
the Z alkenyl isomer, in which coordination through the
carboxylate fragment is allowed. In fact, when trying
to perform the vinylidene formation and subsequent
vinylphosphonium stabilization by protonation reaction
of σ-alkynyl complexes lacking carboxylate substituents
as in fac-[Mn(CtCPh)(CO)3(dppm)], only decomposition
products were observed.
alkyne into a C-H bond, formation of a σ-alkynyl
complex by intramolecular alkyne deprotonation, and
insertion of a vinylidene ligand into a metal-phospho-
rus bond.
Experimental Section
General Remarks. All reactions and manipulations were
performed under a atmosphere of dry nitrogen by using
standard Schlenk techniques. Solvents were distilled over
appropriate drying agents under dry nitrogen prior to use.
Compound [Mn(CO)4{(PPh2)2CH}] (1) was prepared as de-
scribed elsewhere.16
Synthesis of 2 and 3. A solution containing 1 (0.20 g, 0.364
mmol) and methyl propiolate (162 µL, 1.82 mmol) in toluene
(20 mL) was stirred at reflux temperature for 5 h. The color
changed from yellow to red. The solvent was then evaporated
to dryness and the remaining solid chromatographed through
an alumina column (activity degree III). Elution with CH2Cl2/
hexane (1:1) allowed the separation of compound 2 (0.069 g,
30%) from the first band (yellow) and compound 3 (0.055 g,
25%) from the second band (yellow). 2: Anal. (%) Calcd for
C33H25MnO6P2: C 62.47, H 3.97. Found: C 62.13, H 4.12. IR
1
(CH2Cl2): ν 2076 (s), 1995 (vs), 1967 (m) cm-1 (CO). H NMR
(300 MHz, CDCl3): δ 7.83-7.46 (21H, m), 4.84 (1H, d, 3JHH
)
14), 3.60 (3H, s). 31P{1H} NMR (121.5 MHz, CDCl3): δ 2.8 (br).
3: Anal. (%) Calcd for C32H25MnO5P2: C 63.38, H 4.16.
Found: C 63.56, H 4.28. IR (CH2Cl2): ν 2093 (w) cm-1 (CtC),
2016 (vs), 1950 (s), 1935 (s) cm-1 (CO). 1H NMR (300 MHz,
CDCl3): δ 7.71-7.20 (20H, m), 4.84 (1H, m), 4.37 (1H, m), 3.22
(3H, s). 31P{1H} NMR (121.5 MHz, CDCl3): δ 21.6 (br).
Synthesis of 4. To a solution of 3 (0.05 g, 0.082 mmol) in
10 mL of CH2Cl2 was added tetrafluoroboric acid/diethyl ether
complex (54%, 15 µL, 0.109 mmol) with stirring. The solvent
was then evaporated, and the oil obtained was washed with
diethyl ether (3 × 5 mL). Recrystallization in CH2Cl2/hexane
provided 4 as yellow crystals; yield 0.057 g (90%). Anal. (%)
Calcd for C32BF4H26MnO5P2: C 55.36, H 3.77. Found: C 55.54,
H 3.65. IR (CH2Cl2): ν 2033 (vs), 1966 (s), 1918(s) cm-1 (CO).
1H NMR (300 MHz, CD2Cl2): δ 7.99-7.40 (20H, m), 6.45 (1H,
3
4
2
dd, JPH ) 25, JPH ) 7, CdCH), 5.40 (1H, ddd, JPH ) 16,
2JPH ) 10, JHH ) 5, CH2), 3.90 (1H, td, JPH ) 15, JHH ) 5,
2
2
2
CH2), 3.59 (3H, s, CO2CH3). 31P{1H} NMR (121.5 MHz,
2
2
CDCl3): δ 63.5 (d, JPP ) 34, MnPPh2), 26.4 (d, JPP ) 34,
PPh2).
NMR Detection of 5. To a NMR sample of 3 (0.02 g, 0.033
mmol) in CD2Cl2 was added tetrafluoroboric acid/diethyl ether
complex (54%, 10 µL, 0.109 mmol) at 200 K. Keeping a low
temperature, NMR experiments were performed. 1H NMR (400
MHz, CD2Cl2): δ 7.50 (20H, br), 5.90 (1H, br, CdC(H)(CO2-
Me)), 4.85 (2H, m, P2CH2), 3.18 (3H, br, CO2CH3). 31P{1H}
NMR (161.99 MHz, CD2Cl2): δ 11.48 (s, (PPh2)2).
In conclusion, up to three rare reaction pathways are
observed in the treatment of the diphosphinomethanide
complex 1 with methyl propiolate: insertion of the
Crystallography. Diffraction data were collected on an
Enraf-Nonius KappaCCD diffractometer at 100 K. The struc-
tures were solved by direct methods and refined using full-
matrix least-squares on F2 with all non-hydrogen atoms
anisotropically refined. Crystal data for 3 (C32H25MnO5P2): Mr
) 604.4, triclinic, space group P1h, a ) 9.50925(1) Å, b )
17.3418(2) Å, c ) 18.1765(2) Å, R ) 69.7090(5)°, â ) 88.5567-
(5)°, γ ) 89.6242(5)°, V ) 2810.52(5) Å3, Z ) 4, Fcalcd ) 1.433
g/cm-3, F(000) ) 1248, Mo KR radiation (λ ) 0.71073 Å)R,
crystal dimensions 0.36 × 0.24 × 0.20 mm. For 9477 reflections
with [I > 2σI] R indices: R1 ) 0.0320 and wR2 ) 0.0939. For
all 11005 unique reflections R indices: R1 ) 0.0394 and wR2
(8) (a) Bianchini, C.; Peruzzini, M.; Zanobini, F.; Frediani, P.;
Albinati, A. J. Am. Chem. Soc. 1991, 113, 5453. (b) Proulx, G.;
Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 9802. (c) Wiedemann,
R.; Steiner, P.; Scha¨fer, M.; Werner, H. J. Am. Chem. Soc. 1993, 115,
9864. (d) Beckhaus, R.; Sang, J.; Trixie, W.; Ganter, B. Organometallics
1996, 15, 1176. (e) Kerstin, I.; Weberndo¨rfer, B.; Werner, H. Organo-
metallics 2000, 19, 3145.
(9) Chevrier, B.; Weiss, R. J. Am. Chem. Soc. 1981, 103, 2899.
(10) Daniel, T.; Mahr, N.; Braun, T.; Werner, H. Organometallics
1993, 12, 1475.
(11) O’Connor, J. M.; Hiibner, K.; Merwin, R.; Pu, L. J. Am. Chem.
Soc. 1995, 117, 8861.
(12) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.
(13) (a) Bianchini, C.; Meli, A.; Peruzzini, M.; Zanobini; F.; Zanello,
P. Organometallics 1990, 9, 241. (b) Bianchini, C.; Meli, A.; Peruzzini,
M.; Zanobini, F.; Bruneau, C.; Dixneuf, P. H. Organometallics 1990,
9, 1155. (c) Bianchini, C.; Innocenti, P.; Meli, A.; Peruzzini, M.;
Zanobini, F.; Zanello, P. Organometallics 1990, 9, 2514.
(14) Werner; H.; Wiedemann, R.; Laubender, M.; Windmu¨ller, B.;
Steiner, P.; Gevert, O.; Wolf, J. J. Am. Chem. Soc. 2002, 124, 6966.
(15) (a) Chin, C. S.; Park, Y.; Kim, J.; Lee, B. J. Chem. Soc., Chem.
Commun. 1995, 1495. (b) Allen, A.; Lin, W. Organometallics 1999, 18,
2922. (c) Tanase, T.; Begun, R. A. Organometallics 2001, 20, 106.
(16) Ruiz, J.; Riera, V.; Vivanco, M.; Garc´ıa-Granda, S.; Garc´ıa-
Ferna´ndez, A. Organometallics 1992, 11, 4077.

Notes
Organometallics, Vol. 24, No. 10, 2005 2545
) 0.1016. Crystal data for 4 (C32H26BF4MnO5P2): Mr ) 694.22,
monoclinic, space group P21/c, a ) 10.2407(2) Å, b ) 16.6566-
(4) Å, c ) 18.3683(4) Å, â ) 95.650(1)°, V ) 3117.96(12) Å3, Z
) 4, Fcalcd ) 1.479 g/cm-3, F(000) ) 1416, Mo KR radiation (λ
) 0.71073 Å)R, crystal dimensions 0.44 × 0.24 × 0.20 mm. For
4655 reflections with [I > 2σI] R indices: R1 ) 0.0373 and
wR2 ) 0.0945. For all 5480 unique reflections R indices: R1
) 0.0472 and wR2 ) 0.1010.
Acknowledgment. This work was supported by the
Spanish Ministerio de Ciencia y Tecnolog´ıa (PGE and
FEDER funding, Project BQU2003-01011) and by
FAPESP, Brazil.
Supporting Information Available: Crystallographic
data of 3 and 4 (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
OM050146C