Reactions of [Ru(CO)2(PPh3)3] with alkynylphosphonium salts: A phosphinoallene complex

Article abstract of DOI:10.1021/om900621v

[Ru(CO)₂(PPh₃)₃] reacts with either HC=CCH₂Br or [HC=CCH₂SMe₂]Br to provide the σ-allenyl complex [Ru(CH=C=CH₂)Br(CO)₂(PPh ₃)₂]; however, with [HC=CCH₂PPh₃]Br, the salt [Ru(γ²-H₂C=C=CHPPh₃)(CO) ₂(PPh₃)₂]Br is obtained, which may be described as a complex of a phosphonioallene on the basis of crystallographic data for [Ru(γ²-H₂C=C=CHPPh₃)(CO) ₂(PPh₃)₂]₂Br(PF₆) and a comparison of spectroscopic data with those for the simple allene complex [Ru(γ²-H₂C=C=CH₂)(CO) ₂(PPh₃)₂].

Full text of DOI:10.1021/om900621v

5568 Organometallics 2009, 28, 5568–5574
DOI: 10.1021/om900621v
Reactions of [Ru(CO)2(PPh3)3] with Alkynylphosphonium Salts: A
Phosphinoallene Complex
Wee Han Ang,† Richard L. Cordiner,† Anthony F. Hill,*,† Tamara L Perry,† and
†,‡
€
Jorg Wagler
†Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra,
‡
ACT, Australia, and Institut fu€r Anorganische Chemie, Technische Universitat Bergakademie Freiberg,
Freiberg, Germany
€
Received July 16, 2009
[Ru(CO)2(PPh3)3] reacts with either HCtCCH2Br or [HCtCCH2SMe2]Br to provide the
σ-allenyl complex [Ru(CHdCdCH2)Br(CO)2(PPh3)2]; however, with [HCtCCH2PPh3]Br, the salt
[Ru(η2-H2CdCdCHPPh3)(CO)2(PPh3)2]Br is obtained, which may be described as a complex of
a phosphonioallene on the basis of crystallographic data for [Ru(η2-H2CdCdCHPPh3)(CO)2-
(PPh3)2]2Br(PF6) and a comparison of spectroscopic data with those for the simple allene complex
[Ru(η2-H2CdCdCH2)(CO)2(PPh3)2].
Introduction
bi- and polymetallic tricarbido (C3) bridged complexes.
Although a large number of such complexes have been
prepared, the limiting factor is that mononuclear propargy-
lidyne reagents are only known for molybdenum and
tungsten.4-7 We have therefore turned our attention to other
reagents that might serve as “C3” building blocks. One such
candidate is the phosphonium salt [HCtCCH2PPh3]Br, the
organometallic chemistry of which is essentially unexplored,
other than its hydroruthenation by [RuHCl(CO)(PPh3)3]
to provide [Ru(CHdCHCH2PPh3)Br(CO)(PPh3)2]þ,8 and
in cobalt-mediated Diels-Alder cyclizations.9 Herein we
report the reactions of this salt and related propargylic elec-
trophiles with the zerovalent ruthenium complex [Ru(CO)2-
(PPh3)3],10 none of which afford the anticipated γ-func-
tionalized alkynyl complexes.
Since the synthesis of the first allenylidene complex
[Ru(dCdCdCPh2)(PMe3)2(η-C5H5)]þ (Scheme 1),1 the vast
majority of allenylidene syntheses rely on variants of Sele-
gue’s propargyl alcohol dehydration protocol, with most
examples being based on divalent ruthenium.2 One situation
where this approach has not met with success is in the
synthesis of complexes of the parent allenylidene itself
LnMdCRdCβdCγH2 from HCtCCH2OH.3 That is not to
say that the protocol fails, per se. Rather, the resulting parent
allenylidenes are highly reactive and prone to binuclear
decomposition routes or the scavenging of nucleophilic
species by the highly electrophilic and exposed Cγ. We have
previously reported at length4 on the use of silylpropargyli-
dyne complexes LnMtC;CtC-SiMe3 as precursors for
(5) Fischer, E. O.; Kalder, H. J.; Koehler, F. H. J. Organomet. Chem.
1974, 81, C23.
*To whom correspondence should be addressed. E-mail: a.hill@anu.
edu.au.
(6) (a) Hart, I. J.; Hill, A. F.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1989, 2261. (b) Foreman, M. R. St.-J.; Hill, A. F.; White, A. J. P.;
Williams, D. J. Organometallics 2003, 22, 3831. (c) Cabioch, J.-L.; Dossett,
S. J.; Hart, I. J.; Pilotti, M. U.; Stone, F. G. A. J. Chem. Soc., Dalton Trans.
1991, 519. (d) Bruce, G. C.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
J. Chem. Soc., Dalton Trans. 1992, 2685. (e) Bruce, G. C.; Stone, F. G. A.
Polyhedron 1992, 11, 1607. (f) Carr, N.; Dossett, S. J.; Stone, F. G. A. J.
Organomet. Chem. 1991, 413, 223. (g) Cabioch, J. L.; Dossett, S. J.; Hart, I.
J.; Pilotti, M. U.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1991, 519. (h)
Dossett, S. J.; Hart, I. J.; Pilotti, M. U.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1991, 511. (i) Dossett, S. J.; Hart, I. J.; Pilotti, M. U.; Stone, F. G. A.
1990, 3489. (j) Dossett, S. J.; Hart, I. J.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1990, 3481. (k) Etches, S. J.; Hart, I. J.; Stone, F. G. A. 1989, 2281.
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Organomet. Chem. 2002, 641, 134. (b) Schwenzer, B.; Fischer, H. J.
Organomet. Chem. 2003, 667, 16. (c) Bruce, M. I.; Cole, M. L.; Gaudio,
M.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2006, 691, 4601.
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Rawles, H. M. J. Chem. Soc., Chem. Commun. 1995, 369. (b) Hill, A. F. J.
Chem. Soc., Chem. Commun. 1995, 741. (c) Liu, S. H.; Xia, H.; Wan, K. L.;
Yeung, R. C. Y.; Hu, Q. Y.; Jia, G. J. Organomet. Chem. 2003, 683, 331.
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Hengst, C. Synlett 2006, 3247.
(1) Selegue, J. Organometallics 1982, 1, 217.
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Met. Rev. 2006, 50, 81. (d) Bruneau, C.; Dixneuf, P. H. Angew. Chem., Int.
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Organometallics 2005, 24, 3043. (d) Dewhurst, R. D.; Hill, A. F.; Smith,
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r
pubs.acs.org/Organometallics
Published on Web 08/13/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 18, 2009 5569
Scheme 1. Reactions of 1 with CtC and CtP Triply Bonded
Reagents (L = PPh3)a
The reaction of [HCtCCH2PPh3]Br with 1 takes a differ-
ent course. The product isolated after (attempted) bromide/
PF6 metathesis is not the desired salt [RuH(CtCCH2-
PPh3)(CO)2(PPh3)2]PF6 (2 PF6) as suggested by various in-
3
consistencies in the elemental microanalytical data (which
correspond to the double salt 22 Br PF6 (CH2Cl2)2) and
3
3
3
spectroscopic data. Encouragingly, the FAB-mass spectrum
for the product did include an isotopic cluster with the gross
composition attributable to the anticipated molecular ion 2þ
in addition to peaks due to loss of phosphine and/or carbonyl
ligands. However, in the 1H NMR spectrum, the only signal
to low frequency of SiMe4 was a curiously structured triplet
(Figure S1, Supporting Information) at δH -0.32 for which
the coupling was not resolved. The chemical shift, the small
magnitude of the coupling to phosphorus and the integral
(2H) were each inconsistent with this being due to a hydride
ligand. A second resonance was observed at 6.89 ppm as a
doublet of triplets that integrates for one proton.
The 31P{1H} spectrum (CD2Cl2) was uninformative other
than to confirm the presence of two weakly coupled (J=5.5Hz,
i.e., remote) phosphorus environments (A2B: δP =48.2 (2P),
9.44(1P)). The complex gradually decomposes in CDCl3 (δP=
48.1, 9.4) to provide cct-[RuCl2(CO)2(PPh3)2] (δP=18.0), which
is in contrast to the behavior of complexes of the form
[RuH(CtCR)(CO)2(PPh3)2], which react with chloroform to
provide [RuCl(CtCR)(CO)2(PPh3)2]12 (typically δP ≈ 22-24).
Among the characterizational data, the following are note-
worthy: The infrared spectrum includes two νCO absorptions
for the cis-Ru(CO)2 unit at 2003 and 1939 cm-1 (CH2Cl2).
The relative intensities were not, however, consistent with an
octahedral geometry, but rather suggest an intercarbonyl
angle of about 110°.13 The C-H oxidative addition pro-
duct [RuH(CtCC6H4Me-4)(CO)2(PPh3)2]12a has νCO
=
2026, 1988 cm-1 (νCtC=2113 νRuH=1894 cm-1), while the
π-adducts [Ru(η2-PhCtCR)(CO)2(PPh3)2] have νCO=1963,
1875 (R=Ph)11a or 1978, 1917 (R=CtCPh) cm-1 11b,11c
The
.
data for the product in the present study are intermediate
between these values and, therefore, do not offer definitive
insight, in part because the electronic effect of the phosphonium
group is not easy to quantify a priori. Conspicuously absent
from the IR spectrum are any bands that might be confidently
assigned to either νRuH or νCtC modes. The aromatic region of
the 13C{1H} spectrum includes two sets of four resonances for
the two phosphine environments, with one set showing the
virtual triplet patterns indicative of a trans-Ru(PPh3)2 geome-
try. Two carbonyl resonances are observed for the chemically
inequivalent carbonyl ligands. One appears as a simple triplet
a Reagents and Conditions: (a) HCtCR; (b) PtCMes*, Mes* = C6Ht2-
Bu3-2,4,6; (c) PhCtCPh, Δ; (d) PhCtCR (R = Ph, CtCPh, 25 °C);
(e) (μ-C6){W(CO)2(L0)}2 (L0 = HB(pz)3, HB(pzMe2)3, pz = pyrazol-1-yl;
(f) S(C2H4SCtCMe)2.
Results and Discussion
Roper’s complex [Ru(CO)2(PPh3)3] (1) features an elec-
tron-rich metal center and a labile phosphine ligand, which is
readily replaced by internal alkynes, diynes, dimetallaocta-
tetraynes, and phosphaalkynes (Scheme 1).10,11 In the case of
terminal alkynes and diynes, however, oxidative addition
(C-H activation) typically proceeds to provide hydri-
do-alkynyl complexes, albeit reversibly.4a,12
2
(δC=203.5, JPC=13.9 Hz), however, the second resonance
appears as an unresolved double-triplet (δC = 204.7 ppm).
A third triplet resonance appears at δC 213.1 such that un-
ambiguous assignment is not possible.
Prior to the eventual structural characterization of 32 Br
3
3
PF6(CH2Cl2)2 (vide infra), the variously plausible formulations
included an allene-type coordination of the “H2CdCdCH-
PPhþ3 ” ligand. Accordingly, in an attempt to interrogate the
spectroscopic data for “2þ” from an informed perspective, the
parent allene complex [Ru(η2-H2CdCdCH2)(CO)2(PPh3)2]
(4) was prepared. The ethene10 and maleic anhydride14 com-
plexes [Ru(η2-alkene)(CO)2(PPh3)2] have been reported as
(11) (a) Hill, A. F.; Schultz, M.; Willis, A. C. Organometallics 2004,
23, 5729. (b) Alcock, N. W.; Hill, A. F.; Melling, R. P.; Thompsett, A. R.
Organometallics 1993, 12, 641. (c) Hill, A. F.; Rae, A. D.; Schultz, M.;
Willis, A. C. Organometallics 2007, 26, 1325. (d) Bedford, R. B.; Hill, A. F.;
Wilton-Ely, J. D. E. T.; Francis, M. D.; Jones, C. Inorg. Chem. 1997, 36,
5142. (e) Hill, A. F.; Rae, A. D.; Schultz, M.; Willis, A. C. Organometallics
2004, 23, 81. (f) Hill, A. F.; Schultz, M.; Willis, A. C. Organometallics 2005,
24, 2027. (g) Dewhurst, R. D.; Hill, A. F.; Rae, A. D.; Willis, A. C.
Organometallics 2005, 24, 4703.
(12) (a) Bedford, R. B.; Hill, A. F.; Thompsett, A. R.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Chem. Commun. 1996, 1059. (b) Bartlett, M.
J.; Hill, A. F.; Smith, M. K. Organometallics 2005, 24, 5795. (c) Dewhurst,
R. D.; Hill, A. F.; Smith, M. K. Angew. Chem., Int. Ed. 2004, 43, 476.
(13) Beck, W.; Melnikoff, A.; Stahl, R. Chem. Ber. 1966, 99, 3721.
(14) (a) Rickard, C. E. F.; Roper, W. R.; Wright, L. J.; Young, L. J.
Organomet. Chem. 1989, 364, 391. (b) Burrell, A. K.; Clark, G. R.; Rickard,
C. E. F.; Roper, W. R.; Ware, D. C. J. Organomet. Chem. 1990, 398, 133.

5570 Organometallics, Vol. 28, No. 18, 2009
Ang et al.
resulting from simple displacement of a sterically labilized
phosphine of 1. This approach proved successful for the
synthesis of 4 from 1 and allene, however, the complex 4 was
found to be considerably more labile than the ethene complex
and attempts to obtain elemental microanalytical data were
thwarted by the inevitable contamination of 4 with the dioxy-
gen complex [Ru(η-O2)(CO)2(PPh3)2] (5),10 which in other
work we have recently structurally characterized.11a Never-
theless, so long as an atmosphere of allene is maintained over a
solution of 4, full spectroscopic data could be obtained.
Although dissociation of allene from 4 occurs on the chemical
time scale, it is not manifest in any broadening of the 1H NMR
spectra of 4 and the allene present (CD2Cl2: δH=4.73 ppm),
that is, exchange between free and coordinated allene is slow on
the 1H NMR time scale (at 300 MHz). Distinct resonances are
observed at 0.37 ppm (cf -0.35 for 3þ) for the metallacyclic
methylene group and at 4.95 and 5.46 ppm corresponding to
the exometallacyclic methylene unit. Infrared data for 4 include
Scheme 2. Synthesis of Allene and Allenyl Complexes (L = PPh3)a
two strong carbonyl absorbances (1974, 1908 cm-1, kCK
=
15.20 N cm-1), which when compared to those of 3þ would
seem to suggest that the phosphonio group does indeed trans-
mit its electronic influences to some extent to the ruthenium
center. The 13C{1H} NMR spectrum of 4 included resonances
due to the three carbon nuclei of the allene at δC = 170.4, 108.1,
and 10.87. The resonance at 170.4 displayed coupling to
phosphorus (7.3 Hz), while that at 10.87 is noticeably broa-
dened, but not sufficiently as to allow resolution of the coupling
to phosphorus. These data taken together would appear to
substantiate the formulation of 3þ as a π-complex of a phos-
honioallene (Scheme 2), a supposition that was eventually
confirmed by a crystallographic study.
The complex was found to crystallize as the double salt
32 Br PF6(CH2Cl2)2, indicating only partial counteranion
metathesis had occurred. The results of the study are sum-
marized in Figure 1.
a Reagents and condition: (a) H2CdCdCH2; (b) O2; (c) [HCt
CCH2L]Br; (d) HCtCCH2Br; (e) [HCtCCH2SMe2]Br, -SMe2.
3
3
extent in the ratio of the free to coordinated “double” bonds
of the allene. This ratio currently ranges from 1.04-1.11
(mean value 1.07) with the mean bond lengths for free
Although alternative resonance forms might be enter-
tained (Chart 1), the metrical parameters associated with
the RuCC interaction are certainly consistent with a con-
tribution from a phosphonio allene complex (aTb).
Complex 3þ is the first structurally characterized phos-
phonioallene complex in which the double bond remote from
phosphorus coordinates and accordingly structural data for
comparison are not available. Two previous examples of
phosphonioallene complexes have been reported15 albeit via
different strategies, however, in each case it is the CdC bond
to which phosphorus is attached that coordinates to either
platinum15a or rhodium (Scheme 3).15b
˚
and coordinated CdC bonds being 1.309 and 1.404 A,
respectively. Although the ratio of free and coordinated
CdC bonds in 3þ (1.059) falls within this range, C3-C4
(1.421(4) A) lies toward the long end of the range, while
˚
C(4)-C(5) is well beyond the range for the “free” CdC bond
˚
of coordinated allenes (1.288-1.322 A) and the C(3)-C-
(4)-C5) angle of 139.9(3)° is smaller than the typical range
for allene complexes (145-158°). Each of these features may
be in part attributed to the steric bulk of the phosphonio
group, but might also be taken as indicative of stronger
allene binding. Thus, it might appear that the various
resonance contributions that involve mesomeric participa-
tion of phosphorus and reduce the bond multiplicity assume
some importance, steric responses notwithstanding. It might
be reasonably inferred that because the allene complex 4 is
labile, while 32 Br PF6(CH2Cl2)2 is readily isolable, the
Structural data for parent allene complexes (where steric
factors will be minimal) are tabulated (Table S1)16 and the
strength of binding might be expected to be reflected to some
(15) Bennett, M. A.; Kwan, L.; Rae, A. D.; Wenger, E.; Willis, A. C.
J. Chem. Soc., Dalton Trans. 2002, 226. (b) Esteruelas, M. A.; Lahoz, F. J.;
Martin, M.; Onate, E.; Oro, L. A. Organometallics 1997, 16, 4572.
(16) Cambridge Crystallography Data Centre Conquest, January
2009 database release. (a) Ipaktschi, J.; Rooshenas, P.; Dulmer, A.
Eur. J. Inorg. Chem. 2006, 1456. (b) Okamoto, K.; Kai, G.; Yasuoka, N.;
Kasai, N. J. Organomet. Chem. 1974, 65, 427. (c) Briggs, J. R.; Crocker, C.;
McDonald, W. S.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1981, 121. (d)
Diversi, P.; Ingrosso, G.; Immirzi, A.; Porzio, W.; Zocchi, M. J. Organomet.
Chem. 1977, 125, 253. (e) Bruce, M. I.; Hambley, T. W.; Rodgers, J. R.;
Snow, M. R.; Wong, F. S. Aust. J. Chem. 1982, 35, 1323. (f) Lentz, D.;
Willemsen, S. Organometallics 1999, 18, 3962. (g) Lundquist, E. G.;
Folting, K.; Streib, W. E.; Huffman, J. C.; Eisenstein, O.; Caulton, K. G. J.
Am. Chem. Soc. 1990, 112, 855. (h) Pu, J.; Peng, T.-S.; Arif, A. M.; Gladysz,
J. A. Organometallics 1992, 11, 3232. (i) Werner, H.; Schwab, P.; Mahr, N.;
Wolf, J. Chem. Ber. 1992, 125, 2641.
3
3
latter has the “allene” bond more strongly bound and these
alternative bonding descriptions presumably play a role in
this respect.
The isolation of a salt of 3þ raises questions as to how this
final complex eventuates. The precursor [HCtCCH2PPh3]-
Br is prone to propargylic rearrangement to the allenylpho-
sphonium salt [H2CdCdCHPPh3]Br, but only in the pre-
sence of very strong bases (KOtBu). Special care was taken
to ensure that the salt [HCtCCH2PPh3]Br, which was
used, was scrupulously free of the isomer [H2CdCd
CHPPh3]Br within spectroscopically determinable limits

Article
Organometallics, Vol. 28, No. 18, 2009 5571
Scheme 3. Syntheses of Phosphonioallene Complexes15
Figure 1. Molecular geometry of the complex 3þ in a crystal of
the double salt 32 Br PF6(CH2Cl2)2 (100 K, 60% displacement
ellipsoids, phenyl groups simplified). Selected bond lengths
Chart 2. Trihapto (a) Enynyl/butatrienyl and (b) Allenyl/pro-
pargyl Ligands (Nu = a Generic Nucleophile)
3
3
˚
(A) andangles(deg): Ru1-C21.918(3), Ru1-C11.936(3), Ru1-
C4 2.068(3), Ru1-C3 2.161(3), Ru1-P3 2.3572(8), Ru1-P2
2.3634(8), P1-C5 1.777(3), C3-C4 1.421(4), C4-C5 1.342(4),
C2-Ru1-C1 105.95(13), C2-Ru1-C4 114.25(12), C1-Ru1-
C3 100.61(13), C4-Ru1-C3 39.19(12), C4-Ru1-P3 91.15(9),
C3-Ru1-P3 91.49(10), C4-Ru1-P2 89.99(9), C3-Ru1-P2
91.82(10), P3-Ru1-P2 176.00(3), C4-C3-Ru1 66.87(17),
C5-C4-C3 139.9(3), C5-C4-Ru1 146.1(2), C3-C4-Ru1
73.95(18), C4-C5-P1 123.6(3).
Chart 1. Canonical Forms To Describe the Bonding in 3þ
(1H and 31P NMR) before stoichiometric treatment with 1.
Thus, we may say with considerable confidence that the
propargylic rearrangement is mediated by the metal center.
Scheme 4 suggests various pathways that might plausibly
lead to the final product. Points to consider include: (i)
acetylenic C-H activation is likely to be a reversible tangent
to the process, based on the observation that the butadiynyl
complex [RuH(CtCCtCH)(CO)2(PPh3)2] (from 1 and
butadiyne) reversibly dissociates butadiyne to provide “Ru-
(CO)2(PPh3)2”, which may be trapped with dioxygen or
tolane as [Ru(η2-O2)(CO)2(PPh3)2] or [Ru(η2-PhCtCPh)-
(CO)2(PPh3)2], respectively.12b (ii) The typical acidity of pro-
pargylic protons would be enhanced by coordination to a
Lewis acidic metal center facilitating intramolecular proton
transfers. (iii) The relief of strain around ruthenium upon
ultimately arriving at the final product 3þ presumably con-
tributes to the thermodynamics.
or via the metal center (oxidative β-Ru-H elimination, A0)
to provide a hydrido-allenyl complex that undergoes reduc-
tive coupling to afford 3þ. Path B involves multiple phos-
phine migrations, which might be expected to require
sterically encumbered transition states and intermediates
to be traversed and is perhaps less likely. Path C invokes
the weak basicity of liberated triphenylphosphine to assist
in intermolecular proton transfer from the γ-carbon to the
R-carbon. The synthesis of “Ru(CO)2(PPh3)2” in the absence
of “free” triphenylphosphine has not been achieved17 and
so we are not in a position to explore path C. Path D is
(17) Analogues with more sterically demanding phosphine ligands
are, however, available: (a) Ogasawara, M.; Macgregor, S. A.; Streib,
W. E.; Folting, K.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc.
1995, 117, 8869. (b) Ogasawara, M.; Macgregor, S. A.; Streib, W. E.; Folting,
K.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1996, 118, 10189.
Path A envisages multiple hydrogen shifts to initially
provide a γ-phosphonio vinyl carbene which might trans-
fer the β-hydrogen either directly to the carbene carbon (A00)

5572 Organometallics, Vol. 28, No. 18, 2009
Scheme 4. Mechanistic Conjecture on the Formation of 3þ (L = PPh3)
Ang et al.
perhaps the most attractive, proceeding via phosphine
dissociation through a parent allenylidene that undergoes
migratory insertion followed by nucleophilic attack at an
η3-allenyl ligand, however, we are able in this case to provide
strong circumstantial evidence to the contrary.
The reactions of trihapto-allenyl (propargyl, Chart 2) li-
gands with nucleophiles have been extensively explored by
both Casey18 and Wojcicki19 and, in general, nucleophiles
are found to attack at the central carbon. In contrast,
trihapto-enynyl complexes in this system, for which some
analogy might be entertained (Chart 2), react with nucleo-
philes at the metal center, indicating metallacycle hemilabi-
lity.11b,20 Further insights that argue against route D follow
from the reactions of 1 with alternative phosphine-free
propargylic electrophiles.
We have briefly investigated the analogous reaction of 1
with [HCtCCH2SMe2]Br given that C-S bonds are typi-
cally more fragile than C-P bonds and that SMe2 should be
a good leaving group. It transpired that this was indeed the
case, with the product devoid of the SMe2 component being
the allenyl complex [Ru(CHdCdCH2)Br(CO)2(PPh3)2] (6)
rather than the hydrido-allenylidene isomer [RuH(dCdC=
CH2)(CO)2(PPh3)2]Br (7 Br) implicated in route D. The
3
complex [Ru(CHdCdCH2)Br(CO)2(PPh3)2] (6) is also the
product of the reaction of 1 directly with HCtCCH2Br.
Thus, because 1 equiv of PPh3 is liberated in any reactions of
1, its presence during the formation of 6 does not compete
with bromide ion, that is, no 3þ is observed to form during
these reactions.
The formulation of 6 rests on spectroscopic and elemental
microanalytical data and an imprecise crystallographic ana-
lysis21 that nevertheless confirms the connectivity and SMe2
elimination. Other than those associated with the allenyl
ligand, the spectroscopic data for 6 do not require comment.
The 1H NMR spectrum includes two resonances for the
(18) (a) Casey, C. P.; Boller, T. M.; Samec, J. S. M.; Reinert-Nash, J.
R. Organometallics 2009, 28, 123. (b) Casey, C. P.; Boller, T. M.; Kraft, S.;
Guzei, I. A. J. Am. Chem. Soc. 2002, 124, 13215. (c) Casey, C. P.; Chung, S.
Inorg. Chim. Acta 2002, 334, 283. (d) Casey, C. P.; Brady, J. T. Organo-
metallics 1998, 17, 4620. (e) Casey, C. P.; Nash, J. R.; Yi, C. S.; Selmeczy, A.
D.; Chung, S.; Powell, D. R.; Hayashi, R. K. J. Am. Chem. Soc. 1998, 120,
722. (f) Casey, C. P.; Selmeczy, A. D.; Nash, J. R.; Yi, C. S.; Powell, D. R.;
Hayashi, R. K. J. Am. Chem. Soc. 1996, 118, 6698.
(19) (a) Schuchart, C.; Willis, A.; Wojcicki, A. J. Organomet. Chem.
1992, 11, 3232. (b) Schuchart, C. E.; Willis, R. R.; Wojcicki, A. J.
Organomet. Chem. 1992, 424, 185. (c) Jolly, P. W.; Pettit, R. J. Organomet.
Chem. 1968, 12, 491. (d) Arryantne, J. K. P.; Green, M. L. H J. Organomet.
Chem. 1964, 1, 90. (e) Daniel, K. L.; Furilla, J. L.; Wojcicki, A. J.
Organomet. Chem. 2002, 655, 192. (f) Wojcicki, A. Inorg. Chem. Commun.
2002, 5, 82. (g) Blosser, P. W.; Calligaris, M.; Schimpff, D. G.; Wojcicki, A.
Inorg. Chim. Acta 2001, 320, 110. (h) Graham, J. P.; Wojcicki, A.; Bursten,
B. E. Organometallics 1999, 18, 837. (i) Wojcicki, A. New J. Chem. 1997,
21, 733. (i) Baize, M. W.; Blosser, P. W.; Plantevin, V.; Schimpff, D. G.;
Gallucci, J. C.; Wojcicki, A. Organometallics 1996, 15, 164. (j) Baize, M.
W.; Furilla, J. L.; Wojcicki, A. Inorg. Chim. Acta 1994, 223, 1. (k) Wojcicki,
A.; Shuchart, C. E. Coord. Chem. Rev. 1990, 105, 35.
3
4
HR (δH = 5.70, JPH = 3.3, JHH = 6.6, see Scheme 2 for
designations) and the two chemically equivalent Hγ protons
(δH = 3.34; 5JPH = 4.9, 4JHH = 6.6 Hz). These data compare
well with those for the complex [Ru(CHdCdCH2)(CO)2(η-
C5H5)] reported by Wojcicki (δH=5.37(t), 3.99 (d), 4JHH
=
6.4 Hz).19 In the 13C{1H} NMR spectrum, a triplet at δC=
86.6 (2JPC=12.8) may be assigned to the ruthenium-bound
carbon atom, while the terminal carbon of the allenyl ligand
gives rise to a singlet at δC=61.0. The central carbon atom
of the σ-allenyl ligand gives rise to a resonance at 205.5 ppm
in a low field region typical of the central carbon of allenes,
including σ-allenyls.19 Again, Wojcicki’s complex [Ru(CHd
CdCH2)(CO)2(η-C5H5)] serves as a benchmark with reso-
nances being observed at δC = 206.1, 63.1, and 58.4 ppm.19b
(20) (a) Hill, A. F.; Melling, R. P. J. Organomet. Chem. 1990, 396,
C22. (b) Hill, A. F.; Melling, R. P.; Thompsett, A. R. J. Organomet. Chem.
1991, 402, C8. (c) Hill, A. F.; Harris, M. C. J.; Melling, R. P. Polyhedron
1992, 11, 781.
(21) White, A. J. P.; Williams, D. J. private communication.

Article
Organometallics, Vol. 28, No. 18, 2009 5573
Scheme 5. Attack by Nucleophiles and Metal Centers at Pro-
pargylic Electrophiles
protocol.10a The propargylic electrophiles HCtCCH2Br. [HCt
CCH2SMe2]Br and [HCtCCH2PPh3]Br were obtained com-
mercially (Aldrich).
Synthesis of [Ru(η2-H2CdCdCHPPh3)(CO)2(PPh3)2]2Br
3
PF6 (32 Br PF6). Propargyl triphenylphosphonium bromide
3
3
(0.13 g, 0.35 mmol) was added to a solution of [Ru(CO)2-
(PPh3)3] (1: 0.22 g, 0.23 mmol) in dichloromethane (10 mL).
After stirring for 30 min, ammonium hexafluorophosphate
(0.038 g, 0.23 mmol) was added followed by toluene (10 mL).
The mixture was concentrated to ca. 10 mL under dynamic
vacuum and the resulting beige crystals were isolated by filtra-
tion, washed successively with toluene (10 mL) and hexane
(10 mL), and dried in vacuo. Crystals of the double salt 32
Br PF6 CH2Cl2 suitable for elemental and crystallographic
3
3
3
analysis were obtained by slow diffusion of toluene into a
saturated solution of the salt in dichloromethane. Yield 0.21 g
(0.18 mmol, 79%). IR Nujol: 1994 s, 1930 vs νCO; 1716 νCdC
;
.
846 νPF cm-1. CH2Cl2: 2003s, 1939vs νCO; 1610w νCdC cm-1
1H NMR (25 °C, CD2Cl2): δH=-0.35 (m, 2H, RuCHH0, see
2
4
Figure S1), 6.89 (dt, 1H, JPH=33 Hz, JPH apparent but not
resolved), 7.32, 7.62-8.2 (m ꢀ 5, 45H, C6H5). 13C{1H} (CD2-
Cl2): δC =213.1(t), 204.7, 203.5(t), 134.2, 128.8 [C2,3,5,6(P2C6-
H5)], 134.1 [t, JPC = 27.5, C1(P2C6H5)], 131.0 [C4(P2C6H5)],
132.3 (d, JPC=22.0, C1(PC6H5)], 133.9, 129.8 [C2,3,5,6(PC6H5)],
129.9 [C4(PC6H5)], 95.42 (d, JPC=73.2), 12.81 (s.br, RuCH2).
ESI (þve)-MS (MeOH/MeCN): m/z (%) [assignment]=983(9)
[M]þ, 955(6) [M - CO]þ, 721(8) [M - PPh3 þ MeCN]þ, 693(66)
[M - PPh3 - CO þ MeCN]þ, 365(54) [Ph3PCH2CCH þ 2Me-
OH]þ, 333(100) [Ph3PCH2CCH þ MeOH]þ, 301(55) [Ph3PCH2-
CCH]þ. FAB-MS (nba): m/z (%) [assignment] = 983(15) [M]þ,
955(12) [M-CO]þ, 721(42) [M-PPh3]þ, 693(24) [M-CO -
PPh3]þ, 665(9) [M - PPh3 - 2CO]þ. Anal. Calcd. for C60H48-
Br0.5Cl2F3O2P3.5Ru(CH2Cl2): C, 61.05; H, 4.42%. Found:
C, 61.47; H, 4.37%. Crystal data for 32 Br PF6(CH2-
Concluding Remarks
Propargylic nucleophilic substitution may take one of two
courses depending on whether the nucleophile attacks at the
sp3 (Scheme 5a) or sp terminus (Scheme 5b). If the first step in
oxidative addition of propargyl halides is viewed as the metal
acting as nucleophile, then it might appear that the forma-
tion of allenyl rather than propargyl ligands simply reflects
the alternative sites for attack. The results described herein
point toward a different mechanism leading to allenyl
ligands (Scheme 5c), that is, oxidative addition of the alkyne
C-H bond followed by dissociation of the nucleofuge (Br-
or SMe2) to generate an electrophilic allenylidene intermedi-
ate that undergoes migratory coupling with the hydride
ligand (Scheme 5). In support of this, we have isolated the
stable complexes [RuH(CtCCR2OH)(CO)2(PPh3)2] (R=H,
Ph), which only convert to allenyl derivatives [RuCl(CHd
CdCR2)(CO)2(PPh3)2] upon treatment with HCl.22 While
this route appears to be the case in reactions of 1 with
HCtCCH2Br and [HCtCCH2SMe2]Br, the poorer nucleo-
fuge PPh3 remains bound to the propargyl unit, resulting via
prototropy in the formation of a phosphonioallene.
3
3
Cl2)2: C60H50Br0.50Cl2F3O2P3.50Ru, Mw =1180.32, monoclinic,
˚
P2/c, a=16.4415(3), b=12.2233(3), c=27.9952(6) A, β=v
3
107.0630(10) °, V=5378.5(2) A , Z=4, Fcalc=1.458 Mgm-3
,
˚
μ(Mo KR) = 0.920 mm-1, colorless plate 0.16 ꢀ 0.10 ꢀ
0.05 mm, T = 100(2) K, 9349 independent measured reflec-
tions (2θ e 50°), R1 = 0.0417, wR2 = 0.0833 for 7414 inde
pendent observed absorption-corrected reflections [I >
2σ(I)], 748 parameters, 47 restraints, residual electron den-
sity between -0.579 and 0. 0.544 eA-3 (CCDC 699398).
˚
Synthesis of [Ru(η2-H2CdCdCH2)(CO)2(PPh3)3] (4). Under
an atmosphere of allene, a solution of [Ru(CO)2(PPh3)3] (1:
0.200 g, 0.21 mmol) in dichloromethane (20 mL) was stirred
vigorously for 40 min. Ethanol (15 mL) was added and the
mixture was concentrated under dynamic vacuum, occasionally
backfilling the vessel with allene. The resulting white precipitate
was isolated by filtration and washed with hexane. Yield 0.11 g
(0.13 mmol, 62%). NB: Anaerobic dissolution of the complex in
CDCl3 leads to slow formation of cct-[RuCl2(CO)2(PPh3)2]
(δP=18.06). Dissolving the complex in C6D6 without exclusion
of air results in about 40% conversion to [Ru(η2-O2)(CO)2-
(PPh3)2] (δP = 35.65) over 10 min. After 3 h, complete conver-
sion to [Ru(η2-O2)(CO)2(PPh3)2] and OPPh3 (δP = 26.10) was
observed. NMR data could however be obtained from deox-
ygenated CD2Cl2 that was subsequently saturated with allene
(δH = 4.730). 1H NMR (CD2Cl2): δH = 0.37 (m, AA0XX0, 1H,
P2RuCH2), 4.95, 5.46 (m.br ꢀ 2, 1H ꢀ 2, CdCH2), 7.43 [m, 18H,
H3-5(C6H5)], 7.65 [m, 12H, H2,6(C6H5)]. 1H (C6D6): δH = 0.78
(m.br, 1H, P2RuCH2), 4.22, 4.45 (m.br ꢀ 2, 1H ꢀ 2, CdCH2),
6.97 [m, 18H, H3-5(C6H5)], 7.34 [m, 12H, H2,6(C6H5)]. (CDCl3):
δH =0.30 (m, AA0XX0, 1H, P2RuCH2), 4.89, 5.45 (m.br ꢀ 2,
1H ꢀ 2, CdCH2), 7.37, 7.64, 7.92 (m ꢀ 3, 30H, C6H5), 7.65 [m,
12H, H2,6(C6H5)]. 13C{1H} (CD2Cl2): δC = 213.0 (dCd, free
Experimental Section
General Considerations. All manipulations involving [Ru-
(CO)2(PPh3)3] (1) were carried out under a dry and oxygen-free
nitrogen atmosphere using standard Schlenk, vacuum line, and
inert atmosphere drybox techniques, with dried and degassed
dichloromethane, which was distilled from calcium hydride
(CH2Cl2). NMR spectra were obtained at 25 °C on Varian
Gemini 300BB (1H at 299.944 MHz, 13C at 75.420 MHz, 31P at
121.470 MHz) spectrometer. Chemical shifts (δ) are given
relative to residual protio solvents (1H, 13C) or external
D3PO4 (31P), with coupling constants given in Hz. Elemental
microanalytical data were obtained commercially from the
University of North London Analytical Service or from the
microanalytical service of the Australian National University.
For salts, “M” refers to the cationic metal complex in mass
spectrometry assignments. The compound [Ru(CO)2(PPh3)3]
(1) was prepared by a modification10b of Roper’s original
2
allene, obscures RuCO), 170.4 (t, RudCd, JPC=7.3), 134.6,
134.1(d), 130.1, 128.2 (C6H5), 108.1 (dCH2), 73.86 (dCH2,
free allene), 10.87 (br, RuCH2). 31P{1H}: δP=51.48 (CD2Cl2),
(22) Bedford, R. B.; Cartwight, J.; Hill, A. F. unpublished results.
51.83 (CDCl3), 52.03 (C6D6). IR Nujol: 1973s, 1893vs νCO;

5574 Organometallics, Vol. 28, No. 18, 2009
Ang et al.
1716 νCdC cm-1. CH2Cl2: 1974s, 1908vs νCO cm-1. ESI(þve)-MS
(MeOH/CH2Cl2): m/z (%) [assignment] = 754(2) [HM þ Me-
OH]þ, 741(5) [HM þ H2O]þ, 727(43) [HM þ MeOH - CO]þ,
698(19) [HM þ MeOH - C3H4]þ, 655(100) [HRu(CO)(PPh3)2]þ.
Satisfactory elemental microanalytical data were not obtained
due to air sensitivity and difficulties in obtaining a sample
completely free of [Ru(η2-O2)(CO)2(PPh3)2] (5) and PPh3.
Synthesis of [Ru(CHdCdCH2)Br(CO)2(PPh3)2] (6). Propar-
gyl dimethylsulfonium bromide (0.058 g, 0.32 mmol) was
added to a solution of [Ru(CO)2(PPh3)3] (0.22 g, 0.23 mmol)
in dichloromethane (10 mL), and the mixture was stirred for
20 min. Degassed ethanol (10 mL) was added, and the mixture
was concentrated under dynamic vacuum to provide a micro-
crystalline precipitate that was isolated by filtration and re-
crystallized from a mixture of dichloromethane and ethanol
at -18 °C to provide pale orange crystals. Yield 0.13 g (74%).
Comparable yields were obtained when propargyl dimethyl-
sulfonium bromide was replaced with propargyl bromide
(commercial 70% w/w solution in toluene). IR CH2Cl2:
2041vs, 1981vs νCO cm-1. Nujol: 2036vs, 1974vs νCO cm-1. 1H
NMR (CDCl3, 25 °C, 270 MHz): δH=3.34 (m, 2H, 3JHH=6.6,
2JHH=4.9 Hz, dCH2), 5.70 (m, 1H, 3JHH = 6.6, 3JPH = 3.3 Hz,
RuCH), 7.36 - 7.37, 7.71 - 7.76 (m ꢀ 2, 30H, C6H5). 13C{1H}:
205.5 (dCd), 196.3, 192.9 (RuCO), 134.3-128.0 (C6H5), 86.6
2
(t, JPC=12.8 Hz, RuCH), 61.0 (dCH2). 31P{1H}: δP = 22.1.
FAB-MS (nba matrix), 773 [M - CO]þ, 763 [M - C3H3]þ, 746
[M - 2CO]þ, 735 [M - CO - C3H3]þ, 721[M - Br]þ. Anal.
Calcd. for C41H33BrO2P2Ru: C, 61.51; H, 4.15%. Found:
C, 61.22; H, 4.35%.
Acknowledgment. We thank the Australian Research
Council (ARC) for financial support (Grant No.
DP0556236) and the Deustcher Akademischer Aus-
tauschdienst for the award of a fellowship (to J.W.).
Supporting Information Available: Full details of the crystal
structure determination of 32 BrPF6(CH2Cl2)2 (CCDC 699398)
3
in CIF format; 1H NMR spectrum (0 to -0.5 pm) for complex
3þ (Figure S1); Selected structural data for allene complexes
(Table S1). This material is available free of charge via the
Internet at http://pubs.acs.org.