Reactions of [Ru(CO)2(PPh3)3] with alkynylphosphonium salts: Phosphaallenylidene vs phosphonioacetylide coordination

Article abstract of DOI:10.1021/om9003384

[Ru(CO)₂(PPh₃)₃] reacts with [Me ₃SiC≡CPPh₃]-OTf in the presence of moist [ ⁿBu₄N]F to provide the C-H activation product [RuH(C≡CPPh₃)(CO)₂(PPh₃

Full text of DOI:10.1021/om9003384

4880 Organometallics 2009, 28, 4880–4885
DOI: 10.1021/om9003384
Reactions of [Ru(CO)2(PPh3)3] with Alkynylphosphonium Salts:
Phosphaallenylidene vs Phosphonioacetylide Coordination
†
Richard L. Cordiner, Anthony F. Hill,* and Jorg Wagler
,†
†,‡
€
†Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra,
‡
Australian Capital Territory, Australia, and Institut fu€r Anorganische Chemie, Technische Universitat
€
Bergakademie Freiberg, Freiberg, Germany
Received April 29, 2009
Scheme 1. Synthesis and Reactions of 11
Summary: [Ru(CO)2(PPh3)3] reacts with [Me3SiCtCPPh3]-
OTf in the presence of moist [nBu4N]F to provide the C-H
activation product [RuH(CtCPPh3)(CO)2(PPh3)2]OTf,
spectroscopic and structural data for which are used to assess
the previously proposed analogy between phosphonioacetylide
and phosphaallenylidene (cf. isonitriles) bonding descriptions
in an organometallic context.
In a combined experimental and computational study1
Bestmann and co-workers considered a possible analogy
between the nonisolable molecule “Ph3PCC” (1) and the
more familiar isonitrile class of compounds, RNC. The
elegant synthetic approach to 1 involved fluorodesilylation
of the salt [Me3SiCtCPPh3]OTf (2 OTf)2 by [Me3NCH2-
3
Ph]F at -100 °C (Scheme 1), and while the compound
1
decomposes upon warming to room temperature, H, 13C,
and 31P NMR data could be obtained at -78 °C which
supported the formulation. These data are reproduced in
Chart 1. Valence Bond Descriptions of “Ph3PCC” (2): (a)
Table S1 (Supporting Information) for reasons that should
become apparent (vide infra).
Phosphaallenylidene (cf. Isonitriles); (b) Phosphonioacetylide
The detailed computational study led, inter alia, to the
conclusion that “it is not possible to formulate a single Lewis
structure for Ph3PCC that correctly reproduces the geometry
and charge distribution.”1 The same might be said for iso-
nitriles, CNR, and indeed a key theme of the paper was the
isoelectronic relationship between 1 and isonitriles: i.e., to
(Ph3SiNC (iso-3) vs Ph3SiCN (3)) was a matter for unre-
solved debate (vide infra).
Chemical evidence in support of the 1:isonitrile analogy
was gleaned from reactions with a range of electrophiles
(HX, MeOTf, BPh3), which invariably attacked at the
what extent do the phosphaallenylidene and phosphonioa-
cetylide descriptions (Chart 1) contribute? In principle,
triphenylisocyanosilane, Ph3SiNC (iso-3) would be the
carbon atom β to the phosphorus center (Ph3P-CR-Cβ-
most closely related isoelectronic analogue of 1, though
ylides are typically nucleophilic at CR); the computational
this compound has lain dormant in the literature for the
50 years since its discovery,3 at which time its formulation
results suggest Cβ contributed substantially to the HOMO in
the form of a lone pair. The HOMO-1 and HOMO-2 were
found to be an orthogonal set of π orbitals associated with
the C-C multiple bond; however, the paper was silent on the
nature of unoccupied orbitals. From an organic perspective,
the unoccupied orbitals of a demonstrably potent nucleo-
phile would be of little interest. However, in an organome-
tallic context, the invocation of an analogy with isonitriles
immediately raises the issue of metalfcarbon retrodonation
to such orbitals, a question to which we will return.
*To whom correspondence should be addressed. E-mail: a.hill@anu.
edu.au.
(1) Bestmann, H. J.; Wilhelm, F.; Moll, C.; Pohlschmidt, A.; Clark,
€
T.; Goller, A. Angew. Chem., Int. Ed. 1998, 37, 338.
(2) Stang, P. J.; Critell, C. M. J. Org. Chem. 1992, 57, 4305.
(3) (a) McBride, J. J.Jr. J. Org. Chem. 1959, 24, 2029. (b) Bither, T. A.;
Knoth, W. H.; Lindsey, R. V.Jr.; Sharkey, W. H. J. Am. Chem. Soc. 1958, 80,
4151. (c) We find that calculations at the same level of theory (B3LYP, 6-
311G*) used to investigate the bonding in Ph3PCC1 suggest that cyanotri-
phenylsilane is ca. 13.6 kJ mol-1 more stable than isocyanotriphenylsilane, i.
e., for 3 f iso-3, K300 K ≈ 6 ꢀ 10-3. (assuming ΔG ≈ ΔH). Nevertheless, in
the presence of transition metals, cyanosilanes have been found on occasion
to rearrange to complexes of isocyanosilanes: (d) Seyferth, D.; Kahlen, N. J.
Am. Chem. Soc. 1960, 82, 1080. (e) Bessler, E.; Barbosa, B. M.; Hiller, W.;
Weidelin, J. Z. Naturforsch. 1991, 46B, 490. (f) da Silva, M. F. C. G.; Lemos,
M. A. N. D. A.; Frausto, J. J. R.; Pombeiro, A. J. L.; Pellinghelli, M. A.;
Tiripicchio, A. Dalton Trans. 2000, 373. (g) Pombeiro, A. J. L.; Hughes, D.
L.; Pickett, C. J.; Richards, R. L. J. Chem. Soc., Chem. Commun. 1986, 246.
(4) (a) Kaska, W. C.; Mitchell, D. K.; Reichelderfer, R. F.; Korte, W.
D. J. Am. Chem. Soc. 1974, 96, 2847. (b) Kaska, W. C.; Mitchell, D. K.;
Reichelderfer, R. F. J. Organomet. Chem. 1973, 47, 391. (c) Goldberg, S. Z.;
Duesler, E. N.; Raymond, K. N. Inorg. Chem. 1972, 11, 1397. (d) Raymond,
K. N.; Goldberg, S. Z.; Duesler, E. N. Chem. Commun. 1971, 826. (e) Petz,
W.; Weller, F. Z. Naturforsch. 1996, 51B, 1598. (f) Rosche, F.; Heckmann,
G.; Fluck, E.; Weller, F. Z. Anorg. Allg. Chem. 1996, 622, 974.
r
pubs.acs.org/Organometallics
Published on Web 07/30/2009
2009 American Chemical Society

Note
Organometallics, Vol. 28, No. 16, 2009 4881
Scheme 2. Previous Synthetic Routes to Phosphonioacetylide
Scheme 3. Fluoride-Mediated Protodesilylation of Alkynylsi-
lanes: (a) X = CtCSiMe3;10b (b) X = CtW(CO)2L (L =
HB(pz)3, HB(pzMe2)3);10c (c) X = PPh3(OTf)
Complexes:4-7 (i) Ylide Route (X = PR3 (H)SiMe3, (H)U(η-
C5H5)3); (ii) Haloalkyne/Phosphine Coupling; (iii) Phosphi-
noalkynyl Alkylation
Complexes of 1 (and related CCPR3 derivatives) are
known but are rare, and none arise from the intermediacy
of free 1. Rather, they all derive from one of three synthetic
approaches. These involve the reactions of the metal carbo-
nyls with various “double” ylides, reminiscent of the Wittig
reaction (Scheme 2),4,5 the reactions of dichloroethyne with
labile phosphine complexes,6 or the alkylation of (somewhat
rare) phosphinoalkynyl ligands.7 Though only briefly ex-
plored by Dahlenburg, this last approach perhaps offers the
greatest potential for general applicability.
Herein, we wish to address the 1:CNR analogy from an
organo-transition-metal standpoint and have investigated
the generation of 1 in the presence of a suitable trapping
complex, [Ru(CO)2(PPh3)3] (4).8 The complex 4 is known to
react via phosphine substitution with internal alkynes,
diynes, and dimetallaoctatetraynes to form simple π ad-
ducts,9 at least in the first instance, though subsequent
transformations may ensue. Terminal alkynes and diynes
and metalladiynes (propargylidynes), in contrast, undergo
oxidative addition (C-H activation),10 while phosphaalk-
ynes coordinate in the rare, linear η1-σ(P) manner.11
4 provides the parent butadiynyl hydrido complex [RuH(Ct
CCtCH)(CO)2(PPh3)2] (5)10b and that a similar strategy
employing [W(tCCtCSiMe3)(CO)2L] (L =HB(pz)3, HB-
(pzMe2)3; pz=pyrazol-1-yl) affords the tricarbido complexes
[RuH{CtCCtW(CO)2L}(CO)2(PPh3)2] (6).10c We find that
treating 2 with TBAF in the presence of 4 affords a salt
formulated as [RuH(CCPPh3)(CO)2(PPh3)2]OTf (7 OTf) on
3
the basis of spectroscopic and crystallographic data (Scheme 3).
We will return to the nature of the RuCCP linkage;
however, the gross formulation follows from high- and
low-resolution ESI mass spectrometry and elemental micro-
analytical data. Specifically, in addition to a molecular ion,
isotopic clusters attributable to loss of CO and/or phosphine,
but not “CCPPh3”, are readily identifiable. The stereochem-
istry at ruthenium, subsequently confirmed crystallographi-
cally, follows from spectroscopic data and involves trans
phosphine and cis carbonyl ligands: thus, an A2B system is
observed in the 31P{1H} NMR spectrum with a barely
resolved AB coupling (4 Hz), indicative of remote, very
Results and Discussion
1
It has been previously shown that fluoride-mediated pro-
todesilylation of bis(trimethylsilyl)butadiyne with commer-
cial (i.e., moist) [nBu4N]F (“TBAF”) in the presence of
weakly coupled nuclei. The H NMR spectrum features a
2
doublet of triplets resonance at -5.80 ppm with JPH cou-
pling (18.3 Hz) typical of the mer-trans RuH(PPh3)2 arrange-
2
ment (e.g., δH - 5.30, JHP = 20.0 Hz for 510b). Two
chemically distinct carbonyl environments are indicated by
triplet resonances in the 13C{1H} NMR spectrum (δC 197.6,
195.5), while doublet resonances for the two carbon nuclei of
the RuCβCRP spine appear at 176.7 (Cβ) and 87.31 (CRP),
respectively, without coupling to phosphorus nuclei of the
ruthenium-bound phosphines being resolved. The infrared
(5) (a) Blau, H.; Griessmann, K.-H.; Malisch, W. J. Organomet.
Chem. 1984, 263, C5. (b) Cramer, R. E.; Higa, K. T.; Gilje, J. W.
Organometallics 1985, 4, 1140.
(6) (a) Suenkel, K. J. Organomet. Chem. 1992, 436, 101. (b) Sunkel, K.;
Birk, U. Polyhedron 1999, 18, 3187. It is not clear that the ligand necessarily
forms within the coordination sphere, given that phosphines react indepen-
dently with haloalkynes to provide alkynylphosphonium salts: (c) Dickstein,
J. I.; Miller, S. I. J. Org. Chem. 1972, 37, 2168.
spectrum of 7 OTf in CH2Cl2 is consistent with the formula-
3
(7) (a) Dahlenburg, L.; Weiss, A.; Block, M.; Zahl, A. J. Organomet.
Chem. 1997, 541, 465. (b) Dahlenburg, L.; Weiss, A.; Moll, M. J. Organo-
met. Chem. 1997, 535, 195.
tion in that three intense absorptions are observed (2038,
1988, 1959 cm-1) in addition to one weak, somewhat broad,
absorption (1891 cm-1). However, caution should be exer-
cised when assigning these individually to νs(CO), νas(CO),
ν(CtC) and ν(RuH) modes, since these oscillations are all
likely to be strongly coupled.4,6,12 Notably, the simple com-
plex [RuH(CtCC6H4Me-4)(CO)2(PPh3)2] (8)10a has absorp-
tions in CH2Cl2(Nujol) at 2113 (2112) m, 2031 (2026) vs,
1983 (1981) vs, and 1894 (1902) w cm-1, while the precursor
2þ has νCC 2128 cm-1 (CH2Cl2). Thus, the bands that appear
most common to 5, 7þ, and 8 would appear to occur at
(8) (a) Cavit, B. E.; Grundy, K. R.; Roper, W. R. J. Chem. Soc.,
Chem. Commun. 1972, 60. (b) Hill, A. F.; Tocher, D. A.; White, A. J. P.;
Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2005, 24, 5342.
(9) (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) Hill, A. F.; Rae, A. D.;
Schultz, M.; Willis, A. C. Organometallics 2004, 23, 81. (e) Hill, A. F.;
Schultz, M.; Willis, A. C. Organometallics 2005, 24, 2027. (f) Dewhurst, R.
D.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organometallics 2005, 24, 4703.
(10) (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.
(11) Bedford, R. B.; Hill, A. F.; Wilton-Ely, J. D. E. T.; Francis, M.
D.; Jones, C. Inorg. Chem. 1997, 36, 5142.
(12) (a) Vaska, L. J. Am. Chem. Soc. 1961, 83, 756. (b) Vaska, L.;
DiLuzio, J. W. J. Am. Chem. Soc. 1962, 84, 4989.

4882 Organometallics, Vol. 28, No. 16, 2009
Cordiner et al.
1
uncharacteristically complex H NMR spectrum of 7þ in
the phenyl region, suggesting arrested, or at least restricted,
rotation about the Ru-P or P-C bonds of the phosphines.
The 1H NMR spectrum of the precursor 2 is by comparison
quite conventional and unremarkable (δH(CDCl3) 7.76,
7.88, m ꢀ 2), as is the 31P{1H} spectrum (δP 5.74), notwith-
standing the ca. 11 ppm shift that occurs upon replacement
of the SiMe3 group by ruthenium. These features aside, our
interest centers on the RuCCP spine and whether this is best
described as the coordination of neutral 1 to cationic “RuH-
(CO)2(PPh3)þ2 ”, drawing upon the isonitrile analogy, e.g.
[RuH(CNR)(CO)2(PPh3)2]ClO4 (9 ClO4: R=C6H4Me-4),15
3
or if it is more akin to a conventional σ-alkynyl (cf. 5 and 8)
with a remote cationic phosphonium substituent. There is
an enormous amount of structural data available for octa-
hedral (or pseudo-octahedral half-sandwich) acetylides of
ruthenium(II),17 and although these have previously been
tabulated,17b the growth of the field in the interim has been
most notable. The question arises as to whether there is
anything untoward in the metrical parameters associated
with the RuCCPPh3 spine which might point toward a
phosphaallenylidene canonical form having a role to play
in understanding the bonding. On comparison of the struc-
tural data for these previously reported ligands, the CC bond
Figure 1. Molecular geometry of the complex 7þ in a crystal of
the salt 7 OTf CH2Cl2 (60% displacement ellipsoids at 100 K,
phenyl groups simplified, solvent and counteranion omitted).
3
3
˚
Selected bond lengths (A) and angles (deg): Ru1-C1=1.898(7),
Ru1-C2=1.952(6), Ru1-C3=2.041(6), Ru1-P3=2.3623(15),
Ru1-P2=2.3761(15), Ru1-H1=1.64(6), P1-C4=1.698(6),
C3-C4 = 1.235(9); C1-Ru1-C2 = 93.7(2), C2-Ru1-C3 =
94.2(2), C1-Ru1-P3 = 91.51(18), C2-Ru1-P3 = 94.87(17),
C3-Ru1-P3=87.24(16), P3-Ru1-P2=168.10(5), C4-C3-
Ru1=177.4(5), C3-C4-P1=172.4(5).
˚
spans the range 1.21-1.23 A while the C-PPh3 bonds span
ca. 2030 and 1990 cm-1; therefore, we would suggest that
these are predominantly νCO in character while the more
substituent-dependent band (1959 cm-1) is most likely pri-
marily νCC in character. While this is somewhat lower than
the values assigned to most other complexes (2050-2105
cm1), it should be noted that ruthenium(II) is a compara-
tively π-basic metal center, and in the absence of competing
π-acidic ligands values as low as 1932 cm-1 have been
assigned for the salt [Ru(CtCPtBu2Bu)(PPh3)2(η-C5Me5)]-
Br.7 In this respect the response of νCC to the π-basicity of a
metal might well appear to mimic that of isonitriles, though
the separation of σ-dative and π-retrodative contributions to
νCN for isonitriles is less straightforward than for νCO in
carbonyl complexes.13
þ
˚
1.68-1.71 A. Thus, 7 would appear to not show remarkable
departure from this albeit limited precedent. There is no
obvious correlation between the values of “νCC” and the
geometric parameters of the MCCP spines; however, this
may simply reflect the low precision of these structural data
and variations in the media used for IR measurements. The
˚
Ru1-C3 bond length of 2.041(6) A falls within the range
˚
(1.91-2.10 A) typical of conventional ruthenium alkynyls,
˚
as does the C3-C4 bond length of 1.235(9) A; i.e., there is
no structural evidence for significant contributions from
the phosphaallenylidene description. The Ru-C3-C4-P1
spine does not depart significantly from linearity, in contrast
to [Fe(CCPPh3)(CO)4] (10), which has the phosphine bent
off the FeCC axis (162.1°),4e most likely a soft response to
crystal -packing effects.
The formulation of 7 OTf was confirmed by a crystal-
3
lographic study of the solvate 7.OTf.CH2Cl2, the results of
which are summarized in Figure 1.
An Isonitrile Analogue or a Phosphoniacetylide? We may
approach this from two perspectives-empirical or computa-
tional. The characterization of LnMCCPPh3 complexes is
somewhat patchy (Table S1, Supporting Information), re-
flecting the historical availability of various spectroscopic
techniques such that only two examples, [(OC)4FeCCPPh3]
(10)4e and now 7þ, offer both full spectroscopic and struc-
tural data. The structural data are somewhat unresponsive to
variations in substitution at either the metal or phosphorus,
with differences failing to attain statistical significance.
Upon coordination, there is a significant upfield shift in
the Cβ resonance from 229 ppm in free 1 to 197.4 ppm (for 10)
or 176.7 ppm (for 7þ). Alkylphosphonium derivatives span a
wider range (147-223 ppm), and the chemical shift is
responsive to variations in phosphorus substituents, e.g.,
δ(Cβ) values for the series [Ru(CCPR3)(PPh3)2(η-C5H5)]þ
The geometric features of the “RuH(CO)2(PPh3)2” unit
are generally unremarkable, other than to note the charac-
teristic bending of ligands toward the small hydride, which
exerts a trans influence upon the CO to which it is trans
coordinated. Although the position of the ruthenium hy-
dride ligand is typically imprecise, the ruthenium-hydride
˚
bond length (Ru1-H1 = 1.64(6) A) is comparable to that
˚
observed for 5 (1.57 A). It is perhaps noteworthy that one
ortho C-H group of each trans-disposed phosphine
approaches the hydride ligand (Ru-H H-C = 2.24,
3 3 3
˚
2.44 A). Such Ru-H H-C hydrogen-bonding interac-
3 3 3
tions have been noted previously by Junk for the complex
[RuH2(CO)(PPh3)3]14 and more recently for the methima-
zolylborate complexes [RuH(CO)(PPh3){HB(mt)3}] (mt =
methimazolyl)15a and [RuH(PPh3)2{HB(mt)3}]15b and may
well be more widespread than previously appreciated. Equi-
vocal evidence that such interactions may persist to some
extent in solution is provided by the observation of an
(15) (a) Foreman, M. R.; St, J.; Owen, G. R.; White, A. J. P.;
ꢀ
Williams, D. J. Organometallics 2003, 22, 4446. (b) Jimenez-Tenorio,
M.; Puerta, M. C.; Valerga, P. Organometallics 2009, 28, 2787.
(16) Christian, D. F.; Roper, W. R. Chem. Commun. 1971, 1271.
(17) (a) Cambridge Crystallographic Data Centre Conquest, January
2009 database release. (b) Hill, A. F. In Comprehensive Organometallic
Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press: Oxford, U.K., 1995; Vol. 7, pp 411-417.
(13) Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem. 1983,
22, 209.
(14) Junk, P. C.; Steed, J. W. J. Organomet. Chem. 1999, 587, 191.

Note
Organometallics, Vol. 28, No. 16, 2009 4883
Table 1. Infrared Data for Selected Complexes
[RuH(CO)2(L)(PPh3)2]n
L
n
ν
CO (cm-1
)
kCO
CtCC6H4Me
CtCPPh3
CtNC6H4Me
CtO
0
2031, 1983
2038, 1988
2085, 2045
16.24
16.34
17.20
1þ
1þ
1þ
2072, 2050, 2010
Table 2. Infrared Data for Selected Complexes [Mn(CO)2(L)(η-
C5H5)]n
L
n
ν
CO (cm-1
)
kCO
CMe19
1þ
1þ
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2095, 2056
2088, 2047
2015, 1963
2010, 1959
2009, 1955
2002 1960
1995, 1945
1995 1935
1996, 1932
1980, 1918
1977,1919
1944, 1890
1930, 1860
1923, 1855
1887, 1852
1906, 1823
17.37
17.24
15.95
15.88
15.84
15.83
15.65
15.57
15.56
15.32
15.30
14.82
14.48
14.39
14.09
14.02
CPh20
CSe21
CS22
CdCHPh23
CBrPh24
CdCdCPh2
CClPh24
25
19
CdCH2
CFPh24
CPh2
26
CNCy27
CNNPPh3
28
PiPr3
27
CCPMe2Ph5b
C(NMeCH)2
29
span the range 191-206 ppm. This range impinges upon
those typical of coordinated CO and isonitriles but is far
downfield of the region in which metal-bound terminal
acetylide carbons resonate (100-120 ppm). There are two
spectroscopic parameters which do appear to show some
variation within the PPh3 series of compounds. (i) The first
is δP for the phosphorus nucleus, which so far appears
between -0.44 and -10.4 ppm for metal complexes,
cf. -13.85 ppm for free 1 and þ5.22 ppm for 2þ, in which
the addend may be considered primarily σ-interactive.
(ii) There is a dramatic increase in the coupling bet-
ween phosphorus and both CR (50-60 Hz) and Cβ (10-
15 Hz, ca. doubling) upon coordination of 1 to a metal,
suggesting an increase in the s character of the orbitals
involved (conversely a decrease in the p character). The
HOMO for free 1 in addition to having s lone pair character
is also C-C bonding in character with some modest C-P
σ-antibonding contribution; i.e., coordination of a (σ)
Lewis acid to Cβ should indeed reduce the C-P bond
strength.
Figure 2. Topologies and relative energies of the frontier orbi-
tals of 1 and relevant compounds.
To further assess the nature of MCCPR3 bonding, we have
therefore turned to infrared data associated with ancillary
ligands. The complex [RuH(CNC6H4Me-4)(CO)2(PPh3)2]þ
(9þ) is most closely akin to 7þ (and the alkynyl 8), having the
same stereochemistry at ruthenium. Putting aside the caveats
associated with coupled oscillations of coligands, Table 1
collates infrared data for 7þ, 8, 9þ and the tricarbonyl salt
[RuH(CO)3(PPh3)2]PF6, though the Cotton-Kraihanzel
force constant (kCO) is not directly comparable.
Table 1 provides a somewhat brief list of C1 ligands for
comparison, though it does indicate that the net donor
strength is comparable to a (formally anionic) alkynyl ligand
rather than a neutral isonitrile: i.e., the effect of the positive
charge on phosphorus is not strongly felt at the metal center.
A more extensive listing is provided by adducts of the
familiar “RCpMn(CO)2” fragment, and although no com-
plex with 1 has been isolated, adducts of CCPMe3 and
CCPMe2Ph are known.5 Spectroscopic data for these and a
range of C1 ligands are given in Table 2.
(18) (a) Sherlock, S. J.; Boyd, D. C.; Moasser, B.; Gladfelter, W. L.
Inorg. Chem. 1991, 30, 3626. (b) Johnson, B. F. G.; Segal, J. A. J. Chem.
Soc., Dalton Trans. 1973, 478.
(19) Terry, M. R.; Mercando, L. A.; Kelley, C.; Geoffroy, G. L.;
Nombel, P.; Lugan, N.; Mathieu, R.; Ostrander, R. L.; Owens-Waltermire,
B. E.; Rheingold, A. L. Organometallics 1994, 13, 843.
(20) Fischer, E. O.; Schambeck, W. J. Organomet. Chem. 1980, 201,
311.
(21) Butler, I. S.; Cozak, D.; Stobart, S. R. J. Chem. Soc., Chem.
Commun. 1975, 103.
(22) Butler, I. S.; Fenster, A. E. J. Chem. Soc., Chem. Commun. 1970,
933.
(23) Antonova, A.-B.; Kolobova, N. E.; Petrovsry, P. V.; Lokshin, B.
V.; Obezyuk, N. S. J. Organomet. Chem. 1977, 137, 55.
(24) Fischer, E. O.; Chen, J.; Scherzer, K. J. Organomet. Chem. 1983,
253, 231.
(25) Berke, H. Chem. Ber. 1980, 113, 1370.
(26) Herrmann, W. A. Chem. Ber. 1975, 108, 486.
(27) Mueller, J.; Herberhold, M. J. Organomet. Chem. 1968, 13, 399.
(28) Weinberger, B.; Fehlhammer, W. P. Chem. Ber. 1985, 118, 42.
(29) Lappert, M. F.; Pye, P. L. J. Chem. Soc., Dalton Trans. 1977,
2172.
These data would appear to suggest that 2 is a poor
acceptor ligand, weaker than conventional isonitriles, and
far weaker than alkylidenes and cumulenic ligands such as

4884 Organometallics, Vol. 28, No. 16, 2009
Cordiner et al.
vinylidenes and allenylidenes. Among the neutral C1 ligands
(cf. charged alkylidynes), carbon monoselenide is the stron-
gest π acid, while Lappert’s N-heterocyclic carbenes are by a
considerable margin the most electron releasing. To investi-
gate the individual contributions to the net bonding, the
energies of π-donor, σ-donor, and π-acceptor orbitals of 1
are compared with those of CO, CNCH3, and CNSiPh3 (iso-
3, isoelectronic with 1) at the level of theory previously
employed1 for 1 (B3LYP, 6-311G*). Figure 2a-c demon-
strates that, from the perspective of an incoming metal
center, the relevant orbitals (π-acceptor, σ-donor, and
π-donor) have remarkably similar topology. Figure 2d dis-
plays the relative energetics of these orbitals in addition to
those for CO and CNSiPh3. The relative energies of the
σ-donor and π-acceptor orbitals for CO and CNMe rein-
force the accepted wisdom that isonitriles in general are
both stronger σ-donors and weaker π-acceptors than CO.
The relative energies of these orbitals do not change mark-
edly between CNMe and CNSiPh3, and the π-acceptor
orbitals for 1 are essentially identical in energy with those
for CNMe and iso-3. The distinctive feature of 1 in this
scheme is that both the σ-donor orbital and the degenerate
π-donor orbitals are significantly higher in energy, account-
ing for 1 being a potent donor ligand with very modest
retrodative capacity.
Concluding Remarks. Previous routes to CCPR3 com-
plexes are somewhat substrate specific. The ylide route
requires sufficiently electrophilic carbonyl ligands and pro-
ceeds via sterically encumbered intermediates, while the
haloalkyne route requires sufficiently electron rich metal
centers for oxidative addition to be viable. Dahlenburg’s
phosphinoalkynyl alkylation approach promises some gen-
erality, yet to be explored, so long as the precursor complexes
can be obtained. At present, isolable mononuclear phosphi-
noalkynyl complexes remain extremely rare.30 The route
demonstrated herein offers broad applicability, whether
the transfer reagent is [HCtCPPh3]OTf or, in this case, its
conjugate base, 1. Furthermore, the potential exists with the
current strategy to vary both the electronic and steric proper-
ties by employing different phosphines in place of PPh3.
In terms of the coordination properties of 1, carbonyl
coligand infrared data suggest that 1 is a stronger net donor
ligand than are isonitriles. While the use of carbonyls as
reporter ligands for the comparative π-basicity of a metal has
a long and illustrious history, deconvoluting σ-donor,
π-acceptor, and π-donor contributions for a ligand of inter-
est can be problematic. In the case of 1, the energies of the
π-acceptor orbitals are comparable to those of a conven-
tional isonitrile. Thus, the principal features that therefore
distinguish 1 from isonitriles relate to both the σ-donor
and π-donor orbitals being substantially higher in energy,
making 1 a potent net donor. In this respect, the interactions
with a metal center assume character more akin to σ-alkynyls
(albeit neutral).
degassed dichloromethane which was distilled from calcium
hydride (CH2Cl2) or THF which was distilled from sodium
benzophenone ketyl. NMR spectra were obtained at 25 °C on a
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 85%
D3PO4 (31P), with coupling constants given in Hz. Elemental
microanalytical data were obtained from the microanalytical
service of the Australian National University. The compound
[Ru(CO)2(PPh3)3] was prepared by a minor modification8b of
Roper’s original protocol.8a The salt [Ph3PCtCSiMe3]OTf
(2 OTf) was prepared as described previously.2
3
Synthesis of [RuH(CtCPPh3)(CO)2(PPh3)2]OTf (7 OTf).
3
(a) A solution of [Me3SiCtCPPh3]OTf (0.109 g, 0.21 mmol)
in dichloromethane (10 mL) was cooled (dry ice/propanone),
treated with a tetrahydrofuran solution of [nBu4N]F (Aldrich
“TBAF”, 1.0 mol L-1, 0.22 mL, 0.22 mmol), and stirred for
30 min. Solid [Ru(CO)2(PPh3)3] (0.200 g, 0.22 mmol) was added,
and the mixture was stirred for 15 min and then warmed to 0 °C
and stirred for 1 h. The resulting pale yellow solution was filtered
through diatomaceous earth and freed of volatiles in vacuo. The
residue was crystallized from a mixture of dichloromethane and
ethanol. Yield: 0.062 g (26%).
(b) It transpired that commercial grade THF is sufficiently
moist that the desilylation may be achieved without fluoride
mediation: to an intimate mixture of [Me3SiCtCPPh3]OTf
(0.545 g, 1.06 mmol) and [Ru(CO)2(PPh3)3] (1.00 g, 1.06 mmol)
was added thoroughly degassed but otherwise benchtop grade
tetrahydrofuran (50 mL) and the resulting mixture stirred for 1 h
to provide a pale solid and dark supernatant. Dilution with
hexane afforded a precipitate that was isolated by filtration and
recrystallized from a mixture of dichloromethane and hexane as
a dichloromethane monosolvate. Yield: 0.763 g (64%). Crystals
of this dichloromethane solvate suitable for crystallographic
and elemental microanalysis were grown by slow diffusion
of hexane into a saturated solution of the salt in dichloro-
methane. IR (CH2Cl2): 2038 s, 1988 vs νCO, 1959 s νCC, 1891
w br νRuH cm-1. NMR (CD2Cl2): 1H, δH -5.80 (dt, 1 H, 2JPH
=
18.3, 4JPH=1.5 Hz, RuH), 6.80, 6.85 (dd ꢀ 2, 6 H, 3JHH=8.4,
4JHH=1.2, H1(C6H5)), 7.17-7.33 (m ꢀ 7, 24 H, H3,5(C6H5)),
3
7.45-7.52 (m, 12 H, H3,5(C6H5)), 7.59 (ttd, 3 H, JHH =7.7,
5
4JHH =2, JPH =4, H4(C6H5)); 13C{1H}, δC 197.6 (t, RuCO,
2
2
2JPC=16), 195.5 (t, RuCO, JPC=12), 176.7 (d, JPC=24.6),
134.0 (C3,5(P2C6H5)), 133.8 (C3,5(þPC6H5)), 132.8 (C3,5(þPC6-
H5)), 129.9 (C4(þPC6H5)), 128.7 (C2,6(P2C6H5)), 131.0 (C4(P2-
C6H5)), C1(PC6H5) obscured, 87.31 (d, 1JPC=183.1 Hz, RuCt
CP); 31P{1H}, -5.87 (t, 1 P, 4JPP=5), 44.20 (d, 2 P, 4JPP=4 Hz).
ESI-MS (positive ion, high resolution): found (calcd) m/z
969.1806 (969.1779). ESI-MS (positive ion, low resolution):
m/z(%) [assignment] 969.5 (7) [7]þ, 939.5 (100) [7 - H - CO]þ,
913 (4) [7 - 2CO]þ, 677.3 (7) [7 - PPh3]þ, 649.2 (7) [7 - PPh3 -
CO]þ. Anal. Found: C, 59.62; H, 3.88. Calcd for C60H48Cl2-
F3O5P3RuS: C, 59.91; H, 4.02. Crystal data for 4 OTf CH2-
3
3
Cl2: C60H48Cl2F3O5P3RuS, Mw = 1202.92, triclinic, P1, a =
˚
˚
˚
10.0272(2) A, b = 14.6376(4) A, c = 19.3095(7) A, R =
86.3740(10)°, β = 78.064(2)°, γ = 79.451(2)°, V = 2725.05(14)
A , Z=2, Fcalcd =1.466 Mg m-3, μ(Mo KR)=0.572 mm-1
,
3
˚
colorless plate 0.40 ꢀ 0.10 ꢀ 0.03 mm, T = 100(2) K, 9482
independent measured reflections (2θ e 50°), R1 = 0.0619,
wR2=0.1684 for 8225 independent observed absorption-cor-
rected reflections (I > 2σ(I)), 696 parameters, 9 restraints,
Experimental Section
residual electron density between -0.985 and 0.616 e A-3. Data
˚
were collected from a twinned crystal and were detwinned by
employing an initial structural model using TWINROTMAT as
implemented in WinGX PLATON. An HKL5 format data set
thus derived was employed for the final refinement. Twin
populations were refined to 83% and 17% (CCDC 699397).
General Considerations. All manipulations involving [Ru-
(CO)2(PPh3)3] (1)8 were carried out under a dry and oxygen-
free nitrogen atmosphere using standard Schlenk, vacuum-line,
and inert-atmosphere drybox techniques, with dried and
Acknowledgment. We wish to thank Bernhard Wahl
€
€
(Technische Universitat Munchen) for assistance in the
(30) Cadierno, V.; Zablocka, M.; Donnadieu, B.; Igau, A.; Majoral,
J.-P.; Skowronska, A. Chem. Eur. J. 2001, 7, 221.

Note
Organometallics, Vol. 28, No. 16, 2009 4885
solution and refinement of the structure of 4 OTf
Supporting Information Available: A table giving selected
spectroscopic and structural data for phosphonioacetylide com-
plexes and a CIF file giving details of the crystal structure
determination of 7 OTf CH2Cl2. This material is available free
3
3
CH2Cl2. We thank the Australian Research Council
(ARC) for financial support (Grant No. DP0556236)
and the Deustcher Akademischer Austauschdienst for
the award of a fellowship (to J.W.).
3
3
of charge via the Internet at http://pubs.acs.org.