A bimetallic complex spanned by the CeH ligand: Synthesis of [Cl(CO) 2L2RuC=CCH=C=RuL2(η-C5H 5)]PF6 (L = PPh3)

Article abstract of DOI:10.1021/om050800o

The synthesis of the first example of a bime-tallic complex spanned by the C₄H alkynylvinylidene ligand, [Cl(CO)₂L ₂RuC≡CCH=C-RuL₂(η-C₅H ₅]PF₆ (L = PPh₃), is reported: the reaction of [Ru(CO)₂L₃] with butadiyne provides [RuH(C≡CC≡ CH)(CO)₂L₂], which is converted to the chloro derivative [RuCl(C≡CC≡CH)-(CO)₂L₂] by N-chlorosuccinimide. Subsequent treatment with [Ru(thf)L₂(η- C₅H₅)]PF₆ provides [Cl(CO)₂L ₂RuC≡ CCH=C=RuL₂(η-C₅H ₅)]PF₆, deprotonation of which affords [Cl(CO) ₂L₂RuC≡CC≡CRuL₂(η-C ₅H₅)].

Full text of DOI:10.1021/om050800o

Organometallics 2005, 24, 5795-5798
5795
A Bimetallic Complex Spanned by the C4H Ligand:
Synthesis of [Cl(CO)2L2RuCtCCHdCdRuL2(η-C5H5)]PF6
(L ) PPh3)
Michael J. Bartlett, Anthony F. Hill,* and Matthew K. Smith
Research School of Chemistry, Institute of Advanced Studies, Australian National University,
Canberra, Australian Capital Territory, Australia
Received September 16, 2005
Chart 1. Plausible Binuclear Bridging Modes for
the C4H Ligand and Associated Valence Electron
Contributions [x,y]
Summary: The synthesis of the first example of a bime-
tallic complex spanned by the C4H alkynylvinylidene
ligand, [Cl(CO)2L2RuCtCCHdCdRuL2(η-C5H5)]PF6 (L
) PPh3), is reported: the reaction of [Ru(CO)2L3] with
butadiyne provides [RuH(CtCCtCH)(CO)2L2], which is
converted to the chloro derivative [RuCl(CtCCtCH)-
(CO)2L2] by N-chlorosuccinimide. Subsequent treatment
with [Ru(thf)L2(η-C5H5)]PF6 provides [Cl(CO)2L2RuCt
CCHdCdRuL2(η-C5H5)]PF6, deprotonation of which af-
fords [Cl(CO)2L2RuCtCCtCRuL2(η-C5H5)].
While there has been enormous and rapid progress
in recent times in the synthesis of dimetalated buta-
diynes, LnM-(CtC)2-MLn,1 far less is known about
how partially reduced carbon chains, e.g., C4H or C4H2,
might bridge two metal centers. For C4H Chart 1
presents how one might envisage possible coordination
modes on the basis of the number of valence electrons
[x,y] provided to each metal terminus and the position
of the single-proton substituent. One complex in which
two metals are spanned by a C4H ligand has been
reported from the reaction of [W(CtCCtCH)(CO)3(η-
C5H5)] with [Pt(η-C2H4)(PPh3)2], in which the unstable
product is suggested to adopt coordination mode e.2
Protonation of the complexes [Fe2(µ-C4)(CO)2(R2PCH2-
The complex [Ru(CO)2(PPh3)3] (1)5 is known to π-co-
ordinate internal alkynes6 and diynes,7 to cyclocodimer-
ize R,ω-diynes with CO,8 and to cleave one single C-C
bond of dimetallaoctatetraynes.9 However, with termi-
Scheme 1a
i
CH2PR2)(η-C5Me5)2] (R ) Ph, Pr) has been suggested
to provide examples of the butatrienylidene form d,3
although spectroscopic data and the facile deprotonation
are also consistent with form e. Of the various possibili-
ties shown in Chart 1, it is the alkynyl-vinylidene form
(a) with which this paper is concerned. Such a coordina-
tion mode is likely as an intermediate in the double-
deprotonation reactions that have been reported for a
range of bis(vinylidenes);4 however, isolated examples
have yet to be described. We report herein the multistep
synthesis of one such complex.
* To whom correspondence should be addressed. E-mail: a.hill@
anu.edu.au.
(1) (a) Bruce, M. I.; Low, P. J. Adv. Organomet. Chem. 2004, 50,
179. (b) Low, P. J.; Bruce, M. I. Adv. Organomet. Chem. 2002, 48, 71.
(2) Bruce, M. I.; Low, P. J.; Ke, M.; Kelly, B. D.; Skelton, B. W.;
Smith, M. E.; White, A. H.; Witton, N. B. Aust. J. Chem. 2001, 54,
453.
(3) Coat, F.; Guillemot, M.; Paul, F.; Lapinte, C. J. Organomet.
Chem. 1999, 578, 76.
(4) (a) Bruce, M. I.; Ellis, B. G.; Low, P. J.; Skelton, B. W.; White,
A. H. Organometallics 2003, 22, 3184. (b) Bruce, M. I.; Hall, B. C.;
Kelly, B. D.; Low, P. J.; Skelton, B. W.; White, A. H. J. Chem. Soc.,
Dalton Trans. 1999, 3719. (c) Bruce, M. I.; Hinterding, P.; Tiekink, E.
R. T.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1993, 450,
209. (d) Bruce, M. I.; Ellis, B. G.; Gaudio, M.; Lapinte, C.; Melino, G.;
Paul, F.; Skelton, B. W.; Smith, M. E.; Toupet, L.; White, A. H. Dalton
Trans. 2004, 1601.
a L ) PPh3. Legend: (i) [Bu4N]F/H2O; (ii) N-chlorosuccin-
imide; (iii) [Ru(THF)(CO)2(η-C5H5)]PF6; (iv) Et2NH; (v) HPF6.
10.1021/om050800o CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/21/2005

5796 Organometallics, Vol. 24, No. 24, 2005
Communications
firm the stereochemistry inferred from spectroscopic
data. Of the two CtC triple bonds, that adjacent to
ruthenium (C1-C2 ) 1.210(4) Å) is somewhat longer
(ca. 9σ) than the terminal one (C3-C4 ) 1.176(4) Å),
consistent with a retrodative role for the ruthenium
center, despite the disposition of a carbonyl ligand trans
to C1.
The complex 2 was found to decompose11 during the
time required for the acquisition of 13C{1H} NMR data;
however, the more stable derivative [RuCl(CtCCtCH)-
(CO)2(PPh3)2] (3)12 could be obtained via the reaction of
2 with N-chlorosuccinimide (NCS). Spectrocopic data for
3 are conclusive but generally unremarkable. Treating
3 with a filtered solution of [Ru(THF)(PPh3)2(η-C5H5)]-
PF6 (generated in situ from [RuCl(PPh3)2(η-C5H5)] and
AgPF6 in THF) provides the salt [Cl(CO)2L2RuCtCCHd
CdRuL2(η-C5H5)]PF6 (4-PF6),13 in which two ruthenium
centers are linked in an unprecedented manner by the
C4H ligand bound to one ruthenium as a σ-alkynyl
species and the other as a vinylidene (Scheme 1). The
Figure 1. Molecular geometry of 2 in a crystal of 2‚C6H6
(phenyl groups simplified, 50% displacement ellispsoids).
Selected bond distances (Å) and angles (deg): Ru1-C3 )
2.063(3), Ru1-P1 ) 2.3557(9), Ru1-P2 ) 2.3560(10), C3-
C4 ) 1.210(4), C5-C6 ) 1.176(4), C5-C4 ) 1.386(4), Ru1-
H1 ) 1.57(4), C6-H6 ) 0.95(2); P1-Ru1-P2 ) 168.00(3),
C4-C3-Ru1 ) 177.2(3), C6-C5-C4 ) 178.7(3), C3-C4-
C5 ) 178.1(4).
13C{1H} NMR spectrum proved most diagnostic, reveal-
2
ing two alkynyl resonances (δC: 95.3; 127.7, t, JPC
≈
5.1 Hz) in addition to those for the two carbons of the
vinylidene linkage (δC: 120.3; 335.1, t, 3JPC ) 10.9 Hz).
The vinylidene proton resonance was not directly ob-
served in the 1H NMR spectrum due to coincidence with
the plethora of phenyl resonances; however, it could be
identified (δH 7.26) by HMQC NMR measurements,
which revealed a correlation with the resonance at δC
120.3.
nal alkynes C-H activation occurs with oxidative ad-
dition to provide hydrido-alkynyl derivatives of ruthe-
nium(II).5 We have therefore investigated the reaction
of 1 with butadiyne (generated in situ from Me3SiC4-
SiMe3 and moist [Bu4N]F, “TBAF”), which proceeds to
provide the complex [RuH(CtCCtCH)(CO)2(PPh3)2] (2)
in 85% yield. Notably, there was no indication of the
formation of the bimetallic derivative (µ-C4)[RuH(CO)2-
(PPh3)2]2 and isolated 2 did not react with a further
equivalent of 1. The characterization of 210 included a
crystallographic analysis, the results of which are
summarized in Figure 1. The geometry at the octahedral
ruthenium center is unremarkable, other than to con-
In principle, the proton (the acidity of which is
demonstrated below) could reside on either of the two
carbons â to a ruthenium center (Chart 2). Vinylidene/
1-alkyne tautomerism is particularly facile at divalent
ruthenium centers, and it may therefore be assumed
(11) If left to stand in solution under air, the complex 2 provides
[Ru(η2-O2)(CO)2(PPh3)2], while under anaerobic conditions in the
presence of PhCtCPh the complex [Ru(η2-PhCtCPh)(CO)2(PPh3)2]
slowly forms. Since these complexes are also the products of the
reactions of 1 with air5 and PhCtCPh,6 respectively, we conclude that
2 decomposes via reversible reductive elimination of butadiyne.
(12) 3: N-chlorosuccinimide (0.04 g, 0.3 mmol) and 2 (0.18 g, 0.25
mmol) were dissolved in THF (30 mL) and the mixture stirred for 5
min. Ethanol was added, and the solvents were reduced to provide a
pale yellow solid, which was isolated by filtration and recrystallized
from CH2Cl2/EtOH to provide straw-colored crystals. Yield: 0.16 g
(85%). IR (CH2Cl2): 2150 (νCtC), 2058, 1999 (νCO) cm-1. IR (Nujol):
2147 (νCtC), 2057, 1997 (νCO) cm-1. NMR (C6D6, 25 °C): 1H, δH 1.43 (t,
(5) Cavit, B. E.; Grundy, K. R.; Roper, W. R. Chem. Commun. 1972,
60. (b) Preparative details: Hill, A. F.; Tocher, D. J.; White, A. J. P.;
Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2005, 24,
om050514c.
(6) Hill, A. F.; Schultz, M.; Willis, A. C. Organometallics 2004, 23,
5729.
6
1 H, CtCH, JHP ) 1.2 Hz), 6.97, 8.19 (m × 2, 30 H, C6H5); 13C{1H},
2
(7) Alcock, N. W.; Hill, A. F.; Melling, R. P.; Thompsett, A. R.
Organometallics 1993, 12, 641.
δC 58.3 (CtCH), 71.9 (CtCH), 97.3 (RuCtC), 104.0 (t, JCP ) 19.7,
RuCtC), 128.5 (vt, JCP ) 4.98, C3,5 (C6H5)), 130.7 (C4 (C6H5)), 132.9
(vt, JCP ) 24.21, C1 (C6H5)), 134.4 (vt, JCP ) 5.32, C2,6 (C6H5)), 191.7
(8) (a) Hill, A. F.; Rae, A. D.; Schultz, M.; Willis, A. C. Organome-
tallics 2004, 23, 81. (b) Hill, A. F.; Schultz, M.; Willis, A. C. Organo-
metallics 2005, 24, 2027.
2
2
(t, JCP ) 8.98, CO), 193.8 (t, JCP ) 10.6 Hz, CO); 31P{1H}, δP 22.1.
ESI-MS: m/z 806.8 [M + NCMe]+. Anal. Found: C, 62.65; H, 4.04; N,
0.00. Calcd for C42H31ClO2P2Ru‚0.66CH2Cl2: C, 62.32; H, 3.97; N, 0.00
(CH2Cl2 estimated by 1H NMR integration).
(9) Dewhurst, R. D.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organo-
metallics 2005, 24, 4703.
(10) 2: to Me3SiC4SiMe3 (2.47 g, 12.7 mmol) in ethanol (20 mL) was
added [Bu4N]F (50.4 mL, 50.4 mmol, 1.00 mol L-1 in THF, Aldrich)
and the mixture stirred for 15 min before anaerobic cannula transfer
to a suspension of 1 (6.00 g, 6.35 mmol)5b in THF (100 mL). The mixture
was stirred for 15 min and then concentrated to ca. 20 mL. The
resulting white solid was isolated by filtration and recrystallized
from CH2Cl2/EtOH to yield pale brown crystals. Yield: 3.96 g (85%).
IR (CH2Cl2): 2143 (νCtC), 2040, 1987 (νCO), 1999 (νRuH) cm-1. IR
(Nujol): 2141 (νCtC), 2040, 1989 (νCO), 2004 (νRuH) cm-1. NMR (C6D6,
25 °C): 1H, δH - 5.30 (t, 1H, RuH, 2JHP ) 20.0), 1.21 (t, 1H, -CtCH,
6JHP ) 1.2 Hz), 6.97, 7.92 (m × 2, 30H, C6H5); 31P{1H} δP 44.1. ESI-
MS: m/z 772.8 [M + H + NCMe]+. Anal. Found: C, 68.87; H, 4.79; N,
0.00. Calcd for C42H32O2P2Ru: C, 68.84; H, 4.40; N, 0.00. Crystal data
for 2‚C6H6: C48H38O2P2Ru, Mw) 809.79, P1h (No. 2), triclinic, a ) 10.010-
(2) Å, b ) 13.520(3) Å, c ) 15.669(3) Å, R ) 100.96(3)°, â ) 93.85(3)°,
γ ) 106.40(3)°, V ) 1980.7(7) Å3, Z ) 2, Fcalcd ) 1.358 Mg m-3, T )
200(2) K, colorless prism, F2 refinement, R1 ) 0.045, wR2 ) 0.122, for
9060 independent observed absorption corrected reflections (I > 2σ(I),
2θmax ) 49.68°), 478 parameters, CCDC 247962.
(13) 4-PF6: [RuCl(PPh3)2(η-C5H5)] (0.10 g, 0.14 mmol) and AgPF6
(0.035 g, 0.14 mmol) were stirred in THF (25 mL) for 10 min, the
mixture was then transferred, via filter cannula, to a flask containing
3 (0.11 g, 0.14 mmol), and the resulting mixture was stirred for 10
min. The solvent volume was then reduced in vacuo and ethanol added
to precipitate the orange-brown product, which was recrystallized from
THF/ethanol as a THF monosolvate (1H NMR). Yield: 0.17 g (75%).
IR (CH2Cl2): 2052, 1994 (νCO), 1969 (νCdCdRu) cm-1. IR (Nujol): 2046,
1986 (νCO), 1967 (νCdCdRu) cm-1. NMR (CHCl3, 25 °C): 1H, δH 4.66 (s,
5H, C5H5), 7.11, 7.73, 7.78 (m × 3, 61 H, C6H5, and CHdCdRu
correlated to δC 120.3); 13C{1H}, δC 91.4 (C5H5), 95.3 (RuCtC), 120.3
2
(RudCdCH), 127.7 (t, JPC ) 5.1, RuCtC), 128.5 (vt, JCP ) 4.00,
RuCO C3,5 (C6H5)), 128.8 (vt, JCP ) 5.13, RuCp C3,5 (C6H5)), 130.5
(RuCO C4 (C6H5)), 131.3 (RuCp C4 (C6H5)), RuCp C1 (C6H5) resonances
obscured, 133.3 (vt, JCP ) 5.21, RuCp C2,6 (C6H5)), 133.3 (vt, JCP
)
)
2
5.13, RuCO C2,6 (C6H5)), 191.9 (CO), 195.1 (CO), 335.1 (t, JCP
10.9 Hz, RudCdCH); 31P{1H}, δP 23.4, 47.1. ESI-MS: m/z 1422.8 [M
- PF6 - Cl]+ Anal. Found: C, 62.78; H, 4.43; N, 0.00. Calcd for
.
C83H66ClF6O2P5Ru2‚C4H8O: C, 62.36; H, 4.45; N, 0.00.

Communications
Organometallics, Vol. 24, No. 24, 2005 5797
Chart 2. Alternative Alkynyl-Vinylidene
Tautomers: 4+ and iso-4+
that the adopted isomer in which Ru-C multiple
bonding occurs specifically to the Ru(PPh3)2(η-C5H5) end
(4+ vs iso-4+), represents the thermodynamic prefer-
ence. This has been further confirmed by the observa-
tion that protonation of the butadiynediyl complex
[Cl(CO)2(Ph3P)2RuCtCCtCRu(PPh3)2(η-C5H5)] (5; vide
infra) with HPF6 exclusively (re)generates 4-PF6, with
no evidence for the transient intermediacy of iso-4+
being detectable within the time required to measure
the 31P NMR spectrum. Notably, the spectroscopic data
associated with the RuCl(CO)2(PPh3)2 terminus are
essentially invariant in the sequence 3 f 4+, (δP:
22.1f23.4); indeed, the mean νCO value actually de-
creases marginally (mean νCO: 2027 f 2023 cm-1),
inconsistent with the formation of a cationic [(Ph3P)2-
Cl(CO)2RudCR2]+ terminus.14 Thus, structural changes
may be assumed to be remote from the CO-ligated end
of the metallacumulene. We have previously shown that
the addition of CO trans to the vinylidene ligand in
[RuCl2{dCdC(SeiPr)Ph}(PPh3)2] results in rapid for-
mation of [RuCl2(CO)2(PPh3)2] (ttt isomer) and free
PhCtCSeiPr.15 In a similar manner, it has been noted
that the reactions of electrophiles with the complex
[RuCl(CtCPh)(CO)2(PPh3)2] (an analogue of 3) do not
result in the formation of vinylidene derivatives, while
HCl results in liberation of the alkyne and formation
of [RuCl2(CO)2(PPh3)2] (cct isomer).16 Thus, any putative
intermediate in which the superlatively π-acidic vi-
nylidene ligand is coordinated trans to a carbonyl ligand
at an octahedral ruthenium(II) center would appear to
be destabilized due to competitive π-acceptance. Rear-
rangement of the vinylidene to an alkyne tautomer
would alleviate this. However, this in turn introduces
a further labilization resulting from the repulsive
interaction of the filled alkyne bonding orbital (orthogo-
nal to the RuC2R2 coordination plane) with the occupied
(t2g)6 set of metal orbitals. Thus, the stability of 4+ and
isomeric preference (cf. iso-4+) may be traced to the
disparate electronic natures of the two chemically
distinct ruthenium termini.
Figure 2. Molecular geometry of 5 in a crystal of 5‚3C6H6
(phenyl groups simplified, 50% displacement ellispsoids).
Selected bond distances (Å) and angles (deg): Ru1-C2 )
1.864(5), Ru1-C1 ) 1.927(6), Ru1-C3 ) 2.065(4), Ru1-
P2 ) 2.4071(13), Ru1-P1 ) 2.4112(14), Ru1-Cl1 ) 2.4564-
(13), Ru2-C6 ) 2.020(5), Ru2-P4 ) 2.2824(14), Ru2-P3
) 2.2924(14), C3-C4 ) 1.220(6), C4-C5 ) 1.370(6), C5-
C6 ) 1.224(6); C6-Ru2-P4 ) 85.16(13), C6-Ru2-P3 )
88.74(14), P4-Ru2-P3 ) 102.85(5), C4-C3-Ru1 ) 177.1-
(4), C3-C4-C5 ) 178.8(5), C6-C5-C4 ) 174.5(5), C5-
C6-Ru2 ) 176.0(4).
σ-alkynyls [Ru(CtCR)(PPh3)2(η-C5H5)].17 Thus, treating
a solution of 4-PF6 in THF with diethylamine provides
the neutral bimetallic butadiynediyl complex [Cl(CO)2-
(Ph3P)2RuCtCCtCRu(PPh3)2(η-C5H5)] (5), the charac-
terization of which included a crystallographic analy-
sis.18 Figure 2 depicts the molecular geometry of the
bimetallic complex, while Table S1 (Supporting Infor-
mation) collates structural data for the range of known
1,4-diruthenated butadiynes. All of these are sym-
metrically substituted, with identical ligand sets at
either end comprising one η5-C5R5 (R ) H, Me) and two
phosphine donors: i.e., strongly π-basic ruthenium
termini. Complex 5 provides a rare opportunity to assess
the effects of varying coligands while keeping the metal
termini the same. Metal-alkynyl bonding is considered
to include a modest π-retrodative component that ap-
pears maximized for octahedral d6-metal centers devoid
of competitive π-acidic co-ligandssa situation exempli-
fied by the Ru(PPh3)2(η-C5H5) terminus in 5. In contrast,
(17) Davies, S. G.; McNally, J. P.; Smallridge, A. J. Adv. Organomet.
Chem. 1990, 30, 1.
(18) 5: diethylamine (1 mL) was added to a solution of 4-PF6 (0.10
g, 0.06 mmol) in THF (20 mL) and the mixture stirred for 20 min.
Concentration under reduced pressure precipitated the lemon yellow
product, which was recrystallized from CH2Cl2/EtOH as an ethanol
monosolvate (analysis) or a benzene solvate from benzene (X-ray).
Yield: 0.06 g (66%). IR (CH2Cl2): 2048, 1987 (νCO) cm-1. IR (Nujol):
2044, 1983 (νCO) cm-1. NMR (C6D6, 25 °C): 1H, δH 4.43 (s, 5H, C5H5),
6.94, 7.04, 7.73, 8.36 (m × 4, 60 H, C6H5); 13C{1H}, δC 80.3 (br,
CtCRu(Cp)), 85.9 (C5H5), 95.7 (br, (OC)RuCtC), 102.1 ((OC)-
RuCtC), 106.5 (CtCRu(Cp)), the phenyl region was obscured by the
solvent peak, no unambiguous assignments could be made, 192.1 (CO),
195.8 (CO); 31P{1H}, δP 21.8, 51.3. ESI-MS: m/z 1461.7 [M - Cl +
We have not yet succeeded in obtaining crystal-
lographic grade crystals of 4-PF6; however, further
support for its formulation is provided by the simple
deprotonation reaction that is typical of vinylidenes of
the form [Ru(dCdCHR)(PPh3)2(η-C5H5)]+ to provide the
(14) The comparable conversion of [OsCl{C(H)dS}(CO)2(PPh3)2}] to
[OsCl{dC(H)SCH3}(CO)2(PPh3)2}]+ is accompanied by an expected
increase in mean νCO from 2010 to 2023 cm-1: Collins, T. J.; Roper,
W. R. J. Organomet. Chem. 1978, 159, 73.
(15) Hill, A. F.; Hulkes, A. G.; White, A. J. P.; Williams, D. J.
Organometallics 2000, 19, 371.
(16) Bedford, R. B.; Hill, A. F.; Thompsett, A. R.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Chem. Commun. 1996, 1059.
NCMe]+, 1420.6 [M - Cl]+ Anal. Found: C, 67.89; H, 4.89; N, 0.00.
.
Calcd for C83H65ClO2P4Ru2‚EtOH: C, 67.90; H, 4.76; N, 0.00. Crystal
data for 5‚3C6H6: C101H83ClO2P4Ru2, Mw ) 1690.14, monoclinic,
P21/n, a ) 13.189(3) Å, b ) 25.805(5) Å, c ) 24.164(5) Å, â ) 90.13(3)°,
V ) 8224(3) Å3, Z ) 4, Fcalcd ) 1.365 Mg m-3, T ) 200(2) K, yellow
prisms, R1 ) 0.064, wR2 ) 0.151, for 14 527 independent, observed,
absorption-corrected reflections (I > 2σ(I), 2θmax ) 44.30°), 1084
parameters, CCDC 284088.

5798 Organometallics, Vol. 24, No. 24, 2005
Communications
Ru1 is ligated by two strong π-acids, one of which
interacts with both of the t2g-type orbitals that might
otherwise be exploited for retrodonation to the C4 ligand.
This is reflected in the significant (9σ) lengthening of
Ru1-C3 relative to Ru2-C6, the former being the
longest in Table S1. The cis Ru1(CO)2 arrangement
allows an internally referenced indication of the trans
influence of the C4 ligand relative to chloride. The
Ru1-C1 bond is markedly (12σ) lengthened relative to
Ru1-C2, possibly suggesting a degree of competitive
π-acidity on the part of the C4 ligand.
Acknowledgment. We are grateful to one reviewer
for identifying an erroneous spectroscopic assignment
of the 13C{1H} NMR data for 4+.
Supporting Information Available: Full details of the
crystal structure determinations of 2‚C6H6 (CCDC 247962) and
5‚3C6H6 (CCDC 284088) in CIF format and Table S1, collating
structural data for 5 and diruthenated butadiynes. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM050800O