Probing the Ruthenium-Cumulene Bonding Interaction: Synthesis and Spectroscopic Studies of Vinylidene- and Allenylidene-Ruthenium Complexes Supported by Tetradentate Macrocyclic Tertiary Amine and Comparisons with Diphosphine Analogues of Ruthenium and Osmium

Article abstract of DOI:10.1021/ja0380648

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru=C=CHR]PF₆ (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C₆H ₄X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh₂ (5)), trans-[Cl(16-TMC)Ru=C=C=C(C₆H₄X-4)₂]PF ₆ (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm) ₂M=C=C=C(C₆H₄X-4)₂]PF₆ (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C _α and C_α-C_β distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E_1/2 values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp₂Fe^+/0, and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at λ_max ≤ 310 nm (ε_max ≥ 10⁴ dm³ mol^-1 cm^-1), while weak absorptions at λ_max ≥ 400 nm (ε_max ≤ 10² dm³ mol^-1 cm^-1) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal v _c=c stretch mode of the vinylidene ligand at 1629 cm^-1. The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at λ_max = 479-513 nm (ε_max = (2-3) × 10⁴ dm³ mol^-1 cm^-1). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm^-1 for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl-(NH₃)₄Ru=C=C=CPh ₂]⁺ at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at λ_max = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal v_c=c=c stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru=C and Ru-N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C=C=C unit in the electronic excited state.

Full text of DOI:10.1021/ja0380648

Published on Web 01/30/2004
Probing the Ruthenium-Cumulene Bonding Interaction:
Synthesis and Spectroscopic Studies of Vinylidene- and
Allenylidene-Ruthenium Complexes Supported by
Tetradentate Macrocyclic Tertiary Amine and Comparisons
with Diphosphine Analogues of Ruthenium and Osmium†
Chun-Yuen Wong, Chi-Ming Che,* Michael C. W. Chan, King-Hung Leung,
David Lee Phillips,* and Nianyong Zhu
Contribution from the Department of Chemistry and HKU-CAS Joint Laboratory on New
Materials, The UniVersity of Hong Kong, Pokfulam Road, Hong Kong SAR, China
Received August 22, 2003; E-mail: cmche@hku.hk
Abstract: The synthesis and spectroscopic properties of trans-[Cl(16-TMC)RudCdCHR]PF6 (16-TMC )
1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R ) C6H4X-4, X ) H (1), Cl (2), Me (3), OMe (4);
R ) CHPh2 (5)), trans-[Cl(16-TMC)RudCdCdC(C6H4X-4)2]PF6 (X ) H (6), Cl (7), Me (8), OMe (9)), and
trans-[Cl(dppm)2MdCdCdC(C6H4X-4)2]PF6 (M ) Ru, X ) H (10), Cl (11), Me (12); M ) Os, X ) H (13),
Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-CR and CR-Câ
distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two
reversible redox couples are observed by cyclic voltammetry for 6-9, with E1/2 values ranging from -1.19
to -1.42 and 0.49 to 0.70 V vs Cp2Fe+/0, and they are both 0.2-0.3 and 0.1-0.2 V more reducing than
those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are
dominated by intense high-energy bands at λmax e 310 nm (ꢀmax g 104 dm3 mol-1 cm-1), while weak
absorptions at λmax g 400 nm (ꢀmax e 102 dm3 mol-1 cm-1) are tentatively assigned to d-d transitions. The
resonance Raman spectrum of 5 contains a nominal νCdC stretch mode of the vinylidene ligand at 1629
cm-1. The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption
at λmax ) 479-513 nm (ꢀmax ) (2-3) × 104 dm3 mol-1 cm-1). Similar electronic absorption bands have
been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm-1
for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl-
(NH3)4RudCdCdCPh2]+ at the MP2 level, and imply that the HOMO is not localized purely on the metal
center or allenylidene ligand. The absorption band of 6 at λmax ) 479 nm has been probed by resonance
Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that
the nominal νCdCdC stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating
that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization
of the allenylidene ligand is accompanied by rearrangement of the RudC and Ru-N (of 16-TMC) fragments,
which supports the existence of bonding interaction between the metal and CdCdC unit in the electronic
excited state.
Introduction
π-bonding/back-bonding interaction. Extensive synthetic inves-
tigations and numerous X-ray structural determinations, theoreti-
The chemistry of metallacumulenes M(dC)nCR2 is of con-
siderable interest from several perspectives.1 In the context of
materials science, π-conjugated linear (dC)n moieties funda-
mentally allow communication between metal centers and
remote functional groups, and potential applications as nonlinear
optical materials and molecular wires have been advocated.2
Metallacumulenes also represent an interesting class of metal-
carbon multiple-bonded compounds for the study of the bonding
interaction in M(dC)nCR2, particularly with regard to the
oxidation state assignment of the metal ion and the degree of
cal calculations, and vibrational mode studies have been
undertaken for metallacumulenes.3 The majority of these
complexes are supported by phosphine and/or cyclopentadienyl
ligands, while P,O-4 and N-chelating5 groups have also been
described.
(2) (a) Hurst, S. K.; Cifuentes, M. P.; Morrall, J. P. L.; Lucas, N. T.; Whittall,
I. R.; Humphrey, M. G.; Asselberghs, I.; Persoons, A.; Samoc, M.; Luther-
Davies, B.; Willis, A. C. Organometallics 2001, 20, 4664-4675. (b) Uno,
M.; Dixneuf, P. H. Angew. Chem., Int. Ed. Engl. 1998, 37, 1714-1717.
(c) Lang, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 547-550. Examples
of other metal analogues and acetylide relatives: (d) McDonagh, A. M.;
Humphrey, M. G.; Samoc, M.; Luther-Davies, B.; Houbrechts, S.; Wada,
T.; Sasabe, H.; Persoons, A. J. Am. Chem. Soc. 1999, 121, 1405-1406.
(e) Bartik, T.; Weng, W.; Ramsden, J. A.; Szafert, S.; Falloon, S. B.; Arif,
A. M.; Gladysz, J. A. J. Am. Chem. Soc. 1998, 120, 11071-11081.
† In memory of Dr. Vincent M. Miskowski.
* For correspondence regarding Raman spectroscopy: phillips@hku.hk.
(1) (a) Bruce, M. I. Chem. ReV. 1998, 98, 2797-2858. (b) Bruce, M. I. Chem.
ReV. 1991, 91, 197-257.
9
10.1021/ja0380648 CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 2501-2514
2501

A R T I C L E S
Wong et al.
Due to their conjugated nature, the bonding of metallacu-
mulenes may be represented by mesomeric structures, such as
M--CtC-C+R2 T MdCdCdCR2, for allenylidene com-
plexes.6 To facilitate the development of these materials,
particularly for optoelectronic applications, it is important to
understand the excited states arising from the electronic transi-
tions associated with M(dC)nCR2 moieties. Techniques such
as UV-vis and resonance Raman spectroscopy can be employed
to investigate the properties of such excited states, and they
can also provide information regarding the interaction between
the metal and cumulene ligand in both the ground and excited
states. However, there have been few spectroscopic studies on
metallacumulenes, and the ubiquitous incorporation of unsatur-
ated organic ancillary ligands in M(dC)nCR2 complexes has
hampered spectral assignment and interpretation.
ruthenium-porphyrin catalysts.9 Ruthenium-allenylidene com-
plexes have also recently been employed as catalysts for ring-
closing olefin metathesis and propargylation of aromatic
compounds.10 Nevertheless, despite their demonstrated capabili-
ties and versatility, investigations regarding the spectroscopic
nature of RudC moieties remain sparse in the literature. We
recently initiated research activities for organoruthenium com-
plexes containing the macrocyclic tertiary amine 1,5,9,13-
tetramethyl-1,5,9,13-tetraazacyclohexadecane (16-TMC).5d,11 This
ligand is optically transparent in the UV-vis spectral region
and is ideally suited to allow examination of the electronic
transitions associated with the Ru(dC)nCR2 fragment. Further-
more, 16-TMC is a pure σ-donor and does not compete with
the (dC)nCR2 ligand for π-bonding (either direct dπ-pπ (filled)
or π-back-bonding) interactions. This and closely related
macrocyclic ligands have been widely used to stabilize metal-
oxygen and -nitrogen multiple-bonded systems.12
Previous reports have shown that stable oxoruthenium(IV)
and -(VI) complexes of 16-TMC can be obtained at relatively
low reduction potentials.13 In this account, we prepared a series
of aryl-substituted vinylidene- and allenylidene-ruthenium
complexes supported by 16-TMC. Rational methodologies
toward the targeted organometallic species have been devised,
and a hydrogen-atom addition reaction by the allenylidene
complexes is also described. To provide a comparative study
on the ligand effect upon the spectroscopic and electrochemical
properties of the [RudCdCdCR2] moiety, (dppm)2-ligated
ruthenium and osmium congeners have also been prepared and
investigated. Theoretical calculations on the ground state of the
model complex [Cl(NH3)4RudCdCdCPh2]+ have been per-
formed. Resonance Raman spectroscopy has been utilized to
probe the electronic transitions associated with the vinylidene
and allenylidene complexes in order to gain insight into the
nature of the Ru(dC)nCR2 bonding interaction.
We are interested in ruthenium-carbon multiple-bonded
complexes, which have been established as novel and diverse
catalysts for important organic transformations.7 For example,
the Grubbs alkylidene complexes RuCl2(dCHR)(PR3)2 and
more recent congeners containing N-heterocyclic carbene
ligands are highly active and functional-group-tolerant catalysts
for olefin metathesis reactions.8 Ruthenium-carbene species
have been proposed as active intermediates for carbene inser-
tions into CdC and C-H bonds, as highlighted by reports on
(3) For examples, see: (a) Ilg, K.; Werner, H. Chem. Eur. J. 2002, 8, 2812-
2820. (b) Rigaut, S.; Monnier, F.; Mousset, F.; Touchard, D.; Dixneuf, P.
H. Organometallics 2002, 21, 2654-2661. (c) Bustelo, E.; Jime´nez-Tenorio,
M.; Mereiter, K.; Puerta, M. C.; Valerga, P. Organometallics 2002, 21,
1903-1911. (d) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J.;
Rodr´ıguez, M. A. Organometallics 2002, 21, 203-209. (e) Cadierno, V.;
Gamasa, M. P.; Gimeno, J.; Gonza´lez-Bernardo, C.; Pe´rez-Carren˜o, E.;
Garc´ıa-Granda, S. Organometallics 2001, 20, 5177-5188. (f) Gonza´lez-
Herrero, P.; Weberndo¨rfer, B.; Ilg, K.; Wolf, J.; Werner, H. Organometallics
2001, 20, 3672-3685. (g) Moigno, D.; Kiefer, W.; Callejas-Gaspar, B.;
Gil-Rubio, J.; Werner, H. New J. Chem. 2001, 25, 1389-1397. (h) Bruce,
M. I.; Low, P. J.; Costuas, K.; Halet, J.-F.; Best, S. P.; Heath, G. A. J. Am.
Chem. Soc. 2000, 122, 1949-1962. (i) Re, N.; Sgamellotti, A.; Floriani,
C. Organometallics 2000, 19, 1115-1122. (j) Moigno, D.; Kiefer, W.; Gil-
Rubio, J.; Werner, H. J. Organomet. Chem. 2000, 612, 125-132. (k)
Touchard, D.; Haquette, P.; Daridor, A.; Romero, A.; Dixneuf, P. H.
Organometallics 1998, 17, 3844-3852. (l) Colbert, M. C. B.; Lewis, J.;
Long, N. J.; Raithby, P. R.; Younus, M.; White, A. J. P.; Williams, D. J.;
Payne, N. N.; Yellowlees, L.; Beljonne, D.; Chawdhury, N.; Friend, R. H.
Organometallics 1998, 17, 3034-3043. (m) Touchard, D.; Dixneuf, P. H.
Coord. Chem. ReV. 1998, 178-180, 409-429. (n) Oliva´n, M.; Eisenstein,
O.; Caulton, K. G. Organometallics 1997, 16, 2227-2229. (o) Werner, H.
Chem. Commun. 1997, 903-910.
Experimental Section
General Procedures. All reactions were performed under a nitrogen
atmosphere using standard Schlenk techniques unless otherwise stated.
All reagents were used as received, and solvents were purified by
(9) (a) Li, Y.; Huang, J.-S.; Zhou, Z.-Y.; Che, C.-M.; You, X.-Z. J. Am. Chem.
Soc. 2002, 124, 13185-13193. (b) Miller, J. A.; Jin, W.; Nguyen, S. T.
Angew. Chem., Int. Ed. 2002, 41, 2953-2956. (c) Munslow, I. J.; Gillespie,
K. M.; Deeth, R. J.; Scott, P. Chem. Commun. 2001, 1638-1639. (d) Che,
C.-M.; Huang, J.-S.; Lee, F.-W.; Li, Y.; Lai, T.-S.; Kwong, H.-L.; Teng,
P.-F.; Lee, W.-S.; Lo, W.-C.; Peng, S.-M.; Zhou, Z.-Y. J. Am. Chem. Soc.
2001, 123, 4119-4129. (e) Li, Y.; Huang, J.-S.; Zhou, Z.-Y.; Che, C.-M.
J. Am. Chem. Soc. 2001, 123, 4843-4844. (f) Hamaker, C. G.; Mirafzal,
G. A.; Woo, L. K. Organometallics 2001, 20, 5171-5176. (g) Galardon,
E.; Maux, P. L.; Simonneaux, G. Tetrahedron 2000, 56, 615-621. (h) Wolf,
J. R.; Hamaker, C. G.; Djukic, J.-P.; Kodadek, T.; Woo, L. K. J. Am. Chem.
Soc. 1995, 117, 9194-9199. (i) Smith, D. A.; Reynolds, D. N.; Woo, L.
K. J. Am. Chem. Soc. 1993, 115, 2511-2513.
(10) (a) Nishibayashi, Y.; Inada, Y.; Hidai, M.; Uemura, S. J. Am. Chem. Soc.
2002, 124, 7900-7901. (b) Nishibayashi, Y.; Yoshikawa, M.; Inada, Y.;
Hidai, M.; Uemura, S. J. Am. Chem. Soc. 2002, 124, 11846-11847. (c)
Se´meril, D.; Oliver-Bourbigou, H.; Bruneau, C.; Dixneuf, P. H. Chem.
Commun. 2002, 146-147. (d) Fu¨rstner, A.; Liebl, M.; Lehmann, C. W.;
Picquet, M.; Kunz, R.; Bruneau, C.; Touchard, D.; Dixneuf, P. H. Chem.
Eur. J. 2000, 6, 1847-1857.
(4) (a) Mart´ın, M.; Gevert, O.; Werner, H. J. Chem. Soc., Dalton Trans. 1996,
2275-2283. (b) Braun, T.; Steinert, P.; Werner, H. J. Organomet. Chem.
1995, 488, 169-176.
(5) (a) Ru¨ba, E.; Hummel, A.; Mereiter, K.; Schmid, R.; Kirchner, K.
Organometallics 2002, 21, 4955-4959. (b) Tenorio, M. A. J.; Tenorio,
M. J.; Puerta, M. C.; Valerga, P. Organometallics 2000, 19, 1333-1342.
(c) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Iglesias, L.; Garc´ıa-Granda,
S. Inorg. Chem. 1999, 38, 2874-2879. (d) Yang, S.-M.; Chan, M. C. W.;
Cheung, K.-K.; Che, C.-M.; Peng, S.-M. Organometallics 1997, 16, 2819-
2826. (e) Slugovc, C.; Mereiter, K.; Zobetz, E.; Schmid, R.; Kirchner, K.
Organometallics 1996, 15, 5275-5277.
(6) (a) Tamm, M.; Jentzsch, T.; Werncke, W. Organometallics 1997, 16, 1418-
1424. (b) Bruce, M. I.; Hinterding, P.; Low, P. J.; Skelton, B. W.; White,
A. H. Chem. Commun. 1996, 1009-1010. (c) Touchard, D.; Pirio, N.;
Toupet, L.; Fettouhi, M.; Ouahab, L.; Dixneuf, P. H. Organometallics 1995,
14, 5263-5272.
(7) (a) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. ReV. 2001, 101,
2067-2096. (b) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. ReV. 1998,
98, 2599-2660. (c) Doyle, M. P.; Forbes, D. C. Chem. ReV. 1998, 98,
911-935. (d) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311-
323.
(8) (a) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc. 2001,
123, 749-750. (b) Weskamp, T.; Kohl, F. J.; Hieringer, W.; Gleich, D.;
Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1999, 38, 2416-2419. (c)
Huang, J.; Stevens, E. D.; Nolan, S. P.; Petersen, J. L. J. Am. Chem. Soc.
1999, 121, 2674-2678. (d) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R.
H. Org. Lett. 1999, 1, 953-956. (e) Weskamp, T.; Schattenmann, W. C.;
Spiegler, M.; Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1998, 37,
2490-2493. (f) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem.
Soc. 1996, 118, 100-110. (g) Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W.
J. Am. Chem. Soc. 1993, 115, 9858-9859.
(11) (a) Choi, M.-Y.; Chan, M. C. W.; Peng, S.-M.; Cheung, K.-K.; Che, C.-
M. Chem. Commun. 2000, 1259-1260. (b) Choi, M.-Y.; Chan, M. C. W.;
Zhang, S.; Cheung, K.-K.; Che, C.-M.; Wong, K.-Y. Organometallics 1999,
18, 2074-2080. (c) Yang, S.-M.; Chan, M. C. W.; Peng, S.-M.; Che, C.-
M. Organometallics 1998, 17, 151-155. (d) Yang, S.-M.; Cheng, W.-C.;
Peng, S.-M.; Cheung, K.-K.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1995,
2955-2959.
(12) (a) Chan, P.-M.; Yu, W.-Y.; Che, C.-M.; Cheung, K.-K. J. Chem. Soc.,
Dalton Trans. 1998, 3183-3190. (b) Che, C.-M.; Lai, T.-F.; Wong, K.-Y.
Inorg. Chem. 1987, 26, 2289-2299. (c) Che, C.-M.; Wong, K.-Y.; Poon,
C.-K. Inorg. Chem. 1986, 25, 1809-1813.
(13) Che, C.-M.; Yam, V. W.-W. AdV. Inorg. Chem. 1992, 39, 233-325.
9
2502 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004

Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
standard methods. Zinc amalgam was prepared by adding zinc turning
(0.3 g) to a methanolic solution (10 mL) of mercury acetate (0.1 g),
followed by washing with methanol. [Ru(16-TMC)Cl2]Cl,12c RuCl2(d
CHPh)(PCy3)2,8f RuCl2(dCdCHPh)(PCy3)2,14 trans-[Cl(dppm)2Rud
CdCdC(C6H4X-4)2]PF6 (X ) H, Cl, Me (10-12)),15 and cis-
[Os(dppm)2Cl2]16 were prepared according to published procedures.
1H, 13C{1H}, DEPT-135, and 31P{1H} NMR spectra were recorded
on Bruker 400 DPX, 500 DRX, and 600 DRX FT-NMR spectrometers.
Peak positions were calibrated with solvent residue peaks as internal
standard for 1H and 13C{1H} spectra, while the 31P NMR spectra were
referenced to external 85% H3PO4. In the 1H and 13C{1H} NMR spectra,
multiple resonances corresponding to different conformations of 16-
TMC were observed. This is because the 16-TMC ligand, like its
congeners 14- and 15-TMC, can exhibit several possible conformations
upon coordination to the metal center12b,17 (the crystal structures in this
work also show that some (CH2)3 groups are disordered, and the methyl
groups attached to N atoms are often disordered and occupy at least
two positions). Variable-temperature 1H and 13C{1H} NMR spectra
(-75 and 35 °C) for complex 7 have been recorded, and the minimal
differences observed suggest that the conformations are not inter-
changeable in this temperature range. In the 13C{1H} and (to some
extent) 1H NMR spectra, all positions of the 16-TMC ligand have been
assigned and the peak(s) listed for each position correspond to signal-
(s) of greater intensity (see Supporting Information for spectra of 6).
Fast atom bombardment (FAB) mass spectra were obtained on a
Finnigan MAT 95 mass spectrometer with a 3-nitrobenzyl alcohol
matrix. Infrared spectra were recorded as KBr plates on a Bio-Rad FT-
IR spectrometer. UV-vis spectra were recorded on a Perkin-Elmer
Lambda 19 spectrophotometer. Elemental analyses were performed by
the Institute of Chemistry, Chinese Academy of Sciences, Beijing.
Cyclic voltammetry was performed with a Princeton Applied
Research Model 273A potentiostat. A conventional two-compartment
electrochemical cell was used. The glassy-carbon electrode was polished
with 0.05 µm alumina on a microcloth, sonicated for 5 min in deionized
water, and rinsed with acetonitrile before use. An Ag/AgNO3 (0.1 M
in CH3CN) electrode was used as reference electrode. All solutions
were degassed with argon before experiments. E1/2 values are the
average of the cathodic and anodic peak potentials for the oxidative
and reductive waves. The E1/2 value of the ferrocenium/ferrocene couple
(Cp2Fe+/0) measured in the same solution was used as an internal
reference, and all reported E1/2 values are referenced to the Cp2Fe+/0
couple.
solvent bands, the Rayleigh line, and the quartz cell background signal
from the resonance Raman spectrum.
Computational Methodology. The ab initio calculations were
performed on the model complex [Cl(NH3)4RudCdCdCPh2]+ (with
C1 symmetry), which was used as a computational model for [Cl(16-
TMC)RudCdCdCAr2]+ (6-9). The geometry of the complex was
optimized at second-order Møller-Plesset (MP2) level. The large orbital
basis sets with relativistic effective core potential CRENBL ECP
proposed by Christiansen et al.19 were employed, i.e., H (4s), C, N, Cl
(ECP, 4s, 4p), and Ru (ECP, 5s, 5p, 4d), and the number of valence
electrons involved for Ru, C, N, and Cl were 16, 4, 5, and 7,
respectively. Therefore, the calculations employed 448 basis functions
and 124 electrons. The natural charges were calculated using natural
population analysis.20 The calculations were accomplished using the
Gaussian 98 program21 on a PC, natural population analysis was
performed using NBO version 3.122 distributed in Gaussian 98, and
the molecular graphics are presented using MOLEKEL version 4.3.23
Synthesis. [Cl(16-TMC)RudCdCH(C6H4X-4)]PF6 (1-4). Excess
HCtCC6H4X-4 (1 mmol) was added to a mixture containing [Ru(16-
TMC)Cl2]Cl (0.10 g, 0.20 mmol) and zinc amalgam in methanol (30
mL). After refluxing for 2 h, the resultant green solution was filtered
and added to a saturated methanolic solution of NH4PF6 to afford a
green crystalline solid. This solid was recrystallized by slow diffusion
of Et2O into a CH2Cl2 solution to give bright green crystals. Complex
1 (X ) H): yield 0.09 g, 67%. Anal. Calcd for C24H42N4RuClPF6: C,
43.15; H, 6.34; N, 8.39. Found: C, 42.99; H, 6.36; N, 8.28. 1H NMR
(500 MHz, (CD3)2CO): δ 1.50-1.58, 1.86-2.26 (m, 16H, CH2), 2.47,
2.70, 2.73 (singlets, 12H, NCH3), 3.29-4.13 (m, 8H, CH2), 4.83, 4.89
(2 × s, 1H, dCH), 7.16-7.55 (m, 5H, C6H5). 13C{1H} NMR (126
MHz, (CD3)2CO): δ 20.9, 21.0 (NCH2CH2); 45.0, 48.1, 50.5, 51.3,
55.2 (NCH3); 57.8, 58.1, 61.1, 62.4, 65.7, 66.1, 67.2, 68.6 (NCH2);
111.1, 111.4 (Câ); 126.5, 126.6, 128.5, 128.6, 129.2 (aryl C); 127.4,
127.7 (Cipso); 349.4, 351.5 (CR). IR (cm-1): νCdC ) 1593, 1607, νP-F
) 834. FAB-MS: m/z 523 [M+]. See Supporting Information for 2-4.
[Cl(16-TMC)RudCdCHCHPh2]PF6 (5). The procedure for 1-4
was adopted, but 1,1-diphenyl-2-propyn-1-ol was used instead of the
acetylene substrate. Addition of a saturated methanolic solution of NH4-
PF6 afforded a pale red crystalline solid, which was recrystallized from
CH2Cl2/Et2O to give bright red crystals. Yield 0.11 g, 73%. Anal. Calcd
for C31H48N4RuClPF6: C, 49.11; H, 6.38; N, 7.39. Found: C, 48.99;
H, 6.41; N, 7.44. 1H NMR (500 MHz, (CD3)2CO): δ 1.46-1.52, 1.80-
(19) (a) Pacios, L. F.; Christiansen, P. A. J. Chem. Phys. 1985, 82, 2664-
2671. (b) LaJohn, L. A.; Christiansen, P. A.; Ross, R. B.; Atashroo, T.;
Ermler, W. C. J. Chem. Phys. 1987, 87, 2812-2824. Basis sets were
obtained from the Extensible Computational Chemistry Environment Basis
Set Database, Version 6/19/03, as developed and distributed by the
Molecular Science Computing Facility, Environmental and Molecular
Sciences Laboratory which is part of the Pacific Northwest Laboratory,
P.O. Box 999, Richland, WA 99352 and funded by the U.S. Department
of Energy. The Pacific Northwest Laboratory is a multiprogram laboratory
operated by Battelle Memorial Institute for the U.S. Department of Energy
under contract DE-AC06-76RLO 1830. Contact David Feller or Karen
Schuchardt for further information.
Resonance Raman Spectroscopy.The resonance Raman apparatus
and methods have previously been described in detail,18 and a summary
is given here. The first anti-Stokes Raman-shifted line of the second
harmonic of an Nd:YAG laser provided the excitation frequency for
the resonance Raman experiment. The laser beam was loosely focused
onto the sample using ∼130° backscattering geometry, and reflective
optics were used to collect the Raman-scattered light and image it
through a depolarizer and entrance slit of a 0.5 m spectrograph equipped
with a 1200 groove/mm ruled grating blazed at 250 nm. The light was
dispersed onto a liquid nitrogen cooled CCD detector. Accumulations
of about 1 min were acquired from the CCD, and about 30 of these
scans were added to afford the resonance Raman spectrum. Known
acetonitrile solvent bands were used to calibrate the Raman shifts of
the resonance Raman spectrum. Appropriately scaled solvent and quartz
cell background spectra (accumulated simultaneously with the sample
spectra on a different part of the CCD) were subtracted to remove the
(20) (a) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83,
735-746. (b) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066-
4073.
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.;
Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98 (Revision
A.7); Gaussian, Inc.: Pittsburgh, PA, 1998.
(22) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO 3.1.
Board of Regents of the University of Wisconsin System on behalf of the
Theoretical Chemistry Institute, 1996-2003.
(23) (a) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. MOLEKEL 4.3; Swiss
Center for Scientific Computing: Manno, Switzerland, 2000-2002. (b)
Portmann, S.; Luthi, H. P. Chimia 2000, 54, 766-770.
(14) Katayama, H.; Ozawa, F. Organometallics 1998, 17, 5190-5196.
(15) Touchard, D.; Pirio, N.; Dixneuf, P. H. Organometallics 1995, 14, 4920-
4928.
(16) Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1982, 21, 1037-1040.
(17) (a) Che, C.-M.; Cheng, W.-K.; Lai, T.-F.; Poon, C.-K.; Mak, T. C. W.
Inorg. Chem. 1987, 26, 1678-1683. (b) Che, C.-M.; Wong, K.-Y.; Mak,
T. C. W. Chem. Commun. 1985, 988-990. (c) Mak, T. C. W.; Che, C.-
M.; Wong, K.-Y. Chem. Commun. 1985, 986-988. (d) Che, C.-M.; Wong,
K.-Y.; Mak, T. C. W. Chem. Commun. 1985, 546-548.
(18) Zheng, X.; Phillips, D. L. J. Chem. Phys. 1998, 108, 5772-5783.
9
J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2503

A R T I C L E S
Wong et al.
Scheme 1
2.28 (m, 16H, CH2), 2.42, 2.58, 2.61 (singlets, 12H, NCH3), 3.18-
3
4.06 (m, 8H, CH2), 4.68, 4.74 (2 × d, 1H, JHH ) 10.5 Hz, dCH,),
3
6.01, 6.03 (2 × d, 1H, JHH ) 10.5 Hz, CHPh2), 7.23-7.60 (m, 10H,
C6H5). 13C{1H} NMR (126 MHz, (CD3)2CO): δ 20.9, 21.6 (NCH2CH2);
42.1, 42.4 (CHPh2); 44.8, 48.0, 50.4, 50.8, 54.8 (NCH3); 57.5, 57.9,
61.0, 62.4, 65.7, 66.0, 67.1, 69.4 (NCH2); 112.1, 112.4 (Câ); 126.8,
128.0, 128.9 (aryl C); 145.9, 146.0 (Cipso); 347.4, 350.5 (CR). IR (cm-1):
νCdC ) 1631, νP-F ) 839. FAB-MS: m/z 613 [M+].
[Cl(16-TMC)RudCdCdC(C6H4X-4)2]PF6 (6-9). A methanolic
solution (30 mL) of [Ru(16-TMC)Cl2]Cl (0.10 g, 0.20 mmol) was
refluxed in the presence of zinc amalgam for 10 min. This was filtered
to give a green solution, and excess HCtCC(C6H4X-4)2OH (0.40 mol)
was then added. After refluxing for 2 h, the resultant deep red solution
was filtered and added to a saturated methanolic solution of NH4PF6
to afford a red crystalline solid. The crude red solid was dissolved in
a minimum amount of CH2Cl2, and slow diffusion of Et2O into this
solution afforded deep red crystals. Complex 6 (X ) H): yield 0.11 g,
73%. Anal. Calcd for C31H46N4RuClPF6: C, 49.24; H, 6.13; N, 7.41.
of the associated C atom. For 1‚CH2Cl2, two formula units were located
in the asymmetric unit. Disorder is observed in the (CH2)3 units of the
16-TMC ligands, and some restraints had been applied. In the final
stage of least-squares refinement, the disordered atoms and C(50) of
the solvent molecule were refined isotropically. For 5‚CH2Cl2, one
crystallographic asymmetric unit consists of one formula unit. The CH3
and two CH2 groups bound to N(3) in the 16-TMC ligand, plus the
PF6- unit, are disordered. For 6, one crystallographic asymmetric unit
consists of one formula unit. Disorder was found concerning groups
bound to N(3) and N(4), which were refined isotropically. For 8, one
crystallographic asymmetric unit consists of one-half of one formula
unit. The (CH2)3 groups of the 16-TMC ligand are disordered, and
restraints have been applied.
1
Found: C, 49.29; H, 6.20; N, 7.65. H NMR (500 MHz, (CD3)2CO):
δ 1.38-1.48, 1.67-2.28 (m, 16H, CH2), 2.36, 2.39, 2.52 (singlets, 12H,
NCH3), 3.05-4.04 (m, 8H, CH2), 7.35-7.48 (m, 4H, Ho), 7.85-7.91
(m, 2H, Hp), 8.07-8.11 (m, 4H, Hm). 13C{1H} NMR (126 MHz, (CD3)2-
CO): δ 20.9, 21.6 (NCH2CH2); 44.6, 48.1, 50.6, 50.7, 54.4 (NCH3);
57.6, 57.8, 58.0, 61.3, 61.7, 65.9, 66.2, 67.0, 69.9 (NCH2); 127.1, 129.7,
130.0 (aryl C); 150.1, 150.7 (Cγ); 150.9, 151.0 (Cipso); 248.7, 250.7
(Câ); 302.9, 308.6 (CR). IR (cm-1): νCdCdC ) 1884, νP-F ) 841. FAB-
MS: m/z 611 [M+]. See Supporting Information for 7-9.
[Cl(dppm)2OsdCdCdC(C6H4X-4)2]PF6 (13-15). To a CH2Cl2
solution (30 mL) of HCtCC(C6H4X-4)2OH (0.50 mol) and NaPF6 (0.1
g, 0.60 mmol) was added cis-[Os(dppm)2Cl2] (0.15 g, 0.27 mmol). After
stirring for 3 h at room temperature, the color of the solution turned
deep violet then deep orange-red. The reaction mixture was stirred for
an additional 12 h and filtered. All volatile components were removed
under vacuum. The resultant red solid was washed with Et2O (3 × 15
mL) and recrystallized by slow diffusion of Et2O into a CH2Cl2 solution
to give bright red crystals. Complex 13 (X ) H): yield 0.25 g, 75%.
Anal. Calcd for C65H54OsClP5F6: C, 58.72; H, 4.09. Found: C, 58.81;
H, 4.03. 1H NMR (400 MHz, (CD3)2CO): δ 5.99-6.25 (m, 4H,
PCH2P), 6.69-7.78 (m, 50H, aryl H). 13C{1H} NMR (100 MHz, (CD3)2-
CO): δ 50.6 (PCH2P), 128.0-133.3 (aryl C), 150.3 (Cipso), 155.4 (Cγ),
225.6 (Câ), 270.8 (CR). 31P{1H} NMR (162 MHz, (CD3)2CO): δ -57.7
Results
Synthesis and Characterization. In the literature, extensive
studies on the preparation of vinylidene- and allenylidene-
ruthenium complexes [formulated as Ru(II)] supported by
phosphine and arene ligands have appeared.3 In the present
work, we synthesized ruthenium derivatives containing the
macrocyclic amine ligand 16-TMC. Unlike other literature
methods, a Ru(III) rather than Ru(II) precursor was used because
the Ru(II) species [Ru(16-TMC)Cl2] cannot be isolated. The in
situ reduction of [Ru(16-TMC)Cl2]Cl by zinc amalgam resulted
in the generation of a Ru(II) species, the chloride ligands of
which are more reactive to substitution.27 Hence, reaction of
[Ru(16-TMC)Cl2]Cl and HCtCR in the presence of zinc amal-
gam in refluxing methanol afforded the vinylidene-ruthenium
complexes 1-4 (Scheme 1) with an overall yield of around 70%
(for synthesis of the related derivative 5, see below). Slow
diffusion of Et2O into a CH2Cl2 solution under inert-atmosphere
conditions yielded analytically pure crystalline solids. The
vinylidene complexes are mildly unstable upon exposure to air
in both solid and solution forms; oxidative cleavage of the
vinylidene ligands occurs within 10 h in solution to give a
carbonyl complex (characterized by its νC≡O at 1917 cm-1).
No reaction was observed between 1-5 and methanol upon
refluxing for 48 h, although there have been reports of
vinylidene-ruthenium complexes that react with methanol to
give methoxyalkylcarbene complexes.1b,3m Their resistance to
attack by methanol is presumably a result of both steric and
electronic factors; the four NMe groups of 16-TMC may provide
protection for the CR atom, while the 16-TMC ligand is a pure
σ-donor that increases the π-basicity of the ruthenium ion,
making CR less susceptible to nucleophilic attack. By monitoring
the vinylidene proton signal of complex 1 by 1H NMR
1
(s), -144.1 (sept, PF6, JPF ) 708 Hz). IR (cm-1): νCdCdC ) 1924,
νP-F ) 839. FAB-MS: m/z 1183 [M+]. See Supporting Information
for 14 and 15.
X-ray Crystallography. The crystal data and details of data
collection and refinement for 1‚CH2Cl2, 5‚CH2Cl2, 6, and 8 are
summarized in Table S1 (see Supporting Information). A MAR
diffractometer with a 300 mm image plate detector using graphite-
monochromatized Mo KR radiation (λ ) 0.71073 Å) was employed
for data collection. The images were interpreted and intensities
integrated using program DENZO,24 and structures were solved by
direct methods employing the SIR-97 program25 on a PC. The Ru, Cl,
and many non-H atoms were located according to the direct methods.
The positions of the other non-hydrogen atoms were found after
successful refinement by full-matrix least-squares using program
SHELXL-97 on PC.26 Except for disordered atoms, non-hydrogen atoms
were refined anisotropically in the final stage of least-squares refine-
ment. Unless otherwise stated, the positions of H atoms were calculated
based on riding mode with thermal parameters equal to 1.2 times that
(24) DENZO: In The HKL Manual-A description of programs DENZO,
XDISPLAYF and SCALEPACK; written by Gewirth, D. with the cooperation
of the program authors Otwinowski, Z.; Minor, W.; Yale University: New
Haven, CT, 1995.
(25) SIR-97: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1998, 32, 115-119.
(26) SHELXL-97: Sheldrick, G. M. Programs for Crystal Structure Analysis
(release 97-2); University of Goetingen: Germany, 1997.
(27) Poon, C.-K.; Che, C.-M.; Kan, Y.-P. J. Chem. Soc., Dalton Trans. 1980,
128-133.
9
2504 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004

Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
Scheme 2
Scheme 3
in methanol. The resultant pale green solution was then filtered
and refluxed with 1,1-diphenyl-2-propyn-1-ol in the absence of
zinc amalgam. A deep red product was isolated and found to
exhibit an intense IR stretching band at 1884 cm-1, which is
comparable to reported νCdCdC values for ruthenium-
allenylidene complexes.1a On the basis of FAB-MS and 1H and
13C NMR data, the deep red product was identified as [Cl(16-
TMC)RudCdCdCPh2]PF6 (6). This synthetic route was there-
fore employed to synthesize the substituted allenylidene de-
rivatives 7-9 (Scheme 3).
Our observations suggest that the vinylidene complex 5 was
formed via the allenylidene derivative 6 (its deep red color was
observed en route to the generation of 5), and this is strongly
supported by the fact that 6 can be converted to 5 upon refluxing
in methanol in the presence of Zn/Hg. It is interesting to note
that the apparent hydrogen-atom addition process only occurs
at Câ/Cγ but not CR/Câ, plus this reaction does not ensue for
the vinylidene complexes.
spectroscopy, deprotonation of the vinylidene ligand was
achieved upon addition of sodium methoxide but not triethyl-
amine. This is in contrast to the reactivity of phosphine-
supported analogues such as trans-[Cl(dppe)2RudCdCHR]PF6
and trans-[Cl(dppm)2RudCdCHR]PF6, which have been ob-
served to interact with triethylamine to give the corresponding
acetylide complexes.28
The vinylidene complexes have been characterized by various
1
spectroscopic techniques. The H signals at 4.83-4.91 ppm,29
together with typical low-field 13C NMR signals at 347.4-353.1
ppm, confirm the presence of the vinylidene moiety. The IR
spectra also show νCdC stretching frequencies at 1593-1631
cm-1, which are among the lowest reported for vinylidene-
ruthenium derivatives.1b For example, the νCdC values (1593
and 1607 cm-1) for trans-[Cl(16-TMC)RudCdCHPh]PF6 (1)
are noticeably lower than that of 1628 cm-1 for trans-[Cl-
(dppe)2RudCdCHPh]PF6 and 1658 cm-1 for trans-[Cl-
(dppm)2RudCdCHPh]PF6.28
Although there have been accounts of allenylidene-ruthen-
ium complexes which react with methanol to give unsaturated
carbene derivatives, no reaction was observed between 6-9 and
methanol upon refluxing for 48 h. In addition, complex 6
remained intact after treatment with NaOMe (20 equiv) in
methanol for 48 h at room temperature. In contrast, the
diphosphine analogues trans-[Cl(dppm)2RudCdCdCR2]PF6
react with NaOMe to give trans-[Cl(dppm)2Ru-CtC-C(OMe)-
R2] derivatives.15 Also, no reaction was detected between
complex 6 and 100 equiv of CF3COOH in CH2Cl2 after 10 h.
Complexes 6-9 display low-field 13C NMR signals for CR
(294.6-308.6 ppm), Câ (229.1-257.3 ppm), and Cγ (149.1-
150.7 ppm). Like the vinylidene complexes, the νCdCdC in this
work are among the lowest reported for allenylidene-ruthenium
Preparation of allenylidene derivatives were attempted using
propargylic alcohols following the synthetic strategy depicted
at the top of Scheme 2. Upon refluxing a mixture of 1,1-
diphenyl-2-propyn-1-ol and [Ru(16-TMC)Cl2]Cl in the presence
of zinc amalgam in methanol, a pale red solid was isolated that
exhibits an IR band at 1631 cm-1. Its mass spectrum revealed
a parent molecular ion peak at 613, and the 1H NMR spectrum
contained a vinylidene proton (4.68, 4.74 ppm) that is coupled
to another deshielded proton (6.01, 6.03 ppm, JHH ) 10.5 Hz).
This complex was formulated as the vinylidene derivative [Cl-
(16-TMC)RudCdCH-CHPh2]PF6 (5), and the molecular struc-
ture was confirmed by X-ray crystal analysis (see below).
We suspected that the presence of the zinc amalgam reagent
throughout the reaction caused the formation of complex 5.
Therefore, the synthetic methodology was modified and per-
formed in sequence (see bottom of Scheme 2). [Ru(16-TMC)-
Cl2]Cl was first reduced to a Ru(II) species by zinc amalgam
derivatives. For example, the νCdCdC for 6 appears at 1884 cm-1
,
while for the phosphine-supported congeners trans-[Cl(dppm)2-
RudCdCdCPh2]PF6 (10) and trans-[Cl(dppe)2RudCdCd
CPh2]PF6, νCdCdC is observed at 1928 and 1923 cm-1 respec-
tively.15,30
It was found that the reaction of [Ru(16-TMC)Cl2]+ with
1-phenyl-2-propyn-1-ol according to Scheme 3 did not cleanly
yield an allenylidene complex. When the reaction was carried
out in methanol, a mixture of [Cl(16-TMC)RudCdCH-CH-
(OMe)Ph]PF6 (νCdC ) 1608 cm-1; 1H NMR: 3.35 (OMe), 4.12,
(28) (a) Touchard, D.; Haquette, P.; Guesmi, S.; Pichon, L. L.; Daridor, A.;
Toupet, L.; Dixneuf, P. H. Organometallics 1997, 16, 3640-3648. (b)
Touchard, D.; Haquette, P.; Pirio, N.; Toupet, L.; Dixneuf, P. H.
Organometallics 1993, 12, 3132-3139.
3
4.17 (dCdCH), 6.10, 6.13 ppm (dCdCH-CH), JHH ) 8.2
Hz; M+ ) 567) and [Cl(16-TMC)RudCdCdCHPh]PF6 (νCdC
) 1887 cm-1 1H NMR: 8.35, 8.37 ppm (dCdCdCH);
;
(29) Two singlets are observed for the vinylidene proton in the 1H NMR spectra
of 1-4 due to the existence of two prevalent conformations for the 16-
TMC ligand in solution (see Experimental Section and Supporting
Information).
(30) Touchard, D.; Guesmi, S.; Bouchaib, M.; Haquette, P.; Daridor, A.; Dixneuf,
P. H. Organometallics 1996, 15, 2579-2581.
9
J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2505

A R T I C L E S
Wong et al.
Figure 1. Perspective view of one of the two cations in 1 (30% probability
ellipsoids).
Figure 2. Perspective view of the cation in 5 (30% probability ellipsoids).
Scheme 4
M+ ) 534) was obtained. If CH2Cl2 was used as solvent, both
[Cl(16-TMC)RudCdCH-CH(OH)Ph]PF6 and the desired com-
plex [Cl(16-TMC)RudCdCdCHPh]PF6 were isolated.
Allenylidene-ruthenium15 and -osmium complexes sup-
ported by the bidentate phosphine ligand dppm (bis(diphe-
nylphosphino)methane) were prepared according to Scheme 4.
Reaction of cis-[M(dppm)2Cl2] and propargylic alcohols in the
presence of NaPF6 in CH2Cl2 gave trans-[Cl(dppm)2MdCd
CdCR2]PF6 (M ) Ru, 10-12; M ) Os, 13-15). The osmium
derivatives 13-15 also display low-field 13C NMR signals for
CR (266.9-271.0 ppm), Câ (218.2-231.3 ppm), and Cγ (150.7-
156.3 ppm). It is interesting to note that the νCdCdC for 13-15
are comparable to the ruthenium analogues. For example, the
νCdCdC for trans-[Cl(dppm)2MdCdCdCPh2]PF6 appears at
1924 and 1928 cm-1 for M ) Os (13) and Ru (10),15
respectively.
Figure 3. Perspective view of the cation in 6 (30% probability ellipsoids).
16-TMC plus the chloro and vinylidene or allenylidene ligands
that are trans to each other. The disorder of the 16-TMC moiety
in these structures demonstrate that several conformations can
exist upon coordination to the Ru center,12b,17 and those where
the four N-methyl groups adopt the ‘two up, two down’ and
‘three up, one down’ configurations are prevalent. The Ru(1)-
C(1)-C(2) angle for the vinylidene and allenylidene complexes
approach linearity. The Ru(1)-C(1) [1.780(8)-1.862(7) Å],
C(1)-C(2) [1.239(10)-1.352(10) Å], and C(2)-C(3) distances
[6, 1.339(7) Å; 8, 1.378(10) Å] and C(1)-C(2)-C(3) angles
[6, 170.1(5)°; 8, 180°] are comparable to those for analogous
Crystal Structures. The molecular structures of 1, 5, 6, and
8 have been determined by X-ray crystallography. Perspective
views of the complex cations of 1, 5, and 6 are shown in Figures
1, 2, and 3, respectively. Relevant bond lengths and angles are
listed in Table 1. In each case, the Ru atom resides in a distorted
octahedral environment comprising the four nitrogen atoms of
9
2506 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004

Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
Table 1. Selected Bond Length (Å) and Angles (deg)
1
5
6
8
Ru-C(1)
1.780(8)
1.352(10)
1.474(11)
2.488(2)
172.6(7)
178.4(2)
1.802(7)
1.309(10)
1.523(10)
2.489(2)
1.849(4) 1.862(7)
1.262(7) 1.24(1)
1.339(7) 1.378(10)
2.478(1) 2.449(2)
C(1)-C(2)
C(2)-C(3)
Ru-Cl(1)
Ru-C(1)-C(2)
Cl-Ru-C(1)
177.8(6)
177.6(4)
180
179.7(2)
126.2(7)
2.247
178.0(2)
170.1(5)
2.258
180
180
2.260
C(1)-C(2)-C(3) 134.2(8)
mean Ru-N
2.253
Table 2. Electrochemical Data for
trans-[Cl(16-TMC)RudCdCH-CHPh2]PF6 (5),
trans-[Cl(16-TMC)RudCdCdC(C6H4X-4)2]PF6 (6-9), and
trans-[Cl(dppm)2MdCdCdC(C6H4X-4)2]PF6 (M ) Ru, 10-12; M )
Os, 13-15)a
complex
E
1/2/V vs Cp2Fe+/0
5
0.81b
0.64
0.70
0.57
0.49
1.02
1.06
0.92
0.82
0.88
0.75
-2.16c
-1.27
-1.19
-1.32
-1.42
-0.98
-0.92
-1.02
-1.14
-1.05
-1.20
6 (X ) H)
7 (X ) Cl)
8 (X ) Me)
9 (X ) OMe)
10 (X ) H)
11 (X ) Cl)
12 (X ) Me)
13 (X ) H)
14 (X ) Cl)
15 (X ) Me)
Figure 4. Cyclic voltammograms for [Cl(16-TMC)RudCdCdCPh2]PF6
(6) and [Cl(dppm)2MdCdCdCPh2]PF6 [M ) Ru (10) and Os (13)] in
CH3CN with [nBu4N]PF6 (0.1 M) as supporting electrolyte. Conditions:
a Supporting electrolyte: 0.1 M [nBu4N]PF6 in CH3CN. The potential
E1/2 ) (Epc + Epa)/2 at 25 °C for reversible couples. b Irreversible; the
working electrode, glassy-carbon; scan rate, 50 mV s-1
.
recorded potential is the anodic peak potential at a scan rate of 50 mV s-1
.
c Irreversible; the recorded potential is the cathodic peak potential at a scan
rate of 50 mV s-1
(X ) Me); 0.88, -1.05 V for 14 (X ) Cl); 0.82, -1.14 V for
13 (X ) H); 0.75, -1.20 V for 15 (X ) Me)]. The E1/2 values
for the two waves of 10-12 are around 270-380 mV more
anodic than those of the 16-TMC analogues 6-8. In the liter-
ature, a reduction couple was reported for trans-[Cl(dppe)2-
RudCdCdC(C6H4X-4)2]PF6 with a comparable trend for the
shift in E1/2 values [-0.97, -1.05, -1.06, and -1.24 V for
X ) Cl, F, H, and OMe, respectively].3k Recently, Dixneuf and
co-workers reported two redox couples for [Cl(dppe)2RudCd
CdCPh2]PF6 (Eox ) 0.99 and Ered ) -1.03 V),3b which are
350 and 240 mV more anodic than the corresponding values
for 6, respectively.
Electronic Spectroscopy. The UV-vis absorption data of
complexes 1-15 (in CH3CN) and RuCl2{(dC)nHPh}(PCy3)2
(n ) 1 and 2; in CH2Cl2) are summarized in Table 3. The
absorption spectra of 2, 4, 5, and RuCl2{(dC)nHPh}(PCy3)2 (n
) 1 and 2) are depicted in Figure 5. For the vinylidene
complexes, the intense high-energy bands at λmax e 310 nm
(ꢀmax g 104 dm3 mol-1 cm-1) for 1-4 are similar, but they are
distinct from that of 5 where the RudCdC and phenyl moieties
are separated by a saturated carbon atom. Nevertheless, com-
plexes 1-5 all exhibit weak low-energy bands at λmax ) 460-
640 nm with ꢀ values below 102 dm3 mol-1 cm-1. The spectrum
of RuCl2(dCdCHPh)(PCy3)2 is similar to those of the vi-
nylidene complexes 1-4. It is interesting to note that the UV-
vis absorption spectrum of the Grubbs catalyst RuCl2-
.
complexes in the literature1 [vinylidene: Ru-C(1) ) 1.76-
1.91 Å, C(1)-C(2) ) 1.14-1.34 Å; allenylidene: Ru-C(1) )
1.84-2.00 Å, C(1)-C(2) ) 1.18-1.27 Å, C(2)-C(3) ) 1.35-
1.41 Å]. For 5, the angles around the C(3) atom are consistent
with sp3 hybridization. The molecular structures show that the
CR atoms of the vinylidene/allenylidene ligands are shielded
by the NMe groups of the 16-TMC ligand. The Ru-CR distances
in the allenylidene complexes 6 and 8 are slightly longer than
those in 1 and 5, and the CR-Câ bonds for 6 and 8 are
significantly shorter. The Ru-CR and CR-Câ bond lengths in
6 and 8 are thus intermediate compared to those of vinylidene
and acetylide relatives (for trans-[Ru(16-TMC)(CtCPh)2],11b
Ru-CR ) 2.077(4) Å, CR-Câ ) 1.198(6) Å).
Electrochemistry. Cyclic voltammetry was used to examine
the electrochemistry of the vinylidene-ruthenium complex 5
and the allenylidene-ruthenium (6-12) and -osmium (13-
15) complexes. The electrochemical data are listed in Table 2,
and the cyclic voltammograms of 6, 10, and 13 are depicted in
Figure 4. Complex 5 gives two irreversible couples at -2.16
and 0.81 V vs Cp2Fe+/0. The cyclic voltammograms of
complexes 6-9 contain two reversible couples, namely, a
reduction wave at E1/2 ) -1.42 to -1.19 V and an oxidation
wave at E1/2 ) 0.49 to 0.70 V. The E1/2 value of each couple
decreases with an increase in the electron-donating capacity of
the C6H4X-4 substituents [0.70, -1.19 V for 7 (X ) Cl); 0.64,
-1.27 V for 6 (X ) H); 0.57, -1.32 V for 8 (X ) Me); 0.49,
-1.42 V for 9 (X ) OMe)]. The change in the E1/2 values from
X ) Cl to OMe is around 200 mV for each couple. Complexes
10-12 and 13-15 also show two reversible couples, and similar
trends in E1/2 values are observed [1.06, -0.92 V for 11 (X )
Cl); 1.02, -0.98 V for 10 (X ) H); 0.92, -1.02 V for 12
(dCHPh)(PCy3)2 shows an intense absorption band at λmax
)
334 nm and a weak low-energy absorption at λmax ) 520 nm.
The UV-vis absorption spectra of 6-15 are illustrated in
Figure 6. The absorption spectra of 6-9 feature an intense low-
energy absorption band at λmax ) 479-513 nm with ꢀmax values
in excess of 103 dm3 mol-1 cm-1, indicating a dipole-allowed
electronic transition. The absorption maximum is solvatochromic
9
J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2507

A R T I C L E S
Wong et al.
Table 3. UV-Visible Absorption Data for
trans-[Cl(16-TMC)RudCdCHR]PF6 (1-5),
trans-[Cl(16-TMC)RudCdCdC(C6H4X-4)2]PF6 (6-9), and
trans-[Cl(dppm)2MdCdCdC(C6H4X-4)2]PF6 (M ) Ru, 10-12; M )
Os, 13-15) (in CH3CN), RuCl2(dCHPh)(PCy3)2, and
RuCl2(dCdCHPh)(PCy3)2 (in CH2Cl2)
3
complex
1 (R ) Ph)
λ
max, nm(ꢀmax/dm mol-1 cm-1
)
273 (19700), 311 (7360), 351 (590),
464 (68), 585 (38), 644 (37)
277 (21510), 315 (12790), 354 (3250),
470 (78), 578 (48), 638 (46)
273 (25040), 311 (10740), 350 (900),
464 (68), 582 (33)
273 (28830), 310 (10130), 365 (570),
465 (71), 585 (37)
237 (22850), 304 (2200), 395 (83),
466 (82), 589 (21, br, sh)
2 (R ) C6H4Cl-4)
3 (R ) C6H4Me-4)
4 (R ) C6H4OMe-4)
5 (R ) CHPh2)
6 (X ) H)
258 (14110), 283 (13160), 335 (7390),
479 (20200)
7 (X ) Cl)
8 (X ) Me)
292 (15360), 335 (9790), 483 (21740)
260 (14780), 291 (12830), 341 (11510),
492 (24430)
9 (X ) OMe)
264 (14540), 279 (13370), 382 (17510),
513 (29760)
10 (X ) H)
11 (X ) Cl)
12 (X ) Me)
13 (X ) H)
273 (46900), 357 (9010), 506 (17120)
274 (49940), 366 (12590), 510 (19970)
273 (48370), 374 (14170), 519 (20210)
252 (56640), 350 (7330), 468 (22370),
525 (13350, sh)
14 (X ) Cl)
15 (X ) Me)
252 (57610), 350 (10690), 473 (25210),
527 (13690, sh)
252 (68380), 359 (15690), 474 (28400),
527 (23770, sh)
254 (14320), 334 (8060), 520 (360)
264 (36440), 306 (34100), 363 (2060),
494 (230), 594 (160)
RuCl2(dCHPh)(PCy3)2
RuCl2(dCdCHPh)(PCy3)2
(e.g., for 6, λmax ) 479 nm in CH3CN, 488 nm in CHCl3) and
red-shifts in energy as the electron-donating ability of the
Figure 5. (Top) UV-vis absorption spectra of trans-[Cl(16-TMC)Rud
CdCHR]PF6 (R ) C6H4Cl-4 (2), C6H4OMe-4 (4), CHPh2 (5)) in CH3CN
at 25 °C. (Bottom) UV-vis absorption spectra of RuCl2(dCHPh)(PCy3)2
and RuCl2(dCdCHPh)(PCy3)2 in CH2Cl2 at 25 °C.
substituent at C6H4X-4 increases, except for X ) Cl [λmax
)
479 nm for 6 (H), 483 nm for 7 (Cl), 492 nm for 8 (Me), 513
nm for 9 (X ) OMe)]. This anomaly may be rationalized by
the negative inductive and positive mesomeric effects of the
chloro substituent. Like 6-8, the UV-vis absorption spectra
of 10-12 contain an intense low-energy absorption band with
ꢀmax values in excess of 103 dm3 mol-1 cm-1 in a similar spectral
region, and the λmax value decreases as X changes from Me to
Cl and H (λmax ) 519, 510, and 506 nm, respectively).
Interestingly, the absorption maxima are red-shifted by 1060-
1110 cm-1 compared with the 16-TMC analogues 6-8. The
UV-vis absorption spectra of 13-15 show an intense absorp-
tion band at λmax ) 468-474 nm with a prominent shoulder at
525-527 nm (ꢀmax g 103 dm3 mol-1 cm-1), signifying dipole-
allowed electronic transition(s). The shift in the absorption
maximum also parallels the trend observed for 6-8 and 10-
12 [λmax ) 474 nm for 15 (Me), 473 nm for 14 (Cl), 468 nm
for 13 (H)].
the 435.7 and 502.9 nm spectra together with the absolute
Raman cross sections for the nominal νCdCdC stretch mode are
listed in Table 4.
We simulated the 479 nm absorption band and the resonance
Raman intensities of 6 in order to obtain semiquantitative
information about the structural changes in the excited state
relative to the ground state. The methodology for the resonance
Raman intensity analysis is the same as that reported in a number
of our previous studies.31 Table 5 presents the best-fit parameters
for the simulations and the vibrational reorganization energies
determined from the normal mode displacements. The top of
Figure 8 depicts a comparison of the calculated and experimental
absorption spectrum and its Gaussian deconvolution. The bottom
of Figure 8 represents a comparison of the computed absolute
Raman cross sections with the experimental values for the 13
combination bands and overtones as well as the 12 fundamental
vibrational modes observed in the resonance Raman spectrum
of 6. The calculated absorption spectrum in Figure 8 exhibits
good correlation with the Gaussian deconvolution of the
experimental spectrum. Similarly, the calculated absolute Raman
Resonance Raman Spectroscopy. Figure 7 shows the
resonance Raman spectrum of 6 obtained with 435.7 nm
excitation. A similar spectrum was also obtained with 502.9
nm excitation (see Supporting Information). The largest reso-
nance Raman progression is the fundamental and overtone of
the nominal νCdCdC stretch mode at 1889 and 3786 cm-1
,
(31) (a) Leung, K. H.; Phillips, D. L.; Mao, Z.; Che, C.-M.; Miskowski, V. M.;
Chan, C.-K. Inorg. Chem. 2002, 41, 2054-2059. (b) Che, C.-M.; Mao, Z.;
Miskowski, V. M.; Tse, M.-C.; Chan, C.-K.; Cheung, K.-K.; Phillips, D.
L.; Leung, K.-H. Angew. Chem., Int. Ed. 2000, 39, 4084-4088. (c) Che,
C. M.; Tse, M.-C.; Chan, M. C. W.; Cheung, K. K.; Phillips, D. L.; Leung,
K.-H. J. Am. Chem. Soc. 2000, 122, 2464-2468. (d) Leung, K. H.; Phillips,
D. L.; Tse, M.-C.; Che, C.-M.; Miskowski, V. M. J. Am. Chem. Soc. 1999,
121, 4799-4803. (e) Kwok, W. M.; Phillips, D. L., Yeung, P. K.-Y.; Yam,
V. W.-W. J. Phys. Chem. A 1997, 101, 9286-9295.
respectively (this nominal νCdCdC mode was observed at 1884
cm-1 in the IR spectrum). The nominal νCdCdC mode at 1889
cm-1 also forms weaker combination bands with eight other
fundamental Franck-Condon active modes. The resonance
Raman shifts and intensities for the Raman bands observed for
9
2508 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004

Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
Table 4. Resonance Raman Bands for 6 in CH3CN
Raman
shifta/cm-1
relative intensityb relative intensityb
at 435.7 nm at 502.9 nm
Raman band
300
351
468
5
5
7
3
3
5
600
723
766
17.5
9
3
12
6.5
4
996
2
2
1116
1276
1484
1591
1889
1317
1719
2186
2375
2485
2615
2729
3005
3375
3496
3632
3786
4091
17
2
2.6
7
100
1
2
4
4.5
7
3
2
7
1
4
3
22
5
11
2
3
9
100
1
1
4
3.5
7
3
νCdC
νCdCdC
600 + 723
600 + 1116
νCdC + 600
νCdCdC +468
νCdCdC + 600
νCdCdC + 723
νCdC + 1116
νCdCdC + 1116
νCdCdC + 1484
νCdCdC + νCdC
νCdCdC + 1116 + 600
2 × νCdCdC
5
νCdCdC + νCdC + 600
absolute Raman cross section
expt.
0.58 × 10-7
0.69 × 10-7
0.65 × 10-7
for νCdCdC (in /Å2/molecule)
calcdc
0.60 × 10-7
a Estimated uncertainties are about 4 cm-1 for the Raman shifts.
b Relative intensities are based on integrated areas of Raman bands.
Estimated uncertainties are about 5% for intensities greater than 50, 10%
for intensities between 10 and 50, and 20% for intensities below 10.
c Calculated using parameters from Table 5 and model described in text
and ref 31.
Figure 6. UV-vis absorption spectra of trans-[Cl(16-TMC)RudCdCd
C(C6H4X-4)2]PF6 (6-9) and trans-[Cl(dppm)2MdCdCdC(C6H4X-4)2]PF6
(M ) Ru, 10-12; M ) Os, 13-15) in CH3CN at 25 °C.
Table 5. Parameters for Simulations (using Exponential Damping
Function) of Resonance Raman Intensities and Absorption
Spectrum of 6 in CH3CNa
ground-state
vib. freq./cm
excited-state
vib. freq./cm
vib. reorg.
energy/cm
-1
-1
-1
∆
300
300
0.783
0.719
0.760
0.932
0.550
0.364
0.210
0.520
0.200
0.193
0.350
1.060
92
351
351
91
468
468
135
261
109
51
22
151
26
28
97
1061
600
600
723
723
766
766
996
996
1116
1276
1484
1591
1889
1116
1276
1484
1591
1889
a Total λv ) 2124; E0 ) 19 200 ( 100 cm-1; M ) 1.75 ( 0.10 Å; n )
1.344; homogeneous broadening, Γ ) 780 ( 80 cm-1 HWHM; inhomo-
geneous broadening, G ) 250 ( 50 cm-1 standard deviation.
cross sections show reasonable agreement with experimental
counterparts.
The resonance Raman spectrum of 5 was also obtained with
309.1 nm excitation (see Supporting Information). The largest
resonance Raman progression is the fundamental of the nominal
ν
CdC stretch mode at 1629 cm-1 (this νCdC mode was observed
at 1631 cm-1 in the IR spectrum). The nominal νCdC mode at
1629 cm-1 generates an overtone at 3258 cm-1 and similarly
affords combination bands with some fundamental Franck-
Condon active modes.
Ab Initio Calculations. The ground-state structure of the
model complex trans-[Cl(NH3)4RudCdCdCPh2]+ is depicted
in Figure 9 (top), and the optimized structural data are
Figure 7. Resonance Raman spectrum of 6 obtained with 435.7 nm
excitation wavelength in CH3CN at 25 °C (solvent and laser subtraction
artifacts marked by * and +, respectively).
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J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2509

A R T I C L E S
Wong et al.
Figure 8. (Top) Comparison of the calculated absorption spectrum with the experimental and Gaussian deconvolution absorption spectra. (Bottom) Comparison
of the calculated Raman cross sections with the experimental values observed in the 435.7 and 502.9 nm resonance Raman spectra of 6. The calculations
used the parameters given in Table 5 and the model described in references for the simple exponential decay dephasing description of the solvent.31
summarized in the Supporting Information. All the optimized
structural data are in satisfactory agreement with the crystal
structure of [Cl(16-TMC)RudCdCdCPh2]+ (6), except that the
calculated CdCdC bond angle is linear. The compositions of
the HOMO and LUMO [depicted in Figure 9 (bottom)], together
with the Mulliken and natural charges, are listed in the
Supporting Information. The major components of the frontier
molecular orbitals originate from the orbitals of Ru, CdCdC,
and Ph rings, while the total contribution from the orbitals of
chloride and amine ligands is less than 10%. In the HOMO,
the contributions from Ru, CdCdC, and Ph rings are 23%,
22%, and 49%, respectively, while in the LUMO they are 13%,
48%, and 36%, respectively. We note that along the CdCdC
unit, the HOMO contains contribution mainly from the central
carbon atom Câ (2.3% for CR, 15.4% for Câ, 4.2% for Cγ) while
the LUMO is mainly composed of participation by the odd-
numbered carbon atoms CR and Cγ (18.0% for CR, 2.6% for
Câ, 27.2% for Cγ). The Mulliken net charges on Ru, CR, Câ,
and Cγ are 0.55, 0.17, -0.72, and 0.04, respectively (the
corresponding natural charges20 are 0.48, -0.07, -0.15, and
-0.01, respectively), which signifies that (1) the metal center
is more positively charged than the CdCdC unit and (2) Câ is
more negatively charged than CR or Cγ.
Discussion
Nature of Bonding in [Ru(dC)nCR2]. In this work, we
presented the crystal structures of a number of vinylidene- and
allenylidene-ruthenium complexes supported by the 16-TMC
ligand. The Ru-CR bonds are slightly longer and the CR-Câ
distances are significantly shorter for the allenylidene complexes.
By comparison with acetylide complexes such as trans-[Ru-
(16-TMC)(CtCPh)2],11b it is apparent from the Ru-CR and
CR-Câ distances that the bonding character of the allenylidene
fragment is intermediate between vinylidene and acetylide, i.e.,
the CR-Câ bonds of trans-[Cl(16-TMC)RudCdCdCR2]PF6
exhibit partial triple-bond character. In the literature, this has
been attributed to the alkynyl mesomer: MndCdCdCR2 T
Mn-1-C+dCdCR2 T Mn-1-CtC-C+R2. For example, Dix-
neuf and co-workers suggested that for trans-[(dppm)2Ru-(d
CdCdC(OMe)CHdCPh2)2](BF4)2, which features long Ru-
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Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
2-methylfuran gives [(Cp*)(dippe)RudCdCH-C(2-pyrrolyl)-
PhH]+ and [(Cp*)(dippe)RudCdCH-C(5-methyl-2-furanyl)-
PhH]+, respectively, only when HBF4‚Et2O is present.3c Werner
and co-workers also reported that the neutral vinylidene
complexes [Cl2L2RudCdCRH] (L ) PCy3, PiPr3; R ) Ph,
tBu) are susceptible to electrophilic attack by H+ to give [Cl2L2-
RutC-CRH2]+.3f
Theoretical calculations also provide information regarding
the charge distribution along the [RudCdCdCR2] unit. Es-
teruelas et al. performed EHT-MO calculations on [Ru(Cp)-
(CdCdCH2)(CO)(PH3)]+, and the Mulliken atomic net charges
on the carbon atoms are -0.36 (CR), -0.13 (Câ), and -0.05
(Cγ).32 Auger et al. reported DFT calculations on the model
ruthenium cumulene complexes [Cl(PH3)4Ru(dC)nH2]+ (n )
1-8).33 In each case, the Mulliken net charge on the metal center
is positive while the (dC)n chain is negatively charged (e.g.,
for n ) 3, Mulliken net charges on Ru, CR, Câ, and Cγ are
0.60, -0.28, -0.03, and 0.21, respectively). In the ab initio
calculations (at MP2 level) performed in this work on the model
complex [Cl(NH3)4RudCdCdCPh2]+, the Mulliken charges
alternate along the CdCdC moiety (for Ru, CR, Câ, and Cγ )
0.55, 0.17, -0.72, and 0.04, respectively; the corresponding
natural charges20 are 0.48, -0.07, -0.15, and -0.01, respec-
tively). This indicates that like the related calculations described
above,32,33 the metal center is more positive than the CdCdC
unit. Interestingly, with respect to the ruthenium-allenylidene
interaction, these results are consistent with the polarized
Mδ+[(dC)2CR2]δ- description. We note that theoretical calcula-
tions for the neutral rhodium vinylidene complex trans-[RhCl-
(dCdCH2)(PMe3)2] show that the metal center is more negative
than the carbon atom in the RhdC bond,3g but it is clear that
Rh(I) is generally more electron-rich than ruthenium in oxida-
tion state g2. The alternation of Mulliken charges along the
CdCdC unit in [Cl(NH3)4RudCdCdCPh2]+, which is not
observed in [Ru(Cp)(CdCdCH2)(CO)(PH3)]+ 32 and [Cl(PH3)4-
Ru(dC)3H2]+,33 presumably arises because of the use of
diphenyl-substituted (CdCdCPh2) rather than nonsubstituted
(CdCdCH2) allenylidene groups in the calculation.
In [Cl(NH3)4RudCdCdCPh2]+, the contributions in the
HOMO from Ru, CdCdC, and Ph rings constitutes 94% of
the total and the percentage contributions are 23%, 22%, and
49%, respectively. This implies the HOMO is not localized
solely on the metal center or allenylidene ligand but is
delocalized along the RudCdCdCAr2 unit. This is in ac-
cordance with the electrochemical data (see below), which show
that the metal ion affects the electrochemical oxidation potential
of the MdCdCdCAr2 unit. On the other hand, the contributions
from Ru, CdCdC, and Ph rings add up to 97% of the total for
the LUMO (percentage contributions are 13%, 48%, and 36%,
respectively), suggesting the LUMO is localized more on the
allenylidene ligand and especially the CdCdC unit.
Figure 9. Optimized structure (top), HOMO (left), and LUMO (right) of
the model compound [Cl(NH3)4RudCdCdCPh2]+.
CR and Câ-Cγ but short CR-Câ distances, the electron-donating
OMe group can stabilize the mesomeric forms: [Ru+dCdCd
C-OMe] T [Ru-CtC-C+-OMe] T [Ru-CtC-Cd(+O)-
Me].6c Similarly, Bruce et al. rationalized the deviations in bond
lengths between [Ru{CdCdCMe(NPh2)}(PPh3)2(η-C5H5)]+ and
[Ru{CdCdCPh2}(PMe3)2(η-C5H5)]+ by proposing that the N
lone pair electrons can stabilize the [Ru(CtCCMedNPh2)]+
tautomer.6b Tamm et al. reported the allenylidene complex with
a tropylium substituent, [CpRudCdCdC(cycloheptatrienyl-
idene)(PPh3)]PF6, and concluded that the cycloheptatrienyl unit
can stabilize a positive charge, and thus the Ru-CtC-CR+
mesomeric form is important.6a
We conceive that, in this study, the contribution of the Mn-1
-
CtC-C+R2 form to the RudCdCdCR2 bonding in trans-[Cl-
(16-TMC)RudCdCdCR2]PF6 is less important than that in the
phosphine/Cp-stabilized analogues described above and in the
literature. First, 16-TMC is an effective σ-donor, and this would
destabilize the Mn-1-CtC-C+R2 form. This is supported by
the νCdC and νCdCdC values in this work being the lowest
reported for vinylidene- and allenylidene-ruthenium deriva-
tives. Second, complexes 6-9 do not contain any heteroatoms
or conjugated systems that can stabilize a positive charge on
the allenylidene ligand. Third, 6-9 are stable in refluxing
MeOH, and no reaction is observed between 6 and NaOMe;
this is in stark contrast to phosphine-supported cationic conge-
ners such as 10-12, which have been reported to react with
strong nucleophiles such as methoxide to afford functionalized
alkynyl compounds.1a However, 6 does not react with the Lewis
acid CF3COOH, therefore, it appears that the allenylidene ligand
in trans-[Cl(16-TMC)RudCdCdCR2]PF6 is not sufficiently
electron-rich to exhibit nucleophilic character. At this juncture,
we note that accounts of the reactivity of nucleophilic alle-
nylidene ligands have appeared in the literature. Valerga and
co-workers reported that [(Cp*)(dippe)RudCdCdCPh2]+ reacts
with H+ to afford [(Cp*)(dippe)RutC-CHdCPh2]2+, and
treatment of [(Cp*)(dippe)RudCdCdCPhH]+ with pyrrole and
Electrochemical Comparisons. The electrochemical behav-
ior of the allenylidene complexes reported in this work can
provide insight into the nature of MdCdCdCR2 bonding.
Taking the series where R ) Ph (6, 10, and 13) as an example,
the E1/2 values of 6 (E1/2 ) -1.27, 0.64 V) and 10 (E1/2 ) -0.98,
1.02 V) show that changing the ligand system from N [16-TMC]
(32) Esteruelas, M. A.; Go´mez, A. V.; Lo´pez, A. M.; Modrego, J.; On˜ate, E.
Organometallics 1997, 16, 5826-5835.
(33) Auger, N.; Touchard, D.; Rigaut, S.; Halet, J.-F.; Saillard, J.-Y. Organo-
metallics 2003, 22, 1638-1644.
9
J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2511

A R T I C L E S
Wong et al.
to P [(dppm)2] donors increases the E1/2 values of these two
couples by 290 and 380 mV, respectively. Because the equatorial
dppm and 16-TMC auxiliaries would influence the oxidation
potential of ruthenium through π-back-bonding and/or σ-bond-
ing interactions, such an impact upon the E1/2 values suggests
that the electrochemical reactions involve the metal ion and are
unlikely to be localized solely on the CdCdCPh2 unit. In
Insight from Electronic and Resonance Raman Spectros-
copy. The vinylidene complexes 1-4 show similar absorption
patterns in the UV region (λmax e 310 nm, ꢀmax g 104 dm3
mol-1 cm-1), and these are clearly different from 5. As the main
difference between 1-4 and 5 is the nature of the vinylidene
ligand, we suggest that these high-energy transition bands
involve the vinylidene moiety. Support for this assignment is
provided by the resonance Raman spectrum of 5 obtained with
309.1 nm excitation, which shows large resonance Raman
enhancement in the fundamental of the nominal νCdC stretch
mode at 1629 cm-1. This indicates that the electronic transition
involves large structural distortion of the vinylidene unit.
The UV-vis absorption spectra of the vinylidene complexes
addition, the difference between the E1/2 values of 10 (E1/2
)
-0.98, 1.02 V) and 13 (E1/2 ) -1.14, 0.82 V) demonstrate the
effect of the metal center. However, the electrochemical
reactions do not appear to be purely metal-localized, and this
is indicated by the substituent effect of the C6H4X-4 rings upon
the E1/2 values of the two couples; the variations in E1/2 values
of both couples are around 200 mV upon changing X from Cl
(7) to OMe (9). Therefore, a reasonable proposal is that the
electrochemical reactions occur at the delocalized MdCdCd
CR2 unit. To obtain further information regarding the electro-
chemical reaction of the MdCdCdCR2 unit, we note the
following: (1) the difference in E1/2 value for the metal-centered
Ru(III)/(II) couple between trans-[(dppm)2RuCl2]+/0 (0.14 V)34
and [(16-TMC)RuCl2]+/0 (-0.60 V)12c is 740 mV, which is
significantly greater than that between [Cl(16-TMC)RudCd
CdCPh2]+ and [Cl(dppm)2RudCdCdCPh2]+ (290 and 380
mV for the +/0 and 2+/+ couples respectively), (2) the increase
in E1/2 value for the M(III)/(II) couple of trans-[(16-TMC)-
MCl2]+/0 as M changes from Os to Ru is 770 mV, while the
difference in E1/2 value for trans-[(dppm)2MCl2]+/0 and [Cl-
(dppm)2MdCdCdCPh2]+, for M ) Ru and Os, is 240 mV16
and 160/200 (for the +/0 and 2+/+ couples respectively) mV,
respectively. These observations are consistent with the notion
that the redox couples for the allenylidene-ruthenium (6-12)
and -osmium (13-15) complexes are not purely metal- or
ligand-centered.
1-5 show weak absorptions in the low-energy region (λmax
)
.
460-640 nm), with ꢀmax values below 102 dm3 mol-1 cm-1
We propose that these absorption bands are likely to be d-d
transitions in nature. The alternative assignment to spin-
forbidden analogues of the intense UV electronic transitions is
unfavored because (1) the excessively large S-T splitting is
unreasonable and (2) such spin-forbidden transitions in Ru
complexes are expected to be substantially weaker compared
to the visible absorption bands observed in this study. For a
Ru(IV)-ligand multiple bond (d4) formalism, there emerges an
obvious assignment to dxy f (dxz, dyz) transitions. The theoretical
framework for interpreting such transitions and the nature of
the ground states have been established for metal mono-oxo
analogues.35 Interestingly, the spin-allowed dxy f (dxz, dyz)
transition in d4 Ru(IV)dO complexes occurs at a similar spectral
region to the proposed d-d transitions of the vinylidene
complexes 1-5, namely, λmax 460-600 nm.12b A complication
for the compounds in the present study is that the dxz and dyz
orbitals are not degenerate in energy; in particular, this may
account for the complexity of the ∼600 nm absorption of 2.
The UV-vis absorption spectrum of the vinylidene complex
RuCl2(dCdCHPh)(PCy3)2 shows similar absorption patterns to
those of 1-4. As the PCy3 ligand is also optically transparent
in this region, the nature of the electronic transitions for trans-
[Cl(16-TMC)RudCdCHAr]PF6 and RuCl2(dCdCHPh)(PCy3)2
are likely to be similar. The corresponding alkylidene complex
RuCl2(dCHPh)(PCy3)2, which differs by one cumulene carbon
unit, also displays low-energy absorption bands at similar
energies and extinction coefficients to those of RuCl2(dCd
CHPh)(PCy3)2. From the viewpoint that the differences between
the high-energy absorption spectra of RuCl2{(dC)nHPh}(PCy3)2
(n ) 1 and 2) are due to modification of the cumulene ligand,
we suggest that perturbation of the metal-centered d-d transition
would be less dramatic, since the Ru-CR distance in RuCl2(d
CHR)(PCy3)2 (1.838(3)8f and 1.851(21)8g Å for R ) C6H4Cl-4
and CHdCPh2, respectively) and RuCl2(dCdCHPh)(PCy3)2
(1.761(2) Å)14 are comparable. Thus, the ruthenium-carbon
bonding interaction in RudCHR and RudCdCHR are envis-
aged to be alike in these complexes. Incidentally, one would
expect such weak visible band(s) to be present in the absorption
spectra of 6-9, but they are presumably obscured by the intense
electronic transition at λmax ) 479-513 nm.
Compared with the diphosphine analogue 10 (E1/2 ) -0.98,
1.02 V), the E1/2 values of the two couples for 6 (E1/2 ) -1.27,
0.64 V) occur at more negative potentials, indicating the ability
of the strongly σ-donating 16-TMC ligand to increase electron
density at the metal center. The E1/2 values of the two couples
for the osmium derivative 13 (E1/2 ) -1.14, 0.82 V) also occur
at more negative potentials than 10, as would be expected since
osmium has a lower oxidation potential.
With regard to the assignment of the two couples, it is
interesting to compare the redox couples of trans-[(TMC)-
ClRuL]n+, which have been extensively studied.12b,c The 2+/+
couples of trans-[(16-TMC)ClRuIIICl]+, trans-[(14-TMC)-
ClRuIVdO]+, and trans-[(14-TMC)ClRuII-NtCCH3]+ occur
at 1.16, 1.10, and 0.15 V, respectively. The couples of trans-[
(16-TMC)ClRudCdCdCR2]2+/+ (6-9) in this work (0.49-
0.70 V) exist between those of [(16-TMC)ClRudO]2+/+ and
[(14-TMC)ClRu-NtCCH3]2+/+, implying that the ease of
oxidation for trans-[(16-TMC)ClRudCdCdCR2]+ is between
those of [RuII-NtCCH3]+ and [RuIVdO]+. We suggest that
the other reversible wave of 6-9 (-1.19 to -1.42 V) corre-
sponds to the trans-[(16-TMC)ClRudCdCdCR2]+/0 couple,
which is generally more cathodic than that of trans-[(16-TMC)-
ClRuCl]+/0 (-0.60 V). This is in agreement with the above
observation that [Cl-RudCdCdCR2]+ is more electron-rich
than the trans-[Cl-RuIII-Cl]+ moiety.
The UV-vis absorption spectra of the allenylidene-
ruthenium complexes bearing 16-TMC (6-9) and dppm (10-
12) feature an intense low-energy absorption band at λmax
)
(34) Champness, N. R.; Levason, W.; Pletcher, D.; Webster, M. J. Chem. Soc.,
Dalton Trans. 1992, 3243-3247.
(35) Miskowski, V. M.; Gray, H. B.; Hopkins, M. D. AdV. Transition Met. Coord.
Chem. 1996, 1, 159-186.
9
2512 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004

Ruthenium−Cumulene Bonding Interaction
A R T I C L E S
479-513 and 506-519 nm, respectively, with ꢀmax values in
excess of 103 dm3 mol-1 cm-1. The UV-vis absorption spectra
of the allenylidene-osmium dppm complexes 13-15 also
contain an intense absorption at λmax ) 468-474 nm with a
prominent shoulder near 525-527 nm (ꢀmax g 103 dm3 mol-1
cm-1). It has been suggested by Tamm et al. that the electronic
absorption associated with [CpRudCdCdC(cycloheptatrienyl-
idene)(PPh3)]PF6 (λmax ) 496-601 nm) is due to charge-transfer
excitation represented by the resonance structures Ru+dCd
CdCR2 T Ru-CtC-C+R2.6a In this work, we found that the
absorption maximum of trans-[Cl(16-TMC)RudCdCd
C(C6H4X-4)2]PF6 is sensitive to the nature of the solvent (e.g.,
λmax ) 479 nm in CH3CN, 488 nm in CHCl3 for 6). The
absorption maximum red-shifts in energy as the electronic-
donating affinity of the C6H4X-4 ring system increases, which
is consistent with charge transfer from allenylidene to ruthenium.
The general red shift of the absorption maximum (ca. 1100
cm-1) from trans-[Cl(16-TMC)RudCdCdC(C6H4X-4)2]PF6
(6-8) to trans-[Cl(dppm)2RudCdCdC(C6H4X-4)2]PF6 (10-
12) provides useful information for spectral assignment pur-
poses. For an electronic transition involving ligand-to-metal
charge transfer (LMCT), the π-back-bonding between Ru(dπ)
orbitals and the phosphine ligands would decrease the electron
density around Ru to give a red shift. Furthermore, this
assignment is in accordance with the observed blue shift in λmax
from trans-[Cl(dppm)2RudCdCdC(C6H4X-4)2]PF6 (10-12) to
the Os analogues (13-15), which would be expected for an
LMCT transition upon descending the periodic table. Neverthe-
less, it is apparent that the participation of the metal is small
compared to a pure LMCT transition. For example, the energy
difference between the λmax of trans-[Cl(dppm)2MdCdCd
electronic communication between Ru and the peripheral phenyl
rings in the excited state is small.
General Remarks. Metal-carbon double-bonded complexes
are conventionally categorized as Fischer- or Schrock-type. The
Fischer carbene description involves coordination of a neutral
carbene ligand to low-valent metal ion through σ- and π-back-
bonding interactions. The Schrock alkylidene nomenclature
entails a polarized MdC bond (1σ + 1π) with electronic charge
localized on the carbon atom. Because of the strong covalent
character of a metal-carbon double bond, it is often difficult
to clearly distinguish between Fischer and Schrock MdC
species. Moreover, the distinction between such bonding
descriptions becomes rather ambiguous in the case of ruthenium-
vinylidene and -allenylidene derivatives. In the literature,3-5
the metal oxidation state in such compounds are generally
assigned as II, which implies that the vinylidene and allenylidene
ligands are neutral (i.e., Fischer description). However, the
Grubbs catalyst RuCl2(dCHR)(PCy3)2 and its congeners are
often regarded as alkylidene complexes.8
In this work, a definitive assignment of the Ru oxidation state
in trans-[Cl(16-TMC)RudCdCHR]PF6 and trans-[Cl(16-TMC)-
RudCdCdCR2]PF6 may be inappropriate given the strong
covalency of the RudCdCdCR2 bonding interaction. However,
it is interesting to note that the proposed d-d transition for the
vinylidene complexes trans-[Cl(16-TMC)RudCdCHR]PF6
(1-5) occurs at a similar spectral region as the spin-allowed
dxy f (dxz, dyz) transition for d4 Ru(IV)dO complexes. We
suggest that the use of strongly σ-donating ligands such as 16-
TMC can facilitate stabilization of species of the Mδ+[(dC)n-
CR2]δ- type with respect to the ruthenium-cumulene interac-
tion. Our spectroscopic results signify that the low-energy
electronic transition associated with trans-[Cl(L4)MdCdCd
CR2]+ for 6-15 involves a degree of charge transfer from
allenylidene to metal. Complexes 6-9 bearing 16-TMC are inert
toward nucleophilic attack by methoxide, which implies that
the contribution of the Mn-1-CtC-C+R2 form to the Rud
CdCdCR2 bonding in trans-[Cl(16-TMC)RudCdCdCR2]PF6
is not important. The Mulliken and natural population analyses
in the ab initio calculations also indicate that the Ru center is
more positively charged than the CdCdC chain. Overall, since
the 16-TMC- and dppm-ligated allenylidene complexes are
spectroscopically and electrochemically alike (bearing in mind
that the inability of dppm ligands to stabilize cationic ruthenium
centers at high oxidation states is well established), it may be
appropriate to consider the allenylidene ligand in these deriva-
tives as neutral, although we favor the polarized Ruδ+[(dC)2-
CR2]δ- description for complexes such as 6.
CPh2]PF6 for M ) Ru (506 nm) and Os (468 nm) is 1605 cm-1
,
while the pπ(Cl)-to-dπ(M) LMCT transitions of trans-[RuIII(en)2-
Cl2]+ (λmax ) 343 nm) and trans-[OsIII(en)2Cl2]+ (λmax ) 284
nm) show an energy difference of 6056 cm-1 17a
Moreover, it
.
is evident from the resonance Raman spectroscopic data that
the transition involves substantial intraligand π f π* character.
We therefore assign the intense low-energy absorption band of
6-15 to a metal-perturbed intraligand transition with some
allenylidene-to-metal LMCT character.
Characterization by resonance Raman spectroscopy (Table
4) showed that the 479-513 nm charge-transfer bands originate
from a transition that is associated with the RudCdCdC
moiety. By simulating the 479 nm absorption band and the
resonance Raman intensities of 6, it was found that the nominal
νCdCdC stretch mode accounts for approximately 50% of the
total vibrational reorganization energy, which indicates that the
absorption band is strongly coupled to the allenylidene ligand.
Furthermore, the reorganization of this ligand in the excited state
is accompanied by partial reorganization of the RudC and
Ru-N (of 16-TMC) fragments (Franck-Condon active modes
below 1000 cm-1). In other words, significant interaction exists
between the Ru center and the CdCdC moiety in the excited
state. It is noteworthy that from our results and calculations the
contribution from the νCdC stretch mode associated with the
phenyl units to the total vibrational reorganization energy is
only 97 cm-1, which is less than 10% of the nominal νCdCdC
contribution (1061 cm-1) (Table 5). This means that the
contribution from the phenyl groups to the reorganization energy
of the 479 nm electronic transition is minor and signifies that
The apparent similarities between the electronic transitions
associated with the Grubbs alkylidene complex RuCl2(dCHPh)-
(PCy3)2, RuCl2(dCdCHPh)(PCy3)2, and trans-[Cl(16-TMC)-
RudCdCHPh]PF6 indicate that the Ru(dC)nCR2 interactions
in these three systems are comparable. On the basis of the
resonance Raman studies on complex 6, there is significant
delocalization within the linear RudCdCdC unit in the charge-
transfer (presumably intraligand and allenylidene-to-Ru) excited
state. Because the spectroscopic and electrochemical properties
of trans-[Cl(L4)MdCdCdCR2]+ show close resemblance for
M ) Ru and Os as well as for L4 ) tetraamine and (dppm)2,
the bonding description postulated here is expected to be
generally applicable to these allenylidene complexes.
9
J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004 2513

A R T I C L E S
Wong et al.
Acknowledgment. This work was supported by the Research
Grants Council of the Hong Kong SAR, China to C.M.C. (HKU
7077/01P), and The University of Hong Kong Foundation for
Educational Development and Research. We thank Dr. B.-H.
Xia and Ms. P. Y. Chan for technical assistance regarding the
theoretical calculations, and we are grateful to the reviewers
for helpful comments and suggestions.
2/4/2004. The final Web version and the print version are
correct.
Supporting Information Available: CIF and crystallography
1
data for 1, 5, 6, and 8; perspective view of the cation in 8; H
and 13C{1H} NMR spectra of 6; resonance Raman spectra of 5
and 6 (obtained with 309.1 and 502.9 nm excitation wavelength
respectively) in CH3CN at 25 °C; supplementary characterization
data; tables of selected structural parameters, partial molecular
orbital compositions, and the associated Mulliken and natural
charges for the optimized structure of the model complex trans-
[Cl(NH3)4RudCdCdCPh2]+, plus illustrations of selected
molecular orbitals. This material is available free of charge via
the Internet at http://pubs.asc.org.
Note Added after ASAP Publication: In the version
published on the Web 1/30/2004, the cathodic current in Figure
4 was displayed upward and the anodic current was displayed
downward. Figure 4 has been redisplayed with the cathodic
current directed downward and the anodic current directed
upward (according to Wong, K.-Y.; Che, C.-M.; Anson, F. C.
Inorg. Chem. 1987, 26, 737-741) in the version published
JA0380648
9
2514 J. AM. CHEM. SOC. VOL. 126, NO. 8, 2004