Bonding and substituent effects in electron-rich mononuclear ruthenium σ-arylacetylides of the formula [(η2-dppe) (η5-C5Me5)Ru(C≡C)-1,4-(C 6H4)X][PF6]n (n = 0, 1; X = NO 2, CN, F, H, OMe, NH2)

Organometallics 2006, 25, 649-665

649

Bonding and Substituent Effects in Electron-Rich Mononuclear

Ruthenium σ-Arylacetylides of the Formula

[(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X][PF₆]_n(n ) 0, 1; X )

NO₂, CN, F, H, OMe, NH₂)

Fre´de´ric Paul,*^,†Benjamin G. Ellis,^†,‡Michael I. Bruce,*^,‡Loic Toupet,^§Thierry Roisnel,^|

Karine Costuas,^|Jean-Franc¸ois Halet,^|and Claude Lapinte^†

Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires, UMR CNRS 6509,

Institut de Chimie, UniVersite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France,

Department of Chemistry, UniVersity of Adelaide, South Australia 5005, Australia, Groupe Matie`re

Condense´e et Mate´riaux, UMR CNRS 6626, UniVersite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes

Cedex, France, and Laboratoire de Chimie du Solide et Inorganique Mole´culaire, UMR CNRS 6511,

Institut de Chimie, UniVersite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France

ReceiVed September 16, 2005

This study reports the isolation and the structural (X-ray), UV-vis, and NMR characterization of a

series of electron-rich Ru(II) acetylide complexes of the formula (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-

(C₆H₄)X (1a-f; X ) NO₂, CN, F, H, OMe, NH₂) and (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,3-(C₆H₄)F

(1c-m), as well as the spectroscopic (near-IR and ESR) in situ characterization of the corresponding

elusive Ru(III) radical cations. The spectroscopic data are discussed in connection with DFT computations,

and a consistent picture of the electronic structure of these Ru(II) and Ru(III) acetylide complexes is

proposed. Notably, the strong reactivity of the Ru(III) radicals evidenced in this contribution constitutes

a major difference with the relative stability of the known iron analogues.

VIII metal-acetylide complexes have recently been demon-

strated to constitute very interesting functional groups for redox

switching of a given molecular property.^1a,e,12-13Central to their

use in such applications is the question of electronic com-

Introduction

Over the last few years, electron-rich mono- or polynuclear

metal acetylides have attracted particular attention for the

realization of molecular devices.¹These organometallic frag-

ments have shown interesting properties when used as electro-

active end groups in conjunction with various unsaturated

bridges.^2-7Depending on the nature of the metal, on the

structure and connectivity of the central spacer, and on the redox

state of the compound, molecular wires exhibiting quite different

magnetic, optic, or electronic properties have been syn-

thesized.^{2b,3b-d,5,7-11}Alternatively, several electron-rich group

(3) (a) Venkatesan, K.; Fox, T.; Schmalle, H. W.; Berke, H. Organo-

metallics 2005, 24, 2834-2847. (b) Venkatesan, K.; Blacque, O.; Fox, T.;

Alfonso, M.; Schmalle, H. W.; Berke, H. Organometallics 2004, 23, 1183-

1186. (c) Fernandez, F. J.; Venkatesan, K.; Blacque, O.; Alfonso, M.;

Schmalle, H.; Berke, H. Chem. Eur. J. 2003, 9, 6192-6209. (d) Venkatesan,

K.; Fernandez, F. J.; Blacque, O.; Fox, T.; Alfonso, M.; Schmalle, H. W.;

Berke, H. Chem. Commun. 2003, 2006-2008. (e) Kheradmandan, S.;

Heinze, K.; Schmalle, H.; Berke, H. Angew. Chem., Int. Ed. Engl. 1999,

38, 2270-2273.

(4) Yam, V. W.-W. Acc. Chem. Res. 2002, 35, 555-563.

* To whom correspondence should be addressed. Fax: (33) 2 23 23 56

(5) (a) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M.

AdV. Organomet. Chem. 1998, 42, 291-362. (b) Whittall, I. R.; McDonagh,

A. M.; Humphrey, M. G.; Samoc, M. AdV. Organomet. Chem. 1998, 43,

349-405.

37 (F.P.); (61)

8 8303 4358 (M.I.B.). E-mail: frederic.paul@

univ-rennes1.fr (F.P.); michael.bruce@adelaide.edu.au (M.I.B.).

^†UMR CNRS 6509, Universite´ de Rennes 1.

^‡University of Adelaide.

(6) (a) Weyland, T.; Ledoux, I.; Brasselet, S.; Zyss, J.; Lapinte, C.

Organometallics 2000, 19, 5235-5237. (b) Weyland, T.; Costuas, K.;

Toupet, L.; Halet, J.-F.; Lapinte, C. Organometallics 2000, 19, 4228-4239.

(c) Weyland, T.; Costuas, K.; Mari, A.; Halet, J.-F.; Lapinte, C. Organo-

metallics 1998, 17, 5569-5579. (d) Weyland, T.; Lapinte, C.; Frapper, G.;

Calhorda, M. J.; Halet, J.-F.; Toupet, L. Organometallics 1997, 16, 2024-

2031.

(7) (a) Bruce, M. I. Coord. Chem. ReV. 1997, 166, 91-119. (b) Bruce,

M. I. Chem. ReV. 1998, 98, 2797-2858. (c) Bruce, M. I.; Low, P. J. AdV.

Organomet. Chem. 2004, 50, 179-444.

(8) Szafert, S.; Gladysz, J. A. Chem. ReV. 2003, 103, 4175-4205.

(9) (a) Paul, F.; Lapinte, C. In Unusual Structures and Physical Properties

in Organometallic Chemistry; Gielen, M., Willem, R., Wrackmeyer, B.,

Eds.; Wiley: San Francisco, 2002; pp 219-295. (b) Paul, F.; Lapinte, C.

Coord. Chem. ReV. 1998, 178/180, 427-505.

(10) (a) Roue´, S.; Le Stang, S.; Toupet, L.; Lapinte, C. C. R. Chim. 2003,

6, 353-366. (b) Le Narvor, N.; Toupet, L.; Lapinte, C. J. Am. Chem. Soc.

1995, 117, 7129-7138. (c) Le Narvor, N.; Lapinte, C. C. R. Acad. Sci.,

Ser. IIc: Chim. 1998, 745-749. (d) Coat, F.; Lapinte, C. Organometallics

1996, 15, 476-479. (e) Coat, F.; Paul, F.; Lapinte, C.; Toupet, L.; Costuas,

K.; Halet, J.-F. J. Organomet. Chem. 2003, 683, 368-378.

(11) Ren, T. Organometallics 2005, 24, 4854-4870 and references cited

therein.

^§UMR CNRS 6626, Universite´ de Rennes 1.

^|UMR CNRS 6511, Universite´ de Rennes 1.

(1) See for instance: (a) Cifuentes, M. P.; Humphrey, M. G.; Morall, J.

P.; Samoc, M.; Paul, F.; Roisnel, T.; Lapinte, C. Organometallics 2005,

24, 4280-4288. (b) Blum, A. S.; Ren, T.; Parish, D. A.; Trammell, S. A.;

Moore, M. H.; Kushmerick, J. G.; Xu, G.-L.; Deschamps, J. R.; Polack, S.

K.; Shashidar, R. J. Am. Chem. Soc. 2005, 127, 10010-10011. (c) Fillaut,

J.-L.; Perruchon, J.; Blanchard, P.; Roncali, J.; Gohlen, S.; Allain, M.;

Migalska-Zalas, A.; Kityk, I. V.; Sahraoui, B. Organometallics 2005, 24,

687-695. (d) Qi, H.; Sharma, S.; Li, Z.; Snider, G. L.; Orlov, A. O.; Lent,

S. S.; Fehlner, T. P. J. Am. Chem. Soc. 2003, 125, 15250-15259. (e) Wong,

K. M.-C.; Lam, S. C.-F.; Ko, C.-C.; Zhu, N.; Yam, V. W.-W.; Roue´, S.;

Lapinte, C.; Fathallah, S.; Costuas, K.; Kahlal, S.; Halet, J.-F. Inorg. Chem.

2003, 42, 7086-7097. (f) Powell, C. E.; Humphrey, M. G. Coord. Chem.

ReV. 2004, 248, 725-756. (g) Hu, Q. Y.; Lu, W. X.; Tang, H. D.; Sung,

H. H. Y.; Wen, T. B.; Williams, I. D.; Wong, G. K. L.; Lin, Z.; Jia, G.

Organometallics 2005, 24, 3966-3973.

(2) (a) Rigaut, S.; Touchard, D.; Dixneuf, P. H. Coord. Chem. ReV. 2004,

248, 1585-1601. (b) Rigaut, S.; Perruchon, J.; Le Pichon, L.; Touchard,

D.; Dixneuf, P. H. J. Organomet. Chem. 2003, 670, 37-44. (c) Wong,

C.-Y.; Che, C.-M.; Chan, M. C. W.; Han, J.; Leung, K.-H.; Phillips, D. L.;

Wong, K.-Y.; Zhu, N. J. Am. Chem. Soc. 2005, 127, 13997-14007.

Publication on Web 12/27/2005

650 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Chart 1

Results

Synthesis and Characterization of the Ru(II) Complexes.

Many of the complexes were obtained by the traditional route

developed by Bruce et al. for Ru complexes: i.e., activation of

the preformed functional arylacetylide starting from the known

chloride precursor (η²-dppe)(η⁵-C₅Me₅)RuCl (3).^16c,19This

synthetic approach is quite versatile and allows for the isolation

of most compounds in a straightforward way (Scheme 1).²⁰As

shown in the case of Me₃SiCtCC₆H₄NO₂-4, prior deprotection

of the silyl group of the phenylalkyne is not necessary, since it

occurs spontaneously during the course of the reaction. The

vinylidene complexes formed as intermediates were not isolated

munication between the metal and the rest of the molecule via

the alkynyl bridge.^14,15In this respect, and following the recent

synthesis of polynuclear architectures bearing “(η²-dppe)(η⁵-

C₅Me₅)Ru(CtC)-” electroactive end groups,¹⁶we were inter-

ested in comparing the electronic substituent effects in a series

of mononuclear model complexes of the formula [(η²-dppe)(η⁵-

C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X][PF₆]_n(n ) 0, 1; 1a-f/1a-f⁺)

(Chart 1) with those operative in the series of iron analogues

[(η²-dppe)(η⁵-C₅Me₅)Fe(CtC)-1,4-(C₆H₄)X][PF₆]_n(n ) 0, 1;

2a-f/2a-f⁺), previously investigated by some of us.^12,17Given

the significantly larger electronegativity of ruthenium relative

to iron, we anticipated that the bonding and the properties in

each redox state might be somewhat different, as observed for

the dinuclear butadiynediyl complexes.^16aFor instance, in line

with previous hyperpolarizability measurements,¹²a smaller

degree of back-donation from filled d metal-based (M ) Ru,

Fe) molecular orbitals (MOs) into the empty alkynyl π* MOs

was expected in the Ru(II) case.¹⁸

t

but deprotonated in situ using BuOK to yield several of the

desired acetylide complexes (1a,c-f). The quantitative formation

1

of the vinylidene salts was checked by H and ³¹P NMR each

time.

In the case of the cyano and fluoride substituents, the previous

reaction did not work properly. Small amounts of unidentified

compounds were always isolated with the desired acetylide

complex during the workup, and conversion of the starting

chloro complex 3 was uncomplete. We therefore devised another

way to access the Ru(II) acetylides with these particular

substituents and found it more convenient to use a Sonogashira-

type catalytic coupling procedure with the terminal acetylide

complex (η²-dppe)(η⁵-C₅Me₅)RuCtCH (4). Such a procedure,

starting from electron-rich metalated alkynes such as 4, has

already been proven to be quite versatile^21-24and presently

allowed the isolation of the target complexes 1b (X ) CN) and

1c (X ) F) and also of the meta isomer of 1c (1c-m) with good

yields (Scheme 2). By this route, 1a was isolated with a lower

yield (see Experimental Section) than by the previous one

(Scheme 1). However, with this particular substituent, it is the

separation of 1a from excess BrC₆H₄NO₂-4 which proves

detrimental to the final yield, since NMR reveals that 1a is

quantitatively formed by the reaction given in Scheme 2. For

other substituents, the crude samples of the Ru(II) complexes

isolated by extraction right after the reaction are usually fairly

clean. The compounds can then be further purified by flash

chromatography on alumina, before being crystallized from

solvent mixtures.

We therefore report in the following (i) the synthesis and

characterization of several such Ru(II) complexes (1a-f), (ii)

the in situ characterization of the corresponding Ru(III) parents

generated after chemical oxidation (1a-f⁺), (iii) DFT computa-

tions on several Ru(II) and Ru(III) representatives, and (iv)

correlations of selected data with electronic substituent param-

eters (ESP). The bonding within the “Ru-CtC-1,4-C₆H₄-”

core is then discussed along with the X-substituent electronic

effects and subsequently compared to results previously obtained

with the known iron analogues (2a-f/2a-f⁺).^17cThis work

actually reveals several notable differences between these series

of isoelectronic and isolobal complexes.

Unambiguous solid-state characterization of each of the

Ru(II) acetylide complexes (1a-f) was carried out by a single-

crystal X-ray structural determination. In addition, correct

elemental analyses and LSI-MS were obtained. Notably, during

LSI-MS characterization, quite intense peaks corresponding to

the carbonyl ruthenium (5⁺) adduct were detected (Chart 2),

while such complexes were always absent from the original

samples.^25,26An analogous Fe(II) cation was also often detected

by MS when 2a-f were subjected to LSI-MS analysis.

(12) Paul, F.; Costuas, K.; Ledoux, I.; Deveau, S.; Zyss, J.; Halet, J.-F.;

Lapinte, C. Organometallics 2002, 21, 5229-5235.

(13) (a) Powell, C. E.; Cifuentes, M. P.; Morall, J. P.; Stranger, R.;

Humphrey, M. G.; Samoc, M.; Luther-Davies, B.; Heath, G. A. J. Am. Chem.

Soc. 2003, 125, 602-610. (b) Powell, C. E.; Humphrey, M. G.; Cifuentes,

M. P.; Morall, J. P.; Samoc, M.; Luther-Davies, B. J. Phys. Chem. A 2003,

107, 11264-11266. (c) Cifuentes, M. P.; Powell, C. E.; Humphrey, M. G.;

Heath, G. A.; Samoc, M.; Luther-Davies, B. J. Phys. Chem. A 2001, 105,

9625-9627.

(14) Manna, J.; John, K. D.; Hopkins, M. D. AdV. Organomet. Chem.

1995, 38, 80-154.

(15) (a) Lichtenberger, D. L.; Renshaw, S. K. Organometallics 1993,

12, 3522-3526. (b) Lichtenberger, D. L.; Renshaw, S. K.; Bullock, R. M.

J. Am. Chem. Soc. 1993, 115, 3276-3285. (c) Lichtenberger, D. L.; Gruhn,

N. E.; Renshaw, S. K. J. Mol. Struct. 1997, 405, 79-86.

(19) Bruce, M. I.; Wallis, R. C. J. Organomet. Chem. 1978, 161, C1-

C4.

(20) Bitcon, C.; Whiteley, M. W. J. Organomet. Chem. 1987, 336, 385-

392.

(16) (a) Bruce, M. I.; Costuas, K.; Davin, T.; Ellis, B. G.; Halet, J.-F.;

Lapinte, C.; Low, P. J.; Smith, M. E.; Skelton, B. W.; Toupet, L.; White,

A. H. Organometallics 2005, 24, 3864-3881. (b) Bruce, M. I.; Ellis, B.

G.; Low, P. J.; Skelton, B. W.; White, A. H. Organometallics 2003, 22,

3184-3198. (c) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N.

N. J. Organomet. Chem. 2002, 650, 141-150.

(21) (a) Bruce, M. I.; Ke, M.; Low, P. J. J. Chem. Soc., Chem. Commun.

1996, 2405-2406. (b) Bruce, M. I.; Ke, M.; Low, P. J.; Skelton, B. W.;

White, A. H. Organometallics 1998, 17, 3539-3549.

(22) Denis, R.; Weyland, T.; Paul, F.; Lapinte, C. J. Organomet. Chem.

1997, 545/546, 615-618.

(23) Hurst, S. K.; Cifuentes, M. P.; MacDonagh, A. M.; Humphrey, M.

G.; Samoc, M.; Luther-Davies, B.; Asselberghs, I.; Persoons, A. J.

Organomet. Chem. 2002, 642, 259-267.

(17) (a) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics

2000, 19, 4240-4251. (b) Paul, F.; Mevellec, J.-Y.; Lapinte, C. Dalton

Trans. 2002, 1783-1790. (c) Costuas, K.; Paul, F.; Toupet, L.; Halet, J.-

F.; Lapinte, C. Organometallics 2004, 23, 2053-2068. (d) Paul, F.; Toupet,

L.; The´pot, J.-Y.; Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics

2005, 24, 5464-5478.

(24) Courmarcel, J.; Le Gland, G.; Toupet, L.; Paul, F.; Lapinte, C. J.

Organomet. Chem. 2003, 670, 108-122.

(25) This known compound presents a characteristic²⁷and intense infrared

absorption (ν_COat 1972 cm^-1) and a ³¹P shift around 72 ppm.²⁶

(26) Bruce, M. I.; Ellis, B. G.; Skelton, B. W.; White, A. H. J.

Organomet. Chem. 2005, 690, 792-801.

(18) Delfs, C. D.; Stranger, R.; Humphrey, M. G.; MacDonagh, A. M.

J. Organomet. Chem. 2000, 607, 208-212.

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 651

Scheme 1

Table 2. UV-vis Data for

Scheme 2

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC-C₆H₄X) Complexes in CH₂Cl₂

X

abs, nm (10^-3ꢀ, M^-1cm^-1

)

4-NO₂(1a)

4-CN (1b)

3-F (1c)

264 (113.2); 322 (sh, 10.1); 500 (18.9)

250 (sh, 23.1); 338 (sh, 9.3); 384 (19.2)

328 (17.9)

4-F (1c-m)

4-H (1d)

4-OMe (1e)

4-NH₂(1f)

248 (sh, 26.0); 306 (19.0)

252 (sh, 24.5); 318 (21.1)

252 (sh, 37.2); 300 (21.4)

254 (sh, 25.4); 304 (23.2)

Chart 2

these compounds. Thus, a single peak is observed by ³¹P{¹H}

NMR near 82 ppm for the two equivalent phosphorus atoms in

solution and a triplet with a coupling constant of ca. 25 Hz,

characteristic of the R-acetylide carbon atom, can be identified

in the ¹³C NMR spectrum in each case (see Experimental

Section).²⁶For all complexes, a strong ν(CtC) band near 2050

cm^-1is also apparent in solution and in the solid state, which

can be detected by either infrared or Raman spectroscopy. In

solution, this absorption is split respectively by 31 and 21 cm^-1

for the nitro- and cyano-containing complexes (1a,b), presum-

ably by reason of Fermi coupling.^17b

Table 1. Infrared Data for

[(η²-dppe)(η⁵-C₅Me₅)Ru(CtC-C₆H₄X)]^0/+Complexes in

CH₂Cl₂Solution (cm^-1

)

ν_CtC

For all compounds a rather intense electronic transition is

observed in the 300-500 nm range, which explains the purple

(1a) or orange-yellow (1b-f) color of the complexes (Table

2).¹²We attribute this electronic transition to an MLCT process

by analogy with 2a-f.^17c,30This electronic transition is ipso-

chromically shifted by electron-releasing substituents, a sub-

stituent effect which also would be in accordance with an MLCT

process.^17cFor all complexes, more intense absorptions, possibly

corresponding to ligand-based π-π* or n-π* transitions, are

also observed above 250 nm, while for the nitro complex 1a,

an additional weak transition is detected near 320 nm. We

tentatively attribute this to a nitro-based n-π* transition.^17a

Cyclic voltammograms (CVs) of all Ru(II) complexes were

recorded between 1.0 and -1.5 V vs the standard calomel

electrode (SCE). All complexes display an apparently reversible

or quasi-reversible (in the chemical sense) one-electron wave

(Table 3) in the range 0.05-0.40 V, corresponding to the metal-

centered Ru(II)/Ru(III) oxidation. As expected, electron-releas-

ing substituents facilitate this process, shifting the redox potential

toward more negative values from ca. 350 mV on going from

the nitro (1a) to the amino complex (1f) (Figure 1a). For 1a, an

additional nonreversible process is observed near -1.3 V (Figure

1b), which presumably corresponds to the reduction of the

nitroaryl group.^17aFor complex 1f, a second nonreversible

process is also observed at 0.59 V, which possibly corresponds

b

X

Ru(II)^a

Ru(III)

1942

∆ν_CtC

4-NO₂(1a)

2048

2017

2060

2039

2072

2058

2072

2071

2074

2075

2050 (sh)

-90^d

-105^d

/

4-CN (1b)^c

3-F (1c-m)

1944

nd^e

4-F (1c)

4-H (1d)

4-OMe (1e)

4-NH₂(1f)

1930

1930^f

1929

1940^f

-142

-141

-145

-135^d

^aSolid-state ν_CtCvalues obtained in KBr for isolated complexes are

given in the Experimental Section. ^bNeutral vs oxidized ν_CtCdifference.

^cFor this complex, the ν_CtNvalue is shifted from 2218 cm^-1to 2227 cm^-1

^dMean ∆ν_CtCvalue. ^eNot determined. ^fTentative assignment.

.

These carbonyl complexes are probably formed in situ, by

reaction of the M(II) acetylide complexes (M ) Ru, Fe) with

traces of molecular oxygen²⁸or water, either before or after

ionization/protonation²⁹by the matrix.

The acetylide complexes 1a-f were also characterized by

the usual spectroscopic methods. NMR, infrared (Table 1), and

Raman spectra contained the spectral signatures expected for

(27) Conroy-Lewis, F. M.; Simpson, S. J. J. Organomet. Chem. 1987,

322, 221-228.

(28) Paul, F.; Toupet, L.; Roisnel, T.; Hamon, P.; Lapinte, C. C. R. Chim.

2005, 8, 1174-1185.

(30) In accordance with such an assignment and as stated for 2a, we

overall observe a positive solvatochromic behavior for this transition in 1a

(∆λ of ca. 50 nm between pentane and acetone).

(29) Bruce, M. I.; Swincer, A. G.; Wallis, R. C. J. Organomet. Chem.

1979, 171, C5-C8.

652 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Figure 1. Cyclic voltammograms showing the metal-centered oxidations of (a) 1a (X ) NO₂), 1d (X ) H), and 1f (X ) NH₂) and (b) of

1a and of the corresponding analogous Fe(II) complex 2a in dichloromethane at 20 °C (0.1 M tetrabutylammonium hexafluorophosphate,

scan rate 0.1 V/s).

Table 3. Electrochemical Data for

comparatively high esds of 1c-m, no striking differences are

apparent between the coordination spheres of the metal for the

meta- and para-substituted fluoro complexes, the meta isomer

having just a more bent acetylide bridge than the para isomer.

More specifically along the series of para-substituted complexes,

a lengthening of the Ru-C37 bond seems to take place on going

from the most electron-withdrawing substituent (X ) NO₂) to

the most electron-releasing one (X ) NH₂), from 1.997(6) Å

for 1a to 2.026(3) Å for 1f. Although these changes are within

the experimental error, their consistency suggests a real underly-

ing effect. The acetylide bond apparently preserves its usual

length around 1.22 Å but deviates somewhat from strict linearity

(angle C37-C38-C39 * 180°), as was also previously

observed with iron(II) analogues. Concerning the various X

substituents, the bond lengths are quite classical, given the

reported esds.³²The nitro, methoxy, and amino substituents in

1a,e,f are roughly coplanar with the phenyl ring (dihedral angles

for 1a,e,f, respectively: C41-C42-N1-O1 ) 12.2-10.1°;

C41-C42-O1-C45 ) -15.8°; C41-C42-N1-H ) 1.8°),

which suggests some slight π-interaction between these two

fragments.

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC-C₆H₄X) Complexes

b

X

∆E_p(V)

E₀(V)^a

i_c/i_a

4-NO₂(1a)

0.09

0.12

0.08

0.09

0.08

0.40

-1.25

0.36

0.29

0.25

0.23

0.15

0.59

0.05

>0.95

ca. 1.30

>0.95

>0.80

>0.85

>0.90

>0.95

nr^c

4-CN (1b)

3-F (1c)

4-F (1c-m)

4-H (1d)

4-OMe (1e)

4-NH₂(1f)

0.09

> 0.85

^aAll E values in V vs SCE. Conditions: CH₂Cl₂solvent, 0.1 M

[n-Bu₄N⁺][PF₆^-] supporting electrolyte, 20 °C, Pt electrode, sweep rate

0.100 V s^-1. The ferrocene/ferrocenium couple (Fc/Fc⁺) was used as an

internal reference for potential measurements (Fc/Fc⁺taken at 0.460 V vs

SCE in CH₂Cl₂).³³^bRatio (0.05. ^cIrreversible oxidation.

to the oxidation of the amino group (Figure 1a). Overall, very

similar features were observed with the Fe(II) analogues 2a-f,

except that fully reversible electrochemical responses were

obtained for the metal-centered oxidation for each substituent

(Figure 1b).^17a

X-ray Structures of Ru(II) Complexes. The para-substituted

complexes 1a-f, as well as the meta-substituted complex 1c-

m, crystallize in triclinic or monoclinic space groups (Table 4,

parts a-g of Figure 2), as previously observed with iron(II)

analogues.^17cThe bond lengths and angles in the coordination

sphere of the metal are the usual ones for such acetylide

complexes (Table 5).^16,31A noticeable change in comparison

to previous structures is the conformation roughly perpendicular

to the Ru/C₅centroid adopted by the functional aryl ring in

1a-f or 1c-m, while close-to-parallel conformations were

previously observed with complexes possessing nonpermethy-

lated cyclopentadienyl ligands.³¹On consideration of the

In Situ Study of Ru(III) Analogues. The observation of

reversible or quasi-reversible peaks for the metal-centered

oxidation led us to check if complexes 1a⁺-1f⁺were suf-

ficiently stable to be isolated. We therefore tried first to isolate

these species after chemical oxidation with silver(I) salts

(Scheme 3).³³Chemical oxidation was performed using a slight

deficiency of silver triflate in dichloromethane followed by

sonication to help dissolution of the triflate salt in dichlo-

romethane. The oxidation reaction is signaled by a rapid color

change of the reaction media. The intense color of the starting

Ru(II) complexes bleaches upon addition of oxidant before

turning darker, often blue in the case of strongly electron-

releasing substituents. Unfortunately, all attempts at isolation

of oxidized Ru(III) congeners failed. For instance, in the case

of 1a, dark red crystals could be recovered from the reaction

(31) (a) Powell, C. E.; Cifuentes, M. P.; McDonagh, A.; Hurst, S. K.;

Lucas, N. T.; Delfs, C. A.; Stranger, R.; Humphrey, M. G.; Houbrechts,

S.; Asselberghs, I.; Persoons, A.; Hockless, D. C. Inorg. Chim. Acta 2003,

352, 9-18. (b) Whittall, I. R.; Humphrey, M. G.; Hockless, D. C. R.;

Skelton, B. W.; White, A. H. Organometallics 1995, 14, 3970-3979. (c)

Bruce, M. I.; Humphrey, M. G.; Snow, M. R.; Tiekink, E. R. T. J.

Organomet. Chem. 1986, 314, 213-225. (d) Wisner, J. M.; Bartczk, T. J.;

Ibers, J. A. Inorg. Chim. Acta 1985, 100, 115-123.

(32) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.

G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1-S19.

(33) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910.

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 653

Table 4. Crystal Data, Data Collection, and Refinement Parameters for 1a-f and 1c-m

1a (X ) NO₂)

1b (X ) CN)

1c (X ) F)

1c-m (X ) F)

1d (X ) H)

1e (X ) OMe) 1f (X ) NH₂)

formula

2(C₄₄H₄₃NO₂-

P₂Ru)‚CH₂Cl₂

823.26

120(2)

triclinic

C₄₅H₄₃NP₂-

Ru‚C₆H₆

838.92

293(2)

triclinic

C₄₄H₄₃FP₂-

Ru‚C₅H₁₂

789.87

120(2)

triclinic

P1h

11.9933(3)

12.0696(3)

15.8540(5)

91.458(2)

104.174(1)

118.673(1)

1924.5(1)

2

C₄₄H₄₃FP₂Ru

C₄₄H₄₄P₂Ru‚

H₂O

753.86

293(2)

triclinic

P1h

12.026(5)

12.072(5)

15.671(5)

73.609(5)

89.080(5)

61.644(5)

1901.9 (13)

2

C₄₅H₄₆O-

P₂Ru

765.83

150(2)

monoclinic

P2₁/c

15.3442(2)

11.5119(1)

22.1852(3)

90

C₄₄H₄₅N-

P₂Ru

750.82

293(2)

monoclinic

P2₁/c

15.602(5)

11.132(5)

22.277(5)

90

108.800(5)

90

fw

753.79

293(2)

monoclinic

P2₁/n

8.7321(2)

19.3489(5)

22.1105(7)

90

98.459(1)

90

3695.1(1)

4

temp (K)

cryst syst

space group

a (Å)

b (Å)

c (Å)

P1h

12.8706(2)

14.6699(3)

22.5006(5)

89.720(1)

85.854(1)

66.620(1)

3888.1(1)

2

12.3797(2)

13.5627(2)

14.3431(3)

72.6573(8)

88.1280(7)

66.8617(8)

2104.03(6)

2

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

108.085(1)

90

3725.2(1)

4

3663(2)

4

1.362

D

_calcd(g cm^-3

)

1.406

1.324

1.363

1.355

1.320

1.365

cryst size (mm)

0.36 × 0.25 ×

0.30 × 0.28 × 0.45 × 0.32 × 0.38 × 0.36 × 0.60 × 0.30 × 0.35 × 0.35 × 0.19 × 0.16 ×

0.22 0.32 0.24 0.20 0.32 0.07

872 972 1560 784 1592 1560

0.22

F(000)

1700

diffractometer (NONIUS)

radiation

Kappa CCD

Mo KR

Kappa CCD

Mo KR

Kappa CCD

Mo KR

Kappa CCD

Mo KR

Kappa CCD

Mo KR

Kappa CCD

Mo KR

Kappa CCD

Mo KR

abs coeff (mm^-1

data collection

2θ_max(deg)

)

0.593

0.484

0.528

0.546

0.528

0.541

0.548

60

506

60

114

54

320

54

472

55

129

54

190

55

172

no. of frames

Ω rotation (deg)

frames/s

0.8

16

2.0

16

2.0

170

0.6

17

2.0

50

1.6

16

1.6

288

θ range (deg)

hkl ranges

1.79-27.45

2.20-27.51

1.95-27.57

-14 to +14

-15 to +15

-20 to +20

50 379

8864

2.58-27.46

0-11

0-25

-28 to +28

33 926

8396

3.40-27.51

-15 to +15

-20 to +20

13 286

8516

2.02-27.49

0-19

0-14

-28 to +28

33 478

8440

2.65-27.54

-20 to +20

-12 to +14

-26 to +28

38 712

8338

0-16

-18 to +18

-29 to +29

53 280

17 060

-15 to +17

-18 to +18

19 532

9467

total no. of rflns

no. of unique rflns

no. of obsd rflns (I > 2σ(I)) 12 607

8183

0/497

7823

0/467

5446

0/443

6908

0/443

7348

0/443

5875

0/434

no. of restraints/params

0/926

w ) 1/[σ²(F_o)²+ (aP)²+-

bP]^a

a

0.089

0

0.073

2.94

0.109

4.98

0.068

0.164

0.1214

0.2005

1.023

1.2

1.247, 0.890

0.084

1.246

0.061

2.73

0.044

0.485

0.039

0.084

0.0733

0.0956

1.035

0.4

b

0

final R

final R_w

R (all data)

0.073

0.183

0.1041

0.2032

1.069

3.02

3.023, -2.268

0.035

0.087

0.044

0.094

1.063

0.65

0.044

0.118

0.0509

0.1236

0.999

0.67

0.0494

0.1380

0.0644

0.1510

1.059

0.037

0.100

0.0454

0.1075

1.070

1.1

R

_w(all data)

goodness of fit/F²(S_w)

∆F_max(e Å^-3

)

1.1

1.083, 0.728

largest diff peak,

0.646, -0.501 1.685, 1.262

1.018, -0.970 0.441, -0.400

hole (e Å^-3

)

2

^aP ) [F_o+ F_c]/3.

Scheme 3

to change, yielding several new absorptions in the 1500-2000

cm^-1spectral range, while the Ru(III) ν(CtC) band decreases.

The presence of the carbonyl adduct 5⁺(Chart 2) could never

be evidenced at early stages,²⁵possibly because no oxygen^28,35-36

or water^26,29,37was available for its formation in the spectro-

scopic cell. Upon standing, the solution eventually returns to

its original color and the re-formation of the starting Ru(II)

complexes is observed with electron-withdrawing substituents.³⁸

After total decay of the Ru(III) ν(CtC) band, NMR reveals

the presence of several unidentified diamagnetic complexes in

the medium, among which possibly lies the corresponding

vinylidene salt.

mixture, but these proved to correspond to the vinylidene triflate

salt 6[OTf]³⁴(Chart 2), rather than the desired 1a[OTf].

Infrared monitoring suggests that the desired Ru(III) acetylide

complex is the primary product, since a transient absorption

around 1950 cm^-1develops (Table 1), which would typically

correspond to the spectral signature expected for a Ru(III)

ν(CtC) band.³⁵Unfortunately, the reaction mixture continues

ESR in dichloromethane/1,2-dichloroethane glasses at 80 K

reveals that a single radical is generated following oxidation of

the Ru(II) precursor using ferrocenium hexafluorophosphate.

A rhombic signal (Figure 3), typical of a piano-stool metal-

(36) Choi, M.-Y.; Chan, M. C.-W.; Zhang, S.; Cheug, K.-K.; Che, C.-

M.; Wong, K.-Y. Organometallics 1999, 18, 2074-2080.

(37) Le Lagadec, R.; Roman, E.; Toupet, L.; Mu¨ller, U.; Dixneuf, P. H.

Organometallics 1994, 13, 5030-5039.

(38) This is notably the case for the nitro (1a) and cyano (1b) complexes

(see the Supporting Information for an example).

(34) The identity of this complex was confirmed by a poor-quality X-ray

diffraction study (see the Supporting Information).

(35) Adams, C. J.; Pope, S. J. A. Inorg. Chem. 2004, 43, 3492-3499.

654 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Figure 2. ORTEP plots (50% probability level) of (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X: (a) X ) NO₂(1a); (b) X ) CN (1b); (c)

X ) F (1c); (d) X ) H (1d); (e) X ) OMe (1e); (f) X ) NH₂(1f); (g) (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,3-(C₆H₄)F (1c-m).

centered radical, is observed in each case (Table 6).^17d,39No

hyperfine structure is detected, but such features could easily

be hidden underneath the signals observed for g₁, g₂, and g₃,

which respectively have half-height widths of ca. 40, 50 and

70 G. With the most electron-releasing substituents, the ESR

signal proved quite elusive when samples were warmed to room

temperature, after thawing. The sample stability improves in

the solvent glass. Thus, the signal of a sample of 1f⁺(X )

NH₂) in a vacuum-sealed ESR tube was monitored over 56 h

at 77 K in a THF/dichloromethane (2:1) glass. The signal

disappeared after 20 min at 300 K, dark residues being present

in the tube after this period. At ambient temperature, an isotropic

signal at g ) 2.04 (∆g ) 26 G peak to peak) could also be

transiently observed with this sample. Possibly, the latter signal

originates from an organic radical. The instability of these

Ru(III) radicals is likely to be kinetic in origin. Moreover, the

selective observation of one type of rhombic ESR signature for

all compounds at low temperature suggests that oxidation

essentially forms one metal-centered radical.

(39) Rieger, P. H. Coord. Chem. ReV. 1994, 135/136, 203-286.

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 655

Table 5. Selected Bond Lengths (Å) and Angles (deg) for 1a-f and 1c-m

1a (X ) NO₂)^a

1.891/1.889

1b (X ) CN) 1c (X ) F) 1c-m (X ) F) 1d (X ) H) 1e (X ) OMe) 1f (X ) NH₂)

Selected Bond Lengths

Ru-(Cp*)_centroid

Ru-P1

1.895

1.890

1.895

1.884

1.894

1.901

2.2639(14)/2.2676(14)

2.2747(14)/2.2650(15)

1.997(6)/2.004(6)

1.221(8)/1.225(8)

1.437(8)/1.413(8)

1.410(8)/1.405(8)

1.379(8)/1.379(8)

1.389(8)/1.382(8)

1.384(8)/1.383(8)

1.379(8)/1.380(8)

1.403(8)/1.411(8)

2.2639(5)

2.2755(6)

2.004(2)

1.209(3)

1.434(3)

1.399(3)

1.379(4)

1.390(4)

1.387(3)

1.379(3)

1.401(3)

2.2583(7)

2.2715(7)

2.014(3)

1.209(4)

1.445(4)

1.404(4)

1.392(4)

1.373(5)

1.362(5)

1,386(5)

1.404(4)

1.365(4)

2.2663(14)

2.2709(13)

2.017(5)

1.195(7)

1.441(7)

1.383(9)

1.393(9)

1.374(11)

1.369(11)

1.342(8)

1.408(8)

1.337(8)

2.2622(12)

2.2563(12)

2.011(4)

1.215(5)

1.431(5)

1.394(6)

1.380(7)

1.358(9)

1.332(9)

1.379(7)

1.387(6)

2.2652(2)

2.2643(6)

2.015(2)

1.216(3)

1.433(3)

1.398(4)

1.382(4)

1.366(4)

1.382(4)

1.398(4)

1.399(4)

2.2622(11)

2.2625(11)

2.026(3)

1.202(4)

1.444(4)

1.399(4)

1.383(4)

1.379(5)

1.389(5)

1.384(4)

1.388(4)

Ru-P2

Ru-C37

C37-C38

C38-C39

C39-C40

C40-C41

C41-C42

C42-C43

C43-C44

C44-C39

C42-F1

C42-O1

C45-O1

C42-C45

N1-C45

C42-N1

N1-O1

1.379(3)

1.410(4)

1.435(4)

1.137(4)

1.465(7)/1.456(8)

1.232(7)/1.232(7)

1.227(7)/1.235(7)

1.404(4)

N1-O2

Selected Bond Angles

P1-Ru-P2

83.58(5)/83.63(5)

82.33(16)/86.94(16)

87.16(16)/82.56(16)

178.8(5)/177.9(5)

171.6(6)/172.2(6)

120.7(5)/117.9(5)

122.2(5)/122.2(5)

83.78(2)

83.65(3)

80.24(8)

85.76(8)

178.9(3)

172.6(3)

117.7(3)

123.1(3)

118.2(3)

118.7(3)

84.02(5)

82.78(15)

80.92 (14)

172.9(4)

172.9(5)

117.3(5)

117.5(6)

118.2(6)

117.3(7)

83.73(4)

85.37(11)

81.67(11)

179.1(3)

173.7(4)

116.6(4)

119.6(5)

83.01(2)

85.57(7)

79.01(6)

175.4(2)

171.1(3)

116.9(2)

119.9(2)

83.12(3)

79.10(8)

85.46(8)

176.1(3)

172.7(3)

116.6(3)

118.3(3)

P1-Ru-C37

P2-Ru-C37

Ru-C37-C38

C37-C38-C39

C40-C39-C44

C41-C42-C43

C41-C42-F1

C43-C42-F1

C41-C42-O1

C43-C42-O1

C42-O1-C45

C41-C42-N1

C43-C42-N1

C42-C45-N1

O1-N1-O2

80.50(6)

85.09(6)

176.9(2)

172.1(3)

117.5(2)

119.2(2)

115.7(3)

124.5(3)

116.9(3)

118.5(5)/119.4(5)

119.3(5)/118.4(5)

121.2(3)

120.5(3)

177.7(4)

123.2(5)/122.9(6)

Ru-(Cp*)_centroid/C39-C40^b-71.47/-73.19

-91.8

110.2

-108.7

-108.5

-104.8

-104.2

^aTwo molecules in the asymmetric unit. ^bDihedral angle in degrees (Cp* ) pentamethylcyclopentadienyl ligand).

Table 6. ESR Spectroscopic Data^afor

[(η²-dppe)(η⁵-C₅Me₅)Ru(CtC-C₆H₄X)][PF₆] Complexes

X

g₁

g₂

g₃

g

∆g

4-NO₂(1a⁺)

4-NO₂(1a⁺)^b

4-CN (1b⁺)

3-F (1c-m⁺)^c

4-F (1c⁺)

1.971

1.973

1.980

1.985

1.988

1.990

1.998

2.067

2.069

2.068

2.064

2.063

2.057

2.059

2.043

2.040

2.333

2.320

2.327

2.301

2.279

2.227

2.239

2.145

2.131

2.123

2.120

2.123

2.115

2.109

2.091

2.096

2.062

2.056

0.362

0.347

0.354

0.321

0.294

0.239

0.249

0.135

0.142

4-H (1d⁺)

4-OMe (1e⁺)

4-NH₂(1f⁺)

4-NH₂(1f⁺)^b

Figure 3. ESR spectrum of the 1b[PF₆] radical (X ) CN) in 1,2-

CH₂Cl₂/C₂H₄Cl₂(1:1) at 80 K.

^aAt 77 or 80 K in CH₂Cl₂-C₂H₄Cl₂(1:1) glass. ^bAt 77 or 80 K in

CH₂Cl₂-THF (1:2) glass. ^c1,3-substituted isomer.

These Ru(III) radical cations could also be characterized by

electronic spectroscopy at ambient temperature (300 K) in

dichloromethane. On the basis of previous work with Fe(III)

analogues,^17dwe anticipated that these radical species should

present a weak but characteristic absorption in the near-IR range,

corresponding to a forbidden LF transition. After chemical

oxidation, assessed by its diagnostic color change, a weak

absorption around 1300 nm was observed each time (Table 7,

Figure 4), except in the case of the amino complex 1f⁺.

Expectedly, this weak spectral feature disappears upon standing.

It was also confirmed that neither the starting Ru(II) parent

complex nor the silver triflate has absorptions in this spectral

range. For the amino complex 1f⁺, the missing absorption is

either hidden (it could correspond to a very weak shoulder

around 1050 ( 50 nm on the low-energy side of the absorption

detected at 813 nm) or not detected at all. The extinction

coefficients reported for these bands in Table 5 were computed

by considering a total conversion of the initial Ru(III) com-

plexes. As a consequence, these “apparent” values are lower

than the real ones, since the actual concentration of the Ru(III)

radicals present in the cell is evidently lower.

Transient absorptions could also be observed in the UV-

visible range. Given the number of species which are generated

by oxidation and which are likely to absorb in this spectral

region, no definitive data concerning the Ru(III) radical data

could be obtained from these experiments. There are, however,

strong analogies between the transient absorptions immediately

observed following oxidation (Supporting Information) and

those previously reported for the stable Fe(III) analogues.^17d

656 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Figure 4. Near-IR spectra of 1d and 1d[OTf] in CH₂Cl₂.

Table 7. Solution^aNear-IR Data for

Figure 5. Energy (eV) of the frontier MOs of the (H₃P)₂(η⁵-C₅H₅)-

Ru(CtC)-1,4-(C₆H₄)X model complexes 1a-H (X ) NO₂), 1d-H

(X ) H), and 1f-H (X ) NH₂).

[(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X][OTf]

X

ν_max( 25^b(ꢀ ( 5^c)

NO₂(1a⁺)

CN (1b⁺)

F (1c⁺)

1430/6990 (144)

1370/7300 (90)

1310/7630 (300)

1330/7520 (23)

1240/8070 (82)

nd^d

cally computed, on proceeding from a nitro (1a-H) to an amino

(1f-H) substituent, is apparently reproduced in the available

solid-state data,³¹although these changes remain below the

experimental uncertainty with 1a-f. Geometric optimizations

confirm that the most stable configuration is that where the

functional aryl ring is roughly parallel to the Cp plane (see X-ray

structures) but also suggest that rotation of the functional aryl

group around the acetylide axis should be easy in solution.

Energies of the frontier MOs for Ru(II) complexes are shown

in Figure 5, and their orbital composition is given in Table 9.

The NO₂-containing complex shows a smaller HOMO-LUMO

gap due to an empty MO (52a) essentially localized on the NO₂

fragment which lies between the HOMO (50a) and the first

antibonding MO centered on the metal (53a). Without this

particular MO, the HOMO-LUMO gap would slightly decrease

on going from the most electron-withdrawing substituent to the

most electron-releasing one.

Two closely lying MOs with sizable metal acetylide character

(ca. 16-43% and 33-43%, respectively) constitute the HOMO

and HOMO - 1 of these Ru(II) complexes. These MOs roughly

correspond to the perpendicular π-manifolds on the acetylide

ligand. The HOMO corresponds to the π-manifold conjugated

with the X substituent for the compounds 1d-H and 1f-H,

containing the most electron releasing groups (X ) H, NH₂),

as observed for the Fe(II) analogues.^17cThis MO is stabilized

with the nitro substituent and constitutes the HOMO - 1 in

complex 1a-H (X ) NO₂; Figure 5). This illustrates the

influence of the X substituent on the π-bonding in these

compounds. Additionally, the phenylacetylide character of these

two MOs slightly increases, with a concomitant decrease in Ru

character, on going from the nitro (1a-H) to the amino (1f-H)

complexes (see Table 9). For all of the systems except for X )

NO₂, the LUMO is an Ru-Cp antibonding orbital, while for X

) NO₂(1a-H), the corresponding MO is the LUMO + 1, 0.50

eV higher in energy than the LUMO, which is localized on the

aryl-NO₂moiety.

H (1d⁺)

OMe (1e⁺)

NH₂(1f⁺)

^aIn CH₂Cl₂in the absorbance mode at 20 °C. ^bGiven in nm/cm^-1

.

^cTentative estimate in M^-1cm^-1(see text). ^dNot detected.

Table 8. Selected Bond Distances Computed for

(PH₃)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X (1a-H/1d-H/1f-H)

Compared to the X-ray Data Available for the Complexes

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X/

(η²-dppe)(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X/

(Ph₃P)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X (X ) NO₂, H, NH₂)^a

1a-H (X ) NO₂)

1d-H (X ) H)

1f-H (X ) NH₂)

Ru-C37 2.02 (2.00^b/1.99^c/1.99^d) 2.03 (2.01/2.01^e/2.02^e)

C37-C38 1.23 (1.22^b/1.21^c/1.20^d) 1.23 (1.21/1.20^e/1.21^e)

C38-C39 1.42 (1.44^b/1.42^c/1.43^d) 1.43 (1.43/1.44^e/1.46^e)

2.04 (2.03)

1.23 (1.20)

1.43 (1.44)

1.42 (1.40)

1.39 (1.38)

1.40 (1.39)

1.39 (1.38)

1.42 (1.39)

1.98 (1.90)

2.30 (2.26)

1.41 (1.40)

88 (104)

C39-C40 1.42 (1.41^b//1.43^d)

C40-C41 1.39 (1.38^b//1.41^d)

C41-C42 1.40 (1.39^b//1.37^d)

C42-C43 1.40 (1.38^b//1.36^d)

C43-C44 1.39 (1.38^b//1.37^d)

C44-C45 1.42 (1.40^b//1.40^d)

Ru-(Cp)^f1.96 (1.89^b)

1.42 (1.39)

1.39 (1.38)

1.40 (1.35)

1.40 (1.33)

1.39 (1.38)

1.42 (1.39)

1.99 (1.88)

2.29 (2.26/2.24^e/2.31^e)

2.29 (2.25/2.25^e/2.29^e)

/

Ru-P1

Ru-P2

C42-X

δ^g

2.31 (2.26^b//2.30^d)

2.31 (2.27^b//2.30^d)

1.46 (1.47^b//1.47^d)

88 (71^b)

88 (108)

^aRefer to Figure 2 for labeling (experimental values are given in

parentheses). ^bExperimental value given for a selected molecule in the

asymmetric unit of 1a. ^cValues taken from ref 31b. ^dValues taken from

ref 31a. ^eValues taken from ref 31c. ^f(Cp) ) Cp centroid. ^gDihedral angle

Fe-(Cp)-C1-C6.

DFT Computations on Model Compounds. Theoretical

computations on the model Ru(II/III) complexes 1a-H/1a-H⁺

(X ) NO₂), 1f-H/1f-H⁺(X ) H), and 1j-H/1j-H⁺(X ) NH₂),

where the chelating dppe ligand has been replaced by two PH₃

ligands and where the C₅Me₅ligand has been replaced by C₅H₅,

have been performed.⁴⁰The optimized bond lengths and angles,

obtained without symmetry constraints, match quite well not

only the geometric features of the (η²-dppe)(η⁵-C₅Me₅)Ru-

(CtC)-1,4-(C₆H₄)X complexes presently obtained in the solid

state but also those previously published for some (η²-dppe)-

(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X and (Ph₃P)₂(η⁵-C₅H₅)Ru-

(CtC)-1,4-(C₆H₄)X complexes (X ) NO₂, H; Table 8).³¹

Notably, the slight increase in the Ru-C bond length theoreti-

The Ru-C bond dissociation energies were next computed

for the Ru(II) complexes bearing the most electron-withdrawing

substituents (1a-H, X ) NO₂; 1b-H, X ) CN). These were

obtained from complexes with idealized C_ssymmetry, consider-

ing a heterolytic process, i.e. the bond dissociation energy (BDE)

between [(H₃P)₂(η⁵-C₅H₅)Ru]⁺and [(CtC)-1,4-(C₆H₄)X]^-

fragments, according to the general transition state method of

Ziegler and Rauk,^42,43as previously done for the Fe(II)

analogues.^17cThe data are given in Table 10 along with the

results previously obtained for the Fe(II) analogues. The two

families of complexes have very similar bond dissociation

energies, and all energetic terms compare quite well. Apparently,

(40) DFT computations on similar model compounds have been per-

formed by Koentjoro et al. and Powell et al. in the framework of larger

theoretical investigations, but the detailed MO compositions (in terms of

AOs) of these compounds were not published.^31a,41

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 657

Table 9. Energy, Electron Occupancy, and Decomposition of Frontier MOs in (PH₃)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X Model

Complexes (X ) NO₂, H, NH₂)^a

Compound 1a-H (X ) NO₂)

MO

55a

54a

53a

52a

51a

50a

49a

48a

47a

ꢀ (eV)

occ

-1.27

0

-1.72

0

-2.39

0

-2.98

0

-4.81

2

-4.89

2

-5.52

2

-6.15

2

-6.28

2

% Ru

% C (Cp)

% P

% C_R

% C_â

0

99

0

46

18

16

15

4

44

26

29

0

1

0

6

0

27

63

43S

7

1

10

27

0

32

0

1

12

21

17

4

48

19

4

6

2

0

96

53

0

9

0

% C (Ph)

% NO₂

0

1

0

16

0

Compound 1d-H (X ) H)

MO

47a

46a

45a

44a

43a

42a

41a

40a

39a

ꢀ (eV)

occ

-0.73

0

-0.98

0

-1.36

0

-2.03

0

-4.28

2

-4.35

2

-5.07

2

-5.75

2

-5.78

2

% Ru

% C (Cp)

% P

% C_R

% C_â

23

3

48

5

0

2

0

15

2

47

8

14

17

4

46

25

30

0

27

0

17

21

24

40

6

0

12

28

0

47

17

4

6

1

57

0

5

0

97

% C (Ph)

80

0

4

20

Compound 1f-H (X ) NH₂)

MO

50a

49a

48a

47a

46a

45a

44a

43a

42a

ꢀ (eV)

occ

-0.63

0

-0.67

0

-1.24

0

-1.20

0

-3.89

2

-4.21

2

-4.89

2

-5.31

2

-5.72

2

% Ru

% C (Cp)

% P

% C_R

% C_â

0

98

0

20

3

23

3

0

16

0

43

7

29

15

4

51

25

29

0

16

0

18

15

30

8

39

6

0

13

28

0

49

14

1

3

0

40

3

1

8

0

94

0

% C (Ph)

% NH₂

0

9

4

17

12

0

^a“0” means less than 1%.

Table 10. Heterolytic Bond Dissociation Energies and

Energy Decomposition of the M-C Bond in

(PH₃)₂(η⁵-C₅H₅)M(CtC)-1,4-(C₆H₄)X Complexes (M ) Ru,

Fe; X ) NO₂, CN)

substituent is becoming more and more electron-withdrawing.

The effect of oxidation on the energies of the molecular orbitals

is depicted in Figure 6 for 1d and 1d-H⁺(X ) H). As can be

seen in this diagram, the HOMO-LUMO gap slightly increases

upon oxidation. In the Ru(III) model complexes, the LUMO

for these electron-rich compounds has a dominant d_xycharacter

M ) Ru

M ) Fe

X ) NO₂

X ) CN

X ) NO₂

X ) CN

2

and the LUMO + 1 a dominant d_zcharacter. The SOMO, and

∆E_Pauli

-8.86

+4.44

+2.38

+1.68

+0.41

+10.77

+6.55

-8.60

+4.39

+2.77

+1.60

+0.42

+10.88

+6.76

-7.37

+3.82

+1.74

+1.68

+0.40

+10.20

+6.66

-7.37

+3.97

+1.95

+1.59

+0.43

+10.19

+6.77

a

∆E_orb

the two MOs below correspond to the “t_2g” set of the Fe(III)

ion (pseudo-O_hsymmetry). The SOMO and SOMO - 1,

however, retain their important acetylide character (Table 11).

∆E_σ

∆E_π,MfL

∆E_π,LfM

∆E_el

The energies of the six frontier spin MOs (R and â) possessing

a sizable metal character in 1a-H⁺-1f-H⁺(two unoccupied and

four occupied) are shown in Figure 7. The metal contribution

to the higher lying spin MOs is dominated by one type of d

atomic orbital (Table 11). In contrast, the metal contribution to

the lower lying ones is more accurately described by a mixture

of two d AOs. In the case of the complex 1a-H⁺, three aryl-

and nitro-based MOs are found between the filled-spin MOs.

The spin distributions computed for 1a-H⁺, 1d-H⁺, and 1f-

H⁺are given in Table 12. The largest positive spin density is

found on the metal and, to a lesser extent, on the â-carbon atom

of the acetylide. It is strongly influenced by the X substituent,

being larger on these two atoms with the most electron-

withdrawing substituents. The spin delocalization on the aryl-

acetylide fragment is clearly favored for the most electron-

releasing substituents, spreading more and more on the aryl

BDE (∆H)

^a∆E_orb) ∆E_σ+ ∆E_π,MfL+ ∆E_π,LfM

.

the Ru(II) complexes present a somewhat larger orbital σ-sta-

bilizing contribution (∆E_orb), which is compensated by a larger

destabilizing Pauli term (∆E_Pauli).

Upon oxidation, the electron is removed from a delocalized

molecular orbital, being more and more heavily weighted on

the metal center (i.e. 16/27/43% for 1f-H/1d-H/1a-H) as the

(41) Koentjoro, O. F.; Rousseau, R.; Low, P. J. Organometallics 2001,

20, 4502-4509.

(42) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558-1565.

(43) Bickelhaupt, F. M.; Baerends, E. J. In ReViews of Computational

Chemistry; Lipkowitz, K. B., Boyd, D. B., Eds.; Wiley: New York, 2000;

Vol. 15, pp 1-86.

658 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Table 11. Decomposition of Frontier MOs in [(PH₃)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X]⁺Model Complexes (X ) NO₂, H, NH₂)

for Selected Frontier MOs^a

Compound 1a-H⁺(X ) NO₂)

MO

54a(R)

54a(â)

52a(R)

52a(â)

51a(R)

51a(â)

50a(R)

50a(â)

48a(R)

49a(â)

45a(R)

45a(â)

ꢀ (eV)

occ

-5.55

0

-5.46

0

-6.21

0

-6.11

0

-8.77

1

-8.47

0

-8.98

1

-8.62

1

-9.33

1

-9.20

1

-10.18

1

-10.00

1

% Ru

% Cp

% P

% C_R

% C_â

% C (Ar)

% NO₂

43

11

9

15

3

45

20

10

15

3

47

28

24

0

33

21

19

2

0

7

36

4

0

10

23

13

0

33

2

0

12

21

16

0

27

5

0

39

5

1

10

23

9

52

25

3

4

1

46

19

2

5

0

47

8

0

4

0

47

4

0

7

0

9

19

17

1

0

12

23

0

25

0

13

0

Compound 1d-H⁺(X ) H)

MO

45a(R)

45a(â)

44a(R)

44a(â)

43a(R)

43a(â)

42a(R)

42a(â)

41a(R)

41a(â)

39a(R)

39a(â)

ꢀ (eV)

occ

-5.20

0

-5.11

0

-5.80

0

-5.72

0

-8.33

1

-8.00

0

-8.50

1

-8.21

1

-8.88

1

-8.76

1

-9.77

1

-9.53

1

% Ru

% Cp

% P

% C_R

% C_â

% C (Ph)

40

19

6

16

3

44

20

8

16

4

49

27

24

0

44

27

24

0

43

7

3

8

25

1

28

0

14

19

24

27

0

13

16

29

43

7

2

9

1

52

24

3

5

1

52

23

3

6

1

23

9

0

4

0

49

3

0

6

0

3

0

23

27

Compound 1f-H⁺(X ) NH₂)

MO

48a(R)

48a(â)

47a(R)

47a(â)

46a(R)

46a(â)

45a(R)

45a(â)

44a(R)

44a(â)

43a(R)

43a(â)

ꢀ (eV)

occ

-4.70

0

-5.60

0

-5.25

0

-5.19

0

-7.74

1

-7.34

0

-7.82

1

-7.74

1

-8.34

1

-8.23

1

-8.99

1

-8.75

1

% Ru

% Cp

% P

% C_R

% C_â

% C (Ar)

% NH₂

41

15

4

17

4

44

20

11

15

4

43

28

25

0

44

27

23

0

21

0

14

12

33

12

20

0

15

14

32

11

45

9

2

7

25

0

45

8

1

7

25

0

52

25

5

1

50

23

2

4

1

45

0

5

45

0

6

18

2

0

1

2

21

13

21

13

0

^a“0” means less than 1%.

Figure 7. Energy (eV) of the frontier molecular spin orbitals of

the model complexes [(H₃P)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X]⁺

(1a-H⁺-1c-H⁺; X ) NO₂, H, NH₂). Metallic AOs involved in

frontier MOs having a sizable metallic character are shown on the

left-hand side. In the case of 1a-H⁺(X ) NO₂), intercalating nitro-

based MOs are also shown.

Figure 6. Orbital diagram for [(H₃P)₂(η⁵-C₅H₅)Ru(CtCC₆H₅)]^0/+

(1d-H/1d-H⁺) showing the effect of oxidation on the energy levels

(eV). The arrows indicate the possible excitations leading to MLCT,

LMCT, or LF transitions in the visible range.

ring.⁴⁴This shows that the spatial localization of the unpaired

spin density in the arylacetylide is strongly tuned by the

substituent.

Overall, these theoretical results support and usefully comple-

ment recent DFT calculations of Rousseau and Low⁴¹and of

Humphrey and Stranger^31aon similar model compounds.⁴⁰

Correlations of Characteristic CV and Spectroscopic Data

with ESPs. A very good correlation (R²) 0.99) is obtained

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 659

fragment,²⁴we have derived experimentally the Hammett ESP’s

of the “(η²-dppe)(η⁵-C₅Me₅)Ru-CtC-” fragment by means

of ¹⁹F NMR, using the simple procedure described by Taft and

co-workers (Experimental Section).⁴⁷The measurement gives

values of -0.40 and -0.47 for σ_mand σ_p,^45,46respectively,

which indicates a quite strong electron-releasing character for

the “(η²-dppe)(η⁵-C₅Me₅)Ru-CtC-” fragment. This organo-

ruthenium(II) substituent apparently behaves as an electron-

releasing group via both the π- and σ-molecular orbital

manifolds, as suggested by the values of the inductive (σ_I)

-0.33) and resonance (σ_R) -0.09) contributions. Such

electron-releasing capabilities are in fact slightly higher than

those derived for the analogous Fe(II) fragment (σ_m) -0.29

and σ_p) -0.37). Notably, these values are significantly lower

than the σ_pvalue of -0.81 previously derived by Sato and co-

workers for the “(Ph₃P)₂(η⁵-C₅H₅)Ru-CtC-” fragment by

electrochemical means.⁴⁸

Table 12. Calculated Spin Densities for

[(PH₃)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X]⁺Complexes (X )

NO₂, CN, Br, H, OMe, NH₂)

1a-H⁺(X ) NO₂) 1d-H⁺(X ) H) 1f-H⁺(X ) NH₂)

Ru

C_R

0.405

0.077

0.295

0.165

0.018

0.015

0.026

0.352

0.138

0.243

0.277

-0.012

0.005

0.242

0.187

C_â

0.143

-1,4-C₆H₄-

0.323

X

0.126

C₅H₅

2 PH₃

-0.004

-0.005

-0.001

between the σ Hammett ESPs^45,46and the redox potentials

corresponding to the Ru(II)/Ru(III) oxidation of 1a-f (eq 1 and

E₀(V) ) 0.235σ + 0.217

(1)

Figure 8a). Notably, the inclusion of the data for the meta-

substituted complex 1c-m does not change the quality of the

linear fit. The positive slope reflects the fact that an electron-

releasing substituent renders the ruthenium-centered oxidation

more facile. The linear correlation evidences an essentially

electronic substituent effect.

In addition, significant linear fits are also obtained with the

acetylide stretch expressed in cm^-1(R²) 0.96), the energy (in

cm^-1) of the lowest-lying electronic (MLCT) transition (R²)

0.95), and the ¹³C NMR shifts of the R- (R²) 0.96) or â-carbons

(R²) 0.93) of the acetylide ligand vs the σ^-ESPs (eqs 2-4).

Discussion

In the following, we will compare the data obtained for 1a-

f/1a-f⁺and 1a-f-H/1a-f-H⁺with these previously obtained

for the corresponding Fe(II) analogues (2a-f/2a-f⁺and 2a-

f-H/2a-f-H⁺)¹⁷in order to determine the influence of the nature

of the metal on the bonding and reactivity of these compounds,

in line with related investigations.

Ru(II) Complexes. The bonding in this series of Ru(II)

complexes strongly resembles that previously found for the

series of Fe(II) analogues (Figure 10)^17cwith, however, slightly

increased acetylide character in the HOMO and HOMO - 1.

Thus, replacing the Fe(II) center by the more electronegative

Ru(II) center does not drastically change the bonding in these

electron-rich d⁶piano-stool acetylide complexes but results in

more delocalized frontier MOs. Since we anticipated that

changing the metal center should affect back-bonding, we tried

to derive its magnitude for Ru(II) complexes bearing electron-

withdrawing groups such as 1a-H and 1b-H (X ) NO₂, CN),

as previously done for 2a-f-H.^17cAlthough the latter is weak

in a bonding scheme dominated by filled-filled (repulsive)

interactions between the d MOs on the Ru(II) fragment and π

MOs of the acetylide fragment,^15b,31aback-bonding should

become sizable with electron-withdrawing substituents.^18,49The

energetic importance of back-bonding on the Ru-C bond is

given by the ∆E_π,MfLterm in Table 10 (i.e. bonding contribu-

tions to the BDE),^49,50The latter does not change much between

1a-H and 1b-H (X ) NO₂, CN) and, in contrast to our initial

expectations, compares quite well with values previously derived

for the Fe(II) analogues. Such a statement is in line with the

computations of Stranger and co-workers, who found close

values for back-donation in related Fe(II) and Ru(II) acetylide

analogues.¹⁸It evidences that back-bonding cannot be envisioned

as the primary cause of the large hyperpolarizabilities measured

by EFISH for these compounds.¹²Dissociation energies derived

for the M-C bonds in these compounds are also quite close.

ν

_CtC(cm^-1) ) -25.8σ^-+ 2070

(2)

(3)

E

_MLCT(cm^-1) ) -7944σ^-+ 31 862

δ(C_R) (ppm) ) 19.1σ^-+ 127

δ(C_â) (ppm) ) 3.1σ^-+ 110

(4a)

(4b)

Poorer linear fits were obtained in these correlations when the

regular Hammett ESPs (σ) were used, as previously found for

Fe(II) acetylides.^17cThe use of σ^-reveals the dominance of

mesomeric interactions in these substituent effects.

In the case of Ru(III) complexes some linear correlations

could also be obtained with ESR data (parts a and b of Figure

9). This has already been noted for Fe(III) analogues.^17dMore

remarkably, better fits were obtained in these cases with

Hammett ESPs rather than with σ⁺ESPs, suggesting a more

balanced influence of the substituent mesomeric and inductive

effects. The equations of the linear fits for g and ∆g are given

in eqs 5a,b.

g ) 0.0402σ_p+ 2.0975

∆g ) 0.1496σ_p+ 0.2597

(5a)

(5b)

Derivation of Hammett Electronic Substituent Parameters

(ESP’s) of the “(η²-dppe)(η⁵-C₅Me₅)Ru-CtC-” Fragment.

As previously done for the “(η²-dppe)(η⁵-C₅Me₅)Fe(CtC)-”

(47) (a) Taft, R. W.; Price, E.; Fox, I. R.; Lewis, I. C.; Andersen, K. K.;

Davies, G. T. J. Am. Chem. Soc. 1963, 85, 709-724. (b) Taft, R. W.; Price,

E.; Fox, I. R.; Lewis, I. C.; Andersen, K. K.; Davies, G. T. J. Am. Chem.

Soc. 1963, 85, 3146-3156.

(48) Sato, M.; Shintate, H.; Kawata, Y.; Sekino, M.; Katada, M.; Kawata,

S. Organometallics 1994, 13, 1956-1962.

(49) McGrady, J. E.; Lovell, T.; Stranger, R.; Humphrey, M. G.

Organometallics 1997, 16, 4004-4011.

(50) ∆E_π,MfLterms are identified with back-bonding which corresponds

to a net electron transfer from occupied metallic orbitals toward the empty

π* orbitals of the alkynyl ligand, in contrast to forward-bonding ∆E_π,LfM

terms, which correspond to the transfer of electronic density from the filled

π-MO of the acetylide fragment to empty MOs of the metallic fragment.^17c,49

(44) As a result of the avoided crossing mentioned above, the unpaired

spin density is located in the π-manifold conjugated with the aryl ring for

the compounds bearing the electron-releasing substituents and in the

perpendicular π-manifold for the electron-accepting X substituents, while

for compounds with moderate substituents such as 1f-H⁺, the spin density

is located around the acetylide bridge in both π_x- and π_y-manifolds. See

ref 17d for an analogous behavior.

(45) March, J. AdVanced Organic Chemistry. Reactions, Mechanisms and

Structures, 4th ed.; Wiley: New York, Chichester, Brisbane, Toronto,

Singapore, 1992.

(46) Hansch, C.; Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165-195.

660 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Figure 8. Plots of (a) the Ru(III)/Ru(II) oxidation potentials (V) vs Hammett ESPs (σ) in CH₂Cl₂, (b) the ν_CtC(cm^-1) values recorded in

CH₂Cl₂, (c) the MLCT energies (cm^-1) in CH₂Cl₂, and (d) the alkynyl ¹³C NMR shifts (ppm) in CDCl₃of the C_R(b) or C_â(2) vs σ^-ESPs

for (η²-dppe)(η⁵-C₅Me₅)Ru(CtC-1,4-C₆H₄-X) complexes (X ) NO₂, CN, F, H, OMe, NH₂).

Figure 9. Plots of (a) the ESR mean g value and (b) the g-tensor anisotropy vs Hammett ESPs for the complexes [(η²-dppe)(η⁵-C₅Me₅)-

Ru(CtC)-1,4-(C₆H₄)X][PF₆] (X ) NO₂, CN, F, H, OMe, NH₂) and [(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,3-(C₆H₄)F][PF₆].

Apparently, the less favorable energy match between the filled

d MOs of the Ru(II) fragment and the empty π* MOs of the

acetylide fragment which should result from the increased

ruthenium electronegativity is compensated by a better overlap

between these MOs, owing to the larger spatial extension (and

better polarizability) of the Ru-based MOs, in line with the

improvement of the Pauli term (∆E_Pauli) in the decomposition

analysis.⁵¹

Despite the apparent similarities between MOs of 1a-H/1d-

H/1f-H and 2a-H/2d-H/2f-H, the HOMO-LUMO gap is

significantly larger for the Ru(II) complexes (Figure 10). The

blue shift observed for the electronic MLCT transition (Figure

6) detected in the UV-visible range for 1a-f is consistent with

this observation. The lower lying HOMO for Ru(II) complexes

is also certainly at the origin of another notable difference

between the two families of complexes, which resides in their

oxidation potentials. Indeed, as shown in Figure 1 for the two

nitro-substituted complexes, the Ru(II)/Ru(III) oxidation is more

difficult by ca. 350 mV for a given substituent with respect to

that in the iron(II) analogues.^17aIn apparent conflict with the

higher lying LUMO of 1a-H relative to the Fe(II) analogue 2a-

H, the nitro-centered reduction of 1a is slightly easier (-1.25

V) than for the Fe(II) analogue 2a (-1.28 V).^17aThis suggests

a slightly lower electron-releasing capability for the Ru(II) center

relative to the Fe(II) center, which also contrasts somewhat with

the ESP derived for the “(η²-dppe)(η⁵-C₅Me₅)M-CtC-”

fragments (M ) Fe, Ru). Indeed, according to the σ values

found, the Ru(II)-containing fragment should be slightly more

electron-releasing than the Fe(II) one (σ_p) -0.47 for Ru(II)

vs σ_p) -0.37 for Fe(II)).²⁴However, our data also tell us that

if the Ru(II)-containing fragment is a comparatively better

σ-donor than the Fe(II)-containing one (σ_I) -0.33 for Ru(II)

vs -0.20 for Fe(II)), it has a slightly poorer π-donor ability

(51) The Pauli term in the Fe-C bond is mostly due to repulsive

interaction between the filled π-orbitals of the acetylide and the filled π-type

orbitals (with strong d character) of the metallic fragment.^17c,49

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 661

Figure 10. Comparison of the energies (eV) of the frontier MOs of the model complexes [(H₃P)₂(η⁵-C₅H₅)Ru(CtCC₆H₅)]ⁿ⁺(n ) 0, 1;

1d-H/1d-H⁺) and the corresponding [(H₃P)₂(η⁵-C₅H₅)Fe(CtCC₆H₅)]ⁿ⁺analogues (n ) 0, 1; 2d-H/2d-H⁺).

cm^-1) is much larger than that for the Fe(III) center (ú ) 460

Chart 3

cm^{-1 55}

) for a comparable ∆₁value (DFT diagrams actually give

a comparable SOMO/SOMO - 1 gap within 0.05 eV), we

should observe a much larger g₃(respectively ∆g) value.

Actually, this is not the case, and a significantly smaller value

is obtained for g₃(respectively ∆g) in Ru(III) compounds. This

can only be reconciled with eq 6 by considering a much more

delocalized unpaired electron (i.e. lower c₀value) in 1a-f[PF₆],

a trend also shown by the DFT computations (Table 12).

The oxidized species 1a-f⁺could also be characterized by

infrared spectroscopy. A transient absorption located at ca. 1940

cm^-1was detected each time, concomitant with the disappear-

ance of the characteristic ν(CtC) band of the starting Ru(II)

precursor. This absorption is typically in the range found for

other ν(CtC) values of mononuclear Ru(III) acetylide com-

plexes such as 7a-c⁺.³⁵Notably, while a decrease in the ν-

(CtC) energy is expected upon oxidation (Table 1), the shift

was less than that observed with dinuclear butadiynediyl

ruthenium complexes.^16a,b,56However, depending on the sub-

stituent, this shift is larger (ca. 140 cm^-1for 1a⁺to 35 cm^-1

for 1e⁺) than for the corresponding Fe(III) analogues 2a-

f[PF₆].^17aThis suggests a greater bond weakening of the triple

bond in the phenylacetylide spacer for 1a-f⁺than for 2a-f⁺,

in line with the enhanced delocalization of the unpaired electron

in 1a-H/1f-H⁺relative to 2a-H/2f-H⁺found by DFT calcula-

tions.

Finally, our attempts to characterize 1a-f⁺by electronic

spectroscopy revealed a transient absorption of very weak

intensity in the near-IR domain. Electronic transitions in the

same spectral range were recently reported by Humphrey and

co-workers for the related Ru(III) acetylide complexes 8a,b⁺

(Chart 3).^13aThese transitions were, however, much more intense

than for 1a-e[OTf] and were accordingly assigned to LMCT

processes. Much more related to the low-energy transition of

1a-f⁺is certainly the electronic absorption detected in the near-

IR range for the Fe(III) analogues, which was assigned to a

Laporte-forbidden (d-d) SOMO - 2/SOMO transition.^17dBy

comparison, this transition would now have experienced a

sizable blue shift (ca. 1800-2300 cm^-1), a trend that can be

roughly retrieved in the SOMO/SOMO - 2 differences in the

MO diagrams in the case of the NO₂- and NH₂-substituted

complexes, but not between 1d-H⁺and 2d-H⁺. Such a discrep-

(σ_R) -0.09 for Ru(II) vs -0.12 for Fe(II)).²⁴This lower

π-donor capability can presently explain the ordering found for

the potentials of the nitro-centered reduction, especially if large

electronic relaxation comes in play.

Ru(III) Complexes. Oxidation of the Ru(II) complexes yields

the corresponding Ru(III) radicals, which proved to be quite

reactive species in comparison to the isolable Fe(III) analogues.

Again, the DFT computations reveal that the most striking

differences reside in a larger delocalization of the unpaired

electron on the functional arylacetylide ligand and a larger

SOMO-LUMO gap (Figure 10), but the bonding scheme

remains rather close to that obtained for the Fe(III) radicals.^9b,17d,52

Mononuclear Ru(III) acetylide radicals being scarce

species,^35-36,39,53we have attempted to gain further insight into

their bonding by spectroscopy.

Thus, rhombic ESR signatures with g₃> g₂> g_e> g₁(where

g_estands for the free-electron value), were observed for the

oxidized Ru(III) complexes which are reminiscent of those

obtained for the Fe(III) analogues.^17dIt turns out that the

anisotropy found for 1a-f[PF₆] is slightly less than that recently

reported by Adams et al. for the Ru(III) acetylide radical cations

7a-c⁺(Chart 3).^35,53We have previously shown for the Fe-

(III) analogues 2a-f[PF₆] that the anisotropy (∆g) of the signal

is related to the extent of delocalization of the unpaired electron

on the arylalkynyl ligand.^17dAccording to this work, the largest

diagonal value of the g tensor (g_zz), which roughly corresponds

to g₃for 1a-f[PF₆], should be given by eq 6.⁵⁴Considering

g_zz) g_e+ 2ú(c₀c₁)²/∆₁

(6)

that the spin-orbit coupling for the Ru(III) center (ú ) 1250

(52) Connelly, N. G.; Gamasa, M. P.; Gimeno, J.; Lapinte, C.; Lastra,

E.; Maher, J. P.; Le Narvor, N.; Rieger, A. L.; Rieger, P. H. J. Chem. Soc.,

Dalton Trans. 1993, 2575-2578.

(53) Adams, C. J.; Boven, L. E.; Humphrey, M. G.; Morrall, J. P. L.;

Samoc, M.; Yellowlees, L. J. Dalton Trans. 2004, 4130-4138.

(54) In these equations, g_estands for the free-electron g value, c_nvalues

are the coefficients of the d AOs in the frontier MOs, and ∆₁is the SOMO

- 1/SOMO transition energy.

(55) Dunn, T. M. Trans. Faraday Soc. 1961, 57, 1441-1444.

(56) (a) Bruce, M. I.; Low, P. J.; Costuas, K.; Halet, J.-F.; Best, S. P.;

Heath, G. H. J. Am. Chem. Soc. 2000, 122, 1949-1962. (b) Bruce, M. I.;

Denisovich, L. I.; Low, P. J.; Peregudova, S. M.; Ustynyuk, N. A. J. Chem.

Soc., MendeleeV Commun. 1996, 200-201.

662 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Scheme 4

ancy is not surprising, since open-shell compounds often show

large electronic relaxation energies, not apparent in the MO

diagrams.

Thus, despite the apparent similarity between the Ru(III)

radical species 1a-f⁺and the known Fe(III) analogues 2a-f⁺,

the experimental data and DFT calculations point to a larger

delocalization of the unpaired electron in the former species.

This improved delocalization translates to a sizable radical

character not only on the â-carbon atom in these Ru(III)

complexes but also on the aryl ring (and even on the X

substituent for most electron-releasing groups). It explains the

comparably higher reactivity of the Ru(III) complexes, as well

as the elusiveness of 1f⁺. It also rationalizes (see Table 12) the

formation of the vinylidene complex 6[OTf] in the case of 1a⁺,

which possibly results from hydrogen abstraction from the

solvent. The instability of 1a-f⁺radicals, presumably of kinetic

origin, has ample precedence with mononuclear Ru(III) acetyl-

ides.^35,36Finally, it is worth mentioning that the cathodic peak

potential corresponding to the oxidation of the amino group is

slightly lower (0.59 V) than that of the Fe(III) analogue (0.68

V). This tends to indicate that the cationic “[(η²-dppe)(η⁵-

C₅Me₅)Ru-CtC-]⁺” fragment is slightly more electron-releas-

ing than the “[(η²-dppe)(η⁵-C₅Me₅)Fe-CtC-]⁺” fragment.

Substituent Effect and Valence Bond Scheme. When

studying the substituent effect with (η²-dppe)(η⁵-C₅Me₅)Fe-

(CtC)-1,4-(C₆H₄)X, we had previously evidenced linear cor-

relations between CV data or between characteristic spectro-

scopic data and various ESP sets. Likewise here, similar

correlations were sought and observed (Figures 8 and 9). The

various correlations obtained for the Ru(II/III) complexes 1a-

f/1a-f⁺confirm the sizable electronic influence exerted by the

X substituent in both redox states, an effect also indicated by

DFT computations.⁴¹Again, a very good linear correlation

between redox potential and Hammett ESPs was observed. The

recent work of Hurst et al.⁵⁷along with ours on 2a-f/2a-f^{+ 17c}

seems to indicate that this might be a general feature of redox-

active electron-rich acetylide complexes. Relative to the iron

analogues 2a-f/2a-f⁺, the slope is more pronounced for 1a-

f/1a-f⁺, evidencing a slightly stronger substituent effect on the

metal-centered M(II)/M(III) oxidation potential in the case of

ruthenium.

Scheme 5

1a-f. This makes sense, considering the lower hyperpolariz-

abilities (â₀)_EFISHfound for 1a,b relative to those for the

corresponding iron analogues.¹²

The situation is slightly different for the Ru(III) derivatives,

where larger differences in bonding have been established by

DFT calculations, essentially in terms of electronic delocaliza-

tion. Here, no significant correlation with ν(CtC) could be

obtained, in contrast to Fe(III) derivatives,^17bbut a significant

correlation with ESR data was found. These fits were poorer

than those obtained with Fe(III) analogues and were obtained

with σ ESPs rather than with σ⁺ESPs, suggesting a stronger

inductive influence of the substituent in 1a-f⁺than in 2a-f⁺.

Presently, on the basis of a perturbational approach of ESR

shifts,^17d,39,58this stronger inductive influence might be traced

back to the larger spread on the functional arylacetylide ligand

of the higher lying spin orbitals having a sizable metal character

along with a sizable σ-character, and particularly in the SOMO

- 2 among the frontier MOs (Figure 7).⁵⁹The larger slopes

found for the regression lines (eqs 5a,b) can easily be understood

as due to the larger spin-orbit coupling parameter operative

for Ru(III) relative to Fe(III) metal centers. Owing to the strong

similarities between 1a-f⁺and 2a-f⁺suggested by the

spectroscopic data, we also propose a VB scheme similar to

that previously advanced for the Fe(III) derivatives to rationalize

the substituent effects in 1a-f⁺in the GS (Scheme 5).

Similarly to the Fe(II) analogues, the Ru(II) complexes also

have linear correlations between σ^-ESP and ν(CtC), the

energy of the lowest electronic transition (MLCT) and the ¹³

C

acetylide shifts. While this was expected, given the very similar

bonding along the “M^II-CtC-1,4-(C₆H₄)X” core, the quite

similar slopes found for the regression lines in these correlations

were more surprising to us (see Supporting Information). These

similarities suggest that changes in composition and energy of

the frontier MOs induced by the replacement of the Ru(II) atom

by an Fe(II) atom in such compounds do not markedly affect

the transmission of the electronic (inductive/mesomeric) effects

affecting these spectroscopic signatures. This is certainly because

these signatures mostly originate from atoms or functional

groups on the arylacetylide ligand, close to the substituent and

therefore less dependent on the nature of the metal center.

Considering a valence bond (VB) description (Scheme 4) similar

to that previously proposed to rationalize the substituent effects

for Fe(II) complexes 2a-f,^17cν(CtC), the energy of the lowest

electronic transition (MLCT), and the ¹³C acetylide shifts point,

however, to a slightly lower weight of the cumulenic VB

mesomers (B/D) in the ground state (GS) of Ru(II) complexes

Conclusion

We have reported here the isolation and characterization of

several electron-rich Ru(II) acetylide complexes of the formula

(58) Rieger, A. L.; Rieger, P. H. Organometallics 2004, 23, 154-162.

(59) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. L. J. Am. Chem.

Soc. 1979, 101, 585-591.

(57) Hurst, S. K.; Xu, G.-L.; Ren, T. Organometallics 2003, 22, 4118-

4123.

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 663

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)X (1a-f) and also the

in situ characterization of the corresponding Ru(III) congeners

(1a-f⁺). In contrast to the known Fe(III) analogues (2a-f/2a-

f⁺), these radical cations proved to be too reactive to be isolated.

DFT computations on [(H₃P)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X]^0/+

model complexes along with available experimental data on 1a-

f/1a-f⁺indicate that, despite presenting very close electronic

structures to those of the known iron analogues, the frontier

MOs are slightly more weighted on the acetylide spacer in the

case of ruthenium. This leads to a stronger delocalization of

the unpaired electron on the arylacetylide ligand in Ru(III)

complexes and explains their enhanced reactivity. Very good

correlations between oxidation potentials or selected infrared,

UV, or NMR spectral data and various ESP sets were obtained

for the Ru(II) complexes, while good linear correlations with

the ESR rhombic g tensors were found with Ru(III) derivatives,

which overall confirm a comparable or slightly improved

electronic communication between the functional aryl group and

the metal center in comparison to the iron analogues in both

redox states. Finally, we also showed that the magnitude of the

d_M-π*_CtCback-donation is quite unaffected when ruthenium

replaces iron in these M(II) acetylide complexes.

g, 0.46 mmol), and Me₃SiCtC(C₆H₄NO₂)-4 (0.100 g, 0.45 mmol)

were introduced under argon in a Schlenk flask. Subsequently, 15

mL of methanol were added and the mixture was refluxed for 20

h. The solvent was evacuated, and the orange residue was analyzed

(infrared and NMR) to check the complete conversion into the

corresponding vinylidene (³¹P{¹H} NMR (δ, CDCl₃, 200 MHz):

72.3 (s, dppe); 143.1 (septuplet, J_PF) 712 Hz, PF₆^-)). Then,

1

potassium tert-butoxide (0.050 g, 0.45 mmol) and 15 mL of

methanol were introduced and the reaction medium was stirred for

12 h at ambient temperature. The desired alkynyl complex (η²-

dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)NO₂(1a) precipitated as a

purple powder, which was filtered on a frit, washed with methanol

(3 × 5 mL), and dried in vacuo. Yield: 0.180 g (80%).

Method B, via Catalytic Sonogashira Coupling. The orange

complex (η⁵-C₅Me₅)(η²-dppe)Ru(CtCH) (4; 0.100 g, 0.15 mmol),

the (PPh₃)₂PdCl₂catalyst precursor (0.005 g, ca. 5%), and CuI

cocatalyst (0.003 g, ca. 10%) were introduced in a Schlenk flask

under argon. Subsequently p-BrC₆H₄NO₂(0.091 g, 0.45 mmol) was

added into 10 mL of HNPrⁱ₂and the mixture was refluxed for 12

h. The solvent was cryogenically trapped, and the dark residue was

extracted with toluene and the extract filtered on a Celite pad. The

extract is a mixture of the desired complex (ca. 80% by ¹H NMR)

and p-BrC₆H₄NO₂. Evaporation of the toluene and elution through

a neutral alumina column using an n-pentane/diethyl ether gradient,

followed by repeated methanol washings (3 × 10 mL), allowed

isolation of the desired complex (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-

1,4-(C₆H₄)NO₂(1a) as a purple powder in a pure state, albeit with

a lower yield (0.055 g, ca. 20%) after drying in vacuo. Anal. Calcd

for C₄₄H₄₃NO₂P₂Ru: C, 67.68; H, 5.55; N. 1.79. Found: C, 67.24;

H, 5.71; N. 1.88. MS (positive LSI, 3-NBA, m/z): 781 ([1a]⁺, 90%);

635 ([(dppe)(C₅Me₅)Ru]⁺, 100%). FT-IR (ν, KBr, cm^-1): 2050

Experimental Section

General Data. All manipulations were carried out under an inert

atmosphere. Solvents or reagents were used as follows: Et₂O and

n-pentane, distilled from Na/benzophenone; CH₂Cl₂, distilled from

CaH₂and purged with argon; HNPrⁱ₂, distilled from KOH and

purged with argon; aryl bromides (Acros, >99%), opened/stored

under Ar. High-field NMR spectra experiments were performed

on a multinuclear Bruker 300 or 200 MHz instrument (AM300WB

and 200DPX). Chemical shifts are given in parts per million relative

to tetramethylsilane (TMS) for ¹H and ¹³C NMR spectra and

external H₃PO₄for ³¹P NMR spectra. Transmittance FTIR spectra

were recorded using a Bruker IFS28 spectrometer (400-4000

cm^-1). Raman spectra of the solid samples were obtained by diffuse

scattering on the same apparatus and recorded in the 100-3300

cm^-1range (Stokes emission) with a laser excitation source at 1064

nm, using a 1.05-1.06 µm laser source (15 mW) and a quartz

separator with a FRA 106 detector. Liquid near-IR spectra were

recorded on Cary 5 and JASCO V-570 spectrometers. UV-visible

spectra were recorded on an UVIKON 942 spectrometer. Cyclic

voltammograms were recorded using a PAR 263 instrument in CH₂-

Cl₂(0.1 M [NBu₄][PF₆]) at 25 °C at a platinum electrode, using a

SCE reference electrode and ferrocene as internal calibrant (0.460

V).³³EPR spectra were recorded on a Bruker EMX-8/2.7 (X-band)

spectrometer. LSI/ESI-MS analyses were carried out at the “Centre

Regional de Mesures Physiques de l’Ouest” (CRMPO, Rennes,

France) on a high-resolution MS/MS ZabSpec TOF Micromass

spectrometer (8 kV). Elemental analyses were performed at the

Centre for Microanalyses of the CNRS at Lyon-Solaise, France, at

the CRMPO.

(vs, CtC); 2014 (m, CtC); 1577, 1320 (vs, NO₂). Raman (ν, cm^-1

)

2046 (m, CtC); 2011 (w, CtC); 1578 (m, NO₂); 1322 (vs, NO₂).

1

³¹P NMR (δ, CDCl₃, 81 MHz): 81.7 (s, 2P, dppe). H NMR (δ,

CDCl₃, 200 MHz): 7.90 (d, 2H, ³J_HH) 9.0 Hz, H_ortho/ArNO); 7.69

2

(m, 4H, H_{ortho/Ar/dppe}); 7.37-7.19 (m, 16H, H_Ar/dppe); 6.67 (d, 2H,

³J_HH) 9.0 Hz, H_meta/ArNO2); 2.65 (m, 2H, CH_2dppe); 2.11 (m, 2H,

CH_2dppe); 1.58 (s, 15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ, CDCl₃, 75

2

MHz): 153.0 (t, J_CP) 25 Hz, Ru-CtC); 142.5 (s, C_quat); 138.8

(s, C_quat); 138.8-127.7 (m, 8C_Ar/dppe+ C-H_ArNO); 123.9 (s,

2

C-H_ArNO); 114.6 (s, J_CH) 4.4 Hz, C_quat); 93.7 (s, C₅(CH₃)₅);

2

29.9 (m, CH_2,dppe); 10.4 (s, C₅(CH₃)₅).

Crystals of 1a were grown by slow diffusion of methanol into a

chloroform solution of 1a (layer/layer).

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)CN (1b). Complex

1b was isolated by following method B as a yellow solid from the

complex (η⁵-C₅Me₅)(η²-dppe)Ru(CtCH) (3) and p-BrC₆H₄CN.

Yield: 88%. Anal. Calcd for C₄₅H₄₃NP₂Ru: C, 71.04; H, 5.70; N,

1.84. Found: C, 70.03; H, 5.69; N, 1.82. MS (positive LSI, 3-NBA,

m/z): 761 ([1b,H]⁺, 95%); 635 ([(dppe)(C₅Me₅)Ru]⁺, 100%). FT-

IR (ν, KBr, cm^-1): 2286 (m, CtN); 2071 (sh, CtC); 2059 (vs,

CtC); 2034 (m, CtC). Raman (ν, cm^-1): 2219 (m, CtN); 2074

(vs, CtC); 2060 (sh, CtC); 2048 (sh, CtC). ³¹P NMR (δ, CDCl₃,

81 MHz): 81.8 (s, 2P, dppe). ¹H NMR (δ, CDCl₃, 200 MHz): 7.71

(m, 4H, H_{ortho/Ar/dppe}); 7.36-7.24 (m, 18H, H_Ar/dppe+ H_ortho/ArCN);

The complexes (η⁵-C₅Me₅)(η²-dppe)RuCl (3) and (η⁵-C₅Me₅)-

(η²-dppe)Ru(CtCH) (4)⁶⁰as well as the functionalized alkynes

RCtC-1,4-(C₆H₄)X (R ) SiMe₃, H; X ) NO₂, CN, F, H, OMe,

NH₂)⁶¹were synthesized by reported procedures. Other compounds

were commercially available and were used as such.

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)NO₂(1a). Method A,

via Alkyne Activation. The orange chloro precursor complex (η⁵-

C₅Me₅)(η²-dppe)RuCl (3; 0.200 g, 0.29 mmol), [NBu₄][PF₆] (0.005

2

6.69 (d, J_HH) 8.4 Hz, 2H, H_meta/ArCN); 2.63 (m, 2H, CH_2,dppe);

2.07 (m, 2H, CH_2,dppe); 1.57 (s, 15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ,

2

CDCl₃, 75 MHz): 145.7 (t, J_CP) 24 Hz, Ru-CtC); 136.2 (s,

C_quat); 139.2-127.4 (m, 8C_Ar/dppe+ 2C-H_ArCN+ C_quat/ArCN); 121.1

(s, Ar-CN); 112.0 (s, C_quat); 104.4 (s, C_quat); 93.6 (s, C₅(CH₃)₅);

29.8 (m, CH_2dppe); 10.5 (s, C₅(CH₃)₅).

Crystals could be grown by slow evaporation of a benzene

solution of 1b.

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)F (1c). Complex 1c

was isolated by following method B as a yellow solid from the

complex (η⁵-C₅Me₅)(η²-dppe)Ru(CtCH) (3) and p-BrC₆H₄F.

Yield: 77%. Anal. Calcd for C₄₄H₄₃FP₂Ru: C, 70.11; H, 5.75.

(60) 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, 1601-1609.

(61) Lavastre, O.; Ollivier, L.; Dixneuf, P. H.; Sinbandhit, S. Tetrahedron

1995, 52, 5495-5504.

664 Organometallics, Vol. 25, No. 3, 2006

Paul et al.

Found: C, 70.14; H, 5.80. MS (positive LSI, 3-NBA, m/z): 754

([1c]⁺, 50%); 635 ([(dppe)(C₅Me₅)Ru]⁺, 10%). FT-IR (ν, KBr,

cm^-1): 2086 (s, CtC). Raman (ν, neat, cm^-1): 2085 (s, CtC).

³¹P NMR (δ, CDCl₃, 81 MHz): 82.1 (s, 2P, dppe). ¹⁹F{¹H} NMR

¹J_CH) 158 Hz, C-H_ArOMe); 108.8 (s, Ru-CtC); 92.9 (s,

C₅(CH₃)₅); 55.7 (s, OCH₃), 29.8 (m, CH_2,dppe); 10.5 (s, C₅(CH₃)₅).

Crystals could be grown by slow evaporation of a dichloro-

methane solution of 1e.

1

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)NH₂(1f). Complex

1f was isolated by following method A as an orange solid from

the complex (η⁵-C₅Me₅)(η²-dppe)RuCl (2) and HCtC(C₆H₄NH₂)-

4. Yield: 43%. Anal. Calcd for C₄₄H₄₅NP₂Ru: C, 70.38; H, 6.04;

N, 1.87. Found: C, 70.38; H, 6.05; N, 2.08. MS (positive, ESI,

CH₂Cl₂, m/z): 752 ([1f,H]⁺, 85%); 635 ([(dppe)(C₅Me₅)Ru]⁺, 40%).

FT-IR (ν, KBr, cm^-1) 2072 (vs, CtC). Raman (ν, cm^-1): 2074

(δ, CDCl₃, 188 MHz, ppm): -120.3 (s, C₆H₄F). H NMR (δ,

CDCl₃, 200 MHz): 7.82 (m, 4H, H_ortho/dppe); 7.60-7.20 (m, 16H,

H_Ar/dppe); 6.72 (d, 4H, H_ArF); 2.68 (m, 2H, CH_2,dppe); 2.07 (m, 2H,

CH_2,dppe); 1.57 (s, 15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ, CDCl₃, 125

1

2

MHz, ppm): 160.0 (d, J_CF) 241 Hz, F-C_ArF); 128.3 (t, J_CP

)

25 Hz, Fe-CtC); 139.8-127.8 (m, 8C_Ar/dppe+ C_quat/ArF); 131.9

(d, ²J_CF) 7 Hz, C-H_meta/ArF); 114.9 (d, ²J_CF) 21 Hz, C-H_ortho/ArF);

108.9 (s, Fe-CtC); 93.2 (s, C₅(CH₃)₅); 30.1 (m, CH_2,dppe); 10.8

(s, C₅(CH₃)₅).

1

(s, CtC). ³¹P NMR (δ, CDCl₃, 81 MHz): 82.3 (s, 2P, dppe). H

NMR (δ, CDCl₃, 200 MHz): 7.82 (m, 4H, H_{ortho/Ar/dppe}); 7.50-

7.10 (m, 20H, H_Ar/dppe); 6.67 (d, ²J_HH) 7.8 Hz, 2H, H_ArNH); 6.45

Crystals could be grown by layering a dichloromethane solution

of 1c with n-pentane.

2

(d, J_HH) 7.8 Hz, 2H, H_ArNH); 3.43 (s, 2H, NH₂); 2.75 (m, 2H,

2

CH_2,dppe); 2.10 (m, 2H, CH_2,dppe); 1.59 (s, 15H, C₅(CH₃)₅). ¹³C-

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,3-(C₆H₄)F (1c-m). Complex

1c-m was isolated by following method B as a yellow solid from

the complex (η⁵-C₅Me₅)(η²-dppe)Ru(CtCH) (3) and m-BrC₆H₄F.

Yield: 70%. Anal. Calcd for C₄₄H₄₃FP₂Ru: C, 70.11; H, 5.75.

Found: C, 69.98; H, 5.71. MS (positive LSI, 3-NBA): m/z 754

([1c-m]⁺, 45%); 635 ([(dppe)(C₅Me₅)Ru]⁺, 15%). FT-IR (ν, KBr,

cm^-1): 2070, 2057 (vs, CtC). Raman (ν, neat, cm^-1): 2060 (s,

CtC). ³¹P NMR (δ, CDCl₃, 81 MHz): 82.0 (s, 2P, dppe). ¹⁹F{¹H}

{¹H} NMR (δ, C₆D₆, 50 MHz): 143.7 (s, C_quat); 139.8-127.2 (m,

8C_Ar/dppe+ 2C-H_ArNH); 123.1 (s, Ru-CtC); 121.1 (t, ²J_CP) 25

2

Hz, Ru-CtC); 115.6 (s, C-H_ArNH); 110.7 (s, CCtC); 93.2 (s,

2

C₅(CH₃)₅); 30.4 (m, CH_2,dppe); 11.1 (s, ¹J_CH) 127 Hz, C₅(CH₃)₅).

Crystals could be grown by layering a dichloromethane solution

of 1f with n-pentane.

Attempted Oxidation of (η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-

(C₆H₄)NO₂(1a). A 0.92 equiv portion of AgOTf (0.014 g, 0.054

mmol) was added to a solution of 1a (0.050 g, 0.059 mmol) in 10

mL of dichloromethane, resulting in a darkening of the solution.

Stirring was maintained for 3 h at room temperature, and the

solution was concentrated in vacuo to ca. 2 mL. Addition of 10

mL of diethyl ether precipitated a brown-orange solid, after

decantation and subsequent washing with 2 × 3 mL portions of

toluene followed by 2 × 3 mL of diethyl ether and drying in vacuo.

Extraction with 5 mL of dichloromethane, followed by filtration

on a Celite plug and evaporation of the solvent, yielded a brown-

green solid. The latter proved to be a mixture of several compounds,

containing no more starting 1a. Small red-orange needles were

isolated after concentration of the washings to dryness (0.030 g),

redissolution in dichloromethane, and slow evaporation of the

solvent. The solid-state structure of the compound was solved. The

latter proved to be the vinylidene complex [(η²-dppe)(η⁵-C₅Me₅)-

Ru(dCdCH)-1,4-(C₆H₄)NO₂][OTf] (6[OTf]); relevant parameters

are given in the Supporting Information. No other compound could

be purified or identified in the resulting mixture.

Infrared and Near-IR Measurements on Ru(III) Complexes.

The Ru(II) complexes were dissolved in dichloromethane (ca. 5 ×

10^-3M), and the spectrum of the Ru(II) sample was recorded for

comparison purposes. A slight excess of silver triflate (AgOTf) was

next suspended in the solution, and the mixture was sonicated for

a few minutes before being transferred to the spectrometer. The

spectra were then immediately recorded at 20 °C.

ESR Measurements on Ru(III) Complexes. The Ru(II) com-

plexes were ground with a slight excess of [(η⁵-C₅H₅)₂Fe][PF₆] and

introduced in a ESR tube under an argon-filled atmosphere, a 1:1

mixture of degassed dichloromethane/1,2-dichloroethane was trans-

ferred to dissolve the solid, just before being frozen at 77 K, and

the tubes were sealed and transferred into the ESR cavity. The

spectra were immediately recorded at that temperature.

1

NMR (δ, CDCl₃, 188 MHz, ppm): -116.3 (s, C₆H₄F). H NMR

(δ, CDCl₃, 200 MHz): 7.76 (m, 4H, H_ortho/dppe); 7.60-7.20 (m, 16H,

H

_Ar/dppe); 7.00-6.30 (m, 4H, H_ArF); 2.68 (m, 2H, CH_2,dppe); 2.09

(m, 2H, CH_2,dppe); 1.57 (s, 15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ,

CDCl₃, 125 MHz, ppm): 163.3 (d, ¹J_CF) 243 Hz, F-C_Ar); 133.5

(t, ²J_CP) 25 Hz, Fe-CtC); 129.2 (d, ³J_CF) ca. 10 Hz, CtCC_ArF);

3

139.8-128.0 (m, 8C_Ar/dppe); 129.2 (d, J_CF) ca. 9 Hz, C-H_ArF);

126.6 (s,⁴J_CF< 2 Hz, C-H_ArF); 117.2 (d, ²J_CF) ca. 20 Hz, ¹J_CH

)

2

1

163 Hz, C-H_ArF); 109.8 (d, J_CF) ca. 21 Hz, J_CH) 164 Hz,

C-H_ArF); 109.8 (s, Fe-CtC, ⁴J_CF) ca. 3 Hz); 93.3 (s, C₅(CH₃)₅);

30.4 (m, CH_2,dppe); 10.7 (s, C₅(CH₃)₅).

Crystals could be grown by layering a dichloromethane solution

of 1c-m with n-pentane.

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC-C₆H₅) (1d). This complex was

prepared as previously described.^16c,20Anal. Calcd for C₄₄H₄₄P₂-

Ru: C, 71.82; H, 6.03. Found: C, 71.66; H, 5.88. MS (positive

ESI, CH₂Cl₂, m/z): 737 ([1d,H]⁺, 85%); 663 ([(dppe)(C₅Me₅)-

RuCO]⁺, 90%); 635 ([(dppe)(C₅Me₅)Ru]⁺, 100%). FT-IR (ν, KBr,

cm^-1): 2068 (vs, CtC). Raman (ν, cm^-1): 2066 (s, CtC). ³¹P

NMR (δ, CDCl₃, 81 MHz): 82.3 (s, 2P, dppe). ¹H NMR (δ, CDCl₃,

200 MHz): 7.96 (m, 4H, H_{ortho/Ar/dppe}); 7.60-6.90 (m, 21H, H_Ar/dppe

+ H_Ph); 2.85 (m, 2H, CH_2,dppe); 2.22 (m, 2H, CH_2,dppe); 1.74 (s,

15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ, CDCl₃, 50 MHz): 129.3 (t, ²J_CP

) 25 Hz, Ru-CtC); 131.7 (s, CCtC); 139.8-127.2 (m, 8C_Ar/dppe

1

3

+ 2C-H_Ph); 122.9 (s, J_CH) 161 Hz, C-H_Ph); 110.2 (s, J_CH

)

4.5 Hz, Ru-CtC); 92.9 (s, C₅(CH₃)₅); 29.8 (m, CH_2,dppe); 10.5 (s,

C₅(CH₃)₅).

Crystals were grown by slow evaporation of a dichloromethane/

n-pentane (50/50) solution of 1d.

(η²-dppe)(η⁵-C₅Me₅)Ru(CtC)-1,4-(C₆H₄)OMe (1e). Complex

1e was isolated by following method A as a yellow solid from the

complex (η⁵-C₅Me₅)(η²-dppe)RuCl (2) and HCtC(C₆H₄OMe)-4.

Yield: 68%. Anal. Calcd for C₄₅H₄₆OP₂Ru: C, 70.57; H, 6.05.

Found: C, 70.50; H, 5.95. MS (positive ESI, CH₂Cl₂, m/z): 767

([1e,H]⁺, 65%); 663 ([(dppe)(C₅Me₅)RuCO]⁺, 100%); 635 ([(dppe)-

(C₅Me₅)Ru]⁺, 90%). FT-IR (ν, KBr, cm^-1): 2073 (vs, CtC).

Raman (ν, cm^-1): 2075 (s, CtC). ³¹P NMR (δ, CDCl₃, 81 MHz):

¹⁹F NMR Derivation of Hammett Parameters for “(η²-dppe)-

(η⁵-C₅Me₅)Ru-CtC-”. Samples of the compounds 1c and 1c-m

(0.05 mmol) were each dissolved in 1 mL of freshly distilled and

degassed CCl₄. These solutions were then transferred into NMR

tubes under argon, and 5 µL (0.076 mmol) of fluorobenzene was

syringed into the tube, as internal reference. After homogenization

of the solution, the ¹⁹F{¹H} NMR spectra were recorded at 25 °C.

The values of σ_Iand σ_Rwere derived from the values of the various

¹⁹F NMR shift differences, using the correlations established by

Taft and co-workers for m- and p-fluorobenzene derivatives.⁴⁶From

these values, σ_pand σ_mwere then computed.

1

82.3 (s, 2P, dppe). H NMR (δ, CDCl₃, 200 MHz): 7.86 (m, 4H,

H_{ortho/Ar/dppe}); 7.60-7.00 (m, 20H, H_Ar/dppe); 6.78-6.70 (m, 4H,

H_ArOMe); 3.78 (s, 3H, OCH₃); 2.80 (m, 2H, CH_2,dppe); 2.15 (m, 2H,

CH_2,dppe); 1.63 (s, 15H, C₅(CH₃)₅). ¹³C{¹H} NMR (δ, CDCl₃, 50

MHz): 156.0 (s, C_quat); 139.8-127.2 (m, 8C_Ar/dppe+ 2C-H_ArOMe);

2

124.8 (s, CCtC); 124.6 (t, J_CP) 25 Hz, Ru-CtC); 124.1 (s,

Mononuclear Ruthenium σ-Arylacetylides

Organometallics, Vol. 25, No. 3, 2006 665

Computational Details. DFT calculations were carried out using

the Amsterdam Density Functional (ADF) program.^62-64The model

compounds [(PH₃)₂(η⁵-C₅H₅)Ru(CtC)-1,4-(C₆H₄)X]ⁿ⁺(X ) NO₂,

H, NH₂; n ) 0, 1) were used in order to reduce computational

effort. Electron correlation was treated within the local density

approximation (LDA) in the Vosko-Wilk-Nusair parameteriza-

tion.⁶⁵The nonlocal corrections of Becke⁶⁶and of Perdew⁶⁷were

added to the exchange and correlation energies, respectively. The

numerical integration procedure applied for the calculations was

developed by te Velde et al.^62-64The basis set used for the metal

atoms was a triple-ú Slater-type orbital (STO) basis for Ru 4d and

5s and a single-ú function for Ru 5p. A triple-ú STO basis set was

employed for H 1s and for 2s and 2p of C, N and O, extended

with a single-ú polarization function (2p for H; 3d for C, N, and

O) for X groups. The valence orbitals of the atoms of the other

groups (C₅H₅, PH₃) were described by a double-ú STO basis set.

Full geometry optimizations (assuming C₁symmetry) were carried

out on each complex, using the analytical gradient method

implemented by Versluis and Ziegler.⁶⁸Spin-unrestricted calcula-

tions were performed for all the considered open-shell systems.

Decomposition of the Ru-C_Rinteraction energy was done accord-

ing to the transition state method of Ziegler and Rauk,^42,43as

previously described.^17cOptimized geometries with C_ssymmetry

were used. The latter were calculated to be not more than 1 kcal/

mol less stable than the systems optimized without symmetry

constraints.

38 712, and 33 926 reflections for 1a-f and 1c-m, respectively.

Data reduction with Denzo and Scalepack⁶⁹gave the independent

reflections (Table 1). The structures were solved with SIR-97, which

revealed the non-hydrogen atoms.⁷¹After anisotropic refinement,

the remaining atoms were found in Fourier difference maps. The

complete structures were then refined with SHELXL97⁷²by the

full-matrix least-squares technique (use of F²magnitude; x, y, z,

â_ijfor Fe, P, C, N, and/or O atoms, x, y, z in riding mode for H

atoms with variables “N(var)”, observations and “w” used as defined

in Table 1). Atomic scattering factors were taken from the

literature.⁷³ORTEP views of 1a-f and 1c-m were realized with

PLATON98.⁷⁴All the calculations were performed on a Pentium

NT Server computer.

Acknowledgment. These studies were facilitated by travel

grants (ARC of Australia, and CNRS of France). F.P., K.C.,

and J.-F.H. thank the Poˆle de Calcul Intensif de l’Ouest (PCIO)

of the University of Rennes and the Institut de De´veloppement

et de Ressources en Informatique Scientifique (IDRIS-CNRS)

for computing facilities.

Supporting Information Available: Figures displaying an

ORTEP diagram of 6[OTf], IR monitoring of the oxidation of 1b,

and UV spectra of 1b[OTf] and 1e[OTf], comparative tables of

slopes and R²indices for the correlations obtained between

spectroscopic data for Fe(II) and Ru(II) complexes, tables giving

full details of the X-ray structure of 6[OTf], including tables of

atomic positional parameters, bond distances and angles, anisotropic

and isotropic thermal displacement parameters, and CIF files giving

crystal data for 1a-f and 1c-m. This material is available free of

charge via the Internet at http://pubs.acs.org.

Crystallography. Crystals of 1a-f and 1c-m were obtained as

described above. The samples were studied on a NONIUS Kappa

CCD diffractometer with graphite-monochromatized Mo KR radia-

tion. The cell parameters were obtained with Denzo and Scalepack

with 10 frames (ψ rotation: 1° per frame).⁶⁹The data collection⁷⁰

(2θ_max, number of frames, Ω rotation, scan rate, and hkl ranges are

given in Table 1) gave 53 280, 19 532, 50 379, 13 286, 33 478,

OM050799T

(69) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C.

W., Sweet, R. M., Eds.; Academic Press: London, 1997; Vol. 276, pp 307-

326.

(70) Nonius, B. V. Kappa CCD Software; Enraf-Nonius, Delft, The

Netherlands, 1999.

(71) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,

C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.

Chem. 1998, 31, 74-77.

(72) Sheldrick, G. M. SHELX97-2. Program for the Refinement of

Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997.

(73) Reidel: D. International Tables for X-ray Crystallography; Kynoch

Press (present distributor D. Reidel, Dordrecht, The Netherlands): Bir-

mingham, U.K., 1974; Vol. IV.

(62) te Velde, G.; Bickelhaupt, F. M.; Fonseca Guerra, C.; van Gisbergen,

S. J. A.; Baerends, E. J.; Snijders, J.; Ziegler, T. Theor. Chim. Acc. 2001,

22, 931-967.

(63) Fonseca Guerra, C.; Snijders, J.; te Velde, G.; Baerends, E. J. Theor.

Chim. Acc. 1998, 99, 391-403.

(64) ADF2.3 and ADF2002.01; Theoretical Chemistry, Vrije Universiteit,

Amsterdam, The Netherlands, SCM.

(65) Vosko, S. D.; Wilk, L.; Nusair, M. Can. J. Chem. 1990, 58, 1200-

1211.

(66) (a) Becke, A. D. J. Chem. Phys. 1986, 84, 4524-4529. (b) Becke,

A. D. Phys. ReV. A 1988, 38, 3098-3100.

(67) (a) Perdew, J. P. Phys. ReV. B 1986, 33, 8822-8824. (b) Perdew,

J. P. Phys. ReV. B 1986, 34, 7406.

(74) Spek, A. L. PLATON. A Multipurpose Crystallographic Tool;

Utrecht University: Utrecht, The Netherlands, 1998.

(68) Versluis, L.; Ziegler, T. J. Chem. Phys. 1988, 88, 322-328.

Article Doi

Bonding and substituent effects in electron-rich mononuclear ruthenium σ-arylacetylides of the formula [(η2-dppe) (η5-C5Me5)Ru(C≡C)-1,4-(C 6H4)X][PF6]n (n = 0, 1; X = NO 2, CN, F, H, OMe, NH2)

DOI: 10.1021/om050799t

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