Spectroscopic properties and electronic structures of 17-electron half-sandwich ruthenium acetylide complexes, [Ru(C{triple bond, long}CAr)(L2)Cp′]+ (Ar = phenyl, p-tolyl, 1-naphthyl, 9-anthryl; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp*)

Journal of Organometallic Chemistry 692 (2007) 3277–3290

www.elsevier.com/locate/jorganchem

Spectroscopic properties and electronic structures of 17-electron

half-sandwich ruthenium acetylide complexes, [Ru(CCAr)(L₂)Cp⁰]⁺

(Ar = phenyl, p-tolyl, 1-naphthyl, 9-anthryl; L₂= (PPh₃)₂,

Cp⁰= Cp; L₂= dppe; Cp⁰= Cp^*)

a

b

a,

*

ˇ

Mark A. Fox , Rachel L. Roberts , Wan M. Khairul , Frantisek Hartl , Paul J. Low

a

Department of Chemistry, Durham University, South Rd., Durham DH1 3LE, UK

Van’t Hoﬀ Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands

b

Received 29 January 2007; received in revised form 26 March 2007; accepted 26 March 2007

Available online 5 April 2007

Abstract

A series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(C„CAr)(L₂)Cp⁰] (Ar = phenyl, p-tolyl, 1-naphthyl,

9-anthryl; L₂= (PPh₃)₂, Cp⁰= Cp; L₂= dppe; Cp⁰= Cp^*) have been examined using electrochemical and spectroelectrochemical meth-

ods. One-electron oxidation of these complexes gave the corresponding radical cations [Ru(C„CAr)(L₂)Cp⁰]⁺. Those cations based on

Ru(dppe)Cp^*, or which feature a para-tolyl acetylide substituent, are more chemically robust than examples featuring the Ru(PPh₃)₂Cp

moiety, permitting good quality UV–Vis-NIR and IR spectroscopic data to be obtained using spectroelectrochemical methods. On the

basis of TD DFT calculations, the low energy (NIR) absorption bands in the experimental electronic spectra for most of these radical

cations are assigned to transitions between the b-HOSO and b-LUSO, both of which have appreciable metal d and ethynyl p character.

However, the large contribution from the anthryl moiety to the frontier orbitals of [Ru(C„CC₁₄H₉)(L₂)Cp⁰]⁺suggests compounds con-

taining this moiety should be described as metal-stabilised anthryl radical cations.

Keywords: Ruthenium; Acetylide; Radical cation; Spectroelectrochemistry; TD DFT

1. Introduction

conclusion being that iron gives rise to much greater metal

character in the frontier orbitals, whilst the ruthenium ana-

logues exhibit far greater Ru(d)–acetylide(p) mixing [12–

16]. This greater delocalisation is also found to persist after

one-electron oxidation of the ruthenium complexes, and

has been used to rationalise the greater chemical reactivity

of the 17-electron radical cations [Ru(C„C-1,4-C₆H₄X)-

(dppe)(g⁵-C₅Me₅)]⁺[13] when considered alongside the

radical cations [Fe(C„CC₆H₄-X)(dppe)Cp^*]⁺(X = CN,

CF₃, Br, F, Me, ^tBu, OMe, NH₂, NMe₂), which have been

isolated as the [PF₆]^ꢀsalts [16].

Metal acetylide complexes have been objects of intense

research activity for decades [1–7]. While much of the early

work was naturally concerned with synthetic and structural

issues, there is a considerable and growing body of contem-

porary interest concerning the electronic, optical, non-lin-

ear optical and magnetic properties of these compounds

[8–11]. Comparisons of the properties of half-sandwich

ruthenium acetylides [Ru(C„CR)(L₂)(g⁵-C₅R₅)], where

L₂usually represents supporting phosphine ligands, with

analogous iron complexes have been made, with the general

In this report we describe the cation radicals generated

from the series [Ru(C„CAr)(L₂)Cp⁰] [Ar = C₆H₅(1),

C₆H₄Me-4 (2), C₁₀H₉(3), C₁₄H₉(4); L = PPh₃, Cp⁰= g⁵-

C₅H₅(a); L₂= dppe, Cp⁰= g⁵-C₅Me₅(b)]. Whilst the

*

Corresponding author. Tel.: +44 191 334 2114; fax: +44 191 384 4737.

E-mail address: p.j.low@durham.ac.uk (P.J. Low).

doi:10.1016/j.jorganchem.2007.03.042

3278

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

17-electron cation radicals derived from the Ru(PPh₃)₂Cp

fragment are generally very reactive even on the timescale

of the CV experiment, the para-tolyl compound

[Ru(C„CC₆H₄Me-4)(PPh₃)₂Cp] gives rise to an almost

completely reversible oxidation, and good quality IR

[m(C„C)] and electronic (UV–Vis-NIR) spectra are readily

obtained in the absence of atmospheric oxygen and mois-

ture using spectroelectrochemical methods. The complexes

featuring the more electron-donating Ru(dppe)Cp^*moiety

are relatively stable across the series, and we have suc-

ceeded in obtaining good quality spectroscopic data from

each compound 1b, 2b, 3b and 4b. These data are presented

and discussed here.

Ru

C

Ru

C

Ph₃P

Ph₂P

PPh₂

1b

1a

Ru

C

Me

Ru

C

Me

Ph₃P

Ph₂P

PPh₂

2b

2a

2. Results and discussion

Ru

C

Ru

C

Acetylide complexes [Ru(C„CR)(L₂)(g⁵-C₅H₅)] are

conveniently prepared by reactions of the analogous chlo-

ride with a terminal alkyne, and deprotonation of the result-

ing vinylidene [17]. It is also possible to prepare such

complexes from trimethylsilyl protected terminal alkynes

when the metallation reaction is carried out in the presence

of ﬂuoride ions [18]. Together, these methods allow the con-

venient preparation of not only simple phenyl acetylide

complexes such as [Ru(C„CPh)(PPh₃)₂Cp] (1a) [19] and

[Ru(C„CPh)(dppe)Cp^*] (1b) [20], but also substituted

derivatives far too numerous to list in detail here [13,21–

25]. We have used these methods in the preparation of

half-sandwich ruthenium acetylide complexes bearing sim-

ple aromatic substituents (1–4) (Chart 1). We note that only

a small number of related half-sandwich ruthenium acety-

lide complexes of fused-ring aromatic alkynes, such as ethy-

nyl naphthalimide and ethynyl pyrone, are known [25]. The

iron analogue of 3b has recently been reported [26].

Ph₃P

Ph₂P

PPh₂

3b

3a

Ru

C

Ru

C

Ph₃P

Ph₂P

PPh₂

4a

4b

Chart 1. The complexes studied in this work.

corresponding radical cations. Their redox potentials and

chemical stability are sensitive to both the supporting

ligands on the ruthenium centre and the acetylide substitu-

ent [13,20,21d,25a]. In this work we have examined the

anodic behaviour of [Ru(C„CC₆H₅)(L₂)Cp⁰] (1a,b),

[Ru(C„CC₆H₄Me-4)(L₂)Cp⁰] (2a,b), [Ru(C„CC₁₀H₇)-

(L₂)Cp⁰] (3a,b) and [Ru(C„CC₁₄H₉)(L₂)Cp⁰] (4a,b).

The cyclic voltammogram of [Ru(C„CC₆H₅)(PPh₃)₂

Cp] (1a) in dichloromethane is characterised by an oxida-

tion event at 0.59 V (Table 1), the chemical reversibility

of which improves at lower temperatures (i_pa:i_pc= 1.7 at

The IR spectra of complexes 1–4 exhibit m(C„C) bands

for the coordinated acetylide moiety at ca. 2070 (1, 2), 2055

(3) and 2040 (4) cm^ꢀ1, somewhat lower in energy than the

organic alkynes [15b,27,28]. It is interesting to note that

whilst these IR bands are remarkably insensitive to the

other supporting ligands at the metal centre, the m(C„C)

frequency is attenuated by the nature of the aromatic acet-

ylide substituent. The carbons of the acetylide moieties

were observed in the ¹³C NMR spectra as triplets (C_a,

J_CP= 25 Hz) and singlets (C_b). The C_aresonances were

progressively deshielded by the larger aromatic substitutent

[e.g. d_C1b (128.8) ꢁ 2b (126.4) < 3b (135.1) < 4b (144.6)].

The Cp and Cp^*ligand resonances were found as singlets

ꢀ78 ꢁC, m = 100 mV s^ꢀ1

)

and at faster scan rates

(i_pa:i_pc= 1.1 at ꢀ78 ꢁC, m = 800 mV s^ꢀ1). At higher poten-

tials, a second anodic wave was also observed, which was

completely irreversible (Table 1). The behaviour of the

naphthyl (3a) and anthryl (4a) substituted derivatives were

similar to those described for the phenyl acetylide complex,

with the ﬁrst oxidation event associated with 4a being

rather more thermodynamically favourable (Table 1).

The chemical reversibilities of the naphthyl (3a) and

anthryl (4a) substituted derivatives were poor under all

conditions examined.

1

in the H and ¹³C NMR spectra in the usual regions (Cp/

Cp^*: d_H= 4.3–4.6/1.5–1.6 ppm; d_C= 85–86/10.0–10.5,

92–93 ppm) whilst the supporting phosphine ligands gave

rise to singlets in the ³¹P NMR spectra at ca. 50.5–51.5

(PPh₃) or 81–83 (dppe) ppm.

3. Electrochemical characterisation

In contrast, the oxidation of the p-tolyl compound

[Ru(C„CC₆H₄Me-4)(PPh₃)₂Cp] (2a) proved to be fully

chemically reversible at room temperature (i_pa:i_pc= 1),

with the variation in DE_pbeing no greater than that of

Typically, half-sandwich ruthenium acetylides undergo

single electron oxidation in common solvents to give the

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

3279

Table 1

Electrochemical data for complexes 1–4

4. IR spectroelectrochemical studies

E^a_(1/2)

DE^b_p

i_pa:i_pc

E(2)^c_pa

The reactivity of [Ru(C„CPh)(PPh₃)₂Cp]⁺(1a)

implied by the CV study was brieﬂy investigated by spec-

troelectrochemical methods. For this study, and those

which are described in more detail below, we employed

an air-tight spectroelectrochemical cell ﬁtted with CaF₂

windows to provide transparency across the spectroscopic

region of interest [30]. During rapid oxidation of 1a the

m(C„C) band at 2074 cm^ꢀ1, which is characteristic of

the 18-electron ruthenium acetylide, shifted to give rise

to a transient species with an IR bands at 1937 and

1529 cm^ꢀ1. By comparison with results obtained from

2a, and the Ru(dppe)Cp^*series 1b–4b these bands are

attributed to [Ru(C„CPh)(PPh₃)₂Cp]⁺([1a]⁺) (vide

infra). However, [1a]⁺proved to be unstable under the

conditions of the spectroelectrochemical experiment, and

rapidly converted to a second species with IR bands at

1a^d

2a^e

3a^d

4a^d

1b^e

2b^e

3b^e

4b^e

a

0.59

0.53

0.55

0.42

0.34

0.31

0.36

0.29

115

120

85

130

80

90

110

90

1.7

1.0

4.3

7.7

1.0

1.39

1.40

1.44

1.60

1.19

1.17

1.28

1.07

All E values in Volt vs. SCE. Conditions: CH₂Cl₂solvent, 10^ꢀ1M

NBu₄PF₆electrolyte, Pt working, counter and pseudo-reference elec-

trodes, m = 100 mV s^ꢀ1. The decamethyl ferrocene/decamethyl ferroce-

+

nium F_c^*/F_ccouple was used as an internal reference for potential

*

+

*

measurements F_c^*/F_c

taken as ꢀ0.02 V vs. SCE in CH₂Cl₂/0.1 M

[NBu₄]PF₆[29].

b

DE_p= jE_paꢀ E_pcj.

c

Anodic peak potential of a totally irreversible process.

d

e

ꢀ78 ꢁC.

20 ꢁC.

2362, 2173 and 1650 cm^ꢀ1

.

Whilst the band at

2173 cm^ꢀ1is in the appropriate region for an organic

alkyne, we have not pursued the nature of the decompo-

sition species further. However, we do note that there is

no evidence for the formation of the carbonyl cation

[Ru(CO)(PPh₃)₂Cp]⁺, which gives a characteristic m(CO)

band near 1970 cm^ꢀ1[13].

the internal decamethyl ferrocene/decamethyl ferrocenium

reference couple and independent of scan rate. Plots of

i_pavs. m^1/2were also linear for this species. This improved

chemical reversibility over the compounds 1a, 3a and 4a

suggests the involvement of the ring hydrogen in the posi-

tion para to the metal acetylide fragment in at least one of

the chemical pathways responsible for the reactivity of the

[Ru(C„CAr)(PPh₃)₂Cp]⁺systems.

The same trend in electrode potentials as a function of

the acetylide substituent observed in the Ru(PPh₃)₂Cp ser-

ies was also apparent in the Ru(dppe)Cp^*complexes, with

the anthryl derivative being oxidised at signiﬁcantly lower

potentials than the other members of the series 1b–4b.

The introduction of the bulky and more electron-donating

Cp^*and dppe ligands around the ruthenium acetylide

framework rendered the ﬁrst oxidation event of the

[Ru(C„CAr)(dppe)Cp^*] series ca. 100–200 mV more

favourable than the analogous [Ru(C„CAr)(PPh₃)₂Cp]

complexes. These processes are completely electrochemi-

cally and chemically reversible at room temperature and

moderate scan rates (m = 100 mV s^ꢀ1), with linear plots of

i_pavs. m^1/2being obtained and DE_pvalues of comparable

magnitude as the internal reference couple (Table 1).

The greater chemical stability of the [Ru(C„CAr)

(dppe)Cp^*] series 1b, 2b, 3b and 4b under the conditions

of the cyclic voltammetry experiments prompted us to con-

sider spectroscopic characterisation of the products derived

from their one-electron oxidation more thoroughly by

spectroelectrochemical means. Oxidation of 1b was moni-

tored in both the IR and UV–Vis-NIR spectroscopic

regions. The intensity of the characteristic m(C„C) band

of 1b at 2072 cm^ꢀ1decreased, being replaced by a new

band at 1929 cm^ꢀ1as the oxidation proceeded (Table 2).

In addition, new bands in the aromatic m(CC) region were

also observed (Table 2). The original spectrum was fully

recovered after back-reduction, which conﬁrmed the

assignment of the new bands to [1b]⁺, and not to some

product of an EC process (Fig. 1). This spectroelectro-

chemical work conﬁrms the tentative assignment of this

m(C„C) band to [1b]⁺by Paul et al. from chemically oxi-

dised samples of 1b [13]. The shift of the m(C„C) band

by 143 cm^ꢀ1upon oxidation indicates the appreciable

Table 2

IR data (cm^ꢀ1) for compounds 1b–4b and the corresponding cations^a

Neutral species

Oxidised (cation radical) complex

m(CC)

m(Aryl)

m(CC)

m(Aryl)

1b

2a

2b

3b

4b

a

2072(s)

2077(s)

2073(s)

2053(s)

2041(s)

1593(w)

1606(vw)

1606(w)

1567(w)

1561(vw)

1929(s)

1925(s)

1928(s)

1916(s)

1925(s)

1614(m), 1551(s), 1540(s), 1520(m)

1587(s)

1588(s)

1634(m), 1594(m), 1549(s)

1610(w), 1597(w), 1588(w), 1534(w)

Data from CH₂Cl₂solutions containing 0.1 M NBu₄BF₄supporting electrolyte at ambient temperature.

3280

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

orbitals are summarised in Table 4 for 1-H, [1-H]⁺, 4-H

and [4-H]⁺, while Fig. 2 illustrates the labelling scheme.

The Ru–C_a, Ru–P, C_a„C_band C_b–C(1) bond lengths in

4-H are comparable with those found in 1-H. At the level

of theory employed, the aromatic substituents in the neu-

tral systems 1-H and 4-H lie in the plane approximately

parallel to the Cp ring, although there is a barrier to rota-

tion of the aromatic group around the C(2)–C(3) bond of

only ca. 0.3 kcal mol^ꢀ1for 1-H. In contrast, the plane of

the aromatic substituents in the mono-oxidised species [1-

H]⁺and [4-H]⁺are found approximately bisecting the P–

Ru–P angle. The barrier to rotation of the aromatic group

around the C(2)–C(3) bond is considerable at ca.

6 kcal mol^ꢀ1for [1-H]⁺.

The electronic structure of 1-H has been described

before [13], and only pertinent details will be summarised

here. The HOMO and [HOMO ꢀ 1] are approximately

orthogonal and derived from mixing of the metal d and

acetylide p-systems, with the HOMO also containing

appreciable contributions from the phenyl p-system (Table

4, Fig. 3).

Occupied orbitals comprised largely of metal and Cp,

metal phosphine and phenyl p-character are found lower

in the occupied orbital manifest. The LUMO and

[LUMO + 1] of 1-H are largely Ru–Cp anti-bonding in

character, with the phenyl p^*system some 1.35 eV higher

in energy than the LUMO, and comprising the

[LUMO + 3] (Fig. 4).

The frontier orbitals of 4-H feature important contribu-

tions from the anthryl substituent (Table 4, Fig. 5). Thus,

while the HOMO and [HOMO ꢀ 1] are approximately

orthogonal p-type orbitals, the HOMO features a large

(67%) contribution from the atoms of the anthryl substitu-

tent and is somewhat removed from the other occupied

orbitals. The LUMO is essentially the anthryl p^*orbital,

which is suﬃciently low in energy to lie below the unoccu-

pied Ru–Cp based orbitals that comprise the [LUMO + 1]

and [LUMO + 2].

A

2100

2000

1900

1800

1700

1600

1500

Wavenumber / cm^-1

Fig. 1. IR spectra on back reduction of [1b]⁺to 1b in a spectroelectro-

chemical cell (CH₂Cl₂/0.1 M NBu₄PF₆, ambient temperature).

depopulation of an orbital with C„C bonding character.

Similar results were obtained from 2b, 3b and 4b, with oxi-

dation resulting in a shift of the m(C„C) band by 145, 137

and 116 cm^ꢀ1, respectively, and with the original spectra

being fully recovered after the back-reduction in the spec-

troelectrochemical cell.

In the case of the remaining members of the

Ru(PPh₃)₂Cp series, we note here that the introduction of

the para-methyl group in 2a instills signiﬁcant chemical sta-

bility at room temperature to this simple complex. Upon

oxidation of 2a, the m(C„C) band at 2077 cm^ꢀ1shifts by

some 150 cm^ꢀ1to give a new band at 1925 cm^ꢀ1, which

is assigned to the m(C„C) band in [2a]⁺. The comparable

shift in the spectra of 2a/[2a]⁺compared with 2b/[2b]⁺is

revealing, and implies similar acetylide bonding character

in the radical cations, regardless of the electron-donating

ability of the supporting ligands.

5. Electronic structure calculations

A theoretical investigation was conducted at the DFT

level, initially on the model systems [Ru(C„CC₆H₅)

(PH₃)₂Cp] (1-H) and [Ru(C„CC₁₄H₉)(PH₃)₂Cp] (4-H),

which were used to mimic complexes 1a, 1b and 4a, 4b,

and the corresponding radical cations [1-H]⁺and [4-H]⁺.

The discussion which follows refers to results obtained

from calculations at the B3LYP/3-21G^*level of theory

with no symmetry constraints (Table 3), as results obtained

from other functionals and basis sets are in good general

agreement (vide infra). There is excellent agreement

between the crystallographically determined structures of

1a [31,32] and 1b [13] with the DFT optimised geometries

determined here, and also with calculations previously

reported [13]. Energies and composition of the frontier

The model radical cation [1-H]⁺features an Ru–C bond

somewhat shorter than 1-H (Table 3). The metal–phos-

phine bond lengths are sensitive to the net electron density

available for p-back bonding and as such are elongated in

[1-H]⁺relative to 1-H. The elongation of the acetylide

C„C bond in [1-H]⁺when compared with the neutral

model system 1-H is consistent with a decrease in the net

acetylide p-bonding character. This is also supported by

the calculated m(C„C) frequencies of 1-H (2058 cm^ꢀ1

)

and [1-H]⁺(1938 cm^ꢀ1) [33]. The contraction of the C(2)–

C(3), C(4)–C(5) and C(7)–C(8) bonds and elongation of

the remaining C–C bonds in the phenyl substituent is con-

sistent with the evolution of a degree of cumulenic charac-

ter in the radical cation. The frontier orbitals of the one-

electron oxidation product [1-H]⁺are similar to those of

1-H, with the a-HOSO and b-LUSO displaying appreciable

Ru(d) and acetylide (p) character and the next highest

unoccupied orbitals being largely centred on the

Ru(PH₃)₂Cp fragment (Table 4, Fig. 3).

Table 3

+

˚

Optimised bond lengths (A) for 1-H, [1-H] , 4-H and [4-H]

1-H

[1-H]⁺

D

4-H

[4-H]⁺

D

Ru–P(1,2)

Ru–C_a

C_a„C_b

2.278

2.018

1.228

1.426

1.412

1.392

1.398

2.324

1.944

1.247

1.400

1.423

1.386

1.403

+0.046

ꢀ0.074

+0.019

ꢀ0.026

+0.011

ꢀ0.006

+0.005

2.280

2.013

1.230

1.420

1.425

1.444

1.400

2.309

1.954

1.246

1.385

1.448

1.437

1.407

+0.029

ꢀ0.060

+0.016

ꢀ0.035

+0.023

ꢀ0.007

+0.007

C_b–C(1)

C(1)–C(2,6)

C(2,6)–C(3,5)

C(3,5)–C(4)

Table 4

Energy, occupancy, and composition of frontier orbitals in the model complexes 1-H, [1-H]⁺, 4-H and [4-H]⁺(B3LYP/3-21G^*)

MO

LUMO + 3

LUMO + 2

LUMO + 1

LUMO

HOMO

HOMO ꢀ 1

HOMO ꢀ 2

HOMO ꢀ 3

HOMO ꢀ 4

1-H

e (eV)

Occ

+0.09

0

ꢀ0.03

ꢀ0.15

ꢀ0.78

ꢀ4.91

2

ꢀ5.09

ꢀ5.72

ꢀ6.46

ꢀ6.65

0

53

3

0

62

16

13

8

0

50

24

27

0

2

46

8

2

46

26

14

6

2

0

2

58

3

%Ru

%Cp

%PH₃

%C_a

%C_b

%Ph

27

2

30

2

0

12

10

1

11

6

1

4

0

8

16

22

29

10

28

4

0

4

2

0

1

0

1

48

26

0

6

100

27

4-H

e (eV)

Occ

ꢀ0.08

ꢀ0.30

ꢀ0.92

ꢀ1.38

ꢀ4.53

ꢀ5.32

ꢀ5.68

ꢀ6.07

2

ꢀ6.25

0

75

3

0

60

17

13

9

0

50

24

27

0

2

11

1

2

47

8

2

49

12

7

2

0

%Ru

%Cp

%PH₃

%C_a

36

17

9

0

21

1

0

1

4

0

6

11

8

9

1

8

0

%C_b

0

25

7

8

13

18

0

%Anth

0

91

67

23

100

MO

88b

88a

87b

87a

86b

86a

85b

85a

84 b

84a

83 b

83a

82 b

82a

81 b

81a

80 b

80a

b-[LUSO + 4] a-[LUSO + 3]

b-[LUSO + 3]

a-[LUSO + 2]

b-[LUSO + 2]

a-[LUSO + 1]

b-[LUSO + 1]

a-LUSO b-LUSO a-HOSO b-HOSO a-[HOSO ꢀ 1]

b-[HOSO ꢀ 1]

a-[HOSO ꢀ 2]

b-[HOSO ꢀ 2]

a-[HOSO ꢀ 3]

b-[HOSO ꢀ 3]

a-[HOSO ꢀ 4]

[1-H]⁺

e(eV)

Occ

ꢀ3.28

ꢀ3.29

ꢀ3.67

ꢀ4.03

ꢀ4.15

ꢀ4.26

0

ꢀ4.82

ꢀ4.95

ꢀ7.27

0

ꢀ9.00

1

ꢀ9.51

ꢀ9.67

ꢀ9.85

ꢀ9.95

ꢀ9.92

1

ꢀ10.19

ꢀ10.08

ꢀ10.41

0

64

2

0

64

2

0

7

0

5

0

55

20

16

9

0

48

26

0

47

27

26

0

1

51

3

1

50

4

1

41

29

10

8

1

39

37

11

7

1

0

1

0

1

20

29

9

%Ru

%Cp

53

20

15

10

1

33

6

23

7

29

17

6

3

1

0

%PH₃33

34

0

2

4

2

0

%C_a

%C_b

%Ph

0

16

3

19

7

10

21

26

11

16

38

11

30

4

11

29

3

11

0

6

0

1

0

3

5

0

70

68

0

9

1

37

100

35

MO

114b

114a

113b

113a

112b

112a

111b

111a

110b

110a

109b

109a

108b

108a

107b

107a

106b

106a

b-[LUSO + 4] a-[LUSO + 3] b-[LUSO + 3] a-[LUSO + 2] b-[LUSO + 2] a-[LUSO + 1] b-[LUSO + 1] a-LUSO b-LUSO a-HOSO b-HOSO a-[HOSO ꢀ 1] b-[HOSO ꢀ 1] a-[HOSO ꢀ 2] b-[HOSO ꢀ 2] a-[HOSO ꢀ 3] b-[HOSO ꢀ 3] a-[HOSO ꢀ 4]

[4-H]⁺

e (eV) ꢀ3.13

ꢀ3.27

ꢀ3.63

ꢀ3.71

ꢀ4.28

ꢀ4.35

ꢀ4.73

ꢀ5.12

ꢀ6.78

0

ꢀ8.08

ꢀ8.75

ꢀ9.11

ꢀ9.03

ꢀ9.22

1

ꢀ9.37

ꢀ9.43

1

ꢀ9.67

ꢀ9.74

Occ

0

56

20

15

9

0

55

20

15

9

0

49

26

25

0

48

26

0

4

0

3

1

12

3

1

30

8

1

55

8

1

56

6

1

43

29

11

7

1

0

1

0

%Ru

%Cp

%PH₃

%C_a

%C_b

17

3

32

14

6

40

29

10

8

0

1

0

1

2

4

0

8

9

10

58

8

0

7

1

0

1

0

8

11

46

22

5

22

4

11

37

8

10

2

0

%Anth 100

100

0

87

67

2

100

3282

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

Dm(C„C) = 143 cm^ꢀ1

;

4b/[4b]⁺Dm(C„C) = 116 cm^ꢀ1

)

C₁₂C₁₃

C₁₁C₁₄

C₂C₃

C₁C₄C₁₅

C₆

C₇

C₈C₉

and model systems [1-H/[1-H]⁺Dm(C„C) = 120 cm^ꢀ1

4-H/[4-H]⁺Dm(C„C) = 86 cm^ꢀ1].

;

The frontier orbitals of [4-H]⁺are similar to those of

4-H. The a-HOSO and a-LUSO of [4-H]⁺oﬀer an apprecia-

ble anthryl character (a: 67%, 87%, respectively). It may

therefore be more appropriate to consider species such as

[4b]⁺as metal-stabilised anthryl radicals. The optimised

geometries of 4-H and [4-H]⁺supported this point of view,

as do calculated spin densities, with the atoms comprising

the anthryl ring system contributing some 60% of the frac-

tional electronic charge in [4-H]⁺compared with the phenyl

ring system contribution of some 25% in [1-H]⁺(Table 5).

Ru

C_α

C_β

P₂

C

5

P₁

C₁₀

Fig. 2. The labelling scheme used in the discussion of the DFT results, and

¹³C NMR spectra.

The optimised geometry of [4-H]⁺displays elongated

Ru–P bond lengths and evidence of an increased cumulenic

character in the ethynyl anthryl portion of the molecule

when compared with the bond distances in 4-H (Table 3).

While the trends in the structures and calculated m(C„C)

frequencies of [4-H] [m(C„C) = 2038 cm^ꢀ1] and [4-H]⁺

[m(C„C) = 1952 cm^ꢀ1] follow those observed for 1-H and

[1-H]⁺, it is interesting to compare the pairs of structures

1-H/[1-H]⁺and 4-H/[4-H]⁺and note the relative diﬀer-

ences in the individual bond lengths (Table 3). Although

the magnitude of individual deviations are small

6. UV–Vis spectroelectrochemical studies

Comparison of the electronic absorption spectra of 1b,

2b, 3b and 4b reveals a strong, and in the case of 4b, rela-

tively narrow, absorption band between 33000 and

˚

(<0.05 A) there is a clear trend indicating that the anthryl

fragment in [4-H]⁺experiences a greater relative structural

distortion than the phenyl ring in [1-H]⁺. Conversely, the

metal ethynyl fragment is more signiﬁcantly aﬀected in

[1-H]⁺than in [4-H]⁺, which is neatly reﬂected in the diﬀer-

ences between the m(C„C) frequencies of the 18- and 17-

electron compounds in both the experimental (1b/[1b]⁺

Fig. 4. The [LUMO + 3] of 1-H plotted with contour values 0.04

(e/bohr³)^1/2

.

Fig. 3. The (a) [HOMO ꢀ 1], (b) HOMO, (c) LUMO, (d) [LUMO + 1] of 1-H together with (e) b-HOSO, (f) b-LUSO, (g) b-[LUSO + 1],

(h) b-[LUSO + 2] of [1-H]⁺and (i) a-[HOSO ꢀ 1], (j) a-HOSO, (k) a-LUSO, (l) a-[LUSO + 1] of [1-H]⁺plotted with contour values 0.04 (e/bohr³)^1/2

.

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

3283

Fig. 5. The (a) [HOMO ꢀ 1], (b) HOMO, (c) LUMO, (d) [LUMO + 1] of 4-H together with (e) b-HOSO, (f) b-LUSO, (g) b-[LUSO + 1],

(h) b-[LUSO + 2] of [4-H]⁺and (i) a-[HOSO ꢀ 1], (j) a-HOSO, (k) a-LUSO, (l) a-[LUSO + 1] of [4-H]⁺plotted with contour values 0.04 (e/bohr³)^1/2

.

Table 5

20000 cm^ꢀ1, which becomes progressively red-shifted as a

function of the size of the aromatic substituent and

accounts for the colour of these complexes (Table 6, Figs.

6 and 8). The analogous bands in [Ru(C„CC₆H₄X-

4)(dppe)Cp^*] (X = H, CN, F, OMe, NH₂) have been

assigned to MLCT processes by analogy with assignments

made for iron complexes [13]. Although electronic struc-

ture calculations on [Ru(C„CPh)(PH₃)Cp] model systems

have been performed on previous occasions [13,14], only

limited use has been made of TD DFT based studies to

provide further insight into the nature of the electronic

transitions responsible for the characteristic absorption

spectra of related systems [21a,34,35].

Spin densities computed for the model radical cations, [1-H]⁺and [4-H]⁺

[1-H]⁺

[4-H]⁺

D

Ru

P

Cp

C_a

0.413

0.000

0.041

0.043

0.269

0.246

0.220

0.000

0.021

0.079

0.114

0.598

0.193

0.000

ꢀ0.079

ꢀ0.036

0.155

C_b

C₆H₅/C₁₄H₉

ꢀ0.352

Table 6

The principal UV–Vis absorption bands ½ꢀm_max=cm^ꢀ1ðe_max=M^ꢀ1cm^ꢀ1Þꢂ

observed from CH₂Cl₂/10^ꢀ1M NBu₄PF₆solutions of [1b]ⁿ⁺, [2a]ⁿ⁺

[2b]ⁿ⁺, [3b]ⁿ⁺and [4b]ⁿ⁺(n = 0, 1)

,

n

On the basis of TD DFT calculations the characteristic

absorption band observed in 1b, and by analogy 2b and 3b,

can be likened, in the most general terms, to a (d/p) – phe-

nyl p^*charge transfer band (HOMO ﬁ [LUMO + 3])

rather than a purely MLCT band. In the case of 4b there

is a critical distinction and the band at 20600 is better

described as an anthryl-centred p–p^*transition (HOMO ﬁ

LUMO). This distinction in assignment is consistent with

the diﬀerent band shapes observed for 1b–3b on one hand,

and 4b on the other (Figs. 6 and 8).

0

+1

1b 29500

(9500)

2a 30700

(7000)

2b 33400

(7000)

3b 26200

(7000)

22600 (3900), 21100 (4300), 11200 (5100), 8100 (600)

30300 (4500), 19100 (1200), 14300 (1500), 11900 (900),

7500 (100)

29800 (4500), 26200 (2700), 16900 (800), 13900 (1800),

8600 (200)

20200 (3100), 18600 (2500), 11000 (3900), 7600 (700)

4b 20600

(11600)

27200 (8000), 17900 (14000), 15200 (5900), 10100

(1900), 7800 (600)

3284

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

10000

8000

6000

4000

(b)

ε

2000

(a)

25000

0

30000

20000

15000

10000

5000

Wavenumber / cm^-1

Fig. 6. The UV–Vis-NIR spectra of (a) 1b and (b) [1b]⁺(CH₂Cl₂/0.1 M NBu₄PF₆).

The UV–Vis-NIR spectrum of [1b]⁺, obtained spectro-

by Paul et al., and attributed to forbidden ligand-ﬁeld type

transitions centred on the Ru(III) centre [13]. The TD DFT

calculations carried out in the present study suggest that the

lowest energy transition should be attributed to the b-

HOSO to b-LUSO transition, with the low intensity of

the observed band reproduced by the low calculated oscilla-

tor strength and easily explained by the relative, approxi-

mately orthogonal orientation of these two orbitals. Other

NIR bands of slightly greater intensity and higher energy

are attributable to Ru/Cp based b-[HOSO ꢀ 1] to the b-

LUSO.

electrochemically from 1b, exhibits strong absorption enve-

lopes centred near 21100 and 11200 cm^ꢀ1, and a weaker

series of bands between 8000 and 4000 nm (Fig. 6). The

spectrum of 1b was fully recovered after back-reduction,

which strongly supports the assignment of these character-

istic absorption bands to the 17-e species [1b]⁺. TD DFT

calculations using the [1-H]⁺model indicate that the highest

energy transition can be attributed to charge transfer from

the metal fragment (including the acetylide p-system) to the

phenyl (p^*) ring being comprised of electronic transitions

from the a-HOSO (highest occupied spin orbital) to the a-

[LUSO]. The band centred near 11200 cm^ꢀ1can be approx-

imated in terms of transitions between occupied orbitals

with large amounts of Ru/Cp character (b-[HOSO ꢀ 1],

b-[HOSO ꢀ 2], Table 4, Fig. 7) to the b-LUSO. The pres-

ence of low energy (NIR) bands in 17-e cation radicals of

the general type [Ru(C„CAr)(dppe)Cp^*]⁺has been noted

The tolyl-substituted derivatives [2a]⁺and [2b]⁺, and the

naphthyl derivative [3b]⁺oﬀer similar electronic spectra to

each other, and that of [1b]⁺. Low NIR energy bands are

observed, together with a more intense band envelope in

the visible region, the precise shape and composition of

which vary only slightly with the nature of the Cp⁰and

phosphine co-ligands. In the case of [3b]⁺the characteristic

absorption bands are somewhat red-shifted compared with

the analogous features in [1b]⁺, [2a]⁺and [2b]⁺. Given the

similar proﬁles of these compounds, and the similar chem-

ical behaviour of each member of the series, we are reason-

ably conﬁdent in attributing these spectroscopic absorption

bands to transitions similar to those described for [1-H]⁺.

The anthryl derivative [4b]⁺oﬀers four principal absorp-

tion bands near 27000, 18200, 15000 and 10000 cm^ꢀ1

,

Fig. 7. The (a) b-[HOSO ꢀ 1] and (b) b-[HOSO ꢀ 2] of [1-H]⁺plotted

together with weaker bands tailing further into the NIR

region (Fig. 8). On the basis of TD DFT calculations using

with contour values 0.04 (e/bohr³)^1/2

.

16000

12000

8000

4000

0

(b)

ε

(a)

34000

29000

24000

19000

14000

9000

4000

Wavenumber / cm^-1

Fig. 8. The UV–Vis-NIR spectra of (a) 4b and (b) [4b]⁺(CH₂Cl₂/0.1 M NBu₄PF₆).

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

3285

As a test of the reliability of the B3LYP/3-21G^*calcula-

tions presented above, the geometry optimisation, fre-

quency calculations and TD DFT calculations on the

models [1-H] and [1-H]⁺were repeated using a range of

other functionals and basis sets (Table 7). There is a little

signiﬁcant variation in the optimised geometries with com-

putational method. The electronic structures calculated

from these various methods are largely consistent, with

perhaps the most notable feature being the relative order

of the predominantly metal centred orbitals lying below

the b-HOSO in [1-H]⁺.

Time-dependent density functional theory calculations

of the ﬁrst vertical transition energies of both the neutral

and monocationic models are particularly revealing. Whilst

the energy of electronic transitions computed using the dif-

ferent methods varies signiﬁcantly, the net assignment of

the absorption spectra is the same regardless of the func-

tional or basis set employed. Given the gas-phase nature

of the calculation and the use of static model systems, the

strong electrolyte solution used in the spectroelectrochem-

ical measurement of the absorption spectra and the likely

low energy barriers to rotation of the aromatic acetylide

substituent around the acetylide–aromatic single bond, it

is not possible to pass comment on the true precision of

the various computational methods. It is clear, however,

that the computationally expedient B3LYP/3-21G^*calcu-

lations are not signiﬁcantly less accurate than any of the

higher level calculations also examined.

Fig. 9. The b-[HOSO ꢀ 4] of [4-H]⁺plotted with contour values 0.04

(e/bohr³)^1/2

.

As a further test of the reliability of the calculations,

the compounds [1b]ⁿ⁺and [4b]ⁿ⁺were also studied using

B3LYP/3-21G^*, the results of which are summarised in

Tables 8 and 9, together with the experimental data and

that from the models [1-H] and [4-H] for ease of compar-

ison. The agreement between the data calculated from the

systems containing the full ligand sets and those observed

experimentally is better than obtained from any of

the calculations using the model ligand sets. However,

the assignments of the electronic absorption bands in

the experimental systems [1b]ⁿ⁺and [4b]ⁿ⁺are not signif-

icantly changed.

Fig. 10. The b-[HOSO ꢀ 1] of [4-H]⁺plotted with contour values 0.04

(e/bohr³)^1/2

.

[4-H]⁺as a model, the highest-energy band observed in the

UV–Vis-NIR spectrum of [4b]⁺is due to electronic excita-

tions from the largely metal/ethynyl based b-HOSO and

a-[HOSO ꢀ 2] to the b-[LUSO + 1] and a-[LUSO], which

are anthracene p^*in character. The intense band at

18200 cm^ꢀ1is comprised of electronic transitions between

a-HOSO and a-LUSO (i.e. the anthryl radical p–p^*transi-

tion), and is red-shifted from the analogous band in 4b.

The less intense band at 15200 cm^ꢀ1is largely associated

with electronic excitation from the b-[HOSO ꢀ 4] to the

b-LUSO (Fig. 9), and is approximately an MLCT band.

7. Conclusion

A relatively intense NIR band (k_max= 10000 cm^ꢀ1

_max= 2000 M^ꢀ1cm^ꢀ1) is calculated to arise from excita-

,

One-electron oxidation of the half-sandwich bis(phos-

phine) ruthenium acetylide complexes [Ru(C„CAr)(L₂)

Cp⁰] aﬀords the corresponding radical cations [Ru(C„

CAr)(L₂)Cp⁰]⁺. These cations are sensitive to atmospheric

conditions. However, the stability of these species is

improved through the use of p-tolyl acetylide substituents

or the bulky Ru(dppe)Cp^*metal end-cap and in situ spec-

troelectrochemical methods may be used to record the

infrared and UV–Vis-NIR spectra of these relatively ‘reac-

tive’ cations. The compounds derived from phenylacety-

lene, 4-ethynyltoluene and 1-ethynylnapthalene oﬀer

frontier orbitals with appreciable metal character, which

in the case of the HOMO is also admixed with the ethynyl

and aromatic p system. There is a critical distinction in the

e

tions involving occupied orbitals with the metal–ethynyl–

anthryl character (b-HOSO and a-HOSO) and the

b-LUSO and a-LUSO, which are both rather more heavily

centred on the anthryl ring systems (Fig. 5). The very weak

NIR bands found at even longer wavelengths are assigned

to metal to anthryl charge transfer processes, involving

excitations largely between the b-[HOSO ꢀ 1] and b-LUSO

(Fig. 10). The critical distinction between the assignments

of the optical transitions in compounds modelled by [1-

H]⁺and [4-H]⁺is the greater localisation of the b-LUSO

and a-HOSO on the aromatic ring in the anthracene

derivative.

3286

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

Table 7

Optimised bond lengths, important vibration frequencies and major electronic excitations for 1-H, [1-H]⁺, [1b] and [1b]⁺determined by TD DFT methods using diﬀerent functionals and basis sets, with selected

experimental data for comparison

Expt [1b]ⁿ⁺[13]

B3LYP/3-21G^*[1-H]ⁿ⁺B3LYP/Gen [1-H]ⁿ⁺B3LYP/Gen2 [1-H]ⁿ⁺PBE1PBE/3-21G^*[1-H]ⁿ⁺PBE1PBE/Gen [1-H]ⁿ⁺P86/3-21G^*[1-H]ⁿ⁺BP86/Gen [1-H]ⁿ⁺B3LYP/3-21G^*[1b]ⁿ⁺

˚

Bond lengths/A

n = 0

Ru–C 2.011(4)

C„C 1.215(5)

C–Ph 1.431(5)

2.018

1.228

1.426

2.028

1.229

1.428

2.291

2.011

1.222

1.424

2.310

1.999

1.228

1.423

2.250

2.010

1.229

1.425

2.264

2.003

1.242

1.426

2.260

2.012

1.244

1.427

2.273

2.015

1.231

1.425

2.287

Ru–P 2.262(1), 2.256(1) 2.278

n = 1

Ru–C

C„C

C–Ph

Ru–P

1.944

1.246

1.400

2.324

1.946

1.250

1.403

2.335

1.932

1.241

1.399

2.356

1.929

1.248

1.397

2.283

1.929

1.251

1.400

2.299

1.943

1.260

1.404

2.294

1.942

1.263

1.406

2.311

1.957

1.243

1.411

2.350

Vibrational frequencies (IR)/cm^ꢀ1(intensity)

n = 0

C„C 2072(s)

2101 (218)

1547 (54)

2084 (248)

1573 (64)

2081 (327)

1556 (76)

2121 (230)

1568 (54)

2108 (256)

1599 (61)

2020 (318)

1494 (71)

2005 (330)

1523 (80)

2077 (374)

1545 (68)

Ring

1593(m,w)

n = 1

C„C 1929(s)

1980 (310)

1529 (291)

1965 (209)

1551 (290)

1906 (271)

1537 (298)

1993 (339)

1548 (310)

1983 (210)

1574 (309)

1920 (29)

1910 (14)

1952 (520)

1496 (91)

Ring

1551(m)

1482 (165)

1508 (161)

electronic structure of the compounds based on 9-ethynyl-

anthracene, which instead feature frontier orbitals largely

localised on the anthracene moiety. Thus compounds such

as [4b]⁺might be better regarded as metal-stabilised

anthryl radicals than as radical cations derived from oxida-

tion of the metal centre.

accelerating voltage and trans-2-[3-(4-tert-Butylphenyl)-2-

methyl-2-propenylidene]maleonitrile (DCTB), purchased

from Sigma–Aldrich, used as matrix. Samples were pre-

pared from solutions containing 10 mg/1 L of the matrix

and 1 mg/1 L of the sample and mixed 1:9 sample:matrix.

Only 1 lL of the mixtures was used for analyses.

Cyclic voltammograms were recorded at v = 100–

800 mV s^ꢀ1from solutions of approximately 10^ꢀ4M in

analyte in dichloromethane containing 10^ꢀ1M NBu₄PF₆,

using a gastight single-compartment three-electrode cell

equipped with platinum disk working, coiled platinum wire

auxiliary, and platinum wire pseudo-reference electrodes.

The working electrode surface was polished before scans

with an alumina paste. The cell was connected to a com-

puter-controlled Autolab PGSTAT-30 potentiostat. All

redox potentials are reported against the saturated calomel

electrode, and referenced against the decamethylferrocene/

decamethylferrocenium F_c/F_credox couple used as an

internal reference system [29]. Cyclic voltammetric mea-

surements at sub-ambient temperatures were performed

with the electrochemical cell immersed into a bath of ace-

tone/dry ice.

8. Experimental

All reactions were carried out under an atmosphere of

nitrogen using standard Schlenk techniques. Reaction sol-

vents were puriﬁed and dried using an Innovative Technol-

ogy SPS-400, and degassed before use. No special

precautions were taken to exclude air or moisture during

work-up. The compounds [RuCl(PPh₃)Cp] [36], [RuCl(dp-

pe)Cp^*] [37], [Ru(C„CPh)(PPh₃)Cp] [38], [Ru(C„CC₆H₄-

Me-4)(dppe)Cp^*] [39], Ru(C„CPh)(dppe)Cp^*[20] and

1-trimethylsilylethynylanthracene (puriﬁed by column

chromatography on silica gel, eluting with hexane) [40],

were prepared by the literature methods. Other reagents,

including 4-ethynylnaphthalene (Aldrich) and 4-ethynyltol-

uene (Aldrich) were purchased and used as received.

+

*

NMR spectra were recorded on a Bruker Avance (¹H

400.13 MHz, ¹³C 100.61 MHz, ³¹P 161.98 MHz) or Varian

Mercury (³¹P 161.91 MHz) spectrometers from CDCl₃

solutions and referenced against solvent resonances (¹H,

¹³C) or external H₃PO₄(³¹P). IR spectra were recorded

using a Nicolet Avatar spectrometer from solutions in a

cell ﬁtted with CaF₂windows. Electrospray ionisation mass

spectra were recorded using Thermo Quest Finnigan Trace

MS-Trace GC or WATERS Micromass LCT spectrome-

ters. Samples in dichloromethane (1 mg/mL) were 100

times diluted in either methanol or acetonitrile, and ana-

lysed with source and desolvation temperatures of

120 ꢁC, with cone voltage of 30 V. High resolution spectra

were recorded using a Thermo Electron Finnigan LTQ FT

mass spectrometer with capillary temperature 275 ꢁC and

capillary voltage 100 V. MALDI-TOF spectra were

recorded using an ABI Voyager STR spectrometer, with

a 337 nm desorption laser, linear ﬂight path and 2500 V

UV–Vis-NIR and IR spectroelectrochemical experi-

ments at room temperature were performed with an air-

tight optically transparent thin-layer electrochemical

(OTTLE) cell equipped with a Pt minigrid working elec-

trode (32 wires cm^ꢀ1) and CaF₂windows [30]. The cell

was positioned in the sample compartment of either a Nic-

olet Avatar spectrometer (1 cm^ꢀ1spectral resolution, 16

scans) or a Perkin–Elmer Lambda 900 spectrophotometer.

The controlled-potential electrolyses were carried out with

a homebuilt potentiostat.

8.1. Complex 1a

¹³C NMR (CDCl₃, 100 MHz) for 1a: d 85.2 (Cp); 114.4

(C_b); 116.1 (t, J_CP= 25 Hz, C_a); 123.0 (C4), 127.6 (C3);

3

130.5 (C2); 130.6 (C1); 127.2 (dd, J_CP/⁶J_CPꢁ 5 Hz, C_m);

2

128.4 (C_p); 133.9 (dd, J_CP/⁵J_CPꢁ 5 Hz, C_o); 139.0 (dd,

¹J_CP/⁴J_CPꢁ 11 Hz C_i).

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

3287

8.2. Preparation of [Ru(C„CC₆H₄Me-4)(PPh₃)₂Cp]

(2a)

A suspension of [RuCl(PPh₃)₂Cp] (200 mg, 0.28 mmol),

HC„CC₆H₄Me (32 mg, 0.28 mmol) and NH₄PF₆(45 mg,

0.28 mmol) in MeOH (15 mL) was heated at reﬂux for

20 min to form a bright red solution, 2–3 drops of 1,8-

Diazabicyclo[5.4.0]undec-7-ene (DBU) were added to

form yellow precipitate which was collected by ﬁltration,

washed with cold MeOH, and air-dried to aﬀorded 2a as

a yellow solid (125 mg, 56%). IR(Nujol): m(C„C)

1

2076 cm^ꢀ1. H NMR (CDCl₃, 400 MHz): d 2.30 (s, 3H,

Me), 4.31 (s, 5H, Cp), 6.95–7.52 (m, 34H, Ar). ³¹P{¹H}

NMR (CDCl₃, 162 MHz): d 50.6 (s, PPh₃). ¹³C{¹H}

NMR (CDCl₃, 100 MHz): d 21.2 (Me), 85.1 (Cp); 113.5

(t, J_CP= 25 Hz, C_a); 114.0 (C_b); 127.8 (CH), 128.4,

3

130.3 (CH), 132.3 (C1–C4); 127.2 (dd, J_CP/⁶J_CPꢁ 5 Hz,

2

C_m); 128.3 (C_p); 133.9 (dd, J_CP/⁵J_CPꢁ 5 Hz, C_o); 139.1

1

(dd, J_CP/⁴J_CPꢁ 11 Hz C_i). MALDI-TOF(+)-MS (m/z):

806, [M⁺]. High resolution (m/z): calculated for

RuP₂C₅₀H₄₃[M + H]⁺807.18780; found 807.18698.

8.3. Preparation of [Ru(C„CC₁₀H₇)(PPh₃)₂Cp] (3a)

A suspension of [RuCl(PPh₃)₂Cp] (200 mg, 0.275 mmol),

NH₄PF₆(100 mg, 0.613 mmol) and HC„CC₁₀H₇(50 mg,

0.329 mmol) in methanol (20 mL) was heated at reﬂux for

90 min under a nitrogen atmosphere. The red/orange solu-

tion formed was treated with a methanolic solution of

NaOMe and the yellow precipitate formed collected,

washed with MeOH and hexane and dried to give 3a as

a yellow powder (167 mg, 72%). IR(Nujol): m(C„C)

1

2057 cm^ꢀ1. H NMR (CDCl₃, 200 MHz): d 4.59 (s, 5H,

Cp); 8.58–7.10 (m, 37H, Ph, C₁₀H₇). ³¹P{¹H} NMR

(CDCl₃, 81 MHz): d 51.56 (s, PPh₃). ¹³C{¹H} NMR

(CDCl₃, 100 MHz): d 85.5 (Cp); 112.5 (C_b); 122.6 (t,

J_CP= 25 Hz, C_a);122.8 (CH), 124.8 (CH), 125.3 (CH),

125.8 (CH), 127.4, 127.7 (CH), 128.1 (CH), 128.4, 133.7

3

(CH), 134.6 (C1–C10); 127.3 (dd, J_CP/⁶J_CPꢁ 5 Hz, C_m);

2

128.5 (C_p); 133.9 (dd, J_CP/⁵J_CPꢁ 5 Hz, C_o); 139.0 (dd,

¹J_CP/⁴J_CPꢁ 11 Hz, C_i). ES(+)-MS (m/z): 842, [M⁺]. High

resolution: calculated for RuP₂C₅₃H₄₃[M + H]⁺

843.18780; found 843.19002.

8.4. Preparation of [Ru(C„CC₁₄H₉)(PPh₃)₂Cp] (4a)

A suspension of [RuCl(PPh₃)₂Cp] (200 mg, 0.28 mmol),

Me₃SiC„CC₁₄H₉(75 mg, 0.28 mmol) and KF (30 mg,

0.56 mmol) in methanol (20 mL) was heated and the

orange solution formed allowed to reﬂux for 2 h under a

nitrogen atmosphere. The yellow precipitate formed was

collected and washed with cold MeOH and hexane and

dried to give 4a (230 mg, 93%). IR(Nujol): m(C„C)

1

2042 cm^ꢀ1. H NMR (CDCl₃, 200 MHz): d 4.49 (s, 5H,

Cp); 8.76–7.06 (m, 39H, Ph, C₁₄H₉). ³¹P{¹H} NMR

(CDCl₃, 81 MHz): d 51.24 (s, PPh₃). ¹³C{¹H} NMR

(CDCl₃, 100 MHz): d 85.8 (Cp); 112.7 (C_b); 131.7

3288

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

Table 9

Selected IR vibrational frequencies (as wavenumbers), together with major electronic excitations for [4b]ⁿ⁺and [4-H]ⁿ⁺determined by TD DFT methods

using B3LYP/3-21G^*, with selected experimental data for comparison

Expt 4b

Calc 4b

IR intensity/oscillator

strength

Calc 4-H

IR intensity/oscillator

strength

Vibrational frequencies (IR)/cm^ꢀ1

n = 0

C„C

Ring

2041(s)

1561(vw)

2044

1575

723

27

2081 385

1577 18

n = 1

C„C

Ring

1925(s)

1590(w)

1934

1563

81

12

1994 628

1551 42

Electronic transitions/cm^ꢀ1(Molar absorption coeﬃcient/M^ꢀ1cm^ꢀ1or calculated oscillator strength, <1)

n = 0

HOMO ﬁ LUMO

n = 1

20600(11600) 21100(21100) 0.2147

23310(23300) 0.2817

9120(9100) 0.0021

11390(11400) 0.1248

19840(19800) 0.0442

17480(17500) 0.2714

b-[HOSO ꢀ 1] ﬁ b-LUSO

7800(600)

6500(6500)

9710(9700)

0.0035

0.1163

b-[HOSO] ﬁ b-LUSO a-HOSO ﬁ a-LUSO 10100(1900)

b-[HOSO ꢀ 4] ﬁ b-LUSO

15200(5900)

17900(14000) 16530(16500) 0.0998

15550(15500)^a0.0525

a-HOSO ﬁ a-LUSO

a

b-[HOSO ꢀ 3] ﬁ b-LUSO

0

(t, J_CP= 25 Hz, C_a); 120.3, 123.8 (CH), 124.9 (CH), 126.0,

128.1 (CH), 129.2 (CH), 132.0 (CH), 132.6 (C1–C14); 127.4

(dd, J_CP/CCPꢁ 5 Hz, C_m); 128.6 (C_p); 133.9 (dd, J_CP/

(C1–C4); 127.4, 127.2 (dds, J_CP/CCPꢁ 5 Hz, C_m;m); 128.8

0

(C_p;p); 133.8, 133.2 (dds, J_CP/CCPꢁ 5 Hz, C_o;o); 137.1,

+

0

139.0 (m, C_i;i). ES(+)-MS (m/z): 751, [M + H] . High res-

_CCPꢁ 5 Hz, C_o); 139.0 (dd, J_CP/⁴J_CPꢁ 11 Hz, C_i).

olution: calculated for RuP₂C₄₅H₄₇[M + H]⁺751.21910;

1

ES(+)-MS (m/z): 892, [M⁺]. High resolution: calculated

found 751.21305.

for RuP₂C₅₇H₄₅[M + H]⁺893.20345; found 893.20428.

8.7. Preparation of [Ru(C„CC₁₀H₇)(dppe)Cp^*] (3b)

8.5. Complex 1b

A solution of [RuCl(dppe)Cp^*] (150 mg, 0.22 mmol),

HC„CC₁₀H₇(39 mg, 0.22 mmol) and ammonium hexaﬂu-

orophosphate (37 mg, 0.22 mmol) in stirring MeOH

(10 mL) were heated at reﬂux for 20 min to form a bright

red solution, 2–3 drops of DBU were added to form yellow

precipitate which was collected by ﬁltration, washed with

cold MeOH (3 mL), and air-dried to aﬀord 3b as a yellow

¹³C NMR (CDCl₃, 100 MHz) for 1b: d 10.0 (Me); 92.5

(Cp); 109.6 (C_b); 128.8 (t, J_CP= 25 Hz, C_a); 122.4 (C4),

127.4 (C3); 130.2 (C2); 131.3 (C1); 127.1, 127.4 (dd,

3

J_CP/⁶J_CPꢁ 5 Hz, C_m;m); 128.8, 128.8 (C_p;p); 133.2, 133.7

0

(dd, J_CP/⁵J_CPꢁ 5 Hz, C_o;o); 136.9, 138.9 (m, C_i;i).

2

0

8.6. Preparation of [Ru(C„CC₆H₄Me-4)(dppe)Cp^*] (2b)

solid (97 mg, 55%). IR (Nujol): m(C„C) 2055 cm^ꢀ^{1 1}H

.

NMR (CDCl₃, 400 MHz): d 1.60 (s, 15H, Cp^*); 2.11

(2 · dd, 2H, J_HP= J_HH= 6 Hz, dppe), 2.78 (2 · dd, 2H,

J_HP= J_HH= 6 Hz, dppe); 6.75–7.78 (m, 27H, Ar).

³¹P{¹H} NMR (CDCl₃, 81 MHz): d 82.5 (s, dppe).

¹³C{¹H} NMR (CDCl₃, 100 MHz): d 10.2 (Me), 29.4 (dd,

J_CP/CCPꢁ 23 Hz, CH₂); 92.8 (Cp); 108.4 (C_b); 135.1 (t,

J_CP= 25 Hz, C_a); 122.2 (CH), 125.0 (CH), 125.5 (CH),

127.4, 127.6 (CH), 128.1 (CH), 128.4, 133.5 (CH), 134.3

A suspension of [RuCl(dppe)Cp^*] (100 mg, 0.15 mmol),

HC„CC₆H₄Me (35 mg, 0.30 mmol) and NH₄PF₆(50 mg,

0.3 mmol) in methanol (15 mL) was heated at reﬂux for

1 h under a nitrogen atmosphere to form a bright red solu-

tion, 2–3 drops of NaOMe were added to form yellow pre-

cipitate which was collected by ﬁltration, washed with cold

MeOH followed by hexane, and air-dried to aﬀord 2b as a

yellow solid (60 mg, 54%). IR(Nujol): m(C„C) 2078 cm^ꢀ1

.

(C1–C10); 127.4, 127.5 (dd, J_CP/CCPꢁ 5 Hz, C_m;m); 128.8,

0

¹H NMR (CDCl₃, 400 MHz): d 1.54 (s, 15H, Cp^*), 2.21 (s,

3H, Me), 2.04 (2 · dd, 2H, J_HP= J_HH= 6 Hz, dppe), 2.68

(2 · dd, 2H, J_HP= J_HH= 6 Hz, dppe); 6.83 (d,

J_HH= 8 Hz, 2H, C₆H₄); 6.85 (d, J_HH= 7.6 Hz, 2H,

C₆H₄); 7.17–7.79 (m, Ar 20H). ³¹P{¹H} NMR (CDCl₃,

162 MHz): d 81.1 (s, dppe). ¹³C{¹H} NMR (CDCl₃,

100 MHz): d 10.0 (Me at Cp); 21.1 (Me); 29.5 (dd, J_CP/

_CCPꢁ 23 Hz, CH₂); 92.5 (Cp); 109.2 (C_b); 126.4 (t,

J_CP= 25 Hz, C_a); 128.2 (CH); 128.5; 130.0 (CH); 131.9

128.9 (C_p;p); 133.3, 133.8 (dd, J_CP/CCPꢁ 5 Hz,

0

+

0

C

_o;o);137.1, 139.0 (C_i;i). ES(+)-MS (m/z): 787, [M + H] .

High resolution: calculated for RuP₂C₄₈H₄₇[M + H]⁺

787.21910; found 787.22099.

8.8. Preparation of [Ru(C„CC₁₄H₉)(dppe)Cp^*] (4b)

A suspension of [RuCl(dppe)Cp^*] (100 mg, 0.15 mmol),

Me₃SiC„CC₁₄H₉(45 mg, 0.16 mmol), and KF (25 mg,

M.A. Fox et al. / Journal of Organometallic Chemistry 692 (2007) 3277–3290

3289

0.43 mmol) in methanol (15 mL) was heated at reﬂux for

References

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formed was collected and washed with MeOH and hexane

and dried to give 4b (91 mg, 73%). IR(Nujol): m(C„C)

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2039 cm^ꢀ1. H NMR(CDCl₃, 400 MHz): d 1.70 (s, 15H,

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The barriers in the rotations between the phenyl and the

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Article Doi

Spectroscopic properties and electronic structures of 17-electron half-sandwich ruthenium acetylide complexes, [Ru(C{triple bond, long}CAr)(L2)Cp′]+ (Ar = phenyl, p-tolyl, 1-naphthyl, 9-anthryl; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp*)

DOI: 10.1016/j.jorganchem.2007.03.042

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