The synthesis, structure, reactivity and electrochemical properties of ruthenium complexes featuring cyanoacetylide ligands

Inorganica Chimica Acta 359 (2006) 946–961

www.elsevier.com/locate/ica

The synthesis, structure, reactivity and electrochemical properties

of ruthenium complexes featuring cyanoacetylide ligands

a

´

Richard L. Cordiner , Mark E. Smith , Andrei S. Batsanov , David Albesa-Jove ,

b

a

a,

*

Frantisˇek Hartl , Judith A.K. Howard , Paul J. Low

a

Department of Chemistry, University of Durham, South Road, Durham, DH1 3LE, UK

Vanꢀt Hoﬀ Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands

b

Received 19 May 2005; accepted 13 June 2005

Available online 15 August 2005

Ruthenium and Osmium Chemistry Topical Issue.

Abstract

The complex [Ru(C„CC„N)(dppe)Cp*] (1) is readily obtained (ca. 70%) from the sequential reaction of [Ru(C@CH₂)(dp-

n

pe)Cp*]PF₆with BuLi and phenyl cyanate. The complex behaves as a typical transition metal acetylide upon reaction with tetra-

cyanoethene, aﬀording a metallated pentacyanobutadiene. Complex 1 is a useful metalloligand, and its reactions with [W(thf)(CO)₅],

[RuCl(PPh₃)₂Cp], [RuCl(dppe)Cp*] or cis-[RuCl₂(dppe)₂] all aﬀorded products featuring the M–C„CC„N–M⁰motif, for which

ground state structures indicate a degree of polarisation. Electrochemical and spectroelectrochemical studies reveal moderate inter-

actions between the metal centres in the 35-electron dications [{Cp*(dppe)Ru}(l-C„CC„N){RuL₂Cp⁰}]²⁺(RuL₂Cp⁰=

Ru(PPh₃)₂Cp, Ru(dppe)Cp*).

Keywords: Ruthenium; Spectroelectrochemistry; Cyanide; Cyanocarbon

1. Introduction

ligands such as cyanide [1] and the diethynylaromatics

[2], together with a ground-swell of studies dealing with

metal-supported carbon chains [3] and the coordination

chemistry of polyynes [4].

The continued interest in the fundamentals of the

electron transfer processes, together with the potential

for exploitation of controlled electron transfer processes

in mixed-valence materials for modern materials appli-

cations, and related magnetic and optical phenomena,

has led to intense contemporary research eﬀort in the

synthesis and characterisation of metal complexes fea-

turing two (or more) metal centres bridged by some li-

gand that permits electronic eﬀects to be passed

between them. As a consequence, there has been some-

thing of a renaissance in the chemistry of well-known

In this context, the cyanoacetylide ligand,

[C„CC„N]^ꢀ, is a potentially useful bridging moiety,

being isoelectronic with the diyndiyl ligand and having

obvious relationships with the ubiquitous cyanide li-

gand. Although some [M(C„CC„N)L_n] type com-

plexes have been prepared and structurally

characterised [5], the development of this area has been

handicapped by the paucity of synthetic routes to such

species. Recently, we have prepared a metallocyanoacet-

ylide complex [Ru(C„CC„N)(PPh₃)₂Cp] from sequen-

n

tial reaction of [Ru(C„CH)(PPh₃)₂Cp] with BuLi and

*

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

PhOCN [6]. In the present paper, we detail the syntheses

4737.

and molecular structures of [Ru(C„CC„N)(dppe)Cp*]

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

doi:10.1016/j.ica.2005.06.044

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

947

(1) and a range of metal complexes derived from it, and

compare the structural and electrochemical properties of

cyanoacetylide complexes with cyanide, acetylide and

diyndiyl analogues.

2. Results and discussion

Reaction of the vinylidene complex [Ru(C@CH₂)(dp-

n

pe)Cp*]PF₆with two molar equivalents of BuLi, fol-

lowed by trapping of the nucleophilic acetylide anion

formed in situ [7] with phenyl cyanate, PhOCN, gave

the bright yellow complex 1 in 71% yield after chro-

matographic puriﬁcation and crystallisation (Scheme

1). Complex 1 was readily characterised by spectroscopy

and the structure conﬁrmed by X-ray crystallography.

The expected resonances from the Cp* ligand were ob-

served in both the ¹H (1.51 ppm, C₅Me₅) and ¹³C

(93.09 ppm, C₅Me₅; 8.79 ppm, C₅Me₅) NMR spectra.

The protons of the C₂H₄backbone of the dppe ligand

were detected as unresolved multiplets at d_H2.14 and

2.62 ppm. The carbon atoms of the cyanoacetylide li-

gand C_a„C_bC_c„N were observed in the ¹³C NMR

spectrum, with signals from C_a, C_band C_cat d 150.41

(J_CP= 22.5 Hz), 77.05 and 107.35 ppm, respectively.

The dppe ligand gave rise to a singlet in the ³¹P NMR

spectrum at 80.22 ppm. In the IR spectrum, the cyano-

acetylide ligand gives two strong absorption bands at

Fig. 1. Molecular structure of [Ru(C„CC„N)(dppe)Cp*] (1) pro-

jected on the P1/P2/C1 plane. Here, and forthwith thermal ellipsoids

are drawn at the 50% probability level, H atoms are omitted.

group, and hence a shift of the bonding pattern towards

the ꢁcumulatedꢀ structure 1⁰(Scheme 1).

However, whilst the chemical shift of C_ain 1 (150.41

ppm) is somewhat higher than in ethynyl and butadiynyl

complexes (Table 3), indicating a relative reduction in

the electron density at C_ain the case of 1, cumulated sys-

tems typically give rise to d(C_a) ca. 250–300 ppm [14].

Furthermore, the other bond distances in 1 give no def-

inite support to the increased back-bonding model and

the C_a„C_bbond in 1, although longer than in solid

1994 and 2176 cm^ꢀ1

.

The crystallographically determined molecular struc-

ture of 1 is shown in Fig. 1, and the relevant bond dis-

tances and angles in this and other products are

summarised for comparison in Tables 1 and 2. The Ru

atom has the usual ꢁpiano-stoolꢀ coordination geometry.

The cyanoacetylide ligand is nearly linear (Table 2), and

the structural features of this moiety is in general agree-

ment with that in previously reported X-ray structures of

Co(C„CC„N)₂(PPh₃)Cp (9) [5b], Pt(CN)(C„CC„ N)-

(PPh₃)₂(10) [5c] and [NEt₄]₂[Ni(C„CC„N)₄] (11) [5d]

(Table 1).

The Ru–P distances in 1 are essentially the same as in

those in closely related ethynyl and butadiynyl com-

plexes 12–17 [8–13] (Table 3), but the Ru–C(1) bond

in the cyanoacetylide complex 1 is substantially shorter

than in the ynyl and diynyl systems. This observation

prompts consideration of an increase of Ru ! C back-

bonding interactions in the cyanoacetylide systems

brought about by the electron-withdrawing cyano-

˚

acetylene (1.186(4) A at 131 K [15]), is not substantially

longer than in 14a,b and actually shorter than in the diy-

nyl complexes 16 and 17a,b (Table 3). There is clear evi-

dence for an alternating single/triple bond structure

along the Ru–C„C–C„N chain.

It is of course possible that the eﬀects of these under-

lying electronic factors on the molecular structure are

simply not large enough in comparison with random

experimental errors to be signiﬁcant [16]. X-ray diﬀrac-

tion determines bond lengths as the distances between

the centroids of the atomsꢀ electron clouds, assuming

the latter to be spherically symmetrical and co-centric

with the nuclei. Whilst this approximation is reasonable

in most cases, it is less appropriate in the case of triple

bonded moieties, i.e., in acetylenic, cyano and carbonyl

Me₅

PF₆

1) 2eq. nBuLi

Ru C CH₂

PPh₂

Ru C_αC_βC_γ

PPh₂

N

Ru C C C N

PPh₂

Ph₂P

2) PhOCN

1

1'

Scheme 1.

948

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

Table 1

Selected bond distances in complexes 1–[8][PF₆]₂(this work), Co(C„CC„N)(PPh₃)Cp (9) [5b], Pt(CN)(C„CC„N)(PPh₃)₂(10) [5c] and [NEt₄]₂

[Ni(C„CC„N)₄] (11)[5d]

Ru–C_a

C_a„C_b

C_b–C_c

C„N

N–M^a

Ru–P(1)

Ru–P(2)

Ru–X^b

1

1.961(2)

1.985(3)

1.967(3)

2.060(2)

1.946(3)

1.996(3)

2.003(3)

1.944(3)

1.941(6)

1.942(4)

1.948(4)

1.87(1)

1.221(3)

1.366(3)

1.153(3)

1.162(3)

1.154(4)

1.151(3)

1.162(5)

1.193(4)

1.180(4)

1.154(4)

1.168(7)

1.159(5)

1.160(5)

1.15(1)

2.2704(6)

2.2838(7)

2.2826(7)

2.3623(6)

2.292(1)

2.289(1)

2.302(1)

2.294(1)

2.285(2)

2.285(1)

2.289(1)

2.2637(6)

2.2664(7)

2.2578(8)

2.3327(6)

2.287(1)

2.289(1)

2.288(1)

2.296(1)

2.278(2)

2.277(1)

2.281(1)

1.901(2)

1.900(3)

1.895(3)

1.941(2)

1.896(4)

1.889(3)

1.885(3)

1.923(3)

1.911(7)

1.903(4)

1.905(5)

2

1:3

4

1.220(4)

[1.471(3)]

1.232(5)

1.193(4)

1.180(4)

1.240(4)

1.232(8)

1.230(5)

1.235(5)

1.19(1)

1.367(4)

1.473(3)

1.344(5)

1.354(4)

5

2.169(3)

1.996(3)

2.003(3)

2.044(2)

2.027(5)

2.075(3)

2.086(3)

[6]PF₆

[7]PF₆

[8][PF₆]₂

1.357(4)

1.359(8)

1.348(5)

1.36(1)

1.31(5)

1.37

c

9^d

10

11^d

a

1.96(3)

1.86

1.24(5)

1.21

1.16(6)

1.14

M = W for 5, otherwise M = Ru.

Centroid of the Cp* ligand.

In [7]PF₆Æ 3CH₂Cl₂.

b

c

d

Average.

Table 2

Selected bond angles (ꢁ) in complexes 1–[8][PF₆]₂

Ru–C_a–C_b

C_a–C_b–C_c

172.2(2)

C_b–C_c-N

C_c–N–M

u^crange/average

1

175.1(2)

173.3(2)^a

176.7(2)

116.0(1)

178.0(4)

172.5(3)

168.7(3)

177.4(3)

178.2(5)

173.0(3)

175.7(4)

178.8(2)

4.5–8.6/6.2

5.1–8.5/7.0

4.2–8.8/6.2

7.7–14.2/11.2

2.5–10.3/6.0

4.9–11.5/6.7

2

1:3

4

173.6(3)

118.0(2)

168.3(4)

174.3(4)

178.7(4)

175.1(3)

176.4(6)

178.4(5)

176.2(5)

178.9(3)

172.3(2)

177.9(5)

178.7(4)

174.3(4)

177.8(3)

179.4(6)

179.3(4)

178.2(4)

5

166.9(3)

168.7(3)

172.5(3)

177.3(2)

175.7(5)

177.5(3)

178.6(3)

[6]PF₆

[7]PF₆

6.1–11.5/8.2

4.5–9.0/6.9

3.6–8.5/6.2

b

[8](PF₆)₂

a

Ru–C(1)–N(1) angle.

In [7]PF₆Æ 3CH₂Cl₂.

Tilt of the C–Me bonds out of the Cp plane in Cp*.

b

c

Table 3

Selected bond distances (A) and ¹³C chemical shifts (ppm) in ethynyl and butadiynyl derivatives

˚

Complex

Ru–C_a

C_a„C_b

C_b–C_c

C_c„C_d

Ru–P (average)

d(C_a)

d(C_b)

Ref.

Ru(C„CH)(dppe)Cp* (12a)

2.015(2)

2.029(3)

2.017(2)

2.006(4)

2.015(4)

1.983(2)

1.979(4)

1.988(3)

1.994(4)

1.202(3)

1.186(7)

1.217(3)

1.216(6)

1.186(5)

1.231(2)

1.225(5)

1.227(5)

1.206(5)

2.262

2.274

2.269

2.271

2.312

2.268

2.270

2.251

2.263

2.315

120.58

120.26

113.20

a

92.99

93.01

112.40

[8]

[9]

[10]

[9]

[11]

[12]

[13]

Ru(C„CH)(dppm)Cp* (12b)

Ru(C„C^tBu)(dppm)Cp* (13)

Ru(C„CPh)(dppm)Cp* (14a)

Ru(C„CPh)(PPh₃)₂Cp* (14b)

Ru(C„CC„CH)(dppe)Cp* (15)

Ru(C„CC„CSiMe₃)(dppe)Cp* (16)

Ru(C„CC„CFc)(dppe)Cp (17a)

Ru(C„CC„CFc)(dppm)Cp (17b)

Ru(C„CC„CPh)(PPh₃)₂Cp (18)

a

122.56

124.90

120.06

115.75

114.95

80.47

113.04

91.73

115.84

1.387(6)

1.371(2)

1.373(5)

1.360(5)

1.389(6)

1.193(6)

1.222(3)

1.188(5)

1.214(6)

1.200(6)

a

Not observed or not assigned.

groups, and the resulting systematic errors may run into

hundredths of an Angstrom. Furthermore, because low-

angle X-ray reﬂections depend more on the valence elec-

tron density (which is distorted) and the high-angle

reﬂections on the core electron density (which is not)

the structural result depends on the angular range of

the data available and hence, indirectly, on the temper-

ature of the measurement. For example, the C„C bond

length in diphenylacetylene (tolan) at 123 K is deter-

˚

mined as 1.196(2) A on low-angle and 1.211(2) A on

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

949

˚

high-angle data, cf. 1.215(2) A from gas-phase electron

diﬀraction [17]. These crystallographic issues, together

with results of various computational and PES-based

analyses of metal–acetylide bonding interactions suggest

that it is an over-simpliﬁcation to interpret the molecu-

lar parameters in terms of metal–ligand back-bonding

variations alone, and the shortening of the Ru–C dis-

tance in 1 is due to a combination of electrostatic and

orbital-mixing eﬀects rather than to any appreciable in-

crease in the Ru ! C back-bonding [18].

For purposes of comparison, we also determined the

molecular structure of the corresponding cyanide

complex [Ru(C„N)(dppe)Cp*] (2) (Fig. 2) [19]. The

Ru–C(1) distance in 2 is somewhat longer than in the

cyanoacetylide complex 1, while the Ru–P bonds in 2

are slightly but signiﬁcantly longer than in 1 (on average,

˚

by 0.008 A or 11 e.s.d.ꢀs), indicating that the cyanoacet-

ylide ligand is a more eﬀective donor, or a less eﬀective

acceptor, than cyanide. The g¹(C)-bound cyanide moi-

ety is a good p-accepting ligand, and this accounts for

the diﬀerences in the Ru–CN distances in 2 (1.985(3)

Fig. 3. Molecular structure of compound 3, crystallised as solid

solution with 1.

˚

A) and Ru(C„N)(PPh₃)₂Cp (2.025(2) A) [20]. A signif-

icant portion of the excess electron density introduced

by the supporting ligands in 2 also results in stronger

Ru ! P back-bonding, with the Ru–P distances average

stituent of 3, whilst the position of all other atoms of

both components coincide. The resulting molecular

geometry is very similar to that of pure 1, except for a

slight asymmetry of the Ru–P bond distances, which dif-

˚

2.275 A in 2 against 2.310 A in Ru(CN)(PPh₃)₂Cp.

On one occasion, an attempted synthesis of 1 yielded

a mixture of 1 and the unusual species [Ru(C„

˚

fer by 0.035(1) A in 1:3 against only 0.007(1) A in 1. The

deprotonation and functionalisation of a coordinated

diphosphinoalkane by trapping with an appropriate

nucleophile is not unprecedented [21].

CC„N){Ph₂PCH₂CH(CN)PPh₂}Cp*] (3),

a conse-

quence of accidental over-deprotonation of the [Ru(C@

CH₂)(dppe)Cp*]⁺reagent (Fig. 3). Thus, a crystal

grown for an X-ray diﬀraction study turned out to be

a solid solution between 1 (37%) and 3 (63%), so that

one position at the methylene C(4) atom of the dppe li-

gand is shared by a hydrogen atom of 1 and a CN sub-

Metal acetylide complexes often undergo facile [2+2]

cycloaddition reactions with tetracyanoethene (TCNE)

to aﬀord metallocyclobutene complexes. While these

cycloadducts can be isolated when the pendent metal

group features electron withdrawing carbonyl ligands,

in the case of metal complexes featuring electron donat-

ing substituents the cycloadducts undergo spontaneous

ring-opening to give 1,1,4,4-tetracyano-2-metallo-but-

adienes [22]. It was therefore of some interest to examine

the reactivity of 1, in which the acetylide fragment bears

the electron withdrawing group, with TCNE. Addition

of one molar equivalent of TCNE to a CH₂Cl₂solution

of

1 resulted in the complex [Ru[C{@C(CN)₂}-

C{@C(CN)₂}CN](dppe)Cp*] (4) (Scheme 2). The IR

spectrum of 4 clearly indicated the cyanoacetylide ligand

to be the site of reaction, with the two-band pattern

characteristic of 1 being replaced by m(CN) bands at

2253, 2213 and 2177 cm^ꢀ1and a lower frequency vibra-

tion assigned to the formally C@C portion of the ligand

Me₅

C(CN)₂

C_β

Me₅

C_γN

TCNE

C_α

Ru

Ru C_αC_βC_γ

PPh₂

N

Ph₂P

PPh₂C(CN)₂

4

1

Fig. 2. The asymmetric unit of [Ru(CN)(dppe)Cp*] Æ MeOH (2),

showing the hydrogen bonded methanol solvent molecule.

Scheme 2.

950

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

[m(C@C) 1608 cm^ꢀ1]. The mass spectrum is consistent

with the proposed composition, with an ion centred at

m/z 814 being observed with the correct isotopic pattern

for the [M + H]⁺ion.

ously, in 4 this distortion is much stronger than in 1 or

other complexes (see the tilt angles u in Table 2).

The coordination sphere of the Ru atom in 4 is steri-

cally crowded. The C(73)„N(5) cyano group is con-

strained within the pocket formed by the Cp* methyl

groups and the P(1)Ph₂moiety. This renders the P(1)

and P(2) atoms non-equivalent in both the solid state,

The X-ray structure of 4 reveals the 1,1,3,4,4-penta-

cyanobutadienyl ligand, formed by the usual sequence

of cycloaddition and ring opening, g¹-bonded to the

ruthenium centre through C(1) (Fig. 4). Although hexa-

cyanobutadiene [23] and many of its anion-radical salts

and molecular complexes have been extensively studied,

as well as a number of complexes with 1,1,4,4-tetracy-

ano-3-phenyl-butadien-2-yl ligand [10,22a], to our

knowledge no structure containing a pentacyanobuta-

dienyl ligand (or indeed any substituted derivative of

this material) has been reported previously. The cyano-

carbon ligand adopts a twisted conformation with the

C(71)@C(1)–C(2)@C(61) torsion angle of 74.5(3)ꢁ (cf.

140ꢁ in hexacyanobutadiene [23]). The C(1)@C(71) and

˚

with the Ru–P distances diﬀering by 0.03 A, and also

in solution with the ³¹P NMR spectrum of this complex

being characterised by a pair of doublets (d_P76.90,

56.91, J_PP= 15 Hz). Similar complexes containing the

even bulkier 1,1,4,4-tetracyano-3-phenyl-butadien-2-yl

ligand, [RuR(dppm)Cp*], [RuR(dppe)Cp*] [10] and

[RuR(dppe)Cp] [22a], where R = C{@C(CN)₂}C(Ph)@

C(CN)₂, display an even more pronounced asymmetry

in their solid state and solution structures.

We have previously reported the reactions of

[Ru(C„CC„N)(PPh₃)₂Cp] with [RuCl(PPh₃)₂Cp] and

[FeCl(dppe)Cp] which gave bimetallic complexes

[{Cp(PPh₃)₂Ru}(l-C„CC„N){ML₂Cp}]PF₆[6]. With

a view to exploring the use of metallocyanoacetylide

complexes as ligands in more detail we have investigated

the reactions of 1 with other metal complexes bearing la-

bile ligands (Scheme 3).

˚

C(2)@C(61) bonds (1.368(3) and 1.354(3) A, respec-

tively) have essentially double character, although the

twists around these bonds are signiﬁcant (3.4ꢁ and

14.7ꢁ, respectively).

˚

The Ru–C(1) bond length in 4 (2.060(2) A) lies in the

normal range for Ru–C(sp²) single bonds, and is some

˚

0.1 A longer than the Ru–C(sp) bond in the parent com-

Reaction of 1 with [W(thf)(CO)₅] resulted in the dis-

placement of the labile thf ligand and formation of the

bright yellow crystalline complex [Cp*(dppe)Ru(l-

C„CC„N)W(CO)₅] (5) in moderate yield (35%) after

preparative thin-layer chromatography. The complex

was readily identiﬁed from the solution spectroscopic

data and the structure was conﬁrmed by an X-ray dif-

fraction study (Fig. 5), which revealed the cyanoacety-

lide ligand bridging the Ru and W atoms in a linear

fashion (Table 2). The tungsten atom has a pseudoctahe-

dral coordination environment, the W(CO)₅group dis-

playing the usual three-band m(CO) pattern in the IR

spectrum. Not unexpectedly, the W–CO bond trans to

pound 1. The Ru–P bonds and the Ru–Cp(centroid) dis-

tance in 4 are both much longer than in 1 and the other

cyanoacetylide, cyano, or acetylenic analogues deriva-

tives of the Ru(dppe)Cp* metal fragment (Tables 1

and 3). Both eﬀects are indicative of reduced back-dona-

tion from the metal to these ligands, consistent with the

strongly electron-withdrawing nature of the pentacya-

nobutadienyl ligand. As always in g⁵-Cp* complexes,

the methyl groups are tilted out of the cyclopentadienyl

ring plane, in the direction opposite to the metal. Curi-

˚

the r–donor N(1) atom (1.967(4) A) is shorter than

˚

those in cis positions (2.018(5)–2.048(5) A, average

2.03(1) A). The diﬀerence is also evident in the ¹³C

˚

NMR spectrum (d_C200.67 and 197.21 for the trans

and cis groups, respectively).

The slight contraction of Ru(1)–C(1) and C(2)„C(3)

and elongation of C(1)–C(2) and C(3)„N(1) bonds

compared to 1 are on the border of statistical signiﬁ-

cance and do not alter the essentially single/triple bond-

ing mode along the chain. The m(C„CC„N)

frequencies (2197 and 2069 cm^ꢀ1) in 5 are higher than

those found in 1, possibly due to a combination of kine-

matic eﬀects and depopulation of a cyanocarbon r*-

orbital [24], and it is therefore not appropriate to invoke

a cumulated structure for the cyanacetylide ligand. Sim-

ilar structural variations have been found in the molec-

ular

structures

of

[Ru(C„N)(PPh₃)₂Cp]

and

[Ru(C„NBF₃)(PPh₃)₂Cp] [25]. However, the electron

density at the ruthenium centre in 5 is deﬁnitely reduced

Fig. 4. Molecular structure of [Ru{C{@C(CN)₂}C{@C(CN)₂}Ph}(dp-

pe)Cp*] (4).

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

951

Me₅

W(thf)(CO)₅

Ru C C C N W(CO)₅

PPh₂

Ru C_αC_βC_γ

PPh₂

N

Ph₂P

5

1

cis-RuCl₂(dppe)₂

NH₄PF₆

RuCl(L₂)Cp'

Me₅

NH₄PF₆

[PF₆]₂

Ru(dppe)Cp*

C

PF₆

PPh₂

C

N

Ru C C C N RuL₂Cp'

PPh₂

Ph₂P Ru N C C C Ru(dppe)Cp*

Ph₂P

PPh₂

L₂= dppe, Cp' = Cp* ([6]PF₆)

L = PPh₃, Cp' = Cp ([7]PF₆)

[8][PF₆]₂

Scheme 3.

1

relative to 1, as indicated by elongation of the Ru–P dis-

The H and ¹³C NMR spectra of [6]PF₆and [7]PF₆

contained the expected singlet resonances for the two

Cp* ligands ([6]PF₆: d_H1.37, 1.45; d_C9.79/92.12,

10.02/94.78) or Cp* and Cp ([7]PF₆: d_H1.51, 4.25; d_C

10.03/95.10, 83.44), while the ³¹P NMR spectra con-

tained the expected singlet resonances arising from the

phosphine ligands. In the case of [6]PF₆, the carbon nu-

clei of the cyanocarbon ligand were also observed at

158.11 (C_a), 78.84 (C_b) and 113.85 ppm (C_c), although

the phosphorus coupling to C_awas not resolved. The

m(C„CC„N) bands at 2195, 1987 cm^ꢀ1([6]PF₆) and

2194, 1980 cm^ꢀ1([7]PF₆) may be compared with those

found in the ‘‘metalloligand’’ 1 (2176, 1994 cm^ꢀ1) and

in this context it is interesting to note the much smaller

diﬀerences in m(CN) between PhC„N (2229 cm^ꢀ1) and

˚

tances (by ca. 0.02 A) reﬂecting a decrease of Ru ! P

back-bonding, and by the higher chemical shift of C_a

(a broad resonance at 165.32 ppm).

The demonstration of a degree of polarisation in the

ground-state structure of 5, together with the rich redox

response of diyndiyl complexes featuring [Ru(PPh₃)₂Cp],

[Ru(PMe₃)(PPh₃)Cp] [26] and [Ru(dppe)Cp*] [8] end-

caps prompted us to consider the use of 1 in the con-

struction of analogous cyanoacetylide-bridged species.

The complexes [{Ru(dppe)Cp*}₂(l-C„CC„N)]PF₆

([6]PF₆) and [{Cp*(dppe)Ru}(l-C„CC„N){Ru(PPh₃)₂-

Cp}]PF₆([7]PF₆) were readily prepared from reactions

of 1 with [RuCl(dppe)Cp*] and [RuCl(PPh₃)₂-Cp],

respectively, carried out in the presence of NH₄PF₆.

The products were unambiguously identiﬁed from the

solution spectroscopic data, and were conﬁrmed in each

case by a single-crystal X-ray diﬀraction study.

[Ru(N„CPh)(dppe)Cp*] (2227 cm^ꢀ1

)

[27] or

[Ru(N„CPh)(PPh₃)₂Cp]PF₆(2233 cm^ꢀ1) [6]. Electro-

spray mass spectrometry conﬁrmed the proposed com-

position, with isotopic envelopes corresponding to the

bimetallic cations 6⁺and 7⁺being observed in the posi-

tive ion spectra.

Fig. 6. A plot of the [{Cp*(dppe)Ru}₂(l-C„CC„N)]⁺cation in the

crystal of 6 Æ 1.5CH₂Cl₂, illustrating the disorder of the cyanoacetylide

ligand.

Fig. 5. Molecular structure of [Cp*(dppe)Ru(l-C„CC„N)W(CO)₅]

(5). The disorder of phenyl ring A is not shown.

952

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

The crystal structure of [6]PF₆comprises discrete cat-

ions (Fig. 6) and anions. The X-ray study unexpectedly

revealed the cyanoacetylide bridge to be statically disor-

dered between two orientations of opposite polarity, i.e.,

Ru(1)–C„C–C„N ! Ru(2) and Ru(1) N„C–

C„C–Ru(2), with the terminal N and C atoms overlap-

ping too closely to be resolved. Thus, the parameters

presented in Tables 1 and 2 refer to the superposition

of both orientations of the complex. Consequently, the

Ru–C, Ru–N and Ru–P bonds in [6]⁺are of intermedi-

ate length when compared with 1 and cationic nitrile

complexes such as [Ru(NCPh)(dppe)Cp*]⁺(Ru–N

˚

2.027(5) A; Ru–P 2.315(1) A) [27]. The two Ru(dp-

pe)Cp* moieties in [6]PF₆adopt a staggered orientation

with respect to the bridge, with the torsion angle (Cp*-

centroid)–Ru(1)–Ru(2)–(Cp*-centroid), s, of 79ꢁ.

No such disorder can occur in the structure of [7]PF₆

where the two ruthenium centres are distinguished by

their supporting ligands and the orientation of the

bridge is as expected from the synthetic pathway, i.e.,

[{Cp*(dppe)Ru}C„CC„N{Ru(PPh₃)₂Cp}]PF₆. The

X-ray diﬀraction study was carried out twice, on a sol-

vent-free crystal and a tri-solvate with CH₂Cl₂; the sol-

vent disorder in the latter reducing the accuracy of the

structure determination. In both cases the cation has a

cisoid conformation about the cyanoacetylide bridge,

s = ꢀ17.5ꢁ and 21.5ꢁ, respectively, although the PPh₃li-

gands adopt somewhat diﬀerent orientations in each

structure (Fig. 7).

The bond lengths in the cyanoacetylide moieties diﬀer

only slightly from those in 1 and are practically the same

as in ruthenium-tungsten complex 5, indicating a degree

of polarisation along the bridge (see above). The trans-

fer of electron density from Ru(1) to Ru(2) is also indi-

cated by the Ru–P bond distances: the Ru(1)–P(1) and

Ru(1)–P(2) bonds are longer than in the parent 1 by

Fig. 7. [Cp*(dppe)Ru(l-C„CC„N)Ru(PPh₃)₂Cp]⁺cations in the

crystals of 7 (top) and 7 Æ 3CH₂Cl₂(bottom), projected onto the P1/P2/

C1 planes.

[d_P46.10, 46.83 (2· d, J_PP(trans)= 20 Hz); 76.81, 79.54

(2· d, J_PP(cis)= 15 Hz)] and single-crystal X-ray diﬀrac-

tion (Fig. 8).

˚

up to 0.03 A while the Ru(2)–P(3) and Ru(2)–P(4) dis-

The dication 8²⁺comprises two ligands of 1 whose ter-

minal N atoms are bonded to the octahedral Ru(3) atom.

The entire dication has an approximate C₂symmetry, the

Ru(C₃N)Ru(C₃N)Ru moiety being planar with the aver-

˚

tances (2.317(1) and 2.322(1) A in [7]PF₆, 2.318(2) and

˚

2.329(2) A in [7]PF₆Æ 3CH₂Cl₂) are shorter than in the

cation [Ru(NCPh)(PPh₃)₂Cp]⁺(2.335(1) A), but similar

˚

to those in [Ru(NCC₆H₄NMe₂-4)(PPh₃)₂Cp]⁺(2.323(1)

˚

age atomic deviation of only 0.04 A. The bond distances

A) [27].

in the two cyanoacetylide bridges are practically identi-

cal, and similar to the related bridges in 5, 6⁺and 7⁺

(see above), while the elongation of the Ru(1, 2)–P bond

lengths relative to 1 is consistent with the donor nature of

the metallocyanoacetylide ligands towards the Ru(3)

centre (Table 1).

The coordination of Ru(3) may be explained on the

basis of the trans-inﬂuence of the supporting ligands.

The P(31) and P(41) atoms, which lie trans to each

other, form longer Ru–P bonds (2.381(1) and 2.399(1)

Given the ready displacement of the chloride ligand

from the half-sandwich complexes described above, we

chose to investigate similar reactions of 1 with the diha-

lide complex cis-RuCl₂(dppe)₂, also in the presence of

NH₄PF₆. The trimetallic species cis-[Ru{N„CC„C

Ru(dppe)Cp*}₂(dppe)₂][PF₆]₂([8](PF₆)₂) was readily

formed (Scheme 3), and characterised by the usual spec-

troscopic methods, which included the observation of

both the [M ꢀ PF₆]⁺monocation and the complex ion

[Ru{N„CC„CRu(dppe)Cp*}₂(dppe)₂]²⁺, with the dis-

tinct ions which comprise the isotopic envelope of the

latter displaying the half-amu separation appropriate

for a dication. The cis-geometry at the central metal cen-

tre conﬁrmed by both solution ³¹P NMR spectroscopy

˚

A) than do P(32) and P(42) (both 2.355(1) A) which

are trans to the N atoms. Given the relatively high chem-

ical shifts of P(32) and P(42), the strengthening of the

Ru(3)–P(42) and Ru(3)–P(32) bonds are likely due to a

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

953

Fig. 8. (Top) cis-[Ru{N„CC„CRu(dppe)Cp*}₂(dppe)₂]²⁺dication in the crystal of 8 Æ 7MeOH; (bottom) the same with only the ipso carbons of

the phenyl groups shown, for clarity. Thermal ellipsoids are drawn at the 30% probability level.

greater Ru P r-donation than increased Ru ! P

p-back-bonding. The Ru(3) coordination environment

may be compared with that found in [Ru(dppm)₂(NC-

Me)₂](BF₄)₂, the only other structurally characterised

complex with a cis-RuN₂P₄motif [28] and which dem-

onstrates similar trends in structure.

As a ﬁnal point on the structural characterisation of

the cyanoacetylide complexes reported here, we note

that in all cases the RuC₃NM six-atom chain is essen-

tially linear (Table 2) and the minor deviations which

are apparent, the largest of which occur in molecule 5,

probably result from packing eﬀects [29].

The interest in the potential use of the cyanoacetylide

moiety as a bridge capable of permitting the transfer of

electronic eﬀects between remote metal centres

prompted us to investigate a number of the complexes

described above by electrochemical methods (Table 4).

The cyclic voltamogram (CV) of 1 revealed a single,

reversible oxidation event at 0.69 V. The eﬀect of the

electron-withdrawing CN moiety on the oxidation po-

tential of the metal fragment is clearly evident when this

oxidation potential is compared with that of

[Ru(C„CPh)(dppe)Cp*] (0.25 V) collected under iden-

tical conditions [30]. The redox potentials of 1 and 2

support the conclusions drawn from the crystallographic

Table 4

Electrode potentials of the oxidation of the complexes studied in this

work^a

Complex

E_1/2(1) (V)

E_1/2(2) (V)

1

0.69

0.78

0.25

0.71

0.78

0.96^c

1.10

2

Ru(C„CPh)(dppe)Cp*^d

[6]PF₆

[7]PF₆

1.17^b

1.37^b

[8][PF₆]₂

[Ru(NCPh)(dppe)Cp*]PF₆

e

a

Conditions: Pt disk working microelectrode, CH₂Cl₂/10^ꢀ1

M

Bu₄NPF₆, scan rate 100 mV s^ꢀ1, 293 K, potentials referenced against

SCE via conversion from an internal ferrocene standard (E_1/2Fc/

Fc⁺= 0.46 V vs SCE).

b

Chemically irreversible anodic process (I_c/I_a< 1).

Unresolved oxidation of the two Ru(dppe)Cp* termini.

Ref. [30].

Ref. [27].

c

d

e

954

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

data concerning the relative donor properties of these li-

gands (Table 4). Unsurprisingly, the cis-geometry

around the central metal in [8][PF₆]₂eﬀectively insulates

the Ru(dppe)Cp* fragments from each other, and only a

single oxidation event was detected in the CV of

[8][PF₆]₂at 0.96 V. The peak-to-peak separation of the

anodic and cathodic portions of the wave (0.13 V) is

consistent with the unresolved transfer of two electrons

in a stepwise fashion, with the shift in oxidation poten-

tial relative to 1 no doubt being a consequence of the

dicationic nature of this complex. The oxidation process

associated with the Ru(dppe)₂fragment was not ob-

served in the solvent potential window, as might be ex-

pected for a process which involves further oxidation

of a tetracation.

The considerable interest in polycarbon-bridged

bimetallic complexes [3] prompted us to investigate

complexes [6]PF₆and [7]PF₆, which are isoelectronic

with the diyndiyl complexes [{Ru(PPh₃)₂Cp}₂(l-

C„CC„C)] and [{Ru(dppe)Cp*}₂(l-C„CC„C)], in

more detail. Both [6]PF₆and [7]PF₆gave rise to two

oxidation processes, the ﬁrst of which was chemically

reversible in each case. The ﬁrst oxidation potential of

[6]PF₆, which features two Ru(dppe)Cp* centres, was

found at 0.71 V, only some 20 mV higher than the

oxidation potential of 1 under the same conditions.

The second, chemically irreversible oxidation was

found with a peak potential at 1.17 V, which is com-

parable with the oxidation of [Ru(N„CPh)(dp-

pe)Cp*]PF₆(1.10 V) [27]. The ﬁrst, reversible

oxidation of complex [7]PF₆, which features the less

electron-donating Ru(PPh₃)₂Cp group at the N termi-

nus, was found at 0.78 V, and a second, chemically

irreversible process with a peak potential at 1.37 V.

On the basis of these relative oxidation potentials

the oxidation chemistry of the anodic behaviour of

[6]PF₆and [7]PF₆can be approximately described in

terms of an oxidation which is more heavily weighted

on the C(1) bonded Ru(dppe)Cp* centre, with the sec-

ond oxidation aﬀecting the N(1) bonded metal centre

to a greater extent.

Spectroelectrochemical methods provide a conve-

nient way of gaining spectroscopic data from com-

pounds in a range of electrochemically accessible

oxidation states [32]. The m(C„CC„N) bands in the

IR spectra of complexes 1, [6]PF₆and [7]PF₆provided

a convenient spectroscopic probe for the eﬀect of oxida-

tion on the ligand structure. While on the CV timescale

the oxidation of 1 was fully chemically reversible, 1⁺

proved to be unstable on the longer time scale of

minutes required for the electrolysis in an OTTLE spec-

troelectrochemical cell at room temperature. Conse-

quently, infra-red spectroelectrochemical experiments

with 1 were carried out in an OTTLE cell at ꢀ90 ꢁC

in butyronitrile solution. In this solvent at room temper-

ature, 1 displays two bands at 2178 and 1994 cm^ꢀ1; at

ꢀ90 ꢁC, the lower-frequency band splits into bands at

2010 and 1996 cm^ꢀ1. Oxidation to 1⁺caused these sig-

nature bands associated with 1 to collapse and be re-

placed by new bands at 2188 and 2163, and 1963

cm^ꢀ1. It should be stressed, however, that the shifts

are relatively small: the change in vibrational frequen-

cies between the limiting structures C„N and C@N is

as much as 600 cm^ꢀ1and the same applies to the varia-

tion in the formal valence descriptions of C„C and

C@C bonds. It is clear from the variation in IR data re-

ported for the complexes 1, 5, [6]PF₆, [7]PF₆and

[8][PF₆]₂that both C„N and C„C portions of the

cyanoacetylide ligand are sensitive to electronic changes

in the supporting metal fragments, as a consequence of

changes in metal-to-ligand p-back-bonding, remixing

of p(CCCN) and p*(CCCN) orbitals (polarisation), or

kinematic eﬀects. Obviously, whilst kinematic eﬀects

are unlikely to be sensitive to oxidation processes, the

electronic factors may be expected to be primarily

responsible for changes in the IR signature of the CCCN

moiety upon oxidation, and in turn points toward a sig-

niﬁcant degree of delocalisation between the metal cen-

tre and the cyanocarbon ligand.

The UV–Vis–NIR spectrum of 1 features a single

absorption band near 300 nm (33300 cm^ꢀ1), which

was not aﬀected by oxidation to 1⁺and is therefore

likely associated with transitions centred on the phenyl

groups of the supporting phosphine ligands. During oxi-

dation of 1 to 1⁺a new weak band arose at 500 nm

(20000 cm^ꢀ1), which might be approximated as a

LMCT band. The NIR region was transparent in both

1 and 1⁺.

The ﬁrst oxidation of each of the bimetallic com-

plexes [6]PF₆and [7]PF₆proved to be reversible at room

temperature. Complex [6]PF₆exhibits strong

m(C„CC„N) bands at 2197 and 1988 cm^ꢀ1, which dis-

appear during oxidation, being replaced by bands at

2056 and 1856 cm^ꢀ1, accompanied by two further bands

of low intensity at 2106 and 1940 cm^ꢀ1. The thin-layer

cyclic voltammogram collected in the IR spectroelectro-

chemical cell is completely chemically reversible, and the

However, the task of evaluating interactions between

metal centres in bimetallic complexes based on compar-

isons of redox potentials with model complexes can be

complicated by diﬀerences in the underlying electronic

structures of the compound of interest and the models

and the possible misinterpretations that might arise

from comparisons of, for example, metal centred redox

events with redox processes that involve more exten-

sively delocalised orbitals. Solvation eﬀects can also al-

ter E^ꢁvalues, and it is important to bear in mind that

direct comparisons of electrode potentials of bimetallic

complexes with those of model comparisons are only va-

lid if the relative solvation energies of the compounds in

their various oxidation states do not diﬀer signiﬁcantly

[31].

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

955

bands at 2073 and 1868 cm^ꢀ1being formed, associated

with the ﬁrst oxidation product, 7²⁺(Fig. 9). The large

shift in the frequency of the ligand vibrations from those

in [6]PF₆and [7]PF₆to those in the associated 35-elec-

tron oxidation products (6²⁺ca. 140 cm^ꢀ1; 7²⁺ca.

ꢀ120 cm^ꢀ1) indicates that the oxidation event is not

purely metal centred, but rather the redox active orbital

has a considerable degree of cyanoacetylide character.

The electronic spectra of [6]PF₆and [7]PF₆, and the

products of one-electron oxidation, were also collected

using spectroelectrochemical methods [33]. The spectra

of the parent species (i.e., [6]PF₆and [7]PF₆) were, as

might be expected, similar, with only a broad, relatively

featureless absorption band tailing from the UV into the

visible region being apparent. Upon oxidation of cation

6⁺, a new series of bands grew in the red and NIR re-

gions of the spectrum, tailing into the IR region, and

while the bands in the NIR region were heavily over-

lapped, the absorption envelope could be well described

as a sum of three Gaussian-shaped curves (Fig. 10(a),

Table 5). The recovery of the original spectrum after

back-reduction clearly indicates that these bands are

associated with the 35-electron species. Oxidation of

the cation 7⁺also gave a set of overlapping bands in

the NIR region, which were successfully deconvoluted

into three Gaussian-shaped curves (Fig. 10(b), Table 5).

The three NIR bands observed in the electronic spec-

tra of both 6²⁺and 7²⁺are consistent with the three

separate electronic transitions that can arise from the

three ﬁlled d_porbitals in a d⁶metal centre [i.e., Ru(II)]

to the hole in a d⁵site [i.e., Ru(III)]. As noted by

Meyer and colleagues in a recent review [34], the obser-

vation of these three formally forbidden transitions with

A

2200

2100

2000

1900

1800

1700

Wavenumbers (cm^-1)

Fig. 9. The IR spectroelectrochemical response of [7]PF₆during one-

electron oxidation.

cycle of oxidation to give the 35-electron, dicationic spe-

cies 6²⁺and back-reduction to 6⁺could be carried out

several times with no noticeable loss in absorption inten-

sity. The low-intensity bands are therefore not attrib-

uted to a decomposition product, and most likely arise

from a second, minor isomer in solution. For example,

the cisoid and transoid forms of [{Ru(PPh₃)₂Cp}₂(l-

C„CC„C)] display very diﬀerent m(CC) patterns in

their IR spectra [13]. Further oxidation of 6²⁺to the

34-electron di-oxidised species 6³⁺gave new bands at

2178, 2160(sh) and 2015 cm^ꢀ1, but this oxidation step

was chemically irreversible, with back-reduction giving

a new (unidentiﬁed) species with IR absorption bands

at 2209w and 2032 cm^ꢀ1

.

In the case of [7]PF₆, the IR absorption bands at 2200

and 1990 cm^ꢀ1collapsed upon oxidation, with new

7000

3000

a

6000

5000

4000

3000

2000

1000

0

b

2500

2000

1500

1000

500

0

13000

11000

9000

7000

5000

3000

13000

11000

9000

7000

5000

3000

wavelength (cm^-1)

Fig. 10. The deconvoluted NIR band envelope of (a) [6]²⁺and (b) [7]²⁺

.

Table 5

The NIR band shape parameters and derived electronic coupling terms associated with the one-electron oxidation products 6²⁺and 7²⁺

6²⁺

7²⁺

Band 1

Band 2

Band 3

Band 1

Band 2

Band 3

ꢀm_maxðcm^ꢀ1

Þ

6610

2600

3630

7.68

670

8710

1430

1810

7.68

400

10322

820

2750

7.68

410

6150

870

1070

7.71

200

7990

3200

1710

7.71

550

8330

3000

4000

7.71

840

e_max(M^ꢀ1cm^ꢀ1

)

Dꢀm₁₌₂ðcm^ꢀ1

Þ

˚

d (A)

H_ab

956

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

signiﬁcant intensity requires a combination of low-

symmetry ligand ﬁelds about the metal centres, spin-

orbit coupling (albeit a small eﬀect in lighter ﬁrst and

second row transition metal elements contributing to

the small separation in energy of the three transitions

observed here) and mixing of the metal-based orbitals

with the ligand p and p* orbitals. The IR spectroelectro-

chemical results clearly indicate a signiﬁcant contri-

bution from the ligand to the redox active orbitals in

keeping with these suggestions.

denced by the pronounced shifts in the m(C„CC„N)

bands compared with the 36-electron precursors, and

the observation of multiple NIR transitions) make it

clear that the cyanoacetylide moiety allows an apprecia-

ble degree of interaction between metal centres located

at the C and N termini. We are presently pursuing a rig-

orous analysis of the solvent dependence of the elec-

tronic spectra of mixed-valence systems such as 6²⁺

and 7²⁺, and DFT-based computational studies in order

to probe this eﬀect in greater detail.

The relative band energies, intensities and half-height

bandwidths are summarised in Table 5, together with

the coupling parameter H_abderived from Hushꢀs expres-

4. Experimental

sion (1)

pﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ

4.1. General conditions

ꢀ

0.0205 m_maxe_maxDm₁₌₂

H_ab

¼

;

ð1Þ

d

All reactions were carried out in dry solvents, puriﬁed

using an Innovative Technology Inc. solvent puriﬁcation

system, in oven dried glassware under an atmosphere of

nitrogen as a routine precaution. The complexes

[RuCl(dppe)Cp*] [8], [Ru(C@CH₂)(dppe)Cp*]PF₆[8],

[RuCl(PPh₃)₂Cp] [38], [Ru(CN)(dppe)Cp*] [19] and

[W(thf)(CO)₅] [24a] were prepared as described previ-

ously. Commercial tetracyanoethene was sublimed prior

to use, other reagents were used as received. Infrared

spectra were recorded from nujol mulls on NaCl plates

using a Nicolet Avatar spectrometer. NMR spectra were

recorded from solutions in CDCl₃unless indicated

otherwise, and referenced against residual solvent reso-

nances (¹H, ¹³C) or external H₃PO₄(³¹P).

where d is the electron transfer distance, approximated as

the metal–metal separation. Although originally derived

for weakly coupled systems, Eq. (1) has been shown to

also hold true for more strongly coupled systems, and

therefore is appropriate for estimation of H_abin the pres-

ent case [35]. However, given the ligand involvement in

the oxidation event, the electron transfer distance is over-

estimated in this manner and, therefore, the calculated

H_abterms presented here represent a lower limit [36].

In order to contextualise these lower estimates, the

coupling constant H_abgiven in Table 5 may be com-

pared with those obtained from other complexes con-

taining similar metal fragments and more common

bridging ligands. For example, the highly (or fully) delo-

calised 35-electron systems featuring C₄bridges such as

[{Ru(PPh₃)₂Cp}₂(l-C₄)]⁺and [{Ru(dppe)Cp*}₂(l-C₄)]⁺

4.2. Cyclic voltammetry

give rise to intense NIR bands and coupling terms (cal-

Conventional cyclic voltammograms were recorded

with a PAR EG&G Model 283 potentiostat, using an

airtight single-compartment cell placed in a Faraday

cage. The working electrode was a Pt disk (0.42 mm²

apparent surface area), polished with a 0.25 lm dia-

mond paste between the scans. Coiled Pt and Ag wires

served as an auxiliary and pseudoreference electrode,

respectively. The concentration of the analyte was typi-

ꢀm_max

culated from H_ab

¼

) [35] of approximately 5000–

2

5500 cm^ꢀ1. If treated with Eq. (1), the C₄systems yield

coupling terms of ca. 1500 cm^ꢀ1. The 35-electron cya-

nide-bridged species [{Cp(PPh₃)₂Ru}(l-CN){Fe(dp-

pe)Cp}]²⁺exhibits an apparently single transition at

690 nm and, assuming this to be the MMCT band, from

which a coupling term of H_ab= 2250 cm^ꢀ1can be ex-

tracted [24a]. For the mixed valence complex

[{Cp(PPh₃)Ru}(l-CN){Ru(NH₃)₅}]³⁺a single, highly

solvatochromic NIR band is observed with H_abca.

2000 cm^ꢀ1[37].

cally 10^ꢀ3mol dm^ꢀ3in CH₂Cl₂containing 10^ꢀ1

M

NBu₄PF₆as supporting electrolyte. Ferrocene (Fc) was

used as the internal standard to provide potentials

against SCE (E_1/2(Fc/Fc⁺) = 0.46 V vs SCE) [33] for

the determination of electrode potentials and compari-

son of peak-to-peak potential diﬀerences. Conversion

of the Fc/Fc⁺potential scale to other reference systems

can be found elsewhere [39].

3. Conclusions

The cyanoacetylide motif is a useful synthetic tool in

the assembly of bimetallic complexes. The combination

of spectroscopic and structural data suggests a degree

of polarisation in the ground-state structures of bimetal-

lic complexes such as 5, [6]PF₆, [7]PF₆and [8][PF₆]₂.

These data, taken with the signiﬁcant metal–ligand mix-

ing in the mixed-valence complexes 6²⁺and 7²⁺(evi-

4.3. Infrared spectroelectrochemical studies

Infrared spectroelectrochemical experiments at low

temperatures were performed with a cryostated optically

transparent thin-layer electrochemical (OTTLE) cell

equipped with CaF₂windows and a Pt minigrid working

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

957

electrode (32 wires per cm) [41]. The electrolyses at room

temperature were conducted with another home-made

demountable OTTLE cell [42]. The solutions were typi-

acetylide had disappeared the solvent was removed. The

resultant dark blue/green residue was crystallised by

slow diﬀusion of methanol into a CH₂Cl₂solution to

yield the product 4 (Scheme 1) as dark blue crystals

(72 mg, 0.092 mmol, 63%). ¹H NMR (CD₂Cl₂): d

6.56–7.96 (m, 20H, Ph); 2.83–5.58 (m, 4 H, dppe); 1.47

(s, 15H, Cp*); 1.22 (s, 15H, Cp*). ³¹P NMR (CDCl₃):

d 76.90, 56.91 (2· d, J_PP= 15 Hz). ES(+)-MS (m/z):

814 [M + H]⁺. IR(CH₂Cl₂): m(C„N) 2253m, 2213br,

cally 3 · 10^ꢀ3

M

in the supporting electrolyte

(NBu₄PF₆) and 10^ꢀ3M in the analyte. The working

electrode potential of the spectroelectrochemical cell

was controlled with a PA4 potentiostat (EKOM, Czech

Republic). The IR spectra were recorded with Bio-Rad

FTS-7 and Bruker Vertex 70 FT-IR spectrometers (16

scans, 1–2 cm^ꢀ1spectral resolution).

2177w cm^ꢀ1, m(C@C) 1608 cm^ꢀ1

.

4.4. UV–Vis–NIR spectroelectrochemical studies

4.7. Preparation of

[{Ru(dppe)Cp*}(C„CC„N){W(CO)₅}] (5)

UV–Vis–NIR spectroelectrochemical experiments

were carried out in an OTTLE cell similar to that de-

scribed previously [33], from solutions in CH₂Cl₂con-

taining 10^ꢀ1M NBu₄BF₄as supporting electrolyte

using a Varian Cary 5 spectrophotometer. Typically

analyte concentrations were 10^ꢀ1mM.

A Schlenk tube was charged with [W(CO)₆] (51 mg,

0.146 mmol) in thf (30 mL). The solution was irradiated

for 90 minutes with a medium pressure Hg lamp during

which time it became a deep yellow colour. Compound 1

(100 mg, 0.146 mmol) was added and the solution was

stirred for a further 10 minutes before the solvent was

removed. The yellow residue was puriﬁed by passage

up a preparative TLC plate using 3:7 acetone:hexane.

The yellow band was collected, dried and recrystallised

from slow diﬀusion of methanol into a CH₂Cl₂solution

4.5. Preparation of [Ru(C„CC„N)(dppe)Cp*] (1)

A Schlenk ﬂask was charged with [Ru(@C@CH₂)(dp-

pe)Cp*][PF₆] (1.0 g, 1.24 mmol) and thf and cooled to

ꢀ78 ꢁC. To the resulting yellow solution was added

dropwise ⁿBuLi (1.65 mL, 2.64 mmol of a 1.6 M solution

in hexanes). The colour changed from bright yellow to a

paler yellow and the solution was stirred for 1 h at ꢀ78

ꢁC. The solution was then allowed to warm to ca. ꢀ20

ꢁC before being cooled to ꢀ78 ꢁC and PhOCN (1.0

mL, 8.75 mmol) added dropwise. The yellow solution

was stirred a further 1 h at ꢀ78 ꢁC and then allowed

to warm slowly to r.t. The solvent was removed and

the resulting dark yellow/brown residue extracted with

CH₂Cl₂and puriﬁed by passage down a silica column

eluting with acetone/hexane, 3/7. The yellow band was

collected and the solvent removed. Slow evaporation

of a CH₂Cl₂/MeOH solution yielded crystals of 1 (600

mg, 71%). ¹H NMR (CDCl₃): d 1.51 (s, 15H, Cp*);

2.14 (m, 2H, dppe); 2.62 (m, 2H, dppe); 7.61–7.16 (m,

1

to give bright yellow crystals (52 mg, 35%). H NMR

(CDCl₃): d 7.17–7.58 (m, 20H, Ph); 2.64 (m, 2H, dppe);

2.16 (m, 2H, dppe); 1.53 (s, 15H, Cp*). ³¹P NMR

(CDCl₃): 79.68 (dppe). ¹³C NMR (CDCl₃): d 200.67

(s, trans-CO); 197.21 (s, cis-CO, J_WC= 65 Hz); 165.32

(br, C_a); 136.84–128.14 (m, Ph); 112.08 (s, CN); 95.06

(s, C₅Me₅); 77.72 (s, C_b); 29.78–29.40 (m, dppe); 10.12

(s, C₅Me₅). ES(+)-MS (m/z): 1010 [M + H]⁺; 686

[Ru(C₃N)(dppe)Cp*+H]⁺. IR (CH₂Cl₂): m(C„CC„N)

2192m, 2071m cm^ꢀ1; m(CO) 1977m, 1929s, 1882m

cm^ꢀ1. IR (cyclohexane): m(C„CC„N) 2197w, 2069w

cm^ꢀ1; m(CO) 1990w, 1932s, 1904m cm^ꢀ1

.

4.8. Preparation of

[{Ru(dppe)Cp*}₂(C„CC„N)](PF₆) ([6]PF₆)

20H, Ph). ³¹C{H} NMR (CDCl₃):

d

150.41 (t,

A ﬂask was charged with 1 (100 mg, 0.146 mmol),

[RuCl(dppe)Cp*] (98 mg, 0.146 mmol), NH₄PF₆(95

mg, 0.583 mmol) and ﬁnally MeOH (20 mL). The reac-

tion mixture was heated at reﬂux for 90 min, during

which time the solution became bright yellow and a yel-

low precipitate formed. The solution was allowed to

cool, and the bright yellow solid collected by ﬁltration,

washed with cold methanol and air-dried to give

J_CP= 22.5 Hz, C_a); 126.67–136.14 (m, Ph); 107.35 (s,

CN), 93.09 (s, C₅Me₅); 77.05 (s, C_b); 28.06–28.43 (m,

P–C–C–P); 8.79 (s, C₅Me₅). ³¹P{H} NMR (CDCl₃): d

80.22 (s, dppe). ES(+)-MS (m/z) 686.2 [M + H]⁺. IR

(CH₂Cl₂): m(C„CC„N) 2176, 1994 cm^ꢀ1

.

4.6. Reaction of 1 with TCNE

1

[6]PF₆(157 mg, 74%). H NMR (CDCl₃): d 7.48–7.07

A ﬂask was charged with 1 (100 mg, 0.146 mmol) and

the solid dissolved in dry, degassed CH₂Cl₂(10 mL). To

the resulting yellow solution, TCNE (19 mg, 0.146

mmol) was added upon which the solution rapidly ac-

quired a dark green and ﬁnally a deep blue colour.

The reaction was followed by infra-red spectroscopy

and when the m(C„CC„N) bands of the parent cyano-

(m, 40H, Ph); 2.23, 2.17 (2· br, 8H, 2· dppe); 1.45,

1.37 (2· s, 30H, 2 xCp*). ¹³C{H} NMR (CDCl₃): d

158.11 (br, C_a); 136.41–127.78 (m, Ph); 113.85 (s, CN);

94.78 (s, C₅Me₅), 92.12 (C₅Me₅), 78.84 (s, C_b); 29.51–

29.15 (m, dppe); 28.64–28.28 (m, dppe); 10.02 (s,

C₅Me₅); 9.79 (s, C₅Me₅). ³¹P{H} NMR (CDCl₃): d

79.58 (s, dppe); 75.64 (s, dppe); ꢀ143.21 (ht, J_PF= 713

958

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

Hz, [PF₆]^ꢀ). ES(+)-MS (m/z) 1319 [{Ru(dppe)Cp*}₂-

(C„CC„N)]⁺; 635 [Ru(dppe)Cp*]⁺. IR(CH₂Cl₂):

free crystals, while slow diﬀusion of hexane into a CH₂Cl₂

solution yielded [7]PF₆Æ 3CH₂Cl₂.

m(C„CC„N) 2195, 1987 cm^ꢀ1

.

The X-ray diﬀraction data were collected on Bruker

3-cicle diﬀractometers equipped with CCD area detec-

tors SMART APEX (for 2 Æ MeOH and 4), SMART

6K (for 1:3, 5, 7, [8]PF₆Æ 7MeOH) or SMART 1K (for

[6]PF₆Æ 1.5CH₂Cl₂, [7]PF₆Æ 3CH₂Cl₂), using graphite-

monochromated Mo Ka radiation from a 60W micro-

focus Bede Microsource^ꢂwith glass polycapillary optics

(2 Æ MeOH and 4) or a sealed tube. The crystals were

cooled to T = 120 K using Cryostream (Oxford cryosys-

tem) open ﬂow N₂cryostats, except for [8]PF₆Æ 7MeOH

which was studied at 200 K because the crystals (air-

unstable at room temperature) cracked on further cool-

ing, probably due to a phase transition.

4.9. Preparation of

[{Ru(dppe)Cp*}(C„CC„N){Ru(PPh₃)₂Cp}](PF₆)

([7]PF₆)

An analogous procedure using 1 (100 mg, 0.146

mmol), [RuCl(PPh₃)₂Cp] (106 mg, 0.146 mmol),

NH₄PF₆(95 mg, 0.583 mmol) resulted in a clear yellow

solution. This was allowed to cool and the solvent was

removed. The yellow residue was then extracted with

CH₂Cl₂, ﬁltered and the solvent was removed to give

1

[7]PF₆as a yellow powder (209 mg, 94%). H NMR

(CDCl₃): d 7.02–7.50 (m, 50H, Ph); 4.25 (s, 5H, Cp);

2.54, 2.18 (2· m. 4H, dppe); 1.51 (s, 15H, Cp*).

¹³C{H} NMR (CDCl₃): d 136.69–127.93 (m, Ph);

95.10 (s, C₅Me₅), 83.44 (s, Cp); 29.80–29.43 (m, dppe);

10.03 (s, C₅Me₅). ³¹P{H} NMR (CDCl₃) : d 79.34 (s,

dppe); 42.12 (s, PPh₃); ꢀ143.20 (ht, J_PF= 713 Hz

[PF₆]^ꢀ). ES(+)-MS (m/z) 1376 [{Ru(dppe)Cp*}(C„

CC„N){Ru(PPh₃)₂Cp}]⁺. IR (CH₂Cl₂): m(C„CC„N)

Reﬂection intensities were integrated using ^SAINTsoft-

ware [43] and corrected for absorption by numerical

integration based on crystal face indexing (1, 1:3,

[7]PF₆) or by semi-empirical method [44] based on Laue

equivalents (2 Æ MeOH, 5, [7]PF₆Æ 3CH₂Cl₂, [8]PF₆Æ 7-

MeOH). The structures were solved by direct methods

and reﬁned by full-matrix least-squares against F²of

all data using ^SHELXTLsoftware [45]. All non-hydrogen

atoms where reﬁned in anisotropic approximation (ex-

cept minor positions of the disordered atoms) with

hydrogen atoms treated in riding model (methyl groups

as rigid bodies). In [8]PF₆Æ 7MeOH, all phenyl groups

were reﬁned as rigid bodies, PF₆^ꢀanions were restrained

to octahedral symmetry.

2194, 1980 cm^ꢀ1

.

4.10. Preparation of cis-

[Ru{Ru(C„CC„N)(dppe)Cp*}₂(dppe)₂][PF₆]₂

([8][PF₆]₂)

A Schlenk ﬂask was charged with 1 (104 mg, 0.152

mmol), [RuCl₂(dppe)₂] (74 mg, 0.076 mmol) and NH₄PF₆

(99 mg, 0.607 mmol). The mixture was suspended in

MeOH (15 mL) and heated to reﬂux. After two hours at

reﬂux a pale yellow suspension had formed. The reaction

was allowed to cool and the solvent removed. The result-

ing yellow residue was extracted with CH₂Cl₂and ﬁltered.

The solvent was then removed to aﬀord [8][PF₆]₂a pale

yellow powder (143 mg, 74%). ¹H NMR (CDCl₃): d

6.15–8.05 (m, 80H, Ph); 1.57 (s, 15H, Cp*);1.54 (s, 15H,

Cp*). ³¹P NMR (CDCl₃): d 46.10, 46.83 (2· d,

J_PP(trans)= 20 Hz; 76.81, 79.54, 2· d, J_PP(cis)= 15 Hz);

32.48 (s, Ru(dppe)Cp*); ꢀ143.01 (ht, J_PF= 713 Hz,

In structure 5, one phenyl ring shows librational dis-

order (rationalised as two positions with equal probabil-

ity). In [6]PF₆Æ 1.5CH₂Cl₂, the packing of cations

creates large but enclosed voids, around crystallographic

inversion centres (0,0,0), (1/2,1/2,1/2), etc. Each void is

ꢀ

occupied by two (inversion-related) PF₆anions and

three CH₂Cl₂molecules, one of which lies near the

inversion centre and is disordered between two positions

related by it, and the other two occupy (inversion-

related) general positions and show minor disorder of

one of the Cl atoms. In the structure of [7]PF₆Æ 3CH₂Cl₂

the packing of cations leaves inﬁnite channels (parallel

ꢀ

to the x axis) occupied by PF₆anions alternating with

[PF₆]^ꢀ). ES(+)-MS (m/z): 2411 ½M þ PF ^ꢀꢂ^þ1135

groups of three CH₂Cl₂molecules. The anion shows

librational disorder with the F(1) as a pivotal atom;

which was rationalised as two orientations occupied

with 3:2 probability ratio. Two of the three independent

CH₂Cl₂molecules have CH₂groups disordered by libra-

tion around Cl atoms.

6

[M]²⁺

;

686 [Ru(C₃N)(dppe)Cp*+H]⁺. IR(CH₂Cl₂):

m(C„CC„N) 2178, 1966 cm^ꢀ1

.

5. X-ray crystallography

The structure of [8]PF₆Æ 7MeOH contains layers of

cations, parallel to the (11ꢀ1) plane, alternating with

mixed anions/methanol layers. Such packing easily ex-

plains the instability of the crystals in air, and is also

responsible for the chaotic disorder of the methanol

molecules of crystallisation, which were very diﬃcult

to rationalise. The ﬁnal reﬁnement of the structure

included 10 partially occupied methanol sites compris-

X-ray quality crystals of 1 and 1:3 were obtained by

slow evaporation of a CH₂Cl₂/MeOH solution, those of

2 Æ MeOH, 4, 5, [6]PF₆Æ 1.5CH₂Cl₂and [8]PF₆Æ 7MeOH

by slow diﬀusion of methanol into a CH₂Cl₂solution.

In the case of 2 Æ MeOH a small amount of acetone was

found to help the formation of high quality crystals. Crys-

tallisation of [7]PF₆from acetone and EtOH gave solvent-

Table 6

Crystal data and experimental parameters for

C₃₉H₃₉NP₂Ru (1), C₃₇H₃₉NP₂Ru (2), C₄₀H₃₈N₂P₂Ru (3), C₄₅H₃₉N₅P₂Ru (4), C₄₄H₃₉NO₅P₂RuW (5), [C₇₅H₇₈NP₄Ru₂]PF₆([6]PF₆),

[C₈₀H₇₄NP₄Ru₂]PF₆([7]PF₆), [C₁₃₀H₁₂₆N₂P₈Ru₃][PF₆]₂([8][PF₆]₂)

Compound

1

2 Æ MeOH

1_0.37Æ 3_0.63

4

5

[7]PF₆Æ 1.5 CH₂Cl₂

[7]PF₆

[7]PF₆Æ 3CH₂Cl₂

[8](PF₆)₂Æ 7MeOH

CCDC deposition number

Formula weight

T (K)

Crystal system

Space group (No.)

271415

684.72

120(2)

orthorhombic

Pbca (61)

19.121(3)

17.516(5)

19.594(4)

90

6562(3)

8

1.386

271416

692.74

120(2)

monoclinic

P2₁/c (14)

14.264(2)

12.143(2)

19.665(2)

90

99.34(1)

90

3361.0(7)

4

271417

700.35

120(2)

orthorhombic

Pbcn (60)

17.260(3)

18.897(3)

20.810(3)

90

6787(2)

8

1.371

271418

812.82

120(2)

monoclinic

P2₁/c (14)

13.657(2)

12.626(2)

21.838(3)

90

93.32(1)

90

3759(1)

4

271419

1008.62

120(2)

orthorhombic

Pbca (61)

22.727(2)

11.747(1)

30.664(3)

90

8186(1)

8

1.637

271420

1591.76

120(2)

271421

1520.39

120(2)

monoclinic

Pn (7)^a

12.982(3)

17.707(4)

15.540(3)

90

107.00(2)

90

3416(1)

2

271422

1775.17

120(2)

monoclinic

P2₁/n (14)^a

13.342(2)

43.508(8)

14.392(3)

90

104.27(1)

90

8096(3)

4

271423

2781.53

200(2)

triclinic

ꢀ

P1 ð2Þ

˚

a (A)

13.984(2)

15.455(2)

17.815(2)

87.35(1)

71.54(1)

83.49(1)

3628.2(7)

2

17.505(1)

17.590(1)

23.514(1)

104.21(1)

99.48(1)

95.29(1)

6856.3(6)

2

˚

b (A)

˚

c (A)

a (ꢁ)

b (ꢁ)

c (ꢁ)

3

˚

V (A )

Z

D_calc(g cm^ꢀ3

)

1.369

0.59

1.436

0.54

1.454

0.70

1.478

0.62

1.456

0.73

1.347

0.51

l (mm^ꢀ1

)

0.60

0.59

3.30

Reﬂections total

Reﬂections unique

R_int

72508

7532

0.049

27301

10206

0.040

87305

9904

0.041

28618

11362

0.027

70053

12480

0.063

42062

19680

0.054

46012

19567

0.043

42417

17310

0.040

70291

32578

0.039

Reﬂections [I > 2r(I)]

Variables

5991

398

8444

398

8137

417

9135

593

8673

445

13375

879

17458

857

13903

919

21496

1320

R(F) [I > 2r(I)]

wR(F²) (all data)

0.027

0.065

0.049

0.116

0.043

0.105

0.037

0.090

0.037

0.085

0.049

0.106

0.038

0.088

0.079

0.162

0.054

0.181

a

Non-standard setting.

960

R.L. Cordiner et al. / Inorganica Chimica Acta 359 (2006) 946–961

(l) G.A. Stark, A.M. Arif, J.A. Gladysz, Organometallics 16

(1997) 2909.

[2] (a) K.M.C. Wong, S.C.F. Lam, C.C. Ko, N.Y. Zhu, V.V.W.

Yam, S. Roue, C. Lapinte, S. Fathallah, K. Costuas, S. Kahlal,

J.F. Halet, Inorg. Chem. 42 (2003) 7086;

ing 4.25 molecules per asymmetric unit, but the diﬀer-

ence Fourier map still showed high level of diﬀuse elec-

tron density. Alternatively, the structure was analysed

using ^PLATONsoftware [46]. The volume in the unit cell,

not occupied by the cations and anions and thus avail-

(b) S. Roue, S. Le Stang, L. Toupet, C. Lapinte, Comp. Rend.

Chem. 6 (2003) 353;

(c) T. Weyland, I. Ledoux, S. Brasselet, J. Zyss, C. Lapinte,

Organometallics 19 (2000) 5235;

(d) T. Weyland, K. Costuas, L. Toupet, J.F. Halet, C. Lapinte,

Organometallics 19 (2000) 4228;

(e) M.S. Khan, M.R.A. Al-Mandhary, M.K. Al-Suti, F.R. Al-

Battashi, S. Al-Saadi, B. Ahrens, J.K. Bjernemose, M.F. Mahon,

P.R. Raithby, M. Younas, N. Chawdhury, A. Kohler, E.A.

Marseglia, E. Tedesco, N. Feeder, S.J. Teat, Dalton Trans. (2004)

2377;

(f) N. Chawdhury, N.J. Long, M.F. Mahon, L.L. Ooi, P.R.

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Chem. 689 (2004) 840;

(g) C.E. Powell, J.P. Morrall, S.A. Ward, M.P. Cifuentes, E.G.A.

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(2004) 12234;

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Humphrey, Organometallics 22 (2003) 708;

3

˚

able for the solvent, exceeds 1400 A (over 20% of the

total). An electron count over the solvent region in the

diﬀerence electron-density map gave 258 electrons. Both

ﬁgures agree with the assumption that the crystal con-

tains 7 methanol molecules per asymmetric unit. A mod-

el without any methanol molecules was reﬁned against

F²with subtracted solvent contributions [47], converg-

ing at R = 0.045 for 21525 reﬂections with I > 2(I) and

wR(F²) = 0.124 for all 32596 unique data. Although

the e.s.d. of geometrical parameters were slightly lower

than in the conventional reﬁnement, the diﬀerences in

the parameters were statistically insigniﬁcant.

Crystal data and experimental details are listed in Ta-

ble 6, full structural information has been deposited at

the Cambridge Crystallographic Data Centre, deposi-

tion numbers 271415–271423.

(i) A. Barbieri, B. Ventura, F. Barigelletti, A. De Nicola, M.

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J.E. Guerchias, P. LꢀHaridon, J. Organomet. Chem. 367 (1989)

143;

Acknowledgements

We thank Taasje Mahabiersing (UvA) for assistance

with the electrochemical and spectroelectrochemical

work, and Dmitri S. Yuﬁt for help with the crystallo-

graphic studies. We thank the EPSRC and the EU

EESD HPMT-CT-2001-00311 Marie Curie Training

Site (Amsterdam, The Netherlands) for ﬁnancial assis-

tance, and Johnson Matthey plc for generous loan of

RuCl₃Æ nH₂O. R.L.C. held a doctoral scholarship from

the University of Durham Chemistry EPSRC Doctoral

Training Account.

´

(b) R. Kergoat, L.C. Gomes de Lima, C. Jegat, N. Le Berre,

M.M. Kubicki, J.E. Guerchais, P. LꢀHaridon, J. Organomet.

Chem. 389 (1990) 71;

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The synthesis, structure, reactivity and electrochemical properties of ruthenium complexes featuring cyanoacetylide ligands

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