Some chemistry of trans-Ru(CCCCH)2(dppe)2: Syntheses of bi- and tri-metallic derivatives and cycloaddition of tcne

Inorganica Chimica Acta 382 (2012) 6–12

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Some chemistry of trans-Ru(C„CC„CH)2(dppe)2: Syntheses of bi- and tri-metallic derivatives and cycloaddition of tcne Michael I. Bruce a,⇑, Susanne Büschel a,b, Marcus L. Cole c, Nancy Scoleri a, Brian W. Skelton d, Allan H. White d, Natasha N. Zaitseva a a

School of Chemistry & Physics, University of Adelaide, South Australia 5005, Australia Institüt fur Nanotechnologie, Karlsrühe Institut fur Technologie (KIT), P.O. Box 3640, D-76021 Karlsrühe, Germany School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia d School of Biomedical, Biomolecular & Chemical Sciences, Chemistry M313, University of Western Australia, Crawley, Western Australia 6009, Australia b c

a r t i c l e

i n f o

Article history: Received 3 June 2011 Received in revised form 19 September 2011 Accepted 21 September 2011 Available online 1 October 2011 Keywords: Ruthenium dppe complexes Diynyl Gold Tricobalt cluster X-ray crystal structure

a b s t r a c t Conventional reactions of trans-Ru(C„CC„CH)2(dppe)2 1 with RuCl(PP)Cp0 or AuCl(PPh3) have given the complexes trans-Ru(C„CC„CR)(C„CC„CR0 )(dppe)2 [R = H, Ru(PP)Cp0 , Au(PPh3); R0 = Ru(PP)Cp0 , (PP)Cp0 = (PPh3)2Cp, (dppe)Cp, (dppe)Cp⁄ (not all combinations)]. The Au(PPh3) derivatives react with Co(l3-CBr)(l-dppm)(CO)7 to give trans-Ru(C„CC„CH){C„CC„CC[Co3(l-dppm)(CO)7]}(dppe)2 and trans-Ru{C„CC„CC[Co3(l-dppm)(CO)7]}2(dppe)2, which contain respectively four- and five-carbon and two five-carbon chains linking the metal centres. Also described is the addition of tcne to transRu(C„CC„CH)2(dppe)2 to give the bis(g1-tetracyanobutadienyl) complex trans-Ru{C„CC[@C(CN)2] CH@C(CN)2}2(dppe)2 11, of which the single crystal X-ray structure is reported. Ó 2011 Elsevier B.V. All rights reserved.

1. Introduction Metal complexes with a conjugated carbon bridge linking two metal–ligand moieties have attracted great attention because of their potential applications in molecular electronics (modelling molecular wires) [1–5], non-linear optics [6–8], luminescence [9,10] or liquid crystals [11,12]. Many diyndiyl compounds {LnM}C„CC„C{MLn} (where MLn is a redox-active metal–ligand fragment) have been prepared with metal termini such as W(CO)(dppe)2 [13], M(dppe)(g-C7H7) (M = Mo, W) [14], Mn(dmpe)Cp [15], Re(PPh3)(NO)Cp⁄ [16], Fe(dppe)Cp⁄ [17], Ru(PPh3)2Cp, Ru(dppe)Cp⁄ [18], trans-RuCl(dppe)2 [19] or Ru2(dmb)4 [20]. These complexes show strong electronic interactions between the two redox-active metal termini via the conjugated C4 chain and detailed calculations using density functional theoretical methods (DFT) have afforded some insight into the mechanism of electron transfer. An exciting development in this chemistry has been the synthesis of bis(metalla-diynyl)metal complexes of the general formula {LnM}C„CC„C„{M00 L00 p}C„CC„C{M0 L0 m}, in which the central metal–ligand fragment is linking two metalla-diynyl groups which

⇑ Corresponding author. Fax: + 61 8 8303 4358. E-mail address: [email protected] (M.I. Bruce). 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.09.051

may be the same or different. Of interest here is the effect of the central metal–ligand fragment in a carbon chain on electronic interaction between the end-groups, i.e., whether the central fragment acts as a conductor, as an amplifier or as an insulator. Relatively few bis(diyndiyl) complexes of this type are known and there has been no systematic study of their electronic properties. Some previously described systems include transPd{C„CC„C[Re(NO)(PPh3)Cp⁄]}2(PEt3)2, oxidation of which gives a mono-cation, for which EPR studies showed that the unpaired electron is localised on the rhenium atom [21]. Bis(alkynyl)ruthenium systems such as {cis-Ru(C„CFc)2(dppm)2}CuI and trans, trans, trans-Ru(C„CFc)2(CO)(L)(PBu3)2 [L = CO, pyridine or P(OMe)3] show electronic interactions between the terminal ferrocenyl groups, presumably occurring through the central Ru atom [22]. In trans-Ru(C„CC„CFc)2(dppe)2, obtained from RuCl2(dppe)2 and FcC„CC„CH in the presence of Na[PF6] and NEt3, electronic interaction between the two ferrocenyl moieties occurs via the central Ru(dppe)2 moiety (a strong electron-donating group), which acts as a conductor (possibly even as an amplifier), as a result of the excellent overlap which occurs between the central Ru d orbitals and the p orbitals of the C4 fragments [23]. More recently, electronic interaction between the end-groups in the tri-ruthenium system trans-Ru{C„CC„C[Cp⁄(dppe)Ru]}2(dppe)2 was found to be superior to that in {Cp⁄(dppe)Ru}2(l-C8), i.e., introduction of the Ru(dppe)2 moiety enhanced the

M.I. Bruce et al. / Inorganica Chimica Acta 382 (2012) 6–12

electronic interactions between the Ru(dppe)Cp⁄ groups [24]. Similarly, the binuclear ruthenium units Ru2(LL)4 have an exceptional ability to mediate electron mobility between ferrocene and ferricenium groups in oxidised systems obtained from trans(FcC„CC„C)Ru2(LL)4(C„CC„CFc) (LL = N,N0 -dimethylbenzamidinate, N,N0 -dimethyl(3-methoxy)benzamidinate [20] and 2-(3, 5-dimethoxyanilino)pyridine [25]). In contrast, the complex Hg{C„CC„C[Ru(dppe)Cp⁄]}2, prepared from Ru(C„CC„CH)(dppe)Cp⁄ and Hg(OAc)2, was found to have an unusually bent Ru–C4–Hg–C4–Ru sequence [Hg–C„C 166.5(2)°] [26], although analysis of its electronic structure by extended Hückel (EH) and density functional theory (DFT) methods suggested that the bending was due to ‘‘crystal packing forces’’. Of more interest was the finding that in the model complex Hg{C„CC„C[Ru(dHpe)Cp⁄]}2 [dHpe = H2P(CH2)2PH2] there is no Hg contribution to the HOMO, thus precluding any electronic communication between the ruthenium termini, i.e., the Hg atom acts as an insulator. This was confirmed by cyclic voltammetry which showed only one oxidation process. Following these studies, we decided to explore other examples of complexes of the general formula {LnM}C„CC„C{Ru(dppe)2} C„CC„C{M0 L0 m}, in which the two transition metal fragments, MLn, M0 L0 m, are linked by a trans-(–C„CC„C)2Ru(dppe)2 moiety. This paper describes the syntheses and characterisation of several examples of complexes of this type. Two different routes to these complexes can be envisaged: (a) double addition of transition metal fragments to a central C4–Ru(dppe)2–C4 group to give symmetrical complexes (i.e., where LnM = M0 L0 m) or (b) sequential addition of two different groups to the Ru(dppe)2 fragment to give asymmetric complexes (where LnM – M0 L0 m). We have also studied the cycloaddition of the electron-poor alkene tetracyanoethene (tcne) to the bis(diynyl) complex, whereby the bis(g1-tetracyanobutadienyl) trans-Ru{C„CC[@C(CN)2]CH[@C(CN)2]}2(dppe)2 is formed. We note that earlier work from the Dixneuf/Touchard/Rigaut group has described the syntheses of trans-Ru(C„CC„CR)2(dppe)2 (R = SiMe3, H) and their use as building blocks for molecular electronics [19], a particular success being the coupling of the diynyl and allenylidene complexes to give di-ruthenium systems with C7 or C9 bridges [27].

2. Results and discussion The new complexes described below have been identified by a combination of elemental microanalyses, which were consistent with the proposed formulations, and spectroscopy, including IR, 1 H, 13C and 31P NMR, and ES–MS. Limited solubilities have precluded the observation of 13C resonances for the C4 chain in most cases.

2.1. Some bis(diyndiyl)ruthenium complexes containing two or three metal centres We have previously described some examples of bis(diyndiyl)ruthenium complexes in which metal-containing end-groups may be the same or different [24]. These include the symmetrical complexes Ru{C„CC„C[Ru(PP)Cp0 ]}2(dppe)2 [where (PP)Cp0 = (dppe)Cp⁄, (dppe)Cp or (PPh3)2Cp], mentioned above, achieved by the reaction of trans-Ru(C„CC„CH)2(dppe)2 1 [19] with two equivalents of RuCl(PP)Cp0 in presence of an excess of NEt3 and Na[BPh4], and their asymmetric counterparts, transRu{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„C[Ru(dppe)Cp]}(dppe)2 and trans-Ru{C„CC„C[Ru(PPh3)2Cp]}{C„CC„C[Ru(dppe)Cp]}(dppe)2. Further studies reported below have given the bi- and tri-metallic complexes summarised in Scheme 1.

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2.1.1. Complexes trans-Ru(C„CC„CH){C„CC„C[Ru]} (dppe)2 ([Ru] = Ru(dppe)Cp⁄ 2, Ru(dppe)Cp 3, Ru(PPh3)2Cp) 4) Reactions of trans-Ru(C„CC„CH)2(dppe)2 1 with only one equivalent of the appropriate chloro-ruthenium complex RuCl(PP)Cp0 , in a refluxing CH2Cl2/MeOH solvent mixture for 1 h in the presence of an excess of Na[BPh4] and NEt3, afford the related asymmetric bimetallic bis(diyndiyl) complexes trans-Ru(C„CC„CH) {C„CC„C[Ru(dppe)Cp⁄]}(dppe)2 2 and trans-Ru(C„CC„CH) {C„CC„C[Ru(dppe)Cp]}(dppe)2 3, which were obtained as green solids in 80% and 85% yields, respectively, and transRu(C„CC„CH){C„CC„C[Ru(PPh3)2Cp]}(dppe)2 4, which was synthesised in 85% yield as a brown powder. The three complexes were readily identified from their spectroscopic data and elemental analyses. The characteristic peaks for the Ru(dppe)Cp⁄, Ru(dppe)Cp, Ru(PPh3)2Cp and Ru(dppe)2 ligands are present in the various IR and NMR spectra. Singlets for the terminal „CH hydrogens, at d 1.44, 1.41 and 1.40, are present in the 1H NMR spectra of 2, 3 and 4, respectively. The IR spectra of the three complexes each contain two m(C„C) bands at 2022, 1968 cm1 (for 2) or between 1995 and 1896 cm1 (3, 4) and a m(„CH) band at ca 3055 cm1 in all cases. The ES–MS contain strong M+ ions, together with the appropriate [Ru(PP)Cp0 ]+ fragment ions. 2.1.2. Complexes trans-Ru{C„CC„C[Ru(PP)Cp0 ]}{C„CC„C[Au(PPh3)]} (dppe)2 ([Ru] = Ru(dppe)Cp⁄ 5, Ru(dppe)Cp 6, Ru(PPh3)2Cp 7) and trans-Ru{C„CC„C[Au(PPh3)]}2(dppe)2 8 Some gold(I) complexes of 1,3-butadiyne have been reported recently, the copper-catalysed coupling of AuCl(PPh3) and buta1,3-diyne under Cadiot-Chodkiewicz conditions giving Au(C„CC„CH)(PPh3), which reacts further with AuCl(PPh3) under similar conditions to afford {Au(PPh3)}2(l-C„CC„C) [28]. In further studies, diynyl complexes of general formula {MLn}(C„CC„CH) were found to react with AuCl(PPh3) to afford complexes of the type {MLn}(C„CC„C){Au(PPh3)}. For example, W{C„CC„C[Au(PPh3)]}(CO)3Cp was made from the reaction between W(C„CC„CH)(CO)3Cp and AuCl(PPh3). Similarly, the reactions of Ru(C„CC„CH)(PP)Cp0 [(PP)Cp0 = (PPh3)2Cp, (dppe)Cp⁄] with AuCl(PPh3) in the presence of K[N(TMS)2] afforded the two Ru–C4–Au complexes Ru{C„CC„C[Au(PPh3)]}(PP)Cp0 [28]. Complexes 2–4 each react with one equivalent of AuCl(PPh3) in the presence of NaOMe in a 1/4 MeOH–THF mixture to give the pale yellow trimetallic complexes trans-Ru{C„CC„C[Ru(PP)Cp0 ]}{C„CC„C[Au(PPh3)]}(dppe)2 [(PP)Cp0 = (dppe)Cp⁄ 5, (dppe)Cp 6, (PPh3)2Cp 7; Scheme 1] in 70%, 62% and 69% yields, respectively. Complexes 5–7 were fully characterised by NMR and IR spectroscopy and elemental analyses. The NMR spectra confirmed the presence of the different Au- and Ru-bonded ligands, with the various phosphine ligands giving signals at dP ca 44 [Au(PPh3)], 53–55 [Ru(dppe)2], 51 [Ru(PPh3)2Cp], 74 [Ru(dppe)Cp⁄] and 81 [Ru(dppe)Cp]. The C4 chains give rise to two m(C„C) bands at 2012, 1957 (5), 2013, 1882 (6), 1970, 1899 cm1 (7). The ES–MS are characterised by the presence of [MAu(PPh3)]+ ions. Following the chemistry described above, transRu(C„CC„CH)2(dppe)2 1 was coupled with two equivalents of AuCl(PPh3) using NaOMe to give lemon-yellow transRu{C„CC„C[Au(PPh3)]}2(dppe)2 8 in 89% yield (Scheme 1). Complex 8 was characterised by NMR, IR, ES–MS and elemental analysis. The IR spectrum contains two m(C„C) bands at 1974 and 2084 cm1. The 1H NMR spectrum of 8 shows multiplets at d 2.51–2.61, 3.59–3.76 (dppe CH2) and 7.07–7.61 (Ph). The 31P NMR spectrum contains singlets at d 46.1 (PPh3) and 53.1 (dppe). In the 13C NMR spectrum, two multiplets were present at d 30.91–33.27 (dppe CH2) and 127.28–134.53 (Ph). The ES–MS contains M+ at m/z 1916 and ions [Au(PPh3)n]+ (n = 1, 2) at m/z 459 and 721, respectively.

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M.I. Bruce et al. / Inorganica Chimica Acta 382 (2012) 6–12

C

C

C

C

[Ru]Cl / Na[BPh4] / NEt3

PPh2

Ph2P [Ru]

Ru

C

C

C

C

C

C

C

PPh2

Ph2P

PPh2

Ph2P H

H

C

Ru

AuCl(PPh3) / NaOMe

C

C

C

C

C

H tcne

NC

CN

NC

AuCl(PPh3) / NaOMe

C

C C C

NC

C

Ru

C

C

CN

C C C

CN

C C

PPh2

NC

CN

11 C

C

C

Au(PPh3)

PPh2

Ph2P

PPh2

Ph2P

Ru

Ph2P

H

H

PPh2

Ph2P

C

PPh2

Ph2P C

C

1

[Ru] = Ru(dppe)Cp* 2, Ru(dppe)Cp 3, Ru(PPh3)2Cp 4

[Ru]

C PPh2

Ph2P

(Ph3P)Au

C

C

C

C

C

Ru

[Ru] = Ru(dppe)Cp* 5, Ru(dppe)Cp 6, Ru(PPh3)2Cp 7

C

C

C

Au(PPh3)

PPh2

Ph2P 9

Co3(µ3-CBr)(µ-dppm)(CO)7 Co3(µ3-CBr)(µ-dppm)(CO)7

PPh2 Ph2P PPh2

Ph2P [Ru]

C

C

C

C Ph2P

Ru

C

(OC)2Co C

PPh2

C

C

C

PPh2 Co(CO)2

Co (CO)3

Ph2P (OC)2Co

Co(CO)2 C C

(OC)3Co

C

C

C

Ph2P

PPh2

Ph2P Ru

C

C

C

PPh2

Ph2P

C

(OC)2Co C

PPh2 Co(CO)2

Co (CO)3

10 [Ru] = Ru(dppe)Cp* 8

Scheme 1. Reactions and subsequent chemistry of trans-Ru(C„CC„CH)2(dppe)2 1.

2.1.3. Complexes trans-Ru{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„CC„[Co3 (l-dppm)(CO)7]}(dppe)2 9 and trans-Ru{C„CC„CC„[Co3(l-dppm) (CO)7]}2(dppe)2 10 In a variant of the well-known Sonogashira reaction [29,30], reactions between aurated poly-ynes and halo-alkynes in ether solvents at moderate temperatures in the presence of a Pd(0)/ Cu(I) catalyst result in the formation of new C(sp)–C(sp) bonds via facile elimination of AuX(PR3) [31]. For example, coupling of Me3SiC„CC„CAu(PPh3) with Co3(l3-CBr)(l-dppm)(CO)7 afforded Co3(l3-CC„CC„CSiMe3)(l-dppm)(CO)7 [31b]. In the present work, the reaction of trans-Ru{C„CC„C[Ru(dppe)Cp⁄]} {C„CC„C[Au(PPh3)]}(dppe)2 5 with one equivalent of Co3(l3CBr)(l-dppm)(CO)7 in the presence of CuI and Pd(PPh3)4 similarly affords trans-Ru{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„CC„[Co3(ldppm)(CO)7]}(dppe)2 9 in 33% yield (Scheme 1). The IR spectrum of 9 has two m(C„C) bands at 2010 and 1978 cm1, as well as m(CO) bands at 2069 and 2058 cm1. The 1H NMR spectrum contains a singlet at d 1.51 for the Cp⁄ ligand, together with resonances at d 2.45–2.55, 2.77–2.85 (dppe CH2), 3.43–3.48, 4.40–4.45 (dppm CH2) and 6.83–7.70 (Ph of dppm, dppe). The 31P NMR spectrum contains peaks at d 30.6 (dppm), 55.9 [Ru(dppe)2] and 72.8 [Ru(dppe)Cp⁄]. In the 13C NMR spectrum of 9, signals occur at d 10.11, 96.86 (Cp⁄), 29.63–30.40 (dppe CH2), 32.22–33.95 (dppm CH2), 132.77–139.37 (Ph) and 200.02–203.29 [Co(CO)]. The ES– MS contains peaks at m/z 2370 ([MCO]+), 898 ([Ru(dppe)2]+) and 675 ([Ru(dppe)Cp⁄]+). Complex 9 is the first example of a complex containing both even- (C4) and odd-numbered (C5) carbon chains linked by the Ru(dppe)2 unit. The reaction of Co3(l3-CBr)(l-dppm)(CO)7 with Ru{C„CC„C[Au (PPh3)]}2(dppe)2 8 at ca 20 °C in thf in the presence of the Pd(0)/ Cu(I) catalyst afforded bright orange trans-Ru{C„CC„CC„[Co3 (l-dppm)(CO)7]}2(dppe)2 10 in 54% yield. This reaction results in the formation of a complex with two C5 chains linking the three metal-containing groups. Complex 10 was identified from its spectroscopic data. The IR spectrum shows m(CO) bands at 2062, 2057, 2033 and 1999 cm1 and a m(C„C) band at 2084 cm1. The 1H NMR spectrum contains two pairs of multiplets at d 2.19–2.32, 2.56–2.68 (dppe CH2) and

3.48–3.54, 4.40–4.45 (dppm CH2) and a broad multiplet at d 6.82–7.48 (Ph). In the 31P NMR spectrum, two resonances at d 33.2 and 51.0 arise from the dppm and dppe ligands, respectively. In the 13C NMR spectrum, multiplets at d 29.40–30.61 (dppe), 32.87–33.49 (dppm), 126.55–134.56 (Ph) and 206.21–221.31 [Co(CO)] are found.

2.2. Cycloaddition of tcne to 1: transRu{C„„CC[@C(CN)2]CH@C(CN)2}2(dppe)2 11 [2+2]-Cycloaddition of the electron-deficient alkene tcne to

r-alkynyl- or r-poly-ynyl-metal complexes gives cyclobutenyl complexes which readily ring-open to form 1,1,4,4-tetracyanobuta-1,3-dien-2-yl complexes [32]. Addition of two equivalents of tcne to a solution of 1 in dichloromethane afforded bright purple trans-Ru{C„CC[@C(CN)2]CH@C(CN)2}2(dppe)2 11 in 93% yield (Scheme 1). It is reasonable to assume that this reaction goes via an (unobserved) cyclobutenyl intermediate. Characteristic spectroscopic properties of 11 include IR m(C„C) and m(CN) bands at 1973 and 2220 cm1, respectively. The 1H NMR spectrum contained a singlet at d 1.41 (CH) and multiplets at d 2.17–2.25, 2.99–3.08 (CH2) and 7.14–7.43 (Ph). The 31P NMR spectrum shows only one peak at d 47.4 (dppe). The 13C NMR spectrum shows two C(CN)2 signals at d 30.47, 30.61 together with four resonances for the CN groups between d 110.10 and 115.11. Atoms in the cyanocarbon skeleton give four resonances between d 90.82 and 152.78. The ES–MS contains ions at m/z 1251, 1225 and 898 assigned to M+, [MCN]+ and [Ru(dppe)2]+, respectively. The CV of Ru{C„CC[@C(CN)2]CH[@C(CN)2]}2(dppe)2 11 shows two partially reversible redox processes at 0.65 V and +1.21 V (versus SCE) (ic/ia = 0.6 and 0.8, respectively). Reduction of the cyanocarbon moiety occurs at the lower potential, the added electron being stabilised by delocalisation onto the dicyanomethylene group. The presence of the strongly electron-withdrawing CN groups results in oxidation of the Ru(dppe)2 moiety occurring at higher potential than for trans-Ru(C„CC„CSiMe3)2(dppe)2, which displays a reversible wave at +0.596 V and an irreversible wave at +1.458 V [33].

M.I. Bruce et al. / Inorganica Chimica Acta 382 (2012) 6–12

The molecular structure of 11 was determined by an XRD study from a single crystal grown from benzene/CH2Cl2. A plot of a molecule, which lies with the ruthenium atom on a crystallographic twofold axis, is shown in Fig. 1; selected bond distances and angles are given in the caption. [2+2]-Cycloaddition of tcne to the C„C triple bonds furthest from Ru, followed by ringopening, has given the ethynyl-tetracyanobutadienyl ligands which occupy mutually trans positions on the metal [Ru–C(1) 2.007(7) Å]. The other four positions on the essentially octahedral Ru centre accommodate the four P atoms of the dppe ligands [Ru–P(1,2) 2.392, 2.386(2) Å]. Within the cyanocarbon ligand, the interplanar dihedral angles between planes C(3,30,31,32) and C(4,40,41,42) and between these and the plane C(2,3,4,30) are 62.5(3), 2.2(3) and 60.8(3)°, respectively. The three planes lie at 86.1(3), 47.4(2), 88.1(3)° to the P4 plane. The C(1)–C(2) and C(2)– C(3) separations [1.231(9), 1.404(10) Å, respectively] are suggestive of some electron delocalisation, while along the Ru–C(1–3) chain, angles at C(1,2) are quasi-linear. Comparison with the structures of trans-Ru(C„CC„CX)2(dppe)2 (X = H, SiMe3) [34] shows similar Ru–C separations of 2.041(13) and 2.050(4) Å, respectively, but shorter C„C bonds lengths of 1.179(17) and 1.198(5) Å, which also support the existence of some electron delocalisation in 11. Selected bond lengths: Ru(1)–P(1,2) 2.392(2), 2.386(2), Ru–C(1) 2.007(7), C(1)–C(2) 1.231(9), C(2)–C(3) 1.404(10), C(3)–C(4) 1.485(10), C(3)–C(30) 1.376(10), C(4)–C(40) 1.334(10) Å. Bond angles: P(1)–Ru–P(2) (cis, trans) 82.61(6), 175.59(6), P(1,2)–Ru–C(1) 90.8(2), 84.8(2), P(1,2)–Ru–C(10 ) 91.0(2), 93.5(2), C(1)–Ru–C(10 ) 177.4(4), Ru–C(1)–C(2) 176.3(6), C(1)–C(2)–C(3) 177.5(8), C(2)–

9

C(3)–C(4) 115.3(6), C(2)–C(3)–C(30) 123.9(7), C(3)–C(4)–C(40) 124.8(7)°. 3. Conclusions The complex trans-Ru(C„CC„CH)2(dppe)2 1 [19] has been used as a precursor for several symmetric and asymmetric ruthenium(II) complexes containing a trans-Ru(dppe)2 moiety as the central linking group. The preparation of transRu(C„CC„CH){C„CC„C[Ru(PP)Cp0 ]}(dppe)2 complexes [where (PP)Cp0 = (dppe)Cp⁄ 2, (dppe)Cp 3, (PPh3)2Cp 4] has in turn allowed the construction of asymmetric complexes of general formula trans-Ru{C„CC„C[Ru(PP)Cp0 ]}{C„CC„C[Au(PPh3)]}(dppe)2 [where (PP)Cp0 = (dppe)Cp⁄ 5, (dppe)Cp 6, (PPh3)2Cp 7]. Incorporation of the Au(PPh3) fragment and subsequent trans-metallation reactions has enabled access to complexes with extended carbon chains. For example, complex 5 was further reacted with the cobalt cluster Co3(l3-CBr)(l-dppm)(CO)7 to give complex 8 containing both even- and odd-numbered Cx linkages. In the same way, the reaction between trans-Ru(C„CC„CH)2(dppe)2 1 and AuCl(PPh3) occurs readily to afford trans-Ru{C„CC„C[Au(PPh3)]}2(dppe)2 9 which in turn reacts with Co3(l3-CBr)(l-dppm)(CO)7 to give trans-Ru{C„CC„CC[Co3(l-dppm)(CO)7]}2(dppe)2 10 which has two C5 chains linking the three metal centres. The reaction of bis-diynyl 1 with tcne afforded the bis(g1-tetracyanobutadienyl) trans-Ru{C„CC[@C(CN)2]CH[@C(CN)2]}2(dppe)2 11 in very good yield. The X-ray crystal study of 11 has confirmed that the cyanocarbon attacks the outer C„C triple bond, probably because of steric protection of the inner C„C triple bond by the two bulky dppe ligands. 4. Experimental 4.1. General All reactions were carried out under dry nitrogen, although normally no special precautions to exclude air were taken during subsequent work-up. Common solvents were dried, distilled under nitrogen and degassed before use. Separations were carried out by preparative thin-layer chromatography on glass plates (20  20 cm2) coated with silica gel (Merck, 0.5 mm thick). 4.2. Instruments

Fig. 1. Plot of a molecule of trans-Ru{C„CC[@C(CN)2]CH[@C(CN)2]}2(dppe)2 11.

IR spectra were obtained on a Bruker IFS28 FT-IR spectrometer. Spectra in CH2Cl2 were obtained using a 0.5 mm path-length solution cell with NaCl windows. Nujol mull spectra were obtained from samples mounted between NaCl discs. NMR spectra were recorded on a Varian Gemini 2000 instrument (1H at 300.145 MHz, 13 C at 75.479 MHz, 31P at 121.501 MHz). Unless otherwise stated, samples were dissolved in CDCl3 contained in 5 mm sample tubes. Chemical shifts are given in ppm relative to internal tetramethylsilane for 1H and 13C NMR spectra and external H3PO4 for 31P NMR spectra. Electrospray mass spectra (ES–MS) were obtained from samples dissolved in MeOH unless otherwise indicated. Solutions were injected into a Varian Platform II spectrometer via a 10 ml injection loop. Nitrogen was used as the drying and nebulising gas. Chemical aids to ionisation were used as required [35]. Electrochemical samples (1 mM) were dissolved in CH2Cl2 containing 0.5 M [NBu4]BF4 as the supporting electrolyte. The cyclic voltammogram of 11 was recorded using a PAR model 263 apparatus, with a saturated calomel electrode, with ferrocene as internal calibrant (FeCp2/[FeCp2]+ = +0.46 V versus SCE). A 1 mm path-length cell was used with a Pt-mesh working electrode, Ptwire counter and pseudo-reference electrodes. Elemental analyses

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were carried out by Campbell Microanalytical Laboratory, University of Otago, Dunedin, New Zealand. 4.3. Reagents The compounds trans-Ru(C„CC„CH)2(dppe)2 1 [19], RuCl(dppe)Cp⁄ [36], RuCl(dppe)Cp [37], RuCl(PPh3)2Cp [38], Ru(C„CC„CH)(dppe)Cp⁄ [39], Co3(l3-CBr)(l-dppm)(CO)7 [40], AuCl(PPh3) [41], and Pd(PPh3)4 [42] were all prepared by standard literature methods. Na[BPh4], CuI, dbu and tcne were used as received from Sigma–Aldrich or Fluka. 4.3.1. trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp⁄]}(dppe)2 2 trans-Ru(C„CC„CH)2(dppe)2 1 (50 mg, 0.05 mmol), RuCl(dppe)Cp⁄ (34 mg, 0.05 mmol), Na[BPh4] (17 mg, 0.05 mmol) and NEt3 (0.01 ml, 0.07 mmol) were combined and a 6:1 mixture of CH2Cl2/MeOH (25 ml) was added. The resulting suspension was heated at reflux point for 1 h. The solvent was then removed and the resulting green residue dissolved in a minimum amount of CH2Cl2 and filtered through cotton wool into stirred hexane (40 ml). The precipitate was collected and washed with hexane to yield trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp⁄]}(dppe)2 2 as a green powder (66 mg, 80%). Anal. Calc. (C96H88P6Ru2): C, 70.75; H, 5.44; M, 1631. Found: C, 70.73; H, 5.54%. IR (CH2Cl2, cm1): m(„CH) 3055 (m); m(C„C) 2022 (w), 1968 (w). 1H NMR: d 1.44 (s, H), 1.56 (s, 15H, Cp⁄), 2.03–2.10, 2.44–2.47 (2 m, 12H, CH2CH2), 7.12–7.99 (m, 60H, Ph). 13C NMR (CD2Cl2): d 10.64 (s, C5Me5), 30.22–31.51 (m, CH2CH2), 96.91 (s, C5Me5), 127.32– 136.32 (m, Ph). 31P NMR: d 46.1 (s, Ru(dppe)2), 70.5 (s, Ru(dppe)Cp⁄). ES–MS (m/z): 1631, M+; 898, [Ru(dppe)2]+; 635, [Ru(dppe)Cp⁄]+. 4.3.2. trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp]}(dppe)2 3 Similarly, from trans-Ru(C„CC„CH)2(dppe)2 1 (51 mg, 0.05 mmol) and RuCl(dppe)Cp (32 mg, 0.05 mmol) was obtained trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp]}(dppe)2 3 as a green powder (67 mg, 85%). Anal. Calc. (C91H78P6Ru2): C, 70.08; H, 5.04; M, 1560. Found: C, 70.11; H, 5.12%. IR (CH2Cl2, cm1): m(„CH) 3053 (w); m(C„C) 1995 (m), 1919 (m). 1H NMR (C6D6): d 1.41 (s, H), 2.04–2.11, 2.51–2.55 (2 m, 12H, CH2CH2), 4.50 (s, 5H, Cp), 6.87–7.42 (m, 60H, Ph); 13C NMR (CD2Cl2): d 29.27–30.54 (m, CH2CH2), 84.84 (s, Cp),125.22–136.01 (Ph); 31P NMR (C6D6): d 56.4 [s, Ru(dppe)2], 81.5 [s, Ru(dppe)Cp]; ES–MS (MeCN, m/z): 1560, M+; 898, [Ru(dppe)2]+; 605, [Ru(NCMe)(dppe)Cp]+; 563, [Ru(dppe)Cp]+. 4.3.3. trans-Ru(C„CC„CH){C„CC„C[Ru(PPh3)2Cp]}(dppe)2 4 Similarly, from trans-Ru(C„CC„CH)2(dppe)2 1 (51 mg, 0.05 mmol) and RuCl(PPh3)2Cp (37 mg, 0.05 mmol) was obtained trans-Ru(C„CC„CH){C„CC„C[Ru(PPh3)2Cp]}(dppe)2 4 as a brown powder (67 mg, 85%). Anal. Calc. (C101H84P6Ru2): C, 71.96; H, 5.02; M, 1685. Found: C, 72.03; H, 5.08%. IR (CH2Cl2, cm1): m(„CH) 3055 (w), m(C„C) 1981 (m), 1896 (m). 1H NMR: d 1.40 (s, H). 2.06–2.10, 2.37–2.39 (2 m, 8H, CH2CH2); 4.20 (s, 5H, Cp); 6.91–7.76 (m, 70H, Ph); 13C NMR (CD2Cl2): d 30.22–31.03 (m, CH2CH2), 81.48 (s, Cp); 125.72–133.97 (Ph). 31P NMR: d 40.0 (s, PPh3), 53.0 (s, dppe). ES–MS (MeCN, m/z): 1685, M+; 898, [Ru(dppe)2]+; 690, [Ru(PPh3)2Cp]+; 429, [Ru(PPh3)Cp]+. 4.3.4. transRu{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„C[Au(PPh3)]}(dppe)2 5 To a solution of trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp⁄]}(dppe)2 2 (50 mg, 0.04 mmol) and NaOMe (3 mg, 0.15 mmol) in a 1:4 mixture of MeOH/THF (25 ml) was added AuCl(PPh3) (15 mg, 0.03 mmol). The reaction mixture was stirred at r.t. for 3 h and the solvent was then evaporated. The residue

was dissolved in the minimum amount of CH2Cl2 and dropped into rapidly stirred hexane. The pale yellow precipitate was collected by filtration, washed with hexane (2  20 ml) and air-dried to afford trans-Ru{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„C[Au(PPh3)]}(dppe)2 5 (55 mg, 70%). Anal. Calc. (C114H102AuP7Ru2): C, 65.58; H, 4.92; M, 2086. Found: C, 65.89; H, 5.20%. IR (Nujol, cm1): m(C„C) 2012 (w), 1957 (m). 1H NMR: d 1.57 (s, 15H, Cp⁄), 2.30–2.37, 3.15– 3.52, (2 m, 12H, CH2CH2), 7.04–7.69 (m, 75H, Ph). 13C NMR: d 9.48 (s, C5Me5), 29.65–30.63 (m, CH2CH2); 98.80 (s, C5Me5), 121.36–139.31 (Ph). 31P NMR: d 44.6 [s, Au(PPh3)], 55.3 [s, 4P, Ru(dppe)2], 73.8 (s, 4P Ru(dppe)Cp⁄). ES–MS (m/z): 2086, M+; 1626, [MAu(PPh3)]+. 4.3.5. trans-Ru{C„CC„C[Ru(dppe)Cp]}{C„CC„C[Au(PPh3)]}(dppe)2 6 Similarly, from trans-Ru(C„CC„CH){C„CC„C[Ru(dppe)Cp]}(dppe)2 3 (40 mg, 0.03 mmol) and AuCl(PPh3) (13 mg, 0.03 mmol) was obtained pale yellow trans-Ru{C„CC„C[Ru(dppe)Cp]}{C„CC„C[Au(PPh3)]}(dppe)2 6 (33 mg, 62%). Anal. Calc. (C109H93AuP7Ru2): C, 64.85; H, 4.64; M, 2018. Found: C, 65.13; H, 5.11%. IR (CH2Cl2, cm1): m(C„C) 2013 (w), 1882 (w). 1H NMR: d 2.24–2.33, 2.49–2.56 (2 m, 12H, CH2CH2), 4.57 (s, 5H, Cp), 6.91–7.87 (m, 55H, Ph). 13C NMR: d 29.79–30.83 (m, CH2CH2), 84.97 (s, Cp), 122.00–142.68 (Ph). 31P NMR: d 44.6 [s, 1P, Au(PPh3)], 53.3 [s, 4P, Ru(dppe)2], 80.7 [s, 2P, Ru(dppe)Cp]. ES–MS (m/z): 2018, M+; 898, [Ru(dppe)2]+; 565 [Ru(dppe)Cp]+. 4.3.6. transRu{C„CC„C[Ru(PPh3)2Cp]}{C„CC„C[Au(PPh3)]}(dppe)2 7 Similarly, trans-Ru{C„CC„C[Ru(PPh3)2Cp]}{C„CC„C[Au (PPh3)]}(dppe)2 7 was obtained from trans-Ru(C„CC„CH){C„CC„C[Ru(PPh3)2Cp]}(dppe)2 4 (41 mg, 0.03 mmol) and AuCl(PPh3) (13 mg, 0.03 mmol) as a pale yellow powder (36 mg, 69%). Anal. Calc. (C119H99AuP7Ru2): C, 66.63; H, 4.65, M, 2145. Found: C, 66.95; H, 5.22%. IR (CH2Cl2, cm1): m(C„C) 1970 (w), 1899 (w). 1H NMR: d 1.88–1.99, 2.25–2.30 (2 m, 8H, CH2CH2), 4.36 (s, 75H, Cp), 6.86– 7.79 (m, 65H, Ph). 13C NMR: d 29.25–31.12 (m, CH2CH2), 84.05 (s, Cp), 121.85–136.01 (m, Ph). 31P NMR: d 43.2 [s, 1P, Au(PPh3)], 51.4 [s, 2P, Ru(PPh3)2Cp], 53.9 [s, 4P, Ru(dppe)2]. ES–MS (m/z): 2037, [MPPh]+; 898, [Ru(dppe)2]+; 429, [Ru(PPh3)Cp]+. 4.3.7. trans-Ru{C„CC„C[Au(PPh3)]}2(dppe)2 8 To a solution of trans-Ru(C„CC„CH)2(dppe)2 1 (100 mg, 0.1 mmol) and NaOMe (28 mg, 0.5 mmol) in a 1:4 mixture of MeOH/THF (25 ml) was added AuCl(PPh3) (100 mg, 0.2 mmol). The reaction mixture was stirred at r.t. for 5 h. The bright yellow precipitate was collected by filtration, washed with hexane (2  10 ml) and air-dried to afford transRu{C„CC„C[Au(PPh3)]}2(dppe)2 8 (0.17 mg, 89%). Anal. Calc. (C96H78Au2P6Ru): C, 60.29; H, 4.11; M, 1916. Found: C, 60.31; H, 4.17%. IR (CH2Cl2, cm1): m(C„C) 2084 (w), 1974 (m). 1H NMR: d 2.51–2.61, 3.59–3.76 (2 m, 8H, CH2CH2), 7.07–7.61 (m, 35H, Ph). 13C NMR: d 30.91–33.27 (m, CH2CH2), 127.28–134.53 (Ph). 31 P NMR: d 46.1 [s, 1P, Au(PPh3)], 53.1 [s, 4P, Ru(dppe)2]. ES–MS (m/z): 1916, M+; 721, [Au(PPh3)2]+; 459, [Au(PPh3)]+. 4.3.8. trans-Ru{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„CC„[Co3(l-dppm) (CO)7]}(dppe)2 9 Co3(l3-CBr)(l-dppm)(CO)7 (16 mg, 0.02 mmol), CuI (7 mg, 0.04 mmol), Pd(PPh3)4 (41 mg, 0.03 mmol) and trans-Ru{C„CC„C[Ru(dppe)Cp⁄]}{C„CC„C[Au(PPh3)]}(dppe)2 5 (41 mg, 0.02 mmol), were dissolved in thf (30 ml) and stirred at r.t. for 4 h. The solution was filtered and the solvent was then evaporated. The brown residue was then dissolved in acetone and filtered through cotton wool into stirred hexane (40 ml). The precipitate was collected and washed with hexane to afford trans-Ru{C„CC„-

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C[Ru(dppe)Cp⁄]}{C„CC„CC„[Co3(l-dppm)(CO)7]}(dppe)2 9 as a brown powder (15 mg, 33%). Anal. Calc. (C129H109Co3O7P8Ru2): C, 64.61; H, 4.58; M, 2398. Found: C, 64.66; H, 4.61%. IR (CH2Cl2, cm1): m(CO): 2069 (m), 2058 (s); m(C„C) 2010 (w); 1978 (m). 1 H NMR: d 1.51 (s, 15H, Cp⁄), 2.45–2.55, 2.77–2.85 (2 m, 12H, CH2CH2), 3.43–3.48 (m, 2H, CH2), 4.40–4.45 (m, 2H, CH2), 6.83– 7.70 (m, 80H, Ph). 13C NMR: d 10.11 (s, C5Me5), 29.63–30.40 (m, CH2CH2), 32.22–33.95 (m, CH2), 96.86 (s, C5Me5), 132.77–139.37 (Ph), 200.02–203.29 (m, CO). 31P NMR: d 30.6 (s, 2P, dppm), 55.9 [s, 4P, Ru(dppe)2], 72.8 [s, 2P, Ru(dppe)Cp⁄]. ES-MS (MeCN, m/z): 2370, [MCO]+; 898, [Ru(dppe)2]+; 675, [Ru(dppe)Cp⁄]+. 4.3.9. trans-Ru{C„CC„CC„[Co3(l-dppm)(CO)7]}2(dppe)2 10 Co3(l3-CBr)(l-dppm)(CO)7 (88 mg, 0.1 mmol), transRu{C„CC„C[Au(PPh3)]}2(dppe)2 8 (110 mg, 0.05 mmol), CuI (18 mg, 0.1 mmol) and Pd(PPh3)4 (137 mg, 0.1 mmol) were dissolved in THF (50 ml) and stirred at r.t. for 4 h. The solution was filtered and the solvent was evaporated to dryness. The residue was purified by column chromatography on silica gel, eluted with acetone/hexane (3:7) to afford bright orange transRu{C„CC„CC„[Co3(l-dppm)(CO)7]}2(dppe)2 10 (70 mg, 54%). Anal. Calc. (C126H92Co6O14P8Ru): C, 59.76; H, 3.66; M, 2529. Found: C, 59.84; H, 3.58%. IR (CH2Cl2, cm1): m(C„C) 2084 (w); m(CO) 2062 (w), 2057 (s), 2033 (m), 1999 (w). 1H NMR: d 2.19–2.32, 2.56–2.68 (2 m, 8H, CH2CH2), 3.48–3.54 (m, 2H, CH2), 4.40–4.45 (m, 2H, CH2), 6.82–7.48 (m, 80H, Ph). 13C NMR: d 29.40–30.61 (m, CH2CH2), 32.87–33.49 (m, CH2), 126.55–134.56 (Ph), 206.21–221.31 (m, CO). 31 P NMR: d 33.2 [s, 2P, dppm], 51.0 [s, 4P, Ru(dppe)2]. ES–MS (m/z): 2552, [M + Na]+; 2528, [MH]+. 4.3.10. trans-Ru{C„CC[@C(CN)2]CH@C(CN)2}2(dppe)2 11 To a solution of trans-Ru(C„CC„CH)2(dppe)2 1 (50 mg, 0.05 mmol) in CH2Cl2 (40 ml) was added tcne (12 mg, 0.09 mmol) and the reaction mixture was stirred at r.t. for 16 h, gradually changing in colour from yellow to purple. The solvent was then removed and the residue was dissolved in minimum amount of benzene and purified by preparative TLC, eluted with CH2Cl2 to afford bright purple Ru{C„CC[@C(CN)2]CH@C(CN)2}2(dppe)2 11 (52.2 mg, 93%) (Rf 0.32). Single crystals suitable for X-ray studies were grown from CH2Cl2/benzene. Anal. Calc. (C72H50N8P4Ru): C, 69.00; H, 4.02; N, 8.95; M, 1251. Found: C, 68.97; H, 4.14; N, 8.86%. IR (CH2Cl2, cm1): m(CN) 2220 (m); m(C„C) 1973 (w). 1H NMR: d 1.41 (s, 2H, C„CH), 2.17–2.25, 2.99–3.08 (2 m, 8H, CH2CH2), 7.14–7.43 (m, 40H, Ph). 13C NMR: d 29.98–30.47 (m, CH2CH2), 30.47, 30.61 [2 s, 2  C(CN)2], 90.82, 126.12, 142.85, 152.78 (4 s, 4 C of chain), 110.10, 111.31, 113.75, 115.11 (4 s, CN), 128.64–134.16 (Ph). 31P NMR: d 47.4 [s, Ru(dppe)2]. ES– MS (m/z): 1251, M+; 1225, [MCN]+; 898, [Ru(dppe)2]+.

5.1. Crystal data and refinement details Complex 11. Ru{C„CC[@C(CN)2]CH@C(CN)2}2(dppe)2 „ C72H50N8P4Ru, M = 1252.15. Monoclinic, space group C2/c, a = 28.247(8), b = 12.214(4), c = 18.853(6) Å, b = 113.087(5)°, V = 5984(3) Å3, qc = 1.390 g cm3, Z = 4. l(Mo-Ka) = 0.42 mm1, Tmin/max = 0.79. Crystal 0.11  0.10  0.04 mm, 2hmax = 50°. R1 = 0.067, wR2 = 0.21. T ca 153 K. Acknowledgements S.B. worked in Adelaide as part of her Vertiefungspraktikum. We thank Professor B.K. Nicholson, University of Waikato, Hamilton, New Zealand, for measuring mass spectra. We acknowledge financial support of this work by the A.R.C. and Johnson Matthey plc for a generous loan of RuCl3.nH2O. Appendix A. Supplementary material CCDC 789508 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.ica.2011.09.051. References [1] [2] [3] [4] [5] [6] [7]

[8]

[9] [10] [11] [12] [13] [14]

5. Structure determination A full sphere of diffraction data was measured using a CCD areadetector instrument with monochromatic Mo-Ka radiation, k = 0.71073 Å. 22112 reflections were merged to 5339 unique (Rint 0.073) after ‘‘empirical’’/multiscan absorption correction (proprietary software) and used in the full matrix least squares refinements on F2, 3048 with F > 4r(F) being considered ‘‘observed’’. Anisotropic displacement parameter forms were refined for the non-hydrogen atoms; hydrogen atoms were treated with a riding model [weights: (r2(Fo)2 + (0.077P)2 + 47P)1; P = (Fo2 + 2Fc2)/3]. Neutral atom complex scattering factors were used; computation used the SHELXL 97 program [43]. Pertinent results are given in Fig. 1 (which shows non-hydrogen atoms with 50% probability amplitude displacement ellipsoids and hydrogen atoms with arbitrary radii of 0.1 Å) and in the text.

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[15] [16] [17] [18]

[19] [20] [21] [22]

F. Paul, C. Lapinte, Coord. Chem. Rev. 178–180 (1998) 431. P.J. Low, J. Chem. Soc., Dalton Trans. (2005) 2821. D.K. James, J.M. Tour, Topics Curr. Chem. 257 (2005) 33. T. Ren, Organometallics 24 (2005) 4854. (a) M.I. Bruce, P.J. Low, Adv. Organomet. Chem. 50 (2004) 179; (b) M.I. Bruce, Coord. Chem. Rev. 248 (2004) 1603. N.J. Tao, Nat. Nanotech. 1 (2006) 173. (a) I.R. Whittall, A.M. McDonagh, M.G. Humphrey, M. Samoc, Adv. Organomet. Chem. 42 (1998) 291; (b) I.R. Whittall, A.M. McDonagh, M.G. Humphrey, M. Samoc, Adv. Organomet. Chem. 43 (1999) 349; (c) J.P. Morrall, G.T. Dalton, M.G. Humphrey, M. Samoc, Adv. Organomet. Chem. 55 (2008) 61; (d) C.E. Powell, M.G. Humphrey, Coord. Chem. Rev. 248 (2004) 725. (a) K.A. Green, M.P. Cifuentes, T.C. Corkery, M. Samoc, M.G. Humphrey, Angew. Chem., Int. Ed. 48 (2009) 7867; (b) M.P. Cifuentes, M.G. Humphrey, J. Organomet. Chem. 689 (2004) 3968; (c) B. Babgi, L. Rigamonti, M.P. Cifuentes, T.C. Corkery, M.D. Randles, T. Schwich, S. Petrie, R. Stranger, A. Teshome, I. Asselberghs, K. Clays, M. Samoc, M.G. Humphrey, J. Am. Chem. Soc. 131 (2009) 10293. C. Olivier, B. Kim, D. Touchard, S. Rigaut, Organometallics 27 (2008) 509. (a) V.W.-W. Yam, K.M.-C. Wong, Topics Curr. Chem. 257 (2005) 1; (b) V.W.-W. Yam, J. Organomet. Chem. 689 (2004) 1393. T. Kaharu, H. Matsubara, S. Takahashi, J. Mater. Chem. 2 (1992) 43. S.K. Varshney, D.S.S. Rao, S. Kumar, Mol. Cryst. Liq. Cryst. 357 (2001) 55. S.N. Semenov, O. Blacque, T. Fox, K. Venkatesan, H. Berke, Angew. Chem., Int. Ed. 48 (2009) 5203. (a) N.J. Brown, D. Collison, R. Edge, E.C. Fitzgerald, M. Helliwell, J.A.K. Howard, H.N. Lancashire, P.J. Low, J.J.W. McDouall, J. Raftery, C.A. Smith, D.S. Yufit, M.W. Whiteley, Organometallics 29 (2010) 1261; (b) H.N. Lancashire, N.J. Brown, L. Carthy, D. Collison, E.C. Fitzgerald, R. Edge, M. Helliwell, M. Holden, P.J. Low, J.J.W. McDouall, M.W. Whiteley, Dalton Trans. 40 (2011) 1267. K. Venkatesan, T. Fox, H.W. Schmalle, H. Berke, Organometallics 24 (2005) 2834. M. Brady, W. Weng, Y. Zhou, J.W. Seyler, A.J. Amoroso, A.M. Arif, M. Bohme, G. Frenking, J.A. Gladysz, J. Am. Chem. Soc. 119 (1997) 775. N. Le Narvor, L. Toupet, C. Lapinte, J. Am. Chem. Soc. 117 (1995) 7129. (a) M.I. Bruce, P.J. Low, K. Costuas, J.-F. Halet, S.P. Best, G.A. Heath, J. Am. Chem. Soc. 122 (2000) 1949; (b) M.I. Bruce, B.G. Ellis, B.W. Skelton, A.H. White, J. Organomet. Chem. 690 (2005) 792. S. Rigaut, J. Perruchon, L. Le Pichon, D. Touchard, P.H. Dixneuf, J. Organomet. Chem. 670 (2003) 37. G.L. Xu, R.J. Crutchley, M.C. De Rosa, Q.-J. Pan, H.-X. Zhang, X. Wang, T. Ren, J. Am. Chem. Soc. 127 (2005) 13354. W. Weng, T. Bartik, M. Brady, B. Bartik, I.A. Ramsden, A.M. Arif, J.A. Gladysz, J. Am. Chem. Soc. 117 (1995) 11922. Y. Zhu, O. Clot, M.O. Wolf, G.P.A. Yap, J. Am. Chem. Soc. 120 (1998) 1812.

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