Synthesis and reactivity studies of cyclopentadienyl derivatives of ruthenium iridium and osmium iridium mixed metal clusters 3

The reaction of tetrahedral clusters with internal and terminal alkynes often results in cluster opening to give butterfly structures [9].. Tetrahedral clusters are known to react with a

Chapter 3 Reactivity of Cp*- containing ruthenium-iridium and

osmium-iridium mixed metal clusters towards alkynes

3.1 Introduction

Mixed-metal alkyne clusters have generated much interest in recent years largely due

to their catalytic potential in hydrogenation reactions [1] They have been proven to

serve as models for the carbon-carbon triple bond activation on metal surfaces and

also for chemisorption of small molecules on metal surfaces [2-7] Braunstein and

co-workers have recently found that silica-tethered alkyne mixed metal clusters obtained

by the sol-gel method have the potential to function as precursors to bimetallic nano

particles (Scheme 3.1) [8]

The reaction of tetrahedral clusters with internal and terminal alkynes often results in cluster opening to give butterfly structures [9] The butterfly clusters are quite interesting because they represent an intermediate arrangement between the tetrahedral clusters and the planar clusters The relationship between tetrahedral, butterfly and “spiked” triangular clusters is depicted in Scheme 3.2

M M

M M

M M

Tetrahedron Butterfly "Spiked" triangle

Scheme 3.2

Sappa and coworkers have classified butterfly clusters into 13 classes (A-M) Tetrahedral clusters are known to react with alkynes to give class B butterfly clusters where the M3M’ skeleton takes the form of a butterfly and the alkyne C2 unit bonds to the metal framework in a μ4,η2 fashion to form a quasi-octahedral M3M’C2 skeleton (Figure 3.1) [10-12] The acetylenic C≡C bond is disposed parallel to the “hinge” metal–metal bond of the butterfly, and the alkyne interacts with all four metal atoms

C C

M'

M

Wing tip metal atoms

πσ

ππ

σ

π

Hinge metal atoms

Figure 3.1 M3M’C2 butterfly cluster core

The alkyne is coordinated to the two “hinge” metal atoms via σ bonds and to the two

“wing-tip” metal atoms via its π bonds The total electron count for these clusters depends on the method used for counting Considering the alkyne as a four-electron donor, as is conventional in the EAN formalism, these clusters are 60-electron systems This gives an implication that they are electron deficient, since a M3M’ butterfly cluster consistent with the noble gas rule would require 62 electrons However, according to Wade’s system, they are considered as octahedral M3M’C2 clusters, with each CR unit donating three electrons to the skeletal bonding The clusters are therefore 62-electron “electron precise” butterflies or 14-electron closo octahedra [13]

The acetylenic C-C bond lengths in the coordinated “alkyne” in these clusters show considerable variations, ranging from 1.34 to 1.56 Å, indicating considerable bond lengthening and possible deactivation Following a criterion used by Muetterties, the elongation of the alkyne C≡C bond after coordination to more than one metal centre is taken as a parameter of activation upon coordination and used for comparison with the behaviour of these molecules on surfaces [14] According to his hypothesis, the stronger the interaction of the alkyne with the cluster, either for σ−bound or for σ-π-bound alkynes, the greater is the probability of finding long C-C bond distances, sometimes close to C-C single bond The nature of the metal is also thought to play a role in the activation process with the longest C-C bonds observed in the complexes

of the heaviest metals [9, 15, 16] The dihedral angle between the two M’MM planes usually lies in very narrow range between 112º and 118º, because of the restrictions imposed on the metal framework by the coordinated alkyne

Various isomers are possible for the M3M’C2 skeleton and for the coordinated alkynes It can be seen that in Figure 3.2 (a) and (c) the alkyne is disposed parallel to a

Table 3.1 summarises some of the reactions of tetrahedral mixed metal clusters with alkynes It can be seen that most heterometallic tetrahedral clusters reacted with alkynes to afford butterfly clusters Most of these reactions afforded products exhibiting either hinge-apex or alkyne, or both types of isomerisms In some cases the reactions were found to be highly stereoselective For example, the reaction of [CpMRu3(CO)12]⎯ (M=W, Mo), IrRu3(μ-H)(CO)13 and [Ru3Ir(CO)13]⎯ towards internal alkynes afforded M-Ru (M = W, Mo and Ir ) clusters with alkyne insertion into the Ru-Ru bond as the only product However, the reaction of [CpMRu3(CO)12]⎯ (M=W, Mo) clusters with phenyl acetylene afforded M-Ru cis and trans isomers

heterometallic MM’ bond (MM’) whereas in (b) the alkyne is disposed parallel to a homometallic MM bond (MM) and thus they are related as hinge-apex isomers; (c) differs from both (a) and (b) in the orientation of the alkyne and thus they are related

as alkyne isomers

Figure 3.2 (a), (b) Metal hinge-apex isomers (c) alkyne isomer

C C

Table 3.1 Reactions of tetrahedral mixed-metal clusters with alkynes

hinge apex hinge apex

hinge apex, alkyne

Hexane reflux

15 min

Fe-Ru, 48%

Fe-Ru, 5%

Fe-Ru, (Ph cis to Fe) 31%

Fe-Ru, (Ph trans to Fe) 10%

Ru-Ru, 17%

Ru-Ru, 25%

Ru-Ru, 41%

[18]

[MoRu3Cp(CO)12][PPh4] MeC≡CMe PhC≡CH alkyne - THF reflux, 2 h Mo-Ru (Ph cis to Mo) Mo-Ru, 65%

Mo-Ru (Ph trans to Mo) }50%

- alkyne THF reflux, 7 h

Co-Ru, 75%

Co-Ru (Ph cis to Co)

Co-Ru (Ph trans to Co) }73%

The reaction of FeRu3(μ-H)2(CO)13 with alkynes is quite interesting as it afforded hinge-apex as well as alkyne isomers (Figure 3.3)

C C R

Fe

Ru

ia: R = R' = Ph iia: R = R' = Me iiia: R = Ph; R' = Me

ib: R = R' = Ph iib: R = R' = Me iiib: R = Me R' = Ph iiic: R = Ph; R' = Me R

Figure 3.3 Hinge-apex and alkyne isomerism in FeRu3(CO)12(RCCR’) clusters

In the reaction of both CpRhRu3(μ-H)4(CO)9 and FeRu3(μ-H)2(CO)13 towards alkynes, hinge-apex isomerism was observed and the isomer with the heterometal atom at the hinge (Rh-Ru or Fe-Ru) was obtained as the major isomer from the reaction However, this isomer readily isomerised to the Ru-Ru isomer with the heterometal at the wingtip in both cases In the case of CpRhRu3(μ-H)4(CO)9, the isomerisation was observed on purification of the product on TLC plates while in the case of FeRu3(μ-H)2(CO)13, isomerisation occurred upon heating The reverse isomerisation was not facile in these systems This suggested that for these two systems, the isomer with the heterometal atom in the hinge was the kinetically favored product and that with the heterometal atom in the wingtip was the thermodynamically stable product

The reactions of the neutral cluster IrRu3(μ-H)(CO)13, and the anionic cluster [Ru3Ir(CO)13]⎯, towards alkynes were found to afford clusters exhibiting μ3,η2

coordination mode of the alkynes on a face of a tetrahedral metal framework, in addition to the μ4,η2 coordination mode (Scheme 3.3) IrRu3(μ-H)(CO)13 was found

to be an excellent catalyst for the hydrogenation of diphenylacetylene to stilbene and the alkyne substituted clusters were found to represent side-channels of the catalytic cycle

Ir

Ru H

H

C C R

3.2 Reaction of Cp*IrRu3(μ-H)2(CO)10, 3a, with internal alkynes

3.2.1 Reaction of 3a with RCCR (R = Ph, Et)

The thermal reaction of 3a with RCCR (R = Ph, Et) in hexane afforded a dark red

solution which after separation by TLC on silica-gel plates afforded three bands In both the reactions the fastest moving band 1 afforded red crystals which were characterized by IR and 1H NMR spectroscopy, microanalyses and further characterized by single X-ray crystallographic studies; the compounds were identified

as the novel clusters, Cp*Ru3Ir(CO)9(RCCR) [R = Ph = 10a; R = Et = 10b] The IR

spectrum of 10b recorded in hexane is shown in Figure 3.4 and the ORTEP diagram

of 10a is shown in Figure 3.5

Figure 3.4 IR spectrum of 10b in hexane

Figure 3.5 ORTEP diagram of Cp*Ru3Ir(CO)9(PhCCPh),10a Thermal ellipsoids are drawn at the 50% probability level The phenyl hydrogens are omitted for clarity

The molecular structure of 10a consisted of a butterfly skeleton; the butterfly

backbone consisted of ruthenium and iridium atoms which were bonded to two tip ruthenium atoms Each of the three ruthenium atoms were bonded to 3 carbonyls and the iridium atom was bonded to a Cp* ring All carbonyls were terminal The PhCCPh ligand was coordinated to the Ru3Ir metal core in a μ4,η2 fashion One of the carbon atoms (C50) was σ−bonded to Ir(1), and the second one (C60) was σ−bonded

wing-to Ru(3) Both carbon awing-toms were π-bonded wing-to the two wingtip ruthenium awing-toms The

C-C bond of the alkyne was disposed almost parallel to the hinge [(Ru(3)–Ir(1)] of the butterfly

The other two products from the reactions were the previously reported clusters, Ru3(CO)8(C4R4) [R = Ph = 12a, R = Et = 12b], which were identified by their IR and

1H NMR spectroscopic data [22], and the novel trinuclear clusters Cp*IrRu2(CO)7C2R2 [R = Ph = 11a, R = Et = 11b] The latter were characterized by

IR and 1H NMR spectroscopy, FAB-MS, microanalyses and single crystal X-ray crystallographic studies

The IR spectrum of 11b recorded in hexane is shown in Figure 3.6 and the ORTEP diagram of 11a is shown in Figure 3.7 Selected bond lengths and bond angles for 11a and 11b are presented in Table 3.2

Figure 3.6 IR spectrum of 11b in hexane

Figure 3.7 ORTEP diagram of Cp*IrRu2(CO)7C2(C6H5)2, 11a Thermal ellipsoids are drawn at 50% probability level The phenyl hydrogens are omitted for clarity

The overall molecular structures of 11a and 11b were similar, with the ruthenium and

iridium atoms forming a closed triangle The clusters had the expected 48-electron count for trinuclear clusters thus satisfying the noble gas rule A comparison of both structures showed that the distances Ru(2)-C(7) [2.094 (7) Å] and Ir(1)-C(6) [2.067

(6) Å] in 11b were similar to the analogous distances in 11a [Ru(2)-C(7) = 2.116(5)

and Ir(1)-C(6) = 2.090(6) (Å)] suggesting that changing the substituents on the alkyne had not affected the metal-carbon bond distances significantly Three terminal carbonyls each were bonded to Ru(3) and Ru(2) An asymmetric bridging carbonyl

was found to span the Ir(1)-Ru(2) edge The carbonyl bridged Ir(1)-Ru(2) bond was

longer than the unbridged Ir(1)- Ru(3) bond The alkyne ligand was coordinated in a

μ3,η2 fashion over the Ru2Ir triangle [21, 23] The alkyne C(6)-C(7) bond was

disposed almost parallel to the Ir(1)-Ru(2) edge of the metal triangle; this type of

bonding mode has been given the notation μ3,η2 It is generally considered to

donate four electrons to the cluster This type of bonding mode has been observed in

Co2Ru(CO)9(C2Ph2), Ru2Ni(CO)4Cp2(PhCCPh), and OsW2(CO)7Cp2(TolCCTol)

[24-27]

Table 3.2 Selected bond lengths (Å) and bond angles (º) of compounds 11a and 11b

11a 11b

Ir(1)-Ru(2) 2.7977(5) 2.8034(5) Ir(1)-Ru(3) 2.7091(5) 2.7022(5) Ru(2)-Ru(3) 2.6852(6) 2.6892(7) Ir(1)-C(6) 2.090(6) 2.067(6) Ru(2)-C(7) 2.116(5) 2.094(7) Ru(3)-C(6) 2.196(5) 2.196(5) Ru(3)-C(7) 2.250(5) 2.214(6) C(6)-C(7) 1.393(8) 1.402(9) Ir(1)-C(11) 1.880(6) 1.893(7) Ru(2)-C(11) 2.422(6) 2.362(7)

All the metal-metal bond distances were different but were within the range of Ru-Ru and Ru-Ir single bonds [28, 29] The C(6) and C(7) carbon atoms of the alkyne were σ−bonded to Ir(1) as well as Ru(2), and were both π-bonded to Ru(3) The

coordinated alkyne carbon-carbon bond length for 11a and 11b were found to be

1.393(8) Å and 1.402(9) (Å), respectively, which suggested that the formal bond order was less than two The C≡C bond lengths were slightly longer than those in the related clusters, [IrRu2(CO)9(μ3-η2C2Ph2)]⎯, [IrRu2(CO)9(μ3-η2PhC2Me)]⎯ and [Co2Ru(CO)9(C2Ph2)], in which the C-C bond lengths measured 1.363(11) , 1.372(9) and 1.370(3) Å, respectively [21, 24]

Prolonged heating of cluster 3a with PhCCPh and EtCCEt resulted in increased yields

of clusters 11a and 11b at the expense of 10a and 10b, respectively This suggested that 11a and 11b were derived from the butterfly alkyne clusters 10a and 10b, respectively To verify this, thermolyses of clusters 10a and 10b were carried out and the reaction afforded 11a and 11b, thus confirming that the former were the precursors to the latter Furthermore, photolysis of solutions of 10a and 10b under UV also yielded 11a and 11b This suggested that the butterfly alkyne clusters were not

very stable at high temperatures as well as under photolytic conditions and were prone

to undergo fragmentation to yield the stable triangular clusters (Scheme 3.4)

Thermolysis or photolysis of 10a and 10b did not yield the triruthenium clusters 12a and 12b, which suggested that 10a and 10b were not their precursors and that the formation of 12a and 12b probably followed a different pathway Reactions of

Cp*Ir(CO)2 with 12a or 12b were attempted under thermolytic and photolytic

conditions to see whether 10a and 10b were formed IR monitoring of the reactions

did not indicate any reaction

C C R R'

3.2.2 Reaction of 3a with MeCCBu t

Thermal reaction of 3a with 4, 4-dimethyl 2-pentyne afforded red crystals of 10c, with IR spectroscopic characteristics similar to those of 10a and 10b The identity of

10c has been confirmed by a single crystal X-ray structural study as Cp*Ru3Ir(CO)9(MeCCBut) The ORTEP plot of 10c is shown in Figure 3.8 The overall structure of 10c was similar to 10a and 10b However, it was noted that in this

case, the bonding mode appeared to be highly stereoselective, with the tBu group in the alkyne being positioned away from the iridium atom The 1H NMR spectrum did not suggest the presence of isomers IR monitoring of the reaction showed strong peaks due to Cp*Ir(CO)2, suggesting fragmentation of the cluster Trinuclear ruthenium clusters were not isolated in this reaction, unlike with the other alkynes, as most of the bands were not stable on the TLC plates

Figure 3.8 ORTEP diagram of Cp*IrRu3(CO)7(MeCCBut), 10c Thermal ellipsoids

are drawn at 50% probability level Organic hydrogens are omitted for clarity

3.2.3 Reaction of 3a with R 3 SiCCSiR 3 (R = Me, Et)

The thermal reaction of 3a with R3SiCCSiR3 (R = Me, Et) in hexane afforded two

products (Scheme 3.5) One of them were the known triruthenium clusters Ru3(CO)9(μ-H)(C2SiR3) (R = Me , 13; R = Et , 14), obtained in ~ 30% yields as yellow crystalline solids, identified by their IR and 1H NMR spectroscopic data [30]

A second red, crystalline product was obtained in ~ 15% yields The IR spectra

recorded in hexane solution were similar to 10a-c, suggesting a similar structure

R 3 SiCCSiR 3 / 60 °C intramolecular -C-R bond cleavage

C C

Ru Ir

+

13 R = Me

14 R = Et

10d R = Me 10e R = Et

10d ; R = Et, 10e) The ORTEP plot of 10d is shown in Figure 3.9

The 1H NMR and FAB-MS data were consistent with the suggestion that a trialkylsilyl group was lost and replaced by hydrogen The singlets at ~ δ 10.5 ppm corresponded to the alkenic hydrogens on the alkynes and the values were in agreement with similar compounds reported in the literature (δ 9.18 ppm in Ru3(CO)10HCCSiMe3 and δ 10.56 ppm in Os3(CO)10HCCSiMe3, [31]) 1H NMR monitoring of the reaction with Me3SiCCSiMe3 showed that the trimethylsilyl group was lost during the course of reaction and not during workup procedure GC analysis

of an aliquot of the crude reaction mixture suggested that the trimethylsilyl group was lost as octamethyl trisiloxane, which suggested that the hydrogen might have originated from trace amounts of water However, the desilylation product was observed in almost similar yields even when the reaction was carried out with

thoroughly dried solvents and glassware, which ruled out the above postulation Since Cp*Ir(CO)2 is known to bring about C-H activation of hydrocarbons, it is also possible that the Cp*Ir(CO) fragment in these clusters might be responsible for the hydride exchange with the SiMe3 group

Figure 3.9 ORTEP diagram of Cp*Ru3Ir(CO)9(Me3SiCCH), 10d Thermal ellipsoids are drawn at 50% probability level Organic hydrogens are omitted for clarity

Desilylation has been reported by Schneider and coworkers in their attempt to synthesize Fe-Ni heteronuclear clusters by the vaporisation of nickel atoms into a solution of (bistrimethylsilyl)acetylene and Fe(CO)5 [32] The reaction had unexpectedly afforded the cluster Fe3(CO)9(μ-H)(C≡CSiMe3), which was similar to

13 and 14 in that desilylation of one of the trimethylsilyl groups had occurred However, in their reactions they have not reported compounds similar to 10d and 10e

where one of the trialkylsilyl groups was replaced by a hydrogen, although it was

suggested that cleavage might have occurred during chromatographic work-up Vahrenkamp and coworkers have also reported desilylation in the reaction of RuCo2(CO)11 with Me3SiC≡CMe The initial product, RuCo2(CO)9(μ3-Me3SiC≡CMe), formed in the reaction underwent subsequent desilylation to give RuCo2(CO)9(μ3-HC≡CMe) [33]

3.3 Reaction of 3a with terminal alkynes

3.3.1 Reaction of 3a with PhCCH

Reaction of cluster 3a with phenyl acetylene afforded three red crystalline products

The major product, obtained in 28% yield, was identified as Cp*IrRu3(CO)9(PhCCH),

10f 3; it was characterized spectroscopically and analytically, as well as by a single

crystal X-ray structure analysis The ORTEP plot of 10f 3 is shown in Figure 3.10 The other two products were obtained in very low yields A single crystal X-ray

structural study on one of them showed it to be a hinge-apex isomer of 10f 3 The

ORTEP diagram of this isomer, 10f 2, is shown in Figure 3.11 The IR spectrum of the

third product had a pattern similar to 10a-e Its 1H NMR showed a multiplet between

δ 7.00 and 7.77 ppm due to aromatic protons, a singlet at δ 1.82 ppm which could be assigned to Cp* methyl protons, and a singlet at δ 10.58 ppm due to the alkyne C-H

Based on these spectroscopic characteristics it was tentatively identified as 10f 1, a third isomer of Cp*IrRu3(CO)9(PhCCH), 10f3

The three isomers, 10f 1 , 10f 2 and 10f 3, differed in the relative orientation of the alkyne with respect to the butterfly cluster core; they are depicted in Scheme 3.6, together with the notation employed

Figure 3.10 ORTEP diagram of Cp*Ru3Ir(CO)9(PhCCH), 10f3 Thermal ellipsoids are drawn at 50% probability level Organic hydrogens are omitted for clarity

Figure 3.11 ORTEP diagram of Cp*Ru3Ir(CO)9(PhCCH), 10f2 Thermal ellipsoids are drawn at 50% probability level Organic hydrogens are omitted for clarity

C C Ph H

C C Ph H

Ru

Ru

PhCCH -CO,-2H

In the reaction of 3a with internal alkynes, only the Ru-Ir isomer was observed;

prolonged heating of this isomer did not lead to isomerisation but to cluster

fragmentation instead In contrast, the reaction of 3a with phenyl acetylene yielded theRu-Ru isomer (10f 3) as the major product; the Ru-Ir cis and Ru-Ir trans isomers were obtained as minor products This suggested that there was an electronic

preference for the formation of theRu-Ru isomer; the extremely low yield of 10f 2

could be due to the steric effect of having both the bulky phenyl ring on the alkyne, and the Cp* ring on the iridium, close to each other

It was observed by the IR spectroscopy that on standing, a solution of 10f 3 converted

slowly to 10f 1 and 10f 2 NMR monitoring of a deuterated benzene solution of 10f 3 atambient temperature indicated the formation of two new singlets at δ 1.82 ppm and δ

1.87 ppm, assignable to the Cp* signals of 10f 1 and 10f 2,respectively, and also two

singlets at δ 10.58 ppm and δ 11.37 ppm, due to the respective C-H protons of the

phenyl acetylene However, complete conversion to either 10f 2 or 10f 3 was not

observed even after a month Prolonged heating of 10f 3 finally afforded a 1.2:1.0:5.4 equilibrium mixture of 10f 1 :10f 2 :10f 3. This showed that the equilibrium was always

towards the Ru-Ru isomer, 10f 3,indicating that it was the thermodynamically stable isomer This is in agreement with the earlier observations on the FeRu3 and RhRu3 systems [17, 18]

3.3.2 Reaction of 3a with n BuCCH

The reaction of 3a with 1-hexyne afforded a red solid in very low yield The IR spectral profile was similar to that of 10f 1, suggesting a similar structure Further characterization was not possible because of the low yield The compound was tentatively identified as Cp*IrRu3(CO)9(nBuCCH), 10g

3.3.3 Reaction of 3a with Me 3 SiCCH

The reaction of cluster 3a with Me3SiCCH afforded two products which were identified as 10d (17% yield) and Ru3(CO)9(μ-H)(C2SiR3), 13 (30% yield) Thus the reaction of 3a with both bis(trimethylsilyl)acetylene (an internal alkyne) and

trimethylsilyl acetylene (a terminal alkyne) yielded similar products

3.3.4 Reaction of 3a with 1-hexene

The reaction of 3a with 1-hexene was investigated in an attempt to prepare

cluster-olefin complexes but none could be isolated Instead, it was found that the cluster catalysed isomerisation of 1-hexene to give a mixture of cis and trans 2-hexenes The reaction was carried out in an NMR tube and monitored by 1H NMR (Figure 3.12) However, complete isomerisation was not observed even after long hours The

infrared spectrum of the reaction mixture after 7 h showed that 3a remained mainly

unreacted However, further investigations were not carried out to isolate and quantify the products

Figure 3.12 1H NMR spectrum (δ 4.0 - 6.0 ppm region) of (a) 1-hexene (b)

(d)

(c)

(b) (a)

immediately after mixing (c) after 3 h (d) 2-hexene

3.4 Reaction of Cp*IrOs3(μ-H)2(CO)10, 3c and Cp*IrOs3(μ-H)4(CO)9, 4b, towards alkynes

The mixed metal clusters, Cp*IrOs3(μ-H)2(CO)10, 3c, and Cp*IrOs3(μ-H)4(CO) , 9 4b ,

did not react with excess alkyne even at 120 ºC Photochemical activation (Hanovia lamp, 450 W, quartz vessel) afforded some reaction but the products were in low

yields Chemical activation of 3c and 4b with excess triethylamine afforded alkyne

substituted mixed metal clusters Cp*IrOs (CO) (RCCR) 3 9

3.4.1 Reaction of 4b with RCCR (R = Ph, Et)

Reaction of 4b with RCCR (R = Ph, Et) in the presence of excess triethyl amine

afforded two products The IR spectral pattern of one of the products were similar to

those of 10, in which the alkyne was disposed parallel to a Ru-Ir hinge Further

characterization of one of them by single crystal X-ray analysis revealed the identity

as Cp*IrOs3(CO)9(PhCCPh), 15a1; The identity of Cp*IrOs3(CO)9(EtCCEt), 15b1

was confirmed by its IR and FAB-MS characteristics The ORTEP plot of 15a 1 is shown in Figure 3.13 Its overall structure was similar to those of the Cp*IrRu3(CO)9(RCCR’) clusters 10a-e, in that the alkyne was oriented parallel to the Os-Ir hinge (Os-Ir), with two osmium atoms occupying the wingtip positions of the Os3Ir butterfly core

The IR spectral profile of the other product in both the reactions was similar to that of

10f 3 in which the alkyne was oriented parallel to a Ru-Ru bond Single crystal X-ray structural studies confirmed their identities as Cp*IrOs3(CO)9(RCCR) [R = Ph, 15a2;

R = Et, 15b 2 ], the hinge apex isomers of 15a 1 and 15b 1, respectively The ORTEP

plot of 15a 2 is shown in Figure 3.14

Figure 3.13 ORTEP diagram of Cp*Os3Ir(CO)9(PhCCPh), 15a1 Thermal ellipsoids are drawn at 50% probability level Phenyl hydrogens are omitted for clarity

Figure 3.14 ORTEP diagram of Cp*Os3Ir(CO)9(PhCCPh), 15a2 Thermal ellipsoids are drawn at 50% probability level Phenyl hydrogens are omitted for clarity

3.4.2 Reaction of 4b with PhCCH

Reaction of 4b with phenyl acetylene afforded two bands in relatively low yields The

fast moving band 1 was identified as Cp*IrOs3(CO)9(PhCCH) (Os-Ir), 15c 1, from its IR, FAB-MS and 1H NMR characteristics The structure was further confirmed by

a single crystal X-ray analysis Recrystallization of band 2 from a mixture of hexane and dichloromethane gave both red and orange crystals Mechanical separation of the red crystals followed by IR and FAB-MS characterization revealed its identity as Cp*IrOs3(CO)9(PhCCH) (Os-Os), 15c 2

The orange crystals were identified as Cp*IrOs (CO) (PhCCH)3 9 2, 16, by a single

crystal X-ray crystallographic study The ORTEP plot of 16 together with selected bond parameters is shown in Figure 3.15 A schematic diagram of 16 is shown in Figure 3.16 The structure of 16 consisted of an Os3Ir butterfly core Two PhCCH

units were found to be coordinated to the cluster core One of the alkyne C-C unit was bound to three osmium atoms via σ and π-bonding The second alkyne unit was bonded to two osmium atoms and an iridium atom, exhibiting both σ and π bonding The metal-metal bond distances were in the expected range for Os-Os and Os-Ir single bonds[34, 35]

Figure 3.15 ORTEP diagram of Cp*Os3Ir(CO)9(PhCCH)2, 16 Thermal ellipsoids are drawn at 50% probability level Organic hydrogens are omitted for clarity Ir(1)-Os(4) = 2.7251(4) Å; Ir(1)-Os(2) = 2.7456(4) Å; Os(2)-Os(3) = 2.8594(4) Å; Os(3)-Os(4) = 2.8541(5) Å; Ir(1)-Os(2)-Os(3) = 89.523(13)º; Ir(1)-Os(4)-Os(3) = 90.044(13) Å

Os

Os Os

Ir

C

C C

Ph H

C H Ph Figure 3.16 Schematic diagram of 16