Synthesis of [Ir3Rh(CO)12] and Fluxional Behaviour of Some of Its Substituted Derivatives

The redox condensation of [Ir(CO)₄]^–, [Ir(cod)(THF)₂]⁺, and [Rh(cod)(THF)₂]⁺ (cod = cycloocta-1,5-diene) followed by saturation with CO (1 atm) in THF afforded the first synthetic route to pure [Ir₃Rh(CO)₁₂] ( 1 ). Substitution of CO by monodentate ligands gave [Ir₃Rh(CO)₈(μ₂-CO)₃L] (L = Br^–, 2 ; I^–, 3 ; bicyclo[2.2.1]hept-2-ene, 4 ; PPh₃, 5 ). Clusters 2 – 5 have C_s symmetry with the ligand L bound to the basal Rh-atom in axial position. They are fluxional in solution at the NMR time scale due to two CO scrambling processes: the merry-go-round of basal CO's and changes of basal face. An additional process takes place in 5 above room temperature: the intramolecular migration of PPh₃ from the Rh- to a basal Ir-atom. Substitution of CO by polydentate ligands gave [Ir₃Rh(CO)_7–x(μ₂-CO)₃(η⁴-L)x] (L = bicyclo[2.2.1]hepta-2,5-diene (= norbornadiene; nbd), x = 1, 6 ; L = nbd, x = 2, 13 ; L = cod, x = 1, 7 ; L = cod x = 2, 15 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η²-diars)] (diars = 1,2-phenylenebis-(dimethylarsine); 8 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η⁴-L)] (L = methylenebis(diphenylphosphine), bonded to 2 basal Ir-atom ( 9a ) or one Ir- and one Rh-atom ( 9b )), [Ir₃Rh(CO)₆(μ₂-CO)₃(η⁴-nbd)PPh₃] ( 12 ), and [Ir₃Rh(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, 10 ; L = CH(PPh₂)₃, 11 ). Complexes 6 – 8 , 9a , 10 , and 11 have C_s symmetry, the others C₁ symmetry. They are fluxional in solution due to CO scrambling processes involving 1, 3, or 4 metal centres as deduced from 2D-EXSY spectra. Comparison of the activation energies of these processes with those of the isostructural Ir₄ and Ir₂Rh₂ compounds showed that substitution of Ir by Rh in the basal face of an Ir₄ compound slows the processes involving 3 or 4 metal centres (merry-go-round and change of basal face), but increases the rate of carbonyl rotation about an Ir-atom.     

Synthesis,Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2]

The synthesis of [Ir₂Rh₂(CO)₁₂] ( 1 ) by the literature method gives a mixture 1 /[IrRh₃(CO)₁₂] which cannot be separated using chromatography. The reaction of [Ir(CO)₄]^? with 1 mol-equiv. of [Rh(CO)₂(THF)₂]⁺ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir₂Rh₂(CO)₅(μ₂-CO)₃(norbornadiene)₂] which were analysed using X-ray diffraction. The ground-state geometry of 1 in solution has three edge-bridging CO's on the basal IrRh₂ face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D- and VT-¹³C-NMR. Substitution of CO by X^? in 1 takes place at a Rh-atom giving [Ir₂Rh₂(CO)₈(μ₂-CO)₃X]^? (X = Br, I). Substitution by bidentate ligands gives [Ir₂Rh₂(CO)₇(μ₂-CO)₃(η⁴-L)] (L = norbornadiene, cycloocta-1,5-diene) where the ligand L is chelating a Rh-atom of the basal IrRh₂ face. Carbonyl substitution by tridentate ligands gives [Ir₂Rh₂(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C₃ axis on the apical Ir-atom.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge-bridging bidentate ligands

The fluxionality of [Ir₄(CO)₈(μ₂-CO)₃L] (L = Br^?, I^?, SCN^?, NO₂^?, P(4-ClC₆H₄)₃, PPh₃, P(4-MeOC₆H₄)₃, P(4-Me₂NC₆H₄)₃), as studied by 2D-¹³C-NMR in solution, is due to two successive scrambling processes: the merry-go-round of six basal CO's and CO bridging to alternative faces of the Ir₄ tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir₄(CO)₇(μ₂-CO)₃(PMePh₂)₂] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir₄(CO)₁₀(μ₂-L? L)] with one edge-bridging ligand have a ground-state geometry with three edge-bridging CO's (L? L = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (L? L = CH₃SCH₂SCH₃). In all cases, the fluxional process of lowest activation energy in the merry-go-round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir-atoms residing on the mirror plane of the unbridged intermediate.     

Ruthenium cluster chemistry: Monodentate bis(diphenylphosphino)acetylene-ligated cluster modules in chain and dendrimer formation

Reaction of Ru₃(μ-dppm)(CO)₁₀ [dppm = bis(diphenylphosphino)methane] with one equivalent of dppa [dppa = bis(diphenylphosphino)acetylene] afforded Ru₃(μ-dppm)(CO)₉(η¹-dppa) which possesses a monodentate dppa ligand,an X-ray structural study revealing that all phosphorus donor atoms are arranged in equatorial coordination sites with respect to the triruthenium cluster plane.Reaction of Ru₃(CO)₉(NCMe)₃ with excess dppa afforded fair yields of Ru₃(CO)₉(η¹-dppa)₃,which possesses three monodentate dppa ligands.Reaction of three equivalents of Ru₃(μ-dppm)(CO)₉(η¹-dppa) with Ru₃(CO)₉(NCMe)₃ or reaction of Ru₃(CO)₉(η¹-dppa)₃ with excess Ru₃(μ-dppm)(CO)₁₀ afforded low yields of the dodecanuclear first-generation dendrimer Ru₃(CO)₉{PPh₂C₂PPh₂Ru₃(μ-dppm)(CO)₉}₃.Reaction of WIr₃(μ-CO)₃(CO)₈(η-C₅Me₅) with excess Ru₃(μ-dppm)(CO)₉(η¹-dppa) afforded fair yields of the decanuclear dppa-bridged tri-cluster WIr₃(CO)₉{PPh₂C₂PPh₂Ru₃(μ-dppm)(CO)₉}₂(η-C₅Me₅).     

Reaction of [M(CO)4] (M = Ir, Rh) with cyclopropenyl tetrafluoroborate - Ring opening and coupling of cyclopropenyl ligands to form dinuclear metal complexes

Reaction of the iridium tetracarbonylate [PPN][Ir(CO)₄] (1a) with triphenylcyclopropenyl tetrafluoroborate [C₃Ph₃][BF₄] afforded two dinuclear species Ir₂(CO)₄(μ,η¹:η²-C₃Ph₃)(μ,η²:η³-C₃Ph₃) (2) and Ir₂(CO)₄(μ,η⁴:η⁴-C₆Ph₆) (3a) resulting from the ring opening and in the latter case, coupling of the resulting acyclic, propenyl ligands. The analogous reaction with [PPN][Rh(CO)₄] (1b) afforded only the rhodium analogue for 3a.     

A synthetic route to heteronuclear clusters containing iridium and rhodium: X-ray crystal structures of [IrOs3(μ-H)2(μ-Cl)(CO)12] and [Ir2Rh2(μ-CO)(μ3-CO)2(CO)4(η-C5Me5)2]

The iridium and rhodium complexes [MCl(CO)₂(NH₂C₆H₄Me-4)] (M = Ir or Rh) react with [Os₃(μ-H)₂(CO)₁₀] to give the tetranuclear clusters [MOs₃(μ-H)₂(μ-Cl)(CO)₁₂]; the iridium compound being structurally identified by X-ray diffraction. Similarly, [IrCl(CO)₂(NH₂C₆H₄Me-4)] and [Rh₂(μ-CO)₂(η-C₅Me₅)₂] afford the tetranuclear cluster [Ir₂Rh₂(μ-CO)(μ₃-CO)₂(CO)₄(η-C₅Me₅)₂], also characterised by single-crystal X-ray crystallog     

Conversion of allene into μ-dimethylcarbene at a diruthenium centre

Treatment of [Ru₂(CO)(μ-CO) {μ-C(O)C₂Ph₂} (η-C ₅H₅)₂] with allene in toluene at 100°C displaces diphenylacetylene and produces [Ru(CO)(η-C₅H₅)-{η³-C₃H₄Ru(CO)₂(η-C₅H₅)}]; upon protonation a 1-methylvinyl cation [Ru₂(CO)₂(μ-CO){μ-C(Me)CH₂}(η-C₅H₅)₂]⁺ is formed which undergoes nucleophillic attack by hydride to yield the μ-dimethylcarbene complex [Ru₂(CO)₂-(μ-CO)(μ-CMe₂)(η-C₅H₅)₂].     

Tetrairidium carbonyl clusters of mono- and di-olefins

The reactions of NEt₄ [Ir₄(CO)₁₁ Br] (I) with mono- and di-olefins in the presence of AgBF₄ gave high yields ( > 90%) of Ir₄(CO)₁₁ (olefin) (II) and Ir4(CO)₁₀(η⁴-diolefin) (III). Oxidation of Ir₄(CO)₁₁ (L = PPh₃, AsPh₃) in the presence of an excess of diolefin by 1 eq. ON(CH₃)₃ gave the clusters Ir₄(CO)₉L(η⁴-diolefin) (IV) and Ir₄(CO)₇L(η⁴-diolefin)₂ (V). Sulphur dioxide quantitatively displaces the monoolefin ligand from II to give Ir₄(CO)₉(μ₂-CO)₂(μ₂-SO₂), which is the first example of a tetrairidium- SO₂ cluster.     

Preparation and Characterization of an Unusual Di-Cobalt Complex; X-Ray Crystal Structure of Co(CO)2(μ-CO)(μ:η2,η4-C4Ph4)Co(CO)2(PPh3)

Reaction of [MoCo(CO)₅(PPh₃)₂(η⁵-C₅H₅)] (1) with diphenylacetylene in tetrahydrofuran at 50 °C yielded two heterobimetallic compounds, [MoCo(CO)₄.(PPh₃){μ-PhC ? CPh}(η⁵-C₅H₅)] (4) and [MoCo(CO)₅{μ-PhC ? CPh} (η⁵-C₅H₅)] (5). However, an unexpected product, Co(CO)₂(μ-CO)(μ:η₂,η⁴-C₄Ph₄)Co(CO)₂(PPh₃) (6), was observed while attempting to grow the crystals for structural determination of 4. The X-ray crystal structure of 6 was determined: triclinic, $ {\rm P}\bar 1 $, a = 11.654(2) Å, b = 12.864(2) Å, c = 13.854(2) Å, α = 89.67(2)°, β = 86.00(2)°, γ= 83.33(2)°, V = 2057.9(6) ų Z=2. In 6, two cobalt fragments are at apical and basal positions of the pseudo-pentagonal pyramidal structure, respectively. The electron count for the apical cobalt fragments is 20, which is rather unusual. It is believed that 6 was formed after the fragmentation and recombination of the fragmented species of 4.     

Metathetical reactions of carbonylate anions with dichlororuthenium complexes: Preparation and characterization of ruthenium—molybdenum and ruthenium—manganese complexes

The possibility of making metal—metal bonded heterobimetallic species by metathesis of ruthenium dichlorides with anionic carbonylates is demonstrated by the isolation of MoRu(μ-Cl)(μ-CO)(CO)₂(PPh₃)₂(η-C₅H₅) (1) and MnRuCl(μ-CO)₂(CO)₃(μ-dppm)₂ (2), obtained by action of [Mo(CO)₃(η-C₅H₅]^? on RuCl₂(PPh₃)₃ and of Mn(CO)₅^? on RuCl₂(dppm)₂, respectively. In contrast, reaction of Mn(CO)₅^? with RuCl₂(PMe₃)₄ yielded an ionic species 3 containing the diruthenium cation Ru₂Cl₃(PMe₃)₆⁺. More interestingly, the action of Mn(CO)₅^? on RuCl₂(PPh₃)₃ resulted in the formation of the unexpected complex MnRu(μ-PPh₂)(CO)₆(PPh₃)₂ (4) in which the phosphido group PPh₂ bridges the two metals; this process is shown to involve a hydride intermediate, and elimination of a molecule of benzene, both identified in the reaction mixture.     

Synthesis and structural characterisation of [Ru8(μ8-P)(μ2-η1,η6-CH2C6H5)(μ2-CO)2(CO)17]: example of phosphorus encapsulated in a square anti-prism of ruthenium atoms and of an unusual coordination mode for the benzyl group

Reaction of [Ru₃(CO)₁₂] with an equimolar amount of PPh₂H affords a range of products including an octaruthenium species [Ru₈(μ₈-P)(μ₂-η¹,η⁶-CH₂C₆H₅)(μ₂-CO)₂(CO)₁₇], in which, as established X-ray crystallographically, a phosphorus atom is encapsulated in a square anti-prism of ruthenium atoms and a benzyl group is coordinated to two of these rutheniums through all seven carbon atoms.     

Variable-Temperature and -Pressure 31P-NMR Study of the Intramolecular PPh3 Migration in the Cluster Compound [Ir2Rh2(CO)11PPh3]

The reaction of [Ir₂Rh₂(CO)₁₂] with 1 mol-equiv. of PPh₃ yields [Ir₂Rh₂(CO)₁₁PPh₃] ( 1 ) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh-atom in the kinetically preferred isomer 1 R or to one basal Ir-atom in the thermodynamically preferred isomer 11 . Both isomers are fluxional on the ¹³C-NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R?11 , i.e. the intramolecular migration of the reputedly inert PPh₃ ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh₃ is dissociative in character. This article reports the first application of variable pressure ³¹P-NMR to mechanistic studies.     

The cleavage of a coordinated SCNR group in [Fe(CO)2L2(η2-SCNR)] by [Co(η-C5H5)(PPh3)2] to give complexes containing μ3-CNR ligand. The preparation and structure of [{Co(η-C5H5)}2{Fe(CO)2(PPh3)}(μ3-S){μ3-CNC(O)C6H5}]

The reaction of [Fe(CO)₂(PPh₃)₂{η²-SCNC(O)Ph}] with [Co(η-C₅H₅)(PPh₃)₂] in benzene solution at room temperature results in the facile cleavage of the CS bond of the SCNC(O)Ph ligand to give [{Co(η-C₅H₅)}₂{Fe(CO)₂(PPh₃)}(μ₃-S{μ₃-CNC(O)Ph}], whereas [Fe(CO)₂(PPh₃)₂(η²-SCNMe)] gives [{Co(η-C₅H₅)} ₂₂{Fe(CO)(CNMe)(PPh₃)(μ₃-S)(μ₃-CO)]. The structure of [{Co(η-C₅H₅)}₂{Fe(CO)₂(PPh₃)} (μ₃-CNC(O)Ph}] has been confirmed by X-ray diffraction.     

Coordination chemistry of the [Pt2(μ-S)2(PPh3)4] metalloligand with π-hydrocarbon derivatives of d ruthenium(II), osmium(II), rhodium(III) and iridium(III)

The reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards [RuCl₂(η⁶-arene)]₂ (arene=C₆H₆, C₆Me₆, p-MeC₆H₄Prⁱ=p-cymene), [OsCl₂(η⁶-p-cymene)]₂ and [MCl₂(η⁵-C₅Me₅)]₂ (M=Rh, Ir) have been probed using electrospray ionisation mass spectrometry. In all cases, dicationic products of the type [Pt₂(μ-S)₂(PPh₃)₄ML]²⁺ (L=π-hydrocarbon ligand) are observed, and a number of complexes have been prepared on the synthetic scale, isolated as their BPh₄⁻ or PF₆⁻ salts, and fully characterised. A single-crystal X-ray structure determination on the Ru p-cymene derivative confirms the presence of a pseudo-five-coordinate Ru centre. This resists addition of small donor ligands such as CO and pyridine. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with RuClCp(PPh₃)₂ (Cp=η⁵-C₅H₅) gives [Pt₂(μ-S)₂(PPh₃)₄RuCp]⁺. In addition, the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with the related carbonyl complex [RuCl₂(CO)₃]₂, monitored by electrospray mass spectrometry, gives [Pt₂(μ-S)₂(PPh₃)₄Ru(CO)₃Cl]⁺.     

Synthesis of the compounds [Re(CR)(CO)2(η5-C9H7)][BF4] (R = C6H4Me-4 or C6H3Me2-2,6) and the preparation of complexes with FeRe bonds

The salts [Re(CR)CO)₂(η⁵-C₉H₇)][BF₄] [R = C₆H₄Me-4 or C₆H₃Me-2,6; η⁵- C₉H₇ = indenyl] have been prepared and used to synthesize the dimetal compounds [FeRe(μ-CR)(μ-NO)(CO)₄(η⁵-C₉H₇)]. The iron-rhenium species containing a bridging p- tolylmethylidyne ligands react with [Fe₂(CO)₉] or with [Ru(CO)₄(η-C₂H₄)], respectively, to yield the trimetal compounds ([FeMRe(μ₃-CC₆H₄Me-4)(μ-CO)(μ-NO)(CO)₆(η ₅-C₉H₇)] (M = Fe or Ru).     

Unusual tetra- and penta-ruthenium complexes from linking of ethylidyne and vinylidene ligands

The complexes [Ru₂(CO)₂(μ-CO)(μ-CMe)(η-C₅H₅)₂]^? and [Ru₂CO₂(μ-CO)(μ-CCH₂)(η-C₅H₅)₂] react together to give [{Ru₂CO)₃(η-C₅H₅)₂}₂(μ-CMeCHCH)]⁺ and [{Ru₃(CO)₃(η-C₅H₅)₃}(μ-CCH₂CHC){Ru₂(CO)₃(η-C₅H₅)₂}], each characterised by X-ray diffraction. The former results from ethylidyne-vinylidene linking followed by an alkylidyne to vinyl rearrangement.     

Synthesis and structural characterization of the first transition metal cluster containing a PPh2AuPPh3 ligand,Ir4(CO)8(μ-CO)3(PPh2AuPPh3), and its conversion into Ir4(CO)9(μ-CO)(μ-PPh2)(μ-AuPPh3)

Deprotonation of Ir₄(CO)₁₁PPh₂H (1) in the presence of [AuPPh₃][PF₆] yields the novel species Ir₄(CO)₁₁(PPh₂AuPPh₃) (2), which possesses a tetrahedral framework bearing a terminally bound PPh₂AuPPh₃ ligand. When heated in toluene, 2 is converted into the phosphido species Ir₄(CO)₁₀(μ-PPh₂)(μ-AuPPh₃).     

Transformation of C2 units on a bimetallic tetranuclear cluster.: Reactivity of [Ru3Mo(μ3-η-CC)(μ-CO)3(CO)2(η-C5H4R)3(η-C5H5)] (R = H, Me)

The reactivity of [Ru₃Mo(μ₄-η²-CC)(μ-CO)₃(CO)₂(η-C₅H₄R)₃(η-C₅H₅)] (R = H; Me) have been investigated, initially to elucidate the nature of the starting material, and, latterly, to define the reactivity of an interesting ethane-1,2-bis(ylidyne) species. While the mixed RuMo clusters were unreactive towards simple electrophiles and carbonyl substitution by phosphine ligands they did react with atmospheric oxygen or carbon monoxide to give substantially different products. In all instances oxygen was incorporated either at the metal centre or at the C₂ fragment. High-pressure carbonylations yielded [Ru₃(μ-CO)₃(η-C₅H₅)₃(μ₃-C-C(O)O{Ru(CO)₂(η-C₅H₅)})] and [{Ru₂(μ-CO)(CO)₂(η-C₅H₄Me)₂}(μ₄-η²-CC){Ru(CO)(η-C₅H₄Me)Mo(η-C₅H₅)(=O)(μ-O)}], an ethane-1,2-bis(ylidene) complex, this exemplifying a relatively rare raft geometry which further reacted with Cl₂CCCl₂ to give [Mo₃(μ₄-C₂(Ru(CO)₂(η-C₅H₄Me))(CO)(μ-CO)(η-C₅H₅)₃(Cl)₂] having a similar geometry and undergone halogenation. In order to extend the extant examples of these raft clusters we explored the reaction of [{Ru(CO)₂(η-C₅H₄R)₂}₂(μ-C₂)] with [{Ru(CO)₂(η-C₅H₅)₂}₂] to provide a rational synthetic pathway leading to very reactive [Ru(μ₄-η²-CC)(μ₂-CO)₂(CO)₄(η-C₅H₄Me)₂(η-C₅H₄R)₂] rafts.     

Synthesis and characterisation of novel selenium-containing clusters; crystal structures of [Ru4(μ4-Se)2(CO)8(μ-CO)3] and [Ru3(μ3-Se)2(CO)7(Ph2P(CH2)3PPh2)]

The compound [Ru₄(μ-Se)₂(CO)₈(μ3-CO)₃] (1), has been obtained in good yield by vacuum pyrolysis of [RU₃(CO)₁₂] with [Ph₂Se₂] at 185°C. Reaction of 1 with 1,3-bis(diphenylphosphino)propane at room temperature affords the novel cluster [RU₃(μ₃-Se)₂(CO)₇(Ph₂P(CH₂)₃PPh₂)] (2). The structures of 1 and 2 have been determined by an X-ray diffraction study.     

Molybdenum alkyl- and aryl-thiolates

The reaction between [(η⁵-C₅H₅)MoH(CO)₃] and disulphides gives dimeric or trimeric complexes depending upon the conditions. The syntheses of the novel trinuclear molybdenum carbonyl complex [{Mo(η⁵-C₅H₅)(SR)(μ-CO)(CO)}₃] (R = Me), and dinuclear compounds [Mo₂(η⁵-C₅H₅)(μ-SR)₃(CO)₄] (R = Me) and [Mo₂(η⁵-C₅H₅)₂(SR)₂(CO)₂(μ-SR)(μ-Br)] (R = Me or Ph) are reported.