[Ir(COD)(diphos)Cl配合物活化sp^3 C-H键及其促进CO、CO2插入Ir-C键反应性能的研究

本文利用[Ir(COD)(μ-Cl)]2与双膦螯合配位体之间的反应合成了三个新的配合物[Ir(COD)(diphos)]Cl(diphos=dmpe、depe、dppe),用IR、NMR、电导和元素分析测定了结构.以CH3CN为反应底物分别考察了它们活化sp^3C-H键的能力及其反应规律.在此基础上进一步研究了使CO、CO2插入生成的Ir-CH2CN键的可能性.结果表明:在温和条件下进行这一插入反应是可能的,并用光谱方法证实有相应的含羰基、羧基的金属配合物的生成.     

An iridium-pyridylpyrrolide complex exhibiting reversible binding of H2

The synthesis and characterization of a series of iridium(I) and iridium(III) complexes supported by a 3,5-bis(trifluoromethyl)-2-(2'-pyridyl)pyrrole (L(-)) ligand are reported. Compound [Ir(L)(COD)] (COD = 1,5-cyclooctadiene) demonstrates reversible binding of hydrogen to form a dihydride complex [Ir(L)(H)(2)(COD)] with no hydrogenation of COD.     

Bis(alkoxycarbonyl) complexes of platinum: preparation,reactivity and their role in carbonylation reactions

bis(alkoxycarbonyl) complexes of platinum of the type [Pt(COOR)₂L] [L = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), l,4-bis(diphenylphosphino)butane (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppf) or 1,2-bis-(diphenylphosphino)benzene (dpb); R = CH₃, C₆H₅ or C₂H₅] were obtained by reaction of [PtCl₂L] with carbon monoxide and alkoxides. Palladium and nickel complexes gave only carbonyl complexes of the type [M(CO)L] or [M(CO)₂L]. The new complexes were characterized by chemical and spectroscopic means. The X-ray structure of [Pt(COOCH₃)₂(dppf] · CH₃OH is also reported. The reactivity of some alkoxycarbonyl complexes was also investigated.     

Synthesis and Structures of RhI and IrI Complexes Supported by N‐Heterocyclic Carbene‐Phosphinidene Adducts

N‐Heterocyclic carbene‐phosphinidene adducts of the type (IDipp)PR [R = Ph ( 5 ), SiMe₃ ( 6 ); IDipp = 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene] were used as ligands for the preparation of rhodium(I) and iridium(I) complexes. Treatment of (IDipp)PPh ( 5 ) with the dimeric complexes [M(μ‐Cl)(COD)]₂ (M = Rh, Ir; COD = 1,5‐cyclcooctadiene) afforded the corresponding metal(I) complexes [M(COD)Cl{(IDipp)PPh}] [M = Rh ( 7 ) or Ir ( 8 )] in moderate to good yields. The reaction of (IDipp)PSiMe₃ ( 6 ) with [Ir(μ‐Cl)(COD)]₂ did not yield trimethylsilyl chloride elimination product, but furnished the 1:1 complex, [Ir(COD)Cl{(IDipp)PSiMe₃}] ( 9 ). Additionally, the rhodium‐COD complex 7 was converted into the corresponding rhodium‐carbonyl complex [Rh(CO)₂Cl{(IDipp)PPh}] ( 10 ) by reaction with an excess of carbon monoxide gas. All complexes were fully characterized by NMR spectroscopy, microanalyses, and single‐crystal X‐ray diffraction studies.     

Stereoselectivity in Diphos Addition to Molybdenum Complex with Pyridine‐2‐thionate (pyS) and η3‐Methallyl Coordinated Ligands

The conformational isomers endo‐ and exo‐[Mo{η³‐C₃H₄(CH₃)}(η²‐pyS)(CO)(η²‐diphos)] (diphos: dppm = {bis(diphenylphosphino)methane}, 2 ; dppe = {1,2‐bis(diphenylphosphino)ethane}, 3 ) are prepared by reacting the double‐bridged pyridine‐2‐thionate (pyS) complex [Mo{η³‐C₃H₄(CH₃)}(CO)₂]₂(η¹:η²:μ‐pyS)₂, 1 with diphos in refluxing acetonitrile. Stereoselectivity of the methallyl, C₃H₄(CH₃), ligand improves the formation of the exo‐conformation of 2 and 3 . Orientations and spectroscopy of these complexes are discussed.     

Stabilisation of iridium(III) fluoride complexes with NHCs

The first neutral, [IrClF(2)(NHC)(COD)] and [IrClF(2)(CO)(2)(NHC)] (NHC = IMes, IPr), and cationic, [IrF(2)py(IMes)(COD)][BF(4)] and [IrF(2)L(CO)(2)(NHC)][BF(4)] (NHC = IMes, L = PPh(2)Et, PPh(2)CCPh, py; NHC = IPr, L = py), NHC iridium(III) fluoride complexes, have been synthesised by the xenon difluoride oxidation of iridium(I) substrates. The stereochemistries of these iridium(III) complexes have been confirmed by multinuclear NMR spectroscopy in solution and no examples of fluoride-trans-NHC arrangements were observed. Throughout, CO was found to be a better co-ligand for the stabilisation of the iridium(III) fluoride complexes than COD. Attempts to generate neutral trifluoroiridium(III) complexes, [IrF(3)(CO)(NHC)], via the ligand substitution reaction of [IrF(3)(CO)(3)] with the free NHCs were unsuccessful.     

New cationic monocarbonyls of manganese(I) with nitriles and isonitriles

Summary Monocarbonyls of manganese(I) with two chelating diphosphinestrans-[Mn(CO)(diphos)₂(L)]A, [diphos = 1,2-bis(diphenylphosphino)ethane, dppe, or bis(diphenylphosphino)methane, dppm; L=nitriles, NCR (NCMe, NCEt, NCPh, or NCCH₂Ph), dinitriles, NCGCN (NCCH₂CN, NCCH₂CH₂CN, oro-(NC)₂C₆H₄), isonitriles, CNR, (CNPh, or CNBu^t); A = C1O ₄ ^– or PF ₆ ^– ],trans-[(Mn(CO)(dppm)₂)₂(-NCCH₂CH₂CN)](ClO₄)₂ and the monocarbonyl with one diphosphine,mer-[Mn(CO)(dppe)(CNBu^t)₃]ClO₄, have been prepared fromtrans-[Mn(CO)(diphos)₂Br].In this paper we have adopted the convention that gives positive shift to signals at higher frequency of ext. H₃PO₄.     

Synthesis of Ir Catalysts Featuring Amide-functionalized NHC Ligands and Survey of their Activity on Formic Acid Dehydrogenation

2 a and 2 b , [Ir(CI)(COD)(NHC)] (COD=1,5-cyclooctadiene), have been prepared via transmetallation from NHC−Ag complexes. [Rh(CI)(COD)(NHC)] ( 4 ) was prepared analogously. [Ir({κ-C,N-(NHC-acetamide−1H)}(COD)] ( 3 c ) has been synthesized via transmetallation from the deprotonated NHC−Ag complex. [IrCp*({κ-C,N-(NHC-acetamide−1H)}] ( 5 ) (Cp*=pentamethylcyclopentadienyl), has been obtained analogously. [Ir(CI)(CO)₂(NHC)] ( 6 ) and [Ir({κ-C,N-(NHC-acetamide−1H)}(CO)₂] ( 7 ) have been prepared by carbonylation of 2 b and 3 c , respectively. The catalytic activity of these complexes has been evaluated in the dehydrogenation of formic acid, under solventless conditions, in the presence of water as a cosolvent, and in a 5 : 2 HCOOH/Et₃N mixture, with the best TOF values being obtained in the case of the latter. Stoichiometric experiments suggest COD hydrogenation as the preactivation step.     

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

The reaction of [Ir(IMes)(COD)Cl], [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene] with pyridazine (pdz) and phthalazine (phth) results in the formation of [Ir(COD)(IMes)(pdz)]Cl and [Ir(COD)(IMes)(phth)]Cl. These two complexes are shown by nuclear magnetic resonance (NMR) studies to undergo a haptotropic shift which interchanges pairs of protons within the bound ligands. When these complexes are exposed to hydrogen, they react to form [Ir(H)₂(COD)(IMes)(pdz)]Cl and [Ir(H)₂(COD)(IMes)(phth)]Cl, respectively, which ultimately convert to [Ir(H)₂(IMes)(pdz)₃]Cl and [Ir(H)₂(IMes)(phth)₃]Cl, as the COD is hydrogenated to form cyclooctane. These two dihydride complexes are shown, by NMR, to undergo both full N-heterocycle dissociation and a haptotropic shift, the rates of which are affected by both steric interactions and free ligand pK_a values. The use of these complexes as catalysts in the transfer of polarisation from para-hydrogen to pyridazine and phthalazine via signal amplification by reversible exchange (SABRE) is explored. The possible future use of drugs which contain pyridazine and phthalazine motifs as in vivo or clinical magnetic resonance imaging probes is demonstrated; a range of NMR and phantom-based MRI measurements are reported.     

Coordination complexes containing multidentate ligands : V. The reactions between trans-carbonylchlorobis(triphenylphosphine)iridium and trans-carbonylchloro(triphenylarsine)iridium and some tridentate group VB ligands

Bis[3-(dimethylarsino)propyl]phenylarsine, (tas), reacts with trans-Ir(CO)(EPh₃)₂ X (E = P, As; X = F, Cl, Br, I) to yield the (Ir(CO)(tas)] X complexes. In contrast, the similar ligand bis[3-(dimethylarsino)propyl]phenylphosphine, (dap), reacts with trans-Ir(CO)(EPh₃)₂X (E = P, As; X = Cl, Br, I) to yield a mixture of [Ir(CO)(dap)X] and [Ir(CO)(dap)]X, and with trans Ir(CO)(EPh₃)₂F (E = P, As) to yield solely [Ir(CO)(dap)F]. The cations [Ir(CO)(L)]⁺ (L = tas, dap) readily yield tetraphenylborate derivatives, [Ir(CO)(L)]BPh₄. The oxygenation of [Ir(CO)(tas)]⁺ in solution proceeds almost to completion after 15 h, whereas [Ir(CO)(dap)]⁺ does not appear to undergo oxygenation.     

Tetrafluorobenzobarreleneiridium complexes with 1,10- phenanthroline,2,2′-bipyridine and diketonate ligands. Crystal structure of [IrI2(TFB)(phen)]ClO4·(CH32CO (TFB = 5,6,7,8- tetrafluoro-1,4-dihydro-1,4-ethenonapthalene,phen = 1,10- phenanthroline)

The preparations os some new β-diketonate iridium(I) complexes of formula [Ir(β-diketonate)(diolefin)] and [Ir(β-diketonate-C³)(diolefin)(LL)] (β-diketone = acetyl acetone (Hacac), 1-phenyl, butane-1,3-dione (HBzac), 1,3-diphenyl,propane-1,3-dione (HBz₂ac); diolefin = tetraflurobenzobarrelene (TFB), trimethyltetrafluorobenzobarrelene (Me₃TFB); LL = 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy) (not all possible combinations)) are reported. The neutral complexes [IrI(TFB)₂] and [IrI(TFB)(phen)] were prepared by metathetical reactions from the corresponding chlorides. The oxidative addition of iodine to [Ir(acac-C³)(TFB)-(phen)] or (Ir(TFB)(phen)][ClO₄] results in formation of the trans or cis isomers of the iridium(III) cation [IrI₂(TFB)(phen)]⁺, respectively. The rans isomer has been structurally characterized by X-ray diffraction methods; the lattice constants of the monoclinic P2₁/n cell are a 12.6841(4), b 17.7550(7), c 13.8500(4) Å with β 108.874(2)°. The R factor was 0.058 for 3552 observed reflections. The octahedral coordination of the metal is distorted as to make an I-Ir-I angle of 160.43(4)°.     

Carbonyl cationic rhodium(I) and iridium(I) complexes with sulphur donor and triphenylphosphine ligands

Summary The reaction of previously reported Rh^I and Ir^I cationic complexes towards carbon monoxide and triphenylphosphine has been studied. Carbonyl rhodium(I) mixed complexes of the formulae [Rh(CO)L₂(PPh₃)]ClO₄, (L=tetrahydrothiophene(tht), trimethylene sulfide(tms), SMe₂, or SEt₂), [(CO)(PPh₃)Rh{-(L-L)}₂Rh(PPh₃)(CO)](ClO₄)₂ (L-L= 2,2,7,7-tetramethyl-3,6-dithiaoctane (tmdto), (MeS)₂(CH₂)₃ (dth), or 1,4-dithiacyclohexane (dt), [Rh(CO)L(PPh₃)₂]ClO₄ (L= tht, tms, SMe₂, or SEt₂), and carbonyl iridium(I) complexes of the formulae [Ir(CO)₂(COD)(PPh₃)]ClO₄, [Ir(CO)(COD)(PPh₃)₂]ClO₄, [(CO)(COD)(PPh₃) Ir{-(L-L)} Ir(PPh₃)(COD)(CO)](ClO₄)₂ (L-L = tmdto or dt), [(CO)₂ (PPh₃)Ir(-tmdto)Ir(PPh₃)(CO)₂](ClO₄)₂, [(CO)₂(PPh₃) Ir(-dt)₂Ir(PPh₃)(CO)₂](ClO₄)₂, were prepared by different synthetic methods.     

Catalytic polymerization of phenylacetylene by cationic rhodium and iridium complexes of ferrocene-based ligands

Some new Rh(I) and Ir(I) complexes of the types [(COD)M(LL)]ClO₄ and [(COD)MCl]₂ [COD = cyclooctadiene; M = Rh, Ir; LL = 1,1′-bis(diphenylphosphino)ferrocene (DPPF), 1-diphenylphosphino-2-(N,N-dimethylamino)methylferrocene (FcNP), 1,6-diferrocenyl-2,5-diazahexane (FcNN)] were prepared, and their catalytic activities toward polymerization of phenyl acetylene were examined. The rhodium complexes proved to be very effective catalysts to yield highly stereoregular polyphenylacetylene (cis-transoidal-PPA) in high yields under mild conditions. The number-average molecular weight (M _n) of the PPA obtained is in the range of 19,000–33,000 and the weight-average molecular weight (M _ω) is in the range of 47,000–95,000. Comparative studies revealed that of various catalysts employed, the cationic mononuclear [Rh(FcNN)(COD)]ClO₄ complex exhibited the best results to give exclusively the cis-transoidal-PPA (cis content ∼100%) with the highest molecular weight (M _n = 33,340) in the highest chemical yield (94%). Other reaction parameters such as the softness of the ligand, the solvent, the relative amount of catalyst, and the reaction temperature were also investigated to find that all these factors played crucial roles. The iridium systems worked better for the trimerization rather than polymerization to yield 1,3,5-triphenybenzene as major product. © 1996 John Wiley & Sons, Inc.     

Rhodium and Iridium Complexes of Anionic Thione and Selone Ligands Derived from Anionic N-Heterocyclic Carbenes

The lithium salts of anionic N-heterocyclic thiones and selones [{(WCA-IDipp)E}Li(toluene)] ( 1 : E=S; 2 : E=Se; WCA=B(C₆F₅)₃, IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene), which contain a weakly coordinating anionic (WCA) borate moiety in the imidazole backbone were reacted with Me₃SiCl, to furnish the silylated adducts (WCA-IDipp)ESiMe₃ ( 3 : E=S; 4 : E=Se). The reaction of the latter with [(η⁵-C₅Me₅)MCl₂]₂ (M=Rh, Ir) afforded the rhodium(III) and iridium(III) half-sandwich complexes [{(WCA-IDipp)E}MCl(η⁵-C₅Me₅)] ( 5 – 8 ). The direct reaction of the lithium salts 1 and 2 with a half or a full equivalent of [M(COD)Cl]₂ (M=Rh, Ir) afforded the monometallic complexes [{(WCA-IDipp)E}M(COD)] ( 9 – 12 ) or the bimetallic complexes [μ₂-{(WCA-IDipp)E}M₂(COD)₂(μ₂-Cl)] ( 13 – 16 ), respectively. The bonding situation in these complexes has been investigated by means of density functional theory (DFT) calculations, revealing thiolate or selenolate ligand character with negligible metal-chalcogen π-interaction.     

Die photochemische synthese von μ-(1-2-η:2-3-η-allen)-octacarbonyldimangan(0)

Novel dihydroiridium(III) complexes containing mono- and bi-dentate sulfur ligands have been isolated. The cationic complexes [Ir(COD)L₂]ClO₄ (COD = 1,5-cyclooctadiene, L = tetrahydrothiophene (tht) or trimethylene sulfide (tms); L₂ = (CH₃S)₂(CH₂)₃ (dth)), [Ir(COD)(L-L)]₂(ClO₄)₂ (L-L = 1,4-dithiacyclohexane (dt) or (t-BuS)₂(CH₂)₂ (tmdto)) and [Ir(CO)₂(tmdto)]₂-(ClO₄)₂ react with H₂ to give the corresponding iridium(III) dihydrides: [IrH₂COD)L₂]ClO₄ (Ia: L = tht, Ib: L = tms, Ic: L₂ = dth), [IrH₂(COD)-(L-L)]₂(ClO₄)₂ (IIa: L-L = tmdto, IIb: L-L = dt) and [IrH₂(CO)₂(tmdto)]₂-(ClO₄)₂ (III). The ¹H NMR chemical shifts and ν(IrH) data are discussed.     

Transition metal complexes with bidentate ligands spanning trans-positions. IV. Preparation and properties of some rhodium and iridium complexes of 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene

The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene ( 1 ) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)( 1 )] and trans-[M(CO)(CH₃CN)( 1 )][BF₄] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O₂ and SO₂ is significantly lower than that of the corresponding Ph₃P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) ( 1 )] with hydrogen halides give the six-coordinate species [IrHX₂(CO) ( 1 )]. The complexes [IrH₂I (CO) ( 1 )] and [IrH₂L (CO) ( 1 )] [BF₄] (L = CO and CH₃CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph₂PCH₂Ph)₂] (M = Rh, Ir), trans-[Ir (CO) (CH₃CN) (Ph₂PCH₂Ph)₂] [BF₄], [IrHCl₂(CO)(Ph₂PCH₂Ph)₂] and [IrH₂(CO)₂(Ph₂PCH₂Ph)₂] [BF₄] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1 . The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed.     

Reactions of S4N4 with phosphineiridium(I) complexes. Synthesis and crystal structures of [(dppen)2Ir(S2N2)](BPh4) · 0.5CH3COCH3 and (dppen)2Ir(S2N2)[W(CO)5](BPh4) · 0.5CH2Cl2

The iridium(I) complexes [(diphos)₂Ir(CO)](Bph₄) react with S₄N₄ to give the octahedral derivatives [(diphos)₂Ir(S₂N₂)](BPh₄), (diphos = bis(diphenylphosphino)ethylene, dppen, (1); diphos = bis(diphenylphosphino_methane, dppm, (2). Reaction of 1 with W(CO)₆ gave the carbonyl derivative (dppen)₂Ir(S₂N₂)[W(CO)₅](BPh₄), 3). The crystal structures of 1 and 3 have been determined by X-ray diffraction. In both compounds the iridium atom shows a distorted octahedral geometry, being surrounded by two bidentate phosphine ligands and by the sulfur and a nitrogen atom of the open-chain disulfur dinitride ligand. In 3 the nitrogen atom of the S₂N₂ group which is not coordinated to the iridium atom is linked to the tungsten atom of a W(CO)₅ residue. The ³¹P NMR spectra of 1 and 3 are indicative of a rigid structure in solution at room temperature.     

Synthesis, structure and catalytic activity of the first iridium(I) siloxide versus chloride complexes with 1,3-mesitylimidazolin-2-ylidene ligand

The first iridium(I) complex containing siloxyl and N-heterocyclic carbene ligand such as [Ir(cod)(IMes)(OSiMe₃)] (1) and [Ir(CO)₂(IMes)(OSiMe₃)] (3) have been synthesized and their structures solved by spectroscopy and X-ray methods as well as catalytic properties in selected hydrogenation reactions have been presented in comparison to their chloride analogues, i.e. [Ir(Cl)(cod)(IMes)] (2) and [Ir(Cl)(CO)₂(IMes)] (4). The attempts at synthesis of iridium(I) complex with tert-butoxyl ligand has failed as leading instead to the iridium hydroxide complex [Ir(cod)(OH)(IMes)] (5) whose X-ray structure has also been solved. All complexes (1)-(5) show square planar geometry typical of the four-coordinated iridium complexes. Catalytic activity of complexes 1 and 2 was tested in transfer hydrogenation of acetophenone and hydrogenation of olefins.     

Synthesis,Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

A series of iridium tetrahydride complexes [Ir(H)₄(PSiP‐R)] bearing a tridentate pincer‐type bis(phosphino)silyl ligand ([{2‐(R₂P)C₆H₄}₂MeSi]⁻, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me₄N ⋅ BH₄ under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)–dinitrogen complexes, [Ir(H)₂(N₂)(PSiP‐R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)₂(N₂)(PSiP‐Cy)] with PMe₃ required heating at 150 °C to give the expected [Ir(H)₂(PMe₃)(PSiP‐Cy)] and a trigonal bipyramidal iridium(I)–dinitrogen complex, [Ir(N₂)(PMe₃)(PSiP‐Cy)]. The reaction of [Ir(H)₄(PSiP‐Cy)] with three equivalents of 2‐norbornene (nbe) in benzene afforded [Ir^I(nbe)(PSiP‐Cy)] in a high yield, while a similar reaction of [Ir(H)₄(PSiP‐R)] with an excess of 3,3‐dimethylbutene (tbe) in benzene gave the C H bond activation product, [Ir^III(H)(Ph)(PSiP‐R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir^III(H)(Ph)(PSiP‐Cy)] in the presence of PPh₃ in benzene resulted in reductive elimination of benzene, coordination of PPh₃, and activation of the C H bond of one aromatic ring in PPh₃. [Ir^III(H)(Ph)(PSiP‐R)] catalyzed a direct borylation reaction of the benzene C H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single‐crystal X‐ray analysis.     

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