Chemo- and Stereoselective Coordination of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene by d8- and d6-Metal Carbonyls. Diels-Alder reactivity of Dienes Perturbed by Remote Olefin Complexation

The endocyclic double bond C(2), C(3) in 5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene ( 1 ) can he coordinated selectively on its exo-face before complexation of the exocyclic s-cis-butadiene moiety. Irradiation of Ru₃(CO)₁₂ or Os₃(CO)₁₂ in the presence of 1 gave tetracarbonyl [(1R,2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene)]ruthenium ( 6 ) or -osmium ( 8 ). Similarly, irradiation of Cr(CO)₆ or W(CO)₆ in the presence of 1 gave pentacarbonyl[(1R, 2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]chromium (10) or -tungsten (11) . Irradiation of complexes 6 and 11 in the presence of 1 led to further CO substitution giving bed-tricarbonyl-ae-bis[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]ruthenium ( 7 ) and trans-tetracarbonyl[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo-[2.2.1]hept-2-ene)]tungsten (12) , respectively. The diosmacyclobutane derivative cis-m?-[(1R,3R,3S,4S)-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hepta-2,3-diyl)]bis(tetracarbonyl-osmium) (Os-Os) (9) wa also obtained. The Diels-Alder reactivity of the exocyclic s-cis-butadiene moiety in complexs 7 and 8 was found to be significantly higher than that of the free triene 1 .     

Cyclodimerization of 1-(Dimethoxyniethyl)-5,6-dimethylidene-7-oxa-bicyclo[2.2.1]hept-2-ene Induced by Nonacarbonyldiiron. Crystal Structure of (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)- Tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl)-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)]iron

The transition-metal-carbonyl-induced cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene is strongly affected by substitution at C(1) While 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept–2-ene-l-methanol ( 7 ) refused to undergo [4 + 2]-cyclodimerization in the presence of [Fe₂(CO)⁹] in MeOH, 1-(dimethoxymethyl)-5,6-di-methylidene-7-oxabicyclo[2.2.1]hept-2-ene ( 8 ) led to the formation of a 1.7:1 mixture of ‘trans’ ( 19, 21, 22 ) vs. ‘cis’ ( 20, 23, 24 ) products of cyclodimerization together with tricarbonyl[C, 5,6, C-η-(l-(dimethoxymethyl)-5,6-di-methylidenecyclohexa-1,3-diene)]iron ( 25 ) and tricarbonyl[C,3,4, C-η-(methyl 5-(dimethoxymethyl)-3,4-di-methylidenecyclohexa-1,5-diene-l-carboxylate)]iron ( 26 ). The structures of products 19 and of its exo ( 21 ) and endo ( 22 ) [Fe(CO)₃(1,3-diene)]complexes) and 20 (and of its exo ( 23 ) and endo (24) (Fe(CO)₃(1,3-diene)complexes) were confirmed by X-ray diffraction studies of crystalline (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)-tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl])-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)iron ( 21 ). In the latter, the Fe(CO)₃(1,3-diene) moiety deviates significantly from the usual local C_s symmetry. Complex 21 corresponds to a ‘frozen equilibrium’ of rotamers with η-alkyl, η³-allyl bonding mode due to the acetal unit at the bridgehead centre C(1).     

The synthesis and characterisation of some mixed-metal carbonyl hydrides containing tungsten: The X-ray crystal structure of [(Ph3P)2N][Os3WH(CO)14]

The mixed-metal cluster anion [Os₃W(μ-H)(μ-CO)(CO)₁₃]^? has been prepared by the reaction of [Os₃(μ-H)(CO)₁₁]^? with W(CO)₃(MeCN)₃, and the dianion, [Os₃W(CO)₁₄]^2?, may be obtained by subsequent deprotonation. An X-ray analysis of the monoanion shows that the metals adopt a closo-tetrahedral geometry with the W atom coordinated to four terminal and one bridging carbonyl groups. The neutral clusters [Os₃WH₂(CO)₁₄] and [Os₃WH(CO)₁₄] are formed upon treatment of the monoanion with sulphuric acid and iodine, respectively.     

Negative ion mass spectra of Os3(CO)12X2 and Os3(CO)10X2 complexes (X = Br,I)

The negative-ion mass spectra at 70 eV of the compounds Os₃(CO)₁₂X₂ and Os₃(CO)₁₀X₂ (X =Br, I) are reported. Negative molecular ions are absent and only Os₃-containing fragments due to the loss of carbonyl groups are observed. [M  CO]^? is the base peak in the spectrum of Os₃(CO)₁₀I₂ and has a very high abundance in that of Os₃(CO)₁₀Br₂, whereas it is very weak in the spectra of Os₃(CO)₁₂X₂, where [M  3 CO]^? is the base peak. This change in the ionic intensities is related to the closed and open structure of the Os₃ unit in Os₃(CO)₁₀X₂ and Os₃(CO)₁₂X₂ respectively.     

New triosmium–iridium clusters: Synthesis and molecular structure of [Os3Ir2(Cp1)2(μ-OH)(μ-CO)2(CO)8Cl] (1), [Os3IrCp1(μ-OH)(CO)10Cl] (2), [Os3IrCp1(μ-H)(μ-Cl)(η3,μ3-C5H2N(NH2)Br)(CO)9] (3) and [Os3IrCp1(μ-Cl)2(η2,μ3-C5H3N(NH)Br)(CO)7] (4)

The trinuclear osmium carbonyl cluster, [Os₃(CO)₁₀(MeCN)₂], is allowed to react with 1 equiv. of [IrCp¹Cl₂]₂ (Cp¹ = pentamethylcyclopentadiene) in refluxing dichloromethane to give two new osmium–iridium mixed-metal clusters, [Os₃Ir₂(Cp¹)₂(μ-OH)(μ-CO)₂(CO)₈Cl] (1) and [Os₃IrCp¹(μ-OH)(CO)₁₀Cl] (2), in moderate yields. In the presence of a pyridyl ligand, [C₅H₃N(NH₂)Br], however, the products isolated are different. Two osmium–iridium clusters with different coordination modes of the pyridyl ligand are afforded, [Os₃IrCp¹(μ-H)(μ-Cl)(η³,μ₃-C₅H₂N(NH₂)Br)(CO)₉] (3) and [Os₃IrCp¹(μ-Cl)₂ (η²,μ₃-C₅H₃N(NH)Br)(CO)₇] (4). All of the new compounds are characterized by conventional spectroscopic methods, and their structures are determined by single-crystal X-ray diffraction analysis.     

Stereospecific functionalisations of iron carbonyl complexes of 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]oct-2-ene. Crystal and molecular structure of (C12H12)Fe2(CO)6

When the reaction between an excess of Fe₂(CO)₉ and the pentaene 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]oct-2-ene(I) is carried out in hexane/methanol the endo,exo-bis(tetrahaptotricarbonyliron) isomer (C₁₂H₁₂)Fe₂(CO)₆(IIa)is the major product. The structure of this complex has been determined by X-ray diffraction.The asymmetric positions of the two Fe(CO)₃ groups with respect to the roof-shaped organic skeleton was used to induce either stereo-specific functionalisation of the uncoordianted endocyclic CC double bond or stereo-and regiospecific functionalisation of one of the two coordinated s-cis-butadiene groups of the pentaene. Thus, hydroboration/oxidation of Ila gave the endo-exo-bis(tetrahaptotricarbonyliron)isomer of 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]octane-2-ol (IV). cis deuteration of the exocyclic double bond was achieved by treating IIa with D₂/PtO₂ in n-hexane.Protonation of IIa by HCl/AlCl₃/CH₂Cl₂ to give the η⁴-diene : η²-ene : η³-dienyl cationic complex Va, followed by quenching of Va with NaHCO₃/CH₃OH, resulted in a 1,4-addition of methanol to one coordinated s-cis-butadiene system. In contrast, quenching with NaOCH₃/CH₃OH resulted in the corresponding 1,2-addition of methanol. This gave the η⁴-1,3-diene : η⁴-1,4-diene complex VIIIa in which, suprisingly, one Fe(CO)₃ group is coordinated to two CC double bonds in gauche positions with respect to each other.     

Displacement of benzene by an alkyne in a tetraosmium cluster; synthesis and structural characterisation of the novel cluster [H2Os4(CO)9(μ3-η2-Ph2C2)(η2-Ph2C2)]

The benzen ligand in [H₂Os₄(CO)₁₀(η⁶-C₆H₆)] is displaced in the reaction with Ph₂C₂ in the presence of Me₃NO/MeCN. The cluster produced has been characterised as [H₂Os₄(CO)₉(PH₂C₂)₂] spectroscopically, and an X-ray crystallographic study has shown that one of the diphenylacetylene ligands is coordinated to one metal atom in a η²-mode and donates four electrons.     

Oxidative addition of 2-formyl-furan and related pyrrole and thiophene compounds at triosmium clusters

The bridging acyl complexes [Os₃H(μ-COC₄H₃X)(CO)₁₀] (X = NH, O, or S) have been prepared by oxidative addition of the 2-formyl derivatives of pyrrole, furan, or thiophene (C₄H₃XCHO) at [Os₃(CO)₁₀(MeCN)₂] with cleavage of the aldehydic CH bonds. On heating double decarbonylation of the acyl complexes occurs, to afford high yields of the compounds [Os₃H₂(CO)₉(μ₃-C₄H₂X)], reported previously for X = NH or O. For X = NH, two isomers with this formulation were characterised by ¹H NMR and IR data; the one containing the μ₃-2,3-C₄H₃N ligand isomerises to one containing μ₃-1,2-C₄H₃N. The direct reaction of pyrrole with [Os₃(CO)₁₂] has been re-examined at lower temperatures than before, and observed to give new products, including [Os₃H(CO)₁₀(C₄H₄N)], which contains a bridging non-aromatic tautomeric form of pyrrole. The ability of Os₃ clusters to stabilize non-aromatic tautomers of aromatic ligands is discussed.     

Synthesis, Characterization and Structural Properties of Some Heterobimetallic Carbonyl Clusters Derived from Diethynylsilane and Diethynyldisilane Ligands

We report the synthesis of some heterobimetallic carbonyl clusters of groups 8 and 9 derived from diethynylsilane and diethynyldisilane ligands. The triosmium carbonyl clusters containing a pendant acetylene unit [(μ-CO)Os₃(CO)₉(μ₃-η²-HC≡C-E-C≡CH)] [E = Si(CH₃)₂, Si(CH₃)₂–Si(CH₃)₂ and SiPh₂] were prepared and subsequently used for mixed-metal cluster formation. New diyne complexes of the type [{(μ-CO)Os₃(CO)₉}{Co₂(CO)₆}(μ₃-η²:η²-diyne)] and [{(μ-CO)Os₃(CO)₉}{(μ-H)Ru₃(CO)₉}(μ₃-η²:μ₃-η², η²-diyne)] [diyne = HC≡CSi(CH₃)₂C≡CH, HC≡CSi(CH₃)₂–Si(CH₃)₂C≡CH or HC≡CSi(Ph)₂C≡CH] have been prepared in good yields from the reaction of [(μ-CO)Os₃(CO)₉(μ₃-η²-HC≡C-E-C≡CH)] with a molar equivalent of [Co₂(CO)₈] and [Ru₃(CO)₁₂], respectively. All the new heterobimetallic compounds have been characterized by IR and ¹H NMR spectroscopy and mass spectrometry. The X-ray crystal structures and computational analyses based on density functional theory of these three molecules have been studied. Structurally, the dicobalt species adopts a pseudo-tetrahedral Co₂C₂ core with the alkyne bond which lies essentially perpendicular to the Co–Co vector. For the mixed osmium–ruthenium analogue, the hexanuclear carbonyl cluster consist of two trinuclear metal cores with the μ₃-(η²-||) bonding mode for the acetylene group in the former case and the μ₃-η², η² bonding mode in the latter one.     

d6 and d8 Metal Carbonyl Complexes of 7,7-Dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene. Stereoselective Hydroformylation of an [Fe(CO)4(olefin)] Complex

Reaction of 7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene ( 2 ) with various metal carbonyls and their derivatives gave the η²-M(CO)₄ (M = Fe ( 17 ), Ru ( 18 )), η⁴-M(CO)₃ (M = Fe ( 19x, 19n ), Ru ( 20n )), and η²-M(CO)₅ and η⁶-M(CO)₃ (M = Cr, Mo, W) complexes. The trigonal bipyramidal η²-M(CO)₄ complexes present an exceptional C_3v symmetry at the metal with the C,C-double bond in an axial position. In all the η²-complexes, this double bond is stereospecifically coordinated by its exo-vs. endo-η⁴-Fe(CO)₃ configuration was established by chemical correlation (hydrolysis, hydrogenation) with the corresponding complexes ( 24x, 24n ) of 7,7-dimethoxy-2,3-dimethylidenebicyclo[2.2.1]heptane ( 5 ). The relative rates of hydrolysis (AcOH/H₂O 2:1, 50°C) of ligands 2 and 5 and of complexes 19x, 19n, 24x , and 24n to the corresponding ketones showed an acceleration effect only when the metal is coordinated to the exo-face. This was attributed to an F-strain effect on the leaving group of the substrate. Compound 17 was further metallated by [Fe₂(CO)₉] giving the bimetallic isomers 21xn and 21xx . The endocyclic C,C-double bond of the latter can be stereospecifically hydroformylated (1 atm CO, AcOH/H₂O, 25°C) giving 29x (49%). Hydroformylation of 17 gave the corresponding uncoordinated aldehydes 30x/30n in better yields (76%) but with lower selectivity (3:1). These are the first examples of hydroformylation of an isolated [Fe(CO)₄(olefin)] complex.     

Use of the Cationic Fragments [Ru(η5-C5H5) (MeCN)3]+ and [M(η6-C6H5R)(MeCN)3]+ (M=Os, Ru; R=H, Me) as Ionic Coupling Reagents in the Synthesis of the Clusters [Os4M2(CO)12(η6-C6H5R)], [Os4M(CO)12(η6-C6H6)(Au2dppm)] and [Os5Ru(CO)15(η5-C5H5)(AuPPh3)]*

The clusters [H₂Os₄M(CO)₁₂eta⁶-C₆H₆)] (M=Os, Ru) may be deprotonated to generate anions [Os₄M(CO)₁₂eta⁶-C₆H₆)]^2- which react with [M′eta⁶-C₆H₅R) (MeCN)₃]²⁺(M^′=Os, Ru; R=H, Me) to give the bicapped tetrahedral clusters [Os₄(CO)₁₂MM′eta⁶-C₆H₅R)₂]. Whereas [Os₄(CO)₁₂M₂eta⁶-C₆H₆)₂] (M=Os, Ru) have one Meta⁶-C₆H₆) unit in a site connected to three other metals, {3}, and one in a site connected to four other metals, {4}, [Os₄(CO)₁₂OsRueta⁶-C₆H₆)₂] has the Rueta⁶-C₆H₆) unit in the {3} site irrespective of whether the Os or Ru anion is capped. Coupling of these anions with Au₂dppm yields [Os₄M(CO)₁₂eta⁶-C₆H₆)(Au₂dppm)] (M=Os, Ru), which have the arene ligand in the axial site of a trigonal bipyramid and the digold unit capping two faces. Reduction of [H₂Os₅(CO)₁₅] with K/Ph₂CO and coupling with [Rueta⁵-C₅H₅)(MeCN)₃]²⁺yields the monoanion [Os₅(CO)₁₅Rueta⁵-C₅H₅)]^? which reacts with [AuPPh₃]⁺ generating [Os₅(CO)₁₅Rueta⁵-C₅H₅)(AuPPh₃)] with the “Ru(C₅H₅)” unit in the terminal {3} site.     

Ironcarbonyl Complexes of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene Derivatives. Synthesis of Substituted Tricarbonyl(ortho-quinodimethane)iron Complexes and 2-Indanones

The l-dimethoxymethyl-5,6-dimethyldene-7-oxabicyclo[2.2.1]hept-2-ene ( 9 ) has been prepared. On treatment with Fe₂(CO)₉, the endocyclic double bond C(2)?C(3) was coordinated first giving the corresponding exo-Fe(CO)₄ complex 10 . The latter reacted with Fe₂(CO)₉ and afforded cis-heptacarbonyl-μ-[1RS,2SR,3RS,4SR,5RS,6SR-2,3-η: C5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]diiron ( 11 ) as a major product. On heating, 11 underwent deoxygenation of the 7-oxabicyclo[2.2.1]heptene moiety yielding tricarbonyl[C,5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidenecyclohexa-1,3-diene)]iron ( 13 ). In MeOH, a concurrent, regioselective methoxycarbonylation was observed giving tricarbonyl[C,3,4,C-η-(methyl 5-(dimethoxymethyl)-3,4-dimethylidenecyclohexa-1,5-diene-1-carboxylate)]iron ( 14 ). Oxidative removal of the Fe(CO)₃ moiety in 13 and 14 did not afford the expected ortho-quinodimethane derivatives but led to CO insertions giving 2,3-dihydro-2-oxo-1Hindene-4-carbaldehyde ( 20 ) and methyl 7-formyl-2-3-dihydro-2-oxo-lH-indene-5-carboxylate ( 21 ), respectively.     

Synthesis and X-ray structure of the osmium carbonyl anion [HOs3(CO)10 · O2C · Os6(CO)20]−

The reaction of [HOs₃(CO)₁₁]⁻¹¹ with [Os₃(CO)₁₀(MeCN)₂] in acetone gives the green-blue anion [HOs₃(CO)₁₀·O₂C·Os₆(CO)₂₀]⁻ (1) amongst several other products; this anion has been structurally characterised by a single crystal X-ray study of its Bu₄P⁺ salt.     

Triosmium clusters containing diphosphine and triphosphine ligands

The isomeric butadiene compounds 1,1- and 1,2-[Os₃(C₄H₆)(CO)₁₀] and the acetonitrile compound 1,2-[Os₃(CO)₁₀(MeCN)₂] react with the diphosphines Ph₂P(CH₂)_nPPh₂ (n = 2, 3 or 4) to give separable isomers of [Os₃(CO)₁₀(diphosphine)] in which the diphosphine is either bridging or chelating, whereas dppm (n = 1) gives only the 1,2-isomer. The mono-acetonitrile compound [Os₃-(CO)₁₁(MeCN)] reacts to give two series of compounds: [Os₃(CO)₁₁(diphosphine)], containing one coordinated and one free phosphorus atom, and [Os₆(CO)₂₂(diphosphine)] with two Os₃(CO)₁₁ groups bridged by the diphosphine. The triphosphine, Ph₂PCH₂CH₂PPhCH₂CH₂PPh₂ (triphos), reacts similarly to give two separable isomers of [Os₃(CO)₁₁(triphos)] and two inseparable isomers of [Os₆(CO)₂₂(triphos)]. Whereas [Os₃(CO)₁₁(dppm)] readily undergoes decarbonylation to give 1,2-[Os₃(CO)₁₀(dppm)], other compounds of the type [Os₃(CO)₁₁(diphosphine)] are not decarbonylated under the same conditions, but react with Me₃NO to give the 1,2-but not the 1,1-isomers of [Os₃(CO)₁₀(diphosphine)].     

Dirhenium carbonyl complexes bearing 2-vinylpyridine,morpholine and 1-methylimidazole ligands

Treatment of the labile compound [Re₂(CO)₈(MeCN)₂] with 2-vinylpyridine in refluxing benzene affords exclusively the new compound [Re₂(CO)₈(μ-η¹:η²-NC₅H₄CHCH₂)] (1) in 39% yield in which the μ-η¹:η²-vinylpyridine ligand is coordinated to one Re atom through the nitrogen and to the other Re atom via the olefinic double bond. Reaction of [Re₂(CO)₈(MeCN)₂] with morpholine in refluxing benzene furnishes two compounds, [Re₂(CO)₉(η¹-NC₄H₉O)] (2) and [Re₂(CO)₈(η¹-NC₄H₉O)₂] (3) in 5% and 29% yields, respectively. Reaction of [Re₂(CO)₈(MeCN)₂] with 1-methylimidazole gives [Re₂(CO)₈{η¹-NC₃H₃N(CH₃)}₂] (4) and the mononuclear compound fac-[ReCl(CO)₃{η¹-NC₃H₃N(CH₃)}₂] (5) in 18% and 26% yields, respectively. In the disubstituted compounds 2 and 4, the heterocyclic ligands occupy equatorial coordination sites. The mononuclear compound 5 consists of three CO groups, two N coordinated η¹-1-methylimidazole ligands and a terminal Cl ligand. The XRD structures of complexes 1, 3 and 5 are reported.     

Metal cluster-induced desulphurization of N-(p-methoxybenzoyl)-S-benzoylsulphenamide. Crystal and molecular structures of [Os6(CO)20(μ4-S)(MeCN)]

Reaction of N-(p-methoxybenzoyl)-S-benzoylsulphenamide1 with [Os₃(CO)₁₀(MeCN)₂] at room temperature gives Os₃(CO)₁₀(μ₃-S)]2 and [Os₆(CO)₂₀(μ₄-S)(MeCN)]3 in moderate yield. The crystal structure of 3 has been determined. Complex 2 is an intermediate in the formation of 3. Complex 3 undergoes dissociation of CO to give [Os₆(CO)₁₉(μ₃-S)] and [Os₅(CO)₁₅(μ₄-S)].     

Asymmetric diosmium sawhorse complexes

Three asymmetric diosmium(I) carbonyl sawhorse complexes have been prepared by microwave heating. One of these complexes is of the type Os₂(μ‐O₂CR)(μ‐O₂CR′)(CO)₄L₂, with two different bridging carboxylate ligands, while the other two complexes are of the type Os₂(μ‐O₂CR)₂(CO)₅L, with one axial CO ligand and one axial phosphane ligand. The mixed carboxylate complex Os₂(μ‐acetate)(μ‐propionate)(CO)₄[P(p‐tolyl)₃]₂, ( 1 ), was prepared by heating Os₃(CO)₁₂ with a mixture of acetic and propionic acids, isolating Os₂(μ‐acetate)(μ‐propionate)(CO)₆, and then replacing two CO ligands with two phosphane ligands. This is the first example of an Os₂ sawhorse complex with two different carboxylate bridges. The syntheses of Os₂(μ‐acetate)₂(CO)₅[P(p‐tolyl)₃], ( 3 ), and Os₂(μ‐propionate)₂(CO)₅[P(p‐tolyl)₃], ( 6 ), involved the reaction of Os₃(CO)₁₂ with the appropriate carboxylic acid to initially produce Os₂(μ‐carboxylate)₂(CO)₆, followed by treatment with refluxing tetrahydrofuran (THF) to form Os₂(μ‐carboxylate)₂(CO)₅(THF), and finally addition of tri‐p‐tolylphosphane to replace the THF ligand with the P(p‐tolyl)₃ ligand. Neutral complexes of the type Os₂(μ‐O₂CR)₂(CO)₅L had not previously been subjected to X‐ray crystallographic analysis. The more symmetrical disubstituted complexes, i.e. Os₂(μ‐formate)₂(CO)₄[P(p‐tolyl)₃]₂, ( 8 ), Os₂(μ‐acetate)₂(CO)₄[P(p‐tolyl)₃]₂, ( 4 ), and Os₂(μ‐propionate)₂(CO)₄[P(p‐tolyl)₃]₂, ( 7 ), as well as the previously reported symmetrical unsubstituted complexes Os₂(μ‐acetate)₂(CO)₆, ( 2 ), and Os₂(μ‐propionate)₂(CO)₆, ( 5 ), were also prepared in order to examine the influence of axial ligand substitution on the Os—Os bond distance in these sawhorse molecules. Eight crystal structures have been determined and studied, namely μ‐acetato‐1κO:2κO′‐μ‐propanoato‐1κO:2κO′‐bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP′‐bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os₂(C₂H₃O₂)(C₃H₅O₂)(C₂₁H₂₁P)₂(CO)₄]·CH₂Cl₂, ( 1 ), bis(μ‐acetato‐1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os₂(C₂H₃O₂)₂(CO)₆], ( 2 ) (redetermined structure), bis(μ‐acetato‐1κO:2κO′)pentacarbonyl‐1κ²C,2κ³C‐[tris(4‐methylphenyl)phosphane‐1κP]diosmium(Os—Os), [Os₂(C₂H₃O₂)₂(C₂₁H₂₁P)(CO)₅], ( 3 ), bis(μ‐acetato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os) p‐xylene sesquisolvate, [Os₂(C₂H₃O₂)₂(C₂₁H₂₁P)₂(CO)₄]·1.5C₈H₁₀, ( 4 ), bis(μ‐propanoato‐1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os₂(C₃H₅O₂)₂(CO)₆], ( 5 ), pentacarbonyl‐1κ²C,2κ³C‐bis(μ‐propanoato‐1κO:2κO′)[tris(4‐methylphenyl)phosphane‐1κP]diosmium(Os—Os), [Os₂(C₃H₅O₂)₂(C₂₁H₂₁P)(CO)₅], ( 6 ), bis(μ‐propanoato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os₂(C₃H₅O₂)₂(C₂₁H₂₁P)₂(CO)₄]·CH₂Cl₂, ( 7 ), and bis(μ‐formato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os), [Os₂(CHO₂)₂(C₂₁H₂₁P)₂(CO)₄], ( 8 ).     

The reduction of triosmium dodecacarbonyl by sodium borohydride. The preparation and X-ray structure of the cluster anion [H2Os4(CO)12]2−

The reduction of Os₃(CO)₁₂ by NaBH₄ in tetrahydrofuran has been studied, and the formation of the anionic clusters [HOs₃(CO)₁₁]^?, [H₃Os₄(CO)₁₂]^? and [H₂Os₄(CO)₁₂]^2? observed. The previously unreported dianion [H₂Os₄(CO)₁₂]^2? was prepared in satisfactory yield, and characterised as the bis(triphenylphosphine)iminium salt. This compound crystallizes in the space group P$\text{1}$, with Z = 1, and cell dimensions of a 11.014(2), b 14.751(3), c 15.168(3) Å, α 123.95(2)°, β 95.77(2)°, γ 98.73(2)°. The structure was solved by a combination of multisolution sign expansion and Fourier methods, and final residuals were R 0.067 and R_W 0.066 for 5972 observed intensity data. The dianion comprises a distorted tetrahedron of osmium atoms, each metal also bonding to three terminal carbonyl ligands, which as staggered with respect to the metalmetal bonds. Unlike the cation, the cluster anion is statistically disordered between two centrosymmetrically related sites.     

Indene in a novel bonding mode in a carbonyl cluster: isolation,characterisation, and crystal and molecular structure of [HOs4(CO)9(C9H6)(C9H7)]

The reaction of [Os₃(CO)₁₂] with indene at 150°C under reflux affords the known compounds [H₂Os₃(CO)₉(C₉H₆)] (2) and [Os₄(CO)₁₂(C₉H₆)] (3). When the reaction temperature is increased to 170°C, the yield of 2 is greatly reduced, and a new tetraosmium cluster [HOs₄(CO)₉(C₉H₆)(C₉H₇)] (1) is isolated. An X-ray diffraction study of 1 has shown that one face of the Os₄ tetrahedron is capped by an indyne ligand coordinated in a μ₃-η²-− bonding mode, while the indenyl ligand (C₉H₇) is coordinated to a single Os atom in a η⁵ bonding mode through the five-membered ring.     

Synthesis, characterization and reactivity studies of the new compound [Os3(CO)9(μ3-η,η,η-{C5H5FeC5H3CCC(S)C(Fc)CHO}]

Processes such as S-C and C-H bond activations as well as C-C coupling reactions have taken place in the synthesis of the new compound [Os₃(CO)₉(μ₃-η²,η³,η³-{C₅H₅FeC₅H₃CCC(S)C(Fc)CHO}] (Fc = C₅H₄FeC₅H₅), which contains an aldehyde oxametallacycle. A reactivity study of it has been carried out. In addition, other new triosmium clusters such as [Os₃(CO)₉(μ₃,η²-CCFc)(μ,η¹-SCCFc)], [Os₃(CO)₁₀(μ,η²-CCFc)(μ,η¹-SCCFc)] and [Os₃(CO)₉(μ-CO)(μ₃,η²-FcCCSCCFc)] have been prepared from the reaction of [Os₃(CO)₁₀(NCMe)₂] and FcCCSCCFc. All the compounds have been characterized by analytical and spectroscopic techniques. The crystal structures of [Os₃(CO)₉(μ₃,η²-CCFc)(μ,η¹-SCCFc)] and [Os₃(CO)₉(μ₃-η²,η³,η³-{C₅H₅FeC₅H₃CCC(S)C(Fc)CHO}] have been determined by X-ray crystallography and some electrochemical studies have also carried out.