Glycal-ruthenium carbonyl clusters: Syntheses, characterization, and anticancer activity

Four new chiral ruthenium carbonyl cluster complexes Ru₃(μ-H)₂(CO)₉(L-2H) (1), Ru₃(μ-H)₂(CO)₇(L-2H)(dppm) (2), Ru₃(μ-H)₂(CO)₇(L-2H)(PPh₃)₂ (3), Ru₃(μ-H)₂(CO)₇(L-2H)(dppe) (4) containing a dehydrogenated form (L-2H) of 3,4,6-tri-O-benzyl-d-galactal (L) as a chiral ligand have been prepared and characterized. The anticancer activity of five compounds 1-4 and Ru₃(μ-H)₂(CO)₉(L-2H) 5 (L = tribenzyl glucal) against six types of human cancer cell lines was studied and compared to cisplatin. Compound 1 was chosen to produce more detailed growth curves based on overall highest activity profile. The structure of compound 2 was established by a single-crystal X-ray diffraction analysis. The structure based on triangular metal framework contains a bridging dehydrogenated tribenzyl galactal ligand bonded in a parallel μ₃-η²-bonding mode and a bridging dppm ligand. Variable-temperature NMR studies show that the two hydride ligands in compounds 1 and 2 are dynamically active on the NMR time scale at room temperature.     

Two gold-ruthenium clusters derived from Ru3(μ-H)3(μ3-CBr)(CO)9

The reaction between AuMe(PPh₃) and Ru₃(μ-H)₃(μ₃-CBr)(CO)₉ (1) affords the novel heptanuclear cluster Au₄Ru₃(μ₃-CMe)(Br)(CO)₉(PPh₃)₃ (2), containing an Au/Ru₃/Au trigonal pyramidal cluster face-capped by two Au(PPh₃) groups and a CMe ligand, together with Au₂Ru₃(μ-H)(μ₃-CMe)(CO)₉(PPh₃)₂ (3), formed by isolobal replacement of two of the three μ-H atoms in 1 by Au(PPh₃) groups. The latter co-crystallises with the analogous μ₃-CH complex, as also shown spectroscopically.     

Diphenylphosphine and diphenylphosphido derivatives of [Ru3(μ-H)(μ3-ampy)(CO)9] (Hampy = 2-amino-6-methylpyridine)

The reactions of [Ru₃(μ-H)(μ-ampy)(CO)₉] (1) (Hampy = 2-amino-6-methylpyridine) with one or two equivalents of PPh₂H lead to the complexes [Ru₃(μ-H)(μ₃-ampy)(CO)₈(PPh₂H)] (2) or [Ru₃(μ-H)(μ₃-ampy)(CO)₇(PPh₂H)₂] (3), in which the PPh₂H ligands are cis to the bridging NH fragment and cis to the hydride. Complex 2 can be transformed in refluxing THF into the phosphido-bridged derivative [Ru₃(μ₃-ampy)(μ-PPh₂)(μ-CO)₂(CO)₆] (4), which contains the PPh₂ ligand spanning one of the two RuRu edges unbridged by the amido moiety, and presents an extremely high ³¹P chemical shift of 386.9 ppm. Under similar conditions, complex 3 gives a mixture of two isomers of [Ru₃(μ-H)(μ₃-ampy)(μ-PPh₂)₂(CO)₆] in a 5:1 ratio; the major product (5) has a plane of symmetry, whereas the minor one (6) is asymmetric.     

Syntheses and molecular structures of Ru3(μ-H)(μ3-CPh2CCCCPh)(CO)9 and Ru3{μ3-CPhCHCC(CPh2)CHCPh}(μ-CO)(CO)8

The reaction between Ru₃(μ-H){μ₃-C₂CPh₂(OH)}(CO)₉ and HCCPh, carried out in the presence of HBF₄ · Me₂O, afforded the cluster complexes Ru₃(μ-H)(μ₃-CPh₂CCCCPh)(CO)₉ (5) and Ru₃{μ₃-CPhCHCC(CPh₂)CHCPh}(μ-CO)(CO)₈ (6), both of which were characterised by single-crystal X-ray studies.     

Studies on the reactivity of the clusters [Ru3(CO)8(μ-H)2(μ-PR2)2] (R=But,Cy) towards phosphine ligands

The reaction behavior of the 48e-clusters [Ru₃(CO)₈(μ-H)₂(μ-PR₂)₂] (R=Bu^t, 1a; R=Cy, 1b) towards phosphine ligands has been studied. Whereas 1a reacts spontaneously with many phosphines at room temperature, a lack of reactivity for 1b under similar conditions is observed. Thus 1a reacts with dppm (Ph₂PCH₂PPh₂) to the known 46e-cluster [Ru₃(μ-CO)(CO)₄(μ₃-H)(μ-H)(μ-PBu^t₂)₂(μ-dppm)] (2a), and the reaction of 1a with dppe (Ph₂PC₂H₄PPh₂) yields analogously [Ru₃(μ-CO)(CO)₄(μ₃-H)(μ-H)(μ-PBu^t₂)₂(μ-dppe)] (3). Reactions of 1a with dmpm (Me₂PCH₂PMe₂), dmpe (Me₂PC₂H₄PMe₂) and PBuⁿ₃, respectively, gave in each case a mixture of products which could not be characterized. Contrary to the reaction behavior at room temperature, 1b reacts with phosphines in THF under reflux yielding the novel complexes [Ru₃(CO)₆(μ-H)₂(μ-PCy₂)₂L₂] (L=Cy₂PH, 4a; L=Bu^t₂PH, 4b; L=Ph₂PH, 4c; L=P(OEt)₃, 4d). 4a is also obtained directly by the reaction of [Ru₃(CO)₁₂] with an excess of Cy₂PH. The molecular structure of 4a has been determined by a single-crystal X-ray analysis. Moreover, the thermolysis of 1a in octane affords [Ru₃(CO)₈(μ-H)₂(μ₃-PBu^t)(Bu^t₂PH)] (6) as the main product, and the thermolysis of [Ru₃(CO)₉(Bu^t₂PH)(μ-dppm)] (7) yields 2a to a considerable extent. Treatment of 1a with carbon tetrachloride leads to [Ru₃(CO)₇(μ-H)(μ-PBu^t₂)₂(μ-Cl)] (8) as the main product.     

Synthesis and structural characterization of mesitylphosphinidene-capped ruthenium and osmium clusters

Thermal reaction of [Ru₃(CO)₁₂] with PH₂Mes (Mes = mesityl) in refluxing toluene afforded mesitylphosphinidene-capped ruthenium carbonyl clusters, [Ru₃(CO)₉(μ-H)₂(μ₃-PMes)] (1), [Ru₃(CO)₈(PH₂Mes)(μ-H)₂(μ₃-PMes)] (2), [Ru₃(CO)₉(μ₃-PMes)₂] (3), [Ru₄(CO)₁₀(μ-CO)(μ₄-PMes)₂] (4), and [Ru₅(CO)₁₀H₂(μ₄-PMes)(μ₃-PMes)₂] (5). All products were fully characterized and structurally confirmed by X-ray crystal structure analysis. Complexes 2-4 were also obtained in high yields by stepwise reaction starting from 1. Fluxional behavior of carbonyl groups was observed in case of 4. Complex 5 reveals a new type of skeletal structure, bicapped-octahedron having μ₃- and μ₄-phosphinidene ligands at the capping positions. Similar reaction of [Os₃(CO)₁₂] with PH₂Mes yielded a phosphido-bridged osmium cluster [Os₃(CO)₁₀(μ-H)(μ-PHMes)] (6) and a phosphinidene-capped cluster [Os₃(CO)₉(μ-H)₂(μ₃-PMes)] (7).     

Synthesis of homo- and heteronuclear ruthenium-gold clusters with diphosphine and thiolato bridged ligands. Single crystal molecular structure of [Ru3(CO)10(μ-AuPPh3)(μ-SC5H4N)] and [Ru3(CO)8(μ-H)(μ-SC5H4N)(μ-dppe)]

The reaction between [Ru₃(CO)₁₀(NCMe)₂] and [AuClPPh₃] gave compound [Ru₃(CO)₁₀(μ-Cl)(μ-AuPPh₃)] (1) in quantitative yield under very mild conditions. The reaction of 1 with 4-mercaptopyridine (4-pyS) using ultrasonic reaction conditions gave the heteronuclear compound [Ru₃(CO)₁₀(μ-AuPPh₃)(μ-SC₅H₄N)] (2) in moderate yield. There was no spectroscopic evidence that indicates the formation of the hydride isolobal analog in this reaction. The homonuclear cluster [Ru₃(CO)₈(μ-H)(μ-SC₅H₄N)(μ-dppe)] (3) was prepared by a selective reaction employing the ruthenium-diphosphine derivative [Ru₃(CO)₁₀(μ-dppe)] (dppe = 1,2-bis(diphenylphosphine)ethane) with 4-pyS in THF solution. The isolobal analog to compound 3, compound [Ru₃(CO)₈(μ-AuPPh₃)(μ-SC₅H₄N)(μ-dppe)] (4) was synthesized by the reaction between compound 2 and dppe in refluxing dichloromethane. Compounds 1-4 were characterized in solution by spectroscopic methods and the molecular structure of compounds 2 and 3 in the solid state was obtained by single crystal X-ray diffraction studies.     

Dppm-substituted ruthenium clusters with capping sulfido and selenido ligands derived from thiourea, tetramethylthiourea and elemental selenium

Treatment of [Ru₃(CO)₁₀(μ-dppm)] (4) [dppm = bis(diphenylphosphido)methane] with tetramethylthiourea at 66 °C gave the previously reported dihydrido triruthenium cluster [Ru₃(μ-H)₂(μ₃-S)(CO)₇(μ-dppm)] (5) and the new compounds [Ru₃(μ₃-S)₂(CO)₇(μ-dppm)] (6), [Ru₃(μ₃-S)(CO)₇(μ₃-CO)(μ-dppm)] (7) and [Ru₃(μ₃-S){η¹-C(NMe₂)₂}(CO)₆(μ₃-CO)(μ-dppm)] (8) in 6%, 10%, 32% and 9% yields, respectively. Treatment of 4 with thiourea at the same temperature gave 5 and 7 in 30% and 10% yields, respectively. Compound 7 reacts further with tetramethylthiourea at 66 °C to yield 6 (30%) and a new compound [Ru₃(μ₃-S)₂{η¹-C(NMe₂)₂}(CO)₆(μ-dppm)] (9) (8%). Thermolysis of 8 in refluxing THF yields 7 in 55% yield. The reaction of 4 with selenium at 66 °C yields the new compounds [Ru₃(μ₃-Se)(CO)₇(μ₃-CO)(μ-dppm)] (10) and [Ru₃(μ₃-Se)(μ₃-η³-PhPCH₂PPh(C₆H₄)}(CO)₆(μ-CO)] (11) and the known compounds [Ru₃(μ-H)₂(μ₃-Se)(CO)₇(μ-dppm)] (12) and [Ru₄(μ₃-Se)₄(CO)₁₀(μ-dppm)] (13) in 29%, 5%, 2% and 5% yields, respectively. Treatment of 10 with tetramethylthiourea at 66 °C gives the mixed sulfur-selenium compounds [Ru₃(μ₃-S)(μ₃-Se)(CO)₇(μ-dppm)] (14) and [Ru₃(μ₃-S)(μ₃-Se){η¹-C(NMe₂)₂}(CO)₆(μ-dppm)] (15) in 38% and 10% yields, respectively. The single-crystal XRD structures of 6, 7, 8, 10, 14 and 15 are reported.     

μ-Amido complexes of ruthenium carbonyl. Asymmetric versus symmetric bridging preference of the monodeprotonated derivatives of 1,2-arenediamines. Crystal structure of [Ru3(μ-H)(μ-H3N2-4,5-Me2-1,2-phenylene)]

[Ru₃(CO)₁₂] reacts with 1,2-arenediamines (H₄N₂arene), under CO, to give the very asymmetric clusters [Ru₃(μ-H)(μ-H₃N₂arene)(CO)₉] (arene = 1,2-phenylene (1a) or 4,5-Me₂-1,2-phenylene (1b)) in which the three Ru atoms bear two, three, and four CO ligands, respectively. Under similar conditions, reaction of [Ru₃(CO)₁₂] with 1,8-diaminonaphthalene (H₄N₂naph) leads to break up of the cluster framework to give the binuclear ruthenium(I) compound [Ru₂(μ-H₂N₂naph)(CO)₆] (3). The crystal structure of compound 1b has been determined by an X-ray diffraction study.     

Cluster chemistry: XXXV. Reactions of some ruthenium cluster complexes with hydrogen: Cleavage of element-carbon bonds

Hydrogenation (20 atm, 80°C, 2 h) of trinuclear Ru₃(CO)_12-nL_n (L= tertiary phosphine or phosphite; n = 1–3) resulted in aggregation to give mixtures of H₄Ru₄(CO)12-n(L)_n (n = 0–4), but Ru₃(CO)₁₀(L-L) (L-L=dppm, dpam) gave Ru₃(μ-H)(μ₃-PhECH₂EPh₂)(CO)₉ (E = P, As, respectively) and Ru₃(μ-H)₂(μ₃-PPh)(CO)₈(PMePh₂), and Ru₃(μ-H)(μ₃-SBu^t)(CO)₉ gave Ru₃(μ-H)₂(μ₃-S)(CO)₉ by cleavage of PC, AsC, or SC bonds. Both types of reaction occurred with Ru₃(CO)₁₀(dppe) and [Ru₃(CO)₁₁]₂(μ-dppe).     

Synthesis and structure of sulfur and selenium capped dihydride triruthenium clusters [Ru3(CO)7(μ-H)2(μ-dppm)(μ3-E)] (E = S, Se)

Reaction of [Ru₃(CO)₁₀(μ-dppm)] (1) with H₂S at 66 °C affords high yields of the sulfur-capped dihydride [Ru₃(CO)₇(μ-H)₂(μ-dppm)(μ₃-S)] (2), formed by oxidative-addition of both hydrogen-sulfur bonds. Hydrogenation of [Ru₃(CO)₇(μ-dppm)(μ₃-CO)(μ₃-S)] (3) at 110 °C also gives 2 in similar yields, while hydrogenation of [Ru₃(CO)₇(μ-dppm)(μ₃-CO)(μ₃-Se)] (4) affords [Ru₃(CO)₇(μ-H)₂(μ-dppm)(μ₃-Se)] (5) in 85% yield. The molecular structures of 2 and 5 reveal that the diphosphine and one hydride simultaneously bridge the same ruthenium-ruthenium edge with the second hydride spanning one of the non-bridged edges. Both 2 and 5 are fluxional at room temperature being attributed to hydride migration between the non-bridged edges. Addition of HBF₄ to 2 affords the cationic trihydride [Ru₃(CO)₇(μ-H)₃(μ-dppm)(μ₃-S)][BF₄] (6) in which the hydrides are non-fluxional due to the blocking of the free ruthenium-ruthenium edge.     

Reaction of the heteronuclear cluster RuOs3(μ-H)2(CO)13 with toluene

The heteronuclear cluster RuOs₃(μ-H)₂(CO)₁₃ (4) reacts with refluxing toluene to form the clusters Ru₂Os₃(μ-H)₂(CO)₁₆ (5) RuOs₃(CO)₉(μ-CO)₂(η⁶-C₆H₅Me) (6) and Ru₂Os₃(CO)₁₂(μ-CO)(η⁶-C₆H₅Me) (7). Cluster 5 exists as a mixture of five isomers. The inter-relationship among the clusters has also been investigated.     

Reactivity of the heteronuclear cluster RuOs3(μ-H)2(CO)13 with indene

The heteronuclear cluster RuOs₃(μ-H)₂(CO)₁₃ (1) reacts with indene under thermal activation to afford the novel clusters RuOs₃(μ-H)(CO)₉(μ-CO)₂(η⁵-C₉H₇) (3), RuOs₃(μ-H)(CO)₉(μ₃,η⁵:η²:η²-C₉H₇) (4) and Ru₂Os₃(μ-H)(CO)₁₁(μ₃,η⁵:η²:η²-C₉H₇) (5), the latter two possessing indenyl ligands in the μ₃,η⁵:η²:η² bonding mode. Cluster 5 exists as a mixture of two isomers. The inter-relationship among the clusters has also been investigated.     

Open Pentaruthenium Cluster Complexes Formed from the Addition of Benzoic Acid to Ru<Subscript>5</Subscript>(C)(CO)<Subscript>15</Subscript>

Two isomers of Ru₅(C)(CO)₁₄(O₂CC₆H₅)(μ-H): Ru₅(C)(CO)₁₄(η²-O₂CC₆H₅)(μ-H), 2 and Ru₅(C)(CO)₁₄(μ-O₂CC₆H₅)(μ-H), 3 were obtained from the reaction of Ru₅(C)(CO)₁₅ with benzoic acid (PhCO₂H). Both compounds were characterized structurally by X-ray diffraction analysis. Compound 2 contains an opened pentaruthenium cluster with a chelating benzoate ligand on the ruthenium atom that was opened. Compound 3 contains an opened pentaruthenium cluster with a benzoate ligand on that bridges a pair of ruthenium atoms which are not mutually bonded. Compound 2 can be converted partially to 3 and 3 partially back to 2 and they form a 1.54/1.0 ratio (3/2) at equilibrium in solution at 95 °C.     

Reaction of the heteronuclear cluster RuOs3(μ-H)2(CO)13 with azulenes

Reaction of the heteronuclear cluster RuOs₃(μ-H)₂(CO)₁₃ (1) with azulene under thermal activation afforded the novel clusters RuOs₃(μ-H)(CO)₉(μ₃,η⁵:η²:η²-C₁₀H₉) (3) and Ru₂Os₃(μ-H)₂(CO)₁₃(μ-CO)(μ₃,η⁵:σ²-C₁₀H₈) (5a), with 4,6,8-trimethylazulene to give RuOs₃(μ-H)(CO)₈(μ-CO)(μ,η⁵:η⁴-C₁₀H₆Me₃) (4) and Ru₂Os₃(μ-H)₂(CO)₁₃(μ-CO)(μ₃,η⁵:σ²-C₁₀H₅Me₃) (5b), and with guaiazulene to give Ru₂Os₃(CO)₁₁(μ₃,η⁵:η³:η³-C₁₀H₅Me₂ⁱPr) (6), respectively. In 3–5, cluster-to-ligand hydrogen transfer appears to have taken place, with the organic moiety capping a trimetallic face in 3, bridging a metal–metal bond in 4 and via a μ₃,η⁵:σ² bonding mode in 5a and 5b. Cluster 6 contains a trigonal bipyramidal metal framework with the guaiazulene ligand over a triangular metal face. All five clusters have been completely characterised, including by single-crystal X-ray diffraction analysis.     

Synthesis and characterization of triosmium and triruthenium pyrene clusters

The reaction between 1-pyrenecarboxaldehyde (C₁₆H₉CHO) and the labile triosmium cluster [Os₃(CO)₁₀(CH₃CN)₂] gives rise to the formation of two new compounds by competitive oxidative addition between the aldehydic group and an arene C-H bond, to afford the acyl complex [Os₃(CO)₁₀(μ-H)(μ-COC₁₆H₉)] (1) and the compound [Os₃(CO)₁₀(μ-H) (C₁₆H₈CHO)] (2), respectively. Thermolysis of [Os₃(CO)₁₀(μ-H)(μ-C₁₆H₉CO)] (1) in n-octane affords two new complexes in good yields, [Os₃(CO)₉(μ-H)₂(μ-COC₁₆H₈)] (3) and the pyryne complex [Os₃(CO)₉(μ-H)₂(μ₃-η¹:η¹:η²-C₁₆H₈)] (4).In contrast, when 1-pyrenecarboxaldehyde reacts with [Ru₃(CO)₁₂] only one product is obtained, [Ru₃(CO)₉(μ-H)₂(μ₃-η¹:η¹:η²-C₁₆H₈)] (5), a nonacarbonyl cluster bearing a pyrene ligand. All compounds were characterized by analytical and spectroscopic data, and crystal structures for 1, 2, 4 and 5 were obtained.     

Novel carbonyl complexes of ruthenium with α-substituted oxime derivatives of terpenes

The reactions of Ru₃(CO)₁₂ with 1R,4S,6S-4-dimethylamino-4,7,7-trimethylbicyclo[4.1.0]heptane-3-one oxime (dimethylaminocaraneoxime) (I), 1R,4S,6S-4-methylamino-4,7,7-trimethylbicyclo[4.1.0]heptane-3-one oxime (methylaminocarane oxime) (II), and 1R,2R,5R-2-benzylthio-2,6,6-trimethylbicyclo[3.1.1]heptane-3-one oxime (benzylthiopinaneoxime) (III) were studied. The binuclear complex Ru₂(CO)₄{μ-η³(O,N,X)-L}₂ was formed as the main product in every reaction, when Ru₃(CO)₁₂ was heated with terpenoid to 80°C. In the above complex, two terpene ligands are coordinated in the form of ‘head-to tail’ bridge by the oxime groups at a binuclear metal fragment Ru-Ru. The heteroatom of the second functional group of every bridging ligand (nitrogen of amino group in I and II, sulfur of the thio group in III) is additionally coordinated to the ruthenium atom to give the chelate five-membered ring. Also the reactions of terpenoids I, II, III with Ru₃(CO)₁₂ were performed at room temperature using Me₃NO. In this case, as in the thermal reactions, the main product was the binuclear complex. However, in the reactions of Ru₃(CO)₁₂ with I and II, the trinuclear clusters were isolated that readily transformed to binuclear complexes in a solution. The complexes synthesized can exist as two diasteromers due to their chiral metal core. However, in all the cases, only one diastereomer was isolated, which indicates stereospecific nature of the above reactions. The compounds obtained were characterized by IR, ¹H-, ¹³C{¹H}-, COSY, and HXCOBI-NMR spectroscopy, the specific optical rotation angles were measured. For the binuclear complexes with ligands I, III and for trinuclear cluster with ligand II, single crystals were obtained and studied by X-ray diffraction.     

NEW DINUCLEAR ASYMMETRIC COMPLEXES OF RUTHENIUM AND RHENIUM

Abstract

New dinuclear asymmetric complexes of ruthenium and rhenium, of formula [(bpy)(CO)₃ Re^I(4,4′-bpy)Ru^II/III(NH₃)₅]^3+/4+ have been prepared and characterized by spectroscopic and electrochemical techniques. In the mixed-valent species [Re^I, Ru^III], the back electron transfer reaction Ru^II → Re^II, that occurs after light excitation, is predicted to be in the Marcus inverted region. This fact is consistent with the observed quenching of the luminiscence of the Re chromophore in [(bpy)(CO)₃Re^I(4,4′-bpy)Ru^III(NH₃)₅]⁴⁺, when compared to the parent complex [(bpy)(CO)₃Re^I(4,4′-bpy)]⁺. A theoretical treatment due to Creutz, Newton and Sutin has been successfully applied to predict the electronic coupling element in the mixed-valent complex.     

Synthesis,structure, and some reactions of the cluster complex [(μ-H)<Subscript>2</Subscript>Fe<Subscript>5</Subscript>(μ<Subscript>3</Subscript>-Se)<Subscript>2</Subscript>(CO)<Subscript>14</Subscript>]

In the reaction of Na₂Se with [Fe(CO)₅] in isopropanol with subsequent acidification with HCl, which is used to synthesize [(μ-H)₂Fe₃(μ₃-Se)(CO)₉] (II), the cluster [(μ-H)₂Fe₅(μ₃-Se)₂(CO)₁₄] (I) was detected. In assumption that compound I could serve as a suitable synthon for preparing the bulky heterometallic clusters, its reactions with the Rh-containing complexes were studied. The reaction of I with [Rh(CO)₂Cp*] (Cp* is pentamethylcyclopentadienyl) was found to give a mixture of the products. The main reaction products were isolated and their structures were determined: [Fe₂Rh(μ₃-Se)₂(CO)₆Cp*], [Fe₂Rh(μ₃-Se)(μ₃-CO)(CO)₆Cp*], [FeRh₂(μ₃-Se)(μ-CO)(CO)₃Cp ₂ ^* ], [Fe₂Rh₂(μ₄-Se)(μ-CO)₄(CO)₂Cp ₂ ^* ]. Potassium hydride treatment of II with subsequent addition of [Cp*Rh(CH₃CN)₃](CF₃SO₃)₂ leads to the well-known cluster complex [Fe₃Rh(μ₄-Se)(CO)₉Cp*]. A set of the reaction products indicates that the {Fe₅Se₂} core cannot be used as one-piece “building block” in the synthesis of heterometallic clusters.     

Synthesis and X-ray crystal structure of the electron-deficient metal carbonyl cluster [Os3(CO)5(μ3-H)(μ-H)(μ-PtBu2)2(μ-Ph2PCH2PPh2)]

The reaction of [Os₃(CO)₁₀(μ-dppm)] (1) with ^tBu₂PH in refluxing diglyme results in the electron-deficient metal cluster complex [Os₃(CO)₅(μ₃-H)(μ-P^tBu₂)₂(μ-dppm)] (2) (dppm = Ph₂PCH₂PPh₂) in good yields. The molecular structure of 2 has been established by a single crystal X-ray structure analysis. In contrast to the known homologue [Ru₃(μ-CO)(CO)₄(μ₃-H)(μ-H)(μ-P^tBu₂)₂(μ-dppm)] (3), no bridging carbonyl ligand was found in 2. The electronically unsaturated cluster 2 does not react with carbon monoxide under elevated pressure, therefore 2 seems to be coordinatively saturated by reason of the high steric demands of the phosphido ligands.