Shariff E. Kabir

Cluster chemistry in the Noughties: new developments and their relationship to nanoparticles

Over the past decade, the chemistry of low-valent transition metal clusters has again come to the fore, primarily as a result of the development of nanochemistry and the realization that large clusters are on the cusp of the nano-domain. This perspective focuses on these recent developments in low-valent transition metal cluster chemistry, specifically looking at cluster-nanoparticles, the use of small and medium sized clusters as nanoparticle precursors, the development of clusters as homogeneous catalysts and hydrogen uptake and storage systems, together with fundamental discoveries relating to novel transformations that can take place within the cluster framework.

Dinuclear iron carbonyl complexes with dithiolate ligands: X-ray structures of [Fe2(CO)6{μ-SS}] and [Fe2(CO)5{μ-SS}(PPh3)]

Abstract The reactions of Na2[Fe(CO)4] with 3,4-toluenedithiol and 1,3-propanedithiol at room temperature give the dinuclear complexes [Fe2(CO)6{μ-S CCHCHC(CH 3 )CHC S}] (1) and [Fe2(CO)6(μ-SCH2CH2CH2S)] (2), respectively. Compounds 1 and 2 both react with triphenylphosphine at ambient temperature to give [Fe2(CO)5{μ-S CCHCHC(CH 3 )CHC S}(PPh3)] (3) and [Fe2(CO)5(μ-SCH2CH2CH2S)(PPh3)] (4), respectively. The compounds have been characterized by spectroscopic data together with single crystal X-ray diffraction studies for 1 and 3. The toluenedithiolate anion acts as a bidentate ligand with both the sulfur atoms forming symmetrical bridges across the metalmetal bond.

Electron deficient bonding of benzoheterocycles to triosmium clusters: synthesis and applications to organic chemistry

Abstract A new synthetic methodology for the addition of carbon based nucleophiles to the carbocyclic ring of quinolines has been developed which is based on the electron deficient bonding of the C(8) carbon and the protective coordination of the nitrogen atom to the metal core in the complexes [Os3(CO)9(μ3-η2-C9H5(R)N)(μ-H)] (R can be a wide range of substituents in the 3-, 4-, 5- and 6-positions of the quinoline ring). These complexes react with a wide range of carbanions (R′Li, R′=Me, nBu, tBu, Bz, Ph, CHCH2, C2(CH2)3CH3, CH2CN, (CH3)2CCN, –CHS(CH2)2S–; CH2CO2tBu, R′MgBr, R′=CH3, CH2CHCH2) to give the nucleophilic addition products [Os3(CO)9(μ3-η3-C9H7(5-R′)N)(μ-H)] (2a–2l), after quenching with trifluoracetic acid, in isolated yields of 43–86%. Substitution at the 3- or 4-position is well tolerated giving the expected nucleophilic addition products [Os3(CO)9(μ3-η3-C9H6(3 or 4-R)(5-R′)N)(μ-H). The 6-substituted derivatives give >95% of the cis-diastereomer, [(Os3(CO)9(μ3-η3-C9H6(5-R′)(6-R)N)(μ-H)]. The stereochemistry is preserved even in the case of less bulky carbanions (R′=CH3). In the case of the 6-Cl derivative, a second product is obtained on reaction with the isobutyryl carbanion, [Os3(CO)9(μ3-η2-C9H5(6-Cl)(5-C(CH3)2CN)N)(μ-H)2] (4) which is the result of protonation at the metal core and rearrangement of the carbocyclic ring. The trans-diastereomer of the addition products obtained from the 6-substituted derivatives can be synthesized by reaction of the unsubstituted complex with R′Li followed by quenching with (CH3O)2SO2. Acetic anhydride can also be used as the quenching electrophile for the intermediate anions generated from R′Li [(trans-Os3(CO)9(μ3-η3-C9H6(6-CH3CO)(5-CH3)N)(μ-H)] (5). Nucleophilic addition occurs across the 3,4-bond in the cases where the 5-position is occupied by a substituent. The nucleophilic addition products can be rearomatized by reaction with DBU/DDQ or by reaction of the intermediate anion with trityl cation or DDQ. The resulting rearomatized complexes can be cleanly cleaved from the cluster by reflux in acetonitrile under a CO atmosphere yielding the functionalized quinoline and Os3(CO)12 as the only two products. An overview of this previously reported work along with additional examples of this novel chemistry is given here as well as an extention of the synthesis of the electron deficient triosmium clusters to a wide range of heterocycles structurally related to quinoline. These complexes include those containing the heterocycles: phenanthridine (7), 5,6-benzoquinoline (8), 2-CH3-benzimidazole (9), 2-methyl benzotriazole (10), 2-methyl-benzoxazole (11), 2-R-benzothiazole (R=H, 12; CH3, 13) and quinoxaline (14). The solid state structures of 7–10, 12, and 14 are reported.

Reactivity of [(μ-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}] with organic heterothiols; X-ray structures of [H(μ-H)Os3(CO)8(η2-pyS){Ph2PCH2P(Ph)C6H4}] and [Os3(CO)8(μ-η2-pyS){Ph2PCH2P(Ph)C6H4}]

Abstract The reaction of [(μ-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}] (3) with pyridine-2-thiol (pySH, C5H4NSH) at room temperature gave two novel clusters [(μ-H)Os3(CO)8(μ-pyS)(μ-dppm)] (4) and [H(μ-H)Os3(CO)8(η2-pyS){Ph2PCH2P(Ph)C6H4}] (5) in 55 and 15% yields, respectively. Compound 4 is formed by simple oxidative addition of pySH and demetallation of the phenyl ring of dppm ligand whereas the 50-electron cluster 5 results from oxidative addition of pySH and coordination of the thiolate moiety as a chelating ligand and cleavage of one of the metalmetal bonds. The analogous reaction of 3 with pySH at 80°C gave the new compound [Os3(CO)8(μ-η2-pyS){Ph2PCH2P(Ph)C6H4}] (6) in 20% yield together with 4 and 5 in 40 and 7% yields, respectively. Compound 6 contains a chelating/bridging pyS ligand and an orthometallated dppm ligand. In contrast, the reaction of 3 with pyrimidine-2-thiol (pymSH, C4H3N2SH) at room temperature and at 80°C affords only the simple oxidative addition product [(μ-H)Os3(CO)8(μ-pymS)(μ-dppm)] (7). Compound 6 reacts with molecular hydrogen to give 5 and 4 in 20 and 10% yields, respectively. Compound 5 was converted to 6 (30%) with the formation of 3 (10%) by refluxing in heptane at 98°C. The new complexes 4, 5, 6 and 7 have been characterized by spectroscopic data together with X-ray structure determinations for 5 and 6.

Some pyridine-2-thiolato and 6-methylpyridine-2-thiolato complexes of manganese: crystal structure of [Mn2(μ-pyS)2(CO)6] (pyS = pyridine-2-thiolato ligand)

Abstract The complexes [Mn 2 (μ-pyS) 2 (CO) 6 ] ( 1 ) and [Mn 2 (μ-MepyS) 2 (CO) 6 ] ( 2 ), where pySH = pyridine-2-thiol and MepySH = 6-methylpyridine-2-thiol, have been made by reaction of Mn 2 (CO) 10 with the appropriate pyridinethiol in refluxing hexane. In these complexes pyS and MepyS act as both six electron donor chelating and bridging groups which form four-membered N,S chelate rings at one metal centre and bridge to the other metal atom through sulphur. Complex 2 reacts with PPh 3 and Ph 2 PCH 2 PPh 2 (dppm) in refluxing cyclohexane to give [Mn(MepyS)(PPh 3 (CO) 3 ] ( 3 ) and [Mn(MepyS)( η 1 -dppm) 2 (CO) 2 ] ( 4 ) respectively. The crystal structure of 1 was determined.

Reactivity of triruthenium thiophyne and furyne clusters: competitive S–C and P–C bond cleavage reactions and the generation of highly unsymmetrical alkyne ligands

The synthesis and reactivity of the thiophyne and furyne clusters [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, O) is reported. Addition of P(C4H3E)3 to [Ru3(CO)10(mu-dppm)] (1) at room temperature in the presence of Me3NO gives simple substitution products [Ru3(CO)9(mu-dppm)(P(C4H3E)3)] (E = S, 2; E = O, 3). Mild thermolysis in the presence of further Me3NO affords the thiophyne and furyne complexes [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 4; E = O, 6) resulting from both carbon-hydrogen and carbon-phosphorus bond activation. In each the C4H2E (E = S, O) ligand donates 4-electrons to the cluster and the rings are tilted with respect to the mu-dppm and the phosphido-bridged open triruthenium unit. Heating 4 at 80 degrees C leads to the formation of the ring-opened cluster [Ru3(CO)5(mu-CO)(mu-dppm)(mu3-eta3-SC4H3)(mu-P(C4H3S)2)] (5) resulting from carbon-sulfur bond scission and carbon-hydrogen bond formation and containing a ring-opened mu3-eta3-1-thia-1,3-butadiene ligand. In contrast, a similar thermolysis of 3 affords the phosphinidene cluster [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2O)(mu3-P(C4H3O))] (7) resulting from a second phosphorus-carbon bond cleavage and (presumably) elimination of furan. Treatment of 4 and 6 with PPh3 affords the simple phosphine-substituted products [Ru3(CO)6(PPh3)(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 8; E = O, 9). Both thiophyne and furyne clusters 4 and 6 readily react with hydrogen bromide to give [Ru3(CO)6Br(mu-Br)(mu-dppm)(mu3-eta2-eta1-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 10; E = O, 11) containing both terminal and bridging bromides. Here the alkynes bind in a highly unsymmetrical manner with one carbon acting as a bridging alkylidene and the second as a terminally bonded Fisher carbene. As far as we are aware, this binding mode has only previously been noted in ynamine complexes or those with metals in different oxidation states. The crystal structures of seven of these new triruthenium clusters have been carried out, allowing a detailed analysis of the relative orientations of coordinated ligands.

Methylene chain length and coordination geometry in triosmium clusters containing diphosphine ligands X-ray crystal structures of [Os3(CO)10{μ-Ph2P(CH2)n}](n = 4 or 5) and [Os3(CO) 8{μ-Ph2PCH2PPh2}2]

Abstract The bis-acetonitrile compound [Os3(CO)10(MeCN)2] and the butadiene compound [Os3(CO)10(η4-cis-C4H6)] react with dppp {dppp = Ph2P(CH2)5PPh2} to give only [Os3(CO)10(μ-dppp)] (1). Protonation of 1 with trifluoroacetic acid le [(μ-H)Os3(CO)10(μ-dppp)]+ (2) with the hydride bridging the same osmium atoms as the dppp. The bridging dppp compound [Os3(CO)10(μ-dppp)] (1) reacts with dppp at 110°C to give [Os3(CO)9(η1-dppp)(μ-dppp)] (4) whereas [Os3(CO)10(μ-dppm)] under the same conditions reacts with dppm (dppm = Ph2PCH2PPh2) to give [Os3(CO)8(μ-dppm)2] (5). Protonation of 5 with trifluoroacetic acid gives [(μ-H)Os3(CO)8(μ-dppm)2]+ (6) with the hydride bridging the unsubstituted Os — Os edge. The monoacetonitrile compound [Os3(CO)11(MeCN)] reacts with dppp at 0°C to give two compounds: [Os3(CO)11(η1-dppp)] (7) containing one coordinated and one free phosphorus atoms and [{Os3(CO)11}2(μ-dppp)] (8) with one dppp ligand bridging two Os3(CO)11 moities. Solid-state structures for 1, 5 and the previously reported cluster [Os3(CO)10(μ-dppb)] (3) {dppb = Ph2P(CH2)PPh2) are reported. Compound 1 crystallizes in the space group P212121 with unit cell parameters a = 11.770(2) A , b = 16.957(3) A , c = 21.681(5) A , V = 4327(2) A 3 and Z = 4 . Least-squares refinement of 6188 reflections gave a final agreement factor of R = 0.077 (Rw = 0.087). Compound 3 crystallizes in the space group P21/c with unit cell parameters a = 12.361(2) A , b = 16.804(2) A , c = 20.935(2) A , β = 116.66(11)°, V = 3886(2) A 3 and Z = 4 . Least-squares refinement of 2284 reflections gave a final agreement factor of R = 0.028 (Rw = 0.032). Compound 5 crystallizes in the space group Pca21 with unit cell parameters a = 21.398(3) A , b = 15.684(4) A , c = 18.219(4) A , V = 6115(4) A 3 and Z = 4 . Least-squares refinement of 5376 reflections gave a final agreement factor of R = 0.060 (Rw = 0.062).

Dithiolate complexes of ruthenium and osmium: X-ray structures of [Ru2(CO)6(μ-SCH2CH2S)] and [{(μ-H)M3(CO)10)}2(μ-SCH2CH2CH2S)] (M=Ru, Os)

Abstract A comparison between the reactivity of [Ru3(CO)12] and [Os3(CO)10(MeCN)2] with 1,2-ethanedithiol (HSCH2CH2SH) and 1,3-propanedithiol (HSCH2CH2CH2SH) is reported. The reaction of [Ru3(CO)12] with 1,2-ethanedithiol at 68°C afforded [Ru2(CO)6(μ-SCH2CH2S)] (1) in 40% yield, whereas the reaction with 1,3-propanedithiol yielded [{(μ-H)Ru3(CO)10}2(μ-SCH2CH2CH2S)] (2) and [Ru2(CO)6(μ-SCH2CH2CH2S)] (3) in 30 and 19% yields respectively. Treatment of [Os3(CO)10(MeCN)2] with 1,2-ethanedithiol gave [(μ-H)Os3(CO)10(μ-SCH2CH2SH)] (4) in 60% yield and with 1,3-propanedithiol it afforded [{(μ-H)Os3(CO)10}2(μ-SCH2CH2CH2S)] (5) in 30% yield. Compounds 1 and 3 both react with equimolar amounts of PPh3 at room temperature to give the monosubstituted products [Ru2(CO)5(μ-SCH2CH2S)(PPh3)] (6) and [Ru2(CO)5(μ-SCH2CH2S)(PPh3)] (7) respectively. When heated to 68°C, compound 2 transformed into 3. The compounds have been characterized by spectroscopic studies, and in the case of 1, 2 and 5 by X-ray crystallography.

X-ray structure of [Os3(CO)10(μ-Ph2PCH2PPh2)]

Decacarbonyl-μ-bis(diphenylphosphino)methane triosmium crystallizes in the monoclinic space group P21/c with a = 24.422(5), b = 12.381(2), c = 24.788(5) Å, β = 103.69(3)°, V = 7282 (2) Å3, and Z = 8. The molecule consists of a triangular arrangement of osmium atoms with the organic ligand bridging two adjacent osmium atoms at equatorial sites. The Os—Os distances lie in the close range 2.8563(9)–2.8895(11) Å with an average value of 2.87(1) Å.

Triruthenium clusters derived from the reactions of [Ru3(CO)12] with benzothiazole, pyrimidine-2-thione and benzimidazole-2-thione; X-ray structures of [Ru3(μ-H)(μ-2,3-η2-NSC7H4)(CO)10] and [Ru3(μ-H)(μ3-η2-SN2C4H3)(CO)9]

The reaction of [Ru 3 (CO) 12 ] with benzothiazole (C 7 H 5 NS) in THF at 68°C yields [Ru 3 (μ-H)(μ-2,3-η 2 -NSC 7 H 4 )(CO) 10 ] 3 and [Ru 3 (μ-H)(μ 3 -1,2,3-η 3 -NSC 7 H 4 )(CO) 9 ] 4 . An X-ray diffraction analysis of 3 shows that the benzothiazolide ligand is coordinated through the imino-nitrogen and C-2 carbon atoms. The organic ligand in 4 is coordinated through the sulfur, the imino nitrogen and the C-2 carbon atoms as suggested by IR, 1 H-NMR and MS data. Compound 3 converts to 4 on thermolysis in cyclohexane. The reactions of pyrimidine-2-thione (C 4 H 4 N 2 S) and benzimidazole-2-thione (C 7 H 6 N 2 S) with [Ru 3 (CO) 12 ] give the new compounds [Ru 3 (μ-H)(μ 3 -η 2 -SN 2 C 4 H 3 )(CO) 9 ] ( 5 ) and [Ru 3 (μ-H)(μ 3 -η 2 -N 2 SC 7 H 5 )(CO) 9 ] ( 6 ), respectively. An X-ray structure analysis of 5 shows that the pyrimidine-2-thiolato ligand bridges two ruthenium atoms through the sulfur atom and bonds to a third ruthenium through one of the ring N atoms.