Subas Rajbangshi Lecturer, Department of Chemistry

Research Interest

Organometallics, Cluster compounds of Fe, Ru and Os containing Phosphorous, Nitrogen and Sulpher Donor ligands.

Conference Papers

New tertiary phosphine derivatives of Os3(CO)12: X-ray structures of 1,2-[Os3(CO)10{PhP(o-Tol)2}2], 1,2,3-[Os3(CO)9{(4-FC6H4)3P}3], 1,2,3-[Os3(CO)9{PhP(Cy)2}3] and [Os3(µ-OH)2(CO)8{(4-FC6H4)3P}2]

Tertiary phosphines, PR3, are well-known to be valuable ligands in inorganic and organometallic chemistry because they constitute one of the few series of ligands in which the steric and electronic properties of the ligands can be altered in a periodic and systematic fashion by varying the nature of the R-group. The chemistry of tertiary phosphine substituted derivatives of triosmium dodecacarbonyl has been fairly extensively studied1-5. One interesting aspect of these complexes is the almost-exclusive tendency of the phosphine ligands to occupy an equatorial site with respect to the triosmium plane5-6. Electronically, axial substitution is favoured because this leaves a stable fac tricarbonyl unit. The axial CO ligands in Os3(CO)12 are more weakly coordinated and would therefore be expected to be more readily substituted than the equatorial ligands. However, the axial sites are more crowded. Steric effects dominate in most cases and only the smallest ligands prefer axial position, bulky ligands such as tertiary phosphines occupy equatorial position6

Conference paper

Conference Paper:  


(1)  Synthesis of [Ru3(CO)9(µ-dppf){P(C4H3E)3}] (E = O, S) and          


      thermally-induced cyclometalation to form [(µ-H)Ru3(CO)7(µ-dppf)


     {µ3-(C4H3E)2P(C4H2E)}](dppf=1,1      


      bis(diphenylphosphino)ferrocene). Bangladesh Crystallographic Association Conference, Dhaka University, 05 December 2013.


 


 

Journals Papers

Oxidative-addition of the NeH bond of saccharin (sacH) to a triosmium centre: Synthesis, structure and reactivity of Os3(CO)10(m-H)(m-sac)

Saccharin (sacH) is a widely-used sweetener and consequently its chemistry has been extensively
studied, but here we report a rare example of its reactivity towards a multinuclear metal centre. Lightlystabilized
Os3(CO)10-n(NCMe)n (n ¼ 1, 2) react with sacH to afford Os3(CO)10(m-H) (m-sac) (1) in which the
sac ligand bridges an osmiumeosmium vector via nitrogen and the carbonylic oxygen (m-N,O). The
reactivity of 1 towards monodentate phosphines, PR3 (R ¼ Ph, Th, Fu), has been investigated. Carbonyl
substitution affords both mono- and bis-phosphine substituted derivatives Os3(CO)9(PR3) (m-H) (m-sac)
(2) and Os3(CO)8(PR3)2(m-H) (m-sac) (3) respectively. In the mono-substituted derivatives, the phosphine
occupies an equatorial position on the osmium that is directly bonded to the carbonylic oxygen of
saccharinate, while in the bis-(phosphine) substituted derivatives the second phosphine is bound to the
remote osmium also occupying an equatorial site. In all complexes the saccharinate ligand remains in the
bidentate N,O coordination mode thus playing a directing spectator role in these reactions.

Reaction of electron-deficient triosmium cluster Os3(CO)8{μ3-Ph2PCH(CH3)P(Ph)C6H4}(μ-H) with HCl: X-ray structure of two isomers of Os3(CO)8{μ-Ph2PCH(CH3)PPh2}(μ-Cl)(μ-H)

Treatment of electron-deficient Os3(CO)83-Ph2PCH(CH3)P(Ph)C6H4}(μ-H) (1) with HCl at room temperature furnishes the adduct Os3(CO)8{μ-Ph2PCH(CH3)PPh2}(μ-Cl)(μ-H) (2) in almost quantitative yield via oxidative addition of H‒Cl bond. Cluster 2 is electron-precise and contains bridging chloride and hydride ligands which rearranges upon heating at 110°C to form isomeric 3. Both clusters have been characterized by a combination of elemental analyses, IR and NMR spectroscopic data together with single crystal X-ray diffraction studies.

Thermolysis of Ru3(CO)10(μ-dppm) and Ru3(CO)9(PRPh2)(μ-dppm) (R = Ph, H) in presence of O2: Synthesis and structure of triruthenium clusters containing a capping-oxo ligand

Thermolysis of Ru3(CO)10(μ-dppm) [dppm = bis(diphenylphosphino)methane] in boiling xylene in presence of molecular oxygen (O2) affords the trinuclear oxo-capped cluster Ru3(CO)73-CO)(μ3-O)(μ-dppm) (1). A similar reaction between Ru3(CO)9(PPh3)(μ-dppm) and O2 in refluxing benzene also furnishes the oxo-capped Ru3(CO)6(PPh3)(μ3-CO)(μ3-O)(μ-dppm) (2). Crystal structures of 1 and 2 reveal that both contain a capping oxygen at one face and a triply-bridging carbonyl on the opposite face of the triruthenium plane. In contrast, Ru3(CO)9(PHPh2)(μ-dppm) does not react with O2 under similar conditions, but undergoes thermal transformations to give Ru3(CO)7(μ-H)(μ-PPh2){μ3-PhPCH2P(C6H4)Ph} (3) and Ru3(CO)6(μ-CO)(μ-PPh2)23-CH2PPh)] (4) via C–P, P–H and C–H bond activation. All the new clusters have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.

Reactivity of [CpMo(CO)2]2 towards heterocyclic thiols: Synthesis, structure, and bonding in the sulfido-ligated cluster Cp3Mo3(μ-CO)2(μ-κ2-C7H4NS)(μ-S)(μ3-S)


Abstract


The electronically unsaturated dimolybdenum complex [CpMo(CO)2]2 (1) reacts with the π-excessive heterocycle 2-mercapto-1-methylimidazole at 110 °C to afford the mononuclear molybdenum complex CpMo(CO)22-C4H5N2S) (2) and the trimolybdenum cluster Cp3Mo3(μ-CO)2(μ-κ2-C4H5N2)(μ-S)(μ3-S) (3) in 22% and 20% yields, respectively. A similar reaction between 1 and the benzoannulated heterocycle 2-mercaptobenzothiazole furnishes CpMo(CO)22-C7H4NS2) (4) and Cp3Mo3(μ-CO)2(μ-κ2-C7H4NS)(μ-S)(μ3-S) (5) in 17% and 20% yields, respectively. Compounds 2 and 4 consist of a single molybdenum atom with two carbonyl groups, a cyclopentadienyl ligand, and a chelating heterocyclic thiolato ligand. The trimolybdenum clusters 3 and 5 consist of three cyclopentadienyl ligands, a metalated heterocyclic ligand, edge-bridging and face-capping sulfido ligands, and a pair of semi-bridging carbonyl ligands. All new compounds have been fully characterized in solution by IR and NMR spectroscopy, and the solid-state structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses. The bonding in cluster 3 has been computationally investigated by Density Functional Theory (DFT), and the data support a cluster that is electronically saturated with 48e and where both sulfido ligands function as 4e donor groups.



 

Synthesis, structure and reactivity of triosmium clusters derived from the reactions of [Os3(CO)10(µ-dppm)] and [(µ-H)Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}] with tris(4-fluorophenyl)phosphine and tris(cyanoethyl)phosphine

The reactions of [Os3(CO)10(µ-dppm)] (1) with tris(4-fluorophenyl)phosphine, P(4-FC6H4)3, and tris(cyanoethyl)phosphine, P(CH2CH2CN)3, in the presence of Me3NO in refluxing dichloromethane gives the mono-substituted clusters [Os3(CO)9(µ-dppm){P(4-FC6H4)3)}] (2) and [Os3(CO)9(µ-dppm){P(CH2CH2CN)3)}] (3), respectively, in which the phosphine is bound to the non-dppm-substituted osmium center. The 46-electron compound [(µ-H)Os3(CO)83-Ph2PCH2P(Ph)C6H4}] (6) reacts with an excess of P(4-FC6H4)3 and P(CH2CH2CN)3 at ambient temperature to yield (2) and (3), respectively. Heating (2) or (3) in refluxing toluene at 110 oC afforded the electron-deficient clusters [(µ-H)Os3(CO)73-Ph2PCH2PPh(C6H4)}{P(4-FC6H4)3)}] (4) and [(µ-H)Os3(CO)73-Ph2PCH2PPh(C6H4)}{P(CH2CH2CN)3}] (5) resulting from C-H bond scission of the coordinated dppm and metal hydride bond formation. The molecular structures of (2), (3) and (4) have been determined by single- crystal X-ray diffraction studies

New tertiary phosphine derivatives of Os3(CO)12: X-ray structures of 1,2-[Os3(CO)10{PhP(o-Tol)2}2], 1,2,3-[Os3(CO)9{(4-FC6H4)3P}3], 1,2,3-[Os3(CO)9{PhP(Cy)2}3] and [Os3(μ-OH)2(CO)8{(4-FC6H4)3P}2]

Abstract


    Reactions of 1,2-[Os3(CO)10(NCMe)2] (1) with tertiary phosphines such as tris(4-fluorophenyl)phosphine(4-FC6H4)3P, bis(o-tolyl)(phenyl)phosphine PhP(o-Tol)2 and dicyclohexyl(phenyl)phosphine PhP(Cy)2 have been examined at room temperature and found to yield the di- and tri-substituted products 1,2-[Os3(CO)10(PR3)2] {(2), PR3 = (4-FC6H4)3P;(3), PR3 = PhP(o-Tol)2; (4), PR3 = PhP(Cy)2} and 1,2,3-[Os3(CO)9(PR3)3] {(5), PR3 = (4-FC6H4)3P; (6), PR3 = PhP(o-Tol)2; 7, PR3 = PhP(Cy)2} as the major products, in addition to the dihydroxyl-bridged complexes 1,2-[Os3(CO)8(PR3)2(µ-OH)2] {(8), PR3 = (4-FC6H4)3P; (9), PR3 = PhP(o-Tol)2; (10), PR3 = PhP(Cy)2} in trace amounts. Compounds (2)-(10) have been characterized by a combination of elemental analyses, infrared, NMR and mass spectral data together with single crystal X-ray diffraction studies for (3), (5), (7) and (8).

Phenazine-substituted polynuclear osmium clusters: Synthesis and DFT evaluation of the C-metalated derivatives Os3(CO)9(m3,h2-C12H7N2)(m-H) and Os3(CO)9(m3,h2-C12H6N2)(m-H)2

Abstract


Os3(CO)12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os3(CO)932-C12H7N2)(μ-H) (1) in 18% yield and the dihydride cluster Os3(CO)932-C12H6N2)(μ-H)2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os3(CO)10(μ,η2-C12H7N2)(μ-H) (3) and with PPh3 to afford the addition product Os3(CO)9(μ,η2-C12H7N2)(PPh3)(μ-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double C–H bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two σ–Os–C bonds and the third osmium atom via an aryl π bond in an η2 fashion. Compound 4 exhibits a closed trimetallic Os3(CO)9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non-phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os3(CO)12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os3(CO)11.

Backbone Modified Small Bite-Angle Diphosphines:Synthesis, Structure, Fluxionality and Regioselective Thermally-Induced Transformations of Ru3(CO)10{l-Ph2PCH(Me)PPh2}

Abstract


The synthesis of Ru3(CO)10{µ-Ph2PCH(Me)PPh2} (1) has been achieved from the radical-catalysed reaction of Ru3(CO)12 with 1,1′-bis(diphenylphosphino)ethane and the fluxionality, protonation and regioselective thermally-induced on-metal transformations of the small bite-angle diphosphine have been studied. Cluster 1 is fluxional in solution and variable temperature 13C{1H} NMR spectroscopy shows that the six carbonyls on the phosphine-bound metal centers interconvert rapidly on the NMR timescale. Protonation of 1 is facile at room temperature and affords the cationic-hydride [Ru3(CO)10{µ-Ph2PCH(Me)PPh2}(μ-H)][BF4] (1H +) which is fluxional, the hydride migrating between bridged and non-bridged ruthenium–ruthenium vectors, location across an unbridged metal–metal bond being thermodynamically favoured. Thermolysis of 1 in heptane affords moderate amounts of the expected benzene-CO elimination product, Ru3(CO)8(µ-CO){µ3-PhPCH(Me)PPh(C6H4)} (2), along with smaller amounts of Ru3(CO)10{μ-PhP(CHMe)(C6H4)PPh} (3) containing a novel doubly-bridged diphosphine ligand. Hydrogenation of 1 in refluxing cyclohexane affords the hydride cluster Ru3(CO)93-PhPCH(Me)PPh2}(μ-H) (4), the same species also being obtained when 2 was treated with hydrogen under similar conditions. All thermally-induced transformations are regioselective, with only a single isomer being generated. In light of the observed regioselectivity a mechanism is proposed for the formation of 2 from 1 which results from an intermediate in which the methyl-group is held over the triruthenium framework.

Experimental and computational studies on the reaction of silanes with the diphosphine-bridged triruthenium clusters Ru3(CO)10(μ-dppf), Ru3(CO)10(μ-dppm) and Ru3(CO)9{μ3-PPhCH2PPh(C6H4)}

Abstract


Reactions of Ru3(CO)10(μ-dppf) (1) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), Ru3(CO)10(μ-dppm) (2) (dppm = bis(diphenylphosphino)methane), and the orthometalated derivative Ru3(CO)93-PPhCH2PPh(C6H4)} (3) with silanes (Ph3SiH, Et3SiH, Ph2SiH2) are reported. Treatment of 1 with Ph3SiH and Ph2SiH2 at room temperature leads to facile Si–H bond activation to afford Ru3(CO)9(μ-dppf)(SiPh3)(μ-H) (4) (60% yield) and Ru3(CO)9(μ-dppf)(SiPh2H)(μ-H) (6) (53% yield), respectively. The reaction of 1 with Ph3SiH has been investigated by electronic structure calculations, and these data have facilitated the analysis of the potential energy surface leading to 4. Compound 1 does not react with Et3SiH at room temperature but reacts at 68 °C to give Ru3(CO)9(μ-dppf)(SiEt3)(μ-H) (5) in 45% yield. Reaction of 2 with Ph3SiH at room temperature yields two new products: Ru3(CO)9(μ-dppm)(SiPh3)(μ-H) (7) in 40% yield and Ru3(CO)63-O)(μ-dppm)(SiPh3)(μ-H)3 (8) in 15% yield. Interestingly, at room temperature compound 7slowly reverts back to 2 in solution with decomposition and liberation of Ph3SiH. Complex 8 can also be prepared from the direct reaction between 7 and H2O. Similar reactions of 2 with Et3SiH and Ph2SiH2 give only intractable materials. The orthometalated compound 3 does not react with Ph3SiH, Et3SiH and Ph2SiH2 at room temperature but does react at 66 °C to give Ru3(μ-CO)(CO)73-PPhCH2PPh(C6H4)}(SiR2R1)(μ-H)](9, R = R′ = Ph, 71% yield; 10, R = R′ = Et, 60% yield; 11, R = Ph, R′ = H, 66% yield) by activation of the Si–H bond. Compounds 4 and 811 have been structurally characterized. In 4, both the dppf and the hydride bridge a common Ru–Ru vector, whereas NMR studies on 7 indicate that two ligands span different Ru–Ru edges. Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh3ligand, and three bridging hydride ligands, whereas 911 represent simple oxidative addition products. In all of the compounds examined, the triruthenium framework retains its integrity and the silyl groups occupy equatorial sites.

Synthesis of [Ru3(CO)9(µ-dppf){P(C4H3E)3}] (E = O, S) and thermally-induced cyclometalation to form [(µ--H)Ru3(CO)7(µ-dppf){µ3-(C4H3E)2P(C4H2E)}](dppf=1,1’-bis(diphenylphos-phino)ferrocene)

Abstract


The new clusters [Ru3(CO)9(μ-dppf){P(C4H3E)3}] (1, E = O; 2, E = S) have been prepared from the Me3NO-induced decarbonylation of [Ru3(CO)10(μ-dppf)] in the presence of PFu3 (E = O) and PTh3 (E = S), respectively. Upon thermolysis in benzene, the major products are the cyclometalated clusters [(μ-H)Ru3(CO)7(μ-dppf){μ3-(C4H3E)2P(C4H2E)}] (3, E = O; 4, E = S). This thermolytic behavior is in marked contrast to that previously noted for the analogous bis(diphenylphosphino)methane (dppm) complexes [Ru3(CO)9(μ-dppm){P(C4H3E)3}], in which both carbon–hydrogen and carbon–phosphorus bond activation yields furyne- and thiophyne-capped clusters. The crystal structures of 1, 3 and 4 are presented and reveal that phosphine migration has occurred during the transformation of 1,2 into 3,4, respectively. The possible relation of the observed reactivity to the relative flexibilities of the diphosphine ligands is discussed. Density functional calculations have been performed on the model cluster [Ru3(CO)9(μ-Me4-dppf){P(C4H3O)3]}], and these data are discussed relative to the ground-state energy differences extant between the different isomeric forms of this cluster. The dynamic NMR behavior displayed by the metalated thienyl ring in cluster4 has also been investigated by computational methods, and the free energy of activation for the “windshield wiper” motion of the activated thienyl moiety determined.

Synthesis and characterization of tungsten carbonyl complexes containing thioamides

Abstract:


Tungsten pentacarbonyl complexes are isolated from the reactions between [W(CO)5(NCMe)] and thioamides, the former being generated in situ upon addition of  equimolar amount of Me3NO into an acetonitrile solution of W(CO)6. Room temperature reactions between [W(CO)5(NCMe)] and acyclic thioamides such as thioacetamide and benzamide afford [W(CO)51-(S)-RCSNH2}] in which the thioamides are coordinated to tungsten through sulfur. Similar S-coordinated complexes, namely, [W(CO)51-(S)-thiolactam}] are also isolated from the reactions with cyclic thioamides or thiolactams under the same reaction conditions. All the new complexes have been adequately characterized by spectroscopic data together with single crystal X-ray diffraction studies for four complexes.