Shaikh M. Mobin

Catalytic transformation of bio-derived furans to valuable ketoacids and diketones by water-soluble ruthenium catalysts

Bio-derived furans such as 2-furfural (furfural), 5-hydroxymethyl-2-furfural (5-HMF) and 5-methyl-2-furfural (5-MF) were successfully transformed to a ketoacid, levulinic acid (LA), and diketones, 1-hydroxyhexane-2,5-dione (1-HHD), 3-hydroxyhexane-2,5-dione (3-HHD) and hexane-2,5-dione (HD), under moderate reaction conditions using water soluble and recyclable 8-aminoquinoline coordinated arene–ruthenium(II) complexes. Under the optimized reaction conditions using 1 mol% catalyst in the presence of 12 equivalents of formic acid at 80–100 °C, complete conversion of furfural to LA with high selectivity was achieved. Several experiments along with 1H NMR spectral studies are described which provide more insights into the mechanism underlying the transformation of furans to open ring components. Experiments performed using structural analogues of the active catalyst inferred a structure–activity relationship for the observed superior catalytic activity of the 8-aminoquinoline coordinated arene–ruthenium(II) complex. Furthermore, due to the high aqueous solubility of the studied complexes, high recyclability, up to 4 catalytic runs, was achieved without any significant loss of activity. Molecular identities of the studied 8-aminoquinoline coordinated arene–ruthenium(II) complex were also confirmed using single-crystal X-ray diffraction studies.

Ruthenium and Formic Acid Based Tandem Catalytic Transformation of Bioderived Furans to Levulinic Acid and Diketones in Water

Efficient tandem catalytic transformations of bioderived furans, such as furfural, 5‐hydroxymethylfurfural (5‐HMF), and 5‐methylfurfural (5‐MF), to levulinic acid (LA) and diketones, 1‐hydroxyhexane‐2,5‐dione (1‐HHD), 3‐hydroxyhexane‐2,5‐dione (3‐HHD), and hexane‐2,5‐dione (2,5‐HD), was achieved by using water‐soluble arene–RuII complexes, containing ethylenediamine‐based ligands, as catalysts in the presence of formic acid. The catalytic conversion of furans depends on the catalyst, ligand, formic acid concentration, reaction temperature, and time. Experimental evidence, including time‐resolved 1Hu2005NMR spectral studies, indicate that the catalytic reaction proceeds first with formyl hydrogenation followed by hydrolytic ring opening of furans. The ruthenium–formic acid tandem catalytic transformation of fructose to diketones and LA was also achieved. Finally, the molecular structures of the four representative arene–RuII catalysts were established by single‐crystal X‐ray diffraction studies.

Synthetic, spectral and structural aspects of some Rh(III) pentamethylcyclopentadiene complexes containing N,N′-donor bridging ligands

Abstract Reactions of the chloro-bridged dimeric rhodium complex [{(η5-C5Me5)Rh(μ-Cl)Cl}2] with the N,N′-donor bridging ligands pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)aldamine (pbp) or p-biphenylene-bis(picoline)aldamine (bbp) in 1:1 molar ratio in methanol led in the formation of cationic binuclear complexes [(η5-C5Me5)ClRh(μ-L)RhCl(η5-C5Me5)]2+ (L=paa, pbp or bbp) in high yield. It was further observed that reactions of the chloro-bridged dimeric rhodium complex [{(η5-C5Me5)Rh(μ-Cl)Cl}2], with an excess of the above mentioned ligands also, resulted in binuclear complexes. The reaction products have been characterized by microanalyses and spectroscopic studies (IR, 1H-, 13C-NMR, ESMS/FAB mass and electronic spectra). Molecular structure of the representative binuclear complex [(η5-C5Me5)ClRh(μ-paa)RhCl(η5-C5Me5)](BF4)2 has been confirmed by single crystal X-ray analysis. Crystal data: monoclinic, P21/n, a=10.2050(7), b=15.4470(7), c=24.959(2) A, β=97.904(6)°, V=3897.1(5) A3, Z=4, R=0.0609.

Molecular precursors for the preparation of homogenous zirconia-silica materials by hydrolytic sol-gel process in organic media. Crystal structures of [Zr{OSi(O(t)Bu)3}4(H2O)2]·2H2O and [Ti(O(t)Bu){OSi(O(t)Bu)3}3].

[Zr(OPr(i))(4)·Pr(i)OH] reacts with [HOSi(O(t)Bu)(3)] in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy zirconosiloxane precursors of the types [Zr(OPr(i))(3){OSi(O(t)Bu)(3)}] (A) and [Zr(OPr(i))(2){OSi(O(t)Bu)(3)}(2)] (B), respectively. Further reactions of A or B with glycols in 1:1 molar ratio afforded six chemically modified precursors of the types [Zr(OPr(i))(OGO){OSi(O(t)Bu)(3)}] (1A-3A) and [Zr(OGO){OSi(O(t)Bu)(3)}(2)] (1B-3B), respectively [where G = (-CH(2)-)(2) (1A, 1B); (-CH(2)-)(3) (2A, 2B) and (-CH(2)CH(2)CH(CH(3)-)} (3A, 3B)]. The precursors A and B are viscous liquids, which solidify on ageing whereas the other products are all solids, soluble in common organic solvents. These were characterized by elemental analyses, molecular weight measurements, FAB mass, FTIR, (1)H, (13)C and (29)Si-NMR studies. Cryoscopic molecular weight measurements of all the products, as well as the FAB mass studies of 3A and 3B, indicate their monomeric nature. However, FAB mass spectrum of the solidified B suggests that it exists in dimeric form. Single crystal structure analysis of [Zr{OSi(O(t)Bu)(3)}(4)(H(2)O)(2)]·2H(2)O (3b) (R(fac) = 11.9%) as well as that of corresponding better quality crystals of [Ti(O(t)Bu){OSi(O(t)Bu)(3)}(3)] (4) (R(fac) = 5.97%) indicate the presence of a M-O-Si bond. TG analyses of 3A, B, and 3B indicate the formation of zirconia-silica materials of the type ZrO(2)·SiO(2) from 3A and ZrO(2)·2SiO(2) from B or 3B at low decomposition temperatures (≤200 °C). The desired homogenous nano-sized zirconia-silica materials [ZrO(2)·nSiO(2)] have been obtained easily from the precursors A and B as well as from the glycol modified precursors 3A and 3B by hydrolytic sol-gel process in organic media without using any acid or base catalyst, and these were characterized by powder XRD patterns, SEM images, EDX analyses and IR spectroscopy.

Phosphine-free ruthenium-arene complex for low temperature one-pot catalytic conversion of aldehydes to primary amides in water

A highly active phosphine-free ruthenium-arene complex, [(η6-C6H6)RuCl2(C6H5NH2)], exhibits excellent catalytic performance for a one-pot conversion of aldehydes to primary amides at low temperature (60 °C), in water and without any inert gas protection. The reported catalyst performed exceptionally well for a huge range of aldehydes, including aromatic, heteroaromatic, aliphatic and conjugated systems, with a high tolerance for other functional groups. The development of such highly active catalysts using simple reagents will offer new opportunities for the development of improved phosphine-free catalytic systems for this and other related catalytic reactions.

Reactivity of metal acetylides with chalcogen-bridged metal carbonyl cluster in presence of free alkyne molecule: synthesis and characterisation of [(η5-C5Me5)MFe3(μ3-S){(μ3-C(H)=C(R)S}(CO)6(μ3-CCPh)] (R=Ph, n-Bu and M=W, Mo) and [(η5-C5Me5)MFe3(μ3-S){(μ3-C(Fc)=C(H)S}(CO)7(μ3-CCPh)] (M=W, Mo)

Photolysis of benzene solution of [Fe3(CO)9(μ3-S)2] (1), [(η5-C5Me5)M(CO)3(C≡CPh)] (2a: M=W, 2b: M=Mo) and HC≡CR (3a: R=Ph, 3b: R=n-Bu, 3c: R={(η5-C5H5)(η5-C5H4)Fe}(Fc) yields two types of clusters: [(η5-C5Me5)MFe3(μ3-S){(μ3-C(H)ue605C(R)S}(CO)6(μ3-CCPh)] (4: M=W, R=Ph; 5: M=Mo, R=Ph: 6: M=W, R=n -Bu; 7: M=Mo, R=n-Bu) and [(η5-C5Me5)MFe3(μ3-S){(μ3-C(Fc)ue605C(H)S}(CO)7(μ3-CCPh)] (8: M=W; 9: M=Mo) featuring new C–S bond formation. The formation of 8 and 9 involve an unusual head to tail flip of the coordinated acetylide group. All compounds have been characterised by IR and 1H- and 13C-NMR spectroscopy. The structures of 5 and 8 have been established by X-ray crystallography.

Insertion of CS2 into a metal acetylide bond and conversion of the bonding mode of S2CCCPh from η2 to η3

Photolysis of a benzene solution containing [(L)Mo(CO) 3 (Cue606CPh)] (L=η 5 -C 5 H 5 1 ; η 5 -C 5 Me 5 2 ) and CS 2 leads to the formation of dithiopropiolato containing complexes, [(L)Mo(CO) 2 (η 2 -S 2 CCue606CPh)] (L=η 5 -C 5 H 5 4 ; L=η 5 -C 5 Me 5 5 ). In presence of air, [(η 5 -C 5 H 5 )Mo(CO) 3 (Cue606CPh)] reacts with CS 2 to give 4 as the major and [(η 5 -C 5 H 5 )Mo(O)(η 3 -S 2 CCue606CPh)] ( 6 ) as minor products. Similarly, [(η 5 -C 5 Me 5 )Mo(CO) 3 (Cue606CPh)] reacts with CS 2 under aerobic conditions to give compound 5 along with [(η 5 -C 5 Me 5 )Mo(O)(η 3 -S 2 CCue606CPh)] ( 7 ) as minor product. When solutions of 4 or 5 are photolysed under a constant purge of air, 4 gives 6 , and 5 gives 7 in high yields. Room temperature stirring of 5 with [W(CO) 5 (THF)] forms [η 5 -C 5 Me 5 )Mo(CO) 2 CS 2 {W(CO) 5 } 2 Cue606CPh] ( 9 ). All new compounds have been characterised by IR and 1 H-NMR spectroscopy and the structures of 4 , 6 , 7 and 9 have been established crystallographically.

Chalcogen-acetylide interaction and unusual reactivity of coordinated acetylide with water: synthesis and characterisation of [(η5-C5R5)Fe3(CO)6(μ3-E)(μ3-ECCH2RI)] (R = H, Me; RI = Ph, Fc; E = S, Se) and [(η5-C5R5)MoFe2(CO)6(μ3-S)-(μ-SCCH2Ph)] (R = H, Me)

Abstract Photolysis of a benzene solution containing [Fe3(CO)9(μ3-E)2] (E=S, Se), [(η5-C5R5)Fe(CO)2(Cue606CRI)] (R=H, Me; RI=Ph, Fc), H2O and Et3N results in formation of new metal clusters [(η5-C5R5)Fe3(CO)6(μ3-E)(μ3-ECCH2RI)] (R=H, RI=Ph, E=S 1 or Se 2; R=Me, RI=Ph, E=S 3 or Se 4; R=H, RI=Fc, E=S 5; R=Me, RI=Fc, E=S 6 or Se 7). Reaction of [Fe3(CO)9(μ3-S)2]with [(η5-C5R5)Mo(CO)3(Cue606CPh)] (R=H, Me), under same conditions, produces mixed-metal clusters [(η5-C5R5)MoFe2(CO)6(μ3-S)(μ-SCCH2Ph)] (R=H 8; R=Me 9). Compounds 1–9 have been characterised by IR and 1H and 13C-NMR spectroscopy. Structures of 1, 5 and 9 have been established crystallographically. A common feature in all these products is the formation of new C-chalcogen bond to give rise to a (ECCH2RI) ligand.

C−H Bond Activation/Arylation Catalyzed by Arene–Ruthenium–Aniline Complexes in Water

Water-soluble arene-ruthenium complexes coordinated with readily available aniline-based ligands were successfully employed as highly active catalysts in the C-H bond activation and arylation of 2-phenylpyridine with aryl halides in water. A variety of (hetero)aryl halides were also used for the ortho-C-H bond arylation of 2-phenylpyridine to afford the corresponding ortho- monoarylated products as major products in moderate to good yields. Our investigations, including time-scaled NMR spectroscopy and mass spectrometry studies, evidenced that the coordinating aniline-based ligands, having varying electronic and steric properties, had a significant influence on the catalytic activity of the resulting arene-ruthenium-aniline-based complexes. Moreover, mass spectrometry identification of the cycloruthenated species, {(η6 -arene)Ru(κ2 -C,N-phenylpyridine)}+ , and several ligand-coordinated cycloruthenated species, such as [(η6 -arene)Ru(4-methylaniline)(κ2 -C,N-phenylpyridine)]+ , found during the reaction of 2-phenylpyridine with the arene-ruthenium-aniline complexes further authenticated the crucial roles of these species in the observed highly active and tuned catalyst. At last, the structures of a few of the active catalysts were also confirmed by single-crystal X-ray diffraction studies.

Cycloaddition of Cyclohexa-2,4-dienones with Nitroolefins: An Unusual Regioselectivity and Expeditious Entry into Nitro-bicyclo[2.2.2]octenones

Abstract Cycloaddition of electron-deficient cyclohexa-2,4-dienones with nitroolefins leading to functionalized bicyclo[2.2.2]octenones with nitro groups is reported. A highly unusual regioselectivity was observed. Crystal structure of one of adducts has also been reported.