Reversible C-H bond activation at a triosmium centre: A comparative study of the reactivity of unsaturated triosmium clusters Os3(CO)8(μ-dppm)(μ-H)2 and Os3(CO)8(μ-dppf)(μ-H)2 with activated alkynes

Heating a benzene solution of the unsaturated cluster Os3(CO)8(μ-dppm)(μ-H)2 (1) [dppm = bis(diphenylphosphino)methane] with MeO2CCtriple bond; length of mdashCCO2Me (DMAD) or EtO2CCtriple bond; length of mdashCCO2Et (DEAD) at 80 °C furnished the dinuclear compounds Os2(CO)4(μ-dppm)(μ-η2;η1;к1-RO2CCCHCO2R)(μ-H) (3a, R = Me, 3b, R = Et) and the saturated trinuclear complexes Os3(CO)7(μ-dppm)(μ3-η2;η1;η1-RO2CCCCO2R)(μ-H)2 (4a, R = Me, 4b, R = Et). In contrast, similar reactions using unsaturated Os3(CO)8(μ-dppf)(μ-H)2 (2) [dppf = bis(diphenylphosphino)ferrocene] afforded only the trinuclear complexes Os3(CO)8(μ-dppf)(μ-η2;η1-RO2CCHCCO2R)(μ-H) (5a, R = Me; 5b, R = Et) and Os3(CO)7(μ-dppf)(μ3-η2;η1;η1-RO2CCCCO2R)(μ-H)2 (6a, R = Me; 6b, R = Et). Control experiments confirm that 5a and 5b decarbonylate at 80 °C to give 6a and 6b, respectively. Both 5a and 5b exist as a pair of isomers in solution, as demonstrated by 1H NMR and 31P{1H} NMR spectroscopy. DFT calculations on cluster 5a (as the dppf-Me4 derivative) indicate that the isomeric mixture derives from a torsional motion that promotes the conformational flipping of the cyclopentadienyl groups of the dppf-Me4 ligand relative to the metallic plane. VT NMR measurements on clusters 6a and 6b indicate that while the hydride ligand associated with the dppf-bridged Os-Os bond is nonfluxional at room temperature, the second hydride rapidly oscillates between the two non-dppf-bridged Os-Os edges. DFT examination of this hydride fluxionality confirms a “windshield wiper” motion for the labile hydride that gives rise to a time-average coupling of this hydride to both phosphorus centers of the dppf ligand. Thermolysis of 6a and 6b in refluxing toluene yielded Os3(CO)7(μ-dppf)(μ-η2;η1;к1-CCHCO2R) (7a, R=Me; 7b, R=Et). The vinylidene moieties in 7a and 7b derive from the carbon-carbon bond cleavage of coordinated alkyne ligands, and these two products exhibit high thermal stability in refluxing toluene

Rasiowa–Sikorski deduction systems in computer science applications

AbstractA Rasiowa-Sikorski system is a sequence-type formalization of logics. The system uses invertible decomposition rules which decompose a formula into sequences of simpler formulae whose validity is equivalent to validity of the original formula. There may also be expansion rules which close indecomposable sequences under certain properties of relations appearing in the formulae, like symmetry or transitivity. Proofs are finite decomposition trees with leaves having “fundamental”, valid labels. The author describes a general method of applying the R-S formalism to develop complete deduction systems for various brands of C.S and A.I. logic, including a logic for reasoning about relative similarity, a three-valued software specification logic with McCarthy's connectives and Kleene quantifiers, a logic for nondeterministic specifications, many-sorted FOL with possibly empty carriers of some sorts, and a three-valued logic for reasoning about concurrency

Reactivity of 1,2,3-triselena[3]ferrocenophane towards transition metal carbonyls

Reactions of 1,2,3-triselena[3]ferrocenophane with [Mn2(CO)(10)], [Fe(CO)(5)] and [Os-3(CO)(12)] have been investigated under photolytic or thermolytic conditions. Clusters with contrasting structures have been isolated from these reactions: [{Fe(eta-C5H4Se)(2)Mn(CO)(3)}(2)] (1), [Fe(eta-C5H4Se)(2)Fe-2(CO)(6)] (2), 1Fe(eta-C5H4Se)(2)OS3(CO)(10)] (3), [Fe(eta-C5H4Se)(2)(mu(2)-Se)Os-2(CO)(6)] (4) and [Fe(eta-C5H4Se)(2)(mu(3)-Se)Os-4(CO)(11)] (5). Formally, these new clusters are formed by substitution of the central selenium of 1,2,3-triselena[3] ferrocenophane by metal carbonyl units, as in 1-3 or insertion of two Os(CO)(3) groups or an Os-4(CO)(11) unit into the Se Se bond as in 4 and 5, respectively. (C) 2015 Elsevier B.V. All rights reserved

Serendipitous and acid catalyzed synthesis of spirolactones

Formation of three diasteroisomeric spirodilactones 14a--c and 11 has been reported from diester 13 and 9, respectively, under the influence of mineral acid. (C) 2011 Elsevier Ltd. All rights reserved

P-Cl bond-induced lactamization of 2(2 '-hydroxyl)-phenyloxazoline to form a cyclic phosphinite, 3-(2-chloroethyl)-2-phenyl-2H-benzo[e][1,3,2]oxazaphosphinin-4(3H)-one: synthesis, structural studies and transition metal complexes

The equimolar reaction between 2(2'-hydroxy)phenyloxazoline (1) and PPhCl2 in the presence of triethylamine afforded an unexpected cyclic product, phenyl-benzo-oxazaphosphininone (2), instead of a simple phosphinite derivative A. A similar reaction between 1 and PPhCl2 in 2 : 1 ratio also yielded the same product 2, but with one equivalent of 2(2'-hydroxy) phenyloxazoline (1) left unreacted. The formation of the cyclic product 2 is due to the P-Cl bond induced oxazoline ring opening followed by the formation of a six-membered gamma-lactam type product, 3-(2-chloroethyl)-2-phenyl-2H-benzo[e][1,3,2] oxazaphosphinin-4(3H)-one (2 also referred to as L). The reactions of 2 with H2O2, elemental sulphur or elemental selenium yielded the corresponding chalcogenides, LE (3, E = O; 4, E = S; 5, E = Se) in quantitative yield. Treatment of 2 with [Ru(eta(6)-Cymene)Cl-2](2), [Pd(COD)Cl-2] and [Pd(eta(3)-C3H5)Cl](2) resulted in the formation of [RuCl2(eta(6)-cymene)(L)] (6), [PdCl2{L}(2)] (7), and [Pd(eta(3)-C3H5)Cl(L)] (8), respectively. The compound 2 obtained in the 2 : 1 reaction when treated with [Pd(eta(3)-C3H5)Cl](2) gave the same palladium complex 8 (referred to as 9a), but co-crystallized with bis(oxazolyl)palladacycle (9b) as confirmed by single crystal X-ray analysis

Simple, Efficient, and Stereoselective Synthesis of Functionalized Spiro[4.5]decane and Spiro[5.5]undecane Systems

A stereoselective entry into spiro[4.5]decanes and spiro[5.5]undecanes via oxidative cleavage of tricyclo[5.2.2.0(1,5)]undecanes and tricyclo[6.2.2.0(1,6)]dodecanes, which are readily available from simple aromatic precursors, is described

Recognition of fractional non-innocent feature of osmium coordinated 2,2 '-biimidazole or 2,2 '-bis(4,5-dimethylimidazole) and their interactions with anions

Mononuclear complexes [Os-II(bpy)(2)(H2L1)](ClO4)(2) ([1](ClO4)(2)) and [Os-II(bpy)(2)(H2L2)](ClO4)(2) ([2](ClO4)(2)) incorporating two free NH protons at the back face of the coordinated H2L, and deprotonated L2- bridged symmetric dinuclear complexes [(bpy)(2)Os-II(mu-L-1(2-))Os-II(bpy)(2))](ClO4)(2) ([3](ClO4)(2)) and [(bpy)(2)Os-II(mu-L-2(2-))Os-II(bpy)(2))](ClO4)(2) ([4](ClO4)(2)) (bpy = 2,2'-bipyridine, H2L1 = 2,2'-biimidazole and H2L2 = 2,2'-bis(4,5-dimethylimidazole)) have been characterised. Crystal structures of [1](ClO4)(2) and the meso (Delta Delta) diastereomeric form of [3](ClO4)(2) have been determined. The crystal structure of [1](ClO4)(2) also reveals the hydrogen bonding interactions between its free acidic NH protons and the oxygen atoms of the perchlorate anion in the nearby asymmetric unit. Experimental and DFT/TD-DFT calculations have divulged the non-innocent feature of the doubly deprotonated L2- in 3(3+) and 4(3+), leading to the resonating formulation of {Os-II(mu-L2-)Os-III} {Os-II(mu-L-.)Os-II}, instead of a simple mixed valent situation {Os-II(mu-L2-)Os-III}. The dinuclear complexes 3(3+) and 4(3+) display one broad and moderately intense near-IR transition near 1000 nm corresponding to a mixed Os(d pi)/L(pi) -> Os(d pi)/L(pi(star)) MLLMCT (metal/ligand to ligand/metal charge transfer) transition. Different experimental studies have also established the interaction of 1(2+) and 2(2+) with the selective anions

Synthesis of Biaryl Derivatives by Using Ruthenium-Mediated [2+2+2] Cyclotrimerization and Suzuki-Miyaura Cross-Coupling as Key Steps

Functionalized biaryl derivatives have been prepared by applying [2+2+2] cyclotrimerization with the aid of Grubbs' first-generation catalyst (G-I). The trimerized products were subjected to the Suzuki-Miyaura cross-coupling reaction sequence to generate highly functionalized biaryl derivatives

Intramolecular cycloaddition in cyclohexa-2,4-dienone and photochemical reactions: An efficient route to azatriquinane and azasterpurane frameworks

A novel, efficient and stereoselective entry to azatriquinane and azasterpurane frameworks from simple aromatic precursor, is described. The methodology involves in situ generation of cyclohexa-2,4-dienones containing a tether and intramolecular pi 4s+pi 2s cycloaddition that leads to a bicyclo[2.2.2]octenone-annulated five-membered ring that contains nitrogen. Further manipulation of the resulting adduct followed by photochemical sigmatropic shifts readily furnished the azatriquinane and azasterpurane frameworks

New Molybdaborane Clusters with a Bridged Phosphido Ligand

Treatment of [Cp*MoCl(4)], 1 (Cp* = eta(5)-C(5)Me(5)), with [LiBH(4)center dot thf] in toluene at -40 degrees C, followed by thermolysis with [(thf)Li{CH(PPh(2)-BH(3))(2)}] results in the formation of a new class of phosphido bridged molybdaborane [(Cp*Mo)(2)B(4)H(7) (mu-PPh(2))], 2 which has been characterized crystallographically. In addition, the above reaction also produces known [(Cp*Mo)(2)B(5)H(9)], 3 and an unusual molybdaborane [(Cp*Mo)(2)B(5)H(8)(O(i)Pr)], 4 ((i)Pr = -CH(CH(3))(2)). All the new compounds have been characterized in solution by (1)H, (11)B, (13)C, (31)P NMR spectroscopy and the structural types were unambiguously established by X-ray crystallographic analysis of compounds 2 and 4