Toward the synthesis of norzoanthamine: complete fragment assembly

The complex marine alkaloid norzoanthamine (2) was envisioned to be assembled from three key building blocks: the C1-C5 fragment A, the C6-C10 fragment B, and the C11-C24 fragment C. The synthesis of fragment A was achieved in 14 steps and 33% overall yield from (R)-gamma-hydroxymethyl-gamma-butyrolactone. Fragment B was made in two steps from PMB-protected 4-pentynol in 76% yield. The C11-C24 fragment C was made from (S)-carvone via (R)-isocarvone in 18 steps (6% overall yield). The convergent stereoselective synthesis of the entire carbon framework (C1-C24) of the target molecule was achieved via the following assemblage. Alkenyl iodide 20 derived from the C11-C24 fragment C was coupled to fragment B (C6-C10) through a high-yielding Stille coupling reaction of these two sterically very demanding coupling partners, affording the key Diels-Alder precursor 24. The intramolecular Diels-Alder reaction proceeded smoothly in excellent yield and diastereoselectivity, generating the tricyclic trans-anti-trans perhydrophenanthrene motif of norzoanthamine (C6-C24). The final fragment coupling between lithiated fragment A (C1-C5) and aldehyde 40 (C6-C24) has also been successfully accomplished affording the entire carbon framework of the natural product.     

Total synthesis of the epidermal growth factor inhibitor (-)-reveromycin B

The total synthesis of the epidermal growth factor inhibitor reveromycin B (2) in 25 linear steps from chiral methylene pyran 13 is described. The key steps involved an inverse electron demand hetero-Diels-Alder reaction between dienophile 13 and diene 12 to construct the 6,6-spiroketal 11 which upon oxidation with dimethyldioxirane and acid catalyzed rearrangement gave the 5,6-spiroketal aldehyde 9. Lithium acetylide addition followed by oxidation/reduction and protective group manipulation provided the reveromycin B spiroketal core 8 which was converted into the reveromycin A (1) derivative 6 in order to confirm the stereochemistry of the spiroketal segment. Introduction of the C1-C10 side chain began with sequential Wittig reactions to form the C8-C9 and C7-C6 bonds, and a tin mediated asymmetric aldol reaction installed the C4 and C5 stereocenters. The final key steps to the target molecule 2 involved a Stille coupling to introduce the C21-C22 bond, succinoylation, selective deprotection, oxidation, and Wittig condensation to form the final C2-C3 bond. Deprotection was effected by TBAF in DMF to afford reveromycin B (2) in 72% yield.     

C-F activation of fluorinated arenes using NHC-stabilized nickel(0) complexes: selectivity and mechanistic investigations

The reaction of [Ni2((i)Pr2Im)4(COD)] 1a or [Ni((i)Pr2Im)2(eta(2)-C2H4)] 1b with different fluorinated arenes is reported. These reactions occur with a high chemo- and regioselectivity. In the case of polyfluorinated aromatics of the type C6F5X such as hexafluorobenzene (X = F) octafluorotoluene (X = CF3), trimethyl(pentafluorophenyl)silane (X = SiMe3), or decafluorobiphenyl (X = C6F5) the C-F activation regioselectively takes place at the C-F bond in the para position to the X group to afford the complexes trans-[Ni((i)Pr2Im)2(F)(C6F5)]2, trans-[Ni((i)Pr2Im)2(F)(4-(CF3)C6F4)] 3, trans-[Ni((i)Pr2Im)2(F)(4-(C6F5)C6F4)] 4, and trans-[Ni((i)Pr2Im)2(F)(4-(SiMe3)C6F4)] 5. Complex 5 was structurally characterized by X-ray diffraction. The reaction of 1a with partially fluorinated aromatic substrates C6H(x)F(y) leads to the products of a C-F activation trans-[Ni((i)Pr2Im)2(F)(2-C6FH4)] 7, trans-[Ni((i)Pr2Im)2(F)(3,5-C6F2H3)] 8, trans-[Ni((i)Pr2Im)2(F)(2,3-C6F2H3)] 9a and trans-[Ni((i)Pr2Im)2(F)(2,6-C6F2H3)] 9b, trans-[Ni((i)Pr2Im)2(F)(2,5-C6F2H3)] 10, and trans-[Ni((i)Pr2Im)2(F)(2,3,5,6-C6F4H)] 11. The reaction of 1a with octafluoronaphthalene yields exclusively trans-[Ni((i)Pr2Im)2(F)(1,3,4,5,6,7,8-C10F7)] 6a, the product of an insertion into the C-F bond in the 2-position, whereas for the reaction of 1b with octafluoronaphthalene the two isomers trans-[Ni((i)Pr2Im)2(F)(1,3,4,5,6,7,8-C10F7)] 6a and trans-[Ni((i)Pr2Im)2(F)(2,3,4,5,6,7,8-C10F7)] 6b are formed in a ratio of 11:1. The reaction of 1a or of 1b with pentafluoropyridine at low temperatures affords trans-[Ni((i)Pr2Im)2(F)(4-C5NF4)] 12a as the sole product, whereas the reaction of 1b performed at room temperature leads to the generation of trans-[Ni((i)Pr2Im)2(F)(4-C5NF4)] 12a and trans-[Ni((i)Pr2Im)2(F)(2-C5NF4)] 12b in a ratio of approximately 1:2. The detection of intermediates as well as kinetic studies gives some insight into the mechanistic details for the activation of an aromatic carbon-fluorine bond at the {Ni((i)Pr2Im)2} complex fragment. The intermediates of the reaction of 1b with hexafluorobenzene and octafluoronaphthalene, [Ni((i)Pr2Im)2(eta(2)-C6F6)] 13 and [Ni((i)Pr2Im)2(eta(2)-C10F8)] 14, have been detected in solution. They convert into the C-F activation products. Complex 14 was structurally characterized by X-ray diffraction. The rates for the loss of 14 at different temperatures for the C-F activation of the coordinated naphthalene are first order and the estimated activation enthalpy Delta H(double dagger) for this process was determined to be Delta H(double dagger) = 116 +/- 8 kJ mol(-1) (Delta S(double dagger) = 37 +/- 25 J K(-1) mol(-1)). Furthermore, density functional theory calculations on the reaction of 1a with hexafluorobenzene, octafluoronaphthalene, octafluorotoluene, 1,2,4-trifluorobenzene, and 1,2,3-trifluorobenzene are presented.     

A joint study based on the electron localization function and catastrophe theory of the chameleonic and centauric models for the Cope rearrangement of 1,5-hexadiene and its cyano derivatives

A novel interpretation of the chameleonic and centauric models for the Cope rearrangements of 1,5-hexadiene (A) and different cyano derivatives (B: 2,5-dicyano, C: 1,3,4,6-tetracyano, and D: 1,3,5-tricyano) is presented by using the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) on the reaction paths calculated at the B3LYP/6-31G(d,p) level. The progress of the reaction is monitorized by the changes of the ELF structural stability domains (SSD), each being change controlled by a turning point derived from CT. The reaction mechanism of the parent reaction A is characterized by nine ELF SSDs. All processes occur in the vicinity of the transition structure and corresponding to a concerted formation/breaking of C(1)-C(6) and C(3)-C(4) bonds, respectively, together with an accumulation of charge density onto C(2) and C(5) atoms. Reaction B presents the same number of ELF SSDs as A, but a different order appears; the presence of 2,5-dicyano substituents favors the formation of C(1)-C(6) bonds over the breaking of C(3)-C(4) bond process, changing the reaction mechanism from a concerted towards a stepwise, via a cyclohexane biradical intermediate. On the other side, reaction C presents the same type of turning points but two ELF SSD less than A or B; there is an enhancement of the C(3)-C(4) bond breaking process at an earlier stage of the reaction by delocalizing the electrons from the C(3)-C(4) bond among the cyano groups. In the case of competitive effects of cyano subsituents on each moiety, as it is for reaction D, seven different ELF SSDs have been identified separated by eight turning points (two of them occur simultaneously). Both processes, formation/breaking of C(1)-C(6) and C(3)-C(4) bonds, are slightly favored with respect to the parent reaction (A), and the TS presents mixed electronic features of both B and C. The employed methodology provides theoretical support for the centauric nature (half-allyl, half-radical) for the TS of D.     

Unsuccessful/successful attempts to produce penta(heteroaryl)-phosphoranes/-arsoranes R5E (E = P, As; R = 2-furyl, 2-thienyl)

Tri(2-thienyl)phosphine (1) has been transformed into chlorotri(2-thienyl)phosphonium chloride (3) in the reaction with hexachloroethane, into tetra(2-thienyl)phosphonium bromide (4) in a NiBr2-catalyzed quaternization with 2-bromothiophene, and into the p-tolylsulfonyliminotri(2-thienyl)phosphorane (6) using "chloramine T". Attempts to generate the homoleptic penta(2-thienyl)phosphorane (2-C4H3S)5P (5) by treating 3, 4, 6 or the known (PhO)3P=NSO2C6H4-2-Me (9) with 2-thienyllithium were unsuccessful. Tri(2-furyl)phosphine (2) was converted into the related imine 7, but the reaction of 7 or of 9 with 2-furyllithium failed to give (2-C4H3O)5P (8). It was only with the strained phosphorane Ph(C12H8)P=NSO2C6H4-4-Me (C12H8= 2,2'-biphenylylene) (10) that with 2-C4H3OLi the corresponding phosphorane Ph(C12H8)P(C4H3O-2)2 (11) could be obtained (31P NMR: delta-106.7 ppm). In the arsenic series, tri(2-thienyl)- and tri(2-furyl)arsine (12, 13) were converted into the tosylimino compounds (14, 15) and successfully transformed into the homoleptic arsoranes with 2-C4H3E-Li: penta(2-thienyl)- (16) and penta(2-furyl)-arsorane (17) are stable colourless crystalline solids, the NMR spectra of which indicate rapid pseudo-rotation in solution. The single crystal structure analysis of 17 shows an only slightly distorted trigonal-bipyramidal configuration. In crystals of the phosphine 2 and the arsine 13 the molecules have a propeller configuration with approximate C3v symmetry for the former, but Cs symmetry for the latter. The crystal structures of the precursors or intermediates 3, 4, 6, 9, and 10 have also been determined.     

DFT study of the fragmentation mechanism of uracil RNA base

The fragmentation process of the uracil RNA base has been investigated via DFT calculations in order to assign fragments to the ionisation mass spectrum obtained after dissociation induced by collision experiments. The analysis of the electronic distribution and geometry parameters of the cation allows selection of several bonds that may be cleaved and lead to the formation of various fragments. Differences are observed in the electronic behaviour of the bond breaking as well as the energy required for the cleavage. It is reported that N(3)-C(4) and N(1)-C(2) bonds are more easily cleaved than the C(5)-C(6) bond, since the corresponding energy barriers amount to ΔG = +1.627, +1.710, +5.459 eV, respectively, which makes the C(5)-C(6) bond cleavage almost prohibited. Among all possible formed fragments, the formation of the OCN(+) fragment for the peak at m/z = 42 Da is excluded because of an intermediate that was not observed experimentally and too a large free energy barrier. Based on the required free energy, it is observed that two fragment derivatives: C(2)H(4)N(+) and C(2)H(2)O˙(+) may be formed, with a small preference for C(2)H(4)N(+). This latter product is not formed through a retro Diels Alder reaction in contrast to C(2)H(2)O˙(+). The following sequence is proposed for the peak at 42 Da: C(2)H(4)N(+) (from N(1)-C(2), C(4)-C(5) cleavages) > C(2)H(2)O˙(+) (from N(3)-C(4), N(1)-C(2) and C(5)-C(6) cleavages) > C(2)H(4)N(+) (from N(1)-C(2), N(3)-C(4) and C(4)-C(5)) > C(2)H(2)O˙(+) (from C(5)-C(6), N(1)-C(2) and N(3)-C(4) cleavages) > NCO(+) (from N(1)-C(2), C(4)-C(5) and N(3)-C(4) cleavages). Finally the peak at 28 Da is assigned to CNH(2)(+) derivatives that can be formed through two different paths, the easiest one requiring 5.4 eV.     

Chelate and pincer carbene complexes of rhodium and platinum derived from hexaphenylcarbodiphosphorane, Ph3P=C=PPh3

The reaction of [(cod)RhCl]2 with Ph3P=C=PPh3 (1) gave the bidentate Rh(I) carbene complex, (cod)Rh[eta2-C{P(C6H4)Ph2}{PPh3}] (2), in which one of the Ph groups in 1 underwent orthometalation to form the chelate. Displacement of cod by 2 equiv of PMe3 transformed 2, via a second orthometalation event, into the Rh(III) C,C,C pincer carbene complex, HRh(PMe3)2[eta3-C{P(C6H4)Ph2}2] (3). The reaction of [Me2Pt(SMe2)]2 with 1 led directly to the analogous C,C,C pincer carbene complex of Pt(II), (Me2S)Pt[eta3-C{P(C6H4)Ph2}2] (4). DFT calculations on a model form of 3 suggest a net single sigma-bonding interaction between Rh and an sp2-hybridized carbene center, with a HOMO that is predominantly carbene pz in character.     

Facile oxidative addition of water at iridium: reactivity of trans-[Ir(4-C5NF4)(H)(OH)(PiPr3)2] towards CO2 and NH3

A reaction of trans-[Ir(4-C(5)NF(4))(η(2)-C(2)H(4))(PiPr(3))(2)] (1) with an excess of water in THF at room temperature affords the hydrido hydroxo complex trans-[Ir(4-C(5)NF(4))(H)(OH)(PiPr(3))(2)] (2). Treatment of 2 with CO furnishes trans-[Ir(4-C(5)NF(4))(H)(OH)(CO)(PiPr(3))(2)] (3). Reductive elimination of water from 3 leads to the formation of the iridium(I) carbonyl complex trans-[Ir(4-C(5)NF(4))(CO)(PiPr(3))(2)] (4). The insertion of CO(2) into the Ir-O bond of 2 forms the hydrido hydrogencarbonato complex trans-[Ir(4-C(5)NF(4))(H)(κ(2)-(O,O)-O(2)COH)(PiPr(3))(2)] (5). Treatment of 2 with NH(3) in C(6)D(6) yields trans-[Ir(4-C(5)NF(4))(H)(OH)(NH(3))(PiPr(3))(2)] (6). Storage of the reaction mixture at room temperature reveals the formation of the N-H activation product [Ir(4-C(5)NF(4))(H)(μ-NH(2))(NH(3))(PiPr(3))](2) (7).     

High nuclearity ruthenium-tin clusters from the reactions of triphenylstannane with pentaruthenium carbonyl carbido cluster complexes

The reaction of Ru(5)(CO)(15)(mu(5)-C), 1, with Ph(3)SnH in the presence of UV irradiation has yielded the Ph(3)SnH adduct Ru(5)(CO)(15)(SnPh(3))(mu(5)-C)(mu-H), 3, by SnH bond activation and cleavage of one Ru-Ru bond in the cluster of 1. The reaction of 1 with Ph(3)SnH at 127 degrees C yielded the high nuclearity cluster compound Ru(5)(CO)(10)(SnPh(3))(mu-SnPh(2))(4)(&mu(5)-C)(mu-H), 4, that contains five tin ligands. Four of these are SnPh(2) groups that bridge each edge of the base of the Ru(5) square pyramidal cluster. The reaction of Ph(3)SnH with the benzene-substituted cluster Ru(5)(CO)(12)(C(6)H(6))(mu(5)-C), 2, at 68 degrees C yielded two products: Ru(5)(CO)(11)(SnPh(3))(C(6)H(6))(mu(5)-C)(mu-H), 5, and Ru(5)(CO)(10)(SnPh(3))(2)(C(6)H(6))(mu(5)-C)(mu-H)(2), 6. Both contain square pyramidal Ru(5) clusters with one and two SnPh(3) groups, respectively. At 127 degrees C, the reaction of 2 with an excess of Ph(3)SnH has led to the formation of two new high-nuclearity cluster complexes: Ru(5)(CO)(8)(mu-SnPh(2))(4)(C(6)H(6))(mu(5)-C), 7, and Ru(5)(CO)(7)(mu-SnPh(2))(4)(SnPh(3))(C(6)H(6))(mu-H), 8. Both compounds contain square pyramidal Ru(5) clusters with SnPh(2) groups bridging each edge of the square base. Compound 8 contains a SnPh(3) group analogous to that of compound 4. When treated with CO, compound 8 is converted to 4. When heated to 68 degrees C, compound 5 was converted to the new compound Ru(5)(CO)(11)(C(6)H(6))(mu(4)-SnPh)(mu(3)-CPh), 9, by loss of benzene and the shift of a phenyl group from the tin ligand to the carbido carbon atom to form a triply bridging benzylidyne ligand and a novel quadruply bridging stannylyne ligand.     

Steric Effects in the Tuning of the Diastereoselectivity of the Intramolecular Free-Radical Cyclization to an Olefin As Exemplified through the Synthesis of a Carba-Pentofuranose Scaffold

Two free-radical cyclization reactions with the radical at the chiral C4 of the pentose sugar and the intramolecularly C1-tethered olefin (on radical precursors 8 and 17) gave a new diastereospecific C4-C8 bond in dimethylbicyclo[2.2.1]heptane 9, whereas the new C4-C7 bond in 7-methyl-2-oxabicyclo[2.2.1]heptanes 18a/18b gave trans and cis diastereomers, in which the chirality of the C4 center is fully retained as that of the starting material. It has been shown how the chemical nature of the fused carba-pentofuranose scaffolds, dimethylbicyclo[2.2.1]heptane 9 vis-a-vis 7-methyl-2-oxabicyclo[2.2.1]heptanes 18a/18b (C7-Me in the former versus 2-O- in the latter), dictates the stereochemical outcome both at the Grignard reaction step as well as in the free-radical ring-closure reaction. The formation of pure 1,8-trans-bicyclo[2.2.1]heptane 9 from 8 suggests that the boat-like transition state is favored due to the absence of steric clash of the bulky 1(S)-O-p-methoxybenzyl (PMB) and 7(R)-Me substituents (both in the α-face) with that of the 8(R)-CH(2)(?) radical in the β-face. The conversion of 17 → 18a-7(S) and 18b-7(R) in 6:4 ratio shows that the participation of both the chair- and the boat-like transition states is likely.     

Synthesis, characterization and optical properties of pi-conjugated systems incorporating closo-dodecaborate clusters: new potential candidates for two-photon absorption processes

Non-centrosymmetric pi-conjugated systems incorporating closo-dodecaborate clusters, [NC-C6H4-C(H=N(H)-B12H11]-(2), [NC-C6H4-C(H)=C(H)-C(6)H(4)-C(H)=N(H)-B12H11]-(3), and [NC-C6H4-C(H)=C(H)-C6H4-C(H)=C(H)-C6H4-C(H)=N(H)-B12H11]-(4) have been synthesized by reaction of the monoamino derivative of B12, [B12H11NH3]-(1), with various arylaldehydes, R-C6H4-CHO. These Schiff base-like compounds were fully characterized by multinuclear NMR spectroscopy and mass spectrometry. In order to evaluate these boron rich pi-systems as potential materials for two-photon absorption (TPA) processes, UV linear absorption curves were recorded for 3 and 4, and comparatively studied with those of the boron-free pi-systems NC-C6H4-C(H)=N-CH3(5) and NC-C6H4-C(H)=C(H)-C6H4-C(H)=N-CH3(6). The donor effect of the boron cluster was evidenced by a shift to the lower energy of the absorption band in the spectra of systems incorporating B12. The two photon absorption (TPA) spectrum of compound , obtained by the up-conversion method, shows a resonance at 720 nm with a cross-section sigma(TPA) of 35 x 10(-50) cm(4) s photon(-1) molecule(-1). This value suggests the potential of B12 clusters to be used as new donor groups for the synthesis of non-linear materials.     

Pentafluorophenyl transfer: a new group-transfer reaction in organoborate salts

[reaction: see text] Irradiation of isoquinolinium hydroxytris(pentafluorophenyl)borate, 1, and phenanthridium hydroxytris(pentafluorophenyl)borate, 2, in either CH2Cl2 or CH3CN resulted in C6F5 transfer to the isoquinolinium and phenanthridium cations, generating 2-methyl-1-(2,3,4,5,6-pentafluorophenyl)-1,2-dihydroisoquinoline, 3, and 2-methyl-1-(2,3,4,5,6-pentafluorophenyl)-1,2-dihydrophenanthridine, 4, respectively. In addition, photogeneration of H2O x B(C6F5)3 resulted from 1. Photogeneration of C6F5-C6F4H from HO-B(C6F5)3(-) and of C6H5-C6F4H from C6H5-B(C6F5)3(-) was discovered.     

Synthesis, coupling, and condensation reactions of 1,2-diborylated benzenes: an experimental and quantum-chemical study

1,2-Bis(pinacolboryl)benzene (1,2-C(6) H(4) (Bpin)(2) , 2) was synthesized in preparatively useful yields from 1,2-C(6) H(4) Br(2) , iPrO?Bpin, and Mg turnings in the presence of 1,2-C(2) H(4) Br(2) as an entrainer. Compound 2 is a versatile starting material for the synthesis of (un)symmetrically substituted benzenes (i.e., 1,2-C(6) H(4) (Ar(1) )(Ar(2) )) through sequential Suzuki-Miyaura coupling reactions. Alternatively, it can be transformed into bis-borate Li(2) [1,2-C(6) H(4) (BH(3) )(2) ] (3) through reduction with Li[AlH(4) ]. In the crystal lattice, the diethyl ether solvate 3?OEt(2) establishes a columnar structure that is reinforced by an intricate network of B?(μ-H)?Li interactions. Hydride-abstraction from compound 3 with Me(3) SiCl leads to the transient ditopic borane 1,2-C(6) H(4) (BH(2) )(2) , which can either be used in situ for subsequent hydroboration reactions or trapped as its stable NMe(2) Et diadduct (6). In SMe(2) solution, the putative diadduct 1,2-C(6) H(4) (BH(2) ?SMe(2) )(2) is not long-term stable but rather undergoes a condensation reaction to give 9,10-dihydro-9,10-diboraanthracene, HB(μ-C(6) H(4) )(2) BH, and BH(3) . 9,10-Dihydro-9,10-diboraanthracene was isolated from the reaction mixture as its SMe(2) monoadduct (7), which dimerizes in the solid state through two B?H?B bridges ((7)(2) , elucidated by X-ray crystallography). In contrast, hydride-abstraction from compound 3 in THF or CH(2) Cl(2) provides the unique exo-adduct H(2) B(μ-H)(2) B(μ-C(6) H(4) )(2) B(μ-H)(2) BH(2) (8, elucidated by X-ray crystallography). Quantum-chemical calculations on various conceivable isomers of [1,2-C(6) H(4) (BH(2) )(2) ](2) revealed that compound 8 was the most stable of these species. Moreover, the calculations confirmed the experimental findings that the NMe(2) Et diadduct of 1,2-C(6) H(4) (BH(2) )(2) is significantly more stable than the corresponding SMe(2) complex and that the latter complex is not able to compete successfully with borane-dimerization and -condensation. The reaction cascade in SMe(2) , which proceeds from 1,2-C(6) H(4) (BH(2) )(2) to the observed adducts of HB(μ-C(6) H(4) )(2) BH, has been elucidated in detail and the important role of B?C?B-bridged intermediates has been firmly established.     

Seven-minute synthesis of pure C(s)-C60Cl6 from [60]fullerene and iodine monochloride: first IR, Raman, and mass spectra of 99 mol % C60Cl6

Three previously reported procedures for the synthesis of pure C(s)-C60Cl6 from C60 and ICl dissolved in benzene or 1,2-dichlorobenzene were shown to actually yield complex mixtures of products that contain, at best, 54-80% C(s)-C60Cl6 based on HPLC integrated intensities. MALDI mass spectrometry was used for the first time to identify other components of the reaction mixtures. An improved synthetic procedure was developed for the synthesis of about 150 mg batches of chlorofullerenes containing 90% C(s)-C60Cl6 based on HPLC intensities. The optimum reaction time was decreased from several days to seven minutes. Small amounts of the product were purified by HPLC (toluene eluent) to 99% purity. The pure compound C(s)-C60Cl6 is stable for at least three months as a solvent-free powder at 25 degrees C. The Raman, far-IR, and MALDI mass spectra of pure C(s)-C60Cl6 are reported for the first time. The Raman and far-IR spectra, the first reported for any C60Cl(n) chlorofullerene, were used to carry out a vibrational analysis of C(s)-C60Cl6 at the DFT level of theory.     

Synthesis and Characterization of Linked Clusters Capped by Alkylidyne

1 INTRODUCTION Constructing higher nuclearity clusters with well-defined dimensions and structures provide a rather active field of chemistry with potential applications in areas including nanotechnology, molecular recognition and catalysis[1~4]. A continuing effort has been directed toward developing a better methodology for systematic synthesis of supracluster compounds through molecular design [5,6]. On the basis of extensive investigation on the metal exchange reaction in cluster com…     

Synthesis and Crystal Structure of 2,3-Diethoxycarbonyl-4-phenyl-5-morpholinyl Thiophene

1INTRoDUCTIONa-Thiocarbonylthioformamidesweresynthesizedin198o[l~2i,however,thereisnoreportofthesecompoundsconcerningtheirpropertiesandreactionactivitiest33.Accordingtotheirstructure,theyseemtohavereactionwithdienophi1es,likesubsti-tutedolefinicandacetylenicdienophilestoleadcorrespondingDiels-Alderproduct.xylene(15ml),diethylbutynedioicester(O.2g,1.2mmol)wasadded,themix-turewasrefluxedfor20h,thencooledtoroomtemperatureandconcentrated.Theresiduewaspurifiedbysilicagelcolumnusingacetone/petr…     

Role of the NH2 functionality and solvent in terdentate CNN alkoxide ruthenium complexes for the fast transfer hydrogenation of ketones in 2-propanol

The reaction of [RuCl(CNN)(dppb)] (1; HCNN=6-(4-methylphenyl)-2-pyridylmethylamine) with NaOiPr in 2-propanol/C6D6 affords the alcohol adduct alkoxide [Ru(OiPr)(CNN)(dppb)].n iPrOH (5), containing the Ru-NH2 linkage. The alkoxide [Ru(OiPr)(CNN)(dppb)] (4) is formed by treatment of the hydride [Ru(H)(CNN)(dppb)] (2) with acetone in C6D6. Complex 5 in 2-propanol/C6D6 equilibrates quickly with hydride 2 and acetone with an exchange rate of (5.4+/-0.2) s(-1) at 25 degrees C, higher than that found between 4 and 2 ((2.9+/-0.4) s(-1)). This fast process, involving a beta-hydrogen elimination versus ketone insertion into the Ru-H bond, occurs within a hydrogen-bonding network favored by the Ru-NH2 motif. The cationic alcohol complex [Ru(CNN)(dppb)(iPrOH)](BAr(f)4) (6; Ar(f)=3,5-C6H3(CF3)2), obtained from 1, Na[BAr(f)4], and 2-propanol, reacts with NaOiPr to afford 5. Complex 5 reacts with either 4,4'-difluorobenzophenone through hydride 2 or with 4,4'-difluorobenzhydrol through protonation, affording the alkoxide [Ru(OCH(4-C6H4F)2)(CNN)(dppb)] (7) in 90 and 85 % yield of the isolated product. The chiral CNN-ruthenium compound [RuCl(CNN)((S,S)-Skewphos)] (8), obtained by the reaction of [RuCl2(PPh3)3] with (S,S)-Skewphos and orthometalation of HCNN in the presence of NEt3, is a highly active catalyst for the enantioselective transfer hydrogenation of methylaryl ketones (turnover frequencies (TOFs) of up to 1.4 x 10(6) h(-1) at reflux were obtained) with up to 89% ee. Also the ketone CF3CO(4-C6H4F), containing the strong electron-withdrawing CF3 group, is reduced to the R alcohol with 64% ee and a TOF of 1.5 x 10(4) h(-1). The chiral alkoxide [Ru(OiPr)(CNN)((S,S)-Skewphos)]n iPrOH (9), obtained from 8 and NaOiPr in the presence of 2-propanol, reacts with CF3CO(4-C6H4F) to afford a mixture of the diastereomer alkoxides [Ru(OCH(CF3)(4-C6H4F))(CNN)((S,S)-Skewphos)] (10/11; 74% yield) with 67% de. This value is very close to the enantiomeric excess of the alcohol (R)-CF3CH(OH)(4-C6H4F) formed in catalysis, thus suggesting that diastereoisomeric alkoxides with the Ru-NH2 linkage are key species in the catalytic asymmetric transfer hydrogenation reaction.     

Titanium "constrained geometry" complexes with pendant arene groups

The synthesis of the proligands C(5)Me(4)HSiMe(2)N(H)R) (R = CMe(2)Ph 1, 2-C(6)H(4)Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe(2)(C(5)Me(5)H). Generation of the dilithio salt and reaction with TiCl(3)·(THF)(3) followed by oxidation gave C(5)Me(4)SiMe(2)N(C(6)H(4)Ph)TiCl(2) (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me(2)N)(2)TiCl(2) afforded C(5)Me(4)(SiMe(2)NR)Ti(NMe(2))(2) (R = CMe(2)Ph 4, 2-C(6)H(4)Ph 5), respectively, in good yields Treatment with MeI gave the analogs C(5)Me(4)(SiMe(2)NR)TiI(2) (R = CMe(2)Ph 6, 2-C(6)H(4)Ph 7). Reduction of 7 with potassium graphite afforded C(5)Me(4)(SiMe(2)NC(6)H(4)Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C(5)Me(4)(SiMe(2)NR)TiMe(2) (R = CMe(2)Ph 9, 2-C(6)H(4)Ph 10). Complexes 9 and 10 in combination with the activator [Ph(3)C][B(C(6)F(5))(4)] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C(5)Me(4))SiMe(2)(NtBu)]TiMe(2).     

B(C6F5)3 adducts of transition metal acyl compounds

The transition metal acyl compounds [Co(L)(CO)3(COMe)] (L = PMe3, PPhMe2, P(4-Me-C6H4)3, PPh3 and P(4-F-C6H4)3), [Mn(CO)5(COMe)] and [Mo(PPh3)(eta(5)-C5H5)(CO)2(COMe)] react with B(C6F5)3 to form the adducts [Co(L)(CO)3(C{OB(C6F5)3}Me)] (L = PMe3, 1, PPhMe2, 2, P(4-Me-C6H4)3, 3, PPh3, 4, P(4-F-C6H4)3), 5, [Mn(CO)5(C{OB(C6F5)3}Me)] 6 and [Mo(eta(5)-C5H5)(PPh3)(CO)2(C{OB(C6F5)3}Me)], 7. Addition of B(C6F5)3 to a cooled solution of [Mo(eta(5)-C5H5)(CO)3(Me)], under an atmosphere of CO gave [Mo(eta(5)-C5H5)(CO)3(C{OB(C6F5)3}Me)] 8. In the presence of adventitious water, the compound [Co{HOB(C6F5)3}2{OP(4-F-C6H4)3}2] 9, was formed from [Co(P(4-F-C6H4)3)(CO)3(C{OB(C6F5)3}Me)]. The compounds 4 and 9 have been structurally characterised. The use of B(C6F5)3 as a catalyst for the CO-induced migratory-insertion reaction in the transition metal alkyl compounds [Co(PPh3)(CO)3(Me)], [Mn(CO)5(Me)], [Mo(eta(5)-C5H5)(CO)3(Me)] and [Fe(eta(5)-C5H5)(CO)2(Me)] has been investigated.     

Synthesis, characterization and some properties of mononuclear Ni and trinuclear NiFe2 complexes related to the active site of [NiFe]-hydrogenases

The [N(2)S(2)]-type ligand 1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4) (L) is prepared in 84% yield by a new method and its structure has been confirmed by X-ray crystallography. The new synthetic method involves sequential reaction of 1,2-phenylenedithiol with EtONa followed by treatment of the resulting disodium salt of 1,2-phenylenedithiol with in situ generated 2-(chloromethyl)pyridine from its HCl salt. Further treatment of ligand L with NiCl(2)·6H(2)O or NiI(2) affords the expected new mononuclear Ni complexes Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]Cl(2) (1) and Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]I(2) (3) in 87-88% yields, whereas reaction of L with NiBr(2) under similar conditions results in formation of the expected new mononuclear complex Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]Br(2) (2) and one unexpected new mononuclear complex Ni[1-(2-C(5)H(4)NCH(2)S)-2-(2-C(5)H(4)NCH(2)SC(6)H(4)S)C(6)H(4)]Br(2) (2*) in 82% and 5% yields, respectively. More interestingly, the ligand L-containing novel trinuclear NiFe(2) complex Ni{[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)}Fe(2)(CO)(6)(μ(3)-S)(2) (4) is found to be prepared by sequential reaction of (μ-S(2))Fe(2)(CO)(6) with Et(3)BHLi, followed by treatment of the resulting (μ-LiS)(2)Fe(2)(CO)(6) with mononuclear complex 1, 2, or 3 in 12-20% yields. The new complexes 1-4 and 2* are fully characterized by elemental analysis and various spectroscopies, and the crystal structures of 1, 2* and 3 as well as some electrochemical properties of 1-4 are also reported.