Copper-Catalyzed Regioselective Aminothiolation of Aromatic and Aliphatic Alkenes with N-Fluorobenzenesulfonimide and Thiols through Three-Component Radical Coupling.

Copper-catalyzed regioselective aminothiolation of terminal and internal alkenes with N-fluorobenzenesulfonimide and thiols has been developed. The three-component reaction is promoted by the addition of dimethyl sulfide. In addition to aromatic alkenes, aliphatic alkenes are subjected to the reaction, affording various aminothiolation adducts as single regioisomers. The radical process is proposed by preliminary mechanistic studies, involving radical trap and radical clock experiments.

Stereoselective Construction of Spiro-Fused Tricyclic Frameworks by Sequential Reaction of Enynes, Imines, and Diazoalkenes with Rh(I) and Rh(II) Catalysts.

Stereoselective construction of spiro-fused tricyclic compounds from enynes having a tethered imine with diazoalkenes was achieved by Rh(I)- and Rh(II)-catalyzed sequential reactions. This method consists of three reactions, i.e., Rh(I)-catalyzed cyclization of enynes with a tethered imine, Rh(II)-catalyzed cyclopropanation with diazoalkenes, and Cope rearrangement. Notably, the sequential reactions can be operated in one pot, in which Rh(I) and Rh(II) catalysts work in relay without any serious catalyst deactivation to afford the spirocycles in a stereoselective manner.

Coordination Structure Conversion of Hydrazone-Palladium(II) Complexes in the Solid State and in Solution.

We prepared hydrazone-palladium(II) complexes of [PdCl2(HL(n))] and [PdCl(L(n))] (n = 1-3) by the reaction of [PdCl2(cod)] or [PdCl2(PhCN)2] and the hydrazone ligands of HL(n) {N'-(pyridin-2-ylmethylene)picolinohydrazide (HL(1)), N'-[1-(pyridin-2-yl)ethylidene]picolinohydrazide (HL(2)), and N'-[(6-methylpyridin-2-yl)methylene]picolinohydrazide (HL(3))}. The structures of the complexes were determined by X-ray analysis. The hydrazone ligands had κN(py1),κN(imine) and κN(amidate),κN(py2) bidentate coordination modes in [PdCl2(HL(n))] (1, n = 1; 2, n = 2) and in [PdCl2(HL(3))] (3), respectively. In contrast, tridentate coordination modes of κN(py1),κN(imine),κN(py2) and κN(py1),κN(amidate),κN(py2) were observed in [PdCl(L(n))] (4, n = 1; 5, n = 2) and in [PdCl(L(n))] (6, n = 1; 7, n = 2; 8, n = 3). Thermal conversion of complexes 1-3 to complexes 6-8 proceeded in acetonitrile. Complexes 4 and 5 were obtained from complexes 1 and 2, respectively, in a basic acetonitrile solution under dark conditions. Complex 4 reverted immediately to complex 1 in an acidic acetonitrile solution that included hydrochloric acid. However, under room light, in the basic acetonitrile solution that included trimethylamine, complex 4 converted photochemically to complex 6. The thermochromic or vapochromic structure conversion of these complexes also occurred in the solid state. On heating at 180 °C, the color of the crystals of complexes 1, 2, and 3 changed from yellow to orange in the solid state. (1)H NMR and/or UV-vis absorption spectroscopy confirmed that the orange complexes 6-8 were produced. The reddish-orange crystals of complexes 4 and 5 were exposed to hydrogen chloride vapor to yield the yellow products of complexes 1 and 2, respectively.

Palladium-catalyzed peri-selective chalcogenation of naphthylamines with diaryl disulfides and diselenides via C-H bond cleavage.

A palladium-catalyzed and picolinamide-directed C-H thiolation of naphthylamine derivatives with diaryl disulfides has been developed to provide a convenient route to 8-sulfenyl-1-naphthylamines. The reaction proceeds via a 5-membered palladacycle intermediates to afford the peri-thiolated products exclusively, in contrast to the conventional ortho-functionalization. Moreover, the related direct selenation was also achieved with diaryl diselenides, giving the corresponding selenated products with perfect site-selectivity.

Selective synthesis of multisubstituted olefins utilizing gem- and vic-diborylated vinylsilanes prepared by silylborylation of an alkynylboronate and diborylation of alkynylsilanes.

The synthesis of a series of gem- and vic-diborylated vinylsilanes was accomplished via highly selective transition-metal-catalyzed syn-dimetalation to the alkynylmetal species. This protocol served as a general synthetic method toward regio- and stereodefined multisubstituted olefins. The key steps are the diastereoselective Suzuki-Miyaura cross-coupling reactions of gem- and vic-diborylated vinylsilanes, in which the two boron groups showed discrete reactivities to afford diverse precursors of multisubstituted olefins.

Synthesis of methoxy-substituted picenes: substitution position effect on their electronic and single-crystal structures.

A series of picenes having methoxy groups was synthesized through Pd-catalyzed Suzuki-Miyaura couplings or Wittig reaction/intramolecular cyclization sequences, and their physicochemical properties and single-crystal structures were evaluated. The substitution position effects between the outer 1,12-, 2,11-, and 4,9-position and the inner 3,10-position are quite different; the former showed the same electronic structure as that of picene, but the latter results in a HOMO geometry different from those of picene and other methoxy picenes. In addition, crystal structures of four types of methoxy-substituted picenes 4a-c,e strongly depend on their substitution position and number of methoxy groups, which dramatically changes the structures from the fully anisotropic 1D π-stacked structure to a unique 3D herringbone structure due to steric hindrance of methoxy groups. The calculations of transfer integrals based on their single-crystal structures reveal that the methoxy picenes have intermolecular overlaps less effective than that of the parent nonsubstituted picene. These results are attributed not only to the packing structure but also to electronic structures such as the HOMO distribution. The preliminary OFET of the representative 4c,e showed hole mobilities significantly lower than that of picene due to their less effective intermolecular overlaps, as predicted by the calculated transfer integrals.

Photoinduced dimerization reaction coupled with oxygenation of a platinum(II)-hydrazone complex.

Photoreactivities of Ni(II)- and Pt(II)-hydrazone complexes, [NiCl(L)] (Ni1) and [PtCl(L)] (Pt1), respectively [HL = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone], were investigated in detail via UV-vis absorption, (1)H nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry; the two photoproducts obtained from the photoreaction of Pt1 were also successfully identified via X-ray analysis. The absorption bands of the Ni1 and Pt1 complexes were very similar, centered around 530 nm, and were assigned as an intraligand charge transfer transition of the hydrazone moiety. The absorption spectrum of Pt1 in a CH3CN solution changed drastically upon photoirradiation (λ = 530 nm), whereas no change was observed for Ni1. (1)H NMR and ESI-TOF mass spectra under various conditions suggested that the photoexcited Pt1* reacts with dissolved dioxygen to form a reactive intermediate, and the ensuing dark reactions afforded two different products without any decomposition. In contrast to the simple photo-oxidation of HL to form a phosphine oxide HL(P═O), the X-ray crystallographic analyses of the photoproducts clearly indicate the formation of a mononuclear Pt complex with the oxygenated hydrazone ligand (Pt1O) and a dinuclear Pt complex with the oxygenated and dimerized hydrazone ligand (Pt2). The photosensitized reaction in the presence of an (1)O2-generating photosensitizer, methylene blue (MB), also produced Pt1O and Pt2, indicating that the reaction between (1)O2 and ground-state Pt1 is the important step. In a highly viscous dimethyl sulfoxide solution, Pt1 was slowly, but quantitatively, converted to the mononuclear form, Pt1O, without the formation of the dinuclear product, Pt2, upon photoirradiation (and in the reaction photosensitized by MB), suggesting that this photoreaction of Pt1 involves at least one diffusion-controlled reaction. On the other hand, the same complexes Pt1O and Pt2 were also produced in the degassed solution, probably because of the reaction of the photoexcited Pt1* with the biradical character and H2O.

Iron-induced regio- and stereoselective addition of sulfenyl chlorides to alkynes by a radical pathway.

The radical addition of the Cl-S σ-bond in sulfenyl chlorides to various C-C triple bonds has been achieved with excellent regio- and stereoselectivity in the presence of a catalytic amount of a common iron salt. The reaction is compatible with a variety of functional groups and can be scaled up to the gram-scale with no loss in yield. As well as terminal alkynes, internal alkynes underwent stereodefined chlorothiolation to provide tetrasubstituted alkynes. Preliminary mechanistic investigations revealed a plausible radical process involving a sulfur-centered radical intermediate via iron-mediated homolysis of the Cl-S bond. The resulting chlorothiolation adducts can be readily transformed to the structurally complex alkenyl sulfides by cross-coupling reactions. The present reaction can also be applied to the complementary synthesis of the potentially useful bis-sulfoxide ligands for transition-metal-catalyzed reactions.

Coupling of titanacyclopentadienes with a Cp ligand and elimination of one substituent.

Titanacyclopentadienes, prepared from [Cp2TiBu2] and either two equivalents of an alkyne or a diyne, were treated with PMe3 (3 equiv) at 50 °C for 3 h and then with azobenzene at room temperature for 12 h to give 4,5,6-trisubstituted indene derivatives with the loss of one substituent in good yields. This reaction contrasts sharply with our previously reported reaction for the formation of 4,5,6,7-tetrasubstituted indene derivatives without the loss of substituents by the treatment of titanacyclopentadienes with azobenzene without PMe3. (13)C NMR spectroscopy of the product derived from a (13)C-enriched complex revealed that the five carbon atoms originating from a Cp ligand were arranged linearly in the trisubstituted indene derivatives, in contrast to the 4,5,6,7-tetrasubsituted indene derivatives, in which the corresponding five carbon atoms are arranged in a ring.

Kinetic resolution of planar-chiral 1,2-disubstituted ferrocenes by molybdenum-catalyzed asymmetric intraannular ring-closing metathesis.

Planar chirality: Ring-closing metathesis of 1,2-diallylmetallocenes afforded the corresponding 4,7-dihydroindenyl species in high yields. The metallocenes are planar chiral with two different allylic substituents, and kinetic resolution of the racemic 1,2-diallylmetallocene derivatives was realized by molybdenum-catalyzed asymmetric ring-closing metathesis with excellent enantioselectivity (see scheme).

Dehydro side coupling of substituted pentacene derivatives.

1,2,3,4,8,9,10,11-Octaalkylpentacenes were synthesized in high yields from tetrahydropentacenes by the pentacene-DDQ adduct method in the presence of amine. Dehydro side-coupling reactions of pentacene derivatives proceeded to give the corresponding 6,6'-dipentacenyl derivatives in high yields in the presence of a catalytic amount of CSA and 0.5 equiv of DDQ. The structures of dehydro side-coupling products of substituted pentacenes were determined by NMR and X-ray analysis. The combination of acid and DDQ was necessary for the dehydro side coupling of substituted pentacenes.

Preparation of 6,13-bis(trimethylsilyl)pentacene and formation of second-ring Diels-Alder adduct of pentacene.

6,13-Bis(trimethylsilyl)pentacene was synthesized by a coupling reaction of bicyclic dilithiobutadiene with diiodonaphthalene followed by aromatization. Diels-Alder reaction of 6,13-bis(trimethylsilyl)pentacene with dienophiles afforded the corresponding second-ring adducts. Elimination of two silyl groups gave the second-ring Diels-Alder adducts of parent pentacene.

Dimensionality control of vapochromic hydrogen-bonded proton-transfer assemblies composed of a bis(hydrazone)iron(II) complex.

We describe the novel synthesis of a bis(hydrazone)iron(II) complex in protonated [Fe(Hpbph)(2)]Cl(2) (1) and deprotonated [Fe(pbph)(2)] (2) forms and several hydrogen-bonded proton-transfer (HBPT) assemblies having different dimensionalities of hydrogen-bonded network structures, [Fe(Hpbph)(2)](CA)·2CH(3)OH (3), [Fe(Hpbph)(2)](HCA)(2)·2THF (4), and [Fe(Hpbph)(2)](CA)(H(2)CA)(2)·2CH(3)CN (5) (Hpbph = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone), consisting of a deprotonated Fe(II)-hydrazone complex (2) as a proton acceptor (A) and chloranilic acid (H(2)CA) as a proton donor (D). The deprotonated complex 2 exhibited two-step reversible protonation reactions to form the double-protonated form 1, and the acid-dissociation constants were determined to be 7.6 and 10.3 in methanol solution. Utilizing this proton-accepting ability of 2, we succeeded in synthesizing HBPT assemblies 3, 4, and 5 from the reactions in CH(3)OH, THF, and CH(3)CN, respectively, with the same D/A ratio of H(2)CA/[Fe(pbph)(2)] = 10:1. These assemblies were found to have one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) hydrogen-bonded networks with D/A ratios of 1:1, 2:1, and 3:1 for 3, 4, and 5, respectively. In 3, a 1-D hydrogen-bonded chain composed of the alternate arrangement of [Fe(Hpbph)(2)](2+) and CA(2-), {···[Fe(Hpbph)(2)](2+)···CA(2-)···}(∞), was surrounded by solvated methanol molecules to form isolated 1-D hydrogen-bonded chains. In the HBPT assembly 4, a 2-D hydrogen-bonded sheet was formed from two types of hydrogen-bonded chains, {···[Fe(Hpbph)(2)](2+)···HCA(-)···HCA(-)···}(∞) and {···HCA(-)···HCA(-)···}(∞), and solvated THF molecules did not form any hydrogen bonds. In 5, two orthogonal hydrogen-bonded chains constructed from the neutral chloranilic acid molecules, {···CA(2-)···2(H(2)CA)···}(∞), were formed in addition to the 1-D hydrogen-bonded chain similar to that in 3, resulting in the formation of a rigid 3-D hydrogen-bonded network structure. By controlling the dimensionality of the hydrogen bond network, we found that the 2-D HBPT assembly 4 is sufficiently flexible to exhibit interesting vapochromic behavior in response to various organic vapors.

Estimating Effective Steric and Electronic Impacts of a Ferrocenyl Group in Organophosphines.

A series of monodentate ferrocenylphosphines, Fc3P (1a), Fc2PhP (1b), and Fc2ArP (1c; Fc = ferrocenyl, Ar = 3,4-methylenedioxyphenyl), were prepared, and their electronic and steric properties were quantitatively determined. By the IR measurements of their respective Ni(CO)3(phosphine) complexes, the electronic properties of the ferrocenyl group in organophosphines were estimated to be similar to those of primary alkyl groups. The ferrocenyl group is a better electron donor than a methyl group and a poorer donor than an ethyl group. The gold(I) chloride complexes of 1a-c were prepared and their X-ray crystal structures were determined. The %V bur parameters for 1a-c were calculated using the X-ray structural data, and their ″Tolman cone angles″ were estimated. The steric influence of the ferrocenyl group in organophosphines was clarified to be larger than those of cyclohexyl, tert-butyl, and o-tolyl groups and is comparable to that of a mesityl group.

Enantioselective synthesis of planar-chiral phosphaferrocenes by molybdenum-catalyzed asymmetric interannular ring-closing metathesis.

Enantioselective synthesis of planar-chiral phosphaferrocenes was realized for the first time by molybdenum-catalyzed asymmetric ring-closing metathesis (ARCM) in up to 99% ee, which is the first application of ARCM to induction of chirality in molecules devoid of stereogenic centers.

Synthesis of metal-hydrazone complexes and vapochromic behavior of their hydrogen-bonded proton-transfer assemblies.

We synthesized and investigated a new series of metal-hydrazone complexes, including deprotonated [MX(mtbhp)] and protonated forms [MX(Hmtbhp)](ClO(4)) (M = Pd(2+), Pt(2+); X = Cl(-), Br(-); Hmtbhp = 2-(2-(2-(methylthio)benzylidene)hydrazinyl)pyridine) and hydrogen-bonded proton-transfer (HBPT) assemblies containing [PdBr(mtbhp)] and bromanilic acid (H(2)BA). The mtbhp hydrazone ligand acts as a tridentate SNN ligand and provides a high proton affinity. UV-vis spectroscopy revealed that these metal-hydrazone complexes follow a reversible protonation-deprotonation reaction ([MX(mtbhp)] + H(+) ⇋ [MX(Hmtbhp)](+)), resulting in a remarkable color change from red to yellow. Reactions between proton acceptor [PdBr(mtbhp)] (A) and proton donor H(2)BA (D) afforded four types of HBPT assemblies with different D/A ratios: for D/A = 1:1, {[PdBr(Hmtbhp)](HBA)·Acetone} and {[PdBr(Hmtbhp)](HBA)·2(1,4-dioxane)}; for D/A = 1:2, [PdBr(Hmtbhp)](2)(BA); and for D/A = 3:2, {[PdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)·2Acetonitrile}. The proton donor gave at least one proton to the acceptor to form the hydrogen bonded A···D pair of [PdBr(Hmtbhp)](+)···HBA(-). The strength of the hydrogen bond in the pair depends on the kind of molecule bound to the free monoanionic bromanilate OH group. Low-temperature IR spectra (T < 150 K) showed that the hydrogen bond distance between [PdBr(Hmtbhp)](+) and bromanilate was short enough (ca. 2.58 Å) to induce proton migration in the [PdBr(Hmtbhp)](2)(BA) assembly in the solid state. The hydrogen bonds formed not only between [PdBr(Hmtbhp)](+) and HBA(-) but also between HBA(-) and neutral H(2)BA molecules in the {[PdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)·2Acetonitrile} assembly. The H(2)BA-based flexible hydrogen bond network and strong acidic host structure result in an interesting vapor adsorption ability and vapochromic behavior in this assembly because the vapor-induced rearrangement of the hydrogen bond network, accompanied by changes in π-π stacking interactions, provides a recognition ability of proton donating and accepting properties of the vapor molecule.

Coupling of the R-Cp or indenyl ligand with the diene moiety of bis(substituted cyclopentadienyl)- or bis(indenyl)zirconacyclopentadienes.

When bis(substituted cyclopentadienyl)- or bis(indenyl)zirconacyclopentadienes were treated with TiCl(4), a coupling reaction between the substituted cyclopentadienyl or indenyl ligand and the diene moiety proceeded to give indene or fluorene derivatives in moderate to high yields. With the sterically hindered t-Bu-substituted Cp ligand, the coupling products were obtained in high yields.

Metal-dependent regioselective homocoupling of stannyl- and alkyl-substituted alkynes on group 4 elements. Formation of unsymmetrical titanacyclopentadienes and symmetrical zircona-cyclopentadienes.

Homocoupling of stannyl- and alkyl-substituted alkynes with Cp2TiBu2 gave unsymmetrical titanacyclopentadienes (αß isomers) with >95% regioselectivities, whereas the coupling with Cp2ZrBu2 provided symmetrical zirconacyclopentadienes (αα isomers) with >93% selectivities. This is the first example of metal-dependent regioselective homocoupling of unsymmetrical alkynes on group 4 elements.

Once cleaved C-C bond was reformed: reversible C-C bond cleavage of dihydroindenyltitanium complexes.

The once cleaved carbon-carbon bond of the Cp moiety in 2 was recombined in indene products. Aslo, we propose a novel mechanism for the cleavage of the carbon-carbon bond of the Cp moiety.

Selective linear triene formation from different alkynes using Zr/Cu system.

Selective synthesis of linear trienes from three different alkynes was achieved in one-pot procedure using the Zr/Cu system. Zirconacyclopentadiene prepared from two different alkynes such as an alkyl-substituted alkyne and an aryl-substituted alkyne reacted with NCS gave chlorodienylzirconocene. It reacted with the third alkyne with electron-withdrawing groups in the presence of CuCl to afford the corresponding linear triene.