Guochen Jia

Ruthenium-catalyzed azide-alkyne cycloaddition: scope and mechanism.

The catalytic activity of a series of ruthenium(II) complexes in azide-alkyne cycloadditions has been evaluated. The [Cp*RuCl] complexes, such as Cp*RuCl(PPh 3) 2, Cp*RuCl(COD), and Cp*RuCl(NBD), were among the most effective catalysts. In the presence of catalytic Cp*RuCl(PPh 3) 2 or Cp*RuCl(COD), primary and secondary azides react with a broad range of terminal alkynes containing a range of functionalities selectively producing 1,5-disubstituted 1,2,3-triazoles; tertiary azides were significantly less reactive. Both complexes also promote the cycloaddition reactions of organic azides with internal alkynes, providing access to fully-substituted 1,2,3-triazoles. The ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) appears to proceed via oxidative coupling of the azide and alkyne reactants to give a six-membered ruthenacycle intermediate, in which the first new carbon-nitrogen bond is formed between the more electronegative carbon of the alkyne and the terminal, electrophilic nitrogen of the azide. This step is followed by reductive elimination, which forms the triazole product. DFT calculations support this mechanistic proposal and indicate that the reductive elimination step is rate-determining.

Iridium‐Catalyzed Intermolecular Azide–Alkyne Cycloaddition of Internal Thioalkynes under Mild Conditions

An iridium-catalyzed azide-alkyne cycloaddition reaction (IrAAC) of electron-rich internal alkynes is described. It is the first efficient intermolecular AAC of internal thioalkynes. The reaction exhibits remarkable features, such as high efficiency and regioselectivity, mild reaction conditions, easy operation, and excellent compatibility with air and a broad spectrum of organic and aqueous solvents. It complements the well-known CuAAC and RuAAC click reactions.

Electrophilic substitution reactions of metallabenzynes.

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.

Structural, acidity and chemical properties of some dihydrogen/hydride complexes of Group 8 metals with cyclopentadienyls and related ligands

Abstract The structures of Group 8 metal complexes [LMH2(L′)(L′′)]+ (L=cyclopentadienyls, hydrotris(pyrazolyl)borate (Tp)) and [LMH2(L′)(L′′)]2+ (L=1,4,7-triazacyclononane derivatives (RCn), 1,3-(Ph2PCH2)2C5H3N (PMP)) are compared. While complexes [(C5R5)MH2(L′)(L′′)]+ (M=Fe, Ru, Os) at room temperature can exist in either the dihydride form, or the dihydrogen form, or a mixture of both, the analogous Tp, RCn, and PMP complexes are all in the dihydrogen form. Equilibrium studies have shown that the relative acidities of these hydride complexes are strongly affected by the auxiliary ligands, metals, and possibly also the H–H interaction. [TpM(H2)(PR3)2]+ (M=Ru, Os) were found to be slightly more acidic than the analogous [CpMH2(PR3)2]+ complexes, and the dicationic RCn dihydrogen complexes [RCnM(H2)(L′)(L′′)]2+ are much more acidic than the corresponding Cp and Tp analogs. Significant acidity enhancement upon substitution of PPh3 for CO is observed for related dihydrogen complexes such as [RuCl(H2)(L)(PMP)]+, [TpRu(H2)(L)(PPh3)]+, and [HCnRu(H2)(L)(PPh3)]2+ (L=CO, PPh3). At the end of the article, several reactions which may involve heterolytic cleavage of the dihydrogen ligand and proton transfer from coordinated dihydrogen to olefin ligands are described.

Synthesis and Characterization of a Rhenabenzyne Complex

There has been much interest in the chemistry of transitionmetal-containing metallaaromatic compounds. In particular metallabenzenes, which are organometallic compounds derived by the formal replacement of a C H group in benzene with an isolobal transition metal fragment, have attracted considerable attention. Previous studies have led to the isolation and characterization of an impressive number of stable metallabenzenes, especially those of osmium, iridium, platinum, ruthenium, 11] and rhenium. Metallabenzynes, which are organometallic compounds derived from formal replacement of a carbon atom or a C H group in benzyne with an isolobal transition metal fragment, are closely related to metallabenzenes. At first sight, one might expect that metallabenzynes may be too unstable to be isolated, because organic compounds with a C C bond in the six-membered ring, for example, benzyne and cyclohexyne, are thermally highly unstable because of ring strain. Nevertheless, in recent years, several stable osmabenzynes have been isolated and their interesting chemical properties have been demonstrated. For example, osmabenzynes, such as metallabenzenes and aromatic compounds, can undergo electrophilic substitution reactions. Compared with the chemistry of metallabenzenes, that of metallabenzynes is much less developed. For instance, while stable metallabenzenes with several metals are known, to date, isolated metallabenzynes are limited to those containing an osmium center. The synthesis and characterization of metallabenzynes with metals other than osmium remain important goals in the development of the chemistry of these compounds. Herein, we report the preparation and structural characterization of the first stable rhenabenzyne complex. The rhenabenzyne complex was synthesized by the synthetic route outlined in Scheme 1. Reaction of [ReH5(PMe2Ph)3] (1) with alkynol 2 in the presence of HCl produced the dichlorocarbyne complex 3. Treatment of 3 with tert-butylmagnesium chloride produced the hydridochlorocarbyne complex 4, likely through the intermediate [Re( C-CH=C(tBu)C CSiMe3)Cl(tBu)(PMe2Ph)3], which underwent b-H elimination. Experimentally, the side product CH2=CMe2 has indeed been detected by in situ H NMR spectroscopy. Complex 4 was isolated as a blue solid in 63% yield, and could be stored under nitrogen at room temperature for a week without appreciable decomposition. The Me3Si group in 4 could be easily removed by treatment of 4 with nBu4NF to give carbyne complex 5. The new carbyne complexes 3–5 can be readily identified by NMR spectroscopy. For example, the H NMR spectrum of 5 shows the Re–H signal at 1.85 ppm as a doublet of triplets with P–H coupling constants of 50.0 and 28.0 Hz, the Re CCH signal at 4.42 ppm, and the C CH signal at 3.22 ppm; the C{H} NMR spectrum of 5 shows the Re C signal at 254.1 ppm and the C CH signals at 88.4 and 83.8 ppm. In the solid state, complex 5 can be stored under nitrogen for at least three days without any decomposition, however, it is thermally unstable in solution. When a solution of 5 in benzene was stored at room temperature for three days, complex 5 completely rearranged to form complex 6. The rearrangement reaction was complete within 4 h when a solution of 5 in benzene/hexane was heated at 50 8C. Complex Scheme 1. Preparation of rhenabicyclo[3.1.0]hexatriene 6 and rhenabenzyne 7.

Palladium-Catalyzed Three-Component Cascade Cyclization Reaction of Bisallenes with Propargylic Carbonates and Organoboronic Acids : Efficient Construction of cis-Fused Bicyclo[4.3.0]nonenes

A bicycle built for two: The title reaction affords cis-fused bicyclo[4.3.0]nonenes from readily available 1,5-bisallenes with structurally diverse propargylic carbonates and arylboronic acids (see scheme; X = NTs, C(E(1))(2) with E(1) = CO(2)Bn, SO(2)Ph, dba = trans,trans-dibenzylidenacetone). The reaction may involve a sequential oxidative addition, two different types of three carbopalladations, and a Suzuki-type coupling.

Selective and Efficient Cycloisomerization of Alkynols Catalyzed by a New Ruthenium Complex with a Tetradentate Nitrogen-Phosphorus Mixed Ligand

The new ruthenium complex [Ru(N(3)P)(OAc)][BPh(4)] (4), in which N(3)P is the N,P mixed tetradentate ligand N,N-bis[(pyridin-2-yl)methyl]-[2-(diphenylphosphino)phenyl]methanamine was synthesized. The complex was found to be catalytically active for the endo cycloisomerization of alkynols. The catalytic reactions can be used to synthesize five-, six-, and seven-membered endo-cyclic enol ethers in good to excellent yields. A catalytic cycle involving a vinylidene intermediate was proposed for the catalytic reactions. Treatment of complex 4 with PhC[triple bond]CH and H(2)O gave the alkyl complex [Ru(CH(2)Ph)(CO)(N(3)P)][BPh(4)] (30), which supports the assumption that the catalytic reactions involve addition of a hydroxyl group to the C=C bond of vinylidene ligands.

DIMERIC AND POLYMERIC RUTHENIUM COMPLEXES WITH RU-VINYL LINKAGES

Abstract The carbonyl hydrido complex RuHCl(CO)(PPh 3 ) 3 reacted with diynes HC≡C-R-C≡CH (R = p -C 6 H 4 , p -C 6 H 4 -C 6 H 4 ) to give the five-coordinate vinyl ruthenium dimeric compounds [RuCl(CO)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) in high yields. Additions of 2,6-di-methylphenyl isocyanide (CNC 8 H 9 ) or 4-phenylpyridine (Ph-Py) to the vinyl complexes produced the six-coordinate adducts [RuCl(CO)(C 8 H 9 NC)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) and [RuCl(CO)(Ph-Py)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) respectively. Reactions of [RuCl(CO)(PPh 3 ) 2 ] 2 (μ-CH=CH-R-CH=CH) with L (L = 2,3,5,6-tetramethylphenyl diisocyanide or 4,4′-bipyridine) produced [RuCl(CO)(PPh 3 ) 2 (μ-CH=CH-R-CH=CH)RuCl(CO)(PPh 3 ) 2 (μ-L)] x .

A triple-decker complex with a central metallabenzene

It was established in the 1980s that benzene can act as a bridging ligand to form triple-decker complexes.[1, 2] Recent studies on the chemistry of metallabenzenes revealed that transition metal containing metallabenzenes can display chemical properties similar to those of benzene.[3] For example, they can undergo electrophilic substitution reactions[4] and can form 6-metallabenzene complexes.[5] These results imply that metallabenzenes may also function as bridging ligands in tripleor poly-decker complexes. However, such complexes have not yet been reported, although the possibility of obtaining triple-decker complexes with a central metallabenzene was suggested in 1994.[5e] Here we describe the synthesis and characterization of the first tripledecker complex with a central metallabenzene. Treatment of [Cp*Ru(H2O)(nbd)]BF4 (1; Cp* -C5Me5, nbd norbornadiene)[6] with HCO2Na in dry THF produced the bimetallic complex 2 along with nortricyclene and a small amount of the known complex [Cp*RuH(nbd)] (Scheme 1).[7] Analytically pure samples of 2 were obtained by column chromatography. The structure of 2 was deduced on the basis of its mass spectrum and 1H as well as 13C{1H} NMR spectroscopic data. The ion peak at m/z 566 corresponding to the composition {Cp* 2 Ru2(C7H8)} suggests that 2 is a bimetallic complex. The 1H and 13C{1H} NMR data indicate that 2 is a fluxional hydride complex. The room-temperature 1H NMR spectrum in C6D6 displayed a hydride signal at 16.57 and a broad Cp* signal at 1.88. However, the 1H NMR spectrum at 250 K in CD2Cl2 showed a sharp hydride signal at 16.85 and two Cp* signals at 1.77 and 1.85, that is, the two Ru atoms in 2 are inequivalent at this temperature. The presence of the bridging C7H7 ligand is supported by its 13C and 1H NMR spectroscopic data. In particular, the 13C{1H} NMR spectrum at 250 K in CD2Cl2 showed the signals of the and -CH groups of the , vinylic group at 156.31 and 60.84, respectively; that of the bridgehead CH group at 47.02; and those of the olefinic CH groups of the cyclopentadiene at 26.24, 49.86, 58.86, and 66.37. In the 1H NMR spectrum, the signals of the and -CH groups of the , -vinylic group were observed at 5.94 and 3.91, that of the bridgehead proton at 3.47, and Scheme 1. Preparation of the triple-decker complex 4.

Theoretical Studies on the Regioselectivity of Iridium-Catalyzed 1,3-Dipolar Azide–Alkyne Cycloaddition Reactions

Iridium-catalyzed cycloaddition of thioalkynes and bromoalkynes with azides have been investigated with the aid of density functional theory (DFT) calculations at the M06 level of theory. Our investigation focused on the different regioselectivity observed for the reactions of the two classes of alkynes. The DFT results have shown that the mechanisms of cycloaddition reactions using thioalkynes and bromoalkynes as substrates are similar yet different. The reactions of thioalkynes occur via a metallabicyclic Ir-carbene intermediate formed through alkyne-azide oxidative coupling via attack of the azide terminal nitrogen toward the β alkyne carbon, whose carbene ligand is stabilized by an alkylthio/arylthio substituent. Reductive elimination from the intermediate leads to the formation of the experimentally observed 5-sulfenyltriazole. In the reactions of bromoalkynes RC≡CBr, the reaction mechanism involves the initial formation of a six-membered-ring metallacycle intermediate in the oxidative coupling step. The six-membered-ring intermediate then undergoes isomerization via migrating the terminal azide nitrogen from the β carbon to the α carbon to form a much less stable metallabicyclic Ir-carbene species from which reductive elimination gives 4-bromotriazole.