Linear Hydrocarbon Chain Growth from a Molecular Diruthenium Carbide Platform.

The formation of linear hydrocarbon chains by sequential coupling of C1 units on the metal surface is the central part of the Fischer-Tropsch (F-T) synthesis. Organometallic complexes have provided numerous models of relevant individual C-C coupling events but have failed to reproduce the complete chain lengthening sequence that transforms a linear Cn hydrocarbon chain into its Cn+1 homologue in an iterative fashion. In this work, we demonstrate stepwise growth of linear Cn hydrocarbon chains and their conversion to their Cn+1 homologues via consecutive addition of CH2 units on a molecular diruthenium carbide platform. The chain growth sequence is initiated by the formation of a µ-η1:η1-C═CH2 ligand from a C + CH2 coupling between the µ-carbido complex [(Cp*Ru)2(η-NPh)(µ-C)] (1; Cp* = η5-C5Me5) and Ph2SCH2. Then, the chain propagates via a general C═CHR + CH2 coupling and subsequent hydrogen-assisted isomerization of the resulting allene ligand µ-η1:η3-H2C═C═CHR to a higher vinylidene homologue µ-η1:η1-C═CH(CH2)R. By repeating this reaction sequence, up to C6 chains have been synthesized in a stepwise fashion. The key step of this chain homologation sequence is the selective hydrogenation of the µ-η1:η3-allene unit to the corresponding µ-alkylidene ligand. Isotope labeling and computational studies indicate that this transformation proceeds via the hydrogenation of the allene ligand to a terminal alkene form and its isomerization to the µ-alkylidene ligand facilitated by the coordinatively unsaturated diruthenium platform.

Ruthenium-Sulfonamide-Catalyzed Direct Dehydrative Condensation of Benzylic C-H Bonds with Aromatic Aldehydes.

The first catalytic dehydrative condensation of the benzylic C-H bonds of toluene and p-xylene with aromatic aldehydes is reported herein. This protocol provides highly atom-economical access to stilbene and p-distyrylbenzene derivatives, whereby water is the sole byproduct. The reaction is based on the deprotonation-functionalization of benzylic C-H bonds through η6-complexation of the arenes, which is realized for the first time using a catalytic amount of a transition metal activator. The key to the success of this method is the use of a sulfonamide anion as a catalyst component, which appears to facilitate not only the deprotonation of the benzylic C-H bonds but also the formation of a C-C bonds via an electrophilic tosylimine intermediate.

A diruthenium µ-carbido complex that shows singlet-carbene-like reactivity.

Low-temperature deprotonation of the cationic µ-methylidyne complex [(Cp*Ru)2(µ-NPh)(µ-CH)][BF4] (Cp* = η(5)-C5Me5) with KN(SiMe3)2 affords a thermally unstable µ-carbido complex [(Cp*Ru)2(µ-NPh)(µ-C)] (2), as evidenced by trapping experiments with elemental S or Se and (13)C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S(+)CH2(-), EtOH, and an intramolecular C-H bond indicates that the µ-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger σ-donor and weaker π-donor to the carbene center than amino substituents in N-heterocyclic carbenes.

Nucleophile-catalyzed, facile, and highly selective C-H activation of fluoroform with Pd(II).

Exceedingly facile (23 °C) and chemoselective H-CF3 activation with [(dppp)Pd(Ph)(OH)] in the presence of a Lewis base promoter such as n-Bu3P leads to Pd-CF3 bond formation in nearly quantitative yield. A combined experimental and computational study points to a new mechanism that involves H-bonding Pd-O(H)···H-CF3 and nucleophilic attack of the promoter on the metal, followed by a push-pull-type collapse of the resultant five-coordinate Pd(II) intermediate via a polar transition state.

Synthesis and N-H reductive elimination study of dinuclear ruthenium imido dihydride complexes.

Diruthenium imido dihydride complexes [(Cp*Ru)(2)(µ-NAr)(µ-H)(2)] (Ar = Ph (2a), p-MeOC(6)H(4) (2b), p-ClC(6)H(4) (2c), 2,6-Me(2)C(6)H(3) (2d); Cp* = η(5)-C(5)Me(5)) have been synthesized by hydrogenation of the corresponding bis(amido) complexes [Cp*Ru(µ-NHAr)](2) (1a-d). Reductive elimination of the N-H bond from 2a-c in the presence of arene yields the amido hydride complexes [(Cp*Ru)(2)(µ-NHAr)(µ-H)(µ-η(2):η(2)-arene)] containing a π-bound arene. The rate and kinetic isotope effect for this reaction are consistent with a mechanism involving initial rate-determining reductive elimination of an N-H bond to produce the coordinatively unsaturated amido hydride species {(Cp*Ru)(2)(µ-NHAr)(µ-H)} (A) followed by rapid trapping of this species by an arene. The existence of A is also supported by the reversible interconversion of [(Cp*Ru)(2)(µ-NHPh)(µ-H)(µ-η(2):η(2)-C(7)H(8))] with the tetranuclear complex [(Cp*Ru)(4)(µ(4)-NHPh)(µ-NHPh)(µ-H)(2)] (4), a dimerization product of A through a µ(4)-NHPh bridge. DFT calculations provide structures of A and transition states for the N-H reductive elimination. Two distinct reaction pathways are found for the N-H reductive elimination, one of which involves direct migration of a µ-hydride to the µ-NAr ligand, and the other involves formation of a transient terminal hydride species.

Metal-metal multiple bond formation induced by σ-acceptor Lewis acid ligands.

The reaction of [Cp*Ru(µ-NHPh)]2 (Cp* = η5-C5Me5) with Lewis acids of the type MX2 (M = Zn, Sn, Pb; X = Cl, OTf) affords Ru2 → M donor-acceptor adducts characterized as π complexes of a Ru[double bond, length as m-dash]Ru double bond with M(ii) Lewis acids. The results illustrate for the first time the ability of σ-acceptor Lewis acid ligands to induce the formation of a metal-metal multiple bond via stabilizing dative interactions.

A bimetallic Ru2Pt complex containing a trigonal-planar mu3-carbido ligand: formation, structure, and reactivity relevant to the Fischer-Tropsch process.

The bimetallic Ru(2)Pt complex [(Cp*Ru)(2)(mu(2)-NHPh)(mu(2)-H)(mu(3)-C)PtMe(PMe(3))(2)][OTf] (3; Cp* = eta(5)-C(5)Me(5)) containing a planar three-coordinate carbido ligand has been prepared in 93% yield by thermal isomerization of the bridging methylene precursor [(Cp*Ru)(2)Me(mu(3)-NPh)(mu(2)-CH(2))Pt(PMe(3))(2)][OTf] (2) via cleavage of the methylene C-H bonds. Exposure of the carbido complex 3 to carbon monoxide (1 atm) induced coupling of the carbido ligand with the nearby methyl and hydride ligands to produce the diruthenium ethylidene complex [(Cp*Ru)(2)(mu(2)-CHMe)(mu(2)-NHPh)(CO)(2)][OTf] (4) and the known triplatinum complex [Pt(CO)(PMe(3))](3). The crystal structures of 2, 3, and 4 (BPh(4) salt) are reported.

Induction of one-handed helical oligo(p-benzamide)s by domino effect based on planar-axial-helical chirality relay.

One-handed helical oligo(p-benzamide)s were induced via the domino effect based on the planar-axial-helical chirality relay triggered by a planar chiral transition-metal complex at the terminal position as the single chiral source.

Bis(bipyridine) ruthenium(ii) bis(phosphido) metalloligand: synthesis of heterometallic complexes and application to catalytic (E)-selective alkyne semi-hydrogenation.

The first phosphido derivative of the bis(bipyridine) ruthenium(ii) fragment, cis-[(bpy)2Ru(PPh2)2] ([RuP2]), has been developed and applied as a P-donor metalloligand to form new Ru-Rh, Ru-Ir and Ru2Cu2 heterometallic complexes. The Ru-Ir hydride complex [([RuP2])IrH(NCMe)3][BF4]2 exhibits significant catalytic activity for (E)-selective semi-hydrogenation of alkynes.

Divalent dirhodium imido complexes: formation, structure, and alkyne cycloaddition reactivity.

Dirhodium amido complexes [(Cp*Rh)2(mu2-NHPh)(mu2-X)] (X = NHPh (2), Cl (3), OMe (4); Cp* = eta5-C5Me5) were prepared by chloride displacement of [Cp*Rh(mu2-Cl)]2 (1) and have been used as precursors to a dirhodium imido species [Cp*Rh(mu2-NPh)RhCp*]. The imido species can be trapped by PMe3 to give the adduct [Cp*Rh(mu2-NPh)Rh(PMe3)Cp*] (5) and undergoes a formal [2 + 2] cycloaddition reaction with unactivated alkynes to give the azametallacycles [Cp*Rh(mu2-eta2:eta3-R1CCR2NPh)RhCp*] (R1 = R2 = Ph (6a), R1 = H, R2 = t-Bu (6b), R1 = H, R2 = p-tol (6c)). Isolation of a relevant unsaturated imido complex [Cp*Rh(mu2-NAr)RhCp*] (7) was achieved by the use of a sterically hindered LiNHAr (Ar = 2,6-diisopropylphenyl) reagent in a metathesis reaction with 1. X-ray structures of 2, 6a, 7 and the terminal isocyanide adduct [Cp*Rh(mu2-NAr)Rh(t-BuNC)Cp*] (8) are reported.

Nickel-catalyzed [3+1+1] cycloaddition reactions of alkenyl Fischer carbene complexes with methylenecyclopropanes.

Methylenecyclopentanones were synthesized by the nickel-catalyzed [3+1+1] cycloaddition reactions of alkenyl Fischer carbene complexes with methylenecyclopropanes. The methylenecyclopropane was transformed into the C(2)-symmetric bis-cyclopentapyridazine derivative by reacting with p-toluenesulfonyl hydrazine.

Synthesis of Ru-Pt and Ru-Pd mixed-metal imido clusters from a diruthenium imido-methylene scaffold [(Cp*Ru)2(mu2-NPh)(mu2-CH2)].

The diruthenium mu2-imido mu2-methylene complex [(Cp*Ru)2(mu2-NPh)(mu2-CH2)] serves as a bifunctional scaffold for cluster synthesis, producing a mu3-imido Ru2Pt cluster [(Cp*Ru)2(mu3-NPh)(mu2-CH2)Pt(PMe3)2] on treatment with [Pt(eta2-C2H4)(PMe3)2] and a mu3-methylidyne Ru4Pd2 cluster [(Cp*Ru)2(mu2-NPh)(mu3-CH)PdCl]2 with [PdMeCl(cod)].

Ti-Mo heterobimetallic thiacalix[4]arene complex containing an unusual alpha-agostic micro2-eta5:eta2-cyclopentadienyl ligand.

A stepwise reaction of p-tert-butylthiacalix[4]arene (TC4A-(OH)(4)) with [CpTiCl3]-NEt(3) and cis-[Mo(N(2))(2)(PMe(2)Ph)(4)] afforded a new Ti-Mo heterobimetallic complex [TC4A-(O)(4)Ti(micro2-C(5)H(5))MoH(PMe(2)Ph)(2)] which shows an unusual alpha-agostic micro2-eta5:eta2-coordination of a cyclopentadienyl ligand.

Synthesis of Heterobimetallic Fe-M (M = Ni, Pd, Pt) Complexes Containing the 1,1'-Ferrocenedithiolato Ligand and Their Conversion to Trinuclear Complexes.

The reaction of [NiCl(2)(PMe(2)Ph)(2)] with fc(SH)(2) (fcS(2) = 1,1'-ferrocenedithiolato) afforded the Ni-Fe heterobimetallic complex containing an Fe-->Ni dative bond [Ni(S(2)fc)(PMe(2)Ph)] (1) with concurrent liberation of one of the PMe(2)Ph ligands. In contrast, similar treatment of [MCl(2)(dppe)] (M = Ni, Pd, Pt; dppe = Ph(2)PCH(2)CH(2)PPh(2)) gave a series of group 10 metal-ferrocenedithiolato complexes [M(S(2)fc)(dppe)] (2) which do not contain such a dative bond. Furthermore, oxidation of complexes 2 with 1 equiv of [(eta(5)-C(5)H(5))(2)Fe][PF(6)] resulted in the formation of 1,1'-ferrocenedithiolato-bridged complexes [{M(dppe)}(2)(&mgr;-S(2)fc)][PF(6)](2) (3) along with poly(1,1'-ferrocenylene disulfide). Complexes 2 were also converted into the Fe-Ru-M heterotrimetallic complexes [(p-cymene)RuCl(&mgr;-S(2)fc)M(dppe)][PF(6)] (4; p-cymene = 4-isopropyltoluene) by the reaction of 2 with [(p-cymene)RuCl(2)](2) and NH(4)PF(6) in acetonitrile. The detailed structures of 1, [Ni(S(2)fc)(dppe)] (2a), [Pd(S(2)fc)(dppe)] (2b), [{Ni(dppe)}(2)(&mgr;-S(2)fc)][PF(6)](2) (3a), and [(p-cymene)RuCl(&mgr;-S(2)fc)Ni(dppe)][PF(6)] (4a) have been determined by X-ray crystallography.

Synthesis of helicenes utilizing palladium-catalyzed double C-H arylation reaction.

[5]- and [6]helicenes were synthesized in moderate to good yields from Z,Z-bis(bromostilbene)s by palladium-catalyzed double C-H arylation reaction. This method can be applied to the syntheses of helicenes possessing electron-deficient substituents.

Stereoselective synthesis of both enantiomers of N-aryl indoles with axially chiral N-C bonds.

N-Aryl indoles with axially chiral N-C bonds were synthesized by stereoselective nucleophilic aromatic substitution reactions of planar chiral tricarbonyl(2,6-disubstituted-1-fluorobenzene)chromium complexes. The stereochemistry of the products is highly dependent on the position of the substituent in the indole. When indoles devoid of a substituent at the 2-position were used, N-aryl indole chromium complexes having anti orientation with respect to the tricarbonylchromium fragment were obtained diastereoselectively. In contrast, 2-substituted indoles gave the N-aryl indoles with syn orientation between the tricarbonylchromium fragment and the benzene ring of the indole. These results demonstrate that we have succeeded in synthesizing both enantiomers of N-aryl indoles utilizing an identical planar chiral arene chromium complex.

Diiron amido-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)]: synthesis and a net hydrogen atom abstraction reaction to form a bis(imido) complex.

A reaction between [CpFeCl]x and LiNHPh (1 equiv to Fe) produces a new paramagnetic Fe(II)-Fe(III) mu2-amido-mu2-imido complex [(CpFe)2(mu2-NHPh)(mu2-NPh)] (1), which, upon interaction with 2,2'-azobis(2,4-dimethylvaleronitrile), undergoes a net N-H hydrogen atom abstraction reaction to give a diamagnetic Fe(III)-Fe(III) mu2-imido dimer [CpFe(mu2-NPh)]2 (2). The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction.

Reactivity of amido ligands on a dinuclear Ru(II) center: formation of imido complexes and C-N coupling reaction with alkyne.

Treatment of a dinuclear Ru(II) amido complex [Cp*Ru(mu2-NHPh)]2 (Cp* = eta5-C5Me5) with small organic substrates including CO, tert-butyl isocyanide, a sulfur ylide Ph2S=CH2, and diphenylacetylene resulted in an unexpected disproportionation reaction of the bridging amido ligands to produce a free amine and a series of imido-bridged diruthenium complexes [(Cp*Ru)2(mu2-L)(mu2-NPh)] (L = CO, t-BuNC, CH2). In the case of diphenylacetylene, the bridging imido ligand underwent subsequent coupling reaction with the coordinated alkyne to form an iminoalkenyl complex [(Cp*Ru)2(mu2-PhNCPhCPh)].