Trigonal-Bipyramidal Pt(0) and Pd(0) Anions.

Anionic Pt(0) and Pd(0) complexes with unprecedented trigonal-bipyramidal geometry have been prepared and thoroughly characterized by experimental and computational means. Coordination of a σ-acceptor borane moiety supported by three phosphine buttresses enhances the electrophilicity of M(0) and triggers the binding of soft anions (X = Br, I, CN).

Square-Planar Anionic Pt0 Complexes.

A T-shaped Pt0 complex with a diphosphine-borane (DPB) ligand was prepared. The Pt→B interaction enhances the electrophilicity of the metal and triggers the addition of Lewis bases to give the corresponding tetracoordinate complexes. For the first time, anionic Pt0 complexes are isolated and structurally authenticated. X-ray diffraction analyses show the anionic complexes [(DPB)PtX]- (X=CN, Cl, Br, I) to be square-planar. The d10 configuration and Pt0 oxidation state of the metal were unambiguously established by X-ray photoelectron spectroscopy and DFT calculations. The coordination of Lewis acids as Z-type ligands is a powerful mean to stabilize elusive electron-rich metal complexes and achieve uncommon geometry.

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.

Pd/Ni-Catalyzed Germa-Suzuki coupling via dual Ge-F bond activation.

Pd/Ni → Ge-F interactions supported by phosphine-chelation were found to trigger dual activation of Ge-F bonds under mild conditions. This makes fluoro germanes suitable partners for catalytic Ge-C cross-coupling and enables Germa-Suzuki reactions to be achieved for the first time.

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.

Fluorosilane Activation by Pd/Ni→Si-F→Lewis Acid Interaction: An Entry to Catalytic Sila-Negishi Coupling.

A new mode of bond activation involving M→Z interactions is disclosed. Coordination to transition metals as σ-acceptor ligands was found to enable the activation of fluorosilanes, opening the way to the first transition-metal-catalyzed Si-F bond activation. Using phosphines as directing groups, sila-Negishi couplings were developed by combining Pd and Ni complexes with external Lewis acids such as MgBr2. Several key catalytic intermediates have been authenticated spectroscopically and crystallographically. Combined with DFT calculations, all data support cooperative activation of the fluorosilane via Pd/Ni→Si-F→Lewis acid interaction with conversion of the Z-type fluorosilane ligand into an X-type silyl moiety.

Experimental and Theoretical Investigation of an SN2-type Pathway for Borate-Fluorine Bond Cleavage by Electron-Rich Late-Transition Metal Complexes.

B-F σ-bond activation of a fluoroborate has been experimentally achieved through reactions with electron-rich iridium(I) and palladium(0) complexes. The selectivity of B-F σ-bond cleavage by iridium complexes was improved through the high nucleophilicity of the iridium center, implying that a different pathway from that of well-accepted F- abstraction was in effect. The palladium(0) complex was found to promote exclusive B-F σ-bond cleavage even at ambient temperature. Density functional theory (DFT) calculations suggested that B-F σ-bond activation occurred through an SN2-type pathway, which is, to our knowledge, the first proposal of SN2-type borate-fluorine σ-bond cleavage mediated by a transition metal complex. The high feasibility of the SN2-type pathway appears to be attributed to the relatively low deformation energy of the transition state. It was also found that countercation Cs+ effectively stabilized the transition state and product by serving as a F- acceptor.

Palladium-Borane Cooperation: Evidence for an Anionic Pathway and Its Application to Catalytic Hydro-/Deutero-dechlorination.

Metal-Lewis acid cooperation provides new opportunities in catalysis. In this work, we report a new type of palladium-borane cooperation involving anionic Pd0 species. The air-stable DPB palladium complex 1 (DPB=diphosphine-borane) was prepared and reacted with KH to give the Pd0 borohydride 2, the first monomeric anionic Pd0 species to be structurally characterized. The boron moiety acts as an acceptor towards Pd in 1 via Pd→B interaction, but as a donor in 2 thanks to B-H-Pd bridging. This enables the activation of C-Cl bonds and the system is amenable to catalysis, as demonstrated by the hydro-/deutero-dehalogenation of a variety of (hetero)aryl chlorides (20 examples, average yield 85 %).

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.

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.

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.

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.

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.

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.

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.

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.

Stereoselective synthesis of axially chiral N-C bonds in N-aryl indoles.

[reaction: see text] N-Aryl indoles with axially chiral N-C bonds were synthesized by stereoselective nucleophilic aromatic substitution reactions of planar chiral arene chromium complexes. Stereoselective chromium tricarbonyl migration was achieved in the sterically hindered N-aryl indole chromium complex by refluxing in toluene.