N-Alkylation of carbamates and amides with alcohols catalyzed by a CpIr complex

New atom-economical catalytic systems consisting of [Cp^∗IrCl₂]₂/NaOAc (Cp^∗=pentamethylcyclopentadienyl) for the N-alkylation of carbamates and amides using alcohols as alkylating agents under solvent-free conditions have been developed. For example, the reaction of n-butyl carbamate with benzyl alcohol in the presence of [Cp^∗IrCl₂]₂ (5.0 mol % Ir) and NaOAc (5.0 mol %) at 130 °C under the absence of solvent gives n-butyl N-benzylcarbamate in the yield of 94%. The present catalytic system is applicable to not only carbamates but also amides, and only harmless water is produced as co-product.     

Catalyzed hydroboration of nitrostyrenes and 4-vinylaniline: a mild and selective route to aniline derivatives containing boronate esters

Transition metal catalyzed reactions of catecholborane (HBcat; cat = 1,2-O₂C₆H₄) with β-nitrostyrene and 3-nitrostyrene lead to products derived from competing hydrogenation and hydroboration of the alkene unit along with reduction of the nitro group. Hydroboration of 4-vinylaniline gave regioselective formation of either the branched or the linear organoboronate ester depending upon the catalyst precursors (i.e., RhCl(PPh₃)₃ or Rh(acac)(dppe) vs [Cp^∗IrCl₂]₂) used to facilitate this reaction. Hydroboration products were converted to air-stable primary amines by addition of pinacol.     

The transition metal catalyzed hydroboration of enamines

The addition of catecholborane (HBcat, cat = 1,2-O₂C₆H₄) to 9-vinylcarbazole can give either the branched or linear hydroboration product depending upon the judicious choice of metal catalyst used in these reactions. Analogous reactions with pinacolborane (HBpin, pin = 1,2-O₂C₂Me₄) and HBBzpin (Bzpin = 1,2-O₂C₂Ph₄) using catalytic amounts (5 mol%) of either Rh(acac)(dppb) or [Cp^∗IrCl₂]₂ gave the linear hydroboration product selectively. Hydroborations of 1-pyrrolidino-1-cyclopentene and 1-pyrrolidino-1-cyclohexene were complicated by a competing dehydrogenative borylation pathway. The branched isomer was not observed to any significant extent in these reactions, suggesting that the directing effect of the nitrogen atom is negligible. Although catalyzed additions of HBcat to 1-vinyl-2-pyrrolidinone gave complicated product distributions arising from competing reactions, addition of HBpin effectively generated the corresponding linear hydroboration product in good yields.     

Hydrogenation of cyclohexene catalyzed by ruthenium nitrosyl complexes: Crystal structures of catalyst precursors [CpRu(μ2-NO)2RuCp] and [CpRu(NO)(η-C6H10)] (Cp = η-C5(CH3)5)

Hydrogenation of cyclohexene with 0.1 mol% of the (nitrosyl)ruthenium catalyst [Cp^∗Ru(NO)(C₆H₅)₂] (1; Cp^∗ = η⁵-C₅(CH₃)₅) under 1.0 MPa of H₂ in water at 90 °C for 13 h afforded cyclohexane in 94% yield. The nitrosyl-bridged dinuclear complex [Cp^∗Ru(μ₂-NO)₂RuCp^∗] (2) and the mononuclear cyclohexene complex [Cp^∗Ru(NO)(η²-C₆H₁₀)] (3), which also serve as catalyst precursors, have been obtained from the reaction mixture. X-ray crystallographic analyses of 2 and 3 have revealed that the bridging nitrosyl ligands in 2 form an almost planar Ru₂N₂ four-membered ring with the Ru–Ru distance of 2.5366(5) Å, whereas the nitrosyl ligand in 3 is linear. On the other hand, a ruthenium complex without a nitrosyl ligand [Cp^∗Ru(CH₃CN)₃][OSO₂CF₃] proved to be less effective for this hydrogenation.     

[CpIrCl2]2-catalysed cyclization of 2-alkynylanilines into indoles

[Cp^∗IrCl₂]₂ catalyses the cyclization of 2-alkynylanilines into indoles. A wide variety of substrates is tolerated. A reaction pathway involving intramolecular hydroamination is proposed.     

Synthesis, structure and characterization of dimolybdaheteroboranes

Chalcogen-stabilized dimolybdaboranes 3-5 (3: [(Cp^∗Mo)₂B₄H₅Se(Ph)], 4: [(Cp^∗Mo)₂B₄H₃Se₂(SeCH₂Ph)] and 5: [(Cp^∗Mo)₂B₃H₆(BSR)(μ-η¹-SR)] (R = 2,6-(^tBu)₂-C₆H₂OH)) have been isolated from the mild pyrolysis of dichalcogenide ligands, RE-E‘R (R = Ph: E = S, E‘ = Se; R = CH₂Ph, [2,6-(^tBu)₂-C₆H₂OH]: E = E‘ = Se, S) and [(Cp^∗Mo)₂B₄H₈], 2, an intermediate generated from the reaction of [Cp^∗MoCl₄] (1) (Cp^∗ = η⁵-C₅Me₅), with [LiBH₄.thf]. The geometry of [(Cp^∗Mo)₂B₄H₅Se(Ph)] is similar to that of [(Cp^∗Mo)₂B₅H₉], in which one BH₃ unit on the open face is replaced by a triple bridged selenium atom. All the compounds have been characterized in solution by ¹H, ¹¹B, ¹³C NMR and IR spectroscopy and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 3-5.     

Half-sandwich Ru(II), Ir(III) and Rh(III) complexes with bridging or chelating N-heterocyclic bis-carbene ligand: Synthesis and characterization

N-heterocyclic bis-carbene ligand (bis-NHC) which was derived from 1,1′-diisopropyl-3,3′-ethylenediimidazolium dibromide (L·2HBr) via silver carbene transfer method, reacted with [(η⁶-p-cymene)RuCl₂]₂ and [Cp^∗MCl₂]₂ (Cp^∗ = η⁵-C₅Me_5, M = Ir, Rh) respectively, afforded complexes [(η⁶-p-cymene)RuCl₂]₂(L) (1), [Cp^∗IrCl₂]₂(L) (2) and [Cp^∗RhCl(L)][Cp^∗RhCl₃] (3). When [Cp^∗IrCl₂]₂ was treated with 2 equiv AgOTf at first, and then reacted with bis-NHC ligand, [Cp^∗IrCl(L)]OTf (4) was obtained. The molecular structures of complexes 1-4 were determined by X-ray single crystal analysis, showing that 1 and 2 adopted bridging coordination mode, 3 and 4 adopted chelating coordination mode. All of these complexes were characterized by ¹H, ¹³C NMR spectroscopy and element analysis.     

Reactions of 2-pyridinethiolate cobalt(III) complexes with pyridinethiolate or benzenethiolate ligands

Four half-sandwich cobalt complexes, Cp^∗Co(2-PyS)₂ (2), Cp^∗Co(2-PyS)₂ · HI (3), Cp^∗Co(2-PyS) (4-PyS) (4), (Cp^∗Co)₂(μ-PhS)₂(μ-2-PyS)I (5) [Cp^∗ = pentamethylcyclopentadienyl, 2-PyS = 2-pyridinethiolate, 4-PyS = 4-pyridinethiolate, PhS = benzenethiolate] were successfully synthesized by the reactions of 2-pyridinethione, lithium 4-pyridinethiolate and lithium benzenethiolate with Cp^∗Co(2-PyS)I (1), respectively. Complexes 2 and 3 have the structures with two 2-pyridinethiolates ligands coordinated to the cobalt atom. Two different pyridinethiolates ligands can be identified in complex 4. The molecular structure of 5 consists of two Cp^∗-Co fragments, which are triply bridged by three sulfur atoms from different ligands. The molecular structures of 3 and 5 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Synthesis of sulfido- and thiolato-bridged Ir3 cluster and its reactions with alkyne and isocyanide including highly regioselective cyclotrimerization of methyl propiolate

Reactions of a sulfido- and thiolato-bridged diiridium complex [(Cp^∗Ir)₂(μ-S)(μ-SCH₂CH₂CN)₂] (Cp^∗ = η⁵-C₅Me₅) with [(Cp^∗MCl)₂(μ-Cl)₂] (M = Ir, Rh) afforded the sulfido- and thiolato-bridged trinuclear clusters [(Cp^∗M)(Cp^∗Ir)₂(μ₃-S)(μ₂-SCH₂CH₂CN)₂(μ₂-Cl)]Cl (4: M = Ir, 5: M = Rh). Upon treatment with XyNC (Xy = 2,6-Me₂C₆H₃) in the presence of KPF₆ at 60 °C, 4 was converted into a mixture of a mononuclear XyNC complex [Cp^∗Ir(SCH₂CH₂CN)(CNXy)₂][PF₆] (6) and a dinuclear XyNC complex [{Cp^∗Ir(CNXy)}₂(μ-S)(μ-SCH₂CH₂CN)][PF₆] (7). On the other hand, reactions of 4 and 5 with methyl propiolate in the presence of KPF₆ at 60 °C resulted in the formation of a cyclic trimer of the alkyne 1,3,5-C₆H₃(COOMe)₃ as the sole detectable organic product. The reactions proceeded catalytically with retention of the cluster cores of 4 and 5, whereby the activity of the former was much higher than that of the latter.     

Straightforward synthesis of phosphametallocenium cations of Rh and Ir

Reaction of 3,4-dimethylphospholylthallium (Tl-1) with [Cp^∗MCl₂]₂ (M = Rh, Ir) leads to the formation of the dimeric species [(Cp^∗M)₂(Me₂C₄H₂P)₃]⁺2 and 3 with bridging μ-η¹:η¹-phospholyl ligands. The phosphametallocenium sandwich complexes [Cp^∗M(Me₂C₄(SiMe₃)₂P)]⁺7 (M = Rh) and 8 (M = Ir) could be obtained from the reaction of [Cp^∗MCl₂]₂ and the 2,5-bis(trimethylsilyl)-1-trimethylstannylphosphole 6, with the bulky trimethylsilyl groups preventing the phosphole from η¹- and enforcing a η⁵-coordination. The structures of phospharhodocenium cation 7 and a byproduct 9 containing a phosphairidocenium moiety could be determined by X-ray diffraction.     

Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.     

Synthesis, characterization, and crystal structures of the osmium triflate complexes CpOs(P-P)(OTf) and [CpOs(P-P)(OH2)][OTf]

Treatment of the osmium(II) hydrides Cp^∗Os(P-P)H (Cp^∗ = pentamethylcyclopentadienyl) with methyl trifluoromethanesulfonate (MeOTf) affords osmium(II) triflate complexes with the general formula Cp^∗Os(P-P)(OTf), where P-P = bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), or 1,2-bis(dimethylphosphino)ethane (dmpe). The aqua complexes [Cp^∗Os(dmpm)(OH₂)][OTf] and [Cp^∗Os(dppm)(OH₂)][OTf] are synthesized by the addition of water to the corresponding anhydrous triflates. The complexes Cp^∗Os(dppm)(OTf) and [Cp^∗Os(dmpm)(OH₂)][OTf] have been examined crystallographically, and all compounds have been characterized by NMR spectroscopy.     

Preparation of substituted 1,2,3,4-tetrahydroquinoxalines and 2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepines from catalytic CpIr hydrogen transfer N-heterocyclization of anilino alcohols

The [Cp^∗IrCl₂]₂/K₂CO₃ catalyzed hydrogen transfer N-heterocyclization on a series of anilino alcohols has been investigated. The catalyst (20% loading) converts anilino alcohols to 1,2,3,4-tetrahydroquinoxalines and 2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepines in 30-84% isolated yield.     

Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N-B-PTA(BH3): X-ray crystal structures of [CpRhCl2{N-B}-PTA(BH3)] and [CpRh{N-B-PTA(BH3)}(η-CH2 = CHPh)]

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N-B-PTA(BH₃) and [Cp^∗RhCl(μ-Cl)]₂ affords [Cp^∗Rh{N-B-PTA(BH₃)}Cl₂] (3) or [Cp_∗Rh{N-B-PTA(BH₃)}₂Cl]Cl (5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp_∗Rh{N-B-PTA(BH₃)}H₂] (8) was also obtained by reaction of 3 with NaBH₄ and alternatively by direct hydroboration of [Cp^∗Rh(PTA)Cl₂] with excess NaBH₄. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H₃BO₃ and the corresponding PTA derivatives, including the water-soluble dihydride [Cp^∗Rh(PTA)H₂] (9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp^∗Rh{N-B-PTA(BH₃)}(η²-CH₂ = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η²-coordinated to rhodium without affecting the N-BH₃ moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.     

Rapid and facile Lewis acid catalysed Boc protection of amines

Efficient Boc protection of amines was carried out using (Boc)₂O in the presence of a catalytic amount of ZrCl₄ (10 mol %) in acetonitrile at room temperature. The reaction times are very short and the yields are generally high.     

Synthesis and characterization of half-sandwich iridium complexes containing 2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene and ancillary ortho-carborane-1,2-dichalcogenolato ligands

The binuclear half-sandwich iridium complexes {Cp^∗IrCl₂}₂(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (3) and {Cp^∗Ir[E₂C₂(B₁₀H₁₀)]}₂(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (E = S(5a), Se(5b)) were prepared from the reaction of [Cp^∗IrCl(μ-Cl)]₂ or the “pseudo-aromatic” half-sandwich iridium complex Cp^∗Ir[E₂C₂(B₁₀H₁₀)] (E = S(4a), Se(4b)) with a tetrathiafulvalene (TTF) derivative 2,6-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene (2) at room temperature. The complexes (3, 5a and 5b) have been fully characterized by IR and NMR spectroscopy, as well as elemental analysis. And the molecular structures of 2 and 5a were established through X-ray crystallography. It is interesting that infinite tunnels are created by repeating ‘buckled bowl’ molecules of 5a.     

Formations and electrochemical behavior of mononuclear and binuclear molybdenum dithiolene complexes with nitrosyl ligands: Evidence for the formation of a coordinatively unsaturated species [CpMo(NO)(dithiolene)]

The one-pot reaction of [Cp^∗Mo(NO)(CO)₂] with elemental sulfur and dimethyl acetylenedicarboxylate (C₂Z₂ (Z = COOMe)) gave the [2+2] cycloadduct of the mononuclear molybdenum dithiolene complex [Cp^∗Mo(NO)(S₂C₂Z₂)(C₂Z₂)] (1), and some binuclear complexes:[Cp^∗Mo(NO)(S₂C₂Z₂)]₂ (2), [Cp^∗₂Mo₂(NO)₂S₂(S₂C₂Z₂)] (3) and [Cp^∗Mo(NO)S₂]₂ (4).The reaction of [Cp^∗Mo(NO)(Cl)(μ-Cl)]₂ with OC{S₂C₂(COOMe)₂} in the presence of sodium methoxide also produced complex 2 and the paramagnetic Cp^∗Mo bisdithiolene complex [Cp^∗Mo(S₂C₂Z₂)₂] (5, Z = COOMe).The structures of complexes 1-5 were determined by X-ray crystal structure analysis.The nitrosyl ligands of complexes 1-4 showed a linear coordination to the molybdenum center (the Mo-N-O bond angles = 169-174°), and their N-O bond lengths were 1.17-1.20 Å.In the binuclear complexes 2-4, two nitrosyl ligands were placed at cis-position.Complexes 1 and 2 were characterized by cyclic voltammetry and spectroelectrochemistry (visible and IR). The electrochemical reduction of the dimeric complex 2 formed the monomeric dithiolene complex[Cp^∗Mo(NO)(S₂C₂Z₂)]⁻ (X⁻) whose lifetime was several minutes. When the anion X⁻ was electrochemically oxidized, the coordinatively unsaturated species X was generated, but it was immediately dimerized to afford the original dimeric complex 2. The reduction of the complex 1 included the elimination of the bridged DMAD moiety (C₂Z₂) to give the anion X⁻.     

N-Alkylation of amines with alcohols catalyzed by a Cp*Ir complex

A new effective catalytic system consisting of [Cp*IrCl₂]₂/K₂CO₃ (Cp*=pentamethylcyclopentadienyl) for the N-alkylation of primary amines with alcohols has been developed. As an example, the reaction of aniline with benzyl alcohol in the presence of [Cp*IrCl₂]₂ (5.0 mol%Ir) and K₂CO₃ (5.0 mol%) in toluene at 110°C for 17 h gave benzylaniline in an isolated yield of 88%.     

Sulfur-alkylation-initiated CpRu thiyl radicals

The formation of thiyl radicals from [Cp^∗Ru^III{κ³SSS′-tpdt}] (1A) and [Cp^∗Ru^III{κ³SSN-apdt}] (1B) {Cp^∗ = η⁵-C₅Me₅; tpdt = S(CH₂CH₂S⁻)₂; apdt = HN(CH₂CH₂S⁻)₂} has been initiated by thiolate alkylation or oxidation with iodine. Subsequent electron transfer processes yielded disulfide-bridged dinuclear complexes. The mechanistic pathways of these processes will be discussed.     

Stepwise formation of metallo-prisms of iridium and rhodium complexes bearing pentamethylcyclopentadienyl ligands

Reactions of [M(Cp^∗)Cl(μ-Cl)]₂ (M = Ir(1a); M = Rh(1b)) with tridentate ligands tpt (tpt = 2,4,6-tripyridyl-1,3,5-triazine) gave the corresponding trinuclear complexes [M₃(Cp^∗)₃(μ₃-4-tpt-κN)Cl₆] (M = Ir(2a); M = Rh(2b)), which can be converted into hexanuclear complexes [M₆(Cp^∗)₆(μ₃-4-tpt-κN)₂(μ-Cl)₆](O₃SCF₃)₆ (M = Ir(3a); M = Rh(3b)) by treatment with AgO₃SCF₃, respectively. X-ray of 3b revealed that each of six pentamethylcyclopentadienyl metal moieties was connected by two μ-Cl-bridged atoms and a tridentate ligand to construct a cation triangular metallo-prism cavity with the volume of about 273 Å³ based on the distance of the two triazine moieties is 3.62 Å.