Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Synthesis and structural characterization of [Bse]Ni(PPh3)(NO), a nickel complex with a bent nitrosyl ligand

The nickel nitrosyl compound [Bse^Me]Ni(PPh₃)(NO) has been synthesized by the reaction of Ni(PPh₃)₂(NO)Br with potassium bis(2-seleno-1-methylimidazolyl)hydroborate, [Bse^Me]K. X-ray diffraction studies demonstrate that (i) the B–H group of the [Bse^Me] ligand interacts with the nickel center and (ii) the nitrosyl ligand is bent, with Ni–N–O bond angles of 149.1(3)° and 153.1(3)° for the two crystallographically independent molecules. The bent nature of the nitrosyl ligand in [Bse^Me]Ni(PPh₃)(NO) is in marked contrast to the linearity observed for the tris(2-seleno-1-mesitylimidazolyl)hydroborato counterpart [Tse^Mes]NiNO (180.0°). Density functional theory geometry optimization calculations demonstrate that the Ni?H–B interaction is not responsible for causing the nitrosyl ligand to bend, but rather the difference between [Tse^Mes]NiNO and [Bse^Me]Ni(PPh₃)(NO) is due to the [Tse^Mes] ligand allowing the former molecule to adopt a structure with C₃ symmetry. In contrast, the steric and electronic asymmetry of [Se₂P] donor array of the [Bse^Me] and PPh₃ ligand combination prevents [Bse^Me]Ni(PPh₃)(NO) from having C₃ symmetry and the nitrosyl ligand bends to stabilize the occupied M–N σ^∗ antibonding orbital.     

Spectroscopic and structural characterization of O,O′-(diphenylphosphineoxide)amidate and acetylacetonate complexes of pentacoordinate nickel(II)

Heteroleptic nickel pentacoordinate complexes with the macrocyclic ligands 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me₃-mcN₃) or its 9-methyl derivative (Me₄-mcN₃), as ancillary ligands, and O,O′-(diphenylphosphineoxide)amidate ligands, [RC(O)NP(O)Ph₂]^¯ (R = C₆H₆ (1), C₅H₄N (2), C₄H₃S (3)), have been prepared as well as related acetylacetonate derivatives. The complexes have been studied by spectroscopic methods (IR, UV-Vis and ¹H NMR). In acetone solution, the complexes exhibit isotropically shifted ¹H NMR resonances. The full assignment of these resonances has been achieved using one- and two-dimensional ¹H NMR techniques. The single-crystal structures of {(Me₄-mcN₃)Ni[OP(Ph₂)NC(Tf)O]}[PF₆] (9) and {(Me₃-mcN₃)Ni(acac)}[PF₆] (10) have been established by X-ray diffraction.     

Half-sandwich ruthenium(II) complexes containing a tricyclic β-iminophosphine ligand: Catalytic activity in Diels–Alder reactions

The diastereoselective κ²-P,N-coordination of a chiral tricyclic β-iminophosphine ligand to the half-sandwich ruthenium(II) fragments [RuCl(η⁶-arene)]⁺ (arene = C₆H₆, p-cymene, 1,3,5-C₆H₃Me₃, C₆Me₆), [Ru(η⁶-p-cymene)(NCMe)]²⁺ and [Ru(η⁵-C₅H₅)(NCMe)]⁺ is described. The structures of the resulting mono- and dicationic cymene derivatives have been confirmed by X-ray crystallography. Studies on the catalytic activity of these Ru(II) compounds in Diels–Alder cycloaddition processes are also reported.     

Synthesis and reactivity of [2]disilaniobocenophanes

The paramagnetic ansa-niobocene [(Me₂Si)₂(η⁵-C₅H₄)₂NbCl₂] (1) was obtained from the reaction of Li₂[(Me₂Si)₂(C₅H₄)₂] with [NbCl₄(thf)₂]. Further treatment with Li[AlH₄] yielded [(Me₂Si)₂(η⁵-C₅H₄)₂NbH₃] (3), which is prone to decomposition within a few days at room temperature both in solution and in the solid-state, thus affording primarily an insoluble black material. However, after heating or irradiation of a solution of 3 small quantities of the dimeric niobium hydride species, [(Me₂Si)₂{μ-(η¹:η⁵-C₅H₃)}(η⁵-C₅H₄)NbH]₂ (4), were isolated and characterized by X-ray diffraction.     

Me3SiCl-promoted intramolecular cyclization of aromatic compounds tethered with N,O-acetals leading to the facile preparation of 1,4-benzodiazepine skeletons

The Me₃SiCl-promoted intramolecular aminomethylation of a novel type of N,O-acetals, which were prepared via a facile three-step synthesis from N-alkylaniline derivatives and N-alkyl-2-oxazolidinones that leads to the production of pharmaceutically useful 1,4-benzodiazepine skeletons with a variety of functional groups is described. This method was successfully applied to the facile preparation of both tricyclic benzodiazepine derivatives and a 1,4-benzoxazepine derivative via 7-exo-trig cyclization.     

Sulfide oxygenation by tert-butyl hydroperoxide with mononuclear (Me3TACN)Mn catalysts

Mononuclear (Me₃TACN)MnX₃ compounds, where X is Cl⁻, Br⁻, or N₃⁻, and Me₃TACN is 1,4,7-N,N′,N″-trimethyl-1,4,7-triazacyclononane, have been tested for catalyzing both sulfide oxygenation and styrene epoxidation by tert-butyl hydroperoxide (TBHP) and display turnover frequencies (TOF) up to 200 h⁻¹ at room temperature. Sulfoxides or sulfones may be produced selectively by varying reaction conditions. Product distribution from the oxygenation reactions of ethyl phenyl sulfide, 2-chloroethyl phenyl sulfide, and styrene is consistent with a mechanism involving an early single-electron transfer (SET) step.     

A practical approach to non-natural or N-unsubstituted α-arylglycine derivatives: Hf(OTf)4-doped Me3SiCl system-catalyzed aminomethylation of electron-rich arenes with a new type of N,O-acetal

The authors have demonstrated the Hf(OTf)₄-doped Me₃SiCl system-catalyzed aminomethylation of electron-rich aromatic compounds, such as indoles and anilines, with new types of N,O-acetals having a variety of functional groups, such as cyano, ester, bis(trimethylsilyl)amino, diallylamino, and cyclic amino moieties, for the preparation of non-natural aromatic amino acid derivatives. Aminomethylation using an N,O-acetal with a bis(trimethylsilyl)amino group was particularly successful in the direct preparation of an N-unsubstituted α-indolylglycine derivative, which required only a standard aqueous workup.     

Highly efficient trialkylsilylcyanation of aldehydes, ketones and imines catalyzed by a nucleophilic N-heterocyclic carbene

The synthetic utility of N-heterocyclic carbenes was demonstrated by the trialkylsilylcyanation of aldehydes, ketones and imines. In the presence of a catalytic amount of 3a, the reactions with Me₃SiCN proceeded smoothly to give the corresponding cyanohydrin trimethylsilyl ethers or amino nitrile derivatives in good to excellent yields.     

Thermolysis of titanocene methyl compounds bearing t-butyl- and benzyltetramethylcyclopentadienyl ligands

Elimination of methane during thermolysis of title compounds results in the formation of σ-Ti-C bond to t-butyl or benzyl group. The t-butyl-containing titanocene methyl compound [Ti(III)Me(η⁵-C₅Me₄t-Bu)₂] (5) eliminates methane at 110 °C to give cleanly [Ti(III)(η⁵:η¹-C₅Me₄CMe₂CH₂)(η⁵-C₅Me₄t-Bu)] (6). The methyl derivative of analogous benzyl-containing titanocene [Ti(III)Me(η⁵-C₅Me₄CH₂Ph)₂] was not isolated because it eliminated methane at ambient temperature to give [Ti(III)(η⁵:η¹-C₅Me₄CH₂-o-C₆H₄)(η⁵-C₅Me₄CH₂Ph)] (7) with one phenyl ring linked to titanium atom in ortho-position. The corresponding titanocene dimethyl compound [TiMe₂{η⁵-C₅Me₄t-Bu)}₂] (9) eliminates two methane molecules at 110 °C to give the singly tucked-in 1,1-dimethylethane-1,2-diyl-tethered titanocene [Ti{η⁵:η¹:η¹-C₅Me₃(CH₂)(CMe₂CH₂)}(η⁵-C₅Me₄t-Bu)] (11). In distinction, the analogous benzyl derivative [TiMe₂(η⁵-C₅Me₄CH₂Ph)₂] (10) eliminates at 110 °C only one methane molecule to afford [TiMe(η⁵:η¹-C₅Me₄CH₂-o-C₆H₄)(η⁵-C₅Me₄CH₂Ph)] (12) containing one phenyl group attached to titanium in o-position and one methyl group persisting on the titanium atom. This compound is stable at 150 °C for at least 3 h. The crystal structures of 5, 6, 7, and 10 were determined.     

Synthesis and properties of novel ortho-metalated cobalt(I) and iron(II) complexes through Csp2-H bond activation of dibenzylphenylphosphine

Dibenzylphenylphosphine in the reaction with CoMe(PMe₃)₄ afforded complex [(Me₃P)₃Co((ortho-C₆H₄)∩P(C₆H₅)(CH₂C₆H₅))] (1) by C_sp2-H activation via ortho-metalation with P atom as anchoring group. An unexpected dinitrogen iron(II) complex [(Me₃P)₂(N₂)Fe((ortho-C₆H₄)₂∩P(C₆H₅))] (2) stabilized by two five-membered chelate rings as [CPC]-pincer ligand was formed through the reaction of dibenzylphenylphosphine with FeMe₂(PMe₃)₄ via double C_sp2-H activation. The reactions of complexes 1 and 2 with carbon monoxide delivered carbonyl complexes [(Me₃P)(CO)₂Co((ortho-C₆H₄)∩P(C₆H₅)(CH₂C₆H₅))] (3) and [(Me₃P)₂(CO)Fe((ortho-C₆H₄)₂∩P(C₆H₅))] (4). An iodo methyl cobalt(III) complex [(Me₃P)₂(Me)(I)Co((ortho-C₆H₄)∩P(C₆H₅)(CH₂C₆H₅))] (5) was isolated through the reaction of 1 with iodomethane. The structures of 1, 2, 3, 4 and 5 were determined by X-ray diffraction.     

Synthesis, structural characterization and reactivity of new tin bridged ansa-bis(cyclopentadiene) compounds: X-ray crystal structures of Me2Sn(C5Me4R-1)2 (R = H, SiMe3)

The organo-tin compounds, Me₂Sn(C₅H₄R-1)₂ (R = Me (1), Prⁱ (2), Bu^t (3), SiMe₃ (4)) and Me₂Sn(C₅Me₄R-1)₂ (R = H (5), SiMe₃ (6)), were prepared by the reaction of Me₂SnCl₂ with the lithium or sodium derivative of the corresponding cyclopentadiene. Compounds 1-6 have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn). In addition the molecular structures of 5 and 6 were determined by single crystal X-ray diffraction studies. The transmetalation reaction of 1-6 with ZrCl₄ or [NbCl₄(THF)₂] gave the corresponding metallocene complexes in high yields.     

Ru(II) complexes imparting N2O2 donor bis chelating ligand N,N-bis(salicylidine)-hydrazine in unusual coordination mode

The synthesis and characterization of binuclear ruthenium complexes [{(η⁶-C₆H₆)Ru}₂(μ-bsh)₂] (1), [{(η⁶-C₁₀H₁₄)Ru}₂(μ-bsh)₂] (2), [{(η⁶-C₆Me₆)Ru}₂(μ-bsh)₂] (3), and rhodium complex [{(η⁵-C₅Me₅)RhCl}₂(μ-bsh)] (4) (bsh=N,N^′-bis(salicylidine)-hydrazine dianion) are reported. The complexes have been fully characterized by analytical and spectral techniques and unusual coordination mode of the ligand H₂bsh has been confirmed by single crystal X-ray analysis of the complex 2. Structural data revealed extensive inter- and intra-molecular C-H?O and C-H?π interactions and involvement of methyl and isopropyl hydrogen from the p-cymene in hydrogen bonding.     

Stereoselective radical cyclizations of N-(2-halobenzoyl)-cyclic ketene-N,X(X=O, S)-acetals

2-Alkyloxazolines and 2-alkylthiazolines react with 2-halobenzoyl chlorides to form N-(2-halobenzoyl)-cyclic ketene-N,O-acetals and N-(2-halobenzoyl)-cyclic ketene-N,S-acetals in excellent yields, respectively. These ketene acetals readily undergo stereocontrolled aryl radical cyclizations to afford the central six-membered rings of substituted-2,3,10,10α-tetrahydrooxazolo[3,2-b]isoquinolin-5-ones and their 2,3,10,10α-tetrahydrothiazolo[3,2-b]isoquinolin-5-one analogs. The tertiary N,O- and N,S-radicals formed upon aryl radical reaction at the ketene-N,X(X=O, S)-acetal double bond appear to have reasonable stability. The stereoselectivity in hydrogen abstractions by these intermediate radicals from both Bu₃SnH and (Me₃Si)₃SiH was investigated. The N,S-heterocyclic fused ring products may have potential medical value.     

Aminosilylene-bridged ansa-zirconocenes for branched polyethylenes with bimodal molecular weight distributions

Reactions of the dilithium salt of aminosilylene-bridged ligands with (Me₂N)₂ZrCl₂(THF)₂ followed by the treatment of Me₃SiCl are found to be an efficient synthetic route to aminosilylene-bridged ansa-zirconocenes, R₂N(Me)Si(η⁵-C₅H₄)₂ZrCl₂ (R = Me (1), Et (2)) and Me₂N(Me)Si(η⁵-C₅H₄)(η⁵-C₅Me₄)ZrCl₂ (3). Crystal structure of 3 determined by X-ray diffraction study reveals the presence of π-bonding interaction between N and Si atoms, which is further supported by DFT calculation results. These complexes are very active (>1 × 10³ Kg/(mol Cat.·atm·h)) for homopolymerization of ethylene in the presence of methylalumoxane (MAO) cocatalyst, generating polyethylenes that contain branches as well as bimodal molecular weight distribution (MWD). Methyl, ethyl, butyl, and other longer branches (n ≥ 6) are observed in the resulting polyethylenes. The polyethylenes from 1, 2 and 3/MAO show a broad MWD range (6.3-42.2, 3.5-4.0 and 2.6-3.4, respectively).     

Mg(0)-promoted debromometalation of gem-difluoropropargyl bromides

Mg(0)/Me₃SiCl was found to be effective for the preparation of difluoropropargylsilanes. This method, using Me₃SnCl, produced the corresponding propargylstannane.     

In vitro and in vivo antitumor activity of novel 3D-organotin supramolecular coordination polymers based on CuCN and pyridine bases

Two novel organotin supramolecular coordination polymers (SCP), namely, ³_∞[Me₃SnCu(CN)₂·(EN)₂], 1 and ³_∞[Ph₃SnCu(CN)₂·(3-mpy)₂], 2 are obtained by the reactions of K₃[Cu(CN)₄], ethyl nicotinate (EN) or 3-methylpyridine (3-mpy) and Me₃SnCl or Ph₃SnCl in H₂O/acetonitrile solution at room temperature. 2D-layers are constructed via H-bonds between the parallel 1D-puckered chains which contain nanometer-sized [-CN(R₃Sn)NC-] spacers connecting the tetrahedral (T-4) copper sites. The network structures of 1 and 2 consist of infinite layers connected by interlayer H-bonds forming 3D-framworks. 2 is the first compound in this family containing the Ph₃Sn cation. The electronic absorption spectra of 1 and 2 reveal a broad band at 320 nm due to CT transition while the emission spectra exhibit high energy bands at 400-460 nm due to metal-centered (MC) transitions and low energy bands at 485-530 nm corresponding to MLCT. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the in vitro antitumor effects of the SCP 1 and 2 on human breast cancer cell line, ZR-75-1. Cell cycle analysis revealed that the SCP 1 and 2 induced apoptosis in ZR-75-1 breast cancer cell line through activating caspase-3. Moreover, in vivo model, the compound SCP 2 suppressed tumor growth developed mammary carcinoma by 52.3%. Taken together, our novel compounds selectivity exhibit specific in vivo and in vitro antitumor effects.     

Synthesis, characterization and catalytic behaviour of ansa-zirconocene complexes containing tetraphenylcyclopentadienyl rings: X-ray crystal structures of [Zr{Me2Si(η-C5Ph4)(η-C5H3R)}Cl2] (R = H, Bu)

The ansa-bis(cyclopentadiene) compounds, Me₂Si(C₅HPh₄)(C₅H₄R) (R = H (2); Bu^t (3)), have been prepared by the reaction of C₅HPh₄(SiMe₂Cl) (1) with Na(C₅H₅) or Li(C₅H₄Bu^t), respectively, and transformed to the di-lithium derivatives, Li₂{Me₂Si(C₅Ph₄)(C₅H₃R)} (R = H (4); Bu^t (5)), by the action of n-butyllithium. The ansa-zirconocene complexes, [Zr{Me₂Si(η⁵-C₅Ph₄)(η⁵-C₅H₃R)}Cl₂] (R = H (6); Bu^t (7)), were synthesized from the reaction of ZrCl₄ with 4 or 5, respectively. Compounds 6 and 7 have been tested in the polymerization of ethylene and compared with their methyl-substituted analogues, [Zr{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃R)}Cl₂] (R = H (8); Bu^t (9)). Whilst 8 and 9 are catalytically active, the tetraphenyl-substituted complexes 6 and 7 proved to be inactive in the polymerization of ethylene. This phenomenon has been explained by DFT calculations based on the reaction intermediates in the polymerization processes involving 6 and 7, which showed that the extraction of a methyl group from the zirconocene complex to form the cationic active specie is endothermic and therefore unfavourable.     

Structure of N,C,N-chelated organotin(IV) fluorides

The set of starting tri-, di- and monoorganotin(IV) halides containing N,C,N-chelating ligand (L^NCN = {1,3-[(CH₃)₂NCH₂]₂C₆H₃}⁻) has been prepared (1-5) and two compounds structurally characterized ([L^NCNPh₂Sn]⁺I₃⁻ (1c), L^NCNSnBr₃ (5)) in the solid state. These compounds were reacted with KF with 18-crown-6, NH₄F or L^CNnBu₂SnF to give derivatives containing fluorine atom(s). Triorganotin(IV) fluorides L^NCNMe₂SnF (2a) and L^NCNnBu₂SnF (3a) revealed monomeric structural arrangement with covalent Sn-F bond both in the coordinating and non-coordinating solvents, except the behaviour of 3a that was ionized in the methanol solution at low temperature. The products of fluorination of L^NCNSnPhCl₂ (4) and 5 were described by NMR in solution as the ionic hypervalent fluorostannates or the oligomeric species reacting with chloroform, methanol or moisture to zwitterionic monomeric stannate L^NCN(H)⁺SnF₄⁻ (5c), which was confirmed by XRD analysis in the solid state.     

Synthesis and selective silylation of ω-hydroxy functionalized (η-alkenyl)carbene complexes of chromium(0) and tungsten(0) Part 11. The chemistry of metallacyclic alkenylcarbene complexes

Tungsten(0) carbene complexes of the type (OC)₅WC(NMeCH₂CHCHCH₂OH)R 2 (R=Me: 2a; R=Ph: 2b) were generated by aminolysis of (OC)₅WC(OMe)R with cis-NHMeCH₂CHCHCH₂OH. Like their Cr-congeners 1, complexes 2 exist at room temperature as mixtures of Z- and E-isomers with regard to the C-N bond. The metallacyclic complexes (OC)₄WC(η²-NMeCH₂CHCHCH₂OH)R (4) were obtained in good yields upon photo-decarbonylation of 2. Deprotonation/silylation of the complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)Me (M=Cr: 3a; M=W: 4a) with one equivalent of ⁿBuLi/Me₃SiCl gave (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₃ (M=Cr: 5; M=W: 6), whereas with two equivalents of ⁿBuLi/Me₃SiCl complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₂SiMe₃ (M=Cr: 7; M=W: 8) were formed. Hydrolysis of the latter yielded selectively (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)CH₂SiMe₃ (M=Cr: 9; M=W: 10). The complexes 1-10 were analyzed in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ²⁹Si, ¹H/¹H COSY, ¹H/¹H NOESY, ¹³C/¹H HETCOR).