Bond Of 1a Research Articles

Synthesis and Some Coordination Chemistry of Phosphane-Difunctionalized Bis(amidinato)-Heavier Tetrylenes: A Previously Unknown Class of PEP Tetrylenes (E = Ge and Sn).

The bis(amidinato)-heavier tetrylenes E(bzamP)2 (E = Ge (2a) and Sn (2b); bzamP = N-isopropyl-N'-(diphenylphosphanylethyl)benzamidinate), which are equipped with one heavier tetrylene (germylene or stannylene) and two phosphane fragments (one on each amidinate moiety) as coordinable groups, have been synthesized from the benzamidinum salt [H2bzamP]Cl and GeCl2(dioxane) or SnCl2 in 2:1 mol ratio. A preliminary inspection of their coordination chemistry has shown that their amidinate group can also be involved in the bonding with the metal atoms as tridentate ENP and tetradentate PENP' coordination modes have been observed for the ECl(bzamP)2 ligand of [Ir{κ3E,N,P-ECl(bzamP)2}(cod)] (E = Ge (3a) and Sn (3b); cod = η4-1,5-cyclooctadiene) and the E(bzamP)2 ligand of [Ni{κ4E,N,P,P'-E(bzamP)2}] (E = Ge (4a) and Sn (4b)), which are products of reactions of 2a and 2b with [IrCl(cod)]2 (1:0.5 mol ratio) and [Ni(cod)2] (1:1 mol ratio), respectively. These products contain a 5-membered NCNEM ring that results from the insertion of the metal M atom into an E-N bond of 2a and 2b. Additionally, while iridium(I) complexes 3a and 3b are chloridotetryl derivatives (insertion of the tetrylene E atom into the Ir-Cl bond has also occurred) that have an uncoordinated phosphane group, nickel(0) complexes 4a and 4b contain a tetrylene fragment that, maintaining the lone pair, behaves as a σ-acceptor (Z-type) ligand.

Synthesis, characterization, DFT studies and biological assessment of palladium(II) complexes with imidazole derivatives

Six palladium(II) complexes (1–6) with 2-phenylimidazole (L1) and 1,2-dimethylimidazole (L2), were synthesized and characterized by elemental analyses, IR and NMR spectroscopy. The crystal structure of one of them ([Pd(2-phenylimidazole)2Br2], 1) was determined by X-ray crystallography. The palladium(II) ion in complex 1 is coordinated by two nitrogen atoms of 2-phenylimidazole and two bromide ions at trans positions, adopting a nearly regular square planar geometry. The structures of PdBr2 complexes {[Pd(2-phenylimidazole)2Br2] (1) and [Pd(1,2-dimethylimidazole)2Br2] (4)} as well as their chloride analogues, {[Pd(2-phenylimidazole)2Cl2] (1a) and [Pd(1,2-dimethylimidazole)2Cl2] (4a)} were predicted by DFT calculations. Complexes 1 and 1a appeared to be stabilized by a weak agostic interaction between palladium and hydrogen atoms. The energy of Pd⋯H bond was estimated to be 1.6 kcal/mol for both complexes that was comparable to the strength of Cl⋯H hydrogen bond in 1a (1.7 kcal/mol). The complexes were examined for various biological activities including; antimicrobial, antioxidant and anti-diabetic assays. The complexes exhibited moderate antimicrobial activities but they were not good as antioxidants. However, the alpha amylase inhibition assay showed the excellent anti-diabetic effect of the complexes.

Supramolecular chemistry of organoplatinum(IV) complexes: A syndiotactic polymer with uracil substituents

The reaction of RCH2X with [PtMe2(DPA)], 1, (DPA = di-2-pyridylamine) has given [PtXMe2(CH2R)(DPA)] by cis oxidative addition to give 2a, when R = 6-uracil, X = Cl, or 3a, when R = CO2H, X = Br, but by a mixture of cis and trans oxidative addition to give 4a/4b when R = 4-C6H4CO2H, X = Br. The unusual cis stereochemistry of oxidative addition is rationalized thermodynamically by the formation of an intramolecular hydrogen bond in 2a and 3a but not 4a, and kinetically by the role of the ligand DPA NH group in hydrogen bonding to halide. Complex 2a in the solid state forms an unusual supramolecular syndiotactic polymer by forming two different intermolecular NH..O=C hydrogen bonds to neighbouring molecules.

Electrochemical Oxidation Dearomatization of Anisol Derivatives toward Spiropyrrolidines and Spirolactones

Spiro compounds are widely prevalent in biological activities and natural products. However, developing new strategies for their efficient synthesis and derivatization remains a challenge. Outstand...

Synthesis, Characterization, and Reactivity of Cyclometalated Gold(III) Dihalide Complexes in Aqua Regia

A range of N,C‐chelated, cyclometalated gold(III) complexes Au(ppyR)X2 have been prepared and characterized by spectroscopic, crystallographic, and computational means. Here, ppyH is 2‐phenylpyridine dicarboxylic acid (series 1), ppyEt is diethyl 2‐phenylpyridine dicarboxylate (series 2), and X is trifluoroacetate OAcF (a), Cl (b), Br (c), or I (d) anion. The dihalo complexes 1b‐d and 2b‐d are obtained when Au(ppyR)(OAcF)2 (1a and 2a) are treated with HNO3/HX mixtures (aqua regiaX). Good to high yields are obtained with short reaction times (< 30 min) and simple work‐up. Notably, the strongly acidic medium does not cause protolytic cleavage of the Au–C or Au–N bonds in the chelate, nor is ester hydrolysis of complexes 2b‐d seen. Ethylene inserts into an Au–O bond of 1a and 1b, and the resulting trifluoroacetoxyethyl–Au complexes can be further elaborated in aqua regia without cleavage of the two Au–C bonds in the molecule. Facile, mutual halide exchange reactions between complexes with different halides (1b and 1d, 1c and 1d) were observed and led to formation of mixed‐halide complexes Au(ppyH)(X)(Y). These exchange reactions occurred with complete stereoselectivity. The stereoisomer produced was the one expected based on the relative trans influence of the halides (I > Br > Cl), i.e. the highest trans influence halide was located trans to N which is the lowest trans influence end of the chelate. These thermodynamic preferences were also investigated by DFT computations.

Unexpected reactivity of ferrocenyl-iminoboronates: Breaking ortho-imine bonds by oxidation in the presence of non-aqueous sodium chloride

The boronic acid moiety in the proximity of electron-donating structures in ((ferrocenylimino)methyl)phenylboronic acid 1 significantly improves the reactivity of the molecule. The ortho regioisomer 1a exhibits a two-fold higher affinity to NaCl compared to its meta1b and para1c isomers, respectively. Moreover, the double imine bond in 1a was broken by the interaction with NaCl in methanol upon activation by electrochemical oxidation.

Trapping a Highly Reactive Nonheme Iron Intermediate That Oxygenates Strong C-H Bonds with Stereoretention.

An unprecedentedly reactive iron species (2) has been generated by reaction of excess peracetic acid with a mononuclear iron complex [Fe(II)(CF3SO3)2(PyNMe3)] (1) at cryogenic temperatures, and characterized spectroscopically. Compound 2 is kinetically competent for breaking strong C-H bonds of alkanes (BDE ≈ 100 kcal·mol(-1)) through a hydrogen-atom transfer mechanism, and the transformations proceed with stereoretention and regioselectively, responding to bond strength, as well as to steric and polar effects. Bimolecular reaction rates are at least an order of magnitude faster than those of the most reactive synthetic high-valent nonheme oxoiron species described to date. EPR studies in tandem with kinetic analysis show that the 490 nm chromophore of 2 is associated with two S = 1/2 species in rapid equilibrium. The minor component 2a (∼5% iron) has g-values at 2.20, 2.19, and 1.99 characteristic of a low-spin iron(III) center, and it is assigned as [Fe(III)(OOAc)(PyNMe3)](2+), also by comparison with the EPR parameters of the structurally characterized hydroxamate analogue [Fe(III)(tBuCON(H)O)(PyNMe3)](2+) (4). The major component 2b (∼40% iron, g-values = 2.07, 2.01, 1.95) has unusual EPR parameters, and it is proposed to be [Fe(V)(O)(OAc)(PyNMe3)](2+), where the O-O bond in 2a has been broken. Consistent with this assignment, 2b undergoes exchange of its acetate ligand with CD3CO2D and very rapidly reacts with olefins to produce the corresponding cis-1,2-hydroxoacetate product. Therefore, this work constitutes the first example where a synthetic nonheme iron species responsible for stereospecific and site selective C-H hydroxylation is spectroscopically trapped, and its catalytic reactivity against C-H bonds can be directly interrogated by kinetic methods. The accumulated evidence indicates that 2 consists mainly of an extraordinarily reactive [Fe(V)(O)(OAc)(PyNMe3)](2+) (2b) species capable of hydroxylating unactivated alkyl C-H bonds with stereoretention in a rapid and site-selective manner, and that exists in fast equilibrium with its [Fe(III)(OOAc)(PyNMe3)](2+) precursor.

Reactivity of Traditional Metal–Carbon (Alkyl) versus Nontraditional Metal–Carbon (Cage) Bonds in Organo-Rare-Earth Metal Complexes [η5:σ-(C9H6)(C2B10H10)]Ln(CH2C6H4-o-NMe2)(THF)2

Equimolar reaction of 1-indenyl-1,2-carborane with Ln(CH2C6H4-o-NMe2)3 in THF gave highly constrained-geometry complexes [η5:σ-(C9H6)C2B10H10]Ln(CH2C6H4-o-NMe2)(THF)2 (Ln = Y (1a), Gd (1b), Dy (1c)). They reacted with RN═C═NR or 2,6-Me2C6H3NCS to generate the Ln–Calkyl insertion products [η5:σ-(C9H6)C2B10H10]Ln[η2-(RN)2C(CH2C6H4-o-NMe2)](THF) (R = TMS, Ln = Y (2a), Gd (2b); R = tBu, Ln = Y (3a)) or [η5:σ-(C9H6)C2B10H10]Dy[η2-(2,6-Me2C6H3)NC(CH2C6H4-o-NMe2)S](THF)2 (4c). Treatment of 2a with 1 equiv of R′N═C═NR′ to give the Y–Ccage insertion complexes [η5:σ-(C9H6){N(R′)C(═NR′)}C2B10H10]Y[η2-{(TMS)N}2C(CH2C6H4-o-NMe2)] (R′ = Cy (5a), iPr (6a)). Similarly, unsaturated compounds Ph2C═C═O and Py2C═O (Py = 2-pyridyl) also inserted into the Y–Ccage bond in 2a to yield [η5:σ-(C9H6){OC(═CPh2)}C2B10H10]Y[η2-{(TMS)N}2C(CH2C6H4-o-NMe2)] (7a) and [η5:σ-(C9H6){OC(Py)2}C2B10H10]Y[η2-{(TMS)N)}2C(CH2C6H4-o-NMe2)](THF) (8a), respectively. In sharp contrast to the earlier reports that the nontraditional metal–Ccage σ bonds ...

Theoretical Studies of Ring-Opening Reactions of Phenylcyclobutabenzenol and Its Reactions with Alkynes Catalyzed by Rhodium Complexes

DFT calculations have been carried out to study the Rh-catalyzed site selective ring-opening reactions of phenylcyclobutabenzenol (1a). Our calculations supported that the mechanism involves β-carbon elimination in a rhodium(I) phenylcyclobutabenzenolato complex followed by alcoholysis. The favorable β-carbon elimination involves the cleavage of the C(sp(2))-C(sp(3))(OH)(Ph) bond in 1a, which determines the site selectivity. The mechanism and regioselectivity of the related Rh-catalyzed insertion reaction of the asymmetric alkyne MeC≡CPh with phenylcyclobutabenzenol (1a) was also investigated. The key step involves the alkyne insertion into the Rh-C σ bond of a species resulting from the favorable β-carbon elimination in the rhodium(I) phenylcyclobutabenzenolato complex. The favorable insertion couples the metal-bonded carbon with the methyl-substituted carbon of MeC≡CPh.

Competition Between Azido Cleavage and Triplet Nitrene Formation in Azidomethylacetophenones

Photolysis of p- and m-azidomethylacetophenone (1a, 1b) in argon-saturated solutions yields predominantly imine 2a, 2b, whereas irradiation of 1a, 1b in oxygen-saturated solutions results in heterocycles 3a, 3b, aldehydes 4a, 4b and nitriles 5a, 5b. Density functional theory calculations place the energy of the first and second excited state of the triplet ketones (T1K and T2K) in 1a, 1b in close proximity to each other. The triplet transition state for cleaving the C–N bond in 1a, 1b to form azido and benzyl radicals 1aB, 1bB is located only 3 kcal mol–1 (1 kcal = 4.184 kJ) above T1K, indicating that azido cleavage is feasible. The calculations place the energy of the triplet azido group (TA) in 1a, 1b ∼25 kcal mol–1 below T1K; thus, this process is also easily accessible via energy transfer. Further, the transition state barrier for TA to expel N2 and form triplet nitrenes is less than 1 kcal mol–1 above TA in 1a, 1b. Laser flash photolysis of 1a, 1b reveals the formation of the triplet excited ketones of 1a, 1b, which decay to form benzyl radicals 1aB, 1bB and triplet alkylnitrenes. The triplet ketones and the benzyl radicals are quenched with molecular oxygen at rates close to diffusion, whereas the triplet nitrenes react more slowly with oxygen (∼5 × 105 M–1 s–1). We conclude that the triplet alkylnitrenes intercept the benzyl radicals to form 2 in argon-saturated solution, whereas the benzyl radicals are trapped to form 4 in oxygen-saturated solution; thus, the triplet nitrenes react with oxygen to form 3.

Synthesis and Characterization of Dicobalthexacarbonyl-Alkyne Derivatives of Amino Acids, Peptides, and Peptide Nucleic Acid (PNA) Monomers

The reaction of Co(2)(CO)(8) with alkyne-containing amino acids [1a: phenylalanine (Phe) and 1b: methionine (Met)], two suitably alkyne-functionalized derivatives of the neuropeptide enkephalin (Enk) [3: Ac-Enk-Prop and 5: Ac-Enk(Pgl)-NH(2) (Ac--Acetyl; Pgl--propargylglycine; Prop--propargylamine)], a thymine Peptide Nucleic Acid (T-PNA) monomer (7), and a PNA-like monomer (9) derivative gave the respective dicobalthexacarbonyl bioconjugates in very good yields. Two different sites for labeling of the biomolecules were successfully used: The organometallic moiety was reacted with the C-terminus of alkyne-containing amino acids, peptide or PNA thymine monomers, and alternatively the organometallic compound was complexed to an internal site in the peptide or PNA. To this end, a simple glycine was replaced by propargylglycine in peptides, and a new alkyne-containing PNA-like monomer, in which an alkyne chain replaces the nucleobase, was used for PNA chemistry. For the synthesis of the two alkyne-containing enkephalin derivatives 3 and 5, two different resins, namely sulfamylbutyryl and Rink amid, were used as they allow to selectively insert, on the solid phase, an alkyne moiety at the C-terminus and on a side-chain of a peptide sequence, respectively. The identity and constitution of all cobalt complexes were confirmed by different analytical methods (IR, FAB, ESI-MS, and NMR). Most notably, IR spectroscopy shows intensive bands in the 2100-2000 cm(-1) region because of the Co(2)(CO)(6) moiety. In both (1)H NMR spectra of the dicobalthexacarbonyl PNA monomer derivatives 8 and 10, all signals are doubled because of the cis-trans isomerism about the central amide bond. The X-ray structure of a dicobalthexacarbonyl phenylalanine derivative (2a) confirms the proposed composition of the bioconjugates and shows that, as anticipated, the alkyne group of 2a is no longer linear upon complexation in comparison to the alkyne group of the bioconjugate precursor 1a, as indicated by a C-C[triple bond]C angle of about 143 degrees in 2a. Moreover, the C[triple bond]C bond of 1a was elongated by about 0.15 A upon Co(2) coordination.

Phosphorus and Olefin Substituent Effects on the Insertion Chemistry of Nickel(II) Hydride Complexes Containing Amido Diphosphine Ligands

A series of nickel(II) hydride complexes supported by amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2]− ([R-PNP]−; R = Ph, iPr, Cy) and unsymmetrical [N(o-C6H4PPh2)(o-C6H4PiPr2)]− ([Ph-PNP-iPr]−), have been prepared for the investigation of olefin insertion chemistry. The unsymmetrical ligand precursor H[Ph-PNP-iPr] (1d) that features different substituents (phenyl and isopropyl) at the two phosphorus donors was prepared in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with H[R-PNP] (R = Ph (1a), iPr (1b), Cy (1c)) or 1d produced the corresponding four-coordinate nickel hydride complexes 2a−d. Attempts to isolate 2a led instead to the cyclooct-4-en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni−H bond of 2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, respectively, generated cleanly the corresponding ethyl (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quantitative formation of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni−H bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP-iPr]NiCH(Me)Ph (7d) quantitatively. The selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [iPr-PNP]NiCH(Me)CO2Me (8b), [Cy-PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP-iPr]NiCH(Me)CO2Me (8d) were also isolated from the reactions of methyl acrylate with the corresponding nickel hydride complexes 2a−d. The effects of the phosphorus and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed. In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of 1d, 2b−d, 3a, and 5d−7d are reported.

Reversible N−N Coupling of NO Ligands on Dinuclear Ruthenium Complexes and Subsequent N2O Evolution: Relevance to Nitric Oxide Reductase

Unprecedented N−N coupling of two nitrosyl ligands on dinuclear complexes was discovered, which is proposed as a critical step in the bacterial NO reductase (NOR). The N−N coupled complex (TpRu)2(μ-Cl)(μ-pz){μ−κ2-N(O)−N(O)} (2a) (Tp = BH(pyrazol-1-yl)3) was prepared from the reaction of TpRuCl2(NO) (1) with pyrazole in the presence of Et3N. The curious N−N bond distance was X-ray crystallographically determined to be 1.861(3) A for the N−N coupled analogue with a 4-methylpyrazolato bridge, and was confirmed by DFT calculation. The N−N bond of 2a was cleaved by oxidation to give [{TpRu(NO)}2(μ-Cl)(μ-pz)](BF4)2 (4a·(BF4)2), which on reduction reformed 2a. It is interesting to note that the N−N coupled complex 2a was also transformed into the oxo-bridged dinuclear species 5a with the evolution of N2O. These findings would provide valuable information regarding the mechanism of NO reduction to N2O by NOR.

Gold(I)-Catalyzed Dynamic Kinetic Enantioselective Intramolecular Hydroamination of Allenes

Treatment of benzyl 6-methyl-2,2-diphenyl-4,5-octadienyl carbamate (2a) with a catalytic 1:2 mixture of [(S)-3,5-t-Bu-4-MeO-MeOBIPHEP]Au2Cl2 [(S)-1] and AgClO4 (5 mol %) led to isolation of a 3.1:1 mixture of (R,Z)-3a and (R,E)-3a in 94% combined yield with 96 and 76% ee, respectively. Analyses of concentration versus time and/or conversion plots for the reaction of both racemic and enantiomerically enriched 2a with 1 were consistent with conversion of (R)-2a to (R,Z)-3a in the matched reaction manifold and conversion of (S)-2a to (R,E)-3a in the mismatched reaction manifold via the net anti-addition of Au and N across the internal CC bond of 2a.

Characteristics of Antiaromatic Ring π Multi-Hydrogen Bonds in (H2O)n−C4H4(n= 1, 2) Complexes

By counterpoise-corrected optimization method, the six antiaromatic ring pi multi-hydrogen bond structures with diversiform shapes for (H2O)n-C4H4 (n = 1,2) have been obtained at the MP2/aug-cc-pVDZ level. At the CCSD(T)/aug-cc-pVDZ level, the interaction energy obtained mainly depends on the numbers of H2O and fold numbers of the pi multi-hydrogen bond. The interaction energy order is -2.342 (1a with pi mono-hydrogen) < -2.777 (1b with pi bi-hydrogen) << -4.683 (2a with pi bi-hydrogen) < -4.734 (2b with pi tri-hydrogen) < -4.782 (2c with pi tri-hydrogen) < -5.009 kcal/mol (2d with pi tetra-hydrogen bond). Strangely, why is the interaction energy of the pi bi-hydrogen bond in 1b close to that of the pi mono-hydrogen bond in 1a (their difference is only 15.7%)? The reason is that a pi-type H-bond (as an accompanying interaction) between two lone pairs of the O-atom and a near pair of H-atoms of C4H4 exists shoulder by shoulder in structures 1a, 2a, 2b, and 2c and contributes to the interaction energy. Another accompanying interaction, a repulsive interaction between the pi H-bond (using the H-atom(s) of H2O) and the near pair of H-atoms of C4H4, is also found. For the structures and interaction energies, the pi-type H-bond produces four effects: bending the strong pi H-bond, attracting the pair of H-atoms of C4H4 so that they deviate from the C4 ring plane, showing the interaction energy contribution, and bringing the larger electron correlation contribution. The repulsive interaction also produces four effects: pushing the pair of H-atoms of C4H4 so that they deviate from its ring plane, elongating the distance of the pi H-bond, promoting the formation of pi-type H-bond, and slightly influencing the interaction energy. In the present paper, one C=C bond with two H2O (over and below the ring plane) forms a pi H-bond link in two ways: a strong-weak pi H-bond link and a strong-strong pi H-bond link. The stability contribution of the former is more favorable than the latter. One H2O forms a pi H-bond with C4H4 in two ways. One strong pi H-bond part (over or below the ring plane) always is accompanied by another H-bond part. The accompanying part is either a weak pi H-bond or pi-type H-bond.

Heterobimetallic Activation of Dioxygen: Characterization and Reactivity of Novel Cu(I)−Ge(II) Complexes

Reaction of the known germylene Ge[N(SiMe3)2]2 and a new heterocyclic variant Ge[(NMes)2(CH)2] with [L(Me2)Cu]2 (L(Me2) = the beta-diketiminate derived from 2-(2,6-dimethylphenyl)amino-4-(2,6-dimethylphenyl)imino-2-pentene) yielded novel Cu(I)-Ge(II) complexes L(Me2)Cu-Ge[(NMes)2(CH)2] (1a) and L(Me2)Cu-Ge[N(SiMe3)2]2 (1b), which were characterized by spectroscopy and X-ray crystallography. The lability of the Cu(I)-Ge(II) bond in 1a and b was probed by studies of their reactivity with benzil, PPh3, and a N-heterocyclic carbene (NHC). Notably, both complexes are cleaved rapidly by PPh3 and the NHC to yield stable Cu(I) adducts (characterized by X-ray diffraction) and the free germylene. In addition, the complexes are highly reactive with O2 and exhibit chemistry which depends on the bound germylene. Thus, oxygenation of 1a results in scission and formation of thermally unstable L(Me2)CuO2, which subsequently decays to [(L(Me2)Cu)2(mu-O)2], while 1b yields L(Me2)Cu(mu-O)2Ge[N(SiMe3)2]2, a novel heterobimetallic intermediate having a [Cu(III)(mu-O)2Ge(IV)]3+ core. The isolation of the latter species by direct oxygenation of a Cu(I)-Ge(II) precursor represents a new route to heterobimetallic oxidants comprising copper.

DFT and FT-IR analyses of hydrogen bonding in 3-substistuted-3-oxo-arylhydrazonopropanenitriles

Ab initio calculations, FT-IR and X-ray crystal analysis, indicated that the most stable configuration of 3-oxo-2-(phenylhydrazono)-3-(thien-2-yl)-propionitrile is the anti phenylhydrazone structure 1. Stability of such a conformation, over the possible E-form, 2, that would be stabilized by intramolecular hydrogen bonding, is due to interaction between electron-pair domains of the N, S and O atoms. However, the simulated and experimental IR frequency data indicated intermolecular hydrogen bonding between NH and CN, the latter being lowered to 2214cm−1. Studies on 3-oxo-3-phenyl-2-(phenylhydrazono)-propionitrile showed the same result, as well as, another intramolecular hydrogen association of the type NH⋯O. This was clearly indicated by the absorbance of the carbonyl stretch at 1605cm−1.These data indicated the existence of a bifurcated hydrogen bond in 1a and a single intermolecular association in 1b.

Reactivity of silyl-substituted heterobimetallic iron–platinum hydride complexes towards unsaturated molecules: Part II. Insertion of trifluoropropyne and hexafluorobutyne into the platinum–hydride bond

Insertion of hexafluorobutyne into the Pt–H bond of the heterobimetallic complexes [(OC) 3Fe{Si(OMe) 3}(μ-Ph 2PXPPh 2)Pt(H)(PPh 3)] ( 1a X = CH 2; 1b X = NH) yields the σ-alkenyl complexes [(OC) 3Fe{μ-Si(OMe) 2(OMe)}(μ-Ph 2PXPPh 2)Pt{C(CF 3) C(H)CF 3}] ( 3a X = CH 2; 3b X = NH). This insertion reaction is accompanied by dissociation of the platinum bound PPh 3 ligand and saturation of the vacant coordination site by a dative μ−η 2-Si–O → Pt interaction. Addition of the Pt–H bond of 1a across the triple bond of 3,3,3-trifluoropropyne affords in a regiospecific manner [(OC) 3Fe{μ-Si(OMe) 2(OMe)}(μ-dppm)Pt{C(CF 3) CH 2}] ( 2) having the trifluoromethyl substituent on the α-carbon. Addition of RN C to 3 affords the isocyanide adducts [(OC) 3Fe{Si(OMe) 3}(μ-Ph 2PXPPh 2)Pt(CNR){C(CF 3) C(H)CF 3}] ( 4a R = t-Bu, X = CH 2; 4b R = 2,6-xylyl, X = CH 2; 4c R = 2,6-xylyl, X = NH). In dichloromethane solution 3a is gradually transformed into the C 4F 6-bridged compound [(OC) 3Fe(μ-dppm)(μ-CF 3C CCF 3)Pt(CO)] 5. The Pt-bound carbonyl ligand of 5 is displaced by xylylisocyanide or trimethylphosphite affording the derivatives [(OC) 3Fe(μ-dppm)(μ-CF 3C CCF 3)Pt(CNxylyl)] 6 and [(OC) 3Fe(μ-dppm)(μ-CF 3C CCF 3)Pt{P(OMe) 3}] 7. The molecular structures of 4a, 5 and 6 have been determined by X-ray diffraction studies.

Regio‐ and stereochemistry of Michael addition of methanol to Thiele's ester

AbstractAcid‐promoted esterification of Thiele's acid with methanol was found to afford three products. In addition to the expected major product (i.e. the corresponding dimethyl ester, 2a), two minor products are obtained, one of which, 3, results from subsequent Michael addition of methanol to the norbornene CC double bond in 2a. Analysis of its one‐ and two‐dimensional NMR spectra indicates that this minor product possesses structure 3a in which the (C‐5)—OCH3 and (C‐6)—CO2CH3 bonds are exo and endo, respectively. This conclusion is reinforced by the results of thermodynamics calculations and associated chemical shift calculations. In addition, theoretical analysis of competing transition states for Michael addition of methanol to 2a suggests that exo approach of methanol towards the (C‐5)(C‐6) double bond in the substrate is preferred kinetically over the corresponding endo reaction pathway. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Isolation and characterization of iridium(iii) and iridium(v) complexes of 2-(arylazo)pyridine and studies of amine fusion reactions at the coordinated diazo-ligandElectronic supplementary information (ESI) available: Fig. S1: 1H NMR spectra of 1a and tcc-[RuCl2(HL1a)2] in CDCl3. Inset: Methyl resonances of 1b. Fig. S2: 13C NMR spectra of 1a and tcc-[RuCl2(HL1a)2] in CDCl3. Fig. S3: Cyclic voltammogram of 1a in CH3CN. Fig.

The reaction of IrCl3.3H2O with 2-(arylazo)pyridine (HL1) in boiling methanol has afforded [Ir(III)Cl2(L1)(HL1)](1) and [Ir(V)Cl4(HL1)]Cl (2). In complex , one of the two ligands [L1]- is orthometallated via coordination of an ortho-carbon of the aryl ring of [L1]- and one of the two azo nitrogens to form a five-membered chelate. X-Ray crystal structures of the two representative complexes, viz. 1a and 2a, have been solved. Notably, the Ir-N length (2.140(3) A)trans to the Ir-C bond in 1a is appreciably longer than the other three Ir-N lengths present in the same molecule. The N-N lengths in these two compounds lie close to that observed in the uncoordinated ligand. Thorough NMR studies were made to authenticate the carbon-bonded structure of compound 1a. In its 13C NMR spectrum, the resonance near delta 148 is assigned to the carbon bonded to the iridium metal center. UV-visible spectra along with the redox properties of these complexes are reported. The iridium(V) complex, 2 showed a reversible response near 1.40 V, presumably due to the iridium(V)-iridium(VI) couple. Several reductive responses at cathodic potentials, due to ligand reductions, were also observed. Metal promoted aromatic ring amination reactions at the coordinated HL1 ligand in complexes 1 and 2 were investigated. The products were characterized using X-ray diffraction.