Syntheses, structural, photophysical and theoretical studies of heteroleptic cycloplatinated guanidinate(1-) complexes bearing acetylacetonate and picolinate ancillary ligands.

Cycloplatination of symmetrical N,N',N''-triarylguanidines, (ArNH)2C[double bond, length as m-dash]NAr with cis-[Pt(TFA)2(S(O)Me2)2] in toluene afforded cis-[Pt(TAG)(TFA)(S(O)Me2)] (TAG = triarylguanidinate(1-)-κC,κN; TFA = OC(O)CF3; 6-9) in 75-82% yields. The reactions of 6-9 and the previously known cis-[Pt(TAG)X(S(O)Me2)] (X = Cl (1) and TFA (2-5)) with acetylacetone (acacH) or 2-picolinic acid (picH) in the presence of a base afforded [Pt(TAG)(acac)] (acac = acetylacetonate-κ2O,O'; 10-18) and [Pt(TAG)(pic)] (pic = 2-picolinate-κN,κO; 19) in high yields. The new complexes were characterised by analytical, IR and multinuclear NMR spectroscopies. Further, molecular structures of 11, 12, 13·0.5 toluene and 14-19 were determined by single crystal X-ray diffraction. Absorption spectra of 10-19 in solution and their emission spectra in crystalline form were measured. Platinacycles 10-19 are bluish green light emitter in the crystalline form, and emit in the λPL = 488-529 nm range (11 and 13-19) while 12 emits at λPL = 570 nm. Unlike other platinacycles, the emission band of 12 is broad, red shifted, and this pattern is ascribed to the presence of an intermolecular N-H⋯Pt interaction involving the endocyclic amino unit of the six-membered [Pt(TAG)] ring and the Pt(ii) atom in the adjacent molecule in an asymmetric unit of the crystal lattice. Lifetime measurements were carried out for all platinacycles in crystalline form, which revealed lifetime in the order of nanoseconds. The origin of absorption and emission properties of 11, 15, 18 and 19 were studied by TD-DFT calculations.

Ruthenium-Catalyzed Chemo-Selective Carbene Insertion into C-H Bond of Styrene over Cyclopropanation: C-C Bond Formation.

The C-C bond formation reactions are important in organic synthesis. Heck reaction is known to arylate the terminal carbon of olefins; however, direct alkylation of the terminal carbon of olefin is limited. Herein, we report a novel ruthenium-catalyzed selective cross-coupling reaction of styrene and α-diazoesters to form a new C-C bond over cyclopropanation via the C-H insertion process for the first time. Using this novel methodology, a wide variety of substrates have been utilized and a variety of α-vinylated benzylic esters and densely functionalized olefins have been synthesized with good stereoselectivity under mild reaction conditions. The overall reaction process proceeds through the carbene insertion into styrene to form the desired products in good to excellent yields with proper stereoselectivity. The selective C-H inserted product, wide substrate scope, and excellent functional group tolerance are the best features of this work.

Synthesis of ß-Lactams through Carbonylation of Diazo Compounds Followed by the [2 + 2] Cycloaddition Reaction.

Reporting an efficient method for the synthesis of ß-lactams by the carbonylation of diazo compounds, using [Co2(CO)8] to corresponding ketenes, followed by [2 + 2] cycloaddition with imines. The newly developed strategy was successfully applied to electronically and structurally diverse substrates to produce the corresponding ß-lactams under mild reaction conditions. Fourier transform infrared spectroscopy was employed to monitor ketene formation and the transformation of ketene into ß-lactam. All the products were fully characterized by using various analytical and spectroscopic techniques.

Carboxylic Acid Functionalization Using Sulfoxonium Ylides as a Carbene Source.

Functionalization of carboxylic acids using sulfoxonium ylides in the presence of [VO(acac)2] as a catalyst is reported. The usual carbene source, diazo compounds, failed to produce α-carbonyloxy esters in good yield when compared to sulfoxonium ylides. Various standard spectroscopic and analytical techniques were used to characterize the products formed.

Iridium catalyzed acceptor/acceptor carbene insertion into N-H bonds in water.

The chemistry of A and D/A carbenes (D and A are donor and acceptor groups, respectively) is known to a great extent in the literature. Nevertheless the chemistry of the A/A class of carbenes is less explored, although the A/A class of carbenes is more important in natural product synthesis. The known catalysts for A/A carbene chemistry are also less in number and are found to be efficient only in typical organic solvents. These limitations prompted us to search for new catalysts and environmentally benign reaction conditions for the A/A class of carbenes. The present study reveals that [(COD)IrCl]2 is found to be an efficient catalyst for the A/A class of carbenes, and Pd2(dba)3 for the D/A class of carbenes, for insertion into N-H bonds in water under mild reaction conditions. A reactivity comparison study with different classes of carbenes revealed that silver based catalysts are the right choice for the D/D class of carbenes for insertion into N-H bonds in water. A large number of α-amino malonates and amino esters, which are important for the synthesis of heterocycles and several natural products, have been synthesized by following the current methodology, and characterized using standard analytical and spectroscopic techniques.

A Green Approach to the Synthesis of α-Amino Phosphonate in Water Medium: Carbene Insertion into the N-H Bond by Cu(I) Catalyst.

Synthesis of amino phosphonates is more important owing to their significant applications in the biological systems. There are few methods already known in the literature to make these molecules; however, known methods have their own disadvantages. In this regard, synthesis of different kinds of amino phosphonates have been achieved via phosphonate substituted carbene insertion into the N-H bond of aniline catalyzed by readily available copper salt under mild reaction conditions in water. In order to find an efficient catalyst for carbene insertion reaction in neat water, a large number of transition metal catalysts were screened, and we found that the [Cu(CH3CN)4]ClO4 was the best catalyst under employed reaction conditions. Using this environmentally benign methodology (copper catalyzed reaction in water), a large number of biologically important amino phosphonates have been synthesized, isolated (37 examples), and characterized using standard analytical and spectroscopic techniques.

Synthesis of Aminobenzoic Acid Derivatives via Chemoselective Carbene Insertion into the -NH Bond Catalyzed by Cu(I) Complex.

Phosphine ligand stabilized air-stable Cu(I) complexes have been successfully used to functionalize the aromatic aminobenzoic acids in a chemoselective manner without implementing protection and deprotection strategy under mild reaction conditions. This chemoselective carbene insertion into -NH bond over -COOH and -OH bonds leads to the wide range of carboxy and hydroxy functionalized α-amino esters (27 examples). All of the isolated new products have been fully characterized using standard analytical methods.

Chemoselective Carbene insertion into the N-H Bond over O-H Bond Using a Well-Defined Single Site (P-P)Cu(I) Catalyst.

Phosphine-coordinated air-stable Cu(I) catalyst (1) has been synthesized and characterized. Catalyst 1 is found to be active toward highly chemoselective carbene insertion into the N-H bond over the O-H bond and also over the formation of olefins when numerous aminophenols were treated with a variety of α-aryl diazoesters under normal experimental conditions.

Calix[2]bispyrrolylarenes: new expanded calix[4]pyrroles for fluorometric sensing of anions via extended π-conjugation.

Two new expanded calix[4]pyrroles 3 and 4 were synthesized by '2 + 2' cyclocoupling of easily prepared diboryldipyrromethane 7 (by Ir-catalyzed CH-bond activation) with appropriate diiodoarenes using the Suzuki protocol. Owing to the unique design, both macrocycles exhibited extended π-conjugation and enhanced fluorescence. Upon complexation with anions (fluoride and acetate), receptor 3 displayed turn-on sensing of fluorescence, whereas 4 showed turn-off sensing.

A [Fe(CB6)] platform for binding of small molecules: insights from DFT calculations.

The viability of making [Fe(CB(6))L] (L = H(2), N(2), O(2), nitric oxide [NO(-), NO, and NO(+)], CO(2), and hydrocarbons [CH(4), C(2)H(6), C(2)H(4), and C(6)H(6)]) has been investigated by density functional theory (DFT) calculations. The complexes 2-18 are thermodynamically stable and may be synthesized. The small molecules are activated to some extent after complexation. Molecular orbital and ΔG calculation revealed that the molecular hydrogen and hydrocarbons can be chemically adsorbed and desorbed on [Fe(CB(6))] without any significant chemical modification and therefore [Fe(CB(6))] may serve as a storage material. The N(2), O(2), and nitric oxide (NO(-), NO, and NO(+)) can be activated using [Fe(CB(6))]. Proton, carbon, boron, and nitrogen NMR chemical shift calculation predicts drastic chemical shift difference before and after the complexation of [Fe(CB(6))] with small molecules. This new findings suggest that the CB(6)(2-) ligand-based complex may provide several applications in the future.

Colorimetric sensing of fluoride ion by new expanded calix[4]pyrrole through anion-π interaction.

Three new expanded calix[4]pyrroles were synthesized, where the two dialkylldipyrromethane units are linked via C-C double bonds. One of them, calix[2]bispyrrolylethene, colorimetrically senses fluoride ion only, owing to anion-π interaction in polar aprotic solvents.

Energetics and mechanism of ammonia synthesis through the Chatt Cycle: conditions for a catalytic mode and comparison with the Schrock Cycle.

Through a series of DFT calculations the energy profile of the Chatt cycle is evaluated. This is the counterpiece of our earlier investigations of the Schrock cycle (Angew. Chem. 2005, 117, 5783; Angew. Chem. Int. Ed. 2005, 44, 5639), applying the same quantumchemical methodology and approximations. As for the Schrock cycle, decamethylchromocene acts as reductant. The protonation reactions are considered to be mediated by HBF4/diethyl ether or lutidinium. For all protonation and reduction steps the corresponding free reaction enthalpy changes are calculated. The derived energy profile and corresponding reaction mechanism bear strong similarities to the Schrock cycle. In particular, the most endergonic reaction is the first protonation of the N2 complex and the most exergonic reaction is the cleavage of the N--N bond. If lutidinium is employed as acid and Cp2*Cr as reductant, the reaction course involves steps that are not thermally allowed. For HBF4/diethyl ether as the acid and Cp2*Cr as reducant, however, a catalytic cycle consisting of thermally allowed reactions is principally feasible. This cycle involves a Mo I-fluoro complex as dinitrogen intermediate. It is shown that regeneration to the Mo 0-bis(dinitrogen) complex is thermally not accessible in this system. Moreover, the Mo I fluoro-dinitrogen complex is labile towards disproportionation. The implications of these results with respect to the realization of a catalytic system on the basis of Mo and W phosphine complexes are discussed.

Double deprotonation of coordinated ethylimide to CH3CN: molecular mechanism and relevance to the chemistry of Mo and W organoimides.

Reaction of [MCl(NEt)(dppe)2)Cl (M = Mo, W) with n-BuLi in tert-butyl methyl ether under an N2 atmosphere yields the M0 bis(dinitrogen) complexes [M(N2)2(dppe)2] and acetonitrile. A mechanism is proposed for this reaction which involves an anionic chloro-acetonitrile intermediate. The implications of these findings to the chemistry of Mo and W organoimides are discussed.