Phenalenyl Based Aluminum Compound for Catalytic C-H Arylation of Arene and Heteroarenes at Room Temperature.

Main group metal based catalysis has been considered to be a cost-effective alternative way to the transition metal based catalysis, due to the high abundance of main group metals in the Earth's crust. Among the main group metals, aluminum is the most abundant (7-8%) in the Earth's crust, making the development of aluminum based catalysts very attractive. So far, aluminum based compounds have been popularly used as Lewis acids in a variety of organic reactions, but chemical transformation demanding a redox based process has never utilized an Al(III) complex as a catalyst. Herein, we tuned the redox noninnocence behavior of a phenalenyl ligand by coupling with Al(III) ion, which subsequently can store the electron upon reduction with K to carry out direct C-H arylation of heteroarenes/mesitylene at ambient temperature. A mechanistic investigation revealed that a three-electron reduced phenalenyl based triradical aluminum(III) complex plays the key role in such catalysis. The electronic structure of the catalytically active triradical species has been probed using EPR spectroscopy, magnetic susceptibility measurements, and electronic structure calculations using a DFT method.

The non-innocent phenalenyl unit: an electronic nest to modulate the catalytic activity in hydroamination reaction.

The phenalenyl unit has played intriguing role in different fields of research spanning from chemistry, material chemistry to device physics acting as key electronic reservoir which has not only led to the best organic single component conductor but also created the spin memory device of next generation. Now we show the non-innocent behaviour of phenalenyl unit in modulating the catalytic behaviour in a homogeneous organic transformation. The present study establishes that the cationic state of phenalenyl unit can act as an organic Lewis acceptor unit to influence the catalytic outcome of intermolecular hydroamination reaction of carbodiimides. For the present study, we utilized organoaluminum complexes of phenalenyl ligands in which the phenalenyl unit maintains the closed shell electronic state. The DFT calculation reveals that the energy of LUMO of the catalyst is mainly controlled by phenalenyl ligands which in turn determines the outcome of the catalysis.

Abnormal N-heterocyclic carbene main group organometallic chemistry: a debut to the homogeneous catalysis.

Abnormal N-heterocyclic carbene (aNHC) adducts of zinc(II) (1) and aluminum(III) (2) were synthesized. The compounds were characterized by NMR spectroscopy and elemental analysis. The solid state structures of these complexes (1 and 2) were determined by single crystal X-ray study. Furthermore, these organozinc and organoaluminum adducts (1 and 2) were tested for the ring opening polymerization of cyclic esters. These adducts were found to be quite efficient catalysts for the polymerization of cyclicesters such as rac-lactide (rac-LA), ε-caprolactone (ε-CL), and δ-valerolactone (δ-VL). Furthermore, aNHC zinc adduct has been used as catalyst for the synthesis of a tri-block copolymer.

Synthesis, structure, spectroscopic characterization, and protein binding affinity of new water-soluble hetero- and homometallic tetranuclear [Cu(II)2Zn(II)2] and [Cu(II)4] clusters.

Two new water-soluble hetero- and homometallic tetranuclear clusters, Na4[Cu2Zn2(ccdp)2(µ-OH)2]·CH3OH·6H2O (1) and K3[Cu4(ccdp)2(µ-OH)(µ-OH2)]·14H2O (2), have been synthesized in methanol-water at room temperature by exploiting the flexibility, chelating ability, and bridging potential of a carboxylate-rich dinucleating ligand, N,N'-bis(2-carboxybenzomethyl)-N,N'-bis(carboxymethyl)-1,3 diaminopropan-2-ol (H5ccdp). Complex 1 is obtained through the self-assembly of two monoanionic [CuZn(ccdp)](-)fragments, which are, in turn, exclusively bridged by two µ-OH(-)groups. Similarly, complex 2 is formed through the self-assembly of two monoanionic [Cu2(ccdp)](-) species exclusively bridged by one µ-OH(-) and one µ-OH2 groups. Complexes 1 and 2 are fully characterized in the solid state as well as in solution using various analytical techniques including a single-crystal X-ray diffraction study. The X-ray crystal structure of 1 reveals that two Cu(II) centers are in a distorted square-pyramidal geometry, whereas two Zn(II) centers are in a distorted trigonal-bipyramidal geometry. The solid-state structure of 2 contains two dinuclear [Cu2(ccdp)](-) units having one Cu(II) center in a distorted square-pyramidal geometry and another Cu(II) center in a distorted trigonal-bipyramidal geometry within each dinuclear unit. In the powder state, the high-field EPR spectrum of complex 1 indicates that two Cu(II) ions are not spin-coupled, whereas that of complex 2 exhibits at least one noninteracting Cu(II) center coordinated to a nitrogen atom of the ligand. Both complexes are investigated for their binding affinity with the protein bovine serum albumin (BSA) in an aqueous medium at pH ~7.2 using fluorescence spectroscopy. Synchronous fluorescence spectra clearly reveal that complexes 1 and 2 bind to the active sites in the protein, indicating that the effect is more pronounced toward tyrosine than tryptophan. Density functional theory calculations have been carried to find the Fukui functions at the metal sites in complexes 1 and 2 to predict the possible metal centers involved in the binding process with BSA protein.

Interface-engineered templates for molecular spin memory devices.

The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices, opening avenues for developing multifunctional molecular spintronics. Such ideas have been researched extensively, using single-molecule magnets and molecules with a metal ion or nitrogen vacancy as localized spin-carrying centres for storage and for realizing logic operations. However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task. In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl, have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets. Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.

Substitution effect on phenalenyl backbone in the rate of organozinc catalyzed ROP of cyclic esters.

A series of zinc complexes (1-6) supported by substituted phenalenyl ligands was synthesized by reacting the phenalenyl ligands with diethyl zinc under ethane evolution. The solid state structures of these complexes (1-6) were determined by single crystal X-ray crystallography. Furthermore, the organozinc complexes (4-6) were tested for the polymerization of cyclic esters as efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) in the presence of benzyl alcohol (BnOH) as initiator. Complex 4 exhibited remarkably higher rate of polymerization under identical reaction condition than complexes 5 and 6. The polymerization of ε-caprolactone produced polymer with narrow polydispersities (M(w)/M(n) = 1.06 to 1.22), while the polymerization of lactide monomers afforded polylactides with polydispersity values ranging from 1.08 to 1.8. The kinetic experiments unravelled a controlled polymerization. The controlled nature of polymerization was further utilized in the preparation of the block copolymer poly(CL)block-poly(rac-LA).

Phenalenyl-based organozinc catalysts for intramolecular hydroamination reactions: a combined catalytic, kinetic, and mechanistic investigation of the catalytic cycle.

Herein, we report the synthesis and characterization of two organozinc complexes that contain symmetrical phenalenyl (PLY)-based N,N-ligands. The reactions of phenalenyl-based ligands with ZnMe(2) led to the formation of organozinc complexes [N(Me),N(Me)-PLY]ZnMe (1) and [N(iPr),N(iPr)-PLY]ZnMe (2) under the evolution of methane. Both complexes (1 and 2) were characterized by NMR spectroscopy and elemental analysis. The solid-state structures of complexes 1 and 2 were determined by single-crystal X-ray crystallography. Complexes 1 and 2 were used as catalysts for the intramolecular hydroamination of unactivated primary and secondary aminoalkenes. A combined approach of NMR spectroscopy and DFT calculations was utilized to obtain better insight into the mechanistic features of the zinc-catalyzed hydroamination reactions. The progress of the catalysis for primary and secondary aminoalkene substrates with catalyst 2 was investigated by detailed kinetic studies, including kinetic isotope effect measurements. These results suggested pseudo-first-order kinetics for both primary and secondary aminoalkene activation processes. Eyring and Arrhenius analyses for the cyclization of a model secondary aminoalkene substrate afforded ΔH(≠) =11.3 kcal mol(-1) , ΔS(≠) =-35.75 cal K(-1) mol(-1) , and E(a) =11.68 kcal mol(-1) . Complex 2 exhibited much-higher catalytic activity than complex 1 under identical reaction conditions. The in situ NMR experiments supported the formation of a catalytically active zinc cation and the DFT calculations showed that more active catalyst 2 generated a more stable cation. The stability of the catalytically active zinc cation was further supported by an in situ recycling procedure, thereby confirming the retention of catalytic activity of compound 2 for successive catalytic cycles. The DFT calculations showed that the preferred pathway for the zinc-catalyzed hydroamination reactions is alkene activation rather than the alternative amine-activation pathway. A detailed investigation with DFT methods emphasized that the remarkably higher catalytic efficiency of catalyst 2 originated from its superior stability and the facile formation of its cation compared to that derived from catalyst 1.

Abnormal N-heterocyclic carbene palladium complex: living catalyst for activation of aryl chlorides in Suzuki-Miyaura cross coupling.

Palladium complexes bearing abnormal N-heterocyclic carbene were used as catalysts in Suzuki-Miyaura cross coupling of aryl chlorides at 25 °C. The catalyst remained active for 10 successive catalytic runs and can activate 4-chlorotoluene at 25 °C with 0.01 mol% catalyst loading resulting in a TON of 9500 within 6 h.

Introduction of abnormal N-heterocyclic carbene as an efficient organocatalyst: ring opening polymerization of cyclic esters.

The recently isolated abnormal N-heterocyclic carbene (aNHC) has been established as an efficient organocatalyst in ring opening polymerization of three different cyclic esters rac-lactide (rac-LA), ε-caprolactone (ε-CL), and δ-valerolactone (δ-VL). Preliminary DFT calculations indicate that aNHC can be a better organocatalyst than the corresponding nNHC counterpart.