Role of Bis(phosphinimino)methanides as Universal Ligands in the Coordination Sphere of Metals across the Periodic Table.

The coordination chemistry of bis(phosphinimino)methanide ligands is widespread and accompanies a large number of metal ions in the periodic table ranging from lithium to neptunium. This unique class of ligand systems show copious coordination chemistry with the main-group, transition, rare-earth, and actinide metals and are considered to be among the most attractive ligand systems to researchers. The bis(phosphinimino)methanide metal complexes offer an extensive range of applications in various fields and have been demonstrated as one of the universal ligand systems to stabilize the metal ions in not only their usual but also their unusual oxidation states. The main-group and transition metal chemistry using bis(phosphinimino)methanides as ligands was last updated almost a decade ago. In this review, we provide a comprehensive overview of various state-of-the-art bis(phosphinimino)methanide-supported metal complexes by dealing with their synthesis, characterization, reactivity, and catalytic studies which were not included in the last critical reviews.

Hydrosilylation of nitriles and tertiary amides using a zinc precursor.

We report a competent and selective hydrosilylation of nitriles and tertiary amides catalyzed by the readily available zinc bis(hexamethyldisilazide) under solvent-free and mild conditions, making it a sustainable and desirable alternative to existing methods. Both protocols afforded high conversion, superior selectivity, and a broad substrate scope, from electron-withdrawing to electron-donating and heterocyclic substitutions.

Zinc Catalyzed Hydroboration of Esters and Nitriles with Pinacolborane.

We developed a bench-stable iminopyridine-ligated zinc complex for the effective catalytic hydroboration of esters and nitriles under solvent-free conditions. Various esters and nitriles bearing different functionalities were selectively reduced to form corresponding alcohols and amines in good yields. Detailed Hammett plots are provided to explain the electronic effects on the phenyl ring.

Correction: NHC-Zn alkyl catalyzed cross-dehydrocoupling of amines and silanes.

Correction for 'NHC-Zn alkyl catalyzed cross-dehydrocoupling of amines and silanes' by Adimulam Harinath et al., Org. Biomol. Chem., 2023, https://doi.org/10.1039/d3ob00453h.

NHC-Zn alkyl catalyzed cross-dehydrocoupling of amines and silanes.

An N-heterocyclic carbene-zinc alkyl complex [ImDippZn(CH2CH3)2] (Im = imidazol-2-ylidene and Dipp = 2,6-diisopropylphenyl) acts as a catalyst in the cross-dehydrogenative coupling (CDC) of a wide range of primary and secondary amines and hydrosilanes to yield a substantial quantity of the corresponding aminosilanes with good chemoselectivity at room temperature. A broad substrate scope was observed during the zinc-catalyzed CDC reaction. Two zinc complexes, [{ImMesZn(µ-NHPh)(NHPh)}2] (Mes = mesityl) (3) and [{ImDippZn(CH2CH3)(µ-H)}2] (4), were isolated and structurally characterized as intermediates through controlled reactions to ascertain the CDC mechanism.

Metal/Non-Metal Catalyzed Activation of Organic Nitriles.

Nitrile activation is a prominent topic in recent developments in chemistry, especially in organic, inorganic, biological chemistry, as well as in the natural synthesis of products and in the pharmaceutical industry. The activation of nitriles using both metal and non-metal precursors has attracted several researchers, who are exploring newer ways to synthesize novel compounds. Nitrile activation can be achieved by combining various catalytic double hydroelementation reactions, such as hydrosilylation, hydroboration, and hydrogenation of organonitriles using silanes, pinacolborane, and other sources of hydrogen. These methodologies have garnered considerable attention since they are effective in the reduction of organonitriles, whose end products are extensively applied in synthetic organic chemistry. In this review, we summarize the development of selective hydroborylation, hydrosilylation, dihydroborysilylation, and hydrogenation of organonitriles, as well as their reaction mechanisms and the role of metal complexes in the catalytic cycles. This review article explains various synthetic methodologies applied toward the reduction of organonitriles into corresponding amines.

Hydroboration and reductive amination of ketones and aldehydes with HBpin by a bench stable Pd(II)-catalyst.

A palladium(II) complex [(κ4-{1,2-C6H4(NCH-C6H4O)2}Pd] (1) supported by a dianionic salen ligand [1,2-C6H4(NCH-C6H4O)2]2- (L) was synthesised and used as a molecular pre-catalyst in the hydroboration of aldehydes and ketones. The molecular structure of Pd(II) complex 1 was established by single-crystal X-ray diffraction analysis. Complex 1 was tested as a competent pre-catalyst in the hydroboration of aldehydes and ketones with pinacolborane (HBpin) to produce corresponding boronate esters in excellent yields at ambient temperature under solvent-free conditions. Further, the complex 1 proved to be a competent catalyst in the reductive amination of aldehydes with HBpin and primary amines under mild and solvent-free conditions to afford a high yield (up to 97%) of corresponding secondary amines. Both protocols provided high conversion, superior selectivity and broad substrate scope, from electron-withdrawing to electron-donating and heterocyclic substitutions. A computational study based on density functional theory (DFT) revealed a reaction mechanism for Pd-catalysed hydroboration of carbonyl species in the presence of HBpin. The protocols also uncovered the dual role of HBpin in achieving the hydroboration reaction.

Alkali and Alkaline Earth Metal Complexes as Versatile Catalysts for Ring-Opening Polymerization of Cyclic Esters.

Biodegradable polyesters such as poly(ϵ-caprolactone) (PCL) and poly(lactic acid) (PLA) have been considered for use in several areas, such as drug delivery devices, sutures, tissue engineering, and GBR membranes, due to its bio-renewability, biodegradability, and biocompatibility. Several synthetic techniques for the preparation of polyesters have been reported in the literature, amongst which the ring-opening polymerization (ROP) of cyclic esters is the most efficient. A convenient approach to access iso-selective PLAs is polymerization of racemic lactide (rac-LA), which shows excellent stereoregularity without the need for costly chiral auxiliaries or ligands. In this personal account, we review a series of methods that have been practiced to the synthesis of biodegradable polyesters from various cyclic monomers using alkali and alkaline earth metal complexes as efficient catalysts.

Recent advances in the carbon-phosphorus (C-P) bond formation from unsaturated compounds by s- and p-block metals.

Researchers around the globe have witnessed several breakthroughs in s- and p-block metal chemistry. Over the past few years, several applications in catalysis associated with these main group metals have been established, and owing to their abundance and low cost and they have proved to be essential alternatives to transition metal catalysts. In this review, we present a detailed discussion on the catalytic addition of P-H bonds from various phosphine reagents to multiple bonds of unsaturated substrates for the synthesis of organophosphorus compounds with C-P bonds promoted by various s- and p-block metal catalysts, as published in the last decade.

Calcium mediated efficient synthesis of N-arylamidines from organic nitriles and amines.

Amidines are a preeminent group of organic compounds having wide applications in various industries. Here, we have developed a simple one-step reaction protocol for the facile synthesis of N-arylamidines catalysed by calcium bis(hexamethyldisilazide) [Ca{N(SiMe3)2}2(THF)2]. The amidine synthesis was readily achieved from organic nitriles and amines which provided a broad substrate scope ranging from electron-withdrawing to electron-donating substitutions as well as heterocyclic substitution. The reaction was carried out in a solvent-free medium under ambient conditions. The nucleophilic addition of aromatic amines to aryl nitriles led to good to excellent yields of the corresponding amidines. The reactivity of the amidines was further examined and the respective urea derivatives were achieved in excellent yields. The plausible mechanism involves the generation of an active calcium amido pre-catalyst that helps in the activation of nitriles in the reaction course.

Ring Opening Polymerization and Copolymerization of Cyclic Esters Catalyzed by Group 2 Metal Complexes Supported by Functionalized P-N Ligands.

We report the preparation of alkali and alkaline earth (Ae) metal complexes supported by 2-picolylamino-diphenylphosphane chalcogenide [(Ph2P(=E)NHCH2(C5H4N)] [E = S (1-H); Se (2-H)] ligands. The treatment of the protic ligand, 1-H or 2-H, with alkali metal hexamethyldisilazides at room temperature afforded the corresponding alkali metal salts [M(THF)2(Ph2P(=E)NCH2(C5H4N)] [M = Li, E = S (3a), Se (3b)] and [{M(THF) n(Ph2P(=E)NCH2(C5H4N)}2] [M = Na, E = S (4a), Se (4b); M = K, E = Se (5b)] in good yield. The homoleptic Ae metal complexes [κ2-(Ph2P(=Se)NCH2(C5H4N)Mg(THF)] (6b) and [κ3-{(Ph2P(=Se)NCH2(C5H4N)}2M(THF) n] (M = Ca (7b), Sr (8b), Ba (9b)] were synthesized by the one-pot reaction of 2-H with [KN(SiMe3)2] and MI2 in a 2:2:1 molar ratio at room temperature. The molecular structures of the protic-ligands 1-H and 2-H, as well as complexes 3a,b-5a,b and 6b-9b were established using single-crystal X-ray analysis. The Ae metal complexes 6b-9b were tested for ring-opening polymerization (ROP) of racemic lactide ( rac-LA) and copolymerization of rac-LA and ε-caprolactone (ε-CL) at room temperature. In the ROP of rac-LA, the calcium complex 7b exhibited high isoselectivity, with Pi = 0.89, whereas both the barium and strontium complexes showed lower isoselectivity with Pi = 0.78-0.62. In the copolymerization of rac-LA and ε-CL, both barium and strontium complexes proved to be efficient precatalysts for the formation of the block copolymer rac-LA-CL, but the reactivity of 9b was found to be better than that of 8b. All the polymers were fully characterized using differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography analyses. Kinetic studies on the ROP reaction of LA confirmed that the rate of polymerization followed the order Ba ≫ Sr ≈ Ca.

Highly Active Dinuclear Titanium(IV) Complexes for the Catalytic Formation of a Carbon-Heteroatom Bond.

A series of mononuclear titanium(IV) complexes with the general composition κ3-[R{NHPh2P(X)}2Ti(NMe2)2] [R = C6H4, X = Se (3b); R = trans-C6H10, X = S (4a), Se (4b)] and [{κ2-N(PPh2Se)2}2Ti(NMe2)2] (6b) and two dinuclear titanium(IV) complexes, [C6H4{(NPh2PS)(N)}Ti(NMe2)]2 (3c) and [{κ2-N(PPh2Se)}Ti(NMe2)2]2 (6c), are reported. Dinuclear titanium(IV) complex 6c acts as an efficient catalyst for the chemoselective addition of an E-H bond (E = N, O, S, P, C) to heterocumulenes under mild conditions. The catalytic addition of aliphatic and aromatic amines, alcohol, thiol, phosphine oxide, and acetylene to the carbodiimides afforded the corresponding hydroelemented products in high yield at mild conditions with a broader substrate scope. The catalytic efficiency of the dinuclear complex depends on the cooperative effect of the TiIV ions, the systematic variation of the intermetallic distance, and the ligand's steric properties of the complex, which enhances the reaction rate. Most interestingly, this is the first example of catalytic insertion of various E-H bonds into the carbodiimides using a single-site catalyst because only the titanium-mediated insertion of E-H into a C═N unsaturated bond is reported to date. The amine and alcohol insertion reaction with the carbodiimides showed first-order kinetics with respect to the titanium(IV) catalyst as well as substrates. A most plausible mechanism for hydroelementation reaction is also proposed, based on the spectroscopic data of the controlled reaction, a time-course study, and the Hammett plot.

Highly Active and Iso-Selective Catalysts for the Ring-Opening Polymerization of Cyclic Esters using Group†2 Metal Initiators.

A series of alkali and alkaline earth (Ae) metal complexes bearing 1,2-phenylene(bis-diphenylphosphinothioic/selenoic amine) [{Ph2 P(E)NH}2 C6 H4 ] (E=S (1-H2); Se (2-H2) ligands are reported. Alkali metal complexes [{Ph2 P(S)N}2 C6 H4 ]Na(THF)4 (3 a) [{Ph2 P(Se)N}2 C6 H4 ]Na(THF)4 (3 b), and [{Ph2 P(Se)N}2 C6 H4 ]K(THF)5 (4 b) were obtained in good yield by treating protic ligands 1-H2 or 2-H2 with metal hexamethyldisilazides [MN(SiMe3 )2 ] (M=Na or K) at ambient temperature. The Ae metal complexes formulated as [{Ph2 P(E)N}2 C6 H4 ]M(THF)3 [E=S, M=Ca (5 a), Sr (6 a), Ba (7 a); E=Se, M=Ca (5 b), Sr (6 b), Ba (7 b)] can be synthesized by using two routes. The molecular structures of the free ligand 1-H2 and metal complexes 5 a,b-7 a,b in their solid states were established. Complexes 3 a and 3 b are isostructural; however, in complex 4 b, an attachment different from ligand 2 was observed. The complexes 5 a,b-7 a,b are isostructural and each metal ion exhibits a distorted pentagonal bipyramidal geometry around it. All Ae metal complexes 5 a,b-7 a,b were tested for the ring-opening polymerization (ROP) of racemic lactide (rac-LA) and ϵ-caprolactone (ϵ-CL) at room temperature. Calcium complexes 5 a and 5 b show excellent iso-selectivity, with Pi values of 0.78-0.87 at 298 K and with a high degree of polymerization control, whereas the corresponding strontium complexes 6 a and 6 b exhibit moderate iso-selectivity, and barium complexes 7 a and 7 b yield only atactic polylactides (PLAs). In all cases, the catalyst initiates the ROP catalytic cycle in the absence of any external initiator. Kinetic studies of the polymerization reactions indicate the relative order of polymerization rate increases with increase in the size of the metal ion: Ba>Sr>Ca.

Imidazolin-2-iminato Ligand-Supported Titanium Complexes as Catalysts for the Synthesis of Urea Derivatives.

The reactions of tetrakis(dimethylamido)titanium(IV) [Ti(NMe2)4] with three different imidazolin-2-imines (Im(R)NH; R = tert-butyl (tBu), mesityl (Mes), and 2,6-diisopropylphenyl (Dipp)) afforded the corresponding titanium imidazolin-2-iminato complexes [(Im(R)N)Ti(NMe2)3] (R = tBu, 1a; R = Mes, 1b; R = Dipp, 1c). Treatment of complex 1a with two different carbodiimides [R'N═C═NR'; R' = cyclohexyl (Cy) and isopropyl (iPr)] resulted in the formation of imidazolin-2-iminato titanium mono(guanidinate) complex of the type [(Im(R)N)Ti(R'NC(NMe2)NR') (NMe2)2 (R' = iPr; R = tBu (2a), R = Dipp (2c); R' = Cy, R = tBu (3a)], as yellow solid in 94% yield. However, a similar reaction of 1b and 1c with 2 equiv of phenyl isocyanates at ambient temperature resulted in the formation of corresponding titanium bis(ureate) complexes [(Im(R)N)Ti{κ(2)-OC(NMe2)NPh}2(NMe2)] (R = Mes, 4b and R = Dipp, 4c). Three equivalents of phenyl isothiocyanate reacted with complex 1c to afford respective titanium tris(thioureate) complex [(Im(Dipp)N)Ti{κ(2)-SC(NMe2)NPh}2{κ(1)-SC(NMe2)NPh}] (6c). The molecular structures of 1a-c, 2a, 2c, 3a, 4c, and 6c were established by X-ray diffraction analyses, and, from the solid-state structures of 1a-c, 2a, 2c, 3a, 4c, and 6c, it was confirmed that the imidazolin-2-iminato titanium bond in each case is very short and possesses a multiple-bonding character. The imidazolin-2-iminato titanium complex 1c was utilized as a precatalyst for the addition of amine N-H bond to phenyl isocyanate. High yields of the corresponding urea derivatives were achieved under mild conditions. The mechanistic study of the aforementioned catalytic reaction was performed, and the active catalyst complex 7b was isolated using 2 equiv of iminopyrrole [2-(2,6-iPr2C6H3N═CH)C4H3NH] and the complex 4b. The molecular structure of 7b was thereafter established.

Pd(OAc)2-catalyzed dehydrogenative C-H activation: An expedient synthesis of uracil-annulated ß-carbolinones.

An intramolecular dehydrogenative C-H activation enabled an efficient synthesis of an uracil-annulated ß-carbolinone ring system. The reaction is simple, efficient and high yielding (85-92%).

Synthesis of algal-bacterial sludge activated carbon/Fe3O4 nanocomposite and its potential in antibiotic ciprofloxacin removal by simultaneous adsorption and heterogeneous Fenton catalytic degradation.

The extensive use of pharmaceuticals has increased their presence in the environment, posing significant ecological and public health concerns. The current study reports the magnetic nanocomposite (M-ABAC) synthesis using the algal-bacterial sludge as the precursor for activated carbon and evaluates its potential in fluoroquinolone antibiotics removal. The activated carbon from algal-bacterial sludge was composited with Fe3O4 nanoparticles using the co-precipitation method. The M-ABAC was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Brunauer-Emmett-Teller (BET) analysis, and vibrating sample magnetometry (VSM). M-ABAC was employed for antibiotic ciprofloxacin (CIP) removal by combined adsorption and heterogenous Fenton degradation. The adsorption studies reveal that the Langmuir isotherm best fits the experimental data, with a maximum adsorption capacity of 81.6 mg/g. Pseudo-second-order kinetic model well describes adsorption kinetics. Fenton catalytic degradation was performed using H2O2 as the activating agent. The optimal H2O2 dosage was observed to be 10 mM. A CIP adsorptive removal efficiency of 75% was observed at 2 g/L dosage of M-ABAC in a 200 ppm CIP solution. Simultaneous adsorption and Fenton catalytic degradation further enhanced the removal efficiency to 92%. Radical scavengers experiment revealed that the hydroxyl radical (•OH) was the dominant reactive oxidation species. The degradation products of the CIP were identified using liquid chromatography quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS). The possible CIP degradation mechanisms include decarboxylation, piperazine moiety degradation, defluorination, and hydroxylation.

Tri-coordinated zinc alkyl complexes with N

A series of tri-coordinated zinc alkyl complexes with the general molecular formula [κ2NE-{NHIRP(Ph)(E)N-Dipp}ZnEt] [R = Dipp (2,6-diisopropylphenyl), E = S (3a), Se (3b) and R = tBu (tert-butyl), E = S (4a), Se (4b)] bearing imino-phosphanamidinate chalcogenide ligands were prepared in good yields from the reaction between the protic imino-phosphanamidinate chalcogenide ligand [NHIRP(Ph)(E)NH-Dipp] [R = Dipp, E = S (1a), Se (1b) and R = tBu, E = S (2a), Se (2b)] and diethylzinc at room temperature. The molecular structures of all the zinc complexes were established by single-crystal X-ray diffraction analysis. In the solid state, all complexes exhibited a distorted trigonal planar geometry around the zinc ion. Metal-chalcogenide (Zn-S/Se) interactions were observed in the coordination sphere. These zinc alkyl complexes were employed as pre-catalysts in the hydroboration reaction of nitriles and esters to obtain the corresponding N,N-diborylamines and boronate esters, respectively, under ambient conditions. A wide substrate scope of nitriles and esters is presented.

Crafting sustainable solutions: architecting biodegradable copolymers through controlled ring-opening copolymerization.

Polylactic acid (PLA) is a biodegradable and biocompatible polymer with versatile applications in packaging and medicine. It is derived from lactic acid and thus represents an eco-friendly option sourced from renewable raw materials. Despite its advantages, PLA exhibits few drawbacks, such as brittleness and relatively high melting and glass transition temperatures. However, these limitations can be addressed through copolymerization with other monomers like ε-caprolactone (ε-CL), resulting in a composite material with improved physical properties. This paper comprehensively reviews achievements in PLA-PCL copolymerization using organometallic catalysts, discussing scientific findings and various copolymer architectures obtained, including random or block configurations. It also demonstrates various sustainable catalysts for achieving the required microstructure under mild reaction conditions without the aid of any external initiator.

Magnesium-Catalyzed Dye-Embedded Polylactide Nanoparticles for the Effective Killing of Highly Metastatic B16F10 Melanoma Cells.

In the current research, dye-embedded polylactic acid (PLA) conjugate materials were synthesized using one-pot ring-opening polymerization (ROP), i.e., (dtHPLA) (2-[(2,4,6-trimethylphenyl) imino]-1(2H)-acenaphthylenone-reduced-PLA) and (dmHPLA) (monoiminoacenaphtheneone-reduced-PLA), and then, nanoparticles (NPs) were engineered in the size range of 150 ± 30 nm. P(dtHPLA) NPs were employed in the treatment of melanoma, an aggressive type of skin cancer, which mandates the development of novel techniques to enhance healing outcomes and eliminate adverse effects related to existing treatments. In addition to exhibiting strong intracellular absorption in the spheroid model, the P(dtHPLA) NPs exhibited a strong cytotoxic effect on B16F10 cells, which resulted in oxidative stress from the generation of reactive oxygen species (ROS) and cell death. Additionally, a live/dead experiment using P(dtHPLA) NPs revealed a notable reduction in cell viability.

Unprecedented ROP of quinazolinones to polyacylamidines using a cesium catalyst.

Unprecedented ring-opening polymerization of quinazolinones to produce novel polyacylamidines, led by a unique cooperation between a cesium metal center and imino-phosphanamidinate ligand, was developed. Morphological studies revealed the formation of a unique macromolecular assembly producing nanofibers in the absence of a templating agent with excellent control of molecular weights and polydispersity index.