Kulsum Bano

In this report, we describe the synthesis and structural characterization of two zinc alkyl complexes supported by anionic PN-morpholine ligand moieties with the general formula [κ²-{Ph₂P(X)N-(CH₂)₂N(CH₂CH₂)₂O}Zn(C₂H₅)]₂ [X = Se (2a); S (2b)]. Both zinc complexes were fully characterized by ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, and single-crystal X-ray diffraction analysis was performed to determine their molecular structures in the solid state. Complexes 2a and 2b have dimeric structures comprising an eight-membered intermolecular-metalacyclic ring adopting the most stable chair form. Furthermore, zinc complex 2a demonstrated exceptional catalytic activity for hydrosilylation of a wide range of aldehydes and ketones under mild reaction conditions. Hydrosilylated derivatives were confirmed by ¹H and ¹³C{¹H} NMR spectroscopy.

Herein, we report the synthesis of three indium complexes (1–3) supported by different chelating ligands (L1–L3). The indium metal complexes were characterized by using multinuclear NMR, and their solid-state structures were confirmed by single-crystal X-ray crystallography. The indium complex 1 (5 mol%) effectively reduced nitroarenes in the presence of phenylsilane and NaI. Nitroarenes containing different functionalities were reduced under standard conditions to give the corresponding amines in good yields.

Described herein is an efficient ring‐opening polymerization (ROP) of rac‐lactide and ϵ‐caprolactone (ϵ‐CL) using novel bimetallic and monometallic aluminum complexes supported by functionalized P−N ligands. All the aluminum complexes were seen to be active catalysts in the ROP of both rac‐lactide and ϵ‐CL in toluene at 60 °C. Bimetallic aluminum complex, [Al(Me)₂{Ph₂P(Se)N(CH₂)₂N−(CH₂CH₂)₂O}(AlMe₃)] containing an uncoordinated Se atom and an auxiliary Al atom within the proximity of another central Al cation was observed to exhibit the highest catalytic activity among all the catalysts studied. Kinetic experiments, comparing bimetallic and related monometallic complexes revealed that bimetallic cooperativity among the two metallic centers in bimetallic complex plays an essential role in driving such superior reactivity. We synthesized several isoselective polylactides (PLAs) and polycaprolactones (PCLs) with controlled molecular weights and narrow molecular weight distributions and characterized by ¹H, ¹³C NMR, DSC and TGA.

The synthesis and characterisation of two mononuclear aluminium alkyl complexes with the general composition [Al(Me)₂{Ph₂P(E)N(CH₂)₂N(CH₂CH₂)₂O}] (E = Se (2a); S (2b)), and two binuclear aluminium complexes, [Al(Me)₂{Ph₂P-(E)N(CH₂)₂N(CH₂CH₂)₂O}(AlMe₃)] (E = Se (3a) and S (3b)), are described. The binuclear aluminium alkyl complex 3a proved to be a proficient catalyst for the addition of simple nucleophiles to heterocumulenes, leading to the synthesis of a variety of products such as urea, biuret, isourea, isothiourea, phosphorylguanidine, and quinazolinone derivatives, in contrast to its mononuclear analogues. Complex 3a is the first example of a single competent catalyst, which is also low-cost and eco-friendly and derived from a main-group metal, under solvent-free conditions either at room temperature or mild temperatures. Complex 3a possessed a wide functional group tolerance including heteroatoms, yielding the corresponding insertion products in good quantities and with high selectivity.

A novel amidophosphine sulfur‐supported magnesium complex, [Ph₂P(S)NCH₂CH₂N−(CH₂CH₂)O]Mg(C₄H₉)(THF)] (2) enabling efficient ring‐opening polymerization of rac‐lactide (LA) and ϵ‐caprolactone (CL) is disclosed. Achieved incredible selectivity for ROP of rac‐lactide for the first time using a magnesium catalyst affording isoselective PLA with a P_i value of 0.77. The polymerization of rac‐LA as well as ϵ‐CL proceeded under mild reaction conditions in absence of any external initiator, to yield corresponding polyesters with a great control over the molecular weight. The kinetic studies reveal that both sulfur and magnesium centers simultaneously work together to drive high yield and selectivity.

Three zinc complexes, with the general formula {κ²‐C₄H₃NH[2‐CH=NCH₂CH₂N(CH₂CH₂)₂O]ZnX₂} [X=Cl (2 a), Br (2 b), I (2 c)], supported by a neutral iminopyrrole‐morpholine ligand, were synthesized by the reaction between {C₄H₃NH‐2‐[CH=NCH₂CH₂N (CH₂CH₂)₂O]} (1) and anhydrous zinc dihalides (ZnCl₂, ZnBr₂, ZnI₂) at ambient temperature in dry methanol. The zinc complexes were fully characterized using multinuclear NMR spectroscopic techniques and the molecular structures of complexes 2 a and 2 c in their solid states were determined by single‐crystal X‐ray diffraction analysis. The zinc diiodo complex (2 c) proved to be a competent precatalyst in the formation of a wide range of benzimidazole and benzothiazole compounds, via aerobic oxidative condensation of several benzylamines with o‐phenylenediamine, N‐phenyl‐o‐phenylene‐diamine, and o‐mercaptoaniline. The benzimidazole and benzothiazole derivatives were successfully characterized using ¹H and ¹³C{¹H} NMR spectroscopy.

A series of new heteroleptic alkaline earth (Ae) metal complexes of general formula [{(Ph₂CHNCH)₂C₄H₂N}AeI(THF)₃] {Ae = Ca (2), Sr (3), and Ba (4)} were synthesized via salt metathesis by reacting potassium salt of ligand 1-K [{(Ph₂CHNCH)₂C₄H₂N}K(THF)₂] with anhydrous alkaline earth metal diiodides (AeI₂). The homoleptic calcium and barium complexes [{(Ph₂CHNCH)₂C₄H₂N}₂Ae] [Ae = Ca (5), Ba (6)] were prepared by treating metal bis-hexamethyldisilazide [Ae{N(SiMe₃)₂}₂(THF)₂] with the protic ligand 1-H [(Ph₂CH–NCH)₂C₄H₂NH] in a 1 : 2 molar ratio. Calcium complex 5 was used as an active pre-catalyst for the addition of N–H bond of arylamines across the heterocumulenes such as phenylisocyanate (PhNCO) and phenylisothiocyanate (PhNCS) under neat conditions, and up to 99% yields of the corresponding urea and thiourea derivatives were obtained.

Brønsted acidic ionic liquids (BAILs) have been used as catalyst and solvent in organic synthesis, due to their negligible volatility, remarkable solubility, good catalytic activity, and easily structurally tunable properties. In the present study, we have investigated the catalytic efficiency of economically viable ionic liquids bearing different cations pyridinium ([PyH] ⁺ and triethylammonium [TEAH] ⁺ ) for the esterification of aromatic acid with various aliphatic alcohols and crossed aldol condensation of aromatic aldehydes with cyclohexanone under ambient condition. We also examined the effect of various process parameters on the yield of aromatic esters and α,α’‐bis(arylidene)cycloalkanones.

We report a series of titanium and zirconium complexes supported by dianionic amidophosphine–borane ligands, synthesized by amine elimination and salt metathesis reactions. The Ti^IV complex [{Ph₂P(BH₃)N}₂C₆H₄Ti(NMe₂)₂] (1) was obtained by the reaction between tetrakis-(dimethylamido)titanium(IV) and the protic aminophosphine–borane ligand [{Ph₂P(BH₃)NH}₂C₆H₄] (LH2) at ambient temperature. Both the heteroleptic zirconium complexes—[η⁵-(C₅H₅)₂Zr{Ph₂P(BH₃)N}₂C₆H₄] (2) and [[{Ph₂P(BH₃)N}₂C₆H₄]ZrCl₂] (3)—and the homoleptic zirconium complex [[{Ph₂P(BH₃)N}₂C₆H₄]₂Zr] (4) were obtained in good yield by the salt metathesis reaction of either zirconocene dichloride [η⁵-(C₅H₅)₂ZrCl₂] or zirconium tetrachloride with the dilithium salt of the ligand [{Ph₂P(BH₃)NLi}₂C₆H₄] (LLi2), which was prepared in situ. The molecular structures of the complexes 1, 2, and 4 in their solid states were confirmed by single-crystal X-ray diffraction analysis. Of these complexes, only titanium complex 1 acts as an effective catalyst for the facile hydroboration of terminal alkynes, yielding exclusive E-isomers. The hydroboration of organic nitriles yielded diborylamines with a broad substrate scope, including broad functional group compatibility. The mechanism of hydroboration occurs through the formation of titanium hydride as an active species.