Priyanku Nath

A zinc complex bearing imino‐phosphanamidinate chalcogenide ligands efficiently promotes the ring‐opening polymerization (ROP) of rac ‐lactide ( rac ‐LA) and ε‐caprolactone (ε‐CL), as well as their copolymerization. The complex demonstrated good control over the ROP of rac ‐LA, affording isotactic poly (lactic acid) (PLA) with high stereoselectivity ( P _m = 0.82) and narrow dispersity (Ð < 1.3). One‐pot ring‐opening copolymerization (ROCOP) of rac ‐LA and ε‐CL in the presence of the zinc complex has been shown to produce random copolymers with predictable molecular weights. The fact that the randomization of the copolymers is driven concurrently by the formation of a gradient/partially random copolymer species and slow transesterification was established via in situ NMR spectroscopy. PLA‐ co ‐CL copolymers with varying CL/LA ratios were synthesized, displaying a single glass transition temperature ( T _g ) within the range between the T _g values of the corresponding homopolymers.

This study explores the coordination chemistry and catalytic behavior of cesium‐based multinuclear complexes supported by bis(diphenylphosphino)chalcogenide ligands {CH ₂ (P(E)Ph ₂ ) ₂ } [where E = S ( 1 ) and Se ( 2 )] in the ROP of cyclic esters. By reacting {CH ₂ (P(E)Ph ₂ ) ₂ } with cesium amide [Cs{N(SiMe ₃ ) ₂ }], we isolated two distinct structural motifs: a one‐dimensional coordination polymer [CH{PPh ₂ S} ₂ Cs] _∞ ( 3 ) and a dimeric complex [CH{PPh ₂ Se} ₂ Cs] ₂ ( 4 ). Furthermore, the intervention of 18‐crown‐6 in 1D polymeric ladder ( 3 ) commands the formation of contact pair [{18C6}Cs{CH(Ph ₂ PS) ₂ }] ( 5 ), whereas dimeric complex ( 4 ) leads to ion‐separated cesium complex [(18C6) ₂ Cs] ⁺ [CH(PPh ₂ Se) ₂ ] ⁻ ( 6 ). This is one of the rare reports on the structural characterization of a discrete cesium molecular complex featuring a direct Cs–Se interaction, while only ionic solids were known. Complex 6 is the first ion‐pair to display the [HC(PPh ₂ Se) ₂ ] ⁻ anion in its unbound state, which has predominantly been observed in coordinated form with various metals. All complexes were characterized in solution by spectroscopic analysis ( ¹ H and ³¹ P{ ¹ H} NMR), and their solid‐state structures were confirmed by single‐crystal X‐ray diffraction analysis. Notably, the coordination polymer exhibited superior activity in ROP of rac ‐lactide and caprolactone compared to its dimeric or monomeric analog, suggesting a key role for extended metal–ligand cooperativity.

Herein, we synthesize and characterize three diprotic hybrid E ^ N ^ N ^ N ^ E (E = BH ₃ , S, Se) amidophosphineborane and chalcogenide multidentate ligands [{Ph ₂ P(E)NHCH ₂ } ₂ C ₅ H ₃ N] (E = BH ₃ ( 1‐H2 ); S ( 2‐H2 ); Se ( 3‐H2 )) and probed their reactions with alkaline earth (Ae) metal amides [Ae{N(SiMe ₃ ) ₂ } ₂ (THF) ₂ ] [Ae = Mg, Ca, Sr] in THF. The Ae metal silylamides smoothly trigger the deprotonation of 1‐H2, 2‐H2 and 3‐H2 , which produce complexes represented by generic notation [κ ⁵ ‐({Ph ₂ P(E)NCH ₂ } ₂ C ₅ H ₃ N)‐Ae(THF) ₂ ]; [E = BH ₃ ; Ae = Mg ( 1a ), Ca ( 1b ), E = S; Ae = Mg ( 2a ), Ca ( 2b ), Sr ( 2c ), and E = Se; Ae = Mg ( 3a ), Ca ( 3b ), Sr ( 3c )] in 90–98% yield with the elimination of volatile [NH(SiMe ₃ ) ₂ ]. Additionally, the barium analogue, 2d , was obtained in good yield by a salt metathesis reaction of the diprotic ligand 2‐H2 , potassium benzyl (KCH ₂ Ph), and barium iodide (BaI ₂ ). Solid state structures of ligands ( 2‐H2, and 3‐H2 ) and metal complexes ( 1a , 1b , 2b , 2c , 3a , and 3b ) reveal that non‐planar coordinating sites of ligands (N, P, E) enforce a co‐planar penta‐coordination to alkaline earth metals (Mg, Ca, Sr). Moreover, the Ae metal complexes exhibited multitasking catalytic activity for the hydroboration of heterocumulenes (e.g., isocyanates and carbodiimides) and the ROP polymerization of cyclic esters ( rac ‐lactide, ε‐caprolactone).

Designing a multimetallic catalyst based on the principle of metalloenzymes has emerged as a promising route to enhance catalytic performance owing to the combined action of different metal centers in a cooperative fashion. The cooperativity of metal centers with the surrounding ligand environment in metalloenzymes plays a crucial role in driving efficient catalysis. However, the replication of such cooperativity in a synthetic system is very challenging. In this work, we report the synthesis and characterization of diverse cesium coordination polymeric networks, a 2D sheet, [Cs{κ²‐C₄H₃N‐2(CH = N(2,6‐iPr₂C₆H₃))}]_∞ (1), an infinite ladder chain, [Cs{κ³‐C₄H₃N‐2(CH = N(CHPh₂))}]_∞ (2), and a 3D cage [Cs₂{κ³‐(C₄H₃N‐2(CH = NCH₂CH₂N(CH₂CH₂)₂O))}]_∞ (3). This was accomplished by a variation of the substituent on the iminopyrrolyl ligand. Moreover, we studied a breakdown of the 2D sheet coordination polymer (1) into contact pair monomeric cesium complex [(18‐Cr‐6)Cs(κ²‐C₄H₃N‐2(CH = N(2,6‐iPr₂C₆H₃)))] (4). In the coordination polymers, multiple Cs centers are held together within a proximal distance (3.5–6 Å) via an iminopyrrolyl ligand. The Cs coordination polymer 2 displays the highest catalytic efficiency in ring opening polymerization of rac‐lactide (ROP), giving a turnover frequency (TOF) value of 49.5 h⁻¹ compared to 15.7 h⁻¹ and 24.0 h⁻¹ for 1 and 3. The higher reactivity of 2 in comparison to 1 and 3 is due to the metal‐metal cooperativity in cesium coordination polymeric networks.

An efficient route to synthesize block copolymers of ε-CL and rac -LA via ROCOP and sequential addition in the presence of a magnesium catalyst is reported. All the reactions were performed without using any external initiator.

A novel β‐ketimine ligand‐supported titanium complex, [Ti (DippNHC(Me) = CHC(Me)O₂)Cl₂] (2) enabling competent ring‐opening polymerization (ROP) of cyclohexene oxide (CHO) and copolymerization (ROCOP) of CHO and glutaric anhydride (GA) is unveiled. Incredibly well‐controlled poly(cyclohexene oxide) (PCHO) with a range of molecular weights and narrow polydispersity index (PDI) is achieved. The ROP reaction proceeded under mild reaction conditions without the aid of any exogenous initiator. The thermal properties of the polyethers showed a glass transition temperature (T_g) ranging from 60 °C to 69 °C in the DSC curve and high thermal stability of the polymers up to 387 °C in the TGA curve. The Ti(IV) catalyst additionally showed superior activity in the ROCOP of CHO and GA. ROCOP reactions were performed using a diverse range of CHO and GA monomer equivalents, demonstrating the random insertion of epoxide units per glutaric anhydride and forming a random copolymer.

The catalytic ring-opening polymerization of ε-caprolactone using (DBTEMDA)Br₂ efficiently produces controlled PCLs with precise molecular weight control and recyclable catalytic activity for up to six cycles.

Comprehensive studies concerning the synthesis of PCL–PLA copolymers towards generating novel biodegradable materials by controlling their macromolecular architecture using well-defined organometallic catalysts.

A series of high-performance imine-spaced aromatic polyamide materials, prepared with excellent control of molecular weights and polydispersity index from catalytic ring-opening polymerization of quinazolinones using a cesium catalyst, are reported.

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.