Vanadium Alkylidyne Initiated Cyclic Polymer Synthesis: The Importance of a Deprotiovanadacyclobutadiene Moiety

Biobased Cyclic Polycarbonate: Synthesis and Applications via Dynamic Bis(hindered amino)disulfide Linkers

Cyclic polymers have garnered significant interest due to their unique structure; however, their synthesis remains challenging, often hindered by low yields and limited selectivity. Considering that the cyclization step during the synthesis of cyclic polymers is presumably the most challenging, using a spontaneous and selective cyclization system is ideal. Here, we present a topology transformation from linear to cyclic, which is achieved through the error-checking ability provided by the dynamic covalent bonding between bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS) and its stable radicals with a high bond exchange rate. When applying this method to biobased poly(isosorbide carbonate) (PIC), an attractive alternative to conventional petroleum-based polycarbonates, high-molecular-weight cyclic polymers were unexpectedly obtained. Since the functionalization of PICs has been traditionally limited to copolymerization techniques, we aimed to introduce dynamic covalent bonds to establish novel functionalization methods for PICs. Interestingly, the synthesis of cyclic PICs through intramolecular cyclization using dynamic covalent bonds in a heterogeneous system proceeded via a ring-expansion polymerization-like mechanism, affording high-molecular-weight cyclic polymers consisting of a PIC backbone and BiTEMPS units as dynamic units. The resulting PIC-based cyclic polymers with BiTEMPS units were applied to bond exchange reactions, providing an effective approach for the synthesis of cyclic block polymers and end-functionalized linear block polymers with a PIC skeleton. These results demonstrate the potential of dynamic covalent chemistry in polymer synthesis.

Synthesis of Linear and Cyclic Poly(allenamer)s by Powerful Cyclic-Alkyl-Amino-Carbene (CAAC) Ruthenium Catalysts and Facile Post-modification

Cyclic polymers are very attractive due to their unique properties; however, so far, they have simple and less reactive backbone structures due to synthetic limitations, restricting their further post-modification. Notably, allenes present a potentially useful platform in polymer chemistry due to their well-established toolbox in organic chemistry. Nevertheless, the biggest challenge remains in synthesizing poly(allenamer)s with high allene contents or polymerization efficiency, as well as synthesizing different types of cyclic poly(allenamer)s. Herein, we synthesized linear and cyclic poly(allenamer)s via ring-opening metathesis polymerization (ROMP) and ring-expansion metathesis polymerization (REMP), employing highly efficient cyclic-alkyl-amino-carbene (CAAC) ruthenium catalysts. Mechanistic studies suggested CAAC ligands enhanced stability of propagating Ru vinylidene, enabling various linear and cyclic poly(allenamer)s with turnover number up to 1360 and molecular weight reaching 549 kDa. Their cyclic architecture was thoroughly characterized by multiangle light scattering size-exclusion chromatography (MALS SEC) with viscometer. Moreover, controlled ROMP of a highly reactive α-substituted cyclic allene was achieved using third-generation Grubbs' catalyst. Finally, we demonstrated highly efficient and selective post-modifications on poly(allenamer)s with primary and secondary alcohols. This broadens the scope of cyclic polymers with improved efficiency and structural control, affording a practical platform for diverse macromolecules.

Pnictogen-based vanadacyclobutadiene complexes

The reactivity of the V[triple bond, length as m-dash]C t Bu multiple bonds in the complex (dBDI)V[triple bond, length as m-dash]C t Bu(OEt2) (C) (dBDI2- = ArNC(CH3)CHC(CH2)NAr, Ar = 2,6- i Pr2C6H3) with unsaturated substrates such as N[triple bond, length as m-dash]CR (R = Ad or Ph) and P[triple bond, length as m-dash]CAd leads to the formation of rare 3d transition metal compounds featuring α-aza-vanadacyclobutadiene, (dBDI)V(κ2- C , N - t BuCC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ2- C , C - t BuCPCAd) (3). Complexes 1-3 are characterized using multinuclear and multidimensional NMR spectroscopy, including the preparation of the 50% 15N-enriched isotopologue (dBDI)V(κ2- C , N - t BuCC(Ad)15N) (1-15N). Solid-state structural analysis is used to determine the dominant resonance structures of these unique pnictogen-based vanadacyclobutadienes. A systematic comparison with the known vanadacyclobutadiene (dBDI)V(κ2- C , C - t BuCC(H)C t Bu) (4) is also presented. Theoretical investigations into the electronic structure of 2-4 highlight the crucial role of unique V-heteroatom interactions in stabilizing the vanadacyclobutadienes and identify the most dominant resonance structures.

Cyclic polymers from alkynes: a review

Cyclic polymers have applications across various fields, including material science, biomedicine, and inorganic chemistry. Cyclic polymers derived from alkyne monomers have expanded the application scope to include electronic materials and polyolefins. This review highlights recent advancements in the synthesis of cyclic polymers from both mono- and disubstituted alkynes. The aim is to provide a comprehensive overview of the synthetic methodologies and the application of cyclic polymers derived from alkynes. Additionally, this review will facilitate a comparative analysis of the advantages and limitations of various synthetic methods and describe opportunities for future development of novel catalytic systems to synthesize cyclic polymers from alkynes.

Decreasing the Bond Order between Vanadium and Oxo Ligand to Form 3d Schrock Carbynes

Preserving vanadium in a high oxidation state during chemical transformations can be challenging due to the oxidizing nature of V(+5) species. Oxo and similar isoelectronic ligands have been utilized to stabilize V(+5) by extensive π-donation. However, decreasing the bond order between V and the oxo ligand often results in a reduction of the metal center. Herein, we report a unique transformation involving anionic V(+5) alkylidene that converts a V(+5) oxo complex to a V(+5) alkylidyne in three steps without altering the oxidation state of the metal center. This method has been used to obtain rare 3d Schrock carbynes, which provide easy and scalable access to V(+5) alkylidynes.

Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage

Reactions between tungsten alkylidyne [tBuOCO]W≡CtBu(THF)2 1 and sulfur containing small molecules are reported. Complex 1 reacts with CS2 to produce intermediate η2 bound CS2 complex [O2C(tBuC═)W(η2-(S,C)-CS2)(THF)] 8. Heating complex 8 provides a mixture of a monomeric tungsten sulfido complex 9 and a dimeric complex 10 in a 4:1 ratio, respectively. Heating the mixture does not perturb the ratio. Addition of excess THF in a solution of 9 and 10 (4:1) converts 10 to 9 (>96%) with concomitant loss of (CS)x. Both 9 and 10 can be selectively crystallized from the mixture. An alternative synthesis of exclusively monomeric 9 involves the reaction between 1 and PhNCS. Demonstrating ring expansion metathesis polymerization (REMP), tethered tungsten alkylidene 8 polymerizes norbornene to produce cis-selective syndiotactic cyclic polynorbornene (c-poly(NBE)).

A General Concept for the Electronic and Steric Modification of 1-Metallacyclobuta-2,3-dienes: A Case Study of Group 4 Metallocene Complexes

The synthesis of group 4 metal 1-metallacyclobuta-2,3-dienes as organometallic analogues of elusive 1,2-cyclobutadiene has so far been limited to SiMe3 substituted examples. We present the synthesis of two Ph substituted dilithiated ligand precursors for the preparation of four new 1-metallacyclobuta-2,3-dienes [rac-(ebthi)M] (M=Ti, Zr; ebthi=1,2-ethylene-1,10-bis(η5-tetrahydroindenyl)). The organolithium compounds [Li2(RC3Ph)] (1 b: R=Ph, 1 c: R=SiMe3) as well as the metallacycles of the general formula [rac-(ebthi)M(R1C3R2)] (2 b: M=Ti, R1=R2=Ph, 2 c: M=Ti, R1=Ph, R2=SiMe3; 3 b: M=Zr, R1=R2=Ph; 3 c: M=Zr, R1=Ph, R2=SiMe3) were fully characterised. Single crystal X-ray diffraction and quantum chemical bond analysis of the Ti and Zr complexes reveal ligand influence on the biradicaloid character of the titanocene complexes. X-band EPR spectroscopy of structurally similar Ti complexes [rac-(ebthi)Ti(Me3SiC3SiMe3)] (2 a), 2 b, and 2 c was carried out to evaluate the accessibility of an EPR active triplet state. Cyclic voltammetry shows that introduction of Ph groups renders the complexes easier to reduce. 13C CPMAS NMR analysis provides insights into the cause of the low field shift of the resonances of metal-bonded carbon atoms and provides evidence of the absence of the β-C-Ti interaction.

Ynamide and Azaalleneyl. Acid-Base Promoted Chelotropic and Spin-State Rearrangements in a Versatile Heterocumulene [(Ad)NCC(tBu)]. Angew Chem Int Ed Engl 2024;63:e202401433. [PMID: 38433099 DOI: 10.1002/anie.202401433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

We introduce the heterocumulene ligand [(Ad)NCC(tBu)]- (Ad=1-adamantyl (C10H15), tBu=tert-butyl, (C4H9)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid-base chemistry, which promotes an unprecedented spin-state change of the [VIII] ion. These unique scaffolds are prepared via addition of 1-adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡CtBu(OTf)] (A) (BDI-=ArNC(CH3)CHC(CH3)NAr), Ar=2,6-iPr2C6H3) and [(dBDI)V≡CtBu(OEt2)] (B) (dBDI2-=ArNC(CH3)CHC(CH2)NAr). Complex A reacts with C≡NAd, to generate the high-spin [VIII] complex with a κ1-N-ynamide ligand, [(BDI)V{κ1-N-(Ad)NCC(tBu)}(OTf)] (1). Conversely, B reacts with C≡NAd to generate a low-spin [VIII] diamagnetic complex having a chelated κ2-C,N-azaalleneyl ligand, [(dBDI)V{κ2-N,C-(Ad)NCC(tBu)}] (2). Theoretical studies have been applied to better understand the mechanism of formation of 2 and the electronic reconfiguration upon structural rearrangement by the alteration of ligand denticity between 1 and 2.