The reactivity of 2‐alkenylpyridine derivatives with trimethylphosphane‐supported iron– and cobalt–methyl adducts were investigated and provided a series of C,N‐cyclometalated complexes through ...smooth vinyl C(sp2)–H activation. The reactions of Co(CH3)(PMe3)4 with 2‐vinylpyridine, 2‐(1‐phenylvinyl)pyridine, and 2‐vinylpyrazine provided dark green crystals of the five‐membered metallacycles (κ2‐C,N‐R1R2C=CH)Co(PMe3)3 (1: R1 = C5H4N, R2 = H; 2: R1 = C5H4N, R2 = Ph; 3: R1 = C4H3N2,R2 = H). The oxidative addition of 1–3 with iodomethane afforded the mer‐trans trivalent cobalt complexes (κ2‐C,N‐R1R2C=CH)Co(CH3)I(PMe3)2 (4: R1 = C5H4N, R2 = H; 5: R1 = C5H4N, R2 = Ph; 6: R1 = C4H3N2, R2 = H) in modest yields. The reaction of 2 with an additional equivalent of 2‐(1‐phenylvinyl)pyridine incorporated a second C,N metallacycle with an η2‐bonded alkenyl moiety to provide (κ2‐C,N‐C5H4N–CH=CH)(κ3,η2‐C,C,N‐C5H4N–CH=CH2)Co(PMe3) (7). No cyclometalation was observed with 8‐vinylquinoline and Co(CH3)(PMe3)4, which afforded (κ3,η2‐C,C,N‐C9H6N–CH=CH2)Co(CH3)(PMe3)2 (8) with retention of the Co–CH3 group; therefore, a suitable bite angle is required for C–H activation. No N coordination was observed with Fe(CH3)2(PMe3)4 and 8‐vinylquinoline (reductive elimination of C2H6), which afforded a low‐valent Fe(PMe3)3 moiety bound in an η4‐fashion with the exocyclic vinyl group and the ortho‐carbon atoms to give (κ4,η4‐C,C,C,C‐C9H6N–CH=CH2)Fe(PMe3)3 (9). In polar solvents, an equilibrium of cyclometalated 7,8‐benzoquinoline exists between the mer‐trans (90 %) and mer‐cis (10 %) configurations of (κ2‐C,N‐C13H6N)Fe(CH3)(PMe3)3 (10). At variance with the previously reported bicyclometalation of 2‐(2‐naphthalene‐1‐ylvinyl)pyridine with iron adducts, similar reactions with methylcobalt species provided the monocyclometalated η2,σ1‐bound coordination motif (κ3,η2‐C,C,N‐C5H4N–CH=CH–C10H6)Co(PMe3)2 (11). The reaction of 11 with carbon monoxide provided the monocarbonyl complex (κ3,η2‐C,C,C‐C5H4N–CH=CH–C10H6)Co(CO)(PMe3)2 (12), accompanied by the release of the N‐coordination site. The carbonylation of (κ3‐C,C,N‐C5H4N–CH=C–C10H6)Fe(PMe3)3 resulted in the exchange of one PMe3 ligand with the retention of the coordination sites to generate (κ3‐C,C,N‐C5H4N–CH=C–C10H6)Fe(CO)(PMe3)2 (13). All new compounds were identified by NMR spectroscopy and structurally characterized by single‐crystal X‐ray crystallography (with the exception of 10 and 13).
The regioselective cyclometalation reactions of 2‐alkenylpyridine/‐pyrazine derivatives with Co(CH3)(PMe3)4 provide cobalt complexes by vinylic C(sp2)–H activation. These cobalt complexes smoothly add iodomethane but readily demetalate with carbon monoxide. Conversely, reductive elimination through the release of ethane is the dominant reaction with the same ligands and Fe(CH3)2(PMe3)4.
Steric control dictates the cyclometalation of aromatic substrates containing imine anchoring groups upon reaction with basic iron or cobalt complexes. As structural isomers, the azadiene systems 1 ...and 2 undergo regiospecific activation of the (vinylic or aromatic) CH bond of the CH group that has switched places with the N atom.
The novel tetranuclear mixed valent iron(II)/iron(0) complex (1) was prepared by ortho-metalation of benzophenone with zerovalent Fe(PMe3)4 (d8) followed by a subsequent insertion of an additional ...equivalent of benzophenone under ring expansion (seven-membered metallacycle). Dimerization and spontaneous dihydrogen loss, constitutes a four membered Fe2O2 core structure in which both incorporated chelating phenylrings are additionally attached by low-valent Fe(PMe3)3-fragments in η4-mode. In a single electron transfer reaction, by C–C-coupling of two molecules benzophenone with zerovalent Co(PMe3)4 (d9), cyclometalated mononuclear five-membered cobalt(II) alcoholate complex (2) is obtained. The crystal structures of 1 and 2 were determined and supported by gas phase DFT calculations and the formation mechanisms of both complexes are discussed.
Reaction cascade: Ortho-metalation of benzophenone with zerovalent iron and cobalt is observed followed by a subsequent addition/insertion of an additional equivalent benzophenone. Display omitted
•Reaction cascade of benzophenone includes C–H activation and C–C coupling steps.•Subsequent insertion/addition sequence with low valent Fe(PMe3)4 and Co(PMe3)4.•Dimerization constitutes a four membered Fe2O2 core structure.•Single electron transfer reaction afforded cyclometalated mononuclear cobalt complex.•Formation mechanisms of both complexes explain the key steps of the proposed sequence.
Come together: Catalyst 1, which contains a diethylboryl‐protected pyridyl unit, copolymerizes ethylene and cyclic olefins such as norborn‐2‐ene (NBE) and cis‐cyclooctene (COE) to give multiblock ...copolymers. Both vinyl insertion polymerization and ring‐opening metathesis polymerization are in effect within a single polymer chain, and the respective NBE and COE blocks can be obtained in different ratios.
Polyurethanes (PUs) constitute one of the most versatile class of polymers with respect to composition, properties, and applications. Having an excellent elastomeric performance, PUs has been used in ...a wide range of applications. Additionally, silane terminated modified polyurethanes (STPUs) combine advantageous characteristics of PUs and organosilicon. Two PUs and four STPUs modified by a silane end‐capper N‐ethyl‐3‐trimethoxysilyl‐2‐methylpropanamine and N‐cyclohexyl aminomethyltriethoxysilane were synthesized and acted as an adhesives or coatings which could be suitable for use in moisture‐curing compositions at room temperature without releasing CO2. The effect of isocyanate groups in the polyurethane backbone and organofunctional groups in the aminosilane structure (R1–NH–R2–SiOC2H53), R1 (alkyl or aryl), the spacer R2 (α or γ) was examined. The chemical and physical structures of the PUs and STPUs were investigated by nuclear magnetic resonance (13C and 1H), dynamical mechanical analysis (DMA), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT‐IR) and the mechanical properties were evaluated by universal tensile tests. The results showed that STPUs were successfully synthesized as moisture curable, exhibiting low viscosity with adequate tensile strength and elongation can be prepared environmentally benign by utilizing secondary aminosilane end‐cappers and an optimal combination of the polyol molecular weight and NCO/OH ratio.
STPUs combine the advantages of silicones and polyurethanes without their respective drawbacks and they allow to develop products addressing various applications wide range of mechanical properties without hazard labelling.
The propensity of a half-sandwich (η⁵-tetramethylcyclopentadienyl) dimethylsilylamido Ti(IV)-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by ...methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3).
Polyaspartic ester polyurea coatings are known for their eco-friendly properties due to the absence of VOCs and free isocyanates. While these coatings offer many advantages to the industry, achieving ...durability often requires the use of trimers with high NCO content. In such cases, applicators face challenges due to their notably short pot life. Furthermore, the second component used is a petroleum-based polyisocyanate, which limits its classification as a sustainable material. In this study, bio-based polyisocyanates were employed in polyaspartic coatings for the first time, thereby positioning them as sustainable alternatives without compromising their conventional properties. Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance Spectroscopy (13C and 1H) were utilized to characterize the structure of polyaspartic ester coatings derived from biobased polyisocyanates along with solvent-free and catalyst-free PAEs. It was determined that the coating formulation had a convenient working time at room temperature. Pendulum hardness and contact angle measurements indicated that hard coatings with hydrophobicity were obtained with the addition of SiO2 and TiO2 particles without reducing the working time. The results revealed a notable 37% increase in tensile strength with the addition of 3 wt% silica compared to the base coating, and a remarkable 43 wt% increase when the coating obtained an equal proportion of titanium and silica at the same concentration. Additionally, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) studies revealed that the composite coatings comprising titanium and silica particles exhibited higher glass transition temperatures and residual char yields compared to the base coating. The morphology and surface roughness of the coatings were characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).
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•Solventless and catalyst-free Polyaspartic esters were synthesized.•SiO2 and TiO2 were added to PAEs and coatings were formed by using bio-polyisocyanates.•SiO2 and TiO2 were combined to make a high gloss coating with improved surface hardness.•The coating with a higher contact angle was obtained and supported by AFM results.•It was revealed that bio-polyisocyanates could be used to create stronger PAE coatings.
CoCH3(PMe3)4 is known for a long time for its potential to activate less reactive C-H Bonds under extremely mild conditions by methane elimination. A spontaneous second C-H bond activation at the ...same center of cobalt complex is not expected. In contrast to previous investigations with certain aryl-iminophosphane chelating ligands, in this work two consecutive metalation steps at the same complex center lead to a rare example of a cobalt metallabicycle. In the first step a C-H activation results in a five-membered chelate ring, whereas the second ring is formed by an incomplete C-H activation which stops at a stable, rarely observed delta-C-H agostic interaction. The results are supported by NMR spectroscopy, X ray structure analysis and density functional theory (DFT) calculations. Knowledge of such agostic interactions are essential in order to understand catalytic reaction paths and studies of such molecular structures of their ring sizes, bite angles and electronic properties have shown that these ligands allow sensitive control within the metal coordination sphere.
CoCH3(PMe3)4 is known for a long time for its potential to activate less reactive C–H Bonds under extremely mild conditions by methane elimination. A spontaneous second C–H bond activation at the ...same center of cobalt complex is not expected. In contrast to previous investigations with certain aryl‐iminophosphane chelating ligands, in this work two consecutive metalation steps at the same complex center lead to a rare example of a cobalt metallabicycle. In the first step a C–H activation results in a five‐membered chelate ring, whereas the second ring is formed by an incomplete C–H activation which stops at a stable, rarely observed δ‐C–H agostic interaction. The results are supported by NMR spectroscopy, X ray structure analysis and density functional theory (DFT) calculations. Knowledge of such agostic interactions are essential in order to understand catalytic reaction paths and studies of such molecular structures of their ring sizes, bite angles and electronic properties have shown that these ligands allow sensitive control within the metal coordination sphere.
“Snapshot”: A double metalation through the coordination of an ortho‐iminophosphane anchoring group can initiate a new bicyclometalation reaction affording the mononuclear cobalt complex (16 valence electrons) (1, 2). The first ring closing step involves a C–H activation, while the second one stops at the level of a rarely observed δ‐C–H agostic interaction supported by quantum chemical calculations.
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