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1.
iScience ; 7: 120-131, 2018 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-30267674

RESUMO

Neutral zinc alkoxide complexes show high activity toward the ring-opening polymerization of cyclic esters and carbonates, to generate biodegradable plastics applicable in several areas. Herein, we use a ferrocene-chelating heteroscorpionate complex in redox-switchable polymerization reactions, and we show that it is a moderately active catalyst for the ring-opening polymerization of L-lactide, ɛ-caprolactone, trimethylene carbonate, and δ-valerolactone. Uniquely for this type of catalyst, the oxidized complex has a similar polymerization activity as the corresponding reduced compound, but displays significantly different rates of reaction in the case of trimethylene carbonate and δ-valerolactone. Investigations of the oxidized compound suggest the presence of an organic radical rather than an Fe(III) complex. Electronic structure and density functional theory (DFT) calculations were performed to support the proposed electronic states of the catalytic complex and to help explain the observed reactivity differences. The catalyst was also compared with a monomeric phenoxide complex to show the influence of the phosphine-zinc interaction on catalytic properties.

2.
Chem Sci ; 9(8): 2168-2178, 2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-29719690

RESUMO

Poly(l-lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/l-lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(µ-OCH2Ph)}2 ([(fcP,B)Zn(µ-OCH2Ph)]2, fc = 1,1'-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated.

3.
Dalton Trans ; 45(37): 14581-90, 2016 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-27334096

RESUMO

Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp(Ph,Me)) ligand is described. Exposure of Tp(Ph,Me)NiCH2Ph (1a) and Tp(Ph,Me)NiCH2Si(CH3)3 (1b) to CS2 resulted in formation of the insertion products Tp(Ph,Me)Ni(η(2)-CS2)CH2Ph (2a) and Tp(Ph,Me)Ni(η(2)-CS2)CH2Si(CH3)3 (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1 : 1 ratio, identified as Tp(Ph,Me)Ni(η(2)-MeNC)CH2Ph (3) and Tp(Ph,Me)Ni(η(2)-MeNCS)SCH2Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.(t)BuNC), which resulted in isolation of Tp(Ph,Me)Ni(η(2-t)BuNC)CH2Ph (5a) and Tp(Ph,Me)Ni(η(2-t)BuNC)CH2Si(CH3)3 (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species Tp(Ph,Me)NiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (Tp(Ph,Me)Ni(η(2)-CO)CH2TMS (7b) and Tp(Ph,Me)Ni(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.

4.
Inorg Chem ; 54(4): 1778-84, 2015 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-25607817

RESUMO

The first example of a ferrocene-chelating heteroscorpionate, [Li(THF)2][fc(PPh2)(BH[(3,5-Me)2pz]2)] ((fc(P,B))Li(THF)2, fc = 1,1'-ferrocenediyl) is described. Starting from a previously reported compound, fcBr(PPh2), a series of ferrocene derivatives, fc(PPh2)(B[OMe]2), [Li(OEt2)][fc(PPh2)(BH3)], [Li(THF)2][fc(PPh2)(BH[(3,5-Me)2pz]2)] (pz = pyrazole), was isolated and characterized. Compound (fc(P,B))Li(THF)2 allowed the synthesis of the corresponding nickel and zinc complexes, (fc(P,B))NiCl, (fc(P,B))NiMe, (fc(P,B))ZnCl, and (fc(P,B))ZnMe. All compounds were characterized by NMR spectroscopy, while the zinc and nickel complexes were also characterized by X-ray crystallography. The redox behavior of (fc(P,B))NiCl, (fc(P,B))NiMe, (fc(P,B))ZnCl, and (fc(P,B))ZnMe was studied by cyclic voltammetry and supported by density functional theory calculations.

5.
Inorg Chem ; 52(19): 11650-60, 2013 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-24024833

RESUMO

Syntheses of neutral halide and aryl vanadium bisimides are described. Treatment of VCl2(NtBu)[NTMS(N(t)Bu)], 2, with PMe3, PEt3, PMe2Ph, or pyridine gave vanadium bisimides via TMSCl elimination in good yield: VCl(PMe3)2(N(t)Bu)2 3, VCl(PEt3)2(N(t)Bu)2 4, VCl(PMe2Ph)2(N(t)Bu)2 5, and VCl(Py)2(N(t)Bu)2 6. The halide series (Cl-I) was synthesized by use of TMSBr and TMSI to give VBr(PMe3)2(N(t)Bu)2 7 and VI(PMe3)2(N(t)Bu)2 8. The phenyl derivative was obtained by reaction of 3 with MgPh2 to give VPh(PMe3)2(N(t)Bu)2 9. These neutral complexes are compared to the previously reported cationic bisimides [V(PMe3)3(N(t)Bu)2][Al(PFTB)4] 10, [V(PEt3)2(N(t)Bu)2][Al(PFTB)4] 11, and [V(DMAP)(PEt3)2(N(t)Bu)2][Al(PFTB)4] 12 (DMAP = dimethylaminopyridine, PFTB = perfluoro-tert-butoxide). Characterization of the complexes by X-ray diffraction, (13)C NMR, (51)V NMR, and V L(3,2)-edge X-ray absorption near-edge structure (XANES) spectroscopy provides a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene analogues. The electronic structure is dominated by π bonding to the imides, and localization of electron density at the nitrogen atoms of the imides is dictated by the cone angle and donating ability of the axial neutral supporting ligands. This phenomenon is clearly seen in the sensitivity of (51)V NMR shift, (13)C NMR Δδ(αß), and L3-edge energy to the nature of the supporting phosphine ligand, which defines the parameters for designing cationic group 5 bisimides that would be capable of breaking stronger σ bonds. Conversely, all three methods show little dependence on the variable equatorial halide ligand. Furthermore, this analysis allows for quantification of the electronic differences between vanadium bisimides and the structurally analogous mixed Cp/imide system CpV(N(t)Bu)X2 (Cp = C5H5(1-)).

6.
Dalton Trans ; 42(29): 10525-32, 2013 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-23748480

RESUMO

The synthesis of several nickel(II) and manganese(II) alkyl complexes supported by hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp(Ph,Me)) ligand is reported. The metal halide complexes Tp(Ph,Me)MnCl(CH3CN) (1) and Tp(Ph,Me)NiCl (4) were used as precursors for synthesis of Tp(Ph,Me)MnCH2Si(Me)3 (2), Tp(Ph,Me)MnCH2Ph (3), Tp(Ph,Me)NiCH2Si(Me)3 (5) and Tp(Ph,Me)NiCH2Ph (6). The resulting Mn(II) and Ni(II) alkyl complexes, 2-3 and 5-6, were characterized by X-ray crystallography, NMR spectroscopy, and FT-IR spectroscopy. X-ray crystallographic analysis revealed distorted tetrahedral geometries for complexes 2-3 and 5 with a κ(3)-Tp(Ph,Me). Complex 6, on the other hand, was found to have a distorted square planar geometry with κ(2)-Tp(Ph,Me) and an η(3)-benzyl ligand. Transformations of 4 and Tp(Ph,Me)CoCl (10) via treatment with NaN3 to yield Tp(Ph,Me)NiN3 (11), Tp(Ph,Me)CoN3 (12), along with the synthesis of (Tp(Ph,Me))2Ni (8) and Tp(Ph,Me)NiCl(3-Ph-5MepzH) (9) are also reported.

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