No abstract

A series of Ti(IV), Zr(IV) and Hf(IV) benzotriazole phenoxide (BTP) complexes were synthesized and characterized by various spectroscopic techniques, elemental analysis and X-ray crystallography. The monosubstituted Zr(IV) BTP complexes [(μ-L)Zr(O(i)Pr)3]2 1-3 [L = (C1)BTP-H (1), (TCl)BTP-H (2), (pent)BTP-H (3)] and tetrasubstituted Zr(IV), Hf(IV) complexes ZrL4 4-6 [L = (C1)BTP-H (4), (TCl)BTP-H (5), (pent)BTP-H (6)] and HfL4 7-9 [L = (C1)BTP-H (7), (TCl)BTP-H (8), (pent)BTP-H (9)] were prepared by the reaction of Zr(O(i)Pr)4·((i)PrOH) and Hf(O(t)Bu)4 in toluene with the respective ligands in different stoichiometric proportions. The reaction between BTP and TiCl4 and ZrCl4 and HfCl4 in a 2 : 1 stoichiometric reaction resulted in the formation of disubstituted group IV chloride complexes L2MCl2 10-12 [L = (C1)BTP-H, M = Ti, Zr and Hf]. The molecular structures of complexes 1, 4, 7, 10, 11, and 12 were determined by single-crystal X-ray studies. The X-ray structure of 1 reveals a dimeric Zr(IV) complex containing a Zr2O2 core bridged through the oxygen atoms of the phenoxide groups. Each Zr atom is distorted from an octahedral symmetry. These complexes were found to be active towards the ring-opening polymerization (ROP) of L-lactide (L-LA) and rac-lactide (rac-LA). Complex 1 produced highly heterotactic poly(lactic acid) (PLA) from rac-LA under melt conditions with narrow molecular weight distributions (MWDs) and well controlled number average molecular weights (M(n)). Additionally, epoxide polymerizations using rac-cyclohexene oxide (CHO), rac-propylene oxide (PO), and rac-styrene oxide (SO) were also carried out with these complexes. The yield and molecular weight of the polymer was found to increase with the extension of reaction time. Compounds 1-12 were activated by methylaluminoxane (MAO) and show good activity for ethylene polymerization and produced high molecular weight polyethylene.

The design of facile synthetic routes to well-defined block copolymers (BCPs) from direct polymerization of one-pot comonomer mixtures, rather than traditional sequential additions, is both fundamentally and technologically important. Such synthetic methodologies often leverage relative monomer reactivity toward propagating species exclusively and therefore are rather limited in monomer scope and control over copolymer structure. The recently developed compounded sequence control (CSC) by Lewis pair polymerization (LPP) utilizes synergistically both thermodynamic (K eq ) and kinetic (k p ) differentiation to precisely control BCP sequences and suppress tapering and misincorporation errors. Here, we present an in-depth study of CSC by LPP, focusing on the complex interplay of the fundamental K eq and k p parameters, which enable the unique ability of CSC-LPP to precisely control comonomer sequences across a variety of polar vinyl monomer classes. Individual Lewis acid equilibrium and polymerization rate parameters of a range of commercially relevant monomers were experimentally quantified, computationally validated, and rationalized. These values allowed for the judicious design of copolymerizations which probed multiple hypotheses regarding the constructive vs conflicting nature of the relationship between K eq and k p biases, which arise during CSC-LPP of comonomer mixtures. These relationships were thoroughly explored and directly correlated with resultant copolymer microstructures. Several examples of higher-order BCPs are presented, further demonstrating the potential for materials innovation offered by this methodology.

The syntheses and structural characterization of the CS 2 -metal complexes [(η 5 -C 5 Me 5 M)(η 2 -S 2 CH 2 )(η 3 -S 2 CH)] (1: M = Mo; 2: M = W), which feature partially and fully reduced CS 2 , are reported. In addition, the cis and trans isomers of the dimetallic (sulfido)molybdenum complexes [(η 5 -C 5 Me 5 Mo) 2 (μ-S 2 CH 2 S) 2 ] (3-cis and 4-trans) are described. The [Mo 2 S 4 ] cores of 3-cis and 4-trans represent paddlewheel-like arrays. All the new compounds were characterized in solution by mass spectrometry, IR spectroscopy, and 1 H and 13 C NMR spectroscopy. Their structural architectures were established by X-ray crystallographic [a] 4914 successive addition of reduced CS 2 to the Mo and W centers leads to the release of borane and finally the formation of 1 and 2, respectively. Crystal Data for 2: C 12 H 18 S 4 W, M r = 474.35, triclinic, space group P1, a = 7.1497(7) Å, b = 8.3944 (8) Å, c = 13.2781(13) Å, α = 82.816(3)°, = 80.741(3)°, γ = 67.621(3)°, V = 725.52(12) Å 3 , Z = 2, ρ calcd. = 2.171 g cm -3 , μ = 8.512 mm -1 , F(000) = 456, R 1 = 0.0144, wR 2 = 0.0339, 3320 independent reflections (2θ ≤ 50.48°), and 159 parameters. Crystal Data for 3-cis: C 22 H 34 Mo 2 S 6 , M r = 682.73, monoclinic, space group P2 1 /n, a = 8.4477(8) Å, b = 30.668(3) Å, c = 10.5569(9) Å, = 108.643(4)°, V = 2591.5(4) Å 3 , Z = 4, ρ calcd. = 1.750 g cm -3 , μ = 1.461 mm -1 , F(000) = 1384, R 1 = 0.0786, wR 2 = 0.1531, 5709 independent reflections (2θ ≤ 50°), and 212 parameters. Crystal Data for 4-trans/5: 0.5(C 22 H 34 S 6 Mo 2 ) + 0.5(C 22 H 30 S 6 Mo 2 ), M r = 680.71, monoclinic, space group C2/c, a = 18.9517(4) Å, b = 9.5854(2) Å, c = 15.9295(3) Å, = 114.1740(10)°, V = 2639.98(9) Å 3 , Z = 4, ρ calcd. = 1.713 g cm -3 , μ = 1.434 mm -1 , F(000) = 1376, R 1 = 0.0368, wR 2 = 0.0837, 2587 independent reflections (2θ ≤ 52°), and 155 parameters.Computational Details: Quantum-chemical calculations of the DFT type were performed on model compounds 1′, 2′, 3′-cis, and 4′trans (the Cp analogues of 1, 2, 3-cis, and 4-trans, respectively) with the Gaussian 09 program package. [41] All compounds were fully optimized in the gas phase (no solvent effects) with and without symmetry constraints with the PBE0 functional [42] and a triple-quality Def2TZVP basis set for all atoms. The WBIs [22] were obtained from an NBO [21] analysis. The AOMix program [43] was used for the molecular orbital (MO) composition analysis, and the Chemcraft software [44] was used for visualization. Multiwfn V.3.1 [45] was used for the topological analyses of the electron densities.

No abstract