ABSTRACT:A zirconium precatalyst, (salfan)Zr(O t Bu)2 (salfan = 1,1'-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene), shows activity for the redox controlled block copolymerization of L-lactide and cyclohexene oxide. The role of the oxidant is examined and several diblock (AB, BA) and triblock copolymers (ABA and BAB) were synthesized and characterized.

The dinuclear complex {[mu-kappa(1),kappa(3)-B(mim(Bu(t)))(3)]Pd}(2), which features a Pd-->B dative bond, may be obtained by the reaction of [Tm(Bu(t))]K with Pd(OAc)(2); treatment of {[mu-kappa(1),kappa(3)-B(mim(Bu(t)))(3)]Pd}(2) with PMe(3) affords the mononuclear boratrane derivative [kappa(4)-B(mim(Bu(t)))(3)]Pd(PMe(3)), for which a molecular orbital analysis indicates that the palladium center possesses a d(8) configuration.

Linear nickel nitrosyl compounds supported by tridentate nitrogen and selenium ligands, namely the tris(3,5-dimethylpyrazolyl)hydroborato and tris(2-seleno-1-mesitylimidazolyl)hydroborato complexes, [TpMe2]NiNO and [TseMes]NiNO, have been synthesized and structurally characterized by X-ray diffraction. Computational studies demonstrate that the linear nitrosyl ligand behaves as a trivalent X3 ligand such that the Ni-N interaction has multiple bond character.

Several aspects of the copolymerization of L-lactide (LA) and cyclohexene oxide (CHO) by a redox switchable zirconium catalyst, (salfan)Zr(O t Bu)2 (salfan = 1,1'-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene), were examined such as the mechanism of cyclohexene oxide polymerization, the reactivity of [(salfan)Zr(O t Bu)2][BAr F ] (BAr F = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) toward lactide, and co-monomer effects on polymerization rates. Experimental methods and DFT calculations indicate that the likely mechanism of CHO polymerization by [(salfan)Zr(O t Bu)2][BAr F ] is coordination insertion and not a cationic pathway, as employed by the majority of cationic catalysts. Furthermore, DFT calculations showed that the polymerization of LA by [(salfan)Zr(O t Bu)2][BAr F ] is not thermodynamically favored, in agreement with experimental results. Lastly, we found that the conversion times of CHO or LA from block to block correlate with the amount of monomer left from the previous block rather than other factors.

The synthesis and characterization of (thiolfan*)Zr(OtBu)2 (thiolfan* = 1,1′-di(2,4-di-tert-butyl-6-thiophenoxide)ferrocene) is reported, as well as its activity toward the ring-opening polymerizations of l-lactide and ε-caprolactone.

Abstract. An indium complex supported by a ferrocene-derived Schiff base ligand has an unprecedented high activity toward ε-caprolactone, δ-valerolactone, and β-butyrolactone. L-lactide, D,L-lactide, and trimethylene carbonate polymerizations also showed moderate to high activity.Over the past two decades, the ring-opening polymerization of cyclic esters has been increasingly studied because of the promise to produce biodegradable polymers from biomass. In our recent studies, a cerium complex supported by a Schiff base ligand with a ferrocene backbone polymerized L-lactide in a controlled fashion. 24 Phosphinimine analogues with yttrium and indium also demonstrated good activity in lactide and trimethylene carbonate polymerizations. 22 Therefore, we decided to combine indium's activity with the Schiff base, ferrocene-derived ligand in order to study the activity of the resulting complexes toward a broad range of cyclic ester polymerizations. Additional motivation was found from recent studies that point to the biocompatibility, robustness, and high activity of indium catalysts in the ring opening polymerization of cyclic esters. 10,25 Herein, we report a ferrocene-derived Schiff base indium complex that possesses a remarkable range of activity toward cyclic esters and exceptionally fast polymerization rates with lactones. Compound (salfen)In(O t Bu) (salfen = 1,1'-di(2,4-di-tert-butyl-6-iminephenoxy)ferrocene) represents the first indium precatalyst capable of δ-valerolactone polymerization and the most active indium catalyst to date in the polymerization of β-butyrolactone and ε-caprolactone. The polymerization rates of ε-caprolactone are even competitive with those of current industrial catalysts.Compound (salfen)In(O t Bu) was synthesized from the reaction of (salfen)InCl and freshly sublimed KO t Bu. In turn, (salfen)InCl was synthesized by combining InCl3 with K2(salfen), which was generated from H2(salfen) and two equivalents of KH (Eq 1). Needle crystals of (salfen)InCl were isolated from a diethyl ether solution. The solid state molecular structure (Figure 1) shows a distorted octahedral indium center and a THF molecule coordinated trans to the chloride ligand. Similarly to the phosphinimine indium chloride analogue previously reported by us, 22 a long In-Fe distance (3.98 Å) and a staggered configuration of the Cp rings were apparent. Elongation of the In-heteroatom distances compared to other compounds, such as (salen)InCl (salen = N,N ' -bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine (rac-or (R,R)-H2(ONNO))) 9 and (phosfen)In(OPh) (phosfen = 1,1'-di(2-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), 22 by about 0.25 Å possibly compensates for the distortion caused by the staggered Cp rings.

An electrochemically controlled synthesis of multiblock copolymers by alternating the redox states of (salfan)Zr-(O t Bu) 2 (salfan = 1,1′-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene) is reported. Aided by electrochemistry with a glassy carbon working electrode, an in situ potential switch alters the catalyst's oxidation state and its subsequent monomer (Llactide, β-butyrolactone, or cyclohexene oxide) selectivity in one pot. Various multiblock copolymers were prepared, including an ABAB tetrablock copolymer, poly(cyclohexene oxide-b-lactide-bcyclohexene oxide-b-lactide), and an ABC triblock copolymer, poly(hydroxybutyrate-b-cyclohexene oxide-b-lactide). The polymers produced using this technique are similar to those produced via a chemical redox reagent method, displaying moderately narrow dispersities (1.1−1.5) and molecular weights ranging from 7 to 26 kDa.

SummaryNeutral 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.