Synthesis, structures and ring-opening polymerization studies of new zinc chloride and amide complexes supported by amidinate heteroscorpionate ligands

Abstract

The reaction of the heteroscorpionate lithium salts [Li(pbpamd)(THF)] [pbpamd = N,N'-diisopropylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] and [Li(tbpamd)(THF)] [tbpamd = N-ethyl-N'-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] with 1 equivalent of ZnCl2 in THF affords very high yields of the neutral heteroscorpionate chloride zinc complexes [ZnCl(NNN)] (NNN = pbpamd 1 and tbpamd 2). Compound 1 was used as a convenient starting material for the synthesis of aromatic amide zinc compounds [Zn(NHAr)(pbpamd)], where NHAr = 4-methylphenylamide (NH-4-MeC6H4) 3, 2,4,6-trimethylphenylamide (NH-2,4,6-Me3C6H2) 4 and 2,6-diethylphenylamide (NH-2,6-Et2C6H3) 5, by the reaction of the corresponding aromatic primary amide lithium salts. Alternatively, aliphatic amide derivatives [Zn(NR2)(pbpamd)] (R = SiMe3 6, SiHMe2 7 and iPr 8) were cleanly prepared by reacting the amidine-heteroscorpionate compound Hpbpamd with the corresponding bis(amide) zinc complexes [Zn(NR2)2] (R = SiMe3, SiHMe2 and iPr). The single-crystal X-ray structures of complexes 2, 3 and 6 confirm a 4-coordinate arrangement in all cases, with the zinc metal surrounded in a distorted tetrahedral geometry and the heteroscorpionate ligands arranged in a kappa3 coordination mode. Whereas aliphatic amide heteroscorpionates 6-8 can act as efficient single-component initiators for the ring-opening polymerization of epsilon-caprolactone at room temperature, aromatic amide derivatives were not capable of yielding polymers even at high temperature. Epsilon-caprolactone is polymerized within minutes to give medium-high molecular weight polymers under mild conditions and with narrow polydispersities (M(w)/M(n) = 1.26). Polymer end group analysis shows that the polymerization mediated by aliphatic amide zinc complexes is initiated by amide transfer to the monomer.

Synthesis of new bulky bis(pyrazolyl)methane carboxylate (heteroscorpionate) ligands and their complexes with iron, manganese and nickel

“…130-132°C. 1 General procedure for conversion of 3,5-disubstituted-1H-pyrazoles into bis(3,5-bis(2-aryl)-1H-pyrazol-1-yl)methanes A stirred mixture of 3,5-bis(aryl)-1H-pyrazole 3 (1 mol), KOH (4 mol equiv. ), K 2 CO 3 (4 mol equiv.)…”

“…1 3,5-Bis(2,6-dimethoxyphenyl)-1H-pyrazole 31 (1.00 g, 2.94 mmol), KOH (0.658 g, 11.7 mmol), K 2 CO 3 (1.62 g, 11.7 mmol), benzyltriethylammonium chloride (0.109 g, 0.59 mmol), CH 2 Br 2 (30 mL) were treated according to the general procedure to afford a solid, which was purified by flash chromatography using EtOAc as eluent then the major fraction was recrystallised from pentane to afford the title compound 4d as a colourless solid (0.725 g, 71%). 1 General procedure for preparation of ethyl 2,2-bis(3,5-bis(aryl)-1H-pyrazol-1-yl)acetates 5 n BuLi (1.6 M in hexanes, 1.1 mol equiv.) was added to a stirred mixture of bis(3,5-diaryl)-1H-pyrazol-1-yl)methane 4 (1 mol equiv.)…”

“…144-145°C. 1 Bis(3,5-bis(2,6-dimethoxyphenyl)-1H-pyrazol-1-yl)methane 4d. A mixture of 3,5-bis(2,6-dimethoxyphenyl)-1H-pyrazole 3d (1.00 g, 2.94 mmol), KOH (0.658 g, 11.7 mmol), K 2 CO 3 (1.62 g, 11.7 mmol) and TEBAC (0.109 g, 0.59 mmol) in CH 2 Br 2 (30 mL) was treated by the general procedure to afford a solid, which was purified by flash chromatography using EtOAc as eluent then the major fraction was recrystallised from pentane to afford the title compound 4d as a colourless solid (0.725 g, 71%).…”

“…Their coordination chemistry has been explored with metals such as Zn, Y, Ti and Sc in the context of catalysis 1,2 whereas with Tc and Re 3-6 the focus moved in part to radiopharmaceuticals. The coordination chemistry of this class of ligand has been the subject of several reviews.…”

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

“…These trends are frequently observed in ROP of cyclic esters. [45][46][47] In an attempt to distinguish between a less-controlled polymerization due to slow initiation versus transesterification, the single-component initiator 5 was studied (Table 1, entry 12). M w /M n for the resulting polymer was not significantly different to that obtained for PLA under similar conditions using 4/BnOH (Table 1, Entry 11).…”