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Synthesis, Structure, and Reactivity of Alkylzinc Complexes Stabilized with 1,1,3,3-Tetramethylguanidine

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journal contribution
posted on 02.04.2020, 15:42 by Scott D. Bunge, Jacob M. Lance, Jeffrey A. Bertke
The synthesis and structural characterization of several novel alkylzinc guanidinate, alkoxide, and aryloxide complexes are reported. 1,1,3,3-Tetramethylguanidine, H-TMG, was successfully reacted with (Et)2Zn in a 4:3 and a 1:1 ratio to yield the corresponding linear [Zn3(μ-TMG)4(Et)2] (1) and cyclic [Zn(μ-TMG)(Et)]3 (2) complexes. Further investigations have shown 2 to react with alcohols, HOR, to form complexes with the general formula [Zn(Et)(OR)(H-TMG)]n, where OR = OCH2C(CH3)3 {ONep, n = 2 (3)}, OC6H3(CMe3)2-2,6 {DBP, n = 1 (4)}, and OC6H2But2-2,6-Me-4 {DBP-4-Me, n = 1 (5)}. The addition of (Et)2Zn to a solution of 4 yielded the unusual [Zn2(μ-TMG)(μ-DBP)(Et)2] (6). Complex 5 readily reacts with the alcohol, HOR‘, yielding dinuclear compounds with the formula [Zn(μ-OR‘)(DBP-4-Me)(H-TMG)]2, where OR‘ = OCH3 (OMe, 7) and OCH2CH3 (OEt, 8). Additionally, compound 4 was reacted with EtOH, yielding a complex with the formula [Zn(μ-OEt)(DBP)(H-TMG)]2 (9). The utility of compound 8 for use as a catalyst in the ring-opening polymerization of rac-lactide was additionally investigated. Compounds 19 were characterized by single-crystal X-ray diffraction. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FT-IR spectroscopy, and 1H and 13C NMR studies. The polymer was characterized by multi-nuclear NMR spectroscopy and MALDI-TOF mass spectrometry.