Toward Stereoselective Lactide Polymerization Catalysts: Cationic Zinc Complexes Supported by a Chiral Phosphinimine Scaffold

Abstract

The P-stereogenic phosphinimine ligands (dbf)MePhP═NAr (7: Ar = Dipp; 8: Ar = Mes; dbf = dibenzofuran, Dipp = 2,6-diisopropylphenyl, Mes = 2,4,6-trimethylphenyl) were synthesized as racemates via reactions of the parent phosphines (rac)-(dbf)MePhP (6) with organoazides. The ligands 7 and 8 were protonated by Brønsted acids to afford the aminophosphonium borate salts [(7)-H][BAr(4)] (9: Ar = C(6)F(5); 11: Ar = Ph) and [(8)-H][BAr(4)] (10: Ar = C(6)F(5); 12: Ar = Ph). The protonated ligands 9 and 10 were active toward alkane elimination reactions with diethylzinc and ethyl-[methyl-(S)-lactate]zinc to give the heteroleptic complexes [{(dbf)MePhP═NAr}ZnR][B(C(6)F(5))(4)] (Ar = Dipp, 13: R = Et; 15: R = methyl-(S)-lactate; Ar = Mes, 14: R = Et; 16: R = methyl-(S)-lactate). By contrast, reaction of the tetraphenylborate derivative 11 with diethylzinc yielded a phenyl transfer product, [(dbf)MePhP═NDipp]ZnPh(2) (17). Complex 15 was found to catalyze the ring-opening polymerization of rac-lactide.

ZnII Chlorido Complexes with Aliphatic, Chiral Bisguanidine Ligands as Catalysts in the Ring‐Opening Polymerisation of rac‐Lactide Using FT‐IR Spectroscopy in Bulk

“…These systems can show high activity in the polymerisation and produce colourless polymers. Phosphinimines, iminopyridines, trispyrazolylmethanes, carbenes, piperidinyl‐benzyl‐anilines and guanidine systems have been used as neutral ligand compounds. The group of Jeong investigated dichloridozinc complexes bearing ligands based on camphorylimine.…”

β‐Diketiminato–Alkaline Earth Cationic Complexes: Synthesis, Structures, Lactide Polymerization and Unusual Oxidative Reactivity of the Ancillary Ligand

“…By contrast, occurrences of discrete Zn, Mg and Ae cationic complexes remain rather scarce. Recent achievements14 with discrete cations include the cyclohydroamination of aminoalkenes catalyzed by (aminotroponiminato)Zn complexes,15 the synthesis of allylcalcium cations,16 and the ROP of cyclic esters promoted by Zn–Mg17 and Ca–Ba18 cationic complexes bearing neutral (bis)phosphinimine17a–17e or monoanionic amino ether phenolate ancillary ligands 17f,18. Somewhat surprisingly, well‐defined Ae cations supported by the ubiquitous {BDI i Pr } – β‐diketiminate have not been reported to date.…”

Crystal structures of [IrCl2(NHCHPh)((dppm)(C(N2dppm))-κ3 P,C,P′)]Cl·5.5MeCN and [IrI(NHCHPh)(((dppm)C(N2))-κ2 P,C)(dppm-κ2 P,P′)]I(I3)·0.5I2·MeOH·0.5CH2Cl2: triazene fragmentation in a PCN pincer iridium complex

“…Both the N1-C1 bond length [1.280 (5) Å ] and the N1-N2 bond length [1.445 (5) Å ] are typical for a C N double bond and an N-N single bond, respectively. The P3-N2 bond length [1.586 (4) Å ] is in the range of P N double bonds observed for iminophosphoranes (Ireland et al, 2010;Peng et al, 2011;Sun et al, 2011). Corresponding bond lengths in other phosphazene systems exhibit values of 1.62-1.64 Å for P-N, 1.36-1.39 Å for N-N and 1.31 Å for C-N. (Bethell et al, 1992;Supurgibekov et al, 2011;Galina et al, 2013;Nikolaev et al, 2016).…”