Synthesis, Structure, and Ring‐Opening Polymerization Catalysis of Zinc Complexes Containing Amido Phosphinimine Ligands

Abstract

A series of amido phosphinimine ligands of the type [(NAr1)‐o‐(Ph2P=NAr2)C6H4]– (2a: Ar1 = 2,6‐C6H3iPr2, Ar2 = 2,6‐C6H3iPr2; 2b: Ar1 = 2,6‐C6H3iPr2, Ar2 = 2,4,6‐C6H2Me3; 2c: Ar1 = 2,6‐C6H3Me2, Ar2 = 2,4,6‐C6H2Me3), which are electronic variations of monoanionic β‐diketiminates, have been employed to examine the coordination chemistry of zinc. Alkane elimination reactions of ZnR2 (R = Me, Et) with H[2a–c] in toluene or ethereal solutions at –35 °C afforded cleanly the corresponding organozinc complexes [2a–c]ZnMe (3a–c) and [2a–c]ZnEt (4a–c). Deprotonation of H[2a–c] with nBuLi at –35 °C generated [2a–c]Li (5a–c), which may be isolated as either solvent‐free complexes or solvated adducts depending on the reaction solvents employed (toluene, OEt2, or THF). Metathetical reactions of 5a·OEt2 with Zn(OAc)2 in THF at –35 °C produced [2a]Zn(OAc) (6a). These amido phosphinimine derivatives all display solution Cs symmetry on the NMR timescale. The mononuclear nature of the three‐coordinate alkyls 3–4 and four‐coordinate acetate 6a was confirmed by single‐crystal X‐ray diffraction analyses. Interestingly, the alkyl complexes 3a–c and 4a–c are all active initiators for the catalytic ring‐opening polymerization of ϵ‐caprolactone, whereas the acetate 6a is comparatively inactive.

The Role of Nitrogen Donors in Zinc Catalysts for Lactide Ring-Opening Polymerization

“…In particular, zinc complexes supported by a wide array of ligands have been prevalent due to their ease of synthesis, low cost and toxicity, and relative stability toward monomer impurities . Zinc complexes supported by ketiminate, tripodal, polyamino, binolates, amino acid, N -heterocyclic carbene, and phosphinimine, among others, have been reported.…”

Reactivity of N-Phosphinoguanidines of the Formula (HNR)(Ph2PNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from N-Phosphinoguanidinates to Phosphinimine-Amidinates

“…The P1–N2 distance in the phosphinimine moiety, of 1.603(1) Å, is comparable to those measured in related amido-phosphinimide compounds of the formula [Al­{κ 2 - N,N ′-1,2-C 6 H 4 (NDipp)­(Ph 2 P = NR)}­R′ 2 ] (R = Mes or Dipp, SiMe 3 ; R′ = H, Me, Et, or t Bu), ca. 1.60–1.61 Å and compatible with a PN double bond but slightly elongated compared to “free” amino-phosphinimines 1,2-C 6 H 4 (NHAr)­(Ph 2 P = NR) (Ar = Dipp or 2,6-xylyl and R = Mes, 2- i Pr–C 6 H 4 , Dipp, or SiMe 3 ), with P–N distances in the range 1.55–1.57 Å. , This may account for the almost identical Al–N distances measured in 3a of 1.926(1) Å for Al–N amidinate and 1.909(1) Å for Al–N phosphinimine , implying charge delocalization along both Al–N bonds (a partial negative charge on both coordinated N atoms). Similar Al–N distances were also found for the aforementioned amido-phosphinimine Al compounds .…”