The synthesis of retinol initiated polylactide (PLA) by ring opening polymerization (ROP) of l-lactide via in situ calcium alkoxide formation with all-trans-retinol and Ca[N(SiMe3)2]2(THF)2 is described.

The comb polymers are synthesized in three independent steps by ROP, CROP, and RAFT.

N-(2,6-Diisopropylphenyl)-N'-(2-pyridylethyl)pivalamidine (Dipp-N=C(tBu)-N(H)-C2 H4 -Py) (1), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp-N=C(tBu)-N-C2 H4 -Py}] (6), [Mg{Dipp-N=C(tBu)-N-C2 H4 -Py}2 ] (3), and heteroleptic [{(Me3 Si)2 N}Ae{Dipp-N=C(tBu)-N-C2 H4 -Py}], with Ae being Ca (2 a) and Sr (2 b). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β-metalation and an immediate deamidation reaction yielding [(thf)2 Na{Dipp-N=C(tBu)-N(H)}] (4 a) or [(thf)2 K{Dipp-N=C(tBu)-N(H)}] (4 b), respectively, as well as 2-vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI2 in tetrahydrofuran yields N-(2,6-diisopropylphenyl)pivalamidine (Dipp-N=C(tBu)-NH2 ) (5), or [(thf)4 Ca{Dipp-N=C(tBu)-N(H)}2 ] (7), respectively. The reaction of AN(SiMe3 )2 (A=Na, K) with less bulky formamidine Dipp-N=C(H)-N(H)-C2 H4 -Py (8) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 a) or [(thf)K{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 b), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β-metalation/deamidation of N-(2-pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single-crystal X-ray structure analysis and are maintained in solution.

Metalation of 1,3-bis(2,4,6-trimethylphenyl)triazene () with KH, Mg(nBu)2, and [(L)2Ae{N(SiMe3)2}2] (Ae/L = Ca/thf, Sr/dme) yields the dinuclear complexes [(thf)2K{μ-N3(Mes)2}]2 () and [(dme)K{μ-N3(Mes)2}]2 () as well as mononuclear [(thf)2Mg{N3(Mes)2}2] (), [(tmeda)Mg(nBu){N3(Mes)2}] (), [(thf)2Ca{N3(Mes)2}2] (), and [(tmeda)Sr{N3(Mes)2}2] (), respectively, with high yields depending on applied stoichiometry and donor solvent [tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), 1,2-bis(dimethylamino)ethane (TMEDA)]. The 1,3-bis(2,4,6-trimethylphenyl)triazene () forms a strand-like structure in the solid state, stabilized by N-HN hydrogen bridges and intermolecular π-stacking of the mesityl groups. The 1,3-bis(2,4,6-trimethylphenyl)triazenide anions of the s-block metal complexes show charge delocalization within the triazaallylic systems and act as bidentate chelate ligands.