Comments on the ring-opening polymerization of morpholine-2,5-dione derivatives by various metal catalysts and characterization of the products formed in the reactions involving R2SnX2, where X = OPri and NMe2 and R = Bun, Ph and p-Me2NC6H4

(3S,6S)-3-Isopropyl-6-methyl-morpholine-2,5-dione (1), and (3S,6S)-3,6-diinethyl-morpholine-2,5-dione (2), do not enter into ring-opening polymerization reactions with metal catalyst precursors commonly employed for lactides, and with Sn(II) octanoate, only low molecular weight oligomers are obtained. Reactions with R2SnX2 compounds, where R = Ph, Bu-n and p-Me2NC6H4 and X = OPr1 or NMe2, reveal that ring-opening of the morpholine-2,5-diones does occur, but that polymerization is terminated by the formation of kinetically-inert products such as {Ph2Sn[mu,eta(3)-OCH(Me)CONCH(Pr-1)-COOPr1]}(2) (3), and {[Bu-n)(2)Sn[mu,eta(3)-OCH(Me)CONCH(Me)CONMe2]}(2) (4), with elimination of HX. Ph3SnOPr1 is seen to react reversibly with morpholine-2,5-diones in toluene-d(8) by H-1 NMR spectroscopy while (Bu-n)(3)SnNMe2 reacts by ring opening to give (Bu-n)(3)SnOCH(Me)C(O)NHCHMeC-(O)NMe2. The new organotin compounds have been characterized by H-1, C-13{H-1} and Sn-118 NMR spectroscopy and compounds 1, 2, 3 and 4 by single crystal X-ray crystallography.