Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONER1,R2]-) {[R1 = tBu, R2 = Me, E = NMe (L1); R1= R2 = tBu, E = NMe (L2); R1 = R2 = tBu, E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1H, 13C{1H}, and 27Al NMR spectroscopy, and X-ray crystallography. Reactions of AlMe3 with two equivalents of L1H-L3H gave {[ONER1,R2]2AlMe} (1–3), while reaction of Et2AlCl with two equivalents of L1H and L3H afforded {[ONER1,R2]2AlCl} (4 and 5) as monometallic complexes. The catalytic activity of complexes 1–3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogues for ROP of rac-lactide. Characteristics of the polymer as well as polymerization kinetics and mechanism were studied. Polymer end-group analyses were achieved using 1H NMR spectroscopy and MALDI-TOF MS. Eyring analyses were performed, and the activation energies for the reactions were determined, which were significantly lower for 1 and 2 compared with 3. This could be for several reasons: (1) the methylamine (NMe) group of 1 and 2, which is a stronger base than the ether (O) group of 3, might activate the incoming monomer via noncovalent interactions, and/or (2) the ether group is able to temporarily coordinate to the metal center and blocks the vacant coordination site toward incoming monomer, while the amine cannot do this. Preliminary studies using 4 and 5 toward copolymerization of cyclohexene oxide with carbon dioxide have been performed. 4 was inactive and 5 afforded polyether carbonate (66.7% epoxide conversion, polymer contains 54.0% carbonate linkages)

Tris(amido)tingold complexes in different oxidation states: first structural characterization of a Sn-Au-Au-Sn linear chain

The reaction of MeSi{Me2SiN(Li)(p-tol)}3(Et2O)2 with SnCl2 in a 1:1 molar ratio leads the tris(amido)stannate MeSi{Me2SiN(p-tol)}3SnLi(Et2O) (1), which further reacts with neutral AuCl(PPh3) and anionic PPNAuCl2, PPNAuRCl (R = C6F5. mes), and chlorogold(I) complexes yielding Au(MeSi{Me2SiN(p-tol)}3Sn)(PPh3) (2) and PPNAu(MeSi{Me2SiN(p-tol)}3Sn)2 (3) and Au(MeSi{Me2SiN(p-tol)}3Sn)(R) (R = C6F5, 4; R = mes, 5), respectively. The reaction of 1 with the dinuclear gold(II) derivative Au2(CH2PPh2CH2)2Cl 2 in a 1:2 ratio affords Au2(CH2PPh2CH2)2(Me 2i{Me2SiN(p-tol)}3Sn)2 (6). In a similar way but starting from PPNAu(C6F5)3,Cl and reacting with 1 in a 1:1 ratio, the Au(III) complex PPNAu(MeSi{Me2SiN(p-tol)}3Sn)(C6F 5)3 (7) has been obtained. X-ray crystal structure analyses were performed for compounds 2 and 6, establishing the Sn-Au bonds d(Au-Sn) = 2.5651(13) and 2.6804(13) Ã , respectively). Compound 6 has a nearly linear Sn-Au-Au-Sn array and features the first examples of tin-gold(II) bonds