Synthetic pathways to (salcy)CoX (salcy = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane; X = halide or carboxylate) complexes are described. Complexes (R,R)-(salcy)CoCl, (R,R)-(salcy)CoBr, (R,R)-(salcy)CoOAc, and (R,R)-(salcy)CoOBzF(5) (OBzF(5) = pentafluorobenzoate) are highly active catalysts for the living, alternating copolymerization of propylene oxide (PO) and CO(2), yielding poly(propylene carbonate) (PPC) with no detectable byproducts. The PPC generated using these catalyst systems is highly regioregular and has up to 99% carbonate linkages with a narrow molecular weight distribution (MWD). Inclusion of the cocatalysts [PPN]Cl or [PPN][OBzF(5)] ([PPN] = bis(triphenylphosphine)iminium) with complex (R,R)-(salcy)CoCl, (R,R)-(salcy)CoBr, or (R,R)-(salcy)CoOBzF(5) results in remarkable activity enhancement of the copolymerization as well as improved stereoselectivity and regioselectivity with maximized reactivity at low CO(2) pressures. In the case of [PPN]Cl with (R,R)-(salcy)CoOBzF(5), an unprecedented catalytic activity of 620 turnovers per hour is achieved for the copolymerization of rac-PO and CO(2), yielding iso-enriched PPC with 94% head-to-tail connectivity. The stereochemistry of the monomer and catalyst used in the copolymerization has dramatic effects on catalytic activity and the PPC microstructure. Using catalyst (R,R)-(salcy)CoBr with (S)-PO/CO(2) generates highly regioregular PPC, whereas using (R)-PO/CO(2) with the same catalyst gives an almost completely regiorandom copolymer. The rac-PO/CO(2) copolymerization with catalyst rac-(salcy)CoBr yields syndio-enriched PPC, an unreported PPC microstructure. In addition, (R,R)-(salcy)CoOBzF(5)/[PPN]Cl copolymerizes (S)-PO and CO(2) with a turnover frequency of 1100 h(-1), an activity surpassing that observed in any previously reported system.

Synthetic routes to a series of new (salen-1)CoX (salen-1 = N,N'-bis(salicylidene)-1,2-diaminoalkane; X = halide or carboxylate) species are described and the X-ray crystal structures of two (salen-1)CoX (salen- = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane; X = Cl, I) complexes are presented. (R,R)-(salen-)CoX (X = Cl, Br, I, OAc, pentafluorobenzoate (OBzF(5))) catalysts are active for the copolymerization of cyclohexene oxide (CHO) and CO(2), yielding syndiotactic poly(cyclohexene carbonate) (PCHC), a previously unreported PCHC microstructure. Variation of the salen ligand and reaction conditions, as well as the inclusion of [PPN]Cl ([PPN]Cl = bis(triphenylphosphine)iminium chloride) cocatalysts, has dramatic effects on the polymerization rate and the resultant PCHC tacticity. Catalysts rac-(salen-)CoX (salen- = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminopropane; X = Br, OBzF(5)) have high activities for CHO/CO(2) copolymerization, yielding syndiotactic PCHCs with up to 81% r-centered tetrads. Using Bernoullian statistical methods, PCHC tetrad and triad sequences were assigned in the (13)C NMR spectra of these polymers in the carbonyl and methylene regions, respectively.

A highly active cobalt complex ((salph)CoOAc; salph = N,N'-bis(3,5-di-tert-butylsalicylidine-1,2-benzenediamine)) was discovered for the isospecific polymerization of rac-propylene oxide.

Synthetic routes to a series of new (salen)CoX (salen ¼ N,N 0 -bis(salicylidene)-1,2-diaminoalkane; X ¼ Br or pentafluorobenzoate (OBzF 5 )) species are described. Several of these complexes are active for the copolymerization of propylene oxide (PO) and CO 2 , yielding regioregular poly(propylene carbonate) (PPC) without the generation of propylene carbonate byproduct. Variation of the salen ligand, as well as the inclusion of organic-based ionic or Lewis basic cocatalysts, has dramatic effects on the resultant (salen) CoX catalytic activity. Highly active (R,R)-(salen-1)CoOBzF 5 (salen-1 ¼ N,N 0 -bis(3,5di-tert-butylsalicylidene)-1,2-diaminocyclohexane) catalysts with [Ph 4 P]Cl or [PPN]Y ([PPN] ¼ bis(triphenylphosphine)iminium; Y ¼ Cl or OBzF 5 ) cocatalysts exhibited turnover frequencies up to 720 h À1 for rac-PO/CO 2 copolymerization, yielding PPC with greater than 90% head-to-tail connectivity. Additionally, the (R,R)-(salen-1)CoOBzF 5 / [PPN]Cl catalyst system demonstrated a k rel of 9.7 for the enchainment of (S)-over (R)-PO when the copolymerization was carried out at low temperatures. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5182-5191, 2006

Flavin mononucleotide (FMN, 1) provides a dynamic conformational probe for studying the covalent cross-linking of dopants into silica. Excitation of FMN 1 leads to photodecomposition only when the side chain is in an appropriate geometry to allow a six-membered ring transition state. Our investigations indicate that the rate of photodecomposition dramatically changes in the sol-gel through the course of the gelation and aging process. Rapid changes in the decomposition rate were observed in the sol very early in the gelation process, indicating that the hydroxyl groups of 1 become covalently fixed within the silicate matrix and that silicate structure is formed around this site very early in the sol-gel process.