Phototriggered DNA phosphoramidate ligation in a tandem 5'-amine deprotection/3'-imidazole activated phosphate coupling reaction.

We report the preparation and use of an N-methyl picolinium carbamate protecting group for applications in a phototriggered nonenzymatic DNA phosphoramidate ligation reaction. Selective 5'-amino protection of a modified 13-mer oligonucleotide is achieved in aqueous solution by reaction with an N-methyl-4-picolinium carbonyl imidazole triflate protecting group precursor. Deprotection is carried out by photoinduced electron transfer from Ru(bpy)(3)(2+) using visible light photolysis and ascorbic acid as a sacrificial electron donor. Phototriggered 5'- amino oligonucleotide deprotection is used to initiate a nonenzymatic ligation of the 13-mer to an imidazole activated 3'-phospho-hairpin template to generate a ligated product with a phosphoramidate linkage. We demonstrate that this methodology offers a simple way to exert control over reaction initiation and rates in nonenzymatic DNA ligation for potential applications in the study of model protocellular systems and prebiotic nucleic acid synthesis.

Photorelease of primary aliphatic and aromatic amines by visible-light-induced electron transfer.

Visible-light-absorbing tris(bipyridyl)ruthenium(II) has been used to mediate electron transfer to N-methylpicolinium carbamates that undergo C-O bond fragmentation followed by spontaneous carbon dioxide release to give free amines. Release of several aliphatic and aromatic primary amines has been demonstrated under mild conditions using visible light.

Cyclopolymerization of Nonconjugated Dienes with a Tridentate Phenoxyamine Hafnium Complex Supported by an sp(3) -C Donor: Isotactic Enchainment and Diastereoselective cis-Ring Closure.

Cyclopolymerization of nonconjugated dienes produces poly(methylene-1,3-cycloalkanes) and provides a pathway to a number of stereochemically complex polymers. Activation of a diastereomeric mixture of a six-membered metallacycle complex (rac-1) in the presence of 1,5-hexadiene produced poly(methylene-1,3-cyclopentane) (PMCP) with >98% cyclization of the diene monomer. The catalyst was found to cyclopolymerize 1,5-hexadiene with relatively high activity. The microstructure of the PMCP furnished by rac-1 was found to contain a high proportion of cis-cyclopentane rings (σ = 0.70-0.74) and a relatively high isotactic content (α = 0.93-0.96). These are the first cis-enriched isotactic cyclopolymers of 1,5-hexadiene. Cyclopolymerization of 1,6-heptadiene with rac-1/B(C(6) F(5) )(3) produced poly(methylene-1,3-cyclohexane) containing 97% cis-isotactic rings. This is the first report of this highly isotactic and diastereomerically-pure microstructure.

Synthesis of a new olefin polymerization catalyst supported by an sp3-C donor via insertion of a ligand-appended alkene into the Hf-C bond of a neutral pyridylamidohafnium trimethyl complex.

A new living and isoselective propylene polymerization precatalyst was generated via the intramolecular insertion of a ligand-appended vinyl group into the Hf-C bond of a neutral pyridylamidohafnium trimethyl complex.

Fluorinated bis(phenoxyketimine)titanium complexes for the living, isoselective polymerization of propylene: multiblock isotactic polypropylene copolymers via sequential monomer addition.

A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, alpha = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between approximately 790-1000%.