The synthesis of bis(oligophenyleneethynylenes): novel potential nonlinear optical materials

Organotrifluoroborates: protected boronic acids that expand the versatility of the Suzuki coupling reaction

Organotrifluoroborates represent an alternative to boronic acids, boronate esters, and organoboranes for use in Suzuki-Miyaura and other transition-metal-catalyzed cross-coupling reactions. The trifluoroborate moiety is stable toward numerous reagents that are often problematic for other boron species. Consequently, remote functional groups within the organotrifluoroborates can be manipulated, while retaining the valuable carbon-boron bond.

Solid-Phase Synthesis of m-Phenylene Ethynylene Heterosequence Oligomers

Both homo- and heterosequence m-phenylene ethynylene oligomers are synthesized using a conceptually simple iterative solid-phase strategy. Oligomers are attached to Merrifield's resin through a known triazene-type linkage. The phenylene ethynylene molecular backbone is constructed through a series of palladium-mediated cross-coupling reactions. The strategy employs two types of monomers that bear orthogonal reactivity, one being a monoprotected bisethynyl arene and the other being a 3-bromo-5-iodo arene. The catalyst conditions are tailored to the requirements of each monomer type. The monoprotected bisethynyl arene is coupled to the growing chain in 2 h at room temperature using a Pd(I) dimer precatalyst ((t)Bu3P(Pd(mu-Cl)(mu-2-methyl allyl)Pd)P(t)Bu3) in conjunction with ZnBr2 and diisopropylamine. In alternate steps, the resin is deprotected in situ with TBAF and coupled to the 3-bromo-5-iodo arene using the iodo selective Pd(tri-2-furylphosphine)4 catalyst in conjunction with CuI and piperidine; this reaction is also completed in 2 h at room temperature. These cross-coupling events are alternated until an oligomer of the desired length is achieved. The oligomer is then cleaved from the resin using CH(2)I(2)/I(2) at 110 degrees C and purified using preparatory GPC. Using this method, a series of homo- and heterosequence oligomers up to 12 units in length in excellent yield and purity were synthesized on the 100 mg scale. Longer oligomers were attempted; however, deletion sequences were found in oligomers longer than 12 units.

Synthesis and Optical Properties of Bis(oligophenyleneethynylenes)

Bis(oligophenyleneethynylenes) 1-4 were prepared as representative members of a new class of potential nonlinear optical materials. The optical properties of 1-4 were examined for evidence of restricted rotation of the aryl rings when compared to their single-strand precursors, which could potentially increase their nonlinear response through more effective conjugation. The effect of altering the electron density of the terminating functional group of these compounds on their properties was also investigated.