William R. Dolbier

Parylene-AF4: a polymer with exceptional dielectric and thermal properties

[2.2]Paracyclophanes are useful chemical vapor deposition (CVD) precursors of thin film polymers, known as Parylenes. Parylenes are ideally suited for use as conformal coatings in a wide variety of applications, such as in the automotive, medical, electronics, and semiconductor industries. Parylene coatings are inert and transparent and have excellent barrier properties. The bridge-fluorinated 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (AF4) is the CVD precursor of Parylene-AF4 polymer, which combines a low dielectric constant with high thermal stability, low moisture absorption, and other advantageous properties. With such properties, and because its in vacuo deposition process ensures conformality to microcircuit features and superior submicron gap-filling capability, Parylene-AF4 has considerable promise as an interlayer dielectric for on-chip high-speed semiconductor device interconnection. This paper reviews the synthesis and properties of Parylene-AF4 and its paracyclophane precursor, including a discussion of the importance of the fluorinated bridges, the advantages of the dimeric precursor, and why Parylene-AF4 has the potential to meet the needs of the semiconductor industry with respect to the key properties of a potential interlayer dielectric.

Nucleophilic trifluoromethylation of acyl chlorides using the trifluoromethyl iodide/TDAE reagent

Chemoselective bis-trifluoromethylation of acyl chlorides using the CF3I/TDAE-derived nucleophilic trifluoromethyl anion reagent is reported. Very high yields are obtained of an ester product formed by sequential nucleophilic bis-trifluoromethylation, followed by acylation of the resultant alcoholate.

The thermodynamic effect of fluorine as a substituent: Vinylic CF2 and CFH and allylic CF2C

Abstract I 2 -catalyzed isomerizations of 3-fluoropropene and 3,3 - difluoropropene, and a Cope rearrangement of 1,1 - difluoro - 1,5 - hexadiene provide thermodynamic data which allow the determination of a number of important group values for contributions to ΔH o f which when combined with those determined in the preceding paper allow the calculations of ΔH o f s of most simple F-substituted hydrocarbons: [C d (F)(H)] = − 38.4, [C d (F) 2 ] = − 88.0, [C(F) 2 (C)(C d )] = − 103.9, [C(F) 2 (C) 2 ] = − 104.9 kcal/mole. A kinetic study of the conversion of 1,1 - difluoro- to 3,3 - difluoro - 1,5 - hexadiene provided activation parameters for the process: Log A = 10.8, E a = 33.0 kcal/mole and ΔS ≠ = − 12.2 e.u. Incremental geminal stabilizations of F and other substituents are discussed and contrasted.

Fluorinated allenes: the syntheses of 1-fluoropropadiene, 1,1-difluoropropadiene and 1,1-difluoro-3-methyl-1,2-butadiene

Abstract Improved syntheses of 1-fluoropropadiene and 1,1-difluoropropadiene are presented as is the synthesis of a third reactive allene, 1,1-difluoro-3- methyl-1,2-butadiene. Gram quantities of these highly reactive fluorinated allenes may be prepared conveniently in high yield and purity. All three are reactive dienophiles and cycloadd regiospecifically using their non- fluorine-substituted double bonds.

Strain energies of gem-difluorocyclopropanes and related molecules

Abstract Ab initia calculations using the 4–31G basis set are employed to evaluate strain energies of gem-difluoro derivatives of cyclopropane. The increased strain energies of these molecules account for the relative ease of their thermal rearrangements. Similarities between gem-difluoro, carbonyl and carbocationic centers are explored. The strain energy of hexafluorocyclopropane is almost triple that in cyclopropane while the strain in octafluorocyclobutane is less than double that in cyclobutane.

Synthesis of 1,1-difluoroalkenes via α,α-difluoro-β-lactones

Abstract A new method for the general synthesis of 1,1-difluoroalkenes from ketones is presented. The procedure involves initial condensation of a ketone with the difluoro Reformatsky reagent, hydrolysis to form the α,α-difluoro-β-hydroxy acids, followed by cyclization to make the novel α,α-difluoro-β-lactones. These are then thermally decarboxylated to form the 1,1-difluoroalkenes.

The in Situ generation and trapping of some fluorine-substituted ketenes

Abstract Fluoroketene, difluoroketene, methylfluoroketene, trifluoromethylfluoroketene, and phenylfluoroketene were each generated, in situ , via dehydrohalogenation of the respective acid chlorides. In the presence of cyclopentadiene [2 + 2] adducts were obtained in all but the difluoroketene case. In the absence of cyclopentadiene, low temperature 19 F nmr indicated the presence of acyl ammonium salts and enolates, potential precursors of the ketenes, but no actual ketene species could unambiguously be detected. The stereochemical results were consistent with the currently accepted steric-based mechanistic rationale for stereochemical determination in ketene cycloadditions.

Anomalous elimination of HCl from 2-chloro-1,1-difluoroethane. Likely involvement of a 1,2-FCl interchange mechanism

A novel 1,2-FCl interchange mechanism is proposed to be involved in the unexpected thermal conversion of CH2ClCHF2 to 1,2-difluoroethylene.

Kinetic effects of fluorine substituents in free-radical chemistry. Hydrogen-atom abstraction reactions of perfluoro-n-alkyl radicals

Abstract Using competitive methods, the rates of hydrogen-atom abstraction by a typical perfluoro-n-alkyl radical, n-C 7 F 15 ·, have been determined for a series of silane and stannane reductants including n Bu 3 SnH (2.03×10 8 M −1 s −1 ), Et 3 SiH (7.5×10 5 ), (TMS) 2 SiMeH (1.63×10 7 ) and (TMS) 3 SiH (5.1×10 7 ), all of which exhibited substantial rate enhancements relative to their analogous reductions of hydrocarbon radicals. The reduction by PhSH is, in contrast, ∼400-times slower than for hydrocarbon radicals. Transition state polar effects are invoked to rationalize the relative reactivity of perfluoro- versus hydrocarbon radicals in these hydrogen-transfer reactions. A Hammett study for H-atom transfer from arene thiols ( p + = −0.56) provided further substantiation for this conclusion. A discussion of the relative reactivity of t-butoxyl and perfluoro-n-alkyl radicals is presented.

The reactions of n-benzoylperoxycarbamic acid with azines and imines

Abstract N-Benzoylperoxycarbamic acid (BPC) was found to react generally with imines and azines to form oxaziridines rather than N-oxides. The imine products were stable, but those found from azines apparently were unstable and converted to ketones or aldehydes plus diazo compounds.