The first substituent‐induced “flip” from p‐ to n‐type conductivity as well as enhanced thermal stability and volatility are found for fluorocarbon‐functionalized sexithiophene 1 (relative to the fluorine‐free analogues 2 and 3). Evaporated films of 1 behave as n‐type semiconductors, and can be used to fabricate thin‐film transistors with field‐effect mobilities as high as 0.02 cm2 V−1 s−1—some of the highest reported to date for n‐type organic semiconductors.
Templated ZnO thin-film growth from the vapor phase is achieved on docosyltrichloro- silane-patterned Si substrates using atomic layer epitaxy (ALE) combined with soft lithography. Patterned hydrophobic self-assembled monolayers (SAMs) are first transferred to single-crystal Si surfaces by hot microcontact printing. Using diethylzinc and water as ALE precursors, crystalline ZnO layers are then grown selectively on the SAM-free surface regions where native hydroxy groups nucleate growth from the vapor phase. High-resolution ZnO patterns with 1.0–40 μm feature sizes are readily achieved, demonstrating that soft lithography combined with ALE is a simple and promising methodology for selective area in situ vapor phase fabrication of patterned oxide thin films.
The palladium-catalyzed copolymerization of carbon monoxide and
ethylene to give
polyketone polymers,
[CH2CH2C(O)]
n
,
has been accomplished by the use of either (dppp)Pd(OAc)2 or
(dppp)Pd[C(O)tBu]Cl in the presence of a
tert-butyl alumoxane,
[(tBu)Al(μ3-O)]
n
(n = 6, 7, 9) or
[(tBu)7Al5(μ3-O)3(μ-OH)2]
cocatalyst. The effects on the catalytic activity of
the alumoxane and palladium concentrations, the alumoxane structure,
and the identity of
the phosphine ligands were determined. The function of the
alumoxane is shown to depend
on the choice of palladium catalyst precursor. With
(dppp)Pd[C(O)tBu]Cl the
alumoxane
abstracts chloride to give a catalytically active cationic palladium
complex directly. In
contrast, the alumoxane initially alkylates the palladium in
(dppp)Pd(OAc)2 and subsequently
abstracts the remaining acetate anion, yielding the active cationic
palladium complex. The
catalytic activity is highly dependent on the structure of the
alumoxane. A comparative
study indicates the cocatalytic activity to be
[(tBu)Al(μ3-O)]7
>
[(tBu)Al(μ3-O)]6
> [(tBu)Al(μ3-O)]9 ≫
[(tBu)7Al5(μ3-O)3(μ-OH)2].
This observed cocatalytic activity correlates with
the
predicted latent Lewis acidity of the alumoxanes. A discussion of
the palladium−alumoxane
complex is presented with respect to the model compound
[(tBu)6Al6(μ3-O)4(μ-OH)2(μ-O2CCCl3)2], prepared by the reaction of
[(tBu)Al(μ3-O)]6
with HO2CCCl3. The steric effects
of
the catalyst active site, as determined by the alkyl bridge length
(n) in
R2P(CH2)
n
PR2
and
the alkyl substituents R, were probed for the catalyst precursor
compounds
[R2P(CH2)
n
PR2]Pd[C(O)tBu]Cl (R = Ph,
n = 2 (dppe), 3 (dppp), 4 (dppb); R = Me (dmpe),
C6H11 (dcpe),
n = 2). The concept of “pocket angle” has been
developed to account for the observed steric
effects. The detection of vinyl end groups on low-molecular-weight
oligomers is indicative
of catalyst turnover via a β-hydride-elimination chain termination.
A proposed catalyst
mechanism and a pathway to catalyst activation are presented. The
molecular structures
of (dppp)Pd[C(O)tBu]Cl,
(dppe)Pd[C(O)tBu]Cl,
(dmpe)Pd[C(O)tBu]Cl,
(dcpe)Pd[C(O)tBu]Cl,
and
[(tBu)6Al6(μ3-O)4(μ-OH)2(μ-O2CCCl3)2]
have been determined by X-ray crystallography.
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