Predictive modelling of structure formation in semiconductor films produced by meniscus-guided coating.

Meniscus-guided coating methods, such as zone casting, dip coating and solution shearing, are scalable laboratory models for large-area solution coating of functional materials for thin-film electronics. Unfortunately, the general lack of understanding of how the coating parameters affect the dry-film morphology upholds trial-and-error experimentation and delays lab-to-fab translation. We present herein a model that predicts dry-film morphologies produced by meniscus-guided coating of a crystallizing solute. Our model reveals how the interplay between coating velocity and evaporation rate determines the crystalline domain size, shape anisotropy and regularity. If coating is fast, evaporation drives the system quickly past supersaturation, giving isotropic domain structures. If coating is slow, depletion due to crystallization stretches domains in the coating direction. The predicted morphologies have been experimentally confirmed by zone-casting experiments of the organic semiconductor 4-tolyl-bithiophenyl-diketopyrrolopyrrole. Although here we considered a small molecular solute, our model can be applied broadly to polymers and organic-inorganic hybrids such as perovskites.

Insights into functional-group-tolerant polymerization catalysis with phosphine-sulfonamide palladium(II) complexes.

Two series of cationic palladium(II) methyl complexes {[(2-MeOC6 H4 )2 PC6 H4 SO2 NHC6 H3 (2,6-R(1) ,R(2) )]PdMe}2 [A]2 ((X) 1(+) -A: R(1) =R(2) =H: (H) 1(+) -A; R(1) =R(2) =CH(CH3 )2 : (DIPP) 1(+) -A; R(1) =H, R(2) =CF3 : (CF3) 1(+) -A; A=BF4 or SbF6 ) and neutral palladium(II) methyl complexes {[(2-MeOC6 H4 )2 PC6 H4 SO2 NC6 H3 (2,6-R(1) ,R(2) )]PdMe(L)} ((X) 1-acetone: L=acetone; (X) 1-dmso: L=dimethyl sulfoxide; (X) 1-pyr: L=pyridine) chelated by a phosphine-sulfonamide were synthesized and fully characterized. Stoichiometric insertion of methyl acrylate (MA) into all complexes revealed that a 2,1 regiochemistry dominates in the first insertion of MA. Subsequently, for the cationic complexes (X) 1(+) -A, ß-H elimination from the 2,1-insertion product (X) 2(+) -AMA-2,1 is overwhelmingly favored over a second MA insertion to yield two major products (X) 4(+) -AMA-1,2 and (X) 5(+) -AMA . By contrast, for the weakly coordinated neutral complexes (X) 1-acetone and (X) 1-dmso, a second MA insertion of the 2,1-insertion product (X) 2MA-2,1 is faster than ß-H elimination and gives (X) 3MA as major products. For the strongly coordinated neutral complexes (X) 1-pyr, no second MA insertion and no ß-H elimination (except for (DIPP) 2-pyrMA-2,1 ) were observed for the 2,1-insertion product (X) 2-pyrMA-2,1 . The cationic complexes (X) 1(+) -A exhibited high catalytic activities for ethylene dimerization, affording butenes (C4 ) with a high selectivity of up to 97.7 % (1-butene: 99.3 %). Differences in activities and selectivities suggest that the phosphine-sulfonamide ligands remain coordinated to the metal center in a bidentate fashion in the catalytically active species. By comparison, the neutral complexes (X) 1-acetone, (X) 1-dmso, and (X) 1-pyr showed very low activity towards ethylene to give traces of oligomers. DFT analyses taking into account the two possible coordination modes (O or N) of the sulfonamide ligand for the cationic system (CF3) 1(+) suggested that the experimentally observed high activity in ethylene dimerization is the result of a facile first ethylene insertion into the O-coordinated PdMe isomer and a subsequent favored ß-H elimination from the N-coordinated isomer formed by isomerization of the insertion product. Steric hindrance by the N-aryl substituent in the neutral systems (CF3) 1 and (H) 1 appears to contribute significantly to a higher barrier of insertion, which accounts for the experimentally observed low activity towards ethylene oligomerization.

Catalyst activity and selectivity in the isomerising alkoxycarbonylation of methyl oleate.

The synthesis of unsymmetrical diphosphine ligands (3a-g) with an o-tolyl backbone and tert-butyl, adamantyl, cyclohexyl and isopropyl substituents on the phosphorus moiety is described (1,2-(CH2PR2)(PR'2)C6H4; 3a: R=tBu, R'=tBu, 3b: R=tBu, R'=Cy, 3c: R=tBu, R'=iPr, 3d: R=Ad, R'=tBu, 3e: R=Ad, R'=Cy, 3f: R=Cy, R'=Cy, 3g: R=Ad, R'=Ad). The corresponding diphosphine-Pd(II) ditriflate complexes [(P^P)Pd(OTf)2] (5a-g) were prepared and structurally characterised by X-ray crystallography. These new complexes were studied as catalyst precursors in the isomerising methoxycarbonylation of methyl oleate, and were found to convert methyl oleate into the corresponding linear α,ω-diester (L) with 70-80% selectivity. The products of this catalytic reaction with the known [{1,2-(tBu2PCH2)2C6H4}Pd(OTf)2] complex (5h) were fully analysed, and revealed the formation of the linear α,ω-diester (L, 89.0%), the methyl-branched diester B1 (4.3%), the ethyl-branched diester B2 (1.0%), the propyl-branched diester B3 (0.6%) and all diesters from butyl- to hexadecyl-branched diesters B4-B16 (overall 4.8%) at 90 °C and 20 bar CO. The productivity of the catalytic conversion of methyl oleate with complexes 5a-g varied with the steric bulk of the alkyl substituent on the phosphorus. Ligands with more bulky groups, like tert-butyl or adamantyl (e.g., 5a, 5d, 5g), were more productive systems. The formation of the catalytically active hydride species [(P^P)Pd(H)(MeOH)](+) (6-MeOH) was investigated and observed directly for complexes 5a-e and 5g, respectively. These hydride species were isolated as the corresponding triphenylphosphine complexes (6-PPh3) and fully characterised, including by X-ray crystallography. The catalytic productivity of 6a-PPh3 was virtually identical to that of 5a, thereby confirming the efficient hydride formation of 5a under catalytic conditions.

Mechanistic insights into polar monomer insertion polymerization from acrylamides.

N-Isopropyl acrylamide (NIPAM), N,N-dimethyl acrylamide (DMAA), and 2-acetamidoethyl acrylate (AcAMEA) were copolymerized with ethylene employing [(P^O)PdMe(DMSO)] (1-DMSO; P^O = κ(2)-P,O-Ar(2)PC(6)H(4)SO(2)O with Ar = 2-MeOC(6)H(4)) as a catalyst precursor. Inhibition studies with nonpolymerizable polar additives show that reversible κ-O-coordination of free amide retards polymerization significantly. Retardation of polymerization increases in the order ethyl acetate ≪ methyl ethyl sulfone < acetonitrile < N,N-dimethylacetamide ≈ N-methylacetamide ≈ propionic acid < dimethylsulfoxide. Pseudo-first-order rate constants for the insertion into 1-DMSO were determined to increase in the order DMAA < AcAMEA < NIPAM < methyl acrylate. Exposure of 1-DMSO to NIPAM resulted in the formation of consecutive insertion products [(P^O)Pd(C(6)H(11)NO(2))(n)Me] (n ≤ 3), as determined by electrospray ionization mass spectrometry. The solid-state structure of the methanol adduct of the 2,1-insertion product of NIPAM into 1-DMSO, [(P^O)Pd{η(1)-CH(CONHiPr)CH(2)CH(3)}(κ(1)-O-MeOD)] (2-MeOD), was determined by single crystal X-ray diffraction. Both 2,1- and 1,2-insertions of DMAA into the Pd-Me bond of a [(P^O)PdMe] fragment occur to afford a ca. 4:1 mixture of chelates [(P^O)Pd{κ(2)-C,O-C(CH(2)CH(3))C(O)NMe(2)}] (3) and [(P^O)Pd{κ(2)-C,O-CH(2)C(CH(3))C(O)NMe(2)}] (4). The four-membered chelate of 3 is opened by coordination of 2,6-lutidine (3 + 2,6-lutidine ⇌ 3-LUT) with ΔH° = -41.8(10.5) kJ and ΔS° = -115(37) J mol(-1) K(-1).

Breaking the regioselectivity rule for acrylate insertion in the Mizoroki-Heck reaction.

In modern methods for the preparation of small molecules and polymers, the insertion of substrate carbon-carbon double bonds into metal-carbon bonds is a fundamental step of paramount importance. This issue is illustrated by Mizoroki-Heck coupling as the most prominent example in organic synthesis and also by catalytic insertion polymerization. For unsymmetric substrates H(2)C = CHX the regioselectivity of insertion is decisive for the nature of the product formed. Electron-deficient olefins insert selectively in a 2,1-fashion for electronic reasons. A means for controlling this regioselectivity is lacking to date. In a combined experimental and theoretical study, we now report that, by destabilizing the transition state of 2,1-insertion via steric interactions, the regioselectivity of methyl acrylate insertion into palladium-methyl and phenyl bonds can be inverted entirely to yield the opposite "regioirregular" products in stoichiometric reactions. Insights from these experiments will aid the rational design of complexes which enable a catalytic and regioirregular Mizoroki-Heck reaction of electron-deficient olefins.