Demonstration of the utility of a commercially available heterogeneous palladium catalyst in the synthesis of a relevant high performance molecular semiconductor.

High electron mobility in a series of phthalimide–thiophene small molecules has been demonstrated when incorporated into thin film transistors.

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We describe the results of our combined experimental and computational investigation of structurally analogous (N-phosphinoamidinate)metal(N(SiMe 3 ) 2 ) precatalysts ((PN)M; M = Mn 2+ , Fe 2+ , Co 2+ , and Ni 2+ ; d 5 −d 8 ) in the isomerization−hydroboration of 1-octene, cis-4-octene, or trans-4-octene (1a−c) with HBPin. As part of this investigation, the synthesis and crystallographic characterization of diamagnetic (PN)Ni, ((PN)NiH) 2 , (PN)NiH(L) (L = pyridine or DMAP), and (PN)Ni(NHdipp) (dipp = 2,6-iPr 2 C 6 H 3 ) are reported. Divergent catalytic reactivity and selectivity was noted for members of the (PN)M series; (PN)Mn and (PN)Ni afforded poor hydroboration yields, whereas the use of (PN)Fe or (PN)Co afforded high conversion and selectivity for the terminal borylation product, (n-octyl)BPin (2a). DFT calculations involving (PN)M as well as stoichiometric reactivity studies featuring (PN)Ni confirmed that (PN)MH intermediates generated upon reaction of (PN)M with HBPin represent viable catalytic species whereby formation of putative (PN)Ni(H 2 BPin) is reversible. Conversely, poor catalytic performance was noted for ((PN)NiH) 2 and (PN)NiH(L) (L = pyridine or DMAP).Using DFT calculations, the relative reactivity of (PN)M precatalysts was found to be a function of their spin-state energy gaps. For reaction of (PN)MnH with trans-4-octene (1c) there is no viable spin crossover mechanism and migratory insertion is slow, resulting in poor reaction yields. In contrast, (PN)FeH can access a lower barrier through spin crossover, whereas (PN)CoH has a very low migratory insertion barrier from its low spin state. While (PN)NiH has a reasonable migratory insertion barrier, it is plausible that off-catalytic cycle intermediates are responsible for the diminished reaction rate and product yields that are observed experimentally. On the basis of the computed isomerization and borylation energy landscapes, a Curtin−Hammett-type scenario with fast isomerization through β-hydride elimination and migratory insertion steps is proposed, giving rise to a catalytic equilibrium of isomeric (PN)M(octyl) resting states, followed by slow product-forming borylation. The significantly lower barriers calculated for borylation of terminal (PN)M(n-octyl) species versus isomeric internal (PN)M(CHR 2 ) intermediates provides a rationale for the experimentally observed terminal isomerization−hydroboration selectivity.

Screening reveals (PN)Ni(x) pre-catalysts to be effective for the hydrosilative reduction of amides under mild conditions.