Dehydrocoupling of phosphine- and amine-boranes is reported using an iron­(II) β-diketiminate complex. Dehydrocoupling of amine-boranes is far more facile than the phosphine counterpart, the former proceeding at room temperature with 1 mol% iron precatalyst. This low loading is sufficient to allow in situ kinetic analysis and deuterium labeling studies to be carried out. An iron amido-borane complex has also been isolated, which is believed to be the catalyst resting state. Overall, this has allowed us to postulate a catalytic cycle which proceeds via release of diborazane, iron hydride, and iron amido-borane intermediates.

An iron catalyst has been developed for the transfer hydrogenation of carbon–carbon multiple bonds. Using a well-defined β-diketiminate iron­(II) precatalyst, a sacrificial amine and a borane, even simple, unactivated alkenes such as 1-hexene undergo hydrogenation within 1 h at room temperature. Tuning the reagent stoichiometry allows for semi- and complete hydrogenation of terminal alkynes. It is also possible to hydrogenate aminoalkenes and aminoalkynes without poisoning the catalyst through competitive amine ligation. Furthermore, by exploiting the separate protic and hydridic nature of the reagents, it is possible to regioselectively prepare monoisotopically labeled products. DFT calculations define a mechanism for the transfer hydrogenation of propene with n BuNH2 and HBpin that involves the initial formation of an iron­(II)-hydride active species, 1,2-insertion of propene, and rate-limiting protonolysis of the resultant alkyl by the amine N–H bond. This mechanism is fully consistent with the selective deuteration studies, although the calculations also highlight alkene hydroboration and amine–borane dehydrocoupling as competitive processes. This was resolved by reassessing the nature of the active transfer hydrogenation agent: experimentally, a gel is observed in catalysis, and calculations suggest this can be formulated as an oligomeric species comprising H-bonded amine–borane adducts. Gel formation serves to reduce the effective concentrations of free HBpin and n BuNH2 and so disfavors both hydroboration and dehydrocoupling while allowing alkene migratory insertion (and hence transfer hydrogenation) to dominate.

A detailed synthetic investigation into the dehydrocoupling of silanes with amines, phosphines, and alcohols using an iron precatalyst (1) is presented. We have furnished over 30 examples of aminosilane synthesis along with kinetic studies using MeBnNH and MePhSiH 2 as coupling partners. The kinetic studies suggest a reversible reaction with silane which generates aminosilane and an Fe-hydride dimer that undergoes rate-limiting protonolysis with amine with N−H bond cleavage in the transition state, consistent with a primary KIE of 2.42(3). The presence of dimers as on-cycle intermediates was analyzed in depth. Beyond this we have explored the substrate scope of phosphinosilane formation which shows a preferential heterodehydrocoupling to give the phosphinosilane with primary and secondary silanes. Silylethers can also be prepared and alcohols that contain alkene functionality do not show any tendency to reduce the double bond.

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The synthesis and isolation of a phosphinine selenide was achieved for the first time by reacting red selenium with 2,6-bis(trimethylsilyl)phosphinine. The rather large coupling constant of 1 J P,Se = 883 Hz is in line with a PÀ Se bond of high s-character. The σ-electron donating Me 3 Sisubstituents significantly increase the energy of the phosphorus lone pair and hence its basicity, making the heterocycle considerably more basic and nucleophilic than the unsubstituted phosphinine C 5 H 5 P, as confirmed by the calculated gas phase basicities. NBO calculations further reveal that the lone pairs of the selenium atom are stabilized through donor-acceptor interactions with antibonding orbitals of the aromatic ring. The novel phosphinine selenide shows a distinct reactivity towards hexafluoro-2-butyne, Au(I) Cl as well as i PrOH. Our results pave the way for new perspectives in the chemistry of phosphorus in low coordination.