The catalytic addition of phosphines to alkenes and alkynes is a very attractive process that offers access to phosphines in a 100% atom-economic reaction using readily available and inexpensive materials. The products are potentially useful ligands and organocatalysts. Herein we report the first example of intramolecular hydrophosphination of a series of non-activated phosphino-alkenes and phosphino-alkynes with a simple iron β-diketiminate complex. Kinetic studies suggest that this transformation is first order with respect to both the phosphine and the catalyst. A mechanistic interpretation of the iron-catalyzed hydrophosphination is presented, supported by the experimental evidence collected.

Iron-catalyzed hydroboration (HB) of alkenes and alkynes is reported. A simple change in ligand structure leads to an extensive change in catalyst activity. Reactions proceed efficiently over a wide range of challenging substrates including activated, unactivated and sterically encumbered motifs. Conditions are mild and do not require the use of reducing agents or other additives. Large excesses of borating reagent are not required, allowing control of chemo- and regioselectivity in the presence of multiple double bonds. Mechanistic insight reveals that the reaction is likely to proceed via a highly reactive iron hydride intermediate.

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.

Abstract:The importance of phosphines in synthetic chemistry cannot be underestimated. Catalytic hydrophosphination offers an ideal method to prepare P À C bonds without the need for harsh reaction conditions or stoichiometric amounts of waste by-product. We herein report our studies into two biocompatible iron(III) complexes in hydrophosphination chemistry using diphenylphosphine under mild and benign reaction conditions (room temperature, solvent-free) and our extended exploration of hydrophosphination with phenylphosphine, which can be tuned to operate in the absence of catalyst under thermal conditions for single hydrophosphination or solvent-free with an iron(III) precatalyst to generate the products of double hydrophosphination.

Addition of ZnMe2 to cationic and neutral ruthenium hydride complexes bearing NHC ligands affords new Ru–Zn heterobimetallic complexes.