Synthesis and catalytic performance of nickel phosphinite pincer complexes in deoxygenative hydroboration of amides.

A series of imino-POCN, amino-POCN, and bis(phosphinite) POCOP pincer complexes of Ni(II) were prepared and tested in catalytic deoxygenative hydroboration of amides with HBPin to the corresponding amines. In contrast to the deoxygenative hydrosilylation approach, primarily developed for tertiary amides, superior reactivity in Ni-catalyzed deoxygenative hydroboration was demonstrated for secondary carboxamides. The bis(phosphinite) hydride complex (POCOP)NiH proved the most active in these reactions, tolerating potentially reducible functionalities such as internal alkenes, esters, nitriles, heteroaromatic compounds, and tertiary amides.

Hydroboration of isocyanates: cobalt-catalyzed catalyst-free approaches.

Hydroboration of isocyanates with HBPin was demonstrated using both catalytic and catalyst-free approaches. In arene solvents, the reactions employed the commercially available and bench-stable Co(acac)/dpephos (dpephos = bis[(2-diphenylphosphino)phenyl] ether) pre-catalyst and proved chemodivergent, showing the formation of either formamides or -methylamines, depending on the concentration of HBPin and the reaction conditions used. Catalytic monohydroboration of isocyanates to formamides was found to be highly chemoselective, tolerating alkenes, alkynes, aryl halides, esters, carboxamides, nitriles, nitroarenes and heteroaromatic functionalities.

Efficient Co-Catalyzed Double Hydroboration of Nitriles: Application to One-Pot Conversion of Nitriles to Aldimines.

The commercially available and bench-stable Co(acac) /dpephos system is employed as a precatalyst for selective and efficient room temperature hydroboration of organic nitriles with HBPin to produce a series of N,N-diborylamines [RN(BPin) ], which react in situ with aldehydes to give aldimines. Formation of aldimines from N,N-diborylamines does not require a dehydrating agent, is applicable to a wide range of N,N-diborylamine and aldehyde substrates and is highly chemoselective, being unaffected by various common functional groups, such as alkenes, alkynes, secondary amines, ketones, esters, amides, carboxylic acids, pyridines, nitriles, and nitro compounds. The overall transformation represents a synthetically valuable approach to aldimines from nitriles and can be performed in a sequential one-pot manner, tolerating ester, lactone, carboxamide and unactivated alkene functionalities.

POCN Ni(ii) pincer complexes: synthesis, characterization and evaluation of catalytic hydrosilylation and hydroboration activities.

A series of iminophosphinite POCN pincer Ni(ii) complexes, (POCN)NiMe and (POCN)NiL(BX) (L = CHCN, n = 0, 1; X = F, Ph, CF), have been developed and subjected to catalytic hydrosilylation of alkenes, aldehydes and ketones and hydroboration of carbonyl compounds. The stoichiometric reactivity of (POCN)NiMe and (POCN)Ni(BF) with PhSiH and HBPin suggests that catalytic reactions proceed via the hydride intermediate (POCN)NiH. With regard to reactions with HBPin, efficient and mild hydroboration of a variety of carbonyl compounds, including highly chemoselective hydroboration of benzaldehyde in the presence of other common potent reductive functional groups, such as alkenes, alkynes, esters, amides, nitriles, nitro compounds and even ketones, and the first example of base metal catalyzed hydroboration of amides, including mild direct hydroborative reduction of primary and secondary amides to borylated amines were demonstrated for (POCN)NiMe.