NHC-Silyliumylidene Cation-Catalyzed Hydroboration of Isocyanates with Pinacolborane

Abstract

The low-oxidation-state silicon-catalyzed hydroboration of isocyanates with pinacolborane (HBpin) using the NHC-silyliumylidene cation catalyst [(IMe) 2 SiH]I (1, IMe = :C{N(Me)C(Me)} 2 ) is described. In the catalysis, the Si lone pair electrons activate isocyanates, and the latter react with HBpin to form N-boryl formamides at room temperature. Catalyst 1 further activates N-boryl formamides at 70 °C, the intermediates of which react with HBpin to form N-boryl methylamines and (pinB) 2 O.

Tetryliumylidene ions in synthesis and catalysis

“…The NHC-stabilised parent-silyliumylidene ion [NHC 2 SiH] + 11 shows unprecedented abilities in the catalytic hydroboration of CO 2, aldehydes, ketones, and pyridines with a catalyst loading of 10 mol%, as well as isocyanates with a catalyst loading of 1 mol% (Scheme 11). 52,54…”

“…For instance, hydrosilylation and hydroboration reactions were catalysed by [H–E:] + . 52–54 In this minireview, we have summarised the recent developments in the chemistry of tetryliumylidene ions, including their reactivity towards small molecules, as precursors to a variety of additional low-valent species and catalytic applications. While some tetryliumylidene ions were isolated and employed in catalysis by taking advantage of cooperative effects between transition metals and group 14 elements, 55–66 this review highlights only the main-group examples.…”

Mixed Lithium–Aluminum Hydrides Bearing Ar-Bian Ligands: Reactivity Toward Heteroallenes

“…So, the first examples of catalytic hydroboration of isocyanate by pinacolborane (HBpin) to form N , O -bis­(boryl)­hemaminals or N -borylmethyl amines were achieved by using β-diketiminato and hydridotriphenylborate magnesium complexes. Pioneer studies of the catalytic hydroboration of carbodiimides were carried out by Hill and Okuda, utilizing the same magnesium compounds. , Further studies have discovered a wide range of catalytic systems, including derivatives of transition metals, − main group elements, ,− or actinides, , that are able to catalyze these reactions. However, the hydroboration of isocyanates and carbodiimides typically results in the formation of mixtures of products.…”