Iron(II)‐Catalyzed Hydrophosphination of Isocyanates

Abstract

The first transition metal catalyzed hydrophosphination of isocyanates is presented. The use of low-coordinate iron(II) precatalysts leads to an unprecedented catalytic double insertion of isocyanates into the P-H bond of diphenylphosphine to yield phosphinodicarboxamides [Ph PC(=O)N(R)C(=O)N(H)R], a new family of derivatized organophosphorus compounds. This remarkable result can be attributed to the low-coordinate nature of the iron(II) centers whose inherent electron deficiency enables a Lewis-acid mechanism in which a combination of the steric pocket of the metal center and substrate size determines the reaction products and regioselectivity.

The first ring-expanded NHC–copper(i) phosphides as catalysts in the highly selective hydrophosphination of isocyanates

“…These mid-dblock systems, however, are prone to redox-switching and single-electron transfer reactions which, coupled with the stability of phosphorus centred radicals, often result in undesirable side reactions. [5][6][7] The propensity of copper(I) towards the well-defined isohypsic reaction steps of s-bond metathesis, and insertion of unsaturated substrates should allow copper(I) phosphides to overcome such issues. Despite this appeal, copper phosphides often form only as complex oligomers, with a concomitant reduction in reactivity.…”

Low-coordinate first-row transition metal complexes in catalysis and small molecule activation

“…The iron(II) m-terphenyl complexes 16 and 18 (Scheme 11a) are effective catalysts for the hydrophosphination of isocyanates. 77 This reaction affords a mixture of phosphinocarboxamide and phosphinodicarboxamide products, corresponding to both mono-and diinsertion of the isocyanate into the P-H bond (Scheme 13a). Such diinsertion reactions are rare 78 and the double insertion of an isocyanate into a P-H bond has led to a family of phosphinodicarboxamide compounds.…”

“…Poisoning experiments have suggested that the reaction is homogeneous and does not involve radical processes; and a catalytic cycle where the transition metal acts as a Lewis acid was proposed to account for these observations (Scheme 13c). 77 Scheme 11 Cyclotrimerisation of isocyanates with low coordinate m-terphenyl metal complexes. (a) Metal complexes used as precatalysts in the cyclotrimerisation reaction.…”

A Practical and General Amidation Method from Isocyanates Enabled by Flow Technology

“…This led to a detailed exploration of the previously reported reaction of Grignard reagents with isocyanates (Table ). From these explorations it was observed that a successful reaction required a sterically bulky isocyanate, otherwise formation of a deleterious acylurea side product ( 4 aa and 4 ab ) was observed in significant quantities . Attempts to prevent the formation of the acylurea through modulating temperature, addition regime, and reactant stoichiometry delivered no practicable improvement…”

“…From these explorations it was observed that asuccessful reaction required asterically bulky isocyanate, otherwise formation of ad eleterious acylurea side product (4aa and 4ab)was observed in significant quantities. [15] Attempts to prevent the formation of the acylurea through modulating temperature,a ddition regime, and reactant stoichiometry delivered no practicable improvement. [16] We then focused on am ore detailed study of the lowyielding and inefficient coupling of the unhindered reaction partners 1a and 2a.Surprisingly,the rate of Grignard reagent addition was found to have asignificant impact upon reaction performance ( Figure 2).…”