Structural and Mechanistic Insights into s‐Block Bimetallic Catalysis: Sodium Magnesiate‐Catalyzed Guanylation of Amines

Abstract

To advance the catalytic applications of s-block mixed-metal complexes, sodium magnesiate [NaMg(CH SiMe ) ] (1) is reported as an efficient precatalyst for the guanylation of a variety of anilines and secondary amines with carbodiimides. First examples of hydrophosphination of carbodiimides by using a Mg catalyst are also described. The catalytic ability of the mixed-metal system is much greater than that of its homometallic components [NaCH SiMe ] and [Mg(CH SiMe ) ]. Stoichiometric studies suggest that magnesiate amido and guanidinate complexes are intermediates in these catalytic routes. Reactivity and kinetic studies imply that these guanylation reactions occur via (tris)amide intermediates that react with carbodiiimides in insertion steps. The rate law for the guanylation of N,N'-diisopropylcarbodiimide with 4-tert-butylaniline catalyzed by 1 is first order with respect to [amine], [carbodiimide], and [catalyst], and the reaction shows a large kinetic isotopic effect, which is consistent with an amine-assisted rate-determining carbodiimide insertion transition state. Studies to assess the effect of sodium in these transformations denote a secondary role with little involvement in the catalytic cycle.

Molecular Manipulations of a Utility Nitrogen–Heterocyclic Carbene by Sodium Magnesiate Complexes and Transmetallation Chemistry with Gold Complexes

“…We started by investigating the reactivity of IPr with sodium magnesiate NaMgR 3 (R=CH 2 SiMe 3 ). This ate was first developed by our group and has already shown great promise as an efficient precatalyst in hydroamination reactions of isocyanates and carbodiimides . Performing this reaction at room temperature in a hexane/benzene non‐Lewis basic solvent mixture, using equimolar amounts of IPr and NaMgR 3 led to the isolation of sodium tetra(alkyl) magnesiate [ IPr 2 Na 2 MgR 4 ] ( 1 ) as colourless crystals in a 13 % yield (note that the maximum possible yield for this reaction is 50 %, Scheme a).…”

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

“…31 Breaking new ground in this area, we recently reported sodium tris(alkyl)magnesiate NaMg(CH 2 SiMe 3 ) 3 32 as an efficient precatalyst for hydroamination of a variety of carbodiimides and isocyanates. 33,34 Operating synergistically, this bimetallic precatalyst displays an enhanced catalytic ability compared to those found for its homometallic components NaCH 2 SiMe 3 and Mg(CH 2 SiMe 3 ) 2 , allowing hydroaminations to take place under very mild reaction conditions (mostly at ambient temperature) in nearly quantitative yields.…”

Alkali metal and stoichiometric effects in intermolecular hydroamination catalysed by lithium, sodium and potassium magnesiates

“…We have also reported the applications of this mixed Na/Mg system as an efficient precatalyst for the guanylation and hydrophosphination of amines, proceeding by a similar reaction pathway. 12 Related to these findings, Westerhausen has demonstrated that potassium calciates [K2Ca(NPh2)4] and [K2Ca{(N(H)Dipp}4] can catalyse the hydroamination reactions of diphenylbutadiyne with a variety of anilines. 13 Exemplifying the cooperative effect of the ate compound as a catalyst, no reaction product is observed when adding diphenylamine to 1,4-diphenylbutadiyne in presence of Ca(NPh2)2 or KNPh2.…”