1,1‐Hydroboration and a Borane Adduct of Diphenyldiazomethane: A Potential Prelude to FLP‐N₂ Chemistry

Abstract

Diphenyldiazomethane reacts with HB(C 6 F 5 ) 2 and B(C 6 F 5 ) 3 ,r esulting in 1,1-hydroboration and adduct formation, respectively.The hydroboration proceeds via aconcerted reaction involving initial formation of the Lewis adduct Ph 2 CN 2 BH(C 6 F 5 ) 2 .T he highly sensitive adduct Ph 2 CN 2 (B-(C 6 F 5 ) 3 )l iberates N 2 and generates Ph 2 CB(C 6 F 5 ) 3 .D FT computations reveal that formation of Ph 2 CN 2 B(C 6 F 5 ) 3 from carbene,N 2 ,a nd borane is thermodynamically favourable, suggesting steric frustration could preclude carbene-borane adduct formation and affect FLP-N 2 capture. Scheme 1. Metal-N 2 -borane and diazomethane-borane reactions.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Bimetallic Cooperative Cleavage of Dinitrogen to Nitride and Tandem Frustrated Lewis Pair Hydrogenation to Ammonia

“…[4,5] These catalytic cycles are based on sequential biomimetic protonation/reduction of M-N 2 linkages,c ontrasting the direct cleavage of N 2 /H 2 in HB chemistry.Indeed, molecular species that spontaneously cleave N 2 to N 3À are rare, [6] and none of the resulting metal nitrides react with H 2 ;other metal nitrides can react with H 2 ,t om ake am etal amide,M -NH 2 ,o rN H 3 , but they derive from azides rather than N 2 splitting. [17] Herein, we report the homogeneous reductive cleavage of N 2 to N 3À by aT i-Mg complex supported by as imple triamidoamine ligand, and the conversion of N 3À into NH 3 using hydrogen from H 2 split by an FLP.H eterobimetallic cooperativity facilitates reductive cleavage of N 2 ,and by using aFLP,the barrier to activating and cleaving H 2 is overcome. [10] Weakly acidic M-H 2 complexes can effect protonation of M-N 2 complexes to give M-NNH 2 , [11] and in one case,N H 3 was formed.…”

“…[11b] Thus,i n contrast to HB NH 3 synthesis,a ctivating and cleaving H 2 appears to be the impediment to progress.I na na lternative approach that sidesteps the H 2 activation issue,t ransitionmetal hydrides can activate N 2 and cleave it to N 3À , [12] but no subsequent hydrogenation occurs, [12a,b] or reactions stop at m-N(H) or m-NH 2 stages. [17] Herein, we report the homogeneous reductive cleavage of N 2 to N 3À by aT i-Mg complex supported by as imple triamidoamine ligand, and the conversion of N 3À into NH 3 using hydrogen from H 2 split by an FLP.H eterobimetallic cooperativity facilitates reductive cleavage of N 2 ,and by using aFLP,the barrier to activating and cleaving H 2 is overcome. [14] However, despite the burgeoning nature of FLP-mediated hydrogenations of organic substrates, [15] combining this concept with N 2 activation to make NH 3 has remained an unmet goal, [16] but mono-/diprotonation of metal-N 2 units,borylation/silylation of M-N 2 -B FLPs,and amodel for FLP N 2 activation have now been realised.…”

“…[9,12c,d, 13] It has been proposed that frustrated Lewis pairs (FLPs), which are capable of activating and splitting H 2 ,c ould be combined with metal-based reductive cleavage of N 2 . [17] Herein, we report the homogeneous reductive cleavage of N 2 to N 3À by aT i-Mg complex supported by as imple triamidoamine ligand, and the conversion of N 3À into NH 3 using hydrogen from H 2 split by an FLP.H eterobimetallic cooperativity facilitates reductive cleavage of N 2 ,and by using aFLP,the barrier to activating and cleaving H 2 is overcome. [17] Herein, we report the homogeneous reductive cleavage of N 2 to N 3À by aT i-Mg complex supported by as imple triamidoamine ligand, and the conversion of N 3À into NH 3 using hydrogen from H 2 split by an FLP.H eterobimetallic cooperativity facilitates reductive cleavage of N 2 ,and by using aFLP,the barrier to activating and cleaving H 2 is overcome.…”

“…[14] However, despite the burgeoning nature of FLP-mediated hydrogenations of organic substrates, [15] combining this concept with N 2 activation to make NH 3 has remained an unmet goal, [16] but mono-/diprotonation of metal-N 2 units,borylation/silylation of M-N 2 -B FLPs,and amodel for FLP N 2 activation have now been realised. [17] Herein, we report the homogeneous reductive cleavage of N 2 to N 3À by aT i-Mg complex supported by as imple triamidoamine ligand, and the conversion of N 3À into NH 3 using hydrogen from H 2 split by an FLP.H eterobimetallic cooperativity facilitates reductive cleavage of N 2 ,and by using aFLP,the barrier to activating and cleaving H 2 is overcome. Thebridging nature of the nitride renders it amenable to full protonation to give NH 3 ,w hich can be removed by vacuum distillation without the need for acidification, thereby introducing FLPs to NH 3 synthesis.Previously, [5j] we reported that [Ti(Tren TMS )Cl] [1; Tr en TMS = {N(CH 2 CH 2 NSiMe 3 ) 3 } 3À ]c an be reduced by K( K mirror,KC 8 ,orKC 10 H 8 )togive [Ti(Tren TMS )];this species can bind to N 2 to give the end-on:end-on N 2 complex [{Ti(Tren TMS )} 2 (N 2 )],a nd further reduction with Kg ives [{Ti(Tren TMS )} 2 (N 2 K 2 )] (2), which formally contains N 2…”

A Step Closer to Metal‐Free Dinitrogen Activation: A New Chapter in the Chemistry of Frustrated Lewis Pairs

“…[7] This synergistic effect to weaken the nitrogen-nitrogen bond was subsequently likened to an FLP mechanism by Simonneau in which the "push" effect was provided by the Lewis base component of an FLP (a lowvalent Group 6metal) and the "pull" effect was mimicked by the Lewis acidic component of an FLP [B(C 6 F 5 ) 3 ]. [9] Diazo compounds are highly reactive yet useful building blocks in organic synthesis and have been widely used as versatile intermediates in am ultitude of transformations.A sr eagents,t hey have the benefit of generating N 2 as the only byproduct upon liberation of the corresponding carbenes.H owever,t heir use in maingroup chemistry is under-represented although BÀCinsertion reactions of B(C 6 F 5 ) 3 are known. These results represent as ignificant leap in FLP chemistry,i ndicating that the FLP activation of N 2 is certainly possible.…”