β-Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Isocyanides

Abstract

The β-diketiminato nickel(I) species [Me 3 NN]Ni(2-picoline) (1) serves as an efficient catalyst for carbodiimide (RNCNR′) formation in the reactions of a range of organoazides N 3 R with isocyanides R′NC. [Me 3 NN]-Ni(CNR) 2 (R = t Bu, Ar (Ar = 2,6-Me 2 C 6 H 3 )) species provide carbodiimides RNCNAr′ upon reaction with Ar′N 3 (Ar′ = 3,5-Me 2 C 6 H 3 ). Nitrene transfer takes place via the intermediacy of nickel imides. Reaction of [Me x NN]Ni(2-picoline) (x = 2 or 3) with Ar′N 3 gives the new dinickel imides {[Me x NN]Ni} 2 (μ-NAr′) (4 (x = 3) and 5 (x = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me 2 NN]Ni} 2 (μ-NAr′) (5) features short Ni−N imide distances of 1.747(2) and 1.755(2) Å along with a short Ni−Ni distance of 2.7210(3) Å. These dinickel imides 4 and 5 react stoichiometrically with t BuNC to provide the corresponding carbodiimides t BuNCNAr′ in good yield. Azide transfer takes place upon reaction of 1 with TMS-N 3 to give the square planar nickel(II) azide [Me 3 NN]Ni(N 3 )(2-picoline) (7). Stoichiometric reaction of dinickel dicarbonyl {[Me 3 NN]Ni} 2 (μ-CO) 2 with organoazides such as Ar′N 3 is sluggish, indicating that 1 is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO.

Tuning steric and electronic effects in transition-metal β-diketiminate complexes

“…As a result, dimeric/polymeric metal complexes are more often formed with less sterically hindered β-diketiminate ligands. For example, comparisons with more hindered monomeric analogues were reported for [LScCl 2 ] n (L tBu,iPr , 16 n=1; L Me,iPr , 17 n=2), [LSc(CH 3 ) 2 ] n (L tBu,iPr , 16 n=1; L Me,iPr , 17 n=2), [LFeCl] n (L tBu,iPr , 18 n=1; L Me,iPr , 19 Me L Me,Me , 20 n=2), [LFeF] n (L tBu,iPr , n=1; L Me,iPr , n=2), 21 [LCoCl] n (L tBu,iPr , 22 n=1; L Me,iPr , 23 n=2), [LNiCl] n (L tBu,iPr , 22 n=1; L Me,iPr , 24 L Me,Me , 25 n=2), [LNi(CO)] n , (L tBu,iPr , 26 L Me,iPr , 27 n=1; L Me,Me , 28 n=2), [L R,iPr CuCl] n (L Me,iPr , 29 Cl L Me,iPr , 29 n=1; Ph L H,iPr , 30 L Me,Cl , 31 n=2), and [LPd(μ-OAc)] n (L Me,iPr , 32 n=1; L Me,H 32 Cl L Me,H , 33 n=2). The angle between the two β-diketiminate ligand planes in dimeric metal complexes is often influenced by the different substituents on the ligand (Table 3.1.1).…”

“…and neutral ligands (CO, PPh 3 , etc.) can be coordinated to a metal center with less sterically hindered β-diketiminate in LScCl 2 (THF) n (L tBu,iPr , 16 n=0; L Me,iPr , 47 n = 1) LSc(CH 3 ) 2 (THF) n (L tBu,iPr , 16 n=0; L Me,iPr , 16 n = 1), LSc(Cl)(NHAr)(THF) n L tBu,iPr , 48 n=0; L Me,iPr , 49 n = 1), [LSc(CH 3 )(arene) n ] + (L tBu,iPr , 50 n=0; L Me,iPr , 50 n = 1), LTiCl 2 (THF) n (L tBu,iPr , 51 L tBu,Me3 , 52 L Me,Tbt/Me3 , 53 n=0; L Me,iPr , 54 n=1; L Me,H , 55 n=2), LVCl 2 (THF) n (L Me,iPr , 52, 56 L Me,Et , 34 L Me,Me3 , 34 L Ph,iPr , 34 n=0; L Me, H , 55 n=2), [LCr(μ-Cl)(Solvent) n ] 2 (L tBu,iPr , 35 n=0; L Me,iPr , 36 L Me,Me , 37 n = 1; Solvent = THF, benzene), LFe(NHdipp)(THF) n (L tBu,iPr , 19 n=0; L Me,iPr , 28 n = 1), and LCu(PPh 3 ) n ( Ph L H,iPr , 57 L Me,Me , 58 L Me,iPr , 59 L Me,Me3 , 60 n=1; Ph L H,Me , 57 L CF3, m -CF3 , 61 n=2). Steric conflict between N -aryl substituents and metal can also push the metal center out of the β-diketiminate ligand plane in some metal complexes, especially for early transition metals (Table 3.1.2).…”

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The transition metal mediated reaction of organic azides with isocyanide and CO 2 gives easy access to a variety of carbodiimide and isocyanate compounds that are important intermediates in organic synthesis [299]. The Ni−NHC complexes effectively catalyzed the formation of unsymmetrical carbodiimides and isocyanates via the nitrene transfer reactions (Scheme 47).…”

Nitrene Insertion into CC and CH Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] For certain metals,nitrene-like activity is inferred by the products derived from inter-a nd intramolecular insertions into CÀH bonds, [20][21][22][23][24][25][26][27] aziridinations, [28][29][30][31] and related reactions. [32][33][34][35][36][37][38][39][40] In many instances,i mide radical character is inferred from the reactivity and supported by calculations, [41,42] and the chemistry can be related to biological transformations such as the oxygenations by cytochrome P450. [43][44][45][46][47][48][49] During the course of examining chromium and iron complexes chelated by adiamide diimine tetradentate ligand, unusual azide-dependent reactivity featuring CÀCa nd CÀH bond activations was discovered in conjunction with redox non-innocence (RNI).…”