Backbone Reactivity of Lithium β‐Diketiminate (NacNac) Complexes with CO₂, tBuNCO and iPrNCO

Abstract

Though alkali metal NacNac (β‐diketiminate) complexes have been utilised in synthesis as NacNac‐transfer agents, studies of them in their own right with small molecules are exceptionally rare. Here, the lithium compound of the common 2,6‐diisopropylphenyl‐β‐methyldiketiminate [NacNac(Dipp, Me)] ligand is investigated with carbon dioxide and isocyanates. In all four cases reaction occurs at the backbone γ‐C atom of the NacNac ligand, which redistributes electronically into a diimine. Insertion of CO2 gives an eight‐atom carboxylate (Li2O4C2) ring at the γ‐C site in a dimer. Insertion of tBuNCO gives a secondary amide at the γ‐C site in a monomer with TMEDA chelating lithium. Double insertion of tBuNCO and (adventitious) oxygen gives a dimer with a (LiO)2 central core involving the latter source. Insertion of less bulky (iPrNCO) gives a dimer with dimerisation through the C=O bonds of the emergent secondary amide function.

Synthesis and Reactivity of Heteroleptic Ga‐P‐C Allyl Cation Analogues

“…Nucleophilic bond‐forming reactions involving the γ‐carbon have been previously reported for β‐diketiminate stabilized cationic transition metal [32] and Al complexes [33] as well as neutral metal complexes [34] with heteroallenes, that is, CO 2 , CS 2 , diphenylketene, iso(thio)cyanates, and other unsaturated substrates including oxygen and ethylene [35] . However, to the best of our knowledge, the formation of a tripodal N,N′,N′′ ligand as observed in compound 7 was only reported for the reaction between [LMg( n ‐Bu)] 2 and phenylisothiocyanate, [36] while the C−C bond forming reaction of LLi with t ‐BuNCO yielded the isocyanate insertion product [{(MeCN‐2,6‐ i ‐Pr 2 C 6 H 3 ) 2 C(CONH( t ‐Bu))}Li⋅TMEDA], in which the Li cation is coordinated in an N,O‐chelating mode [37] …”

A Phosphine Functionalized β‐Diketimine Ligand for the Synthesis of Manifold Metal Complexes

“…[11,12] b-Diketiminates are an omnipresentl igand system in coordination chemistry, mainly due to their convenient synthetic accessibility ande asily adjustable scaffold, allowing a fine tuning of the electronic and sterice nvironment. [13][14][15][16] This has led to awide scope of applications [17] rangingf rom the formation of redox-active systems, [3] enhanceds pectroscopic properties, [18] supporting ligandsf or metal-mediated cataly-metals within an organometallic structure, ar esearch field which hasb een comprehensively studied in recent years. [42][43][44] To the best of our knowledge,r elated phosphine functionalized b-diketimine systems (see Figure 1, top right), exhibiting a PNNP type pocket, have not been reported yet.…”

“…β‐Diketiminates are an omnipresent ligand system in coordination chemistry, mainly due to their convenient synthetic accessibility and easily adjustable scaffold, allowing a fine tuning of the electronic and steric environment . This has led to a wide scope of applications ranging from the formation of redox‐active systems, enhanced spectroscopic properties, supporting ligands for metal‐mediated catalysis as well as the activation of small molecules . In this regard, β‐diketiminate ligands have been proven capable of supporting metal ions in a number of oxidation states as well as chemical environments .…”

Expected and Unexpected Reactivities of Homoleptic LiNacNac and Heteroleptic NacNacMg(TMP) β-Diketiminates toward Various Small Unsaturated Organic Molecules

“…Repeating the reaction but heating the mixture to reflux temperature still afforded 1 as confirmed by NMR spectra of the isolated product, with a 1 H resonance at 5.02 ppm, corresponding to the still intact backbone γ-hydrogen atom in contrast to the sigmatropic rearrangement of this C—H atom to the N=C bond of the previously studied isocyanate systems. 39 …”

“… 34 − 38 Our first expedition in this area found that the electrophilic species CO 2 , t -BuNCO, and i -PrNCO all reacted with lithium NacNac at the γ-C site of the ligand backbone, instead of at the “frontal” polar Li–N bonds, expelling the innocent, spectator image of alkali-metal-attached NacNac ligands. 39 Here, the picture becomes more complicated when the outcomes of exposing LiNacNac to carbodiimide and phosphine oxide molecules are revealed. Moreover, bringing NacNacMg(TMP) into this study for the first time by treating it with isocyanate and isothiocyanate molecules reveals surprising reactivities out of kilter with those of conventional Mg TMP-containing compounds.…”