Early Main Group Metal Catalysis: How Important is the Metal?

Abstract

Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph2N−][Me4N+] and [Ph3C−][Me4N+]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of ArNCO and RNCNR (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated CC bonds in H2CCHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.

Cationic Magnesium π–Arene Complexes

“…13 These even weaker metal•••alkene interactions can be a requirement for CC double bond activation and subsequent functionalization. 14 Very recently, we described synthesis and structure of the first unsupported Mg•••alkyne coordination in (BDI)Mg + •EtC CEt (III in Figure 1) that crystallized as its B(C 6 F 5 ) 4 − salt (BDI = CH[C(CH 3 )N-Dipp] 2 ; Dipp = 2,6-diisopropylphenyl). 15 The same report presented the first metal•••benzene bonds for the lighter metals Mg 2+ and Ca 2+ in the crystal structures of (BDI)M + •C 6 H 6 (M = Mg 2+ and Ca 2+ ).…”

Formation and Properties of the Trichloroberyllate Ion

“…I n the past decade, interest in alkaline-earth-metal chemistry has grown immensely because of the evolution of Lewis acidic molecular catalysts based on magnesium, calcium, strontium, and barium. 1 For example, CaI 2 , in combination with a strong organic Schwesinger base, is able to activate unreactive CC double bonds, 2 while simple alkaline-earth-metal (Mg−Ba) bisamides can be used as precatalysts for the 100% atom-efficient assembly of imidazolidin-2-ones. 3 Magnesium and calcium βdiketiminato compounds have also been shown to reduce CO 2 in the presence of the strong Lewis acid B(C 6 F 5 ) 3 .…”

“…It is known that PMe 3 partly dissociates from (Me 3 P) 2 BeCl 2 (1a) in solution. 11 This leads presumably to the presence of small amounts of tricoordinated monophosphane adducts to BeCl 2 (2) in solution, which act as Lewis acids and may form adducts to chlorinated solvents (3) via coordination to a chlorine atom. The electron-deficient beryllium atom polarizes the C−Cl bond, which enables nucleophilic attack of the dissociated phosphane at the carbon atom, leading to the formation of phosphonium salts (Scheme 1).…”

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

“…47 − 52 It has previously been shown by the Harder group that activation of carbodiimides is possible under metal-free conditions, although it was noted that in this case the “extent of activation is less than that in carbodiimide···Li+ complexes”, with harsh conditions necessary under a metal-free environment. 53 It is likely that the bulk of the DCC molecule prevents formation of an amidinate in this system, with the DCC being too sterically congested to allow for nucleophilic addition of the NacNac in this case. As alluded to earlier, solution NMR data are in agreement with the solid-state structure (see the Supporting Information for full details), suggesting that its composition is maintained in solution.…”