The insertion of 1,1-diphenylethylene into the Mg-Mg bond of two magnesium(I) dimers, [(Nacnac)Mg-] (Ar = CHMe-2,4,6 (Mes); CHEt-2,6 (Dep)), yielding 1,2-dimagnesioethane products, [{(Nacnac)Mg}(μ-CHCPh)], is described. These reactions are readily reversible at room temperature and thus represent the first examples of room-temperature reversible redox processes for s-block metal complexes. The 1,2-dimagnesioethane products are highly activated magnesium alkyls and show unprecedented, uncatalyzed reactivity toward H, CO, and ethylene. Computational studies have investigated the mechanisms of all presented reaction types.

The first examples of magnesium(I) dimers bearing tripodal ligands, [(Mg{κ(3) -N,N',O-(ArNCMe)2 (OCCPh2 )CH})2 ] [Ar=2,6-iPr2 C6 H3 (Dip) 7, 2,6-Et2 C6 H3 (Dep) 8, or mesityl (Mes) 9] have been prepared by post-synthetic modification of the β-diketiminato ligands of previously reported magnesium(I) systems, using diphenylketene, OCCPh2 . In contrast, related reactions between β-diketiminato magnesium(I) dimers and the isoelectronic ketenimine, MesNCCPh2 , resulted in reductive insertion of the substrate into the MgMg bond of the magnesium(I) reactant, and formation of [{(Nacnac)Mg}2 {μ-κ(2) -N,C-(Mes)NCCPh2 }] (Nacnac=[(ArNCMe)2 CH](-) ; Ar=Dep 10 or Mes 11). Reactions of the four-coordinate magnesium(I) dimer 8 with excess CO2 are readily controlled, and cleanly give carbonate [(LMg)2 (μ-κ(2) :κ(2) -CO3 )] 12 (L=[κ(3) -N,N',O-(DepNCMe)2 (OCCPh2 )CH](-) ; thermodynamic product), or oxalate [(LMg)2 (μ-κ(2) :κ(2) -C2 O4 )] 13 (kinetic product), depending on the reaction temperature. Compound 12 and CO are formed by reductive disproportionation of CO2 , whereas 13 results from reductive coupling of two molecules of the gas. Treatment of 8 with an excess of N2 O cleanly gives the μ-oxo complex [(LMg)2 (μ-O)] 14, which reacts facilely with CO2 to give 12. This result presents the possibility that 14 is an intermediate in the formation of 12 from the reaction of 8 and CO2 . In contrast to its reactions with CO2 , 8 reacts with SO2 over a wide temperature range to give only one product; the first example of a magnesium dithionite complex, [(LMg)2 (μ-κ(2) :κ(2) -S2 O4 )] 16, which is formed by reductive coupling of two molecules of SO2 , and is closely related to f-block metal dithionite complexes derived from similar SO2 reductive coupling processes. On the whole, this study strengthens previously proposed analogies between the reactivities of magnesium(I) systems and low-valent f-block metal complexes, especially with respect to small molecule activations.

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Redox transmetallation protolysis reactions between HgPh2, elemental metals, M = Ca, Eu, or Yb, and the bulkyl arylsilylamine PhL†H (HN(SiPh3)(Ar†), Ar† = C6H2Pri{C(H)Ph2}2-4,2,6), or the borylsilylamine PhLBoH (HN(SiPh3){B(DipNCH)2}, Dip = C6H3Pri2-2,6) pro-ligands yielded complexes incorporating doubly deprotonated, N,C-chelating amido/organyl ligands, viz. [M(L-H) (thf)x]n, L-H = PhL†-H (1-3) or PhLBo-H (4-5); M = Ca (1, 4), Eu (2) or Yb (3, 5); x = 0 (5) or 2 (1-4); n = 1 (1-4) or 2 (5). Structural differences between 4 and 5 represent a rare divergence in the chemistry of divalent calcium and ytterbium. Utilisation of a less hindered bis(aryl) amine, DLMH (HN(Dip)(Mes), Mes = C6H2Me3-2,4,6) in a similar reaction yielded a three-coordinate, trigonal planar ytterbium complex [Yb(DLM)2(thf)] (6). Direct redox transmetallation reactions between an amido-mercurial iodide [(MeL†)HgI] (7, MeL† = -N(SiMe3)(Ar†)) and ytterbium or europium metal afforded homoleptic [Yb(MeL†)2] (8) and heteroleptic [{Eu(MeL†)(μ-I)(thf)}2] (9) respectively. This study highlights the versatility of redox transmetallation pathways to amido-lanthanoid complexes, especially where such compounds are difficult to access using conventional salt metathesis pathways.

This study details the isolation and characterisation of three novel silver(I) amides in solution and solidstate, [Ag(Cy 3 P)(HMDS)] 2,[ Ag(Cy 3 P){N(TMS)(Dipp)}] 3 and [Ag(Cy 3 P) 2 (NPh 2 )] 4.T heir catalytic abilities have proved successfuli nh ydroboration and hydrosilylation reactions with af ull investigation performed with complex 2.B oth protocols proceed under mild conditions, displaying exceptional functional-groupt olerance and chemoselectivity, in excellent conversions at competitive reactiont imes. This work reveals the first catalytic hydroboration of aldehydes and ketones performed by as ilver(I) catalyst.

The first examples of magnesium acyls, [(Nacnac)Mg{μ-C(Ph)O}(μ-OR)Mg(Nacnac)] (R=Me, tBu or Ph; Nacnac=[HC(MeCNAr) ] ; Ar=C H Me -2,4,6 ( Nacnac), C H Et -2,6 ( Nacnac), C H iPr -2,6 ( Nacnac)), have been prepared by reductive cleavage of a series of esters using dimeric magnesium(I) reducing agents, [{(Nacnac)Mg} ]. Crystallographic studies reveal the complexes to be dimeric, being bridged by both phenyl-acyl and alkoxide/aryloxide fragments. The crystal structures, combined with results of spectroscopic and computational studies suggest that the nature of the acyl ligands within these complexes should be viewed as lying somewhere between anionic umpolung acyl and oxo-carbene. However, reactions of the acyl complexes with a variety of organic electrophiles did not provide evidence of umpolung acyl reactivity. A number of attempts to prepare alkoxide free magnesium acyls were carried out, and while these were unsuccessful, they did lead to unusual products, the crystallographic and spectroscopic details of which are discussed.

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