Here we report that attempted preparation of low-valent CaI complexes in the form of LCa-CaL (where L is a bulky β-diketiminate ligand) under dinitrogen (N2) atmosphere led to isolation of LCa(N2)CaL, which was characterized crystallographically. The N22ˉ anion in this complex reacted in most cases as a very potent two-electron donor. Therefore, LCa(N2)CaL acts as a synthon for the low-valent CaI complex LCa-CaL, which was the target of our studies. The N22ˉ anion could also be protonated to diazene (N2H2) that disproportionated to hydrazine and N2. The role of Ca d orbitals for N2 activation is discussed.

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The reagent RK [R=CH(SiMe3)2 or N(SiMe3)2] was expected to react with the low‐valent (DIPPBDI)Al (DIPPBDI=HC[C(Me)N(DIPP)]2, DIPP=2,6‐iPr‐phenyl) to give [(DIPPBDI)AlR]−K+. However, deprotonation of the Me group in the ligand backbone was observed and [H2C=C(N‐DIPP)−C(H)=C(Me)−N−DIPP]Al−K+ (1) crystallized as a bright‐yellow product (73 %). Like most anionic AlI complexes, 1 forms a dimer in which formally negatively charged Al centers are bridged by K+ ions, showing strong K+⋅⋅⋅DIPP interactions. The rather short Al–K bonds [3.499(1)–3.588(1) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C6H6 and monomeric in THF, but slowly reacts with both solvents. In reaction with C6H6, two C−H bond activations are observed and a product with a para‐phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in (DIPPBDI)Al. Calculations show that both AlI and K+ work in concert and determines the reactivity of 1.

Tw oseries of bulkyalkaline earth (Ae) metal amide complexes have been prepared:A e[N(TRIP) 2 ] 2 (1-Ae) and Ae[N(TRIP)(DIPP)] 2 (2-Ae) (Ae = Mg, Ca, Sr,B a; TRIP = SiiPr 3 ,D IPP = 2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized.M onomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene.I ti sa lso active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species,w hich can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate sizeb ut it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has an oticeable influence on the thermodynamics for formation of the (amide)AeH species.C omplex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts,t he substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene. Scheme 4. Energy profiles (DH in kcal mol À1 )for a) the hydrogenation of ethylene by catalysts 1-Ca(orange), 1-Ba (black) and CaN'' 2 (red), and b) benzene hydrogenation by 1-Ba;B3PW91/def2tzvpp including correction for dispersion (GD3BJ) and solvent (PCM = benzene).

The reaction of (tBuBDI)­ZnEt with [Ph3C+]­[B­(C6F5)4 −] yielded the cation (tBuBDI)­Zn+ (tBuBDI = CH­[C­(tBu)­N-DIPP]2, DIPP = 2,6-diisopropylphenyl). The cation is sterically too shielded to interact with the ion B­(C6F5)4 – but forms complexes with arenes (benzene, toluene, m-xylene) or halobenzenes (PhX: X = F, Cl, Br, I). Crystal structures of these complexes are compared with those of the corresponding Mg complexes. Although Mg2+ and Zn2+ are of equal size, the Zn···arene and Zn···XPh contacts are generally 0.1–0.2 Å shorter than comparable contacts to (tBuBDI)­Mg+. This originates from differences in bond character: bonding to Mg has a more electrostatic nature. A major difference between Mg and Zn is observed for PhF complexation. While the hard Mg2+ cation prefers Mg···FPh bonding, the softer Zn2+ shows a Zn···(π)­PhF interaction. Heavier halobenzenes with softer halogens (Cl, Br, I) show Zn···XPh bonding. DFT calculations on (tBuBDI)­Zn+···XPh (X = F, Cl, Br, I) show decreasing Zn···X–Ph angles from PhF to PhI on account of the increase in the halogen’s σ-hole. Zn···XPh interactions result in C–X bond lengthening, but C–X bond activation is less pronounced than in corresponding Mg···XPh complexes. Weak (tBuBDI)­Zn+···XPh bonding could not be detected in solution but is believed to play a role in the functionalization of organohalides by Zn reagents.