We report the isolation and spectroscopic identification of the eight-coordinated alkaline earth metal–dinitrogen complexes M(N 2 ) 8 (M=Ca, Sr, Ba) possessing cubic ( O h ) symmetry in a low-temperature neon matrix. The analysis of the electronic structure reveals that the metal-N 2 bonds are mainly due to [M(d π )]→(N 2 ) 8 π backdonation, which explains the observed large red-shift in N-N stretching frequencies. The adducts M(N 2 ) 8 have a triplet ( 3 A 1g ) electronic ground state and exhibit typical bonding features of transition metal complexes obeying the 18-electron rule. We also report the isolation and bonding analysis of the charged dinitrogen complexes [M(N 2 ) 8 ] + (M=Ca, Sr).

Chemical reactions involving quantum mechanical tunneling (QMT) increasingly attract the attention of scientists. In contrast to the hydrogen-tunneling as frequently observed in chemistry and biology, tunneling solely by heavy atoms is rare. Herein, we report heavy-atom tunneling in trifluoroacetyl nitrene, CF C(O)N. The carbonyl nitrene CF C(O)N in the triplet ground state was generated in cryogenic matrices by laser (193 or 266 nm) photolysis of CF C(O)N and characterized by IR and EPR spectroscopy. In contrast to the theoretically predicted activation barriers (>10 kcal mol ), CF C(O)N undergoes rapid rearrangement into CF NCO with half-life times of less than 10 min and unprecedentedly large N/ N kinetic isotope effects (1.18-1.33) in solid Ar, Ne, and N matrices even at 2.8 K. The tunneling disappearance of CF C(O)N becomes much slower in the chemically active toluene and in 2-methyltetrahydrofuran at 5 K.

We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n−1)d AOs of M and strong backdonation from the occupied (n−1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals.