Group 3 Transition Metal, Lanthanide, and Actinide–Dinitrogen Complexes

Formation of the End-on Bound Lanthanide Dinitrogen Complexes [(R2N)3Ln–N═N–Ln(NR2)3]2– from Divalent [(R2N)3Ln]1– Salts (R = SiMe3)

“…X-ray crystallography revealed that the reduced dinitrogen unit in 2-Tb is bound end-on, as shown in Figure . Previously, all crystallographically characterized Ln 2 N 2 complexes of the lanthanide metals have had side-on bound structures. − Only with scandium, eq , was an end-on structure found …”

“…Initial reduction could form an endon {[(R 2 N) 3 Ln][N 2 ]} 1− radical that is quickly trapped by another [Ln(NR 2 ) 3 ] 1− unit to form the end-on bimetallic complex, {[(R 2 N) 3 Ln] 2 [μ-η 1 :η 1 -N 2 ]} 2− , described for the first time in this study. These complexes could thermally decompose to reform the Ln(II) precursors, [Ln(NR 2 ) 3 ] 1− , as observed here, or, if an (NR 2 ) 1− ligand is substituted by THF, a monoanionic complex of the type isolated in this study, {[(THF)(R 2 N) 2 Ln][μ-η 2 :η 2 -N 2 ][Ln(NR 2 ) 3 ]} 1− , 8-Ln, could form. A reviewer has pointed out that the substitution of an (NR 2 ) 1− ligand in {[(R 2 N) 3 Ln] 2 [μ-η 1 :η 1 -N 2 ]} 2− by THF would increase the electrophilicity of the Ln(III) ion, and this could lead to the end-on to side-on conversion.…”

“…45,46 In the case of smaller titanium, however, both C 5 Me 5 and C 5 Me 4 H ligands are large enough to give endon bound dinitrogen complexes [(C 5 Me 4 R) 2 Ti] 2 (μ-η 1 :η 1 -N 2 ) (R = H, Me), 47,48 and a trimethylcyclopentadienyl ligand is n e e d e d t o ob s er v e th e s i d e -o n b i n d i n g m od e, [(C 5 Me 3 H 2 ) 2 Ti] 2 (μ-η 2 :η 2 -N 2 ). 49,50 Temperature is also crucial: under the conditions of the previously reported Ln(NR 2 ) 3 /K/N 2 reactions, [(THF)-(R 2 N) 2 Ln] 2 [μ-η 2 :η 2 -N 2 ], 7-Ln, would be the only isolated product. To observe the Ln(II) and Ln−NN−Ln intermediates, low temperatures and fast reaction times are necessary.…”

“… Since that initial discovery, dozens of Ln 2 N 2 (Ln = rare-earth metal, i.e. Sc, Y, and lanthanides) complexes have been isolated, and all of the lanthanide compounds display side-on μ-η 2 :η 2 -N 2 bonding, eq . − These reactions differed from eq in that the starting material was not a Ln­(II) complex, but a combination of a Ln­(III) starting material and potassium. Because molecular Ln­(II) complexes for many of the metals in eq were unknown when the dinitrogen reduction was discovered, the mode of formation of the (NN) 2– products was not obvious.…”

Dipnictogen f-Element Chemistry: A Diphosphorus Uranium Complex

“…As the first member of the heavier homologues of N 2 , it is notable that the principal U–P binding mode in 5quin is of A­(π g= ) character. Thus, P 2 joins a family of two donor-atom π-bonded ligands at uranium that includes N 2 , C 2 H 4 , As 2 H 2 , and larger π-bonded ligands such as cyclobutadienyl and -pentadienyl . In contrast, cyclo -P 5 and larger η 6–8 -ligands , adopt δ-bonding, emphasizing the greater use of 5f-orbitals for π-bonding to small ligands that require more angular overlap, whereas 6d-orbital participation becomes more significant for more expansive, less angular overlap ligands.…”