The previously reported and experimentally isolated cobalt dinitrogen1 and dihydrogen2 complexes stabilized by SiP3 (tris(phosphino)silyl) and TPB (tris(phosphino)borane) ligands, designated as (SiP3)Co(N2) (1), (TPB)Co(N2) (2), (SiP3)Co(H2) (3) and (TPB)Co(H2) (4), have been studied by quantum mechanical calculations using density functional theory. The geometry optimizations at BP86-D3(BJ)/Def2TZVPP level suggest an end-on binding mode for N2 and side-on for H2. NBO calculations reveal the accumulation of charge on N2 in both complexes 1 and 2, indicating Co→N2 π-back donation. Whereas no such accumulation of charge on H2 is observed in complexes 3 and 4. Positive Laplacian ∇2ρ(r) and ƞ value less than unity from AIM analysis suggests metal ligand closed-shell interactions. The EDA-NOCV calculations demonstrate the covalent nature of the CoN bond with dominant Co→N2 π back donations and the electrostatic nature of the CoH bond with strong H→Co σ donation in 3 and slightly strong Co→H σ back donations in 4. The results of EDA-NOCV are well correlated with the NBO, QTAIM and bond dissociation analysis. According to the calculations, N2 behave as good π acceptor, whereas H2 as a good σ donor. Relatively large HOMO-LUMO gap suggests the stability of silicon substituted complexes 1, 3 over boron substituted 4, 5.

Co-N2 Vs Co-H2: AN INSIGHT INTO THE BONDING ANALYSIS OF SIGMA COMPLEXES

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27th CRSI National Symposium in Chemistry

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