Metal-ligand bonding and bonding energetics in zerovalent lanthanide, group 3, group 4, and group 6 bis(arene) sandwich complexes. A combined solution thermochemical and ab initio quantum chemical investigation

Wayne A. King, Santo Di Bella, Giuseppe Lanza, Karl Khan, David J. Duncalf, F. Geoffrey N Cloke, Ignazio L. Fragala, Tobin J Marks

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Abstract

In this paper we report a comparative experimental thermochemical and ab initio quantum chemical study of metal-ligand bonding and bonding energetics in the group 3, lanthanide, group 4, and group 5 zerovalent bis(arene) sandwich complexes Sc(TTB)2 (1) Y(TTB)2 (2), Gd(TTB)2 (3), Dy(TTB)2 (4), Ho(TTB)2 (5), Er(TTB)2 (6), Lu(TTB)2 (7), Ti(TTB)2 (8), Zr(TTB)2 (9), Hf(TTB)2 (10), Ti(toluene)2 (11), and Nb(mesitylene)2 (12) (TTB = η6-(1,3,5-tBu)3C6H3). Derived D̄(M-arene) values by iodinolytic batch titration calorimetry in toluene for the process M(arene)2(solution) → Mo + 2arene(solution) are rather large (kcal/mol): 45(3) (1), 72(2) (2), 68(2) (3), 47(2) (4), 56(2) (5), 57(2) (6), 62(2) (7), 49(1) (8), 55(2) (11), 64(3) (9), 67(4) (10), and 73(3) (12). Ab initio relativistic core potential calculations on M(C6H6)2, M = Ti, Zr, Hf, Cr, Mo, W, reveal that the metal-ligand bonding is dominated by strong (greater in group 4 than in the group 6 congeners) δ back-bonding from filled metal dxy and dx2-y2 orbitals to unoccupied arene π orbitals, which decreases in the order Hf > Zr > Ti > W > Mo > Cr. Calculated geometries and D̄(M-C6H6) values (at the MP2 level) yield parameters in favorable agreement with experiment. The latter analyses evidence a great sensitivity to electron correlation effects. Marked, group-centered dependences of the measured D̄(M-arene) values on the sublimation enthalpies of the corresponding bulk metals, on the metal atomic volumes, and, for the lanthanides and Y, on the corresponding free atom f → d promotion energies are also evident.

Original languageEnglish
Pages (from-to)627-635
Number of pages9
JournalJournal of the American Chemical Society
Volume118
Issue number3
Publication statusPublished - 1996

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ASJC Scopus subject areas

  • Chemistry(all)

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