beta-Agostic Interactions in 15-Valence-Electron 9-BBN Hydroborate Half-Sandwich Titanium(III) Complexes

초록

A series of new mono-Cp- or Cp*-based titanium(III) 9-BBN hydroborate derivatives with either 15- or 17-valence-electron configurations were synthesized, and their structures were determined by single-crystal X-ray diffraction analysis. These studies revealed that the 15-valence-electron complexes[Cp*Ti(III)Cl{mu-H)(2)BC(8)H(14)}(THF)] (2) and [Cp*Ti(III){(mu-H)(2)BC(8)H(14)}(2)] (6) show the presence of beta-agostic interactions between the Ti(III) metal center and the alpha-hydrogens on the 9-BBN ligand in the solid state, while the 17-valence-electron complexes [CpTi(III){(mu-H)(2)BC(8)H](14)}(2)(THF)] (3), [Cp*Ti(III){(mu-H)(2)BC(8)H(14)}(2)(THF)] (4), and [Cp*Ti(III){(mu-H)(2)BC(8)H(14)}(2)(NC(5)H(5))] (7) display no agostic interactions. Agostic interactions in Ti(III) species are uncommon. While the Ti center dot center dot center dot H distance can be indicative of an agostic interaction, other structural parameters provide more reliable indication of such an interaction. These are the shortening of the Ti-B distance, the lengthening of the B-C(alpha) distance, the sharpening of the Ti-B-C(alpha) angle, and the narrowing of the dihedral angle between the TiH(2) and H(2)B planes in 9-BBN ligands that adopt an agostic interaction with titanium.

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