Details

Autor(en) / Beteiligte

• Zhang, Xiuhui
• Li, Qian-shu
• Xie, Yaoming
• King, R. Bruce
• Schaefer, Henry F

Titel

Possibilities for Titanium−Titanium Multiple Bonding in Binuclear Cyclopentadienyltitanium Carbonyls: 16-Electron Metal Configurations and Four-Electron Donor Bridging Carbonyl Groups as Alternatives

Ist Teil von

• Inorganic chemistry, 2010-02, Vol.49 (4), p.1961-1975

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2010

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The structures for the binuclear Cp2Ti2(CO) n derivatives (Cp = η5-C5H5; n = 8, 7, 6, 5, 4, 3, 2) have been optimized using density functional theory. Furthermore, the thermodynamics of CO dissociation, disproportionation into Cp2Ti2(CO) n+1 + Cp2Ti2(CO) n−1, and dissociation into mononuclear fragments of these Cp2Ti2(CO) n derivatives have been studied. An unbridged Cp2Ti2(CO)8 structure with a long ∼3.9 Å Ti−Ti bond is found. As expected from the long Ti−Ti bond, the predicted dissociation energy of this dimer into CpTi(CO)4 fragments is relatively low at 7 ± 3 kcal/mol. The lowest energy Cp2Ti2(CO)6 structure has two CpTi(CO)3 units linked by a formal ∼2.8 Å TiTi triple bond and thus is the next member of the MM triply bonded series Cp2V2(CO)5, Cp2Cr2(CO)4, Cp2Mn2(CO)3, all three of which are stable compounds. The lowest energy structures of Cp2Ti2(CO)7, Cp2Ti2(CO)5, and Cp2Ti2(CO)4 all contain one or two four-electron donor bridging η2-μ-CO groups. However, they are not likely to be stable molecules since their disproportionation energies into Cp2Ti2(CO) n+1 + Cp2Ti2(CO) n−1 are either nearly thermoneutral (n = 5) or exothermic (n = 7 and 4). The lowest energy structure of Cp2Ti2(CO)3, in which all three carbonyl groups are four-electron donor η2-μ-CO groups bridging a ∼3.05 Å formal Ti−Ti single bond, is a promising synthetic target since it is thermodynamically stable with respect to both CO dissociation and disproportionation into Cp2Ti2(CO)4 + Cp2Ti2(CO)2. In the lowest energy Cp2Ti2(CO)2 structure both carbonyl groups are four-electron donor η2-μ-CO groups bridging a formal 2.74 Å TiTi triple bond. These low energy Cp2Ti2(CO) n (n = 3, 2) structures have only a 16-electron titanium configuration rather than the usually favorable 18-electron configuration for metal carbonyl complexes.