Binuclear pentalene titanium carbonyls: Comparison with related cyclopentadienyltitanium carbonyls

摘要

> The structures and energetics of the binuclear pentalene titanium carbonyls PnTi ₂ (CO) _n (Pn = η 5 ,η 5 ‐C ₈ H ₆ ; n ?=?8, 7, 6, 5, 4, 3, 2) and their 1,4‐bis(triisopropylsilyl) derivatives related to experimentally studied systems have been examined by density functional theory. Geometric constraints within a η 5 ,η 5 ‐PnTi ₂ unit having exclusively pentahapto ring‐titanium bonds limit the Ti?Ti distances to a maximum of ~3.1 ? in the PnTi ₂ (CO) _n derivatives in contrast to the cyclopentadienyl analogues Cp ₂ Ti ₂ (CO) _n where bonding Ti?Ti distances as long as ~3.9 ? are found. Furthermore, at least one 4‐electron donor η 2 ‐μ‐CO group but never more than 2 such groups are found in the lowest energy PnTi ₂ (CO) _n structures. The lowest energy PnTi ₂ (CO) _n structures ( n ?=?4, 3, 2) by margins of at least 10 kcal/mol have 2 η 2 ‐μ‐CO groups and formal Ti?Ti triple bonds in the singlet spin state. The carbonyl rich species PnTi ₂ (CO) _n and Pn ? Ti ₂ (CO) _n