Displacement of ethene from the decamethyltitanocene-ethene complex with internal alkynes, substituent-dependent alkyne-to-allene rearrangement, and the electronic transition relevant to the back-bonding interaction

摘要: The titanocene-ethene complex [Ti(II)(η2-C2H4)(η5-C5Me5)2] (1) with simple internal alkynes R1CCR2 gives complexes [Ti(II)(η2-R1CCR2)(η5-C5Me5)2] {R1, R2: Ph, Ph (3), Me (4), Me, SiMe3 (5), (6), t-Bu, (7), and SiMe3, (8). In contrast, R1 = R2 t-Bu or i-Pr afford allene [Ti(II)(η2-CH2CCHR2)(η5-C5Me5)2] (11) (12), whereas for Et a mixture of alkyne (13A) minor (13) is obtained. Crystal structures 4, 6, 7 11 have been determined; the latter structure proved back-bonding interaction terminal double bond. Only synthesis 8 from 1 was inefficient because equilibrium constant reaction [1] + [Me3SiCCSiMe3] ⇌ [8] [C2H4] approached 1. Compound 9 (R1, Me), not obtainable 1, together compounds 3–6 10 Et) were also prepared by exchange 8, however this did take place in attempts to obtain 7. Compounds 3–9 display longest-wavelength electronic absorption band range 670–940 nm due HOMO → LUMO transition. assignment first excitation be predominantly b2 a1 transition confirmed DFT calculations. calculated energies followed order hypsochromic shifts relative that induced acetylene substituents: > ≫ SiMe3. Computational results affirmed nature alkyne-to-metal coordination.