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

Dalton Transactions : an International Journal of Inorganic Chemistry
Jiří PinkasKarel Mach

Abstract

The titanocene-ethene complex [Ti(II)(η(2)-C2H4)(η(5)-C5Me5)2] (1) with simple internal alkynes R(1)C≡CR(2) gives complexes [Ti(II)(η(2)-R(1)C≡CR(2))(η(5)-C5Me5)2] {R(1), R(2): Ph, Ph (3), Ph, Me (4), Me, SiMe3 (5), Ph, SiMe3 (6), t-Bu, SiMe3 (7), and SiMe3, SiMe3 (8). In contrast, alkynes with R(1) = Me and R(2) = t-Bu or i-Pr afford allene complexes [Ti(II)(η(2)-CH2=C=CHR(2))(η(5)-C5Me5)2] (11) and (12), whereas for R(2) = Et a mixture of alkyne complex (13A) and minor allene (13) is obtained. Crystal structures of 4, 6, 7 and 11 have been determined; the latter structure proved the back-bonding interaction of the allene terminal double bond. Only the synthesis of 8 from 1 was inefficient because the equilibrium constant for the reaction [1] + [Me3SiC≡CSiMe3] ⇌ [8] + [C2H4] approached 1. Compound 9 (R(1), R(2): Me), not obtainable from 1, together with compounds 3–6 and 10 (R(1), R(2): Et) were also prepared by alkyne exchange with 8, however this reaction did not take place in attempts to obtain 7. Compounds 1 and 3–9 display the longest-wavelength electronic absorption band in the range 670-940 nm due to the HOMO → LUMO transition. The assignment of the first excitation to be of predominantly a b2 → a1 transition was confir...Continue Reading

References

Mar 18, 2000·Journal of Computer-aided Molecular Design·G Schaftenaar, J H Noordik
Aug 12, 2000·Chemistry : a European Journal·M HoracekK Mach
Dec 26, 2001·Chemical Reviews·G Frenking, N Fröhlich
Oct 13, 2005·Journal of the American Chemical Society·Marco W BouwkampBart Hessen
Mar 17, 2011·Chemical Communications : Chem Comm·Shichao Yu, Shengming Ma

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Citations

Nov 17, 2015·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Neha Phadke, Michael Findlater
Dec 2, 2020·Inorganic Chemistry·Anders ReinholdtDaniel J Mindiola
Sep 18, 2021·Chemical Communications : Chem Comm·Skye Fortier, Alejandra Gomez-Torres

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