871502-36-2Relevant articles and documents
Nonclassical bonding in titanasilacyclohexadiene compounds resulting from highly methyl-substituted titanocene-bis(trimethylsilyl)ethyne complexes and bis((trimethylsilyl)ethynyl)silanes
Horacek, Michal,Stepnicka, Petr,Gyepes, Robert,Cisarova, Ivana,Kubista, Jiri,Lukesova, Lenka,Meunier, Philippe,Mach, Karel
, p. 6094 - 6103 (2008/10/09)
Reactions at elevated temperatures (150°C) of titanocene-η2- bis(trimethylsiryl)ethyne (btmse) complexes [(η5-C 5H5-nMen)2Ti(η2- btmse)] (n = 3-5; 1b-d) with bis((trimethylsilyl)-ethynyl)dimethylsilane (2a) afford the unusual 1,1-bis(η5-cyclopentadienyl)-4,4-dimethyl-3,5- bis(trimethylsilyl)-1-titana-4-silacyclohexa-2,5-diene complexes [(η5-C 5H5-nMen)2Ti{C=C(SiMe 3)}2SiMe2] (4b-d), whereas the nonmethylated precursor [(η-C5H5)2Ti(η2- btmse)] (1a) gives under similar conditions the known dinuclear, acetylide-bridged complex [{(η5-C5H5) 2-Ti(μ-η1:η2-C≡CSiMe 3)}2] (3a). In contrast, analogous reactions with bis((trimethylsilyl)-ethynyl)diphenylsilane (2b) give the product of simple ligand exchange [(η-C5Me5)2Ti(η 2-Me3SiC≡CSiPh2C≡CSiMe 3)] (6d) from 1d and mixtures containing the similar complex [(η5-C5HMe4)2Ti(η 2-Me3SiC≡CSiPh2C≡CSiMe 3)] (6c) and the titanasilacyclohexadiene [Ti(η5- C5HMe4)2Ti{C=C(SiMe3)} 2SiPh2] (5c) from 1c. Hydrogenolysis of 5c (1 bar/3 h) affords 1,4-bis(trimethylsilyl)-5,5-diphenyl-5-silacyclopenta-1,3-diene (7). Compounds 4 and 5 possess a surplus of two bonding electrons at the titanium-bonded carbon atoms (Cα) with paired spins, whose presence is reflected by extremely short Ti-Cα bond lengths (1.981(4)-1.998(3) A) and Cα-Cα contacts (1.821(4)-1.933(2) A), the latter excluding the presence of a 3-silacyclopenta-1,4-diene moiety simply bonded to titanium via two a bonds. DFT calculations showed that the two singly occupied p orbitals at C α interact with the titanocene 1a1 orbital, giving rise to a three-center-two-electron, Δ-shaped bond.
