Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

0430955 - ÚFCH JH 2015 RIV US eng J - Článek v odborném periodiku
Pinkas, Jiří - Gyepes, Robert - Císařová, I. - Kubišta, Jiří - Horáček, Michal - Mach, Karel
Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes.
Organometallics. Roč. 33, č. 13 (2014), s. 3399-3413. ISSN 0276-7333. E-ISSN 1520-6041
Grant CEP: GA ČR(CZ) GAP207/12/2368; GA ČR GP203/09/P276
Institucionální podpora: RVO:61388955
Klíčová slova: atoms * complexation * Electron spin resonance spectroscopy
Kód oboru RIV: CF - Fyzikální chemie a teoretická chemie
Impakt faktor: 4.126, rok: 2014

Titanocene hydride [Cp-2*TiH] (Cp* = eta(5)-C5Me5) (1) readily inserts simple internal alkynes (RC)-C-1 CR2 into its Ti-H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp-2*Ti((RC)-C-1=CHR2)] (2a-e) contain a sigma(1)-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R-1 = SiMe3; R-2 = SiMe3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti-H agostic bond of the sigma(1)-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a-4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d(1) electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC C)(2) to give eta(3)-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a-2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) diloro-alkenyl complexes [Cp-2*TiCl((RC)-C-1=CHR2)] 3a-3e and chloro-alkenynes 6a and 6b, respectively. H-1 and C-13 NMR spectra of 3a-3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable pi-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d(8) solutions 7 dissociated at 80 degrees C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable pi-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti(C5Me4CH2)].
Trvalý link: http://hdl.handle.net/11104/0235628