Bis(η5:η1-pentafulvene)titanium Complexes: Catalysts for Intramolecular Alkene Hydroamination and Reagents for Selective Reactions with N−H Acidic Substrates

• Published in: Organometallics 2010-04, Vol.29 (7), p.1806-1817
• Main Authors: Janssen, Thomas, Severin, René, Diekmann, Mira, Friedemann, Marion, Haase, Detlev, Saak, Wolfgang, Doye, Sven, Beckhaus, Rüdiger
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om100056q

Intramolecular catalytic hydroamination reactions of geminally disubstituted amino alkenes employing the bulky substituted bis(η5:η1-pentafulvene)titanium complexes 1a and 1b and the corresponding benzannelated derivative 2 as catalysts are presented. While all three complexes are competent hydroamination catalysts, best results are achieved with the bis(benzofulvene) derivative 2. In addition, a series of Ti−N-containing compounds became available by stoichiometric reactions of 1 with N−H acidic substrates. In such a way, using aniline derivates (H2N−Ar, Ar: p-tolyl, 1-naphthyl) the bisamides (η5-C5H4−CHR2)2Ti(NHAr)2 (CHR2: adamantyl, Ar: p-tolyl 5a; R: p-tolyl, Ar: p-tolyl 5b; R: p-tolyl, Ar: 1-naphthyl 5c; CHR2: adamantyl, Ar: 1-naphthyl 5d) are prepared in high yields under mild conditions. In contrast to this, the employment of the catalytically relevant amine H2NCH2C(Ph)2CH2CHCH2 (3a) in a reaction with (η5:η1-C5H4CR2)2Ti (CR2: adamantylidene, 1a) leads to the titanium monoamide (η5:η1-C5H4CR2)(η5-C5H4−CHR2)Ti(NHCH2C(Ph)2CH2CHCH2) (6), characterized by X-ray diffraction. In reaction of 1a and 1b with benzophenone imine the titanocene bis(enamides) (η5-C5H4−CHR2)2Ti(NCPh2)2 7a and 7b are formed. Titanium nitrogen double bonds are formed by treatment of 1a with 1,1-diphenylhydrazine. In that manner the hydrazido titanocene (η5-C5H4−CHR2)2TiN−N(Ph)2 (CHR2: adamantyl) was structurally characterized as the pyridine adduct 9. Three different Ti−N bonds are formed in one step by reaction of (η5:η1-C5H4CR2)2Ti (R: p-tolyl, 1b) with 1,1-diphenylhydrazine and pyridine (py), leading to (η5-C5H4−CHR2)Ti(N−NPh2)(−N−NPh2)py 10b (dative Ti−N bond: Ti−py 2.211(2) Ǻ, single Ti−N bond: Ti−NNPh2 − 1.968(2) Ǻ, double Ti−N bond: Ti−NNPh2 2− 1.738(1) Ǻ). The formation of 10b is accompanied by the liberation of one C5H5CHR2 ligand. Generally, the bis(η5:η1-pentafulvene)titanium complexes 1 and 2 are valuable catalysts in hydroamination reactions and reagents in order to prepare Ti−N-containing metallocene-type derivatives.