Synthesis, Reactivity, and Insights into the Lewis Acidity of Mononuclear Titanocene Imido Complexes Bearing Sterically Demanding Terphenyl Moieties

• Published in: Organometallics Vol. 39; no. 17; pp. 3232 - 3239
• Main Authors: Fischer, Malte, Wolff, Marie Christin, del Horno, Estefanía, Schmidtmann, Marc, Beckhaus, Rüdiger
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 14.09.2020; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; ALKYLIDENE; DINITROGEN COMPLEX; CYCLOADDITION; HYDROGENATION; NONRIGID ORGANOMETALLIC MOLECULES; POLYMERIZATION; CYCLOPENTADIENYL; HYDROAMINATION; COUPLING-CONSTANTS; TITANIUM IMIDO
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.0c00452

The titanocene imido complex 2 with a m-terphenyl moiety is synthesized by reacting Cp2Ti­(η2-Me3SiC2SiMe3) (1) with m-terphenyl azide. Subsequent reactivity studies with tetrahydrofuran, pyridine, and nitriles verify that these substrates act as two-electron donors, thus binding end-on to the titanium center to give the donor-stabilized titanocene imides 3a,b and 4a–c. Given the potential of the titanium center to act as an electron acceptor, 2 was reacted with phosphine oxides (OPEt3/OPPh3) according to the Gutmann–Beckett method to get information about the Lewis acidity of 2 and to yield 5a,b. Complex 5a is one of the rare examples of structurally characterized titanium complexes with an η1-bound cyclopentadienyl ligand. Further insights into the Lewis acidity of 2 were obtained from the nitrile adducts 4a–c through IR spectroscopy and NMR spectroscopy (δ­(19F) and 1 J C,F employing 4-fluorobenzontrile). In reactions of 2 with terminal alkynes, the respective titanium amido acetylides 6a,b were obtained, whereas reactions with internal alkynes demonstrate that 2 is not very prone to undergoing [2 + 2] cycloaddition reactions.