Half-sandwich complexes of niobium and tantalum bearing o-xylylene, anthracene, or cyclooctatetraene: crystal structures of ( η5-C 5Me 5)Nb{ o-(CH 2) 2C 6H 4}Cl 2, ( η5-C 5Me 5)Ta( η4-anthracene)(CH 2Ph) 2, and ( η5-C 5Me 5)Nb( η4-butadiene)( η3-cyclooctatetraene)

• Published in: Journal of organometallic chemistry Vol. 557; no. 1; pp. 3 - 12
• Main Authors: Mashima, Kazushi, Nakayama, Yuushou, Kaidzu, Michitaka, Ikushima, Naoko, Nakamura, Akira
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: Anthracene; Crystal structure; Cyclooctatetraene; Niobium; o-xylylene; Tantalum; Tantalum; Anthracene; Cyclooctatetraene; o-xylylene; Niobium; Crystal structure
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/S0022-328X(97)00730-4

Half-sandwich complexes of niobium and tantalum having an extended conjugated 1,3-diene ligand such as o-xylylene, anthracene, and cyclooctatetraene have been synthesized and characterized. The molecular structures of Cp*Nb{ o-(CH 2) 2C 6H 4}Cl 2 ( 1) (Cp*= η 5-pentamethylcyclopentadienyl), Cp*Ta( η 4-C 14H 10)(CH 2Ph) 2 ( 14), and Cp*Nb( η 4-C 4H 6)( η 3-C 8H 8) ( 16) were determined by X-ray crystallographic studies. Complexes 1 and 14 adopted a four-legged piano stool geometry and their o-xylylene and anthracene ligands coordinated to the metal center in the η 4-coordination mode. X-ray analysis together with their NMR spectral data revealed that the o-xylylene complex 1 has a large contribution of the 2 σ–1 π canonical form, but otherwise the anthracene complexes have an increased contribution of 2 π– η 4-diene canonical form compared with the butadiene complexes. Thus, the electronic structures of η 4- o-xylylene and η 4-anthracene ligands are deviated from that of η 4-butadiene into the opposite direction. The 1H NMR singlet signal of the cyclooctatetraene ligand in 16 indicated the presence of the dynamic fluxionality in solution, while it coordinated to the metal in η 3-fashion in the crystal.