Synthesis, x-ray structure and nucleophilic properties of mixed bis(diene)tantalum complexes Ta(.eta.5-C5R5)(.eta.4-C4H6)(.eta.4-C6H10)

Diene complexes of early transition metals: ideas and progresses at Osaka University

“…These results were obtained in competition with ErkerÕs group, who reported essentially the same insertion reactions with the butadiene complex of zircononce [91][92][93][94]. Furthermore, we carried out the reactions of diene complexes of group 5 metals and found that essentially the same carbonyl additions proceeded in the cases of the bis(diene) complexes of niobium and tantalum [60,62].…”

“…In the case of the diene complexes of niobium and tantalum, the diene ligand was found to be much stronger bound to the metal and therefore such addition reactions are sluggish [62]. Thus, we realized that the diene ligand bound to the group 5 metals works as a spectator ligand for some organometallic catalyses, and that the monodiene complexes with two halo ligands, Cp(diene)MX 2 , are isoelectronic to the metallocene dihalides of the corresponding group 4 metals.…”

Niobium and Tantalum

“…464 All structures examined show an (r\-C 5 R 5 )Ta(supine-but2idiene)(prone-butadiene 1 ) geometry in which the larger of the two dienes appears to prefer the supine (exo) position. Since the mono(butadiene) complexes contain a supine butadiene, when (Tj-C 5 R 5 )Ta(T|-C 4 H 6 )(T|-2,3-Me 2 C 4 H 4 ) is prepared from (r|-C 5 R 5 )Ta(r|-SMpme-C 4 H 6 )C1 2 and Mg(2,3-Me 2 C 4 H 4 ), the initial geometry of the coordinated r\-supine-C 4 H 6 rearranges to prone in the final product.…”

Some selected chapters from the (butadiene)zirconocene story

“…Complex 11 was characterized by X-ray diffraction. (s-trans-g 4 -Butadiene)complexes have been described from quite a number of metal complex frameworks from d-elements throughout the Periodic Table. A selection of typical examples is depicted in Scheme 7 [12][13][14][15][16][17].…”

“…The stable (butadiene)zirconocene isomers (2) react via the unsaturated (g 2 -butadiene)zirconocene intermediate (3). Ketones are in this way coupled with the butadiene ligand to initially form a metallacyclic (r-allyl)zirconocene complex (12) that is in most cases subsequently stabilized by formation of a metallacyclic seven-membered ring isomer (13,see Scheme 8) [18]. In a few special cases an additional CC-coupling reaction with a second ketone equivalent is observed to yield 14 [19].…”