Group 5 Metal Complexes with Cyclooctatetraene: Formation and Characterization of (Butadiene)(cyclooctatetraene)(cyclopentadienyl)tantalum Systems

Abstract

Keywords: Diene complexes / η 3 -Cyclooctatetraene metal complex / B(C 6 F 5 ) 3 addition / Tantalum / Bicyclo[5.1.0]octadienyl metal complexThe [(η 4 -diene)(η 5 -R Cp)TaCl 2 ] complexes 6a-e (diene = Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and prone orientation of the butadiene, isoprene or 2,3-dimethylbutadiene; R Cp = pentamethylcyclopentadienyl, methylcyclopentadienyl or (diene)CpTa subunit] were found for the (η 4 -butadiene)(η 3cot)CpTa system (7e/7eЈ = 95:5). Complex 7e cleanly adds cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li 2 ]) to yield the (η 4 -diene)(η 3 -the organometallic Lewis acid B(C 6 F 5 ) 3 to yield the betaine system [(η 4 -C 4 H 6 ){C 8 H 8 B(C 6 F 5 ) 3 }Cp*Ta] 8, which contains a cyclooctatetraene)(η 5 -R Cp)tantalum complexes 7. The η 3 -cot coordination was confirmed by an X-ray crystal structure substituted bicyclo[5.1.0]octadienyl ligand. analysis of the compound [(supine-s-cis-η 4 -C 4 H 6 )(η 3 -cot)(η 5 -

Structurally Distinct Homoleptic Anthracene Complexes, [M(C14H10)3]2−, M=Titanium, Zirconium, Hafnium: Tris(arene) Complexes for a Triad of Transition Metals

“…Steric effects do not appear to favor this structure over that of the unknown [Hf(1‐4‐η 4 ‐cot) 3 ] 2− 24. Previously, only Group 5 complexes, e.g., [Nb(η 4 ‐cot)(η 3 ‐cot) 2 ] −[31] and [Cp*M(η 4 ‐butadiene)(η 3 ‐cot)] (Cp*=C 5 Me 5 , M=Nb,35 and Ta ( 8 ))36 were established to possess this unusual cot binding mode. The η 4 ‐cot group in 7 is normal and quite similar to that present in [Cp*Zr(allyl)(cot)] 37.…”

“…Erker et al. previously proposed that the almost structurally identical η 3 ‐cot group in 8 was effectively a dianionic ligand, comprising coordinated allylic and uncoordinated exo ‐pentadienyl anion units 36. Interestingly, a computational study on neutral [Zr(η 8 ‐cot)(η n ‐cot)] indicated that the known ( n =4)33 and unknown ( n =3) isomers have essentially equal stabilities and should be regarded as Zr IV complexes 34.…”

Enantioselective Total Synthesis of the Cyclophilin-Binding Immunosuppressive Agent Sanglifehrin A

“…[6] Herein, we report useful refinements in these protocols as well as the successful conjoining of components 2 ± 4 to arrive at 1 having all of its seventeen stereogenic centers properly installed. [6] Herein, we report useful refinements in these protocols as well as the successful conjoining of components 2 ± 4 to arrive at 1 having all of its seventeen stereogenic centers properly installed.…”

“…[2] Cryptands, which are the most fascinating macrobicyclic systems, possess intramolecular cavities that are available for the encapsulation of ionic guests. [6] Herein we report a rational high-yield (70 ± 85 %) strategy for preparing organometallic cryptands that is based on iridium coordination chemistry (Scheme 1) Scheme 1. [4] Recently Bowman-James and co-workers have elegantly shown that a bicyclic polyammonium receptor can encapsulate two nitrate anions.…”

“…[3] In a spectacular demonstration by Lehn and co-workers a bis-(tren) chelate receptor was used to encapsulate fluoride anions. Although the coordination chemistry of cations is well developed, the chemistry of anion encapsulation is still in its infancy: [7] only one example of a metallo-helicate encapsulating a PF 6 À ion has been described by Steel and co-workers and two supramolecular tetrahedron complexes encapsulating a BF 4 À ion have been reported by the groups of Huttner, and Ward and McCleverty. [5] Although the chemistry of organic cryptands is steadily expanding, less is known about metallocryptands.…”