Synthesis and catalysis of novel mono- and bis(diene) complexes of niobium and x-ray structures of binuclear [Nb(.mu.-Cl)(C5H5)(s-cis-butadiene)]2 and mononuclear Nb(C5H5)(s-cis-2,3-dimethylbutadiene)2

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].…”

Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using α,β‐Unsaturated Carbonyl Ligands

“…[19] The distortion due to the formation of the metallacycle makes the Nb-O-C angles (about 88°) clearly more acute than in alkoxido compounds (over 120°) preventing the π-bonding contribution in the oxygen-niobium bond. The Nb-C(terminal) bonds are slightly shorter than in related (butadiene)mono(cyclopentadienyl) complexes [2] for compounds 1a and 2a and in the same range for complex 2c, in which the terminal carbon atom supports two methyl groups. Finally, the Nb-C(internal) bond lengths are also in the range observed for butadiene [2] and diazabutadiene derivatives.…”

“…The Nb-C(terminal) bonds are slightly shorter than in related (butadiene)mono(cyclopentadienyl) complexes [2] for compounds 1a and 2a and in the same range for complex 2c, in which the terminal carbon atom supports two methyl groups. Finally, the Nb-C(internal) bond lengths are also in the range observed for butadiene [2] and diazabutadiene derivatives. [20] Reaction with Triflic Acid HOTf (Tf = CF 3 SO 2 )…”

“…The reduction of the niobium compound [NbCp*Cl 4 ] in toluene with Na/Hg amalgam in the presence of MMA has been reported previously, [7] and we have applied this method using the α,β-unsaturated carbonyl compounds CH 2 . The whole process can be considered as a reduction of the metal center followed by the oxidative coupling of the α,β-unsaturated carbonyl ligand.…”

“…Hence, complexes with this type of ligand are better represented with contributions from two main canonical forms, σ 2 ,π-metallacyclic or π 2 -butadiene ( Figure 1). [1][2][3][4][5] 2b and 3b to give the three-membered metallacyclic (or η 2 -enone) compounds [NbCp R Cl 2 {η 2 -CH 2 =CHC(OMe){O· E(C 6 F 5 ) 3 }}] [Cp R = C 5 H 4 SiMe 2 Cl, E = B (5), Al (6); Cp R = C 5 H 4 SiMe 3 , E = B (7), Al (8)], which decomposed to the corresponding adducts MA·E(C 6 F 5 ) 3 . The same reaction with the 2a and 3a derivatives only allowed the observation of the corresponding adducts MMA·E(C 6 F 5 ) 3 Replacement of at least one of the terminal CR 2 moieties by an isolobal fragment such as NR, O, S, etc.…”