X-Ray evidence for a mononuclear s-trans-η⁴-1,3-diene complex; molecular structure of Zr(η⁵-C₅H₅)₂(s-trans-PhCHCH–CHCHPh)

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

“…Only recently, such data for the ansazirconocene diene complexes 18 [39] and 28 [73] have been reported [34]. These unique features are listed in Table 1.…”

“…Our collaborative study clarified the precise parameters of the s-trans-diene ligand for the first time in early 1982 (see Fig. 7) [34].…”

(Alkyl)(monocyclopentadienyl)niobium and ‐tantalum Complexes in Insertion Processes

“…This is the most relevant detail of the molecular structure ( Figure 6) because, frequently, in diene mono(cyclopentadienyl)niobium and -tantalum complexes [57a,57d,58] the diene ligand forms a metallacyclopent-3-ene system with a preferred supino conformation, although there are examples with a prono conformation. Furthermore, the diene ligand can adopt an s-trans conformation, as observed in bis(cyclopentadienyl)zirconium, [59] mono(cyclopentadienyl)tantalum [60] and cationic bis(cyclopentadienyl)tantalum [61] complexes. In our case, the crystallographic data do not correspond to the same bonding system and, therefore, we propose a moiety consisting of a ''diene'' C31ϪC32ϪC33ϪC34 fragment linked to the metal atom through the C33ϪC34 atoms, forming a niobacyclopropane ring, and the donor vinyl substituent C31ϪC32.…”

Remarkable features of intermediates in the early transition metal catalyzed conversion of monosubstituted alkenes, dienes and alkynes

“…Air oxidation of the zirconium complex containing a tail-to-tail isoprene dimer resulted in the liberation of a 1:9 mixture of 2,7-dimethyl-l,3,6-octatriene and 2,7-dimethyl-2,4,6-octatriene at 40°C. The addition of 2 equivalents of 1,4-diphenyl-l,3-butadiene to the complex 4 releases a mixture of 2,7-dimethyl-2,4,6-octatriene (70%) and 2,7-dimethyl-l,3,5-octatriene (30%) together with CP2Zr(l,4-diphenylbutadiene [46]. PEt 3, NEt 3 and pyridine are not able to expel the coordinated diene.…”

“…In the latter case, the addition of a large excess of On the basis of the stereo-and regiochemistry of the product, we propose the following mechanism for the cyclic trimerization (Scheme 6). The coordination of the s-trans-conjugated diene to a mononuclear metal species is already known for Zr [46,74], Hf [75], and Mo [76] complexes. These systems also catalyze the codimerization of isoprene with 2,3-dimethylbutadiene to give 1,2,5,10-tetramethyl-l,5,9-cyclododecatriene in 85% selectivity, and the codimerization of isoprene with butadiene to give l-methyl-l,5,9-cyclododecatriene in 65% selectivity.…”