Buta-1,3-diene complexes

Metal carbonyls Allyl and buta-1,3-diene complexes... 

Fig. 24.7 (a) The four tt-MOs of buta-1,3-diene (the energy scale is arbitrary) the symmetry labels apply to Ci buta-1,3-diene with the C and H atoms lying in the yz plane. These symmetry labels are not applicable to the ligand in a complex of other symmetry, (b) Axis definition for a metal-buta-1,3-diene complex and the combinations of metal and ligand orbitals that lead to transfer of charge frran a 1,3-diene to metal (top diagram) and from metal to 1,3-diene (lower diagram). 

It can also be considered to be an analogue of a metal-1,3-buta-diene complex since the BAH9 unit is isoelectronic with 1,3-buta-diene. A similar complex, arachno-[Ir(B< H9) (CO) (PMe3)2] has been isolated in about 1% yield from the reaction of trans-[Ir(CO)Cl(PMe3)2] with nido-B9H12 (l). 

The key of this success lies in the opening of the synthesis in which Roush and Wada utilize the various possibilities offered by the buta-diene-Fe(CO), chemistry for acyclic stereocontrol. They thus impressively demonstrate that the use of transition metal 7r-complexes as synthetic building blocks opens new and powerful strategies for the synthesis of complex target molecules. 

AG ii c = 14.3 kcal/mol). ( -c -Butadiene)- and -2,3-substituted buta-diene)zirconocene complexes exhibit markedly lower barriers (Table III) 50-52). In general, the corresponding bis(Tj-cyclopentadienyl)hafnium... 

By palladium (O)-catalyzed carbonylation of l,2-diaza-l,3-buta-dienes. Boeckman et al. (01OL3651) (Scheme 42) reported that stable l-(l,2-diphenylethenyl)-2-phenyldiazene 180 when treated with 10 or 1 mol% of Pd(Ph3P)4 or Pd(dppe)2 catalysts, respectively, in toluene under 1 or 2 atm of carbon monoxide, at room temperature or 100 °C for 0.25-30 h, afforded pyrazol-3-one 184 in excellent yields. Although no intermediates were detected, by analogy to the previously studied cyclopalladation of azobenzene, the mechanism shown in Scheme 42 was proposed. The mechanism involves formation of a cr-complex 181 between 180 and Pd(0)-catalyst, cycloaddition by n—>-n isomerization to... 

We have shown [13,79, 80] that the electronic spectra of c -l,3-buta-diene [81], cyclopentadiene, aromatic five-membered heterocycles [48,79], and norbornadiene [80] can be understood on the basis of a model with two interacting double bonds. Cyclopentadiene (CP) is the prime example of a ring-shaped molecule with a conjugated rr-electron system, and its structure can be related to that of short polyenes such as cM-1,3-butadiene (CB) and the simplest heterocycles, such as pyrrole (PY), furan (FU), and thiophene (TP). In the series, ci5-l,3-butadiene, cyclopentadiene, norbornadiene (NB), the latter is the most complex system, with the two ethylenic units coupled through indirect conjugation and 77, a interaction. One more system will be added here to the set of molecules with two interacting double bonds methylenecyclopropene (MCP) [(1) in Fig 3] the simplest cross-conjugated 77-electron system. 

C2—C3) and 141 pm (C3—C4). Just as for alkene coordination, we can draw two limiting resonance structures (24.25) for a buta-1,3-diene (or other 1,3-diene) complex. ... 

Treatment of [Cp Ru(Ti -C4H6)(X)] (X = Cl, Br) with excess buta-l,3-dicne in the presence of silver trifluoromethanesulfonate (AgOTf) followed by carbon monoxide afforded OS the cycloocta-1,5-diene complex [Cp Ru(Ti -COD)(CO)]+[(OTf)], by means of a (4 + 4] cycloaddition reaction. Similar dimerisation, both stoichiometric and catalytic, was observed with other conjugated dienes. 

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