Tetraene ligand

Table 9 Late transition metal complexes from diene, triene, and tetraene ligands, prepared by the metal atom/ligand cocondensation method...

Like the alkenes, dienes have a very limited chemistry with Re. Photolytic reactions of (1) in the presence of dienes give complex mixtures of products, with -allyl and bridging alkenyl structures, in a similar manner to the alkene dimers (8). Reaction of ReBr(CO)3(THF)2 with the cyclooctateraene dianion [CsHs] " produces a dimer (CO)3Re(/u-C8H8)Re(CO)3 (81). Each Re atom is coordinated to one half of the fluxional tetraene ligand. While the fragment [Re(CO)5]+ reacts with MeC=CMe to give the complex in equation (4), the fragment... 

Me02CCH CHCH=CHCH2CCSiMe3)]. Desilyation by treatment with fluoride ion afforded [Fe(CX))3( n4-Me02CCH=CHCH=CHCHsC=CH2)] which contains an aUene vicinal to the inMi-diene moiety Decomplexatkm by oxidadcm widi ceric salts tod to dw fiee tetraene ligand. The... 

Another catalytic system that promotes the coupling of alkyl electrophiles with C(sp )-organozincs is based on the use of tetraene ligands such as 442. Exemplified by the formation of product 441 with an amide functional group, under the... 

Scheme 4.100 Ni-catalyzed cross-coupling of dialkylzincs with alkyl bromides in the presence of a tetraene ligand [302].

The meso- and ra -isomers derived from polyenes did not interconvert thermally in the absence of free polyene, but it was found that there was a very efficient photoinduced face inversion, which was studied for tetraene ligands on a Pd-Pd-Pd moiety.Starting from a rac meso 73 27 ratio, irradiation with a xenon lamp (>510 nm) for 7 h leads to a rac meso 1 99 ratio. Moreover, irradiation with visible light for 38h lead to a rac meso 21 79 ratio. 

Since the early work dealing with Zeise s salt, many complexes have been prepared with the formula [PtL(C2H4)X2], where L = quinoline, pyridine, or ammonia and X=C1 , Br , I, or N()2. Similar compounds have been prepared that contain other alkenes than C2H4. Many of the complexes containing dienes, trienes, and tetraenes as ligands also contain carbonyl ligands. In fact, metal carbonyls are frequently starting complexes from which alkene complexes are obtained by substitution reactions. 

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

Cyclic ligands Square brackets designate that the ligand is cyclic and the number within the brackets is the number of atoms in the macrocyclic ring. Saturated macrocycles are designated by ane , while, for unsaturated ligands, ene is used preceded by a prefix to identify the number of double bonds (e.g. diene or tetraene). The donor atoms are then identified. Substituents attached to the macrocycle are indicated by either a prefix or suffix. 

Bicyclo[4,3,0]nona-2,4,8-triene(C9Hio) gives a brick-red, diamagnetic complex [Mo(CO)3(C9Hl0)] which absorbs one molecule of hydrogen (HI, 142). The complex is thus given structure (VIII), in which the ligand is the monocyclic tautomer cyclonona-l,3,5,7-tetraene, rather than structure (IX). 

The TCNE adducts of a variety of other [nq4-Fe(CO)3]- complexed trienes and tetraenes have been investigated. In most cases the adducts have been oxidatively cleaved from the metal with CeIV and the free ligands recovered in good yields. Reactivity patterns generally follow those described above for cy-cloheptatriene and cyclooctatetraene complexes. Specific complexes investigated include [Fe(2,4,6-cy-clooctatrieneone)(CO)3],61 [Fe(tropone)(CO)3],62,63 [Fe(heptafulvalene)(CO)3] and various 8-substituted... 

---