Complexes Derived from Conjugated Dienes

C6H5R)(PF3)3] (R = H, Ph) afforded the highly fluxional agostic diene complex (20), characterised by X-ray diffraction for R = Ph. The nucleophilic attack of hydride on a variety of (Ti 5-arene)chromium tricarbonyl complexes has been studied and the X-ray crystal structure of (21), derived from the reaction with [Cr( n6-dibenzofuran)(CO)3], has been reported . 

The reaction of diisopropylidenecyclobutene with [Cr(MeCN)3(CO)3] afforded [Cr(CX))3( n -diisopropylidenecyclobutene)], (22), which was characterised by X-ray diffraction. 

The X-ray crystal structures of the cycloheptatrienc complexes [M(q6-C7Hg)(CO)3] (M = Cr, W) have been determined and their solution structure investigated. The chromium cycloheptatrienc complexes [Cr(n C7H8)(CO)3] was rcported to react with a variety of alkenes to give photoinduced [6jt + 2n] reactions. 

Electrophilic addition of aldehydes to [CpMo(CO)2(Tl -6-R-cyclohexadien-l-yl)] (R = H, Me, Ph) catalysed by boron trifluoride was reported to afford isolable (Tj -diene) cationic salts of molybdenum. Demetallation by trimethylamine-N-oxide afforded functionalised cyclohexadiene compounds in good yields. The stereochemistry of the carbon-carbon bond forming reaction was clarified. 

The X-ray crystal structures of the (Tj -tetraphenylcyclobutadiene) complexes [CpM(Ti -C4Ph4)Cl2] (M = Nb, Mo) have been determined 5 and the structures compared with those of the bent sandwich compounds[Cp2MCl2] by means of Extended Huckel molecular orbital calculations. 

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Complexes Derived from Conjugated Dienes and Polyolefins... 

Danishefsky et al. were probably the first to observe that lanthanide complexes can catalyze the cycloaddition reaction of aldehydes with activated dienes [24]. The reaction of benzaldehyde la with activated conjugated dienes such as 2d was found to be catalyzed by Eu(hfc)3 16 giving up to 58% ee (Scheme 4.16). The ee of the cycloaddition products for other substrates was in the range 20-40% with 1 mol% loading of 16. Catalyst 16 has also been used for diastereoselective cycloaddition reactions using chiral 0-menthoxy-activated dienes derived from (-)-menthol, giving up to 84% de [24b,c] it has also been used for the synthesis of optically pure saccharides. 

Other conjugated diene systems readily react with either H4Ru4-(CO)i2 or Ru3(CO)i2, to yield 7r-allyl complexes. Thus, butadiene yields the crotyl derivative HRu3(CO)9C4H5. The X-ray structure of the related adduct formed from cis-trans- or trans-trans-2,4-diene is shown in Fig. 12. The hydride is considered to bond to the Ru(l)-Ru(2) edge, as this is the longest metal-metal bond in the structure and in the... 

The addition of olefins to olefins426 can also be accomplished by bases427 as well as by the use of catalyst systems428 consisting of nickel complexes and alkylaluminum compounds (known as Ziegler catalysts), 29 catalysts derived from rhodium chloride,430 and other transition metal catalysts. These and similar catalysts also catalyze the 1,4-addition of olefins to conjugated dienes,431 e.g.,... 

Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, 1, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365 Diene-Iron Carbonyl Complexes, 1,1... 

Although zirconium is only one out of over 50 potentially usable metals in this class (including the lanthanides and actinides), virtually all synthetic applications of hydrometallation with transition metals involve zirconium Why is this so The primary reason derives from the near requirement of a d -metal center for hydrometallation of a general alkene or alkyne. For later transition metals, hydrometallation to give a stable organometallic product can usually be achieved only for special cases—conjugated dienes, alkenes with electronegative substituents, etc. This is due to the relative stability of the ti -complex, as discussed previously. 

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