Cyclopentadienyl analogs

Highly (>95-98%) syndiotactic polystyrene is obtained using a variety of soluble titanium initiators such as CpTiCl3 and Cp2TiCl2, and various substituted cyclopentadienyl analogs with MAO [Coates, 2000 Ishihara et al., 1988 Minieri et al., 2001 a,b Pellecchia et al., 1987 Po and Cardi, 1996 Schellenberg and Tomotsu, 2002 Schwecke and Kaminsky, 2001 Zambelli et al., 1989]. Zirconium initiators are also useful, but their activity is lower than that of the titanium initiators. 

The photochemical synthesis of the tungsten carbonyl metallocarborane [Eq. (18) ] is also effective in the preparation of the molybdenum carbonyl analog. The resulting air-sensitive complexes show chemical behavior similar to the cyclopentadienyl analogs, C5H5M(CO)3, in that they undergo protonation with anhydrous HOI and met.hylation with CH3I. They also react further with metal hexacarbonyls to afford bimetallic complexes 54) ... 

Cyclopentadienyl analogs of the bi- and trimetallic chain complexes were prepared recently (69). These compounds, as well as the carborane-capped compounds, exhibit reversible 1-electron redox couples, indicating that the electrons are added to and removed from delocalized molecular orbitals rather than localized metal centers. 

The azametallocenes, such as 206 and 208, are less stable than their cyclopentadienyl analogs.158 The pKa for azaferrocene (206) is similar to that of quinoline, whereas the manganese compound was a much weaker base.158 Azaferrocene yields a picrate and a methiodide, but, as might be expected, it does not undergo electrophilic substitution.158 The mass spectra of azametallocenes have been discussed.1636 The preparation of cyclopentadienyliodobis(imidazole)cobalt(III)iodide has been reported.1630... 

The Et2BH catalysed condensation of polyborylated hydrocarbons offers attractive alternative routes to novel carboranes. Owing to the exceptional thermal stability of the majority of the new carboranes, further useful transformations can be envisaged. The easy access to cyclopentadienyl-analogous borate anions is another promising aspect of the synthetic potential. 

Evans et al. also reported the synthesis of the divalent lanthanide COT complexes [Zr2(OPr )9Ln]2(COT) (Ln = Yb, Sm) from [Zr2(OPr )9LnI]2 and K2COT (Scheme 226). The monoanionic [Zr2(OPr )9]- unit is used as a cyclopentadienyl analog. X-ray diffraction studies show the bimetallic Ln(ll) complexes with the Sm centers coordinated to the bridging COT ligand in an -fashion.264 [Zr2(OPr )9Sm]2(COT) reacts with 1,3,5,7-COT to form the hexane-soluble Sm(m) complex [Zr2(OPr )9]Sm(COT), in a manner analogous to the reduction of COT by Cp Sm(COT). The molecular structure shows the monomeric complex with one -coordinated COT ligand and the monoanionic [Zr2(OPr )9]- unit attached to the Sm in a tetradentate fashion.2... 

Fig. 12. Amide and alkoxide moieties as cyclopentadienyl-analogous ligands...

The heteroatom cyclopentadienyl analog 1,4,2-P2SbC2Bu 2 has been coordinated to T1(I) via equation (2), producing zigzag polymer (2). Thallium coordination has played an important role in crystallographic characterization of metal-fullerene complexes, providing the first structurally characterized pentahapto metal complexes of Cgo (3) and C70 (4). The key to the formation of these monothallium (I) compounds was the arylation of the fullerenes. Methylated Cgo forms a thallium complex as well. ... 

TpMn(CO)3 (50), (pzTp)Mn(CO)3 (51) and Tp Mn(CO)3 (52) were all prepared from Mn(CO)5Br, and IR spectroscopy suggests that these systems are more electron-rich than the cyclopentadienyl analogs.The phosphine complexes... 

When coordinated to palladium, the rr-indenyl ligand tends to slip from the if - to the 77 -coordination mode, and most of the complexes synthesized show severe distortions or clear -indenyl coordination. Thus, although being a cyclopentadienyl analog, it is rare to find a true Tj -indenyl coordination to palladium, however common for other transition metals. Metathesis with Li[indenide] and ligand-substitution reactions are common preparative routes for indenyl derivatives. The insertion of an alkyne into Pd-G bonds of vinyl substituted aryls, followed by intramolecular alkene insertion, also leads to highly substituted indenyl palladium complexes. Equation (66) shows one of these examples. ... 

MesSiCl gives substitution product 3.638 and with fluorenyl-lithium, the adduct 3.640 is produced. The successive introduction of substituents can be achieved by a sequence of reactions with electrophiles and nucleophiles. Thus electrophile Ei gives fulvene 3.642, followed by attack by nucleophile Nu to afford adduct 3.643, and again by electrophile Ei to give product 3.644. These reactions can lead to the preparation of a unique series of homogeneous catalysts for olefin polymerization for it is known that the indenyl complexes are often better catalysts for olefin polymerization than cyclopentadienyl analogs (Scheme 3.58) [308,315]. 

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