Cyclopentadienyl rings coordination chemistry

In Chapter 2, the chemistry of metallocene-based polymers was reviewed. Herein, other classes of polymers containing cyclopentadienyl rings coordinated to transition metal moieties are described (5). The chemistry of polymers containing 4-membered rings coordinated to transition metal moieties has been investigated however, there are fewer reports on the synthesis and characterization of this type of polymer (6). Within each of these classes of polymers, the synthesis of dendrimeric and/or star-shaped polymers will also be highlighted. 

The interaction of [MN(SiMe3)2] (M = Li, Na, K) and LiTMP with carbenes (1) (R = i-Pr, R = Me), (3) (R = i-Pr) and (4) (R = Me) in solution was also reported. Evidence of complexation of these carbenes with the Li, Na, and K species in solution was given by the NMR shifts for the relevant carbene center. Recently, the reaction of carbene (1) with lithium l,2,4-tris(trimethylsilyl)cyclopentadienide was reported to result in monomeric carbene complexes with 1 1 stoichiometry (R = H R = f-Bu (6), adamantyl (7), or 2,4,6-trimethylphenyl(8)). The crystal structure of (6) showed that the cyclopentadienyl ring is coordinated in an -fashion to the lithium center (see Alkali Metals Organometallic Chemistry) and there is a single a-interaction present between the lithium and the carbene center (Li-C(carbene)... 

One promising approach to the adjustment of coordinative saturation is to alter the number of cyclopentadienyl rings. Since the great bulk of titanium, zirconium, and hafnium organometallic chemistry is that of ( 5115)2X1X2 systems, compounds such as the recently reported ( 5115)2-UCI2 (95) would seem to be ideal precursors. We (96) as well as others (97) have found this to be an incorrect formulation of the reaction product of U U and 2Tl 5H5. When the reaction is carried out in dimethoxy-ethane (DME) we find (96) by NMR that the product is actually a mixture of ( 5H5)3U land ( 5H5)U l3 DME (98). 

Garces A, Sanchez-Barba LF, Alonso-Moreno C, et al. Hybrid scorpionate/ cyclopentadienyl magnesium and zinc complexes synthesis, coordination chemistry, and ring-opening polymerization studies on cyclic esters. Inorg Chem. 2010 49 2859-2871. 

N) and rf n) fashion. Besides in the complexes containing the fused cyclopentadienyl or phenyl ring, the coordination is fulfilled via the latter and these complexes possess valuable catalytic properties. Ruthenium and osmium compounds present a variety of the /(N)-coordinated structures, although in osmium chemistry, the rj2(C,C) coordination is also possible. 

The chemistry of titanium and zirconium, bis(ij-pentamethylcyclopen-tadienyl) systems is essentially that of monomeric fo-CsfCH iM units. With the cyclopentadienyl systems, nearly all of the chemistry observed is that of dimers. Although the dimeric hydride fi-(tj5 tj5-C,0H8 )-/x(H2 C5H5)2Ti2 (3) is coordinatively saturated and relatively unreactive, the partially unsaturated, dimeric metallocene /t-( 1 i -C H )(,i>-CjH )3Ti1 (10) shows considerable chemical reactivity toward N2 (Section III,D) as well as interesting catalytic properties (Section VI). The behavior of dimer units in the cyclopentadienyl systems is exemplified by the unusual naphthalene ring binding in the naphthyl hydride zirconocene derivative... 

As with cyclopentadienyl metal carbonyls, the coordination of the net donor arene ligand trans to three 7i-acidic CO ligands confers considerable thermodynamic stability. Relative to the free arene, the coordination of a Cr(CO)3 unit to an arene face removes electron density, to an extent comparable to the inclusion of a nitro ring substituent. The chemical implications of this electron drift from the arene to chromium, and the basis for much chemistry, are an increase in the acidity of protons bound to the arene ring or to the a- and P-carbons of substituents, and... 

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