Pentamethylcyclopentadienyl ligands, synthesis

The development of the chemistry of organometallic compounds containing the pentamethylcyclopentadienyl ligand has been hampered by the lack of a simple, high yield synthesis of 1,2,3,4,5-pentamethylcyclopentadiene (14). We have recently expanded the method first reported by Sorensen et al. (15) to a large scale preparation which follows Scheme 1 (16). This procedure is applicable... 

Evans, W.J., Mueller, T.J., and Ziller, J.W. (2009) Reactivity of (CsMestsLaLx complexes synthesis of a tris(pentamethylcyclopentadienyl) complex with two additional ligands, (CsMe5)3La(NCCMe3)2. Journal of the American Chemical Society, 131, 2678. 

Tetrahydrido(i -pentamethylcyclopentadienyl)iridium was synthesized in 1982, and proved to be a useful precursor for several iridium complexes of varied oxidation state.The tetrahydride and its derivatives are among the very few iridium(V) polyhydrides that do not contain phosphine ligands. No alternative preparation of the title complex has been reported. The key feature of the synthesis described here is the oxidation of the iridium(III) intermediate to the iridium(V) product during work-up of the reaction mixture. ... 

Unusual mono(pentamethylcyclopentadienyl)actinide complexes containing a 15-membered trianionic hexaoxo ligand built from catechol and catecholborate have been prepared and structurally characterized. As depicted in Scheme 36, the synthesis of these complexes has been achieved by reacting Cp 2AnMe2 (An = Th, U) with an excess of catecholborane that contains 5% dimethylsulfide (DMS) in benzene at room temperature for 24 h. The DMS ligand could be replaced by THF.95... 

A method which uses a primary amine - diol pair in AT-heterocyclization has been developed. It features the catalytic activity of an iridium complex bearing pentamethylcyclopentadienyl (Cp ) ligands, and produces only water as a byproduct. The method was used in the two-step asymmetric synthesis of (S )-2-phenylpiperidine 145 from (7 )-phenylethylamine 146 <04OL3525>. 

In our work on Cp2TiR compounds vide supra) we noticed that hydrogen abstraction from the cyclopentadienyl ligands is the exclusive route followed in thermal decomposition. It was expected that introduction of pentamethylcyclopentadienyl instead of cyclopentadienyl ligands would improve the thermal stability of the alkyl and aryl derivatives and moreover, by steric and electronic induction, would modify the reactions with unsaturated substrates, such that they could be studied under moderate reaction conditions. For these reasons we started to explore CpJTiR chemistry a few years ago. Some of the preliminary results on synthesis and carbonylation of Cp TiCl have been published [27]. 2... 

In search for new active catalysts of the olefin polymerization over the last years several REM monocyclopentadienyl complexes containing a-bonded ligands have been synthesized (Table 1.7) [39, 58, 136-138]. Neutral derivatives of CpLnX2 as well as heterobimetallic complexes [Li(B)][CpLnCl3] have been utilized in these synthesis as the initial compounds. It should be noted that in all cases, except CpHo(C=CPh)2 obtained in 1975 [139], pentamethylcyclopentadienyl derivatives have been used. 

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