Cyclopentadienyl hydride complexes

Immobilization of Rare-Earth Metal Hydride, Alkyl, and Cyclopentadienyl Complexes... 

The same group also showed that mono(cyclopentadienyl) mixed hydride/ aryloxide dimer complexes of several lanthanide elements (Y, Dy, Lu) could be synthesized easily by the acid-base reaction between the mixed hydride/alkyl complexes and an aryl alcohol [144]. These complexes reacted with C02 to generate mixed formate/carboxylate derivatives, which were moderately active initiators for the copolymerization of C02 and cyclohexene oxide, without requiring a co-catalyst. The lutetium derivative 21 was the most active (at 110°C, TOF = 9.4 h ), yet despite a good selectivity (99% carbonate linkages), the molecular weight distribution remained broad (6.15) (Table 6). 

This volume also gives a description of the evolution in Nd-catalyzed polymerization of dienes from the early works to the current state of the art. The authors highlight the tremendous variety of investigated catalyst systems and both articles order the catalyst systems according to the type of anions carboxylates, alcoholates, halides, hydrides, phosphates, phosphonates, allyls, tetraalkylaluminates, cyclopentadienyl complexes, amides, acetylacetonates,... 

It is interesting that the [ (CHsIskTi, 14-electron metallocene car-benoid even inserts into the hydrocarbon-like C—H bond of a penta-methylcyclopentadienyl ligand. Significantly, however, the reaction is reversible, whereas with bis(T)-cyclopentadienyl) systems the formation of complex hydrides (Sections II,A,1 and 2) seems to be an irreversible pro-... 

Figure 10 Cyclopentadienyl-amide hydride complex of yttriiun...

Lanthanide monohydride complexes, such as bi(cyclopentadienyl) lanthanide hydrides, can be conveniently prepared by the reactions of lanthanide mono-alkyl or -aryl complexes with organosilanes under mild reaction conditions (Figure 8.27) [82]. 

The stereocontrol in the polymerization of MMA mediated by chiral organolanthanide metallocenes has been investigated. Flydride, hydrocarbyl, and amido bis(cyclopentadienyl) complexes (Scheme 268) were used as precatalysts for the processes. The achiral hydride precatalysts yielded syndiotactic PMMA with narrow polydispersities (Mw/Mn = 1.02-1.05). The polydispersities of PMMA from the chiral and achiral hydrocarbyl precatalysts are larger then those from the hydride precatalysts, and amide precatalysts gave the largest polydispersities.982... 

The first known complex in this class, frans-bis(triethylphosphine)-platinum chlorohydride, was prepared by Chatt and co-workers (86). In the light of other hydrides known at that time, in particular the carbonyl hydrides of iron and cobalt and bis(7r-cyclopentadienyl)rhenium hydride, the great stability of this complex was quite unique. It rapidly became clear that tertiary phosphine ligands were markedly effective in stabilizing the metal-hydrogen bond, and ligands such as PhjP, EtjP, o-CaH PlVfe, ... 

The reverse transfer of a hydrogen from the metal to a 7r-cyclopentadieny] ring presumably occurs in the formation of 7r-cyclopentadienylcyclopen-tadienedicarbonylrhenium from bis-(7r-cyclopentadienyl)rhenium hydride and carbon monoxide 56, 107). Cationic complexes in this class, prepared by protonation reactions, are discussed in Section III,E. 

The complex, formally derived from a double oxidative addition of benzene to two Ir centers , is in contrast to the mononuclear product obtained with the pentamethylcyclopentadienyl derivative . In the absence of light there is no reaction presumably photolysis displaces one carbonyl ligand to give a coordinatively unsaturated precursor. An apparent intermediate in the photolysis has H NMR resonances in the aromatic, cyclopentadienyl and hydride regions and may be IrGp-j/ (GO)H(G6H5), but its nature remains uncertain. 

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