Zirconium complexes binuclear

The electronic spectra of niobium(IV) and -(V) and zirconium(IV) complexes 126,127) have been reported but not interpreted. The spectrum of Nb(ethyl-dtp)4 is of particular interest since the compound is probably 8-co-ordinate. Discussion of the spectrum of binuclear molybdenum complexes 130,131) employed the molecular orbital model of Blake, Cotton and Wood for MO2O3LX complexes s). 

This type of complex is derived from the mononuclear superoxo species via a further one-electron reduction of the dioxygen moiety. Cobalt is the only metal to form these complexes by reaction with dioxygen in the absence of a ligating porphyrin ring. Molybdenum and zirconium form peroxo-bridged complexes on reaction with hydrogen peroxide. In most cases the mononuclear dioxygen adducts of cobalt will react further to form the binuclear species unless specific steps are taken to prevent this. 

A binuclear zirconium(IV) complex with o-,7r-cyclopentadienyI and phosphine bridges, Cp2(H)Zr 7 7 -CsH4 -P(Ph-.)CH-. Zr CH->PPh-> Cp (83), has been prepared as the minor product from Cp2Zr(CH2PPh2)CI by reduction with sodium amalgam (246,247). Both the free and coordinated... 

Metal chloride complexes (59) with structures analogous to that of the samarium complex (50) have been obtained by the reaction of (57) with titanium or zirconium tetrachlorides via elimination of LiCl. Equimolar reaction of (57) and CrCl2(thf)2 has been shown to yield binuclear chromium complex (60), whilst reaction with a twofold excess of CrCl2(thf)2 affords a partially substituted tetranuclear complex (61). ... 

In the absence of donor ligands, the binuclear zirconium fulvalene complex reacts with Ph3C[B(C6F5)4] to give the relatively inert (g-CH2)(g-CH3) doubly-bridged binuclear cationic complex 71 7550 (Equation (45)). This C-H activation process via ct-H elimination and loss of CH4 is facile even at — 60 °C. 

The introduction of bridged binuclear complexes, the so-called Tebbe reagents, to achieve alkylidene transfer to carbonyl species was a useful discovery. However, developments of these systems such that substituted examples could also be prepared was necessary. Recently, substituted alkylidene-bridged zirconium reagents have been prepared and briefly examined as suitable transfer reagents. ... 

This mechanism has been corroborated by the isolation of a binuclear zirconium (IV) complex... 

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