Fragment linking structures

The acidic hydrogen in terminal alkynes can readily be replaced by silver, in a diagnostic test. [(Me3P)Ag(C=CPh)] has a polymeric structure while [(Ph3P)Ag(C=CPh)]4 is made of [Ag(PPh3)2]+ and [Ag(C=CPh)2] fragments linked so that the silver atoms form a square [147]. 

The first cyclopentadienylzinc compound that was structurally characterized by an X-ray crystallographic study is cyclopentadienyl(methyl)zinc, Cp(Me)Zn (57) ". The structure of 57 in the solid state consists of puckered chains of methylzinc fragments, linked by bridging cyclopentadienyl groups (Figure 28). 

The work described in this review shows that the organometallic chemistry of the heavier alkali metals has ceased to be an exotic backwater. A good deal of information about the interaction between metal cations and carbanionic fragments has been obtained. Much of it has come from studies on crystalline solids, and although it may be reasonable to expect that the species found in the solid are also present in solution, this has to be established experimentally in each case. Some evidence has been obtained from multinuclear or multidimensional NMR spectroscopy, but so far there have been few studies using solid-state NMR to link structures found in the solid with those in solution. Even when the dominant species in solution is established, still more work is required to determine which species react fastest with particular substrates. The active species in a reaction may be present only in low concentration. 

C-O bonds of the alkoxides Cp 2LnOEt were cleaved also by [Cp 2Ln(/r-H)]2 to give bimetallic complexes [Cp 2Ln]2(/r-0). The structure of the THF adduct [Cp 2Ce(THF)]2(/r-0) was determined by X-ray diffraction. The complex consists of two Cp 2Ce fragments linked by a nearly linear oxygen bridge. In contrast to ethers, activation of organic sulfides by [Cp 2Y(/t-H)]2 led to the corresponding metallation products (Scheme 143). 

Fig. 4 Attempt at generating hits through a fragment linking strategy Details of the crystal structures of the active site (see legend to Fig. lc) and selected solvent molecules for the structures of (a) compound 16, (b) compound 17, (c) compounds 16 and 17 and (d) compounds 18 and 17 bound to the active site of Nt-Hsp90...

The FAB-CAB (Fast Atom Bombardment-Collision Activated Dissociation) linked scan (constant B/E) mass spectra of trinervine (16) and vene-curine (35) have been examined by Das et al. (247). In contrast to the El mass spectra, the FAB-CAD linked scan (constant B/E) spectra exhibited prominent fragment ion peaks at m/z 293 and m/z 251 for 16 and at m/z 307 and m/z 265 for 35 (Figs. 13 and 14). The fragments giving structurally useful information are due to losses of H20 (18 mass units) and CH3COOH (60 mass units) from 16H+ (m/z 311) and 35 (m/z 325) (Scheme 26). 

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