Three-electron ligands

Pure n -allyl complexes are best prepared by treatment of suitable metal salts with allyl Grignard reagents such as freshly prepared allyl magnesium bromide. 

Mixed n -allyl complexes may also be prepared by this route [34], e.g. 

Allyl halides react with a variety of anionic metal complexes forming nt-allyl metal bonds. The reactions are thought to proceed via a o-allyl intermediate. Suitable anions are the metal carbonyl anions, 

The formation of 7i-enyl complexes from a mono-olefin probably proceeds via the prior formation of an unstable olefin-metal complex, followed by the loss of a hydrogen atom. The reaction may be compared to that of allyl halides which lose the halogen. Examples are 

With diene olefins, the formation of a rnc-enyl ligand requires the addition to the diene of another group. Thus in the above equation a hydrogen atom has been acquired, presumably from the solvent, by a qrclohexa-1,3-diene, whilst the equations below show the addition of a chlorine or hydrogen atom to butadiene. The addition of [(CN)jCoH]3- to butadiene is discussed on pp. 323-325. 

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Wong, Y.S., Paik, Fl.N., Chieh, P.C., and Carty, A.J., Two-carbon three-electron ligands. Phosphonium-betaine complexes via nucleophilic attack by phosphites on a o-rc-acetylide di-iron hexacarbonyl derivative, /. Chem. Soc., Chem. Commun., 309, 1975. 

Their x-ray structure determination revealed that the acyl group was bonded to zirconium via both acyl carbon and acyl oxygen atoms. While they consider the acyl group as a three-electron ligand bonded to zirconium by both [Pg.150]

Co4(CO),(GeMe)2 The GeMe group is a three-electron ligand, with the methyl group taking up one of the four Ge valence electrons. Thus P is 64 and N = 4. The most plausible figure whereby four Co atoms form just four Co-Co bonds is a square plane, as observed experimentally. 

A. Complexes Having Three-Electron Ligands 1. 1,3-Diborolene ( -C Bt)... 

J. Powell Organometallic complexes containing three-electron ligands. 

Figure 2. Stuctural types of compounds with three-electron ligands...

Figure 23. The example of obtaining the values of the Wiener index for hypergraph and graph representations of the molecular structure with three-electron ligands hydrogens are suppressed in these representations...

Nitric oxide, a three-electron ligand, is too volatile to be cocondensed at —196°C for macroscale preparations. The BF3 adduct of NO, which is less volatile, has been used. Deposition of BF3-NO and appropriate metal/ligand systems yields the corresponding complexes. The codeposition of a wide series of isocyanides gives macroscale amounts of NiL4 and FeLf. 

Three-electron ligands n-allyl and w-enyl complexes... 

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