Eight-electron donor

The reader is referred to Table II of ref. 112 for relevant crystallographic details of compounds containing the R-DAB ligand in the two electron, four electron, six electron and eight electron donor bonding modes. Some data including new information will be discussed in this chapter. 

An interesting point is that up till now it has been very difficult to prepare complexes containing the six electron donor mode with other substituents on the rf -bonded C=N unit. The only exception is MnCo(CO)6(Prc-DAB Me,Me ) with a cyclopropyl substituent on the N atoms.137 No doubt steric reasons are important but it should be noted that in the case of the eight electron donor mode for R-DAB R, R" stable complexes could also be obtained for R = R" = Me.158... 

In addition to compounds containing six electron donor R-DAB ligands compounds with bonding modes have also been formed. 

The P2 and As2 molecules can bind in a variety of ways, formally as four-, six-, or eight-electron donors ... 

Of the aminophosphines, tris(dimethylamino)phosphine is the most widely used. It has the feature of combining three hard nitrogen and the soft phosphorus sites, thus being potentially an eight-electron donor hgand. In complexes such as [M(CO)5P(NMe2)3], it is a two-electron P-donor ligand. ... 

An example of cyclooctatetraene functioning as an eight-electron donor to a dimer also exists. 

The participation of both the p i electrons pairs of X2 in a donations enables the consideration of the unit as an eight electron donor. Thus, in contrast with previous suggestions, 1 can be counted a 34 rather than a 32 electron complex. 

The electron count for these compounds requires some assumptions to be made about the contributions of the two types of imido ligand. While the simple imido ligand contributes four electrons to the cluster electron count, the para-tolylimido ligand that contains an additional cyclohexadienyl rhodium coordination can be considered overall as an eight electron donor (taking into account the coordination... 

A rare case of the bridging function of 6-methyl-2,2 -bipyridine, where the 6-methyl group is cyclometalated, is 73 (080M3018). Rollover cyclometalation 74 is among the less-common coordination modes of 2,2 -bipyridine. Moreover, the unusual dinuclear species 75 with a double C—bond activation also exists (090M2150). The ligand is doubly deprotonated and acts as a 7t-delocalized eight-electron donor. 

Ans Both (C3H3) and are eight-electron donors four Pd-Pd bonds... 

---