Donor pair electron counting

There are two filled molecular orbitals on the allyl ligand that act as good fT-donors. Thus, the allyl ligand is a four-electron donor in the donor pair electron counting formalism. 

FI in donor pair electron counting formalism. Both Fischer-type (low oxidation number) and Schrock-type (high oxidation number) compounds are now known to exist. 

As the cluster nuclearity increases, the structures and electron counting of saturated clusters conform to the polyhedral skeletal electron pair (SEP) theory. For organometallic clusters the carbon fragments of the hydrocarbyl ligands are frequently part of the cluster skeleton. Thus, Fc3(PhCCPh)(CO)9 (1) would be considered to be unsaturated according to the 18-electron rale, as the alkyne ligand is a four-electron donor to a Fc3(CO)9 cluster, which requires... 

Pentahapto-C5H5 is considered by this method as CsHs , a donor of 3 electron pairs it is a 6-electron donor. As in the first example, CO is counted as a 2-electron donor. Chloride is considered CF, a donor of 2 electrons. Therefore, (if) -C5H5)Fe(CO)2Cl is formally an iron(II) complex. Iron(II) has 6 electrons beyond its noble gas core. Therefore, the electron count is Fe(n) 6 electrons... 

The carbyne ligand has a lone pair of electrons in an sp hybrid on carbon this lone pair can donate to a suitable orbital on Cr to form a a bond. In addition, the carbon has two p orbitals that can accept electron density from d orbitals on Cr to form tt bonds. Thus, the overall function of the carbyne ligand is as both a a donor and tt acceptor. (For electron counting purposes, a CR ligand can be considered a 2-electron donor it is usually more convenient to count neutral CR as a 3-electron donor.)... 

A chromium atom has six electrons outside its noble gas core. For transition metals the only electrons that are counted are the 5 and d electrons beyond the noble gas core. Each CO is considered to act as a donor of 2 electrons (from an electron dot standpoint, C=0 , the donated electrons correspond to the lone pair on carbon). Thus, the total electron count is... 

For the donor-pair method, treat C as a chloride anion, CP, and CH>=CH2 as a neutral, two-electron donor as stated in the exercise (and Table 22.2). Considering that the anion of Zeise s salt has -loverall charge, the charge on Pt centre must be +2. Since Pt has 10 valence electrons, Pt(II) must have eight and electronic configuration d. Then, the electron count is 8 (from Pt(ll)) + 3x2e (from 3 Cl") + l 2e (from CHi CHj) = 16 electrons. This is a common electron count for d square planar complexes like this one. 

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