The CpM Fragment Orbitals

Suppose the three carbonyl ligands are removed from CpMn(CO)3 this generates the CpMn fragment, 20.11. Three empty hybrid orbitals are produced which point toward the missing carbonyls. This is exactly the same pattern produced by the 

An orbital interaction diagram for the MCp fragment, which shows the orbital occupancy for the d case. 

Contour plots at the B3LYP level for the important valence orbitals in MnCp fragment. The 62(A) and ei(A) orbitals are plotted in the yz plane, displaced 1A along the x axis. 

The advantage in knowing the form of the valence orbitals in ML3 and MCp fragments can be illustrated for triple-decker sandwiches, 20.16. Based on our previous experience, we expect that a stable metal configuration will be one where 

An orbital interaction diagram for a triple decker sandwich complex in Osh symmetry. 

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The reader should carefully compare these valence orbitals with those of a ML3 fragment in Figure 20.1. The ML3 fragment has the same three below, three above level pattern and almost identical atomic composition at the metal. In the CpM fragment it is clear that the cs set is of 8 symmetry and is of tt symmetry. However, c in ML3 is primarily 8 with some tt character and 2e is mainly Trwilh... 

Answer. A B H fragment possesses three orbitals (two of tt and one of a symmetry) containing two electrons. Hence, a CpM fragment with M = a group-9 metal is the appropriate choice (Figure 4.7). This leads to metal derivatives of B5H9 of the type (CpM) (BH) 5(H)4 for M = Co, Rh or Ir. The square pyramidal mVio-clustcr possesses two types of vertices, one apical and four basal. Hence, for n= 1, two isomers are possible whereas for n = 2, three isomers are possible. The structures... 

Zaric and HalF predicted a weakly bound structure and a strongly bound intermediate in the reaction path of the activation of methane with the fragment [Tp Rh(CO)] [Tp = HB(3,5-dimethylpyraz()lyl)5 before oxidative addition. Subsequent studies using (microsecond- to femtosecond-scale) time-resolved IR spectroscopy proved that the second intermediate has a strongly bound r -C,H moiety. Similar structures were determined for the transition states in the C-H activation of methane by the [CpM(PH3)CH3)] (M = Rh, Ir) fragment by ab initio orbital theory methods. ... 

The more appropiate axis choice for CpM(CO)2 is one in which the 2-axis is along the future Fe-thiophene bond. The mirror plane of this complex lies in theyz plane. The [CpFe(CO)2l fragment of 67, point group symmetry has at low energy three occupied metal-based orbitals (see left side of Figure 2) 17a (2, 3% yz, 18% —y, 52%), 18a ... 

Figures Schematic diagram showing limiting torsional alignments of the E—H bond in half-sandwich sigma complexes (left) vertical orientation, (center) horizontal orientation, and (right) overlap of HOMO of a 16-electron [CpM(CO)2l fragment with E—H o -orbital in horizontal alignment.

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