100
T. Wang et al.
Fig. 3.2 Top and side views of the molecular structure of the cyclotrimer 68 in the crystal (for
clarity only the ipso-carbon atoms of the Mes* substituents at phosphorus and of the C 6 F 5 groups
at boron are depicted)
Ph 3 P
BEt 2
Et 2 B O
BEt 2
O
Ph 3 P
PPh 3
CO
BEt 2
O
Ph 3 P
69
70
71
P
P
Pt
B(C 6 F 5 ) 3
P
P
Pt
H
B(C 6 F 5 ) 3
P
P
Pt
O
B(C 6 F 5 ) 3
P
P
Pt
O
B(C 6 F 5 ) 3
P
P
:
P
t
Bu 2
P
t
Bu 2
72
73
74
75
CO
Scheme 3.21 Examples of CO insertion into the B–C bond
3.5 Reaction of Carbon Monoxide at d 0 -Metallocene
Cations
Transition metal complexes of d
0 electron configuration are special as they lack electron density for back donation. The group 4 bent metallocene cations Cp 2 M(IV)R
+
with d
0 electron configuration are Lewis acidic [87, 88]. Group 4 bent metallocene
cations have found extensive use in homogeneous Ziegler-Natta olefin polymerization catalysis [89–91]. Selected examples have also been used as bulky Lewis acid
components in FLP chemistry. Stephan et al. [92] and Wass et al. [12, 93–101] have
described a variety of intra- and intermolecular Cp 2 ZrR
+ combinations with bulky
Lewis bases, usually bulky phosphanes, that showed typical FLP behavior, e.g., in the