Semi-bridging ligands

Rhodium also provides a very rare crystallographically characterized example of a boryl ligand adopting a semi-bridging mode of coordination 

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The increased abundance of the C3 isomer with increasing ligand basicity presumably occurs because the semi-bridging carbonyl attached to the substituted metal can become more full-bridging and remove the excess electron density released by the basic phosphine. Consistent with this hypothesis is the... 

Reaction with S-Donors. A somewhat similar (o+ir) 4-electron donation is also exhibited by thioketones in their adducts with Cp2Mo2(C0h (22). In this instance, one of the carbonyls trans to the R2CS ligand adopts a semi-bridging bonding mode (eq. 22). 

There exist a vast number of discrete, polymetallic coordination clusters both of the metal-metal bonded type and linked by a tremendous variety of bridging ligands, notably carboxylates. Such compounds are not coordination polymers but oligomers and hence can be more soluble, more well-defined and easier to characterise than coordination polymers, for which they can serve as useful model systems. We will discuss discrete, self-assembled complexes of semi-protected metal ions that act as hosts in solution or as 3D capsules in the next chapter and we will not cover these systems in detail here except to note in passing a couple of examples that are of particular interest. One particularly prominent cluster is Muij-acetate, the mixed-valence compound... 

The reactivity of the aminoborylene complexes 1 and 2 under thermal conditions leads to the formation of semi-bridged borylene or bis-borylene complexes (vide infra). The photochemical transfer of the borylene ligand is useful for the preparation of borirenes [23], turned out to be an alternative for the synthesis of 1, and was also used for the synthesis of the first half-sandwich borylene complex [(775-C5H5)(OC)3V=B=N(SiMe3)2] (5) [24] (Scheme 4). In the crystal, the borylene ligand adopts the expected linear geometry (V-B-N 177.9(4)°) and the B-N bond (137.8(7) pm) is... 

Fig. 30 Structures of dinuclear rhodium and platinum complexes featuring semi-bridging Beat ligands...

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