Bonds in Dinuclear Complexes

The reactions of alkynes and alkenes with metal-metal multiple bonds in dinuclear complexs have important catalytic implications, but less attention is paid to their insertions into metal-metal single bonds. A 1965 publication comprehensively reviewing insertions of compounds of metals and metalloids involving unsaturated substrates lists insertions into metal-metal bonds prior to 1965. 

In his review on highly polar metal-metal bonds in early-late heterodi-metalhe eomplexes Gade expected the topological approach to find more widespread use in future studies of metal-metal bond polarity. A consistent picture of the nature of the Ti-Co bonds in dinuclear complexes was obtained by a combination of AIM and an ELF analysis. The covalent metal-metal bond order was less than 0.5, and high partial charges of > 0.5e emphasized the highly polar character of the Ti-Co bonds. 

As earlier mentioned, one of the reasons of the poor stability of gold(II) complexes is the unfavorable energy of the odd electron. The formation of a metal—metal bond in dinuclear gold(II) complexes giving diamagnetic species provides an extra stability. Thus, the number of... 

Bimetallic biconnective bridging can also be symmetric or can display a variable degree of unsymmetry (Scheme 4). This coordination mode occurs in dinuclear complexes and in supramolecular chain-like arrays. When a metal-metal bond is present five-membered rings are formed. 

Acid Strength of Water Ligands in Dinuclear Complexes with Negligible Intramolecular Hydrogen Bond Interaction at 25°C and / = 1.0 M... 

A number of attempts have been made over the years to develop reproducible synthetic routes to six- and seven-coordinate isocyanide complexes of molybdenum and tungsten. Two of the older methods, namely, the reaction of the hexacarbonyls with halogens in the presence of an isocyanide (775,116) or reactions of the salt Ag4Mo(CN)8 with isocyanides (74), have given six- and seven-coordinate products. Recently, however, the discovery of the reductive or nonreductive cleavage of multiple metal - metal bonds in dinuclear group VIA compounds by isocyanides has provided a facile route to the synthesis of a variety of homoleptic and related isocyanide complexes of these metals in reasonable yields. 

In dinuclear complexes, the bond valence of the metal-metal (M-M) bond can be calculated from its number of bonding electrons, gM. A simple procedure for counting the metal-metal bond valence is as follows ... 

The crystal structures of in excess of 70 hexacarbonylalkyne-dicobalt complexes have been determined by X-ray diffraction. In all cases the basic structural features are the same and can be illustrated by the structure of [Co -FjCQCFjXCO), shown in Fig. 1,Z7 The molecule has pseudo C2v symmetry in which the two cobalt atoms and the two acetylenic carbon atoms form a quasi-tetrahedral core. The carbon-carbon bond of the alkyne is in a perpendicular orientation relative to the cobalt-cobalt bond, as opposed to the parallel orientation which is also observed in dinuclear complexes with bridging alkyne ligands. The coordination around the cobalt atoms is distorted octahedral and the two tricarbonylcobalt moieties are eclipsed. 

Bonding mode M3 is truly acetylenic in character, and is common in dinuclear complexes (17). It has been observed in the trinuclear platinum cluster Pt3((PEt3)4(PhCCPh)2 (151). The three Pt atoms adopt... 

Our knowledge of dioxygen complexes has increased considerably since Vaska s review of 1976. Theoretical and spectroscopic studies have given a description of the bonding in these complexes which rationalises the structures observed experimentally, and which provides a useful basis for the discussion of the reactivity. Very few theoretical studies on dinuclear complexes have appeared however, and we know of only one investigation of the relative merits of the and rf bridging peroxo structures . ... 

In spite of a wide occurrence of ROH OR hydrogen bonding in dinuclear alkoxide complexes, it can be interrupted by competing effects. For example, the complex Nb2Cl4(OMe)4(MeOH) (175) adopts the structure V with a planar... 

In dinuclear complexes containing a metal-metal single bond, the major consequence of irradiation is homolytic cleavage to form reactive metal-carbonyl radicals. Many simple substitutions can be explained by a mechanism involving thermal substitution of these radicals. This mechanism is especially helpful in explaining the formation of a disubstituted product ... 

Photoinduced Cleavage of Metal-Metal Bonds 13.3.1. in Dinuclear Complexes... 

---