Compounds with Homonuclear Transition Metal Bonds

Compounds with Homonuclear Transition Metal Bonds 

1 Group 4.- As in 1990 and 1991, there appear to be no reports of direct metal-metal bonds in (Hganometallic complexes of diis group. 

13 Group 6.- Reaction of the cyclopentadienyl dimers [C (Dr(CO)j2 (n=2,3) with Ph (E=S,Se) affords chakogen-bridged complexes [Cpl02(il-E)( -EPh)2], which upon thermolysis 

CHj)] , the synthesis of [Cp2Mo2(NO)(=CHBu )Oi-CHBu )( i. NO)] which contains a unique i-ti T -NO ligand , and trimethylphosphine adducts of [Mo(CH2Ph)(OPr )3]2. The S3mthesis and X-ray structure of the trinuclear alkylidyne complex [MOj( ls-CMe)(M3-0)(M.-PhC02) (MeOH),] is reported .  

Reaction of [FcjfCO),] with [Cp 3Ta3(fi -P4)(p -P2)] (Cp =l,3-Bu2C5H3) (5) affords an iron tetracarbonyl adduct, shown crystallographically to contain three weak tantalum-tantalum interactions.  

As in the past four years, there appears to be no report of direct metal-metal bonds in organometallic complexes of this group. 

Larger rhenium complexes are also the subject of a number of publications. Reaction of an excess of thietane with the thietane complex fRe3(CX))jQ(p-H)3(p-cyclo-SCH2CH2CH2)] affords a number of ring-opening oligomerisation products from which sulfur containing macrocycles such as 12-S-4, 16-S-4 and 24-S-6 can be eliminated upon addition of pyridine . Addition of 

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Compounds with Homonuclear Transition Metal Bonds... 

The activation of simple organic molecules by more than one transition metal constitutes an area of research which has grown in interest since the mid 1970s. Transition metal clusters, homonuclear and later heteronu-clear compounds, have been widely studied because of the potential for application in catalysis. The chemistry of such complexes has been the topic of many review articles, some of which appeared in this series (1-5). The concept of utilizing binuclear complexes with metal-metal bonds for ligand activation has been recognized (6-8), and, as stated by Casey and Audett, there is some hope that a smooth transition from the chemistry of mononuclear compounds to dinuclear compounds to metal clusters to metal surfaces may be found (9). 

Whereas certain bonding features are considered most unusual in a molecule, similar features are quite normal in solid state compounds, lb give an example, the unusual coordination of the carbon atom in the discrete molecule [ligQ is suggestive of hypervalency, [1, 2] however the occurrence of octahedrally coordinated carbon atoms is often observed in transition metal carbides having the rocksalt type structure, thus a quite normal situation. From a simple ionic representation as [(Ii )5C (e )2], the only surprise is the surplus of electrons. Yet, even this feature is familiar with such interstitial carbides as V2C in which, the valence electrons of V (li) which are not used for heteronuclear V-C (li-Q bonds are used to form homonuclear V-V (li-Ii) bonds, as suggested by the (8-N) rule. [3]... 

Rogl and Nowotny (1978) have observed that the type of homonuclear linkage in borides can be correlated in simple form with the metal boron ratio of the compound. All ternary rare earth-transition metal borides are listed in table 20, arranged according to decreasing metal boron ratio, and the observed homonuclear linkage of the B atoms. One notes that if the ratio is larger than 1.75 only isolated B atoms occur. Boron dumbbells are found with values between 1,3 and 1.0. Two homonuclear bonds occur first with a metal to boron ratio of 1 and three... 

The term Zintl phase is applied to solids formed between either an alkali- or alkaline-earth metal and a main group p-block element from group 14, 15, or 16 in the periodic table. These phases are characterized by a network of homonuclear or heteronuclear polyatomic clusters (the Zintl ions), which carry a net negative charge, and that are neutralized by cations. Broader definitions of the Zintl phase are sometimes used. Group 13 elements have been included with the Zintl anions and an electropositive rare-earth element or transition element with a filled d shell (e.g. Cu) or empty d shell (e.g. Ti) has replaced the alkali- or alkaline-earth element in some reports. Although the bonding between the Zintl ions and the cations in the Zintl phases is markedly polar, by our earlier definition those compounds formed between the alkali- or alkaline-earth metals with the heavier anions (i.e. Sn, Pb, Bi) can be considered intermetallic phases. 

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