Compounds with Heteronuclear Transition Metal Bonds

Compounds with Heteronuclear Transition Metal Bonds 

Due to a the limitation of space a discussion of individual publications in this section is not 

The number of literature reports pertaining to OTganometallic compounds ctmtaining hetercHiuclear metal-metal bonds continues to increase and therefore a discussion of individual publications is beyond the scope of this review. Hence for both binuclear and polynuclear complexes, lists of relevant exaiiq les will be given followed by a brief discussion d those examples which, in the authors q inion, represent the more interesting and novel reports. 

The complex CWOs (CO) g (PMe3) 3, with an unbrldged, dative bond Os - 299fiacistsin solution as two isomeric forms In a dynamic equilibrium, probably involving non-dissociative CO migration between metal atom  

In related donor-acceptor complex [(OC)cRuOsBr(SiCl,)(CO)-3 partial 

Pt- Pd bond is probably present in the bridged complex C PtPd (y-dppm), 

The large majority of newly reported blnuclear complexes that, at least formally, contain a direct metal-metal bond also contain bridging ligemds. Single hydride bridges euce observed in CMFe (p-H) (CO) g] and CMM (u-H) (C0)5(PR3)3 - (M = Cr,Mo,W M = Au,Ag) and from 

X-Ray determined structures of heterobinuclear metal-metal bonded complexes 

Molybdenum and Tungsten (continued) CMoCo(y-H)2Br2(NCMe)Cp23  

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Compounds with Heteronuclear Transition Metal Bonds... 

The subject of heteronuclear cluster compounds of the transition metals remains an active area of research interest, and was reviewed in the early 1980s by Geoffroy el al. (1,2). Clusters with novel architectures, exemplified by the star clusters of Stone and co-workers (5), continue to be synthesized. Whereas there is undoubtedly strong academic interest in the structure, bonding, and chemical reactivity of heteronuclear clusters in their own right, additional impetus to this field is given by the important relationship between heteronuclear clusters and bimetallic alloy catalysts. This relationship was the subject of a published symposium (4). 

Robert D.A., Geoffroy G.L. Compounds with heteronuclear bonds between transition metals. In Comprehensive Organometallic Chemistry, Wilkinson G., Stone F.G.A., Abel E.W. Eds., Perga-mon, Oxford, UK, 1982 Vol. 6, pp. 821-877 and references therein Rogovin, M., Neumann, R. Silicate xerogels containing cobalt as heterogeneous catalysts for the side-chain oxidation of alkyl aromatic compounds with tert-butyl hydroperoxide. J. Mol. Catal. A Chem. 1999 138 315-318... 

Silicon-transition metal chemistry is a relatively new area. The work of Hein and his associates (1941) on Sn—Co derivatives established the possibility of forming bonds between a Group IVB metal and a transition element 139), but it was another fifteen years before CpFe(CO)2SiMej 203), the first of many silyl derivatives, was synthesized. The interest in these compounds derives from (1) comparison with the corresponding alkyl- and Ge-, Sn-, and Pb- transition metal (M) complexes, including the role of ir-back-bonding from filled d orbitals of M into empty d orbitals on Si (or other Group IVB metal), and (2) expectation of useful catalytic properties from such heteronuclear derivatives. 

The general reactions proposed herein for M = M compounds with symmetrical substrates are not exhaustive but merely pertinent to some recent experimental observations. The reaction schemes involving unsymmetrical substrates and heteronuclear M-M multiple bonded compounds are virtually unlimited, all of which indicates the growth potential of this area of transition metal chemistry. 

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]... 

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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