Transition-metal-halide cluster

Early transition metal halide clusters, see Group 5 metal halide clusters Group 6 metal halide clusters... 

The bulk of binary metal-halide clusters involve the early transition metals, however, later transition metal-halide clusters are known. [Pt6(M2-Cl)i2] is one example. 

The lack of late transition-metal halide clusters and the poor bonding which results when they are formed can be easily rationalized. In binary metal halide clusters the metal atoms are in a high oxidation state. The valence orbital contraction in these high oxidation state metals is much greater for the later transition metals than it is for the early ones. The diminished radical extension of the valence shell inhibits metal-metal bonding. 

The octahedral early transition-metal-halide clusters [Mo Clg]" and [M6Xi2] + (M = Nb, Ta, Re X = F, Cl, 1 n = 2, 3, 4) contain both strongly anchored inner halide ligands that bridge metals and substitution-labile outer chloride ligands that are terminal in the six axial/equatorial positions and give rise to a rich hexasubstitution chemistry. 

A second feature of metal halide cluster chemistry is that the early transition metals are more prone to form metal -metal bonds than are the later noble metals and coinage metals. Again the polynuclear metal carbonyls differ in this facet of metal-metal bond behavior, and, in fact, metal carbonyl clusters become more common on going from the left to the right of the Periodic Table. 

Little is known about the oxidative addition of organohaUdes to early transition metal atoms. Nevertheless, macroscale amounts of solvated transition metal halides in lower valency states have been obtained. Re yields interesting clusters in reactions with 1,2-dibromoethane and oxalyl chloride... 

The hexanuclear molybdenum halide clusters (Mo6Xs)X4, i.e. (Mo6X 8)CP2CF 4/2, are known to react with some transition metal halide compounds forming two different types of cluster polymeric clusters with bridging outer halide ligands (X ) and discrete clusters with terminal halide ligands (X ). 

If PhN(SnMc3)2 is allowed to react with certain transition metal halide derivatives at higher temperatures (e. g. in refluxing toluene), the formation of NPh-bridged cluster compounds can be observed. [87] Some of these are outlined in Scheme 3-17. 

Remarkably, it has not proved possible to synthesize heterometallic clusters from 53 (the SeSiMe3 derivative of 52) or other transition metal halide derivatives (with the exception of the syntheses of 61 and 62). [158, 159] It has been possible to synthesize larger palladium clusters, however. The reaction of with [CpCrQ2(THF)] or [PdQ2(PPh3)2], for example, has led to the formation of Pdj, Pdy, and Pds complexes (Scheme 3-24). The isolation of these compounds is not an easy task. 

It is possible to extend the synthetic prindples which were presented above to the preparation of polynuclear complexes having Cp, allyl, and CO ligands. Preliminary results from the reactions of cyclopentadienyl, allyl, and CO complexes of the transition metal halides with E(SiMc3)2 (E = S, Se, Te) indicate that MesSiQ is eliminated and a series of novel compounds are formed. The reaction between [CpFe(CO)2Br] and Se(SiMe3)2 produces a diamagnetic compound composed of the heterocubane cluster anion [Fe4Se4Br4] and two [Se Fe(CO)2Cp 3] cations (Eq. 3.52). 

Organometallic derivatives of the less electron rich transition metals have been used by several investigators as precursors to polynuclear complexes. Cp-substi-tuted transition metal halides, for example, have been allowed to react with M2E, (M = Li, Na E = S, Se x = 1,2) or elemental sulfur or selenium. [251-254] S(SiMe3)2 and Se(SiMe3)2 have also been used successfully. Thus, the reaction of [CpCrCl2(P Bu3)] with Se(SiMc3)2 furnishes the heterocubane cluster [Cp4Cr4Se4]. [255]... 

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