Phosphines cluster compounds

Mixed-Metal-Gold Phosphine Cluster Compounds 279... 

MIXED-METAL-GOLD PHOSPHINE CLUSTER COMPOUNDS... 

Phosphine palladium and phosphine platinum carbonyl cluster compounds. N. K. Eremenko, E. G. Mednikov and S. S. Kurasov, Russ. Chem. Rev. (Engl Transl.), 1985, 54, 394 (69). 

We have restricted the discussion in the section primarily to mixed carbonyl, carbonyl-hydride, or phosphine-substituted cluster compounds. On the basis of electronegativity, there should be an enhance-... 

The Ni3S2 fragments in the two complexes (263) and (265) have a trigonal bipyramidal geometry with the two S atoms in the apical positions and the three nickel atoms in the equatorial plane, as found in other organometaUic compounds which contain the same Ni unit.1939 The formation of the enneanuclear complex (264), on the contrary, is exceptional and no other complex of this stoichiometry was isolated with analogous tertiary phosphines, with selenium, or with metals other than nickel. It is not possible to assign any definite oxidation number to nickel in complex (264). The lack of two electrons with respect to the situation of nine nickel(II) ions was reported to be essential for the existence of complex (264) because the oxidation is spontaneous and its reduction invariably leads to the decomposition of the cluster compound.19 ... 

To relieve the strain of sterically demanding ligands, a metal often remains coordinatively unsaturated. Copper(I) halides and phosphines form cubane-like metal cluster compounds, Lm(CuX) ,12 With the bulky trimesitylphosphine, a monomeric two-coordinate [CuBr(Pmes)3] is formed, Br—Cu—P = 173.7°.252 The d(Cu—P) of 2.193 A is comparable to that in normal tet-rameric complexes, but d(Cu—Br) at 2.225 A is shorter, no doubt due to the reduced coordination number. Heating crowded complexes can also result in a reduction in coordination number (see equation 65). 

A second example of cluster formation involves the antagonism between molybdenum and copper. The presence of high concentrations of molybdenum in pasture soils is known to lead to symptoms of copper deficiency in animals. This has been attributed to the formation of thiomolyb-dates in the rumen of grazing animals, which then interfere with the metabolism of copper through the formation of cluster compounds of molybdenum and copper. It has been shown that thiomolyb-date, MoS42, readily forms such clusters on reaction with phosphines and copper(II) salts under appropriate conditions. Structures are shown in Figure 38.992,993 Reaction between thiomolybdate and copper compounds in aqueous solution have also been reported.994... 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

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