Unsupported metal chains

In this chapter, we describe linear metal chain compounds, consisting of at least three metal ions, supported by ligand systems. Extended metal atom chains (EMACs) of Cr, Co, Ni, and Cu, supported by polypyridylamide ligands, are discussed. This is followed by linear and bent Pd chains sandwiched by unsaturated hydrocarbons. Unsupported linear metal chain compounds are discussed in subsequent sections. Because synthetic protocols and the bonding schemes are different for different metals, our discussion is classified according to metal ions. 

The mixed-valent, square-planar cation [Rh (CO)2(CH3CN)2] was reported to form one-dimensional stack in the solid state. The chain is composed of the repeat unit [ Rh2 (02CCF3)2(C0)4 Rh2 °(02CCF3)4 Rh (02CCF3)2(C0)4 ] , in which an Rh",Rh" unit is connected with two dimeric Rh, Rh units. A linear chain composed of dirhodium units is not limited to acetonitriles and carbonyls. Metal chains of the type [ Rh2(OAc)2(LL)2 (BF4)] (LL = 1,10-phenanthroline 2,2 -bipyridyl) have been prepared by one-electron reduction of the corresponding dirhodium(II,II) precursors [Rh2(OAc)2 (LL)2] in aqueous ethanol. For the phen compound, three different Rh-Rh separations are noted in the Rh chain. The carboxylate bridged Rh-Rh distance is 2.652 A the unsupported interdimer Rh-Rh distance is 2.739 A and the resultant tetranuclear fragments are linked into an infinite chain by Rh-Rh... 

In Chapter 5, M. Majumdar and J. K. Bera describe the properties of and synthetic protocols for preparing extended linear metal (Cr, Co, Ni and Cu) chain compounds that contain at least three metal ions and are supported by ligand systems. In addition, they describe bent Pd chains that are sandwiched between unsaturated hydrocarbons and unsupported linear metal chain compounds. 

Molecular wires, 208 211 in which two metal centers are connected by an unsupported C3 chain, as in compound 191, have been generated by addition of BF3 to binuclear bridged (l-alkynyl)carbene complex lw (Scheme 80).27 29,212 Similar compounds were derived from tungsten, rhenium, and iron moieties. A binuclear complex 192 containing a C5 bridge has been also obtained 27... 

The presence of the cyclopentadienyl ligand at the chromium center provides a catalyst with a unique high response to hydrogen as a chain transfer agent (97). A number of ir- and O-bonded transition metal compounds in solution or supported (34) have been described as polymerization catalysts. Unsupported and supported transition metal-ally 1 compounds have been proposed to initiate polymerization by reaction with monomer in a manner illustrated by Reaction 22 for (allyl)3ZrBr/Si02 and ethylene. 

X-ray structure revealed the hexametallic chain formed by an almost linear array in which two A isomers sandwich a B isomer (Figure 27). The six iridium atoms are linked by metal-metal bonds, two of whieh are unsupported. The unsupported Ir-Ir distances are (range 2.7757(14) 2.7929(14) A) longer... 

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