Trinuclear metal complexes

All three members of the isoelectronic series CoBFe3 BH2 B (CO)9S ( = 0.1,2) are known.1-3 They may be prepared by acidification of solutions containing the [FeH(CO)4]- and the [Co(CO)4]- anions in the presence of sodium sulfide.2,3 The yields of this method are only moderate, however, 

The methods described here are based on the thermal stability of such clusters under CO pressure.4 In the case of Co2Fe(CO)9S, the complex itself is stable under hydroformylation conditions (130-180 °C, 50-150 bar CO and H2) and is formed under such conditions from almost every sulfur-containing substance, iron, cobalt, and carbon monoxide.1 Ethanethiol is used in the procedure as the sulfur source because of its reactivity. The dihydride cluster Fe3H2(CO)9S is not directly accessible by this method because it is a thermally much less stable species but the anion Fe3H(CO)9S can be prepared in this way and its acidification yields the desired complex. 

The two phases are separated and the lower layer is extracted four times with 80-mL portions of hexane. The combined hexane solutions are washed with 40 mL of water and the hexane layer is separated and dried over Na2 S04, filtered under Ar, and cooled to — 78 °C. The separating crystals usually do not need further purification, their purity can be checked by infrared (IR) 

The complex forms dark brown crystals that are sensitive to air. It is highly soluble in nonpolar organic solvents. Its IR spectrum in the region (hexane, 

A rocking autoclave (100 mL) is charged with Co2(CO)8 (5 mmol, 1.71 g), Fe(CO)s (5 mmol, 0.69 mL), C2H5SH (6 mmol, 0.44 mL), and hexane (50 mL). The autoclave is flushed with CO and pressurized with a CO-H2 (2 1) gas mixture at room temperature to 210bar. The reaction is carried out at 150 °C for 3 h (the pressure rises to about 300 bar) after which the autoclave is cooled, and the gas is slowly vented into a well-ventilated hood. The product, a brown solution containing some crystals is poured under Ar into a Schlenk tube (100 mL). The solvent is evaporated under vacuum and the solid residue dissolved in hexane (120 mL). The solution is filtered under Ar and chilled to - 78 °C. Yield 1.5 g (65%). 

Inorganic Syntheses, Volume 26 Edited by Herbert D. Kaesz Copyright 1989 by Inorganic Syndieses, Inc. Polynuclear Transition Metal Complexes 

The complex forms shining black crystals that are moderately stable in air. It is highly soluble in organic solvents. Its IR spectrum in the Vco region (hexane, cm-i) 2104(w), 2066(vs), 2053.5 (vs), 2041.5(s), 2028.5(m), 1984(m). 

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The ability to switch a molecular unit on and off is a key component of an efficient molecular device, since it allows modulation of the physical response of such a device by external physical or chemical triggers. A molecular device, based on a trinuclear metal complex, shown in Figure 59, functions as an electroswitchable-photoinduced-electron-transfer (ESPET) device.616 Electrochemical switching of the redox state of a spacer intervening between a donor-acceptor pair can dictate the type of the observable charge separation and the lifetime of the resulting ion pair.616... 

Figure 59 A trinuclear metal complex that functions as an electroswitchable-photoinduced-electron-transfer...

Studies on di- and trinuclear metal complexes bridged by carbonate or hydrogencarbonate are mainly noted from three areas (i) fixation and activation of C02 from the viewpoint of environmental protection 462 164 (ii) functional models for zinc-containing carbonic anhydrase (Volume 8) and (iii) the relationship between the bridging modes of carbonate and magnetic properties. 

The presence of multiple donor sites enables cyclophosphines cyclo-(PR) n = 3-6) to function as versatile two-electron ligands in mono- di- or trinuclear metal complexes as discussed in Section 7.1.1 (see structures 7.1-7.3) in some case the reaction of cyclo-(PR)5 with transition metal complexes results in P-P bond activation, which may occur either with retention or fragmentation of the oligophosphine (for examples, see structures 7.4-7.5). ... 

On protonation with H[BF4] OEt2 in THF the anionic trinuclear metal complexes 5 and 7 afford the neutral hydrido compounds [2,2-(CO)2-7,ll-(p-H)2-2,7,... 

Electron-precise cluster systems can be seen to be a more complex version (three-connect units) of chains (one-connect units) and rings (two-connect units), leading up to an extended solid (four-connect units, e.g. the diamond structure). This is most easily appreciated for homonuclear examples, for example, (1) and (2). For the mixed systems like (3), two distinct descriptions are possible - as a 4-atom cluster or as a trinuclear metal complex with a /U.3-P cap. In many cases, the difference is of little consequence however, in others, proper choice of description can lead to analyses of significant conceptual value. 

Treatment of the ferrio-silanol 1 with cyclopentadienyltrichlorotitanium 8 yields, under the conditions of Eq. (1), the tris(ferrio-siloxy)-substituted complex 9. In contrast, the analogous reaction of the tungsten-silanols 5a,b does not succeed in the substitution of all chloro atoms, but leads to the incorporation of only two metallo-siloxy groups to give the trinuclear metal complexes 10a,b, irrespective of the molar ratio (Fig. 2). 

R.P. White, N.C. Sa-ard, S.K. Bollen, R.D. Cannon, U.A. Jayasooriya, S.T. Robertson, U. Steigenberger J. Tomkinson (1990). Spectrochim. Acta, 46A, 903-910. Vibrational spectroscopy of oxo-centred trinuclear metal complexes an inelastic neutron scattering study. 

Reaction of the thiocarbyne TpW( = CSMe)(CO)2 with the Ni(I) dimer Cp2Ni2(At-CO)2 generates a trinuclear metal complex based on a Ni2W triangle TpCp2WNi2(/t3-CSMe)(CO)2 (Scheme 71). Two infrared stretches at 1875 and 1806 cm are consistent with a semi-bridging role for the tungsten carbonyls. 

A frequently employed strategy to generate more effective hydrolytic enzyme models is the use of bi- or even trinuclear metal complexes. The active center of natural enzymes often contains two or three divalent metal ions, lying close together with a metal-metal distance of a variety of biomimetic bi- or trinuclear... 

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