ansa-Metallocene derivatives xv *. Reversible coordination of a second CO ligand to (CSHS)2Cr(CO) and its tetramethylethanediyl-bridged analogue. Evidence for an electron-transfer catalysed ringslippage reaction. IR studies at elevated gas pressure. II * *

Decamethylchromocen, (C5(CH3)5)2 Cr, bildet mit CO den 18‐Elektronen‐Komplex (C5(CH3)5)2Cr(CO). Unter höheren CO‐Drucken entsteht der Dicarbonyl‐Komplex (C5(CH3)5)2Cr(CO)2, der auch in Abwesenheit von CO stabil ist. Eine Röntgenstrukturanalyse ergibt, daß diese Verbindung einen η3‐ und einen η5‐koordinierten Ringliganden enthält und damit ebenfalls als 18‐Elektronen‐Teilchen vorliegt.

IR studies of toluene solutions of «CsHshTiClh under elevated CO pressures indicate the formation of a carbonyl complex, probably (CsHshTi(CO)CI, with ,,(CO) 2068 cm-I. This species predominates at CO pressures above 100 bar, and is reasonably stable at temperatures around-30 0 C. At higher temperatures, disproportionation to (CsHshTi(COh and (CsHshTiCI2 occurs. This disproportionation is reversible; at + 30 0 C and 1 bar of CO, roughly equal concentrations of «CsHshTiClh and of dicarbonyl and dichloride products are in equilibrium with each other. Practically complete formation of these products occurs at CO pressures above 10 bar. Rate laws and reaction mechanisms have been studied for the disproportionation reaction and for its reverse, the comproportionation of (CsHshTi(COh and (CsHshTiC12 to «CsHshTiClh, which predominates at lower CO pressures.

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285ChemInform Abstract Decamethylchromocene (I) reacts with CO (II) at ambient pressure to form the 18-electron complex (III). At elevated CO pressure, the dicarbonyl complex (IV) is formed. An X-ray structure determination of (IV) (space group C2/c) shows the presence of one η3-and one η5-coordinated ring ligand and hence an 18-electron configuration even for this compound.