CO-induced ring-slippage reactions of molybdenocene and tungstenocene carbonyl complexes. Electrochemical and elevated-pressure infrared evidence for an electron-transfer catalysis
Abstract Infrared studies at a CO pressure of 120 bar show (η 5 -C 5 H 5 ) 2 W(CO) to be completely resistant to an excess of CO in the absence of oxidants, but cyclovoltammetric measurements with this complex and with (η 3 -C 5 H 5 )(η 5 -C 5 H 5 )W(CO) 2 in THF solution at 0°C indicate that the ring-slipped dicarbonyl complex is catalytically generated by a one-electron oxidation of the tungstenocene monocarbonyl under CO at ambient pressure. Similar results are found for the reaction of (η 5 -C 5 H 5 ) 2 Mo(CO) with CO.
Mono‐ und Dicarbonyl‐Komplexe des Decamethylchromocens Eine CO‐induzierte η5 → η3 ‐ Ringverschiebung
Decamethylchromocen, (C5(CH3)5)2 Cr, bildet mit CO den 18-Elektronen-Komplex (C5(CH3)5)2Cr(CO). Unter hoheren CO-Drucken entsteht der Dicarbonyl-Komplex (C5(CH3)5)2Cr(CO)2, der auch in Abwesenheit von CO stabil ist. Eine Rontgenstrukturanalyse ergibt, das diese Verbindung einen η3- und einen η5-koordinierten Ringliganden enthalt und damit ebenfalls als 18-Elektronen-Teilchen vorliegt. 
 
 
 
Mono- and Dicarbonyl Complexes of Decamethylchromocene 
 
 
 
Decamethylchromocene, (C5(CH3)5)2Cr, reacts with CO at ambient pressure to form the 18-electron species (C5(CH3)5)2Cr(CO). At elevated CO pressures, the dicarbonyl complex (C5(CH3)5)2Cr(CO)2 is formed, which persists in the absence of CO. An X-ray structure determination of (C5(CH3)5)2Cr(CO)2 shows the presence of one η3- and one η5-coordinated ring ligand and hence an 18-electron configuration even for this compound.
Some bonding questions prompted by studies of the fluxional molecule triscyclopentadienylnitrosylmolybdenum
The compound (C5H5)3MoNO has been prepared. Its proton magnetic resonance spectrum in solution has been studied as a function of temperature down to –110°. The crystal structure has been determined with relatively high precision at 22°. The combined results of these studies lead to some new observations concerning the manner in which cyclopentadienyl rings may be bonded to metal atoms. Specific conclusions are (a) that a trihapto (i.e., π-allylic) form of bonding is not a real possibility, and (b) unsymmetrical relationships of ring to metal, which cannot be readily described in terms of any simple limiting structure, are possible under certain conditions.