Understanding the interaction of chiral ligands, alkynes, and alkenes with cobaltcarbonyl sources is critical to learning more about the mechanism of the catalytic, asymmetric Pauson-Khand reaction. We have successfully characterized complexes of the type [Co2(alkyne)(binap)(CO)4] (BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine)) and shown that diastereomer interconversion occurs under Pauson-Khand reaction conditions when alkyne=HC[triple bond]CCO2Me. Attempts to isolate [Co2(alkyne)(binap)(CO)x] complexes with coordinated alkenes led to the formation of cobaltacyclopentadiene species.

Heating (alkyne)(binap)tetracarbonyldicobalt(0) complexes bearing pendant alkenes leads to cleavage of the cobalt−cobalt bond and generation of the mononuclear hydride (binap)(CO)2CoH at 45−55 °C.

Four (binap)(enyne)tetracarbonyldicobalt(0) complexes have been synthesised and their reactivity monitored by variable temperature (31)P NMR spectroscopy. Formation of (binap)dicarbonylhydridocobalt(-1) 12 occurred at temperatures between 35 and 55 degrees C, depending on the nature of the alkene and alkyne components of the enyne. The structure of 12 was determined by X-ray crystallography, and its presence under Pauson-Khand reaction conditions was verified by NMR spectroscopy.

A study of the Pauson-Khand reaction (PKR) based on Co2(CO)8 and binap has revealed that a key precatalyst is (binap)Co2(CO)6, and that alkynes add to this species to generate isomers that interconvert under typical PKR conditions. A 31P NMR study of (binap)(N-(prop-2-enyl)-N-(prop-2-ynyl)-p-toluenesulfonamide)Co2(CO)4 revealed that heating this species gives rise to an unexpected cobalt hydride species (binap)Co(CO)2H together with (binap)Co2(CO)6. Observation of a PKR reaction by 31P NMR spectroscopy revealed that the hydride species is generated during the course of the reaction.

Coordination chemistry Z 0150 Metal Carbonyl Complexes and Chirality -[12 refs.]. -(GIBSON, S. E.; KAUFMANN, K. A. C.; LOCH, J. A.; MIYAZAKI, A.; Pure Appl. Chem. 80 (2008) 5, 903-911; Dep. Chem., Imp. Coll., London SW7 2AZ, UK; Eng.) -Lindner 40-221