A Study of (Binap)(enyne)tetracarbonyldicobalt(0) Complexes

A "catch-and-release" protocol for alkyne-tagged molecules based on a resin-bound cobalt complex for peptide enrichment in aqueous media

The development of new and mild protocols for the specific enrichment of biomolecules is of significant interest from the perspective of chemical biology. A cobalt-phosphine complex immobilised on a solid-phase resin has been found to selectively bind to a propargyl carbamate tag, that is, "catch", under dilute aqueous conditions (pH 7) at 4 °C. Upon acidic treatment of the resulting resin-bound alkyne-cobalt complex, the Nicholas reaction was induced to "release" the alkyne-tagged molecule from the resin as a free amine. Model studies revealed that selective enrichment of the alkyne-tagged molecule could be achieved with high efficiency at 4 °C. The proof-of-concept was applied to an alkyne-tagged amino acid and dipeptide. Studies using an alkyne-tagged dipeptide proved that this protocol is compatible with various amino acids bearing a range of functionalities in the side-chain. In addition, selective enrichment and detection of an amine derived from the "catch and release" of an alkyne-tagged dipeptide in the presence of various peptides has been accomplished under highly dilute conditions, as determined by mass spectrometry.

Metal carbonyl complexes and chirality

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.