BArF

At first, the reaction was investigated in batch mode, by use of different ionic liquids with wealdy coordinating anions as the catalyst medium and compressed CO2 as simultaneous extraction solvent. These experiments revealed that the activation of Wilke s catalyst by the ionic liquid medium was clearly highly dependent on the nature of the ionic liquid s anion. Comparison of the results in different ionic liquids with [EMIM] as the common cation showed that the catalyst s activity drops in the order [BARF] > [Al OC(CF3)2Ph 4] > [(CF3S02)2N] > [BFJ . This trend is consistent with the estimated nucleophilicity/coordination strength of the anions. 

BARF tetra[3,5-bis(trifluoromethyl)phenyl]borate BINAP 2,2 -bis(diphenylphosphanyl)-1,1 -binaphthyl BOC t-butoxycarbonyl... 

Catalyst screen at 90 psi hydrogen at r.t. and 60 °C for 20 h - No product detected Pfaltz-lr-BARF-cat, (Et-Duphos)Rh(COD)BF4,(BINAP)Ru(ll)CI2, Phanephos/(COD)2RhBF4, Josiphos SL-J009-1/(COD)RhCI,... 

BArF Tetra(perfluorophenyl)borate or tetra(3,5-trifluoromethylphenyl)bortate... 

The ionic iridium(III) carbene complex (47) is prepared from the reaction of IrHCl(03SCF3)-(CO)(PPh3)2] with [RC=NMe](03SCF3).61 Addition of Na(barf) (barf = B(3,5-C6H3 (CF3)2)4) to [Ircp (PMe3)(CH3)(0S02CF3)] in CH2C12 yields the structurally determined species... 

Scheme 8.4. Catalytic hydrogenation of imines using cationic iridium catalysts with the C02-philic BARF anion...

This complex is not the actual catalyst for the hydrovinylation, but needs to be activated in the presence of a suitable co-catalyst. The role of this additive is to abstract the chloride ion from the nickel centre to generate a cationic allyl complex that further converts to the catalytically active nickel hydride species. In conventional solvents this is typically achieved using strong Lewis acids such as Et2AlCl. Alternatively, sodium or lithium salts of non-coordinating anions such as tetrakis-[3,5-bis(trifluoromethyl)phenyl]borate (BARF) can be used to activate hydrovinylation... 

Scheme 14.17 Hydrogenation of sorbic acid by [Cp Ru( /4-sor-bic acid)]"X" (52). X"=CF3SOi or BARF".

In general, the choice of counteranion has a minor effect on catalyst performance, with typical examples being selected from BF4, OTD, PFg, or BARF-. In one example, however, it was noted that [(R.R)-Et-DuPhos Rh CODJOTf gave superior selectivity for the reduction of / -/ disubstituted a-dehydroamino acid derivatives than the corresponding BARF complex when performed in a range of solvents, including supercritical carbon dioxide [39]. 

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