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Promoting Difficult Carbon-Carbon Couplings: Which Ligand Does Best?

Authors :: Gioria E
Del Pozo J
Martínez-Ilarduya JM
Espinet P
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2016 Oct 10; Vol. 55 (42), pp. 13276-13280.
Publication Year :: 2016
Abstract: A Pd complex, cis-[Pd(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>2</subscript> (THF) <subscript>2</subscript> ] (1), is proposed as a useful touchstone for direct and simple experimental measurement of the relative ability of ancillary ligands to induce C-C coupling. Interestingly, 1 is also a good alternative to other precatalysts used to produce Pd <superscript>0</superscript> L. Complex 1 ranks the coupling ability of some popular ligands in the order P <superscript>t</superscript> Bu <subscript>3</subscript> >o-TolPEWO-F≈tBuXPhos>P(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>3</subscript> ≈PhPEWO-F>P(o-Tol) <subscript>3</subscript> ≈THF≈tBuBrettPhos≫Xantphos≈PhPEWO-H≫PPh <subscript>3</subscript> according to their initial coupling rates, whereas their efficiency, depending on competitive hydrolysis, is ranked tBuXPhos≈P <superscript>t</superscript> Bu <subscript>3</subscript> ≈o-TolPEWO-F>PhPEWO-F>P(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>3</subscript> ≫tBuBrettPhos>THF≈P(o-Tol) <subscript>3</subscript> >Xantphos>PhPEWO-H≫PPh <subscript>3</subscript> . This "meter" also detects some other possible virtues or complications of ligands such as tBuXPhos or tBuBrettPhos.<br /> (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)