INSERTION REACTIONS OF BENZYNE-NICKEL(O) COMPLEXES WITH ACETYLENES

Complexes of nickel(0) containing eta(2)-4,5-difluorobenzyne, Ni((1,2-eta)-4,5-F2C6H2)(PEt(3))(2) (10) and Ni((1,2-eta)-4,5-F2C6H2)(dcpe) (11; dcpe = 1,2-bis(dicyclohexylphosphino)ethane, Cy(2)PCH(2)-CH(2)PCy(2)) have been synthesized by alkali-metal reduction of the appropriate (2-halo-genoaryl)nickel(II) halides. Spectroscopic measurements (C-13 NMR, FAB-MS) indicate that 10, 11, and the parent benzyne complex Ni((1,2-eta)-C6H4)(PEt(3))(2) (2) are monomeric, analogous to the structurally characterized species Ni((1,2-eta)-C6H4)(Cy(2)PCH(2)CH(2)PCy(2)). Complexes 2 and 10 undergo rapid intermolecular exchange with PEt(3) at room temperature and react with disubstituted acetylenes by double insertion into the metal-benzyne bond to form 1,2,3,4-tetrasubstituted naphthalenes. With electrophilic acetylenes (MeO(2)CC(2)CO(2)Me, MeC(2) . CO(2)Me, HC(2)CO(2)Me, and CF3C2CF3) an aromatic cyclotrimer is also formed; exceptionally, hexafluorobut-2-yne also gives with 10 a phenanthrene derived from two benzyne units and the acetylene. The unsymmetrical acetylenes tert-butylacetylene and methyl 2-butynoate give rise to good regioselectivity in the resulting naphthalenes, the favored isomers being very dependent on the steric and electronic influence of the substituents. The dcpe complexes react similarly but more slowly with acetylenes, and with MeO(2)CC(2)CO(2)Me the monoinsertion complexes Ni{C(CO(2)Me)=C(CO(2)Me)C(6)H(2)R(2)-o}(dcpe) (R = H, F) can be observed.