NAPHTHALENE COMPLEXES. V. ARENE EXCHANGE REACTIONS IN NAPHTHALENECHROMIUM COMPLEXES

Article abstract of DOI:10.1016/0022-328X(85)88005-0

Di-η⁶-naphthalenechromium(0) (1) reacts at 150 deg C with benzene to yield (η⁶-naphthalene)(η⁶-benzene)chromium(0) (3) in 76percent yield.In the presence of THF, 1 undergoes Lewis base catalyzed arene exchange at 80 deg C.Reactions of 1 with substituted arenes yield the mixed sandwich complexes 4 and 6-10 (arene=1,4-C6H4Me2, 1,3,5-C6H3Me3, C6Me6, 1,4-C6H4(OMe)2, 1,4-C6H4F2 and 1,4-C10H6Me2).In all but one case (witih 1,4-dimethylnaphthalene) exchange of a single naphthalene ligand is observed.In marked contrast to the lability of 1, dimesitylenechromium(0) (5) is inert to arene diplacement in benzene up to 240 deg C.The molecular structure of 3 has been determined by X-ray crystallography.The crystal data are as follows: a 7.784(1), b 13.411(2), c 22.772(5) Angstroem, Z=8, space group Pbca.The structure was refined to a R_W value of 0.043.The naphtahlene ligand in 3 is nearly planar and parallel to the approximately eclipsed benzne ring.Metal atom-ring distances are 1.631(9) and 1.611(4) Angstroem for naphthalene and benzene, respectively.Catalyzed and uncatalyzed naphtahlene exchanges in the sandwich complex are compared to the analogous reactions with the Cr(CO)3 complex 2.Naphthalene exchange in 2 in benzene is 1E3 to 1E4 times fastere than arene exchange in other arenetricarbonylchromium compounds.The mild conditions for Lewis base catalyzed naphthalene exchange make 2 a good precursor of other arenetricarbonylchromium compounds.Examples include the Cr(CO)3 complexes of styrene, benzocyclobutene, 1-ethoxybenzocyclobutene, 1,8-diemthoxy-9,10-dihydroanthracene and 1,4-dimethylnaphthalene.