Carbon-carbon bond formation using yttrium(III) and the lanthanide elements

The synthesis and characterization of a series of yttrium and lanthanide complexes that incorporate the macrocyclic bis(amidophosphine) ligand PhP(CH2SiMe2NSiMe2CH2)(2)PPh, [P2N2], are described. The starting materials, {[P2N2]M}(2)(mu -Cl)(2), (M = Y, Sm, Ho, Yb, Lu), are prepared by the reaction of syn-Li-2(dioxane)[P2N2] with MCl3(THF)(3) in toluene. The reactivity of these complexes toward PhLi and other arylating agents is dependent on the size of the M3+ ion. M = Y and Ho undergo C-C bond formation reactions to give biphenyldiide compounds {[P2N2]M}(2){mu-eta (6):eta (6 ')-(C6H5)(2)} and {[P2N2]Y}(2){mu-eta (6):eta (6 ')-(C6H4-p-Ph)(2)} These have been structurally characterized and show the biphenyl dianion bridging two [P2N2]M fragments. These [P2N2]M fragments migrate over the bridging ligand's pi -surface on the NMR time scale. M = Yb yields the paramagnetic monophenyl derivative [P2N2]Yb-(C6H5), where the Yb center is coordinatively unsaturated and resides in a distorted square-pyramidal environment. M = Lu results in a mixture of "ate" complexes of the formulation "[P2N2]LuPh . LiCl", as evidenced by Li-7 NMR. However, the biphenyl product {[P2N2]Lu}(2)-{mu-eta (6):eta (6 ')-(C6H5)(2)} can be synthesized via a reductive route. The presence of THF was found to be deleterious to the coupling reaction; in this case, the THF adduct [P2N2]Y(C6H4-p-Me)-(THF) was isolated and structurally characterized. The mechanism for the C-C bond formation reaction is described based on the isolation of these yttrium and lanthanide complexes.