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(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh, [P 2 N 2 ], are described. The starting materials, {[P 2 N 2 ]M} 2 (μ-Cl) 2, (M = Y, Sm, Ho, Yb, Lu), are prepared by the reaction of syn -Li 2 (dioxane)[P 2 N 2 ] with MCl 3 (THF) 3 in toluene. The reactivity of these complexes toward PhLi and other arylating agents is dependent on the size of the M 3+ ion. M = Y and Ho undergo C−C bond formation reactions to give biphenyldiide compounds {[P 2 N 2 ]M} 2 {μ-η 6:η 6 ‘ -(C 6 H 5 ) 2 } and {[P 2 N 2 ]Y} 2 {μ-η 6:η 6 ‘ -(C 6 H 4 - p- Ph) 2 }. These have been structurally characterized and show the biphenyl dianion bridging two [P 2 N 2 ]M fragments. These [P 2 N 2 ]M fragments migrate over the bridging ligand's π-surface on the NMR time scale. M = Yb yields the paramagnetic monophenyl derivative [P 2 N 2 ]Yb(C 6 H 5 ), 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 “[P 2 N 2 ]LuPh·LiCl”, as evidenced by 7 Li NMR. However, the biphenyl product {[P 2 N 2 ]Lu} 2 {μ-η 6:η 6 ‘ -(C 6 H 5 ) 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 [P 2 N 2 ]Y(C 6 H 4 -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.