Transition metal–carbon bonds. Part XXIX. Some internal metallation reactions of tertiary phosphine ligands with bulky substituents

Abstract

Complexes of the type trans-[PtX₂L₂][X = Cl, Br, or I; L = PBu^tPh₂, PBu^t(p-tolyl)₂, PBu^t₂Ph, PBu^t₂(p-tolyl), PBu^tPrⁿ₂, PBu^t₂Prⁿ, PPh(o-tolyl)₂, or PMe₂(o-tolyl)] have been prepared. Bulky substitents on tertiary phosphine ligands, e.g. t-butyl or o-tolyl, promote internal platinum–carbon bond formation to give complexes of the type trans-[PtX(P–C)L][X = Cl, Br, or I; (P–C)= internally metallated tertiary phosphine; L = tertiary phosphine]. Tertiary phosphine ligands with two t-butyl groups undergo internal metallation (ring-closure) more readily than those with only one t-butyl group. o-Tolylphosphines can also promote ring-closure reactions but the tertiary phosphines with smaller steric requirements show no tendency to metallate internally. The internal metallation reactions give five-membered rings if possible. Generally, the tendency to internally metallate increased in the order of anionic ligands Cl < Br < I. The corresponding palladium(II) complexes, trans-[PdX₂L₂](X = Cl, Br, or I; L = bulky tertiary phosphine) show no tendency to form internal metal–carbon bonds.