Roof-Shaped Halide-Bridged Bimetallic Complexes via Ring Expansion Reaction

Binucleating behavior of rigid triptycene-based ligands has been studied. It has been demonstrated that trans-spanned transition-metal mononuclear complexes bearing 1,8-bis(diisopropylphosphino)triptycene (L1) and 1-diisopropylphosphino-8-diphenylphosphinotriptycene (L2) react with an appropriate transition-metal precursor via a
ring-expansion pathway to form unusual bimetallic quasi-closed structures. New palladium and rhodium complexes
featuring strongly bent (ca. 115°) M2(μ-Cl2) cores with very closely spanned metal centers (less than 3 Å) have
been prepared using the described ring-expansion reaction and have been fully characterized. Despite a constrained
arrangement of the binuclear system, halogen bridges in all new compounds were stable in both the solid state
and solution showing no tendency for dissociation even in the presence of added Lewis bases. Spontaneous
resolution of the dissymmetric Pd2(μ-Cl)2Cl2(1-diisopropylphosphino-8-diphenylphosphinotriptycene) (2) into enantiopure
antipodes is discussed as well.