Binding, Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

Abstract

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu₂ (μ,η¹ : η¹ -MeCN)][X]₂ (X=weakly coordinating anion, NTf₂ (1 a), FAl[OC₆ F₁₀ (C₆ F₅ )]₃ (1 b), Al[OC(CF₃ )₃ ]₄ (1 c)) was replaced by white phosphorus (P₄ ) or yellow arsenic (As₄ ) to yield [(DPFN)Cu₂ (μ,η² : η² -E₄ )][X]₂ (E=P (2 a-c), As (3 a-c)). The molecular structures in the solid state reveal novel coordination modes for E₄ tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E₄ tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E₄ tetrahedra with release of P₄ or As₄ and formation of [(DPFN)Cu₂ (μ,η¹ : η¹ -^Me NHC)][X]₂ (4 a,b) or to an opening of one E-E bond leading to an unusual E₄ butterfly structural motif in [(DPFN)Cu₂ (μ,η¹ : η¹ -E₄ ^Dipp NHC)][X]₂ (E=P (5 a,b), E=As (6)). With a cyclic alkyl amino carbene (^Et CAAC), cleavage of two As-As bonds was observed to give two isomers of [(DPFN)Cu₂ (μ,η² : η² -As₄ ^Et CAAC)][X]₂ (7 a,b) with an unusual As₄ -triangle+1 unit.

Keywords: carbenes; coordination modes; copper; metal-metal interactions; pnictogens.