Crystal and molecular structure of [Pd3{C3Ph(p-MeOC6H4)2}2(acac)2], derived from a tri-arylcyclopropenium salt and a palladium(0) complex

Abstract

The crystal and molecular structure of [Pd₃{C₃Ph(p-MeOC₆H₄)₂}₂(acac)₂](2){obtained from [Pd₂(PhCH: CHCOCH:CHPh)₃(CHCI₃)] and [C₃Ph(p-MeOC₆H₄)₂] Br followed by reaction of the product with Tl(acac)} has been determined. Crystals are monoclinic, space group C2/c(C⁶_2h, No. 15) with a= 14.99(1), b= 21.88(2), c= 18.98(2)Å, β= 90.5(1)°. U= 6 227 ų. and Z= 4; R= 0.060 for 2 259 independent reflections. The compound is composed predominantly (67%) of enantiomers of one isomer which arises from the addition of the C₃R¹R²₂ moiety (R¹= phenyl, R²=p-MeOC₆H₄) to Pd(1) by ring-opening of the CR²–CR² bond [R²C(1)-C(2)R¹= 1.370(17); R¹C(2)-C(3)R²= 1.443(19); R²C(1)⋯ C(3)R²= 2.116(17)Å]. Pd(1) is also O,O′-bonded to the acac (pentanedionato) ligand. Two such units are linked by Pd(2) such that the three Pd atoms form a triangular framework [Pd(1)–Pd(2)= 2.662(2) A; Pd(1)–Pd(1′)= 4.769(2)Å; Pd(1)–Pd(2)-Pd(1′)= 127 °], the two halves of the molecule being related by a two-fold axis of symmetry through Pd(2). The structure may be viewed either as having the acyclic C₃R¹R²₂ ligands bridging Pd(1)–Pd(2)[and Pd(2)-Pd(1′)] or as two palladiacyclo-butenyl ligands [> Pd(1)C₃R¹R²₂]π⁴-bonded to Pd(2). The presence of other isomers of (2)(33%) is deduced from the electron densities in the p-positions of the C₃-aryl substituents; these isomers arise from cleavage of CR¹–CR² bonds in the original C₃R¹R²₂ salt.