Diastereomeric metallatetrahedron complexes of the type Re2(AgPR3)2(μ-PCy2)(CO)7Z (R = Et and Ph; Z = (−)- and (+)-camphanate): synthesis, structure and CD data

Abstract

Diastereomeric pairs of metallatetrahedron clusters of the type Re₂(AgPR₃)₂(μ-PCy₂)(CO)₇(ax-(+)/(−)-camph) ((+)-auxiliary, R = Ph 4a, 4b or Et: 6a, 6b and (−)-auxiliary, R = Ph 5a, 5b or R = Et: 7a, 7b) were prepared from the η¹-carboxylate substituted dirhenium salt Li[Re₂(μ-H)(μ-PCy₂)(CO)₇(ax-η¹-(+)/(−)-camph)] (camph = camphanate) and less than stoichiometric amounts of [Ag(PR₃)BF₄] (R = Ph or Et) in solution at room temperature. The diastereomers were separated using PLC and identified by means of IR, ¹H and ³¹P NMR, UV/VIS and CD spectroscopy. Using single crystal X-ray analysis the molecular structure of 4a/4b in material I and 4a/5a in II have been determined to assign the absolute configuration of the clockwise (C) and anticlockwise (A) configurated tetrahedral Re₂Ag₂ framework in a ligand sphere of C₁ symmetry. These are the first structures which show a chelate like co-ordination of the carboxylic group of the camphanate ligand in a heterometallic cluster complex. Based on their CD spectra the absolute configuration of other chiral carboxylate substituted metallatetrahedra of the type Re₂(MPR₃)₂(μ-PCy₂)(CO)₇(ax-OC(O)R) (M = Au or Ag) can be assigned.