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 Re 2 (AgPR 3 ) 2 (µ-PCy 2 )(CO) 7 (ax-(ϩ)/(Ϫ)-camph) ((ϩ)-auxiliary, R = Ph 4a, 4b or Et: 6a, 6b and (Ϫ)-auxiliary, R = Ph 5a, 5b or R = Et: 7a, 7b) were prepared from the η 1 -carboxylate substituted dirhenium salt Li[Re 2 (µ-H)(µ-PCy 2 )(CO) 7 (ax-η 1 -(ϩ)/(Ϫ)-camph)] (camph = camphanate) and less than stoichiometric amounts of [Ag(PR 3 )BF 4 ] (R = Ph or Et) in solution at room temperature. The diastereomers were separated using PLC and identified by means of IR, 1 H and 31 P 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 Re 2 Ag 2 framework in a ligand sphere of C 1 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 Re 2 (MPR 3 ) 2 (µ-PCy 2 )(CO) 7 (ax-OC(O)R) (M = Au or Ag) can be assigned.

Diastereomeric metallatetrahedron complexes of the type Re2(MPPh3)(M′PPh3)(µ-PCy2)(CO)7(–)-thiocamphanate (M = Ag, Au, M′ = Cu, Ag, Au): synthesis, structure and CD data

“…They show maximum absorptivity at the limit of the experimentally accessible wavelength range at 196/ 197 nm (Table 1), similar to the cluster complexes Re 2 (AgPR 3 ) 2 -(µ-PCy 2 )(CO) 7 (ax-OC(O)R 1 ) (R = Ph, Et; OC(O)R 1 = (ϩ)-, (Ϫ)-camphanate) described earlier. 3 Also, the spectral features at longer wavelengths are insignificant in both types of cluster complexes. Even with derivative spectroscopic methods it was not possible to identify distinct bands including the lowest energy absorption, which is responsible for the colour of these clusters.…”

“…elsewhere. 3 There are slight variations in the intensities and positions of the absorption maxima as a function of the metal substitution, but there is no exception to this correlation. This series of three bands is followed, toward higher energy, by several narrow bands with alternating signs in a more or less regular pattern.…”

“…The coupling between the 31 P atom and the silver isotopes 107 Ag and 109 Ag ranging from 435 to 467 Hz is larger for 1 J P 109 Ag than for 1 J P 107 Ag . 3,8 The signal for the second coin metal fragment degenerates into a double triplet.…”

“…Present knowledge comprises only some examples of tetrahedral cluster complexes with a triangular metal arrangement capped by a phosphido, sulfido, selenido, alkylidyne or arsenido group (see references within ref. 3).…”

“…In a previous paper, we reported the synthesis of diastereomerically pure metallatetrahedron clusters of the type Re 2 -(AgPR 3 ) 2 (µ-PCy 2 )(CO) 7 (ax-OC(O)R 1 ) (R = Ph, Et; OC(O)R 1 = (ϩ)-, (Ϫ)-camphanate). 3 The CD spectra of these compounds were correlated with the absolute configuration of the metallatetrahedral framework (clockwise (C ) and counterclockwise (A)), which was determined by single crystal X-ray analysis of the C-diastereomer of Re 2 (AgPPh 3 ) 2 (µ-PCy 2 )(CO) 7 -(ϩ)-camphanate and the A-diastereomer of Re 2 (AgPPh 3 ) 2 -(µ-PCy 2 )(CO) 7 (Ϫ)-camphanate.…”