Insight into the mechanism of diazocompounds transformation catalyzed by hetero cuboidal clusters [Mo3CuQ4(MeBPE)3X4]+, (Q = S, Se; X = Cl, Br): The catalytically active species

Article abstract of DOI:10.1016/j.jorganchem.2007.12.029

Two enantiomerically pure trinuclear compounds of formula (P)-[Mo₃S₄{(R,R)-Me-BPE}₃Br₃]Br and (P)-[Mo₃Se₄{(R,R)-Me-BPE}₃Cl₃]Cl, (P)-1b.Br and (P)-1c.Cl, respectively, have been synthesized in a good yield and a stereospecific manner by excision of polymeric [Mo₃Q₇X₄]_n (Q = S or Se, X = Cl or Br) phases with (R,R)-Me-BPE{1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane}. They have been transformed into chiral hetereo cuboidal compounds [Mo₃S₄{(R,R)-Me-BPE}₃Br₃]PF₆, (P)-2b.PF₆, and [Mo₃Se₄{(R,R)-Me-BPE}₃Cl₃]PF₆, (P)-2c.PF₆, by reaction with copper salts. All these compounds have been characterized by ³¹P NMR, IR, UV-Vis, mass spectrometry, elemental analysis, and chiral dichroism. The catalytic potential of tetranuclear cuboidal compounds has been assessed in the paradigm intermolecular cyclopropanation reaction of styrene with ethyl diazoacetate. Results are compared with those obtained for the analogue [Mo₃S₄{(R,R)-Me-BPE}₃Cl₃]PF₆, (P)-2a.PF₆. The catalytic data demonstrate that the Se derivative (P)-2c.PF₆ is less reactive than the S analogues, but it leads to a similar product distribution as the sulfide analogue (P)-2a.PF₆. By contrast, exchange of chlorine by the bulky bromine gives rise to a catalyst which makes the carbene dimerization more competitive. These data agree with temporal breaking of one of the Cu-Q bonds to generate an active catalytic species.