Heterobimetallic Bismuth(III)/Molybdenum(VI) and Antimony(III)/Molybdenum(VI) Calix[5]arene Complexes. Progress toward Modeling the SOHIO Catalyst

The treatment of the monometallic bismuth or antimony complexes [M{tBuC5(H)2}] (M = Bi, Sb) with 1.5 equiv of MoO2(OtBu)2 in 1,2-dimethoxyethane (DME) produced soluble BiIII/MoVI and SbIII/MoVI heterometallic calix[5]arene complexes [Bi2Mo4O11{tBuC5(H)}2] 1 and [Sb2Mo4O11{tBuC5(H)}2] 2 in 55 and 45% yields, respectively. In solution the 1H NMR patterns for 1 and 2 are characteristic of a Cs symmetry with three pairs of doublets for the methylene protons and three singlets in a 1:2:2 ratio for the tert-butyl groups. Complex 1 crystallizes in the P1̅ space group and consists of a dimeric heterometallic Bi/Mo (1:2 ratio) complex featuring an overall Mo4Bi2O21 oxo cluster. The remarkable oxo-rich core structure of 1 contains Bi(μ-O)Mo, Mo(μ-O)Mo, MoO···Mo, and Bi−O−Bi interactions that resemble aspects of the proposed SOHIO catalyst active site and the crystal structure of the Bi2Mo2O9 oxide phase.