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{(t)BuC5(H)(2)}] (M = Bi, Sb) with 1.5 equiv of MoO(2)(O(t)Bu)(2) in 1,2-dimethoxyethane (DME) produced soluble Bi(III)/Mo(VI) and Sb(III)/Mo(VI) heterometallic calix[5]arene complexes [Bi(2)Mo(4)O(11){(t)BuC5(H)}(2)] 1 and [Sb(2)Mo(4)O(11){(t)BuC5(H)}(2)] 2 in 55 and 45% yields, respectively. In solution the (1)H NMR patterns for 1 and 2 are characteristic of a C(s) 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 P1 space group and consists of a dimeric heterometallic Bi/Mo (1:2 ratio) complex featuring an overall Mo(4)Bi(2)O(21) oxo cluster. The remarkable oxo-rich core structure of 1 contains Bi(mu-O)Mo, Mo(mu-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 Bi(2)Mo(2)O(9) oxide phase.