SYNTHESIS AND CHARACTERIZATION OF A SERIES OF IRON CARBONYL CLUSTERS CONTAINING SELENIUM AND TELLURIUM

The reaction of TeO2 With Fe(CO)5/KOH/MeOH produces [Te{Fe(CO)4}3]2-, which can be easily isolated as its [PPN]+ salt, [PPN]2[I].0.5 THF, which crystallizes in the trigonal space group P3BAR with a = b = 25.447(4) angstrom, c = 22.432(4) angstrom, v = 12579.7(36) angstrom3, and Z = 6. The Te atom is coordinated to three Fe(CO)4 fragments in a pyramidal arrangement with an average Te-Fe distance of 2.642(8) angstrom and an average Fe-Te-Fe angle of 109.56(6)degrees. When [PPN]2[I] is left in solution, it slowly converts to [PPN]2[TeFe3(CO)9] ([PPN]2[II). This process can accelerated by either mild photolysis or thermolysis. [II]2- can also be prepared from [Et4N]2[Fe2(CO)8] and TeCl4. [Et4N]2[II] crystallizes in the monoclinic space group P2(1)/n with a = 24.79(2) angstrom, b = 11.041(2) angstrom, c = 25.209(11) angstrom, b = 110.49(5)degrees, V = 6465.0(69) angstrom3, and Z = 8. The tetrahedral cluster is composed of a ''naked'' Te atom capping a closed Fe3 triangle. SeO2 also reacts with Fe(CO)5/KOH/MeOH, analogously to TeO2, to produce a compound thought to be [Se{Fe(CO)4}3]2- ([III]2-). [III]2- rapidly converts in solution to [SeFe3(CO)9]2- ([IV]2-). [PPN]2[IV].CH2Cl2 crystallizes in the monoclinic space group Cc with a = 29.393(6) angstrom, b = 14.724(3) angstrom, c = 21.477(4) angstrom, b = 123.65(3)degrees, V = 7737.4(27), and Z = 4. [IV]2- was found to be isostructural with [II]2-.