The trinuclear MoIV 3 incomplete cuboidal cluster [Mo3S4(H2O)9]4+ in 2 M HCl reacts rapidly (green to intense blue-green color change) with AsO2 - or HAsO4 2- in the presence of H3PO2 as reductant to give the new air-sensitive corner-shared double cube [Mo6AsS8(H2O)18]8+. Purification by Dowex 50W-X2 cation-exchange chromatography requires 4 M H(pts) (pts = p-toluenesulfonic acid) for elution, consistent with a high charge. The X-ray structure has been determined for crystals obtained from 4 M H(pts) solution, full formula [Mo6AsS8(H2O)18](pts)8·28H2O. The Mo6AsS8 core structure was confirmed from ICP elemental analysis for Mo, As, and S (6:1:8) and the 8+ charge from the 3:1 stoichiometries with [Co(dipic)2]- and [Fe(H2O)6]3+ as oxidant. Rate constants for the oxidation of [Mo6AsS8(H2O)18]8+ with [Co(dipic)2]- have been determined and indicate strong reduction properties as compared to other heteroatom clusters. The existence of short (bonding) Mo−Mo separations, 2.716 Å average, and long (nonbonding) Mo−As separations at 3.554 A, together with similar features for other heteroatom clusters, has led to a classification of the clusters into different categories. The nine 8+ double cubes, most of which contain a main group heteroatom M, are classified as (Mo3S4 4+)2 M0, with retention of two metal−metal bonded Mo3S4 4+ units. The single cubes, on the other hand, can be classified as Mo3S4 4+M0, with M a transition metal, or Mo3S4 4+M x , with M a main group element (x depends on group involved).

The phosphido-bridged diiron allenyl complex [Fe2(CO)6(μ-PPh2)(μ-η1:η2 α , β-(H)CαCβCγH2)] (1) reacts with primary amines to afford the amido-functionalized alkenyl complexes [Fe2(CO)5(μ-PPh2)(μ-η1(O):η1(C):η2(C)-{OC(NRH)CH2}CCH2)] (R = tBu (2a), Ph (2b)) via a novel coupling sequence involving a terminal carbonyl, the α-carbon of the allenyl, and a hydrogen migration step, as well as dimetallacyclopentanes [Fe2(CO)6(μ-PPh2)(μ-η1:η1-CH2C(NRH)CH2] (R = tBu (3a), Cy (3b)) via nucleophilic attack at Cβ.