M3Q4 Cluster Complexes

The reaction mechanism in acetonitrile or water/acetonitrile mixtures occurs with three kineticaUy distinctive steps according to Eqs. (3)-(6), a kinetics significantly more complicated than that observed for the substitution of the aqua ligands in [M3Q4(H20)9f complexes [35, 36]. 

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A systematic study of this class of compounds did not start until twenty years later and led to the preparation of a series of M3Q7X4 (M = Mo, W Q = S, Se and X = C1, Br) inorganic polymers by high-temperature reactions (ca. 350 °C) of the elements in a sealed tube [10-14]. The interest on these cluster phases was mainly motivated by their excellent role as synthons for the preparation of molecular M3Q7 and M3Q4 cluster complexes, as will be presented in this section. 

Synthesis and Structure of Molecular M3Q4 and M3Q7 Cluster Complexes 107 7.2... 

An unprecedented stereoselective procedure to obtain enantiomerically pure transition cluster M3Q4 complexes consists of the direct excision of the M3Q7X4 n polymers using chiral diphosphanes, namely (+)-l,2-bis[(2J ,5R)-2,5-(dimethylphospholano)]ethane [(R,R)-Me-BPE] and its respective enantiomer [(S,S)-Me-BPE] to afford the trinuclear complexes (P)-[Mo3S4Cl3(J ,J -Me-BPE)3] and (Af)-[Mo3S4Cl3(S,S-Me-BPE)3] , respectively [30]. The structures of both enantiomers are shown in Fig. 7.3. The symbols (P) and (M) refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulfur pointing towards the viewer. 

The structure of [Mo3S4(dmit)3] (dmit=l,3-dithiole-2-thione-4,5-dithiolate) represents one of the rare examples of M3S4 clusters where each metal atom appears as pentacoordinate instead of its more common type-I structure octahedral environment [39]. Complexes [M3Q4(dmit)3] (M = Mo, W Q = S, Se) degrade in air with an almost quantitative yield and afford a series of M(V) dimers of formula [M202(//-Q)2(dmit)2] where the oxygen atoms are in a syn configuration. 

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