Fomitchev Dmitry V, McLauchlan Craig C, Holm R H
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Inorg Chem. 2002 Feb 25;41(4):958-66. doi: 10.1021/ic011106d.
A series of heterometal cubane-type clusters containing VFe(3)S(4) and MoFe(3)S(4) cores has been prepared. Ligand substitution of (DMF)(3)VFe(3)S(4)Cl(3) affords (Tpms)VFe(3)S(4)L(3)(-) (L = Cl(-) (8), EtS(-) (9), p-MeC(6)H(4)S(-), p-MeC(6)H(4)O(-)). A new procedure for the preparation of molybdenum single cubanes is introduced by the reaction of recently reported (Tp)MoS(S(4)) with FeCl(2)/NaSEt to afford (Tp)MoFe(3)S(4)Cl(3) (1, 75% yield). This procedure is more efficient that the existing multistep synthesis of single cubanes, which generally affords clusters of mirror symmetry. Also prepared were (Tp)MoFe(3)S(4)L(3) (L = EtS(-) (2), p-MeC(6)H(4)S(-)). Reduction of 1 with borohydride gives (Tp)MoFe(3)S(4)Cl(3) (5, 67%). Owing to the nature of the heterometal ligand, all clusters have idealized trigonal symmetry, reflected in their (1)H NMR spectra. Trigonal structures are demonstrated by crystallography of (Bu(4)N)[1,2], (Bu(4)N)(2)[5] x MeCN, and (Me(4)N)(2)[8,9]. The availability of 1 and 5 allows the first comparison of structures and (57)Fe isomer shifts of MoFe(3)S(4) in a constant ligand environment. Small increases in most bond distances indicate that an antibonding electron is added in the reduction of 1. Collective synthetic and electrochemical results from this and other studies demonstrate the existence of the series of oxidation states VFe(3)S(4) and MoFe(3)S(4) whose relative stabilities within a given series are strongly ligand dependent. Isomer shifts indicate that the reduction of 1 largely affects the Fe(3) subcluster and are consistent with the formal descriptions MoFe(3+)(2)Fe(2+)S(4) (1) and MoFe(3+)Fe(2+)(2)S(4) (5). Reaction of 1 with excess Li(2)S in acetonitrile affords the double cubane (Tp)MoFe(3)S(4)Cl(2)(mu(2)(-)S)(-), whose sulfide-bridged structure is supported by two sequential reductions separated by 290 mV, in analogy with previously reported double cubanes of higher charge. Trigonally symmetric single cubanes eliminate isomers in the formation of double cubanes and other cluster structures, and may be of considerable value in the preparation of new types of M-Fe-S clusters. (Tpms = tris(pyrazolyl)methanesulfonate(1-); Tp = hydrotris(pyrazolyl)borate(1-).)
已制备出一系列含有[VFe₃S₄]²⁺和[MoFe₃S₄]³⁺、²⁺核心的异金属立方烷型簇合物。[(DMF)₃VFe₃S₄Cl₃]⁻的配体取代反应得到[(Tpms)VFe₃S₄L₃]²⁻（L = Cl⁻ (8)、EtS⁻ (9)、对甲基苯硫酚根、对甲基苯氧根）。通过最近报道的[(Tp)MoS(S₄)]⁻与FeCl₂/NaSEt反应，引入了一种制备钼单立方烷的新方法，得到[(Tp)MoFe₃S₄Cl₃]⁻（1，产率75%）。该方法比现有的单立方烷多步合成更有效，现有的多步合成通常得到镜像对称的簇合物。还制备了[(Tp)MoFe₃S₄L₃]⁻（L = EtS⁻ (2)、对甲基苯硫酚根）。用硼氢化物还原1得到[(Tp)MoFe₃S₄Cl₃]²⁻（5，产率67%）。由于异金属配体的性质，所有簇合物都具有理想的三角对称性，这在它们的¹H NMR谱中有所体现。三角结构通过(Bu₄N)[1,2]、(Bu₄N)₂[5]·MeCN和(Me₄N)₂[8,9]的晶体学得到证实。1和5的可得性使得首次能够在恒定配体环境下比较[MoFe₃S₄]³⁺、²⁺的结构和⁵⁷Fe异构体位移。大多数键长的小幅增加表明在1的还原过程中添加了一个反键电子。这项研究以及其他研究得出的综合合成和电化学结果表明，存在[VFe₃S₄]³⁺、²⁺、¹⁺和[MoFe₃S₄]⁴⁺、³⁺、²⁺系列氧化态，在给定系列中它们的相对稳定性强烈依赖于配体。异构体位移表明1的还原主要影响Fe₃亚簇，并且与形式描述[MoFe₃⁺₂Fe₂⁺S₄]³⁺ (1)和[MoFe₃⁺Fe₂⁺₂S₄]²⁺ (5)一致。1与过量Li₂S在乙腈中反应得到双立方烷[[(Tp)MoFe₃S₄Cl₂]₂(μ₂⁻S)]²⁻，其硫化物桥连结构由两个相隔290 mV的连续还原过程支持，这与先前报道的更高电荷的双立方烷类似。三角对称的单立方烷在形成双立方烷和其他簇结构时消除了异构体，并且在制备新型M - Fe - S簇合物中可能具有相当大的价值。（Tpms = 三(吡唑基)甲磺酸盐(1⁻)；Tp = 氢三(吡唑基)硼酸盐(1⁻)。）
