Geometric Isomerism Based on Metal-Metal Bonds

Abstract

The stereodynamics of metal-metal bonds has remained virtually unexplored until very recently. It is now known that the barriers for the degenerate reorientation of metal-metal bonds can be substantial.1•1 2 This opens the way for the preparation of clusters which differ on the basis of their metalmetal bonding networks. A test of this idea entails demonstration that clusters can exist as geometric isomers based exclusively on the relative positions of -M bonds. This type of process assumes added significance to the extent that -M bonding provides an electrochemically addressable means of controlling the structures of multimetallic frameworks.The reaction of (CsMeshRuaS^w ith 2 equiv of (CsHsjRu-(MeCN)g+ 4 (MeCN solution, 25 °C) proceeds according to eq l.5 The red-brown salt [(CsHsMCsMeshRuqSa](PFe)2 ([!]-(PF6)2) was obtained in high yield and good purity.6•7 (C5Me5)2Ru2S4 + 2(C5H5)Ru(MeCN)3+ -(C5H5)2(C5Me5)2Ru4S42+ + 6MeCN (1)

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“…This was first achieved by grafting on to the same [Ru 4 E 4 ] 2+ core different types of cyclopentadienyl ligands, namely C 5 H 5 , and C 5 Me 5 (Cp*). 28 Only one type of crystal structure was characterized, and the [(Cp) 2 (Cp*) 2 Ru 4 E 4 ] 2+ cluster looks quite similar to the parent compound with four identical Cp ligands: a distorted cubane with three bonding Ru-Ru contacts and three nonbonding Ru…Ru distances. However, the three metal-metal bonds are not distributed at random: the Cp*Ru centers each support two metal-metal bonds, suggesting that the corresponding metal atoms can be assigned as Ru IV (Scheme 9, form 4).…”

“…At 290 °C, isomers 4 and 5 are present to the extent of 77 and 23%, respectively. 28 The metal-metal interactions in Cp…”

Metastable states associated with a change in the metal–metal bonding network of (MoV)6polyoxoanions: a DFT study of [(Mo2VO4)3(μ6-CO3)(μ-CO3)3(μ-OH)3]5−

“…See http:// www.rsc.org/suppdata/dt/b3/b304119k/ can be distinguished by replacing for instance C 5 H 5 by C 5 Me 5 , real isomers based exclusively on the relative positions of the M-M bonds can be characterized from low-temperature NMR spectroscopy. 5 This form of isomerism, termed "geometric isomerism" by Rauchfuss et al, 5 is in fact relevant to the more general concept of "bond-stretch isomerism" defined by Stohrer and Hoffmann, 6 and later by Parkin, 7 in the sense that isomers retain the same atomic arrangement in the same molecular topography -the cubane cage -and differ only in the distance between the pairs of metal atoms displaying or not a localized bond. 8 Theoretical studies in polyoxometalate chemistry have also shown that the localization/delocalization duality of electron pairs in reduced polyoxoanions could lead to multiple energy minima and to bond-stretch isomerism.…”

“…This form of isomerism was investigated first by Rauchfuss et al in cubane-like Ru 4 E 4 Cp 4 clusters (E = S, Se, Te) oxidized into dicationic species. 4, 5 The neutral clusters can be viewed as nested dimers of Ru 2 E 2 Cp 2 butterfly moieties displaying each a single metal-metal bond and two bridging chalcogen atoms. A two-electron oxidation yields a mixed-valence Ru III /Ru IV cluster with a third, localized Ru-Ru bond.…”

Hybridization vs. Bond Stretching Isomerism in Ru(II) Cyclometalated Complexes of 2-Phenylpyridine

“…Thus, structural variability caused by deviation in bond length was found in the dinuclear ruthenium compound, [(Cp*RuCl) 2 (μ-Cl) 2 ] [ 10 , 11 ], in trinuclear cobalt [ 4 , 12 , 13 , 14 ] and chromium complexes [ 15 ]. Recently, two conformations of a dinuclear iron complex differing in valence angles and bond length were reported by Hammann et al [ 16 ].…”