Sodiated β‐Diphosphonate Carbanions: Characterization of the Tetrameric Cubane and the Hexameric Ladder Complexes [{(iPrO)₂P(O)}₂CHNa]₄ and [{(EtO)₂P(O)}₂CHNa]₆

Abstract

Reaction of the methylene diphosphonates [(RO)2P(O)]2CH2, where R = iPr or Et, with the metalating reagents NaH, nBuNa or the superbasic mixture tBuONa/nBuLi leads to monodeprotonation, and formation of the complexes [{(iPrO)2P(O)}2CHNa]4 (1) and [{(EtO)2P(O)}2CHNa]6 (2). Single‐crystal X‐ray diffraction studies revealed that 1 is tetrameric in the solid state, with a central Na4O4 cubane core. Each metal in 1 is rendered pentacoordinate by binding to three μ3‐O phosphoryl bridges within the cubane, a chelating phosphoryl unit, and also a single iPrO group. In contrast, the structure of 2 is hexameric, and is composed of an unusual six‐rung Na6O6 ladder core. Three distinct sodium environments as well as μ1‐, μ2‐ and μ3‐O phosphoryl units are present within the ladder framework. No Na−C interactions are present in either 1 or 2. All of the six‐membered NaOPCPO chelate rings display localized P=O double bonds and partial multiple bonding on the P−C−P linkages (mean P−O: 1.49 Å, and mean P−C: 1.69 Å). Ab initio molecular orbital calculations (HF/6−31G*) on model complexes indicate that the hexameric arrangement found for 2 is thermodynamically more stable than the cubane structure of 1, in the absence of steric effects. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Regio- and Stereoselective Enolizations Using Calcium Bis(hexamethyldisilazide) as a Base: Synthetic, Solid-State, and Solution Studies

“…This unusual motif can be described as a quadruple open cubane, an extension of the more common double open cubane found for 18 (see later). This core structure has previously been observed for a relatively small number of hexanuclear metal complexes and can be considered as structurally related to a section of the CdI 2 layer structure . Only a handful of hexanuclear calcium complexes have previously been characterized, none of which adopt a structure similar to that found for 17 …”

Bis[μ2-bis(diphenylphosphinoyl)methanido-κ2O:O′]hexamethyldi-μ3-oxo-tetraaluminium(III) tetrahydrofuran disolvate

“…Carbanions stabilized by two , H -electron-withdrawing groups constitute an important class of reagents in CÐC bond-forming reactions (Johnson, 1993). We are interested in the emerging structure±reactivity relationships of doubly stabilized carbanions with various metallic partners (Nassar et al, 2003;Henderson et al, 2000Henderson et al, , 2002Henderson et al, , 2003. During our studies, the unexpected title compound, (I), was prepared as colourless crystals from a reaction mixture containing {Ph 2 P(O)} 2 CH 2 , AlMe 3 and t BuLi.…”

3 Alkali and alkaline-earth metals

“…84 Metallation of methylene diphosphonates, {(RO) 2 P(O)} 2 CH 2 (R ~Et or Pr i ) yields [NaCH{(EtO) 2 P(O)} 2 ] 6 , which contains a six-rung (NaO) ladder and [NaCH{(Pr i O) 2 P(O)} 2 ] 4 with a cubane core; ab initio calculations indicate that the hexamer is more stable than the tetramer in the absence of steric effects. 85 4 Potassium, rubidium and caesium 86 The preparation of [M(C 5 Me 4 )SiMe 2 (CH 2 CHLCHCHCH 2 )] (M ~Li or K) and [K(C 5 Me 4 H)(dme)] ' has been described; the latter was crystallographically characterized. 87 EPR evidence for zwitterionic radicals with metal-ligand interactions has been obtained from cyclooctatriene-g 2 -ynyl salts of potassium and caesium.…”