ABSTRACT
Three examples of the rare 8,1,2-closo-MC2B9 isomeric form of an icosahedral metallacarborane have been isolated as unexpected trace products in reactions. Seeking to understand how these were formed we considered both the nature of the reactions that were being undertaken and the nature of the coproducts. This led us to propose a mechanism for the formation of the 8,1,2-closo-MC2B9 species. The mechanism was then tested, leading to the first deliberate synthesis of an example of this isomer. Thus, deboronation of 4-(η-C5H5)-4,1,8-closo-CoC2B10H12 selectively removes the B5 vertex to yield the dianion [nido-(η-C5H5)CoC2B9H11](2-), oxidative closure of which affords 8-(η-C5H5)-8,1,2-closo-CoC2B9H11 in moderate yield.
ABSTRACT
A Sc NHC complex readily activates three equivalents of CO2 showing 'Frustrated Lewis Pair' type reactivity with each metal-carbene bond, but whilst CS2 is also activated by the labile carbenes, no metal involvement is observed.
ABSTRACT
The reaction between Zn and a pyrene-based ligand decorated with benzoate fragments (H(4)TBAPy) yields a 2D layered porous network with the metal coordination based on a paddlewheel motif. Upon desolvation, the structure undergoes a significant and reversible structural adjustment with a corresponding reduction in crystallinity. The combination of computationally assisted structure determination and experimental data analysis of the desolvated phase revealed a structural change in the metal coordination geometry from square-pyramidal to tetrahedral. Simulations of desolvation showed that the local distortion of the ligand geometry followed by the rotation and displacement of the pyrene core permits the breakup of the metal-paddlewheel motifs and the formation of 1D Zn-O chains that cross-link adjacent layers, resulting in a dimensionality change from the 2D layered structure to a 3D structure. Constrained Rietveld refinement of the powder X-ray diffraction pattern of the desolvated phase and the use of other analytical techniques such as porosity measurements, (13)C CP MAS NMR spectroscopy, and fluorescence spectroscopy strongly supported the observed structural transformation. The 3D network is stable up to 425 °C and is permanently porous to CO(2) with an apparent BET surface area of 523(8) m(2)/g (p/p° = 0.02-0.22). Because of the hydrophobic nature, size, and shape of the pores of the 3D framework, the adsorption behavior of the structure toward p-xylene and m-xylene was studied, and the results indicated that the shape of the isotherm and the kinetics of the adsorption process are determined mainly by the shape of the xylene isomers, with each xylene isomer interacting with the host framework in a different manner.
Subject(s)
Organic Chemicals/chemistry , Zinc/chemistry , Crystallography, X-Ray , Magnetic Resonance Spectroscopy , Spectrometry, FluorescenceABSTRACT
The synthesis and isolation of low coordinate methylenebis-(N-DIPP-imidazole-2-ylidene)iron((II))hydrides, (((DIPP)C)(2)CH(2))FeH(2-y)I(y) ((DIPP = 2,6-di-isopropylphenyl, y = 1 or 0), was complicated by competitive reactions with solvent, rapid reductive elimination of H(2) and/or dissociation of the bis-N-heterocyclic carbene ligand. Addition of KH to (((DIPP)C)(2)CH(2))FeI(2) in THF/haloalkane mixtures enabled a short lived mono-hydride to be trapped by reaction with CH(2)Cl(2) or cyclo-heptylbromide to form (((DIPP)C)(2)CH(2))FeI(X) (X = Cl or Br, respectively). Toluene coordination stabilises iron-mono hydride complexes as (((DIPP)C)(2)CH(2))Fe(II)H{η(6)-(toluene)} species, which can be isolated in low yield from combination of borohydride salts and (((DIPP)C)(2)CH(2))FeI(2) in toluene, including an imidazole C4 deprotonated carbene-borane, methylene(N-DIPP-imidazole-2-ylidene)(N-DIPP-4-triethyl-borane-imidazole-2-ylidene)](hydrido)(η(6)-toluene)iron. In the absence of toluene, or at short reaction times compounds with empirical formula (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI (R = Et or sec-Bu) that function as a masked Fe((II))-dihydride are isolated. Whilst (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI was stable for days in Et(2)O, more polar solvents (MeCN, THF) led to formation of the carbene borane adducts (((DIPP)C)(2)CH(2))(BR(3))(2). The addition of CO or cyclo-heptylbromide to (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI formed (((DIPP)C)(2)CH(2))Fe(CO)(3) and (((DIPP)C)(2)CH(2))FeBr(2), respectively with BR(3) evolved from both reactions as a by-product.
ABSTRACT
The d (0) yttrium N-heterocyclic carbene compound YL 3 (L = OCMe 2CH 2[C{N(CHCH)NPr ( i )}]) has been made and structurally characterized. It adopts a mer configuration of the three bidentate ligands. A comparison of this with the isostructural d (1) titanium complex TiL 3 is made in order to seek experimental evidence of a pi-bonding contribution to the M-C bond. This has been augmented by DFT calculations. Experimentally, the metal radius-corrected Ti-C distance is shorter than the Y-C distance, suggesting a pi-bonding contribution in the d (1) complex, but the computational data suggest that a shorter sigma bond might simply be formed by the more strongly polarizing titanium cation. From the potassium reduction of TiL(OPr ( i )) 3, only a byproduct arising from silicone grease activation was isolable, identified as a mixed-valent, multinuclear, d (0)/d (1) cluster [Ti (III)L 2{Pr ( i )OSiMe 2O}K 2OTi (IV)(OPr ( i )) 4] 2 in which the carbene ligands are bound to the Ti (III) centers in preference to Ti (IV), with longer Ti-C distances than those found in TiL 3.
ABSTRACT
The 2e-reduction of 1,12-Ph2-1,12-closo-C(2)B(10)H(10) followed by oxidation or metallation gives products that arise from [7,9-Ph2-7,9-nido-C(2)B(10)H(10)](2-), formed by unexpectedly facile isomerisation of the kinetic 7,10-isomer: the 4,1,6-MC(2)B(10) compounds which result are progressively isomerised to 4,1,8- and 4,1,12-isomers for M = {CpCo} but to an equilibrium mixture of 4,1,8- and 4,1,12-isomers for M = {(arene)Ru}.
