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ABSTRACT: Two new metallaphosphacarboranes have been synthesised from [7, 8-nido-CPB9H11]– by deprotonation followed by treatment with a metal fragment. Starting with [HNMe3][7, 8-nido-CPB9H11] deprotonation and reaction with a source of {(indenyl)Co}2+ affords the η-bonded cobaltaphosphacarborane 3-(η-C9H7)-3, 1, 2-closo-CoCPB9H10 (1) the first “half-sandwich“ 3, 1, 2-metallaphosphacarborane. The indenyl ligand conformation in 1 (cisoid between the indenyl bridgehead carbon atoms and cage heteroatoms, with the cage carbon atom lying below the indenyl C–C bond) reveals that the structural trans effect in a phosphacarborane ligand is weakest for carbon and therefore varies in the order B > P > C. Starting with [HNC5H11][7, 8-nido-CPB9H11] deprotonation and reaction with half an equivalent of [Ru(p-cymene)Cl2]2 affords the σ-bonded ruthenaphosphacarborane 8-{Ru(p-cymene)Cl(C5H11N)}-7, 8-nido-CPB9H11 (2), the first example of a molecule with a phosphacarborane σ-bonded to a metal to be crystallographically characterised.
Zeitschrift für anorganische und allgemeine Chemie 04/2013; 639:1095. · 1.25 Impact Factor
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ABSTRACT: A high-yielding synthesis of the 13-vertex cobaltacarborane 4-Cp-4,1,12-closo-CoC(2)B(10)H(12) is described and this compound used to prepare the known 14-vertex species 1,14-Cp(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(12) () and 1-(p-cymene)-14-Cp-1,14,2,10-closo-RuCoC(2)B(10)H(12) (), the latter by a new route. The related species 1,14-Cp(2)-2,10-Me(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(10) () and 1,14-(η-C(9)H(7))(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(12) () are also reported. Polyhedral expansion of 4,1,8-CoC(2)B(10) compounds affords a different isomer of the 14-vertex bimetallacarboranes, 1,14,2,9-Co(2)C(2)B(10), and three examples, 1,14-Cp(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(12) (), 1,14-Cp(2)-2,9-Me(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(10) () and 1,14-(η-C(9)H(7))(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(12) (), are prepared and characterised. Patterns in (11)B NMR chemical shifts and in <δ(11)B>, the weighted average (11)B chemical shift, within and between related isomers of the 14-vertex compounds and are discussed. Compounds , , , and were studied crystallographically, with cage C atom positions in these and related bicapped hexagonal antiprismatic 1,14,2,x-M(2)C(2)B(10) species analysed by the Vertex-to-Centroid Distance method.
Dalton Transactions 09/2012; · 3.84 Impact Factor
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ABSTRACT: Replacing a boron vertex in a [B(n)H(n)](2-) cluster with a smaller atom, e.g. carbon, results in the distance from that atom to the polyhedral centroid being shorter. This forms the basis of a simple but very effective method of distinguishing between B and C atoms in (hetero)carboranes that have been studied crystallographically, the Vertex-to-Centroid Distance (VCD) method. Examples of well-characterised icosahedral and sub-icosahedral closo carboranes, nido carboranes, icosahedral metallacarboranes and supraicosahedral metallacarboranes are used to illustrate the generality of the VCD method. In this process a number of structures are identified in which the method suggests B/C disorder not previously recognised and some structures in which it appears that a cage C atom has been wrongly assigned. The largest sub-group of heterocarboranes is the family of 3,1,2-MC(2)B(9) compounds, and for these species consideration of Exopolyhedral Ligand Orientation (ELO) can sometimes be used to quickly suggest when a literature structure is suspect in terms of cage C atom positioning. The crystal structure of one such compound, 3,3-NO(3)-3-PPh(3)-3,1,2-closo-RhC(2)B(9)H(11), has been redetermined and the correct location of the cage C atoms established.
Dalton Transactions 09/2012; · 3.84 Impact Factor
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ABSTRACT: Reduction of the tethered carborane 1,2-μ-(CH(2)SiMe(2)CH(2))-1,2-closo-C(2)B(10)H(10) followed by metallation with {CpCo} or {(p-cymene)Ru} fragments affords both C,C'-dimethyl 4,1,2-MC(2)B(10) and 4,1,6-MC(2)B(10) species. DFT calculations indicate that the barriers to isomerisation of both 4-Cp-4,1,2-closo-CoC(2)B(10)H(12) and 4-(η-C(6)H(6))-4,1,2-closo-RuC(2)B(10)H(12) to their respective 4,1,6-isomers are too high for this to be the origin of the unexpected formation of 4,1,6-MC(2)B(10) products (in marked contrast to the related isomerisation of 1,2-closo-C(2)B(11)H(13) to 1,6-closo-C(2)B(11)H(13)), and, indeed, the 4,1,2-species are recovered unchanged from refluxing toluene. Equally, the DFT-calculated profile for the isomerisation of [7,8-nido-C(2)B(10)H(12)](2-) to [7,9-nido-C(2)B(10)H(12)](2-) suggests that the unexpected formation of 4,1,6-metallacarboranes is unlikely to result from isomerisation of a reduced (nido) carborane following desilylation. Instead, the source of the 4,1,6-MC(2)B(10) compounds is traced to desilylation of 1,2-μ-(CH(2)SiMe(2)CH(2))-1,2-closo-C(2)B(10)H(10) by Li or Na prior to reduction. The supraicosahedral metallacarboranes 1,8-Me(2)-4-Cp-4,1,8-closo-CoC(2)B(10)H(10), 1,12-Me(2)-4-Cp-4,1,12-closo-CoC(2)B(10)H(10) and 1,12-Me(2)-4-(p-cymene)-4,1,12-closo-RuC(2)B(10)H(10) are also reported with all new species characterised both spectroscopically and crystallographically.
Dalton Transactions 08/2012; 41(36):10957-69. · 3.84 Impact Factor
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Angewandte Chemie International Edition 12/2011; 50(51):12339-41. · 13.45 Impact Factor
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Hugo Tricas,
Marta Colon,
David Ellis,
Stuart A Macgregor,
David McKay,
Georgina M Rosair, Alan J Welch,
Ivan V Glukhov,
Fulvio Rossi,
Franco Laschi,
Piero Zanello
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ABSTRACT: The icosahedral carboranes 1-C(6)F(5)-2-Ph-1,2-closo-C(2)B(10)H(10) (1), 1-(4'-F(3)CC(6)H(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (2), 1,2-(4'-F(3)CC(6)H(4))(2)-1,2-closo-C(2)B(10)H(10) (3), 1-(4'-H(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (4), 1-(4'-F(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (5), 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10) (6), 1,7-(4'-F(3)CC(6)F(4))(2)-1,7-closo-C(2)B(10)H(10) (7) and 1,12-(4'-F(3)CC(6)F(4))(2)-1,12-closo-C(2)B(10)H(10) (8), with fluorinated aryl substituents on cage carbon atoms, have been prepared in good to high yields and characterised by microanalysis, (1)H, (11)B and (19)F NMR spectroscopies, mass spectrometry, single-crystal X-ray diffraction and (spectro)electrochemistry. By analysis of <δ(11)B>, the weighted average (11)B chemical shift, a ranking order for the ortho carboranes 1-6 is established based on the combined electron-withdrawing properties of the C-substituents, and is in perfect agreement with that established independently by electrochemical study. In a parallel computational study the effects of a wide range of different substituents on the redox properties of carboranes have been probed by comparison of ΔE values, where ΔE is the energy gap between the DFT-optimised [7,9-R(2)-7,9-nido-C(2)B(10)](2-) anion and its DFT-optimised basket-shaped first oxidation product. The overall conclusion from the NMR spectroscopic, electrochemical and computational studies is that strongly electron withdrawing substituents significantly stabilise [7,9-nido-C(2)B(10)](2-) dianions with respect to oxidation, and that the best practical substituent is 4-F(3)CC(6)F(4). Thus attention focussed on the reduction of 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10), compound 6. The sequence 6/[6](-)/[6](2-) appears reversible on the cyclic voltammetric timescale but on the longer timescale of macroelectrolysis the radical anion is only partially stable. EPR study of the electrogenerated monoanions from the ortho-carboranes 1-6 confirms the cage-centred nature of the redox processes. In contrast, the reduction of the meta- and para-carboranes 7 and 8, respectively, appears to be centred on the aromatic substituents, a conclusion supported by the results of DFT calculation of the LUMOs of compounds 6-8. Bulk 2-electron reduction of 6 affords a dianion which is remarkably stable to reoxidation, surviving for several hours in the open laboratory in the absence of halogenated solvents.
Dalton Transactions 03/2011; 40(16):4200-11. · 3.84 Impact Factor
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ABSTRACT: The first supraicosahedral bis(heteroborane), 1-(4'-Cp-4',1',6'-closo-CoC(2)B(10)H(11))-4-Cp-4,1,6-closo-CoC(2)B(10)H(11) has been synthesised as a mixture of racemic and meso diastereoisomers. Analysis of the molecular structures reveals clear evidence of internally crowded molecules.
Chemical Communications 10/2010; 46(39):7394-6. · 6.17 Impact Factor
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Angewandte Chemie International Edition 07/2010; 49(29):4943-5. · 13.45 Impact Factor
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Greig Scott,
Amelia McAnaw,
David McKay,
Alan S F Boyd,
David Ellis,
Georgina M Rosair,
Stuart A Macgregor, Alan J Welch,
Franco Laschi,
Fulvio Rossi,
Piero Zanello
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ABSTRACT: 13-vertex indenyl cobaltacarboranes with 4,1,6-, 4,1,10- and 4,1,2-CoC(2)B(10) architectures have been synthesised by reduction of the corresponding closo carborane and metallation with an {(eta-C(9)H(7))Co} fragment. Variants of the 4,1,6-isomer were prepared with no, one and two methyl groups on cage C atoms, whilst 4,1,2-species were obtained both with two methyl groups and a trimethylene tether on the cage C atoms. Thermolysis of the 4,1,6-isomers yielded the corresponding 4,1,8-isomers, which in turn were converted to 4,1,12-isomers by thermolysis at higher temperatures. Alternatively relatively mild heating of the 4,1,10-isomer led to the 4,1,12-isomer directly. Products were characterised by mass spectrometry, (1)H and (11)B NMR spectroscopies and, in most cases, elemental analysis, and nine compounds were studied crystallographically. The 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- species have docosahedral cages whilst the 4,1,2-species are henicosahedral. In the structural studies attention focused on the orientation of the indenyl ligand with respect to the carborane ligand since this affords experimental information on the metal-cage bonding through the structural indenyl effect. There is a general tendency for the indenyl ligand to adopt orientations in which the ring junction C atoms lie trans to cage B atoms. In cases where the orientation is not compromised by the presence of a non-H substituent on the face of the carborane there is generally good agreement between the experimental orientation and that computed by DFT calculations for the related naphthalene ferracarboranes (eta-C(10)H(8))FeC(2)B(10)H(12). The presence of C-methyl substituents in the indenyl cobaltacarboranes tends to override this preference except in the case of 1,6-Me(2)-4-(eta-C(9)H(7))-4,1,6-closo-CoC(2)B(10)H(10) where the indenyl ligand instead is forced to incline away from the cage methyl groups. In DCM solution the 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- isomers of (eta-C(9)H(7))CoC(2)B(10)H(12) exhibit two, stepwise, 1-electron reductions assigned to Co(III)/Co(II)/Co(I) couples at less negative potentials than those of the corresponding Cp compounds. Moreover these reductions are easier for those isomers (4,1,6- and 4,1,10-) in which there are two cage C atoms in the carborane face to which the metal atom is bound. By spectroelectrochemical and EPR measurements it is concluded that the reductions of these indenyl cobaltacarboranes are largely metal-based.
Dalton Transactions 06/2010; 39(22):5286-300. · 3.84 Impact Factor
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ABSTRACT: The stannacarborane 1,2-mu-(CH(2))(3)-4,1,2-closo-SnC(2)B(10)H(10) (1) and its adducts with 2,2'-bipyridine (bipy), 1,10-phenanthroline (o-phen) and 4,4'-diphenyl-2,2'-bipyridine (Ph(2)bipy), 1,2-mu-(CH(2))(3)-4-(bipy)-4,1,2-closo-SnC(2)B(10)H(10) (2), 1,2-mu-(CH(2))(3)-4-(o-phen)-4,1,2-closo-SnC(2)B(10)H(10) (3) and 1,2-mu-(CH(2))(3)-4-(Ph(2)bipy)-4,1,2-closo-SnC(2)B(10)H(10) (4), respectively, together with the analogous compound 1,2-mu-{C(6)H(4)(CH(2))(2)}-4-(bipy)-4,1,2-closo-SnC(2)B(10)H(10) (5) have been prepared and characterised. In solution at ambient temperature, compounds 1-5 all display NMR spectra which are interpreted in terms of (time-averaged) C(s) molecular symmetry, but whilst (effectively) C(s) symmetry is retained in the structures of 2-5 in the crystal (i.e. henicosahedral cage structures are observed), 1 has a (C(1)-symmetric) docosahedral structure. A method for quantifying the "percentage docosahedral character" of 13-vertex 1,2-C(2) heteroboranes is described, based on the angles around the C1C2B9B5 quadrilateral. The structures of "carbons adjacent" 1-5 all reveal less slipping of the Sn atom (or {SnL(2)} fragment) across the C(2)B(4) carborane face than has previously been observed in analogous "carbons apart" 4,1,6-closo-SnC(2)B(10) species, a surprising result in the context of previous studies of slipping in icosahedral platinacarboranes. A computational study of "carbons adjacent" and "carbons apart" icosahedral and supraicosahedral platinacarboranes has revealed that the origin of this observation is steric control of the slipping distortion in both "carbons apart" species and in the "carbons adjacent" 13-vertex species, with orbital interactions proving dominant only in the case of the "carbons adjacent" icosahedral compound.
Dalton Transactions 03/2010; 39(9):2412-22. · 3.84 Impact Factor
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ABSTRACT: Novel p-block metallacarboranes with 4,1,10-SnC2B10 and 4,1,12-SnC2B10 architectures are described; the structures of bipyridyl adducts of these compounds reveal very different bipyridyl orientations yielding unique experimental information on the relative trans influences of facial B and C atoms in the cage.
Chemical Communications 10/2009; · 6.17 Impact Factor
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ABSTRACT: The 13-vertex stannacarborane 1,6-Me(2)-4,1,6-closo-SnC(2)B(10)H(10) reacts with the Lewis bases 2,2'-bipyridine, 1,10-phenanthroline, 4,4'-dimethybipyridine and 4,4'-diphenylbipyridine, in toluene, to precipitate bright-yellow adducts 1,6-Me(2)-4-(L(2))-4,1,6-closo-SnC(2)B(10)H(10) (, respectively) in good yield. Compounds have been characterised by NMR spectroscopy and single-crystal X-ray diffraction. Compound is somewhat less stable in solution but has also been studied crystallographically. Adduct formation retains the docosahedral structure of 1,6-Me(2)-4,1,6-closo-SnC(2)B(10)H(10) but is accompanied by polyhedral distortion arising from significant increases in Sn-C and Sn-B2 distances. This distortion is described in terms of either a slipping or hinging of the {SnL(2)} fragment. In the molecular structures of it is evident that the Sn lone pair of electrons is stereochemically active since the L(2) ligand is clearly inclined with respect to the polyhedron. Both the inclination and orientation of L(2) are rationalised by the results of DFT calculations on 4,1,6-closo-SnC(2)B(10)H(12). Calculations on models of the adducts , and reproduce the structural distortion that accompanies adduct formation, but appear to underestimate somewhat the strength of Sn-L(2) bonding.
Dalton Transactions 05/2009; · 3.84 Impact Factor
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Brian W Hutton,
Fraser MacIntosh,
David Ellis,
Fabien Herisse,
Stuart A Macgregor,
David McKay,
Victoria Petrie-Armstrong,
Georgina M Rosair,
Dmitry S Perekalin,
Hugo Tricas, Alan J Welch
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ABSTRACT: The reduction and subsequent oxidation of meta-carboranes containing bulky groups attached to the cage C atoms affords sterically-crowded ortho-carboranes with unprecedentedly long C-C connectivities.
Chemical Communications 12/2008; · 6.17 Impact Factor
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ABSTRACT: Reduction of 1,12-closo-C2B10H12 followed by reaction with the appropriate metal halide and metathesis with either [K(18-crown-6)]Br or [BTMA]Cl ([BTMA] = [C6H5CH2N(CH3)3]+) affords isolable salts of the supraicosahedral metallacarborane sandwich anions [4,4-M-(1,10-closo-C2B10H12)2]n- in moderate to good yield. Compounds prepared are [BTMA][4,4-Co-(1,10-closo-C2B10H12)2] ( 1), [K(18-crown-6)][4,4-Co-(1,10-closo-C2B10H12)2] ( 2), [K(18-crown-6)]2[4,4-Ni-(1,10-closo-C2B10H12)2] ( 3), [K(18-crown-6)]2[4,4-Fe-(1,10-closo-C2B10H12)2] ( 4), [BTMA]2[4,4-Fe-(1,10-closo-C2B10H12)2] ( 5) and [K(18-crown-6)]2[4,4-Ti-(1,10-closo-C2B10H12)2] ( 6). Oxidation of the iron(II) species 4 and 5 with FeCl3 in THF generates the iron(III) analogues [K(18-crown-6)][4,4-Fe-(1,10-closo-C2B10H12)2] ( 7) and [BTMA][4,4-Fe-(1,10-closo-C2B10H12)2] ( 8), respectively. All diamagnetic compounds were characterised spectroscopically and the structures of 1, 3, 4, 6, 7 and 8 were established by single crystal X-ray diffraction. All anions have the anticipated cluster structures with two docosahedral 13-vertex cages joined at the central metal atom (the common degree-six vertex 4). Carbon atoms occupy the degree-four vertex 1 and the degree-five vertex 10. 11B NMR spectroscopy suggests the anions have, on the NMR timescale, C2h symmetry in solution at room temperature, consistent with free rotation, or at least substantial libration, of cage units about the long molecular axis. In the solid state the relative conformations of the two cages may be rationalised by simple bonding arguments, the single exception being the conformation of 4, in which both cages are subject to directional B-H...K+ interactions to the [K(18-crown-6)]+ counterion. The salts 3, 6 and 7 also show B-H...K+ interactions but involving one cage only.
Dalton Transactions 03/2008; · 3.84 Impact Factor
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Angewandte Chemie International Edition 07/2007; 46(35):6706 - 6709. · 13.45 Impact Factor
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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}.
Chemical Communications 07/2007; · 6.17 Impact Factor
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ABSTRACT: Symmetric 4,5,2,3-M(2)C(2)B(9) 13-vertex bimetallacarboranes of cobalt and ruthenium with 14 skeletal electron pairs are afforded by reduction and metallation of 3,1,2-MC(2)B(9) icosahedra; the symmetric species can be converted to their asymmetric 4,5,1,6-M(2)C(2)B(9) isomers by heat, but an easier route is by thermolysis of the reduced species before metallation.
Chemical Communications 07/2007; · 6.17 Impact Factor
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Kelly J Dalby,
David Ellis,
Stefan Erhardt,
Ruaraidh D McIntosh,
Stuart A Macgregor,
Karen Rae,
Georgina M Rosair,
Volker Settels, Alan J Welch,
Bruce E Hodson,
Thomas D McGrath,
F Gordon A Stone
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ABSTRACT: The docosahedral metallacarboranes 4,4-(PMe(2)Ph)2-4,1,6-closo-PtC(2)B(10)H(12), 4,4-(PMe(2)Ph)2-4,1,10-closo-PtC(2)B(10)H(12), and [N(PPh(3))2][4,4-cod-4,1,10-closo-RhC(2)B(10)H(12)] were prepared by reduction/metalation of either 1,2-closo-C(2)B(10)H(12) or 1,12-closo-C(2)B(10)H(12). All three species were fully characterized, with a particular point of interest of the latter being the conformation of the {ML2} fragment relative to the carborane ligand face. Comparison with conformations previously established for six other ML(2)C(2)B(10) species of varying heteroatom patterns (4,1,2-MC(2)B(10), 4,1,6-MC(2)B(10), 4,1,10-MC(2)B(10), and 4,1,12-MC(2)B(10)) reveals clear preferences. In all cases a qualitative understanding of these was afforded by simple MO arguments applied to the model heteroarene complexes [(PH3)2PtC(2)B(4)H(6)]2- and [(PH3)2PtCB(5)H(6)]3-. Moreover, DFT calculations on [(PH3)2PtC(2)B(4)H(6)]2- in its various isomeric forms approximately reproduced the observed conformations in the 4,1,2-, 4,1,6-, and 4,1,10-MC(2)B(10) species, although analogous calculations on [(PH3)2PtCB(5)H(6)]3- did not reproduce the conformation observed in the 4,1,12-MC(2)B(10) metallacarborane. DFT calculations on (PH3)2PtC(2)B(10)H(12) yielded good agreement with experimental conformations in all four isomeric cases. Apparent discrepancies between observed and computed Pt-C distances were probed by further refinement of the 4,1,2- model to 1,2-(CH2)3-4,4-(PMe3)2-4,1,2-closo-PtC(2)B(10)H(10). This still has a more distorted structure than measured experimentally for 1,2-(CH2)3-4,4-(PMe(2)Ph)2-4,1,2-closo-PtC(2)B(10)H(10), but the structural differences lie on a very shallow potential energy surface. For the model compound a henicosahedral transition state was located 8.3 kcal mol(-1) above the ground-state structure, consistent with the fluxionality of 1,2-(CH2)3-4,4-(PMe(2)Ph)2-4,1,2-closo-PtC(2)B(10)H(10) in solution.
Journal of the American Chemical Society 04/2007; 129(11):3302-14. · 9.91 Impact Factor
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Angewandte Chemie International Edition 02/2007; 46(35):6706-9. · 13.45 Impact Factor
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Angewandte Chemie International Edition 07/2006; 45(26):4313-6. · 13.45 Impact Factor
