53687-46-0Relevant academic research and scientific papers
Metallacarboranes in Catalysis. 8. I: Catalytic Hydrogenolysis of Alkenyl Acetates. II: Catalytic Alkene Isomerization and Hydrogenation Revisited
Belmont, James A.,Soto, Jorge,King, Roswell E.,Donaldson, Andrew J.,Hewes, John D.,Hawthorne, M. Frederick
, p. 7475 - 7486 (2007/10/02)
Part I of this study describes the facile hydrogenolysis (and deuteriolysis) of alkenyl acetates, such as isopropenyl acetate (D) and 1-phenylvinyl acetate (E), with rhodacarborane catalyst precursors to yield acetic acid and the corresponding alkene.The catalyst precursors employed were (I), (II), and (III).The hydrogenolysis of alkenyl acetates D and E produced propene and styrene, respectively, along with acetic acid in essentially quantitativeyields.Deuterium at Rh was demonstrated not to enter the hydrogenolysis reaction.Use of D2 as the reducing agent with I and E resulted in the incorporation of deuterium into reactant E and products.Styrene produced in these reactions was predominantly d1 with appreciable quantities of d0 and d2.Ethylbenzene, a byproduct resulting from the hydrogenation of styrene, contained only traces of d0 species and was largely d1, d2, and d3.The acetic acid formed in these reactions was isotopically pure CH3COOD.The rate law for E hydrogenolysis with I contained no term showing hydrogen dependence.These results suggest a reaction mechanism for hydrogenolysis that is based upon the relatively slow formation and decomposition of a very reactive rhodium(III) monohydride formed through the regioselective oxidative addition of Rh(I) (in the exo-nido tautomer of the rhodacarborane) to terminal B-H bonds.The monohydride produced in this fashion then enters a cyclic heterolysis process with H2 which leads to rapid product formation.This mechanism suggests that slow B-D/C-H exchange should occur between I-d9 (B-D at all vertices of I) and anisotopically normal alkane, such as 1-hexene (B), during alkene isomerization.Such exchange was observed and shown to be regioselective.This new information predicated part II of this study, which is devoted to a modification of previously advanced proposals for the mechanisms of alkene isomerization and hydrogenation with rhodacarborane precursors.The facile and regioselective exchange of B-H in (IV) with D2 was examined and shown to be electrophilic in character and to apparently proceed through very reactive monohydride intermediates.These new data coupled with previously reported results allow the formulation of unified mechanisms for B-H/D2 and B-H/C-D exchange, alkenyl acetate hydrogenolysis, alkene isomerization, and alkene hydrogenation based upon the key B-Rh(III)-H species formed by the regioselective oxidative addition of terminal B-H bonds to Rh(I) centers.Thus, the effective catalytic sites in all of these reactions appear to be an array of B-Rh(III)-H centers formed reversibly from the Rh(I) present in exo-nido-rhodacarborane tautomers which are, in turn, in equilibrium ...
Synthesis, structural characterization, and reactions of closo-rhodacarborane anions containing a formal d8 metal vertex
Walker, John A.,Knobler, Carolyn B.,Hawthorne, M. Frederick
, p. 2688 - 2697 (2008/10/08)
Deprotonation of three neutral closo hydrido complexes [(L)2-H-RhC2B9H11] under carefully controlled reaction conditions yields the corresponding isomeric [closo-L2RhC2B9H11]- species. Two of these have been structurally characterized. K[18-crown-6][closo-3,3-(PPh3)2-3,1,2-RhC 2B9H11]·C4H 8O·H2O (2a) crystallized in the monoclinic space group P21/c with a = 13.931 (4) A?, b = 19.954 (5) A?, c = 21.665 (7) A?, β = 100.97 (2)°, V = 5913 A?3, and Z = 4. Data were collected on a Syntex P1 diffractometer (Mo Ka radiation) to a maximum 2θ = 50°, giving 10521 unique reflections, and the structure was solved by conventional heavy-atom techniques. The final discrepancy index was R = 0.062, Rw = 0.072 for 6149 independent reflections. The d8-rhodacarborane anion adopts a closo structure similar to that found in the parent hydrido complex. The Rh-P2 plane lies almost perpendicular to the least-squares plane that passes through the bonding face of the carborane ligand and lies parallel to a line joining the two ortho carbon atoms of this ligand, in accord with theoretical studies. [Me4N][closo-2,2-(PPh3)2-2,1,7-RhC 2B9H11] (2b) crystallized in the triclinic space group P1 with a = 12.355 (13) A?, b = 14.896 (16) A?, c = 15.186 (22) A?, α = 68.00 (9)°, β = 102.86 (6)°, γ = 112.17(5)°, V = 2389 A?3, and Z = 2. Data were collected on a Picker FACS-1 diffractometer (Mo Ka radiation) to a maximum in 2θ of 45°, giving 6180 unique reflections, and the structure was solved by conventional heavy-atom techniques. The final discrepancy index was R = 0.063, Rw = 0.067 for 4761 independent reflections. Unlike 2a, this d8-rhodacarborane anion adopts a significantly distorted icosahedral structure. Carbon atoms of the significantly nonplanar C2B3 face are bent back into the cage and away from the metal. Rh-C bonds in 2b are 2.340 (9) and 2.442 (9) A?, while those in 2a are 2.314 (8) and 2.301 (7) A?. The plane containing RhP2 is nearly perpendicular to the C2B3 face and nearly parallel to the noncrystallographic mirror plane in the carborane ligand (the calculated preferred conformation). Salts of 2a-, 2b-, and [closo-2,2-(PPh3)2-2,1,12-RhC2B 9H11]- (2c) were treated with dilute mineral acids in ethanol to produce the neutral hydrido closo complexes and with π-acceptor ligands L = CO or C2H4 to produce the corresponding [closo-(PPh3)(L)-RhC2B9H11] salts. Anions [closo-3,3-(PPh3)2-3,1,2-IrC2B 9H11]-, [closo-3-(PPh3)-3,3-(H)2-3,1,2-IrC2B 9H11]-, and [closo-3-(PPh3)-3-(CO)-3,1,2-IrC2B9H 11]- have also been prepared.
REACTIONS AT THE RHODIUM VERTEX OF ISOMERIC closo-BIS(TRIPHENYLPHOSPHINE)HYDRIDORHODACARBORANES, ALKENYL ACETATE CLEAVAGE AND SUBSEQUENT REACTIONS
King, R. E.,Busby, D. C.,Hawthorne, M. F.
, p. 103 - 114 (2007/10/02)
The isomeric hydridophosphinorhodacarboranerhodium(III) clusters, (1a); (1b); and (1c) react with isopropenyl acetate and vinylacetate under mild conditions to give ester C-O bond scission, expulssion of alkene, and formation of bidentate or monodentate acetate complexes of the form (PPh3))(η2-CH3COO)RhC2B9H11 or (PPh3)2(η1-CH3COO)RhC2B9H11.These acetate complexes react readily with hydrogen to regenerate the parent compounds.A very stable alkyl complex through the carbonyl oxygen could be isolated from the reaction of 1b with vinyl acetate at lower temperatures, whereas the reaction of 1a with either isopropenyl acetate or vinyl acetate at higher temperatures led to the formation of an ortho-metallated complex whose crystal structure is reported.When allyl acetate was employed as substrate, complexes of the form (PPh3)(η3C3H5)RhC2B9H11 resulted with concomitant elimination of acetic acid.The relevance of the novel compounds reported here to the catalytic hydrogenolysis of alkenyl acetates using 1a-1c as catalyst precursors is discussed.
Metallacarboranes in Catalysis. 2. Synthesis and Reactivity of Closo Icosahedral Bis(phosphine)hydridorhodacarboranes and the Crystal and Molecular Structures of Two Unusual closo-Phosphinerhodacarborane Complexes
Baker, R. Thomas,Delaney, Mark S.,King, Roswell E.,Knobler, Carolyn B.,Long, Judith A.,et al.
, p. 2965 - 2978 (2007/10/02)
A series of closo icosahedral rhodacarboranes bearing substituents at carbon has been synthesized by the reaction of with the correspondingly C-substituted nido-carborane anions: from (1-) where R = R' = H; R = R' = D; R = H and R' = Ph, Me, and n-Bu; from (1-) where R = H, Ph, and Me; and from (1-).These closo icosahedral rhodacarboranes are catalytically active in alkene isomerization and hydrogenation reactions, among others.The B-D-B-bridge deuterated (1-) gave when reacted with , establishing the regiospecific transfer of BHB hydrogen to Rh-H in the synthesis reaction.The complex is apparently transformed to by a polytopal rearrangement under mild conditions.The optically active catalyst was employed to hydrogenate ethyl α-phenylacrylate to give ethyl α-phenylpropionate in 3percent enantiomeric excess.In the absence of hydrogen this chiral catalyst reacted with certain esters of the acrylic type to yield alkyl chelates in which the alkene function of the ester had undergone migratory insertion into the Rh-H and the ester carbonyl oxygen became bound to Rh.One of these chelates, derived from the d-catalyst and n-butyl acrylate, was characterized crystallographically.The compound crystallizes in the space group P212121 with unit cell parameters a = 24.578 (5) Angstroem, b = 12.543 (2) Angstroem, and c = 10.377 (2) Angstroem, four molecules per unit cell.The structure was solved by conventional heavy-atom methods and refined to a final value of R = 0.069, Rw = 0.080 (3159 reflections).The absolute configuration of the d-catalyst and the (1-), from which it was derived, was thus established.Reaction of the unsubstituted compounds and (L = PPh3) with more basic phosphines gave the corresponding L2 compounds with L = PEt3, PMe2Ph, and for the 3,1,2-isomer, L2 = Ph2PCH2CH2PPh2.Reaction of the unsubstituted 3,1,2-isomer (L = PPh3) with HCl in CHCl3 gave .The analogous chloro compound in which L = PMe2Ph was prepared by the reaction of the Rh-H species with CH2Cl2.Reaction of with HCl/CHCl3 produced the coordinatively unsaturated 16-electron species .This complex reacted with CO and ligands to produce coordinatively saturated adducts.A crystallographic study of the 16-electron 2,1,7-chloride was carried out.This compound crystallizes in the monoclinic system P21/n, a = 13.840 (5) Angstroem, b = 17.000 (7) Angstroem, c = 13.771 (6) Angstoem, and β = 118.98 (2) deg, four molecules of complex and...
Metallacarboranes in Catalysis. 5. Interconversion of closo-Bis(phosphine)hydridorhodacarboranes by Rhodium Transfer between η5-nido-Carborane Anions
Long, Judith A.,Marder, Todd B.,Hawthorne, M. Frederick
, p. 3004 - 3010 (2007/10/02)
Both the hydride and dicarbollide ligands of a series of closo, formally six-coordinate Rh(III), bis(triphenylphosphine)hydrido η5-(nido-C2B9H9RR') complexes were easily replaced by a series of (1-) ligands using thermal reactions.The following trend for ease of displacement of the nido-carborane anion in cage-carbon-substituted complexes has been found: 7,8-disubstituted > 7,8-monosubstituted > 7,8-unsubstituted > 7,9-unsubstituted ca. 2,9-unsubstituted.Kinetic studies of the reaction of (R = Me, R' = H) (IVd) with (1-) (Ia) and (1-) (III) in THF at 29 deg C showed no anion concentration dependence and a common first-order rate constant for the two reactions although in the case of (1-) (II), anion dependence was observed.Similar kinetic studies of the reaction of (IVf) with anions Ia, II, and III in THF at -63 deg C proved these exchanges with exo-nido substrates to be much faster than the reactions involving closo substrates.In the cases of Ia and II, the less stable kinetic product of the reaction, the exo-nido tautomer, was initially observed along with its conversion to the more stable closo tautomer.Analysis of the anion concentration dependence of the rates of these reactions suggested the existence of a spectroscopically invisible intermediate, presumably an isomer of the exo-nido starting complex.Formation of an analogous intermediate appears to be the rate-determining step in reaction of closo-IVd with anions Ia and III.In addition, the dissociation of either PPh3 or nido-carborane anion does not appear to be involved in any of these cage exchange reactions.Anion III was found to be a more effective nucleophile than Ia which, in turn, was more nucleophilic than II.
Reactions at the metal vertex of a monometal metallacarborane cluster. Chemistry of [closo-3,3-(PPh3)2-3-HSO4-3,1,2-RhC 2B9H11] and [coso-3-PPh3-3,3-NO3-3,1,2-RhC2B 9Hn]
Kalb, William C.,Demidowicz, Zenon,Speckman, Donna M.,Knobler, Carolyn,Teller, Raymond G.,Hawthorne, M. Frederick
, p. 4027 - 4036 (2008/10/08)
Reaction of [closo-3,3-(PPh3)2-3-H-3,1,2-RhC2B 9H11] (1) with sulfuric or nitric acid affords [closo-3,3-(PPh3)2-3-HSO4-3,1,2-RhC 2B9H11] (2) or [closo-3-PPh3-3,3-NO3-3,1,2-RhC 2B9H11] (3), respectively. Compound 3 can also be prepared from nitric acid and the dimeric metallacarborane [{closo-Rh(PPh3)(C2B9H11)} 2] or from NO2/N2O4 and 1. Complexes 2 and 3 have been used to prepare other new metallacarboranes, namely, [closo-3-PPh3-3,3-{C(Ph)-C(PPh 3)-C(H)-C-(Ph)}-3,1,2-RhC2B9H11] (5), [{closo-3-PPh3-3-(μ-CN)-3,1,2-RhC 2B9H11}4] (7), [closo-3-PPh3-3-L-3-NO3-3,NO3-3,1,2-RhC 2B9H11] (L = CO (8); L = PPh3 (9)), [closo-3,3-(PMe2Ph)2)2-3-NO 3-3,1,2-RhC2B9H11] (10), and [closo-3-PPh3-3-CO-3-Cl-3,1,2-RhC2B9H11] (11). Complexes 5 and 7 have been characterized by X-ray crystallography. The reactions of these new metallacarboranes described herein are representative of interconversions carried out at a discrete transition-metal vertex of a cluster species. Complex 5 crystallizes in space group P1 with 2 formula units in a cell of dimensions a = 12.763 (6) A?, b = 13.348 (5) A?, c = 14.561 (7) A?, α = 91.58 (3)°, β = 93.72 (3)°, and γ = 74.64 (3)°. Data were collected at -154 °C on a Picker FACS-1 diffractometer with the θ-20 scan method. Least-squares refinement, including anisotropic vibration parameters for Rh and P and isotropic vibration parameters for other non-hydrogen atoms, with each phenyl group described as a rigid group having a single isotropic vibration parameter, led to final conventional agreement indices (on F) of R = 0.048 and Rw = 0.051, based on 4493 unique reflections having I > 3σ(I). The molecule consists of a [C2B9H11]2- cage and a triphenylphosphine ligand bound to the metal atom of the trisubstituted metallapentacycle Rh-C(Ph)-C-(PPh3)-C(H)-C(Ph). Rh-C, Rh-B, B-B, B-C, and C-C distances are normal for a 3,1,2-RhC2B9 closo rhodacarborane fragment, and the pattern of short-long-short C-C bond lengths in the RhC4 ring is reminiscent of a pentasubstituted cis-butadiene. The complex 7-5C6H6 crystallizes in space group P2/a with 4 formula units in a cell of dimensions a = 26.046 (8) A?, b = 15.626 (3) A?, c = 30.355 (8) A?, and β = 106.71 (2)°. Data were collected at -154 °C on a Syntex P1 diffractometer with the θ-20 scan method. Least-squares refinement, including vibration parameters and rigid-group assignments as described above, led to final conventional agreement indices (on F) of R = 0.063 and Rw = 0.078, based on 9732 unique reflections having I > 3σ(I). The molecules consist of four discrete closo phosphinorhodacarborane moieties joined together through their respective metal vertices by cyano ligand bridges. Each tetramer possesses a crystallographic 2-fold axis; the two noncrystallographically equivalent tetramers are very similar. The Rh-Rh separation is approximately 5 A?. Bond distances within each icosahedral fragment are normal for such a closo Rh(III) metallacarborane.
