Stephen S. Basson

Mechanism for the oxidative addition of lodomethane to carbonyl(N-hydroxy-N-nitrosobenzenaminato-O,O′)triarylphosphinerhodium(I) complexes and crystal structure of [Rh(cupf)(CO)(CH3)(1)(PPh3)]

Abstract Rh(I) complexes, [Rh(cupf)(CO)(PX 3 )] (cupf= cupferrate; PX 3 = PCy 3 , P( o -Tol) 3 , PPh 3 , PPh 2 C 6 F 5 , P( p -ClC 6 H 4 ) 3 and P( p -MeOC 6 H 4 ) 3 ), react with iodomethane to form Rh(III) alkyl compounds. The reaction was studied in the solvents Bz, EtOAc, Me 2 CO, MeOH, CH 3 CN and DMSO having different polarities and donocities. The reaction proceeds through two competing rate determining steps, one of which is first-order in [CH 3 I]. A reaction mechanism, which includes specific solvent effects, is given. The structure determination of [Rh(cupf)(CO)(CH 3 )(I)(PPh 3 )] shows the complex to crystallize in space group P 1 with a =9.912(2), b = 11.534(1), c = 12.514(2) A, α = 67.84(2), β = 84.41(2), γ = 73.15(1)°, Z = 2 and D m = 1.73 g cm −3 . The molecule has distorted octahedral geometry with CH3 and I cis -bonded. Bond distances: RhPue5f8I = 2.708(2), Rhue5f8P = 2.327(4), Rhue5f8O(hydroxy) = 2.04(1), Rhue5f8O(nitroso) = 2.175- (9), Rhue5f8C(carbonyl) = 1.81(2) and Rhue5f8C(methyl) = 2.08(1) A. Rates for the slow alkyl → acyl conversion in Me 2 CO and CH 3 CN are also given for this complex.

First structural confirmation of different geometrical isomers in the same crystal lattice: the crystal structure of benzoylacetonatocarbonyltriphenylphosphinerhodium(I)

Abstract The first structural confirmation of two different [Rh(BA)(CO)(PPh3)] isomers (BA = benzoylacetonate, CH3(CO)CH(CO)C6H5), namely one with PPh3 cis to the oxygen atom nearest to the phenyl group and the second isomer with PPh3 trans to the oxygen nearest to the phenyl group, in the same crystal lattice is reported. The small influence of the different substituents is illustrated by the near equal Rhue5f8O, Rhue5f8P and Rhue5f8C bond distances in the two different isomers. The structure crystallizes in the triclinic system, space group P 1 with a = 15.625(2), b = 19.138(2), c = 8.891(2) A , α = 95.66(1), β = 74.43(1), γ = 90.52(1)° and Z = 4 . The Rhue5f8P, Rhue5f8CO and Rhue5f8O bond distances for isomer I are 2.249(3), 1.739(14), 2.032(8) and 2.079(8) A. respectively, while the corresponding bond distances for isomer II are 2.248(3), 1.768(14), 2.018(8) and 2.057(7) A, respectively.

Bromide catalysis in the oxidative addition of iodomethane to iridium(I) complexes

Abstract [Ir(cod)(β-dik)] complexes (β-dik=2,4-pentanedionato or 1,1,1-trifluoro-2,4-pentanedionato ligands; cod=cycloocta-1,5-diene) react with CH 3 I in acetone to form Ir(III) alkyl compounds. The addition of Br − led to the formation of a five-coordinate intermediate which enhanced the reaction rate of the acac complex and gave the same oxidative addition product compared to the uncatalysed reaction. A reaction mechanism is given.

Crystal structure of carbonyl(N-hydroxy-N-nitroso-benzenaminato-O,Otau; )-triphenylphosphinerhodium(I)

Le compose du titre cristallise dans le systeme triclinique groupe despace P1 et sa structure est affinee jusqua R=0,059

Crystal structure determination and properties of hydrogen hexacyanododeca-?-chloro-octahedro-hexatantalate(4?)-Dodecahydrate

SummaryThe cluster compound H4[Ta6Cl12(CN)6] · 12H2O was prepared and identified by potentiometric titrations, i.r. and visible spectra and by three-dimensional single-crystal x-ray diffraction methods. Discrete [Ta6Cl12(CN)6]4− ions contain a linear Ta−C≡N unit with Ta−C=2.21(4) and C−N=1.16(5) Å, respectively. Each nitrogen atom is hydrogen bonded [2.63(12)Å] to two oxygen atoms.

Di-μ-hydroxo bridge-cleavage reactions between [Co(nta)(μ-OH)]22− and different monodentate ligands

The cleavage of the di-μ-hydroxo bridges of [Co(nta)(μ-OH)]22− by dimethylaminopyridine (dmap) and pyridine (py) has been investigated. [Co(nta)(μ-OH)]22− equilibrates rapidly in aqueous basic solutions with a mono-μ-hydroxo bridged CoIII species [pKOH = 3.26(2)] and both these species react with the incoming ligand to form different ion associated species which react in the subsequent rate-determining steps (k1 and k2) to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co-μ-OH-Co(nta)(L)]2−. Values for k2, the preferred mono-μ-hydroxo bridged substitution pathway for these reactions, vary between 6.8(2) × 10−4 s−1 (py) and 8.5(4) × 10−2 s−1 (dmap).

The photolytic reaction between [ReN(H2O)(CN)4]2− and 1,2-ethanediamine. The crystal structure of tetraphenylphosphonium μ-1,2-ethanediamine-N,N′-bis[tetracyanonitridorhenate(V)] tetrahydrate

An aqueous solution of [ReN(H2O)(CN)4]2− and 1,2-ethanediamine was irradiated in a photolytic reactor. The reaction product, which was isolated as yellow crystals suitable for X-ray structure determination, is a novel complex with the 1,2-ethanediamine acting as a bridge between two rhenium atoms. The crystal structure of (PPh4)4[{ReN(CN)4}2(μ-en)] · 4H2O was determined from three-dimensional X-ray diffraction data. The [{ReN-(CN)4}2(μ-en)]4− anion has a distorted octahedral geometry around both rhenium atoms with Re(1) displaced by 0.35 and Re(2) by 0.31 Å towards the respective nitrido ligands from the equatorial planes formed by the carbon atoms of the four cyano ligands of each rhenium atom.

Kinetic study of the protonations and substitutions of different cobalt(III)–nta complexes

The behaviour of the Cobalt(III)–nta (nta = nitrilotriacetate) system in an acidic medium was investigated. The acid dissociation constant, pKa1, of [(nta)(H2O)Co(μ-OH)Co(H2O)(nta)]− was determined as 3.09(3) and the pKa of the cis-[Co(nta)(H2O)2]/[Co(nta)(H2O)(OH)]− equilibrium was determined as 6.71(1). cis-[Co(nta)(H2O)2] undergoes ring-opening upon acidification below pH = 2.0. The formation of [Co(η3-nta)(H2O)3]+ was also studied. The substitutions between cis-[Co(nta)(H2O)2] and NCS− ions were investigated in the pH = 2–7 ranges. [Co(nta) (H2O)(OH)]− reacts ca. 70 times faster at 24.7 °C with NCS− ions than cis-[Co(nta)(H2O)2], indicating a cis-labilising effect of the OH− ligand.