Monika Moszner

Studies on reaction of dirhodium(II) aquo cation with dioxygen

Abstract The reactions of dirhodium(II) aquo cation {Rh2(aq)4+} with dioxygen were examined. It has been found that the nature of the oxidation product depends upon the concentration of dioxygen in the solution. The dimeric or polymeric Rh(III)(aq) cationic species with a charge of greater than +3 is formed when air oxygen slowly diffuses into a solution containing Rh2(aq)4+. The paramagnetic cation of proposed formula [(H2O)4Rh(O2−)(OH)2Rh(H2O)4]3+ is formed when molecular oxygen is bubbled through a 2–3 M HClO4 solution of Rh2(aq)4+. This species has been isolated and characterized in solution.

Synthesis and characterization of a novel tetranuclear bimetallic complex containing rhodium(II) and zinc(II) as metal centres

Rh(Hdmg)2(PPh3)Cl (Hdmg=monoanion of dimethylglyoxime) undergoes reduction with zinc amalgam to give the tetranuclear bimetallic compound [Rh(Hdmg)(ClZndmg)(PPh3)]2, characterized by elemental analysis, electronic, IR and NMR spectroscopy and X-ray crystallography. It crystallizes in the triclinic space group P1 with: a=14.262(4), b=14.675(4), c=14.698(4) A, α=82.15(4), β=87.57(4), γ=65.89(3)°, Z=2. The structure was refined up to R=0.13 for 4704 reflections. The molecule consists of two [Rh(dmg)(Hdmg)(PPh3)] subunits linked by an [Rh(II)(II)] bond of length equal to 2.852(3) A and by two Zn ions bridging the oxygens of the equatorial ligands. The binding with zinc relieves the equivalence among the atoms of each subunit.

Rhodium complexes with diacetyl monoxime ligands; crystal structure of [Rhcis- (C4H6NO)2cis-(PPh3)2]ClO4·CHCl3

Abstract The reaction of RhCl 3 ·3H 2 O with Hdamo and PPh 3 (Hdamo = diacetyl monoxime = C 4 H 7 NO), both in the absence ( 1 ) and in the presence of HClO 4 ( 2 ) afforded the complex Rh(damo)(PPh 3 ) 2 Cl 2 . The reaction of the acidic water/ethanolic solution of [Rh(H 2 O) 6 ] 3+ with Hdamo and PPh 3 ( 3 ) gave the mixture of the isomers of the compound [Rh(damo) 2 (PPh 3 ) 2 ]ClO 4 ( 3A and 3B ). A similar mixture of isomers was formed when [Rh(H 2 O) 6 ] 3+ reacted with H 2 dopn (H 2 dopn = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) and PPh 3 ( 4 ). Two isomers ( 4A = 3B ) and [Rh cis -(damo) 2 cis -(PPh 3 ) 2 ]ClO 4 ·CHCl 3 ( 4B ) have been isolated. All the compounds were characterized by elemental analysis NMR and IR spectroscopy. Single-crystal X-ray diffraction studies were carried out on the complex 4B . In this compound the coordination environment around rhodium(III) is pseudooctahedral composed of two cis -oxime nitrogen atoms [av. RhN = 2.031(3) A], two trans -oxime oxygen atoms [av. RhO = 2.026(2) A] and two cis -phosphine phosphorus atoms [av. RhP = 2.403(1) A].

Electrocatalytic dioxygen reduction in the presence of a rhodoxime

Polarographic and voltammetric evidences are reported for the production of intermediates superoxo [Rh]OO and hydroperoxo [Rh]OOH derivatives at the electrode surface, in the reduction of dioxygen in the presence of rhodium bis(dimethylglyoximato) chloro triphenylphosphine, [ClRh(III)(DMG)2(PPh3)] (I), in the absence and in the presence of protons in non-aqueous solvents. In the latter case the electrocatalytic reduction of dioxygen is observed. From the trends of the concentrations of dioxygen vs the rhodium complexes, a mechanism for the electrochemical process is proposed. The molar ratio of dioxygen to the rhodium complex when the latter is completely consumed for the formation of the adduct, as compared with the 1:1 stoichiometric ratio determined by the Hill plot, together with the influence of the electrode material, suggests that the reduction of dioxygen involves adsorbed species.

CATIONIC RHODIUM(III) BISDIMETHYLGLYOXIMATES WITH WATER AND TRIPHENYLPHOSPHINE AXIAL LIGANDS

Preparations of [Rh(Hdmg) 2 (H 2 O) 2 ]ClO 4 ( 1 ) (Hdmg=dimethylgyoximate) from [Rh(H 2 O) 6 ](ClO 4 ) 3 and dimethylglyoxime and of [Rh(Hdmg) 2 (PPh 3 ) 2 ]ClO 4 ( 2 ) from 1 and PPh 3 are described. 1 crystallizes in the space group with a =14.910(3), b =6.058(1), c =18.617(4), A, β =107.649(8)°, Z =4. The structure was refined up to R =0.021 for 1849 reflections. The IR and NMR spectra and electrochemical behavior of 1 and 2 are discussed and compared with other rhodoximes. Three polarographic and CV processed can be detected for 2 , the first two, respectively to Rh(II) and Rh(I), being followed by fast reactions.

Synthesis and structure of Rh(I) tris(pyrazolyl)borate complexes of the type TpPh,MeRhL1L2

The complex Tp Ph,Me Rh(CO) 2 ( 1 ) was prepared from the reaction of the appropriate potassium pyrazolyl borate, Tp Ph,Me K, with Rh(acac)(CO) 2 in warm benzene. Reaction of Rh(acac)(CO) 2 with Tp Ph,Me K and PPh 3 gave the compound Tp Ph,Me Rh(CO)(PPh 3 ) ( 2 ). The complexes 1 and 2 were characterized by elemental analysis and IR, 1 H-, 13 C-, and 31 P-NMR spectroscopies. The structures of both compounds were determined by X-ray crystallography. The complex 1 crystallizes in the triclinic space group P 1 with a =11.227(2), b =12.219(2), c =12.262(2) A, α =63.61(3), β =87.67(3), γ =88.17(3)°, V =1505.4(4) A 3 , and Z =2. Crystals of 2 are triclinic, space group P 1, with a =11.114(2), b =11.913(2), c =18.071(4) A, α =82.69(3), β =82.02(3), γ =64.01°, V =2123.9(7) A 3 , Z =2. The fluxional behavior of 1 and 2 was studied by variable-temperature 1 H-NMR spectroscopy. In the case of 1 the κ 2 ↔ κ 3 conversion is fast on the NMR time-scale even at −90°C, whereas complex 2 is a unique example of two well-separated κ 2 ↔ κ 3 equilibria (by 21 kJ mol −1 Δ G ≠ gap).

Polarographic Studies of Dimeric and Monomeric Rhodium(II) and Rhodium(III) Complexes

Abstract The polarographic behaviour of [Rh2(O− 2)(OH)2(H2O)n]3+, [I], [Rh2(H2O)10]4+ (Rh2 4+ (aq)), [II], [Rh(H2O)6]3+, [III], in 3 M HCIO4 and Rh2(CH3CO2)4(H2O)2, [IV], and [Rh2(CH3CO2)4(H2O)2]+, [V], in 3 M HC1O4 and 3 M NaCIO4 has been investigated at a Pt (planar) electrode. The cation [I], which is the reaction product of [II] with molecular oxygen, produced a single electron cyclic polarogram, while cations [II], Rh2 4++(aq), and [III] do not show any wave. Formal potentials of the following couples were evaluated: [Rh2(O2)(OH)2(H2O)n]3+/[Rh2(O2 2-)(OH)2(H2O)n]2+, Eo f = 1.032 ± 0.002 V in 3M HCIO4; [Rh2(CH3CO2)4(H2O)2]+/[Rh2(CH3CO2)4(H2O)2], Ef o = 1.208 ± 0.002 V in 3M HCIO4, Ef o = 1.228 ± 0.002 V vs SHE in 3 M NaCIO4.

Multiple rhodium(II)–rhodium(III) bond in the dimer [Rh2(O2CMe)4(H2O)2][ClO4]·H2O; X-ray crystal structure

The crystal and molecular structure of tetra-µ-acetatorhodium(II)–rhodium(III) perchlorate has been determined; the complex contains the bimolecular species [Rh2(O2CMe)4(H2O)2]+ with a very short RhII–RhIII distance of 2·3165(20)A.

Rhodium complexes with dioximes as catalysts of hydroformylation and hydrogenation of 1-hexene

Abstract Rhodium(II) complexes with dioximes [Rh(Hdmg) 2 (PPh 3 )] 2 [ I ] (Hdmg=monoanion of dimethylglyoxime) and [Rh(Hdmg)(ClZndmg)(PPh 3 )] 2 [ II ] catalyse hydroformylation and hydrogenation reactions of 1-hexene at 1 MPa CO/H 2 and 0.5 MPa H 2 at 353 K, respectively. Hydroformylation with complex [ I ] produces 94% of aldehydes ( n / iso =2.2) and 6% 2-hexene whereas the second catalyst [ II ] gives ca. 40% of aldehydes ( n / iso =2.1) and 60% of 2-hexene. Corresponding Rh(III) complexes are inactive in hydroformylation except of RhH(Hdmg) 2 (PPh 3 ) [ III ], which shows activity similar to [ I ]. Complexes [Rh(Hdmg) 2 (PPh 3 )] 2 [ I ], [Rh(Hdmg)(ClZndmg)(PPh 3 )] 2 [ II ], RhH(Hdmg) 2 (PPh 3 ) [ III ] and [Rh(Hdmg) 2 (PPh 3 ) 2 ]ClO 4 [ V ] catalyse 1-hexene hydrogenation with an average TON ca. 18 cycles/mol [Rh]×min. Complex [ II ] has also been found to catalyse hydrogenation of cyclohexene, 1,3-cyclohexadiene and styrene.

Synthesis and Characterization of Superoxo Rhodium(III) Carboxylates

Abstract Treatment of an aqueous HC1O4 solution of [Rh2(O− 2)(OH)2(H2O)n]+2 (I) with OH−1 yields at pH ca 6 a dark, greenish-blue, gel assumed to be [Rh2(O− 2)(OH)2+m(H2O)n-m] (II). Reactions of (II) and RCO2H gave three new superoxo rhodium(III) carboxylates, which on the basis of electronic, IR, ESR and Raman evidence, elemental analysis, redox equivalent determination and magnetic susceptibility measurements have been formulated as [Rh2(O− 2)(OH)m(RCO2)n·xH2O] [R = CH3 (III), CHC12 (IV), n = 8, m = 3; R = CF2 (V), n = 9, m = 2].