CH2Cl2 Solvent Research Articles

Synthesis and dynamic nuclear magnetic resonance studies of pentafluorobenzenethiolate complexes of molybdenum and tungsten. The crystal and molecular structures of [W(SC6F5)3(CO)(η5-C5H5)]·0.5CH2Cl2and [N(PPh3)2][Mo(SC6F5)4(η5-C5H5)

The reaction between [WBr3(CO)2(η5-C5H5)] and excess of Tl(SC6F5)(CH2Cl2, 20 °C) affords Tl[W(SC6F5)4(η5-C5H5)](2b) as the major product and [W(SC6F5)3(CO)(η5-C5H5)](3) as the minor product. Complex (3) has been structurally characterised as its 0.5 CH2Cl2 solvate by X-ray diffraction. Chiral molecules of [W(SC6F5)3(CO)(η5-C5H5)] adopt a distorted square-based ‘piano-stool’ geometry with the trans W–S bond [2.443 6(15)A] longer than the cis W–S bonds (mean 2.358 A). The SC6F5 ligands lie with S–C bonds approximately in the plane of the square base and, all C6F5 groups have the same rotational orientation about the central W atom. However, dynamic 19F n.m.r. studies of (3) reveal that two isomeric forms exist at low temperature due to different orientations of the SC6F5 ligands but these undergo exchange at ambient temperature as a result of rotation about the W–SC6F5 bonds or inversion at sulphur. Similar studies of complex (2b) established that apparent rotation of the SC6F5 groups is solvent dependent and occurs in conjunction with ionic dissociation into Tl+ and [W(SC6F5)4(η5-C5H5)]–. The TlI in (2b) and related complexes Tl[Mo(SC6F5)4(η5-C5H5)] and Tl[Mo(SC6F5)2(CO)2(η5-C5H5)] can be replaced by non-co-ordinating cations to give X+[M(SC6F5)4(η5-C5H5)]–[M = Mo, X = NBun4(4a) or N(PPh3)2(4b); M = W, X = NMe4] and N(PPh3)2+[Mo(SC6F5)2(CO)2(η5-C5H5)]– which also exhibit fluxional behaviour according to 19F n.m.r. studies. The structure of complex (4b), determined in the solid state by X-ray diffraction, comprises discrete ions [(Ph3P)N(PPh3)]+ and [Mo(SC6F5)]4[(η5-C5H5)]–. The complex anion has a ‘piano-stool’ geometry with a square base defined by four SC6F5 ligands (mean Mo–S 2.420 A) and the C6F5 groups form a ‘swastika-like’ arrangement about the square plane. Reactions of (2b) with tertiary phosphines (L) in CH2Cl2 at 20 °C afford 1:2 adducts Tl[W(SC6F5)4L2(η5-C5H5)][L = PPh3(6b), PMe2Ph (6c), or PEt3(6d)]. Dynamic 19F n.m.r. studies established a different structure for (6b) in solution compared to (6c) and (6d).

Metallaheteroborane chemistry. Part 7. Synthesis, crystal structure, and characterisation of two dinuclear rhodatelluraboranes, [{(PPh3)2RhTeB10H10}2] and [(PPh3)(CO)Rh2Te2B20H20

The dinuclear rhodatelluraborane closo-[(PPh3)(CO)Rh2Te2B20H20](2) was obtained from the reaction between either [Os3H2(CO)10] and closo-[2,2-(PPh3)-2-H-1,2-TeRhB10H10](1) in dichloromethane solvent, or [Rh(cod)(PPh3)Cl](cod = cyclo-octa-1,5-diene) and Cs[TeB10H11] in ethanol. The reaction between [Mo(CO)6] and closo-[2,2-(PPh3)2-2-H-1,2-TeRhB10H10] in tetrahydrofuran afforded [{closo-(PPh3)RhTeB10H10}2], (3). X-Ray crystallographic analysis of compound (2) shows it to crystallise with a monoclinic space group (P21/c), containing four molecules in a unit cell of dimensions a= 16.213(4), b= 13.082(4), c= 17.048(3)A, and β= 95.29(2)°, The final R factor was 0.028 for 5 992 observed reflections. X-Ray analysis of the CH2Cl2 solvate of (3) shows the crystal to be monoclinic, space group P21/a with four molecules in a unit cell that measures a= 16.384(5), b= 16.197(6), c= 19.879(5)A, and β= 70.84(2)°. The final R factor was 0.039 for 3 973 observed reflections. Both (2) and (3) contain two {RhTeB10} cages bonded by Rh–Rh′, Rh–B′, Rh′–B, Rh–H′–B′, and Rh′–H–B′, interactions. Principal interatomic distances are Rh–Rh′ 2.737 1 (3), Rh–B′ 2.380(4), Rh′–B 2.329(4), Rh–Te 2.565 3(3), Rh′–Te′ 2.581 7(3)A in (2) with the corresponding distances in (3), 2.834 4(12), 2.354(12), 2.341(13), 2.604 7(12), and 2.581 1 (10)A respectively. The exo-cage ligands (PPh3 or CO) in both (2) and (3) adopt cis configurations about the central Rh–Rh′ portions of the molecules. The 1H, 11B, and 31P n.m.r. data for (2) and (3) show close similarities with those of (1).

Synthesis and structures of two new mixed antimony-iron carbonyl clusters: [R4N][SbFe4(CO)16] (R = Me, Et) and [Et4N]2[Sb2Fe6(CO)20

[R4N][SbFe4(CO)16] ([R4N][I], R = Me, Et) was prepared by the oxidation of [R4N]3[SbFe4(CO16)] with two equivalents of [Cu(MeCN)4][BF4]. Single crystal X-ray diffraction of [Me4N][I] shows that it crystallizes in the triclinic centrosymmetric space group P1 with a 11.840(3) Å, b 12.550(3) Å, c 10.500(2) Å, α 94.41(2)°, β 101.14(2)°, γ 89.20(2)°, V 1526.3(6) Å3 and Z = 2. Full matrix least squares refinement on a basis of 5072 unique reflections led to R = 0.036, Rw = 0.049. The anion has a highly distorted tetrahedral core in which the four-coordinate antimony atom is surrounded by two isolated Fe(CO)4 units and an Fe2(CO)8 group. Photolysis of [Et4N][I] with UV light gave as the only cluster product [Et4N]2[Sb2Fe6(CO)20] ([Et4N]2[II]) which can also be prepared by the reaction of [Et4N]2[Fe4(CO)13] with SbCl3. It crystallizes with 0.941(9) molecule of solvent CH2Cl2 in orthorhombic accentric space group P212121 with a 15.962(6) Å, b 25.878(6) Å, c 10.035(2) Å, V 5384(2) Å3 and Z = 4. The anion has a distorted trans-Sb2Fe4 octahedral core in which each Sb atom is bonded to an external Fe(CO)4 unit. Full matrix least squares refinement on a basis of 4007 unique reflections converged with R = 0.040 and Rw = 0.049.

Raman and infrared study of reorientational dynamics in trifluorobenzene

AbstractThe Raman spectral bandwidths of two A1′ vibrations of 1,3,5‐trifluorobenzene (TFB) were measured in the neat liquid as a function of temperature and in the solvents CH2Cl2 and CS2. The Raman and IR linewidths of two E′ modes were also measured in solution. Derived values of the two rotational diffusion constants, D⊥ and D∥, were compared with the predictions of several current theories. It was observed that the Hynes–Kapral‐Weinberg (HKW) theory is superior to both the microviscosity–free rotor and Hu–Zwanzig ‘slip’ models of reorientational diffusion. Calculated values of D⊥ and D∥ for TFB in solution using the HKW model are in excellent agreement with the experimentally measured diffusion constants.

ChemInform Abstract: Adducts and Cyclometalated Derivatives of Palladium(II) with Some 1,4‐Benzodiazepin‐2‐ones. Crystal and Molecular Structure of trans‐Dichlorobis(7‐chloro‐1‐(cyclopropylmethyl)‐1,3‐dihydro‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐one)palladium(II).

AbstractIn the adducts (IV), prepared as shown, the benzodiazepines act as monodentate ligands through the 4‐nitrogen atom, as determined by an X‐ray structure analysis of (IVb) (it crystallizes as a CHCl3 solvate in the space group P21/n, Z=2 and as a CH2Cl2 solvate in P21/c, Z=4).

ChemInform Abstract: Reactivity of Cationic Molybdenum(II) Complexes. Part 2. Electrochemical Reduction of the Eighteen‐Electron Complexes (Mo(CO)3(η5‐C5Me5)L)+ (L: CO, p‐MeC6H4NC, or P(OMe)3). Crystal Structure of (Mo2(CO)6(η5‐C5Me5)2).

AbstractThe 18‐electron cationic complexes (I) undergo in CH2Cl2 solvent, a one‐electron cationic process which gives rise to the different products, the dimer (II) or (III), depending on the nature of L. The dimer (II) (space group P21/c, Z=2) is characterized by an X‐ray structure determination.

Ein ringförmiger zirkonium-Dreikernkomplex mit fünffach koordinierten zentralatomen: Darstellung und Struktur von tris[(di-π-cyclopentadienyl)(μ-terephthalato)zirkonium(IV)]-dichlormethan(1/1)

The reaction of zirconocene dichloride with disodium terephthalate in the two-phase system H2O/CHCl3 yields the novel cyclic three-nuclear complex tris[di(π-cyclopentadienyl) (μ-terephthalato)zirconium(IV)] (5), which can be isolated as the CH2Cl2 solvate (sol:11). The three dicarboxylato bridges act as (2 + 1)-dentate ligands, such that each Zr atom has three ligating O atoms in addition to its Cp ligands and thus has an 18-electron configuration. The twenty-seven-membered central ring of 5 is puckered. The structure of 5 has been solved by an X-ray diffraction study. The complex crystallizes in the monoclinic space group P21/n, with Z = 4, and the lattice parameters a 30.123(5), b 13.427(2), c 12.843(2) Å, β 99.11(2)°.

Kinetics of overall decomposition of hydroxyhydrotrioxides

1. The decomposition of hydroxyhydrotrioxides is described by a first order equation. The electron-donor substituents increase the stability of the hydrotrioxides. 2. There is a compensational effect for the preexponential factors and energies of activation of thermal overall decomposition of (CH3)2C(OH)OOOH in solvents CHCl3, CCl4. CH3CN, n-C6H14, (C2H5)2O and in C2H5OH-H2O mixtures. 3. The influence of the solvent on the rate constant of the overall decomposition of (CH3)2C(OH)OOOH is described for the range when the Koppel'-Pal'm equation holds.

ChemInform Abstract: The Chloromethylation of Triethylamine in Dichloromethane. Crystal and Molecular Structure of (Chloromethyl)triethylammonium Tetrachloroplatinate(II), (N(C2H5)3(CH2Cl))2(PtCl4).

AbstractIn the reaction system shown leading to the preparation of the platinum aminothiolate complex (III), a side reaction occurs in which the CH2Cl2 solvent acts as alkylating agent towards NEt3, yielding the salt (IV).

Investigation of transmitting ability of Sn-O binuclear bridge grouping by means of19F NMR

1. On the basis of an investigation of19F-{1H} NMR spectra of a series of 4-fluororphenolates of triaryltins, Ar3SnOC6H4F-4, it has been established that the transmission ability (TA) of the SN-O binuclear bridge grouping differs slightly from that of the Sn bridge atom and the CH2O group. 2. In contrast to the weak proton-donor solvent CHCl3, aprotic polar solvents — either noncoordinating or coordinating — reduce the electron conductivity of Ar3SnOC6H4F-4.

ChemInform Abstract: Cobalt Metallacycles. Part 16. X‐Ray Structures of 4‐Iminocobaltacyclobutene Complexes.

Three 4-iminocobaltacyclobutene complexes, [[graphic omitted](NC6H4Me-p)}(η5-C5H5)(PPh3)] have been analysed by single-crystal X-ray analyses. Crystals of (1)(R1= Ph, R2= CO2Me; CH2Cl2 solvate) are triclinic, space group P, with a= 12.381(3), b= 13.987(4), c= 11.209(4)A, α= 91.16(3), β= 103.30(2), γ= 77.14(2)°, Z= 2, and R= 0.066 for 3 055 reflections. Crystals of (2)(R′= Me, R2= CO2Me) are monoclinic, space group P21/c, with a= 12.062(5), b= 14.945(4), c= 17.817(5)A, β= 113.70(4)°, Z= 4, and R= 0.052 for 2 842 reflections. Crystals of (3)(R1= CO2Me, R2= Ph) are triclinic, space group P, with a= 12.271(6), b= 13.216(5), c= 10.833(4)A, α= 96.07(3), β= 98.77(4), γ= 102.23(3)°, Z= 2, and R= 0.048 for 4 324 reflections. The Co–C(R1) distance in these complexes depends on the bulkiness of the substituent R1, varying from 1.966(8)A for R1= Ph (1), to 1.931(5)A for R1= CO2Me (3), and to 1.908(7)A for R1= Me (2). In all cases the substituent of the imino group, C6H4Me-p, is located syn with respect to the metal. Treatment of (1) with methyl iodide gives a cationic complex which has been isolated as [[graphic omitted](NMeC6H4Me-p)}(η5-C5H5)(PPh3)]PF6(4). Crystals of (4) are triclinic, space group P, with a= 13.658(3), b= 14.142(2), c= 10.517(3)A, α= 94.42(2), β= 95.39(1), γ= 102.62(1)°, Z= 2, and R= 0.082 for 2 314 reflections. The methyl group originating from methyl iodide is bound to the imino nitrogen. Metallacyclobutadiene character in (4) is apparent from the shorter metal–carbon bonds and more averaged C–C distances than in the parent complex (1).

Living polymerization of isobutyl vinyl ether by HI/I2 initiator in polar solvents

AbstractThis study has shown a nearly perfect living polymerization of isobutyl vinyl ether (IBVE) to proceed not only in nonpolar media (e.g., n‐hexane) but in relatively polar CH2Cl2 solvent, provided that the HI concentration is sufficiently high. The produced polymers had a nearly monodisperse molecular weight distribution (Mw/Mn ≤ 1.1); the number‐average molecular weight (Mn) increased in direct proportion to IBVE conversion and its increase continued on the addition of a fresh feed of the monomer at the end of the polymerization. The use of a more polar medium (PhNO2/CH2Cl2) or a lower HI concentration leads to chain transfer reactions, by promoting the ionic dissociation of the “nondissociated” living propagating species. The successful living polymerization by HI/I2 in CH2Cl2 indicates a very strong interaction between the iodide anion and the growing end.

Complexes of hybrid ligands. Comparative studies on two cationic Pt2+ complexes of a fluorinated alkoxy-thioether ligand: solid-state structures and evidence for coupled ring-thioether inversion in solution

Complete structural determinations are reported for two cationic platinum(II) complexes of the chelating, hybrid, alkoxythioether ligand CH3SCH2O(CF3)2O− with phosphine coligands and BF4− counterions. Complex 1, [Pt(PPh3)2{CH3SCH2C(CF3)2O}]BF4, C42H37BCl2F10OP2PtS (CH2Cl2 solvate) is monoclinic, space groupP21/c, with a = 12.2534(9), b = 18.584(2), c = 19.612(3) Å, β = 97.36(1)°, V = 4466(1) Å3, Z = 4. Complex 2, [Pt(PPh2Me)2{CH3SCH2C(CF3)2O}]BF4, C31H31BF10OP2PtS, is orthorhombic, space group Pna21, with a = 23.093(4), b = 11.362(3), c = 12.880(2) Å, V = 3379(2) Å3, Z = 4. The structures show the five-membered chelate ring to have similar conformations in the two complexes, the CH3S and axial CF3 groups being in an anti conformation.The structural results are discussed in relation to previous nmr studies on these and related complexes. It is concluded that an anisotropic shielding effect on the CH3S and CF3 resonances is present in both complexes, but that it is significantly greater in 1, where PPh3 is the coligand, and anomalies in the 19F nmr spectra are explained on this basis. A careful consideration of the nmr data, in light of the crystal structures, demonstrates the persistence of preferred chelate ring conformations in solution. Thioether inversion induces ring inversion in these complexes.

Cobalt metallacycles. Part 16. X-Ray structures of 4-iminocobaltacyclobutene complexes

Three 4-iminocobaltacyclobutene complexes, [[graphic omitted](NC6H4Me-p)}(η5-C5H5)(PPh3)] have been analysed by single-crystal X-ray analyses. Crystals of (1)(R1= Ph, R2= CO2Me; CH2Cl2 solvate) are triclinic, space group P, with a= 12.381(3), b= 13.987(4), c= 11.209(4)Å, α= 91.16(3), β= 103.30(2), γ= 77.14(2)°, Z= 2, and R= 0.066 for 3 055 reflections. Crystals of (2)(R′= Me, R2= CO2Me) are monoclinic, space group P21/c, with a= 12.062(5), b= 14.945(4), c= 17.817(5)Å, β= 113.70(4)°, Z= 4, and R= 0.052 for 2 842 reflections. Crystals of (3)(R1= CO2Me, R2= Ph) are triclinic, space group P, with a= 12.271(6), b= 13.216(5), c= 10.833(4)Å, α= 96.07(3), β= 98.77(4), γ= 102.23(3)°, Z= 2, and R= 0.048 for 4 324 reflections. The Co–C(R1) distance in these complexes depends on the bulkiness of the substituent R1, varying from 1.966(8)Å for R1= Ph (1), to 1.931(5)Å for R1= CO2Me (3), and to 1.908(7)Å for R1= Me (2). In all cases the substituent of the imino group, C6H4Me-p, is located syn with respect to the metal. Treatment of (1) with methyl iodide gives a cationic complex which has been isolated as [[graphic omitted](NMeC6H4Me-p)}(η5-C5H5)(PPh3)]PF6(4). Crystals of (4) are triclinic, space group P, with a= 13.658(3), b= 14.142(2), c= 10.517(3)Å, α= 94.42(2), β= 95.39(1), γ= 102.62(1)°, Z= 2, and R= 0.082 for 2 314 reflections. The methyl group originating from methyl iodide is bound to the imino nitrogen. Metallacyclobutadiene character in (4) is apparent from the shorter metal–carbon bonds and more averaged C–C distances than in the parent complex (1).

X-Ray structure analysis of the salts [N(PPh3)2][M4H3(CO)12](M = Ru or Os); confirmation of the existence of discrete structural isomers for a hydridocarbonyl cluster in the solid state

X-Ray analysis has shown that the salt [N(PPh3)2][Ru4H3(CO)12] crystallizes in two forms, (1) and (2), which correspond to two different structural isomers (tautomers) of the anion. These have overall geometries of virtual C2[(1)] and C3v[(2)] symmetry, and provide the first confirmation of the existence of such isomers in the solid state. Crystals of (1) and (2) are triclinic, space group P. For (1), a= 17.361(4), b= 11.735(2), c= 12.321(2)A, α= 94.61 (2), β= 98.44(2), γ= 88.52(2)°, Z= 2; refinement of atomic parameters using 7 210 data converged at R= 0.0473. For (2), a= 15.608(3), b= 15.370(3), c= 11.219(2)A, α= 99.26(2), β= 103.27(2), γ= 105.72(2)°, Z= 2; refinement of atomic parameters using 10 945 data converged at R= 0.0432. Although three crystalline modifications, (3), (4), and (5), of the corresponding salt [N(PPh3)2][Os4H3(CO)12] were isolated, X-ray analysis has shown that in all three the same isomer of the monoanion, of virtual C2 symmetry, is present. Crystals of the osmium salt (3), which are isomorphous with those of the ruthenium salt (1), are triclinic, space group P, a= 17.378(4), b= 11.691(2), c= 12.308(2)A, α= 94.40(2), β= 98.62(2), γ= 88.41(2)°, Z= 2. Modification (4) crystallizes as a 0.5CH2Cl2 solvate, orthorhombic, space group Pna21, a= 17.648(4), b= 19.597(4), c= 15.429(3)A, Z= 4. Modification (5) is monoclinic, space group P21/c, a= 11.683(2), b= 28.976(4), c= 14.733(3)A, β= 100.13(2)°, Z= 4. Complete structure analysis was carried out for modification (4) only, for which refinement of atomic parameters using 3 347 data converged at R= 0.0426.

The Effect of H2O and HCl on isobutylene polymerization coinitiated by BCl3

The effect of H2O and HCl initiators on the BCl3 coinitiated polymerization of isobutylene was investigated by comparative experiments carried out in CH2Cl2 solvent in the range range from −50 to −100°C under high vacuum (superdry conditions) and in the dry box (conventional condition). H2O is a much more efficient initiator than HCI and the reasons for this are discussed.

Dinuclear metal complexes. Part 4. Electrochemical studies of macrocyclic dicopper(II) complexes. Investigation of the effect of solvents, donor groups, and steric constraints on the stability of mixed-valence copper(II)–copper(I) complexes

Two series of macrocyclic dicopper(II) complexes of stoicheiometry [Cu2L][ClO4]2·2H2O have been synthesized and characterized. Compounds belonging to series (1) are derived from the 6,12,18,24-substituted (H,H,Me,Me; H,H,Me,Ph; Me,Me,Me,Ph; Me,Me,Ph,Ph) macrocycie 7,11;19,23-dimetheno-9,21-dimethyl-1,5,13,17-tetra-azacyclotetracosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H2L). Complexes belonging to series (2) are related to those of series (1) by replacement of two of the –CHN– linkages by –CH2–NH– groups and the segment containing two azomethine linkages having the 6,12-substituents H,H; Me,Me; Me,Ph; Ph,Ph. The electrochemistry of these compounds has been investigated in MeCN and CH2Cl2 solvents using platinum and glassy carbon electrodes. In all cases cyclic voltammograms show sequential one-electron transfers at two different potentials, and from these data the conproportionation constant (Kc) and free energy of the mixed-valent species (ΔGc) have been evaluated. Electrochemical results have been analysed in terms of the effect due to solvent, donor groups, and steric constraints. Values of Kc for all of the compounds are greater in MeCN than those in CH2Cl2, and the Kc value for any compound belonging to series (1) is greater than its analogue in series (2). Factors affecting stability and intramolecular electron-transfer rates of CuIICuIL+ species are discussed.

Living cationic polymerization of isobutyl propenyl ether as β‐substituted vinyl ether

AbstractIsobutyl propenyl ether [IBPE; CH3CH=CHOCH2CH(CH3)2] was polymerized with a mixture of hydrogen iodide and iodine (HI/I2 initiator) in n‐hexane at −40°C to yield living polymers with a nearly monodisperse molecular weight distribution (MWD) (M̄w/M̄n ≈ 1.1). The number‐average molecular weight (M̄n) of the polymers increased proportionally to IBPE conversion and further increased when a new monomer feed was added to a completely polymerized solution. The M̄n was controlled by the initial concentration of hydrogen iodide if the acid was charged in excess over iodine. In polymerization by iodine alone the M̄n of the polymers obtained in nonpolar solvents (n‐hexane and toluene) also increased with conversion, but their MWD was broader (M̄w/M̄n = 1.3–1.4) than in the HI/I2‐initiated systems under similar conditions. The iodine‐initiated polymerization in polar CH2Cl2 solvent, in contrast, led to nonliving polymers with a broad MWD (M̄n/M̄n = 1.6–1.8) and M̄n, independent of conversion. The living polymerization of IBPE was also compared with that of the corresponding isobutyl vinyl ether, to determine the effect of the β‐methyl group in IBPE.

Synthesis of polynuclear complexes containing the tridentate bis(diphenylphosphino)methanide ligand. Crystal structures of the compounds [(C6F5)2Au(Ph2PCHPPh2)Au(C6F5)] and [(C6F5)2Au(Ph2PCHPPh2)Au(Ph2PCHPPh2)Au(C6F5)2]ClO4

Reaction of NaH with [Au(C6F5)2(Ph2PCH2PPh2)]ClO4 causes both deprotonation of the methylene group and elimination of the anion and leads to the neutral bis(diphenylphosphino)methanide complex [Au(C6F5)2(Ph2PCHPPh2)], which further reacts with gold(I) or silver(I) derivatives to give bi- or tri-nuclear complexes. The structures of a binuclear and a trinuclear gold derivative have been confirmed by X-ray crystallography. Crystals of [(C6F5)2Au(Ph2P[graphic omitted]u(C6F5)] are monoclinic, space group P21/m, with a= 10.003(2), b= 17.389(4), c= 11.754(3)A, β= 103.53(2)°, and Z= 2; R= 0.034 for 4 016 reflections. Crystals of [(C6F5)2Au(Ph2P[graphic omitted]HPPh2)Au(C6F5)2]ClO4(CHCl3 solvate) are monoclinic, space group P21/m, with a= 17.456(6), b= 17.704(6), c= 17.749(8)A, β= 92.86(5)°, and Z= 2; R= 0.096 for 5 230 reflections.

Reduction–oxidation properties of organotransition-metal complexes. Part 18. The stabilisation of paramagnetic cyclopentadienylrhodium compounds via o-quinone complexation : X-ray crystal structure of [Rh(PPh3){o-C(O)OC6Cl4O}(η-C5H5)]·0.25CH2Cl2

o-Chloranil (3,4,5,6-tetrachloro-o-benzoquinone) and [Rh(CO)L(η-C5R5)] in n-hexane give yellow [[graphic omitted]}(η-C5R5)](1; R = H or Me, L = CO or PPh3); an X-ray study of (1; R = H, L = PPh3) as its CH2Cl2 solvate reveals that the linking of catecholate and carbonyl ligands has occurred. The Rh atom is therefore co-ordinated by an η-C5H5 ligand and a PPh3 moiety, and in addition forms part of a six-membered [graphic omitted](O) metallacycle. Mean bond lengths are Rh–P 2.298(3), Rh–C (of metallacycle) 1.994(12), and Rh–O 2.079(6)A. The metallacycle adopts a distorted boat conformation, partly because it is fused to the aryl C6Cl4 moiety. Complex (1; R = H, L = PPh3) reacts with HBF4·OEt2 to give [Rh{o-OC6Cl4(OH)}(CO)(PPh3)(η-C5H5)][BF4], via cleavage of the bond linking the CO and catecholate groups. When dissolved in CH2Cl2, the carbonyls (1; L = CO) rapidly lose 2 equivalents of CO to give the deep blue or purple chelated catecholato-complexes [Rh(o-O2C6Cl4)(η-C5R5)](2; R = H or Me). By contrast, the phosphine derivatives (1; L = PPh3) slowly decarbonylate to [RhL(o-O2C6Cl4)(η-C5R5)](3; R = H or Me, L = PPh3); related complexes [3; R = H, L = PPh3, AsPh3, P(OPh)3, or pyridine (py); R = Me, L = PPh3 or AsPh3] result from the reaction between (2) and L. Complexes (3) undergo reversible one-electron oxidation at a platinum electrode in CH2Cl2, and reaction with AgPF6 yields the stable, paramagnetic salts [RhL(o-O2C6Cl4)(η-C5R5)][PF6][4; R = H, L = PPh3, AsPh3, P(OPh)3, or py; R = Me, L = PPh3 or AsPh3]. The e.s.r. spectra of salts (4) suggest that the unpaired electron resides mainly on the semiquinone ligand, but hyperfine coupling to rhodium and to the donor atom (P or As) of L implies some delocalisation.