PPh3 Adduct Research Articles

(Ph3P)4C4P4: Effect of substitution on the Oligomerization of carbon phosphide radicals

AbstractDehalogenation of (PBr)2C2(PPh3)2 with potassium graphite, KC8, leads to Cs‐P4C4(PPh3)4, which can be viewed as a PPh3 adduct of a Cs‐symmetric P4C4 cage. An isolable intermediate was found and in combination with DFT calculations, the structure of a S4‐symmetric P4C4(PPh3)4 cage is proposed for this species. That a 1,3‐diphosphete type Ph3P→P2C2←PPh3 heterocycle is a short‐lived intermediate in the dehalogenation reaction is indicated by trapping experiments which allowed to isolate and fully characterize the [Fe(CO)4] complexes [Fe(CO)4(κ‐P−P2C2{PPh3}2] and [(Fe(CO)4)2(μ2‐κ‐P−P2C2{PPh3}2]. The conversion of S4‐P4C4(PPh3)4 to Cs‐P4C4(PPh3)4 prompted a (re)investigation of the isomerization of various P4X4 species (X=S, NH, NMe; CH2), which shows that these proceed on Minimum Energy Reaction Pathways (MERPs) with two transition states embracing one intermediate. In contrast, the isomerization S4‐P4C4(PR3)4 to Cs‐P4C4(PR3)4 is a one‐step process.

Partially fluorinated Scorpionate [HB(3-(CF3),5-(Ph)Pz)3]− as a supporting ligand for silver(I)-benzene, -carbonyl, and -PPh3 complexes

The benzene, CO, and PPh3 adducts [HB(3-(CF3),5-(Ph)Pz)3]AgL (L=C6H6, CO, or PPh3) have been synthesized by a metathesis process using [HB(3-(CF3),5-(Ph)Pz)3]Na(THF), CF3SO3Ag, and the corresponding co-ligands. These silver(I) adducts have been characterized by NMR spectroscopy, and by X-ray crystallography. In all cases the Scorpionate is bound to silver in typical κ3-fashion. The X-ray crystallographic data of [HB(3-(CF3),5-(Ph)Pz)3]Ag(η2-C6H6) show that it has a η2-bound benzene molecule. NMR data point to fluxional behavior in solution. The 13C NMR resonance corresponding to the CO moiety of [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) appears as a single peak at δ 177.4ppm and the ν¯co is observed at 2148cm−1. These values indicate the presence of a fairly Lewis acidic silver atom in [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) and significantly diminished Ag→CO π-backbonding. Interesting coupling is observed in the solution 19F and 31P NMR spectra of the Ag(I) adduct [HB(3-(CF3),5-(Ph)Pz)3]Ag(PPh3). A detailed analysis of the spectral and structural features of these complexes has been described herein.

Addition reactions of Cp*Ru(1-5-η-CH2CHCRCHSO2) (R = H, Me) with carbon monoxide, phosphorus, sulfur and nitrogen ligands: Spectroscopic and structural characterization of Cp*Ru(1-2,5-η-butadienesulfonyl)(L)

A series of chiral compounds Cp*Ru(1-2,5-η-butadienesulfonyl)(L) (Cp* = C5Me5; butadienesulfonyl = CH2CHCRCHSO2) were prepared by treating Cp*Ru(1-5-η-CH2CHCRCHSO2) [R = H (1), Me (1Me)] with CO, P(OMe)3, a variety of phosphines, sulfur and nitrogen ligands. All addition reactions were selective, with the exception of PMe3 and P(OMe)3. Even in solution, NMR experiments show a rigid structure for the PPh3 adduct, while PPh2Me adduct shows dynamic behavior. 1H NMR demonstrates the formation and equilibrium reactions for both protio and deuterated adducts of the type Cp*Ru(1-2,5-η-CH2CHCRCHSO2)(L) [R = H, L = CH3CN; R = Me, L = CH3CN, DMSO and Py] in different deuterated solvents, such as C6D6, (CD3)2CO and CD3CN. Addition of deuterated donor ligands into 1 or 1Me occur at faster rate than non-deuterated analogues. X-ray crystal structure data are reported for Cp*Ru(1-2,5-η-CH2CHCRCHSO2)(L) [R = H, L = CO (2), PPh3 (3), PMe3 (6), P(OMe)3 (7), DMSO (8); R = Me, L = PPh3 (3Me), DMSO (8Me), Py (9Me), Py-d5 (9DMe)], as well as the side-product Cp*RuCl(P(CD3)2) (12D).

Half-Sandwich B-Oxy Boratabenzene Ruthenium Complexes: Synthesis, Characterization, and Reactivity of (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, Me)

The first examples of half-sandwich boratabenzene ruthenium complexes have been prepared and well-characterized. Treatment of RuCl2(PPh3)3 with the anionic boratabenzene ligands C5H5BORNa (R = Et, Me) produced the B-alkoxy complexes (η6-C5H5BOR)RuCl((PPh3)2 (R = Et, 1a; Me, 1b), while the reaction of RuCl2(PPh3)3 with the neutral borabenzene–PPh3 adduct C5H5BPPh3 led to the formation of the dinuclear complex (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2), with an oxo-bis(boratabenzene) bridging ligand connected by the B–O–B linkage. The B-hydroxy complex (η6-C5H5BOH)RuCl(PPh3)2 (3) was obtained from the nucleophilic substitution of complexes 1a, 1b, or 2 with water at the boron atoms, and the complexes 1a, 1b, 2, and 3 could interconvert through the nucleophilic substitution reactions. While the reaction of 1a with phenylacetylene did not successfully afford the vinylidene complex as expected, reactions of 1a with terminal ω-alkynols HC≡C(CH2)nCH(R)OH (R = H, n = 1, 2; R = Me, n = 1) proceeded smoothly to provide the neutral oxacyclocarbene complexes (η6-C5H5BOEt)RuCl(═CCH2CH2CH2O)(PPh3) (4), (η6-C5H5BOEt)RuCl(═CCH2CH2CH2CH2O)(PPh3) (5), and (η6-C5H5BOEt)RuCl(═CCH2CH2CH(Me)O)(PPh3) (6) via intramolecular nucleophilic attack of the hydroxyl group to the corresponding vinylidene intermediates.

A new enantiopure d-camphor-derived palladacycle

d-Camphor O-methyloxime (HL, 1) was prepared as a 92:8 mixture of E and Z isomers in 74% yield from d-camphor, methoxyamine hydrochloride and NaOAc in ethanol. Reaction of oxime 1 with Na2PdCl4 in a 2:1 ratio in MeOH at rt provided the coordination complex PdCl2(HL)2 (2) in 67% yield. Cyclopalladation of oxime 1 using Pd(OAc)2 in acetic acid at 80 °C followed by treatment with LiCl furnished the chloro-bridged dimeric cyclopalladated complex [μ-ClPdL]2, 3, in 66% yield. Compound 3 was converted to the mononuclear PPh3 adduct 4 in 98% yield. The proposed structures of new complexes 2–4 were confirmed by 1H, 13C{1H}, DEPT, and 2D NMR spectra. X-ray crystal study of complex 3 revealed the anti geometry of two cyclopalladated ligands as well as the presence of the (sp3)C–Pd bond.

On the ambiguity of 1,3,2-benzodiazaboroles as donor/acceptor functionalities in luminescent molecules

A series of 1,3-bis(perfluoroaryl)-2-(hetero)aryl-1,3,2-benzodiazaboroles, 1,3-(F)Ar2-2-Ar-1,3,2-N2BC6H4 (Ar = Ph, (F)Ar = C6F5 5; Ar = Ph, (F)Ar = 4-C5F4N 6; Ar = Ph, (F)Ar = 4-NCC6F4 7; Ar = 2-C4H3S, (F)Ar = C6F5 8; Ar = 2-C4H3S, (F)Ar = 4-C5F4N 9; Ar = 2-C4H3S, (F)Ar = 4-NCC6F4 10), were synthesised by cyclocondensation of the adducts PhBBr2·PPh3 or 2-thienylBBr2·PPh3 with N,N'-bis(perfluoroaryl)-o-phenylenediamines in the presence of 2,2,6,6-tetramethylpiperidine. Similar treatments of the PPh3 adducts of 4-(1',3'-diethyl-1',3',2'-benzodiazaborolyl)-phenyldibromoborane with the corresponding diamines gave rise to the push-pull compounds, C6H4(NEt)2B-1,4-C6H4-B(N(F)Ar)2C6H4 ((F)Ar = C6F5 11; 4-C5F4N 12) and C6H4(NEt)2B-2,5-C4H2S-B(N(F)Ar)2C6H4 ((F)Ar = C6F5 13; 4-C5F4N 14). The X-ray structures of 8, 11, 12 and 13 were determined. Electronic structure calculations reveal that the LUMOs are located at the perfluoroaryl groups in 5-14; thus the fluorinated benzodiazaborolyl groups are considered as electron-withdrawing moieties. These moieties differ from alkylated benzodiazaborolyl groups which are regarded as donors. The emission spectra for 5-14 show charge transfer bands with significant solvatochromism and large Stokes shifts (6100-12,500 cm(-1) in cyclohexane and 8900-15,900 cm(-1) in CH2Cl2). The emissions of the benzodiazaboroles, 5-10, arise from a different charge transfer (CT) process to the local charge transfer (LCT) process typically found in many fluorescent benzodiazaboroles. This novel remote charge transfer (RCT) process involving the perfluoroaryl groups is supported by CAM-B3LYP computations. The push-pull systems 11-14 here give fluorescent emissions with moderate to high fluorescence quantum yields (65-97%) that arise from the usual LCT process only.

Do Solid-State Structures Reflect Lewis Acidity Trends of Heavier Group 13 Trihalides? Experimental and Theoretical Case Study

Lewis acidity trends of aluminum and gallium halides have been considered on the basis of joint X-ray and density functional theory studies. Structures of complexes of heavier group 13 element trihalides MX(3) (M = Al, Ga; X = Cl, Br, I) with monodentate nitrogen-containing donors Py, pip, and NEt(3) as well as the structure of the AlCl(3)·PPh(3) adduct have been established for the first time by X-ray diffraction studies. Extensive theoretical studies (B3LYP/TZVP level of theory) of structurally characterized complexes between MX(3) and nitrogen-, phosphorus-, arsenic-, and oxygen-containing donor ligands have allowed us to establish the Lewis acidity trends Al > Ga, Cl ≈ Br > I. Analysis of the experimental and theoretical results points out that the solid state masks the Lewis acidity trend of aluminum halides. The difference in the Al-N bond distances between AlCl(3)·D and AlBr(3)·D complexes in the gas phase is small, while in the condensed phase, shorter Al-N distances for AlBr(3)·D complexes are observed with 9-fluorenone, mdta, and NEt(3) donors. The model based on intermolecular (H···X) interactions in solid adducts is proposed to explain this phenomenon. Thus, the donor-acceptor bond distance in the solid complexes cannot always be used as a criterion of Lewis acidity.

Mechanochemical and solution synthesis, X-ray structure and IR and 31P solid state NMR spectroscopic studies of copper(i) thiocyanate adducts with bulky monodentate tertiary phosphine ligands

A number of adducts of copper(I) thiocyanate with bulky tertiary phosphine ligands, and some nitrogen-base solvates, were synthesized and structurally and spectroscopically characterised. CuSCN:PCy3 (1:2), as crystallized from pyridine, is shown by a single crystal X-ray study to be a one-dimensional polymer ...(Cy3P)2CuSCN(Cy3P)2CuSCN... (1) with the four-coordinate copper atoms linked end-on by S-SCN-N bridging thiocyanate groups. A second form (2), obtained from acetonitrile, was also identified and shown by IR and 31P CPMAS NMR spectroscopy to be mononuclear, with the magnitude of the dν(Cu) parameter measured from the 31P CPMAS and the ν(CN) value from the IR clearly establishing this compound as three-coordinate [(Cy3P)2CuNCS]. Two further CuSCN/PCy3 compounds CuSCN:PCy3 (1:1) (3), and CuSCN:PCy3:py (1:1:1) (4) were also characterized spectroscopically, with the dν(Cu) parameters indicating three- and four-coordinate copper sites, respectively. Attempts to obtain a 1:2 adduct with tri-t-butylphosphine have yielded, from pyridine, the 1:1 adduct as a dimer [(Bu(t)3P)((SCN)(NCS))Cu(PBu(t)3)] (5), while similar attempts with tri-o-tolylphosphine (from acetonitrile and pyridine (= L)) resulted in solvated 1:1:1 CuSCN:P(o-tol)3:L forms as dimeric [{(o-tol)3P}LCu((SCN)(NCS))CuL{P(o-tol)3}] (6 and 8). The solvent-free 1:1 CuSCN:P(o-tol)3 adduct (7), obtained by desolvation of 6, was characterized spectroscopically and dν(Cu) measurements from the 31P CPMAS NMR data are consistent with the decrease in coordination number of the copper atom from four (for 6) (P,N(MeCN)Cu,S,N) to three (for 7) (PCuS,N) upon loss of the acetonitrile of solvation. These results are compared with those previously reported for mononuclear and binuclear PPh3 adducts which demonstrate a clear tendency for the copper centre to remain four-coordinate. The IR spectroscopic measurements on these compounds show that bands in the far-IR spectra provide a much more definitive criterion for distinguishing between bridging and terminal bonding than does an often-used empirical rule based on ν(CN) in the mid-IR, which leads to the wrong conclusion in some cases.

Reactivities of the N-Atom-inserted Ligands, NSC(NR2)S2− and SN=C(NR2)S2−, in Iridium(III) Complexes

Abstract Reactions of [Cp*Ir{NSC(NR2)S}] (Cp* = η5-C5Me5, R = Me or Et,) with alkyl halides (MeI or BnBr) in acetonitrile gave the N-alkylated products, [Cp*Ir{R′NSC(NR2)S}]+ (R′ = Me or Bn). These complexes readily reacted with PPh3 to give adducts. In contrast, [Cp*Ir{SN=C(NR2)S}] formed their PPh3 adducts, which gave thermally stable S-alkylated products by reactions with alkyl halides.

Activation of nitrite ion by biomimetic iron(III) complexes

The rate of reaction of NO 2 − ion with various FeIII porphyrins in the presence of PPh3 is shown to depend on the redox potential of the FeIII center. There is a linear relationship between the ease of reduction of the FeIII to FeII and the kinetics for the formation of the FeII porphyrin nitrosyl adduct, with concomitant oxidation of PPh3 to PPh3O. Cyclic voltammograms show reversible one-electron reductions that can be ascribed to the FeIII/FeII couple ranging from E1/2 = −343 to −145 mV (versus Ag/AgCl). The order of increasing half-wave reduction potentials for the FeIII/FeII porphyrin redox centers studied is octaethylporphyrin > etioporphyrin I > deuteroporphyrin IX dimethyl ester > protoporphyrin IX dimethyl ester > α,β,γ,δ-tetraphenylporphyrin. This sequence of redox potentials complements the pseudo first-order kinetics ( ${k_{\rm obs}=2.2\times10^{-3}}$ to ${13\times10^{-3}}$ m s −1) for the oxidation of PPh3 and subsequent FeII porphyrin nitrosyl adduct formation. The rates of reaction of biomimetic FeIII porphyrins with NO 2 − ion demonstrate how metal center redox properties are influenced by the surrounding ligand. In this paper we have elucidated a possible mechanistic control for the rate of this reaction.

Endo-Effect-Driven Regioselectivity in the Cyclopalladation of (S)-2-tert-Butyl-4-phenyl-2-oxazoline

Direct cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline using palladium acetate in acetic acid or acetonitrile provided a mixture of two isomeric compounds, the endo μ-AcO dimeric complex with a C(sp3)−Pd bond and the corresponding exo derivative with a C(sp2)−Pd bond, with the former being the major product. The μ-AcO dimeric complexes were converted to the corresponding μ-Cl analogues 3 and 4 by treatment with LiCl in acetone; the latter compounds were transformed to the corresponding PPh3 adducts 5 and 6. The NMR data suggested the puckered structure of the endo palladacycle in complexes 3 and 5, the twisted λ(S) conformation of the oxazoline ring in 3, 4, and 6, and the δ(S) conformation of the heterocycle in complex 5. The X-ray crystal structure of 5 confirmed the δ(S) conformation of the oxazoline ring in the solid state and the twisted conformation of the palladacycle and revealed a P-propeller chiral configuration of the PPh3 ligand. A series of ab initio quantum chemical calculations were performed on two model compounds generated by replacing the PPh3 ligands with NH3 in complexes 5 and 6. The structures and energies of the two model exo and endo isomers were calculated at the RHF, BLYP, and MP2 levels of theory with a 6-31G* basis for the light atoms and LANL2DZ ECP for the palladium and were found to be comparable. Single point coupled cluster calculations, with single double excitations (CCSD), corroborated the results.

Tridentate Copper Ligand Influences on Heme−Peroxo−Copper Formation and Properties: Reduced, Superoxo, and μ-Peroxo Iron/Copper Complexes

In cytochrome c oxidase synthetic modeling studies, we recently reported a new mu-eta2:eta2-peroxo binding mode in the heteronuclear heme/copper complex [(2L)Fe(III)-(O2(2-))-CuII]+ (6) which is effected by tridentate copper chelation (J. Am. Chem. Soc. 2004, 126, 12716). To establish fundamental coordination and O2-reactivity chemistry, we have studied and describe here (i) the structure and dioxygen reactivity of the copper-free compound (2L)FeII (1), (ii) detailed spectroscopic properties of 6 in comparisons with those of known mu-eta2:eta1 heme-peroxo-copper complexes, (iii) formation of 6 from the reactions of [(2L)FeIICuI]+ (3) and dioxygen by stopped-flow kinetics, and (iv) reactivities of 6 with CO and PPh3. In the absence of copper, 1 serves as a myoglobin model compound possessing a pyridine-bound five-coordinate iron(II)-porphyrinate which undergoes reversible dioxygen binding. Oxygenation of 3 below -60 degrees C generates the heme-peroxo-copper complex 6 with strong antiferromagnetic coupling between high-spin iron(III) and copper(II) to yield an S = 2 spin system. Stopped-flow kinetics in CH2Cl2/6% EtCN show that dioxygen reacts with iron(II) first to form a heme-superoxide moiety, [(EtCN)(2L)FeIII-(O2-)...CuI(EtCN)]+ (5), which further reacts with Cu(I) to generate 6. Compared to those properties of a known mu-eta2:eta1-heme-peroxo-copper complex, 6 has a significantly diminished resonance Raman nu(O-O) stretching frequency at 747 cm(-1) and distinctive visible absorptions at 485, 541, and 572 nm, all of which seem to be characteristics of a mu-eta2:eta2-heme-peroxo-copper system. Addition of CO or PPh3 to 6 yields a bis-CO adduct of 3 or a PPh(3) adduct of 5, the latter with a remaining FeIII-(O2-) moiety.

Silver(I) Complexes of a Sterically Demanding Fluorinated Triazapentadienyl Ligand [N{(C3F7)C(Dipp)N}2]- (Dipp = 2,6-Diisopropylphenyl)

Sterically demanding triazapentadiene [N((C3F7)C(Dipp)N)2]H affords the isolation of thermally stable, two- and three-coordinate silver complexes. The free ligand [N((C3F7)C(Dipp)N)2]H has a W-shaped ligand backbone in the solid state.[N((C3F7)C(Dipp)N)2]H reacts with silver(I) oxide in acetonitrile leading to CH(3)CNAg [N((C3F7)C(Dipp)N)2]HIt features a two-coordinate silver center and a kappa(1)-coordinated triazapentadienyl ligand. This silver acetonitrile complex serves as an excellent precursor to obtain thermally stable, silver isocyanide t-BuNCAg [N((C3F7)C(Dipp)N)2]Hand silver phosphine [[N((C3F7)C(Dipp)N)2]HAgPPh(3) adducts. IR spectroscopic data for the silver(I) isocyanide t-BuNCAg [N((C3F7)C(Dipp)N)2]Hshows nu(CN) at 2219 cm(-)(1). The silver ion coordinates to the triazapentadienyl ligand via the central nitrogen atom. The silver PPh(3) adduct,[N((C3F7)C(Dipp)N)2]HAgPPh(3), was synthesized by treating CH3CNAg [N((C3F7)C(Dipp)N)2]Hwith PPh(3). It displays relatively large Ag-P coupling in the (31)P NMR spectrum. The triazapentadienyl ligand in[N((C3F7)C(Dipp)N)2]HAgPPh(3) acts as a chelating kappa(2)-donor. The Ag-P bond is relatively short (2.3487(10) A).

A Chloro-Bridged (Arene)Ru Complex with a Polymerizable Side Chain

An [(arene)RuCl2](2) complex with a methacrylate side chain (2) has been prepared in two steps using commercially available starting materials. This complex reacts with PPh3, pyridine, or toluidine to give the corresponding mononuclear adducts (3-5). The structure of 4 was determined by single-crystal X-ray diffraction. Complex 2 and the PPh3 adduct 3 were immobilized by copolymerization with divinylbenzene (DVB) or ethyleneglycol dimethacrylate (EGDMA). The resulting EGDMA copolymer was tested as a catalyst in asymmetric transfer hydrogenations. Using (1R,2R)-(-)-N-p-tosyl-1,2-diphenylethylenediamine as the chiral ligand and azeotropic NEt3/HCO2H as the reducing agent, aromatic ketones were converted to the corresponding alcohols with selectivities between 87 and 97% ee.

Aerosol-assisted chemical vapour deposition (AACVD) of silver films from triorganophosphine adducts of silver carboxylates, including the structure of [Ag(O2CC3F7)(PPh3)2

Silver carboxylates [Ag(O2CR): R=Me, tBu, 2,4,6-Me3C6H2], fluorocarboxlyates [Ag(O2CRf): Rf=C3F7, C6F13, C7F15] and their phosphine adducts [Ag(O2CR)·nPR3′: R=Me, tBu, 2,4,6-Me3C6H2, R′=Me, Ph, n=2; R=Me, R′=Me, n=3; Ag(O2CRf).2PPh3, Rf=C3F7, C6F13, C7F15] have been synthesised, characterised spectroscopically and used as precursors in the aerosol-assisted chemical vapour deposition of silver films. All the phosphine adducts produced films, though in general PMe3 adducts, proved more successful than PPh3 analogues. The fluoro-carboxylates and their PPh3 adducts all generated silver films, though the growth rate for the adducts was lower. All these latter films showed carbon impurities while fluorine was also evident in most cases. The X-ray structure of AgO2CC3F7·2PPh3 is also reported.

Degradation and Modification of Metallaboranes: Reactions of the Hexaborane(10) Analoguenido-(PPh3)2(CO)OsB5H9with Phosphines and the Crystal and Molecular Structure of [2,2,2-(PPh3)2(CO)-nido-2-OsB4H7-3-BH2·PPh2Me

The reaction between the osmahexaborane [2,2,2-(PPh3)2(CO)-nido-2-OsB5H9] (1) and bases such as PPh3, PPh2Me, and PMe3 in refluxing CH2Cl2 affords unique adducts of the type [2,2,2-(PPh3)2(CO)-nido-2-OsB4H7-3-BH2·PR3] (2) for which spectroscopic data suggest the presence of a pendent boryl group. This was confirmed by a crystal structure determination for the PPh2Me adduct which shows that 2 is a nido-osmapentaborane with a terminal BH2·PPh2Me moiety on a basal boron atom adjacent to the metal. The reaction is reversible in the case of PPh3 and to a lesser extent PPh2Me, but not for PMe3. Heating the PPh3 adduct affords the osmahexaborane 1, liberating PPh3, but degradation to the osmapentaborane [2,2,2-(PPh3)2(CO)-nido-2-OsB4H8] (6) and BH3·PPh3 competes. The tendency to degrade to phosphine·borane increases markedly down the series R3 = Ph3, Ph2Me, and Me3. When the bidentate bases [1,2-(PPh2)2(CH2)2] and [1,3-(PPh2)2(CH2)3] (abbreviated as dppe and dppp, respectively) are used, two major products are o...

Synthesis, properties and crystal structures of diastereomeric areneruthenium(II) chiral Schiff-base complexes

Diastereomers (SRu,Sc)-1a and (RRu,Sc)-1b, in a ratio of 85: 15 and formulated as [Ru(η-MeC6H4Pri-p)Cl(L*)], have been prepared by treating [{Ru(η-MeC6H4Pri-p)Cl2}2] with the sodium salt of (S)-α-methylbenzylsalicylaldimine (HL*) in tetrahydrofuran at –70 °C. The reaction of 1(1a+1b) with AgClO4 in acetone followed by an addition of PPh3 or 4-methylpyridine (4Me-py) leads to the formation of adducts [Ru(η-MeC6H4Pri-p)(PPh3)(L*)]ClO42[(SRu,Sc)2a, (FRu,Sc)2b] and [Ru(η-MeC6H4Pri-p)(4Me-py)(L*)]ClO43[(SRu,Sc)3a, (RRu,Sc)3b] in the diastereomeric ratios (SRu,Sc) : (RRu,Sc) of 2 : 98 and 76 : 24, respectively. Complex 1 crystallises with equal numbers of 1a and 1b molecules in an asymmetric unit of monoclinic space group P21 with a= 10.854(1), b= 17.090(1), c= 12.808(4)A, β= 110.51(1)°, and Z= 4. The structure was refined to R= 0.0552 and R′= 0.0530 with 2893 reflections having I[gt-or-equal] 1.5σ(I). The absolute configurations of the chiral centres in the optically pure single crystal of the PPh3 adduct have been obtained from an X-ray study. Crystals of formulation [Ru(η-MeC6H4Pri-p)-(PPh3)(L*)]2[ClO4][PF6]·1.5 CHCl3, obtained in presence of both ClO4 and PF6 anions, belong to the non-centric triclinic space group P1 with a= 10.852(2), b= 14.028(1), c= 15.950(2)A, α= 91.51(1), β= 105.97(1), γ= 106.11(1)°, and Z= 2. The final residuals were R= 0.0713, R′= 0.0752 with 7283 reflections having I[gt-or-equal] 2.5σ(I). The crystal structures of 1a,1b, and the PPh3 adduct (2b,2b′) consist of a ruthenium(II) centre bonded to a η-p-cymene, a bidentate chelating Schiff base, and a unidentate ligand (Cl or PPh3). The chirooptical properties of the complexes have been studied using 1H NMR and CD spectral data. The presence of a low-energy barrier for the intermediate involved in these reactions, showing both retention as well as inversion of the metal configuration, is discussed.

Syntheses, structures and redox properties of tetrakis-(μ-benzamidato)dirhodium(II) complexes

The reaction of Rh 2(O 2CCh 3) 4 with an excess of molten PhCONH 2 gave Rh 2(PhCONH) 4(PhCONH 2) 2 ( 1) which contains a dirhodium unit having four bridging benzamidato anions and two axial, neutral benzamide ligands. The compound has been characterized by elemental analysis and infrared spectroscopic data. Reactions of ( 1) with SbPh 3 and pyridine in CH 2Cl 2 ( 2) and Rh 2(PhCONH) 4(py) 2 ( 3), respectively, The structures ( 2) and ( 3) were determined from single-crystal X-ray diffraction data. Compound ( 2) crystallizes in the triclinic space group P1 with half of the dinner and half of the CH 2Cl 2 molecule constituting the asymmetric unit. The cell dimensions for ( 2) are: a = 12.927(7) Å, b = 13.661(5) Å, c = 10.242(6) Å α = 103.45(4)°, β = 99363(4)°, γ = 67.44(4)°, V = 1622(1) Å 3, and Z = 1. The molecule, which has a crystallographic center of inversion, consists of a dirhodium unit bridged by four benzamidato ligands. Each rhodium has one axial ligand, SbPh 3. The RhRh distance is 2.463(1) Å and the RhSb bond length is 2.681(1) Å. The mean RhO and RhN distances are 2.029[4] Å and 2.056[3] Å, respectively. The RhRhSb angle is essentially linear having a value of 176.40(2)°. The compound (3) crystallizes in the orthorhombic space group Pbca with the following unit cell dimensions: a = 16.395(2) Å, b = 18.250(2) Å, c = 11.754(1) Å, α = β = γ = 90.0°, V = 3517(1) Å 3, and Z = 4. Half of the molecule has two pyridine ligands in the axial positions. The equatorial positions are occupied by four anionic benzamidato ligands as in (2). The RhRh distance is 2.437(1) Å. The distance between the rhodium and the axial pyridine nitrogen atoms is 2.227(7) Å and the angle RhRhN(3) is 175.5(2)°. The averages of the RhO and RhN bond lengths are 2.059[6] Å and 2.050[7] Å, respectively. Electron transfer behavior of (1) in different solvents and in the presence of strong neutral donor ligands has been investigated. The compound ( 1) in THF, DMF and CH 3CN exhibits a prominent oxidation wave at E 1/2 = 0.42 Λ (Δ E p = 100 m V), = 0.23 V (58 mV), and +0.36 V (65 mV), respectively. The pyridine, dithiane, PPh3 adducts of ( 1) in CH 2Cl 2 show the first oxidation at +0.39 V (60 m V), +0.48 V (90 mV), +0.46 V (65 mV) and +0.47 V (200 mV), respectively. The PPh 3 adduct displays another quasireversible oxidation at +1.1 V (90 mV). In the THF, the pyridine and PPh 3 adducts undergo oxidation at +0.35 V and +0.60 V, respectively. In DMF, the PPh 3 adduct show oxidation at +0.50 V. In most of the cases, a second, less prominent oxidation wave was observed at slightly higher potential than the prominent oxidation peak. The electronic spectra of the pyridine, PPh 3 and SbPh 3 adducts show low energy absorption at 460 nm (shoulder), 445 nm (shoulder), and 508 nm (ϵ = 1520 M −1 cm −1, respectively. The electronic spectra of ( 1) studied in several polar solvents display bands in the range 440–563 nm.