Low temperature matrix photochemistry of M2(CO)4(μ-S-t-Bu)2 and [M(CO)2Cl2] anions, where M = Rh and Ir

Photolysis of M₂(CO)₄(μ-S-t-Bu)₂, where M = Rh or Ir, in Nujol matrices at ca. 90 K results in simple CO loss to form a tricarbonyl intermediate analogous to that observed for Rh₂(CO)₄(μ-Cl)₂. Photolysis of the anions, [M(CO)₂Cl₂]¹⁻, where M = Rh or Ir, in inert ionic matrices at ca. 90 K, results in CO-loss to form an intermediate analogous to that formed by Rh(CO)₂(i-Pr₂HN)Cl. Finally, photolysis of trans-Ir(CO)(PMe₃)₂Cl in a Nujol matrix at ca. 90 K gives rise to a new species whose carbonyl band is shifted slightly down in energy as has been observed for trans-Rh(CO)(PMe₃)₂Cl. In all cases the iridium compounds behave similarly to the rhodium species although the photon energy for iridium photochemistry is typically above that of the rhodium compounds.     

Synthesis, structures, and characterization of benzildiimine complexes of rhodium(III) and iridium(I)

The reactions of trans-[(PPh₃)₂M(CO)Cl] (M = Rh and Ir) with benzildiimine (H₂BDI = 2) derived from benzil-bis(trimethylsilyl)diimine (Si₂BDI) (1) in a 1:2 and 1:1 molar ratio afforded the cationic bis-benzildiiminato complexes [Rh(PPh₃)₂(HBDI)₂]Cl (3) and the mono-benzildiimine complex [Ir(PPh₃)₂(CO)(H₂BDI)]Cl (4), respectively. Both complexes are fully characterized using IR, FAB-MS, NMR spectroscopy and elemental analysis. The single crystal X-ray structure analysis reveals a distorted octahedral coordination geometry for the Rh(III) in 3 and a highly distorted square pyramidal geometry for Ir(I) in 4. In addition, the solid-state structure of Si₂BDI is reported here for the first time showing the substituents highly twisted because of steric reasons.     

Rhodium(I) complexes with phosphinooxathiane (POT) and phophinooxazolidine (POZ) ligands: the crystal structures of [(POT)Rh(CO)Cl] and [(POZ)Rh(CO)Cl]

The reactions of two equivalents of the ligands POT or POZ with one equivalent of the rhodium complex [Rh(μ-Cl)(CO)₂]₂ afford the complexes [(POT)Rh(CO)Cl] (1) and [(POZ)Rh(CO)Cl] (2), respectively. The crystal structures of both complexes have been determined showing the rhodium centers to be into slightly distorted square planar environments. Preliminary screening of the catalytic systems POT/Rh and POZ/Rh in the asymmetric hydroformylation of styrene has been carried out.     

Equilibrium, solid state behavior and reactions of four and five co-ordinate carbonyl stibine complexes of rhodium. Crystal Structures of trans-[Rh(Cl)(CO)(SbPh3)2], trans-[Rh(Cl)(CO)(SbPh3)3] and trans-[Rh(I)2(CH3)(CO)(SbPh3)2]

The crystal structures of the four-coordinate trans-[Rh(Cl)(CO)(SbPh₃)₂] (1) and the five-coordinate trans-[Rh(Cl)(CO)(SbPh₃)₃] (2) are reported, as well as the unexpected oxidative addition product, trans-[Rh(I)₂(CH₃)(CO)(SbPh₃)₂] (3), obtained from the reaction of 2 with CH₃I. The formation constants of the five-coordinate complex were determined in dichloromethane, benzene, diethyl ether, acetone and ethyl acetate as 163±8, 363±10, 744±34, 1043±95 and 1261±96 M⁻¹, respectively. While coordinating solvents facilitate the formation of the five-coordinate complex, the four-coordinate complex could be obtained from diethyl ether due to the favorable low crystallization energy. The tendency of stibine ligands to form five-coordinate rhodium(I) complexes is attributed mainly to electron deficient metal centers in these systems, with smaller contributions by the steric effects. The average effective cone angle for the SbPh₃ ligand in the three crystallographic studies was determined as 139° with individual values ranging from 133 to 145°.     

Complexes of the imine/thioether mixed-donor ligand 8-methylthioquinoline with d-configurated transition metal centers: synthesis, structures and comparison with complexes of 1-methyl-2-(methylthiomethyl)-1H-benzimidazole

Coordination compounds of chelating 8-methylthioquinoline (MTQ) with the complex fragments Re^I(CO)₃Cl, [Ru^II(bpy)₂]²⁺, [Rh^III(C₅Me₅)Cl]⁺, [Ir^III(C₅Me₅)Cl]⁺, and Pt^IVMe₄ were synthesized and structurally characterized. Whereas the ruthenium(II) complex displays the strongest preference of bonding to N versus S, the compound (MTQ)PtMe₄ shows the most balanced metal-donor bonding within the chelate ring due to a relatively short bond to S (2.319 Å) versus N (2.150 Å). The complex fac-(MTQ)Re(CO)₃Cl exhibits a particularly long metal-sulfur bond at 2.472 Å. Cyclic voltammetry of [(MTQ)Ru(bpy)₂](PF₆)₂ reveals one reversible oxidation to Ru^III and three closely spaced reduction waves for the coordinated ligands. In comparison with the imine/thioether chelate ligand 1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) the MTQ ligand with its more rigid chelate setting N(sp²)-C(sp²)-C(sp²)-S forms generally shorter M-S bonds and displays stronger π acceptor behaviour.     

Investigation of the electron density of iridium(I) Vaska-type complexes using DFT calculations and structural results: Structure of trans-carbonyl-chloro-bis(tricyclohexylphosphine)-iridium(I)

[Ir(CO)Cl(PCy₃)₂] was obtained by the slow attack of 1,2-dichloromethane on (Bu₄N)[Ir₂(μ-Dcbp)(CO)₂(PCy₃)₂] (Dcbp = 3,5-dicarboxylatepyrazole). The Ir-CO, Ir-Cl and Ir-P bond distances are 1.778(10), 2.374(3) and 2.3486(8) Å, respectively. The Ir-P bond distances for a number of different Vaska complexes indicate the shortest bond distances for phoshines containing electron withdrawing groups. An excellent correlation between DFT (OLYP/ZORA/TZP) and experimental structures is obtained as reflected by the RMSD values (H excluded) of between 0.083 and 0.268 Å for the different complexes studied. The calculated Ir-P bond distances and ν(CO) stretching frequencies closely follow the trends obtained from the experimental results.     

Synthetic, electrochemical and structural aspects of a series of ferrocene-containing dicarbonyl β-diketonato rhodium(I) complexes

Treatment of [Rh(β-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO)₂] than by treating [Rh(Cl)(CO)₂]₂ with FcCOCH₂COR, R = CF₃ (Hfctfa), CH₃ (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc = ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C₁₆H₁₀F₃FeO₄Rh], monoclinic, C 2/c(15), a = 13.266(3) Å, b = 19.553(3) Å, c = 13.278(3) Å, β = 100.92(2)°, Z = 8 showed both rotational and translational displacement disorders for the CF₃ group. An electrochemical study revealed that the formal reduction potential, E⁰′, for the electrochemically reversible one electron oxidation of the ferrocenyl group varied between 0.304 (for the fctfa complex) and 0.172 V (for the dfcm complex) versus Fc/Fc⁺ in a manner that could be directly traced to the group electronegativities, χ_R, of the R groups on the β-diketonato ligands, as well as to the values of the free β-diketones. Anodic peak potentials, E_pa,Rh, for the dominant cyclic voltammetry peak associated with rhodium(I) oxidation were between 0.718 (bfcm complex) and 1.022 V (dfcm complex) versus Fc/Fc⁺. Coulometric experiments implicated a second, much less pronounced anodic wave for the apparent two-electron Rh^I oxidation that overlaps with the ferrocenyl anodic wave and that the redox processes associated with these two Rh^I oxidation waves are in slow equilibrium with each other.     

New acylhydridorhodium(III) complexes containing terdentate PNN ligands from the reaction of diolefinic rhodium(I) complexes with o-(diphenylphosphino)benzaldehyde in the presence of chelating amino ligands

[{Rh(cod)Cl}₂] (cod=1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh₂(o-C₆H₄CHO)) (Rh:P=1:1) in the presence of aromatic diamines or 8-aminoquinoline (NN) to give acylhydride [Rh(Cl)(H){PPh₂(o-C₆H₄CO)}(NN)] species. The oxidative addition of PPh₂(o-C₆H₄CHO) in the presence of (NN) and PPh₃ gives cationic species [Rh(H){PPh₂(o-C₆H₄CO)} (PPh₃)(NN)]⁺ containing mutually trans phosphorus atoms. When (NN)=8-aminoquinoline, a mixture of two isomers is obtained. These isomers differ in the nitrogen cis to the hydride, amino or quinolinic. By using Rh:PPh₂(o-C₆H₄CHO)=1:2 stoichiometric ratios, oxidative addition of one PPh₂(o-C₆H₄CHO) and P-coordination of another PPh₂(o-C₆H₄CHO) occurs. The aldehyde group undergoes then a condensation reaction with the coordinated amine to afford new PNN terdentate ligands, phosphine-amino-imine when (NN)=diamine or phosphine-diimine when (NN)=8-aminoquinoline. These reactions give selectively the corresponding complexes [Rh(H){PPh₂(o-C₆H₄CO)}(PNN)]⁺ containing trans phosphorus atoms and the hydride cis to the new imino group. X-ray diffraction studies of the PNN complexes are reported.     

Oxidative addition of methyl iodide to [Rh(CO)2I]2: synthesis, structure and reactivity of neutral rhodium acetyl complexes, [Rh(CO)(NCR)(COMe)I2]2

Reaction of [Rh(CO)₂I]₂ (1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I₂]₂ (R=Me, 3a; ^tBu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography for 3a and 3b. The complexes are centrosymmetric with approximate octahedral geometry about each Rh centre. The iodide bridges are asymmetric, with Rh-(μ-I) trans to acetyl longer than Rh-(μ-I) trans to terminal iodide. In coordinating solvents, 3a forms mononuclear complexes, [Rh(CO)(sol)₂(COMe)I₂] (sol=MeCN, MeOH). Complex 3a reacts with pyridine to give [Rh(CO)(py)(COMe)I₂]₂ and [Rh(CO)(py)₂(COMe)I₂] and with chelating diphosphines to give [Rh(Ph₂P(CH₂)_nPPh₂)(COMe)I₂] (n=2, 3, 4). Addition of MeI to [Ir(CO)₂(NCMe)I] is two orders of magnitude slower than to [Ir(CO)₂I₂]⁻. A mechanism for the reaction of 1 with MeI in MeCN is proposed, involving initial bridge cleavage by solvent to give [Rh(CO)₂(NCMe)I] and participation of the anion [Rh(CO)₂I₂]⁻ as a reactive intermediate. The possible role of neutral Rh(III) species in the mechanism of Rh-catalysed methanol carbonylation is discussed.     

Tripodal oxygen and tripodal nitrogen ligands in hydroformylation reactions: formation of novel rhodium(III) carbonyl bis(acyl) complexes

The rhodium(I) complexes TpmsRh(CO)₂ (1) and TpmsRh(cod) (2) of the tripodal nitrogen ligand tris(pyrazolyl)methanesulfonate, Tpms⁻=[(pz)₃CSO₃]⁻, catalyze the hydroformylation of 1-hexene. Addition of phosphine has a negative effect on the activity. The hydroformylation activity reaches a maximum at about 60 °C. At temperatures above 80 °C hydrogenation becomes an important secondary reaction. When the catalysis is performed at 60 °C in acetone with 1 or 2 as catalyst precursor all of the rhodium is recovered in the form of the rhodium(III) bis(acyl) complex TpmsRh(CO)(COC₆H₁₃)₂ (9). A similar behaviour is observed with rhodium(I) complexes bearing the tripodal oxygen ligand L_OMe⁻=[(cyclopentadienyl)tris(dimethylphosphito-P) cobalt O,O^′,O″]⁻. In this case all of the rhodium is transformed into L_OMeRh(CO)(COC₆H₁₃)₂ (10). These hitherto unknown bis(acyl) rhodium(III) complexes show the same catalytic activity as the rhodium(I) starting compounds.     

Synthesis and characterisation of ferrocene-containing β-diketonato complexes of rhodium(I) and rhodium(III)

The synthesis of new β-diketonato rhodium(I) complexes of the type [Rh(FcCOCHCOR)(CO)₂] and [Rh(FcCOCHCOR)(CO)(PPh₃)] with Fc=ferrocenyl and R=Fc, C₆H₅, CH₃ and CF₃ are described. ¹H, ¹³C and ³¹P NMR data showed that for each of the non-symmetric β-diketonato mono-carbonyl rhodium(I) complexes, two isomers exist in solution. The equilibrium constant, K_c, which relates these two isomers in an equilibrium reaction, are concentration independent but temperature and solvent dependent. Δ_rG, Δ_rH and Δ_rS values for this equilibrium have been determined and a linear relationship between solvent polarity on the Dimroth scale and K_c exists. The relationship between RhP bond lengths, d(RhP), and ³¹P NMR peak positions as well as coupling constants ¹J(³¹P¹⁰³Rh) has been quantified to allow calculation of approximate d(RhP) values. Variations in d(RhP) for [Rh(RCOCHCOR′)(CO)(PPh₃)] complexes have also been related to the group electronegativities (Gordy scale) of the terminal β-diketonato R groups trans to PPh₃. A measure of the electron density on the rhodium centre of [Rh(RCOCHCOR′)(CO)(PPh₃)] may be expressed in terms of the IR carbonyl stretching wave number, ν(CO), the sum of the group electronegativities of the R and R′ groups, (χ_R+χ_R′), or the observed pK_a^′ values of the free β-diketones RCOCH₂COR^′. An empirical relationship between ν(CO) and either pK_a^′ or (χ_R+χ_R′) has also been quantified.     

Effect of outer sphere anions on the structure and color of nitrosylpentaamminechromium complex

Three kinds of crystalline compounds containing the nitrosylpentaamminechromium complexes [Cr(NO)(NH₃)₅]²⁺(A) were obtained: chloride ACl₂ (red-orange), chloride perchlorate ACl(ClO₄) (brown), and perchlorate A(ClO₄)₂ (green). The cause of the color change of the complex A with the change of outer sphere anions was sought using X-ray structural data of ACl₂, ACl(ClO₄), and A(ClO₄)₂. Crystal data: ACl₂, orthorhombic, space group Cmcm, a=10.0236 (9) Å, b=9.098 (3) Å, c=10.357(1) Å, V=944.5 (5) ų, Z=4; ACl(ClO₄), tetragonal, space group P4/nmm, a=7.6986 (8) Å, c=9.9566(8) Å, V=590.1 (1) Å^3,Z=2; A(ClO₄)₂, orthorhombic, space group Pnma, a=15.760 (2) Å, b=11.480(2) Å, c=7.920 (2) Å, V=1432.9 (4) ų, Z=4. The complex cation in ACl₂ has a distorted octahedral structure with a linear CrNO moiety. The short CrN (nitrosyl) distance of 1.692 (7) Å indicates the presence of multiple bonding between the chromium atom and the nitrogen atom in the nitrosyl group. The interatomic distances and angles within the complex cations hardly change with the change of the counter anions, while the distances between the complex cations in each crystal increase in the order ACl₂<ACl(ClO₄)<A(ClO₄)₂. The bulky perchlorate anions seems to separate the complex cations, while smaller chloride anions are not large enough to separate them. The distance (3.213(5) Å) between O(NO) and N(NH₃ in the adjacent complex cation) is rather short in the crystal of ACl₂, and there are six hydrogen bonds, where the NO group is surrounded by four NH₃ ligands. The distance (4.002(5) Å) between O(NO) and N(NH₃) is much longer in the crystal of A(ClO₄)₂, indicating the presence of no hydrogen bonding. In the crystal of ACl(ClO₄) the distance (3.452(4) Å) between O(NO) and N(NH₃) is in between those of ACl₂ and A(ClO₄)₂. The presence of hydrogen bonding between O(NO) and N(NH₃ in the adjacent complex cation) seems to cause the color change with the change of outer sphere anions.     

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium-carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR₃)(CO)Cl]⁺ (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh₃)(CO)Cl]PF₆, [Ru(tpy)(P(p-tolyl)₃)(CO)Cl]PF₆ and [Ru(tpy)(PPh₃)(CH₃CN)Cl]PF₆ were determined by X-ray crystallography.     

Structural and spectroscopic studies of Mo 2Cl 4(PR 3) 4 compounds with phosphines of varied basicity

The influence of the π acidity of the PR ₃ ligands in Mo ₂Cl ₄(PR ₃) ₄ compounds on the strength of the Mo−Mo quadruple bond has been studied for twenty such compounds. The main result is that reasonable correlations exist between the δ → δ* transition energy (TE) and two accepted measures of π-acidity for phosphine ligands, namely Tolman's v̄(CO) IR criterion and Bodner's Δδ(CO) ¹³C NMR criterion. For a plot of TE versusv̄(CO) a correlation coefficient of −0.892 was obtained employing data for 15 compounds. For TE versus Δδ(CO), a correlation coefficient of 0.982 was obtained for 13 compounds (excluding three for which a steric factor may be important). An attempt to correlate the Mo−Mo bond lengths with π-acidity was unsuccessful since few compounds were obtained in satisfactory form for structure determination, and for the four compounds with known structure there was no correlation. In addition to the PMe ₃ compound whose structure was previously known, those of the PEt ₃, PMe ₂Ph and PHPh ₂ compounds have been determined and are reported here.     

Quantifying the trans influence of triphenylarsine. Crystal and molecular structures of cis-[PtCl2(SMe2)(AsPh3)] and cis-[PtCl2(AsPh3)2]·CHCl3

Reaction between a mixture of cis-trans-[PtCl₂(SMe₂)₂] and 1 equiv. AsPh₃ in chloroform gives cis-[PtCl₂(SMe₂)(AsPh₃)] crystallizing in P2₁/n with a=10.397(2), b=14.876(3), c=13.956(3) Å, β=90.86(3)° and Z=4. Selected geometrical parameters are PtAs 2.3531(10), PtS 2.262(2), PtCl (trans to S) 2.301(2), PtCl (trans to As) 2.328(2) Å and SPtAs 88.85(6), SPtCl(2) 90.77(8), AsPtCl(1) 91.07(6) and ClPtCl 89.42(7)°. cis-[PtCl₂(AsPh₃)₂]·CHCl₃ crystallizes in P2₁/c with a=20.557(4), b=9.5951(19), c=20.147(4) Å, β=96.77(3)° and Z=4. Selected geometrical parameters are PtAs(1) 2.3599(9), PtAs(2) 2.3770(9), PtCl(1) (trans to As(1)) 2.3515(18), PtCl(2) (trans to As(2)) 2.3251(18) Å and AsPtAs 97.87(3), As(1)PtCl(2) 88.67(5), As(2)PtCl(1) 84.30(5) and ClPtCl 89.32(7)°. By comparison with related structures from the literature the following trans influence series was established PMe₂Ph>PPh₃>AsPh₃≈SbPh₃>Me₂SO≈SMe₂≈SPh₂>NH₃≈olefin>Cl⁻>MeCN.     

Electrochemical reduction properties of A-frame compounds and crystal structure of Pd2(dppm)2(Me)2(Br) dimer

Two series of A-frame complexes, [Pd₂(dppm)₂(R)₂(μ-X)]⁺ (R = Me and X = Cl, Br, I, H; R = Mes and X = Br, I), were investigated by cyclic voltammetry (CV). The 2-electron reduction potentials for the first series increase from I (−1.10), Br (−1.17), Cl (−1.25) to H (−1.65 V versus SCE, in CHCl₃), as well as in the second series; Br (−1.35) and I (−1.38 V versus SCE, in THF). The nature of the LUMO where the electron reduction takes place is qualitatively addressed by DFT on the corresponding model complexes [Pd₂(H₂PCH₂PH₂)₂(R)₂(μ-X)]⁺. The LUMO and (LUMO + 1) of the halide derivatives exhibit the presence of Pd d_x²-y² atomic orbitals interacting in an anti-bonding fashion with the n-donor orbitals of X⁻, P, and Me⁻, explaining in part the observed reactivity upon reduction. The X-ray structure of [Pd₂(dppm)₂(Me)₂(μ-Br)]⁺ compound exhibits the typical A-frame structure with a Pd?Pd non-bonding distance of 3.036(1) Å, and long Pd-Br bonds of 2.5623(5) and 2.5793(5) Å.     

Siloxane functionalized cyclopentadienyl-molybdenum complexes: Synthesis, characterization and catalytic application

A series of compounds of the type CpMoR(CO)₃ and RCpMo(CO)₃CH₃ (R = (CH₂)₃Si(OMe)₃ or CH₂Si(OEt)₃), containing a (CH₂)_nSi(OR)₃ functionality as a side chain, either fixed to the metal itself or to the cyclopentadienyl ligand are prepared and spectroscopically characterized. These molecules are applicable as precursors for both homogeneous and heterogeneous phase catalysts. Their homogeneous catalytic activity in the olefin epoxidation is in the same order of magnitude as that of their methyl and chloro analogues of the types CpMo(CO)₃R and CpMo(CO)₃Cl.     

Kinetics of CO substitution in Co4(CO)12 and Rh4(CO)12

The kinetics of rapid CO substitution by PPh₃ in Co₄(CO)₁₂ and Rh₄(CO)₁₂ have been examined by stopped-flow and low temperature FT-IR methods. In Co₄(CO)₁₂ rapid (k_obs ∼ 1.8 s⁻¹) substitution of CO occurs after a 1–15 s induction period at 28 °C in C₆H₅Cl solvent by a catalytic process. Addition of PPh₃ to Rh₄(CO)₁₂ yields Rh₄(CO)₁₁(PPh₃) according to a predominantly second order rate law k₁[Rh₄- (CO)₁₂] + k₂[Rh₄(CO)₁₂][PPh₃] with k₁ = 25 ± 11 s⁻¹ and k₂ = 2.97 ± 0.27 X 10⁴ M⁻¹ s⁻¹ at 28 °C. Substitution of a second CO ligand also occurs rapidly with k₁ = 0.15 ± 0.09 s⁻¹ and k₂ = 6.54 ± 0.07 X 10² M⁻¹ s⁻¹ at 28 °C. The reactivity of Rh₄(CO)₁₂ toward associative substitution is 10⁴– 10¹¹ faster than for the Co and Ir analogues, In Rh₄(CO)₁₁(PPh₃) the increase in CO substitution rates over Co and Rh analogues is 10²–10⁷. The ordering of associative substitution rates Co << Rh >>> Ir in these clusters exaggerates the trend seen in mononuclear metal complexes.     

Transition metal nitrosyls as nitrosylation agents. IV. 51V NMR characteristics of dinitrosyl and carbonylmononitrosyl vanadium complexes

The action of [Co(X)(NO)₂]₂ (X = Cl, Br, L) on [V(H)(CO)_6?nL_n] (L = 1/ndi- and tritertiary phosphine; n = 2, 3) in thf yields [V(CO)_5?n(NO)L₂] and [V(NO)₂(thf)₄]X as the two main products. Thf is easilty replaced by other ligands L′, leading to the complexes cis-[V(NO)₂(thf)_4?nL′_n]X, where n = 1 to 4. In the case of L′= CNR (R = Cy, iPr, tBu), the species [VX(NO)₂L′₃] are formed. The presence of X in the first coordination sphere is established by the normal halogen dependence (Cl < Br < I) of ⁵¹V shielding.δ(⁵¹V) values have been obtained for the two series of complexes and compared with δ of other nitrosylvanadium species, including [VX(NO)L′₄]X. for [V(NO)₂L′₄]br, ⁵¹V shielding increases in the sequence {O} < {S} < NR₃ < NCMe < AsEt₃ < SbEt₃ < PEt₂Ph < P(OMe)₃ < CNR, reflecting a general increase of shielding as the polarizability of the ligand function increases and its electronegativity decreases. Superimposed effects arising from electronic influences (PEtPh₂) < PMe₃ < P(OMe)₃ and steric conditions (chelate-4 ring < 7 ring < 6 ring < 5 ring) are also discussed. Steric factors are especially pronounced in the [V(CO)₃(NO)Ph₂P(CH₂)_mPPh₃] series (m = 1–4). The thermo-labile parent compound, [V(CO)₅NO], has been characterized by its δ(⁵¹V) = ?1489 ppm at 245 K.     

Palladium-catalysed asymmetric allylation and complex formation involving P,N-bidentate diamidophosphites with 1,3,2-diazaphospholidine cycles

New chiral P,N-bidentate 1,3,2-diazaphospholidine ligands were obtained by one-step phosphorylation of (2S,3S)-2-(ferrocenylideneamino)-3-methylpentan-1-ol and (4S,5S)-(−)-2-methyl-4-hydroxymethyl-5-phenyl-2-oxazoline. Complexation of the new ligands with [Rh(CO)₂Cl]₂ and [Pd(allyl)Cl]₂ was found to give chelate complexes [Rh(CO)Cl(η²-P,N)] and , correspondingly. With the new P,N-ligands, up to 70% ee was achieved in the asymmetric Pd-catalysed sulfonylation of 1,3-diphenyl-2-propenyl acetate with sodium p-toluenesulfinate. In the enantioselective alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate, up to 91% enantioselectivity was achieved by using complexes as chiral catalysts.