PR3 Ligands Research Articles

Ligation of phosphorus ligands to silver(I). 2. Electronic and steric effects in the coordination of one to four P(OR)3 and PR3 ligands

Synthese et etude par RMN de 31 P des complexes {Ag[P(OPh) 3 ] 3 }BF 4 , {Ag[P(O-iPr) 3 ] 3 }BPh 4 , {Ag[P(O-i-Pr) 3 ] 4 }X (X=BF 4 , BPh 4 ), {Ag[P(O-t-Bu) 3 ] 2 }BF 4 {Ag[P(O-t-Bu) 3 X} (X=I, Cl, CN), {Ag[P(O-t-Bu) 3 ] 2 NO 3 } et {Ag[P(O-Me 2 C 6 H 3 -2,6) 3 ] BF 4 }

Elektrochemische Synthesen, IX [1]Darstellung CO-freier Metallkomplexe / Electrochemical Synthesis, IX [1] Preparation of CO Free Metal Complexes

Abstract The electrochemical synthesis of metal acetylacetonates (M = Cr, Mo, V, Ti) from metal anodes and acetylacetone is reported. In the presence of oxygen the oxo compounds OM(acac)2 are formed for M = Mo, V and Ti instead of M(acac)3. The electrochemical production of| Ni(PPh3)4 and Fe(PMe3)4 starting from Ni(acac)2 and Fe metal, respectively, has been investi­gated. Successful carbonylation to Ni(CO)n(PPh3)4-n (n = 1,2) or Fe(CO)m(PMe3)5-m (m = 2, 3) proves the hypothesis that replacement of PR3 ligands by CO takes place after reduction of the central metal to the oxidation state 0.

Synthesis of platinum–manganese and –rhenium complexes with bridging thiocarbonyl ligands; crystal structure of [MnPt(µ-CS)(CO)2(PMePh2)2(η-C5H5)

Addition of the compounds [M(CO)2(CS)(η-C5H5)](M = Mn or Re) to the species [Pt(C2H4)(PR3)2] in light petroleum at 0 °C affords the dimetal complexes [MPt(µ-CS)(CO)2(PR3)2(η-C5H5)](M = Mn, PR3= PMe2Ph or PMePh2; M = Re, PR3= PMe2Ph). The structure of [MnPt(µ-CS)(CO)2(PMePh2)2(η-C5H5)] has been established by X-ray diffraction. Crystals are monoclinic, space group P21/c, Z= 4, in a unit cell with a= 16.655(4), b= 9.684(3), c= 21.409(5)A, β= 114.57(2)°. The structure was refined to R 0.043 (R′ 0.043) for 4 358 independent absorption-corrected intensities with 2.9 ⩽ 2θ⩽ 50°(Mo-KαX-radiation) collected at room temperature. The Pt–Mn bond [2.641(1)A] is bridged by the CS ligand [C–Mn 1.878(8), C–Pt 2.015(8)A] and strongly semi-bridged by a CO group [Mn–C–O 154.0(8)°; C–Mn 1.798(8), C–Pt 2.220(9)A]. Variable-temperature n.m.r. studies revealed that the compounds [MPt(µ-CS)(CO)2(PR3)2(η-C5H5)] undergo dynamic behaviour in solution, and possible mechanisms for site exchange of PR3 and CO ligands are discussed. Treatment of [MnPt(µ-CS)(CO)2(PMe2Ph)2(η-C5H5)] with [OMe3][BF4] gave the salt [MnPt(µ-CSMe)(CO)2(PMe2Ph)2(η-C5H5)][BF4] containing the µ-CSMe thiocarbyne ligand.

Facile lithiation of co-ordinated t-methylphosphines in bis-(2,6-dimethoxyphenyl)nickel(II) complexes

Reactions of n-butyl-lithium with the bis-(2,6-dimethoxyphenyl)nickel(II) complexes, trans-[Ni{C6H3(OMe)2-2,6}2(PR3)2](PR3= PMe3 and PMe2Ph), in di-ethyl ether resulted in the facile lithiation at the methyl carbon in the PR3 ligands.

ChemInform Abstract: CARBONYLATION OF (PTX(PH)(PR3)2). NEW INTERMEDIATES IN THE CO INSERTION SEQUENCE

Phosphorus-31 n.m.r. studies of the reaction of trans-[PtX(Ph)(PR3)2] with carbon monoxide have led to the identification of several new intermediates and reaction pathways involved in the CO insertion process to produce trans-[PtX(COPh)(PR3)2]. Carbonyl addition forms a metastable five-co-ordinate compound in non-polar solvents, which eliminates a halide to form ionic species trans-[Pt(Ph)(CO)(PR3)2]X in polar solvents. Loss of PR3 from five-co-ordinate intermediates produces two isomers of [PtX(Ph)(CO)(PR3)] which convert to the remaining isomer with Ph trans to PR3 before migration of Ph proceeds to form a benzoyl complex. A direct carbonyl insertion route from a five-co-ordinate intermediate also operates, independently of the phosphine elimination pathways, and this becomes the predominant pathway with more nucleophilic PR3 ligands. The use of elemental sulphur to remove PR3 from the reaction mixtures was instrumental in identifying some intermediates, and this method has potential synthetic value in replacing PR3 by weaker ligands at platinum.

Carbonylation of [PtX(Ph)(PR3)2]. New intermediates in the CO insertion sequence

Phosphorus-31 n.m.r. studies of the reaction of trans-[PtX(Ph)(PR3)2] with carbon monoxide have led to the identification of several new intermediates and reaction pathways involved in the CO insertion process to produce trans-[PtX(COPh)(PR3)2]. Carbonyl addition forms a metastable five-co-ordinate compound in non-polar solvents, which eliminates a halide to form ionic species trans-[Pt(Ph)(CO)(PR3)2]X in polar solvents. Loss of PR3 from five-co-ordinate intermediates produces two isomers of [PtX(Ph)(CO)(PR3)] which convert to the remaining isomer with Ph trans to PR3 before migration of Ph proceeds to form a benzoyl complex. A direct carbonyl insertion route from a five-co-ordinate intermediate also operates, independently of the phosphine elimination pathways, and this becomes the predominant pathway with more nucleophilic PR3 ligands. The use of elemental sulphur to remove PR3 from the reaction mixtures was instrumental in identifying some intermediates, and this method has potential synthetic value in replacing PR3 by weaker ligands at platinum.

Zur kenntnis Metallorganischer ytterbium-komplexe mit direkter ytterbium—phosphor-bindung: einflüsse der ligandenvariation auf die optischen spektren

Extensive studies of the system Cp 3Yb III /PR 3, (Cp ' η 5-C 5H 5; R  alkyl, ary] and/or H) indicate that 1/1 adducts of the type CP 3YbPR 3 are readily formed in solution; most attempts of their isolation are, however, hampered by decomposition reactions. In the course of the NIR/VIS spectroscopic characterisation of the adducts in solution we found that variations of the ligand field experienced by the central ion appear to a lesser degree governed by the actual basicity of the PR 3-ligand than by essentially steric influences. Complimentary studies of the system Cp 2Yb IIICI/LiPR 2, suggest that the main decomposition products of the adducts Cp 3YbPR 3 are oligomeric rather than mono- or binuelear species of the type [Cp 2YbPR 2]η.

Solution Studies of the Dynamic Stereochemistry of Palladium(II) Carboxylate Complexes

A series of dimeric tertiary phosphine carboxylate complexes of palladium(II) of the general types [(PR3)Pd(O2CR)2]2 and [(PR3)Pd(O2CR)(O2CR)]2 have been synthesized and struc-turally characterized. The dynamic stereochemistry of the complexes where PR3 = Me2PhP has been investigated using variable temperature n.m.r. techniques. Exchange of the stereochemically nonequivalent methyl groups of the coordinated Me2PhP ligand occurs via a solvent assisted process involving ring opening of the "Pd2(OCO)2" bridged structure. For the trifluoroacetate complexes solution equilibria between monomer and dimer are readily apparent at low temperatures in the 19F n.m.r. The observed equilibrium constants are a function of the solvent and the size of the PR3 ligand. The reaction of [(PMe2Ph)Pd(O2CCF3)2]2 with excess AgO2CCF3 gives an unusual crystalline complex of stoichiometry Ag[(PMe2Ph)Pd(O2CCF3)3]. A quantitative measure of the ability of a coordinated carboxylate to stabilize intermediate species via chelation has been obtained from a variable temperature n.m.r. study of [(Π-2-methylallyl)Pd(O2CR)(Me2PhP)] (R=CH3, CH2Cl, CHCl2, CCl3, CF3, CMe3, CPh3, CH2Ph).

Further N.M.R. Studies of the Dynamic Stereochemistry of π-Allylic Palladium(II) – Tertiary Phosphine Systems

A series of cations of the type 1,2-bis(diphenylphosphino)ethane(π-all)palladium(II) (all = allyl, 2-methylallyl, 2-tert-butylallyl, 1-methylallyl, 1,1-dimethylallyl, syn-1-tert-butyl-2-methylallyl) have been isolated as PF6− and/or BF4− salts. Variable temperature n.m.r. data fully substantiate the proposal that pyridine promoted exchange of syn and anti proton sites in such complexes occurs via a π → σ → π mechanism that involves consecutive SN2 ligand substitutions. Comparison of this variable temperature n.m.r. data with that obtained for the complexes 1,2-bis(diphenylphosphino)ethane(π-all)palladium(II) chloride (prepared in situ) has shown that the chloride ion, functioning as a nucleophile, is also effective in promoting π → σ → π reactions. Studies of bis(dimethylphenylphosphine) (π-1,1-dimethylallyl)palladium(II) chloride in CDCl3 below −30° have shown that rapid consecutive SN2 substitution reactions, in which chloride acts as a nucleophile, are also occurring in systems containing monodentate tertiary phosphine ligands. As such the PR3 promoted syn–syn and anti–anti proton site interchange observed in complexes of the type [(π-2-methylallyl)PdCl(PR3)] has been reinterpreted in terms of consecutive ligand substitution reactions involving PR3 and Cl ligands instead of the original proposal which involved an in plane rotation of the π-allylic ligand.