Evidence of colloidal rhodium formation during the biphasic hydroformylation of 1‐octene with thermoregulated phase‐transfer phosphine rhodium(I) catalyst

A thermoregulated phase‐transfer (TRPT) Rh(I) complex catalyst A prepared from Rh(acac)(CO)₂ and a thermoregulated ligand CH₃(OCH₂CH₂)_mPPh₂ (M_w = 918) was applied to the biphasic hydroformylation of 1‐octene, and a high activity with an aldehyde yield of 97.5% was demonstrated. After three recycling steps, the aldehyde yield gradually decreased. Transmission electron microscopy (TEM) revealed that after the first cycle Rh colloids were generated in situ in the aqueous phase, and in subsequent runs Ostwald ripening occurred. An independently prepared colloidal Rh(0) TRPT catalyst D also exhibited high hydroformylation activity under identical experimental conditions, and after two times of recycling an activity decrease was also observed. It is suggested that in situ from Rh(acac)(CO)₂ colloidal Rh particles are generated, which demonstrate thermomorphic behaviour and a high hydroformylation activity. Subsequently, agglomeration processes result in an activity decay, as observed in the TRPT Rh(I) complex catalyst system. Copyright © 2005 John Wiley & Sons, Ltd.     

Bildung und reaktivität kationischer rhodiummethyl- trimethylphosphit-komplexes;eine weitere metall- organische variante der Michaelis—Arbuzov-reaktion

C₅H₅Rh(P(OCH₃)₃]₂ (I) reacts CH₃I and (CH₃)₃OBF₄ at low temperatures to give [C₅H₅RhCH₃{P(OCH₃)₃}₂]X (II: X = I; III: X = BF₄). Elimination of CH₃I from II yields the phosphonate complex C₅H₅RhCH₃[P(OCH₃)₃]- [P(O)(OCH₃)₂] (IV) which reacts with (CH₃)₃OBF₄ to give III.     

Oxidative addition of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH2)3CCH3)]: an experimental and computational study

The reaction rate of the oxidative addition and CO insertion steps of methyl iodide with [Rh(PhCOCHCOPh)(CO)(P(OCH₂)₃CCH₃)] are presented. Large negative experimental values for the activation entropy and results from a density functional theory computational chemistry study indicated trans addition of the CH3I to [Rh(PhCOCHCOPh)(CO)(P(OCH₂)₃CCH₃)]. A study of the molecular orbitals gives insight into the flow of electrons during the oxidative addition reaction. CO insertion leads to a square pyramidal [Rh(PhCOCHCOPh)(P(OCH₂)₃CCH₃)(COCH₃)(I)] acyl product with the COCH3 moiety in the apical position. The strong electron donation of the P(OCH₂)₃CCH₃ ligand accelerates the oxidation addition step of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH₂)₃CCH₃)] by ca. 265 times faster (at 35°C) than that of the Monsanto catalyst, but inhibits the CO insertion step.     

A density functional theory study of the oxidative addition of methyl iodide to square planar [Rh(acac)(P(OPh)3)2] complex and simplified model systems

The transition state for the oxidative addition reaction [Rh(acac)(P(OPh)₃)₂] + CH₃I, as well as two simplified models viz. [Rh(acac)(P(OCH₃)₃)₂] and [Rh(acac)(P(OH)₃)₂], are calculated with the density functional theory (DFT) at the PW91/TZP level of theory. The full experimental model, as well as the simplified model systems, gives a good account of the experimental Rh-ligand bond lengths of both the rhodium(I) and rhodium(III) β-diketonatobis(triphenylphosphite) complexes. The relative stability of the four possible rhodium(III) reaction products is the same for all the models, with trans-[Rh(acac)(P(OPh)₃)₂(CH₃)(I)] (in agreement with experimental data) as the most stable reaction product. The best agreement between the theoretical and experimental activation parameters was obtained for the full experimental system.     

Atran-analoge Verbindungen III. Atran-analoge Verbindungen des Typs Me2DCH2CH2OSi(Me) (OCH2CH2)2D′ Me (I) und Me2DCH2CH2OSi(Me) (OCH2CH2D′Me2)OCH2CH2D″ Me2 (II) (MeCH3; D,D′, D‴N,P, As)

Atrane-analogous Compounds. III. Atrane-analogous Compounds of the Type Me₂DCH₂CH₂OSi(Me)(OCH₂ CH₂)₂ D′Me (I) and Type Me₂DCH₂CH₂OSi(Me) OCH₂CH₂₂D″Me₂ (II) (Me?CH₃; D, D′, D″?N, P, As) Atrane analogous compounds I and II (Abb. 1) have been prepared by condensation reactions of trifunctional silanes RSiX₃ (X?Cl, OEt, NMe₂) with N-methyldiethanolamine, ß-chloroethanol, ß-dimethylaminoethanol, and ß-dimethylarsanoethanol according to eqn. (1) to (3) and reaction schemes of Figs. 2 and 3, respectively. For compounds of type I weak N→Si adduct bonding is indicated for the MeN-donor of the eight-membered ring by significant shifts of the MeNCH₂ and OCH₂ proton n.m.r. signals. For compounds of type II there is no n.m.r. evidence for D→Si interactions. In spite of equal Lewis acidity of the Si atoms differences in adduct formation are observed for cage, ring, and acyclic podand systems, which can be explained mainly by entropy effects connected to the formation of five-membered rings.     

Neue Rhodium(I)‐Komplexe mit Donor/Akzeptor‐Chelatliganden

Alternative Ligands. XXXVI. Novel Rhodium(I) Complexes with Donor/Acceptor Chelating Ligands In order to generate metal base/Lewis‐acid interactions in rhodium(I) phosphane complexes the binuclear complex [Rh(CO)₂Cl]₂ was reacted in benzene with dipod ligands of the type R₂M′(OCH₂PMe₂)_x(CH₂CH₂PMe₂)_2–x (R = F, Me; M′ = Si, Ge; x = 0–2) using the Ziegler dilution principle with the aim to produce mononuclear compounds in which with formation of five‐membered chelate rings in principle Rh → M′ contacts are possible. The reactions of ligands 1 – 7 (Table 1) with [Rh(CO)₂Cl]₂ proceed under CO elimination and, in spite of large turnovers, lead to a variety of products 8 – 14 (Table 1), in case of 11 , 13 and 14 accompanied by degradation of the corresponding ligands. Intact ligands are present in the 16‐membered rings of the binuclear complexes 8 – 10 and 12 , for which, due to the molecular structure, Rh → M′ interactions can be excluded. In the reaction of Me₂Si(OCH₂PMe₂)₂ ( 4 ) with [Rh(CO)₂Cl]₂ the unusual binuclear system 11 with a central Rh₂O₂ four‐membered ring and two RhO(SiMe₂OCH₂PMe₂) six‐membered rings is formed. Small amounts of the mononuclear compounds Rh(CO)Cl(Me₂PCH₂OH)₂ ( 13 ) and Rh(CO)Cl₃(Me₂PCH₂OH)₂ ( 14 ), respectively, are obtained in crystalline form from the reaction mixtures of [Rh(CO)₂Cl]₂ with Me₂Ge(OCH₂PMe₂)(CH₂CH₂PMe₂) ( 6 ) or Me₂Ge(OCH₂PMe₂)₂ ( 7 ). The new complexes were characterized by analytic (C, H), spectroscopic (NMR, IR, MS) and, except for 12 , by single crystal structural analyses.     

35Cl,79Br,81Br,and127I NQR spectra of HgHal2·XCH2CH2X complexes,X = OCH3, SCH3, and N(CH3)2

Conclusions From the NQR spectra of the halides HgHal₂ -D (Hal = Cl, Br, or I; D = SCH₃CH₂CH₂SCH₃, N(CH₃)₂ CH₂CH₂N(CH₃)₂, or OCH₃CH₂CH₂OCH₃) it follows that in their complexing ability the sulfur, nitrogen, and oxygen atoms can be arranged in the order: S > N > I. A structure with equivalent halogens is realized in the considered complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1895–1897, August, 1973.The authors consider it their duty to thank G. K. Semin for his valuable advice and interest in the work.     

Heteronuclear Alkoxide Compounds Containing Copper and Alkaline Earth Metals

The tetrameric Cu(β-diketonate) alkoxide complex [Cu(thd)(OCH₂CH₂OCH₃)]₄ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate; 1a ) reacts with the alkaline earth metal alkoxides [M(OCH₂CH₂OCH₃)₂] (M = Ca, 2a ; M = Sr, 2b ; M = Ba, 2c ) to yield the heteronuclear compounds [Cu₂M(thd)₃(OCH₂CH₂OCH₃)₃] (M = Ca, 6a ; M = Sr, 6b ). These heterometallic complexes were also obtained in the reaction of 1a and the mixed Ca and Sr complexes of β-diketonate-alkoxide [M_x(thd)_y(OCH₂CH₂OCH₃)_2x?y] (M = Ca, x = 7, y = 6, 3 ; M = Sr, x = 5, y = 3, 4 ), respectively. In comparison, 1a reacts with the analogous [Ba(thd)(OCH₂CH₂OCH₃)] ( 5a ) to yield a[Ba₂Cu₂(thd)₄(OCH₃)₄(HOCH₂CH₂OCH₃)₂] species ( 8a .) The in situ prepared mixed-ligand Ba Compounds [Ba(thd)OR)] (R = CH₂CH₂OCH₂CH₂OCH₃, ( 5b ); R = CH₂CH₂CH₂OCH₃ ( 5c ) react with the corresponding Cu complexes [Cu(thd)(OR)]_n (R = CH₂CH₂OCH₂CH₂OCH₃), n = 4 ( 1b ); R = CH₂CH₂OCH₂CH₂OCH₃ ( 8b ); R = CH₂CH₂CH₂OCH₃ ( 8c ). However, [Cu(hfd)(OCH₂CH₂OCH₃)]₄ (hfd = 1,1,1,5,5,5,-hexafluoroacetylacetonate; 1e ) is converted in the presence of 2a–c to the simple metathesis products [M(hfd)₂] (M = Ca, Sr, Ba) and [Cu(OCH₂CH₂OCH₃)₂]. Crystalline [Ba₂Cu₂(hfd)₂(thd)₂(OCH₂CH₂CH₂OCH₃)₄(HOCH₂CH₂CH₂OCH₃)₂] ( 9 ) was isolated from the reaction of 1a with in situ prepared [Ba((hfd)OCH₂CH₂CH₂OCH₃)] ( 5d ) in 2-, methoxyethanol. X-Ray crystallographic structure determinations are reported for 6a , 6b , 8b , and 8c .     

Schwingungsspektren und Kraftkonstanten der Übergangsreihen OP (CH3)3–OP(OCH3)3 und SP(CH3)3–SP(OCH3)3

Vibrational Spectra and Force Constants of the Series OP(CH₃)₃? OP(OCH₃)₃ and SP(CH₃)₃? SP(OCH₃)₃ The vibrational spectra of OP(CH₃)₂(OCH₃), OP(CH₃)(OCH₃)₂, SP(CH₃)₂(OCH₃), and SP(CH₃)(OCH₃)₂, are recorded and assigned to the normal vibration. The valence force constants are calculated by a simplified force field. The results are disscussed for both series and compared with former results.     

Geminal interactions in ClZ(CH3)2X molecules (Z = C, Si, Ge) according to ab initio calculations

The structure and electronic parameters of ClZ(CH₃)₂X molecules (Z = C, Si, Ge, X = CH₃, OCH₃) were calculated by the RHF/6–31G(d) and RHF/6–311G(d,p) methods with full geometry optimization; calculations of ClZ(CH₃)₂OCH₃ molecules were also performed by the RHF/6–31G(d) method with partial geometry optimization. The ³⁵Cl NQR frequencies calculated from the populations of less diffuse 3p constituents of valence p orbitals of chlorine [RHF/6–31G(d)] were in agreement with the experimental values. The ³⁵Cl NQR frequencies for molecules with X = OCH₃ are lower than those for molecules with X = CH₃ (the Z atom being the same), due mainly to direct through-field polarization of the Z-Cl bond, induced by the effect of unshared electron pair of the oxygen atom in the trans position with respect to that bond. The difference in the ³⁵Cl NQR frequencies decreases in going from Z = C to Z = Si, Ge, in parallel with variation of the Z-Cl bond polarization as the size of Z increases.     

Synthesen zweizähniger P‐Donor/Sn‐Akzeptor‐Liganden: Koordinationsstudien mit Cp*Rh(CO)2 und CpRh(C2H4)2

Alternative Ligands. XXXV. Syntheses of Bidentate P‐Donor/Sn‐Acceptor Ligands: Coordination Experiments with Cp*Rh(CO)₂ and CpRh(C₂H₄)₂ Donor/acceptor ligands Me₂Sn(CH₂CH₂PMe₂)₂ ( 1 ) and Me₂Sn(OCH₂PMe₂)₂ ( 2 ) have been prepared by radical reaction of Me₂PVi with Me₂SnH₂ and by substitution of chlorine in Me₂SnCl₂ or of ethoxy groups in Me₂Sn(OEt)₂ by MOCH₂PMe₂ (M = Li, Na) and HOCH₂PMe₂, respectively. 2 cannot be isolated in pure form from the product mixture because, due to condensation reactions, the “ladder structure” [Me₂Sn(OCH₂PMe₂)₂OSnMe₂]₂ ( 3 ) is formed. The molecular structure of 3 was determined by X‐ray diffraction studies of single crystals. Attempts to produce the thiophosphoryl derivative of 3 result in the degradation of the ladder structure giving the thermally labile phosphane sulfide Me₂Sn(OCH₂P(S)Me₂)₂. Ligands 1 and 2 besides Me₂PCH₂CH₂SnMe₃ ( 4 ) have been used for the preparation of rhodium(I) complexes from Cp*Rh(CO)₂ ( 5 ) or CpRh(C₂H₄)₂ ( 10 ) as educts. The thermal reaction of 5 with 4 yields Cp*Rh(CO)PMe₂CH₂CH₂SnMe₃ ( 6 ), that of 5 with 1 a mixture of the mononuclear derivative Cp*Rh(CO) · PMe₂CH₂CH₂SnMe₂CH₂CH₂PMe₂ ( 7 ) and the binuclear complex [Cp*Rh(CO)PMe₂CH₂CH₂]₂SnMe₂ ( 8 ). The related system [Cp*Rh(CO)PMe₂CH₂O]₂SnMe₂ produced by reaction of 5 with 2 can only be detected in solution but, because of some side‐products, was not fully characterized. From 10 and 4 a mixture of mono‐ and disubstituted products, CpRh(C₂H₄)PMe₂CH₂CH₂SnMe₃ ( 11 ) and CpRh(PMe₂CH₂CH₂SnMe₃)₂ ( 12 ), is obtained. Reaction of 1 with 10 yields a mixture of the complexes CpRh(C₂H₄)PMe₂CH₂CH₂SnMe₂CH₂CH₂PMe₂ ( 13 ) and CpRh(Me₂CH₂CH₂)₂SnMe₂ ( 14 ). Some of the NMR data (¹³C, δδ_Sn) of 14 can be interpreted in terms of the expected Rh → Sn interaction. A definite proof by X‐ray diffraction on single crystals, so far, was not possible.     

Darstellung und katalytische Eigenschaften von Rhodium(I)-Komplexsalzen des Typs [Rh(COD)o-Py(CH2)2P(Ph)(CH2)3ZR)]PF6 (Z = O,NH)

Preparation and Catalytic Properties of Rhodium(I) Complex Salts of the Type [Rh(COD)(o-Py(CH₂)₂ P(Ph)(CH₂)₃ZR)]PF₆ (Z = O, NH) . In dichloromethane solutions were reacted [Rh(COD)Cl]₂ (COD = cis,cis-1.5-cyclooctadiene) with each of the four new ligands of the type o-Py(CH₂)₂P(Ph)(CH₂)₃ZR in the presence of the halogen scavenger TIPF₆ at 0°C to complex salts [Rh(COD) (o-Py(CH₂)₂P(Ph)(CH₂)₃ZR]PF₆ (ZR = OC₂H₅, I ; OPh, II ; NHPh, III ; NHcyclo? C₆H₁₁, IV ). The Rh¹ complex cation in the obtained compounds I – IV coordinates besides the bedentate COD group the ligand donor atoms P und pyridinic N and the remaining donor atom Z is uncoodinated in an assumed square planar ligand geometry at the Rh central atom. In 1.4 dioxane solutions the complex catalysts I – IV polymerize at 25°C the substrate phenylacetylene (PA) to polyphenylacetylene (PPA): values of TON [h^?1] between 352 ( I ) and 876 ( IV ), and average molecular weights M_w (GPC measurements) between 238 000 ( I ) and 199 900 ( IV ). These given values exhibit a dependency on the ZR group in complexes I – IV . The microstructure of isolated PPA is cis-transoidal. It is formed stereospezific and, based on MNDO calculations, is thermodynamically favoured. For the purpose of comparison, from both the newly synthesized compounds of the type [Rh(COD)DBN- (or DBU)Cl] (DBN = 1.5-Diazabi-cyclo[4.3.0.]non-5-en, DBU = 1.8-Diazabicycl0[5.4.0]- undec-7-en) was obtained a larger value of TON with 1292 (or 1327) [h^?], but a lower value of M, with 166200 (or 131200). These catalysts including I –IV polymerize PA to PPA at a lower reaction temperature with improved selectivity and larger values of M_w as hitherto known catalyst systems.     

Some reactions of π-cyclopentadienylbis(triphenylphosphine) rhodium(I)

Reactions of π-cyclopentadienylbis(triphenylphosphine)rhodium(I) (I) with alkyl halides, olefins, acetylenes, carbon disulfide and elementary sulfur have been investigated. Methyl iodide gives the oxidative-addition product [πC₅H₅ Rh(PPh₃)₂CH₃]I but isopropyl iodide produces the alkyl substituted-cyclopentadienyl complex (π-i-C₃H₇C₅H₄)Rh(PPh₃)I₂. Under a nitrogen atmosphere, olefins and acetylenes give compounds of the composition π-C₅H₅ Rh(PPh₃)(L) (L = CH₂—CHCN, CH₂—CHCO₂CH₃, CH₃O₂—CCOO₂CH₃).In the presence of air, however, complexes of the composition π-C₅H₅Rh(L)₂ (L = CH₂—CHCN, CH₂—CHCO₂CH₃, CH₂—C(CH₃)CN) and π-C₅H₅Rh(L)₃ (L = CH₃O₂ CC—CCO₂ CH₃, PhC—CCO₂ CH₃) are formed. The reaction of carbon disulfide or sulfur with (I) also gives the compounds π-C₅H₅Rh(PPh₃)(L) (L = CS₂, CS₃, S₅).     

Periodic mesoporous organosilica grafted palladium organometallic complex: efficient heterogeneous catalyst for water‐medium organic reactions

Water‐medium organic reactions were studied over periodic mesoporous silica (PMO) containing Pd(II) organometallic complex. This heterogeneous catalyst was achieved by Pd(II) compound coordinated with the PPh₂‐ligand onto the pore surface of phenylene‐bridged PMO support. This catalyst displayed ordered mesoporous channels, which ensured the high dispersion of Pd(II) active sites and the convenient diffusion of reactant molecules into the pore channels. Meanwhile, the phenyl group in the pore wall of PMO could enhance the surface hydrophobicity which promoted the adsorption of organic reactant molecules on the catalyst in aqueous environment. As a result, this elaborated catalyst exhibited comparable activity and selectivity with the corresponding PdCl₂(PPh₃)₂ homogeneous catalyst in the water‐medium organic reactions, and could be used repeatedly, showing a good potential in industrial applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of ferrocenylalkoxygermatranes and crystal structures of FcCH2OGe (OCH2CH2)3N and FcCH(CH3)OGe(OCH2CH2)3N1

Germatranes bearing a ferrocenylalkoxyl moiety have been obtained by the reaction of HOGe(OCH₂CH₂)₃N with various ferrocenyl alcohols. A convenient new synthesis method of FcCH₂OGe(OCH₂CH₂)₃N was reported. FcCH₂OGe(OCH₂CH₂)₃N was prepared in 93% yield when FcCH₂OH reacted with HOGe(OCH₂CH₂)₃N in chloroform at room temperature in the presence of molecular sieves (3 Å) as a dehydrating agent. All compounds were characterized by elemental analysis, ¹H NMR and IR spectroscopy. The molecular structures of FcCH₂OGe(OCH₂CH₂)₃N and FcCH(CH₃)OGe(OCH₂CH₂)₃N have been determined by X‐ray diffraction. The antitumor activities of FcCH₂OGe(OCH₂CH₂)₃N and p‐FcC₆H₄CH₂OGe(OCH₂CH₂)₃N were determined. Copyright © 2005 John Wiley & Sons, Ltd.     

Oxidative addition of dimethylphosphite to iridium(I) and rhodium(I) complexes: Stereoselective reduction of 4-t-butylcyclohexanone

Dimethylphosphite, (CH₃O)₂P(O)H, adds oxidatively to iridium(I) and rhodium(I) complexes to give hydrido-iridium(III) or -rhodium(III) dimethylphosphonate complexes. A complex Ir(H)Cl[P(O)(OCH₃)₂][P(OH)(OCH₃)₂]₃ obtained from [IrCl(C₈H₁₄)₂]₂ and dimethylphosphite catalyses the stereo-selective reduction of 4-t-butylcyclohexanone to $\text{97}\text{3}$cis/trans-4-t-butylcyclohexanol, the ratio being identical with that obtained using the Henbest catalyst iridium(IV) chloride, phosphorous acid or one of its esters, and aqueous isopropanol.     

A comparison of local structures in crystalline P(EO)3LiCF3SO3 and glyme-LiCF3SO3 systems

The newly discovered crystal structures of CH₃(OCH₂CH₂)OCH₃(LiCF₃SO₃)₂, monoglyme:(LiTf)₂, and CH₃(OCH₂CH₂)₃OCH₃(LiCF₃SO₃)₂, triglyme:(LiTf)₂, are briefly described. The coordination of lithium cations and the CF₃SO₃⁻ anions in these structures is compared with the cation and anion coordination in the crystalline phase of high molecular weight P(EO)₃LiCF₃SO₃. Comparison is also made with the previously reported crystalline phase of CH₃(OCH₂CH₂)₂OCH₃LiCF₃SO₃, diglyme:LiTf. A tendency to form trans-gauche-trans conformations for the bond order -O-C-C-O- is noted in adjacent ethylene oxide sequences interacting with a five-coordinate lithium ion.     

Investigations on the Synthesis,Structural Characterization,and Crystal Structures of Three Diiron and Tetrairon Azadithiolate Complexes

Three diiron and tetrairon azadithiolate complexes as models for the active site of [FeFe] hydrogenase were prepared. Reaction of complex Fe₂(SCH₂OH)₂(CO)₆ and NH₂CH₂CH₂CH₂OCH₃ resulted in the diiron azadithiolate hexcarbonyl complex Fe₂[(SCH₂)₂NCH₂CH₂CH₂OCH₃](CO)₆ ( 1 ) in moderate yield. Furthermore, treatment of complex 1 with mono phosphine ligand PPh₃ and diphosphine ligand Ph₂PCH₂CH₂PPh₂ in the presence of decarbonylation reagent Me₃NO · 2H₂O yielded the phosphine‐substituted azadithiolate complexes Fe₂[(SCH₂)₂NCH₂CH₂CH₂OCH₃]CO)₅(PPh₃) ( 2 ) and {Fe₂[(SCH₂)₂NCH₂CH₂CH₂OCH₃](CO)₅}₂(Ph₂PCH₂CH₂PPh₂) ( 3 ) respectively. The new complexes 1 – 3 were fully characterized by elemental analysis, IR, ¹H, ¹³C, ³¹P NMR spectroscopy and X‐ray crystallography. It is worthy to note that the crystallographic studies show the unusual difference of the methoxypropanyl substituent on the N atom of complexes 1 and 2 , largely because of the affection of phosphine ligand PPh₃. In addition, complex 1 was found to be a catalyst for H₂ production under electrochemical condition.     

Unterscheidung enantiotoper/diastereotoper Protonen und regioselektive Spinentkopplung in metallorganischen Komplexen mit Hilfe von Shiftreagenzien

Dimethylphosphonate HP(O)(OCH₃)₂ and the dimethylphosphonate complexes [(C₅H₅)MX{P(O) (OCH₃)₂}{P(OCH₃)₃}] (M=Co, Rh; X=I, CH₃), [(C₅H₅)Co{P(O)(OCH₃)₂}₂ {P(OH)(OCH₃)₂}] and [(C₅H₅)Ni{P(O)(OCH₃)₂}{P(OCH₃)₃}] have been studied by ¹H n.m.r. spectroscopy. The chiral shift reagent Eu(tfc)₃ has been used to resolve the spectra of the enantiomeric mixtures of [(C₅H₅)MX {P(O)(OCH₃)₂}{P(OCH₃)₃}]. The substituent X in [(C₅H₅)MX{P(O)(OCH₃)₂}{P(OCH₃)₃}] has a strong influence on the anischrony of the diastereotopic phosphonate methyls in the presence of Eu(tfc)₃. The same shift reagent also resolves the enantiotopic protons in HP(O)(OCH₃)₂ but not in [(C₅H₅)Ni {P(O)(OCH₃)₂}{P(OCH₃)₃}]. The addition of Eu(tfc)₃ to [(C₅H₅)Ni{P(O)(OCH₃)₂}{P(OCH₃)₃}] eliminates the ³J(POCH) coupling in the coordinated dimethylphosphonate. The cobalt complex [(C₅H₅)Co{P(O)(OCH₃)₂}₂{P(OH)(OCH₃)₂}] reacts as a chelating ligand with Eu(tfc)₃ to give one tfcH per Eu(tfc)₃.     

Gas-phase ion–molecule reactions in dilute mixtures of dimethyl ether in krypton. Bimolecular and clustering reactions

The results of high-pressure variable-temperature and variable ionizing electron energy studies of gas-phase ion-molecule reactions of dimethyl ether in krypton are presented. Near the ionization threshold a series of peaks corresponding to (CH₃OCH₃)_nH⁺ (n = 1-4) clusters are observed. At higher ionizing electron energies, two new series of peaks appear, corresponding to [CH₃OCH₂]⁺(CH₃OCH₃)_n and [(CH₃)₃O]⁺ (CH₃OCH₃)_n clusters. The onium ion, [(CH₃)₃O]⁺, has been previously reported at elevated temperatures under methane chemical ionization conditions. It was suggested that the onium ion is formed by reaction of (CH₃)₂OH⁺ with CH₃OCH₃ with subsequent elimination of methanel, i.e. by fragmentation of an adduct ion. The present results strongly suggest that, under our conditions, [CH₃OCH₂]⁺ rather than thermal (CH₃)₃OH⁺, is the precursor to [(CH₃)₃O]⁺.