Platinum-catalyzed double silylations of alkynes with bis(dichlorosilyl)methanes

Bis(dichlorosilyl)methanes 1 undergo the two kind reactions of a double hydrosilylation and a dehydrogenative double silylation with alkynes 2 such as acetylene and activated phenyl-substituted acetylenes in the presence of Speier’s catalyst to give 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes 4 as cyclic products, respectively, depending upon the molecular structures of both bis(dichlorosilyl)methanes (1) and alkynes (2). Simple bis(dichlorosilyl)methane (1a) reacted with alkynes [R¹-CC-R²: R¹ = H, R² = H (2a), Ph (2b); R¹ = R² = Ph (2c)] at 80 °C to afford 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 as the double hydrosilylation products in fair to good yields (33-84%). Among these reactions, the reaction with 2c gave a trans-4,5-diphenyl-1,1,3,3-tetrachloro-1,3-disilacyclopentane 3ac in the highest yield (84%). When a variety of bis(dichlorosilyl)(silyl)methanes [(Me_nCl_3 − nSi)CH(SiHCl₂)₂: n = 0 (1b), 1 (1c), 2 (1d), 3 (1e)] were applied in the reaction with alkyne (2c) under the same reaction conditions. The double hydrosilylation products, 2-silyl-1,1,3,3-tetrachloro-1,3-disilacyclopentanes (3), were obtained in fair to excellent yields (38-98%). The yields of compound 3 deceased as follows: n = 1 > 2 > 3 > 0. The reaction of alkynes (2a-c) with 1c under the same conditions gave one of two type products of 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes (4): simple alkyne 2a and terminal 2b gave the latter products 4ca and 4cb in 91% and 57% yields, respectively, while internal alkyne 2c afforded the former cyclic products 3cc with trans form between two phenyl groups at the 3- and 4-carbon atoms in 98% yield, respectively. Among platinum compounds such as Speier’s catalyst, PtCl₂(PEt₃)₂, Pt(PPh₃)₂(C₂H₄), Pt(PPh₃)₄, Pt[ViMeSiO]₄, and Pt/C, Speier’s catalyst was the best catalyst for such silylation reactions.     

Synthesis,spectral characterization and biological evaluation of novel 1-(2-(4,5-dimethyl-2-phenyl-1H-imidazol-1-yl)ethyl)piperazine derivatives

A simple, highly useful synthesis of 1-(2-(4,5-dimethyl-2-phenyl-1H-imidazol-1-yl)ethyl)piperazine derivatives is achieved by a four component cyclo condensation of diacetyl, aromatic aldehyde, 2-(piperazin-1-yl)ethanamine and ammonium acetate using SO₄²⁻/Y₂O₃ as a catalyst in ethanol. The synthesized compounds were characterized by IR, ¹H and ¹³C NMR and mass spectral studies. All the synthesized compounds were screened for their in vitro antimicrobial studies. Among the newly synthesized compounds 5d, 5e, 5h and 5m showed excellent antibacterial and antifungal activities when compared to the standard drugs.     

From bis(silylamino)tin dichlorides via di(1-alkynyl)-bis(silylamino)tin to new heterocycles by 1,1-organoboration

Bis(silylamino)tin dichlorides 1 [X₂SnCl₂ with X=N(Me₃Si)₂ (a), N(9-BBN)SiMe₃ (b), N(^tBu)SiMe₃ (c), and N(SiMe₂CH₂)₂ (d)] were prepared from the reaction of two equivalents of the respective lithium amides (Li-a-d) with tin tetrachloride, SnCl₄, or from the 1:1 reaction of the respective bis(amino)stannylene with SnCl₄. The compounds 1 react with two equivalents of lithium alkynides LiCCR¹ to give the di(1-alkynyl)-bis(silylamino)tin compounds X₂Sn(CCR¹)₂, 2 (R¹=Me), 3 (R¹=^tBu), and 4 (R¹=SiMe₃). Problems were encountered, mainly with LiCC^tBu as well as with 1b, since side reactions also led to the formation of 1-alkynyl-bis(silylamino)tin chlorides 5-7 and tri(1-alkynyl)(silylamino)tin compounds 8 and 9. 1,1-Ethylboration of compounds 2-4 led to stannoles 10, 11, and in the case of propynides, also to 1,4-stannabora-2,5-cyclohexadiene derivatives 12. The molecular structure of the stannole 11b (R¹=SiMe₃) was determined by X-ray analysis. The reaction of 2a and d with triallylborane afforded novel heterocycles, the 1,3-stannabora-2-ethylidene-4-cyclopentenes 14. These reactions proceed via intermolecular 1,1-allylboration, followed by an intramolecular 1,2-allylboration to give 14, and a second intramolecular 1,2-allylboration leads to the bicyclic compounds 15.     

Silver(I) catalyzed oxidation of thiocarboxylic acids into the corresponding disulfides and synthesis of some new Ag(I) complexes of thiophene-2-thiocarboxylate

Aromatic thiocarboxylic acids in presence of a base on treatment with silver nitrate under ambient conditions were oxidized to the corresponding disulfides. The reactions were found to be catalyzed by Ag⁺ ions. The catalytic oxidation is paralleled by the Ag(SCOAr) complex formation reaction which could be considerably subsided by adjustment of the reaction conditions. Attempts to use [Ag(PPh₃)₂]⁺ or [Ag(PPh₃)]⁺ ion as the catalyst were unsuccessful as these resulted in the formation of the corresponding thiocarboxylate complexes. The products, ArCOSSCOAr (1, 2), [Ag(SCOAr)(PPh₃)₂] (3, 4) and [Ag(SCOAr)(PPh₃)]₄ (5) (Ar = C₆H₅, C₄H₃S) were characterized by single crystal X-ray analysis. Compounds 3 and 4 are monomeric while 5 is a cyclic tetramer in the crystalline phase.     

Intramolecular asymmetric C–H insertion of N-arylalkyl,N-bis(trimethylsilyl)methyldiazoamides mediated by chiral rhodium(II) catalysts. Synthesis of (R)-β-benzyl-γ-aminobutyric acid

The enantio- and site-selectivity of the intramolecular C–H insertion reactions of acyclic N-arylalkyl, N-bis(trimethylsilyl)methyl α-diazoacetamides, and α-carboalkoxy-α-diazoacetamides 1a–g, catalyzed by chiral Rh(II) carboxamidates and Rh(II) carboxylates were studied. In general, the reaction showed good to excellent chemoselectivity. Regioselectivity for most of the reactions was high, but was also found to be influenced by the structure of the diazo substrate and the chiral Rh(II) catalyst employed. The highest enantioselectivity for the reactions catalyzed by chiral Rh(II) carboxamidates was 69% and Rh₂(4R-MEOX)₄ was found to be the most effective. For the chiral Rh(II) carboxylate catalyzed reactions, the highest ee obtained was 75% and Rh₂(S-PTTL)₄ is the optimal catalyst. The method was applied toward the synthesis of a GABA analogue, (R)-β-benzyl-γ-aminobutyric acid.     

Radikalkomplexe vom typ Cp(CO)2MnXR. (X = S,Se)

CpMn(CO)₂ER (E = S, Se) compounds [1] belong to the rare radical derivatives of the CpMn(CO)₂ fragment. We describe herein the syntheses, electrochemistry, and organometallic reactions of CpMn(CO)₂SR ¹ (1a: R = t-C₄H₉, 1b: R = 2-adamantyl) and CpM(CO)₂SePh (2).     

Synthesis,crystal structure and reactivity of a new pentacoordinated chiral dioxomolybdenum(VI) complex

The novel tridentate chiral ligand 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-yl]}pyridine (1) was readily prepared by reaction of 2,6-dilithiopyridine with (R)-(−)-fenchone. Reaction of 1 with [MoO₂(acac)₂] resulted in the formation of the new metal-oxo five-coordinated complex [MoO₂(ONO)] (2) [ONO = (1 – 2H)]. The reactivity of 2 has been studied and the derivatives [MoS₂(ONO)] (3) and [MoO(O₂)(ONO)] (4) were prepared. The compounds 1–4 have been characterised by ¹H and ¹³C{¹H} NMR, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. The behaviour of 2 as catalyst in oxotransfer and in nucleophilic substitution of propargylic alcohols reactions has been tested.     

New cadmium(II) halides modified by N-heterocyclic molecules

Under the solvothermal condition, the reaction of CdI₂, bpp and KI at pH = 8 afforded compound [CdI₂(bpp)] (bpp = 1,2-bis(4-pyridyl)propane) 1, while at the ambient conditions, the reactions of CdX₂, dabco and KX at pH = 4–5 produced compounds [H₂(dabco)][CdBr₄]·H₂O (dabco = 1,4-diazabicyclo[2,2,2]octane) 2 and [(Hdabco)CdI₃] 3. X-ray single-crystal diffraction analysis reveals that (i) compound 1 possesses a one-dimensional (1-D) zigzag chain structure. The large volume bpp molecule controls the Cd²⁺ ion to adopt a tetrahedral geometric configuration; (ii) both compounds 2 and 3 are mononuclear. Interestingly, in the same pH environments, dabco was in situ diprotonated in compound 2, while dabco was in situ monoprotonated in compound 3. The templating effect as well as the X⁻ ion maybe plays a key role in the protonated degree for dabco in an acidic environment. The photoluminescence analysis indicates that compound 1 emits the strong green light, which should be attributed to a combination of two types of charge transfers: the charge transfer between Cd²⁺ and I⁻; the charge transfer between Cd²⁺ and bpp.     

Oxidative addition of MeI to cationic Rh(I) carbonyl complexes with pyridyl bis(carbene) ligands

A series of cationic Rh(I) carbonyl complexes of the form [Rh(CO)(L)]PF₆ (where L = 2,6-bis (alkylimidazol-2-ylidene)-pyridine; alkyl = Me (1a), Et (1b), CH₂Ph (1c)) have been prepared by the reactions of [Rh(CO)₂(OAc)]₂ with diimidazolium pyridine salts in the presence of NEt₃. The ν(CO) values for 1 are ca. 1982 cm⁻¹, indicating that the N-heterocyclic carbene ligands impart high electron density on the Rh(I) centres, despite the overall cationic charge. Each of the Rh(I) complexes reacts with MeI to form two isomeric Rh(III) methyl species, and a third unidentified species. Kinetic measurements on the MeI oxidative addition reactions give second-order rate constants (MeCN, 25 °C) of 0.0927, 0.0633 and 0.0277 M⁻¹ s⁻¹ for 1a, 1b and 1c, respectively. Comparison of these data with those for related Rh(I) carbonyl complexes shows that 1 have remarkably high nucleophilicity for cationic species.     

Synthesis and characterization of insoluble cobalt(II), nickel(II), zinc(II) and palladium(II) Schiff base complexes: Heterogeneous catalysts for oxidation of sulfides with hydrogen peroxide

The condensation reaction of 1,2-bis(2′-aminophenoxy)benzene with 2-pyridinecarbaldehyde in a mole ratio of 1:2 gives a new Schiff base ligand (L). Four Schiff base complexes, CoL(NO₃)₂ (1), NiLCl₂ (2), ZnL(NO₃)₂ (3) and Pd₂LCl₄ (4) have been prepared by direct reaction of the ligand (L) and appropriate metal salts. The Schiff base ligand (L) has been characterized by IR, ¹H NMR and ¹³C NMR spectroscopy and elemental analysis. Also, all complexes have been characterized by IR and XRD spectroscopy techniques and elemental analysis. The synthesized complexes have very poor solubility in all polar and non-polar solvents such as: H₂O, MeOH, EtOH, CH₃CN, DMSO, DMF, CHCl₃, CH₂Cl₂, THF, etc; therefore, they have been used as heterogeneous catalysts. Catalytic performance of the complexes was studied in oxidation of thioanisole using hydrogen peroxide (H₂O₂) as the oxidant. Various factors including the reaction temperature, amount of oxidant and catalyst amount were optimized. The palladium Schiff base complex, Pd₂LCl₄ (4), shows better catalytic activity than other complexes. Therefore, the Pd(II) Schiff base complex has been used as a catalyst for oxidation of different sulfides to their corresponding sulfones in acetonitrile with hydrogen peroxide as the oxidant. The palladium Schiff base complex, Pd₂LCl₄ (4), has shown a very good recyclability, up to five times, without any appreciable decreases in catalytic activity and selectivity.     

Schiff bases of 1′-hydroxy-2′-acetonaphthone containing chalcogen functionalities and their complexes with and (p-cymene)Ru(II), Pd(II), Pt(II) and Hg(II): Synthesis, structures and applications in C-C coupling reactions

Schiff bases of 1′-hydroxy-2′-acetonaphthone (HAN) containing chalcogen functionalities, 1-HO-C₁₀H₆-2-CH₃)CN-(CH₂)_nEC₆H₄-4-R (R = H or OMe; n = 2 or 3; E = S (L¹-L²), Se (L³-L⁴) or Te (L⁵-L⁶)) have been synthesized in yield 90-95%. They show characteristic ¹H, ¹³C{¹H} ⁷⁷Se{¹H} and ¹²⁵Te{¹H} (in case of selenated and tellurated species, respectively) NMR spectra. Their complexation with Pd(II), Pt(II), Hg(II) and (p-cymene)Ru(II) has been explored. The single-crystal structures of ligands L¹, L³ and L⁶ and complexes of Pd(II) with L¹, L², L³ and L⁵ have been determined. The geometry of Pd is close to square planar in all the complexes and the ligands coordinate in a uni-negative tridentate mode. The Pd-N bond lengths are in the range 1.996(7)-2.019(5) ?. The Pd-Se bond distance is 2.3600(5) ? whereas Pd-Te is 2.5025(7) ?. The Pd(II) complexes of L¹-L⁵ have been found promising as homogeneous catalyst for Heck and Suzuki reactions. The yields obtained were up to 85%.     

Chelate structures of 5-(H/Br)-2-hydroxybenzaldehyde-4-allyl-thiosemicarbazones (H2L): Synthesis and structural characterizations of [Ni(L)(PPh3)] and [Ru(HL)2(PPh3)2]

The reactions of 5-R-2-hydroxybenzaldehyde-4-allyl-thiosemicarbazone {R: H (L¹); Br (L²)} with [M^II(PPh₃)nCl₂] (M = Ni, n = 2 and M = Ru, n = 3) in a 1:1 molar ratio have given stable solid complexes corresponding to the general formula [Ni(L)(PPh₃)] and [Ru(HL)₂(PPh₃)₂]. While the 1:1 nickel complexes are formed from an ONS donor set of the thiosemicarbazone and the P atom of triphenylphosphine in a square planar structure, the 1:2 ruthenium complexes consist of a couple from each of N, S and P donor atoms in a distorted octahedral geometry. These mixed-ligand complexes have been characterized by elemental analysis, IR, UV–Vis, APCI-MS, ¹H and ³¹P NMR spectroscopies. The structures of [Ni(L²)(PPh₃)] (II) and [Ru(L¹H)₂(PPh₃)₂] (III) were determined by single crystal X-ray diffraction.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

Di-t-butyl(ferrocenylmethyl)phosphine: air-stability, structural characterization, coordination chemistry, and application to palladium-catalyzed cross-coupling reactions

Di-t-butyl(ferrocenylmethyl)phosphine (1) has been isolated and structurally characterized. This ligand was found to be reasonably air stable as a solid and it has been shown to possess electron donating ability similar to that of tri-i-propylphosphine. A palladium catalyst bearing this ligand performed room temperature Suzuki-Miyaura coupling reactions with aryl bromides. Modest Heck coupling reactivity with aryl bromides was also observed at 100 °C. Complexation of 1 with Pd₂(dba)₃ led to formation of (1)₂Pd⁰. Addition of 4-bromoanisole to solutions containing both 1 and Pd₂(dba)₃ led to formation of an oxidative addition product when 1:Pd ratios were ?1. With a 2:1 ratio of 1:Pd, monophosphine complex formation and oxidative addition were significantly inhibited.     

Half sandwich complexes of Ru(II) and complexes of Pd(II) and Pt(II) with seleno and thio derivatives of pyrrolidine: Synthesis, structure and applications as catalysts for organic reactions

The reactions of PhSe⁻, PhS⁻ and Se²⁻ with N-{2-(chloroethyl)}pyrrolidine result in N-{2-(phenylseleno)ethyl}pyrrolidine (L1), N-{2-(phenylthio)ethyl}pyrrolidine (L2), and bis{2-pyrrolidene-N-yl)ethyl selenide (L3), respectively, which have been explored as ligands. The complexes [PdCl₂(L1/L2)] (1/7), [PtCl₂(L1/L2)] (2/8), [RuCl(η⁶-C₆H₆)(L1/L2)][PF₆] (3/9), [RuCl(η⁶-p-cymene)(L1/L2)][PF₆] (4/10), [RuCl(η⁶-p-cymene)(NH₃)₂][PF₆] (5) and [Ru(η⁶-p-cymene)(L1)(CH₃CN)][PF₆]₂·CH₃CN (6) have been synthesized. The L1-L3 and complexes were found to give characteristic NMR (Proton, Carbon-13 and Se-77). The crystal structures of complexes 1, 3-6, 9 and 10 have been solved. The Pd-Se and Ru-Se bond lengths have been found to be 2.353(2) and 2.480(11)/2.4918(9)/2.4770(5) Å, respectively. The complexes 1 and 7 have been explored for catalytic Heck and Suzuki-Miyaura coupling reactions. The value of TON has been found up to 85 000 with the advantage of catalyst’s stability under ambient conditions. The efficiency of 1 is marginally better than 7. The Ru-complexes 3 and 9 are good for catalytic oxidation of primary and secondary alcohols in CH₂Cl₂ in the presence of N-methylmorpholine-N-oxide (NMO). The TON value varies between 8.0 × 10⁴ and 9.7 × 10⁴ for this oxidation. The 3 is somewhat more efficient catalyst than 9.     

非对称N-(亚水杨基)二亚乙基三胺铜(Ⅱ)配合物的合成、结构分析和催化活性评价(英文)

A new copper(Ⅱ) complex of a non‐symmetric Schiff base, [CuII(saldien)(H2O)]+(1), has been synthesized and characterized by elemental analysis and several other spectroscopic methods (Hsaldien = N‐(salicylidene)diethylenetriamine). The crystal structure of 1 has also been determined by X‐ray crystallography. The geometry of the complex cation in 1 was found to be distorted square pyramidal with the mononegative Schiff base coordinating to the copper in a tetradentate mode via the O,N,N’, and N’’‐donor atoms. The remaining coordination site was occupied by the O atom of a H2O molecule in the axial position. The catalytic potential of 1 was tested in the oxidation reactions of cyclooctene and cyclohexene with aqueous 30% H2O2/NaHCO3 in acetonitrile. These reactions proceeded smoothly to give the corresponding epoxides with selectivity levels greater than 99%. This catalytic system also showed high levels of activity and selectivity towards the oxidation of cyclohexane (i.e., cyclohexanol 37% and cyclohexanone 54%) in comparison with most of the other Cu‐based systems reported in the literature.     

Catalytic hydrogenation reactions by a monobenzene complex of ruthenium, [Ru(η6-C6H6)(CH3CN)3](BF4)2, in biphasic medium

The water soluble monobenzene complex of ruthenium, [Ru(η⁶-C₆H₆)(CH₃CN)₃](BF₄)₂ (1) is an effective catalyst or catalyst precursor for the hydrogenation of olefinic functions in benzene/H₂O biphasic medium. The catalyst can be recycled by simple decantation. Complex 1 is capable of catalyzing H/D exchange reaction between H₂ and D₂O. A two-loop reaction mechanism for the catalytic hydrogenation reactions with 1 is postulated. In this mechanism, water acts as the base to assist the heterolytic hydrogen cleavage in one of the loops, but is not an active participant in the other.     

Reactions of half-sandwich rhodium(III) and iridium(III) compounds with pyridinethiolate ligands: Mono-, di-, and tri-nuclear complexes

Neutral trinuclear metallomacrocycles, [Cp^*RhCl(μ-4-PyS)]₃ (3) and [Cp^*IrCl(μ-4-PyS)]₃ (4) [Cp^* = pentamethylcyclopentadienyl, 4-PyS = 4-pyridinethiolate], have been synthesized by self-assembly reactions of [Cp^*RhCl₂]₂ (1) and [Cp^*IrCl₂]₂ (2) with lithium 4-pyridinethiolate, respectively. In situ reaction of complex 3 with three equivalent of lithium 4-pyridinethiolate resulted in [Cp^*Rh(μ-4-PyS)(4-PyS)]₃ (5) containing both skeleton and pendent 4-PyS groups. Chelating coordination of 2-pyridinethiolate broke down the triangular skeleton to give mononuclear metalloligands Cp^*Rh(2-PyS)(4-PyS) (6) and Cp^*Ir(2-PyS)(4-PyS) (7) [2-PyS = 2-pyridinethiolate], which could also be synthesized from Cp^*RhCl(2-PyS) (10) and Cp^*IrCl(2-PyS) (11) with lithium 4-pyridinethiolate. The coordination reactions of 6 with complexes 1 and 2 gave dinuclear complexes [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*RhCl₂] (8) and [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*IrCl₂] (9), respectively. Molecular structures of 3, 4, 6 and 11 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Tricarbonylrhenium(I) and manganese(I) complexes of 2-(pyrazolyl)-4-toluidine

A series of tricarbonyl rhenium(I) and manganese(I) complexes of the electroactive 2-(pyrazolyl)-4-toluidine ligand, H(pzAn^Me), has been prepared and characterized including by single crystal X-ray diffraction studies. The reactions between H(pzAn^Me) and M(CO)₅Br afford fac-MBr(CO)₃[H(pzAn^Me)] (M = Mn, 1a; Re, 1b) complexes. The ionic species {fac-M(CH₃CN)(CO)₃[H(pzAn^Me)]}(PF₆) (M = Mn, 2a; Re, 2b) were prepared by metathesis of 1a or 1b with TlPF₆ in acetonitrile. Complexes 1a and 1b partly ionize to {M(CH₃CN)(CO)₃[H(pzAn^Me)]⁺}(Br⁻) in CH₃CN but retain their integrity in less donating solvents such as acetone or CH₂Cl₂. Each of the four metal complexes reacts with (NEt₄)(OH) in CH₃CN to give poorly-soluble crystalline [fac-M(CO)₃(μ-pzAn^Me)]₂ (M = Mn, 3a; Re, 3b). The solid state structures of 3a and 3b are of centrosymmetric dimeric species with bridging amido nitrogens and with pyrazolyls disposed trans- to the central planar M₂N₂ metallacycle. In stark contrast to the diphenylboryl derivatives, Ph₂B(pzAn^Me), none of the tricarbonyl group 7 metal complexes are luminescent.     

Metallacrown ethers with a symmetric bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene: Synthesis, characterization and hydroformylation of styrene

To better understand the effects of ligand configuration on hydroformylation reactions carried out in the presence of LiBPh₄·3dme (dme = 1,2-dimethoxyethane), a conformationally restrained bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene, {[(2,2′-O₂C₁₂H₈)P(C₂H₄O₂)]₂C₆H₄}, 1, has been prepared and its Rh(I) metallacrown ether complex has been evaluated as a catalyst for the hydroformylation of styrene. Both the activity and regioselectivity of the catalyst are sensitive to the amount of the LiBPh₄·3dme added with the activity decreasing by 16% and the regioselectivity for the iso increasing by 9% at a 8:1 LiBPh₄:Rh ratio.Model complexes for the octahedral, cis-Mo(CO)₄(1), 2, and square planar, cis-PtCl₂(1), 3, and cis-PdCl₂(1), 4, complexes in the catalytic cycle has been have been studied using multinuclear NMR spectroscopy and X-ray crystallography. Although the X-ray crystal structure of 2 suggests that the metallacrown ether ring could adopt a configuration capable of binding alkali metal cations, this does not appear to occur in a dichloromethane-d₂ solution of 2 because no shift in the ³¹P NMR resonance 2 is observed upon the addition of an excess of LiBPh₄·3dme. The ³¹P{¹H} NMR spectra of chloroform-d solutions of 2 (in the presence of a catalytic amount of HgCl₂) and of 4 and the X-ray crystal structures of the complexes indicate that the bis(phosphite) ligands are cis coordinated in these complexes in both the solution and in the solid state. This is particularly surprising for 4 because related PdCl₂{Ph₂P(CH₂CH₂O)_nCH₂CH₂PPh₂} (n = 3-5) complexes exhibit both cis-trans and monomer-oligomer equilibria in solution.