Presence Of Donor Ligands Research Articles

Pyridine-2-thione and pyrimidine-2-thione derivatives of silver(I): Synthesis and structures of unusual dinuclear and polynuclear coordination compounds, [Ag2Cl2(pytH)2(dppm)], [Ag2Br2(pymtH)(PPh3)3] and {AgCl(pytH)2}n

The chemical reactivity of heterocyclic-2-thiones towards silver halides in presence of donor ligands, such as tertiary phosphines, is poorly explored relative to that with other anions (such as NO3, OAc etc). It was observed in a research report that chemical reactivity of silver(I) chloride/bromide with pyridine-2-thione (pytH) in the presence of a tertiary phosphine, was different in terms of nuclearity. In this manuscript some unusual products from reactions of silver(I) halides with pyridine-2-thione (pytH)/pyrimidine-2-thione (pymtH) in presence of tertiary phosphines are reported. In one case, reaction of a bis(diphenylphosphino)methane (dppm) with silver(I) chloride yielded a crystalline product of stoichiometry, [Ag2Cl2)(pytH)2(µ-P,P-Ph2PCH2PPh2)] 1. Silver(I) chloride with pytH in the presence of tri-p-tolylphosphine ligand did not form the expected, AgCl(pytH)(p-tolyl3P)2 complex, rather it has formed a compound of stoichiometry, {AgCl(pytH)2} 2. The crystal structures of these compounds revealed the formation of a triply bridged di-nuclear compound, [(κ1Cl)Ag(µ-Cl)(µ-P,P-Ph2PCH2PPh2)(µ-S-pytH)Ag(κ1S-pytH)] 1, and a polymeric product, {AgCl(κ1S-pytH)(µ-S-pytH)-}n,2, respectively. The chemical reactivity of pyrimidine-2-thione (pymtH) is found to be different. A reaction of silver(I) bromide with PPh3 and pymtH, yielded a bromo-bridged unsymmetrical dinuclear compound, [(PPh3)2Ag(µ-Br)2Ag(PPh3)(κ1S-pymtH)] 3. Reaction of AgNO3 with pytH and PPh3 in the presence of Et3N base did not yield the expected [Ag(κ1S-pyt)(PPh3)3] compound, rather it formed the ionic complex, [Ag(κ1S-pytH)(PPh3)3](NO3)·CH3OH·0.25H2O 4. In compound 1, there is a short Ag···Ag distance of 3.1127(3) Å, suggesting possibility of argentophillic interaction.

Trans‐Influence in Heavy Main Group Compounds: A Case Study on Tris(pyrazolyl)borate Bismuth Complexes

Compounds of heavy main group elements possessing polarized primary bonds exhibit trans‐influence. The extent of secondary interactions at the electrophilic sites trans to the primary bonds provides an understanding on the Lewis acidity exhibited by the main group element center, thus forming the basis for designing Lewis acid catalysts. Hydridotris(3,5‐dimethylpyrazolyl)borate(TpMe2), a C3v symmetric tridentate σ‐donor ligand, offers an opportunity to explore trans‐influence in Bi(III) compounds in the presence of donor ligands with varying nucleophilicity. We have examined a series of TpMe2Bi species by accessing five new moieties [TpMe2BiCl3]–, (TpMe2)2Bi+, TpMe2BiCl(OTf), TpMe2Bi(OTf)2 and [TpMe2Bi(solvent)3]2+ in addition to the recently reported TpMe2BiCl2, TpMe2Bi2+, [TpMe2Bi]2[Bi3Cl13] and K[TpMe2Bi(OTf)3]. Analysis of structures by X‐ray crystallographic studies and computational analysis on TpMe2Bi species establish the variation of trans‐influence and demonstrate a continuum in bonding of TpMe2 to bismuth correlating with the degree of nucleophilicity of the trans‐ligands.

Trianionic Pincer Complexes of Niobium and Tantalum as Precatalysts for ROMP of Norbornene

This report details the synthesis and characterization of a series of Nb complexes and one tantalum complex supported by the [CF3–ONO]3– trianionic pincer-type ligand. Access to the trianionic Nb dichloride complex, [CF3–ONO]NbCl2(OEt2) (3-Et2O), allows for the synthesis of Nb-dialkyl complexes, [CF3–ONO]NbR2 (where R = benzyl (5), neopentylsilyl (6), neophyl (7)). The sterically encumbered Nb-neophyl complex (7) is thermally stable and fails to convert to the alkylidene even in the presence of donor ligands. Complex 7, however, promotes catalytic ring-opening metathesis polymerization (ROMP) of norbornene, suggesting the plausible intermediacy of a Nb-alkylidene. The corresponding Ta analogue, [CF3–ONO]Ta(CH2C(CH3)2(C6H5))2 (9), requires dramatically higher temperatures to initiate ROMP and provides poor yields of polymer. Complexes 5 and 6 also promote ROMP of norbornene. Characterization of all new complexes includes multinuclear NMR spectroscopy and combustion analysis. For complex 7, characterization also includes solid-state structure elucidation via a single crystal X-ray diffraction experiment.

Mechanistic Study of Rhodium/xantphos-Catalyzed Methanol Carbonylation

Rhodium/iodide catalysts modified with the xantphos ligand are active for the homogeneous carbonylation of methanol to acetic acid using either pure CO or CO/H2. Residues from catalytic reactions contain a Rh(III) acetyl complex, [Rh(xantphos)(COMe)I2] (1), which was isolated and crystallographically characterized. The xantphos ligand in 1 adopts a “pincer” κ3-P,O,P coordination mode with the xanthene oxygen donor trans to the acetyl ligand. The same product was also synthesized under mild conditions from [Rh(CO)2I]2. Iodide abstraction from 1 in the presence of donor ligands (L = MeCN, CO) gives the cationic acetyl species [Rh(xantphos)(COMe)I(L)]+, whereas in CH2Cl2 migratory CO deinsertion gives [Rh(xantphos)(Me)I(CO)]+ (4), which reacts with H2 to liberate methane, as observed in catalytic reactions using syngas. A number of Rh(I) xantphos complexes have been synthesized and characterized. Oxidative addition of methyl iodide to the cation [Rh(xantphos)(CO)]+ is very slow but can be catalyzed by addition of an iodide salt, via a mechanism involving neutral [Rh(xantphos)(CO)I] (6). IR spectroscopic data and DFT calculations for 6 suggest the existence in solution of conformers with different Rh–O distances. Kinetic data and activation parameters are reported for the reaction of 6 with MeI, which proceeds by methylation of the Rh center and subsequent migratory insertion to give 1. The enhancement of nucleophilicity arising from a Rh- - -O interaction is supported by DFT calculations for the SN2 transition state. A mechanism for catalytic methanol carbonylation based on the observed stoichiometric reaction steps is proposed. A survey of ligand conformations in xantphos complexes reveals a correlation between P–M–P bite angle and M–O distance and division into two broad categories with bite angle <120° (cis) or >143° (trans).

New types of alumosiloxanes by the reaction of the bicyclic compound Al2[(OPh2Si)2O]3·2 Et2O with water in the presence of donor ligands – A status report

Abstract The selective synthesis of new types of alumosiloxanes can be achieved by the reaction of the bicyclic compound Al 2 [(OPh 2 Si) 2 O] 3 ·2 Et 2 O ( 3 ) with water in donor solvents like acetone or THF, leading to the polycyclic THF adduct [(Ph 2 SiO) 8 (AlO 1,5 ) 4 ]·2 THF, ( 7 ), and to the polycyclic alumosiloxane [(Ph 2 SiO) 8 (AlO(OH)) 4 ]·4 Me 2 C O ( 8 ), respectively. In the presence of the base triethylamine, the starting compound 3 gives rise to two other condensation products. At medium temperatures (50--60 °C) in toluene the dispiro “alumosilicate” [(Ph 2 SiO) 2 O] 2 {Al[(Ph 2 SiO) 2 OH·NEt 3 ]} 2 ( 9 ) is formed and at higher temperatures under reflux in toluene, the product [(Ph 2 SiO) 2 O]Al[(Ph 2 SiO) 2 OH·NEt 3 ] ( 10 ) is generated. The spirocyclic compounds 9 and 10 present the first isolated “alumosilicates” with six-membered O(SiO) 2 Al cycles. These new types of alumosiloxanes and “alumosilicates” have been characterised by spectroscopic methods as well as by single crystal X-ray analyses.

Synthesis of Bis(indenyl)zirconium Dihydrides and Subsequent Rearrangement to η5,η3-4,5-Dihydroindenediyl Ligands: Evidence for Intermediates during the Hydrogenation to Tetrahydroindenyl Derivatives

Exposure of eta9,eta5-bis(indenyl)zirconium sandwich complexes to 4 atm of H2 resulted in facile oxidative addition to furnish the corresponding zirconocene dihydrides, (eta5-C9H5-1,3-R2)2ZrH2 (R = SiMe3, SiMe2Ph, CHMe2). Continued hydrogenation completed conversion to the tetrahydroindenyl derivatives, (eta5-C9H9-1,3-R2)2ZrH2. Deuterium labeling studies established that dihydrogen (dideuterium) addition to the benzo rings is intramolecular and stereospecific, occurring solely from the endo face of the ligand, proximal to the zirconium. In the absence of dihydrogen, the bis(indenyl)zirconium dihydrides rearranged to new zirconium monohydride complexes containing an unusual eta5,eta3-4,5-dihydroindenediyl ligand, arising from metal-to-benzo ring hydrogen transfer. Mechanistic studies, including a normal, primary kinetic isotope effect measured at 23 degrees C, are consistent with a pathway involving regio- and stereoselective insertion of a benzo C=C bond into a zirconium hydride. The stereochemistry of the insertion reaction, and hence the eta5,eta3-4,5-dihydroindenediyl product, is influenced by the presence of donor ligands and controlled by the preferred conformation of the indenyl rings. Exposure of the zirconium hydrides containing the eta5,eta3-4,5-dihydroindenediyl rings to 1 atm of dihydrogen afforded the tetrahydroindenyl zirconium dihydride complexes, establishing the intermediacy of this unusual coordination environment during benzo ring hydrogenation.

Titanium hydrazido and imido complexes: synthesis, structure, reactivity, and relevance to alkyne hydroamination.

Treatment of Ti(NMe(2))(2)(dpma) (1) with aniline results in the protonation of the dimethylamido ligands, which are retained as dimethylamines, and generation of a titanium imido complex Ti(NPh)(NHMe(2))(2)(dpma) (2) in 94% yield. The monomeric imido 2 is converted to the reactive dimeric micro-imido [Ti(NPh)(dpma)](2) (3) on removal of the labile dimethylamine donors. The dimer 3 is converted to monomeric terminal imido complexes in the presence of added donors, e.g., 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)-bpy) and DME. Compounds 1-3 exhibit the same rate constant for 1-phenylpropyne hydroamination by aniline and are all kinetically competent to be involved in the catalytic cycle. Attempts to use 1 as a catalyst for hydroaminations involving 1,1-dimethylhydrazine resulted in only a few turnovers under the best conditions. Consequently, the chemistry of 1 with hydrazines to generate hydrazido complexes was scrutinized for comparison with the imido species. Through these studies, titanium hydrazido complexes including Ti(eta(2)-NHNC(5)H(10))(2)(dpma) (5), Ti(eta(2)-NHNMe(2))(2)(dpma) (6), and [Ti(micro:eta(1),eta(2)-NNMe(2))(dpma)](2) (7) were characterized. In addition, a terminal hydrazido(2-) complex was available by addition of Bu(t)-bpy to 1 prior to 1,1-dimethylhydrazine addition, which provided Ti(eta(1)-NNMe(2))(Bu(t)-bpy)(dpma) (8). Compound 8 was structurally characterized and compared to Ti(NPh)(Bu(t)-bpy)(dpma) (4b), an imido derivative with the same ancillary ligand set. Compound 8 has a nucleophilic beta-nitrogen consistent with a hydrazido(2-) formulation, as determined by reaction with MeI to form the ammonium imido complex [Ti(NNMe(3))(Bu(t)-bpy)(dpma)]I (9). Analogous pyridinium imido complexes [Ti(N-1-pyridinium)(Bu(t)-bpy)(dpma)](+) (10) are available by addition of 1-aminopyridinium iodide to 1. From the investigations, some conclusions regarding the activity of titanium pyrrolyl complexes in hydroamination were drawn. The lack of conversion of the bis[micro-hydrazido(2-)] 7 to monomeric species in the presence of donor ligands is put forth as one explanation for the poor hydrazine hydroamination activity of 1. This problem was combated in the synthesis of Ti(NMe(2))(2)(dap)(2), which is an active catalyst for hydrazine hydroamination of alkynes.

Unprecedented cage-carbon to cage-boron NMe(3) transfer in a monocarbon Molybdenacarborane.

The reagent Li(2)[7-NMe(3)-nido-7-CB(10)H(10)] reacts with [Mo(CO)(3)(NCMe)(3)] in THF-NCMe (THF = tetrahydrofuran) to give a molybdenacarborane intermediate which, upon oxidation by CH(2)[double bond]CHCH(2)Br or I(2) and then addition of [N(PPh(3))(2)]Cl, gives the salts [N(PPh(3))(2)][2,2,2-(CO)(3)-2-X-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (X = Br (1) or I (2)). During the reaction, the cage-bound NMe(3) substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives. When [Rh(NCMe)(3)(eta(5)-C(5)Me(5))][BF(4)](2) is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)(3)-7-mu-H-2,7,11-[Rh(2)(mu-CO)(eta(5)-C(5)Me(5))(2)]-closo-2,1-MoCB(10)H(9)] (10) is formed, the NMe(3) group being lost. Reaction of 1 in CH(2)Cl(2) with Tl[PF(6)] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)(3)-2-L-3-NMe(3)-closo-2,1-MoCB(10)H(10)] for L = PPh(3) (4) or CNBu(t) (5), and [2-Bu(t)C[triple bond]CH-2,2-(CO)(2)-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (6) when L = Bu(t)C[triple bond]CH. When 1 is treated with CNBu(t) and X(2), the metal center is oxidized, and in the products obtained, [2,2,2,2-(CNBu(t))(4)-2-Br-3-X-closo-2,1-MoCB(10)H(10)] (X = Br (7), I (8)), the B-NMe(3) bond is replaced by B-X. In contrast, treatment of 2 with I(2) and cyclo-1,4-S(2)(CH(2))(4) in CH(2)Cl(2) results in oxidative substitution of the cluster and retention of the NMe(3) group, giving [2,2,2-(CO)(3)-2-I-3-NMe(3)-6-[cyclo-1,4-S(2)(CH(2))(4)]-closo-2,1-MoCB(10)H(9)] (9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies upon 6, 7, 9 and 10.

Selective C−C vs C−H Bond Activation by Rhodium(I) PCP Pincer Complexes. A Computational Study

A theoretical study of the oxidative addition of C−C vs C−H bonds to a rhodium(I) complex with PCP-type ligands has been carried out. Special attention has been paid to the effect of different bulky substituents at the phosphorus atoms of the chelate ligand. Therefore, B3LYP/lanl2dz+p//B3LYP/lanl2dz and ONIOM(B3LYP/lanl2dz+p:B3LYP/lanl2dz)//ONIOM(B3LYP/lanl2dz:HF/lanl1mb) methods have been utilized. According to the calculations, C−H activation is always the kinetically favored process (ΔΔE⧧ 20 kJ·mol-1), though the C−C activation product is more stable (ΔΔE 20 kJ·mol-1). C−H addition is a reversible process; the product of the C−H activation can interconvert to the C−C activation product via an intermediate structure. Bulky substituents are found to increase the barrier for C−H activation relative to that for C−C activation. With additional ligands (e.g., phosphines), hexacoordinate complexes are formed. This is more favorable for the C−C activation products. Our calculations show that the activation reaction proceeds via complexes with a pentacoordinated rhodium atom. Thus, in the presence of donor ligands, the activation reaction is inhibited.

Regiochemical control of a Pt-promoted alkylation of the phenyl ring

The reactivity of cationic PtII–phenyl complexes of the type [PtPh(CH2CHR)(phen)]+ (R = H or Me) has been investigated. In all cases, insertion of the alkene into the Pt–Ph bond has been observed. The fate of the resulting Pt–CH2CHRPh (R = H or Me) derivative depends on the experimental conditions. In the presence of donor ligands (e.g. excess olefin, pyridine or triphenylphosphine) the product is stable, while in the absence of them a rapid rearrangement to form Pt–C6H4(CHRMe)-2 occurs.

Framework chirality and optical activity of organometallic cluster compounds

The contributions by the author's research group towards the preparation and the investigation of physical and chemical properties of optically active clusters are reviewed. Such clusters with EM 3 tetrahedrane frameworks can be prepared by stepwise synthesis or by metal exchange. Enantiomer separation is possible by means of optically active phosphine ligands via the intermediate formation of diastereomeric substitution derivatives or by means of chromatography on triacetyl cellulose. The optical properties of the diastereoisomers and the enantiomers (molar rotations, rotatory dispersion) are extreme. The optical activity of the clusters containing light transition elements is lost in the presence of donor ligands (CO, phosphines, catalysis substrates) due to the opening of metalmetal bonds. Reactions in the ligand sphere, however, can be performed with up to 100% diastereoselectivity.

Study of the interaction between iron(0) and carbon dioxide, carbonyl sulphide and carbon disulphide: “ab initio” calculations on the model compounds Fe(CO) 2(PH 3) 2(η 2-CO 2), Fe(CO) 2(PH 3) 2(η 2-COS), Fe(CO) 2(PH 3) 2(η 2-CS 2), and Fe(PH 3) 4(η 2-CO 2)

“Ab initio” calculations have been performed on the model systems Fe(CO) 2(PH 3) 2(η 2-CO 2), Fe(CO) 2(PH 3) 2(η 2-COS), Fe(CO) 2(PH 3) 2(η 2-CS 2) in order to investigate the nature and energetics of the interaction between iron and CO 2, COS, CS. The results suggest that the main bonding interaction between the fragment Fe(CO) 2(PH 3) 2 and the unsaturated molecule is the π-back-donation from the transition metal to the π-acceptor ligand and that the strength of the coordination bond increases in the order CO 2 < COS < CS 2. Partial geometry optimizations obtained by gradient calculations show that carbonyl sulphide prefers the η 2-C,S rather than the η 2-C,O coordination mode because of the increased π-back-donation. The study of the system Fe(PH 3) 4(η 2-CO 2) reveals that the presence of donor ligands, such as phosphine, by increasing the electronic population at the metal centre, enhances the π-back-donation and thus the strength of the interaction.

Solution and matrix photochemistry of (η-cyclopentadienyl)bis(ethane)rhodium

Solution photolysis of (η-C5H5)Rh(C2H4)2 leads to substitution of ethane in the presence of donor ligands and to oxidative addition with R3SiH (R = Me or Et); photolysis in inert matrices causes reversible loss of ethane, but in reactive matrices substitution by N2 and CO takes place.

Synthesis and reactivity of nickel o-semiquinolate complexes

The hindered catecholate complex ▪ was obtained by the reaction of nickel halides with the dipotassium derivative of 3,5-di-t-butylcatechol. The oxidation of this complex leads to a compound with a semiquinolate structure ▪ which is identical to the previously prepared Balch complex. Reactions of bis(3,5-di-t-butyl-l,2-benzosemiquinolate)-nickel with acids, alkali, benzoyl peroxide and some complex molecular compounds were investigated. The reduction of Ni(SQ) 2 with BuLi in the presence of donor ligands can be a convenient method of synthesising nickel zerovalent complexes. Tetrakis(triphenylphosphine)nickel prepared by this procedure undergoes oxidative addition reactions with allyl chloride and benzoyl peroxide. The mono- o-semiquinolate nickel derivative allylnickel-3,5-di-t-butyl-l,2-benzo-semiquinolate was produced. This novel allylnickel complex is air-stable and paramagnetic both in solution and in the solid state.

Substituierte halogencarbonylmetallate des chroms, Molybdäns und Wolframs : II. Photochemische phosphin-abspaltung, ein neuer weg zu metall (VI A) carbonylderivaten

Irradiation of bis(phosphine) tetracarbonyl complexes L 2M(CO) 4 (M = Cr, Mo, W) in the presence of donor ligands (amine, nitrile, halide ion) leads, via loss of one phosphine ligand, to neutral (LL′M(CO) 4) or ionic ([LM(CO) 4X] −) metal carbonyl compounds. The use of this reaction as the first step in a general synthesis of unsymmetrically disubstituted derivatives of Group VIA hexacarbonyls is discussed.