Synthesis and structure of titanium alkoxide complexes with bulky ligands derived from natural products: Asymmetric epoxidation of cinnamyl alcohol

A family of titanium(IV) alkoxide compounds [{Ti(OPrⁱ)₃(OR)}₂], [{Ti(OPrⁱ)₂(OR)₂}₂], and Ti(OR)₄ (1-12) have been prepared using two different routes: by metathesis reaction of TiCl(OPrⁱ)₃ and TiCl₂(OPrⁱ)₂ with ROH in the presence of Et₃N and alternatively by alcohol exchange of Ti(OPrⁱ)₄ and the corresponding higher boiling alcohol (ROH=adamantanol, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose, 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose, 1R,2S,5R-(−)-menthol). These tetra alkoxide titanium(IV) compounds have been characterized by spectroscopic techniques. In addition, some of these chiral Lewis acid titanium compounds, derived from diacetone galactose and diacetone glucose, have been studied in the asymmetric epoxidation of cinnamyl alcohol in order to evaluate their catalytic activity and stereoselectivity.     

Homometallic glycolates containing hydroxyl functionality for anchoring another metal: synthesis and characterization of heterometallic alkoxide–glycolates of Ti and Zr incorporating Al and Nb

Reaction of Ti(OPrⁱ)₄ with 2-methyl-2,4-pentanediol [HOGOH, where G = CMe₂CH₂CH(Me)] in 1?:?3 M ratio under reflux afforded the monomeric [Ti(OGO)(OGOH)₂] (1), which on further reactions with [Al(OPrⁱ)₃] or [Nb(OPrⁱ)₅] in 1?:?1 and 1?:?2 M ratios afforded heterometallic derivatives, [Ti(OGO)₃{M(OPrⁱ)_n?2}] and [Ti(OGO)₃{M(OPrⁱ)_n?1}₂] [where M = Al (n = 3), Nb (n = 5)], respectively. Similar reactions of Zr(OPrⁱ)₄?PrⁱOH with a number of glycols [HOGOH, where G = CH(Me)CH(Me), CMe₂CMe₂, CMe₂CH₂CH(Me)] yielded dimeric [Zr₂(OGO)₂(OGOH)₄]. [Zr₂(OGO)₆{M(OPrⁱ)_n?2}₂] and [Zr₂(OGO)₄(OGOH)₂M(OPrⁱ)_n?2] [M = Al (n = 3), Ti (n = 4), Nb (n = 5)] were prepared by 1?:?2 and 1?:?1 reactions, respectively, of [Zr₂(OGO)₂(OGOH)₄] with Al(OPrⁱ)₃, Ti(OPrⁱ)₄, or Nb(OPrⁱ)₅. Surprisingly, a 1?:?2 reaction of [VO(OPrⁱ)₃] with 2,2-diethyl-1,3-propanediol in benzene followed a different reaction and produced a neutral tetranuclear derivative [V₄(O)₄(μ-OCH₂CEt₂CH₂O)₂(OCH₂CEt₂CH₂O)₄] (18). All of these derivatives were characterized by elemental analysis, molecular weight measurements, FT-IR, and ¹H NMR (and wherever possible, by ²⁷Al or ⁵¹V NMR) spectroscopic studies. The derivatives [Zr₂(OCMe₂CH₂CH(Me)O)₂(OCMe₂CH₂CH(Me)OH)₄] (9 and 18) were additionally characterized by single-crystal X-ray structure analysis.     

Formation of mixed-metal alkoxides mediated by the reactivity of coordinated pinacol: Synthesis and molecular structures of Ce2Ti2(μ3-O)2(μ,η2-OCMe2CMe2O)4(OPri)4(PriOH)2 and of Ce2Nb2(μ3-O)2(μ,η2-OCMe2CMe2O)4(OPri)6

The addition of pinacol to mixtures of titanium and cerium isopropoxides as well as the use of insoluble titanium and cerium pinacolate synthons was investigated as a route to M-Ce (M=Ti, Nb) species. Pinacol was able to promote the formation of mixed-metal species and the first Ce-Ti and Ce-Nb species namely Ce_2Ti(pin)₂(OPrⁱ)₈ and [M₂Ce₂(μ₃-O)₂(μ,η²pin)₄(OPrⁱ)₆H_x] [M=Ti, x=2; M=Nb, x=0; pin=OCMe₂-COMe₂] were isolated and characterized by FT-IR and ¹H NMR. The latter were also characterized by X-Ray diffraction. Their structures are based on a rhombus compressed along the M⋯M direction with 6-coordinated metals. The pinacolate moieties act as bridging-chelating ligands. The metal–oxygen bond lengths vary according to M–O(pin)<M-μ₃–O<Mμ–O(pin)<Ce–OPrⁱ<Ce–μ₃O.     

AACVD of WO3 thin films from W(O)(OPri)3[O(CH2)nNMe2] (n = 2, 3)

Monomeric tungsten oxo‐aminoalkoxides W(O)(OPrⁱ)₃(L) [L = O(CH₂)_nNMe₂; n = 2 (dmae, 1) and 3 (dmap, 2 )] were synthesized by alcohol exchange with [W(O)(OPrⁱ)₄]₂ and characterized spectroscopically. 1, 2 and [W(O)(OPrⁱ)₄]₂ were used as precursors for the aerosol‐assisted chemical vapour deposition of WO₃ thin films, which were characterized by glancing angle X‐ray diffraction, SEM and transmission‐reflectance measurements. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of the molar ratio [H<Subscript>2</Subscript>O]/[Ti(OR)<Subscript>4</Subscript>] on the kinetics of the titanium-oxo-alkoxy clusters nucleation

The influence of the molar ratio h = [H₂O]/[Ti(OR)₄] (R = Pr ⁱ ) on the kinetics of the titanium-oxo-alkoxy clusters (TOAC) nucleation was studied. Clusters were formed by the titanium tetraisopropoxide Ti(OPr ⁱ )₄ chemical reaction with H₂O in n-propanol solution, with the fixed concentration of Ti(OPr ⁱ )₄ (c = 0.04 M), molar ratio h ∈ {11, 14, 17, 20} and temperature T ∈ {298, 308, 318} K. It was determined that the isothermal rate of clusters nucleation is a power law function of the molar ratio h. The kinetic parameter β value changes complexly as h and T change. The value of apparent activation energy of the nucleation process (E _a) decreases with the increase of value h. It was found that nucleation is a reaction with complex kinetics whose elementary stages are hydrolysis Ti(OR)₄ to Ti(OR)₃OH and formation of titanium-oxo-alkoxy clusters [Ti _{n + β}O_β](OR)_{4n + 2β} through the alcoxolation reaction.     

Glycol modified titanosiloxane as molecular precursor for homogenous titania–silica material: synthesis and characterization

Ti(OPrⁱ)₄ reacts with HOSi(O^tBu)₃ in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPrⁱ)₃{OSi(O^tBu)₃}] (A) and [Ti(OPrⁱ)₂{OSi(O^tBu)₃}₂] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPrⁱ)(O–G–O){OSi(O^tBu)₃}] (1A–3A) and [Ti(O–G–O){OSi(O^tBu)₃}₂] (1B–3B), respectively [where G = (CH₂)₂ (1A, 1B); (CH₂)₃ (2A, 2B) and {CH₂CH₂CH(CH₃)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and ¹H, ¹³C & ²⁹Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors. Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO₂·SiO₂ in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO₂·SiO₂. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses.     

Synthesis and some properties of furylacrylates of aluminium(III) and titanium(IV)

Summary Compounds of the type [M(OPrⁱ)_m–n(FA)_n] (where m = 3 and n = 1 to 3 when M = Al; and m = 4 and n = 1 to 4 when M = Ti) have been synthesised by the reactions of aluminium and titanium isopropoxides with furylacrylic acid (HFA) in benzene. The corresponding tertiary butoxide derivatives, [M(OBu^t)_m–n(FA)_n], were also obtained by the alcohol-interchange technique. These compounds have been characterised by elemental analysis, and i.r. and p.m.r. spectra.     

Synthesis of novel termetallic isopropoxides

Novel termetallic isopropoxides are reported which may be represented by the general formulae: [(PrⁱO)₃M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂], [(PrⁱO)₂M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂]₂ [where M = Ti(IV), Zr(IV) and Hf(IV)] and [(PrⁱO)₄M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] [where M = Nb(V) and Ta(V)]. Attempts to synthesize derivatives with the general formula, [(PrⁱO)₇M₂(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] [where M = Ti(IV), Zr(IV) or Hf(IV)], were unsuccessful and in all such cases a mixture of M(OPrⁱ)₄ and [(PrⁱO)₃M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] was obtained. All these derivatives are soluble in common organic solvents and with the exception of titanium(IV) derivatives, they can be volatilised without noticeable disproportionation. These products have been characterized by elemental analyses, molecular weights, IR, ¹H NMR and (in representative cases) mass spectral studies also.     

Heterobimetallic diethanolaminate complexes of titanium and zirconium with alkaline earth metals

Ti(OPr ⁱ )₄ or Zr(OPr ⁱ )₄ · Pr ⁱ OH react with hydrocarbon-insoluble complexes M{(OCH₂CH₂)NH(CH₂CH₂OH)}₂ (M = Mg, Ca, Sr, Ba) in a 2:1 molar ratio to yield hydrocarbon-soluble heterobimetallic diethanolaminate isopropoxide complexes [M{(OCH₂CH₂)₂NH}₂{M(OPr ⁱ )₃}₂] (M = Mg, Ca, Sr, Ba; M = Ti, Zr), which have been characterized by elemental analyses, molecular weight measurements and spectroscopic [i.r., n.m.r. (¹H and ¹³C)] studies.     

Synthesis and structure of [Cp2Zr(OPr)(HOPr)] and its activity in the polymerisation of propene oxide

The reaction of Cp₂Zr(OPrⁱ)₂ with [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] in dichloromethane at room temperature gives [Cp₂Zr(OPrⁱ)(HOPrⁱ)]⁺[H₂N{B(C₆F₅)₃}₂]⁻ · Et₂O in high yield. The crystal structure is reported. The complex contains a short Zr-alkoxide and a longer Zr-alcohol bond; the OH group of the coordinated isopropanol is hydrogen-bonded to a diethyl ether molecule. The complex initiates the polymerisation of propylene oxide, most probably via a cationic mechanism.     

ɛ‐caprolactone and lactide polymerization promoted by an ionic titanium(IV)/iron(III) polynuclear halo‐alkoxide

The ionic [Ti₃(µ₃‐OPrⁱ)₂(µ‐OPrⁱ)₃(OPrⁱ)₆][FeCl₄] halo‐alkoxide ( A ) was investigated for its activity towards the bulk polymerization of rac‐lactide (rac‐LA) and ?‐caprolactone (?‐CL) in various temperatures, monomer/ A molar proportions, and reaction times. The reactivity of A in the ring‐opening polymerization (ROP) of both monomers is mainly due to the cationic [Ti₃(OPrⁱ)₁₁]⁺ unity and proceeds through the coordination–insertion mechanism. Molecular weights ranging from 6,379 to 13,950 g mol^?1 and PDI values varying from 1.22 to 1.52 were obtained. Results of ROP kinetic studies for both ?‐CL and rac‐LA confirm that the reaction rates are first‐order with respect to monomers. The production of poly(?‐caprolactone) shows a higher sensitivity of the reaction rate to temperature, while the polymerization of rac‐LA is slower and more dependent on the thermal stability of the active species during the propagation step. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2509–2517     

New sol–gel precursors for binary oxides of antimony,Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> (senarmonite) and α-Sb<Subscript>2</Subscript>O<Subscript>4</Subscript>: synthesis and characterization of some ketoximate modified antimony(III) alkoxides

Hydrolysis of pure Sb(OPrⁱ)₃ by sol–gel method followed by sintering at 500 °C yields microcrystallites of Sb₂O₃ (senarmonite phase). Under similar conditions bimetallic alkoxide, [NaSb(OPrⁱ)₄], yields a mixture of binary oxides Sb₂O₃ and Sb₂O₄. Chemical modification of Sb(OPrⁱ)₃ with oximes forms monomeric products of the type [Sb(OPrⁱ)_3−n {ON=C(CH₃)R} _n ] {where R = CH₃, n = 1 [1]; n = 2 [2]; n = 3 [3]; R = 2-C₅H₄N, n = 1 [4]; n = 2 [5]; n = 3 [6]; R = 2-C₄H₃O, n = 1 [7]; n = 2 [8]; n = 3 [9]; R = 2-C₄H₃S, n = 1 [10]; n = 2 [11]; n = 3 [12]}. The liquid products [1–3, 7 & 10] were purified by distillation while the solids by recrystallization. All these products were characterized by elemental analyses, IR, NMR (¹H and ¹³C{¹H}) and representative derivatives [1], [2] and [3] by FAB mass studies. On the basis of these studies, a distorted pyramidal structure for all the derivatives may be assumed in the solution state containing an end-on coordination of oximes with the metal atom. Hydrolysis of the distilled precursors [1], [2] and [3] under sol–gel conditions yields pure nano-sized α-Sb₂O₄. All the oxides were characterized by XRD, SEM and EDX analysis exhibiting minimum particle size for the oxide obtained from the precursor [3].     

Heterotri- and -tetrametallic alkoxides of chromium(III) containing aluminium(III), gallium(III) and niobium(V)

CrCl₃ · 3THF reacts with two equivalents of potassium alkoxometallates K{M(OPr ⁱ ) _x } [M = Al(A), Ga(B), x = 4; M = Nb(C), x = 6] to give heterobimetallic chloride isopropoxides [Cr{M(OPr ⁱ ) _x }₂Cl(THF)] [M = Al(A – 1), Ga(B – 1), and Nb(C – 1)], in which the replacement of the chloride with an appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) results in the formation of novel heterotrimetallic derivatives. The 'single pot synthesis of an heterotetrametallic isopropoxide [Cr{Nb(OPr ⁱ )₆}{Al(OPr ⁱ )₄}{Ga(OPr ⁱ )₄}] (7) has been carried out by the sequential addition of (A), (B), and (C) to a benzene suspension of CrCl₃ · 3THF. Alcoholysis of [Cr{Al(OPr ⁱ )₄}₂{Nb(OPr ⁱ )₆}] (1) and [Cr{Al(OPr ⁱ )₄}₂{Ga(OPr ⁱ )₄}] (5) with t-BuOH has also been studied and the derivatives characterized by elemental analyses, molecular weight determinations, spectroscopic [Electronic, i.r., ²⁷Al-n.m.r.] and magnetic susceptibility studies.     

Synthesis and Spectroscopic [Electronic,IR, NMR (1H, 13C, 89Y)] Characterization of Hexaisopropoxoniobates and ‐Tantalates of Yttrium(III) and Lanthanides(III)

Hexaisopropoxoniobates/tantalates of lathanides of the type [Ln{(μ‐OPrⁱ)₂M(OPrⁱ)₄}₃] (M = Nb, Ln = Y( 1 ), La( 2 ), Nd( 3 ), Er( 4 ), Lu( 5 ); M = Ta, Ln = Y( 6 ), Gd( 7 )) have been prepared by the reactions of LnCl₃.3PrⁱOH with three equivalents of KM(OPrⁱ)₆ in benzene. Reactions in 1:2 molar ratio of LnCl₃.3PrⁱOH with KTa(OPrⁱ)₆ yielded derivatives of the type [{(PrⁱO)₃Ta(μ‐OPrⁱ)₃}Ln{(μ‐OPrⁱ)₂Ta(OPrⁱ)₄}(Cl)] (Ln = Y( 8 ), Gd( 9 )), which on interactions with one equivalent of KOPrⁱ afforded [{(PrⁱO)₃Ta(μ‐OPrⁱ)₃}Ln {(μ‐OPrⁱ)₂Ta(OPrⁱ)₄}(OPrⁱ)] (Ln = Y( 10 ), Gd( 11 )). All these derivatives have been characterized by elemental analyses and molecular weight measurements as well as by their spectroscopic [IR, ¹H and ¹³C NMR (Y, La, Lu), electronic (Nd, Er)] studies. ⁸⁹Y NMR studies have also been carried out on derivatives ( 6 ), ( 8 ), and ( 10 ).     

Reaction of silicon with alcohols in autoclave

A reaction of activated silicon with alcohols in an autoclave at 240—270 °C was studied. It was found that primary alcohols form tetraalkoxysilanes Si(OR)₄ with high selectivity (up to 97%), while the secondary PrⁱOH gave a mixture of compounds HSi(OPrⁱ)₃, Si(OPrⁱ)₄, HSi(OPrⁱ)₂OSi(OPrⁱ)₂H, HSi(OPrⁱ)₂OSi(OPrⁱ)₃, and Si(OPrⁱ)₃OSi(OPrⁱ)₃ with the predominance of trialkoxysilane (up to 67%). Carrying out the reaction under the indicated conditions has the advantage of experimental simplicity, reagent availability, high conversion of silicon, good isolated yields of products.     

Synthesis,characterization, volatilization,alcoholysis and hydrolytic studies of nonaalkoxodititanatocopper(II) complexes

Heterobimetallic alkoxides of Cu(II) of the types [Cu{η⁴-Ti₂(OEt)₉}Cl] (1) and [Cu{η³-Ti₂(OR)₉}₂] [R = Prⁱ (2), R = Et(3)] have been prepared for the first time by the reactions of CuCl₂ · xROH with KTi₂(OR)₉ in 1:1 and 1:2 molar ratios, respectively, in benzene medium. The chloro(nonaalkoxo dititanato)copper(II) complexes undergo chloride replacement reactions by a variety of monodentate alkoxo (⁻OPrⁱ, ⁻OEt) and chelating [Al(OPrⁱ) ₄ ⁻ , Al(OEt) ₄ ⁻ , Nb(OPrⁱ) ₆ ⁻ , Zr₂(OPrⁱ) ₉ ⁻ , Sn₂(OPrⁱ) ₉ ⁻ , and Sn₂(OEt) ₉ ⁻ ] ligands to form interesting hetero(bi-and tri-)metallic complexes. Alcoholysis (with methyl alcohol and tert-butyl alcohol) and hydrolytic [with Ba(OH)₂ · 8H₂O powder] reactions of a few typical compounds have also been investigated. All of these have been characterized by elemental analyses, molecular weight determinations, spectral (i.r. and visible) and magnetic studies. On attempted volatilization under reduced pressure these complexes liberated titanium alkoxides as a volatile component leaving nonvolatile residues.     

Tantalum(v) oxoalkoxides. Synthesis and structure

Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPrⁱ)₅ afford crystalline oxoisopropoxide Ta₂O(OPrⁱ)₈ · PrⁱOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPrⁱ)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M _n O _m (OR) _p , oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta₂O(OPrⁱ)₈ (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)₅ (Alk = Me, Et, Prⁱ, or Bu¹¹). When compound1 is heated invacuo (10^–2–10^–3 Torr), Ta(OPrⁱ)₅ is sublimated. Crystals of Ta₇O₉(OPrⁱ)₁₇ (2) were formed upon prolonged storage of solutions of1 in PrⁱOH. Heptanuclear molecule2 consists of two [Ta₄] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one ₃-oxo and two ₂-OPrⁱ groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996.     

Synthesis and characterization of a new type of heterometallic derivative of zirconium

ZrCl₄ reacts with the potassium salt of the bifunctional tridentate Schiff base HOC₆H₄C(H)=NCH₂CH(Me)OH (LH₂) in a 1:1 molar ratio in benzene to give a new complex Zr(L)Cl₂ which, on reaction with different potassium isopropoxymetallates [e.g., KAl(OPr ⁱ )₄, KTi(OPr ⁱ )₅, and KNb(OPr ⁱ )₆], yield novel heterobimetallic derivatives. These new homo and heteronuclear coordination compounds have been characterized by elemental (N, Cl, Al, Ti, and Nb) analyses, molecular weight (ebullioscopic) measurements and spectral [i.r., n.m.r. (¹H, ¹³C and ²⁷Al)] studies and probable structures for them have been suggested.     

Syntheses and characterization of a new class of zirconia precursors of oxime-modified zirconium(IV) isopropoxide

Some oxime modified complexes of the type [Zr{OPrⁱ}_4?n{L}_n] {where, n = 1–4 and LH=(CH₃)₂C=NOH (1–4) and C₉H₁₆C=NOH (5–8)} have been synthesized by the reaction of [Zr(OPrⁱ)₄·PrⁱOH] with oximes, in anhydrous refluxing benzene. These synthesized complexes were characterized by elemental analyses, molecular weight measurements, ESI-mass, FT-IR and NMR (¹H and ¹³C{¹H}) spectral studies. The ESI-mass spectral studies indicate dimeric nature for [Zr{OPrⁱ}₂{ONC(CH₃)₂}₂] (2), [Zr{OPrⁱ}₃{ONC₁₀H₁₆}] (5) and [Zr{OPrⁱ}{ONC₁₀H₁₆}₃] (7) and monomeric nature for [Zr{ONC₁₀H₁₆}₄] (8). Oximato ligands appear to bind the zirconium in side on manner in all the complexes. Thermogravimetric curves of (2) and (8) exhibit multi-step decomposition with the formation of ZrO₂, under nitrogen atmosphere. Sol–gel transformations of precursors (5), (6), (7) and (8) in organic medium, yielded nano-sized tetragonal phase of zirconia samples (a), (b), (c) and (d), respectively, on sintering at ~600 °C. All these samples were characterized by Powder XRD patterns and EDX analyses. Surface morphologies of these samples were investigated by SEM images.     

Synthesis and structural properties of a series of pentacoordinate rhodium nitrosyl complexes: Crystal and molecular structures of cis-dibromonitrosylbis(methoxydiphenylphosphine)rhodium and trans-dibromonitrosylbis(iso-propoxydiphenylphosphine)rhodium

The pentacoordinate rhodium nitrosyl complexes [RhBr₂(NO)L₂ [L = P(OPh)₂Ph, P(OMe)Ph₂ or P(OPrⁱ)Ph₂] have been synthesized and the structures of [RhBr₂(NO){P(OMe)Ph₂}₂] and [RhBr₂(NO){P(OPrⁱ)Ph₂}₂] have been determined X-ray crystallographically. Both of these latter compounds are tetragonal pyramidal with the nitrosyl group apical. The methoxydiphenylphosphine ligands in [RhBr₂(NO){P(OMe)Ph₂}₂] are cis-disposed whereas the larger cis-propoxydiphenylphosphine ligands in [RhBr₂(NO){P(OPrⁱ)Ph₂}₂] are mutually trans. The nitrosyl group in trans-[RhBr₂(NO){P(OPrⁱ)Ph₂}₂] eclipses an Rh-P axis but in cis-[RhBr₂(NO){P(OMe)Ph₂}₂] it is staggered with respect to the P-Rh-P linkage. The isomeric behaviour of nitrosyl complexes of type [RhX₂(NO)L₂] (X = halogen, L = phosphorus donor ligand) is rationalized in terms of the size of the ligand L.