Phenoxide Complexes Research Articles

Preparation, structure and properties of triphenylphosphine rhodium aryloxides

The reaction of Wilkinson's catalyst with NaOAr in toluene cleanly affords the corresponding aryloxide complexes Rh(PPh 3) 3OAr ( 1). In solution, 1 exists in equilibrium with PPh 3 and the corresponding Rh(PPh 3) 2(π-ArO) ( 2). The addition of HOAr shifts the equilibrium completely toward the corresponding adducts 2·2HOAr, due to hydrogen bonding between the oxygen atom of the π-coordinated OAr ligand and two molecules of HOAr. Heating of 1a-d in toluene at 60–80°C leads to the elimination of HOAr with concomitant cyclometallation of a phenyl ring of one PPh 3 ligand, affording mixtures of 1, 2·2HOAr, a cyclometallated Rh complex and PPh 3. At room temperature, a reverse reaction slowly occurs to give equilibrium mixtures of 1, 2 and PPh 3. Complexes 1 readily with water, CO and H 2, affording Rh 2(PPh 3) 4(μ-OH) 2, Rh(PPh 3) 2(CO)OAr ( 3) and HRh(PPh 3) 3, respectively. The latter complex was also obtained when complexes 1 were treated with methanol. The structures of the phenoxide complexes 1 and 2·2PhOH and of p-nitrophenoxide complex 3 were established by X-ray diffraction.

Crystal structures of aryloxide complexes of zinc embracing sodium aryl group interactions: Na[Zn(2,6-diphenylphenoxide) 3(H 2O)] and Na[Zn 2(2,6-diisopropylphenoxide) 4Cl]·3THF

The addition of Na(2,6-diphenylphenoxide) to a diethyl ether solution of the monomeric Zn(2,6-diphenylphenoxide) 2(THF) 2 derivative affords the trisphenoxide complex, Na[Zn(2,6-diphenylphenoxide) 3(H 2O)] ( 1). An X-ray crystal structure analysis of 1 reveals the zinc to possess a distorted tetrahedral geometry and that the sodium counterion is essentially six-coordinate, being bound to the three oxygen atoms of the aryloxide ligands and the aromatic carbon atoms of one of the phenyl substituent on each of these ligands. An additional zinc phenoxide complex, Na[Zn 2(2,6-diisopropylphenoxide) 4Cl]·3THF ( 2), was obtained during the synthesis of Zn(2,6-diisopropylphenoxide) 2(THF) 2 in the presence of NaCl. The X-ray structure of 2 again shows the sodium ion to be six-coordinate, involved in an η 6-interaction with the phenoxide π-system and bound to two THF ligands and a chloride ion.

Rhodium aryloxide complexes containing terdentate nitrogen ligands, C-O bond formation, hydrogen bonding with phenol and oxidative addition reactions. Molecular structure of an Rh(III)-acetyl complex

The new rhodium(I) phenoxide complexes [Rh(OPh) (2,6-(CH=R 2) 2C 5H 3N)] (R 2 = i-Pr( 3), t-Bu( 4)) containing strongly electrondonating N-N′-N ligands, have been prepared by a metathesis reaction of [RhCl(2,6-(CH=R 2) 2C 5H 3N)] (R 2 = i-Pr ( 1), t-Bu ( 2)) with NaOPh. These rhodium(I) phenoxide complexes 3 and 4, which are very sensitive to O 2 but stable towards H 2O, give with phenol the adducts [Rh(OPh) (2,6-(CH=NR 2) 2C 5H 3N)] · HOPh (R2 = i-Pr ( 5), t-Bu ( 6)), which contain strong O-H⋯O hydrogen bonds. The hydrogen bonded phenol could not be extracted with diethyl ether, while no exchange of the hydrogen bonded phenol and the phenoxide ligand in 4 is observed on the NMR time scale. However, a small excess of phenol results in exchange of the hydrogen bonded phenol, the coordinated phenoxide ligand and free phenol on the NMR time scale. Reaction of 3 and 4 with p-nitrophenol afforded [Rh(OC 6H 4-(NO 2-4))(2,6-(CH=R 2) 2C 5H 3N)] · HOPh (R 2 = i-Pr ( 7), t-Bu ( 8)) in which the formed phenol is hydrogen bonded to the Rh(I)-OC 6H 4-(NO 2-4) moiety. The O-H⋯O bond is less strong than in 5 and 6, as the hydrogen bonded phenol could be removed by diethyl ether. Treatment of 3 with acetyl chloride and benzoyl chloride in benzene at room temperature gave phenylacetate and RhCl 2(C(O)C 6H 3) (2,6(C(H)=N-i-Pr) 2C 5H 3N)] ( 15), and phenylbenzoate and [RhCl 2(C(O)Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 19), respectively. Complex 15 and the analogous complex [RhCl 2(C(O)CH 3) (2,6-(C(H)=N-t-Bu) 2C 5H 3N)] ( 16) could also be prepared directly from acetyl chloride and 1 or 2, respectively. The single crystal X-ray determination of complex 16, monoclinic, space group P2 1/ c , a = 10.0477(5), b= 11.7268(6), c= 19.2336(9) Å, β = 92.041(4)°, Z = 4, R 1 = 0.0281, shows that the acetyl group occupies an axial position, while the N-N′-N ligand is positioned equatorially. In solution this geometry remains unchanged as was shown by variable temperature 1H NMR measurements. When the oxidative addition of acetyl chloride to 3 was carried out at −78°C in toluene the intermediate complex [RhCl(OPh) (C(O)Me) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 11) could be isolated, which at room temperature reductively eliminates phenylacetate with formation of 1. Oxidative addition of acetyl chlori de to 4 at room temperature gives [RhCl(OPh) (C(O)Me) (2,6-(C(H)=Nt-Bu) 2C 5H 3N)] ( 12) which yields phenylacetate and 2 at 70°C in benzene by inductive elimination. Treatment of 3 with two equivalents of benzyl chloride afforded a mixture of [RhCl(OPh) (CH 2Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 13) and [RhCl 2(CH 2Ph) (2,6-(C(H)=N-i-Pr) 2C 5H 3N)] ( 17) and some non-characterizable organic products, while 4 only yielded [RhCl(OPh) (CH 2Ph) (2,6-(C(H)=N-tBu) 2C 5H 3N)] ( 14).

A three-coordinate copper(i)-phenoxide complex that models the reduced form of galactose oxidase

A novel 3-coordinate Cu(I)-phenoxide complex with N-donor supporting ligation was structurally characterized and shown to be highly reactive towards dioxygen, similar to the reduced form of galactose oxidase.

Structural Diversity in Monomeric Cadmium Phenoxides.

Three monomeric Cd(II) phenoxide complexes have been prepared by reacting Cd[N(SiMe(3))(2)](2) with 2 equiv of 2,6-disubstituted phenols bearing sterically bulky tert-butyl or phenyl groups. The strongly coordinating solvents THF, tetrahydrothiophene (THT), and pyridine used for these reactions were incorporated into the metal's coordination sphere, leading to complexes with a general formulation of Cd(O-2,6-R(2)C(6)H(3))(2)(solv)(2)(-)(3). The Cd complexes obtained have been characterized crystallographically and have been found to adopt differing solid-state geometries. The X-ray crystal structure of Cd(O-2,6-(t)BuC(6)H(3))(2)(THF)(2), 1, previously reported by Buhro, displayed unusual square-planar coordination of the metal center. Complex 2, Cd(O(t)BuC(6)H(3))(2)(THT)(2), has been found to take on the same square-planar geometry, even with the more strongly donating thioether ligand. Alternatively, complex 3, Cd(O-2,6-Ph(2)C(6)H(3))(2)(THF)(2), has been found to adopt distorted-tetrahedral geometry, quite similar to its zinc congener. The O(1)-Cd-O(2) angle between the phenoxide ligands in 3 is 150.1(2) degrees, and the angle between the ether ligands is 83.1(3) degrees. When the strongly basic solvent pyridine was used, a five-coordinate complex 4, Cd(O-2,6-(t)BuC(6)H(3))(2)(py)(3), was isolated. This complex 4 is best described as having trigonal bipyramidal geometry with the phenoxide ligands and one pyridine defining the equatorial plane and two axial pyridine ligands having an angle of 169.7(2) degrees. The angle between the phenoxide ligands in 4 is 156.1(2) degrees. These complexes 1-4 have also been characterized in noncoordinating solvent solutions by (1)H, (13)C, and (113)Cd NMR spectroscopy and have been found to contain labile donor ligands. Preliminary studies indicate that, in a noncoordinating solvent, a rapid equilibrium exists between species with and without coordinated donor solvent ligands.

Diamino-ligated platinum(II) and platinum(IV) phenoxide complexes; syntheses and crystal structures

The reaction of the diamino-ligated dimethylplatinum(II) complex [Pt(Me) 2(bpy)] (bpy = 2,2′-bipyridyl) with phenol affords the new complex [Pt(Me)(OPh)(bpy)] ( 1). The X-ray crystal structure of square-planar 1 is reported: orthorhombic, space group P2 12 12 1 No. 19), a = 9.1625(12), b = 12.3922(12), c = 13.3181(13) A ̊ , Z = 4 . Reaction of complex 1 with MeI or benzyl bromide affords the novel six-coordinate platinum(IV) aryloxide complexes [Pt(Me) 2(I)(OPh)(bpy)] ( 2) and [Pt(Me)(CH 2Ph)(Br)(OPh)(bpy)] ( 3), respectively. The X-ray crystal structure of octahedral 2 is reported: monoclinic, space group P2 1/ c (No. 14), a = 10.0194(6), b = 10.5126(10), c = 17.6596(14) A ̊ , β = 104.159(6)°, Z = 4 . The iodide complex 2 exists as a mixture of two isomers in solution (the major one corresponds to that of trans oxidative addition), whereas the bromide complex 3 is found only as the trans oxidative addition product.

Catalytic activity of supported tungsten phenoxide complexes in olefin metathesis; XPS characterization; application of molecular modelling to surface organometallic chemistry

Heterogeneous catalysts with respect to the metathesis of olefins has been prepared by a controlled thermal reaction between W(O-2,6-C 6H 3X 2) 2Cl 4 (X = t-Bu, Me, Br, and Cl) or W(MBPD)Cl 4 and a silica support. Surface characteristics of the powder catalysts and a model catalyst have been determined by conventional XPS and Angle-Resolved XPS (AR-XPS). The catalytic activity has been related to the structure of the molecular entities on the surface of the precursor. Furthermore, a model for hydroxylated silica is described. The surface structure ( SiO) 2W(O-2,6-C 6H 3X 2) 2Cl 2 is modeled to determine the preferred arrangement of the tungsten diphenoxide species on the hydroxylated support.

Phenyl-to-Oxo Migration in an Electrophilic Rhenium(VII) Dioxo Complex

Reaction of (HBpz3)ReO(Ph)(OTf) with oxygen atom donors leads to oxidation of the phenyl group [HBpz3 = hydrotris(1-pyrazolyl)borate, OTf = triflate, OSO2CF3]. Reaction with Me2SO gives the adduct [(HBpz3)ReO(Ph)(OSMe2)]OTf, which undergoes phenyl-to-oxo migration at 25 °C to give the phenoxide complex [(HBpz3)ReO(OPh)(OSMe2)]OTf and Me2S. The Me2SO adduct readily and reversibly loses Me2S (k = 2.9(4) s-1 at 25 °C) as indicated by isotope exchange reactions and magnetization transfer. The Me2SO adduct also slowly oxidizes Me2SO to Me2SO2. These reactions all proceed via an intermediate rhenium(VII) dioxo complex, [(HBpz3)ReO2(Ph)]OTf. This dioxo complex can be observed at low temperature on reaction of (HBpz3)ReO(Ph)(OTf) with pyridine N-oxide. It rearranges at 0 °C by phenyl-to-oxo migration to give phenoxide products and the catecholate complex (HBpz3)ReO(O2C6H4). The kinetics of this migration have been measured (ΔH⧧ = 14.8(7) kcal/mol, ΔS⧧ = −20.5(25) eu). From these data and the activation parameters for reactions of [(HBpz3)ReO(Ph)(OSMe2)]OTf, a detailed free energy surface for the reactions of [(HBpz3)ReO2(Ph)]OTf is constructed. The dioxo complex reacts very rapidly with Me2S (1.7 × 105 M-1 s-1) with essentially no enthalpic barrier, consistent with the action of a highly electrophilic oxo ligand. Electrophilicity of the oxo groups is suggested to be a critical factor in facilitating the phenyl-to-oxo migration. A general explanation for the relative ease of various organometallic migration reactions, based on analogies with organic [1,2]-shifts, is presented.

Synthesis of Allylnickel Aryloxides and Arenethiolates: Study of Their Dynamic Isomerization and 1,3-Diene Polymerization Activity

A new family of allylnickel(I1) complexes, [Ni(η^3-+allyl)(µ-X)]_2 (X = ArO, ArS), have been synthesized by anion metathesis of the sodium or lithium salts of aryloxides or arenethiolates with [Ni(η^3-allyl)(µ-Br)]_2. The complexes are proposed to be dimeric and to consist of a mixture of cis and trans isomers. A dynamic process rapidly equilibrates the cis and trans isomers of the pentafluorophenoxide, 2,6-difluorophenoxide, and 3,5-bis(trifluoromethyl)phenoxide complexes on the ^1H NMR time scale. The 2,6-dimethylphenoxide, 2,6-diisopropylphenoxide, 2,4,6- tris(trifluoromethyl)phenoxide, and pentafluorothiophenoxide complexes are static at room temperature. A variable-temperature NMR study of the 3,5-bis(trifluoromethyl)phenoxide complex provided activation enthalpy and entropy values of 12.9 kcal/mol and -6.6 cal/ (K mol), respectively. Allyl rotation or cleavage of one of the µ-X bridges is proposed as the mechanism for the isomerization. The pentafluorophenoxide, 3,5-bis(trifluoromethyl)phenoxide, and 2,4,6-tris(trifluoromethy1)phenoxide complexes initiate the rapid polymerization of 1,3-cyclohexadiene and 1,3-butadiene to form high-molecular weight, 1,4-linked polymers.

Palladium and platinum diphenoxide and aryl phenoxide complexes with amine donors: effect of hydrogen bonding on structure and properties

Palladium and platinum diphenoxide and aryl phenoxide complexes with amine donors: effect of hydrogen bonding on structure and properties

Alkyl and hydrido phenoxo complexes of nickel(II), palladium(II), and platinum(II). Hydrido amido complexes of palladium

The compound trans-NiHCl(PBz{sub 3}){sub 2}, where Bz=CH{sub 2}C{sub 6}H{sub 5}, has been synthesized in good yield by the reduction of NiCl{sub 2}(PBz{sub 3}){sub 2} with Super-Hydride, whereas the Pd and Pt analogues may be prepared by reduction of the corresponding MCl{sub 2}(PBz{sub 3}){sub 2} complexes with sodium naphthalide under an ethylene atmosphere, followed by the addition of HCl. Addition of NaOPh to trans-NiHCl(P{sup 1}Pr{sub 3}){sub 2} or trans-NiHCl(PCy{sub 3}){sub 2}, where {sup i}Pr = i-C{sub 3}H{sub 7} and Cy = c-C{sub 6}H{sub 11}, produces the corresponding hydrido phenoxo complexes, while the addition of NaOPh to trans-NiHCl(PBz{sub 3}){sub 2} yields trans-NiH(OPh)(PBz{sub 3}){sub 2}{center dot}HOPh. Addition of phenol to Pd(CH{sub 3}){sub 2}(dmpe), where dmpe = 1,2-bis(dimethyl-phosphino)ethane, yields Pd(CH{sub 3})(OPh)(dmpe). The reactivity of these late-transition-metal phenoxides suggests a high nucleophilicity for the metal-bound phenoxide, as evidenced by alkylation at oxygen by methyl iodide or by the insertion of an electrophile such as phenyl isocyanate. Thermally unstable hydrido anilido complexes trans-PdH(NHPh)L{sub 2}, where L = P({sup i}Pr){sub 3} or PCy{sub 3}, were prepared by addition of NaNHPh to the corresponding hydrido chloro complexes. With the use of Na{sup 15}NHPh it was possible to definitively characterize the solution structures of these unstable species by NMRmore » spectroscopy. Besides exhibiting alkylation and insertion reactivity similar to the phenoxide complexes, these compounds were extremely susceptible to reductive elimination of aniline on addition of ligands, such as acrylonitrile. A consideration of bond strengths, along with the observed tendencies for reductive elimination, suggests that catalytic animation of olefins by a cycle that requires N-H oxidative addition has thermodynamic limitations for the late transition metals.« less

New Addition Reactions of Cyclic Ethers with Esters and Thioesters Catalyzed by Quaternary Ammonium Salts or Crown Ether Complexes

Abstract A new addition reaction of 3-benzyloxymethyl-3-methyloxetane with S-phenyl thioacetate proceeded to give 3-benzyloxy-2-methyl-2-phenylthiomethylpropyl acetate catalyzed by 18-crown-6-potassium phenoxide complex. N-(2-Acetoxyethyl)-N-(2-phenoxyethyl)acetamide was also synthesized in high yield by the addition reaction of 5-methyl-4,6-dioxa-1-azabicyclo[3.3.0]octane with phenyl acetate, using tetrabutylammonium salts as catalysts.

Preparation and properties of methylplatinum fluoroalkoxide and phenoxide complexes, PtMe(OR)(PMe 3) 2 and PtMe(OR)(HOR)(PMe 3) 2 (R = CH(CF 3) 2, C 6H 5)

Reactions of cis-PtMe 2(PMe 3) 2 with 1,1,1,3,3,3-hexafluoro-2-propanol in 1/1 and 1/2 ratios give cis-PtMe(OCH(CF 3) 2)(PMe 3) 2 ( 1) and its hydrogen-bonded alcohol adduct, cis-PtMe(OCH(CF 3) 2)(HOCH(CF 3) 2)(PMe 3) 2 ( 2), respectively. Complex 2 undergoes exchange of the fluoroalkoxide ligand on addition of phenol to give cis-PtMe(OC 6H 5)(PMe 3) 2 ( 3) or its phenol adduct, cis-PtMe(OC 6H 5)-(HOC 6H 5)(PMe 3) 2 ( 4), depending on the ratio of added phenol to the complex. IR and NMR data of 2 and 4 indicate the presence of OH ··· O hydrogen bonding between the alkoxide (or phenoxide) ligand and the associated alcohol (or phenol) both in the solid state and in solution. Thermodynamic parameters for the association of the HOCH(CF 3) 2 with 1 in toluene have been obtained by means of 1H NMR spectroscopy as Δ H° −5.1 kcal mol −1, Δ G° −2.6 kcal mol −1, and Δ S° −9.1 e. u. at 273 K. Reaction of 1 with CO at room temeprature gives cis-PtMe(COOCH(CF 3) 2)(PMe 3) 2 ( 7a) produced through CO insertion into the PtO bond as confirmed by 31P{ 1H} and 13C{ 1H} NMR spectroscopy. The cis complex 7a is isomerized into trans-PtMe(COOCH(CF 3) 2)(PMe 3) 2 ( 7b) under the reaction conditions. Reaction of the phenoxide complex 3 with CO does not cause insertion of CO into the PtO bond, and gives trans-PtMe(OPh)(PMe 3) 2.

ChemInform Abstract: Monomeric Rhenium(IV) Phenoxides and Their Development from Mononuclear Rhenium Halides with Oxygen and Sulfur Donor Ligands.

AbstractThe homoleptic phenoxide complexes (IIIa) (space group P21/c, Z=4) and (IIIb) are prepared according to the scheme.

Uranium alkoxide chemistry. 3. tert-Butylisocyanide adducts of tris(2,6-di-tert-butylphenoxy)uranium(III)

The solution reactions of a uranium(III) phenoxide complex, U(O-2,6, t-Bu{sub 2}C{sub 6}H{sub 3}){sub 3}, with tert-butyl isocyanide (t-BuCN), a sterically unencumbered ligand, are described. The tert-butyl isocyanide has been reported to form both 1:1 and 1:2 adducts in solution with the cerium(III) complex, Ce(O-2, 6,-t-Bu{sub 2}C{sub 6}H{sub 3}){sub 3}. Results of {sup 1}H NMR spectral studies indicated that the U complex is capable of binding one or two t-BuCN ligands in solution. At room temperature, the isonitile exchange between the base-free complex and the 1:1 adduct was noted to occur at a rate close to the NMR time scale, and the 1:1 adduct was found to rapidly exchange with the free t-BuCN in solution. 11 refs., 4 figs.

Synthesis and redox and structural chemistry of monomeric rhenium(IV) phenoxide complexes

Synthesis and redox and structural chemistry of monomeric rhenium(IV) phenoxide complexes

ChemInform Abstract: Synthesis and Reactivity of Two Monomeric Tungsten(IV) Phenoxide Complexes.

AbstractThe monomeric W(IV) phenoxide complexes (III) are synthesized according to the scheme.

Synthesis and reactivity of two monomeric tungsten(IV) phenoxide complexes

Synthese de W(L) 4 avec L=O-2,6-C 6 H 3 -iPr 2 ou O-2,6-C 6 H 3 Me 2 . Structure cristalline

The crystal structures of the 1:1:1 complexes of dicyclohexano-18-crown-6 (isomer B) with potassium phenoxide and phenol and dicyclohexano-18-crown-6 (isomer A) with sodium phenoxide and phenol

The crystal structures of the 1:1:1 complexes of dicyclohexano-18-crown-6 (isomer B) with potassium phenoxide and phenol, and of dicyclohexano-18-crown-6 (isomer A) with sodium phenoxide and phenol have been determined. The potassium phenoxide complex crystallizes in space group Pnca with a = 14.150(3), b = 23.794(6), c = 9.491(1) Å, and Z = 4. Thesodium phenoxide complex crystallizes in space group Pbca with a = 21.201(4), b = 24.406(6), c = 12.492(3) Å, and Z = 8. Both structures were solved by direct methods and refined by full matrix least-squares calculations to residuals, R, of 0.059 for the potassium phenoxide complex, and 0.069 for the sodium phenoxide complex. In the potassium phenoxide complex, the cation sits on a centre of symmetry, in the centre of the cavity formed by the crown ether in its regular conformation. The potassium is coordinated to all six crown oxygens as well as to two phenol/phenoxides, one on each side of the crown. Groups of phenol/phenoxide–potassium–phenol/phenoxide are linked by the hydrogen atoms to form a chain: K+… O … H … O … K+. The distance between the oxygens of the phenol/phenoxides is short, 2.48(1) Å. The hydrogen was initially located halfway between the two oxygens, on a 2-fold axis special position. Inspection of the difference Fourier map and refinement on the hydrogen position revealed, however, the presence of statistical or dynamical disordering. In the sodium phenoxide complex, the hexaether adopts an irregular conformation. The distances between the sodium and the crown oxygens range from 2.45 to 2.89 Å, while a distance of 2.363 Å is found with the phenoxide oxygen. Strong hydrogen bonding is found between the oxygens of the phenol and phenoxide. The O ….O distance is 2.471(4) Å.

Sterically congested tris phenoxide complexes of tantalum(V). The x-ray crystal structures of [TaCl 2(2,6-di-t-Butylphenoxide) 3] and [Ta 2Cl(μ-Cl) 2(2,6-di-isopropylphenoxide) 5(μ-O)

TaCl 5 reacts with two equivalents of lithium 2,6-di-t-butylphenoxide in benzene to give [TaCl 3(2,6-di-t-butylphenoxide) 2] ( 1) in 70% yield and with three equivalents of the lithium phenoxide in diethyl ether to give [TaCl 2(2,6-di-t-butylphenoxide) 3] ( 2) which can also be prepared by reaction of ( 1) with one equivalent of the lithium phenoxide. Three equivalents of lithium 2,6-di-isopropylphenoxide react with TaCl 5 to give [TaCl 2(diethylether)(2,6-di-isopropylphenoxide) 3] ( 4) which, on attempted recrystallization in the presence of air, gave [Ta 2Cl(μ-Cl) 2(2,6-di-isopropylphenoxide) 5(μ-O)] ( 5). Complexes ( 1), ( 2), and ( 4) were characterized by elemental analysis, IR, and 1H and 13C NMR spectra. Coordination of the phenoxide ligand in ( 2) is accompanied by downfield shifts of the phenyl ring ipso, ortho and para carbon resonances of 9.6, 3.6 and 3.1 ppm respectively, compared with the free ligand. For complex ( 4) the relative shifts are 5.9, 6.1 and 2.9 ppm. The structures of ( 2) and ( 5) have been determined by single-crystal X-ray diffraction methods. Crystals of ( 2) are monoclinic, space group P2 1/ c with a = 18.902(6) Å, b = 10.815(8) Å, c = 20.259(4) Å and β = 92.62(2)°; crystals of ( 5) are monoclinic, space group P2 1/ c with a = 11.174(1) Å, b = 20.402(4) Å, c = 27.143(3) Å and β = 94.58(1)°. Both structures were solved by Patterson and Fourier methods and refined to R values of 0.063 for the 1690 observed data for ( 2) and 0.062 for the 3693 observed data for ( 5). Complex ( 2) is monomeric with a square pyramidal coordination geometry about Ta. Observed distances are: TaO axial 1.83(2) Å; TaO basal each 1.90(2) Å; TaCl basal each 1.37(1) Å. Complex ( 5) is binuclear with a distorted octahedral geometry about each tantalum atom. The structure consists essentially of TaCl 2(2,6-di-isopropylphenoxide) 3 and TaCl 2(O)(2,6-di-isopropylphenoxide) 2 units bridged through the oxygen and Cl atoms. Observed distances are TaO bridge 1.69(1) and 2.10(1) Å; TaCl bridge 2.498(7), 2.396(8), 2.634(7) and 2.781(7) Å; TaCl terminal 2.309(8) Å. The TaO phenoxide distances range from 1.77(2) to 2.19(2) Å. In both ( 2) and ( 5) the phenyl rings are orientated such as to minimise interactions between the 2- and 6-substituents. In both molecules electron counts are maximized using π-electron density from the terminal ligands.