Diol Ligands Research Articles

Synthesis and Evaluation of New 1,7-Dioxaspiro[5.5]undecane Ligands: Implications for the Use of Diols in the Desymmetrization of meso Epoxides

The synthesis and preliminary evaluation of two new chiral 1,7-dioxaspiro[5.5]undecane ligands is described. The compounds of interest are readily available in enantiomerically pure form. Chiral organotitanium complexes prepared from these ligands catalyze the ring opening reaction of meso epoxides by TMSN3. A key observation suggests that silylation of the ligand competes with catalyst turnover in this application. Implications for the use of diol ligands are discussed.

Asymmetric Synthesis of Rigid C2-Symmetric Bis(ferrocenyl) Diol and Diamine Ligands

We report herein the asymmetric synthesis of C2-symmetric fused diferrocenyl diamine and diol ligands. The synthesis begins with the Cu(II)-mediated coupling of the diastereomerically and enantiome...

Pinane-Type Tridentate Reagents for Enantioselective Reactions: Reduction of Ketones and Addition of Diethylzinc to Aldehydes.

The reduction of aryl and alkenyl methyl ketones using lithium aluminum hydride modified with (1R,2S,3S,5R)-(+)-10-anilino-3-ethoxy-2-hydroxypinane (10b) afforded chiral secondary alcohols in 83-96% chemical yields and 50-91% ee with dominance of R enantiomers. The reduction of acetophenone in the presence of lithium iodide gave the alcohol product with higher ee. On the other hand, the addition reaction of diethylzinc to benzaldehyde using the pinane-based diols 5-9 as promoters gave 1-phenylpropanol in favor of the S enantiomer up to 88% ee. Using the pinane-based alcohols 10a-e as promoters, the R enantiomer was obtained as the major product. The addition reactions of diethylzinc to various substituted benzaldehydes, employing the diol ligands 5c and 8e, afforded predominantly the corresponding (S)-alcohols. The chiral modifiers 5-10 were prepared from (1R)-(-)-myrtenol and were readily recovered (>90%) after the asymmetric reactions. In this study, LAH reduction and Et(2)Zn addition are complementary methods for the preparation of optically active secondary alcohols. The ligand 10-butylanilino-2,3-dihydroxypinane 5c promoted the Et(2)Zn additions effectively, whereas the modifier 10-anilino-3-ethoxy-2-hydroxypinane 10binduced the LAH reductions in a highly enantioselective manner.

A New Entry to Enantioselective Synthesis of .ALPHA.-Methylene-.BETA.-hydroxy Ketones by the Chalcogeno-Baylis-Hillman Reaction.

Chiral hydroxy chalcogenides in the presence of TiCl4 achieved the asymmetric version of the chalcogeno-Baylis-Hillman reaction. The reaction proceeded under atmospheric pressure for 1h. 10-Methylthioisoborneol (9) achieved the best enantioselectivity. A methoxy derivative 10 of 10-methylthioisoborneol resulted in lower-selectivity than that obtained by 10-methylthioisoborneol (9). A hydroxyl group is required to perform good asymmetric induction. The asymmetric chalcogeno-Baylis-Hillman reaction with a C2 symmetric bidentate ligand-TiCl4 complex was also examined. Diol ligands gave the adduct in low to good yields with low or no enantiomeric excess. The adduct was also obtained in low to high yields with low or no enantiomeric excess using bisoxazoline ligands.

Mono(pentamethylcyclopentadienyl)titanium and -zirconium Complexes Supported by Chiral Diolate Ligands. X-ray Crystal Structures of [(η-C5Me5)TiCl(μ-η1,η1-2-CF3-dpbd)]2 and [HNEt3][(η-C5Me5)2Zr2Cl2(μ-Cl)(μ-η1,η2-3,5-Me2-dpbd)2

Reaction of optically pure (S,S)-butadiene diepoxide (1) with 2 equiv of Grignard reagent ArMgBr (Ar = 2-CF3C6H4 or 3,5-Me2C6H3) in the presence of copper(I) iodide produces the chiral substituted diphenylbutanediols (dpbd) (2S,3S)-ArCH2CH(OH)CH(OH)CH2Ar (Ar = 2-CF3C6H4 (2), abbreviated 2-CF3-dpbdH2; Ar = 3,5-Me2C6H3 (3), abbreviated 3,5-Me2-dpbdH2). The mono(pentamethylcyclopentadienyl) halide complex (η-C5Me5)TiCl3 reacts with 1 equiv of diol 2 in the presence of triethylamine to produce the dimeric species [(η-C5Me5)TiCl(μ-η1,η1-2-CF3-dpbd)]2 (4). An analogous reaction employing the zirconium halide (η-C5Me5)ZrCl3 and the diol 3 leads to isolation of the salt complex [HNEt3][(η-C5Me5)2Zr2Cl2(μ-Cl)(μ-η1,η2-3,5-Me2-dpbd)2] (5). Compounds 4 and 5 have been subjected to single-crystal X-ray diffraction studies. The solid-state structure of 4 consists of two titanium metal centers, each bearing a pentamethylcyclopentadienyl ligand and a terminal chloride ligand, bridged by two diolate ligands such that a central 10-membered ring is formed. The terminal Ti−Cl bond length is 2.306(2) Å, and the Ti−O distances range from 1.783(4) to 1.830(5) Å. The two bridging diolate ligands adopt widely differing conformations such that one diolate ligand possesses Ti−O−C angles of 172.3(4) and 172.4(4)° while the other displays acute Ti−O−C angles of 125.2(4)°. The molecular geometry of the anion in 5 is comprised of two (η-C5Me5)ZrCl moieties bridged by a single μ2-Cl ligand and two diolate ligands. One oxygen atom within each diolate ligand acts as a μ2 bridge between the zirconium metal centers whereas the other is bound in a terminal fashion to one metal center, thus forming a central Zr2O2 four-membered ring and two ZrO2C2 five-membered rings. Bridging Zr−Cl distances are 2.606(4) and 2.737(3) Å, and terminal Zr−Cl bond lengths are 2.499(4) and 2.584(4) Å. Terminal Zr−O distances are 1.989(9) and 1.972(9) Å, and bridging Zr−O distances range from 2.125(9) to 2.222(8) Å. Crystal data for 4 (at −90 °C): monoclinic space group P21, a = 12.399(1), b = 22.229(2), c = 13.275(1) Å, β = 111.208(6)°, V = 3411 Å3, Z = 2, Dcalc = 1.338 g cm-3. Crystal data for 5 (at −90 °C): orthorhombic space group P212121, a = 13.615(2), b = 13.623(2), c = 36.042(5) Å, V = 6685 Å3, Z = 4, Dcalc = 1.246 g cm-3.

Facile Syntheses of TiCl2(TADDOLate)(L2), Efficient Asymmetric Ethylation of PhCHO, and an Unexpected Rearrangement of the Tetramethyl Analogue of the TADDOL Ligand

Facile syntheses of TiCl2(TADDOLate)L2 (TADDOL = α,α,α‘,α‘-tetraphenyl-1,3-dioxolane-4,5-dimethanol; L = THF (1), AcOEt (2)) were developed from reactions of TiCl4 with the TADDOL ligand in coordinating solvent L. The labile solvent ligands L can be replaced by a neutral bidentate ligand such as 1,2-bis(diphenylphosphino)ethane (dppe) or 3,3-dimethyl-2,4-pentanedione (diketone) to give TiCl2(TADDOLate)(L2) (L2 = dppe (3), diketone (4)). The molecular structure of complex 3 shows a structure with two chlorides in trans positions, and the dppe ligand is trans to the strong alkoxide ligands. The most significant features of the structure are the long Ti−P(phosphine) bond distances observed, indicating considerable steric hindrance arising from the TADDOLate ligand in the complex. In a reaction of the TADDOL analogue α,α,α‘,α‘-tetramethyl-1,3-dioxolane-4,5-dimethanol with TiCl4 in Et2O, the unexpected complex 6 derived from rearrangement of the chiral diol ligand was obtained. This rearrangement is apparently...

Synthesis of Zirconium Pinacolate and Mechanism of Its Thermal Transformation to ZrO2: Impact of a Vicinal Diol Ligand

Reaction of Zr2(OiPr)8(HOiPr)2 with a slight excess of pinacol (HOCMe2CMe2OH) yields Zr2(OCMe2CMe2O)2(OCMe2CMe2OH)4, as confirmed by X-ray crystallography. Inter- and intramolecular hydrogen bonding results in the polymeric solid-state structure and the subsequent nonvolatility and reduced solubility of the species. The thermal transformation of zirconium pinacolate occurs in two distinct steps, as seen by the thermal gravimetric analysis (TGA), and occurs at <300 °C, yielding ZrO2, as determined by X-ray powder diffraction. GC−MS analysis of the thermolysis byproducts reveals six species: pinacol, pinacolone, 2,3-dimethyl-2-butene (tetramethylethylene) (trace amounts), 2,3-dimethylbutadiene (DMBD), 2,3-dimethyl-3-buten-2-ol (DMB-ol), 2,2,5,6,6-pentamethyl-4-hepten-3-one (PMH), and 1,3,5-tri-tert-butylbenzene (TTB). Real-time monitoring of the thermal transformation is achieved by carrying out the experiment inside a mass spectrometer. This novel experiment confirms that while only pinacol is lost in step I, step II consists of two phases. In step IIA, pinacolone, DMB-ol, PMH, and TTB are evolved, while in step IIB, only pinacolone and DMBD are formed. The observations support a primary mechanism for the formation of all C6 products except DMBD, which is a dehydration product of pinacolone. Mechanistic studies involving isotopic labeling experiments suggest that the C12 and C18 products are formed by a secondary process involving the interaction of evolved pinacolone with the metal oxide species. Crystallographic data (P1̄/−169 °C) for Zr2(OCMe2CMe2O)2(OCMe2CMe2OH)4 are as follows: a = 21.2305(5) Å, b = 22.905(5) Å, c = 10.508(3) Å, β = 104.01(1)°, with Z = 2.

New homochiral cyclic diol ligands for titanium alkoxide catalyzed phosphonylation of aldehydes

An investigation of the structural effects of chiral diol ligands on the enantioselectivity of phosphonylation was performed. Cyclic diols, and cyclohexanediol in particular, were identified as effective ligands for titanium alkoxide catalyzed asymmetric phosphonylation.

C2-Symmetric Ligands for Asymmetric Catalysis based on Feist's Acid

We describe a study of some of the chemistry of Feist's acid and attempts to prepare new diol and diamine ligands as well as a bis(indene) derivative.

ChemInform Abstract: The Titanium‐Catalyzed, Asymmetric Epoxidation of Allylic Alcohols with Optically Active Hydroperoxides in the Presence of Achiral Diol Ligands.

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The titanium-catalyzed, asymmetric epoxidation of allylic alcohols with optically active hydroperoxides in the presence of achiral diol ligands

The titanium-catalyzed, asymmetric epoxidation of dialkyl- and phenyl-substituted allylic alcohols with various enantiomerically pure hydroperoxides has been examined in the presence of achiral diol ligands. Enantioselectivities with ee values up to 50% were achieved in the oxygen transfer from (−)-(S)-1-phenylethyl 1a and (−)-(S)-1-phenylpropyl 1b hydroperoxides to 3-methyl-2-buten-1-ol 2a and geraniol 2b in the presence of the diethyl 2-hydroxy-2-hydroxymethylmalonate (DHHM) as an achiral multidentate diol ligand. The DHHM additive was ineffective in the asymmetric epoxidation of the phenyl-substituted allylic alcohols 3c-f, and only low ee values (up to 15%) were obtained. The optically active hydroperoxides (−)-(S)- 1c and (−)- 1d gave only moderate enantioselectivities (ee values up to 24%) with or without the achiral malonate additive DHHM. The concept of titanium-catalyzed, asymmetric epoxidation with optically active hydroperoxides as oxygen donors in the presence of multidentate diols as achiral ligands is less effective in its enantioselectivity than the Sharpless modus operandi of employing t-butyl hydroperoxide as achiral oxygen donor and the C 2-symmetric tartrate as chiral auxiliary.

Dinuclear (d(3)-d(3)) Diolate Complexes of Molybdenum and Tungsten. 1. Preparation and Characterization of Complexes Derived from 2,5-Dimethylhexane-2,5-diol.

Reaction of M(2)(O(t)Bu)(6) (M = Mo, W) with 3 equiv of 2,5-dimethylhexane-2,5-diol (LH(2)) in hexane/THF produces orange crystals of M(2)(&mgr;-L(3))(2), Ia (M = Mo), Ib (M = W), in high yield (80%). Treatment of M(2)(NMe(2))(6) with excess (>8 fold) LH(2) in THF/hexane solution at -20 degrees C produces exclusively green crystals of M(2)(&mgr;-L)(eta(2)-L)(2)(HNMe(2))(2), IIa (M = Mo), IIb (M = W), in high yield (75%). Dissolving IIa and IIb in toluene at room temperature slowly produces Ia and Ib, respectively, the process being accelerated by heat (t(1/2) = 10 min at 60 degrees C). Compounds Ia, Ib, IIa, and IIb were characterized by (1)H NMR, IR, melting point, and microanalysis, and Ib and IIb were also characterized by X-ray crystallography. Addition of excess HNMe(2) to a solution of Ia or Ib at -50 degrees C does not produce any IIa or IIb after 2 months, but at +25 degrees C, 40% IIa and IIb are produced with HNMe(2) after 2 days. Crystal data for Ib: W(2)(&mgr;-L)(3) at -171 degrees C, a = 12.568(2) Å, b = 12.568(3) Å, c = 37.075(8) Å, Z = 8, d(calcd) = 1.822 g/cm(3), space group I4(1)/a. The molecule Ib adopts an "ethane-like" staggered conformation with three eight-membered diolate rings spanning the W-W triple bond: W&tbd1;W = 2.3628(11) Å; W-O = 1.87 Å (average). Crystal data for compound IIb: W(2)(&mgr;-L)(eta(2)-L)(2)(HNMe(2))(2) at -170 degrees C, a = b = 20.198(3) Å, c = 17.819(3) Å, Z = 8, d(calcd) = 1.629 g/cm(3), space group P4/ncc. IIb has two essentially square planar WO(3)N units connected by a W-W triple bond, W&tbd1;W = 2.3196(12) Å, W-O = 1.95 Å (average), and W-N = 2.294(11) Å, and one bridging eight-membered diolate ring. The other two diolate ligands chelate at opposite ends of the molecule forming two seven-membered rings.

Cp ∗Ru(NO) (catecholate) compounds. Synthesis, redox behavior, extended Hückel molecular orbital calculations, and X-ray diffraction structure of the pentamethylcyclopentadienylruthenium complex Cp ∗Ru(NO) (2,3-naphthalenediolate)·CH 2Cl 2

Eight new catecholate- and naphthalenediolate-substituted pentamethylcyclopentadienylruthenium, compounds have been prepared from the reaction between Cp ∗Ru(NO)Cl 2 and the appropriate aromatic diol in methanolic KOH. Each new compound has been isolated and fully characterized in solution by IR and NMR ( 1H and 13C) spectroscopy, in addition to X-ray diffraction analysis which has established the solid-state structure of the naphthalenediolate compound Cp ∗Ru(NO)(2,3-O 2C 10H 6). Cp ∗Ru(NO)(2,3-O 2C 10H 6) crystallizes, as the CH 2Cl 2 solvate, in the monoclinic space group P2 1/ n with a = 11.0176(8), b = 16.041(2), c = 13.0504(9) A ̊ , β = 112.024(6)° , V = 2138.1(3) A ̊ 3 and Z=4. Full-matrix least-squares refinement yielded R=0.0376 for 1893 ( l.3 ϱ( l)) reflections. Cyclic voltammetric studies have been carried out, and two redox responses were observed, assignable to the 0/1− and 0/1+ redox couples. Whereas the reduction wave in each of the compounds is essentially independent of the nature of the ancillary diolate ligand, the stability of the oxidation couple is modulated by the electronic properties of the diolate ligand. The molecular orbital properties of several model CpRu(NO)(diolate) compounds were explored by extended Hückel calculations. The calculated HOMO and LUMO energies of each compound displayed good agreement with the cyclic voltammetry data, allowing for generalizations to be made concerning the site of electron addition to and electron removal from the new Cp ∗Ru(NO)(diolate) compounds.

Competitive Interactions of Phenol Derivatives and Aliphatic Alcohols for Alkenyl and Diol Silica Surfaces

A thermodynamic equation is used to analyze the retention behavior of phenolic solutes at low modifier concentrations on alkenyl and diol chemically modified silica packings. These materials were prepared by attaching alkenyl and diol ligands with four, six, eight and ten carbon atoms to the surface of LiChrosorb Si-60 silica. The thermodynamic analysis of the capacity ratios of various phenolic solutes measured at different concentrations of simple aliphatic alkohols (used as modifiers) in n-hexane have provided information about solute and solvent interactions with the alkenyl and diol modified silicas. This analysis shows that the solute-alcohol competitive interaction for the alkenyl bonded phases changes significantly with chain length, whereas this effect is not observed for the diol phases. Also, the influence of polarity and geometric structure of functional groups on solute retention have been examined.

Synthesis and characterization of phosphorus complexes of meso-tetraphenylporphyrin (tpp), and X-ray crystal structure of [P(tpp)(OCH(CH 3) 2) 2] +Cl −

Three cationic phosphorus(V) porphyrin complexes of the type [P(ttp)(L) 2] + [tpp = meso-tetraphenylphorphyrin; the axial ligand L = OCH(CH 3) 2, O(CH 2) 4OH, O- p-C 6H 4OH] have been prepared. All compounds were characterized by 1H and 13C NMR and mass spectrometry. The structure of the new compound di(2-propanolato)( meso-tetraphenylporphyrinato)phosphorus(V) chloride, [P(tpp)(OCH(CH 3) 2) 2] +Cl −, was determined by a single-crystal X-ray structure analysis. The cation of [P(tpp)(OCH(CH 3) 2) 2] +Cl − displays an octahedral coordination about the phosphorus atom and exhibits a ruffled porphyrin geometry with a core size of 1.866 Å. The displacement of the phosphorus atom from the porphyrin mean plane is 0.016 Å. The geometry around the phosphorus centre of the [P(tpp)(OCH(CH 3) 2) 2] +Cl − molecule has P(1)— O(1) = 1.650(3) A ̊ , P(1)— O(2) = 1.622(3) A ̊ and PNp = 1.866(4) A ̊ . NMR spectroscopy provides a convenient method for investigating the ring current effect (Δσ) between di(1,4-butanediolato) ( meso-tetraphenylporphyrinato)phosphorus(V) chloride, [P(tpp)(OCH 2CH 2CH 2CH 2OH) 2] +Cl −, with fluxional 1,4-butanediolate ligands, and di(1,4-hydroxy-benzeneato)( meso-tetraphenylporpyrinato)phosphorus(V) chloride, [P(tpp)(O- p-C 6H 4OH) 2] +Cl −, with rigid 1,4-hydroxybenzeneate ligands. It also differentiates the ring current effect for the diolate ligands of [P(tpp)(O(CH 2) n OH) 2] +Cl − with different chain lengths by increasing n from 2 to 4.

Synthesis of New Chiral Ligands and Their Group VI Metal Alkylidene Complexes

The new chelating chiral diol ligands (1S,2S)- and (1R,2R)-1,2-bis(2-hydroxy-2,2-bis(trifluoromethyl)ethyl)cyclopentane (TBEC-H2; 1) were synthesized. The dilithium alkoxide of TBEC was reacted with Mo(CHCMe2Ph)(NAr)(OTf)2dme (2; Ar = 2,6-(i-Pr)2C6H3) to give the chiral alkylidene complex Mo(CHCMe2Ph)(NAr)(TBEC) (3). The ligand also reacts with W(η2-diphenylcyclopropene)Cl2(O)[P(OMe)3]2 (4), W(CHCHCOCH2CH2CH2O)(O)Cl2[P(OMe)3] (5), and W(CHCHCPh2)(NAr)Cl2[P(OMe)3]2 (6; Ar = 2,6-(i-Pr)2C6H3) to the give stable corresponding tungsten oxo vinylalkylidene complexes and tungsten amide vinylalkylidene complexes, respectively. These group VI alkylidene complexes show excellent catalytic activity in both ring-opening metathesis polymerization and in ring-closing metathesis processes.

First examples of metal and ligand accelerated catalysis of the Baylis–Hillman reaction

Lanthanides and group III metal triflates (especially La, Sm) accelerate the Baylis–Hillman reaction (reaction between an unsaturated ester and aldehyde catalysed by DABCO, for example) and further acceleration can be obtained upon addition of diol ligands such as binol.

Dioxomolybdenum(VI) Complexes with New Enantiomerically Pure Amino Diol Ligands.

(R)-Phenylglycinol is shown to be an efficient building block for the synthesis of chiral amino diols in pure diastereomeric form by epoxide ring-opening reactions. The reaction with rac-trans-stilbene oxide gives [HOCH(2)-(R)-PhCH]NH[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)-HNO(2)H(2)] in 32% yield, which can be methylated at nitrogen to give enantiomerically pure [HOCH(2)-(R)-PhCH]NCH(3)[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)-MeNO(2)H(2)]. These amino diol ligands have been used to prepare chiral dioxomolybdenyl complexes of the formula N(R)-2(R)-3(R)-4(S)-(HNO(2))MoO(2) (1) and N(R)-2(R)-3(R)-4(S)-(MeNO(2))MoO(2) (2). The absolute configuration at each stereocenter in the Mo(VI) complexes has been established by (1)H NOESY spectroscopy. The configuration determined for 1 has been confirmed by an X-ray analysis. Crystal data: orthorhombic P2(1)2(1)2(1), a =7.620(3), b = 13.589(2), c = 20.339(3) Å, Z = 4, R = 0.0336. The structure consists of a polymeric chain of N(R)-2(R)-3(R)-4(S)-(HNO(2))MoO(2) molecules connected through unsymmetrical Mo=O --> Mo bridges. Each metal center is coordinated in a distorted octahedral geometry by a cis dioxo unit and by two trans alkoxo atoms. The coordination polyhedron is completed by a nitrogen atom and by a bridging oxo oxygen atom from an adjacent molecule. Compound 2 catalyzes the oxidation of PPh(3) to OPPh(3) by DMSO through a mechanism that involves the intermediacy of a Mo(IV) species.

Alkene epoxidation catalysed by camphor-derived β-ketophosphonate complexes of molybdenum(VI)

New β-ketophosphonates (L) have been prepared from (R)- or (S)-camphor with various substituents on the phosphorus atom [EtO, (R)- or (S)-BusO, Ph or binaphthoxy] and reacted with [MoO2CI2] to form complexes [MoO2CI2L]. These complexes have been used to give highly active catalysts for epoxidation of alkenes by ButOOH. Very fast initial rates (ca. 400 catalyst turnovers in the first minute) gave way to much slower rates because the hemi-labile β-ketophosphonate is displaced by a diol ligand. In the presence of molecular sieves, the fast initial stage of the reaction is extended and for styrene, which gives low conversions followed by degradation in the absence of molecular sieves, styrene oxide can be formed with 98% conversion and 94% selectivity. It is demonstrated that both the ButOOH and the catalyst bind to the molecular sieves, the latter with loss of the β-ketophosphonate ligand.

A Torsionally Constrained Diolate Ligand: Novel Complexes of Octahydrobinaphthol with Titanium(IV)

A Torsionally Constrained Diolate Ligand: Novel Complexes of Octahydrobinaphthol with Titanium(IV)