Syntheses for the new multidentate chelating ligands ((6,6′-((1,4-diazepane-1,4-diyl)bis(methylene))bis(pyridine-6,2-diyl))bis(methylene))bis(diphenylphosphine oxide) (2) and 6,6′-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2-((diphenylphosphoryl)methyl)pyridine 1-oxide) (3), based upon a 1,4-diazepane platform functionalized with 2-(diphenylphosphinoylmethyl)pyridine P-oxide and 2-(diphenylphosphinoylmethyl)pyridine N,P-dioxide fragments, respectively, are reported. Results from studies of the coordination chemistry of the ligands with selected lanthanide nitrates and Cu(BF4)2 are outlined, and crystal structures for two complexes, [Cu(2)](BF4)2 and [Cu(3)](BF4)2, are described along with survey Eu(III) and Am(III) solvent extraction analysis, for 3.New pre-organized, hexadentate chelating phosphinoylmethyl pyridine and –pyridine N-oxide ligands, based upon a 1,4-diazepane platform, form stable complexes with Ln(III) and Cu(II) ions. Solvent extraction analyses for Eu(III) and Am(III) in nitric acid with the pyridine N-oxide derivative show improved performance, at the highest nitric acid concentrations, compared to the parent bidentate phosphinoylmethyl pyridine N-oxide ligand.

Syntheses and spectroscopic characterization data for two new hybrid chelating ligands, 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene (2) and 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene 5,5-dioxide (3), that contain two CMPO fragments grafted onto dibenzothiophene and dibenzothiophene sulfone platforms, respectively, are presented. Coordination chemistry with selected lanthanide nitrates is described along with a X-ray crystal structure determination for an unexpected Eu(III) complex, Eu(4)(NO3)3 that contains the intermediate ligand oxidation species 4,6-bis[(diphenyl-N,N-diethylcarbamoylmethylphosphine oxide)methyl]dibenzothiophene 5-oxide (4).New hybrid donor ligands based on the dibenzothiophene and dibenzothiophene-5,5-dioxide platforms decorated with C-attached carbamoylmethylphosphine oxide substituents have been prepared. The potential chelation behavior of the ligands has been explored with molecular mechanics calculations and selected coordination chemistry with Ln(NO3)3 salts examined. The acid dependence of the solvent extraction performance of the dibenzothiophene-5,5-dioxide derivative for Am(III) and Eu(III) has also been surveyed.

Syntheses for new ligands based upon dibenzothiophene and dibenzothiophene sulfone platforms, decorated with phosphine oxide and methylphosphine oxide donor groups, are described. Coordination chemistry of 4,6-bis(diphenylphosphinoylmethyl)dibenzothiophene (8), 4,6-bis(diphenylphosphinoylmethyl)dibenzothiophene-5,5-dioxide (9) and 4,6-bis(diphenylphosphinoyl)dibenzothiophene-5,5-dioxide (10) with lanthanide nitrates, Ln(NO3)3·(H2O)n is outlined, and crystal structure determinations reveal a range of chelation interactions on Ln(III) ions. The nitric acid dependence of the solvent extraction performance of 9 and 10 in 1,2-dichloroethane for Eu(III) and Am(III) is described and compared against the extraction behavior of related dibenzofuran ligands (2, 3; R = Ph) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (4) measured under identical conditions.

Stepwise syntheses of 2-{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]C5H4NO (6), 2-{[2-(diphenylphosphoryl)acetamido]methyl}-6-[(diphenylphosphoryl)methyl]pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]-6-[Ph2P(O)CH2]C5H3NO (7) and 2,6-bis{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3NO (8), are reported along with spectroscopic characterization data and single crystal X-ray diffraction structure determination for 6·2H2O, 7 and 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3N·MeOH 18·MeOH, the pyridine precursor of 8. Molecular mechanics computations indicate that 6, 7 and 8 should experience minimal steric hindrance to donor group reorganization that would permit tridentate, tetradentate and pentadentate docking structures for the respective ligands on lanthanide cations. However, crystal structure determination for the lanthanide complexes, {[Yb(6)(NO3)3]·(MeOH)}n, {[Lu(6)(NO3)3]·(MeOH)}n, [Er(6)2(H2O)2](NO3)3·(H2O)4}n, {[La(13)(NO3)3(MeOH)]·(MeOH)}n, {[Eu(7)(NO3)2(EtOAc)0.5(H2O)0.5](NO3)}2·MeOH and [Dy3(7)4(NO3)4(H2O)2](NO3)5·(MeOH)5·(H2O)2 reveal solid-state structures with mixed chelating/bridging ligand:Ln(III) interactions that employ lower than the maximal denticity. The binding of 6 and 7 with Eu(III) in the solid state and in MeOH solutions is also accessed by emission spectroscopy. The acid dependence for solvent extractions with 6 and 7 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared with the behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO, 1b) and 2-[(diphenyl)phosphinoylmethyl]pyridine N-oxide (DPhNOPO, 4a).

Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented.

Syntheses for a set of new ligands containing one or two carbamoylmethylphosphine oxide (CMPO) fragments appended to pyridine and pyridine N-oxide platforms are described. Molecular mechanics analyses for gas phase lanthanide–ligand interactions for the pyridine N-oxides indicate that the trifunctional NOPOCO molecules, 2-{[Ph2P(O)][C(O)NEt2]C(H)}C5H4NO (7) and 2-{[Ph2P(O)][C(O)NEt2]CHCH2}C5H4NO (8), and pentafunctional NOPOP′O′COC′O′ molecules, 2,6-{[Ph2P(O)][C(O)NEt2]C(H)}2C5H3NO (9) and 2,6-{[Ph2P(O)][C(O)NEt2]CHCH2}2C5H3NO (10), should be able to adopt, with minimal strain, tridentate and pentadentate chelate structures, respectively. As a test of these predictions, selected lanthanide coordination chemistry of the N-oxide derivatives was explored. Crystal structure analyses reveal the formation of a tridentate NOPOCO chelate structure for a 1:1 Pr(III) complex containing 7 while 8 adopts a mixed bidentate/bridging monodentate POCO/NO binding mode with Pr(III). Tridentate and tetradentate chelate structures are obtained for several 1:1 complexes of 9 while a pentadentate chelate structure is observed with 10. Emission spectroscopy for one complex, [Eu(9)(NO3)3], in methanol, shows that the Eu(III) ion resides in a low-symmetry site. Lifetime measurements for methanol and deuterated methanol solutions indicate the presence of four methanol molecules in the inner coordination sphere of the metal ion, in addition to the ligand, with the nitrate anions most likely dissociated. The solvent extraction performance of 7–10 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions was analyzed and compared with the performance of 2,6-bis(di-n-octylphosphinoylmethyl)pyridine N-oxide (TONOPOP′O′) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO) measured under identical conditions.

A four-step synthesis for 4,6-bis(diphenylphosphinoylmethyl)dibenzofuran (4) from dibenzofuran and a two-step synthesis for 4,6-bis(diphenylphosphinoyl)dibenzofuran (5) are reported along with coordination chemistry of 4 with In(III), La(III), Pr(III), Nd(III), Er(III), and Pu(IV) and of 5 with Er(III). Crystal structure determinations for the ligands, 4·CH3OH and 5, the 1:1 complexes [In(4)(NO3)3], [Pr(4)(NO3)3(CH3CN)]·0.5CH3CN, [Er(4)(NO3)3(CH3CN)]·CH3CN, [Pu(4)Cl4]·THF and the 2:1 complex [Nd(4)2(NO3)2]2(NO3)2·(H2O)·4(CH3OH) are described. In these complexes, ligand 4 coordinates in a bidentate POP′O′ mode via the two phosphine oxide O-atoms. The dibenzofuran ring O-atom points toward the central metal cations, but in every case it is more than 4 Å from the metal. A similar bidentate POP′O′ chelate structure is formed between 5 and Er(III) in the complex, {[Er(5)2(NO3)2](NO3)·4(CH3OH)}0.5, although the nonbonded Er···Ofuran distance is reduced to ∼3.6 Å. The observed bidentate chelation modes for 4 and 5 are consistent with results from molecular mechanics computations. The solvent extraction performance of 4 and 5 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared against the extraction behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (OΦDiBCMPO) measured under identical conditions.

The reactions of (Me3Si)3Al, Me3Al, Et3Al, and i-Bu3Al with 1,3,4,5,6-pentamethyl-2-aminoborazine have been examined. An amine alane adduct (Me3Si)3Al·NH2B3(Me)2N3Me3 (1) and several elimination products [(Me3Si)2AlN(H)B3(Me)2N3Me3]2 (2), [(Me3SiAl)4(Me3SiN)3NH] (3), [Me2AlN(H) B3(Me)2N3Me3]2 (4), [Et2AlN(H) B3(Me)2N3Me3]2 (5), and [i-Bu2AlN(H) B3(Me)2N3Me3]2 (6) have been isolated. Compounds 1, 2, 4−6 have been spectroscopically characterized, and single crystal X-ray diffraction structure determinations have been completed for 1−4 and 6. The molecular chemistry provides insight into the reaction of Me3Al and 1,3,5-N-trimethyl-2,4,6-B-triaminoborazine that, upon pyrolysis, produces AlN/BN composite ceramic materials.

An efficient three step synthesis of (benzoxazol-2-ylmethyl)phosphonic acid (6-H2) is described along with IR, mass spectrometry (MS), and 1H, 13C, and 31P NMR spectroscopic characterization data, and a single crystal X-ray diffraction structure determination. 6-H2 is unstable in acidic aqueous solutions (pH < 4) undergoing ring-opening to give [(2-hydroxyphenylcarbamoyl)methyl] phosphonic acid (7-H2) that is characterized by IR, MS, and NMR methods. The protonation constants (pKa) for 7-H2 have been measured, and crystal structure determinations for (NH4)(7-H) and K(7-H)·DMF are described. Reactions of NaOH and KOH with 6-H2 in MeOH/H2O solutions led to isolation and crystal structure determinations of the salts [Na(6-H)·H2O]2, K(6-H), Na3(6)(6-H)·H2O, and [K2(6)]2·3H2O. The complexation reactions of 7-H2 with La(III), Nd(III), and Gd(III), as a function of pH, were also examined by titrametric methods, and a model for the 1:1 anion binding with Ln(III) cations is proposed.

Phosphinoyl Grignard-based substitutions on 2,6-bis(chloromethyl)pyridine followed by N-oxidation of the intermediate 2,6-bis(phosphinoyl)methylpyridine compounds with mCPBA give the target trifunctional ligands 2,6-bis[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine 1-oxide (2a) and 2,6-bis[bis(3,5-bis(trifluoromethyl)phenyl)phosphinoylmethyl]pyridine 1-oxide (2b) in high yields. The ligands have been spectroscopically characterized, the molecular structures confirmed by single crystal X-ray diffraction methods, and the coordination chemistry surveyed with lanthanide nitrates. Single crystal X-ray diffraction analyses are described for the coordination complexes Nd(2a)(NO3)3, Nd(2a)(NO3)3·(CH3CN)0.5, Eu(2a)(NO3)3, and Nd(2b)(NO3)3·(H2O)1.25; in each case the ligand binds in a tridentate mode to the Ln(III) cation. These structures are compared with the structures found for lanthanide coordination complexes of the parent NOPOPO ligand, [Ph2P(O)CH2]2C5H3NO.

A synthetic route for the formation of 2-[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1c) and 2-[bis(3,5-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1d) was developed and the new ligands characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The coordination chemistry of 1c was examined with Yb(NO3)3 and the molecular structure of one complex, [Yb(1c)(NO3)3(DMF)]·DMF·0.5H2O, was determined by single-crystal X-ray diffraction methods. The ligand is found to coordinate in a bidentate fashion, and this is compared against lanthanide coordination chemistry observed for the related ligand, [Ph2P(O)CH2] C5H4NO.

The transamination reactions between Ti(NMe2)4 and 1,3,4,5,6-pentamethyl-2-aminoborazine, (Me)3N3(Me)2B3(NH2), and diphenylamine (Ph2NH) and between [Zr(NMe2)4]2 and 1,3,4,5,6-pentamethyl-2-aminoborazine, aniline (PhNH2) and diphenylamine have been studied and the molecular product species have been isolated, spectroscopically characterized and single crystal X-ray structure analyses completed. The results of these studies have been used to interpret the outcome of reactions of Ti(NMe2)4 and Zr(NMe2)4 with borazinylamine preceramic polymers that, upon pyrolysis, produce TiN/BN, ZrN/BN and ZrH0.6N/BN composite powders.The transamination reactivity of a two-point poly(borazinylamine) oligomer having terminal –NH2 amino groups with Ti(NMe2)4 and Zr(NMe2)4 has been used to obtain metallated preceramic oligomers that, upon pyrolysis, give TiN/BN and ZrN/ZrH0.6N/BN nanocomposites. Model reactions of 1,3,4,5,6-pentamethyl-2-amino borazine, aniline and Ph2NH2 with Ti(NMe2)4 and Zr(NMe2)4 are also described as models for the formation of the metallated oligomers. Molecular structure determinations for the metal amides are presented.Open image in new window

The trifunctional ligands, [(HO)2P(O)CH2]2C6H2(R)OH, (5-H4) (R = CH3, Br) were prepared in good yield via an Arbusov reaction between P(OEt)3 and the respective 4-R-2,6-bis(chloromethyl)phenols followed by acidic aqueous hydrolysis and they were spectroscopically characterized by IR and NMR techniques. The ligand 5-H4–CH3 readily dissolves lanthanide hydroxide residues and it forms a crystalline complex from aqueous LaCl3 solutions. This complex was characterized by single crystal X-ray diffraction methods and found to adopt a complex 2-D lamellar network in the bc plane. The La(III) inner coordination sphere is seven coordinate formed by oxygen atoms from two water molecules and five phosphonate oxygen atoms from three different ligands. The phenolic oxygen atom is not involved in the ligand binding to La(III).

The trifunctional ligand 2,6-[(C6H5)2P(O)CH2]2C5H3NO forms stable complexes with trivalent and tetravalent f-element cations and it acts as an effective liquid–liquid extraction reagent when it is dissolved in CHCl3. In a search for more hydrocarbon solvent soluble extraction reagents, derivative ligands having alkyl substituents in the 4-pyridyl ring position, 4-R′-2,6-[(C6H5)2P(O)CH2]2C5H2NO (R′ = Et, Oct), have been prepared and characterized. A single crystal X-ray diffraction analysis for the Et derivative shows that the ligand molecular structure is closely related to the parent ligand, 2,6-[(C6H5)2P(O)CH2]2C5H3NO. The coordination chemistry of the ligands with Nd(NO3)3 has been examined, and the molecular structures of two complexes obtained with 1 ∶ 1 and 2 ∶ 1 ligand ∶ metal reactant ratios are reported.

The trifunctional mixed donor ligands 2,6-[R2P(S)CH2]2C5H3N 1 (R = Ph 1a, Tol 1b, n-Bu, 1c) and 2,6-[R2P(S)CH2]2C5H3NO 2 (R = Ph 2a, Tol 2b, n-Bu, 2c) have been prepared and characterized by spectroscopic (MS, IR, NMR) techniques. The coordination chemistry of one derivative 1a has been examined and the complex {[Ph2P(S)CH2]2C5H3N}Ni(NO3)2 has been crystallized and characterized by single-crystal X-ray diffraction methods. The structure contains a six coordinate Ni(II) ion bonded to a tridentate ligand 1a with Ni–Npyr 2.110(3) Å and Ni–S 2.481(1) and 2.402(1) Å, a bidentate nitrate anion and a monodentate NO3− anion.

The reaction of LiP(H)B(NiPr2)[N(SiMe3)2]·DME with Cp2ZrCl2 in a 2:1 ratio yields the metallodiphosphane Cp2Zr{P(H)B(NiPr2)[N(SiMe3)2]}2 (3a). Combination of 3a with Mo(CO)4 (norbornadiene) provides the adduct Cp2Zr{P(H)B(NiPr2)[N(SiMe3)2]}2·Mo(CO)4 (4a) in which the metallo-diphosphane 3a acts as a chelating ligand. The compounds have been characterized by spectroscopic methods and the molecular structures of 3a and 4a have been determined by single-crystal X-ray diffraction methods. The chemical and structural features are compared and contrasted with related metallo-diphosphanes that contain organic substituents on the diphosphane P atoms.

The bifunctional ligand 2-[(C6H5)2P(O)CH2]C5H4NO (2), in EtOH, combined in a 1 ∶ 1 ratio with Pu(IV) in an aqueous nitric acid solution, produced an orange–brown coordination complex. The complex was characterized in MeOH solution by UV/vis/near-IR spectroscopy and in the solid state by single-crystal X-ray diffraction analysis. In the solid state, the complex exists as a 2 ∶ 1 coordination complex, [Pu(2)2(NO3)3+][Pu(NO3)62−]0.5, with the two ligands (2) bonded to the Pu(IV) ion in a bidentate fashion. Six oxygen atoms from three bidentate nitrate ions also occupy inner-sphere coordination positions. The complex cation charge is balanced by a hexanitratoplutonium(IV) dianion that resides on an inversion center between two monocationic [Pu(2)2(NO3)3+] units. The ten-vertex coordination polyhedron of the cation is distorted from square antiprismatic towards a sphenocorona. Optical absorbance spectra of the Pu(IV) in MeOH containing varying concentrations of nitrate and 2, show that multiple complexes form in solution.

Stepwise syntheses of 2-{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]C5H4NO (6), 2-{[2-(diphenylphosphoryl)acetamido]methyl}-6-[(diphenylphosphoryl)methyl]pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]-6-[Ph2P(O)CH2]C5H3NO (7) and 2,6-bis{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3NO (8), are reported along with spectroscopic characterization data and single crystal X-ray diffraction structure determination for 6·2H2O, 7 and 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3N·MeOH 18·MeOH, the pyridine precursor of 8. Molecular mechanics computations indicate that 6, 7 and 8 should experience minimal steric hindrance to donor group reorganization that would permit tridentate, tetradentate and pentadentate docking structures for the respective ligands on lanthanide cations. However, crystal structure determination for the lanthanide complexes, {[Yb(6)(NO3)3]·(MeOH)}n, {[Lu(6)(NO3)3]·(MeOH)}n, [Er(6)2(H2O)2](NO3)3·(H2O)4}n, {[La(13)(NO3)3(MeOH)]·(MeOH)}n, {[Eu(7)(NO3)2(EtOAc)0.5(H2O)0.5](NO3)}2·MeOH and [Dy3(7)4(NO3)4(H2O)2](NO3)5·(MeOH)5·(H2O)2 reveal solid-state structures with mixed chelating/bridging ligand:Ln(III) interactions that employ lower than the maximal denticity. The binding of 6 and 7 with Eu(III) in the solid state and in MeOH solutions is also accessed by emission spectroscopy. The acid dependence for solvent extractions with 6 and 7 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared with the behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO, 1b) and 2-[(diphenyl)phosphinoylmethyl]pyridine N-oxide (DPhNOPO, 4a).

A synthetic route for the formation of 2-[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1c) and 2-[bis(3,5-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1d) was developed and the new ligands characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The coordination chemistry of 1c was examined with Yb(NO3)3 and the molecular structure of one complex, [Yb(1c)(NO3)3(DMF)]·DMF·0.5H2O, was determined by single-crystal X-ray diffraction methods. The ligand is found to coordinate in a bidentate fashion, and this is compared against lanthanide coordination chemistry observed for the related ligand, [Ph2P(O)CH2] C5H4NO.