Lanthanide and uranium complexes with an SPS-based pincer ligand

Reactions of Ln(BH4)3(THF)n and [Li(Et2O)]SPS(Me)], the lithium salt of an anionic SPS pincer ligand composed of a central hypervalent lambda4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide sidearms, led to the monosubstituted compounds [Ln(BH4)2(SPS(Me))(THF)2] [Ln = Ce (1), Nd (2)], while the homoleptic complexes [Ln(SPS(Me))3] [Ln = Ce (3), Nd (4)] were obtained by treatment of LnX3 (X = I, BH4) with [K(Et2O)][SPS(Me)]. The [UX2(SPS(Me))2] complexes [X = Cl (5), BH4 (6)] were isolated from reactions of UX4 and the lithium or potassium salt of the [SPS(Me)]- anion. The X-ray crystal structures of 1.1.5THF, 2.1.5THF, 3.2THF.2Et2O, and 5.4py reveal that the flexible tridentate [SPS(Me)]- anion is bound to the metal as a tertiary phosphine with electronic delocalization within the unsaturated parts of the ligand.     

Homoleptic 12-coordinate lanthanoids with eta(2)-nitroso ligands

The complexes [Et(4)N](3)[Ln(eta(2)-dcnm)(6)] (Ln = La, Ce, Nd, Gd, dcnm = dicyanonitrosomethanide) have discrete N, O 12-coordination owing to symmetrical chelation of the nitroso donor groups.     

Mono-phosphacyclopentadienyl bis(tetramethylaluminate) lanthanide complexes

Homoleptic complexes Ln(AlMe(4))(3) (Ln = La, Nd) can be straightforwardly utilized in salt metathetic exchange reactions with potassium 2,3,4,5-tetramethylphospholide (KTmp) or 3,4-dimethyl-2,5-bis(trimethylsilyl)phospholide (KDsp) affording monophosphacyclopentadienyl hydrocarbyl complexes (eta(5)-PC(4)Me(4))Ln(AlMe(4))(2) and [eta(5)-PC(4)Me(2)(SiMe(3))(2)]Ln(AlMe(4))(2) (Ln = La, Nd). The solid-state structures reveal distinct metal size effects as evidenced by X-ray diffraction analyses of monomeric neodymium Tmp and Dsp derivatives as well as the dimeric lanthanum Tmp complex. Dimerization is accomplished by intermolecular P --> La donor contacts. Upon activation with [PhMe(2)NH][B(C(6)F(5))(4)] the monophosphacyclopentadienyl complexes initiate the polymerization of isoprene producing 1,4-trans-polyisoprene (tPIP > 87%) with moderate activity (approximately 30 kg(PIP) mol(Ln)(-1) h(-1)).     

Cerium(III) dialkyl dithiocarbamates from [Ce[N(SiMe3)2]3] and tetraalkylthiuram disulfides, and [Ce(kappa2-S2CNEt2)4] from the Ce(III) precursor; Tb(III) and Nd(III) analogues

The synthesis and characterisation of the first neutral cerium dialkyl dithiocarbamate complexes, using a novel oxidative displacement of the amido ligands of [Ce[N(SiMe3)2]3] by tetraalkylthiuram disulfides [R2NC(S)S]2(R = Me, Et) in thf solution, are reported. In the absence of other donors, the complexes [Ce(kappa2-S2CNMe2)3(thf)2] and Ce(kappa2-S2CNEt2)3) 3 were obtained. The addition of a polypyridyl ligand allowed easy access to a range of complexes of general formula [Ce(kappa2-S2CNR2)3(L[intersection]L)][R = Me and L([intersection])L = 2,2'-bipy (4), or 4,7-diphenyl-1,10-phenanthroline (6); or R = Et and L[intersection]L = 2,2'-bipy (5)]. Brief exposure of the Ce(III) dithiocarbamate to oxygen gas afforded in high yield the diamagnetic, crystalline Ce(IV) dithiocarbamate [Ce(kappa2-S2CNEt2)4)] 7. The neodymium (8) and terbium (10) complexes, isoleptic with 2, were prepared from the appropriate 4f metal (Ln) bis(trimethylsilyl)amide [Ln[pN(SiMe3)2]3][Ln = Nd or Tb (9)] and [Me2NC(S)S]2. The structures of the crystalline complexes, 2, 4, 6, 7, 9 and 10 have been determined by X-ray crystallography. Some evidence has been obtained for the formation of the cerium(IV) complex Ce[N(SiMe3)2]2(kappa2-S2CNMe2)2. The cerium(IV) complex 7 has the metal coordinated to eight sulfur atoms of four planar chelating S2CNC2 moities and its geometry is intermediate between dodecahedral and square prismatic; the mean Ce-S bond length of 2.803 A in 7 compares with the 2.950 A in the Ce(III) complex 2.     

Half-sandwich bis(tetramethylaluminate) complexes of the rare-earth metals: synthesis, structural chemistry, and performance in isoprene polymerization

The protonolysis reaction of [Ln(AlMe(4))(3)] with various substituted cyclopentadienyl derivatives HCp(R) gives access to a series of half-sandwich complexes [Ln(AlMe(4))(2)(Cp(R))]. Whereas bis(tetramethylaluminate) complexes with [1,3-(Me(3)Si)(2)C(5)H(3)] and [C(5)Me(4)SiMe(3)] ancillary ligands form easily at ambient temperature for the entire Ln(III) cation size range (Ln=Lu, Y, Sm, Nd, La), exchange with the less reactive [1,2,4-(Me(3)C)(3)C(5)H(3)] was only obtained at elevated temperatures and for the larger metal centers Sm, Nd, and La. X-ray structure analyses of seven representative complexes of the type [Ln(AlMe(4))(2)(Cp(R))] reveal a similar distinct [AlMe(4)] coordination (one eta(2), one bent eta(2)). Treatment with Me(2)AlCl leads to [AlMe(4)] --> [Cl] exchange and, depending on the Al/Ln ratio and the Cp(R) ligand, varying amounts of partially and fully exchanged products [{Ln(AlMe(4))(mu-Cl)(Cp(R))}(2)] and [{Ln(mu-Cl)(2)(Cp(R))}(n)], respectively, have been identified. Complexes [{Y(AlMe(4))(mu-Cl)(C(5)Me(4)SiMe(3))}(2)] and [{Nd(AlMe(4))(mu-Cl){1,2,4-(Me(3)C)(3)C(5)H(2)}}(2)] have been characterized by X-ray structure analysis. All of the chlorinated half-sandwich complexes are inactive in isoprene polymerization. However, activation of the complexes [Ln(AlMe(4))(2)(Cp(R))] with boron-containing cocatalysts, such as [Ph(3)C][B(C(6)F(5))(4)], [PhNMe(2)H][B(C(6)F(5))(4)], or B(C(6)F(5))(3), produces initiators for the fabrication of trans-1,4-polyisoprene. The choice of rare-earth metal cation size, Cp(R) ancillary ligand, and type of boron cocatalyst crucially affects the polymerization performance, including activity, catalyst efficiency, living character, and polymer stereoregularity. The highest stereoselectivities were observed for the precatalyst/cocatalyst systems [La(AlMe(4))(2)(C(5)Me(4)SiMe(3))]/B(C(6)F(5))(3) (trans-1,4 content: 95.6 %, M(w)/M(n)=1.26) and [La(AlMe(4))(2)(C(5)Me(5))]/B(C(6)F(5))(3) (trans-1,4 content: 99.5 %, M(w)/M(n)=1.18).     

Complexes of lanthanide nitrates with bis(diphenylphosphino)methane dioxide

The reactions of lanthanide nitrates, Ln(NO(3))(3), with bis(diphenylphosphino)methane dioxide, Ph(2)P(O)CH(2)P(O)Ph(2) (L), lead to complexes with three distinct classes of structure. At low ratios of Ln:L (<1:1.5) in acetonitrile the ionic complexes [Ln(NO(3))(2)L(2)](+)[Ln(NO(3))(4)L](-) (Ln = Pr, Eu) have been isolated. When carried out with a 1:2 or higher ratio in ethanol the reaction yields Ln(NO(3))(3)L(2) (Ln = La,Ce) and [Ln(NO(3))(2)L(2)H(2)O](+)[NO(3)](-) (Ln = Nd, Gd, Ho). Geometrical isomerism is found for the cations [Ln(NO(3))(2)L(2)H(2)O](+) and is attributed to the extent of hydrogen bonding to the coordinated water. Ligand redistribution occurs on heating in the solid state giving yellow solids in all cases. Crystallization of these materials from ethanol or acetonitrile gives [Ln(NO(3))L(3)](2+).2[NO(3)](-), which have been structurally characterized for Ln = Gd and Yb. Electrospray mass spectra indicate that extensive ligand exchange reactions occur in solution.     

Structural and near-IR photophysical studies on ternary lanthanide complexes containing poly(pyrazolyl)borate and 1,3-diketonate ligands

The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3-(2-pyridyl)pyrazol-1-yl]dihydroborate (L2, potentially tetradentate) have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm). [Eu(L1)(dbm)2] is eight-coordinate, with L1 acting only as a tetradentate chelate (with one potentially bidentate arm pendant) and two bidentate dbm ligands. [Nd(L1)(dbm)2] was also prepared but on recrystallization some of it rearranged to [Nd(L1)2][Nd(dbm)4], which contains a twelve-coordinate [Nd(L1)2]+ cation (two interleaved hexadentate podand ligands) and the eight-coordinate anion [Nd(dbm)4]- which, uniquely amongst eight-coordinate complexes having four diketonate ligands, has a square prismatic structure with near-perfect O8 cubic coordination. Formation of this sterically unfavourable geometry is assumed to arise from favourable packing with the pseudo-spherical cation. The isostructural series of complexes [Ln(L2)(dbm)2](Ln = Pr, Nd, Eu, Gd, Tb, Er, Yb) was also prepared and all members structurally characterised; again the metal ions are eight-coordinate, from one tetradentate ligand L2 and two bidentate dbm ligands. Photophysical studies on the complexes with Ln = Pr, Nd, Er, and Yb were carried out; all show the near-IR luminescence characteristic of these metal ions, with longer lifetimes in CD3OD than in CH3OH. For [Yb(L2)(dbm)2], two species with different luminescence lifetimes were observed in CH3OH solution, corresponding to species with zero or one coordinated solvent molecules, in slow exchange on the luminescence timescale. For [Nd(L2)(dbm)2] a single average solvation number of 0.7 was observed in MeOH. For [Pr(L2)(dbm)2] a range of emission lines in the visible and NIR regions was detected; time-resolved measurements show a particularly high susceptibility to quenching by solvent CH and OH oscillators.     

Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

This report covers studies in trivalent lanthanide complexation by two simple cyclohexanetriols that are models of the two coordination sites found in sugars and derivatives. Several complexes of trivalent lanthanide ions with cis,cis-1,3,5-trihydroxycyclohexane (L(1)()) and cis,cis-1,2,3-trihydroxycyclohexane (L(2)()) have been characterized in the solid state, and some of them have been studied in organic solutions. With L(1)(), Ln(L)(2) complexes are obtained when crystallization is performed from acetonitrile solutions whatever the nature of the salt (nitrate or triflate) [Ln(L(1)())(2)(NO(3))(2)](NO(3)) (Ln = Pr, Nd); [Ln(L(1)())(2)(NO(3))H(2)O](NO(3))(2) (Ln = Eu, Ho, Yb); [Ln(L(1)())(2)(OTf)(2)(H(2)O)](OTf) (Ln = Nd, Eu). Lanthanum nitrate itself gives a mixed complex [La(L(1)())(2)(NO(3))(2)][LaL(1)()(NO(3))(4)] from acetonitrile solution while [La(L(1)())(2)(NO(3))(2)](NO(3)) is obtained using dimethoxyethane as reaction solvent and crystallization medium. With L(2)(), Ln(L)(2) complexes have also been crystallized from methanol solution [Ln(L(2)())(2)(NO(3))(2)]NO(3), (Ln = Pr, Nd, Eu). Single-crystal X-ray diffraction analyses are reported for these complexes. Complex formation in solution has been studied for several triflate salts (La, Pr, Nd, Eu, and Yb) with L(1 )()and L(2)(), respectively in acetonitrile and in methanol. In contrast to the solid state, both structures Ln(L) and Ln(L)(2) equilibrate in solution, as was demonstrated by low-temperature (1)H NMR and electrospray ionization mass spectrometry experiments. Competing experiments in complexing abilities of L(1)() and L(2)() with trivalent lanthanide cations have shown that only L(2)() exhibits a small selectivity (Nd > Pr > Yb > La > Eu) in methanol.     

Regioselective C-H activation of lanthanide-bound N-heterocyclic carbenes

The reaction of Ln(L)N'2 (Ln = Nd, Ce; L = t-BuNCH2CH2[C{NCHCHNt-Bu}], N' = N(SiMe3)2) with trimethylsilyl iodide regiospecifically functionalises the carbene backbone at the C4-carbene ring position to afford the silylated complex Ln(L')N'I; Ln(L')N'2 is isolated after attempted reduction (L' = t-BuNCH2CH2[C{NC(SiMe3)CHNt-Bu}]) which allows a comparison of the structurally characterised complexes Nd(L)N'2, [Nd(L')N'I]2, and Nd(L')N'2.     

Steric modulation of coordination number and reactivity in the synthesis of lanthanoid(III) formamidinates

Reactions of a range of the readily prepared and sterically tunable N,N'-bis(aryl)formamidines with lanthanoid metals and bis(pentafluorophenyl)mercury (Hg(C6F5)2) in THF have given an extensive series of tris(formamidinato)lanthanoid(III) complexes, [Ln(Form)3(thf)n], namely [La(o-TolForm)3(thf)2], [Er(o-TolForm)3(thf)], [La(XylForm)3(thf)], [Sm(XylForm)3], [Ln(MesForm)3] (Ln=La, Nd, Sm and Yb), [Ln(EtForm)3] (Ln=La, Nd, Sm, Ho and Yb), and [Ln(o-PhPhForm)3] (Ln=La, Nd, Sm and Er). [For an explanation of the N,N'-bis(aryl)formamidinate abbreviations used see Scheme 1.] Analogous attempts to prepare [Yb(o-TolForm)3] by this method invariably yielded [{Yb(o-TolForm)2(mu-OH)(thf)}2], but [Yb(o-TolForm)3] was isolated from a metathesis synthesis. X-ray crystal structures show exclusively N,N'-chelation of the Form ligands and a gradation in coordination number with Ln3+ size and with Form ligand bulk. The largest ligands, MesForm, EtForm and o-PhPhForm give solely homoleptic complexes, the first two being six-coordinate, the last having an eta1-pi-Ar--Ln interaction. Reaction of lanthanoid elements and Hg(C6F5)2 with the still bulkier DippFormH in THF resulted in C--F activation and formation of [Ln(DippForm)2F(thf)] (Ln=La, Ce, Nd, Sm and Tm) complexes, and o-HC6F4O(CH2)4DippForm in which the formamidine is functionalised by a ring-opened THF that has trapped tetrafluorobenzyne. Analogous reactions between Ln metals, Hg(o-HC6F4)2 and DippFormH yielded [Ln(DippForm)2F(thf)] (Ln=La, Sm and Nd) and 3,4,5-F3C6H2O(CH2)4DippForm. X-ray crystal structures of the heteroleptic fluorides show six-coordinate monomers with two chelating DippForm ligands and cisoid fluoride and THF ligands in a trigonal prismatic array. The organometallic species [Ln(DippForm)2(C[triple chemical bond]CPh)(thf)] (Ln=Nd or Sm) are obtained from reaction of Nd metal, bis(phenylethynyl)mercury (Hg(C[triple chemical bond]CPh)2) and DippFormH, and the oxidation of [Sm(DippForm)2(thf)2] with Hg(C[triple chemical bond]CPh)2, respectively. The monomeric, six-coordinate, cisoid [Ln(DippForm)2(C[triple chemical bond]CPh)(thf)] complexes have trigonal prismatic geometries and rare (for Ln) terminal C[triple chemical bond]CPh groups with contrasting Ln--C[triple chemical bond]C angles (Ln=Nd, 170.9(4) degrees; Ln=Sm, 142.9(7) degrees). Their formation lends support to the view that [Ln(DippForm)2F(thf)] complexes arise from oxidative formation and C--F activation of [Ln(DippForm)2(C6F5)] intermediates.     

Lanthanide metallocene complexes of the 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato Ligand, (hpp)1-

Reaction of the lanthanide metallocene allyl complexes, (C(5)Me(5))(2)Ln(eta(3)-CH(2)CHCH(2))(THF) (Ln = Ce, Sm, Y) with 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, Hhpp, forms a series of metallocene complexes, (C(5)Me(5))(2)Ln(hpp) (Ln = Ce, Sm, Y) in which the (hpp)(1-) anion coordinates as a terminal bidentate ligand. Isomorphous structures were observed by X-ray crystallography regardless of the size of the metal. The acetonitrile adduct, (C(5)Me(5))(2)Sm(hpp)(MeCN), was also crystallographically characterized to provide an unusual pair of eight- and nine-coordinate complexes. The coordination mode of the (hpp)(1-) anion in these complexes is compared with that in other heteroallylic metallocenes like the caprolactamate (C(5)Me(5))(2)Y(ONC(6)H(10)) and the dithiocarbamate (C(5)Me(5))(2)Sm(S(2)CNEt(2)), which was also structurally characterized.     

Synthesis and structural comparison of a series of divalent Ln(Tp(R,R)')2 (Ln = Sm, Eu, Yb) and trivalent Sm(Tp(Me2))2X (X = F, Cl, I, BPh4) complexes

Reaction of LnI2 (Ln = Sm, Yb) with two equivalents of NaTp(Me2) or reduction of Eu(Tp(Me2))2OTf gives good yields of the highly insoluble homoleptic Ln(II) complexes, Ln(Tp(Me2))2 (Ln = Sm (1a), Yb (2a), Eu (3a)). Use of the additionally 4-ethyl substituted Tp(Me2,4Et) ligand produces the analogous, but soluble Ln(Tp(Me2,4Et))2 (1-3b) complexes. Soluble compounds are also obtained with the Tp(Ph) and Tp(Tn) ligands (Tn = thienyl), Ln(Tp(Ph))2 (Ln = Sm, 1c; Yb, 2c) and Ln(Tp(Tn))2 (Ln = Sm, 1d; Yb, 2d). To provide benchmark parameters for structural comparison the series of Sm(Tp(Me2))2X complexes (X = F, 1e; Cl, 1f; Br, 1g; I, 1h; BPh4, 1j) were prepared either via oxidation of the Sm(Tp(Me2))2 or salt metathesis from SmX3 (X = Cl, Br, I). The solid-state structures of 1-3a, 1b, 1-2c and 1e, 1f, 1h, and 1j were determined by single-crystal X-ray diffraction. The homoleptic bis-Tp complexes are all six-coordinate with trigonal antiprismatic geometries, planes of the kappa(3)-Tp ligands are parallel to one another. In the series of Sm(Tp(Me2))2X complexes the structure changes from seven-coordinate molecular compounds, with intact Sm-X bonds, for X = F, Cl, to six-coordinate ionic structures [Sm(Tp(Me2))2]X (X = I, BPh4), suitable crystals of the bromide compound could not be obtained. The dependence of the structures on the size of X is understandable in terms of the interplay between the size of the cleft that the [Sm(Tp(Me2))2](+) fragment can make available and the donor ability of the anionic group toward the hard Sm(III) center.     

Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl,carbonato, carbamato,thiocarbamate, and thioureide complexes of palladium(II)

Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh]]. Similarly, the reaction of [Pd(bipy)(C(6)F(5))(OH)] with PhNCO in methanol gives the N-phenyl-O-methylcarbamate complex [Pd(bipy)(C(6)F(5))[NPhC(O)OR]]. The reactions of [(N[bond]N)Pd(C(6)F(5))(OH)] with PhNCS in the presence of Et(2)NH yield the corresponding thioureidometal complexes [Pd(N[bond]N)(C(6)F(5))[NPhCSNR(2)]]. The crystal structures of [Pd(tmeda)(C(6)F(5))(CO(2)Me)], [Pd(2)(Me(2)bipy)(2)(C(6)F(5))(2)(mu-eta(2)-CO(3))].2CH(2)Cl(2), and [Pd(tmeda)(C(6)F(5))[SC(OMe)NPh]] have been determined.     

Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

A series of lanthanide amide complexes supported by bridged bis(amidinate) ligand L, LLnNHAr(1)(DME) (L = [Me(3)SiNC(Ph)N(CH(2))(3)NC(Ph)NSiMe(3)], Ar(1) = 2,6-(i)Pr(2)C(6)H(3), DME = dimethoxyethane, Ln = Y (1), Pr (2), Nd (3), Gd (4), Yb (5)), [Yb(μ(2)-NHPh)](2)(μ(2)-L)(2) (6) and [LYb](2)(μ(2)-NHAr(2))(2) (7) (Ar(2) = (o-OMe)C(6)H(4)), were synthesized by reaction of LLnCl(THF)(2) with the corresponding lithium amide in good yields and structurally characterized by X-ray crystal structure analyses. All complexes were found to be precatalysts for the catalytic addition of aromatic amines to aromatic nitriles to give monosubstituted N-arylamidines. The catalytic activity was influenced by lanthanide metals and the amido groups with the active sequence of Y (1) < Gd (4) < Nd (3) < Pr (2) ～ Yb (5) for the lanthanide metals and -NHAr(2) < -NHPh < -NHAr(1) for the amido groups. The catalytic addition reaction with complex 5 showed a good scope of aromatic amines. Some key reaction intermediates were isolated and structurally characterized, including the amidinate complexes LLn[NPhCNAr(1)](PhCN) (Ln = Y (8), Ln = Yb (9)), LYb[NAr(2)CNAr(1)](Ar(2)CN) (10), and amide complex 5 prepared by protonation of 9 by Ar(1)NH(2). Reactivity studies of these complexes suggest that the present catalytic formation of monosubstituted N-arylamidines proceeds through nucleophilic addition of an amido species to a nitrile, followed by amine protonolysis of the resultant amidinate species.     

Expanding dinitrogen reduction chemistry to trivalent lanthanides via the LnZ3/alkali metal reduction system: evaluation of the generality of forming Ln2(mu-eta2:eta2-N2) complexes via LnZ3/K

The Ln[N(SiMe(3))(2)](3)/K dinitrogen reduction system, which mimicks the reactions of the highly reducing divalent ions Tm(II), Dy(II), and Nd(II), has been explored with the entire lanthanide series and uranium to examine its generality and to correlate the observed reactivity with accessibility of divalent oxidation states. The Ln[N(SiMe(3))(2)](3)/K reduction of dinitrogen provides access from readily available starting materials to the formerly rare class of M(2)(mu-eta(2):eta(2)-N(2)) complexes, [[(Me(3)Si)(2)N](2)(THF)Ln](2)(mu-eta(2):eta(2)-N(2)), 1, that had previously been made only from TmI(2), DyI(2), and NdI(2) in the presence of KN(SiMe(3))(2). This LnZ(3)/alkali metal reduction system provides crystallographically characterizable examples of 1 for Nd, Gd, Tb, Dy, Ho, Er, Y, Tm, and Lu. Sodium can be used as the alkali metal as well as potassium. These compounds have NN distances in the 1.258(3) to 1.318(5) A range consistent with formation of an (N=N)(2)(-) moiety. Isolation of 1 with this selection of metals demonstrates that the Ln[N(SiMe(3))(2)](3)/alkali metal reaction can mimic divalent lanthanide reduction chemistry with metals that have calculated Ln(III)/Ln(II) reduction potentials ranging from -2.3 to -3.9 V vs NHE. In the case of Ln = Sm, which has an analogous Ln(III)/Ln(II) potential of -1.55 V, reduction to the stable divalent tris(amide) complex, K[Sm[N(SiMe(3))(2)](3)], is observed instead of dinitrogen reduction. When the metal is La, Ce, Pr, or U, the first crystallographically characterized examples of the tetrakis[bis(trimethylsilyl)amide] anions, [M[N(SiMe(3))(2)](4)](-), are isolated as THF-solvated potassium or sodium salts. The implications of the LnZ(3)/alkali metal reduction chemistry on the mechanism of dinitrogen reduction and on reductive lanthanide chemistry in general are discussed.     

Coordination ability of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) towards lanthanide(III) ions

The proton and metal complex equilibria of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (CDTP) with lanthanide(iii) ions, where Ln(III) = La(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Ho(III) and Lu(III) were studied. The stoichiometry, protonation and complex formation constants were determined by potentiometric titration at 25.0 degrees C and ionic strength of 0.1 mol dm(-3) (KCl). All metal ions form several species: [LnH4L]-, [LnH3L](2-), [LnH2L](3-), [LnHL](4-), [LnL](5-), [LnH(-1)L](6-) and [LnH(-2)L](7-) in the pH range between 2 and 11. The stability constants log beta(LnL) were found to be between 14.7 and 16.7. The studied complexes were also characterized by spectroscopic methods (31P NMR, UV-Vis absorption and emission spectroscopy). These studies allowed to reveal a distinct structural change of the Ln(III)-CDTP complex which occurs between protonated and hydroxy species in solutions at pH around 7.5. The major change is caused by the involvement of both nitrogen donors in the metal ion coordination occurring in ML species. The data obtained from UV-Vis spectroscopy allowed to draw conclusions about complex symmetry and to estimate a number of coordinated water molecules. The hydration number or more precisely the number of two OH oscillators was found to be approximately one in all species formed over the pH range between 5 and 10. The structure of the major hydroxy complex was supported by X-ray crystallographic data. The crystal structures of the Eu(III) and Tb(III) complexes clearly show that the CDTP ligand is coordinated to the Ln(III) ion by two nitrogen and four oxygen atoms in such a way that only one oxygen atom from each phosphonic group is placed in the lanthanide inner sphere. The monomeric complex anion is connected to a symmetry related ion through short hydrogen bonds formed by two hydroxy ions and one water molecule. In this way the two neighbouring anions form a quasi-dimer in which one of the Ln(III) ion is seven-coordinate (two N atoms, four O atoms and one hydroxy ion) and the other is eight-coordinate (two N atoms, four O atoms, one hydroxy ion and one water molecule).     

LnIIAlIII2(alkyl)8]x: donor addition instead of donor-induced cleavage

(SmAl2Me8)x and (SmAl2Et8)x are obtained via a silylamide elimination reaction from Sm[N(SiMe3)2]2(THF)2 and excess AlR3 (R = Me, Et); (LnAl2Et8)x (Ln = Sm, Yb) react with THF, pyridine, and 1,10-phenanthroline to form the first donor adducts of homoleptic peralkylated Ln-Al heterobimetallic complexes.     

Trivalent [(C5Me5)2(THF)Ln]2(mu-eta2:eta2-N2) complexes as reducing agents including the reductive homologation of CO to a ketene carboxylate, (mu-eta4-O2C-C=C=O)2-

The [Z(2)Ln(THF)](2)(mu-eta(2)():eta(2)()-N(2)) complexes (Z = monoanionic ligand) generated by reduction of dinitrogen with trivalent lanthanide salts and alkali metals are strong reductants in their own right and provide another option in reductive lanthanide chemistry. Hence, lanthanide-based reduction chemistry can be effected in a diamagnetic trivalent system using the dinitrogen reduction product, [(C(5)Me(5))(2)(THF)La](2)(mu-eta(2)():eta(2)()-N(2)), 1, readily obtained from [(C(5)Me(5))(2)La][BPh(4)], KC(8), and N(2). Complex 1 reduces phenazine, cyclooctatetraene, anthracene, and azobenzene to form [(C(5)Me(5))(2)La](2)[mu-eta(3):eta(3)-(C(12)H(8)N(2))], 2, (C(5)Me(5))La(C(8)H(8)), 3, [(C(5)Me(5))(2)La](2)[mu-eta(3):eta(3)-(C(14)H(10))], 4, and [(C(5)Me(5))La(mu-eta(2)-(PhNNPh)(THF)](2), 5, respectively. Neither stilbene nor naphthalene are reduced by 1, but 1 reduces CO to make the ketene carboxylate complex {[(C(5)Me(5))(2)La](2)[mu-eta(4)-O(2)C-C=C=O](THF)}(2), 6, that contains CO-derived carbon atoms completely free of oxygen.     

Synthesis, structure and catalytic activity of alkali metal-free bent-sandwiched lanthanide amido complexes with calix[4]-pyrrolyl ligands

Simple silylamine elimination reactions of calix[4]-pyrrole [R(2)C(C(4)H(2)NH)](4) (R = Me (1), {-(CH(2))(5)-}(0.5) (2)) with 2 equiv. of [(Me(3)Si)(2)N](3)Ln(μ-Cl)Li(THF)(3) (Ln = Nd, Sm, Dy) in reflux toluene, afforded the novel dinuclear alkali metal-free trivalent lanthanide amido complexes (η(5):η(1):η(5):η(1)-R(8)-calix[4]-pyrrolyl){LnN(SiMe(3))(2)}(2) (R = Me, Ln = Nd (3), Sm (4), Dy (5); R = {-(CH(2))(5)-}(0.5), Ln = Nd (6), Sm(7)). The complexes were fully characterized by elemental analyses, spectroscopic analyses and single-crystal X-ray analyses. X-ray diffraction studies showed that each lanthanide metal was supported by bispyrrolyl anions in an η(5) fashion and along with three nitrogen atoms from N(SiMe(3))(2) and two other pyrroyl rings in η(1) modes formed the novel bent-sandwiched lanthanide amido bridged trivalent lanthanide amido complexes, similar to ansa-cyclopentadienyl ligand-supported lanthanide amides with respect to each metal center. The catalytic activities of these organolanthanide complexes as single component l-lactide polymerization catalysts were studied.     

Reduction of dinitrogen with an yttrium metallocene hydride precursor, [(C5Me5)2YH]2

Treatment of [(C(5)Me(5))(2)YH](2), 1, with KC(8) under N(2) in methylcyclohexane generates the unsolvated reduced dinitrogen complex, [(C(5)Me(5))(2)Y](2)(μ-η(2):η(2)-N(2)), 2, and extends the range of yttrium and lanthanide LnZ(2)Z'/M (Z = monoanion; M = alkali metal) dinitrogen reduction reactions to (Z')(-) = (H)(-). The hydride complex, 1, is unique in this reactivity compared to other alkane-soluble yttrium metallocenes, [(C(5)Me(5))(2)YX](x) {X = [N(SiMe(3))(2)](-), (Me)(-), (C(3)H(5))(-), and (C(5)Me(5))(-)} which did not generate 2 when treated with KC(8). [(C(5)Me(5))(2)LnH](x)/KC(8)/N(2) reactions with Ln = La and Lu did not give isolable dinitrogen complexes. Complex 2 and the unsolvated lutetium analogue, [(C(5)Me(5))(2)Lu](2)(μ-η(2):η(2)-N(2)), 3, were obtained using benzene as a solvent and [(C(5)Me(5))(2)Ln][(μ-Ph)(2)BPh(2)] as precursors with excess KC(8). Complex 2 functions as a reducing agent with PhSSPh to form [(C(5)Me(5))(2)Y(μ-SPh)](2), 4, in high yield.