Facile construction of lanthanide metallomacrocycles with the bridging imidazolate and triazolate ligands and their ring expansions

Four novel tri- or tetranuclear organolanthanide metallomacrocycles [Cp2Ln(mu-Im)(THF)3 (Cp = C5H5, Ln = Yb (1), Er (2)], [Cp2Dy(mu-Im)]4(THF)]3 x 2THF (3), and [Cp'2Yb(mu-eta1:eta2-Tz)]4 x 2THF (Cp' = CH3C5H4) (4) have been synthesized through protolysis of Cp3Ln or Cp'3Yb with imidazole or triazole, indicating that both the bridge-ligand size and the lanthanide-ion radii can be applied in the modulation of the metallomacrocycles. Further investigations on the reactivity of complexes 1, 3, and 4 toward phenyl isocyanate reveal that PhNCO inserts readily into the simple bridge Ln-N bonds of 1 and 3 to yield the corresponding insertion products [Cp2Ln(mu-eta1:eta2-OC(Im)NPh)]3 (Ln = Yb (5), Dy (6)) but cannot insert into the Ln-N bond with a mu-eta1:eta2-bonding mode in 4. The novel bridge ligand [OC(Im)NPh] can expand the numbers of the ring members from 12 to 18 in 5 or 16 to 18 in 6. The number of metal atoms in the metallacycles with the ligand [OC(Im)NPh] is independent of the lanthanide-ion size; both trinuclear lanthanide macrocycles are observed in 5 and 6. All of these new complexes have been characterized by elemental analysis and spectroscopic properties, and their structures have also been determined through X-ray single-crystal diffraction analysis.     

Reactivity of organolanthanide and organolithium complexes containing the guanidinate ligands toward isocyanate or carbodiimide: synthesis and crystal structures

The direct reactions of (C5H5)2LnCl with LiN=C(NMe2)2 proceeded at room temperature in THF under pure nitrogen to yield the lanthanocene guanidinate complexes [(C5H5)2Ln(mu-eta1:eta2-N=C(NMe2)2)]2 (Ln = Gd (1), Er (2)). Treatment of phenyl isocyanate with complexes 1 and 2 results in monoinsertion of phenyl isocyanate into the Ln-N(mu-Gua) bond to yield the corresponding insertion products [(C5H5)2Ln(mu-eta1:eta2-OC(N=C(NMe2)2)NPh)]2 (Ln = Gd (3), Er (4)), presenting the first example of unsaturated organic small molecule insertion into the metal-guanidinate ligand bond. Further investigations indicate that N,N'-diisopropylcarbodiimide does not react with complexes 1 and 2 under the same conditions; however, it readily inserts into the lithium-guanidinate ligand bond of LiN=C(NMe2)2. As a synthon of the insertion product Li[(iPrN)2C(N=C(NMe2)2)], its reaction with (C5H5)2LnCl gives the novel organolanthanide complexes containing the guanidinoacetamidinate ligand, (C5H5)2Ln[(iPrN)2C(N=C(NMe2)2)] (Ln = Yb (5), Er (6), Dy (7)). All complexes were characterized by elemental analysis and spectroscopic properties. The structures of complexes 1, 3, 5 and 7 were determined through X-ray single-crystal diffraction analysis.     

Bridging mu-eta(5):eta(4)-coordination of an indenyl ligand and reductive coupling of diazabutadienes in the assembly of di- and tetranuclear mixed-valent ytterbium indenyldiazabutadiene complexes

The redox reaction of [Yb(C(9)H(7))(2)(thf)(2)] with the diazabutadiene PhN==C(Me)--C(Me)==NPh (DAD) has been found to depend on the molar ratio of the reactants. Reaction in a 1:2 molar ratio affords the dinuclear mixed-valent complex [Yb(2)(mu-eta(5):eta(4)-C(9)H(7))(eta(5)-C(9)H(7))(2){mu-eta(4):eta(4)-PhNC(Me)==C(Me)NPh}] containing an indenyl ligand with an unusual mu-eta(5):eta(4) bridging coordination. Reaction of equimolar amounts of these compounds results in an organolanthanide-mediated reductive coupling of the DAD ligands and formation of the tetranuclear mixed-valent complex [Yb(2)(mu-eta(5):eta(4)-C(9)H(7))(eta(5)-C(9)H(7))(2){mu-eta(4):eta(4)-PhNC(CH(2))==C(Me)NPh}](2) with a novel tetradentate tetraimine ligand.     

Reactivity of lanthanocene hydroxides toward ketene, isocyanate, lanthanocene alkyl, and triscyclopentadienyllanthanide complexes

The reactivity of [Cp(2)Ln(mu-OH)(THF)]2 (Ln = Y (1), Er (2), Yb (3)) toward PhEtCCO, PhNCO, Cp3Ln, [Cp2Ln(mu-CH3)]2, and the LiCl adduct of Cp2Ln(n)Bu(THF)x was examined. In all cases, OH-centered reactivity is observed: complexes 1-3 react with PhEtCCO to form the O-H addition products [Cp2Ln(mu-eta1:eta2-O2CCHEtPh)]2 (Ln = Yb (5), Er (6), Y (7), respectively, for 1-3), whereas treatment of 1 with PhNCO affords the addition/CpH-elimination/rearrangement product [{Cp2Y(THF)}2(mu-eta2:eta2-O2CNPh)] (8), which contains an unusual PhNCO(2) dianionic ligand. Analogous compound [Cp2Ln(THF)]2(mu-eta2:eta2-O2CNPh) (Ln = Yb (9), Er (10)) and 8 can be obtained in a higher yield by treatment of [Cp2Ln(mu-OH)(THF)]2 with PhNCO followed by reaction with the corresponding Cp3Ln. However, attempts to prepare the corresponding heterobimetallic complex by reacting stoichiometric amounts of [Cp2Y(mu-OH)(THF)]2 with PhNCO followed by treating it with Cp3Yb are unsuccessful. Instead, only rearrangement products 8 and 9 are obtained. Furthermore, the reaction of 3 with [Cp2Yb(mu-CH3)]2 or Cp3Yb forms oxo-bridged compound [Cp2Yb(THF)]2(mu-O) (11), whereas the reaction of [Cp2ErCl]2 with Li(n)Bu followed by treatment with 2 affords unexpected mu-oxo lanthanocene cluster (Cp2Er)3(mu-OH)(mu3-O)(mu-Cl)Li(THF)4 (12). In contrast to 1 and 2, 3 shows a strong tendency to undergo the intermolecular elimination of CpH at room temperature, giving trinuclear species [Cp2Yb(mu-OH)]2[CpYb(THF)](mu3-O) (4). The single-crystal X-ray diffraction structures of 1, 2, and 4-12 are described. All the results offer an interesting contrast to transition- and main-metal hydroxide complexes.     

Yttrium and lanthanide complexes having a chiral phosphanylamide in the coordination sphere

The chiral phosphanylamides {N(R-CHMePh)(PPh(2))}(-) and {N(S-CHMePh)(PPh(2))}(-) were introduced into rare earth chemistry. Transmetalation of the enantiomeric pure lithium compounds Li{N(R-CHMePh)(PPh(2))} (1a) and Li{N(S-CHMePh)(PPh(2))} (1b) with lanthanide bis(phosphinimino)methanide dichloride [{CH(PPh(2)NSiMe(3))(2)}LnCl(2)](2) in a 2:1 molar ratio in THF afforded the enantiomeric pure complexes [{CH(PPh(2)NSiMe(3))(2)}Ln(Cl){eta(2)-N(R-CHMePh)(PPh(2))}] (Ln = Er (2a), Yb (3a), Lu (4a)) and [{CH(PPh(2)NSiMe(3))(2)}Ln(Cl){eta(2)-N(S-CHMePh)(PPh(2))}] (Ln = Er (2b), Yb (3b), Lu (4b)). The solid-state structures of 2a and 3a,b were established by single-crystal X-ray diffraction. Attempts to synthesize compounds 3 in a one-pot reaction starting from K{CH(PPh(2)NSiMe(3))(2)}, YbCl(3), and 1 resulted in the lithium chloride incorporated complex [{(Me(3)SiNPPh(2))(2)CH}Yb(mu-Cl)(2)LiCl(THF)(2)] (5). In an alternative approach to give chiral rare earth compounds in a one-pot reaction 1a or 1b was reacted with LnCl(3) and K(2)C(8)H(8) to give the enantiomeric pure cyclooctatetraene compounds [{eta(2)-N(R-CHMePh)(PPh(2))}Ln(eta(8)-C(8)H(8))] (Ln = Y (6a), Er (7a), Yb (8)) and [{eta(2)-N(S-CHMePh)(PPh(2))}Ln(eta(8)-C(8)H(8))] (Ln = Y (6b), Er (7b)). The structures of 6a,b, 7a, and 8 were confirmed by single-crystal X-ray diffraction in the solid state.     

Reactivity of lanthanocene amide complexes toward ketenes: unprecedented organolanthanide-induced conjugate electrophilic addition of ketenes to arenes

This paper presents some unusual types of reactions of lanthanocene amide complexes with ketenes, and demonstrates that these reactions are dependent on the nature of amide ligands and ketenes as well as the stoichiometric ratio under the conditions involved. The reaction of [{Cp(2)LnNiPr(2)}(2)] with four equivalents of Ph(2)CCO in toluene affords the unexpected enolization dearomatization products [Cp(2)Ln(OC{2,5-C(6)H(5)(==CPhCONiPr(2)-4)}==CPh(2))] (Ln = Yb (1 a), Er (1 b)) in good yields, representing an unprecedented conjugate electrophilic addition to a non-coordinated benzenoid nucleus. Treatment of [{Cp(2)LnNiPr(2)}(2)] with four equivalents of PhEtCCO under the same conditions gives the unexpected enolization dearomatization/rearomatization products [{Cp(2)Ln(OC{C(6)H(4)(p-CHEtCONiPr(2))}==CEtPh)}(2)] (Ln = Yb (2 a), Er (2 b), Dy (2 c)). However, reaction of [{Cp(2)YbNiPr(2)}(2)] with PhEtCCO in THF forms only the mono-insertion product [Cp(2)Yb{OC(NiPr(2))==CEtPh}](THF) (3). Hydrolysis of 2 afforded aryl ketone PhEtCHCOC(6)H(4)(p-CHEtCONiPr(2)) (4) and the overall formation of aryl ketone 4 provides an alternative route to the acylation of aromatic compounds. Moreover, reaction of [{Cp(2)LnNHPh}(2)] with excess of PhEtCCO or Ph(2)CCO in toluene affords only the products from a formal insertion of the C==C bond of the ketene into the N--H bond, [(Cp(2)Ln{OC(CHEtPh)NPh})(2)] (Ln = Yb (5 a), Y (5 b)) or [(Cp(2)Er{OC(CHPh(2))NPh})(2)] (6), respectively, indicating that an isomerization involving a 1,3-hydrogen shift occurs more easily than the conjugate electrophilic addition reaction, along with the initial amide attack on the ketene carbonyl carbon. [{Cp(2)ErNHEt}(2)] reacts with an excess of PhEtCCO to give [(Cp(2)Er{PhEtCHCON(Et)COCEtPh})(2)] (7), revealing another unique pattern of double-insertion of ketenes into the metal-ligand bond without bond formation between two ketene molecules. All complexes were characterized by elemental analysis and by their spectroscopic properties. The structures of complexes 1 b, 2 a, 2 b, 5 a, 5 b, 6, and 7 were also determined through X-ray single-crystal diffraction analysis.     

Lanthanide-potassium wheels

Mixed potassium-lanthanide wheel-shaped-structured, hexanuclear coordination oligomers of composition [(eta5-C5H5)Ln(NPh2)2{N(PPh2)2}2K2(THF)4]2 (Ln = Er (1a), Yb (1b)) and an octanuclear coordination polymer of composition [(eta5-C5H5)Sm(NPh2)2{N(PPh2)2}K]infinity (2) were synthesized. All presented compounds can be obtained in moderate yields in a one-pot procedure, in which the potassium salts KNPh2 and [K(THF)(n)N(PPh2)2] as well as NaC5H5 are reacted with anhydrous samarium, erbium, and ytterbium trichloride in THF.     

Flexibility in the coordination chemistry of the 2,3-dimethylindolide ligand with potassium,yttrium, and samarium

The coordination chemistry of the 2,3-dimethylindolide anion (DMI), (Me(2)C(8)H(4)N)(-), with potassium, yttrium, and samarium ions is described. In the potassium salt [K(DMI)(THF)](n), 1, prepared from Me(2)C(8)H(4)NH and KH in THF, the dimethylindole anion binds and bridges potassium ions in three different binding modes, namely eta(1), eta(3), and eta(5), to form a two-dimensional extended structure. In the dimethoxyethane (DME) adduct [K(DMI)(DME)(2)](2), 2, prepared by crystallizing a sample of 1 from DME, DMI exists as a mu-eta(1):eta(1) ligand. Compound 1 reacts with SmI(2)(THF)(4) in THF to form the distorted octahedral complex trans-(DMI)(2)Sm(THF)(4), 3, in which the dimethyindolide anions are bound in the eta(1) mode to samarium. Reaction of 2,3-dimethylindole with Y(CH(2)SiMe(3))(3)(THF)(2) afforded the amide complex (DMI)(3)Y(THF)(2), 4, in which the dimethylindolide anions are also bound in the eta(1) mode to yttrium. Compound 1 also reacts with (C(5)Me(5))(2)LnCl(2)K(THF)(2) (Ln = Sm, Y) to form unsolvated amide complexes (C(5)Me(5))(2)Ln(DMI) (Ln = Sm, 5; Y, 6), in which DMI attaches primarily through nitrogen, although the edge of the arene ring is oriented toward the metals at long distances.     

Catalytic addition of amine N-H bonds to carbodiimides by half-sandwich rare-earth metal complexes: efficient synthesis of substituted guanidines through amine protonolysis of rare-earth metal guanidinates

Reaction of [Ln(CH(2)SiMe(3))(3)(thf)(2)] (Ln=Y, Yb, and Lu) with one equivalent of Me(2)Si(C(5)Me(4)H)NHR' (R'=Ph, 2,4,6-Me(3)C(6)H(2), tBu) affords straightforwardly the corresponding half-sandwich rare-earth metal alkyl complexes [{Me(2)Si(C(5)Me(4))(NR')}Ln(CH(2)SiMe(3))(thf)(n)] (1: Ln = Y, R' = Ph, n=2; 2: Ln = Y, R' = C(6)H(2)Me(3)-2,4,6, n=1; 3: Ln = Y, R' = tBu, n=1; 4: Ln = Yb, R' = Ph, n=2; 5: Ln = Lu, R' = Ph, n=2) in high yields. These complexes, especially the yttrium complexes 1-3, serve as excellent catalyst precursors for the catalytic addition of various primary and secondary amines to carbodiimides, efficiently yielding a series of guanidine derivatives with a wide range of substituents on the nitrogen atoms. Functional groups such as C[triple chemical bond]N, C[triple chemical bond]CH, and aromatic C--X (X: F, Cl, Br, I) bonds can survive the catalytic reaction conditions. A primary amino group can be distinguished from a secondary one by the catalyst system, and therefore, the reaction of 1,2,3,4-tetrahydro-5-aminoisoquinoline with iPrN==C==NiPr can be achieved stepwise first at the primary amino group to selectively give the monoguanidine 38, and then at the cyclic secondary amino unit to give the biguanidine 39. Some key reaction intermediates or true catalyst species, such as the amido complexes [{Me(2)Si(C(5)Me(4))(NPh)}Y(NEt(2))(thf)(2)] (40) and [{Me(2)Si(C(5)Me(4))(NPh)}Y(NHC(6)H(4)Br-4)(thf)(2)] (42), and the guanidinate complexes [{Me(2)Si(C(5)Me(4))(NPh)}Y{iPrNC(NEt(2))(NiPr)}(thf)] (41) and [{Me(2)Si(C(5)Me(4))(NPh)}Y{iPrN}C(NC(6)H(4)Br-4)(NHiPr)}(thf)] (44) have been isolated and structurally characterized. Reactivity studies on these complexes suggest that the present catalytic formation of a guanidine compound proceeds mechanistically through nucleophilic addition of an amido species, formed by acid-base reaction between a rare-earth metal alkyl bond and an amine N--H bond, to a carbodiimide, followed by amine protonolysis of the resultant guanidinate species.     

Synthesis and crystal structure of the first lanthanide complex of N-confused porphyrin with an eta2 agostic C-H interaction

The reaction of Ln[N(SiMe3)2]3.[LiCl(THF)3](x)(Ln = Yb and Er) with N-confused tetraphenylporphyrin (H2NCTPP) followed by Na(L(OMe))(L(OMe)=(eta5-C5H5)Co[P(=O)(OMe)2]) gives (NCTPP)Ln(L(OMe)), whose X-ray structures exhibit an eta2 agostic interaction between the metal centre and the inner C-H bond of the NCTPP ligand.     

Reactions of lanthanoid metals with 3,5-diphenylpyrazole at elevated temperatures: synthesis and structures of both homoleptic, [Ln3(Ph2pz)9] (Ln = La, Nd), [Ln2(Ph2pz)6] (Ln = Er, Lu), and heteroleptic, [Ln(Ph2pz)3(Ph2pzH)2] (Ln = La, Nd, Gd, Tb, Er or Yb), pyrazolate complexes

The direct reaction of lanthanoid metals with 3,5-diphenylpyrazole (Ph2pzH) at 300 degrees C under vacuum in the presence of mercury gives the structurally characterized [Ln3(Ph2pz)9] (Ln = La or Nd), [Ln2(Ph2pz)6] (Ln = Er or Lu). Similar reactions provided heteroleptic [Ln(Ph2pz)3(Ph2pzH)2] (Ln = La, Nd, Gd, Tb, Er and Y). The last was obtained only from impure Ph2pzH, but was subsequently prepared by treatment of [Yb(Ph2pz)3(thf)2] with Ph2pzH. Reactions of Yb with Ph2pzH at 200 degrees C gave a poorly soluble divalent species which was converted by 1,2-dimethoxyethane into [Yb(Ph2pz)2(dme)2]. Single crystal X-ray structures established a bowed trinuclear pyrazolate-bridged structure for [Ln3(Ph2pz)9] (Ln = La or Nd), Ln...Ln...Ln being 135.94(1) degrees (La) and 137.41(1) degrees(Nd). There are two eta2-Ph2pz ligands on the terminal Ln atoms and one on the central metal with adjacent Ln atoms linked by one mu-eta2:eta2 and one mu-eta5 (to terminal Ln):eta2 pyrazolate group. Thus the terminal Ln atoms are formally nine-coordinate and the central Ln, ten-coordinate. By contrast, [Ln2(Ph2pz)6] (Ln = Er or Lu) complexes are dimeric with two terminal (eta2) and two bridging (mu-eta2:eta2) pyrazolates and eight-coordinate lanthanoids. All six heteroleptic complexes [Ln(Ph2pz)3(Ph2pzH)2] (Ln = La, Nd, Gd, Tb, Er or Yb) are isomorphous with three equatorial eta2-Ph2pz groups, transoid(N-Ln-N 158.18(6)-161.43(9) degrees) eta1-pyrazole ligands, and eight-coordinate Ln throughout.     

Homolysis of the Ln-N (Ln = Yb, Eu) bond. Synthesis, structural characterization and catalytic activity of ytterbium(II) and europium(II) complexes with methoxyethyl functionalized indenyl ligands

The interaction of methoxyethyl functionalized indene compounds (C(9)H(6)-1-R-3-CH(2)CH(2)OMe, R =t-BuNHSiMe(2)(1), Me(3)Si (2), H (3)) with [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5)) produced a series of new ytterbium(II) and europium(II) complexes via tandem silylamine elimination/homolysis of the Ln-N (Ln=Yb, Eu) bond. Treatment of the lanthanide(III) amides [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5) with 2 equiv. of, 1,2 and 3, respectively, produced, after workup, the ytterbium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Yb(II) (6), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Yb(II) (7), (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Yb(II)(8) and the corresponding europium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Eu(II)(9), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Eu(II)(10) and (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Eu(II)(11) in moderate to good yield. In contrast, interaction of the corresponding indene compounds 1, 2 or 3 with the lanthanide amides [(Me(3)Si)(2)N](3)Ln (Ln = Yb, Eu) was not observed, while addition of 0.5 equiv. of anhydrous LiCl to the corresponding reaction mixture produced, after workup, the corresponding ytterbium(II) or europium(II) complexes. All the new compounds were fully characterized by spectroscopic and elemental analyses. The structures of complexes, and were determined by single-crystal X-ray analyses. The catalytic activity of all the ytterbium(II) and europium(II) complexes on MMA polymerization was examined. It was found that all the ytterbium(II) and europium(II) complexes can function as single-component MMA polymerization catalysts. The temperature, solvent and ligand effects on the catalytic activity were studied.     

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.     

Dinitrogen reduction by TmII,DyII, and NdII with simple amide and aryloxide ligands

Dinitrogen can be reduced to the planar M2(mu-eta2:eta2-N2) structure without employing cyclopentadienyl or complicated polydentate ligands using the recently discovered divalent oxidation states of Tm(II), Dy(II), and Nd(II). Complexes of these ions with common monodentate amide and aryloxide ligands can effect N2 reduction. THF solutions of LnI2 (Ln = Tm, Dy) in the presence of 2 equiv of NaN(SiMe3)2 reduce dinitrogen to form {[(Me3Si)2N]2(THF)Ln}2(mu-eta2:eta2-N2) complexes that have planar Ln2N2 units and 1.264(7) and 1.305(6) A NN bonds consistent with (N2)2- moieties. With the stronger reductant Nd(II), aryloxides are sufficient ancillary ligands: the NdI2/2KOC6H3tBu2-2,6 (KOAr) system forms [(ArO)2(THF)2Nd]2(mu-eta2:eta2-N2), which has a 1.242(7) A NN bond.     

Rare-earth metal-mediated addition/cyclization of the 2-cyanobenzoamino anion

Reaction of two equiv of [2-NCC(6)H(4)HNLi(THF)](n) (1) with Cp(2)LnCl(THF) yields the heterobimetallic complexes Cp(2)Ln[κ(3)-(4-NH[double bond, length as m-dash](C(8)N(2)H(4))(2-NHC(6)H(4))]Li(THF)(3) (Cp = C(5)H(5); Ln = Er (2), Y(3)), indicating an organolanthanide-mediated nucleophilic addition/cyclization of the 2-cyanobenzoamino anion to construct the 4-iminoquinazolinate dianionic ligand.     

New mode of coordination for the dinitrogen ligand: formation, bonding, and reactivity of a tantalum complex with a bridging N(2) unit that is both side-on and end-on.

The reaction of a mixture of 1 equiv of PhPH(2) and 2 equiv of PhNHSiMe(2)CH(2)Cl with 4 equiv of Bu(n)Li followed by the addition of THF generates the lithiated ligand precursor [NPN]Li(2).(THF)(2) (where [NPN] = PhP(CH(2)SiMe(2)NPh)(2)). The reaction of [NPN]Li(2).(THF)(2) with TaMe(3)Cl(2) produces [NPN]TaMe(3), which reacts under H(2) to yield the diamagnetic dinuclear Ta(IV) tetrahydride ([NPN]Ta)(2)(mu-H)(4). This hydride reacts with N(2) with the loss of H(2) to produce ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)), which was characterized both in solution and in the solid state, and contains strongly activated N(2) bound in the unprecedented side-on end-on dinuclear bonding mode. A density functional theory calculation on the model complex [(H(3)P)(H(2)N)(2)Ta(mu-H)](2)(mu-eta(1):eta(2)-N(2)) provides insight into the molecular orbital interactions involved in the side-on end-on bonding mode of dinitrogen. The reaction of ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)) with propene generates the end-on bound dinitrogen complex ([NPN]Ta(CH(2)CH(2)CH(3)))(2)(mu-eta(1):eta(1)-N(2)), and the reaction of [NPN]Li(2).(THF)(2) with NbCl(3)(DME) generates the end-on bound dinitrogen complex ([NPN]NbCl)(2)(mu-eta(1):eta(1)-N(2)). These two end-on bound dinitrogen complexes provide evidence that the bridging hydride ligands are responsible for the unusual bonding mode of dinitrogen in ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)). The dinitrogen moiety in the side-on end-on mode is amenable to functionalization; the reaction of ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N(2)) with PhCH(2)Br results in C-N bond formation to yield [NPN]Ta(mu-eta(1):eta(2)-N(2)CH(2)Ph)(mu-H)(2)TaBr[NPN]. Nitrogen-15 NMR spectral data are provided for all the tantalum-dinitrogen complexes and derivatives described.     

Nitrophenolate as a building block for lanthanide chains, layers, and clusters

Potassium o-nitrophenolate (1) was reacted with various lanthanide trichlorides under different reaction conditions. By using the smaller lanthanides and working under rigorous exclusion of air, infinite chains of composition [(THF)4[K(o-O2N-C6H4-O)4Ln]4]n (Ln = Y (2a), Er (2b), Lu (2c)) were obtained. Using the same conditions but performing the crystallization under air, tetradecanuclear clusters of composition H18[Ln14(micro-eta2-o-O2N-C6H4-O)8(eta2-o-O2N-C6H4-O)16(micro4-O)2(micro3-O)16] (Ln = Dy (3a), Er (3b), Tm (3c), Yb (3d)) were isolated. Using larger center metals such as samarium, europium, and terbium and working under rigorous exclusion of air, infinite layers of composition [[K2(o-O2N-C6H4-O)5Tb]n] (4) and [[K2(o-O2N-C6H4-O)5Ln)]n] (Ln = Sm (5a), Eu (5b)) were obtained. In 4 the layers have a closer packing than those in compound 5. The closer packing is a result of the increased coordination number of the lanthanide metal and the potassium atoms. In contrast, the more open structures of 5 results in channels which are rectangular through the layers. All compounds reported including 1 have been investigated by single-crystal X-ray diffraction.     

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.     

Synthesis and controlled hydrolysis of organolanthanide complexes with mono- and dianionic benzimidazole-2-thiolate ligands

Treatment of Cp(3)Er with one equivalent of benzimidazole-2-thiol (H(2)Bzimt) in THF affords the monoanionic HBzimt(-) complex Cp(2)Er(η(2)-HBzimt)(THF)(2) (1). Reaction of Cp(3)Yb with two equivalents of H(2)Bzimt gives complex CpYb(η(2)-HBzimt)(2)(THF) (2) at room temperature. Treatment of Cp(3)Ln with three equivalents of H(2)Bzimt in reflux THF affords the homoleptic Ln(η(2)-HBzimt)(3)(THF)(2) (Ln = Er (3), Y (4)). Cp(3)Ln reacts with 0.5 equivalents of H(2)Bzimt to afford the dianionic Bzimt(2-) complexes [(Cp(2)Ln)(THF)](2)(μ-Bzimt) (Ln = Yb (5), Er (6), Dy (7), Y (8)) in good yields, in which the Bzimt(2-) ligand bridges the two metals in an μ-η(2):η(2) coordination mode. Interestingly, controlled hydrolysis of complexes Cp(2)Ln(η(2)-HBzimt)(THF)(2), CpLn(η(2)-HBzimt)(2)(THF) and [(Cp(2)Ln)(THF)](2)(μ-Bzimt) produces the same tetranuclear complexes [CpLn(μ(3)-OH)(μ-η(1):η(2)-HBzimt)](4) (Ln = Yb (9), Er (10), Y (11)), indicating that the hydrolysis selectivity greatly depends on the number of coordinated cyclopentadienyl groups. All complexes were characterized by elemental analysis, spectroscopic properties and X-ray single crystal diffraction analysis.     

Selective reaction based on the linked diamido ligands of dinuclear lanthanide complexes

The dinuclear ytterbium pyridyl diamido complexes [Cp(2)Yb(THF)](2)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,6)] (1a) and [Cp(2)Yb(THF)](2)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,3)] (1b) are easily prepared by protonolysis of Cp(3)Yb with 0.5 equiv of the corresponding diaminopyridine in accepted yields, respectively. Treatment of 1a with 2 equiv of dicyclohexylcarbodiimide (CyN=C=NCy) in THF at low temperature leads to the isolation of the formal double N-H addition product (Cp(2)Yb)(2)[mu-eta(2):eta(2)-(CyN(CyNH)CN)(2)(C(5)H(3)N-2,6)] (2) in 42% yield. Compound 2 is unstable to heat and slowly isomerized to the mixed neutral/dianionic diguanidinate complex (Cp(2)Yb)(2)[mu-eta(2):eta(2)-(CyNH)(2)CN(C(5)H(3)N-2,6)NC(NCy)(2)](THF) (3) at room temperature. Similarly, treatment of 1b with 2 equiv of CyN=C=NCy gives the addition/ isomerization product (Cp(2)Yb)(2)[mu-eta(2):eta(2):eta(1)-(CyNH)(2)CN(C(5)H(3)N-2,3)NC(NCy)(2)] (4). Moreover, the reaction of various ytterbium aryl diamido complexes (prepared in situ from [Cp(2)YbMe](2) and aryldiamine, respectively) with CyN=C=NCy affords the corresponding addition products (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,4)] (5), (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,3)](6), and (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(13)H(8)-2,7)] (7), respectively. In contrast to pyridyl-bridged bis(guanidinate monoanion) complexes, aryl-bridged bis(guanidinate monoanion) complexes 5-7 are stable even with prolonged heating at 110 degrees C. All the results not only demonstrate that the presence of the pyridyl bridge can impart the diamido complexes with a unique reactivity and initiate the unexpected reaction sequence but also indicate evidently that the number and distribution of negative charges of the diguanidinate ligand is tunable from double monoanionic units to mixed neutral/dianionic isomers. All the complexes are characterized by elemental analysis and IR spectroscopies. The structures of complexes 1a, 3, 5, 6, and 7 are also determined through X-ray single-crystal diffraction analysis.