Use of calix[4]arenes in the redox chemistry of lanthanides: the reduction of dinitrogen by a calix[4]arene-samarium complex.

The synthesis and structural characterization of a samarium-dinitrogen complex supported by a calix[4]arene ligand in which the N-N bond distance has been stretched to 1.611(16) Angstrom are described. The central mu(3)-eta(2):eta(2):eta(2)-hydrazido tetraanion formed is bonded to three Sm(III) centers with an overall butterfly-type arrangement.

Alkali and alkaline-earth-metalated forms of calix[4]arenes: synthons in the synthesis of transition metal complexes.

This is the first coherent report on the metalation of calix[4]arene by alkali and alkaline-earth metals, thus providing a high-yield production of appropriate synthons for the synthesis of transition metal calix[4]arenes. In addition, various facets of the coordination chemistry by calix[4]arene anions of alkali and alkaline-earth metal ions have been singled out. Among them: 1) the exo and endo coordination of metal ions by the calix[4]arene skeleton; 2) the pi solvation of the ions by the phenyl rings; 3) the ion-carrier properties of metallacalix[4]arenes; 4) the simulation of the kinetically labile coordination sphere of alkali and alkaline-earth metal ions by a polyoxo rigid skeleton. The peculiarities of the complexation of alkali and alkaline-earth metal ions by calix[4]arenes outlined are deduced from the synthesis and the structural characterization both in solution ((1)H NMR) and in the solid state (X-ray structure analysis) of the following classes of compounds: 1) [p-tBu-calix[4](OMS(n))(4)](2) (M=Li, Na, K); 2) [p-tBu-calix[4](OR)(2)(O)(2)ML] (M=Mg, L=THF, R=C(5)H(9); M=Ca, L=TMEDA (tetramethylethylenediamine), R=C(5)H(9); M=Ca, L=DME (dimethoxyethane), R=C(5)H(9); M=Ba, L=TMEDA, R=C(5)H(9); M=Ba, L=none, R=C(5)H(9)); 3) [p-tBu-calix[4](OC(5)H(9))(2)(O)(2)Ca(2)I(2)(MeCN)(2)]; 4) [(p-tBu-calix[4](OR)(2)(O)(2))(2)BaNa(2)].

Photochemical Activation of the N≡N Bond in a Dimolybdenum-Dinitrogen Complex: Formation of a Molybdenum Nitride.

Photoinduced cleavage of the residual N-N bond in the dimetallahydrazone 1 (Mes=2,4,6-Me3 C6 H2 ) led to a transient monomeric nitrido complex, which reacts further with 1 to form 2. Compound 1 was synthesized by the reductive arylation of MoCl4 ⋅DME by MesMgBr under an N2 atmosphere.

From Oligomers to Conducting Polymers of the Metal-Dinitrogen Functionality.

A new avenue is opened up in the potential use of dinitrogen. Oligomerization of the metalla-dinitrogen functionality leads to the formation of polymers based on a [-(Mes)3 W-N2 -] nq moiety.

Ruthenium Nitrides: Redox Chemistry and Photolability of the Ru-Nitrido Group.

Tunable electrophilicity/nucleophilicity by means of the redox properties of the Ru≡N group and reversible interconversion of mononuclear and dinuclear species as a result of the photolability of the Ru=N=Ru group are characteristic of the nitrido derivatives of Ru porphyrinogens. For example, 2, the product of reversible reduction of a Ru≡N precusor, reacts with 1 in the dark to form 3, which undergoes photocleavage to 1 and 2.

Acetylenes Rearranging on Ruthenium-Porphyrinogen and Leading to Vinylidene and Carbene Functionalities.

Through a proton-transfer reaction a porphyrinogen assists the transformation of terminal acetylenes into Ru-vinylidenes, which are the entry point to a variety of Ru-carbenes and Ru-cumulenes. The scheme (in which the porphyrinogen is stylized) shows the reversible interconversion of an acetylide into a divinylidene unit.

Reactivity of a Vanadium(III) Center over an Oxo Surface Modeled by Calix[4]arene.

Metalation of the monomethoxycalix[4]arene [p-Bu(t)-calix[4]-(OMe)(OH)(3)], 1, using [VMes(3).THF] led to the coordinatively unsaturated V(III)-d(2) fragment [p-Bu(t)-calix[4]-(OMe)(O)(3)V] collapsing to the dimer [{&mgr;-p-Bu(t)-calix[4]-(OMe)(O)(3)}V](2), 2, where each calix[4]arene shares a bridging oxygen donor atom. The dimeric complexity remains intact in the reaction with Bu(t)NC and PhCN, which bond to the metal inside the cavity of the calix[4]arene leading to [{&mgr;-p-Bu(t)-calix[4]-(OMe)(O)(3)}(V-L)](2) [L = Bu(t)NC, 3; L = PhCN, 4]. In contrast, the reaction of 2 with pyridine and 4,4'-dipyridyl cleaves the dimeric form into a monomeric complex [{&mgr;-p-Bu(t)-calix[4]-(OMe)(O)(3)}V(Py)], 5, or to a different dimer containing a bridging 4,4'-dipyridyl, [{p-Bu(t)-calix[4]-(OMe)(O)(3)}(2)V(2)(&mgr;-4,4'-dipyridyl)], 6. Complex 2 undergoes one electron oxidation by I(2) to the corresponding vanadium(IV) dimer [{&mgr;-p-Bu(t)-calix[4]-(O)(4)}(2)V(2)], 7, and by p-benzoquinone to [{p-Bu(t)-calix[4]-(OMe)(O)(3)}V](2)(&mgr;-C(6)H(4)O(2)), 8. A two-electron oxidation of the V(III)-d(2) to vanadium(V) derivatives has been achieved using styrene epoxide and diphenyldiazomethane. In the former case the oxovanadium(V) derivative was obtained [p-Bu(t)-calix[4]-(OMe)(O)(3)V=O], 9, and in the latter case a metallahydrazone complex [p-Bu(t)-calix[4]-(OMe)(O)(3)V&tbd1;N-N=CPh(2)], 10. The dimeric d(2) and d(1) derivatives display significant antiferromagnetic couplings between the two metal centers, namely as follows: 2, J = -74.6 cm(-)(1); 3, J = -17 cm(-)(1); 4, J = -33.4 cm(-)(1); 7, J = -131.7 cm(-)(1). The extended Hückel calculations gave an appropriate picture of the two-electron reduction of the diphenyldiazomethane substrate. The proposed structures have been supported by X-ray analyses on 3, 7, 9, and 10.

Cyclopentadienyl Behavior of Pyrrolyl Anions within the meso-Octaethylporphyrinogen-Binding Lanthanides: Carbon-Hydrogen and Metal-Carbon Bond Rearrangements.

The complexation of Ln(III) ions by the meso-octaethylporphyrinogen [Et(8)N(4)H(4)], 1, has been achieved by reacting the sodium derivative [Et(8)N(4)Na(4).THF(3)], 2, with [LnCl(3).THF(2)]. Depending on the reaction or crystallization solvent, a variety of structural categories of Ln-porphyrinogen complexes have been isolated and structurally characterized. When the reaction was carried out in THF and the final complex recrystallized from THF, [{(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))Ln(THF)}-eta(3)-Na(THF)(2)] complexes [Ln = Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Yb (8)] were obtained in a monomeric form. When their recrystallization was performed in dioxane, a dimerization occurred thanks to dioxane bridging the sodium cations of the monomeric units [{(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))Ln(DME)}-eta(3)-Na](dioxane)(1.5)] [Ln = Nd, 14; Ln = Sm, 15]. In a third category we isolated complexes where two monomeric monoanions [(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))Ln](-) are eta(2):eta(3) sandwiching two sodium cations, which are exclusively solvated by the pyrrolyl anions [{(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))Ln}(2)-eta(2):eta(3)-Na(2)] [Ln = Pr, 16; Ln = Sm, 17]. The three classes of compounds mentioned above, all of them containing the monomeric unit [Ln-porphyrinogen-Na], are characterized by the following structural parameters: Ln-eta(5)(pyrrole)(av), 2.490(7) Å for 7, 2.556(2) Å for 14, 2.543(2) Å for 16; Ln-eta(1)(pyrrole)(av), 2.43(1) Å for 7, 2.494(4) Å for 14, 2.485(4) Å for 16; centroid-Ln-centroid, 174.6(3) degrees for 7, 168.1(1) degrees for 14, 169.7(2) degrees for 16; Na-eta(3)(pyrrole), 2.50(1) Å for 7, 2.515(3) Å for 14. The recrystallization of complexes 3-8 from DME led to dimeric organometallic complexes, where the dimerization has been via the desolvation of the Ln ion and the formation of a Ln-C sigma bond with the beta-carbon of a pyrrole of an adjacent Ln-porphyrinogen unit. Such dimers occur in the ion-separated form [(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))(2)Ln(2)][NaS(n)()](2) [Ln = Pr (9), Nd (10), Sm (11), Gd (12), Eu (13)]. Their recrystallization from THF led to the ion-pair derivatives in which two sodium cations are eta(2)-bonded to the eta(1)-pyrrolyl anions of the dimer [{(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))(2)Ln(2)}-eta(2)(NaS(n)())(2)] [Ln = Pr (18), Nd (19), Sm (20), Gd (21); S = DME, THF; n = 2]. When the crystallization of 9-13 was carried out from THF/dioxane, polymeric structures were isolated, where cations are bridged by dioxane molecules [{(eta(5):eta(1):eta(5):eta(1)-Et(8)N(4))(2)Ln}(2)-eta(2){Na(THF)}(2)(&mgr;-dioxane)][Ln = Nd, 22; Ln = Gd, 23]. In the three classes made up from the dimeric building block, the structural leit-motiv is constant and two structural parameters are very close [Ln-eta(5)(pyrrole)(av), 2.538(3) Å for 11, 2.578(1) Å for 18; centroid-Ln-centroid, 172.3(2) degrees for 11, 170.4(1) degrees for 18; Ln-C, 2.471(7) Å for 11, 2.512(2) Å for 18].

Neutral, Cationic, and Anionic Alkyl Derivatives of Tungsten Bonded to a Calix[4]arene Oxo Surface.

The chemically reversible reduction of [(Me)2 W(calix)] to the diamagnetic [(Me)2 W(calix)Na2 ] [Eq. (1)], without major changes in the connectivity of the molecule, illustrates the flexibility of the calixarene ligand and stresses its potential as a molecular functional model of heterogeneous oxo surfaces.

The π Complexation of Calcium inside the meso-Octaethylporphyrinogen Tetraanion Cavity.

A possible binding cavity for alkali and alkaline earth metal ions: The synthesis and structural characterization of the complex shown, which was obtained from meso-octaethylporphyrinogen and calcium metal, shows that the porphyrinogen functions as a binucleating ligand with four η3 -azaallyl binding sites for two calcium cations.

Porphomethenes and Porphodimethenes Synthesized by the Two- and Four-Electron Oxidation of the meso-Octaethylporphyrinogen.

Stepwise dealkylation of meso-octaethylporphyrinogen 1 yields porphomethene 2 and porphodimethene 3, providing access to large quantities of these valuable intermediates. The synthetic sequence relies on SnCl4⋅2 THF, Li, and H2O; the extent of dealkylation depends on the amount of SnCl4⋅2 THF employed.

Role of o-Methylene-Bridged Bis(aniline) as a Spectroscopic Probe for the Metal Coordination Environment.

Reaction of the bidentate ligand 2,2'-methylenebis(5-(dimethylamino)aniline) (2, L) with PdCl(2) and K(2)PtCl(4) and the bidentate ligand 2,2'-methylenebis(5-(acetylamino)aniline (5, L') with K(2)PtCl(4) in polar solvents gave the complexes [PdCl(2)(L)] (6), [PtCl(2)(L)] (8), and [(L')PtCl(2)] (7), respectively. Treatment of 2 with K(2)PtCl(4) in the presence of DMSO resulted in the solvolysis of a chloride ion to give [(L)Pt(Cl)(DMSO)]Cl (9). The resulting eight-membered metallocyclic rings have rigid elongated chair conformations forcing one of the two bridging methylene hydrogens (H(endo)) in close proximity to the metal centre. An (1)H NMR study revealed that they are now diastereomeric (H(endo), H(exo)); the higher field signal position does not vary irrespective of the ligand or metal, whereas the proton corresponding to the lower field signal is apparently more sensitive to the metal coordination environment. The ability of this spectroscopic probe to predict the bonding mode of the metal was also studied by reacting 2 with K[PtCl(3)(C(2)H(4))].H(2)O to give [Pt(2)(&mgr;-L)Cl(4)(C(2)H(4))(2)] (10), which occurred irrespective of the L/Pt ratio. The corresponding methylene hydrogens were not diastereomeric, showing only one singlet in the (1)H NMR spectrum. Crystal structures of 6 and 9 have been determined: 6 is triclinic, space group P&onemacr;, a = 10.179(2) Å, b = 12.136(2) Å, c = 9.686(2) Å, alpha = 97.79(1) degrees, beta = 95.98(2) degrees, gamma = 78.02(1) degrees, V = 1156.1(4), Z = 2, and R = 0.034; 9 is triclinic, space group P&onemacr;, a = 12.348(1) Å, b = 12.407(1) Å, c = 10.159(1) Å, alpha = 103.02(1) degrees, beta = 104.87(2) degrees, gamma = 117.09(1) degrees, V = 1313.0(3), Z = 2, and R = 0.035.

The Synthesis and Characterization of Two-Dimensional Ferromagnetic Extended Structures Containing High-Spin (S = (5)/(2)) and Low-Spin (S = (1)/(2)) Iron(III) Bridged by Cyanide Groups.

The reaction of [Fe(salen)](+) and {A(3)[Fe(CN)(6)]} (A = NEt(4), K), depending on the countercation A(+) and on the reaction solvent, led to [(NEt(4)){Fe(salen)}(2){Fe(CN)(6)}](n)(), 4, and [{Fe(salen)}(3){Fe(CN)(6)}(MeOH)(2)](n)().3nH(2)O, 5 [NEt(4) = tetraethylammonium cation, salen = N, N'-ethylenebis(salicylideneiminato) dianion], displaying a similar extended 2D structure. Complex 5 crystallizes in the monoclinic, space group P2(1)/n, a = 13.495(7) Å, b = 14.220(9) Å, c = 33.137(5) Å, beta = 96.74(2) degrees, and Z = 4. It assumes a two-dimensional network layer structure consisting of cyclic octanuclear [-Fe(h.s.)-NC-Fe(l.s.)-CN-](4) units with [Fe(salen)(MeOH)(2)](+) located between the interlayer as a countercation. Complex 4 exhibits a metamagnetic behavior with a field-induced transition from an antiferromagnetic to a ferromagnetic-like state and a Neel temperature of ca. 6 K.

The Intra- and Intermolecular Oxidative Coupling of Ni(II)-meso-Octaethyl Mono(pyridine)-Tris(pyrrole) Complex Leading to C-C Bonds: Pathways to Oligomeric Porphyrinogens.

This paper reports the oxidative transformations of the unprecedented meso-octaalkyl mono(pyridine)-tris(pyrrole) macrocycle [Et(8)(C(5)H(3)N)(C(4)H(2)NH)(3)], 1, which was obtained by a homologation of the corresponding porphyrinogen, [Et(8)(C(4)H(2)NH)(4)], A. The metallation of 1 was obtained via its deprotonation with LiBu, followed by the reaction with MCl(2).thf(n)(), leading to the bimetallic complexes: [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)M{Li(thf)(2)}] [M = Fe, 3; M = Co, 4; M = Ni, 6; M = Cu, 7]. The cobalt derivative occurs also in the separated ion-pair form [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Co](-)[{Li(thf)(4)}](+), 5. The reaction of 4 and 6 with an excess of Cp(2)FeBPh(4) led to the oxidation of the macrocycle with the formation of a cyclopropane functionality [Et(8)(C(5)H(3)N){(C(4)H(2)N)(3)(Delta)}Ni](+)BPh(4)(-), 8. The cyclopropane unit underwent reductive cleavage back to the initial macrocycle using lithium metal. The use of a Ni/Cp(2)Fe(+) 1:1 ratio allowed the identification of a dimer derived formally from the monoelectronic oxidation of the macrocycle 1, which formed a radical coupling to 9, [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Ni](2). The same compound formed from a disproportionation redox reaction occurring between 6 and 8. The C-C bond across the two metallamacrocycles involved the beta position of the pyrrole. Deprotonation of 9 by LiBu led to a dianionic form 10 [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Ni{Li(thf)(2)}]. The formation of the cyclopropane functionality was also achieved via the oxidation of [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Li(3)(thf)(2)}], 2, forming [Et(8)(C(5)H(3)N){(C(4)H(2)N)(3)(Delta)}Li(thf)], 11, which was ready to be used in metallation reaction. The proposed structures were supported by X-ray analyses on 4, 7, 8, 9, and 11.

The π-Pyrrole Complexation of Alkali Metal Ions by Zirconium meso-Octaalkylporphyrinogens: Encapsulation of Li4 H4 and Li2 O in Sandwich Structures.

Complexation of metal ion and counterion by the same compound is possible with zirconium meso-octaalkylporphyrinogens (structure of a dimeric complex with four encapsulated equivalents of LiH is depicted): they carry salts in the molecular ion-pair form in hydrocarbons, and function as acid-base bifunctional compounds.