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Ab initio Hartree-Fock and Moller-Plesset calculations are performed on the reduction chemistry of (Ni(salophen)). Results show that no oxidation state change follows the addition of two electrons to the system because no localized-on-nickel and low-energy orbitals are present to accomodate them. Instead, the two electrons form a new C-C bond which can be broken to give the original product. Moreover, the Ni2+ functions as a shield among the negative charges of the ligand during the redox reaction.

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.

Density functional calculations have been performed on some calix[4]arenes complexes of early transition metals. Particular emphasis has been placed on the comparison of the main properties of these metal complexes with the analogous metal complexes based on four monodentate phenolate ligands to study the effect of the geometrical constraints imposed by the calixarenes framework on the electronic structure. The results show that the most stable geometry of titanium and molybdenum tetraphenolates is pseudotetrahedral (slightly flattened for molybdenum) and that the distortion to a square planar coordination requires, respectively, 52.0 and 21.5 kcal x mol(-1). However, a significant energy decrease is found when the four phenolate groups are bent in the same hemisphere, reproducing the calix[4]arene geometry. Such a coordination determines the energy decrease of the unoccupied metal d orbitals of sigma and pi symmetry, which leads to an increase of the electron-accepting properties of these metal fragments.

The syntheses of the parent compounds [(p-Bu(t)-calix[4]-(O)2(OR)2)Fe-L] [R = Me, L = THF, 5; R = Bu(n), L = THF, 6; R = PhCH2, L = THF, 7; R = SiMe3, L = none, 8] have been performed by reacting the protonated form of the dialkylcalix[4]arene with [Fe2Mes4] [Mes = 2,4,6-Me3C6H2]. All of them undergo one-electron oxidative functionalization. By use of different oxidizing agents, the following iron(III) derivatives have been obtained: [(p-Bu(t)-calix[4]-(O)2(OR)2)Fe-X] [X = Cl, R = Me, 9; X = I, R = Me, 10] and [(p-Bu(t)-calix[4]-(O)2(OR)2)2Fe2(mu-X] [X = O, R = Me, 11; X = O, R = Bu(n), 12; X = S, R = Me, 13], 9 and 10 being particularly appropriate for a further functionalization of the metal. The last three display typical antiferromagnetic behavior [J = -78.6 cm-1, 11; J = -64.1 cm-1, 13]. In the case of 7 and 8, the reaction with O2 led to the dealkylation of one of the alkoxo groups, with the formation of a dimeric iron(III) derivative ([mu-p-Bu(t)-calix[4]-(O)3(OR))2Fe2] [R = PhCH2, 14; R = SiMe3, 15] [J = -9.8 cm-1]. The reaction of the parent compounds with ButNC and diazoalkanes led to the formation of [Fe=C] functionalities supported by a calix[4]arene oxo surface. The following compounds have been isolated and characterized: ([p-Bu(t)-calix[4]-(O)2(OR)2)Fe=CNBut] [R = SiMe3, 16, nu CN = 2175 cm-1], ([p-Bu(t)-calix[4]-(O)2(OR)2)Fe=CPh2] [R = Me, 17; R = PhCH2, 18; R = SiMe3, 19]. The three carbene complexes 17-19 display quite an unusual high-spin state, which is a consequence of the formation of a weak pi interaction between the metal and the carbene carbon, as confirmed by the extended Hückel calculations. The carbene functionality has been removed from the iron center in the reaction with O2 and HCl. The proposed structures have been supported by X-ray analyses of complexes 8, 9, 12, 14, 16, 17, and 19.

Sodium, potassium, and cesium salts (iodides, nitrates, acetates, and tetraphenylborates) form 1/1, 1/2 and 2/3 adducts with MLn [M = Co, Ni, Cu, and Zn; n = 1-4; H2L1 = N,N'-(3-methoxysalicyliden)ethane-1,2-diamine; H2L2, H2L3, and H2L4 are the -propane-1,2-diamine, -o-phenylenediamine, and -propane-1,3-diamine analogues of H2L1). Metal salicyladimine, alkali metal, and anion all exert influence on stoichiometry and reactivity. Sodium ions tend to reside within the planes of the salicylaldimine oxygens, as in Na(NO3)(MeOH).NiL4 (1), Na(NO3)(MeOH).CuL1 (2; both with unusual seven-coordinated sodium), and Na.(NiL4)2I.EtOH.H2O (3; with dodecahedral sodium coordination geometry). Potassium and cesium tend to locate between salicylaldimine ligands as in KI.NiL4 (4) and [Cs(NO3).NiL4]3.MeOH (5; structures with infinite sandwich assemblies), CsI.(NiL2)2.H2O (6), CsI3.(NiL4)2 (7; simple sandwich structures), and [K(MeCN)]2.(NiL4)3 (8; a triple-decker sandwich structure). Crystal data for 1 are the following: triclinic, P1, a = 7.3554(6) A, b = 11.2778(10) A, c = 13.562(2) A, alpha = 96.364(10) degrees, beta = 101.924(9) degrees, gamma = 96.809(10) degrees, Z = 2. For 2, triclinic, P1, a = 7.2247(7) A, b = 11.0427(6) A, c = 13.5610(12) A, alpha = 94.804(5) degrees, beta = 98.669(7) degrees, gamma = 99.26(6) Z = 2. For 3, orthorhombic, Pbca, a = 14.4648(19) A, b = 20.968(3) A, c = 28.404(3) A, Z = 8. For 4, triclinic, P1, a = 12.4904(17) A, b = 13.9363(13) A, c = 14.1060(12) A, alpha = 61.033(7) degrees, beta = 89.567(9) degrees, gamma = 71.579(10) degrees, Z = 2. For 5, monoclinic. P2(1)/n, a = 12.5910(2) A, b = 23.4880(2) A, c = 22.6660(2) A, beta = 99.3500(1) degree, Z = 4. For 6, orthorhombic, Pbca, a = 15.752(3) A, b = 23.276(8) A, c = 25.206(6) A, Z = 8. For 7, triclinic, P1, a = 9.6809(11) A, b = 10.0015(13) A, c = 11.2686(13) A, alpha = 101.03 degrees, beta = 90.97 degrees, gamma = 100.55 degrees, Z = 2. For 8, monoclinic, C2/c, a = 29.573(5) A, b = 18.047(3) A, c = 23.184(3) A, beta = 122.860(10) degrees, Z = 8.

Density functional calculations were performed on a series of M(OH3)-substituted (M = Ti,V) cyclopolyenes as simple models is metal carbides. We studied the oligomerization of the metal acetylide complexes [MLn]2 (mu-C2) as a possible precursor of these [(OH)3MC]n (n = 4,6) hypothetical species. Special emphasis was placed on the comparison of the main properties of these metal substituted cyclopolyenes with those of the corresponding cyclopolyenes in an attempt to study the effects of the metal substituents on the organic C4 and C6 cyclic moieties. Whereas for the titanium species, the pi system of the polyene moiety is slightly perturbed, the electronic structures and molecular geometries found for the vanadium species suggest a metalla radialene nature for these compounds, with the endocyclic conjugation of carbon-carbon double bonds replaced by an exocyclic arrangement of carbon-metal double bonds.

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].

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.

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 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.

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 diacetone glucose (DAGH, 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose) monoanion DAG binds as a terminal alkoxo ligand to a variety of transition metals. When it is used in excess, with respect to the oxidation state of the metal, homoleptic anionic complexes [M'(DAG)(6)](3)(-) are formed. Such complexes contain oxygen-rich cavities between pairs of DAG ligands appropriate for binding alkali metal cations. The anionic complexes have been obtained by using [Li(DAG)], 1, and [Na(DAG)], 2, whose syntheses and characterization are reported here. The reaction of 1 and 2 with [V(DAG)(3)] gave [V(DAG)(6)Li(3)], 3, and [V(DAG)(6)Na(3)], 4, respectively. An alternative synthesis of 3 and 4 involves the metathesis reaction of 1 and 2 with [VCl(3)(thf)(3)]. This strategy also led to the synthesis of [Cr(DAG)(6)Li(3)], 5, and [Ti(DAG)(6)Li(3)], 6. Three pairs of DAG shape a cavity appropriate for three lithium cations in the case of complexes 3, 5, and 6; a cavity is formed for three sodium cations in the case of 4, where the alkali cation is in a tetrahedral O(4) environment. In the anionic manganese derivative [Mn(Cl)(DAG)(4)](3)(-), the four DAG units arrange in such a way as to bind four Li cations, which form a cationic cage [Mn(Cl)(DAG)(4)Li(4)](+), and Cl(-) is bound inside as [Mn(Cl)(DAG)(4)Li(4)(&mgr;(4)-Cl)], 7. Crystallographic details: 4, prism, P2(1), a = 14.735(10) Å, b = 15.033(9) Å, c= 21.021(10) Å, beta = 107.34(2) degrees, V= 4445(5) Å(3), Z = 2, and R = 7.60; 5, prismatic, C2, a = 22.671(9) Å, b = 18.785(5) Å, c = 13.886(4) Å, beta = 126.39(2) degrees, V= 4761(3) Å(3), Z = 2, and R = 7.32; 6, prismatic, P2(1), a= 13.888(5) Å, b = 18.750(5) Å, c= 17.933(5) Å, beta = 91.84(2) degrees, V = 4667(2) Å(3), Z = 2, and R = 8.75; 7, prismatic, P2(1), a = 13.306(7) Å, b= 21.311(11) Å, c = 13.376(6) Å, beta = 95.01(2) degrees, V = 3779(3) Å(3), Z = 2, and R = 9.33.

The multistep synthesis of the novel diphosphine reference ligand L(2), 6, Ph(2)P(o-C(6)H(4)CH(2)C(6)H(4)-o)PPh(2), has been streamlined and can be prepared on a ca. 20 g scale. It forms metallacycles with a variety of metal fragments. The resulting, and very rigid, boat-boat conformation forces a proton (H(endo)()) of the bridging methylene in close proximity to the metal, which in turn renders these protons (H(endo)(), H(exo)()) diastereotopic. The NMR spectra of [L(2)MCl(2)] [M = Pd, 9; M = Pt, 10] and of the organometallic derived compounds [L(2)Pd(PPh(3))], 11, and [L(2)Pd(Cl)(eta(2)-CH(2)Ph)], 12, consist of a pair of doublets, with the H(endo)() coupled to the P of the metallacycle. The CH(2)-metal close proximity drives the electrophilic metalation of the bridging methylene by RhCl(3) to form [L(2)Rh(Cl)(2)(MeCN)], 13, [L(2) = Ph(2)P(o-C(6)H(4)CHC(6)H(4)-o)PPh(2)]. A significant example, which shows how the coordination number of the metal can affect the H(exo)()-H(endo)() resonance separation, is provided by the couple [L(2)Ni(C(2)H(4))], 14, and [L(2)Ni(CO)(2)], 15. In order to show that the metallacycle size is crucial for the bridging methylene to function as a spectroscopic probe, we complexed the same [Fe(CO)(3)] fragment to L(2), 6, and L'(2), 17, [L'(2) = Ph(2)PO(o-C(6)H(2)(4,6Bu(t)(2))CH(2)(4,6Bu(t)(2))C(6)H(2)-o)OPPh(2)], to give [L(2)Fe(CO)(3)], 19, and [L'(2)Fe(CO)(3)], 18, respectively. In complex 17 the diastereotopic nature of these protons and hence the spectroscopic information was lost because of the presence of a 10-membered metallacycle. Crystal data: 9 is triclinic, space group P&onemacr;, a = 11.987(1) Å, b = 15.990(2) Å, c = 10.872(1) Å, alpha = 91.42(1) degrees, beta = 111.01(2) degrees, gamma = 99.86(2) degrees, V = 1908.2(5) Å(3), Z = 2, and R = 0.053; 11 is monoclinic, space group C2/c, a = 39.071(5) Å, b = 13.657(4) Å, c = 19.848(5) Å, beta = 92.45(2) degrees, V = 10581(5) Å(3), Z = 8, and R = 0.047; 12 is triclinic, space group P&onemacr;, a = 11.289(1) Å, b = 18.769(2) Å, c = 11.077(1) Å, alpha = 91.20(1) degrees, beta = 111.27(1) degrees, gamma = 105.26(1) degrees, V = 2107.7(4) Å(3), Z = 2, and R = 0.039; 13 is orthorhombic, space group P2(1)2(1)2(1), a = 15.346(2) Å, b = 18.188(3) Å, c = 12.072(2) Å, V = 3369.5(9) Å(3), Z = 4, and R = 0.042.

This report concerns the carrier properties of [Mn(acacen)]-derived compounds toward polar organometallics, inorganic ion pairs, and salts. Such properties are the consequence of Mn(II) behaving as a Lewis acid and the O&arcraise;O bite of the bidentate Schiff base ligand toward alkali cations. The starting compounds, which occur in a dimeric form, [Mn(acac-L-en)](2) [L' = CH(2)CH(2) (1); L" = C(6)H(10) (2); L"' = R,R-C(6)H(10) (3)] have been synthesized either via a metathesis reaction from MnCl(2) or using [Mn(3)Mes(6)]. The reaction of 1-3 with lithium organometallics allowed the isolation of [Mn(acac-L-en)(R)Li(DME)] [R = Me, L = L' (4); R = Ph, L = L' (5); R = Mes, L = L' (6); R = Me, L = L" (7); R = Me, L = L"' (8)] as metalated forms, where the alkyl or aryl group is sigma-bonded to Mn(II), while the lithium cation is anchored to the Schiff base ligand. The metalated forms 4-8 react with PhCHO to give the corresponding lithium alkoxide, which remains bound in its ion-pair form to the [Mn(acacen)] skeleton in [Mn(2)(acac-L'-en)(2)Li(2)(OCH(Ph)Me)(2)](n)() (9). The use of 8, which has a chiral bridge across two nitrogen atoms, did not lead to a significant asymmetric induction in the reaction with PhCHO, because of the long separation between the lithium cation and the stereogenic center. The metalated form 4 was able to transfer the methyl group to the nitrile function to give the corresponding lithium-imide which then remains bonded to [Mn(acacen)] as the ion pair in a dimeric structure, as revealed for [Mn(2)(acac-L'-en)(2)Li(2)(DME){N=C(Ph)Me}(2)](n)() (10). Their reaction with 1 appears to depend on the steric bulkiness of the alkyl group in NaOR, resulting in either monomeric adducts, i.e. in [Mn(acac-L'-en)(2,6-Bu(t)(2)C(6)H(3)O)Na(DME)(2)] (11.2DME), or polymeric structures, like in [Mn(acac-L'-en)Na(DME)(&mgr;-OEt)](n)() (13). All the dimeric units reported in this paper show a slight antiferromagnetic coupling between the two Mn(II) assisted by bridging alkoxo groups.

Density functional calculations were performed on a series of Cu(PH(3))-substituted cyclopolyenes as simple models of molecular metal carbides. We studied the oligomerization of the copper acetylide PH(3)CuC&tbd1;CCuPH(3) as a possible precursor of these (PH(3)CuC)(n)() (n = 4, 6, 8) hypothetical species. Special emphasis was placed on the comparison of the main properties of these metal-substituted cyclopolyenes with those of the corresponding cyclopolyenes in an attempt to study the effects of metal substituents on the organic C(4), C(6), and C(8) cyclic moieties. We found comparable geometries of the C(n)() units and, for n = 3, a thermodynamically stable species with respect to dissociation toward dinuclear copper acetylides.

p-tert-Butylcalix[4]arene tetrakis(diphenylphosphinite), calix[4]-(PPh(2))(4) (1), and tetrakis(dimethylphosphinite), calix[4]-(PMe(2))(4) (2), provide a phosphorus surface consisting of four coplanar trivalent phosphorus atoms for binding two metal ions into a close geometrical proximity. Homodimetallic complexes have been obtained in the reaction of 1 with [(COD)MCl(2)] [COD = cycloocta-1,5-diene], namely, [{calix[4]-(PPh(2))(4)}(MCl(2))(2)] [M = Pd (3), Pt (4)]. Characterizations by (1)H and (31)P NMR were particularly informative and showed how the bridging methylene of the calix[4]arene skeleton may function as a spectroscopic probe. A dimeric complex was obtained by reacting 1 with [Rh(CO)(2)Cl](2) to give [{calix[4]-(PPh(2))(4)}{Rh(CO)Cl}(2)] (5). Reaction of 1 with excess NiCl(2) gave exclusively the monometallic complex, [{calix[4]-(PPh(2))(4)}NiCl(2)] (6), regardless of the stoichiometry used. The analogous Pd monometallic complex (7) undergoes a ligand disproportionation reaction, while the corresponding Pt analogue does not exist under the same conditions. Complex 6 represents a good entry to dinuclear heterodimetallic complexes. In fact, its reaction with [(NBD)Mo(CO)(4)] [NBD = norbornadiene] led to [{calix[4]-(PPh(2))(4)}NiCl(2){Mo(CO)(4)}] (8). The use of the more basic and less sterically demanding ligand 2 led to the synthesis of homonuclear bimetallic complexes [{calix[4]-(PMe(2))(4)}(MCl(2))(2)] [M = Ni (9), Pd (10), Pt (11)].