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The [{calix[4]-(O)4}W(η²-C6H10)], 2, has been used as a source of W^IV-d² center-bonded to an oxo surface, which has been modeled by the calix[4]arene tetraanion in the reaction with diazoalkanes and organic azides. The olefin is easily displaced by both substrates. The reaction with Ph2CN2 led to the formation of metallahydrazone, [{calix[4]-(O)4}W&dbd;N−NCPh2], 5, which binds Bu^tNC inside the cavity, 6, or it can be reduced to a dinuclear W^V derivative [W−W, 2.646(1) Å], where the two metals are bridged by a diphenylhydrazido ligand in complex 7, [{calix[4]-(O)4}2W2(μ-N−N&dbd;CPh2)2Na2]. The reaction of 2 with organic azides (RN3) is strongly dependent on the nature of the R substituent at the azide functionality. The reaction with RN3 [R = SiMe3; CPh3] occurs at the metal in the exo position, leading to alkylimido derivatives [{calix[4]-(O)4}W&dbd;N−R] [R = SiMe3, 8; R = CPh3, 9], which bind inside the cavity Bu^tNC, leading to 10 and 11, respectively. The reaction of 2 with PhN3, on the contrary, occurs inside the calixarene cavity, leading to the triazenido derivative [{μ-calix[4]-(O)4}2(W&dbd;N−N&dbd;NPh)2], 12. The results of 2 with organic azides show that two different pathways are followed at the metal in the exo and endo positions. In the former case, for steric reasons, the 1,3 dipolar addition of the azide to the carbenoid metal precedes the formation of the alkylimido. In the case of PhN3, the size of the calix cavity prevents the same pathway. In the case of HN3 the reaction is supposed to proceed with HN3 binding the metal with the protonated nitrogen inside the cavity and decomposing to the imido functionality [{μ-calix[4]-(O)4}2(W&dbd;NH)2], 13. An alternative synthetic route to arylimido derivatives of W^VI has been reported. The reaction of [calix[4]-(ONa)4(THF)2] with [p-tolyl-N&tbd1;WCl4] led to [μ-calix[4]-W&tbd1;N-p-tolyl], 14, which is in equilibrium in solution with the corresponding dimeric form [{μ-calix[4]}2-W&tbd1;N-p-tolyl], 15.

This report deals with the deprotonation of [W(η²-alkene)] complexes to the corresponding 1-metallacyclopropene, which can be equally well obtained via hydride addition to the corresponding [W(η²-alkyne)]. The ancillary ligand supporting the metal is [p-Bu^t-calix[4]-(O)4],^4- which mimics an oxo surface. The [W(η²-2-methyl-2-butene)] complex 2 undergoes deprotonation to give the corresponding anionic 1-metallacyclopropene species 7. The latter can be protonated back to 2, alkylated using MeTf to give the corresponding [W(η²-2,3-dimethyl-2-butene)] complex 3 or metalated at the alkylidene functionality using ClSnPh3 to give 8. The one-electron oxidation of 7 led to the homolytic cleavage of the W−C bond within the 1-metallacyclopropene unit, thus forming a free radical dimerizing to the dinuclear W−alkylidene 9. The [W(η²-alkyne)] complexes 12 and 14 produce the 1-metallacyclopropenes 10 and 16, respectively, in the reaction with LiHBEt3. The former undergoes reversible protonation−deprotonation to the corresponding [W(η²-trans-stilbene)] derivative 4, while alkylation using MeTf occurs at one of the oxygens of the calixarene tetraanion, thus forming the neutral metallacyclopropene complex 11. In the case of a strained alkene, such as acenaphthylene (complex 5), the deprotonation occurs with the concomitant, homolytic cleavage of a W−C bond and the formation of a free radical alkylidene dimerizing to the ditungsten(V)−dialkylidene species 17, which has been oxidized using [Cp2Fe]⁺ to the corresponding diamagnetic form 18. The electronic structure and reactivity pathway of the 1-metallacyclopropene functionality has been analyzed using the DFT (density functional theory) approach.

The organometallic chemistry of titanium− and vanadium−macrocycle was investigated using meso-octaethyl mono(pyridine)−tris(pyrrole), [Et8(C5H3N)(C4H2NH)3], 1, and meso-octaethyl cis-bis(pyridine)−bis(pyrrole), [Et8cis-(m-MeC5H2N)(C5H3N)(C4H2NH)2], 7, as ligands for titanium(IV) and vanadium(III), respectively. The metalation of 1 with LiBu followed by the reaction with TiCl4·thf2 led to [Et8(C5H3N)(C4H2N)3Ti−Cl], 3, which was alkylated to [Et8(C5H3N)(C4H2N)3Ti−Me], 4. The Ti−C bond in 4 underwent a migratory insertion reaction with Bu^tNC and carbon monoxide. In the former case the corresponding η²-iminoacyl was isolated and structurally characterized as [Et8(C5H3N)(C4H2N)3Ti(η²-C(Me)NBu^t)], 6, while the reaction of 4 with carbon monoxide led to the homologation of one pyrrolyl anion, thus converting the mono(pyridine)−tris(pyrrole) into a cis-bis(pyridine)−bis(pyrrole) macrocycle and the oxotitanium(IV) functionality in [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2Ti&dbd;O], 5. The homologation occurs via a carbenium ion η²-acyl which was not intercepted. The synthesis of [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2V−Cl], 9, was carried out from the lithiated form, 8, of 7 followed by reaction with VCl3·thf3. Complex 9 was converted into the corresponding methyl derivative [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2V−Me], 10, which underwent a migratory insertion of CO and Bu^tNC. The reaction of 10 with Bu^tNC led to the expected η²-iminoacyl [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2V{η²-C(Me)&dbd;NBu^t}], 12, while in the case of CO, the intermediate η²-acyl, behaving as a nucleophilic carbenoid, reacted preferentially with the pyridine α-position, leading to [Et8(m-MeC5H3N)μ(O−CMe)(C4H2N)}(C4H2N)(C5H3N)V], 11. The proposed structures were supported by the X-ray analysis of 5, 6, 8, 9, and 11.

This report contains the chemistry of the ruthenium−carbene functionality bonded to the dibenzotetramethyltetraaza[14]annulene dianion, tmtaa. [{Ru(tmtaa)}2(μ-C8H12)], 1, was the most appropriate starting material, as it contains a labile olefin, which can be displaced by a number of ligands to give [Ru(tmtaa)(L)(L‘)] [L = L‘ = Py, 2; L = CO, L‘ = thf, 3; L = Bu^tNC, L‘ = thf, 4; L = L‘ = Bu^tNC, 5]. Reaction of 1 with diazoalkanes led to the displacement of the olefin and gave the corresponding carbene derivatives [Ru(tmtaa)(CRR‘)] [R = R‘ = Ph, 6; R = Ph, R‘ = H, 7; R = Ph, R‘ = COOMe, 8], which have square-pyramidal structures. Complexes 7 and 8 underwent a remarkable labilization of the carbene functionality in the reaction with carbon monoxide, while 6 was only converted to the corresponding carbonyl [Ru(tmtaa)(CPh2)(CO)], 10, by CO. The reaction of 7 with both CO and Bu^tNC led to the migration of the carbene to one of the metalladiimino rings of the ligands in 12 and 13, while the reaction of 8 with both CO and Bu^tNC enabled us to intercept the preliminary product of a free-radical-type migration of the carbene to the tmtaa ligand, with the isolation of 11 and 14. The ligand (CO or Bu^tNC)-induced migration of the CR2 fragment to the macrocycle seemed to proceed via a carbene mechanism in the case of 7, while 8 seemed to prefer a free-radical-like pathway. This assumption was further supported by extended Hückel calculations and by the reaction of 6−8 with ligands of different σ/π donor/acceptor capability. The pyridine converted 6−8 to the corresponding coordinate adducts, 15−17, while the reaction of 7 with PMe3 led to the formation of [Ru(tmtaa)(PMe3)2] and stilbenes, via a plausible carbene mechanism. The reaction of 8 with PMe3 proceeded through a free-radical pathway leading to 19, which has a structure similar to 11 and 14. The ligand-induced labilization of the metallacarbene functionality in the macrocyclic environment was analyzed using the extended Hückel calculations.

This report deals with the first examples of butadienes bonded to a Zr−O matrix provided by a calix[4]arene skeleton and their reactivity. The reaction of [{p-Bu^t-calix[4]-(OMe)2(O)2}ZrCl2], 2, with Mg(C4H6)(thf)2 and Mg(Ph2C4H4)(thf)3 led to [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr(η⁴-C4H6)], 3, and [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr(η⁴-Ph2C4H4)], 4. The butadiene fragment exhibits a π²,η⁴ bonding mode, as shown by an X-ray analysis on both compounds. Extended Hückel calculations confirmed the energetically preferred s-cis conformation and the π²,η⁴ bonding mode vs the σ²,π,η⁴ one. The parent compound 3 of this series behaves, however, both as a source of zirconium(II) in displacement reactions or as a dialkyl derivative of zirconium(IV) in insertion reactions. In the former class of transformations, the reaction of 3 with Ph2CO and PhCOCOPh led to the dioxo metallacycles [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−OC(Ph)2−C(Ph)2O−}], 5, and [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−OC(Ph)&dbd;C(Ph)O−})], 6, respectively. Butadiene was also displaced by diphenylacetylene leading to [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr(η²-Ph2C2)], 7, and by a phenylnitrene source [PhN3] forming the dinuclear phenylimido-bridged complex [{p-Bu^t-calix[4]-(OMe)2(O)2}2Zr2(μ-NPh)2], 8. Unlike at room temperature, Ph2CO reacted with 3 at low temperature without displacing the butadiene, but leading, instead, to the stepwise insertion of the ketone to form [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{CH2CH&dbd;CHCH2C(Ph)2O}], 10, and [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−OC(Ph)2CH2CH&dbd;CHCH2C(Ph)2O−}], 11. Using 2 mol of acetone, [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−OC(Me)2CH2CH&dbd;CHCH2C(Me)2O−}], 12, was obtained. MeCN and EtCN inserted in a single Zr−C bond (of a formal σ²,π,η⁴ structure) yielding [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−CH2CH&dbd;CHCH2C(Me)&dbd;N−}], 13, and [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−CH2CH&dbd;CHCH2C(Et)&dbd;N−}], 14. Bu^tNC engaged 3 in a multistep insertion reaction leading to [{p-Bu^t-calix[4]-(OMe)2(O)2}Zr{−(Bu^t)NC(C4H6)C(C&dbd;NBu^t)N(Bu^t)−}], 15, via a pathway which has been observed in the reaction of Bu^tNC with dialkylzirconium calix[4]arene derivatives. The σ² behavior of butadiene in 3 was further verified in the reaction with H2O to give [{p-Bu^t-calix[4]-(OMe)2(O)2}2Zr2(μ-O)2], 9, and butenes.

This report deals with the chemistry of V−C functionalities anchored to a quasi-planar O4 matrix represented here by the [p-Bu^t-calix[4]-(OMe)2(O)2]^2- macrocycle. The starting material [p-Bu^t-calix[4]-(OMe)2(O)2V−Cl], 2, has been converted into the corresponding alkyl and aryl derivatives [p-Bu^t-calix[4]-(OMe)2(O)2V−R] (R = Me, 3; R = CH2Ph, 4; R = p-MeC6H4, 5) by conventional procedures. The structure of 5 reveals the self-assembling of the monomeric unit into a columnar arrangement with the p-tolyl substituent functioning as a guest moiety in a neighboring unit. Complexes 3−5 undergo migratory insertion reactions with CO and Bu^tNC to the corresponding η²-acyls [p-Bu^t-calix[4]-(OMe)2(O)2V(η²-COR)] (R = Me, 6; R = CH2Ph, 7) and η²-iminoacyls [p-Bu^t-calix[4]-(OMe)2(O)2V{η²-C(NBu^t)R}] (R = Me, 8; R = CH2Ph, 9; R = p-MeC6H4, 10), the reaction with CO being strongly dependent on the R substituent. The structural model for the hexacoordinate intermediate leading to the inserted product is exemplified by the d² high-spin [p-Bu^t-calix[4]-(OMe)2(O)2V(Cl)(CNBu^t], 11, and proves the presence of four available orbitals at the metal for driving the reactivity in the [p-Bu^t-calix[4]-(OMe)2(O)2V] fragment. The bonding mode of the organic functionalities at the metal and the conversion of the alkyl substituent into the η²-acyl have been inspected by extended Hückel calculations. The oxidative demethylation of 3 and 5 by a controlled amount of iodine opened an interesting synthetic route to the corresponding vanadium(IV) organometallic derivatives [p-Bu^t-calix[4]-(OMe)(O)3V−X] (X = Cl, 12; X = p-MeC6H4, 13). A structural report on 2, 5, and 9 is included.

Solubilization of the highly insoluble polymeric ZrCl4 is achieved using 1,2,4,5-Me4C6H2 (durene) as a carrier in a halogenated solvent, such as CH2Cl2, CHCl3, 1,2-Cl2C2H4, or o-Cl2C6H4. Solubilization can reach the level of 40 g of ZrCl4 in 100 mL of CH2Cl2 using an equimolar amount of durene. This is a very successful approach to making available soluble ZrCl4 in a noncoordinating solvent. The solubilization occurs via the formation of a η⁶-arene complex, which has been structurally characterized in the form of the hexamethylbenzene derivative [(η⁶-Me6C6)Zr2(μ-Cl)3Cl5] (3). This complex is in equilibrium, as revealed by the ¹H NMR spectrum in CH2Cl2, with free C6Me6 and a complex (4) which contains a higher Zr/C6Me6 ratio. A careful analysis of the CH2Cl2 solution, containing originally ZrCl4 and durene, showed that durene underwent transformation to C6Me5H and C6Me6. These species have been trapped, bonded to zirconium in complex [(η⁶-C6Me5R)Zr2(μ-Cl)3Cl5] (2, R = H, 50%; R = Me, 50%), which has been structurally characterized. The methyl redistribution reaction in CH2Cl2 can result in the inconvenient formation of byproducts derived from the Zr-assisted Friedel−Craft reaction of CH2Cl2 on the arene. The intermediate of such a reaction has been isolated as [C6Me6CHCl2]⁺[Zr2Cl9]^- (5), whose X-ray structure is available. In order to avoid the intervention of the solvent and to speed up the reaction, the ZrCl4 rearrangement of methylbenzenes was carried out in neat hydrocarbon at 90 °C for 6 h. This rearrangement has a number of peculiarities:  (i) unlike the original Jacobsen reaction, it involves intermolecular methyl transfer; (ii) it reaches an equilibrium of methyl distribution; and (iii) it is catalytic in zirconium. The very high stability of 3 accounts for the isolation of the same compound derived from the ZrCl4-assisted trimerization of 2-butyne in n-hexane.

A bimetallic complex, in which a RuCl2(η²-C2H4)(PCy3) fragment is connected via three chloro bridges to a (η⁶-p-cymene)RuCl2 fragment, has been synthesized and characterized by single-crystal X-ray crystallography. This complex was used to catalyze the atom transfer radical addition of CCl4 and CHCl3 to olefins at temperatures between 0 and 40 °C. Turnover frequencies of up to 1550 h^-1 were observed, making the new complex one of the most active catalysts for this type of reaction described so far.

[p-Bu^t-calix[4]-(O)4-Mo^IV], generated in situ from [MoCl4·THF2] and the alkali salts of p-Bu^t-calix[4]arene, displays the reactivity expected for a d²-carbenoid metal. The reaction carried out in the presence of azobenzene led to the cleavage of the N&dbd;N bond and the formation of a dimeric Mo^VI-phenylimido derivative, [{μ-p-Bu^t-calix[4]-(O)4}2{Mo^VI&tbd1;NPh}2], while the reaction with acetylenes led to 2-metallacyclopropene complexes [{p-Bu^t-calix[4]-(O)4-Mo}(η²-C2R2)], which converted to 1-metallacyclopropenes, the precursor of alkylidene and alkylidyne functionalities, in the reaction with a hydride source.

The cis-dichloro-meso-hexaethylporphodimethene−zirconium(IV) complex has been functionalized to the corresponding dialkyl derivatives [R = Me, PhCH2, Ph], 3−5, displaying a variety of migratory pathways. In the case of benzyl derivative 4, the spontaneous migration of the first benzyl to the ligand, 6, is followed by the second one, photochemically induced, thus forming a Zr−porphyrinogen complex, 7. The methyl derivative undergoes thermally induced methane elimination with the metalation of the meso ethyl chains, 8. Migration of both methyl groups has been observed in the reaction of 3 with Bu^tNC, with the preliminary formation of η²-imine, rearranging to the corresponding enamine, 9.

The (meso-octaethylporphyrinogenato)zirconium(IV) species [(Et8N4)Zr(thf)] (1) binds the acetophenone potassium enolate [PhCOCH2K] (2) in its ion-pair form, [(η⁵:η¹:η¹:η¹-Et8N4)Zr{PhC(CH2)O}K(thf)3] (3), and thus drives the aldol condensation reaction with acetophenone. The resulting aldolate, which occurs in a metallacyclic form due to the solvation of potassium by a phenyl ring, remains η¹ (O)-bonded to zirconium, [(η⁵:η¹:η¹:η¹-Et8N4)Zr{PhC(CH2)OC(O)C(Me)Ph}K]n (4).

The reaction of a Ti&sbd;Me species with carbon monoxide occurred with the complete cleavage of the C&sbd;O bond and formation of the Ti&dbd;O unit, while the [Me&sbd;C] fragment homologated a pyrrole to a 4-methylpyridine ring within the meso-octaethyl tris(pyrrole)−mono(pyridine) macrocycle.

[(Calix[4]OMe)TaCl2] (2), formed from [calix[4](OMe)2] (1) and TaCl5 via a demethylation reaction, undergoes exhaustive alkylation to [(calix[4]OMe)TaR2] (3−5), which give photochemically or thermally induced concerted dealkylation at the metal and at the methoxy group, to give [calix[4]TaR] (6−8). Double migration of alkyl groups has been observed in the reaction of 3−5 with CO and Bu^tNC to form the corresponding η²-ketones [(calix[4]OMe)Ta(η²-COR2)] (9−11) and η²-imines [(calix[4]OMe)Ta{η²-N(Bu^t)CR2}] (12−14).

A reactive coordinatively unsaturated iron(II) bonded to a quasi-planar O4 environment in [calix[4](OMe)2(O)2Fe] (2) has been obtained from the reaction of the free ligand 1 with Fe2Mes4 (Mes = 1,3,5-Me3C6H2). The reaction of 2, which adds a variety of monodentate ligands, [calix[4](OMe)2(O)2FeL] (L = thf, 3; Bu^tNC, 4), with Ph2CN2 led to the first high-spin iron(II) carbene bonded to an oxo matrix, [calix[4](OMe)2(O)2Fe&dbd;CPh2] (5).

The doubly homologated meso-octaethylporphyrinogen 1, containing two pyridine and two pyrrole rings in cis arrangements, allowed the synthesis of highly reactive vanadium(III) organometallics, via the intermediacy of 2, [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2Li2(THF)2], and 3, [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2V−Cl]. This latter complex has been converted to the corresponding [V−Me] derivative 4, [Et8(m-MeC5H2N)(C5H3N)(C4H2N)2V−Me], which undergoes a facile carbonylation to 5, Et6(m-MeC5H2N)(C5H3N)(C4H2N)2V−OC(CEt2)(Me)]. The intermediate η²-acyl derivative thus found displayed an unusual carbenoid reactivity inserting into a C−C bond.