Linear CuI2 Pd0 , CuI Pd02 , and AgI2 Pd0 Metal Chains Supported by Rigid N,N'-Diphosphanyl N-Heterocyclic Carbene Ligands and Metallophilic Interactions.

Selective copper(I) to palladium(0) transmetallation of P-donors from the rigid N,N'-diphosphanyl-imidazol-2-ylidene C3 H2 [NP(tBu)2 ]2 (PCNHC P) was observed when known [Cu3 (µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)3 was reacted with [Pd(PPh3 )4 ]. When 1.2 equivalents of [Pd(PPh3 )4 ] was used, the product [Cu2 Pd(µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (2(OTf)2 ) was obtained, which features a CuI -CuI -Pd0 chain and appears to be the first linear heterotrinuclear complex with d10 -d10 interactions between Pd0 and CuI . When the Cu3 precursor was reacted with 3.0 equivalents of [Pd(PPh3 )4 ], the complex [CuPd2 (µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (3(OTf)2 ) was obtained, which, on the basis of magnetic measurements, DFT calculations, and computed nuclear shieldings, was formulated as containing a Pd0 -CuI -Pd0 chain with an electron hole delocalized over the whole cation, including the metal chain. Similarly, selective transmetallation of the P-donors in [Ag3 (µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)3 from silver to palladium (originating from [Pd(PPh3 )4 ]) gave the linear chain [Ag2 Pd(µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (5(OTf)2 ), which on the basis of NMR spectroscopy comprises an AgI -AgI -Pd0 metal core. However, X-ray diffraction data collected on various samples of 5(OTf)2 were modeled with 50:50 metal disorder at the terminal positions, corresponding to a (AgI /Pd0 )-AgI -(AgI /Pd0 ) formulation. Upon standing in solution, 5(OTf)2 transformed to 6(OTf)2 , the regioisomer of 5(OTf)2 in which the Pd center has migrated to the central position of an AgI -Pd0 -AgI chain. Prolonged standing in CH2 Cl2 or by reaction with [PtCl2 (NCMe)2 ] converts complex 6(OTf)2 to the AgI /PdII complex [Ag2 PdCl2 (µ3 -PCNHC P,κP,κCNHC ,κP)2 ](OTf)2 (7(OTf)2 ). The structural data of 2(OTf)2 , 3(OTf)2 , and 7(OTf)2 establish significant heterometallophilic interactions.

Photocatalytic Aminodecarboxylation of Carboxylic Acids.

Aminodecarboxylation of unactivated alkyl carboxylic acids has been accomplished utilizing an organic photocatalyst. This operationally simple reaction utilizes readily available carboxylic acids to chemoselectively generate reactive alkyl intermediates that are not accessible via conventional two-electron pathways. The organic radical intermediates are efficiently trapped with electrophilic diazo compounds to provide aminated alkanes.

Normal-to-Abnormal NHC Rearrangement of Al(III) , Ga(III) , and In(III) Trialkyl Complexes: Scope, Mechanism, Reactivity Studies, and H2 Activation.

The present contribution reports experimental and theoretical mechanistic investigations on a normal-to-abnormal (C2-to-C4-bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3-di-tert-butylimidazol-2-ylidene; M=Al, Ga, In; 1 a-c) readily rearrange to quantitatively afford the corresponding C4-bonded complexes (aItBu)MMe3 (4 a-c), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC-to-aNHC process converting the Al-nNHC (1 a) to its aNHC analogue 4 a. A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF-AlMe3 . The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2 -O-AlMe3 ) (6), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors.

Steric congestion at, and proximity to, a ferrous center leads to hydration of α-nitrile substituents forming coordinated carboxamides.

The question of the conversion of nitrile groups into amides (nitrile hydration) by action of water in mild and eco-compatible conditions and in the presence of iron is addressed in this article. We come back to the only known example of hydration of a nitrile function into carboxamide by a ferrous [Fe(II)] center in particularly mild conditions and very efficiently and demonstrate that these unusual conditions result from the occurrence of steric stress at the reaction site and formation of a more stable end product. Two bis(cyano-substituted) (tris 2-pyridyl methyl amine) ligands have been prepared, and the structures of the corresponding FeCl2 complexes are reported, both in the solid state and in solution. These two ligands only differ by the position of the nitrile group on the tripod in the α and ß position, respectively, with respect to the pyridine nitrogen. In any case, intramolecular coordination is impossible. Upon action of water, the nitrile groups are hydrated however only if they are located in the α position. The fact that the ß-substituted ß-(NC)2TPAFeCl2 complex is not water sensitive suggests that the reaction proceeds in an intramolecular way at the vicinity of the metal center. In the bis α-substituted α-(NC)2TPAFeCl2 complex, both functions are converted in a very clean fashion, pointing out that this complex exhibits ligand flexibility and is not deactivated after the first hydration. At a preparative scale, this reaction allows the one-pot conversion of the bis(cyano-substituted) tripod into a bis(amido-substituted) one in particularly mild conditions with a very good yield. Additionally, the XRD structure of a ferric compound in which the two carboxamido ligands are bound to the metal in a seven-coordinate environment is reported.

Copper(II) complexes of bis(aryl-imino)acenaphthene ligands: synthesis, structure, DFT studies and evaluation in reverse ATRP of styrene.

Two new Ar-BIAN Cu(II) complexes (where Ar-BIAN = bis(aryl-imino)acenaphthene) of formulations [CuCl2(Mes-BIAN)] (1) (Mes = 2,4,6-Me3C6H2) and [CuCl2(Dipp-BIAN)] (2) (Dipp = 2,6-iPr2C6H3) were synthesised by direct reaction of CuCl2 suspended in dichloromethane with the respective ligands Mes-BIAN (L1) and Dipp-BIAN (L2), dissolved in dichloromethane, under an argon atmosphere. Attempts to obtain these compounds by solubilising CuCl2 in methanol and adding a dichloromethane solution of the corresponding ligand, under aerobic conditions, gave also compound 1, but, in the case of L2, the Cu(I) dimer [CuCl(Dipp-BIAN)]2 (3) was obtained instead of compound 2. The compounds were fully characterised by elemental analyses, MALDI-TOF mass spectrometry, FT-IR, (1)H NMR and EPR spectroscopic techniques. The solid-state molecular structures of compounds 1-3 were determined by single crystal X-ray diffraction, showing the expected chelation of the Ar-BIAN ligands and two chloride ligands completing the coordination sphere of the Cu(II) centre. In the case of the complex 1, an intermediate coordination geometry around the Cu(II) centre, between square planar and tetrahedral, was revealed, while the complex 2 showed an almost square planar geometry. The structural differences and evaluation of energetic changes were rationalised by DFT calculations. Analysis of the electrochemical behaviour of complexes 1-3 was performed by cyclic voltammetry and the experimental redox potentials for Cu(II)/Cu(I) pairs have been compared with theoretical values calculated by DFT in the gas phase and in dichloromethane and methanol solutions. The complex 1 exhibited good activity in the reverse atom transfer radical polymerisation (ATRP) of styrene.

Reactions of trinuclear platinum clusters with electrophiles: ionisation isomerism with [Pt3(µ2-I)(µ-PPh2)2(PPh3)3]I and [Pt3(µ-PPh2)2I2(PPh3)3]. Structures of [Pt3(µ2-Cl)(µ-PPh2)2(PPh3)3]PF6, [Pt3(µ-PPh2)2I2(PPh3)3] and of the Pt-Ag cluster [Pt3{µ3-AgBF4}(µ2-I)(µ-PPh2)2(PPh3)3]BF4.

A reaction of the 44 electron cluster [Pt3(µ-PPh2)3Ph(PPh3)2] (1) with wet AgBF4 afforded the cationic cluster [Pt3(µ2-OH)(µ-PPh2)2(PPh3)3]BF4 (3(BF4)) which slowly transformed into [Pt3(µ2-Cl)(µ-PPh2)2(PPh3)3]BF4 (4(BF4)) upon recrystallization from CH2Cl2. These 44 electron clusters have been characterized by (31)P{(1)H} NMR, and the crystal structure of 4(PF6) has been determined by X-ray diffraction, as well as that of [Pt3(µ-PPh2)2I2(PPh3)3] (5), which was obtained by recrystallization of the known cluster [Pt3(µ2-I)(µ-PPh2)2(PPh3)3]I (2(I)) from toluene and represents a neutral formula isomer of the latter. In addition, we have prepared the adducts of cluster 1 containing the moieties [Cu(NCMe)2](+) and [Au(PPh3)](+) in 6 and 7, respectively, and on the basis of their spectroscopic data, it was concluded that these complexes have similar structures to that previously established for the adduct of 1 with Ag(TFA) (TFA = OC(O)CF3), [Pt3{µ3-Ag(TFA)}(µ-PPh2)3Ph(PPh3)2] (8). The cationic clusters in 3(BF4) and 4(BF4) react with Ag(TFA) to afford cationic adducts in [Pt3{µ3-Ag(TFA)}(µ2-X)(µ-PPh2)2(PPh3)3]BF4 (9(BF4), X = OH; 10(BF4), X = Cl). The structure of the mixed-metal cluster [Pt3(µ3-AgBF4)(µ2-I)(µ-PPh2)2(PPh3)3]BF4 (11(BF4)), obtained by reaction of the complex 2(I) with AgBF4, was determined by X-ray diffraction.

Structural, magnetic and optical properties of an Fe(III) dimer bridged by the meridional planar divergent N,N'-bis(salicyl)hydrazide and its photo- and electro-chemistry in solution.

{Fe(III)Cl(DMF)(2)}(2)(L) where L is N,N'-bis(salicyl)hydrazide has been synthesized as red crystals and characterized using single-crystal diffraction, infrared and UV-vis spectroscopies, and its magnetic properties studied. The dimeric unit in the structure is formed through the two meridional sets of divergent O, N, O coordinating atoms of the hexacoordinated and quadruply charged ligand. With the presence of the inversion symmetry the Fe atoms are strictly planar with the ligand. The magnetic exchange interaction is found to be antiferromagnetic with a J = -5.98(3) cm(-1) through the rare Fe-N-N-Fe pathway. Irradiation of the FeCl(3)/H(4)L red DMF solution in the visible region of the spectrum resulted in its complete discoloration and from which the unknown colorless salt [Fe(II)(DMF)(6)][Fe(II)Cl(4)] and the neutral ligand have been identified by single crystal diffraction. The UV-visible spectra of FeCl(3), H(4)L and their mixture in DMF solution indicate that the iron complex is the absorbing species and the presence of the free ligand in the irradiated solution suggests that the ligand is potentially acting as a catalyst to the photoreduction of Fe(III) to Fe(II), while electrochemistry points to a mixed-valent (Fe(II)-Fe(III)) intermediate in the process.

Matrix-assisted laser desorption/ionisation time of flight spectrometry for the fast screening of oxosteroids using aromatic hydrated hydrazines as versatile probes.

To make the use of MALDI-based mass spectrometry feasible for the fast analysis of oxosteroids, three new aromatic probes have been designed to be used simultaneously as derivatisation agents and MALDI matrices. This concept brings a number of benefits: the sample handling is reduced, the workflow is less time consuming allowing high throughput and the interferences caused by the MALDI matrix are avoided. Identification was successfully attained for all oxosteroids used in this study. As proof-of-concept, the identification of oxosteroids in urine was performed to evaluate the robustness of the new methodology. The oxosteroids 17-α-methyltestosterone, nandrolone, boldenone, 17-α-Trenbolone, fluoxymesterolone, mesterolone and bolasterone were identified in human urine at the minimum concentration level recommended by the world anti-doping agency, 2 ng/mL.

Highly active zinc alkyl cations for the controlled and immortal ring-opening polymerization of ε-caprolactone.

Zinc alkyl cations supported by N,N-BIAN-type bidentate ligands were found to be highly active in the immortal ROP of ε-caprolactone to yield narrowly disperse and chain length-controlled poly(ε-caprolactone), whether in solution or bulk polymerization conditions.

Binucleating behaviour of a proximally-diphosphinated calix[4]arene.

The long diphosphine 5,11-diphenylphosphanyl-25,26-dipropyloxy-27,28-bis(2-propenyloxy) calix[4]arene (cone) (5), in which the two phosphorus atoms are separated by a semi-rigid linking unit, was prepared in four steps starting from calix[4]arene. Reaction of 5 with AuCl(SEt(2)) or [RuCl(2)(p-cymene)](2) led to calixarenes bearing two metallated pendant arms, [5·(AuCl)(2)] and [5·{RuCl(2)(p-cymene)}(2)], respectively. In the presence of AgBF(4) or [Ni(C(5)H(5))(1,5-cyclooctadiene)]BF(4), diphosphine 5 displayed a marked tendency to form oligomeric material, but under high dilution conditions dimeric species were obtained selectively. The inability of 5 to form chelate complexes was further illustrated by its reaction with [PdCl(2)(1,5-cyclooctadiene)(2)], which led quantitatively to a rare complex in which a diphosphine spans across the dinuclear [PdCl(µ-Cl)(2)PdCl] unit.

Comparison of the structure and stability of new α-diimine complexes of copper(I) and silver(I): density functional theory versus experimental.

New compounds of the general formulas [M(Ar-BIAN)(2)]BF(4) and [M(Ar-BIAN)(NCMe)(2)]BF(4), where M = Cu(I) or Ag(I) and Ar-BIAN = bis(aryl)acenaphthenequinonediimine, were synthesized by the direct reaction of [Cu(NCMe)(4)]BF(4) or [Ag(NCMe)(4)]BF(4) with the corresponding Ar-BIAN ligand in dried CH(2)Cl(2). The synthesized compounds are [M(o,o',p-Me(3)C(6)H(2)-BIAN)(2)]BF(4) where M = Cu(I) (1) and Ag(I) (2), [M(o,o'-iPr(2)C(6)H(3)-BIAN)(NCMe)(2)]BF(4) where M = Cu(I) (3) and Ag(I) (4), and [Ag(o,o'-iPr(2)C(6)H(3)-BIAN)(2)]BF(4) (5). The crystal structures of compounds 1-3 and 5 were solved by single-crystal X-ray diffraction. In all cases copper(I) or silver(I) are in a distorted tetrahedron that is constructed from the four nitrogen atoms of the two α-diimine ligands or, in 3, from one α-diimine ligand and two acetonitrile molecules. All compounds were characterized by elemental analyses, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry, and IR, UV-vis, and (1)H NMR spectroscopy. The analysis of the molecular geometry and the energetic changes for the formation reactions of the complexes, in a CH(2)Cl(2) solution, were evaluated by density functional theory calculations and compared with the experimental results.

Novel Cr(III) dinuclear complexes supported by salicyloylhydrazono dithiolane and dithiane ligands: synthesis, stability, crystal structures and magnetic properties.

We hereby report the synthesis, crystal structures and magnetic characterizations of three novel Cr(III) complexes: a mononuclear Cr(III)(HL((1)))3 species along with two dinuclear µ-methoxo Cr(III)2(µ-OMe)2(HL)4 (H2L((1)): 2-salicyloylhydrazono-1,3-dithiolane; H2L((2)): 2-salicyloylhydrazono-1,3-dithiane). EPR studies indicate that both dinuclear complexes (2a and 2b) are stable in solution (CHCl3). Both Cr(III) dinuclear complexes exhibit a strong antiferromagnetic coupling. DFT calculations performed for complex 2a are in agreement with a strong antiferromagnetic exchange interaction in these new dinuclear Cr(III) complexes.

Unusual reactivity in organoaluminium and NHC chemistry: deprotonation of AlMe3 by an NHC moiety involving the formation of a sterically bulky NHC-AlMe3 Lewis adduct.

A sterically congested NHC-AlMe(3) Lewis adduct (NHC = 1,3-di-tert-butylimidazol-2-ylidene) was found to either isomerize to an "abnormal" NHC-AlMe(3) species or to be involved in the deprotonation of AlMe(3) to form the corresponding imidazolium species along with an AlMe(3)-stabilized methylene aluminium anion.

Solid state and solution study of some phosphoramidate derivatives containing the P(O)NHC(O) bifunctional group: crystal structures of CCl(2)HC(O)NHP(O)(NCH(3)(CH(2)C(6)H(5)))(2), p-ClC(6)H(4)C(O)NHP(O)(NCH(3)(CH(2)C(6)H(5)))(2), CCl(2)HC(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2) and p-BrC(6)H(4)C(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2).

Synthetic methods for several novel phosphoramidate compounds containing the P(O)NHC(O) bifunctional group were developed. These compounds with the general formula R(1)C(O)NHP(O)(N(R(2))(CH(2)C(6)H(5)))(2), where R(1)=CCl(2)H, p-ClC(6)H(4), p-BrC(6)H(4), o-FC(6)H(4) and R(2)=hydrogen, methyl, benzyl, were characterized by several spectroscopic methods and analytical techniques. The effects of phosphorus substituents on the rotation rate around the P-N(amine) bond were also investigated. (1)H NMR study of the synthesized compounds demonstrated that the presence of bulky groups attached to the phosphorus center and electron withdrawing groups in the amide moiety lead to large chemical-shift non-equivalence (Deltadelta(H)) of diastereotopic methylene protons. The crystal structures of CCl(2)HC(O)NHP(O)(NCH(3)(CH(2)C(6)H(5)))(2), p-ClC(6)H(4)C(O)NHP(O)(NCH(3)(CH(2)C(6)H(5)))(2), CCl(2)HC(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2) and p-BrC(6)H(4)C(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2) were determined by X-ray crystallography using single crystals. The coordination around the phosphorus center in these compounds is best described as distorted tetrahedral and the P(O) and C(O) groups are anti with respect to each other. In the compound Br-C(6)H(4)C(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2) (with two independent molecules in the unit cell), two conformers are connected to each other via two different N-H...O hydrogen bonds forming a non-centrosymmetric dimer. In the crystalline lattice of other compounds, the molecules form centrosymmetric dimers via pairs of same N-H...O hydrogen bonds. The structure of CCl(2)HC(O)NHP(O)(N(CH(2)C(6)H(5))(2))(2) reveals an unusual intramolecular interaction between the oxygen of C=O group and amine nitrogen.

Heterometallic chains and clusters with gold-transition metal bonds: synthesis and interconversion.

Anionic, metal-metal bonded heterotrinuclear chain complexes of the type [M{MoCp(CO)(3)}(2)](-) with M = Cu(I), Ag(I), and Au(I) have been prepared by reaction between a d(10) metal precursor complex and the carbonylmetalate [MoCp(CO)(3)](-). These complexes have been structurally characterized by X-ray diffraction and used as precursors to neutral 2-D hexa- or octanuclear mixed-metal clusters of the general formula [MMoCp(CO)(3)](n) (M = Cu, n = 3; M = Ag or Au, n = 4), which are characterized by a central core constituted of interacting d(10) metal ions, surrounded by the molybdenum atoms. When M = Cu, the six metal atoms form a nu(2)-triangular core whereas when M = Ag or Au, a nu(2)-square structure is observed for the octanuclear metal core. It is shown in the case of M = Cu and Ag that interconversion between the metal chain complexes of stoichiometry M[m](2) and the clusters {M[m]}(n) is possible, and the position of the equilibrium depends solely on the respective stoichiometry of the reagents. The new nu(2)-square, octanuclear, trimetallic complexes [CuAg(3){MoCp(CO)(3)}(4)] (7) and [CuAu(3){MoCp(CO)(3)}(4)] (8) have also been obtained and characterized in the solid-state by X-ray diffraction, as well as the unexpected double pentanuclear complex [{Na(dme)}{Cu(2)[MoCp(CO)(3)](3)}](2) (9).

Calixarene-monophosphines as supramolecular chelators.

The calix[4]arenes 5-diphenylphosphino-17-R1-11,23-diR2-25,26,27,28-tetrapropoxycalix[4]arene (1, R1 = R2 = Br; 2, R1 = Br, R2 = H; 3, R1 = R2 = p-tolyl; 4, R1 = p-tolyl, R2 = H; 5, R1 = R2 = H; 20, R1 = p-tolyl, R2 = H), all bearing a diphenylphosphino group attached to the calixarene upper rim, have been synthesised starting from 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4]arene. Reaction of 1-5 with [RuCl2(p-cymene)]2 leads quantitatively to monophosphine complexes, [RuCl2(p-cymene)L], in which the endo-oriented ruthenium atom unit sits inside the cone delineated by the four phenoxy rings. The particular orientation of the P-Ru vector appears to result from pi-pi interactions between the p-cymene ligand and two aromatic cavity walls. Overall, in each case the calixarene end of the ligand behaves as a supramolecular receptor towards the Ru(p-cymene) fragment. Formation of complexes with exo-oriented P-M bonds were observed in the complexes cis-[PtCl2 x 1(2)] and in [RuCl2(p-cymene) x 20]. As shown by a variable temperature study carried out on [RuCl2(p-cymene) x 3], in which the ruthenium is embedded in an expanded cone, the p-cymene ring undergoes a fast oscillation about the Ru-arene bond which can be frozen out at low temperatures. Reaction of [RuCl2(p-cymene) x 3] with AgBF4 in CH3CN results in an intra-cavity reaction, with one chloride ligand being replaced by acetonitrile.

Di- and trinuclear phosphido-bridged platinum complexes. Crystal structures of [Pt{CH(2)=CHC(O)OMe}(PPh(3))(2)], trans-[Pt(2)(micro-PPh(2))(2)I(2)(PPh(3))(2)] and cis,cis,cis-[Pt(3)(mu-I)(2)(mu-PPh(2))(2)Cl(0.5)I(1.5)(PPh(3))(2)].

The readily available Pt(0) methyl acrylate complex [Pt{CH2CHC(O)OMe}(PPh3)2] (2) allows access to the known, mixed-valence trinuclear cluster [Pt3(mu-PPh2)3Ph(PPh3)2] (3) in 64% yield. Oxidation of 3 with 2 equivalents of I2 afforded the new trinuclear complex [Pt3(mu-I)2(mu-PPh2)2I2(PPh3)2] (4) whose molecular structure is similar to that of the related compound of empirical formula [Pt3(mu-I)2(mu-PPh2)2Cl0.5I1.5(PPh3)2] ( 5) which has been generated by oxidation of 3 with successively 1 equivalent of I2 and 1 equivalent of C6H5ICl2. In these complexes, the four halogen atoms lie on the same side of the almost aligned platinum atoms and the nearly square-planar coordination planes of the metal atoms adopt a japanese screen, chair-like conformation. The reaction of the dinuclear, metal-metal bonded Pt(I)-Pt(I) complex [Pt2(mu-PPh2)2(PPh3)2] with one equivalent of I2 afforded the Pt(II) complex [Pt2(mu-PPh2)2I2(PPh3)2] (6). The molecular structures of complexes 2 x CH2Cl2, [Pt3(mu-I)2(mu-PPh2)2(I1.3Cl0.7)(PPh3)2][Pt3(mu-I)2(mu-PPh2)2(I1.7Cl0.3)(PPh3)2] x C6H5Cl x 3CH2Cl2 (5A x 5B x C6H5Cl x 3CH2Cl2) and 6 have been established by single crystal X-ray diffraction studies.

Regiospecific intramolecular O-demethylation of the ligand by action of molecular dioxygen on a ferrous complex: versatile coordination chemistry of dioxygen in FeCl(2) complexes with (2,3-dimethoxyphenyl) alpha-substituted tripods in the tris(2-pyridylmethyl)amine series.

We report in this article one of the first examples of a reaction of O-demethylation carried out at a Fe(II) center by molecular dioxygen, in the homogeneous phase in non-porphyrinic chemistry. This reaction parallels at the intramolecular level a very important process found in biology leading to the derivatization and elimination of drugs by oxygen-dependent enzymes that contain nonheme iron centers. To get insight into some reactivity aspects of this reaction, we have used dioxygen and iron complexes coordinated to ligands that are substituted by methoxy groups. We detail in this work the coordination chemistry of FeCl(2) to the series of mono- (L(1)), di- (L(2)), and tris(2,3-dimethoxyphenyl) (L(3)) alpha-substituted ligands in the tris(2-pyridylmethyl)amine series and the behavior of the complexes upon reaction with molecular dioxygen. As main outcomes of this study, we demonstrate that the methoxy group does not need to be coordinated to the metal center to undergo O-demethylation, but needs to be properly orientated close to an oxygenated form of the metal. We also demonstrate the importance of the environment in the reactivity with molecular dioxygen: whereas a regular 18-electron Fe(II) reacts with O(2), a five- coordinate, 16-electron center may be oxygen-stable, if the access of dioxygen to the reaction site is locked.