Remarkable reactions of cyclooctatetraene diiron-bridging carbyne complexes with amino and amido compounds: nucleophilic addition to and breaking of the cyclooctatetraene ring

The reactions of the cationic, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(8)-C(8)H(8))]BF(4) (1, Ar=C(6)H(5); 2, Ar=p-CH(3)C(6)H(4); 3, Ar=p-CF(3)C(6)H(4)) with LiN(C(6)H(5))(2) in THF at low temperature gave novel N-nucleophilic-addition products, namely, the neutral, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(7)-C(8)H(8)N(C(6)H(5))(2))] (4, Ar=C(6)H(5); 5, Ar=p-CH(3)C(6)H(4); 6, Ar=p-CF(3)C(6)H(4))). Cationic bridging carbyne complexes 1-3 react with (C(2)H(5))(2)NH, (iC(3)H(7))(2)NH, and (C(6)H(11))(2)NH under the same conditions with ring cleavage of the COT ligand to produce the novel diiron-bridging carbene inner salts [Fe(2)[mu-C(Ar)C(8)H(8)NR(2)](CO)(4)] (7, Ar=C(6)H(5), R=C(2)H(5); 8, Ar=p-CH(3)C(6)H(4), R=C(2)H(5); 9, Ar=p-CF(3)C(6)H(4), R=C(2)H(5); 10, Ar=C(6)H(5), R=iC(3)H(7); 11, Ar=p-CH(3)C(6)H(4), R=iC(3)H(7); 12, Ar=p-CF(3)C(6)H(4), R=iC(3)H(7); 13, Ar=C(6)H(5), R=C(6)H(11); 14, Ar=p-CH(3)C(6)H(4), R=C(6)H(11), 15, Ar=p-CF(3)C(6)H(4), R=C(6)H(11)). Piperidine reacts similarly with cationic carbyne complex 3 to afford the corresponding bridging carbene inner salt [Fe(2)[mu-C(Ar)C(8)H(8)N(CH(2))(5)](CO)(4)] (16). Compound 9 was transformed into a new diiron-bridging carbene inner salt 17, the trans isomer of 9, by heating in benzene. Unexpectedly, the reaction of C(6)H(5)NH(2) with 2 gave a novel COT iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NHC(6)H(5)](mu-CO)(CO)(3)(eta(8)-C(8)H(8))] (18). However, the analogous reactions of 2-naphthylamine with 2 and of p-CF(3)C(6)H(4)NH(2) with 3 produce novel chelated iron-carbene complexes [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(10)H(7)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (19) and [Fe(2)[=C(C(6)H(4)CF(3)-p)NC(6)H(4)CF(3)-p](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (20), respectively. Compound 18 can also be transformed into the analogous chelated iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(6)H(5)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (21). The structures of complexes 6, 9, 15, 17, 18, and 21 have been established by X-ray diffraction studies.     

HP-Ca2Si5N8--a new high-pressure nitridosilicate: synthesis, structure, luminescence, and DFT calculations

HP-Ca(2)Si(5)N(8) was obtained by means of high-pressure high-temperature synthesis utilizing the multianvil technique (6 to 12 GPa, 900 to 1200 degrees C) starting from the ambient-pressure phase Ca(2)Si(5)N(8). HP-Ca(2)Si(5)N(8) crystallizes in the orthorhombic crystal system (Pbca (no. 61), a=1058.4(2), b=965.2(2), c=1366.3(3) pm, V=1395.7(7)x10(6) pm(3), Z=8, R1=0.1191). The HP-Ca(2)Si(5)N(8) structure is built up by a three-dimensional, highly condensed nitridosilicate framework with N([2]) as well as N([3]) bridging. Corrugated layers of corner-sharing SiN(4) tetrahedra are interconnected by further SiN(4) units. The Ca(2+) ions are situated between these layers with coordination numbers 6+1 and 7+1, respectively. HP-Ca(2)Si(5)N(8) as well as hypothetical orthorhombic o-Ca(2)Si(5)N(8) (isostructural to the ambient-pressure modifications of Sr(2)Si(5)N(8) and Ba(2)Si(5)N(8)) were studied as high-pressure phases of Ca(2)Si(5)N(8) up to 100 GPa by using density functional calculations. The transition pressure into HP-Ca(2)Si(5)N(8) was calculated to 1.7 GPa, whereas o-Ca(2)Si(5)N(8) will not be adopted as a high-pressure phase. Two different decomposition pathways of Ca(2)Si(5)N(8) (into Ca(3)N(2) and Si(3)N(4) or into CaSiN(2) and Si(3)N(4)) and their pressure dependence were examined. It was found that a pressure-induced decomposition of Ca(2)Si(5)N(8) into CaSiN(2) and Si(3)N(4) is preferred and that Ca(2)Si(5)N(8) is no longer thermodynamically stable under pressures exceeding 15 GPa. Luminescence investigations (excitation at 365 nm) of HP-Ca(2)Si(5)N(8):Eu(2+) reveal a broadband emission peaking at 627 nm (FWHM=97 nm), similar to the ambient-pressure phase Ca(2)Si(5)N(8):Eu(2+).     

Eta6-mesityl,eta1-imidazolinylidene-carbene-ruthenium(II) complexes: catalytic activity of their allenylidene derivatives in alkene metathesis and cycloisomerisation reactions

The reaction of electron-rich carbene-precursor olefins containing two imidazolinylidene moieties [(2,4,6-Me(3)C(6)H(2)CH(2))NCH(2)CH(2)N(R)Cdbond;](2) (2a: R=CH(2)CH(2)OMe, 2 b R=CH(2)Mes), bearing at least one 2,4,6-trimethylbenzyl (R=CH(2)Mes) group on the nitrogen atom, with [RuCl(2)(arene)](2) (arene=p-cymene, hexamethylbenzene) selectively leads to two types of complexes. The cleavage of the chloride bridges occurs first to yield the expected (carbene) (arene)ruthenium(II) complex 3. Then a further arene displacement reaction takes place to give the chelated eta(6)-mesityl,eta(1)-carbene-ruthenium complexes 4 and 5. An analogous eta(6)-arene,eta(1)-carbene complex with a benzimidazole frame 6 was isolated from an in situ reaction between [RuCl(2)(p-cymene)](2), the corresponding benzimidazolium salt and cesium carbonate. On heating, the RuCl(2)(imidazolinylidene) (p-cymene) complex 8, with p-methoxybenzyl pendent groups attached to the N atoms, leads to intramolecular p-cymene displacement and to the chelated eta(6)-arene,eta(1)-carbene complex 9. On reaction with AgOTf and the propargylic alcohol HCtbond;CCPh(2)OH, compounds 4-6 were transformed into the corresponding ruthenium allenylidene intermediates (4-->10, 5-->11, 6-->12). The in situ generated intermediates 10-12 were found to be active and selective catalysts for ring-closing metathesis (RCM) or cycloisomerisation reactions depending on the nature of the 1,6-dienes. Two complexes [RuCl(2)[eta(1)-CN(CH(2)C(6)H(2)Me(3)-2,4,6)CH(2)CH(2)N- (CH(2)CH(2)OMe)](C(6)Me(6))] 3 with a monodentate carbene ligand and [RuCl(2)[eta(1)-CN[CH(2)(eta(6)-C(6)H(2)Me(3)-2,4,6)]CH(2)CH(2)N-(CH(2)C(6)H(2)Me(3)-2,4,6)]] 5 with a chelating carbene-arene ligand were characterised by X-ray crystallography.     

Binding N2, N2H2, N2H4, and NH3 to transition-metal sulfur sites: modeling potential intermediates of biological N2 fixation

In the quest for low-molecular-weight metal sulfur complexes that bind nitrogenase-relevant small molecules and can serve as model complexes for nitrogenase, compounds with the [Ru(PiPr(3))('N(2)Me(2)S(2)')] fragment were found ('N(2)Me(2)S(2)'(2-)=1,2-ethanediamine-N,N'-dimethyl-N,N'-bis(2-benzenethiolate)(2-)). This fragment enabled the synthesis of a first series of chiral metal sulfur complexes, [Ru(L)(PiPr(3))('N(2)Me(2)S(2)')] with L=N(2), N(2)H(2), N(2)H(4), and NH(3), that meet the biological constraint of forming under mild conditions. The reaction of [Ru(NCCH(3))(PiPr(3))('N(2)Me(2)S(2)')] (1) with NH(3) gave the ammonia complex [Ru(NH(3))(PiPr(3))('N(2)Me(2)S(2)')] (4), which readily exchanged NH(3) for N(2) to yield the mononuclear dinitrogen complex [Ru(N(2))(PiPr(3))('N(2)Me(2)S(2)')] (2) in almost quantitative yield. Complex 2, obtained by this new efficient synthesis, was the starting material for the synthesis of dinuclear (R,R)- and (S,S)-[micro-N(2)[Ru(PiPr(3))('N(2)Me(2)S(2)')](2)] ((R,R)-/(S,S)-3). (Both 2 and 3 have been reported previously.) The as-yet inexplicable behavior of complex 3 to form also the R,S isomer in solution has been revealed by DFT calculations and (2)D NMR spectroscopy studies. The reaction of 1 or 2 with anhydrous hydrazine yielded the hydrazine complex [Ru(N(2)H(4))(PiPr(3))('N(2)Me(2)S(2)')] (6), which is a highly reactive intermediate. Disproportionation of 6 resulted in the formation of mononuclear diazene complexes, the ammonia complex 4, and finally the dinuclear diazene complex [micro-N(2)H(2)[Ru(PiPr(3))('N(2)Me(2)S(2)')](2)] (5). Dinuclear complex 5 could also be obtained directly in an independent synthesis from 1 and N(2)H(2), which was generated in situ by acidolysis of K(2)N(2)(CO(2))(2). Treatment of 6 with CH(2)Cl(2), however, formed a chloromethylated diazene species [[Ru(PiPr(3))('N(2)Me(2)S(2)')]-micro-N(2)H(2)[Ru(Cl)('N(2)Me(2)S(2)CH(2)Cl')]] (9) ('N(2)Me(2)S(2)CH(2)Cl'(2-) =1,2-ethanediamine-N,N'-dimethyl-N-(2-benzenethiolate)(1-)-N'-(2-benzenechloromethylthioether)(1-)]. The molecular structures of 4, 5, and 9 were determined by X-ray crystal structure analysis, and the labile N(2)H(4) complex 6 was characterized by NMR spectroscopy.     

1,4-dicyanobenzene as a scaffold for the preparation of bimetallic actinide complexes exhibiting metal-metal communication

Reaction of two equivalents of [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) or [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [{(C(5)Me(4)Et)(2)(Cl)U}(2)(mu-{N==C(CH(3))-C(6)H(4)-(CH(3))C==N})] (8) and [{(C(5)Me(5))(2)(Br)Th}(2)(mu-{N==C(CH(3))-C(6)H(4)- (CH(3))C==N})] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U(IV)/U(IV) (5f(2)-5f(2)) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the pi system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U(IV)/U(IV) system decrease substantially compared to the related monometallic ketimide chloride complex, [(C(5)Me(5))(2)U(Cl){-N==C(CH(3))-(3,4,5-F(3)-C(6)H(2))}] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) and [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C(5)Me(4)Et)(2)UCl(2)] (3), [(C(5)Me(4)Et)(2)U(CH(3))(2)] (4), [(C(5)Me(4)Et)(2)U{-N==C(CH(3))-C(6)H(4)-C==N}(2)] (10), and 11.     

Unsymmetrically substituted 9,10-dihydro-9,10-diboraanthracenes as versatile building blocks for boron-doped π-conjugated systems

The targeted hydrolysis of the 9,10-dihydro-9,10-diboraanthracene adduct (Me(2)S)HB(C(6)H(4))(2)BH(SMe(2)) (1) with 0.5 equiv of H(2)O leads to formation of the borinic acid anhydride [(Me(2)S)HB(C(6)H(4))(2)B](2)O (2) and thereby provides access to the field of unsymmetrically substituted 9,10-dihydro-9,10-diboraanthracenes. Compound 2 reacts with tBuC≡CH to give the corresponding vinyl derivative in an essentially quantitative conversion. Subsequent cleavage of the B-O-B bridge by LiAlH(4) with formation of hydridoborate functionalities is possible but is accompanied by partial B-C(vinyl) bond degradation. This situation changes when the related mesityl derivative [MesB(C(6)H(4))(2)B](2)O (7) is employed, which can be synthesized from BrB(C(6)H(4))(2)BBr (6) by treatment with 1 equiv of MesMgBr and subsequent hydrolysis. The reaction of 7 with LiAlH(4) in tetrahydrofuran (THF) furnishes Li[MesB(C(6)H(4))(2)BH(2)] (8); hydride elimination with Me(3)SiCl leads to formation of the THF adduct MesB(C(6)H(4))(2)BH(THF) (9·THF). Alternatively, 7 can be transformed into the bromoborane MesB(C(6)H(4))(2)BBr (10) by treatment with BBr(3). A Br/H-exchange reaction between 10 and Et(3)SiH yields the donor-free borane MesB(C(6)H(4))(2)BH (9), which forms B-H-B bridged dimers (9)(2) in the solid state. The vinyl borane MesB(C(6)H(4))(2)BC(H)=C(H)Mes (14) is accessible from MesC≡CH and either 9·THF or 9. Compared with the related compound Mes(2)BC(H)=C(H)Mes, the electronic absorption and emission spectra of 14 reveal bathochromic shifts of Δλ(abs)=17 nm and Δλ(em)=74 nm, which can be attributed to the rigid, fully delocalized π framework of the [MesB(C(6)H(4))(2)B] chromophore.     

Molecular nitrides containing group 4 and 5 metals: single and double azatitanocubanes

Treatment of [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) with the imido complexes [Ti(NAr)Cl(2)(py)(3)] (Ar=2,4,6-C(6)H(2)Me(3)) and [Ti(NtBu)Cl(2)(py)(3)] in toluene affords the single azatitanocubanes [[Cl(2)(ArN)Ti]( micro(3)-NH)(3)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (2.C(7)H(8)) and [[Cl(2)Ti](micro(3)-N)(2)(micro(3)-NH)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (3), respectively. Similar reactions of complex 1 with the niobium and tantalum imido derivatives [[M(NtBu)(NHtBu)Cl(2)(NH(2)tBu)](2)] (M=Nb, Ta) in toluene give the single azaheterometallocubanes [[Cl(2)(tBuN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (M=Nb (4), Ta (5)), both complexes react with 2,4,6-trimethylaniline to yield the analogous species [[Cl(2)(ArN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (Ar=2,4,6-C(6)H(2)Me(3), M=Nb (6.C(7)H(8)), Ta (7.C(7)H(8))). Also the azaheterodicubanes [M[micro(3)-N)(2)(micro(3)-NH)](2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2C(7)H(8) [M=Ti (8.2C(7)H(8)), Zr (9.2C(7)H(8))], and [M[(micro(3)-N)(5)(micro(3)-NH)][Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2 C(7)H(8) (Nb (10.2C(7)H(8)), Ta (11.2C(7)H(8))) were prepared from 1 and the homoleptic dimethylamido complex [M(NMe(2))(x)] (x=4, M=Ti, Zr; x=5, M=Nb, Ta) in toluene at 150 degrees C. X-ray crystal structure determinations were performed for 6 and 10, which revealed a cube- and double-cube-type core, respectively. For complexes 2 and 4-7 we observed and studied by DNMR a rotation or trigonal-twist of the organometallic ligands [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) and [(micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]](1-). Density functional theory calculations were carried out on model complexes of 2, 3, and 8 to establish and understand their structures.     

The nature of unsupported uranium-ruthenium bonds: a combined experimental and theoretical study

Four new uranium-ruthenium complexes, [(Tren(TMS))URu(η(5)-C(5)H(5))(CO)(2)] (9), [(Tren(DMSB))URu(η(5)-C(5)H(5))(CO)(2)] (10), [(Ts(Tolyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (11), and [(Ts(Xylyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (12) [Tren(TMS)=N(CH(2)CH(2)NSiMe(3))(3); Tren(DMSB)=N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts(Tolyl)=HC(SiMe(2)NC(6)H(4)-4-Me)(3); Ts(Xylyl)=HC(SiMe(2)NC(6)H(3)-3,5-Me(2))(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(η(5)-C(5)H(5))(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(η(5)-C(5)H(5))(3)URu(η(5)-C(5)H(5))(CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.     

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.     

Convenient syntheses of fluorous aryl iodides and hypervalent iodine compounds: ArI(L)n reagents that are recoverable by simple liquid/liquid biphase workups,and applications in oxidations of hydroquinones

Iodinations of the ortho, meta, and para fluorous arenes (R(f8)CH(2)CH(2)CH(2))(2)C(6)H(4) (R(f8)=(CF(2))(7)CF(3)) with I(2)/H(5)IO(6) in AcOH/H(2)SO(4)/H(2)O give 3,4-(R(f8)CH(2)CH(2)CH(2))(2)C(6)H(3)I (5) and the analogous 2,4- (6) and 2,5- (7) isomers, respectively. Spectroscopic yields are >90 %, but 5 and 7 must be separated by chromatography from by-products (yields isolated: 70 %, 97 %, 61 %). Reaction of 1,3,5-(R(f8)CH(2)CH(2)CH(2))(3)C(6)H(3) with PhI(OAc)(2)/I(2) gives 2,4,6-(R(f8)CH(2)CH(2)CH(2))(3)C(6)H(2)I (8) on multigram scales in 97 % yield. The CF(3)C(6)F(11)/toluene partition coefficients of 5-8 (24 degrees C: 69.5:30.5 (5), 74.7:25.3 (6), 73.9:26.1 (7), 98.0:2.0 (8)) are lower than those of the precursors, but CF(3)C(6)F(11)/MeOH gives higher values (97.0:3.0 (5), 98.6:1.4 (6), 98.0:2.0 (7), >99.3:<0.3 (8)). Reactions of 5-8 with excess NaBO(3) in AcOH yield the corresponding ArI(OAc)(2) species 9-12 (9, 85 % as a 90:10 9/5 mixture; 10, 97 %; 11, 95 %; 12, 93 % as a 95:5 12/8 mixture). These rapidly oxidize 1,4-hydroquinones in MeOH. Subsequent additions of CF(3)C(6)F(11) give liquid biphase systems. Solvent removal from the CF(3)C(6)F(11) phases gives 5-8 in >99-98 % yields, and solvent removal from the MeOH phases gives the quinone products, normally in >99-95 % yields. The recovered compounds 5-8 are easily reoxidized to 9-12 and used again.     

Solubilizing sodium fluoride in acetonitrile: synthesis, molecular structure, and complexation behavior of bis(organostannyl)methyl-substituted crown ethers

The synthesis of the crown-ether-substituted bis(organostannyl)methanes Ph(3)SnCH(2)Sn(Ph(2))-CH(2)-[16]crown-5 (1) and Ph(2)ISnCH(2)Sn(I)(Ph)-CH(2)-[16]crown-5 (2) is reported. Both compounds have been characterized by elemental analyses, (1)H, (13)C, (19)F, and (119)Sn NMR spectroscopy, and in the case of compound 2 also by electrospray ionization mass spectrometry. Single-crystal X-ray diffraction analysis revealed for the aqua complex 2.H(2)O trigonal-bipyramidal-configured tin atoms with intramolecular Sn(1)-O(1) and Sn(2)-O(1W) distances of 2.555(2) and 2.440(3) A, respectively. The water molecule is trapped in a sandwich-like fashion between the crown ether oxygen atoms O(2) and O(4) and the Sn(2) atom. NMR spectroscopy unambiguously proved the ability of compound 2 in acetonitrile to overcome the high lattice energy of sodium fluoride and to complex the latter under charge separation.     

N,N'-ethylenebis(pyridoxylideneiminato) and N,N'-ethylenebis(pyridoxylaminato): synthesis, characterization, potentiometric, spectroscopic, and DFT studies of their vanadium(IV) and vanadium(V) complexes

The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.     

Strong intramolecular secondary si.N bonds in trifluorosilylhydrazines

The simple silylhydrazines F(3)SiN(Me)NMe(2) (1), F(2)Si(N(Me)NMe(2))(2) (2), and F(3)SiN(SiMe(3))NMe(2) (3) have been prepared by reaction of SiF(4) with LiN(Me)NMe(2) and LiN(SiMe(3))NMe(2), while F(3)SiN(SnMe(3))NMe(2) (4) was prepared from SiF(4) and (Me(3)Sn)(2)NNMe(2) (5). The compounds were characterized by gas-phase IR and multinuclear NMR spectroscopy ((1)H, (13)C, (14/15)N, (19)F, (29)Si, (119)Sn), as well as by mass spectrometry. The crystal structures of compounds 1-5 were determined by X-ray crystallography. The structures of free molecules 1 and 3 were determined by gas-phase electron diffraction. The structures of 1, 2, and 4 were also determined by ab initio calculations at the MP2/6-311+G** level of theory. These structural studies constitute the first experimental proof for the presence of strong Si.N beta-donor-acceptor bonds between the SiF(3) and geminal NMe(2) groups in silylhydrazines. The strength of these non-classical Si.N interactions is strongly dependent on the nature of the substituent at the alpha-nitrogen atom of the SiNN unit, and has the order 3>4>1. The valence angles at these extremely deformed alpha-nitrogen atoms, and the Si.N distances are (crystal/gas): 1 104.2(1)/106.5(4) degrees, 2.438(1)/2.510(6) A; 3 83.6(1)/84.9(4) degrees, 2.102(1)/2.135(9) A; 4 89.6(1) degrees, 2.204(2) A.     

A combination of lacunary polyoxometalates and high-nuclear transition-metal clusters under hydrothermal conditions. Part II: From double cluster, dimer, and tetramer to three-dimensional frameworks

The hydrothermal reactions of trivacant Keggin A-alpha-XW(9)O(34) polyoxoanions (X=P(V)/Si(IV)) with transition-metal ions (Ni(II)/Cu(II)/Fe(II)) in the presence of amines result in eight novel high-nuclear transition-metal-substituted polyoxotungstates [{Ni(7)(mu(3)-OH)(3)O(2)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))][{Ni(6)(mu(3)-OH)(3)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))][Ni(dap)(2)(H(2)O)(2)]4.5 H(2)O (1), [Cu(dap)(H(2)O)(3)](2)[{Cu(8)(dap)(4)(H(2)O)(2)}(B-alpha-SiW(9)O(34))(2)]6 H(2)O (2), (enH(2))(3)H(15)[{Fe(II) (1.5)Fe(III) (12)(mu(3)-OH)(12)(mu(4)-PO(4))(4)}(B-alpha-PW(9)O(34))(4)]ca.130 H(2)O (3), [{Cu(6)(mu(3)-OH)(3)(en)(3) (H(2)O)(3)}(B-alpha-PW(9)O(34))]7 H(2)O (4), [{Ni(6)(mu(3)-OH)(3)(en)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))]7 H(2)O (5), [{Ni(6)(mu(3)-OH)(3)(en)(2)(H(2)O)(8)}(B-alpha-PW(9)O(34))]7 H(2)O (6), [{Ni(6)(mu(3)-OH)(3)(dap)(2)(H(2)O)(8)}(B-alpha-PW(9)O(34))] 7 H(2)O (7), and [{Ni(6)(mu(3)-OH)(3)(en)(3)(H(2)O)(6)}(B-alpha-SiW(9)O(34))][Ni(0.5)(en)] 3.5 H(2)O (8) (en=ethylenediamine, dap=1,2-diaminopropane). These compounds have been structurally characterized by elemental analyses, IR spectra, diffuse reflectance spectra, thermogravimatric analysis, and X-ray crystallography. The double-cluster complex of phosphotungstate 1 simultaneously contains hepta- and hexa-Ni(II)-substituted trivacant Keggin units [{Ni(7)(mu(3)-OH)(3)O(2)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))](2-) and [{Ni(6)(mu(3)-OH)(3)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))]. The dimeric silicotungstate 2 is built up from two trivacant Keggin [B-alpha-SiW(9)O(34)](10-) fragments linked by an octa-Cu(II) cluster. The main skeleton of 3 is a tetrameric cluster constructed from four tri-Fe(III)-substituted [Fe(III) (3)(mu(3)-OH)(3)(B-alpha-PW(9) O(34))](3-) Keggin units linked by a central Fe(II) (4)O(4) cubane core and four mu(4)-PO(4) bridges. Complex 4 is an unprecedented three-dimensional extended architecture with hexagonal channels built by hexa-Cu(II) clusters and trivacant Keggin [B-alpha-PW(9)O(34)](9-) fragments. The common feature of 5-8 is that they contain a B-alpha-isomeric trivacant Keggin fragment capped by a hexa-Ni(II) cluster, very similar to the hexa-Ni(II)-substituted trivacant Keggin unit in 1. Magnetic measurements illustrate that 1, 2, and 5 have ferromagnetic couplings within the magnetic metal centers, whereas 3 and 4 reveal the antiferromagnetic exchange interactions within the magnetic metal centers. Moreover, the magnetic behavior of 4 and 5 have been theoretically simulated by the MAGPACK magnetic program package.     

Assembly of hybrid organic-organometallic materials through mechanochemical acid-base reactions

Manual grinding of the organometallic complex [Fe(eta(5)-C(5)H(4)COOH)(2)] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2]octane, C(6)H(12)N(2), 1,4-phenylenediamine, p-(NH(2))(2)C(6)H(4), piperazine, HN(C(2)H(4))(2)NH, trans-1,4-cyclohexanediamine, p-(NH(2))(2)C(6)H(10), and guanidinium carbonate [(NH(2))(3)C](2)[CO(3)], generates quantitatively the corresponding adducts, [HC(6)H(12)N(2)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (1), [HC(6)H(8)N(2)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (2), [H(2)C(4)H(10)N(2)][Fe(eta(5)-C(5)H(4)COO)(2)] (3), [H(2)C(6)H(14)N(2)][Fe(eta(5)-C(5)H(4)COO)(2)].2 H(2)O, (4.2 H(2)O), and [C(NH(2))(3)](2)[Fe(eta(5)-C(5)H(4)COO)(2)].2 H(2)O, (5.2 H(2)O), respectively. Crystallization from methanol in the presence of seeds of the ground sample allows the growth of single crystals of these adducts; therefore we were able to determine the structures of the adducts by single-crystal X-ray diffraction. This information was used in turn to identify and characterize the polycrystalline materials obtained by the grinding process. In the case of [HC(6)N(2)H(12)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (1), the base can be removed by mild treatment regenerating the starting dicarboxylic acid, while in all other cases decomposition is observed. The solid-solid processes described herein imply molecular diffusion through the lattice, breaking and reassembling of hydrogen-bonded networks, and proton transfer from acid to base.     

Ring currents as probes of the aromaticity of inorganic monocycles : P5-, As5-, S2N2, S3N3-, S4N3+, S4N42+, S5N5+, S42+ and Se42+

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G** (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles: S(4) (2+), Se(4) (2+), S(2)N(2), P(5) (-) and As(5) (-) with 6 pi electrons; S(3)N(3) (-), S(4)N(3) (+) and S(4)N(4) (2+) with 10 pi electrons; and S(5)N(5) (+) with 14 pi electrons. Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry- and energy-based selection rules. All nine systems were found to support diatropic pi currents, reinforced by sigma circulations in P(5) (-), As(5) (-), S(3)N(3) (-), S(4)N(3) (+), S(4)N(4) (2+) and S(5)N(5) (+), but opposed by them in S(4) (2+), Se(4) (2+) and S(2)N(2). The opposition of pi and sigma effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).     

Solid state NMR characterization of individual compounds and solid solutions formed in Sc(2)O(3)--V(2)O(5)--Nb(2)O(5)--Ta(2)O(5) system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).     

Formation of two isomeric closo-[(eta5-C5H5)FePC2B8H10] phosphadicarbaborane analogues of ferrocene via isolable eta1-bonded complexes of the [7-[(eta5-C5H5)Fe(CO)2]-(eta1-nido-PC2B8H10)] type

The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed.     

Unusual iron(III) ate complexes stabilized by Li-pi interactions

Several iron(III) complexes incorporating diamidoether ligands are described. The reaction between [Li(2)[RN(SiMe(2))](2)O] and FeX(3) (X=Cl or Br; R=2,4,6-Me(3)Ph or 2,6-iPr(2)Ph) form unusual ate complexes, [FeX(2)Li[RN(SiMe(2))](2)O](2) (2, X=Cl, R=2,4,6-Me(3)Ph; 3, X=Br, R=2,4,6-Me(3)Ph; 4, X=Cl, R=2,6-iPr(2)Ph) which are stabilized by Li-pi interactions. These dimeric iron(III)-diamido complexes exhibit magnetic behaviour characteristic of uncoupled high spin (S= 5/2 ) iron(III) centres. They also undergo halide metathesis resulting in reduced iron(II) species. Thus, reaction of 2 with alkyllithium reagents leads to the formation of iron(II) dimer [Fe[Me(3)PhN(SiMe(2))](2)O](2) (6). Similarly, the previously reported iron(III)-diamido complex [FeCl[tBuN(SiMe(2))](2)O](2) (1) reacts with LiPPh(2) to yield the iron(II) dimer [Fe[tBuN(SiMe(2))](2)O](2) but reaction with LiNPh(2) gives the iron(II) product [Fe(2)(NPh(2))(2)[tBuN(SiMe(2))](2)O] (5). Some redox chemistry is also observed as side reactions in the syntheses of 2-4, yielding THF adducts of FeX(2): the one-dimensional chain [FeBr(2)(THF)(2)](n) (7) and the cluster [Fe(4)Cl(8)(THF)(6)]. The X-ray crystal structures of 3, 5 and 7 are described.     

Diferratricarbaboranes of the subcloso-[(eta5-C5H5)2Fe2C3B8H11] type, the first representatives of the 13-vertex dimetallatricarbaborane series

Treatment of the [2-Cp-9-tBuNH-closo-2,1,7,9-FeC(3)B(8)H(10)] (1) ferratricarbollide (Cp = eta(5)-C(5)H(5) (-)) with Na(+) C(10)H(8) (-) in 1,2-dimethoxyethane (DME) at room temperature produced an air-sensitive transient anion with a tentatively identified nido-[tBuNH-CpFeC(3)B(8)H(10)](2-) constitution. In-situ reaction of this low-stability ion with [CpFe(CO)(2)I] or [CpFe(CO)(2)](2) generated three violet diferratricarbaboranes identified as paramagnetic subcloso complexes [4,5-Cp(2-)-4,5,1,6,7-Fe(2)C(3)B(8)H(11)] (2; yield 2 %), [4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(11)] (3; yield 2 %), and [7-tBuNH-4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(10)] (4; yield 14 %). These first representatives of the 13-vertex dimetallatricarbaborane family were characterized by EPR and IR spectroscopy, and mass spectrometry, and their structures were determined by X-ray diffraction analysis.