Alkali metal complexes of sterically demanding amino-functionalized secondary phosphanide ligands

The reaction between {(Me(3)Si)(2)CH}PCl(2) (4) and one equivalent of either [C(6)H(4)-2-NMe(2)]Li or [2-C(5)H(4)N]ZnCl, followed by in situ reduction with LiAlH(4) gives the secondary phosphanes {(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))PH (5) and {(Me(3)Si)(2)CH}(2-C(5)H(4)N)PH (6) in good yields as colourless oils. Metalation of 5 with Bu(n)Li in THF gives the lithium phosphanide [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]Li(THF)(2)] (7), which undergoes metathesis with either NaOBu(t) or KOBu(t) to give the heavier alkali metal derivatives [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]Na(tmeda)] (8) and [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]K(pmdeta)] (9) after recrystallization in the presence of the corresponding amine co-ligand [tmeda = N,N,N',N'-tetramethylethylenediamine, pmdeta = N,N,N',N',N'-pentamethyldiethylenetriamine]. The pyridyl-functionalized phosphane 6 undergoes deprotonation on treatment with Bu(n)Li to give a red oil corresponding to the lithium compound [{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]Li (10) which could not be crystallized. Treatment of this oil with NaOBu(t) gives the sodium derivative [{[{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]Na}(2) x (Et(2)O)](2) (11), whilst treatment of with KOBu(t), followed by recrystallization in the presence of pmdeta gives the complex [[{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]K(pmdeta)](2) (12). Compounds 5-12 have been characterised by (1)H, (13)C{(1)H} and (31)P{(1)H} NMR spectroscopy and elemental analyses; compounds 7-9, and 12 have additionally been characterised by X-ray crystallography. Compounds 7-9 crystallize as discrete monomers, whereas 11 crystallizes as an unusual dimer of dimers and 12 crystallizes as a dimer with bridging pyridyl-phosphanide ligands.     

Synthesis of zirconium, hafnium, and tantalum complexes with sterically demanding hydrazide ligands

The bulky hydrazine t-BuN(H)NMe2 was synthesized via hydrazone and t-BuN(H)N(H)Me intermediates as the major component in a 90:5:5 mixture consisting of t-BuN(H)NMe2, t-BuN(Me)N(H)Me, and t-BuN(Me)NMe2. Reacting the mixture with n-BuLi followed by distillation and fractional crystallization led to the isolation of the ligand precursor LiN(t-Bu)NMe2. Lithium hydrazides, LiN(R)NMe2, were reacted with metal chlorides to afford the hydrazide complexes M(N(Et)NMe2)4 (M = Zr or Hf), MCl(N(R)NMe2)3 (M = Zr, R = i-Pr or t-Bu; M = Hf, R = t-Bu), and TaCl3(N(i-Pr)NMe2)2. The X-ray crystal structures of [LiN(i-Pr)NMe2]4, [LiN(t-Bu)NMe2.THF]2, ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu), and TaCl3(N(i-Pr)NMe2)2 were determined. The structural analyses revealed that the hydrazide ligands in ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu) and TaCl3(N(i-Pr)NMe2)2 are eta2 coordinated.     

A new coupling reaction for the synthesis of ruthenium half-sandwich complexes with sterically demanding cyclopentadienyl ligands

The reaction of RuCl(3)(solv.)(n) with tert-butylacetylene in methanol or ethanol leads to the formation of chloro-bridged half-sandwich complexes with sterically demanding cyclopentadienyl ligands, which are of high interest as starting materials for the synthesis of novel Ru catalysts.     

Mono- and dinuclear nickel(II) complexes of resolved Schiff-base ligands with extended quinoline substituents

The coordination chemistry of four enantiopure tetradentate bis(iminoquinoline) ligands with nickel(II) salts is reported. The previously reported ligands CBQ, CPQ, BBQ, and BPQ result from the condensation of (1R,2R)-cyclohexyldiamine or (R)-BINAM with two equivalents of 2-formylbenzo[h]quinoline or 8-isopropyl-2-quinolinecarboxaldehyde {CBQ = (1R,2R)-cyclohexanediamine-N,N'-bis(benzo[h]quinoline-2-ylmethylene), CPQ = (1R,2R)-cyclohexanediamine-N,N'-bis[[(8-isopropyl)-2-quinolinyl]methylene], BBQ = [(R)-1,1'-binaphthalene]-2,2'-diamine-N,N'-bis(benzo[h]quinoline-2-ylmethylene), BPQ = [(R)-1,1'-binaphthalene]-2,2'-diamine-N,N'-bis[[(8-isopropyl)-2-quinolinyl]methylene]}. Reaction of NiI(2) with the (1R,2R)-cyclohexyl ligands gives the mononuclear distorted trigonal-bipyramidal (TBP) complexes [Ni(N(3)-CBQ)I(2)] and [Ni(N(3)-CPQ)I(2)]. Incomplete iodide abstraction from [Ni(N(3)-CPQ)I(2)] with AgOTf leads to partial replacement of the iodide with hydroxide from adventitious water to give [Ni(N(3)-CPQ)I(1.6)(OH)(0.4)] (distorted TBP). The corresponding reaction with [Ni(N(3)-CBQ)I(2)] again fails to remove all of the iodide, resulting instead in conversion to the syn dinuclear [Ni(2)(CBQ)(μ-X)(2)I(2)] (X = Cl(0.925)I(0.075)) complex, where chloride abstraction from the solvent (CH(2)Cl(2)) has resulted in a mixed halide system and the metal centers are square-pyramidal. Reaction of Ni(OTf)(2) with CBQ leads to the isolation of the octahedral cation [Ni(CMBQ)(2)](2+), with CMBQ [(1R,2R)-cyclohexanediamine-mono-N-(benzo[h]quinoline-2-ylmethylene)] being the partial hydrolysis product of CBQ. [Ni(CMBQ)(2)][OTf](2) crystallizes as a 1:1 mixture of P and M helical diastereomers. The coordination of NiI(2) with the (R)-BINAM derived ligands yields the anti dinuclear P-helical complexes [Ni(2)(BBQ)(μ-I)(2)I(2)] and [Ni(2)(BPQ)(μ-I)(2)I(2)]: one nickel ion is coordinated in each bidentate iminoquinoline pocket and the geometry at the metal centers is distorted square-pyramidal. Characterisation by (1)H NMR, UV-Vis, electronic circular dichroism (ECD) spectroscopy, combustion analysis, and HRMS is reported in addition to structural and halide abstraction studies.     

Preparation and properties of sterically demanding and chiral distibine ligands

A series of new rigid distibines, 1,8-bis(R(2)Sb)naphthalene (R = Me: (); R = Ph: ()), and chiral distibines, 2,2'-bis(R(2)Sb)-1,1'-binaphthyl (R = Me: (); R = Ph: () obtained as racemic mixtures) and the discrete enantiomers of 4,5-bis((R(2)Sb)methyl)-2,2-dimethyl-1,3-D/L-dioxolane (R = Me: () (l), () (d); R = Ph: () (l), () (d)) have been obtained in high yields, using either electrophilic halostibine reagents with di-lithium reagents (()-()) or nucleophilic stibide reagents with dibromo-derivatives (()-()). The distorted octahedral complexes [Mo(CO)(4)(L)], L = ()-(), planar [PtCl(2)(L)], L = (), (), (), (), and neutral, five-coordinate [RhCl(cod)(L)], L = (), (), (), are reported and trends in the spectroscopic data are discussed in terms of the ligand donor properties. Crystal structures of () and [Mo(CO)(4)()] reveal significant structural changes occur upon coordination, and these are also reflected in the solution NMR spectroscopic parameters. Changes in the C-Sb-C angles and C-Sb bond distances upon coordination of () are discussed in term of increased s/p orbital mixing. Air oxidation of () forms a very unusual stibine oxide, the structure of which shows a distorted Sb(4)O(4) cubane core (bridging O atoms) with two orthogonal naphthalene units.     

Complexes of manganese, iron and cobalt with sterically demanding indenyl ligands

A series of manganese, iron and cobalt complexes bearing sterically demanding 1,3-disubstituted indenyl ligands, 1,3-(Me(3)C)(2)C(9)H(5) (Ind(tBu)) (1) and 1,3-(C(6)H(11))(2)C(9)H(5) (Ind(cHexyl)) (2), has been prepared. These complexes have been fully characterised by various spectroscopic techniques, elemental analysis, and X-ray diffraction experiments. In addition the electronic and steric properties of these ligands have been evaluated. Although the cone angles and electronic properties are similar to 1,2,4-(Me(3)C)(3)C(5)H(2) (Cp'), indenyl iron half-sandwich complexes are only stable at low temperature. This has been demonstrated for 1-FeI using suitable trapping experiments such as CO or NaCp' addition to yield 1-Fe(CO)(2)I and 1-FeCp', respectively. Overall the metal-ligand bonds in these indenyl compounds are weaker than in the corresponding cyclopentadienyl derivatives. In addition, the bis(indenyl)manganese complexes, 1-Mn and 2-Mn, are high-spin, as established by solid state magnetic susceptibility studies in the temperature range 2-300 K.     

Mono- and dinuclear tricarbonyltechnetium(I) complexes with thiosemicarbazones

[NEt4]2[Tc(CO)3Cl3] reacts with thiosemicarbazones derived from 2,2'-dipyridyl ketone (HL3) and 4-acetylpyridine (HL4) to form stable technetium(I) complexes of the compositions [Tc(CO)3Cl(HL3-Npy,Npy)] and [Tc2(CO)6Cl2(micro-HL4-Npy,S)]. Whereas exclusively the pyridine nitrogen atoms are involved in coordination in the monomeric complex, the binuclear compound represents the first technetium complex with a coordinated thiosemicarbazone functionality.     

Reactions of cationic dinuclear molybdenum complexes containing μ-sulfido and μ-thiolate ligands

Cationic dinuclear molybdenum complexes with bridging sulfido and thiolate ligands of the formula [(CpMo)₂(µ-S₂CH₂)(µ-S)(µ-SR)]^– have been found to show extensive reactivity with molecular hydrogen and with organic molecules that results in the cleavage of C-C, C-N, and C-O bonds. The scope of the reactivity and mechanistic information are reviewed in this paper, and the potential relevance of the reactions to those of heterogeneous molybdenum sulfide catalysts in the hydrotreating process is discussed. Studies of the complex redox chemistry and of the electrophilic and nucelophilic sites within the dinuclear derivatives provide an important basis for understanding the bond cleavage reaction mechanisms, and these topics are also reviewed here.     

Mono- and dinuclear copper(II) complexes with meta-phenylene-bridging ligands: Synthesis,structure and magnetic properties

The new double-Schiff-base ligand H₆ipa-bhea has been synthesized by condensation of a 4,6-diformylresorcinol derivative (ipa) with two equivalents of N,N-bis-(2-hydroxyethyl)ethylenediamine (bhea). Reaction with copper(II) perchlorate leads to the formation of two different products depending on the reaction conditions. The directed synthesis of either a mononuclear or dinuclear copper(II) complex is reported. The reaction in methanol results in the formation of a dinuclear complex [Cu₂(H₄ipa-bhea)](ClO₄)₂ (1). Whereas in the presence of water as solvent for the reaction, one imine side chain of the ligand is hydrolyzed regenerating the formyl moiety with the mononuclear complex [Cu(H₃hyforsa-bhea)]ClO₄ · 2H₂O (2) as final product. Subsequent reaction of complex 2 with N,N-bis-(pyridin-2-ylmethyl)ethylenediamine (unspenp) as additional amine component results in the formation of the mononuclear complex [Cu(Hhyforsa-unspenp)]ClO₄ (3). All complexes are characterized by IR spectroscopy, elemental analysis and X-ray crystallography. Temperature-dependent magnetic measurements on the dinuclear complex indicate weak antiferromagnetic exchange interactions between the copper(II) ions with a coupling constant of J = ?16.4 cm^?1. Density functional calculations have been used to evaluate the magnetic properties. The exchange coupling constant can be nicely reproduced with the use of the broken symmetry approach. The exchange pathway through the meta-phenylene-linkage is discussed in terms of a competitive spin-polarization and superexchange mechanism as well as geometrical changes at the copper(II) ions.     

Boron and aluminum complexes of sterically demanding phosphinimines and phosphinimides

Reactions of sterically demanding phosphinimines R3PNH [R=i-Pr (1), t-Bu (2)] were examined. Reactions with B(C6F5)3 formed the adducts (R3PNH)B(C6F5)3 [R=i-Pr (3), t-Bu (4)] in high yield. On the other hand, 2 reacts with HB(OBu)2, evolving H2 to give t-Bu3PNB(OBu)2 (5). The reaction of 2 equiv of 2 with BH3.SMe2 affords the species (t-Bu3PN)2BH (6). In contrast, the reaction of n-Bu(t-Bu)2PNH with BH3.SMe2 results in the formation of the robust adduct n-Bu(t-Bu)2PNH.BH3 (8). An alternative route to borane-phosphinimide complexes involves Me3SiCl elimination, as exemplified by the reaction of BCl2Ph with n-Bu3PNSiMe3, which gives the product n-Bu3PNBCl(Ph) (9). The corresponding reactions of the parent phosphinimines 1 and 2 with AlH3.NMe2Et give the dimers [(mu-i-Pr3PN)AlH2]2 (10) and [(mu-t-Bu3PN)AlH2]2 (11). Species 11 reacts further with Me3SiO3SCF3 to provide [(mu-t-Bu3PN)AlH(OSO2CF3)]2 (12). The reaction of the lithium salt [t-Bu3PNLi]4 (13) with BCl3 proceeds smoothly to give t-Bu3PNBCl2 (14), which is readily alkylated to give t-Bu3PNBMe2 (15). Subsequent reaction of 15 with B(C6F5)3 results in methyl abstraction and the formation of [(mu-t-Bu3PN)BMe]2[MeB(C6F5)3]2 (16). The reaction of 13 in a 2:1 ratio with BCl3 gives the salt [(t-Bu3PN)2B]Cl (17). This species can be methylated to give (t-Bu3PN)2BMe (18), which undergoes subsequent reaction with [Ph3C][X] (X=[B(C6F5)4], [PF6]) to form the related salts [(t-Bu3PN)2B][B(C6F5)4] (19) and [(t-Bu3PN)2B][PF6] (20), respectively. Analogous reactions with [Ph3C][BF4] afforded [t-Bu3PNBF2]2 (21). Compounds 3, 4, 6, 8, 11, 12, 17, 19, and 21 were characterized by X-ray crystallography.     

Mono- and dinuclear ruthenium carbonyl complexes with redox-active dioxolene ligands: electrochemical and spectroscopic studies and the properties of the mixed-valence complexes

The mononuclear complex [Ru(PPh(3))(2)(CO)(2)(L(1))] (1; H(2)L(1) = 7,8-dihydroxy-6-methoxycoumarin) and the dinuclear complexes [[Ru(PPh(3))(2)(CO)(2)](2)(L(2))][PF(6)] [[2][PF(6)]; H(3)L(2) = 9-phenyl-2,3,7-trihydroxy-6-fluorone] and [[Ru(PBu(3))(2)(CO)(2)](2)(L(3))] (3; H(4)L(3) = 1,2,3,5,6,7-hexahydroxyanthracene-9,10-dione) have been prepared; all complexes contain one or two trans,cis-[Ru(PR(3))(2)(CO)(2)] units, each connected to a chelating dioxolene-type ligand. In all cases the dioxolene ligands exhibit reversible redox activity, and accordingly the complexes were studied by electrochemistry and UV/vis/NIR, IR, and EPR spectroscopy in their accessible oxidation states. Oxidation of 1 to [1](+) generates a ligand-centered semiquinone radical with some metal character as shown by the IR and EPR spectra. Dinuclear complexes [2](+) and 3 show two reversible ligand-centered couples (one associated with each dioxolene terminus) which are separated by 690 and 440 mV, respectively. This indicates that the mixed-valence species [2](2+) has greater degree of electronic delocalization between the ligand termini than does [3](+), an observation which was supported by IR, EPR, and UV/vis/NIR spectroelectrochemistry. Both [2](2+) and [3](+) have a solution EPR spectrum consistent with full delocalization of the unpaired electron between the ligand termini on the EPR time scale (a quintet arising from equal coupling to all four (31)P nuclei); [3](+) is localized on the faster IR time scale (four CO vibrations rather than two, indicative of inequivalent [Ru(CO)(2)] units) whereas [2](2+) is fully delocalized (two CO vibrations). UV/vis/NIR spectroelectrochemistry revealed the presence of a narrow, low-energy (2695 nm) transition for [3](+) associated with the catecholate --> semiquinone intervalence transition. The narrowness and solvent-independence of this transition (characteristic of class III mixed-valence character) coupled with evidence for inequivalent [Ru(CO)(2)] termini in the mixed-valence state (characteristic of class II character) place this complex at the class II-III borderline, in contrast to [2](2+) which is clearly class III.     

Mono- and dinuclear complexes of chiral tri- and tetradentate Schiff-base ligands derived from 1,1'-binaphthyl-2,2'-diamine

The synthesis and characterization of the bis(bidentate) Schiff-base ligand [(R)-2] formed by the condensation reaction of (R)-1,1'-binaphthyl-2,2'-diamine [(R)-BINAM] with pyridine-2-carboxaldehyde is presented. The coordination chemistry of (R)-2 with Ni(ClO(4))(2).6H(2)O, Co(ClO(4))(2).6H(2)O, CuCl(2), and CuSO(4) has been investigated. Reaction of (R)-2 with the first two metal salts leads to complexes of the type [M((R)-4)(2)](ClO(4))(2) (M = Ni(II), Co(II)), where (R)-4 is a tridentate ligand resulting from the hydrolytic cleavage of one of the pyridyl groups from (R)-2. Both complexes were characterized by X-ray crystallography, which showed that the Lambda absolute configuration of the metal center is favored in both cases. (1)H NMR spectroscopy suggests that the high diastereoselectivity of Lambda-[Co((R)-4)(2)](ClO(4))(2) is maintained in solution. The reaction of (R)-2 with CuCl(2) leads to the dinuclear complex [Cu(2)((R)-2)Cl(4)], which has a [Cu(2)(mu(2)-Cl(2))] core. The reaction of CuSO(4) with (R)-2 gives a dimeric complex, [Cu((R)-4)SO(4)](2), which features a [Cu(2)(mu(2)-(SO(4))(2))] core. This complex can be prepared directly by the reaction of (R)-BINAM with pyridine-2-carboxaldehyde and CuSO(4). The use of rac-BINAM in this synthetic procedure leads to the heterochiral dimer [Cu(2)((R)-4)((S)-4)(SO(4))(2)]; that is, the ligands undergo a self-sorting (self/nonself discrimination) process based on chirality. The reaction of rac-BINAM, pyridine-2-carboxaldehyde, and Co(ClO(4))(2).6H(2)O proceeds via a homochiral self-sorting pathway to produce a racemic mixture of [Co((R)-4)(2)](2+) and [Co((S)-4)(2)](2+). The variable-temperature magnetic susceptibilities of the bimetallic complexes [Cu(2)((R)-2)Cl(4)], [Cu((R)-4)(mu(2)-SO(4))](2), and [Cu(2)((R)-4)((S)-4)(mu(2)-SO(4))(2)] all show weak antiferromagnetic coupling with J = -1.0, -0.40, and -0.67 cm(-)(1), respectively.     

Olefin metathesis featuring ruthenium indenylidene complexes with a sterically demanding NHC ligand

The synthesis and characterization of two new ruthenium indenylidene complexes [RuCl(2)(SIPr)(Py)(Ind)] 6 and [RuCl(2)(SIPr)(3-BrPy)(Ind)] 7 featuring the sterically demanding N-heterocyclic carbene 1,3-bis(2,6-di isopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) are reported. Remarkable activity was observed with these complexes in ring closing, enyne, and cross metathesis of olefins at low catalyst loadings. The performance of SIPr-bearing complexes 6 and 7 as well as [RuCl(2)(SIPr)(PCy(3))(Ind)] 5 in ring opening metathesis polymerization is also disclosed. This work highlights the enormous influence of the neutral "spectator" ligands on catalyst activity and stability.     

Mono- and dinuclear complexes of sulfones with the tetrachlorides of group 4

The reactions of dialkyl sulfones [R(2)SO(2): R = Me, Et, Ph, R(2)=-(CH(2))(4)-] with the metal tetrachlorides of Group 4 [MCl(4): M = Ti, Zr, Hf] give different products mainly depending on the sulfone/M molar ratio. Compounds of formula [M(2)Cl(8)(R(2)SO(2))(2)][M = Ti, R(2)=-(CH(2))(4)-; M = Zr, R = Et, R = Ph] and [MCl(4)(R(2)SO(2))(2)](sulfone/M = 2)[M = Ti, R = Me; M = Zr, R = Me, R = Ph, R(2)=-(CH(2))(4)-; M = Hf, R = Me, R(2)=-(CH(2))(4)-] have been obtained. By X-ray diffraction methods the dinuclear titanium and zirconium adducts, [Ti(2)Cl(8)(mu-sulfolane-O,O')(2)] and [Zr(2)Cl(8)(mu-Ph(2)SO(2)-O,O')(2)] have been established to contain bridging sulfone and hexacoordinated metal centres, while the mononuclear zirconium complex [ZrCl(4)(Me(2)SO(2))(2)] has cis-monodentate sulfones in a slightly distorted octahedral geometry. The reaction between TiCl(4) and sulfolane (tetrahydrothiophene 1,1-dioxide) in SOCl(2) affords the 1:1 adduct independent of the sulfone/Ti molar ratio. Ligand-exchange and inter-conversion between mononuclear and dinuclear species have been observed by NMR, while the spectral features of the SO(2) moiety have been assigned by IR- and Raman spectroscopies.     

Neutral and cationic aluminium complexes of a sterically demanding N-imidoylamidine ligand

The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2 was prepared. Direct reactions with AlI3 or AlMe3 afforded [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3 and [i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4].AlMe3, 4 respectively. Thermolysis of 4 gave (i-Pr2C6H3NC(=CH2)(NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe2 6. Subsequent reaction with B(C6F5)3 gave the zwitterionic species [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe(mu-MeB(C6F5)3)] 7. In a related reactions of 2, [Ph3C][B(C6F5)4] and AlMe3, AlH3.NEtMe2 or AlD3.NMe3, the complexes [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4] (R = Me 5, H 8, D 9) and [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlH][B(C6F5)4] 10 are formed. Single-crystal X-ray data for 2, 3, 5 and 10 are reported.     

Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes

We report the synthesis of free 1,6,7,12-tetraazaperylene (tape). Tape was obtained from 1,1'-bis-2,7-naphthyridine by potassium promoted cyclization followed by oxidation with air. Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes of the general formulas [Ru(L-L)(2)(tape)](PF(6))(2), [1](PF(6))(2)-[5](PF(6))(2), and [{Ru(L-L)(2)}(2)(μ-tape)](PF(6))(4), [6](PF(6))(4)-[10](PF(6))(4), with{L-L = phen, bpy, dmbpy (4,4'-dimethyl-2,2'-bipyridine), dtbbpy (4,4'-ditertbutyl-2,2'-bipyridine) and tmbpy (4,4'5,5'-tetramethyl-2,2'-bipyridine)}, respectively, were synthesized. The X-ray structures of tape·2CHCl(3) and the mononuclear complexes [Ru(bpy)(2)(tape)](PF(6))(2)·0.5CH(3)CN·0.5toluene, [Ru(dmbpy)(2)(tape)](PF(6))(2)·2toluene and [Ru(dtbbpy)(2)(tape)](PF(6))(2)·3acetone·0.5H(2)O were solved. The UV-vis absorption spectra and the electrochemical behavior of the ruthenium(ii) tape complexes were explored and compared with the data of the analogous dibenzoeilatin (dbneil), 2,2'-bipyrimidine (bpym) and tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazin (tpphz) species.     

Mono- and dinuclear Zn(II) complexes of Schiff-base ligands: syntheses,characterization and studies of photoluminescence

Six Schiff-bases HL¹-HL⁴, L⁵ and L⁶ [HL¹ = 2,6-bis[1-(2-aminoethyl)pyrolidine-iminomethyl]-4-methyl-phenol, HL² = 2,6-bis[1-(2-aminoethyl)piperidine-iminomethyl]-4-methyl-phenol, HL³ = N-{1-(2-aminoethyl)pyrolidine}salicylideneimine, HL⁴ = N-{1-(2-aminoethyl)piperidine}salicylideneimine, L⁵ = 2-benzoyl pyridine-N-{1-(2-aminoethyl)pyrolidine}, L⁶ = 2-benzoylpyridine-N-{1-(2-aminoethyl)piperidine}] have been synthesized and characterized. Zn(II) complexes of those ligands have been prepared by conventional sequential route as well as by template synthesis. The same complexes are obtained from the two routes as evident from routine physicochemical characterizations. All the Schiff-bases exhibit photoluminescence originating from intraligand (π–π*) transitions. Metal mediated fluorescence enhancement is observed on complexation of HL¹-HL⁴ with Zn(II), whereas metal mediated fluorescence quenching occurs in Zn(II) complexes of L⁵ and L⁶.     

Fischer type carbene ligands in dinuclear complexes

A large number of iron and ruthenium dinuclear complexes containing heteroatom substituted carbene ligands have been obtained by two different synthetic routes. The first method consists in reacting heteroatom substituted -carbyne cationic complexes with CN^– ion. The second involves the displacement of the SMe₂ molecule in the sulfonium [Fe₂{-C(CN)(SMe₂)}(-CO)(CO)₂CP₂]SO₃CF₃ by appropriate nucleophilesX ^– (X=OR, SR, NR₂, PR₂). Spectroscopic (IR, NMR) and structural investigations together with reactivity studies on these complexes have greatly contributed to better understanding the factors which favor bridging vs. terminal coordination of heteroatom substituted carbene ligands.     

Mono- and dinuclear zinc complexes derived from unsymmetric binucleating ligands: synthesis, characterization, and formation of tetranuclear arrays

Zinc complexes of the unsymmetric, binucleating Schiff base ligands 3-(N-[2-(dimethylamino)ethyl]iminomethyl)-salicylic acid (H2L1) and 3-[N-(2-pyridylmethyl)iminomethyl]-salicylic acid (H2L2) have been studied in the solid state as well as in solution. Reaction of ZnX2 (X = NO3-, CH3CO2-) with 3-formylsalicylic acid and N,N-dimethylethylenediamine at neutral or slightly acidic pH afforded the dinuclear complexes [Zn2(HL1)2(H2O)2](NO3)2.2H2O (1a) and [Zn2(HL1)2(CH3CO2)2].6H2O (1b). The Zn ions, which are 3.126(1) A (1a) and 3.2665(7) A (1b) apart, are bridged by two phenolate oxygens. Further coordination sites of the ligand are the imine nitrogen and carboxylate oxygen, while the amino nitrogen is protonated. On dissolution in DMSO or DMF, 1a and 1b are converted into the mononuclear species [Zn(HL1)]+. Cleavage of the dinuclear complexes is accompanied by migration of the ammonium proton to the carboxylate group and coordination of the amino nitrogen to Zn. Reaction of 1b with base yielded the novel tetranuclear Zn complex [Zn4(L1)4].6.5H2O (2) that exhibits coordination number asymmetry. The four Zn ions having N2O3 and N2O4 coordination environments are located at the corners of a nearly square-planar rectangle. H2L2 binds Zn via the phenolate oxygen and, imine and pyridine nitrogens in acidic solution. Deprotonation of the carboxyl group in alkaline solution gave the tetranuclear compound [Zn4(L2)4].4.5H2O (4) with a cubane-like Zn4O4 core.