Synthesis of molybdenum complexes that contain "hybrid" triamidoamine ligands, [(hexaisopropylterphenyl-NCH2CH2)2NCH2CH2N-aryl]3-, and studies relevant to catalytic reduction of dinitrogen

In the Buchwald-Hartwig reaction between HIPTBr (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = hexaisopropylterphenyl) and (H2NCH2CH2)3N, it is possible to obtain a 65% isolated yield of (HIPTNHCH2CH2)2NCH2CH2NH2. A second coupling then can be carried out to yield a variety of "hybrid" ligands, (HIPTNHCH2CH2)2NCH2CH2NHAr, where Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, 3,5-(MeO)2C6H3, 3,5-Me2NC5H3, 3,5-Ph2NC5H3, 2,4,6-i-Pr3C6H2, or 2,4,6-Me3C6H2. The hybrid ligands may be attached to Mo to yield [hybrid]MoCl species. From the monochloride species, a variety of other species such as [hybrid]MoN, {[hybrid]MoN2}Na, and {[hybrid]Mo(NH3)}+ can be prepared. [Hybrid]MoN2 species were prepared through oxidation of {[hybrid]MoN2}Na species with ZnCl2, but they could not be isolated. [Hybrid]Mo=N-NH species could be observed as a consequence of the protonation of {[hybrid]MoN2}- species, but they too could not be isolated as a consequence of a facile decomposition to yield dihydrogen and [hybrid]MoN2 species. Attempts to reduce dinitrogen catalytically led to little or no ammonia being formed from dinitrogen. The fact that no ammonia was formed from dinitrogen in the case of Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, or 3,5-(MeO)2C6H3 could be attributed to a rapid decomposition of intermediate [hybrid]Mo=N-NH species in the catalytic reaction, a decomposition that was shown in separate studies to be accelerated dramatically by 2,6-lutidine, the conjugate base of the acid employed in the attempted catalytic reduction. X-ray structures of [(HIPTNHCH2CH2)2NCH2CH2N{3,5-(CF3)2C6H3}]MoCl and [(HIPTNHCH2CH2)2NCH2CH2N(3,5-Me2C6H3)]MoN2}Na(THF)2 are reported.     

Synthesis and reactions of molybdenum triamidoamine complexes containing hexaisopropylterphenyl substituents

We have synthesized a triamidoamine ligand ([(RNCH(2)CH(2))(3)N](3)(-)) in which R is 3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3) (hexaisopropylterphenyl or HIPT). The reaction between MoCl(4)(THF)(2) and H(3)[HIPTN(3)N] in THF followed by 3.1 equiv of LiN(SiMe(3))(2) led to formation of orange [HIPTN(3)N]MoCl. Reduction of MoCl (Mo = [HIPTN(3)N]Mo) with magnesium in THF under dinitrogen led to formation of salts that contain the ((Mo(N(2)))(-) ion. The (Mo(N(2)))(-) ion can be oxidized by zinc chloride to give Mo(N(2)) or protonated to give MoN=NH. The latter was found to decompose to yield MoH. Other relevant compounds that have been prepared include (Mo=N-NH(2))(+) (by protonation of MoN=NH), M=1;N, (Mo=NH)(+) (by protonation of M=N), and (Mo(NH(3)))(+) (by treating MoCl with ammonia). (The anion is usually (B(3,5-(CF(3))(2)C(6)H(3))(4))(-) = (BAr'(4))(-).) X-ray studies were carried out on (Mg(DME)(3))(0.5)[Mo(N(2))], MoN=NMgBr(THF)(3), Mo(N(2)), M=N, and (Mo(NH(3)))(BAr'(4)). These studies suggest that the HIPT substituent on the triamidoamine ligand creates a cavity that stabilizes a variety of complexes that might be encountered in a hypothetical Chatt-like dinitrogen reduction scheme, perhaps largely by protecting against bimolecular decomposition reactions.     

An electrochemical investigation of intermediates and processes involved in the catalytic reduction of dinitrogen by [HIPTN3N]Mo (HIPTN3N = (3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N)

The redox properties of [HIPTN(3)N]Mo complexes (where HIPTN(3)N = (3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)NCH(2)CH(2))(3)N) involved in the catalytic dinitrogen reduction cycle were studied using cyclic voltammetry in fluorobenzene with Bu(4)NPF(6) as the electrolyte. MoN(2) (Mo = [HIPTN(3)N]Mo, E(1/2) = -1.96 V vs. Fc(+)/Fc at a Pt electrode), Mo≡N (E(1/2) = -2.68 V vs. Fc(+)/Fc (Pt)), and [Mo(NH(3))]BAr'(4) (Ar' = 3,5-(CF(3))(2)C(6)H(3), E(1/2) = -1.53 V vs. Fc(+)/Fc (Pt)) each undergo a chemically reversible one-electron reduction, while [Mo=NNH(2)]BAr'(4) (E(1/2) = -1.50 V vs. Fc(+)/Fc (Pt)) and [Mo=NH]BAr'(4) (E(1/2) = -1.26 V vs. Fc(+)/Fc (Pt)) each undergo a one-electron reduction with partial chemical reversibility. The acid employed in the catalytic reduction, [2,4,6-collidinium]BAr'(4), reduces irreversibly at -1.11 V vs. Fc(+)/Fc at Pt and at -2.10 V vs. Fc(+)/Fc at a glassy carbon electrode. The reduction peak potentials of the Mo complexes shift in the presence of acids. For example, the reduction peak for MoN(2) in the presence of [2,4,6-collidinium]BAr'(4) at a glassy carbon electrode shifts positively by 130 mV. The shift in reduction potential is explained in terms of reversible hydrogen bonding and/or protonation at a nitrogen site in Mo complexes. The significance of productive and unproductive proton-coupled electron transfer reactions in the catalytic dinitrogen reduction cycle is discussed.     

Catalytic reduction of dinitrogen to ammonia by molybdenum: theory versus experiment

Molybdenum complexes that contain the triamidoamine ligand [(RNCH(2)CH(2))(3)N](3-) (R = 3,5-(2,4,6-iPr(3)C(6)H(2))(2)C(6)H(3)) catalyze the reduction of dinitrogen to ammonia at 22 degrees C and 1 atm with protons from 2,6-dimethylpyridinium and electrons from decamethylchromocene. Several theoretical studies have been published that bear on the proposed intermediates in the catalytic dinitrogen reduction reaction and their reaction characteristics, including DFT calculations on [(HIPTNCH(2)CH(2))(3)N]Mo species (HIPT =hexaisopropylterphenyl = 3,5-(2,4,6-iPr(3)C(6)H(2))(2)C(6)H(3)), which contain the actual triamidoamine ligand that is present in catalytic intermediates. Recent theoretical findings are compared with experimental findings for each proposed step in the catalytic reaction.     

Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)3N]3- ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)3N]Mo), [Mo=NNH2][BAr'4] (Ar' = 3,5-(CF3)2C6H3), [Mo=NH][BAr'4], and Mo(NH3). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)+, which is formed upon treatment of MoH with [2,6-LutH][B(C6F5)4]. We focus on the synthesis of compounds that have not yet been isolated, which include Mo=NNH2, Mo=NH, and Mo(NH2). Mo=NNH2, formed by reduction of [Mo=NNH2]+, has not been observed. It decomposes to give mixtures that contain two or more of the following: MoN=NH, Mo triple bond N, Mo(NH3)+, Mo(NH3), and ammonia. Mo=NH, which can be prepared by reduction of [Mo=NH]+, is stable for long periods in the presence of a small amount of CrCp*2, but in the absence of CrCp*2, and in the presence of Mo=NH+ as a catalyst, Mo=NH is slowly converted into a mixture of Mo triple bond N and Mo(NH2). Mo(NH2) can be produced independently by deprotonation of Mo(NH3)+ with LiN(SiMe3)2 in THF, but it decomposes to Mo triple bond N upon attempted isolation. Although catalytic reduction of dinitrogen could involve up to 14 intermediates in a "linear" sequence that involves addition of "external" protons and/or electrons, it seems likely now that several of these intermediates, along with ammonia and/or dihydrogen, can be produced in several reactions between intermediates that themselves behave as proton and/or electron sources.     

Synthesis of triamidoamine ligands of the type (ArylNHCH(2)CH(2))(3)N and molybdenum and tungsten complexes that contain an [ArylNCH(2)CH(2))(3)N]3- ligand

Aryl bromides react with (H(2)NCH(2)CH(2))(3)N in a reaction catalyzed by Pd(2)(dba)(3) in the presence of BINAP and NaO-t-Bu to give the arylated derivatives (ArylNHCH(2)CH(2))(3)N [Aryl = C(6)H(5) (1a), 4-FC(6)H(4) (1b), 4-t-BuC(6)H(4) (1c), 3,5-Me(2)C(6)H(3) (1d), 3,5-Ph(2)C(6)H(3) (1e), 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3) (1f), 2-MeC(6)H(4) (1g), 2,4,6-Me(3)C(6)H(2) (1h)]. Reactions between (ArNHCH(2)CH(2))(3)N (Ar = C(6)H(5), 4-FC(6)H(4), 3,5-Me(2)C(6)H(3), and 3,5-Ph(2)C(6)H(3)) and Mo(NMe(2))(4) in toluene at 70 degrees C lead to [(ArNHCH(2)CH(2))(3)N]Mo(NMe(2)) complexes in yields ranging from 64 to 96%. Dimethylamido species (Ar = 4-FC(6)H(4), 3,5-Me(2)C(6)H(3)) could be converted into paramagnetic [(ArNHCH(2)CH(2))(3)N]MoCl species by treating them with 2,6-lutidinium chloride in tetrahydrofuran (THF). The "direct reaction" between 1a-f and MoCl(4)(THF)(2) in THF followed by 3 equiv of MeMgCl yielded [(ArNHCH(2)CH(2))(3)N]MoCl species (3a-f) in high yield. If 4 equiv of LiMe instead of MeMgCl are employed in the direct reaction, then [(ArNHCH(2)CH(2))(3)N]MoMe species are formed. Tungsten species, [(ArNHCH(2)CH(2))(3)N]WCl, could be prepared by analogous "direct" methods. Cyclic voltammetric studies reveal that MoCl complexes become more difficult to reduce as the electron donating ability of the [ArylNCH(2)CH(2))(3)N]3- ligand increases, and the reductions become less reversible, consistent with ready loss of chloride from ([(ArNHCH(2)CH(2))(3)N]MoCl)(-). Tungsten complexes are more difficult to reduce, and reductions are irreversible on the CV time scale.     

Reduction of dinitrogen to ammonia at a well-protected reaction site in a molybdenum triamidoamine complex

We have synthesized a triamidoamine ligand ([(RNCH2CH2)3N]3-) in which R is 3,5-(2,4,6-i-Pr3C6H2)2C6H3 (HexaIsoPropylTerphenyl or HIPT). The reaction between MoCl4(THF)2 and H3[HIPTN3N] in THF followed by 3.1 equiv of LiN(SiMe3)2 led to formation of orange [HIPTN3N]MoCl. Reduction of [HIPTN3N]MoCl with magnesium in THF under dinitrogen led to formation of salts that contain the {[HIPTN3N]Mo(N2)}- ion. The {[HIPTN3N]Mo(N2)}- ion can be oxidized by zinc chloride to give [HIPTN3N]Mo(N2) or protonated to give [HIPTN3N]Mo-N=N-H. Other relevant compounds that have been prepared include {[HIPTN3N]Mo-N=NH2}+, [HIPTN3N]MoN, {[HIPTN3N]Mo=NH}+, and {[HIPTN3N]Mo(NH3)}+. (The anion is usually {B(3,5-(CF3)2C6H3)4}- = {BAr'4}-.) Reduction of [HIPTN3N]Mo(N2) with CoCp2 in the presence of {2,6-lutidinium}BAr'4 in benzene leads to formation of ammonia and {[HIPTN3N]Mo(NH3)}+. Preliminary X-ray studies suggest that the HIPT substituent creates a deep, three-fold symmetric cavity that protects a variety of dinitrogen reduction products against bimolecular decomposition reactions, while at the same time the metal is left relatively open toward reactions near the equatorial amido ligands.     

Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation

The reactions of the bulky amino-bis(phenol) ligand Me(2)NCH(2)CH(2)N[CH(2)-3,5-Bu(t)(2)-C(6)H(2)OH-2](2)(1-H(2)) with Zn[N(SiMe(3))(2)](2)(4), [Mg[N(SiMe(3))(2)](2)](2)(5) and Ca[N(SiMe(3))(2)](2)(THF)(2)(6) yield the complexes 1-Zn, 1-Mg and 1-Ca in good yields. The X-ray structure of 1-Ca showed the complex to be dimeric, with calcium in a distorted octahedral coordination geometry. Five of the positions are occupied by an N(2)O(3) donor set, while the sixth is taken up by an intramolecular close contact to an o-Bu(t) substituent, a rare case of a Ca...H-C agostic interaction (Ca...H distances of 2.37 and 2.41 Angstroms). Another sterically hindered calcium complex, Ca[2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)O](2)(THF)(2).(C(7)H(8))(2/3)(7), was prepared by reaction of 6 with the iminophenol 2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)OH (3-H). According to the crystal structure 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2)(2-Ti) was prepared by treatment of Ti(OPr(i)(4)) with the new amino-bis(phenol) Me(2)NCH(2)CH(2)N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)OH-2](2)(2-H(2)). The reduction of 2-Ti with sodium amalgam gave the titanium(III) salt Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2).Na(THF)(2)(8). A comparison of the X-ray structures of 2-Ti and 8 showed that the additional electron in 8 significantly reduced the intensity of the pi-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1-Ca and 8 were active initiators for the ring-opening polymerisation of epsilon-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.     

Imido Complexes Derived from the Reactions of Niobium and Tantalum Pentachlorides with Primary Amines: Relevance to the Chemical Vapor Deposition of Metal Nitride Films

Reactions of niobium and tantalum pentachlorides with tert-butylamine (>/=6 equiv) in benzene afford the dimeric imido complexes [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (90%) and [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (79%). The niobium complex exists as two isomers in solution, while the tantalum complex is composed of three major isomers and at least two minor isomers. Analogous treatments with isopropylamine (>/=7 equiv) give the monomeric complexes NbCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2) (84%) and TaCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2) (84%). The monomeric complexes are unaffected by treatment with excess isopropylamine, while the dimeric complexes are cleaved to the monomers MCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)(2) upon addition of excess tert-butylamine in chloroform solution. Treatment of niobium and tantalum pentachlorides with 2,6-diisopropylaniline affords insoluble precipitates of [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (100%) and [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[TaCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (100%), which react with 4-tert-butylpyridine to afford the soluble complexes [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (45%) and [4-t-C(4)H(9)C(5)H(4)NH](2)[TaCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] (44%). Sublimation of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), MCl(2)(N(i)Pr)(NH(i)Pr)(NH(2)(i)Pr)(2), and [NH(3)(2,6-(CH(CH(3))(2))(2)C(6)H(3))](2)[MCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] leads to decomposition to give [MCl(3)(NR)(NH(2)R)](2) as sublimates (32-49%), leaving complexes of the proposed formulation MCl(NR)(2) as nonvolatile residues. By contrast, [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) sublimes without chemical reaction. Analysis of the organic products obtained from thermal decomposition of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) showed isobutylene and tert-butylamine in a 2.2:1 ratio. Mass spectra of [NbCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), [TaCl(2)(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), and [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2) showed the presence of dimeric imido complexes, monomeric imido complexes, and nitrido complexes, implying that such species are important gas phase species in CVD processes utilizing these molecular precursors. The crystal structures of [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))], [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2), [NbCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2), and [TaCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) were determined. [4-t-C(4)H(9)C(5)H(4)NH](2)[NbCl(5)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))] crystallizes in the space group P2(1)/c with a = 12.448(3) ?, b = 10.363(3) ?, c = 28.228(3) ?, beta = 94.92(1) degrees, V = 3628(5) ?(3), and Z = 4. [NbCl(3)(N(i)Pr)(NH(2)(i)Pr)](2) crystallizes in the space group P2(1)/c with a = 9.586(4) ?, b = 12.385(4) ?, c = 11.695(4) ?, beta = 112.89(2) degrees, V = 1279.0(6) ?(3), and Z = 2. [NbCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) crystallizes in the space group P2(1)/n with a = 10.285(3) ?, b = 11.208(3) ?, c = 23.867(6) ?, beta = 97.53 degrees, V = 2727(1) ?(3), and Z = 2. [TaCl(3)(N(2,6-(CH(CH(3))(2))(2)C(6)H(3)))(NH(2)(2,6-(CH(CH(3))(2))(2)C(6)H(3)))](2) crystallizes in the space group P2(1)/n with a = 10.273(1) ?, b = 11.241(2) ?, c = 23.929(7) ?, beta = 97.69(2) degrees, V = 2695(2) ?(3), and Z = 2. These findings are discussed in the context of niobium and tantalum nitride film depositions from molecular precursors.     

From quantum motifs to assemble nanoaggregates: the preparation of organo-molybdenum hybrid nanostructures

Nanoaggregates such as nanowires, nanoparticles, nanotubules, and nanoribbons were prepared from bulk crystals, which are shaped as needles (1), blocks (2), tubules (3α), and plates (3β), respectively, by grinding and ultrasonication. Nanowires have diameters of approximately 2 nm, lengths of thousands of nanmeters, and the distance between adjacent nanowires is approximately 2 nm. The diameters of nanoparticles range from 3 to 5 nm. Nanotubules display diameters of 70 nm and lengths of thousands of nanometers, and nanoribbons exhibit widths of approximately 50 nm and lengths of hundreds of nanometers. All of the bulk crystals have been synthesized by the wet chemical method. Single-crystal X-ray diffraction reveals that crystal 1 is constituted by infinite one-dimensional {[NH(3)CH(2)CH(NH(2))CH(3)](C(6)H(4)O(2))[μ(2)-OC(6)H(4)O](Mo(VI)-O-Na-O)[NH(2)CH(2)CH(NH(2))CH(3)]}(n) (1), which acts as a parallel aligned quantum wire forming lamellas that assemble themselves into multilayered architecture. Crystal 2 consists of discrete [NH(3)CH(2)CH(NH(2))CH(3)](2)[Mo(VI)O(2)(O(2)C(6)H(4))(2)] (2), which presents as quantum particles and repeats itself along a three-dimensional crystal lattice. Crystal 3α, formed under 5 °C, and 3β, crystallized above 10 °C, are both composed of (NH(3)CH(2)CH(2)NH(2))(2)[Mo(VI)O(2)(O(2)C(6)H(4))(2)](NH(2)CH(2)CH(2)NH(2))(0.5) (3) but are packed in different ways. In crystal 3α, four [Mo(VI)O(2)(O(2)C(6)H(4))(2)](2-) circle into a quantum tube that is further assembled into multitubular architecture. However, in crystal 3β, two [Mo(VI)O(2)(O(2)C(6)H(4))(2)](2-) form a bilayered quantum lamellar motif that is piled into multilayered architecture. TEM reveals that all of the morphologies of the nanoaggregates are associated with the structures of the quantum motifs in their crystal lattices, which provide successful and effective access to assemble controlled nanostructures from quantum motifs of fine-desired and well-ordered bulk crystals. The technology of grinding and ultrasonication to prepare nanoaggregates is simple and available.     

Unsymmetrical tren-based ligands: synthesis and reactivity of rhenium complexes

Reaction of bis(2-aminoethyl)(3-aminopropyl)amine with C(6)F(6) and K(2)CO(3) in DMSO yields unsymmetrical [(C(6)F(5))HNCH(2)CH(2)](2)NCH(2)CH(2)CH(2)NH(C(6)F(5)) ([N(3)N]H(3)). The tetraamine acts as a tridentate ligand in complexes of the type H[N(3)N]Re(O)X (X = Cl 1, Br 2) prepared by reacting Re(O)X(3)(PPh(3))(2) with [N(3)N]H(3) and an excess of NEt(3) in THF. Addition of 1 equiv of TaCH(CMe(2)Ph)Br(3)(THF)(2) to 1 gives the dimeric compound H[N(3)N]ClReOReBrCl[N(3)N]H (3) in quantitative yield that contains a Re(V)[double bond]O[bond]Re(IV) core with uncoordinated aminopropyl groups in each ligand. Addition of 2 equiv of TaCH(CMe(2)Ph)Cl(3)(THF)(2) to 1 leads to the chloro complex [N(3)N]ReCl (4) with all three amido groups coordinated to the metal, whereas by addition of 2 equiv of TaCH(CMe(2)Ph)Br(3)(THF)(2) to 2 the dibromo species H[N(3)N]ReBr(2) (5) with one uncoordinated amino group is isolated. Reduction of 4 under an atmosphere of dinitrogen with sodium amalgam gives the dinitrogen complex [N(3)N]Re(N(2)) (6). Single-crystal X-ray structure determinations have been carried out on complexes 1, 3, 5, and 6.     

Synthesis of [(HIPTNCH2CH2)3N]V compounds (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an evaluation of vanadium for the reduction of dinitrogen to ammonia

Green [HIPTN3N]V(THF) ([HIPTN3N]3- = [(HIPTNCH2CH2)3N]3-, where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) can be prepared in a 70-80% yield via the addition of H3[HIPTN3N] to VCl3(THF)3 in THF, followed by the addition of LiN(SiMe3)2. From [HIPTN3N]V(THF), the following have been prepared: {[HIPTN3N]VN2}K, [HIPTN3N]V(NH3), [HIPTN3N]V=NH, [HIPTN3N]V=NSiMe3, [HIPTN3N]V=O, [HIPTN3N]V=S, and [HIPTN3N]V(CO). No ammonia is formed from dinitrogen using {[HIPTN3N]VN2}K, [HIPTN3N]V=NH, or [HIPTN3N]V(NH3) as the initial species under conditions that were successful in the analogous [HIPTN3N]Mo system. X-ray structural studies are reported for [HIPTN3N]V(THF) and [HIPTN3N]V(NH3).     

Synthesis of [(HIPTNCH2CH2)3N]Cr Compounds (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an evaluation of chromium for the reduction of dinitrogen to ammonia

Red-black [HIPTN3N]Cr (1) ([HIPTN3N]3- = [(HIPTNCH2CH2)3N]3- where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = HexaIsoPropylTerphenyl) can be prepared from CrCl3, while green-black [HIPTN3N]Cr(THF) (2) can be prepared from CrCl3(THF)3. Reduction of {1|2} (which means either 1 or 2) with potassium graphite in ether at room temperature yields [HIPTN3N]CrK (3) as a yellow-orange powder. There is no evidence that dinitrogen is incorporated into 1, 2, or 3. Compounds that can be prepared readily from {1|2} include red [HIPTN3N]CrCO (4), blood-red [HIPTN3N]CrNO (6), and purple [HIPTN3N]CrCl (7, upon oxidation of {1|2} with AgCl). The dichroic (purple/green) Cr(VI) nitride, [HIPTN3N]CrN (8) was prepared from Bu4NN3 and 7. X-ray studies have been carried out on 4, 6, and 7, and on two co-crystallized compounds, 7 and [HIPTN3N]CrN3 (65:35) and [HIPTN3N]CrN3 and 8 (50:50). Exposure of a degassed solution of {1|2} to an atmosphere of ammonia does not yield "Cr(NH3)" as a stable and well-behaved species analogous to Mo(NH3). An attempt to reduce dinitrogen under conditions described for the catalytic reduction of dinitrogen by [HIPTN3N]Mo compounds with 8 yielded a substoichiometric amount (0.8 equiv) of ammonia, which suggests that some ammonia is formed from the nitride but none is formed from dinitrogen.     

Synthesis and Evaluation of Thioether-Based Tris-Melamines as Components of Self-Assembled Aggregates Based on the CA.M Lattice

Two new tris-melamine derivatives, triazine-thio-M(3) (5) (C(3)N(3)-2,4,6-[SCH(2)C(6)H(4)-3-N(CH(2)C(6)H(4)-4-C(CH(3))(3))COC(6)N(3)-2-NHC(3)N(3)(NH(2))(NHCH(2)CH(2)C(CH(3))(3))-5-Br](3)) and benzene-thio-M(3) (6) (C(6)H(3)-1,3,5-[SCH(2)C(6)H(4)-3-N(CH(2)C(6)H(4)-4-C(CH(3))(3))COC(6)H(3)-2-NHC(3)N(3)(NH(2))(NHCH(2)CH(2)C(CH(3))(3))-5-Br](3)), were synthesized by reactions of 2,4,6-trithiocyanuric acid and 1,3,5-trimercaptobenzene with a bromobenzyl melamine derivative 19 (BrCH(2)C(6)H(4)-3-N(CH(2)C(6)H(4)-4-C(CH(3))(3))COC(6)H(3)-2-NHC(3)N(3)(NH(2))(NHCH(2)CH(2)C(CH(3))(3))-5-Br). These two compounds formed stable and structurally well-defined 1 + 3 supramolecular aggregates with neohexyl isocyanurate (R'CA) (9) as shown by NMR spectroscopy and gel permeation chromatography. (1)H NMR competition experiments indicated that the stability of triazine-thio-M(3).(R'CA)(3) (1) was similar to that of benzene-thio-M(3).(R'CA)(3) (2). The order of stabilities of tris-melamine-based 1 + 3 complexes was hubM(3).(R'CA)(3) (3) > triazine-thio-M(3).(R'CA)(3) (1) approximately benzene-thio-M(3).(R'CA)(3) (2) > flexM(3).(R'CA)(3) (4). Computational simulations were also carried out on triazine-thio-M(3).(R'CA)(3) and hubM(3).(R'CA)(3) fully solvated in CHCl(3). Values of DP (the deviation from planarity of the cyanuric acid and melamine rosette) obtained from these simulations correlated correctly with the observed stabilities and suggested a structural reason why triazine-thio-M(3).(R'CA)(3) was less stable than hubM(3).(R'CA)(3).     

Solid state structure and solution behaviour of organoselenium(II) compounds containing 2-{E(CH2CH2)2NCH2}C6H4 groups (E = O, NMe)

Cleavage of the Se-Se bond in [2-{O(CH(2)CH(2))(2)NCH(2)}C(6)H(4)](2)Se(2) (1) and [2-{MeN(CH(2)CH(2))(2)NCH(2)}C(6)H(4)](2)Se(2) (2) by treatment with SO(2)Cl(2), bromine or iodine (1 : 1 molar ratio) yielded [2-{O(CH(2)CH(2))(2)NCH(2)}C(6)H(4)]SeX [X = Cl (3), Br (4), I (5)] and [2-{MeN(CH(2)CH(2))(2)NCH(2)}C(6)H(4)]SeI (6). The compounds were characterized in solution by NMR spectroscopy (1H, 13C, 15N, 77Se, 2D experiments). The solid-state molecular structures of 1-3, 4.HBr, 5 and 6 were established by single crystal X-ray diffraction. In all cases T-shaped coordination geometries, i.e. (C,N)SeSe (1, 2), (C,N)SeX (3, 5, 6; X = halogen) or CSeBr(2) (4.HBr), were found. Supramolecular associations in crystals based on hydrogen contacts are discussed.     

Structure and Properties of [Fe(4)S(4){2,6-bis(acylamino)benzenethiolato-S}(4)](2)(-) and [Fe(2)S(2){2,6-bis(acylamino)benzenethiolato-S}(4)](2)(-): Protection of the Fe-S Bond by Double NH.S Hydrogen Bonds

Iron-sulfur clusters containing a singly or doubly NH.S hydrogen-bonded arenethiolate ligand, [Fe(4)S(4)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), [Fe(4)S(4){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), [Fe(2)S(2)(S-2-RCONHC(6)H(4))(4)](2)(-) (R = CH(3), t-Bu, CF(3)), and [Fe(2)S(2){S-2,6-(RCONH)(2)C(6)H(3)}(4)](2)(-), were synthesized as models of bacterial [4Fe-4S] and plant-type [2Fe-2S] ferredoxins. The X-ray structures and IR spectra of (PPh(4))(2)[Fe(4)S(4){S-2,6-(CH(3)CONH)(2)C(6)H(3)}(4)].2CH(3)CN and (NEt(4))(2)[Fe(2)S(2){S-2,6-(t-BuCONH)(2)C(6)H(3)}(4)] indicate that the two amide NH groups at the o,o'-positions are directed to the thiolate sulfur atom and form double NH.S hydrogen bonds. The NH.S hydrogen bond contributes to the positive shift of the redox potential of not only (Fe(4)S(4))(+)/(Fe(4)S(4))(2+) but also (Fe(4)S(4))(2+)/(Fe(4)S(4))(3+) in the [4Fe-4S] clusters as well as (Fe(2)S(2))(2+)/(Fe(2)S(2))(3+) in the [2Fe-2S] clusters. The doubly NH.S hydrogen-bonded thiolate ligand effectively prevents the ligand exchange reaction by benzenethiol because the two amide NH groups stabilize the thiolate by protection from dissociation.     

O-atom-transfer oxidation of [molybdenum(IV) oxo{3,6-(acylamino)2- 1,2-benzenedithiolato}2]2- promoted by intramolecular NH...S hydrogen bonds

Novel molybdenum dithiolene compounds having neighboring amide groups as models for molybdoenzymes, (NEt(4))(2)[Mo(IV)O{1,2-S(2)-3,6-(RCONH)(2)C(6)H(2)}(2)] (R = CH(3), CF(3), t-Bu, Ph(3)C), were designed and synthesized. The contributions of the NH...S hydrogen bond to the electrochemical properties of the metal ion and the reactivity of the O-atom-transfer reaction were investigated by a comparison with [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-). The MoOS(4) core of [Mo(IV)O{1,2-S(2)-3,6-(CH(3)CONH)(2)C(6)H(2)}(2)](2)(-) shows no significant geometrical difference from that of [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-) in the crystal. The hydrogen bonds positively shifted the Mo(IV/V) redox potential and accelerated the reduction of Me(3)NO.     

Flexible N,N,N-chelates as supports for iron and cobalt chloride complexes; synthesis, structures, DFT calculations and ethylene oligomerisation studies

The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH and (ArNHCH(2)CH(2))(2)NH (Ar = 2,6-Me(2)C(6)H(3), 2,4,6-Me(3)C(6)H(2)), have been prepared by employing palladium-catalysed N-C(aryl) coupling reactions of the corresponding primary amines with aryl bromide. Treatment of MCl(2) with (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH affords [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 1a; 2,4,6-Me(3)C(6)H(2)) 1b and [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]FeCl(2)](n)(n= 1, Ar = 2,6-Me(2)C(6)H(3) 2a; n= 2, 2,4,6-Me(3)C(6)H(2) 2b) in high yield. The X-ray structures of 1a and 1b are isostructural and reveal the metal centres to adopt distorted trigonal bipyramidal geometries with the N,N,N-chelates adopting fac-structures. A facial coordination mode of the ligand is also observed in bimetallic 2b, however, in 2a the N,N,N-chelate adopts a mer-configuration with the metal centre adopting a geometry best described as square pyramidal. Solution studies indicate that mer-fac isomerisation is a facile process for these systems at room temperature. Quantum mechanical calculations (DFT) have been performed on 1a and 2a, in which the ligands employed are identical, and show the fac- to be marginally more stable than the mer-configuration for cobalt (1a) while for iron (2a) the converse is evident. Reaction of (ArNHCH(2)CH(2))(2)NH with CoCl(2) gave the five-coordinate complexes [[(ArNHCH(2)CH(2))(2)NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 3a, 2,4,6-Me(3)C(6)H(2) 3b), in which the ligand adopts a mer-configuration; no reaction occurred with FeCl(2). All complexes 1-3 act as modest ethylene oligomerisation catalysts on activation with excess methylaluminoxane (MAO); the iron systems giving linear alpha-olefins while the cobalt systems give mixtures of linear and branched products.     

Synthesis, structure, and electrochemical studies of molybdenum and tungsten dinitrogen, diazenido, and hydrazido complexes that contain aryl-substituted triamidoamine ligands

One-electron reduction of [ArN(3)N]MoCl complexes (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3)) yields complexes of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N], while two-electron reduction yields ([ArN(3)N]Mo-N=N)(-) derivatives (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3), 3,5-Ph(2)C(6)H(3), and 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3)). Compounds that were crystallographically characterized include ([t-BuC(6)H(4)N(3)N]Mo)(2)(N(2)), Na(THF)(6)([PhN(3)N]Mo-N=N)(2)Na(THF)(3), [t-BuC(6)H(4)N(3)N]Mo-N=N-Na(15-crown-5), and ([Ph(2)C(6)H(3)N(3)N]MoNN)(2)Mg(DME)(2). Compounds of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N] do not appear to form when Ar = 3,5-Ph(2)C(6)H(3) or 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3), presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN(3)N]Mo-N=N-Na(THF)(x)) with electrophiles such as Me(3)SiCl or MeOTf yielded [ArN(3)N]Mo-N=NR complexes (R = SiMe(3) or Me). These species react further to yield ([ArN(3)N]Mo-N=NMe(2))(+) species in the presence of methylating agents. Addition of anionic methyl reagents to ([ArN(3)N]Mo-N=NMe(2))(+) species yielded [ArN(3)N]Mo(N=NMe(2))(Me) complexes. Reduction of [4-t-BuC(6)H(4)N(3)N]WCl under dinitrogen leads to a rare ([t-BuC(6)H(4)N(3)N]W)(2)(N(2)) species that can be oxidized by two electrons to give a stable dication (as its BPh(4)(-) salt). Reduction of hydrazido species leads to formation of Mo=N in low yields, and only dimethylamine could be identified among the many products. Electrochemical studies revealed expected trends in oxidation and reduction potentials, but also provided evidence for stable neutral dinitrogen complexes of the type [ArN(3)N]Mo(N(2)) when Ar is a relatively bulky terphenyl substituent.     

Synthesis and characterization of ionic liquids containing copper, manganese, or zinc coordination cations

Copper-, manganese-, and zinc-based ionic liquids (Cu{NH(2)CH(2)CH(2)OH}(6)[CH(3)(CH(2))(3)CH(C(2)H(5))CO(2)](2) (2), Cu{NH(CH(2)CH(2)OH)(2)}(6)[CH(3)(CH(2))(3)CH(C(2)H(5))CO(2)](2) (3A), Cu{NH(CH(2)CH(2)OH)(2)}(6)[CF(3)SO(3)](2) (3B), Cu{NH(CH(2)CH(2)OH)(2)}(6)[(CF(3)SO(2))(2)N](2) (3C), Mn{NH(CH(2)CH(2)OH)(2)}(6)[CF(3)SO(3)](2) (4), and Zn{NH(2)CH(2)CH(2)OH}(6)[CF(3)SO(3)](2) (5)) are synthesized in a single-step reaction. Infrared data suggest that ethanolamine preferentially coordinates to the metal center through the amine group in 2 and the hydroxyl group in 5. In addition, diethanolamine coordinates through the amine group in 3A, 3C, and 4 and the hydroxyl group in 3B. The compounds are viscous (>1000 cP) at room temperature, but two (3C and 4) display specific conductivities that are reasonably high for ionic liquids (>20 mS cm(-1)). All of the compounds display a glass transition (T(g)) below -50 °C. The cyclic voltammograms (CVs) of 2, 3A, 3B, and 3C display a single quasi-reversible wave associated with Cu(II)/Cu(I) reduction and re-oxidation while 5 shows a wave attributed to Zn(II)/Zn(0) reduction and stripping (re-oxidation). Compound 4 is the first in this new family of transition metal-based ionic liquids (MetILs) to display reversible Mn(II)/Mn(III) oxidation and re-reduction at 50 mV s(-1) using a glassy carbon working electrode.