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Bidentate 5,5ʹ-alkyl-3,3ʹ-bi-1H-pyrazole and 2-(5-alkyl-1H-pyrazol-3-yl)pyridine ligands, L5 and L6, have been shown to be stronger synergists for the solvent extraction of Ni(II) from sulfate solutions by dinonylnaphthalene sulfonic acid (DNNSAH) than the structurally related tridentate ligand 2,6-bis-[5-n-nonylpyrazol-3-yl]pyridine, L1, previously reported by Zhou and Pesic. The bidentate ligands are highly selective, providing the option of sequential recovery of Ni(II) and Co(II) and rejection of other metals commonly found in the liquors resulting from the acidic sulfate leaching of laterite ores. They were the strongest synergists identified in a screening carried out on 18 types of bidentate and tridentate N-heterocyclic ligands, including the recently reported 2-(2ʹ-pyridyl)imidazoles, L9−11. X-ray crystal structures of Ni(II) complexes of model ligands for L5 and L6, having t-butyl rather than long-chain alkyl groups and with 2-naphthalene sulfonate rather than DNNSA− as counteranions, show that the [Ni(L)3]2+ complexes form strong H-bonds from the pyrazolyl NH groups to the oxygen atoms of the sulfonate groups, an arrangement that will stabilize [Ni(L)3·(DNNSA)2] assemblies and shield their polar functionalities from diluent molecules of the water-immiscible phase. UV–visible spectra and mass spectrometry provide evidence for the strong synergists displacing all water molecules from the inner coordination sphere of the Ni(II) ions.

Eight new amido functionalized reagents, L-1-L-8, have been synthesized containing the sequence of atoms R2N-CH2-NR'-CO-R '', which upon protonation forms a six-membered chelate with a hydrogen bond between the tertiary ammonium N-H+ group and the amido oxygen atom. The monocationic ligands, LH+, extract tetrachloridometal(II)ates from acidic solutions containing high concentrations of chloride ions via a mechanism in which two ligands address the "outer sphere" of the [MCl4](2-) unit using both N-H and C-H hydrogen bond donors to form the neutral complex as in 2L + 2HCl + MCl2 reversible arrow [(LH)(2)MCl4]. The strengths of L-1-L-8 as zinc extractants in these pH-dependent equilibria have been shown to be very dependent on the number of amide groups in the R3-nN(CH2NR'COR '')(n) molecules, anti-intuitively decreasing with the number of strong hydrogen bond donors present and following the order monoamides > diamides > triamides. Studies of the effects of chloride concentration on extraction have demonstrated that the monoamides in particular show an unusually high selectivity for [ZnCl4](2-) over [FeCl4](-) and Cl-. Hybrid-DFT calculations on the tri-, di-, and monoamides, L-2, L-3, and L-4, help to rationalize these orders of strength and selectivity. The monoamide L-4 has the most favorable protonation energy because formation of the LH+ cation generates a "chelated proton" structure as described above without having to sacrifice an existing intramolecular amide amide hydrogen bond. The selectivity of extraction of [ZnCl4](2-) over Cl-, represented by the process 2[(LH)Cl] + ZnCl42- reversible arrow [(LH)(2)ZnCl4] + 2Cl(-), is most favorable for L-4 because it is less effective at binding chloride as it has fewer highly polar N-H hydrogen bond donor groups to interact with this "hard" anion.

Alkyl-substituted phenolic pyrazoles such as 4-methyl-2-[5-(n-octyl)-1H-pyrazol-3-yl]phenol (L2H) are shown to function as Cu-extractants, having similar strength and selectivity over Fe(iii) to 5-nonylsalicylaldoxime which is a component of the commercially used ACORGA® solvent extraction reagents. Substitution in the phenol ring of the new extractants has a major effect on their strength, e.g. 2-nitro-4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L4H) which has a nitro group ortho to the phenolic hydroxyl group unit and has an extraction distribution coefficient for Cu nearly three orders of magnitude higher than its unsubstituted analogue 4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L8H). X-ray structure determinations and density functional theory (DFT) calculations confirm that inter-ligand hydrogen bonding between the pyrazole NH group and the phenolate oxygen atom stabilise the Cu-complexes, giving pseudomacrocyclic structures. Electron-accepting groups ortho to the phenol oxygen atoms buttress the inter-ligand H-bonding, enhancing extractant strength but the effectiveness of this is very dependent on steric factors. The correlation between the calculated energies of formation of copper complexes in the gas phase and the observed strength of comparably substituted reagents in solvent extraction experiments is remarkable. Analysis of the energies of formation suggests that big differences in strength of extractants arise principally from a combination of the effects of the substituents on the ease of deprotonation of the proligands and, for the ortho-substituted ligands, their propensity to buttress inter-ligand hydrogen bonding.

A series of 22 tridentate unsaturated mono-anionic ligands having the atom-sequence Y-C[double bond, length as m-dash]C-N=CH-C=C-Z(-1), with Y = N, O, or S and Z = O or S, has been studied to establish whether this backbone could be used to develop strong solvent extractants for nickel(II) which will preferably also show a high selectivity over iron(III) in the pH-dependent process: 2LH(org) + NiSO4 ⇌ [(L)2Ni]org + H2SO4. All are capable of forming octahedral [(L)2Ni] complexes with a mer-arrangement of the YNZ(-1) donor set. X-ray crystal structures of three salicylaldimine proligands derived from 3-bromo-5-t-butyl-2-hydroxybenzaldehyde show these to have pre-organised donor sets in which the three donors are held in an approximately orthogonal arrangement by intramolecular hydrogen bonds. The tautomers observed are dependent on the nature of the Y atom and the extent to which it is favourable for this to form a bonding interaction with the acidic hydrogen atom on the salicylaldimine unit. X-ray crystal structure determinations of seven of the [(L)2Ni] complexes show these to have significantly distorted octahedral coordination geometries which partly account for the proligands proving to be fairly weak Ni-extractants. DFT calculations show that extractant strength is dependent on a combination of the binding strength of the YNZ(-1) donor set to the nickel ion and on the ease of deprotonation of the extractant. On this basis 3-nitro-4-t-octyl-6-(quinolin-8-imino)phenol is predicted, and is found, to be the strongest Ni-extractant. The extractants have low hydrolytic stability, reverting to their aldehyde precursors when solutions in water-immiscible solvents are contacted with aqueous acid, making them poor candidates for development as reagents for nickel recovery based on pH-swing processes of the type shown above.

The facile syntheses and the structures of five new Cu(I) alkynyl clusters, [Cu(12)(hfac)(8)(C[triple chemical bond]CnPr)(4)(thf)(6)]xTHF (1), [Cu(12)(hfac)(8)(C[triple chemical bond]CtBu)(4)] (2), [Cu(12)(hfac)(8)(C[triple chemical bond]CSiMe(3))(4)] (3), [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)]/[Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(3)(C[triple chemical bond]CnPr)(diethyl ether)] (4) and [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)] (5) are reported, in which hfacH=1,1,1,5,5,5-hexafluoropentan-2,4-dione. The first independent molecule found in the crystals of 4 (4 a) proved to be chemically identical to 5. The Cu(10) and Cu(12) cores in these clusters are based on a central "square" Cu(4)C(4) unit. Whilst the connectivities of the Cu(10) or Cu(12) units remain identical the geometries vary considerably and depend on the bulk of the alkynyl group, weak coordination of ether molecules to copper atoms in the core and CuO intramolecular contacts formed between Cu-hfac units on the periphery of the cluster. Similar intermolecular contacts and interlocking of Cu-hfac units are formed in the simple model complex [Cu(2)(hfac)(2)(HC[triple chemical bond]CtBu)] (6). When linear alkynes, C(n)H(2n+1)C[triple chemical bond]CH, are used in the synthesis and non-coordinating solvents are used in the workup, further association of the Cu(4)C(4) cores occurs and clusters with more than eighteen copper atoms are isolated.

The application of the reagent (Ipc)BCl(2) (Ipc = isopinocampheyl) in the synthesis of a new tris(pyrazolyl)borate ligand having an Ipc substituent on boron is described. The sodium salt is a convenient precursor for the preparation of the complexes [(Ipc)tris(pyrazolyl)borato]tricarbonylmanganese and [[(Ipc)tris(pyrazolyl)borato](p-cymene)ruthenium](+), whose X-ray crystal structures are reported. While little distortion of the B(pz)(3)M unit is observed in these complexes, steric interaction between the Ipc group and the 3-positions of the pyrazolyl rings is noted to lead to distortion of the angles around the B-C bond.

A new high-yield synthesis of [(PhCH(2))(2)Mg(thf)(2)] and [[(PhCH(2))CH(3)Mg(thf)](2)] via benzylpotassium has allowed a simple entry into benzylmagnesium coordination chemistry. The syntheses and X-ray crystal structures of both [(eta(2)-Me(2)NCH(2)CH(2)NMe(2))Mg(CH(2)Ph)(2)] and [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] (Ar'=2,6-diisopropylphenyl) are reported. The latter beta-diketiminate complex reacts with dioxygen to provide a 1:2 mixture of dimeric benzylperoxo and benzyloxo complexes. The benzylperoxo complex [[eta(2)-HC[C(CH(3))NAr'](2)Mg(mu-eta(2):eta(1)-OOCH(2)Ph)](2)] is the first example of a structurally characterised Group 2 metal-alkylperoxo complex and contains the benzylperoxo ligands in an unusual mu-eta(2):eta(1)-coordination mode, linking the two five-coordinate magnesium centres. The O[bond]O separation in the benzylperoxo ligands is 1.44(2) A. Reaction of the benzylperoxo/benzyloxo complex mixture with further [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] results in complete conversion of the benzylperoxo species into the benzyloxo complex. This reaction, therefore, establishes the cleavage of dioxygen by this system as a two-step process that involves initial oxygen insertion into the Mg[bond]CH(2)Ph bond followed by O[bond]O/Mg[bond]C sigma-bond metathesis of the resulting benzylperoxo ligand with a second Mg[bond]CH(2)Ph bond. The formation of a 1:2 mixture of the benzylperoxo and benzyloxo species indicates that the rate of the insertion is faster than that of the metathesis, and this is shown to be consistent with a radical mechanism for the insertion process.

A number of new complexes of the tris(methimazolyl)hydroborate (Tm) ligand have been synthesised: [(Tm)RuCl(DMSO) 2 ] ( 1 ), [(Tm)Ru( p -cymene)]Cl ( 2 ), [(Tm)RuCp] ( 3 ) and [(Tm)Mn(CO) 3 ] ( 4 ). Complexes 2 and 4 have been characterised structurally by X-ray crystallography and a partial crystallographic analysis was obtained for 1 . The Tm ligand is found to coordinate as a tripod ligand through its sulphur donors in all complexes except 3 , for which there is evidence of bidentate coordination and formation of a 16-electron species.

By employment of monoanionic hfac(1,1,1,5,5,5-hexafluoroacetylacetonate) as a “capping ligand”, it is possible to modulate the facile accretion of [{Cu(C⋮CR)}n] moieties to yield discrete high-nucl...

Two novel high nuclearity copper(I) alkynyl complexes, [Cu16(hfac)8(CCBut)8] (1) and [Cu20(hfac)8(CCCH2Ph)12] (2), that consist of complicated alkynyl bridged Cu(I) cores ‘capped’ by peripheral hfac ligands have been synthesised and characterised by X-ray structure determination. The photoluminescent properties of 1 and 2 together with the clusters, [Cu18(hfac)10(CCBun)8] (4) and [Cu26(hfac)11(CCPrn)15] (5) and the monomeric species, [Cu(hfac)(HCCCH2OMe)] (3), [Cu(hfac)(Me3SiCCSiMe3)] (6) and [Cu(hfac)(COD)] (7) are reported. A comparison of the photoluminescent spectra of the high nuclearity species with the related monomeric complexes have shown that the cluster luminescence is derived from transitions within the delocalised Cu-hfac chelate ring.

Treatment of the heterocycle 5-thioxo-4,5-dihydro-3,4-dimethyl-1,2,4-triazole (thioxotriazole) with sodium tetrahydroborate at 210 degrees C provides the new [N(3)/S(3)] ambidentate tripod ligand hydridotris(thioxotriazolyl)borate (Tt) as its sodium complex salt. Complexes of this ligand with sodium, bismuth(III), tin(IV), and manganese(I) have been synthesized and characterized by X-ray crystallography. The structures of these complexes illustrate the ambidentate character of the ligand with the softer metals bismuth and tin exhibiting sulfur coordination, while sodium and manganese(I) bond via the ligand nitrogen donors. In the [S(3)] coordination mode the ligand creates eight-membered chelate rings with the metal with the consequence that the metal ligand unit adopts a propeller-type conformation with C(3)-symmetry. However, in the [N(3)] mode six-membered chelate rings are formed analogous to the familiar hydrotris(pyrazolyl)borate (Tp) ligand.

Treatment of the phosphonium salt [PhP(CH2Ph)3]Cl with three molar equivalents of nBuLi gives the dilithiated species [Li2PhP(CHPh)3]. The crystal structure of the monolithiated species as its TMEDA adduct has been determined. Treatment of the dilithiate species with [((η-C5Me5)MX2]2 (M=Cr, X=Br; M=Rh, X=Cl) provides [(η-C5Me5)M{η2-PhP(CH2Ph)(CHPh)2}X] containing chelating phosphoniodiylide ligands which are thought to be the hydrolysis products of the target complexes [{PhP(CHPh)3}M(C5Me5)].

Treatment of dimethylmagnesium with Ar‘NC(tBu)CHC(tBu)NHAr‘ (Ar‘ = 2,6-diisopropylphenyl) in THF provides the β-diketiminate complex [CH3Mg(THF){η2-(Ar‘NCtBu)2CH}]. The THF ligand may be removed fr...

Treatment of the dimeric ruthenium halide complex [Ru(η-C6H6)Cl2]2 with 1,2,3-triphenylguanidine provided the tris-chelate [Ru{η2-(NPh)2CNHPh}3] with loss of the aromatic ligand and metal oxidation. This product may also be prepared by treatment of the previously reported [Ru(η-p-PriC6H4Me){η2-(NPh)2CNHPh}Cl] with bases (KOH, LiNiPr2, NEt3). Complexes containing chelating guanidinate ligands are also available by means of metathesis of the monolithiated ligands Li[C(NR)2NR2] with metal halide complexes, as exemplified by the synthesis of the square planar bis-chelate [Pt{η2-(NPh)2CNHPh}2] from [Pt(PhCN)2Cl2] and [Ti{η2-(NPh)2CN(Et)2}2Cl2] from [TiCl4(THF)2]. The characterisation of these complexes allows a comparison of the co-ordination properties of chelating guanidinates with early, middle and late transition metals.

Treatment of the Grignard reagent MeMgCl with the lithiates Li[L–X] (Li[L–X] = lithium β-diketiminate [HC{C(Me)NAr′}2Li] (Ar′ = 2,6-diisopropylphenyl) or lithium N,N′-diisopropylaminotroponiminate, Li[(iPr2)ATI]) in THF provided four-co-ordinate methylmagnesium complexes [Mg(η2-L–X)Me(THF)]. The β-diketiminate complex has been characterised by X-ray crystallography, however the aminotroponiminate complex is an oil. Both complexes readily react with oxygen to provide methoxide-bridged dimeric complexes [Mg(μ-OMe)(η2-L–X)]2 and the complex [Mg(μ-OMe){η2-(iPr2)ATI}]2 has structurally been characterised. The methyl-bridged dimeric complex [Mg(μ-Me){HC[C(Me)NAr′]}2]2 may be obtained by removal of THF from the adduct under vacuum at 150 °C or by treatment of the β-diketimine (L–XH) with dimethylmagnesium in toluene with elimination of methane, and has also been characterised crystallographically. In contrast to this, treatment of MgMe2 with the aminotriponimine H[(iPr2)ATI] provides only the bis-chelate complex [Mg{(iPr2)ATI}2] which has also been characterised structurally. However the methyl bridged dimer [Mg(μ-Me){η2-(iPr2)ATI}]2 may be formed by removal of THF from [MgMe{η2-(iPr2)ATI}(THF)] at 110 °C under vacuum.

The phosphonium salt [PhP(NHiPr)3]Br has been synthesized, and the ligand properties of its deprotonated forms have been investigated. Treatment of its dilithiate Li2[PhP(NiPr)3] with the dimer [(η-p-cymene)RuCl2]2 provides the unsaturated 16-electron cation [(η-p-cymene)Ru{η2-(iPrN)2PPh(NHiPr)}]+ which adds cyanide and carbon monoxide (reversibly) and has been structurally characterized as its tetraphenylborate salt.

The quadruply bonded molybdenum dimer [Mo2{μ-η2-(NPh)2CNHPh}4] (1), bridged by four triphenylguanidine anion (guanidino) ligands, has been synthesized and structurally characterized. The guanidino ligands greatly stabilize the oxidized forms of this complex, and it is reversibly oxidized to the red monocation and the blue dication at readily accessible potentials (E1/2 = −0.05 and +0.85 V vs Ag/AgCl, respectively). The [Mo2{μ-η2-(NPh)2CNHPh}4]+ cation (2) has also been structurally characterized as its [BF4]- salt showing that the Mo−Mo distance increases from 2.0839(9) to 2.2902(12) A on oxidation, an unprecedented increase for such systems and almost 4 times that previously observed for a [Mo2]4+/5+ pair. The N−Mo−Mo−N torsion angle is also found to increase from 4.5 to 7.6° on oxidation. The crystallographic data are as follows. 1·2.2Et2O: C84.8H86Mo2N12O2.2, monoclinic, P2/n, a = 13.127(3) A, b = 14.335(3) A, c = 22.752(3) A, β = 90.434(13)°, Z = 2. 2[BF4]-·3CH2Cl2: C79H70BCl6F4Mo2N12, monoclinic, P...

Two complexes exhibiting monodentate metal co-ordination of a neutral guanidine have been synthesized and structurally characterised. Treatment of CoCl2 with 1,2,3-triphenylguanidine in tetrahydrofuran solution produced the tetrahedral complex [Co{(PhN)C(NHPh)2}2Cl2] 1 in which the guanidine ligands are co-ordinated through their imine nitrogen atoms alone. Similarly, treatment of the guanidine with Ag[SO3CF3] in toluene provided the linear complex [Ag{(PhN)C(NHPh)2}2][SO3CF3] 2 in which the triflate counter ion remains unco-ordinated, but is hydrogen bonded to the guanidine hydrogen atoms. Both complexes have been characterised by X-ray crystallography.

A simple and convenient route to η(5)-coordinated Ru and Rh aminofulvene-aldiminate (AFA) complexes is described. The metalloligands [Cp*Ru{η(5)-(Ph(2)AFAH)}][BF(4)] (3), [Cp*Ru{η(5)-(benzyl(2)AFAH)}][OTf] (7), [Cp*Rh{η(5)-(Cy(2)AFA)H}][BF(4)](2) (8) and [Cp*Rh{η(5)-(Cy(2)AFA)}][BF(4)] (9) have been synthesised and characterised. The basicity of 9 has been found to be significantly less than its neutral analogue and thus eliminates the need for a deprotonation step to ligate to a second metal in the κ(2)-N,N'-coordination mode. The reaction of 9 with a palladium precursor provides a mixed-metal complex [Cp*Rh(η(5)/κ(2)-Cy(2)AFA)PdCl(2)][BF(4)] (12). Cyclic voltammetry studies of the Ph(2)AFAH ligand shows an irreversible one electron oxidation peak at +1.0 V (vs. Fc/Fc(+)). Complex 3 shows an irreversible oxidation at +1.5 V and a reduction peak at -1.0 V. The oxidation of 3 occurs on the AFA ligand backbone whereas the structurally analogous neutral 1,2-bis(imidoyl)pentamethyl-ruthenocene shows reversible oxidation at the Ru center.

The thermolysis of [Ru3(CO)12]1 in the presence of 1,3,5-trimethylbenzene yielded, in addition to hexaruthenium carbido products, the tetracapped octahedral carbido cluster anion [Ru10H(C)(CO)24]–2 which has been fully characterised as its [N(PPh3)2]+ salt. Deprotonation of 2 yielded the dianion [Ru10C(CO)24]2–3 which has been similarly characterised. The isostructural decaruthenium nitrido anion [Ru10N(CO)24]–4 may be synthesised by condensation of the required stoichiometric quantities of [Ru3(CO)12] with the preformed nitrides [Ru5N(CO)14]– or [Ru6N(CO)16]– under thermolysis in bis(2-methoxyethyl) ether (diglyme), or alternatively directly from [Ru3(CO)12] by reaction with 1/3 equivalent of [N(PPh3)2][N3] under the same conditions. The anion 4 as its [N(PPh3)2]+ salt forms crystals isomorphous to those of 2, and conclusive evidence for its containing an interstitial nitride was therefore obtained by observation of its 14N NMR resonance at δ 30 [δ(14N, MeNO2)= 0]. Reaction of 3 with 1 atm CO in solution leads to rapid degradation to [Ru6C(CO)16]2– and [Ru3(CO)12] whilst under the same conditions 4 yields [Ru5N(CO)14]– and [Ru3(CO)12].

The introduction of carbido atoms into hexaruthenium clusters is discussed in terms of the cleavage of susceptible carbonyl ligands coordinated to non-carbido precursors. The isolation of an intermediate containing dihapto-carbonyl ligands in the well established synthesis of [Ru 6 C(CO) 14 (η 6 -arene)] species by thermolysis of [Ru 3 (CO) 12 ] in the presence of the arene, and its demonstrated conversion to the carbide a second hexaruthenium product and carbon dioxide, is interpreted in terms of a bimolecular mechanism involving cleavage of a dihapto-carbonyl ligand. With reference to this mechanism, the virtually quantitative conversion of [Ru 6 (CO) 18 ] 2− ( 5 ) into [Ru 6 C(CO) 16 ] 2− ( 6 ) and carbon dioxide which occurs at high temperature in solution is discussed, and an autocatalytic mechanism involving a bimolecular CO cleavage step is suggested. Finally, the conversion of [Ru 6 (CO) 18 ] 2− ( 5 ) into the neutral carbide [Ru 6 C(CO) 17 ] ( 1 ) by carbonyl ligand CO cleavage induced by reaction with trifluoromethanesulfonic or trifiuoroethanoic anhydrides is discussed.

Diffusion barrier properties of electrochemically deposited Ni, Co, and Ni‐Co alloys were examined in the binary system and the Au/Ni/Cu ternary system. Ni and Co were electrodeposited from sulfate or sulfamate (Ni) solutions in the presence of boric acid, at pH 3.30. Electroless Ni and Co deposited either from sulfate or sulfamate solution using sodium hypophosphite or dimethylamine borane as the reducing agent. Electroless gold was deposited from cyanide solutions using potassium borohydride as the reducing agent. The deposits were annealed at 400°C for 14 h in a forming gas atmosphere (10% , 90% ). Auger electron spectroscopy and electron probe analysis were used to assess the extent of interdiffusion as a result of the heat‐treatment. Only electrolessly deposited 1000 A thick Ni, Co, and Ni‐Co alloys have barrier properties for Cu diffusion. For 1000 A thick barriers, annealed for 14 h, the amount of the interdiffused copper into was less than 1 atomic percent. Thicker barriers of , , and are required for the same degree of Cu diffusion. thin films deposited from nickel sulfamate solutions are better diffusion barriers than those deposited under the same experimental conditions, from nickel sulfate solutions. Electrochemically deposited barriers were compared with Ni, Co, and Cr barriers produced by evaporation. The differences between the diffusion barrier properties of deposited from the sulfamate and the sulfate solutions were interpreted in term of microstructural data and grain growth mechanism.

The synthesis of a new charge-neutral zwitterionic tripodal borate ligand based on 2-hydroxypyridine is reported. (Dimethylaminopyridinium)tris(2-pyridonyl)borate, (DMAP)Thp, has been complexed to copper(I) chloride to give a pseudo-C-3 symmetric complex. The propensity for this ligand and other flexible scorpionates to exhibit such helical chirality upon complexation is discussed.

The reaction of the carbido dianion [Ru 6 C(CO) 16 ] 2− with Au 2 {Ph 2 PCH 2 PPh 2 }Cl 2 , in dichloromethane, in the presence of TIPF 6 , affords the neutral cluster Ru 6 C(CO) 16 Au 2 {Ph 2 PCH 2 PPh 2 } ( 1 ) in 90% yield. An X-ray analysis of 1 shows that the octahedral ruthenium core has remained intact, and that the two Au atoms of the chelating gold phosphine bridge two adjacent edges of one of the triangular faces of the Ru 6 octahedron. In marked contrast, the reaction of the non-carbido dianion [Ru 6 (CO) 18 ] 2− with Au 2 {Ph 2 PCH 2 PPh 2 }Cl 2 under similar reaction conditions leads to the breakdown of the octahedral ruthenium core and the formation of Ru 5 (CO) 15 Au 2 {Ph 2 PCH 2 PPh 2 } ( 2 ) in ca . 50% yield. The X-ray analysis of 2 shows that the ruthenium atoms adopt a trigonal bipyramidal framework with the Au atoms of the Au 2 {Ph 2 PCH 2 PPh 2 } ligand μ 3 - capping adjacent faces of the trigonal bipyramid in a manner not previously observed for mixed ruthenium-gold clusters.

The dimethylamine in the adducts [(HNMe2)B(azolyl)(3)] (azolyl = methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe2)(3), can readily be Substituted with a range of nitrogen donors to provide new charge-neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)(3)] (nmi = N-methylimidazole) have been compared with their anionic analogues [HB-(azolyl)(3)](-) by synthesis of their manganese(I)-tricarbonyl complexes and comparison of their infrared v(CO) energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl),] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand.

Bis(N,N'-2,6-diisopropylphenyl)-6-aminofulvene-2-aldimine (4) has been synthesised and characterised. The synthesis and characterisation of two zwitterionic Pd(ii) complexes [(Ph(2)AFA)Pd(Me)DMAP] (1) and [(Ph(2)AFA)Pd(N,N-dimethylbenzylamine-2-C,N)] (2) are reported. Activation of 1 and 2 for ethene polymerisation with Lewis acids such as BF(3) and B(C(6)F(5))(3) were not successful. Attempted synthesis of halide-bridged dimers of the form [(Ph(2)AFA)Pd(mu-X)](2) resulted in formation of bis-chelated complexes [(Cy(2)AFA)(2)Pd] (3) and [((t)Bu(2)AFA)(2)Pd] (5).

The nature of the crystallographically isostructural hydrido-cluster anions [HOs10C(CO)24]- (1) and [HRu10C(CO)24]- (2) in solution has been probed by variable-temperature 13C-NMR and two-dimensional {1H}13C-EXSY spectroscopy. The results of the study are interpreted in terms of both localised and global intramolecular exchange of the carbonyl and hydrido ligands which appear to occur by the same mechanisms in both clusters. The significance of the derived model for the understanding of the dynamic behaviour of more complicated systems such as [H4Os10(CO)24]2- (4) is discussed. The latter is at present the best molecular model for the structural aspects of synthesis gas adsorption at high density on metal surfaces.

The reinvestigation of an early synthesis of hexaruthenium carbido clusters has lead to the isolation of a number of new clusters which have been fully characterised by spectroscopic and crystallographic techniques. The thermolysis of Ru 3 (CO) 12 in the presence of mesitylene (1,3,5-trimethylbenzene) at moderate temperatures yields two new clusters, [Ru 6 (μ 4 -η 2 -CO) 2 (CO) 13 (η 6 -C 6 H 3 Me 3 )] (I) and [HRu 6 (μ 4 -η 2 -CO)(CO) 13 (μ 2 -η 7 -C 6 H 3 Me 2 CH 2 )] (II), the structures and reactivity of which indicate the origin and mechanism of formation of the carbido-carbon in the hexaruthenium carbido clusters [Ru 6 C(CO) 14 (η 6 -C 6 H 3 Me 3 )] (III) and [Ru 6 C(CO) 17 ] (IV). A further product of the reaction is the decaruthenium carbido cluster dianion [Ru 10 C(CO) 24 ] 2− (V) which has the tetracapped octahedral geometry. The monohydrido-cluster anion [HRu 10 C(CO) 24 ] − (VI) may be synthesised quantitatively from V by protonation. The nature of the hydrido-ligand in VI has been investigated in the solid state by NMR spectroscopy and it has been found to be fluxional, its location being temperature dependent. The decanuclear dianion V has been found to react with mercury salts to yield the 21 metal atom cluster dianion [Ru 18 Hg 3 C 2 (CO) 42 ] 2− (VII) which consists of two tricapped octahedral nonaruthenium “subclusters” fused by a bi-facecapping (Hg 3 ) 2+ unit.

The activation of tris(dimethylamino)borane towards reaction with a chiral methimazole by N-methylimidazole has been used to prepare the first example of a chiral tris(methimazolyl)borate ligand. Coordination of this neutral ligand to Ru(II) has been achieved by reaction with [(p-cymene)RuCl(2)](2) to provide a single diastereomer complex in which the chirality of the methimazolyl substituents dictate the chirality of the bicyclo[3.3.3]cage formed by the ligand on coordination to the metal. The alternative approach to chiral tris(methimazolyl)borate ligands involving the introduction of a chiral group onto the boron atom has been explored by replacing N-methylimidazole in the above reaction by chiral oxazolines as activating bases in reaction with simple methimazole. However, although the B(NMe(2))(3) is activated to reaction with methimazole by these oxazolines, an intramolecular oxazoline ring-opening by a coordinated methimazolyl sulfur occurs and prevents the successful synthesis of these ligands.

The 6-aminofulvene-2-aldiminate (AFA) ligand contains both cyclopentadienyl and diimine donors. The ligand preferentially coordinates to transition metals via the nitrogen atoms; however once these are occupied, the cyclopentadienyl ring may be coordinated to a Cp*Ru+ unit, providing bi- and trimetallic species. In the tetrahedral [Zn(Ph2AFA)2] (2) the metal is located approximately in the planes of the two ligands; however in the square-planar [Pd(Ph2AFA)2] (1) there is a severe distortion of the coordination and the metal is located almost 1.3 Å out of the planes of the two ligands. This situation arises to avoid the steric interaction of the ligand phenyl substituents. Treatment of 2 with [Cp*Ru(NCMe)3][BF4] gives [Cp*Ru(η5-Ph2AFA)] (3), providing the first example of the cyclopentadienyl coordination of an AFA ligand in which the nitrogen donors are vacant, and it is thought to form as a result of the fragmentation of an intermediate mixed Zn/Ru species. The X-ray structure of 3 provides some evidence for an interaction between the Ru center and one of the exocyclic carbon atoms, thus suggesting a fulvene form of the ligand in this complex. Similar treatment of 1 with [Cp*Ru(NCMe)3][BF4] provides a trimetallic PdRu2 species (4) in which both of the cyclopentadienyl rings in the complex 2 are coordinated to Ru. The complex [(Ph2AFA)Pd(Me)PPh3] (5) is formed on treatment of [(COD)PdMe(Cl)] with NaPh2AFA in the presence of PPh3, and preliminary investigations have shown that its activation with [Ni(COD)2] as a phosphine scavenger provides species active toward ethylene oligomerization and polymerization.

The facile syntheses and the structures of five new Cu(I) alkynyl clusters, [Cu(12)(hfac)(8)(C[triple chemical bond]CnPr)(4)(thf)(6)]xTHF (1), [Cu(12)(hfac)(8)(C[triple chemical bond]CtBu)(4)] (2), [Cu(12)(hfac)(8)(C[triple chemical bond]CSiMe(3))(4)] (3), [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)]/[Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(3)(C[triple chemical bond]CnPr)(diethyl ether)] (4) and [Cu(10)(hfac)(6)(C[triple chemical bond]CtBu)(4)(diethyl ether)] (5) are reported, in which hfacH=1,1,1,5,5,5-hexafluoropentan-2,4-dione. The first independent molecule found in the crystals of 4 (4 a) proved to be chemically identical to 5. The Cu(10) and Cu(12) cores in these clusters are based on a central "square" Cu(4)C(4) unit. Whilst the connectivities of the Cu(10) or Cu(12) units remain identical the geometries vary considerably and depend on the bulk of the alkynyl group, weak coordination of ether molecules to copper atoms in the core and CuO intramolecular contacts formed between Cu-hfac units on the periphery of the cluster. Similar intermolecular contacts and interlocking of Cu-hfac units are formed in the simple model complex [Cu(2)(hfac)(2)(HC[triple chemical bond]CtBu)] (6). When linear alkynes, C(n)H(2n+1)C[triple chemical bond]CH, are used in the synthesis and non-coordinating solvents are used in the workup, further association of the Cu(4)C(4) cores occurs and clusters with more than eighteen copper atoms are isolated.

The tripodal ligands hydrotris(N-ethyl-2-mercaptoimidazol-1-yl)borate (NaTm E t ) (1) and hydrotris(N-benzyl-2-mercaptoimidazol-1-yl)borate (NaTm B n ) (2), analogues of the hydrotris(N-methyl-2-mercaptoimidazol-1-yl)borateligand (Tm) containing alternative nitrogen substituents, have been employed to examine the racemization of their C 3 -symmetric complexes with both four- and six-coordinate metals. The ligands react at room temperature with metal halides to provide C 3 -symmetric metal complexes. The syntheses of the four-coordinate complexes [Tm E t ZnCl] (3), [Tm E t CdBr] (4), [Tm E t HgCl] (5), [Tm E t CuPPh 3 ] (6), [Tm E t AgPPh 3 ] (7), and [Tm B n ZnCl] (8) are reported. The six-coordinate complexes [Tm E t RU(p-cymene)]Cl (9), [Tm E t Ru(p-cymene)]PF 6 (10), and [Tm E t Mn(CO) 3 ] (11) were also synthesized. The X-ray crystal structures of 3, 4, 6, and 9 are reported. The diastereotopic nature of the ethyl and benzyl hydrogen atoms in the ligands allows the enantiomeric forms of these complexes to be distinguished by 1 H NMR spectroscopy. Variable-temperature (VT) 1 H NMR spectra have thus been used to investigate the energies of the racemization processes occurring in these chiral complexes. In solvents the activation energies to racemization for the four-coordinate complexes lay in the range of 53-77 kJ mol - 1 . In non-donor solvents the energies are reduced and a dissociative mechanism is therefore implicated. No interconversion could be observed by VT NMR for the six-coordinate complexes in any solvent. To further explore the racemization mechanisms ab initio density functional theory calculations have been conducted on the ground- and transition-state structures of representative six-coordinate [Mn(I)] and four-coordinate [Zn(ll)] complexes following a proposed nondissociative mechanism of racemization. The calculated energy barriers to racemization are 163 and 121 kJ mol - 1 , respectively. It is concluded that the low-energy racemization of substitution-labile four-coordinate complexes occurs via a dissociative mechanism, while substitution-inert six-coordinate complexes experience a significantly higher barrier to racemization. Whether this is due to the operation of a dissociative mechanism with a higher activation barrier or to a nondissociative mechanism remains unknown.

Treatment of the chloro-bridged dimers [{Rh(η-C5Me5)Cl2}2] and [{Ru(η-MeC6H4Pri-p)Cl2}2] with 1,2,3-triphenylguanidine in toluene solution led to the formation of [Rh(η-C5Me5){η2-(NPh)2CNHPh}Cl]1 and [Ru(η-MeC6H4Pri-p){η2-(NPh)2CNHPh}Cl]2 respectively. These represent the first examples of complexes containing guanidine anions as chelating ligands. Crystal structure analyses of both complexes have been performed.

Species containing the Y-shaped CN3 unit have recently attracted increasing attention as electronically and sterically flexible ligands. Neutral guanidines [(R2N)2CNR], guanidinates(−1) [(RN)2CNR2]− and guanidinates(2) [(RN)2CNR]2− are capable of exhibiting a variety of coordination modes and a range of donor properties leading to compatibility with a remarkably wide range of metal ions from all parts of the periodic table. The coordination chemistry of these species is reviewed up to July 2000, and aspects of their electronic structures and metal-ligand bonding characteristics discussed.

The reaction of the octahedral dianion [Ru 6 (CO) 18 ] 2− with trifluoromethanesulphonic (triflic) anhydride [(CF 3 SO 2 ) 2 O] quantitatively yields the neutral carbido-cluster [Ru 6 C(CO) 17 ] as a result of the cleavage of a coordinated carbonyl ligand.

The thiazolidinediones are novel insulin sensitizers that serve as orally active antidiabetic agents, in rodents, nonhuman primates, and man. We have examined the effects of 4-week oral administration of three thiazolidinediones (AD-5075, BRL 49653, and CS-045) on plasma glucose and triglyceride concentrations in obese hyperglycemic db/db mice. All three agents lower plasma glucose and triglyceride concentrations. Normal levels of glucose are achieved after treatment with AD-5075 (1.7 mg/kg) or BRL 49653 (or = 30 mg/kg), whereas CS-045 (100 or 300 mg/kg) produces only modest reductions in either parameter. Although the thiazolidinediones have demonstrated insulin-sensitizing activities both in vivo and in vitro, their primary molecular target has been unclear. We have compared the in vivo antidiabetic actions described above with the in vitro activities on peroxisomal proliferator-activated receptor-gamma (PPAR gamma). Hamster PPAR gamma 1 was transiently expressed in COS-1 cells to study the binding of [3H]AD-5075. The concentrations of compounds needed to displace radiolabeled AD-5075 from PPAR gamma correlate with their in vivo potency; the Ki values for displacement by cold AD-5075, BRL 49653, and CS-045 are 22, 68, and 1600 nM, respectively. To examine activation of the receptor, it was transiently cotransfected into COS-1 cells with a reporter plasmid containing two copies of a peroxisome proliferator response element. The EC50 values for activation are 2, 6, and 140 nM for AD-5075, BRL 49653, and CS-045, respectively. We have also analyzed limited proteolytic digests of in vitro translated hamster PPAR gamma. The thiazolidinediones produce a conformational change in PPAR gamma analogous to those produced by agonists of other nuclear hormone receptors. In the presence of saturating concentrations of either AD-5075 or BRL 49653, a receptor fragment of 27 kDa is protected from proteolysis by trypsin. These data support the conclusion that the antidiabetic actions of the thiazolidinediones are directly mediated through binding to PPAR gamma and the resulting active conformation of the receptor. Therefore, binding and transactivation assays using PPAR gamma should serve to identify other novel therapeutic agents with potential antidiabetic activities.

The pursuit of heteroleptic 'half-sandwich' complexes of boron substituted anionic and charge-neutral tris(methimazolyl)borate ligands is described. The formation of the homoleptic 'sandwich' complexes was found to be favoured when the metal precursor contains labile ligands. When unable to form these homoleptic complexes Tm is shown to preferentially coordinate in a κ²-[S,S] fashion. This study reinforces previous assertions that the Tm ligand preferentially adopts the κ²-[S,S] mode when coordinated to electron rich metal centres and demonstrates the strong electron donor properties of substituted Tm ligands.

Interactions, particularly hydrogen bonds, between ligands in the outer coordination spheres of metal complexes have a major effect on their stabilities in the hydrocarbon solvents used in commercial solvent extraction and it is now possible to use these interactions to tune the strength and selectivity of extractants.

Two magnesium complexes of the 6-aminofulvene-2-aldimine (AFA) system bearing cyclohexyl groups on the donor nitrogen atoms have been synthesised; in the first the ligand is coordinated via the two nitrogen donors while in the second it is found to ligate magnesium via the cyclopentadienyl and the imine donors.

The synthesis, crystallography and solution luminescence properties of [Cu18(hfac)10(CCC4Hn9)8] are reported.

The title compound 2-(2,6-diiso­propyl­phenyl­amino)-4-(2,6-diiso­propyl­phenyl­imino)­pent-2-ene crystallizes as a toluene solvate, C29H42N2·0.5C7H8; the observed bond lengths are consistent with delocalization of the imino and alkene double bonds across the N—C—C—C—N backbone.

Treatment of dimethylmagnesium with the alpha-diimine ligands Ar'N=C(R)C(R)=NAr' [R = naphth-1,8-diyl (1), H (2), CH3 (3); Ar' = 2,6-diisopropylphenyl] in diethyl ether provides the neutral methyl-bridged dimeric complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET) to the coordinated diimine and elimination of a methyl radical. These biradical species have been characterised by EPR spectroscopy and, for the ligand , X-ray crystallography. In the presence of THF the reaction of ligand proceeds to the diamagnetic [(ene-1,2-diamide)Mg(THF)3] complex in which the diimine ligand has been doubly reduced to an ene-diamide by two successive SET processes. Comparison of the structural data for the free ligand with that obtained for the alpha-diimine radical anion and ene-diamide complexes shows the expected increases in C-N, and decreases in C-C, bond lengths within the N-C-C-N unit consistent with the progressive reduction of the ligand. In the case of ligand , reaction at low temperature provides the complex [Mg(mu2-Me){Ar'NC(Me)2C(Me)NAr'}]2 in which methyl transfer to a ligand imine carbon atom has occurred. This species has also been structurally characterised. This contrasts with the formation of the radical species at room temperature, and indicates the involvement of an intermediate in which the radical products of the SET process are held in close proximity by the solvent cage. Two competing processes of methyl radical escape and methyl transfer to the ligand account for the formation of the observed products at different temperatures.

The title compound, 1,3-bis[(S)-(-)-1 -phenylethyl]thiourea, C 7 H 20 N 2 S, exhibits bond lengths and angles consistent with the build-up of negative charge on the S atom. There are weak hydrogen bonds between molecules leading to helices disposed about crystallographic 3 1 axes.