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The title compound, (C6H8N4)[Mn(H2O)6](SO4)2, was obtained by cocrystallization of 2,2′-biimidazolium sulfate and bis(tetrabutylammonium) tetrachloridomanganate(II). The asymmetric unit contains one isolated (SO4)2− anion, one half of an octahedral [Mn(H2O)6]2+ dication and one half of a 2,2′-biimidazolium dication, each of which lies on an inversion centre. Molecules are connected by a three-dimensional N—H...O and O—H...O hydrogen-bond network.

The structure of the centrosymmetric title compound, [Cu2Cl6(C10H15N4)2]·2H2O, consists of a dimeric [{(HMe4bpz)CuCl3}2] unit (HMe4bpz is 3,3′,5,5′-tetramethyl-4,4′-bipyrazol-1-ium) with two solvent water molecules. Each [HMe4bpz]+ cation is bonded to a CuCl3 unit through a Cu—N dative bond, effectively making square-planar geometry at the Cu atom. Two of these units then undergo a face-to-face dimerization so that the Cu atoms have a Jahn–Teller distorted square-pyramidal geometry with three chlorides and an N atom in the basal plane and one chloride weakly bound in the apical position. Several N—H...Cl, O—H...Cl and N—H...O hydrogen bonds form a three-dimensional network.

The asymmetric unit of the title compound, (C4H5N2O)2[Cu2Cl6(C4H4N2O)2]·2H2O, consists of one cation, one half of a centrosymmetric dianion and one water molecule. The centrosymmetric dianion formed by dimerization in the crystal structure has neutral pyrimidin-2-one ligands coordinated to each copper(II) centre through Cu—N bonds. The Cu atoms each have a distorted trigonal bipyramidal geometry, with the N atom of the pyrimidin-2-one ligand in an axial position, and dimerize by sharing two equatorial Cl atoms. N—H...Cl, O—H...Cl and N—H...O hydrogen bonds connect the anions, cations and water molecules, forming a three-dimensional network.

The title compound, (C4H5N2O)5[Cd3Cl11], was obtained from the reaction of 2-hydroxypyrimidine hydrochloride and cadmium(II) chloride in concentrated HCl solution. The crystal structure consists of planar 2-oxo-1,2-dihydropyrimidin-3-ium cations with both N atoms protonated and the O atom unprotonated, and a complex trinuclear [Cd3Cl11]5− anion of approximately D3h symmetry, which has a triangle of three octahedrally coordinated CdII centres bonded to 11 chloride ions. Three of the chloride ions bridge adjacent Cd atoms, two cap the faces of the Cd3 triangle and the remaining six are terminally bonded and act as hydrogen-bond acceptors. Various N—H...Cl hydrogen bonds connect the anions and cations and, in addition, intermolecular N—H...O hydrogen bonds contribute to the formation of a three-dimensional network.

In the title compound, [CuCl2(C4H4N2O)(H2O)], the CuII cation is coordinated by two chloride anions, one pyrimidin-2-one N atom and one water molecule, giving a slightly distorted square-planar geometry. In the crystal structure, the pyrimidin-2-one rings stack along the b axis, with an interplanar distance of 3.306 Å, as do the copper coordination planes (interplanar spacing = 2.998 Å). The coordination around the Jahn–Teller-distorted CuII ion is completed by long Cu...O [3.014 (5) Å] and Cu...Cl [3.0194 (15) Å] interactions with adjacent molecules involved in this stacking. Several N—H...Cl, O—H...Cl and O—H...O intermolecular hydrogen bonds form a polar three-dimensional network.

The two-step mechanochemical preparation of carbene–pyridine complexes of palladium and platinum is reported. The organometallic products, which represent a class of commercially available catalysts, are rapidly formed in excellent yield proving solvent-free synthesis to be a viable synthetic alternative even in the case of NHC-containing compounds. [ABSTRACT FROM AUTHOR]

The tricarbonyl [Mn(CO)3{HC(pz′)3}][PF6] 1+[PF6]−(pz′ = 3,5-dimethylpyrazolyl) reacts with a range of P-, N- and C-donor ligands, L, in the presence of trimethylamine oxide to give [Mn(CO)2L{HC(pz′)3}]+{L = PEt33+, P(OEt)34+, P(OCH2)3CEt 5+, py 6+, MeCN 7+, CNBut8+and CNXyl 9+}. The complex [Mn(CO)2(PMe3){HC(pz′)3}]+2+is formed by reaction of 7+with PMe3. Complexes 2+and 6+were structurally characterised by X-ray diffraction methods. Reaction of 7+with half a molar equivalent of 4,4′-bipyridine gives a purple compound assumed to be the bridged dimer [{HC(pz′)3}Mn(CO)2(μ-4,4′-bipy)Mn(CO)2{HC(pz′)3}]2+102+. The relative electron donating ability of HC(pz′)3has been established by comparison with the cyclopentadienyl and tris(pyrazolyl)borate analogues. Cyclic voltammetry shows that each of the complexes undergoes an irreversible oxidation. The correlation between the average carbonyl stretching frequency and the oxidation potential for complexes of P- and C-donor ligands is coincident with the correlation observed for [Mn(CO)3−mLm(η-C5H5−nMen)]. The data for complexes of N-donor ligands, however, are not coincident due to the presence of a node (and phase change) between the metal and the N-donor in the HOMO of the complex as suggested by preliminary DFT calculations. [ABSTRACT FROM AUTHOR]

A series of crystalline salts based on the complex dianion [Fe(dto)2(NO)]2−(dto = 1,2-dithiooxalate) with hydrogen-bond donor cations have been synthesised. The preparation and structural characterisation of the new crystalline phases [4,4′-H2bipy][Fe(dto)2(NO)]·H2O (1), [3,3′-H2bipy][Fe(dto)2(NO)] (2) and [H2Me4bipyz][Fe(dto)2(NO)]·2H2O (3) (Me4bipyz = 3,3′,5,5'-tetramethyl-4,4′-bipyrazole) are reported, and show that a charge-assisted NHdto synthon is formed in each of compounds 1–3. In compound 1the anion forms a dimer in the solid-state, and variable temperature magnetic susceptibility measurements reveal a weak antiferromagnetic interaction with a best fit superexchange parameter J= –3.18 (2) cm−1, where H= –2JS1S2. [ABSTRACT FROM AUTHOR]

The homodiphosphanes CgP–PCg (1) and PhobP–PPhob (2) and the heterodiphosphanes CgP–PPhob (3), CgP–PPh2(4a), CgP–P(o-Tol)2(4b), CgP–PCy2(4c), CgP–PtBu2(4d), PhobP–PPh2(5a), PhobP–P(o-Tol)2(5b), PhobP–PCy2(5c), PhobP–PtBu2(5d) where CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been prepared from CgP(BH3)Li or PhobP(BH3)Li and the appropriate halophosphine. The formation of 1is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1. Restricted rotation about the P–P bond of the bulky meso-1is detected by variable temperature 31P NMR spectroscopy. Diphosphane 3reacts with BH3to give a mixture of CgP(BH3)–PPhob and CgP–PPhob(BH3) which was unexpected in view of the predicted much greater electron-richness of the PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in order to determine their propensity for diphosphination. The homodiphosphanes 1and 2did not react with DMAD. The CgP-containing heterodiphosphanes 4a–dall added to DMAD to generate the corresponding cisalkenes CgPCH(CO2Me)CH(CO2Me)PR2(6a–d) which have been used in situto form chelate complexes of the type [MCl2(diphos)] (7a–d) where M = Pd or Pt. The PhobP-containing heterodiphosphanes 3and 5a–dreact anomalously with DMAD and do not give the products of diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and dioxide of diphosphane 1, and the platinum chelate complex 7chave been determined and their structures are discussed. [ABSTRACT FROM AUTHOR]

para-Phenylenediamine (ppda) may be ground together with metal chloride salts MCl2to produce the coordination network compounds [{(ppda)MCl2}n] {M = Zn (2), Cd (4), Cu (6)}. Its dihydrochloride salt [H2ppda]Cl2can be ground with MCl2to produce the layered salt structures [H2ppda][MCl4] {M = Zn (1), Cd (3), Cu (5)}, which (when M = Zn or Cd) may then be converted into 2or 4respectively by grinding with solid KOH. Alternatively, [H2ppda][MCl4] will react directly with appropriate basic metal compounds (hydroxides and/or carbonates) to give 2or 4, which can then be converted back to the salts by reaction with gaseous HCl. The interconversion of 5and 6is more complicated, with different combinations of starting material giving different products. The crystal structure of 2has been solved ab initiofrom the powder-diffraction data, and is shown to consist of zigzag polymeric chains containing alternating ppda and MCl2units. [ABSTRACT FROM AUTHOR]

Reaction of [Pd(PPh3)4] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl2(PPh3)(C3(Ar)2)] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)2] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl2(C3(Ar)2)]2(Ar = Ph 7, p-(OMe)C6H48, p-(F)C6H49). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl2(NCMe)(C3(Ar)2)] (Ar = Ph 10, p-(OMe)C6H411and p-(F)C6H4) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7or acetonitrile adducts 11and 12gave complexes of the type cis-[PdCl2(PR3)(C3(Ar)2)] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C6H4, R = Ph 14, Ar = p-(F)C6H4, R = Ph 15). Crystal structures of complexes 6·3.25CHCl3, 10, 11·H2O and 12–15are reported. DFT calculations of complexes 10–12indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5–9were tested for catalytic activity in C–C coupling (Mizoroki–Heck, Suzuki–Miyaura and, for the first time, Stille reactions) and C–N coupling (Buchwald–Hartwig amination) showing excellent conversion with moderate to high selectivity. [ABSTRACT FROM AUTHOR]

The potassium salts of the new S2N-heteroscorpionate ligand hydrobis(methimazolyl)(3,5-dimethylpyrazolyl)borate [HB(mt)2(pz3,5-Me)]−and its known analogue hydrobis(methimazolyl)(pyrazolyl)borate [HB(mt)2(pz)]−(prepared from KTp′ or KTp and methimazole, Hmt), and the adduct KTp·Hmt have polymeric structures in the solid state (the first a ladder and the other two chains). The iridaboratranes [IrHLL′{B(mt)2X}] (X = pz3,5-Meor pz), prepared from the heteroscorpionate anion and [{Ir(cod)(μ-Cl)}2] (LL′ = cod), subsequent carbonylation [LL′ = (CO)2] and then reaction with phosphine [LL′ = (CO)(PR3), R = Ph or Cy], have a pendant pyrazolyl ring and a bicyclo-[3.3.0] cage formed by an S2-bound B(mt)2fragment. The binuclear species [(cod)HIr{μ-B(mt)3}IrCl(cod)], the only isolated product of the reaction of KTm with [{Ir(cod)(μ-Cl)}2], also has an S2-bound iridaboratrane unit but with the third mt ring linked to square planar iridium(i). [ABSTRACT FROM AUTHOR]

[{(4,4′-bipy)ZnCl2}n] (4) is known in three different polymorphs, in the space groups C2/c(4a), Pnma(4b) and Pban(4c). Solution synthesis produces a mixture of 4aand 4b, but solid-state synthesis, either by grinding together 4,4′-bipy and ZnCl2or by heating [4,4′-H2bipy][ZnCl4] 3to thermally eliminate HCl, generates only the 4bform, demonstrating that solid-state synthesis can exert control over polymorph formation; other solid-state preparations of 4such as reaction of basic zinc carbonate with [4,4′-H2bipy]Cl2or reaction of [4,4′-H2bipy][ZnCl4] 3with KOH also increase the amount of 4bgenerated relative to the solution synthesis. It is also possible to form the mixed-metal phases [{(4,4′-bipy)Co1−xZnxCl2}n] 4xas effectively homogeneous solid-solutions by the same techniques, and when x< 0.5 (i.e.there is more cobalt present than zinc) then only the Pbanpolymorph of the solid-solution is observed. When x> 0.5, the amount of this polymorph is still greater than would be expected for a predominantly zinc-containing phase. [ABSTRACT FROM AUTHOR]

The reaction of potassium hydrotris(methimazolyl)borate {KTm = HB(mt)3} with [{Rh(cod)(μ-Cl)}2] gave [Rh(cod)Tm] while the complexes [Rh(CO)(PR3)Tm] (R = Ph or NMe2) and [Rh{P(OPh)3}2Tm] were isolated from light-sensitive [Rh(CO)2Tm], prepared in situfrom KTm and [{Rh(CO)2(μ-Cl)}2], and PR3or P(OPh)3under CO. The complexes [Rh(cod)Tm] and [Rh(CO)(PR3)Tm] (R = Ph or NMe2) adopt κ3-S2Hstructures in the solid state but in all cases rapid dynamic exchange processes render the three mt rings equivalent in solution. Oxidation of [Rh(CO)(PPh3)Tm] with [Fe(η-C5H5)2][PF6] in the presence of NHPri2gave a mixture containing two monocationic rhodaboratranes. One is assigned as [Rh(CO)(PPh3){B(mt)3}][PF6] on the basis of IR and NMR spectroscopy, with boron transto the phosphine ligand. The second, structurally characterised as [Rh(PPh3){B(mt)3}][PF6], has boron transto an empty coordination site, vacated by CO. Similar oxidation of [Rh(cod)Tm] gave small quantities of the boron-fluorinated bis(scorpionate) [Rh{FB(mt)3}2][PF6]. [ABSTRACT FROM AUTHOR]

A series of symmetric and unsymmetric N,N-bis(diarylphosphino)amine (‘PNP’) ligands (Ar2PN(R)PNAr′2: R = Me, Ar2= o-anisyl, Ar′2= Ph, 1, R = Me, Ar2= o-tolyl, Ar′2= Ph, 2, R = Me, Ar2= Ph(o-ethyl), Ar′2= Ph, 3, R = Me, Ar2= Ar′2= o-anisyl, 4, R = iPr, Ar2= Ar′2= Ph, 5) and symmetric N,N′-bis(diarylphosphino)dimethylhydrazine (‘PNNP’) ligands (Ar2PN(Me)N(Me)PAr2: Ar2= o-tolyl, 6, Ar2= o-anisyl, 7) have been synthesised. Catalytic screening for ethene/styrene co-trimerisation and isoprene trimerisation was performed viathe in situcomplexation to [CrCl3(THF)3] followed by activation with methylaluminoxane (MAO). PNNP catalytic systems showed a significant increase in activity and selectivity over previously reported PNP systems in isoprene trimerisation. Comparing the symmetric and unsymmetric variants in ethene and styrene co-trimerisation resulted in a switch in selectivity, an unsymmetric catalytic (o-anisyl)2PN(Me)PPh2(1) ligand system affording unique incorporation of two styrenic monomers into the co-trimer product distribution differing from the familiar two ethene and one styrene ω-substituted alkenes. Complexes of the type [(diphosphine)Cr(CO)4] 8–11were also synthesised, the single-crystal X-ray diffraction of which are reported. We propose the mechanisms of these catalytic transformations and an insight into the effect of the ligand series on the chromacyclic catalytic intermediates. [ABSTRACT FROM AUTHOR]

We describe the development of a ligand knowledge base designed to capture the properties of C-donor ligands coordinating to transition metal centres, LKB-C. This knowledge base has been developed to describe both singlet (Arduengo and Fischer) and triplet (Schrock) carbenes, as well as related neutral monodentate C-donor ligands. The descriptors evaluated and used have been derived from a range of coordination environments to maximise their transferability and hence utility for the investigation of such ligands. These descriptors have been analysed with different statistical approaches, both individually to determine their chemical context, and collectively by principal component analysis thereby allowing the derivation of maps of ligand space for different ligand sets. The utility of such maps for investigating ligand similarity and identification of target areas for future ligand designs has been discussed. In addition, linear regression models have been fitted for the prediction of a calculated response variable, highlighting further potential applications of such a knowledge base. [ABSTRACT FROM AUTHOR]

The optically pure monophosphites P(OAr)(BINOLate) (7, where Ar = 2,4-di-tert-butylphenyl) have been prepared by treatment of PCl2(OAr) with R- or S-BINOL. Treatment of [PdCl2(NCMe)2] with 7gave [PdCl2(7)2] (9) or the binuclear orthometallated complex [Pd2Cl2(7-H)2] (8) depending on the reaction conditions. Bridge cleavage reactions of 8gave [PdCl(7-H)(L)] with L transto carbon when L = PPh3or 7and cisto carbon when L = N-heterocyclic carbene. Treatment of [PtCl2(NCtBu)2] with 7gave [PtCl2(7)2] (18) which upon further reaction with PtCl2furnished a mixture of binuclear [Pt2Cl2(7-H)2] (17) and cis-[PtCl(7-H)(7)] (19). The palladium complexes containing cyclometallated 7were screened for catalysis of 1,4-conjugate addition of phenylboronic acid to cyclohexen-2-one and the allylation of benzaldehyde with allyltributyltin. Conversions were generally high in each case but enantioselectivities were low (15% e.e. at best). The X-ray crystal structures of 8, 17and [PdCl(7-H)(NHC)] (10a, where NHC = 1,3-(dimesityl)imidazolidin-2-ylidene) have been determined. [ABSTRACT FROM AUTHOR]

The new sterically encumbered facially coordinating N3-donor ligand cis,cis-1,3,5-tris(mesitylideneimino)cyclohexane (L1) has been synthesised. Reaction with [Cu(NCCH3)4]PF6 gives [Cu(L1)NCCH3]PF6(1), the bound acetonitrile being labile and readily replaced by CO to yield [Cu(L1)CO]PF6 (2); both 1 and 2 have been structurally characterised. Complexes 1 and 2 do not undergo a substitution reaction with ethylene. This is in contrast to the related bidentate ligand complexes [Cu(L2)NCCH3]BF4 (3) or [Cu(L2)CO]BF4 (4) (L2 = 1,2-bis(mesitylideneamino)cyclohexane) which rapidly form the ethylene complex under the same conditions. [ABSTRACT FROM AUTHOR]

The new sterically encumbered facially coordinating N3-donor ligand cis,cis-1,3,5-tris(mesitylideneimino)cyclohexane (L1) has been synthesised. Reaction with [Cu(NCCH3)4]PF6gives [Cu(L1)NCCH3]PF6(1), the bound acetonitrile being labile and readily replaced by CO to yield [Cu(L1)CO]PF6(2); both 1and 2have been structurally characterised. Complexes 1and 2do not undergo a substitution reaction with ethylene. This is in contrast to the related bidentate ligand complexes [Cu(L2)NCCH3]BF4(3) or [Cu(L2)CO]BF4(4) (L2= 1,2-bis(mesitylideneamino)cyclohexane) which rapidly form the ethylene complex under the same conditions. [ABSTRACT FROM AUTHOR]

The homologous series of diphosphines (CH2)n−1P(CH2)3P(CH2)n−1where n= 5 (L5), 6 (L6), or 7 (L7) have been synthesized from the corresponding PhP(CH2)n−1. Treatment of [PtCl2(cod)] with L5–7gave the 6-membered chelates cis-[PtCl2(L5–7)], the crystal structures for which reveal that L5–7have very similar steric bulk and bite angles. Treatment of [Rh2Cl2(CO)4] with L5–7gave the binuclear trans-[Rh2Cl2(CO)2(μ-L5–7)2] with synand antiorientations of the CO and Cl ligands suggested by the 31P NMR spectra and the crystal structures of syn–trans-[Rh2Cl2(CO)2(μ-L5)2] and anti–trans-[Rh2Cl2(CO)2(μ-L7)2]. The ν(CO) values for trans-[Rh2Cl2(CO)2(μ-L5–7)2] indicate that the donor strength increases in the order L5 L6> L7. [ABSTRACT FROM AUTHOR]

The d4halide complexes [MX(CO)(η-RCCR)Tp′] {R = Me, M = W, X = F; R = Ph, M = Mo or W, X = F or Cl; Tp′ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo two-electron oxidation in the presence of a halide source to give the d2monocations [MX1X2(η-PhCCPh)Tp′](R = Me, M = W, X1= X2= F; R = Ph, M = Mo, X1= X2= F or Cl; M = W, X1= X2= F or Cl; X1= F, X2= Cl). Each monocation (R = Ph) shows two reversible one-electron reductions (the second process was not detected for R = Me) corresponding to the stepwise formation of the neutral d3and monoanionic d4analogues, [MX1X2(η-PhCCPh)Tp′] and [MX1X2(η-PhCCPh)Tp′]−respectively; the potentials for the two processes can be ‘tuned’ over a range of ca.1.0 V by varying M and X. Chemical one-electron reduction of [MX2(η-PhCCPh)Tp′]膫 [MX2(η-PhCCPh)Tp′] (M = Mo or W, X = F or Cl). X-Ray structural studies on the redox pairs [WX2(η-PhCCPh)Tp′]z(X = F and Cl, z= 0 and 1) show the alkyne to bisect the X–W–X angle in the d2cations but align more closely with one M–X bond in the neutral d3molecules, consistent with the anisotropic ESR spectra of the latter; the solution ESR spectrum of [MoF2(η-PhCCPh)Tp′] showed equivalent fluorine atoms, i.ethe alkyne oscillates at room temperature. The successful isolation of [MX2(η-PhCCPh)Tp′]橷 [MX2(η-PhCCPh)Tp′] completes a series in which d6to d2alkyne complexes are linked in a redox family tree by sequential one-electron transfer and substitution reactions. The implications for such trees in the production of new species and the selective synthesis of paramagnetic complexes acting as synthetically useful ‘alkyne radicals’ are discussed. [ABSTRACT FROM AUTHOR]

The preparation of the complex salts [H2im]2[MCl4] (H2im = imidazolium, M = Co, 1; Zn, 2; Cu, 3) and coordination compounds [MCl2(Him)2] (M = Co, 4; Zn, 5; Cu, 6) by a range of solid-state and solid-gas reactions is reported. Compounds 4–6and the related [{MCl2(4,4′-bipy)}n] (M = Co, 7; Zn, 8) were prepared by the solid state reactions of metal hydroxide or carbonate salts (or their equivalent) with the hydrochloride salt of the appropriate ligand (imidazole or 4,4′-bipy). [ABSTRACT FROM AUTHOR]

Rhodium and iridium complexes of flexible scorpionate ligands based on azaindole were synthesised in good yields. The complexes were characterised in solution and in the solid state. Structural characterisation revealed a B–H–metal interaction, which is retained in solution. Given the greater flexibility of the ligand and potential cooperative effect of boron, the complexes were tested for their activity in the transfer hydrogenation of ketones. [ABSTRACT FROM AUTHOR]

The reaction of [Mn(CN)L′(NO)(η5-C5R4Me)] with cis- or trans-[MnBrL(CO)2(dppm)], in the presence of Tl[PF6], gives homobinuclear cyanomanganese(i) complexes cis- or trans-[(dppm)(CO)2LMn(µ-NC)MnL′(NO)(η5-C5R4Me)]+, linkage isomers of which, cis- or trans-[(dppm)(CO)2LMn(µ-CN)MnL′(NO)(η5-C5R4Me)]+, are synthesised by reacting cis- or trans-[Mn(CN)L(CO)2(dppm)] with [MnIL′(NO)(η5-C5R4Me)] in the presence of Tl[PF6]. X-Ray structural studies on the isomers trans-[(dppm)(CO)2{(EtO)3P}Mn(µ-NC)Mn(CNBut)(NO)(η5-C5H4Me)]+ and trans-[(dppm)(CO)2{(EtO)3P}Mn(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)]+ show nearly identical molecular structures whereas cis-[(dppm)(CO)2{(PhO)3P}Mn(µ-NC)Mn{P(OPh)3}(NO)(η5-C5H4Me)]+ and cis-[(dppm)(CO)2{(PhO)3P}Mn(µ-CN)Mn{P(OPh)3}(NO)(η5-C5H4Me)]+ differ, effectively in the N- and C-coordination respectively of two different optical isomers of the pseudo-tetrahedral units (NC)Mn{P(OPh)3}(NO)(η5-C5H4Me) and (CN)Mn{P(OPh)3}(NO)(η5-C5H4Me) to the octahedral manganese centre. Electrochemical and spectroscopic studies on [(dppm)(CO)2LMn(µ-XY)MnL′(NO)(η5-C5R4Me)]+ show that systematic variation of the ligands L and L′, of the cyclopentadienyl ring substituents R, and of the µ-CN orientation (XY = CN or NC) allows control of the order of oxidation of the two metal centres and hence the direction and energy of metal–metal charge-transfer (MMCT) through the cyanide bridge in the mixed-valence dications. Chemical one-electron oxidation of cis- or trans-[(dppm)(CO)2LMn(µ-NC)MnL′(NO)(η5-C5R4Me)]+ with [NO][PF6] gives the mixed-valence dications trans-[(dppm)(CO)2LMnII(µ-NC)MnIL′(NO)(η5-C5R4Me)]2+ which show solvatochromic absorptions in the electronic spectrum, assigned to optically induced Mn(i)-to-Mn(ii) electron transfer via the cyanide bridge. [ABSTRACT FROM AUTHOR]

The salts [NEt4][Ru(CN)(CO)2L(o-O2C6Cl4)] {L = PPh3 or P(OPh)3}, which undergo one-electron oxidation at the catecholate ligand to give neutral semiquinone complexes [Ru(CN)(CO)2L(o-O2C6Cl4)], react with the dimers [{Ru(CO)2L(µ-o-O2C6Cl4)}2] {L = PPh3 or P(OPh)3} to give [NEt4][(o-O2C6Cl4)L(OC)2Ru(µ-CN)Ru(CO)2L′(o-O2C6Cl4)] {L or L′ = PPh3 or P(OPh)3}. The cyanide-bridged binuclear anions are, in turn, reversibly oxidised to isolable neutral and cationic complexes [(o-O2C6Cl4)L(OC)2Ru(µ-CN)Ru(CO)2L′(o-O2C6Cl4)] and [(o-O2C6Cl4)L(OC)2Ru(µ-CN)Ru(CO)2L′(o-O2C6Cl4)]+ which contain one and two semiquinone ligands respectively. Structural studies on the redox pair [(o-O2C6Cl4)(Ph3P)(OC)2Ru(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]− and [(o-O2C6Cl4)(Ph3P)(OC)2Ru(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)] confirm that the C-bound Ru(CO)2(o-O2C6Cl4) fragment is oxidised first. Uniquely, [(o-O2C6Cl4){(PhO)3P}(OC)2Ru(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]− is oxidised first at the N-bound fragment, indicating that it is possible to control the site of electron transfer by tuning the co-ligands. Crystallisation of [(o-O2C6Cl4)(Ph3P)(OC)2Ru(µ-CN)Ru(CO)2{P(OPh)3}(o-O2C6Cl4)] resulted in the formation of an isomer in which the P(OPh)3 ligand is cis to the cyanide bridge, contrasting with the trans arrangement of the X–Ru–L fragment in all other complexes of the type RuX(CO)2L(o-O2C6Cl4). [ABSTRACT FROM AUTHOR]

The triazenide-bridged tetracarbonyls [(OC)2Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2] (M = Rh or Ir) undergo oxidative addition of iodine across the dimetal centre, giving the [RhM]4+ complexes [I(OC)2Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2I], structurally characterised for M = Ir. The anionic tricarbonyl iodide [I(OC)Rh(µ-p-MeC6H4NNNC6H4Me-p)2Rh(CO)2]− forms [I2(OC)Rh(µ-p-MeC6H4NNNC6H4Me-p)2Rh(CO)I]− by initial one-electron transfer whereas the analogous tricarbonyl phosphine complexes [(OC)(Ph3P)Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2] (M = Rh or Ir) undergo bridge cleavage, giving mononuclear [Rh(p-MeC6H4NNNC6H4Me-p)I2(CO)(PPh3)] and dimeric [I(OC){RNNN(R)C(O)}M(µ-I)2M{C(O)N(R)NNR}(CO)I] (M = Rh or Ir, R = C6H4Me-p) in which CO has been inserted into a metal–nitrogen bond. [ABSTRACT FROM AUTHOR]

Complexes of the type [(diphosphine)Cr(CO)4] (diphosphine = Ph2PN(iPr)PPh2, Ar2PN(Me)PAr2 or Ar2PCH2PAr2 (Ar = 2-C6H4(MeO)) have been synthesised. In the solid state, these complexes show tight phosphine bite angles in the range 67.82(4)° to 71.52(5)° and the nitrogen atom in N,N-bis(diarylphophino)amine ligands adopts an almost planar (sp2) geometry. All of the complexes are readily oxidised electrochemically or chemically to corresponding Cr(i) species. There is no evidence for coordination of the pendant ether group in derivatives with Ar = 2-MeO-C6H4 in either Cr(0) or Cr(i) species. Treatment of the [(diphosphine)Cr(CO)4] complexes with [NO]BF4 yields [(diphosphine)Cr(NO)(CO)3]BF4. Removal of CO ligands to generate an oligomerisation-active species is not observed with amine oxides but triethyl aluminium is effective in this role, and active catalysts can be produced. The use of weakly coordinating anions seems crucial in achieving oligomerisation catalysis. [ABSTRACT FROM AUTHOR]