Oxidation of [Ir(η-C5Me5)(C8H4S8)] and crystal structures of [IrI(η-C5Me5)(C8H4S8)](I3) and [IrI(η-C5Me5)(C8H4S8)](I3)1/2(I7)1/2

[Ir(η⁵-C₅Me₅)(C₈H₄S₈)] (1) [ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] was reacted with iodine in dichloromethane to afford one-electron- and two-electron-oxidized species [IrI(η⁵-C₅Me₅)(C₈H₄S₈)] (2), [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₃) (3) and [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₅) (4). The oxidized species exhibit electrical conductivities of (1.1-5.0) × 10⁻⁶ S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized complexes 3 and 4 revealed the Ir-I bonds for both of them and the presence of for 3 and ions for 4 as the counter anions. They have many S-S and S-I non-bonding contacts to form two-dimensional molecular interaction sheets in the solid state.     

Reactions of the pentamethylcyclopentadienyl trisulfido tungsten with M′Cl2 (M′ = Zn, Cd, Hg): Isolation and structural characterization of [PPh4][(η-C5Me5)WS3(ZnCl2)] and [{(η-C5Me5)WS3}2Hg]

Reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] with equimolar M′Cl₂ (M′ = Zn, Cd) in MeCN or 0.5 equiv. of HgCl₂ in DMF afforded two binuclear clusters [PPh₄][(η⁵-C₅Me₅)WS₃(M′Cl₂)] (1: M′ = Zn; 2: M′ = Cd) and one trinuclear cluster [{(η⁵-C₅Me₅)WS₃}₂Hg] (3). Compounds 1-3 were characterized by elemental analysis, IR, UV-Vis, ¹H NMR and X-ray crystallography. Compound 1 may be viewed as a 1:1 composite of [PPh₄][(η⁵-C₅Me₅)WS₃] and ZnCl₂, in which one [(η⁵-C₅Me₅)WS₃]⁻ anion binds a ZnCl₂ moiety via two μ-S atoms. In the structure of 3, two [(η⁵-C₅Me₅)WS₃]⁻ anions coordinate the central Hg atom via two μ-S atoms, forming an unique bent linear structure. In addition, internal redox reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] under the presence of M′Cl₂ (M′ = Zn, Cd, Hg) in high concentrations were discussed.     

Metal-sulfur dπ-pπ buffering of the oxidations of metal-thiolate complexes: Photoelectron spectroscopy of (η-C5H5)Fe(CO)2SR (SR = SCH3, SBu) and (η-C5H5)Re(NO)(PR3)SCH3 (PR3 = PPr3, PPh3)

The metal-sulfur bonding present in the transition metal-thiolate complexes CpFe(CO)₂SCH₃, CpFe(CO)₂S^tBu, CpRe(NO)(PⁱPr₃)SCH₃, and CpRe(NO)(PPh₃)SCH₃ (Cp = η⁵-C₅H₅) is investigated via gas-phase valence photoelectron spectroscopy. For all four complexes a strong dπ-pπ interaction exists between a filled predominantly metal d orbital of the [CpML₂]⁺ fragment and the purely sulfur 3pπ lone pair of the thiolate. This interaction results in the highest occupied molecular orbital having substantial M-S π^∗ antibonding character. In the case of CpFe(CO)₂SCH₃, the first (lowest energy) ionization is from the Fe-S π^∗ orbital, the next two ionizations are from predominantly metal d orbitals, and the fourth ionization is from the Fe-S π orbital. The pure sulfur pπ lone pair of the thiolate fragment is less stable than the filled metal d orbitals of the [CpFe(CO)₂]⁺ fragment, resulting in a Fe-S π^∗ combination that is higher in sulfur character than the Fe-S π combination. Interestingly, substitution of a tert-butyl group for the methyl group on the thiolate causes little shift in the first ionization, in contrast to the shift observed for related thiols. This is a consequence of the delocalization and electronic buffering provided by the Fe-S dπ-pπ interaction. For CpRe(NO)(PⁱPr₃)SCH₃ and CpRe(NO)(PPh₃)SCH₃, the strong acceptor ability of the nitrosyl ligand rotates the metal orbitals for optimum backbonding to the nitrosyl, and the thiolate rotates along with these orbitals to a different preferred orientation from that of the Fe complexes. The initial ionization is again the M-S π^∗ combination with mostly sulfur character, but now has considerable mixing among several of the valence orbitals. Because of the high sulfur character in the HOMO, ligand substitution on the metal also has a small effect on the ionization energy in comparison to the shifts observed for similar substitutions in other molecules. These experiments show that, contrary to the traditional interpretation of oxidation of metal complexes, removal of an electron from these metal-thiolate complexes is not well represented by an increase in the formal oxidation state of the metal, nor by simple oxidation of the sulfur, but instead is a variable mix of metal and sulfur content in the highest occupied orbital.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.     

The reaction between orthodiphenylphosphinobenzaldehyde and [(η-C5Me5)MCl(μ-Cl)]2 (M=Rh and Ir)

The benzaldehyde functionalized phosphine Ph₂PC₆H₄CHO-2 underwent reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂ (M=Rh, Ir) to form (η⁵-C₅Me₅)MCl₂(κP-Ph₂PC₆H₄CHO-2), which underwent activation of the aldehyde C-H bond to form (η⁵-C₅Me₅)MCl(κP,κC-Ph₂PC₆H₄CO-2). Formally the reaction involves oxidative addition of C-H across the metal and reductive elimination of HCl. The structure of (η⁵-C₅Me₅)RhCl(κP,κC-Ph₂PC₆H₄CO-2) has been determined by single-crystal X-ray diffraction.     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

Crystallographic and theoretical studies of (η-C5Me5)Ru(2,4-dimethyl-η-pentadienyl) and [(η-C5Me5)Rh(2,4-dimethyl-η-pentadienyl)][BF4]

The determination of the solid state structure of Cp*Ru(2,4-dimethyl-η⁵-pentadienyl) (1), where Cp* = pentamethylcyclopentadienyl, fills the gap in the series of previously established structures of closely related compounds. Compound 1 does not exhibit the ideal C_S symmetry and its conformation is intermediate between the C_S-synperiplanar eclipsed and C_S-antiperiplanar arrangements of the ligands. Density functional theory studies indicate that the C_S-synperiplanar eclipsed, C_S-antiperiplanar, and intermediate conformations of 1 and Cp*Rh(2,4-dimethyl-η⁵-pentadienyl)⁺ (2) do not differ by more than a few tenths of 1 kcal/mol. The geometrical features of cation 2 are similar to those of 1, and in both complexes the pentadienyl ligands are not planar. The metal-carbon distances to the Cp* ligands in 1 and 2 are comparable, while the metal-carbon distances to the pentadienyl moiety are somewhat shorter in the Ru complex. A study of the conformational flexibility of the Cp* ligand in 5610 organometallic complexes showed that it usually shields the central metal by 36.2(10)%, provided the metal-centroid(Cp*) distances are normalized to 2.28 Å. The corresponding values in 1 and 2 are 37.2% and 37.4%, respectively.     

First crystallographic determination of dichloro-bridged dinuclear rhodium Cp* complex with neutral Me2CO molecules. [Rh2(Cp*)2(μ-Cl)2(Me2CO)2](BF4)2 (Cp* = η-C5Me5)

The single crystals of dichloro-bridged dinuclear Rh-Cp* complex with neutral Me₂CO molecules, [Rh₂(Cp*)₂(μ-Cl)₂(Me₂CO)₂](BF₄)₂ (Cp* = η⁵-C₅Me₅), was isolated and the structure was in first determined crystallographically.     

Five-coordinate gold(III) complexes of the Kläui ligands [(η-C5H5)Co{P(O)(OR)2}3] (R = Me, Et)

The reactions of cycloaurated gold(III) dichloride complexes [LAuCl₂] (L = 2-C₆H₄CH₂NMe₂ or 2-C₆H₄PPh₂NPh) with monoanionic tripodal oxygen donor Kläui ligands [(η⁵-C₅H₅)Co{P(O)(OR)₂}₃]⁻ (R = Me or Et) results in the formation of cationic gold(III) salts [LAu{OP(OR)₂}₃Co(η⁵-C₅H₅)]⁺. An X-ray structure determination on [(2-C₆H₄PPh₂NPh)Au{OP(OR)₂}₃Co(η⁵-C₅H₅)]BF₄ shows that the Kläui ligand coordinates strongly to the gold through two oxygen atoms, and weakly through the third, giving the gold(III) a distorted square pyramidal geometry. This is the first structurally characterised example of this geometry for gold(III) with ligands other than those containing rigid bipyridine or phenanthroline backbones. In solution at room temperature there is rapid interchange (on the NMR timescale) between the oxygen atoms of the Kläui ligands, which is frozen out on cooling.     

Syntheses and structural analyses of chiral rhenium containing amines of the formula (η-C5H5)Re(NO)(PPh3)((CH2)nNRR′) (n = 0, 1)

The reaction of the racemic chiral methyl complex (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (1) with CF₃SO₃H and then NH₂CH₂C₆H₅ gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(NH₂CH₂C₆H₅)]⁺ ([4a-H]⁺; 73%), and deprotonation with t-BuOK affords the amido complex (η⁵-C₅H₅)Re(NO)(PPh₃)(NHCH₂C₆H₅) (76%). Reactions of 1 with Ph₃C⁺ X⁻ and then primary or secondary amines give [(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NHRR′)]⁺ X⁻ ([6-H]⁺ X⁻; R/R′/X = a, H/NH₂CH₂C₆H₅/BF₄; a′, H/NH₂CH₂C₆H₅/PF₆; b, H/NH₂CH₂(CH₂)₂CH₃/PF₆; c, H/(S)-NH₂CH(CH₃)C₆H₅/BF₄); d, CH₂CH₃/CH₂CH₃/PF₆; e, CH₂(CH₂)₂CH₃/CH₂(CH₂)₂CH₃/PF₆; f, CH₂C₆H₅/CH₂C₆H₅/PF₆; g, -CH₂(CH₂)₂CH₂-/PF₆; h, -CH₂(CH₂)₃CH₂-/PF₆; i, CH₃/CH₂CH₂OH/PF₆ (62-99%). Deprotonations with t-BuOK afford the amines (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NRR′) (6a-i; 99-40%), which are more stable and isolated in analytically pure form when R ≠ H. Enantiopure 1 is used to prepare (R_ReS_C)-[6c-H]⁺, (R_ReS_C)-6c, (S)-[6g-H]⁺, and (S)-6g. The crystal structures of [4a-H]⁺, a previously prepared NH₂CH₂Si(CH₃)₃ analog, [6a′,d,f,h-H]⁺, (R_ReS_C)-6c, and 6f are determined and analyzed in detail, particularly with respect to cation/anion hydrogen bonding and conformation. In contrast to analogous rhenium containing phosphines, 6a-i show poor activities in reactions that are catalyzed by organic amines.     

A facile reaction of bibenzyl trisulfide with [(η-C5H5)Cr(CO)3]2: formation of a thiolato-bridged dichromium complex of [CpCr(CO)2(SBz)]2 (Bz = PhCH2-)

The reaction of [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅) (1) with an equivalent of Bz₂S₃ at ambient temperature gave [CpCr(CO)₂]₂S (3) [L.Y. Goh, T.W. Hambley, G.B. Robertson, Organometallics 6 (1987) 1051], novel complexes of [CpCr(CO)₂(SBz)]₂ (4) and together with [CpCr(SBz)]₂S (5) as main products. Thermolytic studies showed that 4 underwent complete decarbonylation to give [CpCr(SBz)]₂S (5). Final thermal decomposition of 3 and 5 eventually yielded Cp₄Cr₄S₄ (6) (Goh et al., 1987) after prolonged reaction at 100 °C. However, the reaction of [CpCr(CO)₂]₂ (CrCr) (2) with Bz₂S₃ was much slower at ambient temperature which required 72 h to complete eventually yielding 3 and 5. All the products have been characterized by elemental and spectral analyses. 4 has been structurally determined.     

Macropolyhedral boron-containing cluster chemistry: two-electron variations in intercluster bonding intimacy. Contrasting structures of 19-vertex [(η-C5Me5)HIrB18H19(PHPh2)] and [(η-C5Me5)IrB18H18(PH2Ph)]

Fused double-cluster [(η⁵-C₅Me₅)IrB₁₈H₁₈(PH₂Ph)] (8), from syn-[(η⁵-C₅Me₅)IrB₁₈H₂₀] (1) and PH₂Ph, retains the three-atoms-in-common cluster fusion intimacy of 1, in contrast to [(η⁵-C₅Me₅)HIrB₁₈H₁₉(PHPh₂)] (6), from PHPh₂ with 1, which exhibits an opening to a two atoms-in-common cluster fusion intimacy. Compound 8 forms via spontaneous dihydrogen loss from its precursor [(η⁵-C₅Me₅)HIrB₁₈H₁₉(PH₂Ph)] (7), which has two-atoms-in-common cluster-fusion intimacy and is structurally analogous to 6.     

Synthesis of (β-phenylethynyl)-gem-diphenyltrifluorocyclotriphosphazene and its reaction with RCpCo(PPh3)2 [R = MeOC(O)]

Reaction of gem-diphenyltetrafluorocyclotriphosphazene with in situ generated lithiated phenylacetylene resulted in the formation of the first example of a gem-diphenyltrifluorophosphazene based alkyne (β-phenylethynyl)-gem-diphenyltrifluorocyclotriphosphazene (NPPh₂)(NPF₂)[NP(F)CCPh] 1. Reaction of this alkyne with η⁵-(MeOC(O)C₅H₄)Co(PPh₃)₂ resulted in the formation of a CpCo stabilized cyclobutadiene complex [η⁵-carbomethoxycyclopentadienyl][η⁴-1,3-bis(gem-diphenyltrifluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene]cobalt 2, having two gem-diphenyltrifluorophosphazene moieties trans to each other on the cyclobutadiene ring. The reaction also yielded two structural isomers of the PPh₃ stabilized cobaltacyclopentadiene compounds 3 and 4 having gem diphenyl trifluorophosphazene moieties present in the 2,4 and 2,5 positions of the metallacycle. The reaction in addition yielded a novel spirocyclic phosphazacyclopentadiene compound bound to a CpCo unit in the η⁴-mode 5. All the compounds were characterized by ¹H, ¹³C, ³¹P and ¹⁹F NMR spectroscopy and compounds 2, 3 and 5 were also structurally characterized by X-ray crystallography.     

Syntheses and crystal structures of mononuclear [2.2]paracyclophane complexes of rhodium and iridium supported by the pentamethylcyclopentadienyl ligand [M(η-pcp)(η-C5Me5)](BF4)2 (M=Rh and Ir)

Mononuclear [2.2]paracyclophane complexes of Rh and Ir, [M(η⁶-pcp)(η⁵-C₅Me₅)](BF₄)₂ (M=Rh (1) and Ir (2); pcp=[2.2]paracyclophane) were crystallized and their structures were first characterized crystallographically. On both pcp complexes the metal atom is bonded to the benzene ring on one side of the pcp ligand in the η⁶-coordination mode. The metal atom is also supported by the η⁵-C₅Me₅ ligand to afford a triple-decker sandwich structure. In Rh pcp complex 1 the average RhC(pcp) and RhC(C₅Me₅) distances are 2.284(2) and 2.161(2) Å, respectively. The average C(pcp)C(pcp) distance of 1.407(4) Å with the Rh atom is longer than that (1.388(4) Å) without a Rh atom. Similarly, the average IrC(pcp) and IrC(C₅Me₅) distances in Ir pcp complex 2 are 2.275(3) and 2.174(3) Å, respectively. The average C(pcp)C(pcp) distance of 1.410(4) Å with the Ir atom is longer than that (1.388(4) Å) without an Ir atom. It is interesting that the average interannular distances of 2.97 Å for 1 and 2 between two decks of the pcp ligand are shorter than that (3.09 Å) of the metal-free pcp ligand, indicative of the decrease of the repulsive π-interaction between benzene rings. The Rh pcp complex gave the well-resolved ¹H NMR signals of [Rh(η⁶-pcp)(η⁵-C₅Me₅)]²⁺, whereas the Ir pcp complex exhibited two kinds of ¹H NMR signals which were assigned as [Ir(η⁶-pcp)(η⁵-C₅Me₅)]²⁺ and [Ir₂(η⁶-pcp)(η⁵-C₅Me₅)₂]⁴⁺ in (CD₃)₂CO at 23 °C.     

Synthesis of σ-π-phosphinidene sulfide complexes [Mn2(CO)n(μ-η,η-P(NR2)S)] (n = 8, 9) via direct sulfuration of electrophilic μ-phosphinidenes and photochemical transformation to a trigonal prismatic Mn2P2S2 cluster

The μ-phosphinidene complexes [Mn₂(CO)₈{μ-P(TMP)}] (1) (TMP = tetramethylpiperidyl) and [Mn₂(CO)₈{μ-P(NⁱPr₂)}] (2) react with elemental sulfur to form rare phosphinidene sulfide complexes [Mn₂(CO)₉{μ-η¹,η²-P(TMP)S}] (3) and [Mn₂(CO)₈{μ-η¹,η²-P(NⁱPr₂)S}] (4), respectively. Photolysis of 3 results in the unprecedented conversion to [Mn₂(CO)₆(μ-{κPκ²S}₂-(TMP)(S)P-P(S)(TMP)] (5), which contains a novel 10-electron donor diphosphene disulfide ligand (TMP)(S)P-P(S)(TMP).     

Variation of the electron population by four units in the cluster series [(η-Cp′)3Mo3S4Co(L)] (L = I, CO, PPh3, NO; n = 0, 1)

The versatility of cuboidal Mo₃S₄Co clusters for the preparation of complexes with different numbers of valence shell electrons (VSE) in the cluster is described. The reaction of the geometrically incomplete cuboidal cluster salt [(η⁵-Cp′)₃Mo₃S₄][pts] (pts = p-toluenesulfonate) with one molar equivalent of [Co₂(CO)₈] afforded almost quantitatively the electroneutral 60 VSE cluster [(η⁵-Cp′)₃Mo₃S₄Co(CO)] (1), which previously has been prepared in low yield by Curtis et al. in autoclave syntheses [M.D. Curtis, U. Riaz, O.J. Curnow, J.W. Kampf, Organometallics 14 (1995) 5337]. Cluster 1 was also obtained in high yield by reaction of [(η⁵-Cp′)₃Mo₃S₄][pts] with [(η⁵-Cp^∗)Co(CO)₂]. Reaction of [(η⁵-Cp′)₃Mo₃S₄][pts] with two molar equivalents of [Co(I)(CO)₃(PPh₃)] led to a complex mixture of products, of which the electron deficient 58 VSE cluster salt [(η⁵-Cp′)₃Mo₃S₄Co(I)][Co(I)₃(thf)] ([2][Co(I)₃(thf)]) was isolated as single crystals. In the crystal structures of 1 and [2][Co(I)₃(thf)], the Co-Mo bond lengths are almost identical, indicating a delocalization of the electron deficiency in [2]⁺. The reduced form of [2]⁺, [(η⁵-Cp′)₃Mo₃S₄Co(I)] (2), was prepared by oxidative substitution of the carbonyl ligand in 1 by I₂. Further reactions of 1 with PPh₃ and NO leading to the 60 and 61 VSE cluster complexes [(η⁵-Cp′)₃Mo₃S₄Co(PPh₃)] (3) and [(η⁵-Cp′)₃Mo₃S₄Co(NO)] (4), respectively, enabled the preparation of Mo₃S₄Co clusters in altogether four different oxidation states.     

Crystal and molecular structures of {Cu(μ-CCPh)(triphos)}2 [triphos = (PPh2CH2)3CMe]

The binuclear complex {Cu(μ-CCPh)(triphos)}₂ [triphos = (PPh₂CH₂)₃CMe] has been obtained from a reaction between {Cu(CCPh)}_n and triphos. The two copper atoms are bridged unsymmetrically by two CCPh groups, each attached through one carbon only [Cu-C, 2.016(4) Å], the separation between the two coppers being 2.4663(8) Å. Only two of the three phosphorus atoms in each ligand are coordinated to copper [Cu-P(1,2) 2.281, 2.273(1) Å]. The observed structure may be rationalised using a recent theoretical study [C. Mealli, S.S.M.C. Godinho, M.J. Calhorda, Organometallics 20 (2001) 1734] and differs from that assumed for the rationalisation of its luminescence properties [V. Pawlowski, G. Knör, C. Lennartz, A. Vogler, Eur. J. Inorg. Chem. (2005) 3167].     

Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U⁴⁺ cyclooctatetraenyl complex, [(C₅Me₅)(C₈H₈)U]₂(μ-C₈H₈), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me₂bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η⁵-C₅Me₅)(η⁸-C₈H₈)U(Me₂bipy-κ²N,N′) and (η⁵-C₅Me₅)(η⁸-C₈H₈)U(bipy-κ²N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U⁴⁺ complexes of bipyridyl radical anions. Hence, only one of the (C₈H₈)²⁻ ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C₈H₈)²⁻, Me₂bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.     

Synthesis, characterization and applications in ethylene polymerization of asymmetric ansa-titanocene complexes. Molecular structure of [Ti{Me2Si(η-C5Me4)(η-C5H3iPr)}Cl2]

The ansa-titanocene complexes, [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃R)}Cl₂] (R = Me (5), iPr (6), tBu (7), SiMe₃ (8)), were obtained from the reaction of Li₂{Me₂Si(C₅Me₄)(C₅H₃R)} (R = Me (1), iPr (2), tBu (3), SiMe₃ (4)) with [TiCl₄(THF)₂], respectively. Compounds 5-8 have been tested as catalysts in the polymerization of ethylene and compared with the ansa-titanocene complexes [Ti{Me₂Si(η⁵-C₅H₄)₂}Cl₂] and [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂]. The resulting polyethylene showed molecular weights of about 200 000 g mol⁻¹ and polydispersity values of approximately 3. In addition, the molecular structure of 6 has been determined by single crystal X-ray diffraction studies.     

Hydrido-derivatives of [Ir4(CO)10(diphosphine)]: X-ray analyses of [Ir4H(CO)9(μ-Ph2PH(CH3)PPh2)] and [Ir4 H(CO)9(μ-Ph2P(CH2)nPPh2)] (n = 2, 3)

Some novel hydrido-anions of general formula [Ir₄H(CO)₉(μ-L-L)]⁻ (L-L = Ph₂PCH(CH₃)PPh₂, Ph₂P(CH₂)₂PPh₂, Ph₂P(CH₂)₃PPh₂ and Ph₂AsCH₂AsPh₂) have been obtained by the reaction of [Ir₄(CO)₁₀(μ-L-L)] with the base 1,8-diazabicyclo[5.4.0]undec-7-ene in wet dichloromethane. According to IR and ¹H, ³¹P and ¹³C NMR data at low temperature, these anionic derivatives display a single conformation in solution: three edge-bridging COs around the triangular basal face and both the hydride and the bidentate ligands located in axial positions relative to this face. The structures of four compounds were established by X-ray diffraction studies, which confirmed the configuration proposed on the basis of spectroscopic data.