Interligand H?Si interactions in tungsten silyl trihydride complexes

The dichloride complex Cp∗(Am)WCl₂ (1, Am = [(iPrN)₂CMe]⁻) reacted with the primary silanes PhSiH₃, (p-tolyl)SiH₃, (3,5-xylyl)SiH₃, and (C₆F₅)SiH₃ to produce the W(VI) (silyl)trihydrides Cp∗(Am)W(H)₃(SiHPhCl) (2), Cp∗(Am)W(H)₃(SiHTolylCl) (3), Cp∗(Am)W(H)₃(SiHXylylCl) (4), and Cp∗(Am)W(H)₃[SiH(C₆F₅)Cl] (5). In an analogous manner, 1 reacted with PhSiH₂Cl to give Cp∗(Am)W(H)₃(SiPhCl₂) (6). Complex 6 can alternatively be quantitatively produced from the reaction of 2 with Ph₃CCl. NMR spectroscopic studies and X-ray crystallography reveal an interligand H?Si interaction between one W-H and the chlorosilyl group, which is further supported by DFT calculations.     

Mono and dinuclear half-sandwich platinum group metal complexes bearing pyrazolyl-pyrimidine ligands: Syntheses and structural studies

Reactions of 0.5 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = η⁶-C₆H₆, η⁶-p-ⁱPrC₆H₄Me) and [(Cp∗)M(μ-Cl)Cl]₂ (M = Rh, Ir; Cp∗ = η⁵-C₅Me₅) with 4,6-disubstituted pyrazolyl-pyrimidine ligands (L) viz. 4,6-bis(pyrazolyl)pyrimidine (L1), 4,6-bis(3-methyl-pyrazolyl)pyrimidine (L2), 4,6-bis(3,5-dimethyl-pyrazolyl)pyrimidine (L3) lead to the formation of the cationic mononuclear complexes [(η⁶-C₆H₆)Ru(L)Cl]⁺ (L = L1, 1; L2, 2; L3, 3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(L)Cl]⁺ (L = L1, 4; L2, 5; L3, 6), [(Cp∗)Rh(L)Cl]⁺ (L = L1, 7; L2, 8; L3, 9) and [(Cp∗)Ir(L)Cl]⁺ (L = L1, 10; L2, 11; L3, 12), while reactions with 1.0 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ and [(Cp∗)M(μ-Cl)Cl]₂ give rise to the dicationic dinuclear complexes [{(η⁶-C₆H₆)RuCl}₂(L)]²⁺ (L = L1, 13; L2, 14; L3, 15), [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(L)]²⁺ (L = L1, 16; L2, 17; L3, 18), [{(Cp∗)RhCl}₂(L)]²⁺ (L = L1, 19; L2, 20; L3, 21) and [{(Cp∗)IrCl}₂(L)]²⁺ (L = L1 22; L2, 23; L3 24). The molecular structures of [3]PF₆, [6]PF₆, [7]PF₆ and [18](PF₆)₂ have been established by single crystal X-ray structure analysis.     

Metallacarboranes and triple-decker complexes with the (C4Me4)Pt fragment

Complex Cp∗PtCl₂ (Cp∗ = η-C₄Me₄) reacts with the carborane anions [7,8-C₂B₉H₁₁]²⁻ and [9-SMe₂-7,8-C₂B₉H₁₀]⁻ giving platinacarboranes Cp∗Pt(η-7,8-C₂B₉H₁₁) (1) and [Cp∗Pt(η-9-SMe₂-7,8-C₂B₉H₁₀)]⁺ (2), respectively. Reactions of the [Cp∗Pt]²⁺ fragment (as a labile nitromethane solvate) with the sandwich compounds Cp∗Fe(η-C₅H₃Me₂BMe) and Cp∗Rh(η⁵-C₄H₄BPh) afford the triple-decker cations [Cp∗Pt(μ-η:η-C₅H₃Me₂BMe)FeCp∗]²⁺ (3) and [Cp∗Pt(μ-η⁵:η⁵-C₄H₄BPh)RhCp∗]²⁺ (4) with bridging boratabenzene and borole ligands. The structures of 1 and 3(CF₃SO₃)₂ were determined by X-ray diffraction.     

Insertion of nitrene and chalcogenolate groups into the Ir-C σ bond in a cyclometalated iridium(III) complex

Treatment of [Cp∗Ir(ppy)Cl] (Cp∗ = η⁵-C₅Me₅, ppyH = 2-(2-pyridyl)phenyl) with Ag(OTf) (OTf⁻ = triflate) in MeOH and MeCN gave the solvento complexes [Cp∗Ir(ppy)(solv)][OTf] (solv = MeOH (1) and MeCN (2)). Complex 1 is capable of catalyzing oxidation and azirdination of styrene with PhIO and PhINTs (Ts = tosyl), respectively. Treatment of 2 with a stoichiometric amount of PhINTs resulted in the insertion of the NTs group into the Ir-C(ppy) bond and formation of [Cp∗Ir(η²-ppy-NTs)(MeCN)][OTf] (3). Treatment of 1 with R₂E₂ afforded [Cp∗Ir(ppy)(η¹-R₂E₂)][OTf] (E = S (4), Se (5), Te (6)). Reactions of 4 and 5 with Ag(OTf) resulted in cleavage of the E-E bond and insertion of an ER group into the Ir-C(ppy) bond. The crystal structures of complexes 2-6 and [Cp∗Ir(η²-ppy-S-p-tol)(H₂O)][OTf]₂ have been determined.     

Metallaheteroborane clusters of group 5 transition metals derived from dichalcogenide ligands

Treatment of group 5 metal polychlorides such as, [Cp_nMCl_4-x] (M = V: n, x = 2; M = Nb: n = 1, x = 0), or [Cp∗TaCl₄] (Cp = η⁵-C₅H₅, Cp∗ = η⁵-C₅Me₅), with [LiBH₄·THF] followed by thermolysis in the presence of diphenyl diselenide yielded metallaheteroborane clusters [{CpV(μ-SePh)}₂(μ-Se)], 1 [(CpNb)₂B₄H₉(μ-SePh)], 2 and [(Cp∗Ta)₂B₄H₁₁(SePh)], 3 in modest yields. Compound 1 is an organovanadium selenolato cluster in which two (CpV) moieties bridged by (μ-Se) and two (μ-SePh) ligands. Compound 2 exhibits a bicapped tetrahedral core with one (μ-SePh) ligand. 3 is a tantalahexaborane cluster in which one of the terminal BH protons is substituted by SePh. Compounds 1-3 have been characterized by mass spectrometry, ¹H, ¹¹B, ¹³C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis of 1-3.     

Half-sandwich binuclear carbaborane compounds: Closo-carbaboranes as good σ-donar ligands

The synthesis of half-sandwich binuclear transition-metal complexes containing the Cab^C,C chelate ligands (Cab^C,C = C₂B₁₀H₁₀ (1)) is described. 1Li₂ was reacted with chloride-bridged dimers [Cp∗RhCl(μ-Cl)]₂ (Cp∗ = η⁵-C₅(CH₃)₅), [Cp′RhCl(μ-Cl)]₂ (Cp′ = η⁵-1,3-^tBu₂C₅H₃), [Cp∗IrCl(μ-Cl)]₂ and [(p-cymene)RuCl(μ-Cl)]₂ to give half-sandwich binuclear complexes [Cp∗Rh(μ-Cl)]₂(Cab^C,C) (2), [Cp′Rh(μ-Cl)]₂(Cab^C,C) [3),[Cp∗Ir(μ-Cl)]₂(Cab^C,C) (4) and [(p-cymene)Ru(μ-Cl)]₂(Cab^C,C) (5), respectively. Addition reactions of the ruthenium complex 5 with air gave [(p-cymene)₂Ru₂(μ-OH)(μ-Cl)](Cab^C,C) (6), rhodium complex 2 with LiSPh gave [Cp∗Rh(μ-SPh)]₂(Cab^C,C) (7). The complexes were characterized by IR, NMR spectroscopy and elemental analysis. In addition, X-ray structure analysis were performed on complexes 2-7 where the potential C,C-chelate ligand was found to coordinate in a bidentate mode as a bridge.     

Aqueous organometallic chemistry. 3. Catalytic hydride transfer reactions with ketones and aldehydes using [Cp∗Rh(bpy)(H2O)](OTf)2 as the precatalyst and sodium formate as the hydride source: Kinetic and activation parameters, and the significance of steric and electronic effects

The reaction of a precatalyst, [Cp∗Rh(bpy)(H₂O)](OTf)₂ (1), with sodium formate provided the hydride complex, [Cp∗Rh(bpy)(H)]⁺ (2), in situ, at pH 7.0, which was then evaluated in an aqueous, catalytic hydride transfer process with water soluble substrates that encompass 2-pentanone (3), cyclohexanone (4), acetophenone (5), propionaldehyde (6), benzaldehyde (7), and p-methoxybenzaldehyde (8). The initial rates, r_i, of appearance of the reduction product alcohols at 23 °C provided a relative rate scale: 8 > 7 ≈ 6 > 5 > 4 > 3, while the effect of concentration of substrate, precatalyst, and sodium formate on r_i, using 7 as an example, implicates [Cp∗Rh(bpy)(H)]⁺ formation as the rate-limiting step. The experimental kinetic rate expression was found to be: d[alcohol]/dt = k_cat[1][HCO₂Na]; substrate being pseudo zero order in water. The steric effects were also analyzed and appeared to be of less importance intra both the ketone and aldehyde series, but an inter series comparison appeared to show that the aldehydes had less of a steric effect on the initial rate, i.e., 7 > 4 by a factor of 3.6, while the aldehyde series appeared to have some moderate electronic influence on rates, presumably via electron donation to increase binding to the Cp∗Rh metal ion center, in accordance with these proposed concerted binding/hydride transfer reactions. A proposed catalytic cycle will also be presented.     

Synthesis and characterization of scandium complexes with reduced ligands: Crystal structures of Cp∗ScI2, [Cp∗ScI(bpy)]2, and [Cp∗ScCl(bpy)]2

The synthesis and characterization of complexes containing a Cp∗Sc(R₂bpy) (Cp∗ = pentamethylcyclopentadienyl, bpy = 4,4′-R,R-2,2′-bipyridine, R = H, Me) motif are described. Cp∗ScI₂ (1) was prepared from Cp∗Sc(acac)₂ (acac = acetylacetonate) and AlI₃ (2 equiv) in pentane. Compound 1 reacted with bipyridine and 4,4′-dimethyl-2,2′-bipyridine (dmb) in benzene to yield Cp∗ScI₂(bpy) (3) and Cp∗ScI₂(dmb) (4), respectively. Compound 3 was reduced by alkali metal reductants such as Na/Hg, NaK₂, and K in aromatic solvents to yield [Cp∗ScI(bpy)]₂ (5). The chloride analog of 5, [Cp∗ScCl(bpy)]₂ (7), was prepared from Cp∗ScCl₂ by salt metathesis with Li₂(dme)₂bpy (6) (dme = dimethoxyethane) in toluene. Compounds 1, 5, and 7 have been structurally characterized. Analysis of the bond distances of the bipyridine ligands in 5 and 7, together with infrared and UV/vis spectroscopic data, suggest that the bipyridine ligands in these molecules exist as radical anions. The bipyridine ligands in 5 and 7 are arranged co-facially and are in close proximity (?3.30 Å), suggesting the presence of a π-π interaction.     

Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III) complexes containing various types of bidentate ligands

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp∗) group, [Cp∗Ir(N₃)₂(Ph₂Ppy-κP)] (1: Ph₂Ppy = 2-diphenylphosphinopyridine), [Cp∗Ir(N₃)(Ph₂Ppy-κP,κN)]CF₃SO₃ (2), [Cp∗Ir(N₃)(dmpm)]PF₆ (3: dmpm = bis(dimethylphosphino)methane), [Cp∗Ir(N₃)(Ph₂Pqn)]PF₆·$·$CH₃OH (4·$·$CH₃OH: Ph₂Pqn = 8-diphenylphosphinoquinoline), and [Cp∗Ir(N₃)(pybim)] (5: Hpybim = 2-(2-pyridyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffraction. In complex 1, the Ph₂Ppy ligand is only coordinated via the P atom (-κP), while in 2 it acts as a bidentate ligand through the P and N atoms (-κP,κN) to form a four-membered chelate ring. Comparing the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring formed by Ph₂Pqn in 4, it became apparent that the angular distortion in the Ph₂Ppy-κP,κN ring was remarkable, although the Ir–P and Ir–N bonds in the Ph₂Ppy-κP,κN ring were not elongated very much from the corresponding bonds in the Ph₂Pqn-κP,κN ring. In the pybim complex 5, the five-membered chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III) complexes analyzed previously, comparison of the structural parameters of the Ir–N₃ moiety in [Cp∗Ir^III(N₃)(L–L′)]^+/0 complexes reveals an anomalous feature of the 2,2′-bipyridyl (bpy) complex, [Cp∗Ir(N₃)(bpy)]PF₆.     

Some ruthenium complexes of fluorinated alkynylcyclopentenes

Reactions between 1,2-dichlorohexafluorocyclopentene and Ru(CCH)(dppe)Cp∗ or Ru(CCCCLi)(dppe)Cp∗ have given Ru(CC-c-C₅F₆Cl-2)(dppe)Cp∗ 4 and Ru(CCCC-c-C₅F₆Cl-2)(dppe)Cp∗ 7, respectively. Ready hydrolysis of 4 to the ketone Ru{CC[c-C₅F₄Cl(O)]}(dppe)Cp∗ 5 occurs, which can be converted to Ru{CC(c-C₅F₄Cl[C(CN)₂])}(dppe)Cp∗ 6 by treatment with CH₂(CN)₂/basic alumina. Spectroscopic, electrochemical and XRD structural studies for 4-7 are reported: for 6, these suggest that the cyanated fluorocarbon ligand is a very powerful electron-withdrawing group.     

Half-sandwich Ru(II), Ir(III) and Rh(III) complexes with bridging or chelating N-heterocyclic bis-carbene ligand: Synthesis and characterization

N-heterocyclic bis-carbene ligand (bis-NHC) which was derived from 1,1′-diisopropyl-3,3′-ethylenediimidazolium dibromide (L·2HBr) via silver carbene transfer method, reacted with [(η⁶-p-cymene)RuCl₂]₂ and [Cp^∗MCl₂]₂ (Cp^∗ = η⁵-C₅Me_5, M = Ir, Rh) respectively, afforded complexes [(η⁶-p-cymene)RuCl₂]₂(L) (1), [Cp^∗IrCl₂]₂(L) (2) and [Cp^∗RhCl(L)][Cp^∗RhCl₃] (3). When [Cp^∗IrCl₂]₂ was treated with 2 equiv AgOTf at first, and then reacted with bis-NHC ligand, [Cp^∗IrCl(L)]OTf (4) was obtained. The molecular structures of complexes 1-4 were determined by X-ray single crystal analysis, showing that 1 and 2 adopted bridging coordination mode, 3 and 4 adopted chelating coordination mode. All of these complexes were characterized by ¹H, ¹³C NMR spectroscopy and element analysis.     

Trimetallic complexes containing 1,1′-Rc′(CC)2 units [Rc′ = ruthenocene-1,1′-diyl, Ru(η-C5H4-)2]

Reactions between 1,1′-(Me₃SiCC)₂Rc′ [Rc′ = ruthenocen-1,1′-diyl, Ru(η-C₅H₄-)₂] and RuCl(PP)Cp′ in the presence of KF gave 1,1′-{Cp(PP)RuCC}₂Rc′ [Cp′ = Cp, PP = PPh₃1, P(m-tol)₃2, dppe 3, dppf 4; Cp′ = Cp^∗, PP = dppe 5]. Compounds 1 and 2 react with tcne to give two diastereomers a/b of the allylic (vinylcarbene) complexes 6 and 7, while methylation of 5 gave the bis-vinylidene [1,1′-{Cp^∗(dppe)RuCCMe}₂Rc′](BPh₄)₂ (8). The X-ray structures of 4, 6b and 8 have been determined. Cyclic voltammograms indicate that there is some electronic communication between the ruthenium end-groups through the Rc′ centre.     

Iodo-alkynyl- and iodo-butadiynyl-ruthenium complexes

Addition of [I(py)₂]BF₄ to Ru(CCH)(dppe)Cp∗ gave the iodovinylidene [Ru(CCHI)(dppe)Cp∗]BF₄1, which could be deprotonated to Ru(CCI)(dppe)Cp∗ 2. The attempted preparation of Ru(CCCCI)(dppe)Cp∗, followed by derivatisation with tcne, gave the dienynyl Ru{CCC[C(CN)₂]CIC(CN)₂}(dppe)Cp∗ 3. The Pd(0)/Cu(I)-catalysed reaction of 3 with Ru{CCCCAu(PPh₃)}(dppe)Cp∗ afforded Ru{CCCC(CN)₂CC(CN)₂Au(PPh₃)}(dppe)Cp∗ 4 by formal replacement of I⁺ by [Au(PPh₃)]⁺. XRD structures of 1-4 are reported.     

Nucleophilic properties of Ru(CCH)(dppe)Cp∗: Synthesis and structure of Ru{c-CCArC(O)C(O)O}(dppe)Cp∗ [Ar = 2,4-(NO2)2C6H3]

The complex Ru{c-CCArC(O)C(O)O}(dppe)Cp∗ [Ar = 2,4-(NO₂)₂C₆H₃] 2, containing a dihydrofuran-3,4-dione ligand, was obtained from a reaction between the strong nucleophile Ru(CCH)(dppe)Cp∗ 1 and bis(2,4-dinitrophenyl) oxalate. The X-ray determined molecular structure of 2 is reported, together with a plausible route for its formation.     

Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N-B-PTA(BH3): X-ray crystal structures of [CpRhCl2{N-B}-PTA(BH3)] and [CpRh{N-B-PTA(BH3)}(η-CH2 = CHPh)]

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N-B-PTA(BH₃) and [Cp^∗RhCl(μ-Cl)]₂ affords [Cp^∗Rh{N-B-PTA(BH₃)}Cl₂] (3) or [Cp_∗Rh{N-B-PTA(BH₃)}₂Cl]Cl (5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp_∗Rh{N-B-PTA(BH₃)}H₂] (8) was also obtained by reaction of 3 with NaBH₄ and alternatively by direct hydroboration of [Cp^∗Rh(PTA)Cl₂] with excess NaBH₄. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H₃BO₃ and the corresponding PTA derivatives, including the water-soluble dihydride [Cp^∗Rh(PTA)H₂] (9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp^∗Rh{N-B-PTA(BH₃)}(η²-CH₂ = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η²-coordinated to rhodium without affecting the N-BH₃ moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.     

Synthesis, characterization and electrochemical behavior of some N-heterocyclic carbene-containing active site models of [FeFe]-hydrogenases

Treatment of parent compounds [(μ-SCH₂)₂X]Fe₂(CO)₆ (A, X = O; B, X = NBu-t; C, X = NC₆H₄OMe-p) with N-heterocyclic carbene I_Mes (I_Mes = 1,3-bis(mesityl)imidazol-2-ylidene) generated in situ through reaction of imidazolium salt I_Mes ·HCl with n-BuLi or t-BuOK afforded the monocarbene-substituted complexes [(μ-SCH₂)₂X]Fe₂(CO)₅(I_Mes) (1, X = O; 2, X = NBu-t; 3, X = NC₆H₄OMe-p). Similarly, the monocarbene and dicarbene-substituted complexes [(μ-SCH₂)₂NBu-t]Fe₂(CO)₅[I^∗_Mes(CH₂)₃I^∗_Mes]·HBr (4) and [(μ-SCH₂)₂CH₂Fe₂(CO)₅]₂[μ-I^∗_Mes(CH₂)₃I^∗_Mes] (5, I^∗_Mes = 1-(mesityl)imidazol-2-ylidene) could be prepared by reactions of parent compound B with the mono-NHC ligand-containing imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · HBr and parent compound [(μ-SCH₂)₂CH₂]Fe₂(CO)₆ (D) with di-NHC ligand I^∗_Mes(CH₂)₃I^∗_Mes (both NHC ligands were generated in situ from reaction of n-BuLi with imidazolium salt [I^∗_MesI^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr), respectively. The imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr was prepared by reaction of 1-(mesityl)imidazole with Br(CH₂)₃Br. All the new model compounds 1-5 and imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr were fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. On the basis of electrochemical studies of 1 and 2, compound 2 was found to be a catalyst for proton reduction to hydrogen. In addition, an EECC mechanism for this electrocatalytic reaction is preliminarily suggested.     

Synthesis and characterization of new paramagnetic tetraaryl derivatives of chromium and molybdenum

The low-temperature reaction of [CrCl₃(thf)₃] with LiC₆H₃Cl₂-2,6 yields the organochromium(III) compound [Li(thf)₄][Cr^III(C₆H₃Cl₂-2,6)₄] (1) in 48% yield. The homoleptic, anionic species [Cr^III(C₆H₃Cl₂-2,6)₄]⁻ is electrochemically related to the neutral one [Cr^IV(C₆H₃Cl₂-2,6)₄] (2) through a reversible one-electron exchange process (E_1/2 = 0.16 V, ΔE_p = 0.09 V, i_pa/i_pc = 1.18). Compound 2 was isolated in 74% yield by chemical oxidation of 1 with [N(C₆H₄Br-4)₃][SbCl₆]. Attempts to prepare the salt [NBu₄][Cr^III(C₆Cl₅)₄] (4) by direct arylation of [CrCl₃(thf)₃] with LiC₆Cl₅ in the presence of [NBu₄]Br gave the organochromium(II) salt [NBu₄]₂[Cr^II(C₆Cl₅)₄] (3) instead, as the result of a reduction process. The salt [NBu₄][Cr^III(C₆Cl₅)₄] (4) was cleanly prepared by comproportionation of 3 and [Cr^IV(C₆Cl₅)₄]. The reaction of [MoCl₄(dme)] with LiC₆Cl₅ in Et₂O solution proceeded with oxidation of the metal center to give the paramagnetic (S = 1/2), five-coordinate salt [Li(thf)₄][Mo^VO(C₆Cl₅)₄] (5). The crystal and molecular structures of 1 and 2 have been established by X-ray diffraction methods. The magnetic properties of 1 and 4 (S = 3/2) as well as those of 2 (S = 1) have been established by EPR spectroscopy as well as by ac and dc magnetization measurements.     

Syntheses and molecular structures of half-sandwich iridium metallarectangles containing bridging 2,5-dihydroxy-1,4- benzoquinonato (dhbq) ligands

Binuclear complex (Cp∗IrCl)₂(dhbq) (dhbq = 2,5-dihydroxy-1,4-benzoquinonato) (1) was obtained by the reaction of (Cp∗IrCl₂)₂ with bridging ligand 2,5-dihydroxy-1,4-benzoquinone(H₂dhbq) in the presence of the base n-BuNH₂. After treatments of 1 with AgX (X = ) and then with N-linkers (pyrazine, 4,4′-bipyridine), the corresponding tetranuclear metallarectangular complexes [(Cp∗Ir)₄(dhbq)₂(pyrazine)₂] (NO₃)₄·CH₂Cl₂·5H₂O (2) and [(Cp∗Ir)₄(dhbq)₂(4,4′-bipyridine)₂](SO₃CF₃)₄(3) were obtained in good yields. Both the products were characterized by IR, ¹H NMR and single crystal X-ray analyses and revealed that these tetranuclear complexes were constructed from half-sandwich metal corners with both dhbq and N-linkers to form rectangular cavities with the dimensions 8.0 × 6.9 Å (Ir-Ir separations) for 2, 8.0 × 11.2 Å (Ir-Ir separations) for 3, respectively. In additionally, in the solid structure of 2 the counteranions are located out of the cavities with the observed water molecules by hydrogen bonding of the type N-O?H-O-H?O-N. One-dimensional channels are observed in 3 along the b axis with intramolecular stacking, the similar arrangement is not found in the solid of 2.     

Synthesis, X-ray structures, and syndiospecific polymerization behavior of styrene of new (pentamethylcyclopentadientyl) titanatranes containing modified tetradentate triethanolamine ligands

A series of monomeric pentamethylcyclopentadienyltitanatranes, [n = 0, 1; n = 1, 2; n = 2, 3], were synthesized by the reaction of Cp∗TiCl₃ with corresponding triethanolamines such as (HOCH₂CH₂)_nN(CH₂CMe₂OH)_{3 − n} (n = 0, L1H₃; n = 1, L2H₃; n = 2, L3H₃), which varied by the number of CMe₂ groups adjacent to an OH functionality from 3 (L1H₃) to 2 (L2H₃) to 1 (L3H₃), in the presence of NEt₃. All complexes were characterized by elemental analysis and solution ¹H and ¹³C{¹H} NMR spectroscopy. Moreover, their solid state structures, which are slightly distorted three-legged piano stool geometry, have been confirmed by single crystal X-ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activity for the polymerization of styrene producing syndiotactic polystyrene (SPS) with high molecular weights. Compounds 1 and 2 bearing more than two pairs of methyl substituents on the side arms of triethanolamines showed the enhanced catalytic activities as the polymerization temperature went up from 50 °C to 110 °C, whereas less bulky complexes 3 and Cp∗Ti(OCH₂CH₂)₃N (4) gave the decreased activities as polymerization temperature rose. Unlike 3 and 4, complexes 1 and 2 in the presence of MAO as a cocatalyst gave SPS with controlled bimodal molecular weight distribution. Bimodal properties were much distinct at low polymerization temperature.     

Synthesis of bulky tris[(dimethyl(alkyl/aryl)silyl)methyl]stannanes as radical based reducing agents

The synthesis of novel bulky tris[dimethyl(ethyl/benzyl/p-tolyl/α-naphthyl)silylmethyl]stannanes (1-4) is described. Alkylation of SnCl₄ with Me₂(ethyl/p-tolyl)SiCH₂MgBr (10-11) gave mainly the triorganotin chlorides [(Me₂(ethyl/p-tolyl)SiCH₂)]₃SnCl 14 and 15, which were isolated by silica gel chromatography. Reduction of 14 and 15 with LiAlH₄ in THF gave the corresponding triorganotin hydrides 1 and 2, respectively. [Me₂(benzyl/α-naphthyl)SiCH₂]₃SnCl 16 and 17, generated by the alkylation of SnCl₄ with Me₂(benzyl/α-naphthyl)SiCH₂MgBr 12 and 13, were inseparable from the minor product [Me₂(benzyl/α-naphthyl)SiCH₂]₂SnCl₂18 and 19, respectively. Treatment of the mixtures of 16/18 and 17/19 with NaOH furnished the corresponding mixtures of stannoxanes, from which the hexakisdistannoxanes [Me₂(benzyl/α-naphthyl)SiCH₂]₆Sn₂O 20 and 22 were isolated from the minor dialkyltin oxide derivatives [Me₂(benzyl/α-naphthyl)SiCH₂]₂SnO in good yields. Reduction of 20 and 22 with BH₃ in THF gave [Me₂(benzyl/α-naphthyl)SiCH₂]₃SnH (3 and 4), respectively in good yields. ¹H, ¹³C, ¹¹⁹Sn, ²⁹Si NMR characteristics of the newly synthesized compounds are included.