Synthesis and structure of halogen derivatives of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-Me2S-7,8-C2B9H11]

Halogenation of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-SMe₂-7,8-C₂B₉H₁₁] with N-chlorosuccinimide, bromine and iodine gave the expected corresponding halogen derivatives [9-SMe₂-11-X-7,8-C₂B₉H₁₀], where X = Cl (1), Br (2), I (3). In the bromination reaction, [9-SMe₂-6-Br-7,8-C₂B₉H₁₀] (4) was isolated as a minor product being the first example of substitution at a “lower” belt of the 7,8-dicarba-nido-undecaborate cage. The use of excess of bromine resulted in dibromo derivative [9-SMe₂-6,11-Br₂-7,8-C₂B₉H₉] (5). Structures of the compounds prepared were determined using ¹¹B-¹¹B COSY NMR spectroscopy (for all halogen derivatives) and single crystal X-ray diffraction (for compounds 2, 3, and 5).     

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.     

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.     

The first metallacarborane triple-decker complexes with a bridging borole ligand

The (borole)iodide complex [(η⁵-C₄H₄BPh)RhI]₄ reacts with the carborane anion [Carb′]⁻ (Carb′ = 9-SMe₂-7,8-C₂B₉H₁₀) giving (Carb′)Rh(η⁵-C₄H₄BPh) (2). Reactions of 2 with dicationic fragments [LM]²⁺ afford the μ-borole triple-decker complexes [(Carb′)Rh(μ-η⁵:η⁵-C₄H₄BPh)ML]²⁺ [LM = Cp^∗Ir (4), (Carb′)Rh (7)] or the arene-type complexes [(Carb′)Rh(μ-η⁵:η⁶-C₄H₄BPh)ML]²⁺ [LM = Cp^∗Rh (3), (Carb′)Ir (8)]. The structure of 4(BF₄)₂ was determined by X-ray diffraction.     

(1,2,3,4,7-Pentamethylindenyl)rhodium complexes with arene ligands

The reaction of (η⁵-C₉H₂Me₅)Rh(1,5-C₈H₁₂) (1) with I₂ gives the iodide complex [(η⁵-C₉H₂Me₅)RhI₂]₂ (2). The solvate complex [(η⁵- C₉H₂Me₅)Rh(MeNO₂)₃]²⁺ (generated in situ by treatment of 2 with Ag⁺ in nitromethane) reacts with benzene and its derivatives giving the dicationic arene complexes [(η⁵-₉H₂Me₅)Rh(arene)]²⁺ [arene = C₆H₆ (3a), C₆Me₆ (3b), C₆H₅OMe (3c)]. Similar reaction with the borole sandwich compound CpRh(η⁵-C₄H₄BPh) results in the arene-type complex [CpRh(μ-η⁵:η⁶-C₄H₄BPh)Rh(η⁵-C₉H₂Me₅)]²⁺ (4). Treatment of 2 with CpTl in acetonitrile affords cation [(η⁵-C₉H₂Me₅)RhCp]⁺ (5). The structure of [3c](BF₄)₂ was determined by X-ray diffraction. The electrochemical behaviour of complexes prepared was studied. The rhodium-benzene bonding in series of the related complexes [(ring)Rh(C₆H₆)]²⁺ (ring = Cp, Cp^∗, C₉H₇, C₉H₂Me₅) was analyzed using energy and charge decomposition schemes.     

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.     

Complexes of titanium and zirconium based on [C5Me4CH2-(2-C5H4N)] ligand

Half-sandwich [η⁵:η¹-κN-C₅Me₄CH₂-(2-C₅H₄N)]MCl₃ (M = Ti (4), Zr (5)) and sandwich [η⁵-C₅Me₄CH₂-(2-C₅H₄N)][η⁵-C₅Me₅]ZrCl₂ (6) ring-peralkylated complexes have been prepared and characterized. Evidence of the intramolecular coordination of the side-chain pyridyl group both in 4 and 5 in solutions is provided by NMR spectroscopy data. Crystal structure of an adduct 5-py with one molecule of pyridine has been established by X-ray diffraction analysis.     

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.     

Trimetallic FePd2 and FePt2 4-ferrocenyl-NCN pincer complexes

Ferrocene-bridged NCN pincer complexes of structural type Fe(η⁵-C₅H₄-4-NCN-1-MX)₂ (X = I: 6, M = Pd; 7, M = Pt; X = Cl: 8, M = Pt; NCN = [4-C₆H₂(CH₂NMe₂)₂-2,6]⁻) are accessible by the subsequent reaction of Fe(η⁵-C₅H₄-4-NCNH)₂ (4) with ⁿBuLi and [PtCl₂(SEt₂)₂] (synthesis of 8) or treatment of Fe(η⁵-C₅H₄-4-NCN-1-I)₂ (5) with [Pd₂(dba)₃] (synthesis of 6) or [Pt(tol)₂(SEt₂)]₂ (synthesis of 7) (dba = dibenzylidene acetone, tol = 4-tolyl). In addition, the Sonogashira cross-coupling of Fe(η⁵-C₅H₄I)₂ (1) with HCC-4-NCNH (2) gives Fe(η⁵-C₅H₄-CC-4-NCNH)₂ (3). The reaction behavior of 3 towards ^tBuLi is reported as well.Cyclovoltammetric studies show that the ferrocene entity can be oxidized reversibly. The Fe(II)/Fe(III) potential decreases with increasing electron density at the NCN pincer units due to the presence of the M-halide moiety (M = Pd, Pt).The solid state structure of Fe(η⁵-C₅H₄-4-NCN-1-PdI)₂ (6) is presented. In 6 the Fe(η⁵-C₅H₄)₂ unit connects two NCN-PdI pincer entities with palladium in a square-planar environment. The cyclopentadienyl ligands show a staggered conformation. The C₆H₂ rings are tilted by 23.5(3)° towards the C₅H₄ entities and the C₆H₂ plane is almost coplanar with the coordination plane (10.3(3)°).     

An unexpected cluster opening upon the formation of electronically unsaturated η-(cyclooctenyl)metallacarboranes of rhodium(III) and iridium(III) with sterically reduced [(PhCH2)2C2B9H9] ligand

The room-temperature metallation reactions of the K⁺ salt of the [7,8-(PhCH₂)₂-7,8-nido-C₂B₉H₁₀]⁻ anion (1) with the COD-metal μ-chloride dimers [(η⁴-C₈H₁₂)₂Rh₂(μ-Cl)₂] (2) and [(η⁴-C₈H₁₂)₂Ir₂(μ-Cl)₂] (3) in benzene/ethanol solution gave formally 16-electron pseudocloso-type complexes with the η³-cyclooctenyl ligand at the metal vertices, [3-{(1-3-η³)-C₈H₁₃}-1,2-(PhCH₂)₂-pseudocloso-3,1,2-MC₂B₉H₉] [4, M = Rh(III); 5, M = Ir(III)]. No evidence supporting the existence of an agostic C-H?M bonding interaction in these compounds was obtained either from the crystallographic or the phase-sensitive 2-D [¹H-¹H] NOESY/EXSY studies of 4. The extraordinary stability of complexes 4 and 5 can therefore be associated with their cage-deformed cluster structures, where electronically-deficient (16-electron) metal centers are believed to be stabilized by additional electron density released from the polyhedral C-C bond cleavage. DFT solid-state calculations performed for closo (18-electron) and pseudocloso (16-electron) Rh(III) complexes, [3-(η⁵-C₅Me₅)-1,2-(PhCH₂)₂-closo-3,1,2-RhC₂B₉H₉] (6, C-C, 1.7397 Å) and [3-{(1-3-η³)-C₈H₁₃}-1,2-(4′-MeC₆H₄)₂-pseudocloso-3,1,2-RhC₂B₉H₉] (9, C?C, 2.420(2) Å), showed that the electron density transfer from the carborane moiety to the rhodium center is marginally greater for complex 9, in accordance with the idea that electronics rather than sterics play a crucial role in the stabilization of 16-electron pseudocloso-metallacarborane species.     

Synthesis and characterization of three nickel(ii) carborane complexes containing nido- or closo-carborane diphosphine ligand

Three nickel(II) carborane complexes, [Ni₂(μ-Cl)₂{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂] (1), [Ni{7-(OPPh₂)-8-(PPh₂)-7,8-C₂B₉H₁₀}{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] (2) and [NiBr₂{1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀}] · CH₂Cl₂ (3), have been synthesized by the reactions of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane with NiCl₂ · 6H₂O or NiBr₂ · 6H₂O in ethanol under different conditions, respectively. For complex 1, it could also be obtained under the solvothermal condition. All the three complexes were characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal analysis shows that the molecular symmetry of complex 1 is centrosymmetric, containing two same structure units - Ni(7,8-(PPh₂)₂-7,8-C₂B₉H₁₀) linked by two bridged-Cl atoms. The central square plane formed by the [Ni₂Cl₂] unit is almost parallel to the two side NiPP planes. For complex 2, the coordination environment of the Ni atom is a seriously distorted square-planar, in which two positions come from the chelating diphosphine ligand [7,8-(PPh₂)₂-7,8-C₂B₉H₁₀]⁻ degraded from the closo species, while the other two are occupied by an unsymmetrical chelating phosphine oxide ligand [7-(OPPh₂)-8-(PPh₂)-7,8-C₂B₉H₁₀]⁻. As for complex 3, the geometry at the Ni atom is a slightly distorted square-planar. The closo carborane diphosphine ligand 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ was coordinated bidentately to the metal ion through the two phosphorus atoms, and the two Br atoms are at cis position which can fulfill the four coordination mode of the metal.     

Synthetic, X-ray structural and protonation studies of CpCr(CO)2SPy and CpCr(CO)2SPym (SPy = C5H4NS, SPym = C4H3N2S)

The facile reaction of [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅) (1) with one mole equivalent of 2,2′-dithiodipyridine ((C₅H₄NS)₂(SPy)₂) at ambient temperature led to the isolation of dark brown crystalline solids of CpCr(CO)₂(η²-SPy) (2) in ca. 72% yield. 2 undergoes quantitative conversion to CpCrCl₂(η¹-SPyH) (3) with HCl. The reaction 1 with one mole equivalent of 2-mercaptopyrimidine (C₄H₃N₂SHHSPym) at ambient temperature led to the isolation of reddish-brown crystalline solids of CpCr(CO)₂(η²-SPym) (4) and green solids of CpCr(CO)₃H (5) in yields of ca. 42% and 46%, respectively. Reaction of 4 with HCl and subsequent workup in acetonitrile resulted in the cleavage of the thiolate ligand, giving the 15-electron chromium(III) species CpCrCl₂(CH₃CN) (6) and free 2-mercaptopyrimidine. The complexes 2-4 have been determined by single X-ray diffraction analysis.     

Dicationic triple-decker complexes with a bridging boratabenzene ligand

New dicationic triple-decker complexes with a bridging boratabenzene ligand [Cp*Fe(μ-η:η-C₅H₅BMe)ML]X₂ (ML=CoCp*, 6(CF₃SO₃)₂; RhCp, 7(BF₄)₂; IrCp, 8(CF₃SO₃)₂; Ru(η-C₆H₆), 9(CF₃SO₃)₂; Ru(η-C₆H₃Me₃-1,3,5), 10(CF₃SO₃)₂; Ru(η-C₆Me₆), 11(CF₃SO₃)₂) were synthesized by stacking reactions of Cp*Fe(η-C₅H₅BMe) (2) with the corresponding half-sandwich fragments [ML]²⁺. The structure of 10(CF₃SO₃)₂ was determined by X-ray diffraction study.     

Synthesis and characterization of hetero-binuclear Co-Rh complexes [CpCoS2C2(B9H10)][Rh(COD)] and [CpCoSe2C2(B10H10)][Rh(COD)]

Two hetero-binuclear complexes [Cp^∗CoS₂C₂(B₉H₁₀)][Rh(COD)] (2a) and [Cp^∗CoSe₂C₂(B₁₀H₁₀)][Rh(COD)] (2b) [Cp^∗ = η⁵-pentamethylcyclopentadienyl, COD = cyclo-octa-1,5-diene (C₈H₁₂)] were synthesized by the reactions of half-sandwich complexes [Cp^∗CoE₂C₂(B₁₀H₁₀)] [E = S (1a), Se (1b)] with low valent transition metal complexes [Rh(COD)(OEt)]₂ and [Rh(COD)(OMe)]₂. Although the reaction conditions are the same, the structures of two products for dithiolato carborane and diselenolato carborane are different. The cage of the carborane in 2a was opened; However, the carborane cage in 2b was intact. Complexes 2a and 2b have been fully characterized by ¹H, ¹¹B NMR and IR spectroscopy, as well as by elemental analyses. The molecular structures of 2a and 2b have been determined by single-crystal X-ray diffraction analyses and strong metal-metal interactions between cobalt and rhodium atoms (2.6260 Å (2a) and 2.7057 Å (2b)) are existent.     

Photochemical arene exchange in the iron dicarbollide complex [(η-9-SMe2-7,8-C2B9H10)Fe(η-C6H6)]+

Visible light irradiation of the dicarbollide complex [(η-9-SMe₂-7,8-C₂B₉H₁₀)Fe(η-C₆H₆)]⁺ (2a) in the presence of the benzene derivatives in CH₂Cl₂/MeNO₂ resulted in cations [(η-9-SMe₂-7,8-C₂B₉H₁₀)Fe(η-C₆R₆)]⁺ (2b-g; arene is anisole (b), toluene (c), m-xylene (d), mesitylene (e), durene (f), and hexamethylbenzene (g)) due to the arene exchange. The structures of [2g]PF₆ and related tricarbollide complex [(η-1-Bu^tNH-1,7,9-C₃B₈H₁₀)Fe-(η-C₆H₆)]PF₆ (1) were confirmed by X-ray diffraction analysis. The nature of bonding in cations 1, 2a, and [CpFe(η-C₆H₆)]⁺ was analyzed by an energy decomposition analysis.     

Reactivity of electron-poor decamethyl-1,3-diboraruthenocene with sulfur and phosphorus compounds

Decamethyl-1,3-diboraruthenocene [(η⁵-C₅Me₅)Ru{η⁵-(CMe)₃(BMe)₂}] (1) reacts with cyclo-octasulfur in hexane to give [(η⁵-C₅Me₅){η⁵-(CMe)₃(BMe)₂}RuS] (3), which may also be obtained from 1 and propylene sulfide. 1 reacts with H₂S to form the ruthenathiacarboranyl complex [(η⁵-C₅Me₅)Ru{η⁴-(CMe)₃(BMe)₂S}] (6), for which a nido-structure is proposed. The isomeric compounds 3 and 6 have different stabilities: 3 loses sulfur and unexpectedly the closo-cluster [(η⁵-C₅Me₅)₂Ru₂H(CMe)₃(BMe)₂] (4) is formed with hydrogen bridging the basal and apical Ru centers. Reaction of 1 with carbonylsulfide (COS) yields the dinuclear ruthenium compound [(η⁵-C₅Me₅)Ru{η⁵-(CMe)₃(BMe)₂(S)(COBMe)}]₂ (7) in which two B-O groups bridge two ruthenium complexes. Its formation results from a complex reaction sequence: sulfur inserts into the diborolyl ring and the ligand CO forms an oxygen-boron bridge to a second molecule, followed by insertion of the carbonyl carbon into the double bond of the diboraheterocycle. Carbon disulfide reacts with 1 to give the dinuclear complex 8 with two CS₂ molecules connecting the ruthenium centers. When 1 and P₄ are heated in toluene, the sandwich 9 is obtained by formal insertion of a P-H group into the diborolyl ring of 1 and the triple-decker [{η⁵-(C₅Me₅)Ru}₂{μ-(MeC)₃P(MeB)₂} (10) is detected in the mass spectrum. The phosphaalkyne PCtBu inserts into 1 to give the ruthenaphosphacarborane [(η⁵-C₅Me₅)Ru{(CMe)₂(BMe)(PCtBu)(CMe)(BMe)}] (11) in high yield. Phosphanes react with 1 to give weak donor-acceptor complexes 1 · PH₂R (12) (R=Ph, H). The compositions of the compounds are deduced from spectroscopic and analytical data and are confirmed for 4 and 7 by X-ray structural analyses.     

Synthesis and crystal structure of four Pd(II) complexes containing nido or closo carborane diphosphine ligands

Three Pd(II) complexes [Pd₂(μ-Cl)₂{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂] · 0.25CH₂Cl₂ (1), [Pd{7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂] · 4CHCl₃ (2) and [PdCl₂(1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀)] (3) have been synthesized by the reactions of 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ with PdCl₂ in acetonitrile, cyanophenyl and dichloromethane, respectively. A fourth complex, [PdI₂(1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀)] (4), was obtained by a ligand exchange reaction through the substitution of the Cl⁻ of complex 3 with I⁻. All four complexes have been characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal X-ray determination showed that the carborane cage, nido for 1, 2 and closo for 3, 4, was coordinated bidentately to the Pd atom through the two P atoms, and the geometry at the Pd atom was square-planar in all the complexes.     

The effect that 6-tert-butoxyhexyl functionalization has on ethylene polymerization in ansa-zirconocene dichlorides

Ethylene polymerization studies have been carried out with novel precatalysts of the type: [(η⁵-C₁₃H₈)-X(t-BuOC₆H₁₂)Me-(η⁵-C₅H₄)]ZrCl₂ [X=C [1a], Si [2a]], [(η⁵-C₁₃H₈)-XMe₂-(η⁵-(t-BuOC₆H₁₂C₅H₃))] ZrCl₂ [X=C [3a], Si [4a]] in the presence of excess methylalumoxane (MAO) to compare their catalytic activity and to delineate the effect of the 6-t-butoxyhexyl functionality on ethylene polymerization. The precatalysts [1a] and [2a] with the bridge functionality showed higher activity in ethylene polymerization than the corresponding complexes [3a] and [4a] which have it on the Cp ring moiety. On the other hand the silyl bridged complexes [2a] and [4a] produced a higher molecular weight polyethylene than the carbon-bridged one, regardless of the location of functional group.     

Syntheses and catalytic activities of Group 4 metal complexes derived from C(cage)-appended cyclohexyloxocarborane trianion

The reaction of Li[closo-1-Me-1,2-C₂B₁₀H₁₀] with cyclohexene oxide produced closo-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (1) in 86% yield. Decapitation of (1) with potassium hydroxide in refluxing ethanol gave the corresponding cage-opened potassium salt of the carborane anion, [nido-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₉H₁₀]⁻ (2) in 82% yield. Deprotonation of (2) with two equivalents of n-butyllithium in THF at −78 °C, followed by its further reaction with anhydrous MCl₄ · 2THF (M = Ti, Zr) produced the corresponding d⁰-half-sandwich metallacarboranes, closo-1-M(Cl)-2-Me-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (3 M = Zr; 4 M = Ti), in 59% and 51% yields, respectively. Reaction of Li[closo-1,2-C₂B₁₀H₁₁] with Merrifield’s peptide resin (1%) in refluxing THF gave the ortho-carborane-functionalized polymer (5) in 88% yield. The corresponding closo-1-polystyryl-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (6) was produced in 94% yield by refluxing a mixture of the lithium salt of (5) and cyclohexene oxide in THF for 2 days. Compound (6) was decapitated, deprotonated and then reacted with ZrCl₄ · 2THF to produce a polymer-supported d⁰-half-sandwich metallacarborane closo-1-Zr(Cl)-2-polystyryl-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (7) in 41% yield. Compounds (3) and (7), in the presence of MMAO-7 (13% ISOPAR-E), were found to catalyze the polymerization of ethylene and vinyl chloride in toluene to give high molecular weight PE (9.4 × 10³ (M_w/M_n = 1.8)) and PVC (2.1 × 10³ (M_w/M_n = 1.6)), respectively.     

Synthesis and reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η-C5H4SiMe3)Cl2{NC6Me4-4-(N(SiMe3)2)}]

The reaction of [1,4-{SiMe₃(H)N}₂C₆Me₄] (1) with 2 equivalents of LiBuⁿ followed by the addition of SiMe₃Cl gave the diamine compound [1,4-{(SiMe₃)₂N}₂C₆Me₄] (2). [Ta(η⁵-C₅H₄SiMe₃)Cl₄] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (3), and mononuclear, [Ta(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η⁵-C₅H₄SiMe₃)Cl₄] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl₃(CH₃CN)₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (5) has been prepared by the reaction of one molar equivalent of TaCl₅ with 2 in a CH₃CN/CH₂Cl₂ solvent mixture. The synthesis of the niobium complexes, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (6) and [Nb(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η⁵-C₅H₄SiMe₃)RCl{NC₆Me₄-4-(N(SiMe₃)₂)}] (R = η⁵-C₅H₄SiMe₃ (8), PhC(NSiMe₃)₂ (9), NMe₂ (10)). In an attempt to form the hetero bimetallic complex, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}(μ-1,4-NC₆Me₄N){Ta(η⁵-C₅H₄SiMe₃)Cl₂}] (11), the reaction of 7 with [Ta(η⁵-C₅H₄SiMe₃)Cl₄] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.