Pentamethylcyclopentadienyl Complexes Research Articles

Iridium Complexes with Bidentate Pyridinylidene/N-Amidate Ligands for Transfer Hydrogenation Catalysis.

A series of iridium pentamethylcyclopentadienyl (Cp*) complexes, [Cp*Ir(κ2-RLp/m)Cl], that contain the strongly coordinating bidentate ligands RLp/m were synthesized. The donor groups of the bidentate ligands were an N-amidate and either a para-pyridinylidene remote N-heterocyclic carbene (RLp) or a meta-pyridinylidene remote N-heterocyclic carbene (RLm). For each type of bidentate ligand, a set of iridium complexes was synthesized, which differed only according to the substituents (R) on the phenyl ring associated with the amidate group. The iridium complexes were all fully characterized and molecular structures were obtained by single-crystal X-ray diffraction studies for representative examples. The complexes were found to be good precatalysts in iso-propanol for the transfer hydrogenation of benzaldehyde to give benzyl alcohol. The catalytic activity correlated with the Hammett σm/p parameters of the phenyl ring substituents, with more electron-donating substituents leading to increased catalytic activity. In all cases, the meta-pyridinylidene complexes, [Cp*Ir(κ2-RLm)Cl], performed better than the corresponding para analogues, [Cp*Ir(κ2-RLp)Cl].

Cell Death Mechanism of Organometallic Ruthenium(II) and Iridium(III) Arene Complexes on HepG2 and Vero Cells.

Due to side effects and toxicity associated with platinum-derived metal-based drugs, extensive research has been conducted on ruthenium (Ru) complexes. We aim to synthesize a highly oil soluble Ru(II)-p-cymene complex (Ru1) with an aliphatic chain group, a bimetallic Ru(II)-p-cymene complex (Ru2) with N,S,S triple-coordination and a bimetallic Ir(III)-pentamethylcyclopentadienyl complex (Ir1) with S,S double-coordination. Subsequently, we investigate the effects of these complexes on Vero and HepG2 cell lines, focusing on cell death mechanisms. Characterization of the complexes is performed through nuclear magnetic resonance spectroscopy (1H and 13C NMR) and Fourier-transform infrared spectroscopy. The effective doses are determined using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) (MTT) assay, applying different doses of the complexes to the two cell lines for 24 and 48 h, respectively. Immunoreactivities of Bax, Bcl2, caspase-3, RIP3, and RIPK1 are analyzed using the indirect immunoperoxidase technique. Notably, all the complexes (Ru1, Ru2, and Ir1) exhibit distinct cell death mechanisms, showing greater effectiveness than cisplatin. This study reveals the diverse mechanisms of action of Ru and Ir complexes based on different ligands. To the best of our knowledge, this study represents the first investigation of a novel RAED-type complex (Ru1) and unexpected bimetallic complexes (Ru2 and Ir1).

Structural Effect of Water-Soluble Zinc Porphyrins in a Visible-Light Driven NADH Regeneration System Catalyzed by Rhodium Pentamethylcyclopentadienyl Complex

Abstract The effect of ionic substituents (4-sulfonatophenyl, 4-carboxyphenyl, 4-methylpyridyl, and 4-N,N,N-trimethylaminophenyl-groups) of water-soluble zinc porphyrin (ZnP) on the visible light-driven NADH regeneration by a system of triethanolamine, ZnP, and rhodium complex [Cp*Rh(bpy)(H2O)]2+ (Cp* = pentamethylcyclopentadienyl, bpy = 2,2′-bipyridyl) was studied to provide significant guidance for hybridization with a wide range of oxidoreductases.

Utility of a Ferrocene Unit in a Cyclometallated Cp*Ir(III) Catalyst during Water Oxidation: Exploring Bimetallic Cooperativity

AbstractFerrocene functionalized 2‐phenylpyridine iridium(III) pentamethylcyclopentadienyl complex is synthesized and probed for oxygen evolution from water. The excellent activity of this system has been rationalized by proposing a Fe(III)/Ir(IV) transient intermediate where bimetallic redox synergism between the Fe and Ir centres possibly provide an alternative pathway rather than a conventional Ir(V) based cycle.

Pentamethylcyclopentadienyl Complexes of Cerium(IV): Synthesis, Reactivity, and Electrochemistry.

Treatment of Cp*2CeCl2K(THF) with alkali-metal alkoxides and siloxides in the presence of hexachloroethane generates the monomeric bis(pentamethylcyclopentadienyl) cerium(IV) complexes Cp*2Ce(OR)2 (Cp* = C5Me5; R = Et, iPr, CH2tBu, tBu, SiMe3, or SiPh3). Large substituents R trigger ligand scrambling to half-sandwich complexes Cp*Ce(OR)3, which could be isolated for R = tBu and SiPh3. Similar reactions with sodium aryloxide NaOAr (OAr = OC6H3iPr2-2,6) led to Cp*2Ce(OAr)Cl. Treatment of tris(cyclopentadienyl) complexes CpR3CeCl (CpH = Cp = C5H5; CpMe = C5H4Me) with NaOAr afforded CpMe2Ce(OAr)2 and Cp3Ce(OAr). The cerium(IV) complexes display a pseudotetrahedral geometry in the solid state. Cyclic voltammetry revealed mostly chemically reversible as well as electrochemically quasi-reversible redox processes with potentials ranging from -0.84 to -1.61 V versus Fc/Fc+. Switching from sandwich to half-sandwich complexes decreased the electrochemical potentials drastically, showing better stabilization of the cerium(IV) center in the case of Cp*Ce(OR)3 than in the case of Cp*2Ce(OR)2. Enhanced stabilization of the cerium +IV oxidation state could be further demonstrated in the series alkoxy > siloxy > aryloxy as well as C5Me5 > C5HMe4.

Synthesis and antiproliferative activity of novel organometallic cobalt(III) complex encapsulated in polydiacetylene-phospholipid nanoformulation

Organometallic complexes are considered as promising anticancer agents with the aim to overcome the limitations of platinum drugs but until very recently the development of organometallic cobalt-based anticancer active compounds has remained scarce. Two novel half-sandwich Cobalt(III)-pentamethylcyclopentadienyl complexes containing Schiff base ligands of the general formula [Cp*Co(NN)CH3CN](ClO4)2(Cp*Co(L1) and Cp*Co(L2)), where Cp* is pentamethylcyclopentadiene and NN is bis(anthracen-9-ylmethylene)benzene-1,2-diamine (L1) or bis(4-isopropylbenzylidene)benzene-1,2-diamine (L2), have been synthesized and characterized by elemental analysis, spectroscopic techniques, DFT method and cyclic voltammogram analysis. The facile reduction behaviour of complexes illustrates the observed potency of their oxidative DNA cleavage. Cp*Co(L1) complex displays oxidative DNA cleavage in presence of ascorbic acid more prominent than Cp*Co(L2) by generating OH radicals. Cp*Co(L1) complex shows remarkable cytotoxicity (IC50: ∼0.5 μM) towards A549 lung and HeLaS3 cervical cancer cells but moderate to normal human lung fibroblast cells (IC50: 6.02 μM). Also, the cytotoxic potency of Cp*Co(L1) is significantly higher than its analogue complex as well as cis-platin due to its redox behaviour and enhanced hydrophobicity of the ligand moieties. The AO/EB staining assay reveals that the complexes are able to induce late apoptotic mode of cell death in lung and cervical cancer cells. In order to improve the biocompatibility and anticancer activity of Cp*Co(L1) complex, it is encapsulated into polymer-supported liposomes and the size and morphology of nanoformulation is characterized by suitable techniques. The toxic effect of the complex after being encapsulated into liposome is reduced towards normal cells. However, the nanoformulation is less active in lung and cervical cancer cells compared to non-encapsulated complex.

Synthesis and Characterization of an Oxo-Centered Homotrimetallic Uranium(IV)–Cyclobutadienyl Dianion Complex

Reaction of [Li2{C4(SiMe3)4}(THF)2] (1) with [U(η5-C5Me5)I2(THF)] (2) produced the oxo-centered homotrimetallic uranium–pentamethylcyclopentadienyl complex [{U(η5-C5Me5)(μ-I)2}3{μ3-O}{Li(THF)3}0.5]...

Pyrrole thioamide complexes of organo-rhodium(III), -iridium(III) and -ruthenium(II)

Reactions of the pentamethylcyclopentadienyl complexes [(η5-Cp*)MCl2]2 (M = Rh, Ir) and the ruthenium arene complex [(η6-C6Me6)RuCl2]2 with pyrrole-2-thioamide ligands (containing various substituents on the pyrrole ring) and triethylamine base were investigated. A set of new dinuclear complexes were obtained in which the pyrrole thioamide ligand bonds as a dianion, through the deprotonated pyrrole, and the sulfur atom bridging the two metal centres, as confirmed by a X-ray structure determination on an iridium derivative. When triphenylphosphine was included in the reaction mixture, mononuclear complexes were obtained, with the pyrrole thioamide dianion ligand coordinating through sulfur and the pyrrole nitrogen, forming a five-membered chelate ring. The complexes were characterised by NMR and IR spectroscopies, and ESI mass spectrometry. A preliminary investigation of the activity of a selection of compounds towards A549 (adenocarcinomic human alveolar basal epithelial) cells was also carried out.

Pentamethylcyclopentadienyl osmium complexes that contain diazoalkane, dioxygen and allenylidene ligands: preparation and reactivity.

Diazoalkane complexes [Os(η5-C5Me5)(N2CAr1Ar2)(PPh3){P(OR)3}]BPh4 (1, 2) [R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C12H8 (fluorenyl) (c)] were prepared by reacting bromo-compounds OsBr(η5-C5Me5)(PPh3){P(OR)3} with an excess of diazoalkane in ethanol. The treatment of diazoalkane complexes 1 and 2 with acetylene under mild conditions (1 atm, RT) led to dipolar (3 + 2) cycloaddition affording 3H-pyrazole derivatives [Os(η5-C5Me5)(η1-[upper bond 1 start]N[double bond, length as m-dash]NC(C12H8)CH[double bond, length as m-dash]C[upper bond 1 end]H)(PPh3){P(OR)3}]BPh4 (6, 7) [R = Me (6), Et (7)] whereas reactions with terminal alkynes R1C[triple bond, length as m-dash]CH (R1 = Ph, p-tolyl, COOMe) gave vinylidene derivatives [Os(η5-C5Me5){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)R1}(PPh3){P(OR)3}]BPh4 (8b-d, 9b-d) [R = Me (8), Et (9); R1 = Ph (b), p-tolyl (c), COOMe (d)]. Exposure to air of dichloromethane solutions of complexes 1 and 2 produced dioxygen derivatives [Os(η5-C5Me5)(η2-O2)(PPh3){P(OR)3}]BPh4 (10, 11) [R = Me (10), Et (11)]. Allenylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CR1R2 (12-14) [R1 = R2 = Ph (12, 13); R1 = Ph, R2 = Me (14)], vinylvinylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C(H)C(Ph)[double bond, length as m-dash]CH2 (15) and 3-hydroxyvinylidene [Os][double bond, length as m-dash]C[double bond, length as m-dash]C(H)C(H)R2(OH) (16, 17) [R2 = Ph (16), H (17)] derivatives were also prepared. The vinylidene complex [Os(η5-C5Me5)([double bond, length as m-dash]C[double bond, length as m-dash]CH2)(PPh3){P(OMe)3}]BPh4 (8a) reacted with PPh3 to afford the alkenylphosphonium derivative [Os(η5-C5Me5){η1-C(H)[double bond, length as m-dash]C(H)PPh3}(PPh3){P(OMe)3}]BPh4 (18) whereas vinylidene complexes 8 and 9 reacted with water leading to the hydrolysis of the alkyne and the formation of carbonyl complexes [Os(η5-C5Me5)(CO)(PPh3){P(OR)3}]BPh4 (19, 20). The complexes were characterised by spectroscopic data (IR and NMR) and by X-ray crystal structure determination of [Os(η5-C5Me5){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)p-tolyl}(PPh3){P(OEt)3}]BPh4 (9c), [Os(η5-C5Me5)(η2-O2)(PPh3){P(OMe)3}]BPh4 (10) and [Os(η5-C5Me5)(CO)(PPh3){P(OMe)3}]BPh4 (19).

Tetranuclear Ruthenium Cyclopentadienyl and Pentamethylcyclopentadienyl Complexes Containing Bridging Nitrido Ligands

Tetranuclear Ru μ-nitrido complexes have been synthesized by reactions of Ru(II) cyclopentadienyl and pentamethylcyclopentadienyl complexes with Ru(VI) terminal nitrides. Treatment of [RuCp2] (Cp = η5-C5H5) with [LOEtRuVI(N)Cl2] (LOEt– = [CpCo{P(O)(OEt)2}3]−) (1) afforded a tetranuclear RuIV2-RuIII2 μ-nitrido complex, [CpRu{(μ-N)RuCl2LOEt}{(μ-Cl)RuClLOEt}{(μ-NC5H4NH)RuCl2LOEt}] (2), that contains a bridging monodeprotonated cyclopent-4-ene-1,3-diimine ligand. The formation of 2 possibly involves the migratory insertion of the Ru nitride with a Ru-η1-C5H5 intermediate derived from the η5–η1 ring slippage of [RuCp2] and subsequent C–H activation of the cyclopentadienylimido ligand by another molecule of 1. Treatment of [Cp*Ru(MeCN)3](PF6) (Cp* = η5-C5Me5) with [LOEtM(N)Cl2] afforded [{Cp*Ru(μ-N)M(LOEt)}2(μ-Cl)4](PF6)2 (M = Ru (3), Os (4)). Treatment of [Cp*Ru(MeCN)3](PF6) with mer-[Ru(N)Cl3(AsPh3)2] yielded [{Cp*Ru(μ-N)RuCl(AsPh3)}2(μ-Cl)4(μ-O2PF2)](PF6) (5), which contains a bridging difluorophosphate liga...

A pyrazine amide – 4-aminoquinoline hybrid and its rhodium and iridium pentamethylcyclopentadienyl complexes; evaluation of anti-mycobacterial and anti-plasmodial activities

The synthesis and characterization of N-(2-((7-chloroquinolin-4-yl)amino)ethyl)pyrazine-2-carboxamide (L), an aminoquinoline – pyrazinamide hybrid, and the complexes (N-(2-((7-chloroquinolin-4-yl)amino)ethyl)pyrazine-2-carboxamide)(cyclopentadienyl) chlorido-rhodium or iridium hexafluorophosphate ([M(L)(Cp*)Cl] PF6; M = Rh, Ir) and the corresponding chlorido salts ([M(L)(Cp*) Cl]Cl; M = Rh, Ir) are described. The ligand and the hexafluorophosphate salts of the metal complexes have been evaluated for anti-plasmodial and anti-mycobacterial activity. The rhodium and the iridium complexes were significantly more active against M. tuberculosis than the free ligand. The crystallographically determined molecular structures of complexes (N-(2-((7-chloroquinolin-4-yl)amino)ethyl)pyrazine-2-carboxamide)(cyclopentadienyl)chlororhodium hexafluoro-phosphate and (N-(2-((7-chloroquinolin-4-yl)amino)ethyl)pyrazine-2-carboxamide)(cyclopentadienyl)chloro-iridium chloride are presented.

Rhodium(III) and iridium(III) pentamethylcyclopentadienyl complexes with tris(2-carboxyethyl)phosphine, properties and cytostatic activity

New pentamethylcyclopentadienyl complexes [M(C5Me5)Cl2(TCEP)] (M = Rh 1, M = Ir 2) with P(C2H4COOH)3 (TCEP) were investigated using IR, 1H, 13C, 31P NMR and ESI-MS spectroscopies. Geometry optimization in the gas phase at the B3LYP/3-21G** level indicated that complex 1 has stable pseudooctahedral structure with large HOMO–LUMO gap. Calculated and experimental IR spectra of 1 agree very well. Cytostatic activity of compounds 1 and 2 was investigated against melanoma and breast tumor cells. Complexes 1 and 2 show very promising activity towards MDA-MB-231 triple negative breast cancer cells.

SnCl2 insertion into Ir–Cl and Rh–Cl bonds: Synthesis, characterization and catalytic activity of three-legged piano-stool trichlorostannyl iridium and rhodium complexes

Facile insertion reaction of SnCl2 across pentamethylcyclopentadienyl complexes of Ir(III) and Rh(III) resulted in the formation of Ir–SnCl3 and Rh–SnCl3 heterobimetallic complexes. Treatment of SnCl2 with [Cp*IrCl2]2 and [Cp*Ir(NH2tBu)Cl2] afforded [Cp*Ir(SnCl3)2{SnCl2(H2O)2}] (1) and [Cp*Ir(SnCl3)3][NH3tBu] (3), respectively. Similarities in NMR data for complexes 1 and 3 suggested that complex 1 converts to anionic [Cp*Ir(SnCl3)3] species in solution via rapid chloride exchange. Similarly, insertion reaction of SnCl2 with [Cp*Ir(PPh3)Cl2] and [Cp*Rh(PPh3)Cl2] afforded single insertion complex [Cp*Ir(PPh3)(SnCl3)Cl] (2) and double insertion complex [Cp*Rh(PPh3)(SnCl3)2] (4), respectively. All these new complexes were characterized by multinuclear NMR spectroscopy, while complexes 1, 3 and 4 were structurally characterized by single crystal X-ray diffraction technique. Complexes 1–4 were also tested as catalyst for bisarylation of aldehyde with arene and it was observed that only complexes 1 and 3 were active. Scope of this organic reaction was examined for different arenes and heteroarenes and in all the cases very good yields of triarylmethane derivatives were achieved.

Contrasting Reactivity and Cancer Cell Cytotoxicity of Isoelectronic Organometallic Iridium(III) Complexes

Replacing the N,N-chelating ligand 2,2'-bipyridine (bpy) in the Ir(III) pentamethylcyclopentadienyl (Cp*) complex [(η(5)-C(5)Me(5))Ir(bpy)Cl](+) (1) with the C,N-chelating ligand 2-phenylpyridine (phpy) to give [(η(5)-C(5)Me(5))Ir(phpy)Cl] (2) switches on cytotoxicity toward A2780 human ovarian cancer cells (IC(50) values of >100 μM for 1 and 10.8 μM for 2). Ir-Cl hydrolysis is rapid for both complexes (hydrolysis equilibrium reached in <5 min at 278 K). Complex 2 forms adducts with both 9-ethylguanine (9-EtG) and 9-methyladenine (9-MeA), but preferentially with 9-EtG when in competition (ca. 85% of total Ir after 24 h). The X-ray crystal structure of [(η(5)-C(5)Me(5))Ir(phpy)(9-EtG-N7)]NO(3)·1.5CH(2)Cl(2) confirms N7 binding to guanine. Two-dimensional NMR spectra show that complex 2 binds to adenine mainly through N1, consistent with density functional theory (DFT) calculations. DFT calculations indicate an interaction between the nitrogen of the NH(2) group (9-MeA) and carbons from phpy in the adenine adduct of complex 2. Calculations show that the most stable geometry of the adduct [(η(5)-C(5)Me(5))Ir(phpy)(9-EtG-N7)](+) (3b) has the C6O of 9-EtG orientated toward the pyridine ring of phpy, and for [(η(5)-C(5)Me(5))Ir(phpy)(9-MeA-N1)](+) (4(N1)a), the NH(2) group of 9-EtA is adjacent to the phenyl ring side of phpy. Complex 2 is more hydrophobic than complex 1, with log P values of 1.57 and -0.95, respectively. The strong nucleobase binding and high hydrophobicity of complex 2 probably contribute to its promising anticancer activity.

Chemical implantation of Group 4 cations on silica via cyclopentadienyl- and N,N-dialkylcarbamato derivatives

Chemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild conditions by the reaction of polycyclopentadienyl- (MCpn; M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed cyclopentadienyl/N,N-dialkylcarbamato (MLx(O2CNEt2)y; M = Ti, L = Cp, C5Me5 (Cp*), x = 2, y = 1; M = Hf, L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O2CNR2)n, M = Ti, n = 3, R = iPr; M = Ti, Hf, n = 4, R = Et; M = Zr, n = 4, R = iPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process. The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl complex being less reactive than the unsubstituted congener. The starting complexes and the final products have been characterized by EPR or by 13C CP-MAS NMR spectroscopy.

N‐(2‐benzimidazolylquinolin‐8‐yl)benzamidate half‐titanocene chlorides: Synthesis, characterization and their catalytic behavior toward ethylene polymerization

AbstractA series of N‐(2‐benzimidazolyquinolin‐8‐yl)benzamidate half‐titanocene chlorides, Cp′TiLCl (C1–C8: Cp′ = C5H5, MeC5H4, or C5Me5; L = N‐(benzimidazolyquinolin‐8‐yl)benzamides)), was synthesized by the KCl elimination reaction of half‐titanocene trichlorides with the correspondent potassium N‐(2‐benzimidazolyquinolin‐8‐yl)benzamide. These half‐titanocene complexes were fully characterized by elemental and NMR analyses, and the molecular structures of complexes C2 and C8 were determined by the single‐crystal X‐ray diffraction. The high stability of the pentamethylcyclopentadienyl complex (C8) was evident by no decomposing nature of its solution in air for one week. The oxo‐bridged dimeric complex (C9) was isolated from the solution of the corresponding cyclopentadienyl complex (C3) solution in air. Complexes C1–C8 exhibited good to high catalytic activities toward ethylene polymerization and ethylene/α‐olefin copolymerization in the presence of methylaluminoxane (MAO) cocatalyst. In the typical catalytic system of C1/MAO, the polymerization productivities were enhanced with either elevating reaction temperature or increasing the ratio of MAO to titanium precursor. In general, it was observed that higher the catalytic activity of the catalytic system lower the molecular weight of polyethylene. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3154–3169, 2009

Study of novel η 5-cyclopentadienyl and η 6-arene platinum group metal complexes containing a N 4-type ligand and their structural characterization

The mononuclear η 5-cyclopentadienyl complexes [(η 5-C 5H 5)Ru(PPh 3) 2Cl], [(η 5-C 5H 5)Os(PPh 3) 2Br] and pentamethylcyclopentadienyl complex [(η 5-C 5Me 5)Ru(PPh 3) 2Cl] react in the presence of 1 eq. of the tetradentate N, N′-chelating ligand 3,5-bis(2-pyridyl)pyrazole (bpp-H) and 1 eq. of NH 4PF 6 in methanol to afford the mononuclear complexes [(η 5-C 5H 5)Ru(PPh 3)(bpp-H)]PF 6 ([ 1]PF 6), [(η 5-C 5H 5)Os(PPh 3)(bpp-H)]PF 6 ([ 2]PF 6) and [(η 5-C 5Me 5)Ru(PPh 3)(bpp-H)]PF 6 ([ 3]PF 6), respectively. The dinuclear η 5-pentamethylcyclopentadienyl complexes [(η 5-C 5Me 5)Rh(μ-Cl)Cl] 2 and [(η 5-C 5Me 5)Ir(μ-Cl)Cl] 2 as well as the dinuclear η 6-arene ruthenium complexes [(η 6-C 6H 6)Ru(μ-Cl)Cl] 2 and [(η 6- p- iPrC 6H 4Me)Ru(μ-Cl)Cl] 2 react with 2 eq. of bpp-H in the presence of NH 4PF 6 or NH 4BF 4 to afford the corresponding mononuclear complexes [(η 5-C 5Me 5)Rh(bpp-H)Cl]PF 6 ([ 4]PF 6), [(η 5-C 5Me 5)Ir(bpp-H)Cl]PF 6 ([ 5]PF 6), [(η 6-C 6H 6)Ru(bpp-H)Cl]BF 4 ([ 6]BF 4) and [(η 6- p- iPrC 6H 4Me)Ru(bpp-H)Cl]BF 4 ([ 7]BF 4). However, in the presence of 1 eq. of bpp-H and NH 4BF 4 the reaction with the same η 6-arene ruthenium complexes affords the dinuclear salts [(η 6-C 6H 6) 2Ru 2(bpp)Cl 2]BF 4 ([ 8]BF 4) and [(η 6- p- iPrC 6H 4Me) 2Ru 2(bpp)Cl 2]BF 4 ([ 9]BF 4), respectively. These compounds have been characterized by IR, NMR and mass spectrometry, as well as by elemental analysis. The molecular structures of [ 1]PF 6, [ 5]PF 6 and [ 8]BF 4 have been established by single crystal X-ray diffraction studies and some representative complexes have been studied by UV–vis spectroscopy.

Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N– B–PTA(BH 3): X-ray crystal structures of [Cp ∗RhCl 2{ N– B}–PTA(BH 3)] and [Cp ∗Rh{ N– B–PTA(BH 3)}(η 2-CH 2 = CHPh)

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N– B–PTA(BH 3) and [Cp ∗RhCl(μ-Cl)] 2 affords [Cp ∗Rh{ N– B–PTA(BH 3)}Cl 2] ( 3) or [Cp ∗Rh{ N– B–PTA(BH 3)} 2Cl]Cl ( 5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp ∗Rh{ N– B–PTA(BH 3)}H 2] ( 8) was also obtained by reaction of 3 with NaBH 4 and alternatively by direct hydroboration of [Cp ∗Rh(PTA)Cl 2] with excess NaBH 4. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H 3BO 3 and the corresponding PTA derivatives, including the water-soluble dihydride [Cp ∗Rh(PTA)H 2] ( 9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp ∗Rh{ N– B–PTA(BH 3)}(η 2-CH 2 = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η 2-coordinated to rhodium without affecting the N–BH 3 moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.

Synthesis and Structure of Strontium and Barium Guanidinates and Mixed-Ligand Guanidinate Pentamethylcyclopentadienyl Complexes

A new family of strontium and barium guanidinate complexes were synthesized from SrI2, [Sr{N(SiMe3)2}2]2, [Ba{N(SiMe3)2}2(THF)1.6], Sr(Cp*)2, and Ba(Cp*)2(THF)1.7 metal reactants and appropriate guanidine or guanidinate ligand (Cp* = pentamethylcyclopentadienide). Treatment of [Sr{N(SiMe3)2}2]2 with 4.0 equiv of iPrN═C(NMe2)N(H)iPr (1LH) or iPrN═C(N(iPr)2)N(H)iPr (2LH) gave dimeric complexes [(η2-1L)Sr(μ2,η2:η2-1L)(μ2,η1:η1-1L)Sr(η2-1L)] (3) and [(η2-2L)Sr(μ2,η2:η2-2L)2Sr(η2-2L)] (4), respectively. Related reactions of 1LH and 2LH with 1.0 equiv of Sr(Cp*)2 afforded the mixed-ligand complexes [(Cp*)Sr(μ2,η2:η2-1L)2Sr(Cp*)] (5) and [(Cp*)Sr(μ2,η2:η2-2L)2Sr(Cp*)] (6), respectively, with simultaneous liberation of Cp*H. Treatment of [Ba{N(SiMe3)2}2(THF)1.6] with 2.0 equiv of 2LH gave the dimer [(η2-2L)Ba(μ2,η2:η2-2L)2Ba(η2-2L)] (7), while reaction of Ba(Cp*)2(THF)1.7 with 2LH afforded guanidinate-bridged [(Cp*)Ba(μ2,η2:η2-2L)2Ba(Cp*)] (8). Reaction of SrI2 with 2.0 equiv of Na[(iPr)NC(N(SiMe3)2)N(iPr)] (9LNa) in diethyl ether gave monomeric [Sr(η2-9L)2OEt2] (10). The solid-state structures of 3, 4, 6, 7, 8, and 10 are reported. Reactions of 4 and 6 with certain Lewis bases are also described.

Synthesis and Characterization of the Octahydrotriborate Complexes Cp*V(B3H8)2 and Cp*Cr(B3H8)2 and the Unusual Cobaltaborane Cluster Cp*2Co2(B6H14)

The new compounds CpV(B(3)H(8))(2), CpCr(B(3)H(8))(2), and Cp(2)Co(2)(B(6)H(14)) have been synthesized by treating the pentamethylcyclopentadienyl complexes [CpVCl(2)](3), [CpCrCl(2)](2), and [CpCoCl](2) with NaB(3)H(8). X-ray crystallography shows that CpV(B(3)H(8))(2) and CpCr(B(3)H(8))(2) have the same ligand sets but different molecular structures: the vanadium compound contains two bidentate B(3)H(8) ligands (i.e., bound to the metal center via two vicinal hydrogen atoms), whereas the chromium compound has one bidentate B(3)H(8) ligand and one B(3)H(8) ligand bound in an unprecedented fashion via two geminal hydrogen atoms. The "gem-bound" B(3)H(8) group itself has an atypical structure consisting of a BH(2)-BH(2)-BH(3) triangle with one additional hydrogen atom bridging the unique BH(2)-BH(2) edge. The B-B distances are nearly identical within experimental error at 1.790(5), 1.792(5), and 1.786(6) Angstrom. The relationship between the electronic and molecular structures of the V and Cr compounds is briefly discussed. The structure of Cp(2)Co(2)(B(6)H(14)) can be viewed in two different ways: as a dicobalt complex in which two CpCo units are each bound to four adjacent boron atoms of an S-shaped B(6)H(14) ligand, or as an eight-vertex hypho cluster compound. In the former case, the B(6)H(14) ligand is best regarded as a dianionic bi-borallyl group H(3)B(mu-H)BH(mu-H)BHBH(mu-H)BH(mu-H)BH(3) in which one hydrogen at each end of the chain is involved in an agostic interaction. From a cluster point of view, the structure of Cp(2)Co(2)(B(6)H(14)) can be generated by removing three adjacent high-connectivity vertices from the eleven-vertex closo polyhedron. The Co-B distances vary from 2.008(5) to 2.183(4) Angstrom, and the B-B distances within in the S-shaped chain range from 1.734(8) to 1.889(6) Angstrom. Finally, a new synthesis of the known molybdenum compound Cp(2)Mo(2)(B(5)H(9)) is described; its structure as established by X-ray crystallography closely resembles that of the previously described (C(5)H(4)Me) analogue.