Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(L-L)(NCBH3) (M = Mo, W; L-L = dppe, bipy, en)

Compounds M(CO)₂(η³-C₃H₅)(L-L)(NCBH₃) (L-L = dppe, M = Mo(1), W(2); L-L = bipy, M = Mo(3), W(4); L-L = en, M = Mo(5), W(6)) were prepared and characterized. The single crystal X-ray analyses of 2-6 revealed that the cyanotrihydroborate anion bonds to the metal through a nitrogen atom, the open face of the allyl group being pointed toward the two carbonyls (endo-isomer). In compounds 2, 5, and 6, the two donor atoms of the bidentate ligand occupy equatorial and axial positions, respectively. In the solid state structures of compounds 3 and 4 both nitrogen atoms of the bipy ligand occupy equatorial positions. The NMR spectroscopy reveals a fluxional behavior of compounds 1, 2, 5, and 6 in solution. Although the fluxional behavior of compounds 5 and 6 ceased at about −40 °C, that of compound 1 could not be stopped even at −90 °C. Their low temperature conformations are consistent with their solid state structures. Both the endo- and exo-isomers coexist in solution for compounds 3 and 4.     

HMB and Cp* ruthenium(II) complexes containing bis- and tris-(mercaptomethimazolyl)borate ligands: Synthetic, X-ray structural and electrochemical studies (HMB = η-C6Me6, Cp* = η-C5Me5)

The reactions of [(HMB)RuCl₂]₂ with K[HB(mt)₃] and Na[H₂B(mt)₂] (mt = N-methyl-2-mercaptoimidazol-1-yl) led to the isolation of [(HMB)Ru{HB(mt)₃}]Cl (1) (ca. 66% yield) and [(HMB)Ru{H₂B(mt)₂}]Cl (2) (ca. 70% yield), respectively. The reaction of [Cp*RuOMe]₂ with Na[H₂B(mt)₂] yielded Cp*Ru[H₂B(mt)₂] (3) (ca. 85% yield). Single crystal X-ray diffraction analyses were carried out on all three complexes, together with cyclic voltammetric measurements.     

New ferrocenylmethylphosphines - Preparation, characterisation and coordination chemistry of PH(CH2Fc)2, P(CH2Fc)3 [Fc = Fe(η-C5H5)(η-C5H4)] and their derivatives

The new ferrocenylmethylphosphines PH(CH₂Fc)₂ (1) [Fc = Fe(η⁵-C₅H₅)(η⁵-C₅H₄)] and P(CH₂Fc)₃ (2) and the phosphonium salt [P(CH₂Fc)₃(CH₂OH)]I (3) were synthesised from P(CH₂OH)₃ and [FcCH₂NMe₃]I. [P(CH₂Fc)(CH₂OH)₃]Cl (4) was obtained from P(CH₂Fc)(CH₂OH)₂, CH₂O and HCl. The new phosphines and phosphonium salts were fully characterised by NMR and IR spectroscopy and MS. [Mo(CO)₆] reacts with 1 to give [Mo(CO)₅{PH(CH₂Fc)₂}] (5) in high yield, but attempts to employ 2 as a ligand failed. The reaction of [P(CH₂Fc)₃(CH₂OH)]I (3) and [PH(CH₂Fc)₃]I (obtained in situ from 3 and Na₂S₂O₅) with [WI₂(CO)₃(NCMe)₂] gave the complex salts [P(CH₂Fc)₃(CH₂OH)][WI₃(CO)₄] (6) and [PH(CH₂Fc)₃][WI₃(CO)₄] (7), respectively. [P(CH₂Fc)₄]I (8) was synthesized from PH₂CH₂Fc and [FcCH₂NMe₃]I. Crystal structures were obtained for 1, 3-8.     

Stilbene analogues incorporating the Co(η-C4Ph4)(η-C5H4-) end group

A number of organometallic stilbenes of the general type [Co(η⁴-C₄Ph₄)(η⁵-C₅H₄CHCHR] are reported where R is C₆H₄X-4 (X = H, OMe, Br, NO₂), 1-naphthyl, 9-anthryl, 1-pyrenyl, (η⁵-C₅H₄)Co(η⁴-C₄Ph₄), and (η⁵-C₅H₄)Fe(η⁵-C₅H₄Y) {Y = CHO, CHC(CN)₂ and CHCHC₅H₄-η⁵)Co(η⁴-C₄Ph₄)}. They were prepared by Wittig or Horner-Wadsworth-Emmons reactions which yield both E and Z or only E products respectively. The isomers were separated and all compounds characterised by standard spectroscopic techniques as well as by X-ray diffraction methods in many cases. The electrochemistry of the stilbene analogues in dichloromethane solution is also reported. In most, the (η⁵-C₅H₄)Co(η⁴-C₄Ph₄) functional group undergoes a reversible one-electron oxidation. For those molecules that also include (η⁵-C₅H₄)Fe(η⁵-C₅H₄Y), this is preceded by the reversible oxidation of the ferrocenyl group. Spectroscopic and structural data suggests that for most compounds there is little electronic interaction between Co(η⁴-C₄Ph₄)(η⁵-C₅H₄) and the R end groups which are effectively independent of one another. The only exceptions to this are Z and E-[Co(η⁴-C₄Ph₄)(η⁵-C₅H₄CHCHC₆H₄NO₂-4], and [Co(η⁴-C₄Ph₄)(η⁵-C₅H₄CHCHC₅H₄-η⁵)Fe{η⁵-C₅H₄CHC(CN)₂}] where the electronic spectra are respectively consistent with a significant Co(η⁴-C₄Ph₄)(η⁵-C₅H₄)/NO₂ donor/acceptor interaction and a less significant Co(η⁴-C₄Ph₄)(η⁵-C₅H₄)/C(CN)₂ one. However, OTTLE studies show that in the electronic spectra of [Co(η⁴-C₄Ph₄)(η⁵-C₅H₄CHCHR]⁺ there are low energy absorption bands (950-1800 nm) which are attributed to R → Co(η⁴-C₄Ph₄)(η⁵-C₅H₄)⁺ or, when R is a ferrocenyl-base group, Co(η⁴-C₄Ph₄)(η⁵-C₅H₄) → (η⁵-C₅H₄)Fe(η⁵-C₅H₄Y)⁺ charge transfer transitions. The ferrocenyl compounds undergo cis/trans isomerisation on the OTTLE experiment timescale.     

Aldol condensation reactions of [Co(η-C4Ph4){η-C5H4C(O)CH3}]

The aldol condensation reaction between [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] and a range of aromatic aldehydes [RCHO] and [RCHCH-CHO] gives a series of α,β-unsaturated ketones [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-R}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-CHCH-R}] (3). The reaction is promoted by various bases: NaH proved to be the most effective whilst ⁿBuLi gave [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(OH)(ⁿBu)CH₃}] as the major product. NaOH was ineffective, perhaps indicating that that the methyl protons in [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] are less acidic than those in [Fe(η⁵-C₅H₅){η⁵-C₅H₄C(O)CH₃}]. Compounds 3 were characterised spectroscopically. Their ¹H NMR spectra are consistent with a trans configuration about their CC bond, and this was confirmed by X-ray crystallography in five cases, which showed that all have the same basic structure with parallel cyclobutadiene and cyclopentadienyl ligands, but they are not identical. The C₅H₄C(O)(CHCH)_n-R (n = 1 or 2) moieties show little evidence for delocalisation and often deviate from planarity. The UV/Vis spectra of those 3 with smaller aromatic rings (R = C₆H₅, 4-C₆H₄NMe₂, 2-C₄H₃S and 1-C₁₀H₇) suggest that these are donor-π-acceptor systems, but as the annellation of R increases (R = 9-C₁₄H₉, 1-C₁₆H₉ and 1-C₂₀H₁₁) the spectra increasingly resemble those of the parent polycyclic aromatic hydrocarbon, RH. Reduction of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-C₁₀H₇-1}] with DIBAL gives a mixture of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₂CH₂-C₁₀H₇-1}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄CH(OH)CHCH-C₁₀H₇-1}]. A minor product from the preparation of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] was shown by X-ray crystallography to be the η⁴-butadiene complex [Co{η⁴-Ph(H)CC(Ph)-C(Ph)C(H)Ph}{η⁵-C₅H₄C(O)CH₃}].     

Synthesis and reactivity of asymmetrically substituted ansa-bridged zirconocene complexes: X-ray crystal structures of [Zr{R(H)C(η-C5Me4)(η-C5H4)}Cl2] (R = Bu, Bu) and [Zr{Bu(H)C(η-C5Me4)(η-C5H4)}(CH2Ph)2]

The dialkyl complexes, (R = Prⁱ, R′ = Me (2a), CH₂Ph (3a); R = Buⁿ, R′ = Me (2b), CH₂Ph (3b); R = Bu^t, R′ = Me (2c), CH₂Ph (3c); R = Ph, R′ = Me (2d), CH₂Ph (3d)), have been synthesized by the reaction of the ansa-metallocene dichloride complex, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (R = Prⁱ (1a), Buⁿ (1b), Bu^t (1c), Ph (1d)), and two molar equivalents of the alkyl Gringard reagent. The insertion reaction of the isocyanide reagent, CNC₆H₃Me₂-2,6, into the zirconium-carbon σ-bond of 2 gave the corresponding η²-iminoacyl derivatives, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}{η²-MeCNC₆H₃Me₂-2,6}Me] (R = Prⁱ (4a), Buⁿ (4b), Bu^t (4c), Ph (4d)). The molecular structures of 1b, 1c and 3b have been determined by single-crystal X-ray diffraction studies.     

Cyclopalladation of N-phenyl-4-ferrocenylmethylpyrazoles: Crystal structure of [Pd{κ-C,N-C6H4-1-[(3,5-Me2-C3N2)-CH2-(η-C5H4)Fe(η-C5H5)]}Cl(PPh3)] · CH2Cl2

The synthesis and characterization of pyrazole derivatives of general formula [C₆H₄-4-R-1-{(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}] [R = OMe (1a) or H (1b)] with a ferrocenylmethyl substituent are described.The study of the reactivity of compounds 1 with palladium(II) acetate has allowed the isolation of complexes (μ-AcO)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (2) [R = OMe (2a) or H (2b)] that contain a bidentate [C(sp², phenyl), N]⁻ ligand and a central “Pd(μ-AcO)₂Pd” unit.Furthermore, treatment of 2 with LiCl produced complexes (μ-Cl)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (3) [R = OMe (3a) or H (3b)] that arise from the replacement of the acetato ligands by the Cl⁻.Compounds 2 and 3 also react with PPh₃ giving the monomeric complexes [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}X(PPh₃)] {X⁻ = AcO⁻ and R = OMe (5a) or H (5b) or X⁻ = Cl⁻ and R = OMe (6a) or H (6b)}, where the phosphine is in a cis-arrangement to the metallated carbon atom. Treatment of 3 with thallium(I) acetylacetonate produced [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}(acac)] (7) [R = OMe (7a) or H (7b)]. Electrochemical studies of the free ligands and the cyclopalladated complexes are also reported. The dimeric complexes 3 also react with MeO₂C-CC-CO₂Me (in a 1:4 molar ratio) giving [Pd{(MeO₂C-CC-CO₂Me)₂C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}Cl] (8) [R = OMe (8a) or H (8b)], which arise from the bis(insertion) of the alkyne into the σ{Pd-C(sp², phenyl)} bond of 3.     

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.     

Synthesis and properties of carboxy-substituted half-sandwich ruthenium complexes with chelating bisphosphine ligands (η-C5H4CO2H)Ru(η-L)X (X = I, H)

Several Ru(II) complexes (η⁵-C₅H₄CO₂H)Ru(η²-L)I have been prepared by the hydrolysis of the ester linkage in (η⁵-C₅H₄CO₂t-Bu)Ru(η²-L)Cl with trimethylsilyl iodide. The hydrides (η⁵-C₅H₄CO₂H)Ru(η²-L)H may be prepared by reduction of the iodide complexes in KOH/MeOH solutions followed by acidification. Complexes with several chelating bisphosphine ligands have been prepared in this way. The carboxylate anions [(η⁵-C₅H₄CO₂)Ru(η²-L)H]⁻ are readily protonated by weak acids to give the carboxyCp complexes. The pK_a of the carboxy proton of (η⁵-C₅H₄CO₂H)Ru(dppe)H (dppe = 1,2-bis(diphenylphosphino)ethane) is 11.3 in DMSO. Protonation of the neutral hydride complex (η⁵-C₅H₄CO₂H)Ru(dppf)H gives the cationic dihydride (η⁵-C₅H₄CO₂H)Ru(dppf)H⁺₂; the dihydride structure has been confirmed by measuring the T₁ of its ¹H NMR hydride resonance over a range of temperatures. The oxidations of the halide complexes (η⁵-C₅H₄CO₂H)Ru(dppf)I and (η⁵-C₅H₄CO₂t-Bu)Ru(dppf)Cl (dppf = 1,1′-bis(diphenylphosphino)ferrocene) have been studied by cyclic voltammetry.     

A study of β-hydride abstraction from alkanediyl homobimetallic complexes [{Cp(CO)2Fe}2{μ-(CnH2n)}] (n = 4-10, Cp = η-C5H5)

The alkyl-bridged iron(II) complexes [{Cp(CO)₂Fe}₂{μ-(C_nH_2n)}] (n = 6-10, Cp = η⁵-C₅H₅) undergo both single and double hydride abstraction when reacted with one equivalent of Ph₃CPF₆ to give both the monocationic complexes, [{Cp(CO)₂Fe}₂{μ-(C_nH_2n−1)}]PF₆, and the dicationic complexes, [{Cp(CO)₂Fe}₂{μ-(C_nH_2n−2)}](PF₆)₂. The ratios of monocationic to dicationic complexes decrease with the increase in the value of n. The complexes where n = 4 and 5 undergo only single hydride abstraction under similar conditions. When reacted with two equivalents of Ph₃CPF₆, the complexes where n = 6-10 undergo double hydride abstraction to give dicationic complexes only. In contrast, the complex where n = 5 gives equal amounts of the monocationic and the dicationic complexes, while the complex where n = 4 only gives the monocationic complex. ¹H and ¹³C NMR data show that in the monocationic complexes one metal is σ-bonded to the carbenium ion moiety while the other is bonded in a η²-fashion forming a chiral metallacylopropane type structure. In the dicationic complexes both metals are bonded in the η²-fashion. The monocationic complexes where n = 4-6, react with methanol to give η¹-alkenyl complexes[Cp(CO)₂Fe(CH₂)_nCHCH₂] (n = 2-4) as the major products and σ-bonded ether products [{Cp(CO)₂Fe}₂{μ-(CH₂)_nCH(OCH₃)CH₂}] as the minor products. The complex where n = 8 reacted with iso-propanol to give the η¹-alkenyl complex [Cp(CO)₂Fe(CH₂)₆CHCH₂]. The dicationic complexes where n = 5, 8 and 9 were reacted with NaI to give the respective α, ω-dienes and [Cp(CO)₂FeI].     

Insertion reaction of elemental sulfur into the Ln–C bond: Synthesis and characterization of [(C5H4SiMe2Bu)2Ln(μ-SR)]2 (R = Me,Ln = Yb,Er, Dy,Y; R = Bu,Ln = Yb,Dy)

Treatment of (C₅H₄SiMe₂^tBu)₂LnR with 1 equiv of elemental sulfur in toluene at ambient temperature gives dimeric complexes [(C₅H₄SiMe₂^tBu)₂Ln(μ-SR)]₂ [R = Me, Ln = Yb (1), Er (2), Dy (3), Y (4); R = ⁿBu, Ln = Yb (5), Dy (6)]. All these complexes have been characterized by elemental analysis, IR and mass spectroscopies. The structures of complexes 1, 3, 5 and 6 are also determined through X-ray single crystal diffraction analysis, indicating that only one sulfur atom from elemental sulfur inserts into Ln–C σ-bond.     

Synthesis and structure of the monometallic cationic complex [Cp(CO)2Fe{η-(CH2CHCH2CH3)}]PF6 (Cp = η-C5H5)

The bimetallic carbocation complex [{Cp(CO)₂Fe}₂(μ-C₄H₇)]PF₆ reacted with trifluoroacetic acid to give the mononuclear cationic complex [Cp(CO)₂Fe{η²-(CH₂CHCH₂CH₃)}]PF₆, which formed yellow orthorhombic crystals in the space group P2₁2₁2₁ with a = 7.652(4), b = 13.422(7), c = 14.037(7); α = β = γ = 90.00 and Z = 4. The carbocation is coordinated to the metal in a η²-fashion forming a chiral metallacyclopropane type structure. The β-CH carbon (C9) is disordered over two positions (C9A and C9B), each having about 50% occupancy. This is attributed to there being both the R and S enantioface isomers in equal amounts in the crystal sample. NMR data indicate that the metallacyclopropane structure observed in the solid state is preserved in solution.     

A series of multinuclear homo- and heterometallic complexes with bridging tellurolato ligands derived from [CpIr(CO)(TeTol)2] (Cp = η-C5Me5, Tol = p-tolyl)

Reactions of [Cp^∗Ir(CO)(TeTol)₂] (1; Tol = p-tolyl) with certain organometallic Pd(II), Pt(II), Ir(III), Rh(III), and Ru(II) species afforded IrPd, IrPt, IrPt₂, Ir₂, IrRh, IrRu₃, and IrRu complexes having tellurolato-bridged dinuclear or trinuclear cores. This finding demonstrates that 1 is a versatile precursor to synthesize a variety of multinuclear homo- and heterometallic μ-tellurolato complexes, whose chemistry is still less advanced as compared with that of μ-thiolato complexes.     

Synthesis, characterization and catalytic behaviour of ansa-zirconocene complexes containing tetraphenylcyclopentadienyl rings: X-ray crystal structures of [Zr{Me2Si(η-C5Ph4)(η-C5H3R)}Cl2] (R = H, Bu)

The ansa-bis(cyclopentadiene) compounds, Me₂Si(C₅HPh₄)(C₅H₄R) (R = H (2); Bu^t (3)), have been prepared by the reaction of C₅HPh₄(SiMe₂Cl) (1) with Na(C₅H₅) or Li(C₅H₄Bu^t), respectively, and transformed to the di-lithium derivatives, Li₂{Me₂Si(C₅Ph₄)(C₅H₃R)} (R = H (4); Bu^t (5)), by the action of n-butyllithium. The ansa-zirconocene complexes, [Zr{Me₂Si(η⁵-C₅Ph₄)(η⁵-C₅H₃R)}Cl₂] (R = H (6); Bu^t (7)), were synthesized from the reaction of ZrCl₄ with 4 or 5, respectively. Compounds 6 and 7 have been tested in the polymerization of ethylene and compared with their methyl-substituted analogues, [Zr{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃R)}Cl₂] (R = H (8); Bu^t (9)). Whilst 8 and 9 are catalytically active, the tetraphenyl-substituted complexes 6 and 7 proved to be inactive in the polymerization of ethylene. This phenomenon has been explained by DFT calculations based on the reaction intermediates in the polymerization processes involving 6 and 7, which showed that the extraction of a methyl group from the zirconocene complex to form the cationic active specie is endothermic and therefore unfavourable.     

Reactions of diferrocenyl dichalcogenides with [W(CO)5(THF)]: X-ray crystal structures of Fc2Te2 and [W2(μ-SeFc)2(CO)8] (Fc = [Fe(η-C5H5)(η-C5H4)])

Treatment of [W(CO)₅THF] with diferrocenyl diselenide, Fc₂Se₂, yielded the novel metal-metal bonded tungsten(I) complex, [W₂(μ-SeFc)₂(CO)₈] (1: Fc = ferrocenyl, [Fe(η⁵-C₅H₅)(η⁵-C₅H₄)]), which was characterised by NMR and IR spectroscopy, mass spectrometry, and X-ray crystallography. The corresponding tellurium derivative could not be prepared by an analogous route. The X-ray crystal structure of Fc₂Te₂ has also been determined.     

Cyclopentadienyl chromium and tungsten complexes with halide, methyl and σ-phenylethynyl ligands: Structures of (η-C5H5)Cr(NO)2(-CC-C6H5), (η-C5H5)Cr(NO)2I and [(η-C5H4)-COOCH3]W(CO)3Cl

With copper(I) iodide as catalyst, σ-alkynyls, compounds (η⁵-C₅H₅)Cr(NO)₂(CC-C₆H₅) (5), [(η⁵-C₅H₄)-COOCH₃]Cr(NO)₂(CC-C₆H₅) (10), and [(η⁵-C₅H₄)-COOCH₃]W(CO)₃(CC-C₆H₅) (13), were prepared from their corresponding metal chloride 1, 6 and 12. Structures of compound 3, 5 and 12 have been solved by X-ray diffraction studies. In the case of 5, there is an internal mirror plane passing through the phenylethynyl ligand and bisecting the Cp ring. The phenyl group is oriented perpendicularly to the Cp with an eclipsed conformation. The twist angle is 0° and 118.4° for -CC-Ph and two NO ligands, respectively. The orientation is rationalized in terms of orbital overlap between ψ₃ of Cp, dπ of Cr atom, and π^∗ of alkynyl ligand, and complemented by molecular orbital calculation. The opposite correlation was observed on the chemical shift assignments of C(2)-C(5) on Cp ring in compounds 6 and 12, using HetCOR NMR spectroscopy. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data and compared with the calculations via density functional B3LYP correlation-exchange method.     

A laser flash photolysis, matrix isolation, and DFT investigation of (η-C6H5Y)Cr(CO)3 (Y = NH2, OCH3, H, CHO, or CO2CH3)

The quantum yield for arene displacement from (η⁶-C₆H₅Y)Cr(CO)₃ was measured in 1,1,2-trifluorotrichloroethane (Y = NH₂, OCH₃, H, CHO, or CO₂CH₃). Values of 0.24, 0.27, 0.15, 0.17, and 0.32 were obtained respectively (λ_exc. = 355 nm). These values are significantly higher than those measured for photoinduced arene loss in hydrocarbon solvents using the same excitation wavelength. Laser flash photolysis of (η⁶-C₆H₅Y)Cr(CO)₃ in 1,1,2-trifluorotrichloroethane (λ_exc. = 355 nm) resulted in the rapid formation (<10 ns) of Cr(CO)₆. Matrix isolation experiments on (η⁶-C₆H₅Y)Cr(CO)₃ (Y = H or CHO) at 12 K in CH₄ or CO-doped CH₄ matrixes using monochromatic irradiation confirmed the presence of two discrete excited states, one leading to CO-loss and the other to arene-loss. The results correlate with the calculated electron drift in the excited state derived from density functional theory and time dependent density functional theory calculations.     

Synthesis of the cyclooctadiene and cyclooctenediyl cobalt complexes. Structures of [(η2,η2-cyclooctadiene)Co(η-1,2,4,5-C6H2Me4)]BF4 and [(η1,η3-cyclooctenediyl)Co(η-9-SMe2-7,8-C2B9H10)

Cobaltacarboranes (η¹, η³-cyclooctenediyl)Co(Carb) (Carb = η-9-SMe₂-7,8-C₂B₉H₁₀, η-1-tBuHN-1,7,9-C₃B₈H₁₀) were synthesized by the reaction of the carborane anions [Carb]⁻ with the acetonitrile complex [(η¹, η³-cyclooctenediyl)Co(MeCN)₃]⁺ generated in situ upon the dissolution of [(η¹, η³-cyclooctenediyl)Co(η-1,4-C₆H₄Me₂)]⁺ in MeCN. The structures of (η¹,η³-cyclooctenediyl)Co(η-9-SMe₂-7,8-C₂B₉H₁₀ and [(η²,η²-cyclooctadiene)Co((η-1,2,4,5-C₆H₂Me₄)]BF₄ were determined by X-ray diffraction analysis.