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.     

Allyl complexes of molybdenum with Schiff base ligands. The crystal structures of [MoCl(CO)2{N(C6H4-2-OMe)C(Me)C5H4N}(η-C3H5)] and [MoCl(CO)2{N(Me)C(Ph)C5H4N}(η-C3H5)] are described

Treatment of the molybdenum tetracarbonyl complexes of [Mo(CO)₄L₂] (L₂=pyridyl amine Schiff base ligands) with allyl chloride in refluxing THF afforded η³-allyl complexes [MoCl(CO)₂L₂(η³-allyl)] (1-9). These complexes have been characterised by various techniques including ¹H-NMR, IR and FABMS spectroscopies and the single crystal X-ray structure determinations of the complexes [MoCl(CO)₂{N(C₆H₄-2-OMe)C(Me)C₅H₄N}(η³-C₃H₅)] (3) and [MoCl(CO)₂{N(Me)C(Ph)C₅H₄N}(η³-C₃H₅)] (4).     

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}].     

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 synthetic, structural and reactivity study of [(η-C4R4)Co(η-C5H4X)] complexes, R = Me or Et; X = CHO, CHCHFc, CHCH(η-C5H4)Co(η-C4Ph4), CHC(CN)2: Unexpected formation of [(η-cyclopentadienyl)(η-3,4,5,6-tetraethyl-α-pyrone)cobalt]

The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η⁴-C₄R₄)Co(η⁵-C₅H₄CHO)] R = Et, 5, R = Me, 7, and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CO₂Me)] R = Et, 6, R = Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η⁴-C₄R₄)Co(η⁶-C₆H₅Me)]⁺ in acetonitrile, and subsequent treatment with Na[C₅H₄CHO] or Na[C₅H₄CO₂Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH₂PPh₃]I and CH₂(CN)₂, to form [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=CHFc)] and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=C(CN)₂], 11 and 15, respectively. The Horner-Wittig reaction of [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH₂P(O)(OEt)₂] with [(η⁴-C₄Ph₄)Co(η⁵-C₅H₄CHO)] yields [(η⁴-C₄R₄)Co(η⁵:η⁵-C₅H₄CHCH-C₅H₄)Co(η⁴-C₄Ph₄)], 12 and 13. [(η⁴-C₄Me₄)Co(η⁵-C₅H₄CHO)] also reacts with t-BuLi and FcLi to furnish the corresponding secondary alcohols, 16 and 17, respectively. Surprisingly, the attempted direct synthesis of 5 by reaction of Na[C₅H₅] and ethyl formate with [(η⁴-C₄Et₄)Co(CO)₂I], 1, instead yielded [(η⁵-C₅H₅)Co(η⁴-3,4,5,6-tetraethyl-α-pyrone)], 18, and a mechanistic proposal is advanced. The X-ray crystal structures of 1, 7, 8, 11(Z), 15 and 18, and also the isocobaltocenium salts [(η⁴-C₄Et₄)Co(η⁶-C₆H₅Me)][PF₆], 2, and [(η⁴-C₄Et₄)Co(η⁶-1,3,5-C₆H₃Me₃)][PF₆], 4, are reported.     

Palladium (II) complexes with mono-oxide 1,1′-bis(diphenylphosphino)metallocene ligands [Fe(η-C5Me4PPh2)(η-C5Me4P{O}Ph2)] and [Os(η-C5H4PPh2)(η-C5H4P{O}Ph2)]

The monoxides [Fe(η⁵-C₅Me₄PPh₂)(η⁵-C₅Me₄P{O}Ph₂)] (1) and [Os(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄P{O}Ph₂)] (2) have been prepared by treatment of the corresponding diphosphines with CCl₄ and methanol.These ligands react with [Pd(PhCN)₂Cl₂] to give dichloride complexes of different structure.The dimeric complex [{Os(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄P{O}Ph₂)}PdCl(μ-Cl)]₂ (4) contains the monodentate P-coordinated osmocene ligand with the free P{O}Ph₂ group, while the octamethylferrocene ligand gives the chelate k²-P,O complex [{Fe(η⁵-C₅Me₄PPh₂)(η⁵-C₅Me₄P{O}Ph₂)}PdCl₂] (3).The structures of 3 and 4 have been determined crystallographically.Treatment of 3 and 4 with silver salts in CH₂Cl₂ or acetonitrile leads to the corresponding dicationic complexes[{M(η⁵-C₅R₄PPh₂)(η⁵-C₅R₄P{O}Ph₂)}Pd(MeCN)_x]²⁺ (5, M = Fe, R = Me; 6, M = Os, R = H). Complex 5 decomposes upon isolation, in contrast 6 is rather stable, probably due to Os-Pd bonding. The dichlorides 3 and 4 catalyze catalytic amination of p-bromotoluene with N-(4-tolyl)morpholine with lower activity than (dppf)PdCl₂, however they perform comparable to (dppf)PdCl₂ activity in coupling of p-bromotoluene with p-methoxyphenyl boronic acid.     

双核Fe配合物[(η5-C5H4)C6H10(C4H3S)Fe(CO)2]2的合成和晶体结构

由侧链带有噻吩的环戊二烯基配体C5H5C6H10C4H3S与Fe(CO)5在二甲苯中加热回流,合成了1个新颖的四羰基二铁配合物[(η5-C5H4)C6H10(C4H3S)Fe(CO)2]2。通过元素分析、IR、1H NMR对其结构进行了表征,用X-射线单晶衍射确定了其结构。X-射线单晶衍射表明配合物中有2个桥羰基和2个端羰基,Fe-Fe的键长为0.25465(10)nm。     

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.     

Knoevenagel condensation of [NC-CH2C(O)-NH-CH(CO2Et)-S]2 with ferrocenecarbaldehyde and the activation of the σ(C-S) bond of [(η-C5H5)Fe{(η-C5H4)-CHC(CN)-C(O)-NH-CH(CO2Et)-CH2-S-}]2 induced by palladium(II)

The results obtained from the Knoevenagel condensation between the aldehydes R-CHO {with R=4-MeO-C₆H₄, 4-NO₂-C₆H₄, 4-Cl-C₆H₄, C₆H₅, 2,4,6-Me₃-C₆H₂ or (η⁵-C₅H₅)Fe(η⁵-C₅H₄)} and [NC-CH₂C(O)-NH-CH(CO₂Et)-S]₂ under different experimental conditions are reported. These studies have allowed the isolation and characterisation of three optically pure polyamides of general formula [R-CHC(CN)-C(O)-NH-CH(CO₂Et)-CH₂-S-]₂ with R=4-MeO-C₆H₄ (3a), 4-NO₂-C₆H₄ (3b) or (η⁵-C₅H₅)Fe(η⁵-C₅H₄) (3f). The reactions of 3f with Na₂[PdCl₄] or Pd(AcO)₂ are also studied. The treatment of Pd(AcO)₂ with 3f in a 2:1 molar ratio in refluxing toluene leads to the formation of [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHC(CN)-C(O)-NH-C(CO₂Et)CH₂}] (5f). Electrochemical studies based on cyclic voltammetry of compounds 3f and 5f are also reported.     

Derivatisation of boryl substituted titanium half-sandwich complexes - Molecular structures of [Ti{(η-C5H4)B(NiPr2)N(H)tBu}Cl2(NMe2)] and [{TiCl2(μ-{OB(NHMe2)-η-C5H4})}2-μ-O]

The half-sandwich complex [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}(NMe₂)₃] (6) was prepared from (η¹-C₅H₅)B(NiPr₂)N(H)iPr (5) and [Ti(NMe₂)₄] with cleavage of one equivalent of HNMe₂ and further converted into the corresponding constrained geometry complex [Ti{(η⁵-C₅H₄)B(NiPr₂)NiPr}(NMe₂)₂] (7) by elimination of a second equivalent of HNMe₂. Reaction of the half-sandwich complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}(NMe₂)₃] (R = iPr, tBu) with excess Me₃SiCl yielded the corresponding dichloro complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}Cl₂(NMe₂)] (R = tBu (10), iPr (11)). The intermediate species [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}Cl(NMe₂)₂] (9) could also be spectroscopically characterised. Partial hydrolysis of 10 and 11, respectively, resulted in formation of [{TiCl₂(μ-{OB(NHMe₂)-η⁵-C₅H₄})}₂-μ-O] (12). The molecular structures of 10 and 12 have been determined by X-ray crystallographic analyses. Complex 10, when activated with MAO, was found to be a highly active styrene polymerisation catalyst while being inactive towards the polymerisation of ethylene.     

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.     

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.     

Synthesis, characterization and reactivity studies of the new compound [Os3(CO)9(μ3-η,η,η-{C5H5FeC5H3CCC(S)C(Fc)CHO}]

Processes such as S-C and C-H bond activations as well as C-C coupling reactions have taken place in the synthesis of the new compound [Os₃(CO)₉(μ₃-η²,η³,η³-{C₅H₅FeC₅H₃CCC(S)C(Fc)CHO}] (Fc = C₅H₄FeC₅H₅), which contains an aldehyde oxametallacycle. A reactivity study of it has been carried out. In addition, other new triosmium clusters such as [Os₃(CO)₉(μ₃,η²-CCFc)(μ,η¹-SCCFc)], [Os₃(CO)₁₀(μ,η²-CCFc)(μ,η¹-SCCFc)] and [Os₃(CO)₉(μ-CO)(μ₃,η²-FcCCSCCFc)] have been prepared from the reaction of [Os₃(CO)₁₀(NCMe)₂] and FcCCSCCFc. All the compounds have been characterized by analytical and spectroscopic techniques. The crystal structures of [Os₃(CO)₉(μ₃,η²-CCFc)(μ,η¹-SCCFc)] and [Os₃(CO)₉(μ₃-η²,η³,η³-{C₅H₅FeC₅H₃CCC(S)C(Fc)CHO}] have been determined by X-ray crystallography and some electrochemical studies have also carried out.     

Unsaturation in binuclear cyclopentadienylchromium carbonyl thiocarbonyls: Viability of (η-C5H5)2Cr2(CS)2(CO)3 in contrast to (η-C5H5)2Cr2(CO)5

The cyclopentadienylchromium carbonyl thiocarbonyls Cp₂Cr₂(CS)₂(CO)_n (n = 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The lowest energy Cp₂Cr₂(CS)₂(CO)₄ structure can be derived from the experimentally characterized unbridged Cp₂Cr₂(CO)₆ structure by replacing the two terminal carbonyl groups furthest from the Cr-Cr bond with two terminal CS groups. The two lowest energy Cp₂Cr₂(CS)₂(CO)₃ structures have a single four-electron donor η²-μ-CS group and a formal Cr-Cr single bond of length ∼3.1 Å. In contrast to the carbonyl analogue Cp₂Cr₂(CO)₅ these Cp₂Cr₂(CS)₂(CO)₃ structures are viable with respect to disproportionation into Cp₂Cr₂(CS)₂(CO)₄ and Cp₂Cr₂(CS)₂(CO)₂ and thus are promising synthetic targets. The lowest energy Cp₂Cr₂(CS)₂(CO)₂ structures have all two-electron donor CO and CS groups and short CrCr distances around ∼2.3 Å suggesting the formal triple bonds required to give the chromium atoms the favored 18-electron configurations. These Cp₂Cr₂(CS)₂(CO)₂ structures are closely related to the known structure for Cp₂Cr₂(CO)₄. In addition, several doubly bridged structures with four-electron donor η²-μ-CS bridges are found for Cp₂Cr₂(CS)₂(CO)₂ at higher energies. The global minimum Cp₂Cr₂(CS)₂(CO) structure is a triply bridged triplet with a CrCr triple bond (2.299 Å by BP86). A higher energy singlet Cp₂Cr₂(CS)₂(CO) structure has a shorter Cr-Cr distance of 2.197 Å (BP86) suggesting the formal quadruple bond required to give each chromium atom the favored 18-electron configuration.     

Crystal structure and spectral characteristics of {[(C6H5)NH]2C=NH(C6H5)}[B(C6H5)4]·C2H5OH

A novel compound of {[(C₆H₅)NH]₂C=NH(C₆H₅)}[B(C₆H₅)₄]·C₂H₅OH is prepared and examined by single crystal X-ray diffraction. Crystal data: C₄₅H₄₄BN₃O, M = 653.64, monoclinic, space group P2₁/c, unit cell parameters: a = 24.375(2) Å, b = 17.5829(15) Å, c = 18.090(1) Å, β = 105.277(2)°, V = 7479.0(11) ų, Z = 8, d _calc = 1.161 g/cm³, T = 293 K, R ₁ = 0.064. The structure contains two crystallographically independent cations, two anions, and two solvate ethanol molecules. Three types of interactions occur between them: interionic N-H(N)⋯π and N(H)⋯π⋯H(C), π-delocalized system of Ph rings of the anions, and interaction of ions with ethanol molecules N-H⋯O-H(O)⋯π. The compound is characterized by IR and luminescence spectra. At room temperature, the emission intensity grows with time of exposure to UV irradiation. Original Russian Text Copyright ? 2008 by T. M. Polyanskaya, E. A. Il’inchik, V. V. Volkov, M. K. Drozdova, O. P. Yur’eva, and G. V. Romanenko __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 3, pp. 512–521, May–June, 2008.     

An NMR study of the rotational barriers in cobalt-stabilized carbocations: X-ray crystal structures of (η-C4Ph4)Co-(η-C5H4R), where R is CH3CO, CHO, CH(Bu)OH

Treatment of the aldehyde (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CHO) (4b) with tert-butyllithium or phenyllithium yields the secondary alcohols (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CH(R)OH), where R=tert-butyl (5) or phenyl (6). Protonation of 5 and 6 at −80 °C furnishes the deep purple, cobalt-stabilized cations, 7 and 8, respectively, both of which exhibit restricted rotation about the external C₅H₄-CHR⁺ linkage on the NMR time-scale. These data indicate a minimum value for the barrier to rotation of 15 kcal mol⁻¹, but it is certainly much higher, indicating a considerable degree of C-C double bond character. X-ray crystal structures of 4b, 5 and also of the ketone (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-C(O)CH₃ (4a) are reported. The secondary alcohol 5 exhibits disorder in the solid state because of the presence of diastereomers as a consequence of the stereogenic center at the α-carbon and the clockwise or anticlockwise propeller orientations of the tetraphenylcyclobutadiene ligand.     

Dynamic behavior of [(η-C5H4CH3)Cr(CO)2(μ-SBu)Pt(PPh3)2] in solution

The structure and dynamic behavior of complex [(η⁵-C₅H₄CH₃)Cr(CO)₂(μ-SBu)Pt(PPh₃)₂] in solution was studied by multinuclear (¹H, ¹³C, ³¹P) NMR spectroscopy including a phase-sensitive NOESY experiment. Increasing temperature causes rupture of the Cr-Pt bond in the three-membered ring of the complex and rotation of the S-Pt(PPh₃)₂ unit around the Cr-S bond line, followed by formation of a new Cr-Pt bond to close the ring. All activation parameters for this dynamic process have been determined.