Synthesis and electrochemical behaviour of the cyanamide-isocyanide complexes of rhenium, trans-[ReL(CNR)(Ph2PCH2CH2PPh2)2] ( L = NCNH2 or NCNH)

Reaction of trans-[ReCl(CNR)(dppe)₂] (R = Me (Ia) or ^tBu (Ib); DPPE = Ph₂PCH₂CH₂PPh₂) in CH₂Cl₂ with cynamide in the presence of TlBF₄ forms the new cynamide-isocyanide complexes trans-[Re(CNR)(NCNH₂)(dppe)₂][BF₄] (R = Me (IIa) or ^tBu (IIb)), which upon treatment by ^tBuOK or Et₃N give trans-[Re(NCNH)(CNR)(dppe)₂] (R = Me (IIIa) or ^tBu (IIIb)). The electrochemical behaviour of these species was studied by cyclic voltammetry and controlled potential electrolysis at a Pt electrode in an aprotic solvent, and cathodic reduction of II results in the formation of III.     

Syntheses of low-valent nitrosyl complexes of rhenium and X-ray structure oftrans-[ReCl(NO)(Ph2PCH2CH2PPh2)2][NO3]2 with nitrosyl derived nitrates

The nitrosyl complexes trans-[ReCl(NO)(dppe)₂]A₂ (1; A = BF₄ or NO₃; dppe = Ph₂PCH₂CH₂₋PPh₂) and trans-[ReCl(NO)(dppe)₂][BF₄] (2) have been prepared from the reactions of NO[BF₄] or NO with trans-[ReCl(N₂)dppe)₂]. An unusual facile oxidation of NO to nitrate is involved in the formation of (1, A = NO₃), the X-ray structure of which is reported.     

Reactivity of niobocene dihalogenides toward nitroso derivatives. EPR and IR characterization of the first niobium(IV) complexes containing an ArNO-N,O ligand

The reaction of [Nb(η⁵-C₅H₄R)₂X₂] [1: R = SiMe₃, X = Cl; 2: R = SiMe₃, X = Br; 3: R = H, X = Cl; 4: R =^t, X = Cl] with nitroso derivatives ArNO [a: Ar = Ph; b: Ar = o-CH₃-C₃H₄; c: Ar = p-(CH₃)₂NC₆H₄] yields paramagnetic complexes formulated as [Nb(η⁵-C₅H₄R)(η³-C₅H₄R)X₂(ArNO-N,O) 1a, 1b, 1c, 2a, 3a, 4a and 4c, which have been characterized by ESR and IR spectroscopy.     

Organometallic complexes for nonlinear optics: Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

The complexes trans-[Os(CCPh)Cl(dppe)₂] (1), trans-[Os(4-CCC₆H₄CCPh)Cl(dppe)₂] (2), and 1,3,5-{trans-[OsCl(dppe)₂(4-CCC₆H₄CC)]}₃C₆H₃ (3) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os^II/III couple. In situ oxidation of 1–3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1⁺–3⁺; a low-energy band is observed in the near-IR region (11 000–14 000 cm⁻¹) in each case, in contrast to the neutral complexes 1–3 which are optically transparent below 20 000 cm⁻¹. Density functional theory calculations on the model compounds trans-[Os(CCPh)Cl(PH₃)₄] and trans-[Os(4-CCC₆H₄CCPh)Cl(PH₃)₄] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.     

Synthesis and structure of neutral and cationic pentahaloarylpalladium(II) isonitrile complexes

Complexes of the types (a) trans- and cis-[Pd(C₆X₅)₂ (CNR)₂], (b) trans- [Pd(C₆X₅)Cl(CNR)₂] and (c) [Pd(C₆X₅)(CNR)₃]ClO₄ (X = F or Cl;R = Bu^t cyclohexyl or p-tolyl) have been made by replacement of the tetrahydrothiophen or Cl groups of appropriate precursors by isonitrile. Their structures have been assigned on the basis of their IR and ¹H NMR spectra.     

Success and serendipity during studies aimed at preparing carbenerhodium(I) complexes

The preparation of a series of new square-planar and half-sandwich type carbenerhodium(I) complexes will be described. The key to success is the use of the bis(stibane)rhodium compound trans-[RhCl(C₂H₄)(SbiPr₃)₂] as starting material from which in a stepwise manner the complexes trans-[RhCl(=CRR′)(SbiPr₃)₂] (L = PiPr₃, AsiPr₃, SbEt₃) and [C₅H₅Rh(=CCR′)L] (L = SbiPr₃, PiPr₃, PMe₃, CO, CNtBu) have been obtained. Displacement of the carbene ligand in either trans-[RhCl(=CPH₂)L₂]L = SbiPr₃, PiPr₃ or [C₅H₅Rh(=CPh₂)(PiPr₃)] by CO or CNtBu leads to the formation of the corresponding carbonyl- or isocyanidrhodium compounds and the C---C coupling products Ph₂C=C=O and Ph₂C=C=NtBu, respectively. The carbene ligand is also involved in the selective formation of the isomeric olefins CH₂=CHCPh₂H and Ph₂C=CHCH₃ on treatment of trans-[RhCl(=CPh₂)(SbiPr₃)₂] and trans-[RhCl(=CPh₂)(PiPr₃)₂] with ethene. The most spectacular reaction of the bis(triisopropylstibane) complexes, however, occurs on warming of trans-[RhCl(=CRR′)(SbiPr₃)₂] in the absence of any substrate which yields the first representatives of dinuclear transition-metal compounds containing a tertiary stibane ligand in a bridging position. Some exploratory studies on the reactivity of the Rh₂(μ-SbiPr₃) complexes indicate that the triisopropylstibane can be replaced by SbMe₃, SbEt₃ or CNtBu without destroying the dimetallic core of the molecule.     

A study of ortho- and para-siloxyanilines for the synthesis of mono-, bi-, and tetra-nuclear early transition metal–imido complexes

The siloxyanilines o-Me₃SiOC₆H₄NH₂ (1) and p-RMe₂SiOC₆H₄NH₂ (R=H (2); R=Me (3)), and their N-silylated derivatives p-Me₃SiOC₆H₄NHSiMe₃ (4) and p-Me₃SiOC₆H₄N(SiMe₃)₂ (5) have been prepared from ortho- or para-aminophenol and used in the synthesis of imido complexes. Thus, binuclear [{Ti(η⁵-C₅H₅)Cl}{μ-NC₆H₄(p-OSiMe₃)}]₂ (6) and mononuclear [TiCl₂{NC₆H₄(p-OSiMe₃)}(py)₃] (7) imido complexes have been obtained from the reaction of 3 and [Ti(η⁵-C₅H₅)Cl₃] or [TiCl₂(N^tBu)(py)₃], respectively. In contrast, the reaction of 1 with TiCl₄ and ^tBupy affords the titanocycle [TiCl₂{OC₆H₄(o-NH)---N,O}(^tBupy)₂] (8). Compound 5 has also been used to prepare the niobium imide complex [NbCl₃{NC₆H₄(p-OSiMe₃)}(MeCN)₂] (9), by its reaction with NbCl₅ in CH₃CN. These findings have been applied to the synthesis of polynuclear systems. Thus, chlorocarbosilane Si[CH₂CH₂CH₂Si(Me)₂Cl]₄ (CS–Cl) has been functionalized with the ortho- and para-aminophenoxy groups to give 10 and 11, respectively. The use of 11 has allowed the formation of the tetranuclear compound 12. Attempts to synthesize terminal imido titanium complexes from 10 and TiCl₄ in the presence of ^tBupy and Et₃N, give complex 8 and carbosilane CS–Cl.     

Synthesis, structure and reactions of organometallic compounds of Groups 1–3 containing bulky silicon-substituted alkyl groups

Complexes trans-[PtX(L)(PPh₃)₂]A [1: X = CF₃; A = BF₄; L = NCNH₂, NCNMe₂, NCNEt₂, or NCNC(NH₂)₂. 2: X = Cl; A = BPh₄; L = NCNMe₂ or NCNEt₂] and cis-[PtCl(L)(PPh₃)₂][BPh₄] [3: L = NCNH₂ or NCNC(NH₂)₂], which appear to be the first cyanamide or cyanoguanidine complexes of platinum to be reported, have been prepared by treatment of trans-[PtBr(CF₃)(PPh₃)₂] (in CH₂Cl₂/acetone and in the presence of Ag[BF₄]) or of cis-[PtCl₂(PPh₃)₂] (in THF and in the presence of Na[BPh₄]), respectively, with the appropriate substrate. In KBr pellets or in solution 1 (L = NCNMe₂ or NCNEt₂) undergoes ready replacement of the organocyanamide (under the trans influence of CF₃) by bromide to regenerate trans-(PtBr(CF₃)(PPh₃)₂]. The X-ray structure of 1 (X = CF₃, A = BF₄, L = NCNEt₂) is also reported, and shows the presence of two apical intramolecular contacts of the metal with two ortho-hydrogen atoms of the phosphines, whereas the amine N atom of the diethylcyanamide is trigonal planar in the linear NCN framework with a delocalized π system.     

A simple synthesis of tetraethynylethenes and representative molecular structures of some dicobalt derivatives

Palladium–copper catalysed cross-coupling reactions of tetracholoroethene with terminal acetylenes RCCH (R=SiMe₃, C₆H₅, C₆H₄CN-4) in refluxing triethylamine afford the corresponding tetraethynylethenes in 30–60% isolated yields. The reaction of 1,6-bis(trimethylsilyl)-3,4-bis(trimethylsilylethynyl)-hex-3-ene-1,5-diyne with [Co₂(CO)₆(L₂)] [L₂=(CO)₂ or μ-dppm] affords complexes in which one or two (trans) acetylene moieties are coordinated by a dicobalt fragment.     

Binuclear methyplatinum and phenylplatinum complexes with bis(dimethylphosphino)methane ligands

Reaction of cis-[Ptph₂(SMe₂)₂] with Me₂PCH₂PMe₂ (dmpm) gave cis-[PtPh₂(dmpm-P)₂] (1) or cis,cis-[Pt₂Ph₄(μ-dmpm)₂] (2) and reaction of 1 with [Pt₂Me₄(μ-SMe₂)₂] gave cis,cis-[Ph₂Pt(μ-dmpm)₂PtMe₂] (3). Reaction of 1 with trans-[PtClR(SMe₂)₂] gave cis,trans-[Ph₂Pt(μ-dmpm)₂PtClR], R = Me (5) or Ph (6), and in polar solvents, these isomerized to give [Ph₂Pt(μ-dmpm)₂PtR]⁺Cl⁻. When R = Me, further isomerization via the phenyl group transfer gave [PhMePt(μ-dmpm)₂PtPh]⁺Cl⁻. Oxidative addition of methyl iodide occurred reversibly at the cis-[PtMe₂P₂ unit of 3 to give cis,fac-[Ph₂Pt(μ-dmpm)₂PtIMe₃] but complex 2 failed to react with MeI. A comparison with similar known complexes of Ph₂PCH₂PPh₂ (dppm) is made and differences are attributed primarily to the lower steric hindrance of dmpm.     

The first 2,3-dihydro-1H-[1,2,4] triphosphole

Protonation of the lithium triphospha-cyclopentenyl salt Li (P₃C₂Bu^t₂RR′) (R=(Me₃Si)₂CH-, R′=Buⁿ) with HCl affords the new 2,3-dihydro-1H-[1,2,4] triphosphole P₃C₂Bu^t₂(H) (Buⁿ)CH(SiMe₃)₂ which has been structurally characterised as its [W(CO)₅] complex.     

Synthesis and characterization of cationic heteronuclear complexes of platinum(II) and silver( I) bridged by alkynyl ligands

The dialkynyl complexes cis-[Pt(C CR)₂L₂] [R = Ph, L₂ = 2PPh₃, 2PEt₃, dppe (dppe = 1,2-bis(diphenylphosphino)ethane]; R ---^tBu, L₂ = 2PPh₃, dppe) react with silver perchlorate in a molar ratio 1:0.5 to give platinum-silver perchlorate salts of the type [Pt₂ Ag(C CR)₄L₄](ClO₄) in excellent yield. The X-ray crystal structure of [Pt₂Ag(C = CPh)₄(PPh₃)₄](ClO₄) 1 shows that the cation is formed by two nearly orthogonal cis-[Pt(C CPh)₂(PPh₃)₂] units connected through a silver cation which is unsymmetrically π-bonded to all four acetylene fragments. Similar reactions of cis-[Pt(C CR)₂L₂] with one equivalent of AgClO₄ afford cationic complexes of general formula [PtAg(C CR)₂L₂](ClO₄), which are believed to be salts, [Pt₂Ag₂(C CR)₄L₄](ClO₄)₂.     

Equilibrium constants and kinetics of carbon monoxide insertion in alkyl complexes of ruthenium(II)

The equilibrium constants of the reaction of cis, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mc) with carbon monoxide to give cis, trans[Ru(CO)₂(PMe₃)₂ (COMe)i] (Ac) and trans, trans[Ru(CO)₂(PMe₃)₂(COMe)I] (At) were measured at various temperatures in toluene. The thermodynamic parameters are compared with those obtained for the isoelectronic complexes of iron, and the trend is discussed. The kinetics of the carbonylation reaction of Mc, as well as those of the inverse decarbonylation reaction of At were measured. The kinetics of the carbonylation of the new complex trans, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mt) were also investigated. All the results afford further support to the previously proposed CO insertion mechanism occurring via methyl migration. The comparison of these kinetic results with those of isoelectronic complexes of iron indicates that ruthenium is more reactive than iron, which is reflected by its greater aptitude to act as catalyst in many processes.     

Group 4 metallacarboranes of constrained geometries derived from B(cage)- and C(cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

The reactions of RNHSi(Me)₂Cl (1, R=t-Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2,3-(SiMe₃)₂-2,3-C₂B₄H₅ (3) and Li[closo-1-R′-1,2-C₂B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2,3-(SiMe₃)₂-2,3-C₂B₄H₅, (5, R=t-Bu) and closo-1-R′-2-[Si(Me)₂N(H)R]-1,2-C₂B₁₀H₁₀ (6, R=t-Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH)₂C₆H₃)]-1,2-C₂B₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [nido-3-{Si(Me)₂N(2,6-(Me₂CH)₂C₆H₃)}-1,3-C₂B₁₀H₁₁]³⁻ (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2-[1′-η¹σ-N(2,6-(Me₂CH)₂C₆H₃)(Me)₂Si]-2,4-η⁶-C₂B₁₀H₁₁ (M=Ti (9), n=0; M=Zr (10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2₁/c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) ų, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.     

Synthesis, structure and reactions of seven-coordinate, phosphine-supported, halide-activated carbonyl- and alkyne-complexes of niobium(I)

The complexes (Hal)Nb(CO)₃(PR₃)₃ (PR₃ = PEt₃, Hal = I; PR₃ = PMe₂Ph, Hal = Cl, Br, I) and (Hal)Nb(CO)_4/2(dppe)_1/2 (Hal = Br, I) have been prepared by oxidative halogenation of carbonylniobate with pyridinium halides (Hal = Cl, Br) or iodine (Hal = I). In the tricarbonyls, one CO and one PR₃ are labile and can be displaced by a four-electron donating alkyne to give all-trans-[(Hal)Nb(CO)₂(RCCR′)(PR₃)₂] (PR₃ = PMe₂Ph; Hal = Cl, Br, I: R, R′ = H, Et, Ph; R = H, R′ = Ph. PR₃ = PEt₃, Hal = I: R, R′ = Pr; R = H, R′ = Bu, Ph; R = Me, R′ = Et). In the case of acetylene, INb(CO)(HCCH)₂(PEt₃)₂ is also formed. PR₃ can be displaced by P(OMe) ₃. In the tetracarbonyls, two CO ligands are replaced by two isonitriles to form INb(CO)₂(CNR)₂dppe (R = ^tBu, Cy), or by one alkyne to form (Hal)Nb(CO)₂(PhCCPh)dppe (Hal = Br, I). In these complexes, the remaining CO ligands occupy cis positions. The structure of BrNb(CO)₂(dppe)₂·THF, INb(CO)₂(dppe)₂·hexane and INb(CO)₂(PEt₃)₂(MeCCEt) have been determined by a single crystal X-ray diffraction study. The alkyne complexes are best regarded as octahedral with the centre of the alkyne ligand occupying the positions trans to the halide and the CC axis aligned with the OC---Nb---CO axis. The complexes (Hal)Nb(CO)₂(dppe)₂ adopt a trigonal prismatic structure with the halide capping the tetragonal face spanned by the four phosphorus functions. The crystal structure of a by-product, Br₂Nb(CO)(H₂CPhPCH₂CH₂PPh₂)₂·1/2THF has also been determined. The geometry is pentagonal bipyramidal, with one of the bromine atoms and the CO on the axis. Some ⁹³ Nb NMR data for the Nb^I complexes are presented, and preliminary observations on the reactions between the π-alkyne complexes and H₂ or H⁻ are reported.     

Übergangsmetall-carbin-komplexe : LXXXIII. Neue anionische mer-dihalogeno-tricarbonyl-dialkylamino-carbin-komplexe des wolframs

The reaction of trans-X(CO)₄WCNR₂ (X = Br, R = ^c hex (cyclohexyl); X = Cl, R = ^c hex, ⁱpr (isopropyl) with M⁺X⁻ (M⁺ = NEt₄⁺, X⁻ = Br⁻; M⁺ = PPN⁺, X⁻ = Cl⁻) leads under substitution of one CO ligand to new anionic dihalo(tricarbonyl)carbyne-tungsten complexes of the type M⁺ mer-[(X)₂(CO)₃WCNR₂]⁻ (M⁺ = NEt₄⁺, X = Br, R = ^c hex; M⁺ = PPN⁺, X = Cl, R = ^c hex, ⁱ pr), whose composition and structure were determined by elemental analysis as well as by IR, ¹H and ¹³C NMR spectroscopy. In the anionic carbyne complexes the entered halogen ligand, coordinated in a cis position relative to the carbyne ligand on the metal, can be easily substituted by neutral nucleophiles, as the reaction of PPN⁺ mer-[(Cl)₂(CO)₃WCN^chex₂]⁻ with PPh₃ demonstrates yielding the neutral carbyne complex mer-[Cl(CO)₃(PPh₃)WCN^chex₂].     

Substituted cyclopentadienyl ligands—10. Intramolecular steric interactions in [(η-C5H3(SiMe3)2)Mo(CO)2(L)I]

Reaction of C₅H₄(SiMe₃)₂ with Mo(CO)₆ yielded [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₃]₂, which on addition of iodine gave [(η⁵-C₅H₃(SiMe₃)₂Mo(CO)₃I]. Carbonyl displacement by a range of ligands: [L = P(OMe)₃, P(OPrⁱ)₃,P(O-o-tol)₃, PMe₃, PMe₂Ph, PMePh₂, PPh₃, P(m-tol)₃] gave the new complexes [(η⁵-C₅H₃(SiMe₃)₂ MO(CO)₂(L)I]. For all the trans isomer was the dominant, if not exclusive, isomer formed in the reaction. An NOE spectral analysis of [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₂(L)I] L = PMe₂Ph, P(OMe)₃] revealed that the L group resided on the sterically uncongested side of the cyclopentadienyl ligand and that the ligand did not access the congested side of the molecule. Quantification of this phenomenon [L = P(OMe)₃] was achieved by means of the vertex angle of overlap methodology. This methodology revealed a steric preference with the trans isomer (less congestion of CO than I with an SiMe₃ group) being the more stable isomer for L = P(OMe)₃.     

P and C NMR investigation of the system tetracarbonyldi-μ-chlorodirhodium(I) — tertiary phosphine

¹³C and ³¹P{¹H} NMR data at low temperature prompted us to characterize cis-[Rh(CO)₂(PR₃)Cl] (3) (3a, PR₃ = PPh₃; 3b, PR₃ = PMe₂Ph), as surprisingly stable products of the reaction between [{Rh(CO)₂(μ-Cl)}₂] (1) and tertiary phosphines in toluene (P : Rh = 1). Every attempt to isolate solid 3a led to the cis- and trans- halide-bridged dimers [{Rh(CO)₂(μ-Cl)}₂] (5a) and 6a which are formed from 3a by slow decarbonylation, a process which is greatly accelerated by the evaporation of the solvent under vacuum.

The analogous reaction of 1 with dimethylphenylphosphine follows a similar pathway; in this case, however, low temperature NMR spectra allowed us to characterize the pentacoordinated dinuclear species [{Rh(CO)₂(μ-Cl)}₂] (2b) as the unstable intermediate of the bridge-splitting process.

The reaction of 3 with a second equivalent of phosphine (P : Rh = 2) leads, at room temperature, to the well known product trans-[Rh(CO)(PR₃)₂Cl] (8) accompanied by evolution of CO; however our data show that when the reaction is performed at 200 K, decarbonylation is prevented and spectroscopic evidence of trigonal bipyramidal pentacoordinate [Rh(CO)₂(PR₃)₂Cl] (7), stable only at low temperature, can be obtained.     

Direct electrosynthesis of halo and mixed-halo complexes of palladium(II and IV) by the dissolution of a sacrificial palladium anode in aqueous medium

A rapid single-step method for the electrosynthesis of chloro and bromo complexes of palladium(II and IV), viz. M₂[PdX₄] and M₂[PdX₆], by the dissolution of a palladium anode in chloride or bromide containing media is described. Electrolysis of dilute HX solution in the presence of pyridine, 2,2′-bipyridyl or 1,10-phenanthroline gives rise to non-electrolytes, e.g. trans-[PdX₂(py)₂], [PdX₂(bipy)] and [PdX₂(phen)]. Anodic oxidation of palladium in HX medium in the presence of acetonitrile and benzonitrile also gives the non-electrolytes trans-[PdX₂(CH₃CH₂NH₂)₂] and trans-[PdX₂(C₆H₅CH₂NH₂)₂], respectively.     

Half-sandwich and mixed-ring uranium complexes

The monocyclooctatetraene uranium complex [U(COT)(I)₂(THF)₂] (COT=η-C₈H₈; THF=tetrahydrofuran), isolated from the reaction of bis(cyclooctatetraene)uranium with iodine, is a precursor for the synthesis of the alkyl derivatives [U(COT)(CH₂Ph)₂i (HMPA) ₂], [U(COT)(CH₂SiMe₃)₂(HMPA)] (HMPA=hexamethyl phosphorous triamide) and [U(COT)CH₂SiMe₃)₃] [Li(THF)₃] and of the mixed-ring compounds [U(COT)(η-C₅R₅)(I)] (R=H or Me). The last were used to prepare the amide and alkyl complexes [U(COT)(η-C₅H₅)(N{SiMe₃}₂)] and [U(COT)(η-C₅Me₅)(CH₂SiMe₃)].