A new cumulene diiron complex related to the active site of Fe-only hydrogenases and its phosphine substituted derivatives: synthesis, electrochemistry and structural characterization

A new cumulene diiron complex related to the Fe-only hydrogenase active site [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₆] (1) was obtained by treatment of (μ-LiS)₂Fe₂(CO)₆ with excess 1,4-dichloro-2-butyne. By controllable CO displacement of 1 with PPh₃ and bis(diphenylphosphino)methane (dppm), mono- and di-substituted complexes, namely [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅L] (2: L = PPh₃; 3: L = dppm) and [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄L₂] (4: L = PPh₃; 5: L = dppm) could be prepared in moderate yields. Treatment of 1 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅]₂(μ-dppe) (7). With dppm in refluxing toluene, a dppm-bridged complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄(μ-dppm)] (6) was obtained. These model complexes were characterized by IR, ¹H, ³¹P NMR spectra and the molecular structures of 1, 2 and 5-7 were determined by single crystal X-ray analyses. The electrochemistry of 1-3 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of HOAc.     

Organometallic π-tweezers incorporating pyrazine- and pyridine-based bridging units

Pyrazine- and pyridine-based π-conjugated σ-donor molecules, such as 4,4′-bipyridine, 1,2-di(4-pyridyl)ethylene, 3,5-dipyridyl-1,2,4-triazole, N,N′-bis(4-pyridylmethylidene)benzene-1,4-diamine, 2,5-di(pyridylmethylidene)cyclopentanone, 2,6-di(4-pyridylmethylidene)cyclohexanone (LL, 2a-2g) can successfully be used to span heterobimetallic π-tweezer units of the type [{[Ti](μ-σ,π-CCSiMe₃)₂}M]⁺ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = Cu, Ag). The thus accessible di-cationic species [{[Ti](μ-σ,π-CCSiMe₃)₂}MLLM{(Me₃SiCC-μ-σ,π)₂[Ti]}]²⁺ (4), which are formed via the formation of [{[Ti](μ-σ,π-CCSiMe₃)₂}MLL]⁺ (3) complexes, can be isolated in yields between 66% and 99%.However, when C₅H₄NCHCHC₆H₄CHCHNC₅H₄ (5a) and C₅H₄NCHNC₆H₄CHCHNC₅H₄ (5b), respectively, are reacted with {[Ti](μ-σ,π-CCSiMe₃)₂}AgBF₄(1c) in a 1:1 molar ratio, then the silver(I) ion is released from the organometallic π-tweezer 1c and coordination polymers [AgBF₄ · 5a]_n (6a) and [AgBF₄ · 5b]_n (6b) along with [Ti](CCSiMe₃)₂ (7) are formed in quantitative yield.     

Synthesis and characterization of triphenylphosphine stabilized silver α,β-unsaturated carboxylate: Crystal structure of [Ag(O2CCHC(CH3)2)(PPh3)2]

A series of triphenylphosphine coordinated silver α,β-unsaturated carboxylates of type [Ag(O₂CR)(PPh₃)_n: n = 1, R = CH₃CHCH (2a), (CH₃)₂CCH (2b), CH₃CH₂CHCH (2c), CH₃CH₂CH₂CHCH (2d), PhCHCH (2e), CH₂CH (2f); n = 2, CH₃CHCH (3a), (CH₃)₂CCH (3b), CH₃CH₂CHCH (3c), CH₃CH₂CH₂CHCH (3d)] were prepared by reaction of relative silver carboxylates (1a-1f) with triphenylphosphine in chloroform. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P NMR and IR spectroscopy. Thermal stability of the complexes has been determined by TG analysis. The molecular structure of [Ag((O₂CCHC(CH₃)₂))(PPh₃)₂] (3b) shows that the senecioato ligand is chelated with silver atom and generate, a distorted tetrahedron.     

Ketimine synthesis in the coordination sphere of thallium (I)

[AuTl(C₆F₅)₂(en)] (en = ethylenediamine) reacts with cyclic ketones as cyclopentanone (Cy⁵O), cyclohexanone (Cy⁶O) or cycloheptanone (Cy⁷O) in 1:1 or 1:2 molar ratio leading to products of stoichiometry [AuTl(C₆F₅)₂{Cy^xN(CH₂)₂NH₂}] (x = 5 1, 6 2 or 7 3), or [AuTl(C₆F₅)₂{Cy^xN(CH₂)₂NCy^x}] (x = 5 4, 6 5 or 7 6). Addition of ethylenediamine to the ketimine complexes in chloroform regenerates [AuTl(C₆F₅)₂(en)], the starting material, and the free ketimines, as their NMR and mass spectra evidenced. The ketimine complexes display luminescence in solid state at room temperature and at 77 K at higher wavelengths than the diamine starting product (505 nm). The excited states responsible for this behaviour are assigned to orbitals due to the gold-thallium interactions.     

One-pot syntheses of alkenyl-phosphonio complexes of ruthenium(II), rhodium(III) and iridium(III) bearing p-cymene or pentamethylcyclopentadienyl groups

Reaction of [(p-cymene)RuCl₂(PPh₃)] (1) or [Cp^∗MCl₂(PPh₃)] (Cp^∗ = C₅Me₅) (3a: M = Rh; 4a: M = Ir) with 1-alkynes and PPh₃ were carried out in the presence of KPF₆, generating the corresponding alkenyl-phosphonio complexes, [(p-cymene)RuCl(PPh₃){CHCR(PPh₃)}](PF₆) (2a: R = Ph; 2b: R = p-tolyl) or [Cp^∗MCl(PPh₃){CHCPh(PPh₃)}](PF₆) (5: M = Rh; 6: M = Ir). Similar reactions of complexes [Cp^∗RhCl₂(L¹)] (3a: L¹ = PPh₃; 3c: L¹ = P(OMe)₃) with L² (L² = PPh₃, PMePh₂, P(OMe)₃) gave [Cp^∗RhCl(L¹)(L²)](PF₆) (7bb: L¹ = L² = PMePh₂; 7ca: L¹ = P(OMe)₃, L² = PPh₃; 7cc: L¹ = L² = P(OMe)₃). Alkenyl-phosphonio complex 5 was treated with P(OMe)₃ or 2,6-xylyl isocyanide, affording [Cp^∗RhCl(L){CHCPh(PPh₃)}](PF₆) (8a: L = P(OMe)₃; 8b: L = 2,6-xylNC). X-ray structural analyses of 2a, 6 and 8a revealed that the phosphonium moiety bonded to the C_β atom of the alkenyl group are E configuration.     

Spectroscopic properties of mono- and binuclear platinum(II) alkynyl complexes with phosphine ligands: A theoretical study

Based on their MP2 optimized structures in the ground states, we obtained solution absorption spectra for trans-[Pt^II(CCR)₂(PH₃)₂] (R = H (1) and Ph (2)) and trans-[Pt^II(CCH)₂(PH₂CH₂PH₂)]₂ (3) under the time-dependent density functional theory calculations. These absorptions agree with experimental observations. The unrestricted MP2 optimization performed for 3 in the lowest-energy triplet excited state shows that upon excitation the PtPt distance shortens about 0.347 Å with respect to the 3.188 Å one in the ground state. The UMP2 calculations estimated that its ³[σ^∗(d_z²)σ(p_z)] excited state produces the 531 nm emission, corresponding to the 580 nm one of trans-[Pt^II(CCPh)₂(PPh₂CH₂PPh₂)]₂ in the solid state at 298 K.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of molybdenum Me2Si[CHMo(NAr)(ORF3)2]2 and PhVinSi[CHMo(NAr)(ORF3)2]2

Bimetallic alkylidene complexes of molybdenum (R_F3O)₂(ArN)MoCH-SiMe₂-CHMo(NAr)(OR_F3)₂ (1) and (R_F3O)₂(ArN)MoCH-SiPhVin-CHMo(NAr)(OR_F3)₂ (2) (Ar = 2,6-C₆H₃; R_F3 = CMe₂CF₃) have been prepared by the reactions of vinyl silicon reagents Me₂Si(CHCH₂)₂ and PhSi(CHCH₂)₃ with known alkylidene compound PhMe₂C-CHMo(NAr)(OR_F3)₂. Complexes 1 and 2 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1 and 2 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and predominant cis-units content in the case of 2.     

Novel long bipyridine-type linking ligands containing an intervening naphthalene fragment: [Zn(L)(NO3)2], [Zn(L)(NO3)2], and [Cd(L)1.5(NO3)2] (L = (4-py)-CHN-C10H6-NCH-(4-py); L = (3-py)-CHN-C10H6-NCH-(3-py))

Novel bipyridine-type linking ligands L¹ ((4-py)-CHN-C₁₀H₆-NCH-(4-py)) and L² ((3-py)-CHN-C₁₀H₆-NCH-(3-py)), a pair of isomers due to possessing different pairs of terminal pyridyl groups, were prepared by the Schiff-base condensation. In ligand L¹, the N?N separation between the terminal pyridyl groups is 16.0 Å, with their nitrogen donor atoms at the para positions (4,4′). The corresponding N?N separation in ligand L² is 14.2 Å, with the nitrogen donor atoms at the meta positions (3,3′). 1-D zigzag-chain coordination polymers [Zn(L¹)(NO₃)₂] (1) and [Zn(L²)(NO₃)₂] (2) were prepared by reactions of Zn(NO₃)₂ · 6H₂O with ligands L¹ and L², respectively, by solution diffusion. Polymer 3, [Cd(L¹)_1.5(NO₃)₂], prepared from Cd(NO₃)₂ · 4H₂O and L¹, exhibits a 1-D ladder structure, whose repeating ladder unit consists of four Cd metals and four L¹ ligands to create a large 76-membered ring with dimensions of 20.8 × 20.8 Å. All products were structurally characterized by X-ray diffraction.     

Co and Cu complexes of reduced Schiff bases: Generation of phenoxyl radical species

The three complexes [Co^IIIL¹Cl] (1), [Co^IIIL²]⁺·ClO₄⁻ (2⁺·ClO₄⁻), and [Cu^IIH₂L²]²⁺·2ClO₄⁻ (H₂3²⁺·2ClO₄⁻) [where H₂L¹ = N,N′-dimethyl-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H₂L² = N,N′-bis(2-pyridylmethyl)-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine] have been prepared. The bis-phenolate and bis-phenol complexes, 2⁺ and H₂3²⁺ respectively, have been characterized by X-ray diffraction, showing a metal ion within an elongated octahedral geometry. 1-2 exhibit in their cyclic voltammetry curves two anodic reversible waves attributed to the successive oxidation of the phenolates into phenoxyl radicals. The cobalt radical species (1)⁺, (2)²⁺, and (2)³⁺ have been characterized by combined UV-Vis and EPR spectroscopies. In the presence of one equivalent of base, one phenolic arm of H₂3²⁺ is deprotonated and coordinates the metal. The resulting complex (H3⁺) exhibits a single reversible redox wave at ca. 0.3 V. The electrochemically generated oxidized species is EPR silent and exhibits the typical features of a radical compound, with absorption bands at 411 and 650 nm. The fully deprotonated complex 3 is obtained by addition of two equivalents of nBu₄N⁺OH⁻ to H₂3²⁺. It exhibits a new redox wave at a lower potential (−0.16 V), in addition to the wave at ca. 0.3 V. We assigned the former to the one-electron oxidation of the uncoordinated phenolate into an unstable phenoxyl radical.     

A closer look at the phosphorus-phosphorus double bond lengths in meta-terphenyl substituted diphosphenes

The single crystal X-ray structure of DmpPPDmp (1, Dmp = 2,6-Mes₂C₆H₃), which was previously reported to have a relatively short PP bond distance of 1.985(2) Å at room temperature, has been reexamined at variable temperatures. Crystallographic analyses of 1 at 100 K allow for resolution of disorder of the two phosphorus atoms (which is unresolvable from room temperature diffraction data), and for determination of a more conventional PP bond length of 2.029(1) Å. Single crystals of the closely related diphosphene DxpPPDxp (2, Dxp = 2,6-(2,6-Me₂C₆H₃)₂C₆H₃) show similar disorder in one of two crystallographically independent molecules in the unit cell. A value of 2.0276(4) Å is found for the non-disordered PP bonds at 100 K for 2. A new diphosphene Ar′PPAr′ (3, Ar′ = 2,6-Mes₂-4-OMe-C₆H₃) has been prepared and its structure has also been examined. The PP bond length for 3 was determined to be 2.0326(9) Å and relatively free of the effects of disorder.     

Organometallic complexes for nonlinear optics. Part 36. Quadratic and cubic optical nonlinearities of 4-fluorophenylethynyl- and 4-nitro-(E)-stilbenylethynylruthenium complexes

The complexes trans-[Ru(CC-4-C₆H₄F)X(dppe)₂] [X = Cl (1), CCPh (2), CC-4-C₆H₄NO₂ (3)], trans-[Ru{CC-4-C₆H₄-(E)-CHCH-4-C₆H₄NO₂}X(dppe)₂] [X = CCPh (4), CC-4-C₆H₄CCPh (5)], and [C₆H₃-1,3-{CC-trans-[RuCl(dppe)₂]}₂-5-(CC-4-C₆H₄F)] (6) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetry reveals a metal-centered oxidation, the potential of which is largely invariant on alkynyl ligand replacement across the series 1-5; the diruthenium complex 6 shows two oxidation processes, consistent with weakly interacting metal centers. Hyper-Rayleigh scattering (HRS) studies at 1064 nm using ns pulses suggest quadratic nonlinearities for 3-5 that are amongst the largest thus far for organometallic complexes, a trend maintained with the two-level-corrected data. HRS studies at 800 nm using fs pulses and amplitude modulation to remove multi-photon fluorescence contributions reveal significant fluorescence-free nonlinearities for 3-5; the frequency-independent nonlinearities calculated from the 800 nm results are suggestive of fluorescence contributions to the 1064 nm data. Z-scan studies at 820 nm reveal cubic nonlinearities that increase with the size of the π-system, although error margins are significant.     

Halo-complexes of titanium(III): The thermochromic behaviour of [NBu4][TiCl4(THF)2]

TiCl₃(thf)₃ reacts with ACl (A = NBu₄, PPN; PPN = Ph₃PNPPh₃) in dichloromethane solution, affording the compounds A[TiCl₄(thf)₂] (A = NBu₄, 1; A = PPN, 2). Compound 1, dissolved in CH₂Cl₂, exhibits thermochromic behaviour which has been the subject of variable-temperature UV-Vis investigations.     

Construction of carbon chains on ruthenium and osmium carbonyl clusters

We have used the elimination of AuX(PR₃) (X = halide, R = Ph, tol) that occurs in reactions of alkynylgold(I)-phosphine complexes with M₃(μ-H)₃ (μ₃-CBr) (CO)₉ (M = Ru, Os) to prepare the complexes M₃(μ-H)₃(μ₃-CCCR)(CO)₉ [M = Ru, R = Ph 2, CCSiMe₃3, Fc 4, CCFc 6-Ru, CC[Ru(PPh₃)₂Cp] 8; M = Os, R = CCFc 6-Os, CCCCFc 7], Fc′{(μ₃-CCC)Ru₃(μ-H)₃(CO)₉}₂5, and bis-cluster-capped carbon chain complexes {M₃(μ-H)₃(CO)₉}₂{μ₃:μ₃-C(CC)_nC} (M = Ru, n = 2 9, 3 10-Ru; M = Os, n = 3 10-Os) and {(L)(OC)₈(μ-H)₃M₃}C(CC)_nC{Co₃(μ-dppm)(CO)₇} (n = 1, M = Ru, L = CO 11, PPh₃12-Ru/P; n = 2, L = CO 12-Ru, PPh₃13; M = Os, L = CO 12-Os) in good to excellent yields. X-ray structural determinations of 2-5, 6-Ru, 6-Os, 7, 9, 11, 12-Ru, 12-Os and 12-Ru/P are reported.     

Addition of protic nucleophiles to alkynyl methoxy carbene ligands in diiron complexes

Different protic nucleophiles (i.e.Ph₂CNH, PhSH, MeCO₂H, PhOH) can be added to the CC bond of [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CCTol}(Cp)₂][SO₃CF₃] (1), affording new diiron alkenyl methoxy carbene complexes.The additions of Ph₂CNH and MeCO₂H are regio and stereoselective, resulting in the formation of the 5-aza-1-metalla-1,3,5-hexatriene [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)(NCPh₂)}(Cp)₂][SO₃CF₃] (2), and the 2-(acyloxy)alkenyl methoxy carbene complex [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)OC(O)Me)}(Cp)₂][CF₃SO₃] (5); the E isomer of the former and the Z of the latter are formed exclusively.Conversely, the addition of PhSH is regio but not stereoselective; thus, both the E and Z isomers of [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)(SPh)}(Cp)₂][SO₃CF₃] (3) are formed in comparable amounts.Compounds 3 and 5 are demethylated upon chromatography through Al₂O₃, resulting in the formation of the acyl complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(O)C_βHC_γ(Tol)(SPh)}(Cp)₂] (4) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(O)C_βHC_γ(Tol)OC(O)Me}(Cp)₂] (6), respectively, both with a Z configured C_βC_γ bond.Finally, the reaction of 1 with PhOH proceeds only in the presence of an excess of Et₃N affording the 2-(alkoxy)alkenyl acyl complex [Fe₂{μ-CN(Me)(Xyl)}(μ- CO)(CO){C_α(O)C_βHC_γ(Tol)(OPh)}(Cp)₂] (7). The crystal structures of 4 · CH₂Cl₂ and 7 · 0.5CH₂Cl₂ have been determined by X-ray diffraction experiments.     

The syntheses, structures and redox properties of phosphine-gold(I) and triruthenium-carbonyl cluster derivatives of tolans

The syntheses of several ethynyl-gold(I)phosphine substituted tolans (1,2-diaryl acetylenes) of general form [Au(CCC₆H₄CCC₆H₄X)(PPh₃)] are described [X = Me (2a), OMe (2b), CO₂Me (2c), NO₂ (2d), CN (2e)]. These complexes react readily with [Ru₃(CO)₁₀(μ-dppm)] to give the heterometallic clusters [Ru₃(μ-AuPPh₃)(μ-η¹,η²-C₂C₆H₄CCC₆H₄X)(CO)₇(μ-dppm)] (3a-e). The crystallographically determined molecular structures of 2b, 2d, 2e and 3a-e are reported here, that of 2a having been described on a previous occasion. Structural, spectroscopic and electrochemical studies were conducted and have revealed little electronic interaction between the remote substituent and the organometallic end-caps.     

Novel stable five-coordinate diorgano cobalt(III) complexes: Formation, structure, and reaction with carbon monoxide

A series of new five-coordinate acyl vinyl cobalt(III) complexes Co{η¹-C(CCPh)CHPh}[C(O)CCO] L₂(L = PMe₃) (6-10) were prepared via formal insertion of diphenylbutadiyne into Co-H function of mer-octahedral hydrido-acyl(phenolato)-cobalt(III) complexes. The complexes are diamagnetic. One square pyramidal structure of complex 6 was confirmed by X-ray diffraction analysis. These complexes are stable in solid state. In solution, six-coordinate acyl vinyl carbonyl cobalt(III) complex 11 is approved through the reaction of complex 7 with CO and the structure of complex 11 was determined by X-ray method.     

Modification of aminoallenylidene complexes of chromium via exchange of the C3-bound amino group

The aminoallenylidene(pentacarbonyl)chromium complexes [(CO)₅CrCCC(NR¹R²)Ph] (1a-c) react with dimethylamine by addition of the amine to the C1C2 bond of the allenylidene ligand to give alkenyl(amino)carbene complexes [(CO)₅CrC(NMe₂)CHC(NR¹R²)Ph] (2a-c) (R¹ = Me: R² = Me (a), Ph (b); R¹ = Et: R² = Ph (c)). In contrast, addition of a large excess (usually 20 equivalents) of ammonia or primary amines, H₂NR, to solutions of [(CO)₅CrCCC(NMe₂)Ph] (1a) affords the aminoallenylidene complexes [(CO)₅CrCCC(NHR)Ph] (1d-w) in which the dimethylamino group is replaced by NH₂ or NHR, respectively. In addition to simple amines such as methylamine, butylamine, and aniline, amines carrying a functional group (allylamine, propargylamine) and amino acid esters as well as amino terpenes and amino sugars can be used to displace the NMe₂ substituent. Usually the Z isomer (with respect to the partial C3-N double bond) is formed exclusively. Products derived from addition of H₂NR to the C1C2 bond of 1a are not observed. The amino group in 1d-w is rapidly deprotonated by excess of amine to form iminium alkynyl chromates [1d-w]⁻, thus protecting 1d-w from addition of free amine to either C3 or across the C1C2 bond. The iminium alkynyl chromates are readily reprotonated by acids or by chromatography on wet SiO₂ to reform 1d-w.     

Synthesis and characterization of CpMCl(PR3)(S or W-η-butadienesulfonyl) compounds of rhodium and iridium

A metathesis reaction of [Cp^∗MCl₂(PR₃)] [M = Rh, R = Ph (1), Me (3); M = Ir, R = Ph (2), Me (4)] takes place in the presence of potassium butadienesulfinate (SO₂CHCHCHCH₂)K (9) to afford the mononuclear compounds [Cp^∗M(Cl)(PR₃)(η¹-SO₂CHCHCHCH₂)] [M = Rh, R = Ph (11S), (11W); M = Rh, R = Me (13S), (13W)] and [M = Ir, R = Ph (12S); M = Ir, R = Me (14S), (14W)] under different reaction conditions. The addition of PR₃ (R = Ph, Me) to Cp^∗Ir(Cl)[(1,2,5-η)-SO₂CHCHCHCH₂] (7) affords the corresponding iridium isomers 12S, 12W and 14S, in a non-selective reaction, along with the corresponding dichloride compounds 2 or 4. The ¹H and ¹³C{¹H} NMR data are consistent with the butadienesulfonyl ligands coordinated exclusively through the sulfur atom, and they show the presence of two isomers, described as the S and W conformers, which can be isolated separately. There is clear evidence that these isomers correspond to the kinetic and thermodynamic derivatives, respectively.     

Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.