1,2-dihydro-1,2,4,3-triazaphospholo[4,5-a]quinolines as electron carriers in the electrochemical reduction of 1,1-dichloro-2-methoxycarbonyl-2-methylcyclopropane

Electrochemical reduction of 1-X-1-R¹-5-methyl-2-phenyl-7-R²-1,2-dihydro-1,2,4,3-tri-azaphospholo[4,5-a]quinolines1–5 (1: X is the lone electron pair (LEP), R¹=Et₂N, R²=Me;2: X=LEP, R¹=Ph, R²=H;3: X=S, R¹=Et₂N, R²=H;4: X=LEP, R¹=Et₂N, R²=H;5: X=LEP, R¹=MeO, R²=H) in DMF with 0.1M Bu₄NI as supporting electrolyte is reversible and results in metastable radical anions. Radical anions of compounds1–3 efficiently reduce 1,2-dichloro-2-methoxycarbonyl-2-methylcyclopropane both in the presence and in absence of Ni¹¹ ions. Effective reduction rate constants have been evaluated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2088–2091, November, 1999.     

Tin Tetrachloride Adducts with Arylphosphoramidates: A Multinuclear (31P, 19F,and 119Sn) NMR Characterization in Solution

Abstract

The synthesis of octahedral complexes [SnCl₄L₂] (L = R₂NP(O)(OCH₂CF₃)(O-p-tolyl): R₂N = Me₂N (1), Et₂N (2), CH₂(CH₂CH₂)₂N (3), and O(CH₂CH₂)₂N (4), or L = R₂NP(O)(OCH₂CF₃)(O-p-PhNO₂): R₂N = Me₂N (5), Et₂N (6), and O(CH₂CH₂)₂N (7) is described. The new adducts have been characterized by multinuclear (³¹P, ¹⁹F, ¹¹⁹Sn) NMR, IR spectroscopy, and elemental analyses. The solution NMR data show the presence of a mixture of cis and trans isomers. The structure of the complexes in solution was further confirmed by ¹¹⁹Sn NMR spectra, which display a triplet for each isomer, indicating an octahedrally coordinated tin center. The effects of the nature of R and Ar substituents on the donor ability of the P=O group in the ligands R₂NP(O)(OCH₂CF₃)(OAr) were investigated on the basis of ¹¹⁹Sn NMR chemical shifts and used to classify these ligands according to their Lewis basicity.     

Polarity and Conformatios of Phosphorylethylenes and Phosphorylacetates in Solution

Abstract

A series of derivatives R¹R²P(X)R³, where R¹=R²=Ph. R³= -CH=CH-Me, X=O(I); R¹=Me, R²=Ph, R³= -CH=CH₂, X=O(II); R¹=R²=Ph, R³= -CH=CH₂, X=Se(III) and R¹R²P(O)-CH₂C(O)OX, where R¹=Ph, R²= -CH=CH₂, X=Ment?(IV); R¹=Ph-2-OMe, R²=Ph, X=Ment?(V); R¹=R²=CH₂Ph, X=Et(I), were investigated by means of dipole moments method. The problem of conjugation in phosphorylethylenes and conformation behaviour of phosphorylacetates was considered. DM (exp.) of (I-IV), determined in CC1₄ solution are 4.48(I), 4.27(II), 4.97(III), 4.21(IV), 5.21(V) and 4.02 D (VI). The intramolecular electronic interactions of phosphoryl group with unsaturated fragment did not displays in polarity properties of compounds (I-III). The experimental dipole moments of derivatives (I-III) are equal to the calculated values of DM. DM (IV-VI) is very sensitive to orientation of the P=O and C=O polar bonds. Because DM (exp.) of these compounds very sensitive to its orientation. DM (calc.) for cis- and trans- orientation of P=O and C=O dipoles are really different, that allows to drow the conclution that, in the contrast to the crystal state, the corresponded dipoles prefer an anti array in solution.     

Effect of electron donating substituents on supramolecular structure of salts having phenylphosphonic acid and pyrazoles

The reactions of phenylphosphonic acid [(OH)₂POC₆H₅] (PPA) with a variety of ditopic pyrazoles Pz^R1,R2H (where R₁ = R₂ = H for 1, R₁ = R₂ = Me for 2, R₁ = Ph, R₂ = Me for 3 and R₁ = R₂ = iPr for 4) produce salts 1–4. Due to the presence of different substituents on pyrazole, each salt shows different structure. This study demonstrates that the presence of different substituents on the pyrazole moieties provides sufficient non-covalent interactions which are responsible for the different supramolecular structures adopted. Theoretical studies reveal that the proton affinity increases on the nitrogen having lone pair of electron with the increase of electron density on pyrazole ring but the orientation remains the same in both the solid and gaseous phase.     

Tailoring the Structure of Two‐Dimensional Self‐Assembled Nanoarchitectures Based on NiII–Salen Building Blocks

The synthesis of a series of Ni^II–salen‐based complexes with the general formula of [Ni(H₂L)] (H₄L=R²‐N,N′‐bis[R¹‐5‐(4′‐benzoic acid)salicylidene]; H₄L1: R²=2,3‐diamino‐2,3‐dimethylbutane and R¹=H; H₄L2: R²=1,2‐diaminoethane and R¹=tert‐butyl and H₄L3: R²=1,2‐diaminobenzene and R¹=tert‐butyl) is presented. Their electronic structure and self‐assembly was studied. The organic ligands of the salen complexes are functionalized with peripheral carboxylic groups for driving molecular self‐assembly through hydrogen bonding. In addition, other substituents, that is, tert‐butyl and diamine bridges (2,3‐diamino‐2,3‐dimethylbutane, 1,2‐diaminobenzene or 1,2‐diaminoethane), were used to tune the two‐dimensional (2D) packing of these building blocks. Density functional theory (DFT) calculations reveal that the spatial distribution of the LUMOs is affected by these substituents, in contrast with the HOMOs, which remain unchanged. Scanning tunneling microscopy (STM) shows that the three complexes self‐assemble into three different 2D nanoarchitectures at the solid–liquid interface on graphite. Two structures are porous and one is close‐packed. These structures are stabilized by hydrogen bonds in one dimension, while the 2D interaction is governed by van der Waals forces and is tuned by the nature of the substituents, as confirmed by theoretical calculations. As expected, the total dipolar moment is minimized     

üBER DIE INSERTION VON RPS2 IN DIE PN-BINDUNG VON AMINOPHOSPHINEN

Abstract

Aminophosphine des Typs R_n P(NR′₂)_3-n (n= 2, 1, 0; R = Ph, c-Hex, (-)Men, t-Bu; R′= Me, Et, n-Bu) reagieren mit 2, 4-Bis(aryl)-1, 3, 2, 4-dithiadiphosphetan-2, 4-disulfiden (ArPS₂)₂(Ar: Ph, 4-Methoxyphenyl = An, Naphthyl, Thienyl) unter formaler Insertion monomerer {ArPS₂)-Einheiten in eine oder in zwei der λ³-P—N-Bindung zu chiralen Organophosphorverbindungen Ar(R′₂N)P(S)—S—PR_n (NR′₂)_2-n(n = 2, 1, 0) und [Ar(R′₂N)P(S)—]₂PR₂(NR′₂)_1-n (n = 1.0). In diesen werden bei Raumtemperatur bevorzugt die λ³—P—N—und λ³—P—S-Bindungen durch H₂O oder Methanol unter Bildung von Produktgemischen solvolysiert. Mit Chlorwasserstoff bildet sich aus An(Et₂N)P(S)—S—PPh(NEt₂) das An(Et₂ N)P(S)—S—PPh(C1). Addition von Schwefel führt zu Ar(R′₂N)P(S)—S—P(S)R_n (NR′)_2-n (n=2, 1). Die Stereoisomerenbildung der neuen Verbindungen wird besprochen und ihre Struktur sowie die Zusammensetzung der Reaktionsmischungen aus den ³¹P-Spektren hergeleitet.

Aminophosphines R_n P(NR′₂)_3-n (n = 2, 1, 0; R = Ph. c-Hex, (-)Men, t-Bu; R′= Me, Et, n-Bu) react with 2, 4-Bis(aryl)-1, 3, 2, 4-dithiadiphosphetane-2, 4-disulfides (ArPS₂)₂ (Ar: Ph, 4-Methoxyphenyl = An, Naphthyl, Thienyl) under formal insertion of monomeric {ArPS₂)-units in one or in two of the λ³-P—N-bonds to yield chiral organophosphorus compounds Ar(R′₂N)P(S)—S—]₂PR_n (NR′₂)₂ (n = 2, 1, 0) and [Ar(R′₂N)P(S)—S—]₂ PR₂ (NR′₂)_2-n (n = 1, 0). At room temperature chiefly the A—P—N and A³—P—S-bonds in these products are solvolyzed by H, O or methanol with formation of mixtures of compounds. With hydrogen chloride An(Et₂N)P(S)—S—PPh(NEt₂) is converted into An(Et₂N)P(S)—S—PPh(Cl). Addition of sulfur yields Ar(R′₂N)P(S)—S P(S)R_n (NR′₂)_2-n (n = 2, 1). Stereoisomerism of the new compounds is discussed and their structures as well as the composition of reaction mixtures are deduced from “P-NMR-spectra”.     

Double stereoselective coordination of chiral N,S ligands: Synthesis,coordination chemistry and utilization in Pd‐catalyzed allylic alkylation

A series of chiral pentane‐2,4‐diyl‐based thioether‐amine ligands [ 4 and 5 ; (R,S)‐ and (S,S)‐R¹SCH(CH₃)CH₂CH(CH₃)NHR², respectively, where 4a R¹ = iPr, R² = Ph; 4b R¹ = tBu, R² = Ph; 4c R¹ = 1‐Ad, R² = Ph; 5a R¹ = iPr, R² = Ph; 5b R¹ = tBu, R² = Ph; 5c R¹ = 1‐Ad, R² = Ph; 5d R¹ = iPr, R² = 4‐MeOC₆H₄; 5e R¹ = iPr, R² = 4‐MeC₆H₄; 5f R¹ = iPr, R² = 3,5‐Me₂C₆H₃] with stereogenic S‐ and N‐donor atoms has been prepared starting from cyclic sulfates via optically pure γ‐aminoalcohol or 2,4‐dimethylazetidine intermediates. The synthesis of the novel diastereomerically related ligand sets 4 and 5 was accomplished starting from the same source of chirality. The modular ligand structure and the novel synthetic strategies developed for their synthesis allowed the easy modification of the ligands’ (i) S‐ and (ii) N‐substituents, as well as (iii) the relative stereochemistry within the ligand backbone. Six‐membered [Pd(N,S)Cl₂]‐type chelate complexes of the diastereomerically related ligands 4a and 5a were synthesized and characterized by X‐ray crystallography in the solid phase, by density functional theory calculations and in solution by NMR spectroscopy. The coordination of 5a resulted in the formation of a single chair conformation by the stereospecific locking of both stereolabile (N and S) donor atoms. In contrast, compound 4a forms rapidly equilibrating palladium species due to the fast inversion of the sulfur donor. Ligands with stereochemically fixed donor atoms provided robust and efficient catalytic systems that can be effectively applied in alkylene carbonates as green reaction media. Remarkably, the phosphine‐free catalysts are air‐stable, and at room temperature in the presence of moisture gave excellent ee’s (up to 93%) in asymmetric allylation processes thanks to the double stereoselective coordination.     

Phosphorylacetaladehydes in Reactions with N-Electro-Philes. Synthesis of new Promising Synthons

Abstract

The reactions of phosphorylacetaldehydes I with N-electro-philes (⁺NO, ⁺N₂Ar) proceed selectively via intermediate A in accordance with one of the three directions depending on the nature of the substituents X and R. The nature of the end product is determined by the competitive electrofugic power of R₂P(O), X and CHO.     

Syntheses,crystal structures,and electrochemistry of novel Fe2SN and FeSN carbonyl complexes with pendant bases

Reactions of Fe₂(CO)₉ with thioacylhydrazones ArCH=NNHCSPh in THF afford Fe₂(CO)₆(μ-κ²S:κ²N-PhC(S)=NNCHArCHArN(CHAr)N=CSPh) (1, Ar?=?C₆H₅; 3, Ar?=?4-CH₃C₆H₄) and Fe(CO)₃(κ²S:N-PhC(=S)NHNCHArCHArN(CHAr)N=CSPh) (2, Ar?=?C₆H₅; 4, Ar?=?4-CH₃C₆H₄). They have been characterized by elemental analyses, IR, ¹H NMR, and ¹³C NMR and structurally determined by X-ray crystallography. Electrochemical studies reveal that when using HOAc as a proton source, they exhibit high catalytic H₂-production.     

Synthesis,characterization and in vitro antitumour activity of diorganotin bisxanthates [R2Sn(S2COR′)2] (R=Me,Et, nBu,Ph; R′=Et,iPr, Hex) and crystal structure of bis(O-ethyldithiocarbonato)diphenyltin(IV)

A series of diorganotin bisxanthate compounds, [R₂Sn(S₂COR′)₂] (R=Me, Et, nBu, tBu, and Ph; R′?Et, iPr and cHex) have been prepared and characterized by spectroscopic methods (IR, NMR and FAB MS). The xanthate ligands chelate the R₂Sn moieties forming disparate Sn–S bonds leading to skew-trapezoidal biypramidal tin atom geometries. The crystal structure of a representative compound, [Ph₂Sn(S₂COEt)₂], confirms the spectroscopic results and shows the tin atom to be coordinated by two asymmetrically chelating xanthate ligands [Sn–S(1) 2.486(1), Sn–S(2) 3.052(1) Å and Sn–S(3) 2.484(1), Sn–S(4) 3.220(1) Å] with the two phenyl substituents lying over the weaker Sn–S interactions so that C–Sn–C is 126.5(1)°. Crystal data for [Ph₂Sn(S₂COEt)₂]: monoclinic space group P2₁/n: a=9.645(1), b=23.723(3), c=9.798(2) Å, ß=100.23(1)°, V=2206.2 ų, Z=4; 2708 data refined to final R 0.023. A selection of these compounds has been evaluated for activity against the L1210 mouse leukaemia cell line.     

Evidence of Long-Range 13C-31P Couplings: A 13C NMR Investigation of Some Aryl Esters of Phosphor-Amidochloridic Acid and the Related Compounds

Abstract

In ¹³ NMR study organophosphorus compounds, sign and magnitude of ¹³ C-³¹ P spin-spin couplings has been of great interest to elucidate stereochemistry and electronic state of phosphorus central atom. However, a discussion about the mechanisms of carbon-phosphorus couplings is still complicated specially in the case of long-range couplings that also are not frequently observed. In this study, ¹³ C NMR chemical shifts and coupling constants have been determined for a series of aryl esters of phosphoramidochloridic acid with the general formula: R₂NP(O)(OAr)Cl, in which R = methyl and/or benzyl, Ar = p-tolyl. p-nitrophenyl, and phenyl. Besides usual W-couplings that could be found in these systems, we detected long-range couplings through five and six bonds. It has been shown that, these couplings are highly dependent on substituents on phosphorus nuclei. The data for some related compounds have been also obtained for a comparison.     

四个基于间苯二(取代水杨醛酰腙)的有机锡配合物的溶剂热合成、结构和荧光性能

采用间苯二（取代水杨醛酰腙）（H₄L）与R₃²SnOH溶剂热反应,或间苯二甲酰肼、3-叔丁基水杨醛和三环己基氢氧化锡一锅溶剂热法反应,合成了4个新的有机锡配合物（SnR²）₂L（1~4）,其中,H₄L=m-Ph（CONH—N=CH（o-OH） PhR¹）₂;R¹=NEt₂,R²=Ph（1）;R¹=3,5-di-tert-butyl=3,5-t-2Bu,R²=Ph（2）;R¹=3,5-t-2Bu,R²=Cy（3）;R¹=3-tert-butyl=3-t-Bu,R²=Cy（4）。经元素分析、红外光谱和（¹H、¹³C、¹¹9Sn）核磁共振谱表征,并用X射线衍射方法确证配合物1~4的结构。配体H₄L的2个取代水杨醛酰腙链向内取向并与锡原子配位形成3个内向E型配合物1~3,取代水杨醛酰腙链向外取向并与锡原子配位形成外向E型配合物4。配合物1、2和4属于三斜晶系P1空间群,配合物3属于单斜晶系P2₁/c空间群。中心锡与配位原子构成畸形双角三锥构型。配体、配合物-三氯甲烷溶液的荧光性能表明,当具有弱荧光的配体m-Ph（CONH—N=CH（o-OH） PhNEt₂）₂（H₄L¹）和无荧光的配体m-Ph（CONH—N=CH（o-OH） Ph（3,5-t-2Bu））₂（H₄L²）分别与苯基锡、环己基锡配位后,配合物-三氯甲烷溶液发出强荧光。     

Interaction of Tris(3-Hydroxymethyl)Phosphine with Cinnamic Acids

Abstract

Phosphonium zwitterions of the known type R₃P⁺CH(Ar)CH₂CO₂ ^? (II) are obtained as a racemic mixture in moderate yield via a 1:1 reaction of cinnamic acids (Ar = phenyl, or substituted phenyl) with [HO(CH₂)₃]₃P in acetone at room temperature under Ar. The products are characterized by elemental analysis, ³¹P{¹H}-, ¹H-, and ¹³C{¹H}-NMR spectroscopies, and mass spectrometry, although they contain a minor coproduct formed via neutralization of the positive and negative charges of II with the respective acid and phosphine reactants (see Experimental Section). In CD₃OD, the monodeuterated salts R₃P⁺CH(Ar)CH(D)CO₂ ^? are formed as a mixture of diastereomers with d.r. values of ～2 to 8, depending on substituent groups present in the organic acid; in these studies, 2-HO-cinnamic acid is the most reactive, and β-methylcinnamic acid is the least reactive.     

Ligand Substituent Effects on Ruthenium (III/II) Redox Properties: An Advanced Inorganic Laboratory Experiment

A convenient inorganic laboratory exercise is presented that exposes the student to the influences of ligand substituents on a metal centers redox properties. Students prepare a series of compounds with the general formula [Ru(bpy)₂(R¹,R²mal)](PF₆), where bpy is 2,2-bipyridine and R¹,R²mal is an anionic -diketone ligand with various R¹ and R² substituents. Each complex is prepared in a single synthetic step, and the Ru(III)/Ru(II) couple is characterized by cyclic voltammetry. The potential of the Ru(III)/Ru(II) couple shifts upon varying R¹ and R² from 0.64 to 1.10 volts vs. SSCE in the following order: (R¹ = R² = Me) < (R¹ = R² = Ph) < (R¹ = Me, R² = CF₃) < (R¹ = R² = CF₃). The inductive effects of the R substituents on the Ru(III)/Ru(II) couple are consistent with their electron-donating and electron-withdrawing properties. Hammett constants for the substituents provide an approximate measure of these effects. A linear relationship is observed when the Hammett constants are plotted against the Ru(III)/Ru(II) potential. This laboratory exercise applies a versatile electroanalytical method, cyclic voltammetry, to measure the substituent effects on a metal centers electron density. Student results of the syntheses and redox characterizations of a series of [Ru(bpy)₂(R¹,R²mal)]⁺ complexes are presented and discussed.     

Cyclopentadienyl diruthenium metal carbonyl complexes bearing pendant thienyl ligands

Abstract  

Reactions of the thienyl side chain functionalized cyclopentadienyls (C₄H₃S)C(R₁R₂)C₅H₅[R₁, R₂ = CH₃ (1); R₁, R₂ = (CH₂)₅ (2); R₁, R₂ = C₂H₅ (3)] with Ru₃(CO)₁₂ in refluxing xylene gave the corresponding cyclopentadienyl diruthenium carbonyl complexes [(η ⁵-C₄H₃S)CR₁R₂(C₅H₄)Ru(CO)₂]₂ (R₁, R₂ = CH₃ (4); R₁, R₂ = (CH₂)₅ (5); R₁, R₂ = C₂H₅ (6)), which were characterized by elemental analysis, IR and ¹H NMR spectra. The molecular structures of 4, 5 and 6 were determined by single crystal X-ray diffraction.     

Primary Studies on Variation in Position of Trifluoromethyl Groups in Several Aromatic Group‐14 Derivatives by 19F‐NMR Spectroscopy

Variation in the position of CF₃ groups in several aromatic Group‐14 compounds was studied by ¹⁹F‐NMR spectroscopy. In these compounds R_nECl_4?n (n=1 or 2; E=Si, Ge, or Sn; R=2,4,6‐(CF₃)₃C₆H₂ (=Ar), 2,6‐(CF₃)₂C₆H₃ (=Ar′), or 2,4‐(CF₃)₂C₆H₃ (=Ar″)), Ar, Ar′, and Ar″ are all bulky, strongly electron‐withdrawing ligands. The ¹⁹F‐NMR studies of the variation in position of the CF₃ substituents in these compounds as revealed by chemical shifts could be correlated with the electronegativities of the central elements E, and with intramolecular E–F interactions derived from single‐crystal X‐ray diffraction data. These interactions are considered to play an important role in the stabilization of these compounds.     

The Influence of the Steric Effect of the Substituents on the Phosphorus Acids Dissociation

Abstract

The dissociation processes of a series of phosphoric, phosphonic, and phosphinic acids have been studied by the modified method of potentiometry in water and water-ethanol media at 25°C. The influence of substituents on the acidic properties of these compounds has been investigated. As a measure of the substituents steric effects the R_s constants, calculated on the basis of frontal steric model (1), nave been used. A good linear relationship between pKa values in different media has been found. For all series of acids a linear relationship between pKa values and R_s constants of substituents at phosphorus has also been established. In the case of dialkylphosphates in water, for example, such a relationship is expressed by equation:

pKa = (-0.717 ± 0.028)-(0.556 ± 0.009) R_s

N = 7, R = 0.9932, S_o = 0.011

pKa value rises with the increase of the steric effect of the substituents at phosphorus which may be conditioned by the steric hindrance to the anion solvatation.     

Hydroalumination and Hydrogallation Reactions with Tri(ethynyl)silanes – Generation of Compounds with up to Three Coordinatively Unsaturated Aluminium Atoms

Hydroalumination or hydrogallation of tri(ethynyl)silanes, RSi(C≡C‐Ar)₃ ( 1a , R = Ph, Ar = Ph; 1b , R = Me, Ar = Ph; 1c , R = Me, Ar = C₆H₄Me), with the element hydrides H‐EtBu₂ (E = Al, Ga) in stoichiometric ratios of 1:1 to 1:3 at ambient temperature yielded the addition products (PhC≡C)₂(R)Si[(tBu₂E)C=C(H)Ph] ( 2 , R = Ph, E = Ga; 3a , R = Me, E = Al; 3b , R = Me, E = Ga), (PhC≡C)(Me)Si[(tBu₂E)C=C(H)Ph]₂ ( 4a , E = Al, 4b , E = Ga) and (Me)Si[(tBu₂Al)C=C(H)Ar]₃ ( 5 , Ar = Ph; 6 , Ar = C₆H₄Me). Compounds 2 – 4 show a relatively close interaction between the coordinatively unsaturated aluminium or gallium atoms and one of the C_α(≡C) atoms of unreacted alkyne substituents [245 (E = Al) and 266 pm (E = Ga)] that stabilises the kinetically favoured cis addition products with E and hydrogen on the same side of the resulting C=C double bonds. In the absence of these stabilising effects the compounds were found to isomerise to the thermodynamically favoured trans isomers.     

The Formation of Phosphacycloheptatrienes in Ring Enlargement Reaction

Abstract

The forrmation of substituted phosphacycloheptatrienes in ring expansion reaction(s) is describzd. From thc: reac-tion of 3,4-dimethyl-l-phenyl-3-phospholene-l-oxide(1,R¹ = c₆H₅, R₂=R₃ = CH₃) with dichlorocarbene under liquid-liquid phase transfer circumstances not the expected adduct but the appropriate phoshacycloheptatrisne (4, R_l, R₂,R₃ as above) was prepared. The formation of this product can be explained assuming two ring expansions effected by two series of dichlorocarbene addition and cyclopropane ring opening. In the similar reaction of the methoxy-phospholenc derivative (1, R¹=CH₃O, R² = R³ = CH3 four other products are also formed beside the phosphacyclohcptatriene. Again phosphacycloheptatrienes (4) are formed as the result of dichlorocarbene addition to the regioisoners of dihidrophosphorins (2) obtained from the phospholene-dichlorocarbene adducts by thermolysis. The same product can be derived from each regioisomeric pair.     

Homogeneous and Solid-Gas Hydrogenation of Alkynes in the Presence of the Clusters Fe3(CO)9(ε-RC2 R 1) {R=R 1=Ph, Et; R=Me, R 1=Ph}: Characterization of New Metallacyclic Derivatives

The clusters Fe₃(CO)₉(RC₂ R ¹) (R=R ¹=Ph, Et; R=Me, R ¹=Ph), complexes 1a, 1b, 1c, containing an alkyne bound in perpendicular fashion with respect to a cluster edge, catalyze the hydrogenation of some acetylenes either under homogeneous and solid–gas conditions. We hypothesize that cluster catalysis occurs and that the catalytic activity is related to the coordinating ability of the alkynic substrates. Competition between hydrogenation and formation of metallacyclic byproducts occurs. The new metallacyclic derivatives Fe₃(CO)₆(-CO)₂{(RC₂ R ¹)(R ²C₂ R ³)}, Fe₂(CO)₆{(RC₂ R ¹)(R ²C₂ R ³)} {R=R ¹=Et, R ²=R ³=H, Ph; R ²=Me, R ³=Et, Ph; R ²=H, R ³=Bu ^t . R=R ¹=Ph, R ²=Me, R ³=Et, Ph} (complexes 2, 3) were found both in the homogeneous reaction mixtures and after the solid–gas reactions. The formation of these products lowers the catalytic activity.