Alkyne Ligands Research Articles

Defective TiO2-supported Cu nanoparticles as efficient and stable electrocatalysts for oxygen reduction in alkaline media.

Nanocomposites based on TiO2-supported copper nanoparticles were prepared by a hydrothermal method where copper nanoparticles with or without the passivation of 1-decyne were chemically grown onto TiO2 nanocolloid surfaces (and hence denoted as CuHC10/TiO2 and Cu/TiO2, respectively). Transmission electron microscopy measurements showed that the size of the hybrid nanoparticles was 5-15 nm in diameter with clearly defined lattice fringes for anatase TiO2(101) and Cu(111). The formation of anatase TiO2 nanoparticles was also observed by X-ray diffraction measurements. FTIR measurements confirmed successful attachment of alkyne ligands onto the surface of the copper nanoparticles via Cu-C≡ interfacial bonds in CuHC10/TiO2. XPS measurements suggested the formation of CuO in both samples with a higher concentration in Cu/TiO2, and interestingly Ti(3+) species were found in CuHC10/TiO2 but were absent in Cu/TiO2 or TiO2 nanoparticles. Electrochemical studies demonstrated that both Cu/TiO2 and CuHC10/TiO2 exhibited a markedly improved electrocatalytic performance in the oxygen reduction reaction, as compared to TiO2 nanocolloids alone, in the context of the onset potential, the number of electrons transferred and the kinetic current density. Importantly, among the series, CuHC10/TiO2 exhibited the best ORR activity with a high current density, an almost four-electron reduction pathway and long-term stability after 4000 cycles at high potentials, which may be ascribed to the defective TiO2 structures in combination with surface ligand engineering.

Crystal Structures of Homoleptic Propynyloargentates AI[Ag(C3H3)2] with AI = Ag, Li, Na Solved and Refined from X‐ray Powder Diffraction Data

AbstractThe crystal structures of three isostructural homoleptic propynyloargentates, namely Ag[Ag(C3H3)2], Li[Ag(C3H3)2], and Na[Ag(C3H3)2] were solved and refined from laboratory X‐ray powder diffraction data (Iba2, Z = 4). Almost linear [H3C–C≡C···Ag···C≡C–CH3]– anions are found: The alkali metal cations or the second silver cation coordinate side‐on to the C≡C triple bond of the alkyne ligand (CN = 8) so that layer‐like structural fragments are formed, which are stacked in an AB fashion along [100]. These crystal structures are corroborated by IR and solid‐state NMR spectra. Powder SHG measurements confirm the acentric space group Iba2. On the other hand, these methods also supported a first structural model obtained earlier, in which very unusual bent [Ag(CCCH3)2]– units were found in a smaller unit cell (Amm2, Z = 2). Bond‐analytical COHP calculations clearly indicate that this structural motif cannot be stable. A close re‐inspection of the diffraction data, now also including high‐resolution synchrotron powder diffraction data (HASYLAB, beamline B2), reveal the existence of one weak additional reflection indicating a larger unit cell. Hence, this investigation clearly shows that under very specific circumstances – e.g. ligands with a weak scattering power compared to the central metal ion – wrong structural models can be obtained from X‐ray powder diffraction data, even when additional information from complementary spectroscopic methods is taken into account. Additional electronic‐structure calculations are therefore needed to elucidate the correct structural arrangement.

Carbon–Carbon Bond Forming Reactions with Tantalum Diamidophosphine Complexes That Incorporate Alkyne Ligands

The incorporation of o-phenylene-linked diamidophosphine ligands onto the readily available alkyne complexes Ta(alkyne)Cl3(DME) (where alkyne = hex-3-yne or 1,2-bis(trimethylsilylacetylene); DME = 1,2-dimethoxyethane) results in the formation of a versatile set of starting materials of the general formula [PhNPN*]Ta(alkyne)Cl (where [PhNPN*] = PhP(2-(N-mesityl)-5-Me-C6H3)2). Upon reaction with KBEt3H, the synthesis of the corresponding hydride complexes [PhNPN*]Ta(alkyne)H can be achieved; these complexes feature extremely downfield (δ ∼21 ppm) doublet resonances (2JHP = ∼35 Hz) in the respective 1H NMR spectra that are assigned to the newly formed Ta–H moieties. Subsequent reaction of these Ta hydrides with 2,6-dimethylphenylisocyanide and phenylacetylene results in the insertion of these species into the Ta–H bond and the formation of the corresponding iminoformyl and phenylvinyl complexes, respectively. While the former intermediate cannot be detected, the latter was characterized by NMR spectroscopy. Both of these processes result in the further transformation to generate C–C coupled products by a reductive elimination sequence with the coordinated alkyne; in the case of the iminoformyl, an azadiene results, whereas with the phenylvinyl derivative a butadienyl fragment is generated. Single-crystal X-ray diffraction and a suite of NMR spectroscopic techniques were used to characterize these species. A discussion of the bonding of the products in the context of the process by which they form is presented. The rate of formation of the butadienyl moiety from the phenylvinyl intermediate results in the activation parameters of ΔH⧧ = 22.2 ± 0.3 kcal/mol and ΔS⧧ = −8.7 ± 0.2 cal/(mol)(K).

Photoluminescent Gold(I) Complex with Biphenyl Acetylene Ligand Showing Stable Nematic Liquid-Crystalline Phase

A novel liquid-crystalline (LC) gold(I) complex (Biph6) having biphenyl acetylene ligand was designed and synthesized, and its LC behavior and photoluminescence properties were compared with those of a previously reported gold complex (Ph6) with phenyl acetylene ligand. Biph6 exhibited an enantiotropic nematic phase in a temperature range wider than that of Ph6. Ph6 and Biph6 showed intense photoluminescence with different colors in the crystalline phase: blue and yellowish green luminescence, respectively. We demonstrated that the color of luminescence of the gold complexes could be changed by changing the structure of the molecules and molecular aggregates.

Crystal structures of trans-acetyl-dicarbon-yl(η(5)-cyclo-penta-dien-yl)(di-methyl-phenyl-phosphane)molybdenum(II) and trans-acetyl-dicarbon-yl(η(5)-cyclo-penta-dien-yl)(ethyl-diphenyl-phosphane)molybdenum(II).

The title compounds, [Mo(C5H5)(COCH3)P(CH3)2(C6H5)(CO)2], (1), and [Mo(C5H5)(COCH3)P(C2H5)(C6H5)2)(CO)2], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C5H5)(CO)3(CH3)]. Both complex mol-ecules exhibit a four-legged piano-stool geometry with trans-disposed carbonyl ligands along with Mo-P bond lengths and C-Mo-P angles that reflect the relative steric pressure of the respective phosphine ligand. The structure of compound (1) exhibits a layered arrangement parallel to (100). Within the layers mol-ecules are linked into chains along [001] by non-classical C-H⋯O inter-actions between the acetyl ligand of one mol-ecule and the phenyl and methyl phosphine substituents of another. In the structure of complex (2), a chain motif of centrosymmetrical dimers is found along [010] through C-H⋯O inter-actions.

Crystal structures of (μ2-η(2),η(2)-4-hydroxybut-2-yn-1-yl 2-bromo-2-methylpropanoate-κ(4) C (2),C (3):C (2),C (3))bis[tricarbonylcobalt(II)](Co-Co) and [μ2-η(2),η(2)-but-2-yne-1,4-diyl bis(2-bromo-2-methyl-propanoate)-κ(4) C (2),C (3):C (2),C (3)]bis[tricarbonylcobalt(II)](Co-Co).

The title compounds, [Co2(C8H11BrO3)(CO)6], (1), and [Co2(C12H16Br2O4)(CO)6], (2), result from the replacement of two carbonyl ligands from dicobalt octa-carbonyl by the alkynes 4-hy-droxy-but-2-ynyl 2-bromo-2-methyl-propano-ate and but-2-yne-1,4-diyl bis-(2-bromo-2-methyl-propano-ate), respectively. Both mol-ecules have classic tetra-hedral C2Co2 cluster cores with the Co(II) atoms in a highly distorted octa-hedral coordination geometry. The alkyne ligands both adopt a cis-bent conformation on coordination. In the crystal structure of (1), classical O-H⋯O and non-classical C-H⋯O contacts form inversion dimers. These combine with weak O⋯O and Br⋯O contacts to stack the mol-ecules into inter-connected columns along the b-axis direction. C-H⋯O and C-H⋯Br contacts stabilize the packing for (2), and a weak Br⋯O contact is also observed. Inter-connected columns of mol-ecules again form along the b-axis direction.

Synthesis and reactivity of oxygen ligated molybdenum(II) carbonyl complexes

Bis(acetylacetonate) and bis(tropolonate) complexes of MoII were synthesized by combining [NEt4][Mo(CO)4(I)3] and two equivalents of the ligand, followed by trapping with either an alkyne or phosphine. Alkyne complexes (trop)2Mo(CO)(PhCCH) (1b) and (acac)2Mo(CO)(PhCCR) (R=Me (2a), H (2b)) were characterized crystallographically. The alkyne ligands undergo rapid rotation at room temperature on the NMR time scale and the barrier to rotation for the butyne complexes (LX)2Mo(CO)(MeCCMe) (LX=trop (1c), acac (2c)) were measured by variable temperature NMR. The rotational barrier of the tropolonate derivative 1c is 1.6kcal/mol lower than that of the acetylacetonate derivative 2c despite the fact that trop is both smaller and less basic than acac. The coordinated alkynes will readily undergo exchange with free alkyne in solution and, on a slower time scale, the CO ligand can be displaced to form the bis(alkyne) species (LX)2Mo(RCCR)2 (4). The CO ligand of (LX)2Mo(CO)(PhCCH) can also be readily displaced by P(OMe)3 to form (LX)2Mo(P(OMe)3)(PhCCH), but larger phosphorus donors do not react. Alkyne complexes 1 and 2 will oxidize in air to the d2 species (LX)2Mo(O)(RCCR) in which the alkyne has been rotated perpendicular to the Mo–O bond and locked in position. The synthesis of the (LX)2Mo(CO) fragment reported here provides access to oxygen ligated low-valent Mo species which have thus far remained elusive.

ChemInform Abstract: Three‐Component [2 + 2 + 1] Cross‐cyclotrimerization of Carboryne, Unactivated Alkene, and Trimethylsilylalkyne Co‐Mediated by Zr and Ni.

A three-component [2+2+1] cross-cyclotrimerization of carboryne, alkene, and trimethylsilylalkyne has been achieved under the cooperative action of zirconium and nickel, leading to the synthesis of a series of dihydrofulvenocarboranes. The bulkiness of the alkyne and phosphine ligand plays a key role in the selective formation of the products.

Electrocatalytic activities of alkyne-functionalized copper nanoparticles in oxygen reduction in alkaline media

Stable alkyne-capped copper nanoparticles were prepared by chemical reduction of copper acetate with sodium borohydride in the presence of alkyne ligands. Transmission electron microscopic measurements showed that nanoparticles were well dispersed with a diameter in the range of 4–6 nm. FTIR and photoluminescence spectroscopic measurements confirmed the successful attachment of the alkyne ligands onto the nanoparticle surface most likely forming Cu–C interfacial bonds. XPS measurements indicated the formation of a small amount of CuO in the nanoparticles with a satellite peak where the binding energy red-shifted with increasing Cu(II) concentration. Cu2O was also detected in the nanoparticles. Similar results were observed with commercial CuO nanoparticles. Electrochemical studies showed that the as-prepared alkyne-capped copper nanoparticles exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, a performance that was markedly better than those reported earlier with poly- or single-crystalline copper electrodes; and the fraction of peroxides in the final products decreased with decreasing concentration of oxide components in the nanoparticles.

Synthesis of branched tetranuclear alkynylplatinum(II) terpyridine complexes and their photophysical properties

Herein we report the synthesis of two luminescent branched tetranuclear alkynylplatinum(II) complexes {[Pt(tBu3-tpy)]2[Ar(CC)4][Pt(tBu3-tpy)]}2(PF6)4 (I and II; tBu3-tpy=4,4′,4″-tri-tertbutyl-2,2′:6′,2″-terpyridine; Ar=[(C6H4)2(CCCC)]). Two terminal alkyne ligands were synthesized by oxidative coupling in the air, and subsequently reacted with a chloroplatinum(II) terpyridine complex. Their photophysical properties have been studied by both steady-state spectroscopy and transient spectroscopy. The final two platinum(II) complexes were found to show long-lived excited states in solution at room temperature. The longest lifetime of ∼17μs for the twisted branched molecule was observed in toluene at room temperature. Application of the two complexes as a light-harvesting chromophore in photocatalytic hydrogen production was further examined.

Study on the anti‐sulfur‐poisoning characteristics of platinum–acetylide–phosphine complexes as catalysts for hydrosilylation reactions

A series of platinum–acetylide–phosphine complexes were synthesized and their anti‐sulfur‐poisoning characteristics investigated. In comparison with Speier's and Karstedt's catalysts, the platinum–acetylide–phosphine complexes exhibited both higher catalytic activity and selectivity for the β‐adduct for the hydrosilylation reactions under the same conditions. Furthermore, the complexes also exhibited a strong ability to resist to sulfur‐poisoning. This indicated that the alkyne ligands containing the silyl group had a strong impact on the hydrosilylation reaction. Copyright © 2014 John Wiley & Sons, Ltd.

Hydrazone–diacetyl platinum(II) complexes: Substituent effect on intramolecular N–H⋯O hydrogen-bond strength

Bis(benzylamine)diacetylplatinum(II) (3) reacted with 2-pyridyl-functionalized hydrazones and with diacetyl dihydrazone to yield diacetyl platinum(II) complexes [Pt(COMe)2(2-pyCRNNH2)] (R = H, 4a; Me, 4b; Ph, 4c) and [Pt(COMe)2(H2NNCMe–CMeNNH2)] (5). These complexes showed weak intramolecular N–H⋯O hydrogen bonds where the hydrazone and the acetyl ligand act as H donor and H acceptor, respectively. Using hydrazones 2-pyCRNNHR′ substituted with electron-withdrawing groups R′ resulted in complexes [Pt(COMe)2(2-pyCRNNHR′)] (R/R′ = H/C6H4-p-F, 6d; Me/C6H4-p-F, 6e; H/COMe, 7a; Me/COMe, 7b; H/COPh, 7c; Me/COPh, 7d; H/CO(C6H4-p-F), 7e; Me/CO(C6H4-p-F), 7f) with stronger intramolecular N–H⋯O hydrogen bonds. The isolation of the analogous phenylhydrazone complexes (R′ = Ph) failed on this way, but reactions of the 1D coordination polymer [{Pt(COMe)2}n] (2) with phenylhydrazones resulted in the formation of the desired complexes [Pt(COMe)2(2-pyCRNNHR′)] (R/R′ = H/Ph, 6a; Me/Ph, 6b; Ph/Ph, 6c; H/C6F5, 6f). The constitution of all complexes was unambiguously confirmed analytically, spectroscopically and, in part, by single-crystal X-ray diffraction analyses. Structural and NMR parameters gave evidence that the strength of the N–H⋯O hydrogen bond is increased in the order 5 ≈ 4a–c < 6a–e < 6f ≈ 7a–f. This goes parallel with an activation of the acetyl ligand, but in no case the reaction with amines resulted in the formation of iminoacetyl platinum(II) complexes as it was found in analogous oxime–diacetyl complexes [Pt(COMe)2(2-pyCRNOH)] which have stronger (even than in type 6f/7a–f complexes) intramolecular O–H⋯O hydrogen bonds.

Titanocene and Zirconocene Complexes with Diaminoacetylenes: Formation of Unusual Metallacycles and Fulvene Complexes

The reaction of dipiperidinoacetylene (pipC≡Cpip, pip = NC5H10, 1a) with [Cp2Ti(η2-btmsa)] (2) or with [Cp2Zr(η2-btmsa)(py)] (4) (btmsa = bis(trimethylsilyl)acetylene, py = pyridine) afforded the metallacyclopentadienes [Cp2M(C4pip4)] (3, M = Ti; 5, M = Zr), which in the solid state exhibit twisted five-membered metallacycles with an unusual half-chair conformation. In contrast, the sterically more demanding decamethyltitanocene (Cp*2Ti) and -zirconocene (Cp*2Zr) complex fragments can only accommodate one alkyne ligand. Thus, the titanacyclopropene [Cp*2Ti(C2pip2)] (7) was isolated from the reaction of 1a with [Cp*2Ti(η2-btmsa)] (6) or with [Cp*2TiCl] in the presence of magnesium, whereas the zirconacyclopropenes [Cp*2Zr(C2X2)] (8a, X = pip; 8b, X = NC5H9-4-Me; 8c, X = NEt2) were prepared by the reduction of [Cp*2ZrCl2] with magnesium in the presence of 1a, bis(4-methylpiperidino)acetylene (1b), and bis(diethylamino)acetylene (1c), respectively. NMR studies showed that complexes 8 are in equilibrium with ...

Abstraction of a Vinylic Hydrogen to Form Alkynes. Multinuclear and Multidimensional NMR Spectroscopy and Computational Studies Elucidating Structural Solution Behavior of Acetylene and Propyne Complexes of Titanium

The alkyne complexes [(PNP)Ti(η2-HC≡CH)(CH2tBu)] (2) and [(PNP)Ti(η2-HC≡CMe)(CH2tBu)] (3) have been prepared by treatment of [(PNP)Ti═CHtBu(OTf)] (1) with the Grignard reagents H2C═CHMgCl and MeHC═CHMgBr, respectively. Complex 3 can be also prepared using the Grignard H2C═C(Me)MgBr and 1. The 2-butyne complex [(PNP)Ti(η2-MeC≡CMe)(CH2tBu)] (4) can be similarly prepared from 1 and MeHC═C(Me)MgBr. Complexes 2 and 3 have been characterized with a battery of multidimensional and multinuclear (1H, 13C, and 31P) NMR spectroscopic experiments, including selectively 31P decoupled 1H{31P}, 1H–31P HMBC, 1H–31P HOESY, and 31P EXSY. Variable-temperature 1H and 31P{1H} NMR spectroscopy reveals that the acetylene ligand in 2 exhibits a rotational barrier of 11 kcal mol–1, and such a process has been corroborated by theoretical studies. Formation of the titanium alkyne ligand in complexes 2 and 3 proceeds via the vinyl intermediate [(PNP)Ti═CHtBu(CH═CHR)] followed by a concerted, metal-mediated β-hydrogen abstraction step that has been computed to have a barrier of 20–22 kcal mol–1. The geometry and rotational mechanism of the alkyne ligand in 2 are presented and compared with those of the ethylene derivative [(PNP)Ti(η2-H2C═CH2)(CH2tBu)] (5), which does not display rotation of the bound ethylene under the same conditions.

Three-Component [2+2+1] Cross-cyclotrimerization of Carboryne, Unactivated Alkene, and Trimethylsilylalkyne Co-mediated by Zr and Ni

A three-component [2+2+1] cross-cyclotrimerization of carboryne, alkene, and trimethylsilylalkyne has been achieved under the cooperative action of zirconium and nickel, leading to the synthesis of a series of dihydrofulvenocarboranes. The bulkiness of the alkyne and phosphine ligand plays a key role in the selective formation of the products.

Activation of Acetyl Ligands through Hydrogen Bonds: A New Way to Platinum(II) Complexes Bearing Protonated Iminoacetyl Ligands

The dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] (1) reacted with 2-pyridyl-functionalized monoximes and with dioximes in the presence of NaOMe to yield oxime–diacetyl platinum(II) complexes [Pt(COMe)2(2-pyCR═NOH)] (R = H, 4a; Me, 4b; Ph, 4c) and [Pt(COMe)2(HON═CR–CR═NOH)] (R/R = Me/Me, 5a; Ph/Ph, 5b; (CH2)4, 5c; NH2/NH2, 5d), respectively. The strong intramolecular O–H···O hydrogen bonds in these complexes give rise to an activation of the acetyl ligands for Schiff-base type reactions, thus forming with primary amines iminoacetyl platinum complexes [Pt(COMe)(CMe═NHR′)(2-pyCR═NO)] (R/R′ = H/Bn, 6a; Me/Bn, 6b; Ph/Bn, 6c; H/CH2CH2Ph, 6d; H/CH2CH═CH2, 6e; Bn = benzyl) and [{Pt(CMe═NHR′)2(ON═CR–CR═NO)}2] (R/R = Me/Me, 7a–d; Ph/Ph, 8a–d; (CH2)4, 9a; R′ = Bn, a; CH2CH2Ph, b; CH2CH═CH2, c; CH2CH2OH, d). The intramolecular N–H···O hydrogen bonds in type 6–9 complexes make clear that protonated iminoacetyl ligands (i.e., aminocarbene ligands) and deprotoanted oxime ligands are present. These complexes coul...

Synthesis, Characterization and Reactivity of Group 4 Metallocene Bis(diphenylphosphino)acetylene Complexes—A Reactivity and Bonding Study

A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C≡C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'2M(L)(η(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged η(5)-cyclopentadienyl), the expected mononuclear complexes Cp*2Ti(η(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(η(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(η(2)-Me3SiC2SiMe3) with Ph2P-C≡C-PPh2, the dinuclear complex [Cp2Zr(η(2)-Ph2PC2PPh2)]2 (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C≡C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)2Ni(η(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(μ-PPh2)]2 (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C≡C-PR2 ligand. For compound 7b, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.

Cationic, Two‐Coordinate Gold π Complexes

Cationic, two-coordinate gold π complexes that contain a phosphine or N-heterocyclic supporting ligand have attracted considerable attention recently owing to the potential relevance of these species as intermediates in the gold-catalyzed functionalization of C-C multiple bonds. Although neutral two-coordinate gold π complexes have been known for over 40 years, examples of the cationic two-coordinate gold(I) π complexes germane to catalysis remained undocumented prior to 2006. This situation has changed dramatically in recent years and well-defined examples of two-coordinate, cationic gold π complexes containing alkene, alkyne, diene, allene, and enol ether ligands have been documented. This Minireview highlights this recent work with a focus on the structure, bonding, and ligand exchange behavior of these complexes.

Structural Characterization of (C5H5)Co(PPh3)(η2-alkyne) and (C5H5)Co(η2-alkyne) Complexes of Highly Polarized Alkynes

The solid state structures of the cobalt–alkyne complexes (η5-C5H5)(PPh3)Co{η2-(R3Si)C≡C(SO2Ar)} (3-TMS, R = Me, Ar = C6H5; 3-TIPS, R = CH(CH3)2, Ar = p-C6H4CH3) and the noncoordinated alkyne (Me3Si)C≡C(SO2Ph) (6-TMS) have been characterized by X-ray crystallography and, in the case of 3-TMS, 6-TMS, and (η5-C5H5)Co{η2-(Me3Si)C≡C(SO2Ph)} (5-TMS-calc), by B97D/Def2-TZVPP computational analysis. The phosphine-dissociated complex 5-TMS-calc is determined to be a ground state singlet. Analysis of bond angle and distance metrics, calculated NMR chemical shift data, and molecular orbital analysis provide strong evidence for a four-electron-donor alkyne ligand in 5-TMS-calc. The degree of asymmetry in metal–alkyne bonding, as defined by the Gladysz alkyne-slippage parameter, is dramatically reduced in 5-TMS-calc relative to that in the precursor complex 3-TMS-calc.

Trans-Acetyldicarbonyl(η5-cyclopentadienyl)[tris(furan-2-yl)phosphane-κP]molybdenum(II)

The title compound, [Mo(C5H5)(C2H3O)(C12H9O3P)(CO)2], was prepared by reaction of [Mo(C5H5)(CO)3(CH3)] with tris­(furan-2-yl)phosphane. The MoII atom exhibits a four-legged piano-stool coordination geometry with the acetyl and phosphine ligands trans to each other. The O atom of the acetyl ligand points down, away from the Cp ring. In the crystal, mol­ecules form centrosymmetrical dimers via π–π inter­actions between furyl rings [the centroid–centroid distance is 3.396 (4) Å]. The dimers are linked by C—H⋯O hydrogen bonds into layers parallel to (100).