Alkyne Adducts Research Articles

Dioxygen Activation by a Bioinspired Tungsten(IV) Complex.

An increasing number of discovered tungstoenzymes raises interest in the biomimetic chemistry of tungsten complexes in oxidation states +IV, +V, and +VI. Bioinspired (sulfur-rich) tungsten(VI) dioxido complexes are relatively prevalent in literature. Still, their energetically demanding reduction directly correlates with a small number of known tungsten(IV) oxido complexes, whose chemistry is not well explored. In this paper, a reduction of the [WO2(6-MePyS)2] (6-MePyS = 6-methylpyridine-2-thiolate) complex with PMe3 to a phosphine-stabilized tungsten(IV) oxido complex [WO(6-MePyS)2(PMe3)2] is described. This tungsten(IV) complex partially releases one PMe3 ligand in solution, creating a vacant coordination site capable of activating dioxygen to form [WO2(6-MePyS)2] and OPMe3. Therefore, [WO2(6-MePyS)2] can be used as a catalyst for the aerobic oxidation of PMe3, rendering this complex a rare example of a tungsten system utilizing dioxygen in homogeneous catalysis. Additionally, the investigation of the reactivity of the tungsten(IV) oxido complex with acetylene, substrate of a tungstoenzyme acetylene hydratase (AH), revealed the formation of the tungsten(IV) acetylene adduct. Although this adduct was previously reported as an oxidation product of the tungsten(II) acetylene carbonyl complex, here it is obtained via substitution at the sulfur-rich tungsten(IV) center, mimicking the initial step of the first shell mechanism for AH as suggested by computational studies.

Synthesis and Reactivity of Molybdenum and Tungsten Alkyne Complexes Containing 6‐Methylpyridine‐2‐thiolate Ligands

AbstractA series of M(II) and M(IV) (M=Mo, W) alkyne adducts employing two 6‐methylpyridine‐2‐thiolate (6‐MePyS) ligands was synthesized and investigated towards the nucleophilic attack of PMe3 on the coordinated alkynes. For this approach, 2‐butyne (C2Me2), phenylacetylene (HC2Ph), and diphenylacetylene (C2Ph2) were used. For the exploration of an intramolecular attack, but‐3‐yn‐1‐ol (HCCCH2CH2OH) was coordinated to the metal centers. A nucleophilic attack of PMe3 was observed in [W(CO)(HC2Ph)(6‐MePyS)2] yielding an η2‐vinyl compound. Reaction of [W(CO)(C2Ph2)(6‐MePyS)2] with excess PMe3 resulted in the selective coordination of one molecule of PMe3 concomitant with decoordination of the nitrogen atom of one 6‐MePyS ligand. In contrast, the W(IV) complexes did not react with PMe3. While no selectivity was observed in the reaction of the Mo(II) compounds with PMe3, alkynes in the Mo(IV) compounds were replaced by PMe3. Addition of Et3N to the but‐3‐yn‐1‐ol complexes did not lead to the anticipated formation of 2,3‐dihydrofuran.

Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)

The Co(I) complex, [Co(N2)(CyPNP)] (CyPNP = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of internal alkynes under 2 bar of H2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E- and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, [Co(PMe3)(CyPNP)], results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, [CoH(CyPNP)], can also be generated by treatment of degassed solutions of [Co(N2)(CyPNP)] with H2. The CoII-hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.

Additive-Free Conversion of Internal Alkynes by Phosphanylalumanes: Production of Phosphorus/Aluminum Frustrated Lewis Pairs.

Internal and terminal alkynes react with phosphanylalumanes, i. e., P-Al single-bond species, through heating but without any additional additives. The reactions with internal alkynes afforded the corresponding adducts with cis-1,2-form in moderate yields (54-80 %). In addition, alkyne adducts thus obtained function as P/Al-based C2 -vicinal FLPs, and the FLP addition reactions with benzaldehyde and CO2 were demonstrated. Furthermore, in the reaction of 2,4,6-trimethylphenyl-substituted alkyne adducts with dimethyl acetylenedicarboxylate, an unexpected CAr -CMe bond cleavage characteristic of this system was demonstrated.

Mononuclear Fe(I) and Fe(II) Acetylene Adducts and Their Reductive Protonation to Terminal Fe(IV) and Fe(V) Carbynes.

The activity of nitrogenase enzymes, which catalyze the conversion of atmospheric dinitrogen to bioavailable ammonia, is most commonly assayed by the reduction of acetylene gas to ethylene. Despite the practical importance of acetylene as a substrate, little is known concerning its binding or activation in the iron-rich active site. "Fischer-Tropsch" type coupling of non-native C1 substrates to higher-order C≥2 products is also known for nitrogenase, though potential metal-carbon multiply bonded intermediates remain underexplored. Here we report the activation of acetylene gas at a mononuclear tris(phosphino)silyl-iron center, (SiP3)Fe, to give Fe(I) and Fe(II) side-on adducts, including S = 1/2 FeI(η2-HCCH); the latter is characterized by pulse EPR spectroscopy and DFT calculations. Reductive protonation reactions with these compounds converge at stable examples of unusual, formally iron(IV) and iron(V) carbyne complexes, as in diamagnetic (SiP3)Fe≡CCH3 and the paramagnetic cation S = 1/2 [(SiP3)Fe≡CCH3]+. Both alkylcarbyne compounds possess short Fe-C triple bonds (approximately 1.7 Å) trans to the anchoring silane. Pulse EPR experiments, X-band ENDOR and HYSCORE, reveal delocalization of the iron-based spin onto the α-carbyne nucleus in carbon p-orbitals. Furthermore, isotropic coupling of the distal β-CH3 protons with iron indicates hyperconjugation with the spin/hole character on the Fe≡CCH3 unit. The electronic structures of (SiP3)Fe≡CCH3 and [(SiP3)Fe≡CCH3]+ are discussed in comparison to previously characterized, but heterosubstituted, iron carbynes, as well as a hypothetical nitride species, (SiP3)Fe≡N. Such comparisons are germane to the consideration of formally high-valent, multiply bonded Fe≡C and/or Fe≡N intermediates in synthetic or biological catalysis by iron.

Synthesis, Photophysical Properties, and Computational Analysis of Di- and Tetranuclear Alkyne Complexes of Copper(I) Supported by a Highly Fluorinated Pyrazolate

This work describes the reaction of a cyclic trinuclear complex, {[3,5-(CF3)2Pz]Cu}3, with internal alkynes to construct di- and tetranuclear copper(I) complexes with short cuprophilic contacts and the study of their intriguing bonding and photophysical properties, both experimentally and theoretically. For comparison, we have also investigated the related copper(I) trifluoroacetate 3-hexyne complexes so as to deduce and isolate the role played by the supporting pyrazolate ligand on the luminescence of these and related complexes. Some adducts reported herein feature bridging (i.e., μ2–η2,η2-) alkyne coordination modes, which is rare for copper(I)–alkyne complexes documented in the literature. Raman data show red shifts in the average υC≡C stretching frequency from 2260 cm–1 in free 3-hexyne to 2050 cm–1 in the terminal η2-/2e-donor alkyne adduct Cu2(μ-[3,5-(CF3)2Pz])2(EtC≡CEt)2 (1) and, more drastically, to 1874 cm–1 in the bridged μ2–η2,η2-/4e-donor adduct Cu4(μ-[3,5-(CF3)2Pz])4(μ-EtC≡CEt)2 (2). The te...

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

AbstractThe synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S‐Phoz (2‐(4′,4′‐dimethyloxazolin‐2′‐yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W–acetylene adducts. The featured complexes [W(C2H2)(CO)(S‐Phoz)2] (2) and [WO(C2H2)(S‐Phoz)2] (3) are extremely rare from a synthetic and structural point of view as very little is known about W–C2H2 adducts. Upon exposure to visible light, 3 can release C2H2 from its coordination sphere to yield the 14‐electron species [WO(S‐Phoz)2] (4). Under light‐exclusion 4 re‐activates C2H2 making this the first fully characterized system for the reversible activation of acetylene.

The reactivities of iminoboranes with carbenes: BN isosteres of carbene-alkyne adducts.

The first examples of adducts of cyclic alkyl(amino) carbenes (CAAC) and N-heterocyclic carbenes (NHCs) with iminoboranes have been synthesized and isolated at low temperature (-45 °C). The adducts show short BN bonds and planarity at boron, mimicking the structures of the isoelectronic imine functionality. When di-tert-butyliminoborane was reacted with 1,3-bis(isopropyl)imidazol-2-ylidene (IPr), the initially formed Lewis acid-base adduct quickly rearranged to form a new carbene substituted with an aminoborane at the 4-position. Warming the iminoborane-CAAC adduct to room temperature resulted in an intramolecular cyclization to give a bicyclic 1,2-azaborilidine compound.

Nitrogen atom transfer from a dinitrogen-derived vanadium nitride complex to carbon monoxide and isocyanide.

Reduction of [(ONO)V(THF)] with KH under an N2 atmosphere cleaves the N≡N bond to afford a bis(μ-nitride) V(IV) dimer. This complex is oxidized to generate a V(V) nitride. The reactions of the V(V) nitride with carbon monoxide and isocyanide led to formation of cyanate and carbodiimide complexes. Following treatment of the cyanate complex with alkyne produces an alkyne adduct along with the release of potassium cyanate. Dissolution of the alkyne adduct in THF regenerates the starting complex [(ONO)V(THF)], thereby closing a synthetic cycle for conversion of N2 and CO into [NCO](-).

Al/P-Based Frustrated Lewis Pairs: Limitations of Their Synthesis by Hydroalumination and Formation of Dialkylaluminum Hydride Adducts

Aluminum–phosphorus-based frustrated Lewis pairs (Al/P FLPs) are valuable reagents for the dipolar activation or coordination of small molecules or ionic compounds. They are accessible by hydroalumination of alkynylphosphines. However, as reported in this article, the application of this simple method for the synthesis of a broad variety of different compounds is limited to sterically shielded systems. Hydroalumination of Mes2PC≡CPh with small dialkyl- or diarylaluminum hydrides HAlR2 (R = Me, iBu, Ph) afforded unique adducts in which an HAlR2 molecule was coordinated by the Al/P FLP Mes2PC(═CHPh)AlR2 via an Al–P and an Al–H–Al 3c bond. A new Al/P FLP was obtained with equimolar quantities of dineopentylaluminum hydride. The less shielded alkynylphosphine Ph2PC≡CPh yielded a hydride adduct with HAlNp2 and an alkyne adduct with HAltBu2. The latter compound resulted from triple-bond activation and had a five-membered AlPC3 heterocycle in which a C═C bond was bonded to the P and Al atoms of an Al/P FLP. Both...

Hydrotris(3-mesitylpyrazolyl)borato-copper(i) alkyne complexes: synthesis, structural characterization and rationalization of their activities as alkyne cyclopropenation catalysts

The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of stable Tp(Ms)Cu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3). The spectroscopic and structural features of these compounds and their relative reactivity have been examined, indicating the existence of a low π back-bonding from the copper(I) centre to the alkyne. Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction catalysed by the Tp(x)Cu complexes can be rationalized and correlated with their relative stability.

Carbon−Hydrogen Bond Oxidative Addition of Partially Fluorinated Aromatics to a Ni(PiPr3)2Synthon: The Influence of Steric Bulk on the Thermodynamics and Kinetics of C−H Bond Activation

The reaction of (PiPr3)2NiCl2 with the anthracene adduct (THF)3Mg(η2-C14H10) in THF provides the anthracene adduct (PiPr3)2Ni(η2-C14H10). In aromatic solvents (benzene, toluene, mesitylene) a thermal equilibrium exists between the bis(phosphine)nickel(0) anthracene adduct, (PiPr3)2Ni(η2-C14H10), and the monophosphine solvent adduct, (PiPr3)Ni(η6-solvent). The reaction of (PiPr3)2Ni(η2-C14H10) with 1,2,4,5-C6F4H2 affords the C−H activation product trans-(PiPr3)2NiH(2,3,5,6-C6F4H). The thermodynamic C−F activation product is not obtained even after hours of heating at 100 °C. Similar reactions with 1,2,3,5-C6F4H2 and pentafluorobenzene produce the desired C−H activation products, trans-(PiPr3)2NiH(2,3,4,6-C6F4H) and trans-(PiPr3)2NiH(C6F5), respectively, in >95% yield. The reaction with 1,2,3,4-tetrafluorobenzene did not produce an observable C−H activation product. Unlike previously reported analogous C−H activation products with Ni(PEt3)2 synthons, the bulkier Ni(PiPr3)2 moiety did not provide observable mononuclear or dinuclear η2-fluoroarene adducts. Solutions of Ni(COD)2 with 2 equiv of triisopropylphosphine and 1,2,4,5-C6F4H2 reacted to give the 1,5-cyclooctadiene insertion and rearrangement product, (η3-C8H13)Ni(PiPr3)(2,3,5,6-C6F4H). The same reaction with 1,2,3,5- and 1,2,3,4-C6F4H2 afforded analogous compounds, which demonstrates that C−H bond activation is kinetically accessible at room temperature with 1,2,3,4-tetrafluorobenzene despite the presence of a single ortho-fluorine substituent adjacent to the site of activation. The room-temperature reactions of the C−H activation products (PiPr3)2NiH(ArF) (ArF = 2,3,5,6-C6F4H; C6F5) with 3-hexyne provided a mixture of the alkyne adduct (PiPr3)2Ni(η2-EtC≡CEt), with the liberation of ArFH, and the insertion product (PiPr3)2Ni(CEt═CHEt)(ArF), even in the presence of excess fluorinated aromatic ArFH. The reaction of (PiPr3)2Ni(η2-EtC≡CEt) with 1,2,4,5-C6F4H2 resulted in no reaction at room temperature, but heating at 50 °C provided the insertion product (PiPr3)2Ni(CEt═CHEt)(ArF) as the initial product, followed by the product of reductive elimination, 1,2,4,5-C6F4H-CEt═CHEt. In contrast, the reaction of (PEt3)2Ni(η2-EtC≡CEt) with 1,2,4,5-C6F4H2 at 80 °C slowly produced (PEt3)2Ni(CEt═CHEt)(2,3,5,6-C6F4H), but very little 1,2,4,5-C6F4H-CEt═CHEt.

Halogenated catechols from cycloaddition reactions of η 4-(2-ethoxyvinylketene)iron(0) complexes with 1-haloalkynes

1-Chloroalkynes and 1-bromohexyne undergo cycloaddition reactions with ethoxyvinylketeneiron(0) complexes to form chloro and bromocatechols. With most substituents, the halogen is incorporated ortho to the phenolic hydroxyl group regioselectively. With chloroethyne, chlorohexyne, and methyl chloropropiolate, the reverse regioselection is observed. Ab initio calculations reveal that the products are, in most cases, nearly isoenergetic, which indicates that the intermediate ketene–alkyne adduct geometry must be important in determining the product distribution.

Theoretical Studies of Models of the Active Site of the Tungstoenzyme Acetylene Hydratase

Models of the tungstoenzyme acetylene hydratase (AH), which catalyzes the addition of water to acetylene through a nonredox process, are examined using density-functional theory (DFT). The relative energy of acetylene adduct formation was calculated for several tungsten- and molydbenum-oxo dithiocarbamates (dtc) and dithiolates (dtl). Stronger coordination of acetylene to tungsten and dtc complexes is consistent with experimental Keq values and attributed to the larger W 5d orbitals and the overall negative charge of the dithiolate complexes. The recently solved AH X-ray crystal structure suggests the presence of a water molecule bonded to the metal and the possibility that catalysis occurs via a non-organometallic intermediate. Models of the truncated active site are used to analyze this claim by determining the relative energies of acetylene versus water coordination. Complexation of acetylene is favored over water by 12 kcal/mol with the aquo complex formation endergonic by 7 kcal/mol (ΔG). These resul...

Alkyne adducts of paramagnetic and diamagnetic tripalladium clusters supported by dppm ligands

The unsaturated redox-active cluster [Pd3(dppm)3(CO)]n+ (n = 0,1, or 2) reacts with ethylene dicarboxylic esters and a variety of terminal acetylenes (but not PhC≡CPh) in all three charge states. In particular, the radical cations [Pd3(dppm)3(CO)(RC≡CR′)].+ can be produced by several routes: one-electron electrochemical reduction of the dication adducts, comproportionation of the neutral and dicationic adducts, as well as the direct complexation of alkyne to the known radical cation [Pd3(dppm)3(CO)].+. Compared with the latter, each of the adducts have significantly extended lifetimes and classify as persistent radicals in solution. The alkyne adducts have been characterized by voltammetry (cyclic and rotating disk electrode), by UV – vis titrations and by MALDI-TOF mass spectra from dithranol matrices. Isotropic solution EPR spectra of the adducts with R = R′ = MeOC(O) and EtOC(O), as well as those with R′ = H and R = C6H5, FC6H4, HC≡CC6H4, and EtO have been obtained. Full line shape fitting simulations demonstrate that all display coupling to six different 31P (I = 1/2) and to one to three 106Pd (I = 5/2) nuclei. The A(31P) values range from a low of 3.0 × 104 to a high of 180.5 × 104 cm–1; this variation is caused by changes in the contribution of P s orbitals to the SOMO resulting from structural distortions of the Pd3P6 core upon alkyne coordination.Key words: electrochemistry, redox state, electron paramagnetic resonance, catalytic model, palladium, bridging phosphine.

Vanadium (β-(Dimethylamino)ethyl)cyclopentadienyl Complexes with Diphenylacetylene Ligands

Reduction of the V(III) (β-(dimethylamino)ethyl)cyclopentadienyl dichloride complex [η5:η1-C5H4(CH2)2NMe2]VCl2(PMe3) (1) with 1 equiv of Na/Hg yielded the V(II) dimer {[η5:η1-C5H4(CH2)2NMe2]V(μ-Cl)}2 (2). This compound reacted with diphenylacetylene in THF to give the V(II) alkyne adduct [η5:η1-C5H4(CH2)2NMe2]VCl(η2-PhC≡CPh) (3). Further reduction of 2 with Mg in the presence of diphenylacetylene resulted in oxidative coupling of two diphenylacetylene groups to yield the diamagnetic, formally V(V), bent metallacyclopentatriene complex [η5:η1-C5H4(CH2)2NMe2]V(C4Ph4) (4).

FLUORINATED TRIS(PYRAZOLYL)BORATES AND SILVER(I) COMPLEXES OF GROUP 14 LIGANDS

This review presents an overview of fluorinated tris(pyrazolyl)borate ligands and their role in the development of silver adducts containing group 14 ligands. Tris(pyrazolyl)borates bearing fluorocarbon substituents are sterically somewhat similar but electronically very different from their hydrocarbon counterparts. They have weakly donating nitrogen sites. Fluorinated hydridotris(pyrazolyl)borates also have less reducing B-H groups. These mono-anionic, nitrogen-based donors are ideal supporting ligands to stabilize silver complexes bearing labile donors. For example, fluorinated tris(pyrazolyl)borates have enabled the isolation of thermally stable Ag(I)-CO, Ag(I)-ethylene, and Ag(I)-acetylene adducts. Compounds with unsupported Ag(I)-Ge(II) and Ag(I)-Sn(II) bonds have also been synthesized. Most of these contain easily removable halide groups and silver atoms in the same molecule, but do not show the silver-halide metathesis. Fluorinated tris(pyrazolyl)borate ligands without the problematic B-H moiety have been reported. They afford silver-tris(pyrazolyl) borates with higher solution stability. The κ3-coordination mode is the most common for tris(pyrazolyl)borates but κ2-bonded tris(pyrazolyl)borate silver adducts are also known. Some silver adducts of fluorinated tris(pyrazolyl)borates are excellent tris(pyrazolyl)borato ligand transfer agents, promising homogeneous catalysts and effective antimicrobial agents.

Nonchelated Alkene and Alkyne Complexes of d0 Zirconocene Pentafluorophenyl Cations

This paper describes the generation and properties of nonchelated d(0) zirconocene-aryl-alkene and alkyne adducts that are stabilized by the presence of beta-SiMe(3) substituents on the substrates and the weak nucleophilicity of the -C(6)F(5) ligand. The cationic complexes [(C(5)H(4)R)(2)Zr(C(6)F(5))][B(C(6)F(5))(4)] (4a: R = H, 4b: R = Me) were generated by methide abstraction from (C(5)H(4)R)(2)Zr(C(6)F(5))Me by Ph(3)C(+). NMR studies show that 4a,b contain an o-CF...Zr dative interaction and probably coordinate a PhCl molecule in PhCl solution. Addition of allyltrimethylsilane (ATMS) to 4a,b in C(6)D(5)Cl solution at low temperature produces an equilibrium mixture of (C(5)H(4)R)(2)Zr(C(6)F(5))(H(2)C=CHCH(2)SiMe(3))(+) (7a,b), 4a,b, and free ATMS. Similarly, addition of propargyltrimethylsilane (PTMS) to 4a produces an equilibrium mixture of Cp(2)Zr(C(6)F(5))(HCCCH(2)SiMe(3))(+) (8a), 4a, and free PTMS. The NMR data for 7a,b,and 8a are consistent with highly unsymmetrical substrate coordination and substantial polarization of the substrate multiple bond with significant positive charge buildup at C(int) and negative charge buildup at C(term). PTMS binds to 4a more strongly than ATMS does. The ATMS adducts undergo nondissociative alkene face exchange ("alkene flipping"), i.e., exchange of the (C(5)H(4)R)(2)Zr(C(6)F(5))(+) unit between the two alkene enantiofaces without decomplexation of the alkene, on the NMR time scale.

Low-Valent α-Diimine Iron Complexes for Catalytic Olefin Hydrogenation

A family of low-valent α-diimine iron complexes has been synthesized and their utility in catalytic olefin hydrogenation reactions evaluated. Reduction of the ferrous dichloride complex [ArNC(Me)C(Me)NAr]FeCl2 (Ar = 2,6-(CHMe2)2-C6H3) with sodium amalgam in benzene or toluene furnished the iron arene complexes, [ArNC(Me)C(Me)NAr]Fe(η6-C6H5R) (R = H, Me). The solid-state structure of the toluene adduct revealed a contracted carbon−carbon backbone, short iron−imine bonds, and elongated imine nitrogen−carbon distances, suggesting significant reduction of the α-diimine ligand. The analogous reduction in alkane solvents afforded the bis(α-diimine) complex [ArNC(Me)C(Me)NAr]2Fe, which has also been crystallographically characterized. The arene complexes and the bis(α-diimine) complexes are inactive for catalytic olefin hydrogenation. Performing the reduction in the presence of internal alkynes such as diphenylacetylene and bis(trimethylsilyl)acetylene furnished the alkyne adducts [ArNC(Me)C(Me)NAr]Fe(η2-RC⋮CR) ...

Reactions of Sulfido-Bridged Molybdenum Dimers with Diynes as a Route to Multinuclear Dithiolene Complexes

The bridging sulfido ligands in dunuclear molybdenum complexes of the formula (Me n CpMoμ-S) 2 S 2 CH 2 , where n = 0 or 1, react with alkynes to form alkenedithiolate complexes. These reactions have been extended to a seriesof diynes, including 2,4-hexadiyne, 1,4-diphenyl-1,3-butadiyne, 1,3-diethynylbenzene, and 1,4-bis(trimethylsilylethynyl)benzene, to form bis(alkenedithiolate) complexes. The corresponding mono-adducts have also been synthesized by the reaction of the molybdenum dimer with the diyne in a 1:1 molar ratio. The new alkyne adducts have been characterized by spectroscopic techniques and cyclic voltammetry, and both the 1:1 and 2:1 adducts of 1,4-diphenyl-1,3-butadiyne have been identified by X-ray structural determinations. Synthetic routes to a hexanuclear complex and higher molecular weight oligomers linked by alkenedithiolate ligands are also described. Tetranuclear complexes linked by the 1,3-dialkynes show two closely spaced oxidation waves in the cyclic voltammogram, suggesting a small degree of electronic communication between the dimers.