Mo 2Cp Research Articles

C-C and C-N Couplings Following Hydride Addition on Isocyanide Cyclopolyenyl Dimolybdenum Complexes to Give Tethered Aldimine and Aminocarbene Derivatives.

Reaction of [Mo2 Cp2 (μ-κ1 :κ1 ,η6 -PMes*)(CO)2 ] with S or Se followed by protonation with [H(OEt2 )2 ](BAr'4 ) gave the cationic derivatives [Mo2 Cp2 {μ-κ2P,E :κ1P ,η5 -EP(C6 H3 tBu3 )}(CNR)(CO)2 ](BAr'4 ) (E=S; R=tBu, iPr, Ph, 4-C6 H4 OMe, Xyl; or E=Se; R=tBu; Ar'=3,5-C6 H3 (CF3 )2 ). Reaction of the latter with K[BHsBu3 ] yielded the aldimine complexes [Mo2 Cp2 {μ-κ2P,E :κ2P,N ,η4 -SP(C6 H3 tBu3 (CHNR))}(CO)2 ] and their aminocarbene isomers [Mo2 Cp2 {μ-κ2P,E :κ2P,C ,η4 -SP(C6 H3 tBu3 (NRCH))}(CO)2 ] (R ≠ Xyl), following C-C and C-N couplings, respectively. Monitoring of these reactions revealed that the initial H- attack takes place at a Cp ligand to give cyclopentadiene intermediates [Mo2 Cp{μ-κ2P,S :κ1P ,η5 -SP(C6 H3 tBu3 )}(η4 -C5 H6 )(CNR)(CO)2 ], which then undergo C-H oxidative addition to give the hydride isomers [Mo2 Cp2 {μ-κ2P,S :κ1P ,η3 -SP(C6 H3 tBu3 )}(H)(CNR)(CO)2 ]. In turn, the latter rearrange to give the aldimine and aminocarbene complexes. DFT calculations revealed that the hydride intermediates first undergo migratory insertion of the isocyanide ligand into the Mo-H bond to give unobservable formimidoyl intermediates, which then evolve either by nucleophilic attack of the N atom on the C6 ring (C-N coupling) or by migratory insertion of the formimidoyl ligand into the C6 ring (C-C coupling). Our data suggest that increasing the size of the substituent R at the isocyanide ligand destabilizes the aldimine isomer to a greater extent, thus favoring formation of the aminocarbene complex.

Alkyne to carbyne coupling reactions of the unsaturated methoxycarbyne-bridged complex [Mo 2(η 5-C 5H 5) 2(μ-COMe)(μ-PCy 2)(CO) 2

The 32-electron complex [Mo 2Cp 2(μ-COMe)(μ-PCy 2)(CO) 2] (Cp = η 5-C 5H 5) reacts at 333 K with terminal alkynes HC CR to give the corresponding derivatives [Mo 2Cp 2{μ-κ 2:η 3-CRCHC(OMe)}(μ-PCy 2)(CO) 2], (R = p-tol, CO 2Me), with good yields. These compounds are both obtained selectively as trans-dicarbonyl isomers and display a propenyl-ylidene type ligand bridging the dimetal centre, derived from the specific coupling of the alkyne to the carbyne ligand through the terminal carbon atom of the alkyne. The reaction with the internal alkyne (MeO 2C)C C(CO 2Me) gives the related derivative [Mo 2Cp 2{μ-κ 2:η 3-C(CO 2Me)C(CO 2Me)C(OMe)}(μ-PCy 2)(CO) 2], but now this product is obtained as an equimolar mixture of the corresponding trans- and cis-dicarbonyl isomers. The structures of the new compounds are discussed on the basis of the available spectroscopic data in solution and an X-ray diffraction analysis of the product derived from p-tolylacetylene (Mo−Mo = 2.8646(8) Å).

Reactivity of the unsaturated dimolybdenum anion [Mo 2(η 5-C 5H 5) 2(μ-PCy 2)(μ-CO) 2] − towards electrophiles based on p- and d-block elements

The 30-electron binuclear anion [Mo 2Cp 2(μ-PCy 2)(μ-CO) 2] − reacts with the chlorophosphite ClP(OEt) 2 or the organotin chlorides Cl 2SnPh 2 or ClSnPh 3 to give compounds of the formula trans-[Mo 2Cp 2(μ-E)(μ-PCy 2)(CO) 2], (E = P(OEt) 2, SnPh 3, SnPh 2Cl). In contrast, this anion reacts with the organosilicon chlorides ClSiR 3 (R = Ph, Me) to give unstable silyloxycarbyne-bridged complexes [Mo 2Cp 2(μ-PCy 2)(μ-COSiR 3)(μ-CO)], which rapidly hydrolyze to give the known hydride [Mo 2Cp 2(μ-H)(μ-PCy 2)(CO) 2]. Two main types of products were also observed in the reactions of the title anion with different chlorocomplexes of the transition and post-transition metals. Thus, the reactions with [MCl 2Cp 2] (M = Ti, Zr) give moisture-sensitive isocarbonyl-bridged complexes of the type [Mo 2Cp 2(μ-COMClCp 2)(μ-PCy 2)(μ-CO)]. In contrast, softer metallic electrophiles such as [AuCl(PR 3)] (R = i Pr, ptol) react with the anion at the dimolybdenum site to form new trimetallic clusters of the formula [AuMo 2Cp 2(μ-PCy 2)(CO) 2(PR 3)], also retaining a Mo−Mo triple bond. Subsequent reactions of the latter products with the solvate complexes [Au(PR 3)(THF)][PF 6] give the tetranuclear clusters [Au 2Mo 2Cp 2(μ-PCy 2)(CO) 2(PR 3) 2][PF 6] (Mo−Mo = 2.5674(3) Å and Au−Au = 2.7832(2) Å when R = i Pr). Finally, the reaction of the title anion with HgI 2 gives the pentanuclear cluster [Hg{Mo 2Cp 2(μ-PCy 2)(CO) 2} 2] or the trinuclear cluster [Mo 2Cp 2(μ-HgI)(μ-PCy 2)(CO) 2] depending on the stoichiometry being actually used for the reaction. The trinuclear species is only stable in tetrahydrofuran (THF), and decomposes to give a mixture of the dimeric species [Mo 2Cp 2(μ-HgI)(μ-PCy 2)(CO) 2] 2 along with variable amounts of the known iodide-bridged complex [Mo 2Cp 2(μ-I)(μ-PCy 2)(CO) 2].

Reactivity of the 30-electron dimolybdenum anion [Mo 2(η 5-C 5H 5) 2(μ-PCy 2)(μ-CO) 2] − towards β,γ-unsaturated organic halides: Alkenyl, allenyl and alkoxycarbyne derivatives

The 30-electron dimolybdenum anion [Mo 2Cp 2(μ-PCy 2)(μ-CO) 2] − reacts at room temperature with allyl chloride to give the unsaturated σ:π-bonded alkenyl derivative trans-[Mo 2Cp 2(μ-η 1:η 2-CMeCH 2)(μ-PCy 2)(CO) 2], this requiring a 2,1-hydrogen shift in the allyl moiety probably induced by the unsaturated nature of the dimetal center. In a similar way, the dimolybdenum anion reacts with trans-1-chloro-2-butene (crotyl chloride) to give a mixture of the alkenyl complexes trans-[Mo 2Cp 2(μ-η 1:η 2-CEtCH 2)(μ-PCy 2)(CO) 2] and trans-[Mo 2Cp 2(μ-η 1:η 2-CMeCHMe)(μ-PCy 2)(CO) 2] in a 3:2 ratio, which could not be separated by column chromatography. All these alkenyl species exhibit a dynamic behavior in solution (fast on the NMR timescale even at low temperatures) involving alternative π-bonding of the alkenyl ligand to each metal center. In contrast, the title anion reacts with propargyl chloride (ClCH 2–C CH) without further rearrangement of the propargyl moiety, to afford the allenyl derivative trans-[Mo 2Cp 2{μ-η 2:η 3-CH 2CCH)}(μ-PCy 2)(CO) 2] as the major species. Acryloyl chloride (ClC(O)–CH CH 2) also reacts with the title anion to give a mixture of two products, the carbyne complex [Mo 2Cp 2{μ-COC(O)CHCH 2}(μ-PCy 2)(μ-CO)] and the vinyl trans-[Mo 2Cp 2(μ-η 1:η 2-CHCH 2)(μ-PCy 2)(CO) 2], in a 1:1 ratio. This reaction is a unique case in which a single electrophile can attack both nucleophilic positions in the dimolybdenum anion, these being located at the O(carbonyl) and metal sites, respectively. The formation of the vinyl derivative requires the decarbonylation of a metal-bound acryloyl group, which proved to be an irreversible reaction, since the addition of CO to the above alkenyl complex gave instead the tricarbonyl vinyl derivative cis-[Mo 2Cp 2(μ-η 1:η 2-CHCH 2)(μ-PCy 2)(CO) 3]. The structure of this electron-precise complex was confirmed through a single-crystal X-ray diffraction analysis (Mo−Mo = 3.0858(7) Å).

Activation of propargylic alcohols by dimolybdenum tris(μ-thiolate) complexes: Influence of the substituents R in HC [tbnd]CCR 2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes

Reaction of the bis(nitrile) complex [Mo 2Cp 2(μ-SMe) 3(NCMe) 2](BF 4) ( 1) with dimethylpropargylic alcohol, HC CCMe 2(OH), at room temperature in dichloromethane produced good yields of the μ-alkynol species [Mo 2Cp 2(μ-SMe) 3{μ-CHCCMe 2(OH)}](BF 4) ( 2a) through replacement of the two acetonitrile ligands in 1 by the alkynol. The NMR spectra of 2a indicate a μ-η 1:η 1 coordination mode for the alkyne which is thereby incorporated into a dimetallacyclobutene ring like that found here by X-ray diffraction (XRD) analysis of the related complex [Mo 2Cp 2(μ-SMe) 3(μ-η 1:η 1-CHCCO 2Me)](BPh 4) ( 2b). When 2a was stirred with Et 3N at room temperature in dichloromethane, deprotonation gave high yields of the μ-3-hydroxyalkynyl derivative [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCCMe 2(OH)}] ( 3), together with small amounts of the already-known vinylacetylide [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCC(Me)CH 2}] ( 4) resulting from dehydration of 3. Treatment of 3 with 1 equiv. of HBF 4 · OEt 2 in diethyl ether at room temperature gave the 3-hydroxyvinylidene derivative [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCHCMe 2(OH)}](BF 4) ( 5) as the major product, together with other minor products [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCHC(Me)CH 2}](BF 4) ( 6), [Mo 2Cp 2(μ-SMe) 3(μ-η 1:η 2-CCCMe 2)](BF 4) ( 7), [Mo 2Cp 2(μ-SMe) 3(μ-η 1:η 2-CCH 2)](BF 4) ( 8), [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCH(CHMe 2)}](BF 4) ( 9) and [Mo 2Cp 2(μ-SMe) 3(μ-O)](BF 4) ( 10). The vinylidene ( 6) and allenylidene ( 7) species resulted from dehydration of the 3-hydroxyvinylidene complex 5 whereas the vinylidene derivative 8 was formed by deketonisation of 5. When 3 reacted with a large excess of HBF 4 · OEt 2 in dichloromethane, the 3-isopropylvinylidene complex 9 was obtained nearly quantatively via a H radical process. When left for several days CD 2Cl 2 solutions of 5 afforded mainly the vinylidene species 8 by deketonisation and the side-oxoproduct [Mo 2Cp 2(μ-SMe) 3(μ-O)](BF 4) ( 10) by hydrolysis or reaction with oxygen. Addition of nucleophiles (H −, OMe −, OH −, SMe −) to the allenylidene complex [Mo 2Cp 2(μ-SMe) 3(μ-η 1:η 2-CCCPh 2)](BF 4) ( 11) resulted in the formation of the corresponding μ-acetylide derivatives [Mo 2Cp 2(μ-SMe) 3(μ-η 1:η 2-CCCRPh 2)] [R = H ( 12), OMe ( 16a), OH ( 17), SMe ( 16b)], which by further reaction with tetrafluoroboric acid afforded either the vinylidene species [Mo 2Cp 2(μ-SMe) 3{μ-η 1:η 2-CCH(CRPh 2)}](BF 4) when R = H ( 13), or the starting complex 11 when R is a leaving group (OMe). Reaction of 13 with Na(BH 4) gave the μ-alkylidyne complex [Mo 2Cp 2(μ-SMe) 3(μ-η 1-CCH 2CPh 2H)] ( 14) by nucleophilic attack of H − at the C β carbon atom of the vinylidene chain. Proton addition at C α in 14 led to the formation of a μ-vinylidene compound 15 containing an agostic C–H bond. New complexes have been characterised by elemental analyses and spectroscopic methods, supplemented for 2b and 3 by X-ray diffraction studies.

Chemistry of highly electrophilic binuclear cations. 6. Synthesis of the alkyne-bridged complexes [Mo 2(η 5-C 5H 5) 2{μ-η 2:η 2-HC 2(p-tol)}(CO) 2(μ-L 2)][B{3,5-C 6H 3(CF 3) 2} 4] 2 and their isocyanide derivatives (L 2 = Ph 2PCH 2PPh 2, Me 2PCH 2PMe 2)

One-electron oxidation of the alkyne-bridged radicals [Mo 2Cp 2{μ-η 2:η 2-HC 2(p-tol)}(CO) 2(μ-L 2)] ( BAr 4 ′ ) [Cp = η 5 − C 5H 5; L 2=Ph 2PCH 2PPh 2 (dppm), Me 2PCH 2PMe 2 (dmpm); Ar′ = 3,5-C 6H 3(CF 3) 2] with the ferricenium salts [FeCp 2]X ( X = BAr 4 ′ - , BF 4 - ) gives the dipositive cationic complexes [Mo 2Cp 2{μ-η 2:η 2-HC 2(p-tol)}(CO) 2(μ-L 2)] ( BAr 4 ′ ) (X) which display two isomeric geometries differing in the position ( cis or trans) of the alkyne ligand relative to the diphosphine bridge, with the cis isomer being dominant for the dmpm complex and the reverse for the dppm derivative. These 32-electron complexes turned out to be quite stable and do not experience deprotonation, dehydrogenation or any rearrangement in the bonded alkyne even under heating. However, they react rapidly with CN t Bu at room temperature to give new isocyanide derivatives stepwise. Addition of one equivalent of CN t Bu leads to the monocarbonyl complexes [Mo 2Cp 2{μ-η 2:η 2-HC 2(p-tol)}(CO)(CN t Bu)(μ-L 2)] ( BAr 4 ′ ) 2 (L 2 = dppm, dmpm) resulting from substitution of one carbonyl ligand. Addition of a second equivalent of isocyanide on the dmpm cation replaces the remaining carbonyl to give the diisocyanide complex [Mo 2Cp 2{μ-η 2:η 2-HC 2(p-tol)}(CN t Bu) 2(μ-dmpm)] ( BAr 4 ′ ) 2 , while a large excess of ligand forces the incorporation of a third isocyanide molecule to the unsaturated metal centre, to give the electron-precise triisocyanide derivative [Mo 2Cp 2{μ-η 2:η 2-HC 2(p-tol)}(CN t Bu) 3(μ-dmpm)] ( BAr 4 ′ ) 2 . The latter is a labile cation which dissociates isocyanide in solution at room temperature. All new compounds were characterized on the basis of their spectroscopic IR and NMR ( 1H, 31P, 13C) data.

Mixed μ-phosphido or μ-thiolato μ-halo-dimolybdenum(III) compounds [Mo 2Cp 2(μ-SMe) 2(μ-X)(μ-Y)] (X = PPh 2, Y = Cl; X = SCH 3, Y = Br, I): Electrochemical and structural comparisons – The X-ray structure of [{Mo 2Cp 2Br(μ-O)(μ-SMe) 2} 2(μ-MoO 4)

Mixed μ-phosphido or μ-thiolato μ-halo-dimolybdenum(III) compounds [Mo 2Cp 2(μ-SMe) 2(μ-X)(μ-Y)] (X = PPh 2, Y = Cl ( 1); X = SCH 3, Y = Br ( 3), I( 4)) have been studied. Syntheses and X-ray structures of the new bromo and iodo analogues of [Mo 2Cp 2(μ-SMe) 3(μ-Cl)] ( 2) are reported. While preparing 3 a side-product 5 was obtained and structurally characterised as the Mo 5 system [{Mo 2Cp 2Br(μ-O)(μ-SMe) 2} 2(μ-MoO 4)], containing a {Mo IV–Mo IV–O–(Mo VIO 2)–O–Mo IV–Mo IV} unit. The influence of the bridging groups on the structures and electrochemical behaviour of the complexes [Mo 2Cp 2(μ-SMe) 2(μ-X)(μ-Y)] 1– 4 has been investigated. In MeCN–[NBu 4][PF 6] the first oxidation of [Mo 2Cp 2(μ-SMe) 2(μ-PPh 2)(μ-Cl)] ( 1) is quasi-reversible, contrasting with the essentially irreversible first oxidation of the thiolate analogue [Mo 2Cp 2(μ-SMe) 3(μ-Cl)] ( 2) under similar conditions. The effects of lowering the temperature or increasing the scan rate on the oxidation of 1 were examined: the initial quasi-reversible oxidation at first became irreversible but at still higher scan rates or lower temperatures the oxidation was again quasi-reversible. This suggests that the oxidation of 1 in MeCN is followed by reversible coordination of acetonitrile to afford the species [Mo 2Cp 2(μ-SMe) 2(μ-PPh 2)(Cl)(MeCN)] + ( 7 +). Cyclic voltammetry of [Mo 2Cp 2(μ-SMe) 3(μ-Y)](Y = Br ( 3) or I ( 4)) showed two quasi-reversible diffusion-controlled oxidation steps in CH 2Cl 2–[NBu 4][PF 6] or thf–[NBu 4][PF 6]. In acetonitrile, the fast loss of the halide ligands results in the formation of [Mo 2Cp 2(μ-SMe) 3(MeCN) 2] + species.

Methylation sites in tris(μ-thiolato)dimolybdenum(III) complexes

Attempts at methylating cis-[Mo 2Cp 2(μ-SMe) 3L 2](BF 4) [Cp = η 5-C 5H 5; L = CO ( 1a) CNxyl ( 1b), CNBu t ( 1c), NCMe ( 1d)] with methyl triflate gave the corresponding thioether-bridged cations [Mo 2Cp 2(μ-SMe) 2(μ-SMe 2)L 2] 2+ ( 4 2+), except in the case of 1a which did not react at room temperature. The electronic properties of the ancillary ligands L thus have a crucial influence on the course of this reaction. The dimeric compounds [Mo 2Cp 2(μ-SMe) 3(CNBu t )(CN)] ( 2) and [Mo 2Cp 2(μ-SMe) 3{μ-η 1-N C(CH 3)CH 2CN}] ( 3), which potentially offer the alternatives of S- or N-methylation, reacted with methylating agents to give mainly the S-methylated derivatives 5 and 7. Only in the case of the nucleophilic reactant 2 was N-methylation also observed and isomer 6 was obtained as a minor product together with 5. New complexes have been completely characterised by multinuclear NMR, IR and elemental analysis, supplemented for 5 by X-ray diffraction study at 100 K.

Unexpected formation of the novel mixed μ-oxo, μ-sulfido, bis(μ-thiolato) compound [Mo(IV) 2Cp 2(μ-O)(μ-S)(μ-SMe) 2

A novel example of CS bond cleavage in a dimolybdenum derivative leads to the formation of the quadruply bridged compound [Mo(IV) 2Cp 2(μ-O)(μ-S)(μ-SMe) 2]. This μ-oxo species is formed by reaction of the chloro-bridged complex [Mo(III) 2Cp 2(μ-Cl)(μ-SMe) 3] with PhCCLi and subsequent hydration at the dimolybdenum site. The MoMo bond length of 2.4900(3) Å in [Mo 2Cp 2(μ-O)(μ-S)(μ-SMe) 2] is unusually short.

Reactions of dipropargyl manolate, terephthalate with Co 2(CO) 8, Mo 2Cp 2(CO) 4 and RuCo 2(CO) 11 give the di or tetranuclear clusters. The crystal structure of [CH 2(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 and [ p-(HC 2CH 2OCO)C 6H 4(CO 2CH 2C 2H-μ)][Co 2(CO) 6

The reactions of dipropargyl manolate and terephthalate, respectively, with Co 2(CO) 8 in THF at room temperature gave four new compounds [R(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 (R=CH 2, 1a; R=C 6H 4, 1b) and [(HC 2CH 2OCO)R(CO 2CH 2C 2H-μ)][Co 2(CO) 6] (R=CH 2, 2a; R=C 6H 4-1,4-, 2b), and compounds 2a and b reacted with RuCo 2(CO) 11 to form two new linked clusters [R(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6][RuCo 2(CO) 9] (R=CH 2, 3a; R=C 6H 4-1,4-, 3b). The treatment of two dipropargyl esters, respectively, with RuCo 2(CO) 11 afforded another two new clusters [R(CO 2CH 2C 2H-μ) 2][RuCo 2(CO) 9] 2 (R=CH 2, 4a; R=C 6H 4-1,4-, 4b). The reactions of dipropargyl manolate, terephalate with Mo 2Cp 2(CO) 4 gave rise to the formation of dinuclear complexes [(HC 2CH 2OCO)R(CO 2CH 2C 2H-μ)][Mo 2Cp 2(CO) 4] (R=CH 2, 5a; R=C 6H 4-1,4-, 5b), compound 5a reacted with Co 2(CO) 8 to produce the cluster [CH 2(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6][Mo 2Cp 2(CO) 4] 6a. All the new clusters have been characterized by C/H elemental analysis, IR and 1H NMR spectroscopies. The structure of [CH 2(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 1a and [ p-(HC 2CH 2OCO)C 6H 4(CO 2CH 2C 2H-μ)][Co 2(CO) 6] 2b have been determined by single crystal X-ray diffraction methods.

Reaction of dipropargyl phthalate with Co 2(CO) 8 and Mo 2Cp 2(CO) 4 gives the di or tetranuclear clusters. The crystal structure of [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 and [ o-(HC 2CH 2OCO)C 6H 4(CO 2CH 2C 2H-μ)][Mo 2Cp 2(CO) 4]–CH 2Cl 2

The reaction of dipropargyl phthalate with Co 2(CO) 8 in benzene at room temperature gave a new cluster [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 1, which reacts with the cyclopentadienyl tricarbonyl molybdenum anion [Mo(CO) 3Cp] − to form the tetranuclear clusters [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6][CoMoCp(CO) 5] 2 and [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2] [CoMoCp(CO) 5] 2 3, respectively. The reaction of Mo 2Cp 2(CO) 4 with dipropargyl phthalate gave rise to the formation of the dinuclear cluster [ o-(HC 2CH 2OCO)C 6H 4(CO 2CH 2C 2H-μ)][Mo 2Cp 2(CO) 4] 4 and tetranuclear cluster [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2] [Mo 2Cp 2(CO) 4] 2 5, respectively. The cluster 4 reacted with Co 2(CO) 8 to produce the tetranuclear cluster [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] [Mo 2Cp 2(CO) 4] 6. These clusters were characterized by C/H analyses, IR and 1H NMR. The structure of [C 6H 4-1,2-(CO 2CH 2C 2H-μ) 2][Co 2(CO) 6] 2 1 and [ o-(HC 2CH 2OCO)C 6H 4 (CO 2CH 2C 2H-μ)][Mo 2Cp 2(CO) 4]-CH 2Cl 2 4·CH 2Cl 2 were determined by single crystal X-ray diffraction methods.

The effect of replacing carbonyl with acetonitrile on the reactivity of the bimetallic system [Mo 2Cp 2(μ-SMe) 3(L) 2] + (L=CO, CH 3CN). Crystal structure of [Mo 2Cp 2(μ-SMe) 2(CH 3CN) 4](BF 4) 2

[Mo 2Cp 2(μ-SMe) 3(CH 3CN) 2](BF 4) ( 1) reacts with H[BF 4] in acetonitrile at room temperature to give the tetrakis (acetonitrile) compound [Mo 2Cp 2(μ-SMe) 2(CH 3CN) 4](BF 4) 2 ( 3) through replacement of one SMe bridge by two terminal CH 3CN ligands. In sharp contrast, the carbonyl analogue [Mo 2Cp 2(μ-SMe) 3(CO) 2] + ( 2) fails to undergo a similar reaction. This suggests that the electronic properties of the ancillary ligands L in the [Mo 2Cp 2(μ-SMe) 3L 2] + moiety govern the activation of a sulfur atom in protonation reactions. An X-ray diffraction study shows that 3 contains two CpMo(CH 3CN) 2 units bridged by two SMe groups and linked by a long Mo–Mo bond of 3.000(1) Å.

A dimolybdenum(III) azido compound: its decomposition into amido and nitrido derivatives. Crystal structure of [Mo 3(O)(N)Cp 3(SMe) 4

The thermal reaction of [Mo 2Cp 2( μ-SMe) 3( μ-Cl)] 1 with NaN 3 in THF/EtOH gives a mixture of three compounds: [Mo 2Cp 2( μ-SMe) 3( μ-N 3)] 2, [Mo 2Cp 2( μ-SMe) 3( μ-NH 2)] 3 and [Mo 3(O)(N)Cp 3(SMe) 4] 4. Only the μ-azido derivative 2 is isolated if the time of thermolysis is short. Its formation in the presence of EtOH leads in turn to the products 3 and 4. Production of 3 from 2 requires N 2 loss followed by intermolecular reduction of the bimetallic system. Complete decomposition of the complexes occurs if the time of reaction is prolonged. An X-ray diffraction study shows that 4 contains a [Mo 2Cp 2( μ-SMe) 3( μ-N)] core that is linked through a MoN double bond to a CpMo(O)(SMe) unit. The resulting Mo 3( μ 3-N) fragment, in which the NMo double bond is supported by two MoN single bonds involving the directly bonded metal atoms, is the most striking structural feature of 4. The triply-bridging nitrido nitrogen atom adopts a distorted trigonal planar coordination.

Reactions of di- and poly-nuclear complexes 13. Synthesis, structure and fluxional behaviour of hydrido- and thiolato- or selenato-bridged complexes [Mo 2Cp 2(μ-H)(μ-ER)(CO) 4] (E  S, R  Me, tBu, Bz, or Ph; E  Se, R  Ph)

Oxidative addition of thiols or selenoles across the Mo 2 centre of [Mo 2Cp 2(CO) 4] gives complexes with bridging thiolate or selenate and hydride ligands [Mo 2Cp 2(μ-H)(μ-ER)(CO) 4](E  S, R  Me ( 4), tBu ( 5), Bz ( 6), Ph ( 7); E  Se, R  Ph ( 8)). The complex 4 is also formed on reaction of [Mo 2Cp 2(μ-SMe) 2(CO) 4] with vanadocene [VCp 2] with the possible involvement of a thioaldehyde, hydride derivative of the vanadocene. Crystals of 4 are monoclinic, space group C2/ c, with a = 17.225 (1), b = 8.418 (1) c = 22.960 (2) A ̊ , β = 90.346 (5)°, R = 0.023 for 4213 observed reflections. In the solid state, molecules of 4 contain a planar Mo 2(μ-H)(μ-S) core and the Cp ligands are cis with respect to the MoMo bond, the two CpMo(CO) 2 unites being related by an approximate plane of symmetry which contains the bridging H and S donor atoms and which is normal to the MoMo bond. The fluxional nature of complexes 4–8 in solution is shown from variable-temperature 1H and 13C NMR spectra to arise from cis-trans isomerisation.

Synthesis of [Mo 2{μ-Au(PPh 3)}Cp 2(CO) 4(μ-PPh 2)] and structural comparison with the dimolybdenum complexes [Mo 2Cp 2(CO) 4(μ-H)(μ-PPh 2)] and PPN[Mo 2Cp 2(CO) 4(μ-PPh 2)] (PPN = (PPh 3) 2N +)

[Mo 2{μ-Au(PPh 3)}Cp 2(CO) 4(μ-PPh 2)] ( 4) has been synthesized from K[Mo 2Cp 2(CO) 4(μ-PPh 2)] ( 2) and [AuCl(PPh 3)] and characterized by IR and 31P NMR spectroscopy. X-ray structures of this cluster and of [Mo 2Cp 2(CO) 4(μ-H)(μ-PPh 2)] ( 1) and PPN[Mo 2Cp 2(CO) 4(μ-PPh 2)] ( 3) have been performed and refined to R = 0.026, 0.037 and 0.025, respectively. In all three complexes two MoCp(CO) 2 fragments are bridged by a PPh 2 group and they are additionally bridged by a hydrogen atom or an AuPPh 3 group in 1 and 4. The most striking difference in the structures of the doubly-bridged complexes involves the conformation of the central Mo 2PAu/H unit: it is approximately planar for 1 but strongly folded for 4.

Ligand shift in mixed-cluster complexes: synthesis of alkyne-bridged Co 2Mo 2 clusters with two triply-bridging sulphur atoms: crystal structure of [Co 2Mo 2(η 5-Cp) 2(μ 3-S) 2(μ 4-CF 3C 2Me)(CO) 4

Reaction of the complexes [(CO) 3Co(μ-RC 2R′)Co(CO) 3] (R = R′ = CF 3; R = Ph, CF 3 and R′ = H) with the MoMo dinuclear derivative [Mo 2Cp 2(μ-SMe) 2(CO) 2] leads to cleavage of both CS and CH bonds with the formation of closo-octahedral Mo 2CO 2C 2 clusters stabilised by a μ 4-η 2-bound alkyne. An X-ray diffraction study has shown that the two Mo 2Co faces of the octahedron are capped by triply-bridging sulphur atoms.

Transition metal complexes as electrochemical markers for steroids

The electrochemical behaviour of few Co 2(CO) 6(alkyne-estradiol) and Mo 2Cp 2(CO) 4(alkyne-estradiol) complexes is described. For purposes of comparison the electrochemical responses of free estradiols and of the model compound Co 2(CO) 6(HC 2H) have also been investigated. From the cyclic voltammetric responses of the estradiol-organometallic derivatives, it is clear that the two constituent units, i.e. Co 2″ 6CC″ and the estradiol frame, undergo relatively independent electrochemical processes. Significantly the labelling of steroids by means of bimetallic fragments (having an accessible LUMO) increases their electrochemical activity by adding a well-defined reduction process which makes the molecules cathodically detectable at stationary electrodes. This approach suffers from adsorption and filming problems, but these can be overcome by careful pretreatment of the solid electrodes. A method of evaluating the molecular mobility of such complexes from the 13C-NMR line-width analysis is described.

Synthesis, crystal structure and heterometallic derivatives of [Mo 2Cp 2(μ-σ,π-CN tBu)(PPh 2CH 2PPh 2- P)(CO) 3] ( tBu = C(CH 3) 3, Cp = η-C 5H 5)

The dppm ligand (Ph 2PCH 2PPh 2) in [Mo 2Cp 2(CO) 4(μ-dppm)] (Cp = η-C 5H 5) undergoes ring-opening upon reaction with NCMe or CN tBu ( tBu = C(CH 3) 3), to give [MoCp(CO)(NCMe)(dppm)][MoCp(CO) 3] or [Mo 2Cp 2(μ-σ,π-CN tBu)(dppm-P)(CO) 3], respectively. The crystal structure of the latter complex is described as well as its reactions with sources of the metal fragments ML n [ML n : Fe(CO) 4, Mo(CO) 5, MnBr(CO) 4, CuCl] to give the heterometallic species [ML n (μ-dppm)MoCp(CO)(μ-σ,π-CN tBu)MoCp(CO) 2].

Synthesis and reactivity of the unsaturated dimolybdenum compound [Mo 2(η-C 5H 5) 2(μ-CH 2PPh 2)(μ-PPh 2)(CO) 2]. Crystal structure of [Mo 2(η-C 5H 5) 2(μ-I)(μ-CH 2PPh 2)- (μ-PPh 2)(CO) 2][TlI 4]·CH 2Cl 2

The unsaturated compound [Mo 2Cp 2(μ-CH 2PPh 2)(μ-PPh 2)(CO) 2] (Cp = η-C 5H 5) has been prepared by heating [Mo 2Cp 2(CO) 4-(μ-Ph 2PCH 2PPh 2)] in tetrahydrofuran at 60° C. This compound reacts with elemental E (E = S, Se) to yield [Mo 2Cp 2(μ-CH 2PPh 2)(μ-PPh 2)(μ-E)(CO) 2], and with iodine to give the cation [Mo 2Cp 2(μ-I)(μ-CH 2PPh 2)(μ-PPh 2)(CO) 2] + the crystal structure of which as the [TlI 4] − salt has been determined by an X-ray diffraction study.

A comment on the chemistry and the electrochemistry of [Mo 2Cp 2(CO) 4(μ-SR) 2] 0/2+

A comment on the chemistry and the electrochemistry of [Mo 2Cp 2(CO) 4(μ-SR) 2] 0/2+