Allenylidene Complexes Research Articles

Allenylidene and derived alkynyl complexes of iron(II) with the {FeBr(Et 2PCH 2CH 2PEt 2) 2} + centre

The allenylidene complexes trans-[FeBr{CCC(R)Ph}(depe) 2][BPh 4] (depe=Et 2PCH 2CH 2PEt 2; R=Me 1, Ph 2) were obtained by treatment of a methanolic solution of trans-[FeBr 2(depe) 2] with the appropriate alkynol HCCC(R)Ph(OH), in the presence of Na[BPh 4]. The methylallenylidene ligand in 1 undergoes reversible deprotonation (by NaOMe) to yield the enynyl (or ene–yne) complex of iron(II), trans-[FeBr{CCC(CH 2)Ph}(depe) 2] 3. The diphenylallenylidene ligand in 2 undergoes regioselective hydride γ-addition on reaction with K[B{CH(Me)Et} 3H] to afford the alkynyl complex trans-[FeBr{CCC(H)Ph 2}(depe) 2] 4.

Titanium-containing epoxidation catalysts

Complex [RuCl{κ3(N,N,N)-Tp}(PPh3)(PTA)] (κ3(N,N,N)-Tp = hydridotris(pyrazolyl)borate) containing the water-soluble phosphane 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane (PTA) reacts with terminal alkynes producing to the corresponding neutral alkynyl complexes [Ru(CCR){κ3(N,N,N)-Tp}(PPh3)(PTA)] (R = Ph (1a), nBu (1b), 1-cyclopentenyl (1c), p-methoxyphenyl (1d), 6-methoxynaft-2-yl (1e)). When halide is extracted from complex [RuCl{κ3(N,N,N)-Tp}(PPh3)(PTA)] followed by treatment with propargyl alcohols, the corresponding allenylidene complexes [Ru{κ3(N,N,N)-Tp}(PPh3)(PTA)(CCCPh2)][X] (X = PF6 (2a), CF3SO3 (2b)) and [Ru{κ3(N,N,N)-Tp}(PPh3)(PTA)(CCCC12H8)][PF6] (3) result. Electrophilic attack on the complexes thus obtained leads chemoselectively to the alkynyl complexes [Ru(CCR){κ3(N,N,N)-Tp}(PPh3)(1-CH3-PTA)][CF3SO3] (R = Ph (4a), nBu (4b), and 1-cyclopentenyl (4c)) and to the dicationic allenylidene complexes [Ru{κ3(N,N,N)-Tp}(PPh3)(1-H-PTA)(CCCC12H8)][PF6]2 (5) and [Ru{κ3(N,N,N)-Tp}(PPh3)(1-CH3-PTA)(CCCPh2)][CF3SO3]2 (6).

Ruthenium‐Catalyzed Carbon—Carbon Bond Formation Between Propargylic Alcohols and Alkenes via the Allenylidene‐Ene Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Displacement of tetrahydrofuran in [(CO) 5M(THF)] (M=Cr, W) by the anion [CCC(X)Y] − (X=O; NR; Y=NR′ 2, Ph) followed by alkylation of the resulting metalate with [R″ 3O]BF 4 (R″=Me, Et) offers a convenient and versatile route to π-donor-substituted allenylidene complexes, [(CO) 5MCCC(XR″)Y]. Allenylidene complexes in which the terminal carbon atom of the allenylidene ligand constitutes part of a heterocycle are likewise accessible by this reaction sequence. Reaction of [(CO) 5M(THF)] with Li[CCC(NMe)Ph] − and subsequent protonation of the metalate afford [(CO) 5MCCC(NMeH)Ph] in high yield. As indicated by the spectroscopic data of the compounds and the X-ray analyses of three representative examples, these allenylidene complexes are best described as hybrids of allenylidene and zwitterionic alkynyl complexes with delocalisation of the electron pair at nitrogen towards the metal center. Dimethylamine reacts with the amino( phenyl)allenylidene complex [(CO) 5CrCCC(NMe 2)Ph] ( 7a) by addition of the amine across the C αC β bond to give selectively the E-alkenyl(amino)carbene complex [(CO) 5CrC(NMe 2)CHC(NMe 2)Ph] ( 12). In contrast, the reaction of dimethylamine with the amino( methoxy)allenylidene complex [(CO) 5CrCCC(NMe 2)OMe] ( 1a) proceeds by addition of the amine to the C γ atom and subsequent elimination of methanol to give the substitution product [(CO) 5CrCCC(NMe 2) 2] ( 13). Triphenylphosphane neither adds to the C α nor the C γ atom of 7a but upon irradiation displaces a CO ligand to form a cis-allenylidene(tetracarbonyl)phosphane complex 15.

Synthesis, molecular structure, and C-C coupling reactions of carbeneruthenium(II) complexes with C5H5Ru(=CRR') and C5Me5Ru(=CRR') as molecular units.

The ethene derivatives [(eta(5)-C(5)R(5))RuX(C(2)H(4))(PPh(3))] with R=H and Me, which have been prepared from the eta(3)-allylic compounds [(eta(5)-C(5)R(5))Ru(eta(3)-2-MeC(3)H(4))(PPh(3))] (1, 2) and acids HX under an ethene atmosphere, are excellent starting materials for the synthesis of a series of new halfsandwich-type ruthenium(II) complexes. The olefinic ligand is replaced not only by CO and pyridine, but also by internal and terminal alkynes to give (for X=Cl) alkyne, vinylidene, and allene compounds of the general composition [(eta(5)-C(5)R(5))RuCl(L)(PPh(3))] with L=C(2)(CO(2)Me)(2), Me(3)SiC(2)CO(2)Et, C=CHCO(2)R, and C(3)H(4). The allenylidene complex [(eta(5)-C(5)H(5))RuCl(=C=C=CPh(2))(PPh(3))] is directly accessible from 1 (R=H) in two steps with the propargylic alcohol HC triple bond CC(OH)Ph(2) as the precursor. The reactions of the ethene derivatives [(eta(5)-C(5)H(5))RuX(C(2)H(4))(PPh(3))] (X=Cl, CF(3)CO(2)) with diazo compounds RR'CN(2) yield the corresponding carbene complexes [(eta(5)-C(5)R(5))RuX(=CRR')(PPh(3))], while with ethyl diazoacetate (for X=Cl) the diethyl maleate compound [(eta(5)-C(5)H(5))RuCl[eta(2)-Z-C(2)H(2)(CO(2)Et)(2)](PPh(3))] is obtained. Halfsandwich-type ruthenium(II) complexes [(eta(5)-C(5)R(5))RuCl(=CHR')(PPh(3))] with secondary carbenes as ligands, as well as cationic species [(eta(5)-C(5)H(5))Ru(=CPh(2))(L)(PPh(3))]X with L=CO and CNtBu and X=AlCl(4) and PF(6), have also been prepared. The neutral compounds [(eta(5)-C(5)H(5))RuCl(=CRR')(PPh(3))] react with phenyllithium, methyllithium, and the vinyl Grignard reagent CH(2)=CHMgBr by displacement of the chloride and subsequent C-C coupling to generate halfsandwich-type ruthenium(II) complexes with eta(3)-benzyl, eta(3)-allyl, and substituted olefins as ligands. Protolytic cleavage of the metal-allylic bond in [(eta(5)-C(5)H(5))Ru(eta(3)-CH(2)CHCR(2))(PPh(3))] with acetic acid affords the corresponding olefins R(2)C=CHCH(3). The by-product of this process is the acetato derivative [(eta(5)-C(5)H(5))Ru(kappa(2)-O(2)CCH(3))(PPh(3))], which can be reconverted to the carbene complexes [(eta(5)-C(5)H(5))RuCl(=CR(2))(PPh(3))] in a one-pot reaction with R(2)CN(2) and Et(3)NHCl.

Ruthenium-catalyzed carbon-carbon bond formation between propargylic alcohols and alkenes via the allenylidene-ene reaction.

A novel ruthenium-catalyzed carbon-carbon bond formation between propargylic alcohols and alkenes via the allenylidene-ene reaction has been found to afford the corresponding 2,4-disubstituted-1-hexen-5-ynes in moderate yields. The finding described here discloses a new reactivity of allenylidene complexes. As a synthetic application, intramolecular cyclization of propargylic alcohols bearing an alkene moiety has been developed to give the corresponding syn-substituted chromanes in high yields with an excellent diastereoselectivity.

Structure and Dynamics of Half-Sandwich Ruthenium(IV) Alkynyl Hydrido Complexes

The coordinatively unsaturated complex [Cp*Ru(PMeiPr2)2][BAr‘4] (1; BAr‘4 = B{3,5-C6H3(CF3)2}4) reacts with 1-alkynes in diethyl ether at 0 °C, furnishing the RuIV alkynyl hydrido derivatives [Cp*RuH(C⋮CR)(PMeiPr2)2][BAr‘4]. In an analogous fashion, the reaction of 1 with 1-alkyn-3-ols in diethyl ether at 0 °C leads to the 3-hydroxyalkynyl hydrido complexes [Cp*RuH(C⋮CC(OH)RR‘)(PMeiPr2)2][BAr‘4]. The complexes [Cp*RuH(C⋮CCOOMe)(PMeiPr2)2][BAr‘4] and [Cp*RuH(C⋮CC(OH)Ph2)(PMeiPr2)2][BAr‘4]·Et2O have been structurally characterized, and their crystal structures show a transoid disposition of the hydride and alkynyl ligands. These compounds are stereochemically nonrigid and undergo a rapid equilibrium between possible stereoisomers in solution, which has been studied by variable-temperature NMR spectroscopy and computer simulation. The dynamic NMR study for these processes indicates energy barriers of ca. 11 kcal mol-1, and moreover the differences in energy for the possible stereoisomers are very small (ca. 1 kcal mol-1). The alkynyl hydrido complexes rearrange to their more stable vinylidene or hydroxyvinylidene tautomers. Spontaneous dehydration of the latter leads to either vinylvinylidene or allenylidene complexes.

Ruthenium‐Catalysed Selective Transetherification of Substituted Vinyl Ethers To Form Acetals and Aldehydes

AbstractThe water‐soluble ruthenium allenylidene complex [{RuCl(μ‐Cl)(C=C=CPh2)(TPPMS)2}2]Na4 catalyses the selective transformation of substituted linear and cyclic vinyl ethers with MeOH, under mild non acidic conditions, to give acetals, while aldehydes and ketones are obtained in a CHCl3/H2O mixture, which allows for easy recycling of the catalyst. NMR studies showed that the reaction follows a transetherification mechanism rather than simple acid‐catalysed hydrolysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Ruthenium‐Catalyzed Propargylation of Aromatic Compounds with Propargylic Alcohols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Long-lived higher excited state luminescence from new ruthenium(II)–allenylidene complexes

Resonance Raman spectra of heteroatom substituted ruthenium(II)-allenylidene complexes, obtained by irradiation into the second electronic absorption band, clearly prove the d(Ru)→π*(CCC) MLCT character of the corresponding electronic transition. The complexes are not significantly luminescent at room temperature, but in solvent glasses at 77 K, emission is observed. Only some of the complexes studied are luminescent upon irradiation into their lowest-energy absorption band. The striking finding of this study is that almost all complexes are luminescent on irradiation into their second absorption band. The emission was shown to originate from a higher lying 3MLCT state, which shows that internal conversion to the lowest excited state is very inefficient in these complexes.

(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

AbstractWe describe the allenylidene complexes [TpL2Ru=C=C=CPhR]+ SbF6− [Tp = HB(pz)3−, L2 = 2 PPh3 or 1,1′‐bis(diphenylphosphanyl)ferrocene (dppf), R = Ph or ferrocenyl] and their spectroscopic and electrochemical characteristics. Three of these compounds possess redox‐active, ferrocene‐based substituents or ligands − that are oxidized at lower potentials than the ruthenium center itself − attached either to the terminal carbon atom of the allenylidene ligand or to the ruthenium atom. The Fc/Ph‐substituted complexes 3a and 3b provide unique examples of hindered rotation of the allenylidene substituent around the M=C bond. For 3a (L2 = 2 PPh3), two isomers differing in the orientation of the vertically aligned, unsymmetrically substituted allenylidene ligand are discernible even at 388 K. The dppf‐substituted congener 3b has the allenylidene ligand in a horizontal orientation and exhibits a rotational barrier, as determined by dynamic 31P NMR spectroscopy, of ΔG≠ = 47 kJ/mol at TC = 238 K. The changes in the spectroscopic and electrochemical properties upon replacement of the PPh3 by a dppf ligand and the Ph by an Fc moiety can be explained in terms of the bonding within these systems. These effects are attenuated when the ferrocene‐based redox tags are oxidized, as shown by IR and UV/Vis spectroelectrochemistry. Thus, infrared spectroelectrochemistry reveals a blue shift of the allenylidene stretch upon oxidation of the dppf ligand, while oxidation of the ferrocene covalently linked to the unsaturated C3 ligand has the opposite effect. Oxidation of the ruthenium atom influences the bonding within the unsaturated ligand more profoundly. Results from IR spectroelectrochemistry point to a vinylidene structure in the RuIII state. Reduction enhances the contribution of alkynyl‐type resonance forms to the overall bonding description, as also shown by IR spectroelectrochemistry. For the ferrocenyl‐substituted allenylidene complexes, oxidation and reduction result in bleaching of the intense optical low‐energy absorption band attributed to a ferrocenyl‐to‐allenylidene charge‐transfer process. The EPR spectra of the paramagnetic reduced forms of these complexes also indicate spin delocalization into the aryl substituents attached to the allenylidene ligand. The complexes Tp(dppf)RuCl and [Tp(dppf)Ru=C=C=CPh2]+ SbF6− were also characterized by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Metallacumulenylidene complexes in the [(η 5-C 5Me 5)(η 2-dppe)Fe(=C(=C) nR 2)]X ( n = 0, 1, 2) series: investigations of the iron-carbon bonding by Mössbauer spectroscopy and X-ray analyses

The synthesis of the iron allenylidene complexes [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=C=C(Ph)Ph)][X] ( 5a, X = PF 6, 95%; 5b, X = BPh 4, 91%; dppe = 1,2-bis(diphenylphosphino)ethane) was achieved by reacting the complex (η 5-C 5Me 5)(η 2-dppe)FeCl ( 10) with 1 equiv of 1,1-diphenyl-prop-2-yn-1-ol in methanol in the presence of KPF 6 or NaBPh 4. Surprisingly, when the reaction was carried out in the presence of the tetraphenylborate anion, the final product contained both 5b and the hydroxyvinylidene [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=C(H)C(OH)(Ph) 2)][BPh 4] ( 14b) in the 1:1 ratio. Further treatment of the mixture with Amberlyst 15 in methanol provided the allenylidene 5b as a pure sample. The allenylidene complexes [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=C=C(Me)Ph)][PF 6] ( 6) and [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=C=C(Me)Et)][PF 6] ( 7) were prepared according to the same procedure and they were isolated as purple powders in 90% yield. The X-ray crystal structures were determined for the vinylidene complexes [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=CH 2)][PF 6] ( 3) and [(η 5-C 5Me 5)(η 2-dppe)Fe(=C=C(Ph)H)][PF 6] ( 4), and the allenylidene derivative 5a. In the homogeneous series of complexes [(η 5-C 5Me 5)(η 2-dppe)Fe(=(C) n (R)R’)][PF 6], ( n = 1, R = H, R′ = Me, X = PF 6, 1; n =1, R = H, R’ = OMe, X = PF 6, 2a; n = 1, R = H, R’ = OMe, X = CF 3OSO 2, 2b; n = 2, R = R′ = H, X = PF 6, 3; n = 2, R = H, R′ = Ph, X = PF 6, 4; n = 3, R = R′ = Ph, X = PF 6, 5a; n = 3, R = R′ = Ph, X = BPh 4, 5b; n = 3, R = Me, R′ = Ph, X = PF 6, 6; n = 3, R = Me, R′ = Et, X = PF 6, 7; n = 3, R = Me, R′ = OMe, X = BPh 4, 8), an empiric relationship between the Mössbauer parameters, δ and QS, was found. This observation would indicate that the positive charge on the iron nucleus decreases with the Fe=C bond order. Moreover, in this series of iron cumulenylidene derivatives, comparison of the variation of the metal–carbon bond distances determined by X-ray analyses with the Mössbauer QS values allows the observation of a linear correlation ( R = 0.99). To cite this article: G. Argouarch et al., C. R. Chimie 6 (2003).

1,3-Cycloaddition of pyrazole to the allenylidene ligand in [Re{CCCPh 2}(CO) 2{MeC(CH 2PPh 2) 3}] +

The reaction of the allenylidene complex [Re{CCCPh 2}(CO) 2(triphos)]OTf ( 1) (triphos=MeC(CH 2PPh 2) 3; OTf= −OSO 2CF 3) with pyrazole gave the 1,2,3-diheterocyclization product [Re{CCHCPh 2(N 2C 3H) 3}(CO) 2(triphos)]Y (Y=OTf, 2OTF; Y=BPh 4, 2BPh 4 ). The molecular structure of this complex was determined by a single-crystal X-ray analysis. Treatment of 2 with sodium methoxide gave the pyrazolyl-functionalized alkynyl derivative [Re{CCCPh 2(N 2C 3H 3)}(CO) 2(triphos)] ( 3) via selective deprotonation of the vinylic hydrogen, followed by back opening of the metal-bound heterocycle. Protonation of 3 with triflic acid in dichloromethane re-generated 1 and free pyrazole. The overall result of this deprotonation/protonation sequence allowed us to propose a reliable mechanism for the formation of the 1,2,3-diheterocyclization product 2OTf.

Indenyl–ruthenium(ii) allenylidene complexes containing terpenic substituents as precursors of optically active terminal alkynes: scope and limitations

The optically active allenylidene complex [Ru{CCC(C9H16)}(η5-C9H7)(PPh3)2][PF6] (C(C9H16) = (1R,4S)-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-ylidene) 1 regio- and stereoselectively reacts with unhindered anionic nucleophiles to yield the neutral σ-alkynyl derivatives [Ru{CCC(C9H16)R}(η5-C9H7)(PPh3)2] (R = H 2a, CN 2b, Me 2c, CCPh 2d). Protonation of 2a–d with HBF4·Et2O affords the cationic vinylidene complexes [Ru{CC(H)C(C9H16)R}(η5-C9H7)(PPh3)2][BF4] 3a–d, which can be easily demetalated, by treatment with acetonitrile, yielding the corresponding chiral acetylenic compounds HCC(C9H16)R 4a–d. The novel optically active indenyl–ruthenium(II) allenylidene complexes [Ru{CCC(C9H16)}(η5-C9H7)(PPh3)2][PF6] (C(C9H16) = (1R,4R)-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-ylidene) 9 and [Ru{CCC(C9H14)}(η5-C9H7)(PPh3)2][PF6] (C(C9H14) = (1S,5S)-4,6,6-trimethyl-bicyclo[3.1.1]hept-3-en-2-ylidene) 10 have been prepared by activation of propargylic alcohols derived from the natural ketones (+)-camphor and (−)-verbenone, respectively, with [RuCl(η5-C9H7)(PPh3)2] 6. Treatment of 9 with anionic nucleophiles generates the neutral σ-enynyl complex [Ru{CCC(C9H15)}(η5-C9H7)(PPh3)2] 11 (C(C9H15) = (1R,4R)-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-en-2-yl).

Ruthenium complexes supported by 2,6-bis(pyrazol-1-yl)pyridines

The synthesis and characterization of a series of ruthenium(II) complexes containing the planar tridentate ligands 2,6-bis(pyrazol-1-yl)pyridine (BPP) or 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (Me 4BPP) are described. The reaction of BPP with RuCl 2(PPh 3) 3 yields both the cis ( 1a) and trans ( 1b) isomers of [RuCl(PPh 3) 2(BPP)]Cl. Complexes of the general formula trans-RuCl 2(L)(Me 4BPP) (L=PPh 3, 2; C 2H 4, 3a; CO, 3b; MeCN, 3c) are also reported, and were prepared from either RuCl 2(PPh 3) 3 and Me 4BPP (i.e. 2), Et 3N reductions of RuCl 3(Me 4BPP) in the presence of L (i.e. 2 and 3b, c), or from [RuCl 2( p-cymene)] 2, Me 4BPP and L (i.e. 3a). The neutral vinylidene complex cis-RuCl 2(CCHPh)(Me 4BPP) ( 4), was isolated from reactions of phenylacetylene with either 3a or mixtures of [RuCl 2( p-cymene)] 2 and Me 4BPP, while the cationic allenylidene complex [RuCl(PPh 3)(CCCPh 2)(Me 4BPP)][BF 4] ( 5), was prepared from 2, AgBF 4 and 1,1-diphenyl-2-propyn-1-ol. Complexes 1– 5 were characterized by multinuclear NMR and IR spectroscopy.

Allenylidene-ruthenium-arene precatalyst for ring opening metathesis polymerisation (ROMP)

The ruthenium allenylidene complex [RuCl(CCCPh 2)(PCy 3)( p-cymene)][OTf] constitutes an excellent precatalyst for the ROMP at room temperature of norbornene ( M n=198×10 3, PDI=1.8) and cyclooctene ( M n=143×10 3, PDI=1.9). The activation of the precatalyst by initial heating (25 min, 60 °C) generates a catalytic species that operates at room temperature to produce in 10 min 90% of polyoctenamer ( M n=151×10 3, PDI=1.7).

Generation of polyunsaturated cumulene chains by unprecedented insertions of the ynamine MeC=_NEt2 in ruthenium(II) allenylidene complexes.

Three-fold sequential insertion of the ynamine MeCCNEt2 into ruthenium(II) allenylidene complexes leads to the stereoselective formation of the polyunsaturated complex I.

In Search of Optically Active γ-Keto Acetylenes via Regioselective Coupling of Allenylidene Groups and Cyclic Enolates

(Indenyl)ruthenium(II) allenylidene complexes [Ru{CCC(R)Ph}(η5-C9H7)(PPh3)2][PF6] (R = Ph (1), H (2)) regioselectively react with enolates derived from cyclopentanone and cyclohexanone at the Cγ atom to yield the σ-alkynyl derivatives (R = Ph, n = 1 (3a), 2 (3b); R = H, n = 1 (4a), 2 (4b)). Protonation of these species at Cβ of the alkynyl chain with HBF4 affords vinylidene complexes 5a,b and 6a,b, which can easily be demetalated with acetonitrile to yield the γ-keto acetylenes (7a,b and 8a,b). Compounds 4a,b, 6a,b and 8a,b, derived from the monosubstituted allenylidene complex 2, have been obtained as nonseparable mixtures of two diastereoisomers. The optically active allenylidene [Ru{CCC(C9H16)}(η5-C9H7)(PPh3)2][PF6] (10) (C(C9H16) = (1R)-1,3,3-trimethylbicyclo[2.2.1]hept-2-ylidene) undergoes a selective exo addition of the cyclopentanone enolate to afford the σ-alkynyl diastereoisomers (11a,b). Demetalation of 11a and 11b, via their corresponding vinylidenes, allows the preparation of optically pure te...

Addition of E−H Bonds (E = S, N) across the CαCβ Bond of the Allenylidene Ligand in [Re{CCCPh2}(CO)2(triphos)](OSO2CF3) (Triphos = MeC(CH2PPh2)3)

Reaction of the rhenium(I) allenylidene complex [Re{CCCPh2}(CO)2(triphos)]OTf (1; triphos = MeC(CH2PPh2)3, OTf = -OSO2CF3) with thiophenol, 2-thionaphthol, or allyl mercaptan gave selectively the α,β-unsaturated thiocarbene complexes [Re{C(SR)CHCPh2}(CO)2(triphos)]OTf (R = Ph (2), α-naphthyl (3), CH2CHCH2 (4)). A reversible reaction was observed for PhSH in DMSO at 80 °C. Compounds 2 and 3 have been found to react with sodium alkoxides, yielding the kinetic thioallenyl products [Re{C(SR)CCPh2}(CO)2(triphos)] (R = Ph (6a), α-naphthyl (7a)). These equilibrated in room-temperature solution with the thermodynamic thioalkynyl products [Re{C⋮CC(SR)Ph2}(CO)2(triphos)] (R = Ph (6b), α-naphthyl (7b)) to give stationary states (6a/6b, 40/60; 7a/7b, 20/80). Deprotonation of the thioallyl complex 4 gave the stable allenyl derivative [Re{C(SCH2CHCH2)CCPh2}(CO)2(triphos)] (8). Ammonia, aniline, and propargylamine each reacted with 1 to give the azoniabutadienyl compounds [Re{C(NHR)CHCPh2}(CO)2(triphos)]OTf (R = H (9), Ph (10), CH2C⋮CH (11)) via N−H bond addition across the CαCβ double bond. NMR spectroscopy showed the γ-alkynylammonium complex [Re{C⋮CCPh2(NH3)}(CO)2(triphos)]OTf (12) to be a transient intermediate along the reaction of 1 with ammonia. Treatment of 10 or 11 with sodium methoxide resulted in the selective deprotonation of the nitrogen atom to give the azabutadienyl compounds [Re{C(NR)CHCPh2}(CO)2(triphos)] (R = Ph (13), CH2C⋮CH (14)). The molecular structure of the azoniabutadienyl complex 11 was determined by a single-crystal X-ray analysis. The geometry around the rhenium center conforms to a slightly distorted octahedron, with the polyphosphine sitting on a face of the coordination polyhedron. In keeping with the azoniabutadienyl structure, the Re−Cα bond length is 2.151(7) Å, and the Cα−N distance is 1.300(9) Å.

Reactivity of the Electron-Rich Allenylidene−Ruthenium Complexes [Cp*Ru{CCC(R)Ph}(dippe)][BPh4] (R = H, Ph). X-Ray Crystal Structure of a Novel Dicationic Ruthenium Carbyne (Cp* = C5Me5; dippe = 1,2-bis(diisopropylphosphine)ethane)

The reactions of the allenylidene complexes [Cp*Ru{CCC(R)Ph}(dippe)][BPh4] (R = H (1), Ph (2)) with different substrates have been studied, providing a new form of allenylidene−ruthenium reactivity. The observed reactivity pattern depends strongly on the substituents on the γ-carbon. The secondary allenylidene 1 undergoes addition of weakly nucleophilic reagents such as pyrazole, 3,5-dimethylpyrazole, or thiophenol to the Cβ−Cγ double bond, yielding substituted vinylidene compounds [Cp*Ru{CCHCH(L)Ph}(dippe)][BPh4] (L = pyrazolyl (3), 3,5-dimethylpyrazolyl (4), phenylsulfanyl (5)). The reaction of 1 with pyrrole or 2-methylfuran to afford analogous complexes [Cp*Ru{CCH−CH(L)Ph}(dippe)][BF4] (L = 2-pyrrolyl (6), 5-methyl-2-furanyl (7)) takes place only in the presence of acid. This suggests that an initial protonation at the β-carbon of the allenylidene occurs, enhancing the electrophilic character of the γ-carbon atom. This mechanism involves the formation of dicationic carbyne ruthenium complexes [Cp*Ru{⋮C−CHC(R)Ph}(dippe)]2+ (R = H (8), Ph (9)), which have been isolated and characterized as [B(ArF)4] (ArF = 3,5-(CF3)2C6H3) salts, by protonation of the cationic allenylidenes with [H(Et2O)2][B(ArF)4]. The X-ray crystal structure of the carbyne compound 9 is reported. A series of neutral functionalized alkynyl compounds [Cp*Ru{C⋮CCR(L)Ph}(dippe)] (L = CH3COCH2, R = H (10), R = Ph (11); L = pyrazolyl, R = H (12); R = Ph (13)) have also been synthesized by regioselective addition of anionic nucleophiles such as potassium acetonate or potassium pyrazolate. The structures of 11 and 13 in the solid state have been determined by X-ray diffraction analysis. Protonation of 10 and 11 with HBF4·Et2O yields the vinylidene compounds [Cp*Ru{CCH−CR(CH2COCH3)Ph}(dippe)][BF4] (R = H (14), Ph (15)).