Silvia Bordoni

Catalytic hydroformylation of (1S,5S)-(−)- and (1R,5R)-(+)-β-pinene: stereoselective synthesis and spectroscopic characterization of (1S,2R,5S)-, (1S,2S,5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinane

Abstract (1S,5S)-(−)- and (1R,5R)-(+)-β-pinene have been hydroformylated in toluene to give (1S,2R,5S)- and (1R,2S,5R)-10-formylpinane with up to 95% diastereoselectivity using bimetallic CoRh(CO)7 as a catalyst; the latter was generated in situ from preformed Co2Rh2(CO)12 or a stoichiometric mixture of either [Rh4(CO)12] or [Rh6(CO)16] and [Co2(CO)8]. At 70–125°C and under 60 atm of syngas, the yields of hydroformylated products do not exceed 30% because of the concomitant isomerization of β- to α-pinene. In all cases the catalyst is recovered as a mixture of soluble cobalt carbonyl derivatives and a crystalline precipitate that contains most of the rhodium, mainly as [Rh6(CO)16]. Comparable yields and diastereoselectivities were obtained from reactions in tetrahydrofuran with a mixture of [Rh4(CO)12] and [N(PPh3)2]Cl as the catalyst precursor. The corresponding (1S,2S,5S)- and (1R,2R,5R)-10-formylpinanes, along with the corresponding alcohols, were obtained diastereoselectively by the use of bimetallic CoRh or homometallic Rh carbonyl catalysts modified with bis(diphenylphosphine)ethane (dppe). When unidentate phosphines such as triphenylphosphine were used in place of dppe, as the ligand/metal (L/M) ratio was raised the diastereoselectivity of both the hetero- and the homo-metallic catalytic system fell progressively, and was completely lost for L/M ≥ 4. However, a further increase in L/M to ca. 70–100 allows chemio- and diastereo-selective synthesis of both the (1S,2S,5S)- and (1R,2R,5R)-10-formylpinane. The (1S,2R,5S)-, (1S,2S,5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinane diastereomers were isolated by distillation under reduced pressure and fully characterized by IR, UV, 1H and 13C NMR and circular dicroism (CD) spectroscopy, and mass spectrometry. The possible factors favouring the diastereoselective hydroformylation of β-pinenes under the conditions used are discussed.

Reactions of [Au(C6F5)(SC4H8)] with diazoalkanes. Synthesis and molecular structures of [Au(C6F5)(Ph2CNNCPh2)]

Abstract Treatment of [Au(C6F5)(SC4H5)] (1) (SC4H8=tetrahydrothiophene, tht) with Ph2CN2 affords the azine complex [A u(C 6 F 5 )(Ph 2 CN NCPh2)] (2), whereas HAuC14 reacts with diphenyldiazomethane to form the salt [Ph2CN(H)NCPh2][AuCl4] (3). The molecular structures of both 2 and 3 have been established by single crystal X-ray diffraction studies. Complex 2 (triclinic, P 1 , Z=2, a=10.805(4), b=13.066(2), c=10.094(3) A, α=112.06(3), β=100.63(2), γ=88.45(2)°) exhibits the expected linear coordination with the azine acting as N- monodentate ligand. Bond parameters of interest are AuC(perfluorophenyl) 1.992(6), AuN(azine) 2.069(5) A, CAuN 175.8(2)°. 3 (triclinic, P 1 , Z=1, a=9.145(5), b=9.333(1), c=8.228(3) A, α=100.08(1), β=107.30(3), γ=74.17(2)°) is an ionic species in which the cation is the monoprotonated derivative of the azine coordinated to gold in 2. Bond parameters within the azine motecule in the two derivatives are comparable. Complex 1 promotes dinitrogen elimination from diazofluorene to form fluoren-9-ylidene via carbene-carbene coupling. An interpretation of the different behaviour of the two diazocompounds is presented.

CN coupling between μ-aminocarbyne and nitrile ligands promoted by tolylacetylide addition to [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(NCCMe3)(Cp)2][SO3CF3]: Formation of a novel bridging η1:η2 allene-diaminocarbene ligand

The reaction of the μ-aminocarbyne complex [Fe 2 {μ-CN(Me)(Xyl)}(μ-CO)(CO)(NCCMe 3 )(Cp) 2 ][SO 3 CF 3 ] ( 2 ) (Xyl=2,6-Me 2 C 6 H 3 ) with tolylacetylide, followed by treatment with HSO 3 CF 3 affords the complex [Fe 2 {μ-η 1 :η 3 C(Tol)CC(CMe 3 )N(H)CN(Me)(Xyl)}(μ-CO)(CO)(Cp 2 )][SO 3 CF 3 ] ( 3 ) (Tol=4-MeC 6 H 4 ). The X-ray molecular structure of 3 reveals the peculiar character of the bridging ligand, which exhibits both η 1 :η 2 allene and aminocarbene nature. The formation of 3 proceeds through several intermediate species, which have been detected by IR spectroscopy. Addition of HSO 3 CF 3 at an early stage of the reaction between 2 and LiCCTol leads to the formation of the imine complex [Fe 2 {μ-CN(Me)Xyl}(μ-CO)(CO){NHC(CCTol)CMe 3 }(Cp) 2 ][SO 3 CF 3 ] ( 6 ) indicating that the first step of the reaction consists in the acetylide addition at the coordinated NCCMe 3 . The molecular structure of 6 has been elucidated by an X-ray diffraction study.

Derivatives of [Rh6(CO)13C]2–: solution structure of [Rh6H(CO)13C]– from nuclear magnetic resonance measurements and the X-ray crystal structure of [Rh6(CO)11C(µ-Ph2PCH2CH2PPh2)]2–

Multielement n.m.r. measurements (1H, 1H-{103Rh}, 13C, 13C-{103Rh}, and 103Rh) show that protonation of [Rh6(CO)13C]2– at low temperature gives [Rh6H(CO)13C]– which contains an edge-bridging hydride with the carbonyl distribution being very similar to that found in [Rh6(CO)13C]2– Warming this solution to < –20 °C results in complete CO- and H-migration over the Rh6 octahedron and at –20 °C there is formation of [Rh6H(CO)15C]– together with loss of hydrogen to give [Rh12(CO)24(C)2]2– which has been spectroscopically characterised. Multielement n.m.r. studies on products resulting from the reaction of [Rh6(CO)13C]2–(1 mol equiv.) with diphosphines Ph2P(CH2)nPPh2[0.5 mol equiv.; n= 1,2 (dppe), 3, or 4] or Ph2AsCH2CH2AsPh2 suggest that they all have similar structures and an X-ray crystallographic analysis of the dppe derivative shows it to be [Rh6(CO)11C(µ-dppe)]2–.

The μ-sulfonium–methylidene diiron complexes [Fe2{μ-C(X)SMe2}(μ-CO)(CO)2(Cp)2]SO3CF3 (X=CN, H) as precursors of μ-alkylidene complexes

Abstract The reactions of [Fe 2 {μ-C(X)SMe 2 }(μ-CO)(CO) 2 (Cp) 2 ]SO 3 CF 3 (X=CN 2a , H 2b ; Cp=η-C 5 H 5 ) with Li 2 Cu(CN)R 2 (R=Me, Bu n , Ph, CCC 6 H 4 Me-4, C 4 H 3 S) give the neutral μ-alkylidene complexes [Fe 2 {μ-C(X)R}(μ-CO)(CO) 2 (Cp) 2 ] ( 3 ) arising from nucleophilic attack at the bridging carbon and SMe 2 displacement. Likewise, 2a , b react with the sodium salt of dimethylmalonate, diethylmalonate, ethylacetoacetate, 2,4-pentanedione, dibenzoylmethane and benzylcyanide, resulting in the formation of the corresponding functionalized μ-alkylidene complexes [Fe 2 {μ-C(X)R}(μ-CO)(CO) 2 (Cp) 2 ] ( 5 – 7 ) (X=CN, H; R=CH(COOMe) 2 , CH(COOEt) 2 , CH(COOMe)(COMe), CH(COMe) 2 , CH(COPh) 2 , CH(Ph)CN). The dichetone adducts [Fe 2 {μ-C(X)CH(COR) 2 }(μ-CO)(CO) 2 (Cp) 2 ] (X=CN, H; R=Me, Ph) undergo deacylation upon treatment with alumina, leading to the formation of the complexes [Fe 2 {μ-C(X)CH 2 C(O)R}(μ-CO)(CO) 2 (Cp) 2 ]. Reactions of 2a , b with LiBu or PhLi result in the formation the metallacycles [Fe 2 {μ-C(X)S(Me) CH 2 }(μ-CO)(C O)(CO)(Cp) 2 ] (X=CN, 4a ; H 4b ) which arise from the deprotonation of an SMe group and the intramolecular addition at a terminally coordinated carbonyl. Finally, a comparison of the reactivity of 2a , b with that of the μ-carbyne diiron complexes [Fe 2 (μ-CX)(μ-CO)(CO) 2 (Cp) 2 ]SO 3 CF 3 (X=H, SMe, NMe 2 ) is presented.

Synthesis and reactions of the novel sulfonium-methylidene complex [Fe2(CO)2(cp)2(μ-CO){μ-C(H) (SMe2)}]SO3CF3

Abstract The reaction of [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(H)(SMe)}] (cp=η-C 5 H 5 ) with MeSO 3 CF 3 forms the sulfonium-methylidene complex [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(H)(SMe 2 )}]SO 3 CF 3 ( 3 ). Compared to Caseys methylidyne complex [Fe 2 (CO) 2 (cp) 2 (μ- CO)(μ-CH)]PF 6 ( 1 ), compound 3 appears to be more stable and easier to handle, still maintaining a reactivity centered at the μ-carbon. In fact 3 undergoes replacement of SMe 2 by a variety of nucleophiles X, at room temperature, affording the corresponding cationic [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(H)(X)}]SO 3 CF 3 (XNMe 3 , PMe 3 , PPh 3 , PHPh 2 ) or neutral [Fe 2 (CO) 2 (cp) 2 (μ- CO){μ-C(H)(X)}] (XH − , MeO − , CN − ) μ-methylidene derivatives, in good yield. The phosphonium complex [Fe 2 (CO) 2 (cp) 2 (μ- CO){μ-C(H)(PHPh 2 )}]SO 3 CF 3 has been deprotonated with NEt 3 to yield the novel phosphino-methylidene complex [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(H)(PPh 2 )}]. The presence of the SMe 2 moiety in 3 reduces, compared to 1 , the electrophilic character of the μ-C carbon, as evidenced by the reaction with styrene.

Further applications of the NCO− insertion into a CSR bond: Synthesis of the bis(μ-acylisocyanide) complex [Fe2(CO)2(Cp) 2{μ-CNC(O)SMe}2]

Abstract The complex [Fe 2 (CO) 2 (Cp) 2 (μ-CS)(μ-CSMe)]SO 3 CF 3 ( 1 ) reacts with N n Bu 4 NCO to give [Fe 2 (CO) 2 (Cp) 2 (μ-CS){μ-CNC(O)SMe}] ( 2 ). This reaction has been carried out separately for both the cis and trans isomers of 1 . Complex cis - 2 undergoes S -methylation with MeOSO 2 CF 3 affording the novel thiocarbyne derivative [Fe 2 (CO) 2 (Cp) 2 (μ-CSMe) {μ-CNC(O)SMe}]SO 3 CF 3 ( 3 ), into which in turn an additional NCO − anion inserts to yield the bis(μ-acylisocyanide) complex [Fe 2 (CO) 2 (Cp) 2 {μ-CNC(O)SMe} 2 ] ( 4 ). All the reactions described are stereospecific and the derivatives 2–4 do not exhibit cis-trans isomerization.

Dithiocarbamate derivatives of μ-thiocarbyne complexes: synthesis and X-ray molecular structure of [Fe2(μ-CS)(μ-CSMe)(μ-S2CNMe2)Cp2]

Abstract Reaction of [Fe 2 (μ-CS)(μ-CSMe)Cp 2 (CO) 2 ] + ( 1 ) with sodium N , N -dimethyldithiocarbamate [Me 2 dtc]Na affords a mixture of the dithiocarbene [Fe Fe(μ-CS){μ-C(SMe)S C(S)NMe 2 }Cp(CO)] ( 2 ) and the thiocarbyne [Fe 2 (μ-CS)(μ-CSMe)(μ-S 2 CNMe 2 )Cp 2 ] ( 3 ). Complex 2 is quantitatively converted into 3 by photochemical irradiation. The X-ray molecular structure of 3 demonstrates the presence of three bridging ligands and exhibits the shortest FeFe interaction found in similar systems [2.453(1) A]. Complex 3 can also be obtained by reacting [Me 2 dtc] − with the di-solvento thiocarbyne [Fe 2 (μ-CS)(μ-CSMe)(NCMe) 2 Cp 2 ] + ( 1a ). By contrast no stable addition product has been isolated in analogous reactions involving the thiocarbyne [Fe 2 (μ-CO)(μ-CSMe)Cp 2 (CO) 2 ] + ( 1b ). The [Me 2 dtc] − nucleophilic addition at the μ-C to form [Fe 2 (μ-CO){μ-C(CN)SC(S)NMe 2 }Cp 2 (CO) 2 ] ( 4a ) is obtained starting from [Fe 2 (μ-CO){μ-C(CN)(SMe 2 )}Cp 2 (CO) 2 ]SO 3 CF 3 ( 1d ). Photochemical reaction of the cyanocarbene 4a causes intramolecular ring closure affording [Fe Fe(μ-CO){μ-C(CN)S C(S)NMe 2 }Cp 2 (CO)] ( 5a ).

A new route to diiron bis(µ-thiocarbene) complexes: molecular structure of [{Fe{µ-C(CN)SMe](cp)}2](cp =η-C5H5) containing the unusually folded six-membered metallacycle Fe2C2S2

The bis(µ-thiocarbene)[(cp)(OC)Fe{µC(CN)SMe}{µ-C([graphic omitted]e(cp)](X = H or CN; cp =µ-C5H5) and all the intermediate species obtained from the thiocarbyne derivative cis-[Fe2(µ-CS){µ-C(SMe)}(CO)2(cp)2]-[SO3CF3]viaµ-C stereoselective addition of X–, photochemical formation of [(cp)[graphic omitted]Me)X}(µ-CS)Fe-(CO)(cp)] followed by stepwise addition of MeSO3CF3 and (NBu4n)CN at the bridging CS group have been prepared and characterized. Attempts to obtain the bis(µ-thiocarbene)[{Fe[µ-C(CN)SMe](CO)(cp)}2] failed. The crystal structure of [{[graphic omitted]Me](cp)}2] which demonstrates the presence of two doubly bridging thiocarbene groups has been determined. The results show that bis(µ-thiocarbene) derivatives are stable when at least one of the ligands acta as a double bridge via a S–Fe bond.

Fischer type carbene ligands in dinuclear complexes

A large number of iron and ruthenium dinuclear complexes containing heteroatom substituted carbene ligands have been obtained by two different synthetic routes. The first method consists in reacting heteroatom substituted μ-carbyne cationic complexes with CN− ion. The second involves the displacement of the SMe2 molecule in the sulfonium [Fe2{μ-C(CN)(SMe2)}(μ-CO)(CO)2CP2]SO3CF3 by appropriate nucleophilesX− (X=OR, SR, NR2, PR2). Spectroscopic (IR, NMR) and structural investigations together with reactivity studies on these complexes have greatly contributed to better understanding the factors which favor bridging vs. terminal coordination of heteroatom substituted carbene ligands.