Models for the Homogeneous Hydrodesulfurization of Benzothiophenes. Carbon−Sulfur Bond Cleavage, Hydrogenolysis, and Desulfurization Reactions Mediated by Coordination of the Carbocyclic Ring to Manganese and Ruthenium (original) (raw)
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Inorganic Chemistry, 1991
Several Scoordinatcd 2,Sdihydrothiophene (2,5-DHT) transition-metal complexes were synthesized in order to determine whether or not this type of coordination promotes butadiene elimination from the 2,5-DHT ligand, a step proposed in a mechanism for the hydrodesulfurization (HDS) of thiophene. Thermal decomposition of W(C0)'(2,5-DHT) and Re2(C0)9(2,5-DHT) at 1 10 M OC liberates butadiene and free 2,S-DHT (relative ratio 1:4), Uncoordinated 2,5-DHT itself does not decompose at 120 OC after 3 days. Thus, S-coordination of 2,5-DHT to these metal centers does promote the liberation of butadiene. Upon being heated at 180 OC, MC12(2,5-DHT)2 (M = Pd, Pt) gives off mainly thiophene and free 2,5-DHT (1:l) with only a small amount of butadiene. Thus, depending on the complex either butadiene or thiophene may be evolved. The reaction of R U , (C O)~~ with 2,5-DHT forms the trinuclear (fi2-H)R~J(CO)9(pJ-l-4-?4-DHT), whose X-ray structure determination shows that the sulfur and olefin of the 2,5-DHT coordinate to two different ruthenium atoms but also C-H cleavage occurs at C(2) forming a C-Ru bond. The structure of an S-coordinated DHT complex [Cp(PMe3),Ru(2,5-DHT)](PF6) is also reported.
Journal of the American Chemical Society, 2008
All manipulations were performed using a combination of glovebox, high vacuum, and Schlenk techniques under an argon atmosphere unless otherwise specified. S1 Solvents were purified and degassed by standard procedures. 1 H NMR spectra were measured on Bruker 300 DRX, Bruker 400 DRX, and Bruker Avance 500 DMX spectrometers. 1 H chemical shifts are reported in ppm relative to SiMe 4 (δ = 0) and were referenced internally with respect to the protio solvent impurity (δ 7.16 for C 6 D 5 H; S2 2.09 for C 6 D 5 CHD 2 S3). 2 H NMR spectra are reported in ppm relative to C 6 H 5 D (δ 7.16). 13 C NMR spectra are reported in ppm relative to SiMe 4 (δ = 0) and were referenced internally with respect to the solvent (δ 128.06 for C 6 D 6). S2 31 P chemical shifts are reported in ppm relative to 85% H 3 PO 4 (δ = 0) and were referenced using P(OMe) 3 (δ = 141.0) as an external standard. Coupling constants are given in hertz. Infrared spectra were recorded on Nicolet Avatar 370 DTGS spectrometer and are reported in cm-1. Mass spectra were obtained on a Micromass Quadrupole-Time-of-Flight mass spectrometer using fast atom bombardment (FAB). Mo(PMe 3) 6 , S4 d 1-2-D-benzothiophene S5 and d 1-3-D-benzothiophene S6 were prepared by literature methods or modifications thereof. The isotopic composition of the deuterated benzothiophenes was analyzed by mass spectroscopy. Benzothiophene and selenophene were obtained from Aldrich. Benzoselenophene was obtained from Acros Organics. Reaction of Mo(PMe 3) 6 with benzothiophene (i) Room temperature reaction A mixture of Mo(PMe 3) 6 (12 mg, 0.022 mmol) and benzothiophene (3 mg, 0.022 mmol) in an NMR tube equipped with a J. Young valve was treated with C 6 D 6 (0.6 mL). The reaction was monitored by 1 H NMR spectroscopy, thus revealing the immediate formation of paramagnetic Mo(κ 2-CHCHC 6 H 4 S)(PMe 3) 4 , followed by isomerization to Mo(κ 1 ,η 2-CH 2 CHC 6 H 4 S)(η 2-CH 2 PMe 2)(PMe 3) 3 and Mo(κ 1 ,η 2-CH 2 CC 6 H 4 S)(PMe 3) 4 in a ca.
Journal of The American Chemical Society, 1995
The fragment [(triphos)RhH], generated by thermolysis of (triphos)RhH3 (1) in refluxing THF, reacts with thiophene (T) or benzo[b]thiophene (BT) to yield (triphos)Rh(q3-SCH=CH-CH=CHz) (2) and (triphos)Rh-{ v3-S(C6&)CH=CH2} (3), respectively [triphos = MeC(CH2PPh&]. Compound 2 is selectively protonated at the terminal metal-bonded carbon atom (CZ) by HBF4.OEtz to give, after anion exchange, the v4-C,C,C,S-thiocrotonaldehyde complex anti-[(triphos)Rh{v4-SCHCHCH(CH3)}]BPb (4), which reacts with CO to yield [(triphos)Rh(CO)-{T,~-S=CH-CH=CH(CH~)}]BP~ (5) and thermally isomerizes to syn-[(triphos)Rh{v4-SCHCHCH(CH3)}]BPb (6) in solution. Complex 4 also reacts with Me1 by selective delivery of Me+ to the sulfur atom to give, after anion exchange, [(triphos)Rh(y3-MeSCH=CH-CH=CHz)]BPb (7). On the other hand, Ph$+ selectively attacks the CZ carbon atom to yield [(triphos)Rh{v4-SCHCHCH(CH2CPh3)}]PF6 (S), whose structure has been determined by X-ray diffraction. Complex 8 crystallizes in orthorhombic space group P212121 (no. 19) with a = 10.834(6) A, b = 15.012-(6) A, c = 39.902(9) A, 2 = 4, and V = 6489.66 A3. The cation [(triphos)Rh(q4-SCHCHCH(CHzCPh3)}]+ presents a distorted square pyramidal structure with one P atom occupying the apical position, while the remaining two P atoms plus the C6-S and the C7-C8 bonds occupy the basal sites; the C8 atom bears the trityl substituent. The vinylthiophenolate complex 3 is also selectively protonated at CZ with HBF4.OEt2 to yield [(triphOS)Rh{v4-s(c61&)-CH(CH3)}]BPb (9), which undergoes an intramolecular hydrogen shift from carbon to sulfw slowly at room temperature and rapidly in refluxing THF to produce [(triphos)Rh( q3-HS(C&)CH=CH2}]BPb (10); complex (10) is deprotonated by t-BuOK to reform 3. As in the case of 2, Me1 and Ph3CPF6 react with 3 by selective attack of S and C, yielding [(tripho~)Rh(~~-MeS(C6b)CH==CH~}]BPh4 (11) &d [(triphos)Rh{v4-S(C61&)CH(CH2CPh3)}]-PF6 (12), respectively. All the rhodium complexes obtained by addition of electrophiles to 2 or 3 upon treatment with CO quantitatively transform into [(triphos)Rh(C0)2]Y (Y = B P b , PFs), liberating the thio ligands in solution.
Organometallics, 1994
A series of ql(E)-coordinated (E = S or Se) thiophene, benzo[blthiophene and selenophene complexes [Cp(NO)(PPh3)Re(q1(E)-L)1+, Cp = C5H5, L = thiophene (TI, 2-methylthiophene (2-MeT), 2,5-dimethylthiophene (2,5-MezT), benzo[blthiophene (BT), 3-methylbenzo[blthiophene (3-MeBT), selenophene (Sel), 2-methylselenophene (2-MeSel), and 2,5-dimethylselenophene (2,5-MezSel) are prepared by the reaction of [Cp(NO)(PPhs)Re(ClCsH5)1+ with the appropriate ligand. The T, 2-MeT, BT, 3-MeBT, Sel, 2-MeSel complexes are deprotonated a t C(2) by strong, non-nucleophilic bases to give the neutral Cp(NO)(PPh3)Re(2-L-y1) complexes, where 2-L-yl= 2-thienyl(2-Tyl), 245-methylthienyl) (2-(5-MeTyl)), 2-benzothienyl (2-BTyl), 2-(3-methylbenzothienyl) (2-(3-MeBTyl)), 2-selenyl (2-Selyl), and 2-(5-methylselenyl) (245-MeSelyl)). The pKa of the base required to effect this deprotonation increases with the L ligand in the complex in the following order: Sel < T < BT. The 2-Ty1, 2-BTy1 and 2-Selyl complexes react with either HBFgEtzO or H03SCF3 a t-42 "C to give the corresponding carbene complexes [Cp(NO)(PPh3)Re(2-L-ylcarbene)l+ resulting from protonation a t C(3). The molecular structure of [Cp(NO)(PPh3)Re(2-BTylcarbene)lO3SCF3, as determined by a n X-ray diffraction study, exhibits a Re=C bond distance of 1.992(7) A. The carbene complexes do not react with nucleophiles; however, those nucleophiles that are sufficiently basic deprotonate C(3) to give back the L-yl compound. The pKa values of bases that are strong enough to cause deprotonation increase with the L-ylcarbene ligand in the order: Selylcarbene-Tylcarbene < BTylcarbene. The carbene complexes [Cp(NO)(PPh& Re(2-(5-MeTylcarbene)l+ and [Cp(NO)(PPh3)Re(2-(5-MeSelylcarbene)l+ are unstable and rearrange to their more stable isomers [Cp(NO)(PPh3)Re(r11(S)-2-MeT)lf and [Cp(NO)(PPh3)-Re(q1(Se)-2-MeSel)l+. A new mechanism for H/D exchange of thiophene on hydrodesulfurization catalysts is proposed based on deuterium labeling studies of these thiophene complexes.
Organometallics, 2005
Treatment of the electronically unsaturated cluster Os 3 (CO) 8 (µ 3-η 2-Ph 2 PCH 2 P(Ph)C 6 H 4)-(µ-H) (1) with benzothiophene in refluxing m-xylene afforded Os 3 (CO) 7 (µ-PPh 2)(µ-PMePh)-(µ 3-η 2-C 6 H 4) (2), Os 3 (CO) 7 (µ 3-η 2-PPh(C 6 H 4)CH 2 PPh)(µ 3-η 3-SC 8 H 5)(µ-H) (3), and Os 3 (CO) 8 (µ-CO)(µ 3-η 2-PPh(C 6 H 4)CH 2 PPh) (4). Thermolysis of 1 in refluxing toluene for 35 h afforded only 4, whereas in refluxing m-xylene it gave both 4 and 2. Compound 4 can also be obtained from the thermolysis of Os 3 (CO) 9 (µ 3-η 2-PPh(C 6 H 4)CH 2 PPh 2)(µ-H) (5) in refluxing toluene. All the complexes have been structurally characterized. Compound 3 contains a unique example of a µ 3-η 2 benzothienyl ligand coordinated through the sulfur atom and the CC double bond of the five-membered ring in a σ,π vinyl fashion. This coordination mode results in the rupture of one osmium-osmium bond, whereas the basic triangular metal framework is retained in the case of 2 and 4, which are derived from the activation of P-C and C-H bonds of 1 and do not contain any benzothiophene-derived ligand.
Carbon-Sulfur Bond Cleavage in Thiophene by Group 6 Metallocenes
Organometallics, 1994
Photolysis of CpzMoHz in t h e presence of thiophene leads to the formation of t h e C-H insertion product Cp~Mo(2-thienyl)H as the sole product, which was characterized by conversion to the chloro derivative CpzMo(2-thieny1)Cl. Photolysis of CpZWHz in the presence of thiophene leads to the initial formation of the C-S insertion product CpzWSCH=CHCH=CH. Continued irradiation results in the conversion of this adduct to the C-H insertion product Cp~W(2-thienyl)H. Thermal reaction of CpzW(CH3)H with thiophene gives both C-S a n d-C-H insertion products in a n 11:l kinetic ratio. The complex CpzWSCH=CHCH=CH crystallizes in orthorhombic space group Pbca (No. 61) with a = 7.713(6) A, b = 13.636(5) A, c = 22.290(7) A, V = 2344.4(3.3) Hi3, Z = 8. Introduction The reactions of thiophenes with transition metal complexes has been under investigation recently as a means of modeling the initial steps in the hydrodesulfurization process. A variety of q4 and q5 complexes of thiophene have been prepared and structurally characterized,l some of which react with nucleophiles to give ring-opened products.2 Several other metal complexes have been found to directly cleave the C-S bond, giving metallacycle product^.^-^ The first such report involved the reaction of iron carbonyl with thiophene to give a dinuclear structure (Scheme la).6 The reaction of Cp*Co(CzH4)2 with thiophene and dibenzothiophene gives similar dinuclear products (Scheme lbh7 The q4-thiophene complex Cp*Ir(q4-C4HzMezS) was found to rearrange to the C-S insertion product upon chromatography on basic alumina (Scheme lcL3 The reaction of the reactive fragment [Cp*Rh(PMedI with thiophene was found to give
Journal of the American Chemical Society, 1991
Reactions of the isomers Cp*Ir(v4-2,5-Me2T) (1) and Cp*Ir(CS-2,5-Me2T) (2), where Cp* = qS-C5MeS and 2,5-Me2T = 2,5-dimethylthiophene, with iron carbonyls (Fe(CO)5, Fe2(C0)9, and Fe3(CO),2) give eight different products, 310. Two of them, Cp*Ir(q4-2,5-Me2T.Fe(C0),) (3) and Cp*Ir(v4-2,5-Me2T.Fe2(CO),) (7), retain the v4-2,5-Me2T coordination to the Ir but are also bonded through the sulfur to the Fe atom(s). Both 1 and 2 react with Fej(CO),, to give 8 in which all of the elements of 2,5-Me2T are present but the sulfur has been removed from the thiophene ring. Reaction of 8 with CO (1 atm) 1 2 8 9 gives the totally desulfurized 9. A new mechanism is proposed for thiophene hydrodesulfurization (HDS) based on the C-S bond cleavage reactions which occur when 1 rearranges to 2 and 2 is converted to 8. Structures of 3,7,8, and 9 were established by X-ray diffraction studies. On the basis of organometallic model compound and catalytic reactor studies, a mechanism (Scheme I) was proposed2J in these laboratories for the transition-metal-catalyzed hydrodesulfurization (HDS) of thiophene to give HIS and C4 hydrocarbons. The actual desulfurization step (Scheme I), which involves C-S bond cleavage, occurs after thiophene is partially hydrogenated to dihydrothiophene. Very recently4 we observed another type of C-S bond cleavage (eq 1) in thiophene itself. In this base-catalyzed rearrangement, the iridium in Cp*Ir(q4-2,5-Me2T) (1) inserts into