The ReH6[P(C6H5)3]2 ion as a ligand: complexes with M(CO)3 fragments (M = Cr, Mo, W)

The reactions of [(H₅C₆)₃P]₂ReH₆⁻ with (CH₃CN)₃Cr(CO)₃, (diglyme)Mo(CO)₃ or (C₃H₇CN)₃W(CO)₃ led to the formation of [(H₅C₆)₃P]₂ReH₆M(CO)₃⁻ (M = Cr, Mo, W) complexes. These have been characterized by IR and NMR spectroscopies, as well as elemental analyses. A single crystal X-ray diffraction study has also been carried out for the M = Cr complex as a K(18-crown-6)⁺ salt. The complex crystallizes as a THF monosolvate in the monoclinic space group P2₁/n with a = 22.323(6), B = 9.523(2), C = 27.502(5) Å, β = 104.98(2)⁰ and V = 5648 ų for Z = 4. The Re---Cr separation is 2.5745(12) Å, and the two phosphine ligands are oriented unsymmetrically. Although the hydride ligands were not found, the presence of three bridging hydrides and a dodecahedral coordination geometry about rhenium could be inferred. Low temperature ¹H and ³¹P NMR spectroscopic studies did not reveal the low symmetry of the solid state structure.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

Mixed-metal butterfly acetamidediato clusters derived from a highly reactive ruthenium oxo cluster: synthesis and characterization of [(PPh3)2N][MRu3(CO)12(η-μ3-NC(μ-O)CH3)], (M = Mn or Re)

Analogy with the isolable oxo cluster [Fe₃(CO)₉(μ₃-O)]²⁻, which is structurally interesting and synthetically useful, prompted the present attempt to synthesize its ruthenium analog. Although the high reactivity of [Ru₃(CO)₉(μ₃-O)]²⁻ (I) prevented its isolation, the reaction of this species with [M(CO)₃(NCCH₃)]⁺, where M = Mn or Re, yields [PPN][MRu₃(CO)₁₂(η²-μ₃-NC(μ-O)CH₃]⁻. The high nucleophilicity of the oxo ligand in [Ru₃(CO)₉(μ₃-O)]²⁻ (I) appears to be responsible for the conversion of acetonitrile to an acetamidediato ligand and for the instability of I. The crystal structure of [PPN][MnRu₃(CO)₁₂(η²-μ₃-NC(μ-O)CH₃)]] reveals a hinged butterfly array of metal atoms in which the acetamidediato ligand bridges the two wings with μ₃-N bonding to an Mn and two Ru atoms, and μ-O bonding to an Ru atom.     

The new enneanuclear nickel carbonyl anion [Ni9(CO)16] and its relationships with the [Ni12(CO)21] and [Ni6Rh3(CO)17] clusters

The reaction of [N(PPh₃)₂]₂[Ni₆(CO)₁₂] with Cu(PPh₃)_xCl (x=1, 2), as well as the degradation of [N(PPh₃)₂]₂[H₂Ni₁₂(CO)₂₁] with PPh₃, affords the new and unstable dark orange–brown [N(PPh₃)₂]₂[Ni₉(CO)₁₆].THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni₉(CO)₁₆]²⁻ dianion is directly related to that of the bimetallic [Ni₆Rh₃(CO)₁₇]³⁻ trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni₁₂(CO)₂₁]⁴⁻ by the substitution of one of the two outer [Ni₃(CO)₃(μ−CO)₃]²⁻ layers with a face-bridging carbonyl group.     

CO substitution and diphosphine ligand chelation in the reaction between 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Re(2(CO)8(μ-H)(μ-η,η-C CPh)

The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and the dirhenium compound Re₂(CO)₈(μ-H)(μ-η¹,η²-C CPh) in CH₂Cl₂ at room temperature proceeds by CO loss to give the dirhenium complex Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) (1). This new complex was characterized in solution by IR and NMR (¹H and ³¹P) spectroscopy and in the solid state by X-ray diffraction analysis. Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) crystallizes in the triclinic space group

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γ = 69.240(6)°, V = 2024.9(3) ų, Z = 2, d_calc = 1.862 g cm⁻³ R = 0.0221, R_w = 0.243 for 4066 observed reflections. The bpcd ligand in 1 adopts a chelating mode with a linear phenylacetylide ligand being located on the adjacent rhenium center cis to the bpcd ligand. This complex represents the first structurally characterized example of a hydrido-bridged dirhenium complex possessing both a linear acetylide ligand and a chelating diphosphine ligand.     

Ligand connected metal clusters. The molecular structures and solid state packing of {Ru3(CO)11}2(bis(diphenylphosphino)ethane) and {Ru3(CO)11}2(1,4-bis(diphenylphosphino)benzene)

The preparation and structural characterization of {Ru₃(CO)₁₁}₂(1,4-bis(diphenylphosphino)benzene), a modified synthesis of 1,4-bis(diphenylphosphino)benzene, and the structural characterization of {Ru₃(CO)₁₁}₂(bis(diphenylphosphino)ethane) are reported. In both compounds two metal cluster units are connected through ditertiary-phosphine ligands. Both molecules consist of centrosymmetric units in which the diphosphine ligands are largely covered by the triangular ruthenium clusters. No direct interaction between the two cluster units occurs within individual molecules. Molecular packing in the solid state is dominated by interactions between sets of carbon monoxide ligands in motifs that were previously identified in the solid state structure of the parent cluster, Ru₃(CO)₁₂.     

Five-coordinate rhenium(III)-thiolato complexes: the structure of [Re(SCH2PhOCH3)3(PPh3)2]

A novel five-coordinate rhenium(III)-thiolato complex, Re(SCH₂C₆H₄OCH₃-p)₃(PPh₃)₂ has been isolated during the reaction of trans-ReOCl₃(PPh₃)₂ with p-methoxybenzyl mercaptan. In the unexpected structure that was acquired, the central metal has undergone a reduction from Re(V) to Re(III). The five-coordinate Re(III) complex has been characterized by spectroscopic methods, elemental analysis and X-ray crystallography. X-ray crystallographic studies showed the coordination geometry around rhenium to be that of a trigonal bipyramid. The basal plane is defined by three sulfur atoms of the monodentate ligand, while the two apical positions are occupied by two phosphines of the precursor.     

The structure of (η-C6H5Cl)Cr(CO)2PPh3

In a synthetic route that varies from the standard procedure requiring irradiation, the (η⁶-C₆H₅Cl)Cr(CO)₂PPh₃ complex is obtained upon reacting (η⁶-C₆H₅Cl)Cr(CO)₃ with tetrakis(triphenylphosphine)palladium(0), CuI, and trimethylsilylphenylacetylene in triethylamine. The X-ray crystal structure of the yellow–orange crystals of (η⁶-C₆H₅Cl)Cr(CO)₂PPh₃ allows structural comparisons to related (arene)Cr(CO)₂PR₃ complexes.     

Thermal and photochemical substitution reactions of CpRe(PPh3)2H2 and CpRe(PPh3)H4. Catalytic insertion of ethylene into the C-H bond of benzene

The thermal and photochemical reactions of CpRe(PPh₃)₂H₄ and CpRe(PPh₃)H₄ (Cp = η⁵-C₅H₅) with PMe₃, P(p-tolyl)₃, PMe₂Ph, DMPE, DPPE, DPPM, CO, 2,6-xylylisocyanide and ethylene have been examined. While CpRe(PPh₃)₂H₂ is thermally inert, it will undergo photochemical substitution of one or two PPh₃ ligands. With ethylene, substitution is followed by insertion of the olefin into the C-H bond of benzene, giving ethylbenzene. CpRe(PPh₃)H₄ undergoes thermal loss of PPh₃, which leads to substituted products of the type CpRe(L) H₄. Photochemically, reductive elimination of dihydrogen occurs preferentially. The complex trans-CpRe(DMPE)H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 6.249(6), b = 16.671(8), c = 13.867(7) Å, β = 92.11(6)°, V = 1443.7(2.9) Å and Z = 4. The complex trans-CpRe(PMe₂Ph)₂H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 7.467(3), b = 23.874(14), c = 11.798(6) Å, β = 100.16(4)°, V = 2070.2(3.4) ų and Z = 4.     

Synthesis of monoamine derivatives of [Ir4(CO)12]. X-ray crystal structure of [Ir4(CO)11(4-picoline)]

The mono-substituted amine derivatives [Ir₄(CO)₁₁L] (L = pyridine (1), 4-methylpyridine (2), 4-ter-butyl pyridine (3), 3,5-dimethylpyridine (4), 3,4-dimethylpyridine (5)) were obtained by the reaction of [Ir₄(CO)₁₁Br]⁻ with the corresponding aromatic amine. In the solid state, cluster 2 has an approximate C_s symmetry with all terminal ligands as shown by an X-ray analysis. In solution, this unbridged structure is in dynamic equilibrium with two other isomeric forms having three edge-bridging CO’s on a common basal face and the amine ligand coordinated in axial or in radial position relative to this face.     

Rhenium(IV) cyanate complexes: Synthesis, crystal structures and magnetic properties of NBu4[ReBr4(OCN)(DMF)] and (NBu4)2[ReBr(OCN)2(NCO)3]

Two new rhenium(IV) mononuclear compounds of formula NBu₄[ReBr₄(OCN)(DMF)] (1) and (NBu₄)₂[ReBr(OCN)₂(NCO)₃] (2) (NBu₄ = tetrabutylammonium cation, OCN = O-bonded cyanate anion, NCO = N-bonded cyanate anion and DMF = N,N-dimethylformamide) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with the space group P2₁/n, whereas 2 crystallizes in the triclinic one with as space group. In both complexes the rhenium atom is six-coordinated, in 1 by four Br atoms in the equatorial plane, and two trans-oxygen atoms, one of a DMF molecule and another one from a cyanato group, while in 2 by one bromide anion and five cyanate ligands, two of which are O-bonded and three N-bonded, forming a somewhat distorted octahedral surrounding. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field splitting (|2D| is ca. 41.6 and 39.2 cm⁻¹ for 1 and 2, respectively).     

Heats of reaction of HMo(CO)3(C5R5) (R = H, CH3) with diphenyldisulfide and of formation of the clusters [PhSMo(CO)x(C5H5)]2, X = 1,2. Thermodynamic study of molybdenum-sulfur bond strengths

The enthalpies of reaction of HMo(CO)₃C₅R₅ (R = H, CH₃) with diphenyldisulfide producing PhSMo(CO)₃C₅R₅ and PhSH have been measured in toluene and THF solution (R = H, ΔH= −8.5 ± 0.5 kcal mol⁻¹ (tol), −10.8 ± 0.7 kcal mol⁻¹ (THF); R = CH₃, ΔH = −11.3±0.3 kcal mol⁻¹ (tol), −13.2±0.7 kcal mol⁻¹ (THF)). These data are used to estimate the Mo---SPh bond strength to be on the order of 38–41 kcal mol⁻¹ for these complexes. The increased exothermicity of oxidative addition of disulfide in THF versus toluene is attributed to hydrogen bonding between thiophenol produced in the reaction and THF. This was confirmed by measurement of the heat of solution of thiophenol in toluene and THF. Differential scanning calorimetry as well as high temperature calorimetry have been performed on the dimerization and subsequent decarbonylation reactions of PhSMo(CO)₃Cp yielding [PhSMo(CO)₂Cp]₂ and [PhSMo(CO)Cp]₂. The enthalpies of reaction of PhSMo(CO)₃Cp and [PhSMo(CO)₂Cp]₂ with PPh₃, PPh₂Me and P(OMe)₃ have also been measured. The disproportionation reaction: 2[PhSMo(CO)₂Cp]₂ → 2PhSMo(CO)₃Cp + [PhSMP(CO)Cp]₂ is reported and its enthalpy has also been measured. These data allow determination of the enthalpy of formation of the metal-sulfur clusters [PhSMo(CO)_nC₅H₅]₂, N = 1,2.     

Chiroptical properties of heterotrimetallic ‘wing-tip’ butterflies; synthesis and crystal structure of (μ-H)Ru2Fe2PdC(CO)12 (η-ß-C10H15)

HRu₂Fe₂PdC(CO)₁₂ (η³-ß-C₁₀H₁₅) cluster was prepared in the reaction of (Et₄N) [HFe₂Ru₂C(CO)₁₂] with [Pd(η³-ß-C₁₀H₁₅)Cl]₂. X-ray structural study of HRu₂Fe₂PdC(CO)₁₂ (η³-ß-C₁₀H₁₅) (where ß-C₁₀H₁₅ is ß-pinenyl) revealed a wing-tip butterfly geometry of the metal core and (1R, 2S, 3S, 5R) absolute configuration for both crystallography independent molecules in the crystal. Chiroptical properties of this cluster are compared with other clusters containing a Pd(η³-ß-C₁₀H₁₅) fragment and discussed.     

Main group derivatives of a cyclometallated iron carbonyl anion. Crystal structures of Fe(CO)2{P(OPh)3}{(PhO)2POC6H4}(SnPh3) and two isomers of Fe(CO)2{P(OPh)3}{(PhO)2POC6H4}(I)

The iron hydrido complex HFe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄} (1), was rapidly deprotonated by DBU or [BzMe₃N][OH] in THF to afford the new carbonyl iron anion [Fe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄}]⁻ ([2]⁻), containing an ortho-metallated triphenyl phosphite ligand. Complex [2]⁻ reacted with triorganostannyl and plumbyl salts and with halogens to give the octahedral Fe^II compounds Fe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H₄}(X) (X=SnPh₃, 3; SnMe₃, 4; PbPh₃, 5; PbMe₃, 6; Cl, 7; Br, 8; I, 9). The Group 14 complexes 3-6 were obtained in one isomeric form in which the P^III-donor atoms are mutually cis, the carbonyl ligands are cis and the P(OPh)₃ and MR₃ (M=Sn, Pb; R=Ph, Me) groups are trans as determined by solution-state IR, ³¹P and ¹³C NMR spectroscopic data. This geometry was confirmed for 3 by a single crystal X-ray diffraction study. The halide complexes, however, were obtained as a mixture of isomers. The major isomer (7, X=Cl; 8a, X=Br; 9a, X=I) has cis P atoms, trans CO groups and the halide located trans to the phosphorus atom of the ortho-metallated phosphite ligand. The structure of 9a was confirmed by an X-ray diffraction study. Two other isomers, designated 8b (X=Br) and 9b (X=I), with cis P atoms and cis CO groups were isolated from the reactions of [2]⁻ with Br₂ and I₂, respectively. The structure of the latter was established by X-ray crystallography and is related to 9a by exchange of the P(OPh)₃ ligand and a carbonyl group such that the metal-bound C atom of the five-membered metallacycle is trans to CO. The stereo-geometry of 8b could not be unambiguously assigned from the spectroscopic data; however, two of the seven possible geometric isomers were suggested as plausible structures.     

Synthesis and structures of the cuboidal iron-sulfur-nitrosyl-phosphine clusters [Fe4S3(NO)4(PR3)3] (R = Et, Pr, C6H11)

A series of cuboidal iron-sulfur clusters [Fe₄S₃(NO)₄(PR₃)₃]^0,1+ (R = Et, Prⁱ, Cy) were synthesized by two routes: reductive desulfurization of [Fe₄S₄(NO)₄] by tertiary phosphines, and substitution of triphenylphosphine in [Fe₄4S₃(NO)₄(PPh₃)₃] by a more basic phosphine. The structures of 3[Fe₄S₃(NO)₄(PEt₃)₃] · 0.5Et₂O, [Fe₄S₃(NO)₄(PEt₃)₃] [Fe₄S₃(NO)₇] and partially substituted [Fe₄S₃(NO)₄(PPh₃)_2⁻ (PPrⁱ₃)] have been determined by X-ray diffraction in order to define the cuboidal Fe₄S₃ core, previously known only in Roussin's black anion and its reduced form, [Fe₄S₃(NO)₇7]^1−,2−, and as a part of the iron-molybdenum cofactor of nitrogenase.     

Synthesis and structural characterization of dinuclear iridium hydrido complex with 3,6-bis(2-pyridyl)tetrazine, [Ir2(H)4(PPh3)4(bptz)](PF6)2 · 4CH2Cl2

Reaction of the precursor Ir complex [Ir(H)₂(PPh₃)₂(Me₂CO)₂]PF₆ with 3,6-bis(2-pyridyl)tetrazine (bptz) in CH₂Cl₂ gave a novel dinuclear Ir hydrido complex [Ir₂(H)₄(PPh₃)₄(bptz)](PF₆)₂ · 4CH₂Cl₂. Crystallographic study described an interesting coordination environment having a π-π interaction and ¹H NMR study showed unique upfield shifts of pyridyl rings that are likely induced by the ring current effect of neighboring PPh₃ ligands.     

Photocatalyzed isomerization of 1-pentene by Ru3(CO)12 adsorbed onto porous Vycor glass

UV photolysis of Ru₃(CO)₁₂ physisorbed onto porous Vycor glass leads to the oxidative addition product (μ-H)Ru₃(CO)₁₀(μ-OSi). The latter reacts thermally with 1-pentene to form a stable adduct, HRu₃(CO)₁₀(OSi)(1-C₅H₁₀), and photolysis of the adduct results in isomerization of the alkene. HRu₃(CO)₁₀(OSi)(1-C₅H₁₀) + hv → (μ-H)Ru₃(CO)₁₀(μ-OSi) + 2-pentene As with other photoactivated hybrid systems, the cis-/trans-2-pentene product ratio changes during photolysis. Unlike the other systems, where light generates a thermal catalyst, the data gathered here indicate a photoassisted catalytic process in which photoactivation of HRu₃(CO)₁₀(OSi)(1-C₅H₁₀) leads to an excited state similar to a π-allyl complex.     

Syntheses and properties of organocyanamide, cyanoguanidine and dinitrogen complexes of rhenium. Crystal structure of mer-[ReCl2(NCNEt2) (PMePh2)3]

Treatment of a THF solution of trans-[ReCl(N₂)L₄] (L = PMePh₂) with a cyanamide, NCNR₂ (R = Me, Et or H) or with cyanoguanidine, NCNC(NH₂)₂ , yields mer-[ReCl(N₂)(NCNR₂)L₃] (1) or mer-[Re(N₂)[Re(N₂){NCNC(NH₂)₂}₂L₃]Cl (2), respectively, which, to our knowledge, are the first mixed dinitrogen-cyanamide-type complexes to be reported. The former products (1, R=Me or Et) can also be obtained from reaction of the benzoyldiazenido complex [ReCl₂(NNCOPh)L₃] with NCNR₂ in refluxing methanol; the Re(II) complex mer-[ReCl₂(NCNEt₂)L₃] (3) is also formed (conceivably via an unusual homolysis of the C---N bond of the benzoyldiazenido ligand) and its crystal structure is reported. It shows an unusual pyramidal conformation at the amine N atom of the diethylcyanamide ligand which also exhibits a significant structural trans influence on the phosphine, behaving as a stronger net electron donor than the latter ligand.     

Synthesis and characterization of SrCu2(O2CR)3(bdmap)3 and Bi2(O2CCH3)4(bdmap)2(H2O) (R = CH3, CF3; bdmap = 1,3-bis(dimethylamino)-2-propanolato)

New mixed metal complexes SrCu₂(O₂CR)₃(bdmap)₃ (R = CF₃ (1a), CH₃ (1b)) and a new dinuclear bismuth complex Bi₂(O₂CCH₃)₄(bdmap)₂(H₂O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF₂ and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi₂O₃ at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2J = 34.0(8) cm⁻¹. Crystal data for 1a: C₂₇H₅₁N₆O₉F₉Cu₂Sr/THF, monoclinic space group P2₁/m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) ų, Z = 2; for 1b: C₂₇H₆₀N₆O₉Cu₂Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) ų, Z = 8; for 2: C₂₂H₄₈O₁₁N₄Bi₂, monoclinic space group P2₁/c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) ų, Z = 4.     

Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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