Butterfly diradical intermediates in photochemical reactions of Fe2(CO)6(mu-S2)

Photolysis of the tetrahedrane Fe2(CO)6(mu-S2) at 450 +/- 35 nm in a Nujol matrix at low temperatures gives an isomer characterized by its nu(CO) infrared frequencies. Comparison of these experimental frequencies with those calculated by density functional theory using the BP86 functional indicates this photoisomer to be the butterfly singlet diradical Fe2(CO)6S2 isomer in which the S-S bond of the tetrahedrane is broken but the Fe-Fe bond is retained. Photolysis at higher energies (420-280 nm) results in CO loss from this singlet butterfly diradical as indicated again by comparison of the experimental infrared nu(CO) frequencies with those calculated for an Fe2(CO)5S2 isomer of this type.     

Oxidative addition of phosphine-tethered thiols to iron carbonyl: binuclear phosphinothiolate complexes, (mu-SCH(2)CH(2)PPh(2))(2)Fe(2)(CO)(4), and hydride derivatives

The mononuclear complex Fe(CO)(4)(PPh(2)CH(2)CH(2)SH), 1, is isolated as an intermediate in the overall reaction of PPh(2)CH(2)CH(2)SH with [Fe(0)(CO)(4)] sources to produce binuclear bridging thiolate complexes. Photolysis is required for loss of CO and subsequent S-H activation to generate the metal-metal bonded Fe(I)-Fe(I) complex, (mu-SCH(2)CH(2)PPh(2))(2)Fe(2)(CO)(4), 2. Isomeric forms of 2 derive from the apical or basal position of the P-donor ligand in the pseudo square pyramidal S(2)Fe(CO)(2)P coordination spheres. This position in turn is dictated by the stereochemistry of the mu-S-CH(2) bond, designated as syn or anti with respect to the Fe(2)S(2) butterfly core. Addition of strong acids engages the Fe(I)-Fe(I) bond density as a bridging hydride, [(mu-H)-anti-2](+)[SO(3)CF(3)](-) or [(mu-H)-syn-2](+)[SO(3)CF(3)](-), with formal oxidation to Fe(II)-H-Fe(II). Molecular structures of anti-2, syn-2, and [(mu-H)-anti-2](+)[SO(3)CF(3)](-) were determined by X-ray crystallography and show insignificant differences in distance and angle metric parameters, including the Fe-Fe bond distances which average 2.6 A. The lack of coordination sphere rearrangements is consistent with the ease with which deprotonation occurs, even with the weak base, chloride. The Fe(I)-Fe(I) bond, supported by bridging thiolates, therefore presents a site where a proton might be taken up and stored as a hydride without impacting the overall structure of the binuclear complex.     

NMR parameters of the tetrahedrane [Fe2(CO)6(μ-SNH)], studied by experiment and DFT

The intramolecular dynamic behavior of the tetrahedrane-type cluster [Fe₂(CO)₆(μ-SNH)] 1 was studied by ¹³C NMR spectroscopy. The ⁵⁷Fe chemical shift of 1 and the coupling constants ¹ J(⁵⁷Fe,¹³C) were measured. These NMR parameters, and also ¹ J(⁵⁷Fe,¹⁵N), were found to be in good agreement with data calculated by using density functional theory (DFT) methods (B3LYP), based on the geometry calculated at the 6-311+G(d,p) level of theory. The isolobal replacement of the Fe(CO)₃ with BH fragments leads to the tetrahedranes [Fe(CO)₃(BH)(μ-SNH)] 2 and [(HB)₂(μ-SNH)] 3. Both were identified by calculations as minima on the respective potential energy surface (PES). However, the tetrahedrane-type structure of 3 is much higher in energy when compared with the planar cyclic isomers 3a and 3b.     

Theoretical investigation of water gas shift reaction catalyzed by iron group carbonyl complexes M(CO)5 (M = Fe, Ru, Os)

We have investigated the mechanism of M(CO)(5) (M = Fe, Ru, Os) catalyzed water gas shift reaction (WGSR) by using density functional theory and ab initio calculations. Our calculation results indicate that the whole reaction cycle consists of six steps: 1 → 2 → 3 → 4 → 5 → 6 → 2. In this stepwise mechanism the metals Fe, Ru, and Os behave generally in a similar way. However, crucial differences appear in steps 3 → 4 → 5 which involve dihydride M(H)(2)(CO)(3)COOH(-) (4') and/or dihydrogen complex MH(2)(CO)(3)COOH(-) (4). The stability of the dihydrogen complexes becomes weaker down the iron group. The dihydrogen complex 4_Fe is only 11.1 kJ/mol less stable than its dihydride 4'_Fe at the B3LYP/II(f)++//B3LYP/II(f) level. Due to very low energy barrier it is very easy to realize the transform from 4_Fe to 4'_Fe and vice versa, and thus for Fe there is no substantial difference to differentiate 4 and 4' for the reaction cycle. The most possible key intermediate 4'_Ru is 38.2 kJ/mol more stable than 4_Ru. However, the barrier for the conversion 3_Ru → 4'_Ru is 23.8 kJ/mol higher than that for 3_Ru → 4_Ru. Additionally, 4'_Ru has to go through 4_Ru to complete dehydrogenation 4'_Ru → 5_Ru. The concerted mechanism 4'_Ru → 6_Ru, in which the CO group attacks ruthenium while H(2) dissociates, can be excluded. In contrast to Fe and Ru, the dihydrogen complex of Os is too unstable to exist at the level of theory. Moreover, we predict Fe and Ru species are more favorable than Os species for the WGSR, because the energy barriers for the 4 → 5 processes of Fe and Ru are only 38.9 and 16.2 kJ/mol, respectively, whereas 140.5 kJ/mol is calculated for the conversion 4' → 5 of Os, which is significantly higher. In general, the calculations are in good agreement with available experimental data. We hope that our work will be beneficial to the development and design of the WGSR catalyst with high performance.     

Strained, stable 2-aza-1-phosphabicyclo[n.1.0]alkane and -alkene Fe(CO)4 complexes with dynamic phosphinidene behavior

The synthesis of highly strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes, that is, complexes with 2-aza-1-phosphabicyclo[n.1.0]alkanes and -alkenes (n = 3-5), is explored by using intramolecular cycloaddition of an in situ generated electrophilic phosphinidene complex, [R(iPr)NP=Fe(CO)(4)], to its C=C- and C[triple chemical bond]C-containing R substituent. Saturated bicyclic complexes 7 a-c with n = 4-2 are remarkably stable, as illustrated by the X-ray crystal structure for 7 b (n=3), yet all readily undergo retroaddition to react with phenylacetylene. Shuttling of the phosphinidene iron complex between two equivalent C=C groups is demonstrated for a 1-butene-substituted 2-aza-1-phosphabicyclo[3.1.0]hexane by selective (1)H NMR magnetization transfer from the phosphirane protons to the olefinic protons. Even the more strained unsaturated bicycles 17 a,b (n = 4,3) are surprisingly stable as illustrated by the X-ray crystal structure for 17 a (n = 4), but the smaller phosphabicyclo[3.1.0]hex-5-ene (17 c, n = 2) dimerizes to tricyclic 19 with a unique ten-membered heterocyclic ring; an X-ray crystal structure is reported. Like their saturated analogues also the bicyclic phosphirenes readily undergo retroaddition as shown by the reaction of their phosphinidene iron moiety with phenylacetylene.     

α-酯甲基硫桥羰基铁配合物(μ-RS)[μ-EtO<(O)CH2S]-Fe2(CO)6的合成及构象分析

通过μ-S2Fe2(CO)6的S-S键被Grignard试剂的还原断裂反应及中间物(μ-RS)(μ-XMgS)Fe2(CO)6(2)对氯代乙酸乙酯的亲核取代反应,合成了一系列铁硫原子簇配合物(μ-RS)[μ-EtOC(O)CH2S]Fe2(CO)6(1).1也可由2经三氟醋酸酸解及中月物(μ-RS)(μ-HS)Fe2(CO)6(3)在三乙胺存在下与氯代乙酸乙酯缩合制得.然而前法较后法既操作简便又原料便宜易得.构象分析表明,各配合物一般为ae.ee和ea三种或其中构象体以一定比例存在的混和物.     

Di- and tri-nuclear osmium carbonyl chloride complexes: x-ray structures of Os2(CO)8Cl2 and Os3(CO)12Cl2

Summary Os₂(CO)₈Cl₂ (1) is orthorhombic P2₁2₁2₁ witha=9.3599(9),b=9.879(2),c=16.014(3), V=1480³, D_c=3.03 Mgm^–3 for Z=4. Structure solved by Patterson methods. Final R=0.038, R_w=0.038 [w=(²F)] for 1270 observed reflections and 141 parameters. Os₃(CO)₁₂Cl₂ (2) is monoclinic C2/m witha=12.105(3), b=10.612(3),c=8.798(1) , =117.02(2)°, V=1006³, D_c=3.22 Mgm^–3 for Z=2. Structure solved by Patterson methods. Final R=0.036, R_w=0.037 (w=(²F)^–) for 821 observed reflections and 75 parameters.Complex(1) has an osmium-osmium single bond 2.897(1), with the chloride ligands in equatorial positions,(2) has a linear triosmium chain with osmium-osmium single bonds 2.893(1) and the chloride ligands occupy equatorial sites on the terminal osmium atoms. Both(1) and(2) are isostructural with their osmium carbonyl iodide analogues.     

Synthesis and characterization of tricarbonyl(trimethylenemethane)iron complexes: crystal structure of (2-methylene-6-p-nitrobenzoyloxy-heptan-1,3-diyl)Fe(CO)3

A series of substituted tricarbonyl(trimethylenemethane)-iron complexes were prepared by functionalization of (3-butenyltrimethylenemethane)Fe(CO)3 (3) or (formyltrimethylenemethane)Fe(CO)3 (14). The products are characterized by 1H and 13C-n.m.r., i.r. and high resolution mass spectroscopy. In addition, the X-ray diffraction analysis of one of these derivatives (13a) was accomplished. Reactions of (3), which introduce a new chiral centre, occur in a non-diastereoselective fashion, while reactions of (14) that introduce a new chiral centre proceed with good diastereoselectivity. The remote nature of the reactive functionality and the (TMM)Fe(CO)3 group is responsible for the lack of diastereoselectivity for (3). The present work demonstrates the robust nature of the (TMM)Fe(CO)3 fragment, embodied in its resistance toward oxidation, and to attack by nucleophiles. This revised version was published online in June 2006 with corrections to the Cover Date.     

系列双核Ln(III)配合物的晶体结构和磁性

合成了分子式为[Ln~2(phen)~2L],phen=C~1~2H~8N~2[ALn=Nd,L=(CH~3COO)~4(ONO~2)~2,BLn=Sm,L=(C~6H~5COO)~6,CLn=Eu,L=(C~6H~5COO)~6]3种同双核配合物。用X射线四圆衍射仪测定了3种化合物的结构。在化合物A分子中,2个Nd(III)原子由4个CH~3COO^-基团桥联,以phen和ONO~2^-为端基,构成了一个具有C~2对称性的双核分子。配合物B和C具有完全相同的结构,它们是以4个苯甲酸根为桥,2个phen和2个C~6H~5COO^-为端基的中心对称双核分子,其中6个苯甲酸根的成键状态可分为3种状况。在3种化合物中,每个Ln均为9配位,呈不规则多面体。Ln-Ln距离,A为0.397nm,B和C均为0.405nm。测定了各配合物的变温磁化率,通过对磁性质研究,发现化合物A在低温下具有反铁磁物质行为,并由理论拟合,求得了磁参数g,J值。     

系列双核Ln(III)配合物的晶体结构和磁性

合成了分子式为[Ln~2(phen)~2L],phen=C~1~2H~8N~2[ALn=Nd,L=(CH~3COO)~4(ONO~2)~2,BLn=Sm,L=(C~6H~5COO)~6,CLn=Eu,L=(C~6H~5COO)~6]3种同双核配合物。用X射线四圆衍射仪测定了3种化合物的结构。在化合物A分子中,2个Nd(III)原子由4个CH~3COO^-基团桥联,以phen和ONO~2^-为端基,构成了一个具有C~2对称性的双核分子。配合物B和C具有完全相同的结构,它们是以4个苯甲酸根为桥,2个phen和2个C~6H~5COO^-为端基的中心对称双核分子,其中6个苯甲酸根的成键状态可分为3种状况。在3种化合物中,每个Ln均为9配位,呈不规则多面体。Ln-Ln距离,A为0.397nm,B和C均为0.405nm。测定了各配合物的变温磁化率,通过对磁性质研究,发现化合物A在低温下具有反铁磁物质行为,并由理论拟合,求得了磁参数g,J值。     

Singlet diradical complexes of chromium, molybdenum, and tungsten with azo anion radical ligands from M(CO)6 precursors

The homoleptic diamagnetic complexes M(mer-L)(2), M = Cr, Mo,W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)(6) with the tridentate ligands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(H) (HL(a)) or NH(4)C(5)N=NC(6)H(4)N(H)C(6)H(4)(CH(3)) (HL(b))) in refluxing n-octane. In the case of M = Mo, the dinuclear compounds [Mo(L)(pap)](2)(mu-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction analysis for Cr(L(b))(2) (1b), Mo(L(a))(2) (2a), and W(L(a))(2) (4a) reveals considerably distorted-octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido nitrogen atoms. Whereas the N(azo)-M-N(azo) angle is larger than 170 degrees, the other two trans angles are smaller, at about 155 degrees (M = Cr, 1b) or 146 degrees (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by more than 0.08 A than those to the anilido or azo nitrogen atoms, reflecting negative charge on the latter. The N-N bond distances vary between 1.339(2) A for 1b and 1.373(3) A for 4a, clearly indicating the azo radical anion oxidation state. Considering the additional negative charge on anilido-N, the mononuclear complexes are thus formulated as M(IV)(L*(2-))(2). The diamagnetism of the complexes as shown by magnetic susceptibility and (1)H NMR experiments is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The experimental structures are well reproduced by density functional theory calculations, which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) A for L(a) and 1.340(9) A for pap is also formulated as an azo anion radical-containing molybdenum(IV) species, i.e., [Mo(IV)(L*(2-))(pap*-)](2)(mu-O). All compounds can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. Electron paramagnetic resonance spectroscopy indicates metal-centered spin for 1a+ and 1a- and g approximately 2 signals for 2a-, 3a+, 3a-, and 4a-. Spectroelectrochemistry in the UV-vis-NIR region showed small changes for the reduction of 2a, 3a, and 4a but extensive spectral changes for the reduction and oxidation of 1a.     

Structure and bonding in binuclear metal carbonyls from the analysis of domain averaged fermi holes. 2. Fe2(CO)8(2-) and Fe2(CO)8

The nature of the bonding interactions in individual isomeric structures of the above carbonyls was studied using the analysis of domain averaged Fermi holes (DAFH). The main focus was directed on the confrontation of the picture of the bonding resulting from this analysis with the predictions of empirical 18-electron rule. This rule assumes, namely, the presence of direct metal-metal bond(s) for both carbonyls, but the detailed insights provided by the DAFH analysis show that the straightforward association of metal-metal bond with the favorable electron count only is too simplistic, and provided the actual structure of individual isomeric species is not taken into account, the predictions of this rule may fail. This is, e.g., the case of the C(2v) isomer of the carbonylate anion [Fe2(CO)8](2-) where the DAFH analysis denies the existence of direct metal-metal bond similarly as in the case the isoelectronic Co2(CO)8. Similar discrepancies between the predictions of the 18-electron rule and DAFH analysis were found also in the case of the C(2v) isomer of the neutral Fe2(CO)8 carbonyl, where the DAFH analysis detects the presence of a single bent Fe-Fe bond rather than the double bond anticipated by the 18-electron rule.     

Syntheses,crystal structures,and electrochemical studies of dinuclear coordination compounds with the Fe2(CO)6 core

Reaction of 2-C₅H₄ NCOSPh, generated from 2-C₅H₄NCO₂H and PhSH in the presence of DCC, with Fe₃(CO)₁₂ affords (μ-κ²C,N-2-C₅H₄N)(μ-PhS)Fe₂(CO)₆ (1) and (μ-PhS)₂Fe₂(CO)₆ (2). Reaction of (NC)₂C=C(SMe)₂, formed from NCCH₂CN, CS₂, and MeI in the presence of NaOH, with Fe₃(CO)₁₂ provides (μ-κ²C,S-(NC)₂C=CSMe)(μ-MeS)Fe₂(CO)₆ (3) and (μ-MeS)₂Fe₂(CO)₆ (4). All complexes have been fully characterized by EA, IR, ¹H NMR, and ¹³C NMR spectroscopy and structurally determined by X-ray crystallography. In 1 and 3, the group attached to the bridging S is at the equatorial position. In 2, two phenyl groups are at equatorial positions. Two isomers of 4, ae-4 and ee-4, can be separated by thin-layer chromatography. DFT calculations reveal that the Gibbs energy difference between ae-4 and ee-4 is ?2.17 kcal mol^?1 in THF and ?2.29 kcal mol^?1 in benzene, and the isomerization barrier between ae-4 and ee-4 is 14.92 kcal mol^?1 in THF and 16.84 kcal mol^?1 in benzene. All these results suggest that ae-4 is more stable than ee-4 in either THF or benzene, and the two isomers do not interconvert. Electrochemical studies of 1 and 3 demonstrate that using HOAc as a proton source 1 and 3 can catalyze H₂ production.     

Binuclear cyclopentadienylcobalt sulfur and phosphinidene complexes Cp2Co2E2 (E = S, PX): Comparison with their Iron carbonyl analogues

Density functional theory studies on a series of Cp₂Co₂E₂ derivatives (E = S and PX; X = H, Cl, OH, OMe, NH₂, NMe₂) predict global minimum butterfly structures with one Co-Co bond for the “body” of the butterfly and four Co-E bonds at the edges of the “wings” of the butterfly. Tetrahedrane structures with both Co-Co and E-E bonds are higher in energy for Cp₂Co₂S₂ and Cp₂Co₂(PH)₂ and are not found in the other systems. This differs from the corresponding Fe₂(CO)₆S₂ and Fe₂(CO)₆(PX)₂ derivatives where tetrahedrane structures are predicted to be the lowest energy structures for all cases except X = NR₂ and OH and such a tetrahedrane structure is found experimentally for Fe₂(CO)₆S₂. The butterfly structures for the Cp₂Co₂E₂ derivatives are of two types. For Cp₂Co₂(PX)₂ (X = H, OH, OMe, NH₂, NMe₂) the lowest energy structures are unsymmetrical butterflies Cp₂Co₂(P)(PX₂) with two X groups on one phosphorus atom and a lone pair on the other (naked) phosphorus atom. Related low-energy unsymmetrical butterfly Fe₂(CO)₆(P)(PX₂) structures, not observed in previous theoretical studies, are now found for the corresponding Fe₂(CO)₆(PX)₂ derivatives. Symmetrical butterfly singlet diradical structures with one X group on each phosphorus atom in relative cis or trans positions are also found for the Cp₂Co₂(PX)₂ derivatives and are the global minima for Cp₂Co₂(PCl)₂ as well as Cp₂Co₂S₂. In all cases the cis structures are of lower energy than the corresponding trans structures. Rhombus structures having neither Co-Co nor E-E bonds are also found for all of the Cp₂Co₂(PX)₂ derivatives but always at higher energies than the butterfly structures, ranging from 17 to 29 kcal/mol above the global minima.     

Neutral and monocationic dinuclear (carbonyl)(cyclopentadienyl)(phenylchalcogenate) iron complexes of the general formulas [(RC5H4)Fe(CO)EPh]2 and [(RC5H4)Fe(CO)EPh]2PF6 (E = S or Te; R = H or Me): Synthesis, molecular structures, and EPR spectra

Heating of the compounds (RC₅H₄)Fe(CO)₂TePh (R = H (I) and Me (II)) in heptane afforded the dinuclear complexes [(RC₅H₄)Fe(CO)TePh]₂ (III and IV, respectively). By oxidation with Fc⁺PF ₆ ^? , these complexes were transformed into the paramagnetic cationic complexes [(RC₅H₄)Fe(CO)TePh]₂PF₆ (V and VI, respectively). Structures III–V and [(C₅H₅)Fe(CO)SPh]₂PF₆ (VII) were characterized by X-ray diffraction.