New class of ruthenium sulfide clusters: Ru(4)S(6)(PPh(3))(4), Ru(5)S(6)(PPh(3))(5), and Ru(6)S(8)(PPh(3))(6)

Reaction of RuCl(2)(PPh(3))(3) with S(2)(-) sources yields a family of phosphine-containing Ru-S clusters which have been characterized crystallographically and by MALDI-MS. Ru(4)S(6)(PPh(3))(4) (Ru-Ru(av) = 2.94 A) has idealized T(d)() symmetry whereas Ru(6)S(8)(PPh(3))(6) (Ru-Ru(av) = 2.82 A) adopts the idealized O(h)() symmetry characteristic of Chevrel clusters. Ru(5)S(6)(PPh(3))(5) is formally derived by the addition of Ru(PPh(3)) to one face of Ru(4)S(6)(PPh(3))(4). In terms of its M-S connectivity, the Ru(5)S(6) cluster resembles a fragment of the FeMo cluster in nitrogenase.     

Excited-state properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py)

The photophysical properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF = tetrahydrofuran, PPh(3) = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. Time-resolved absorption shows that all the complexes possess a long-lived transient (3.5-5.0 micros) assigned as an electronic excited state of the molecules, and they exhibit an optical transition at approximately 760 nm whose position is independent of axial ligand. No emission from the Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py) systems was detected, but energy transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to the (3)pipi excited state of perylene is observed. Electron transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to 4,4'-dimethyl viologen (MV(2+)) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (k(q)) of 8.0 x 10(6) and 1.2 x 10(6) M(-1) s(-1) in methanol, respectively. A k(q) value of 2 x 10(8) M(-1) s(-1) was measured for the quenching of the excited state of Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) by O(2) in methanol. The observations are consistent with the production of an excited state with excited-state energy, E(00), between 1.34 and 1.77 eV.     

Synthesis and Chemical and Electrochemical Characterization of Fe-S Carbonyl Clusters. X-ray Crystal Structures of [N(PPh(3))(2)](2)[Fe(5)S(2)(CO)(14)] and [N(PPh(3))(2)](2)[Fe(6)S(6)(CO)(12)

A reinvestigation of the redox behavior of the [Fe(3)(&mgr;(3)-S)(CO)(9)](2)(-) dianion led to the isolation and characterization of the new [Fe(5)S(2)(CO)(14)](2)(-), as well as the known [Fe(6)S(6)(CO)(12)](2)(-) dianion. As a corollary, new syntheses of the [Fe(3)S(CO)(9)](2)(-) dianion are also reported. The [Fe(5)S(2)(CO)(14)](2)(-) dianion has been obtained by oxidative condensation of [Fe(3)S(CO)(9)](2)(-) induced by tropylium and Ag(I) salts or SCl(2), or more straightforwardly through the reaction of [Fe(4)(CO)(13)](2)(-) with SCl(2). The [Fe(6)S(6)(CO)(12)](2)(-) dianion has been isolated as a byproduct of the synthesis of [Fe(3)S(CO)(9)](2)(-) and [Fe(5)S(2)(CO)(14)](2)(-) or by reaction of [Fe(4)(CO)(13)](2)(-) with elemental sulfur. The structures of [N(PPh(3))(2)](2)[Fe(5)S(2)(CO)(14)] and [N(PPh(3))(2)](2)[Fe(6)S(6)(CO)(12)] were determined by single-crystal X-ray diffraction analyses. Crystal data: for [N(PPh(3))(2)](2)[Fe(5)S(2)(CO)(14)], monoclinic, space group P2(1)/c (No. 14), a = 24.060(5), b = 14.355(6), c = 23.898(13) ?, beta = 90.42(3) degrees, Z = 4; for [N(PPh(3))(2)](2)[Fe(6)S(6)(CO)(12)], monoclinic, space group C2/c (No. 15), a = 34.424(4), b = 14.081(2), c = 19.674(2) ?, beta = 115.72(1) degrees, Z = 4. The new [Fe(5)S(2)(CO)(14)](2)(-) dianion shows a "bow tie" arrangement of the five metal atoms. The two Fe(3) triangles sharing the central Fe atom are not coplanar and show a dihedral angle of 55.08(3) degrees. Each Fe(3) moiety is capped by a triply bridging sulfide ligand. The 14 carbonyl groups are all terminal; two are bonded to the unique central atom and three to each peripheral iron atom. Protonation of the [Fe(5)S(2)(CO)(14)](2)(-) dianion gives reversibly rise to the corresponding [HFe(5)S(2)(CO)(14)](-) monohydride derivative, which shows an (1)H-NMR signal at delta -21.7 ppm. Its further protonation results in decomposition to mixtures of Fe(2)S(2)(CO)(6) and Fe(3)S(2)(CO)(9), rather than formation of the expected H(2)Fe(5)S(2)(CO)(14) dihydride. Exhaustive reduction of [Fe(5)S(2)(CO)(14)](2)(-) with sodium diphenyl ketyl progressively leads to fragmentation into [Fe(3)S(CO)(9)](2)(-) and [Fe(CO)(4)](2)(-), whereas electrochemical, as well as chemical oxidation with silver or tropylium tetrafluoroborate, in dichloromethane, generates the corresponding [Fe(5)S(2)(CO)(14)](-) radical anion which exhibits an ESR signal at g = 2.067 at 200 K. The electrochemical studies also indicated the existence of a subsequent one-electron anodic oxidation which possesses features of chemical reversibility in dichloromethane but not in acetonitrile solution. A reexamination of the electrochemical behavior of the [Fe(3)S(CO)(9)](2)(-) dianion coupled with ESR monitoring enabled the spectroscopic characterization of the [Fe(3)S(CO)(9)](-) radical monoanion and demonstrated its direct involvement in the generation of the [Fe(5)S(2)(CO)(14)](n)()(-) (n = 0, 1, 2) system.     

DNA hydrolytic cleavage by the diiron(III) complex Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2): comparison with other binuclear transition metal complexes

The binuclear structure of Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) (DTPB = 1,1,4,7,7-penta (2'-benzimidazol-2-ylmethyl)-triazaheptane, Ac = acetate) was characterized by UV-visible absorption and infrared spectra and NMR and ESR. The binding interaction of DNA with the diiron complex was examined spectroscopically. Supercoiled and linear DNA hydrolytic cleavage by the diiron complex is supported by the evidence from anaerobic reactions, free radical quenching, high performance liquid chromatography experiments, and enzymatic manipulation such as T4 ligase ligation, 5'-(32)P end-labeling, and footprinting analysis. The estimation of rate for the supercoiled DNA double strand cleavage shows one of the largest known rate enhancement factors, approximately 10(10) against DNA. Moreover, the DNA hydrolysis chemistry needs no coreactant such as hydrogen peroxide. The poor sequence-specific DNA cleavage indicated by the restriction analysis of the pBR322 DNA linearized by the diiron complex might be due to the diiron complex bound to DNA by a coordination of its two ferric ions to the DNA phosphate oxygens, as suggested by spectral characterizations. The hydrolysis chemistry for a variety of binuclear metal complexes including Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) is compared. It is established that the dominant factors for the DNA hydrolysis activities of the binuclear metal complexes are the mu-oxo bridge, labile and anionic ligands, and open coordination site(s). Concerning the hydrolytic mechanisms, the diiron complex Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) might share many points in common with the native purple acid phosphatases.     

Synthesis and crystal structures of (fulvalene)W(2)(SH)(2)(CO)(6), (fulvalene)W(2)(mu-S(2))(CO)(6), and (fulvalene)W(2)(mu-S)(CO)(6): low valent tungsten carbonyl sulfide and disulfide complexes stabilized by the bridging fulvalene ligand

Reaction of FvW(2)(H)(2)(CO)(6) with 2/8S(8) in THF results in rapid and quantitative formation of FvW(2)(SH)(2)(CO)(6). The crystal structure of this complex is reported and shows that the two tungsten-hydrosulfide groups are on opposite faces of the fulvalene ligand in an anti configuration. Nevertheless, treatment of FvW(2)(SH)(2)(CO)(6) (1) with PhN[double bond]NPh produces FvW(2)(mu-S(2))(CO)(6) (2) and Ph(H)NN(H)Ph. The crystal structure of the bridging disulfide, which cocrystallizes with 1 in a 2:1 ratio, is also described. Exposure of 2 equiv of *CrCp*(CO)(3) to 1 effects similar H atom transfers yielding 2 HCrCp*(CO)(3) and 2. Attempts to obtain crystals of the latter from solutions derived from this reaction mixture furnished a third product, FvW(2)(mu-S)(CO)(6) (3), which was analyzed crystallographically. The enthalpy of sulfur atom insertion into FvW(2)(H)(2)(CO)(6), yielding 1, has been measured by solution calorimetry.     

Diazo complexes of rhenium: preparations and crystal structures of the bis(dinitrogen), [Re(N2)2(PPh(OEt)2)4][BPh4] and methyldiazenido [ReCl(CH3N2)(CH3NHNH2)(PPh(OEt)2)3][BPh4] derivatives

Depending on experimental conditions and the nature of the hydrazine, the reactions of ReCl3P3 [P = PPh(OEt)2] with RNHNH2 (R = H, CH3, tBu) afford the bis(dinitrogen) [Re(N2)2P4]+ (2+), dinitrogen ReClN2P4 (3), and methyldiazenido [ReCl(CH3N2)(CH3NHNH2)P3]+ (1+) derivatives. In contrast, reactions of ReCl3P3 [P = PPh(OEt)2, PPh2OEt] with arylhydrazines ArNHNH2 (Ar = Ph, p-tolyl) give the aryldiazenido cations [ReCl(ArN2)(ArNHNH2)P3]+ (4+) and [ReCl(ArN2)P4]+ (7+) and the bis(aryldiazenido) cations [Re(ArN2)2P3]+ (5+, 6+). These complexes were characterized spectroscopically (IR; 1H and 31P NMR), and the BPh4 complexes 1, 2, and 7 were characterized crystallographically. The methyldiazenido derivative [ReCl(CH3N2)(CH3NHNH2)(PPh(OEt)2)3][BPh4] (1) crystallizes in space group P1 with a = 15.396(5) A, b = 16.986(5) A, c = 11.560(5) A, alpha = 93.96(5) degrees, beta = 93.99(5) degrees, gamma = 93.09(5) degrees, and Z = 2 and contains a singly bent CH3N2, group bonded to an octahedral central metal. One methylhydrazine ligand, one Cl- trans to the CH3N2, and three PPh(OEt)2 ligands complete the coordination. The complex [Re(N2)2(PPh(OEt)2)4][BPh4] (2) crystallizes in space group Pbaa with a = 23.008(5) A, b = 23.367(5) A, c = 12.863(3) A, and Z = 4. The structure displays octahedral coordination with two end-on N2 ligands in mutually trans positions. [ReCl(PhN2)(PPh(OEt)2)4][BPh4] (7) crystallizes in space group P2(1)/n with a = 19.613(5) A, b = 20.101(5) A, c = 19.918(5) A, beta = 115.12(2) degrees, and Z = 4. The structure shows a singly bent phenyldiazenido group trans to the Cl- ligand in an octahedral environment. The dinitrogen complex ReClN2P4 (3) reacts with CF3SO3CH3 to give the unstable methyldiazenido derivative [ReCl(CH3N2)P4][BPh4]. Reaction of the methylhydrazine complex [ReCl(CH3N2)(CH3NHNH2)P3][BPh4] (1) with Pb(OAc)4 at -30 degrees C results in selective oxidation of the hydrazine, affording the corresponding methyldiazene derivative [ReCl(CH3N=NH)(CH3N2)P3][BPh4] (8). In contrast, treatment with Pb(OAc)4 of the related arylhydrazines [ReCl(ArN2)(ArNHNH2)P3][BPh4] (4) [P = PPh(OEt)2] gives the bis(aryldiazenido) complexes [Re(ArN2)2P3][BPh4] (5). Possible protonation reactions of Br?nsted acids HX with all diazenides, 1, 4, 5, 6, and 8, were investigated and found to proceed only in the cases of the bis(aryldiazenido) complexes 5 and 6, affording, with HCl, the octahedral [ReCl(ArN=NH)(ArN2)P3][BPh4] or [ReCl(Ar(H)NN)(ArN2)P3][BPh4] (10) (Ar = Ph; P = PPh2OEt) derivative.     

Syntheses and Properties of New Layered Alkali-Metal/Ammonium Vanadium(V) Methylphosphonates: M(VO(2))(3)(PO(3)CH(3))(2) (M = NH(4), K, Rb, Tl). Single-Crystal Structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2)

The hydrothermal syntheses of a family of new alkali-metal/ammonium vanadium(V) methylphosphonates, M(VO(2))(3)(PO(3)CH(3))(2) (M = K, NH(4), Rb, Tl), are described. The crystal structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) have been determined from single-crystal X-ray data. Crystal data: K(VO(2))(3)(PO(3)CH(3))(2), M(r) = 475.93, trigonal, R32 (No. 155), a = 7.139(3) ?, c = 19.109(5) ?, Z = 3; NH(4)(VO(2))(3)(PO(3)CH(3))(2), M(r) = 454.87, trigonal, R32 (No. 155), a = 7.150(3) ?, c = 19.459(5) ?, Z = 3. These isostructural, noncentrosymmetric phases are built up from hexagonal tungsten oxide (HTO) like sheets of vertex-sharing VO(6) octahedra, capped on both sides of the V/O sheets by PCH(3) entities (as [PO(3)CH(3)](2-) methylphosphonate groups). In both phases, the vanadium octahedra display a distinctive two short + two intermediate + two long V-O bond distance distribution within the VO(6) unit. Interlayer potassium or ammonium cations provide charge balance for the anionic (VO(2))(3)(PO(3)CH(3))(2) sheets. Powder X-ray, TGA, IR, and Raman data for these phases are reported and discussed. The structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) are compared and contrasted with related layered phases based on the HTO motif.     

A high-pressure iron K-edge x-ray absorption spectral study of the spin-state crossover in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2)

The room temperature iron K-edge X-ray absorption near edge structure spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) have been measured between ambient and 88 and 94 kbar, respectively, in an opposed diamond anvil cell. The iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2)undergoes the expected gradual spin-state crossover from the high-spin state to the low-spin state with increasing pressure. In contrast, the iron(II) in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) remains high-spin between ambient and 78 kbar and is only transformed to the low-spin state at an applied pressure of between 78 and 94 kbar. No visible change is observed in the preedge peak in the spectra of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) with increasing pressure, whereas the preedge peak in the spectra of ((e[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) changes as expected for a high-spin to low-spin crossover with increasing pressure. The difference in the spin-state crossover behavior of these two complexes is likely related to the unusual behavior of (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2) upon cooling.     

A new reaction of [Cp((CO)2Fe(PPh2H)]PF6 with NaBH4 to give Cp(CO)(H)Fe(PPh2H) via Cp(CO)2FeH and PPh2H

[Cp((CO)₂Fe(PPh₂H)]PF₆ reacts with NaBH₄ to give the intermediates CpFe(CO)₂H and PPh₂H, which are then converted into Cp(CO)(H)Fe(PPh₂H). [Cp(CO)₂FeL]PF₆ (L = P(OMe)₃, P(OEt)₃ and P(OⁱPr)₃) reacts with NaBH₄ to give the product Cp(CO)(H)FeL directly without Cp(CO)₂FeH and L even being formed transiently. The proposed reaction mechanism is that H⁻ attacks th phosphorus atom to give a metallaphosphorane complex, followed by coupling between a Cp(CO)₂Fe fragment and H on the hypervalent phosphorus.     

(NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')]: an iron thiolate complex modeling the [Fe(CN)(2)(CO)(S-Cys)(2)] site of [NiFe] hydrogenase centers

In the search for complexes modeling the [Fe(CN)(2)(CO)(cysteinate)(2)] cores of the active centers of [NiFe] hydrogenases, the complex (NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')] (4) was found ('S(3)'(2-)=bis(2-mercaptophenyl)sulfide(2-)). Starting complex for the synthesis of 4 was [Fe(CO)(2)('S(3)')](2) (1). Complex 1 formed from [Fe(CO)(3)(PhCH=CHCOMe)] and neutral 'S(3)'-H(2). Reactions of 1 with PCy(3) or DPPE (1,2-bis(diphenylphosphino)ethane) yielded diastereoselectively [Fe(CO)(2)(PCy(3))('S(3)')] (2) and [Fe(CO)(dppe)('S(3)')] (3). The diastereoselective formation of 2 and 3 is rationalized by the trans influence of the 'S(3)'(2-) thiolate and thioether S atoms which act as pi donors and pi acceptors, respectively. The trans influence of the 'S(3)'(2-) sulfur donors also rationalizes the diastereoselective formation of the C(1) symmetrical anion of 4, when 1 is treated with four equivalents of NEt(4)CN. The molecular structures of 1, 3 x 0.5 C(7)H(8), and (AsPh(4))(2)[Fe(CN)(2)(CO)('S(3)')] x acetone (4 a x C(3)H(6)O) were determined by X-ray structure analyses. Complex 4 is the first complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site. Complex 4 can be reversibly oxidized electrochemically; chemical oxidation of 4 by [Fe(Cp)(2)PF(6)], however, led to loss of the CO ligand and yielded only products, which could not be characterized. When dissolved in solvents of increasing proton activity (from CH(3)CN to buffered H(2)O), complex 4 exhibits drastic nu(CO) blue shifts of up to 44 cm(-1), and relatively small nu(CN) red shifts of approximately 10 cm(-1). The nu(CO) frequency of 4 in H(2)O (1973 cm(-1)) is higher than that of any hydrogenase state (1952 cm(-1)). In addition, the nu(CO) frequency shift of 4 in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state. These results demonstrate that complexes modeling properly the nu(CO) frequencies of [NiFe] hydrogenase probably need a [Ni(thiolate)(2)] unit. The results also demonstrate that the nu(CO) frequency of [Fe(CN)(2)(CO)(thiolate)(2)] complexes is more significantly shifted by changing the solvent than the nu(CO) frequency of [NiFe] hydrogenases by coupled-proton and electron-transfer reactions. The "iron-wheel" complex [Fe(6)[Fe('S(3)')(2)](6)] (6) resulting as a minor by-product from the recrystallization of 2 in boiling toluene could be characterized by X-ray structure analysis.     

NMR studies of Ru(3)(CO)(10)(PMe(2)Ph)(2) and Ru(3)(CO)(10)(PPh(3))(2) and their H(2) addition products: detection of new isomers with complex dynamic behavior

The clusters Ru(3)(CO)(10)L(2), where L = PMe(2)Ph or PPh(3), are shown by NMR spectroscopy to exist in solution in at least three isomeric forms, one with both phosphines in the equatorial plane on the same ruthenium center and the others with phosphines in the equatorial plane on different ruthenium centers. Isomer interconversion for Ru(3)(CO)(10)(PMe(2)Ph)(2) is highly solvent dependent, with DeltaH decreasing and DeltaS becoming more negative as the polarity of the solvent increases. The stabilities of the isomers and their rates of interconversion depend on the phosphine ligand. A mechanism that accounts for isomer interchange involving Ru-Ru bond heterolysis is suggested. The products of the reaction of Ru(3)(CO)(10)L(2) with hydrogen have been monitored by NMR spectroscopy via normal and para hydrogen-enhanced methods. Two hydrogen addition products are observed with each containing one bridging and one terminal hydride ligand. EXSY spectroscopy reveals that both intra- and interisomer hydride exchange occurs on the NMR time scale. On the basis of the evidence available, mechanisms for hydride interchange involving Ru-Ru bond heterolysis and CO loss are proposed.     

Aluminium complexes with thio-phosphorus ligands: syntheses and characterisations of [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] and [Al(S(2)PPh(2))(3)

The novel aluminium complexes [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] and [Al(S(2)PPh(2))(3)] have been prepared as potential models for alumino-thiophosphonate based materials; [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] is the first example of a primary dithiophosphinate to be characterised in the solid state.     

New routes to low-coordinate iron hydride complexes: The binuclear oxidative addition of H2

The oxidative addition and reductive elimination reactions of H₂ on unsaturated transition-metal complexes are crucial in utilizing this important molecule. Both biological and man-made iron catalysts use iron to perform H₂ transformations, and highly unsaturated iron complexes in unusual geometries (tetrahedral and trigonal planar) are anticipated to give unusual or novel reactions. In this paper, two new synthetic routes to the low-coordinate iron hydride complex [L^tBuFe(μ-H)]₂ are reported. Et₃SiH was used as the hydride source in one route by taking advantage of the silaphilicity of the fluoride ligand in three-coordinate L^tBuFeF. The other synthetic method proceeded through the binuclear oxidative addition of H₂ or D₂ to a putative Fe(I) intermediate. Deuteration was verified through reduction of an alkyne and release of the deuterated alkene product. Mössbauer spectra of [L^tBuFe(μ-H)]₂ indicate that the samples are pure, and that the iron(II) centers are high-spin.     

Reaction of bis(phosphine)(hydrotris(3,5-dimethylpyrazolyl)borato)rhodium(I) with phenylacetylene,p-nitrobenzaldehyde,and triphenyltin hydride: structures of [Rh(Tp)(PPh(3))(2)], [Rh(Tp)(H)(C(2)Ph)(P(4-C(6)H(4)F)(3))], [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PPh(3))], and [Rh(Tp)(H)(SnPh(3))(PPh(3))

The complexes [Rh(Tp)(PPh(3))(2)] (1a) and [Rh(Tp)(P(4-C(6)H(4)F)(3))(2)] (1b) combine with PhC(2)H, 4-NO(2)-C(6)H(4)CHO and Ph(3)SnH to give [Rh(Tp)(H)(C(2)Ph)(PR(3))] (R = Ph, 2a; R = 4-C(6)H(4)F, 2b), [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PR(3))] (R = Ph, 3a), and [Rh(Tp)(H)(SnPh(3))(PR(3))] (R = Ph, 4a; R = 4-C(6)H(4)F, 4b) in moderate to good yield. Complexes 1a, 2b, 3a, and 4a have been structurally characterized. In 1a the Tp ligand is bidentate, in 2b, 3a, and 4a it is tridentate. Crystal data for 1a: space group P2(1)/c; a = 11.9664(19), b = 21.355(3), c = 20.685(3) A; beta = 112.576(7) degrees; V = 4880.8(12) A(3); Z = 4; R = 0.0441. Data for 2b: space group P(-)1; a = 10.130(3), b = 12.869(4), c = 17.038(5) A; alpha = 78.641(6), beta = 76.040(5), gamma = 81.210(6) degrees; V = 2100.3(11) A(3); Z = 2; R = 0.0493. Data for 3a: space group P(-)1; a = 10.0073(11), b = 10.5116(12), c = 19.874(2) A; alpha = 83.728(2), beta = 88.759(2), gamma = 65.756(2) degrees; V =1894.2(4) A(3); Z = 2; R = 0.0253. Data for 4a: space group P2(1)/c; a = 15.545(2), b = 18.110(2), c = 17.810(2) A; beta = 95.094(3) degrees; V = 4994.1(10) A(3); Z = 4; R = 0.0256. NMR data ((1)H, (31)P, (103)Rh, (119)Sn) are also reported.     

Interplay among tetrahedrane, butterfly diradical, and planar rhombus structures in the chemistry of the binuclear iron carbonyl phosphinidene complexes Fe2(CO)6(PX)2

Density functional theory studies on a series of Fe2(CO)6(PX)2 derivatives show the tetrahedrane to be the most stable for the alkyl (X = Me, tBu), P-H (X = H), and chloro (X = Cl) derivatives. However, butterfly diradical and planar rhombus structures are found to be more stable than tetrahedranes for the amino (X = NH2, NMe2, and NiPr2) and aryloxy (R = 2,6-tBu2-4-Me-C6H2O) derivatives. For the chloro (X = Cl) and methoxy (X = OMe) derivatives energetically accessible bishomotetrahedrane Fe2(CO)6P2(mu-X)2 isomers are observed in which the X substituents on the phosphorus atoms interact with the iron atom to form two direct Fe-X bonds at the expense of two of the four Fe-P bonds. In addition, the global minimum for the hydroxy (X = OH) derivative is an unusual FeP-butterfly structure with a central Fe-P bond as well as two external Fe-P bonds, one external P-P bond, and one external Fe=Fe double bond. Comparison of calculated with experimental nu(CO) frequencies shows that low-temperature Nujol matrix photolysis of (iPr2NP)2COFe2(CO)6 leads to a planar rhombus rather than a tetrahedrane isomer of Fe2(CO)6(PNiPr2)2.     

Computational study of the energetics of 3Fe(CO)4, 1Fe(CO)4 and 1Fe(CO)4(L), L = Xe, CH4, H2 and CO

Large basis CCSD(T) calculations are used to calculate the energetics of 3Fe(CO)4, 1Fe(CO)4 and 1Fe(CO)4(L), L = Xe, CH4, H2 and CO. . The relative energy of the excited singlet state of Fe(CO)4 with respect to the ground triplet state is not known experimentally, and various lower levels of theory predict very different results. Upon extrapolating to the infinite basis set limit, and including corrections for core-core and core-valence correlation, scalar relativity, and multi-reference character of the wavefunction, the best CCSD(T) estimate for the spin-state splitting in iron tetracarbonyl is 2 kcal mol(-1). Calculation of the dissociation energy of 1Fe(CO)4(L) into singlet fragments, taken together with known experimental behaviour of triplet Fe(CO)4, provides independent evidence for the fact that the spin-state splitting is smaller than 3 kcal mol(-1). These calculations highlight some of the challenges involved in benchmark calculations on transition metal containing systems.