Manganese clusters derived from a 2,6-diacetylpyridine dioximato ligand: structure and magnetic study

Reactions of 2,6-diacetylpyridine dioxime (dapdoH?) with Mn(NO?)? or Mn(SO?CF?)? under a variety of conditions or co-ligands yield compounds with the formula [Mn?O?(OMe)?(dapdo)?(dapdoH)?](X)? in which X = NO?? (1) or SO?CF?? (2), [Mn?O?(dapdo)?(NO?)?]·H?O (3) and [Mn(dapdoH?)(N?)?](n) (4). Compounds 1, 3 and 4 were structurally characterized and equivalent structures for 1 and 2 were inferred from spectroscopic and analytical results. Compounds 1 and 2 consist of hexanuclear Mn?(II)Mn?(III) complexes whereas 3 consists of an octanuclear Mn?(II)Mn?(III) cluster in which the manganese atoms exhibit a rare bicapped elongated octahedral topology. Compound 4 consists of a 1D system bridged by double end-on azido ligands. Variable temperature magnetic studies were performed between 2-300 K, confirming the ground state S = 5 for 1 and 2, S = 0 for 3 and ferromagnetic response for 4.     

Mononuclear and binuclear rhenium carbonyl nitrosyls: comparison with their manganese analogues

The structures and energetics of Re(NO)(CO)n (n = 5, 4, 3, 2) and Re2(NO)2(CO)n (n = 7, 6) have been investigated using density functional theory. For Re(NO)(CO)4 the preferred structure is an equatorially substituted trigonal bipyramid analogous to the known structure of the manganese analogue. The lowest energy structures for the unsaturated Re(NO)(CO)n (n = 3, 2) species can be derived from this structure by removal of carbonyl groups. A structure is found for Re(NO)(CO)5 in which the NO ligand has attached to one of the CO ligands by forming a C-N bond to give an unprecedented eta(2)-OCNO ligand. However, this structure is predicted to undergo exothermic CO loss to give Re(NO)(CO)4. The preferred structures for the binuclear derivatives Re2(NO)2(CO)n (n = 7, 6) are structures unprecedented for the manganese analogues and consist of a Re(CO)5 unit linked to a Re(NO)2(CO)(n-5) unit. However, only slightly higher in energy are structures of the type Re2(mu-NO)2(CO)n with two bridging nitrosyl groups, similar to the global minima for the manganese analogues. These results predict extensive areas of new rhenium carbonyl nitrosyl chemistry. Thus the synthesis of Re(NO)(CO)4 by methods related to the synthesis of the manganese analogue appears to be feasible. In addition, the existence of an extensive series of Re(NO)2(CO)2X derivatives, as well as a Re2(NO)4(CO)4 dimer, is predicted.     

Structure and magnetic properties of a decanuclear Mn(II)₂Mn(III)₂Dy₆ aggregate

Using glycerol (H?gly) as a primary ligand, the decanuclear aggregate [Mn(II)?Mn(III)?Dy?(μ?-OH)?(Hgly)?(H?gly)?-(PhCO?)??(H?O)?]·10CH?CN (1) has been synthesised; it has a structure built up from two Mn?Dy? heterocubane units linked through a central Dy?(μ-benzoate)? paddle-wheel dimer and shows slow relaxation of its magnetisation.     

Manganese carbonyl fluorides: are they viable molecules?

The mononuclear Mn(CO)(5)X and binuclear Mn(2)(CO)(8)(μ-X)(2) manganese carbonyl halides have long been known for the halogens Cl, Br, and I. However, the corresponding manganese carbonyl fluorides (X = F) remain unknown. The structures and thermochemistry of such manganese carbonyl fluorides and their decarbonylation products have now been investigated using density functional theory. In all cases singlet structures were found to have lower energies than the corresponding triplet structures. The expected octahedral structure is predicted for Mn(CO)(5)F. Decarbonylation of Mn(CO)(5)F is predicted to give trigonal bipyramidal Mn(CO)(4)F with equatorial fluorine. Further, decarbonylation gives tetrahedral Mn(CO)(3)F. All of the binuclear Mn(2)(CO)(n)F(2) structures (n = 8, 7, 6) are predicted to have a central Mn(2)F(2) unit with two bridging F atoms, a non-bonding Mn···Mn distance of ~3.1 ?, and exclusively terminal CO groups. The thermochemistry of these manganese carbonyl fluorides indicates that they are viable species. This suggests that the failure to date to synthesize the simple manganese carbonyl fluorides arises from a lack of a suitable synthetic method rather than from the instability of the desired products.     

Dimers and chains of {3d-4f} single molecule magnets constructed from heterobimetallic tectons

A tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni?(valpn)?Dy?(III)(pdca)?(NO?)(H?O)?](NO?)·4H?O 1, and (∞)1[Ni?(H?O)?(valpn)?Dy?(tfa)?]·4CH?CN 2 (valpn2? = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca2? = the dianion of 2,6-pyridinedicarboxylic acid; tfa2? = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K).     

Re

A chair conformation comparable to that observed for six-membered rings composed of tetrahedral carbon atoms is found for the cluster anion [Re(6)(μ-H)(5)(CO)(24)](-) (see picture; black spheres: Re, white spheres: μ-H; CO ligands omitted for clarity) in spite of the octahedral coordination at the Re centers. This is the first example of a carbonyl cluster exhibiting a cyclohexane-like geometry of the metallic framework.     

High nuclearity manganese(III) compounds containing phenol-pyrazole ligands: the influence of the ligand on the core geometry

Three high-nuclearity manganese(III) clusters have been synthesized and characterized: [Mn?(μ?-O)?(phpzH)?(thf)?] (1), [Mn?(μ?-O)?(phpzH)?(EtOH)?]·2EtOH (2), and [Mn?(μ?-O)?(μ?-Br)?(HphpzEt)?(phpzEt)] (3). Compounds 1 and 2 contain a [Mn?(μ?-O?)(phpzH)?] core in which antiferromagnetic interactions between the manganese(III) ions are found. Compound 3 is a hexanuclear manganese(III) cluster in which weak ferromagnetic interactions appear to be operative. The formation and the stability of the cluster cores in relation to the type of phenol-pyrazole ligand and the reaction conditions are discussed.     

Synthesis, Characterization, and Comparative Properties of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)

The reaction of [PPN](2)[Re(6)C(CO)(19)] with Mo(CO)(6) and Ru(3)(CO)(12) under sunlamp irradiation provided the new mixed-metal clusters [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)], which were isolated in yields of 85% and 61%, respectively. The compound [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] crystallizes in the monoclinic space group P2(1)/c with a = 20.190 (7) ?, b = 16.489 (7) ?, c = 27.778 (7) ?, beta = 101.48 (2) degrees, and Z = 4 (at T = -75 degrees C). The cluster anion is composed of a Re(6)C octahedral core with a face capped by a Mo(CO)(4) fragment. There are three terminal carbonyl ligands coordinated to each rhenium atom. The four carbonyl ligands on the molybdenum center are essentially terminal, with one pair of carbonyl ligands (C72-O72 and C74-O74) subtending a relatively large angle at molybdenum (C72-Mo-C74 = 147.2(9) degrees ), whereas the remaining pair of carbonyl ligands (C71-O71 and C73-O73) subtend a much smaller angle (C71-Mo-C73 = 100.5(9) degrees ). The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows signals for four sets of carbonyl ligands at -40 degrees C, consistent with the solid state structure, but the carbonyl ligands undergo complete scrambling at ambient temperature. The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] at 20 degrees C is consistent with the expected structure of an octahedral Re(6)C(CO)(18) core capped by a Ru(CO)(3) fragment. The visible spectrum of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows a broad, strong band at 670 nm (epsilon = 8100), whereas all of the absorptions of [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] are at higher energy. An irreversible oxidation wave with E(p) at 0.34 V is observed for [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)], whereas two quasi-reversible oxidation waves with E(1/2) values of 0.21 and 0.61 V (vs Ag/AgCl) are observed for [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)]. The molybdenum cap in [Re(6)C(CO)(18)Mo(CO(4))](2-) is cleaved by heating in donor solvents, and by treatment with H(2), to give largely [H(2)Re(6)C(CO)(18)](2-). In contrast, [Re(6)C(CO)(18)Ru(CO)(3)](2-) shows no tendency to react under similar conditions.     

Synthesis, functionalization, characterization, and photophysical study of carbonyl-containing isocyano rhenium(I) diimine complexes

New classes of tunable rhenium(I) diimine luminophores with formula of [Re(CO)(CNR)(3)(N-N)]PF(6) and [Re(CO)(L(x))(CNC(6)H(4)Cl-4)(2)(1,10-phenanthroline)]PF(6), (R = C(6)H(5), 4-BrC(6)H(4), 4-ClC(6)H(4), 4-MeOC(6)H(4), 2,6-(i)Pr(2)C(6)H(3); N-N = 1,10-phenanthroline, 5,6-dibromo-1,10-phenanthroline, 4,4'-di-tert-butyl-2,2'-bipyridine; L(x) = MeCN, pyridine and PPh(3)) have been synthesized. Different synthetic routes including photo-ligand substitution and thermal carbonyl ligand substitution through the oxidative decarbonylation with trimethyl amine N-oxide, for the facial and meridional isomeric forms of [Re(CO)(CNR)(3)(N-N)]PF(6) were investigated. On the basis of these synthetic strategies, different ligand modification and functionalization of the rhenium(I) diimine luminophores with tailored excited state properties could be readily achieved. The structures of both facial and meridional conformations of [Re(CO)(CNR)(3)(N-N)]PF(6) and the complex precursors fac-[Re(CO)(3)(CNC(6)H(3)(i)Pr-2,6)(3)]OTf were determined by X-ray crystallography. These complexes display an orange to red (3)MLLCT [dπ(Re) → π*(N-N)] phosphorescence at room temperature. Detailed photophysical investigations revealed that the physical, photophysical, electrochemical, and excited state properties can be fine-tuned and tailored through the modifications of the substituents on isocyanide or diimine ligands.     

NMR study of ligand exchange and electron self-exchange between oxo-centered trinuclear clusters [Fe3(μ3-O)(μ-O2CR)6(4-R'py)3](+/0)

The syntheses, single crystal X-ray structures, and magnetic properties of the homometallic μ?-oxo trinuclear clusters [Fe?(μ?-O)(μ-O?CCH?)?(4-Phpy)?](ClO?) (1) and [Fe?(μ?-O)(μ-O?CAd)?(4-Mepy)?](NO?) (2) are reported (Ad = adamantane). The persistence of the trinuclear structure within 1 and 2 in CD?Cl? and C?D?Cl? solutions in the temperature range 190-390 K is demonstrated by 1H NMR. An equilibrium between the mixed pyridine clusters [Fe?(μ?-O)(μ-O?CAd)?(4-Mepy)(3-x)(4-Phpy)(x)](NO?) (x = 0, 1, 2, 3) with a close to statistical distribution of these species is observed in CD?Cl? solutions. Variable-temperature NMR line-broadening made it possible to quantify the coordinated/free 4-Rpy exchanges at the iron centers of 1 and 2: k(ex)2?? = 6.5 ± 1.3 × 10?1 s?1, ΔH(?) = 89.47 ± 2 kJ mol?1, and ΔS(?) = +51.8 ± 6 J K?1 mol?1 for 1 and k(ex)2?? = 3.4 ± 0.5 × 10?1 s?1, ΔH(?) = 91.13 ± 2 kJ mol?1, and ΔS(?) = +51.9 ± 5 J K?1 mol?1 for 2. A limiting D mechanism is assigned for these ligand exchange reactions on the basis of first-order rate laws and positive and large entropies of activation. The exchange rates are 4 orders of magnitude slower than those observed for the ligand exchange on the reduced heterovalent cluster [Fe(III)?Fe(II)(μ?-O)(μ-O?CCH?)?(4-Phpy)?] (3). In 3, the intramolecular Fe(III)/Fe(II) electron exchange is too fast to be observed. At low temperatures, the 1/3 intermolecular second-order electron self-exchange reaction is faster than the 4-Phpy ligand exchange reactions on these two clusters, suggesting an outer-sphere mechanism: k?2?? = 72.4 ± 1.0 × 103 M?1 s?1, ΔH(?) = 18.18 ± 0.3 kJ mol?1, and ΔS(?) = -90.88 ± 1.0 J K?1 mol?1. The [Fe?(μ?-O)(μ-O?CCH?)?(4-Phpy)?](+/0) electron self-exchange reaction is compared with the more than 3 orders of magnitude faster [Ru?(μ?-O)(μ-O?CCH?)?(py)?](+/0) self-exchange reaction (ΔΔG(exptl)(?298) = 18.2 kJ mol?1). The theoretical estimated self-exchange rate constants for both processes compare reasonably well with the experimental values. The equilibrium constant for the formation of the precursor to the electron-transfer and the free energy of activation contribution for the solvent reorganization to reach the electron transfer step are taken to be the same for both redox couples. The larger ΔG(exptl)(?298) for the 1/3 iron self-exchange is attributed to the larger (11.1 kJ mol?1) inner-sphere reorganization energy of the 1 and 3 iron clusters in addition to a supplementary energy (6.1 kJ mol?1) which arises as a result of the fact that each encounter is not electron-transfer spin-allowed for the iron redox couple.     

Probing Surface Sites of TiO2: Reactions with [HRe(CO)5] and [CH3Re(CO)5]

Two carbonyl complexes of rhenium, [HRe(CO)₅] and [CH₃Re(CO)₅], were used to probe surface sites of TiO₂ (anatase). These complexes were adsorbed from the gas phase onto anatase powder that had been treated in flowing O₂ or under vacuum to vary the density of surface OH sites. Infrared (IR) spectra demonstrate the variation in the number of sites, including Ti⁺³? OH and Ti⁺⁴? OH. IR and extended X‐ray absorption fine structure (EXAFS) spectra show that chemisorption of the rhenium complexes led to their decarbonylation, with formation of surface‐bound rhenium tricarbonyls, when [HRe(CO)₅] was adsorbed, or rhenium tetracarbonyls, when [CH₃Re(CO)₅] was adsorbed. These reactions were accompanied by the formation of water and surface carbonates and removal of terminal hydroxyl groups associated with Ti⁺³ and Ti⁺⁴ ions on the anatase. Data characterizing the samples after adsorption of [HRe(CO)₅] or [CH₃Re(CO)₅] determined a ranking of the reactivity of the surface OH sites, with the Ti⁺³? OH groups being the more reactive towards the rhenium complexes but the less likely to be dehydroxylated. The two rhenium pentacarbonyl probes provided complementary information, suggesting that the carbonate species originate from carbonyl ligands initially bonded to the rhenium and from hydroxyl groups of the titania surface, with the reaction leading to the formation of water and bridging hydroxyl groups on the titania. The results illustrate the value of using a family of organometallic complexes as probes of oxide surface sites.     

Insertion Reactions of [ReH(CO)5–n(PMe3)n] Complexes (n = 2–4) with aldehydes,CO2, and activated acetylenes

The complexes of the type [ReH(CO)_5–n(PMe₃)_n] (n = 4, 3) were reacted with aldehydes, CO₂, and RC?CCOOMe (R = H, Me) to establish a phosphine-substitutional effect on the reactivity of the Re–H bond. In the series 1–3 , benzaldehyde showed conversion with only 3 to afford a (benzyloxy)carbonyltetrakis(trimethylphosphine)rhenium complex 4 . Pyridine-2-carbaldehyde allowed reaction with all hydrides 1–3 . With 1 and 2 , the same dicarbonyl[(pyridin-2-yl)methoxy-O, N]bis(trimethylphosphine)rhenium 5b was formed with the intermediacy of a [(pyridin-2-yl)methoxy-O]-ligated species and extrusion of CO or PMe₃, respectively. The analogous conversion of 3 afforded the carbonyl[(pyridin-2-yl)methoxy-O,N]tris(trimethylphosphine)rhenium ( 1 ) 7b . While 1 did not react with CO₂, 2 and 3 yielded under relatively mild conditions the formato-ligated [Re(HCO₂)(CO)(L)(PMe₃)₃] species ( 8 (L = CO) and 9 (L = PMe₃)). Methyl propiolate and methyl butynoate were transformed, in the presence of 1 , to [Re{C(CO₂Me)?CHR}(CO)₃(PMe₃)₂] systems ( 10a (R = H), and 10b (R = Me)), with prevailing α-metallation and trans-insertion stereochemistry. Similarly, HC≡CCO₂Me afforded with 2 and 3 , the α-metallation products [Re{C(CO₂Me)?CH₂}(CO)(L)(PMe₃)₃] 11 (L = CO) and 12 (L = PMe₃). The methyl butyonate insertion into 2 resulted in formation of a mixture of the (Z)- and (E)-isomers of [Re{C(CO₂Me)?CHMe} (CO)₂(PMe₃)₃] ( 13a , b ). In the case of the conversion of 3 with MeC?CCO₂Me, a Re–H cis-addition product [Re{(E)-C(CO₂Me)?CHMe}(CO)(PMe₃)₄] ( 14 ) was selectively obtained. Complex 11 was characterized by an X-ray crystal-structure analysis.     

Complete family of mono-, bi-, and trinuclear Re(I)(CO)3Cl complexes of the bridging polypyridyl ligand 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinapthalene: syn/anti isomer separation, characterization, and photophysics

The syn and anti isomers of the bi- and trinuclear Re(CO)(3)Cl complexes of 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinapthalene (HATN-Me(6)) are reported. The isomers are characterized by (1)H NMR spectroscopy and X-ray crystallography. The formation of the binuclear complex from the reaction of HATN-Me(6) with 2 equiv of Re(CO)(5)Cl in chloroform results in a 1:1 ratio of the syn and anti isomers. However, synthesis of the trinuclear complex from the reaction of HATN-Me(6) with 3 equiv of Re(CO)(5)Cl in chloroform produces only the anti isomer. syn-{(Re(CO)(3)Cl)(3)(μ-HATN-Me(6))} can be synthesized by reacting 1 equiv of Re(CO)(5)Cl with syn-{(Re(CO)(3)Cl)(2)(μ-HATN-Me(6))} in refluxing toluene. The product is isolated by subsequent chromatography. The X-ray crystal structures of syn-{(Re(CO)(3)Cl)(2)(μ-HATN-Me(6))} and anti-{(Re(CO)(3)Cl)(3)(μ-HATN-Me(6))} are presented both showing severe distortions of the HATN ligand unit and intermolecular π stacking. The complexes show intense absorptions in the visible region, comprising strong π → π* and metal-to-ligand charge-transfer (MLCT) transitions, which are modeled using time-dependent density functional theory (TD-DFT). The energy of the MLCT absorption decreases from mono- to bi- to trinuclear complexes. The first reduction potentials of the complexes become more positive upon binding of subsequent Re(CO)(3)Cl fragments, consistent with changes in the energy of the MLCT bands and lowering of the energy of relevant lowest unoccupied molecular orbitals, and this is supported by TD-DFT. The nature of the excited states of all of the complexes is also studied using both resonance Raman and picosecond time-resolved IR spectroscopy, where it is shown that MLCT excitation results in the oxidation of one rhenium center. The patterns of the shifts in the carbonyl bands upon excitation reveal that the MLCT state is localized on one rhenium center on the IR time scale.     

Binuclear manganese and rhenium carbonyls M2(CO)n (n = 10, 9, 8, 7): comparison of first row and third row transition metal carbonyl structures

The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic binuclear rhenium carbonyls Re2(CO)n (n = 10, 9, 8, 7) were determined using the MPW1PW91 and BP86 methods from density functional theory (DFT) with the effective core potential basis sets LANL2DZ and SDD. In all cases triplet structures for Re2(CO)n were found to be unfavorable energetically relative to singlet structures, in contrast to corresponding Mn2(CO)n derivatives, apparently owing to the larger ligand field splitting of rhenium. For M2(CO)10 (M = Mn, Re) the unbridged structures (OC)5M-M(CO)5 are preferred energetically over structures with bridging CO groups. For M2(CO)9 (M = Mn, Re) the two low energy structures are (OC)4M(micro-CO)M(CO)4 with an M-M single bond and a four-electron donor bridging CO group and (OC)4M[double bond, length as m-dash]M(CO)5 with no bridging CO groups and an M[double bond, length as m-dash]M distance suggesting a double bond. The lowest energy structures for Re2(CO)8 have Re[triple bond, length as m-dash]Re distances in the range 2.6-2.7 A suggesting the triple bonds required to give the Re atoms the favored 18-electron configuration. Low energy structures for Re2(CO)7 are either of the type (OC)(4)M[triple bond, length as m-dash]M(CO)3 with short metal-metal distances suggesting triple bonds or have a single four-electron donor bridging CO group and longer M-M distances consistent with single or double bonds. The 18-electron rule thus appears to be violated in these highly unsaturated Re2(CO)7 structures.     

Heterometallatom-Koordinationsverbindungen Re2(μ-PPh2)2[mer-(CO)3]2-trans-[InX2(H2O)]2 und neue halogenhaltige drei- und vierkernige Rheniumcluster aus Reaktionen zwischen Re2[μ-PPh2)2(CO)8] und InX3 (X = Cl,Br, I)

Heterometallic Coordination Compounds Re₂(μ-PPh₂)₂[mer-(CO)₃]₂-trans-[InX₂(H₂O)]₂ and New Halogene Containing Three- and Four-Nuclear Rhenium Clusters from Reactions between Re₂(μ-PPh₂)₂(CO)₈ and InX₃ (X = Cl, Br, I) In sealed glass tubes equimolar amounts of Re₂(μ-PPh₂)₂(CO)₈ and InX₃ (X = Cl, Br, I) were reacted in the presence of xylene at 220°C to two types of products. The first type comprised the heterometallic coordination compounds Re₂(μ-PPh₂)₂(CO)₆[InX₂(H₂O)]₂ (X = Cl, Br, I) (yield 60%), and the second halogene containing rhenium complexes Re₃(μ₃-H)(μ₃-X)(μ-PPh₂)₃(CO)₆ (unsaturated three-membered metal ring with 46 VE) and Re₄(μ-H)(μ-X)(μ-PPh₂)₄(μ₄-PPh)(CO)₈ and additionally those substances as cis-IRe(CO)₄(PPh₂H), Re₂(μ-PPh₂)(μ-X)(CO)₈ (X = Cl, Br), Re₂(μ-I)₂[μ-(PPh₂)₂O](CO)₆ and Re₄(μ-Cl)₂(μ-PPh₂)₄(μ₄-PPh)(CO)₈ (four-membered metal ring with 66 VE with three Re? Re bonds) which have been observed in one or two of the three reaction systems. A proposal of the reaction course is discussed. The single X-ray analysis of Re₂(μ-PPh₂)₂[mer(CO)₃]₂-trans[InI₂(H₂O)]₂ · 2 Me₂CO shows for the two fold phosphido bridged dirhenium molecular fragment with 34 VE a Re? Re bond of 294.6(1) pm. From two possible transpositions of both In? Re bond vectors, the one found advantageously has sterical reasons. The average In? Re single bond length is 271.1(1) pm. The corresponding determination of the unsaturated three-membered ring compound Re₃(μ₃-H) (μ₃-Cl)(μ-PPh₂)₃(CO)₆ showed three Re? Re bond lenghts of comparable size, of which the mean value of 281.9(1) pm was significantly shortened by π electron delocalization effect compared to that of a saturated phosphido bridged three-membered rhenium ring compound. As it was recognized by further comparison, the structural data of the common molecular fragments in the three examined three-membered rhenium ring clusters (X = Cl, Br, I) are not dependent on the different kind of halogeno ligand atoms. Finally, the crystal structure determination of the substance Re₄(μ-H)(μ-Br)(μ-PPh₂)₄(μ₄-PPh)(CO)₈ shows the presence of square-pyramidal Re₄(μ₄-P) atomic arrangement, of which the planar basic plane has a sequence of up- and downwards orientated four diphenylphosphido bridging groups. The four measured Re? Re single bond lengths (mean value 302.7(3) pm change with the different kind of bridging atoms. The structural features observed are compared with those of a corresponding iodine derivative.     

Unsaturated binuclear cyclopentadienylrhenium carbonyl derivatives: metal-metal multiple bonds and agostic hydrogen atoms

The cyclopentadienylrhenium carbonyls Cp 2Re 2(CO) n (Cp = eta (5)-C 5H 5; n = 5, 4, 3, 2) have been studied by density functional theory. The global minima for the Cp 2Re 2(CO) n ( n = 5, 4, 3, 2) derivatives are predicted to be the singly bridged structure Cp 2Re 2(CO) 4(mu-CO) with a formal Re-Re single bond; the doubly semibridged structure Cp 2Re 2(CO) 4 with a formal ReRe double bond; the triply bridged structure Cp 2Re 2(mu-CO) 3 with a formal ReRe triple bond; and the doubly bridged structure Cp 2Re 2(mu-CO) 2, respectively. The first three of these predicted structures have been realized experimentally in the stable compounds (eta (5)-C 5H 5) 2Re 2(CO) 4(mu-CO), (eta (5)-Me 5C 5) 2Re 2(CO) 4 and (eta (5)-Me 5C 5) 2Re 2(mu-CO) 3. In addition, structures of the type Cp 2Re-Re(CO) n with both rings bonded only to one metal and unknown in manganese chemistry are also found for rhenium but at energies significantly above the global minima. The unsaturated Cp 2Re-Re(CO) n structures ( n = 4, 3, 2) have agostic Cp hydrogen atoms forming C-H-Re bridges to the unsaturated Re(CO) n group with a Re-H distance as short as 2.04 A.     

Boronyl ligand as a member of the isoelectronic series BO(-) → CO → NO(+): viable cobalt carbonyl boronyl derivatives?

Recently the first boronyl (oxoboryl) complex [(c-C(6)H(11))(3)P](2)Pt(BO)Br was synthesized. The boronyl ligand in this complex is a member of the isoelectronic series BO(-) → CO → NO(+). The cobalt carbonyl boronyls Co(BO)(CO)(4) and Co(2)(BO)(2)(CO)(7), with cobalt in the formal d(8) +1 oxidation state, are thus isoelectronic with the familiar homoleptic iron carbonyls Fe(CO)(5) and Fe(2)(CO)(9). Density functional theory predicts Co(BO)(CO)(4) to have a trigonal bipyramidal structure with the BO group in an axial position. The tricarbonyl Co(BO)(CO)(3) is predicted to have a distorted square planar structure, similar to those of other 16-electron complexes of d(8) transition metals. Higher energy Co(BO)(CO)(n) (n = 3, 2) structures may be derived by removal of one (for n = 3) or two (for n = 2) CO groups from a trigonal bipyramidal Co(BO)(CO)(4) structure. Structures with a CO group bridging 17-electron Co(CO)(4) and Co(BO)(2)(CO)(3) units and no Co-Co bond are found for Co(2)(BO)(2)(CO)(8). However, Co(2)(BO)(2)(CO)(8) is not viable because of the predicted exothermic loss of CO to give Co(2)(BO)(2)(CO)(7). The lowest lying Co(2)(BO)(2)(CO)(7) structure is a triply bridged (2BO + CO) structure closely related to the experimental Fe(2)(CO)(9) structure. However, other relatively low energy Co(2)(BO)(2)(CO)(7) structures are found, either with a single CO bridge, similar to the experimental Os(2)(CO)(8)(μ-CO) structure; or with 17-electron Co(CO)(4) and Co(BO)(2)(CO)(3) units joined by a single Co-Co bond with or without semibridging carbonyl groups. Both triplet and singlet Co(2)(BO)(2)(CO)(6) structures are found. The lowest lying triplet Co(2)(BO)(2)(CO)(6) structures have a Co(CO)(3)(BO)(2) unit coordinated to a Co(CO)(3) unit through the oxygen atoms of the boronyl groups with a non-bonding ～4.3 ? Co···Co distance. The lowest lying singlet Co(2)(BO)(2)(CO)(6) structures have either two three-electron donor bridging η(2)-μ-BO groups and no Co···Co bond or one such three-electron donor BO group and a formal Co-Co single bond.     

Rhenium ethoxy- and hydroxycarbene complexes with thiophene substituents

Reaction of mono- and dilithiated thiophene (a), bithiophene (b) and 2,5-dibromothiophene (c) with [Re(2)(CO)(10)] afforded, after subsequent alkylation with triethyloxonium tetrafluoroborate, tetra- and binuclear Fischer carbene complexes, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)X}], n = 1, X = H (1a); n = 2, X = H (1b); n = 1, X = Br (1c); n = 1, X = C(OEt)Re(2)(CO)(9), (2a); n = 2, X = C(OEt)Re(2)(CO)(9) (2b), as major products. The dirhenium acylate intermediates from this reaction not only gave the expected novel ethoxycarbene complexes with alkylation but after rhenium-rhenium bond breaking afforded a number of minor products. The (1)H NMR spectrum of the crude reaction mixture revealed the formation of four metal hydride complexes and aldehydes. Protonation with HBF(4) instead of alkylation with Et(3)OBF(4) significantly increased the yields of the hydride complexes, which enabled the positive identification of three of these complexes. In addition to the known compounds [Re(CO)(5)H] and [Re(3)(CO)(14)H] (3), a unique complex displaying a hydroxycarbene fragment connected to an acyl fragment via an O-H···O hydrogen bond and a Re···H···Re bond linking the two Re centers, [(μ-H){Re(CO)(4)C(OH){C(4)H(2)S}(n)H}{Re(CO)(4)C(O){C(4)H(2)S}(n)H}], n = 1 (4a) or n = 2 (4b), were isolated. The formation of thiophene aldehydes, H{C(O)}(m){C(4)H(2)S}(n)C(O)H (m = 0 or 1 and n = 1 or 2), were observed and the novel monocarbene complexes with terminal aldehyde groups, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)C(O)H}], n = 1 (5a) and n = 2 (5b) could be isolated. A higher yield of 5b was obtained after stirring crystals of 2b in wet THF. The crystal structures of 1a, 2a, 4a and 5b are reported.     

New dirhenium(III) compounds bridged by carboxylate ligands: N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] and Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2)

The solvothermal reaction of (N(C(4)H(9))(4))(2)[Re(2)Cl(8)] with trifluoroacetic acid and acetic anhydride leads to the new rhenium trifluoroacetate dimer N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1) and to the rhenium carbonyl dimer Re(2)(mu(2)-Cl)(2)(CO)(8) as the rhenium-reduced byproduct. The reaction of the precursor complex, N(C(4)H(9))(4)[Re(2)(OOCCF(3))Cl(6)] (1), with the organometallic carboxylic acid (CO)(6)Co(2)HCCCOOH leads to the cluster of clusters compound Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2), which has the dimer structure of Re(2)(OOCR)(4)Cl(2). Cyclic voltammetric measurements show that Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) has one reduction centered on the dirhenium core and a reduction centered on the cobalt atoms. DFT calculations have been used to rationalize the observed displacements of the voltammetric signals in Re(2)(OOCCCHCo(2)(CO)(6))(4)Cl(2) (2) compared to the parent ligand (CO)(6)Co(2)HCCCOOH and rhenium pivalate.     

Systematic synthesis, isolation, and photophysical properties of linear-shaped Re(I) oligomers and polymers with 2-20 units

Systematic synthesis routes have been developed for the linear-shaped rhenium(I) oligomers and polymers bridged with bidentate phosphorus ligands, [Re(N--N)(CO)3-PP-{Re(N--N)(CO)2-PP-}(n)Re(N--N)(CO)3](PF6)(n+2) (N--N = diimine, PP = bidentate phosphine, n = 0-18). These were isolated by size exclusion chromatography (SEC) and identified by (1)H NMR, IR, electrospray ionization Fourier transform mass spectrometry, analytical SEC, and elemental analysis. Crystal structures of [Re(bpy)(CO)3-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)3](PF6)2, [Re(bpy)(CO)3-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)2-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)3](PF6)3 and [Re(bpy)(CO)3-Ph2PC2H4PPh2-{Re(bpy)(CO)2Ph2PC2H4PPh2-}(n)Re(bpy)(CO)3](PF6)(n+2) (bpy = 2,2'-bipyridine, n = 1, 2) were obtained, showing that they have interligand pi-pi interaction between the bpy ligand and the phenyl groups on the phosphorus ligand. All of the oligomers and polymers synthesized were emissive at room temperature in solution. For the dimers, broad emission was observed with a maximum at 523-545 nm, from the (3)MLCT excited-state of the tricarbonyl complex unit, [Re(N--N)(CO)3-PP-]. Emission from the longer oligomers and polymers with > or = 3 Re(I) units was observed at wavelengths 50-60 nm longer than those of the corresponding dimers. This fact and the emission decay results clearly show that energy transfer from the edge unit to the interior unit occurs with a rate constant of (0.9 x 10(8))-(2.5 x 10(8)) s(-1). The efficient energy transfer and the smaller exclusive volume of the longer Re(I) polymers indicated intermolecular aggregation for these polymers in an MeCN solution.