Cationic diiron and diruthenium μ-allenyl complexes: synthesis, X-ray structures and cyclization reactions with ethyldiazoacetate/amine affording unprecedented butenolide- and furaniminium-substituted bridging carbene ligands

The novel cationic diiron μ-allenyl complexes [Fe(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe(2)Cp(2)(CO)(4)]. The solid state structures of [4a][CF(3)SO(3)] and of the diruthenium analogues [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}][BPh(4)] (R = Me, [2a][BPh(4)]; R = Ph, [2c][BPh(4)]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Br?nsted bases result in formation of the μ-allenylidene compound [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(1)-C(α)=C(β)=C(γ)(Ph)(2)}] (5) and of the dimetallacyclopentenone [Fe(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)=C(β)(C(γ)(Me)CH(2))C(=O)}] (6), respectively. The nitrile adducts [Ru(2)Cp(2)(CO)(NCMe)(μ-CO){μ-η(1):η(2)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a,c with MeCN/Me(3)NO, react with N(2)CHCO(2)Et/NEt(3) at room temperature, affording the butenolide-substituted carbene complexes [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(R)(2)OC(=O)C[upper bond 1 end](H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (9) has been detected in the course of the reaction leading to 10a. The addition of N(2)CHCO(2)Et/NHEt(2) to 7a gives the 2-furaniminium-carbene [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (11). The X-ray structures of 10a, 10b and [11][BF(4)] have been determined. The reactions of 4a,b with MeCN/Me(3)NO result in prevalent decomposition to mononuclear iron species.     

1 Pi<--X1 Sigma+ band systems of jet-cooled ScCo and YCo

Rotationally resolved resonant two-photon ionization (R2PI) spectra of ScCo and YCo are reported. The measured spectra reveal that these molecules possess ground electronic states of (1)Sigma(+) symmetry, as previously found in the isoelectronic Cr(2) and CrMo molecules. The ground state rotational constants for ScCo and YCo are B(0)(")=0.201 31(22) cm(-1) and B(0) (")=0.120 96(10) cm(-1), corresponding to ground state bond lengths of r(0) (")=1.812 1(10) A and r(0) (")=1.983 0(8) A, respectively. A single electronic band system, assigned as a (1)Pi<--X (1)Sigma(+) transition, has been identified in both molecules. In ScCo, the (1)Pi state is characterized by T(0)=15,428.8, omega(e)(')=246.7, and omega(e)(')x(e)(')=0.73 cm(-1). In YCo, the (1)Pi state has T(0)=13 951.3, omega(e)(')=231.3, and omega(e)(')x(e) (')=2.27 cm(-1). For YCo, hot bands originating from levels up to v(")=3 are observed, allowing the ground state vibrational constants omega(e)(")=369.8, omega(e)(")x(e)(")=1.47, and Delta G(12)(")=365.7 cm(-1) to be deduced. The bond energy of ScCo has been measured as 2.45 eV from the onset of predissociation in a congested vibronic spectrum. A comparison of the chemical bonding in these molecules to related molecules is presented.     

Luminescence of the nonclassical homoleptic metal carbonyl complex [Rh(CO4]+

The nonclassical [Rh(CO)(4)](+) cation is luminescent at low temperature with a peak maximum at 19640 cm(-1) and a full-width at half-maximum of 2900 cm(-1). Both the solution absorption and low-temperature solid-state luminescence spectra of the [Rh(CO)(4)](1-Et-CB(11)F(11)) salt are reported. The cesium salt of the [1-Et-CB(11)F(11)](-) counterion is also luminescent (with a peak maximum at 22650 cm(-1)), but the emission maximum of [Rh(CO)(4)](+) is lower in energy. The Rh-C bond length changes of approximately 0.07 A in the excited state are calculated. The calculated bond length changes in the nonclassical [Rh(CO)(4)](+) ion are not very different from those in classical complexes.     

Discrete and monodimensional heteropolynuclear structures formed by tetracarboxylatodiruthenium(II,III) and perrhenato fragments

Reaction between cationic units of carboxylate-bridged diruthenium complexes [Ru(2)(mu-O(2)CR)(4)](+) (R = Me, CMePh(2), CMe(3), CH(2)CH(2)OMe, C(Me)=CHEt, C(6)H(4)-p-OMe, Ph) and tetrabutylammonium perrhenate gives complexes with different arrangements in the solid state. Thus, the compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)) [R = Me (1), CMePh(2) (2), CMe(3) (3), CH(2)CH(2)OMe (4), C(Me)=CHEt (5), C(6)H(4)-p-OMe (6), Ph (7)] have polymeric structures with the diruthenium units linked by perrhenate ligands in the axial positions. The structures of complexes 3.THF and 4 were established by single-crystal X-ray diffraction. The tetrahedral geometry of the ReO(4)(-) anion permits the formation of a chain close to the linearity. In contrast to the polymeric chains observed in complexes 1-7, the reaction of [Ru(2)(mu-O(2)CPh)(4)](+) with NBu(4)ReO(4) also affords the compounds Ru(2)(mu-O(2)CPh)(4)(ReO(4))(H(2)O) (8) and NBu(4)[Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)] (9) depending on the reaction conditions. The structure of 8 consists of cationic and anionic units, [Ru(2)(mu-O(2)CPh)(4)(H(2)O)(2)](+) and [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-), linked by hydrogen bonds, which give a three-dimensional net. The structure of complex 9.0.5H(2)O has an anionic unit similar to that of 8, whose counterion is NBu(4)(+). The Ru-Ru bond distances are slightly longer in [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-) than in the polymeric compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)). The magnetic behavior owes to the existence of zero-field splitting (ZFS) and a weak antiferromagnetic coupling. The experimental data are fitted with a model that considers the ZFS effect using the Hamiltonian (D) = SDS. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation.     

Dependence of the chemical properties of macrocyclic [Ni(II)(2)L(μ-O(2)CR)](+) complexes on the basicity of the carboxylato coligands (L(2-) = macrocyclic N(6)S(2) ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.     

Diastereoselective fragmentation of chiral alpha-aminophosphonic acids/metal ion aggregates

Diastereomeric clusters of general formula [MAB(2)](+) and [MA(2)B](+) (M = Li(I), Na(I), Ag(I), Ni(II)-H, or Cu(II)-H; A = (R)-(-)- and (S)-(+)-(1-aminopropyl)phosphonic acid; B = (1R)-(-)- and (1S)-(+)-(1-aminohexyl)phosphonic acid) have been readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissociation (CID) investigated. CID of diastereomeric complexes, e.g. [MA(S)(B(S))(2)](+) and [MA(R)(B(S))(2)](+), leads to fragmentation patterns characterized by R(homo) = [MA(S)B(S)](+)/[M(B(S))(2)](+) and R(hetero) = [MA(R)B(S)](+)/[M(B(S))(2)](+) abundance ratios, which depend upon the relative stability of the diastereomeric [MA(S)B(S)](+) and [MA(R)B(S)](+) complexes in the gas phase. The chiral resolution factor R(chiral) = R(homo)/R(hetero) is found to depend not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB(2)](+) or [MA(2)B](+). The origin of this behavior is discussed.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

Approaching the gas-phase structures of [AgS8]+ and [AgS16]+ in the solid state

Upon treating elemental sulfur with [AgSbF(6)], [AgAl(hfip)(4)], [AgAl(pftb)(4)] (hfip=OCH(CF(3))(2), pftb =OC(CF(3))(3)) the compounds [Ag(S(8))(2)][SbF(6)] (1), [AgS(8)][Al(hfip)(4)] (2), and [Ag(S(8))(2)](+)[[Al(pftb)(4)](-) (3) formed in SO(2) (1), CS(2) (2), or CH(2)Cl(2) (3). Compounds 1-3 were characterized by single-crystal X-ray structure determinations: 1 by Raman spectroscopy, 2 and 3 by solution NMR spectroscopy and elemental analyses. Single crystals of [Ag(S(8))(2)](+)[Sb(OTeF(5))(6)](-) 4 were obtained from a disproportionation reaction and only characterized by X-ray crystal structure analysis. The Ag(+) ion in 1 coordinates two monodentate SbF(6) (-) anions and two bidentate S(8) rings in the 1,3-position. Compound 2 contains an almost C(4v)-symmetric [AgS(8)](+) moiety; this is the first example of an eta(4)-coordinated S(8) ring (d(Agbond;S)=2.84-3.00 A). Compounds 3 and 4, with the least basic anions, contain undistorted, approximately centrosymmetric Ag(eta(4)-S(8))(2) (+) cations with less symmetric eta(4)-coordinated S(8) rings (d(Agbond;S)=2.68-3.35 A). The thermochemical radius and volume of the undistorted Ag(S(8))(2) (+) cation was deduced as r(therm)(Ag(S(8))(2) (+))=3.378+ 0.076/-0.120 A and V(therm)(Ag(S(8))(2) (+))=417+4/-6 A(3). AgS(8) (+) and several isomers of the Ag(S(8))(2) (+) cation were optimized at the BP86, B3LYP, and MP2 levels by using the SVP and TZVPP basis sets. An analysis of the calculated geometries showed the MP2/TZVPP level to give geometries closest to the experimental data. Neither BP86 nor B3LYP reproduced the longer weak dispersive Agbond;S interactions in Ag(eta(4)-S(8))(2) (+) but led to Ag(eta(3)-S(8))(2) (+) geometries. With the most accurate MP2/TZVPP level, the enthalpies of formation of the gaseous [AgS(8)](+) and [Ag(S(8))(2)](+) cations were established as Delta(f)H(298)([Ag(S(8))(2)](+), g)=856 kJ mol(-1) and Delta(f)H(298)([AgS(8)](+), g)=902 kJ mol(-1). It is shown that the [AgS(8)](+) moiety in 2 and the [AgS(8)](2) (+) cations in 3 and 4 are the best approximation of these ions, which were earlier observed by MS methods. Both cations reside in shallow potential-energy wells where larger structural changes only lead to small increases in the overall energy. It is shown that the covalent Agbond;S bonding contributions in both cations may be described by two components: i) the interaction of the spherical empty Ag 5s(0) acceptor orbital with the filled S 3p(2) lone-pair donor orbitals and ii) the interaction of the empty Ag 5p(0) acceptor orbitals with the filled S 3p(2) lone-pair donor orbitals. This latter contribution is responsible for the observed low symmetry of the centrosymmetric Ag(eta(4)-S(8))(2) (+) cation. The positive charge transferred from the Ag(+) ion in 1-4 to the coordinated sulfur atoms is delocalized over all the atoms in the S(8) ring by multiple 3p(2)-->3sigma* interactions that result in a small long-short-long-short Sbond;S bond-length alternation starting from S1 with the shortest Agbond;S length. The driving force for all these weak bonding interactions is positive charge delocalization from the formally fully localized charge of the Ag(+) ion.     

Insertion reactions of alkynes and organic isocyanides into the palladium-carbon bond of dimetallic Fe-Pd alkoxysilyl complexes

Insertion of MeO(2)C-C[triple bond]C-CO(2)Me (DMAD) into the Pd-C bond of the heterodimetallic complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d(dmba-C)] (2) (dppm = Ph(2)PCH(2)PPh(2), dmba-C = metallated dimethylbenzylamine) and [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d(8-mq-C,N)] (3) (8-mq-C,N = cyclometallated 8-methylquinoline) yielded the sigma-alkenyl complexes [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (7) and [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(CO(2)Me)[double bond, length as m-dash]C(CO(2)Me)(CH(2)C(9)H(6)N)}] (8), respectively. The latter afforded the adduct [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(CH(2)C(9)H(6)N)}(CNBu(t))] (9) upon reaction with 1 equiv. of Bu(t)NC. The heterodinuclear sigma-butadienyl complexes [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(Ph=C(Ph)C(CO(2)Me)=(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (11) and [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(Ph)=C(CO(2)Et)C(Ph)=C(CO(2)Et)(CH(2)C(9)H(6)N)}] (13) have been obtained by reaction of the metallate K[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)] (dppm = Ph(2)PCH(2)PPh(2)) with [P[upper bond 1 start]dCl{C(Ph)=C(Ph)C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)N[upper bond 1 end]Me(2))}] or [P[upper bond 1 start]dCl{C(Ph)=C(CO(2)Et)C(Ph)=(CO(2)Et)}(CH(2)C(9)H(6)N[upper bond 1 end])], respectively. Monoinsertion of various organic isocyanides RNC into the Pd-C bond of 2 and 3 afforded the corresponding heterometallic iminoacyl complexes. In the case of complexes [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end][upper bond 1 start]d{C=(NR)(CH(2)C(9)H(6)N[upper bond 1 end])}] (15a R = Ph, 15b R = xylyl), a static six-membered C,N chelate is formed at the Pd centre, in contrast to the situation in [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(=NR)(o-C(6)H(4)CH(2)NMe(2))}] (14a R = o-anisyl, 14b R = 2,6-xylyl) where formation of a mu-eta(2)-Si-O bridge is preferred over NMe(2) coordination. The outcome of the reaction of the dimetallic alkyl complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]dMe] with RNC depends both on the stoichiometry and the electronic donor properties of the isocyanide employed for the migratory insertion process. In the case of o-anisylisocyanide, the iminoacyl complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(=N-o-anisyl)Me}] (16) results from the reaction in a 1 : 1 ratio. Addition of three equiv. of o-anisylisocyanide affords the tris(insertion) product [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{[C(=N-o-anisyl)](3)Me}] (18). After addition of a fourth equivalent of o-anisylNC, exclusive formation of the isocyanide adduct [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d{[C(=N-o-anisyl)](3)Me}(CN-o-anisyl)] (19) was spectroscopically evidenced. In the complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{[C(=N-o-C(6)H(4)COCH(2))](2)Me}] (20), the sigma-bound diazabutadienyl unit is part of a 12-membered organic macrocyle which results from bis(insertion) of 1,2-bis(2-isocyanophenoxy)ethane into the Pd-Me bond of the precursor complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]dMe]. In contrast, addition of two equivalents of tert-butylisocyanide to a solution of the latter afforded [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]Fe(mu-dppm)P[upper bond 1 end]d{C(=NBu(t))Me}(CNBu(t))] (21) in which both a terminal and an inserted isocyanide ligand are coordinated to the Pd centre. In all cases, there was no evidence for competing CO substitution at the Fe(CO)(3) fragment by RNC. The molecular structures of the insertion products 8 x CH(2)Cl(2) and 16 x CH(2)Cl(2) have been determined by X-ray diffraction.     

Comprehensive thermochemistry of W-H bonding in the metal hydrides CpW(CO)2(IMes)H, [CpW(CO)2(IMes)H](•+), and [CpW(CO)2(IMes)(H)2]+. Influence of an N-heterocyclic carbene ligand on metal hydride bond energies

The free energies interconnecting nine tungsten complexes have been determined from chemical equilibria and electrochemical data in MeCN solution (T = 22 °C). Homolytic W-H bond dissociation free energies are 59.3(3) kcal mol(-1) for CpW(CO)(2)(IMes)H and 59(1) kcal mol(-1) for the dihydride [CpW(CO)(2)(IMes)(H)(2)](+) (where IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), indicating that the bonds are the same within experimental uncertainty for the neutral hydride and the cationic dihydride. For the radical cation, [CpW(CO)(2)(IMes)H](?+), W-H bond homolysis to generate the 16-electron cation [CpW(CO)(2)(IMes)](+) is followed by MeCN uptake, with free energies for these steps being 51(1) and -16.9(5) kcal mol(-1), respectively. Based on these two steps, the free energy change for the net conversion of [CpW(CO)(2)(IMes)H](?+) to [CpW(CO)(2)(IMes)(MeCN)](+) in MeCN is 34(1) kcal mol(-1), indicating a much lower bond strength for the 17-electron radical cation of the metal hydride compared to the 18-electron hydride or dihydride. The pK(a) of CpW(CO)(2)(IMes)H in MeCN was determined to be 31.9(1), significantly higher than the 26.6 reported for the related phosphine complex, CpW(CO)(2)(PMe(3))H. This difference is attributed to the electron donor strength of IMes greatly exceeding that of PMe(3). The pK(a) values for [CpW(CO)(2)(IMes)H](?+) and [CpW(CO)(2)(IMes)(H)(2)](+) were determined to be 6.3(5) and 6.3(8), much closer to the pK(a) values reported for the PMe(3) analogues. The free energy of hydride abstraction from CpW(CO)(2)(IMes)H is 74(1) kcal mol(-1), and the resultant [CpW(CO)(2)(IMes)](+) cation is significantly stabilized by binding MeCN to form [CpW(CO)(2)(IMes)(MeCN)](+), giving an effective hydride donor ability of 57(1) kcal mol(-1) in MeCN. Electrochemical oxidation of [CpW(CO)(2)(IMes)](-) is fully reversible at all observed scan rates in cyclic voltammetry experiments (E° = -1.65 V vs Cp(2)Fe(+/0) in MeCN), whereas CpW(CO)(2)(IMes)H is reversibly oxidized (E° = -0.13(3) V) only at high scan rates (800 V s(-1)). For [CpW(CO)(2)(IMes)(MeCN)](+), high-pressure NMR experiments provide an estimate of ΔG° = 10.3(4) kcal mol(-1) for the displacement of MeCN by H(2) to give [CpW(CO)(2)(IMes)(H)(2)](+).     

Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes

The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.     

Heterolytic activation of hydrogen as a trigger for iridium complex promoted activation of carbon-fluorine bonds

The cationic iridium(III) complex [IrCF(3)(CO)(dppe)(DIB)][BARF](2) where DIB = o-diiodobenzene, dppe = 1,2-bis(diphenylphosphino)ethane, and BARF = B(3,5-(CF(3))(2)C(6)H(3))(4)(-) undergoes reaction in the presence of dihydrogen to form [IrH(2)(CO)(2)(dppe)](+) as the major product. Through labeling studies and (1)H and (31)P[(1)H] NMR spectroscopies including parahydrogen measurements, it is shown that the reaction involves conversion of the coordinated CF(3) ligand into carbonyl. In this reaction sequence, the initial step is the heterolytic activation of dihydrogen, leading to proton generation which promotes alpha-C-F bond cleavage. Polarization occurs in the final [IrH(2)(CO)(2)(dppe)](+) product by the reaction of H(2) with the Ir(I) species [Ir(CO)(2)(dppe)](+) that is generated in the course of the CF(3) --> CO conversion.     

Reactions of (di)manganese carbonyl ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN) in the gas phase

The gas-phase reactions of a series of (di)manganese carbonyl positive ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me(3)TACN) have been examined with the aid of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The monomanganese carbonyl ions, [Mn(CO)(n)](+) (n = 2-5), react predominantly by ligand exchange and to a minor extent by electron transfer with the formation of the radical cation of Me(3)TACN. For the [Mn(CO)(n)](+) (n = 2-4) ions, the ligand exchange results in the exclusive formation of a [Mn(Me(3)TACN)](+) complex, whereas small amounts of [Mn(CO)(Me(3)TACN)](+) ions are also generated in the reactions of the [Mn(CO)(5)](+) ion. The [Mn(2)(CO)(n)](+) ions (n = 2, 4 and 5) react also by competing electron transfer and ligand exchange. The reaction of the [Mn(2)(CO)(2)](+) and [Mn(2)(CO)(4)](+) ions is associated with cleavage of the Mn--Mn bond as evidenced by the pronounced formation of [Mn(Me(3)TACN)](+) ions. For [Mn(2)(CO)(5)](+), the ligand exchange leads mainly to the formation of [Mn(2)(CO)(n)(Me(3)TACN)](+) (n = 1-3) ions. These primary product ions react subsequently by the incorporation of a second Me(3)TACN molecule to afford [Mn(2)(CO)(Me(3)TACN)(2)](+) and [Mn(2)(CO)(2)(Me(3)TACN)(2)](+) ions. Both of these latter species incorporate an oxygen molecule with formation of ions with the assigned composition of [Mn(2)(O(2))(CO)(Me(3)TACN)(2)](+) and [Mn(2)(O(2))(CO)(2)(Me(3)TACN)(2)](+).     

Probing the ruthenium-cumulene bonding interaction: synthesis and spectroscopic studies of vinylidene- and allenylidene-ruthenium complexes supported by tetradentate macrocyclic tertiary amine and comparisons with diphosphine analogues of ruthenium and osmium

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru[double bond]C[double bond]CHR]PF(6) (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C(6)H(4)X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh(2) (5)), trans-[Cl(16-TMC)Ru[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm)(2)M[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C(alpha) and C(alpha)-C(beta) distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E(1/2) values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp(2)Fe(+/0), and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at lambda(max) < or = 310 nm (epsilon(max) > or = 10(4) dm(3) mol(-1) cm(-1)), while weak absorptions at lambda(max) > or = 400 nm (epsilon(max) < or = 10(2) dm(3) mol(-1) cm(-1)) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal nu(C[double bond]C) stretch mode of the vinylidene ligand at 1629 cm(-1). The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at lambda(max) = 479-513 nm (epsilon(max) = (2-3) x 10(4) dm(3) mol(-1) cm(-1)). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm(-1) for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl(NH(3))(4)Ru[double bond]C[double bond]C[double bond]CPh(2)](+) at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at lambda(max) = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nu(C[double bond]C[double bond]C) stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru[double bond]C and Ru[bond]N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C[double bond]C[double bond]C unit in the electronic excited state.     

Electrochemical cleavage of N=N bonds at a Mo2(mu-SMe)3 site relevant to the biological reduction of dinitrogen at a bimetallic sulfur centre

The reduction of diazene complexes [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(2)-H-N=N-R)](+) (R=Ph (3 a); Me (3 b)) and of the hydrazido(2-) derivative [Mo(2)Cp(2)(mu-SMe)(3)[mu-eta(1)-N=N(Me)H]](+) (1 b) has been studied by cyclic voltammetry, controlled-potential electrolysis, and coulometry in THF. The electrochemical reduction of 3 a in the presence of acid leads to cleavage of the N=N bond and produces aniline and either the amido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-NH(2))] 4 or the ammine complex [Mo(2)Cp(2)(mu-SMe)(3)(NH(3))(X)] 5, depending on the initial concentration of acid (HX=HTsO or CF(3)CO(2)H). The N=N bond of the methyldiazene analogue 3 b is not cleaved under the same conditions. The ability of 3 a but not 3 b to undergo reductive cleavage of the N=N bond is attributed to electronic control of the strength of the Mo-N(R) bond by the R group. The electrochemical reduction of the methylhydrazido(2-) compound 1 b in the presence of HX also results in cleavage of the N=N bond, with formation of methylamine, 4 (or 5) and the methyldiazenido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(1)-N=N-Me)]. Formation of the last of these complexes indicates that two mechanisms (N=N bond cleavage and possibly H(2) production) are operative. A pathway for the reduction of N(2) at a dinuclear site of FeMoco is proposed on the basis of these results.     

New alkyl-cobalt(III) complexes containing chiral centers in the chelating system

The complex mer-[Co(III)(L(1)Npy)(2)](+) (1') where the L(1)Npy(-) is the tridentate 3-[(2-pyridyl)methylimino]butan-2-one oximate ligand, gives alkyl-cobalt derivatives after reduction with NaBH(4)/Pd(2+) to the Co(I) and alkylation. The formation of the cobalt-carbon bond is accompanied by the reduction to the amino form of one or both imino ligands (depending on the experimental conditions) initially present in 1'. In one series of experiments, complexes of the type fac-[RCo(III)(L(1)Npy)(H-L(1)NHpy)](+) (R = Me, i-Pr, CH(2)Cl, CH(2)Br, CH(2)CF(3), and Bz) were obtained, in which only one of the two ligands was reduced to the amino form (H-L(1)NHpy). The saturation of one azomethine group causes the products to assume a fac configuration and induces the formation of one asymmetric carbon and one asymmetric nitrogen center in the chelating system. When an excess of reducing agent is used, both azomethine groups may be saturated, causing the introduction of one pair of chiral carbons and one pair of chiral nitrogens. Two isomers of the methyl derivative [MeCo(III)(L(1)NHpy)(H-L(1)NHpy)](+) were isolated. The X-ray analysis reveals that these isomers differ from one another in configuration of the C and N chiral centers. Possible reaction mechanisms leading to these different types of complexes are proposed.     

Molecular Orbital Calculation and Spectroscopic Study of the Photochemical Generation of Bis(2,2'-bipyridine)rhodium(I) from Bis(2,2'-bipyridine)(oxalato)rhodium(III)

A planar complex, [Rh(bpy)(2)](+) (bpy = 2,2'-bipyridine), was obtained from [Rh(ox)(bpy)(2)](+) (ox = oxalato) by photoirradiation. A rate constant k for the photoreaction was evaluated as 1 x 10(8) s(-1) in simple first-order kinetics, whereas a ligand dissociation, a reorganization of the coordinated bpy, and a two-electron transfer were involved in the reaction. The process of the Rh(I) complex generation was investigated in terms of a discrete variational (DV)-Xalpha molecular orbital calculation on [Rh(ox)(HN=CHCH=NH)(2)](+) instead of [Rh(ox)(bpy)(2)](+). From the calculation, using the transition-state method, it was predicted that a transition of the ox pi orbital to the metal 4d(z)()2 orbital caused the ligand dissociation and the reorganization of the coordinated bpy occurred in the ox pi to Rh 4d(x)()2(-y)2 excited state stabilized by the ox elimination. Upon release of the ligand and a change from octahedral to square-planar geometry, the electron density on the metal increased and the Rh 4d orbital acquired a d(8) electronic configuration.     

Near-infrared spectra and rovibrational dynamics on a four-dimensional ab initio potential energy surface of (HBr)2

Supersonic jet investigations of the (HBr)(2) dimer have been carried out using a tunable diode laser spectrometer to provide accurate data for comparison with results from a four-dimensional (4-D) ab initio potential energy surface (PES). The near-infrared nu(1) (+/-), nu(2) (+/-), and (nu(1)+nu(4))(-) bands of (H (79)Br)(2), (H (79)Br-H (81)Br), and (H (81)Br)(2) isotopomers have been recorded in the range 2500-2600 cm(-1) using a CW slit jet expansion with an upgraded near-infrared diode laser spectrometer. The 4-D PES has been calculated for (HBr)(2) using second-order M?ller-Plesset perturbation theory with an augmented and polarized 6-311G basis set. The potential is characterized by a global minimum occurring at the H bond structure with the distance between the center of masses (CM) of the monomer being R(CM)=4.10 A with angles theta(A)=10 degrees, theta(B)=100 degrees and a well depth of 692.2 cm(-1), theta(A) is the angle the HBr bond of monomer A makes with the vector from the CM of A to the CM of B, and theta(B) is the corresponding angle monomer B makes with the same CM-CM vector. The barrier for the H interchange occurs at the closed C(2h) structure for which R(CM)=4.07 A, theta(A)=45 degrees, theta(B)=135 degrees, and the barrier height is 73.9 cm(-1). The PES was fitted using a linear-least squares method and the rovibrational energy levels of the complex were calculated by a split pseudospectral method. The spectroscopic data provide accurate molecular parameters for the dimer that are then compared with the results predicted on the basis of the 4-D ab initio PES.     

The rotational spectrum and structure for the argon-cyclopentadienyl thallium van der Waals complex: experimental and computational studies of noncovalent bonding in an organometallic pi-complex

The rotational spectrum of a noble gas-organometallic complex was measured using a pulse molecular beam Fourier transform microwave spectrometer. Rotational transitions for the neutral argon-cyclopentadienyl thallium weakly bound complex were measured in the 4-9 GHz range. Analysis of the spectrum showed that the complex is a prolate symmetric-top rotor with C(5V) symmetry. The experimentally determined molecular parameters for Ar-C(5)H(5) (205)Tl are B=372.4479(3) MHz, D(J)=0.123(2) kHz, and D(JK)=0.45(2) kHz. For Ar-C(5)H(5) (203)Tl, B=373.3478(5) MHz, D(J)=0.113(3) kHz, and D(JK)=0.37(3) kHz. Using a pseudodiatomic model with Lennard-Jones potential yields an approximate binding energy of 339 cm(-1). The argon atom is located on the a-axis of the C(5)H(5)Tl monomer, directly opposite from the thallium metal atom. The measured separation distance between argon and the cyclopentadienyl ring is R=3.56 A. The overall size of the cluster is about 6 A, measuring from argon to thallium. Relatively small D(J) and D(JK) centrifugal distortion constants were observed for the complex, indicating that the structure of Ar-C(5)H(5)Tl is somewhat rigid. MP2 calculations were used to investigate the possible structures and binding energies of the argon-cyclopentadienyl thallium complex. Calculated, counterpoise corrected binding energies are evaluated at R=3.56 A for Ar-C(5)H(5)Tl range from 334 to 418 cm(-1). The experimental binding energy epsilon=339 cm(-1) for Ar-C(5)H(5)Tl falls within this range. The higher-level MP2/aug-cc-pVTZ-PP (thallium)/aug-cc-pVTZ(Ar, C, H) calculation with variable R yielded R(e)=3.46 A and binding energy of 535 cm(-1). Our estimated binding energy for argon-cyclopentadienyl thallium is very similar to the binding energy of argon-benzene. Calculations for the new van der Waals complexes, Ar(C(5)H(5)Tl)(2) and (C(5)H(5)Tl)(2), have been obtained, providing further information on the structures and bonding properties of previously observed cyclopentadienyl thallium polymer chains. The calculated intermolecular distance R(Tl-Cp)=3.05 A for the (CpTl)(2) chain subunit (Cp is cyclopentadienyl, C(5)H(5)) is slightly longer than the measured x-ray value R(M-Cp)(M=Tl)=2.75 A. The x-ray distance R(Tl-Tl)=5.5 A for the chain structure is almost identical to the calculated R(Tl-Tl)=5.51 A for the (C(5)H(5)Tl)(2) dimer.