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PubMed2005

Aerobic catechol oxidation catalyzed by a bis(mu-oxo)dimanganese(III,III) complex via a manganese(II)-semiquinonate complex.

A 3,5-di-tert-butyl-1,2-semiquinonato (DTBSQ) adduct of Mn(II) was prepared by a reaction between Mn(II)(TPA)Cl(2) (TPA = tris(pyridin-2-ylmethyl)amine) and DTBSQ anion and was isolated as a tetraphenylborate salt. The X-ray crystal structure revealed that the complex is formulated as a manganese(II)-semiquinonate complex [Mn(II)(TPA)(DTBSQ)](+) (1). The electronic spectra in solution also indicated the semiquinonate coordination to Mn. The exposure of 1 in acetonitrile to dioxygen afforded 3,5-di-tert-butyl-1,2-benzoquione and a bis(mu-oxo)dimanganese(III,III) complex [Mn(III)(2)(mu-oxo)(2)(TPA)(2)](2+) (2). The reaction of 2 with 3,5-di-tert-butylcatechol (DTBCH(2)) quantitatively afforded two equivalents of 1 under anaerobic conditions. The highly efficient catalytic oxidation of DTBCH(2) with dioxygen was achieved by combining the above two reactions, that is, by constructing a catalytic cycle involving both manganese complexes 1 and 2. It was revealed that dioxygen is reduced to water but not to hydrogen peroxide in the catalytic cycle.

Journal Article↗
PubMed2005

A T-shaped three-coordinate nickel(I) carbonyl complex and the geometric preferences of three-coordinate d9 complexes.

A three-coordinate diketiminate-nickel(I) complex with a carbonyl ligand has been characterized using EPR and IR spectroscopies and X-ray crystallography. The T geometry (bending from the sterically favored C(2)(v)() structure) contrasts with that of isosteric d(9) copper(II) complexes. DFT calculations on a truncated model reproduce experimental geometries, implying that the geometric differences are electronic in nature. Analysis of the charge distribution in the complexes shows that the geometry of the three-coordinate d(9) complexes is affected by differential charge donation of the ligands to the metal center.

Journal Article↗
PubMed2006

Ferromagnetic coupling by orthogonal magnetic orbitals in a heterodinuclear CuIIVIV=O complex and in a homodinuclear CuIICuII complex.

The heterodinuclear complex [LCuIIVIVO] 1 was synthesized by using a new unsymmetric dinucleating ligand based on 1,8-naphthalenediol, whereas the homodinuclear CuIICuII complex 2 has a bridging beta-diketimineamid unit. Here we report on the synthesis, molecular structures, and magnetic properties of 1 and 2. In the solid state, both complexes dimerize to tetranuclear entities 1(2) and 2(2). The intradimer interaction in both complexes is ferromagnetic because of the orthogonality of the magnetic orbitals (J12 = +45.6 cm(-1) in 1 and +4.8 cm(-1) in 2). The interdimer interaction in 1 is also ferromagnetic, giving a St = 2 ground state.

Journal Article↗
PubMed2006

On the paucity of molecular actinide complexes with unsupported metal-metal bonds: a comparative investigation of the electronic structure and metal-metal bonding in U2X6 (X = Cl, F, OH, NH2, CH3) complexes and d-block analogues.

Density functional calculations have been performed on M2X6 complexes (where M = U, W, and Mo and X = Cl, F, OH, NH2, and CH3) to investigate general aspects of their electronic structures and explore the similarities and differences in metal-metal bonding between f-block and d-block elements. A detailed analysis of the metal-metal interactions has been conducted using molecular orbital theory and energy decomposition methods. Multiple (sigma and pi) bonding is predicted for all species investigated, with predominant f-f and d-d metal orbital character, respectively, for U and W or Mo complexes. The energy decomposition analysis involves contributions from orbital interactions (mixing of occupied and unoccupied orbitals), electrostatic effects (Coulombic attraction and repulsion), and Pauli repulsion (associated with four-electron two-orbital interactions). The general results suggest that the overall metal-metal interaction is stronger in the Mo and W species, relative to the U analogues, as a consequence of a significantly less destabilizing contribution from the combined Pauli and electrostatic ("pre-relaxation") effects. Although the orbital-mixing ("post-relaxation") contribution to the total bonding energy is predicted to have a larger magnitude in the U complexes, this is not sufficiently strong to compensate for the comparatively greater destabilization that originates from the Pauli-plus-electrostatic effects. Of the pre-relaxation terms, the Pauli repulsion is comparable in analogous U and d-block compounds, contrary to the electrostatic term, which is (much) less favorable in the U systems than in the W and Mo systems. This generally weak electrostatic stabilization accounts for the large pre-relaxation destabilization in the U complexes and, ultimately, for the relative weakness of the U-U bonds. The origin of the small electrostatic term in the U compounds is traced primarily to MX(3) fragment overlap effects.

Journal Article↗
PubMed1997

Heterobimetallic Complexes with Phenylcyclopentadienyl Ligand: Syntheses and Structures of Tricarbonylchromium-eta(6),eta(5)-Phenylcyclopentadienyl-Transition Metal Complexes(1).

A new synthetic method of heterobimetallic complexes bridging with a pi,pi-phenylcyclopentadienyl ligand, tricarbonylchromium-eta(6),eta(5)-phenylcyclopentadienyl-transition metal complexes, was developed through the reactions of (eta(6)-C(6)H(5)C(5)H(5))Cr(CO)(3) or its sodium salt with transition metal complexes. The method is suitable for most transition metal elements with the advantages of easy manipulation, mild reaction conditions, and moderate to high yields. As indicated by (1)H NMR spectra, the interactions between the two pi systems of phenyl and cyclopentadienyl rings were weak. X-ray crystal structures of seven complexes were studied. Compound 23, [eta(6)-C(6)H(5)Cr(CO)(3)](2)C(10)H(10), crystallizes in orthorhombic space group Pbca with cell constants a = 29.616(8) Å, b = 12.861(5) Å, c = 12.397(7) Å, V = 4721(6) Å(3), Z = 8, R = 0.045, and R(w) = 0.045. Compound 3, (eta(6)-C(6)H(5)C(9)H(7))Cr(CO)(3), crystallizes in monoclinic space group P2(1)/c with cell constants a = 7.901(3) Å, b = 14.799(2) Å, c = 12.917(2) Å, beta = 99.72(2) degrees, V = 1488.7(4) Å(3), Z = 4, R = 0.044, and R(w) = 0.051. Compound 7, Cr(CO)(3)(eta(6),eta(5)-C(6)H(5)C(5)H(4))Ti(CO)(2)(eta(5)-C(5)H(5)), crystallizes in monoclinic space group P2(1)/c with cell constants a = 12.361(4) Å, b = 12.487(6) Å, c = 12.531(7) Å, beta = 93.48(4) degrees, V = 1930 Å(3), Z = 4, R = 0.047, and R(w) = 0.048. Compound 13, Cr(CO)(3)(eta(6),eta(5)-C(6)H(5)C(5)H(4))Mo(CO)(3)Br, crystallizes in monoclinic space group P2(1)/c with cell constants a = 14.685(2) Å, b = 8.509(3) Å, c = 14.960(3) Å, beta = 104.46(1) degrees, V = 1810.0(7) Å(3), Z = 4, R = 0.037, and R(w) = 0.037. Compound 19, Cr(CO)(3)(eta(6),eta(5)-C(6)H(5)C(9)H(6))Mn(CO)(3), crystallizes in triclinic space group P(-)(1) with cell constants a = 11.660(4) Å, b = 12.578(5) Å, c = 6.987(2) Å, alpha = 100.03(3) degrees, beta = 104.19(2) degrees, gamma = 71.99(3) degrees, V = 939.3(6) Å(3), Z = 2, R = 0.048, and R(w) = 0.065. Compound 21, Cr(CO)(3)(eta(6),eta(5)-C(6)H(5)C(5)H(4))Ru(PPh(3))(2)Cl, crystallizes with one molecule of EtOH in triclinic space group P(-)(1) with cell constants a = 14.033(4) Å, b = 16.163(6) Å, c = 10.411(3) Å, alpha = 104.22(3) degrees, beta = 103.50(2) degrees, gamma = 90.81(3) degrees, V = 2219(1) Å(3), Z = 2, R = 0.081, and R(w) = 0.096. Compound 22, Cr(CO)(3)(eta(6),eta(5)-C(6)H(5)C(5)H(4))Co(CO)(2), crystallizes in orthorhombic space group P2(1)2(1)2(1) with cell constants a = 15.083(5) Å, b = 16.391(5) Å, c = 6.351(4) Å, V = 1570(1) Å(3), Z = 4, R = 0.036, and R(w) = 0.039. The trans configurations of the two metal atoms in these molecules were found as expected; the phenyl and cyclopentadienyl or indenyl rings in the molecules were found to be not coplanar.

Journal Article↗
PubMed1996

Reactions of the Dirhenium(II) Complexes Re(2)X(4)(dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) with Isocyanides. 10.(1) Synthesis and Characterization of the Complex [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) and Several Isomeric Forms of [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]Y (Y = PF(6), O(3)SCF(3)).

The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O(3)SCF(3) (3a), PF(6) (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+). Two forms have very similar bis(&mgr;-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(&mgr;-Br)(2)(&mgr;-dppm)(2)Re(CNXyl)(2)]Y (Y = O(3)SCF(3) (4a/4a'), PF(6) (4b/4b')), while the third is an open bioctahedron [(XylNC)(2)BrRe(&mgr;-dppm)(2)ReBr(2)(CO)]Y (Y = O(3)SCF(3) (5a), PF(6) (5b)). While the analogous chloro complex cation [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e. the isomer analogous to 5a and 5b). The reaction of 3a with CO gives the salt [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(&mgr;-Br)(&mgr;-CO)(&mgr;-dppm)(2)ReBr(CO)](+) has an all-cis arrangement of pi-acceptor ligands. The Re-Re distances in the structures of 4b', 5a, and 7 are 3.0456(8), 2.3792(7), and 2.5853(13) Å, respectively, and accord with formal Re-Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](PF(6))(0.78)(ReO(4))(0.22).CH(2)Cl(2) (4b') at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 19.845(4) Å, b = 16.945(5) Å, c = 21.759(3) Å, beta = 105.856(13) degrees, V = 7038(5) Å(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F(o)(2) > 2sigma(F(o)(2))). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3).C(6)H(6) (5a) at 173 K: monoclinic space group P2(1)/n (No. 14) with a = 14.785(3) Å, b = 15.289(4) Å, c = 32.067(5) Å, beta = 100.87(2) degrees, V=7118(5) Å(3), and Z = 4. The structure was refined to R = 0.046 (R(w) = 0.055) for 6962 data (I > 3.0sigma(I)). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3).Me(2)CHC(O)Me (7) at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 14.951(2) Å, b = 12.4180(19) Å, c = 40.600(5) Å, beta = 89.993(11) degrees, V = 7537(3) Å(3), and Z = 4. The structure was refined to R = 0.074 (R(w) = 0.088) for 6595 data (I > 3.0sigma(I)).

Journal Article↗
PubMed1997

Fluoro[eta(3)-hydrotris(3-R-5-methylpyrazol-1-yl)borato]zinc(II): The First TpZnF Complexes, Convenient Precursors to Zinc Hydride Complexes(,).

Fluoro[eta(3)-tris(3-R-5-methylpyrazol-1-yl)hydroborato]zinc(II) complexes, Tp(R,Me)ZnF (with R = p-Tol, t-Bu), have been prepared by metathesis of Tp(p-)()(Tol,Me)ZnOAc with KF in MeOH/THF and by reaction of KTp(t-)()(Bu,Me) with Zn(ClO(4))(2) and KF in MeOH. The molecular structure of Tp(p-)()(Tol,Me)ZnF has been determined by X-ray crystallography. Crystal data: a = 11.8719(12), c = 37.051(3) Å; trigonal, space group R3c (No. 161); Z = 6. The complex contains tetrahedrally coordinated Zn(II). The tolyl rings deviate by 21 degrees from coplanarity with the pyrazolyl plane. The reaction of Tp(p-)()(Tol,Me)ZnF with py.BF(3) leads to the tetrafluoroborate salt [Tp(p-)()(Tol,Me)Zn(py)](+)BF(4)(-). The analogous reaction with Et(2)O.BF(3) probably gives a solvent complex [Tp(p-)()(Tol,Me)Zn(Et(2)O)](+)BF(4)(-) that however could not be isolated. Triethylsilane reacts with Tp(p-)()(Tol,Me)ZnF to yield the zinc hydride Tp(p-)()(Tol,Me)ZnH. Trimethylsilyl derivatives Me(3)Si-X (X = Cl, Br, I, NCO, OAc) similarly give Tp(p-)()(Tol,Me)ZnX, whereas bis(trimethylsilyl) malonate yields the bridged complex Tp(p-)()(Tol,Me)Zn-O-C(O)-CH(2)-C(O)-O-ZnTp(p-)()(Tol,Me).

Journal Article↗
PubMed1997

Hydrotris(pyrazolyl)borato Cycloocta-1,5-diene Complexes of Iridium(I): Synthetic Studies and Equilibria in Solution. X-ray Crystal Structures of a Four- and a Five-Coordinate Iridium(I) Hydrotris(pyrazolyl)borato Complex.

The compounds [Tp(3R,4R,5R)Ir(COD)] (COD = cycloocta-1,5-diene; Tp(3R,4R,5R) = hydrotris(pyrazolyl)borate (1), hydrotris(3-methylpyrazolyl)borate (2), hydrotris(3-isopropylpyrazolyl)borate (3), hydrotris(3,5-dimethylpyrazolyl)borate, hydrotris(3-(trifluoromethyl)-5-methylpyrazolyl)borate, hydrotris(3-phenyl-5-methylpyrazolyl)borate, hydrotris(3,5-diisopropylpyrazolyl)borate, hydrotris(3,4,5-trimethylpyrazolyl)borate, hydrotris(4-chloro-3,5-dimethylpyrazolyl)borate (9), hydrotris(4-bromo-3,5-dimethylpyrazolyl)borate) were prepared and characterized by IR and NMR spectroscopy. The X-ray crystal structure of 9.2MeOH (triclinic, space group P&onemacr; (No. 2); a = 10.044(1) Å, b = 11.186(2) Å, c = 15.499(3) Å; alpha = 77.90(1) degrees, beta = 73.23(1) degrees, gamma = 66.89(1) degrees; Z = 2; R = 0.0276 for 2469 observed reflections) shows that iridium is four-coordinate with an eta(2)-hydrotris(pyrazolyl)borate. The X-ray crystal structure of 1 (triclinic, space group P&onemacr; (No. 2); a = 7.345(1) Å, b = 7.645(1) Å, c = 15.893(5) Å; alpha = 103.17(4) degrees, beta = 90.30(2) degrees, gamma = 93.50(3) degrees; Z = 2; R = 0.0433 for 2606 observed reflections) shows that iridium is five-coordinate with an eta(3)-bonded tris(pyrazolyl)borate. Equilibria between corresponding four- (eta(2)-Tp(3R,4R,5R)) and five-coordinate (eta(3)-Tp(3R,4R,5R)) species of all the complexes are established in solution. The complex containing the ligand HB(Pz(3Me))(3) (Pz = pyrazolyl group) (2) rearranged first to the corresponding complex with HB(Pz(3Me))(2)(Pz(5Me)) and then into that with HB(Pz(3Me))(Pz(5Me))(2). However, 3, which contains HB(Pz(3)()i(Pr))(3), gave only the complex with coordinated HB(Pz(3)()i(Pr))(2)(Pz(5)()i(Pr)).

Journal Article↗
PubMed1998

Mononuclear Platinum(II) and Palladium(II) Dithiolate Complexes as Chelate Metalloligands for Preparation of Heterobimetallic d(8)-d(8) Complexes.

Palladium-rhodium and platinum-rhodium heterobimetallic bridged dithiolate complexes of general formula [(P-P)M(&mgr;-S-S)Rh(COD)]ClO(4) (COD = 1,5-cyclooctadiene. For M = Pt: P-P = (PPh(3))(2) and S-S = EDT(2)(-) (1,2-ethanedithiolate) (1), PDT(2)(-) (1,3-propanedithiolate) (2), and BDT(2)(-) (1,4-buthanedithiolate) (3); P-P = dppb (1,4-bis(diphenylphosphino)butane) and S-S = EDT(2)(-) (4), PDT(2)(-) (5), and BDT(2)(-) (6); P-P = dppp (1,3-bis(diphenylphosphino)propane) and S-S = EDT(2)(-) (7), PDT(2)(-) (8), and BDT(2)(-) (9). For M = Pd: P-P = dppb and S-S = EDT(2)(-) (10), PDT(2)(-) (11), and BDT(2)(-) (12); P-P = dppp and S-S = EDT(2)(-) (13), PDT(2)(-) (14), and BDT(2)(-) (15)) have been prepared. The crystal structures for complexes 1-3, 6, 9, and 12 have been determined, and hinged structures were found with angles between local coordination planes MS(2)Rh ranging from 111.27 degrees for complex 1 to 151.34 degrees for complex 3. Metal-metal distances show nonbonding interactions between metals. X-ray data for 1: triclinic, P&onemacr;, a = 11.311(6) Å, b = 12.991(6) Å, c = 16.140(6) Å, alpha = 84.86(6) degrees, beta = 75.73(6) degrees, gamma = 86.43(6) degrees, Z = 2, R = 0.0427 (R(w) = 0.1151). X-ray data for 2: triclinic, P&onemacr;, a = 11.084(5) Å, b = 13.094(6) Å, c = 16.338(6) Å, alpha = 86.06(6) degrees, beta = 75.67(6) degrees, gamma = 88.55(6) degrees, Z = 2, R = 0.0470 (R(w) = 0.1264). X-ray data for 3: orthorhombic, Pbca, a = 14.439(6) Å, b = 19.807(6) Å, c = 38.156(6) Å, Z = 8, R = 0.0864 (R(w) = 0.2457). X-ray data for 6: monoclinic, P2(1)/c, a = 20.338(6) Å, b = 14.227(6) Å, c = 14.570(6) Å, beta = 100.94(6) degrees, Z = 4, R = 0.0536 (R(w) = 0.1449). X-ray data for 9: monoclinic, P2(1)/c, a = 20.326(6) Å, b = 14.109(6) Å, c = 14.368(6) Å, beta = 100.90(6) degrees, Z = 4, R = 0.0380 (R(w) = 0.0990). X-ray data for 12: monoclinic, P2(1)/c, a = 20.365(6) Å, b = 14.186(6) Å, c = 14.592(6) Å, beta = 101.04(6) degrees, Z = 4, R = 0.0507 (R(w) = 0.1500).

Journal Article↗
PubMed1998

Ruthenium Complexes Containing "Noninnocent" o-Benzoquinone Diimine/o-Phenylenediamide(2-) Ligands. Synthesis and Crystal Structure of the Nitrido-Bridged Complex [{LRu(o-C(6)H(4)(NH)(2))}(2)(&mgr;-N)](PF(6))(2).3CH(3)CN.C(6)H(5)CH(3).

Reaction of LRu(III)Cl(3) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) with 1,2-phenylenediamine (opdaH(2)) in H(2)O in the presence of air affords [LRu(II)(bqdi)(OH(2))](PF(6)) (1), where (bqdi) represents the neutral ligand o-benzoquinone diimine. From an alkaline methanol/water mixture of 1 was obtained the dinuclear species [{LRu(II)(bqdi)}(2)(&mgr;-H(3)O(2))](PF(6))(3) (1a). The coordinated water molecule in 1 is labile and can be readily substituted under appropriate reaction conditions by acetonitrile, yielding [LRu(II)(bqdi)(CH(3)CN)](PF(6))(2) (2), and by iodide and azide anions, affording [LRu(II)(bqdi)I](PF(6)).0.5H(2)O (3) and [LRu(bqdi)(N(3))](PF(6)).H(2)O (4), respectively. Heating of solid 4 in vacuum at 160 degrees C generates N(2) and the dinuclear, nitrido-bridged complex [{LRu(o-C(6)H(4)(NH)(2))}(2)(&mgr;-N)](PF(6))(2) (5). Complex 5 is a mixed-valent, paramagnetic species containing one unpaired electron per dinuclear unit whereas complexes 1-4 are diamagnetic. The crystal structures of 1, 1a.3CH(3)CN, 3, 4.H(2)O, and 5.3CH(3)CN.0.5(toluene) have been determined by X-ray crystallography: 1 crystallizes in the monoclinic space group P2(1)/m, Z = 2, with a = 8.412(2) Å, b = 15.562(3) Å, c = 10.025 Å, and beta = 109.89(2) degrees; 1a.3CH(3)CN, in the monoclinic space group C2/c, Z = 4, with a = 19.858(3) Å, b = 15.483(2) Å, c = 18.192(3) Å, and beta = 95.95(2) degrees; 3, in the orthorhombic space group Pnma, Z = 4, with a = 18.399(4) Å, b = 9.287(2) Å, and c = 12.052(2) Å, 4.H(2)O, in the monoclinic space group P2(1)/c, Z = 4, with a = 8.586(1) Å, b = 15.617(3) Å, c = 16.388(5) Å, and beta = 90.84(2) degrees; and 5.3CH(3)CN.0.5(toluene), in the monoclinic space group P2(1)/c, Z = 4, with a = 15.003(3) Å, b = 16.253(3) Å, c = 21.196(4) Å, and beta = 96.78(3) degrees. The structural data indicate that in complexes 1-4 the neutral o-benzoquinone diimine ligand prevails. In contrast, in 5 this ligand has predominantly o-phenylenediamide character, which would render 5 formally a mixed-valent Ru(IV)Ru(V) species. On the other hand, the Ru-N bond lengths of the Ru-N-Ru moiety at 1.805(5) and 1.767(5) Å are significantly longer than those in other crystallographically characterized Ru(IV)=N=Ru(IV) units (1.72-1.74 Å). It appears that the C(6)H(4)(NH)(2) ligand in 5 is noninnocent and that formal oxidation state assignments to the ligands or metal centers are not possible.

Journal Article↗
PubMed1998

Structural and (99)Tc NMR Investigations of Complexes with fac-[Tc(CO)(3)](+) Moieties and Macrocyclic Thioethers of Various Ring Sizes: Synthesis and X-ray Structure of the Complexes fac-[Tc(9-ane-S(3))(CO)(3)]Br, fac-[Tc(2)(tosylate)(2)(18-ane-S(6))(CO)(6)], and fac-[Tc(2)(20-ane-S(6)-OH)(CO)(6)][tosylate](2).

Starting originally from the organometallic precursor [NEt(4)](2)[TcBr(3)(CO)(3)] (1b), substitution reactions were performed with the macrocyclic thioethers 1,4,7-trithiacyclononane (9-ane-S(3)), 1,4,7,10,13,16-hexathiacyclooctadecane (18-ane-S(6)), and 3,6,9,13,16,19-hexathiacycloicosanol (20-ane-S(6)-OH). The corresponding complexes fac-[Tc(9-ane-S(3))(CO)(3)]Br (2), fac-[Tc(2)(tosylate)(2)(18-ane-S(6))(CO)(6)] (3), and fac-[Tc(2)(20-ane-S(6)-OH)(CO)(6)][tosylate](2) (5) were isolated in good yields and characterized spectroscopically by IR, (1)H, (99)Tc NMR, and X-ray diffraction methods. In the case of 18-ane-S(6) and 20-ane-S(6)-OH the formation of the 1:2 as well as the 1:1 complex could be observed in the (99)Tc NMR experiment, depending on the ligand to metal ratio. Complex 2crystallizes in the monoclinic space group P2(1)/c, a = 14.79(2) Å, b = 11.691(2) Å, c = 16.94(2) Å, beta = 94.88(6) degrees, Z = 8. The tripodal ligand is coordinated through the sulfur atoms to the metal center, forming three favorable five-membered chelate rings. Complex 3 crystallizes in the monoclinic space group C2/c, a = 26.073(4) Å, b = 9.288(1) Å, c = 17.898(3) Å, beta = 99.84(1) degrees, Z = 4. The binuclear unit is formed by two fac-[Tc(tosylate)(CO)(3)] moieties which are trans, bidentate coordinated to the macrocyclic ligand. Compound 5 crystallizes in the monoclinic space group Pc, a = 25.737(4) Å, b = 14.009(1) Å, c = 26.479(3) Å, beta = 149.56(2) degrees, Z = 4. In the case of the dicationic compound 5, the two Tc(I) centers are tripodal, cis coordinated toward the thia crown ether. A detailed analysis of the ring conformation in the solid state structure explained to a certain extent the formation of only one isomer (trans in the case of 3 and cis in the case of 5, respectively) during the substitution reaction.

Journal Article↗
PubMed2000

Vibronic coupling in dicyano-complex-bridged mixed-valence complexes. Relaxation of vibronic constraints in systems with degenerate bridging-ligand and electron-transfer excited states.

Intense near-infrared (NIR) absorption bands have been found in mixed-valence Ru(NH3)5(2+,3+) complexes bridged by trans-Ru(py)4(CN)2 and cis-Os(bpy)2(CN)2, epsilonmax approximately 1.5 x 10(3) cm(-1) and deltav1/2 approximately 5 x 10(3) cm(-1) for bands at 1,000 and 1,300 nm, respectively. The NIR transitions implicate substantial comproportionation constants (64 and 175, respectively) characteristic of moderately strong electronic coupling in the mixed-valence complexes. This stands in contrast to the weakly forbidden electronic coupling of Ru(NH3)5(2+,3+) couples bridged by M(MCL)(CN)2+ complexes (MCL = a tetraazamacrocyclic ligand) (Macatangay; et al. J. Phys. Chem. 1998, 102, 7537). A straightforward perturbation theory argument is used to account for this contrasting behavior. The electronic coupling between a cyanide-bridged, donor-acceptor pair, D-(CN-)-A, alters the properties of the bridging ligand. Such systems are described by a "vibronic" model in which the electronic matrix element, HDA, is a function of the nuclear coordinates, QN, of the bridging ligand: HDA = HDA degrees + bQN. Electronic coupling in the dicyano-complex-bridged, D-[(NC)M(CN)]-A, systems is treated as the consequence of the perturbational mixing of the "local", D(NC)M and M(CN)A, vibronic interactions. If M is an electron-transfer acceptor, then the nuclear coordinates are assumed to be configured so that bQN is larger for D(NC)M but very small (bQN approximately 0) for M(CN)A. When the vertical energies of the corresponding charge-transfer transitions, EDM and EDA, differ significantly, a perturbation theory treatment results in HDA = HDAHAM/Eave independent of M and consistent with the earlier report. When EDM approximately equals EDA, configurational mixing of the excited states leads to HDA proportional to HDM, consistent with the relatively intense intervalence bands reported in this paper. Some implications of the model are discussed.

Journal Article↗
PubMed2000

Preparation and crystal structures of formato complexes of the [MIV3O4]4+ and [MIV3S4]4+ (M = Mo, W) clusters. Convenient precursors to the corresponding aqua complexes.

In the aqueous chemistry of molybdenum(IV) and tungsten(IV), trinuclear, incomplete cubane-like, oxo and sulfido clusters of the type [M3E4]4+ (M = Mo, W; E = O, S) play a central role. We here describe how formato complexes of all these cluster cores can be prepared in high yields by crystallization from methanol-water or ethanol-water mixtures. Since potassium and ammonium formate are very soluble in these alcohol-water mixtures, high formate concentrations could be accomplished in the solutions from which the corresponding salts of cluster formato complexes crystallized. The [Mo3O4]4+ compounds could be synthesized without requiring the use of noncomplexing acids in the process. Some [M3E4]4+ compounds were characterized by single-crystal structure determinations. [NH4]3.20[K]0.80[H3O][Mo3O4(HCO2)8][HCO2].H2O was triclinic, space group P1 (No. 2) with a = 11.011(2) A, b = 13.310(2) A, c = 9.993(1) A, alpha = 106.817(7) degrees, beta = 91.651(9) degrees, gamma = 88.340(9) degrees, and two formula units per cell. [K]6[W3S4(HCO2)9][HCO2].2.27H2O.0.73CH3OH was monoclinic, space group C2/m (No. 12) with a = 19.605(6) A, b = 14.458(7) A, c = 13.627(5) A, beta = 118.94(2) degrees, and four formula units per cell. Generally, the nine coordination sites of [M3E4]4+ were occupied either by a mixture of monodentate and mu 2-bridging formato ligands or by monodentate formato ligands only. By dissolution in noncomplexing strong acid, all the formato complexes immediately hydrolyzed to form [M3E4(H2O)9]4+ aqua complexes. This allows, for example, high concentrations of [Mo3S4(H2O)9]4+ in CF3SO3H to be obtained and these solutions to be used for the synthesis of bimetallic clusters containing the cubane-like motif Mo3M'S4.

Journal Article↗
PubMed2001

Molecular recognition in cyclodextrin complexes of amino acid derivatives. 1. Crystallographic studies of beta-cyclodextrin complexes with N-acetyl-L-phenylalanine methyl ester and N-acetyl-L-phenylalanine amide pseudopeptides.

Cyclodextrins (CDs) are widely utilized in studies of chiral and molecular recognition. By changing the functionality of the guest molecule, the effect of such changes on recognition by the host CD molecule can be examined. We report crystal structure determinations for two nearly isomorphous complexes of phenylalanine derivatives: beta-CD/N-acetyl-L-phenylalanine methyl ester and beta-CD/N-acetyl-L-phenylalanine amide. The complexes crystallize as hydrated head-to-head host dimers with two included guest molecules in space group P1. The crystal packing is such that it presents a nonconstraining hydrophobic pocket adjacent to a hydrophilic region, where potential hydrogen-bonding interactions with hydroxyl groups of neighboring cyclodextrin molecules and waters of hydration can occur. The two host molecules display very similar conformations; only a few of the primary hydroxyl groups are conformationally disordered. There are a number of changes in the location of water of hydration molecules, some of which are the result of different hydrogen-bonding interactions. For the different guest molecules, similar modes of penetration are observed in the CD torus; however, there is a 0.985-A shift in the position of the guest molecules in the host torus, which takes place without changing the hydrophobic interactions displayed by the phenyl side chains. This observation and the thermal motion of the guest molecules in the ester complex are taken as evidence that complex binding forces are weak. The pseudopeptides experience a significant degree of flexibility in the crystalline environment provided by CD dimers. Conformational differences of the pseudopeptide backbones and the presence of disordered water molecules in the host-guest interface provide examples of different hydrogen-bonding schemes of similar potential energy. The crystal system presents an opportunity to establish a database of molecular interactions for small peptides and peptide analogues with waters of hydration and functional groups in nonconstraining binding environments.

Crystallography, X-Ray↗
PubMed2001

Physical organic chemistry of transition metal carbene complexes. 23. Kinetic and thermodynamic acidities of cationic benzothienyl- and selenylcarbene complexes of rhenium in aqueous acetonitrile.

The pK(a) values of a cationic selenyl- (5H(+)) and a benzothienylcarbene complex (6H(+)) and rate constants for the reversible deprotonation of these complexes by water, carboxylate ions, primary aliphatic amines, secondary alicyclic amines (5H(+) only), and OH(-) (5H(+) only) were determined in 50% MeCN-50% water (v/v) at 25 degrees C. In comparison with neutral Fischer-type carbene complexes such as 1H, the cationic complexes 5H(+) and 6H(+) are much more acidic, and the intrinsic barriers to proton transfer are substantially higher. This paper discusses a variety of factors that contribute to these differences, with the most important ones being that 5H(+) and 6H(+) are cationic, which makes the C(5)H(5)(NO)(PPh(3))Re moiety a stronger pi-acceptor than the (CO)(5)M moieties, coupled with the fact that the deprotonated forms of 5H(+) and 6H(+ )are aromatic molecules.

Journal Article↗
PubMed2003

Organometallic complexes for nonlinear optics. 30.1 electrochromic linear and nonlinear optical properties of alkynylbis(diphosphine)ruthenium complexes.

A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, time-dependent density functional theory (TD-DFT), and Z-scan measurements employing a modified optically transparent thin-layer electrochemical (OTTLE) cell has been used to identify and assign intense transitions of metal alkynyl complexes at technologically important wavelengths in the oxidized state and to utilize these transitions to demonstrate a facile electrochromic switching of optical nonlinearity. Cyclic voltammetric data for the ruthenium(II) complexes trans-[RuXY(dppe)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane, X = Cl, Y = Cl (1), Ctbd1;CPh (2), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (3); X = Ctbd1;CPh, Y = Ctbd1;CPh (4), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (5)] show a quasi-reversible oxidation at 0.50-0.60 V (with respect to ferrocene/ferrocenium 0.56 V), which is assigned to the Ru(II/III) couple. The ruthenium(III) complex cations trans-[RuXY(dppe)(2)](+) were obtained by the in situ oxidation of complexes 1-5 using an OTTLE cell. The UV-vis-NIR optical spectra of 1(+)-5(+) contain a low-energy band in the near-IR region ( approximately 8000-16 000 cm(-)(1)), in contrast to 1-5, which are optically transparent at wavelengths < 22 000 cm(-)(1). TD-DFT calculations have been applied to model systems trans-[RuXY(PH(3))(4)] [X = Cl, Y = Cl, Ctbd1;CPh, or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh; X = Ctbd1;CPh, Y = Ctbd1;CPh or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh] to rationalize the optical spectra of 1-5 and 1(+)-5(+). The important low-energy bands in the electronic spectra of 1(+)-5(+) are assigned to the promotion of an electron from either a chloride p orbital or an ethynyl p orbital to the partially occupied HOMO. These absorption bands have been utilized to demonstrate a facile switching of cubic nonlinear optical (NLO) properties at 12 500 cm(-)(1) (corresponding to the wavelength of maximum transmission in biological materials such as tissue) using the OTTLE cell, the first electrochromic switching of molecular nonlinear refraction and absorption, and the first switching of optical nonlinearity using an electrochemical cell.

Journal Article↗
PubMed2003

Comparative reactivity of sterically crowded nf3 (C5Me5)3Nd and (C5Me5)3U complexes with CO: formation of a nonclassical carbonium ion versus an f element metal carbonyl complex.

Sterically crowded isoelectronic nf(3) (C(5)Me(5))(3)M complexes of neodymium and uranium, compounds which have unconventionally long metal ligand distances, are found to react very differently with CO as a substrate. The 4f(3) complex (C(5)Me(5))(3)Nd reacts with CO to form a nonclassical carbonium ion complex, (C(5)Me(5))(2)Nd(O(2)C(7)Me(5)), which contains a three-coordinate planar carbon. (C(5)Me(5))(3)U reacts with CO to form an even more crowded CO adduct through a reaction type never observed before for (C(5)Me(5))(3)M compounds. The rare uranium carbonyl complex, (C(5)Me(5))(3)U(CO), has nu(CO) = 1922 cm(-1) and a U-C(CO) distance of 2.485(9) A.

Journal Article↗
PubMed2006

Dynamic processes in silyl palladium complexes: evidence for intermediate Si-H and Si-Si sigma-complexes.

The silyl palladium complexes (dcpe)PdH(SiHtBu2) and (dcpe)Pd(SiHMe2)2 display NMR spectra that vary with temperature. The dynamic NMR behavior is consistent with long-lived sigma-complexes as intermediates. In the case of (dcpe)PdH(SiHtBu2), the intermediate is believed to be a symmetric complex with doubly bridged hydrogen atoms between the silicon and palladium. Dynamic interchange of the two silicon atoms in (dcpe)Pd(SiHMe2)2 is consistent with an intermediate Si-Si sigma-complex.

Journal Article↗