Structural correlation between Rh-P and Rh-C bond distances vs. 31P and 13C NMR parameters in monocarbonylphosphinerhodium(I) complexes: Crystal structure of (methyl 2-(amino)-1-cyclopentene-1-dithio arboxylato-κN, κS)-carbonyl(triphenylphosphine) rhodium(I)

Structural Study of Model Rhodium(I) Carbonylation Catalysts Activated by Indole-2-/Indoline-2-Carboxylate Bidentate Ligands and Kinetics of Iodomethane Oxidative Addition

The rigid-backbone bidentate ligands Indoline-2-carboxylic acid (IndoliH) and Indole-2-carboxylic acid (IndolH) were evaluated for rhodium(I). IndoliH formed [Rh(Indoli)(CO)(PPh3)] (A2), while IndolH yielded the novel dinuclear [Rh1(Indol’)(CO)(PPh3)Rh2(CO)(PPh3)2] (B2) complex (Indol’ = Indol2−), which were characterized by SCXRD. In B2, the Rh1(I) fragment [Rh1(Indol’)(CO)(PPh3)] (bidentate N,O-Indol) exhibits a square-planar geometry, while Rh2(I) shows a ‘Vaska’-type trans-[O-Rh2(PPh3)2(CO)] configuration (bridging the carboxylate ‘oxo’ O atom of Indol2−). The oxidative addition of MeI to A2 and B2 via time-resolved FT-IR, NMR, and UV/Vis analyses indicated only Rh(III)-alkyl species (A3/B3) as products (no migratory insertion). Variable temperature kinetics confirmed an associative mechanism for A2 via an equilibrium-based pathway (ΔH≠ = (21 ± 1) kJ mol−1; ΔS≠ = (−209 ± 4) J K−1mol−1), with a smaller contribution from a reverse reductive elimination/solvent pathway. The dinuclear complex B2 showed the oxidative addition of MeI only at Rh1(I), which formed a Rh(III)-alkyl, but cleaved the bridged Rh2(I) site, yielding trans-[RhI(PPh3)2(I)(CO)] (5B) as a secondary product. A significantly smaller negative activation entropy [ΔH≠ = (73.0 ± 1.2) kJ mol−1; ΔS≠ = (−21 ± 4) J K−1mol−1] via a more complex/potential interchange mechanism (the contribution of ΔS≠ to the Gibbs free energy of activation, ΔG≠, only ±10%) was inferred, contrary to the entropy-driven oxidative addition of MeI to A2 (the contribution of ΔS≠ to ΔG≠ ± 75%).

Rh(I)/(III)-N-Heterocyclic Carbene Complexes: Effect of Steric Confinement Upon Immobilization on Regio- and Stereoselectivity in the Hydrosilylation of Alkynes

Rh(I) NHC and Rh(III) Cp* NHC complexes (Cp*=pentamethylcyclopentadienyl, NHC=N-heterocyclic carbene=pyrid-2-ylimidazol-2-ylidene (Py-Im), thiophen-2-ylimidazol-2-ylidene) are presented. Selected catalysts were selectively immobilized inside the mesopores of SBA-15 with average pore diameters of 5.0 and 6.2 nm. Together with their homogenous progenitors, the immobilized catalysts were used in the hydrosilylation of terminal alkynes. For aromatic alkynes, both the neutral and cationic Rh(I) complexes showed excellent reactivity with exclusive formation of the β(E)-isomer. For aliphatic alkynes, however, selectivity of the Rh(I) complexes was low. By contrast, the neutral and cationic Rh(III) Cp* NHC complexes proved to be highly regio- and stereoselective catalysts, allowing for the formation of the thermodynamically less stable β-(Z)-vinylsilane isomers at room temperature. Notably, the SBA-15 immobilized Rh(I) catalysts, in which the pore walls provide an additional confinement, showed excellent β-(Z)-selectivity in the hydrosilylation of aliphatic alkynes, too. Also, in the case of 4-aminophenylacetylene, selective formation of the β(Z)-isomer was observed with a neutral SBA-15 supported Rh(III) Cp* NHC complex but not with its homogenous counterpart. These are the first examples of high β(Z)-selectivity in the hydrosilylation of alkynes by confinement generated upon immobilization inside mesoporous silica.

Crystal structure of monocarbonyl[2-((cyclopentylmethylene)amino)-5-methylphenolato-κ2N,O] (tricyclohexylphosphine)rhodium(I), C32H48NO2PRh

C32H48NO2PRh, orthorhombic, P212121 (no. 19), a = 26.784(10) Å, b = 8.837(3) Å, c = 12.759(4) Å, V = 3020.0(18) Å3, Z = 4, R gt(F) = 0.0400, wR ref(F 2) = 0.0920, T = 100(2) K.

Diminished electron density in the Vaska-type rhodium(I) complextrans-[Rh(NCBH3)(CO)(PPh3)2]

Vaska-type complexes,i.e. trans-[RhX(CO)(PPh3)2] (Xis a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the RhIatom in these complexes plays an important role in their reactivity. Many cyanotrihydridoborate (BH3CN−) complexes of Group 6–8 transition metals have been synthesized and structurally characterized, an exception being the rhodium(I) complex. Carbonyl(cyanotrihydridoborato-κN)bis(triphenylphosphine-κP)rhodium(I), [Rh(NCBH3)(CO)(C18H15P)2], was prepared by the metathesis reaction of sodium cyanotrihydridoborate withtrans-[RhCl(CO)(PPh3)2], and was characterized by single-crystal X-ray diffraction analysis and IR,1H,13C and11B NMR spectroscopy. The X-ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the RhIatom through the N atom in atransposition with respect to the carbonyl ligand; this was also confirmed by the IR and NMR data. The carbonyl stretching frequency ν(CO) and the carbonyl carbon1JC–Rhand1JC–Pcoupling constants of the Cipsoatoms of the triphenylphosphine groups reflect the diminished electron density on the central RhIatom compared to the parenttrans-[RhCl(CO)(PPh3)2] complex.

Crystal structure of carbonyl(2-oxopyridin-1(2H)-olato-κ2 O, O′)(triphenylphosphine-κP)rhodium(I), C24H19NO3PRh

C24H19NO3PRh, triclinic, P1̅ (no. 2), a = 9.1734(16) Å, b = 9.5433(18) Å, c = 12.342(2) Å, α = 92.400(6)°, β = 105.460(5)°, γ = 99.472(5)°, V = 1023 Å3, Z = 2, R gt (F) = 0.0236, wR ref (F 2 ) = 0.0597, T = 100 K.

Characterization of a Rh(iii) porphyrin–CO complex: its structure and reactivity with an electron acceptor

To analyse the electrocatalytic oxidation of carbon monoxide by Rh porphyrins, we isolated a CO-adduct of Rh octaethylporphyrin, and examined its properties and reactivity by IR, NMR, and X-ray crystallographic analyses.

Perfluorinated Taddol Phosphoramidite as an L,Z-Ligand on Rh(I) and Co(-I): Evidence for Bidentate Coordination via Metal-C6F5 Interaction

Perfluorinated Taddol-based phosphoramidite, CKphos, is a highly selective ligand for formation of the vinylogous amide cycloadduct in the Rh(I) catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and alkynes. CKphos overrides substrate bias of product selectivity in the cycloaddition, providing indolizinones in excellent product and enantioselectivities. Excellent selectivities are attributed to a shortened Rh-P bond and coordination of one C6F5 to rhodium via a Z-type interaction, making the phosphoramidite a bidentate L,Z-ligand on rhodium. Evidence for the shortened Rh-P and C6F5 coordination is provided by X-ray, NMR and DFT computation analyses. Additionally, an anionic cobalt complex with CKphos was synthesized and two Co-C6F5 interactions are seen. Rh(C2H4)Cl•CKphos catalyst in the [2+2+2] cycloaddition of alkenyl isocyanates and alkynes represents a rare example of metal-C6F5 Z-type interaction affecting selectivity in transition metal catalysis.

Dicarbon-yl[4-(2,6-dimethyl-phenyl-amino)-pent-3-en-2-onato-κ(2)N,O]rhodium(I)

In the title compound, [Rh(C₁₃H₁₆NO)(CO)₂], a square-planar coordination geometry is observed around the Rh^I atom, formed by the N and O atoms of the bidentate ligand and two C atoms from two carbonyl ligands. The Rh^I atom is displaced from the plane through these surrounding atoms by 0.0085 (2) Å. The dihedral angle between the benzene ring and the N—C—C—C—O plane is 89.82 (6)°, and the N—Rh—O bite angle for the bidentate ligand is 90.53 (6)°. An inter­molecular C—H⋯O inter­action is observed between a methyl group of the benzene ring and a carbonyl O atom.

4-(2,6-Dibromo-4-fluoro-anilino)pent-3-en-2-one

The title enamino­ketone, C₁₁H₁₀Br₂FNO, has a roughly planar pentenone chain; the maximum displacement of an atom from the pentenone plane is 0.071 (4) Å. The dihedral angle between the benzene ring and the pentenone unit is 77.2 (1)°. Inter­molecular C—H⋯Br and C—H⋯O inter­actions, as well as an intra­molecular N—H⋯O inter­action, are observed. In both methyl groups, each H atom is disordered equally over two sites.

cyclo-Tetra-μ-oxido-tetra-kis-[(acetyl-acetonato-κO,O')bis-(ethano-lato-κO)niobium(V)]

The asymmetric unit of the title tetra­nuclear niobium(V) compound, [Nb₄(C₂H₅O)₈(C₅H₇O₂)₄O₄], contains two Nb^V atoms, two bridging O atoms, two acetyl­acetonate and four ethano­late ligands. Each Nb^V atom is six-coordinated by the bridging O atoms, two ethano­late and one chelating acetyl­acetonate ligands. The Nb—O distances vary between 1.817 (2) and 2.201 (2) Å and the O—Nb—O angles vary between 78.88 (8) and 102.78 (9)°, illustrating the significant distortion from ideal ocahedral geometry. The rest of the tetra­nuclear unit is generated through an inversion centre. The C atoms of two of the ethano­late mol­ecules are disordered over two sites [occupancy ratio 0.601 (12):0.399 (12)].

Tetra-kis(5,7-dimethyl-quinolin-8-olato-κN,O)hafnium(IV) dimethyl-formamide disolvate

In the title compound, [Hf(C(11)H(10)NO)(4)]·2C(3)H(7)NO, the Hf(IV) atom is coordinated by four N,O-donating bidentate 5,7-dimethyl-8-quinolino-late (Ox(-)) ligands arranged to give a distorted square-anti-prismatic coordination polyhedron. The average Hf-O and Hf-N distances are 2.098 and 2.298 Å, respectively, and the average O-Hf-N bite angle is 70.2°. The crystal packing is controlled by π-π inter-actions between Ox(-) ligands of neighbouring mol-ecules, giving rise to a three-dimensional supra-molecular grid network. The inter-planar distances vary from 3.441 (1) to 3.509 (1) Å, while the centroid-centroid distances vary from 3.688 (2) to 3.759 (12) Å. A non-classical C-H⋯O hydrogen bond is observed between the complex and one of the solvate mol-ecules.

Tetra-kis(picolinato-κN,O)zirconium(IV) dihydrate

In the title compound, [Zr(C₆H₄NO₂)₄]·2H₂O, the Zr^IV atom is located on a crystallographic fourfold rotoinversion axis () and is coordinated by four picolinate anions with Zr—O and Zr—N distances of 2.120 (2) and 2.393 (2) Å, respectively. An approximate square-anti­prismatic coordination polyhedron of the N,O-coordination ligand atoms is formed, with a distortion towards dodeca­hedral geometry. The crystal packing is stabilized by inter­molecular π–π inter­actions between adjacent picolinate rings [centroid–centroid distances = 3.271 (1) and 3.640 (2) Å], as well as O—H⋯O hydrogen bonds between the solvent mol­ecules and the coordinated ligands, thereby linking the mol­ecules into a supra­molecular three-dimensional network.

Tetra-kis(1,3-diphenyl-propane-1,3-dionato)hafnium(IV)

In the title compound, [Hf(C₁₅H₁₁O₂)₄], the Hf^IV atom is coordinated by four 1,3-diphenyl­propane-1,3-dionato ligands with an average Hf—O distance of 2.17 (3) Å and O—Hf—O bite angles varying from 74.5 (1) to 75.02 (9)°. The coordination polyhedron shows a slightly distorted Archimedean square-anti­prismatic geometry. The crystal packing is stabilized by weak C—H⋯O inter­actions.

Bis[N,N-bis-(diphenyl-phosphan-yl)cyclo-hexyl-amine-κP,P']platinum(II) bis-(hexa-fluorido-phosphate) dichloro-methane disolvate

In the title compound, [Pt(C₃₀H₃₁NP₂)₂](PF₆)₂·2CH₂Cl₂, the four-coordinated Pt^II atom, situated on an inversion centre, exhibits a highly distorted square-planar geometry illustrated by the P—Pt—P bite angle of 70.76 (3)°. The cyclo­hexyl ring and one of the phenyl rings display 0.630 (7):0.37 (7) and 0.60 (2):0.40 (2) positional disorder, respectively. The dichloro­methane solvent mol­ecule displays 0.526 (4):0.474 (4) positional disorder. C—H⋯F hydrogen bonds stabilize the crystal packing.

Bis[N,N-bis-(diphenyl-phosphan-yl)pentyl-amine-κP,P']platinum(II) bis-(hexa-fluoridophosphate) dichloro-methane disolvate

The Pt(II) atom in the title compound, [Pt(C(29)H(31)NP(2))(2)](PF(6))(2)·2CH(2)Cl(2), is coordinated by four P atoms from two bis-(di-phenyl-phosphan-yl)pentyl-amine ligands with an average Pt-P distance of 2.300 (1) Å. The coordination around the Pt(II) atom shows a highly distorted square-planar geometry, as evidenced by the P-Pt-P bite angles of 70.45 (3) and 70.64 (3)°. The asymmetric unit contains two hexa-fluoridophosphate ions, the metal complex and two dichloro-methane solvent mol-ecules. One of the chloride atoms of one of the dichloro-methane mol-ecules is disordered over two sites in a 0.515 (3):0.485 (3) ratio. C-H⋯F hydrogen bonds stabilize the crystal packing.

(Acetyl-acetonato-κO,O')chlorido-trimethano-latoniobium(V)

In the title compound, [Nb(CH(3)O)(3)(C(5)H(7)O(2))Cl], the Nb(V) atom is coordinated by two O atoms from the chelating acetyl-acetonate ligand, three O atoms from the methano-late groups and one chloride ligand. The octa-hedral environment around niobium is slightly distorted with Nb-O distances in the range 1.8603 (15)-2.1083 (15) Å and an Nb-Cl distance of 2.4693 (9) Å. The O-Nb-O angles vary between 80.74 (6) and 100.82 (7)°, while the trans Cl-Nb-O angle is 167.60 (5)°. There are no hydrogen bonds observed, only an inter-molecular C-H⋯O inter-action.

4-(2-Methyl-anilino)pent-3-en-2-one

The title enamino ketone, C(12)H(15)NO, a derivative of 4-(phenyl-amino)-pent-3-en-2-one, presents a roughly planar [greatest displacement of an atom from the pentenone plane is 0.033 (2) Å] pentenone backbone, enhanced by an intra-molecular N-H⋯O hydrogen bond; the asymmetry in C-C distances in the group suggests the presence of unsaturated bonds. The overall geometry in the free ligand differs significantly from that in other reported compounds, in which it is coordinated to rhodium; this is reflected in the bond distances [the N⋯O distance is significantly increased (0.2 Å) upon coordination to the metal] and the dihedral angle between the benzene ring and the pentenone backbone [49.53 (5)°]. All of the methyl goups are rotationally disordered over two orientations of equal occupancy.

Tetra-kis(8-quinolinolato-κN,O)hafnium(IV) dimethyl-formamide solvate monohydrate

In the title compound, [Hf(C(9)H(6)NO)]·C(3)H(7)NO·H(2)O, the hafnium(IV) atom is coordinated by four 8-quinolinolate (Ox) ligands, forming a slightly distorted square-anti-prismatic coordination polyhedron. The crystal packing is controlled by O-H⋯O and C-H⋯O hydrogen-bonding inter-actions and π-π inter-actions between quinoline ligands of neighbouring mol-ecules. The inter-planar distances vary between 3.150 (1) and 3.251 (2) Å, while centroid-centroid distances vary from 3.589 (1) to 4.1531 (1) Å.

Cooperation between cis and trans influences in cis-Pt(II)(PPh(3))(2) complexes: structural, spectroscopic, and computational studies

The relevance of cis and trans influences of some anionic ligands X and Y in cis-[PtX(2)(PPh(3))(2)] and cis-[PtXY(PPh(3))(2)] complexes have been studied by the X-ray crystal structures of several derivatives (X(2) = (AcO)(2) (3), (NO(3))(2) (5), Br(2) (7), I(2) (11); and XY = Cl(AcO) (2), Cl(NO(3)) (4), and Cl(NO(2)) (13)), density functional theory (DFT) calculations, and one bond Pt-P coupling constants, (1)J(PtP). The latter have allowed an evaluation of the relative magnitude of both influences. It is concluded that such influences act in a cooperative way and that the cis influence is not irrelevant when rationalizing the (1)J(PtP) values, as well as the experimental Pt-P bond distances. On the contrary, in the optimized geometries, evaluated through B3LYP/def2-SVP calculations, the cis influence was not observed, except for compounds ClPh (21), Ph(2) (22), and, to a lesser extent, Cl(NO(2)) (13) and (NO(2))(2) (14). A natural bond order analysis on the optimized structures, however, has shown how the cis influence can be related to the s-character of the Pt hybrid orbital involved in the Pt-P bonds and the net atomic charge on Pt. We have also found that in the X-ray structures of cis-[PtX(2)(PPh(3))(2)] complexes the two Pt-X and the two Pt-P bond lengths are different each other and are related to the conformation of the phosphine groups, rather than to the crystal packing, since this feature is observed also in the optimized geometries.

13C and (15)N NMR Mechanistic Study of Cyanide Exchange on Oxotetracyanometalate Complexes of Re(V), Tc(V), W(IV), Mo(IV), and Os(VI)

A range of complexes with general formula [MO(X)(CN)(4)](n)()(-) of W(IV), Mo(IV), Re(V), Tc(V), and Os(VI) were prepared and characterized by (13)C, (15)N, (17)O, and (99)Tc NMR, utilizing (13)C- and (15)N-enriched cyano complexes. A correlation between M-O and M-CN bond strength from X-ray crystallographic data and |(1)J((183)W-(13)C)| coupling is reported. The cyanide (HCN/CN(-)) exchange kinetics on the trans-dioxotetracyanometalate complexes and protonated/substituted ([MO(X)(CN)(4)](n)()(-)) forms thereof were studied in aqueous medium. The dioxotetracyano complexes show a trend of reactivity M(IV) > M(V) >M(VI), which is in agreement with the increase in M-L bond strength (L = O(2)(-) or CN(-)) and a dissociative activation for the cyanide and the oxygen exchange in these complexes. Rate constants (X, k(Xc)) in s(-)(1) at 298 K for the [MO(X)(CN)(4)](n)()(-) complexes are as follows for Mo(IV): O(2)(-), >0.4; OH(-), (1.7 +/- 0.1) x 10(-)(2); H(2)O, (1.5 +/- 0.1) x 10(-)(2); CN(-), (9.6 +/- 0.8) x 10(-)(3). For W(IV): O(2)(-), (4.4 +/- 0.4) x 10(-)(3); OH(-), (9.6 +/- 0.9) x 10(-)(5); H(2)O, (1.1 +/- 0.1) x 10(-)(4); CN(-), (1.1 +/- 0.1) x 10(-)(2); N(3)(-), (3.1 +/- 0.2) x 10(-)(4); F(-), (4.8 +/- 0.1) x 10(-)(5). For Tc(V): O(2)(-), (4.8 +/- 0.4) x 10(-)(3); H(2)O, <4 x 10(-)(5); NCS(-), <4 x 10(-)(5). For Re(V): O(2)(-), (3.6 +/- 0.3) x 10(-)(6) and (1.2 +/- 0.1) x 10(-)(4) for CN(-) and HCN, respectively; OH(2), <4 x 10(-)(8). For Os(VI): O(2)(-), <4 x 10(-)(9) and (1.2 +/- 0.1) x 10(-)(4) for CN(-) and HCN, respectively. The cyanide exchange kinetics were correlated with previously determined proton and oxygen exchange, spanning a kinetic domain of more than 12 orders of magnitude for the five metal centers studied.