Synthesis, structure, properties, volatility, and thermal stability of molybdenum(II) and tungsten(II) complexes containing allyl, carbonyl, and pyrazolate or amidinate ligands

Treatment of M(allyl)(Cl)(CO)₂(py)₂ (M = Mo, W) with 1 equiv. of potassium pyrazolates in tetrahydrofuran at −78 °C afforded M(allyl)(R₂pz)(CO)₂(py)_n (R₂pz = 3,5-disubstituted pyrazolate; n = 1, 2) in 68-81% yields. X-ray crystal structure analyses of Mo(allyl)((CF₃)₂pz)(CO)₂(py)₂ and W(allyl)(tBu₂pz)(CO)₂(py) revealed η¹- and η²-coordination of the (CF₃)₂pz and tBu₂pz ligands, respectively. Analogous treatment of Mo(allyl)(Cl)(CO)₂(NCCH₃)₂ with 1 equiv. of tBu₂pzK in tetrahydrofuran at −78 °C afforded [Mo(allyl)(tBu₂pz)(CO)₂]₂ in 79% yield. An X-ray crystal structure analysis of [Mo(allyl)(tBu₂pz)(CO)₂]₂ showed a dimeric structure bridged by two μ-η²:η¹-tBu₂pz ligands. Treatment of M(allyl)(Cl)(CO)₂(py)₂ with 1 equiv. of lithium 1,3-diisopropylacetamidinate or lithium 1,3-di-tert-butylacetamidinate in diethyl ether at −78 °C afforded M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) and M(allyl)(tBuNC(Me)NtBu)(CO)₂(py), respectively, in 68-78% yields. The new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. M(allyl)(iPrNC(Me)NiPr)(CO)₂(py) adopt pseudo-octahedral geometry about the metal centers, with the 1,3-diisopropylacetamidate ligand nitrogen atoms spanning one axial site and one equatorial site of the octahedron. By contrast, M(allyl)(tBuNC(Me)NtBu)(CO)₂(py) adopt pseudo-octahedral structures in which the two 1,3-di-tert-butylacetamidinate ligand nitrogen atoms span two equatorial coordination sites. Sublimation of M(allyl)(tBuNC(Me)NtBu)-(CO)₂(py) at 105 °C/0.03 Torr afforded ?7% yields of M(allyl)(tBuNC(Me)NtBu)(CO)₂, along with sublimed M(allyl)(tBuNC(Me)NtBu)(CO)₂(py). W(allyl)(tBuNC(Me)NtBu)(CO)₂ exists in the solid state as a 16-electron complex with distorted square pyramidal geometry. Many of the new complexes undergo dynamic ligand site exchange in solution, and these processes were probed by variable temperature ¹H NMR spectroscopy. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use as precursors in thin film growth experiments.     

Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-β-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh)₃)₂] and [Rh(FcCOCHCOR)(P(OPh)₃)₂(CH₃)(I)], with Fc = ferrocenyl and R = Fc, CH₃ and CF₃, have been synthesized. The reactivity of complexes of the type [Rh(β-diketonato)(P(OPh)₃)₂] increase in the order: β-diketonato = (CF₃COCHCOCF₃)⁻ < (CF₃COCHCOPh)⁻ < (CF₃COCHCOCH₃)⁻ < (PhCOCHCOPh)⁻ < (CF₃COCHCOFc)⁻ < (CH₃COCHCOPh)⁻ < (CH₃COCHCOCH₃)⁻ < (CH₃COCHCOFc)⁻ < (FcCOCHCOFc)⁻, giving linear relationships between the kinetic parameter ln k₂ and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the β-diketonato side groups (χ_R + χ_R′) and the pK_a of the uncoordinated β-diketone RCOCH₂COR′. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF₃)(P(OCH₃)₃)₂] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.     

Olefin-aminocarbyne coupling in diiron complexes: Synthesis of new bridging aminoallylidene complexes

The bridging aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃] (R = Me, 1a; Xyl, 1b; 4-C₆H₄OMe, 1c; Xyl = 2,6-Me₂C₆ H₃) react with acrylonitrile or methyl acrylate, in the presence of Me₃NO and NaH, to give the corresponding μ-allylidene complexes [Fe₂{μ-η¹:η³- C_α(N(Me)(R))C_β(H)C_γ(H)(R′)}(μ-CO)(CO)(Cp)₂] (R = Me, R′ = CN, 3a; R = Xyl, R′ = CN, 3b; R = 4-C₆H₄OMe, R′ = CN, 3c; R = Me, R′ = CO₂Me, 3d; R = 4-C₆H₄OMe, R′ = CO₂Me, 3e). Likewise, 1a reacts with styrene or diethyl maleate, under the same reaction conditions, affording the complexes [Fe₂{μ-η¹:η³-C_α(NMe₂)C_β(R′)C_γ(H)(R″)}(μ-CO)(CO)(Cp)₂] (R′ = H, R″ = C₆H₅, 3f; R′ = R″ = CO₂Et, 3g). The corresponding reactions of [Ru₂{μ-CN(Me)(CH₂Ph)}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃] (1d) with acrylonitrile or methyl acrylate afford the complexes [Ru₂{μ-η¹:η³-C_α(N(Me)(CH₂Ph))C_β(H)C_γ(H)(R′)}(μ-CO)(CO)(Cp)₂] (R′ = CN, 3h; CO₂Me, 3i), respectively.The coupling reaction of olefin with the carbyne carbon is regio- and stereospecific, leading to the formation of only one isomer. C-C bond formation occurs selectively between the less substituted alkene carbon and the aminocarbyne, and the C_β-H, C_γ-H hydrogen atoms are mutually trans.The reactions with acrylonitrile, leading to 3a-c and 3h involve, as intermediate species, the nitrile complexes [M₂{μ-CN(Me)(R)}(μ-CO)(CO)(NC-CHCH₂)(Cp)₂][SO₃CF₃] (M = Fe, R = Me, 4a; M = Fe, R = Xyl, 4b; M = Fe, R = 4-C₆H₄OMe, 4c; M = Ru, R = CH₂C₆H₅, 4d).Compounds 3a, 3d and 3f undergo methylation (by CH₃SO₃CF₃) and protonation (by HSO₃CF₃) at the nitrogen atom, leading to the formation of the cationic complexes [Fe₂{μ-η¹:η³-C_α(N(Me)₃)C_β(H)C_γ(H)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = CN, 5a; R = CO₂Me, 5b; R = C₆H₅, 5c) and [Fe₂{μ-η¹:η³-C_α(N(H)(Me)₂)C_β(H)C_γ(H)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = CN, 6a; R = CO₂Me, 6b; R = C₆H₅, 6c), respectively.Complex 3a, adds the fragment [Fe(CO)₂(THF)(Cp)]⁺, through the nitrile functionality of the bridging ligand, leading to the formation of the complex [Fe₂{μ-η¹:η³-C_α(NMe₂)C_β(H)C_γ(H)(CNFe(CO)₂Cp)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (9).In an analogous reaction, 3a and [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃], in the presence of Me₃NO, are assembled to give the tetrameric species [Fe₂{μ-η¹:η³-C_α(NMe₂)C_β(H)C_γ(H)(CN[Fe₂{μ- CN(Me)(R)}(μ-CO)(CO)(Cp)₂])}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = Me, 10a; R = Xyl, 10b; R = 4-C₆H₄OMe, 10c).The molecular structures of 3a and 3b have been determined by X-ray diffraction studies.     

Photocatalytic properties of new cyclopentadienyl and indenyl rhodium(I) carbonyl complexes with water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA) and tris(2-cyanoethyl)phosphine

Reactions of [(η⁵-R)Rh(CO)₂] (R = cp, ind) with water-soluble phosphines (L = 1,3,5-triaza-7-phosphaadamantane and tris(2-cyanoethyl)phosphine) give the new rhodium(I) complexes of the types [Rh(η⁵-cp)(CO)(PTA)] (1), [Rh(η⁵-cp)(CO)(P(CH₂CH₂CN)₃)] (2), [Rh(η⁵-ind)(CO)(PTA)] (3) and [Rh(η⁵-ind)(CO)(P(CH₂CH₂CN)₃)] (4) in isolated yields of 52-75%. All these compounds have been fully characterized by IR, ¹H, ³¹P{¹H} and ¹³C{¹H} NMR, FAB-MS spectroscopies and elemental analyses. Reactivity for the substitution of phosphine is greater for [(η⁵-ind)Rh(CO)(L)] comparing to [(η⁵-cp)Rh(CO)(L)] because of a flexibility of the indenyl ligand to undergo facile η⁵-η³ coordinative isomerizations. The obtained complexes are active catalyst precursors for the dehydrogenation of propan-2-ol, octane and cyclooctane under photoassisted conditions without any organic hydrogen transfer acceptors, giving TOFs of 26-56 using 3 as precatalyst.     

Oxidative addition of MeI to cationic Rh(I) carbonyl complexes with pyridyl bis(carbene) ligands

A series of cationic Rh(I) carbonyl complexes of the form [Rh(CO)(L)]PF₆ (where L = 2,6-bis (alkylimidazol-2-ylidene)-pyridine; alkyl = Me (1a), Et (1b), CH₂Ph (1c)) have been prepared by the reactions of [Rh(CO)₂(OAc)]₂ with diimidazolium pyridine salts in the presence of NEt₃. The ν(CO) values for 1 are ca. 1982 cm⁻¹, indicating that the N-heterocyclic carbene ligands impart high electron density on the Rh(I) centres, despite the overall cationic charge. Each of the Rh(I) complexes reacts with MeI to form two isomeric Rh(III) methyl species, and a third unidentified species. Kinetic measurements on the MeI oxidative addition reactions give second-order rate constants (MeCN, 25 °C) of 0.0927, 0.0633 and 0.0277 M⁻¹ s⁻¹ for 1a, 1b and 1c, respectively. Comparison of these data with those for related Rh(I) carbonyl complexes shows that 1 have remarkably high nucleophilicity for cationic species.     

Reactions of cationic rhodium(I) carbonyl compounds with nucleophiles to form alkoxo,carboalkoxy and carboxylato complexes. Part II

Summary The rhodium(I) carbonyl compounds [Rh(CO)L₂2] [BF₄]. 1/2CH₂Cl_nn2 (L = PPh₂ or AsPh₃) react with the nucleophiles OMe⁻, RCOO⁻ (R = Me, Et) under nitrogen to form [Rh(OR)(CO)L₂] (1)–(2) and [Rh(OOCR)(CO)L₂] (7)–(₁₀), respectively. Addition of [Rh(CO)₂(PPh₃)₂]-[BF ₄] to OMe⁻ under nitrogen produces [Rh(COOMe)-(CO) (PPh₃)₂]-MeOH (3), whilst reactions of [Rh(CO)-(PPh₃)₂] [BF₄]·1/2CH₂Cl₂ and [Rh(CO)₂(PPh₃)₂] [BF₄] with OR_- (R = Me, Et or n-Pr) in the presence of CO produce [Rh(COOR)(CO)₂(PPh₃)₂] (4)–(6). The products have been characterised by i.r., ¹H, ³¹P, ¹³Cn.m.r. spectroscopy and elemental analysis.     

Hydride addition at μ-vinyliminium ligand obtained from disubstituted alkynes

New μ-vinylalkylidene complexes cis-[Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αHN(Me)(R)}(μ-CO)(CO)(Cp)₂] (R = Me, R′ = R″ = Me, 3a; R = Me, R′ = R″ = Et, 3b; R = Me, R′ = R″ = Ph, 3c; R = CH₂Ph, R′ = R″ = Me, 3d; R = CH₂Ph, R′ = R″ = COOMe, 3e; R = CH₂ Ph, R′ = SiMe₃, R″ = Me, 3f) have been obtained b yreacting the corresponding vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2a-f) with NaBH₄. The formation of 3a-f occurs via selective hydride addition at the iminium carbon (C_α) of the precursors 2a-f. By contrast, the vinyliminium cis-[Fe₂{μ-η¹:η³-C_γ (R′) = C_β(R″)C_α = N(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R′ = R″ = COOMe, 4a; R′ = R″ = Me, 4b; R′ = Prⁿ, R″ = Me, 4c; Prⁿ = CH₂CH₂CH₃, Xyl = 2,6-Me₂C₆H₃) undergo H⁻ addition at the adjacent C_β, affording the bis-alkylidene complexes cis-[Fe₂{μ-η¹:η²-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], (5a-c). The cis and trans isomers of [Fe₂{μ-η¹:η³-C_γ(Et)C_β(Et)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4d) react differently with NaBH₄: the former reacts at C_α yielding cis-[Fe₂{μ-η¹:η³-C_γ(Et)C_β(Et)C_αHN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], 6a, whereas the hydride attack occurs at C_β of the latter, leading to the formation of the bis alkylidene trans-[Fe₂{μ-η¹:η²-C(Et)C(H)(Et)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (5d). The structure of 5d has been determined by an X-ray diffraction study. Other μ-vinylalkylidene complexes cis-[Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αHN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], (R′ = R″ = Ph, 6b; R′ = R″ = Me, 6c) have been prepared, and the structure of 6c has been determined by X-ray diffraction. Compound 6b results from treatment of cis-[Fe₂{μ-η¹:η³-C_γ(Ph)C_β(Ph)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4e) with NaBH₄, whereas 6c has been obtained by reacting 4b with LiHBEt₃. Both cis-4d and trans-4d react with LiHBEt₃ affording cis-6a.     

31P-NMR and X-ray studies of new rhodium(I) β-ketoiminato complexes Rh(R1C(O)CHC(NH)R2)(CO)(PZ3) where PZ3=PPh3, PCy3, P(OPh)3 or P(NC4H4)3

The substitution of the CO ligand in rhodium(I) β-ketoiminato complexes Rh(R₁{O,N}R₂)(CO)₂ ({O,N}=R₁C(O)CHC(NH)R₂; R₁, R₂=CF₃, Me, CMe₃ in several combinations) by phosphorus ligands PZ₃ (PZ₃=PCy₃, PPh₃, P(OPh)₃, P(NC₄H₄)₃) leads to Rh(R₁{O,N}R₂)(CO)(PZ₃) complexes characterised by ³¹P{¹H}-NMR and X-ray methods. The stronger σ-donor PZ₃ ligands (PZ₃=PCy₃, PPh₃) substitute almost exclusively the CO group trans to N, forming P-trans-to-N isomers. The complexes Rh(CF₃{O,N}Me)(CO)(PCy₃) (II), Rh(CF₃{O,N}CMe₃)(CO)(PCy₃) (III), Rh(CF₃{O,N}Me)(CO)(PPh₃) (IV) and Rh(CF₃{O,N}CMe)(CO)(PPh₃) (V) are of a square-planar geometry with a slight tetrahedral distortion around the rhodium atom in II, III and V. The RhP(PCy₃) bonds are slightly longer than the RhP(PPh₃) bonds. The reaction of stoichiometric amounts of the less basic P(OPh)₃ or P(NC₄H₄)₃ ligands leads to the formation of both isomers of the Rh(R₁{O,N}R₂)(CO)(P(OPh)₃) or Rh(R₁{O,N}R₂)(CO)(P(NC₄H₄)₃) complex in comparable yields. The RhP(P(OPh)₃) distance (2.195(2) Å) in the isomer of Rh(CF₃{O,N}CMe₃)(CO)(P(OPh)₃) with P(OPh)₃ coordinated trans to N (VI) is ca. 0.04 Å longer than in the isomer of that complex with P(OPh)₃ coordinated trans to O (VII). The CO substitution in Rh(R₁{O,N}R₂)(CO)₂ by PZ₃ ligands (PPh₃, PCy₃, P(OPh)₃) causes the shortening of the RhC(CO) bond by ca. 0.04 Å compared to Rh(CF₃{O,N}Me)(CO)₂ (I), making difficult the coordination of another PZ₃ ligand, especially one with stronger σ-donor properties. The more π-acceptor P(OPh)₃ ligands form bis-phosphito complexes and Rh(CF₃{O,N}CMe₃){P(OPh)₃}₂ (VIII) exhibits inequivalence of the two P(OPh)₃ ligands in solution (³¹P-NMR) as well as in solid form (X-ray).     

Iodomethane oxidative addition and CO migratory insertion in monocarbonylphosphine complexes of the type [Rh((C6H5)COCHCO((CH2)nCH3))(CO)(PPh3)]: Steric and electronic effects

The chemical kinetics, studied by UV/Vis, IR and NMR, of the oxidative addition of iodomethane to [Rh((C₆H₅)COCHCOR)(CO)(PPh₃)], with R = (CH₂)_nCH₃, n = 1-3, consists of three consecutive reaction steps that involves isomers of two distinctly different classes of Rh^III-alkyl and two distinctly different classes of Rh^III-acyl species. Kinetic studies on the first oxidative addition step of [Rh((C₆H₅)COCHCOR)(CO)(PPh₃)] + CH₃I to form [Rh((C₆H₅)COCHCOR)(CH₃)(CO)(PPh₃)(I)] revealed a second order oxidative addition rate constant approximately 500-600 times faster than that observed for the Monsanto catalyst [Rh(CO)₂I₂]⁻. The reaction rate of the first oxidative addition step in chloroform was not influenced by the increasing alkyl chain length of the R group on the β-diketonato ligand: k₁ = 0.0333 ([Rh((C₆H₅)COCHCO(CH₂CH₃))(CO)(PPh₃)]), 0.0437 ([Rh((C₆H₅)COCHCO(CH₂CH₂CH₃))(CO)(PPh₃)]) and 0.0354 dm³ mol⁻¹ s⁻¹ ([Rh((C₆H₅)COCHCO(CH₂CH₂CH₂CH₃))(CO)(PPh₃)]). The pK_a^′ and keto-enol equilibrium constant, K_c, of the β-diketones (C₆H₅)COCH₂COR, along with apparent group electronegativities, χ_R of the R group of the β-diketones (C₆H₅)COCH₂COR, give a measurement of the electron donating character of the coordinating β-diketonato ligand: (R, pK_a^′, K_c, χ_R) = (CH₃, 8.70, 12.1, 2.34), (CH₂CH₃, 9.33, 8.2, 2.31), (CH₂CH₂CH₃, 9.23, 11.5, 2.41) and (CH₂CH₂CH₂CH₃, 9.33, 11.6, 2.22).     

Darstellung carboxylatsubstituierter Rhenium-Gold-Metallatetrahedrane Re2(AuPPh3)2(μ-PCy2)(CO)7(η1-OC(R)O) (R = H,Me, CF3, Ph, 3,4-(OMe)2C6H3)

Synthesis of Carboxylate Substituted Rhenium Gold Metallatetrahedranes Re₂(AuPPh₃)₂(μ-PCy₂)(CO)₇(η¹-OC(R)O) (R = H, Me, CF₃, Ph, 3,4-(OMe)₂C₆H₃) The reaction of the in situ prepared salt Li[Re₂(μ-H)(μ-PCy₂)(CO)₇(ax-C(Ph)O)] ( 2 ) with 1,5 equivalents of monocarboxylic acid RCOOH (R = H ( 4 a ), Me ( 4 b ), CF₃ ( 4 c ), Ph ( 4 d ), 3,4-(OMe)₂C₆H₃ ( 4 e ) in tetrahydrofruan (THF) solution at 60 °C gives within 4 h under release of benzaldehyde (PhCHO) the η¹-carboxylate substituted dirhenium salt Li[Re₂(μ-H)(μ-PCy₂)(CO)₇(η¹-OC(R)O)] (R = H ( 4 a ), Me ( 4 b ), CF₃ ( 4 c ), Ph ( 4 d ), 3,4-(OMe)₂C₆H₃ ( 4 e )) in almost quantitative yield. The lower the pK_a value of the respective carboxylic acid the faster the reaction proceeds. It was only in the case of CF₃COOH possible to prove the formation of the hydroxycarbene complex Re₂(μ-H)(μ-PCy₂)(CO)₇(=C(Ph)OH) ( 5 ) prior to elimination of PhCHO. The new compounds 4 a–4 e were only characterized by ³¹P NMR and ν(CO) IR spectroscopy as they are only stable in solution. They are converted with two equivalents of BF₄AuPPh₃ at 0 °C in a so-called cluster expansion reaction into the heterometallic metallatetrahedrane complexes Re₂(AuPPh₃)₂(μ-PCy₂)(CO)₇(η¹-OC(R)O) (R = H ( 7 a ), Me ( 7 b ), CF₃ ( 7 c ), Ph ( 7 d ), 3,4-(OMe)₂C₆H₃ ( 7 e )) (yield 47–71% ). The expected precursor complexes of 7 a–7 e Li[Re₂(AuPPh₃)(μ-PCy₂)(CO)₇(η¹-OC(R)O] ( 8 ) were not detected by NMR and IR spectroscopy in the course of the reaction. Their existence was retrosynthetically proved by the reaction of 7 b with an excess of the chelating base TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-en) forming [(TBD)_xAuPPh₃][Re₂(AuPPh₃)(μ-PCy₂)(CO)₇(η¹-OC(Me)O] ( 8 b ) in solution. The η¹-bound carboxylate ligand in 7 a–7 e can photochemically be converted into a μ-bound ligand in Re₂(AuPPh₃)₂(μ-PCy₂)(μ-OC(R)O)(CO)₆ (R = H ( 9 a ), Me ( 9 b ), CF₃ ( 9 c ), Ph ( 9 d ), 3.4-(MeO)₂C₆H₃ ( 9 e )) under release of one equivalent CO. All isolated cluster complexes were characterized and identified by the following analytical methods: elementary analysis, NMR (¹H, ³¹P) spectroscopy, ν(CO) IR spectroscopy and in the case of 7 d and 9 b by X-ray structure analysis.     

Rhodium(I) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid as active and recyclable catalysts for 1-hexene hydroformylation

The rhodium complex trans-[Rh(CO)(Hdpf-κP)(dpf-κ²O,P)] (1), (Hdpf = 1′-(diphenylphosphino)ferrocenecarboxylic acid) was used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H₂ and 80 °C. After the reaction, unchanged complex 1 was separated from the reaction mixture and used again three times with the same catalytic activity. The effect of modifying ligands, phosphines and phosphites, on the reactivity of 1 was investigated. The active catalytic systems containing 1 or trans-[Rh(CO)(L)(dpf-κ²O,P)] (2) were formed in situ from acetylacetonato rhodium(I) precursors [Rh(CO)₂(acac)] (3) or [RhL(CO)(acac)] (4) and Hdpf or Medpf (L = phosphine, Medpf = methyl ester of Hdpf).     

Rhodium(I) carbonyl complexes of tetradentate chalcogen functionalized phosphines, [P(X)(CH2CH2P(X)Ph2)3] {X = O, S, Se}: Synthesis, reactivity and catalytic carbonylation reaction

The reaction of [Rh(CO)₂Cl]₂ with 0.5 mol equivalent of the ligands [P^′(X)(CH₂-CH₂P(X)Ph₂)₃](P^′P₃X₄) {where X = O(a), S(b) and Se(c)} affords tetranuclear complexes of the type [Rh₄(CO)₈Cl₄(P^′P₃X₄)] (1a-1c). The complexes 1a-1c have been characterized by elemental analyses, mass spectrometry, IR and multinuclear NMR spectroscopy, and the ligands b and c are structurally determined by single crystal X-ray diffraction. 1a-1c undergo oxidative addition (OA) reactions with CH₃I to generate Rh(III) oxidised products. Kinetic data for the reaction of 1a and 1b with excess CH₃I indicate a pseudo first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester show a higher Turn Over Frequency (TOF = 1349-1748 h⁻¹) compared to the well-known species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the similar experimental conditions. However, 1b and 1c exhibit lower TOF than 1a, which may be due to the desulfurization and deselinization of the ligands in the respective complexes under the reaction conditions.     

Theoretical investigation of the scope of sequential ligand tuning using a bifunctional scorpionate tris(1,2,4-triazolyl)borate-based architecture

The donor properties of a series of tripodal mixed N-donor/carbene ligands derived through sequential alkylation of hydrotris(1,2,4-triazolyl)borate have been investigated by density functional theory (DFT) methods. The structures of complexes of the form [Mo(L)(CO)₃]⁻ were optimized (L = [HB(1,2,4-triazolyl)_n(1,2,4-triazol-5-ylidene)_3−n]⁻ (n = 0-3), hydrotris(pyrazolyl)borate, hydrotris(3,5-dimethylpyrazolyl)borate and hydrotris(imidazol-2-ylidene)borate) and ν_CO frequencies for these complexes and partial charges of their Mo(CO)₃ fragments were determined. Results show that ligand donation is highly tunable when compared to similar experimentally known ligands with a shift in the symmetric ν_CO stretching mode of −39 cm⁻¹ on going from the tris(1,2,4-triazolyl)borate complexes to that of the triscarbene hydrotris(1,2,4-triazol-5-ylidene) and an increase in partial charge (distributed multipole analysis) of the Mo(CO)₃ fragment from −0.23 to −0.48.     

Reactions of trans-[RuCl2(CO)2(PEt3)2] with 1,1-dithiolates: Stepwise formation of cis-[Ru(CO)(PEt3)(S2X)] (X = CNMe2, CNEt2, COEt,P(OEt)2, PPh2)

Trans-[RuCl₂(CO)₂(PEt₃)₂] reacts with two equivalents of a series of 1,1-dithiolate ligands to form the bis(dithiolate) complexes, cis-[Ru(CO)(PEt₃)(S₂X)₂] (X = CNMe₂, CNEt₂, COEt, P(OEt)₂, PPh₂). Two intermediates have been isolated; trans-[Ru(PEt₃)₂Cl(CO){S₂P(OEt)₂}] and trans-[Ru(PEt₃)₂(CO)(η¹-S₂COEt)(η²-S₂COEt)], allowing a simple reaction scheme to be postulated involving three steps; (i) initial replacement of cis carbonyl and chloride ligands, (ii) substitution of the second chloride, (iii) loss of a phosphine. Thermolysis of cis-[Ru(CO)(PEt₃)(S₂CNMe₂)₂] with Ru₃(CO)₁₂ in xylene affords trinuclear [Ru₃(μ₃-S)₂(PEt₃)(CO)₈] as a result of dithiocarbamate degradation. Crystal structures of cis-[Ru(CO)(PEt₃)(S₂X)₂] (X = NMe₂, COEt), trans-[Ru(PEt₃)₂Cl(CO){S₂P(OEt)₂}], trans-[Ru(PEt₃)₂(CO)(η¹-S₂COEt)(η²-S₂COEt)] and [Ru₃(μ₃-S)₂(PEt₃)(CO)₈] are reported.     

First examples of [Rh(Bident)(CO)(L)] complexes where L is N-donor ligand: Molecular structure of [Rh(8-Oxiquinolinato)(CO)(NH3)]

Selective oxidation of one (trans to N) carbonyl group in [Rh(8-Oxiquinolinato)(CO)₂] with stoichiometric amount of Me₃NO in MeCN produces a solution containing [Rh(Oxq)(CO)(Me₃N)] and [Rh(Oxq)(CO)(MeCN)]. The ammonia complex, [Rh(Oxq)(CO)(NH₃)], has been prepared by action of NH₃ gas on this solution and characterized by IR, ¹H and ¹³C NMR, and X-ray data. Spectral parameters, ν(CO), δ¹³C, and ¹J(CRh), were measured in situ for a series of complexes [Rh(Oxq)(CO)(L)] (L = NAlk₃, Py, PBu₃, PPh₃, P(OPh)₃, C₈H₁₄) formed upon action of L on [Rh(Oxq)(CO)(NH₃)] in THF. A new ν(CO) and δ¹³C based scale of σ-donor/π-acceptor properties of ligands L is proposed including NH₃ and CO as the natural endpoints.     

Co-ligand effects in the catalytic activity of Pd(II)-NHC complexes

Three cis-chelating di-N-heterocyclic carbene palladium(II) complexes [PdX₂(diNHC)] (X = I, 1; X = SCN, 2; X = CF₃CO₂, 3) bearing different anionic co-ligands were synthesized and fully characterized. A comparison of their catalytic activities in the Mizoroki-Heck reaction and conjugate addition of arylboronic acids to cyclic enones revealed increasing efficiency in the order SCN⁻ < I⁻ < CF₃CO₂⁻. The di(trifluoroacetato) complex 3 showed the best activity in both transformations highlighting the importance of co-ligands effects in catalysis. In addition, the molecular structure of an unusual poly-heteronuclear complex salt 4 is reported, which has been isolated as a byproduct in the synthesis of complex 3.     

Quantum-chemical study of donor-acceptor interactions in rhodium(I) carbonyl carboxylate complexes with phosphine ligands

The DFT B3LYP method was used to optimize the geometries, calculate the IR spectra, and analyze the electronic structures of carbonyl(carboxylato)(phosphine)rhodium(I) complexes, namely, trans-[Rh(Cl)(CO)(PPh₃)₂], trans-[Rh(OCOR)(CO)(PPh₃)₂] (R = H, CH₃, and CF₃), and trans-[Rh(OCOH)(CO)(PX₃)₂], and free PX₃ molecules (X = H, F, CH₃, i-Pr, Cy, and Ph). A linear correlation between v(CO) in the IR spectra of trans-[Rh(OCOH)(CO)(PX₃)₂] and the HOMO energy of the free PX₃ molecule was found for phosphines with nonaromatic substituents X. It was concluded that the electronic state of the CO group is mainly determined by the σ-donor properties of phosphines. The distinctive features of the electronic structure of triphenylphosphine are discussed.     

μ,μ,-bis(alcoholato)- and μ,μ-bis(phenolato)dirhodium(I) tetracarbonyl complexes

Rh₂(CO)₄(OR)₂ complexes (R = Me, Et, Pr, i-pent, Ph, p-chlorophenyl) were prepared from Rh₂(CO)₄Cl₂ and sodium alcoholates or phenolates. They are converted by phosphines into the monomeric Rh(CO)(PR′₃)₂(OR) derivatives (R′ = Bu, Ph) via Rh₂(CO)₃(PR′₃)(OR)₂ intermediates.     

Synthesis of the water-soluble [Rh(Tpms)(CO)(PTA)] compound, the first transition metal complex bearing the 1,3,5-triaza-7-phosphaadamantane (PTA) and the tris(1-pyrazolyl)methanesulfonate (Tpms) ligands

The water-soluble Rh^I compound [Rh(Tpms)(CO)(PTA)] (1) (Tpms = O₃SC(pz)₃⁻, PTA = 1,3,5-triaza-7-phosphaadamantane) has been easily prepared in high yield by a single-pot reaction of [{Rh(CO)₂(μ-Cl)}₂] with PTA and the tris(1-pyrazolyl)methanesulfonate lithium salt Li(Tpms), in a CH₂Cl₂/MeOH solution at room temperature. This synthetic strategy can be easily applied to the preparation of general [Rh(Tpms)(CO)(L)] (L = phosphine) complexes and constitutes a substantial improvement over the previously described procedures. Compound 1 is air stable in the solid state and water-soluble, affording stable solutions under an inert atmosphere. It has been characterized by IR, ¹H, ³¹P{¹H} and ¹³C{¹H} NMR spectroscopies, elemental and single crystal X-ray diffraction structural analyses. The solid state structure of 1 has a square-planar geometry with the Tpms ligand coordinating the metal centre in a (κ²: N,N) bipodal mode. The title compound has also been investigated by cyclic voltammetry in CH₃CN, and values of the E_L Lever and P_L Pickett electrochemical parameters (which measure the ligand net electron-donor character) are proposed for the PTA ligand. Complex 1 represents the first example of a transition metal complex bearing both PTA and Tpms (or any other tris(1-pyrazolyl)methane or derivative) ligands.     

The reaction of H2Os3(CO)10 with trifluoroacetonitrile and the x-ray crystal structure of HOs3(CO)9(μ3-η2-HNCCF3)

The reaction of H₂Os₃(CO)₁₀ with CF₃CN in hexane at 80°C leads to two isomeric products. The isomer constituting the major product contains a 1,1,1-tri-fluoroethylidenimido ligand which bridges one edge of the Os₃ triangle via the nitrogen, atom and may be formulated as (μ-H)Os₃(CO)₁₀(μ-NC(H)CF₃) (I). The minor product, formulated as (μ-H)Os₃(CO)₁₀(μ-η²-HNCCF₃) (II), contains a 1,1,1-trifluoroacetimidoyl ligand which is also edge-bridging, being N-bonded to one Os atom and C-bonded to the other. Thermolysis of I and II in solution results in loss of a CO group in each case to give (μ-H)Os₃(CO)_9^? (μ₃-η²-NC(H)CF₃) (III) and (μ-H)Os₃(CO)₉(μ₃-η²-HNCCF₃) (IV), respectively, which, it is proposed, are structurally related to I and II, but with the CN group coordinated also to the third Os atom in place of a CO group. In the case of IV this proposal has been confirmed by an X-ray crystallographic analysis. The compound crystallises in space group C2/c with a = 14.258(7), b = 13.486(10), c = 18.193(8) Å, β = 92.68(4)°, and Z = 8. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by full-matrix least squares to R = 0.054 for 2489 unique observed diffractometer data. Reaction of I with Et₃P gives a 1 : 2 adduct which is formulated as (μ-H)Os₃(CO)₁₀[μ-N?C(H)(CF₃)PEt₃] (V) on the basis of NMR evidence.