Steric vs. electronic anomaly observed from iodomethane oxidative addition to tertiary phosphine modified rhodium(i) acetylacetonato complexes following progressive phenyl replacement by cyclohexyl [PR3 = PPh3, PPh2Cy, PPhCy2 and PCy3]

Dioxaphosphabicyclooctanes: small caged phosphines from tris(hydroxymethyl)phosphine

Dioxaphosphabicyclo[2.2.2]octanes (L1-L4) have been prepared in a one-pot reaction from tris(hydroxymethyl)phosphine and various α,β-unsaturated ketones. The non-volatile phosphines oxidise very slowly in air. They possess highly upfield 31P chemical shifts (-59 to -70 ppm), small cone angles (121-140°) and a similar electronic parameter to PPh3. Reaction of L1 with [Rh(acac)(CO)2] gave the complex [Rh(acac)(CO)(L1)] with a ν(CO) of 1981.5 cm-1, whereas reaction L1 with [Rh(CO)2Cl]2 gave [Rh(CO)(L1)2Cl] with a ν(CO) of 1979.9 cm-1, remarkably similar to the CO stretching frequencies reported for analogous PPh3 complexes. The cage phosphines were explored as ligands in rhodium catalysed hydroformylation of 1-octene. All of the ligands gave a linear selectivity to n-nonanal of 68%, regardless of the substituents. However the ligand substituents had a significant effect on the catalyst activity, with increased steric bulk around the coordination environment giving a three-fold increase in aldehyde yield. The phosphines undergo ligand subsitution with [Pd(MeCN)2Cl2] forming square planar trans-[Pd(L)2Cl2] complexes. Subsequent reduction with hydrazine furnishes homoleptic tetravalent [Pd(L1)4] which was applied as a catalyst in Suzuki-Miyaura couplings, furnishing the C-C coupled products in moderate yields.

The crystal structure of dicarbonyl-(N-nitroso-N-oxido-phenylamine-κ 2 O,O)-rhodium(I), C8H5N2O4Rh

C8H5N2O4Rh, monoclinic, P21/c (no. 14), a = 14.1998(9) Å, b = 3.6516(2) Å, c = 17.7458(11) Å, β = 92.801(2)°, V = 919.06(10) Å3, Z = 4, R gt(F) = 0.0281, wR ref(F 2) = 0.0702, T = 100 K.

The crystal structure of (carbonato κ2 O,O′)(2-oxopyridin-1(2H)-olato-κN)tris(trimethylphosphine)rhodium(III) water solvate, C15H33NO5P3Rh

C15H33NO5P3Rh, orthorhombic, Pnma (no. 62), a = 19.8694(11) Å, b = 12.5765(7) Å, c = 8.6990(5) Å, V = 2173.8(2) Å3, Z = 1, Rgt (F) = 0.0394, wRref (F 2) = 0.0941, T = 100 K, α = β = γ = 90°.

Kinetic Study of the Oxidative Addition Reaction between Methyl Iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] Complexes, Utilizing UV-Vis, IR Spectrophotometry, NMR Spectroscopy and DFT Calculations

The oxidative addition of methyl iodide to [Rh(β-diketonato)(CO)(PPh)₃] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to [Rh(imino-β-diketonato)(CO)(PPh)₃] complexes, as observed on UV-Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of [Rh(CH₃COCHCNPhCH₃)(CO)(PPh₃)] and two isomers of [Rh(CH₃COCHCNHCH₃)(CO)(PPh₃)] are observed-in agreement with density functional theory (DFT) calculations. Experimentally the [Rh(CH₃COCHCNPhCH₃)(CO)(PPh₃)] + CH₃I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the [Rh(CH₃COCHCNHCH₃)(CO)(PPh₃)] + CH₃I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH₃I to the two [Rh(imino-β-diketonato)(CO)(PPh)₃] complexes of this study was 7-11 times faster than the oxidative addition reaction rate of CH₃I to [Rh(CH₃COCHCOCH₃)(CO)(PPh₃)].

Sterically hindered ortho-substituted phosphatriptycenes as configurationally stable P-chirogenic triarylphosphines

ortho-Substituted and unsymmetrical 9-phospha-triptycenes were synthesized via two synthetic approaches involving densely functionalized ortho-halogenated triarylmethane or phosphine precursors. ortho-Substituents imposed a considerable steric shielding due to the tricyclic cage-shaped structure with the aryl rings p-systems orthogonal to the phosphorus electron pair. A series of Au(i) and Rh(i) complexes were analysed in the solid state to determine Tolman electronic parameters, cone angles and buried volumes of these unprecedented functionalized phosphines. Quantum chemical calculations of electronic and steric descriptors revealed that these cage-shaped phosphines are electron-poor and that single methyl substituent is enough to provide the largest effect on steric shielding reported so far in triarylphosphines. An unsymmetrically substituted 9-phosphatriptycene was resolved by chiral HPLC, opening the avenue towards stable P-chirogenic triarylphosphines with unlimited configurational stability for new catalyst development in asymmetric transition-metal catalysis.

Crystal structure of carbonyl(2-methylquinolin-8-olato-κ2 N,O)(triphenylarsine-κAs)rhodium(I), C29H23AsNO2Rh

C 29 H 23 AsNO 2 ${\text{C}}_{29}{\text{H}}_{23}{\text{AsNO}}_{2}$ Rh, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 9.2778(18) Å, b = 9.8274(16) Å, c = 14.444(3) Å, α = 99.748(6)°, β = 91.330(7)°, γ = 114.197(6)°, V = 1177.6(4) Å3, Z = 2, R g t ${R}_{gt}$ (F) = 0.0552, w R r e f $w{R}_{ref}$ (F 2) = 0.1005, T = 100 K.

Crystal structure of carbonyl(2-oxopyridin-1(2H)-olato-k2 O,O′)(triphenylarsine-κAs)rhodium(I), C24H19AsNO3Rh

C24H19AsNO3Rh, triclinic, P 1 ‾ $‾{1}$ (no. 2), a = 9.1358(5) Å, b = 9.6478(6) Å, c = 12.4509(7) Å, α = 92.303(2)°, β = 106.281(2)°, γ = 99.137(2)°, V = 1035.89(1) Å3, Z = 2, R gt (F) = 0.0336, wR ref (F 2) = 0.0900, T = 100 K.

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.

The crystal structure of trans-carbonyl-(diphenylcyclohexyl-phosphine-κP)iodidomethyl-(2-oxopyridin-1(2H)-olato-κ2 O,O′)rhodium(III), C25H28INO3PRh

C25H28INO3PRh, monoclinic, P21/c (no. 14), a = 11.339(4) Å, b = 9.887(5) Å, c = 23.069(9) Å, β = 91.125(5)°, Z = 4, V = 2585.7(19) Å3, R gt(F) = 0.0463, wR ref(F 2) = 0.1093, T = 293(2) K.

Ambient and high-pressure kinetic investigation of methanol substitution in fac-[Re(Trop)(CO)3(MeOH)] by different monodentate nucleophiles

First report of high-pressure methanol substitution by entering monodentate L forms fac-[Re(CO)₃(Trop)(L)] {ΔV^≠_(kL) = +9 – +14 cm⁻³ mol⁻¹}, indicating dissociative/dissociative interchange activation.

Crystal structure of fac-(acetylacetonato-κ2 O,O′)tricarbonyl(tri-m-tolyl phosphane-κP)rhenium(I), C29H28O5PRe

C29H28O5PRe, monoclinic, P21/n (no. 14), a = 10.548(5) Å, b = 22.996(5) Å, c = 11.022(5) Å, β = 98.011(5)°, V = 2647.4(18) Å3, Z = 4, R gt(F) = 0.0306, wRref (F2) = 0.0911, T = 100 K.

Palladium-catalysed carboxytelomerisation of β-myrcene to highly branched C21-esters

The first example of the highly-efficient palladium-catalysed carboxytelomerisation of β-myrcene to branched C₂₁-esters is presented.

The crystal structure of carbonyl(2-oxopyridin-1(2H)-olato-κ 2 O,O′)-(diphenylcyclohexylphosphine-κ P)rhodium(I), C24H25NO3PRh

C24H25NO3PRh, orthorhombic, P212121 (no. 19), a = 9.5498(1) Å, b = 13.4996(2) Å, c = 17.428(3) Å, V = 2246.7(5) Å3, Z = 4, R gt(F) = 0.0163, wR ref(F 2) = 0.0376, T = 100 K.

Coordination of bis(azol-1-yl)methane-based bisphosphines towards RuII, RhI, PdII and PtII: synthesis, structural and catalytic studies

This paper describes the transition metal chemistry of three bis(X-diphenylphosphino-azol-1-yl)-based bisphosphines: bis(2-Ph₂P-imidazol-1-yl)methane (1), bis(5-Ph₂P-pyrazol-1-yl)methane (2) and bis(5-Ph₂P-1,2,4-triazol-1-yl)methane (3). These show versatility in their coordination behaviour.

Amidine functionalized phosphines: tuneable ligands for transition metals

A diastereomeric, cationic phosphine ligand [α,β-CgPAmMe]⁺ composed of a chiral amidinium substituent and a racemic phosphacycle has been prepared and compared to its neutral parent α,β-CgPAm.

Crystal structure of 3,5,7-tris(morpholinomethyl)tropolone·0.67 hydrate, C22H33N3O5·0.67H2O

C22H33N3O5·0.67H2O, monoclinic, P21/c, a = 11.9915(6) Å, b = 18.9934(10) Å, c = 10.5332(5) Å, β = 112.155(2)°, V = 2221.91(19) Å3, Z = 4, R gt(F) = 0.0417, wR ref(F 2) = 0.1139, T = 100(2) K.

Crystal structure of dicarbonyl(pyridin-2-olate-1-oxido-κ2 O,O′)rhodium(I), C7H4NO4Rh

C7H4NO4Rh, monoclinic, P21/c (no. 14), a = 3.5780(12) Å, b = 10.932(4) Å, c = 20.866(7) Å, β = 94.792(11)°, V = 813.3(12) Å3, Z = 4, R gt (F) = 0.0345, wR ref (F 2 ) = 0.0712, T = 100 K.

Crystal structure of tetraethylammonium fac-tricarbonyl(hexafluoroacetylacetonato-κ 2O,O′)-(nitrato-κO)rhenium(I), C16H21O8N2F6Re

C16H21O8N2F6Re, triclinic, P1̅, a = 9.161(5) Å, b = 10.283(5) Å, c = 12.974(5) Å, α = 87.739(5)°, β = 78.339(5)°, γ = 75.047(5)°, V = 1156.3(10) Å3, Z = 2, R gt (F) = 0.037, wR ref (F 2 ) = 0.1012, T = 100(2) K.

Crystal structure of tetraethylammonium hexachloridotantalate(V), C8H20Cl6NTa

C8H20Cl6N1Ta1, monoclinic, P 2 1/n (no. 14), a = 7.1550(4) Å, b = 10.0090(6) Å, c = 11.6290(4) Å, β = 98.487(5)°, V = 823.7(8) Å3, Z = 2, R gt (F) = 0.0207, wR ref (F 2 ) = 0.0531, T = 100(2) K.

Phosphonium-based aminophosphines as bifunctional ligands for sequential catalysis of one-pot hydroformylation–acetalization of olefins

A series of ionic phosphonium-based aminophosphinesL1–L3were prepared and fully characterized, in each of which the involved bifunctional moieties of the phosphine fragment and Lewis acidic phosphonium were linked together by stable chemical bonds and bridged by one N-atom.

Rational ligand design for the arylation of hindered primary amines guided by reaction progress kinetic analysis

We report the Pd-catalyzed arylation of very hindered α,α,α-trisubstituted primary amines. Kinetics-based mechanistic analysis and rational design have led to the development of two biarylphosphine ligands that allow the transformation to proceed with excellent efficiency. The process was effective in coupling a wide range of functionalized aryl and heteroaryl halides under mild conditions.

Solid state isostructural behavior and quantified limiting substitution kinetics in Schiff-base bidentate ligand complexes fac-[Re(O,N-Bid)(CO)3(MeOH)](n)

A range of N,O-donor atom salicylidene complexes of the type fac-[M(O,N-Bid)(CO)3(L)](n) (O,N-Bid = anionic N,O-bidentate ligands; L = neutral coordinated ligand) have been studied. The unique feature of the complexes which crystallize in a monoclinic isostructural space group for complexes containing methanol in the sixth position (L = MeOH) is highlighted. The reactivity and stability of the complexes were evaluated by rapid stopped-flow techniques, and the methanol substitution by a range of pyridine type ligands indicates significant activation by the N,O-salicylidene type of bidentate ligands as observed from the variation in the second-order rate constants. In particular, following the introduction of the sterically demanding and electron rich cyclohexyl salicylidene moiety on the bidentate ligand, novel limiting kinetic behavior is displayed by all entering ligands, thus enabling a systematic probe and manipulation of the limiting kinetic constants. Clear evidence of an interchange type of intimate mechanism for the methanol substitution is produced. The equilibrium and rate constants (25 °C) for the two steps in the dissociative interchange mechanism for methanol substitution in fac-[Re(Sal-Cy)(CO)3(MeOH)] (5) by the pyridine type ligands 3-chloropyridine, pyridine, 4-picoline, and DMAP are k3 (s(-1)), 40 ± 4, 13 ± 2, 10.4 ± 0.7, and 2.11 ± 0.09, and K2 (M(-1)), 0.13 ± 0.01, 0.21 ± 0.03, 0.26 ± 0.02, and 1.8 ± 0.1, respectively.

Activation of rhenium(I) toward substitution in fac-[Re(N,O'-Bid)(CO)3(HOCH3)] by Schiff-base bidentate ligands (N,O'-Bid)

A series of fac-[Re(N,O'-Bid)(CO)3(L)] (N,O'-Bid = monoanionic bidentate Schiff-base ligands with N,O donor atoms; L = neutral monodentate ligand) has been synthesized, and the methanol substitution reactions have been investigated. The complexes were characterized by NMR, IR, and UV-vis spectroscopy. X-ray crystal structures of the compounds fac-[Re(Sal-mTol)(CO)3(HOCH3)], fac-[Re(Sal-pTol)(CO)3(HOCH3)], fac-[Re(Sal-Ph)(CO)3(HOCH3)], and fac-[Re(Sal-Ph)(CO)3(Py)] (Sal-mTol = 2-(m-tolyliminomethyl)phenolato; Sal-pTol = 2-(p-tolyliminomethyl)phenolato; Sal-Ph = 2-(phenyliminomethyl)phenolato; Py = pyridine) are reported. Significant activation for the methanol substitution is induced by the use of the N,O bidentate ligand as manifested by the second order rate constants, with limiting kinetics being observed for the first time. Rate constants (25 °C) (k1 or k3) and activation parameters (ΔHk‡, kJ mol(-1); ΔSk‡, J K(-1) mol(-1)) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Re(Sal-mTol)(CO)3(HOCH3)] 3-chloropyridine: (k1) 2.33 ± 0.01 M(-1) s(-1); 85.1 ± 0.6, 48 ± 2; fac-[Re(Sal-mTol)(CO)3(HOCH3)] pyridine: (k1) 1.29 ± 0.02 M(-1) s(-1); 92 ± 2, 66 ± 7; fac-[Re(Sal-mTol)(CO)3(HOCH3)] 4-picoline: (k1) 1.27 ± 0.05 M(-1) s(-1); 88 ± 2, 53 ± 6; (k3) 3.9 ± 0.03 s(-1); 78 ± 8, 30 ± 27; (kf) 1.7 ± 0.02 M(-1) s(-1); 86 ± 2, 49 ± 6; fac-[Re(Sal-mTol)(CO)3(HOCH3)] DMAP (k3) 1.15 ± 0.02 s(-1); 88 ± 2, 52 ± 7. An interchange dissociative mechanism is proposed.

Ethylene tri- and tetramerization: a steric parameter selectivity switch from X-ray crystallography and computational analysis

A steric parameter (θN-sub) is introduced to describe the steric bulk at the nitrogen atom on a range of PNP ligands used in ethylene tri- and tetramerization. This parameter was calculated for the free ligands and different metal complexes thereof and compared to catalytic data. A specific tendency is observed for the value of θN-sub and 1-hexene selectivity, and a slight increase in 1-octene selectivity is found with increased bulkiness of the substituents on the nitrogen atom.

2,6-Dichloro-aniline-4-(2,6-dichloro-anilino)-pent-3-en-2-one (1/2)

The asymmetric unit of the title compound, C₆H₅Cl₂N·2C₁₁H₁₁Cl₂NO, is composed of one mol­ecule of an enamino–ketone [i.e. –(2,6-dichloro­phenyl­amino)­pent-3-en-2-one] and half a mol­ecule of 2,6-dichloro­aniline, the whole mol­ecule of the latter component being generated by twofold rotational symmetry. In this latter mol­ecule, there are two intra­molecular N—H⋯Cl contacts. In the enamino–ketone mol­ecule, there is an N—H⋯O hydrogen bond of moderate strength, and the dihedral angle between the benzene ring and penta­none fragment [C—C(—N)=C—C(=O)—C; planar within 0.005 (1) Å] is 81.85 (7)°. In the crystal, two mol­ecules of the enamino–ketone are bridged by a mol­ecule of 2,6-dichloro­aniline via N—H⋯O hydrogen bonds of moderate strength. There are also π–π inter­actions present, involving the benzene rings of inversion-related enamino–ketone mol­ecules [centroid–centroid distance = 3.724 (4) Å].