Vaska-type Complexes Research Articles

Tuning the sterics: Rh-catalyzed hydroformylation reactions with ferrocene based diphosphorus ligands

Tuning the sterics: Rh-catalyzed hydroformylation reactions with ferrocene based diphosphorus ligands

Crystal and molecular structure of trans-[RhCl(CO)(P t Bu2Ph)2

Abstract Treatment of THF solutions containing the rhodium(II) complex trans-[RhCl2(P t Bu2Ph)2] (1) with [Fe2(CO)9] in the same solvent resulted in the formation of the Vaska-type complex trans-[RhCl(CO)(P t Bu2Ph)2] (2) in high yield. The title complex 2 was obtained as pale yellow crystals, characterized by NMR and IR spectroscopy, as well as by microanalyses. Additionally, the molecular structure of 2 has been established by X-ray crystallography. As often reported for similar constituted compounds, the chlorido and carbonyl ligands in crystals of 2 are strongly disordered.

Promotional effect of CH3I on hydroxycarbonylation of cycloalkene using homogeneous rhodium catalysts with PPh3 ligand

Abstract The reaction mechanism of the hydroxycarbonylation of cyclohexene with formic acid to form cyclohexanecarboxylic acid using organorhodium complexes was investigated both experimentally and computationally. It was found that excess CH3I and PPh3 promote this reaction. The active catalyst species was determined to be a five-coordinated rhodium hydride 16-electron complex derived from a mononuclear rhodium 16-electron complex (Vaska-type complex). PPh3 and CH3I played the following roles: i) to promote the formation of the Vaska-type Rh complex from Rh2Cl2(CO)4 (1), ii) to aid the elimination of the PPh3 ligand from the Vaska-type complex by stabilizing the free energy of formation of a mononuclear three-coordinated rhodium 14-electron complex through the formation of phosphonium iodide ([Ph3P(CH3)]I), and iii) to generate the active rhodium hydride species.

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

Vaska-type complexes, i.e. trans-[RhX(CO)(PPh3)2] (X is a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the Rh(I) atom 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 with trans-[RhCl(CO)(PPh3)2], and was characterized by single-crystal X-ray diffraction analysis and IR, (1)H, (13)C and (11)B NMR spectroscopy. The X-ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the Rh(I) atom through the N atom in a trans position 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 carbon (1)JC-Rh and (1)JC-P coupling constants of the Cipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central Rh(I) atom compared to the parent trans-[RhCl(CO)(PPh3)2] complex.

Transformations of the Vaska-type complex trans-[RhCl(CO)(PTA) 2] (PTA = 1,3,5-triaza-7-phosphaadamantane) during stepwise addition of HCl: Synthesis, characterization and crystal structure of trans-[RhCl 2(PTA)(PTAH)

Abstract The new aqua-soluble rhodium(I) complex trans -[RhCl 2 (PTA)(PTAH)] ( 1 ) {PTAH = N -protonated form of 1,3,5-triaza-7-phosphaadamantane (PTA)} has been synthesized via the reaction of trans -[RhCl(CO)(PTA) 2 ] with aqueous HCl or N -chlorosuccinimide, or by the treatment of RhCl 3 with PTA. Compound 1 has been characterized by IR, 1 H and 31 P{H} NMR spectroscopies, ESI–MS(+), elemental and single crystal X-ray diffraction analyses, the latter showing a square planar {RhCl 2 P 2 } geometry. Besides, the stepwise addition of diluted HCl to an aqueous solution of trans -[RhCl(CO)(PTA) 2 ] has been monitored by 31 P{ 1 H} NMR and ESI–MS(+) techniques, allowing to detect a number of intermediate Rh(I) species.

Trans-Carbonylchloridobis[dicyclohexyl(4-isopropylphenyl)phosphane]rhodium(I) acetone monosolvate

The title rhodium Vaska-type complex, trans-[RhCl{P(C6H11)2(C6H4-4-C3H7)2}2(CO)], crystallizes with an accompanying acetone solvent mol­ecule. The metal atom shows a distorted square-planar coordination environment with selected important geometrical parameters of Rh—P = 2.3237 (6) and 2.3253 (6) Å, Rh—Cl = 2.3724 (6) Å, Rh—C = 1.802 (2) Å, P—Rh—P = 173.42 (2)° and Cl—Rh—C = 179.13 (7)°. Effective cone angles for the two P atoms are 165 and 161°, respectively. Both isopropyl groups and the acetone mol­ecule are disordered with occupancy values of 0.523 (5):0.477 (5), 0.554 (8):0.446 (8) and 0.735 (4):0.265 (4), respectively. The crystal packing is stabilized by weak C—H⋯O and C—H⋯Cl contacts.

Solid-state packing behaviour in pseudo Vaska-type complexes

Solid-state packing behaviour in pseudo Vaska-type complexes

Toward autonomously operating molecular machines driven by transition-metal catalyst

A Vaska-type complex carrying a ferrocene-appended diphosphine ligand was developed as a prototype of autonomous molecular machines that is able to undergo continuous scissoring motion in the presence of diphenylphosphoryl azide and aldehyde.

Trans-Carbonylchlorobis[(2-naphthyloxy)diphenylphosphine-κP]rhodium(I)

The title compound, [RhCl(C22H34OP)2(CO)], can be described as one of a few RhI Vaska-type complexes containing a (2-naphth­yloxy)diphenyl­phosphine ligand and has a square-planar geometry about the rhodium(I) metal centre, which lies on an inversion centre, so that the carbonyl and chloro ligands are disordered. The most important bond lengths and angle include Rh—P = 2.305 (1) Å, Rh—Cl = (trans CO) = 2.374 (2) Å, Rh—C (carbon­yl) = 1.818 (6) Å and Rh—C—O = 178.1 (10)°. A weak π–π inter­molecular stacking is observed, with an inter­planar distance of 3.377 (2) Å.

Mild hydrothermal synthesis and structural study of a new nickel pyrazine vanadate

Pseudo Vaska-type complexes, trans-[M(X)(Y)(ZR3)2] (M=Rh, Ir if X=CO, NCS, NCO and M=Pt, Pd if X=Cl, Me; Y=halogen, Z=Group 15 atom, R=aryl, alkyl) can undergo various key step catalytic reactions, e.g. oxidative addition, reductive elimination, substitution, insertion, etc., manifesting them as well-behaved model complexes for various catalytic systems [1]. These complexes are easy to synthesize and can be investigated structurally due to their favorable thermal stability. Data obtained from solid-state investigations can then be correlated with solution IR and 31 P NMR spectroscopy for the CO and PR3 ligands to evaluate different ligand effects. However, these complexes are also well known for their tendency to be statistically disordered along the X-M-Y axis, thus decreasing accuracy of the solid-state data in some cases, leading to incorrect correlations. Complexes to be discussed in this presentation form part of a study to determine which factors govern the packing disorder [2].

Trans-Carbonylchlorobis[diphenyl(4-tolyl)phosphine]rhodium(I)

The title compound, [RhCl(C19H17P)2(CO)], can be characterized as a Vaska-type complex containing a diphenyl(4-tolyl)phosphine ligand. The rhodium(I) metal centre has a square-planar coordination. The molecule is disordered, with the Rh atom lying on an inversion centre. The most important bond lengths and angles include Rh—P = 2.3315 (9) Å, Rh—Cl(trans CO) = 2.405 (2) Å, Rh—C(carbonyl) = 1.724 (11) Å and Rh—C—O = 178.0 (6)°.

Solid–gas carbonylation of aryloxide rhodium(I) complexes: stepwise reaction forming Vaska-type complexes

Abstract Aryloxide rhodium(I) complexes Rh(OAr)(PPh3)3 (1a: Ar=C6Cl5, 1b: Ar=C6F5, 1c: Ar=C6H4–NO2-4) react with CO in toluene solutions to produce Vaska-type complexes trans-Rh(OAr)(CO)(PPh3)2 (2a: Ar=C6Cl5, 2b: Ar=C6F5, 2c: Ar=C6H4–NO2-4). Carbonylation of a similar complex with PMe3 ligands, Rh(OC6H4–NO2-4)(PMe3)3 (3c), also forms trans-Rh(OC6H4–NO2-4)(CO)(PMe3)2 (4c). Molecular structures of the complexes are determined by X-ray crystallography and NMR spectroscopy. Complex 1a reacts with CO in the absence of solvent to produce a mixture of 2a and complex A, the latter of which shows the IR and 13C{1H} signals due to the carbonyl ligand at different positions from those of 2a. Addition of Et2O to the above mixture turns it into analytically pure 2a. Carbonylation of 1b and 1c under the solvent-free conditions produces complexes B and C as the respective products of the solid–gas reaction. Recrystallization of B and C turns them into 2b and 2c, respectively. Complex 3c also reacts with CO in the solid state to form a mixture of 4c and complex D, although the latter complex is converted slowly into 4c even in the solid state.

Quantifying the electronic cis effect of phosphine, arsine and stibine ligands by use of rhodium(I) Vaska-type complexes

The cis effects of phosphine, arsine and stibine ligands have been evaluated by measuring the IR stretching frequency in dichloromethane of the carbonyl ligand in a series of Rh(I) Vaska-type complexes, trans-[RhCl(CO)(L)2]. These data were correlated with those obtained by Tolman for the electronic trans influences in the [Ni(L)(CO)3] complexes. The electronic contribution, χFc, of ferrocenyl was determined as 0.8 from these plots by evaluating PPh2Fc as ligand. In order to accommodate arsine and stibine ligands an additional correction term, to compensate for differences in the donor atom, was added to Tolman’s equation for calculation of the Tolman electronic parameter of phosphine ligands. In the resulting equation: ν(CONi)=2056.1+∑i=13χi+CL values for CL of CP=0, CAs=−1.5 and CSb=−3.1 are suggested for phosphine, arsine and stibine ligands, respectively. The crystal and molecular structures of trans-[RhCl(CO)(PPh2Fc)2] · 2C6H6, trans-[RhCl(CO){P(NMe2)3}2] and trans-[RhCl(CO)(AsPh3)2] are reported. The Tolman cone angles for PPh2Fc and P(NMe2)3 were determined as 169° and 166°, while the effective cone angles for PPh2Fc, P(NMe2)3 and AsPh3 were determined as 171°, 168° and 147°, respectively.

Synthesis, Spectroscopy, and Structure of a Family of Iridabenzenes Generated by the Reaction of Vaska-Type Complexes with a Nucleophilic 3-Vinyl-1-cyclopropene

Seven new iridabenzenes were prepared by the addition of (Z)-1,2-diphenyl-3-(2-lithioethenyl)-1-cyclopropene to the Vaska-type complexes [IrCl(CO)(PR3)2], containing differing phosphine ligands. The iridabenzenes could be isolated from the reaction mixture either by direct means or after heating of the crude solution. In the case of the reactions using PMe3 and PEt3, a σ-vinyl/η2-cyclopropene Ir(I) complex, best described as an iridabenzvalene, could be isolated and fully characterized. The metallabenzvalene intermediate could be cleanly converted to the corresponding iridabenzene by heating in solution. The PEt3-substituted iridabenzene and iridabenzvalene were characterized by X-ray crystallography. Plausible mechanisms for the formation of both iridacycles from the lithiated vinylcyclopropene as well as the isomerization of the benzvalene into the benzene are postulated.

Pseudo Vaska-type complexes: solid state and solution behaviour as model homogeneous catalysts

Pseudo Vaska-type complexes: solid state and solution behaviour as model homogeneous catalysts

A high-yield synthetic approach to trans-[Ir(ER 3) 2(CO)X] (ER 3=PMe 3, PEt 3, PPhMe 2, PPh 2Me, P(OMe) 3, AsMe 3, AsEt 3, AsPh 3, SbPh 3; X=Cl, Br)

Abstract The complex [Ir(CO) 2 X 2 ][NBu 4 ] (X=Cl, Br) forms Vaska-type complexes, trans -[Ir(ER 3 ) 2 (CO)X], when treated with two equivalents of aryl- or alkyl-phosphines, arsines, or stibines under a CO atmosphere. The synthesis is general for a wide range of phosphines, arsines, or stibines irrespective of the cone angle. For small cone-angle ligands, the initial addition of ligand to [Ir(CO) 2 X 2 ][NBu 4 ] is performed at low temperature. The synthesis and characterisation of three new Vaska-type complexes trans -[Ir(P(OMe) 3 ) 2 (CO)Cl], trans -[Ir(AsMe 3 ) 2 (CO)Cl], and trans -[Ir(AsEt 3 ) 2 (CO)Cl] is also reported.

Trans-Carbonylchlorobis(tri-p-tolylphosphine)rhodium(I)

The crystal structure of the square-planar title compound, [RhCl(C 21 H 21 P) 2 (CO)], describes another of the Vaska-type complexes. It is isomorphous with selected Ir I and even Pt II structures. Important bond lengths include Rh-P1 2.3344(11), Rh-P2 2.3305 (11), Rh-C1 2.3581 (12), Rh-C1 1.798 (5) and C1-O1 1.139 (6) A.

A mechanistic study of thermal C-H reductive elimination from a six-coordinate d 6 iridium complex

The thermolysis of trans-IrL2(CO)Cl(H)(C6H5) (1abd; L=P(i-Pr)3; H trans to CO) produces benzene and the Vaska-type complex IrL2(CO)Cl. A mechanistic study of the reaction has shown that 1a reversibly loses CO at 120 °C (as evidenced by the incorporation of 13CO) and isomerizes to the previously unreported 1b (H trans to Cl). It was found that 1b is the complex primarily responsible for the formation of benzene upon thermolysis under CO atmosphere; direct loss of benzene from 1a was determined to be, at most, a minor pathway. Benzaldehyde was also formed as a product of thermolysis of 1a under CO atmosphere. The first-order rate constant for benzene elimination in the absence of CO was found to be 8.5 × 10−5 s−1. The presence of only 5 Torr CO results in a decrease to 2.0 × 10−5 s−1, but little further inhibition is observed above 5 Torr CO. Added dihydrogen (100 Torr) was found to effect a novel catalysis of benzene elimination from 1a in the absence of CO atmosphere; it is suggested that trace amounts of dihydrogen, present in solutions of 1a, are responsible for the enhanced rate of elimination in the absence of CO. The thermolysis of 1-d6 in toluene was found to proceed without any toluene incorporation, implying that arene loss is irreversible.

Iridium complexes with secondary phosphines: synthesis and X-ray crystal structure of [IrCl(Bu 2tPH) 3

Abstract The reaction of [s1rC1(COE)22] (1) (COE = cyclooctene) with Bu2tPH in hexane at room temperature gave the complex [IrCI(Bu2tPH)3] (2) which has been fully characterized by both spectroscopic and crystallographic methods. 1 reacts with carbon monoxide to give the Vaska-type complex trans-[IrCI(CO) (Bu2tPH)2] (3).

A Theoretical Study on the Oxidative Addition of a Si–H σ-Bond to [MCl(CO)(PH3)2] (M = Rh or Ir). Similarities to and Differences from [M′(PH3)2] (M′ = Pd or Pt) and [RhCl(PH3)2

Abstract The Si–H Oxidative Addition to [MCl(CO) (PH3)2] (M = Rh or Ir) was theoretically investigated with ab initio MO/MP2—MP4, SD-CI, and CCD (coupled cluster with double substitutions) methods. This reaction proceeds with a somewhat high activation energy (Ea) and a moderate exothermicity (Eexo); when the oxidative addition occurs in the Cl–M–CO plane, Ea = 19 kcal mol−1 for Rh and 13 kcal mol−1 for Ir, and Eexo = 0.4 kcal mol−1 for Rh and 17.4 kcal mol−1 for M = Ir. This result is in significant contrast to [M′(PH3)2] (M′ = Pd or Pt) and [RhCl (PH3)2] : the Si–H oxidative addition occurs with a very small barrier for [M′(PH3)2], but a zero barrier and significantly high exothermicity for [RhCl(PH3)2]. The low reactivity of [MCl(CO)(PH3)2] is interpreted in terms of the low energy level of the d orbital, a considerable weakening of the M–Cl and M–CO bonds, and an exchange repulsion between SiH4 and the M d orbital in [MCl(CO)(PH3)2]. The above results indicate that Vaska-type complexes are less favorable for an oxidative addition reaction than [M′(PH3)2] and [RhCl(PH3)2], and that they cannot be used for a catalytic reaction including an oxidative addition which requires a high activation energy.