Evaluation of ligand effects in the modified cobalt hydroformylation of 1-octene. Crystal structures of [Co(L)(CO)3]2 (L = PA-C5, PCy3 and PCyp3).

A series of phosphine ligands with different electronic and steric properties were evaluated at fully modified conditions in cobalt catalysed hydroformylation of 1-octene. The steric demand of the ligands was based on the Tolman cone angle model covering a range of 132-175°. The electron donating ability was evaluated through the first order Se-P coupling constants as determined from the corresponding phosphine selenides covering a range of 672-752 Hz. Crystal structures of three phosphine modified cobalt dimers, [Co(CO)(3)(L)](2) (L = PA-C(5), PCy(3) and PCyp(3) with PA-C(5) = 1,3,5,7-tetramethyl-8-pentyl-2,4,6-trioxa-8-phosphatricyclo[3.3.1.1(3,7)]decane), are reported. The Phoban and Lim ligands (Phoban = mixture of 9-phosphabicyclo[3.3.1 and 4.2.1]nonane, Lim = 4,8-dimethyl-2-phosphabicyclo[3.3.1]nonane) resulted in systems about twice as active as most of the other ligands investigated, these ligands have a high Lewis basicity with (1)J(Se-P) values from 684-687 Hz. The linearity of the alcohol product in general decreased for the less electron donating ligands while no clear relationship was evident as a function of steric size. The parallel competing hydrogenation of 1-octene to octane varied from 9-15% for a cone angle range of 132-172°, but a sharp increase of up to 40% was observed for PA-C(5), PCy(3) and PCyp(3), all with cone angles > 169°. The catalytic behaviour provides evidence that is contrary to the dissociative substitution of CO by an alkene as the rate limiting step in all cases. For large symmetrical ligands, such as PA-C(5), PCy(3) and PCyp(3) the rate limiting step may move within the catalytic cycle and may now be situated at the carbonylation step where the chemoselectivity is also determined. The lack of clear correlation between the steric and electronic effect of the ligands and all catalytic parameters may serve as additional proof that the same system, especially in terms of the rate determining step, is not operative in all cases. The Phoban and Lim systems are superior with the highest reactivity and lowest alkene loss through hydrogenation. The unsymmetrical nature of the Phoban and Lim ligands may provide flexibility to adopt geometries inducing both high and low steric crowding, which may be a reason for its beneficial catalytic properties.

The bis(acetonitrile-κN)bis[N,N-bis(diphenylphosphanyl)ethanamine-κ2P,P']iron(II) tetrabromidoferrate(II) and µ-oxido-bis[tribromidoferrate(III)] complex salts.

Orange crystals of bis(acetonitrile-κN)bis[N,N-bis(diphenylphosphanyl)ethanamine-κ(2)P,P']iron(II) tetrabromidoferrate(II), [Fe(CH(3)CN)(2)(C(26)H(25)NP(2))(2)][FeBr(4)], (I), and red crystals of bis(acetonitrile-κN)bis[N,N-bis(diphenylphosphanyl)ethanamine-κ(2)P,P']iron(II) µ-oxido-bis[tribromidoferrate(III)], [Fe(CH(3)CN)(2)(C(26)H(25)NP(2))(2)][Fe(2)Br(6)O], (II), were obtained from the same solution after prolonged exposure to atmospheric oxygen, resulting in partial oxidation of the [FeBr(4)](2-) anion to the [Br(3)FeOFeBr(3)](2-) anion. The asymmetric unit of (I) consists of three independent cations, one on a general position and two on inversion centres, with two anions, required to balance the charge, located on general positions. The asymmetric unit of (II) consists of two independent cations and two anions, all on special positions. The geometric parameters within the coordination environments of the cations do not differ significantly, with the major differences being in the orientation of the phenyl rings on the bidentate phosphane ligand. The ethyl substituent in the cation of (II) and the Br atoms in the anions of (II) are disordered. The P-Fe-P bite angles represent the smallest angles reported to date for octahedral Fe(II) complexes containing bidentate phosphine ligands with MeCN in the axial positions, ranging from 70.82 (3) to 70.98 (4)°. The average Fe-Br bond distances of 2.46 (2) and 2.36 (2) Šin the [FeBr(4)](2-) and [Br(3)FeOFeBr(3)](2-) anions, respectively, illustrate the differences in the Fe oxidation states.

trans-Dichloridobis(4,8-dimethyl-2-phenyl-2-phosphabicyclo[3.3.1]nonane-κP)platinum(II).

The crystal structure of the title compound, trans-[PtCl(2)(C(16)H(23)P)(2)], has been determined at 100 K. The Pt atom is located on a twofold axis and adopts a distorted square-planar coordination geometry. The structure is only the second example of a coordination complex containing a derivative of the 4,8-dimethyl-2-phosphabicyclo[3.3.1]nonane (Lim) phosphine ligand family. The ligand contains four chiral C atoms, with the stereochemistry at three of these fixed during synthesis, therefore resulting in two possible ligand stereoisomers. The compound crystallizes in the chiral space group P4(3)2(1)2 but is racemic, comprising an equimolar mixture of both stereoisomers disordered on a single ligand site. The effective cone angles for both isomers are the same at 146°.

trans-Carbonylchloridobis(ferrocenyldiphenylphosphane-κP)rhodium(I) dichloromethane monosolvate and trans-carbonylchloridobis(ferrocenyldiphenylphosphane-κP)iridium(I) dichloromethane monosolvate.

The isomorphous crystal structures of the title compounds, [Fe(2)M(C(5)H(5))(2)(C(17)H(14)P)Cl(CO)]·CH(2)Cl(2) or trans-[MCl(CO)(PPh(2)Fc)(2)]·CH(2)Cl(2) (M = Rh or Ir, and Fc is ferrocenyl), are reported. The data collection for M = Rh was performed at 293 (2) K, while the M = Ir data were collected at 160 (2) K. The compounds crystallize with two independent half-molecules in the asymmetric unit, both occupying inversion centres, and are accompanied by a single dichloromethane molecule on a general position. Due to the symmetry, there is 0.50/0.50 disorder present in the chloride and carbonyl positions. One molecule in each structure also has a second type of disorder in the chloride and carbonyl positions, which was refined over another two positions of equal distribution. The steric impact of the bulky PPh(2)Fc ligands was evaluated using the Tolman cone-angle model, resulting in an average value of 172° for the four molecules in both structures.

(N-Benzoyl-N'-phenyl-thio-urea-κS)chlorido(η-1,5-cyclo-octa-diene)rhodium(I).

The title compound, [RhCl(C(8)H(12))(C(14)H(12)N(2)OS)], is a rhodium(I) derivative with a functionalized thio-urea ligand. Despite the presence of several heteroatoms, the thio-urea ligand coordinates only in a monodentate fashion via the S atom. The geometry of the coordination sphere is approximately square planar about the Rh(I) atom, with two bonds to the π-electrons of the 1,5-cyclo-octa-diene ligand, one bond to the Cl(-) ligand and one bond to the S atom of the thio-urea ligand. The mol-ecular structure is stabilized by intra-molecular N-H⋯O and N-H⋯Cl hydrogen bonding. Inter-molecular N-H⋯O hydrogen-bonding inter-actions lead to the formation of layers extending parallel to (011).

cis-Dichloridobis{dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine-kappaP}platinum(II).

The title compound, [PtCl(2)(C(13)H(26)NP)(2)], is a rare example of a sterically bulky ligand adopting a cis geometry in a square-planar complex. It crystallizes on a twofold rotation axis which bisects the Pt centre and the P-Pt-P' and Cl-Pt-Cl' angles. The ligand exhibits a random packing disorder in the N,N-dimethylpropylamine substituent, with the two orientations refining to occupancies of 0.404 (15) and 0.596 (15). Weak intermolecular interactions between a Cl and a H atom of the ligand of a neighbouring molecule result in extended chains along the a axis. The effective cone angle for the dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine (Phoban[3.3.1]-C(3)NMe(2)) ligand was determined as being in the range 160-181 degrees , depending on the choice of atoms used in the calculations.

2-Isobutyl-2-phosphabicyclo-[3.3.1]nonane 2-selenide.

The title compound, C(12)H(23)PSe, represents the first structure of a phosphine containing the bicyclic 2-phospha-bicyclo-[3.3.1]nonane (VCH) unit. It contains two chiral centres per mol-ecule which can be either R,R- or S,S and crystallizes as a centrosymmetric, racemic micture of the enanti-omers. The P-Se bond distance of 2.1360 (16) Šis typical for these compounds. The Tolman cone angle (2.28 Šfrom P) was calculated as 163°, and the effective cone angle (using the crystallographically determined P-Se bond distance) is 168°.

Rapid phosphorus(III) ligand evaluation utilising potassium selenocyanate.

Oxidative addition of SeCN(-) to tertiary phosphine ligands has been investigated in methanol at 298 K by use of UV-Vis stopped-flow and conventional spectrophotometry. In most cases k(obs) vs. [SeCN(-)] plots were linear with zero intercepts corresponding to a rate expression of k(obs) = k(1)[SeCN(-)]. Reactions rates are dependent on the electron density of the phosphorus centre with k(1) varying by five orders of magnitude from 1.34 +/- 0.02 x 10(-3) to 51 +/- 3 mol(-1) dm(3) s(-1) for P(2-OMe-C(6)H(4))(3) to PCy(3) respectively. Activation parameters range from 27 +/- 1 to 49.0 +/- 1.3 kJ mol(-1) for DeltaH(double dagger) and -112 +/- 9 to -140 +/- 3 J K(-1) mol(-1) for DeltaS(double dagger) supporting a S(N)2 mechanism in which the initial nucleophilic attack of P on Se is rate determining. Reaction rates are promoted by more polar solvents supporting the mechanistic assignment. Reasonable linear correlations were observed between log k(1)vs. pK(a), (1)J(P-Se) and chi(d) values of the phosphines. The reaction rates are remarkably sensitive to the steric bulk of the substituents, and substitution of phenyl rings in the 2 position resulted in a decrease in the reaction rate. The crystal structures of SePPh(2)Cy and SePPhCy(2) have been determined displaying Se-P bond distances of 2.111(2) and 2.1260(8) A respectively.

Bicyclic phosphines as ligands for cobalt catalysed hydroformylation. Crystal structures of [Co(Phoban[3.3.1]-Q)(CO)(3)](2) (Q = C(2)H(5), C(5)H(11), C(3)H(6)NMe(2), C(6)H(11)).

A range of tertiary bicyclic phosphine ligands derived from cis, cis-1,5-cyclooctadiene (Phoban family) was studied by batch autoclave reactions during the hydroformylation of a mixture of linear internal decenes using a cobalt catalyst system. Comparative runs were performed with PBu(3) as representative of standard trialkyl phosphine behaviour. The Phoban ligands comprise of a cyclooctyl bicycle with a mixture of the [3.3.1] and [4.2.1] isomers where the third substituent was systematically varied, Phoban-Q (Q = CH(2)CH(3), (CH(2))(4)CH(3), (CH(2))(9)CH(3), (CH(2))(19)CH(3), (CH(2))(3)N(CH(3))(2), C(6)H(11) and C(6)H(5)). An increase in ligand concentration resulted in a decrease in the reaction rate while the selectivity towards the n-alcohol product increased in accordance with a move from more unmodified catalysis to more modified catalysis. Alcohol yields of 77-85% were obtained at rates of 1.8-2.4 h(-1) for highly modified catalysis. Under highly modified conditions the linearity of the alcohol ranges in a narrow band from approximately 85-90% from Phoban-Ph to Phoban-Cy respectively. Hydrogenation of the alkene substrate varied from approximately 9-15% for Phoban-Ph and Phoban-Cy respectively the least and most electron donating derivatives. The two phosphine isomers were separated for Phoban-C(2) and the hydroformylation activity were re-evaluated for each isomer. The less electron donating [4.2.1] isomer required slightly higher ligand concentrations to achieve fully modified catalysis and gave rates and linearities comparable to the [3.3.1] isomer but giving slightly higher yields due to less hydrogenation of the olefin. In comparison, at fully modified conditions, PBu(3) gave a rate of 0.6 h(-1), alcohol yield of 77%, linearity of 81% and 17% hydrogenation. The crystal structures of the cobalt dimers [Co(CO)(3)(Phoban[3.3.1]-C(2))](2), [Co(CO)(3)(Phoban[3.3.1]-C(5))](2), [Co(CO)(3)(Phoban[3.3.1]-C(3)NMe(2))](2), and [Co(CO)(3)(Phoban[3.3.1]-Cy)](2) have been determined and indicated very similar geometries with Co-Co and Co-P bond distances ranging from 2.6526(10)-2.707(3) and 2.1963(8)-2.2074(9) A respectively. The cone angles of the Phoban ligands were calculated from the crystallographic data, according to the Tolman model, and ranges from 159-165 degrees.

Synthesis and characterization of a novel cobalt carbonyl N-heterocyclic carbene salt. Crystal structure of [Co(CO)(3)(IMes)(2)](+)[Co(CO)(4)](-).

The disproportionation of dicobalt octacarbonyl induced by the free carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and the X-ray characterization of the cyclohexane solvate of the resulting cobalt carbonyl N-heterocyclic carbene salt, [Co(CO)3(IMes)2]+[Co(CO)4]-.1/4C6H12, is reported. The crystal structure represents the first example of a [Co(CO)3(L)2][Co(CO)4] disproportionate salt reported to date.

Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities.

Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system.

Pseudo-rotation mechanism for fast olefin exchange and substitution processes at orthometalated C,N-complexes of platinum(II).

Bridge splitting in chloroform of the orthometalated chloro-bridged complex [Pt(micro-Cl)(2-Me(2)NCH(2)C(6)H(4))](2)(1), with ethene, cyclooctene, allyl alcohol and phosphine according to 1+ 2L --> 2[PtCl(2-Me(2)NCH(2)C(6)H(4))(L)], where L = C(2)H(4)(3a), C(8)H(14), (3b), CH(2)CHCH(2)OH (3c), and PPh(3)(4a and 4b) gives monomeric species with L coordinated trans or cis to aryl. With olefins the thermodynamically stable isomer with L coordinated cis to aryl is formed directly without an observable intermediate. With phosphine and pyridine, the kinetically controlled trans-product isomerizes slowly to the more stable cis-isomer. Bridge splitting by olefins is slow and first-order in 1 and L, with largely negative DeltaS(++). Substitution of ethene cis to aryl by cyclooctene and allyl alcohol to form 3b and 3c, and substitution of cot from 3b by allyl alcohol to form 3c are first order in olefin and complex, ca. six orders of magnitude faster than bridge cleavage due to a large decrease in DeltaH(++), and with largely negative DeltaS(++). Cyclooctene exchange at 3b is first-order with respect to free cyclooctene and platinum complex. All experimental data for olefin substitution and exchange are compatible with a concerted substitution/isomerization process via a turnstile twist pseudo-rotation in a short-lived labile five-coordinated intermediate, involving initial attack on the labile coordination position trans to the sigma-bonded aryl. Bridge-cleavage reactions of the analogous bridged complexes occur similarly, but are much slower because of their ground-state stabilization and steric hindrance.

Trans-bis(3,5-diaza-1-azonia-7-phosphaadamantane-kappaP)bis(thiocyanato-kappaS)palladium(II) bis(thiocyanate).

The crystal structure of the title compound, trans-[Pd(NCS)(2)(C(6)H(13)N(3)P)(2)](NCS)(2), is one of the few palladium(II) complexes containing two protonated water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA) ligands reported to date. The compound displays a distorted square-planar geometry, with the Pd atom on an inversion centre and with the S atoms of the thiocyanate counter-ions occupying the axial positions above and below the equatorial plane described by the phosphine and thiocyanate ligands. Geometric parameters for the formal coordination polyhedron include a Pd--P distance of 2.2940 (8) A, a Pd--S distance of 2.3509 (8) A and a P--Pd--S angle of 89.45 (3) degrees. The effective cone angle for the PTA ligands was calculated as 114.5 degrees.

trans-Carbonyliodotris(triphenylstibine-kappaSb)rhodium(I).

The crystal structure of the title compound, [RhI(C(18)H(15)Sb)(3)(CO)], represents a rare example of a crystallographically characterized five-coordinate Rh(I)-SbPh(3) complex. The compound crystallizes with the I-Rh-CO core on a threefold rotation axis, with three crystallographically equivalent triphenylstibine ligands. Selected geometric parameters are: Rh-I = 2.7159 (8), Rh-Sb = 2.5962 (4), Rh-C(CO) = 1.825 (6) and C(CO)-O 1.153 (6) A, and Sb-Rh-I = 89.374 (10) and Sb-Rh-C(CO) = 90.626 (10) degrees. The cone angle of the SbPh(3) ligand was determined as 137 degrees, according to the Tolman model.

Structural and mechanistic look at the orthoplatination of aryl oximes by dichlorobis(sulfoxide or sulfide)platinum(II) complexes.

Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes [PtCl(2)L(2)] (2, L = SOMe(2) (a), rac-SOMePh (b), R-SOMe(C(6)H(4)Me-4) (c), and SMe(2) (d)) to afford the corresponding platinacycles cis-(C,S)-[Pt(II)(C(6)H(3)-2-CR'=NOH-5-R)Cl(L)] (3, R, R' = H, Me) have been investigated. The reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent occurs noticeably faster than with sulfide complex 2d due to the fact that the sulfoxide is a much better platinum(II) leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formation of unreactive dichlorobis(N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenone oxime and suggests the importance of pseudocoordinatively unsaturated species for the C-H bond activation by Pt(II). A comparative X-ray structural study of dimethyl sulfoxide platinacycle 3b (R = R' = Me) and its sulfide analogue 3e (R = H, R' = Me), as well as of SOMePh complex 3c (R = H, R' = Me), indicated that they are structurally similar and a sulfur ligand is coordinated in the cis position with respect to the sigma-bound phenyl carbon. The differences concern the Pt-S bond distance, which is notably longer in the sulfide complex 3e (2.2677(11) A) as compared to that in sulfoxide complexes 3b (2.201(2)-2.215(2) A) and 3c (2.2196(12) A). Whereas the metal plane is practically a plane of symmetry in 3b due to the H-bonding between the sulfoxide oxygen and the proton at carbon ortho to the Pt-C bond, an S-bonded methyl of SOMePh and SMe(2) is basically in the platinum(II) plane in complexes 3c and 3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex 3b. An interesting structural feature of complex 3c is that the two independent molecules in the asymmetric unit of the crystal reveal an extremely short Pt-Pt contact of 3.337 A.

Structures of trans-[PtCl(2)(PBz(3))(2)], trans-[PtI(2)(PBz(3))(2)], trans-[Pt(NCS)(2)(PBz(3))(2)].0.5C(6)H(6) and trans-[PdI(2)(PBz(3))(2)].

A series of structures of trans-[MX(2)(PBz(3))(2)] [M = Pt, X = Cl(-); PBz(3) = tribenzylphosphine (1), I(-), trans-diiodobis(tribenzylphosphine)platinum(II) (2), and NCS(-), trans-di(thiocyanate)bis(tribenzylphosphine)platinum(II) (3); M = Pd, X = I(-), trans-diiodobis(tribenzylphosphine)palladium(II) (4)] have been characterized by X-ray crystallography. In all compounds each tribenzylphosphine has one benzylcarbon close to the coordination plane. In (1), (2) and (4) those (in-plane) C atoms, from the two different PBz(3), exhibit an anti conformation along the P-P axis, while (3) has the gauche conformation. Root mean square (RMS) calculations and half-normal probability plots show that the complexes in (2) and (4) are very similar and the only significant differences between them are the M-P bonds, 2.354 (4) and 2.330 (5) A, and the M-I bond distances, 2.604 (1) and 2.611 (2) A, for Pd and Pt, respectively. Calculations of the steric demand of the PBz(3) ligands based on the Tolman model gave values ranging from 155 to 178 degrees for the effective and 156 to 179 degrees for the Tolman angles, respectively.

Reaction Mechanism for Olefin Exchange at Chloro Ethene Complexes of Platinum(II).

Complex equilibria in methanol/chloroform/dichloromethane solutions containing Zeise's anion, [PtCl(3)(C(2)H(4))](-) (1), the solvento species, trans-[PtCl(2)(C(2)H(4))(MeOH)] (2), and the dinuclear complex, trans-[PtCl(2)(C(2)H(4))](2) (3), have been studied by UV-vis, (1)H, and (195)Pt NMR spectroscopy, giving average values of K(Cl) = (1.6 +/- 0.2)10(3) M(-)(1) and K(S) = (0.16 +/- 0.02) M(-)(1) for the equilibrium constants between 2 and 1 and 3 and 2, respectively. The bridged complex 3 is completely split into monomeric solvento complexes 2 in methanol and in chloroform or dichloromethane solutions with [MeOH] > 0.5 M. Ethene exchange at the mononuclear complexes 1 and 2 was studied by (1)H NMR line-broadening experiments in methanol-d(4). Observed overall exchange rate constants decrease with an increase in free chloride concentration due to the displacement of the rapid equilibrium between 1 and 2 toward the more slowly exchanging parent chloro complex 1. Ethene exchange rate constants at 298 K for complexes 1 and 2 are k(ex1) = (2.1 +/- 0.1)10(3) M(-)(1) s(-)(1)and k(ex2) = (5.0 +/- 0.2)10(5) M(-)(1) s(-)(1), respectively, with corresponding activation parameters DeltaH(1)() = 19.1 +/- 0.3 kJ mol(-)(1), DeltaS(1)() = -117 +/- 1 J K(-)(1) mol(-)(1), DeltaH(2)() = 10.2 +/- 0.4 kJ mol(-)(1), and DeltaS(2)() = -102 +/- 2 J K(-)(1) mol(-)(1). The activation process is largely entropy controlled; the enthalpy contributions only amounting to approximately 30% of the free energy of activation. Ethene exchange takes place via associative attack by the entering olefin at the labile site trans to the coordinated ethene, which is either occupied by a chloride or a methanol molecule in the ground state. The intimate mechanism might involve a two-step process via trans-[PtCl(2)(C(2)H(4))(2)] in steady state or a concerted process via a pentacoordinated transition state with two ethene molecules bound to the platinum(II).