Metal Olefin Research Articles

Intramolekulare beweglichkeit des ethylen-liganden in den η 5-cyclopentadienyl- und η 5 -indenyl-komplexen C 5H 5W(CO) 2(C 2H 4)CH 3 und C 9H 7 W(CO) 2(C 2H 4)CH 3

In the η 5-cyclopentadienyl and η 5-indenyl complexes C 5H 5W(CO) 3CH 3 and C 9H 7W(CO) 3CH 3 one CO ligand can be replaced photochemically by ethylene. The resulting substitution products C 5H 5W(CO) 2(C 2H 4)CH 3 and C 9H 7W(CO) 2(C 2H 4)CH 3 are characterized spectroscopically. Temperature dependent 1H NMR spectra of these pseudo-tetragonal pyramidal coordination compounds indicate hindered rotation of the π-bonded olefin ligand around the metal—olefin bond axis. The rotation barriers of the ligand motion are comparatively high, ΔG ≠ 59(±5) kJ mol −l and 57(±5) kJ mol −1.

Activation of CH bonds by transition metals: IV. Partial dehydrogenation of tricyclohexylphosphine by iridium(I) and rhodium(I) leading to the formation of a metal—olefin complex and a five-coordinated metal dihydride, which is a hydrogenation catalyst

Reaction of tricyclohexylphosphine with [(COT) 2MC1] 2 (M = Rh, Ir, COT = cyclooctene) in refluxing toluene, yields the five-coordinated metal(III) complexes H 2[P(C 6H 11) 3] 2MCl and the four-coordinated metal(I) complexes [P(C 6H 11) 3] M[P(C 6 H 9)(C 6H 11) 2]Cl, in which one cyclohexyl group has been dehydrogenated to a cyclohexene group, the double bond of which occupies the fourth coordination site. In refluxing toluene, triisopropylphosphine reacts with [(COT) 2MCl] 2 to give the five-coordinated complex H 2[P(C 3H 7) 3] 2MCl, which suggests a similar dehydrogenation. Reaction of the partly dehydrogenated products with CO yields [P(C 6H 11) 3]M[P(C 6H 9)(C 6H 11) 2]Cl(CO) in which the double bond is not coordinated to the metal. Hydrogen adds oxidatively to the iridium(I) compound, but does not react with the rhodium(I) compound. The mechanism of the dehydrogenation is discussed. The complexes H 2(PR 3) 2MCl are catalysts for hydrogenation of olefins at 100°C and at 1 atmosphere. 1,5-Cyclooctadiene is especially readily hydrogenated at this temperature.

ChemInform Abstract: FLUXIONAL AND NONRIGID BEHAVIOR OF TRANSITION METAL ORGANOMETALLIC Π‐COMPLEXES

Publisher Summary The chapter discusses major developments in the understanding of nonrigidity in π-complexes . The stereochemistry of products derived from reactions of coordinated olefins and the stereochemistry of polymers formed in reactions catalyzed by transition metals are ultimately determined by the conformational stability of π-complexed intermediates. The interconversions rates of these isomers and the thermodynamic preferences of olefin–metal conformations should explain observed product distributions and provide a rational basis for catalyst design. Molecules that undergo intermolecular rearrangements at rates that influence nuclear magnetic resonance (NMR) line shapes in accessible temperature ranges are termed “stereochemically nonrigid.” Nonrigid molecules, of which all observable interconnecting species are chemically and structurally equivalent, are designated as fluxional. The study of nonrigid systems has closely followed the technical advance of NMR instrumentation. The rapid advances in 13 C spectroscopy have made previously undetectable carbonyl rearrangements, conformational interconversions, and fluxionality accessible. This chapter concentrates on recent developments in technique that are likely to be used more extensively, potential problems in interpretation of dynamic NMR spectra, and observations that establish general patterns of rearrangement or conflict with currently accepted mechanisms. Stereochemically nonrigidity can be interpreted in these systems in terms of variations in bond strength with orientation of the olefin. Rotation of the allyl group, in which syn–anti interconversions does not occur, is now known in many instances for complexes with coordination numbers greater than four. NMR spectra consistent with allyl rotation in most square palladium complexes have been shown to result from ligand exchange.

Olefin metathesis: preparation of a carbene–olefin–metal complex

Protonation of the chelated carbene–iron complex (1) in the presence of ethylene yields the complex (5) in which the metal is co-ordinated to separate olefin and carbene ligands.

Reaction of ylides with cationic transition metal olefin and tetrahydrofuran complexes

The reaction of [(η 5-C 5H 5)Fe(CO)(L)(THF)] + (L = CO, PPh 3) with CH 2PPh 3 yields [(η 5-C 5H 5)Fe(CO)(L)CH 2PPh 3] + complexes. This ylide reacts with [(η 5-C 5H 5)Fe(CO)(PPh 3)(η 2-C 2H 4)] + to yield [(η 5-C 5H 5)Fe(CO)(PPh 3)(CH 2CH 2CH 2PPh 3)] + and [PO(OMe) 2] − reacts with this cationic olefin complex to yield (η 5-C 5H 5)Fe(CO)(PPh 3)[CH 2CH 2PO(OMe) 2].

Dehydrogenation of an alkane chain: rhodium(I) and iridium(I) complexes of 1,6-bis(diphenylphosphino)- trans-hex-3-ene

Rhodium(I) and iridium(I) complexes effect the dehyddrogenation of the alkane chain in the ligand 1,6-bis(diphenylphosphino)hexane forming the metal olefin complexes (BDPH)MCl where BDPH = 1,6-bis(diphenylphosphino)- trans-hex-3-ene and M = Rh or Ir.

Rotation of olefins in dithiocarbamatobis(isocyanide)(olefin)rhodium complexes

The π-olefinic complexes, Rh(dtc)(RNC) 2(olefin) (dtc = (CH 3) 2NCS 2 −; R = p-CH 3C 6H 4, 2,4,6-(CH 3) 3 C 6H 2; olefin = tetracyanoethylene, fumaronitrile, maleonitrile, maleic anhydride), have been synthesized. Variable temperature 1H nmr spectra suggest that the olefin rotates around the metalolefin bond accompanying Berry pseudorotation in a trigonal bipyramid. The ν(NC) frequency due to the isocyanide and the free energy of activation (ΔG Tc ≠) for the intramolecular rearrangement are discussed in terms of the π-interactions between the rhodium atom and the olefin ligands.

π-komplexverbindungen der methoxy-substituierten äthylene : I. Das system cyclopentadienyl-mangan-dicarbonyl-olefin

The influence of methoxy substituents upon the coordinative properties of olefin ligands has been investigated for complexes of the type C 5H 5Mn(CO) 2L [L = CH 2CH 2, (CH 3O)CHCH 2, (CH 3O) 2 CCH 2, cis- and trans-(CH 3O)CHCH(OCH 3), (CH 3O) 2CC(OCH 3) 2]. All complexes possess temperature-dependent 1H-NMR spectra which indicate restricted rotation of the π-bonded olefin around the metal—olefin bond at room temperature in solution. In comparison with ethylene, the olefins methyl vinyl ether and 1,1-dimethoxyethylene increase the charge density at the metal, while tetramethoxyethylene — due to the inductive effect of the four CH 3O substituents — causes a decrease of the charge.

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C 5H 5Mn(CO) 2L und C 5H 5Cr(CO)(NO)L

The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C 5H 5Mn(CO) 2L and C 5H 5Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent 1H NMR spectra. The olefinic ligand is arranged preferably in a position where the CC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The 1H NMR spectra of C 5H 5Cr(CO)(NO)( trans-CH 3OOCCHCHCOOCH 3) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C 5H 5Mn(CO) 2L complexes (Δ G ≠( T C) 11–12 kcal mol −1) than in the isoelectric C 5H 5Cr(CO)(NO)L compounds (Δ G ≠( T C) 15–20 kcal mol −1).

Relative olefin—metal bond strengths in some platinum (0) compounds. Part II 1

Measurements are reported for the enthalpies of solution of: ▪ where L is triphenylphosphine and the olefins used were cis- and trans-1,2-diphenyl-ethene. These enthalpies, when combined with other data, lead to the conclusion that the difference in the relative strengths of the platinum—olefin bonds ( trans-1,2- diphenylethene&>; cis-1,2-diphenylethene&>;phenylethene) found previously arises mainly from electronic rather than from steric effects of the olefins in the complexes.

Tris-olefin complexes of rhodium(I) and iridium(I) containing the tetradentate ligands tris(but-3-enyl)phosphine and tris(pent-4-enyl)phosphine

The rhodium(I) and iridium(I) complexes, RhX(tbp), RhX(tpp), X = Cl, Br or I, and IrCl(tbp) and IrCl(tpp) where tbp = P(CH 2CH 2CH=CH 2) 3 and tpp = P(CH 2CH 2CH 2CHCH 2) 3 have been prepared. These compounds, except for RhI(tbp), all exhibit the same “umbrella” type five coordinate structure in the solid state, in which all three olefins are bonded to the metal. At −60° in solution, RhI(tbp) adopts the same five coordinate stereochemistry. Due to restricted rotation, the methylene protons in RhCl(tbp) become inequivalent at low temperature. RhCl(tbp) forms 1 1 adducts with carbon monoxide and triphenylphosphine. Infrared, Raman and PMR studies conclude that the metalolefin bond is stronger for the iridium complexes compared to the corresponding rhodium complexes.

Comments on the Interpretation of NMR. Parameters in some platinum‐olefin complexes

Abstract13C and 195Pt‐NMR. parameters for the complexes trans‐[PtCl2(C5H10N)‐(CH3CHCHCH3)] are presented. It is suggested that conclusions, concerning metal olefin bond strengths, drawn from NMR. studies of nuclei not directly involved in the bonding can be misleading.

ChemInform Abstract: STRUCTURES OF 1,2‐DIMETHYL‐ AND 3‐METHYL‐CYCLOPROPENEBIS(TRIPHENYLPHOSPHINE)PLATINUM(0)

The crystal and molecular structures of the title compounds (I) 1,2-dimethyl- and (II) 3-methyl-cyclopropene-bis(triphenylphosphine)platinum(0) have been each determined from X-ray data collected by counter methods. The structures were determined by the heavy-atom method and refined by least-squares techniques to R 0.032 [(I), 2390 independent reflections] and 0.051 [(II), 905 independent reflections]. The parameters of the cyclopropene ring in (II) are inaccurate owing to disorder in the crystal used.The compounds have the same overall molecular structure. On complex formation the cyclopropene ring remains intact, with CC 1.50 A, and is co-ordinated to the platinum via a metal–olefin interaction with Pt–C 2.28 A. In (II), the methyl group and the metal lie on opposite sides of the cyclopropene-ring plane.Crystals are orthorhombic, space group P21/c with Z= 4 in unit cells of dimensions: (I), a= 12.49(1), b= 17.77(7), c= 16.38(7)A, β= 109.42(5)°(II); a= 11.28(3), b= 20.74(4), c= 17.23(4)A, β= 124.5(2)°.

Organometallic conformational equilibria : XVIII. Preferred orientations and rotational barriers of π-olefins in cyclopentadienyl and indenyl complexes of iron and ruthenium

The synthesis and spectral analysis of a series of some η 5-cyclopentadienyl-and η 5-indenyl-ironolefin complexes have allowed the elucidation of the orientational preferences and dynamic properties of the olefin ligand. The olefins rotate rapidly about the metalolefin bond with the barrier to rotation on the order of 8 kcal as determined by the observation of signal broadening in several of the ethylene complexes. Dissociation of the olefin and rotation about the carbon double bond are excluded as possible mechanisms on the basis of spectral evidence. The mode of rotation is consistent with the behavior of the olefin ligands in η 5-C 5H 5Rh(C 2H 4) 2 first noted by R. Cramer [J. Amer. Chem. Soc., 86 (1964) 217]. Thetermodynamically preferred orientations were defermined for each of the olefin complexes. Chemical shift differences resulting from the substitution of an indenyl ligand for a cyclopentadienyl ligand allow determination of the preferred orientations in the ethylene and propylene complexes. For ethylene, the orientation in which the CC bond is parallel to the plane of the cyclopentadienyl ring is preferred. Methyl substitution of the olefin produces a deviation of preferred orientation. A dihedral angle of about 10° is estimated for the propylene complex.

Structures of 1,2-dimethyl- and 3-methyl-cyclopropenebis(triphenylphosphine)platinum(0)

The crystal and molecular structures of the title compounds (I) 1,2-dimethyl- and (II) 3-methyl-cyclopropene-bis(triphenylphosphine)platinum(0) have been each determined from X-ray data collected by counter methods. The structures were determined by the heavy-atom method and refined by least-squares techniques to R 0.032 [(I), 2390 independent reflections] and 0.051 [(II), 905 independent reflections]. The parameters of the cyclopropene ring in (II) are inaccurate owing to disorder in the crystal used.The compounds have the same overall molecular structure. On complex formation the cyclopropene ring remains intact, with CC 1.50 A, and is co-ordinated to the platinum via a metal–olefin interaction with Pt–C 2.28 A. In (II), the methyl group and the metal lie on opposite sides of the cyclopropene-ring plane.Crystals are orthorhombic, space group P21/c with Z= 4 in unit cells of dimensions: (I), a= 12.49(1), b= 17.77(7), c= 16.38(7)A, β= 109.42(5)°(II); a= 11.28(3), b= 20.74(4), c= 17.23(4)A, β= 124.5(2)°.

ChemInform Abstract: PREPARATION AND CHARACTERIZATION OF RHODIUM(I) COMPLEXES CONTAINING BIDENTATE DIPHENYL(PROP‐2‐ENYLOXO)PHOSPHINE AND (BUT‐3‐ENYL)DIPHENYLPHOSPHINE LIGANDS

AbstractDie Umsetzung von dimerem Chloro‐bis‐[äthylenl‐Rh?) oder Chlorocyclooctadien‐ Rh(I) mit den Titelliganden in Äther führt zu den chelatisierten Phosphin‐Rh(I)‐Dimeren (I), die mit Cyclopentadienyl‐Tl die monomeren Cyclopentadienyl‐Rh(I)‐Komplexe (II) bilden.

Gehinderte ligandenbewegungen in übergangsmetall komplexen : III. Olefinrotation in cclopentadienyl-mangan-dicarbonyl- äthylen und cyclopentadienyl-chrom-carbonyl- nitrosyl-äthylen

The temperature dependence of the 1H NMR spectra indicates that the ethylene ligand in the isoelectronic complexes, cyclopentadienylmanganese dicarbonyl ethylene, C 5H 5Mn(CO) 2(CH 2=CH 2) (I), and cyclopentadienylchromium carbonyl nitrosyl ethylene, C 5H 5Cr(CO)(NO)(CH 2=CH 2) (II), undergoes a hindered rotation around the metalolefin bond axis. In addition to the ethylene complexes I and II, the corresponding complexes containing trans-D 2- ethylene, C 5H 5Mn(CO) 2 ( trans-CHD=CHD)(ID) and C 5H 5Cr(CO)(NO)- ( trans-CHD=CHD) (IID), have been prepared and studied in order to support the analysis of the 1 H NMR spectra of I and II. The activation barriers for the ligand motion were fond to be Δ G ‡ 1 68 = 8.4 ± 0.2 kcal/mole in the case of I and ID, and Δ G ‡ 2 38 = 11.4 ± 0.2 kcal/mole in the case of II and IID.

Palladium(II) and platinum(II) complexes of unsaturated tertiary phosphines

A series of square planar Pd II and Pt II complexes of the type MX 2(L) [X = Cl, Br, I and L = Ph n P(CH 2CH 2CHCH 2) 3 − n ; n = 0–2] have been prepared and studied by 1H and 31P magnetic resonance, and infrared and Raman spectroscopy. The strength of the metalolefin bond is found to be in the order Pt > Pd. When L = PhP(CH 2CH 2CHCH 2) 2 or P(CH 2CH 2CHCH 2) 3, IR and Raman data indicate only one olefin is coordinated in both the solid state and solution. On the PMR timescale, the olefins undergo rapid intramolecular exchange, offering a system in which one observes average HH and PtH coupling.

Approaches towards a comprehensive theory of the cationic polymerisation of olefins

AbstractSome of the factors which influence, or must be contained in, a Comprehensive Theory of the cationic polymerisation of olefins are discussed from new points of view, starting from the author's new theory concerning initiation by metal halides. Alleged determinations of the rate constant k are criticised because they ignored two equilibria which make the concentration of growing polymer chains [P] in general less than the nominal concentration, c0, of initiator. One of them is a binary ionogenic equilibrium involving metal halide MtXn and polymer halide PnX. The other is between metal halide and olefin. An equation relating [P] to c0 is deduced which takes account of these equilibria. The importance of the second equilibrium is illustrated by the way in which it provides simple explanations of hitherto obscure phenomena. Some of these arise during the interaction of aluminium halides with olefins in different circumstances, others concern the different interactions which can take place between titanium tetrachloride and 1,1‐diphenylethylene. The fact that titanium tetrachloride appears to be able to initiate without co‐initiator in some systems, but requires one in others is explained by the self‐ionisation of the metal halide and the effects of impurities.

Preparation and characterization of rhodium(I) complexes containing bidentate diphenyl(prop-2-enyloxo)phosphine and (but-3-enyl)diphenylphosphine ligands

The complexes [LRh(µ-Cl)2RhL] and [RhL(L′)][L′=η-cyclopentadienyl (cp) or pentane-2,4-dionato (acac); L = diphenyl(prop-2-enyloxo)phosphine-P;C2,C3-η(dppp) or (but-3-enyl)diphenylphosphine-P;C3,C4-η(bdpp)] have been prepared and characterized. The strongest metal–olefin bond occurs in the cp complexes and can be recognized by significant changes in spin–spin coupling involving the olefinic protons and a large upfield shift of the terminal olefinic protons (as high as τ 9). Unequal coupling constants 3J(POCH) of 34 and 6·5 Hz for the complex [Rh(cp)(dppp)] and similar values for [Rh(acac)(dppp)] allow assignment of the configuration of the ligand and of the molecular structures of the complexes in solution.