Probing the chemistry of organomanganese complexes. a kinetic study of the role of coordinate bonds in a demetalation reaction.

Dowler, Michael E.; Le, Thuy X.; DeShong, Philip; Philipsborn, W. Von; Vöhler, Markus; Rentsch, Daniel

doi:10.1016/s0040-4020(01)87276-8

Cited by 6 publications

(3 citation statements)

References 17 publications

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“…The chemical shift of a transition metal is a very sensitive probe for electronic and geometric changes in the coordination sphere of the nucleus under scrutiny. − Although there is no a priori reason for an intrinsic relation between NMR shifts and chemical reactivity, a number of empirical correlations of this type have been established. 9b-e,− In a seminal study, Bönnemann and von Philipsborn correlated 59 Co shifts and catalytic properties of substituted cyclopentadienyl Co(I) complexes . Similarly, direct relationships between 103 Rh shifts and rate constants have been described for stoichiometric exchange processes involving cyclopentadienyl Rh(I) 9b and Rh(III) 9c complexes.…”

Section: Introductionmentioning

confidence: 99%

¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

et al. 1999

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Experimental and theoretical methods have been employed to investigate the influence of the chelating phosphine ligand on the 103Rh chemical shift in complexes containing the [(P2)Rh] fragment (P2 = chelating bidentate phosphine). The δ(103Rh) values obtained by 2D(31P,103Rh{1H}) NMR spectroscopy for a series of neutral rhodium complexes [{R2P(CH2) n PR2}Rh(hfacac)] (R = Ar, Ph, Cy, Me, n = 1−4, hfacac = hexafluoroacetylacetonate) have been compared. Systematic variation of the phosphine ligand has allowed separation of electronic and geometrical effects. The purely electronic influence of para substituents in complexes [{(p-XC6H4)2P(CH2)4P(p-XC6H4)2}Rh(hfacac)] correlates directly with the Hammett σP constants of X, but leads to variations in the chemical shift of less than 80 ppm between X = CF3 and X = OMe. In contrast, geometrical changes in complexes [(P2)Rh(hfacac)] lead to variations in the chemical shift over a range of approximately 800 ppm. The individual contributions of various structural parameters on the δ(103Rh) values have been assessed by density-functional-based calculations for suitable model compounds. The same approach has been extended to the rationalization of the trends in 103Rh chemical shifts of cationic complexes with four P donor ligands around a Rh(+I) center and selected anionic Rh(−I) complexes [(P2)2Rh]-. This analysis allows for the first time a direct corroboration of geometrical variations and their effect on 103Rh chemical shifts, demonstrating that correlations of reactivity with 103Rh chemical shifts can give valuable information on structure/reactivity relationships.

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Section: Introductionmentioning

confidence: 99%

¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

et al. 1999

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“…However, a more than qualitative characterization of ligand effects is often difficult. Ligand effects on structure and reactivity can be probed by transition metal NMR spectroscopy, as we have reported for a variety of cases: 59 Co, , 103 Rh, − 55 Mn, , and 57 Fe. − Cyclopentadienyl complexes of group VIII transition metals are vital in several important stoichiometric and catalytic reactions, and annually many synthetic applications are published. , Cyclopentadienyliron complexes in particular have attracted considerable interest as stoichiometric reagents in stereoselective reactions …”

Section: Introductionmentioning

confidence: 99%

⁵⁷Fe NMR Study of Ligand Effects in Cyclopentadienyliron Complexes

et al. 1996

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The first systematic 57Fe NMR study of ligand effects in cyclopentadienyliron complexes is presented. Four series encompassing a total of 35 compounds have been studied. Among the compounds are five new ring-substituted complexes with the formula (C5H4Y)Fe(CO)(PPh3)(Me), Y = Me, SiMe3, NEt2, I, and Ph. The crystal structure of (C5H4I)Fe(CO)(PPh3)(Me) (32) was determined. For the series CpFe(CO)2R (type I), 57Fe shielding was found to decrease with the bulkiness of the alkyl ligand R and to correlate with the CO-insertion rate of the complex. In type III complexes CpFe(CO)(L)(COMe), L = PR3, and CO, it is again the steric requirement of the ligand L that dominates the 57Fe chemical shift which increases with larger cone angles (θ). In contrast, a strong electronic effect was found for type II complexes CpFe(CO)(PPh3)X, X = H, Me, and I. Ligands with higher electronegativity induce a shift of the 57Fe resonance to higher frequencies. In the complexes (C5H4Y)Fe(CO)(PPh3)(Me), Y = Me, H, SiMe3, NEt2, I, Ph, COOMe, and COiPr (type IV), again electronic effects are dominant, whereby electron acceptor substituents (e.g. Y = COiPr, COOMe) cause a deshielding of the iron nucleus, relative to complexes with electron donor substituents (e.g. Y = Me, H, SiMe3). Dominant electronic ligand effects in type IV complexes are also apparent from the correlation of δ(57Fe) with the electronic substituent parameter σI. The 57Fe chemical shift is shown to be very sensitive to changes in the ligand sphere, and the effects are discussed in terms of the paramagnetic shielding constant (σpara). The 1 J(57Fe,13C) coupling constants and longitudinal relaxation times T 1 of 57Fe in selected complexes have been determined and ligand effects are discussed.

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“…Transition-metal NMR spectroscopy can be used to explore both electronic and steric effects in organometallic systems. In addition, its use as a probe to screen the activity of catalysts, correlate rate data, and provide insight into mechanistic pathways is an ongoing area of research in our group, although these attempts have not always been successful we decided to examine this nucleus in more detail as part of our research on the application of transition-metal NMR spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

¹⁸⁷Os NMR Study of (η⁶-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects

et al. 1996

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Osmium-187 NMR data have been collected for 37 Os(arene)X2L type complexes, using inverse two-dimensional (31P, 187Os){1H} and (1H, 187Os) NMR spectroscopy. In the series Os(p-cymene)X2PMe3, shielding increases in the order Cl < Br < I < Me < H. Systematic variation of the phosphite ligand of Os(p-cymene)Cl2P(OR)3 (R = Me, Et, nBu, Ph, iPr) reveals a linear dependence on Tolman's electronic parameter χ with metal shielding increasing as the acceptor character of the P(OR)3 ligand increases. Conversely, the structurally related Os(p-cymene)X2PR3 types (X = Cl, I; PR3 = PMe3, PMe2Ph, PnBu3, PPh2Me, P(CH2Ph)3, PPh3, P(m-tolyl)3, PiPr3, PCy3) exhibit a linear dependence on Tolman's cone angle θ, with shielding decreasing as larger phosphine ligands are introduced. Variation of the arene ligand of Os(C6H5X)Cl2PMe3 (X = H, Me, Et, iPr, tBu) shows a linear dependence of chemical shift on Taft's steric parameter E s for group X. In only one case, for the monohydride complexes Os(p-cymene)HClPR3 (PR3 = PMe3, PMe2Ph, PnBu3, PPh3, PiPr3, PCy3), has it been possible to separate both steric and electronic effects of the phosphorus ligand on the observed 187Os chemical shifts. There are some correlations between 1 J(187Os,31P) and the acceptor character of the phosphorus ligand, and a relationship between Os−P bond lengths and coupling constants was found. Osmium relaxation rates T 1 -1 and their B 0 field dependence are reported for selected complexes. The crystal structures of four Os(p-cymene)Cl2L complexes (L = PMe3 (1), P(OMe)3 (6), PBz3 (13), and PPh3 (15)) have been determined.

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Probing the chemistry of organomanganese complexes. a kinetic study of the role of coordinate bonds in a demetalation reaction.

Cited by 6 publications

References 17 publications

¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

⁵⁷Fe NMR Study of Ligand Effects in Cyclopentadienyliron Complexes

¹⁸⁷Os NMR Study of (η⁶-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects

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Probing the chemistry of organomanganese complexes. a kinetic study of the role of coordinate bonds in a demetalation reaction.

Cited by 6 publications

References 17 publications

103Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

103Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

57Fe NMR Study of Ligand Effects in Cyclopentadienyliron Complexes

187Os NMR Study of (η6-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects

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¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

¹⁰³Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands

⁵⁷Fe NMR Study of Ligand Effects in Cyclopentadienyliron Complexes

¹⁸⁷Os NMR Study of (η⁶-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects