The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

Abstract

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron ...

Indenyl‐ and Fluorenyl‐Functionalized N‐Heterocyclic Carbene Complexes of Rhodium and Iridium – Synthetic, Structural and Catalytic Studies

“…-PEt 2 )(CO), [5,8] and Rh(Ind-PPh 2 )(CO) [8] by the degree of backbonding to the coordinated CO as measured from the position of the ν(CO) in the IR spectra of the complexes. The ν(CO) of 6 appears at slightly lower wave numbers (1927 cm -1 ) than those for the phosphane species (1933 and 1937 cm -1 for PEt 2 and PPh 2 analogues, respectively).…”

“…In a further development, cyclopentadienyl complexes of Co I , Rh I and Ir I with tethered alkyl-and arylphosphanes have also been studied as catalysts for this reaction, and showed higher carbonylation rates under milder conditions. [5] We have recently reported a new class of NHC ligands Flu-NHC, Ind-NHC and derivatives (Scheme 1), where the 1816 been observed. Catalytic studies on the bidentate Rh I complex 6 show that it is weakly active for the hydroformylation of 1-octene with poor linear selectivity, but it shows slightly lower activity than the standard Monsanto system for the carbonylation of methanol.…”

Dicarbonylrhodium(I) Complexes of Bipyridine Ligands with Proximate H‐Bonding Substituents and Their Application in Methyl Acetate Carbonylation

“…[23] Examples are the application of monodentate [24,25] and bidentate phosphane ligands [26][27][28][29][30][31][32][33] as well as cyclopentadienyl ligands [34,35] and combinations thereof. [36] Nitrogen-based ligands such as diimines and pyridine ligands have also been investigated. [37][38][39] Noteworthy, Dutta and co-workers have recently reported improved catalytic behaviour of rhodium catalysts for methanol carbonylation, when monodentate pyridine ligands with carboxylic acid substituents were employed.…”

Quantum Mechanics Calculations: Asymmetric Phosphines for Methanol Carbonylation (Part I)

“…In addition to the high electron density at rhodium [19], ligand steric and electronic effects play a key role in determining organometallic reactivity trends and catalytic behavior [20].…”