54006-05-2Relevant academic research and scientific papers
Synthesis of pyrrolyl-, indolyl-, and carbazolylphosphanes and their catalytic application as ligands in the hydroformylation of 2-pentene
Jackstell, Ralf,Klein, Holger,Beller, Matthias,Wiese, Klaus-Diether,Roettger, Dirk
, p. 3871 - 3877 (2007/10/03)
The synthesis of π-acceptor ligands of the type PArxR3-x (x = 0-2; R = pyrrolyl, indolyl, carbazolyl; Ar = aryl) (1-8, 10, 12, 13) and P(pyrrolyl)2(carbazolyl) (11) is described. These ligands can be prepared in good to excellent yields by treatment of the corresponding free heterocyclic amines with phosphorus chlorides in the presence of base. The utilization of pyrrolyl-, indolyl-, and carbazolylphosphanes in the rhodium-catalyzed hydroformylation of 2-pentene demonstrates the influence of the ligand π-acidity on regioselectivity and activity in the hydroformylation of internal olefins. In general, increasing π-acidity of the ligand results in an increased yield of the linear oxo product. The best n/iso ratios of about 60:40 are obtained at low synthesis gas pressure (10 bar) in the presence of the P(pyrrolyl)3 (1) ligand.
N-pyrrolyl phosphines: An unexploited class of phosphine ligands with exceptional π-acceptor character
Moloy, Kenneth G.,Petersen, Jeffrey L.
, p. 7696 - 7710 (2007/10/02)
The coordination chemistry of N-pyrrolyl phosphines (P-NC4H4) is described. These ligands are prepared in excellent yield from pyrrole, a phosphorus halide, and base, and this synthesis has been applied to the series PPhx(pyrrolyl)3-x (x = 0-2) and the chelate (pyrrolyl)2P(CH2)2P(pyrrolyl)2. These ligands readily form coordination complexes, and the complexes trans-RhCl(CO)[PPhx(pyrrolyl)3-x]2 (x = 0-2) and Mo(CO)4[(pyrrolyl)2P(CH2) 2-P(pyrrolyl)2] are described. The carbonyl stretching frequencies of these complexes are shifted to significantly higher energy relative to "traditional" phosphine ligands, indicating that N-pyrrolyl phosphines are poor σ-donors, exceeding phosphites and approaching fluoroalkylphosphines with respect to this property. For example, νCO for trans-RhCl(CO)-[P(pyrrolyl)3]2 exceeds that of the PPh3 analogue by 59 cm-1. That these ligands are π-acceptors is suggested by the single crystal X-ray structure of trans-RhCl(CO)[P(pyrrolyl)3]2 which shows shortened Rh-P distances and a lengthened Rh-C distance, consistent with enhanced Rh to P back-bonding. The X-ray structure of trans-RhCl(CO)-[P(pyrrolidinyl)3]2 is also reported; this complex possesses longer Rh-P distances which more closely resemble those found for other complexes of this type. The exceptional π-acceptor character of these ligands is convincingly demonstrated by their substitution chemistry with electron rich [PPN][Rh(CO)4]. P(pyrrolyl)3 is found to displace CO in a stepwise manner to give the entire series [PPN][Rh(CO)4-x{P(pyrrolyl)3}xr] (x = 1-4). Similar results are obtained with (pyrrolyl)2P(CH2)2P(pyrrolyl)2, and the anions [PPN][Rh(CO)x{(pyrrolyl)2P(CH2) 2P(pyrrolyl)2}y] (x = 2, y = 1; x = 0, y = 2) are reported. An X-ray structure analysis of [PPN][Rh(CO){P(pyrrolyl)3}3] shows that the Rh-P bonds in this tetrahedral anion are shorter than those found in the Rh(I) complex, consistent with significantly greater π back-bonding in this more electron rich system. The infrared spectra of these anions again show a substantial shift in νCO to higher frequency relative to other phosphine ligands. The structural results further indicate that PPhx(pyrrolyl)3-x (x = 0-2), PPh3, and P(pyrrolidinyl)3 possess nearly identical steric properties (cone angles). The wide range of electronic properties (π-acceptor/σ-donor) exhibited by this isosteric series, together with their ready availability, suggests that they, and N-pyrrolyl phosphines in particular, may find utility in physical inorganic and organometallic chemistry.
