455947-55-4Relevant academic research and scientific papers
Reactions with electrophiles control isomerization from η5(π)- to η1(P)-coordination of phosphinyl-substituted benzophospholide ligands
Baiko, Zoltan,Daniels, J?rg,Gudat, Dietrich,H?p, Stefan,Nieger, Martin
, p. 5182 - 5189 (2008/10/08)
The Ph2P-functionalized phosphoniobenzo[c]phospholide 5 reacts with [Cr(CO)5(cyclooctene)] and [Cr(CO)3(naphthalene)] under site-selective n(P)-complexation at the Ph2P moiety and π-complexation at the five-membered heterocycle, respectively, to give complexes 6 and 7, which were characterized by spectroscopic data and an X-ray diffraction study of 6. The attack of electrophiles E (E = alkyl-, Ag-, S, BH3) on the π-complex 7 occurs at the pendant Ph2P substituent to give unstable quaternization products that were in some cases detectable by NMR. The initial products decay either via decomplexation to metal-free quaternization products (for E = alkyl+) or via a combination of decomplexation/isomerization reactions to give mixtures of free quaternization products and complexes 10a and 13a containing a Cr-(CO)4 unit that is chelated by a n(P)-coordinated benzophospholide moiety and an adjacent sulfur atom (for E = S) or a BH-σ-bond (for E = BH3). These products as well as their tungsten analogues 10b and 13b were likewise accessible from the appropriate ligands and [M(CO)4-(norbornadiene)], and 10a,b and 13b were isolated from these reactions and characterized by spectroscopic and X-ray diffraction studies. The course of the studied reactions of 7 with electrophiles suggests that the destabilization of the primary quaternization products is controlled by increased weakening of the π-donor power of the ligand with increasing phosphonium character of the substituents at the benzophospholide moiety. The observed spontaneous π(η5)/κ2-P,σ-BH-coorainatioii isomerization of a benzophospholide implies that the unusual coordination mode through a phosphorus lone pair and a BH-σ-bond is thermodynamically preferable to π-coordination through the five-membered ring.
Structural and electronic properties of neutral phoshoniobenzo[c]phospholides
Haep, Stefan,Szarvas, Laszlo,Nieger, Martin,Gudat, Dietrich
, p. 2763 - 2772 (2007/10/03)
The neutral monophosphoniobenzo[c]phospholides 2 and 3 were selectively prepared by reduction of bis(triphenylphosphonio)benzophospholide chloride 1[Cl]. Compound 3 was further converted into the borane adduct 6 and the thioxophosphorane 7. All products were characterised by spectroscopic methods and X-ray diffraction. The most notable features of the molecular structures are the significantly different distances of the two P-C bonds adjacent to the two-coordinate phosphorus atom (P2-C1 175.0-176.6, P2-C3 171.7-173.5 pm), and a short exocyclic C-P(phosphonio) bond (C1-P1 172.5-173.7 pm) relative to cationic derivatives such as 1. Structure comparisons revealed further variations in the bond lengths, which can be related to the changes in the inductive electron-withdrawing power of the substituents in the 3-position of the fused ring system. Computational studies of monophosphoniobenzophospholides, as well as the corresponding anions with no phosphonio substituents, and cations with two phosphonio substituents, allowed for the interpretation of the special properties of the neutral species in terms of a partial ?-bond localisation. This, in terms of a VB picture, is equivalent to the prominence of a single resonance structure that can best be described as an ylide-substituted cyclic phosphoalkene. The analysis of these results allows important predictions for th chemical properties of these compounds.
