Structure of triphenylphosphonium cyclopentadienylide. Evaluation of ylene-ylide character from structural data

Abstract

The crystal structure of triphenylphosphonium cyclopentadienylide has been determined from an X-ray crystallographic investigation. Mo Ka radiation was used and the X-ray intensities were measured with a computer-controlled diffractometer. The space group is monoclinic, Plfn; the lattice constants are a = 10.564, b = 8.986, c = 18.708 Á, ß = 93.410; there are four molecules per cell. The amount of ylene-ylide character (ca. 20-80%) is estimated from the P-C bond length, the -electron delocalization in the five ring evaluated from the C-C distances, and from the plus charge on P obtained from the P photoelectron spectrum. These data are compared with the results from a previously reported MO analysis. The conformations about the P-C (five ring) bond in the compound and about the P-Cbonds in a number of other ylides can be explained in terms of the orientations necessary for C p-orbital overlap with the two P d orbitals of symmetry.

Substrate‐Controlled, Phosphine‐Catalyzed Domino Reactions of Activated Conjugated Dienes: Highly Diastereoselective Synthesis of Bicyclic Skeletons

“…Cyclopentenyl phosphoranes may serve as ligands in the synthesis of many inorganic and organic complexes. [13] To the best of our knowledge, no efficient strategy for the synthesis of bicyclic phosphoranes has been reported because the unusual stability of cyclopentenyl phosphoranes makes the traditional stepwise manipulations rather difficult. To solve these problems, we focused on the appropriate domino processes.…”

Coordination complexes of aryl- and alkylphosphonium cyclopentadienylides (cyclopentadienylidene ylides), C5R4PR′R′′R′′′ (R=H, alkyl, aryl; R′, R′′, R′′′=alkyl, aryl)

“…This was the first report of C 5 H 4 PPh 3 being bound in this way. The P-C 5 bond distance (1.748(7)Å) in this compound is elongated relative to the P-C 5 bond distance in C 5 H 4 PPh 3 (1.718(3)Å) [7,28,63], but the C 5 ring bond distances are only nominally shorter than in the free ligand. The bonding at the ␤-carbon (see Fig.…”

“…Further evidence for delocalization of the π electron density was found in the crystal structure, which showed that the P-C 5 , or P-C(ylide), bond was of intermediate length between those expected for P-C single and double bonds. In addition, the C 5 ring CC bond lengths were found to be rather similar to those of benzene although they also alternated somewhat as implied by structure Ia [7]. In addition, the 13 C NMR spectrum exhibited an unusually high field chemical shift for the ylide carbon and a P-C(ylide) coupling constant typical of an aliphatic carbon-P bond [8].…”

“…38 [20]. The P-C 5 bond length of 1.793(12)Å is considerable longer than in free C 5 H 4 PPh 3 (1.718(2)Å [7], as is more akin to a P-C single bond, while the P-C 5 bond is bent significantly out of the plane of the C 5 ring by 19.4(6) • . The major CO stretching band in the IR spectrum is lower in frequency than that of Ru 6 C(CO) 14 ( 6 -C 6 H 6 ) by 17 cm −1 , indicating that the ylide is a better electron donor than is benzene.…”

A New and Efficient Synthesis of Highly Functionalized (Triphenylphosphoranylidene)cyclopentadienes with Zwitterionic Resonance Structures

“…(Triphenylphosphoranylidene)cyclopentadienes are usually prepared by deprotonation of related phosphonium salts; the latter, in turn, are prepared by the reaction of Ph 3 P and a cyclopentadienyl halide [2]. Cyclopentadiene-based ylides are of interest to us, because these compounds may serve as ligands in the synthesis of many inorganic complexes, and since they are usually stable and quite unreactive for ylide species [3].…”