A Versatile Approach toward Phosphinine−Phosphole-Based and Phosphinine−Phosphaferrocene-Based Tridentate Ligands

Abstract

A synthetic approach toward mixed phosphinine−phosphole and phosphinine−phosphaferrocene tridentate ligands has been studied. In the first step, the metallacycle transfer reaction from 2,5-bis(trimethylsilyl)zirconacyclopentadienes to the corresponding phospholes has been investigated. Three metallacycles 2a−c, bearing different groups at the β-positions of the ring (a, R = Ph; b, R = n-Bu; c, R = Me), have been synthesized. Whereas the reaction of PCl3 with 2a,b respectively leads to 1-P chlorophosphirenes 3a,b, complex 2c is readily transformed into the corresponding 1-P bromophosphole 4 upon reaction with PBr3 in dichloromethane. This approach was extended to the synthesis of the bis(dimethylpropynylsilyl)zirconacyclopentadiene compound 5, which was then further converted into the corresponding 1-P chlorophosphole 6. Phospholyl anion 7 was obtained from the reaction of 6 with lithium in THF at room temperature. Three 1-R-2,5-bis(dimethylpropynylsilyl)phospholes (8a, R = CH2CH2Cl; 8b, R = CH2CH2CN; 8c, R = CH2CH2CO2Et) have been obtained from the reaction of anion 7 with the corresponding species RCH2CH2X (X = Cl, Br). The X-ray crystal structure of compound 8b has been determined. The reaction of anion 7 with [FeCp(η6-C9H12)][PF6] and FeCl2 respectively yielded the monophosphaferrocene 9 and the diphosphaferrocene 10. The X-ray crystal structure of 10 has been determined. The three phosphinine−phosphole tridentate ligands 12a−c have been assembled by reacting phospholes 8a−c with diazaphosphinine 1 followed by reaction of the 2,5-bis(dimethyl(1,2-azaphosphininyl)silyl)phospholes 11a−c with (trimethylsilyl)acetylene in excess. Ligands 12b,c have been converted into the anion 13 upon reaction with LDA at low temperature. The 2,5-bis(dimethyl(phosphininyl)silyl)phosphaferrocene ligand 15, which was structurally characterized, has been prepared by following the strategy devised for the synthesis of ligands 12. Reaction of ligands 12a and 15 with [Rh(COD)Cl]2 gave respectively the corresponding Rh chloride complexes 16 and 17. Both complexes adopt a square-planar geometry, and complex 17 has been structurally characterized.