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

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 PCl 3 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 PBr 3 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 = CH 2 CH 2 Cl; 8b, R = CH 2 CH 2 CN; 8c, R = CH 2 CH 2 CO 2 Et) have been obtained from the reaction of anion 7 with the corresponding species RCH 2 CH 2 X (X = Cl, Br). The X-ray crystal structure of compound 8b has been determined. The reaction of anion 7 with [FeCp(η 6 -C 9 H 12 )][PF 6 ] and FeCl 2 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.