Intramolecular Dehydrofluorinative Coupling of the Asymmetric Diphosphine Ph₂PCH₂CH₂PPh(C₅F₄N-4) and Pentamethylcyclopentadienyl Ligands in a Rhodium Complex

Abstract

The tetrafluoropyridyl-substituted diphosphine Ph 2 PCH 2 CH 2 PPh(C 5 F 4 N-4) (1) has been prepared in three steps from dppe. Comparison of the spectroscopic properties between trans-[RhCl(CO){PPh 2 (C 5 F 4 N-4)} 2 ] and analogous complexes of other fluorinated triaryl phosphines reveals the lower basicity of tetrafluoropyridylphosphines relative to pentafluorophenylphosphines. The reaction between [Cp*RhCl(µ-Cl)] 2 and 1 in the presence of [BF 4 -] yielded racemic diastereoisomers of [Cp*RhCl (1)] [BF 4 ]. In the S Rh R P and R Rh S P pair of enantiomers the Cp* and tetrafluoropyridyl groups have a cis disposition about the Rh-P bond, and in the S Rh S P and R Rh R P pair the groups are trans. In situ NMR experiments reveal that the cis pair, in which the Cp* and tetrafluoropyridyl groups are close, underwent rapid dehydrofluorinative C-C coupling to give the respective enantiomers of [{η 5 ,κP,κP-C 5 Me 4 CH 2 -2-C 5 F 3 N-4-PPhCH 2 -CH 2 PPh 2 }RhCl][BF 4 ] (6‚[BF 4 ]). The trans pair did not undergo coupling, but isomerized to the cis pair on heating in ethanol. The reaction between [Cp*RhCl(µ-Cl)] 2 and 1 in refluxing benzene afforded 6‚[BF 4 ] in 64% yield after anion metathesis. The structures of OPPh 2 -(C 5 F 4 N-4), the cis isomer of [Cp*RhCl(1)][BF 4 ], and one enantiomer of 6‚[BF 4 ], which crystallizes as a conglomerate, have been determined by single-crystal X-ray diffraction.

Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

“…This route involves the intramolecular dehydrofluorinative coupling of coordinated h 5 -pentamethylcyclopentadienyl and phosphine ligands. The latter must bear a fluorinated aryl group susceptible to nucleophilic attack at an ortho position, such as pentafluorophenyl or tetrafluoropyridyl [6][7][8]. The development of such an approach to ligands containing an NHC functionality would obviate the problematic synthesis of a non-coordinated cyclopentadienyl-NHC ligand and its complexation.…”

Fluoroarylphosphines as ligands

“…Trimethylsilylphosphines [33,41,42,50] and trimethylstannylphosphines [33] have been reported to react with polyfluoroarenes giving products in high yields. The driving force for the reaction is the strength of the Me 3 Si-F and Me 3 Sn-F bonds.…”

Complexes of η5, κP-cyclopentadienyl-phosphine ligands by chelate-assisted dehydrofluorinative coupling; the coupling of bis{bis(pentafluorophenyl)phosphino}methane to η5-pentamethylcyclopentadienyl in a rhodium complex

“…Intramolecular dehydrofluorinative coupling of methylsubstituted cyclopentadienyl and chelating polyfluoroarylsubstituted phosphine ligands provides a convenient route to rhodium and iridium complexes of trifunctional g 5 ,jP, jL-cyclopentadienyl-phosphine-donor (Cp-PL) ligands (Scheme 1) [1][2][3]. The reactions are rapid and high-yielding, and can be performed directly from [{(g 5 -C 5 Me 5 )MCl(lCl)} 2 ] (M = Rh or Ir) and a chelating phosphine (P 2 ), via the intermediate [(g 5 -C 5 Me 5 )MCl(jP,jP-P 2 )] + [4], as for the synthesis of [{(g 5 ,jP,jP-C 5 Me 4 CH 2 C 5 F 3 N-2-PPhCH 2 -CH 2 PPh 2 )}RhCl] + [2].…”

“…The reactions are rapid and high-yielding, and can be performed directly from [{(g 5 -C 5 Me 5 )MCl(lCl)} 2 ] (M = Rh or Ir) and a chelating phosphine (P 2 ), via the intermediate [(g 5 -C 5 Me 5 )MCl(jP,jP-P 2 )] + [4], as for the synthesis of [{(g 5 ,jP,jP-C 5 Me 4 CH 2 C 5 F 3 N-2-PPhCH 2 -CH 2 PPh 2 )}RhCl] + [2]. Access to ligands of this type had previously been problematic, involving elaborate, multiple step, low-yielding syntheses [5].…”

“…One group of chelating PL ligands that may show this ability are those which give small bite (P-M-L) angles. It has been established that coupling of the phosphine to cyclopentadienyl reduces both the Cp-M-P angle and the M-P bond length [1,2], and this geometric change may disallow coordination of the L functionality.…”