1,2-Bis{(pentafluorophenyl)phenylphosphino}ethane:  A Probe for Configurational Stability in Three-Legged Piano Stool Complexes

Abstract

The pentafluorophenyl-substituted diphosphine (C6F5)PhPCH2CH2PPh(C6F5) has been prepared, as a 1:1.7 mixture of rac (1a) and meso (1b) isomers, in four steps from dppe. The reaction between [Cp*RhCl(μ-Cl)]2 and 1 in the presence of tetrafluoroborate yielded a mixture of racemic diastereoisomers of [Cp*RhCl(κP,κP-1a)][BF4] (4a·BF 4 ) and trans and cis isomers of [Cp*RhCl(κP,κP-1b)][BF4] (4b·BF 4 and 4c·BF 4 , respectively). On addition of Proton Sponge, 4a and 4c, in which at least one pentafluorophenyl group is close to the pentamethylcyclopentadienyl ligand, underwent rapid dehydrofluorinative carbon−carbon coupling giving trans- and cis-[{η5,κP,κP-C5Me4CH2C6F4-2-PPhCH2CH2PPh(C6F5)}RhCl]+ (5 and 6), respectively. The latter underwent further dehydrofluorinative carbon−carbon coupling to give two isomers of [{η5,κP,κP-C5Me3[CH2C6F4-2-PPhCH2]2}RhCl]+ (7). Isomerization of 4b to 4c was observed in chloroform and dimethlysulfoxide. Neither isomerization of 4a to 4b or 4c nor isomerization of 5 to 6 was observed at ambient or elevated temperature in dimethyl sulfoxide. The results provide the first evidence that complexes of η5,κP,κL-cyclopentadienyl-phosphine-donor ligands are configurationally stable at high temperature.

New cyclopentadienylethylphosphane chelate complexes with unsymmetrical phosphane substitution

“…The complexes were characterized spectroscopically. According to HMQC measurements 1 The syntheses as well as reactions of cyclopentadienyl or indenyl rhodium chelate complexes bearing a phosphane tether have been reported by Poilblanc et al, 50 Tani et al, [51][52][53][54][55][56] Nelson et al, 57,58 Saunders et al, [38][39][40][59][60][61] Hidai et al, 62 Jones et al, 63 Green et al, 64 Salzer et al, [65][66][67][68] Cole-Hamilton et al, 69 Lalinde et al, 70 and Whitby et al 71 In most cases the phosphane tether bears phenyl substituents, however, there are also some in which alkyl, pentafluorophenyl or more complicated substituents are present. To our knowledge there are no examples with tert-butyl substituents, which, according to our experience with cobalt complexes, increase the stability of the complexes and improve their crystallization properties.…”

“…The few, in some cases rather special examples of such complexes, have been reported by Nakazawa and Miyoshi et al (Zr, Hf), [31][32][33] Hey-Hawkins et al (Ti, Zr), 34 Ganter et al (Mn, Ru), [35][36][37] and Saunders et al (Rh). [38][39][40][41] Different substituents at phosphorus render the complexes less symmetric and are expected to affect the chemical and spectroscopic properties of the complexes as well as the energy of activation of an ethene rotation, which has earlier been reported for 2. 27 In order to get a deeper insight into these aspects we prepared the first cyclopentadienylethylphosphane chelates of cobalt, rhodium, iridium, nickel, and chromium with tert-butyl and phenyl or with tert-butyl and cyclohexyl substituents at phosphorus.…”

Fluoroarylphosphines as ligands

“…These reagents are nucleophilic and readily react with electrophilic phosphorus reagents, in particular phosphorus mono-, di-and tri-halides. Typically diethyl ether or THF is used as solvent, and low temperatures P(C 6 F 5 ) 3 y A [1,16] (C 6 F 5 ) 2 PCH 2 P(C 6 F 5 ) 2 (dfppm) y A [17,18] PhP(C 6 F 5 )C 6 H 4 SMe-2 A [6] (C 6 F 5 ) 2 PCH 2 CH 2 P(C 6 F 5 ) 2 (dfppe) y A [19,20] Ph 2 P(h 6 -C 6 F 5 )Cr(h 6 -C 6 H 6 ) A [7,8] (C 6 F 5 )PhPCH 2 CH 2 PPh(C 6 F 5 ) A [21] A [9] (C 6 F 5 ) 2 B [53] are used for reactions involving lithium reagents. A polymersupported halodiphosphine, prepared by treating Merrifield's resin with tert-butylamine and 1,2-bis(dichlorophosphino)ethane, has allowed the synthesis of asymmetrically substituted diphosphines, such as (C 6 H 3 F 2 ) 2 PCH 2 CH 2 PPh-(C 6 H 3 F 2 ), in moderate to high yields (Scheme 2) [65].…”

“…This reaction provides a convenient access to rhodium and iridium complexes of trifunctional h 5 ,kP,kL-cyclopentadienyl-phosphine ligands, and a range of complexes has been prepared in high yield using this method [6,21,42,84,111,134]. The same method has been used to link the h 5 -cyclopentadienyl ligand and monodentate phosphines of [(h 5 -C 5 Me 5 )MCl{R 2 P(C 6 F 5 )}(CNR 0 )] + , affording [(h 5 ,kP-C 5 Me 4 CH 2 C 6 F 4 PR 2 )MCl(CNR 0 )] + , but the yields were lower, reaction times were longer and more by-products were formed [6,84].…”

Cobalt, rhodium and iridium

“…of {Ph(C 6 F 5 )PCH 2 } 2 in the presence of NH 4 (BF 4 ) gave the salt 39 as a mixture of isomers (39a, 39b and 39c). 20 42) rhodium(I) thiolato complexes have been prepared using different phosphine ligands. 22 Single crystal X-ray structures of 42 and 43 have been determined and reveal O-HÁ Á ÁO intermolecular H-bonding through the pendant carboxylic acid groups.…”