Intramolecular Dehydrofluorinative Coupling of η⁵-Pentamethylcyclopentadienyl and Pentafluorophenylphosphine Ligands in Rhodium Complexes

Abstract

The rhodium(III) complex [Cp*RhCl(dfppe)]BF4, 1, undergoes rapid stepwise intramolecular dehydrofluorinative carbon−carbon coupling on addition of proton sponge to produce [{η5,κP,κP-C5Me3[CH2C6F4-2-P(C6F5)CH2]2-1,3}RhCl]BF4. The reaction requires less than the stoichiometric quantity of proton sponge and also occurs on addition of Bu n 4NF or in the presence of polymer-supported fluoride. NMR studies of reactions between a series of complexes and proton sponge have revealed the necessary conditions for intramolecular dehydrofluorinative coupling in pentamethylcyclopentadienyl rhodium(III) phosphine complexes. The complex must be cationic, and the phosphine, which can be either part of a chelating ligand or monodentate need have only one pentafluorophenyl substituent. The reaction is rapid where Cp* and C6F5 are held in close proximity. The compounds [Cp*RhCl{(C6F5)2PC6H4SMe-2}]BF4, 7, and the diastereoisomer of [Cp*RhCl{(C6F5)PhPC6H4SMe-2}]BF4, 11a, in which Cp* and C6F5 are cis, undergo rapid coupling on treatment with proton sponge. The diastereoisomer of [Cp*RhCl{(C6F5)PhPC6H4SMe-2}]BF4, in which Cp* and C6F5 are trans, undergoes isomerization to 11a at a much slower rate than that of coupling. Cationic complexes of monodentate phosphines, in which there is rotation about the Rh−P bond, undergo coupling on addition of proton sponge, but at a much slower rate than for 1, 7, and 11a. The structures of [{η5,κP,κP-C5Me4CH2C6F4-2-P(C6F5)CH2CH2P(C6F5)2}RhCl]BF4, [{η5,κP,κS-C5Me4CH2C6F4P(C6F5)C6H4SMe}RhCl]BF4, and [Cp*RhCl2{PEt2(C6F5)}] have been determined by single-crystal X-ray diffraction.

Synthesis of Piano Stool Complexes Employing the Pentafluorophenyl-Substituted Diphosphine (C6F5)2PCH2P(C6F5)2and the Effect of Phosphine Modifiers on Hydrogen Transfer Catalysis

“…The Rh-P distance and Cp † -Rh-P angle are consistent with those of rhodium complexes in which a cyclopentadienyl ring is linked to a phosphine by a tetrafluorobenzyl or similar group. 30,32,50 The Cp † -Rh-P and Cp † -Rh-Cl angles are smaller than those of 5, and the P-Rh-Cl and Cl-Rh-Cl angles are close to 90°. Significantly the Rh-P distance is 0.1 Å shorter than that of 5 and the P-C-P angle is identical to that of 2.…”

Catalysis and Organometallic Chemistry of Monometallic Species

“…217 Several examples of C-F activation have been reported including dihydrogen induced conversion of an iridium() coordinated CF 3 to CO, 218 conversion of hexafluoropropene to 1,1,1-trifluoropropane, 219 diastereoselective C-F bond activation of iridium perflouroalkyl methyl complexes coupled with C-C bond formation, 220 formation of rhodium() and iridium() η 2 -flourobenzyne complexes such as 24, 221 and intramolecular dehydrofluorinative coupling of Cp* and pentafluorophenylphosphine ligands in rhodium() complexes. 222 Complexes containing group 9 metals in unusual oxidation states include a rare example of a rhodium() complex 25, 223 an ESR study of cobalt(0), rhodium(0) and iridium(0) complexes of tropylidene phosphines 224 Several N-heterocyclic carbene complexes and their chemistry have been investigated. Chelating bis(carbene) pyridine complexes of rhodium() catalyse the hydrogenation of imines 226 and iridium() complexes the transfer hydrogenation of ketones.…”

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].…”

“…Access to ligands of this type had previously been problematic, involving elaborate, multiple step, low-yielding syntheses [5]. Rhodium and iridium complexes of bidentate g 5 ,jP-cyclopentadienyl-phosphine (Cp-P) ligands can also be prepared using intramolecular dehydrofluorinative coupling from monodentate polyfluoroaryl-substituted phosphine ligands, but the reaction times are longer, the yields are lower and it has proved difficult to obtain the products pure [1,3].…”

“…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.…”