Rhodium(i) complexes of unsymmetrical diphosphines: efficient and stable methanol carbonylation catalysts

Abstract

Rhodium complexes of unsymmetrical diphosphines of the type Ph 2 PCH 2 CH 2 PAr 2 are catalysts for the carbonylation of methanol; several features of the catalysis are reminiscent of iridium carbonylation catalysts.

Square‐Planar Carbonylchlororhodium(I) Complexes Containing trans‐Spanning Diphosphine Ligands as Catalysts for the Carbonylation of Methanol

“…All complexes displayed a characteristic s in the 1 H-NMR spectrum (CDCl 3 ) at d ca. 8.5 for the amide protons and a strong n Ä(CO) absorption around 1950 cm À1 in the IR spectrum, comparable with the n Ä(CO) reported for other trans-[Rh(PR 3 ) 2 (CO)X] complexes [7] [23] but significantly lower than that of cis-[Rh(dppe)(CO)I] (dppe ethane-1,2-diylbis[diphenylphosphine] [11]. A medium-to-strong absorption at ca.…”

“…Complexes containing P,P-linked bis[phosphine] ligands have also been studied as catalysts for the carbonylation of MeOH [10] [11], they are in general more stable than their complexes containing unlinked bis(monophosphine) analogues. However, since complexes containing P,P-linked bis[phosphines] are usually cis-configured, they are less active than the trans-configured bis(monophosphine) complexes [11]. The stability of such Rh-complexes employed as catalysts under the harsh carbonylation conditions is a crucial point.…”

Fluoroarylphosphines as ligands

“…(Ph 2 PCH 2 CH 2 P(C 6 H 4 F-3) 2 has also been synthesized by addition of [C 6 H 4 F] À to Ph 2 PCH 2 CH 2 PCl 2 [49]. )…”

“…A number of rhodium complexes formed in situ from [Rh(mCl)(CO) 2 ] 2 and analogues of dppe, including the fluorophenyl-substituted phosphines Ph 2 PCH 2 CH 2 P(ArF) 2 (ArF = C 6 H 4 F-3, C 6 H 3 F 2 -3,5 and C 6 H 3 F 2 -3,4,5) and (C 6 H 4 F-3) 2 PCH 2 CH 2 P(C 6 H 4 F-3) 2 , have been assessed as catalysts for methanol carbonylation [49]. All showed good activity, although not approaching that of [RhI 2 (CO) 2 ] À , and the selectivity for acetic acid was >99%, with lower formation of propionic acid than with [RhI 2 (CO) 2 ] À .…”

Metal(II) template assisted syntheses of two P―C―O―P chelating ligands incorporating a bulky 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantyl cage

“…Ph 2 P(CH 2 ) 2 PPh 2 (often abbreviated dppe) are an important class of ligand playing a major role in coordination chemistry and catalysis. While symmetric diphosphines are readily synthesised or indeed commercially available, their nonsymmetric counterparts are often somewhat more challenging to prepare [1,2]. We [3] recently described the synthesis and reactivity of Ad`P(CH 2 ) 2 PPh 2 1, a bulky analogue of dppe by virtue of the 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantyl cage (Ad`).…”