Interplay of bite angle and cone angle effects. A comparison between o-C6H4(CH2PR2)(PR2 ') and o-C6H4(CH2PR2)(CH2PR2 ') as ligands for Pd-catalysed ethene hydromethoxycarbonylation

Tamara Fanjul Solares, Graham Eastham, Joelle Floure, Sebastian J. K. Forrest, Mairi F. Haddow, Alex Hamilton, Paul G. Pringle*, A. Guy Orpen, Mark Waugh

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

18 Citations (Scopus)

Abstract

The following unsymmetrical diphosphines have been prepared: o-C6H4((CH2PBu2)-Bu-t)(PR2) where R = (PBu2)-Bu-t (L-3a); PCg (L-3b); PPh2 (L-3c); P(o-C6H4CH3)(2) (L-3d); P(o-C6H4OCH3)(2) (L-3e) and o-C6H4(CH(2)PCg)(PCg) (L-3f) where PCg is 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl. Hydromethoxycarbonylation of ethene under commercially relevant conditions has been investigated in the presence of Pd complexes of each of the ligands L3a-f and the results compared with those obtained with the commercially used o-C6H4((CH2PBu2)-Bu-t)(2) (L-1a). The Pd complexes of the bulkiest ligands L-3a, L-3b and L-3f are highly active catalysts but the Pd complexes of L-3c, L-3d and L-3e are completely inactive. The crystal structures of the complexes [PtCl2(L-1a)] (1a) and [PtCl2(L-3a)] (2a) have been determined and show that the crystallographic bite angles and cone angles are greater for L-1a than L-3a. Solution NMR studies show that the seven-membered chelate in 1a is more rigid than the six-membered chelate in 2a. Treatment of [PtCl(CH3)(cod)] with L3a-f gave [PtCl(CH3)(L3a-f)] as mixtures of 2 isomers 3a-f and 4a-f. The ratio of the products 4 : 3 ranges from 100 : 1 to 1 : 20, the precise proportion is apparently governed by a balance of two competing factors, steric bulk and the antisymbiotic effect. The palladium complexes [PdCl(CH3)(L-3b)] (5b/6b) and [PdCl(CH3)(L-3c)] (5c/6c) react with labelled (CO)-C-13 to give the corresponding acyl species [PdCl((COCH3)-C-13) (L-3b)] (7b/8b) and [PdCl((COCH3)-C-13)(L-3c)] (7c/8c). Treatment of [PdCl((COCH3)-C-13)(L)] with MeOH gave CH3 (COOMe)-C-13 rapidly when L = L-3b but very slowly when L = L-3c paralleling the contrasting catalytic activity of the Pd complexes of these two ligands.

Original languageEnglish
Pages (from-to)100-115
Number of pages16
JournalDalton Transactions
Volume42
Issue number1
DOIs
Publication statusPublished - 2013

Keywords

  • METHANOLYSIS
  • CARBONYLATION
  • DIPHOSPHINES
  • METHOXYCARBONYLATION
  • HYDROFORMYLATION
  • REACTIVITY
  • CARBON-MONOXIDE
  • ALTERNATING COPOLYMERIZATION
  • METHYL PROPANOATE
  • PALLADIUM(II) COMPLEXES

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