Keywords: Palladium / Platinum / N,P ligands / Ligand design 1,2-Bis-N-[2Ј-(diphenylphosphanyl)benzoyl]diaminobenzene (dppbH; 1) was prepared by peptidic coupling and shown to exist, in the solid state, in the form of hydrogenbonded dimers by single-crystal X-ray structure analysis. As expected, 1 reacts with [MCl 2 (cod)] (M = Pd, Pt; cod = cyclooctadiene) to form square-planar complexes. However, in the case of palladium [PdCl 2 (dppbH)] (2) is obtained, while in the case of platinum [Pt(dppb)] (3) is formed. Thus, the nature of the metal induces a completely different coordination mode: In 2, the dppbH ligand only coordinates through the

Dedicated to Professor Andre Merbach on the occasion of this 65th birthdayThe rhodium(I) complexes trans-[Rh(diphos)(CO)Cl] 7 (diphos pbpb), 8 (diphos nbpb), and 9 (diphos cbpb) were synthesized (Scheme 4) and used as catalysts for the carbonylation of MeOH to AcOH (Scheme 1). The trans coordination imposed by the rigid C-spacer framework of the diphos ligands pbpb, nbpb, and cbpb, demonstrated by 31 P-NMR and IR spectroscopy of 7 ± 9 and unambiguously confirmed by singlecrystal X-ray structure analysis of 7, improved the thermal stability of the rhodium(I) system under carbonylation conditions and, hence, the catalytic performance of the complexes. For the catalytic carbonylation of MeOH, the active catalyst could be prepared in situ from the mixture of [Rh(CO) 2 Cl] 2 and the corresponding diphos ligand pbpb, nbpb, or cbpb, giving the same results as carbonylation in the presence of the isolated complexes 7, 8 or 9 (see Table). The highest activity was observed for complex 7 (or the mixture [Rh(CO) 2 Cl] 2 / pbpb, the catalytic turnover number (TON) being 950 after 15 min (1708, 22 bar). The anion cis-[Rh(CO) 2 I 2 ] À was found to be the initial catalytically active species [3]. As the rate-determining step of the catalytic cycle is the oxidative addition of MeI to cis-[Rh(CO) 2 I 2 ] À [4], electron enrichment at the metal center is expected to facilitate this step and to improve the rate of AcOH formation. Consequently, square-planar rhodium(I) complexes with ligands that increase the electron density at the Rh-atom have been developed and studied as catalysts; they give better or at least comparable activities than the original Monsanto catalyst [5 ± 8]. Introduction. ± The carbonylation of MeOH to generate AcOH is one of the most important homogeneously catalyzed industrial processes [1] (Scheme 1). The production of AcOH by the

Two equivalents of 2-diphenylphosphinobenzoic acid react with 1,2-ethanedithiol and 1,8-diaminonaphthalene under peptidic coupling conditions to give the new ligands 1,2-bis-S-[2 0 -(diphenylphosphino)benzoyl]dithioethane (dppte) (1) and 1,2-bis-N-[2 0 -(diphenylphosphino)benzoyl]diaminonaphthalene (dppan) (2), respectively. 1 and 2 have been characterised by mass spectrometry, elemental analysis, NMR, IR spectroscopy, and by single-crystal X-ray structure analysis. 2 is easily oxidised by air to give the monophosphine oxide derivatives (3). Single-crystal X-ray structure analysis of 3 shows an intramolecular hydrogen bond between an amido and the phosphoryl oxygen atom. Compounds 1 and 2 react with [RuCl 2 (g 6 -p-cymene)] 2 to give the dinuclear complexes [RuCl(g 6 -p-cymene)(dppte)RuCl(g 6 -p-cymene)] 2þ (4) and [RuCl(g 6 -p-cymene)(dppan)RuCl(g 6 -p-cymene)] 2þ (5). As determined by single-crystal X-ray structure analysis, 4 and 5 adopt different coordination modes to the ruthenium atoms. In 4 the symmetric dppte ligand is P ; S coordinated to the ruthenium atom, whereas in 5 the dppan ligand prefers a P ; O coordination mode.

Key indicatorsSingle-crystal X-ray study T = 153 K Mean '(O±C) = 0.013 A Ê R factor = 0.053 wR factor = 0.141 Data-to-parameter ratio = 18.0 For details of how these key indicators were automatically derived from the article, see