Aryl alkyl ketones are among the most important intermediates in chemical industry. The main preparation method, the Friedel-Crafts acylation, is rather limited in substrate scope. The authors disclose herein a simple, efficient and versatile method for the preparation of these compounds starting from aryl and hetero­aryl bromides and aldehydes. The protocol is easy to perform, does not require expensive ligands and allows using highly functionalized substrates.

Ein elegantes Modell: Die Intermediate von Hydrid- und Carbomethoxy-Zyklus sowie des Kettentransfers bei der Carboalkoxylierung von Ethen und der CO-Alken-Copolymerisation wurden für die Reaktion mit einem hochaktiven kationischen Palladium-Diphosphan-Katalysator charakterisiert (siehe Schema). Im Unterschied zu früheren Befunden an Modellsystemen verläuft die Alken-Insertion in PdC(O)OMe- und PdC(O)Me-Bindungen mit vergleichbaren Geschwindigkeiten. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2004/z52369_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Two novel heterometallic octahedral clusters [Rh(4)Pt(2)(CO)(11)(dppm)(2)](1) and [Ru(2)Rh(2)Pt(2)(CO)(12)(dppm)(2)](2) were synthesized by the reaction of [Rh(2)Pt(2)(CO)(6)(dppm)(2)] with [Rh(6)(CO)(14)(NCMe)(2)] and Ru(3)(CO)(12), respectively. Solid state structures of 1 and 2 have been established by a single crystal X-ray diffraction study. Two dppm ligands in 1 are bonded to one platinum and three rhodium atoms, which form an equatorial plane of the Rh(4)Pt(2) octahedron. Two rhodium and two platinum atoms bound to the diphosphine ligands in 2 are nonplanar to give an octahedral C2 symmetric Ru(2)Rh(2)Pt(2)(dppm)2 framework. The (31)P NMR investigation of and (1D, (31)P COSY, (31)P-[(103)Rh] HMQC) and simulation of 1D spectral patterns showed that in both clusters the structures of the M(6)(PP)(2) fragments found in the solid state are maintained in solution.

Alcoholysis of acyl–Pd(II) complexes relevant to palladium catalysed CO/ethene coupling reactions such as polyketone synthesis/alkoxycarbonylation reactions is shown, in a highly active catalyst system, to proceed via coordination of methanol to the Pd centre prior to nucleophilic attack at the acyl carbon.

Multiple‐metal spin transitions which distort the HMQC spectra of rhodium carbonyl clusters are discussed. These effects are seen whenever the detector nucleus, e.g. 13 C or 31 P, couples to more than one metal spin and are not restricted to detector ligands occupying edge‐ or face‐bridging sites. These effects are illustrated in, but not limited to, the 13 C‐{ 103 Rh} and 31 P‐{ 103 Rh} HMQC spectra of [Rh 6 (CO) 15 L], (where L = P(4‐F‐C 6 H 4 ) 3 ), [Rh 4 (CO) 11 {P(OPh) 3 }], [Rh 6 C(CO) 15 ] 2 − and [Rh 2 (carboxylate) 2 PPh 3 ]. The effect is to modulate the intensity and position of the correlations in the metal dimension; cross peaks are displaced from the true chemical shift, additional cross peaks are seen and the intensity of the coherences varies as a function of the preparation delay, d 2 , and coupling constant, and may go to zero at the conventional value of 1/(2 J ). Analyses of the relevant spin systems are given together with experimental strategies to overcome these effects. Copyright © 2004 John Wiley & Sons, Ltd.

The promotional effect of low concentrations of water on the catalytic activity in the Co-catalysed methoxycarbonylation of oct-1-ene to straight and branched chain C-9 methylesters has been demonstrated. Under rigorously anhydrous conditions, only moderate octene conversions are noted. The controlled addition of water leads to enhanced octene conversions, by factors of up to 2.5, ester product selectivity remaining unchanged. Addition of dry pyridine to the anhydrous system results in the known promotional effects on both activity and selectivity towards linear esters. Further addition of water leads to enhanced oct-1-ene conversions, particularly at low pyridine loadings, whilst maintaining the improved product selectivity associated with the presence of pyridine. The role of water, which influences the rate as strongly as pyridine, has been attributed to increasing the effective concentration of HCo(CO)(4), thereby enhancing the hydride mechanistic pathway for methoxycarbonylation. Certain amide/water compositions have also been found to result in significant promotional effects relative to the performance of standard Co-based catalysts. Thus, 4- and 3-amidopyridine (iso-nicotinamide and nicotinamide, respectively) display enhancements in rate and selectivity approaching that of pyridine itself whereas, in total contrast, 2-amidopyridine (picolinamide) acts as an effective poison of both olefin isomerisation and methoxycarbonylation activity. (C) 2003 Elsevier Science B.V. All rights reserved.

The asymmetric copolymerization of styrene with CO catalyzed by Pd−(R,S)-BINAPHOS complexes has been studied using in situ NMR spectroscopy under both diffusion- and reaction-controlled conditions. While a study conducted in a conventional zirconia tube suffered from gas diffusion limitation, use of a high-pressure NMR flow cell allows the observation of potential catalytic intermediates. The formation of Pd−alkyl complexes via 1,2-insertion of styrene into Pd−acyl complexes is confirmed to be the most active catalytic pathway. The 2,1-insertion complexes were found to be quite inactive to further insertion and remarkably stable toward β-hydride elimination, in contrast to our previous expectations.

One of the outstanding problems and challenges in CO activation concerns the lack of a detailed mechanistic understanding of the roles of catalytic promoters used in a number of homogeneously catalysed carbonylation reactions. These problems, and attempts at their resolution, are highlighted with reference to (i) the varied range of promoters that have found use in composite catalysts for the direct synthesis of oxygenates such as ethylene glycol and ethanol from CO/H-2, (ii) the promotional effects of N-bases in the catalytic methoxycarbonylation of alkenes to esters, and (iii) sonic preliminary C-13 NMR spectroscopic evidence which is enabling the definition of a dual role of Ru-promoters as iodide abstraction agents in the Ir-catalysed carbonylation of methanol to ethanoic (acetic) acid. The detection, and characterisation in solution, of an iodide-bridged Ru-Ir dimer is facilitating the development of a plausible, internally consistent model on which to base the catalysis.

All the intermediates involved in the platinum catalysed methoxycarbonylation of ethene have been characterised by in situ NMR; the low activity of platinum catalysts in this reaction is shown to be due to trapping of the active intermediates by carbon monoxide at every step in the catalytic cycle and to the ready reversibility of the product forming reactions.

A detailed spectroscopic study has allowed the solution structure and dynamic properties of all the intermediates in the Pd-catalyzed methoxycarbonylation of ethene to be established. [Pd(L-L)H(solv)](-) 1 (L-L = 1,2-(CH2PBu2t)(2)C6H4; solv = MeOH, 1a; (PrOH)-O-n, 1b; THF, 1c; EtCN, 1d) is static, and the two inequivalent P atoms do not become equivalent through solvent exchange over all the temperatures studied. [Pd(L-L)(CH2CH3)](+), 2, contains a strong beta-agostic C-H interaction which is remarkably stable and is not displaced even in strongly coordinating solvents such as EtCN. C-alpha and C-beta Of the ethyl group in 2 become equivalent via a stereospecific interchange involving [Pd(L-L)H(eta(2)-C2H4)](+) without making the two P atoms equivalent; at higher temperatures these two inequivalent P atoms do become equivalent probably via a T-shaped intermediate. For [Pd(L-L)(C(O)Et)(solv)](+), 6, there is no beta-agostic C-H interaction and multiple C-13-labeling of the C(O)Et group shows that the inequivalent P atoms become equivalent via movement of the intact C(O)Et group. The crystal structure of the related complex [Pd(L-L)(C(O)Et)Cl] cocrystallized with dibenzylacetone has been determined.

A fluorous polymeric phosphine, when combined with supercritical CO2 (scCO2) and rhodium, effects fast and highly chemoselective hydroformylation of acrylates, one of the least reactive olefins in hydroformylation reactions.

The sequence of reaction steps and the role of each reactant, required for the transformation of the Pd(0) precursor [Pd(d(t)bpx)(dba)] [d(t)bpx = 1,2-(CH2PBu2t)(2)C6H4; dba = trans, trans-(PhCH=CH)(2)CO], 1, into [Pd(d(t)bpx)H(MeOH)](+), 2a, the active Pd(II)- hydride catalyst for the methoxycarbonylation of ethene to methylpropanoate, have been delineated using a combination of spectroscopic and crystallographic methods. The preparation and characterisation of a variety of related complexes are described including some unusual examples involving bidentate sulfonate complexes and mono-cationic and neutral palladium hydride complexes. X-Ray crystal structures have been determined for [Pd(d(t)bpx)(eta(2)-O-2)], 3, [Pd(d(t)bpx)(eta(2)-BQ)] (BQ = benzoquinone), 4, [Pd(dcpx)(dbaH)](+) [dcpx = 1,2-(CH2PCy2)(2)C6H4], 7, and [Pd(d(t)bpx)(eta(2)-MeSO3)](+), 9b.

The mechanism of the rhodium-catalyzed hydroformylation reaction using a monodentate phosphorus diamide ligand has been investigated. The system presents an ideal case to illustrate the basics of hydroformylation. A detailed kinetic study and (in situ) spectroscopic techniques revealed that several of the elementary reaction steps are involved in the hydroformylation rate control. Which step is rate-determining depends strongly on the conditions used. Deuterioformylation showed that alkene coordination followed by hydride migration is irreversible under the conditions studied. The rhodium hydride complex HRhL2(CO)(2) and several rhodium-acyl complexes were observed during the hydroformylation reaction. The structures of the rhodium-acyl complexes have been characterized using P-31, C-13, and Rh-103 NMR spectroscopy. The major rhodium-acyl complex formed, RC(O)RhL2(CO)(2), has a trigonal-bipyramidal structure with the two phosphorus ligands coordinated in the equatorial plane. The exchange rates of the equatorial and apical carbonyl ligands with dissolved carbon monoxide differ significantly, the equatorial carbon monoxide being much more labile.

A series of substituted hexarhodium carbonyl clusters [Rh-6(CO)(15)L] (L = PR3 (R = alkyl, aryl), P(OPh)(3), NCMe, I-) has been studied by variable temperature and two-dimensional, X-{Rh-103}, (X = C-13, P-31) HMQC and C-13 EXSY NMR spectroscopy in solution. At low temperatures, the spectra are consistent with retention of the solid state structure. Different localised exchanges of terminal (COt) and face-bridging (COfb) CO's are found to occur over different atoms of the Rh-6-octahedron at higher temperatures and the different pathways of the exchanges are discussed. When L = PR3 (R = alkyl, aryl), the lowest energy scrambling surprisingly involves exchange of COt and COfb, associated with the substituted rhodium ((S) under bar -type), with concomitant exchange of L between the two terminal sites on the substituted rhodium, followed by other localised stereospecific exchanges involving CO's associated with unsubstituted rhodium atoms ((U) under bar -type). For the other substituted clusters (L = P(OPh)(3), NCMe, I-), only (U) under bar -type exchanges are observed. The kinetics of these exchanges are reported at different temperatures and for the (S) under bar -type exchange mechanism, the rate is found to vary with the nature of PR3.

The pathway of the palladium catalysed methoxycarbonylation of ethene to methyl propanoate has been shown to occur via a hydride rather than a methoxycarbonyl cycle and all the intermediates in this cycle have been unambiguously identified by multinuclear NMR spectroscopy and C-13-labelling.

Triple-rhodium quantum effects in the HMQC spectra of [Rh-6(CO)(15)L][L = MeCN, I, PBu3n, P(OPh)(3), P(4-XC6H4)(3); X = H. OMe, F] modulate the intensity and position of the correlations in the rhodium dimension; cross peaks are displaced from the true chemical shift, additional cross peaks are seen, and the intensity of the coherences varies as a function of the mixing time and coupling constant, going to zero at the conventional value of 1/(2J).

Two novel mixed metal rhodium–platinum clusters have been synthesized by the reaction of [Rh4(CO)12] with [Pt(PPh3)3]. The structure of [Rh2Pt3(µ-CO)5(CO)4(PPh3)3] 1 has been established by a single crystal X-ray diffraction study. The tetranuclear cluster [Rh2Pt2(µ-CO)3(CO)4(PPh3)3] 2 has been characterised by FAB mass spectrometry and shown by various multinuclear NMR techniques (13C, 31P, {31P–31P} COSY and {13C–103Rh} and {31P–103Rh} heteronuclear multiple quantum coherence, HMQC) to adopt a butterfly type structure. The carbonyl migration pathways in 2 have been established by a combination of EXSY and 1-D variable temperature measurements; independent localised exchange about the hinge rhodium atoms and interchange of bridging and semi-bridging carbonyls on the Pt–Rh bonds occur.

Solvent-stabilised Pt and Pd nanoparticles, of size range 2.3–2.8 nm and 2.7–3.8 nm, respectively, have been prepared by metal vapour synthesis routes, characterised by transmission electron microscopy (TEM), and their behaviour as catalysts for the enantioselective hydrogenation of ethyl pyruvate (EP) investigated; comparisons have been effected with the performance of standard supported Pt and Pd catalysts. Cinchona alkaloid-modified Pt nanoparticles display parallel behaviour to that exhibited by their conventional supported counterparts both in terms of the sense of the enantioselectivity in the ethyl lactate product and in the acceleration in reaction rate relative to the unmodified system. With Pd, however, significant differences are noted. Here, the sense of the enantioselectivity relative to that reported previously over conventional supported catalysts is reversed, i.e., an (R)- vs. (S)-enantiomer switch occurs, and a rate acceleration rather than retardation is noted on cinchona alkaloid modification. The Pt particle size distribution shows a higher degree of monodispersity after use in catalysis, although the average particle size remains essentially unchanged, whereas the behaviour of the Pd nanoparticles shows evidence of concentration dependence, lower concentrations showing Pt-like behaviour but more highly concentrated preparations showing evidence of significant aggregation during catalysis. With Pt catalysts, the presence of water as a component of the ketonic solvent system is shown to result in a significant acceleration in overall reaction rate with both conventional supported catalysts and their solvent-stabilised counterparts. In sharp contrast, totally aqueous-based colloidal platinum preparations, obtained by conventional salt reduction, display very low reaction rates and enantioselectivities.