Rhodium-catalysed reactions phosphine complexes

Miscellaneous. - Several new optically active tervalent phosphorus acid derivatives have been prepared for use as ligands in asymmetric metal catalysed reactions. These include the cyclic diaminophosphines 57, the cyclic bisamino-phosphine 58, and the compounds 59, 60, 61, and 62 containing a 1,1 -binaphthalene group as the chiral inducer. A new diphosphoramidite (63) has been used for improved regioselectivity of rhodium-catalysed hydroformylations of alkenes. A new sterically hindered chiral phosphite (64) derived from glucose and a Cu(I) complex of 64 have been prepared. ... 

Recent research has shown that this mechanism does not hold for all catalyst and substrate combinations. For instance, the rhodium-catalysed hydrogenation with electron-rich bidentate phosphine (2.11) is thought to proceed via initial oxidative addition of hydrogen to a catalyst-substrate complex. Furthermore, enantioselectivity arises from reaction of the major catalyst-ligand complex, in a lock-and-key process, when using monodentate phosphites as ligands. 

Fig. 12.17 Possible reaction mechanism (associative) for hydroformylation catalysed by rhodium carbonyl phosphine complexes. L = Ph3P. Formation of n (unbranched) product only shown. 16fi complexes square planar, 18e probably trigonal bipyramidal.

The formal 2 -I- 2-cycloaddition reaction of platinum(ll) acetilides (14) with TCNE and TCNQ initially produced 7,7,8,8-tetracyano-p-quinodimethane cyclobuta-1, 3-dienes that undergo retroelectrocyclization to produce feis-cycloadducts (15, 16). In all examples investigated, the triple bond adjacent to the platinum atom did not react with the TCNE or the TCNQ (Scheme 5). The 2-I-2-cycloaddition of substituted cyclobutadiene-AlCl3 complexes (18) with methyl phenylpropynoate (17) produced Dewar benzene intermediates (19) that readily converted to 1,2,3,4-tetramethyl- and 1,2,3,4-tetraethyl-fluorenes (20) (Scheme 6). The first rhodium-catalysed inter-molecular 2-1-2-cycloaddition of terminal alkynes with e-deflcient alkenes yielded substituted cyclobutenes in high yields (99%) and complete regioselectivity. An 8-quinolinolatorhodium/phosphine catalyst (21) was employed in this reaction. ... 

Low-oxidation-state phosphine complexes, particularly of rhodium and of iridium, catalyse the oxidation of cyclohexene, by an autocatalytic free-radical mechanism. The isolation of [IrCl(C2H4)(02)(PPh3)a],CeHe is claimed to furnish the first model intermediate for homogeneous oxidation of alkenes. The reactions of iridium(i) complexes with molecular oxygen are related to this topic of homogeneous oxidation these reactions are dealt with in the chapter on oxidative addition (Chapter 6 of Part IV). 

Hydroformylation of PhCH=CHMe in the presence of RhCl(PPh3)3 produces PhCH(CHO)-CHa-CH3 and PhCH3-CH(CHO)-CH3, as well as some PhCH2 CH2 CH3. Both Rh4(CO)i2 and mixed carbonyl-phosphine complexes derived from Rh4(CO)i2 and from Rh,(CO)ie are active catalysts for hydroformylation of alkenes. Acyl-rhodium intermediates may be important when Rh4(COX2 is the catalyst, for [Rh-(C0)2(02CR)]2 dimers have been isolated from alkene hydroformylations in which this polynuclear carbonyl has been the catalyst. Rh4(CO)i2 also catalyses the reaction between ethylene and carbon monoxide, which produces several products, including octane-3,6-dione, undecane-3,6,9-trione, and tetradecane-3,6,9,12-tetraone. The products obtained indicate a mechanism in which addition of ethylene to rhodium and insertion of carbon monoxide into a rhodium-carbon bond alternate. ... 

The carbonylation of nitrobenzene to phenyl isocyanate is catalysed by [RhCl(CO)2]2 + L (L=MoCl6 or py.H+Cl- >), [RhH(CO)(PPh3)3], = and PdCl2-pyMe+ Carbonylation of allylic substrates has also been studied in detail rhodium phosphine complexes [e.g., RhCl(PPh3)s] are particularly useful for the synthesis of AT-alkyl-2-pyrrolidones [reactions (6)], whereas the carbonylations of allylic alcohols to vinylacetate esters [reaction (7)] are best carried out with [PdCl2(PAr3)a]10MCl2 (M=Sn or Ge). ... 

Hydroformylation of formaldehyde to give glycolaldehyde is an attractive route from syn-gas toward ethylene glycol. The reaction is catalysed by rhodium arylphosphine complexes [39] but clearly phosphine decomposition is... 

Cationic rhodium complexes catalyse the oxidative anti-Markovnikov amination of aromatic alkenes to enamines, a process that is accompanied by a simultaneous formation of 1 equiv. of ethylbenzene. Kinetic and mechanistic studies reveal that the yield and the rate of the reaction increase on increasing the styrene amine ratio. Furthermore, the type of phosphine ligand greatly influences the reaction. The formation of cationic rhodium-alkene-amine complexes has been proposed to be the first step towards the active catalytic species. ... 

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