Asymmetric homogeneous hydrogenation of olefins catalyzed by alkylphosphine complexes of rhodium(I)

Abstract

The cationic rhodium(I) complexes of the optically active ferrocenes, C5H5FeC5H3[CH(CH3)N(CH3)2][ER2]-1,2, catalyze the asymmetric hydrogenation of acetamidoacrylic acid derivatives, itaconic acid and styrene, when ER2 is P(C6H5)2 or P(C(CH3)3)2. The configuration of the product is reversed on substituting C6H5 for C(CH3)3 groups. The catalyst with the tert-butyl groups can afford higher optical yields and is faster overall. The rhodium(I) complexes of the arsenic derivatives ER2 = As(C6H5)2 or As(CH3)2 do not catalyze the hydrogenation reactions. The nmr spectrum of the arsenic complex (ER2 = As(C6H5)2) is temperature dependent which seems to be due to a process involving the making and breaking of the Rh—N bond. The unsuccessful use of the MEM group (β-methoxyethoxymethyl) to protect an alcohol function α to a ferrocene ring is described. The hydrogenation results are discussed in the light of models which are currently used to predict the results of rhodium(I) catalyzed reactions but which are inapplicable to this work.

A kinetic study of the hydrogenation of hexene-1 catalyzed by a ferrocenyl-phosphine derivative of ruthenium(II)

“…Such monohydride catalysts are usually quite active for isomerization via the usual metal hydride addition -elimination sequence involving a metal alkyl intermediate (1,35). Presumably, reduction to the ruthenium(1) state involves hydride formation (eq.…”

“…Apparent reduction to ruthenium (1) complicates the probing of heterolytic cleavage of H2 by Ru(II), while the catalytic hydrogenation system discovered seems inactive, at least under mild conditions, for hydrogenation of the prochiral amino acid precursors, although this may be due to strong chelation to the RuCI,(PPIij)(PPFA) cornplex. Nevertheless, catalytic hydrogenation via the relatively rare ruthenium(1) state is strongly indicated, and further efforts are in hand to isolate the active complex.…”

“…One unsolved problem with catalysis at rutheniuni(I1) centres is the accessibility of the Ru(IV) oxidation state; for example, does reaction [I], a net heterolytic cleavage of HI, involve oxidative addition to give a RuiVH2 intermediate followed by reductive elimination of HCI, or a transition state in which coordinated chloride stabilizes the released proton (1, 5)? Activation parameter data for several ruthenium(I1) systems provide indirect support for a rate-determining oxidative addition (1).…”

The synthesis and structure of

“…We also have an interest in exploring the electrochemistry of chiral surfaces (7,8). For these reasons the synthesis of l c , which contains both a chiral center and planar chirality, and its binding to silica, was an attractive target since, if necessary, it could readily be prepared as an optically pure enantiomer (9,10).…”

The synthesis of primary, secondary, and tertiary ferrocenylethylamines

“…The synthesis of these derivatives was conveniently achieved from 3 by the stepwise reaction with HBr and NH, (eq. [4] For personal use only.…”