Synthesis and Complexation Properties of Allenic Bipyridines, a New Class of Axially Chiral Ligands for Transition Metal Catalysis

Abstract

The allenic bipyridines 3, which represent a new class of axially chiral ligands for transition metal catalysis, were synthesized and their complexation properties were studied. The synthesis was achieved by copper-mediated or palladiumcatalyzed S N 2Ј-substitution of the tertiary propargyl acetates 2. The allenic bipyridines form 1:1 complexes with Cu + and Ag + ions that were characterized by electrospray mass spec-

Synthesis of Allenes Bearing Phosphine Oxide Groups and Investigation of Their Reactivity toward Gold Complexes

“…[1a,b,11] Alternatively,w ea lso used the Pd(0)c oupling reaction between az incr eagent and propargyl acetate 2 to obtain 8 and 9,a sw ella sp yridyl allenes 10a and 10b from acetates 4a and 4b. [3] It should be noted that 10a could also be prepared in slightly better yield (41%), based on the addition of PyZnBr to 2.…”

“…[1] When substituted by Lewis base substituents,t he allenea ssembly can serve as al igand, [2] possibly conveying axial chirality.I llustration of this principle wasi nitially providedi n2 008 by Krause,w ho reported the preparation of allenic bipyridines I and the corresponding silver andc opper complexes. [3] In 2009, Ready developed chiral phosphine oxide allenes II as versatile organocatalysts for the asymmetric ringo pening of meso-epoxides. [4] The same group then furthera dapted the parent structure II to append phosphineg roups bearing CF 3 electronwithdrawing groups in place of the phosphineo xide ones.T he resulting ligand could coordinate to Rh(I), featuring coordination to the allene moiety, and provide complex III,w hich proved to be ah ighly efficient catalyst for the enantioselective arylation of aketo esters( Scheme 1).…”

Bis-phosphine allene ligand: coordination chemistry and preliminary applications in catalysis

“…20 The evaluation of the electronic properties of allene 1 was achieved by measuring the magnitude of 1 J P-Se for the 77 Se isotopomer 21 of the corresponding bis-selenide derivative 2 (Scheme 2). With a 1 J P-Se value of 754 Hz, allene 1 exhibits an intermediate s-donor ability, lower than that of PPh 3 ( 1 J P-Se = 728 Hz) but much higher than that of P(PhO) 3 ( 1 J P-Se = 1027 Hz). 22 We then evaluated the catalytic activity of gold complex rac-7 using the prototypical N-tethered 1,6-enyne precursor 8a.…”

“…Krause reported the formation of silver and copper complexes from allene-containing bipyridine ligands, but no catalytic activity was reported. 3 Chiral diphosphine oxide allenes were first used as organocatalysts by Ready who described the highly enantioselective formation of chlorohydrins from meso-epoxides with SiCl 4 . 4 Later, the same group devised chiral allene-containing bisphosphines that, when coordinated to Rh(I), were able to promote the asymmetric addition of arylboronic acids to a-keto esters with high enantioselectivity.…”

Chiral Allene-Containing Phosphines in Asymmetric Catalysis

“…9 In pioneering work, Krause and coworkers reported allene-containing ligands for silver, but catalysis, asymmetric or otherwise, was not reported. 10 Our own efforts in this area led to the invention of bisphosphine oxide 6 , which promotes the addition of SiCl 4 to meso -epoxides with high enantioselectivity. 11 We report here a new class of phosphine-containing allenes that serve as ligands for transition metals and enable asymmetric catalysis with rhodium.…”