Flexible Coordination of Diphosphine Ligands Leading to cis and trans Pd(0), Pd(II), and Rh(I) Complexes

Abstract

A series of diphosphine ligands (i)Pr2P-C6H4-X-C6H4-P(i)Pr2 (for ligand L(1), X = CH2; for ligand L(2), X = CH2CH2) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium(II), and rhodium(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium(II) complexes, with L(1) coordinating preferentially cis, while L(2) coordinates in a trans fashion. Coordination to Pd(0) leads to L(1)Pd(dba) and L(2)Pd(dba), in which both ligands accommodate a P-M-P angle close to 120°. L(2) was found to coordinate cis in a rhodium(I) complex ([L(2)Rh(nbd)][BF4], where nbd = norbornadiene).

Palladium carbene complexes as persistent radicals

“…Compound [PC(sp 3 )HP]PdCl ( 10 ) was previously reported. 10 a Compound [PC(sp 3 )HP]PdBr ( 4 ) was synthesized using a method analogous to that used for the synthesis of [PC(sp 3 )HP]PdCl: [PC(sp 3 )H 2 P]PdBr 2 ( 12 ) could be isolated by reacting PC(sp 3 )H 2 P ( 13 ) with (COD)PdBr 2 at ambient temperature 21 in 91% yield. This complex undergoes dehydrohalogenation through ligand C–H activation by heating it at 100 °C in toluene to generate [PC(sp 3 )HP]PdBr ( 4 ) in high yield (83%).…”

Metal-ligand cooperation between palladium and a diphosphine ligand with an olefinic backbone

“…Our group has previously synthesized a monomeric trigonal planar palladium(0) species with the wide bite angle ligand i Pr 2 P(o-C 6 H 4 -CH 2 CH 2 -o'-C 6 H 4 )P i Pr 2, L 2 . 38 The metal center is bound to an olefin of a dba ligand, as well as to the two phosphine donors on L 2 . The non-tethered olefin in that situation allows for a more optimal trigonal planar geometry of the metal center (P-Pd-P = 117.117( 17)).…”

“…The non-tethered olefin in that situation allows for a more optimal trigonal planar geometry of the metal center (P-Pd-P = 117.117( 17)). 38 Examples of ligands containing two phosphines and a  system donor in the same ligand framework were reported. 39,40 Agapie and coworkers described a tris(phosphine) triphenyl benzene ligand that supports a palladium(0) metal center.…”

Heterobimetallic Pd–K carbene complexes via one-electron reductions of palladium radical carbenes

“… 50 , 51 We have recently applied dehydrohalogenation reactions 60 to synthesize Pd( ii ) carbene complexes, [{PC(sp 2 )P} R Pd(PMe 3 )] (R = H, [PC(sp 2 )P] H = bis[2-(di-iso-propylphosphino)phenyl]methylene); R = t Bu, ([PC(sp 2 )P] t Bu = bis[2-(di-iso-propylphosphino)-4- tert -butylphenyl]methylene). 61 – 63 Interestingly, the Pd–C carbene bonds in these compounds are best described as ylide-like ( Chart 1 , type B), as demonstrated by their strong nucleophilic reactivity toward polar substrates (MeI, HCl, MeOH, para -toluidine), 61 strong Lewis acids, 62 C–H 64 and Si–H 65 bond activation reactions. Furthermore, our recent study on the redox-induced umpolung of palladium carbenes revealed that the radical carbene [{PC˙(sp 2 )P} t Bu PdI] ( 1 , Chart 1 , type C) bridges cationic and anionic carbenes via reversible one-electron transfer processes.…”