Optical Resolution and the Study of Ligand Effects on the Ortho-Metalation Reaction of Resolved (±)-Diphenyl[1-(1-naphthyl)ethyl]phosphine and Its Arsenic Analogue

Abstract

Two highly air-sensitive asymmetric ligands (+/-)-diphenyl[1-(1-naphthyl)ethyl]phosphine and its arsenic analogue [(+/-)-L] have been prepared and resolved by the fractionalization of a pair of diastereomeric palladium complexes containing the appropriate ligand and ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthylene. X-ray structural analysis revealed that the less soluble isomers in each resolution contained the resolving ligand of the S absolute configuration. The resolved ligands coordinated as monodentates with only the phosphorus or arsenic donor coordinated to the resolving organopalladium unit. Due to the steric congestions between the phenyl and the naphthyl rings, the Ph(2)E-C distances in both monodentate ligands are unusually long [1.885(2) A for E = P and 2.035(7) A for E = As]. The (R)-naphthylamine auxiliary could be removed chemoselectively from the resolved complexes by treatment with concentrated hydrochloric acid to give the corresponding bis(micro-chloro) complexes (-)-[(S)-LPdCl(2)](2). Treatments of these dimeric complexes with sodium acetate in ethanol gave the novel ortho-metalated complex bis(micro-chloro)bis[(S)-1-[1-(diphenylphospha)ethyl]naphthylenyl-C(2),P]dipalladium(II), with [alpha](D) +559 degrees (CH(2)Cl(2)), and the analogous ortho-metalated (S)-arsa complex, with [alpha](D) +349 degrees (CH(2)Cl(2)). The Ph(2)E-C distances recorded for the ortho-metalated phosphine complex are 1.841(6) and 1.846(5) A, and those recorded for the organometallic arsa rings are 1.938(9) and 1.945(9) A. These Ph(2)E-C distances are noticeably shorter than those recorded for their analogous monodentate complexes. The intrachelate E-Pd-C angles of the analogous amino, phospha, and arsa complexes involved in the current study are similar [within the range of 80.5(2)-82.1(3) degrees ] although it is noticeable that As > P > N.

Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

“…23 Cyclometalations that are assisted by oxygen, arsenic, and selenium donors are also known, though they are much rarer. 149,150 Chirality has been incorporated, for example through asymmetric ligand synthesis, [426][427][428][429][430] 436 Monomers are also present in solvents like benzene at high temperatures.…”

“…147 In addition, acid-catalyzed ligand exchange via dissociative Pd-C bond cleavage of 23 has been successfully used for synthesizing metallacycles bearing arsenic 149 or selenium as donor sites. The resulting platinum bis(aryl) complex 29 has been structurally analyzed and can thermally be transformed into the final product 27 and the neutral arene 18a, probably mediated by acidolysis of the Pt-C bond of the monodentate ligand.…”

Phosphines and Related Tervalent Phosphorus Systems

“…249 However, a very common strategy in phosphine synthesis continues to be a final stage reduction of phosphine oxides with silane reagents, of which trichlorosilane is the most popular. Among a considerable range of new monophosphines obtained by trichlorosilane reduction, usually in the final step of the synthesis, are the phosphorus core conjugated triaryl-dendrimer unit (111), 250 a range of triarylphosphines bearing branched fluoroalkyl moieties ('split pony tails'), e.g., (112), 251 and a variety of chiral monophosphines, including the phosphinocarboxylic acid (113), 252 phosphinoaryloxathianes, e.g., (114), 253 a series of axially chiral ortho-aminoarylphosphines, e.g., (115) 254,255 and (116), 256 the axially chiral binaphthylphosphine (117), 257 and the chiral arylferrocenylphosphines (118). 258 Trichlorosilane reduction has also been used in the synthesis of phosphino- [6]-and - [7]-helicenes, e.g., (119), which are also chiral systems, 259,260 and a variety of other chiral diphosphines, including the spiro system (120), 261 the C 2 -symmetric cyclobutane system (121), 262 and the tetraphenylene (122).…”

“…107 The reactions of lithiophosphide reagents with alkyl-halides or -tosylates have been used to prepare chelating ligand systems, e.g., the phosphinoalkylpyrazole (52) 108 and the rigid phosphino-amide donor (53). 109 Related reactions of sodio-organophosphide reagents have also given phosphino-amides, e.g., (54), 110 heteroalkynes, e.g., (55), 111 the chiral naphthyl-(ethyl)phosphine (56), 112 and (3-dimethylphosphino)propanethiol. 113 The secondary phosphine (57), obtained by treatment of a carbonyl-protected bromoalkyl derivative of camphor with lithium phenylphosphide, undergoes a proton-catalysed hydrolysis, followed by a stereoselective, base-catalysed addition of P-H to the carbonyl group to give the phospholane (58).…”

New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

“…Two main approaches to enantiomerically pure palladacycles are commonly used: (i) synthesis from optically active ligands (commercially available, 1-8 pre-resolved [9][10][11][12][13] or prepared by asymmetric synthesis 14 ); and (ii) resolution of racemic cyclopalladated compounds by recrystallization [15][16][17][18][19][20][21][22][23][24][25][26][27][28] or chromatographic separation [29][30][31][32][33] of their diastereomeric derivatives. The third method based on the asymmetric activation of the C-H bond under control of an optically active base [34][35][36][37][38][39] or ligand in the palladation agent [40][41][42] is not so popular and used mainly for prochiral substrates.…”