Reactions of Cyclopalladated Complexes with Lithium Diphenylphosphide

Abstract

Reactions of the cyclopalladated dimer {Pd(η2-L1)(μ-Cl)}2 (7) derived from N,N-dimethylbenzylamine (HL1) with lithium diphenylphosphide were studied under varied conditions. The LiPPh2 reagents used were purchased from Sigma-Aldrich Co. or synthesized from PPh3, ClPPh2, or HPPh2 by known general methods. Depending on the source of lithium phosphide, solvent, and reagent ratio, reactions of LiPPh2 with complex 7 resulted in the formation of different products. The commercial LiPPh2 solutions reacted with compound 7 and several other cyclopalladated dimeric complexes in THF to form the corresponding mononuclear derivatives with Ph2P(CH2)4OH as an auxiliary ligand, Pd(η2-L)Cl{PPh2(CH2)4OH}. The monophosphido-bridged analogue of dimer 7, {Pd(η2-L1)}2(μ-Cl)(μ-PPh2) (17), was the most common product of the 1:2 reactions of dimer 7 with other LiPPh2 solutions in THF. ortho-(Diphenylphosphino)-N,N-dimethylbenzylamine (20) was obtained in the reactions of complex 7 with the synthesized solutions of LiPPh2 using a 1:4.5 molar ratio of the reagents in THF or a 1:2 ratio in toluene. Possible mechanisms of these reactions are discussed.

Reactivity of dimeric cyclopalladated complexes with an (sp)C–Pd bond toward KPPh2

“…The isolation of free preligands was previously reported in KPPh 2 reactions with CPCs containing an (sp 2 )CePd bond [13] as well as in the Pd-catalyzed phosphination reactions of aryl triflates with PPh 3 [26]. The formation of such products can be explained by b-hydride elimination of the alkoxide-containing Pd(II) intermediate, which could be formed after the adventitious cleavage of a CeO bond in THF by the phosphide [11,13].…”

“…Previously, we showed that both LiPPh 2 and KPPh 2 are capable of reacting with dimeric chloro-bridged CPCs [11,12]. However, the outcome of the LiPPh 2 reactions with CPCs was highly sensitive to the phosphide structure in the solution, which in turn, depended on the preparation method, concentration and age of the chemical.…”

“…The 31 P{ 1 H} NMR chemical shift of 123.2 ppm has been reported for complexes with the PAr 2 group as a terminal ligand bonded to Pd(II) [16] (cf. the chemical shift of À7.8 ppm for the terminal PPh 2 ligand bonded to Pt [17]), while the chemical shifts in a range of 20e35 ppm are typical for tertiary phosphines bonded to Pd(II) as terminal ligands [11,18]. The value of the coupling constant suggests [18e20] that there are two phosphorus atoms in complex 5a that are cis to each other.…”

Reactions of m-chloroperoxybenzoic acid with dimeric cyclopalladated complexes derived from 2-phenyl-2-oxazolines

“…Reactions at the C-Pd bond of cyclopalladated complexes (CPCs) [1][2][3][4][5] (e.g., phosphination [6][7][8][9][10], chlorination [11][12][13][14], iodination [15][16][17][18][19], bromination [15,16], acetoxylation [20][21][22][23][24][25] and other transformations [15,[26][27][28][29][30][31]) represent an attractive method for highly regioselective functionalization of organic compounds. These Pd-mediated transformations are gaining importance as a synthetic method, providing access to new organic and organometallic compounds not readily available by other methods.…”

Pyridine‐Directed Palladium‐Catalyzed Phosphonation of C(sp2)H Bonds

“…[1,2] Although a wide variety of transition-metalcatalyzed reactions for functionalizing CÀH bonds are currently available, examples of carbon-phosphorus bond formation are significantly limited, presumably owing to the strong coordinating character of phosphorus reagents. [3,4] Existence of an excess amount of coordinative phosphorus over metal in a reaction media would hamper a process to activate less coordinative CÀH bonds. Very recently, Yu and co-workers reported a pyridine-directed CÀH phosphonation reaction catalyzed by palladium, in which H-phosphonates were directly used.…”