Coordination Chemistry of Cyclopropenylidene‐Stabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes

Abstract

A straightforward synthesis of cyclopropenylidene-stabilized phosphenium cations 1 a–g through the reaction of [(iPr₂N)₂C₃⁺Cl]BF₄ with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L₂](BF₄)₂ and electrochemical methods. The cyclopropenium ring induces a phosphite-type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a–g still act as two-electron donor ligands, forming adducts with Pd^II and Pt^II precursors. Conversely, in the presence of Pd⁰ species, an oxidative insertion of the Pd atom into the C_carbene–phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt^II complexes was tested; all of the cationic phosphines accelerated the prototype 6-endo-dig cyclization of 2-ethynyl-1,1′-biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A

Main Avenues in Gold Coordination Chemistry

“…This idea was based on their previous work with an only one cationic phosphine ancillary ligand (Scheme ), by means of the synthesis of cyclo­propenylylidene stabilized phosphenium adducts. In all cases, the practical efficiency of the corresponding gold complexes bearing these ligands was demonstrated in several mechanistically different transformations, , and the authors even extended this idea to other metal complexes. − Their catalytic activity has been tested in different reactions such as in hydroarylation reactions or in the naphthofurane synthesis, among others …”

α-Cationic Arsines: Synthesis, Structure, Reactivity, and Applications

“…The products were convincingly characterized to confirm the structure and purity, and these data compare well to the reported values. [10][11][12] A high quality, low temperature X-ray diffraction study was also performed on a sample of 18 grown from a CH 2 472,571,693,727,999,1024,1077,1158,1183,1305,1434,1482,150,1955 455,473,485,522,563,574,696,743,752,776,789,848,928,997,1031,1048,1230,1383,1439,1478,1606 458, 469, 521, 573, 643, 691, 741, 895, 997, 1044, 1092, 1145, 1185, 1204, 1359, 1377, 1440, 1568, 1868, 4, -110.9, -113.4, -120.6, -127.6, -134.3, -136.9, -141.4; FT-IR (ν, cm -1 ): 482,573,651,695,736,746,996,1033,1080,1143,1183,1264,1352,…”

Carbeniophosphines versus Phosphoniocarbenes: The Role of the Positive Charge

“…Experimental ν CO values ranging from 1971 to 2003 cm −1 indicate that all α‐cationic phosphine ligands behave as weaker donors than triphenylphosphine ( 14 : ν CO (PPh 3 )=1968 cm −1 ), but remain slightly stronger donors than trimethoxyphosphite ( 15 : ν CO [P(OMe) 3 ]=2011 cm −1 ) . At both extremities of the electronic parameter's scale, cyclopropenio‐ and imidazoliophosphines stand as the most and the least electron‐donating ligands of the carbeniophosphane class, respectively. As the phosphenium acceptor moiety (∼PPh 2 + ) remains the same along the series of Rh(CO) complexes 13 , the ν CO values are directly related to electronic properties of the carbene donor.…”

“…Experimental n CO values rangingf rom 1971 to 2003 cm À1 indicate that all a-cationic phosphine ligands behavea sw eaker donors than triphenylphosphine (14: n CO (PPh 3 ) = 1968cm À1 ), [38] but remain slightly stronger donors than trimethoxyphosphite (15: n CO [P(OMe) 3 ] = 2011cm À1 ). [39] At both extremities of the electronic parameter's scale, cyclopropenio- [40] and imidazoliophosphines [41] stand as the most and the least electron-donating ligands of the carbeniophosphane class, respectively.A s the phosphenium acceptor moiety (~PPh 2 + )r emains the same along the series of Rh(CO) complexes 13,t he n CO values are di-rectly relatedt oe lectronic properties of the carbene donor. The greater the donor properties of the carbene, the more the phosphenium character of the PPh 2 is lowered, as in the case of bis(amino)cyclopropenylidene (bac) [42] (n CO [RhCl(CO) 2 (bac)] = 2031 cm À1 ), which wasr eported to act as as tronger donor than unsaturated NHCs (n CO [RhCl(CO) 2 (NHC)] % 2041 cm À1 ).…”