Palladium(0) phosphine complexes are of great importance as catalysts in numerous bond formation reactions that involve oxidative addition of substrates. Highly active catalysts with labile ligands are of particular interest but can be challenging to isolate and structurally characterize. We investigate here the synthesis and chemical reactivity of Pd 0 complexes that contain geometrically adaptable diferrocenylmercury-bridged diphosphine chelate ligands (L) in combination with a labile dibenzylideneacetone (dba) ligand. The diastereomeric diphosphines 1a (p S p R , meso -isomer) and 1b (p S p S -isomer) differ in the orientation of the ferrocene moieties relative to the central Ph 2 PC 5 H 3 –Hg–C 5 H 3 PPh 2 bridging entity. The structurally distinct trigonal LPd 0 (dba) complexes 2a ( meso ) and 2b (p S p S ) are obtained upon treatment with Pd(dba) 2 . A competition reaction reveals that 1b reacts faster than 1a with Pd(dba) 2 . Unexpectedly, catalytic interconversion of 1a ( meso ) into 1b ( rac ) is observed at room temperature in the presence of only catalytic amounts of Pd(dba) 2 . Both Pd 0 complexes, 2a and 2b , readily undergo oxidative addition into the C–Cl bond of CH 2 Cl 2 at moderate temperatures with formation of the square-planar trans -chelate complexes LPd II Cl(CH 2 Cl) ( 3a , 3b ). Kinetic studies reveal a significantly higher reaction rate for the meso -isomer 2a in comparison to (p S p S )- 2b .
more »
« less
Novel Sulfonated CNN Pincer Ligands for Facile C−H Activation at a Pt(II) Center
Two novel sulfonated CNN‐pincer ligands
- PAR ID:
- 10043509
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Israel Journal of Chemistry
- Volume:
- 57
- Issue:
- 10-11
- ISSN:
- 0021-2148
- Page Range / eLocation ID:
- p. 1010-1022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3‐methylpentyl (H2L2) and cyclohexyl (H2L3) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL2a/3ahave two imino N and two S donors resulting in three five‐member chelate rings (555 isomers). The kinetic isomers CuL2b/3bhave one imino and one hydrazino N donor and two S donors resulting in four‐, six‐, and five‐member rings (465 isomers). The 555 isomers have more accessible CuII/Ipotentials (E1/2=−811/−768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E1/2=−923/‐854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR‐90) using the MTT assay. CuL2awas potent (A549EC50=0.080 μM) and selective (IMR‐90EC50/A549EC50=25) for A549. Its linkage isomer CuL2bhad equivalent A549 activity, but lower selectivity (IMR‐90EC50/A549EC50=12.5). The isomers CuL3aand CuL3bwere less potent withA549EC50 values of 1.9 and 0.19 M and less selective withIMR‐90EC50/A549EC50ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.
-
more » « less
Abstract Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO−, to the NbIVcomplex [(PNP)NbCl2(N
t BuAr)] (1 ) (PNP=N[2‐Pi Pr2‐4‐methylphenyl]2−; Ar=3,5‐Me2C6H3) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(Nt BuAr)] (2 ). Reduction of2 with CoCp*2cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(Nt BuAr)] (3 ). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3 with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(Nt BuAr)] (4 ). -
more » « less
Abstract Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO−, to the NbIVcomplex [(PNP)NbCl2(N
t BuAr)] (1 ) (PNP=N[2‐Pi Pr2‐4‐methylphenyl]2−; Ar=3,5‐Me2C6H3) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(Nt BuAr)] (2 ). Reduction of2 with CoCp*2cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(Nt BuAr)] (3 ). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3 with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(Nt BuAr)] (4 ). -
more » « less
Abstract We report here a “nonspectator” behavior for an unsupported
L ‐function σ3‐P ligand (i.e. P{N[o ‐NMe‐C6H4]2},1a ) in complex with the cyclopentadienyliron dicarbonyl cation (Fp+). Treatment of1a ⋅Fp+with [(Me2N)3S][Me3SiF2] results in fluoride addition to theP ‐center, giving the isolable crystalline fluorometallophosphorane1aF ⋅Fp that allows a crystallographic assessment of the variance in the Fe−P bond as a function of P‐coordination number. The nonspectator reactivity of1a ⋅Fp+is rationalized on the basis of electronic structure arguments and by comparison to trigonal analogue (Me2N)3P⋅Fp+(i.e.1b ⋅Fp+), which is inert to fluoride addition. These observations establish a nonspectator L/X‐switching in (σ3‐P)–M complexes by reversible access to higher‐coordinate phosphorus ligand fragments.
