Synthesis and characterization of bis(diphenylphosphinomethyl)amino ligands and their Ni(II), Pd(II) complexes: Application to hydrogenation of styrene

Abstract

Transition metal

The development of phosphinoamine–Pd(II)–imidazole complexes: implications in room‐temperature Suzuki–Miyauracross‐coupling reaction

“…Electrochemical study of complex 4 demonstrates an irreversible reductive event at −1.29 V (∆ E p = 750 mV), which is shifted to a more negative potential compared to starting compound [PdCl 2 (PPh 2 Etpy–P,N)] ( 3 ) ( E pc = −0.78 V). This feature is consistent with Pd(II)/Pd(0) redox couple . A ligand‐based reduction was also observed at −0.83 V with no peak reversal.…”

“…The 1 H NMR spectrum of complex 2 , in addition to aromatic protons, shows a singlet at δ = 8.21 ppm for H 2′ of N‐BuIm (Scheme ), which is shifted downfield compared to free ligand. The electrochemical study of complex 2 revealed one irreversible reduction at −1.39 V (∆ E p = 670 mV), similar to complex 1 , attributed to Pd(II)/Pd(0) redox couple . The shift of this reduction to a more negative value compared to complex 1 might be due to higher electron‐donating ability of N‐BuIm relative to N‐MeIm ligand.…”

“…The electrochemical behavior of complex 5 showed similar features to the above complexes. An irreversible reductive event at −1.35 V (∆ E p = 630 mV) could be ascribable to Pd(II)/Pd(0) redox couple . The shift of this event to a more negative potential compared to precursor complex [PdCl 2 (PPh 2 Etpy‐P,N)] ( 3 ) ( E pc = −0.78 V ) and the complex 4 may be attributed to the presence of more electron‐donating N‐BuIm ligands.…”

“…Complex 1 in its cyclic voltammogram in acetonitrile exhibited one irreversible reductive response at −1.18 V (∆ E p = 510 mV). This feature could be assigned to the Pd(II)/Pd(0) redox couple, since complexes of π‐acceptor ligands undergo two‐electron reduction with the stabilization of Pd(0) . Extremely high peak‐to‐peak separation value indicated that the redox process is quite non‐Nernstian.…”

“…During positive potential scan the oxidation at +1.52 V with no peak reversal is assumed to lead to the formation of a Pd(IV), accompanied by an increase in coordination number from 4 to 6 . Compared to the precursor complex [PdCl 2 (PPh 2 py–P,N)] ( E pc = −0.75 V) the reduction was shifted to a more negative value, which may be due to the presence of electron‐donating N‐MeIm ligand in 1 …”