Amido PNP pincer complexes of palladium(II) and platinum(II): Synthesis, structure, and reactivity

Abstract

The synthesis of a series of divalent palladium and platinum complexes containing amido PNP pincer ligands of the type [N(o-C 6 H 4 PR 2) 2 ] − (R = Ph (1a), iPr (1b)) is reported. Metathetical reactions of [1a-b]PdCl or [1a-b]PtCl with a variety of alkyl Grignard reagents or LiHBEt 3 in ethereal or arene solutions generate their corresponding alkyl or hydride complexes [1a]PdR 1 (R 1 = Me, Et, nBu), [1b]PdR 1 (R 1 = Me, Et, H), [1a]PtR 1 (R 1 = Me, Et, nBu, nHexyl, H), and [1b]PtR 1 (R 1 = Me, H). Although these organometallic complexes are all thermally stable, including those containing β-hydrogen atoms even at elevated temperatures, compounds [1a]PdH and [1b]PtR 1 (R 1 = Et, nBu, nHexyl) are not isolable due to facile decomposition. The stability and reactivity of these complexes are discussed. The chloro [1a]PdCl is a superior catalyst precursor to [1b]PdCl, [1a]PtCl, and [1b]PtCl in Kumada couplings, affording, for instance, n-butyl arenes nearly quantitatively. The X-ray structures of [1b]PtCl,

Comparative study of CO2insertion into pincer supported palladium alkyl and aryl complexes

“…19 This is consistent with the ethyl or propyl ligand exerting a stronger trans -influence than a chloride ligand. Although, crystallographically characterized examples of palladium ethyl complexes are rare, 15,17,20 the Pd–C bond distance in 1-Et is longer than those typically reported (Pd(1)–C(1) is 2.226(6) Å in 1-Et ) and is most comparable to a PSiP-supported palladium ethyl complex, which also contains a strong trans -influence donor (silyl) opposite the palladium. 15 In 1- n Pr the Pd(1)–C(1) is 2.209(2) Å, which is within error of the Pd–C bond distance in 1-Et .…”

“…13 g In an analogous fashion, treatment of ( t Bu PBP)PdCl ( 1-Cl ) with EtLi or n PrMgCl in benzene results in the formation of ( t Bu PBP)Pd(CH 2 CH 3 ) ( 1-Et ) and ( t Bu PBP)Pd(CH 2 CH 2 CH 3 ) ( 1- n Pr ), which were isolated in yields of 76 and 59%, respectively, after recrystallization (eqn (2)). 16 1-Et is a rare example of an isolated pincer supported palladium ethyl complex, 15,17 while 1- n Pr is to the best of our knowledge only the second example of an isolated palladium propyl complex. 18 1-Et and 1- n Pr are indefinitely stable at room temperature in benzene and β-hydride elimination to generate ethylene or propene and a putative palladium hydride ( vide infra ) only occurs at temperatures greater than 60 °C.…”

Facial–Meridional Isomerization and Reductive Elimination in [(R2P-o-C6H4)2N]PtMe3 (R = Ph, iPr)

“…The production of ethane (δ H 0.80 ppm) and [R-PNP]PtMe from these reactions is evident by their 1 H and 31 P{ 1 H} NMR spectra. In particular, the 1 J PPt coupling constants of [Ph-PNP]PtMe (2983 Hz) 4b and [iPr-PNP]PtMe (2837 Hz) 18 are significantly larger than those of their corresponding fac/mer-[R-PNP]PtMe 3 because of the reduced formal oxidation state of platinum. 19 No intermediate was found prior to reductive elimination.…”