Mono- and di-nuclear palladium(ii) complexes with bulky arsino(phosphino)methanes in different coordination modes

Abstract

The peralkylated arsino(phosphino)methanes R₂AsCH₂PiPr₂ (R = tBu 2, iPr 3) react with trans-[PdCl₂(NCPh)₂] 1 to give the chelate compounds [PdCl₂(κ²-R₂AsCH₂PiPr₂)] 4, 5 which, via salt metathesis with KBr, KI (or NaI) and CF₃CO₂Ag, are converted to the dibromo-, diiodo-, and bis(trifluoracetato)-palladium(II) derivatives 6–11, respectively. Whereas from 2, 3 and [{Pd(μ-Cl)(η³-C₃H₅)}₂] 12 the mono-cationic species [Pd(η³-C₃H₅)(κ²-R₂AsCH₂PiPr₂)]PF₆13, 14 are obtained, treatment of 4, 5 with AgPF₆ in acetonitrile affords the di-cationic complexes [Pd(NCCH₃)₂(κ²-R₂AsCH₂PiPr₂)](PF₆)₂15, 16. Compound 15 (R = tBu) reacts with Na(acac) to give [Pd(κ²-acac)(κ²-R₂AsCH₂PiPr₂)]PF₆17. The reaction of 4, 5 with AgPF₆ in acetone leads to the formation of the di-nuclear complexes [{Pd(μ-Cl)(κ²-R₂AsCH₂PiPr₂)}₂](PF₆)₂18, 19, which in the presence of SbiPr₃ or pyridine undergo bridge cleavage to yield the mono-nuclear chelate derivatives [PdCl(L)(κ²-R₂AsCH₂PiPr₂)]PF₆, mostly as a mixture of cis/trans isomers. The methylpalladium(II) compound [PdCl(CH₃)(κ²-tBu₂AsCH₂PiPr₂)] 25, prepared from [PdCl(CH₃)(η⁴-C₈H₁₂)] 24 and 2, reacts with Na[B(Ar_F)₄] to afford the A-frame type complex [Pd₂(CH₃)₂(μ-Cl)(μ-tBu₂AsCH₂PiPr₂)₂][B(Ar_F)₄] 27. In contrast, the related precursor [PdCl(CH₃)(κ²-iPr₂AsCH₂PiPr₂)], generated in situ from 24 and 3, gives, upon treatment with Na[B(Ar_F)₄], a mixture of two products 28a,b being the corresponding head-to-tail and head-to-head isomers. The mono-nuclear compounds 4 and 13 as well as the A-frame type complex 27 have been characterized by X-ray crystallography.