Diferrocenylmercury‐Bridged Diphosphine: A Chiral, Ambiphilic, and Redox‐Active Bidentate Ligand

Abstract

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox-active and ambiphilic character is reported. Initially generated as its HgCl complex by reaction of 1,2-fc(PPh )(SnMe ) (fc=ferrocenediyl) with HgCl in acetone, treatment with [n-Bu N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg-Cl→Hgfc (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh ) ⋅HgCl where the bridging mercury atom acts as a σ-acceptor. Furthermore, a bis-[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10 and 1.4×10 e/a at the bond critical points.

Mechanistic Studies into the Sn/Hg Exchange Reaction of 1,2-Fc(PPh2)(SnMe3) with HgCl2: Competitive Sn–Me over Sn–Fc Cleavage in Noncoordinating Solvents

“…However, this interaction only modestly influences the geometry, as the Sn atom resides in a distorted-monocapped-tetrahedral configuration. The extent of trigonal-bipyramidal character at Sn as judged by the sum of the equatorial angles of 339.9° is more pronounced than for the trimethylstannyl derivative FcPPh 2 SnMe 3 (∑(equatorial angles) = 332.2°) but significantly less than for the BH 3 -complexed species [Fc­(PPh 2 ·BH 3 )­SnMe 2 Cl] (∑(equatorial angles) = 349.4°). A much shorter Sn1–Cl1 distance of 2.259(2) Å in comparison to that in [Fc­(PPh 2 ·BH 3 )­SnMe 2 Cl] (2.4022(9) Å) further indicates that the P1···Sn1 interaction is rather weak.…”

“…However, in contrast to the reaction of 5 with 2 equiv of HgCl 2 which ultimately gave 6 ·HgCl 2 , upon standing at room temperature slow conversion of 5 ·HgCl 2 into the dimeric species 2 ·HgCl 2 was observed (δ­( 31 P) 27.3 ppm, 35% after 24 h, Figures S27 and S28). The latter crystallized from the reaction mixture, and its structure was confirmed by verification of the previously reported unit cell parameters using X-ray diffraction analysis. Importantly, we found no evidence for “free” Fc­(PPh 2 )­(HgCl) or the formation of its dimer [Fc­(PPh 2 )­(HgCl)] 2 ( 4 , Scheme ) through an intermolecular Hg–P Lewis acid–base reaction.…”

“…HgCl 2 , n -butyllithium (1.6 M in hexanes), and tert -butyllithium (1.7 M in pentane) were purchased from commercial sources and used without further purification. The syntheses of the p S isomer of 1 and the p S ,p S isomer of 2 ·HgCl 2 have been previously reported.…”

“…The presence of the Lewis acidic Hg(II) in close proximity to another metal can give rise to Z-type ligand behavior, where the Hg atom is able to engage in metallophilic 4 interactions. For instance, short M•••Hg contacts have been reported for complexes of ligands III and IV with various d 8 and d 10 metal ions. 5 The requisite diarylmercury species are frequently prepared by reaction of an aryllithium precursor with 0.5 equiv of HgCl 2 or, alternatively, by redistribution of arylmercuric halides in the presence of a soft base.…”

“…6,8 T h i s c o n t e n t i s We previously reported that stirring a mixture of ferrocenylstannane 1 (pS isomer) and HgCl 2 in acetone over a period of 1 h 9 afforded a yellow precipitate that was identified as 2•HgCl 2 (pS,pS isomer) by single-crystal X-ray diffraction analysis (Scheme 1). 10 The unexpected spontaneous formation of this diarylmercury species prompted us to further investigate the reaction mechanism with the aim of identifying possible intermediates or byproducts generated in the process, as well as gaining a better understanding of the role of the reaction conditions on the product distribution. We offer here detailed mechanistic studies into the formation of this unusual complex.…”