Multinuclear and Dynamic NMR Study of trans-[Pt(Cl)(PHCy₂)₂(PCy₂)], [Pt(Cl)(PHCy₂)₃][BF₄], [Pt(Cl)(PHCy₂)₃][Cl], trans-[Pt(Cl)(PHCy₂)₂{P(S)Cy₂}], and trans-[Pt(Cl)(PHCy₂)₂{P(O)Cy₂}]. Influence of Intramolecular PO···H−P and Cl···H−P Interactions on Restricted Rotation about Pt−P Bond. X-ray Structure of trans-[Pt(Cl)(PHCy₂

Abstract

The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, have been characterized by X-ray crystallography as well as by NMR and IR spectroscopy. A short and concise overview is given on the scarce literature on phosphonite related chemistry. Structural differences in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butyl-phenolate groups, led to orthometallated complexes cis-[MCl{1-κ 3 C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)]. These complexes were compared with those formed with ligand 2, bearing 2,2-dioxo-3,3-di-tert-butyl-5,5-dimethoxy-1,1-biphenyl groups, preventing orthometallation. The complexes trans-{PdCl 2 (2)], cis-[PtCl 2 (2)] and trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chemical shifts, Pt-P coupling constants, as well as CO stretch frequencies of Rh-CO complexes as important tools for structural characterization of such complexes. Introduction Progress and development of homogeneous catalysis is very much related and dependent on the synthesis and availability of ligands. In recent years a number of powerful new ligand classes have emerged, most of which are chelating phosphorus-based compounds 1 such as phosphines 2 or phosphites. 3 Phos-phonites however have been widely neglected and only very recently a few examples were reported. Reetz et al. used several backbones, amongst others ferrocene, to prepare chelating diphosphonites and used them in asymmetric Rh-catalyzed hydrogenations of the typical benchmark substrates 4 as well as in conjugate addition of aryl boronic acids. 5 Zanotti-Gerosa et al. also described diphosphonites but they used the para-cyclophane backbone and performed hydrogenation reactions. 6 Pringle andco-workers used binaphthol-derived mono-and bidentate phosphonites for conjugate additions of diethyl zinc to enones. 7 The same monophosphonites were used by Claver and Pringle in asymmetric hydrogenations. 8 Scharf and co-workers used the monodentate phosphonites based on TADDOL as the chiral auxiliary for the rhodum-catalyzed hydrosilylation of ketones. 9 Börner and co-workers have published on the use of both monodentate and bidentate phosphonite ligands in the hydroformylation of alkenes, with varying results. 10 Finally the Reetz group, in line with their earlier work, prepared phosphite-phosphonite bidentate ligands but no applications in catalysis were reported so far. 11 During recent years xanthene-based chelating ligands have been introduced and extensively used in transition metal catalyzed CC bond forming reactions. 12 These backbones provide a unique combination of rigidity and P-P distance in such a way, that specific, large bite-angle coordination modes are supported. Additionally interaction of the central oxygen atom in the backbone with a metal atom coordinated is po...

Uncovering Intramolecular π‐Type Hydrogen Bonds in Solution by NMR Spectroscopy and DFT Calculations

“…The existence of a π‐type hydrogen bond between the PO−H and the C≡C triple bond in solution is also suggested by the sharpness of the 31 P NMR signal of the P 4 HCy 2 ligand. In fact, for systems analogous to 2 , the 31 P NMR signal of the P 4 HCy 2 ligand is expected to be quite broad when the P(OH)Cy 2 in the cis position can freely rotate about the Pt−P bond, and relatively sharp when the rotation of the P(OH)Cy 2 ligand is hindered due to the formation of the PO⋅⋅⋅H⋅⋅⋅X bridge (X=Lewis base) …”

“…The existence of a p-type hydrogen bond between the POÀ Ha nd the CCt riple bond in solution is also suggestedb yt he sharpnesso ft he 31 PNMR signalo ft he P 4 HCy 2 ligand.I nf act, for systems analogoust o2,t he 31 PNMR signal of the P 4 HCy 2 ligand is expected to be quite broad when the P(OH)Cy 2 in the cis positionc an freely rotate about the PtÀPb ond, [21] and rela-tively sharpw hen the rotationo ft he P(OH)Cy 2 ligand is hindered due to the formationo ft he PO···H···X bridge (X = Lewis base). [22][23][24][25][26] Another clue to the presence of the p-type hydrogen bond derives from the analysis of the 1 H-195 Pt HMQC spectrum of 2 ( Figure 1) displaying, besides the correlation between the Cy 2 PH protons and the 195 Pt atoms to which the phosphanes are bonded, intense cross peaks between the POH protona nd Pt 1 (but not Pt 2 ).…”

Stepwise Sulfuration of the Terminal Phosphido Complex trans‐[PtCl(PHCy2)2(PCy2)]: Synthesis of [Pt(κ2S,S′‐PS2Cy2)(PHCy2)2]Cl and [Pt(κ2S,S′‐PS2Cy2){κP‐P(S)Cy2}(PHCy2)] and Crystal Structure of [Pt(κ2‐S,S‐PCy2S2)(κ‐S‐PCy2S2)(PHCy2)]

“…Complexes 2 and 7 were prepared as described elsewhere. [54] Melting points were determined with Gallenkamp equipment and are uncorrected. C, H and S elemental analyses were carried out with a Eurovector CHNS-O Elemental Analyser.…”

“…Such behaviour could be explained invoking a hydrogen bond interaction between the P-H of the cationic complex and the chloride anion, an interaction already found for [PtCl(PCy 2 H) 3 ]Cl. [54] In order to confirm such a hypothesis we have compared the 35 Cl NMR spectra recorded in CD 2 Cl 2 before and after the addition of CD 3 OD as a hydrogen bond breaker. No signal could be observed in the 35 Cl NMR spectrum recorded in CD 2 Cl 2 , as expected for a quadrupolar nucleus surrounded by an asymmetric electron cloud.…”

“…[54] Dissolving 2 in halogenated solvents, the irreversible isomerisation into the thermodynamically favoured cis complex 3 took place as indicated in Scheme 3. This isomerisation was completed in 5 min by heating the reaction mixture at 40°C.…”