Search

The discovery that cyclic (ArO)2PF can support Rh-catalysts for hydroformylation with significant advantages in tuning regioselectivity transformed the study of metal complexes of monofluorophos ligands from one of primarily academic interest to one with potentially important applications in catalysis. In this review, the syntheses of monofluorophosphites, (RO)2PF, and monofluorophosphines, R2PF, are discussed and the factors that control the kinetic stability of these ligands to hydrolysis and disproportionation are set out. A survey of the coordination chemistry of these two classes of monofluorophos ligands with d-block metals is presented, emphasising the bonding of the fluorophos to d-block metals, predominantly in low oxidation states. The application of monofluorophos ligands in homogeneous catalysis (especially hydroformylation and hydrocyanation) is discussed, and it is argued that there is great potential for monofluorophos complexes in future catalytic applications. [ABSTRACT FROM AUTHOR]

The dn number or configuration is a very useful parameter in transition metal chemistry because it conveys information about the expected properties of a d-block metal complex, including its shape, magnetism, thermodynamic stability, kinetic lability, and spectroscopic properties. The dn number can be determined from either the oxidation state (OS) or valence number (VN) of the metal centre, and since, in most cases, these are numerically equal, the derived dn value is the same. However, examples are discussed where the OS and VN are not equal, which results in unavoidable ambiguities in dn values. Following a discussion of these examples, a revised definition of dn is proposed based on the occupation of the frontier molecular orbitals of the complex. [ABSTRACT FROM AUTHOR]

The reactions of R2P–PR2 with R′E–ER′, (where E = Se, S, O, Te) to give R2P–ER′ have been explored experimentally and computationally. The reaction of Ph2P–PPh2 with PhSe–SePh gives Ph2P–SePh (1) rapidly and quantitatively. The P–P/Se–Se reaction is inhibited by the addition of the radical scavenger TEMPO which is consistent with a radical mechanism for the heterometathesis reaction. Compound 1 has been fully characterised, including by X-ray crystallography. A range of other Ar2P–SeR (R = Ph, nBu or CH2CH2CO2H) have also been prepared and characterised. The reaction of 1 with [Mo(CO)4(nbd)] (nbd = norbornadiene) gives two products which, from their characteristic 31P NMR data, have been identified as cis-[Mo(CO)4(Ph2PSePh–P)2] (8) and the mixed-donor complex cis-[Mo(CO)4(Ph2P–SePh–P)(Ph2P–SePh–Se)] (9). It is deduced that the P and Se atoms in ligand 1 have comparable capacity to coordinate to Mo(0). The reaction of Ph2P–PPh2 with PhS–SPh gives Ph2P–SPh (2) quantitatively but no reaction was observed between Ph2P–PPh2 and PhTe–TePh. Heterometathesis between Ph2P–PPh2 and tBuO–OtBu does not occur thermally but has been observed under UV irradiation to give Ph2P–OtBu along with P(V) oxidation by-products. DFT calculations have been carried out to illuminate why heterometatheses with dichalcogenides R′E–ER′ occur readily when E = S and Se but not when E = O and Te. The calculations show that heterometathesis is predicted to be thermodynamically favourable for E = O, S and Se and unfavourable for E = Te. The fact that a metathesis reaction between Ph2P–PPh2 with tBuO–OtBu is not observed in the absence of UV radiation, is therefore due to kinetics. [ABSTRACT FROM AUTHOR]

Radiotracers labelled with technetium-99m (99mTc) enable accessible diagnostic imaging of disease, provided that radiotracer preparation is simple. Whilst 99mTc radiopharmaceuticals for imaging perfusion are routinely prepared from kits, and regularly used in healthcare, there are no 99mTc-labelled receptor-targeted radiopharmaceuticals in widespread clinical use. This is in part due to the multistep radiosyntheses required for the latter. We demonstrate that the diphosphine, 2,3-bis(diphenylphosphino)maleic anhydride (BMA), is an excellent platform for preparation of kit-based, receptor-targeted 99mTc-labelled radiotracers: its conjugates are simple to prepare and can be easily labelled with 99mTc using one-step, kit-based protocols. Here, reaction of BMA with the αvβ3-integrin receptor targeted cyclic peptide, Arg-Gly-Asp-DPhe-Lys (RGD), provided the first diphosphine-peptide conjugate, DP-RGD. DP-RGD was incorporated into a "kit", and addition of a saline solution containing 99mTcO4− to this kit, followed by heating, furnished the radiotracer [99mTcO2(DP-RGD)2]+ in consistently high radiochemical yields (>90%). The analogous [ReO2(DP-RGD)2]+ compound was prepared and characterised, revealing that both [99mTcO2(DP-RGD)2]+ and [ReO2(DP-RGD)2]+ consist of a mixture of cis and trans geometric isomers. Finally, [99mTcO2(DP-RGD)2]+ exhibited high metabolic stability, and selectively targeted αvβ3-integrin receptors, enabling in vivo SPECT imaging of αvβ3-integrin receptor expression in mice. [ABSTRACT FROM AUTHOR]

The water-soluble phosphine P(CH2OH)3 was synthesized from the reaction of (P CH2OH 4)Cl with base. The synthesis of the complexes MX2(P CH2OH 3)2 proceeded from the reaction of the phosphine with the corresponding MX2(COD), where M = Pt or Pd, X = Cl, Br or I and COD = cycloocta-1,5-diene. The treatment of PtCl(CH3)(COD) with P(CH2OH)3 also yielded the stable organoplatinum species cis- and trans-PtCl(CH3)(P CH2OH 3)2, where X = Br and I. The complex Ni(P CH2OH 3)4 was precipitated from a toluene solution of Ni(COD)2 and Pd(P CH2OH 3)4 from Pd(dibenzylideneacetone)2 in toluene.

The hydroformylation of 1-hexene with 12 bar of 1 : 1 H2/CO in the presence of the catalytic system [Rh(acac)(CO)2]/PPh3 was successfully studied by real-time multinuclear high-resolution FlowNMR spectroscopy at 50 °C. Quantitative reaction progress curves that yield rates as well as chemo- and regioselectivities have been obtained with varying P/Rh loadings. Dissolved H2 can be monitored in solution to ensure true operando conditions without gas limitation. 31P{1H} and selective excitation 1H pulse sequences have been periodically interleaved with 1H FlowNMR measurements to detect Rh–phosphine intermediates during the catalysis. Stopped-flow experiments in combination with diffusion measurements and 2D heteronuclear correlation experiments showed the known tris-phosphine complex [RhH(CO)(PPh3)3] to generate rapidly exchanging isomers of the bis-phosphine complex [Rh(CO)2(PPh3)2] under CO pressure that directly enter the catalytic cycle. A new mono-phosphine acyl complex has been identified as an in-cycle reaction intermediate. [ABSTRACT FROM AUTHOR]

Three methods are described for the large scale separation of the secondary phobanes 9-phosphabicyclo[3.3.1]nonane (s-PhobPH) and 9-phosphabicyclo[4.2.1]nonane (a-PhobPH). The n-butyl phobane s-PhobPBu is prepared by using nucleophilic and electrophilic routes and the donor properties of the individual isomers of PhobPBu are assessed.

The results from comparison of the heterobidentate phosphino/phosphonite [L.sub.A] and the monophosphonite/monophosphine analogue M, PMe[Ph.sub.2] are reported. The results revealed that the greater activity of the heteroligand catalysts compared to that of the homoligand catalysts is true for the bidentate and monodentate systems.

The 5- to 8-membered cyclic fluorophosphites L5–8 have been prepared from the corresponding chlorophosphites which are derived from dihydroxyarenes or bis(trimethylsiloxy)arenes. Ligand L5 is very sensitive to hydrolysis but L6–8 are much more kinetically robust. The coordination chemistry of L5–8 has been explored with Mo(0), Pt(0) and Rh(i) and it is shown that the π-acceptor properties of L5–8 increase with decreasing ring size. The IR spectra and X-ray crystal structures of the [Mo(CO)4L2] complexes show that L5–8 lie between PF3 and P(OAr)3 in terms of their σ/π-bonding properties. The [PtL4] complexes are readily prepared from [Pt(nbe)3] and 4 equiv. of L5–8 whereas equilibrium mixtures of PtLx(nbe)y species form when 2 equiv. of L5–8 are added to [Pt(nbe)3]. The CO substitution reactions of [Rh2Cl2(CO)4] with L5–8 to give [Rh2Cl2L4] are evidence of the PF3-like ligand properties of L5–8. The trends in the properties of L5–8 are analysed in terms of their proximity to PF3 or P(OPh)3. [ABSTRACT FROM AUTHOR]

Abstract: Ligand‐enabled aza‐Heck cyclizations and cascades of N‐(pentafluorobenzoyloxy)carbamates are described. These studies encompass the first examples of efficient non‐biased 6‐exo aza‐Heck cyclizations. The methodology provides direct and flexible access to carbamate protected pyrrolidines and piperidines. [ABSTRACT FROM AUTHOR]