Dynamic Motions of Ligands around the Metal Centers Afford a Fidget Spinner-Type AIE Luminogen.

A new type of aggregation-induced emission (AIE) luminogen containing a dimeric metal fragment and two or three phthalazine ligands is described, which shows dynamic motions of ligands around the metal centers in solution. Based on the variable-temperature and EXSY NMR spectroscopy data, X-ray crystallography structures, and computational results, three different pathways (i.e., reversible exchange with haptotropic shifts, circulation of ligands around the dimeric metal fragment, and walking on the spot of ligands on the metal centers) were considered for this dynamic behavior. Restriction of these dynamic processes in the aggregate forms of the compounds (in H2O/CH3CN solvent mixtures) contributes to their AIE. DFT calculations and NMR analysis showed that bright excited states for these molecules are not localized on isolated molecules, and the emission of them stemmed from π-dimers or π-oligomers. The morphologies and the mode of associations in the solvent mixtures were determined by using transmission electron microscopy (TEM) and concentration-dependent NMR spectroscopy. The computational results showed the presence of a conical intersection (CI) between the S0 and S1 excited state, which provides an accessible pathway for nonradiative decay in these systems.

Non-Targeted Spectranomics for the Early Detection of Xylella fastidiosa Infection in Asymptomatic Olive Trees, cv. Cellina di Nardò.

Olive quick decline syndrome (OQDS) is a disease that has been seriously affecting olive trees in southern Italy since around 2009. During the disease, caused by Xylella fastidiosa subsp. pauca sequence type ST53 (Xf), the flow of water and nutrients within the trees is significantly compromised. Initially, infected trees may not show any symptoms, making early detection challenging. In this study, young artificially infected plants of the susceptible cultivar Cellina di Nardò were grown in a controlled environment and co-inoculated with additional xylem-inhabiting fungi. Asymptomatic leaves of olive plants at an early stage of infection were collected and analyzed using nuclear magnetic resonance (NMR), hyperspectral reflectance (HSR), and chemometrics. The application of a spectranomic approach contributed to shedding light on the relationship between the presence of specific hydrosoluble metabolites and the optical properties of both asymptomatic Xf-infected and non-infected olive leaves. Significant correlations between wavebands located in the range of 530-560 nm and 1380-1470 nm, and the following metabolites were found to be indicative of Xf infection: malic acid, fructose, sucrose, oleuropein derivatives, and formic acid. This information is the key to the development of HSR-based sensors capable of early detection of Xf infections in olive trees.

Exploring the xylem-sap to unravel biological features of Xylella fastidiosa subspecies pauca ST53 in immune, resistant and susceptible crop species through metabolomics and in vitro studies.

Xylella fastidiosa subsp. pauca ST53 (Xfp) is a pathogenic bacterium causing one of the most severe plant diseases currently threatening the olive-growing areas of the Mediterranean, the Olive Quick Decline Syndrome (OQDS). The majority of the olive cultivars upon infections more or less rapidly develop severe desiccation phenomena, while few are resistant (e.g. Leccino and FS17), being less impacted by the infections. The present study contributes to elucidating the basis of the resistance phenomenon by investigating the influence of the composition of the xylem sap of plant species on the rate of bacterial multiplication. Xylem saps from Xfp host and non-host species were used for growing the bacterium in vitro, monitoring bacterial growth, biofilm formation, and the expression of specific genes. Moreover, species-specific metabolites, such as mannitol, quinic acid, tartaric acid, and choline were identified by non-targeted NMR-based metabolomic analysis in olive, grapevine, and citrus. In general, the xylem saps of immune species, including grapevine and citrus, were richer in amino acids, organic acids, and glucose. The results showed greater bacterial growth in the olive cultivar notoriously susceptible to Xfp (Cellina di Nardò), compared to that recorded in the resistant cultivar Leccino. Conversely, higher biofilm formation occurred in Leccino compared to Cellina di Nardò. Using the xylem saps of two Xfp-immune species (citrus and grapevine), a divergent bacterial behavior was recorded: low planktonic growth and biofilm production were detected in citrus compared to the grapevine. A parallel evaluation of the expression of 15 genes showed that Xfp directs its molecular functions mainly to virulence. Overall, the results gained through this multidisciplinary study contribute to extending the knowledge on the host-pathogen interaction, while confirming that the host response and resistance mechanism have a multifactorial basis, most likely with a cumulative effect on the phenotype.

Pt(II)-Decorated Covalent Organic Framework for Photocatalytic Difluoroalkylation and Oxidative Cyclization Reactions.

A new covalent organic framework (COF) based on imine bonds was assembled from 2-(4-formylphenyl)-5-formylpyridine and 1,3,6,8-tetrakis(4-aminophenyl)pyrene, which showed an interesting dual-pore structure with high crystallinity. Postmetallation of the COF with Pt occurred selectively at the N donor (imine and pyridyl) in the larger pores. The metallated COF served as an excellent recyclable heterogeneous photocatalyst for decarboxylative difluoroalkylation and oxidative cyclization reactions.

NHCs as Neutral Donors towards Polyphosphorus Complexes.

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η5 -P5 )] (1) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp''Ta(CO)2 (η4 -P4 )] (Cp''=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P3 -containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.

Development of a food class-discrimination system by non-targeted NMR analyses using different magnetic field strengths.

Non-targeted NMR-based approach has received great attention as a rapid method for food product authenticity assessment. The availability of a database containing many comparable NMR spectra produced by different spectrometers is crucial to develop functional classifiers able to discriminate rapidly the commodity class of a given food product. Nevertheless, variability in spectrometer features may hamper the production of comparable spectra due to inherent variations in signal resolution. In this paper, we report on the development of a class-discrimination model for grape juice authentication by application of non-targeted NMR spectroscopy. Different approaches for the pre-treatment of data will be described along with details about the model validation. The developed model performed excellently (95.4-100% correct predictions) even when it was tested against 650 spectra produced by 65 spectrometers with different configurations (magnetic field strength, manufacturer, age). This study may boost the use of non-targeted NMR methods for food control.

(Thio)urea-Based Covalent Organic Framework as a Hydrogen-Bond-Donating Catalyst.

Two-dimensional urea- and thiourea-containing covalent organic frameworks (COFs) were synthesized at ambient conditions at large scale within 1 h in the absence of an acid catalyst. The site-isolated urea and thiourea in the COF showed enhanced catalytic efficiency as a hydrogen-bond-donating organocatalyst compared to the molecular counterparts in epoxide ring-opening reaction, aldehyde acetalization, and Friedel-Crafts reaction. The COF catalysts also had excellent recyclability.

Collaborative Study to Validate Purity Determination by 1H Quantitative NMR Spectroscopy by Using Internal Calibration Methodology.

NMR spectroscopy has recently been utilized to determine the absolute amounts of organic molecules with metrological traceability since signal intensity is directly proportional to the number of each nucleus in a molecule. The NMR methodology that uses hydrogen nucleus (1H) to quantify chemicals is called quantitative 1H-NMR (1H qNMR). The quantitative method using 1H qNMR for determining the purity or content of chemicals has been adopted into some compendial guidelines and official standards. However, there are still few reports in the literature regarding validation of 1H qNMR methodology. Here, we coordinated an international collaborative study to validate a 1H qNMR based on the use of an internal calibration methodology. Thirteen laboratories participated in this study, and the purities of three samples were individually measured using 1H qNMR method. The three samples were all certified via conventional primary methods of measurement, such as butyl p-hydroxybenzoate Japanese Pharmacopeia (JP) reference standard certified by mass balance; benzoic acid certified reference material (CRM) certified by coulometric titration; fludioxonil CRM certified by a combination of freezing point depression method and 1H qNMR. For each sample, 1H qNMR experiments were optimized before quantitative analysis. The results showed that the measured values of each sample were equivalent to the corresponding reference labeled value. Furthermore, assessment of these 1H qNMR data using the normalized error, En-value, concluded that statistically 1H qNMR has the competence to obtain the same quantification performance and accuracy as the conventional primary methods of measurement.

Double addition of phenylacetylene onto the mixed bridge phosphinito-phosphanido Pt(i) complex [(PHCy2)Pt(µ-PCy2){κ2P,O-µ-P(O)Cy2}Pt(PHCy2)](Pt-Pt).

The reaction of the dinuclear phosphinito bridged complex [(PHCy2)Pt(µ-PCy2){κ2P,O-µ-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (1) with phenylacetylene affords the η1-alkenyl-µ,η1:η2-alkynyl complex [(η1-trans-(Ph)HC[double bond, length as m-dash]CH)(PHCy2)Pt(µ-PCy2)(µ,η1:η2-PhC[triple bond, length as m-dash]C)Pt{κP-P(O)Cy2}(PHCy2)] (4) displaying a σ-bonded 2-phenylethenyl ligand and an alkynyl (µ-κCα:η2) bridge between the platinum atoms. Complex 4 was shown to form in two steps: initially, the attack of the first molecule of phenylacetylene gives the σ-acetylide complex [(PHCy2)(η1-PhC[triple bond, length as m-dash]C)Pt1(µ-PCy2)Pt2(PHCy2){κP-P(OH)Cy2}](Pt-Pt) (5) featuring an intramolecular π-type hydrogen bond between the POH and the C[triple bond, length as m-dash]C triple bond; fast reaction of 5 with a second molecule of phenylacetylene results in the oxidative addition of the terminal C-H bond of the second alkyne to Pt1 that, after rearrangements, leads to 4. When left in solution for two weeks, complex 4 spontaneously isomerizes completely to [(PHCy2)(η1-trans-(Ph)HC[double bond, length as m-dash]CH)Pt(µ-PCy2){κ2P,O-µ-P(O)Cy2}Pt(η1-PhC[triple bond, length as m-dash]C)(PHCy2)] (7) displaying a 2-phenylethenyl ligand and a phenylethynyl group both σ-bonded to the metal. Density functional calculations at the B3LYP/LACV3P++**//DFT/LACVP* level were carried out to study the thermodynamics of the formation of all considered complexes and to trace the mechanism of formation of the observed products.

Stable mixed-valence diphenylphosphanido bridged platinum(ii)-platinum(iv) complexes.

The reaction between [NnBu4][(C6F5)2PtII(µ-PPh2)2PtIV(C^N)(I)2] (C^N = κ2-N,C-benzoquinolinate, 1) and (i) bidentate S^S, N^S and O^O anionic ligands or (ii) monodentate S- N- or O-based anionic ligands was studied in order to investigate the factors that may guarantee the stability of Pt(ii),Pt(iv) mixed-valence dinuclear phosphanido complexes. While reactions of 1 with S^S or N^S ligands afforded stable Pt(ii),Pt(iv) species of general formula [(C6F5)2PtII(µ-PPh2)2PtIV(C^N)(L^S)]x- [(L^S)(x-1) = 2-mercaptopyrimidinate (pymS-), 2-mercaptopyridinate (pyS-), dimethyldithiocarbamate (Me2NCS2-), ethyl xanthogenate (EtOCS2-) and 1,2-benzenedithiolate (PhS22-)], the reaction of 1 with the O^O ligand sodium acetylacetonate gave several products, and no pure Pt(ii),Pt(iv) complex could be isolated. The reaction of monodentate ligands such as PhS-, OH- or N3- with 1 led to a stable Pt(ii),Pt(iv) complex only in the case of N3-. The reaction with OH- afforded the Pt(ii),Pt(ii) complex [(C6F5)2PtII(µ-PPh2)(κ2-O,P-µ-O-PPh2)PtII(C^N)]- (8) deriving from reductive coupling of a diphenylphosphanide and an O-donor ligand coordinated to the Pt(iv) centre, while the reaction with PhS- produced the unstable Pt(ii),Pt(iv) complex [NnBu4][(C6F5)2PtII(µ-PPh2)2PtIV(C^N)(PhS)2] (11) that evolved in solution to the Pt(ii),Pt(ii) species [NnBu4][(C6F5)2PtII(µ-PPh2)2PtII(C^N)] (9) by elimination of diphenyldisulfide. Thus, the stability of mixed valence Pt(ii),Pt(iv) phosphanide complexes is affected by several concurrent factors, including the chelating effect of the ligands and the type of ligating atoms.

A community-built calibration system: The case study of quantification of metabolites in grape juice by qNMR spectroscopy.

Nuclear Magnetic Resonance (NMR) is an analytical technique extensively used in almost every chemical laboratory for structural identification. This technique provides statistically equivalent signals in spite of using spectrometer with different hardware features and is successfully used for the traceability and quantification of analytes in food samples. Nevertheless, to date only a few internationally agreed guidelines have been reported on the use of NMR for quantitative analysis. The main goal of the present study is to provide a methodological pipeline to assess the reproducibility of NMR data produced for a given matrix by spectrometers from different manufacturers, with different magnetic field strengths, age and hardware configurations. The results have been analyzed through a sequence of chemometric tests to generate a community-built calibration system which was used to verify the performance of the spectrometers and the reproducibility of the predicted sample concentrations.

31P and 195Pt solid-state NMR and DFT studies on platinum(i) and platinum(ii) complexes.

31P and 195Pt solid state NMR spectra of anti-[(PHCy)ClPt(µ-PCy2)2Pt(PHCy)Cl] (3) and [(PHCy2)Pt(µ-PCy2)(κ2P,O-µ-POCy2)Pt(PHCy2)] (Pt-Pt) (4) were recorded under cross polarization/magic-angle spinning conditions (31P) or with the cross polarization/Carr-Purcell-Meiboom-Gill pulse sequence (195Pt) and compared to the data obtained by relativistic DFT calculations of 31P and 195Pt CS tensors and isotropic shielding at the ZORA spin-orbit level. A good agreement with the experimental results was found and it was possible to rationalize the chemical shift differences of 195Pt and 31P nuclei between compounds 3 and 4 as mostly due to a change (in opposite directions for 195Pt and 31P) of the principal component of the shielding tensor perpendicular to the molecular plane defined by the Pt and P atoms. Paramagnetic and spin-orbit terms were found to be the most important contributions to 195Pt and 31P shielding.

A Borane Platinum Complex Undergoing Reversible Hydride Migration in Solution.

Reaction of [Pt(κ2-C,N-ppy)(dmso)Cl], 1 (Hppy = 2-phenylpyridine), with Na[H2B(mb)2] (Hmb = 2-mercapto-benzimidazole) smoothly afforded the complex {[(κ3-S,B,S-HB(mb)2]Pt(κ2-C,N-ppy)H}, 2, featuring a strong reverse-dative Pt → B σ interaction in the solid state. When dissolved in thf (or acetone) solution, 2 undergoes a reversible Pt-H bond activation, establishing an equilibrium between the hexacoordinated 2 and the tetracoordinate complex {[(κ2-S,S-H2B(mb)2]Pt(κ2-C,N-ppy)}, 3, as ascertained by multinuclear NMR. Hydrolysis of the B-N bond in 2/3 resulted ultimately in the formation of a dimeric half-lantern platinum(II,II) complex [{Pt(κ2-C,N-ppy)(µ2-κ2-N,S-mb)}2], 4. The SC-XRD structures of 2 and 4 are reported.

Interplay of Internal Structure and Interfaces on the Emitting Properties of Hybrid ZnO Hierarchical Particles.

The design of hybrid organic/inorganic nanostructures with controlled assembly drives the development of materials with new or improved properties and superior performances. In this paper, the surface and internal structure of hybrid ZnO poly-N-vinylpyrrolidone (ZnO/PVP) mesocrystals are investigated in detail and correlated with their emitting properties. A photoluminescence study at room temperature reveals that the as-synthesized particles show a remarkable ultraviolet (UV) emission, whereas an emission from defects in the visible region is not observed. On the other hand, a visible emission is achieved upon calcination of the hybrid ZnO/PVP particles in air, and its intensity is found to increase with the calcination temperature and, in some cases, to overwhelm the UV emission. A molecular description is proposed for the absence of a visible emission from defects in the as-synthesized ZnO/PVP mesocrystals on the basis of Fourier transform infrared (FTIR) and solid-state 13C NMR (SSNMR) spectroscopy. An in-depth electron microscopy study sheds light on the internal organization of mesocrystals and reveals the formation of nanoreactors, that is, particles with enclosed porosity, upon thermal treatment.

Ammonia Borane Dehydrogenation Catalyzed by (κ4-EP3)Co(H) [EP3 = E(CH2CH2PPh2)3; E = N, P] and H2 Evolution from Their Interaction with NH Acids.

Two Co(I) hydrides containing the tripodal polyphosphine ligand EP3, (κ4-EP3)Co(H) [E(CH2CH2PPh2)3; E = N (1), P (2)], have been exploited as ammonia borane (NH3BH3, AB) dehydrogenation catalysts in THF solution at T = 55 °C. The reaction has been analyzed experimentally through multinuclear (11B, 31P{1H}, 1H) NMR and IR spectroscopy, kinetic rate measurements, and kinetic isotope effect (KIE) determination with deuterated AB isotopologues. Both complexes are active in AB dehydrogenation, albeit with different rates and efficiency. While 1 releases 2 equiv of H2 per equivalent of AB in ca. 48 h, with concomitant borazine formation as the final "spent fuel", 2 produces 1 equiv of H2 only per equivalent of AB in the same reaction time, along with long-chain poly(aminoboranes) as insoluble byproducts. A DFT modeling of the first AB dehydrogenation step has been performed, at the M06//6-311++G** level of theory. The combination of the kinetic and computational data reveals that a simultaneous B-H/N-H activation occurs in the presence of 1, after a preliminary AB coordination to the metal center. In 2, no substrate coordination takes place, and the process is better defined as a sequential BH3/NH3 insertion process on the initially formed [Co]-NH2BH3 amidoborane complex. Finally, the reaction of 1 and 2 with NH-acids [AB and Me2NHBH3 (DMAB)] has been followed via VT-FTIR spectroscopy (in the -80 to +50 °C temperature range), with the aim of gaining a deeper experimental understanding of the dihydrogen bonding interactions that are at the origin of the observed H2 evolution.

Homoleptic Phosphaalkyne Complexes of Silver(I).

By employing silver salts with a weakly coordinating anion Ag[A] ([A]=[FAl{OC12 F15 }3 ], [Al{OC(CF3 )3 }4 ]), two phosphaalkynes could be coordinated side-on to a bare silver(I) center to form the unprecedented homoleptic complexes [Ag(η2 -P≡CtBu)2 ][FAl{OC12 F15 }3 ] (1) and [Ag(η2 -P≡CtBu)2 ][Al{OC(CF3 )3 }4 ] (2). DFT calculations show that the perpendicular arrangement in 1 is the minimum energy structure of the coordination of the two phosphaalkynes to a silver atom, whereas for 2 a unique square-planar coordination mode of the phosphaalkynes at Ag+ was found. Reactions with donor molecules yield the trigonally planar coordinated silver salts [((CH3 )2 CO)Ag(η2 -P≡CtBu)2 ][FAl{OC12 F15 }3 ] (3) and [(C7 H8 )2 Ag(η2 -P≡CtBu)][FAl{OC12 F15 }3 ] (4). All of the compounds were comprehensively characterized in solution and in the solid state.

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

Reaction between the phosphinito bridged diplatinum species [(PHCy2 )Pt(µ-PCy2 ){κ(2) P,O-µ-P(O)Cy2 }Pt(PHCy2 )](Pt-Pt) (1), and (trimethylsilyl)acetylene at 273 K affords the σ-acetylide complex [(PHCy2 )(η(1) -Me3 SiC≡C)Pt(µ-PCy2 )Pt(PHCy2 ){κP-P(OH)Cy2 }](Pt-Pt) (2) featuring an intramolecular π-type hydrogen bond. Scalar and dipolar couplings involving the POH proton were detected by 2D NMR experiments. Relativistic DFT calculations of the geometry, relative energy, and NMR properties of model systems of 2 confirmed the structural assignment and allowed the energy of the π-type hydrogen bond to be estimated (ca. 22 kJ mol(-1) ).

Polynuclear platinum phosphanido/phosphinito complexes: formation of P-O and P-O-P bonds through reductive coupling processes.

A mixture of the asymmetric complexes of formula [(RF)2Pt(µ-Ph2PO)(µ-PPh2)Pt(µ-PPh2)2Pt(solv)(solv')] [(1-(solv)(solv')] (solv, solv' = acetone, H2O, CH3CN) has been prepared by reaction of [(RF)2Pt(II)(µ-PPh2)2Pt(II)(µ-PPh2)2Pt(II)(NCCH3)2] with AgClO4 in CH3CN/acetone. The lability of the Pt-solvent bonds allows the displacement of the coordinated solvent molecules by dppm or Cl(-) and the isolation of the tri- or hexanuclear phosphanido/phosphinito Pt(ii) complexes [(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(dppm)] (2) or [NBu4]2[(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(µ-Cl)2Pt(µ-PPh2)2Pt(µ-PPh2)(µ-PPh2O)Pt(C6F5)2] (as a mixture of the two possible isomers 4a and 4b). Complex 2 reacts with AgClO4 to form the tetranuclear derivative [(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(dppm)Ag(OClO3)] (3), which displays two Pt-Ag donor-acceptor bonds. The mixture of the hexanuclear isomers 4a-4b reacts with Tl(acac) producing the acetylacetonato complex [NBu4][(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(acac)] (5) which, upon reaction with HCl, yields back the mixture of 4a-4b. The reaction of 4a-4b with PPh3 produces [NBu4][(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(Cl)(PPh3)] (6) as a mixture of isomers with the chloro ligand located syn (6a) or anti (6b) to the PPh2O(-) group. Either the reaction of 6 with AgClO4 or the treatment of 5 with HPPh3ClO4 results in the formation of the species [(C6F5)2Pt(II)(µ-PPh2)2Pt(I)(µ-PPh2OPPh2)Pt(I)(PPh3)] (7) (44 VEC), which can be explained as the consequence of a PPh2O/PPh2 reductive coupling and a rearrangement of ligands in the molecule generating a Pt(ii),Pt(i),Pt(i) compound. All complexes were characterised in the solid state by XRD (only one of the isomers, in the cases of 4 and 6) and in solution by NMR spectroscopy.

Sulfur-Assisted Phenyl Migration from Phosphorus to Platinum in PtW2 and PtMo2 Clusters Containing Thioether-Functionalized Short-Bite Ligands of the Bis(diphenylphosphanyl)amine-Type.

The reactivity of dichloroplatinum(II) complexes containing thioether-functionalized bis(diphenylphosphanyl)amines of formula (Ph2P)2N(CH2)2SR (R = (CH2)5CH3, CH2Ph) toward group 6 carbonylmetalates Na[M(CO)3Cp] (M = Mo or W, Cp = cyclopentadienyl) was explored. Reactions with two or more equivalents of Na[M(CO)3Cp] (M = Mo or W) afforded the trinuclear complexes of general formula [PtPh{M(CO)3Cp}{µ-P(Ph)N(CH2CH2SR)(PPh2)-κ(3)P,P,S}M(CO)2Cp] (3 M = Mo, R = (CH2)5CH3; 4 M = Mo, R = CH2Ph; 9 M = W, R = (CH2)5CH3; 10 M = W, R = CH2Ph), the structure of which consists of a six-membered platinacycle condensed with a four-membered M-P-N- P cycle, together with small amounts of isomeric PtM2 clusters [PtM2(CO)5Cp2{(Ph2P)2N(CH2CH2SR)-κ(2)P,P}] (5 M = Mo, R = (CH2)5CH3; 6 M = Mo, R = CH2Ph; 11 M = W, R = (CH2)5CH3; 12 M = W, R = CH2Ph) in which the ligand (Ph2P)2NR solely chelates the Pt atom or bridges an M-Pt bond as in [PtM2(CO)5Cp2{µ-(Ph2P)2N(CH2CH2SR)-κ(2)P,P}] (7 M = Mo, R = (CH2)5CH3; 8 M = Mo, R = CH2Ph; 13 M = W, R = (CH2)5CH3; 14 M = W, R = CH2Ph). The synthesis of the trinuclear complexes 3, 4, 9, and 10 entails an unexpected P-phenyl bond cleavage reaction and phenyl migration onto Pt. When only 1 equiv of Na[M(CO)3Cp] (M = Mo or W) was used, the heterodinuclear products of monosubstitution [PtCl{M(CO)3Cp}{Ph2PN(R)PPh2-P,P}] (15 M = Mo, R = (CH2)5CH3; 16 M = Mo, R = CH2Ph; 17 M = W, R = (CH2)5CH3; 18 M = W, R = CH2Ph) were obtained, which are the precursors to the bicyclic products 3, 4, 9, and 10, respectively. Density functional calculations were performed to study the thermodynamics of the formation of all the new complexes, to evaluate the relative stabilities of the isomeric chelated and bridged forms, and to trace the mechanism of formation of the phosphanido-bridged products 3, 4, 9, and 10. It was concluded that Pt(II) complexes containing a thioether-functionalized short-bite ligand, [PtCl2{Ph2PN(R)PPh2}], react with Na[M(CO)3Cp] to yield first heterodinuclear Pt-M and then heterotrinuclear PtM2 complexes resulting from the activation of a P-C bond in one of the PPh2 groups and phenyl migration to Pt. The critical role of an intramolecular thioether group was demonstrated.

Multinuclear Solid-State NMR and DFT Studies on Phosphanido-Bridged Diplatinum Complexes.

Multinuclear ((31)P, (195)Pt, (19)F) solid-state NMR experiments on (nBu4N)2[(C6F5)2Pt(µ-PPh2)2Pt(C6F5)2] (1), [(C6F5)2Pt(µ-PPh2)2Pt(C6F5)2](Pt-Pt) (2), and cis-Pt(C6F5)2(PHPh2)2 (3) were carried out under cross-polarization/magic-angle-spinning conditions or with the cross-polarization/Carr-Purcell Meiboom-Gill pulse sequence. Analysis of the principal components of the (31)P and (195)Pt chemical shift (CS) tensors of 1 and 2 reveals that the variations observed comparing the isotropic chemical shifts of 1 and 2, commonly referred to as "ring effect", are mainly due to changes in the principal components oriented along the direction perpendicular to the Pt2P2 plane. DFT calculations of (31)P and (195)Pt CS tensors confirmed the tensor orientation proposed from experimental data and symmetry arguments and revealed that the different values of the isotropic shieldings stem from differences in the paramagnetic and spin-orbit contributions.