The synthesis of a new trisbenzylsilanephosphine P{(o-CHCH)SiMeH} (1) is shown to proceed with high yields from P(o-tolyl). Compound 1 coordinates to the Rh and Ir dimers [MCl(COD)] (M = Rh, Ir) in a tetradentate or tridentate fashion, depending on the strict exclusion of water. The dimeric compounds [ClM(SiMeCH-o-CH)P(o-CH-CHSiMeH)], 2Rh and 2Ir, feature a tetradentate coordination of the starting ligand with P and two Si atoms as well as a non-classical agostic Si-H group. The presence of adventitious water in the solvents leads to the formation of two new complexes [(μ-Cl)M(SiMeCH-o-CH)P(o-CH-CHSiMeOSiMeCH-o-CH-)P(SiMeCH-o-CH)], 3Rh and 3Ir, which feature a siloxane bridge through Si-H bond breaking in 2. Reaction of [RhCl(COD)] with the bisbenzylsilanephosphine PhP{(o-CHCH)SiMeH} leads to the formation of compound 4Rh which features also a dimeric structure with the SiPSi ligand coordinated through the two silicon atoms, one of which occupies the apical position of a square-pyramidal geometry in the solid state, while the second is disposed equatorially trans to π-donor Cl. Finally, bidentate coordination of a PSi ligand is achieved by reaction of [RhCl(COD)] with PhP{(o-CHCH)SiMeH} which leads to the monometallic species [RhCl(SiMeCH-o-CH-PPh)], 5Rh, incorporating two chelating PSi ligands and maintaining a Cl ligand.
Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M −1 ) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.
Incorporating pendant silicon functionalities into phosphine ligands enables to profit from the strong σ‐electron donor and trans influence properties of Si while enhancing the coordination ability of the ligand. Herein, we show that the introduction of bulky sigma donor substituents on the Si atoms and modulation of the number of Si–H functional groups in a series of phosphinobenzylsilanes allow either the stabilization of rare highly unsaturated 14‐electron rhodium(III) and iridium(III) species devoid of agostic interactions or the access to mixed‐valence MI–MIII complexes. Our findings using isopropyl‐substituted silicon are markedly different from those obtained when employing the methyl‐substituted Si series.
Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(III) devoid of agostic interactions. The complexes [X-Rh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2], where X = Cl (Rh-1),...
By using two different multidentate phosphinosilyl ligands, we prepared the two platinum complexes [Pt{PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }PPh 3 ] (3) and [Pt{P((o-C 6 H 4 )CH 2 SiMe 2 ) 2 (o-C 6 H 4 )CHSiMe 2 )}PPh 3 ] (4) exhibiting a trans configuration of the silicon atoms in a typical square-planar geometry around a Pt(II) center. Complex 4 results from intramolecular C− H activation of a methylene moiety by the third silicon atom of the original ligand and displays an anagostic C−H•••Pt interaction, as supported by solution NMR data and solid-state X-ray diffraction analysis. The reactivity of 3 toward small molecules is also discussed. In the case of H 2 and CO, the corresponding dihydride [PtH 2 {PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }PPh 3 ] (5) and dicarbonyl [Pt{PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }(CO) 2 ] (6) complexes were characterized, whereas reduction to Pt(0) and release of PPh 3 and HSiMe 3 were observed upon thermolysis in the presence of HBpin.
Selective anion sensing by luminescent chemosensors capable
of
operating in aqueous conditions is a central field of modern supramolecular
chemistry that impacts analytical and biological chemistry. A cationic
cyclometalated [Pt(N^C^N)NCCH3]OTf complex, 1 [N^C^N = 1,3-bis(1-(p-tolyl)-benzimidazol-2′-yl)benzene,
OTf = triflate], was prepared, structurally described by single-crystal
X-ray diffraction and studied in-depth as a luminescent chemosensor
for anions in aqueous phase and solid state. A series of related neutral
[Pt(N^C^N)X] complexes (X = Cl, 2; CN, 3 and I, 4) were formed readily upon treatment of 1 with the respective NaX salt in aqueous media and were described
structurally by X-ray diffraction. Complex 1 is hydrostable
with phosphorescent green emission originated by intraligand transitions,
and [d
yz
(Pt) → π*(N^C^N)]
charge transfer transitions, as evidenced by TD-DFT calculations and
lifetime. Additions of halides, pseudohalides, oxyanions, and dicarboxylates
to a neutral aqueous solution of 1 modified its green
emission intensity with a pronounced affinity (K =
1.5 × 105 M–1) and turn-on signal
toward Cl– within the micromolar concentration range.
Pt complex 1 is two orders of magnitude more selective
for Cl– than the other halides, CN– and basic oxyanions. Such Cl– affinity for a metal-based
chemosensor in aqueous media is still rare. On the basis of X-ray
crystallographic analysis and multiple spectroscopic tools (NMR, UV–vis,
luminescence, MS, lifetimes) the origin of this selectivity hinges
on the cooperative three-point recognition involving one coordination
bond (Pt–Cl) and two convergent short C–H···Cl– contacts. This strong affinity and efficient optical
response can be utilized in quantitative Cl– sensing
in real samples and solid–liquid extractions. Additionally,
chloro-Pt complex, 2 may be relevant to bioimaging as
a marker for cell nuclei, as revealed by its emission within living
cells and intracellular distribution by confocal microscopic studies.
These results demonstrate the usefulness of the new water-stable luminescent
Pt-N^C^N complexes as effective analytical tools in anion sensing
and extraction agents.
The reactivities
of tris(benzyldimethylsilyl)phosphine [P(o-C6H4-CH2SiMe2H)3] (1) and tris(benzyldiphenylsilyl)phosphine
[P(o-C6H4-CH2SiPh2H)3] (6) toward the same platinum
precursor [Pt(PPh3)3] are strikingly different.
The reaction with 1 renders the trans disilyl platinum(II) complex [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}PPh3] (2) in which the ligand coordinates in a tridentate
fashion while a new Si–C bond is formed from the third Si moiety.
The most prominent feature is an anagostic interaction that is established
at the apical position. In contrast, the reaction of [Pt(PPh3)3] with 6 yields the hexacoordinated hydrido
trisilyl platinum(IV) complex [PtH{P(o-C6H4-CH2SiPh2)3}PPh3] (7). We have studied the effect of the variation
of the monodentate ligand in 2 by simple substitution
reactions. We found a systematic variation of the chemical shift of
the anagostic hydrogen in the 1H nuclear magnetic resonance
spectrum of the corresponding PMe3, P(OPh)3,
and CO complexes that can in principle be ascribed to a varying degree
of the π acceptor character of the ancillary ligand. However,
theoretical calculations at the density functional theory level show
only slight changes in the frontier orbitals in line with predominantly
closed-shell electrostatic interactions.
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