“…It is interesting to note that no substitution occurs between [Pd 2 (μ-dppm) 2 Cl 2 ] and dppm, while [Pt 2 (μ-dppm) 2 Cl 2 ] does react similarly to 1 . The coupling constants ( 1 J Pt - PA = 2930 Hz, 1 J Pt - PC = 2121 Hz, and 2 J PC - PD = 54 Hz) agree with the literature data for species such as [Pt 2 (μ-dppm) 2 Cl(η 1 -dppm)] + ( 1 J Pt - PA = 2885 Hz and 1 J Pt - PC = 2155 Hz) and [Pt 2 (μ-dppm) 2 Cl(PPh 3 )] + ( 1 J Pt - PA = 2856 Hz and 1 J Pt - PC = 2207 Hz) . The resonance of the uncoordinated phosphorus P D of the pendent dppm gives rise to a doublet at δ −26.7, quite close to the chemical shift found for free dppm (δ −21.3).…”
The heterodinuclear d(9)-d(9) title compound 1, whose crystal structure has been solved, reacts with dppm [bis(diphenylphosphino)methane] in the presence of NaBF4 to generate the salt [ClPd(mu-dppm)2Pt(eta(1)-dppm)][BF4] (2a), which contains a Pt-bound dangling dppm ligand. 2a has been characterized by 1H and 31P NMR, Fourier transform Raman [nu(Pd-Pt) = 138 cm(-1)], and UV-vis spectroscopy [lambda(max)(dsigma-dsigma*) = 366 nm]. In a similar manner, [ClPd(mu-dppm)2Pt(eta(1)-dppm=O)][BF4] (2b), ligated with a dangling phosphine oxide, has been prepared by the addition of dppm=O. The molecular structure of 2b has been established by an X-ray diffraction study. 2a reacts with 1 equiv of NaBH4 to form the platinum hydride complex [(eta(1)-dppm)Pd(mu-dppm)2Pt(H)][BF4] (3). Both 2a and 3 react with an excess of NaBH4 to provide the mixed-metal d(10)-d(10) compound [Pd(mu-dppm)3Pt] (4). The photophysical properties of 4 were studied by UV-vis spectroscopy [lambda(max)(dsigma-dsigma*) = 460 nm] and luminescence spectroscopy (lambda(emi) = 724 nm; tau(e) = 12 +/- 1 micros, 77 K). The protonation of 1 and 4 leads to [ClPd(mu-dppm)2(mu-H)PtCl]+ (5) and 3, respectively. Stoichiometric treatment of 1 with cyclohexyl or xylyl isocyanide yields [ClPd(mu-dppm)2Pt(CNC6H11)]Cl (6a) and [ClPd(mu-dppm)2Pt(CN-xylyl)]Cl (6b) ligated by terminal-bound CNR ligands. In contrast, treatment of 1 with the phosphonium salt [C[triple bond]NCH2PPh3]Cl affords the structurally characterized A-frame compound [ClPd(mu-dppm)2(mu-C=NCH2PPh3)PtCl]Cl (6c), spanned by a bridging isocyanide ligand. The electrochemical reduction of 2a at -1.2 V vs SCE, as well as the reduction of 5 in the presence of dppm, leads to a mixture of products 3 and 4. Further reduction of 3 at -1.7 V vs SCE generates 4 quantitatively. The reoxidation at 0 V of 4 in the presence of Cl- ions produces back complex 2a. The whole mechanism of the reduction of 1 has been established.
“…It is interesting to note that no substitution occurs between [Pd 2 (μ-dppm) 2 Cl 2 ] and dppm, while [Pt 2 (μ-dppm) 2 Cl 2 ] does react similarly to 1 . The coupling constants ( 1 J Pt - PA = 2930 Hz, 1 J Pt - PC = 2121 Hz, and 2 J PC - PD = 54 Hz) agree with the literature data for species such as [Pt 2 (μ-dppm) 2 Cl(η 1 -dppm)] + ( 1 J Pt - PA = 2885 Hz and 1 J Pt - PC = 2155 Hz) and [Pt 2 (μ-dppm) 2 Cl(PPh 3 )] + ( 1 J Pt - PA = 2856 Hz and 1 J Pt - PC = 2207 Hz) . The resonance of the uncoordinated phosphorus P D of the pendent dppm gives rise to a doublet at δ −26.7, quite close to the chemical shift found for free dppm (δ −21.3).…”
The heterodinuclear d(9)-d(9) title compound 1, whose crystal structure has been solved, reacts with dppm [bis(diphenylphosphino)methane] in the presence of NaBF4 to generate the salt [ClPd(mu-dppm)2Pt(eta(1)-dppm)][BF4] (2a), which contains a Pt-bound dangling dppm ligand. 2a has been characterized by 1H and 31P NMR, Fourier transform Raman [nu(Pd-Pt) = 138 cm(-1)], and UV-vis spectroscopy [lambda(max)(dsigma-dsigma*) = 366 nm]. In a similar manner, [ClPd(mu-dppm)2Pt(eta(1)-dppm=O)][BF4] (2b), ligated with a dangling phosphine oxide, has been prepared by the addition of dppm=O. The molecular structure of 2b has been established by an X-ray diffraction study. 2a reacts with 1 equiv of NaBH4 to form the platinum hydride complex [(eta(1)-dppm)Pd(mu-dppm)2Pt(H)][BF4] (3). Both 2a and 3 react with an excess of NaBH4 to provide the mixed-metal d(10)-d(10) compound [Pd(mu-dppm)3Pt] (4). The photophysical properties of 4 were studied by UV-vis spectroscopy [lambda(max)(dsigma-dsigma*) = 460 nm] and luminescence spectroscopy (lambda(emi) = 724 nm; tau(e) = 12 +/- 1 micros, 77 K). The protonation of 1 and 4 leads to [ClPd(mu-dppm)2(mu-H)PtCl]+ (5) and 3, respectively. Stoichiometric treatment of 1 with cyclohexyl or xylyl isocyanide yields [ClPd(mu-dppm)2Pt(CNC6H11)]Cl (6a) and [ClPd(mu-dppm)2Pt(CN-xylyl)]Cl (6b) ligated by terminal-bound CNR ligands. In contrast, treatment of 1 with the phosphonium salt [C[triple bond]NCH2PPh3]Cl affords the structurally characterized A-frame compound [ClPd(mu-dppm)2(mu-C=NCH2PPh3)PtCl]Cl (6c), spanned by a bridging isocyanide ligand. The electrochemical reduction of 2a at -1.2 V vs SCE, as well as the reduction of 5 in the presence of dppm, leads to a mixture of products 3 and 4. Further reduction of 3 at -1.7 V vs SCE generates 4 quantitatively. The reoxidation at 0 V of 4 in the presence of Cl- ions produces back complex 2a. The whole mechanism of the reduction of 1 has been established.
“…31 P NMR spectroscopy was used to further characterize the resulting compounds because it is highly diagnostic of the coordination environment. Additionally, the resonance shifts and platinum–phosphorus coupling patterns were consistent with the presence of a combination of cis - 4a , trans - 4b , and combined cis/trans ( 4c ) fully open complexes (Figure a). − As summarized in Figure , the fully open trans species 4b [ trans -Pt 2 Cl 4 (κ 1 :μ:κ 1 -NHC,S)(κ 1 :μ:κ 1 -P,S)] contains two platinum nodes in which the phosphine and carbene are trans to one another; this configuration is evidenced by a resonance at 9.7 ppm with a J P–Pt coupling constant of 2300 Hz. The presence of the cis complex 4a [ cis -Pt 2 Cl 4 (κ 1 :μ:κ 1 -NHC,S)(κ 1 :μ:κ 1 -P,S)] is evidenced by a resonance at 1.8 ppm with a larger J P–Pt of 3740 Hz.…”
Macrocycles capable of host-guest chemistry are an important class of structures that have attracted considerable attention because of their utility in chemical separations, analyte sensing, signal amplification, and drug delivery. The deliberate design and synthesis of such structures are rate-limiting steps in utilizing them for such applications, and coordination-driven supramolecular chemistry has emerged as a promising tool for rapidly making large classes of such systems with attractive molecular recognition capabilities and, in certain cases, catalytic properties. A particularly promising subset of such systems are stimuli-responsive constructs made from hemilabile ligands via the weak-link approach (WLA) to supramolecular coordination chemistry. Such structures can be reversibly toggled between different shapes, sizes, and charges based upon small-molecule and elemental-anion chemical effectors. In doing so, one can deliberately change their recognition properties and both stoichiometric and catalytic chemistries, thereby providing mimics of allosteric enzymes. The vast majority of structures made to date involve two-state systems, with a select few being able to access three different states. Herein, we describe the synthesis of a new allosterically regulated four-state macrocycle assembled via the WLA. The target structure was made via the stepwise assembly of ditopic bidentate hemilabile N-heterocyclic carbene thioether (NHC,S) and phosphino thioether (P,S) ligands at Pt metal nodes. The relatively simple macrocycle displays complex dynamic behavior when addressed with small-molecule effectors, and structural switching can be achieved with several distinct molecular cues. Importantly, each state was fully characterized by multinuclear NMR spectroscopy and, in some cases, single-crystal X-ray diffraction studies and density functional theory computational models. This new structure opens the door to complex multicue switching reminiscent of multistate chemoswitches that could be important in controlling stoichiometric and catalytic transformations as well as generating molecular logic systems.
“…For comparison, the corresponding coupling constant is approximately 80 Hz in the dipalladium complex [Pd 2 (PMe 3 ) 6 ][hfac] 2 and 185 Hz in the mixed-metal complex [PdPt(PMe 3 ) 6 ][hfac] 2 , The 1 J Pt - Pt coupling constant of 1350 Hz falls in the 100−9000 Hz range reported for other diplatinum compounds 2 500 MHz 1 H NMR spectrum of [Pt 2 (PMe 3 ) 6 ][hfac] 2 , 2 , in CD 2 Cl 2 at 25 °C. 3 Bottom: 121.64 MHz 31 P{ 1 H} NMR spectrum of [Pt 2 (PMe 3 ) 6 ][hfac] 2 , 2 , in CD 2 Cl 2 at 25 °C.…”
Comproportionation of the platinum(0) complex
Pt(PMe3)4 with the platinum(II)
hexafluoroacetylacetonate
complexes Pt(hfac)2 or
[Pt(hfac)(PMe3)2][hfac]
yields diplatinum species of stoichiometry
[Pt2(μ-hfac)(PMe3)4][hfac], 1, and
[Pt2(PMe3)6][hfac]2,
2, respectively. The NMR spectra and X-ray crystal
structure of 1 show that
the two platinum centers are chemically inequivalent; one is a
square-planar platinum(II) center, and the other is
trigonal planar platinum(0) center. One of the hfac groups is
anionic while the other bridges between the two
platinum atoms. Each platinum center bears two PMe3
ligands, and the bridging hfac group is bound to one
platinum center in the usual fashion through its two oxygen atoms.
The bridging hfac group, however, is bound
to the other platinum center as an η2 alkene ligand via
its methine carbon and one of the two carbonyl carbons.
The two platinum atoms do not interact directly with one another
and are separated by 3.786(1) Å. The 1H
NMR
spectra of the hexakis(trimethylphosphine)diplatinum complex
2 are consistent with a structure in which the
two
platinum centers are connected by a Pt−Pt bond and the six
PMe3 groups complete two mutually
perpendicular
square-planar coordination environments. Treatment of
Pt(PMe3)4 with
[Pt(PMe3)4][hfac]2 in
tetrahydrofuran
gives the platinum(II) hydride
[PtH(PMe3)4][hfac], 3.
The 1H and 31P{1H}
NMR data of 3 are consistent with a
trigonal bipyramidal structure; the hydride ligand occupies an axial
position. The hydride ligand evidently arises
from adventitious water. Thermolysis of 1 and
2 under vacuum gives the platinum(II) methyl complex
[PtMe(PMe3)3][hfac] as a result of the
cleavage of one of the P−C bonds in the PMe3 ligands.
Crystal data for 1 at
−75 °C: triclinic, space group P1̄, a
= 9.848(2) Å, b = 12.079(3) Å, c
= 15.373(3) Å, α = 84.70(2)°, β =
78.57(2)°, γ = 80.30(2)°, V =
1763(7) Å3, Z = 2,
R
F
= 0.043,
R
w
F
= 0.044 for 400
variables and 3360 reflections
with I > 2.58 σ(I).
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