The behavior of the tetra-υ-pyrophosphito-diplatinum(II) ion Pt2(P2O5H2)4−4 and related species

Applications of Halogen-Atom Transfer (XAT) for the Generation of Carbon Radicals in Synthetic Photochemistry and Photocatalysis

The halogen-atom transfer (XAT) is one of the most important and applied processes for the generation of carbon radicals in synthetic chemistry. In this review, we summarize and highlight the most important aspects associated with XAT and the impact it has had on photochemistry and photocatalysis. The organization of the material starts with the analysis of the most important mechanistic aspects and then follows a subdivision based on the nature of the reagents used in the halogen abstraction. This review aims to provide a general overview of the fundamental concepts and main agents involved in XAT processes with the objective of offering a tool to understand and facilitate the development of new synthetic radical strategies.

Demystifying the Origin of Vibrational Coherence Transfer Between the S1 and T1 States of the Pt-pop Complex

We demonstrate that spin-vibronic coupling is the most significant mechanism in vibrational coherence transfer (VCT) from the singlet (S₁) to the triplet (T₁) state of the [Pt₂(P₂O₅H₂)₄]^4- complex. Our time-dependent correlation function-based study shows that the rate of intersystem crossing (k_ISC) through direct spin-orbit coupling is negligibly small, making VCT vanishingly small due to the ultrashort decoherence time (2.5 ps). However, the inclusion of the spin-vibronic contribution to the net k_ISC in selective normal modes along the Pt-Pt axis increases the k_ISC to such an extent that VCT becomes feasible. Our results suggest that k_ISC for the S₁ →T₂ (τ_ISC = 1.084 ps) is much faster than the S₁ → T₁ (τ_ISC = 763.4 ps) and S₁ → T₃ (τ_ISC = 13.38 ps) in CH₃CN solvent, indicating that VCT is possible from the low-lying excited singlet (S₁) to the triplet (T₁) state through the intermediate T₂ state. This is the first example where VCT occurs solely due to spin-vibronic interactions. This finding can pave the way for new types of photocatalysis.

Experimental and theoretical investigation of a metalloreceptor bearing a [Re(CO)3]+ core incorporating a multifunctional ligand: selective reactivity towards Zn2+ and CN− ions

Novel Re(i) complex containing multifunctional ligand HL shows selective reactivity towards Zn²⁺ and CN⁻.

Grid-Based Projector Augmented Wave (GPAW) Implementation of Quantum Mechanics/Molecular Mechanics (QM/MM) Electrostatic Embedding and Application to a Solvated Diplatinum Complex

A multiscale density functional theory-quantum mechanics/molecular mechanics (DFT-QM/MM) scheme is presented, based on an efficient electrostatic coupling between the electronic density obtained from a grid-based projector augmented wave (GPAW) implementation of density functional theory and a classical potential energy function. The scheme is implemented in a general fashion and can be used with various choices for the descriptions of the QM or MM regions. Tests on H₂O clusters, ranging from dimer to decamer show that no systematic energy errors are introduced by the coupling that exceeds the differences in the QM and MM descriptions. Over 1 ns of liquid water, Born-Oppenheimer QM/MM molecular dynamics (MD) are sampled combining 10 parallel simulations, showing consistent liquid water structure over the QM/MM border. The method is applied in extensive parallel MD simulations of an aqueous solution of the diplatinum [Pt₂(P₂O₅H₂)₄]^4- complex (PtPOP), spanning a total time period of roughly half a nanosecond. An average Pt-Pt distance deviating only 0.01 Å from experimental results, and a ground-state Pt-Pt oscillation frequency deviating by <2% from experimental results were obtained. The simulations highlight a remarkable harmonicity of the Pt-Pt oscillation, while also showing clear signs of Pt-H hydrogen bonding and directional coordination of water molecules along the Pt-Pt axis of the complex.

Synchrotron ultrafast techniques for photoactive transition metal complexes

In the last decade, the use of time-resolved X-ray techniques has revealed the structure of light-generated transient species for a wide range of samples, from small organic molecules to proteins. Time resolutions of the order of 100 ps are typically reached, allowing one to monitor thermally equilibrated excited states and capture their structure as a function of time. This review aims at providing a general overview of the application of time-resolved X-ray solution scattering (TR-XSS) and time-resolved X-ray absorption spectroscopy (TR-XAS), the two techniques prevalently employed in the investigation of light-triggered structural changes of transition metal complexes. In particular, we herein describe the fundamental physical principles for static XSS and XAS and illustrate the theory of time-resolved XSS and XAS together with data acquisition and analysis strategies. Selected pioneering examples of photoactive transition metal complexes studied by TR-XSS and TR-XAS are discussed in depth.

Opening the paddlewheel: unusual coordination of [Mo2] dumbbells in the chain structures of A[Mo2(CF3SO3)5]·2CF3SO3H (A = Na, Rb, Cs)

The reaction of Mo(II)acetate, concentrated triflic acid and the alkaline metal triflates A(CF(3)SO(3)) (A = Na, Rb, Cs) in sealed glass ampoules at 110 °C yielded red single crystals of A[Mo(2)(CF(3)SO(3))(5)]·2CF(3)SO(3)H (A = Na: triclinic, P-1, Z = 4, a = 13.714(1) Å, b = 14.339(1) Å, c = 21.340(2) Å, α = 81.78(1)°, β = 75.21(1)°, γ = 62.65(1)°; A = Rb/Cs: monoclinic, P2(1)/m, Z = 2, a = 11.561(1)/11.584(1) Å, b = 14.817(1)/14.9472(8) Å, c = 11.6208(1)/11.744(1) Å, β = 112.38(1)/113.48(1)°). The crystal structures contain dumbbell shaped [Mo(2)] moieties surrounded by three chelating and four monodentate triflate anions leading to an opening of the typical paddlewheel fragment at one of its edges. The monodentate triflate anions are connected to further [Mo(2)] dumbbells leading to infinite anionic chains according to (∞)(1)[Mo(2)(CF(3)SO(3))(3/1)(CF(3)SO(3))(4/2)](-). The charge balance is achieved by the alkaline metal ions that are additionally coordinated by triflic acid molecules. Theoretical investigations were preformed on the open paddlewheel fragment and are in good agreement with the experimental findings. According to DTA/TG measurements and the XRD investigations the decomposition of the compounds occurs in multiple steps and leads to MoO(2) and A(2)MoO(4).

Palladium(III) in Synthesis and Catalysis

While the organometallic chemistry of Pd in its (0), (+II), and (+IV) oxidation states is well-established, organometallic Pd(III) chemistry remains widely unexplored. Few characterized Pd(III) complexes are known, which has inhibited detailed study of the organometallic chemistry of Pd(III). In this review, the potential roles of both mono- and dinuclear Pd(III) complexes in organometallic chemistry will be discussed. While not widely recognized, Pd in the (+III) oxidation state may play a significant role in a variety of known Pd-catalyzed reactions.

Crystal Structures and Luminescence Behaviour of d10 Metal - Organic Complexes with Multipyridine Ligands

Six d10 metal–organic complexes with multipyridine ligands, [Cd(terpy)2](NO3)2·2H2O (1), [Cd(terpy)(NO3)2(H2O)] (2), [Hg(terpy)I2] (3), [Zn(tpt)(NO3)(H2O)2]NO3 (4), [Zn2(tpt)2(4,4′-bipy)(4H2O)](NO3)4·4H2O (5), [Zn(tpt)(OAc)2]·5H2O (6) (terpy = 2,2′:6′,2′-terpyridine, tpt = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, 4,4′-bipy = 4,4′-bipyridine) were synthesized and structurally characterized. The abundant hydrogen-bonding interactions extend complex 2 into ladder-like 1D chains, discrete molecules of 4 into a 2D layer structure, complex 5 into a 2D hydrogen-bonded network through linking the hydrogen-bonded ribbons with hexagonal and four-sided rings, and complex 6 into a 3D hydrogen-bonded network through combining water helical chains. Fluorescence analyses of 1–6 in the solid state are investigated at both room temperature and 10 K. The emission spectra of 1–2 show a large red shift, which is ascribed to ligand-to-ligand charge transfer combined with ligand-to-metal charge transfer, whereas emissions of 4–6 all originate from intraligand π-π* transitions. In organic solvents, 1–6 behave very differently and their emission spectra exhibit various luminescences, with an obvious blue shift indicating strong solvent effects. The X-ray diffraction and thermal gravimetric analyses for complexes 1–6 are also reported.

Theoretical studies on metal-metal interaction, excited states, and spectroscopic properties of binuclear Au-Au, Au-Rh, and Rh-Rh complexes with diphosphine ligands: buildup of complexity from monomers to dimers

To understand their photocatalytic activity and application in luminescent materials, a series of gold and rhodium phosphine complexes (mononuclear [Au(I)(PH(3))(2)](+) (1) and [Rh(I)(CNH)(2)(PH(3))(2)](+) (2); homobinuclear [Au(I)(2)(PH(2)CH(2)PH(2))(2)](2+) (3) and [Rh(I)(2)(CNH)(4)(PH(2)CH(2)PH(2))(2)](2+) (4); heterobinuclear [Au(I)Rh(I)(CNH)(2)(PH(2)CH(2)PH(2))(2)](2+) (5), [Au(I)Rh(I)(CNH)(2)(PH(2)NHPH(2))(2)Cl(2)] (6), and [Au(I)Rh(I)(CNH)(2)(PH(2)NHPH(2))(2)](2+) (7); and oxidized derivatives [Au(II)Rh(II)(CNH)(2)(PH(2)CH(2)PH(2))(2)](4+) (8), [Au(II)Rh(II)(CNH)(2)(PH(2)NHPH(2))(2)Cl(3)](+) (9), and [Au(II)Rh(II)(CNH)(2)(PH(2)NHPH(2))(2)](4+) (10)) were investigated using ab initio methods and density functional theory. With the use of the MP2 method, the M-M' distances in 3-7 were estimated to be in the range of 2.76-3.02 A, implying the existence of weak metal-metal interaction. This is further evident in the stretching frequencies and bond orders of M-M'. The two-electron oxidation from 5-7 to their respective partners 8-10 was shown to mainly occur in the gold-rhodium centers. Experimental absorption spectra were well reproduced by our time-dependent density functional theory calculations. The metal-metal interaction results in a large shift of d(z(2)) --> p(z) transition absorptions in binuclear complexes relative to mononuclear analogues and concomitantly produces a low-lying excited state that is responsible for increasing visible-light photocatalytic activities. Upon excitation, the metal-centered transition and the metal-to-metal charge transfer strengthen the metal-metal interaction in triplet excited states for 3-6, while the promotion of electrons into the sigma*(d(z(2))) orbital weakens the interaction in 9.

Palladium diselenolenes: a new group of near-infrared lumophores

We describe the photochemical characteristics of two phosphorescent palladium diselenolenes [Pd(2)(Se(2)C(8)H(12))(2)(PBu(3))(2)] (1) and [Pd(2)(Se(2)C(8)H(12))(2)(PPh(3))(2)] (2) which, to the best of our knowledge, are the first reported examples of luminescent Pd-Se compounds. Both compounds exhibit broadband near-infrared phosphorescence in the solid state, with lambda(max) of 717 nm for 1 and 792 nm for 2 at 298 K, and 752 nm for 1 and 785 nm for 2 at 77 K. No phosphorescence was detected for either compound when they were dissolved in nitrogen-purged acetonitrile or toluene solution at 298 K but they do phosphoresce at 77 K in organic glasses with emission quantum yields of 0.12 (+/-0.01) for 1 and 0.13 (+/-0.01) for 2 in an ethanol/diethylether/toluene (1:2:1) (EDT) glass. Emission lifetimes at 77 K are the same whether in the solid state or in an organic glass with first order fit lifetimes of tau = 18.8 (+/-0.7) micros and 11.5 (+/-0.3) micros for 1 and 2, respectively. Combination of these lifetimes with quantum yields gives radiative lifetimes of 151 (+/-13) micros and 86 (+/-7) micros for compounds 1 and 2, respectively, at 77 K in EDT glass. At 77 K solid state quantum yields are estimated to be of the same order of magnitude as those in glasses, and these decrease by a factor of about 3-5 in going from 77 to 298 K. In the solid state at 298 K emission lifetimes are 1.83 (+/-0.02) micros and 7.0 (+/-0.3) micros for 1 and 2, respectively. We could detect no transients by nanosecond flash photolysis which could be assigned to the triplet state in room temperature solution, and no emission assignable to singlet oxygen across the wavelength range 1200-1350 nm upon 550 nm excitation of either 1 or 2 in acetonitrile solution. We estimate the quantum yield of singlet oxygen formation to be less than about 5 x 10(-4), which is also an upper limit for the yield of triplet states of any significant lifetime in fluid solution. Density functional theory (DFT) calculations of the S(0) to S(1) and T(1) transitions show a shift in molecular orbital character from one with significant -ene pi involvement but very little P involvement in the ground-state to one with less -ene pi but greater P involvement in the excited states; there is also a significant shift in the distribution of involvement of atomic orbitals on the four Se atoms.

Theoretical Insight into Electronic Structures and Spectroscopic Properties of [Pt2(pop)4]4-, [Pt2(pcp)4]4-, and Related Derivatives (pop = P2O5H22- and pcp = P2O4CH42-)

The structures of [Pt2(pop)4]4-, [Pt2(pcp)4]4-, and related species [Pt2(pop)4X2]4- and [Pt2(pop)4]2- in the ground states (pop = P2O5H2(2-), pcp = P2O4CH4(2-), and X = I, Br, and Cl) were optimized using the second-order Møller-Plesset perturbation (MP2) method. It is shown that the Pt-Pt distances decrease in going from [Pt2(pop)4]4- to [Pt2(pop)4X2]4- to [Pt2(pop)4]2-. This is supported by the analyses of their electronic structures. The calculated aqueous absorption spectra at the time-dependent density functional theory (TD-DFT) level agree with experimental observations. The unrestricted MP2 method was employed to optimize the structures of [Pt2(pop)4]4- and [Pt2(pcp)4]4- in the lowest-energy triplet excited states. The Pt-Pt contraction trend is well reproduced in these calculations. For [Pt2(pop)4]4-, the Pt-Pt distance decreases from 2.905 A in the ground state to 2.747 A in the excited state, which is comparable to experimental values of 2.91-2.92 A and 2.64-2.71 A, respectively. On the basis of the excited-state structures of such complexes, TD-DFT predicts the solution emissions at 480 and 496 nm, which is closer to the experimental values of 512 and 510 nm emissions, respectively.

Novel Luminescent Mixed-Metal PtTl-Alkynyl-Based Complexes: The Role of the Alkynyl Substituent in Metallophilic and η2(π⋅⋅⋅Tl)-Bonding Interactions

A novel series of [PtTl(2)(C[triple chemical bond]CR)(4)](n) (n = 2, R = 4-CH(3)C(6)H(4) (Tol) 1, 1-naphthyl (Np) 2; n = infinity, R = 4-CF(3)C(6)H(4) (Tol(F)) 3) complexes has been synthesized by neutralization reactions between the previously reported [Pt(C[triple chemical bond]CR)(4)](2-) (R = Tol, Tol(F)) or novel (NBu(4))(2)[Pt(C[triple chemical bond]CNp)(4)] platinum precursors and Tl(I) (TlNO(3) or TlPF(6)). The crystal structures of [Pt(2)Tl(4)(C[triple chemical bond]CTol)(8)]4 acetone, 14 acetone, [Pt(2)Tl(4)(C[triple chemical bond]CNp)(8)]3 acetone1/3 H(2)O, 23 acetone 1/3 H(2)O and [[PtTl(2)(C[triple chemical bond]CTol(F))(4)](acetone)S](infinity) (S = acetone 3 a; dioxane 3 b) have been solved by X-ray diffraction studies. Interestingly, whereas in the tolyl (1) and naphthyl (2) derivatives, the thallium centers exhibit a bonding preference for the electron-rich alkyne entities to yield crystal lattices based on sandwich hexanuclear [Pt(2)Tl(4)(C[triple chemical bond]CR)(8)] clusters (with additional Tlacetone (1) or Tlnaphthyl (2) secondary interactions), in the C(6)H(4)CF(3) (Tol(F)) derivatives 3 a and 3 b the basic Pt(II) center forms two unsupported Pt-Tl bonds. As a consequence 3 a and 3 b form an extended columnar structure based on trimetallic slipped PtTl(2)(C[triple chemical bond]CTol(F))(4) units that are connected through secondary Tl(eta(2)-acetylenic) interactions. The luminescent properties of these complexes, which in solution (blue; CH(2)Cl(2) 1,2; acetone 3) are very different to those in solid state (orange), have been studied. Curiously, solid-state emission from 1 is dependent on the presence of acetone (green) and its crystallinity. On the other hand, while a powder sample of 3 is pale yellow and displays blue (457 nm) and orange (611 nm) emissions, the corresponding pellets (KBr, solid) of 3, or the fine powder obtained by grinding, are orange and only exhibit a very intense orange emission (590 nm).

Synthesis, Characterization, and Electrochemical Relationships of Dinuclear Complexes of Platinum(II) and Platinum(III) Containing Ortho-Metalated Tertiary Arsine Ligands

Reaction of 2-Li-4-MeC6H3AsPh2 with [PtCl2(SEt2)2] gives two isomeric dinuclear platinum(II) complexes, one containing a half-lantern structure with two chelating and two bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(kappa2As,C-C6H3-5-Me-2-AsPh2)2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)2], and the other, a full-lantern with four bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4]. The lantern structure of the latter is retained in the dihalodiplatinum(III) complexes that are formed by oxidative addition of chlorine, bromine, or iodine to the isomeric mixture. The dichloro derivative undergoes metathesis reactions with silver or sodium salts, yielding the corresponding cyano, thiocyanato, cyanato, and fluoro species. The structures of all complexes have been determined by single-crystal X-ray analysis. The oxidative addition products have Pt-Pt distances in the range 2.65-2.79 A (cf. 2.89 A in the lantern diplatinum(II) structure), consistent with the presence of a Pt-Pt bond. Electrochemical data lead to the conclusion that an initial rapid one-electron process and subsequent chemical reactions produce the dihalodiplatinum(III) lantern structure when mixtures of the lantern and half-lantern complexes are oxidized by halogens. The electrochemical data also explain why chemical reduction of the dihalodiplatinum(III) complex produces only the lantern diplatinum(II) complex.

Reactions of a Platinum(III) Dimeric Complex with Alkynes in Water: Novel Approach to α-Aminoketone, α-Iminoketone, and α,β-Diimine via Ketonyl−Pt(III) Dinuclear Complexes

Reaction of the platinum(III) dimeric complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(NO(3))(2)](NO(3))(2) (1), prepared in situ by the oxidation of the platinum blue complex [Pt(4)(NH(3))(8)((CH(3))(3)CCONH)(4)](NO(3))(5) (2) with Na(2)S(2)O(8), with terminal alkynes CH[triple bond]CR (R = (CH(2))(n)CH(3) (n = 2-5), (CH(2))(n)CH(2)OH (n = 0-2), CH(2)OCH(3), and Ph), in water gave a series of ketonyl-Pt(III) dinuclear complexes [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)COR)](NO(3))(3) (3, R = (CH(2))(2)CH(3); 4, R = (CH(2))(3)CH(3); 5, R = (CH(2))(4)CH(3); 6, R = (CH(2))(5)CH(3); 7, R = CH(2)OH; 8, R = CH(2)CH(2)OH; 9, R = (CH(2))(2)CH(2)OH; 10, R = CH(2)OCH(3); 11, R = Ph). Internal alkyne 2-butyne reacted with 1 to form the complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(CH(3))COCH(3))](NO(3))(3) (12). These reactions show that Pt(III) reacts with alkynes to give various ketonyl complexes. Coordination of the triple bond to the Pt(III) atom at the axial position, followed by nucleophilic attack of water and hydrogen shift from the enol to keto form, would be the mechanism. The structures of complexes 3.H(2)O, 7.0.5C(3)H(4)O, 9, 10, and 12 have been confirmed by X-ray diffraction analysis. A competitive reaction between equimolar 1-pentyne and 1-pentene toward 1 produced complex 3 and [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)CH(OH)CH(2)CH(2)CH(3))](NO(3))(3) (14) at a molar ratio of 9:1, suggesting that alkyne is more reactive than alkene. The ketonyl-Pt(III) dinuclear complexes are susceptible to nucleophiles, such as amines, and the reactions with secondary and tertiary amines give the corresponding alpha-amino-substituted ketones and the reduced Pt(II) complex quantitatively. In the reactions with primary amines, the once formed alpha-amino-substituted ketones were further converted to the iminoketones and diimines. The nucleophilic attack at the ketonyl group of the Pt(III) complexes provides a convenient means for the preparation of alpha-aminoketones, alpha-iminoketones, and diimines from the corresponding alkynes and amines.