Stability of the gold(i)-phosphine bond. A comparison with other group 11 elements

The stability of gold phosphine complexes of the form [Au(PH(3))(n)()](+) (n = 1-4) and [AuCl(PH(3))(n)()] (n = 1-3) is analyzed in detail by applying quantum theoretical methods and compared to the coordination behavior of the lighter group 11 elements copper and silver. It is shown that, once [M(PH(3))(2)](+) or [MClPH(3)] (M = Cu, Ag, and Au) is formed, further coordination by PH(3) ligands is relatively weak; i.e., the energy gain to form [M(PH(3))(3)](+) from [M(PH(3))(2)](+) is less than 60 kJ mol(-)(1), and less than 100 kJ mol(-)(1) to form [MCl(PH(3))(2)] from [MClPH(3)]. Relativistic effects in gold significantly influence these factors and reduce the tendency for phosphine coordination beyond two-coordination. This implies that the most favored coordination number for gold is two with either a linear P-Au-P or P-Au-X arrangement (X = a strongly coordinating ligand like Cl(-)). Instead, X-Au-PH(3) units prefer to interact via close Au-Au contacts (aurophilic interactions) keeping the linear structure approximately intact, while the corresponding copper and silver compounds prefer PH(3) coordination to strongly bound M(2)Cl(2) units (M = Cu or Ag) where two chlorine atoms bridge the two metal atoms thus having the formal coordination number of three for copper or silver.     

Ring-opening reactions induced by gold(I) of five- and four-coordinate palladium(II) and platinum(II) complexes containing tripodal or linear polyphosphines

The tripodal ligands NP(3)(tris[2-(diphenylphosphino)ethyl]amine) and PP(3)(tris[2-(diphenylphosphino)ethyl]phosphine), form five-coordinate [Pd(NP(3))X]X [X = Cl (1), Br (2)], [M(PP(3))X]X [M = Pd: X = Cl (4), Br (5), I (6); M = Pt, X = Cl (7), Br (8), I (9)] and four-coordinate[Pd(NP(3))I]I (3) complexes containing three fused rings around the metal. The interaction between Au(tdg)X (tdg = thiodiglycol; X = Cl, Br) or AuI and the respective ionic halo complexes 1-9 in a 1:1 stoichiometric ratio occurs via a ring-opening reaction with formation of the heterobimetallic systems PdAu(NP(3))X(3)[X = Cl (11), Br (12), I (13)], [MAu(PP(3))X(2)]X [M = Pd: X = Cl (14), Br (15), I (16); M = Pt: X = Cl (17), Br (18), I (19)]. The cations of complexes 17 and 18 were shown, by X-ray diffraction, to contain a distorted square-planar Pt(II) arrangement (Pt(P(2)P)X) where PP(3) is acting as tridentate chelating ligand and an almost linear PAuX moiety bearing the dangling phosphorus formed in the ring-opening process. PPh(3) coordinates to Au(I) and not to M(II) when added in excess to 14 and 17. Complexes 14-17 and [Pt(P(4))](BPh(4))(2) (10) (P4=linear tetraphosphine) also react with A(I), via chelate ring-openings to give MAu(2)(PP(3))X(4) [M = Pd: X = Cl (20), Br (21), I (22); M = Pt: X = Cl (23)] and [Pt(2)Au(2)(mu-Cl)(2)(mu-P(4))(2)](BPh(4))(4) (24), respectively.     

Synthesis and DNA-binding properties of cationic 2,2':6',2' '-terpyridineplatinum(II) complexes containing 1,2- and 1,7-dicarba-closo-dodecaborane(12)

The first examples of DNA metallointercalators containing a dicarba-closo-dodecaborane(12) (carborane) moiety are presented. Treatment of the labile platinum(II) complex [Pt(OTf)(terpy)](+) (terpy = 2,2':6',2' '-terpyridine) with the 1,2-carborane monothiol derivatives 1-HS(CH(2))(n)-1,2-C(2)B(10)H(11) (n = 0, 1) or the novel 1,7-carborane ligand, 1-HSCH(2)-1,7-C(2)B(10)H(11), affords the stable, brightly colored species [Pt(1-S(CH(2))(n)-1,Z-C(2)B(10)H(11))(terpy)](+) (Z = 2, n = 0, 1; Z = 7, n = 1) in good yield and purity. Preliminary DNA-binding experiments with calf-thymus DNA indicate an intercalative interaction by the platinum(II) complexes at high r(f) values.     

Metal-metal interactions in dinuclear d(8) metal cyanide complexes supported by phosphine ligands. Spectroscopic properties and ab initio calculations of [M(2)(mu-diphosphine)(2)(CN)(4)] and trans-[M(phosphine)(2)(CN)(2)] (M = Pt,Ni)

Structural, spectroscopic properties on the dinuclear [M(2)(dcpm)(2)(CN)(4)] (M = Pt, 1a; Ni, 2a, dcpm = bis(dicyclohexylphosphino)methane) and [M(2)(dmpm)(2)(CN)(4)] (M = Pt, 1b; Ni, 2b, dmpm = bis(dimethylphosphino)methane) and the mononuclear trans-[M(PCy(3))(2)(CN)(2)] (M = Pt, 3; Ni, 4, PCy(3) = tricyclohexylphosphine) and theoretical investigations on the corresponding model compounds are described. X-ray structural analyses reveal Pt.Pt and Ni.Ni distances of 3.0565(4)/3.189(1) A and 2.957(1)/3.209(8) A for 1a/1b and 2a/2b, respectively. The UV-vis absorption bands at 337 nm (epsilon 2.41 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1a and 328 nm (epsilon 2.43 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1b in CH(2)Cl(2) are assigned to (1)(5d(sigma) --> 6p(sigma)) electronic transitions originating from Pt(II)-Pt(II) interactions. Resonance Raman spectroscopy of 1a, in which all the Raman intensity appears in the Pt-Pt stretch fundamental (93 cm(-)(1)) and overtone bands, verifies this metal-metal interaction. Complexes 1a and 1b exhibit photoluminescence in the solid state and solution. For the dinuclear nickel(II) complexes 2a and 2b, neither spectroscopic data nor theoretical calculation suggests the presence of Ni(II)-Ni(II) interactions. The intense absorption bands at lambda > 320 nm in the UV-vis spectra of 2a and 2b are tentatively assigned to d --> d transitions.     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Electronic excited states of [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm= bis(dimethylphosphine)methane)

We present studies of the resonance Raman and electronic luminescence spectra of the [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm = bis(dimethylphosphine)methane) complex, including excitation into an intense band at 256 nm and into a weaker absorption system centered about approximately 300 nm. The resonance Raman spectra confirm the assignment of the 256 nm absorption band to a (1)(dsigma --> psigma) transition, a metal-metal-localized transition, in that nu(Au-Au) and overtones of it are strongly enhanced. A resonance Raman intensity analysis of the spectra associated with the 256 nm absorption band gives the ground-state and excited-state nu(Au-Au) stretching frequencies to be 79 and 165 cm(-1), respectively, and the excited-state Au-Au distance is calculated to decrease by about 0.1 A from the ground-state value of 3.05 A. The approximately 300 nm absorption displays a different enhancement pattern, in that resonance-enhanced Raman bands are observed at 103 and 183 cm(-1) in addition to nu(Au-Au) at 79 cm(-1) The compound exhibits intense, long-lived luminescence (in room-temperature CH(3)CN, for example, tau = 0.70 micros, phi(emission) = 0.037) with a maximum at 550-600 nm that is not very medium-sensitive. We conclude, in agreement with an earlier proposal of Mason (Inorg. Chem. 1989, 28, 4366-4369), that the lowest-energy, luminescent excited state is not (3)(dsigma --> psigma) but instead derives from (3)(d(x2-y2,xy --> psigma) excitations. We compare the Au(I)-Au(I) interaction shown in the various transitions of the [Au(2)(dmpm)(3)](ClO(4))(2) tribridged compound with previous results for solvent or counterion exciplexes of [Au(2)(dcpm)(2)](2+) salts (J. Am. Chem. Soc. 1999, 121, 4799-4803; Angew. Chem. 1999, 38, 2783-2785; Chem. Eur. J. 2001, 7, 4656-4664) and for planar, mononuclear Au(I) triphosphine complexes. It is proposed that the luminescent state in all of these cases is very similar in electronic nature.     

Electronic structures and spectroscopic properties of mono- and binuclear d(8) complexes: a theoretical exploration on promising phosphorescent materials

The structures of trans-[M(2)(CN)(4)(PH(2)CH(2)PH(2))(2)] (M = Pt (1), Pd (2), and Ni (3)), trans-[Pt(2)X(4)(PH(2)CH(2)PH(2))(2)] (X = Cl (4) and Br (5)), and trans-[M(CN)(2)(PH(3))(2)] (M = Pt (6), Pd (7), and Ni (8)) in the ground state were optimized using the MP2 method. Frequency calculations reveal that the weak metal-metal interaction is essentially attractive for 1, 2, 4, and 5 but not for 3. The TD-DFT calculations associated with the polarized continuum model (PCM) were performed to predict absorption spectra in CH(2)Cl(2) solution. Experimental spectra are well reproduced by our results. With respect to analogous mononuclear d(8) complexes (6-8), a large red shift of the absorption wavelength was calculated for the binuclear d(8) complexes (1-3). Relative to 1 with unsaturated CN- donors, introduction of saturated halogen donors into 4 and 5 changes their electronic structures, especially the HOMO and LUMO. The TD-DFT and subsequent unrestricted MP2 calculations predict that 1 produces the lowest-energy d --> p emission while 2-5 favor the d --> d emissions, agreeing with experimental observations.     

New mu-oxo octanuclear complexes of 3d elements stabilized by dialkylcarbamato ligands. Synthesis and X-ray crystal and molecular structures

The octanuclear aggregates M(8)(mu(4)-O)(2)(O(2)CN(i)()Pr(2))(12) [M = Mn(II) 1, Co(II) 2, Ni(II) 3] have been prepared in good yields by controlled hydrolysis of the corresponding metal carbamate precursors [M(O(2)CN(i)()Pr(2))(2)](n)(). X-ray analysis has shown compounds 1-3 to be isostructural. The core of 2 contains two distorted [M(4)O] tetrahedra related by an inversion center. The hexanuclear carbamates M(6)(O(2)CNEt(2))(12) in toluene undergo a metal redistribution process with formation of the hexanuclear carbamates M'(x)M' '(6-x)(O(2)CNEt(2))(12), M' = Co, M' ' = Mn, as evidenced by mass-spectrometric data. In the presence of moisture, the mixed octanuclear carbamates Co(x)Mn(6-x)(MnO)(CoO)(O(2)CNEt(2))(12) were promptly formed and detected by DCI/MS measurements. Mass spectral data of Co(8)(mu(4)-O)(2)(O(2)CN(i)Pr(2))(12) are also reported.     

Stable diplatinum complexes with functional thiolato bridges from dialkylation of [Pt2(mu-S)2(P-P)2] [P-P=2 x PPh3, Ph2P(CH2)3PPh2

The normally robust monoalkylated complexes [Pt(2)(mu-S)(mu-SR)(PPh(3))(4)](+) can be activated towards further alkylation. Dialkylated complexes [Pt(2)(mu-SR)(2)(P-P)(2)](2+) (P-P=2 x PPh(3), Ph(2)P(CH(2))(3)PPh(2)) can be stabilized and isolated by the use of electron-rich and aromatic halogenated substituents R [e.g. 3-(2-bromoethyl)indole and 2-bromo-4'-phenylacetophenone] and 1,3-bis(diphenylphosphino)propane [Ph(2)P(CH(2))(3)PPh(2) or dppp] which enhances the nucleophilicity of the {Pt(2)(mu-S)(2)} core. This strategy led to the activation of [Pt(2)(mu-S)(mu-SR)(PPh(3))(4)](+) towards R-X as well as isolation and crystallographic elucidation of [Pt(2)(mu-SC(10)H(10)N)(2)(PPh(3))(4)](PF(6))(2) (2a), [Pt(2)(mu-SCH(2)C(O)C(6)H(4)C(6)H(5))(2)(PPh(3))(4)](PF(6))(2) (2b), and a range of functionalized-thiolato bridged complexes such as [Pt(2)(mu-SR)(2)(dppp)(2)](PF(6))(2) [R= -CH(2)C(6)H(5) (8a), -CH(2)CHCH(2) (8b) and -CH(2)CN (8c)]. The stepwise alkylation process is conveniently monitored by Electrospray Ionisation Mass Spectrometry, allowing for a direct qualitative comparison of the nucleophilicity of [Pt(2)(mu-S)(2)(P-P)(2)], thereby guiding the bench-top synthesis of some products observed spectroscopically.     

Mechanistic diversity covering 15 orders of magnitude in rates: cyanide exchange on [M(CN)(4)](2-) (M = Ni, Pd, and Pt)

Kinetic studies of cyanide exchange on [M(CN)(4)](2-) square-planar complexes (M = Pt, Pd, and Ni) were performed as a function of pH by (13)C NMR. The [Pt(CN)(4)](2-) complex has a purely second-order rate law, with CN(-) as acting as the nucleophile, with the following kinetic parameters: (k(2)(Pt,CN))(298) = 11 +/- 1 s(-1) mol(-1) kg, DeltaH(2) (Pt,CN) = 25.1 +/- 1 kJ mol(-1), DeltaS(2) (Pt,CN) = -142 +/- 4 J mol(-1) K(-1), and DeltaV(2) (Pt,CN) = -27 +/- 2 cm(3) mol(-1). The Pd(II) metal center has the same behavior down to pH 6. The kinetic parameters are as follows: (k(2)(Pd,CN))(298) = 82 +/- 2 s(-1) mol(-1) kg, DeltaH(2) (Pd,CN) = 23.5 +/- 1 kJ mol(-1), DeltaS(2) (Pd,CN) = -129 +/- 5 J mol(-1) K(-1), and DeltaV(2) (Pd,CN) = -22 +/- 2 cm(3) mol(-1). At low pH, the tetracyanopalladate is protonated (pK(a)(Pd(4,H)) = 3.0 +/- 0.3) to form [Pd(CN)(3)HCN](-). The rate law of the cyanide exchange on the protonated complex is also purely second order, with (k(2)(PdH,CN))(298) = (4.5 +/- 1.3) x 10(3) s(-1) mol(-1) kg. [Ni(CN)(4)](2-) is involved in various equilibrium reactions, such as the formation of [Ni(CN)(5)](3-), [Ni(CN)(3)HCN](-), and [Ni(CN)(2)(HCN)(2)] complexes. Our (13)C NMR measurements have allowed us to determine that the rate constant leading to the formation of [Ni(CN)(5)](3-) is k(2)(Ni(4),CN) = (2.3 +/- 0.1) x 10(6) s(-1) mol(-1) kg when the following activation parameters are used: DeltaH(2)() (Ni,CN) = 21.6 +/- 1 kJ mol(-1), DeltaS(2) (Ni,CN) = -51 +/- 7 J mol(-1) K(-1), and DeltaV(2) (Ni,CN) = -19 +/- 2 cm(3) mol(-1). The rate constant of the back reaction is k(-2)(Ni(4),CN) = 14 x 10(6) s(-1). The rate law pertaining to [Ni(CN)(2)(HCN)(2)] was found to be second order at pH 3.8, and the value of the rate constant is (k(2)(Ni(4,2H),CN))(298) = (63 +/- 15) x10(6) s(-1) mol(-1) kg when DeltaH(2) (Ni(4,2H),CN) = 47.3 +/- 1 kJ mol(-1), DeltaS(2) (Ni(4,2H),CN) = 63 +/- 3 J mol(-1) K(-1), and DeltaV(2) (Ni(4,2H),CN) = - 6 +/- 1 cm(3) mol(-1). The cyanide-exchange rate constant on [M(CN)(4)](2-) for Pt, Pd, and Ni increases in a 1:7:200 000 ratio. This trend is modified at low pH, and the palladium becomes 400 times more reactive than the platinum because of the formation of [Pd(CN)(3)HCN](-). For all cyanide exchanges on tetracyano complexes (A mechanism) and on their protonated forms (I/I(a) mechanisms), we have always observed a pure second-order rate law: first order for the complex and first order for CN(-). The nucleophilic attack by HCN or solvation by H(2)O is at least nine or six orders of magnitude slower, respectively than is nucleophilic attack by CN(-) for Pt(II), Pd(II), and Ni(II), respectively.     

Gold(I) phosphido complexes: synthesis, structure, and reactivity

Deprotonation of the phosphine complexes Au(PHR(2))Cl with aqueous ammonia gave the gold(I) phosphido complexes [Au(PR(2))](n)() (PR(2) = PMes(2) (1), PCy(2) (2), P(t-Bu)(2) (3), PIs(2) (4), PPhMes (5), PHMes (6); Mes = 2,4,6-Me(3)C(6)H(2), Is = 2,4,6-(i-Pr)(3)C(6)H(2), Mes = 2,4,6-(t-Bu)(3)C(6)H(2), Cy = cyclo-C(6)H(11)). (31)P NMR spectroscopy showed that these complexes exist in solution as mixtures, presumably oligomeric rings of different sizes. X-ray crystallographic structure determinations on single oligomers of 1-4 revealed rings of varying size (n = 4, 6, 6, and 3, respectively) and conformation. Reactions of 1-3 and 5 with PPN[AuCl(2)] gave PPN[(AuCl)(2)(micro-PR(2))] (9-12, PPN = (PPh(3))(2)N(+)). Treatment of 3 with the reagents HI, I(2), ArSH, LiP(t-Bu)(2), and [PH(2)(t-Bu)(2)]BF(4) gave respectively Au(PH(t-Bu)(2))(I) (14), Au(PI(t-Bu)(2))(I) (15), Au(PH(t-Bu)(2))(SAr) (16, Ar = p-t-BuC(6)H(4)), Li[Au(P(t-Bu)(2))(2)] (17), and [Au(PH(t-Bu)(2))(2)]BF(4) (19).     

Palladium(II) and platinum(II) complexes with tridentate iminophosphine ligands; synthesis and structural studies

The previously synthesised Schiff-base ligands 2-(2-Ph(2)PC(6)H(4)N[double bond, length as m-dash]CH)-R'-C(6)H(3)OH (R'= 3-OCH(3), HL(1); 5-OCH(3), HL(2); 5-Br, HL(3); 5-Cl, HL(4)) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino)aniline with the appropriate substituted salicylaldehyde. HL(1-4) react directly with M(II)Cl(2)(M = Pd, Pt) or Pt(II)I(2)(cod) affording neutral square-planar complexes of general formula [M(II)Cl(eta(3)-L(1-4))](M = Pd, Pt, 1-8) and [Pt(II)I(eta(3)-L(1-4))](M = Pd, Pt, 9-12). Reaction of complexes 1-4 with the triarylphosphines PR(3)(R = Ph, p-tolyl) gave the novel ionic complexes [Pd(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(13-20). Substituted platinum complexes of the type [Pt(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(R = P(CH(2)CH(2)CN)(3)21-24) and [Pt(II)(P(p-tolyl)(3))(eta(3)-L(3,4))]ClO(4)( 25 and 26 ) were synthesised from the appropriate [Pt(II)Cl(eta(3)-L(1-4))] complex (5-8) and PR(3). The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O,N,P donor set together with one further atom which is trans to the central nitrogen atom.     

o-Iminobenzosemiquinonato(1-) and o-amidophenolato(2-) complexes of palladium(II) and platinum(II): a combined experimental and density functional theoretical study

From the reaction mixture of [M(II)(bpy)Cl(2)], the ligand 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and 2 equiv of a base (NaOCH(3)) in CH(3)CN under anaerobic conditions were obtained the blue-green neutral complexes [M(II)(L(AP)-H)(bpy)] (M = Pd (1), Pt (2)). (L(AP)-H)(2)(-) represents the o-amidophenolato dianion, (L(AP))(1)(-) is the o-aminophenolate(1-), (L(ISQ))(1)(-) is its one-electron-oxidized, pi-radical o-iminobenzosemiquinonate(1-), and (L(IBQ))(0) is the neutral quinone. Complexes 1 and 2 can be oxidized by ferrocenium hexafluorophosphate, yielding the paramagnetic salts [M(II)(L(ISQ))(bpy)]PF(6) (S = (1)/(2)) (M = Pd (1a), Pt (2a)). The reaction of PtCl(2), 2 equiv of H[L(AP)], and 4 equiv of base in CH(3)CN in the presence of air yields diamagnetic [Pt(L(ISQ))(2)] (3), which is shown to possess an electronic structure that is best described as a singlet diradical. Complexes 1, 1a, 2, 2a, and 3 have been structurally characterized by X-ray crystallography at 100 K. It is clearly established that O,N-coordinated (L(AP)-H)(2)(-) ligands have a distinctly different structure than the corresponding O,N-coordinated (L(ISQ))(1)(-) radicals. It is therefore possible to unambiguously assign the protonation and oxidation level of o-aminophenol derived ligands in coordination compounds. All complexes have been investigated by cyclic voltammetry, spectroelectrochemistry, EPR, and UV-vis spectroscopy. Complexes 1 and 2 can be reversibly oxidized to the [M(II)(L(ISQ))(bpy)](+) and [M(II)(L(IBQ))(pby)](2+) mono- and dications, respectively, and reduced to the [M(L(AP)-H)(bpy(*))](-) anion, where (bpy(*))(1)(-) is the radical anion of 2,2'-bipyridine. Complex 3 exhibits four reversible one-electron-transfer waves (two oxidations and two reductions) which are all shown to be ligand centered. The EPR spectra of the one-electron-reduced species [Pt(L(AP)-H)(L(ISQ))](-) (S = (1)/(2)) and of the one-electron-oxidized species [Pt(L(ISQ))(L(IBQ))](+) (S = (1)/(2)) in CH(2)Cl(2) solutions have been recorded. To gain a better understanding of the electronic structure of 3 and its monooxidized and reduced forms, relativistic DFT calculations have been carried out. Magnetic coupling parameters and hyperfine couplings were calculated and found to be in very good agreement with experiment. It is shown that both the one-electron oxidation and reduction of 3 are ligand centered. A simple MO model is developed in order to understand the EPR properties of the monocation and monoanion of 3.     

Preparation and structural characterization of ionic five-coordinate palladium(II) and platinum(II) complexes of the ligand tris[2-(diphenylphosphino)ethyl]phosphine. Insertion of SnCl(2) into M-Cl bonds (M = Pd,Pt) and hydroformylation activity of the Pt-SnCl(3) systems

The five-coordinate palladium(II) and platinum(II) complexes [M(PP(3))Cl]Cl [M = Pd (1), Pt (2)] (PP(3) = tris[2-(diphenylphosphino)ethyl]phosphine) were prepared by interaction of aqueous solutions of MCl(4)(2-) salts with PP(3) in CHCl(3). Complexes 1 and 2 undergo facile chloro substitution reactions with KCN in 1:1 and 1:2 ratios to afford complexes [M(PP(3))(CN)]Cl [M = Pt (3)] and [M(PP(3))(CN)](CN) [M = Pd (4), Pt (5)] possessing M-C bonds, both in solution and in the solid state. The reaction of 1 and 2 with SnCl(2) in CDCl(3) occurs with insertion of SnCl(2) into M-Cl bonds leading to the formation of [M(PP(3))(SnCl(3))](SnCl(3)) [M = Pd (6), M = Pt (7)]. The isolation as solids of complexes 6 and 7 by addition of SnCl(2) to the precursors requires the presence of PPh(3) which activates the cleavage of M-Cl bonds, favors the SnCl(2) insertion, and does not coordinate to M in any observable extent. Solutions of 6 in CDCl(3) undergo tin dichloride elimination in higher proportion than solutions of 7. The reaction of complexes 1 and 2 with SnPh(2)Cl(2) leads to [M(PP(3))Cl](2)[SnPh(2)Cl(4)] [M = Pd (8)]. Complexes 2, 5, 7, and 8 were shown by X-ray diffraction to contain distorted trigonal bipyramidal monocations [M(PP(3))X](+) [M = Pt, X = Cl(-) (2), X = CN(-) (5), X = SnCl(3)(-) (7); M = Pd, X = Cl(-) (8)], the central P atom of PP(3) being trans to X in axial position and the terminal P donors in the equatorial plane of the bipyramids. The "preformed" catalyst 7 showed a relatively high aldehyde selectivity compared to most of the platinum catalysts.     

Different rotamer states of cytosine nucleobases in heteronuclear PtPd-, PtPd2, and Pt2Pd2Ag complexes derived from [Pt(2,2'-bpy)(1-MeC-N3)2]2+ (1-MeC = 1-methylcytosine): first examples of species with head-head oriented 1-MeC(-) ligands

[Pt(2,2'-bpy)(1-MeC-N3)(2)](NO(3))(2) (1) (2,2'-bpy = 2,2'-bipyridine; 1-MeC = 1-methylcytosine) exists in water in an equilibrium of head-tail and head-head rotamers, with the former exceeding the latter by a factor of ca. 20 at room temperature. Nevertheless, 1 reacts with (en)Pd(II) (en = ethylenediamine) to give preferentially the dinuclear complex [Pt(2,2'-bpy)(1-MeC(-)-N3,N4)(2)Pd(en)](NO(3))(2)·5H(2)O (2) with head-head arranged 1-methylctosinato (1-MeC(-)) ligands and Pd being coordinated to two exocyclic N4H(-) positions. Addition of AgNO(3) to a solution of 2 leads to formation of a pentanuclear chain compound [{Pt(2,2'-bpy)(1-MeC(-))(2)Pd(en)}(2)Ag](NO(3))(5)·14H(2)O (5) in which Ag(+) cross-links two cations of 2 via the four available O2 sites of the 1-MeC(-) ligands. 2 and 5 appear to be the first X-ray structurally characterized examples of di- and multinuclear complexes derived from a Pt(II) species with two cis-positioned cytosinato ligands adopting a head-head arrangement. (tmeda)Pd(II) (tmeda = N,N,N',N'-tetramethylethylenediamine) and (2,2'-bpy)Pd(II) behave differently toward 1 in that in their derivatives the head-tail orientation of the 1-MeC(-) nucleobases is retained. In [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(2,2'-bpy)}(2)](NO(3))(4)·10H(2)O (4), both (2,2'-bpy)Pd(II) entities are pairwise bonded to N4H(-) and O2 sites of the two 1-MeC(-) rings, whereas in [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(tmeda)}(2)(NO(3))](NO(3))(3)·5H(2)O (3) only one of the two (tmeda)Pd(II) units is chelated to N4H(-) and O2. The second (tmeda)Pd(II) is monofunctionally attached to a single N4H(-) site. On the basis of these established binding patterns, ways to the formation of mixed Pt/Pd complexes and possible intermediates are proposed. The methylene protons of the en ligand in 2 are special in that they display two multiplets separated by 0.64 ppm in the (1)H NMR spectrum.     

Interplay between covalent and aurophilic interactions in a series of isostructural 3D Hoffman-like frameworks containing bipyrimidine and dicyanoaurate bridges. X-Ray structure and magnetic properties of {(mu-Au(CN)(2)](2)[(M(NH(3))(2))(2)(mu-bpym)]}[Au(CN)(2)](2) (M = Ni(II), Co(II) and Cu(II))

The isomorphous coordination polymers {micro-Au(CN)(2)](2)[(M(NH(3))(2))(2)(mu-bpym)]}[Au(CN)(2)](2) (M = Co(II) (1), Ni(II) (2), Cu(II) (3)) have been prepared from the reaction of 2 equiv. M(NO(3))(2) x nH(2)O (M = Cu(II), n = 3; M = Ni(II) and Co(II), n = 6) with 1 equiv. of bipyrimidine (bpym) in aqueous ammonia and then with an aqueous solution containing 1 equiv. of K[Au(CN)(2)]. The structures of these complexes are made of bpym bridged centrosymmetric dinuclear [M(NH(3))(2)(mu-bpym)M(NH(3))(2)] units connected by [Au(CN)(2)](-) anions to four other dinuclear units giving rise to a cationic 2D (4,4) rectangular grid network, its charge being balanced by two non-coordinated [Au(CN)(2)](-). The layers are stacked in such a way that the ammonia coordinated molecules are interdigitated and aligned above and below one sheet with cavities in neighbouring sheets, giving rise to an ABAB[dot dot dot] repeat pattern of layers. Gold atoms of bridging and non-bridging dicyanoaurate anions are involved in short aurophilic interactions (Au1-Au2 distances in the range 3.12-3.14 Angstrom), leading to a chain of gold atoms running along the a direction. Neighbouring gold chains are further connected by weaker aurophilic interactions (Au1-Au1 distances in the range 3.43-3.49 Angstrom), affording a honeycomb-like 2D network of gold atoms. The (4,4) rectangular sheets and (6,3) honeycomb sheets share the Au2 atoms, leading to a unique 3D network. Magnetic measurements clearly show the existence of antiferromagnetic exchange coupling between the metal ions with susceptibility maxima at 17 K (1), 22 K (2), and 17 K (3). The data of 1 were analyzed through a full Hamiltonian involving spin-orbit coupling, axial distortion, Zeeman interactions and magnetic exchange coupling between Co(II), and the best fit gives J = -9.23 cm(-1), kappa = 0.99, lambda = -142 cm(-1), Delta = -562 cm(-1). For 2 and 3, magnetic data were fitted to the theoretical equations derived from the isotropic Hamiltonian: H = -JS(1)S(2). The best fit parameters were g = 2.050(1), J = -17.51(1) and P = 0.01(2) for 2 and g = 2.068(5), J = -20.07(8) and P = 0.015(4) for 3, respectively (P takes into account the amount of paramagnetic impurity). In order to explain the weak magnetic interaction between copper(II) ions mediated by the bipyrimidine bridging ligand in 3, we have carried out electronic structure calculations based on the density functional theory (DFT).     

Syntheses, structures, and properties of trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)], constructed with the complexed bridging ligand [M(bpca)(2)] [M, M' = Ni(II), Mn(II); Cu(II), Mn(II); Fe(II), Mn(II); Ni(II), Fe(II); and Fe(II), Fe(II); Hbpca = Bis(2-pyridylcarbonyl)amine, Hhfac = Hexafluoroacetylacetone

Five trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)] (where MM'(2) = NiMn(2), CuMn(2), FeMn(2), NiFe(2), and FeFe(2); Hbpca = bis(2-pyridylcarbonyl)amine; and Hhfac = hexafluoroacetylacetone) were synthesized almost quantitatively by the reaction of [M(bpca)(2)] and [M'(hfac)(2)] in 1:2 molar ratio, and their structures and magnetic properties were investigated. Three complexes, with M' = Mn, crystallize in the same space group, Pna2(1), whereas two complexes, with M' = Fe, crystallize in P4(1), and complexes within each set are isostructural to one another. In all complexes, [M(bpca)(2)] acts as a bis-bidentate bridging ligand to form a linear trinuclear complex in which three metal ions are arranged in the manner M'-M-M'. The central metal ion is in a strong ligand field created by the N(6) donor set, and hence the Fe(II) in the [Fe(bpca)(2)] moiety is in a low-spin state. The terminal metal ions (M') are surrounded by O(6) donor sets with a moderate ligand field, which leads to the high-spin configuration of Fe(II). Three metal ions in all complexes are almost collinear, and metal-metal distances are ca. 5.5 A. The magnetic behavior of NiMn(2) and NiFe(2) shows a weak ferromagnetic interaction between the central Ni(II) ion and the terminal Mn(II) or Fe(II) ions. In these complexes, sigma-spin orbitals of the central Ni(II) ion and those of terminal metal ions have different symmetry about a 2-fold rotation axis through the Ni-N(amide)-M'(terminal) atoms, and this results in orthogonality between the neighboring sigma-spin orbitals and thus ferromagnetic interactions.     

链状三核异金属簇阴离子［Cl_2FeS_2M＇（PPh_3）_2］~－（M＝Mo

在５５０～９０ｃｍ~（－１）波数范围内，测量簇阴离子［Ｃｌ_２ＦｅＳ_２ＭＳ_２Ｍ′（ＰＰｈ_３）_２］~－（Ｍ＝Ｍｏ，Ｍ′＝Ａｇ；Ｍ＝Ｗ，Ｍ′＝Ｃｕ，Ａｇ）的付里叶变换红外光谱，并对标题簇阴离子［Ｃｌ_２ＦｅＳ_２ＷＳ_２Ｃｕ（ＰＰｈ_３）_２］~－，［Ｃｌ_２ＦｅＳ_２ＭｏＳ_２Ａｇ（ＰＰｈ_３）_２］~－和［Ｃｌ_２ＦｅＳ_２ＷＳ_２Ａｇ（ＰＰｈ_３）_２］~－骨架的振动光谱给予经验指认。同时采用＂诱导自洽方法计算振动力常数＂程序，对簇骨架［Ｃｌ_２ＦｅＳ_２ＭＳ_２Ｍ~′Ｐ_２］进行简正坐标分析。振动频率的计算值与观测值符合良好，两者平均偏差小于１．０％，计算结果支持了振动谱带的归属并表明计算力常数的合理性。文中还讨论了主要价键振动频率的变化规律。     

Syntheses, characterization, and luminescence of Pt II-M I (M = Cu, Ag, Au) heterometallic complexes by incorporating Pt(diimine)(dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Reaction of Pt(diimine)(edt) (edt = 1,2-ethanedithiolate) with M(2)(dppm)(2)(MeCN)(2)(2+) (dppm = bis(diphenylphosphino)methane) gave heterotrinuclear complexes [PtCu(2)(edt)(mu-SH)(dppm)(3)](ClO(4)) (11) and [PtCu(2)(diimine)(2)(edt)(dppm)(2)](ClO(4))(2) (diimine = 2,2'-bpyridine (bpy), 12; 4,4'-dibutyl-2,2'-bipyridine (dbbpy), 13; phenanthroline (phen), 14; 5-bromophenanthroline (brphen), 15) when M = Cu(I). The reaction, however, afforded tetra- and trinuclear complexes [Pt(2)Ag(2)(edt)(2)(dppm)(2)](SbF(6))(2) (17) and [PtAu(2)(edt)(dppm)(2)](SbF(6))(2) (21) when M = Ag(I) and Au(I), respectively. The complexes were characterized by elemental analyses, electrospray mass spectroscopy, (1)H and (31)P NMR, IR, and UV-vis spectrometry, and X-ray crystallography for 14, 17, and 18. The Pt(II)Cu(I)(2) heterotrinuclear complexes 11-15 exhibit photoluminescence in the solid states at 298 K and in the frozen acetonitrile glasses at 77 K. It is likely that the emission originates from a ligand-to-metal charge transfer (dithiolate-to-Pt) (3)[p(S) --> d(Pt)] transition for 11 and from an admixture of (3)[d(Cu)/p(S)-pi(diimine)] transitions for 12-16. The Pt(II)(2)Ag(I)(2) heterotetranuclear complexes 17 and 18 are nonemissive in the solid states and in solutions at 298 K but show photoluminescence at 77 K. The Pt(II)Au(I)(2) heterotrinuclear complexes 19-21, however, are luminescent at room temperature in the solid state and in solution. Compounds 19 and 20 afford negative solvatochromism associated with a charge transfer from an orbital of a mixed metal/dithiolate character to a diimine pi orbital.     

Theoretical study of rhodium(III)-catalyzed hydrogenation of carbon dioxide into formic acid. Significant differences in reactivity among rhodium(III), rhodium(I), and ruthenium(II) complexes

The title reaction was theoretically investigated, where cis-[RhH(2)(PH(3))(3)](+) and cis-[RhH(2)(PH(3))(2)(H(2)O)](+) were adopted as models of the catalyst. The first step of the catalytic cycle is the CO(2) insertion into the Rh(III)-H bond, of which the activation barrier (E(a)) is 47.2 and 28.4 kcal/mol in cis-[RhH(2)(PH(3))(3)](+) and cis-[RhH(2)(PH(3))(2)(H(2)O)](+), respectively, where DFT(B3LYP)-calculated E(a) values (kcal/mol unit) are given hereafter. These results indicate that an active species is not cis-[RhH(2)(PH(3))(3)](+) but cis-[RhH(2)(PH(3))(2)(H(2)O)](+). After the CO(2) insertion, two reaction courses are possible. In one course, the reaction proceeds through isomerization (E(a) = 2.8) of [RhH(eta(1)- OCOH)(PH(3))(2)(H(2)O)(2)](+), five-centered H-OCOH reductive elimination (E(a) = 2.7), and oxidative addition of H(2) to [Rh(PH(3))(2)(H(2)O)(2)](+) (E(a) = 5.8). In the other one, the reaction proceeds through isomerization of [RhH(eta(1)-OCOH)(PH(3))(2)(H(2)O)(H(2))](+) (E(a) = 5.9) and six-centered sigma-bond metathesis of [RhH(eta(1)-OCOH)(PH(3))(2)(H(2)O)](+) with H(2) (no barrier). RhH(PH(3))(2)-catalyzed hydrogenation of CO(2) proceeds through CO(2) insertion (E(a) = 1.6) and either the isomerization of Rh(eta(1)-OCOH)(PH(3))(2)(H(2)) (E(a) = 6.1) followed by the six-centered sigma-bond metathesis (E(a) = 0.3) or H(2) oxidative addition to Rh(eta(1)-OCOH)(PH(3))(2) (E(a) = 7.3) followed by isomerization of RhH(2)(eta(1)-OCOH)(PH(3))(2) (E(a) = 6.2) and the five-centered H-OCOH reductive elimination (E(a) = 1.9). From these results and our previous results of RuH(2)(PH(3))(4)-catalyzed hydrogenation of CO(2) (J. Am. Chem. Soc. 2000, 122, 3867), detailed discussion is presented concerning differences among Rh(III), Rh(I), and Ru(II) complexes.