Site selectivity in the protonation of a phosphinito bridged Pt(I)-Pt(I) complex: a combined NMR and density-functional theory mechanistic study

The protonation of the dinuclear phosphinito bridged complex [(PHCy2)Pt(mu-PCy2){kappa(2)P,O-mu-P(O)Cy2}Pt(PHCy2)] (Pt-Pt) (1) by Br?nsted acids affords hydrido bridged Pt-Pt species the structure of which depends on the nature and on the amount of the acid used. The addition of 1 equiv of HX (X = Cl, Br, I) gives products of formal protonation of the Pt-Pt bond of formula syn-[(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(O)Cy2}] (Pt-Pt) (5, X = Cl; 6, X = Br; 8, X = I), containing a Pt-X bond and a dangling kappa P-P(O)Cy2 ligand. Uptake of a second equivalent of HX results in the protonation of the P(O)Cy2 ligand with formation of the complexes [(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(OH)Cy2}]X (Pt-Pt) (3, X = Cl; 4, X = Br; 9, X = I). Each step of protonation is reversible, thus reactions of 3, 4, with NaOH give, first, the corresponding neutral complexes 5, 6, and then the parent compound 1. While the complexes 3 and 4 are indefinitely stable, the iodine analogue 9 transforms into anti-[(PHCy2)(I)Pt(mu-PCy2)(mu-H)Pt(PHCy2)(I)] (Pt-Pt) (7) deriving from substitution of an iodo group for the P(OH)Cy2 ligand. Complexes 3 and 4 are isomorphous crystallizing in the triclinic space group P1 and show an intramolecular hydrogen bond and an interaction between the halide counteranion and the POH hydrogen. The occurrence of such an interaction also in solution was ascertained for 3 by (35)Cl NMR. Multinuclear NMR spectroscopy (including (31)P-(1)H HOESY) and density-functional theory calculations indicate that the mechanism of the reaction starts with a prior protonation of the oxygen with formation of an intermediate (12) endowed with a six membered Pt(1)-X...H-O-P-Pt(2) ring that evolves into thermodynamically stable products featuring the hydride ligand bridging the Pt atoms. Energy profiles calculated for the various steps of the reaction between 1 and HCl showed very low barriers for the proton transfer and the subsequent rearrangement to 12, while a barrier of 29 kcal mol(-1) was found for the transformation of 12 into 5.     

Possible biotransformation reactions of polynuclear Pt(II) complexes

The reactions of the two complexes BBR3464 [{trans-PtCl(NH3)2}2{mu-trans-Pt(NH3)2(NH2(CH2)6NH2)2}](4+) and BBR3610 [{trans-PtCl(NH3)2}2{mu-C2H4(NH2(CH2)6NH2)2}](4+) and the corresponding diaqua complexes with the nucleophiles thiourea (tu) and l-methionine (l-Met), were investigated under pseudo-first-order conditions as a function of concentration and temperature, using UV-vis spectrophotometric and stopped-flow techniques. 1H NMR spectroscopy was used to follow the stepwise substitution of the chloro ligands by guanosine-5'-monophosphate under second-order conditions. For the sulfur donor containing nucleophiles (tu and l-Met), a second reaction step, the displacement of the labilized amine chain linker, as a result of the strong trans-effect of tu and l-Met, was found. The activation parameters for all reactions studied suggest an associative substitution mechanism. The displacement of the chain linker by S-donor nucleophiles illustrates the limit of application of polynuclear complexes with monodentate aliphatic amine bridges and primary ammines, in agreement with previous studies reported in the literature.     

Hydrogen bonds and protonation of carbonyl-containing polynuclear rhodium complexes

According to IR spectroscopy data, the interaction of bi-, tri-, and tetranuclear cyclopentadienylcarbonyl rhodium complexes with rather weak protic acids (phenols, fluoroalcohols) in low-polarity media results in the formation of hydrogen bonds of the OH...O=C type with bridged carbonyl groups. According to¹H NMR data, protonation of these complexes with strong acids (CF₃COOH and HBF₄) occurs at the the Rh-Rh bond to give the symmetrical bridge.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 386–388, February, 1995.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-0461).     

Thin-film oxygen sensors using a luminescent polynuclear gold(I) complex

Robust thin-film oxygen sensors were fabricated by encapsulating a lipophilic, polynuclear gold(I) complex, bis{m-(bis(diphenylphosphino)octadecylamine-P,P′)}dichlorodigold(I), in oxygen permeable polystyrene and ormosil matrices. Strong phosphorescence, which was quenched by gaseous and dissolved oxygen, was observed from both matrices. The polystyrene encapsulated dye exhibited downward-turning Stern–Volmer plots which were well fitted by a two-site model. The ormosil trapped complex showed linear Stern–Volmer plots for dissolved oxygen quenching but was downward turning for gaseous oxygen. No leaching was observed when the ormosil based sensors were immersed in flowing water over an 8 h period. Both films exhibited fully reversible response and recovery to changing oxygen concentration with rapid response times.     

PtCl(PHCy2)[(PCy2O)2H]: a hydrogen bonded phosphinito complex obtained by direct reaction of molecular oxygen with a terminal phosphido complex

Exposure of solid trans-[Pt(PHCy2)2(PCy2)Cl] (1) to dry oxygen unexpectedly leads to [PtCl(PHCy2)[(PCy2O)2H]] (2) as the major product, the formation of which has been followed by NOESY 1H NMR techniques.     

The metal is the kinetic site of protonation of (diimine)Pt dimethyl complexes

Protonolysis of (diimine)PtMe2 (1) complexes in CD2Cl2 containing CD3CN at -78 degrees C yields (diimine)PtMe2(H)(NCCD3)+ (4), (diimine)PtMe(NCCD3)+ (5), and methane. The relative yields of 5 and methane decrease with increasing concentrations of CD3CN. This is consistent with protonation of 1 occurring directly at the metal, rather than at a methyl group. The principle of microscopic reversibility then implies that the deprotonation in "Shilov-type C-H activation" occurs from a Pt(IV) hydridomethyl intermediate, rather than from a Pt sigma-methane complex.     

Imidazolate bridged polynuclear rhodium(I) complexes. X-ray structure of [Rh(2-Meimidazolate)(CO)2]4

The synthesis and properties of polynuclear complexes of general formulae [M(RIm)(diolefin)_x, [M(RIm)(CO)₂]_x and [M(RIm)(CO)L]_x (M  Rh, Ir; RIm  imidazolate, 2-methylimidazolate, 2-benzylbenzimidazolate; L  PPh₃ or P(OPh)₃) are reported. The crystal structure of the novel complex [Rh(2-MeIm)-(CO)₂]₄ (2-MeIm  2-methylimidazolate) has been determined by X-ray methods. The crystals are orthorhombic, space group P2₁2₁2₁, with Z  4 in a unit cell of dimensions a 19.427(12), b 13.419(8), c 12.346(9) Å. The structure has been solved by combined Patterson and direct methods and refined by full-matrix least-squares to R  0.043 for 937 independent observed reflections. It consists of discrete tetrameric complexes in which each Rh atom is in a nearly cis square planar arrangement, bonded to two carbon atoms of carbonyl groups and to two nitrogen atoms of two 2-methylimidazolate ligands, each of which, acting as an exo-bidentate ligand, bridging two metal atoms, so that the four bridging 2-MeIm ligands and the four Rh atoms form a multiatomic ring.     

Dioxygen binding and activation by a new molybdenum (II) polynuclear complex

A new dimolybdenum(II) compound has been synthesized and characterized by physical methods including g.l.c., i.r., n.m.r., mass and X-ray spectrometry. The compound contains a very short (2.079 Å) MoMo quadruple bond.This complex is able to coordinate dioxygen directly and to use this activated molecule to oxidize ligand groups.     

Binuclear complexes of Pt(II) with platinated 2-phenylbenzothiazole and bridged derivatives of pyridin- and benzothiazol-2-thiols

Binuclear complexes of Pt(II) cycloplatinated with 2-phenylbenzothiazole and bridging ligands have been shown to contain the Pt-Pt bond. The complexes have been studied by X-ray diffraction, ¹H NMR and electronic absorption spectroscopy, and electrochemical methods. The complexes cis-N_(bt),S-isomers with antisymmetric positions of the cyclometalated and the bridging ligands have been detected in the crystals as well as in the solutions. The low-wavelength absorption and luminescence of the complexes have been assigned to the metal-metal-ligand charge transfer. The two-electron oxidation and reduction waves in the voltamperograms are associated with the metal- and the ligand-centered processes, respectively.     

Synthesis and characterization of propylene and butylene bridged fac-tricarbonylrhenium(I) biscarbene complexes

Nine new complexes of the type fac-[(CO)(3)ReBr(L)], where L represents a chelating bis-NHC ligand consisting of two alkylene (propylene and butylene) bridged (R') N-substituted (R) imidazoline moieties (1,1'-di-R-3,3'-R'-diimidazolin-2,2'-diylidene), were synthesized. Spectroscopic methods, elemental analysis, mass spectrometry and X-ray crystallography were employed to characterize the complexes both in solution and in solid state. The complexes were compared to the analogous complexes with smaller bridge lengths in order to reveal differences and similarities. Depending on the bridge length and the ligand size in some cases dinuclear complexes were obtained as small scale side products.     

X-band e.p.r. spectra of imidazole/imidazolate bridged polynuclear copper(II) complexes

X-band e.p.r. spectra of polycrystalline, polynuclear complexes of the type [(dien)Cu-im- Cu(dien)]n(ClO4)n and [(dien)Cu-imH- Cu(dien)]n(ClO4)2n are described, where dien = diethylenetriamine, imH and im are imidazole (and 2-methyl- and 2-ethylimidazole) respectively. All the complexes show e.p.r. spectra characteristic of S=1, which yield the value of the zero field splitting parameter, D, in the 0.030±0.001cm–1 range.     

Synthesis and characterization of cationic heteronuclear complexes of platinum(II) and silver( I) bridged by alkynyl ligands

The dialkynyl complexes cis-[Pt(C CR)₂L₂] [R = Ph, L₂ = 2PPh₃, 2PEt₃, dppe (dppe = 1,2-bis(diphenylphosphino)ethane]; R ---^tBu, L₂ = 2PPh₃, dppe) react with silver perchlorate in a molar ratio 1:0.5 to give platinum-silver perchlorate salts of the type [Pt₂ Ag(C CR)₄L₄](ClO₄) in excellent yield. The X-ray crystal structure of [Pt₂Ag(C = CPh)₄(PPh₃)₄](ClO₄) 1 shows that the cation is formed by two nearly orthogonal cis-[Pt(C CPh)₂(PPh₃)₂] units connected through a silver cation which is unsymmetrically π-bonded to all four acetylene fragments. Similar reactions of cis-[Pt(C CR)₂L₂] with one equivalent of AgClO₄ afford cationic complexes of general formula [PtAg(C CR)₂L₂](ClO₄), which are believed to be salts, [Pt₂Ag₂(C CR)₄L₄](ClO₄)₂.     

Pt(II) complexes of 4-amino-4H-1,2,4-triazole

The coordination ability of 4-amino-4H-1,2,4-triazole with Pt(II), both in solution and solid states, is elucidated by conventional and linear-polarized IR spectroscopy of oriented colloid suspensions in nematic host, ¹H- and ¹³C-NMR, UV-Vis spectroscopy, mass spectrometry (ESI and FAB), TGV, and DSC methods. The interpretation of the spectroscopic characteristics of corresponding metal complexes is obtained by comparison with free 4-amino-4H-1,2,4-triazole. In addition, quantum chemical calculations of the last compound are performed to obtain data for electronic structures and optical properties of the ligand, thus supporting the experimental elucidation. The evaluation of the cell viability on a panel of human tumor cell lines is made. The new Pt(II) complexes exerted cytotoxic effects in a concentration-dependent manner.     

Copper(I) and copper(II) complexes of an ethylene cross‐bridged cyclam

The preparation and crystal structures of (4,11‐di­benzyl‐1,4,8,11‐tetra­aza­bi­cyclo­[6.6.2]­hexa­decane‐κ⁴N)copper(I) hexa‐fluorophosphate, [Cu(C₂₆H₃₈N₄)]PF₆, and acetonitrile(4,11‐dibenzyl‐1,4,8,11‐tetraazabicyclo[6.6.2]hexadecane‐κ⁴N)‐copper(II) bis(hexafluorophosphate), [Cu(C₂H₃N)(C₂₆H₃₈‐N₄)](PF₆)₂, are described. The Cu^I ion is tetracoordinated in a very distorted tetrahedron, while the Cu^II analogue is pentacoordinated in a square pyramid.     

Thermolysis of polynuclear platinum(II) acetamidato complexes

The thermolysis of five polynuclear Pt(II) acetamidato complexes with known structures (I-V) and platinum blue of the composition Pt(NHCOCH₃)₂ · H₂O prepared by two different procedures (VI and VIa) has been studied by differential scanning calorimetry and thermogravimetry. The results of studying the thermolysis of these complexes allows one to assume that the structures of VI and VIa are different: complex VI is polynuclear and consists of binuclear fragments[(H₂O)(NHCOCH₃)Pt(μ-NHCOCH₃)₂Pt(NHCOCH₃)(H₂O)], whereas complex VIa is built of fragments [(H₂O)(NHCOCH₃)Pt(μ-OH)(μ-OH)(μ-NHCOCH₃)Pt(NHCOCH₃)₂].     

Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

Six new homobimetallic and heterobimetallic complexes of rhenium(I) and ruthenium(II) bridged by ethynylene spacer [(CO)₃(bpy)Re(BL)Re(bpy)(CO)₃]²⁺ [Cl(bpy)₂Ru(BL)Ru(bpy)₂Cl]²⁺ and [(CO)₃(bpy)Re(BL)Ru(bpy)₂Cl]²⁺ (bpy = 2,2′-bipyridine, BL = 1,2-bis(4-pyridyl)acetylene (bpa) and 1,4-bis(4-pyridyl)butadiyne (bpb) are synthesized and characterized. The electrochemical and photophysical properties of all the complexes show a weak interaction between two metal centers in heterobimetallic complexes. The excited state lifetime of the complexes is increased upon introduction of ethynylene spacer and the transient spectra show that this is due to delocalization of electron in the bridging ligand. Also, intramolecular energy transfer from *Re(I) to Ru(II) in Re–Ru heterobimetallic complexes occurs with a rate constant 4 × 10⁷ s⁻¹.     

Convenient synthesis of Pt(0) olefin complexes by colorimetric reduction of Pt(II) complexes with SmI2

Homoleptic olefin platinum(0) complexes, Pt(C₇H₁₀)₃ and Pt(cod)₂, were synthesized by the colorimetric reduction of platinum(II) complexes with SmI₂ in the presence of 2-norbornene or COD. This is a practically more convenient method for the synthesis of the Pt(0) complexes than the literature method employing Li₂(cot).