A trinuclear Pt(ii) compound with short Pt–Pt–Pt contacts. An analysis of the influence of π–π stacking interactions on the strength and length of the Pt–Pt bond (original) (raw)
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Inorganic Chemistry, 1996
A condensation reaction between two cis-[PtCl 2 (Hmtpo) 2 ] (where Hmtpo) 4,7-H-5-methyl-7-oxo[1,2,4]triazolo-[1,5a]pyrimidine) molecules takes place in neutral aqueous media, giving [Pt 2 (µ-mtpo) 4 ]‚4H 2 O (1). The X-ray structure of the recrystallization product of 1 in DMSO:EtOH (1:1) (DMSO ) dimethyl sulfoxide), namely, [Pt 2 (µ-mtpo) 4 ]‚2DMSO (2) has been determined. Compound 2 crystallizes in the orthorhombic space group Pbcn with unit cell dimensions a ) 14.207(3) Å, b ) 15.187(3) Å, c ) 17.165(3) Å, and Z ) 4. The molecular structure shows that the two Pt atoms are bridged by four mtpo ligands. Thus, it presents two face to face PtN 4 units with a Pt‚‚‚Pt 2.744(2) Å separation. Compound 1 has also been characterized by 1 H and 195 Pt NMR. The very short Pt(II)‚‚‚Pt(II) contact suggests an interaction between the two metal centers, supported by the great deshielding observed for the platinum nuclei in the 195 Pt NMR spectrum (δ ) -2005 ppm) compared to a Pt(II) in a typical N 4 environment. In order to make an approach to the possible bonding nature of the Pt(II)‚‚‚Pt(II) interaction, a theoretical analysis has been performed on the basis of the properties of the electronic charge density distribution, derived from ab initio MO calculations for the model compound {Pt 2 [NHCHN(C(CH 2 )(CH 3 ))] 4 } using RHF/LANL2DZ and B3LYP/LANL2DZ wave functions; both take into account relativistic effects and the second electronic correlation also. A significant directional interaction between the two metal centers has been found. Thus, a bond critical point appears between the two platinum nuclei, with a density of charge F b ) 0.056 e‚bohr -3 , which is half of that found for the platinum nitrogen bond. Moreover, a value of the energy density, E d (r b ) < 0 (E d (r) ) -0.0175 hartree‚bohr -3 ), at this point, shows the bonding nature of the interaction.
Journal of Organometallic Chemistry, 2006
A series of dinuclear platinum complexes where the metal ions are linked by a twofold deprotonated 2,2 0 :6 0 ,2 00 -terpyridine (terpy) has been synthesized. Reaction of cis-[Pt(Me) 2 (DMSO) 2 ] with terpy in toluene at 90°C (molar ratio Pt:terpy 2:1) results in activation of the C(3)-and C(5)-H bonds of the inner pyridinic ring to give the cyclometalated dinuclear derivative [Pt 2 (terpy-2H)(Me) 2 (DMSO) 2 ] (1a), (trans Me-Pt-N). From complex 1a, substitution of DMSO with neutral two-electron donors, L, allows isolation of a number of new species [Pt 2 (terpy-2H)(Me) 2 (L) 2 ] with the same N,C Ù C,N bridging ligand. The ''Pt 2 (terpy-2H)'' fragment is very robust: it is not affected by alkylating reagents such as MeI or acids such as HPF 6 or even HCl. Nevertheless the latter acid cleaves the Pt-Me bond affording another series of complexes having a chloride in place of a methyl, [Pt 2 (terpy-2H)(Cl) 2 (L) 2 ], (trans-Cl-Pt-C). The structure of complex 7, [Pt 2 (terpy-2H)(Cl) 2 (PPh 3 ) 2 ], has been solved by X-ray analysis: the platinum atoms are in a tetrahedrally distorted square planar coordination. The inner framework of the molecule is not flat: the dihedral angle between the best planes of the metal ions is 37.2(1)°. The coordinated chlorides can be abstracted to give cationic solvento derivatives or exchanged with other anions such as iodides. Exchange with [BH 4 ] À allows to obtain the corresponding hydrides, examples of very rare C,N cyclometalated platinum(II) hydrides. Finally a two step approach allows the synthesis of unsymmetric derivatives, [Pt 2 (terpy-2H)(Cl) 2 (L)(L 0 )], with different ligands around each platinum atom. The surprising deprotonation of terpy, typically a neutral ligand, points to the potential of the ''Pt(Me) 2 '' fragment in the intramolecular C-H bond activation.
A neutral Pt3 stack unsupported by any bridging ligand
Dalton Transactions, 2011
Pt ◊ ◊ ◊ Pt ◊ ◊ ◊ Pt interactions via their d 8 orbitals, combined with p-p stacking of deprotonated, chelating 2-(3¢pyrazolyl)pyridine (pyzpy) ligands, are responsible for trans-Pt(pyzpy) 2 (2) crystallization in a stack of three molecules unsupported by any bridging ligand. 2-(3¢-pyrazolyl)pyridine (Hpyzpy) is a N,N¢-chelating biheteroaromatic ligand with a tradition in coordination chemistry 1 and applied sciences. 2 It can occur in its neutral form in six possible isomeric forms (tautomers, rotamers; cf. ESI †) and deprotonation to give the monoanion can take place either at N1¢ or N2¢ of the pyrazolyl entity. When acting as a chelating ligand for d 8 metal ions (Pt II , 2b Pd II , 3 Au III2d) it is the pyridyl-N1 site and the pyrazolyl-N2¢ site which are involved. Unlike 2,2¢-bpy complexes, 4 bis-complexes of pyzpy are perfectly planar, which is a consequence of the compared to 2,2¢-bpy smaller pyrazole moiety and the possibility to form CH ◊ ◊ ◊ N hydrogen bonds following deprotonation of the N1¢H position. Here we report on two products obtained upon reacting K 2 PtCl 4 with Hpyzpy in water (Scheme 1). In both products, Pt(Hpyzpy)Cl 2 (1) and trans Pt(pyzpy) 2 (2) ‡ the (H)pyzpy ligands act as chelating ligands via py-N1 and pyz-N2¢. 1 was obtained in crystalline form as its acetone solvate (Fig. 1). Molecules of 1 stack in the solid state in pairs (Pt ◊ ◊ ◊ Pt, 3.474(2) Å), as is not uncommon in Pt II chemistry. There are no unusual structural features with 1 (cf. ESI †). In contrast, 2 is special in that it crystallizes in a rare fashion 5 in units of three, with the three Pt's stacked right on top of each other. Single crystals of trans-Pt(pyzpy) 2 (2) were grown from CHCl 3. There are two crystallographically different molecules (2a, 2b) present, which differ slightly. One of these, 2a, lies on an inversion center, and is shown in Fig. 2 (top). The two chelate rings within a molecule are oriented trans to each other.
Acta Chimica Slovenica, 2015
A novel platinum(II) complex with 2-hydroxy-6-methylpyridine (Hmhp), trans-[PtCl 2 (dmso)(Hmhp)] • H 2 O, crystallizes in the space group P 2 1 /n with a = 11.5505(1) Å, b = 8.9467(1) Å, c = 14.6047(2) Å and β = 112.3919(6)°. The platinum ion is in the expected square-planar environment. The 2-hydroxy-6-methylpyridine ligand is coordinated to the metal ion in a monodentate manner via nitrogen. The plane of the aromatic ligand is nearly perpendicular to the platinum coordination plane. The Pt(II) ion is shielded with pyridine ortho substituents above and below the square coordination plane of platinum. Hydrogen bonding between the complex molecules and the H 2 O molecules of crystallization produces infinite two-dimensional layers. Weak intermolecular interactions of the C-H•••Cl type link the layers into a three-dimensional structure.
Inorganic Chemistry, 2012
The kinetics and mechanism of substitution reactions of novel monofunctional [Pt(tpdm)Cl] + and [Pd(tpdm)Cl] + complexes (where tpdm = tripyridinedimethane) and their aqua analogues with thiourea (tu), L-methionine (L-met), glutathione (GSH), and guanosine-5′-monophosphate (5′-GMP) were studied in 0.1 M NaClO 4 at pH = 2.5 (in the presence of 10 mM NaCl for reactions of the chlorido complexes). The reactivity of the investigated nucleophiles follows the order tu > L-met > GSH > 5′-GMP. The reported rate constants showed the higher reactivity of the Pd(II) complexes as well as the higher reactivity of the aqua complex than the corresponding chlorido complex. The negative values reported for the activation entropy as well as the activation volume confirmed an associative substitution mode. In addition, the molecular and crystal structure of [Pt(tpdm)Cl]Cl was determined by X-ray crystallography. The compound crystallizes in a monoclinic space group C2/c with two independent molecules of the complex and unit cell dimensions of a = 38.303(2) Å, b = 9.2555(5) Å, c = 27.586(2) Å, β = 133.573(1)°, and V = 7058.3(8) Å 3 . The cationic complex [Pt(tpdm)Cl] + exhibits square-planar coordination around the Pt(II) center. The lability of the [Pt(tpdm)Cl] + complex is orders of magnitude lower than that of [Pt(terpyridine)Cl] + . Quantum chemical calculations were performed on the [Pt(tpdm)Cl] + and [Pt(terpyridine)Cl] + complexes and their reactions with thiourea. Theoretical computations for the corresponding Ni(II) complexes clearly demonstrated that π-back-bonding properties of the terpyridine chelate can account for acceleration of the nucleophilic substitution process as compared to the tpdm chelate, where introduction of two methylene groups prevents such an effective π-back bonding.
Dalton Transactions, 2009
The readily available Pt(0) methyl acrylate complex [Pt{CH 2 =CHC(O)OMe}(PPh 3 ) 2 ] (2) allows access to the known, mixed-valence trinuclear cluster [Pt 3 (m-PPh 2 ) 3 Ph(PPh 3 ) 2 ] (3) in 64% yield. Oxidation of 3 with 2 equivalents of I 2 afforded the new trinuclear complex [Pt 3 (m-I) 2 (m-PPh 2 ) 2 I 2 (PPh 3 ) 2 ] (4) whose molecular structure is similar to that of the related compound of empirical formula [Pt 3 (m-I) 2 (m-PPh 2 ) 2 Cl 0.5 I 1.5 (PPh 3 ) 2 ] (5) which has been generated by oxidation of 3 with successively 1 equivalent of I 2 and 1 equivalent of C 6 H 5 ICl 2 . In these complexes, the four halogen atoms lie on the same side of the almost aligned platinum atoms and the nearly square-planar coordination planes of the metal atoms adopt a "japanese screen", chair-like conformation. The reaction of the dinuclear, metal-metal bonded Pt(I)-Pt(I) complex [Pt 2 (m-PPh 2 ) 2 (PPh 3 ) 2 ] with one equivalent of I 2 afforded the Pt(II) complex [Pt 2 (m-PPh 2 ) 2 I 2 (PPh 3 ) 2 ] (6). The molecular structures of complexes 2·CH 2 Cl 2 , [Pt 3 (m-I) 2 (m-PPh 2 ) 2 (I 1.3 Cl 0.7 )(PPh 3 ) 2 ][Pt 3 (m-I) 2 (m-PPh 2 ) 2 (I 1.7 Cl 0.3 )(PPh 3 ) 2 ]·C 6 H 5 Cl·3CH 2 Cl 2 (5A·5B·C 6 H 5 Cl·3CH 2 Cl 2 ) and 6 have been established by single crystal X-ray diffraction studies.
Intramolecular NH··· Pt Interactions of Platinum (II) Diimine Complexes with Phenyl Ligands
Inorganic …, 2010
Pt(pipNC) 2 (phen) [pipNC -= 1-(piperidylmethyl)phenyl anion; phen = 1,10-phenanthroline] was prepared by the reaction of cis-Pt(pipNC) 2 with phen. Crystallographic and 1 H NMR data establish that the phen ligand is bidentate, whereas each piperidyl ligand is monodentate and bonded to the platinum at the ortho position of the phenyl group. Acidic conditions allowed for isolation of the salts of diprotonated Pt(pipNHC) 2 (diimine) 2þ adducts (diimine = phen, 2,2 0 -bipyridine, or 5,5 0ditrifluoromethyl-2,2 0 -bipyridine). Crystallographic and spectroscopic data for the diprotonated complexes are consistent with H 3 3 3 Pt interactions (2.32-2.51 Å ) involving the piperidinium groups, suggesting that the metal center behaves as a Brønsted base. Metal-to-ligand (diimine) charge-transfer states of Pt(pipNHC) 2 (phen) 2þ in solution are strongly destabilized (>2500 cm -1 ) relative to Pt(pipNC) 2 (phen), in keeping with the notion that NH 3 3 3 Pt interactions effectively reduce the electron density at the metal center. Though N 3 3 3 Pt interactions in Pt(pipNC) 2 (phen) appear to be weaker than those found for outer-sphere two-electron reagents, such as Pt(pip 2 NCN)(tpy) þ [pip 2 NCN -= 1,3-bis(piperidylmethylphenyl anion; tpy = 2,2 0 :6 0 ,2 0 -terpyridine], each of the Pt(pipNC) 2 (diimine) complexes undergoes diimine ligand dissociation to give back cis-Pt(pipNC) 2 and free diimine ligand. Electrochemical measurements on the deprotonated complexes suggest that the piperidyl groups help to stabilize higher oxidation states of the metal center, whereas protonation of the piperidyl groups has a destabilizing influence.
Inorganic Chemistry, 2005
The preparation of the [NBu 4 ][Pt(C 6 F 5) 3 L] complexes (L) triazene, 1; formamidine, 2; 2-aminopyridine, 3) have been carried out. These ligands contain a hydrogen atom, with more or less acidic character, in a position suitable for establishing an intramolecular hydrogen bonding interaction with the metal center. This interaction has been detected in solution for 1; its 1 H NMR spectrum shows that the resonance assignable to this hydrogen has platinum satellites. For 2, this coupling is not observed, and the interaction, if it exists, has to be weaker because of the less acidic character of the hydrogen atom. The 2-aminopyridine ligand is more flexible than the triazene or formamidine, and also in this case, no evidence of the interaction in solution is obtained. Nevertheless, if another potential proton acceptor is present, such as ClO 4in [NBu 4 ] 2 [Pt(C 6 F 5) 3 (C 5 H 6 N 2)](ClO 4) (4), a conventional N−H‚‚‚O−Cl hydrogen bond is formed. The crystal structures of complexes 1−4 have been determined by X-ray diffraction.
Dalton Transactions, 2008
The rate of substitution of the chloride ligand from [Pt(terpy)Cl] + (Pt1) (where terpy = 2,2¢:6¢,2¢¢-terpyridine) and its corresponding analogue [Pt( t Bu 3 terpy)Cl] + (Pt2) (where t Bu 3 terpy = 4,4¢,4¢¢-tri-tert-butyl-2,2¢:6¢,2¢¢-terpyridine) by a series of neutral and anionic nucleophiles, viz. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU), iodide (I -) and thiocyanate (SCN -), was determined under pseudo first-order conditions as a function of concentration and temperature using standard stopped-flow spectrophotometric techniques. The observed pseudo first-order rate constants for the substitution reactions obeyed the simple rate law k obs = k 2 [nucleophile]. Second-order kinetics and negative activation entropies support an associative mode of activation. The rate of substitution of chloride is observed to decrease with an increase in the steric bulk of the neutral nucleophiles, whilst rate of substitution by Iwas observed to be faster than that by SCN -, in correlation with their polarizability and the softness of the metal centre. A comparison of the second-order rate constants, k 2 , at 298 K, obtained for the substitution reactions of Pt1 and Pt2 shows that the introduction of strong s-donating groups on the periphery of the terpyridyl backbone in Pt2 results in a corresponding decrease in the reactivity. DFT calculations at the B3LYP/LACVP** level of theory for the two complexes, Pt1 and Pt2, and a series of similar analogues containing either electron-donating or electron-withdrawing groups in the periphery positions demonstrate that the introduction of electron-donating groups decreases the positive charge on the metal centre and increases energy separation of the frontier molecular orbitals (E HOMO -E LUMO ) of the ground state platinum(II) complexes leading to a less reactive metal centre whilst the introduction of electronwithdrawing groups has an opposite effect leading to increased reactivity of the metal centre.