Mechanism of oxidative addition of mercury(II) compounds to platinum(II)

Supramolecular organometallic chemistry: the platinum(IV) paradigm

Supramolecular chemistry and the chemistry of alkyl derivatives of the transition metals are both topics of considerable current interest, but the combination of the two fields is still underdeveloped. The challenges are, in large part, experimental in nature. For example, the self-assembly of molecules in supramolecular chemistry often relies on intermolecular hydrogen bonding, but most alkyl-transition metal bonds are cleaved by the protic groups used in hydrogen bond formation. Alkyl-platinum(IV) bonds are inert to protonolysis or attack by other electrophiles under mild conditions, and this has allowed an extensive supramolecular chemistry of organoplatinum(IV) complexes to be developed, as outlined in this perspective review. Highlights include a zeolitic structure, a polyrotaxane, a double helix, a nanotube structure and an example of spontaneous resolution to form a chiral sheet structure.

Reactions of Cycloplatinated Guanidine Complexes with Hg(OC(O)CF3)2: Formation of a One-Dimensional Coordination Polymer Containing a Pt2Hg(μ2-S(O)Me2-S,O) Repeating Unit versus a Discrete Pt2Hg2 Complex

Separate reactions of cycloplatinated 2-tolyl- and 2-anisylguanidine complexes, [Pt{κ²(C,N)}(OC(O)CF₃)(S(O)Me₂)] (1 and 2), with Hg(OC(O)CF₃)₂ in 1:0.5 and 1:1 molar ratios afforded the one-dimensional coordination polymer (1D CP) {[Pt^III{κ²(C,N)}(OC(O)CF₃)₂]₂Hg⁰}(μ₂-S(O)Me₂-S,O)·C₇H₈ (3·C₇H₈) as bright red crystals and the discrete tetrametallic complex [Pt^II{κ²(C,N)}(μ₂-OC(O)CF₃)₂Hg^I-]₂ (4) as yellow crystals in good yields. The two different products obtained in the aforementioned reactions are ascribed to the subtle differences in the N substituent of the guanidinate(1-) ligands in 1 and 2. The plausible mechanisms of formation of 3 and 4 are outlined. Complexes 3 and 4 were characterized by elemental analyses and IR and multinuclear NMR (¹H, ¹³C{¹H}, ¹⁹F, and ¹⁹⁵Pt) spectroscopy. Complex 4 was also characterized by ¹⁹⁹Hg NMR spectroscopy. The molecular structures of 3·C₇H₈ and 4 were determined by single-crystal X-ray diffraction studies. 1D CP 3·C₇H₈ contains a Pt(III)-Hg(0)-Pt(III)(μ₂-S(O)Me₂-S,O) repeating unit with a pair of unsupported Pt-Hg covalent bonds, while 4 contains a Pt(II)-Hg(I)-Hg(I)-Pt(II) chain with a pair of trifluoroacetate ligand supported Pt→Hg coordinate bonds. 1D CP 3·C₇H₈ falls apart into a mixture of three species, namely 6-8 and 9-11 in C₆D₆ and CDCl₃, respectively, as revealed by multinuclear NMR spectroscopy. In CDCl₃, 4 partially isomerizes to [Pt^II(OC(O)CF₃)(μ₂-OC(O)CF₃){κ³μ₂(C,N,O)}Hg^I-]₂ (12), wherein each Pt→Hg coordinate bond is supported by one μ₂-bridging trifluoroacetate ligand and one chelating bridging guanidinate(1-) ligand, as inferred from variable-temperature ¹H and ¹⁹F NMR spectroscopy. Complex 12 is the major species and 4 is the minor species in CDCl₃, while opposite situation prevails in C₆D₆. The observance of a mixture of two solution species for 4 is ascribed to a rapid "carboxylate shift" process induced by the oxygen atom of the ═N(C₆H₄(OMe)-2) unit of the guanidinate(1-) ligand through neighboring-group participation. UV-visible absorption and emission spectra of 4 were measured in CHCl₃, and from the outcome of the investigation, the possible existence of [Cl₂(H)C-Cl···Pt^II(OC(O)CF₃)(μ₂-OC(O)CF₃){κ³μ₂(C,N,O)}Hg^I-]₂ (12″) was suggested, which is likely to have a pair of Pt-Hg covalent bonds made possible by CHCl₃ coordination on the sixth site of the Pt(II) atom.

Coordination Isomers of Trinuclear Pt2Hg Complex That Differ in Type of Metal-Metal Bond

New type isomers that differ in metal-metal bond type are isolated. One is the Pt-Hg-Pt complex, which has two metal-metal covalent bonds, Pt-Hg = 2.5459(8) and 2.5483(7) Å, and the other is the Pt→Hg-Pt complex, which has one metal-metal covalent bond, Pt-Hg = 2.5744(6) Å, and one metal-metal dative bond, Pt→Hg = 2.6635(7) Å.

Metal “Capture” by a Heterotrimetalloligand, Heterometallic d10−d10Interactions, and Unexpected Iron-to-Platinum Silyl Ligand Migration: a Combined Experimental and Theoretical Study

The heterotrinuclear chain complex Hg[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)](2) (dppm = Ph(2)PCH(2)PPh(2)) 1 which has a transoid arrangement of the phosphine donors was used as a versatile chelating metallodiphosphine ligand owing to the easy rotation of its metal core about the Fe-Hg sigma-bonds. Its reaction with the labile Pt(0) olefin complex [Pt(C(7)H(10))(3)] yielded [HgPt{Si(OMe)(3)}Fe(2)(CO)(6){Si(OMe)(3)}(mu-dppm)(2)] 5 which resulted, after coordination of the dangling phosphine donors to Pt, from an unprecedented intramolecular rearrangement involving a very rare example of silyl ligand migration between two different metal centers, and the first one in metal cluster chemistry. The major structural differences observed between the heterometallic complexes obtained from 1 and d(10) Cu(I), Pd(0), or Pt(0) precursors have been established by X-ray diffraction. The bonding situation in the silyl migrated Pt complex 5 was analyzed and compared to those in the isoelectronic, but structurally distinct complexes obtained from Cu(I) and Pd(0) precursors, [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Cu](+) (2) and [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Pd] (4), respectively, by means of extended Hückel interaction diagrams. DFT calculations then allowed the energy minima associated with the three structures to be compared for 2, 4, and 5. All three minima are in close competition for the Pd complex 4, but silyl migration is favored by approximately 10 kcal mol(-)(1) for 5, mainly due to the more electronegative character of Pt with respect to Pd.

Modification of Binuclear Pt−Tl Bonded Complexes by Attaching Bipyridine Ligands to the Thallium Site

Complex formation of monomeric thallium(III) species with 2,2'-bipyridine (bipy) in dimethyl sulfoxide (dmso) and acetonitrile solutions was studied by means of multinuclear ((1)H, (13)C, and (205)Tl) NMR spectroscopy. For the first time, NMR signals of the individual species [Tl(bipy)(m)(solv)](3+) (m = 1-3) were observed despite intensive ligand and solvent exchange processes. The tris(bipy) complex was crystallized as [Tl(bipy)(3)(dmso)](ClO(4))(3)(dmso)(2) (1), and its crystal structure determined. In this compound, thallium is seven-coordinated; it is bonded to six nitrogen atoms of the three bipy molecules and to an oxygen atom of dmso. Metal-metal bonded binuclear complexes [(NC)(5)Pt-Tl(CN)(n)(solv)](n)(-) (n = 0-3) have been modified by attaching bipy molecules to the thallium atom. A reaction between [(NC)(5)Pt-Tl(dmso)(4)](s) and 2,2'-bipyridine in dimethyl sulfoxide solution results in the formation of a new complex, [(NC)(5)Pt-Tl(bipy)(solv)]. The presence of a direct Pt-Tl bond in the complex is convincingly confirmed by a very strong one-bond (195)Pt-(205)Tl spin-spin coupling ((1)J((195)Pt-(205)Tl) = 64.9 kHz) detected in both (195)Pt and (205)Tl NMR spectra. In solutions containing free cyanide, coordination of CN(-) to the thallium atom occurs, and the complex [(NC)(5)Pt-Tl(bipy)(CN)(solv)](-) ((1)J((195)Pt-(205)Tl) = 50.1 kHz) is formed as well. Two metal-metal bonded compounds containing bipy as a ligand were crystallized and their structures determined by X-ray diffractometry: [(NC)(5)Pt-Tl(bipy)(dmso)(3)] (2) and [(NC)(5)Pt-Tl(bipy)(2)] (3). The Pt-Tl bonding distances in the compounds, 2.6187(7) and 2.6117(5) A, respectively, are among the shortest reported separations between these two metals. The corresponding force constants in the molecules, 1.38 and 1.68 N/cm, respectively, were calculated using Raman stretching frequencies of the Pt-Tl vibrations and are characteristic for a single metal-metal bond. Electronic absorption spectra were recorded for the [(NC)(5)Pt-Tl(bipy)(m)(solv)] compounds, and the optical transition was attributed to the metal-metal bond assigned.

Cationic thiolate and selenolate complexes of platinum(IV)

The reaction of the adamantanoid compounds [Hg4(EPh)6(L)4][ClO4]2 (E = S or Se, L = PEt3 or PPh3) with [PtMe2(bu2bpy)] (bu2bpy = 4,4'-di-tert-butyl-2,2'-bipyridine) occurs easily to give the first examples of cationic thiolate or selenolate derivatives of platinum(IV), [PtMe2(EPh)L(bu2bpy)][ClO4], and the addition is shown to occur with trans stereochemistry. The new complexes are characterized by NMR spectroscopy and when L = PEt3 by X-ray structure determinations. When L = PPh3, a competitive reaction leads to methyl group transfer from platinum to mercury to give MeHgEPh (E = S or Se).Key words: oxidative-addition, platinum, thiolate, selenolate, mercury.