Reactivity of a Dimethylplatinum(II) Complex with the Bis(2-pyridyl)dimethylsilane Ligand: Easy Silicon–Carbon Bond Activation

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.

Facial-Meridional Isomerization and Reductive Elimination in [(R2P-o-C6H4)2N]PtMe3 (R = Ph, iPr)

Treatment of PtMe₃I in tetrahydrofuran with either in situ prepared [R-PNP]Li ([R-PNP]^- = [(R₂P-o-C₆H₄)₂N]^-; R = Ph, iPr) or H[R-PNP] in the presence of triethylamine at room temperature affords quantitatively fac-[R-PNP]PtMe₃. Thermolysis of fac-[R-PNP]PtMe₃ in benzene solutions generates mer-[R-PNP]PtMe₃ and ultimately [R-PNP]PtMe and ethane. Complexes mer-[R-PNP]PtMe₃ represent the first meridional trialkylplatinum(IV) derivatives to date.

Ligand-Mediated C-Br Oxidative Addition to Cycloplatinated(II) Complexes and Benzyl-Me C-C Bond Reductive Elimination from a Cycloplatinated(IV) Complex

Reaction of the Pt(II) complexes [PtMe₂(pbt)], 1a, (pbt = 2-(2-pyridyl)benzothiazole) and [PtMe(C^N)(PPh₂Me)] [C^N = deprotonated 2-phenylpyridine (ppy), 1b, or deprotonated benzo[h]quinoline (bhq), 1c] with benzyl bromide, PhCH₂Br, is studied. The reaction of 1a with PhCH₂Br gave the Pt(IV) product complex [PtBr(CH₂Ph)Me₂(pbt)]. The major trans isomer is formed in a trans oxidative addition (2a), while the minor cis products (2a' and 2a″) resulted from an isomerization process. A solution of Pt(II) complex 1a in the presence of benzyl bromide in toluene at 70 °C after 7 days gradually gave the dibromo Pt(IV) complex [Pt(Br)₂Me₂(pbt)], 4a, as determined by NMR spectroscopy and single-crystal XRD. The reaction of complexes 1b and 1c with PhCH₂Br gave the Pt(IV) complexes [PtMeBr(CH₂Ph)(C^N)(PPh₂Me)] (C^N = ppy; 2b; C^N = bhq, 2c), in which the phosphine and benzyl ligands are trans. Multinuclear NMR spectroscopy ruled out other isomers. Attempts to grow crystals of the cycloplatinated(IV) complex 2b yielded a previously reported Pt(II) complex [PtBr(ppy)(PPh₂Me)], 3b, presumably from reductive elimination of ethylbenzene. UV-vis spectroscopy was used to study the kinetics of reaction of Pt(II) complexes 1a-1c with benzyl bromide. The data are consistent with a second-order S_N2 mechanism and the first order in both the Pt complex and PhCH₂Br. The rate of reaction decreases along the series 1a ≫ 1c > 1b. Density functional theory calculations were carried out to support experimental findings and understand the formation of isomers.

Linear Bidentate Ligands (L) with Two Terminal Pyridyl N-Donor Groups Forming Pt(II)LCl2 Complexes with Rare Eight-Membered Chelate Rings

NMR and X-ray diffraction studies were conducted on Pt(II)LCl₂ complexes prepared with the new N-donor ligands N(SO₂R)Me _ndpa (R = Me, Tol; n = 2, 4). These ligands differ from N(H)dpa (di-2-picolylamine) in having the central N within a tertiary sulfonamide group instead of a secondary amine group and having Me groups at the 6,6'-positions ( n = 2) or 3,3',5,5'-positions ( n = 4) of the pyridyl rings. The N(SO₂R)3,3',5,5'-Me₄dpa ligands are coordinated in a bidentate fashion in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes, forming a rare eight-membered chelate ring. The sulfonamide N atom did not bind to Pt(II), consistent with indications in the literature that tertiary sulfonamides are unlikely to anchor two meridionally coordinated five-membered chelate rings in solutions of coordinating solvents. The N(SO₂R)6,6'-Me₂dpa ligands coordinate in a monodentate fashion to form the binuclear complexes [ trans-Pt(DMSO)Cl₂]₂( N(SO₂R)6,6'-Me₂dpa). The monodentate instead of bidentate N(SO₂R)6,6'-Me₂dpa coordination is attributed to 6,6'-Me steric bulk. These binuclear complexes are indefinitely stable in DMF- d₇, but in DMSO- d₆ the N(SO₂R)6,6'-Me₂dpa ligands dissociate completely. In DMSO- d₆, the bidentate ligands in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes also dissociate, but incompletely; these complexes provide rare examples of association-dissociation equilibria of N,N bidentate ligands in Pt(II) chemistry. Like typical cis-PtLCl₂ complexes, the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes undergo monosolvolysis in DMSO- d₆ to form the [Pt( N(SO₂R)3,3',5,5'-Me₄dpa)(DMSO- d₆)Cl]⁺ cations. However, unlike typical cis-PtLCl₂ complexes, the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes surprisingly do not react readily with the excellent N-donor bioligand guanosine. A comparison of the structural features of over 50 known relevant Pt(II) complexes having smaller chelate rings with those of the very few relevant Pt(II) complexes having eight-membered chelate rings indicates that the pyridyl rings in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes are well positioned to form strong Pt-N bonds. Therefore, the dissociation of the bidentate ligand and the poor biomolecule reactivity of the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes arise from steric consequences imposed by the -CH₂-N(SO₂R)-CH₂- chain in the eight-membered chelate ring.

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

Organometallic and metal amide reagents react with –OH groups to generate metal–oxygen connectivity, yielding metal-oxo heterobimetallics, clusters and nanoparticles.

The coordination chemistry of the neutral tris-2-pyridyl silicon ligand [PhSi(6-Me-2-py)3]

The first transition metal complexes of Si(iv) tris(2-pyridyl) ligands are reported.

Phosphorescent heterobimetallic complexes involving platinum(iv) and rhenium(vii) centers connected by an unsupported μ-oxido bridge

Heterobimetallic compounds containing an unsupported Pt(iv)–O–Re(vii) bridge are synthesized. The complexes exhibit rare phosphorescence emission in solid and frozen states.

Oxidation of dimethylplatinum(II) complexes with malonyl peroxide derivatives

The reaction of the cyclic peroxides cyclobutane malonoyl peroxide and cyclopentane malonoyl peroxide to dimethylplatinum(II) complexes with the bidentate nitrogen donor ligand 4,4′-di-t-butyl-2,2′-bipyridine (bubpy) gave a mixture of the products of cis and trans oxidative addition, [PtMe2{(O2C)2C(C3H6)}(bubpy)] and [PtMe2{(O2C)2C(C4H8)}(bubpy)], respectively. The cis isomers exist with a chelating dicarboxylate ligand, forming a six-membered ring, while the trans isomers are thought to exist as oligomers, which may react with water or solvent to give complexes containing a monodentate dicarboxylate ligand. Equilibration of the product of cis oxidative addition, cis-[PtMe2{(O2C)2C(C3H6)}(bubpy)], with oxalic or phthalic acid to give equilibria with the oxalate cis-[PtMe2(O4C2)(bubpy)] or phthalate cis-[PtMe2{(O2C)2C6H4}(bubpy)] derivative, respectively, indicated the expected sequence of chelate stability oxalate > cyclobutane malonate > phthalate.

Reactivity comparison of five-and six-membered cyclometalated platinum(ii) complexes in oxidative addition reactions

A six-membered cyclometalated complex [PtMe(bzpy)(PPh₃)] (bzpy = 2-benzylpyridinate) undergoes oxidative addition with methyl iodide to give [PtMe₂I(bzpy)(PPh₃)]. The ring size of the chelating unit has a significant impact on the rate of the reaction.