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.

Metal-Organic Cubane Cage with Trimethylplatinum(IV) Vertices

Herein we describe the synthesis and characterization of the first platinum(IV) metal-organic cage [(Me₃Pt^IV)₈(byp)₁₂](OTf)₈ (2), in which the organometallic moieties trimethylplatinum(IV) (PtMe₃) occupied the corners of a cubane structure and 4,4'-bipyridine ligands used as linkers. The first-principles density functional theory calculations showed that the highest occupied molecular orbitals were localized on the PtMe₃ moieties, while the lowest unoccupied molecular orbitals were distributed on the organic linkers.

Mechanisms of rearrangements in platinacyclobutane chemistry

The mechanisms of formation, decomposition, and isomerisation of platinacyclobutane complexes [PtCl2(C3H6)L2] (L is typically pyridine) are discussed on the basis of density functional theory (DFT). The isomerisation and decomposition reactions occur through 5-coordinate intermediates [PtCl2(C3H6)L] that cannot be directly detected. These 5-coordinate complexes are predicted to have distorted square pyramidal structures, but a pinched trigonal bipyramidal (PTBP) stereochemistry is easily accessible. Both α- and β-elimination from these complexes to give hydride complexes [PtHCl2(C3H5)L] are predicted to have high activation energies. The isomerisation of [PtCl2(C3H6)L2] to the ylide complex [PtCl2{CH(L)CH2CH3)L] is instead predicted to occur after cleavage of a Pt–C bond to give an intermediate that can be considered as a corner platinated cyclopropane, leading to 1,3-hydrogen transfer without a hydridoplatinum intermediate. The reaction of [PtCl2{CH(L)CH2CH3}L] to give the alkene complex [PtCl2(CH2 = CHCH3)L] involves dissociation of the C–L bond followed by a 2,1-hydrogen transfer. The selectivity of related reactions from phenylcyclopropane follows naturally from these mechanisms.

Stable mixed-valence diphenylphosphanido bridged platinum(ii)-platinum(iv) complexes

The reaction between [NnBu4][(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(I)2] (C^N = κ2-N,C-benzoquinolinate, 1) and (i) bidentate S^S, N^S and O^O anionic ligands or (ii) monodentate S- N- or O-based anionic ligands was studied in order to investigate the factors that may guarantee the stability of Pt(ii),Pt(iv) mixed-valence dinuclear phosphanido complexes. While reactions of 1 with S^S or N^S ligands afforded stable Pt(ii),Pt(iv) species of general formula [(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(L^S)]x- [(L^S)(x-1) = 2-mercaptopyrimidinate (pymS-), 2-mercaptopyridinate (pyS-), dimethyldithiocarbamate (Me2NCS2-), ethyl xanthogenate (EtOCS2-) and 1,2-benzenedithiolate (PhS22-)], the reaction of 1 with the O^O ligand sodium acetylacetonate gave several products, and no pure Pt(ii),Pt(iv) complex could be isolated. The reaction of monodentate ligands such as PhS-, OH- or N3- with 1 led to a stable Pt(ii),Pt(iv) complex only in the case of N3-. The reaction with OH- afforded the Pt(ii),Pt(ii) complex [(C6F5)2PtII(μ-PPh2)(κ2-O,P-μ-O-PPh2)PtII(C^N)]- (8) deriving from reductive coupling of a diphenylphosphanide and an O-donor ligand coordinated to the Pt(iv) centre, while the reaction with PhS- produced the unstable Pt(ii),Pt(iv) complex [NnBu4][(C6F5)2PtII(μ-PPh2)2PtIV(C^N)(PhS)2] (11) that evolved in solution to the Pt(ii),Pt(ii) species [NnBu4][(C6F5)2PtII(μ-PPh2)2PtII(C^N)] (9) by elimination of diphenyldisulfide. Thus, the stability of mixed valence Pt(ii),Pt(iv) phosphanide complexes is affected by several concurrent factors, including the chelating effect of the ligands and the type of ligating atoms.

Supramolecular Polymer and Sheet and a Double Cubane Structure in Platinum(IV) Iodide Chemistry: Solution of a Longstanding Puzzle

The complexes [PtMe₂(L)], L = 2-C₅H₄NCH₂NH-x-C₆H₄OH (x = 2, 3, or 4), react with iodine to form [PtI₂Me₂(L)], by trans oxidative addition, when x = 3 or 4, and they are shown to have polymeric or sheet structures formed through NH···I hydrogen bonding. However, ligand dissociation occurs when x = 2 to give [(PtI₂Me₂) _n ] and, with methyl group transfer, the complex [(PtIMe₃·PtI₂Me₂)₂]. This tetraplatinum cluster complex is shown to have a double cubane structure, thus solving a longstanding puzzle.

A route to small clusters: a twisted half-hexagram-shaped M4(OH)4 cluster and its capacity for hosting closed-shell metals

The secret to making a new M₄(OH)₄ core structure lies in combining different oxidation states, coordination geometries and bridging systems. The spatial distribution of Pt(ii) atoms in Pt₄(OH)₄ is capable of cradling incoming Ag(i) centers.