Homo and heteromultimetallic complexes containing a group 8 transition metal and μ-diphosphine bridging ligands involved in anticancer research: A review.

Herein, we present a comprehensive review focusing on synthetic strategies, detailed structural analysis, and anticancer activity investigations of complexes following the general formula [LM(μ-diphosphine)M'L] where M = group 8 metal; M' = any transition metal; μ-diphosphine = bridging ligand; L and L = ligand spheres). Both homo- and heteromultimetallic complexes will be discussed in detail. We review in vitro, in vivo and in silico anticancer activity investigations, in an attempt to draw comparisons between the various complexes and derive structure-activity relationships (SAR).

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions.

The reactions of 2,4-di--butyl-6-(diphenylphosphino)phenol and various Michael acceptors (acrylonitrile, acrylamide, methyl vinyl ketone, several acrylates, methyl vinyl sulfone) yield the respective phosphonium phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form.

Selective synthesis of germasila-adamantanes through germanium-silicon shift processes.

The regioselective synthesis of germasila-adamantanes with the germanium atoms in the bridgehead positions is described starting from cyclic precursors by a cationic sila-Wagner-Meerwein (SWM) rearrangement reaction. The SWM rearrangement allows also a deliberate shift of germanium atoms from the periphery and within the cage structures into the bridgehead positions. This opens the possibility for a synthesis of germasila-adamantanes of defined germanium content and controlled regiochemistry.

Metallacyclosilanes of Calcium, Yttrium, and Iron.

Utilizing a choice of α,ω-oligosilanylene diides, it is possible to synthesize a number of heterocyclosilanes with heteroelements of calcium, yttrium, and iron by metathesis reactions with respective metal halides CaI, YCl, and FeBr. Si NMR spectroscopic analysis of the calcacyclosilanes suggests that these compounds retain a strong oligosilanylene dianion character, which is more pronounced than in the analogous magnesacyclosilanes. As the electronegativity of calcium lies between potassium and magnesium, silyl calcium reagents should be considered as building blocks with an attractive reactivity profile.

Silole allylic anions instead of silanides.

Reaction of a 3,4-diphenylsilole with two neopentasilanyl groups attached to the 2- and 5-positions with one equivalent of KOBu did not result in the expected silanide formation but yielded a silole allylic anion instead. The initially formed silanide added to a neighboring phenyl group, which then transfers a proton to the 2-position of the silole ring.

Osmium Arene Germyl, Stannyl, Germanate, and Stannate Complexes as Anticancer Agents.

Herein, we describe the synthesis, full spectroscopic characterization, DFT (density functional theory) calculations, and single-crystal X-ray diffraction analyses of a series of osmium arene σ-germyl, germanate, σ-stannyl, and stannate complexes, along with their cytotoxic (anticancer) investigations. The known dimer complexes [OsCl(η-CH)] () and [OsCl(η--cymene)] () were reacted with PPh to form the known mononuclear complex [OsCl(η--cymene)(PPh)] () and the new complex [OsCl(η-CH)(PPh)] (); complex was reacted with GeCl·(dioxane) and SnCl to afford, by insertion into the Os-Cl bond, the neutral σ-germyl and stannyl complexes [OsCl(η--cymene)(PPh)(GeCl)] () and [OsCl(η--cymene)(PPh)(SnCl)] (), respectively, as a mixture of enantiomers. Similarly, the reaction of complex with GeCl·(dioxane) afforded [OsCl(η-CH)(PPh)(GeCl)] ().

Rare-Earth-Silyl ate-Complexes Opening a Door to Selective Manipulations.

The reactions of a number of rare-earth (RE) trichlorides and an oligosilanylene diide containing a siloxane unit in the backbone in DME are described. The formed products of the type [(DME)·K][(DME)·RE(Cl){Si(SiMe)SiMe}O] (RE = Y, La, Ce, Pr, Sm, Tb, Dy, and Er) are disilylated dichloro metalate complexes and include the first examples of Si-La and Si-Pr compounds as well as the first structurally characterized example of a Si-Dy complex. A most intriguing aspect of the synthesis of these complexes is that they offer entry into a systematic study of the still largely unexplored field of silyl RE complexes by the possibility of ligand exchange reactions under preservation of the Si-RE interaction.

Oligosilanylated Silocanes.

A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KOBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides.

A review on 1,1-bis(diphenylphosphino)methane bridged homo- and heterobimetallic complexes for anticancer applications: Synthesis, structure, and cytotoxicity.

Herein, we review developments in synthesis, structure, and biological (anti-cancer) activities of 1,1-bis(diphenylphosphino)methane (dppm) bridged homo- and heterobimetallic systems of the type LM(μ-dppm)M'L (M and M' are transition metals which may be different or the same and L are co-ligands) since the first such reported bimetallic system in 1987 until the present time (2020). As the simplest diphosphine, dppm enables facile formation of bimetallic complexes, where, given the short spacer between the PPh groups, close spatial proximity of the metal centres is ensured. We concentrate on complexes bearing no M-M interaction and contrast biological activities of these complexes with mononuclear counterparts and positive control agents such as cisplatin, in an attempt to elucidate patterns in the biological activities of these complexes.

The Combination of Cross-Hyperconjugation and σ-Conjugation in 2,5-Oligosilanyl Substituted Siloles.

Reaction of a 2,5-dilithiated silole with excess dichlorodimethylsilane gives the respective 2,5-bis(chlorodimethylsilyl) substituted silole. This compound can be converted to 2,5-bis(oligosilanyl) substituted siloles by addition of a suitable oligosilanide. In the UV spectra of the thus obtained compounds the lowest energy absorptions are bathochromically shifted compared to the absorptions of the two constituents, namely the 2,5-disilyl substituted silole and a trisilane.

Synthesis, structure and anti-cancer activity of osmium complexes bearing π-bound arene substituents and phosphane Co-Ligands: A review.

While many examples of osmium complexes, as anti-cancer agents, have been reported and some reviews have been devoted to this topic, a particularly interesting and synthetically accessible sub-class of these compounds namely those bearing a π- bound arene and phosphane co-ligand have escaped review. These complexes have made a surprisingly late entry in the literature (2005) in terms of anti-cancer investigations. This is somewhat surprising considering the plethora of analogous complexes that have been reported for the lighter analogue, ruthenium.

A 1,5-Oligosilanylene Dianion as Building Block for Oligosiloxane Containing Cages, Ferrocenophanes, and Cyclic Germylenes and Stannylenes.

Starting out from dipotassium 1,5-oligosiloxanylene diide 2, a 3,7,10-trioxa-octasilabicyclo[3.3.3]undecane was prepared, which represents the third known example of this cage structure type.

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts.

The reactions of the PMe adduct of the silylated germylene [(MeSi)Si]Ge: with GeCl·dioxane were found to yield 1,1-migratory insertion products of GeCl into one or two Ge-Si bonds. In a related reaction, a germylene was inserted with tris(trimethylsilyl)silyl and vinyl substituents into a Ge-Cl bond of GeCl. This was followed by intramolecular trimethylsilyl chloride elimination to another cyclic germylene PMe adduct.

β-Amino- and Alkoxy-Substituted Disilanides.

Our recent study on formal halide adducts of disilenes led to the investigation of the synthesis and properties of β-fluoro- and chlorodisilanides. The reaction of the functionalized neopentasilanes (MeSi)SiSiPhNEt and (MeSi)SiSiMeOMe with KOBu in the presence of 18-crown-6 provided access to structurally related β-alkoxy- and amino-substituted disilanides. The obtained EtNPhSi(MeSi)SiK·18-crown-6 was converted to a magnesium silanide and further on to EtNPhSi(MeSi)Si-substituted ziroconocene and hafnocene chlorides.

Disilene Fluoride Adducts versus β-Halooligosilanides.

Extending the chemistry of disilene fluoride adducts studied earlier by us, we investigated the formation of 1,1-bis(trimethylsilyl)fluorodiphenylsilylsilanide, which was prepared by reaction of (MeSi)SiSiPhF with KOBu. The formed FPhSiSi(MeSi)K displays distinctively different structural and spectroscopic features compared to the earlier reported F(MeSi)SiSi(SiMe)K. While the latter eliminates metal fluoride upon reaction with MgBr, the respective magnesium silanide is formed from FPhSiSi(MeSi)K.

Group 4 Metal and Lanthanide Complexes in the Oxidation State +3 with Tris(trimethylsilyl)silyl Ligands.

A number of paramagnetic silylated d group 4 metallates were prepared by reaction of potassium tris(trimethylsilyl)silanide with group 4 metallates of the type K[CpMCl] (M = Ti, Zr, Hf). The outcomes of the reactions differ for all three metals. While for the hafnium case the expected complex [CpHf{Si(SiMe)}] was obtained, the analogous titanium reaction led to a product with two Si(H)(SiMe) ligands.

Chemistry of a 1,5-Oligosilanylene Dianion Containing a Disiloxane Unit.

Synthesis of a number of disiloxane containing cyclo- and bicyclooligosilanes is described starting from the dipotassium 1,5-oligosiloxanylene diide derived from 1,3-bis[tris(trimethylsilyl)silyl]tetramethyldisiloxane. In addition, the use of this particular fragment as ligand for zinc and group 4 metallocene complexes was studied. Both types of compounds exhibit marked structural differences compared to related compounds containing Si-Si-Si units instead of the Si-O-Si fragment.

Spectroscopic and Structural Study of Some Oligosilanylalkyne Complexes of Cobalt, Molybdenum and Nickel.

Metal induced stabilization of α-carbocations is well known for cobalt- and molybdenum complexed propargyl cations. The same principle also allows access to reactivity enhancement of metal coordinated halo- and hydrosilylalkynes. In a previous study, we have shown that coordination of oligosilanylalkynes to the dicobalthexacarbonyl fragment induces striking reactivity to the oligosilanyl part.

Hypercoordinated Oligosilanes Based on Aminotrisphenols.

The hypercoordinated silicon chlorides ClSi[(-OCH)N] () and ClSi[(OCHMeCH)N] () were used for the synthesis of catenated derivatives (MeSi)SiSi[(-OCH)N] (), (MeSi)SiSiMeSiMeSi(SiMe)Si[(-OCH)N] (), and (MeSi)SiSi[(OCHMeCH)N] () in reactions with (MeSi)SiK·THF () or (MeSi)SiK·[18-crown-6] (). It was found that the nature of the (MeSi)SiK solvate determines the product of interaction, resulting in the formation of (MeSi)Si(CH)OSi[(OCHMeCH)N] () or . Compounds obtained were characterized using multinuclear NMR and UV-vis spectroscopy and mass spectrometry.

Spirocyclic germanes via transannular insertion reactions of vinyl germylenes into Si-Si bonds.

The reactions of two cyclic germylene phosphane adducts with monosubstituted acetylenes caused the formation of spirocyclic germanes, which is postulated to occur by double acetylene insertion into germylene attached bonds. Further insertion of the formed cyclic divinylgermylene into transannular Si-Si or Si-Ge bonds provides the spirocyclic germanes. Thermal treatment of two germacyclopropenes, formed by the reaction of the two cyclic germylene phosphane adducts with tolane, also produced spirocyclogermanes.

Incorporating Methyl and Phenyl Substituted Stannylene Units into Oligosilanes. The Influence on Optical Absorption Properties.

Molecules containing catenated heavy group 14 atoms are known to exhibit the interesting property of σ-bond electron delocalization. While this is well studied for oligo- and polysilanes the current paper addresses the UV-absorption properties of small tin containing oligosilanes in order to evaluate the effects of Sn-Si and Sn-Sn bonds as well as the results of substituent exchange from methyl to phenyl groups. The new stannasilanes were compared to previously investigated oligosilanes of equal chain lengths and substituent pattern.

Tuning the Si-N Interaction in Metalated Oligosilanylsilatranes.

Most known silatrane chemistry is concerned with examples where the attached silatrane substituent atom is that of an element more electronegative than silicon. The current study features silylated silatranes with a range of electropositive elements attached to the silyl group. The resulting compounds show different degrees of electron density on the silatrane-substituted silicon atom.

Using Functionalized Silyl Ligands To Suppress Solvent Coordination to Silyl Lanthanide(II) Complexes.

The reaction of the potassium 1,3-trisilanediide MeSi[Si(MeSi)K] with SmI and YbI was found to give the respective disilylated complexes MeSi[Si(MeSi)]Sm·2THF and MeSi[Si(MeSi)]Yb·2THF. Desolvation of coordinated solvent molecules in these complexes made their handling difficult. However, using a number of functionalized silanide ligands, complexes with a diminished number or even no coordinated solvent molecules were obtained ((RSi)Ln(THF) (x = 0-3)).

Electron Transfer and Modification of Oligosilanylsilatranes and Related Derivatives.

Several silatranyl -substituted oligosilanes were prepared starting from bis(trimethylsilyl)silatranylsilanide. Electrochemical and theoretical investigations of some oligosilanes revealed that electrooxidation occurs by formation of a short-lived cation radical. This species undergoes structural relaxation to form a pair of conformers, with endo and exo relationships with respect to the Si-N interaction.