Microwave-Assisted Organometallic Syntheses: Formation of Dinuclear [(Arene)Ru(μ-Cl)3RuCl(L-L′)] Complexes (L-L′: Chelate Ligands withP-,N-, orS-Donor Atoms) by Displacement of Arene π Ligands

Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This “Green” Method?

Microwave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent.

Alternative Technologies That Facilitate Access to Discrete Metal Complexes

Organometallic complexes: these two words jump to the mind of the chemist and are directly associated with their utility in catalysis or as a pharmaceutical. Nevertheless, to be able to use them, it is necessary to synthesize them, and it is not always a small matter. Typically, synthesis is via solution chemistry, using a round-bottom flask and a magnetic or mechanical stirrer. This review takes stock of alternative technologies currently available in laboratories that facilitate the synthesis of such complexes. We highlight five such technologies: mechanochemistry, also known as solvent-free chemistry, uses a mortar and pestle or a ball mill; microwave activation can drastically reduce reaction times; ultrasonic activation promotes chemical reactions because of cavitation phenomena; photochemistry, which uses light radiation to initiate reactions; and continuous flow chemistry, which is increasingly used to simplify scale-up. While facilitating the synthesis of organometallic compounds, these enabling technologies also allow access to compounds that cannot be obtained in any other way. This shows how the paradigm is changing and evolving toward new technologies, without necessarily abandoning the round-bottom flask. A bright future is ahead of the organometallic chemist, thanks to these novel technologies.

Unprecedented flexibility of the 1,1′-bis(o-carborane) ligand: catalytically-active species stabilised by B-agostic B–H⇀Ru interactions

The compound (p-cymene)Ru[(C₂B₁₀H₁₀)₂], an effective Lewis acid catalyst, is the precursor to a number of products in which the 1,1′-bis(o-carborane) unit displays an unprecedented range of ligating modes.

1,2,3-Triazolylidene ruthenium(ii)(η6-arene) complexes: synthesis, metallation and reactivity

Three bis(1,2,3-triazolylidene) silver(i) complexes were reacted with [RuCl₂(p-cymene)]₂ and the ruthenium complexes [RCH₂N₂(NMe)C₂Ph]RuCl₂(p-cymene) (R = C₆H₂Me₃4a1, C₆H₂iPr₃4b1, Ph 4c1) were isolated as major products with the minor C(sp²)–H activated products [RCH₂N₂(NMe)C₂C₆H₄]RuCl(p-cymene) (R = C₆H₂Me₃4a2, C₆H₂iPr₃4b2, Ph 4c2) and [(C₆H₄)CH₂N₂(NMe)C₂Ph]RuCl(p-cymene) (4c3).

Metal-Arene Complexes with Indolo[3,2-c]-quinolines: Effects of Ruthenium vs Osmium and Modifications of the Lactam Unit on Intermolecular Interactions, Anticancer Activity, Cell Cycle, and Cellular Accumulation

Six novel ruthenium(II)- and osmium(II)-arene complexes with three modified indolo[3,2-c]quinolines have been synthesized in situ starting from 2-aminoindoloquinolines and 2-pyridinecarboxaldehyde in the presence of [M(p-cymene)Cl(2)](2) (M = Ru, Os) in ethanol. All complexes have been characterized by elemental analysis, spectroscopic techniques ((1)H, (13)C NMR, IR, UV-vis), and ESI mass spectrometry, while four complexes were investigated by X-ray diffraction. The complexes have been tested for antiproliferative activity in vitro in A549 (non-small cell lung), SW480 (colon), and CH1 (ovarian) human cancer cell lines and showed IC(50) values between 1.3 and >80 μM. The effects of Ru vs Os and modifications of the lactam unit on intermolecular interactions, antiproliferative activity, and cell cycle are reported. One ruthenium complex and its osmium analogue have been studied for anticancer activity in vivo applied both intraperitoneally and orally against the murine colon carcinoma model CT-26. Interestingly, the osmium(II) complex displayed significant growth-inhibitory activity in contrast to its ruthenium counterpart, providing stimuli for further investigation of this class of compounds as potential antitumor drugs.

Ruthenium- and Osmium-Arene Complexes of 2-Substituted Indolo[3,2-c]quinolines: Synthesis, Structure, Spectroscopic Properties, and Antiproliferative Activity

The synthesis of new modified indolo[3,2-c]quinoline ligands L¹−L⁸ with metal-binding sites is reported. By coordination to ruthenium− and osmium−arene moieties 16 complexes of the type [(η⁶-p-cymene)M(L)Cl]Cl (1a,b−8a,b), where M is Ru^II or Os^II and L is L¹−L⁸, have been prepared. All compounds were comprehensively characterized by elemental analysis, electrospray ionization mass spectrometry, IR, UV−vis, and NMR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction (2a, 4a, 4b, 5a, 7a, and 7b). The complexes were tested for antiproliferative activity in vitro in three human cancer cell lines, namely, CH1 (ovarian carcinoma), SW480 (colon adenocarcinoma), and A549 (non-small-cell lung cancer), yielding IC₅₀ values in the submicromolar or low micromolar range.