New Frontiers on Cooperative Chemistry of Rarely Employed Metals

This project sought to extend the concept of enhanced cooperative reactivity in bimetallic chemistry to metals beyond Mg, Zn or Al, especially, Ga and Mn.Towards new applications of trisalkylgallium in synthesis, studies on gallium NHC (N-heterocyclic carbene) chemistry afforded a novel series of normal, abnormal and anionic NHC complexes derived from Ga(CH2SiMe3)3. These complexes proved excellent platforms for accessing functionalised aNHC ligands via metallation/electrophilic interception and/or thermal isomerisation. Capitalising on these advances, a new FLP system incorporating Ga(CH2SiMe3)3 and bulky NHCs as effective Lewis acid Lewis base combinations was developed. By exploring their reactivity towards carbonyl compounds two distinct types of FLP activation processes were uncovered. Adding the FLP pair across the C=O functionality can occur, forming new C-C and Ga-O bonds, in which NHC can participate through its normal or abnormal position. Alternatively, C-H bond activation can proceed by treating enolizable ketones, or other C-H acidic substrates such as nitriles or terminal alkynes, with the same mixture;Exporting such steric incompatibility into bimetallic chemistry a new multicomponent LiTMP/GaR3 metallating mixture that works in a tandem manner has been established. Lack of co-complexation between the bulky lithium amide LiTMP and trisalkylgallium facilitates substrate deprotonation by LiTMP (the base) and anion trapping by GaR3 (the trap). Thus, introducing the concept of gallium trans-metal-trapping, for the first time formal gallation of aromatic substrates (i.e. diazines and anisole) has been accomplished.The project also developed alkali-metal manganate chemistry. A new family of homoleptic alkali-metal manganates has been prepared and characterized by X-ray crystallographic, EPR spectroscopic and SQUID magnetometric studies. Intriguing structural/synthetic/magnetic correlations were revealed in which aggregation and reactivity of different manganates were largely determined by the alkali-metal. Furthermore, addressing the issue of ill-defined manganese species participating in organic transformations, lithium manganate [(TMEDA)2Li2Mn(CH2SiMe3)4] was disclosed as an effective reagent to promote direct Mn-I exchange and homocoupling processes.This project sought to extend the concept of enhanced cooperative reactivity in bimetallic chemistry to metals beyond Mg, Zn or Al, especially, Ga and Mn.Towards new applications of trisalkylgallium in synthesis, studies on gallium NHC (N-heterocyclic carbene) chemistry afforded a novel series of normal, abnormal and anionic NHC complexes derived from Ga(CH2SiMe3)3. These complexes proved excellent platforms for accessing functionalised aNHC ligands via metallation/electrophilic interception and/or thermal isomerisation. Capitalising on these advances, a new FLP system incorporating Ga(CH2SiMe3)3 and bulky NHCs as effective Lewis acid Lewis base combinations was developed. By exploring their reactivity towards carbonyl compounds two distinct types of FLP activation processes were uncovered. Adding the FLP pair across the C=O functionality can occur, forming new C-C and Ga-O bonds, in which NHC can participate through its normal or abnormal position. Alternatively, C-H bond activation can proceed by treating enolizable ketones, or other C-H acidic substrates such as nitriles or terminal alkynes, with the same mixture;Exporting such steric incompatibility into bimetallic chemistry a new multicomponent LiTMP/GaR3 metallating mixture that works in a tandem manner has been established. Lack of co-complexation between the bulky lithium amide LiTMP and trisalkylgallium facilitates substrate deprotonation by LiTMP (the base) and anion trapping by GaR3 (the trap). Thus, introducing the concept of gallium trans-metal-trapping, for the first time formal gallation of aromatic substrates (i.e. diazines and anisole) has been accomplished.The project also developed alkali-metal manganate chemistry. A new family of homoleptic alkali-metal manganates has been prepared and characterized by X-ray crystallographic, EPR spectroscopic and SQUID magnetometric studies. Intriguing structural/synthetic/magnetic correlations were revealed in which aggregation and reactivity of different manganates were largely determined by the alkali-metal. Furthermore, addressing the issue of ill-defined manganese species participating in organic transformations, lithium manganate [(TMEDA)2Li2Mn(CH2SiMe3)4] was disclosed as an effective reagent to promote direct Mn-I exchange and homocoupling processes

Trans-metal-trapping meets FLP chemistry : Ga(CH2SiMe3)3 induced C-H functionalizations

Merging two topical themes in Main Group chemistry, namely cooperative bimetallics and FLP activity, this Forum Article focuses on the cooperativity-induced outcomes observed when the tris(alkyl)gallium compound GaR3 (R= CH2SiMe3) is paired with lithium amide LiTMP (TMP=2,2,6,6-tetramethylpiperidide) or the sterically hindered NHC ItBu (ItBu = 1,3-bis(tert-butyl)imidazol-2-ylidene). Drawing together some previously published work with new results, unique tandem reactivities are presented which are driven by the steric mismatch between the individual reagents of these multicomponent reagents. Thus the LiTMP/GaR3 combination, which on its own fails to form a co-complex, functions as a highly regioselective base (LiTMP)-trap (GaR3) partnership for metalation of N-heterocycles such as diazines, 1,3 benzo-azoles and 2-picoline in a trans-metal-trapping (TMT) process that stabilizes the emerging sensitive carbanions. Taking advantage of related steric incompatibility, a novel monometallic FLP system pairing GaR3 with ItBu has been developed for activation of carbonyl compounds (via C=O insertion) and other molecules with acidic hydrogen atoms such as phenol and phenylacetylene. Shedding new light on how these non-cocomplexing partnerships operate and showcasing the potential of Ga reagents to engage in metalation reactions or FLP activations, areas where the use of this Group 13 metal is scant, this Forum Article aims to stimulate more interest and activity towards the advancement of organogallium chemistry

Alkali-metal-mediated synergistic effects in polar main group organometallic chemistry

The development of synthetic chemistry since the early 1900s owes much to the service of organolithium reagents. Brilliant bases (e.g., deprotonating C–H bonds), nucleophiles (e.g., adding to unsaturated molecules), and transfer agents (e.g., delivering ligands to other metals), these versatile virtuosi and to a lesser extent the organic derivatives of the other common alkali metals sodium and potassium have proved indispensable in both academia and technology. Today these monometallic compounds are still utilized widely in synthetic campaigns, but in recent years they have been joined by an assortment of bimetallic formulations that also contain an alkali metal but in company with another metal. These bimetallic formulations often exhibit unique chemistry that can be interpreted in terms of synergistic effects, for which the alkali metal is essential, though it is often the second metal that performs the synthetic transformation. Here, this “alkali-metal-mediated” chemistry is surveyed focusing mainly on bimetallic formulations containing two alkali metals or an alkali metal paired with magnesium, calcium, zinc, aluminum, or gallium. In this International Year of the Periodic Table (IYPT), we ponder whether a Pairiodic Table of Element Pairs will emerge in the future

The role of self-esteem and peer pressure in loneliness among adolescents

Glavni cilj ovog istraživanja bio je utvrditi u kojoj mjeri se usamljenost u adolescenciji možeobjasniti samopoštovanjem i vršnjačkim pritiskom. Naime, brojna istraživanja su se većinomusmjerila na bivarijatne odnose među spomenutim varijablama, te do sada na hrvatskom uzorkuadolescenata nije istovremeno provjeravan odnos usamljenosti sa samopoštovanjem i vršnjačkimpritiskom. Iako većina autora smatra da se usamljenost može javiti u svim razvojnim razdobljima,ipak se naglašava da je usamljenost tijekom adolescencije izraženija i to čak najviše u razdobljumlađi adolescencije. Uspostavljanje i održavanje zadovoljavajućih odnosa postaje prioritet, štoneadekvatne i nepodržavajuće odnose s vršnjacima čini rizičnim faktorom za pojavu usamljenosti.Osim vršnjačkih odnosa, značajnu ulogu za uspješan razvoj adolescenata ima i pozitivan stav osebi, odnosno samopoštovanje. Ranija istraživanja su pokazala da je samopoštovanje, koje opadatijekom rane adolescencije, važna odrednica usamljenosti. Stoga su uzorak ovog istraživanjačinile dvije skupine adolescenata, 200 učenika sedmih razreda osnovne škole, koji su predstavljaligrupu mlađih adolescenata, i 200 učenika četvrtih razreda srednjih škola, koji su činili skupinustarijih adolescenata. Primijenjen je upitnik koji se sastojao od tri skupine skala, Kratka verzijaUCLA skale, Revediriana skala samoprihvaćanja i samokompetentnosti te Skala podložnostivršnjačkom pritisku. Rezultati ukazuju na višu razinu usamljenosti kod mlađih adolescenata,te niže samopoštovanje, ali veću razinu podložnosti vršnjačkom pritisku u odnosu na kasneadolescente. Djevojke bez obzira na dob imaju nešto niže samopoštovanje u odnosu na mladiće,dok se razina usamljenosti značajno ne mijenja s obzirom na spol. Međutim, adolescenti suskloniji nego adolescentice rizičnom ponašanju (npr. konzumiranje opijata i rizična seksualnaponašanja) i neadekvatnom ponašanju u školi (npr. neopravdano izostajanje s nastave) podutjecajem vršnjaka. Također je za pojavu usamljenosti u adolescenciji važna negativna slika osebi, odnosno nisko samopoštovanje, te izraženija podložnost vršnjačkom pritisku. Dobivenirezultati su objašnjeni u okvirima razvojnih promjena koje čine adolescente rizičnim za pojavuusamljenosti.The main aim of this study was to determine the extent to which the loneliness in adolescencecan be explained by self-esteem and peer pressure. In fact, numerous studies have mostly focusedon bivariate relation between these variables and so far in the Croatian sample of adolescentsis not examined relations between loneliness, self-esteem and peer pressure simultaneously.Although most authors believe that loneliness can occur in all developmental periods, it has beenemphasized that loneliness is more expressed during adolescence and even the most during theperiod of early adolescence. Establishing and maintaining satisfactory relationships is a priority,as inadequate and unsupported relationships with peers makes a risk for the experience ofloneliness. In addition to peer relationships, a positive attitude about yourself, or self-esteem hasa significant role in the successful development of adolescents. Earlier studies have shown thatself-esteem, which decreases during early adolescence, is an important determinant of loneliness.Therefore, the sample of this study consisted of two groups of adolescents, 200 seventh graders,who represented a group of early adolescents, and 200 students of fourth graders of highschool, who formed a group of late adolescents. The questionnaire, which consisted of threegroups of scale, Short version UCLA scale, Self-liking/self-competence Scale-Revised Versionand Susceptibility to Peer Pressure Scale. The results showed a higher level of loneliness inearly adolescents, and lower self-esteem, but a greater level of susceptibility to peer pressurein relation to the late teens. Girls, regardless of age had slightly lower self-esteem compared toboys, while the level of loneliness does not change significantly with respect to sex. However,male adolescents are more prone to risk behavior (eg, consumption of opiates and risky sexualbehavior) and inappropriate behavior at school (eg. unexcused absence from class) under theinfluence of peers. Finally, negative self-image, or low self-esteem and expressed susceptibility topeer pressure are significant determinants of loneliness in adolescence. The results are explainedin terms of developmental changes that make adolescents at risk for the occurrence of loneliness.</p

Polar organometallic strategies for regioselective C-H metallation of N-heterocyclic Carbenes

N-heterocyclic carbenes (NHCs) have become indispensable ligands across a broad swathe of the synthetic and catalytic landscape, not in small part due to their ease of electronic and steric tuneability. One of the latest additions to this important family of ligands are anionic NHCs, which have become valuable precursors to access abnormal NHC complexes as well as shown great potential for further NHC functionalisation. Deprotonative metallation has emerged as one of the most versatile methodologies to access anionic NHCs, where judicious choice of reaction conditions and metallating agent can finely tune the regioselectivity of the reaction. This Feature Article focuses on the recent emergence of s-block metal-mediated NHC metallations and the new opportunities this methodology offers

Transforming LiTMP lithiation of challenging diazines via gallium alkyl trans-metal-trapping

This study establishes a new trans-metal-trapping (TMT) protocol based on a mixture of LiTMP (the base) and tris(trimethylsilylmethyl)gallium [Ga(CH2SiMe3)3, GaR3] (the trap) that, operating in a tandem manner, is effective for the regioselective deprotonation of sensitive diazines in hydrocarbon solution as illustrated through reactions of pyrazine, pyridazine and pyrimidine, as well as through the N-S heterocycle benzothiazole, the metallo-activated complexes of all of which have been isolated and structurally defined

Trans-metal-trapping : concealed crossover complexes en route to transmetallation?

Defined as the transfer of ligands from one metal to another, transmetallation is a common reaction in organometallic chemistry. Its chemical celebrity stems from its role in important catalytic cycles of cross-coupling reactions such as those of Negishi, Sonogashira, Stille, or Suzuki. This article focuses on trans-metal-trapping (TMT), which could be construed as partially complete transmetallations. On mixing two distinct organometallic compounds, of for example lithium with aluminium or gallium, the two metals meet in a crossover co-complex, but the reaction ceases at that point and full transmetallation is not reached. Though in its infancy, trans-metal-trapping shows promise in transforming failed lithiations into successful lithiations and in stabilising sensitive carbanions through cooperative bimetallic effects making them more amenable to onward reactivity