Synthetic and reactivity studies of hetero-tri-anionic sodium zincates

The synthesis and characterisation of several sodium zincate complexes is reported. The all-alkyl monomeric sodium zincate (PMEDTA)·Na(μ-CH2SiMe3)ZntBu2 2, is prepared by combining an equimolar quantity of tBu2Zn, nBuNa and PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine)]. A similar approach was used to prepare and isolate the unusual dimeric zincate [(PMEDTA)·Na(μ-nBu)ZntBu2]2 3. When an equimolar mixture of nBuNa, tBu2Zn and TMP(H) (2,2,6,6-tetramethylpiperidine) are combined in hexane, the hetero-tri-leptic TMP(H)-solvated zincate (TMPH)Na(μ-TMP)(μ-nBu)ZntBu 4 was forthcoming. Complex 4 can also be prepared using a rational approach [i.e., utilising two molar equivalents of TMP(H)]. When TMEDA is reacted with an equimolar mixture of nBuNa, tBu2Zn and TMP(H), the monomeric sodium zincate (TMEDA)Na(μ-TMP)(μ-nBu)ZntBu 5 was obtained – this complex is structurally similar to the synthetically useful relation TMEDA)·Na(μ-TMP)(μ-tBu)Zn(tBu) 1. By changing the sodium reagent used in the synthesis of 5, it was possible to prepare (TMEDA)Na(μ-TMP)(μ-Me3SiCH2)ZntBu 6. By reacting 5 with cis-DMP(H) (cis-2,6-dimethylpiperidine), the zincate could thermodynamically function as a amide base, to give the transamination product (TMEDA)Na(μ-cis-DMP)(μ-nBu)ZntBu 7, although no crystals could be grown. However, when HMDS(H) (1,1,1,3,3,3-hexamethyldisilazane) or PEA(H) [(+)-bis[(R)-1-phenylethyl]amine] is reacted with 5, crystalline (TMEDA)Na(μ-HMDS)(μ-nBu)ZntBu 8 or (TMEDA)Na(μ-PEA)(μ-nBu)ZntBu 9 are isolated respectively. With PNA(H) (N-phenylnaphthalen-1-amine) the reaction took a different course and resulted in the formation of the dimeric sodium amide complex [(TMEDA)Na(PNA)]2 10. When reacted with benzene, it appears that a TMEDA-free variant of 5 functions thermodyanically as an nBu base to yield the previously reported (TMEDA)Na(μ-TMP)(tBu)Zn(μ-C6H4)Zn(tBu)(μ-TMP)Na(TMEDA) 11. Finally when reacted with TEMPO (2,2,6,6-tetramethylpiperidinyloxy), 5 undergoes a single electron transfer reaction to form (TMEDA)Na(μ-TMP)(μ-TEMPO)ZnnBu 12

Remote functionalisation via sodium alkylamidozincate intermediates : access to unusual fluorenone and pyridyl ketone reactivity patterns

Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)center dot Na(mu-Bu-t)(mu-TMP)Zn(Bu-t)] in hexane solution, gives efficient Bu-t addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively

Synthetic and structural studies of mixed sodium bis(trimethylsilyl)amide/sodium halide aggregates in the presence of η2-N,N-, η3-N,N,N/N,O,N-, and η4-N,N,N,N-donor ligands

When the important utility amide sodium bis(trimethylsilyl)amide is combined with hydrocarbon-soluble molecular forms of sodium halide salts, a complex structural chemistry is observed. Through utilization of several different multidentate donor molecules, it is possible to isolate a series of compounds that have structural motifs previously not observed in sodium chemistry

Monodentate coordination of the normally chelating chiral diamine (R,R)-TMCDA

After isolating an unusual binuclear, but monosolvated NaHMDS complex [{(R,R)-TMCDA}·(NaHMDS)2]∞ which polymerises via intermolecular electrostatic Na···MeHMDS interactions, further (R,R)-TMCDA was added to produce the discrete binuclear amide [κ2-{(R,R)-TMCDA}·(NaHMDS)2{κ1-(R,R)-TMCDA}], whose salient feature is the unique monodentate coordination of one of the chiral diamine ligands

Facile access to hetero-poly-functional arenes and meta-substituted arenes via two-step dimetalation and Mg/halogen-exchange protocol

The Grignard reagent, iPrMgCl and its lithium chloride-enhanced ‘turbo’ derivative iPrMgCl·LiCl have been employed to investigate the single iodo/magnesium exchange reactions of the trisubstituted arenes, 2,5-diiodo-N,N-diisopropylbenzamide 1 , 1,4-diiodo-2-methoxybenzene 2 , and 1,4-diiodo-2-(trifluoromethyl)benzene 3 . These three arenes themselves were initially prepared by a double ortho-, metaʹ-deprotonation of N,N-diisopropylbenzamide, anisole and (trifluoromethyl)benzene respectively, using a sodium magnesiate reagent, and subsequent electrophilic quenching with iodine/THF solution. Thus, by following a combined deprotonation and magnesium/halogen exchange strategy, the simple monosubstituted arenes can be converted to trisubstituted diiodoarenes, which can ultimately be transformed into the corresponding mono-magnesiated arenes, in THF at −40°C, within seconds in good yields. The other functional group (OMe, NiPr2 or CF3 respectively) present on the di-iodoarenes helps direct the exchange reaction to the ortho position whereas subsequent addition of different electrophiles permits the preparation of hetero-poly-functional-arenes, with three different substituents in their structure. Intriguingly, if water is used as the electrophile, a new and facile route to prepare meta-substituted arenes, which cannot be easily obtained by conventional processes, is forthcoming. In contrast to directed ortho-metalation (DoM) chemistry, this reaction sequence can be thought of as InDirect meta-Metalation (IDmM). The scope of the chemistry has been tested further by exposing the initial unreacted iodo-functionality at the meta-position to a second Mg/I-exchange reaction and subsequent functionalization

Templated deprotonative metalation of polyaryl systems : facile access to simple, previously inaccessible multi-iodoarenes

The development of new methodologies to affect non-ortho functionalization of arenes has emerged as a globally important arena for research, which is key to both fundamental studies and applied technologies. Here, a range of simple arene feedstocks (namely, biphenyl, meta-terphenyl, para-terphenyl, 1,3,5-triphenylbenzene and biphenylene) are transformed to hitherto unobtainable multi-iodoarenes via a s-block metal sodium magnesiate templated deprotonative approach. These iodoarenes have potential to be used in a whole host of high impact transformations, as precursors to key materials in the pharmaceutical, molecular electronic and nanomaterials industries. Proving the concept, we have transformed biphenyl to 3,5-bis(N-carbazolyl)-1,1’-biphenyl, a novel isomer of 4,4’-bis(N-carbazolyl)-1,1’-biphenyl (CPB) which is currently widely employed as a host material for organic light-emitting diodes, OLEDs

s-Block cooperative catalysis : alkali metal magnesiate-catalysed cyclisation of alkynols

Mixed s-block metal organometallic reagents have been successfully utilised in the catalytic intramolecular hydroalkoxylation of alkynols. This success has been attributed to the unique manner in which these reagents can overcome the challenges of the reaction: namely OH activation and coordination to and then addition across a C≡C bond. In order to optimise the reaction conditions and to garner vital catalytic system requirements, a series of alkali metal magnesiates were enlisted for the catalytic intramolecular hydroalkoxylation of 4-pentynol. In a prelude to the main investigation, the homometallic magnesium dialkyl reagent MgR2 (where R = CH2SiMe3) was utilised. This reagent was unsuccessful in cyclising the alcohol into 2-methylenetetrahydrofuran 2a or 5-methyl-2,3-dihydrofuran 2b, even in the presence of multidentate Lewis donor molecules such as N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA). Alkali metal magnesiates MIMgR3 (when MI = Li, Na or K) performed the cyclisation unsatisfactorily both in the absence/presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) or PMDETA. When higher-order magnesiates (i.e., MI2MgR4) were employed, in general a marked increase in yield was observed for MI = Na or K; however, the reactions were still sluggish with long reaction times (22–36 h). A major improvement in the catalytic activity of the magnesiates was observed when the crown ether molecule 15-crown-5 was combined with sodium magnesiate Na2MgR4(TMEDA)2 furnishing yields of 87% with 2a : 2b ratios of 95 : 5 after 5 h. Similar high yields of 88% with 2a : 2b ratios of 90 : 10 after 3 h were obtained combining 18-crown-6 with potassium magnesiate K2MgR4(PMDETA)2. Having optimised these systems, substrate scope was examined to probe the range and robustness of 18-crown-6/K2MgR4(PMDETA)2 as a catalyst. A wide series of alkynols, including terminal and internal alkynes which contain a variety of potentially reactive functional groups, were cyclised. In comparison to previously reported monometallic systems, bimetallic 18-crown-6/K2MgR4(PMDETA)2 displays enhanced reactivity towards internal alkynol-cyclisation. Kinetic studies revealed an inhibition effect of substrate on the catalysts via adduct formation and requiring dissociation prior to the rate limiting cyclisation step

Introducing glycerol as a sustainable solvent to organolithium chemistry : ultrafast chemoselective addition of aryllithium reagents to nitriles under air and at ambient temperature

Edging closer towards developing air and moisture compatible polar organometallic chemistry, the chemoselective and ultrafast addition of a range of aryllithium reagents to nitriles has been accomplished using glycerol as a solvent, at ambient temperature in the presence of air, establishing a novel sustainable access to aromatic ketones. Addition reactions occur heterogeneously ("on glycerol conditions"), where the lack of solubility of the nitriles in glycerol and the ability of the latter to form strong intermolecular H-bonds seem key to favouring nucleophilic addition over competitive hydrolysis. Remarkably, PhLi exhibits a greater resistance to hydrolysis working "on glycerol" conditions than "on water". Introducing glycerol as a new solvent in organolithium chemistry unlocks a myriad of opportunities for developing more sustainable, air and moisture tolerant main-group-metal-mediated organic synthesis

Structural and metal-halogen exchange reactivity studies of sodium magnesiate biphenolate complexes

Bimetallic sodium magnesiates have been employed in metal-halogen exchange for the first time. Utilising the racemic phenoxide ligand 5,5´,6,6´-tetramethyl-3,3´-di-tert-butyl-1,1´-biphenyl-2,2´-diol [(rac)-BIPHEN-H2], the dialkyl sodium magnesiates [(rac)-BIPHEN]Na2MgBu2(TMEDA)2 3 and [(rac)-BIPHEN]Na2MgBu2(PMDETA)2 4 have been synthesised. Both 3 and 4 can be easily prepared through co-complexation of di-n-butylmagnesium with the sodiated (rac)-BIPHEN precursor which can be prepared in situ in hydrocarbon solvent. Prior to the main investigation, synthesis of the sodiated precursor [BIPHEN]2Na4(THF)4 1 was explored in order to better understand the formation of sodium magnesiates utilising the dianionic (rac)-BIPHEN ligand as the parent ligand. In addition, a BIPHEN-rich sodium magnesiate [BIPHEN]2Na2Mg(THF)4 2 was prepared and characterised, and its formation was rationalised. Complex 1 and 4 have also been fully characterised in both solid and solution state. In terms of onward reactivity, 3 and 4 have been tested as potential exchange reagents with aryl and heteroaryl iodides to produce aryl and heteroaryl magnesium phenoxides utilising toluene as a non-polar hydrocarbon solvent. Complex 3 reacted smoothly to give a range of aryl and heteroaryl magnesium phenoxides, whilst 4’s reactivity is more sluggish

Structural studies of donor-free and donor-solvated sodium carboxylates

Focusing mainly on sodium 2-ethylhexanoate, this study reveals that the carboxylate exists as a dimer in MeOD solution as evidenced by Diffusion Ordered NMR SpectroscopY (DOSY). Two crystalline varieties with distinct polymeric structures have been synthesised and crystallographically characterised. A mixed 1,10-phenanthroline–water solvate [{(C5H10)(C2H5)COONa.(H2O)[1,10-phen]}2]∞ contains dimeric [Na(OH)2]2 subunits, which propagate through hydrogen bonds between O atoms of the carboxylate and OH water bonds. Adjacent polymeric chains interdigitate with each other through π-π interactions between 1,10-phen rings. Solvent-free sodium 2-ethylhexanoate has five-coordinate cations comprising one bidentate chelating and three monodentate carboxylate oxygen atoms. Here, the packing arrangement is different with the central hydrophilic (NaO2)∞ core surrounded by a wrapping of disordered alkyl groups. A similar polymeric structure is observed for the crystalline DMSO-solvated sodium valproate [{(C3H7)(C4H8)COONa.(DMSO)}]∞. This adopts a layered arrangement comprising alternating sodium carboxylate hydrophilic layers and hydrophobic organic bilayers