Abstract:The reaction of AlMe 3 with tBuLi in the presence of trimethylacetonitrile affords the bimetallic complex [tBu(Me)Al(μ-Me) 2 Li•NC(tBu)] ∞ (1). Pseudotetrahedral Al centers form by the nucelophilic addition of tBuLi to AlMe 3 .The alkali-metal center is stabilized through coordination of the unreacted nitrile and polymer formation via the construction of Al(μ-Me) n Li (n = 1, 2) motifs. Neutron diffraction evidences agostic interactions in the bridging methyl group to give further stabilization. There is only … Show more
“…Remarkably, the NCI surfaces show a high directionality of the interactions in the three examples. It is worth mentioning that, although some alkaline(-earth)···methyl contacts have been previously identified in different crystal structures, they have been traditionally considered as agostic interactions rather than as structure-driving noncovalent bonds 46 . Fig.…”
It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.
“…Remarkably, the NCI surfaces show a high directionality of the interactions in the three examples. It is worth mentioning that, although some alkaline(-earth)···methyl contacts have been previously identified in different crystal structures, they have been traditionally considered as agostic interactions rather than as structure-driving noncovalent bonds 46 . Fig.…”
It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.
“…It is possible to isolate (depending on the stoichiometry) both monolithium and dilithium compounds 2-6, the structure of the dimeric dilithium compound {[PhP(Nt-Bu) 2 ]Li 2 } 2 (1) was reported earlier. 9a All compounds were characterized by 1 H, 7 Li, 13 C and 31 P NMR spectroscopy and molecular structures of 2-4 and 5…”
Section: Resultsmentioning
confidence: 99%
“…9c To prove, whether similar spontaneous tautomerization will occur also with group 14 metals, the reaction between 2 and GeCl 2 .dioxane (or SnCl 2 ) has been carried out (Scheme 3). While expected heteroleptic germylene 12 was isolated in reasonable yield (40 %) as colorless crystalline solid, in the case of the tin a redistribution of ligands occurred and a 1:1 mixture of the stannylene 10 and parent PhP(NHt-Bu) 2 was obtained as judged by 1 H, 13 C and 31 P NMR spectroscopic inspection of the reaction mixture. 18 with the respect to the mutual position of chlorine and phenyl groups on the central PN 2 Ge ring.…”
Section: Figurementioning
confidence: 95%
“…The latter complex has been investigated using the singlecrystal neutron diffraction analysis and contacts were described as C−H···Li agostic interactions involving methyl groups of the alkylaluminum moiety and Li-C bond lengths are 2.357 (19) and 2.282 (19) Å. 13 Although the Li(2)-C(3) distance of 2.498(7) Å in 5, is slightly longer, it is likely, that similar description of the Li(2)···t-Bu contact is also eligible. The reaction of dilithium precursors 1, 3 and 5 with GeCl 2 ·dioxane or SnCl 2 gave corresponding tetrylenes 7-11 (Scheme 2).…”
The deprotonation of aminophosphanes PhP(NHR)2 (R = t-Bu or Dip; Dip = 2,6-i-Pr2C6H3) and t-BuP(NHDip)2 using n-BuLi gave, depending on the stoichiometry, both the dilithium compounds {[PhP(Nt-Bu)2]Li2}2 (), [PhP(Nt-Bu)(NDip)]Li2·(Et2O) (), [t-BuP(NDip)2]Li2·(Et2O)2 () and [t-BuP(NDip)2]Li2·(tmeda)2 (), and the monolithium compounds [PhP(NHt-Bu)(NR)]Li·(tmeda) (R = t-Bu , Dip ) and [t-BuP(NHDip)(NDip)]Li·(tmeda) (). Treatment of , and with GeCl2·dioxane or SnCl2 in a 1 : 1 stoichiometric ratio gave the corresponding tetrylenes [PhP(Nt-Bu)2]E (E = Ge , Sn ), [PhP(Nt-Bu)(NDip)]Ge () and [t-BuP(NDip)2]E (E = Ge , Sn ). The heteroleptic germylene [Ph(H)P(Nt-Bu)2]GeCl () was obtained by the reaction of the monolithium compound [PhP(NHt-Bu)(Nt-Bu)]Li·(tmeda) () with GeCl2·dioxane in a 1 : 1 stoichiometric ratio, as a result of a spontaneous NH → PH tautomeric shift in the ligand backbone. In contrast, an analogous reaction with SnCl2 produced only stannylene along with the PhP(NHt-Bu)2 starting material, suggesting scrambling of the ligands rather than a NH → PH tautomeric shift. Finally, heating in solution led to P-C bond cleavage and formation of the bis(imino)phosphide [DipNPNDip]Li·(tmeda) (). The reaction of with GeCl2·dioxane, SnCl2 or PbCl2 in a 2 : 1 stoichiometric ratio yielded the unprecedented tetrylenes [DipNPNDip]2E (E = Ge , Sn and Pb ), in which the tetrylene center is incorporated within two N2PE rings. Treatment of the monolithium compound with n-BuLi and K (or KC8) gave [t-BuNPNt-Bu]Li·(tmeda) () and{[t-BuNPNt-Bu]K(tmeda)}2 (), respectively. In contrast to the reaction with , similar reactions of with GeCl2·dioxane and SnCl2 resulted in the known compounds cis-[P(μ-Nt-Bu)2P(t-BuN)2]E (E = Ge, Sn); evidently the t-Bu groups do not provide sufficient steric shielding to protect the bis(imino)phosphide backbone as in the case of . The bonding situation in a set of selected compounds (, ) has been subjected to a theoretical survey with particular emphasis on the nature of the bonding between the ligand and the central metal and the bonding within the NPN core of the ligand, showing significant differences among the studied complexes.
“…Hence, metallocycle formation has proved unambiguous in aluminates (where M is Group 13) 46 and zincates (where M is Group 12 and therefore stands comparison with Group 2). 47 However, in recently observed manganates (where M is Group 7 and therefore stands comparison with Groups 2 and 12), 48 closure of the ring via the formation of an agostic bridge 49 to match the amido one was much more ambiguous (Scheme 5). Finally, in the present case (where M is Group 11 and stands comparison with Group 1) the essentially linear geometry at Cu 50 clearly prevents the formation of a metallocycle.…”
Recent advances in the selective deprotometallation of aromatic reagents using alkali metal cuprates are reported. The ability of these synergic bases to effect deprotonation under the influence of a directing group is explored in the context of achieving new and more efficient organic transformations whilst encouraging greater ancillary group tolerance by the base. Developments in our understanding of the structural chemistry of alkali metal cuprates are reported, with both Gilman cuprates of the type R2CuLi and Lipshutz and related cuprates of the type R2Cu(X)Li2 (X = inorganic anion) elucidated and rationalised in terms of ligand sterics. The generation of new types of cuprate motif are introduced through the development of adducts between different classes of cuprate. The use of DFT methods to interrogate the mechanistic pathways towards deprotonative metallation is described. Theoretical modelling of in situ rearrangements undergone by the cuprate base are discussed, with a view to understanding the relationship between R2CuLi and R2Cu(X)Li2, their interconversion and the implications of this for cuprate reactivity. The advent of a new class of adduct between different cuprate types is developed and interpreted in terms of the options for expelling LiX from R2Cu(X)Li2. Applications in the field of medicinal chemistry and (hetero)arene derivatization are explored.
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