Lithiated amidines: syntheses and structural characterisations

Abstract

The reaction of a toluene solution of PhNC(Ph)NHPh (N,N'-diphenylbenzamidine) with n-butyllithium gave the toluene-solvated amidinolithium compound {Li[PhNC(Ph)NPh]}(n) 1. Similarly the same reaction performed in the presence of the Lewis-base donors (Me(2)N)(3)PO (hmpa), Me(2)N(CH2)(2)NMe(2) (tmen) or [Me(2)N(CH2)(2)](2)NMe (pmdien) yielded the amidinolithium complexes {Li[PhNC(Ph)NPh . hmpa]}(2) 2, {Li[PhNC(Ph)NPh]. tmen} 3 and {Li[PhNC(Ph)NPh]. pmdien} 4 respectively. In addition the reaction of a toluene solution of the related amidine PhNC(Me)NHPh(N,N'-diphenylacetamidine) with LiBu(II) in the presence of hmpa afforded {Li[PhNC(Me)NPh]. hmpa}(2) 5. The solid-state structures of 2-5, which have been resolved by single-crystal X-ray diffraction methods, show both similarities and differences The complexes 3 and 4, which contain the di- and tri-dentate ligands tmen and pmdien respectively, are monomeric, whilst use of the unidentate Lewis base hmpa results in dimers 2 and 5. However, the way in which dimerisation is achieved differs. The co-ordination geometry about the lithium cation is clearly influenced by the choice of donor and as such shows how change in the denticity of the donor ligand utilised can have a significant effect on the solid-state structure of the system

New Lanthanide Alkynylamidinates and Diiminophosphinates

“…In the solid state, both lithium propiolamidinates crystallize in the triclinic space group P-1 with one dimeric molecule in the unit cell. The bond lengths and bond angles are in good agreement with similar structures of amidinate ligands [48][49][50][51][52][53][54][55][56][57][58]. The N-C distances in the amidinate N-C-N unit are 1.321(2) and 1.330(2) Å in 1 and 1.3201 (13) …”

“…Full crystallographic data can be found in the Supplementary Information. The crystal structure determinations of Li[Ph-C≡C-C(N i Pr)2] THF (1) and Li[Ph-C≡C-C(NCy)2] THF (2) in both cases revealed the presence of a ladder-type dimeric structure, which is the most characteristic structural motif of most previously characterized lithium amidinates and guanidinates [48][49][50][51][52][53][54][55][56][57][58]. The dimers are centrosymmetric with the central Li2N2 ring being strictly planar.…”

Synthesis of an alkylmagnesium amide and interception of a ring-opened isomer of the important utility amide 2,2,6,6-tetramethylpiperidide (TMP)

“…1). While four-membered dimeric rings are common in s-block amide chemistry, [42,43] that of 2 is interesting for displaying two distinctly different TMP bridging conformations, [44] which renders the structure noncentrosymmetric. One ligand prefers the common chair conformation (N1 ligand in Fig.…”

A sandwich complex of lithium oxide: {Li[BunC(NBut)2]}4·Li2O

“…1b,3-5 Although a wide range of both main-group and transition-metal complexes of these chelating ligands has been characterized, 6 structural information for the lithium derivatives of these important reagents is limited to complexes in which the lithium ions are co-ordinated to Lewis bases such as RCN (R = aryl), 7 THF, 8 HMPA, 9 N,N,NЈ,NЈ-tetramethylethylenediamine 9 or N,N,NЈ,NЈ,NЉpentamethyldiethylenetriamine. 9 The complexes [4-MeC 6 -H 4 C(NSiMe 3 ) 2 Li(THF)] 2 8 and [PhC(NPh) 2 Li(HMPA)] 2 9 form dimeric, step-shaped structures whereas chelating Lewis bases give rise to monomeric structures. 9 We describe here the unexpected generation and crystal structure of the complex {Li[Bu n C(NBu t ) 2 ]} 4 ؒLi 2 O 2 in which a molecule of lithium oxide is trapped between two twisted Li 2 N 4 C 2 ladders of a dimeric lithium amidinate.…”

“…9 The complexes [4-MeC 6 -H 4 C(NSiMe 3 ) 2 Li(THF)] 2 8 and [PhC(NPh) 2 Li(HMPA)] 2 9 form dimeric, step-shaped structures whereas chelating Lewis bases give rise to monomeric structures. 9 We describe here the unexpected generation and crystal structure of the complex {Li[Bu n C(NBu t ) 2 ]} 4 ؒLi 2 O 2 in which a molecule of lithium oxide is trapped between two twisted Li 2 N 4 C 2 ladders of a dimeric lithium amidinate. Compared to other complexes of Li 2 O, 10-14 complex 2 exhibits some novel features that result from the unique ligand behaviour of the Li 2 N 4 C 2 ring.Amidinates Li[RC(NRЈ) 2 ] are readily obtained by the nucleophilic addition of an organolithium reagent (RLi) to a carbodiimide RЈNCNRЈ.…”