Axially asymmetric metal alkyls. Part 1. Lithium alkyls of 2,2′-dimethylbiphenyl and its trimethylsilylmethylated compounds: crystal structures of [{Li(Me₂NCH₂CH₂NMe₂)}₂{(2-CHRC₆H₄)₂}] for R = H (polymeric) and R = SiMe₃(monomeric)

Abstract

Metallation of (2-CH2RC6H4)2, with excess Li(tmen) Bun (tmen = NNN'N'-tetramethylethylenediamine) yields the crystalline compounds [{Li(tmen)}2{(2-CHRC6H4)2}] [R = H (7) or SiMe, (9)] whereas for 2-methyl-2'-trimethylsilylmethylbiphenyl, although selectivity is maintained, the crystalline product is a monolithiated species. This difference has been rationalised on the basis of the results of the crystal structure determination of the lithium complexes ( 7) and ( 9). The structure of ( 7) is polymeric (cf. dimeric in benzene by ebullioscopy) with a ' metallacycle ' lithium and a lithium bridging methylene groups of different ' metallacycles ' (electron-deficient bonding) : Li-C (mean) 2.30 A ; Li-C-Li (mean) 159.5, C-Li-C (mean) 106.5". Compound (9) is best described as a ' contact ion-pair ' structure; Li-C(H)SiMe3 contacts, 2.22(1) and 2.1 9(2) A. Lithiation of 2-[bis(trimethylsilyl)methyl]-2'-methylbiphenyl results in the formation of (9), via an anionic 1,6-silyl migration.

Tin Organometallic Compounds: Classification and Analysis of Crystallographic and Structural Data: Part 1. Monomeric Derivatives

“…The remainder are Sn(IV) compounds with a distorted tetrahedral environment. The structure of Sn(Ph) 3 (ompa) is shown in Figure 4 as an example [87a], There are several types of chomophore: SnC 4 ; SnC 3 X; SnC 2 X 2 ; SnCI 2 XY; SnCX 3 ; as can be found in [122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137], and one monodentate and a tridentate [138] giving the SnC 4 chromophore; two alkyl groups plus a hetero bidentate (C+N) ligand, methyl [169][170][171], tert-butyl [172]; two monodentate C-donors plus heterodentate (C+S or Se) [216]; two monodentate C-donors plus a chelate (N+N) [242,243], (B+B) [247], (S+S) [278][279][280][281][282][283][284][285][286][287][288], (P+P) [289][290][291], (Se+Se) [288,294]; one chelate (C+C) plus two CI atoms [260] and one tridentate (N+N+C) plus a chlorine atom [299].…”

The Directed Lithiation of Benzenoid Aromatic Systems

“…6 Li, 1 H HOESY [122] and one-dimensional 6 Li{ 1 H} spectroscopy [36b] have been employed to probe the 1:1 complex between 1-naphthyllithium and TMEDA (106) with data suggesting chelation of the metals in a dimeric aggregate. Treatment of 106 with nBuLi has long been known to effect the formation of 1,8-Li 2 C 10 H 6 (107), [124] with 6 Li, 1 H HOESY more recently revealing a cross-peak involving the peri hydrogen atom prior to reaction and suggesting activation of this position. [122] …”

“…In this context, the biphenyl derivatives 2-(CH 2 Li·PMDETA)-6-MeC 6 H 3 (C 6 H 3 Me 2 Ϫ2,6) (88) [106] and (the dimer of) 2-(CHRLi·TMEDA)C 6 H 4 (R ϭ H 89, SiMe 3 90) [107] have been characterised. Moreover, the structure of 2,2Ј-bis(TMEDA)lithiomethyl-1,1Ј-binaphthyl (91) has also been reported.…”

Axially asymmetric metal alkyls. Part 5. Synthesis and reduction to ZrIIIspecies of Group 4 metallepines [ML(η-C5H5)2][L =(2-CHRC6H4)22–, R = H, M = Ti, Zr, or Hf)], isomers of [ZrL(η-C5H5)2](R = SiMe3), and meso-[M{1,8-(CHSiMe3)2C10H6}(η-C5H5)2](M = Zr or Hf); X-ray crystal structures of [TiL(η-CEngelhardt1, Leung2, Papasergio3 et al. 1987J. Chem. Soc., Dalton Trans.Self Cite8010View full textAdd to dashboardCite

“…and the metallabicyclic complex [(WL,OTMg(thf),] (thf = tetrahydrofuran),' and, for R = SiMe,, h-SSand 6-RR-[SnLPh2]. 3 Their synthesis involves at some stage a di-Grignard reagent, (2), 3 and/or dilithium reagents, (3) (R = H) and (4) (R = SiMe,) (tmen = NNN"'tetramethylethylenediamine), and metal or metalloid halides. Interestingly, in (3) in the solid, one lithium centre is part of a metallacycle, the other bridging two methylene carbons, whereas in (4) both lithiums are q3-allyl to the hydrocarbyl group.…”

“…Interestingly, in (3) in the solid, one lithium centre is part of a metallacycle, the other bridging two methylene carbons, whereas in (4) both lithiums are q3-allyl to the hydrocarbyl group. 6 In addition, the reaction of (2) with vanadocene dichloride gives the bimetallic complex [{ VCl(q-CsHs)2}2L] (R = H ) 4 rather than a metallacycle.…”