Syntheses and solid-state structures of trimeric dibenzylamidolithium and its diethyl ether and hexamethylphosphoramide dimeric complexes: an explanation of these structures and evidence for Li CH interactions in both solid and solution phases

D R ARMSTRONG, Robert Mulvey, G T WALKER, D BARR, R SNAITH, W CLEGG, D REED

Research output: Contribution to journalArticle

77 Citations (Scopus)

Abstract

Dibenzylamidolithium, [(PhCH2)2NLi]n′(1), and two of its comlexes, [(PhCH2)2NLi·OEt2]n′(2), and [(PhCH2)2NLi·hmpa]n′(3)(hmpa = hexamethylphosphoramide), have been synthesised and characterised, and shown to meet earlier proposed criteria for useful proton abstraction reagents. The X-ray crystal structures of (1), (2), and (3) have been determined. Their solid-state structures contain central (NLi)n rings [n= 3 for (1), n= 2 for (2) and (3)], and the diminution in ring size from six- to four-membered on complexation of (1) has been rationalised via the results from ab initio calculations on model systems. Recent ring-stacking and ring-laddering principles have also been used to show why such rings cannot associate further, so leaving their lithium atoms with abnormally low co-ordination number [formally only 2 in (1), 3 in (2) and (3)]. Evidence that the co-ordinatively unsaturated Li atoms, in (1) in particular, are thereby prompted to engage in compensating interactions with CH units on the (PhCH2)2N ligands is drawn from both solid-state and solution studies. For the former, the implications of relatively short Li HC distances in the structure of (1) have been probed by molecular orbital bond index (MOBI) calculations which show that Li HC interactions constitute ca. 40% of lithium's valency, and that C–H bonds involved are weakened. In the solution studies, cryoscopic, 7Li n.m.r. spectroscopic, and u.v.–visible spectroscopic measurements have shown that the pink-red solution colours of (1) and (2) are caused by a species common to both, monomeric (PhCH2)2NLi; m.o. calculations on this one-co-ordinate Li species imply that it contains enhanced Li benzyl interactions which shift the charge transfer transition h.o.m.o. (benzyl)→l.u.m.o. (Li)(highest occupied and lowest unoccupied molecular orbitals, respectively) into the visible region.
LanguageEnglish
Pages617-628
Number of pages12
JournalJournal of the Chemical Society, Dalton Transactions
Issue number3
DOIs
Publication statusPublished - Mar 1988

Fingerprint

Hempa
Ether
Molecular orbitals
Lithium
Atoms
Complexation
Protons
Charge transfer
Crystal structure
Ligands
Color
X rays

Keywords

  • trimeric dibenzylamidolithium
  • diethyl ether
  • dimeric complexes
  • crystal structures

Cite this

@article{db3b43e386474538800b9f87957f940b,
title = "Syntheses and solid-state structures of trimeric dibenzylamidolithium and its diethyl ether and hexamethylphosphoramide dimeric complexes: an explanation of these structures and evidence for Li CH interactions in both solid and solution phases",
abstract = "Dibenzylamidolithium, [(PhCH2)2NLi]n′(1), and two of its comlexes, [(PhCH2)2NLi·OEt2]n′(2), and [(PhCH2)2NLi·hmpa]n′(3)(hmpa = hexamethylphosphoramide), have been synthesised and characterised, and shown to meet earlier proposed criteria for useful proton abstraction reagents. The X-ray crystal structures of (1), (2), and (3) have been determined. Their solid-state structures contain central (NLi)n rings [n= 3 for (1), n= 2 for (2) and (3)], and the diminution in ring size from six- to four-membered on complexation of (1) has been rationalised via the results from ab initio calculations on model systems. Recent ring-stacking and ring-laddering principles have also been used to show why such rings cannot associate further, so leaving their lithium atoms with abnormally low co-ordination number [formally only 2 in (1), 3 in (2) and (3)]. Evidence that the co-ordinatively unsaturated Li atoms, in (1) in particular, are thereby prompted to engage in compensating interactions with CH units on the (PhCH2)2N ligands is drawn from both solid-state and solution studies. For the former, the implications of relatively short Li HC distances in the structure of (1) have been probed by molecular orbital bond index (MOBI) calculations which show that Li HC interactions constitute ca. 40{\%} of lithium's valency, and that C–H bonds involved are weakened. In the solution studies, cryoscopic, 7Li n.m.r. spectroscopic, and u.v.–visible spectroscopic measurements have shown that the pink-red solution colours of (1) and (2) are caused by a species common to both, monomeric (PhCH2)2NLi; m.o. calculations on this one-co-ordinate Li species imply that it contains enhanced Li benzyl interactions which shift the charge transfer transition h.o.m.o. (benzyl)→l.u.m.o. (Li)(highest occupied and lowest unoccupied molecular orbitals, respectively) into the visible region.",
keywords = "trimeric dibenzylamidolithium , diethyl ether , dimeric complexes , crystal structures",
author = "ARMSTRONG, {D R} and Robert Mulvey and WALKER, {G T} and D BARR and R SNAITH and W CLEGG and D REED",
year = "1988",
month = "3",
doi = "10.1039/DT9880000617",
language = "English",
pages = "617--628",
journal = "Journal of the Chemical Society, Dalton Transactions",
issn = "0300-9246",
number = "3",

}

TY - JOUR

T1 - Syntheses and solid-state structures of trimeric dibenzylamidolithium and its diethyl ether and hexamethylphosphoramide dimeric complexes: an explanation of these structures and evidence for Li CH interactions in both solid and solution phases

AU - ARMSTRONG, D R

AU - Mulvey, Robert

AU - WALKER, G T

AU - BARR, D

AU - SNAITH, R

AU - CLEGG, W

AU - REED, D

PY - 1988/3

Y1 - 1988/3

N2 - Dibenzylamidolithium, [(PhCH2)2NLi]n′(1), and two of its comlexes, [(PhCH2)2NLi·OEt2]n′(2), and [(PhCH2)2NLi·hmpa]n′(3)(hmpa = hexamethylphosphoramide), have been synthesised and characterised, and shown to meet earlier proposed criteria for useful proton abstraction reagents. The X-ray crystal structures of (1), (2), and (3) have been determined. Their solid-state structures contain central (NLi)n rings [n= 3 for (1), n= 2 for (2) and (3)], and the diminution in ring size from six- to four-membered on complexation of (1) has been rationalised via the results from ab initio calculations on model systems. Recent ring-stacking and ring-laddering principles have also been used to show why such rings cannot associate further, so leaving their lithium atoms with abnormally low co-ordination number [formally only 2 in (1), 3 in (2) and (3)]. Evidence that the co-ordinatively unsaturated Li atoms, in (1) in particular, are thereby prompted to engage in compensating interactions with CH units on the (PhCH2)2N ligands is drawn from both solid-state and solution studies. For the former, the implications of relatively short Li HC distances in the structure of (1) have been probed by molecular orbital bond index (MOBI) calculations which show that Li HC interactions constitute ca. 40% of lithium's valency, and that C–H bonds involved are weakened. In the solution studies, cryoscopic, 7Li n.m.r. spectroscopic, and u.v.–visible spectroscopic measurements have shown that the pink-red solution colours of (1) and (2) are caused by a species common to both, monomeric (PhCH2)2NLi; m.o. calculations on this one-co-ordinate Li species imply that it contains enhanced Li benzyl interactions which shift the charge transfer transition h.o.m.o. (benzyl)→l.u.m.o. (Li)(highest occupied and lowest unoccupied molecular orbitals, respectively) into the visible region.

AB - Dibenzylamidolithium, [(PhCH2)2NLi]n′(1), and two of its comlexes, [(PhCH2)2NLi·OEt2]n′(2), and [(PhCH2)2NLi·hmpa]n′(3)(hmpa = hexamethylphosphoramide), have been synthesised and characterised, and shown to meet earlier proposed criteria for useful proton abstraction reagents. The X-ray crystal structures of (1), (2), and (3) have been determined. Their solid-state structures contain central (NLi)n rings [n= 3 for (1), n= 2 for (2) and (3)], and the diminution in ring size from six- to four-membered on complexation of (1) has been rationalised via the results from ab initio calculations on model systems. Recent ring-stacking and ring-laddering principles have also been used to show why such rings cannot associate further, so leaving their lithium atoms with abnormally low co-ordination number [formally only 2 in (1), 3 in (2) and (3)]. Evidence that the co-ordinatively unsaturated Li atoms, in (1) in particular, are thereby prompted to engage in compensating interactions with CH units on the (PhCH2)2N ligands is drawn from both solid-state and solution studies. For the former, the implications of relatively short Li HC distances in the structure of (1) have been probed by molecular orbital bond index (MOBI) calculations which show that Li HC interactions constitute ca. 40% of lithium's valency, and that C–H bonds involved are weakened. In the solution studies, cryoscopic, 7Li n.m.r. spectroscopic, and u.v.–visible spectroscopic measurements have shown that the pink-red solution colours of (1) and (2) are caused by a species common to both, monomeric (PhCH2)2NLi; m.o. calculations on this one-co-ordinate Li species imply that it contains enhanced Li benzyl interactions which shift the charge transfer transition h.o.m.o. (benzyl)→l.u.m.o. (Li)(highest occupied and lowest unoccupied molecular orbitals, respectively) into the visible region.

KW - trimeric dibenzylamidolithium

KW - diethyl ether

KW - dimeric complexes

KW - crystal structures

U2 - 10.1039/DT9880000617

DO - 10.1039/DT9880000617

M3 - Article

SP - 617

EP - 628

JO - Journal of the Chemical Society, Dalton Transactions

T2 - Journal of the Chemical Society, Dalton Transactions

JF - Journal of the Chemical Society, Dalton Transactions

SN - 0300-9246

IS - 3

ER -