Lithiations of mercaptoamines containing =NC(=S)NH-,-NHC(=S)S- and -NHC(=S)NH- units: Syntheses, crystal structures and model molecular-orbital calculations

David R. Armstrong, Robert E. Mulvey, Donald Barr, Richard W. Porter, Paul R. Raithby, Timothy R.E. Simpson, Ronald Snaith, Dominic S. Wright, Karina Gregory, Patrizia Mikulcik

Research output: Contribution to journalArticlepeer-review

Abstract

Three mercaptoamines have been lithiated in the presence of various Lewis bases. 2-Mercaptopyrimidine (I), containing a =NC(=S)NH- (as an amine)/=NC(-SH)=N- (as a thiol) unit, affords [N=CHCH=CH(N-..C- ..S)Li·hmpa]n 1. 2-Mercaptothiazoline (II), with a -SC(=S)NH-/-SC(-SH)=N- unit, gives [SCH2CH2(N- ..C-..S)Li·tmen]n 2. 2-Mercaptobenzimidazole (III), having a -NHC(=S)NH-/-NHC(-SH)=N- unit, gives, when dilithiated, {C6H4[N-..C(- ..S)-..N]Li2·3hmpa}n 3 [hmpa = hexamethylphosphoramide, (Me2N)3P=O; tmen = Me 2NCH2CH2NMe2]. The solid-state structures of complexes 1-3 were solved by X-ray crystallography. Complex 1 is polymeric (n = ∞): each unit contains a (N-..C- ..S)Li chelate feature with a terminal hmpa molecule on Li, and these units are then associated via intermolecular N→Li co-ordinations using the third (N) heteroatom of the organic anion. Complex 2 is a dimeric (n = 2) S-Li compound with each Li bearing a tmen molecule; dimerisation is achieved by N→Li intermonomer interactions, but the third (ring S) heteroatom is not involved with metal centres. The dilithiated species 3 is also a dimer (n = 2) and each Li is chelated by an (N-..C-..S) unit of its organic dianion; the two end-Li atoms of the dimer are each co-ordinated to two terminal hmpa molecules, while the two central Li atoms are linked by two μ-hmpa molecules, which effect dimerisation. The structural diversities displayed by 1-3 have been probed, and thereby in part rationalised, by ab initio (6-31G basis set) and MNDO molecular-orbital calculations on the amine/thiol isomers of I-III, and on their uncomplexed and complexed lithiated derivatives (as monomers). In particular, the optimised structures predict and reproduce the (N-..C-..S)Li chelating modes found in 1 and 3 and help to explain why direct S-Li bonding is found in 2.

Original languageEnglish
Pages (from-to)765-776
Number of pages12
JournalJournal of the Chemical Society, Dalton Transactions
Issue numberS
DOIs
Publication statusPublished - 1991

ASJC Scopus subject areas

  • General Chemistry

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