The coordination chemistry of guanidines and guanidinates

Publisher Summary This chapter discusses the current patterns and perspectives in organolithium chemistry, including the structures of organonitrogenlithium (N-Li) compounds. The chapter explains the compounds with N-Li bonds. These are chiefly lithium imides [iminolithiums (RR’C=NLi) n ] and their complexes with added Lewis bases (L), and lithium amides [amidolithiums (RR’NLi) n ] and their complexes. For the lithium amide species, particularly, only those whose R,R’ groups that do not contain additional functionalities are described—that is, the R,R’ groups remain largely uninvolved with lithium centers. These species are termed “simple” lithium amides. N-Li compounds and, particularly, lithium amides (R 2 NLi) are widely used both in organic and in organometallic syntheses. For the former, these strong bases are employed as proton abstractors to generate new organolithiums. Although synthetic uses have dominated the interest in N-Li compounds, the chapter focuses on the structures. Most of the physical properties of organolithium compounds (the marked exception being conductance) arise, because of the overall size and shape of the units making up these materials and the nature of the peripheries of these units. The basic structural building block of any organolithium is an ion pair, R – L + . The identities and structures of complexed organolithiums are of particular importance.

Structures of Organonitrogen—Lithium Compounds: Recent Patterns and Perspectives in Organolithium Chemistry

The aim of this perspective is to highlight the continued development and application of amidines and guanidines as neutral, N-based donor ligands in coordination chemistry. From a sporadic interest dating back to the 1980s, work on these two closely related classes of compounds has steadily grown, with examples of evermore sophisticated substitution about the common ligand framework being developed to address specific problems in a number of fields of chemistry. These compounds have shown varied coordination modes at metals from across the periodic table, and examples of their application in a number of catalytic processes are emerging as the field matures.

Application of neutral amidines and guanidines in coordination chemistry

‘Old Chemistries’ for new applications: Perspectives for development of precursors for MOCVD and ALD applications

Group 4 ketimide complexes: Synthesis, reactivity and catalytic applications

Reactions in ether between methyl-lithium and diphenylketimine, or between phenyl-lithium and phenyl cyanide, give a red solution of diphenylketiminolithium, Ph2C:NLi, from which unsolvated (Ph2C:NLi)n may be obtained as a yellow amorphous and presumably polymeric solid, m. p. 260°(decomp.). Diphenylketiminolithium forms the coloured crystalline adducts Ph2C:NLi,py, m. p. 108–110°(red) and Ph2C:NLi, tetrahydrofuran, m. p. 127°(orange) which dissociate in benzene and deposit (Ph2C:NLi)n. Phenyl cyanide and methyl-lithium give yellow amorphous (PhCMe:NLi)n, m. p. 196°. t-Butyl cyanide does not react with methyl-or ethyl-lithium at or below 20°, but methyl and ethyl cyanides with these alkyl-lithium compounds cleave alkane to give amorphous insoluble highly reactive solids believed to contain CCN– groups. A similarly reactive and apparently polymeric, insoluble solid results when dimethylcyanamide and methyl-lithium react and evolve methane. NNN′N′-Tetramethylguanidine and methyl-lithium give methane and the crystalline derivative [(Me2N)2C:NLi]2 which is dimeric in benzene (by cryoscopy) and is also soluble in ether and toluene.

Azomethine derivatives. Part V. Reactions between organolithium compounds and diphenylketimine, some cyanides, and NNN′N′-tetramethylguanidine

Reactions between R13Al and R2NH·CO·R3(R1= Me or Et; R2= Me, Et, But, or Ph; R3= Me or Ph) leading to materials (R12Al·NR2·CO·R3)n are described Ir, mass, and 1H nmr spectroscopic details of the products are given Cyclic 8-membered ring structures (n= 2) are proposed for these compounds in the solution phase Cryoscopic studies support dimeric structures for the compounds (Me2Al·NPh·CO·Me)2 and (Me2Al·NBut·CO·Me)2 in benzene, although an X-ray crystallographic study of the former, which can also be prepared from Me3Al and PhNCO, shows a trimeric structure to be more likely in the crystal The related sulphur compound Me2Al·NPh·CS·Me, from Me3Al and PhNCS, probably also has a similar cyclic structure in solution

Reactions between organoaluminium compounds and N-substituted acid amides

The adducts (Me2N)2C:NH,AlX3(X = Me or Et), from (Me2N)2C:NH +½(or more) Al2X6 in hexane, are monomeric in dilute benzene solution and are believed to have a structure co-ordinated through the imino-nitrogen. They lose XH when heated, forming [(Me2N)2C:NAIX2]2, for which four-membered ring structures are suggested. Although the adduct (Me2N)2C:NH,AlCl3 does not similarly afford [(Me2N)2C:NAICl2]2 when heated, the latter can be prepared from (Me2N)2C:NLi and AlCl3. I.r. spectroscopic details are given for all these new compounds. Also discussed are the 1H n.m.r. spectra of the alkylaluminium compounds and the mass spectra of (Me2N)2C:NH,AICl3 and [(Me2N)2C:NAIEt2]2.

Azomethine derivatives. Part X. 1,1,3,3-Tetramethylguanidine adducts of trimethylaluminium, triethylaluminium, and aluminium trichloride: dimethyl-, diethyl-, and dichloro-bis(dimethylamino)methyleneamino-aluminium

Diphenylketimine and trimethylgallium form a crystalline adduct Ph2C:NH,GaMe3 which at 100° loses methane to form the azomethine derivative (Ph2C:N·GaMe2)2. In the systems Ph2C:NH–GaR3(R = Et or Ph) the 1 : 1 mixtures of the components are viscous liquids whose proton magnetic resonance (p.m.r.) spectra provide evidence of weak complex formation. Both systems lose RH readily at 100–120° to form azomethine derivatives (Ph2C:N·GaR2)2. Features of the infrared, p.m.r., and mass spectra of these compounds are discussed.

Azomethine derivatives. Part III. Reactions between diphenylketimine and trimethylgallium, triethylgallium, and triphenylgallium

The alkylideneamino-aluminium dihalides (R2C:NAlCl2)2(R = Ph or But) and (Ph2C:NAIBr2)n(n probably = 2) have been prepared from R2C:NLi and AIX3(X = Cl or Br); (Ph2C:NAICI2)2 has also been prepared from (diphenylmethyleneamino)trimethylsilane and aluminium trichloride. The trialkylideneamino-derivatives (R2C:N)3Al have been prepared from aluminium trichloride and R2C:NLi (3 molar equiv.). Attempts at the preparation of the dialkylideneamino-derivatives, (R2C:N)2AICI, from aluminium trichloride and R2C:NLi (2 molar equiv.) afforded mixtures of the mono- and tri-alkylideneamino-derivatives. The adduct py,AlCl3 was formed during the reaction between (Ph2C:NAICI2)2 and pyridine. Details of the i.r. and 1H n.m.r. spectra of these new moisture-sensitive methyleneamino-compounds are given and discussed, and the mass spectra of two compounds are reported. Four-membered (AIN)2 ring structures are proposed for the dimeric alkylideneaminoaluminium dihalides. For the monomeric trialkylideneamino-derivatives, the i.r. and 1H n.m.r. spectra are consistent with Iinear CN⇌Al units, the shape appropriate for maximum N⇌Al dative π-bonding from the methyleneamino-nitrogens to the three-co-ordinated aluminium.

B. K. Wyatt

Papers

Azomethine derivatives. Part V. Reactions between organolithium compounds and diphenylketimine, some cyanides, and NNN′N′-tetramethylguanidine

Reactions between organoaluminium compounds and N-substituted acid amides

Azomethine derivatives. Part X. 1,1,3,3-Tetramethylguanidine adducts of trimethylaluminium, triethylaluminium, and aluminium trichloride: dimethyl-, diethyl-, and dichloro-bis(dimethylamino)methyleneamino-aluminium

Azomethine derivatives. Part III. Reactions between diphenylketimine and trimethylgallium, triethylgallium, and triphenylgallium

Azomethine derivatives. Part XIV. Dimeric alkylideneaminoaluminium dihalides, and monomeric trialkylideneamino-derivatives of aluminium