Additions to Metal-Activated Organonitriles†

The coordination chemistry of the amidine ligand

The coordination chemistry of guanidines and guanidinates

A highly efficient, mild, practical, and catalytic multicomponent reaction for the synthesis of N-sulfonylamidines has been developed. This reaction has an extremely wide scope with regard to all three coupling components of alkyne, sulfonyl azide, and amine. Two plausible mechanistic pathways involving ketenimine or triazole intermediate are tentatively presented for the copper-catalyzed three-component coupling reactions.

Highly Efficient One-Pot Synthesis of N-Sulfonylamidines by Cu-Catalyzed Three-Component Coupling of Sulfonyl Azide, Alkyne, and Amine

For decades, the organometallic chemistry of the rare earth elements was largely dominated by the cyclopentadienyl ligand and its ring-substituted derivatives. A hot topic in current organolanthanide chemistry is the search for alternative ligand sets which are able to satisfy the coordination requirements of the large lanthanide cations. Among the most successful approaches in this field is the use of amidinate ligands of the general type [RC(NR')(2)](-) (R = H, alkyl, aryl; R' = alkyl, cycloalkyl, aryl, SiMe(3)) which can be regarded as steric cyclopentadienyl equivalents. Closely related are the guanidinate anions of the general type [R(2)NC(NR')(2)](-) (R = alkyl, SiMe(3); R' = alkyl, cycloalkyl, aryl, SiMe(3)). Two amidinate or guanidinate ligands can coordinate to a lanthanide ion to form a metallocene-like coordination environment which allows the isolation and characterization of stable though very reactive amide, alkyl, and hydride species. Mono- and trisubstituted lanthanide amidinate and guanidinate complexes are also readily available. Various rare earth amidinates and guanidinates have turned out to be very efficient homogeneous catalysts e.g. for ring-opening polymerization reactions. Moreover, certain alkyl-substituted lanthanide tris(amidinates) and tris(guanidinates) were found to be highly volatile and could thus be promising precursors for ALD (= Atomic Layer Deposition) and MOCVD (= Metal-Organic Chemical Vapor Deposition) processes in materials science and nanotechnology. This tutorial review covers the success story of lanthanide amidinates and guanidinates and their transition from mere laboratory curiosities to efficient homogeneous catalysts as well as ALD and MOCVD precursors.

Lanthanide amidinates and guanidinates: from laboratory curiosities to efficient homogeneous catalysts and precursors for rare-earth oxide thin films

Electron impact mass spectrometry of a range of amidines (R′NC(R)NHR′) including formamidines, acetamidines, benzamidines and tert-butylamidine, has been undertaken, and comparisons made of the fragmentation pathways followed by the different families of compounds. Fragmentation of all the molecular ions is characterized by skeletal carbon-nitrogen bond cleavage to form [R′NCR]+ and [R′NH]+ fragments, both of which are observed. For formamidines (RH), the positive charge remains with the [R′NH]+ fragment which leads to the base peak at m/z93 corresponding to [R′NH2]+˙. In contrast, for acetamidines and benzamidines the charge prefers to remain with the [R′NCR]+ fragment which gives the base peak for these compounds. The spectra of unsubstituted amidines (HNC(R)NH2) are characterized by cleavage of the carbon substituent from the NCN skeleton, [CN2H3]+ (m/z 43) being produced in all cases.

James Barker

Papers

The coordination chemistry of the amidine ligand

Amidine mass spectral fragmentation patterns