Guanidinates as Alternative Ligands for Organometallic Complexes

Abstract

For decades, ligands such as phosphanes or cyclopentadienyl ring derivatives have dominated Coordination and Organometallic Chemistry. At the same time, alternative compounds have emerged that could compete either for a more practical and accessible synthesis or for greater control of steric and electronic properties. Guanidines, nitrogen-rich compounds, appear as one such potential alternatives as ligands or proligands. In addition to occurring in a plethora of natural compounds, and thus in compounds of pharmacological use, guanidines allow a wide variety of coordination modes to different metal centers along the periodic table, with their monoanionic chelate derivatives being the most common. In this review, we focused on the organometallic chemistry of guanidinato compounds, discussing selected examples of coordination modes, reactivity and uses in catalysis or materials science. We believe that these amazing ligands offer a new promise in Organometallic Chemistry.

Controlled Modification of Triaminoguanidine-Based μ3 Ligands in Multinuclear [VIVO]/[VVO2] Complexes and Their Catalytic Potential in the Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes

“…Coordination chemistry of guanidines and guanidinates has been studied extensively in the past few years. − However, the research group of Robson was the first one to use triaminoguanidine-based μ 3 -ligands [(a) of Chart ] in designing trinuclear Zn­(II) and Pd­(II) complexes having a carbonate-like CN 3 core . However, they observed that during the synthesis of mononuclear Pd­(II) complexes, these ligands undergo the formation of a 1,2,4-triazole ring [(b) of Chart ] by intramolecular oxidative cyclization .…”

Guanidine-centred reactivity of CNN Pd(ii) pincer complexes including carboxylate-assisted N–H activation and –CH2– → –C(O)– oxygenation

“…Transition metal complexes of sym N,N 0 ,N 00 -trisubstituted guanidines, [(RN(H)) 2 C = NR] (R = alkyl-and aryl-substituents; sym = symmetrical), are known for their intriguing structures, reactivity, catalytic activity and bonding feature. [1][2][3][4][5] This class of guanidines are versatile in that the R substituent can be modulated systematically, which would enable one to fine tune their reactivity towards metal precursors. Furthermore, monoand di-deprotonation of guanidines can be carried out by choosing an external base in conjunction with the metal precursors or precursors that already contain basic ancillary ligands resulting in the formation of a great variety of guanidinate(1À) and guanidinate(2À) complexes.…”

Diverse Reactivity of Amidinate-Supported Boron Centers with the Hypersilyl Anion and Access to a Monomeric Secondary Boron Hydride

“…The early 21 st century witnessed enormous interest in the development of bidentate monoanionic nitrogen–donor amidinate ligands of the general formula [R′C­(NR) 2 ] − , as a popular replacement for the cyclopentadienyl ligand, as well as a close association with guanidinates as the ligand architecture . Among a plethora of ligands, amidinates have been designed in such a way that the steric and electronic effects can be readily modified by tailoring the C- and N-centered substituents to stabilize and tune the reactivity of various transition metals, lanthanides, and more recently, main group compounds.…”

“…The early 21 st century witnessed enormous interest in the development of bidentate monoanionic nitrogen–donor amidinate ligands of the general formula [R′C(NR) 2 ] − , as a popular replacement for the cyclopentadienyl ligand, as well as a close association with guanidinates as the ligand architecture. 1 Among a plethora of ligands, amidinates have been designed in such a way that the steric and electronic effects can be readily modified by tailoring the C- and N-centered substituents to stabilize and tune the reactivity of various transition metals, lanthanides, and more recently, main group compounds. Following the first use with rare-earth metals in 1992 by Edelmann et al, 2 the application of amidinates rapidly expanded and fulfilled the quest for the preparation and stabilization of low-valent main group compounds 3 − 10 together with applications in homogeneous catalysis 11 − 15 and materials chemistry.…”