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Probing the factors that influence the conformation of a guanidinato ligand in [(η5-C5Me5)M(NN)X] (NN = chelating N,N′,N′′-tri(o-substituted aryl)guanidinate(1−); X = chloro, azido and triazolato)

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Abstract

Three types of half sandwich complexes, namely, [(η5-Cp*)M(NN)X] (Cp* = C5Me5; NN = chelating N,N′,N′′-tri(o-substituted aryl)guanidinate(1−) ligand; M = Rh/Ir; X = Cl (9–13), N3 (14–18) and N3C2(C(O)OR)2 (19–21)), were prepared and isolated in moderate to good yields. The new complexes were fully characterized and further molecular structures of key complexes from each type were determined by single crystal X-ray diffraction (SCXRD). The new complexes revealed synsyn (10, 12, 15 and 20), antianti (13 and 16) and antisyn (14, 17, 19·CHCl3 and 21) conformations. DFT calculations were performed on four conformers of 14, which revealed the stability order as synsyn (0.00 kcal mol−1) < antisyn (0.23 kcal mol−1) ≪ synanti (3.15 kcal mol−1) ≪ antianti (5.15 kcal mol−1). An intra-ligand repulsive interaction between the o-substituent in two proximal aryl rings in guanidinate ligands of 14 and 17 was invoked as a driving force for the observance of the antisyn conformer in the solid state, which is likely formed from a hypothetical synsyn conformer via a guanidine centered rearrangement. The influence of packing forces upon the antisyn conformation of the guanidinate ligand in 14 was also discussed. NBO analysis was carried out on the N3 moiety of the synsyn conformer of 14 in order to identify the likely resonance form responsible for [3+2] cycloaddition with the alkyne. Several new complexes that contain an o-substituted arylguanidinate ligand were shown to exist as a mixture of conformers in solution as revealed by NMR spectroscopy, and these conformers were shown to arise from a solid state conformer via guanidinine centered rearrangement.

Graphical abstract: Probing the factors that influence the conformation of a guanidinato ligand in [(η5-C5Me5)M(NN)X] (NN = chelating N,N′,N′′-tri(o-substituted aryl)guanidinate(1−); X = chloro, azido and triazolato)

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Publication details

The article was received on 03 Oct 2017, accepted on 18 Dec 2017 and first published on 19 Dec 2017


Article type: Paper
DOI: 10.1039/C7NJ03766J
Citation: New J. Chem., 2018, Advance Article
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    Probing the factors that influence the conformation of a guanidinato ligand in [(η5-C5Me5)M(NN)X] (NN = chelating N,N′,N′′-tri(o-substituted aryl)guanidinate(1−); X = chloro, azido and triazolato)

    R. Kumar, R. Kishan, J. M. Thomas, S. Chinnappan and N. Thirupathi, New J. Chem., 2018, Advance Article , DOI: 10.1039/C7NJ03766J

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