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). (10th January 2018)

• Record Type: Journal Article
• Authors: Kumar, Robin; Kishan, Ram; Thomas, Jisha Mary; Chinnappan, Sivasankar; Thirupathi, Natesan
• Is Part Of: New journal of chemistry. Volume 42:Number 3(2018)
• Page Start: 1853
• Page End: 1866
• Publication Date: 2018-01-10
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c7nj03766j
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : The conformational difference illustrated is ascribed to a subtle repulsive interaction between the o -Cl substituent of two proximal aryl rings in the guanidinate ligand. Abstract : Three types of half sandwich complexes, namely, [(η 5 -Cp*)M( NN )X] (Cp* = C5 Me5 ; NN = chelating N, N ′, N ′′-tri( o -substituted aryl)guanidinate(1−) ligand; M = Rh/Ir; X = Cl (9–13 ), N3 (14–18 ) and N3 C2 (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 syn – syn (10, 12, 15 and20), anti – anti (13 and16 ) and anti – syn (14, 17, 19 ·CHCl3 and21 ) conformations. DFT calculations were performed on four conformers of14, which revealed the stability order as syn – syn (0.00 kcal mol −1 ) < anti – syn (0.23 kcal mol −1 ) ≪ syn – anti (3.15 kcal mol −1 ) ≪ anti – anti (5.15 kcal mol −1 ). An intra-ligand repulsive interaction between the o -substituent in two proximal aryl rings in guanidinate ligands of14 and17 was invoked as a driving force for the observance of the anti – syn conformer in the solid state, which is likely formed from a hypothetical syn – syn conformer via a guanidine centered rearrangement. The influence of packing forces upon the anti – syn conformation of the guanidinate ligand in14 was also discussed. NBO analysis was carried out on the N3 moiety of the syn – syn conformer of14 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.