[(eta(6)-C10H14)RuCl(mu-Cl)](2) (eta(6)-C10H14 = eta(6)-p-cymene) was subjected to a bridge-splitting reaction with N,N',N ''-triarylguanidines, (ArNH)(2)C=NAr, in toluene at ambient temperature to afford [(eta(6)-C10H14)RuCl{kappa(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C6H4Me-4 (1), C6H4(OMe)-2 (2), C6H4Me-2 (3), and C6H3Me2-2,4 (4)) in high yield with a view aimed at understanding the influence of substituent(s) on the aryl rings of the guanidine upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1-3 upon reaction with NaN3 in ethanol at ambient temperature afforded [(eta(6)-C10H14)RuN3{kappa(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C6H4Me-4 (5), C6H4(OMe)-2 (6), and C6H4Me-2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5-7 with RO(O)C-C C-C(O)OR (R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH2Cl2 at ambient temperature afforded [(eta(6)-C10H14)Ru{N3C2(C(O)OR)(2)}{kappa(2)(N,N')((ArN)(2)C-N(H)Ar)}cen ter dot xH(2)O (x = 1, R = Et, Ar = C6H4Me-4 (8 center dot H2O); x = 0, R = Me, Ar = C6H4(OMe)-2 (9), and C6H4Me-2 (10)) in moderate yield. The molecular structures of 1-6, 8 center dot H2O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the aforementioned complexes revealed pseudo octahedral "three legged piano stool" geometry. The guanidinate ligand in 2, 3, and 6 revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN3 unit of the guanidinate ligand in the new complexes was explained by invoking n-pi conjugation involving the interaction of the NHAr/NcoordAr lone pair with C=N pi* orbital of the imine unit. Complexes 1, 2, 5, 6, 8 center dot H2O, and 9 were shown to exist as a single isomer in solution as revealed by NMR data, and this was ascribed to a fast C-N(H)Ar bond rotation caused by a less bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about 1:1:1 and 1.0:1.2:2:7:3.5:6.9 ratios, respectively in solution as revealed by a VT H-1 NMR, H-1-H-1 COSY in conjunction with DEPT-90 C-13 NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the restricted C-N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C-NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around the ruthenium atom in 10.