Combined Spectroscopic and Quantum Chemical Study of [trans-Ru(C≡CC6H4R1-4)2(dppe)2]n+ and [trans-Ru(C≡CC6H4R1-4)(C≡CC6H4R2-4)(dppe)2]n+ (n = 0, 1) Complexes: Interpretations beyond the Lowest Energy Conformer Paradigm

The reaction of trans-RuCl(C≡CC6H4R1-4)(dppe)2 (2: R1 = Me (a), C5H11 (b), OMe (c), CO2Me (d), NO2 (e), C≡CSiMe3 (f), C≡CBut (g), NH2 (h)), prepared in situ from reactions of [RuCl(dppe)2]OTf ([1]OTf) with terminal alkynes in CH2Cl2 solutions containing 1,8-diazabicycloundec-7-ene (DBU) and TlBF4, provides a convenient and rapid route to bis(acetylide) complexes trans-Ru(C≡CC6H4R1-4)2(dppe)2 (3a–h) and trans-Ru(C≡CC6H4R1-4)(C≡CC6H4R2-4)(dppe)2 (4, R1 = C≡CSiMe3, R2 = NH2; 5, R1 = CO2Me, R2 = NH2; 6, R1 = CO2Me, R2 = OMe). However, even in the absence of the chloride abstracting reagent, more strongly electron donating substituents (e.g., R1 = OMe (2c), NH2 (2h)) promote sufficient ionization of the Ru–Cl bond in trans-RuCl(C≡CC6H4R1-4)(dppe)2 to lead to slow conversion to bis(alkynyl) complexes 3c,h in the presence of excess alkyne and DBU. Desilylation of 2f and 3f affords 2i and 3i (R1 = C≡CH), respectively. The molecular structures of 3a–d,f–i have been determined and are reported together with the str...