Ruthenium Carbene and Allenylidene Complexes Supported by the Tertiary Amine−Aromatic Diimine Ligand Set: Structural, Spectroscopic, and Theoretical Studies

Abstract

Ruthenium−methoxycarbene and −allenylidene complexes bearing 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 Tacn) and 1,10-phenanthroline (phen), [(Me 3 Tacn)(phen)Ru═C(OMe)R] 2+ (R = CH 2 Ph ( 1 ), CH═CPh 2 ( 2 ), CH═C(C 6 H 4 Cl-4) 2 ( 3 ), CH═C(C 6 H 4 Me-4) 2 ( 4 )), and [(Me 3 Tacn)(phen)Ru═C═C═CR 2 ] 2+ (R = Ph ( 5 ), C 6 H 4 OMe-4 ( 6 )) have been prepared. The molecular structures of 1 (PF 6 ) 2 and 2 (PF 6 ) 2 reveal Ru−C distances of 1.917(3) and 1.906(4) Å, respectively. The lowest-energy dipole-allowed absorptions for complexes 1 − 4 (λ max ≈ 435 nm) are assigned as d π (Ru II ) → π*(phen) metal-to-ligand charge transfer (MLCT) transitions, while those for complexes 5 and 6 (λ max = 530 and 585 nm, respectively) are assigned as metal-perturbed π−π* [Ru═C═C═CR 2 ] intraligand transitions. Complexes 1 − 4 are emissive in glassy MeOH/EtOH at 77 K: excitation at λ = 430 nm produces emission at λ max = 570−620 nm, which are tentatively assigned as d π (Ru II ) → π*(phen) 3 MLCT in nature. Density functional theory (DFT) calculations, charge decomposition analysis (CDA), and natural bond orbital (NBO) analysis on complexes 1, 2, 5, and 6 suggest that allenylidene ligands are better electron donors and poorer acceptors compared with methoxycarbene ligands, and the Ru−C interactions in ruthenium−allenylidene and −methoxycarbene complexes can be depicted by the polarized formulation Ru δ+ ═C δ− and nonpolarized formulation Ru═C, respectively. The methoxycarbene/allenylidene rotational barriers on 1, 2, and 5 are calculated to be 8.3, 6.3, and 1.5 kcal mol −1, respectively.