| The dirhodium(II,II) tetracarboxylate motif has been shown to serve as a structural template for the self-assembly of carboxylate-appended photoactive units of the form [(tpy)(4'-(4-carboxyphenyl)tpy)Ru](PF6) 2 (tpy = 2,2':6'2" terpyridine). Efficient quenching of the emissive 3MLCT state of these photoactive complexes upon formation of these higher-order assemblies suggested irreversible energy transfer to the non-emissive excited state of the Rh2(II,II) center, which was verified through the preparation of analogous assemblies based upon the triazine-based photoactive units [(2-phenyl-4,6-di(2-pyridyl)triazine)(4'-(4-carboxyphenypl)tpy)Ru](PF 6)2 and [(2-(4-carboxyphenyl)-4,6-di(2-pyridyl)triazine)(tpy)Ru](PF 6)2.;To improve the integrity of the highly-charged Ru(II) assemblies constructed about the Rh2(II,II) motif, amidinate analogues [(4'-( N,N'-dipropylbenzamidine)-tpy)(tpy)Ru](PF6)2 and [(4'-(N,N'-diphenylbenzamidine)-tpy)(tpy)Ru](PF 6)2 were prepared, along with the polytopic amidine ligand N,N'-di-(4'-phenyl-tpy) formamidine. However, coordination of these amidinate-Ru(II) complexes to a Rh2(II,II) center was not possible using conventional methods. Moreover, the elusiveness of the ligand N,N'-di-(4'-phenyl-tpy) formamidine was shown to be due to an unusual and unanticipated susceptibility of this compound to undergo hydrolysis, presumably due to the presence of tpy fragments bound to the amidine nitrogen atoms.;A divergent strategy was therefore developed by creating a family of reactive building blocks based upon the Rh2(N,N'-diphenylbenzamiinate) 4 motif. This family stemmed from the initial creation of Rh2( N,N'-diphenyl-4-bromobenzamidinate)4, from which reactive functionality was installed to the central phenyl ring of the amidinate ligand. Such functionality was shown to include -NH2 and -CCH groups, the periodicity and proportion of which could be controlled based upon the efficient isolation of mixed diphenylketimine/bromine Rh2-complexes from the C-N coupling reaction of benzophenone imine with Rh2(N,N'-diphenyl-4-bromobenzamidinate) 4. As proof of principle, both di- and penta-nuclear Rh2(II,II) complexes were prepared. Where formylation was desired but inaccessible through a 'chemistry-on-the-complex' approach, suitable ligand preparation (i.e. N,N'-diphenyl-4-formyl-benzamidine) gave access to Rh2 (N,N'-diphenyl-4-formyl-benzamidine) 4, from which the carboxylate analogue Rh2 (N,N'-diphenyl-4-carboxybenzamidine) 4 could be prepared. All complexes were unambiguously characterized by 1H NMR, ESI-MS, UV-vis, cyclic voltammetry and, in some cases, single-crystal X-ray crystallography.;Keywords. ruthenium(II), dirhodium(II,II), tpy, triazine, carboxylate, amidinate, self-assembly, templation, photoactive, excited--state, energy transfer.;To expand on the synthetic utility of the dirhodium(II,II) tetracarboxylate motif, a series of homoleptic Ru(II) complexes based on the ligands 4'-(carboxy)tpy, 4'-(4-carboxyphenyl)tpy, and (2-(4-carboxyphenyl)-4,6-di(2-pyridyl)triazine) were prepared. Incorporation of the Rh2(II,II) motif to these dicarboxylates could be performed in the absence of deleterious polymerization to give both bis-Rh2 and mono-Rh2-adducts, which have been unambiguously characterized. To ameliorate the general insolubility of such dicarboxylate complexes, the ligand 4'-(4-carboxyphenyl)-4,4"-di-(tert-butyl)tpy was prepared, along with its subsequent homoleptic Ru(II) complex which was shown to be abundantly soluble in a range of organic solvents and to possess an unusual, porous solid-state structure. |
