Nucleobases team up: the efficient and selective preparation of purine-derived metallanucleosides, metallanucleotides, and metalladinucleotides having M-C bonds (M=Ir(III), Rh(III)) is reported for the first time. The results presented may be applied to the synthesis of functionalized nucleic acids, or DNA/RNA-modified segments.

The reactions of the hexahydride complex OsH 6 (P i Pr 3 ) 2 (1) with 4,5-dimethyl-2,6-bis(4-methylphenyl)pyrimidine (H 2 L1), 2,4,6-tris-(4-methylphenyl)-1,3,5-triazine (H 4 L2), and 2,4,6-triphenylpyrimidine (H 4 L3) have been studied. Complex 1 reacts with H 2 L1 to give a mixture of the metallapolycyclic derivatives OsH 3 (HL1)(P i Pr 3 ) 2 (2) and OsH 2 (L1)(P i Pr 3 ) 2 (3). Compound 2 arises from the coordination of the N3-pyrimidine nitrogen atom to osmium and the ortho-CH bond activation of the C2-bonded phenyl group. The formation of 3 involves the coordination of the N1-pyrimidine nitrogen atom to osmium and the ortho-CH bond activation of both phenyl groups. The reaction of 1 with H 4 L2 leads to a mixture of OsH 2 (H 2 L2)(P i Pr 3 ) 2 (4) and (P i Pr 3 ) 2 H 2 Os-(L2)OsH 2 (P i Pr 3 ) 2 (5), containing five and eight fused rings, respectively. Complex 4 results from the coordination of the N1-triazine nitrogen atom to osmium and the ortho-CH bond activation of the phenyl groups at positions 2 and 6 of the triazine ring. Complex 5 results from the coordination of the N1 and N3 of triazine to two different metal centers along with a double ortho-CH bond activation in each proximal phenyl group. Complex 1 reacts with H 4 L3 to afford OsH 2 (H 2 L3)(P i Pr 3 ) 2 (6) and (P i Pr 3 ) 2 H 2 Os(L3)OsH 2 (P i Pr 3 ) 2 (7), which are related to 4 and 5, respectively. Complexes 2, 3, 4, and 5 have been characterized by X-ray diffraction analysis. The structures prove the planarity of their cores and suggest electron delocalization through the polycyclic system. Quantum chemical calculations (DFT level) on model compounds clearly indicate that the Os-C and Os-N bonds of the newly formed metallapolycycles exhibit a remarkable double-bond character that is higher for the Os-C bond, in very good agreement with the experimental findings.

[6]-Azaosmahelicenes, the first d(4)-heterometallahelicenes, have been synthesised and fully characterised. Their optical properties (UV-Vis absorption and luminescence) are reported.

The capacity of the hexahydride complex OsH 6 (P i Pr 3 ) 2 (1) to discern between the nitrogen atom and the NH unit in the azole assisted aryl C−H bond activation has been investigated. Complex 1 reacts with 2-phenylimidazole to give OsH 3 {κ 2 -C,N-(C 6 H 4 -imidazole)}(P i Pr 3 ) 2 (2), which has been characterized by X-ray diffraction analysis. The structure proves the higher affinity of the metal center for the N atom in the presence of the NH unit, which remains unchanged, and reveals that in the solid state the molecules of this complex form infinite chains by means of intermolecular asymmetric 3-center bifurcated dihydrogen bonds. In solution, 1 H-DOSY NMR experiments suggest that the association degree decreases as the temperature increases. The fused six-membered ring of benzimidazole weakens the NH bond, enhancing its reactivity. As a consequence, complex 1 cannot discern between the N atom and the NH unit of 2-phenylbenzimidazole. Thus, the treatment of 1 with this substrate leads to a mixture of OsH 3 {κ 2 -C,N-(C 6 H 4 -benzimidazole)}(P i Pr 3 ) 2 (3) and the dinuclear species (P i Pr 3 ) 2 H 3 Os(C 6 H 4 -benzimidazolate)OsH(η 2 -H 2 )(P i Pr 3 ) 2 (4). The latter is the result of a N-assisted ortho-C−H bond activation of the phenyl group promoted by 0.5 equiv of 1 and the N−H bond activation promoted by the remaining 0.5 equiv of hexahydride 1 along with the agostic coordination of the remaining ortho-C−H bond to the metal center of the unsaturated fragment OsH(η 2 -H 2 )(P i Pr 3 ) 2 . The comparison of the redox properties of 3 and 4 suggests that the interaction between the metal centers in the dinuclear compound is negligible. The replacement of the NH group of the azoles by a sulfur atom does not modify the behavior of the substrates. Thus, the reactions of 1 with 2-phenylthiazole and 2-phenylbenzothiazole afford OsH 3 {κ 2 -C,N-(C 6 H 4 -thiazole)}(P i Pr 3 ) 2 (5) and OsH 3 {κ 2 -C,N-(C 6 H 4 -benzothiazole)}(P i Pr 3 ) 2 (6). In turn, complexes 2, 3, 5, and 6 are phosphorescent.

In the search for evidence to establish the effect of π conjugation on the variation of the equilibrium torsion angle (θ eq ) in push-pull 4,4Ј-disubstituted biphenyls, a systematic Hammett DFT study has been carried out. The study shows that although reasonable and intuitive, the through-conjugation between donor and acceptor substituents in these systems is only of some relevance when strong donor and strong charged acceptors are involved. In these cases, changes in