New osmium cluster compounds containing the heterocyclic ligand 2,3-bis-(diphenylphosphino)quinoxaline (dppq): Ligand isomerization and crystal structures of dppq, the isomeric clusters Os3(CO)10(dppq), and HOs3(CO)9[μ-2,3-PhP(η1-C6H4)(Ph2P)quinoxaline]

DFT Investigation of the Mechanism of Phosphine-Thioether Isomerization in the Triosmium Cluster Os3(CO)10(Ph2PCH2CH2SMe): Migratory Preference for the Formation of an Edge-Bridged Thioether versus a Phosphine Moiety

“…Scheme outlines this first exchange step, where the conrotatory motion of the six migrating groups furnishes the bridging isomer A2 ; here the thioether moiety is transformed from an initial equatorial position in A1 to an axial site at the cluster. This in-plane migration represents a prevalent manifold for the exchange of CO and phosphine ligands between adjacent metal centers in polynuclear metal clusters. − , Figures and show the geometry-optimized structures and the potential energy surface for the conversion of 1,2-( P eq , S eq )-Os 3 (CO) 10 (Ph 2 PCH 2 CH 2 SMe) to 1,1-( P eq , S ax )-Os 3 (CO) 10 (Ph 2 PCH 2 CH 2 SMe). The transition state TSA1A2 lies 10.9 kcal/mol higher in energy than the starting species A1 , and the product species, A2 , is only marginally less stable than the starting cluster, lying 0.8 kcal/mol above A1 .…”

“…The isomerization of diphosphine ligands about triosmium clusters has been shown to occur through a concerted scrambling of equatorial CO and phosphine ligands via a merry-go-round process. ,, In these examples, where the diphosphine ligands possess an unsaturated backbone, the single-step exchange process is kinetically favored over alternative, multistep sequences involving pairwise ligand exchanges across a single Os–Os vector. In order to rule out a possible merry-go-round manifold in the conversion of 1,2-( P eq , S eq )-Os 3 (CO) 10 (Ph 2 PCH 2 CH 2 SMe) to 1,1-( P eq , S ax )-Os 3 (CO) 10 (Ph 2 PCH 2 CH 2 SMe), the energetics associated with the migration of the phosphine ligand to the MeS-substituted osmium center in species A2 were computationally modeled.…”

“…We have studied these isomerizations kinetically, and they are well-behaved and exhibit first-order kinetics; however, the mechanism responsible for the permutation of the ancillary PS ligand about the cluster frame remains equivocal. Related to the fluxional behavior of the PS ligand in Os 3 (CO) 10 (PS) clusters is the lability of the ancillary ligands in the related clusters Os 3 (CO) 10 (PP), whose diphosphine isomerization behavior has been thoroughly investigated by us experimentally and computationally. , DFT calculations indicate that the concerted bridge-to-chelate isomerization of the diphosphine ligand in Os 3 (CO) 10 (PP) clusters occurs through a merry-go-round sequence that involves the simultaneous rearrangement of a phosphine moiety and a pair of CO groups in a plane coincident with the metallic frame. This phenomenon is illustrated in eq in the case of the cluster containing the ligand 1,2-bis­(diphenylphosphino)­benzene (dppz) …”

Cytotoxic (cis,cis-1,3,5-triaminocyclohexane)ruthenium(ii)-diphosphine complexes; evidence for covalent binding and intercalation with DNA

“…The quinoxaline diphosphine ligand, L2 was prepared by route (ii) following a modified literature procedure. 46 The novel extended quinoxaline dipho- sphine ligand, L3 was prepared by route (iii) from its dichloro precursor (obtained from treatment of 1,4-dihydrodibenzo[f,h] quinoxaline-2,3-dione with PCl 3 in DMF, see ESI †). 47 The ruthenium complexes 3g-i were prepared in an analogous way to 3a-f (route (iv)); their formation was monitored by 31 P{ 1 H} NMR spectroscopy.…”

Synthesis of quinoxaline derivatives via aromatic nucleophilic substitution of hydrogen

“…Regarding metal-free ring funtionalization, quinoxaline (as many other aromatic azines) exhibits electron-deficient properties, hence it is susceptible to nucleophilic attack. Indeed, there are examples of substitution of chlorine in 2-chloro- and 2,3-dichloroquinoxalines with a variety of nucleophiles: 5 a nitrogen, 5 b – d oxygen, 6 sulfur 7 and phosphorus 8 nucleophiles, as well as carbanions. 9 On the other hand, it is surprising that in spite of the high electron-deficiency of the quinoxaline ring, nucleophilic substitution of hydrogen in quinoxalines has received very little attention.…”