Reactions of 2-Substituted Pyridines with Titanocenes and Zirconocenes: Coupling versus Dearomatisation.

Reactions of group 4 metallocene sources with 2-substituted pyridines were investigated to evaluate their coordination type between innocent and reductive dearomatisation as well as to probe the possibility for couplings. A dependence on the cyclopentadienyl ligands (Cp, Cp*), the metals (Ti, Zr), and the substrates (2-phenyl-, 2-acetyl-, and 2-iminopyridine) was observed. While 2-phenylpyridine is barely reactive, 2-acetylpyridine reacts vigorously with the Cp-substituted complexes and selectively with their Cp* analogues. With 2-iminopyridine, in all cases selective reactions were observed. In the isolated [Cp2 Ti], [Cp2 Zr], and [Cp*2 Zr] compounds the substrate coordinates by its pyridyl ring and the unsaturated side-chain. Subsequently, the pyridine was dearomatised, which is most pronounced in the [Cp*2 Zr] compounds. Using [Cp*2 Ti] leads to the unexpected paramagnetic complexes [Cp*2 TiIII (N,O-acpy)] and [Cp*2 TiIII (N,N'-impy)]. This highlights the non-innocent character of the pyridyl substrates.

Crystal structure of di-n-but-yl-bis-(η (5)-penta-methyl-cyclo-penta-dien-yl)hafnium(IV).

The crystal structure of the title compound, [Hf(C10H15)2(C4H9)2], reveals two independent mol-ecules in the asymmetric unit. The diffraction experiment was performed with a racemically twinned crystal showing a 0.529 (5):0.471 (5) component ratio. Each Hf(IV) atom is coordinated by two penta-methyl-cyclo-penta-dienyl and two n-butyl ligands in a distorted tetra-hedral geometry, with the cyclo-penta-dienyl rings inclined to one another by 45.11 (15) and 45.37 (16)°. In contrast to the isostructural di(n-butyl)bis(η (5)-penta-methyl-cyclo-penta-dien-yl)zirconium(IV) complex with a noticeable difference in the Zr-butyl bonding, the Hf-Cbut-yl bond lengths differ from each other by no more than 0.039 (3) Å.

Synthesis, characterization and reactivity of group 4 metallocene bis(diphenylphosphino)acetylene complexes-a reactivity and bonding study.

A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C≡C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'2M(L)(η(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged η(5)-cyclopentadienyl), the expected mononuclear complexes Cp*2Ti(η(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(η(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(η(2)-Me3SiC2SiMe3) with Ph2P-C≡C-PPh2, the dinuclear complex [Cp2Zr(η(2)-Ph2PC2PPh2)]2 (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C≡C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)2Ni(η(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(µ-PPh2)]2 (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C≡C-PR2 ligand. For compound 7b, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.

Melanoma cells use Thy-1 (CD90) on endothelial cells for metastasis formation.

The cell adhesion molecule Thy-1 (CD90) mediates the adhesion of melanoma cells to activated human endothelial cells (EC) via the interaction with the αvß3-integrin on the tumor cells in vitro. Here, we report a strong expression of Thy-1 on both blood vessel and lymphatic EC in melanoma and melanoma metastases. Vascular endothelial growth factor and tumor necrosis factor-α were identified as inducers of Thy-1 expression on EC in vitro. The physiological role of Thy-1 for lymphogenic and hematogenic metastasis of melanoma cells was substantiated in an experimental metastasis model using B16/F10 melanoma cells. Mice lacking Thy-1 showed markedly diminished experimental lung metastasis after injection of B16/F10 melanoma cells compared to wild-type littermate controls. In addition, on generation of a primary subcutaneous tumor, metastasis to regional lymph nodes was clearly reduced in Thy-1(-/-) mice. However, Thy-1 deletion did not affect subcutaneous primary tumor growth, tumor-induced recruitment of inflammatory cells or T cells, angiogenesis, or T-cell activation. In conclusion, Thy-1 contributes to metastasis of melanoma cells by mechanisms likely involving a Thy-1-mediated adhesion of melanoma cells to EC.

Thy-1 (CD90) regulates the extravasation of leukocytes during inflammation.

Human Thy-1 (CD90) has been shown to mediate adhesion of inflammatory cells to activated microvascular endothelial cells via interaction with Mac-1 (CD11b/CD18) in vitro. Since there are no data showing the physiological relevance of Thy-1 for the recruitment of inflammatory cells in vivo, different inflammation models were investigated in Thy-1-deficient mice and littermate controls. In thioglycollate-induced peritonitis, the number of neutrophils and monocytes was significantly diminished in Thy-1-deficient mice. During acute lung inflammation, the extravasation of eosinophils and monocytes into the lung was significantly reduced in Thy-1-deficient mice. Moreover, during chronic lung inflammation, the influx of eosinophils and monocytes was also strongly decreased. These effects were independent of Thy-1 expression on T cells, as shown by the transplantation of WT BM into the Thy-1-deficient mice. In spite of the strong Thy-1 expression on T cells in the chimeric mice, the extravasation of the inflammatory cells in these mice was significantly diminished, compared to control mice. Finally, the altered number and composition of infiltrating leukocytes in Thy-1-deficient mice modified the chemokine/cytokine and protease expression at the site of inflammation. In conclusion, Thy-1 is involved in the control of inflammatory cell recruitment and, thus, also in conditioning the inflammatory microenvironment.