He I and He II photoelectron (PE) spectra of [Fe(η-C5H4)2SiMe2] (1), [Fe(η-C5H3Me)2SiMe2] (2), [Fe(η-C5H4)(η-C5Me4)SiMe2] (3), [Fe(η-C5Me4)2SiMe2] (4), [Fe(η-C5H4)2C2H4] (5), and [Fe(η-C5H4)2S] (6) have been measured and assigned. The d bands of 1−5 show less structure than that of ferrocene, consistent with a loss of degeneracy of the e2 orbitals on bending. Compound 6, which has the largest inter-ring angle of the series, shows two separate d bands. The trend in the first ionization energy closely parallels the variation in oxidation potential. Density functional calculations on 1, 5, and 6 give geometries in good agreement with the structures found from X-ray diffraction. Ionization energies calculated were also in excellent agreement with experiment. Good agreement was also found between the calculated d−d transitions and the position of the first spin-allowed band in the optical spectra of 1 and 6. Estimates of strain energy in bending ferrocene and octamethylferrocene were obtained, and octamethylferrocene was shown to be significantly more difficult to bend. Compounds 1 and 6 were both shown to have a low-lying empty orbital, partially located on the ipso carbon, which is a possible site for nucleophilic attack in the polymerization process undergone by these compounds.

Incompletely condensed silsesquioxanes of the type R7Si7O9(O[SiR'2O]n)OH (R = c-C5H9, c-C6H11; R' = Me, Ph; n = 1-4), containing a siloxane ring of variable size and rigidity and a remaining silanol, are described. Compared with a truly isolated silanol [R7Si8O12(OH)], solution and solid state FT-IR spectra of these compounds show a nu(OH) shift of approximately 150 cm(-1) to lower frequency, which suggests hydrogen bonding of the silanol with the internal siloxane ring. In agreement with this, the relative ion pair acidities of the silanols in THF, determined by UV/Vis, were lowered by 0.8-1.2 compared with a truly isolated silanol. Density functional theory (DFT) calculations on these systems confirm the presence of intramolecular hydrogen bonding. Possible interaction of the silyl ether functionalities with Lewis acidic metal sites was studied for the neutral gallium-substituted systems and cationic titanium silsesquioxane complexes, models for an immobilized titanium olefin polymerization catalyst. The electron donating capability of the siloxide functionalities in 1, 6, and 7 is not sufficient to satisfy the electron deficiency of the corresponding gallium silsesquioxane species, which form dimeric structures with a bridging siloxide unit rather than Lewis base adducts with coordinated siloxide functionalities. Metallation of 1 and 4 with [Cp"Ti(CH2Ph)3] (Cp" = eta5-1,3-C5H3(SiMe3)2) in a 1:1 ratio afforded monomeric titanasilsesquioxanes. To probe the effect of the neighboring siloxane ring on the highly Lewis acidic titanium center, the catalytic activities of the corresponding cationic half-sandwich complexes were tested in 1-hexene polymerization. Compared with the catalyst system based on the isolated silanol [(c-C5H9)7Si8O12OH], the presence of a neighboring siloxane ring causes considerable retardation of the polymerization process but also improves the stability of the catalyst.

The new compounds [W{(η-C 5 H 4 )X(η-C 5 H 4 )}Cl 2 ] 1, [W{(η-C 5 H 4 )X(η-C 5 H 4 )}Me 2 ] 2, [W{(η-C , where X = SiMe 2 , SiEt 2 or CMe 2 CMe 2 , and Y = BF 4 or Cl, have been prepared. The crystal structures of [W{(η-C 5 H 4 )X(η-C 5 H 4 )}Me 2 ] (X = SiMe 2 or CMe 2 CMe 2 ) have been determined.Recently we have described ansa-metallocenes of tungsten and molybdenum and shown that their properties are significantly different from non-ansa analogues. 1,2 In particular we noted that the complex [W{(η-C 5 H 4 )CMe 2 (η-C 5 H 4 )}H 3 ] ϩ PF 6 Ϫ displays exceptional highly temperature variable 1 H NMR spectroscopic data with 2 J(HH) of ca. 16 000 Hz at Ϫ70 ЊC attributed to quantum mechanical exchange coupling. By comparison, [W(η-C 5 H 5 ) 2 H 3 ] ϩ BF 4 Ϫ shows very different temperature independent behaviour. 3 We have prepared a number of related ansa-tungstenocene complexes to investigate the effect that changes in the bridging ring substituents have upon their properties.Compound and analysis a 1a [W{(η-C 5 H 4 )SiMe 2 (η-C 5 H 4 )}Cl 2 ] Green C, 28.7 (28.7); H, 3.7 (3.3) Spectroscopic data b 1 H: c 6.12 (4 H, m, C 5 H 4 ), 5.81 (4 H, m, C 5 H 4 ), 0.09 (6 H, s, Me 2 Si) 13 C-{ 1 H}: c 125.9 (s, C 5 H 4 ), 78.7 (s, C 5 H 4 ), 66.0 (s, C 5 H 4 , C ipso ), Ϫ5.9 (s, SiMe 2 ) Mass (FAB): m/z 442 (M ϩ ), 405 (M ϩ Ϫ Cl) 1b [W{(η-C 5 H 4 )SiEt 2 (η-C 5 H 4 )}Cl 2 ] Green 1

Tin silicate species have shown good catalytic activity in various oxidation reactions. In an attempt to mimic surface tin species, several tin containing silsesquioxanes have been synthesized. Incompletely condensed silsesquioxanes (c-C5H9)7Si7O9(OH)3 and (c-C5H9)7Si7O9(OSiMe3)(OH)2 were reacted with common tin-precursors, which afforded several silsesquioxane ligated tin compounds. Divalent stannasilsesquioxanes form dimers of the type [(c-C5H9)7Si7O11(OX)Sn]2(X=H, SiMe3) with three-coordinated tin centers. The three-coordinated tin(II) are hydrolytically unstable whereas the octahedrally surrounded tetravalent stannasilsesquioxanes [(c-C5H9)7Si7O11(OX)]Sn(acac)2(X=H, OSiMe3) are hydrolytically robust. An unprecedented anionic trimeric cluster, [[(c-C5H9)7Si7O12Sn]3(mu2-OH)3(mu3-OH)]-[HNEt3]+, stabilized by bridging hydroxyl groups was formed when the product formed upon reacting (c-C5H9)7Si7O9(OH)3 with SnCl4 was slowly hydrolyzed. The stannasilsesquioxanes showed no catalytic activity in oxidation reactions.

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