Syed A. A. Shah

Formation of ring-expanded products from certain combinations of tetraphenyldisiloxanediolates [(Ph2SiOM′)2O](M′= Li or Na) and group 4 metal chlorides MCl4

Experimental conditions and combinations of reagents have been varied in reactions between [(Ph2SiOM′)2O](M′= Li or Na) and Group 4 metal halides MCl4, with the broad aim of assessing their affects on the formation of ring-expanded products. Lithium-7 NMR spectroscopy was used to monitor the reaction between [(Ph2SiOLi)2O] and MgCl2·2thf in thf (tetrahydrofuran) which gives a ring-expanded product. The reaction between [(Ph2SiONa)2O], prepared in situ from sodium metal and (Ph2SiOH)2O, and TiCl4 in a 3 : 1 molar ratio gave the sodium-bridged compound [Ti{O(SiPh2O)2}3{Na(py)}2]·py, py = pyridine, the first example of a six-membered titanasiloxane ring. Further reaction with LiI gave the lithium-bridged analogue. The analogous reaction with HfCl4 gave the ring-expanded compound [Hf{Ph2Si(OSiPh2O)2}2(py)2]·2C6H5Me, the first examples of eight-membered hafnasiloxane rings. Results of 7Li, 29Si, and 23Na NMR, IR, and single-crystal X-ray diffraction studies are reported.

Synthesis and crystal structures of the cyclosiloxytin(IV) complexes [Cl2Sn{O(SiPh2O)2}2]-μ-(Li(THF)2)2] and [THF2Sn{(OSiPh2)3O}2]·toluene

Abstract The reaction between the lithium compound [{Ph 2 SiOLi} 2 O] and SnCl 4 gave the lithium-bridged chlorostannasiloxane [Cl 2 Sn{O(SiPh 2 O) 2 } 2 ]-μ-(Li(THF) 2 ) 2 ] ( 1 ) containing six-membered stannasiloxane rings. A similar reaction betwee the corresponding sodium compound [{Ph 2 SiONa} 2 O] and SnCl 4 surprisingly gave the stannasiloxane [THF 2 Sn{(OSiPh 2 ) 3 O} 2 ] (bd crystallised as the mono-toluene solvate) containing eight-membered stannasiloxane [ings. Compounds 1 and 2 were obtained in reactions in which the relative molar ratio of the lithium or sodium reagents to SnCl 4 was varied from 1:1 to 3:1. Compounds 1 and 2 were characterised by 1 H and 29 Si NMR spectroscopy, elemental analysis and single-crystal X-ray diffraction studies.

Synthesis and structural characterisation of the cyclosiloxymagesium compound [(py)2Li]2-µ-Mg[{Ph2SiO}2O][{Ph2SiO}3O] having both six- and eight-membered magnesiasiloxane rings

The dilithium salt, [(Ph2SiOLi·THF)2O], reacts with MgCl2·2THF to give, on addition of pyridine, the unexpected lithium bridged spirocyclic magnesiasiloxane compound [(py)2Li]2-µ-Mg[{Ph2SiO}2O][{Ph2SiO}3O] which is the first example of a molecular magnesium siloxide compound to be characterised and also the first example of a spirocyclic metallasiloxane having rings with different degrees of oligomerisation.

Synthesis, crystal structure and homogeneous catalytic activity towards ethylene polymerisation of the spirocyclic chromium(II) siloxane [C[graphic ommitted])-µ-Na(thf)2}2](thf = tetrahydrofuran)

The chromium(II) compound [C[graphic ommitted])-µ-Na(thf)2}2]1 has been isolated and structurally characterised; in combination with trimethylaluminium, it is a precatalyst for the polymerisation of ethene to linear polyethylene.

A novel route to oxovanadium halides. Synthesis and x-ray structures of VOCl2·3Py and VO2 Cl·2Py

Abstract The oxovanadium halides VOCl2·2Py (1), VOCl2·3Py (2) and VO2Cl·2Py (3) have been isolated as unexpected products from reactions between VCl4 and VOCl3, respectively, with [(Ph2SiOM′)2O] (M′Li or Na). Further reaction of compound 1 with [O(SiPh2OLi)2·2THF], however, gave the cyclosiloxyoxovanadium(IV) complex [VOO(SiPh2O)22-μ-(Li(THF)2)2]. The manner in which 1, 2 and 3 may be formed in these reactions is illustrated. The X-ray structure of 2 and structures of two crystallography distinct forms of 3 are presented.

Formation and X-ray structure of [{O(Ph2SiONa)2}4·(NaOH)·(H2O)·(7 pyridine)]·(toluene)·(pyridine) incorporating a unique assembly of three fused Na4O4 cubane units and a μ3-water molecule

Abstract We report on the isolation and molecular structure of [{O(Ph 2 SiONa) 2 } 4 ·(NaOH)·(H 2 O)·(7pyridine)]·(pyridine)·(toluene) from toluene/pyridine solutions of [O(Ph 2 SiONa) 2 ·Py] in air; a unique structural assembly, of three edge-shared Na 4 O 4 siloxane-bridged cubes, sharing one μ 6 -OH site, where one cube corner is occupied by a μ 3 -OH 2 group.

Synthesis and structural characterisation of the novel metallasiloxane compound [Cp2∗ZrOSiPh2OLiOH]2

Abstract The reactions between Cp 2 ZrCl 2 or Cp 2 ∗ ZrCl 2 with in situ generated Ph 2 Si(OLi) 2 gave unexpected dimeric cyclozirconasiloxane products incorporating LiOH within the chelate-bridging unit OSiPh 2 OLi(OH). The crystal structure of [Cp 2 ∗ ZrOSiPh 2 OLiOH] 2 is reported and the origin of the LiOH discussed.

Lithium bridged cyclosiloxy-niobium( V ) and -tantalum( V ) complexes: thermal decomposition, solid-state and solution structural studies†

Treatment of MCl 5 (M = Nb or Ta) with 3 equivalents of dilithium tetraphenyldisiloxanediolate, [(Ph 2 SiOLi) 2 O], gave the lithium-bridged metallasiloxane complex, [M{O(SiPh 2 O) 2 } 3 ]-µ-[Li(L) 2 ] (M = Nb 1 or M = Ta 2; L = pyridine). The solid-state structure of compound 2 determined by single crystal X-ray diffraction is reported. Variable-temperature 7 Li NMR of 2 revealed two separate exchange processes which may account for the equilibration of non-equivalent silicon environments in 1 and 2. Preparative scale thermal decomposition of the solid samples with L = tetrahydrofuran (thf) gave crystalline LiNbO 3 and LiTaO 3 .

Synthesis and catalytic properties of novel zirconium fluoro-sulfonato and bis(sulfonate) complexes: crystal structure of [(η5-C5Me5)2Zr(OSO2CF3)2]

Abstract Treatment of [( η 5 -C 5 Me 5 ) 2 ZrF 2 ] with Me 3 SiOSO 2 R (R = CF 3 , C 6 H 4 - p -CH 3 ) yield both the monosubstituted [( η 5 -C 5 Me 5 ) 2 ZrF(OSO 2 R)] ( 1 , R = CF 3 ; 2 , R = C 6 H 4 - p -CH 3 ) and disubstituted [( η -C 5 Me 5 ) 2 Zr(OSO 2 R) 2 ] ( 3 , R = CF 3 ; 4 , R = C 6 H 4 - p -CH 3 ) sulfonate complexes, when using stoichiometric amounts of reagents. An X-ray diffraction study of 3 revealed that the trifluoromethanesulfonate ligands are covalently bound to zirconium. Compounds 1–4 along with [( η 5 -C 5 Me 5 ) 2 ZrF(OCOCF 3 )] (5) and [( η 5 -C 5 Me 5 ) 2 Zr(OCOCF 3 ) 2 ] (6) were investigated as catalysts for the polymerization of ethylene in combination with methylaluminoxane (MAO).