Pentamethylcyclopentadienyl compounds

Single crystal neutron diffraction studies on Cp Y(OAr)[CH(SiMe3)2] (Ar = 0-2,6-Buc2C6H3) and Cp La[CH(SiMe3)2]2 have been performed in order to get conclusive evidence for the nature of the close intramolecular contacts between CH(SiMe3)2 and the lanthanide center in these complexes. These intramolecular 

Single crystal X-ray structures of CpDoCp HScCl and CpDoCp HScMe were published. Both molecules showed a similar structure. The Cl complex is one of the very few examples of a di(cyclopentadienyl)scandium chloride without bridging chlorine atoms. This terminal Sc-Cl distance is 2.4574(12) A shorter than in a scandium chloride complex with bridging chlorine atoms like [Cp 2Sc(/r-Cl)]2 with 2.58 A. The scandium metal atom is surrounded by four ligands in a distorted tetrahedral geometry. The coordinated dimethylamino group decreases the Lewis acidity 

Semi-empirical molecular orbital calculations using the INDO/S method have been carried out for organoscandium complexes of the general formula Cp 2ScX (X = C1, I, Me, CH2Ph, NHPh).549 The utility of electrospray mass spectrometry for the characterization of air-sensitive organolanthanides and related species has been demonstrated.550 A wide variety of lanthanide complexes, including divalent and trivalent compounds, neutral and 

The polymeric structure of the pentamethylcyclopentadienyl complex of thulium [Cp 2Tm(/r3-Cl)2K(THF)] is generated by triply bridging chloride ligands, with each chloride being connected to one Cp 2Tm bent metallocene unit and two K(THF) moieties in a T-shaped geometry around the chloride.557 Cp 2Tm(lll) complexes have also been isolated from reactions of TmI2(THF)2 with KCp. 344 Cp 2Nd(/r-Cl)2Na(DME)2 was obtained by the reaction 

The THF adducts display further chemistry and provide a system in which THF coordination and ring opening can be separately defined. This ring opening occurs over a period of days at room temperature in benzene, toluene, 

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The organometallic chemistry of scandium is generally similar to that of the later lanthanides. It thus forms a cyclopentadienyl ScCps that has mixed mono- and pentahapto-coordination like LuCps. An anionic methyl [Li(tmed)]3[M(CH3)6] is formed by scandium, as by the lanthanides. However, there are often subtle differences that should be borne in mind. The pentamethylcyclopentadienyl compound [ScCp 2Me] is a monomer but the lutetium compound is an asymmetric dimer [Cp 2Lu(/u.-Me)LuCp 2Me]. Similarly, whilst triphenylscandium is obtained as a bis(thf) adduct, [ScPh3(thf)2], which has a TBPY structure with axial thf molecules, the later lanthanides form octahedral [LnPh3(thf)3]. Triphenylscandium and the phenyls of the later lanthanides are made by different routes. 

An ether that would not undergo rearrangement to a 3-alkyl derivative during acid-catalyzed removal of — NH protective groups was required to protect the phenol group in tyrosine. Four compounds were investigated (9-cyclohexyl-, (9-isobomyl-, 0-[l-(5-pentamethylcyclopentadienyl)ethyl]-, and O-isopropyltyro-sine. 

Some years ago we were successful in our attempts to synthesize a Jt-complex with divalent silicon as the central atom. Starting from dihalogeno(pentamethylcyclopentadienyl)silanes, we have been able to prepare decamethylsilicocene (1) by reductive elimination processes [1]. Characteristic data concerning the synthesis, structure, and bonding of 1 have been published elsewhere together with preliminary results concerning the chemistry of this compound [2]. Here we describe some further progress in this field. 

Summarizing the available bonding information, decamethylsilicocene (1) is regarded as an electron-rich silicon(II) compound containing a hypercoordinated silicon atom which is sandwiched between two rather weakly 7i-bonded pentamethylcyclopentadienyl ligands and thus is effectively shielded the lone-pair orbital at silicon is part of the frontier orbitals of the molecule. 

Several compounds containing Tt-bonds show reactions with 1 which most likely proceed via [2+1] or [4+1] cycloaddition processes, but no detailed mechanistic studies have been performed so far. Not unexpectedly, the electron-rich species 1 preferentially reacts with electron-poor substrates, and ring-strained or dipolar intermediates rearrange or react further to more stable products in a sometimes rather complicated and surprising fashion. In a few cases even the pentamethylcyclopentadienyl substituents at silicon are involved in the reaction pathways. 

After a decade of research the basic principles in the chemistry of decamethylsilicocene (1) seem to be understood. This compound shows the reactivity of a nucleophilic silylene due to the fact that the Tt-bonded pentamethylcyclopentadienyl ligands are easily transferred to a-bonded substituents during the reaction. The steric requirements of these substituents permit reactions with bulky substrates. The migratory aptitude and the leaving-group character of the pentamethylcyclopentadienyl groups... 

The first isolable alkenetitanium complex, the bis(pentamethylcyclopentadienyl)-titanium—ethylene complex 5, was prepared by Bercaw et al. by reduction of bis(penta-methylcyclopentadienyl)titanium dichloride in toluene with sodium amalgam under an atmosphere of ethylene (ca. 700 Torr) or from ( (n-C5Mc5)2Ti 2(fJ-N2)2 by treatment with ethylene [42], X-ray crystal structure analyses of 5 and of the ethylenebis(aryloxy)trimethyl-phosphanyltitanium complex 6 [53] revealed that the coordination of ethylene causes a substantial increase in the carbon—carbon double bond length from 1.337(2) A in free ethylene to 1.438(5) A and 1.425(3) A, respectively. Considerable bending of the hydrogen atoms out of the plane of the ethylene molecule is also observed. By comparison with structural data for other ethylene complexes and three-membered heterocyclic compounds, the structures of 5 and 6 would appear to be intermediate along the continuum between a Ti(11)-ethylene (4A) and a Ti(IV)-metallacyclopropane (4B) (Scheme 11.1) as... 

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