Scandium cyclopentadienyls

The molecular structure of Sc(C5H6)3 (Fig. 8) exhibits both r - and bridging jji-cyclopentadienyl rings. Each scandium is pentahapto bound to two terminal... 

L5 = carbonyl- ( ]5-cyclopentadienyl)-nitrosotriphenylphosphinomolybdenum trichlorotin. L = dichlorotetrakis(tetrahydrofuran)scandium(III). 

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. 

Cl2Li02ScSi4CjoH , Scandium, bis[i) -l,3-bis(trimethyl ilyl)cyclopentadienyl]di- x-chloro-bis(tetrahydrofuran)lithium-, 27 170... 

Si4Cl2Sc2C44HK4, Scandium, tetrakis[ti -l,3-bis(trimethylsilyl)cyclopentadienyl]di-p,-chloro-di-, 27 171... 

Phosphorus, arsenic, antimony, and bismuth ligands have been discussed in CCC (1987).153 Complexes containing bonds between scandium, yttrium, and phosphorus or arsenic have been reviewed,154 as have complexes with neutral phosphorus ligands.155 Many of the complexes described in these reviews contain organic substituents such as cyclopentadienyl or alkyl groups. 

The reaction of a cyclopentadienyl scandium acac complex [(C5Me5)Sc(acac)3] with tetra-phenyldisiloxanediol (Ph2Si0H)20 results in displacement of the cyclopentaidiene group and the formation of a siloxane complex, [ (Ph2SiO)2OSc(acac)2 2Sc(acac)].19... 

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... 

The scandium, yttrium, or lanthanide atoms in these compounds evidently form such bridges to make better use of their valence shell electrons and orbitals. (C5H5)2MR monomers would contain only 14 valence shell electrons (five from each cyclopentadienyl ligand, one from the alkyl group in addition to the three metal electrons), well short of the 16 or preferably 18 valence shell electrons normally present in stable organotransition metal compounds " dimerization to (C5H5)2M(p-R)2M(C5H5)2 raises the valence shell electron count to 16 and uses a metal orbital that would be vacant in the monomer. 

The hydrides of the early lanthanides may be stabilised by bulky substituted cyclopentadienyl ligands, such as 1,3-di-tert-butylcyclopentadienyl and penta-methylcyclopentadienyl. The late lanthanide hydrides [(C5H4R)2LnH(L)]2, Ln = Lu, Er and Y, may be obtained with less bulky cyclopentadienyl ligands. Only monocyclopentadienyl hydrides of scandium and yttrium of general formula [(CjMe4R)LnH(L)] have been reported [6]. Most of the lanthanide hydrides... 

Complexes of metals in low oxidation state induce rearrangements and isomeiizations of strained and unsaturated hydrocarbons which occur with C-C bond cleavage [68] (Scheme IV.35). 1,4-Pentadiene can be isomerized (with splitting C-C bonds) under the action of hydride cyclopentadienyl complexes of scandium [69a]. Hydrogenolysis of C-C bonds in saturated hydrocarbons has been described in the presence of the system H2-Re2(CO)io-AI2O3 [69b, ... 

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