Ethylenebis titanium complexes

The basic compound of Brintzinger s ansa-titanocene complexes is ethylenebis-(tetrahydroindenyl)titanium dichloride, (EBTHI)TiCl2. Further analogues ((EBTHI)TiH, (EBTHI)Ti(Me)2, and (EBTHI)Ti(CO)2) have been wddely used for asymmetric hydrogenation, hydrosilylation, and Pauson-Khand reaction (121). Novel optically active titanium complexes containing a linked amido-cyclopentadienyl ligand have been developed and used for asymmetric hydrogenation (122). 

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... 

Employing silyated quadridentate Schiff bases, e.g. 0,0 -bis(trimethylsilyl)-JV,JV -ethylenebis(salicylideneimine),105 a range of titanium(IV) complexes Ti(j/5-C5H5)(salen)L (25 L = Cl, OMe, SMe, NMe2, SnPh3, acac) have been prepared. 

Reduction of dichloro-NN -ethylenebis(salicylideneiminato)titanium(rv) by BH4 gives a compound which analyses as [Ci6Hi N202Ti(BH3)2]2. The crystal structure of this showed the presence of amine-boranes as donor groups, and the novel unit (19) in the complex. ... 

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