No abstract

The dinuclear and trivalent complex {[(Me 3 Si)NCH 2 CH 2 ] 2 N(Me 3 Si)} 2 V 2 (µ-Cl) 2 (1) is the precursor to mono-and dinuclear alkyl derivatives that are thermally stable. For example, treatment with MeLi gives a stable methyl derivative, probably isostructural with 1, which upon further treatment with pyridine affords the mononuclear complex {[(Me 3 Si)NCH 2 -CH 2 ] 2 N(Me 3 Si)}V(CH 3 )(pyridine) (2). However, reaction of 1 with Me 2 AlCl, AlMe 3 , or PMAO-IP yields the tetrametallic species { 3), where the central core of 1 was preserved except for the vanadium centers, which were reduced to the divalent state. The two Me 2 Al residues remained coordinated to the amido ligand. The reduction of vanadium to the divalent state relates to the relatively short life of 1 as an ethylene polymerization catalyst. A similar reaction of 1 with AlCl 3 resulted in disproportionation forming the tetravalent complex {[(Me 3 Si)NCH 2 CH 2 ] 2 N(Me 3 Si)}VCl 2 AlCl 3 (4) and the pentanuclear mixed 5). The fact that complex 5 contains a divalent vanadium atom stripped of its ligand system indicates that two different reaction mechanisms are operating to reduce the vanadium center and that the differing Lewis acidity of the two aluminum species is the determining factor.

The new diamagnetic Ti(III) complex (CyNC(H)NCy)(4)Ti(2)Cl(2).2THF (1) containing a short Ti-Ti distance was prepared and crystallographically characterized. Ab initio unrestricted Hartree-Fock calculations suggested the presence of a Ti-Ti bonding interaction. Crystal data for 1 are as follows: C(60)H(108)N(8)Ti(2)Cl(2)O(2), FW 1140.27, monoclinic Pn, a = 10.4688(9) Å, b = 14.4579(9) Å, c = 21.421(1) Å, beta = 100.227(9) degrees, V = 3190.6(7) Å(3), Z = 2, D(calc) = 1.187 g/cm(3), F(000) = 1236, &mgr; = 3.75 cm(-)(1), T = -158 degrees C, R = 0.074, R(w) = 0.075, GOF = 3.64 for 540 parameters and 4630 reflections out of 5771 unique reflections observed.

Reaction of [(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]VCl 2 (1) with 2 equiv of MeLi yielded the corresponding trivalent vanadium derivative [(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]-VMe 2 (3). Subsequent hydrogenolysis afforded the dinuclear hydride complex {[(Me 3 Si)Nd P(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]V} 2 (µ-H) 2 ( 4), where reduction of the metal center to the divalent state had occurred. Hydrogenolysis of solutions of 1 previously treated with lower than stoichiometric amounts of MeLi afforded the two mixed-valent V(II)/V(III) hydrides 7). Hydrolysis of the divalent 4 afforded the trivalent and dinuclear {[(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 d(µ-N)]V(OSiMe 3 )} 2 (5), featuring migration of the Me 3 Si group from the N to the O atom of one incoming molecule of water.

Reaction of the diamagnetic cluster (TMEDA)2Nb2Cl5Li(TMEDA) with the (3,5-Me2Ph)(Ad)NLi (Ad = adamantyl) amide led to a rare case of C−N bond activation and formation of tetravalent, dinuclear, and diamagnetic {(3,5-Me2Ph)(Ad)N]Nb(3,5-Me2Ph)}2(μ-NAd)2·ether (1) containing a Nb−Nb single bond. Conversely, a similar reaction carried out with [Cy2NLi]4 (Cy = cyclohexyl) yielded dinuclear {[(Cy2N)2Nb]2(μ-N)}(μ3-N)Li(TMEDA) (2).