MIGRATORY APTITUDE OF THE ZR-C FUNCTIONALITIES BONDED TO A MACROCYCLIC STRUCTURE - THERMALLY-ASSISTED AND SOLVENT-ASSISTED INTRAMOLECULAR AND INTERMOLECULAR MIGRATIONS IN L(DIBENZOTETRAMETHYLTETRAAZAANNULENE)ZIRCONIUM(IV)

The Zr-C bond chemistry and, particularly, its migration properties ha ve been investigated where the metal is bonded to the dibenzotetrameth yltetraaza[14]annulene (tmtaa) dianion in the model complexes cis-[Zr( tmtaa)R(2)]. In this respect the [Zr(tmtaa)] fragment has been analyze d in comparison with the well-known [cp(2)Zr] moiety, with the support of an extended Huckel analysis. The synthesis of [Zr(tmtaa)R(2)] (R = Me, 2; R = CH(2)Ph, 3) from [Zr(tmtaa)Cl-2] (1) has been achieved und er highly controlled reaction conditions. Complexes 2 and 3 are therma lly labile, and one of the alkyl groups undergoes a thermally-induced migration to one of the imino groups, leading to a trianionic ligand [ Zr(R-tmtaa)R] (R = Me, 4; R = CH(2)Ph, 5). The nature of such complexe s has been elucidated by an X-ray analysis on the THF-solvated form of 4, [Zr(Me-tmtaa)(Me)(THF)] (6). Nucleophiles are even more effective in inducing the alkyl migration to the ligand. In the presence of THF or pyridine 5 may be easily converted to [Zr(R(2)-tmtaa)] (R = CH(2)Ph , 7), in which both alkyl groups have migrated to the imino groups of the ligand. The use of an excess of LiMe during the alkylation of 1 le d to the formation of [Zr(Me(2)-tmtaa)...Li(THF)(2)] (8) via the inter mediacy of 4. Complex 8 is a bifunctional carrier of Lih le. The gener al consequences of two electrophilic sites on the ligand, eventually, in competition with the electrophilic metal have been analyzed. The ne t charge and electrophilic index are significantly higher for the meta l in [Cp(2)Zr](2+) than in [Zr(tmtaa)](2+). The relatively higher ther mal inertness of 3 allowed us to study the migration of the alkyl grou p toward the unsaturated incoming nucleophiles, Bu(t)NC and CO. The re action of 3 with Bu(t)NC led to the formation of the bis(eta(2)-iminoa cyl) compound [Zr(tmtaa)(eta(2)-C(Me)=NBu(t))(2)]. The four low-lying d orbitals can accommodate the two eta(2)-iminoacyl groups. The reacti on of 3 with CO gave [Zr(tmtaa)(eta(2)-OC(CH(2)Ph)(2))] (11) via the i ntermediacy of a very reactive oxycarbene eta(2)-acyl compound and ult imately gave 12 and 13, illustrating the reactivity of both zirconium and the iminato carbons in the [Zr(tmtaa)] fragment. The crystallograp hic details are as follows: 3 is orthorhombic, space group Pnma, a = 1 6.028(3) Angstrom, b = 20.666(4) Angstrom, c = 9.018(2) Angstrom, alph a = beta = gamma = 90 degrees, Z = 4, and R = 0.063. 6 is monoclinic, space group P2(1)/n, a = 19.859(5) Angstrom, b = 14.771(5) Angstrom, c = 9.072(4) Angstrom, alpha = gamma = 90 degrees, beta = 93.85(3)degre es, Z = 4, and R = 0.034. 7 is monoclinic, space group C2/c, a = 23.60 8(6) Angstrom, b = 9.529(3) Angstrom, c = 19.050(4) Angstrom, alpha = gamma = 90 degrees, beta = 99.30(2)degrees, Z = 4, and R = 0.046. 10 i s triclinic, space group P (1) over bar, a = 12.800(4) A, b = 15.795(5 )Angstrom, c = 11.758(1) Angstrom, alpha = 91.8(2)degrees, beta = 93.5 6(1)degrees, gamma = 97.81(2)degrees, Z = 2, and R = 0.042.