Organomolybdenum(VI) and lithium organomolybdate(VI) and -(V) complexes with C,N-chelating aminoaryl ligands

The synthesis and characterization of new, five-coordinate molybdenum bis(i midoaryl) complexes [Mo(NAr)(2)(C-N)X] (Ar = C(6)H(3)i-Pr-2-2,6; C-N = [C6H 4(CH2NMe2)-2](-); X = Cl (1), Me (2), Et (3), Bu (4), CH2SiMe3 (5), (p-toly l) (6), (C-N) (7)) is reported. The solid-state structure of 2 has been elu cidated by single-crystal X-ray analysis. Compounds 2, 3, 4, 5, and 6 react with alkyl- or aryllithium compounds to form lithium molybdate(VI) derivat ives, of which [Li(DME)Mo(NAr)(2)( C-N)(Me)(p-tolyl)] (10), formed by the r eaction of 2 with [Li(p-tolyl)], has been structurally (X-ray) characterize d. Thermal activation of these lithium molybdates leads to the formation of paramagnetic lithium molybdate(V) compounds instead of the anticipated mol ybdenum(VI) alkylidenes. The actual temperature (between -10 and 80 degrees C) at which paramagnetic Mo(V) radical anions are formed is dependent on b oth the type of alkyl or aryl substituent (introduced via LiR') and the sol vent. The synthesis of [LiMo(NAr)2(C-N)(2)] (11) by reaction of 7 with n-Bu Li is described. The initially formed lithium molybdate(VI) compound [Li(DM E),Mo-n(NAr)(2)(C-N)(2)(n-Bu)] is not stable at room temperature and conver ts directly to the lithium molybdate(V) derivative 11. The solid-state stru cture of fl has been elucidated by single-crystal X-ray analysis. None of t he lithium molybdate(VI) nor -(V) derivatives described herein are active c atalysts for ROMP, as thermal activation does not lead to the formation of a molybdenum alkylidene complex but to electron transfer and formation of a lithium molybdate(V) instead. However, upon treatment of a solution of any of the molybdate(TT) derivatives with dry air, catalytic ROMP is observed.