Nitrogen-to-metal multiple bond functionalities: The reaction of calix[4]arene-W(IV) with azides and diazoalkanes

The [{calix[4]-(O)(4)}W(eta (2)-C6H10)], 2, has been used as a source of W-IV-d(2) center-bonded to an oxo surface, which has been modeled by the calix[4] arene tetraanion in the reaction with diazoalkanes and organic azides, The olefin is easily displaced by both substrates. The reaction with Ph2CN2 led to the formation of metallahydrazone, [{calix[4]-(O)(4)}W=N-NCPh2], 5, which binds (BuNC)-N-t inside the cavity, 6, or it can be reduced to a,dinuclear W-V derivative [W-W, 2.646(1) Angstrom], where the two metals are bridged by a diphenylhydrazido ligand in complex 7, [{calix[4]-(O)(4)}(2)W-2(mu -N-N=CPh2)(2)Na-2]. The reaction of 2 with organic azides (RN3) is strongly dependent on the nature of the R substituent at the azide functionality. The reaction with RN3 [R = SiMe3; CPh3] occurs at the metal in the exo position, leading to alkylimido derivatives [{calix[4]-(O)(4)}W=N-R] [R = SiMe3; 8; R = CPh3, 9], which bind inside the cavity ButNC, leading to 10 and 11 respectively. The reaction of 2 with PhN3, on the contrary, occurs inside the calixarene cavity, leading to the triazenido derivative [{mu -calix[4]-(O)(4)}(2)(W=N-N=NPh)(2)], 12. The results of a,with organic azides show that two different pathways are followed at the metal in the exo and endo positions. In the former case, for steric reasons, the 1,3 dipolar addition of the; azide to; the carbenoid metal precedes the formation of the alkylimido. In the case of PhN3, the size of the calix cavity prevents the same pathway. In the case of HN3 the reaction is supposed to proceed with HN3 binding the metal with the protonated nitrogen inside the cavity and decomposing to the imido functionality [{mu -calix[4]-(O)(4)}(2)(W=NH)(2)], 13. An alternative synthetic route to arylimido derivatives of W-VI has been reported, The reaction of [calix[4]-(ONa)(4)(THF)(2)] with [p-tolyl-N=WCl4] led to [mu -calix[4]-W=N-p-tolyl], 14, which is in equilibrium in solution with the corresponding dimeric form [{mu -calix[4]}(2)-W=N-p-tolyl], 15.