Mononuclear and dinuclear molybdenum and tungsten complexes of p-tert-butyltetrathiacalix[4]arene and p-tert-butyltetrasulfonylcalix[4]arene: facile cleavage of the calixarene ligand framework by nickel

Abstract

The reactivity of p-tert-butyltetrathiacalix[4]arene, [S4CalixBut(OH)4], and p-tert-butyltetrasulfonylcalix[4]arene, [(SO2)4CalixBut(OH)4], toward Mo(PMe3)5H2, Mo(PMe3)6, and W(PMe3)4(eta2-CH2PMe2)H has been used to synthesize a series of mononuclear molybdenum and tungsten calixarene compounds that feature both coordinatively saturated and unsaturated metal centers, such as [S4CalixBut(OH)2(O)2]M(PMe3)3H2 (M = Mo, W), [(SO2)4CalixBut(OH)2(O)2]M(PMe3)3H2, [S4CalixBut(OH)2(O)2]Mo(PMe3)3, [(SO2)4CalixBut(OH)2(O)2]Mo(PMe3)3, and [(SO2)4CalixBut(OH)(O)3]M(PMe3)3H. Comparison with the related {[CalixBut(OH)2(O)2]M} complexes indicates that the chemistry of the system is strongly influenced by the nature of the calixarene linker, that is, CH2, S, and SO2. For example, in contrast to the methylene-bridged calixarene system, the thiacalixarene and sulfonylcalixarene systems readily coordinate a second metal center to form homo- and heterodinuclear complexes, namely {[S4CalixBut(O)4]}[M(PMe3)3H2]2, {[(SO2)4CalixBut(O)4]}[Mo(PMe3)3H2]2 and {[S4CalixBut(O)4]}[Mo(PMe3)3H2][W(PMe3)3H2]. Of most interest, incorporation of nickel into [S4CalixBut(OH)2(O)2]M(PMe3)3H2 using Ni(PMe3)4 results in cleavage of a C- bond to give [(SArButOH)(SArButO)3][M(PMe3)3H2][Ni(PMe3)2], an observation that is of relevance to the role that nickel plays in hydrodesulfurization catalysis.