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Preparation of dimolybdenum cations with triply bridged cores [Mo2(μ-F)2(μ-X)(CO)4(PPh3)4]+(X  F, Cl, Br, OH), [Mo2(μ-Br)n(μ-OH)3−n(CO)4(PPh3)4]+(n= 1, 2) and ditungsten cations [W(μ-F)n(μ-Br)3−n(CO)4(PPh3)4]+crystal structure of [Mo2(μ-Br)(μ-F)2(CO)4(PPh3)4]F

Authors
Journal
Polyhedron
0277-5387
Publisher
Elsevier
Publication Date
Volume
13
Issue
4
Identifiers
DOI: 10.1016/s0277-5387(00)84740-3

Abstract

Abstract The reaction of Mo 2Br 2(CO) 2(PPh 3) 2 with aqueous NaBF 4 in CH 2Cl 2 leads to [Mo 2(μ-X)(μ-F) 2(CO) 4(PPh 3) 4] + (X  Br, F, Cl, OH). The initially formed bromide can be isolated under appropriate conditions and crystallographically characterized as the unusual fluroide salt [Mo 2(μ-Br)(μ-F) 2(CO) 4(PPh 3) 4]F (x hexane). The molecular unit is a triply bridged dimer with very long MoBr distances [2.694(3) and 2.693(3) Å], which are accounted for by the trans-influence of two nearly co-linear CO ligands (BrMOCO ca 165°). The bromide is fluxional, MoBr cleavage processes are evident from the variable temperature 31P NMR spectra. Under the reaction conditions the bromide is expelled leading to the formation of [Mo 2(μ-X(μ-F) 2(CO) 4(PPh 3) 4] + (X  F, Cl, OH). Under identical conditions WBr 2(CO) 2(PPh 3) 2 reacts to form [W(μ-F) n (μ-Br) 3− n (CO) 4(PPh 3) 4] + ( n = 1,2) while reaction of Mo 2Br 2(CO) 2(PPh 3) 2 with aqueous KPF 6 leads to the hydroxo bridged dimers [Mo 2(μ-Br) n(μ-OH) 3−n(CO) 4(PPh 3) 4] + ( n = 1,2).

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