Studies of high-valent vanadium complexes binding with non-innocent thiolato ligands / the cleavage of strong C-O and O-H bonds with assistance of hydrogen bonds

Abstract

In our effort to understanding high-valent vanadium sulfur chemistry two tris(thiolato)phosphine ligands [PS3”]H3 and [PS3*]H3 has been untilized to interact with high-valent vanadium species ([PS3”]H3=[P(C6H3-3-Me3Si-2-S)3]3- [PS3*]H3=[P(C6H3-3-Ph-2-S)3]3-) At this work several five vanadium-thiolate complexes have been obtained and characterized They are [V(PS3”)2][NEt4] (1a) [V(PS3*)2][NPr4] (1b) [VIV(PS2”SH)(PS3”)][PPh4] (2a) [VIV(PS3*)(PS2*SH)][NPent4] (2b) and [VIV(PS3*)2] [(NPr4)2] (3) The reactivity of them with air has been explored The evidences were supported by Ultraviolet-visible spectroscopies and ESI-MS studies The hepta-coordinated [VIV(PS2”SH)(PS3”)]- (2a) and [VIV(PS3*)(PS2*SH)]- (2b) proceed air oxidation to form the octa-coordinated [V(PS3”)2]- (1a) and [V(PS3*)2]- (1b) respectively The octa-coordinated [VIV(PS3*)2]2- (3) can be oxidized via one electron oxidation to form complex 1b by air oxidation or [Fe(C5H5)2][BF4] oxidation From ESI-MS studies complex 1a and 1b species with resonance forms between V(V)-thiolate and V(IV)-thiyl radical can reacted with H2O and form 2a and 2b by homolytic cleavage of the O-H bond In addition complex 1a and 1b also reacted with methanol via homolytic cleavage of O-H bond and C-O bond Consequently it led to the formation of 2a [VIV(PS3”)(PS2SCH3”)]- (4a) and 2b [VIV(PS3*)(PS2SCH3*)]- (4b) respectively The kinetic studies of 1a with a series of substrates such as H2O toluene CH3CN fluorene and THF have been investigated From the kinetic isotope effect (KIE) O-H bond cleavage in H2O is an important component of the rate-determining step It is interesting that 1a prefers to cleave stronger O-H bonds rather than C-H bonds This finding was proposed that the preorganization step via the assistant of the hydrogen bonding interaction between substrates and 1a plays a key role which reduces the activation energy barrier

Date of Award	2014 Nov 7
Original language	English
Supervisor	Hua-Fen Hsu (Supervisor)