ESIMS targeted synthesis of novel {Pt2S2} derivatives

Abstract

Electrospray ionisation mass spectrometry (ESIMS) was used to investigate ring- opening reactions of several epoxides with the nucleophilic dinuclear PtII complexes [Pt2(μ-E)2(PPh3)4] (E = S, 1a; Se, 1b) and several activated cyclopropanes, N - tosylaziridine, and thiirane with 1a. Epoxides cyclohexene oxide, styrene oxide, epibromohydrin, and 2,2-dimethyloxirane were found to undergo ring-opening when reacted with 1a and derivatives [Pt2(μ-S)(μ-S C6H10OH)(PPh3)4]BPh4 (5[BPh4], [Pt2(μ-S)(μ-S C8H8OH)(PPh3)4]BETI (6[BETI]), [Pt2(μ-S CH2CH(OH)CH2 μ-S)- (PPh3)4][PF6]2 (3[PF6]2), and [Pt2(μ-S)(μ-S CH2C(Me)2OH)(PPh3)4]BPh4 (7 [BPh4]) were respectively isolated and structurally characterised with 31P{1H} and 195Pt nu- clear magnetic resonance (NMR) spectroscopy, and for 5, 3 and 7 single crystal X- ray diffraction (XRD) studies. 6 was found to be a mixture of isomers, and crystals suitable for a single crystal XRD experiment were not obtained. Both styrene oxide and epibromohydrin underwent ring-opening when reacted with 1b and the respec- tive derivatives [Pt2(μ-Se)(μ-Se C8H8OH)(PPh3)4]+ and [Pt2(μ-Se CH2CH(OH)- CH2 μ-Se)(PPh3)4]2+ were characterised by ESIMS. The fully substituted epoxide 2,3-dimethyl-2,3-epoxybutane did not undergo ring-opening when treated with 1a in refluxing methanol for several hours. 5,6-Epoxy-5,6-dihydro-[1,10]-phenanthro- line resulted in ring-opening when reacted with 1a however the resulting deriva- tive [Pt2(μ-S)(μ-S C12H8N2O)(PPh3)4]+ (8) was found to decompose readily in solution. Cyclopropanes cyclopropyl methyl ketone and trans-1,2-dibenzoylcyclo- propane did not undergo ring-opening when reacted with 1a. The more activated 2,2,3,3-tetracyanocyclopropane and diethylcyclopropane-1,2-dicarboxylate both re- i sulted in ring-opening when reacted with 1a resulting in the isolation of deriva- tives [Pt2(μ-S)(μ-S C(CN)2)(PPh3)4] (12) and [Pt2(μ-S)(μ-S C2H4CH(CO2Et)2)- (PPh3)4]BETI (11[BETI]) respectively which were structurally characterised by het- eronuclear NMR spectroscopy (12 31P{1H}, 195Pt{1H}; 11 1H, 31P{1H}) and single crystal XRD studies. 12 was found to have a carbanionic center and is proposed to result from an intramolecular rearrangement of the initially formed [Pt2(μ-S)(μ- S C(CN)2C(CN)2CH3)(PPh3)4]+ (31). Bromomethylcyclopropane did not result in ring-opening when reacted with 1a, however alkylation resulted in [Pt2(μ-S)(μ- S CH2C3H5)(PPh3)4]+ (10) which was isolated as 10[BPh4] and structurally char- acterised by 31P{1H}-NMR spectroscopy and single crystal XRD. 10[BPh4] did not undergo ring-opening when refluxed in methanol. N -tosylaziridine resulted in the ring-opened derivative [Pt2(μ-S)(μ-S C2H4NHtosyl)(PPh3)4]+ (13) when reacted with 1a and was isolated as 13[PF6] and structurally characterised by 31P{1H}-NMR spectroscopy and single crystal XRD. Thiirane appeared to rapidly undergo ring- opening when reacted with 1a however only polymeric decomposition species were detected by ESIMS. The previously reported reaction of 1a and 2-chloro-N -methyl- pyridinium iodide (14[I]) was reexamined. Salts of 14 sans iodide were synthesized using alkylating agents trimethyloxonium tetrafluoroborate or dimethyl sulfate giv- ing 14[BF4] or 14[CH3SO4] respectively. The reaction of 1a and 14 was found to result in the dicationic complex [Pt2(μ-S)(μ-S C6H7N)(PPh3)4]2+ (2) which was isolated as the bis-hexafluorophosphate salt 2[PF6]2 and structurally characterised with 31P{1H}-NMR spectroscopy, 195Pt{1H}-NMR spectroscopy, and single crystal XRD. The 2-mercapto-N -methylpyridinium ligand in 2 was proposed to be an ex- cellent leaving group and the reaction of 2 with excess bromide resulted in the isola- tion of the mixed-bridged complex [Pt2(μ-S)(μ-Br)(PPh3)4]BPh4 (16[BPh4]) which was structurally characterised with 31P{1H}-NMR spectroscopy and single crystal XRD. The thiols N -acetylcysteamine, 2-mercapto-1-methylimidazole, and 2-amino- thiophenol were reacted with 2 to give [Pt2(μ-S)(μ-S C2H4NHC( O)CH3)(PPh3)4]+ (38), [Pt2(μ-S)(μNS-S C3H2N2CH3)(PPh3)4]+ (17), and [Pt2(μ-S)(μ-S C6H4NH2)- ii (PPh3)4]+ (39) respectively which were isolated as 38[BF4], 17[BETI], and 39[BF4]. 17[BETI] was structurally characterised (31P{1H}-NMR spectroscopy, 195Pt{1H}- NMR spectroscopy, single crystal XRD) and found to contain a novel 6-membered Pt-S-Pt-S-C-N heterocycle. 38 was characterised using NMR spectroscopy (1H, 13C, 31P{1H}, and 195Pt{1H}). 39 was characterised using 31P{1H}-NMR spectroscopy. 2 was reacted with selenourea resulting in the detection by ESIMS of the mixed- bridged [Pt2(μ-S)(μ-Se)(PPh3)4]+ (23) which decomposed over the course of several days to 1a and 1b. When the diaryldichalcogenides Ph2Se2, Ph2Te2, di-4-ethoxy- phenyl-ditelluride were reduced with hydrazine to the corresponding chalcogeno- late anion and reacted with 2, substitution of the 2-mercapto-N -methylpyridinium zwitterion resulted and mixed-bridged derivatives [Pt2(μ-S)(μ-E R)(PPh3)4]+ (E- R = Se-Ph, 18; Te-Ph, 47; Te-C6H4-OEt, 19) detected by ESIMS. 18[BF4] and 19[BF4] were isolated and structurally characterised with heteronuclear NMR spec- troscopy (31P{1H}-NMR, 195Pt{1H}-NMR) and single crystal XRD. A bridging hy- drazine species was observed when reacting 2 with hydrazine reduced diaryldichalco- genides, and the reaction between 2 and hydrazine was found to result in [Pt2- (μ-S)(μ-NH NH2)(PPh3)4]+ (21) which was isolated as 21[BPh4] and structurally characterised with 31P{1H} and 195Pt{1H}-NMR spectroscopy