Analysis of a Hydrodesulfurization Process. 3. Acid Cleavage of Thiaplatinacycles¹

Abstract

Reaction of the thiaplatinacyle [(Et3P)2Pt(C12H8S-C,S)] (3; derived from reaction of [Pt(Et3P)3] and dibenzothiophene (DBT)) with HCl gives largely 2-phenylthiophenol and a small amount of DBT. The thiaplatinacycle [(Et3P)2Pt(C8H6S-C,S)] (2; from benzothiophene (BT)) undergoes reaction with HCl to give 2,3-dihydrobenzothiophene (22%), a small amount of 2-vinylthiophenol, and BT, while the thiaplatinacycle [(Et3P)2Pt(C4H4S-C,S)] (1; from thiophene) regenerates thiophene with HCl; in each case the metal is found as [(Et3P)2PtCl2]. In contrast all the thiaplatinacycles react very similarly with HBF4 to give dinuclear [Pt2(Et3P)4(μ-SR)2](BF4)2 (7c, R = 2-phenylthiophenolate (from 3); 7b, R = 2-vinylthiophenolate (from 2); 7a, R = 1-thiolatobutadiene (from 1)). An X-ray structure determination of 7c confirmed the structure. Reaction of the dications 7a − c with HCl gave C4H6S (59%), 2-vinylthiophenol (83%), and 2-phenylthiophenol (91%), respectively.

C–S Bond Activation and Partial Hydrogenation of Thiophene by a Dinuclear Trihydride Platinum Complex

“…Thiophene was also identified in the reaction of IV, and it was the only additional product in the case of II, both results being consistent with reported data. [52] Overall, the reaction of II-V with HBF 4 or HCl does not involve activation of the second thiophenic C-S bond. Instead, these reactions allow the formation of thiols and, in the case of HCl, the recovery of platinum as [(dppp)-PtCl 2 ].…”

“…Identification of this complex was achieved on the basis of NMR spectroscopic data, which were fully consistent with those reported for the [(PEt 3 ) 4 Pt 2 (µ-SC 4 H 5 ) 2 ]-(BF 4 ) 2 analog, also obtained in a parallel reaction. [52] Remarkably, replacement of II by III in the above reaction led to the unprecedented complex [(dppp) 2 Pt 2 (µ-www.eurjic.orgSC 4 H 6 )](BF 4 ) 2 (V), whose formation involves the insertion of a proton in the thiophenic chain of III without cleavage of the dinuclear species. As shown in Scheme 3, this reaction is easily reversed by addition of a base (NaMeO, NEt 3 ).…”

“…The ease of formation of this complex in related systems is well known. [52] In the case of III-V, various thiols were also detected in the reaction mixture by CG-MS, as depicted in Scheme 3. Thiophene was also identified in the reaction of IV, and it was the only additional product in the case of II, both results being consistent with reported data.…”

“…The solid was unequivocally identified as [(dppp)PtCl 2 ] (65-80 % yield) by NMR spectroscopy. [72,73] The solution was shown to be composed mainly of thiophene in the case of II, thiapentadiene or an isomer thereof (C 4 H 6 S) and thiophene [52] in a 4:1 molar ratio for IV, and a mixture of HS-CH 2 -CH=CH-CH 3 [74] and HS-CH 2 -CH 2 -CH=CH 2 , [47] in 4:1 and 1:1 molar ratios, for III and V, respectively.…”

Reaction Chemistry of Complexes Containing PtH, PtSH, or PtS Fragments: From Their Apparent Simplicity to the Maze of Reactions Underlying Their Interconversion

“…These can be summarized as follows: 1) Essentially electron-rich Pt 0 and also Pt I complexes have been assayed 2) The first step of the HDS reaction usually leads to the insertion of platinum into the C À S bond and therefore to the formation of a six-membered thiaplatinacycle of general formula [Pt(h 2 -S,C-C a H b S)(P) 2 ] (P= phosphane; for T, a = b = 4; for BT, a = 8, b = 6; for BDT, a = 12, b = 8). [7] 3) The presence of protonic acids causes degradation of the thiaplatinacycle without achieving desulfurization of the initially coordinated organosulfur ligand; thus, acids with noncoordinating anions give rise to cleavage of the Pt À C bond and yield dinuclear thiolate complexes of formula [Pt 2 A C H T U N G T R E N N U N G (m-SR) 2 P 4 ] 2 + , while the reaction with HCl cleaves both the PtÀC and PtÀS bonds to afford the very stable [PtCl 2 P 2 ] species together with thiols and/or other sulfurcontaining organic compounds, [8] 4) In contrast, conversion of thiaplatinacycle over time [9] or its further reaction with various hydrides [7a,d] causes cleavage of the Pt-S-C linkage at the SÀC bond thus leading to the formation of dinuclear [Pt 2 A C H T U N G T R E N N U N G (m-S) 2 P 4 ] [9] or [Pt 2 A C H T U N G T R E N N U N G (m-S)A C H T U N G T R E N N U N G (P\P) 2 ], [7d] or mononuclear [Pt(H)(SH)P 2 ] species, [7a] which evidently involve desulfurization of the organic ligand.…”