S-S bond reactivity in metal-perthiocarboxylato compounds

While M-percarboxylato species are elusive intermediates, their sulfur containing analogues are known in some cases. The feasibility of isolation of M-perthioacetato compounds allowed, in this work, to obtain new insights into the pathways that follow the reactivity of M-E-ER (E = O, S) fragments. Herein we report on the isolation of two new M-perthioacetato compounds: trans-[Pt(CH(3)CS(2)S)(2)] () and [Ni(CH(3)CSS)(CH(3)CS(2)S)] (), which have been fully characterized, including X-ray structures. Reactivity of these compounds towards PPh(3) has been studied combining UV-vis monitorization and NMR measurements. Overall the accumulated data suggest that the evolution of the perthioacetato ligand in complexes and by reaction with PPh(3) consists of a complex multistep pathway in which the sulfur transfer is preceded by electron transfer. Cyclic voltammetry measurements indicate that the transference of two electrons from the phosphorus to the sulfur atom is not concerted, suggesting that the first step of the reaction with PPh(3) is the monoelectronic electron transfer followed by P-S bond formation. The results presented here show a novel pathway in the field of S-S bond reactivity processes relevant in biological, synthetic systems and in hydrocarbon desulfurization processes.

Is 2.07 A a record for the shortest Pt-S distance? Revision of two reported X-ray structures

The comparison of the very similar compounds (Ph(3)P)(2)Pt(mu-S)(2)Pt(PPh(3))(2) (1) and (Ph(2)PyP)(2)Pt(mu-S)(2)Pt(PPh(2)Py)(2) (2) raises intriguing questions about the reliability of the reported Pt(2)S(2) core in 1, where the Pt-S bonds are the shortest ever reported. Also, the trans-annular S...S separation of 2.69 A is surprisingly shorter in 1 than in 2 (3.01 A), but no incipient coupling between two S(2-) bridges seems reasonable in this case. Various considerations lead to reformulate 1 as [(Ph(3)P)(2)Pt(mu-OH)(2)Pt(PPh(3))(2)](BF(4))(2), 3. The sets of cell parameters for 1 and 3 are not equal but two axes match, and the volume of 1 is exactly double. Simple matrices may be constructed to interconvert the direct and reciprocal crystalline cells, thus corroborating their identity of the compounds. It is concluded that, in the structure solution of 1, some atoms were either neglected (BF(4)(-) counterions) or ill identified (sulfido in place of hydroxo bridges), while the structure of 3 was solved by collecting only one-half of the possible reflections (hence, also the different space groups). A new preparation, crystallization and X-ray structure of 3 confirms the above points and dismisses any other theoretical conjecture about two electronically different Pt(2)S(2) cores in 1 and 2.

Aromatic C-F activation by complexes containing the {Pt2S2} core via nucleophilic substitution: a combined experimental and theoretical study

The C-F bond activation of perfluorobenzene and perfluoropyridine have been achieved by means of the complex [Pt(2)(mu-S)(2)(dppp)(2)], where dppp denotes 1,3-bis(diphenylphosphino)propane. The reaction with the first substrate requires a long time (five days) and high temperature (reflux in toluene) to yield [Pt(o-S(2)C(6)F(4))(dppp)] and [Pt(3)(mu(3)-S)(2)(dppp)(3)]F(2), and involves replacement of two fluorides in the ortho position. In contrast, the reaction with perfluoropyridine is much faster (15 min at 0 degrees C) yielding [Pt(2)(mu-S){mu-(p-SC(5)F(4)N)}(dppp)(2)]F, which implies the C-F activation in the para position with respect the pyridine nitrogen. The mechanism of both reactions has been studied computationally and the geometries of the transition states are consistent with an S(N)Ar mechanism where a sulfido bridging ligand replaces the fluoride anion. The energy barriers corresponding to the first and the second fluoride substitution are 131.7 and 137.1 kJ mol(-1) for perfluorobenzene and 85.9 and 142.7 kJ mol(-1) for perfluoropyridine, respectively. The different energy barrier of the first substitution explains the different experimental conditions required and the various products obtained for these reactions.

Pressure-Assisted Hetero- and Homodialkylation of Sulfide in [Pt2(μ-S)2(dppp)2]: One-Pot Conversion of {Pt2(μ-S)2} into {Pt2(SR)2} and {Pt2(SR)(SR′)}

Heterodialkylation of [Pt2(mu-S)2(dppp)2] (dppp = Ph2P(CH2)3PPh2) was achieved under high pressure (10 kbar). This enabled the synthesis of rare diplatinum complexes with structurally diverse thiolate bridges, such as [Pt2(mu-SC5H10CO2CH2CH3)(mu-SC3H7)-(dppp)2](PF6)2, which was crystallographically identified. Complete homodialkylation was also achieved under similar conditions (6 kbar at room temperature), thus permitting the isolation of [Pt2(mu-SC2H4CO2CH2CH3)2(dppp)2]-(PF6)2. The isolation of these complexes extends the applications of high-pressure chemistry to thiolato homo- and heterobridged complexes that are otherwise not accessible.

Alkylthio Bridged 44 cve Triangular Platinum Clusters: Synthesis, Oxidation, Degradation, Ligand Substitution, and Quantum Chemical Calculations

Acetylplatinum(II) complexes trans-[Pt(COMe)Cl(L)2] (L = PPh3, 2a; P(4-FC6H4)3, 2b) were found to react with dialkyldisulfides R2S2 (R = Me, Et, Pr, Bu; Pr = n-propyl, Bu = n-butyl), yielding trinuclear 44 cve (cluster valence electrons) platinum clusters [(PtL)3(mu-SR)3]Cl (4). The analogous reaction of 2a-b with Ph2S2 gave SPh bridged dinuclear complexes trans-[{PtCl(L)}2(mu-SPh)2] (5), whereas the addition of Bn2S2 (Bn = benzyl) to 2a ended up in the formation of [{Pt(PPh3)}3(mu3-S)(mu-SBn)3]Cl (6). Theoretical studies based on the AIM theory revealed that type 4 complexes must be regarded as triangular platinum clusters with Pt-Pt bonds whereas complex 6 must be treated as a sulfur capped 48 ve (valence electrons) trinuclear platinum(II) complex without Pt-Pt bonding interactions. Phosphine ligands with a lower donor capability in clusters 4 proved to be subject to substitution by stronger donating monodentate phosphine ligands (L' = PMePh2, PMe2Ph, PBu3) yielding clusters [(PtL')3(mu-SR)3]Cl (9). In case of the reaction of clusters 4 and 9 with PPh2CH2PPh2 (dppm), a fragmentation reaction occurred, and the complexes [(PtL)2(mu-SMe)(mu-dppm)]Cl (12) and [Pt(mu-SMe)2(dppm)] (13) were isolated. Furthermore, oxidation reactions of cluster [{Pt(PPh3)}3(mu-SMe)3]Cl (4a) using halogens (Br2, I2) gave dimeric platinum(II) complexes cis-[{PtX(PPh3)}2(mu-SMe)2] (14, X = Br, I) whereas oxidation reactions using sulfur and selenium afforded chalcogen capped trinuclear 48 ve complexes [{Pt(PPh3)}3(mu3-E)(mu-SMe)3] (15, E = S, Se). All compounds were fully characterized by means of NMR and IR spectroscopy, microanalyses, and ESI mass spectrometry. Furthermore, X-ray diffraction analyses were performed for the triangular cluster 4a, the trinuclear complex 6, as well as for the dinuclear complexes trans-[{Pt(AsPh3)}2(mu-SPh)2] (5c), [{Pt(PPh3)}2(mu-SMe)(mu-dppm)]Cl (12a), and [{{PtBr(PPh3)}2(mu-SMe)2] (14a).

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

The relevance of platinum in the reaction of thiophene and derivatives with homogeneous transition-metal complexes as models for hydrodesulfurization has led us to the study of the reaction chemistry of complexes containing Pt--H, Pt--SH, and Pt--S fragments. Exploration of the reactions triggered by addition of controlled amounts of Na2S or NaSH to [Pt2(H)2(mu-H)(dppp)2]ClO4 (1) has provided evidence of the formation of complexes [Pt2(mu-H)(mu-S)(dppp)2]ClO4 (2), [Pt(H)(SH)(dppp)] (3), [Pt2(mu-S)2(dppp)2] (4), [Pt2(mu-S)(dppp)2] (5) and [Pt(SH)2(dppp)], in which dppp denotes 1,3-bis(diphenylphosphanyl)propane. Consequently, complexes 1, 2, and 5 as well as the already reported 3, 4, and [Pt(SH)2(dppp)] have been obtained and fully characterized spectroscopically. Also the crystal structures of 1 and 2 have been solved. Complexes 1-5 constitute the main framework of the network of reactions that account for the evolution of 1 under various experimental conditions as shown in Scheme 1. Apparently, this network has complexes 2 and 4 as dead-ends. However, their reciprocal interconversion by means of the replacement of one bridging hydride or sulfide ligand in the respective {Pt(mu-H)(mu-S)Pt} and {Pt(mu-S)2Pt} cores enables the closure of the reaction cycle involving complexes 1-5. Theoretical calculations support the existence of the undetected intermediates proposed for conversion from 1 to 2 and from 3 to 2 and also account for the fluxional behavior of 1 in solution. The intermediates proposed are consistent with the experimental results obtained in comparable reactions carried out with labeled reagents, which have provided evidence that complex 1 is the source of the hydride ligands in complexes 2 and 3. Overall, our results show the strong dependence on the experimental conditions for the formation of complexes 1-5 as well as for their further conversion in solution.

Stable diplatinum complexes with functional thiolato bridges from dialkylation of [Pt2(µ-S)2(P–P)2] [P–P = 2 × PPh3, Ph2P(CH2)3PPh2]

The normally robust monoalkylated complexes [Pt(2)(mu-S)(mu-SR)(PPh(3))(4)](+) can be activated towards further alkylation. Dialkylated complexes [Pt(2)(mu-SR)(2)(P-P)(2)](2+) (P-P=2 x PPh(3), Ph(2)P(CH(2))(3)PPh(2)) can be stabilized and isolated by the use of electron-rich and aromatic halogenated substituents R [e.g. 3-(2-bromoethyl)indole and 2-bromo-4'-phenylacetophenone] and 1,3-bis(diphenylphosphino)propane [Ph(2)P(CH(2))(3)PPh(2) or dppp] which enhances the nucleophilicity of the {Pt(2)(mu-S)(2)} core. This strategy led to the activation of [Pt(2)(mu-S)(mu-SR)(PPh(3))(4)](+) towards R-X as well as isolation and crystallographic elucidation of [Pt(2)(mu-SC(10)H(10)N)(2)(PPh(3))(4)](PF(6))(2) (2a), [Pt(2)(mu-SCH(2)C(O)C(6)H(4)C(6)H(5))(2)(PPh(3))(4)](PF(6))(2) (2b), and a range of functionalized-thiolato bridged complexes such as [Pt(2)(mu-SR)(2)(dppp)(2)](PF(6))(2) [R= -CH(2)C(6)H(5) (8a), -CH(2)CHCH(2) (8b) and -CH(2)CN (8c)]. The stepwise alkylation process is conveniently monitored by Electrospray Ionisation Mass Spectrometry, allowing for a direct qualitative comparison of the nucleophilicity of [Pt(2)(mu-S)(2)(P-P)(2)], thereby guiding the bench-top synthesis of some products observed spectroscopically.

Methylation of [Pt2(μ-SR)(μ-S)(PPh3)4]: En Route to Mixed-Thiolato Bridged Complexes

Sequential and independent alkylation of [Pt2(mu-S)2(PPh3)4] by RX followed by methylation with Me2SO4 led to the first successful isolation of novel diplatinum complexes [Pt2(mu-SR)(mu-SCH3)(PPh3)4](PF6)2 (3) (R = CH2C6H5 (a), CH2CHCH2 (b), C5H10CO2CH2CH3 (c), C2H4CO2CH2CH3 (d), CH2CH2CN (e), C2H4CH(O)2C2H4 (f), and C2H4SC6H5 (g)) with asymmetric thiolato bridges. The synthetic methodology can tolerate a range of electronically and sterically contrasting thiolate substituents with different chemical functionalities. The X-ray crystal structures of 3 a-c, g confirm the unusual heterodialkylation with two different thiolato bridging ligands in a syn-exo conformation. A secondary product [Pt2(mu-SC2H4SC6H5)(mu-SCH3)(PPh3)3](PF6)2 (4), which arises from intramolecular phosphine displacement by the thio pendant at the neighboring SC2H4SC6H5 bridge, has been trapped and characterized. This is an unusual diplatinum complex with three different bridging thio ligands and three different phosphines. The heteroalkylation is screened in situ by ESI-MS, and the resultant spectral data provide a convenient guide for one-pot syntheses of {M2(SR)(SR')} from{M2S}. The isolation and X-ray crystal structure of a homoalkylated analogue [Pt2(mu-SCH3)2(PPh3)4](PF6)2 (6) is included for comparison.

Pt(ii) mono-carbonyl complexes of a cyclometallating 2-(2′-thienyl)-(pyridinato-C,3N′) ligand: nature and dynamics of the lowest excited state of the chloro- and thiolato-complexes

The synthesis of a cyclometallated Pt(II) thiolate carbonyl complex Pt(thpy)(CO)(mts), (thpy = 2-(2'-thienyl)-pyridinate, mts = methylthiosalicylate) is reported. A combination of emission and time-resolved infrared (TRIR) techniques revealed for both Pt(thpy)(CO)(mts) and its chloride analogue Pt(thpy)(CO)Cl the predominant intra 2-(2'-thienyl)-pyridinate 3pi pi* character of the lowest electronic excited state. The unusually short lifetime (780 ps) of the intraligand 3pi pi* lowest excited state of Pt(thpy)(CO)(mts) indicates that this electronic state is influenced by another close-lying excited state, probably charge-transfer in origin.

Influence of the terminal ligands on the redox properties of the {Pt2(µ-S)2} core in [Pt2(Ph2X(CH2)2XPh2)2(µ-S)2](X = P or As) complexes and on their reactivity towards metal centres, protic acids and organic electrophiles

In order to explore possible ways for modulating the unusually rich chemistry shown by complexes of formula [L2Pt(mu-S)2PtL2] we have studied the influence of the nature of the terminal ligand L on the chemical properties of the {Pt2(mu-S)2} core. The systematic study we now report allows comparison of the behaviour of [Pt2(dpae)2(mu-S)2](dpae = Ph2As(CH2)2AsPh2) (1) with the already reported analogue [Pt2(dppe)2(mu-S)2](dppe = Ph2P(CH2)2PPh2). Complex 1 as well as the corresponding multimetallic derivatives [Pt(dpae){Pt2(dpae)2(mu-S)2}](BPh4)2 2, [M{Pt2(dpae)2(mu-S)2}2]X2 (M = Cu(II), X = BF4 3; M = Zn(II), X = BPh4 4; M = Cd(II), X = ClO4 5; M = Hg(II), X = Cl 6 or X2 = Cl(1.5)[HCl2](0.5) 6') have been characterized in the solid phase and in solution. Comparison of structural parameters of 1 and 3-6' with those of the corresponding phosphine analogues, together with the results of the electrochemical study for 1, allow us to conclude that replacement of dppe by dpae causes a decrease in basicity of the {Pt2(mu-S)2} core. The study of the reactivity of 1 towards CH2Cl2 and protic acids has led to the structural characterization of [Pt(dpae)(S2CH2)] 9 and [PtCl2(dpae)] 10. Moreover, comparison with the reactivity of [Pt2(dppe)2(mu-S)2] indicates that the stability of the intermediate species as well as the nature of the final products in both multistep reactions are sensitive to the nature of the terminal ligand.