Dedicated to Professor Renji Okazaki on the occasion of his 70th birthdayOxidative additions of cyclic and acyclic disulfides and their oxides to platinum(0) complexes are a topic of recent research. [1][2][3] However, analogous reactions of selenium compounds are limited to diselenides. [3,4] For example, in the diselenation of terminal acetylenes with diselenides in the presence of palladium(0) and platinum(0) complexes, [5,6] diselenolato complexes have been proposed as the intermediates. As far as we know, there are no reports on analogous reactions for oxides of diselenides such as selenoseleninates (RSe(O)SeR), a major reason for which must be that only few isolable selenoseleninates are known. [7, 8] It is important to investigate their reactivity toward low-valent transition-metal complexes and the nature of the resulting selenium metal complexes in relation to the corresponding chemistry of sulfur.Previously we reported the preparation of selenoseleninate 1 by dehydration of selenenic acid 2 or oxidation of diselenide 3 (Scheme 1).[7] Selenoseleninates 1 and 4 are the only such species isolable under ambient conditions. Herein we report the reactions of 1 and its related compounds with a platinum(0) complex. We unexpectedly observed the formation of a five-membered selenaplatinacycle by intramolecular C À H activation.[9] The chemistry of chalcogenametallacycles is also interesting in relation to the mechanistic study of homogeneous hydrodesulfurization of crude oil distillates. The formation of thiaplatinacycles 5[10] and selenametallacycles 6[11] by insertion of low-valent transition metals into C À S and C À Se bonds of the thiophene and selenophene derivatives, respectively, has been revealed.We first examined the reaction of selenoseleninate 1 with [Pt(PPh 3 ) 2 (h 2 -C 2 H 4 )] (7) in the expectation of obtaining the corresponding selenenato selenolato platinum(II) complex [Pt(SeTrip){Se(O)Trip}(PPh 3 ) 2 ]. However, when 1 was treated with 1.1 molar equivalents of 7 in toluene at room temperature, we obtained an unexpected compound (8, 0.72 molar equiv) together with diselenide 3 (0.30 molar equiv, 30 %) [Eq. (1)]. In the 31 P NMR spectrum of the compound, two doublets with accompanying satellite signals from the 195 Pt isotope are observed at d = 22.7 (d, 2 J(P,P) = 20.4 Hz, 1 J(Pt,P) = 1833 Hz) and 25.3 ppm (d, 2 J(P,P) = 20.4 Hz, 1 J-(Pt,P) = 3276 Hz). In the 1 H NMR spectrum, a characteristic signal appears at d = 5.81-5.88 ppm (m, 1 H). The structure was finally shown by X-ray crystallography to be selenaplatinacycle 8 (Figure 1). The signal in the 31 P NMR spectrum at d = 25.3 ppm with 1 J(Pt,P) = 3276 Hz was assigned to the Scheme 1. Formation of selenoseleninates from selenenic acids and diselenides.

The oxidatiVe addition reaction of the oVercrowded selenol TripSeH (1; Trip ) 9-triptycyl) with [Pd(Ph 3 P) 4 ] in toluene produced a noVel dinuclear palladium(I) complex with bridging selenolato ligands, [{Pd(PPh 3 )} 2 (µ-SeTrip) 2 ] (2). In contrast, the reaction of 1 with [Pd(dppe) 2 ] in toluene resulted in the formation of the fiVe-membered selenapalladacycle [Pd(η 2 (C,Se)-Trip)(dppe)] (3).

Dedicated to Professor Renji Okazaki on the occasion of his 70th birthdayOxidative additions of cyclic and acyclic disulfides and their oxides to platinum(0) complexes are a topic of recent research. [1][2][3] However, analogous reactions of selenium compounds are limited to diselenides. [3,4] For example, in the diselenation of terminal acetylenes with diselenides in the presence of palladium(0) and platinum(0) complexes, [5,6] diselenolato complexes have been proposed as the intermediates. As far as we know, there are no reports on analogous reactions for oxides of diselenides such as selenoseleninates (RSe(O)SeR), a major reason for which must be that only few isolable selenoseleninates are known. [7, 8] It is important to investigate their reactivity toward low-valent transition-metal complexes and the nature of the resulting selenium metal complexes in relation to the corresponding chemistry of sulfur.Previously we reported the preparation of selenoseleninate 1 by dehydration of selenenic acid 2 or oxidation of diselenide 3 (Scheme 1).[7] Selenoseleninates 1 and 4 are the only such species isolable under ambient conditions. Herein we report the reactions of 1 and its related compounds with a platinum(0) complex. We unexpectedly observed the formation of a five-membered selenaplatinacycle by intramolecular C À H activation.[9] The chemistry of chalcogenametallacycles is also interesting in relation to the mechanistic study of homogeneous hydrodesulfurization of crude oil distillates. The formation of thiaplatinacycles 5[10] and selenametallacycles 6[11] by insertion of low-valent transition metals into C À S and C À Se bonds of the thiophene and selenophene derivatives, respectively, has been revealed.We first examined the reaction of selenoseleninate 1 with [Pt(PPh 3 ) 2 (h 2 -C 2 H 4 )] (7) in the expectation of obtaining the corresponding selenenato selenolato platinum(II) complex [Pt(SeTrip){Se(O)Trip}(PPh 3 ) 2 ]. However, when 1 was treated with 1.1 molar equivalents of 7 in toluene at room temperature, we obtained an unexpected compound (8, 0.72 molar equiv) together with diselenide 3 (0.30 molar equiv, 30 %) [Eq. (1)]. In the 31 P NMR spectrum of the compound, two doublets with accompanying satellite signals from the 195 Pt isotope are observed at d = 22.7 (d, 2 J(P,P) = 20.4 Hz, 1 J(Pt,P) = 1833 Hz) and 25.3 ppm (d, 2 J(P,P) = 20.4 Hz, 1 J-(Pt,P) = 3276 Hz). In the 1 H NMR spectrum, a characteristic signal appears at d = 5.81-5.88 ppm (m, 1 H). The structure was finally shown by X-ray crystallography to be selenaplatinacycle 8 (Figure 1). The signal in the 31 P NMR spectrum at d = 25.3 ppm with 1 J(Pt,P) = 3276 Hz was assigned to the Scheme 1. Formation of selenoseleninates from selenenic acids and diselenides.

p-Toluoyl 9-triptycyl diselenide (9) wasprepared by reaction of Se-9-triptycyl triptycene-9-selenoseleninate (7)