C À S bonds are known to be efficiently activated by transition metals and lead, through cleavage of C À S bonds, to novel sulfur compounds or sulfide complexes. This transformation allows insight into the related processes that may occur during heterogeneous catalytic processes. [1] The platinum(0)-mediated C À S bond cleavage reactions have been well studied and are established for the C(sp 2 ) À S bonds of thiophene, [2] thioester, [3] and vinyl sulfide. [4] However, to the best of our knowledge, a simple C(sp 3 )ÀS bond activation with platinum(0) complexes has never been explored. Meanwhile, oxametallacycles are of great interest because of their unique structure and catalytic activity. Although there are several reports on the preparation and application of oxametallacycles containing nickel [5,6] or palladium, [7] the chemistry of oxaplatinacycle is limited. Pregosin and co-workers have reported the synthesis of five-membered acyl-(oxa)platinacycle 1 by the reaction of salicylaldehyde with K 2 PtCl 4 in the presence of PPh 3 . [8] Also, Sweigart and coworkers have described that the platinum(0)-mediated C À O bond cleavage reaction of benzofuran afforded the sixmembered oxaplatinacycle 2. [9] As a four-membered analogue, Sharp and co-workers have reported the formation and unique reactivity of platinaoxetane 3 (cod = 1,5-cyclooctadiene). [10] Herein, we report the cleavage of C(sp 3 )ÀS and O À H bonds of 2-hydroxybenzyl sulfide derivatives 4 mediated by platinum(0). This process led to an unusual formation of novel five-membered 1,2-oxaplatinacycles (5 a, 5 b; see Scheme 2 for structures). We also describe the thermal reaction of 5 a involving the unexpected P À C/Pt À O metathesis.We have examined the coordination ability of [OSSO]type diphenolate 6 [11] as a chelate ligand toward transitionmetal complexes. When 6 was treated with 3 equivalents of [Pt(h 2 -nb)(PPh 3 ) 2 ] in toluene, [12] the activation of both benzylic C À S and O À H bonds [13] in 6 occurred unexpectedly and gave novel 1,2-oxaplatinacycle 5 b and cis-(dithiolato)Pt II complex 7 [14] in 72 % and 69 % yields, respectively (Scheme 1). On monitoring this reaction that was carried out in a sealed NMR tube, the generation of H 2 was observed by 1 H NMR spectroscopy (d = 4.21 ppm in C 6 D 6 ).To elucidate the general validity of this platinum(0)mediated benzylic CÀS and phenolic OÀH bond activation, we examined the reactions of alkyl or aryl 2-hydroxybenzyl sulfides 4 a-d, which have only half the framework of 6 (i.e. [Pt(h 2 -nb)(PPh 3 ) 2 ]). The reactions readily proceeded in toluene at room temperature and gave the corresponding 1,2-oxaplatinacycles 5 a or 5 b in 55-84 % yields, together with polymeric thiolato Pt II complexes [Pt(SR) 2 ] n as insoluble materials (Scheme 2). When 4 b was allowed to react with [Pt(h 2 -nb)(PPh 3 ) 2 ] in the presence of an excess amount of PPh 3 in toluene at room temperature, 5 a and the bis(thiolato) Pt II complex cis-[Pt(SPh) 2 (PPh 3 ) 2 ] 8, [15] instead of polymeric thiolato Pt complexes, were formed...
