Several tricyclic phenoxasilin and phenazasiline heterocycles were synthesized from the corresponding 2,2‘-dilithio-diphenyl ether or diphenyl amine precursor and silicon tetrachloride (or trichlorosilane) followed by reduction with lithium aluminum hydride [H2SiAr2: Ar2 = C12H8O (1); Ar2 = C14H12O (2); Ar2 = C13H11N (3); Ar2 = C15H15N (4); Ar2 = C13H9Br2N (5)]. The reactivity of hydrosilanes 1−5 with (Ph3P)2Pt(η2-C2H4) (6) was investigated. At room temperature, mononuclear complexes, (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)2Pt(SiAr2H)2, were generally observed by NMR spectroscopy but were too reactive or unstable to isolate. Dinuclear and in some cases trinuclear Pt−Si-containing complexes were observed as the major products from the reactions. Symmetrical dinuclear complexes, [(Ph3P)Pt(μ-η2-H-SiAr2)]2 (8 and 22, respectively), were produced from the reaction of 1 or 3 with 6. In contrast, reaction of silane 2 with 6 produced a trinuclear complex, [(Ph3P)Pt(μ-SiAr2)]3 (16), as the major product. However, reaction of 4 or 5 with complex 6 produced an unsymmetrical dinuclear complex, [(Ph3P)2Pt(H)(μ-SiAr2)(μ-η2-H-SiAr2)Pt(PPh3)] (26 and 30, respectively), as the major component. The molecular structures of a symmetrical (22) and unsymmetrical dinuclear (30) complex as well as a trinuclear (16) complex were determined by X-ray crystallography.
Mononuclear Pt−Si-containing complexes with the general formulas (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)2Pt(SiAr2H)2 were produced at low temperature from the reaction of the secondary arylhydrosilanes Ph2SiH2, C12H8SiH2 (silafluorene), and C20H24SiH2 (3,7-di-tert-butylsilafluorene) with (Ph3P)2Pt(η2-C2H4). When solutions of the mononuclear complexes were run at low temperature and then warmed to room temperature, or when the reactions were run at room temperature or above, dinuclear Pt−Si-containing complexes were produced, [(Ph3P)Pt(μ-η2-HSiAr2)]2 (Ar = Ph (4)) and [(Ph3P)2Pt(H)(μ-SiAr2)(μ-η2-HSiAr2)Pt(PPh3)] (Ar2 = C12H8 (8), C20H24 (15); both fluxional). A mechanism is proposed for the formation of the unsymmetrical dinuclear complexes (8 and 15) that involves a bimolecular reaction between two mononuclear species, (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)Pt(H)(SiAr2H). VT-NMR studies of complexes 8 and 15 illustrate that a fluxional process occurs which can be explained by elimination and recoordination of a PPh3 ligand. Complex 15 reacted with added P(p-Tol)3 to produce a mixture of dinuclear products consistent with the presence of both types of phosphines in the dinuclear complexes. Reaction of the dinuclear complex 8 with the mononuclear complex 16 as well as the elevated-temperature reaction between 8 and 15 will be described.
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