Reaction of Silafluorenes with (Ph3P)2Pt(η2-C2H4):  Generation and Characterization of Pt−Si Monomers, Dimers, and Trimers

The reaction of silafluorene (1; H 2 SiC 12 H 8 ) with (Ph 3 P) 2 Pt(η 2 -C 2 H 4 ) (2) at room temperature in C 7 D 8  initially provided the mononuclear complex (Ph 3 P) 2 Pt(H)[Si(H)C 12 H 8 ] (3), followed by the appearance of the unsymmetrical dinuclear complex (Ph 3 P) 2 (H)Pt(μ-SiC 12 H 8 )(μ-η 2 -HSiC 12 H 8 )Pt(PPh 3 ) (4) and finally the novel trinuclear complex [(Ph 3 P)Pt(μ-SiC 12 H 8 )] 3  (5). The three complexes were characterized by multinuclear NMR spectroscopy and by X-ray crystallography (5). The molecular structure of 5 exhibits a nonplanar Pt 3 Si 3  core. When the reaction was conducted at low temperature until the silafluorene was consumed and the mixture then warmed to room temperature, the dinuclear complex 4 could be isolated. The related substituted silafluorene system 3,7-di- tert -butylsilafluorene (6; H 2 SiC 20 H 24 ) also reacted with 2 to provide both mono- and dinuclear complexes (7 and 8) analogous to 3 and 4. The dinuclear complex 8 was isolated and crystallographically characterized. Each of the two Pt centers in complex 8 exhibits a unique environment. In solution at low temperature 8 is best described as having one platinum center with a terminal hydride, [Pt(H)(PPh 3 ) 2 ], and the second platinum with a nonclassical [Si···H···Pt(PPh 3 )] unit. However, in the solid state, the two hydrides may both adopt a bridging environment. Heating a sample of the unsymmetrical dimer 8 led to the formation of several products, one of which was the trimer 9, analogous to 5.